CA3037462C - A refractory material for sliding nozzle plate and a method for producing the same - Google Patents

Abstract

ABSTRACT The invention relates to a refractory material for a sliding nozzle plate for use in casting of steel. The refractory material contains 15% to 45% by mass of an A1404C component, 2.0% to 4.5% by mass of a free carbon component, 0.5% 4.0% by mass of a SiO2 component, and 0 to 1.0% by mass of a metallic aluminum component, with the remainder including an A1203 component as a primary component. The refractory material includes a surface serving as a sliding surface, and has a gas-permeability of 5x10-17 m2 to 40x10-17 m2 in a direction orthogonal to said surface, according to J1S-R2115 (2008), and an apparent porosity of 8.0% to 11.0%, as measured according to J1S-R2213 (1995). Also, the invention relates to a method for producing the refractory material. Date recue/Date Received 2020-08-20

Description

DESCRIPTION
TITLE OF INVENTION
A REFRACTORY MATERIAL FOR SLIDING NOZZLE PLATE AND A METHOD
FOR PRODUCING THE SAME
TECHNICAL FIELD
[0001]
The present invention relates to a refractory material for a sliding nozzle plate (hereinafter, also referred to as "plate") for use in opening and closing control and flow rate control during operation of discharging molten steel, particularly molten steel having a low concentration of free oxygen, from a vessel such as a ladle or a tundish, in a steelmaking process, and a method for producing the refractory material.
BACKGROUND ART

[0002]
A surface roughening of a sliding surface, which is one main type of damage of a plate, is a phenomenon that a structure of the sliding surface serving as an operating surface during casting is embrittled, leading to the occurrence of secondary phenomena such as abrasion, wear, and spalling. This surface roughening is considered to be caused by exertion of a complex influence of several factors such as chemical factors and physical factors. It is considered that oxidation and decarburization often serve as a trigger of the surface roughening, wherein oxidation is caused by gas-phase oxidation due to oxygen in atmospheric air and liquid-phase oxidation due to oxygen in molten steel, and decarburization is caused by elution of carbon into molten steel. It is also considered that molten steel, or components in the molten steel, such as inclusions and slag, infiltrate in, adhere to, or react with the structure of the operating surface embrittled by oxidation and decarburization, and further the resulting infiltrated or adhered layer causes spalling of the structure, leading to acceleration of the surface roughening.

[0003]

Meanwhile, recently, oxidation and decarburization mechanisms different from simple gas-phase oxidation, liquid-phase oxidation due to oxygen in molten steel and decarburization due to elution of carbon into molten steel have been reported.
For example, in the following Non-Patent Document 1, based on a test in which three types of steel consisting of extremely-low carbon Al-killed steel (carbon concentration: 20 ppm), low-carbon Al-killed steel (carbon concentration: 410 ppm) and ultralow carbon Si-killed steel (carbon concentration: 20 ppm) were placed in an electric furnace and subjected to reaction with a simple system-type sample composed of an alumina fine powder and carbon, under a temperature condition of 1560 C in an Ar atmosphere replaced under vacuum, evaluation and consideration of an interfacial structure of the sample are made. As a result of the reaction with the extremely-low carbon Al-killed steel (carbon concentration: 20 ppm), formation of an embrittled layer having a thickness of about 200 pm on the operating surface of the sample, i.e., disappearance of carbon and Al2O3 grains, was ascertained.
Similarly, in the low-carbon Al-killed steel (carbon concentration: 410 ppm), formation of the embrittled layer having a thickness of about 100 pm from which carbon and A1203A1 grains disappeared was ascertained.
Further, in the following Non-Patent Document 2, after undergoing operation of pouring molten steel, such as Al-killed steel, having a low concentration of free oxygen, a sliding surface of a plate was observed to ascertain formation of an embrittled layer from which carbon and Al2O3 grains disappeared.

[0004]
As above, during the operation of pouring molten steel, such as Al-killed steel, having a low concentration of free oxygen, an embrittled layer is considered to be formed in a part of the sliding surface of the plate in contact with the molten steel or in a surface of the plate exposed to an inner bore space (this surface will hereinafter be referred to as "operating surface") of the plate, thereby leading to the occurrence of the surface roughening phenomenon.
However, a detailed mechanism, an improvement method, etc., for the surface roughening have not been sufficiently studied.

CITATION LIST
[NON-PARENT DOCUMENT]

[0005]
Non-Patent Document 1: Proceedings of the 1st Iron and Steel Refractories Committee, November 21, 2013, p. 180 ¨ p. 187 Non-Patent Document 2: Proceedings of the 3rd Iron and Steel Refractories Committee, November 26, 2015, p. 167 ¨ p. 174 SUMMARY OF INVENTION
[TECHNICAL PROBLEM]

[0006]
A technical problem to be solved by the present invention is to provide a refractory material for a plate, capable of allowing a sliding surface of the plate to become less likely to undergo surface roughening during operation of pouring molten steel such as Al-killed steel, and a method for producing the refractory material for the plate.
Further, the technical problem to be solved by the present invention is to provide a refractory material for a plate, which is suitable for the operation of pouring molten steel having a low concentration of free oxygen, and a method for producing the refractory material for the plate.
[Solution to Technical Problem]

[0007]
As a result of various researches of the inventor about the mechanism of surface roughening on the sliding surface during the operation of pouring molten steel such as Al-killed steel, particularly molten steel having a low concentration of free oxygen, it was found that the aforementioned embrittled layer in which carbon and Al2O3 grains has disappeared is formed by the occurrence of oxidation-reduction reaction between carbon and oxide, etc.
in the refractory material, and surface roughening accelerates by damage of the embrittled layer.

[0008]
More specifically, carbon in the refractory material is oxidized by oxygen (0) in an Al2O3 component, a S102 component, a ZrO2 component, etc., which are main components in the refractory material, and becomes gas phase as CO gas and disappears, and thereby decarburization is caused. Further, an A1203 component, a SiO2 component, a ZrO2 component, etc. are reduced by carbon to generate gas phase species such as Al gas, A120 gas, SiO gas, and carbide such as ZrC, SIC, etc. Many of the generated gas phase species are considered to migrate to an operating surface and elute into the molten steel. Also, it is considered that a part of the SiO gas forms SiC
in the refractory structure, and similarly to the generation of ZrC, when the carbide is generated from the oxide, its volume shrinks and many voids are generated in the refractory structure adjacent to the operating surface to form an embrittled layer.

