Mold powder and its manufacturing method

Abstract

To produce a mold powder capable of suppressing the generation of white smoke while having a low viscosity suitably applicable to the continuous casting of a medium carbon steel, a high carbon steel and an electromagnetic steel.SOLUTION: One aspect of this invention is a method for producing a mold powder applicable to continuous casting of a medium carbon steel, a high carbon steel and an electromagnetic steel. The method includes a step of obtaining a mold powder from raw material comprising sodium fluoride and a sodium oxoacid salt, where a content of Na2O is 9 mass% or more; a content of Cl is 0.5 mass% or less; and viscosity of the mold powder at 1,300°C is 2dPa s or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to molding powders and methods for making the same. [Background technology]

[0002] Mold powder is added to a mold for continuous casting, melts with the heat of the molten steel, and becomes molten slag, which flows into the gap between the solidified steel and the mold, fulfilling the roles of lubrication and heat removal control. In the continuous casting of medium-carbon steel, high-carbon steel, or electrical steel, due to the characteristics of these steel grades, it is particularly important to prevent operational problems and problems with the quality of the cast slabs. Therefore, the mold powder used in the continuous casting of these steel grades is required to maintain high lubricity.

[0003] In order to maintain high lubricity of the molding powder, it is necessary to keep the viscosity of the molding powder low. To keep the viscosity of the molding powder low, it is conceivable to include a large amount of a sodium source, which is known as a component that adjusts the viscosity of molding powder (see, for example, Patent Document 1), in the molding powder. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-309464 Summary of the Invention [Problem to be solved by the invention]

[0005] As described in Patent Document 1, when a sodium source is contained, it is known that a fluoride or chloride of sodium is used as a raw material. However, according to the investigations of the present inventors, it has been found that when a chloride is used, if the amount of chlorine remaining in the obtained molding powder increases, white smoke may be generated when the molding powder is used.

[0006] Therefore, one aspect of the present invention aims to produce a molding powder that has a low viscosity suitable for use in continuous casting of medium carbon steel, high carbon steel, or electrical steel, while being able to suppress 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, the method comprising a step of obtaining mold powder from raw materials containing sodium fluoride and a sodium oxoacid salt, wherein the mold powder has an NaO content of 9 mass% or more, a Cl content of 0.5 mass% or less, and a viscosity of 2 dPa s or less at 1300°C.

[0008] In this manufacturing method, the NaO 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, so the mold powder contains a sufficient amount of sodium source and the viscosity of the mold powder is kept low, making it possible to exhibit the lubricity required of mold powders for continuous casting of medium carbon steel, high carbon steel, or electrical steel. Also, in this manufacturing method, raw materials containing sodium fluoride and a sodium oxoacid salt are used, and the Cl content in the mold powder is 0.5% by mass or less, making it possible to suppress the generation of white smoke when the mold powder is used.

[0009] The F content in the molding powder may be 6% by mass or more. The sodium oxoacid salt content in the raw materials may be 9% by mass or less, and the molding powder may be hollow granular. The sodium fluoride content in the raw materials may be 5% by mass or more. The residual chlorine content in the sodium fluoride may be 3.5% by mass or less.

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

[0011] According to one aspect of the present invention, it is possible to produce a molding powder that has a low viscosity suitable for use in continuous casting of medium carbon steel, high carbon steel, or electrical steel, while being able to suppress the generation of white smoke. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0013] One embodiment of the present invention is a method for producing a molding powder, comprising the step of obtaining a molding powder from raw materials including sodium fluoride and a sodium oxoacid salt.

[0014] The raw material is obtained by blending sodium fluoride, sodium oxoacid salts, and other raw materials, such as sodium carbonate, sodium sulfate, sodium nitrate, sodium aluminate, sodium phosphate, and sodium silicate.

[0015] The other raw materials are at least one selected from the group consisting of a base material raw material, a flux raw material, a carbonaceous raw material (aggregate carbon), and an organic binder. The base material raw material may be, for example, a premelt base material raw material, specifically, a raw material produced through a heat 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. The flux raw material may be, for example, a metal oxide such as manganese dioxide, a fluoride such as calcium fluoride (excluding sodium fluoride), or a carbonate such as lithium carbonate (excluding sodium oxoacid salts). The carbonaceous raw material may be, for example, carbon powder. The organic binder may be, for example, a water-soluble polymer compound.

[0016] The content of sodium fluoride in the raw materials (content based on the total amount of the raw materials) may preferably be 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 content of the sodium oxoacid salt in the raw materials (content based on the total amount of the raw materials) may preferably be 1 mass% or more, 2 mass% or more, or 3 mass% or more, and may be 9 mass% or less, 8 mass% or less, 7 mass% or less, or 6 mass% or less. When the content of the sodium oxoacid salt in the raw materials is in this range, if the molding powder is in the form of hollow granules, it is possible to prevent an excessive increase in hollow portions, which would result in a decrease in the bulk density and strength of the molding powder.

