JP2020132487A - Production method of magnesia carbon brick for lining of steel refining furnace - Google Patents

Abstract

To provide a production method of brick for lining of steel refining furnace sufficient in damage reduction even when a heat processing temperature is 300°C or lower.SOLUTION: A production method of magnesia carbon brick for lining of steel refining furnace includes steps of: obtaining a compact by kneading and molding a compound containing a magnesia raw material, a graphite raw material, and a binder; heat treating the compact at a temperature of 200°C or higher and lower than 300°C; and impregnating one kind or more selected from the group consisting of tar and pitch to the compact, in which the magnesia raw material and the graphite raw material are main component of the compound, a content of the binder is 0.5 to 2.8 mass% relative to a total content 100 mass% of the magnesia raw material and the graphite raw material.SELECTED DRAWING: None

Description

The present invention relates to a method for producing magnesia carbon brick for steel smelting furnace lining.

In recent years, the operating temperature of steel smelting furnaces has become extremely high with the further improvement of quality of steel products. Furthermore, there are increasing social demands for improving the operating rate to improve productivity and reducing the burden on the global environment. As a result, the steel manufacturing process is becoming more and more demanding for refractories. Damage reduction is also strongly required for magnesia carbon bricks, which are widely used as refractories for steel smelting furnace linings.

Japanese Unexamined Patent Publication No. 2007-076980 JP-A-2002-114567

Patent Document 1 describes magnesia carbon bricks having excellent heat impact resistance (heat resistance spall properties) and corrosion resistance, which are kneaded and molded by adding an organic binder to a fireproof raw material compound containing a magnesia-based raw material as a main component. Disclosed are magnesia carbon bricks impregnated with tar or pitch after heat treatment at ° C. However, when the heat treatment is performed at 300 to 1000 ° C., the strength is greatly reduced due to the decomposition of the organic binder, and there are problems such as breakage and chipping during transportation and furnace construction, and the economy is also inferior. On the other hand, in Patent Document 1, when the heat treatment temperature is less than 300 ° C., the decomposition of the organic binder is insufficient, the closed pores remain in the brick, and the open pores are not sufficiently formed, so that tar or pitch is not easily impregnated to the center of the brick. Also disclosed (paragraph 0024).

Patent Document 2 relates to a refractory material for a converter outlet, which is composed of a sleeve arranged in a converter steel part and a block arranged around the sleeve, as a compound composed of a spinel raw material and a magnesia raw material. On the other hand, an example in which 3 to 20% by mass of a binder (binder) is added, kneaded, molded, dried at 200 ° C., and then pitch-impregnated is disclosed. The purpose of the drying treatment is described as curing the binder and / or removing volatile components in the binder. Since the sleeve has a cylindrical shape with a hollow portion, the pitch is impregnated from both the outer peripheral surface and the inner peripheral surface of the sleeve, and because the wall thickness is thin, the pitch can be adjusted even after a relatively low temperature drying treatment of 300 ° C. or lower. In some cases, it can be evenly impregnated up to the center of the wall thickness. However, the brick for lining of a steel smelting furnace does not have a hollow part and is thick. Therefore, when the drying treatment temperature is 300 ° C. or lower, it is difficult to uniformly impregnate the pitch to the center of the brick, and the damage reduction is not sufficient as the brick for lining the steel smelting furnace.

Aspects of the present invention have been made in view of the above circumstances, and an object of the present invention is to provide a method for producing bricks for steel smelting furnace lining, which can sufficiently reduce damage even when the heat treatment temperature is 300 ° C. or lower. Is.

One aspect of the present invention is a step of kneading and molding a compound containing a magnesia raw material, a graphite raw material, and a binder to obtain a molded product, and heat-treating the molded product at a temperature of 200 ° C. or higher and lower than 300 ° C. It has a step and a step of impregnating the molded product with one or more selected from the group consisting of tar and pitch, and the magnesia raw material and the graphite raw material are the main components of the compound, and the content of the binder is magnesia. The present invention relates to a method for producing magnesia carbon brick for lining of a steel smelting furnace, which is characterized in that the total content of the raw material and the graphite raw material is 0.5 to 2.8% by mass with respect to 100% by mass.

