JP6905202B2 - Magnesia carbon refractory - Google Patents

Description

The present disclosure relates to magnesia carbon refractories used in steel refining process equipment.

A magnesia-carbon refractory containing a magnesia raw material, a graphite raw material, and a binder as main components is widely used in a steel refining process apparatus operated at an extremely high temperature. Magnesia-carbon refractories are required to have improved corrosion resistance and spalling resistance, and the deterioration of wear resistance due to damage to the brick tissue caused by the magnesia-carbon reaction is a major problem. Is also strongly required. For example, Patent Document 1 contains expanded graphite-containing bricks (magnesia carbon material) in which expanded graphite is compressed and then pulverized to a particle size of 1 mm or less to improve corrosion resistance while maintaining spalling resistance. Fireproof material) is described. Further, in Patent Document 2, the magnesia-carbon reaction is an equilibrium reaction described by (Equation 1), and by reducing the amount of the organic binder (binder), the magnesia-carbon-based brick (magnesia-carbon refractory). It is described that the substance) is densified and the magnesia-carbon reaction is suppressed.
MgO (s) + C (s) = Mg (g) + CO (g) (Equation 1)

Japanese Unexamined Patent Publication No. 8-081256 Japanese Unexamined Patent Publication No. 2013-180945

However, since the expanded graphite-containing brick of Patent Document 1 uses expanded graphite, it is bulkier than scaly graphite and the like, and the amount of binder cannot be sufficiently reduced. As a result, the expanded graphite-containing brick is not sufficiently densified, and there is a problem that the brick structure is damaged due to the magnesia-carbon reaction and the wear resistance is lowered accordingly. Further, the magnesia-carbon brick of Patent Document 2 is not sufficiently improved in corrosion resistance and spalling resistance.

One aspect of the present disclosure has been made in view of the above circumstances, and is to maintain and improve corrosion resistance and spalling resistance, and to improve wear resistance by suppressing damage to the brick tissue caused by the magnesia-carbon reaction. The purpose is to provide a magnesia-carbon refractory that is compatible with each other.

(1) One aspect of the present disclosure contains a magnesia raw material, a graphite raw material, and a binder as main components, and the content of the graphite raw material is 100% by mass based on the total content of the magnesia raw material and the graphite raw material. The graphite raw material is 2 to 60% by mass ^{, contains expanded graphite having a bulk density of 0.08 to 0.28 g / cm 3} , and the content of expanded graphite having a particle size of 1.5 to 10 mm is that of the graphite raw material. The present invention relates to a magnesia-carbon refractory having a content of 40 to 100% by mass based on 100% by mass and 2% by mass or more based on a total content of 100% by mass of a magnesia raw material and a graphite raw material.

The magnesia-carbon refractory according to one aspect of the present disclosure contains a magnesia raw material, a graphite raw material, and a binder as main components, and the content of the graphite raw material is 100 mass by mass of the total content of the magnesia raw material and the graphite raw material. ^{The graphite raw material contains expanded graphite having a bulk density of 0.08 to 0.28 g / cm 3} , which is 2 to 60% by mass with respect to%. Therefore, the corrosion resistance is improved while maintaining the spalling resistance. Can be done. Further, in the magnesia carbon refractory, the content of expanded graphite having a particle size of 1.5 to 10 mm is 40 to 100% by mass with respect to the content of 100% by mass of the graphite raw material, and the magnesia raw material and the graphite raw material are used. Since the total content is 2% by mass or more with respect to 100% by mass, the particle size of expanded graphite is large, and the specific surface area is small, the amount of binder can be reduced. As a result, since the magnesia-carbon refractory can be densified, the wear resistance can be improved by suppressing the damage of the brick tissue caused by the magnesia-carbon reaction. That is, it is possible to achieve both corrosion resistance, spalling resistance and wear resistance of magnesia carbon refractories.

(2) In one aspect of the present disclosure, it is preferable that the graphite raw material does not contain the expanded graphite having a particle size of less than 1.5 mm. Since it does not contain expanded graphite having a small particle size and a large specific surface area, the amount of binder can be further reduced. As a result, the magnesia-carbon refractory can be further densified, so that the wear resistance can be further improved by suppressing the damage to the brick tissue caused by the magnesia-carbon reaction.

