JP6546687B1 - Method of manufacturing magnesia carbon brick - Google Patents

Abstract

An object of the present invention is to improve the spalling resistance of a magnesia carbon brick having a graphite content of 5% by mass or less. SOLUTION: A magnesia carbon brick obtained by adding an organic binder to a refractory raw material composition, kneading and forming, and then heat-treating, and the refractory raw material composition contains 50% by mass of magnesia having a particle size of 1 mm or more and less than 5 mm. More than 75 mass%, magnesia with a particle size of 0.075 mm or more and less than 1 mm is 20 mass% or more and 40 mass% or less, magnesia with a particle size of less than 0.075 mm is 1 mass% or more and 10 mass% or less, and aluminum and / or The total amount of aluminum alloy is 1.5% by mass or more and 4% by mass or less, the graphite content is 5% by mass or less (including 0), and the particle size is 3 mm or more for magnesia having a particle size of 1 mm or more and less than 3 mm. A magnesia carbon brick whose mass ratio of magnesia of less than 5 mm is 0.8 or more and 1.2 or less. 【Selection chart】 None

Description

The present invention relates to a method for producing magnesia carbon brick used in a molten metal container, a smelting furnace, and the like.

  Although magnesia carbon brick generally contains graphite as a carbon source, since it contains graphite, it has a high thermal conductivity and there is a problem of heat loss due to heat dissipation of the molten metal and a problem of carbon pickup. In addition, when used in an oxidizing atmosphere such as a converter or a secondary refining facility, the slag component infiltrates into pores formed with the disappearance of graphite due to oxidation, and the dissolution of aggregate is accelerated, resulting in corrosion resistance. There is also the problem of becoming insufficient.

  From these viewpoints, it is desirable that the magnesia carbon brick be as small as possible in graphite, but when the amount of graphite is small, there arises a problem that the spalling resistance is lowered.

  Therefore, various means have been proposed to suppress the decrease in spalling resistance associated with the reduction of the amount of graphite.

For example, in Patent Document 1, the mass ratio of the amount of magnesia particles having a particle diameter of 1 mm or more to the amount of magnesia particles having a particle diameter of less than 1 mm in the refractory material composition is 1.27 to 2.58, and magnesia and graphite A magnesia carbon brick is disclosed in which the blending amount of graphite in the total amount is 10% by mass or less. Since this magnesia carbon brick contains a large number of coarse particles as compared with a general magnesia carbon brick, it is considered that the spalling resistance is good despite the small content of graphite.
However, in the magnesia carbon brick of Patent Document 1, when the graphite content is 5% by mass or less, the spalling resistance may still be insufficient.

  Further, in Patent Document 2, 3.0 mass% or more and 10.0 mass% or less of magnesia with a particle diameter of less than 0.075 mm, and 87.0 mass% or more of magnesia with a particle diameter of 0.075 mm or more and less than 5 mm. The mass ratio of magnesia with a particle size of 1 mm or more and less than 5 mm to a magnesia particle size of 96.0 mass% or less and with a particle size of 0.075 mm or more and less than 1 mm is 1.66 or more and 2.34 or less. A magnesia carbon brick is disclosed. With such a particle size configuration, it is said that densification and low modulus of elasticity are simultaneously satisfied by heat reception at the time of use.

  The present inventors are expanding the use of the magnesia carbon brick of Patent Document 2 centering on secondary refining facilities such as RH, DH and VOD pots, but in these uses, the spalling resistance is further increased. It has been found that there are cases where improvement of

JP, 2013-72090, A Patent No. 6279052 gazette

  The problem to be solved by the present invention is to further improve the spalling resistance in a magnesia carbon brick having a graphite content of 5% by mass or less.

  The present inventors conducted various studies on the content of aluminum in order to improve the spalling resistance of magnesia carbon bricks having a graphite content of 5% by mass or less. When aluminum and / or aluminum alloy is contained in a total amount of 1.5% by mass or more and 4% by mass or less, magnesia carbon having a large amount of conventional graphite, in which the elastic modulus decreases due to heat reception at the time of use It was found that the opposite result to brick was obtained. As a result, even when the graphite content was 5% by mass or less, a magnesia carbon brick excellent in spalling resistance and corrosion resistance could be obtained.

