JPH0826817A - Magnesia carbonaceous refractory brick - Google Patents

Abstract

PURPOSE:To produce a lining refractory brick for a molten steel ladle or a secondary refining container which is one of steel manufacturing process apparatuses. CONSTITUTION:This magnesia carbonaceous refractory brick comprises a blending composition consisting essentially of 10-25wt.% alumina-based raw material, 5-20wt.% carbonaceous raw material, 2-10wt.% silicon carbide-based raw material, 1-5wt.% metallic powder and the remainder of magnesia-based raw material. The magnesia carbonaceous refractory brick is capable of relaxing the expanding stress by using the magnesia-based raw material, alumina-based raw material, carbonaceous raw material, silicon carbide-based raw material and metallic powder in the blending ratio. Thereby, joint fusion loss is prevented. Since other various properties are also excellent, the furnace life is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory brick for lining such as a molten steel ladle and a secondary refining vessel, which is one of steelmaking process equipment.

[0002]

BACKGROUND ART Conventionally, magnesia carbonaceous refractory bricks have been used as refractory bricks for linings such as molten steel ladle and secondary refining vessel. When magnesia carbonaceous refractory bricks are used as refractory bricks for linings such as molten steel ladle and secondary refining vessel, there is a tendency that preceding melting damage of joints occurs. It is presumed that the cause of the preceding erosion of the joint is the cracking of the cell due to the expansion stress of the brick. If various salts such as phosphates, borates, silicates, glass, and low-melting substances such as frits are added to alleviate this expansion stress, even if the preceding erosion damage at the joints can be improved, Corrosion resistance is deteriorated due to the decrease in hot strength and the durability is not improved.

Also, magnesia containing dolomite
Dolomite-carbonaceous refractory brick is also considered. Even in this case, the preceding erosion of joints can be improved, but during use, it is unstable because it absorbs moisture in the atmosphere to cause a digestive reaction. As a solution to the problem of deterioration in hot strength of bricks, magnesia carbonaceous refractory bricks containing Al, Si, Mg,
An example of adding a metal powder such as Al-Mg is disclosed in JP-A-58-58.
185475 and Japanese Patent Laid-Open No. 58-190868.

[0004]

However, although it is effective for improving the hot strength of bricks, it causes a decrease in heat-resistant spalling property, so that the problem of pre-melting of joints still exists. There is. Regarding the form of brick meltdown, not the entire operating surface in contact with the molten steel is melted down, but the meltdown near the joint of the brick is large. That is, due to the expansion stress of the brick, chipping of the joint corner of the brick occurs first. After that, the chipped portion develops due to the drop impact of the molten steel. When the size of the joint melt loss portion reaches the life criterion, there is a problem that it cannot be used any more, no matter how large the size of the brick elsewhere. Therefore, in order to reduce the cost of the furnace material by improving the life, it is required to develop a product that improves the preceding melting loss of the joint portion.

[0005]

Therefore, the inventors of the present invention have investigated the cause of damage to bricks after use in an actual furnace, conducted an offline test,
Through the confirmation test in an actual furnace, we tried to develop a product that alleviates the expansion stress of brick, which is the main cause of joint melting loss, and has excellent properties such as expandability, oxidation resistance, and heat spalling resistance. And, by using magnesia raw material, alumina raw material, carbonaceous raw material, silicon carbide raw material, and metal powder in a specific mixing ratio, the expansion stress of the brick is relaxed, and a product having other various properties is excellent. Was obtained. As a result of an actual machine test of this product, improvement of joint melt loss was verified, and the present invention was completed.

That is, according to the present invention, the alumina raw material: 10
-25 wt%, carbonaceous raw material: 5 to 20 wt%, silicon carbide raw material: 2 to 10 wt%, metal powder: 1 to 5 wt%, the balance is a magnesia carbonaceous refractory brick having a blending composition mainly composed of a magnesia raw material Is. The present invention is intended to prevent stress fracture without impairing the corrosion resistance of bricks, in order to improve the joint preceding melting loss of refractory bricks for lining such as molten steel ladle and secondary refining vessel.