(3) In one aspect of the present disclosure, the particle size of expanded graphite is preferably 2 to 7 mm. The specific surface area of expanded graphite can be reduced and the amount of binder can be reduced. As a result, the magnesia-carbon refractory can be densified, and the damage to the brick tissue caused by the magnesia-carbon reaction can be suppressed.

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

The magnesia carbonaceous fireproof material of the present embodiment contains a magnesia raw material, a graphite raw material, and a binder as main components, and the content of the graphite raw material is 100% by mass of the total content of the magnesia raw material and the graphite raw material. The graphite raw material contains expanded graphite having a bulk density of 0.08 to 0.28 g / cm ³ , and the content of expanded graphite having a particle size of 1.5 to 10 mm is a graphite raw material. It is 40 to 100% by mass with respect to 100% by mass of the content of, and 2% by mass or more with respect to 100% by mass of the total content of the magnesia raw material and the graphite raw material.

<Bulk density>
In the present disclosure, the bulk density is a loose bulk density, which means a value obtained by gently placing an object to be measured in a measuring cylinder and dividing the mass of the object to be measured by its volume.

<Magnesia raw material>
The magnesia raw material is a source of magnesium oxide (MgO). The magnesia raw material may be any material generally used for magnesia-carbon refractories, and examples thereof include electrolytic magnesia, seawater magnesia, natural magnesia, and sintered magnesia. The purity of the magnesia raw material is preferably MgO: 98% by mass or more. In this case, the corrosion resistance of the magnesia-carbon refractory is improved, and the magnesia-carbon reaction can be suppressed.

<Graphite raw material>
The graphite raw material is a source of graphite. The graphite raw material may be any one generally used for magnesia-carbon refractories, and examples thereof include natural graphite such as scaly graphite, scaly graphite, and earthy graphite, and artificial graphite. The graphite raw material of the present embodiment has a bulk density of 0.08 to 0.28 g /, which is obtained by expanding, compressing and crushing a sheet, and classifying the graphite raw material having a particle size of 1.5 to 10 mm. Contains cm ³ expanded graphite. By containing expanded graphite, corrosion resistance can be improved while maintaining spalling resistance. In general, expanded graphite rapidly expands (expands) the graphite layers by rapidly heating a graphite intercalation compound in which sulfuric acid or the like is inserted between layers of natural scaly graphite to a temperature of 800 to 1000 ° C. It is a thing. The bulk density of the expanded graphite after expansion treatment is usually less than 0.05 g / cm ^3, in the present embodiment is about 0.01 g / cm ^3. In the present embodiment, the expanded graphite is then compressed into a sheet and pulverized. Compression, the bulk density of the expanded graphite after grinding is usually 0.05 to 0.3 g / cm ^3, preferably ^{0.08~0.28g / cm 3, 0.08~0.2 / cm} 3 Gayori Preferably, 0.1 to 0.15 g / cm ³ is more preferable. The expanded graphite after compression and crushing is classified using a sieve of the nominal opening auxiliary dimension series specified in JIS Z8801: 2019 to adjust the particle size. The particle size after classification is preferably 1.5 to 10 mm, more preferably 2 to 7 mm. By setting the bulk density and the particle size within this range, the specific surface area of expanded graphite can be reduced and the amount of binder can be reduced. As a result, the magnesia-carbon refractory can be densified, and the damage to the brick tissue caused by the magnesia-carbon reaction can be suppressed. When the amount of expanded graphite having a particle size of less than 1.5 mm increases, the specific surface area of the expanded graphite increases and a large amount of binder is required. Therefore, the magnesia-carbon refractory cannot be densified, and the magnesia-carbon reaction occurs. Inability to control damage to the tissue caused by graphite. On the other hand, when expanded graphite having a particle size of more than 10 mm increases, it becomes difficult to disperse it uniformly.