That is, according to one aspect of the present invention, the following magnesia carbon brick is provided.
After the addition of organic binder to refractory raw material formulation by kneading molding, in the production method of magnesia carbon brick for heat treatment,
The refractory material composition is
50 mass% or more and 75 mass% or less of magnesia with a particle diameter of 1 mm or more and less than 5 mm,
20 mass% or more and 40 mass% or less of magnesia with a particle diameter of 0.075 mm or more and less than 1 mm,
1% by mass or more and 10% by mass or less of magnesia with a particle size of less than 0.075 mm,
And 1.5 to 4 mass% of aluminum and / or aluminum alloy in total.
The content of graphite is 5% by mass or less (including 0),
Method of manufacturing magnesia carbon brick.

  Hereinafter, the configuration of the refractory raw material composition, which is a feature of the present invention, will be described.

  In the present invention, aluminum and / or aluminum alloy (hereinafter collectively referred to as “aluminium metal / alloy”) is used for the purpose of improving spalling resistance and corrosion resistance, among which aluminum metal / alloy is added. Thus, the improvement of the spalling resistance is an opposite effect to the conventional magnesia carbon brick having a high graphite content.

The following mechanism can be considered as the reason.
First, when the aluminum in the brick is subjected to heat during use, part of it is oxidized to form alumina, which reacts with magnesia to form spinel. When this spinel is produced, it causes a volume expansion called a so-called spinel expansion.

  The conventional magnesia carbon brick has a low elastic structure because it contains a large amount of graphite, and if spinel expansion occurs due to heat reception during use, it is considered that this expansion can be absorbed to some extent in the brick structure. For this reason, it is considered that the decrease in elastic modulus due to heat reception at the time of use is small, and rather, the development of sintered bond of spinel advances densification of the structure and the elastic modulus increases and the spalling resistance decreases.

  On the other hand, the magnesia carbon brick of the present invention has a high elasticity structure because it contains a small amount of graphite and a large number of coarse particles and a small amount of fine powder, and it is difficult to absorb spinel expansion in the brick structure. For this reason, when the brick structure expands due to spinel expansion, the contact area between coarse particles (aggregate particles) decreases, and pores or microcracks are formed in the structure to lower the elastic modulus, and It is considered that the polling performance is improved. In addition, the magnesia carbon brick of the present invention is likely to lack bonds in the brick structure due to the small amount of fine powder constituting the matrix, but relatively large amounts of aluminum metal and alloy such as 1.5 to 4 mass%. Since a large amount of bonds such as spinel derived from aluminum are generated during use because of the inclusion, there is also obtained an advantage that the strength is improved and the corrosion resistance is also improved.

  As described above, the refractory material composition of the magnesia carbon brick of the present invention (hereinafter simply referred to as "the refractory material composition of the present invention") is an aluminum metal / alloy for the purpose of improving the spalling resistance and corrosion resistance. Is contained in the range of 1.5% by mass or more and 4% by mass or less. If the content of the aluminum metal or alloy is less than 1.5% by mass, the spinel generation amount is insufficient, so that the spalling resistance is insufficient and the corrosion resistance is also insufficient. On the other hand, if the content of the aluminum metal or alloy exceeds 4% by mass, expansion of the brick due to spinel formation becomes too large, and there is a problem that fractures occur during use. Furthermore, when spalling resistance and corrosion resistance are required more, content of an aluminum metal and an alloy can be 2 mass% or more and 3 mass% or less.

  In addition, the refractory raw material composition of the present invention has a particle size configuration with a small amount of fine powder and a large number of coarse particles in order to improve the spalling resistance. That is, the refractory raw material composition of the present invention contains 50% by mass or more and 75% by mass or less of magnesia with a particle size of 1 mm or more and less than 5 mm. If the magnesia of particle size 1 mm or more and less than 5 mm is less than 50% by mass, the structure becomes too dense and spalling resistance becomes insufficient, and if it exceeds 75% by mass, the structure becomes too porous and the strength and corrosion resistance become insufficient. .

  Furthermore, in the refractory raw material composition of the present invention, the mass ratio of magnesia with a particle diameter of 3 mm or more and less than 5 mm to the magnesia with a particle diameter of 1 mm or more and less than 3 mm (hereinafter "magnesia mass ratio" Can be made 0.8 or more and 1.2 or less. The magnesia mass ratio affects the spalling resistance, and if it is less than 0.8, the spalling resistance is slightly insufficient, and if it exceeds 1.2, coarse particles increase, resulting in a porous structure with strength and corrosion resistance. Is somewhat inadequate.