The magnesia carbon brick for lining of a steel smelting furnace thus obtained can improve corrosion resistance and abrasion resistance, and can reduce crack peeling. It is considered that this is because the heat treatment temperature is 200 ° C. or higher and lower than 300 ° C., so that there is almost no decrease in strength due to decomposition of the binder, and conversely, the strength is improved by curing the binder. Further, when the content of the binder is 0.5 to 2.8% by mass on the outer surface with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass, a coating film of excess binder is formed around the molded body. It is considered that this is because the impregnation of one or more kinds of bricks selected from the group consisting of tar and pitch is not hindered. Furthermore, since the volatile content in the binder that escapes from the molded product is appropriate, pores of an appropriate amount and size are formed, and one or more selected from the group consisting of tar and pitch is uniformly impregnated up to the center of the brick. It is thought that it can be done. Further, it is considered that when the temperature is raised to 300 ° C. or higher as the lining of the steel smelting furnace, there are few pores in the sample due to thermal decomposition of the binder, and the decrease in strength of the brick itself is small.

Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that the present embodiment described below does not unreasonably limit the content of the present invention described in the claims, and all the configurations described in the present embodiment are essential as a means for solving the present invention. Is not always the case.

The method for producing magnesia carbon brick for steel smelting furnace lining of the present embodiment includes a step of kneading and molding a compound containing a magnesia raw material, a graphite raw material, and a binder to obtain a molded product, and the molded product at 200 ° C. It has a step of heat-treating at a temperature of more than 300 ° C. and a step of impregnating the molded product with one or more selected from the group consisting of tar and pitch, and the magnesia raw material and the graphite raw material are the main components of the compound. Yes, the content of the binder is 0.5 to 2.8% by mass in the outer case with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass.

[Compound]
The formulation comprises a magnesia raw material, a graphite raw material and a binder. The magnesia raw material and the graphite raw material are the main components of the compound. The magnesia raw material is a source of magnesium oxide (MgO). The magnesia raw material may be any material generally used for magnesia carbon bricks, and examples thereof include fused magnesia and sintered magnesia. The content of the magnesia raw material is preferably 30 to 99% by mass with respect to the total content of the magnesia raw material and the graphite raw material. The graphite raw material is a source of graphite. The graphite raw material may be any material generally used for magnesia carbon bricks, and examples thereof include artificial graphite, natural graphite, and scaly graphite. The content of the graphite raw material is preferably 1 to 70% by mass with respect to the total content of the magnesia raw material and the graphite raw material.

The binder may be any binder generally used for magnesia carbon bricks, and examples thereof include thermosetting (resole type) or thermoplastic (novolac type) phenolic resins and ethylene glycol. In addition to the resin, the binder may be any binder generally used for non-firing bricks, and examples thereof include polysaccharide solutions such as molasses and silicates. The binder is particularly preferably a novolak type phenol resin. When the binder is a liquid having low viscosity at room temperature, even a small amount of the binder can be uniformly dispersed in the formulation. When the viscosity of the binder at room temperature is high, the viscosity of the binder may be reduced by heating to uniformly disperse the binder in the formulation.

The content of the binder is 0.5 to 2.8% by mass, preferably 1.0 to 2.6% by mass, more preferably 1.0 to 2.6% by mass, based on 100% by mass of the total content of the magnesia raw material and the graphite raw material. Is 1.5 to 2.5% by mass, and particularly preferably 1.7 to 2.2% by mass. It is considered that the coating film due to the excess binder is not formed around the molded product, and the impregnation of one or more bricks selected from the group consisting of tar and pitch is not prevented. Furthermore, since the volatile content in the binder that escapes from the molded product is appropriate, pores of an appropriate amount and size are formed, and one or more selected from the group consisting of tar and pitch is uniformly impregnated up to the center of the brick. It is thought that it can be done. Further, when the temperature is raised to 300 ° C. or higher as the lining of the steel smelting furnace, it is considered that there are few pores in the sample due to thermal decomposition of the binder, and the decrease in strength of the brick itself is small. If the content of the binder is less than 0.5% by mass in the outer cover, the binder is insufficient and a dense molded product cannot be obtained. On the other hand, when the content of the binder exceeds 2.8% by mass in the outer cover, the excess binder forms a coating film around the molded product, and is uniform to one or more types of bricks selected from the group consisting of tar and pitch. It is considered to prevent the impregnation. Further, it is considered that a large amount of large pores are formed after the volatile matter in the binder is removed, which causes a decrease in the strength of the molded body, oxidation, penetration of molten steel and the like. Further, when the temperature is raised to 300 ° C. or higher as the lining of the steel smelting furnace, the pores in the sample increase due to the thermal decomposition of the binder, and it is considered that the strength of the brick itself is greatly reduced.

