JP2739502B2 - Permanent magnet alloy with excellent oxidation resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a rare earth (R) -iron (Fe) having excellent oxidation resistance.
The present invention relates to a permanent magnet alloy comprising boron (B) and carbon (C).

[Conventional technology]

In recent years, many reports have been made since R-Fe-B-based magnets were disclosed by Sagawa et al. As next-generation permanent magnets exceeding the magnetic force of Sm-Co-based magnets. However, although the magnet is excellent in magnetic force as compared with the Sm-Co magnet, the thermal stability and oxidation resistance of its magnetic properties are remarkably inferior. For example, in the case of the permanent magnet material disclosed in JP-A-59-46008, It is difficult to withstand practical use.

In fact, many of the above reports point out disadvantages to oxidation resistance and disclose improvements. The method of improving the oxidation resistance is roughly classified into a method based on the alloy composition and a method in which the surface of the magnet is covered with an oxidation-resistant protective film.

As an example of the former, for example, JP-A-59-64733 discloses Fe
Teaches that corrosion resistance can be imparted to magnets by replacing part of Co with Co. JP-A-63-114939 discloses that a low melting point metal element such as Al, Zn, Sn or Fe, Co,
It teaches that the oxidation resistance is improved by including a high melting point metal element such as Ni. Further, JP-A-62-133040 and JP-A-63-77103 assume that C in a magnet promotes oxidation, and the oxidation resistance is improved by reducing the content of C to a predetermined value or less. Teach.

However, the effect of the oxidation resistance improvement method using these alloy compositions alone is limited, and it is actually difficult to withstand practical use. For this reason, in practical use, the surface of the magnet (the outermost exposed surface of the magnet product) is subjected to an oxidation-resistant protective film through a complicated and numerous steps as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 63-114939. It is necessary to cover with.

With respect to the formation of the oxidation-resistant protective film on the surface of the magnet product, it has been proposed to coat an oxidation-resistant substance by a plating method, a sputtering method, a vapor deposition method, an organic coating method, or the like.
However, in any case, it is necessary to form a strong and uniform protective film layer of several tens of μm or more on the outer surface of the magnet, so that the operation is inevitably complicated and requires many steps. However, the problems of peelability, dimensional accuracy, and cost increase could not be avoided.

[Problems to be solved by the invention]

Thus, the conventional R-Fe-B-based, R-Fe-Co-B-based, and R-Fe-Co-BC-based magnets have not yet achieved a drastic improvement in oxidation resistance. In spite of its excellent magnetic properties compared to the Sm-Co system and the great advantage of stable supply against abundant resources, at the practical level, it has oxidation resistance to shield the magnet surface from the atmosphere. There is a problem that the formation of a protective film is inevitable, and the above advantages are greatly impaired due to an increase in cost and a change in dimensional accuracy.

Generally, an R-Fe-B-based magnet is composed of magnetic crystal grains and a non-magnetic phase including a B-rich phase and a Nd-rich phase. It is said to progress and then shift to the Nd-rich phase. For this reason, in order to improve the oxidation resistance, it is necessary to reduce B as much as possible and to provide oxidation resistance to the Nd-rich phase. In fact, the content of B must be increased, and imparting oxidation resistance to the Nd-rich phase has not achieved remarkable results.

For example, in Japanese Unexamined Patent Publication No.
Although it is proposed to provide corrosion resistance by replacing with o, no mention is made of the B content with respect to oxidation resistance, and the B content is required to ensure coercive force (iHc) of 1 KOe or more. Is assumed to be 2 to 28 atomic%, and the B content must be at least 4 atomic% in order to make iHc 3KOe, and the B content should be further increased in order to obtain practically high iHc. Is taught. Thus, B
In order to ensure high magnetic properties by containing a large amount of
It is actually difficult to sufficiently exhibit oxidation resistance even if corrosion resistance is imparted by addition, and therefore, in order to put such a magnet containing a large amount of B into practical use, the inventors of the gazette must disclose it. Magnet surface as described (the outermost exposed surface of the magnet product)
The formation of a strong oxidation-resistant protective film is essential.

