JP6194257B2 - Magnesia carbon brick - Google Patents

Description

  The present invention relates to a magnesia carbon brick that is suitably used as a lining material for general kilns for carrying, storing, and refining molten metal.

  Magnesia carbon brick (hereinafter referred to as “MgO-C brick”) is a brick with excellent corrosion resistance and spall resistance composed mainly of magnesia and graphite. It is widely used as.

  With the recent severe operation of smelting vessels, MgO-C bricks with better durability have been demanded. In order to improve its durability, not only is it excellent in corrosion resistance and spalling resistance, but the lining material of the kiln furnace is generally used for a long period of time and receives the heat history of heating and cooling, so bricks in the same environment It is important to be able to maintain the tissue for a long period of time, that is, maintain compactness.

  In this regard, Patent Document 1 discloses that by controlling the content of a magnesia-based refractory raw material having a particle size of 0.1 mm or less, it is possible to suppress tissue deterioration even in an environment where the material is exposed to a high temperature for a long time. An MgO-C brick that can maintain the corrosion resistance at the beginning of use is disclosed. Further, Patent Document 2 discloses MgO that can suppress deterioration of various properties due to spalling resistance and structural deterioration due to heat by controlling the content of coarse particles, intermediate particles, and fine particles in the particle size constitution of the magnesia raw material. -C brick is disclosed.

  On the other hand, a carbon-based raw material is used for MgO-C brick, and in order to prevent this oxidation, a metal such as metal Al or metal Si having high affinity with oxygen is often added. In the second and second embodiments, a metal is added as an antioxidant.

  However, although the metal added as the antioxidant suppresses the oxidation of the carbon-based raw material in the brick by its own oxidation, the reaction generally involves expansion. In addition, the oxidation reaction product reacts with the magnesia raw material in which MgO-C brick is present in the structure in a large amount to form a product and expand the structure of the brick. These swelling reactions in the tissue lead to loosening of the brick tissue, which in turn leads to a decrease in corrosion resistance.

JP 2007-297246 A JP-A-1-270564

  The problem to be solved by the present invention is that the occurrence of loosening of the brick structure due to the expansion reaction of the metal added as an antioxidant can be suppressed, and it is exposed to a long-term heat history during use in an actual furnace. Even if it is used, it is to provide a MgO-C brick which can maintain a compactness with little deterioration of a brick structure and can improve durability.

The MgO-C brick of the present invention is premised on adding metal Al as an antioxidant. This metal Al produces Al ₂ O ₃ when used in an actual furnace, and further this Al ₂ O ₃ produces magnesia raw material and spinel in the brick structure. Conventionally, it has been considered that MgO—C brick used under restraint is densified by volume expansion due to the generation of spinel. However, the inventors' research has shown that when volume expansion occurs excessively in a brick tissue, the brick loosens in the tissue and the residual expansion increases, resulting in an increase in porosity.

  On the other hand, since the metal Al also has an antioxidant function of the carbon-based raw material as described above, reducing the content of the metal Al in the brick structure causes a reduction in the oxidation resistance of the brick. Therefore, the present inventors examined the application of boron carbide to ensure oxidation resistance, and found that the deterioration of the brick structure can be suppressed against a long-term thermal history. The mechanism is considered as follows.

