JPH08208313A - Platelike refractory for sliding nozzle - Google Patents

Abstract

PURPOSE: To improve the thermal shock resistance of platelike refractories and the erosion resistance to molten steel having a high oxygen content by regulating the particle size of AlN to a specified value or below at the time of producing the refractories consisting of oxide stock and AlN. CONSTITUTION: Oxide stock may be selected from among oxides used in conventional ceramic bonded platelike refractories, e.g. Al2 O3 , ZrO2 , MgO spinel and MgO. The pref. rate of blending of the oxide stock is 85-99wt.% of the amt. of the entire objective platelike refractories and AlN of <=0.3mm paticloe size is added to such starting material by 5-50vol.% of the amt. of fine particles of <=0.3mm particle size in the oxide stock. The purity of the AlN is 50-99.9wt.% and allowable impurities or components are Al2 O3 , SiO2 , CaO, Y2 O3 , etc. When the AlN is added, a proper amt. of a binder such as PVA, starch or molasses is added if necessary and they are formed in a prescribed plate shape and sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate refractory for a sliding nozzle (hereinafter referred to as SN) used for controlling the flow rate of molten steel in continuous casting of molten steel, particularly for a steel type having a high oxygen level in the steel. The present invention relates to a plate refractory having high durability.

[0002]

2. Description of the Related Art The SN method is widely adopted as a method for controlling the flow rate of molten steel in continuous casting. This is to control the flow rate by a method of sliding plate-like refractories having through-holes and opening and closing the outflow hole of molten steel.

When the refractory material constituting the plate is used,
It is damaged by two factors, physical and chemical. In the former case, spalling due to thermal stress generated due to local heating caused by contact of the hole diameter portion with molten steel, peeling damage (peeling) on the operating surface, and wear due to molten steel flow are mentioned. In the latter case, melting loss due to the reaction of refractory with steel or molten slag can be mentioned.

Currently, Al _{2 is used} as a material for plate refractories.
O ₃ -C (carbon) material (carbon bonding material) is most commonly used. This is a refractory whose thermal shock resistance is improved by mainly selecting Al ₂ O ₃ as a main raw material from the viewpoint of corrosion resistance and adding carbon having good thermal conductivity. However, with the recent diversification of steel grades and the increasing number of castings, Al ₂ O ₃ —C material may be significantly damaged, and the material of the plate is selected according to the conditions of the steel grade to be cast.

In particular, when an Al ₂ O ₃ -C material is used for a steel type having a high oxygen level in the steel, that is, a so-called high oxygen steel, the carbon bond, which is the bond structure, is oxidized and the structure becomes brittle, and the normal steel type is used. It is known that the damage is severe compared to the case. For this reason, so-called ceramic bond materials such as MgO spinel material and Al ₂ O ₃ material are often selected for this type of steel.

However, since the ceramic bond material is inferior in thermal shock resistance to the carbon bond material, there is a drawback that the above-mentioned spalling and peeling from cracks along the operating surface are likely to occur. Another problem is the pickup of N in steel that occurs due to air suction from cracks that penetrate through the plate.

In addition, the high oxygen steel contains a large amount of highly corrosive FeO, which causes the plate refractories to be significantly melted. As a means for preventing this, it has been attempted to make ZrO ₂ having excellent corrosion resistance into a ring shape and insert it into the hole diameter portion of the Al ₂ O ₃ —C material.

However, even with this means, cracks caused by thermal stress have occurred, and a fundamental solution has not been reached. As a means for solving this, Japanese Examined Patent Publication No. 60-296
Japanese Unexamined Patent Publication No. 64 discloses an unfired SN plate brick. This feature is that the bond between the aggregate and the matrix is a resin bond for improving the spalling resistance, and a low melting point metal is mixed for the purpose of preventing the strength deterioration of the resin bond at a high temperature. Further, it is said that this low-melting-point metal can render FeO harmless by reducing FeO to Fe.

In the above invention, metal Al is used as the low melting point metal.
Is recommended, but in this case approximately 700 ° C
It is expected that the resin carbonized above reacts with metallic Al to produce Al ₄ C ₃ . It is known that Al ₄ C ₃ easily reacts with moisture in the air at room temperature and decomposes to decompose bricks, and a non-fired SN plate brick containing both metal Al and a resin serving as a C source is However, it is not suitable for the reuse of plate refractories, which has been actively performed in recent years.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to improve the thermal shock resistance and the melting loss resistance of molten steel having a high oxygen level in steel.
It is to provide a plate refractory for N.