In the above-mentioned Japanese Patent Application Laid-Open No. 63-114939, an active Nd-rich phase is formed by adding a low-melting-point metal element such as Al, Zn, Sn or a high-melting-point metal such as Fe, Co, or Ni to the matrix phase. It teaches that the oxidation resistance is improved. For example, according to the embodiment described in the publication, a weather resistance test (60 ° C. ×
The results (90% RH) indicate that the standing time in which red rust was observed on the magnet surface was improved to 100 hours compared to 25 hours in the comparative example. However, in such a state, it is difficult to use at a practical level, and in practice, it is necessary to form a strong oxidation-resistant protective film on the magnet surface. Therefore, also in this case, it is difficult to drastically improve the oxidation resistance of the magnet itself. This gazette does not mention the content of B with respect to the oxidation resistance at all, and the content of B shown in Examples is 3.5 to 6.7 atomic%. It may be considered that the content of B in the range of 2 to 28 atomic% disclosed in Japanese Patent No. 46008 is intended.

An object of the present invention is to solve the problems of such R-Fe-B-based permanent magnets, especially the problem of oxidation resistance. An object of the present invention is to provide the magnet itself with excellent oxidation resistance while maintaining high magnetic properties without forming a protective film.

[Means for solving the problem]

As a means for solving these problems, the present inventors have proposed a drastic oxidation resistance based on a microscopic idea instead of the conventional macroscopic idea of coating the magnet surface with an oxidation-resistant protective film. As a result of intensive studies on the improvement of the oxidizing properties, a new technology, which was difficult to predict even with the conventional technology of coating each of the magnetic crystal grains in the magnet with an oxidation-resistant protective film, was found. It has made it possible to provide a new permanent magnet alloy that has been further improved. Furthermore, the B content of 2 atomic%, which was no longer high in the prior art and was considered out of the practical range, could not be obtained.
It has been newly found that good magnetic properties that can withstand practical use can be imparted even in a region less than the above.

That is, the present invention provides an R—Fe—B alloy magnet (where R is Y
, At least one of the rare earth elements), each of the magnetic crystal grains of the alloy is covered with an oxidation-resistant protective film,
This oxidation-resistant protective film contains substantially all of the alloying elements constituting the magnetic crystal grains, and 0.1 to 16% by weight of the alloy is C. BC
The present invention provides a permanent magnet alloy. Here, the magnetic crystal grains preferably have a particle size in the range of 0.5 to 50 μm.
The thickness of the oxidation-resistant protective film covering each crystal grain having this particle size is in the range of 0.001 to 15 μm.

The preferred composition of the magnet of the present invention (the entire composition of the magnetic crystal grains and the oxidation-resistant protective film) is as follows: R (at least one of rare earth elements including Y): 10 to 30%, B: less than 2% (0%
), C: 0.5 to 20%, the balance being Fe and unavoidable impurities in production. Even if B is 2% or more, the effect of oxidation resistance can be sufficiently exerted. %, The oxidation resistance is remarkably improved while the magnetic properties are sufficiently exhibited.

Since the permanent magnet according to the present invention has extremely excellent oxidation resistance without having to coat the outermost surface of the magnet with an oxidation-resistant protective film as in the past, for example, the above-mentioned 60 ° C.
Demagnetization of Br and iHc is 0.3 ~ 10% and 0 ~, respectively, even if the magnet surface is left exposed for 5040 hours at constant temperature and humidity of 90% RH.
Very low at 10%. Therefore, it is not necessary to form a protective film covering the surface even in such an environment. Such oxidation resistance and demagnetization resistance of the magnet of the present invention could not be achieved by the conventional magnet, and in this respect it can be said that the magnet is a completely new permanent magnet.

On the other hand, regarding the magnetic characteristics of the magnet of the present invention, Br ≧ 4000 (G), iHc ≧ 4000 (Oe), (BH) max
≧ 4M ・ G ・ Oe, Br ≧ 7000 (G) for anisotropic sintered magnet, iHc
≧ 4000 (Oe), (BH) max ≧ 10M ・ G ・ Oe
It has a value equal to or higher than that of the Nd-Fe-B permanent magnet.

