JP6419555B2 - Cast refractory - Google Patents

Description

  The present invention relates to a cast refractory used for lining a molten metal container such as a tundish or a molten steel ladle, and particularly to a cast refractory excellent in spalling resistance against thermal spalling and mechanical spalling.

  In recent years, the resistance to erosion of molten metal and slag (hereinafter referred to as corrosion resistance) for cast refractories used for the lining of molten metal containers such as tundish and molten steel ladle has improved with the increase in the purity of the raw materials used. Yes. On the other hand, however, the corrosion resistance has been improved and the life of the refractory has been extended, so that damage due to cracks and peeling has flowed in and the proportion of the influence on the life of the refractory has increased.

  The causes of cracking and peeling of cast refractories can be broadly classified as follows. (1) Phenomenon in which stress is generated due to the difference in thermal expansion between the surface and the inside of the cast refractory body when repeated rapid heating / cooling (hereinafter referred to as thermal spalling), (2 ) Phenomena in which stress is generated in the refractory construction body poured by mechanical force from the outside and cracks and peeling occur (hereinafter referred to as mechanical spalling).

  As a method for improving the resistance to each spalling (hereinafter referred to as spalling resistance), a method of using a long columnar refractory aggregate for a part or all of the refractory aggregate in the cast refractory is a conventional method. Proposed. The use of long columnar refractory aggregates extends the propagation path of cracks generated in cast refractories compared to general granular refractory aggregates obtained by pulverizing massive refractory raw materials. The spalling resistance of the cast refractory is improved by improving the resistance of the cast refractory to crack propagation.

  For example, in Patent Document 1, a sintered aggregate of a heat-resistant metal oxide having a diameter of 1 to 30 mm and an aspect ratio expressed by length / diameter of 3 to 50 in a refractory is uniformly 1 to 40% by mass. A spalling refractory material dispersed in is disclosed. Patent Document 1 discloses that, as a result of using this spalling refractory, the bending strength of the refractory brick after a thermal spalling test at 1400 ° C. is increased.

  In Non-Patent Document 1, how rod-like aggregates that are different in shape from ordinary crushed aggregates are used in typical corundum low-cement castables, and how they affect fracture characteristics and heat-resistant spalling properties As a result, it has been disclosed that low cement castables using 20% or more of rod-like aggregates have improved fracture characteristics, and a slight improvement effect was observed in the 1450 ° C heat-resistant spalling test. Has been.

  However, when the long columnar refractory aggregate disclosed in Patent Document 1 and the rod-shaped aggregate described in Non-Patent Document 1 are applied to a cast refractory for tundish lining, cracks on the working surface side are reduced. Although an effect was seen, a large crack that led to peeling occurred at a constant thickness from the working surface side, so it was not possible to obtain the effect of improving the spalling resistance and improving the tundish life .

Japanese Patent Laid-Open No. 53-001205

"Effects of aggregates on the fracture characteristics of amorphous refractories" Makoto Ishikawa, Refractories 41, 80, 1989

  The present inventors inferred the reason why cracks occurred despite the use of the long columnar refractory aggregate as described above.

  The lining construction body of the molten metal container has a temperature gradient between the working surface side and the back surface side during use. The site where a large crack that would lead to peeling occurred was a site where the ambient temperature during use was around 600 ° C. Normally, cast refractories using hydraulic binders break down the hydraulic binder from 300 ° C or higher to form fine pores. It develops its strength while reducing pores. Therefore, in the vicinity of 600 ° C., the hydraulic binder in the matrix is decomposed to have fine pores, but sintering is not progressing. Therefore, the part near 600 ° C in the thickness direction of the construction body is in an unsintered state, so it has a lower strength than the sintered working surface side, and the bonding material has been decomposed and lost. For this reason, the strength is lower than the back side where the binder is not decomposed and remains.

  Here, since the long columnar refractory aggregate having anisotropy has a large specific surface area compared with a general granular refractory aggregate, the resistance to hinder the fluidity during pouring is large, and the long columnar refractory aggregate has a long columnar shape. The cast refractory to which the refractory aggregate is applied has a poor filling property at the time of construction, and has many fine pores when the pouring is completed. For this reason, refractories to which long columnar refractory aggregates are applied have more fine pores, especially in the unsintered area around 600 ° C and where the binder has decomposed. It is thought that the strength is lower than when using a synthetic aggregate, and as a result, a large crack that leads to peeling is likely to occur.

  As a method of preventing the occurrence of cracks due to such a decrease in strength, a method of improving the filling property during the construction of the cast refractory can be considered. However, in order to improve the filling property, for example, there is a problem that the corrosion resistance decreases when the amount of kneading water is increased, and there is a problem that the long columnar refractory aggregate and the matrix part are separated when the vibration time by the vibrator is increased. is there.

