DE69927931T2 - PERMANENT MAGNETIC ALLOY WITH OUTSTANDING HEAT-RESISTANT PROPERTIES AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

technical Field of the invention

The The present invention relates to a permanent magnet alloy which R (where R denotes yttrium (Y) or a rare earth element), Boron (B), carbon (C), cobalt (Co) and iron (Fe) based, which in particular improved thermal resistance such that low degradation in the magnetic force also occurs in the case in which they are under an environment a temperature as big as 200 ° C used becomes.

background the invention

One Sm-Co based magnet is considered to be a. Rare earth magnet known, has improved thermal resistance on, but is expensive. The term "thermal resistance" as used herein in particular means that the magnetic force of the magnet is not by heat demoted. As disclosed in Japanese Patent Publication No. 4-116144 (Patent No. 2740981.) have one of the inventors of the present invention and others, an R-B-C-Co-Fe based permanent magnet alloy proposed as a rare earth magnet, which is included in the cost is reduced and at the same time improved in the thermal resistance. This magnet alloy contains Carbon (C) as an essential alloying element and uses a Combination of a light rare earth element and a heavy one Rare earth element for the rare earth element (R). The revelation teaches that the irreversible Demagnetization of the magnetic alloy is significantly improved (this means, the negative irreversible demagnetization values reach 0%) by the incorporation of C, and that the irreversible demagnetization is further improved by partial incorporation of a heavy rare earth element for R.

Object of the invention

in the Case that a permanent magnet is installed in applications which near of heat-emitting Sources are installed, it is essential that the magnetic Force of the permanent magnet does not fall when it is in higher temperature is brought, that is, that the remaining magnetic flux density (Br) no degradation is subject when heated becomes. However, these are cases in which the magnet is used under conditions such, that the operating temperature reaches about 200 ° C (for example automotive engine applications operated at about 200 ° C and is natural same thing for Engines of electric automotive vehicles). Then you are up Sm-Co based magnets the only type of known magnets, which can be used in this field. However, as above mentioned, expensive on Sm-Co based magnets, and the usual Nd-Fe (Co) -B based ones Rare earth magnets are for Applications at such high temperatures (for example, 200 ° C) unsuitable.

Even though the aforementioned Japanese Patent Publication No. 4-116144 teaches that incorporation of C (carbon) as the alloying element in a permanent magnet improves the irreversible demagnetization, and that partial replacement of R by a heavy rare earth element continues to improve the irreversible demagnetization is here no magnet is shown which does not undergo demagnetization, when he reaches 200 ° C heated becomes.

In Considering such circumstances it is an object of the present invention to provide a permanent magnet which improved thermal resistance has, and is suitable in such high temperatures of 200 ° C, with at the same time low production costs.

Summary the invention

Around the above goal based on the fundamental concept of Incorporation of C to improve the thermal resistance of the permanent magnet alloy as proposed in Japanese Patent Publication No. 4-116144, the present inventors studied and studied the influence of each of the heavy rare earth elements on the thermal resistance. As a result, in addition to the incorporation of basic rare earth elements such as Nd and Dr it re-found that infliction of Dy and Tb in combination and in correct amounts, in particular when added in relation to each other, the thermal resistance the permanent magnet significantly improved.

Consequently is in accordance with the present Invention, a permanent magnet alloy provided, which a improved thermal resistance has, according to claim 1.

Also is a method for producing such a permanent magnet alloy according to claim 7 intended.

preferred embodiments of the present invention from the dependent ones claims to be obtained.

Short description the drawings

1 Fig. 12 is a diagram showing the distribution of irreversible demagnetization in which the values of irreversible demagnetization at 200 ° C of the magnets shown in Table 2 are shown depending on the contents of Dy and Tb;

2 Fig. 12 is a diagram showing the observed irreversible demagnetization values at various temperatures of the magnet disclosed in Example 24 disclosed in Japanese Patent Publication No. 4-116144 and that of Example 2 according to the present invention, in which the specimens are respectively shaped in that the permeability coefficient (Pc) is 3 and is magnetized by application of 50 KOe; and

3 FIG. 13 is a graph showing the observed irreversible demagnetization values similar to those in FIG 2 except that the specimens are shaped to have a permeability coefficient (Pc) of 1.

description the preferred embodiments

At the Design of applications that can be operated in cases such that the magnet installed in it is brought to a temperature of 200 ° C The irreversible demagnetization at 200 ° C serves as one Index. In particular, it is preferable to choose a design that the value (a negative value) of the irreversible demagnetization (200 ° C) according to the above Equation (1) 0% if possible reached.

