JPH1112034A - Zirconia-based refractory for casting use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject refractory improved in corrosion resistance and spalling resistance in yttria-stabilized zirconia, and excellent in serviceability, by compounding an yttria-stabilized zirconia stock, yttria-unstabilized zirconia stock and alumina-based fine powder in specific proportions. SOLUTION: Using a total of >=98 wt.% of a feedstock powder comprising 50-97 wt.% of an yttria-stabilized zirconia stock containing 1-10 wt.% of Y2 O3 , 2-40 wt.% of an unstabilized zirconia stock, and 0.1-10 wt.% of alumina-based fine powder <=100 μm in particle size containing >=75 wt.% (pref. >=95 wt.%) of Al2 O3 , a binder, etc., is added to the feedstock followed by kneading, molding, and then backing at >=1,600 deg.C to obtain the objective zirconia-based refractory for casting use. The respective particle sizes of the yttria-stabilized zirconia stock and unstabilized zirconia stock are pref. as follows: particles exceeding 0.5 mm in size accounts for <=8 wt.% of the total particles, particles 0.01-0.5 mm in size 10-45 wt.%, and particles <=0.01 mm in size 30-70 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an open nozzle,
The present invention relates to a refractory for zirconia casting used as a refractory for casting molten steel, such as a casting nozzle such as an upper nozzle, a lower nozzle or a submerged nozzle, or a stopper.

[0002]

2. Description of the Related Art As casting refractories used for continuous casting of molten steel, casting nozzles such as open nozzles, plate bricks, upper nozzles, lower nozzles and immersion nozzles are used to control the flow rate in a tundish. Uses a stopper.

In general, it is important to extend the continuous casting time in order to improve the quality of steel and reduce costs, but at present, lack of durability of casting refractories is a bottleneck.

[0004] When the cause of insufficient durability is corrosion resistance, a zirconia material is often used.

For example, in open casting in which two to six steel plates are provided at the bottom of a tundish and molten steel is simultaneously injected into respective molds, an open nozzle made of a zirconia material is generally used.

[0006] This open nozzle is used for continuous casting for 5 to 15 hours. However, as the operating time becomes longer, the inner hole is eroded and the diameter of the hole increases, and finally the casting speed increases. We have stopped casting for too long.

[0007] In addition, there is a case where the casting is damaged by a thermal shock during casting, and when it is broken, not only the casting operation is interrupted but also there is a danger of a steel leak accident. Further, when a crack is formed, the flow of molten steel flowing out of the nozzle may be disturbed, or air may be sucked and locally melted.

In order to improve the corrosion resistance of the inner hole surface of the plate brick, not only the plate brick itself is made of zirconia material, but also a case where a cylindrical zirconia refractory is attached to the inner hole is used. is there. This cylindrical zirconia refractory is sometimes used for an upper nozzle, a lower nozzle, or a part of an immersion nozzle.

A zirconia refractory for casting used in such applications is disclosed, for example, in Japanese Patent Application Laid-Open No. 62-241869, in which CaO partially stabilized zirconia is sintered as a sintering aid such as clay, alumina fine powder, phosphoric acid and the like. Add binder and add 1
There is a description of a zirconia brick by a sintered bond fired at 600 to 1900 ° C., and this type is actually widely used.

In the case of the CaO-stabilized zirconia,
In most cases, casting time is limited due to expansion of the bore during use. Observation of the CaO-stabilized zirconia brick used shows that CaO—SiO ₂ —Al ₂ O
It was found that zirconia particles were refined and eluted in the _3- MnO-FeO-based glass layer. In addition, low melt penetration into the grain boundaries is observed throughout.

The phenomenon that zirconia is refined indicates that zirconia has been destabilized. CaO, which has been dissolved in zirconia particles as a stabilizer, is reduced to Al ₂ O ₃ , Si
It is presumed that it was eluted at the grain boundary by O ₂ , MnO, and the like.

