JP2002173744A - SLAB FOR R-Fe-B-C BASED MAGNET ALLOY HAVING EXCELLENT CORROSION RESISTANCE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an R-Fe-B-C based magnet alloy slab in which the reduction of the degree of orientation, pulverization in grinding in its making into a magnet, and the oxidation of the powder can be prevented, and which has excellent corrosion resistance and magnetic properties for solving the problems of the slab obtained from the molten metal of a magnet alloy by rapidly cooling rollers. SOLUTION: The molten metal of an R-Fe-B-C based alloy in which B+C=6 to 10 at.% (wherein, B: 2 to 6 at.%, and C: 4 to 8 at.%) is melted. After that, the molten metal is subjected to primary cooling by rapid cooling rollers at a specified cooling rate, and subsequently, the slab removed from the rollers is subjected to secondary cooling to a solidus temperature or lower at a specified cooling rate to obtain a rapidly cooled slab with a homogeneous structure in which R2Fe14(B1-xCx) type dendritic or columnar crystals having a minor axis grain size with specified dimensions and a minor axis grain size distribution and a specified R rich phase are finely dispersed, so that the R-Fe-B-C based magnet alloy slab having excellent corrosion resistance and magnetic properties can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slab for an R-Fe-BC-based magnet alloy having excellent corrosion resistance and excellent magnetic properties, and quenches a molten R-Fe-BC-based alloy. A slab of specific thickness rapidly solidified by a roll is cooled by a two-stage cooling method under specific conditions to obtain a slab having a specific finely dispersed homogenous structure, which has excellent corrosion resistance and magnetic properties. F
The present invention relates to a slab for an R-Fe-BC-based magnet alloy for obtaining an e-B-C-based magnet.

[0002]

2. Description of the Related Art Today, a typical high performance permanent magnet R
-Fe-B based permanent magnet (JP-A-59-46008)
Has high magnetic properties in a structure having a main phase of a ternary tetragonal compound and an R-rich phase, and is used in a wide range of fields from various household electrical appliances to peripherals of large computers, and is used in various fields. R-Fe-B permanent magnets of various compositions have been proposed to exhibit various magnet properties.

Although the R-Fe-B permanent magnet has extremely excellent magnetic properties, it has problems in corrosion resistance and temperature characteristics. A method of coating the surface of a magnet with a corrosion-resistant metal film or a resin film has been proposed (Japanese Patent Application Laid-Open Nos. 60-54406 and 60-63901). It is proposed to replace a part of Fe in the composition with Co (Japanese Patent Laid-Open No. 59-64733).
However, there has been a problem that it is not yet sufficient, and the cost of the magnet is increased.

Recently, a part of B of an R—Fe—B magnet has been changed to C
To form a boundary phase having excellent corrosion resistance, thereby improving the corrosion resistance and improving the temperature characteristics.
A C-based magnet has been proposed (Japanese Patent Application Laid-Open No. 3-82744).

The R—Fe—BC system magnet has a B content of 2
at% or less and containing a large amount of C. That is, when part of B is replaced with C,
The main phase of R ₂ Fe ₁₄ B tetragonal becomes R ₂ Fe ₁₄ (B _1-x C _x ) tetragonal in which a part of B is substituted by C, but the crystal structure is the same and the grain boundary The phase changes from an R-rich phase to an R-rich phase (R-Fe-C phase) having good corrosion resistance.

[0006] Further, R-F in which a part of Fe is substituted with Co.
The e-Co-B-C magnet, the main phase is _{R 2 (Fe 1-x Co} x) of R ₂ Fe ₁₄ B tetragonal same crystal structure ₁₄ (B
_1-y C _y ) It becomes tetragonal, and the grain boundary phase changes from the R-rich phase to the R-rich phase (R-Fe-Co-C phase) having good corrosion resistance, but contains a large amount of C in the magnet. Then, C reacts with R (rare earth element) to easily form RC (rare earth carbide), and RC is generated in the raw material alloy and the sintered magnet.

[0007] In short, the R-Fe-B-C magnet is an R-Fe-B-based magnet in which R reacts with C to become R-C, and R is consumed. More R is required. Therefore, since there are many RCs that do not contribute to the magnetic properties, the abundance of the main phase is reduced and the R-Fe
Br is lower than that of the -B type, and a large amount of expensive R is required. This causes a problem that the cost is increased and the magnetic properties are deteriorated and varied with an increase in the oxygen content. .