[0009]
Further, in an inner bore of the plate during casting of molten steel, when the degree of opening of the inner bore is reduced, i.e., the opening is narrowed, a region where the molten steel is not filled is generated. In this region, the degree of the narrowing becomes larger, the degree of pressure reduction becomes larger. Thus, generally, a casting time will be extended. It was also found that, in some cases, as compared to a sliding surface of a lower plate member of the plate, a sliding surface of an upper plate member of the plate to be exposed to such pressure reduction for a longer time is more significantly roughened, because, in a structure adjacent to the sliding surface of the upper plate member, an embrittled layer from which carbon, Al2O3 grain and the like disappeared becomes thicker, and the depth of infiltration of the molten steel or the like becomes larger.

[0010]
From these facts, the inventors found that formation of the embrittled layer or the surface roughening phenomenon described above is influenced by temperature, time, and pressure of the inner bore space in addition to oxygen concentration in molten steel. Then, the inventors found that when the free oxygen concentration in molten steel is 30 ppm or less, the higher the temperature, the longer the time, and the greater the extent of the negative pressure in the inner bore space, the greater the degree of formation of the embrittled layer or surface roughening.

[0011]
More specifically, in the refractory structure around the operating surface, in addition to Al2O3 grains, aggregate grains such as A1203 - ZrO2 based raw material and ZrO2 - mullite added as a low thermal expandable raw material have also been observed to suffer significant alteration.
And it was also ascertained that this alteration also tended to be larger in the upper plate than in the lower plate under the throttling pouring condition for a long time.
Further, it was ascertained that in the Al2O3 - ZrO2 based raw material, the ZrO2 grains in the raw material are altered into ZrC, whereas in the ZrO2 - mullite, the SiO2 component in the mullite region of the particle disappears, only A1203 remains, and the SiO2 component gasifies and migrates on the surface layer of the ZrO2 - mullite particle to exist as SiC. Moreover, it was confirmed that not only the SiO2 component of the mullite region but also the Al2O3 component disappears as the alteration progresses. Further, as for the ZrO2 grains, it was confirmed that the ZrO2 grains were altered to ZrC similarly to the ZrO2 grains in the A1203 - ZrO2 raw material.

[0012]
All of these phenomena are caused mainly by the reduction action of carbon in the refractory structure, and under negative pressure conditions, the reduction reaction of the oxide components such as SiO2, ZrO2, and A1203 in the refractory structure for the plate with carbon progresses even more.

[0013]
These mechanisms can mainly be represented by the reactions shown by the following formulas 1 to 5.
SiO2 (s) + 3C (s) =SiC (s) +2C0 (g) Formula 1 3A1203.2Si02 (s) +12C (s) = 3A1203 (s) +2SiC (s) +4C0 (g) +12C (s) Formula ZrO2 (s) +3C (s) =ZrC (s) +2C0 (g) Formula 3 A1203 (s) +3C (s) =2A1 (g) +3C0 (g) Formula 4 A1203 (s) +2C (s) =A120 (g) +2C0 (g) Formula 5

[0014]
As the result of calculating the reactions of these Formulas 1 to 5 under a temperature condition of 1550 C using thermodynamic calculation software Fact Sage, it was found that the reactions prone to progress more under the negative pressure condition. In addition, it was found that the reactions are more likely to progress more in the order of (1)> (2)>
(3)> (4) (5), and the raw materials for general use in the above-mentioned refractory material for the plate are prone to alter in the order of mullite, ZrO2 - mullite > A1203 - Zr02 > A1203. Further, according to this calculation, it was found that although the reduction reactions (4) and (5) by the carbon of A1203 do not progress at a normal pressure of 1 atm, in the case where a small amount of a SiO2 component is contained, a reaction occurs in a very small amount from 1 atm.
This shows that when the SiO2 component is contained, the above-mentioned reduction reaction occurs also on the sliding surface in a region which becomes atmospheric pressure or positive pressure during casting to form the embrittled layer, causing surface roughening.

[0015]
From these findings, the refractory material for the sliding nozzle plate of the present invention is constructed mainly based on the following policies.
(1) The amount of carbon component should be kept to the minimum necessary.
(2) The amount of the SiO2 component and the amount of the ZrO2 component should be kept to the minimum necessary.
(3) The amount of a metal Al component should be kept to the minimum necessary.
(4) The refractory structure should be densified.
Here, the above-mentioned "minimum necessary" means approximately the minimum relative amount/degree necessary in consideration of balancing of strength, thermal shock resistance, corrosion resistance, etc., after employing other alternative means.

[0016]
In addition, the refractory material for the sliding nozzle plate of the present invention contains an A1203 component as a main component in addition to an A1404C
component. The A1203 component, in particular, corundum, has the required properties in the most balanced manner such as corrosion resistance, abrasion resistance, heat resistance, thermal expansion property, etc. necessary as a sliding nozzle plate. Therefore, the refractory material for the sliding nozzle plate of the present invention also contains corundum as an A1203 component as a main component.

[0017]
On the other hand, when the amount of the carbon component described above (1) is reduced, formation of the embrittled layer can be suppressed. However, the thermal shock resistance deteriorates due to an increase in elastic modulus or the thermal expansion coefficient, the progress of sintering by heat receiving during casting, etc., and edge chipping of the plate, radial cracks, etc., occur, which also cause deterioration of durability. In addition, when the amount of the SiO2 component and the amount of the ZrO2 component described above (2) is reduced, formation of the embrittled layer can be suppressed, but then the thermal shock resistance is lowered, and edge chipping of the plate, radial cracks, etc., occur, which also cause deterioration of durability.

[0018]
Therefore, in the present invention, the thermal shock resistance is increased by containing an A1404C component in an amount of 15 to 45 mass% which has a lower thermal expansion than corundum. The A1404C component is a main component of an aluminum oxycarbide composition and has a thermal expansion coefficient of about 4 x 10-6 K, which is about half of that of a corundum, and thus has a high effect of reducing the thermal expansion coefficient. In addition, the A1404C component is reduced under coexistence of carbon as shown in the following formula 6.
2A1404C (s) + 3C (s) = 2A1203 (s) +Al4C3(s) + 2C0 (g) Formula 6 And according to the calculation under the temperature condition of 1550 C
using Fact Sage, it was found that the reaction of this formula 6 occurs even at 1 atm.

[0019]
On the other hand, as a result of observing the structure around the operating surface after actually using a plurality of plates to which the aluminum oxycarbide composition is applied, it was ascertained that a small altered layer having a thickness of about several tens of micrometers is formed only around the surface of the aluminum oxycarbide grains and the deeper structure remains less altered. From this, it was found that the reaction represented by the above Formula 6 occurs only in the surface layer of the aluminum oxycarbide composition on the surface of the operating surface. Further, from the above Formula 6, the above altered layer is considered to be composed of A1203 and A14C3, and both A1203 and Al4C3 are more stable than ZrO2 and SiO2 under coexistence of carbon, and thus they are considered to function as a protective layer for the aluminum oxycarbide composition. From these, it was found that the aluminum oxycarbide composition has higher stability under a reducing atmosphere at high temperature than a composition of A1203 - ZrO2 based composition, ZrO2 - mullite, and A1203 -SiO2 based composition, and is capable of sustaining low thermal expansion property for a long time, and thus it is difficult for the embrittlement of the structure due to the alteration of the composition itself to progress.