Such characteristics are obtained by covering each magnetic crystal grain constituting the magnet of the present invention with a nonmagnetic film having an appropriate C content. That is, the present inventors have found that by adding a predetermined amount of the C (carbon) to the grain boundary phase, which is a nonmagnetic phase, a remarkable oxidation resistance function can be imparted to this nonmagnetic phase. By coating each magnetic crystal grain with the non-magnetic film having the oxidation resistance function, a sufficient oxidation resistance effect can be exhibited even with the same B content as before, and further, the formation of the C-containing protective film is performed by the B It has been found that the oxidation resistance can be remarkably improved while the magnetic properties are at or above the same level as before even at less than 2 atomic%.

[Detailed Description of the Invention]

The magnet of the present invention has a significant feature in the use of C (carbon). Heretofore, this type of magnet has generally been regarded as an impurity element that is unavoidably mixed, and has not been treated as an alloying element that is actively added unless otherwise specified. For example, in the above-mentioned Japanese Patent Application Laid-Open No. 59-46008, the content of B in the magnet is specified to be 2 to 28 atomic%, and it is pointed out that the coercive force iHc becomes less than 1 KOe when the B content is less than 2 atomic%. In addition, it merely states that part of B can be replaced with C from the viewpoint of cost reduction. JP-A-59-163803 discloses an R-Fe-Co-BC-based magnet in which the B content in the magnet is 2 to 28 atomic%,
The content of B is specified as 4 atomic% or less, and the specific combination of B and C is disclosed. However, the content of B is required to be 2 atomic% or more regardless of the combination of C and 2 atomic%. If the amount of B is less than
It is described that iHc is less than 1 KOe as in JP 59-46008 A. That is, as pointed out by the gazette, C is understood to be an impurity that lowers the magnetic properties. For example, it is inevitable to mix C from a lubricant or the like used in molding a powder, and it must be completely removed. Because the removal operation increases the cost, Br40 equivalent to hard ferrite magnet
Up to 00G, it is proposed that the C content can be 4 atomic% or less, and C has a negative effect on the magnetic properties, and C is not necessarily required. Further, there is no suggestion about formation of a C-containing oxidation-resistant protective film (non-magnetic phase).

Further, JP-A-62-13304 discloses that R-Fe-Co-B-
In order to improve the oxidation resistance of C-based magnets, he teaches that a large amount of C is not good, and proposes to suppress the C content to 0.05% by weight or less (about 0.3% by atomic percentage). Furthermore, Japanese Patent Application Laid-Open No. 63-77103 by another applicant also proposes to reduce C to 1000 ppm or less for the same purpose. As described above, conventionally, C has been regarded as a passive element in terms of magnetic properties and oxidation resistance, and has not been regarded as an essential additive element.

The present inventors do not include C as a mere substitution element for B, but use a non-magnetic phase (grain boundary) surrounding magnetic crystal grains.
It has been found that C, if added in such a manner that C is positively contained therein, can greatly contribute to the oxidation resistance of the magnet, contrary to conventional wisdom. It also became clear that improvement could be achieved. That is, due to the inclusion of C in such a non-magnetic phase, even if the B content is within a known normal range, the oxidation resistance is improved as compared with the conventional case, and particularly when the B content is less than 2 atomic%. It was found that the effect was even more remarkable. For example, conventionally, when the B content is less than 2 atomic%, iHc is 1 KOe.
According to the present invention, iHc is 4 KOe or more even with a B content of less than 2 atomic% in the present invention. Such a novel effect according to the present invention is brought about by the formation of the C-containing oxidation-resistant protective film surrounding each of the magnetic crystal grains. It is completely different from the conventional magnet which uses C as the depolarizing element, and has completed the invention of a new magnet which requires C as an essential element.