  In the refractory raw material composition of the present invention, the content of magnesia having a particle diameter of 0.075 mm or more and less than 1 mm is 20% by mass or more and 40% by mass or less. If the content of magnesia with a particle diameter of 0.075 mm or more and less than 1 mm is less than 20% by mass, the structure becomes too porous and the strength and corrosion resistance become insufficient, and when it exceeds 40% by mass, the structure becomes too dense and spalling resistance Sex is reduced.

  Furthermore, in the refractory raw material composition of the present invention, the content of magnesia having a particle size of less than 0.075 mm is 1% by mass or more and 10% by mass or less. Since magnesia with a particle size of less than 0.075 mm forms part of a bond (bonded structure) by receiving heat during use, if it is less than 1% by mass, the structure becomes too porous and the strength and corrosion resistance become insufficient, and 10% by mass When it exceeds, the structure becomes too fine and the spalling resistance decreases.

  In the refractory raw material composition of the present invention, the total amount of magnesia can be 93% by mass or more in order to obtain higher corrosion resistance.

  Here, the particle size referred to in the present invention is the size of the sieve when the refractory raw material particles are separated by sieving, and for example, magnesia having a particle size of less than 0.075 mm has a sieve size of By magnesia which passes a sieve of 0.075 mm, magnesia having a particle diameter of 0.075 mm or more is a magnesia whose sieve does not pass a sieve of 0.075 mm.

  In the refractory raw material composition of the present invention, the content of graphite is 5% by mass or less (including 0). That is, in the present invention, although it may not contain graphite, even when it does not contain graphite, the effect of improving the spalling resistance can be achieved by containing 1.5% by mass or more and 4% by mass or less of aluminum metal or alloy as described above. Is obtained. Therefore, the magnesia carbon brick of the present invention can be used in applications that can not contain graphite. Furthermore, even when graphite can be contained at 5% by mass or less, by containing 1.5% by mass or more and 4% by mass or less of the aluminum metal / alloy, the spalling resistance improvement effect can be obtained. On the other hand, when the content of graphite exceeds 5% by mass, the corrosion resistance is lowered, and the problem of carbon pickup becomes remarkable at the time of use.

Further, when the magnesia carbon brick of the present invention is used in a secondary refining facility such as VOD, the content of graphite is set to 0.5 mass% or more in order to further secure spalling resistance, and carbon is further enhanced. From the viewpoint of suppressing the pickup, the magnesia carbon brick can be made to have a content of graphite of 2% by mass or less. Furthermore, when increasing the effect of suppressing carbon pickup, the content of graphite and 0.5 mass% or more, and the fixed carbon content in the brick can be less than 2 wt%. In order to set the amount of fixed carbon in the brick to less than 2% by mass, the fixed carbon in the brick includes not only graphite but also organic binders such as pitch, carbon black and phenol resin, etc. It is possible to use a refractory material composition and an organic binder such that the total amount of carbon content and graphite content is less than 2% by mass.

  As described above, since the magnesia carbon brick of the present invention has a small graphite content and is excellent in spalling resistance and corrosion resistance, it can be suitably used as a lining brick for RH and VOD pots to be treated with low carbon steel. it can. In particular, it is most suitable for the slag line of a VOD pot or RH lower tank where dissolution loss due to slag is severe.

  Since the magnesia carbon brick of the present invention is excellent in spalling resistance and corrosion resistance even if it contains no graphite or has a small graphite content of 5% by mass or less, sufficient durability can be obtained. In addition, when used in a secondary refining facility, it is possible to suppress the carbon pickup, improve the quality of the steel, and reduce the heat loss.

  Magnesia to be used for the refractory material composition in the present invention may be either fused magnesia or sintered magnesia, and these may be used in combination. The composition is also not particularly limited, but magnesia with high MgO purity can be used to obtain higher corrosion resistance, for example, the MgO purity may be 96 mass% or more, and further 98 mass% or more.

  Any aluminum metal or alloy that is generally used in magnesia carbon brick or the like can be used without any problem. Also, the particle size can be used at less than 0.075 mm.

  As graphite, although scaly graphite used for ordinary magnesia carbon brick can be used, synthetic graphite can also be used. Also, the particle size can be used at less than 0.1 mm.

  A raw material generally used as a raw material of magnesia carbon brick other than magnesia, graphite and aluminum metal / alloy can be used without adverse effect as long as the total amount is about 3% by mass or less. For example, silicon, pitch, carbon black, boron carbide, silicon carbide, fibers, glass and the like.