The production temperature of the reaction product of metallic Al is about 800 ° C. for Al ₄ C _{3 and} about 900 ° C. for Al ₂ O ₃ . On the other hand, the oxidation start temperature of boron carbide is about 500 ° C., and Al ₄ BC starts to be formed at 400 to 500 ° C. in the coexistence of boron carbide and metal Al. B ₂ O ₃ produced by oxidation of boron carbide reacts with Al ₂ O ₃ , 9Al ₂ O ₃ .2B ₂ O ₃ , 2Al ₂ O ₃ .B ₂ O ₃ , and Al ₂ O ₃ and B ₂ O ₃ Produces a liquid phase. From these facts, by containing boron carbide in MgO-C brick to which metal Al is added, it is possible to suppress the generation of Al ₂ O ₃ that causes generation of magnesia raw material and spinel from the stage where the ambient temperature is low. it can. _Further, since the low-melting compound of Al _{2 O 3 -B 2} O 3 system is produced, it is possible to reduce the amount of _Al 2 _{O 3} of brick tissue. Thereby, it is considered that the spinel reaction between Al ₂ O ₃ and the magnesia raw material is suppressed, and as a result, the expansion of the brick structure is suppressed. Furthermore, since the liquid phase these _{9Al 2 O 3 · 2B 2 O} 3, 2Al 2 O 3 · B 2 O 3 and _Al 2 _{O 3} and _B 2 _{O 3} are mixed to act as an oxidation film at a high temperature, metal Al This suppresses or improves the oxidation resistance of MgO-C bricks due to the decrease in the amount of MgO-C brick.

  As a result of various studies, the present inventors have found that the size and content of the metal Al constituting the brick structure, in order to maintain the compactness with little loosening of the brick structure even after receiving a thermal history over a long period of time, and It has been found that it is important to adjust the particle size and content of boron carbide. Furthermore, it has been found that this effect can be further improved by adjusting the particle size composition of the magnesia raw material, using the metal Si together, adjusting the particle size and content thereof, and applying a binder having a high residual carbon ratio.

That is, the present invention provides the following MgO-C brick.
(1) In a magnesia carbon brick containing a magnesia raw material and graphite, the proportion of the total mass of the magnesia raw material and graphite is 8% by mass to 25% by mass, and the mass of the magnesia raw material is 75% by mass to 92% by mass. 1% by mass to 15% by mass with respect to the amount of added graphite, and the content of 45 μm or less in particle size is 85% by mass or more. Boron carbide is contained in an amount of 1% by mass or more and 50% by mass or less with respect to the amount of added metal Al , and the particle size of the magnesia raw material is a proportion of the total amount of the magnesia raw material and graphite, and the particle size is 0.075 mm or more and 1 mm or less. A magnesia raw material containing 35 mass% or more and a magnesia raw material having a particle size of less than 0.075 mm is blended in an amount of 15 mass% or less, and the magnesia raw material has a particle size of less than 0.075 mm. MgO-C bricks having a mass ratio of magnesia raw material having a particle size of 0.075 mm to 1 mm of 4.2 or more .
(2) The MgO-C brick according to (1), wherein the apparent porosity after heat treatment in a reducing atmosphere at 1400 ° C. for 3 hours is 7.8% or less.
( 3 ) The MgO-C brick according to (1) or (2) , wherein metal Si having a particle size of 45 μm or less is contained in an amount of 85% by mass or less with respect to the amount of added graphite.
( 4 ) The MgO-C brick according to any one of (1) to (3) , wherein a phenol resin having a residual carbon ratio of 48% or more is used as a binder.

  Regarding (2) above, there are some examples of the apparent porosity measured by reducing and firing MgO—C bricks in the past, but most of them have a firing temperature of 1200 ° C. or less and a high heat of 1400 ° C. There is no example that has achieved a low porosity of 7.8% or less under load. The inventors of the present invention are able to obtain excellent corrosion resistance and oxidation resistance that are not conventionally obtained by further reducing the apparent porosity of the MgO-C brick after high heat load to 7.8% or less. Obtained knowledge.

  According to the present invention, the occurrence of loosening of the brick structure due to the expansion reaction of the metal Al added as an antioxidant is suppressed, and even if it is used under conditions where it is exposed to a long-term heat history during actual furnace use. As a result, the deterioration of the brick structure is small and the denseness can be maintained, which contributes to the improvement of the durability of the brick and the extension of the life of the furnace. This makes it possible to extend the maintenance period of the furnace and contribute to productivity improvement by reducing the furnace material unit and extending the furnace repair span.