[0020]
Although the metal Al component in the above (3) mainly hasP an effect of increasing the strength by oxidation, it also has strong reducing action. The amount of the metal Al component should be kept to the minimum necessary to inhibit the reaction such as mainly excessive oxidation to suppress deterioration of the thermal shock resistance and to inhibit formation of the embrittled layer due to the reduction of the oxide.

[0021]
The aforementioned mechanisms (reactions) progress through pores in the refractory material, and thus increasing the denseness of the refractory structure contributes to suppression of formation of the embrittled layer or surface roughening. However, the pores are necessary to some extent and cannot be eliminated entirely from the viewpoint of production because the pores are also responsible for mitigation functions of thermal and mechanical stress of the refractory structure. Therefore, the densification of the refractory structure in the above (4) needs to be adjusted mainly in terms of balancing with thermal shock resistance.

[0022]
It is a widely common practice to impregnate with tar, pitch or a thermosetting resin to reinforce a carbon source and perform the densification. However, the carbon added to the refractory structure in this way is active and excess carbon is present, which is thus likely to accelerate formation of the embrittled layer. Further, with respect to such densification, it can be realized by other means, and thus in the present invention, it is preferable free of such impregnating step.

[0023]

Based on the above findings, the present invention is a refractory material for a sliding nozzle plate and a method for producing the refractory material for the sliding nozzle plate in the following 1 to 6.
1. A
refractory material for a sliding nozzle plate for use in casting of steel, the refractory material containing an A1404C component in an amount of 15 to 45 mass%, a free carbon component in an amount of 2.0 to 4.5 mass%, a SiO2 component in an amount of 0.5 to 4.0 mass%, and a metal Al component in an amount of 1.0 mass% or less (including zero), with the remainder including an Al2O3 component as a primary component, wherein the refractory material includes a surface serving as a sliding surface, and has a gas-permeability of 40x10-17 m2 or less as measured for said refractory material including said surface and in a direction perpendicular to said surface, and an apparent porosity of 11.0 % or less.
2. The refractory material as recited in claim 1, wherein the permeability is 5x10'7 to 40x10-17 m2, and the apparent porosity is 8.0 to 11.0 %.
3. The refractory material as recited in claim 1 or 2, which has a thermal expansion coefficient of 0.5 to 0.6 % as measured in a non-oxidizing atmosphere at 1000 C, and a bending strength of 15 to 40 MPa as measured at room temperature.
4. The refractory material as recited in any one of claims 1 to 3, wherein the steel has a free oxygen concentration of 30 ppm or less as measured in a molten state of the steel during casting.
5. A method for producing the refractory material as recited in any one of claims 1 to 4, the method comprising the steps of:
shaping a mixture containing a metal Al or an Al-containing alloy, wherein a total amount of a metal Al component in the metal Al or the Al-containing alloy is 2.0 to 10.0 mass%; and subjecting the mixture to heat treatment in a non-oxidizing atmosphere at 1000 C or more to adjust the content of the metal Al component in the refractory material to fall within a range of 1.0 mass% or less (including zero).
6. The method as recited in claim 5, which is free of a step of impregnating the refractory material with tar, pitch, or a thermosetting resin.

[0024]

In the present invention, the term "free oxygen in molten steel" means dissolved oxygen in molten steel and does not include oxygen contained in inclusions in molten steel present in the form of oxide. Also, in the present invention, the term "free carbon component" means a carbon component that is present alone and excluding carbon components present in the form of a compound with other elements, regardless of crystallinity, shape, etc.
[EFFECT OF THE INVENTION]

[0025]
The present invention can significantly reduce a surface roughening on a sliding surface of a sliding nozzle plate in casting of steel such as Al-killed steel, particularly even when the opening degree is small and the degree of throttling is large or when casting for a long time. This makes it possible to obtain stable high durability.
In particular, in casting of steels having a free oxygen concentration in molten steel of 30 ppm or less, in which has heretofore tended to become large in damage, the present invention can significantly reduce a surface roughening on a sliding surface of a sliding nozzle plate. This makes it possible to obtain stable high durability.
DESCRIPTION OF EMBODIMENTS

[0026]
A refractory material for a plate of the present invention contains an A1404C
component in an amount of 15 to 45 mass%. If the content of the A1404C component is less than 15 mass%, the refractory material has a low effect of reducing the thermal expansion coefficient and has insufficient thermal shock resistance. If the content of the A1404C component exceeds 45 mass%, the thermal expansion amount of the refractory material for the plate becomes relatively smaller than the thermal expansion amount of a metal band shrink-fitted to an outer periphery of the refractory material, resulting in reduction in the binding force of the refractory material for the plate, so that cracks is more likely to occur or expand. In addition, due to shifting of the metal band, and particularly during reusing of the plate, problems of deterioration in workability and safety during handling such as detaching of the plate, are likely to occur.

[0027]

The refractory material for the plate of the present invention contains a free carbon component in an amount of 2.0 to 4.5 mass%. If the content of the free carbon component is less than 2.0 mass%, the refractory material becomes easily wettable with oxides such as slag, so that oxide inclusions and slag in molten steel are more likely to adhere to and infiltrate into an operating surface of the plate and facilitate surface roughening. In addition, the effect of suppressing sintering between oxides to inhibit decrease or increase in elastic modulus is deteriorated, so that the thermal shock resistance is deteriorated, and cracks is more likely to occur or expand. If the content of the free carbon component exceeds 4.5 mass%, the embrittlement of the structure is accelerated by disappearance of carbon due to oxidation in the portion exposed to the outside air.
Furthermore, according to the above Formulas 1 to 5, oxides constituting the refractory material also disappear together with carbon in the refractory structure. As a result, the embrittlement of the structure is more likely to progress, and surface roughening is easily facilitated.

