JP2002194476A - Method for producing low carbon ferroboron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which the content of C in ferroboron is reduced compared with the conventional case and ferroboron satisfactory as the raw material for a rare earth magnet can be produced at a high yield. SOLUTION: The molten metal of high carbon ferroboron is stirred while holding the same to a temperature range of 1,500 to 1,600 deg.C to precipitate and separate carbon and carbides. In this case, preferably, the precipitated and separated carbon and carbides are adsorbed and removed into a refractory.

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 Ferroboron is roughly classified into two types according to quality, that is, high-carbon ferroboron and low-carbon ferroboron. Among them, high-carbon ferroboron is made from boron sources such as boron oxide and boric acid, and iron sources such as iron scrap, iron oxide and iron ore as raw materials, and is mixed with coke, coal, charcoal, graphite debris, etc. as a reducing agent to produce electricity. Mass produced by furnace. High carbon ferroboron is relatively inexpensive, but cannot be used as a raw material for rare earth permanent magnets because of its high carbon content.

[0003] On the other hand, low-carbon ferroboron is produced by reducing the boron source and iron source with silicon, aluminum, magnesium or an alloy thereof by a thermite reaction. C has a low C content but a high Al content. Since it is manufactured by a relatively small-scale method with a low boron yield, it can be used as a raw material for a rare earth permanent magnet, but is expensive. In addition, since Al is high, its use may be limited. For reference, JIS standards for the high carbon ferroboron and the low carbon ferroboron are shown in Table 1.

[0004]

[Table 1]

In view of such circumstances, many attempts have been made to produce low-carbon ferroboron by decarburizing high-carbon ferroboron. For example, JP
Japanese Patent Application Laid-Open No. 260260 discloses a technique of oxidizing and removing aluminum and carbon contained in ferroboron by spraying an oxygen-enriched gas containing an oxygen concentration of 21 to 100% by volume to semi-molten or molten ferroboron. I have. Further, Japanese Patent Application Laid-Open No. 59-126732 discloses a technique for oxidizing and removing aluminum and carbon by bubbling pure oxygen gas into a molten boron alloy.

Further, JP-A-59-232250 discloses that ferroboron produced in an electric furnace is further melted at a melting point of +150.
A technique of obtaining low-carbon ferroboron by completely re-dissolving in the temperature range of ~ 200 ° C, cooling to just above the melting point, and precipitating and separating contained C, and Japanese Patent Application Laid-Open No. 61-195953, Disclosed is a technique in which a refractory cold material is charged onto the surface of molten ferroboron with slag, and a slag is entangled in the cold material to remove graphite and boron carbide to obtain ferroboron with less nonmetallic inclusions. ing.

[0007]

However, when decarburization is attempted by blowing oxygen to ferroboron, unlike the decarburization of pig iron, the C content is low, and the affinity of B with oxygen is lower than that of pig iron. Since it is larger than the affinity and the content of B is high, oxygen injected into the ferroboron melt does not contribute to decarburization, reacts with B to generate boron oxide,
It lowers the B content in the metal and deteriorates the B yield. Further, the produced boron oxide reacts with the magnesia lining of the smelting furnace to form a low melting point slag of MgO-B ₂ O ₃ system, so that the lining is significantly damaged. This damage progresses further due to the rise in the temperature of the molten metal due to the oxidation of B. Therefore, decarburization of high carbon ferroboron with gaseous oxygen is not feasible.

On the other hand, a purification method utilizing the fact that the solubility of C in the ferroboron melt differs depending on the temperature does not have the problem as in the above oxidation method, but the C content of the final product is 0.2% (mass ratio, the same applies hereinafter). It is difficult to reduce the amount of C required as a raw material of the rare earth permanent magnet to 0.1% or less.
Also, the method of removing graphite and boron carbide by smelting slag with cold material has many problems, such as lowering the temperature of the molten metal due to the introduction of the cold material, and further lowering the yield due to mixing of metal into the flux. .

