JP7019421B2 - Plate for sliding nozzle Refractory and its manufacturing method - Google Patents

Description

The present invention is a plate for a sliding nozzle used for opening / closing and flow rate control when discharging molten steel, especially steel having a low free oxygen concentration in molten steel, from a container such as a ladle or a tundish in a steelmaking process (hereinafter referred to as "plate"). It also refers to fireproof materials and their manufacturing methods.

Rough surface of the sliding surface, which is the main form of wear of the plate, is a phenomenon in which the structure of the sliding surface, which is the moving surface, becomes weak during casting, causing phenomena such as wear, melting, and peeling. It is thought that this surface roughness is caused by a complex effect of several factors such as chemical factors and physical factors. In many cases, oxidation and decarburization are considered to be the starting point of surface roughness. Oxidation is caused by vapor phase oxidation by oxygen in the atmosphere and liquid phase oxidation by oxygen in molten steel, and decarburization is carried out to molten steel. It is believed to be caused by the elution of carbon. Components in molten steel and molten steel, such as inclusions and slag, infiltrate, adhere or react with the working surface structure embrittled by oxidation and decarburization, and the infiltration and adhesion layer peel off the structure, resulting in the surface. It is believed that the storm will progress.

On the other hand, recently, a mechanism of oxidation and decarburization, which is different from simple vapor phase oxidation, liquid phase oxidation by oxygen in molten steel, and decarburization by elution of carbon into molten steel, has been reported.
For example, in Non-Patent Document 1, there are three types of steel: ultra-low carbon Al killed steel (carbon concentration; 20 ppm), low carbon Al killed steel (carbon concentration; 410 ppm), and ultra-low carbon Si killed steel (carbon concentration; 20 ppm). Was placed in an electric furnace and reacted with a simple sample composed of alumina fine powder and carbon under a temperature condition of 1560 ° C. under an Ar atmosphere with vacuum substitution, and the texture of the interface was evaluated and considered. There is. As a result, as a result of the reaction test with ultra-low carbon Al killed steel (carbon concentration; 20 ppm), the formation of an embrittlement layer of about 200 μm on the working surface of the sample, that is, the disappearance of carbon and Al ₂ O ₃ grains was confirmed. Similarly, it has been confirmed that a low carbon Al killed steel (carbon concentration; 410 ppm) also forms an embrittlement layer of about 100 μm in which carbon and _{Al2O 3 grains} have disappeared.
Further, in Non-Patent Document 2, the sliding surface of the plate receiving the steel having a low free oxygen concentration in the molten steel such as Al killed steel was observed, and an embrittlement layer in which carbon and Al ₂ O ₃ grains disappeared was formed. I have confirmed that it will be done.

When receiving steel with a low free oxygen concentration in molten steel such as Al killed steel, the sliding surface of the plate is the surface that comes into contact with the molten steel or is exposed to the inner hole space (hereinafter referred to as the "operating surface"). It is considered that the surface roughness phenomenon occurs due to the formation of the embrittled layer in), but the detailed mechanism and improvement method thereof have not been sufficiently investigated.

Proceedings of the 1st Refractory Committee for Steel, November 21, 2013, p. 180-p. 187 Proceedings of the 3rd Refractory Committee for Steel, November 26, 2015, p. 167-p. 174

An object to be solved by the present invention is to provide a plate refractory material in which surface roughness is unlikely to occur on a sliding surface when receiving Al-killed steel or the like, and a method for manufacturing the same.
Further, in particular, it is an object of the present invention to provide a plate refractory material suitable for receiving steel having a low free oxygen concentration in molten steel and a method for producing the same.

As a result of repeated studies by the present inventors on the mechanism of surface roughness on the sliding surface when receiving steel such as Al killed steel, which has a particularly low free oxygen concentration in molten steel, the above-mentioned carbon and Al _2O It was found that the embrittled layer in which the _three grains disappeared was formed by the redox reaction between carbon and oxides in the refractory material, and the surface roughness progressed when the fragile layer was damaged.

More specifically, carbon in the refractory is oxidized by oxygen (O) such as Al ₂ O ₃ component, SiO ₂ component, ZrO ₂ component, etc., which are the main constituents in the refractory, as CO gas. It becomes a gas phase, disappears, and decarburizes. Further, the Al ₂ O ₃ component, the SiO ₂ component, the ZrO ₂ component and the like are reduced by carbon to generate gas phase species such as Al gas, Al ₂ O gas and SiO gas, and carbides such as ZrC and SiC. It is considered that most of the generated gas phase species move to the working surface and elute into the molten steel. Further, it is considered that a part of SiO gas forms SiC in the refractory structure, and similar to the formation of ZrC, when carbide is formed from the oxide, its volume shrinks and many voids are formed in the refractory structure near the working surface. Is considered to form a brittle layer.

In addition, in the inner hole of the plate during casting of molten steel, a region where the molten steel is not filled is generated by reducing the opening, that is, by squeezing, and the greater the degree of squeezing, the greater the degree of decompression in that region. In general, the casting time becomes longer. The structure near the sliding surface of the upper plate, which is exposed to such a reduced pressure region for a long time, is more brittle than the sliding surface of the lower plate, in which carbon and Al ₂ O ₃ grains have disappeared. It was also found that there are cases where the embrittlement layer is thick, the infiltration of the bare metal is deep, and the surface roughness becomes large.

From these, it was found that the above-mentioned phenomenon of embrittlement layer formation or surface roughness is affected by temperature, time, and pressure in the inner pore space in addition to the oxygen concentration in the molten steel. The free oxygen concentration in the molten steel is 30 ppm or less, the higher the temperature, the longer the time, the larger the degree of negative pressure in the inner pore space, the more the embrittlement layer is formed or the degree of surface roughness is. It was found that it would grow.