[0028]
The refractory material for the plate of the present invention contains a SiO2 component in an amount of 0.5 to 4.0 mass%. The SiO2 component contributes to improvement in refractory strength and densification of the structure depending on its starting material or its existence form.
Further, although the metal Al component contributes to improvement of corrosion resistance and oxidation resistance, densification of the structure, it generates A14C3 due to heat receiving, particularly, during casting, and this A14C3 hydrates to break up the structure in some cases. For suppressing hydration of Al4C3, the SiO2 component is effective. In order to suppress the hydration of A14C3, it is necessary that the SiO2 component is contained in an amount of 0.5 mass%
or more, and If the content is less than 0.5 mass%, it is impossible to achieve a sufficient hydration suppressing effect. On the other hand, as shown in Formulas 1 and 2, the SiO2 component reacts partly with carbon under a high temperature condition and precipitates as SiC
and disappears as SiO (g). However, alteration to SiC is accompanied by a decrease in volume, and thus it is also one factor that deteriorates the structure. Further, as described above, according to the calculation using Fact Sage, although the reduction reactions shown in Formulas (4) and (5) by the carbon of A1203 do not progress at 1 atm which is a normal pressure, in the case where a small amount of a SiO2 component is contained, a reaction occurs in a very small amount from 1 atm. The reduction = CA 03037462 2019-03-19 reaction of A1203 is one factor that facilitates embrittlement of the refractory structure. In order to suppress the deterioration of the structure due to the reduction reaction or disappearance of the SiO2 component and the A1203 component, the content of the SiO2 component needs to be 4.0 mass% or less.

[0029]
In the refractory material for the plate of the present invention, the content of the metal Al component is set to 1.0 mass% or less (including zero). If the content of the metal Al component is 1.0 mass% or less, the refractory material contributes the effect of suppressing oxidation of free carbon component or A1404C component in the refractory structure, improvement of corrosion resistance, densification of refractory structure, etc., without largely changing the refractory structure due to heat receiving at the time of use. However, If the content of the metal Al component exceeds 1.0 mass%, it is difficult to ensure the stability of the refractory structure depending on the casting time, the kind of steel, the number of uses, etc., and rather, causing deterioration in durability.

[0030]
The remainder of the refractory material for the plate of the present invention other than the above-mentioned components is mainly composed of an A1203 component as a corundum.
This is because A1203 as corundum has a melting point of 2060 C, which is excellent in heat resistance, and has excellent corrosion resistance against foreign ingredients such as FeO. Further, in addition to the A1203 component, the remainder can contain, for the purpose of preventing oxidation, carbide components such as small amounts of SiC, B4C, A14C3, etc., nitride components such as Si3N4, BN, AIN, etc., and a metal component such as metallic Si, Mg in the Al alloy, etc.
These components also deteriorate denseness of the refractory structure, corrosion resistance, etc., due to oxidation, alteration, etc., so that the total amount of them is preferably about 7.0 mass% or less.

[0031]
In the refractory material for the plate of the present invention, denseness of the structure is an important factor as well as specifying the components as described above. In particular, it is important that the structure of the sliding surface side of the plate, particularly the portion serving as an operating surface, is dense, which is on the high temperature side and is easily affected by the foreign components and has a large degree of alteration such as reduction reaction.
This denseness can be evaluated or specified by a gas-permeability as measured for said refractory material including the surface serving as the sliding surface, and in a direction perpendicular to said surface, and an apparent porosity. Thus, it is necessary that the refractory material for the plate of the present invention includes a surface serving as a sliding surface, and has a gas-permeability of 40x10-17 m2 or less as measured for said refractory material including said surface and in a direction perpendicular to said surface, and the apparent porosity of 11.0 % or less. If the gas-permeability exceeds 40x 10-17 m2 or if the apparent porosity exceeds 11.0 %, decomposition gas from an inside of the refractory material becomes easy to migrate, further infiltration of the foreign component easily progresses, so that deterioration of the refractory structure and damage of the sliding surface (surface roughening) are accelerated. However, if the refractory structure is excessively densified, there is a possibility that the elastic modulus will rise and the thermal shock resistance will be deteriorated, so that, preferably, the lower limit value of the gas-permeability is x 10 -17 m2, and the lower limit value of the apparent porosity is 8.0 %.

[0032]
Preferably, the refractory material for the plate of the present invention has a thermal expansion coefficient of 0.5 to 0.6 % as measured in a non-oxidizing atmosphere at 1000 C. In the refractory material for the sliding nozzle plate, high temperature molten steel passes through the inner bore, and thus thermal shock resistance is required. Particularly when the refractory material for the sliding nozzle plate is set in a sliding nozzle device and used under constraint conditions by a pushing metal member, etc., in order to reduce the thermal stress generated during casting, it is important to reduce the thermal expansion coefficient of the refractory material for the sliding nozzle plate. Generally, the larger the shape of the plate, the higher the possibility of destruction tendency due to the thermal stress becomes. However, from the experience of the plate having generally largest shape heretofore, if the thermal expansion coefficient at 1000 C is about 0.6 % or less, remarkable destruction is avoided. On the other hand, if the amount of thermal expansion of the refractory material for the sliding nozzle plate during casting is too small, the restraining force by the metal band in the outer circumferential direction of the plate decreases, and when it is smaller than the thermal expansion amount of the metal band, the restraining force disappears. Then, in the refractory material for the sliding nozzle plate, problems are likely to occur; for example, cracks is likely to occur, cracks is likely to expand, and when detaching the plate after casting, the metal band greatly shifts and disassembling operation becomes difficult.
For these reasons, the thermal expansion coefficient at 1000 C is preferably about 0.5 % or more.

[0033]
Preferably, the refractory material for the plate of the present invention has a bending strength of 15 to 40 MPa as measured at room temperature. The refractory material for the sliding nozzle plate is set in a sliding nozzle device, and restraint by surface pressure is applied in the thickness direction, and restraint by and restraint by surface pressure is applied in the thickness direction, and restraint by the restraining hardware, etc., is applied from the surroundings. When the mechanical strength of the refractory material for the sliding nozzle plate restrained in this way is low, destruction is caused by the binding force. If the bending strength of the refractory material for the plate of the present invention as measured at room temperature is less than 15 MPa, the inventors have found from the experience that cracks are likely to occur at the time of setting or fixing into the sliding nozzle device, or at the time of the surface pressure loading. Therefore, the bending strength at room temperature is preferably 15 MPa or more. On the other hand, if the bending strength at normal temperature increases, the elastic modulus also increases, which is a factor of deterioration of the thermal shock resistance. If the bending strength of the refractory material for the plate of the present invention as measured at room temperature exceeds 45 MPa, the inventors have found from the experience that the elastic modulus is likely to be excessively high, and cracks due to thermal shock are likely to occur. Therefore, the bending strength at room temperature is preferably 15 to 40 MPa.

[0034]
A method for producing the refractory material for the plate of the present invention will be described below.

[0035]
Generally, the refractory material for the sliding nozzle plate can be produced by a production method including the following steps.

(A) A prescribed amount of raw material to be each component source of the refractory material for the sliding nozzle plate is blended and mixed together to obtain a raw material blend.
(B) A resin which forms a carbon bond after the heat treatment and can be used as a regulator for wet state of a mixture at the time of shaping and further, if necessary, a solvent, etc., are added and kneaded to the raw material blend to obtain a mixture.
(C) The mixture is subjected to pressure forming under an arbitrary method and any pressure to obtain a shaped body of the mixture.
(D) The shaped body is subjected to drying and heat treatment (burning) in a non-oxidation atmosphere.
(E) If necessary, polishing, winding of metal band, etc. are performed.

