JP3176832B2 - Pouring refractories for hot metal pretreatment vessels - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixed iron wheel, a hot metal ladle and a vacuum degassing method (for example, RH method and DH method) for pretreatment of hot metal.
The present invention relates to a cast refractory used for lining containers such as a dip tube for scouring outside a furnace according to the above method.

[0002]

2. Description of the Related Art In recent years, hot metal pretreatments such as desulfurization, desiliconization, and dephosphorization of hot metal have been performed for upgrading and cleaning steel. For a mixed iron wheel, a hot metal pot, and the like used for hot metal pretreatment, bricks containing silicon carbide and carbon, which are excellent in durability, are generally used. On the other hand, in recent years,
As quality safety is evaluated in addition to labor saving, etc.,
The demand for cast refractories is increasing. However, when these molten metal containers are poured and constructed with refractories, they are constrained by iron shells or the construction body itself, so when the refractories are expanded or cooled during heating such as dehydration drying, heating, and receiving pig iron. Thermal stress is generated inside the refractory construction body due to the shrinkage of the refractory. As a result, phenomena such as protrusion and peeling of the construction body are likely to occur. On the other hand, in the case of bricks, such a phenomenon is relatively unlikely to occur because the joint absorbs the stress. As one of the conventional examples of the stress absorption countermeasure in a cast refractory, a refractory to which a low-melting substance is added is cited. That is, by adding a material having a relatively low melting point, such as rubble, to impart a load softening property at a temperature of 1000 ° C. or more during operation to achieve stress absorption, but a reduction in corrosion resistance is inevitable. There are drawbacks. In addition, this method
Such a stress absorbing effect cannot be expected because there is no load softening property in a low temperature range of 1000 ° C. or lower such as during dehydration drying and initial temperature rise.

On the other hand, pitch is conventionally known as a material which softens and melts in a low temperature range of 1000 ° C. or lower. As an example of using a pitch for a cast refractory, the invention described in JP-A-60-215581 is disclosed.
For a refractory raw material containing 1 to 20 wt% of ultrafine powder having a particle size of 5 μm or less, the softening point is different within a range of 80 to 250 ° C. 2
A blast furnace gutter castable refractory made by adding an appropriate amount of a binder and a deflocculating agent with a total amount of 0.5 to 10% by weight of outer pitch in a total amount of more than one kind of pitch. Using two or more types, a steam diffusion path during drying is secured by the difference in the melting point of the pitch to prevent explosion. However, when drying a thick construction body, a gentle temperature gradient is generated in the construction body cross section. In this case, if a pitch with a softening point of 250 ° C or less is used, the pitch melted by rapid heating during drying will be near the surface. The pores are closed, and the diffusion of water remaining inside is hindered, leading to explosion. That is, the explosion is not completely suppressed depending on the effect of the construction thickness. In addition, if a pitch having a particle diameter of 1 mm or less is mixed, it becomes bulky, so that the amount of added water is increased and the filling property is reduced, so that the corrosion resistance is reduced.

In the invention described in Japanese Patent Application Laid-Open No. 62-230679, a refractory raw material impregnated with a carbon source is used as an aggregate, the carbon source is 50% by weight or more of fixed carbon, and the softening point is 20%.
An amorphous refractory having a pitch of less than 0 ° C and a softening point of 20
Aggregates are impregnated with a pitch of less than 0 ° C. under high temperature and high pressure to increase the amount of carbon added without lowering fluidity. However, in the present invention, there is no stress absorbing effect by using the pitch.