More specifically, in the refractory structure near the working surface, in addition to Al ₂ O ₃ particles, Al ₂ O ₃ -ZrO ₂ system raw materials added as low thermal expansion raw materials and aggregate particles such as ZrO ₂ -mullite are added. It was also observed that the upper plate had undergone significant alteration, and it was confirmed that this alteration also tended to be larger in the upper plate than in the lower plate under the condition of being squeezed for a long time. Furthermore, in the Al ₂ O ₃ -ZrO ₂ system raw material, the ZrO ₂ particles in the raw material are transformed into ZrC, and in the ZrO ₂ -mullite, the SiO ₂ component in the mullite region of the particles disappears, and only Al ₂ O ₃ remains. , SiO ₂ component was gasified and moved to the surface layer of ZrO ₂ -mullite particles, and it was confirmed that they existed as SiC. It was also confirmed that as the alteration progressed, not only the SiO ₂ component in the mullite region but also the Al ₂ O ₃ component disappeared. Furthermore, regarding the ZrO ₂ particles, it was confirmed that the ZrO ₂ particles _{were altered to ZrC in the same manner as the ZrO 2 particles} in the _{Al2O3 -} ZrO2 system raw material.

All of these phenomena are mainly caused by the reducing action of carbon in the refractory structure, but under negative pressure conditions, the oxidation of SiO ₂ , ZrO ₂ , Al ₂ O ₃ , etc. in the refractory structure of the plate The reduction reaction by carbon of the substance component proceeds further.

These mechanisms can be mainly shown by the reactions of the following formulas 1 to 5.
SiO ₂ (s) + 3C (s) = SiC (s) + 2CO (g) ... Equation 1
3Al ₂ O _{3.2SiO 2} (s) + 12C (s)
= 3Al ₂ O ₃ (s) + 2SiC (s) + 4CO (g) + 12C (s) ... Expression 2
ZrO ₂ (s) + 3C (s) = ZrC (s) + 2CO (g) ... Equation 3
Al ₂ O ₃ (s) + 3C (s) = 2Al (g) + 3CO (g) ... Equation 4
Al ₂ O ₃ (s) + 2C (s) = Al ₂ O (g) + 2CO (g) ... Equation 5

As a result of calculating the reactions of the formulas 1 to 5 under the temperature condition of 1550 ° C. using the thermodynamic calculation software Fact Sage, it was found that the reaction was more likely to proceed under the negative pressure condition. Further, these reactions are likely to proceed in the order of (1)>(2)>(3)> (4) ≈ (5), and the raw materials generally used for the above-mentioned plate refractory are mullite. It was found that the deterioration was likely to occur in the order of ZrO ₂ -mullite> Al ₂ O ₃ -ZrO ₂ > Al ₂ O ₃ . Furthermore, according to this calculation, the reduction reactions (4) and (5) of Al ₂ O ₃ with carbon do not proceed at 1 atm, which is the normal pressure, but when a small amount of SiO ₂ component is included, the amount is very small from 1 atm. It was found to produce a reaction. This indicates that when the SiO ₂ component is contained, the above-mentioned reduction reaction occurs even on the sliding surface in the region where the atmospheric pressure or positive pressure is applied during casting to form an embrittled layer, which causes surface roughness. ..

Based on these findings, the refractory plate for sliding nozzles of the present invention was mainly constructed based on the following policy.
(1) Keep the amount of carbon component to the minimum necessary.
(2) Keep the amount of SiO ₂ component and the amount of ZrO ₂ component to the minimum necessary.
(3) Keep the amount of metal Al component to the minimum necessary.
(4) The refractory structure is densified.
The above-mentioned "minimum required" refers to the relative minimum amount and degree required in terms of the balance of strength, heat impact resistance, corrosion resistance, etc., after taking other alternative means.

Further, the refractory plate for the sliding nozzle of the present invention contains the Al ₂ O ₃ component as the main component in addition to the Al ₄ O ₄ C component. The Al ₂ O ₃ component, especially corundum, has the most well-balanced characteristics such as corrosion resistance, wear resistance, heat resistance, and thermal expansion characteristics required for a plate for a sliding nozzle. Therefore, the refractory plate for sliding nozzles of the present invention also has corundum as an Al ₂ O ₃ component as a main component.

On the other hand, if the amount of carbon component in (1) is reduced, the formation of the embrittled layer can be suppressed, but on the other hand, the elastic modulus and thermal expansion rate increase, and sintering proceeds due to heat reception during casting. As a result, the thermal impact resistance is lowered, and the edge of the plate is chipped or radial cracks are generated, which causes the durability to be lowered. Further, by reducing the amount of the SiO ₂ component and the amount of the ZrO ₂ component in (2) above, the formation of the embrittlement layer can be suppressed, but the thermal impact resistance is lowered, and the edge of the plate is chipped and radial cracks are generated. This causes a decrease in durability.

Therefore, in the present invention, it is decided to enhance the thermostable impact resistance by containing 15 to 45% by mass of the Al ₄ O ₄ C component, which has lower thermal expansion than corundum. The Al ₄ O ₄ C component is the main component of the aluminum oxycarbide composition, and has a thermal expansion coefficient of about 4 × ^10-6 / K, which is about half that of corundum, and has a high effect of reducing the coefficient of thermal expansion. Further, the Al ₄ O ₄ C component is reduced in the coexistence with carbon as shown in the following formula 6.
2Al ₄ O ₄ C (s) + 3C (s)
= 2Al ₂ O ₃ (s) + Al ₄ C ₃ (s) + 2CO (g) ... Equation 6
Then, it was found that the reaction of this formula 6 occurred even at 1 atm according to the calculation under the temperature condition of 1550 ° C. using Fact Sage.