[0011]

The gist of the present invention is as follows.
For N plate refractory.

A sliding-nozzle plate refractory made of an oxide raw material and AlN, wherein the grain size of AlN is 0.3 mm or less.

The "oxide raw material" referred to here is the main raw material of the plate refractory, and includes Al ₂ O ₃ , ZrO ₂ , and MgO.
It means oxides used in conventional ceramic bond type plate refractories such as spinel and MgO.

The desirable lower limit of the AlN grain size is 1 μm.
It is a degree. The desirable mixing ratio of AlN is 5% or more and 50% or less in terms of volume% with respect to the fine particle portion of 0.3 mm or less of the oxide raw material. The desirable purity range of AlN is about 50 to 99.9% by weight, and the impurities or components that are allowed to be contained are Al ₂ O ₃ , SiO ₂ , CaO, and Y ₂ O ₃ .

[0015]

The SN plate refractory material of the present invention comprises an oxide raw material which is a main raw material and AlN.

As oxide raw materials, Al ₂ O ₃ and ZrO are used.
₂ , selectable from oxides used in conventional ceramic bond type plate refractories such as MgO spinel and MgO. These raw materials are used alone or in a proper proportion, and the desirable proportion of the oxide raw material with respect to the whole plate refractory is 85 to 99% by weight.
Is. The particle size and the combination of raw materials when two or more kinds are mixed and used are not particularly limited.

Such a main raw material is used as a starting raw material, and AlN having a particle size of 0.3 mm or less is mixed therein.

The purpose of compounding AlN is to improve the thermal conductivity of the plate refractory. Table 1 shows examples of material properties of AlN.

[0019]

[Table 1]

As shown in Table 1, AlN has a very high thermal conductivity and is thermally stable. Therefore, by incorporating AlN, the thermal conductivity of the whole plate refractory can be improved. . Therefore, the generation of the temperature gradient generated in the plate refractory is mitigated, and the generation of thermal spalling, which is a disadvantage of the conventional ceramics bond type plate refractory, can be mitigated. In addition, as described above, high oxygen steel contains a large amount of FeO, which is highly corrosive, and is liable to be melted by this.
AlN in contact with eO detoxifies FeO by reducing FeO to Fe according to the reaction shown in the following formula (1).

2AlN (s) + 3FeO (s) → Al ₂ O ₃ (s) + 3Fe (s, l) + N ₂ (g) (1) The desirable purity range of AlN is 50 to 99% by weight. 9
%, And the impurities or components that can be included are Al
₂ O ₃ , SiO ₂ , CaO, Y ₂ O ₃ and the like.

The reason for setting the grain size of AlN to 0.3 mm or less is as follows.

Generally, the composition of the refractory is composed of coarse particles (aggregate) of a certain size and a matrix (continuous phase) which binds them.
And the matrix is composed of fine particles or a liquid phase. AlN in the present invention
Corresponds to the fine particles constituting this matrix.

If the grain size of AlN is 0.3 mm or less, A
The 1N fine particles can be collected in the continuously existing matrix (continuous phase) portion rather than in the discontinuous coarse particles (aggregate). As a result, AlN is present in the matrix (continuous phase) to improve the thermal conductivity of the matrix (continuous phase) portion. This is due to the fact that the thermal conductivity of the entire refractory material is considered. Be advantageous. However, considering the raw material cost of AlN, the desirable lower limit of the particle size of AlN is about 1 μm.

However, since AlN is a material that is difficult to sinter, it is difficult to completely sinter it by ordinary firing. Therefore, A
The continuous presence of 1N in the matrix does not provide the strength required for the plate refractory. Therefore, A
1N is preferably dispersed in the first component (oxide), which is a readily sinterable material, as the second component of the matrix constituent.

To achieve this, the range of the desirable mixing ratio of AlN having the above-mentioned particle size is 5% in volume% with respect to the fine particles having a particle size of 0.3 mm or less in the main raw material of the oxide.
It is above 50%. If it is less than 5%, the improvement of the thermal conductivity is not recognized, and the effect of improving the corrosion resistance to FeO is not recognized. On the other hand, if it exceeds 50%, AlN becomes the first component constituting the matrix, and the strength is remarkably lowered.