The content of the graphite raw material is preferably 2 to 60% by mass with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass. The content of expanded graphite having a particle size of 1.5 to 10 mm is preferably 40 to 100% by mass with respect to 100% by mass of the graphite raw material. If the content of the graphite raw material is less than 2% by mass with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass, the absolute amount becomes too small even if all the graphite raw materials are expanded graphite (100% by mass), which is sufficient. No good spalling resistance can be obtained. On the other hand, if the content of the graphite raw material exceeds 60% by mass with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass, the graphite raw material becomes excessive and the brick structure cannot be densified. As a result, the corrosion resistance is lowered, and at the same time, the damage of the brick tissue due to the magnesia-carbon reaction is increased, and the wear resistance is lowered. The content of the graphite raw material is more preferably 5 to 40% by mass with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass. The content of expanded graphite having a bulk density of 0.08 to 0.28 g / cm ³ and a particle size of 1.5 to 10 mm is 60 to 100% by mass with respect to 100% by mass of the graphite raw material. preferable. As the graphite raw material other than expanded graphite, artificial graphite, natural graphite and the like can be contained in the above range. The purity of the graphite raw material may be one generally used for magnesia carbon refractories, and is often from 85% by mass to 99% by mass.

<Binder>
The binder may be any one generally used for magnesia-carbon refractories, and examples thereof include thermosetting (resole type) or thermoplastic (novolac type) phenol resins and ethylene glycols. The form of the binder is not particularly limited as long as it is generally used, and examples thereof include liquids and powders. A binder having a low viscosity at room temperature or a binder having a reduced viscosity by heating to a constant temperature is particularly preferable because it can be uniformly dispersed by adding a small amount. The binder does not have to be a resin as long as it is generally used for non-firing bricks, and examples thereof include polysaccharide solutions such as molasses and inorganic compounds such as silicates.

<Small amount of additives>
If it is generally used for magnesia carbon refractories, a small amount of additives other than the main component may be added, and examples thereof include antioxidants, carbon black, and powder pitch. As the antioxidant, for _{example, Al, Si, B 4 C} , SiC, Al-Mg alloys.

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

[Creation of test piece]
After obtaining expanded graphite having a bulk density of 0.01 g / cm ³ by expansion treatment, it was compressed into a sheet, pulverized, and classified using a sieve of a nominal opening auxiliary dimension series specified in JIS Z8801: 2019. .. Table 1 shows the particle size and bulk density of the obtained expanded graphite.

The formulation shown in Table 2 was kneaded using the expanded graphite shown in Table 1, formed into a rectangular parallelepiped shape having a length of 900 mm, a width of 180 mm and a height of 150 mm, and then dried at 250 ° C. for 24 hours to obtain a brick. If necessary, the brick was processed into a predetermined shape to prepare a test piece.

In Table 2, "% class", "coarse grain", "medium grain", "fine grain" and "100M or less" are the purity of the raw material, the particle size of 5 to 1 mm, the particle size of 1 mm or less, and the particle size of 0.15 mm or less, respectively. And the particle size is 100 Mesh (0.15 mm) or less.

As expanded graphite, Examples 1, 2 to 10 and 11 to 12 are 95% class expanded graphite having a particle size of 1.5 to 10 mm, and 95% class expanded graphite and grains having a particle size of 2 to 7 mm, respectively. 90% class expanded graphite having a diameter of 2 to 7 mm was used. In Examples 2 to 5 and 9, only expanded graphite was added as a graphite raw material in an amount of 2 to 25% by mass based on 100% by mass of the total content of the magnesia raw material and the graphite raw material. In Examples 1, 6 to 8 and 10 to 12, expanded graphite and scaly graphite were added in an amount of 10 to 20% by mass and 5 to 20% by mass with respect to a total content of 100% by mass of the magnesia raw material and the graphite raw material, respectively. Examples 11 and 12 had the same composition except that the binders were a novolak-type phenol resin (liquid) and an aqueous solution of sodium silicate, respectively.

In Comparative Example 1, expanded graphite was not added. In Comparative Example 2, only expanded graphite was added as a graphite raw material in an amount of 1% by mass based on a total content of 100% by mass of the magnesia raw material and the graphite raw material. In Comparative Example 3, the content of expanded graphite was 65% by mass with respect to the total content of 100% by mass of the magnesia raw material and the graphite raw material. In Comparative Example 4 and Comparative Example 5, expanded graphite having a particle size of 11 mm or more and 1 mm or less was used.

