Abstract:
An R--T--M alloy material, wherein R is at least one rare earth metal including Y, T is Fe or an Fe component partially replaced by Co or Ni, M is B or a B component partially replaced by C as primary components is prepared by heating the alloy at a temperature from room temperature to a specific temperature of less than 500° C. in a non-oxidizing atmosphere and holding it at the given temperature, if necessary; performing hydrogenation by holding the alloy in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas at a specific temperature in the range of 500-1,000° C.; medial annealing the alloy by holding the R--T--M alloy after the hydrogenation step in an inert gas atmosphere at a specific temperature in the range of 500-1,000° C.; and dehydrogenating the alloy by holding the alloy in a vacuum of less than 1 Torr for dehydrogenation, and then cooling the alloy.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a rare earth magnetic powder having high magnetic anisotropy, and to a method for manufacturing a rare earth magnet using the rare earth magnetic powder. 
     2. Description of the Background 
     A method for manufacturing a rare earth magnetic powder is known as described in, for example, Japanese Patent Laid-Open No. 2-04901, in which an alloy material (hereinafter referred to as an R--T--M alloy material) containing at least one rare earth metal including Y (hereinafter referred to as R), Fe or an Fe component, which is partly replaced by Co or Ni (hereinafter referred to as T), and B or a B component, which is partly replaced by C (hereinafter referred to as M) as primary components, and an alloy material (hereinafter referred to as an R--T--M--A alloy material) comprising the R--T--M alloy material and 0.001-5 atomic percent of at least one element selected from the group consisting of Si, Ga, Zr, Nb, Mo, Hf, Ta, W, Al, Ti and V (hereinafter referred to as A) is homogenized, if necessary, in an Ar gas atmosphere at a temperature of 600-1,200° C. The alloy material is heated 500-1,000° C. in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas and held at the specific temperature for a hydrogenation treatment. The alloy is dehydrogenated at a temperature of 500-1,000° C. in a vacuum, cooled and then pulverized. 
     In recent years, the demand for rare earth magnetic powders having higher magnetic anisotropy than conventional powders has increased in order to achieve further miniaturization and higher performance of magnetic parts in the electric and electronic fields. No rare earth magnetic powder having sufficiently high magnetic anisotropy for these purposes has yet been obtained. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a method of manufacturing a rare earth magnetic powder having higher magnetic anisotropy than conventional powders. 
     Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a method of producing a rare earth magnetic powder in which: 
     (a) A rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having a higher magnetic anisotropy can be produced by heating the R--T--M or R--T--M--A alloy material from room temperature to a specific temperature of less than 500° C. in a non-oxidizing atmosphere and holding it at the specific temperature, performing a hydrogenation treatment by holding the R--T--M or R--T--M--A alloy material at a specific temperature in a range of 500-1,000° C. in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas to promote phase transformation by hydrogenation, performing medial annealing by holding the R--T--M or R--T--M--A alloy material after the hydrogenation treatment at a specific temperature in a range of 500-1,000° C. in an inert gas atmosphere, and performing dehydrogenation by holding the R--T--M or R--T--M--A alloy material at a specific temperature in a range of 500-1,000° C. in a vacuum at a final pressure of less than 1 Torr to promote phase transformation by forcibly causing the release of hydrogen from the R--T--M alloy material. 
     (b) It is preferred that the R--T--M or R--T--M--A alloy material be homogenized by holding it at a temperature of 600-1,200° C. in a vacuum or under an Ar gas atmosphere. 
     (c) It is preferred that the medial annealing at a given temperature in a range of 500-1,000° C. of the R--T--M or R--T--M--A alloy material after the hydrogenation treatment be performed in an inert gas atmosphere with a pressure in a range of 0.5-11 atm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein: 
     FIG. 1 is a schematic illustration of a heat treatment pattern of a method of manufacturing a rare earth magnetic powder of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention has been completed based on these findings. Accordingly, one(1) embodiment of the invention is a method for manufacturing a rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having high magnetic anisotropy, comprising: 
     heating an R--T--M alloy material from room temperature to a specific temperature of less than 500° C. in a non-oxidizing atmosphere and optionally holding the alloy at this temperature; 
     performing a hydrogenation treatment on the R--T--M alloy material by holding the R--T--M alloy material at a specific temperature in the range of 500-1,000° C. in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas to promote phase transformation of the R--T--M alloy material by hydrogenation; 
     performing medial annealing by holding the R--T--M alloy material after the hydrogenation treatment at a specific temperature in the range of 500-1,000° C. in an inert gas atmosphere; and 
     performing dehydrogenation by holding the R--T--M alloy material at a specific temperature in the range of 500-1,000° C. in a vacuum of a final pressure of less than 1 Torr to promote phase transformation in the R--T--M alloy material by forcibly releasing hydrogen from the R--T--M alloy material, followed by cooling and pulverizing. 
     In a second embodiment(2) of the invention a rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having high magnetic anisotropy is manufactured, by: 
     heating an R--T--M alloy material, which is homogenized at a temperature of 600-1,200° C. in a vacuum or Ar gas atmosphere, from room temperature to a specific temperature of less than 500° C. in a non-oxidizing atmosphere and optionally holding the alloy at this temperature; 
     performing hydrogenation of the R--T--M alloy material by holding the R--T--M alloy material at a specific temperature in a range of 500-1,000° C. in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas to promote phase transformation of the R--T--M alloy material by hydrogenation; 
     performing medial annealing by holding the R--T--M alloy material after the hydrogenation treatment at a specific temperature in the range of 500-1,000° C. in an inert gas atmosphere; and 
     performing dehydrogenation by holding the R--T--M alloy material at a specific temperature in the range of 500-1,000° C. in a vacuum of a final pressure of less than 1 Torr to promote phase transformation in the R--T--M alloy material by forcibly releasing hydrogen from the R--T--M alloy material, followed by cooling and pulverizing. 
     In a third embodiment(3) of the invention a rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having high magnetic anisotropy is manufactured by: 
     heating an R--T--M--A alloy material from room temperature to a specific temperature of less than 500° C. in a non-oxidizing atmosphere and optionally holding the alloy at this temperature; 
     performing hydrogenation of the R--T--M--A alloy material by holding the R--T--M--A alloy material at a specific temperature in the range of 500-1,000° C. in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas to promote phase transformation of the R--T--M--A alloy material by hydrogenation; 
     performing medial annealing by holding the R--T--M--A alloy material after the hydrogenation treatment at a specific temperature in the range of 500-1,000° C. in an inert gas atmosphere; and 
     performing dehydrogenation by holding the R--T--M--A alloy material at a specific temperature in the range of 500-1,000° C. in a vacuum of a final pressure of less than 1 Torr to promote phase transformation in the R--T--M--A alloy material by forcibly releasing hydrogen from the R--T--M--A alloy material, followed by cooling and pulverizing; 
     In a fourth embodiment (4) of the invention a rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having high magnetic anisotropy is manufactured by; 
     heating the R--T--M--A alloy material, which is homogenized at a temperature of 600-1,200° C. in a vacuum or Ar gas atmosphere, from room temperature to a specific temperature of less than 500° C. in a non-oxidizing atmosphere and optionally holding the alloy at this temperature; 
     performing hydrogenation of the R--T--M--A alloy material by holding the R--T--M--A alloy material at a specific temperature in the range of 500-1,000° C. in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas to promote phase transformation of the R--T--M--A alloy material by hydrogenation; 
     performing medial annealing by holding the R--T--M--A alloy material after the hydrogenation treatment at a specific temperature in the range of 500-1,000° C. in an inert gas atmosphere; and 
     performing dehydrogenation by holding the R--T--M--A alloy material at a specific temperature in the range of 500-1,000° C. in a vacuum of a final pressure of less than 1 Torr to promote phase transformation in the R--T--M--A alloy material by forcibly releasing hydrogen from the R--T--M--A alloy material, followed by cooling and pulverizing. 
     In a fifth embodiment (5) of the invention a rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having high magnetic anisotropy described in embodiments (1)-(4) is subjected to medial annealing in an inert gas atmosphere an atmosphere having a pressure in a range of 0.5-11 atm. 
     In one embodiment of manufacturing a rare earth magnet, a rare earth magnetic powder, which is produced by one of the method embodiments (1)-(5) of the present invention and has a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and high magnetic anisotropy, is combined with an organic binder or a metallic binder, or by hot-pressing or hot-isostatic pressing the powder at a temperature of 600-900° C. 
     In another embodiment of manufacture of a rare earth magnet, a green compact of an embodiment of a rare earth magnetic powder (1)-(5) above is prepared, and then the green compact is hot-pressed or hot-isostatic pressed at a temperature of 600-900° C. 
     The method for manufacturing the rare earth magnetic powder of the present invention has, as a significant aspect, a medial annealing step in which the alloy material is held at a specific temperature in the range of 500-1,000° C. in an inert gas atmosphere having a pressure of 0.5-11 atm between the hydrogenation step and the dehydrogenation step. 
     The medial annealing step after the hydrogenation treatment causes a change in the texture in the alloy in which the phases are decomposed by occlusion of hydrogen in the hydrogenation treatment, and the following dehydrogenation treatment forms a rare earth magnetic powder having fine recrystallization textures in which the c axis in the R 2  T 14  M intermetallic compound phase is further oriented in one direction. Thus, the rare earth magnetic powder has a higher magnetic anisotropy and coercive force than rare earth magnetic powders which are produced by conventional methods. 
     The method for making the rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having high magnetic anisotropy in accordance with the present invention is now described with reference to the drawing. 
     FIG. 1 shows a heat treatment pattern in the method for manufacturing the rare earth magnetic powder having a recrystallization texture of fine R 2  T 14  M intermetallic compound phases and having high magnetic anisotropy of the present invention. That is, the relationship between the temperature, the time and the atmosphere in the heating step, the hydrogenation step, the medial annealing step, and the dehydrogenation step, and the cooling step is shown. In FIG. 1, numerals 1, 2, 3, 4 and 5 represent the heating step, the hydrogenation step, the medial annealing step, and the dehydrogenation step, and the cooling step, respectively. 
     In the heating step 1, the R--T--M or R--T--M--A alloy material is heated to a temperature from room temperature to a specific temperature of less than 500° C. in a non-oxidizing atmosphere (for example, a hydrogen gas atmosphere, a vacuum, or an inert gas atmosphere), or is heated and held at a specific temperature x (for example, 100° C.) of less than 500° C. and then reheated. 
     In the hydrogenation step 2, the R--T--M or R--TM--A alloy material is held in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas at 500-1,000° C. to promote phase transformation in the alloy material by hydrogenation. 
     In the medial annealing step 3, the R--T--M or R--T--M--A alloy material after the hydrogenation treatment is held in an inert gas atmosphere, preferably, at a pressure of 0.5-11 atm, and more preferably 0.5-2 atm, at a specific temperature in a range of 500-1,000° C., preferably, 650-950° C., and more preferably 750-900° C., for a specified time. The medial annealing step 3 is most preferably performed in an Ar gas atmosphere with a pressure of 0.5-2 atm at a temperature of 750-900° C. for 1-30 minutes. The introduction of the inert gas in the medial annealing step 3 is preferred as a substitute for the hydrogen gas atmosphere or the mixed gas atmospheres of hydrogen and an inert gas in the hydrogenation step 2. The medial annealing step 3 is the most characteristic step in the present invention. When the medial annealing step 3 is performed after the hydrogenation step, the texture of the alloy in which the phase is decomposed by hydrogenation changes. Upon the subsequent dehydrogenation treatment, a rare earth magnetic powder having a fine recrystallization texture, in which the c axis of the R 2  Tm 14  M intermetallic compound is further oriented in one direction, is obtained. Thus, the magnetic powder has higher magnetic anisotropy and coercive force than the rare earth magnetic powders produced by conventional processes. 
     In the dehydrogenation step 4, the R--T--M or R--T--M--A alloy is held at a temperature in the range of 500-1,000° C. in a vacuum with a final pressure of less than 1 Torr to forcibly release hydrogen which is not released in the medial annealing step 3. After the dehydrogenation step 4, the alloy material is cooled to room temperature in the cooling step 5 using inert gas (Ar gas). 
     Having now generally described the invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purpose of illustration only and are not intended to be limiting unless otherwise specified. 
     EXAMPLE 1 
     Melts were prepared in a high frequency vacuum-melting furnace and cast to produce ingots a to j of R--T--M or R--T--M--A alloy materials having the compositions shown in Table 1. Each of the ingots of the resulting R--T--M or R--T--M--A alloy materials was shaped into a block with a side of 10 mm or less. Ingot blocks were heated from room temperature to specific temperatures or heated and held at the specific temperatures shown in Tables 2-5. The blocks were subjected to hydrogenation treatment, to medial annealing, and to dehydrogenation under the conditions shown in Tables 2-5, forcibly cooled to room temperature with Ar gas and then pulverized to produce a rare earth magnetic powder having a particle size of 300 μm or less. Invention Methods 1-28 of the present invention, Comparative Methods 1-2 for comparison, and Conventional Methods 1-10 were conducted in such a manner. 
     To the rare earth magnetic powder of each of Invention Methods 1-28, Comparative Methods 1-2 and Conventional Methods 1-10, 3 percent by weight of epoxy resin was added. The materials were kneaded and compressed in a magnetic field of 20 kOe to form green compacts. The green compacts were thermoset in an oven at 150° C. for 2 hours to form bonded magnets with a density of 6.0-6.1 g /cm 3 . The magnetic characteristics of the resulting bonded magnets are shown in Tables 6-9. 
     Anisotropic green compacts were prepared in a magnetic field from the rare earth magnetic powders of Invention Methods 1-28, Comparative Methods 1-2 and Conventional Methods 1-10, placed into a hot press, and hot-pressed at a temperature of 750° C. and a pressure 0.6 Ton/cm 2  for 1 minute in Ar gas so that the green compacts were compressed in the direction in which the magnetic field is applied. Hot press magnets with densities of 7.5-7.7 g/cm 3  were prepared by quenching the compressed compacts. The magnetic characteristics of the resulting hot press magnets are shown in Tables 6-9. 
     