In this case, the C-containing oxidation-resistant protective film surrounding each of the magnetic crystal grains contains substantially all of the alloy elements constituting the magnetic crystal grains in addition to C. Such a C-containing oxidation-resistant protective film can be formed by allowing C to be contained in the grain boundary layer existing between the magnetic crystal grains in the magnet. The reason is presumed as follows. That is, since the protective film contains substantially all of the alloying elements constituting the magnetic crystal grains, it is considered that the protection film is particularly caused by the formation of the R-Fe-C intermetallic compound. It is generally said that rare earth elements are easily rusted and carbides of rare earth elements are easily hydrolyzed. However, it is presumed that the non-stoichiometric R-Fe-C-based intermetallic compound is generated in the protective film according to the present invention, and this is considered to suppress the above-mentioned disadvantage. Therefore, it is necessary that at least R and Fe besides C exist in the protective film so that such a non-stoichiometric R-Fe-C intermetallic compound can be formed. This can be confirmed by the presence of rich R and Fe in the protective film, as shown in the embodiments described later (for example, FIGS. 3 and 4). In addition, B is contained in the protective film to some extent depending on the manufacturing history and the amount of B added. For this reason, the oxidation-resistant protective film according to the present invention contains C as an essential component, and R, Fe,
Further, it contains B.

As described above, the present inventors have found that coating the individual magnetic crystal grains with the C-containing oxidizing protective film significantly increases the oxidation resistance, and furthermore, the effect is further enhanced by reducing the B content. Invented a good permanent magnet, which was difficult with known techniques.

The C-containing oxidation-resistant protective film contains substantially all of the elements constituting the magnetic crystal grains as described above,
And the C content is 0.1 to 16% by weight in the protective film composition.
It is necessary to be. That is, C in the protective film not only imparts oxidation resistance to the magnet but also reduces iHc
The content is preferably 0.1 to 16% by weight, more preferably 0.2 to 12% by weight in the composition of the protective film, but it is not less than 0.7% by weight as described in Examples below. Preferably, it is practically not less than 1.0% by weight and not more than 13% by weight. If the content of C is less than 0.1% by weight, oxidation resistance cannot be imparted, and iHc
Is less than 4KOe. On the other hand, when the amount of C in the protective film exceeds 16% by weight, the Br of the magnet is remarkably reduced, and practical use is no longer practical. In addition, in the magnet of the present invention, the compositional components of the protective film include, in addition to C, substantially all of the alloying elements constituting the magnetic crystal grains, even if the amount ratio differs from that of the magnetic crystal grains. As long as the thickness of the protective film is uniformly covered with the individual magnetic crystal grains, the oxidation resistance is substantially maintained irrespective of the thickness, but if the film thickness is less than 0.001 μm, i
If the decrease of Hc is remarkably more than 15 μm, Br no longer satisfies the value intended in the present invention, so it is preferable to set the range of 0.001 μm to 15 μm, preferably 0.005 μm to 12 μm. The thickness of the protective film includes the triple point of the grain boundary. The thickness of this protective film can be measured using a TEM (this measurement was also used in Examples described later).

On the other hand, each magnetic crystal grain itself surrounded by the oxidation-resistant protective film may have the same composition as that of the periodic R-Fe-B- (C) -based permanent magnet. However, even with a small amount of B, the magnet of the present invention can exhibit good magnetic properties. The composition of the alloy magnet of the present invention (the overall composition of the magnetic crystal grains and the oxidation-resistant protective film in combination) is preferably R: 10 to 30, B:
Less than 2% (excluding 0%), C: 0.5 to 20%, balance: Fe and impurities inevitable in production.

The total C content in the magnet of the present invention is preferably 0.5 to 20 atomic%. If the total C content in the magnet exceeds 20 atomic%, Br
Is significantly reduced, and Br ≧ 4KG as an isotropic sintered magnet and Br ≧ 7KG as an anisotropic sintered magnet in the present invention.
Is not satisfied. On the other hand, if it is less than 0.5 atomic%, it is no longer possible to impart oxidation resistance. As described above, the total C content in the magnet is preferably 0.5 to 20 atomic%. However, the C in the above-described oxidation-resistant protective film not only imparts oxidation resistance but also reduces the B content. Since the effect of suppressing the decrease in iHc is brought about, the content is essential in the composition of the protective film to be 0.1 to 16% by weight, preferably 0.2 to 12% by weight. As a raw material of C, carbon black, high-purity carbon, or an alloy such as Nd-C or Fe-C can be used.