When an appropriate amount of C is incorporated in a sintered RB-Co-Fe-based alloy, where R is representative of Nd or a combination of Nd and Pr, the value (negative value) of the irreversible magnetization (160 ° C ) Zero. This fact is shown in the example of Japanese Patent Publication No. 4-116144. However, the irreversible demagnetization (160 ° C.) described in this disclosure is replaced by replacing A ₂₀₀ with A ₁₆₀ (where A _{160 is} the flux value of a magnet measured on a specimen written at 160 ° C. for was held for a period of 120 minutes and then cooled to room temperature), and is an observed value for a permeability coefficient (Pc) of three. That is, the irreversible demagnetization (160 ° C) is a value obtained by magnetizing a specimen formed such that Pc is three and magnetized with 50 KOe, and measuring the flux value A ₂₅ and A ₁₆₀ . As described in the publication, it is known that incorporation of C is effective for improving heat resistance (and resistance to oxidation). However, nothing is known about the irreversible demagnetization at 200 ° C. Further, among existing R- (Fe, Co) -B based sintered magnet alloys (which do not contain C as the alloying element), no one finds irreversible demagnetization ( 200 ° C) in a range of 0% to -20%.

outgoing from the proposal of the above disclosure, set forth the present Inventor various types of tests and research on the composition the alloy and the process for their preparation, with an object of improving the thermal resistance of the R-Fe-Co-C-B based sintered magnet alloys, and have found that the combined addition of Dy and Tb in proper amounts leads to a magnet alloy which has a significantly lower irreversible demagnetization. The effect of infliction is not remarkable when Dy or Tb are added independently, but a preferred heat resistance is achieved in the case when both are added in combination.

Of the Reason of limitation the amount of each of the components containing the magnetic alloy according to the present invention Invention is described below, together with the method for producing the alloy magnet according to the present invention Invention. In the following description, "at.%" Indicates atomic percent, this means % on an atomic basis.

C: 0.1 to 15 at.%

As in Japanese Patent Publication No. 4-116144, the adverse characteristic of a Rare earth magnets, that is the tendency of the tendency to oxidation, by the addition of C be modified while the magnetic properties of the magnetic alloy preferably obtained become. Carries carbon also to reduce the demagnetization at. If the infliction of C is less than 0.1 at.%, The effect of this is on the improvement the oxidation resistance and the thermal resistance is insufficient. If the addition of C 15 at.% on the other side, the value begins of Br, to fall. Accordingly, C is included in a range of 0.1 to 15 at.%, but a preferred range is 1.0 to 10 at.%, and more preferred is a range of 2.5 to 7 at.%.

B: 0.5 to 15 at.%

boron (B) is necessary to form a magnetic phase, and it should be present with at least 0.5 at.%. However, that worsens infliction from B to too big Quantity reversible the magnetic properties. Accordingly B is added in an amount of 0.5 to 15 at.%, preferably 1.0 to 10 at.%, and more preferably 1.5 to 7 at.%.

C and B total: 2 to 30 at.%

For education a magnetic phase and for the improvement of resistance to oxidation must be C and B total at least 2 at.% Make up. However, the insertion of C and B, which exceeds 30 at.% In total, the magnetic Properties; accordingly C and B total 2 to 30 at.% Make up.

Co: 40 at.% Or less

cobalt raises the Curie point while he gets the magnetic properties. Thus, the addition of Co important, but an addition of which in an amount exceeding 40 at.% decreases significantly the coercive force of the magnet. Accordingly, the addition of Co be 40 at.% Or less.