On the other hand, as a result of observing the microstructure near the working surface of the product after actual use of multiple plates to which the aluminum oxycarbide composition was applied, slight deterioration with a thickness of several tens of μm was observed only near the surface of the aluminum oxycarbide particles. It was confirmed that only the layer was formed, and the tissue deeper than it remained with almost no deterioration. From this, it was found that the reaction represented by the above formula 6 occurred only on the surface layer of the aluminum oxycarbide composition on the surface layer of the working surface. Further, it is considered that the altered layer is composed of Al ₂ O ₃ and Al ₄ C ₃ from the above formula 6, and both Al ₂ O ₃ and Al ₄ C ₃ are considered to be ZrO ₂ or ZrO 2 in the coexistence with carbon. It is more stable than SiO ₂ , and is considered to function as a protective layer for the aluminum oxycarbide composition. From these, the aluminum oxycarbide composition is more stable in a reducing atmosphere at a high temperature than the Al ₂ O ₃ -ZrO ₂ system, ZrO ₂ -mullite, and Al ₂ O ₃ -SiO ₂ system compositions. It can be seen that the low thermal expansion characteristics can be maintained for a long time, and that the embrittlement of the structure due to the alteration of the composition itself does not easily proceed.

The metal Al component of (3) has the effect of oxidizing and mainly increasing the strength, but also has a strong reducing action. The amount of metal Al component is kept to the minimum necessary in order to suppress the deterioration of thermal shock resistance mainly by suppressing the reaction such as excessive oxidation and to suppress the formation of the embrittled layer due to the reduction of the oxide. ..

Since the above-mentioned mechanisms (reactions) proceed through the pores in the refractory, increasing the denseness of the refractory structure contributes to the formation of the embrittlement layer or the suppression of surface roughness. However, since the pores also have the function of relaxing the thermal and mechanical stress of the refractory structure, they are necessary to some extent and cannot be eliminated in manufacturing. That is, it is necessary to adjust the densification of the refractory structure of (4) mainly in the balance with the thermostable impact resistance.

It is generally widely practiced to impregnate tar, pitch or thermosetting resin to reinforce and densify the carbon source. However, the carbon added in the refractory structure in this way is active and also causes excess carbon to be present, which may promote the formation of the embrittlement layer. Further, since the densification can be realized by other means, it is preferable that the present invention does not include such an impregnation step.

Based on the above findings, the present invention is the following methods 1 to 5 for manufacturing a refractory plate for sliding nozzles and a refractory plate for sliding nozzles.
1. 1. A refractory plate for sliding nozzles used for steel casting.
Al ₄ O ₄ C component is 15% by mass or more and 45% by mass or less, free carbon component is 2.0% by mass or more and 4.5% by mass or less, SiO ₂ component is 0.5% by mass or more and 4.0% by mass or less. , Metal Al component is 1.0% by mass or less (including zero), and the balance contains Al ₂ O ₃ component as the main component.
The air permeability in the direction perpendicular to the sliding surface including the sliding surface is 5 × 10 ^-17 m ² or more and 40 × 10 ^-17 m ² or less, and the apparent porosity is 8.0% or more. Refractory plate for sliding nozzles of 11.0% or less.
2 . The refractory plate for sliding nozzles according to 1 above, wherein the thermal expansion rate in a non-oxidizing atmosphere at 1000 ° C. is 0.5% or more and 0.6% or less, and the bending strength at room temperature is 15 MPa or more and 40 MPa or less.
3 . The refractory plate for a sliding nozzle according to 1 or 2 above, wherein the steel has a free oxygen concentration of 30 ppm or less in the molten steel at the time of casting.
4 . A clay containing a metallic Al or an Al-containing alloy and having a total amount of metallic Al components in the metallic Al or Al-containing alloy of 2.0% by mass or more and 10.0% by mass or less is formed, and 1000 in a non-oxidizing atmosphere. The sliding according to any one of 1 to 3 above, which comprises a step of heat-treating at a temperature of ° C. or higher to reduce the content of the metallic Al component in the refractory material to 1.0% by mass or less (including zero). How to manufacture a plate fireproof material for nozzles.
5 . The method for producing a refractory plate for a sliding nozzle according to 4 above, which does not include a step of impregnating with tar, pitch or a thermosetting resin.

In the present invention, "free oxygen in molten steel" means dissolved oxygen in molten steel and does not include oxygen contained in inclusions in molten steel existing in the form of oxides. Further, in the present invention, the "free carbon component" refers to a carbon component existing alone, excluding the carbon component existing in the form of a compound with another element, regardless of the form such as crystallinity or shape.

According to the present invention, in the casting of steel such as Al killed steel, the surface roughness of the sliding surface of the sliding nozzle plate becomes remarkable even when the opening is small and the drawing degree is large or when casting is performed for a long time. It can be reduced and stable high durability can be obtained.
In particular, in the casting of steel with a free oxygen concentration of 30 ppm or less in molten steel, which has tended to be more damaged in the past, the surface roughness of the sliding surface of the sliding nozzle plate can be significantly reduced and stable. High durability can be obtained.

The plate refractory of the present invention contains Al ₄ O ₄ C component in an amount of 15% by mass or more and 45% by mass or less. When the content of the Al ₄ O ₄ C component is less than 15% by mass, the effect of reducing the thermal expansion rate is small and the thermal impact resistance is insufficient. When the content of Al ₄ O ₄ C exceeds 45% by mass, the amount of thermal expansion of the plate refractory is relative to the amount of thermal expansion of the metal band shrink-fitted on the outer periphery of the plate refractory. As the size becomes smaller and the binding force of the refractory plate is reduced, cracks are likely to occur or expand. In addition, the metal band is displaced, and when the plate is reused, problems such as deterioration of workability and safety during handling such as removal of the plate are likely to occur.