Further, zirconia has a coagulant,
Al ₂ O ₃ , clay and the like are used, but it is quite possible that the sintering aid itself promotes destabilization.

Similar results are obtained when MgO-stabilized zirconia is used.

On the other hand, there is a method using a yttria-stabilized zirconia raw material which is difficult to destabilize.
No. 55257 discloses that 100 parts by weight of yttria-stabilized zirconia clinker contains at least one kind of alumina fine powder, metallic aluminum, phosphoric acid and phosphate in the range of 0.8 to 8 parts.
1700 ° C to 1900 ° C after kneading and molding
Is described.

[0015]

By using Y ₂ O ₃ as a stabilizing material, destabilization can be achieved with CaO or Mg.
Although improved over O, the durability is still insufficient.

[0016] That is, Y ₂ O ₃ is very expensive, Y ₂
The price of the zirconia raw material to which O ₃ is added is CaO or Mg.
Approximately 3 to 5 times that of O. Therefore, the durability is required to be at least 3 to 5 times that of CaO and MgO, but at present, the service time is at most 1.5 times and there is no merit of using an expensive yttria stabilized zirconia material. It is. Damage to the refractory for casting is mainly caused by erosion, and the same applies to yttria-stabilized zirconia.

In the casting nozzle stabilized with Y ₂ O ₃ , a crack is observed in the vicinity of a coarse grain of 1 to 2 mm when the cross section of the used product is viewed, and a grain boundary is formed depending on the sintering aid used. Low melt infiltration into the steel and destabilization were observed, and when used under relatively strong thermal shock conditions, cracks in the inner hole were observed. In other words, the penetration of the low melt into the cracks and grain boundaries is the starting point, and the zirconia raw material is eluted.

Accordingly, an object of the present invention is to provide a yttria-stabilized zirconia, a zirconia-based casting refractory having improved corrosion resistance, spalling resistance and the like and excellent durability.

[0019]

SUMMARY OF THE INVENTION The present invention comprises a 50 to 97 wt% yttria stabilized zirconia material of Y ₂ O ₃ containing 10 wt% as a raw material powder, the unstabilized zirconia feedstock 2-40 Weight% and alumina fine powder 0.1 ~
It is a zirconia refractory for casting containing at least 98% by weight of a raw material consisting of 10% by weight (Claim 1).

The yttria-stabilized zirconia raw material containing 1 to 10% by weight of Y ₂ O ₃ and the unstabilized zirconia raw material having a particle size of more than 0.5 mm are 8% by weight or less. Item 2. The zirconia refractory for casting according to Item 1 (Item 2).

With respect to the particle size of the yttria-stabilized zirconia raw material containing 1 to 10% by weight of Y ₂ O ₃ and the unstabilized zirconia raw material, the particle size exceeding 0.5 mm is not more than 8% by weight,
0.5 mm or less and 0.01 mm or more are 10 to 45% by weight,
The zirconia refractory for casting according to claim 1 or 2, wherein 30 to 70% by weight is less than 0.01 mm and the particle size of the alumina fine powder is 0.1 mm or less (Claim 3). ).

The weight of the refractory for zirconia casting is 0.1
The weight is between 10 kg and 10 kg.
Or the zirconia refractory for casting according to claim 3 (claim 4).

[0023] The refractory for zirconia casting according to claim 1, wherein the alumina-based fine powder has an Al ₂ O ₃ content of 98% or more. Section 5).

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The yttria-stabilized zirconia raw material used as the raw material powder has a Y ₂ O ₃ content of 1 to 10%.
% By weight, and can be used in either partially stable or completely stable form. Further, either electrofused or sintered materials may be used. If Y ₂ O ₃ is less than 1% by weight, it does not contribute to stabilization,
If the content exceeds 10% by weight, the stabilization of zirconia is not affected, and conversely, the corrosion resistance is reduced due to the increase of the Y ₂ O ₃ component, which is not preferable.