                       TABLE 1______________________________________Type  Composition (atomic %) (the balance is Fe)______________________________________Ingot  a Nd:12.0%, Co:16.5%, B:6.2%, Zr:0.2%, Al:0.5%  b Nd:11.0%, Dy:1.2%, Pr:0.2%, Co:5.7%, B:6.0%, Zr:0.1%,   Ti:0.3%  c Nd:12.0%, Pr:0.3%, Co:20.0%, B:6.5%, C:0.05%, Zr:0.2%,   Ga:0.5%  d Nd:12.0%, Dy:0.6%, B:7.0%, Hf:0.1%, Nb:0.2%, Si:0.1%  e Nb:6.5%, Pr:6.0%. Co:18.7%. B:5.8%, Hf:0.1%, Ta:0.2%,   Ga:0.5%  f Nd:11.5%, Dy:0.6%, Pr:0.3%, Co:9.0%, B:6.0%, Zr:0.1%,   Ga:0.3%  g Nd:12.3%, Ce:0.1%, Pr:0.2%, Co:16.5%, B:6.2%, Zr:0.5%,   Ga:0.5%  h Nd:14.1%, La:0.1%, Pr:0.2%; Co:20.1%, B:6.5%, Nb:0.5%,   Ga:1.0%  i Nd:12.1%, Pr:0.5%, Co:18.0%, B:6.0%, C:0.1%  j Nd:11.2%, Dy:0.3%, Pr:0.3%, Co:11.7%, Ni:1.0%, B:5.5%,   C:0.2%, Zr:0.05%, Mo:0.2%, Al:0.7%______________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________    Heating   Hydrogen occulusion                         Medial annealing                                    Dehydrogenation    Atmosphere from              H.sub.2                 Holding                     Holding                         Ar Holding                                Holding                                    Final                                        Holding                                            Holding    room temp. to less press temp. time press temp. time press temp. time  Type Ingot than 500° C. (atm) (° C.) (min.) (atm)                                            (° C.) (min.)                                            (Torr) (° C.)                                            (hr.)__________________________________________________________________________Invention&#39;s  Method  1 a Vacuum from room 1 850  20 1 850 10 0.98 830 40  2 b temp. to 100° C., and 5 850  20 1 850 10 0.98 830 40                                               H.sub.2 of 1 atm.                                            from    100° C. to 500° C.  3 c Vacuum from room 1 830  60 1.2 840  5 0.05 820 50  4 d temp. to 200° C., and 1 830  60 1.2 840  5 0.05 820 50                                             5 e H.sub.2 1 atm. from                                            1 830  60 1.2 840  5 0.5                                            820 50    200° C. to 500° C.  6 f Vacuum from room 2 850 120 1 850 10 0.05 850 60  7 g temp. to 100° C., and 1 850 120 2 850 10 0.2 850 60  8 h H.sub.2 of 1 atm. from 1 850 120 2 850 10 0.02 850 60  9 i 100° C. to 500° C. 1 850 120 1 850 10 0.2 850 60                                             10  j  1.5 850 120 1                                            850 10 0.001 850__________________________________________________________________________                                            60 
    
