JP3300274B2 - Mold powder for continuous casting of steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold powder for continuous casting of steel, and more particularly, to a continuous casting of steel capable of remarkably contributing to improvement of working environment, adaptability to automatic feeder, operation stability and steel quality. The present invention relates to a mold powder.

[0002]

2. Description of the Related Art In recent years, the progress of continuous casting of steel has been remarkable, and the maintenance of high-temperature slabs (HCR, HDR), high-speed casting, diversification of mold cross-sectional shapes, and continuous casting have been progressing. Improving and stabilizing the continuous casting machine operation rate by eliminating defects in high-temperature slabs and reducing troubles is the biggest issue in the CC process. Under such circumstances, the role played by the mold powder is significant.

In continuous casting of steel, mold powder is added in a mold. Mold powder added to the molten steel surface injected into the mold through the immersion nozzle forms a layered structure of a molten slag layer and unmelted raw powder layer from the molten steel surface by receiving heat from the molten steel, and plays various roles. While flowing between the solidified shell of steel and the mold. The important roles are lubrication between the mold and the solidified shell, dissolution and absorption of inclusions floating from the molten steel, prevention of oxidation of the molten steel, heat retention, and a heat medium between the solidified shell and the mold.
That is, by flowing a certain amount while ensuring a certain thickness of the molten slag layer, the function of (1) can be performed, and a sound cast piece can be obtained.

[0004] Common mold powders include Portland cement, yellow rinse slag, wollastonite, blast furnace slag, dicalcium silicate (2CaO.Si).
O ₂ ), synthetic calcium silicate, etc. as a main raw material base, and if necessary, a silica raw material for adjusting powder characteristics such as basicity and bulk specific gravity are added, and further, fluorite, cryolite, borax, fluoride A mixed type in which a flux material such as a softening point such as a fluoride such as magnesium, a carbonate such as sodium carbonate or barium carbonate, a flux material as a material for adjusting a melting property such as a viscosity, and a carbonaceous material as a material for adjusting a melting slag rate, There are a pre-melt type in which all of the components excluding the carbonaceous raw material are previously melt-pulverized, and a semi-melt type in which a part is pre-melt-pulverized.
Also, in terms of shape, powder type mixed powder raw material,
There are granule types granulated by various methods.

If the mold powder cannot fulfill these roles, the quality of the slab deteriorates and the operation becomes unstable.
(Such as BO), the development of high quality and stable quality mold powder is being promoted. in recent years,
Further, there is a strong demand for a granule mold powder having an excellent working environment and excellent applicability to automatic feeding.

(1) Improvement of molten slag property In recent years, the operation of blowing an inert gas such as Ar from an upper nozzle, a slide plate, an immersion nozzle, and the like has been actively performed. Since the gas floats in the mold and passes through the mold powder layer, the melting of the mold powder tends to be unstable. That is, as the floating gas passes through the molten slag layer, slag bubbling tends to occur, and the unmelted layer and sintered layer may be covered with the molten slag, resulting in non-uniform molten slag, poor melting, and heat retention. This may lead to operation troubles such as deterioration of the slag bear, enlargement of the slag bear, variation in the thickness of the molten powder slag layer, and finally deterioration of the slab quality, and in some cases, breakout due to poor lubrication.

(2) Applicability to automatic feeding machine From the viewpoint of improving the working environment and saving labor, use of granule powder by automatic feeding has been promoted. However, pneumatic feeding (for example, from powder feeding hopper to feeding machine body). (Pneumatic feeding) or cutting out (such as a screw feeder) in an automatic feeder causes the problem that the grains are broken and powdered. The columnar granules formed by extrusion granulation are easily broken in shape, and are used while being powdered. In addition, spherical granules formed by spray granulation tend to be hollow and have extremely low particle strength, and thus are particularly easy to powder.

(3) Improvement in heat retention Granular powder is inferior to powder in terms of heat retention and is desired to have excellent heat retention, and hollow spherical granules have been proposed. And its applicability to automatic feeders.

