JP2966009B2 - High corrosion resistance, high spalling resistance ZrB (2)-Manufacturing method of graphite refractories - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the production of ZrB ₂ -graphitic refractories suitably used for continuous casting of molten metal, especially molten iron.

[Conventional technology]

Refractory for continuous casting of molten iron is one of the most important refractories in the process of obtaining the final product of iron and steel, and is used for preventing oxidation, scattering and measuring temperature of molten iron after melting or refining. Have been.

Characteristics required for such refractories for continuous casting include high erosion resistance due to being exposed to severe wear and erosion under high temperature due to the flow of molten iron, Because it is rapidly heated, it has thermal shock resistance, and in immersion nozzles and long nozzles,
It must have high corrosion resistance because it comes into contact with molten powder or molten slag in a mold or tundish.

As the material of the refractory for continuous casting, alumina-carbon, zirconia-carbon or the like is used, and a combination of alumina powder or zirconia powder having high fire resistance and carbon powder having excellent thermal conductivity is used. ,
A product excellent in corrosion resistance and spalling resistance has been obtained, and has recently become the mainstream in multiple continuous casting.

In addition, ZrB ₂ quality has been used to further improve corrosion resistance to high oxygen steel, powders and slags. When this ZrB ₂ material is used, ZrB ₂ itself has a disadvantage that the sinterability is very poor, and measures for improving this point are disclosed in JP-A-61-21979 and JP-A-61-72687. And JP-A-62-230674, JP-A-62-230675, JP-A-62-288171, and the like.

However, in any case, in firing the compound material molded body, at least 2000 ° C. under normal pressure, 1900 ° C. or more under a pressurized atmosphere, and an inert atmosphere such as Ar, He as a firing atmosphere is required, Therefore, there is a disadvantage that special baking equipment is required for the production.

For ZrB ₂ quality composite sintered body, no baking equipment is required,
The method of manufacturing a ZrB ₂ containing refractories at low cost, the present inventor has been disclosed in JP-A-63-10071, applying to the spalling resistance of the refractory containing the graphite as the material Can not.

Further, there are disclosed methods in JP 62-288171 discloses for those having a composite composition of the ZrB ₂ and carbon, which is very specific as the production method of firing conditions refractory in the method There is a problem.

The problem to be solved in the present invention is to find a production method which solves the above-mentioned problems in producing a ZrB ₂ -containing refractory excellent in corrosion resistance and spalling resistance.

[Means for solving the problem]

The method for producing a ZrB ₂ -graphitic refractory of the present invention comprises the following steps: 5 to 25% by weight of graphite powder, 1 to 12% by weight of a mixed powder of metallic aluminum and metallic silicon or an alloy powder or a mixed powder of both. 0.5% to 10% by weight of Si, the remainder is particle size + 2mm
Of 30% by weight or less and 20 to 9 of particles having a particle size of +0.044 mm
A resin binder is kneaded or granulated into a composition comprising ZrB ₂ in the range of 0% by weight, and then molded, and then fired at 1300 ° C. or more in carbon powder.

[Action]

Graphite powder, spalling resistance, but is formulated for imparting stability ZrB _2, when the amount added is less than 5 wt%, spalling resistance, improvement in the corrosion resistance can not be expected. On the other hand, if the amount of the graphite powder exceeds 25% by weight, the spalling resistance is reduced, and the corrosion resistance is also reduced, unlike ordinary refractories.

As the graphite powder, natural scale graphite, natural earth graphite, quiche graphite, graphite electrode waste, and the like can be used. It is necessary to select the particle size and purity in consideration of spalling resistance, corrosion resistance, oxidation resistance, and the effectiveness of added Al.

Al generates AlN during firing to promote sintering of the ZrB ₂ -graphite powder. Also to prevent degradation of the ZrB ₂ from the oxygen contained in trace amounts in the firing atmosphere. If the amount is less than 1% by weight, corrosion resistance, oxidation resistance, strength, and spalling resistance decrease. 12
If the content is more than 10% by weight, the spalling resistance decreases. Corrosion resistance also decreases because the amount of alumina formed by oxidizing AlN on the working surface increases and the amount of reaction with zirconia formed by oxidizing ZrB ₂ increases.