The plate refractory of the present invention contains a free carbon component of 2.0% by mass or more and 4.5% by mass or less. When the content of the free carbon component is less than 2.0% by mass, it becomes easy to get wet with oxides such as slag, so oxide-based inclusions and slag in the molten steel adhere to and infiltrate the moving surface. It becomes easy to promote surface roughness. In addition, the effect of suppressing the sintering of oxides to lower the elastic modulus or suppressing the rise is reduced, and the thermal impact resistance is lowered, so that cracking or expansion is likely to occur. When the content of the free carbon component exceeds 4.5% by mass, the embrittlement of the tissue due to the disappearance of carbon due to oxidation in the portion exposed to the outside air becomes large, and further, according to the above formulas 1 to 5. Since the oxides and the like constituting the fire-resistant material disappear together with the carbon in the fire-resistant structure, the embrittlement of the structure is more likely to proceed and the surface roughness is easily promoted.

The plate refractory of the present invention contains a SiO ₂ component of 0.5% by mass or more and 4.0% by mass or less. The SiO ₂ component also contributes to the improvement of the strength of the refractory and the densification of the structure depending on the starting material or the form of existence. In addition, the metallic Al component contributes to the improvement of corrosion resistance and oxidation resistance and the densification of the structure. In particular, Al ₄ C ₄ is generated by heat reception during casting, and this Al ₄ C ₄ is hydrated to form a structure. May collapse. The SiO ₂ component is effective for suppressing the hydration of Al ₄ C ₄ . In order to suppress the hydration of Al ₄ C ₄ , it is necessary to contain 0.5% by mass or more of the SiO ₂ component, and if it is less than 0.5% by mass, a sufficient hydration suppressing effect cannot be obtained. On the other hand, as shown in the above formulas 1 and 2, the SiO ₂ component partially reacts with carbon to precipitate as SiC and disappears as SiO (g) under high temperature conditions, but the conversion to SiC is volumetric. Since it is a deterioration accompanied by a decrease, it is also one of the factors that deteriorate the tissue. Further, as described above, the reduction reaction represented by the above formulas 4 and 5 by the carbon of Al ₂ O ₃ does not proceed at 1 atm, which is the normal pressure, but contains a small amount of SiO ₂ components, according to the calculation using Fact Sage. And, although it is a very small amount, a reaction occurs from 1 atm. This reduction reaction of Al ₂ O ₃ is one factor that promotes the embrittlement of the refractory structure. In order to suppress the tissue deterioration due to the reduction reaction or disappearance of the SiO ₂ component and the Al ₂ O ₃ component, the content of the SiO ₂ component needs to be 4.0% by mass or less.

The content of the metallic Al component in the refractory plate of the present invention is 1.0% by mass or less (including zero). When the content of the metal Al component is 1.0% by mass or less, the refractory structure is not significantly changed by the heat received during use, and the free carbon component and the Al ₄ O ₄ C component in the refractory structure are oxidized. It contributes to the effect of suppressing the corrosion resistance, the improvement of corrosion resistance, and the densification of the refractory structure. However, if the content of the metallic Al component exceeds 1.0% by mass, it becomes difficult to secure the stability of the refractory structure depending on the usage conditions such as casting time, steel type, and number of uses, and rather the durability is improved. It will also reduce it.

In the plate refractory of the present invention, the rest other than the above _- mentioned components is mainly composed of the _Al2O3 component as corundum. This is because Al ₂ O ₃ as corundum has an excellent heat resistance of 2060 ° C. and excellent corrosion resistance to foreign components such as FeO. In addition to the Al ₂ O ₃ component, a small amount of carbide components such as SiC, B ₄ C, Al ₄ C ₃ and nitride components such as Si ₃ N ₄ , BN and Al N, and metals are used for the purpose of preventing oxidation. It can contain a metal component such as Mg in Si and Al alloys. Since these may also deteriorate the fineness and corrosion resistance of the refractory structure due to oxidation and alteration, the total amount is preferably about 7.0% by mass or less.

In the plate refractory of the present invention, the fineness of the structure is an important factor as well as the identification of the components as described above. In particular, it is important that the structure of the sliding surface side, which is on the high temperature side and is easily affected by foreign components and has a large degree of deterioration such as reduction reaction, especially the working surface, is dense. This denseness can be evaluated or specified by the air permeability and the apparent porosity in the direction perpendicular to the surface to be the sliding surface including the surface to be the sliding surface. That is, the plate refractory of the present invention has an air permeability of 40 × 10 ^-17 m ² or less in the direction perpendicular to the sliding surface including the surface to be the sliding surface, and an apparent porosity of 11.0%. It is necessary that: When this air permeability exceeds 40 × 10 ^-17 m ² , or when the apparent porosity exceeds 11.0%, the decomposed gas from the inside of the refractory tends to move, and the infiltration of foreign components also progresses. It becomes easier, and deterioration of the refractory structure and damage to the sliding surface (rough surface) increase. However, if the refractory structure is excessively densified, the elastic modulus may increase and the thermal impact resistance may decrease. Therefore, the lower limit of the air permeability is 5 × 10 ^-17 m ² , and the lower limit of the apparent porosity. Is preferably 8.0%.