  The magnesia carbon brick of the present invention can be manufactured by a general magnesia carbon brick manufacturing method. That is, the magnesia carbon brick of the present invention can be obtained by heat-treating after adding and kneading an organic binder to the above-mentioned fireproofing raw material combination and forming it. The heat treatment temperature can be, for example, 150 to 400 ° C.

  As an organic binder, the organic binder currently used by normal magnesia carbon brick can be used, for example, furan resin, a phenol resin, etc. can be used. The organic binder may be used in the form of powder or liquid dissolved in a suitable solvent, or in combination of liquid and powder. The methods and conditions of kneading, molding and heat treatment also conform to the general method for producing magnesia carbon brick.

  Tables 1 to 3 show the composition of the refractory material blend and the physical properties of magnesia carbon brick obtained from the refractory material blend. These bricks are kneaded by adding an appropriate amount of phenol resin as an organic binder to the refractory raw material compositions of Tables 1 to 3 and formed into a shape of 230 mm × 114 mm × 100 mm by an oil press, and maintained at a maximum temperature of 250 ° C. for 5 hours Obtained by heat treatment of And the sample for physical-property measurement was cut out from the obtained brick, and while measuring the amount of fixed carbon, an apparent porosity, a sonic elastic modulus, and a hot bending strength, corrosion resistance and spalling resistance were evaluated. Moreover, about Example 1 to 4 and Comparative example 2 and Comparative example 3, the residual line change rate was measured.

  The amount of fixed carbon in the brick was measured in accordance with JIS M 8812.

  In the measurement of apparent porosity, a sample of shape 50 × 50 × 50 mm was embedded in coke breath, heated to 1400 ° C. in an electric furnace, held for 5 hours, and naturally cooled. Thereafter, the solvent was changed to white kerosene and the measurement was performed according to JIS R 2205. The lower the apparent porosity, the denser the brick, which is considered to be effective in improving the corrosion resistance.

  In the measurement of the sonic elastic modulus, the sample of the shape 20 × 20 × 80 mm was embedded in the coke breath as in the measurement of the apparent porosity, heated to 1400 ° C. in the electric furnace, held for 3 hours and naturally cooled .

  The hot bending strength was measured at 1400 ° C. in a nitrogen atmosphere in accordance with JIS R 2656.

The corrosion resistance was evaluated by a rotational erosion test. In the rotary erosion test, the inner surface of a drum having a horizontal rotation axis was lined with a test brick, and an eroding agent was charged and heated to erode the brick surface. The heat source is an oxygen-propane burner, the test temperature is 1750 ° C., the composition of the erodible agent is 20% by mass of CaO, 10% by mass of SiO ₂ , 5% by mass of Al, 5% by mass of Fe-Si, steel: 60 The mass% was used, and the discharging and discharging of the eroding agent were repeated 10 times every 30 minutes. The steel melts in the process of being heated by the burner and reacts with oxygen to form FeO, thereby melting the test brick. After the test was completed, the amount of erosion (mm) of the largest erosion portion of each brick was measured, and the erosion resistance (mm) of the brick of "Comparative Example 2" described in Table 1 was represented by 100 as a corrosion resistance index. . The smaller the corrosion resistance index, the better the corrosion resistance.

  In the test of the spalling resistance, a 40 × 40 × 190 mm sample calcined at 1400 ° C. for 3 hours in a reducing atmosphere was used. The test was repeated three times by immersion in hot metal heated to 1600 ° C. for 90 seconds and then water cooling for 30 seconds. After the test, the sample was cut and the cross section was observed to evaluate the spalling resistance. Specifically, ◎ (excellent) that the medium or more cracks occurred in the third, ○ (good) that the medium or more cracks occurred in the second, 回 (good), the medium or more cracks in the first The thing which arose was made into x (improper), and when evaluation was x (improper), it was judged that it was not suitable for actual furnace use.

  The residual linear change rate was measured for a 20 × 20 × 80 mm sample after firing for 3 hours at 1400 ° C. in a reducing atmosphere and after firing for 30 hours at 1400 ° C. in a reducing atmosphere.