     
                                           TABLE 3__________________________________________________________________________    Heating   Hydrogen occulusion                         Medial annealing                                    Dehydrogenation    Atmosphere from              H.sub.2                 Holding                     Holding                         Ar Holding                                Holding                                    Final                                        Holding                                            Holding    room temp. to less press temp. time press temp. time press temp. time  Type Ingot than 500° C. (atm) (° C.) (min.) (atm)                                            (° C.) (min.)                                            (Torr) (° C.)                                            (hr.)__________________________________________________________________________Invention&#39;s  Method  11 a Vacuum from room 1 820 30 1 820 10 0.05 820 40  12 b temp. to 100° C., 3 880 60 1 850 10 0.01 850 30  13 c hydrogen of 1 atm at 0.8 860 10 2 860  5 0.02 840 50  14 d 100° C. for 30 min., 2 800 30 2 820 20 0.02 830 60  15 e and heating in H.sub.2 of 1 920 120 1 850 10 0.01 800 60    1 atm to less than    500° C.  16 f Heating in Ar from 2 800 30 2 820 20 0.005 770 60  17 g room temp. to 0.5 890 60 3 770 60 0.01 800 50  18 h 200° C., Ar at 1 840 60 1 840 20 0.002 770 60  19 i 200° C. for 60 min., 0.7 780 10 0.5 850 10 0.50 850 30                                             20 j and heating in Ar                                            to 1 800 120  0.8 800 40                                            0.1 800 50    less than 500° C.__________________________________________________________________________ 
    