The invention described in Japanese Patent Application Laid-Open No. 1-203277 discloses a softening point of 150-250 ° C., a particle diameter of 3 mm or less, and a fixed carbon content of 55% by weight or more based on 100% by weight of the refractory raw material whose particle size has been adjusted. A castable refractory for hot working of a blast furnace gutter comprising 1 to 6% by weight of a petroleum pitch having a volatile content of 40% by weight or less, a curing retarder, an exothermic agent and the like. The addition is used to soften, melt, and disperse by drying, raising the temperature, or heating during use, and then carbonizing to obtain a refractory structure by carbon bonding. In this case, in order to prevent the pitch from filling the pores on the surface of the refractory in the drying step and hindering the diffusion of water vapor, the pitch has a softening point higher than the conventional one (80 to 130 ° C.) (150 to 250 ° C.). ° C). However, there is no disclosure of any technique for absorbing and relaxing the thermal stress of the refractory from room temperature to 1000 ° C., which is the main subject of the present invention.

In any of the above prior arts, pitch is added to the refractory, but in any case, the effect of absorbing the thermal stress generated during dehydration drying and initial temperature rise cannot be expected.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a heating step in a low temperature range (normal temperature to 1000 ° C.) at the time of dehydration drying and initial temperature rise without impairing the corrosion resistance and spall resistance of the construction. An object of the present invention is to provide a cast refractory for a hot metal pre-treatment vessel, in which a generated thermal stress is relieved to prevent a protrusion and a peeling phenomenon.

[0008]

According to the present invention, there is provided a cast refractory for a hot metal pretreatment vessel, as shown in the drawing, comprising a refractory aggregate comprising silicon carbide and carbon, and a binder. A coarse grain pitch having a particle size of 1 to 10 mm and a softening point higher than 250 ° C. is added in an outer amount of 1 to 5% by weight to 100% by weight of the product.

In the present invention, the refractory aggregate must contain silicon carbide and carbon as a material suitable for hot metal pretreatment. However, it is not necessary to particularly limit other aggregates. Aggregate can be used. As the silicon carbide raw material, those having an SiC content of 90% or more are preferable, but those having an SiC content of 80% or more can also be used. As the carbon raw material, phosphorous graphite, artificial graphite, earthy graphite, carbon black and the like can be used. As the other refractory aggregate, one or a combination of two or more ordinary refractory aggregates including alumina, silica, magnesia, spinel, zircon and the like can be used.

Any binder can be used as long as it is used for the production of cast refractories, but alumina cement is particularly preferred. The amount of the alumina cement is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight.

The coarse-grained pitch has a softening point higher than 250 ° C., a particle size of 1 to 10 mm, a fixed carbon content of 70% or more,
The volatile content is desirably 20% or less. It is necessary that the softening point of the pitch used in the present invention is higher than 250 ° C. If a pitch having a softening point of 250 ° C or less is used, the molten pitch closes the pores near the surface during drying and heating of the construction. Evaporation and diffusion of water remaining inside are hindered, and as a result, explosion and internal cracks due to water vapor are likely to occur. Since the pitch used in the present invention has a softening point higher than 250 ° C. and a coarse particle size of 1 to 10 mm, it is possible to secure a water vapor diffusion path without blocking pores near the surface, thereby preventing water vapor explosion. can do. Further, the preferred softening point is 255-400 ° C.
If the temperature is higher than this, the stress absorption effect at the stage where the thermal stress occurs during drying and heating of the construction body is slightly reduced. The addition amount of the high softening point coarse-grained pitch is 1 to 5% by weight on the outside with respect to 100% by weight of the cast refractory. If the amount is less than 1% by weight, the effect of stress absorption is reduced. If it is more than 5% by weight, the amount of added water increases,
The filling property is reduced, and the strength and corrosion resistance are reduced. The particle size of the high softening point coarse pitch used is 1 to 10 mm, more preferably 3 to 8 mm. If the particle size is smaller than 1 mm, the effect of preventing steam explosion will be lost and bulky, so that the amount of added water increases, the filling property decreases, and the corrosion resistance decreases. If the particle size is larger than 10 mm, the voids after the volatilization of the pitch are large, so that slag infiltration increases, and the corrosion resistance decreases.