  The present invention has been made in view of the above-mentioned problems, and the object thereof is a cast refractory using a long columnar refractory aggregate, which has a low temperature around 600 ° C. due to the shape of the long columnar refractory aggregate. An object of the present invention is to provide a cast refractory material excellent in spalling resistance which can be preferably used for the lining of a molten metal container by preventing the occurrence of cracks by suppressing a decrease in strength in the temperature range.

  As a result of intensive studies to achieve the above object, the present inventors have found that, in a cast refractory using a long columnar refractory aggregate, a high strength long columnar refractory aggregate and metal The inventors have found that a decrease in strength around 600 ° C. can be suppressed by adding an appropriate amount of fiber, and have arrived at the present invention.

  That is, the cast refractory according to the present invention has (A) a substantially circular cross-sectional shape, a maximum cross-sectional diameter of 5 to 20 mm, and an axial length / maximum cross-sectional diameter with respect to 100% by mass of the refractory compound. 5-25% by mass of a long columnar refractory aggregate having a specified aspect ratio of 2-5, a bending strength measured according to JIS R1601 of 60 MPa or more, and (B) a maximum cross-sectional diameter of 0.2- It is characterized in that 1 to 10% by mass of a metal fiber having a length of 1.5 mm and a length of 20 to 35 mm is externally added.

In a further preferred embodiment of the present invention, the refractory composition comprises a refractory aggregate, a refractory fine powder, an alumina cement and a dispersant, the chemical component of which is an alumina-containing 55% by mass or more Al ₂ O _3. It is siliceous and the long columnar refractory aggregate is a sintered mullite containing 55% by mass or more of Al ₂ O ₃ .

  In a further preferred embodiment of the present invention, the cast refractory according to the present invention is a cast refractory for tundish lining.

  According to the cast refractory material using the long columnar refractory aggregate of the present invention, it becomes possible to prevent the occurrence of cracks leading to peeling even in a low temperature region around 600 ° C. And can be suitably used for lining of molten metal containers such as ladle and molten steel ladle.

It is sectional drawing which shows the example of the shape of the metal fiber used with the cast refractory of this invention. 6 is a graph showing the number of channels of life when the cast refractories of Examples 4 and 5 and Comparative Example 1 are applied to a tundish lining.

  Hereinafter, although the form for implementing this invention is demonstrated, prior to that, the technical significance of the cast refractory specified by this invention is demonstrated.

  The feature of the cast refractory of the present invention using the long columnar refractory aggregate is not only the improvement of the resistance to the crack growth in the high temperature region of 1000 ° C or higher, but also the suppression of the strength decrease near 600 ° C. It is to prevent the occurrence of cracks that lead to peeling.

(A) Long columnar refractory aggregate The long columnar refractory aggregate used in the cast refractory of the present invention extends the crack propagation path in a high temperature range of 1000 ° C or higher, and prevents the cast refractory from cracking. By improving the resistance, the spalling resistance of the cast refractory is improved.

  The longest columnar refractory aggregate has a maximum cross-sectional diameter of 5 to 20 mm. A maximum cross-sectional diameter of less than 5 mm is not preferable because the structural strength is weak and the effect of suppressing the progress of cracks cannot be obtained. When the maximum cross-sectional diameter is larger than 20 mm, the flowability of the cast refractory is lowered, which is not preferable.

  The aspect ratio defined by the axial length / maximum cross-sectional diameter is 2-5. If it is less than 2, the effect of resistance to crack growth cannot be obtained. On the other hand, if it exceeds 5, not only the production cost of the aggregate is increased, but also the fluidity of the cast refractory is lowered and the filling property is lowered, so that the resulting structure becomes brittle. The aspect ratio defined here refers to the average aspect ratio of 50 aggregates. For example, a long columnar refractory aggregate having an aspect ratio of 2 may have an average aspect ratio of 2, and a refractory aggregate having an aspect ratio of less than 2 may be included therein.

  The bending strength of the long columnar refractory aggregate is preferably high in order to suppress crack growth in a high temperature range of 1000 ° C. or higher. Specifically, according to JIS R1601: 2008 “Testing method for room temperature bending strength of fine ceramics”, a prismatic specimen with a width of 4.0 mm × thickness of 3.0 mm × total length of 45 mm is subjected to a three-point bending test method. The measured value is 60 MPa or more. When the bending strength is less than 60 MPa, the aggregate itself breaks due to the developed crack, and the effect of suppressing the progress of the crack, which is the purpose of using the long columnar refractory aggregate, cannot be obtained.