Further, the R-Fe-BC-based magnet is prepared by casting a molten alloy into a mold to form an ingot, and then pulverizing the ingot.
Powdering, molding, sintering, or magnetizing by the powder metallurgy method of aging treatment, or, after solution treatment of the ingot or coarse powder after pulverization of the ingot, pulverized, and magnetized by the powder metallurgy method described above To improve the corrosion resistance and temperature characteristics, the magnetic characteristics of the R-Fe-BC-based magnet are (BH) ma
x was at most about 38 MGOe. Furthermore, the R-Fe-BC magnet has a very poor squareness of the demagnetization curve, and is demagnetized with respect to temperature and reverse magnetic field as compared with the R-Fe-B magnet having the same dimensions and shape. There was an easy problem.

Further, in order to prevent coarsening of crystal grains, α-Fe retention and segregation, which are disadvantages of the R-Fe-B alloy powder by the ingot pulverization method, the R-Fe-B alloy is melted by a twin method. By a roll method, a slab having a thickness of 0.03 mm to 10 mm was formed. The slab was coarsely pulverized by a stamp mill, a jaw crusher or the like according to a usual powder metallurgy method, and then a disc mill, a ball mill, and an attritor were obtained. A method is proposed in which a powder having an average particle size of 3 to 5 μm is finely pulverized by a pulverization method such as a jet mill and then pressed, sintered and aged in a magnetic field to improve performance (JP-A-63-317643). No.).

A method of manufacturing a quenched cast for a permanent magnet by a side-cast strip casting method using a single roll of an R-Fe-B-based alloy melt has been proposed by using a nozzle having a required width in the horizontal direction at the tip of a tundish. Is provided adjacent to this nozzle, and a single roll is horizontally supported and placed in a tundish after the molten metal melted in the high-frequency melting furnace. And quenched and solidified to produce a quenched cast slab (JP-A-5-222488, JP-A-6-846).
No. 24).

Further, as a slab for a magnet alloy obtained by casting a molten R-Fe-B magnet alloy with a quenching roll, R, T,
And B as a main component, substantially composed of R ₂ Fe ₁₄ B phase, and composed of columnar crystal grains having an average diameter of 3 to 50 μm and a grain boundary phase mainly composed of an R-rich phase, and a thickness in a cooling direction. Of a magnet alloy having a thickness of 0.1 to 2 mm is proposed (Japanese Patent Laid-Open No.
-295490).

[0012]

However, the R-F
There is a strong demand for cost reduction for eB-based permanent magnet materials, and it is extremely important to efficiently manufacture high-performance permanent magnets. For this reason, it is necessary to improve the manufacturing conditions in order to bring out characteristics close to the limit. In addition, miniaturization and weight reduction of today's electric and electronic devices and (BH) ma
There is a strong demand for high performance of x40MGOe or higher, and it is also required that the demagnetization curve has excellent squareness, and that an improvement in corrosion resistance without surface treatment or the like is required. And cost reduction are required.

In view of the above, the inventor has made various studies on the reduction of the solution heat treatment step for ingots or pulverized grains, the reduction in cost by improving the pulverizability, the high performance of magnetic properties, and the like as in the prior art. That is, the present invention enables efficient and efficient pulverization of an alloy slab for obtaining an R-Fe-BC-based sintered magnet having excellent corrosion resistance and magnet properties, and a powder which accompanies pulverization. Of high-quality R-Fe-BC sintered magnets with high corrosion resistance by increasing the squareness of the demagnetization curve and the degree of orientation of each crystal grain in the direction of easy magnetization. It is another object of the present invention to provide a cast slab for an R-Fe-BC-based magnet alloy.

[0014]

Means for Solving the Problems The inventors of the present invention prepared an alloy slab for an R-Fe-BC based sintered magnet having excellent corrosion resistance by strip casting, and found that primary crystals of Fe, F
e _x Co _1-x is little, milling property is improved, compared to the milling efficiency of the conventional mold melted alloy was confirmed to be improved about twice or more. However, when the casting structure of the slab was examined in detail, the casting structure changed significantly depending on the casting conditions, and the powder was oxidized due to pulverization during pulverization during magnetization, and the degree of orientation of the sintered magnet decreased. Was found to have a significant effect on magnetic properties.