     
                                           TABLE 4__________________________________________________________________________    Heating   Hydrogen occulusion                         Medial annealing                                    Dehydrogenation    Atmosphere from              H.sub.2                 Holding                     Holding                         Ar Holding                                Holding                                    Final                                        Holding                                            Holding    room temp. to less press temp. time press temp. time press temp. time  Type Ingot than 500° C. (atm) (° C.) (min.) (atm)                                            (° C.) (min.)                                            (Torr) (° C.)                                            (hr.)__________________________________________________________________________Invention&#39;s  Method  21 a Vacuum from room 1 830 60 0.3 840 5 0.05 820 50  22 b temp. to 200° C.,  1 830 60 0.5 840 5 0.05 820 50  23 c H.sub.2 of 1 atm. 1 830 60 5.0 840 5 0.05 820 50  24 d at 200° C. for 1 830 60 11.0 840 5 0.05 820 50  25 e 30 min., and 1 830 60 1.2 840 300 0.05 820 50  26 f H.sub.2 of 1 atm. 1 830 60 1.2 840 30 0.05 820 50  27 g from 200° C. 1 830 60 1.2 840 5 0.05 820 50  28 h to 500° C. 1 830 60 1.2 840 0.5 0.05 820 50  Comparative  Method  1 i  1 830 60 13.0* 840 5 0.05 820 50  2 j  1 830 60 1.2 1050* 0.5 0.05 820 50__________________________________________________________________________ 
    