Si reacts with carbon from the binder resin and carbon in the firing atmosphere during firing to form β-SiC, and ZrB ₂
Promotes the binding action during sintering of graphite powder with
Although the reason is not well understood, it has a function of suppressing digestion by AlN. If the added amount of Si is less than 0.5% by weight, the effect of preventing digestion will be insufficient. If it exceeds 10% by weight, β-
As the amount of SiC increases, the corrosion resistance and spalling resistance decrease.

Regarding the addition form of Ai and Si, it is possible to use a mixed powder of each metal, an alloy powder, or a mixed powder of both.

The grain size composition of ZrB ₂ is extremely important in terms of corrosion resistance and spalling resistance, which may be said to determine the performance of fire resistance for continuous casting.

If the particle size of +2 mm exceeds 30% by weight, the thermal expansion is affected by ZrB _{2 which} is larger than graphite, and the spalling resistance is reduced. On the other hand, if the particle size of +0.044 mm is less than 20% by weight, the fine powder becomes excessive and the spalling resistance and the corrosion resistance are reduced. If the content exceeds 90% by weight, fine powder becomes insufficient, and the spalling resistance decreases.

It is more preferable to granulate in order to uniformly disperse ZrB ₂ and graphite having greatly different specific gravities during the production, but the present invention is not limited to this.

Further, as a resin binder to be used, a phenol resin, a furan resin, an acrylic resin, an imide resin, a pitch and the like can be used, but a phenol resin is desirable from the viewpoint of cost and workability.

For forming, it is desirable to use CIP (normal temperature isostatic press) from the viewpoint of uniformity.
An oil press or the like can be optionally used.

Firing the molded body, ZrB ₂ - to prevent oxidation of the graphite powder, Al
In order to form a bond by N, β-SiC, it is fired at 1300 ° C. or more in carbon powder.

As the carbon powder, any material may be used as long as it keeps the firing atmosphere in a non-oxidizing atmosphere, such as scaly graphite, coke powder, anthracite powder, and graphite electrode powder. By firing in such an atmosphere, AlN from Al, proceeds generated a beta-SiC from Si, ZrB ₂ - is promoted sintering of the graphite powder, sufficient by firing at 1300 ° C. or higher temperature A refractory having strength can be obtained.

However, if the firing temperature is lower than 1300 ° C., AlN
Is not sufficient, and AlC ₃ formed before the formation of AlN
Remain, the bonding strength of the sintered body due to AlN decreases, and the digestion resistance decreases due to the formation of Al ₄ C ₃ which is more digestible than AlN.

Regarding firing, firing in a nitrogen stream is also possible.
Although the cost is higher than firing in carbon powder by the nitrogen gas cost, the cost is significantly lower than firing in Ar or He gas flow.

Since the sintering temperature does not require a particularly high temperature of 1300 ° C or higher, sintering using ordinary SiC sheath is possible, and sintering equipment that has been used for ordinary refractory mass firing can be used. There is also an advantage that it is.

〔Example〕

Hereinafter, examples of the present invention are shown together with comparative examples. Rings having an inner diameter of 150 mm, an outer diameter of 210 mm, and a length of 250 mm were formed from the compounds shown in Tables 1 to 8 by CIP and fired at 1450 ° C. in carbon powder.

As shown in Table 1, compounding graphite with ZrB ₂ is inferior in strength to compounding with BN, but excellent in corrosion resistance, spalling resistance, and oxidation resistance, which are the most problematic in practical use. I have. The difference in spalling resistance can be explained by the difference in the size of both scales, but the corrosion resistance and oxidation resistance can be determined to be due to the compounding.

Similarly, when the addition amount of the graphite powder is less than 5% by weight, the corrosion resistance and spalling resistance are greatly reduced, and when it is more than 25% by weight, the corrosion resistance and spalling resistance are greatly reduced. When the added amount of the graphite powder exceeds 25% by weight, the spalling resistance is significantly different from other graphite composite compounds.

From Table 2, it can be seen that when the amount of Al powder added is small, the corrosion resistance, spalling resistance, strength, and oxidation resistance decrease. It can be seen that when the amount of the Si powder added is more than 10% by weight, the corrosion resistance and spalling resistance decrease.

As can be seen from Table 3, when the amount of +2 mm of the ZrB ₂ powder exceeds 30% by weight, the spalling resistance decreases. Also +0.
If the amount of 044 mm is less than 20% by weight, the corrosion resistance and spalling resistance decrease. If it exceeds 90% by weight, the spalling resistance decreases.

It is a feature of the ZrB ₂ composite that the aggregate has a coarser grain size and lower spalling resistance.