The inventors of the present invention have conducted various studies on the relationship between the structure of the cast slab for the R-Fe-BC-based magnet alloy and the magnetic characteristics of the sintered magnet. As a result, the cast slab has various sizes and directions. There is a dendritic or columnar crystal having, the fine dendritic or columnar crystal has a great effect on the oxidation of the powder and the decrease in the degree of orientation of the sintered magnet due to the pulverization at the time of pulverization at the time of magnetization, It has been found that it is important to reduce fine dendritic or columnar crystals in the slab.

The inventors have further studied and found that in order to obtain a slab in which the fine dendritic or columnar crystals in the slab are reduced, a molten alloy at a specific temperature is poured from a nozzle into a quenching roll. , After primary cooling at a specific cooling rate,
It has been found that it is important to perform two-stage cooling in which the slab having the rolls separated is secondarily cooled at a specific cooling rate below the solidus temperature. Furthermore, as a result of various studies on the alloy composition and the squareness of the demagnetization curve, it was found that the squareness can be greatly improved by optimizing the amounts of B and C, and the present invention was completed.

That is, the present invention relates to R12-18at.
%, B + C = 6 to 10 at% (B: 2 to 6 at%,
C: 4 to 8 at%), the balance Fe (a part of Fe is C
o, Ni) (substituted by one or two of Ni), and has an average minor axis crystal grain diameter of 3 to 15 μm containing 10% or less of fine crystals having a minor axis crystal grain diameter of less than 1.0 μm, and a minor axis. R ₂ Fe ₁₄ (B having a grain size distribution of 0.01 μm to 40 μm
_1-x C _x ) type dendritic or columnar crystals and an R-rich phase of 10 μm or less have a finely dispersed homogeneous structure,
An R-Fe-BC-based magnet alloy slab having excellent corrosion resistance and magnet properties, particularly having a square shape of a demagnetization curve, characterized by having a slab thickness of 0.01 mm to 1.0 mm.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a molten R-Fe-BC alloy is melted in a vacuum melting furnace, then poured into a quenching roll from a nozzle at the tip of a tundish, and the molten metal is quenched with a chilling roll. After primary cooling to a specific temperature at a specific cooling rate,
By subjecting the slab separated from the roll to secondary cooling at a specific cooling rate below the solidus temperature, R ₂ Fe ₁₄ (B _1-x C _x )
It is characterized in that a quenched slab of a specific thickness having a homogeneous structure in which a dendritic crystal or a columnar crystal and a specific R-rich phase are finely dispersed is obtained. The R ₂ Fe ₁₄ (B _1-x C _x ) compound is obtained by substituting a part of B in the R ₂ Fe ₁₄ B compound with C, and has the same tetragonal structure as the R ₂ Fe ₁₄ B compound.

The production method of the present invention will be described in detail. R12-18 at%, B + C = 6-10 at% (B: 2-6 at%, C: 4-8 at%), the balance Fe
(However, a part of Fe can be replaced by one or two types of Co and Ni.) A melt of a magnetic alloy mainly composed of a liquidus temperature (solidification starting temperature) of the alloy + 5 ° C. to + 300 ° C. Quenching roll, for example, 2 × 10 ³ ° C./sec to 7
Slab temperature 700 at primary cooling rate of × 10 ³ ° C / sec.
After cooling to about 1000 ° C. to 1000 ° C., and then removing the roll, the slab is cooled to a temperature equal to or lower than the solidus temperature (solidification completion temperature) of the alloy, for example, 50 ° C.
/ Min to 2 × 10 ³ ° C./min. At a secondary cooling rate of 10 μm.
% R ₂ F having an average minor axis crystal grain size of 3 μm to 15 μm and a minor axis crystal grain size distribution of 0.01 μm to 40 μm.
e ₁₄ (B _1-x C _x ) type dendritic or columnar crystal and 10μ
m or less R-rich phase, has a finely dispersed homogeneous structure, for example, corrosion resistance and magnet properties, characterized by obtaining a slab for a magnet alloy having a slab thickness of 0.01 mm to 1.0 mm, especially R-F with excellent squareness of demagnetization curve
This is a method for producing a cast for e-B-C magnet alloy.

That is, the casting structure of the cooling slab is determined at the moment when the molten metal comes into contact with the cooling roll, and the shorter the contact length between the molten metal and the cooling roll and the higher the roll peripheral speed, the thinner the plate becomes and the finer the structure becomes. However, in reality, it has been found that the cast structure changes depending on the temperature of the slab at the time of leaving the quenching roll and the subsequent cooling rate.