Unstabilized zirconia includes CaO, MgO
Alternatively, an electrofused raw material, a sintered raw material or a natural raw material which is not stabilized by a stabilizer such as Y ₂ O ₃ and has a purity of 95% by weight or more can be used. In the present invention, a yttria-stabilized zirconia raw material and an unstabilized zirconia raw material are used in combination for imparting spalling resistance.

When the yttria-stabilized zirconia raw material is
Relative to 97% by weight, by combining the unstabilized zirconia material 2 to 40 wt% as a lower ZrO ₂ thermal expansion reduces the thermal expansion and unstabilized zirconia and yttria-stabilized zirconia expansion coefficient different As a result, micro-cracks are generated to lower the elastic modulus, and in addition to the reduction in expansion coefficient, the thermal shock resistance is improved due to the lower elastic modulus.

On the other hand, alumina-based fine powder is used as a sintering aid. Various sintering aids have been studied, including alumina, but when used as a refractory for casting and added to yttria-stabilized zirconia, it is most effective to use alumina-based fine powder raw materials. It is.

That is, in actual use, since the low-melting-point slag of the SiO ₂ —Al ₂ O ₃ —MnO—FeO system generated from steel penetrates, the sintering aid has as high a melting point as possible and Y It is desirable that a material containing Al ₂ O ₃ as a main component is less likely to generate a low melt even when reacted with ₂ O ₃ and has a high effect as a sintering aid.

On the other hand, conventional examples include zirconia sol, zirconia, zirconium trichloride and the like, but these have poor sinterability and insufficient strength after firing as compared with alumina fine powder.

Accordingly, alumina-based fine powder is the most excellent stabilizer for yttria-stabilized zirconia used in continuous casting.

As the alumina-based fine powder, a fine powder raw material having an Al ₂ O ₃ content of 75% by weight or more is preferable.
As components other than l ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ ,
Raw materials composed of one or more of MgO and CaO can be used. Further, Al ₂ O ₃ and SiO ₂ are added so that the proportion of Al ₂ O ₃ added as a sintering aid is 75% by weight or more.
_{One or two} of ZrO ₂ , TiO ₂ , MgO, CaO
It is also possible to add a mixture of a plurality of raw materials containing at least seeds.

When the alumina fine powder having an alumina content of 95% by weight or more is used among these alumina fine powders, the most excellent effect is obtained in terms of corrosion resistance. As the alumina-based fine powder having an alumina content of 95% by weight, calcined alumina,
Such materials include sintered alumina and fused alumina. Since the alumina-based fine powder is added as a fine powder and is present at the grain boundary of the zirconia particles, it greatly affects the corrosion resistance. When used as a refractory for casting, SiO ₂ —Al ₂ O ₃ —MnO—
The higher the purity of Al ₂ O ₃ , the more difficult it is to generate a low melt with respect to the penetration of the low melt of the FeO system, so that the corrosion resistance is excellent.

Further, the alumina fine powder is used with a particle size of 100 μm or less. Since the purpose of using the alumina-based fine powder is a sintering aid, it needs to be widely and uniformly present at the grain boundaries of the zirconia raw material.

On the other hand, the conventional zirconia refractories are, for example, disclosed in Japanese Patent Application Laid-Open No.
40% by weight of 0.4 mm coarse particles are used. The reason for this is that by adopting a particle size configuration widely distributed from coarse particles to fine powders, a non-uniform structure is obtained and spalling resistance is imparted. Refractories are generally considered to have such a non-uniform structure.

However, when a used product produced by adding a sintering aid to the yttria-stabilized zirconia raw material was observed, cracks were observed around the coarse particles, and the structure around the coarse particles was found. Is insufficient, and a phenomenon in which a low melt permeates around the cracks and coarse particles is observed.

Further, when the structure of the material to which the sintering aid was added was observed after firing, similar cracks were observed. The cracks were more remarkable as the amount of the sintering aid added increased. .

When no sintering aid is added, almost no firing shrinkage is observed. However, when the sintering aid is added, firing shrinkage of 1 to 5% occurs depending on the amount of addition, and this firing shrinkage occurs in the fine powder region. It was presumed that cracks occurred around the coarse grains.