     
                                           TABLE 5__________________________________________________________________________    Heating   Hydrogen occulusion                         Medial annealing                                    Dehydrogenation    Atmosphere from              H.sub.2                 Holding                     Holding                         Ar Holding                                Holding                                    Final                                        Holding                                            Holding    room temp. to less press temp. time press temp. time press temp. time  Type Ingot than 500° C. (atm) (° C.) (min.) (atm)                                            (° C.) (min.)                                            (Torr) (° C.)                                            (hr.)__________________________________________________________________________Conventional  Method  1 a Vacuum from room 1 850  20 -- -- -- 0.98 830 40  2 b temp. to 100° C., and 5 850  20 -- -- -- 0.98 830 40                                               H.sub.2 of 1 atm.                                            from    10° C. to 500° C.  3 c Vacuum from room 1 830  60 -- -- -- 0.05 820 50  4 d temp. to 200° C., and 1 830  60 -- -- -- 0.05 820 50                                             5 e H.sub.2 of 1 atm.                                            from 1 830  60 -- -- --                                            0.5 820 50    200° C. to 500° C.  6 f Vacuum from room 2 850 120 -- -- -- 0.05 850 60  7 g temp. to 100° C., and 1 850 120 -- -- -- 0.2 850 60  8 h H.sub.2 of 1 atm. from 1 850 120 -- -- -- 0.02 850 60  9 i 100° C. to 500° C. 1 850 120 -- -- -- 0.2 850 60                                             10  j  1.5 850 120 --                                            -- -- 0.001 850 60__________________________________________________________________________ 
    
     
                       TABLE 6______________________________________Bonded Magnet       Hot pressed magnet   Br      iHc    BHmax  Br    iHc   BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Invention&#39;s  Method  1 10.1 11.0 22.1 12.6 10.7 36.1  2 8.9 25.4 18.3 11.1 25.1 28.6  3 10.2 11.7 23.0 12.8 11.4 37.6  4 9.1 20.3 18.6 11.4 18.7 30.2  5 9.8 10.7 20.7 12.3 10.3 33.8  6 9.4 21.6 20.3 11.8 20.3 33.0  7 10.1 11.6 22.5 12.6 11.7 35.1  8 9.7 13.1 20.2 12.1 12.8 33.5  9 9.8  7.2 19.4 12.2  7.0 32.0  10  9.4 16.3 19.8 11.8 15.6 32.7______________________________________ 
    