  The present invention relates to a MgO-C brick containing a magnesia raw material and graphite, and by adjusting the particle size and content of metallic Al constituting the brick structure and the particle size and content of boron carbide, It is characterized by suppressing the tissue deterioration and maintaining the denseness against the history exposure.

  As the magnesia raw material, one or more of electrofused magnesia, seawater magnesia, and natural magnesia can be used. Further, the purity does not significantly affect the effect of the present invention, but it is preferable to use a magnesia raw material having a purity of 90% or more in order to avoid the deterioration of corrosion resistance and oversintering due to impurities.

  As the particle size constitution of the magnesia raw material, the proportion of the magnesia raw material and graphite is the proportion of the total amount of magnesia raw material having a particle size of 0.075 mm or more and 1 mm or less, 35 mass% or more, and magnesia raw material having a particle size of less than 0.075 mm, 15 mass %, And the mass ratio of the magnesia raw material having a particle size of 0.075 mm to 1 mm to the magnesia raw material having a particle size of less than 0.075 mm is preferably 4.2 or more.

  That is, when there are too many fine particles having a particle size of less than 0.075 mm, the contact between magnesia raw materials increases and the moldability deteriorates. Therefore, the smaller one is preferable in order to improve the fillability after molding. Specifically, the blending amount of fine particles having a particle size of less than 0.075 mm is preferably 15% by mass or less. If the blending amount of the fine particles exceeds 15% by mass, the moldability is deteriorated, the structure is easily deteriorated after being exposed to the heat history, and the porosity tends to increase, which is not preferable.

  In addition, the magnesia raw material expands and contracts in the process of heating and cooling. However, since the expansion coefficient is larger than that of the surrounding graphite, voids are generated around it when contracting. In particular, relatively large voids are generated around coarse particles having a particle diameter of more than 1 mm, and easily open pores, resulting in a large increase in apparent porosity. Therefore, it is preferable to increase the blending amount of medium grains having a particle size of 0.075 mm or more and 1 mm or less and to reduce coarse particles having a particle diameter of more than 1 mm. Specifically, the blending amount of medium grains having a particle size of 0.075 mm or more and 1 mm or less is preferably 35% by mass or more, and more preferably 43% by mass or more. Moreover, it is preferable that the mass ratio (mass of middle grain / mass of fine grain) of medium grains having a particle diameter of 0.075 mm to 1 mm with respect to fine grains having a particle diameter of less than 0.075 mm is 4.2 or more.

  As the graphite, normal scaly graphite can be used, but expanded graphite, artificial graphite, quiche graphite, or the like may be used instead of or in combination with this. Although the composition is not particularly defined, it is better to use graphite having high C purity in order to obtain higher corrosion resistance, and the C purity is preferably 85% or more, more preferably 98% or more. Since it is difficult to maintain denseness when the particle size is extremely fine, it is better to use graphite having a particle size of 0.04 mm or more, more preferably 0.15 mm or more of the compounding amount of 40% by mass or more.

  The graphite content is 8% by mass or more and 25% by mass or less in terms of the proportion of the total amount of the magnesia raw material and graphite. When the content of graphite is less than 8% by mass, the ratio of the magnesia raw material increases, and the structure stability decreases. That is, the porosity increases after long-term heat history exposure. If the graphite content exceeds 25% by mass, the porosity and the corrosion resistance may be lowered. As the remainder of the graphite content, the content of the magnesia raw material is set to 75% by mass or more and 92% by mass or less in the proportion of the total amount of the magnesia raw material and graphite.

