JPH11100280A - Irregular refractories for tundish lining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the monolithic refractory which is employed for the lining of a tundish continuously used under hot conditions and does not cause buckling fracture or crack extension. SOLUTION: This refractory consists of 80 to 91 wt.% alumina, 4 to 14 wt.% magnesia, 3 to 7 wt.% fumed silica and 2 to 6 wt.% alumuna cement based on 100 wt.% of the mix composition and also, has a weight ratio of (fumed silica)/(alumina cement) of >=0.75. By adjusting the weight ratio of (fumed silica)/(alumima cement) of the refractory to >=0.75, since the ratio of the anorthitic structure formed in a bonding structure of the material at the time of receiving heat, is increased, the hot expansion coefficient at the time of reheating the material is lowered and thereby the amount of fumed silica can be increased without adversely affecting advantageous properties of alumina- magnesia, such as corrosion resistance and slag infiltration resistance. As a result, buckling fracture and crack extension of the refractory material can be inhibited from being caused and thus, the service durability of tundish lining can remarkably be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amorphous refractory for lining a tundish.

[0002]

2. Description of the Related Art Conventionally, refractories for tundish lining represented by castables have been used by applying a basic coating material to the surface thereof. Therefore, the refractory for lining does not come into direct contact with the molten steel, so the material design does not take into account the corrosion resistance and the influence of molten steel contamination,
Material design has been made with emphasis on structural stability. For this reason, as a material for the tundish lining, an alumina-silica castable of 50 to 70% by weight of alumina has been used.

[0003] However, recently, in order to increase the efficiency of tundish operation, save energy, and reduce costs, an operation in which tundish is continuously used hot (hot rotary operation) without using a coating material has been performed. It has become. In such hot-rotating tundishes, the refractory for the lining is directly used in contact with the molten steel and is continuously used at a high temperature.Therefore, low silica is used in consideration of the structural stability, corrosion resistance, and the effect on molten steel contamination. Is required. Therefore,
The castables were further converted to high alumina, and a high alumina castable with 70 to 90% by weight of alumina was applied.

However, this material is still insufficient in durability, and as a result, alumina-magnesia or alumina-spinel having excellent corrosion resistance and slag infiltration resistance has attracted attention as a high corrosion-resistant low-silica castable. It has been studied to apply this to refractories for hot rotating tundish lining. However, conventional alumina-magnesia or alumina-spinel castables have no disadvantages in corrosion resistance, slag infiltration resistance, and contamination of molten steel, but have a disadvantage that cracks and peeling occur greatly and cannot be used for a long time. there were. Therefore, there has been a demand for an improvement in the castable physical properties of the tundish lining structure using these materials.

[0005]

Alumina-magnesia castables are currently performing very well as refractories for lining steel ladles. Nevertheless, when this material is applied to the refractory for tundish lining, it is considered that the cause of the increase in cracking and peeling is due to the difference in the shape of the container.

That is, since the molten steel ladle container has a barrel-shaped structure having a circular horizontal cross section, when the container is heated and the castable expands thermally, the generated seric stress is reduced and absorbed by the castable moving to the back. Therefore, breakage due to buckling hardly occurs. Further, when the container is cooled, the width of the shrinkage crack is reduced by moving the castable to the working surface side. For this reason, it is possible to suppress the occurrence of cracks and peeling in the castable, thereby ensuring high durability.

On the other hand, since the tundish container has a box-shaped structure having a square horizontal section, in other words, since the castable has a linear structure, the castable thermally expands along the wall surface with both ends constrained by an iron shell. As a result, the castable protrudes or buckles on the heated surface due to the cell stress caused by thermal expansion, and the castable is broken. In addition, when cooling, cracks expand due to shrinkage, and a temperature gradient from the working surface to the back surface occurs, so if there is a temperature range where the material strength decreases, stress concentrates there and leads to peeling There are many. Such tissue deterioration is amplified by repeated use.