R is a rare earth element, Y, La, Ce, Nd, Pr, Tb, Dy, Ho, Er,
One or more of Sm, Gd, Eu, Pm, Tm, Yb and Lu are used. Note that a mixture of two or more kinds, such as misch metal and dymium, can also be used. Here, the reason why R is preferably set to 10 to 30 atomic% is that Br is practically excellent in this range.

As B, pure boron or ferroboron can be used. Even if the content exceeds 2 atomic%, which is a known range, the oxidation resistance is remarkably improved as compared with the prior art, and the object of the present invention can be achieved. Preferably, B is less than 2 atomic%, and more preferably 1.8 atomic% or less, which has a further effect. On the other hand, when B is not added, the oxidation resistance is improved, but iHc is extremely reduced, and the object of the present invention cannot be achieved. As the ferroboron, those containing impurities such as Al and Si can also be used.

As described above, the permanent magnet alloy of the present invention has a thickness of preferably 0.001 to 15 μm, more preferably 0.005 to 12 μm, and each magnetic crystal grain is covered with a C-containing oxidation-resistant protective film. However, the particle size of the magnetic crystal grains is preferably in the range of 0.5 to 50 μm, more preferably 1 to 30 μm. IHc becomes 4K when the particle size of magnetic crystal grains is less than 0.5 μm
If it is less than Oe, and if it exceeds 50 μm, the decrease of iHc becomes remarkable, and the characteristics of the magnet of the present invention are impaired. The measurement of the grain size of the crystal grains can be accurately performed by SEM, and the composition analysis can be accurately performed by using EPMA (these measurements were also performed in Examples described later).

As a method for producing the permanent magnet of the present invention, when the permanent magnet alloy is a sintered body, melting, casting, crushing, molding,
Although it can be produced by a conventional method comprising a series of steps of sintering or melting, casting, crushing, molding, sintering, and heat treatment, preferably, in the above production process, the step of heat treating the cast alloy after casting is performed. It can be advantageously produced by introducing a step of secondary addition of part or all of the C raw material during or after the pulverization, or by combining these two steps. On the other hand, when the permanent magnet alloy is a cast alloy, a good permanent magnet alloy of the present invention exhibiting the above-mentioned effects can be produced by using the hot plastic working method.

As described above, the permanent magnet alloy according to the present invention is remarkably excellent in oxidation resistance as compared with conventional ones, is resistant to rust, and has good magnetic properties, so that it is suitably used for various magnet-applied products. Examples of the magnet application products include the following products.

Various motors such as DC brushless motors and servo motors; drive actuators and optical pickups
Various actuators such as F / T actuators; Various audio equipment such as speakers, headphones, and earphones; Various sensors such as rotation sensors and magnetic sensors; Electromagnetic replacement products such as MRI; various relays such as reed relays and polarized relays Various types of magnetic couplings such as brakes and clutches; various types of vibration oscillators such as buzzers and chimes: various types of suction devices such as magnet separators and magnet chucks; various types of opening and closing control devices such as electromagnetic switches, micro switches, and rodless air cylinders An optical isolator,
Various microwave devices such as klystrons and magnetrons; magnet generators; health appliances, toys, etc.

In addition, the above-mentioned magnet application product is an example, and is not limited to these. Further, the feature of the permanent magnet alloy according to the present invention is that it is resistant to rust, and it is possible to maintain high magnetic properties without forming an oxidation-resistant protective coating on the outermost exposed surface of a magnet product unlike conventional materials. The protective coating is not necessary because of its excellent oxidation resistance, and even if a protective coating is required for special environments, there is no rust generated inside the magnet. It has good adhesiveness when forming a film, and eliminates problems such as dimensional accuracy due to film peeling and fluctuations in film thickness.
An optimal permanent magnet can be provided for applications requiring oxidation resistance.

Hereinafter, the characteristics of the magnet of the present invention will be clarified with reference to examples.