Hereinafter, the present invention will be described in more detail. The type of magnesia raw material that can be used in the present invention is not particularly limited, but known ones such as artificial electrofused magnesia and sintered magnesia are known. The particle size is adjusted to coarse particles, medium particles, and fine particles so that a close-packed structure can be obtained, similar to conventional magnesia carbonaceous refractory bricks. Mixing ratio is preferably 40
˜80 wt%. The magnesia raw material is an aggregate having a high melting point and a high density, and if it is less than 40 wt%, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 80 wt%, the expansion rate becomes high and the heat-resistant spalling property is lowered, so that the joint melt loss becomes large, which is not preferable.

As the alumina raw material, general fused alumina and sintered alumina are mainly used. The particle size is not particularly limited, but it is preferable to use fine particles of 1 mm or less in order to facilitate generation of the magnesia raw material and spinel mineral during use. The mixing ratio is 10 to 25 wt%. 1
If it is less than 0% by weight, the residual expansion rate is insufficient and the joint is opened during use. Further, if it exceeds 25 wt%, the corrosion resistance is lowered.

Specific types of carbonaceous raw materials include scaly graphite,
It is one or more selected from earth-like graphite, artificial graphite, coke, carbon black, calcined anthracite, electrode scrap, and the like, and it is preferable to use a high-purity graphite from the viewpoint of corrosion resistance at high temperatures. The carbonaceous raw material prevents penetration of molten steel and slag and improves corrosion resistance. It also has the feature of improving the heat resistant spalling property. Mixing ratio is 5
˜20 wt%. If it is less than 5% by weight, hot strength and corrosion resistance are satisfactory, but the expansion coefficient is not sufficiently reduced, and as a result, the heat-resistant spalling property is insufficient. Also, 20w
This is because if it exceeds t%, wear due to molten steel increases and corrosion resistance remarkably decreases.

A known synthetic material can be used as the silicon carbide raw material, and it is preferable to use one having a SiC content of 90% or more. This is because the main component of impurities contained in the silicon carbide based material is free silica (SiO ₂ ), which causes transformation expansion and deteriorates the heat resistant spalling property. The silicon carbide material is effective in preventing oxidation and improving corrosion resistance, and also exerts a remarkable effect in relaxing expansion stress. The reason for these effects is that the low expansion of SiC itself and MgO-A
It is considered that this is due to the effect of the product of the reaction of the l ₂ O ₃ —SiC system. The blending ratio is 2 to 10 wt%. 2w
If it is less than t%, oxidation and melting loss increase, and the expansion stress also increases. Also, if it exceeds 10 wt%, the corrosion resistance is reduced.

The magnesia carbonaceous refractory brick of the present invention comprises
In addition to the above raw materials, it contains 1 to 5 wt% of metal powder. The specific type of the metal powder is one kind or two or more kinds selected from metal powders such as Al, Si, Mg, Cr and Fe or alloy powders thereof. If the metal powder is less than 1 wt%, the effect of improving the hot strength and the oxidation resistance is insufficient. Also, the metal powder is 5
If it exceeds wt%, the heat-resistant spalling property is deteriorated. In addition, the generation of charcoal during use tends to cause a digestion phenomenon, resulting in unstable brick quality.

In addition to the above raw materials, magnesia carbonaceous refractory bricks may be made of SiO ₂ , as long as the effect of the present invention is not impaired.
ZrO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , CaO, Si
₃ N ₄ , BN, metal fiber, ceramic fiber,
It is also possible to add an appropriate amount of fibers such as carbon fiber and glass.

The magnesia carbonaceous refractory brick can be obtained by the usual steps of kneading, molding and heating the above-mentioned compounds. For kneading, organic binders such as phenol resin, furan resin, pitch, tar, CMC, MC, PVA, or sodium silicate, aluminum sulfate, lignin sulfonate, magnesium sulfate, phosphate, etc. Inorganic binder is 2 to 5 on the whole composition
wt% can be added. The molding is performed by using, for example, an oil press or a friction press according to the purpose of the brick and the existing manufacturing equipment. After molding, for example, 200-6
Heat at 00 ° C. By this heat treatment, the brick prevents smoke and odor from the binder in the initial stage, and imparts the strength of the molded body by the effect of the binder. If necessary, reduction firing can be performed at about 1000 ° C.