As can be seen from Table 4, if the added amount of the Si powder is less than 0.5% by weight, the digestion resistance is greatly reduced, probably because the amount of β-SiC formed is small. As long as the amount of AlN in the present invention is large, even if the amount is large, the amount of the added Si powder is 0.5% by weight.
If it is above, a decrease in digestion resistance is small, and there is no problem.

Similarly, as for the Si metal powder, a mixed powder, an alloy powder or a mixture of both can be used.

The substrate of Example 2 shown in Table 1 was fired under each firing condition shown in Table 5. Table 5 also shows the results. However, for Comparative Example 13, the shape shown in Note * A in Table 5 was cut out and fired due to the restriction on the size of the kiln. Comparative Example 13
Was fired using a special firing furnace capable of high temperature firing.

As can be seen from Table 5, when the firing temperature is lower than 1300 ° C.,
_{Because 4} C ₃ remained and Al ₄ C ₃ was far more digestible than AlN, digestion after firing was intense, cracks occurred after cutting data, and samples could not be taken.

Similarly, firing can be performed even in a nitrogen stream if attention is paid to the oxygen partial pressure of impurities. Even in a nitrogen stream, carbonization of Si occurs at a lower temperature than nitridation, so carbon from the binder resin and Si
Preferentially reacts to generate β-SiC, and there is no significant difference in the physical properties of the difference in the firing conditions between the nitrogen gas stream and the carbon powder.

The inner diameter of the straight body part is φ70 mm and the outer diameter is φ110 mm. The long nozzle is shown in Comparative Example 2, Example 3, Comparative Example 3, Example 7 shown in Table 3, and Comparative Example 10 shown in Table 4 shown in Table 1. Manufactured. Table 6 shows the results.

For users who fix the interface between powder and metal, immersion nozzles having a zirconia-graphite thickness of 18 mm were used in Examples 2 shown in Table 1, Comparative Examples 4 shown in Table 2, and Table 5 shown in Table 2.
Used in Example 16 shown in FIG. Table 7 shows the results.

Table 3 shows a continuous temperature protection tube with an inner diameter of 15 mm and an outer diameter of 45 mm.
Comparative Example 9 and Example 8 shown in Table 1, Example 2 shown in Table 1, and Example 14 shown in Table 4. Table 8 shows the results.

As can be seen from Table 6, problems of digestion of AlN can be prevented by the present invention, and corrosion resistance and spalling resistance are sufficiently exhibited.

Table 6 shows that the present invention provides a refractory having both high corrosion resistance and high spalling resistance to steel.

As shown in Table 7, a refractory having both high corrosion resistance and high spalling resistance to powder was obtained according to the present invention.

Table 8 shows that the present invention provided a refractory having both high corrosion resistance and high spalling resistance to slag.

Although the actual use cases were described only for long nozzles, immersion nozzles, and continuous temperature measurement protection tubes, the examples relate to molten metals that can take advantage of high corrosion resistance, high spalling resistance, and high oxidation resistance to slag, powder, steel, etc. If it is a refractory, it is not limited to the above.

〔The invention's effect〕

Refractory obtained by the present invention has a sufficiently Ikaseru high spalling resistance and high corrosion resistance of ZrB _2.

A method for manufacturing a refractory according to the present invention, for the preparation of ZrB ₂ quality refractory, without the need for special burning facility, it is possible to obtain an excellent refractory corrosion resistance and spalling resistance at a low cost.

Claims (2)

(57) [Claims] (1) 5 to 25% by weight of graphite powder, 1 to 12% by weight of Al, 0.5 to 10% by weight of Si, and 30% by weight or less of particles having a particle size of +2 mm, and the formulations .044mm particles consisting ZrB ₂ Metropolitan which is within the range of 20 to 90 wt%, after the resin binder are kneaded or granule, ZrB ₂ fired at 1300 ° C. or more carbon powder - graphite Manufacturing method of quality refractories. 2. The graphite powder is 5 to 25% by weight, Al is 1 to 12% by weight, Si is 0.5 to 10% by weight, and the balance is 30% by weight or less for particles having a particle size of +2 mm and a particle size of + 0%. A resin binder was kneaded or granulated into a composition comprising .044 mm particles of ZrB ₂ in the range of 20 to 90% by weight, and then molded in a nitrogen stream.
A method for producing a ZrB ₂ -graphitic refractory which is fired at a temperature of 00 ° C. or higher.