Dy and Tb total: 0.5 up to 5 at.%

dysprosium (Dy) and Terbium (Tb) are the characteristic elements of the magnet of the present invention, and their combined addition is reduced noteworthy the irreversible demagnetization. To this end, have to Dy and Tb are added in an amount of 0.5 at.% Or more in total, but their effect on the improvement of thermal resistance saturates if an entire infliction bigger than them 5 at.%, And it can reversible the magnetic properties influence. Accordingly, their addition must total 0.5 to 5 at.% be. As shown below in the comparative example, wears the infliction Dy or Tb alone does not contribute to reducing irreversible demagnetization. It is believed that Dy and Tb work synergistically to reduce the irreversible demagnetization work. Further will be these elements preferably in a Tb (at.%) / Dy (at.%) ratio, expressed in% added on an atomic basis in the range of 0.1 to 0.8. In the described below, it allows the addition of 0.3 to 4.9 at.% Of Dy and 0.1 to 4.7 at.% Of Tb the magnet improved thermal resistance with an irreversible demagnetization at 200 ° C with a permeance coefficient of 1 in a range of 0 to -20%, preferably 0 to -15 %.

R: 8 to 20 at.%

One Rare earth element different from Dy and Tb, at least one element, which is selected from the group consisting of Nd, Pr, Ce, La, Y, Gd, Ho, Er and Tm is selected is, either alone or in combination of it with a lot from 8 to 20 at.% added become. By the addition R becomes a magnetic phase and a grain boundary phase in of the sintered magnet alloy formed to iHc and Br at high Values. Among the elements for R, Nd and Pr are preferred, and the infliction from Nd alone or a combination of Nd with Pr is the most prefers. If the addition R is less than 8 at.%, a high enough Br can not be achieved, and the infliction of R exceeds 20 at.% to an insufficient value of Br. A preferred range of R is 13 to 18 at.%.

A permanent magnet alloy according to the present invention, which is the above together has an irreversible demagnetization (200 ° C) in accordance with the above equation (1) at a low level such as that in the range of 0 to -20%, preferably 0 to -15%, and most preferably 0 to -5%. Thus, for the first time, the present invention provides a permanent magnet alloy other than an Sm-Co based magnet suitable for high temperature use. For high temperature applications, known boron-containing rare earth magnets having higher coercive force have been used by taking demagnetization at higher temperatures into consideration. However, after the magnet according to the present invention is almost free from demagnetization even at elevated temperatures, it can be used as it is as a permanent magnet having a high magnetic force. In particular, the magnet according to the present invention can maintain the magnetic properties for use at elevated temperatures at iHc of 13 KOe or higher, and preferably 15 KOe or higher. Considering that the existing magnets required a fairly high iHc for use in elevated temperature applications, the magnet according to the present invention can be considered as an effective permanent magnet alloy. The permanent magnet alloy according to the present invention can be produced by a method consisting of sequential steps of melting, casting, crushing, molding and sintering. As a melt-casting method, a method such as vacuum melting and casting, melting and casting under an inert gas atmosphere, quench rolling, atomization, etc. may be used. In order to obtain a sintered magnet having improved magnetic characteristics and heat resistance, it is preferable to incorporate a step of heat treatment between the steps of casting and crushing to allow the product to be subjected to a heat treatment at a temperature of 600 ° C or under an inert gas atmosphere prior to crushing ; is exposed. Thus, the irreversible demagnetization can be further reduced. In the sintering step, it is preferable to sinter the molding in the temperature range of 1000 to 1200 ° C under an inert gas atmosphere and to gradually cool it from the sintering temperature to a temperature in the range of 600 to 900 ° C, followed by quenching thereof. The irreversible demagnetization can be further reduced by the quenching carried out after sintering.

The sintered magnet alloy according to the present invention Invention may according to the manufacturing process for one sintered magnets disclosed in Japanese Patent Publication No. 4-116144, with the exception of heat treatment and the quenching treatment after the above-described sintering. The manufacturing method is described below.