Although Example 1 to Example 4 described in Table 1 are cases where the content of aluminum is different, they are within the scope of the present invention and exhibited sufficient spalling resistance and corrosion resistance.
On the other hand, Comparative Example 1 did not contain aluminum, and Comparative Example 2 had 1% by mass of aluminum. The elastic modulus was increased in all cases, the spalling resistance was lowered, and the corrosion resistance was also lowered. On the other hand, Comparative Example 3 is the case where the aluminum content is 5% by mass, and the residual linear change ratio after firing at 1400 ° C. for 30 hours is significantly increased from 1.34% to 0.91% in Example 4. . From the past findings, magnesia carbon brick used in secondary smelting furnace etc. If the residual linear change rate (residual expansion) after firing at 1400 ° C for 30 hours exceeds 1%, the thermal expansion during use is too large and cracking occurs There is a problem that the life of the generated brick is reduced.

Examples 5 to 8 are cases where magnesia mass ratio (mass ratio of particle size 3 mm or more and less than 5 mm particle size to magnesia with particle diameter 1 mm or more and less than 3 mm) is different, but within the scope of the present invention Corrosion resistance and corrosion resistance.
However, in Example 5, since the mass ratio of magnesia is low (the amount of magnesia with a particle diameter of 3 mm or more and less than 5 mm is small), a dense structure is formed, the elastic modulus is slightly increased, and the spalling resistance is slightly reduced. In addition, since Example 8 had a high magnesia mass ratio (small amount of magnesia with a particle diameter of 1 mm or more and less than 3 mm), it had a slightly porous structure, and its strength and corrosion resistance were slightly reduced.

Examples 9 and 10 described in Table 2 are cases where the content of magnesia with a particle diameter of 0.075 mm or more and less than 1 mm is different, but within the scope of the present invention, sufficient spalling resistance and corrosion resistance showed that.
On the other hand, Comparative Example 4 is a case where the content of magnesia with a particle diameter of 0.075 mm or more and less than 1 mm is less than the lower limit value of the present invention, a porous structure is formed, and the strength and the corrosion resistance decrease. On the other hand, Comparative Example 5 is a case where the content of magnesia with a particle diameter of 0.075 mm or more and less than 1 mm exceeds the upper limit value of the present invention, and the spalling resistance is lowered.

Although Example 11 and Example 12 differ in content of magnesia with a particle size of less than 0.075 mm, they were within the scope of the present invention and exhibited sufficient spalling resistance and corrosion resistance.
On the other hand, in Comparative Example 6, the content of magnesia having a particle size of less than 0.075 mm was below the lower limit value of the present invention, resulting in a porous structure and a decrease in strength and corrosion resistance. On the other hand, Comparative Example 7 is the case where the content of magnesia having a particle size of less than 0.075 mm exceeds the upper limit value of the present invention, and the spalling resistance is lowered.

Example 13 described in Table 3 has no graphite, and Examples 14 to 16 have different graphite contents, but all are within the scope of the present invention and sufficient spalling resistance And corrosion resistance. On the other hand, Comparative Example 8 contained 7% by mass of graphite, and the corrosion resistance was lowered.
Example 17 contains silicon, Example 18 contains silicon and pitch, and Example 19 contains silicon and boron carbide. Both show sufficient spalling resistance and corrosion resistance. The

Claims (5)

After the addition of organic binder to refractory raw material formulation by kneading molding, in the production method of magnesia carbon brick for heat treatment,
The refractory material composition is
50 mass% or more and 75 mass% or less of magnesia with a particle diameter of 1 mm or more and less than 5 mm,
20 mass% or more and 40 mass% or less of magnesia with a particle diameter of 0.075 mm or more and less than 1 mm,
1% by mass or more and 10% by mass or less of magnesia with a particle size of less than 0.075 mm,
And 1.5 to 4 mass% of aluminum and / or aluminum alloy in total.
The content of graphite is 5% by mass or less (including 0),
Method of manufacturing magnesia carbon brick. The method for producing a magnesia carbon brick according to claim 1, wherein the mass ratio of magnesia having a particle diameter of 3 mm to 5 mm with respect to magnesia having a particle diameter of 1 mm to 3 mm in the refractory material composition is 0.8 to 1.2. . The manufacturing method of the magnesia carbon brick according to claim 1 or 2 whose content of aluminum and / or aluminum alloy is 2 mass% or more and 3 mass% or less in total in the refractory material composition. The manufacturing method of the magnesia carbon brick as described in any one of Claim 1 to 3 whose content of graphite is 0.5 mass% or more and 2 mass% or less in a refractory raw material combination . In the refractory material composition , the refractory material composition and the organic binder are used such that the content of graphite is 0.5% by mass or more and the amount of fixed carbon in the magnesia carbon brick is less than 2% by mass. The manufacturing method of the magnesia carbon brick as described in any one of Claim 1 to 3.