[0036]
In such method for producing the general refractory material for the sliding nozzle plate, a method for producing a refractory material for the plate of the present invention is characterized in that the method comprises the steps of:
adjusting the content of the metal Al component in the mixture to be in an amount of 2.0 to 10.0 mass%;
shaping the mixture; and subjecting the mixture to heat treatment the mixture in a non-oxidizing atmosphere at 1000 C or more to obtain the refractory material in which the content of the metal Al component is 1.0 mass% or less (including zero).

[0037]
If the content of the metal Al component in the mixture is less than 2.0 mass%, the densified structure after the heat treatment cannot be obtained. In other words, if a shaped body of the mixture containing the metal Al component in an amount of 2.0 mass% or more is heat-treated at 1000 C or more in a non-oxidizing atmosphere, the metal Al component in the shaped body reacts with the other components to produce reaction products such as AIN, Al4C3, A120C, A1404C, Al2O3, etc., causing densification of the structure due to volume expansion accompanying reaction products. The shape of the metal Al as a metal Al component source (raw material) can be atomized grains, flake grains, fibers, or the like. In addition to metal Al alone, an alloy of Al -Si, Al - Mg, etc. can also be used.

[0038]
On the other hand, If the content of the metal Al component in the mixture exceeds 10.0 mass%, the amount of the metal Al component in the refractory material (refractory material for the plate as a product) is highly likely to exceed 1.0 mass%. Even If the content of the metal Al component in the mixture is in an amount of 2.0 to 10.0 mass%, depending on the heat treatment conditions and the form of metal Al or an Al alloy as a metal Al component source (raw material), etc., the metal Al component is likely to not remain in the refractory material after heat treatment.
Including such cases, in the present invention, the content of the metal Al component in the refractory material after the heat treatment is set to 1.0 mass% or less (including zero).

[0039]
The melting point of the metal Al is 660 C. However, for example, in the case where the form of the metal Al is atomized grains in which the surface layer of the grains are covered with an oxide film or in the form of a fiber having a relatively large shape, even the heat treatment temperature is not lower than the melting point of the metal Al, a large amount of metallic Al component is likely to remain at a temperature of less than 1000 C.
Therefore, it is necessary to firing at a high temperature of 1000 C or more to sufficiently react the metal Al component with other components in order to densify the structure.

[0040]
Further, the heat treatment needs to be performed in a non-oxidizing atmosphere. However, as a heat treatment in a non-oxidizing atmosphere, in addition to a nitrogen atmosphere, an argon atmosphere, and a CO atmosphere in which heat treatment is performed by embedding in a coke, it is also possible to be subjected to heat treatment in a simple CO
atmosphere in which a shaped body is placed inside a container made of metal such as SiC or SUS and heated from outside the container with a burner or the like. On the other hand, when subjecting to heat treatment in an oxidizing atmosphere such as in an ambient atmosphere, not only carbon of the shaped body is oxidized but also AIN, A14C3, A120C, A1404C, etc., are not formed, and then it is not possible to densify the structure.

[0041]
In the present invention, in order to obtain the gas-permeability of 40x 10-1' m2 or less as measured for the refractory material including the surface serving as the sliding surface, and in a direction perpendicular to said surface, constitution of various raw materials, etc., as described above, particularly morphology and amount of metal Al and further the heat treatment conditions may be adjusted. In the heat treatment condition, burning is performed in a non-oxidizing atmosphere at a temperature of 1000 C or more (for example, a temperature of 1200 C or more under a nitrogen atmosphere having an oxygen concentration of 100 ppm or less). At that time, a method of finely adjusting the oxygen concentration for each temperature region, the partial pressures of nitrogen and CO, etc., is also effective.
In addition, with respect to each raw material, it is possible to adopt a method of selecting as dense as possible and shaping with oil press or friction press at a pressure of 100 MPa or more, such as, for example, using an A1404C-containing raw material produced by the arc melting method.
Further, the gas-permeability can be matched with the above-mentioned value by methods such as decreasing the diameter of the fine particle fraction, adjusting the structure ratio of large, medium, and small particle size fractions, increasing the pressure applied during shaping, increasing the number of tightening, adjusting the speed at pressurizing, etc.
in such a way as to make the particle size composition of the mixture, especially the fine particle fraction a tendency of tight-packed structure.
Adjustment of the apparent porosity is also similar to these techniques.
In addition, there are aspects that cannot accurately grasp and express denseness of structure only with apparent porosity, and thus it is necessary to judge denseness by comprehensive evaluation with apparent porosity and gas-permeability.

[0042]
A specific method in which the shaped body of the adjusted mixture such that the content of the metal Al component is 2.0 to 10.0 mass% is heat treated to obtain the refractory material containing the metal Al component in an amount of 1.0 mass% or less, includes optimally adjusting, for example, temperature, gas components such as oxygen partial pressure, gas supply rate, etc., for each of the above-mentioned techniques.

[0043]
As described above, in the production of the refractory material for the sliding nozzle plate, it is a widely common practice to impregnate with tar, pitch or a thermosetting resin in order to perform densification of the structure, etc. However, in the method for producing the refractory material for the plate of the present invention, a step of impregnating with tar, pitch or thermosetting resin is not necessarily required.

[0044]
Each of tar, pitch and thermosetting resin finally leaves residual carbon.
Among them, the thermosetting resin forms a continuous rigid amorphous carbon structure and is effective in improving the strength. However, it is likely to cause a reduction in thermal shock resistance. On the other hand, tar and pitch are solid at room temperature, soften in a temperature of several tens C to a hundred and several tens C to form a liquid, and have a high carbonization rate when heat treated at high temperature and become crystalline carbon after heat treatment. Therefore, impregnation of the refractory material for the sliding nozzle plate under a predetermined temperature condition with tar or pitch has a densification effect of greatly lowering the gas-permeability and the apparent porosity, and maintains denseness even after carbonization, resulting in crystalline soft carbon. Thereby, the increase in elastic modulus is suppressed, and the adverse effect of lowering the thermal shock resistance is small. However, when impregnated with tar, pitch or thermosetting resin, carbon will be present so as to fill the voids in the refractory structure. Accordingly, the amount of free carbon component in the refractory material becomes high, and a large amount of carbon exists around the oxide raw material such as A1203 grains. As a result, the oxide material such as A1203 particle, ZrO2, mullite, etc., will be reduced in a so-called high efficiency under long casting conditions. From this, it becomes easier to form an embrittled layer by disappearance or alteration of these oxide materials, etc., in the vicinity of the operating surface, which is likely to further accelerate damage to the sliding surface.
Therefore, according to the method for producing the refractory material for the plate of the present invention, it is preferable not to impregnate with tar, pitch or thermosetting resin.

