JPH11320055A - Multi-layer structural mold powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide multi-layer structural mold powder which has good working circumference, spreading property and reactivity with the air while keeping the original characteristic of the mold powder and can restrain the mutual reactivity between the grains. SOLUTION: Relating to the multi-layer structural mold powder constituted of an inner granular material and at least of a surface layer part formed on the outer surface of the inner granular material, the surface layer part contains >=30 wt.% one or more kinds selected from group composed of carbon black of <8 in pH, carbon-containing compound and metallic carbonate.

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 mold powder having a multi-layer structure capable of remarkably contributing to improvement of working environment, adaptability to automatic feeder, operation stability and steel quality. About.

[0002]

2. Description of the Related Art In recent years, continuous casting technology of steel has been remarkably advanced, and high-temperature cast slabs without maintenance (HCR, HDR), high-speed casting, diversification of mold cross-sectional shapes, and continuous casting have been advanced. Improvement and stabilization of the continuous casting machine operation rate by eliminating defects in high-speed slabs and reducing troubles are the biggest issues in the continuous casting 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. The mold powder added on the surface of the molten steel injected into the mold through the immersion nozzle forms a layered structure of a molten slag layer and an unmelted raw powder layer from the molten steel surface by receiving heat from the molten steel. It plays a role and flows between the solidified shell of steel and the mold and is consumed. The lubricating action between the mold and the solidified shell; the action of dissolving and absorbing inclusions floating from the molten steel; the action of preventing the molten steel from being oxidized and maintaining the heat; and the action as a heat removal control medium between the solidified shell and the mold are important roles. That is, by flowing a certain amount while ensuring a certain thickness of the molten slag layer, the function of (1) can be fulfilled, 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 properties such as basicity and bulk specific gravity, and fluorite, cryolite, borax, magnesium fluoride A mixture of a mixture of a flux material such as a fluoride such as fluoride, sodium carbonate, and carbonate such as barium carbonate, a flux material as a melting property adjusting material such as a viscosity, a carbonaceous material as a melting slag forming speed adjusting material, and a carbon material. Pre-melt type in which all of the components except for the raw materials are previously melt-water granulated,
There is a semi-pre-melt type in which a part is previously melt-water granulated.
In terms of shape, there are a powder type obtained by mixing powder raw materials and a granule type obtained by granulating by various methods.

If the mold powder cannot fulfill these roles, the quality of the slab deteriorates and the operation becomes unstable.
(Break-out, etc.), the development of high-quality and stable-quality mold powder is being promoted. In recent years, there has been a strong demand for granule powders that are more excellent in working environment and more applicable to automatic feeding.

[0006]

As described above, since the mold powder plays various roles simultaneously, the continuous casting operation can be stabilized and the quality of steel can be improved. However, conventional granule mold powders have a homogeneous / uniform composition manufactured by mixing and granulating, so if a particular function is emphasized according to the application and purpose, the other functions will deteriorate. It is the present situation.

[0007] For example, the properties of the surface layer from the inside of the granular mold powder are particularly related to (1) work environment, (2)
Spreading property, (3) reaction with the atmosphere, (4) reaction between grains, and the like. These are particularly important characteristics in the surface layer of the granule mold powder.However, since the conventional granule mold powder has a homogeneous and uniform composition from the inside to the surface layer, if a composition in which these properties are given to the surface layer is used, the mold powder The characteristics (1) and (2) required for the above cannot be sufficiently imparted to the mold powder.

[0008] 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 7 wt%, the balance being CaO / SiO ₂ (wt% ratio) in addition to CaO and SiO ₂ in the range of 0.65 to 1.5, becomes a component composition including unavoidable impurities, agitation granulation method The particle size composition of the particles granulated in the above is 90% by weight or more when the particle diameter is 0.1 mm or more and less than 2.0 mm, and 80% by weight or more and less than 0.1 mm when the particle diameter is 0.3 mm or more and less than 1.2 mm. Is a spherical granule having a distribution of 5% by weight or less and a particle size of 2.0 mm or more and less than 3.0 mm but 5% by weight or less. Melting characteristics characterized by being present on the surface or between grains Excellent casting flux is disclosed. The flux disclosed in this publication is obtained by causing powdered carbon to exist on the surface of the spherical granules or between the granules, and is considered to be effective in suppressing the reaction between particles and sintering. However, according to the publication, the flux is produced by simply mixing the spherical granules and the powdered carbon, so that the powdery carbon is sprinkled into the spherical granules, and the carbon powder is easily spherical. Degradation of the working environment such as dirt due to falling off from the granules and deterioration of the flux quality easily occur.