Generally, solidification of the molten alloy starts at the liquidus temperature and is completed at the solidus temperature. However, if the time for passing through the solid-liquid coexistence region from the liquidus to the solidus temperature is long, the cast structure becomes coarse. In the case of an R-Fe-BC-based alloy, the difference between the liquidus temperature and the solidus temperature is as large as about 500 ° C, so that the coarsening is particularly remarkable.

That is, even if the slab temperature immediately after the quenching roll is separated is equal to or higher than the solidus temperature, a fine structure can be obtained if the subsequent cooling is sufficiently fast, but the subsequent cooling rate is slow and the material passes through the solid-liquid coexistence region. As the time increases, the crystal grains grow, leading to a decrease in iHc of the sintered magnet.

As a result of examination of the relationship between the passing time and the crystal grain size by the inventors, the crystal grain size grows even when the passing time in the solid-liquid coexistence region is only a few minutes, for example, from 800 ° C. to the solidus temperature. When the passage time is 3 minutes, the crystal grain size grows to 20 to 30 μm.

In addition, the cooling of the roll can be strengthened to reduce the temperature of the slab when the roll is removed to the solidus temperature or lower.
In this case, the crystal grains are not coarsened, but the cooling rate by the roll is too fast, and the crystals are too fine, resulting in a decrease in Br of the sintered magnet.

That is, in order to prevent the crystal grain size of the slab from being excessively reduced, the molten alloy is primarily cooled at a specific cooling rate to a specific temperature by a quenching roll, and then separated from the quenching roll. It has been found that a two-stage cooling method of performing secondary cooling at a specific cooling rate below the solidus temperature is important in order to prevent the slab from coarsening its fine structure.

In the method for producing a cast slab according to the present invention, the reason for limiting the temperature of the molten alloy to be cooled and solidified by the quenching roll to the liquidus temperature (solidification starting temperature) + 5 ° C. to + 300 ° C. is that the liquidus temperature is + 5 ° C. If the temperature is lower than 0 ° C., the alloy melt solidifies in the nozzle portion, causing clogging of the nozzle, making casting impossible. If the temperature exceeds the liquidus temperature + 300 ° C., the temperature of the molten metal is too high, and cooling with rolls is insufficient. The average short-axis crystal grain size exceeds 15 μm, and the temperature of the molten metal in contact with the roll is high, so that the life of the cooling roll is shortened.

In the present invention, the primary cooling rate is defined by {(the temperature of the molten metal in contact with the roll) − (the temperature of the slab at the time of roll detachment)} / (the contact time of the roll), and the primary cooling rate is 2 × 10 ³ ° C. / is less than sec insufficient molten metal by the roll cooling, average minor axis crystal grain size undesirably beyond 15 [mu] m, also exceeds 7 × 10 ³ ℃ / sec, average minor axis grain size Is less than 3 μm, and even if the average short-axis crystal grain size is 3 μm or more, it is not preferable because fine crystals having a grain size of 1 μm or less exceed 10%. Also, 1
The preferable range of the secondary cooling rate is 3 × 10 ³ ° C./sec or more.
6 × a 10 ³ ℃ / sec.

After the primary cooling, the temperature of the slab is 700 ° C. to 100 ° C.
The reason for limiting the temperature to 0 ° C. is that if the temperature is less than 700 ° C., the average short-axis crystal grain size becomes fine as less than 3 μm, and even if the average short-axis crystal grain size is 3 μm or more, fine crystals of 1 μm or less exceed 10%. Undesirably, further, when the temperature exceeds 1000 ° C., after the rolls of the slab are released, the cooling time to the solidus temperature or less increases, and the average short-axis crystal grain size exceeds 15 μm.
It is not preferable to use a secondary cooling device which requires a large equipment cost in order to increase the size of the material and to cool it to a temperature not higher than the solidus temperature in a short time. Further, a preferable temperature range of the slab after the primary cooling is 700 ° C to 900 ° C.

In the present invention, the reason for limiting the cooling of the slab after the roll has been separated to the solidus temperature or lower is that in the solid-liquid coexistence region exceeding the solidus temperature, an R-rich liquid phase exists, Even after holding for several minutes, the crystal grows and coarsens,
In particular, since the coercive force is reduced, it is necessary to cool to a temperature below the solidus temperature at which no crystal grows, that is, no liquid phase exists.