  The addition amount of metal Al is suitably 1% by mass or more and 15% by mass or less, and more preferably 10% by mass or less, with respect to the added graphite amount. In this way, by keeping the amount of metal Al added to a relatively small amount, expansion reaction due to metal Al can be suppressed, and pores generated by volatilization of metal Al can be reduced, and as a result, the denseness of MgO-C brick is ensured. can do. In addition, it is preferable that the particle size is small in order to reduce the apparent porosity. This is because the metal Al can be melted and volatilized during the temperature rising process to reduce the pore diameter, and the probability of opening to open pores is reduced. Furthermore, this is considered to be effective for forming an MgO—C brick structure at an early stage. The reason why 1% by mass or more of metallic Al is added is that oxidation resistance is insufficient with an addition amount less than this. The effect by metal Al is remarkably exhibited by using metal Al having a particle size of 75 μm or less and a content of 85% by mass or more.

The addition amount of boron carbide is suitably 1% by mass or more and 50% by mass or less, and more preferably 25% by mass or less, with respect to the added metal Al amount. If the amount of boron carbide is more than 50 mass%, when the thermal history exposure, _B 2 _{O 3} is generated excessively by oxidation, _Al 2 _{O 3} can not be reacted with excess _B 2 _{O 3} and a magnesia raw material It reacts to produce a large amount of a low melting point, which in turn causes a decrease in corrosion resistance. If the amount of boron carbide added is less than 1% by mass, the effect cannot be obtained. The effect of boron carbide is remarkably manifested by using boron carbide having a particle size of 45 μm or less and a content of 85% by mass or more. As boron carbide, commercially available raw materials generally used for refractory bricks can be used.

In the MgO-C brick of the present invention, metal Si can be added in addition to the above-mentioned metal Al and boron carbide. The metal Si generates SiC and then SiO ₂ in the MgO-C brick during the temperature rising process. This SiO ₂ reacts with MgO to produce Enstatite and Forsterite having a relatively low melting point, but the liquid phase of this reaction process fills the fine pores of MgO—C brick and lowers the porosity. Further, in the presence of metal Al, cordierite having a lower melting point is also generated, and the effect of the liquid phase filling the pores more efficiently is exhibited. Also, the smaller the particle size of the metal Si is, the more effective for lowering the porosity. This is the same as the case of the metal Al, and it is possible to reduce the pore diameter generated by melting and volatilization in the temperature rising process, and the probability of open pore formation is small. It is to become.

  The addition amount of metal Si is 5% by mass or less with respect to the amount of added graphite, and it is sufficient, and fine metal Si having a particle size of 45 μm or less, specifically, the content of particle size of 45 μm or less is 85 mass as the particle size constitution. By using more than 1% of metal Si, further effects are exhibited. Excessive addition beyond this increases the amount of low-melt material generated in the MgO-C brick, causing a reduction in corrosion resistance and reducing the durability. The lower limit of the amount of addition of metal Si is not particularly limited, but it is preferably 1% by mass or more with respect to the amount of added graphite in order to significantly express the effect of metal Si.

  As the binder, it is preferable to use a phenol resin. The phenolic resin may be any of a novolak type, a resol type, and a mixed type thereof, but in the case of MgO-C brick, a novolak type that hardly changes with time is more preferable. Either powder or liquid dissolved in an appropriate solvent, or a combination of liquid and powder can be used. Usually, an appropriate amount of a curing material such as hexamethylenetetramine is added to ensure a residual carbon ratio. The residual carbon ratio is preferably 34% or more, more preferably 48% or more, but is not necessarily limited thereto. There are not many known phenol resins for refractories that are commercially available with such a high residual carbon ratio. For example, as disclosed in Japanese Patent Application Laid-Open No. 2010-105891, It is possible to achieve a residual carbon ratio of 50% or more by adjusting the solvent type and amount.

  Examples of the present invention will be described below. In addition, a present Example shows the one aspect | mode of this invention, and is not limited to these Examples.

  Sample preparation was performed using a product line for converters. Raw materials were weighed at the ratios shown in Tables 1 and 2, and kneading was performed using a high speed mixer. Molding was performed at a molding pressure of 180 MPa at maximum with vacuum friction in a standard shape for a side wall having a length of 810 mm. Drying was held in a batch furnace at a maximum of 280 ° C. for 5 hours.