     
                       TABLE 7______________________________________Bonded Magnet       Hot pressed magnet   Br      iHc    BHmax  Br    iHc   BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Invention&#39;s  Method  11 10.0  11.4 21.8 12.5 11.3 34.3  12 9.1 24.6 19.2 11.4 24.1 30.0  13 10.0  11.8 22.0 12.5 11.7 34.7  14 9.2 19.8 19.7 11.5 19.0 29.7  15 9.6 10.7 20.1 12.0 10.8 32.8  16 9.6 21.6 21.2 12.0 20.5 34.0  17 9.7 12.7 20.6 12.2 12.5 33.8  18 9.7 13.5 20.7 12.1 13.2 33.6  19 9.7  7.0 18.8 12.1  7.1 32.1  20 9.2 17.5 18.7 11.5 17.0 30.2______________________________________ 
    
     
                       TABLE 8______________________________________Bonded magnet       Hot pressed magnet   Br      iHc    BHmax  Br    iHc   BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Invention&#39;s  Method  21 9.7 11.4 20.4 12.1 11.0 32.2  22 10.1 12.0 22.1 12.7 11.6 35.5  23 10.0 12.1 21.6 12.5 11.9 34.6  24 9.9 12.3 20.8 12.4 12.1 35.1  25 9.6 5.9 18.6 12.0 5.5 27.1  26 9.9 8.7 20.8 12.3 8.6 32.2  27 10.2 12.0 23.1 12.8 11.4 36.2  28 9.8 12.4 20.6 12.3 12.1 33.7  Comparative  Method   1 8.8 8.3 13.7 10.8 7.7 17.6   2 3.6 1.4 &lt;3 5.3 0.8 &lt;3______________________________________ 
    
     
                       TABLE 9______________________________________Bonded magnet       Hot pressed Magnet   Br      iHc    BHmax  Br    iHc   BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Conventional  Method  1 9.6 11.1 18.8 12.0 10.7 30.4  2 7.6 24.3 13.2 9.5 23.5 20.2  3 9.3 11.9 18.5 11.5 12.2 29.7  4 7.2 20.1 11.8 9.0 19.3 18.0  5 9.4 10.1 18.0 11.7 10.2 29.5  6 6.5 22.3  9.2 8.1 21.8 13.3  7 9.5 11.8 19.7 11.8 11.3 30.0  8 9.2 12.6 18.1 11.4 12.4 28.6  9 8.7  8.4 15.5 11.0  8.3 25.4  10  7.0 17.0 10.8 8.7 17.1 16.7______________________________________ 
    
     The results presented in Tables 1-9 demonstrate that the magnetic characteristics of the bonded magnets prepared from the rare earth magnetic powders of Invention Methods 1-28, the processing including a medial annealing step, are superior to those of the bonded magnets prepared from the rare earth magnetic powders of Conventional Methods 1-10 not including medial annealing. In contrast, the bonded magnets prepared from the rare earth magnetic powders of Comparative Methods 1 and 2, which are out of the range of the present invention, have low magnetic characteristics. 
     The results also demonstrate that the magnetic characteristics of the hot pressed magnets prepared from the rare earth magnetic powders of Invention Methods 1-28, whose processing included medial annealing, are superior to those of the hot pressed magnets prepared from the rare earth magnetic powders of Conventional Methods 1-10 not including medial annealing. In contrast, the hot pressed magnets prepared from the rare earth magnetic powders of Comparative Methods 1 and 2, which are out of the range of the present invention, have low magnetic characteristics. 
     EXAMPLE 2 
     The ingots a to j, which were prepared in Example 1, of the R--T--M or R--T--M--A alloy materials having the compositions shown in Table 1 were subjected to homogenization under the conditions shown in Table 10, and the resulting homogenized ingots A-J were pulverized blocks or powders having the sizes shown in Table 10. These blocks and powders were subjected to heating, hydrogenation, medial annealing, dehydrogenation, and cooling as in Invention Methods 1-28, Comparative Methods 1-2, and Conventional Methods 1-10 in Example 1, and pulverized powders of a particle size of 300 μm or less. The rare earth magnetic powders of Invention Methods 29-56, Comparative Methods 3-4, and Conventional Methods 11-20 were prepared in such a manner. Bonded magnets and hot pressed magnets were prepared from the resulting rare earth magnetic powders as described in Example 1. The magnetic characteristics of the resulting bonded magnets and hot pressed magnets are shown in Tables 11-14. 
     