[Example 1] Electrolytic iron having a purity of 99.9% and a boron content of 19.32 as raw materials
% Of ferroboron alloy, purity of 99.5% carbon black and purity of 98.5% neodymium metal (containing other rare earth metals as impurities), measured and blended so that the composition ratio (atomic ratio) becomes 18Nd 71Fe 1B 3C Then, after melting in a high frequency induction furnace in a vacuum, it was cast into a water-cooled copper mold to obtain an alloy lump. The alloy ingot thus obtained was crushed to 10 to 15 mm by a jaw crusher, then kept at 700 ° C. for 5 hours, and then cooled at a rate of 50 ° C./min. Further, the alloy ingot is -100 m
After crushing to esh, the composition ratio (atomic ratio) is 18Nd 71Fe 1B
Carbon black having a purity of 99.5% was further added to the coarsely ground powder so as to obtain 10C, and then ground to an average particle diameter of 5 µm using a vibration mill. The alloy powder thus obtained was formed at a pressure of 1 ton / cm ^{2 in} a magnetic field of 10 KOe, kept at 1100 ° C. for 1 hour in an argon gas, and quenched to obtain a sintered body.

As Comparative Example 1, except that carbon black was not used, the composition was the same as in the above Example, and the composition ratio (atomic ratio) was measured and blended so as to be 18Nd76Fe6B. (But no carbon black added)
It was roughly crushed, finely crushed, formed by a magnetic field, then sintered and rapidly cooled to obtain a sintered body.

Evaluation of the oxidation resistance (weather resistance test) of the sintered body thus obtained was conducted at a constant temperature and humidity of 60 ° C. and 90% humidity.
Table 1 and FIG. 1 show the BriHc demagnetization rate when left for a period of 50 months (5040 hours).

As is clear from FIG. 1, the sintered body of Example 1 (sintered body in which each magnetic crystal grain is covered with a C-containing protective film) has a thickness of 6 mm.
The demagnetization ratios after a month are extremely small, such as Br (solid line): -0.36% and iHc (dashed line): -0.1%, indicating that the oxidation resistance is extremely good. On the other hand, in the sintered body of Comparative Example 1 having no C-containing protective film, only one month (720
After the time, the demagnetization ratios were Br: -9.8% and iHc: -3.0%, and if left for a longer time, rust was so severe that measurement became impossible.

FIG. 2 shows the result of SEM observation of the structure of the sintered body of Example 1, and FIG. 3 shows the result of line analysis of C and Nd elements using EPMA. FIG. 4 shows the line of each element obtained by copying the line analysis line in the photograph of FIG. From these photographs, it can be seen that the magnetic crystal grains are covered with the oxidation-resistant protective film containing C, and most of the C is present in the Nd-rich protective film. The C content in the protective film was 6.1
% By weight. In addition, the SE of the sintered structure
When measuring 100 pieces from the M photo, the range is 0.7 to 25μ
m. On the other hand, the thickness of the protective film measured by TEM was 0.01 to
It was 5.6 μm. These values are shown in Table 1 below.
In addition, Br, iHc and (B
H) The values of max are shown in Table 1.

Thus, it can be seen that the permanent magnet alloy according to the present invention has remarkably excellent oxidation resistance as compared with the known alloy of Comparative Example 1, and has the same or better magnet properties.

[Examples 2 to 6] A sintered body was obtained by performing the same operations as in Example 1 except that the amounts of boron (B) shown in Table 1 were measured and blended when the raw materials were dissolved.

Comparative Example 2 was an example in which the amount of boron was 0 atomic%, and a sintered body was obtained by the same operation as described above except that boron was not blended.

Oxidation resistance of each obtained sintered body, C content in protective film,
The magnetic crystal grain size, the thickness of the protective film, and the magnetic properties were evaluated in the same manner as in Example 1, and the results are shown in Table 1. FIG. 1 also shows the oxidation resistance evaluation results of Examples 5 and 6.

From these results, it can be seen that the sintered body having the C-containing protective film of the present invention has a very small demagnetization rate over a long period of time and has excellent oxidation resistance. This effect is sufficient even in Example 6 where B = 3 atomic%, but is particularly remarkable in an example where B is less than 2 atomic% (for example, Examples 1 and 5 in FIG. 1).

[Examples 7 to 10] A sintered body was obtained in the same manner as in Example 1, except that carbon black was additionally added at the time of pulverization so that the amount of carbon became the composition ratio shown in Table 2. In addition, Example 7 does not add carbon black at the time of dissolution but only adds at the time of pulverization.