The present invention solves the above problems of the prior art, reduces the C content in ferroboron as compared with the prior art, and can produce ferroboron sufficient as a raw material for rare earth permanent magnets at a high yield. Is proposed.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to focus on the precipitation behavior of C (quiche graphite) and boron carbide (B ₄ C) from a high carbon ferroboron melt, and the adhesion behavior between these and a refractory. This is achieved by precipitating and separating carbon and carbide while stirring the high-carbon ferroboron molten metal while keeping it in the range of 1500 to 1600 ° C. At this time, it is preferable to deposit and remove the carbon and carbide deposited and separated from the refractory.

[0011] At this time, the high-carbon ferroboron melt is efficiently stirred and weakly stirred to separate and separate carbon and carbide, and the high-carbon ferroboron melt is stirred by Mg.
O system, CaO-based, Al ₂ O ₃ system, and preferably to be carried out in a refractory vessel Zr ₂ O ₃ system or a spinel.

It is preferable that the molten ferroboron be finally adjusted to have a mass ratio of C: 0.1% or less and Al: 0.05% or less.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described specifically. First, in the present invention, a high-carbon ferroboron melt is used as a starting material. The reason why high carbon ferroboron is used as a starting material is that it is relatively inexpensive and is suitable for the precipitation and separation of carbon and carbide in the subsequent steps, and JIS FBH1 and FBH2 shown above can be used.
In particular, containing C in an amount of about 0.2 to 0.5% and containing Al in an amount of about 0.1 to 0.2% is advantageous for promptly proceeding the subsequent precipitation and separation of carbon and carbide. Such a high carbon ferroboron melt can be produced, for example, by reduction smelting in an electric furnace.

[0014] Such a high-carbon ferroboron melt contains 15
It is kept in the range of 00 to 1600 ° C. FIG. 1 is a graph showing the effect of the B content on the C solubility just above the melting point of a ferroboron-based alloy containing 5 to 25% of B. As shown here, the solubility of C in the ferroboron melt is 16% for B.
Above is about 0.1% or less. Therefore, if the high-carbon ferroboron melt is melted and kept just above the melting point, a ferroboron ingot having a sufficiently low C content should be obtained. However, simply performing such an operation does not necessarily result in a sufficiently low carbon content, and results in ingot analysis values shown in FIG. The cause is already disclosed in JP-A-61-195953.
As described in the publication, the precipitated Kish graphite remains in the solidified ferroboron, and a considerable amount of carbides of B, such as B ₄ C, remain in the molten ferroboron without being completely separated from the molten metal. It is in.

In the present invention, in order to solve this problem,
Give stirring to the ferroboron melt maintained at the above temperature,
Levitation of precipitated quiche graphite and boron carbide
Promotes separation. Specifically, weak stirring by electromagnetic induction,
Weak stirring by blowing gas into the container holding the molten metal is preferred. Here, "weak stirring" refers to a case where the stirring power is 5 to 23 W / kg when stirring is performed by blowing gas, and 14 to 53 W / kg for electromagnetic induction. These calculation methods are described in detail in “Iron and Steel”, Vol. 67, p. 672 (1981), and Hiroyuki Kajioka, “Ladle Refining Method”, p. 232, published by Jinjinshokan 1997. In addition, in the case of mechanical strong stirring using a refractory stirrer, the adhesion of the alloy is so bad that a favorable result cannot be obtained.

By performing the above-mentioned weak stirring, kish graphite and boron carbide precipitate and separate from the molten ferroboron, which are removed by an appropriate means. As a means, JP-A-61-195953 discloses that
Means for charging a cold material and entangled with slag is disclosed, and this can also be used. However,
In order to prevent the temperature of the molten metal from dropping due to the introduction of the cold material and to prevent the yield of B from decreasing due to mixing of the metal into the flux, it is preferable to remove the B by attaching it to a refractory.

Specifically, the lining of the crucible containing the ferroboron melt is made of MgO, CaO, Al ₂ O ₃ , Zr ₂ O ₃
Or a refractory of the spinel type, or a block of the above-mentioned various refractories may be inserted into a crucible so that quiche graphite or the like may be adhered to them. These various refractories are maintained in a solid state during the processing, and therefore have the advantage of being easy to handle and capable of almost completely removing quiche graphite and the like.