[Evaluation method]
The test pieces were evaluated as follows.

<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 flexural strength was measured according to JIS R2213 (test method for flexural strength of refractory bricks).

<Corrosion resistance (erosion index)>
Corrosion resistance was evaluated by the high frequency lining method. That is, the test temperature was 1700 ° C., and _{synthetic slag having CaO / SiO 2} (mass ratio) 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 continued for a total of 6 hours. The test piece after the test was cut in the direction perpendicular to the working surface, and the erosion area was measured. Corrosion resistance was evaluated by a erosion index with the erosion area of Comparative Example 1 as 100. The smaller the erosion index, the better the wear resistance, and it was evaluated that 95 or less was excellent, 95 or more and 110 or less was acceptable, and 110 or more was not acceptable.

<Abrasion resistance (wear index)>
Abrasion resistance was evaluated according to ASTM C704 (Abrasion Response of Reflectory Materials at Room Temperature). That is, a test piece processed into a rectangular parallelepiped having a predetermined shape: 115 × 115 × 30 mm was fired at 1000 ° C. in a reducing atmosphere, and a surface of 115 × 115 mm was set at an angle of 45 ° with respect to the discharge direction of the abrasion material. The wear material was continuously sprayed on the test piece rotated at 15 rpm. SiC particles having a particle size of 0.3 to 1 mm were used as the abrasion material. The amount of the abrasive material sprayed was 1 kg, and the sprayed air pressure was 0.4 MPa. The mass of the test piece was measured before and after the spray test, 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 a wear index with the wear volume of Comparative Example 1 as 100. The smaller the wear index, the better the wear resistance, and it was evaluated that 70 or less was excellent, 70 or more and 110 or less was acceptable, and 110 or more was not acceptable.

<Spalling resistance (elastic modulus reduction rate)>
The spalling resistance was evaluated by a rapid heating and quenching test. That is, a test piece processed into a rectangular parallelepiped having a predetermined shape: 40 × 40 × 160 mm was fired at 1000 ° C. in a reducing atmosphere. The operation of immersing the test piece in hot metal at 1680 ° C. for 60 seconds and then immersing it in cold water for 15 seconds was repeated twice. The elastic modulus of the test piece before and after the immersion test was measured, the elastic modulus reduction rate was calculated by the following formula, and the spalling resistance was evaluated. The elastic modulus was determined from the ultrasonic propagation velocity in the longitudinal direction (160 mm length direction) of the test piece.
Elastic modulus reduction rate = (elastic modulus before test-elastic modulus after test) / elastic modulus before test x 100

The smaller the elastic modulus reduction rate, the better the spalling resistance, and it was evaluated that 50% or less was excellent, more than 50% and 60% or less was possible, and more than 60% was not possible.

<Magnesia-carbon reaction (weight loss rate)>
The magnesia-carbon reaction was evaluated by the following procedure. That is, a test piece processed into a cylinder having a predetermined shape: diameter 27 mm and height 30 mm was heat-treated at 1500 ° C. in a reducing atmosphere, and then heat-treated at 1700 ° C. for 1 hour in an argon atmosphere. The weight loss rate before and after the heat treatment at 1700 ° C. in an argon atmosphere was measured, and the magnesia-carbon reaction was evaluated. The smaller the weight loss rate, the less the damage to the brick tissue, and the better the suppression of the magnesia-carbon reaction. 6% or less was evaluated as excellent, more than 6% and 7% or less were evaluated, and more than 7% was evaluated as impossible.

<Comprehensive evaluation>
The test pieces in which all the items were excellent or acceptable were evaluated as overall preferable (◯) because the corrosion resistance and the spalling resistance were maintained and improved as well as the wear resistance was improved. Among them, the test pieces with two or more excellent pieces were evaluated as being particularly preferable (⊚) overall. Test pieces with one or more disapprovals were evaluated as totally unfavorable (x).