Further, as Comparative Example 3, after weighing and blending to obtain 18Nd-81Fe-1B, the same operation as in Comparative Example 1 was performed to obtain a sintered body. As Comparative Example 4, the composition ratio was 18Nd-56Fe-1B-25C.
A sintered body was obtained in the same manner as in the above example except that the above conditions were satisfied.

The oxidation resistance of the sintered body thus obtained, the C content in the protective film, the magnetic crystal grain size, and the thickness magnetic properties of the protective film were evaluated in the same manner as in Example 1. The results are shown in Table 2.

As shown in the results of Table 2, the sintered body having the alloy composition (atomic percentage) and the requirement for the protective film according to the present invention was:
Each of them has low demagnetization rate and shows excellent oxidation resistance. In Comparative Example 3, since the protective film did not contain C, rust occurred before the oxidation resistance could not be measured. In Comparative Example 4, the Br value was low because the C content of the protective film was excessive.

[Examples 11 to 13] The amounts of neodymium were measured and measured so as to have the composition ratios shown in Table 3.
Except for blending, all operations were the same as in Example 1 to obtain a sintered body.

The oxidation resistance of the sintered body thus obtained, the C content in the protective film, the magnetic crystal grain size, the thickness of the protective film, and the magnetic properties were evaluated in the same manner as in Example 1. The results are shown in Table 3. Indicated.

As can be seen from the results in Table 3, the sintered body of the present invention has excellent magnetic properties and extremely good oxidation resistance.

[Examples 14 to 22] Except for adding rare earth elements shown in Table 4 in place of neodymium during melting of the raw materials, all operations were the same as in Example 1 to obtain a sintered body.

The oxidation resistance of the sintered body thus obtained, the C content in the protective film, the magnetic crystal grain size, the thickness of the protective film, and the magnetic characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 4. Indicated.

From the results shown in Table 4, it is clear that all of the sintered magnets according to the present invention have excellent magnetic properties and extremely good oxidation resistance.

Example 23 A sintered body was obtained by performing the same operation as in Example 1 except that the alloy fine powder was molded in the absence of a magnetic field.

The oxidation resistance of the thus obtained sintered body, the C content in the protective film, the magnetic crystal grain size, the thickness of the protective film, and the magnetic properties were also evaluated in the same manner as in Example 1. The results are shown in Table 5. Indicated.

[Brief description of the drawings]

FIG. 1 shows a sintered magnet (Examples 1, 5, and 6) of the present invention, in which each magnetic crystal grain is covered with a C-containing oxidation-resistant protective film, at 60 ° C. × FIG. 2 is a graph showing the relationship between the storage time when left in an atmosphere of 90% RH and the demagnetization rate of Br and iHc in comparison with a comparative example having no C-containing oxidation-resistant protective film. Fig. 3 is a photograph showing the metallographic structure of the magnet of the present invention of Example 1, Fig. 3 is a photograph showing the line analysis results of Nd, Fe, C elements in the metallic structure of Fig. 2, and Fig. 4 is FIG. 3 is a diagram in which the line analysis lines of FIG. 3 are copied, for displaying the element names of the respective line lines.

Claims (3)

(57) [Claims] In an R-Fe-BC-based alloy magnet (where R is at least one of rare earth elements including Y), each magnetic crystal grain of the alloy is covered with an oxidation-resistant protective film. The oxidation-resistant protective film contains substantially all of the alloying elements constituting the magnetic crystal grains, and 0.1 to 16% by weight of it is C. Fe-BC permanent magnet alloy. 2. The permanent magnet alloy according to claim 1, wherein the magnetic crystal grains have a particle size in the range of 0.5 to 50 μm and a thickness of the oxidation-resistant protective film in a range of 0.001 to 15 μm. 3. The composition of the magnet alloy (the total composition of the magnetic crystal grains and the oxidation-resistant protective film) is expressed by an atomic percentage of R: 10.
~ 30%, B: less than 2% (excluding 0 atomic%), C: 0.5 ~ 20%,
2. The composition according to claim 1, wherein the balance comprises Fe and impurities inevitable in production.
Or the permanent magnet alloy according to 2.