In the present invention, the secondary cooling rate is
{(Cast temperature at roll separation)-(solidus temperature)} / (cooling time), the secondary cooling rate is 50 ° C /
If it is less than min, the time required to pass through the solid-liquid coexistence region becomes longer, and the crystal grows and becomes coarse, which is not preferable. The higher the secondary cooling rate is, the shorter the time required for passing through the solid-liquid coexistence region is, which is preferable. However, from the viewpoint of mass production, it is preferable to be within 2 × 10 ³ ° C./min. The preferred range of the secondary cooling rate is 100 to
It is 2 × 10 ³ ° C./min.

In the present invention, the secondary cooling is performed by cooling an inert gas such as Ar gas between the quenching roll and the slab storage box, or cooling during transfer by a conveyor or a belt, and further cooling the slab storage box. It can be adjusted by cooling with an inert gas at a temperature, and there is a method of cooling by sandwiching a slab by two pairs of rotating belts, or a method of directly charging the liquid Ar, and a combination of these methods is also available. Good. In order to realize a sufficient secondary cooling rate, it is necessary to provide a sufficient distance between the cooling roll and the slab storage box, and the distance is preferably 1/20 or more of the roll peripheral speed. For example, when the roll peripheral speed is 100 m / min, it is 5 m or more.

In the magnet alloy slab of the present invention, the minor axis grain size means the length of the minor axis in a direction perpendicular to the major axis direction of the dendritic or columnar crystal.

R ₂ Fe ₁₄ (B _1-x C _x ) of magnet alloy slab
Average short-axis crystal grain size of dendritic or columnar crystals is 3 μm
The reason for limiting to 15 μm is that if it is less than 3 μm, it tends to be oxidized when powdered, leading to deterioration of magnetic properties, and the powdered alloy powder becomes polycrystalline, the degree of orientation during press molding is disturbed, Br is lowered, and
If it exceeds 15 μm, the crystal grain size of the sintered magnet increases,
This is not preferable because the coercive force decreases and the squareness of the demagnetization curve decreases.

The short axis crystal grain size distribution is set to 0.01 μm or less.
The reason why the thickness is limited to 40 μm is not preferable because if it is less than 0.01 μm, the crystal is likely to be amorphous, and if it exceeds 40 μm, the coercive force of the magnet is reduced and the squareness of the demagnetization curve is reduced.

The reason why the content of fine crystals having a minor axis crystal grain size of less than 1.0 μm is limited to 10% or less is that if the content exceeds 10%, the proportion of polycrystals in the powdered alloy powder increases. However, the degree of orientation during press molding is disturbed, and Br of the magnet is undesirably reduced.

In the finely dispersed homogenous structure of the slab for a magnet alloy of the present invention, each ratio of the R ₂ Fe ₁₄ (B _1-x C _x ) type dendritic crystal or columnar crystal and the R-rich phase is R ₂ F
e ₁₄ (B _1-x C _x ) type dendritic or columnar crystal is 90
% Or more, more preferably 95% or more,
The R-rich phase is preferably 3 to 10%. In the present invention, the solidus temperature fluctuates depending on the composition of the R-Fe-BC-based magnet, but when the magnet composition is 15Nd-78Fe-2.5B-
For a 4.5 Cat% magnet, the solidus temperature is 660 ° C.

The alloy composition of the alloy slab for producing the R-Fe-BC permanent magnet according to the present invention will be described below.

The rare earth element R contained in the alloy slab for a permanent magnet of the present invention is a rare earth element containing yttrium (Y) and including light rare earth elements and heavy rare earth elements. In general, one kind of R is sufficient, but in practice, a mixture of two or more kinds (mish metal, dymium, etc.) can be used for reasons such as convenience in obtaining, and Sm, Y, La, Ce,
Gd and the like can be used as a mixture with other R, especially Nd, Pr and the like. Note that R may not be a pure rare earth element, and may contain impurities that are unavoidable in production within the industrially available range.

R is an essential element of the alloy slab for producing the R—Fe—BC permanent magnet. If it is less than 12 atomic%, high magnetic properties, especially high coercive force cannot be obtained, and 18 atomic% If it exceeds, the residual magnetic flux density (Br) decreases, and a permanent magnet having excellent characteristics cannot be obtained. Therefore, R is 12 atomic% to 1
The range is 8 atomic%. Preferably, R is between 13 atomic% and 1
7 atomic%.