Since the alumina-magnesia castable and the alumina-spinel castable have higher expansion properties than the alumina-silica castable conventionally used for refractories lined with tundish, the above tendency is more remarkable. became. Particularly, in the case of alumina-magnesia castable, the expansion, the buckling, and the peeling of the crack were further progressed because the expansion greatly changed when the alumina and the magnesia reacted to form the secondary spinel.

On the other hand, since the alumina-spinel castable has a tendency to shrink in linear change rate, cracks cannot be eliminated. Therefore, there has been a demand for the development of an alumina-magnesia castable material that can be applied to a tundish lining material. The present invention has been made to meet this need.

[0010]

To improve the material for preventing cracking, overhang, buckling, and peeling of alumina-magnesia, there have conventionally been provided creep properties, prevention of firing shrinkage due to heating, intermediate temperature and back surface. Although it is recommended to increase the strength, the present inventors have investigated the causes of damage to the tundish lining and found that in addition to these remedies, a reduction in expansion upon reheating is effective.

[0011] The present inventors have studied the above composition, particularly low expansion upon reheating, by examining the composition of the bonding portion in alumina-magnesia, and have completed a refractory for lining a tundish. Things. It is characterized by a blending composition containing 80 to 91% by weight of alumina, 4 to 14% by weight of magnesia, 3 to 7% by weight of fumed silica, and 2 to 6% by weight of alumina cement, and 100% by weight. Fumed silica / alumina cement is an amorphous refractory for lining alumina-magnesia tundish having a composition of 0.75 or more.

By the way, the alumina-magnesia castable conventionally used in the ladle is a cement-bonded product, and no fume silica is used, or 3% even if used.
, And there was no idea to increase the amount of fumed silica. For example, Japanese Patent Application Laid-Open No. 7-242470 states that if the amount of fumed silica exceeds 2% by weight, oversintering at a high temperature is a problem. In addition, Japanese Patent Application Laid-Open
JP-A-3304747 reports that if the amount of fumed silica exceeds 3% by weight, excessive sintering and expansion of shrinkage cracks become problems. However, considering the improvement of the tissue strength of the back of the lining, increasing the amount of fumed silica gives good results.

The present invention solves the problem of adding a large amount of fume silica and increases the structural strength by making the alumina-magnesia amorphous refractory having the above-mentioned composition based on such knowledge and experiments. This is to improve the durability of the tundish lining material by improving the creep characteristic and reducing the expansion upon reheating at the same time.

In the present invention, it is an essential condition that the mixing ratio of the above fumed silica and alumina cement (fumed silica / alumina cement) is 0.75 or more by weight. The reason for this will be described with reference to FIG.
If the fumed silica / alumina cement is 0.75,
The coefficient of linear thermal expansion after firing is 0.95% / 1000 ° C., and if it exceeds 0.75, it is 0.95% / 1000 ° C.
The expansion rate becomes smaller than ° C. In this case, the expansion rate is almost the same as that of the high alumina type.If the amorphous refractory has such an expansion rate, when used in a tundish, buckling, protrusion, and peeling tend to be small. , Fully practical.

On the other hand, when the fumed silica / alumina cement is smaller than 0.75, the coefficient of hot linear expansion after firing becomes sharply larger than 0.95% / 1000 ° C., and buckles, protrudes, and peels during reheating. Easily occur, and the durability decreases. Fumed silica / alumina cement is 0.
The reason for the expansion characteristic of low expansion upon reheating at 75 or more is not completely clear, but the following may be considered.

Alumina cement is involved in coagulation into fumed silica during compounding at the time of hardening, and its mineral composition is not only ordinary calcium-aluminum hydrate but also CaO—SiO ₂ —H ₂ O by a so-called pozzolanic reaction.
Produces system hydrate. The formation ratio is affected by the mixing ratio of fumed silica and alumina cement, and when the fumed silica is large, CaO—SiO ₂ —H ₂ O-based hydrate is
When the amount of alumina cement is large, a large amount of calcium-aluminum hydrate is generated.

