JPH07178520A - Mold powder for continuous casting of steel - Google Patents

Abstract

PURPOSE:To provide mold powder for continuous casting of a steel, which has excellent slag-making and melting characteristic and contributes to the improvement of the stability of operation and steel quality. CONSTITUTION:The mold powder for continuous casting of the steel is composed of 45-90wt.% base raw material (15-90wt.% in the case of containing silica raw material), 5-40wt.% flux raw material and 6-15wt.% carbonaceous raw material. As the base raw material, acicular calcium silicate having 45-500mum average fiber length, 5-65mum average fiber diameter and 7-100 in the range of aspect ratio is contained at 10-90wt.%. Further, silica raw material at <=20wt.% and further, metallic component at <=0wt% can e contained.

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.
The present invention relates to a mold powder for continuous casting of steel, which has excellent melting characteristics and can contribute to improvement of operation stability and stability of steel quality.

[0002]

2. Description of the Related Art In recent years, the progress of continuous casting of steel has been remarkable, and high-temperature slabs have become unmaintained (HCR, HDR), high-speed casting, diversified mold cross-sectional shapes, and multi-casting. Improving and stabilizing the operating rate of the continuous casting machine by reducing defects and eliminating defects in cast slabs are the greatest challenges in the CC process. Under these circumstances, the mold powder plays a large role.

Although the quality of the mold powder is designed to meet various steel components and various casting conditions,
In particular, if the quality design is inappropriate, or if the quality design is appropriate but the quality varies, the continuous casting machine may be stopped due to trouble such as breakout, and the cause of slab defects may be caused. Often becomes. With the improvement of mold powder quality design level, the stability of quality becomes important depending on the steel grade.

Mold powders for continuous casting of steel include Portland cement, yellow phosphorus slag, wollastonite, dicalcium silicate, synthetic calcium silicate and the like as base materials, and powders such as basicity and bulk specific gravity as required. A silica raw material for adjusting body characteristics, a flux raw material as a melting property adjusting agent for sodium carbonate, borax, cryolite, fluorspar, etc., and a mixed type consisting of a carbonaceous raw material as a melting rate adjusting material, and carbon. There is a semi-pre-melt type in which all components except the quality raw material are melt-water granulated in advance. In terms of shape, there are a powder type in which powder raw materials are mixed and a granule type in which granulation is performed by various methods. In addition,
In the conventional mold powder, the wollastonite raw material is adopted by taking advantage of the characteristics that the chemical components are stable and the amount of impurities is small, and the shape etc. are not particularly considered.

In continuous casting of steel, mold powder is added in the mold. The mold powder injected into the mold through the dipping nozzle and added on the surface of molten steel forms a layered structure of molten slag layer, sintered layer and unmelted raw powder layer from the surface of molten steel due to the heat received from the molten steel. , Flows between the solidified shell of steel and the mold while playing various roles, and is consumed. The lubrication between the mold and the solidified shell, the dissolution of inclusions floating from the molten steel, the absorption, the oxidation prevention of the molten steel, and the heat retention function are important roles of the mold powder.

Among the roles of the mold powder mentioned above,
It is important to adjust properties such as softening point and viscosity, and it is important to select the chemical composition. Regarding the heat retention property of, the melting rate adjusted by the carbonaceous raw material,
Powder characteristics such as bulk specific gravity are important.

Particularly, extremely low carbon steel, high carbon steel, stainless steel, etc. are necessary and important for heat retention, and when heat retention is poor,
Skin peeling occurs during casting, and slab defects such as pinholes and inclusions are likely to cause problems. Moreover, the probability of causing a trouble tends to increase due to the generation of the slug bear.

The heat retaining property may be partly due to a metal or the like, but it is basically secured by the carbonaceous raw material, and it is important to adjust the particle size, type and addition amount of the carbonaceous raw material. However, since the carbonaceous raw material also plays a role of adjusting the melting rate, addition of a large amount of the material ensures heat retention, but slows the melting rate, which reduces the molten slag layer thickness and risk of breakout. In addition to the high melting point, when unmelted powder layer and sintered layer come close to the molten steel surface and fluctuations in the molten metal level occur, slab defects such as pinholes and inclusions are more likely to occur. It may be.

[0009]

As described above, in order to ensure the heat retaining property of the powder, it may be partially made of metal, etc., but basically it is made of carbonaceous raw material, and the particle size of carbonaceous raw material is The current situation is that it is made according to the type, type, and amount of addition.