Japanese Patent Application Laid-Open No. Hei 5-131266 discloses a spherical mold additive obtained by granulating a base material, a flux and an aggregate and coating the surface with carbon. Even in the additives, the adhesion of carbon is insufficient, and carbon is easily removed. That is, in the publication, the spherical mold additive performs the coating of carbon in a wet state in the granulation step, but since it becomes a product after the drying step, the adhesion of the carbon coating in the product state after drying is low. There are inferior drawbacks. This is because, during drying, the moisture in the internal granulated material easily passes through the surface layer to make the surface layer brittle, and also causes a difference in drying shrinkage between the internal granulated material and the contraction of the surface layer. Becomes significantly weaker. Therefore, in this publication, the carbon coating is further coated with sodium stearate or the like to prevent the carbon coating from falling off.

Accordingly, it is an object of the present invention to provide a good working environment, spreadability and reactivity with the atmosphere while suppressing the inherent characteristics of the mold powder, and to suppress the reactivity between grains. It is an object of the present invention to provide a mold powder having a multilayer structure.

[0011]

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, the present invention provides a multi-layer structure mold powder comprising an inner granulated material and at least one surface layer formed on the outer surface of the inner granulated material, wherein the surface layer has a carbon black having a pH of less than 8 , A multilayer-structured mold powder comprising at least 30% by weight of at least one selected from the group consisting of carbon-containing compounds, carbonates and metals.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of various studies and studies, the present inventors have found that a mold powder has a multilayer structure comprising at least internal granules and a surface layer, and a carbon black having a pH of less than 8 is formed on the surface layer. It has been found that it is effective to contain at least 30% by weight of at least one selected from the group consisting of carbon-containing compounds, carbonates and metals. In other words, the properties that involve the surface layer of the mold powder particularly from the inside of the mold powder include (1) work environment, (2) spreading, (3) reactivity with the atmosphere, and (4) mutual And the like. These are particularly important characteristics in the surface layer portion of the mold powder, and in the multilayer structure mold powder of the present invention, the surface layer portion can have a composition capable of imparting these characteristics.

In the multilayer structure mold powder of the present invention,
By forming the mold powder from the internal granules and at least one surface layer, the characteristics required for the surface layer can be imparted to the surface layer, and the characteristics of the mold powder can be greatly improved. The improvements are shown below. (1) Work environment If the mold powder contains carbon, the black color of the carbon causes stains and is avoided as deteriorating the work environment. However, when carbon is present in the surface layer of the granule mold powder, it is effective in suppressing the reaction between particles and sintering. Therefore, in the multilayer structure mold powder of the present invention, by using a specific carbon in the surface layer portion, even by a simple method such as simply mixing the internal granulated material and carbon, it was firmly adhered to the internal granulated material surface Since the surface layer can be formed and the surface layer has excellent adhesion,
This is very advantageous in terms of work environment. In the present invention, by forming a carbon-free layer using a carbon-containing compound (organic compound) as a carbon substitute substance on the surface layer, and coating the internal granulated material containing carbon, the disadvantages of the conventional product are obtained. It is also possible to overcome.

(2) Spreadability The spreadability in the mold when the mold powder is charged is as follows.
In addition to the shape and bulk specific gravity of the mold powder, the composition of the surface layer also affects. If there is a gas generating component in the surface layer, the powder moves due to the generated gas and the fluidity is improved, but conversely, if the gas generating component is present excessively inside the mold powder, it leads to deterioration of the melting property and the like. . Therefore, if the surface layer portion and the internal granules have different compositions and the gas generating component is blended only in the surface layer portion, the spreadability can be improved without deteriorating the characteristics of the internal granules. That is, by blending the gas generating component into the surface layer, the drawbacks of the conventional mold powder can be overcome.

(3) Reactivity with the atmosphere In order to impart heat generation to the mold powder, there is a heat generation mold powder containing a heat generation agent such as a metal such as silicon. Unless an oxidizing agent such as sodium, sodium nitrate or iron oxide is contained, an exothermic reaction cannot be smoothly obtained. However, when the above-mentioned exothermic agent is concentrated in the surface layer portion, the reaction with the air proceeds smoothly, and the amount of the oxidizing agent as described above can be reduced or eliminated. That is, by arranging components that need to react with the atmosphere in the surface layer, the disadvantages of the conventional product can be overcome.