                       TABLE 10______________________________________    Conditions of homogenization                       Size of   Used   Holding   Holding        block or  Type ingot temp. (° C.) time (hr.) Atmosphere powder______________________________________Homoge-  nized ingot  A a 1,140 20 1-atm. Ar &lt;15 mm  B b 1,120 30 Vacuum  &lt;5 mm  C c 1,130 15 1-atm. Ar  &lt;8 mm  D d 1,110 40 Vacuum &lt;500 μm  E e 1,120 30 2-atm. Ar &lt;500 μm  F f 1,140 20 1-atm. Ar &lt;10 μm  G g 1,150  5 Vacuum &lt;20 mm  H h 1,100 20 1-atm. Ar &lt;400 μm  I i 1,140 15 1-atm. Ar &lt;30 mm  J j 1,130 30 1.5-atm. Ar &lt;15 mm______________________________________ 
    
     
                       TABLE 11______________________________________ Homoge-   nized  Hydrogen Medial Dehydro-  Type ingot Heating Occlusion annealing genation______________________________________  Inven-  tion&#39;s  Method29    A        The same as Invention&#39;s Method 1 in Example 1  30 B The same as Invention&#39;s Method 2 in Example 1  31 C The same as Invention&#39;s Method 3 in Example 1  32 D The same as Invention&#39;s Method 4 in Example 1  33 E The same as Invention&#39;s Method 5 in Example 1  34 F The same as Invention&#39;s Method 6 in Example 1  35 G The same as Invention&#39;s Method 7 in Example 1  36 H The same as Invention&#39;s Method 8 in Example 1  37 I The same as Invention&#39;s Method 9 in Example 1  38 J The same as Invention&#39;s Method 10 in Example 1______________________________________ 
    
     
                       TABLE 12______________________________________ Homoge-   nized  Hydrogen Medial Dehydro-  Type ingot Heating Occlusion annealing genation______________________________________  Inven-  tion&#39;s  Method39    A        The same as Invention&#39;s Method 11 in Example 1  40 B The same as Invention&#39;s Method 12 in Example 1  41 C The same as Invention&#39;s Method 13 in Example 1  42 D The same as Invention&#39;s Method 14 in Example 1  43 E The same as Invention&#39;s Method 15 in Example 1  44 F The same as Invention&#39;s Method 16 in Example 1  45 G The same as Invention&#39;s Method 17 in Example 1  46 H The same as Invention&#39;s Method 18 in Example 1  47 I The same as Invention&#39;s Method 19 in Example 1  48 J The same as Invention&#39;s Method 20 in Example 1______________________________________ 
    
     
                       TABLE 13______________________________________ Homoge-   nized  Hydrogen Medial Dehydro-  Type ingot Heating Occlusion annealing genation______________________________________  Inven-  tion&#39;s  Method49    C        The same as Invention&#39;s Method 21 in Example 1  50 C The same as Invention&#39;s Method 22 in Example 1  51 C The same as Invention&#39;s Method 23 in Example 1  52 C The same as Invention&#39;s Method 24 in Example 1  53 C The same as Invention&#39;s Method 25 in Example 1  54 C The same as Invention&#39;s Method 26 in Example 1  55 C The same as Invention&#39;s Method 27 in Example 1  56 C The same as Invention&#39;s Method 28 in Example 1  Com-  para-  tive  Method  3 C The same as Comparative Method 1 in Example 1  4 C The same as Comparative Method 2 in Example 1______________________________________ 
    
     
                                           TABLE 14__________________________________________________________________________    Homogenized               Hydrogen                    Medial  Type ingot Heating Occlusion annealing dehydroenation__________________________________________________________________________Conventional  11    A      The same as Conventional Method 1 in Example 1  Method 12 B The same as Conventional Method 2 in Example 1   13 C The same as Conventional Method 3 in Example 1   14 D The same as Conventional Method 4 in Example 1   15 E The same as Conventional Method 5 in Example 1   16 F The same as Conventional Method 6 in Example 1   17 G The same as Conventional Method 7 in Example 1   18 H The same as Conventional Method 8 in Example 1   19 I The same as Conventional Method 9 in Example 1   20 J The same as Conventional method 10 in Example 1__________________________________________________________________________ 
    
     
                       TABLE 15______________________________________Bonded magnet       Hot pressed magnet   Br      iHc    BHmax  Br    iHc   BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Invention&#39;s  Method  29 10.4 11.4 23.1 13.1 11.1 38.8  30 9.3 31.6 19.8 11.7 30.5 31.5  31 10.4 12.6 24.0 13.2 12.6 40.1  32 9.5 24.3 20.6 12.0 23.7 33.6  33 10.1 10.6 22.7 12.7 10.2 35.4  34 9.6 21.5 19.5 12.1 21.6 34.2  35 10.3 12.3 23.7 12.9 11.8 36.5  36 9.9 12.8 21.6 12.4 12.5 34.3  37 10.0  8.7 20.7 12.6  8.3 34.7  38 9.7 18.5 20.1 12.1 17.8 33.0______________________________________ 
    