The formulation may further contain additives as needed. Examples of the additive include a carbon antioxidant. The antioxidant may be any one generally used for magnesia carbon bricks, and examples thereof include Al, Si, and Al—Mg alloys. The content of the antioxidant is 0.5 to 3.0% by mass, preferably 1.0 to 2.0% by mass, based on the total content of the magnesia raw material and the graphite raw material of 100% by mass. In the present embodiment, since the heat treatment temperature is low, the metal is less likely to undergo a chemical change during the production of bricks, and the effect can be fully exhibited. Other additives include those commonly used for magnesia carbon bricks, such as carbon black and boron carbide powder.

[Kneading / molding]
The kneading / molding may be generally used in the process for producing magnesia carbon bricks. For kneading, for example, a Connor mixer, a pressurized high-speed mixer equipped with a high-speed stirring blade, an Erich (registered trademark) mixer, or the like can be used. For molding, a general brick molding press such as a hydraulic press or a friction press can be used. The molding pressure is usually about 100 to 250 MPa, more preferably 120 to 220 MPa, still more preferably 140 to 210 MPa, and particularly preferably 150 to 200 MPa. If it is less than 100 MPa, molding becomes insufficient, and if it exceeds 250 MPa, lamination occurs, which is not preferable.

[Heat treatment (drying treatment)]
The heat treatment after forming the brick is also called a drying treatment, and its purpose is to cure the binder and / or remove volatile substances in the binder. The heat treatment temperature is 200 ° C. or higher and lower than 300 ° C., more preferably 220 ° C. to 295 ° C., and further preferably 230 ° C. to 270 ° C. If the temperature is lower than 200 ° C., drying (removal of volatile components of the binder) becomes insufficient, and one or more kinds selected from the group consisting of tar and pitch cannot be sufficiently impregnated into the inside of the brick. At 300 ° C. or higher, the thermal decomposition of the binder increases the pores in the brick, so that the structure of the brick itself becomes loose and the strength decreases significantly. On the other hand, since the impregnation of the pitch becomes easier as the porosity increases, it is possible to supplement the strength to a certain extent by the impregnation effect. However, since the curing of the binder greatly contributes to the strength of the brick itself, thermal decomposition of the binder by high-temperature heat treatment is not preferable.

[Immersion]
After the heat treatment, one or more impregnation treatments selected from the group consisting of tar and pitch are performed. For the impregnation treatment, for example, an apparatus for impregnating the sliding nozzle plate with pitch can be used. Brick is loaded into an impregnation tank, the inside of the impregnation tank is depressurized, and at least one selected from the group consisting of heated tar and pitch is injected into the impregnation tank and immersed to impregnate the brick. As the pitch, either petroleum-based pitch or coal-based pitch can be used. The heat treatment (drying treatment) may be performed again after the impregnation treatment. By the above manufacturing process, densification and damage reduction are achieved, and magnesia carbon brick suitable for steel smelting furnace lining can be manufactured.

Hereinafter, examples of the present invention will be described in detail.

[Manufacturing of magnesia carbon brick]
A compound containing a magnesia raw material, a graphite raw material, and a binder was kneaded and molded to obtain a molded product, and the molded product was heat-treated for 24 hours to impregnate the molded product with a pitch to obtain a sample of magnesia carbon brick. .. Tables 1 and 2 show the magnesia raw materials, graphite raw materials, binders and additives used in Examples and Comparative Examples, their contents, molding pressure and heat treatment temperature.

In Tables 1 and 2, "% grade", "coarse grain", "medium grain", "fine grain" and "100M or less" are raw material purity, particle size 5 to 1 mm, particle size 1 mm or less, particle size 0. It means 15 mm or less and a particle size of 100 Mesh (0.15 mm) or less.

In Examples 1 to 4, Example 5, Example 6, Example 7 and Example 8, as binders, phenol resin (liquid), phenol resin (liquid) and phenol resin (powder) are used in combination, and phenol resin. A combination of (liquid) and ethylene glycol, sugar honey (liquid) and an aqueous solution of sodium silicate were used.