The raw materials weighed to give the desired alloy composition are melted in a vacuum smelting furnace at a temperature of 1600 ° C or higher, and are cast by quenching in a water-cooled mold. As described above, the ingot thus obtained is treated under gaseous Ar at a temperature of 600 ° C or higher and subjected to coarse crushing by use of a jaw crusher. The thus prepared coarse-grained powder was finely ground by using a vibratory ball mill to obtain a powder consisting of particles having an average diameter in the range of 2 to 10 μm. These steps for such size reduction are carried out under gaseous Ar atmosphere. A part of the raw material for C may be fed in the last step of grinding. That is, part of the raw material at C is charged into the vacuum melt furnace, and the remainder is added in this fine grinding step. Carbon black is suitable as the raw material of C, but organic materials containing C can also be used, such as an aliphatic hydrocarbon, a high-fatty acidic alcohol, a high-grade fatty acid, a high-greasy acid-amide, a metal soap, a fatty acid ester, etc. Then, the powder thus obtained is compaction-molded while applying an external magnetic field. The preferable range for the molding pressure is 1 to 5 t / cm ² , and that for the external magnetic field is 15 KOe or higher. The molding step is also preferably carried out under a gaseous Ar atmosphere. The molded product thus obtained is then sintered under gaseous Ar in the temperature range of 1000 to 1200 ° C for a period of about 2 hours. Then, as mentioned above, the resulting product is gradually cooled to a temperature in the range of 600 to 900 ° C, and quenched from this temperature. In order to initiate quenching from a temperature in the range of 600 to 900 ° C, a method of spraying a low temperature inert gas or a method of immersing the sintered product in water, an oil or a liquid similar thereto may be used, and preferably For example, rapid cooling is performed from the extinguishing triggering temperature in the range of 600 to 900 ° C to a temperature of 400 ° C or less at a cooling rate of -50 ° C / min or higher, preferably -100 ° C / min or higher.

Thus, according to the present invention, a method of manufacturing a permanent magnet alloy having improved heat resistance, which comprises melting and casting each of the alloying material starting materials, exposing the resulting alloy for pulverization, compression molding the resulting powder, and sintering the molding under an inert gas atmosphere in a temperature range of 1000 to 1200 ° C to obtain a sintered magnet alloy characterized in that the alloy prior to the pulverization is thermally treated under an inert gas atmosphere at a temperature of 600 ° C or higher, and / or that the method further, after the sintering of the molded article under an inert gas atmosphere in a temperature range of 1000 to 1200 ° C, gradually cooling the sintering from the sintering temperature in a temperature range of 600 to 900 ° C, followed by quenching. In the process, a part of the raw material of C may be added during the melting, and the remainder may be added during the pulverization of the alloy.

Of the Magnet according to the present The invention will be described in more detail below with reference on representative Examples.

example 1

An alloy having the composition below was prepared by a method which will be described below. [chemical composition of the alloy (at.%)] C: 5.0 at.% B: 1.8 at.% Co: 12.0 at.% Nd: 13.0 at.% Dy: 2.5 at.% tb: 0.5 at.% Fe: 65.2 at.%

In which C and B in total for 6.8 at.%, Dy and Tb in total for 3.0 at.%, And the ratio of Tb / Dy is 0.2.

[Production method]

each of the raw materials, weighed to the desired level above Alloy composition was melted in a vacuum furnace. Part of the raw material of C was not added to the smelting furnace, but instead was canceled. The melt thus obtained became quenched cast in a water cooled copper mold 1600 ° C, to obtain a cast alloy ingot. After the heat treatment under gaseous Ar at a temperature shown in Table 1 or without Application of heat treatment, The cast alloy ingot was roughly broken using a Tongs breaker, and the roughly broken product was put together into a vibratory ball mill with the lifted remainder of the raw material C for carrying out the Mahlens inserted. Thus, a powder was obtained which was an average Having particle diameter of 5 μm.

The powder product thus obtained was molded under a magnetic field using a pressure of 2 t / cm ² and an external magnetic field of 15 KOe. The resulting molded article was sintered under gaseous Ar at 1100 ° C for 2 hours, and was gradually cooled from the sintering temperature to the quenching initiation temperature as shown in Table 1, at which temperature rapid cooling was started with a cooling rate. which is also given in Table 1, by blowing gaseous Ar onto the molding. The magnetic properties, thermal resistance and oxidation resistance of the resulting sintering were determined to obtain the results given in Table 1. The thermal resistance and the oxidation resistance of the sintering were evaluated as follows.