As the composition of the long columnar refractory aggregate, various materials can be used without any particular limitation as long as the above-mentioned bending strength is satisfied, but those having a small difference in thermal expansion coefficient from the matrix portion are used. It is preferable to do. For example, the chemical components of the refractory formulation as described later, Al ₂ O ₃ is 55 percent by weight or greater of the alumina - if a siliceous, long columnar refractory aggregate is the Al ₂ O ₃ less than 55 wt% content It is preferable to use sintered mullite.

  The addition amount of the long columnar refractory aggregate is 5 to 25% by mass on the basis of 100% by mass of the refractory compound. If the addition amount is less than 5% by mass, it is not possible to obtain the effect of preventing the occurrence and progress of the target crack, and if the addition amount exceeds 25% by mass, the filling property at the time of construction is decreased, which is preferable. Absent.

The method for producing the long columnar refractory aggregate of the present invention is not particularly limited, but from the viewpoint of ease of production and production cost, for example, a method of firing a product formed by extrusion of a slurry-like raw material in a rotary kiln or the like. Is preferred. In molding by slurry extrusion, various shapes such as circular and polygonal cross sections can be produced depending on the shape of the die, but from the viewpoint of problems such as corner chipping during firing in a rotary kiln and the flowability of cast refractories, it is almost The thing of circular cross-sectional shape is preferable. Here, when the cross-sectional shape is substantially circular, the circularity of the cross-section [4 × π × S / L ² (where S is the cross-sectional area and L is the cross-sectional circumference)] is 0.8 or more. Say. The circularity is preferably 0.85 or more.

(B) Metal fiber The metal fiber used for the cast refractory of the present invention suppresses a decrease in strength near 600 ° C., which is a particular problem of the cast refractory of the present invention using a long columnar refractory aggregate. This prevents the occurrence of cracks. Moreover, the progress of the cracks generated is also suppressed by the crosslinking effect.

  The metal fiber has a cross-sectional maximum diameter of 0.2 to 1.5 mm. If the maximum cross-sectional diameter is less than 0.2 mm, the effect of suppressing the decrease in fracture strength at around 600 ° C cannot be obtained, and if it exceeds 1.5 mm, the flowability of the cast refractory decreases, so the fillability during construction is reduced. Deteriorate. The length of the metal fiber is more preferably 20 to 35 mm. If the length is less than 20 mm, the effect of dispersing or suppressing cracks below 1000 ° C. cannot be obtained. If the length exceeds 35 mm, the metal fibers tend to be entangled during kneading, and the flowability of the cast refractory is reduced. Therefore, the obtained organization becomes fragile, which is not preferable.

  The addition amount of the metal fiber is 1 to 10% by mass on the basis of 100% by mass of the refractory compound. If the addition amount is less than 1% by mass, the desired effect cannot be obtained. Even if the addition amount exceeds 10% by mass, only the cost is increased, and the desired effect or more cannot be obtained.

  The kind of metal fiber is not particularly limited, and any metal fiber can be used as long as it is generally used for cast refractories. For example, heat-resistant alloys, heat-resistant steels, stainless steels, high-tensile steels, and carbon steels are included, and they contain one or more elements such as Cu, Al, Mo, Ti, Nb, Be, N, and B. Special alloy steel and the like are also included. Examples that are relatively easily available include SUS310S, SUS304, SUH446, and SUS430, which are specified by JIS.

  As the shape of the metal fiber, any of a linear shape and a curved shape (for example, a mountain shape, a corrugated shape, a dog bone shape, etc.) as shown in FIG. 1 can be used as long as the effects of the present invention are not impaired.

(C) Refractory compound The refractory compound used in the cast refractory of the present invention comprises a refractory aggregate, a refractory fine powder, an alumina cement and a dispersant.

  As the refractory aggregate, it is possible to use a substantially spherical one of an electromelted product and a sintered product used for a general cast refractory, and the particle size thereof is 10 mm or less. The composition is selected from the group consisting of alumina, bauxite, kyanite, andalusite, mullite, chamotte, rholite, silica, alumina-magnesia spinel, magnesia, zircon, zirconia, silicon carbide, graphite, carbon, pitch, etc. 1 type, and two or more types can be used together as necessary.

  Similarly, the refractory fine powder is at least one selected from the group consisting of amorphous silica fine powder, silica fine powder, alumina fine powder, magnesia fine powder, titania fine powder, mullite fine powder, zirconia fine powder, chromia fine powder, silicon carbide fine powder, carbon fine powder and the like. It is a seed, and two or more kinds are used together as necessary. In addition, the fireproof fine powder here is a particle of 200 mesh or less, that is, 0.074 mm or less by JIS standard sieve.