B and C are essential elements of alloy slabs for producing R—Fe—BC permanent magnets. If B + C is less than 6 atomic%, a high coercive force (iHc) cannot be obtained and 10 atomic atoms are not obtained. %, The residual magnetic flux density (Br) decreases, so that an excellent permanent magnet cannot be obtained. If B is less than 2 at%, the residual magnetic flux density is reduced and the squareness of the demagnetization curve is degraded. If B exceeds 6 at%, the corrosion resistance is undesirably reduced. If C is less than 4 at%, the corrosion resistance deteriorates, which is not preferable. If C exceeds 8 at%, the RC amount increases, the residual magnetic flux density decreases, and the squareness of the demagnetization curve deteriorates. Therefore, B + C is 6 at% to 10 at% (however, B 2 to 6 at%, C 4 to
8 at%). The preferred range of B + C is 6 to
8 at%.

Fe is an essential element of alloy slabs for producing R—Fe—BC permanent magnets. If it is less than 72 atomic%, the residual magnetic flux density (Br) decreases. Since a high coercive force cannot be obtained, the content of Fe is 72 atomic% to 8 atomic%.
Limited to 2 atomic%. Further, a part of Fe can be replaced by one or two of Co and Ni, which is because the effect of improving the temperature characteristics of the permanent magnet and the effect of further improving the corrosion resistance can be obtained. When one or two kinds of Ni exceed 50% of Fe, a high coercive force cannot be obtained and an excellent permanent magnet cannot be obtained. Therefore, the upper limit of the substitution amount of one or two of Co and Ni is 50% of Fe.

In order to obtain an excellent permanent magnet having both high residual magnetic flux density, high coercive force, excellent squareness of demagnetization curve, and high corrosion resistance in the alloy slab according to the present invention, R13 at. Atomic%, B + C6 atomic% ~
8 atomic%, provided that B2 to 4 at%, C4 to 6 at%, F
e 75 at% to 81 at% is preferred.

The alloy slab according to the present invention has R,
In addition to B, Fe, and C, the presence of unavoidable impurities such as oxygen, Ca, and Mg in industrial production can be tolerated. However, a part of B + C is reduced to 3.5 atomic% or less of P and 2.5 atomic% or less. S, 3.
By replacing at least one of Cu of 5 atomic% or less with a total amount of 4.0 atomic% or less, it is possible to improve the productivity of the magnet alloy and reduce the cost.

Further, R-Fe-B containing one or two of R, B, C, and Fe alloys or Co and Ni.
A 9.5 atomic% or less of Al, 4.5 atomic% or less of Ti, V of 9.5 atomic% or less, Cr of 8.5 atomic% or less, Mn of 8.0 atomic% or less, Bi of 5 atomic% or less,
Nb of 12.5 atomic% or less, T of 10.5 atomic% or less
a, 9.5 atomic% or less of Mo, 9.5 atomic% or less of W,
2.5 atomic% or less of Sb, 7 atomic% or less of Ge, 7 at
% Or less of Ga, 3.5 atomic% or less of Sn, 5.5 atomic%
By adding at least one of the following Zr and 5.5 atomic% or less of Hf, a high coercive force of the permanent magnet alloy can be obtained.

In the R-Fe-BC permanent magnet according to the present invention, it is indispensable that the main phase of the crystal phase is tetragonal, and in particular, a fine and uniform alloy powder is obtained, and excellent magnetic properties are obtained. This is effective for producing a sintered permanent magnet having

In the present invention, the reason why the plate thickness of the magnet alloy slab having a homogeneous structure in which dendritic or columnar crystals and the R-rich phase are finely dispersed are limited to 0.01 mm to 1.0 mm is as follows. If it is less than 01 mm, the quenching effect is large, the average short-axis crystal grain size is smaller than 3 μm, and it is easy to be oxidized when powdered, so that the magnetic properties are deteriorated and the finely pulverized particles become polycrystalline. Since the degree of orientation decreases and Br decreases, it is not preferable.
, The cooling rate _decreases, and α-Fe and Fe 1 to _x
This is because Co _x is easily crystallized, the crystal grain size becomes large, and the Nd-rich phase is unevenly distributed, so that the magnetic properties, particularly the coercive force and the squareness of the demagnetization curve are deteriorated, which is not preferable. More preferably, the thickness is 0.05 mm to 0.8 mm.