[Evaluation of thermal resistance]

(1) measurement of irreversible Degaussing at 200 ° C

The specimen was formed in such a manner that the permeability coefficient (Pc) thereof is one. Specifically, the specimen was cut to a size of 2.5 mm × 2.5 mm × 1.05 mm. The specimen thus obtained was magnetized by applying an external magnetic field of 50 KOe to measure the flow value at room temperature (25 ° C). A flowmeter manufactured by Toyo Jiki Kogyo Co. ltd. was made and equipped with an iron core coil was used to obtain the flux value. The flux value thus obtained was designated A ₂₅ .

The magnetized specimen thus obtained was maintained at 200 ° C for a period of 120 minutes. The heating, which was held for a period of 120 minutes, was carried out in an oil bath filled with silicone oil. The temperature of the oil bath has been precisely controlled so that the fluctuation in temperature can fall in the range of ± 0.1 ° C. The specimen taken out of the oil bath was sufficiently cooled at room temperature to measure the flow value again using the above-mentioned flowmeter. The flux value thus obtained was designated A ₂₀₀ . The irreversible demagnetization was calculated using the observed A ₂₅ and A ₂₀₀ according to the following equation: Irreversible demagnetization (200 ° C) [%] = 100 × (A 200 - A 25 ) / A 25

(2) measurement of irreversible Degaussing at 160 ° C

The same procedure as described in the measurement of irreversible demagnetization at 200 ° C above was carried out to obtain observed values A ₂₅ and A ₁₆₀ except for forming the specimen in such a manner that the permeability coefficient (Pc) was obtained. 3 is similar to the example which is in the example of Japanese Patent Publication No. 4-116144 and for heating the specimen in the oil bath at 160 ° C for a period of 120 minutes. Thus, irreversible demagnetization was calculated according to the above equation.

(3) Magnetization measurement and temperature coeficients of coercive force

After magnetization of the specimen by application of an external magnetic field of 50 KOe, the magnetization measurements at room temperature became RT; 25 ° C performed using a Vibrierproben magnetometer. The temperature coefficient of the coercive force was calculated according to the following equation. Coefficient of Temperature Coefficient (% / ° C) = 100 × (B 1 - B 0 ) / B 0 / (160 - 25)

Where B _{0 is} the coercive force at room temperature, and B ₁ is the coercive force obtained at 160 ° C using the same vibrating sample magnetometer.

(4) Measurement of oxidation resistance

The Progressive formation of rust was by execution of a Pressure cook test (PCT) measured. In particular, the specimen was in a test chamber available from Tabai Espec Corp. was produced, at 120 ° C, 2 atm, and 100% RH (saturated Condition) for a duration of 100 hours, and the generation of rust was visually observed.

As shown in the results in Table 1 were permanent magnet alloys, which have an irreversible demagnetization (200 ° C) of -3% (see for example Table 1a). With reference to Table 1, the irreversible demagnetization (160 ° C) for the alloy a -0.7%, a value which is very close to 0%. Thus it can be understood be that a high magnetic force is achieved for the alloy, even when used at high temperatures.

Under Reference to the manufacturing conditions can be clearly seen By comparing the alloy a with the alloy b, that the irreversible demagnetization can be reduced by performing heat treatment at the cast bar. Furthermore, by comparing the results for the Alloys a, c and d, the coercive force can be improved and The irreversible demagnetization can be achieved by quenching the sintered Alloy reduced from a temperature of at least 700 ° C or higher become.

Examples 2 to 16 and Comparative Examples 1 to 6

Sintered goods were manufactured under the same manufacturing conditions as those which for the Alloy a used in Example 1, except for the exchange the composition of the alloys as shown in Table 2. The Characteristics of the sintered magnets thus obtained were found in the same manner as described in Example 1, and the results were given in Table 2.