Further, the plate refractory of the present invention preferably has a thermal expansion rate of 0.5% or more and 0.6% or less in a non-oxidizing atmosphere at 1000 ° C. In plate refractory materials, heat impact resistance is required because high-temperature molten steel passes through the inner holes. It is important to reduce the thermal expansion rate of the plate refractory in order to reduce the thermal stress generated during casting, especially when it is set in the sliding nozzle device and used under restraint conditions such as holding hardware. be. Generally, the larger the shape of the plate, the stronger the tendency of fracture due to thermal stress, but from the experience with the plate of almost the maximum shape so far, it is remarkable if the thermal expansion rate at 1000 ° C is about 0.6% or less. Escape from such destruction. On the other hand, if the thermal expansion amount of the plate refractory during casting is too small, the binding force of the metal band in the peripheral direction of the plate decreases, and if it is smaller than the thermal expansion amount of the metal band, the binding force is lost. Then, cracks are likely to occur in the refractory plate, cracks are likely to expand, and the metal band is greatly displaced when the plate after casting is removed, making dismantling work difficult. Therefore, the thermal expansion rate at 1000 ° C. is preferably about 0.5% or more.

Further, the plate refractory of the present invention preferably has a bending strength of 15 MPa or more and 40 MPa or less at room temperature. The plate is set in the sliding nozzle device and is constrained by surface pressure in the thickness direction and by restraining hardware from the surroundings. When the mechanical strength of the plate refractory that is restrained in this way is low, the restraining force causes fracture. The present inventors have empirically found that when the bending strength of the refractory plate at room temperature is less than 15 MPa, cracks are likely to occur when the plate refractory is set or fixed in the sliding nozzle device or when a surface pressure load is applied. .. Therefore, the bending strength at room temperature is preferably 15 MPa or more. On the other hand, as the bending strength at room temperature increases, the elastic modulus also increases, which is a factor that lowers the thermal impact resistance. The present inventors have empirically found that when the bending strength at room temperature exceeds 45 MPa, the elastic modulus tends to be excessively high and cracks due to thermal shock are likely to occur. Therefore, the bending strength at room temperature is preferably 15 MPa or more and 45 MPa or less.

Next, a method for manufacturing the plate refractory of the present invention will be described.

Generally, a plate refractory can be manufactured by a manufacturing method including the following steps.
(A) A predetermined amount of a raw material to be a source of each component of a plate refractory is mixed and mixed to obtain a raw material mixture.
(B) A resin that forms carbon bonds after heat treatment and can also be used as an agent for adjusting the wet state of the clay during molding, and if necessary, a solvent or the like is added to this raw material formulation and kneaded to make the complex. Get the soil.
(C) This clay is pressed and molded by an arbitrary method and pressure to obtain a molded body.
(D) This molded product is dried and heat-treated (baked) in a non-oxidizing atmosphere.
(E) If necessary, perform processing such as polishing and winding a metal band.

In such a general method for producing a plate refractory, the method for producing a plate refractory of the present invention has a content of the metal Al component in the soil of 2.0% by mass or more and 10.0% by mass or less. The clay is formed into a non-oxidizing atmosphere and heat-treated at a temperature of 1000 ° C or higher so that the content of the metallic Al component in the refractory is 1.0% by mass or less (including zero). It is characterized by being.

When the content of the metallic Al component in the clay is less than 2.0% by mass, a densified structure cannot be obtained after the heat treatment. In other words, when a molded body of clay containing 2.0% by mass or more of the metal Al component is heat-treated at a temperature of 1000 ° C. or higher in a non-oxidizing atmosphere, the metal Al component in the molded body reacts with other components. Then, products such as AlN, Al ₄ C ₃ , Al ₂ OC, Al ₄ O ₄ C, and Al ₂ O ₃ are produced, and the structure is densified by the volume expansion accompanying the formation of the reactants. The shape of the metal Al as the metal Al component source (raw material) can be atomized particles, flake-shaped particles, fibers, or the like. In addition to the metal Al alone, it can also be used as an alloy such as Al—Si and Al—Mg.

On the other hand, when the content of the metal Al component in the clay exceeds 10.0% by mass, the amount of the metal Al component in the refractory (plate refractory as a product) after the heat treatment exceeds 1.0% by mass. The possibility is high. Even if the content of the metal Al component in the clay is 2.0% by mass or more and 10.0% by mass or less, the heat treatment conditions and the form of the metal Al or Al alloy as the metal Al component source (raw material) Depending on the above, the metallic Al component may not remain in the refractory material after the heat treatment. Including such a case, in the present invention, the content of the metallic Al component in the refractory after the heat treatment is set to 1.0% by mass or less (including zero).

The melting point of the metal Al is 660 ° C. For example, when the form of the metal Al is atomized particles whose particle surface layer is covered with an oxide film or a fiber shape having a relatively large shape, the heat treatment temperature is higher than the melting point of the metal Al. If the temperature is lower than 1000 ° C., a large amount of metallic Al component may remain. Therefore, it is necessary to sufficiently react the metallic Al component with other components by firing at a high temperature of 1000 ° C. or higher in order to densify the structure.

The heat treatment must be performed in a non-oxidizing atmosphere, but the heat treatment in a non-oxidizing atmosphere includes a nitrogen atmosphere, an argon atmosphere, a CO atmosphere in which the heat treatment is performed by embedding in coke, a SiC container, and a metal such as SUS. It is also possible to place the molded body inside the manufactured container and heat it from the outside of the container with a burner or the like in a simple CO atmosphere. On the other hand, when heat treatment is performed in an oxidizing atmosphere such as an atmospheric atmosphere, not only the carbon of the molded body is oxidized, but also AlN, Al ₄ C ₃ , Al ₂ OC, Al ₄ O ₄ C and the like are generated. Therefore, the structure cannot be densified.