[EXAMPLES]

[0045]
Table I presents Inventive Examples and Comparative Examples. In Inventive and Comparative Examples in Table 1, raw materials were weighted and mixed so as to have respective given raw material compositions and given particle distributions, and an organic binder was added and kneaded to the mixed raw materials to obtain a mixture, which was uniaxial pressed into a plate-shaped body under predetermined shaping conditions. The shaped body was subjected to heat treatment at a predetermined temperature and atmosphere to form a refractory material for a sliding nozzle plate. And bulk specific gravity, apparent porosity, gas-permeability, bending strength, elastic modulus and thermal expansion coefficient were evaluated, and for the evaluation of chemical components, A1404C component, Al2O3 component, SiO2 component and free carbon were quantified. In addition, a reaction test with molten steel and a reaction test with molten pig iron were performed using a high frequency induction furnace to evaluate formation of embrittled layer. Furthermore, thermal shock resistance was also evaluated using the high frequency induction furnace. Methods of these evaluations are as follows.

[0046]
The bulk density and the apparent porosity were measured according to HS
R2205.
Samples for use in measuring the bulk density and the apparent porosity had a shape of 40 mm x 40 mm x 40 mm including a surface serving as the sliding surface of the refractory material for the sliding nozzle plate and cut out as measured in a direction perpendicular to the surface serving as the sliding surface of the refractory material for the sliding nozzle plate. When the shape of the refractory material for the sliding nozzle plate is small, it is possible to evaluate samples cut out in the similar shape of 30 mm x 30 mm x 30 mm.

[0047]
The gas-permeability was measured according to JIS R2115 (2008). The samples for use in measuring the gas-permeability was those having a size of cp50 mm including a surface serving as the sliding surface of the refractory material for the sliding nozzle plate and cut out into a shape with a thickness of 20 mm in the direction perpendicular to the surface serving as the sliding surface. In this sample, the surface serving as the sliding surface and a surface of the 20 mm thick-side were parallel. The gas-permeability of this sample in the direction perpendicular to the surface serving as the sliding surface was measured.

[0048]
The bending strength was measured, using a sample cut into a shape of 20 mm ><
20 mm x 80 mm, according to J1S-R 2213 (1995).

[0049]
Elastic modulus was measured by an ultrasonic method. Specifically, terminals were placed at both ends of a sample cut into a shape of 20 mm x 20 mm x 80 mm to measure an acoustic velocity, and the elastic modulus was calculated by calculating a formula between the acoustic velocity and The bulk density measured according to J1S-R2205.

[0050]
The thermal expansion coefficient was measured up to 1000 C in a nitrogen atmosphere by a non-contact method described in JIS-R2207-1.

[0051]
Among the chemical components, A1404C component, A1203 component and metal Al component were quantified by Rietveld method using X-ray diffraction. If there is a standard sample, quantification can also be performed by the internal standard method similarly by X-ray diffraction method. In the analysis by ordinary X-ray fluorescence or wet method, it is very difficult to separate and quantify A1404C and A1203, and thus it is preferable to quantify by X-ray diffraction method. Likewise, with respect to the quantification of the metal Al component, when containing A1404C component, it is practically impossible to separate and quantify the A1404C by analyzing using atomic absorption, ICP , etc., by a wet method.
The SiO2 component was quantified by fluorescent X-ray diffraction method according to J1S-R 2216.
The free carbon component (expressed as "F.C." in Table 1) was quantified according to the method prescribed in JIS-R2011.

[0052]
Formation of the embrittled layer was evaluated by a reaction test with molten steel and a reaction test with molten pig iron, using a high-frequency induction furnace, as described above.

Specifically, the surface serving as the sliding surface of the refractory material for the sliding nozzle plate was lined in the high-frequency induction furnace so as to be the inner surface of the furnace of the high-frequency induction furnace, and the embrittled layer formed by the reaction test with molten steel or molten pig iron was evaluated.
As to the evaluation method of the embrittled layer on the sliding surface of the plate due to the oxygen in the molten steel (oxidation and decarburization is mainly caused for molten steel), SS400 is used as the molten steel and adjustment was made by adding Si and carbon so that the free oxygen concentration during the test was in the range of 30 to 50 ppm.
As to the evaluation method of the embrittled layer formation mainly due to the reduction reaction inside the refractory material, it was ascertained that when the molten pig iron containing almost no in-steel oxygen and having a carbon content of about 4 mass% was used, the oxygen concentration during the evaluation was stably 5 ppm or less.
The reaction tests were performed at 1600 C for 3 hours. After the reaction test, the lining of the high-frequency induction furnace was disassembled and the thickness of the embrittled layer formed on the surface serving as the sliding surface of the refractory material for the sliding nozzle plate (the inner surface of the furnace of the high-frequency induction furnace) was measured. In Table 1, the thickness of the embrittled layer is expressed as an index with the thickness of the embrittled layer of Example being 100. The smaller the index is, the thinner the embrittled layer is, and the better the surface roughness resistance. As described in Non-Patent Document 2, the reaction test with molten pig iron can well reproduce the structure of the sliding surface during the operation of pouring molten steel having a low concentration of free oxygen such as Al-killed steel.

[0053]
The thermal shock resistance was evaluated by a so-called immersion thermal shock test, in which a sample was immersed in the molten pig iron in a high-frequency induction furnace and the degree of cracking of the sample after cooling was evaluated.
Specifically, a sample of 40 mm x 40 mm x 180 mm was cut out from the plate refractory, and a series of tests was repeated three times in which the sample was immersed in molten pig iron at 1600 C for 3 minutes and then air-cooled for 30 minutes. After the test, the degree of cracking of the sample was observed.

,

[0054]
In addition, some examples and comparative examples were applied to an actual machine test (actual operation). In the actual machine test, by pouring two kinds of molten steel, i.e., molten steel of high oxygen content steel (steel having a free oxygen concentration in molten steel of more than 30 ppm) and molten steel of low oxygen content steel (steel having a free oxygen concentration in molten steel of 30 ppm or less), samples were evaluated from damaged state of the refractory material for the sliding nozzle plate, etc., in three stages of o (Excellent), A (Good) and x (NG) in total.