As shown in Table 3, the permanent magnet alloys of Examples 2 to 16, in which FIG chemically both Dy and Tb are incorporated, all a small irreversible demagnetization at 200 ° C, and the irreversible demagnetization at 160 ° C is also very close to 0%. Further, it can be seen that not only do they have a low coercive force temperature coefficient, but they also show excellent oxidation resistance.

in the Contrary to the permanent magnet alloys of the above examples is the irreversible demagnetization at 200 ° C for Comparative Example 1, in which neither Dy nor Tb added is as big as -95%, the one for Comparative Example 2, which does not contain Tb and 0.5 at.% Dy, is -95%, and that for Comparative Example 4, which contains no Dy and 0.5% atomic Tb, is -91%. It can be understood be that these permanent magnet alloys completely their lose magnetic force when heated to 200 ° C. This means, that the infliction from Dy alone or Tb alone has no effect on the irreversible Degaussing at 200 ° C Has. Although the infliction by Dy alone in a big one Amount, as shown in Comparative Example 3, the irreversible demagnetization reduced to a certain extent, the effect is not sufficient. With reference to Comparative Example 5, the oxidation resistance is inferior, because the content of C falls below the range, which is specified in the present invention. The alloy of Comparative Example 6 contains 3.0 at.% Of Tb, but no Dy. It can be seen that though one preferred heat resistance is obtained, the irreversible demagnetization at 200 ° C so small like -30 % is.

1 Fig. 10 is a graph showing how the values of irreversible demagnetization at 200 ° C are affected by the contents of Dy and Tb; all the magnets given in Table 2 are plotted in the diagram, the abscissa showing the content of Dy (at.%) and the ordinate the content of Tb (at.%). The numbers, which in 1 are given, each show the irreversible demagnetization at 200 ° C for the plotted values.

With reference to 1 It can be understood that a maximum value (one point as close as possible at 0%) in irreversible demagnetization at 200 ° C for the range which is by 2 to 3 at.% Dy and 0.3 to 1.5 at.% Tb is defined exists. In particular, the straight lines indicated by numerals (1), (2), (3), (4), (5) and (6) define the areas having a certain content of Dy and Tb and the area which is one irreversible demagnetization at 200 ° C in the range of 0 to -20, can be defined by crossing points A, B, C, and D. Similarly, the area giving an irreversible demagnetization at 200 ° C in the range of 0 to -15% may be defined by the crossing points B, C, H, E, F and G. The straight lines (1) to (6) can be expressed by the following equations:
Line (1): Dy = 0.3
Line (2): Tb + Dy = 0.5
Line (3): Tb = 0.1
Line (4): Tb = 0.1 Dy
Line (5): Tb = 0.8 Dy
Line (6): Tb + Dy = 5.0

The coordinates (Dy at.%, Tb at.%) From points A to H are obtained as follows:
Point A (0,3, 4,7)
Point B (0,3, 0,2)
Point C (0,4, 0,1)
Point D (4,9, 0,1)
Point E (4,5, 0,5)
Point F (2,8, 2,2)
Point G (0,3, 0,24)
Point N (1,0, 0,1)

With reference to the 2 and 3 , shows 2 the observed irreversible demagnetization values at various temperatures for the magnet, which has the highest heat resistance among the magnets disclosed in Japanese Patent Publication No. 4-116144 as in Example 24 thereof and Example 2 according to the present invention, in which the examples are each shaped such that the permeability coefficient (Pc) is 3 and magnetized by using an external magnetic field of 50 KOe. Similar is 3 a diagram showing the observed irreversible demagnetization values similar to those observed in 2 are shown, except that the specimens are shaped to give a permeability coefficient (Pc) of 1. The magnet of Example 24 disclosed in Japanese Patent Publication No. 4-116144 (hereinafter referred to as "of fendened magnet ") has a composition expressed by 9 Nd - 9 Dy - 59 Fe - 15 Co - 1 B - 7 C and an irreversible demagnetization at 160 ° C at Pc = 3, according to the disclosure.