  As the alumina cement, a high-purity high-alumina cement having a CaO content of less than 30% by mass and containing calcium aluminate as a main mineral is used.

  The dispersant is not particularly limited, but inorganic dispersants such as tripolyphosphate, hexametaphosphate, ultrapolyphosphate, and acidic hexametaphosphate, polyacrylate, sulfonate, and polycarboxylic acid Use organic dispersants such as the system.

  In the cast refractory according to the present invention, in addition to the above-described configuration, a thickener, a curing modifier, an explosion-preventing agent, etc. are further added to the refractory compound within a range that does not impair the effects of the invention. You can also.

The refractory composition of the present invention can be used in various combinations according to the purpose of use within the range that does not impair the effects of the present invention. For example, when used suitably for tundish lining, it consists of refractory aggregate such as mullite and chamotte, refractory fine powder such as alumina fine powder and amorphous silica fine powder, JIS class 1 or JIS class 2 alumina cement and dispersant. From the viewpoint of corrosion resistance, it is preferable to use a chemical component having an Al ₂ O ₃ content of 55 wt% or more of alumina-silica.

  Here, experimental results showing the basis of the items defined in the present invention will be described.

(1) Long columnar refractory aggregate
Sintered mullite columnar refractory aggregates with different Al ₂ O ₃ content and shape were produced. The bending strength of the long columnar refractory aggregate is manufactured separately from a rectangular parallelepiped having the same composition as each long columnar refractory aggregate, and a test piece of thickness x width x length = 3 mm x 4 mm x 40 mm The value measured in accordance with the three-point bending test method of JIS R1601: 2008 was adopted. The aspect ratio was determined by randomly collecting 50 aggregates from 10 kg of each long columnar refractory aggregate, measuring the maximum cross-sectional diameter and axial length with calipers, and determining the aspect ratio. The average value was expressed. Table 1 shows the composition, shape, and bending strength of each long columnar refractory aggregate.

(2) Metal fibers Various metal fibers shown in Table 2 were prepared.

(3) Production of cast refractory material Refractory aggregate, refractory fine powder, alumina cement and dispersant were blended in the composition shown in Table 3 to prepare a refractory blend. After adding the long columnar refractory aggregates shown in Table 1 and the metal fibers shown in Table 2 to the obtained refractory composition at the ratio shown in Table 4, and further adding 5% by mass of water, The mixture was kneaded for a minute and cast into a predetermined form. The shape of the molded body was a rectangular parallelepiped of 40 × 40 × 160 mm. The obtained molded body was cured at room temperature for 24 hours, then de-framed and dried at 110 ° C. for 24 hours.

  A fracture energy measurement and a heat-resistant spalling property evaluation test were performed using a sample of the formed body. Fracture energy is the energy required until a sample is gradually stressed, and cracks develop and progress until complete fracture. The greater the fracture energy, the greater the resistance to crack growth, and the better the spalling resistance. Excellent. In the heat spalling evaluation test, the sample was repeatedly subjected to rapid heating and rapid cooling, and the deterioration of the sample was evaluated by the change in elastic modulus. It can be determined that the more the elastic modulus is maintained, the better the heat spalling property. The test method for each test will be described below.

<Measurement of fracture energy>
Prepared the molded body sample prepared by the above method, after heating and firing at 1400 ° C. for 3 hours and after heat treatment at 600 ° C. for 3 hours, until the autograph by the three-point bending method A load-displacement diagram was obtained, and the integrated value was taken as the fracture energy.

<Heat-resistant spalling property evaluation test>
The elastic modulus E ₀ of the test piece prepared by the above method was measured by heating and baking at 1400 ° C. for 3 hours and then gradually cooling to room temperature. (1) Put the specimen in a furnace heated to 1400 ° C, (2) Hold for 30 minutes, (3) Remove the specimen from the furnace, and (4) Elastic modulus after rapid cooling in air Was measured. The rapid heating-rapid cooling cycle of (1) to (4) was defined as 1 cycle, and the elastic modulus after completion of n cycles was defined as En. The modulus of elasticity decreases due to damage such as cracking of the specimen due to rapid heating and rapid cooling. The heat spalling property was evaluated by evaluating the change in the elastic modulus.

The test result was indicated by a ratio E ₃ / E ₀ between the elastic modulus E ₃ and the initial elastic modulus E ₀ after performing the above cycle three times. As E ₃ / E ₀ is larger, the decrease in elastic modulus is smaller, so the heat spalling property is better. The elastic modulus was measured by a dynamic elastic modulus test method (JIS R1602: bending resonance method).