[0038] Then, when an alumina-based sintering additive was added, the optimum particle size configuration for suppressing cracks due to firing shrinkage was also studied.

As a result, the raw material particle size affecting the crack exceeds 0.5 mm, and the ratio of the zirconia raw material particles exceeding 0.5 mm is not more than 8% by weight of the whole. found.

For zirconia raw material particles having a size of 0.5 mm or less, the zirconia raw material particles having a size of 0.5 mm or less and
30 to 70% by weight is preferable if it is less than 0.01%.

If the thickness is 0.5 mm or less and 0.01 mm or more and less than 10% by weight, the structure becomes too dense and the spalling resistance is reduced, and the 0.5 mm or less and 0.01 mm or more exceeds 45% by weight. The structure becomes porous and the corrosion resistance is reduced. On the other hand, if the content is less than 0.01 mm, the sintering is insufficient and the strength is low if the content is less than 30% by weight.
If less than 70% by weight, the structure becomes too dense and the spalling resistance decreases.

In order to enhance the corrosion resistance effect, the purity of the raw material used is preferably as high as possible. However, in the present invention, the refractory raw material powder in which the total amount of yttria-stabilized zirconia, unstabilized zirconia and alumina-based fine powder is 98% by weight or more is used. The desired effect can be obtained by using. That is, unavoidable components are observed up to 2% by weight. A binder or the like is added to these raw material powders, kneaded, and then fired at 1600 ° C. or more after molding to obtain a zirconia refractory for casting.

On the other hand, the refractory for zirconia casting of the present invention preferably has a product weight in the range of 0.1 to 10 kg in the case of the particle size constitution described in claims 2 and 3.

The refractory for zirconia casting according to the second and third aspects of the present invention is fired at a high temperature to form a sintered bond in which zirconia grains of a fine powder material are bonded to each other. Compared with refractories, they have a uniform structure composed of fine powder without using coarse particles, and thus have poor spalling resistance.

Therefore, in order to sufficiently bring out the effect of improving the corrosion resistance, a small shape that is not easily affected by spalling is preferable.

Normally, it is a cylindrical refractory through which molten steel passes through the inner hole. In this case, a refractory of up to 10 kg can be used without any problem. The effect of this comes out.

Specific applications include open nozzles,
A refractory or stopper head mounted in the inner hole of the casting nozzle is suitable.

When the weight exceeds 10 kg, for example, in the case of a plate brick main body, the spalling resistance can be improved by using coarse particles.

[0049]

【Example】

Example 1 In the following Examples and Comparative Examples, as an yttria-stabilized zirconia raw material, an electrofused raw material having a Y ₂ O ₃ content of 5% by weight was used, and as unstable zirconia, a natural raw material containing 98% by weight of ZrO _2. And the calcined alumina has an Al ₂ O ₃ content of 99% by weight.
And a particle size of 44 μm or less.

Table 1 shows the results of an investigation on the effect of the zirconia raw material addition rate.

[0051]

[Table 1] A predetermined composition shown in Table 1 was kneaded with an organic binder in a kneader, formed into a refractory shape of 230 × 110 × 60 mm by a hydraulic press, dried, and fired at 1700 ° C. to obtain a test sample.

The erosion test uses rotary erosion, and 1600
Two cycles were carried out, with one cycle being one hour at a temperature of 1 hour. The slag used in the test was SiO ₂ = 39.8% by weight, Al ₂ O
₃ = 12% by weight, MnO = 23.5% by weight, CaO =
7.6% by weight, MgO = 6.4% by weight Other FeO, F
It is composed of e ₂ O ₃ and trace impurities. In addition, 20 pieces of SUS304 of 30 mm cubic were simultaneously put together with the slag, and physical wear was also evaluated. The sample after the test was cut, and the erosion depth and the slag infiltration depth were measured. The erosion depth and the slag infiltration depth are indices when Comparative Example 5 is set to 100. If the number is 100 or less, the corrosion resistance is good, and if it is 100 or more, the corrosion resistance is inferior.