In the present invention, in order to reduce the air permeability in the direction perpendicular to the sliding surface including the working surface to 40 × 10 ^-17 m ² or less, the components of various raw materials and the like are configured as described above. In particular, the form and amount of the metal Al, the heat treatment conditions, and the like may be adjusted. Under the heat treatment conditions, firing is performed at a temperature of 1000 ° C. or higher in a non-oxidizing atmosphere (for example, a temperature of 1200 ° C. or higher in a nitrogen atmosphere with an oxygen concentration of 100 ppm or less). A method such as finely adjusting the partial pressure of CO is also effective.
Further, for the Al ₄ O ₄ C-containing raw material, for example, the Al ₄ O ₄ C-containing raw material produced by the arc melting method is preferably used, and each raw material is selected as as precise as possible, and oil press or friction. A method such as molding with a pressure of 100 MPa or more can be adopted by a press.
In addition, for example, the diameter of the fine powder area should be reduced, the composition ratio of each of the large, medium, and small particle size areas should be adjusted, and the pressure applied during molding should be applied so that the particle size composition of the clay, especially the fine powder area, tends to be densely filled. It is also possible to match the above-mentioned air permeability by methods such as increasing, increasing the number of times of tightening, and adjusting the speed at the time of pressurization.
The adjustment of the apparent porosity is similar to these methods.
In addition, since there is an aspect that the fineness of the tissue cannot be accurately grasped and expressed only by the apparent porosity, it is necessary to judge the fineness by comprehensive evaluation with the aeration rate.

The molded body adjusted so that the content of the metal Al component is 2.0% by mass or more and 10.0% by mass or less is heat-treated, and the content of the metal Al component in the refractory material is 1.0% by mass or less. As a concrete method to make it (including zero). For each of the above-mentioned methods, for example, the temperature, the gas component such as oxygen partial pressure, the gas supply speed, and the like are optimally adjusted.

As described above, in the production of a plate refractory material, it is generally impregnated with tar, pitch or a thermosetting resin for the purpose of densifying the structure, etc., but the production of the plate fireproof material of the present invention The method does not necessarily require a step of impregnating with tar, pitch or thermosetting resin.

Tar, pitch, and thermosetting resins all retain carbon in the end. Of these, thermosetting resins form a rigid, amorphous, continuous carbon structure, and although they have the effect of improving strength, they tend to cause a decrease in heat impact resistance. On the other hand, tar and pitch are solid at room temperature and soften in the heat of several tens to several tens of degrees Celsius to become liquid, and have a high carbonization rate when heat-treated at high temperature, and become crystalline carbon after heat treatment. Therefore, when tar or pitch is impregnated into a plate refractory under predetermined temperature conditions, it has a densifying effect that greatly reduces the air permeability and apparent porosity, maintains the densification even after carbonization, and becomes crystalline soft carbon. Therefore, there is little adverse effect of suppressing the increase in elastic modulus and reducing the thermal shock resistance. However, when impregnated with tar, pitch or thermosetting resin, carbon is present so as to fill the voids in the refractory structure, so that the amount of free carbon component in the refractory increases and Al ₂ A large amount of carbon is present around the oxide raw material such as O ₃ grains, and under long casting conditions, the oxide raw materials such as Al ₂ O ₃ grains, ZrO ₂ , and mullite can be reduced with high efficiency. Become. Therefore, it becomes easier to form an embrittled layer due to the disappearance or alteration of these oxide raw materials in the vicinity of the working surface, and it tends to be a factor that further promotes damage to the sliding surface. Therefore, in the method for producing a plate refractory of the present invention, it is preferable not to impregnate tar, pitch, thermosetting resin or the like.

Table 1 shows examples and comparative examples of the present invention. In each example of Table 1, the raw materials are weighed and mixed so as to have a predetermined raw material composition and particle size composition, and then the clay obtained by adding an organic binder and kneading is uniaxially formed into a plate shape under predetermined molding conditions. Molded. This molded body is heat-treated at a predetermined temperature and atmosphere to prepare a plate refractory, and the bulk specific density, apparent porosity, air permeability, bending strength, elastic modulus and thermal expansion rate are evaluated, and the chemical components are evaluated. As an evaluation, the Al ₄ O ₄ C component, the Al ₂ O ₃ component, the SiO ₂ component, and the free carbon were quantified. In addition, a reaction test with molten steel and a reaction test with hot metal were conducted using a high-frequency induction furnace to evaluate the formation of the embrittlement layer. Furthermore, the thermostable impact resistance was evaluated using the same high-frequency induction furnace. The methods of these evaluations are as follows.

The bulk specific density and the apparent porosity were measured according to JIS-R2205. The sample for measuring the bulk specific gravity and the apparent porosity is cut out in a shape of 40 mm × 40 mm × 40 mm in the direction perpendicular to the surface to be the sliding surface of the plate refractory, including the surface to be the sliding surface. It was used. If the shape of the refractory plate is small, a sample cut into a shape of 30 mm × 30 mm × 30 mm can be evaluated in the same manner.

The air permeability was measured according to JIS-R2115: 2008. The sample for measuring the air permeability is φ50 mm including the surface of the refractory plate, which is the sliding surface, and is cut out into a shape with a thickness of 20 mm in the direction perpendicular to the sliding surface. It was used. In this sample, the surface to be the sliding surface and the surface on the thickness side of 20 mm were made parallel. Then, the air permeability of this sample in the direction perpendicular to the sliding surface was measured.

The bending strength was measured according to JIS-R2213 (1995) using a sample cut into a shape of 20 mm × 20 mm × 80 mm.

The elastic modulus was measured by the ultrasonic method. Specifically, the sound velocity was measured by applying terminals to both ends of a sample cut into a shape of 20 mm × 20 mm × 80 mm, and the relational expression with the bulk specific gravity measured according to JIS-R2205 was calculated to calculate the elastic modulus.

The thermal expansion rate was measured up to 1000 ° C. in a nitrogen atmosphere by the non-contact method described in JIS-R2207-1.