  The cast refractory of the present invention (Examples 1 to 10) has a high fracture energy both after heat treatment at 600 ° C. and after firing at 1400 ° C. because it has the effect of suppressing crack propagation by the long columnar refractory aggregate. Excellent spalling performance.

  On the other hand, Comparative Example 1 using a long columnar refractory aggregate with an aspect ratio of less than 2 does not provide a crack growth suppression effect, so the fracture energy at 1400 ° C is low and the heat spalling property is also poor. .

  Comparative Example 2 using a long columnar refractory aggregate whose bending strength measured in accordance with JIS R1601 is lower than 60 MPa, and a long columnar refractory aggregate with a cross-sectional maximum diameter of less than 5 mm and weak structural strength. In Comparative Example 3, since the effect of suppressing the progress of the generated crack cannot be obtained, the fracture energy at 1400 ° C. is low and the heat spalling property is also inferior.

  Both Comparative Example 4 using a long columnar refractory aggregate with an aspect ratio exceeding 5 and Comparative Example 5 using a large long columnar refractory aggregate with a cross-sectional maximum diameter exceeding 20 mm are both cast refractories. The structure of the construction body that can be reduced in fluidity of the construction becomes fragile. Therefore, the fracture energy at 600 ° C. and 1400 ° C. is low, and the heat spalling property is inferior.

  In Comparative Example 6 using a metal fiber having a length shorter than 20 mm, the crack suppression effect at 600 ° C. cannot be obtained, so the fracture energy is low and the heat spalling property is also poor.

  Comparative Example 7 using metal fibers longer than 35 mm has a low fracture energy at 600 ° C and 1400 ° C because the flow structure of the cast refractory decreases and the structure of the construction body that can be obtained becomes brittle. Also, the heat spalling property is inferior.

  In Comparative Example 8, in which the amount of metal fiber added is less than 1% by mass, the crack suppression effect at 600 ° C. cannot be obtained, so the fracture energy is low and the heat resistance spalling property is poor.

(Example of tundish application)
The cast refractories of Examples 4 and 5 and Comparative Example 1 were actually used as the lining of the actual tundish. At this time, the moisture at the time of construction was set to 5% by mass, and kneading was performed using a mixer every 2 tons. A predetermined core was set in the tundish, and a kneaded cast refractory was poured. Thereafter, the mixture was cured for 12 hours, the core was removed, and then dried for 52 hours using a drying burner. A magnesia-based coating was applied to complete the installation.

  The completed tundish was used in a continuous casting process. Casting for one molten steel pan is 1 channel, and casting several channels continuously is called “casting”. The conditions of this time were to cast about 400 tons of molten steel for about 10 channels in a single cast. The casting was preheated for 2 hours, and the lining refractory was heated to about 1000 ° C. on the surface. When the casting was finished, the molten steel and slag remaining in the tundish were discharged, and simple maintenance such as removal of deposits was made, coated, and used for the next cast, and used repeatedly.

  The tundish-lined refractory is subjected to thermal shock and mechanical shock in the process of repeated use, cracks are formed, and finally it is peeled off to have a lifetime. The durability of the refractory is expressed by the number of channels used until the end of its life.

FIG. 2 shows the number of life channels when the cast refractories of Examples 4 and 5 and Comparative Example 1 are applied to the tundish lining. It can be seen that Examples 4 and 5 have an approximately 30% longer life ch number than Comparative Example 1, and are excellent in durability. This can be said to be a result showing that crack peeling of the lining refractory is suppressed by the effect of the present invention.

Claims (2)

For 100% by mass of fire-resistant compound,
(A) Bending strength measured according to JIS R1601 with a cross-sectional shape of approximately circular, a maximum cross-sectional diameter of 5 to 20 mm, and an aspect ratio defined by the axial length / maximum cross-sectional diameter of 2 to 5. 5-25% by mass of a long columnar refractory aggregate having a Mn of 60 MPa or more, and
(B) 1 to 10% by mass of a metal fiber having a maximum cross-sectional diameter of 0.2 to 1.5 mm and a length of 20 to 35 mm
Are cast refractories that are respectively added to the outside ,
The refractory composition is composed of refractory aggregate, refractory fine powder, alumina cement, and a dispersant, and the chemical component thereof is alumina-silica having an Al ₂ O ₃ content of 55% by mass or more,
The long columnar refractory aggregate, refractory casting, characterized in that <br/> the Al ₂ O ₃ is sintered mullite containing more than 55 wt%.   The cast refractory according to claim 1, wherein the cast refractory is for tundish lining.