However, since the mold powder added to the mold is melted sequentially from the low melting point raw material, when a large amount of carbonaceous raw material is added, the carbonaceous raw material is covered with the molten glass-like substance and is oxidized and burned. I can't do it
Variations in the melting rate may occur, leading to variations in the thickness of the powder slag layer, which may eventually deteriorate the quality of the slab and hinder stable operation.

In mold powders such as ultra-low carbon steel and stainless steel, addition of a large amount of carbonaceous raw material easily causes a problem of carburization. Therefore, the heat retaining property and the slagging time are adjusted depending on the particle size and type of the carbonaceous raw material. It is difficult to adjust the addition amount.
In addition, the mold powder added to the mold must be melted quickly by receiving the heat from the molten steel, flowing into the space between the mold and the solidified shell and consumed, so it is necessary to adjust the slagging time to match the casting speed. However, it is difficult to add a large amount of carbonaceous raw material in high-speed casting operation.

From this fact, it is difficult to adjust the addition amount of the carbonaceous raw material, so that it is difficult to ensure the heat retaining property in the range where the addition amount of the carbonaceous raw material is small, and the balance of the slagging melting rate is It may cause disintegration, which not only adversely affects the quality of the cast slab but also causes certain troubles.

Therefore, an object of the present invention is to provide a mold powder for continuous casting of steel which is excellent in slag formation and melting characteristics, and can contribute to improvement of operation stability and stability of steel quality.

[0014]

That is, the mold powder for continuous casting of steel of the present invention comprises 45 to 90% by weight of base material, 5 to 40% by weight of flux material, and 0 to 0 of carbonaceous material.
In a mold powder for continuous casting of steel containing 15% by weight, the average fiber length of the base material is 45 to 5
It is characterized by containing acicular calcium silicate having an average fiber diameter of 00 μm, an average fiber diameter of 5 to 65 μm, and an aspect ratio of 7 to 100 in an amount of 10% by weight or more and less than 90% by weight.

Furthermore, the mold powder for continuous casting of steel according to the present invention comprises 15 to 90% by weight of base material, 5 to 40% by weight of flux material, 30% by weight or less of silica material and 0 to 15% by weight of carbonaceous material. In a mold powder for continuous casting of steel containing, needle-like calcium silicate having an average fiber length of 45 to 500 μm, an average fiber diameter of 5 to 65 μm, and an aspect ratio of 7 to 100 as a base material. Is contained in an amount of 10 to 90% by weight.

[0016]

The present inventors have obtained the following findings as a result of various studies. The heat retaining property of the powder is ensured by the sintered layer and the unmelted raw powder layer. Therefore, in order to secure the sintered layer and the unmelted raw powder layer, the addition amount of the carbonaceous raw material is adjusted, but the addition of a large amount of carbonaceous raw material not only reduces the melting rate, but also causes harmful effects. The current situation is that a sufficient effect is not obtained. However, when acicular calcium silicate having the following characteristics is used as all or a part of the base material, proper voids are generated in the powder layer, which improves the heat insulating property of the powder. Moreover, the bulk specific gravity decreases, the volume per unit weight increases, and the raw powder layer can be reliably secured, which can contribute to heat retention.

Further, as compared with ordinary powder, a large amount of carbonaceous raw material can be added, and the powder melt layer, which has been caused by the addition of a large amount of carbonaceous raw material, is reduced, and the harmful effects and powders associated therewith are reduced. It was found that the oxidative combustion of the carbonaceous raw material can be carried out extremely smoothly without the red heat. Moreover, it was also found at the same time that the addition of a very small amount of carbonaceous raw material to steel grades such as ultra-low carbon steel and stainless steel can ensure sufficient heat retention.

It was also found that the decrease in heat retention due to shrinkage during sintering can contribute to the heat retention by using acicular calcium silicate as a base material, which causes a small shrinkage of sintering at 500 to 1000 ° C. did.

The mold powder for continuous casting of steel according to the present invention is based on the above findings. That is, acicular calcium silicate having the following shape was used as a base material.
Mold powder containing 0 to 90% by weight has good heat retention properties, excellent slag formation and melting characteristics, and stability of operation,
It can contribute to improving the stability of steel quality.

The acicular calcium silicate used in the mold powder of the present invention can be obtained by synthesizing it into a needle shape and crushing so as to maintain the acicular shape, but the cost is very high. , Rather, it is more effective to use a natural product obtained by crushing which easily retains the needle-like shape of existing needle-like minerals by means such as impact so as to keep the needle-like shape. Among them, the special crushed product of wollastonite is a promising acicular calcium silicate.