[0014]

The magnesia carbonaceous refractory brick of the present invention provides a refractory brick excellent in durability with no joint damage in the combined action effect of each raw material of magnesia-alumina-silicon carbide-carbon-metal. The main effects of the raw materials are as follows. Magnesia is a main constituent with high fire resistance and high corrosion resistance. Carbon contributes to preventing penetration of molten steel, slag, etc. and improving heat-resistant spalling resistance. The metal powder contributes to strength development, antioxidation, and improvement of corrosion resistance. For these magnesia-carbon-metal systems, the action is the same as for conventional magnesia carbonaceous refractory bricks. When alumina is added to the magnesia-carbon-metal system, the residual expansivity is developed to reduce the joint opening that occurs during heating and cooling, thus preventing joint damage. Silicon carbide has a small expansion coefficient and has a function of remarkably reducing the expansion stress by the reaction product of magnesia-alumina-silicon carbide-carbon-metal. Further, it also contributes to the prevention of oxidation and the improvement of corrosion resistance and prevents joint damage.

[0015]

EXAMPLES Examples of the present invention and comparative examples will be shown below. Table 1 shows examples of the present invention, comparative examples and test results thereof.

[0016]

[Table 1]

In each of the examples, 5 wt% of a phenol resin was added as a binder to the composition shown in the table, and the mixture was kneaded with a kneader.
It was molded in a normal shape with a pressing force of g / cm ² . Then 300
What was heat-processed at 24 degreeC for 24 hours, and what was cooled was made into the sample. Using the specimens thus obtained, chemical analysis in the table, quality, hot strength, residual expansion coefficient, corrosion resistance, oxidation resistance,
A test was performed for heat resistant spalling.

Chemical analysis: According to JIS R2212-55. Apparent porosity, bulk specific gravity; according to JIS R2205-74. Hot strength: Hot bending strength was measured by a three-point bending test in an electric furnace at 1400 ° C. Residual expansion rate; 1500 ° C x 10 hours, 150 in electric furnace
It is a value after heat treatment at 0 ° C. × 20 Hr. However, in order to prevent oxidation, the test piece was heat-treated by putting it in a sheath filled with coke breeze. Corrosion resistance: The rotational erosion method was used to measure the erosion size (mm). The corrosion resistance test was conducted under the following conditions. Temperature and time: 1650 ° C × 200 minutes, erosion agent: steel 80% + converter slag (CaO / SiO ₂ = 3.0, Total
-Fe = 15%) 20%, oxidation resistance; A cubic test piece cut out from the test piece and having a side of 50 mm was subjected to oxidation firing at 1500 ° C x 10 hours. Then, the test piece was cut, and the dimensions of the whitened portion (oxidized portion) were measured. Heat-resistant spalling resistance: A test piece is immersed in molten steel at 1650 ° C. for 5 minutes and air-cooled for 15 minutes, which is defined as 1 cycle, and 1
The number of occurrences of cut loss was measured by performing 0 cycles. The test result was expressed as 10+, meaning that the number of cuts that did not occur after 10 cycles exceeded 10 cycles. Hot expansion stress; 50mm × 50m cut from the specimen
Place the m × 200mm test piece in the electric furnace sideways,
Fix both ends of the test piece. Then, the method was used in which the temperature was raised to 1600 ° C. and the expansion stress at the time of temperature rise was detected with a load cell.

As can be seen from the comparison between the examples of Table 1 and the comparative examples, it is clear that the examples are excellent in all properties of hot strength, corrosion resistance, oxidation resistance, and heat spalling resistance. . Comparative Example 1 is a case where the silicon carbide based material of Example 1 was removed, and the melting loss amount and the oxidation amount increased. Furthermore, as shown in FIG. 1, Comparative Example 1 is not preferable because the expansion stress increases. In Comparative Example 2, the amount of metal powder added is 0.5 w
When it is as small as t%, all of the hot strength, the amount of melting loss, and the amount of oxidation are clearly inferior to those of Example 2. Comparative Example 3
Is an example in which the mixing ratio of the alumina raw material is excessive, and the amount of erosion is increasing. Comparative Example 4 is an example in which the mixing ratio of the carbonaceous raw material is too small, and it can be seen that the heat resistant spalling property is remarkably lowered. Comparative Example 5 is an example in which the mixing ratio of the alumina raw material is too small, and the residual expansion coefficient is the lowest. Further, as shown in the table, it can be seen that there is no expansion after 1500 ° C. × 10 Hr. Comparative Example 6 is an example in which the blending ratio of the silicon carbide based material is excessive, the hot strength is lowered, and the amount of melting loss is increased.