As a result, when these bonds receive heat, the calcium-aluminum hydrate becomes CaO.6Al ₂ O
The _{3, CaO-SiO 2 -H 2} O system hydrate produces anorthite glass. Of these, CaO · 6Al ₂ O ₃
At high temperatures increases the expansion of amorphous refractories and has low creep properties. On the other hand, anorthite glass has a low expansion coefficient and a deformability.

The mineral composition of the alumina-magnesia amorphous refractory after firing is composed of corundum, alumina magnesia spinel, CaO.6Al ₂ O ₃ , anorthite-based glass, and CaO.6Al ₂ O ₃ having a bonding composition of CaO.6Al ₂ O ₃ . It is considered that the formation ratio of the anorthite glass affects the expansion rate of the amorphous refractory after firing. Then, as in the present invention, the fumed silica / alumina cement contains 0.1%.
When the ratio is 75, it is considered that the increase in the generation ratio of the anorthite-based glass contributes to a reduction in the expansion rate and an improvement in the deformability of the amorphous refractory after firing.

As described above, according to the present invention, by forming an anorthite-based composition at the joint portion of the alumina-magnesia amorphous refractory, the alumina-magnesia amorphous refractory is more regenerated than the conventional CaO.6Al ₂ O ₃ -bonded alumina-magnesia. The rate of hot expansion during heating could be reduced. In addition, by using fumed silica in an amount of 3% by weight or more in this composition, the structural strength of the amorphous refractory is improved, and the expansion of the alumina-magnesia lining for tundish is improved in combination with the optimization of the residual expandability. The service life has been achieved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the alumina-magnesia amorphous refractory of the present invention, it is preferable to use a sintered or electrofused high-purity alumina having a purity of 99% or more. If the purity is low, corrosion resistance is undesirably reduced.
Further, the addition amount is 80 to 91% by weight. If it is less than 80% by weight, not only does the volume stability decrease, but also the corrosion resistance decreases. On the other hand, if it exceeds 91% by weight, the amount of other components, especially magnesia, is reduced, and the amount of secondary spinel produced is reduced, so that the residual expansion is reduced and the slag is easily infiltrated.

As for magnesia, it is preferable to use a sintered or electrofused product having a purity of 95% or more. If its purity is low,
It is not preferable because the spinel generation reaction becomes insufficient and the corrosion resistance decreases. Further, the added amount is 4 to 14% by weight. If the content is less than 4% by weight, not only is there no effect on slag infiltration resistance, but also the residual expansion property after firing, which is a basic property of the amorphous refractory of the present invention, cannot be secured. Also, 14
If the amount exceeds 20% by weight, the residual expansion becomes too large due to the formation of a large amount of secondary spinel, or the corrosion resistance is lowered.

Magnesia has a particle size (particle size) of 1 mm.
It is preferred to use: Conventional alumina-magnesia amorphous refractories use fine magnesia powder having a particle size of 0.15 mm or less. However, when only magnesia fine powder having a particle size of 0.15 mm or less was used under the composition of the present invention, shrinkage in firing and oversintering proceeded due to an increase in fume silica, and the spalling resistance was reduced.

On the other hand, when magnesia having a particle size of 1 to 0.15 mm was used in combination, no shrinkage was observed even when the amount of fumed silica was increased, and the spalling resistance was improved. However, a coarser grain size of 3 to 1 mm
When magnesia is used, it is effective in preventing the shrinkage tendency, but voids are formed in the magnesia grain boundary, and these voids loosen the structure and reduce the amount of secondary spinel generated, resulting in structural deterioration and slag resistance. Decreased.

From the above results, it is preferable to use the magnesia of the alumina-magnesia irregular shaped refractory of the present invention having a particle size of 1 mm or less. It is adjusted so that the residual swelling property is maintained even when silica is added in an amount of 3% by weight or more. More specifically, as magnesia, 1 mm
By combining several of the following particle sizes,
Consideration is made so that the linear change rate after firing does not shrink. In this case, a fixed amount of magnesia powder having various particle diameters of 1 mm or less may be added alone, for example, 1 to 0.3 mm
A plurality of types of magnesia having a particle size of 1 mm or less may be used in combination such that two types of magnesia having a particle size of 1 mm or less are combined with two types of magnesia having a particle size of 0.15 mm or less.