The amount of acicular calcium silicate used is preferably in the range of 10% by weight or more, and if it is less than 10% by weight, the heat retaining effect is small. Although the amount of acicular calcium silicate used varies depending on the amount of other calcium silicate used, the upper limit is 90% by weight.

The acicular calcium silicate preferably has an average fiber length of 45 to 500 μm and an average fiber diameter of 5 to 65 μm. The average fiber length of acicular calcium silicate is 4
If the average fiber diameter is less than 5 μm and the average fiber diameter is less than 5 μm, sufficient effect cannot be obtained because sufficient voids that can secure heat retention cannot be obtained. On the contrary, the average fiber length exceeds 500 μm and the average fiber diameter exceeds 65 μm. If it becomes large, the melting rate becomes uneven, and in some cases, the carbonaceous raw material is covered with the molten glass, and there is a risk that it cannot be oxidized and burned and remains.

Similarly, the aspect ratio of acicular calcium silicate is also important, and it is preferably 7 to 100 from the viewpoints of ensuring sufficient heat retention and good slagging property of the carbonaceous raw material.

FIG. 1 is a graph showing the relation between the amount of acicular calcium silicate added to mold powder and the oxidation rate of carbonaceous raw material. As is clear from FIG. 1, when the aspect ratio of acicular calcium silicate is 30 rather than 1, the carbonaceous raw material is rapidly oxidized even if the addition amount increases.
It is understood that when acicular calcium silicate having an aspect ratio of 1 is used, the carbonaceous raw material remains unmelted and adversely affects the melting rate. 2 is a graph showing the relationship between the aspect ratio of acicular calcium silicate and the shrinkage ratio. As is clear from FIG. 2, the larger the aspect ratio is, the smaller the shrinkage ratio tends to be, which contributes to the heat retention.

It is preferable to use needle-like calcium silicate alone as a base material, but other base materials such as Portland cement, yellow phosphorus slag, conventional wollastonite, dicalcium silicate, synthetic calcium silicate. Etc. can be used together.

The mold powder of the present invention is basically composed of 45 to 90% by weight of base material (15 to 90% by weight when silica material is included) and 5 to 40 of flux material.
% By weight and 0 to 15% by weight of carbonaceous raw material,
Further, the silica raw material may be contained in an amount of 30% by weight or less. Further, the metal component may be contained in an amount of 20% by weight or less.

Here, as the base material, acicular calcium silicate is used alone as described above, or is used in combination with another base material. Further, if the blending ratio of the base material is less than 45% by weight (less than 15% by weight when the silica raw material is included), the amount of the other raw materials added becomes relatively large, and the lubricating action and absorption of inclusions are relatively large. The effect of the original role of the mold powder such as action is small, and when it exceeds 90% by weight, the addition amount of other raw materials becomes relatively small,
It is not preferable because the melting characteristics are deteriorated and it is difficult to adjust the powder characteristics such as bulk specific gravity and spreadability.

Examples of the flux raw material used in the mold powder of the present invention include fluorite, sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, alkali metal carbonates such as lithium carbonate, sodium fluoride, and fluoride. Fluorine compounds such as magnesium can be mentioned. Furthermore, B ₂ O ₃ , MnO, T
iO ₂ , MgO and the like can also be used as the flux raw material. If the mixing ratio of the flux raw material is less than 5% by weight, it becomes difficult to adjust the melting characteristics, and if it exceeds 40% by weight, the composition change due to evaporation or the molten steel It is not preferable because it severely damages the immersion nozzle that is injected into the mold.

Examples of the carbonaceous raw material used in the mold powder of the present invention include carbon black, graphite, coke and charcoal. If the ratio of the carbonaceous raw material exceeds 15% by weight, the molten steel condition deteriorates, and in some cases carbon may not be completely oxidized, so the effect is small. Further, under the conditions such as for the front of ultra-low carbon steel where carburization is particularly likely to occur, it is possible to use no carbonaceous raw material from the viewpoint of preventing carburization.

Further, as the siliceous raw material which can be used in the mold powder of the present invention, for example, perlite, fly ash, feldspar, diatomaceous earth, silica stone powder, sodium silicate, potassium silicate, glass powder, silica flour and the like can be used. You can The mixing ratio of the siliceous raw material is 3
If it exceeds 0% by weight, it may cause deterioration of the working environment and is not preferable.