(4) Reactivity between Grains The carbon in the surface layer is effective for suppressing the sintering between the mold powder granules. Further, in ultra-low carbon steel and stainless steel, carburization due to direct contact with carbon in powder becomes a problem. In such a case, it is effective to use a carbon-containing compound (organic compound) as a carbon substitute substance in the surface layer. In particular, an organic compound containing a hydroxyl group, a carboxyl group, a carbonyl group, or the like is more effective because it easily forms a thin layer, has a small amount of carbon, and has an improved spreadability due to a gas generated during combustion. Further, even if a carbon raw material is used for the internal granulated material, if the surface raw material does not contain a carbon raw material, the chance of contact with molten steel is extremely reduced, and carburization can be suppressed.

In the multilayer structure mold powder of the present invention, the composition of the internal granulated material is not particularly limited, and any commonly used one can be used according to the purpose and application. That is, C: 0 to 10% by weight, SiO ₂ : 2
0 to 50% by weight, CaO: 20 to 50% by weight, Al
₂ O ₃ : 0.5 to 20% by weight, MgO: 0 to 15% by weight,
Na ₂ O: 0 to 20% by weight, Li ₂ O: 0 to 10% by weight,
MnO: 0 wt%, TiO _2: 0 wt%,
SrO: 0 wt%, B ₂ O _3: 0 wt%, B
aO-: 0 wt%, Fe ₂ O _3: 0~10 wt%,
F: A composition range of 0 to 20% by weight is preferable.

Next, in the multilayer structure mold powder of the present invention, the surface layer portion contains at least 30% by weight of at least one selected from the group consisting of carbon black having a pH of less than 8, a carbon-containing compound, a carbonate and a metal. The work environment required for the powder as described above,
The composition of other components can be appropriately determined in consideration of characteristics such as spreading properties, reactivity with the atmosphere, and reactivity between grains.

For example, when it is desired to include carbon in the surface layer, a simple method such as simply mixing the internal granulated material and carbon black by using carbon black having a pH of less than 8 in the surface layer is preferred. In this case, the surface layer portion firmly adhered to the surface of the internal granulated material can be formed, and the surface layer portion has excellent adhesion, which is very advantageous in terms of dirt.

In particular, the pH of a carbon-containing compound (organic compound) containing a hydroxyl group, a carboxyl group, and / or a carbonyl group, or a pH having a large number of functional groups to which a functional group has been imparted by oxidation treatment =
A carbon black of less than 8 is effective for forming a thin layer having strong adhesion. In particular, carbon black having a pH of 6 or less is more effective.

In the case where the surface layer is formed only with the specific carbon-containing compound (organic compound) or carbon black having a pH of less than 8, as described above, 0.1% by weight or more of the internal granules may be present. For example, a strong coating can be formed on the outer surface of the inner granulated product by simply mixing with the inner granulated product.

Further, a carbon-free layer can be formed on the surface layer by using a carbon-containing compound (organic compound) as a carbon substitute. Here, as the organic compound, those containing a hydroxyl group, a carboxyl group, a carbonyl group and the like can be used, and specific examples thereof include sugars such as starch, carboxylic acids, and phenol resins.

Further, the composition for forming the surface layer of the multi-layered powder of the present invention uses carbonates such as calcium carbonate, magnesium carbonate, strontium carbonate, lithium carbonate, sodium carbonate, barium carbonate, etc. A wide range of materials such as pure metals such as metallic silicon and alloys can be used. These are effective even when used alone, but are also effective when used as a mixture. As described above, it is possible to select each raw material according to the application and purpose and design the quality.

The characteristics that are particularly important in the surface layer are as described above. Therefore, the surface layer is made of one of carbon black, a carbon-containing compound (organic compound), a carbonate or a metal (alloy) having a pH of less than 8. It is necessary to contain at least 30% by weight of seeds or more. When these contents are less than 30% by weight, the difference from the composition constituting the internal granulated product is small and the improvement effect is small. Further, a composition for forming an internal granulated material may be appropriately used for the remainder of the composition constituting the surface layer portion.

In the multi-layered powder of the present invention, the surface layer preferably has 1 to 3 layers, and the surface layer preferably has a weight ratio of 0.1 to 30% of the internal granulated material. If the proportion of the surface layer portion exceeds 30% by weight, the thickness of the surface layer portion becomes too large, which is not preferable. On the other hand, if the ratio of the surface layer is less than 0.1% by weight, the surface layer is not sufficiently formed as a layer, which is not preferable. More preferably, the content is 0.4 to 15% by weight.