  From this, a sample for measuring physical properties was cut out to measure the apparent porosity, and the oxidation resistance and corrosion resistance were evaluated.

  In measuring the apparent porosity, a sample having a shape of 60 × 60 × 60 mm was used. The apparent porosity was measured after heat treatment in a reducing atmosphere at 1400 ° C. for 3 hours. When the heat treatment temperature is less than 1400 ° C., the reaction inside the MgO—C brick cannot be completed, and the heat load is not sufficient, so that it is not suitable for evaluation of denseness. In addition, sintering proceeds at a temperature exceeding 1400 ° C., and it becomes difficult to separate and evaluate the effect of sintering as an evaluation of denseness, and the load on the furnace for heat treatment is large and a steady measurement method. Unpreferable. If the heat treatment time is less than 3 hours, the reaction inside the MgO-C brick cannot be completed, which is not suitable. Furthermore, if the heat treatment is longer than this, sintering proceeds and it becomes difficult to evaluate the effect separately. In this example, the apparent porosity of a sample after heat treatment in a reducing atmosphere at 1400 ° C. for 3 hours was measured according to the Archimedes method (JIS R 2205) using white kerosene as a liquid medium.

  Evaluation of oxidation resistance was cut out from the sample after drying to φ50 × 50 mm and fired in an electric furnace at 1400 ° C. for 5 hours in an air atmosphere. Thereafter, the center in the height direction of the sample was cut, and the thickness of the portion where the carbon component was decarburized and discolored was measured in four directions, and the average value of these values was taken as the decarburized layer thickness.

Corrosion resistance was evaluated by a rotational erosion test. In the rotary erosion test, a test brick was lined on the inner surface of a drum having a horizontal rotation axis, slag was added, and the brick surface was eroded by heating. The heating source is an oxygen-propane burner, the test temperature is 1700 ° C., the slag composition is CaO / SiO ₂ = 3.4, FeO = 20 mass%, MgO = 3 mass%, and slag is discharged and charged every 30 minutes. Repeated 10 times. After the test was completed, the size of the maximum melted portion of each brick was measured to calculate the erosion amount, and the corrosion resistance index of “Comparative Example 1” shown in Table 1 with the erosion amount being 100 was displayed. This corrosion resistance index indicates that the larger the value, the better the corrosion resistance.

In Reference Examples 1 to 3 and Comparative Examples 1 to 3, in the MgO-C brick having a graphite content (referred to as a proportion of the total amount of the magnesia raw material and graphite; the same shall apply hereinafter) of 13% by mass, the addition amount of metal Al It is the result of investigating the combined use effect of boron carbide when changing. In Reference Example 1, 0.13% by mass of metal Al having a particle size of 75 μm or less and 0.065% by mass of boron carbide having a particle size of 45 μm or less were added, and an apparent porosity of 7.7% was achieved. Both oxidation resistance and corrosion resistance were excellent. On the other hand, in Comparative Example 1, since boron carbide was not added, the apparent porosity was increased, and the oxidation resistance and corrosion resistance were inferior.

Reference Examples 2 and 3 are cases where the addition amount of metal Al is 1.0 mass%, 1.9 mass%, and the boron carbide addition amount is 0.5 mass% and 0.95 mass%, Compared with Reference Example 1, the apparent porosity was further reduced, and the oxidation resistance was excellent. On the other hand, in Comparative Example 2, since boron carbide was not added, the apparent porosity increased as compared with Reference Example 3. In Comparative Example 3, the amount of boron carbide added to the amount of added metal Al was excessive, so the apparent porosity increased and the corrosion resistance decreased.

Reference Example 4 is a case where the amount of boron carbide added to the amount of added metal Al is 1.0% by mass, and an apparent porosity of 7.6% is achieved. Reference Example 5 was a case where the amount of boron carbide added relative to the amount of added metal Al was 20% by mass, and the result was that the apparent porosity was further reduced and the oxidation resistance and corrosion resistance were improved.

