JP2003286535A - Process for producing low-carbon ferroboron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suggest a process for producing ferroboron possessing a sufficient quality as a raw material for rare-earth permanent magnets in a high yield, by reducing its carbon content compared to that of conventional ferroboron. <P>SOLUTION: A molten metal of high-carbon ferroboron is placed in a vessel lined with MgO, CaO, Al<SB>2</SB>O<SB>3</SB>, ZrO<SB>2</SB>or their composite refractories and kept under reduced pressure in a controlled atmosphere at 1,550-1,750°C to remove carbon. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing low carbon ferroboron, and more particularly to a method for producing low carbon ferroboron used as a raw material for rare earth permanent magnets using high carbon ferroboron as a raw material.

[0002]

2. Description of the Related Art Ferroborones are roughly classified into two types according to their quality, namely, high carbon ferrobolone and low carbon ferrobolone. Of these, high carbon ferroboron is
Boron oxide, boric acid, and other boron sources, iron scrap, iron oxide, iron ore, and other iron sources are used as raw materials, and coke, coal, charcoal, graphite, etc. are mixed as a reducing agent, and mass-produced in an electric furnace. . High carbon ferroboron is relatively inexpensive, but cannot be used as a raw material for rare earth permanent magnets due to its high carbon content.

On the other hand, low carbon ferroboron is produced by reducing the boron source and iron source with silicon, aluminum, magnesium or a mixture or alloy thereof by a thermite reaction, and has a low carbon content but contains silicon or aluminum. The quantity is high. In addition, since the thermite reaction is relatively small and the boron yield is low,
It can be used as a raw material for rare earth permanent magnets, but is expensive.
For reference, the JIS standards of these high carbon ferroboron and low carbon ferrobolone are shown in Table 1.

[0004]

[Table 1]

In view of such circumstances, many attempts have been made to decarburize high carbon ferroboron to produce low carbon ferroborone. For example, JP-A-58-2
The 6025 publication discloses a technique of spraying an oxygen-enriched gas containing an oxygen concentration of 21 to 100% by volume onto a semi-molten or molten ferroboron to oxidize and remove aluminum and carbon contained in the ferroboron. ing. Further, JP-A-59-126732 discloses a technique of bubbling pure oxygen gas into a molten boron alloy to oxidize and remove aluminum and carbon.

Further, Japanese Patent Laid-Open No. 59-232250 discloses that ferroboron smelted in an electric furnace has a melting point of +150 to 2
After completely redissolving in the temperature range of 00 ° C, cooling to just above the melting point and depositing and separating the contained carbon to obtain low-carbon ferroboron is disclosed in JP-A-61-195953. A technique of obtaining a ferroboron with less non-metallic inclusions by disposing of a refractory coolant on the surface of the molten ferroboron accompanied with it, slagging the surface of the molten ferroboron to remove graphite and boron carbide is disclosed. There is.

[0007]

However, unlike hot metal, ferrobolone molten metal has a low carbon content, and the affinity of boron for oxygen is greater than that of carbon and oxygen. Is high. Therefore, when you try to decarburize by blowing oxygen to ferroboron, oxygen blown into the ferrobolone melt does not contribute to decarburization,
It reacts with boron to form boron oxide, lowers the boron content in the metal, and deteriorates the boron yield. Further, the generated boron oxide reacts with refractory materials in the smelting furnace and MgO-
B ₂ O ₃ system, to produce a low melting point of the slag of SiO ₂ -B ₂ O ₃ based, therefore damage of the lining is remarkable. This damage progresses further due to the rise in the molten metal temperature due to the oxidation of boron. Therefore, decarburization of high carbon ferroboron with gaseous oxygen is not practical.

On the other hand, the smelting method utilizing the fact that the solubility of carbon in ferrobolone molten metal varies depending on the temperature does not have the problem of the above-mentioned oxidation method, but the carbon content of the final product is 0.2%.
(Mass ratio, the same applies hereinafter), and it is difficult to reduce the carbon content to 0.1% or less required as a raw material for rare earth permanent magnets. In addition, the method of entangling the molten slag in a cold material to remove graphite and boron carbide is a method in which the temperature of the molten metal decreases due to the introduction of the cold material, the amount of metal deposited on the ladle increases, and the yield of boron increases. Aggravate. Further, there is a problem that the main component and the trace element in the flux are mixed in the metal due to the mixing of the metal in the flux, which deteriorates the quality of the metal.

The present invention solves the above-mentioned problems of the prior art, reduces the carbon content in ferroboron as compared with the prior art, and produces ferroboron having a sufficient quality as a raw material for rare earth permanent magnets at a high yield. It proposes a method of gaining money.

[0010]

Means for Solving the Problems In the method for producing low carbon ferroboron of the present invention, high carbon ferroboron is provided in a container lined with MgO, CaO, Al ₂ O ₃ , ZrO ₂ or a composite refractory thereof. The molten metal is contained and kept in a reduced pressure atmosphere gas at 1550 to 1750 ° C to remove carbon.

In carrying out the above invention, it is preferable that the pressure of the reduced pressure atmosphere is 13.3 kPa or less, and the atmosphere gas is one selected from helium, argon and nitrogen, or a mixture of two or more thereof. Gas is preferred.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below.

