Mold powder and method for producing the same

Abstract

To produce a mold powder that has a low viscosity suitable for continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, while suppressing the generation of white smoke. [Solution] One aspect of the present invention is a method for producing mold powder used in continuous casting of medium carbon steel, high carbon steel, or electrical steel, comprising the step of obtaining mold powder from raw materials containing sodium fluoride and sodium oxoate, wherein the Na2O content in the mold powder is 9% by mass or more, the Cl content is 0.5% by mass or less, and the viscosity of the mold powder at 1300°C is 2 dPa·s or less.

Description

Technical Field

[0001] The present disclosure relates to mold powder and a method for manufacturing the same.

Background Art

[0002] Mold powder is put into the mold for continuous casting, melted by the heat of molten steel to become molten slag, flows into the gap between the solidified steel and the mold, and plays a role in lubrication and heat extraction control. In the continuous casting of medium carbon steel, high carbon steel or electromagnetic steel, due to the characteristics of these steel grades, it is particularly required to prevent operation troubles and slab quality troubles. Therefore, the mold powder used for the continuous casting of these steel grades is required to maintain high lubricity.

[0003] When attempting to maintain high lubricity of the mold powder, it is necessary to keep the viscosity of the mold powder low. And in order to keep the viscosity of the mold powder low, for example, it is conceivable to increase the amount of a sodium source (see, for example, Patent Document 1), which is known as a component for adjusting the viscosity of the mold powder, in the mold powder.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described in Patent Document 1, when including a sodium source, it is known to use sodium fluoride or chloride as a raw material. However, according to the study by the present inventors, when using chloride, it has been found that when the residual amount of chlorine in the obtained mold powder increases, white smoke may occur during the use of the mold powder.

[0006] Therefore, one aspect of the present invention aims to produce a mold powder that has a low viscosity suitable for use in continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, while suppressing the generation of white smoke. [Means for solving the problem]

[0007] One aspect of the present invention is a method for producing mold powder used in continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, comprising the step of obtaining mold powder from raw materials containing sodium fluoride and sodium oxoate, wherein the Na2O content in the mold powder is 9% by mass or more, the Cl content is 0.5% by mass or less, and the viscosity of the mold powder at 1300°C is 2 dPa·s or less.

[0008] In this manufacturing method, the Na2O content in the mold powder is 9% by mass or more, and the viscosity of the mold powder at 1300°C is 2 dPa·s or less. As a result, the mold powder contains a sufficient sodium source and its viscosity is kept low, thus exhibiting the lubricity required for mold powder used in continuous casting of medium-carbon steel, high-carbon steel, or electrical steel. Furthermore, in this manufacturing method, raw materials containing sodium fluoride and sodium oxoate are used, and the Cl content in the mold powder is 0.5% by mass or less, thus suppressing the generation of white smoke when using the mold powder.

[0009] The content of F in the mold powder may be 6% by mass or more. The content of sodium oxoate in the raw materials may be 9% by mass or less, and the mold powder may be in the form of hollow granules. The content of sodium fluoride in the raw materials may be 5% by mass or more. The residual amount of chlorine in the sodium fluoride may be 3.5% by mass or less.

[0010] Another aspect of the present invention is a mold powder used for continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, wherein the Na2O content in the mold powder is 9% by mass or more, the Cl content is 0.5% by mass or less, and the viscosity of the mold powder at 1300°C is 2 dPa·s or less. The F content in the mold powder may be 6% by mass or more. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to produce a mold powder that has a low viscosity suitable for use in continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, while suppressing the generation of white smoke. [Modes for carrying out the invention]

[0012] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0013] One embodiment of the present invention is a method for producing mold powder, comprising the step of obtaining mold powder from raw materials containing sodium fluoride and sodium oxoate.

[0014] The raw materials are obtained by blending sodium fluoride, sodium oxoates, and other raw materials. Examples of sodium oxoates include sodium carbonate, sodium sulfate, sodium nitrate, sodium aluminate, sodium phosphate, and sodium silicate.

[0015] Other raw materials are one or more selected from the group consisting of base material raw materials, flux raw materials, carbonaceous raw materials (aggregate carbon), and organic binders. Base material raw materials may be, for example, premelt base material raw materials, and specifically may be raw materials produced through a heating and melting process, such as blast furnace slag and converter slag produced in the ironmaking and steelmaking processes, electric furnace slag produced in electric furnaces and cupolas, yellow phosphorus slag and synthetic calcium silicate. Flux raw materials may be, for example, metal oxides such as manganese dioxide, calcium fluoride fluorides (excluding sodium fluoride), and carbonates such as lithium carbonate (excluding sodium oxoates). Carbonaceous raw materials may be, for example, carbon powder. Organic binders may be, for example, water-soluble polymer compounds.