In addition to the above components, alkali metal salts of condensed phosphoric acid such as sodium hexametaphosphate and alkali metal salts of silicic acid, or organic acids such as carboxylic acid, humic acid, alkylsulfonic acid and aromatic sulfonic acid, and alkali metals thereof. A dispersant such as a metal salt can be blended. The compounding amount of the dispersant is 0.01 to 100% by weight of the refractory composition.
It is preferably set to と す る 2% by weight. In addition to dispersants, those used for ordinary cast refractories, such as pot life and curing time regulators, thickeners, and anti-explosion agents, can be appropriately compounded.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the following embodiments and examples, reference examples and comparative examples.

[0014]

REFERENCE EXAMPLES 1-2 The high softening point pitch (particle size 1-8 mm) used in the present invention was added to the cast refractory composition containing silicon carbide and carbon shown in Table 1. Table 2 shows the physical properties of the high softening point pitch, and Table 3 shows the addition amount.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

The cast refractory composition of each composition was kneaded with the same amount of added water (6.2% outer shell) and then cast into a cylindrical mold to obtain a molded sample having a diameter × length of 50 mm × 100 mm. For these samples, the generated thermal stress was measured using the thermal stress measuring device shown in FIG. The apparatus is a uniaxial stress measuring apparatus for measuring the thermal stress caused only by the expansion of the sample while keeping the initial length of the specimen constant by laser measurement using a controller. FIG. 2 shows the measurement results. As shown in FIG.
According to the results of the generated stress comparison test in which the thermal stress was measured after holding for a long time and the peak value Δδ of the thermal stress was compared, the pitch of the softening point pitch was higher than that of the sample without the high softening point pitch (Reference Example 1). (Reference Example 2) was added at room temperature to 600 ° C.
, The generated stress value is small. For this reason, the high softening point pitch can absorb the thermal stress generated at the time of dehydration drying and initial temperature rise of the cast refractory construction body.

[0019]

Example 1 With respect to 100% by weight of the refractory composition shown in Table 1, high softening point pitches shown in Table 2 were added by changing the particle size (adjusted to a width of ± 1 mm) by 3% by weight on the outside. did. A sample was prepared under the same conditions as in the reference example, and the generated stress was measured. Further, a sample for a rotational erosion test was prepared, and 1
A slag immersion test at 600 ° C. for 5 hours was performed to measure the amount of erosion. FIG. 3 shows the measurement results. Here, the maximum generated stress index is defined as the maximum stress value without pitch addition (Reference Example 1) being 10
The ratio when the value is set to 0 is represented by a numeral, and the larger the maximum generated stress index is, the smaller the stress absorbing effect is. (Figure 2
More stress to absorb the easy of Δσ _f is small. Similarly, the erosion index was 10% when no pitch was added (Reference Example 1).
The corrosion resistance is poorer as the erosion index is set to 0. FIG.
As shown in the figure, when the particle size is smaller than 1 mm, the maximum generated stress index is large, and when it is larger than 10 mm, the erosion index is large.

[0020]

Example 2 To 100% by weight of the refractory composition shown in Table 1, a high softening point pitch having a particle size of 1 to 8 mm having the physical properties shown in Table 2 was externally added while changing the addition amount. Example 1
The generated stress and the amount of erosion were measured under the same conditions as described above. FIG. 4 shows the measurement results. As shown in FIG. 4, when the addition amount is less than 1% by weight, the maximum generated stress index is large, and when the addition amount is more than 5% by weight, the added water amount is large, and the filling property is reduced, so that the erosion index is large.