As the alumina cement, 12CaO.
_{7Al 2 O 3, CaO · Al} 2 O 3, CaO · 2Al 2
It is preferable to use a high-purity calcium aluminate composition mainly composed of an O ₃ mineral. The alumina cement of the present invention is preferably a high-purity fine powder having good dispersibility, which is well-granulated so that calcium and aluminum ions are quickly diffused into water after kneading the compound and curing. The addition amount is used in the range of 2 to 6% by weight. If the content is less than 2% by weight, the strength after curing and drying after application is low, and the structure is destroyed by a small external stress, which is not preferable. On the other hand, if the amount exceeds 6% by weight, the corrosion resistance decreases and the coefficient of hot expansion after firing increases.

Fume silica is also called vaporizable silica, and is an ultrafine powder mainly composed of spherical silica generated during production of metallic silicon and zirconia. And the addition amount is 3 to 7% by weight. If the content is less than 3% by weight, the strength of the middle portion of the structure and the back surface is lower than the sintering strength of the working surface, and the use of a tundish lining material is not effective in reducing peeling. On the other hand, when the content exceeds 7% by weight, the corrosion resistance is lowered due to a decrease in fire resistance, which is not preferable. In addition, oversintering of the operating surface portion also proceeds.

Although the main constitution of the present invention has been described above, a dispersant may be used in order to further exert the effect of the present invention. The present inventors also investigated the relationship between the type of the dispersant and the tissue strength. did. Among the amorphous refractories, the dispersants commonly used for castables include various organic and inorganic dispersants. The application of the dispersant is generally selected based on the fluidity and curability of the castable. However, the present inventors have found that such a small amount of dispersant has a great influence on the bonding composition in a low-cement castable and changes the tissue strength.

That is, a castable using an inorganic dispersant, particularly a condensed phosphate, rather than an organic dispersant was more effective in improving the tissue strength. Although the reason for such an effect is not completely clear, the following may be considered. That is, the connective tissue of the castable with a large amount of fumed silica added was CaO-
Although a SiO ₂ —H ₂ O-based bond is formed, when a condensed phosphate is used as a dispersant, the CaO—SiO ₂ —H ₂ O-based bond reacts with the condensed phosphate to produce CaO—SiO ₂ −P
It believed to produce the ₂ O ₅ -H ₂ O system coupling.

More specifically, CaO--SiO ₂ --H ₂
In the O system, the bond chain is broken when the binding water is lost by heating, whereas in the CaO—SiO ₂ —P ₂ O ₅ —H ₂ O system, the release of the binding water is gradual, There is no disappearance. As a result, it is considered that stable strength can be maintained in each temperature range after drying of the castable and after heating.

Examples of the condensed phosphate include sodium tripolyphosphate, sodium tetrapolyphosphate, sodium hexametaphosphate, sodium acid hexametaphosphate, and sodium ultrapolyphosphate. Further, in addition to these condensed phosphates, polycarboxylic acids, sulfonic acids and other organic dispersants may be used in combination. Further, as a curing regulator, for example, boric acid, ammonium borate, oxalic acid, tartaric acid, sodium carbonate, lithium carbonate and the like are used.

Further, in order to improve the structural stability of the tundish lining material, coarse aggregate having a particle size of about 50 to 10 mm may be externally added as long as the characteristics of the alumina-magnesia amorphous refractory are not impaired. good. Suitable for these coarse aggregates are electrofused and sintered alumina and svinel. In addition, natural alumina and bauxite are also effective. Further, metal fibers, organic fibers, ceramic fibers, aluminum powder, aluminum alloy powder, glass powder and the like may be added for the purpose of improving structural stability and dry explosion resistance.