The cross-sectional structure of the R-Fe-BC-based alloy having a specific composition obtained by the strip casting method of the present invention is such that the main phase R ₂ Fe ₁₄ (B _1-x C _x ) crystal is a conventional mold. About 1/10 of the ingot obtained by casting
Although the above is fine, the short axis crystal grain size is 1.
The average short axis crystal grain size containing 10% or less of fine crystals of less than 0 μm is 3 μm to 15 μm.

[0048]

EXAMPLE 1 An alloy melt having a composition shown in Table 1 (liquidus temperature of 1175 ° C.) at a melt temperature of 1300 ° C. in an atmosphere of Ar reduced pressure of 600 torr and an outer diameter of 300 μm at a rotation speed of 120 rpm from a nozzle.
Primary cooling rate 5 × 10 ³ ℃
After cooling to a slab temperature of 800 ° C./sec, and after the roll is separated, Ar with a pressure of 5 kg / cm ² and a flow rate of 500 l / min from above and below the slab between the quenching roll and the slab storage box (distance 8 m).
Gas is blown, and the pressure is 5kg /
cm ^2, blowing Ar gas at a flow rate of 500l / min,
Cast slab to 610 ° C (solidus temperature 650 ° C) at 200 ° C /
Gas cooling was performed at a secondary cooling rate of min to obtain a slab of 0.40 mm in thickness for composition 1 and a slab of 0.38 mm in thickness for composition 2.

The section of the obtained slab was mirror-polished and observed with an optical microscope (400-fold magnification), and the minor axis crystal grain size of 500 crystals was measured by the line segment method. As described above, a tetragonal structure having an average short-axis crystal grain size of 4.5 μm and a short-axis crystal grain size distribution of 0.3 μm to 12.0 μm containing 3.7% of fine crystals having a short-axis crystal size of 1.0 μm or less. R
₂ Fe ₁₄ (B _1-x C _x ) dendritic crystal and R of 10 μm or less
-Having a homogeneous structure in which the rich phase is finely dispersed, and in composition 2, 4.3% of fine crystals having a minor axis crystal grain size of 1.0 μm or less
Containing tetragonal R ₂ Fe ₁₄ (B _{1-x) having} an average short axis crystal grain size of 4.3 μm and a short axis crystal grain size distribution of 0.3 μm to 11.6 μm.
_Cx ) type dendrites and an R-rich phase of 10 μm or less had a finely dispersed homogeneous structure.

The obtained slab was coarsely pulverized and then finely pulverized by jet mill pulverization to obtain fine powder having an average powder particle size of 3.0 μm. The powder was molded at a magnetic field strength of 15 kOe under a press pressure of 1 ton / cm ² , sintered in vacuum at 1040 ° C. for 4 hours, and then subjected to an aging treatment at 900 ° C. for 1 hour. Table 3 shows the average crystal grain size and the results of the corrosion resistance test. Corrosion resistance test is 80 ℃ × 90% RH ×
Expressed in terms of increased oxidation per unit area under the condition of 500 hours.
In Table 3, Hk is 0.9 × I on the demagnetization curve.
This is the strength of the reverse magnetic field when Br is reached.

Comparative Example 1 Using a molten alloy having the same composition as in Example 1, using the same rolls as in Example 1, and cooling at a primary cooling rate of 7500 ° C./sec. ° C.
Further, the slab after the roll was separated was gas-cooled at a secondary cooling rate of 200 ° C./min to obtain a tetragonal structure of R ₂ Fe ₁₄ (B
_A cast piece having a uniform structure in which _1-x C _x ) type dendritic crystals and an R-rich phase of 10 μm or less were finely dispersed was obtained.

Table 2 shows the thickness of the obtained slab and the result of measuring the short-axis crystal grain size by the same method as in Example 1. Also,
A sintered magnet was obtained under the same conditions as in Example 1 except that each of the obtained cast pieces was finely pulverized to an average powder particle size of 2.8 μm.
Table 3 shows the measurement results of the magnetic properties and the average crystal grain size and the results of the corrosion resistance test.

Comparative Example 2 Using a molten alloy having the same composition as in Example 1, using the same roll as in Example 1, and cooling at a primary cooling rate of 1600 ° C./sec, the slab temperature was 1120 ° C. Further, the slab after the roll was separated was gas cooled at a secondary cooling rate of 100 ° C./min to 600 ° C. to obtain a slab.