Although various granular powders have been proposed so far, there is no practical powder that can overcome the above three points at the same time. For example, Japanese Patent Publication No. 57-20069 discloses a closed spherical hollow body comprising at least one casting powder component, in which case a fine powder mixture of the casting powder component and optionally a flux is used as a raw material. Is used, the raw material is slurried, mixed with the blowing agent, and the mixture of the raw material and the blowing agent is expanded,
In a method for producing a casting powder, a method for producing a casting powder, wherein the hollow body is calcined after foaming, is disclosed. However, the powder for casting produced according to this publication has an air layer inside and thus has poor melting properties. In addition, since it is hollow, it has a low particle strength, and powdering by an automatic feeder cannot be employed violently.

In Japanese Patent Publication No. 4-22663, Al ₂
2 to 20% by weight of O _3, 3 to 30% by weight of fluoride of alkali and alkaline earth metal, CaO is 2 to 30% by weight of oxide of alkali and alkaline earth metal, 0.2 to 7% of carbon powder % By weight, with the balance being CaO and SiO ₂ ,
Moreover consists composition of CaO / SiO ₂ .65 to 1.5, particle size 0.2~0.6mm is at 90% or more by weight of spherical granules, repose angle of 27 degrees or less, the collapse angle is 17 degrees A flux for continuous casting excellent in heat insulation, characterized by the following, is disclosed. However, this flux also has a problem in terms of grain strength and the like, and has a problem in application to an automatic feeder.

Further, JP-A-61-108463 discloses that Al
₂ to 20% by weight of ₂ O3, ₃ to 30% by weight of alkali and alkaline earth metal fluorides, and alkali and alkaline earth metal oxides.
0% by weight and 0.2 to 7% by weight of carbon powder, and the balance is a composition containing CaO and SiO ₂ whose CaO / SiO ₂ ratio is 0.65 to 1.5. Particles having a particle size of 3.0 mm or less, having a particle size of 0.1 to 20 mm: 90% by weight or more, and a particle size of 0.1 mm: 5
Disclosed is a spherical granular flux for casting having good heat retention, characterized by a particle size distribution of not more than 5% by weight and a particle size of 2.0 to 3.0 mm: 5% by weight or less. However, the flux disclosed in this publication is granulated by an agitation granulation method, has a low particle strength, and has a problem in application to an automatic feeder.

Japanese Patent Publication No. 1-20944 discloses Al ₂
2 to 20% by weight of O _{3, 3 to} 30% by weight of alkali and alkaline earth metal fluorides, and oxides of alkali and alkaline earth metals. In the case of ／ 7% by weight, the balance is CaO / SiO ₂ (weight% ratio) in the range of 0.65 to 1.5, in addition to CaO and SiO ₂ , and a component composition containing unavoidable impurities. The particle size composition of the particles granulated in the above is that 90% by weight or more and 0.3 mm
80% by weight or more when less than 1.2 mm, 5% by weight or less when the particle size is less than 0.1 mm, and 2.0 mm or more and 3.0 mm or more.
Less than 5% by weight or less, spherical granules,
In addition, a casting flux excellent in melting properties, characterized in that the whole or a part of the carbon is present in the form of powder in the form of spherical particles on the surface or between the particles, is disclosed. However, the flux disclosed in this publication is also granulated by the stirring granulation method, and has the same problems as described above.

Accordingly, an object of the present invention is to provide a mold powder for continuous casting of steel which can improve the properties of molten slag, can be applied to an automatic feeder, and can improve the heat retention.

[0014]

The present inventors have made various studies to solve the above-mentioned problems, and as a result, have found that all of the above-mentioned drawbacks can be overcome. That is, according to the present invention, the CaO-SiO ₂ -based
O ₂ The feedstocks 0-30 wt%, 0.2 to 8 wt% of carbonaceous material, in a continuous casting mold powder of steel comprising a flux material 3-30 wt%, a swelling clay mineral 0 A mold for continuous casting of steel, which is a granulated product containing 1.5 to 15% by weight, having a particle size of 1.5 mm or less, and having a bulk specific gravity in a range of 1.0 to 1.5. In the powder.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The mold powder of the present invention can improve the properties of molten slag by applying solid, spherical, high-density, small-diameter particles, can be applied to an automatic feeder, and improve heat retention. Is what you can do.