[0018] The chlorine content in the raw materials needs to be adjusted so that the chlorine (Cl) content in the resulting molding 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. Since chlorine may remain in the form of sodium chloride in the sodium fluoride used as a raw material, in such cases, it is preferable to reduce the amount of chlorine remaining in the sodium fluoride. The amount of chlorine remaining in the sodium fluoride may preferably be 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 step of obtaining the mold powder, the raw materials as described above can be powdered to obtain the powdered mold powder. Alternatively, in this step, the raw materials can be dispersed in a dispersion medium to prepare a slurry, and then a granulation step of spraying and drying the slurry can be carried out to obtain the mold powder in the form of hollow granules.

[0020] The mold powder obtained by the above manufacturing method has a NaO 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 a low viscosity, it is suitable for use in the continuous casting of medium carbon steel, high carbon steel, or electrical steel, which require high lubricity, 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 the mold powder.

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

[0022] The Cl content in the molding powder may preferably be 0.4 mass% or less, 0.3 mass% or less, 0.2 mass% or less, 0.1 mass% or less, 0.08 mass% or less, 0.06 mass% or less, 0.05 mass% or less, less than 0.05 mass%, 0.04 mass% or less, or 0.03 mass% or less.

[0023] The molding powder may further contain F. F The content of F 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 F content in the mold powder is within this range, when the mold powder melts in the mold, flows between the mold and the cast piece, and partially solidifies to form a powder film, crystals called cuspidine (Ca4Si2O7F2), which is the main component of the powder film, are more likely to crystallize (because F is the main component of cuspidine), and heat removal in the mold can be stably controlled.

[0024] The molding powder may further contain CaO and SiO2. The CaO content in the molding powder may be 20 mass% or more, 25 mass% or more, or 30 mass% or more, and may be 55 mass% or less, 50 mass% or less, or 45 mass% or less. The SiO2 content in the molding powder may be 20 mass% or more, 25 mass% or more, or 30 mass% or more, and 50 mass% or less, 45 mass% or less, or 40 mass% or less. The ratio of the CaO content to the SiO2 content (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 molding powder may further contain C. The C content (TC) in the molding powder may be 2 mass% or more, 3 mass% or more, or 4 mass% or more, and may be 8 mass% or less, 7 mass% or less, or 6 mass% or less.

[0026] The molding powder may further contain Al2O3. Al 2 O The content of 3 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 molding powder may further contain MgO. The content of MgO in the molding 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 molding powder may further contain Li2O. The content of Li2O in the molding powder may be 0.1 mass% or more, 0.2 mass% or more, or 0.5 mass% or more, and may be 3 mass% or less, 2 mass% or less, or 1 mass% or less.

[0029] The viscosity of the molding 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, or 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 molding powder at 1300°C means the viscosity of the molding 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. After that, it is placed in a vertical tube furnace (EREMA furnace), and the rotor of a Brookfield viscometer is immersed in the molten powder and allowed to stabilize 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 Brookfield viscometer is calibrated in advance using a standard viscometer.

[0030] The molding powder may be in the form of a powder (e.g., solid) or hollow granules. As described above, the molding powder is suitably used for 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. [Example]

[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] (Mold powder manufacturing) 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 powders having the compositions and viscosities shown in Tables 1 and 2. The other raw materials included a base material, a flux material, a carbonaceous material (aggregate carbon), and an organic binder. Table 1 shows the contents and viscosity of Na2O and Cl in the mold powder, and Table 2 shows the contents of other components in the mold powder. Next, water was added to the raw materials to prepare a slurry, and then the slurry was spray granulated to obtain a hollow granular mold powder.

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

[0034] (Evaluation of white smoke) In a high-frequency induction heating furnace, each mold powder was scattered on molten pig iron of the steel types shown in Table 1, held at 1550°C. Five workers were asked whether they found the white smoke emitted from the mold powder unpleasant. Cases in which zero workers answered "yes" were given an "A" rating, one worker answered "B," and two or more workers answered "C." The results are shown in Table 1.

[0035] [Table 1]

[0036] [Table 2]

Claims

1. A method for producing mold powder used in continuous casting of medium carbon steel, high carbon steel, or electromagnetic steel, comprising: The method includes a step of obtaining the molding powder from raw materials containing sodium fluoride and a sodium oxoacid salt, Na in the mold powder ２ The O content is 9% by mass or more, the Cl content is 0.5% by mass or less, and the C content is 6% by mass or less, The manufacturing method, wherein the viscosity of the molding 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 molding powder is 6 mass % or more.

3. 3. The method according to claim 1, wherein the content of the sodium oxoacid salt in the raw material is 9% by mass or less, and the molding 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 the sodium fluoride in the raw material is 5 mass% or more.

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

6. A mold powder used in continuous casting of medium carbon steel, high carbon steel, or electromagnetic steel, Na in the mold powder ２ The O content is 9% by mass or more, the Cl content is 0.5% by mass or less, and the C content is 6% by mass or less, The mold powder has a viscosity of 2 dPa·s or less at 1300°C.

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

Images