Table 2 shows the thickness of the obtained cast slab and the result of measuring the minor axis crystal grain size by the same method as in Example 1. Also,
A sintered magnet was obtained under the same conditions as in Example 1 except that each of the obtained cast pieces was finely pulverized to an average powder particle size of 3.2 μm.
Table 3 shows the measurement results of the magnetic properties and the average crystal grain size and the results of the corrosion resistance test.

Comparative Example 3 The same manufacturing conditions as in Example 1 were used, except that a molten alloy having the same composition as in Example 1 was used, the same roll as in Example 1 was used, and the secondary cooling rate was 20 ° C./min. To obtain a slab.

Table 2 shows the thickness of the obtained cast slab and the result of measuring the minor axis crystal grain size by the same method as in Example 1. Also,
A sintered magnet was obtained under the same conditions as in Example 1 except that each of the obtained cast pieces was finely pulverized to an average powder particle size of 3.4 μm.
Table 3 shows the measurement results of the magnetic properties and the average crystal grain size of the sintered magnet and the results of the corrosion resistance test.

COMPARATIVE EXAMPLE 4 Using a molten alloy having the same composition as in Example 1 and the same roll, gas-cooled to 750 ° C. at a secondary cooling rate of 250 ° C./min, and then cooled to 600 ° C. at 20 ° C./min. A slab was obtained under the same manufacturing conditions as in Example 1 except that the casting was performed.

Table 2 shows the thickness of the obtained cast slab and the result of measuring the minor axis crystal grain size by the same method as in Example 1. Also,
A sintered magnet was obtained under the same conditions as in Example 1 except that each of the obtained cast pieces was finely pulverized to an average powder particle size of 3.3 μm.
Table 3 shows the measurement results of the magnetic properties and the average crystal grain size and the corrosion resistance test results of the obtained sintered magnet.

Comparative Example 5 12.8Nd-1.5Dy-10Co-1.0B-6.
A 4C-68.3Fe composition molten alloy was sized 30 mm x 1
The ingot obtained by casting into a 00 mm × 200 mm mold is broken into 50 mm square or less, and 900 mm in an inert gas atmosphere.
A solution treatment was performed at 10 ° C. × 10 hours. Table 2 shows the results of measuring the crystal grain size of the ingot after the solution treatment. The R-rich phase was locally scattered at a size of 70 μm. Example 1 except that the broken fragments were finely pulverized to an average powder particle size of 3.2 μm.
Under the same conditions as above, a sintered magnet was obtained. Table 3 shows the measurement results of the magnetic properties and the average crystal grain size of the sintered magnet and the results of the corrosion resistance test.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Table 3]

[0063]

According to the present invention, after the molten R-Fe-BC alloy is melted in a vacuum melting furnace, the molten metal is poured from a nozzle at the tip of the tundish into a quenching roll, and the molten metal is specified by the quenching roll. After the primary cooling at the cooling rate, the slab separated from the rolls is secondarily cooled at a specific cooling rate below the solidus temperature to have a short-axis crystal grain size and crystal grain size distribution of a specific size. A quenched slab of a specific thickness having a homogeneous structure in which a R ₂ Fe ₁₄ (B _1-x C _x ) type dendritic or columnar crystal having a tetragonal structure and a specific R-rich phase are finely dispersed is obtained. It is possible to prevent the reduction of the degree of orientation, the pulverization at the time of pulverization at the time of magnetizing, and the oxidation of the powder.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Junichiro Baba 2- 15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Sumitomo Special Metals Co., Ltd. Yamazaki Works F-term (reference) 5E040 AA04 CA01 HB17 NN01

Claims (1)

[Claims] 1. R12-18 at%, B + C = 6-10
at% (B: 2 to 6 at%, C: 4 to 8 at%),
Average short-term content of 10% or less of fine crystals whose main component is the remainder Fe (however, a part of Fe can be replaced by one or two of Co and Ni) and the minor axis crystal diameter is less than 1.0 μm. R ₂ Fe ₁₄ (B _1-x C _x ) type dendritic or columnar crystals having an axial crystal grain size of 3 μm to 15 μm and a short axis crystal grain size distribution of 0.01 μm to 40 μm, and an R-rich phase of 10 μm or less. Is a slab for an R-Fe-BC-based magnet alloy having excellent corrosion resistance, which has a finely dispersed homogeneous structure and a slab thickness of 0.01 mm to 1.0 mm.