     
                       TABLE 16______________________________________Bonded magnet       Hot pressed magnet   Br      iHc    BHmax  Br    iHc   BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Invention&#39;s  Method  39 10.2 12.3 23.3 12.8 12.4 36.1  40 9.4 27.5 20.2 11.8 26.4 32.5  41 10.3 12.3 23.6 13.0 12.1 37.6  42 9.5 22.1 20.5 11.9 21.6 32.5  43 9.8 10.8 20.7 12.3 10.4 34.0  44 9.9 23.7 22.0 12.5 22.8 35.4  45 10.0 13.3 22.7 12.6 13.4 35.0  46 9.9 13.1 21.6 12.4 13.0 34.7  47 9.9 8.4 20.4 12.3  8.2 32.2  48 9.4 17.3 19.1 11.8 17.1 31.1______________________________________ 
    
     
                       TABLE 17______________________________________Bonded magnet       Hot pressed magnet   Br      iHc    BHmax  Br    iHc   BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Invention&#39;s  Method  49 9.9 12.0 21.6 12.4 11.8 34.5  50 10.5 12.2 24.7 13.2 12.1 39.8  51 10.3 12.5 23.1 12.9 12.5 37.6  52 10.2 12.5 22.8 12.8 12.3 37.0  53 9.8 7.6 20.6 12.3 7.5 32.0  54 10.1 10.4 23.0 12.6 9.6 35.1  55 10.4 12.7 24.5 13.0 11.8 37.2  56 9.9 12.5 20.7 12.4 12.1 33.4  Comparative  Method  3 8.7 7.8 14.2 9.8 6.7 16.7  4 4.1 2.0 &lt;3 5.4 0.5 &lt;3______________________________________ 
    
     
                       TABLE 17______________________________________    Bonded magnet                 Hot pressed magnet      Br     iHc    BHmax  Br   iHc  BHmax  Type (kG) (kOe) (MGOe) (kG) (kOe) (MGOe)______________________________________Invention&#39;s  Method  49 9.9 12.0 21.6 12.4 11.8 34.5  50 10.5 12.2 24.7 13.2 12.1 39.8  51 10.3 12.5 23.1 12.9 12.5 37.6  52 10.2 12.5 22.8 12.8 12.3 37.0  53 9.8 7.6 20.6 12.3 7.5 32.0  54 10.1 10.4 23.0 12.6 9.6 35.1  55 10.4 12.7 24.5 13.0 11.8 37.2  56 9.9 12.5 20.7 12.4 12.1 33.4  Comparative  Method  3 8.7 7.8 14.2 9.8 6.7 16.7  4 4.1 2.0 &lt;3 5.4 0.5 &lt;3______________________________________ 
    
     The results shown in Tables 10-18 demonstrate that the magnetic characteristics of the bonded magnets prepared from the rare earth magnetic powders of Invention Methods 29-56, in which these rare earth magnetic powders were obtained by annealing, hydrogenation, medial annealing, dehydrogenation, cooling and pulverizing of the homogenized ingots A-J as in Example 1 and had sizes of 300 μm or less, are superior to those of the bonded magnets prepared from the rare earth magnetic powders of Conventional Methods 11-20 not including medial annealing. In contrast, the bonded magnets prepared from the rare earth magnetic powders of Comparative Methods 3-4, which are out of the range of the present invention, have slightly low magnetic characteristics. 
     These results also demonstrate that the magnetic characteristics of the hot pressed magnets prepared from the rare earth magnetic powders of Invention Methods 29-56 including medial annealing are superior to those of the hot pressed magnets prepared from the rare earth magnetic powders of Conventional Methods 11-20 not including medial annealing. In contrast, the hot pressed magnets prepared from the rare earth magnetic powders of Comparative Methods 3-4, which are out of the range of the present invention, have slightly low magnetic characteristics. 
     Advantages 
     It is clear from the description above that the method of the present invention for manufacturing rare earth magnetic powders, in which a medial annealing treatment is employed between a hydrogenation treatment and a dehydrogenation treatment, produces a rare earth magnetic powder having improved magnetic characteristics over rare earth magnetic powders prepared by conventional methods. Thus the present invention provides a significant industrial advantage in the technology of rare earth metal magnetic powders. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.