In the present invention, since the mold powder is formed into a high-density, small-diameter granule, heat is easily transmitted to the inside of the mold powder. Shows the molten slag formation properties. The particle size of the granulated product is preferably 1.5 mm or less, and more preferably 1.2 mm or less is 90% by weight or more. Here, 9 granules having a particle size of 1.2 mm or less
If it is 0% by weight or more, it exhibits excellent slagging properties close to powder. Further, by setting the granulated material having a size of 1.2 mm or less to have a particle size distribution of 90% by weight or more, the permeability of the unmelted layer can be remarkably reduced, and the passage of heat can be suppressed, and the characteristics excellent in heat retention can be secured. In addition, large particles having a particle size of more than 1.5 mm are not preferable because good slag property cannot be imparted.

Further, in order to reduce the size of the granulated product and obtain high strength, it is necessary to increase the density of the granulated product.
Even if granulation is performed simply by a granulation method such as a stirring granulation method, the density cannot be increased. Therefore, in the present invention, the density of the granulated material is increased by blending a swellable clay mineral. Here, the swellable clay mineral has a property of swelling due to moisture added as a binder during granulation, and can significantly improve the granulation property as compared with general clay. The swellable clay mineral that can be used in the present invention is a montmorillonite-based mineral, such as bentonite. The compounding amount of the swellable clay mineral is 0.5 to 15% by weight, preferably 0.5.
In the range of 10 to 10% by weight. Here, if the blending amount of the swelling clay mineral is less than 0.5% by weight, it is not preferable because the addition effect is not obtained, and if the blending amount exceeds 15% by weight, the granulated material obtained by granulation is not preferable. The particle size tends to be too large, the particle strength becomes too high, the packing becomes excessive, the bulk specific gravity becomes too large, and the melting properties are unfavorably deteriorated.

[0018] Here, the basic composition of the continuous casting mold powder of the steel of the present invention, CaO-SiO ₂ system main raw materials 4
0 wt% or more, the SiO ₂ feedstocks 0-30 wt%, 0.2 to 8 wt% of carbonaceous material, a flux material 3-30
% By weight.

The CaO—SiO ₂ -based main raw material that can be used in the present invention is not particularly limited, and any of those generally used as raw materials for mold powder can be used, for example, wollastonite. , Yellow phosphorus slag, synthetic calcium silicate, dicalcium silicate,
Blast furnace slag, Portland cement and the like. Note that C
If the amount of the aO-SiO ₂ -based main raw material is less than 40% by weight, the amount of other raw materials to be added is relatively large, and it is difficult to adjust the melting characteristics such as viscosity, which is not preferable.

Also, the SiO ₂ raw material usable in the present invention is not particularly limited, and any material usually used as a raw material for mold powder can be used. For example, sodium silicate, Glass powder, silica powder,
Diatomaceous earth, clay, silica flower, spodumene, etc. If the amount of the SiO ₂ raw material exceeds 30% by weight, the composition becomes low in CaO / SiO ₂ , the viscosity becomes too high, and it becomes difficult to adjust the melting characteristics and the like.

Further, the carbonaceous raw material that can be used in the present invention is not particularly limited, and any one commonly used as a raw material of a mold powder can be used. Examples thereof include graphite, coke, and the like. Carbon black,
It is charcoal. If the compounding amount of the carbonaceous raw material is less than 0.2% by weight, slagging is too fast and it is difficult to adjust the slagging rate, which is not preferable.
Exceeding the weight% is not preferable because the slagging becomes too slow and it is difficult to adjust the slagging rate.

In the mold powder of the present invention, expandable graphite can be used for part or all of the carbonaceous raw material. By using expandable graphite as a carbonaceous raw material, it is possible to balance grain strength and slagging properties. The compounding amount of the expandable graphite and the swellable clay mineral is preferably such that the weight ratio of the swellable clay mineral / expandable graphite is within a range of 5/1 or less. If the weight ratio exceeds 5/1, the grain strength is too high, and the slagging tends to be delayed, which is not preferable.

The flux material usable in the present invention is not particularly limited, and any flux material usually used as a mold powder material can be used. Examples of the flux material include sodium carbonate and lithium carbonate. ,
Manganese carbonate, strontium carbonate, potassium carbonate, barium carbonate, magnesium carbonate, sodium fluoride, magnesium fluoride, calcium fluoride, aluminum fluoride, lithium fluoride, cryolite, fluorite, boric acid, borax and the like. If the amount of the flux material is less than 3% by weight, the viscosity and melting point are too high, which is not preferable. If the amount exceeds 30% by weight, the viscosity and the melting point are too low. Not preferred.