FIG. 1 shows the measurement results of the expansion stress of Example 1, Example 2, Comparative Example 1 and Comparative Example 3 in Table 1. Comparative Example 1 has an abnormally large stress value. This is because no silicon carbide based material is used. Further, Comparative Example 3 has a low expansion stress, but is inferior in corrosion resistance, which is not preferable. On the other hand, Examples 1 and 2 have stable expansion stress and are excellent in various properties such as hot strength, corrosion resistance, and heat spalling resistance.

Actual machine test: Among the magnesia carbonaceous refractory bricks manufactured in the actual machine shape by a method substantially similar to that described in the above-mentioned Example, Example 1, Example 2 and Comparative Example 1 were actually 100 t. It was built in the side wall steel bath of the molten steel ladle, and operated under the conditions of molten steel temperature of 1610 ° C. and molten steel residence time of 100 minutes. The lifetimes of Example 1, Example 2, and Comparative Example 1 were 105 ch, 94 ch, and 71 ch, respectively. In relation to it, the opening width and depth of the joint between the bricks is 8 mm.
It was 0 mm, 13 mm · 13 mm, 45 mm · 40 mm. As described above, it was clear that the difference in life between Examples 1 and 2 and Comparative Example 1 was due to the difference in melting loss of the joints.
The building part is a part that is heavily worn by the impact of molten steel when receiving steel. As is clear from this result, the magnesia carbonaceous refractory brick obtained according to the present invention showed a remarkable improvement in joint melting loss even in an actual furnace and exhibited a sufficient effect.

[0022]

The magnesia carbonaceous refractory brick according to the present invention is excellent in hot strength, corrosion resistance and heat spalling resistance, as is clear from the above test results. Moreover, joint melting loss, which has been a problem in the past, has been improved, the life of the furnace has been improved by about 30%, and the cost of the furnace material has been reduced.

[Brief description of drawings]

FIG. 1 is a hot expansion stress curve showing the relationship between temperature and expansion stress.

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[Procedure amendment]

[Submission date] May 23, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

Actual machine test: Among the magnesia carbonaceous refractory bricks manufactured in the actual machine shape by a method substantially similar to that described in the above-mentioned Example, Example 1, Example 2 and Comparative Example 1 were actually 100 t. It was built in the side wall steel bath of the molten steel ladle, and operated under the conditions of molten steel temperature of 1610 ° C. and molten steel residence time of 100 minutes. The lifetimes of Example 1, Example 2, and Comparative Example 1 were 105 ch, 94 ch, and 71 ch, respectively. In relation to it, the opening width and depth of the joint between the bricks is 8 mm.
It was 0 mm, 13 mm · 13 mm, 45 mm · 40 mm. As described above, it was clear that the difference in life between Examples 1 and 2 and Comparative Example 1 was due to the difference in melting loss of the joints.
Furthermore, the bricks used in Examples 1, 2 and Comparative Example 1
Were built on the side wall slag line of the same molten steel ladle under the same conditions.
Started in. The lives of Examples 1, 2 and Comparative Example 1 are
They were 110 ch, 118 ch, and 72 ch, respectively.
In relation to it, the opening width and depth of the joint between bricks is 1
0 mm / 12 mm, 7 mm / 9 mm, 55 mm / 51 m
It was m. The surface of the brick is smooth, with no joint melting and
As a result, it is possible to greatly extend the life of the slag line.
I chose The building part is a part that is heavily worn by the impact of molten steel when receiving steel. As is clear from this result, the magnesia carbonaceous refractory brick obtained according to the present invention showed a remarkable improvement in joint melting loss even in an actual furnace, and exhibited a sufficient effect.

Claims (1)

[Claims] 1. Alumina raw material: 10 to 25 wt%, carbonaceous raw material: 5 to 20 wt%, silicon carbide raw material: 2 to 10
wt%, metal powder: 1 to 5 wt%, the remainder is a magnesia carbonaceous refractory brick having a blending composition whose main component is a magnesia raw material.