When AlN is blended, if necessary, PV
A suitable amount of binder such as A, starch and molasses is added and kneaded with the oxide main material. After that, a desired plate-shaped refractory can be obtained by forming it into a predetermined plate shape using a press or a rammer and firing the formed body in an N ₂ atmosphere.

[0028]

【Example】

(Invention Example 1) Sintered Al ₂ O ₃ clinker having a purity of 99.5% by weight was selected as a main oxide material, of which a grain size of 3 to 1 mm was coarse grain and 1 mm to 0.3 mm. Was a medium particle, and those having a diameter of 0.3 mm or less were fine particles. AlN having a purity of 90% by weight and an average particle size of 0.1 mm with respect to this fine particle part
Was compounded. This composition is 10.7% of Al ₂ O ₃ fine particle part.
It was carried out such that the weight% (40% by volume) was replaced by AlN. The compounding conditions at this time are shown in Table 2.

[0029]

[Table 2]

After kneading this raw material using an Erich mixer, a molding pressure is applied using a hydraulic press to 500 Kg / cm.
Molded in ² . This was fired at 1600 ° C. in an N ₂ atmosphere to make a plate refractory. The prototype shape was the size of a normal brick, and samples for each evaluation test were taken from this.

(Inventive Example 2) A plate fireproof was prepared under the same conditions and method as in Inventive Example 1, except that the compounding ratio of AlN was changed to 5.4% by weight (20% by volume of fine particles of Al ₂ O ₃ ). I made a prototype.

(Comparative Example 1) A plate refractory material was prepared under the same conditions and method as those of Example 1 of the present invention, except that the compounding ratio of AlN was changed to 14.7% by weight (55% by volume of fine particles of Al ₂ O ₃ ). Was prototyped.

(Comparative Example 2) Except that the mixing ratio of AlN was changed to 0.8% by weight (3% by volume of fine particles of Al ₂ O ₃ ).
A plate refractory was manufactured under the same conditions and methods as those of Inventive Example 1.

(Comparative Example 3) The average particle size of AlN is 0.5 mm.
A plate refractory was manufactured under the same conditions and method as those of Example 2 of the present invention.

(Comparative Example 4) Al ₂ O was added without adding AlN.
_A plate refractory was trial-produced under the same conditions and method as those of Example 1 of the present invention except that only ₃ was used as a raw material.

The physical properties and characteristic values of each trial refractory were evaluated. The test procedures are as follows.

(1) Apparent porosity, bulk specific gravity: JIS-R22
Compliant with 05 (2) Compressive strength: Compliant with JIS-R2206 (3) Thermal conductivity: Measured at room temperature by laser flash method (4) Thermal shock resistance: 30 mm x 30 mm x 12 from prototype refractory
A 0 mm sample was cut out and placed in an electric furnace at 1300 ° C.
After heating for 5 minutes, the sample was dropped in liquid nitrogen and rapidly cooled, and then the bending strength was measured. The evaluation was made by setting the bending strength of Comparative Example 4 to 100 and comparing it with that, and the larger the value, the better the thermal shock resistance.

(5) Molten steel erosion test: Each sample was placed in a high frequency induction furnace kept in an Ar atmosphere, and the amount of reduction in cross-sectional area due to melting loss was measured. At this time, the erosion agent is molten steel, the molten steel temperature is 1580 ° C., and the test time is 120 minutes. However, iron oxide was added to the molten steel in a timely manner so that a _{O in} the molten steel was 0.
It was adjusted to be constant at 04. The evaluation was performed by setting the value of Comparative Example 4 to 100 and comparing it with the value, and the smaller the value, the better the corrosion resistance.

Table 2 also shows the compounding conditions of Examples 2 to 3 of the present invention and the evaluation results of each test of Examples.

From the results of Table 2, the SN plate refractory of the present invention is an Al ₂ O ₃ refractory containing no AlN (Comparative Example 4).
It can be seen that the thermal conductivity, the thermal shock resistance, and the corrosion resistance to the high oxygen steel are improved as compared with those in Table 1.

[0041]

EFFECTS OF THE INVENTION The refractory for SN plate of the present invention has improved thermal shock resistance, which is a disadvantage of the conventional ceramic bond type refractory for SN plate. At the same time, it is especially suitable for steel grades having high oxygen level in steel. In contrast, it has high durability.

Claims (1)

[Claims] 1. A sliding-nozzle plate refractory made of an oxide raw material and AlN, wherein AlN has a grain size of 0.3 mm or less.