[0055]
[Table 1]
Example ample Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Chemical component/mass%
A1404C 15.0 30.0 45.0 300 30.0 30.0 300 30.0 300 30.0 29.5 Al2O3 (corundum) 75.0 60.0 45.0 60.0 600 600 60.0 60.0 60.0 60.0 58.7 SiO2 2.0 2.0 20 2.0 20 0.5 4.0 2.0 2.0 20 1.9 F.C. 3.0 3.0 3.0 . 2.0 4.5 3.0 3.0 3.0 3.0 3.0 , 4.5 Al < 1.0 <10 <1.0 <1.0 <10 <1.0 <1.0 <1.0 <1.0 <1.0 <1.0 Total 95.0 95.0 95.0 940 96.5 93.5 970 950 95.0 950 94.6 P

P P P P P. r P P. P
P
Content of metal Al component in 5 5 5 5 5 5 5 5 5 mixture/mass% .1) High- High-Normal Normal Normal Normal Normal Normal Normal Normal Normal Shaping condition (shaping pressure) forming forming , forming forming forming forming forming pressurefo ng pressureforming forming forming Heat treatment temperature/'C (highest 1200C 1200t 1200t 1200t 1200t 1200t 1200'C 1200t 1200t 1000t 1200t temperature, non-oxidizing atmosphere) With/Without impregnation of pitch, etc.
Without Without Without Without , Without Without Without Without Without Without ' With Evaluation Bulk density 3.10 3.00 2.95 3.02 2.92 3.03 294 3.03 3.02 2.96 3.05 Apparent porosity/% 8.5 8.5 8.5 9.0 10.0 , 8.2 9.5 7.8 7.0 11.0 , 45 Gas-permeab ility/1047m2 18 20 23 23 28 18 27 12 Bending strength/MPa 26 25 24 27 20 22 20 30 Elastic modulus/GPa 47 45 44 50 38 48 40 55 Thermal expansion coefficient/% 0.58 0.52 0.46 0.53 0.50 0.53 0.50 0.54 0.56 0.55 0.54 Reaction test with molten steel (Embrittled layer thickness/Index) Reaction test with molten pig 100 89 67 94 122 67 Ill 85 iron (Embrittled layer thickness/Index) Small Small micro Small Small Medium Small Medium Medium Small Small Th ennal shock resistance , crack crack crack crack crack crack crack crack crack crack crack Result of actual machine test (High 0 Mediu OMediu oxygen content steel) m crack m crack Result of actual machine test (Low oxygen OMediu OMediu content steel) m crack m crack , Comparati Comparati Comparati Comparati Comparati Comparati -Comparati Comparati ye ye ye ye ye ye ye ye Example 1 Dample 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Chemical component/mass%
A1404C 13.0 48.0 30.0 30.0 30.0 _ 30.0 30.0 30.0 A1203 75.0 45.0 60.0 60.0 600 60.0 60.0 60.0 SiO2 2.0 2.0 2.0 2.0 0.0 4.5 2.0 2.0 F.C. 3.0 3.0 1.0 5.0 3.0 3.0 , 3.0 3.0 Al <1.0 <1.0 <1.0 <10 <1.0 <1.0 2.5 <1.0 Total 93.0 98.0 93.0 97.0 93.0 96.5 95.0 95.0 V P P I, I, , I, Content of metal Al component in I

inbaure/mass% .1) High- Low-Normal Normal Normal Normal Normal Normal Shaping condition (shaping pressure) forming forming foiming forming forming forming pressure pressure forming forming Heat treatment temperatureC (highest 1200t 1200 C 1200t 1200t 1200 C 1200 C 900t 1200t temperature, non-oxidizing atmosphere) With/Without of impregnation of pitch, Without Without Without Without Without Without Without Without etc.
Evaluation Bulk density 3.12 2.93 3.04 2.90 3.04 /90 2.97 2.85 Apparent porosityi% 9.0 8.4 8.4 10.4 8.1 9.6 120 12.1 Gas-permeability/10-'7m' 17 24 21 29 17 28 39 43 Bending strength/MPa 27 23 42 18 23 ... 18 15 Elastic modulus/GPa 48 43 78 , 33 54 38 31 28 Thermal expansion coefficient/% 962 0.42 0.54 0.49 0.55 0.49 0.54 aso , Reaction test with molten steel (Embrittled layer thickness/Index) . .
Reaction test with molten pig iron (Embrittled layer thiclaiess/Index) Large Small Large Small Large Small Medium Small Thermal shock resistance crack crack crack crack crack crack crack crack '<Shill of Result of actual machine test (High '< Peculiar metal '<Slaking oxygen content steel) band crack '<Shift of xSurface '<Surface Result of actual machine test (Low oxygen metal xSlaking roughenin roughenin content steel) band g g .1 :The total amount of the metal Al component contained in mixute

[0056]
In Table 1, in Examples 1 to 3, the content of A1404C component is in the range of 15.0 to 45.0 mass%, the content of a SiO2 component is in the range of 2.0 mass%, the content of free carbon component is in the range of 3.0 mass%, and the content of the metal Al component is in the range of 1.0 mass% or less, each of which falls within the scope of the present invention, and properties such as an apparent porosity, gas-permeability, a bending strength, thermal expansion coefficient also fall within the scope of the present invention. Therefore, as the result of the reaction test with molten steel and the reaction test with molten pig iron, formation of the embrittled layer was negligible and evaluation of thermal shock resistance was good. As a result of testing the materials of Examples Ito 3 with an actual machine, good durability was obtained.
On the other hand, in Comparative Example 1, the content of the A1404C
component was as low as 13.0 mass%, and the effect of reducing the thermal expansion coefficient was low. Thus, as a result of evaluation of thermal shock resistance, a large crack occurred and good durability cannot be expected.
In Comparative Example 2, the content of A1404C component was as high as 48.0 mass%, and thus the thermal expansion coefficient became remarkably low. As the result, when detaching the plate from the sliding nozzle device after actual use, the shrink-fitted band (HB) on the outer periphery of the plate shifted and the dismantling property was bad. Further, cracks also developed, which made it difficult to recycle and it was evaluated as NG.

[0057]
In Examples 4 and 5, the contents of the free carbon component were, respectively, 2.0 mass%, and 4.5 mass%, the content of the A1404C component was 30.0 mass%, the content of the SiO2 component was 2.0 mass%, and the content of the metal Al component is 1.0 mass% or less, each of which falls within the scope of the present invention, and properties such as an apparent porosity, gas-permeability, a bending strength, thermal expansion coefficient also fall within the scope of the present invention.
Therefore, as the result of the reaction test with molten steel and the reaction test with molten pig iron, formation of the embrittled layer was negligible and evaluation of thermal shock resistance was good.
On the other hand, in Comparative Example 3, the content of the free carbon component was as low as 1.0 mass%, and thus the elastic modulus became high. As the result, Comparative Example 3 was evaluated as being inferior in terms of the thermal shock resistance. Thus, even in actual machine, good durability cannot be expected.
Further, in Comparative Example 4, the content of the free carbon component was as high as 5.0 mass%, and thus as the result of the reaction test with molten steel and the reaction test with molten pig iron, formation of the embrittled layer was became thick. Thus, even in actual machine, good durability cannot be expected.