In Examples 1 to 8, Comparative Example 2 and Comparative Example 3, the content of the binder was changed in the range of 0.3 to 3% by mass with respect to the total content of 100% by mass of the magnesia raw material and the graphite raw material. ..

In Examples 9 to 11, the molding pressure was changed in the range of 122 to 203 MPa based on Example 3.

In Examples 12 to 15, Comparative Example 4 and Comparative Example 5, the heat treatment temperature was changed in the range of 180 to 350 ° C. based on Example 3.

Comparative Example 1 was based on Example 3 and was not impregnated.

After the heat treatment, the sample is loaded into the impregnation tank, the pressure inside the impregnation tank is reduced to 13.3 kPa or less, the heated pitch is injected into the impregnation tank, the sample is immersed in the pitch, and the impregnation pressure is maintained at 0.5 MPa for 2 hours. The impregnation treatment was performed. The shape of the sample was a rectangular parallelepiped having a length of 900 mm, a width of 180 mm, and a height of 150 mm, which was the same as that of a converter brick.

[Evaluation method]
The following items were evaluated for the obtained sample.

<Porosity / flexural strength>
The porosity was measured according to JIS R2205 (measurement method of apparent porosity, water absorption rate, and specific gravity of refractory bricks). The smaller the porosity, the better, and it was evaluated that less than 2.0% was preferable. The flexural strength was measured according to JIS R2213 (test method for flexural strength of refractory bricks). The greater the bending strength, the better, and it was evaluated that 11 MPa or more was preferable, and 16 MPa or more was particularly preferable.

<Corrosion resistance>
Corrosion resistance was measured by the high frequency induction furnace lining method. The test temperature was 1700 ° C., and synthetic slag having a mass ratio (CaO / SiO2) of 2.8 was used as the erosion agent. 400 g of the erosive agent was added at one time and replaced every hour, and the test was conducted for a total of 6 hours. The sample after the test was cut in the direction perpendicular to the working surface to measure the erosion area. Corrosion resistance was evaluated by the erosion index when the erosion area of Comparative Example 1 was 100. The smaller the erosion index, the better the corrosion resistance, and it was evaluated that 79 or less is preferable, and 68 or less is particularly preferable.

<Abrasion resistance>
Abrasion resistance was evaluated according to ASTM C704 (Abrasion Resistance of Refractory Materials at Room Temperature). A test piece having a shape of 115 × 115 × 30 mm was cut out from the sample and fired in a reducing atmosphere at 1000 ° C., and a surface of 115 × 115 mm was set at an angle of 45 ° with respect to the discharge direction of the wear material. While rotating the test piece at 15 rotations / minute around the vertical center line of the 115 × 115 mm surface, 1 kg of the abrasive was continuously sprayed on the 115 × 115 mm surface. As the wear material, SiC particles having a particle size adjusted to 1 to 0.3 mm were used. The sprayed air pressure was 0.4 MPa. The mass of the test piece before and after the test was measured, and the wear volume was calculated from the mass change and the bulk specific density of the test piece. The wear resistance was evaluated by the wear index when the wear volume of Comparative Example 1 was set to 100. The smaller the wear index, the better the wear resistance, and it was evaluated that 84 or less is preferable, and 69 or less is particularly preferable.

<Heat-resistant spall property>
The heat-resistant spall property was evaluated by a rapid heating and quenching test. A test piece having a shape of 40 × 40 × 160 mm was cut out from the sample and fired in a reducing atmosphere at 1000 ° C. The test piece was immersed in hot metal heated to 1680 ° C. for 60 seconds and then in cold water for 15 seconds, and this was repeated twice. The elastic modulus before and after the rapid heating and quenching test was measured, and the elastic modulus reduction rate was calculated by the following formula.
Elastic modulus reduction rate (%) = (elastic modulus before test-elastic modulus after test) ÷ elastic modulus before test × 100
The elastic modulus was determined from the ultrasonic wave velocity in the longitudinal direction of the test piece (160 mm length direction). The heat-resistant spall property was evaluated by the rate of decrease in elastic modulus. The smaller the elastic modulus reduction rate, the better the heat-resistant spall property, and it was evaluated that 39% or less is preferable, and 34% or less is particularly preferable.