With reference to 2 are the values of irreversible demagnetization at 160 ° C for the specimens shaped to give Pc = 3, -1.0% (disclosed magnet) and -0.7% (Example 2 of the present invention); that is, the difference between them is not that big. However, as for the values of irreversible demagnetization at 200 ° C, the value of the magnet according to Example 2 of the present invention is improved to -1.9%, which can be discriminated against the value of -12.9% for the disclosed magnet. This tendency can be seen more clearly from the specimens shaped to give Pc = 1, as in 3 shown. In particular, at Pc = 1, the values of irreversible demagnetization at 160 ° C for the disclosed magnet become -9.4%, and that for the magnet according to Example 2 of the present invention is improved to -1.7%; moreover, the value of the irreversible demagnetization at 200 ° C for the disclosed magnet is -22.3%, and that for the magnet according to Example 2 of the present invention is remarkably improved to -4%.

As detailed above, the present invention provides a permanent magnet alloy which has superior heat resistance and oxidation resistance never in the field of R-Fe (Co) -B based magnets have been achieved. Accordingly, the present sees Invention materials which have excellent magnetic properties at low cost, which have advantages in applications which at elevated Temperatures are usable, can be installed.

Claims (9)

A permanent magnet alloy having improved thermal resistance, which has the following in atomic percent (at.%): 0.1 to 15 at.% C, 0.5 to 15 at.% B, provided that C and B total 2 to 30 at.% include; 40 at.% Or less Co (excluding zero percent), 0.3 to 4.9 at.% Dy, 0.1 to 4.7 at.% Tb, provided that Dy and Tb in a total amount of 0.5 up to 5 at.% are present; 8 to 20 at.% R, wherein R represents at least one member selected from the group consisting of: Nd, Pr, Ce, La, Y, Gd, Ho, Er and Tm; the balance being Fe and unavoidable incidental impurities; Further, the irreversible demagnetization (at 200 ° C) in the following equation (1) is in the range of 0% to -20%, wherein iHc is 13 KOe or higher: Irreversible demagnetization (at 200 ° C) = 100 × (A 200 - A 25 ) / A 25 (1) wherein A ₂₅ represents a flux value of a magnet measured at room temperature (25 ° C) on a sample prepared in a shape such that its permeance coefficient Pc is 1, being magnetized at 50 KOe; and A ₂₀₀ represents a flux value of a magnet measured on the same sample exposed to the measurement of A ₂₅ , the sample being held at 200 ° C for 120 minutes and then cooled to room temperature (25 ° C) for the measurement. A permanent magnet alloy according to claim 1, wherein the content (at.%) Of Dy and Tb as a whole is as shown by the points B, C, H, E, F and G in FIG 1 fall within the defined range and wherein the irreversible demagnetization at 200 ° C in the range of 0% to -15%. A permanent magnet alloy according to claim 1, wherein said irreversible demagnetization (at 200 ° C) is in a range of 0% to -5%. Permanent magnet alloy with improved thermal resistance according to claim 1, where the ratio of Tb (at%) / Dy (at%) ranges from 0.1 to 0.8. Permanent magnet alloy with improved thermal resistance according to one of claims 1 to 4, wherein the content of C is in the range of 1 to 10 at.%. Permanent magnet alloy with improved thermal resistance according to one of the claims 1 to 5, wherein R alone is Nd or a combination of Nd and Pr. A method for producing a permanent magnet alloy with improved thermal resistance according to one of the preceding claims, the method comprising the steps of: melting and to water each of the raw materials of the alloying elements, exposing themselves resulting alloy pulverization, compression molding of the resulting powder and sintering the molding under inert gas atmosphere in one Temperature range from 1000 to 1200 ° C, around a sintered magnetic alloy to obtain, characterized in that the alloy before the Pulverization thermally in an inert gas atmosphere at a Temperature of 600 ° C or higher is treated. Process for producing a permanent magnet alloy according to claim 7, the method further comprising: after sintering of the molded article under an inert gas atmosphere in a temperature range from 1000 to 1200 ° C gradually cooling down of the sintered body from the sintering temperature to a temperature range of 600 to 900 ° C, followed from a cooling process. Process for producing a permanent magnet alloy according to claim 7 or 8, wherein a part of the raw material C is added during melting will and the rest during the pulverization of the alloy is added.