[0016] The sodium fluoride content in the raw materials (content relative to the total amount of raw materials) is preferably 5% by mass or more, 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, or 10% by mass or more, and may be 20% by mass or less, 19% by mass or less, 18% by mass or less, or 17% by mass or less.

[0017] The sodium oxoate content in the raw materials (content relative to the total amount of raw materials) is preferably 1% by mass or more, 2% by mass or more, or 3% by mass or more, and may be 9% by mass or less, 8% by mass or less, 7% by mass or less, or 6% by mass or less. By keeping the sodium oxoate content in the raw materials within this range, it is possible to suppress an excessive increase in the hollow portion when the mold powder is in the form of hollow granules, which can lead to a decrease in the bulk density and strength of the mold powder.

[0018] The chlorine content in the raw materials must be adjusted so that the chlorine (Cl) content in the resulting mold powder is 0.5% by mass or less. Therefore, for example, it is preferable to use a sodium source other than sodium chloride as the sodium source. Sodium fluoride used as a raw material may contain residual chlorine, for example, in the form of sodium chloride. In such cases, it is preferable to reduce the amount of residual chlorine in the sodium fluoride. The amount of residual chlorine in the sodium fluoride is preferably 3.5% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.5% by mass or less, 0.4% by mass or less, or 0.35% by mass or less, and may be 0.01% by mass or more, 0.1% by mass or more, or 0.2% by mass or more.

[0019] In the process of obtaining mold powder, the raw materials described above can be turned into powder to obtain powdered mold powder. Alternatively, in the same process, the raw materials can be dispersed in a dispersion medium to prepare a slurry, and then a granulation process can be carried out in which the slurry is sprayed and dried to obtain hollow granular mold powder.

[0020] The mold powder obtained by the above manufacturing method has a Na2O content of 9% by mass or more, a Cl content of 0.5% by mass or less, and a viscosity of 2 dPa·s or less at 1300°C. Because this mold powder has low viscosity, it is suitable for continuous casting of medium carbon steel, high carbon steel, or electrical steel where high lubricity is required, and can suppress the generation of white smoke. In this specification, unless otherwise specified, the content of each component in the mold powder is the content (by mass) based on the total amount of mold powder.

[0021] The Na2O content in the mold powder is preferably 10% by mass or more, 10.5% by mass or more, 11% by mass or more, or 12% by mass or more, and may be 25% by mass or less, 20% by mass or less, 15% by mass or less, or 13% by mass or less.

[0022] The content of Cl in the mold powder is preferably 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, 0.1% by mass or less, 0.08% by mass or less, 0.06% by mass or less, 0.05% by mass or less, less than 0.05% by mass, 0.04% by mass or less, or 0.03% by mass or less.

[0023] The mold powder may further contain F. The content of F in the mold powder may be 6% by mass or more, 7% by mass or more, 8% by mass or more, or 9% by mass or more, and may be 13% by mass or less, 12% by mass or less, 11% by mass or less, or 10% by mass or less. When the content of F in the mold powder is within this range, when the mold powder melts in the mold, flows between the mold and the slab, and a part of it solidifies to form a powder film, crystals of Cuspidine (Ca4Si2O7F2), which is the main component of the powder film, are likely to crystallize (because F is the main component of Cuspidine), and the heat extraction in the mold can be stably controlled.

[0024] The mold powder may further contain CaO and SiO2. The content of CaO in the mold powder may be 20% by mass or more, 25% by mass or more, or 30% by mass or more, and may be 55% by mass or less, 50% by mass or less, or 45% by mass or less. The content of SiO2 in the mold powder may be 20% by mass or more, 25% by mass or more, or 30% by mass or more, and may be 50% by mass or less, 45% by mass or less, or 40% by mass or less. The ratio of the content of CaO to SiO2 (CaO / SiO2) may be 0.80 or more, 0.90 or more, 1.00 or more, 1.10 or more, or 1.20 or more, and may be 1.80 or less, 1.70 or less, 1.60 or less, 1.50 or less, or 1.40 or less.

[0025] The mold powder may further contain C. The content of C (T.C.) in the mold powder may be 2% by mass or more, 3% by mass or more, or 4% by mass or more, and may be 8% by mass or less, 7% by mass or less, or 6% by mass or less.

[0026] The mold powder may further contain Al2O3. The Al2O3 content in the mold powder may be 2% by mass or more, 3% by mass or more, 4% by mass or more, or 5% by mass or more, and may be 10% by mass or less, 9% by mass or less, 8% by mass or less, or 7% by mass or less.

[0027] The mold powder may further contain MgO. The MgO content in the mold powder may be 0.1% by mass or more, 0.2% by mass or more, or 0.5% by mass or more, and may be 3% by mass or less, 2% by mass or less, or 1% by mass or less.