<Good or bad pitch impregnation>
An organic solvent was sprayed on the cross section of the sample, and the reaction state between the organic solvent and the pitch was confirmed. The quality of pitch impregnation was evaluated by whether the reaction state of the cross section was uniform up to the center of the sample. A sample having a uniform reaction state up to the center was evaluated as having a particularly preferable pitch impregnation into the center (◯), and a sample having a non-uniform reaction state was evaluated as having an insufficient pitch impregnation into the center (×).

<Comprehensive judgment>
Samples in which all items were preferable or particularly preferable were evaluated as overall preferable (◯) because densification and damage reduction were achieved. Among them, the sample in which three or more items are particularly preferable is very suitable for the steel smelting furnace lining, and was evaluated as being particularly preferable overall (⊚). Samples in which one or more items were unfavorable were evaluated as totally unfavorable (x).

[Evaluation results]
The evaluation results are shown in Table 3.

In each of the examples, as compared with the comparative example, both reduction of porosity and uniform pitch impregnation were achieved, and densification was achieved. As a result, corrosion resistance (erosion index), wear resistance (wear index), and heat resistance spall property (elastic modulus reduction rate) were also improved.

Since the overall judgment of Examples 1 to 15 is ○ or ◎, while the overall judgment of Comparative Examples 2 to 3 is ×, the binder content is 100% by mass of the total content of the magnesia raw material and the graphite raw material. It is in the range of 0.5 to 2.8 mass% with respect to the outer hook. Further, since the comprehensive judgments of Examples 2 to 5, Examples 10 to 11 and Examples 13 to 15 are ⊚, the content of the binder is external to the total content of 100% by mass of the magnesia raw material and the graphite raw material. More preferably in the range of 1.5 to 2.5% by mass. Since Comparative Example 2 has a slightly large porosity, it is considered that a dense molded product cannot be obtained if the binder is insufficient. On the other hand, in Comparative Example 3, although the porosity is small and the bending strength is sufficient, the melt loss index, the wear index, and the elastic modulus decrease rate are large. It is considered that this is because when the amount of the binder is large, the excess binder forms a coating film around the molded product, which hinders the uniform impregnation of the pitch bricks. Further, it is considered that when the temperature was raised to 300 ° C. or higher, the pores in the sample increased due to the thermal decomposition of the binder, and the strength of the brick itself decreased significantly.

Since the comprehensive judgment of Examples 3 to 5 is ⊚ and the comprehensive judgment of Examples 6 to 8 is ◯, the binder is preferably a novolak type phenol resin.

Since the comprehensive judgment of Examples 3 and 10 to 11 is ⊚, while the comprehensive judgment of Example 9 is ◯, the molding pressure is in the range of 100 to 250 MPa and the range of 120 to 220 MPa. More preferred.

The heat treatment temperature is 200 ° C. or higher and lower than 300 ° C. because the comprehensive judgment of Examples 3 and 12 to 15 is ◯ or ⊚, while the comprehensive judgment of Comparative Examples 4 to 5 is ×. Further, since the comprehensive judgment of Examples 3 and 13 to 15 is ⊚, the heat treatment temperature is more preferably in the range of 220 ° C. to 295 ° C.

Although the present embodiment has been described in detail as described above, those skilled in the art will easily understand that many modifications that do not substantially deviate from the novel matters and effects of the present invention are possible. Therefore, all such modifications are within the scope of the present invention. For example, in the specification, a term described at least once with a different term having a broader meaning or a synonym may be replaced with the different term at any part of the specification. Further, the configuration and operation of the manufacturing apparatus and the like of the present embodiment are not limited to those described in the present embodiment, and various modifications are possible.

Claims (1)

A step of kneading and molding a compound containing a magnesia raw material, a graphite raw material, and a binder to obtain a molded product.
A step of heat-treating the molded product at a temperature of 200 ° C. or higher and lower than 300 ° C.
A step of impregnating the molded product with one or more selected from the group consisting of tar and pitch.
Have,
The magnesia raw material and the graphite raw material are the main components of the compound.
The content of the binder is 0.5 to 2.8% by mass with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass, which is a magnesia carbon brick for lining a steel smelting furnace. Manufacturing method.