The spalling test was performed at 20 × 20 × 80.
The test piece cut into mm was put into an electric furnace at 1500 ° C., held for 10 minutes, taken out and examined for cracks.

Example 1 uses a mixture of 95% by weight of yttria-stabilized zirconia, 3% by weight of unstabilized zirconia, and 2% by weight of calcined alumina. The unstabilized zirconia of Comparative Example 1 was added. Cracking was not observed after the spalling test as compared with those not performed, and spalling resistance was improved by using unstabilized zirconia.

Examples 2 to 5 differ in the mixing ratio between the yttria-stabilized zirconia raw material and the unstabilized zirconia raw material, but are within the scope of the present invention, and are compared with the conventional yttria-stabilized zirconia. The results were excellent in corrosion resistance and spalling resistance. In Comparative Example 2, the yttria-stabilized zirconia raw material and the unstabilized zirconia raw material were used, and in Comparative Example 3, the unstabilized zirconia raw material was out of the scope of the present invention. Could not be collected.

Comparative Example 4 was a case where no unstabilized zirconia raw material was used, but the spalling resistance was reduced due to densification by a sintering aid.

In Examples 1 to 5, densification was performed with a sintering aid. However, since unstabilized zirconia was used, spalling resistance was improved, and spalling resistance was reduced due to densification of the structure. Is preventing.

Table 2 shows the results of studies on the amount and type of the sintering aid.

[0059]

[Table 2] Table 3 shows the chemical composition of the sintering aid used in the examples.

[0060]

[Table 3] In Example 6, 0.5% by weight of calcined alumina was used as a sintering aid, and it was found that the porosity was reduced and denser than in Comparative Example 7 in which calcined alumina was not used at all. . Examples 7 to 10 are also within the scope of the present invention, and are denser than those of Comparative Example 7. At the same time, by adding unstabilized zirconia, corrosion resistance is improved without lowering spalling resistance.

In Examples 11 to 13, mullite fine powder, alumina zirconia fine powder and spinel fine powder were used as sintering aids, but the results were excellent in corrosion resistance.

In Comparative Example 8, the calcined alumina was 12% by weight, which was out of the range of the present invention. The porosity was 11%, and the structure was too dense, so that the spalling resistance was lowered.

In Comparative Example 9, where clay was used as a sintering aid, the erosion depth was large and the corrosion resistance was poor.

In Comparative Example 10, zirconia sol was used as a sintering aid, and the porosity was high, the effect of densification was small, and the corrosion resistance was unsatisfactory.

Table 4 shows the particle size composition of the raw materials.

[0066]

[Table 4] In Examples 14 to 17, none of the raw materials had a particle size of 0.5 mm or more, and even when the structure of the fired product was observed, the structure was good without cracks around the coarse particles. In Examples 18 to 20, 5% and 7% of 0.5 mm or more were used. However, although microcracks were observed at 7%, they were within the practical range.

On the other hand, in Comparative Example 11, the raw material particle size of 0.5 mm or more exceeded 10% by weight, and when the cut surface of the fired product was observed, cracks were observed in the vicinity of coarse particles and corrosion resistance was poor.

Table 5 shows the size of the refractory for zirconia casting of the present invention.

[0069]

[Table 5] According to the second and third aspects of the present invention, the grain size is reduced as compared with the prior art, and the structure is densified by using a sintering aid. The problem becomes worse. Therefore, there is an optimum size for effective use in actual use.

In Table 5, each nozzle having a cylindrical shape as shown in FIG. 1 and having the dimensions shown in the table was manufactured and evaluated by cracking of the outer surface and cut surface after firing and a spalling test. . Table 4 used the formulation of Example 14.

In the spalling test, the inner hole was 1500 ° C.
Of molten steel was poured, and the occurrence of cracks in the outer peripheral portion was observed.