As the production method, various methods can be selected, but the following steps are effective. (1) Granulation of internal granules-drying-surface layer formation by dryer
(Wet type, dry type) -Drying The internal granulated product is granulated by a granulator such as a stirring granulator, and the obtained granulated product is dried by a dryer such as a fluidized bed dryer. Before the end of the drying step (the moisture content of the internal granulation is 0.3 to 5% by weight)
In, spray the composition for forming the surface layer in hot air, diffused,
A surface layer is formed by adhering around the internal granules. Further, the drying is continued, and the drying is completed to obtain a powder. At this time, there are a dry type where the composition for forming the surface layer portion is sprayed as it is, and a wet type where the composition is sprayed in a slurry form having a water content of 20 to 50% by weight. When the surface layer is formed by a wet method, after the drying of the internal granules is completed (water content of 0.3% by weight)
In the following, a surface layer portion may be formed, and then dried again.

Here, the method for forming the surface layer in the granulation step has the following problems. That is, the internal granulated material usually contains a large amount of water, and when the surface layer is formed and dried, the water in the internal granulated material passes through the surface layer to embrittle the surface layer, and further, the internal granulated material is dried. However, there is a disadvantage that the boundary portion is weak due to the difference in drying shrinkage of the surface layer portion, and the surface layer portion is easily peeled off and easily broken. On the other hand, in the method in which the surface layer is formed after the middle stage of drying, the above-described problem does not occur because the surface layer is formed at the stage when the drying and shrinkage of the internal granules are substantially completed. Therefore, in the above method, the moisture content of the internal granules at the time of forming the surface layer is preferably less than 5% by weight, and is preferably less than 3% by weight in order to increase the bonding strength at the boundary.

(2) Granulation of Internal Granulated Material-Drying-Drying-Drying Machine to Form Surface Layer (Dry Type) In the manufacturing method (1), after the surface layer is completely dried (water content: 0.3% by weight or less). By spraying a composition for forming a surface layer portion in dry or hot air or cold air.

Regarding the granulation method, any of granulation methods such as stirring granulation, fluidized granulation, tumbling granulation and spray granulation can be employed in the production methods (1) and (2). .

The binder may be organic if necessary.
Inorganic binders can be used. Organic binders include, for example, starch, dextrin, alginic acids, C
MC, MC, lignin sulfonic acids, PVA and the like can be used. Further, as the inorganic binder, for example, various sodium silicates, various sodium phosphates, sodium aluminate and the like can be used. The amount, concentration, and the like of the binder can be appropriately selected depending on the granulation method to be employed.

As a granulation method, a stirring granulation method is particularly effective. Further, when the surface layer is a carbon-containing thin layer, the above-mentioned specific carbon black or the above-mentioned organic compound is blown into the dryer by the method of the production method (1) or (2), and the inside is dried. The method of coating the granules is particularly effective. By this method, a strongly adhered surface layer is obtained.

It is preferable to use a fluidized-bed dryer or the like as the dryer. Drying, hot air temperature 150 ° C
As described above, the heat treatment is preferably performed at 200 ° C. or higher. The amount of hot air varies depending on the size of the apparatus and the amount of drying, but it is preferable to use an amount that allows the granulated material to flow sufficiently.

When a thermosetting compound such as a phenol resin is used as the organic compound, the powder particle strength can be greatly improved. That is, the use of the thermosetting compound in the powder has been limited in the conventional use because the temperature of the granulated and kneaded material is increased due to the heat of reaction between the raw materials and the frictional heat. This makes it possible to make the surface layer a cured layer. As the dryer at this time, a fluidized bed dryer is suitable, but other dryers can be manufactured as long as the temperature of the blown hot air is 200 ° C. or higher.

When the surface layer is formed in a fluidized bed dryer,
As a method of introducing the composition for forming a surface layer into the dryer,
A method of introducing a raw material for forming a surface layer portion as a single substance, a method of introducing two or more types of components constituting a composition for forming a surface layer part as a single substance from a plurality of blow openings, and a method of introducing a composition from one place Etc. can be used.

By providing a time difference in introducing two or more kinds of the composition for forming a surface layer into a fluidized-bed dryer, two or more surface layers can be provided in the internal granulated product.

The multilayer structure powder of the present invention having the above-mentioned structure can be suitably used as a mold powder or a powder for a tundish.