In the present invention, a high carbon ferroboron ingot or molten metal is used as a starting material. High carbon ferroboron is used as a starting material because it is relatively inexpensive and suitable for removing carbon and carbide in the subsequent process. The boron content is 5 including JIS FBH1 and FBH2 shown above.
High carbon ferroboron in the range of up to 25% can be preferably used. Such high carbon ferroboron can be produced, for example, by reduction smelting in an electric furnace.

High carbon ferroboron discharged from the electric furnace
Hot water is received in a container lined with MgO-based, CaO-based, Al ₂ O ₃ , ZrO ₂ -based, or a composite refractory of these. These refractories react with carbon in the molten high carbon ferroboron as an oxygen source under reduced pressure at high temperature, and contribute to the decarburization reaction of the molten high carbon ferroboron by the reaction of MgO + C = Mg + CO, for example. This decarburization reaction proceeds most smoothly when MgO is used, although it depends on the temperature and pressure (pressure reduction degree). Further, since the boiling point of Mg produced by this reaction is 1120 ° C., which is lower than the decarburization treatment temperature of the present invention, Mg is discharged out of the system in the form of vapor.

Decarburization by the above reaction is carried out at an atmospheric pressure of 13.3
Setting it to kPa or less facilitates the progress. When the atmospheric pressure exceeds 13.3 kPa, the progress of the decarburization reaction slows down. On the other hand, when the atmospheric pressure is less than 1.3 kPa, the generation of CO due to the decarburization reaction increases, and the molten metal scatters more. Therefore, the atmospheric pressure is preferably 1.3 kPa or more and 13.3 kPa or less.

When the temperature of the molten metal is less than 1550 ° C., a solidified product is formed on the surface of the molten metal, which hinders the progress of decarburization.
Further, since the molten metal is not sufficiently stirred, the reaction between carbon in the molten ferrobolone and the refractory lining that is the oxygen source does not proceed sufficiently. On the other hand, holding temperature is 1750 ℃
In the above case, damage to the refractory lining becomes large, and the melted refractory may be mixed into the product as it is. Therefore, the melt temperature for carrying out the above reaction is
1550 to 1750 ℃

The conditions for promoting decarburization by the above reaction are preferably adjusted depending on the refractory material. For example, when a CaO-based refractory is used, it is preferable to use a high temperature and / or a low pressure (high vacuum side) as compared with the case of using a MgO-based refractory.

When ferroboron having a particularly high boron content is used as a raw material, one or a mixture of two or more gases selected from helium, argon and nitrogen is used as a non-oxidizing atmosphere as an atmosphere gas. Good. This makes it possible to prevent the oxidation loss of boron in the reaction process.

The present invention is for decarburizing by reacting the refractory and carbon (C) in the molten ferroboron under high temperature and reduced pressure as described above. Therefore, completely different from the method of blowing oxygen gas into the high carbon ferroboron melt as disclosed in, for example, the above-mentioned Japanese Patent Laid-Open No. 58-26025, the substance produced by decarburization is a gas and can be easily removed from the system. Therefore, it is possible to produce clean ferroboron with less inclusions. Also, without depending on the boron content of ferroboron,
High carbon ferrobolone with boron content in the range of 5-25% is available.

In carrying out the above invention, the apparatus shown in FIG. 1 can be used. In this device, the Mg in the vacuum chamber 1
A high-frequency induction electric furnace 4 having a lining 2 of O or the like and a water-cooling melting coil 3 arranged on the outer periphery thereof, and a tundish 6 and a mold 7 for solidifying the molten metal 5 decarburized in the electric furnace 4 into a product. Is installed. The vacuum chamber 1 is connected to a vacuum pump 8 and an inert gas tank 9 such as argon, and the inside thereof can be adjusted to a required reduced pressure atmosphere. Further, a replenishment tank 10 is provided so that the raw materials can be replenished as needed during decarburization.

[0021]

EXAMPLE High-carbon ferroboron was charged into a vacuum high-frequency induction heating furnace (shown in FIG. 1) having a crucible made of various materials, and decarburized according to the present invention to melt-produce low-carbon ferroboron. The operating conditions are as shown in Table 2, and the analytical values of the obtained product were as shown in Table 3. As shown in Table 3, in the examples of the present invention, decarburization could be performed without oxidizing boron.

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

According to the present invention, low carbon ferroboron having an extremely low carbon content can be produced extremely economically using high carbon ferroborone as a starting material.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a representative apparatus for carrying out the present invention.

[Explanation of symbols]

1: Vacuum tank 2: Refractory lining 3: Water cooling melting coil 4: High frequency induction electric furnace 5: molten metal 6: Tundish 7: Mold 8: Vacuum pump 9: Inert gas tank 10: Additional tank

Claims (3)

[Claims] 1. A high carbon ferroboron molten metal is housed in a container lined with MgO-based, CaO-based, Al ₂ O ₃ -based, ZrO ₂ -based or a composite refractory of these, and stored in a decompressed atmosphere gas at 1550 to 1750 ° C. A method for producing low carbon ferroboron, which comprises holding and removing carbon. 2. The method for producing low carbon ferroboron according to claim 1, wherein the reduced pressure atmosphere has a pressure of 13.3 kPa or less. 3. The method for producing low carbon ferroboron according to claim 1, wherein the atmosphere gas is one kind selected from helium, argon and nitrogen, or a mixed gas of two or more kinds thereof.