  In Comparative Example 4, the addition amount of boron carbide relative to the added metal Al amount is appropriate, but boron carbide was added as relatively coarse particles having a particle size of 75 μm or less (content of particle size of 45 μm or less is 15% by mass). Apparent porosity has increased.

  Examples 6 and 7 are results of adjusting and evaluating the mass ratio of the magnesia raw material having a particle size of 0.075 mm to 1 mm to the magnesia raw material having a particle size of less than 0.075 mm to 5.38 and 6.63. Apparent porosity was reduced, and oxidation resistance and corrosion resistance were improved.

  Examples 8, 9, and 10 are MgO-C bricks having a graphite content of 8, 18, and 25% by mass, respectively. All of them had a low apparent porosity and showed good oxidation resistance and corrosion resistance. On the other hand, Comparative Example 5 is an MgO—C brick having a graphite content of 7% by mass, but the apparent porosity increased and the oxidation resistance decreased accordingly. It was also confirmed that the apparent porosity increased and the corrosion resistance decreased in Comparative Example 6 having a graphite content of 26% by mass.

  In Example 11, a further reduction in porosity is achieved by refining metal Al. On the other hand, in Comparative Example 7, as a result of adding 1.0% by mass of relatively coarse metal Al of 0.15 mm or less (content of particle size of 75 μm or less is 10% by mass), a sufficient porosity reduction effect is obtained. The results were inferior in oxidation resistance and corrosion resistance compared to Examples 6 and 11.

  Example 12 is a case where metal Si having a particle size of 75 μm or less is used in combination. It was confirmed that the porosity was lowered by using metal Si together. In Example 13, metal Si having a particle size of 45 μm or less was used, and a further reduction in porosity was achieved.

  Example 14 is a case in which finely divided metal Al having a particle diameter of 45 μm or less and a finely divided metal Si having a particle diameter of 45 μm or less are used in combination, and by further using the finely divided metal, a further low porosity is achieved. Was achieved.

  Example 15 is an MgO-C brick using a phenol resin having a residual carbon ratio of 48% as a binder. The characteristics were improved as compared with the case where the residual carbon ratio of Example 14 was 42%.

  Examples 16 and 17 are examples in which a phenol resin having a residual carbon ratio of 30% is used as the binder and the content of the pitch-based raw material is 1 or 2% by mass, but is within the scope of the present invention and is dense. Organization.

Claims (4)

The magnesia carbon brick containing the magnesia raw material and graphite contains 8% by mass or more and 25% by mass or less of graphite and 75% by mass or more and 92% by mass or less of magnesia raw material in the proportion of the total amount of the magnesia raw material and graphite. Furthermore, a metal Al having a particle size of 75 μm or less is added to 85% by mass or more of metal Al. The boron carbide having a content of 1 to 15% by mass and a particle size of 45 μm or less of 85% by mass or more is added to the amount of graphite. A magnesia raw material having a particle size of 0.075 mm or more and 1 mm or less is contained in a proportion of the total amount of the magnesia raw material and graphite as a particle size constitution of the magnesia raw material. A particle size of 35% by mass or more and a magnesia raw material having a particle size of less than 0.075 mm is blended in an amount of 15% by mass or less and a magnesia raw material having a particle size of less than 0.075 mm. The magnesia carbon brick whose mass ratio of the magnesia raw material of 0.075 mm or more and 1 mm or less is 4.2 or more .   The magnesia carbon brick according to claim 1, wherein an apparent porosity after heat treatment in a reducing atmosphere at 1400 ° C for 3 hours is 7.8% or less. The magnesia carbon brick according to claim 1 or 2 , wherein the metal Si having a particle size of 45 µm or less contains 85 mass% or more of metal Si with respect to the amount of added graphite. The magnesia carbon brick according to any one of claims 1 to 3 , wherein a phenol resin having a residual carbon ratio of 48% or more is used as a binder.