[0021]

Examples 3 to 5 and Comparative Examples 1 to 6 For 100% by weight of the refractory composition shown in Table 1, a high softening point pitch shown in Table 2 and a conventionally used low softening point pitch (softening point 115) were used. ° C) was added over the surface. Table 4 shows the addition amount and physical properties. As is evident from Table 4, in Examples 3, 4 and 5, the addition of a high softening point coarse-grained pitch to the cast refractory allows stress absorption without deteriorating the corrosion resistance, spall resistance and explosion resistance. The effect was significantly improved. However, as compared with the Examples, Comparative Example 1 in which no high softening point coarse pitch was added and Comparative Example 2 in which 0.5% by weight was added were inferior in the stress absorbing effect. In Comparative Example 3 in which the high softening point coarse grain pitch was added at 6% by weight, the corrosion resistance was deteriorated because the amount of added water was increased and the filling property was reduced. When a high softening point pitch having a particle size of 1 mm or less is added as in Comparative Example 4, the explosion resistance decreases. Furthermore, in Comparative Examples 5 and 6 in which a conventionally used low softening point pitch was added, there was no stress absorption effect, and the melted pitch closed pores near the surface, and the diffusion of water vapor remaining inside Explosion resistance is also deteriorated.

[0022]

Example 6 A cast refractory having the composition shown in Example 4 in Table 4 was lined on a mixed-iron car (capacity: 350 t). As a result, in the conventional material, after dehydration and drying, 50 to 70
A layered crack parallel to the internal heating surface of mm mm was formed, and in the observation after receiving 70 times of iron, many infiltration and exfoliation of the hot metal were observed in that portion. However, in the case of the product of the present invention, no layered cracks were observed after dehydration and drying, and a good result was obtained without any peeling phenomenon.

[0023]

[Table 4]

As described above, in the present invention, by adding a coarse grain pitch having a high softening point, thermal stress during dehydration drying and subsequent temperature rise is absorbed. That is, at the stage where the stress at the time of drying and temperature rise begins to be generated, the high softening point coarse-grained pitch softens and melts, creating a void at the boundary with the refractory aggregate. The void absorbs thermal stress generated in the construction body, thereby preventing protrusion and peeling.

[0025]

As described in detail above, the present invention provides a method of adding a high softening point coarse grain pitch to a cast refractory.
Obtain a silicon carbide / carbon-containing cast refractory that is free from protrusion and delamination due to dehydration and drying of the cast refractory construction and thermal stress during initial temperature rise without reducing corrosion resistance, spall resistance, and explosion resistance. be able to. Therefore, the cast refractory of the present invention is suitable for use in a mixed iron wheel for hot metal pretreatment, a hot metal ladle, and an immersion pipe for out-of-furnace refining of RH and DH.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an apparatus for measuring thermal stress.

FIG. 2 is a graph showing a relationship between a generated stress of a cast refractory, a temperature, and a holding time.

FIG. 3 is a graph showing the relationship between the particle size of a high softening point pitch, the maximum stress index, and the erosion index.

FIG. 4 is a graph showing the relationship between the amount of addition of a high softening point coarse grain pitch having a particle size of 1 to 8 mm and the maximum stress index and erosion index.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoshihiko Okada 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Inside Yawata Works (72) Inventor Hisato Yoshimoto Tobata-ku, Kitakyushu-shi, Fukuoka No. 1-1 Hibata-machi Nippon Steel Corporation Yawata Works (72) Inventor Itsutoshi Iwasaki 1-1, Makiyama Shinmachi, Tobata-ku, Kitakyushu-shi, Fukuoka Daiko Furnace Materials Co., Ltd. (72) Inventor Toshihiko Takeshige (71) Inventor Hirohide Okuno 1-1 Makiyama Shinmachi, Tobata-ku, Kitakyushu City, Fukuoka Prefecture Inventor Hirohide Okuno Field (Int.Cl. ⁷ , DB name) C04B 35/66

Claims (2)

(57) [Claims] 1. A coarse-grain pitch having a particle size of 1 to 10 mm and a softening point higher than 250 ° C. is externally applied to 100% by weight of a refractory composition comprising a refractory aggregate containing silicon carbide and carbon and a binder. A cast refractory for a hot metal pretreatment vessel, which is added in an amount of 1 to 5% by weight. 2. The coarse-grain pitch having a softening point of 255 to 4
The cast refractory for a hot metal pretreatment vessel according to claim 1, which is at a temperature of 00 ° C.