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

In each of the examples, the erosion index was 110 or less, the wear index was 110 or less, the elastic modulus reduction rate was 60% or less, and the weight reduction rate was 7% or less. Corrosion resistance (erosion resistance index) and erosion resistance were compared with the comparative examples. Abrasion resistance (wear index), spalling resistance (elastic modulus reduction rate), and magnesia-carbon reaction suppression (weight reduction rate) are improved.

<Contents of graphite raw material>
In Comparative Example 2, the porosity and the weight loss rate are small, but the elastic modulus reduction rate is large and the spalling resistance is inferior. It is probable that the content of the graphite raw material was low. Therefore, it is considered that the content of the graphite raw material is preferably 2% by mass or more with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass. In Comparative Example 3, the elastic modulus reduction rate is small, but the melt loss index and the weight loss rate are large, suggesting that the brick structure is deteriorated due to the magnesia-carbon reaction. It is probable that the amount of graphite raw material was excessive and the brick structure could not be densified. Therefore, it is considered that the content of the graphite raw material is preferably 60% by mass or less with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass. The content of the graphite raw material is more preferably 5 to 40% by mass with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass.

<Diameter of expanded graphite>
In Comparative Example 4, the elastic modulus reduction rate is large and the spalling resistance is inferior. It is probable that the particle size of the expanded graphite exceeded 10 mm, making it difficult to disperse it uniformly. In Comparative Example 5, the weight loss rate was large, suggesting that the brick structure deteriorated due to the magnesia-carbon reaction. Since the particle size of expanded graphite is less than 1.5 mm and the specific surface area of expanded graphite increases, a large amount of binder is required, and the magnesia-carbon refractory cannot be densified, which is caused by the magnesia-carbon reaction. It is probable that it became difficult to control the damage to the tissue of graphite. Therefore, it is considered that the particle size of expanded graphite is preferably 1.5 to 10 mm. Comparing Example 1 and Example 7, the compounding composition is almost the same except that the particle size of the expanded graphite is 1.5 to 10 mm for the former and 2 to 7 mm for the latter. However, in Example 7, the melt loss index, the wear index, the elastic modulus reduction rate, and the weight loss rate are improved, and it is considered that the particle size of the expanded graphite is more preferably 2 to 7 mm.

<Content of expanded graphite>
In Comparative Example 1 and Comparative Example 2, the porosity and the weight loss rate are small, but the elastic modulus reduction rate is large and the spalling resistance is inferior. It is probable that the content of expanded graphite was low. On the other hand, the comprehensive judgment of Example 2 is "◯ (preferable)". Therefore, the content of expanded graphite is preferably 40 to 100% by mass with respect to the total content of 100% by mass of the graphite raw material and 2% by mass or more with respect to the total content of 100% by mass of the magnesia raw material and the graphite raw material. Conceivable.

<Binder>
Comparing Example 11 and Example 12, the evaluation results are almost the same. The former does not have to be a resin because the blending composition of both is the same except that the binder is a novolak type phenol resin (liquid) and the latter is an aqueous solution of sodium silicate.

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 new matters and effects of the present disclosure are possible. Therefore, all such variations are within the scope of the present disclosure. 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 (3)

It contains a magnesia raw material, a graphite raw material, and a binder as main components.
The content of the graphite raw material is 2 to 60% by mass with respect to the total content of the magnesia raw material and the graphite raw material of 100% by mass.
The graphite raw material contains expanded graphite having a bulk density of 0.08 to 0.28 g / cm ^3.
The content of the expanded graphite having a particle size of 1.5 to 10 mm is 40 to 100% by mass with respect to the total content of the graphite raw material of 100% by mass, and the total content of the magnesia raw material and the graphite raw material is 100% by mass. A magnesia-carbon refractory characterized by being 2% by mass or more with respect to%. In the magnesia carbon refractory according to claim 1.
The graphite raw material is a magnesia-carbon refractory characterized by not containing the expanded graphite having a particle size of less than 1.5 mm. In the magnesia carbon refractory according to claim 1 or 2.
A magnesia-carbon refractory characterized in that the expanded graphite has a particle size of 2 to 7 mm.