Of the chemical components, the Al ₄ O ₄ C component, the Al ₂ O ₃ component, and the metallic Al component were quantified by the lead belt method using X-ray diffraction. If there is a standard sample, it can also be quantified by the internal standard method by the X-ray diffraction method. Since it is very difficult to separate and quantify Al ₄ O ₄ C and Al ₂ O ₃ by analysis by ordinary fluorescent X-ray or wet method, it is possible to perform quantification by X-ray diffraction method. preferable. Similarly, regarding the quantification of the metal Al component, when the Al ₄ O ₄ C component is contained, it is practically impossible to separate and quantify it by analyzing it by atomic absorption spectrometry or ICP by a wet method. , It is desirable to perform quantification by X-ray diffraction method.
The SiO ₂ component is quantified by the fluorescent X-ray diffraction method using JIS-R2216, and the free carbon component (denoted as "FC" in Table 1) conforms to the method specified in JIS-R2011. And quantified.

The evaluation of the embrittlement layer formation was carried out by a reaction test with molten steel and a reaction test with hot metal using a high-frequency induction furnace as described above.
Specifically, the embrittlement layer formed by the reaction test with molten steel or hot metal was evaluated by lining the high-frequency induction furnace so that the sliding surface of the plate refractory would be the inner surface of the high-frequency induction furnace.
As a method for evaluating the embrittled layer of the plate sliding surface due to oxygen in molten steel (oxidation and decarburization are the main factors for molten steel), SS400 is used as molten steel and the free oxygen concentration during the test is 30 to 50 ppm. It was adjusted by adding Si and carbon so as to be within the range.
As a method for evaluating the formation of the embrittled layer mainly due to the reduction reaction inside the refractory, a hot metal containing almost no oxygen in the steel and having a carbon content of about 4% by mass was used to stabilize the oxygen concentration during the evaluation. It was confirmed that the amount was 5 ppm or less.
The reaction tests were carried out at 1600 ° C. for 3 hours each. After the reaction test, the lining of the high-frequency induction furnace was disassembled, and the thickness of the embrittlement layer formed on the surface to be the sliding surface of the plate refractory (the inner surface of the high-frequency induction furnace) was measured. In Table 1, it is expressed as an index with the thickness of the embrittled layer of Example 1 as 100. The smaller this index is, the smaller the thickness of the embrittlement layer is, and the better the surface roughness resistance is. In the reaction test with the above-mentioned hot metal, as described in Non-Patent Document 2, the structure of the sliding surface when receiving a steel having a low free oxygen concentration in the molten steel such as Al killed steel is used. This is a test that can be reproduced well.

The thermostable impact resistance was evaluated by a so-called immersion thermal impact test in which a sample was immersed in the hot metal in a high-frequency induction furnace and the degree of cracking of the sample after cooling was evaluated. Specifically, a series of tests of 40 mm × 40 mm × 180 mm cut out from a refractory plate, immersed in hot metal at 1600 ° C for 3 minutes, and then air-cooled for 30 minutes were repeated three times, and the degree of cracking in the sample after the test. Was observed.

In addition, some examples and comparative examples were used for actual machine test (actual operation). In the actual machine test, two types of steel, high oxygen-containing steel (steel with a free oxygen concentration of more than 30 ppm in molten steel) and low oxygen-containing steel (steel with a free oxygen concentration of 30 ppm or less in molten steel), were received and plate fire resistance was received. Comprehensively evaluated from the damage state of the object, etc., on a scale of ○ (excellent), △ (good), and × (poor).

In Table 1, Examples 1 to 3 have an Al ₄ O ₄ C component content of 15.0 to 45.0% by mass, a SiO ₂ component content of 2.0% by mass, and a free carbon component content. The amount is 3.0% by mass and the content of the metallic Al component is 1.0% by mass or less, both of which are within the range of the present invention, and have characteristics such as apparent pore ratio, air permeability, bending strength, and thermal expansion ratio. Is also within the scope of the present invention. Therefore, in the reaction test results with molten steel and hot metal, the formation of the embrittlement layer was slight, and the evaluation of thermal impact resistance was also good. As a result of testing the materials of Examples 1 to 3 with an actual machine, good durability was obtained.
On the other hand, in Comparative Example 1, the content of the Al ₄ O ₄ C component is as small as 13.0% by mass, and the effect of reducing the thermal expansion rate is small. Durability cannot be expected. Further, in Comparative Example 2, since the content of the Al ₄ O ₄ C component is as high as 48.0% by mass, the thermal expansion rate becomes extremely low, and when the plate is removed from the sliding nozzle device after actual use, it is formed on the outer periphery of the plate. The band (HB) that was shrink-fitted was displaced, the dismantability was poor, the cracks expanded, and it was difficult to recycle, which was a defect.

In Examples 4 and 5, the content of the free carbon component is 2.0% by mass and 4.5% by mass, respectively, and the content of the Al ₄ O ₄ C component is 30.0% by mass, SiO ₂ The content of the component is 2.0% by mass and the content of the metallic Al component is 1.0% by mass or less, which are within the range of the present invention. The properties are also within the scope of the present invention. Therefore, in the reaction test results with molten steel and hot metal, the formation of the embrittlement layer was slight, and the evaluation of thermal impact resistance was also good.
On the other hand, in Comparative Example 3, since the content of the free carbon component is as small as 1.0% by mass, the elastic modulus is high and the evaluation result of thermal shock resistance is inferior, so that the durability is good even in an actual machine. You can't expect to get it. Further, in Comparative Example 4, since the free carbon component is as large as 5.0% by mass, the formation of the embrittlement layer is thick in the reaction test results with molten steel and hot metal, and it cannot be expected that good durability can be obtained even in an actual machine. ..