[0037]

EXAMPLES The multilayer structure powder of the present invention will be further described below with reference to examples. [Examples] Multilayer structure powders of the present invention and comparative products were manufactured according to the formulations and manufacturing methods described in Tables 1 to 3 below. The production methods 1 to 4 in the table are as follows: Production method 1: First, 11 to 14% by weight of a CMC aqueous solution as a binder was externally added to the composition for forming the internal granules.
After adding and granulating in a granulator, the obtained granules are dried in a fluidized bed dryer at a hot air temperature of 250 ° C. to a water content of 0.2% by weight, and the obtained granules are fluidized. The powder was taken out of the layer dryer, and the granulated material and the composition for forming a surface layer portion were mixed to form a surface layer portion on the surface of the granulated material, thereby obtaining a multilayer structure powder. Production method 2: First, an aqueous CMC solution as a binder was added to the composition for forming the internal granulated material in an amount of 11 to 14% by weight.
After the addition and granulation in a granulator, the obtained granules are charged into a fluidized bed dryer, and heated at a hot air temperature of 250 ° C. until the water content of the granules becomes 0.2% by weight. Drying, and then introducing the composition for forming the surface layer (not containing water) into a fluidized bed dryer in which the granulated material is fluidized by hot air to form a surface layer on the surface of the granulated material. A multilayered powder was obtained. Production method 3: First, an aqueous CMC solution as a binder is added to the composition for forming internal granules in an amount of 11 to 14% by weight.
After the addition and granulation in a granulator, the obtained granules are charged into a fluidized bed dryer, and heated at a hot air temperature of 250 ° C. until the water content of the granules becomes 0.2% by weight. After drying, the composition (water content = 50 to 60% by weight) for forming a surface layer is introduced into a fluidized bed dryer in which the granulated material is in a fluidized state by cold air, and the surface layer is formed on the surface of the granulated material. After the formation, hot air was blown again and dried to a water content of 0.2% by weight to obtain a multilayer structure powder. Production method 4: First, an aqueous solution of CMC as a binder is added to the composition for forming internal granules in an amount of 11 to 14% by weight.
After adding and granulating in a granulator, the surface layer forming composition is charged into the granulator and granulated again to form the surface layer, and then the obtained granulated material is The mixture was charged into a fluidized bed dryer and dried at a hot air temperature of 250 ° C. to a water content of 0.2% by weight to obtain a multilayer structure powder.

The results obtained by using the obtained powder as a mold powder are also shown in Tables 1 to 3. The work environment index was evaluated by visually checking the work site on a scale of 1 to 5, and the larger the numerical value, the better.
The in-mold melting property index was evaluated on a scale of 5 to 5,
The larger the value, the better. Further, the slab defect occurrence index is an index of the defect occurrence rate, and the smaller the numerical value, the better. The BO (breakout) prediction occurrence index is the frequency of occurrence of the BO prediction warning, and the smaller the numerical value, the better. Further, the carburizing index is an index of the amount of carbon increase of the product after casting, and the smaller the value, the better.

[0039]

[Table 1]

From the results in Table 1, it can be seen that: Comparative product 1 is a mixture of carbon black having a general pH = 8, and thus is not a state in which a surface layer is formed. The state was such that carbon black was simply mixed with the internal granules, and dust was generated by the carbon black. Moreover, the result of the comparative product 2 was even worse than that of the comparative product 1 because the surface layer was easily peeled off.
Therefore, the products 1 and 2 of the present invention having an improved method of forming the surface layer portion
The working environment, melting properties, and steel quality are both reduced as compared to On the other hand, in the products 1 and 2 of the present invention, due to the improvement of the method of forming the surface layer, the adhesive force of the surface layer was improved, and the working environment, melting properties, and steel quality were all improved. In the product 3 of the present invention, a simple mixing method was used for forming the surface layer, but the use of a special carbon black having a pH of 3 improved the working environment, melting properties, and steel quality. The product 4 of the present invention uses a special carbon black having a pH of 3 and further improves the working environment, melting properties and steel quality by improving the method of forming the surface layer.

[0041]

[Table 2]

From the results shown in Table 2, the products 8 to 10 of the present invention have an improved working environment because the surface layer is formed with a composition containing no carbon as compared with the comparative product 3, and the surface layer is improved. It contains a gas generating component, so that the spreading property and the melting property in the mold are improved, the slab defects are reduced, and the carburization of the slab is also significantly reduced.

[0043]

[Table 3]

[0044]

According to the present invention, since the powder is composed of the internal granulated material and at least one surface layer, the composition of the surface layer of the powder and the composition of the internal granulated material can be made different. The composition of the surface layer portion and the internal granulated material can be set to an optimum composition as appropriate according to the use of the powder and the like.

Claims (1)

[Claims] 1. A multilayer mold powder comprising an inner granulated product and at least one surface layer formed on an outer surface of the inner granulated product, wherein the surface layer is carbon black having a pH of less than 8; A multilayer structure mold powder comprising at least 30% by weight of at least one selected from the group consisting of a carbon-containing compound, a carbonate and a metal.