In Example 21, the outer diameter was 50 mm and the inner diameter was 40 m.
m, height 30mm, weight 0.1kg cylindrical shape,
No cracks were observed on the outer surface and the cut surface after firing, and no cracks were observed on the appearance after the spalling test.

Examples 22 to 25 are also within the scope of the present invention. In Examples 24 and 25, there was no problem although microcracks were observed only in the outer peripheral portion after the spalling test. Further, in Examples 23 and 24, they were mounted on a tundish as an open nozzle and used continuously for 8 hours, but the spalling resistance was good. Comparative Example 12 weighed 13.3 kg, which was out of the range of the present invention. After the spalling test, cracks were generated from the outer peripheral surface to the inner hole, and were poor.

Using the composition of Example 14, an open nozzle of about 3 kg was manufactured, mounted on an actual tundish, and 20 nozzles were used. The conventional CaO-stabilized zirconia (Comparative Example 5) was on average 5 hours. For 17 hours, the durability was greatly improved.

[0075]

As the raw material powder according to the present invention Y ₂ O ₃ 1 to 10 wt%
50-97 of the yttria-stabilized zirconia raw material
Wt% and 2-40 wt% of unstabilized zirconia raw material
And a total of 98% by weight or more of a raw material composed of 0.1 to 10% by weight of alumina fine powder can improve the corrosion resistance and spalling resistance, and the durability of the casting nozzle and stopper. Improved.

In the yttria-stabilized zirconia raw material containing 1 to 10% by weight of Y ₂ O ₃ and the unstabilized zirconia raw material, those having a particle size of more than 0.5 mm are reduced to 8% by weight or less, so that sintering aid is obtained. Even if the agent is added, the durability of the casting nozzle and the stopper is improved in order to suppress the generation of cracks due to firing shrinkage.

In the particle size of the yttria-stabilized zirconia raw material containing 1 to 10% by weight of Y ₂ O ₃ and the unstabilized zirconia raw material, those having a particle size exceeding 0.5 mm are not more than 8% by weight.
By setting the particle size of 0.5 to 0.001 mm to 92 to 100% by weight and the alumina fine powder to 100 to 0.1 μm,
A sintered body having a dense structure was obtained, and the durability of the casting nozzle and stopper was improved.

The weight of the refractory for zirconia casting is 0.1
By setting the weight to 10 kg, the characteristics of the material to be used can be utilized, and the durability is improved.

When the alumina fine powder has an Al ₂ O ₃ content of 98% by weight or more, the composition of the grain boundaries can be made higher in melting point, and the corrosion resistance is improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a nozzle.

Claims (5)

[Claims] 1. A Y ₂ O ₃ as a raw material powder 1 to 10 wt%
50-97 of the yttria-stabilized zirconia raw material
Wt% and 2-40 wt% of unstabilized zirconia raw material
Characterized in that a total of 98% by weight or more of a raw material comprising 0.1 to 10% by weight of alumina fine powder is used. 2. A raw material of yttria-stabilized zirconia and a raw material of unstabilized zirconia containing 1 to 10% by weight of Y ₂ O ₃ having a particle size exceeding 0.5 mm is 8% by weight or less. The refractory for zirconia casting according to claim 1, wherein the refractory is used. 3. The particle size of the yttria-stabilized zirconia raw material containing 1 to 10% by weight of Y ₂ O ₃ and the unstabilized zirconia raw material has a particle size exceeding 0.5 mm of 8% by weight or less and 0.5 mm or less. The zirconia-based casting according to claim 1 or 2, wherein the diameter of the alumina-based fine powder is 10 to 45% by weight, the particle size of the alumina-based fine powder is 0.1 to 10% or less. For refractories. 4. A zirconia casting refractory having a weight of 0.
The zirconia refractory for casting according to claim 2 or 3, wherein the refractory weight is 1 to 10 kg. 5. An alumina fine powder having an Al ₂ O ₃ content of 98%
The refractory for zirconia-based casting according to claim 1, wherein the refractory is used.