[0028] The mold powder may further contain Li2O. The Li2O content in the mold powder may be 0.1% by mass or more, 0.2% by mass or more, or 0.5% by mass or more, and may be 3% by mass or less, 2% by mass or less, or 1% by mass or less.

[0029] The viscosity of the mold powder at 1300°C may be 1.8 dPa·s or less, 1.6 dPa·s or less, 1.5 dPa·s or less, 1.4 dPa·s or less, 1.3 dPa·s or less, 1.2 dPa·s or less, or 1.1 dPa·s or less, and may be 0.1 dPa·s or more, 0.2 dPa·s or more, 0.3 dPa·s or more, 0.4 dPa·s or more, 0.5 dPa·s or more, or 0.6 dPa·s or more. The viscosity of the mold powder at 1300°C refers to the viscosity of the mold powder measured by the rotating cylinder method according to the following procedure. First, the mold powder to be measured is placed in a crucible and completely melted at 1400°C. Then, it is placed in a vertical annular furnace (Elema furnace), and the rotor of a Type B viscometer is immersed in the molten powder and stabilized at 1300°C for 30 minutes. Next, the rotor is rotated, and the torque due to viscous resistance is measured to determine the viscosity. The Type B viscometer is calibrated in advance using a standard viscometer.

[0030] The mold powder may be in powder form (e.g., solid) or hollow granule form. As described above, the mold powder is suitably used in the continuous casting of medium-carbon steel, high-carbon steel, or electrical steel. Medium-carbon steel is steel with a carbon content of, for example, 0.08 to 0.20 mass%. High-carbon steel is steel with a carbon content of, for example, 0.20 mass% or more. Electrical steel is steel with a silicon content of, for example, 1.0 mass% or more. [Examples]

[0031] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0032] (Manufacturing of mold powder) Raw materials were prepared by blending the amounts of sodium fluoride and sodium carbonate shown in Table 1 with other raw materials to obtain mold powder having the composition and viscosity shown in Tables 1 and 2. The other raw materials include base material, flux material, carbonaceous material (aggregate carbon), and organic binder. Table 1 shows the Na2O and Cl content and viscosity in the mold powder, and Table 2 shows the content of other components in the mold powder. Subsequently, water was added to the raw materials to prepare a slurry, and then the slurry was spray-granulated to obtain hollow granular mold powder.

[0033] The Cl content in the mold powder was measured using the Mohr method. More specifically, the Cl content in the mold powder was determined by potentiometric titration using a silver indicator electrode with an automatic titrator (manufactured by Hiranuma Sangyo Co., Ltd., product name: Automatic Titrator COM-300A) (the titrator was a 0.01 mol / L silver nitrate standard solution).

[0034] (Evaluation of white smoke) In a high-frequency induction heating furnace, each mold powder was sprinkled onto molten iron of the steel types shown in Table 1, which was maintained at 1550°C. Five workers were then asked whether they experienced discomfort from the white smoke generated by the mold powder. The number of workers who answered "yes" to discomfort was categorized as "A" if 0 workers answered "yes," "B" if 1 worker answered "yes," and "C" if 2 or more workers answered "yes." The results are shown in Table 1.

[0035] [Table 1]

[0036] [Table 2]

Claims

1. A method for manufacturing mold powder used in continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, The process includes obtaining the mold powder from raw materials containing sodium fluoride and sodium oxoate, Na in the mold powder ２ The O content is 9% by mass or more, and the Cl content is 0.5% by mass or less, and SiO ２ The ratio of CaO content to (CaO / SiO ２ ) is 1.40 or less, A method for producing the mold powder, wherein the viscosity of the mold powder at 1300°C is 2 dPa·s or less.

2. The manufacturing method according to claim 1, wherein the content of F in the mold powder is 6% by mass or more.

3. The manufacturing method according to claim 1 or 2, wherein the sodium oxoate content in the raw materials is 9% by mass or less, and the mold powder is in the form of hollow granules.

4. The manufacturing method according to any one of claims 1 to 3, wherein the content of sodium fluoride in the raw material is 5% by mass or more.

5. The manufacturing method according to any one of claims 1 to 4, wherein the residual amount of chlorine in the sodium fluoride is 3.5% by mass or less.

6. A mold powder used in continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, Na in the mold powder ２ The O content is 9% by mass or more, and the Cl content is 0.5% by mass or less, and SiO ２ The ratio of CaO content to (CaO / SiO ２ ) is 1.40 or less, A mold powder having a viscosity of 2 dPa·s or less at 1300°C.

7. The mold powder according to claim 6, wherein the content of F in the mold powder is 6% by mass or more.

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