In Examples 6 and 7, the content of the SiO ₂ component is 0.5% by mass and 4.0% by mass, respectively, and the content of the Al ₄ O ₄ C component is 30.0% by mass, and free carbon. The content of the component is 3.0% by mass and the content of the metallic Al component is 1.0% by mass or less, which are within the range of the present invention. The properties are also within the scope of the present invention. Therefore, in the reaction test results with molten steel and hot metal, the formation of the embrittlement layer was slight, and the evaluation of thermal impact resistance was also good.
On the other hand, since Comparative Example 5 did not contain the SiO ₂ component, it could not be digested and regenerated when it was recovered after actual use and processed for recycling and after processing. Further, in Comparative Example 6, since the content of the SiO ₂ component was as high as 4.5% by mass, the formation of the embrittlement layer was remarkable in the reaction test with the hot metal.

In Examples 8 and 9, the content of the Al ₄ O ₄ C component is 30.0% by mass, the content of the SiO ₂ component is 2.0% by mass, and the content of the free carbon component is 3.0% by mass. %, The content of the metallic Al component is 1.0% by mass or less, which is within the range of the present invention, and the characteristics such as apparent pore ratio, air permeability, bending strength, and thermal expansion ratio are also within the scope of the present invention. .. However, since Examples 8 and 9 were produced by high-pressure molding, the apparent porosity was as low as 7.8% in Example 8, and the apparent porosity was 7.0% and the air permeability was 8 × 10 in Example 9. It is as low as ^-17 m ² , and the elastic modulus is high in both cases. Therefore, according to the reaction test results with molten steel and hot metal, the formation of the embrittled layer was extremely slight, but the thermal impact resistance tended to decrease slightly. In the actual machine test, the damage to the sliding surface was slight, but the radial cracks from the nozzle holes tended to be slightly larger. However, overall, better results were obtained than the conventional products for comparison.

In Example 10, the heat treatment temperature was 1000 ° C., the content of the Al ₄ O ₄ C component was 30.0% by mass, the content of the SiO ₂ component was 2.0% by mass, and the content of the free carbon component was 2. 0% by mass and the content of the metallic Al component is 1.0% by mass or less, which is within the range of the present invention, and characteristics such as apparent pore ratio, air permeability, bending strength, and thermal expansion ratio are also within the scope of the present invention. Is. Therefore, in the reaction test results with molten steel and hot metal, the formation of the embrittlement layer was slight, and the evaluation of thermal impact resistance was also good.
On the other hand, in Comparative Example 7, since the firing temperature is as low as 900 ° C., the reaction of the metallic Al during the heat treatment is small and the densification is insufficient even though the high pressure molding is performed, and the content of the metallic Al component is high. It was over 1.0% by mass. Therefore, the formation of the embrittlement layer was remarkable in the reaction test results with molten steel and hot metal, and the surface roughness was remarkable even in the actual machine test, and good durability could not be obtained.

In Comparative Example 8, the bulk density is set low by adjusting the molding pressure at the time of molding the refractory plate. Therefore, in Comparative Example 8, the firing temperature is 1200 ° C., the content of the Al ₄ O ₄ C component is 30.0% by mass, the content of the SiO ₂ component is 2.0% by mass, and the content of the free carbon component is 2.0% by mass and the content of the metallic Al component are 1.0% by mass or less, which are within the range of the present invention, but the apparent pore ratio is 12.1% and the air permeability is 43 × 10 ^-17 m. The precision is insufficient as ² and the bending strength is as low as 14 MPa. Therefore, the formation of the embrittlement layer is remarkable in the reaction test results with molten steel and hot metal, and good durability cannot be expected in the actual machine. In addition, due to insufficient strength, in the actual machine test, peculiar cracks different from the radial cracks caused by normal thermal stress were generated, and the durability was lowered.

In Example 11, pitch impregnation was performed, and although it was within the scope of the present invention, the content of the free carbon component was high, and the carbon component was uniformly present in the refractory structure. In the reaction test, the reduction reaction in the refractory structure proceeded, and the formation of the embrittled layer tended to be thick. However, in the reaction test with molten steel, the formation of the embrittlement layer was slight. In the actual machine test, the damage to the sliding surface was slight for the high oxygen-containing steel, but the damage to the sliding surface tended to be slightly larger when the low oxygen-containing steel was received. However, overall, better results were obtained than the conventional products for comparison.

Claims (5)

A refractory plate for sliding nozzles used for steel casting.
Al ₄ O ₄ C component is 15% by mass or more and 45% by mass or less, free carbon component is 2.0% by mass or more and 4.5% by mass or less, SiO ₂ component is 0.5% by mass or more and 4.0% by mass or less. , Metal Al component is 1.0% by mass or less (including zero), and the balance contains Al ₂ O ₃ component as the main component.
The air permeability in the direction perpendicular to the sliding surface including the sliding surface is 5 × 10 ^-17 m ² or more and 40 × 10 ^-17 m ² or less, and the apparent porosity is 8.0% or more. Refractory plate for sliding nozzles of 11.0% or less. The refractory plate for a sliding nozzle according to claim 1 , wherein the thermal expansion rate in a non-oxidizing atmosphere at 1000 ° C. is 0.5% or more and 0.6% or less, and the bending strength at room temperature is 15 MPa or more and 40 MPa or less. The refractory plate for a sliding nozzle according to claim 1 or 2 , wherein the steel has a free oxygen concentration of 30 ppm or less in the molten steel at the time of casting. A clay containing a metallic Al or an Al-containing alloy and having a total amount of the metallic Al component in the metallic Al or Al-containing alloy of 2.0% by mass or more and 10.0% by mass or less is formed, and 1000 in a non-oxidizing atmosphere. 7 . How to make a plate fireproof material for sliding nozzles. The method for producing a refractory plate for a sliding nozzle according to claim 4 , which does not include a step of impregnating with tar, pitch or a thermosetting resin.