The construction of the tundish lining using the product of the present invention is carried out according to a standard method. In the case of the casting method, about 4 to 8% by weight of construction water is added to the above-mentioned composition by external application, and the formwork is added. This is performed through a process of pouring an amorphous refractory into the voids using a varnish, curing and then drying. At the time of construction, a vibrator is generally attached to the formwork or a rod-shaped vibrator is inserted into the refractory to improve the filling property.

In addition to directly pouring an amorphous refractory into a tundish container, a block of an arbitrary shape may be formed in advance from the amorphous refractory and used as a lining material.

[0034]

Embodiments of the present invention will be described below in detail.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

Table 1 shows the chemical composition of alumina used in Examples and Comparative Examples, Table 2 also shows the chemical composition of magnesia, Table 3 also shows the chemical composition of fumed silica, and Table 4 also shows the chemical composition of alumina cement. Tables and Table 5 are tables of components and test results of Examples and Comparative Examples of the present invention. In each of the examples and comparative examples, a predetermined amount of water was added to the mixture, and the mixture was kneaded, and poured into a mold and dried to produce a test piece. About this, bending strength, linear change rate, corrosion resistance,
Test and measurement of the reheating hot linear expansion coefficient were performed. The measurement of the bending strength was performed according to JIS R1601. Corrosion resistance was measured using a molten steel ladle slag in a rotary erosion test.
At 600 ° C. for 5 hours, the amount of erosion and the amount of permeation were measured. The reheating hot linear expansion coefficient is 1500 ° C. × 3 hours.
It was measured on the sample after firing.

In all of the examples of the present invention, the bending strength after drying and the bending strength after firing at 1000 ° C. are high.
After firing at 1500 ° C. for 3 hours, the rate of linear change is small, indicating a slight residual expansion. Furthermore, the coefficient of expansion upon reheating after baking at 1500 ° C. for 3 hours is low, indicating characteristics effective for structural stability. On the other hand, in Comparative Examples 1 to 3, the bending strength after drying and the bending strength after firing at 1000 ° C. are low, and the expansion after reheating is large. Comparative Example 4 is small in expansion after reheating and excellent in spalling resistance, but inferior in corrosion resistance due to alumina-silica.

In the actual machine test, the slag line was used as a lining material for a 60-ton hot rotating tundish, and the erosion speed of the slag line and the start time of peeling were measured. In the case of a conventionally used high-alumina amorphous refractory of 80% by weight class of alumina (Example 4), the slag line has a erosion rate of 1 mm / c
h, the peeling and cracking were small, but the life of 150 ch (charge) was limited. The alumina-magnesia castable shown in Comparative Example 1 had a slag line erosion rate of 0.5 mm / ch, but had large peeling and cracking, and had a life of 100 ch. In contrast, the castable of Example 3 of the present invention had a slag line erosion rate of 0.6 mm / ch, which was slightly larger than the castable of Comparative Example 2, but with less peeling and cracking.
It withstands the use of 250 channels and shows a significant improvement in durability compared to conventional products.

[0043]

As described above, the alumina-magnesia amorphous refractory of the present invention can improve the strength of the structure, optimize the rate of change of the residual line, and the expansion rate upon reheating by examining the composition of the joint. And the life of the hot rotary tundish lining, which has been damaged by cracking and peeling at the same time as melting, has been drastically extended. In recent years, the operation of the tundish has been changing from the coating operation to the hot rotary operation, and the refractory for lining used therein has been strongly required to be highly durable.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the fumed silica / alumina cement ratio and the expansion rate after reheating.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyohiro Hosokawa 1-3-1, Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside Harima Ceramic Co., Ltd. (72) Inventor Hidetoshi Kamio 1-3-1, Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Harima Ceramics Co., Ltd.

Claims (1)

[Claims] 1. 80 to 91% by weight of alumina, magnesia 4
１４14% by weight, 3-7% by weight of fume silica, 2-6% by weight of alumina cement, and 100% by weight of a blended composition. Amorphous refractory for magnesia tundish lining.