The granulation method is not particularly limited, and any conventional method such as stirring granulation can be used. If necessary, organic and inorganic binders can be used.

Further, it is preferable that the obtained granules are dried by applying hot air while adding fluidity in a fluidized bed or the like.
That is, since the granules are dried and shrunk by the hot air and the flow, the granulated material becomes denser and has high density. The temperature of the hot air is preferably 150 ° C. or higher, and more preferably 200 ° C. or higher. When the temperature of the hot air is lower than 150 ° C., the drying shrinkage is small, and the effect of densification cannot be expected much.

The bulk specific gravity of the mold powder of the present invention is
It is in the range of 1.0 to 1.5. If the bulk specific gravity is less than 1.0, the degree of filling of the unmelted layer is insufficient and the heat retention is poor, which is not preferable. On the other hand, if the bulk specific gravity exceeds 1.5, it is not preferable because overfilling occurs and the slag melting property deteriorates.

[0027]

EXAMPLES Hereinafter, the mold powder of the present invention will be further described with reference to examples. Examples Mold powders of the products 1 to 9 of the present invention and the comparative products 1 to 3 were prepared at the compounding ratios and production conditions shown in Table 1 below. Table 1 also shows the chemical composition of the obtained mold powder and the results of its use.

[0028]

[Table 1]

In Table 1, the workability is a comprehensive evaluation of the uniformity of the molten slag when using the mold powder, the melting properties, the presence or absence of a slag bear, the heat retention, the uniformity of the thickness of the molten powder slag layer, and the like. Where ◎ indicates good, 〇 indicates suitability, △ indicates partial failure, and × indicates failure. The powdering index at the time of passing through the automatic feeder is represented by an index with the powdering amount of the comparative product 1 as 1. Further, the slab defect occurrence index is represented by an index with the slab defect generation amount of the comparative product 1 as 1. The heat retention was evaluated by measuring the temperature of the molten slag layer. Further, the slagging property shows the result of visual observation in actual casting. In addition, the particle strength was evaluated by measuring the amount of fine powder after mixing the mold powder and the cobblestone into a V-shaped mixer at the same time. Indicated as x.

Next, mold powders of Samples 1 to 7 having various bulk specific gravities and particle sizes were obtained by stirring and granulating using the raw material blend of the product 4 of the present invention shown in Table 1. Table 2 below shows the particle strength, applicability of the automatic feeder, heat retention and slagging properties of the obtained sample. For comparison, mold powder agitated and granulated using the raw material composition of comparative product 1 (samples 8 to 10) and mold powder spray granulated using the raw material formulation of comparative product 2 (samples 11 and 12) ), Mold powders (samples 13 and 14) obtained by extrusion granulation using the raw material mixture of Comparative Product 3 were obtained. Table 2 also shows various characteristics of the obtained mold powder.

[0031]

[Table 2]

In Table 2, the applicability of the automatic feeder shows the result of measuring the powdering rate when passing through the automatic feeder.

[0033]

According to the present invention, the molten slag has excellent properties,
When applied to an automatic feeder, it is possible to provide a mold powder for continuous casting of steel that is not powdered and has excellent heat retention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-164459 (JP, A) JP-A-6-198404 (JP, A) JP-A-6-63713 (JP, A) JP-A-5-1984 305403 (JP, A) JP-A-49-115933 (JP, A) JP-A-10-156492 (JP, A) JP-A-61-108463 (JP, A) JP-B-1-20944 (JP, B2) JP-B-57-20069 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/108 C21C 7/076

Claims (2)

(57) [Claims] 1. A 40% by weight CaO—SiO ₂ main raw material.
Although the SiO ₂ feedstocks 0-30 wt%, 0.2 to 8 wt% of carbonaceous material, in a continuous casting mold powder of steel comprising a flux material 3-30 wt%,
It contains 0.5 to 15% by weight of a swelling clay mineral and has a particle size of 1.
Granulated material of 5 mm or less and bulk specific gravity of 1.0 to 1.5
A mold powder for continuous casting of steel. 2. A part or all of a carbonaceous raw material is expandable graphite, and a weight ratio of swellable clay mineral / expandable graphite is 5 /.
The mold powder for continuous casting according to claim 1, which is 1 or less.