[0058]
In Examples 6 and 7, the contents of the SiO2 component were, respectively, 0.5 mass%
and 4.0 mass%, the content of the A1404C component was 30.0 mass%, the content of the free carbon component was 3.0 mass%, and the content of the metal Al component is 1.0 mass% or =

less, each of which falls within the scope of the present invention, and properties such as an apparent porosity, gas-permeability, a bending strength, thermal expansion coefficient also fall within the scope of the present invention. Therefore, as the result of the reaction test with molten steel and the reaction test with molten pig iron, formation of the embrittled layer was negligible and evaluation of thermal shock resistance was good.
On the other hand, Comparative Example 5 does not contain the SiO2 component, and thus slaking occurred at the time of processing and after processing for recovering and recycling after actual use, it could be recycled. Further, in Comparative Example 6, the content of the SiO2 component was as high as 4.5 mass%, and thus formation of the embrittled layer was remarkable in the reaction test with molten pig iron.

[0059]
In Examples 8 and 9, the content of the A1404C component was 30.0 mass%, the content of the SiO2 component was 2.0 mass%, the content of the free carbon component was 3.0 mass%, and the content of the metal Al component was 1.0 mass% or less, each of which falls within the scope of the present invention, and properties such as an apparent porosity, gas-permeability, a bending strength, thermal expansion coefficient also fall within the scope of the present invention.
However, Examples 8 and 9 were produced by high-pressure forming, and thus in Example 8, the apparent porosity was as low as 7.8%, whereas in Example 9, the apparent porosity was as low as 7.0% and the gas-permeability was as low as 8 x 10-17 m2, both of which have high elastic modulus.
Therefore, although the formation of the embrittled layer was extremely slight in the reaction test with molten steel and the reaction test with molten pig iron, the thermal shock resistance tended to deteriorate somewhat. Also in the actual machine test, although the damage on the sliding surface was slight, the radial crack from a nozzle hole tended to be somewhat larger.
Comprehensively, however, better results could be obtained than the comparative conventional product.

[0060]
In Example 10, the heat treatment temperature was 1000 C, the content of the component was 30.0 mass%, the content of the SiO2 component was 2.0 mass%, the content of the free carbon component was 2.0 mass%, and the content of the metal Al component was 1.0 a = CA 03037462 2019-03-19 mass% or less, each of which falls within the scope of the present invention, and properties such as an apparent porosity, gas-permeability, a bending strength, thermal expansion coefficient also fall within the scope of the present invention. Therefore, as the result of the reaction test with molten steel and the reaction test with molten pig iron, formation of the embrittled layer was negligible and evaluation of thermal shock resistance was good.
On the other hand, in Comparative Example 7, a burning temperature is as low as 900 C, and thus despite the high-pressure forming, the reaction of the metal Al during the heat treatment was small. Further, the densification was insufficient, and the content of the metal Al component was more than 1.0 mass%. Therefore, as the result of the reaction test with molten steel and the reaction test with molten pig iron formation of embrittlement layer was also remarkable, even in the actual machine test, remarkable surface roughening occurred, and good durability could not be obtained.

[0061]
In Comparative Example 8, the shaping pressure at the time of shaping of the refractory material for the sliding nozzle plate was adjusted and the bulk density was set low. For this reason, in Comparative Example 8, the burning temperature was 1200 C, the content of component was 30.0 mass%, the content of a SiO2 component was 2.0 mass%, the content of free carbon component was 2.0 mass%, and the content of the metal Al component is 1.0 mass% or less, each of which falls within the scope of the present invention. However, the apparent porosity is 12.1 %, and the gas-permeability is 43 x 10-1' m2, and thus the densification is insufficient. Also, the bending strength is as low as 14 MPa. Therefore, as the result of the reaction test with molten steel and the reaction test with molten pig iron formation of embrittlement layer was also remarkable, even in the actual machine test, good durability could not be expected. In addition, due to insufficient strength, in the actual machine test, a peculiar crack different from radial cracks, etc., caused by normal thermal stress occurred, and the durability was deteriorated.

[0062]
In Example 11, pitch impregnation performed, which falls within the scope of the present invention. However, the content of free carbon component became high, and the carbon component is uniformly present in the refractory structure. Therefore, in the reaction test with molten pig iron, the reduction reaction in the refractory structure progress and the formation of the embrittled layer tended to be slightly thick. On the other hand, as the result of the reaction test with molten steel, formation of the embrittled layer was negligible. In the actual machine test, after the operation of pouring molten steel of high oxygen content steel, damage to the sliding surface was negligible, whereas after the operation of pouring molten steel of low oxygen content steel, damage to the sliding surface tended to be slightly larger.
Comprehensively, however, better results could be obtained than the comparative conventional product.

Claims (6)

1. A refractory material for a sliding nozzle plate for use in casting of steel, the refractory material containing an Al4O4C component in an amount of 15 to 45 mass%, a free carbon component in an amount of 2.0 to 4.5 mass%, a SiO2 component in an amount of 0.5 to 4.0 mass%, and a metal Al component in an amount of 1.0 mass% or less (including zero), with the remainder including an Al2O3 component as a primary component, wherein the refractory material includes a surface serving as a sliding surface, and has a gas-permeability of 40×10 -17 m2 or less as measured for said refractory material including said surface and in a direction perpendicular to said surface, and an apparent porosity of 11.0 % or less.

2. The refractory material as recited in claim I, wherein the permeability is 5×10 -17 to 40×10 -17 m2, and the apparent porosity is 8.0 to 11.0 %.

3. The refractory material as recited in claim 1 or 2, which has a thermal expansion coefficient of 0.5 to 0.6 % as measured in a non-oxidizing atmosphere at 1000 °C, and a bending strength of 15 to 40 MPa as measured at room temperature.

4. The refractory material as recited in any one of claims 1 to 3, wherein the steel has a free oxygen concentration of 30 ppm or less as measured in a molten state of the steel during casting.

5. A method for producing the refractory material as recited in any one of claims 1 to 4, the method comprising the steps of:
shaping a mixture containing a metal Al or an Al-containing alloy, wherein a total amount of a metal Al component in the metal Al or the Al-containing alloy is 2.0 to 10.0 mass%; and subjecting the mixture to heat treatment in a non-oxidizing atmosphere at 1000 °C or more to adjust the content of the metal Al component in the refractory material to fall within a range of 1.0 mass% or less (including zero).

6. The method as recited in claim 5, which is free of a step of impregnating the refractory material with tar, pitch, or a thermosetting resin.