By the above operation, the ferroboron melt
Although the C content is reduced to 0.1% or less, it is preferable to further note the following points. First, since the B and C contents have an inverse correlation as shown in FIG. 1, the B content in the molten ferroboron is preferably at least 16% or more, and more preferably 19% or more. However, if the B content is too high, the melting point will be high, the energy for raising the temperature will be large, the efficiency will be reduced, and the refractory will be greatly worn. Therefore, it is preferable to limit the content to 25% or less. In the treatment according to the present invention, the atmosphere is preferably made inert or weakly oxidizing. Thereby, excessive oxidation of B can be prevented.

[0019]

[Example] (Example 1) High carbon ferroboron (FBH) about 1
000kg is melted in a high frequency induction furnace lined with magnesia, and stirring power is maintained for 30 minutes while maintaining the molten metal at 1500-1600 ° C.
It was kept at 38 W / kg with high frequency induction stirring. The obtained molten metal was cast into a metal pan made of cast iron to form an ingot. Table 2 shows the composition of ferroboron before and after the treatment. As shown here, according to the present invention, only decarburization and de-Al could be performed without oxidizing B.

[0020]

[Table 2]

Example 2 About 1000 kg of FBH melt discharged from an electric furnace for ferroboron production was poured at 1710 ° C. into a high-frequency induction furnace lined with magnesia, and the bath temperature was lowered by natural cooling.
Wait for the temperature to drop to 1600 ° C.
While maintaining the temperature of the molten metal at 1500 to 1600 ° C., the mixture was gently stirred by high-frequency induction for 30 minutes, and cast into a metal pan made of cast iron to form an ingot. The stirring power was 25 W / kg. Table 3 shows the composition of ferroboron before and after the treatment. As shown here, in the present invention, only decarburization and de-Al could be performed without oxidizing B.

[0022]

[Table 3]

(Example 3) A molten FBH melt discharged from an electric furnace for ferroboron production was poured into a container lined with magnesia and provided with a porous plug at the bottom, and the bath temperature was measured by bubbling Ar gas from the porous plug. The stirring was continued gently, and after 45 minutes, the mixture was cast into a metal pan made of cast iron to form an ingot. The stirring power was 9 W / kg. The amount of FBH subjected to the experiment was approximately 1000 kg, the tapping temperature from the electric furnace was 1690 ° C, and the bath temperature at the end of bubbling was 15
55 ° C. Table 4 shows the composition of ferroboron before and after the treatment. As shown here, in the present invention, only decarburization and de-Al could be performed without oxidizing B.

[0024]

[Table 4]

[0025]

According to the present invention, low carbon ferroboron having an extremely low C content can be easily produced from high carbon ferroboron as a raw material.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the B content on the solubility of C immediately above the melting point of a molten ferroboron.

Continued on the front page (72) Inventor Ryoji Kuroda 2-11-8 Ginza, Chuo-ku, Tokyo Nippon Denko Corporation (72) Inventor Yoshitaka Tanaka 62-1 Kono Tachibanacho, Anan-shi, Tokushima Nippon Denko Corporation Inside the research institute (72) Kinue Nakajima 3004 Kojima, Oshima-machi, Imizu-gun, Toyama Pref.

Claims (5)

[Claims] 1. A high carbon ferroboron melt at 1500 to 1600 ° C.
The carbon and carbide are precipitated while stirring within the range of
A method for producing low-carbon ferroboron, which comprises separating. 2. The method for producing low-carbon ferroboron according to claim 1, wherein the carbon and carbide deposited and separated are attached to and removed from the refractory. 3. The method for producing low-carbon ferroboron according to claim 1, wherein the stirring of the high-carbon ferroboron molten metal is performed by weak stirring. 4. The stirring of the high carbon ferroboron molten metal is performed using MgO
The method is performed in a refractory container of a system, CaO, Al ₂ O ₃ , Zr ₂ O ₃ or spinel system.
4. The method for producing low carbon ferroboron according to any one of 2 and 3. 5. The method for producing low-carbon ferroboron according to claim 1, wherein the mass ratio of the ferroboron melt is C: 0.1% or less and Al: 0.05% or less.