The metal component that can be used in the mold powder of the present invention is, for example, magnesium,
Examples thereof include aluminum, silicon, calcium and alloys thereof. The mixing ratio of the metal components is 2
If it exceeds 0% by weight, the oxidation rate will decrease, and a part of it will flow between the mold and the shell in an unoxidized state, and the expected exothermic reaction cannot be obtained, so the effect is small. Further, the effect is small because it causes deterioration of lubricity.

The mold powder of the present invention has a basic composition within the above range, and further, when the ratio of acicular calcium silicate to carbonaceous raw material + metal component is 4 or more,
It is preferable because the oxidation rate is high and the carbonaceous raw material is not covered with the molten glassy substance. When the ratio is less than 4, the oxidation rate is slow and the melting rate varies, which is not preferable. Further, in the conventional mold powder, the combined use of a large amount of carbonaceous raw material and metal has a drawback that the oxidation rate of the metal is delayed and the mold powder flows between the mold and the shell in an unoxidized state, which impairs lubricity and the like. However, when acicular calcium silicate is used as the base material, the metal can be quickly oxidized and almost no unoxidized metal remains in the slag.

The mold powder of the present invention is granulated by using the above-mentioned acicular calcium silicate by a method such as extrusion granulation, stirring granulation, fluidized granulation, tumbling granulation and spray granulation. It can be used in the form of granules, and an organic or inorganic binder can be used if necessary during granulation.

[0034]

EXAMPLES The mold powder for continuous casting of the present invention will be further described below with reference to examples. Examples Table 1 below shows the formulations of the products of the present invention and comparative products, and the results of use in actual machines. In Table 1, the product Nos. 1, 4 and 10 of the present invention and the comparative examples Nos. 13 and 15 are granulated products obtained by hydro-kneading the powder raw material mixture and columnarly granulating the mixture with an extrusion granulator. It is a powder product obtained by mixing the materials with a V-type mixer. In addition, the product No. of the present invention. 1, 4, 6,
The acicular calcium silicates used in Nos. 7, 9, 11, and 12 have an average fiber length of 300 μm, an average fiber diameter of 6 μm, and an aspect ratio of 50. 2,
For 3, 5, 6, 7, 8 and 10 the average fiber length is 49
The one having 0 μm, the average fiber diameter of 5 μm and the aspect ratio of 98 was used. For Comparative Examples 17 and 18, an average fiber length of 300 μm, an average fiber diameter of 297 μm,
The acicular calcium silicate having an aspect ratio of 1 is used.

[0035]

[Table 1]

[0036]

[Table 2]

In the results of use, the heat retention was measured by measuring the temperature of the molten slag layer, and the cast slab inclusion index was obtained by measuring the defects generated per 1 m ² of the steel slab and converting them into an index. Index is cast slab inclusions Index is steel slab 1m ²
Defects that occur per hit are measured and indexed,
The melt stability is a visual observation of the melting state in the mold, and the operation stability is a breakout occurrence frequency.

[0038]

INDUSTRIAL APPLICABILITY The mold powder for continuous casting of steel according to the present invention has at least 1 part of acicular calcium silicate as a base material.
By using 0% by weight, the heat retention is good, and the slag and the melting property are excellent, and it can contribute to the improvement of the operation stability and the stability of the steel quality.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of acicular calcium silicate added to mold powder and the oxidation rate of carbonaceous raw material.

FIG. 2 is a graph showing the relationship between the aspect ratio of acicular calcium silicate and the shrinkage rate.

Claims (3)

[Claims] 1. A mold powder for continuous casting of steel, comprising 45 to 90% by weight of a base material, 5 to 40% by weight of a flux material and 0 to 15% by weight of a carbonaceous material,
As a base material, the average fiber length is 45 to 500 μm, the average fiber diameter is 5 to 65 μm, and the aspect ratio is 7 to 100.
A mold powder for continuous casting of steel, characterized by containing acicular calcium silicate within the range of 10 to 90% by weight. 2. A mold powder for continuous casting of steel, comprising 15 to 90% by weight of base material, 5 to 40% by weight of flux material, 30% by weight or less of silica material and 0 to 15% by weight of carbonaceous material. Containing as a base material a needle-like calcium silicate having an average fiber length of 45 to 500 μm, an average fiber diameter of 5 to 65 μm and an aspect ratio of 7 to 100 in an amount of 10 to 90% by weight. Mold powder for continuous casting of steel characterized by. 3. The mold powder for continuous casting of steel according to claim 1, which contains a metal component in an amount of 20% by weight or less.