CN115116726A

CN115116726A - Method for producing R-T-B sintered magnet

Info

Publication number: CN115116726A
Application number: CN202210157081.0A
Authority: CN
Inventors: 野泽宣介
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2021-03-23
Filing date: 2022-02-21
Publication date: 2022-09-27
Also published as: JP2022147793A

Abstract

The invention provides a heavy rare earth RH reducing agent B _r And H _cJ A method for producing an R-T-B sintered magnet having an excellent balance. The manufacturing method comprises a step of preparing an R-T-B-based sintered magnet material (R is a rare earth element, T is at least 1 selected from the group consisting of Fe, Co, Al, Mn and Si and essentially contains Fe.), a step of preparing an RL-RH-C-M-based alloy, and a diffusion step of attaching at least a part of the RL-RH-C-M-based alloy to at least a part of the surface of the R-T-B-based sintered magnet material and heating the same, wherein the RL-RH-C-M-based alloy has an RL content of 50 to 95 mass%, an RH content of 45 to 45 mass% (including 0 mass%), and a C content of 0.1 to 0.5 mass%)Less than or equal to mass percent, and the content of M is more than or equal to 4mass percent and less than or equal to 49.9mass percent.

Description

Method for producing R-T-B sintered magnet

Technical Field

The present invention relates to a method for producing an R-T-B sintered magnet.

Background

It is known that R-T-B sintered magnets (R is a rare earth element, T is mainly Fe, and B is boron) are magnets having the highest performance among permanent magnets, and are used for various motors such as Voice Coil Motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), and motors for industrial equipment, and household electric appliances. The R-T-B sintered magnet contributes to energy saving and reduction in environmental load by making various motors and the like smaller and lighter.

R-T-B sintered magnet consisting essentially of R ₂ T ₁₄ The main phase of the B compound and a grain boundary phase located in a grain boundary portion of the main phase. R as the main phase ₂ T ₁₄ The B compound is a ferromagnetic material having high saturation magnetization and an anisotropic magnetic field, and is a key to the characteristics of R-T-B sintered magnets.

Coercive force H of R-T-B sintered magnet at high temperature _cJ (hereinafter, abbreviated as "H _cJ ") decreases and irreversible thermal demagnetization occurs. Therefore, in particular, R-T-B sintered magnets used for electric motors for electric vehicles are required to have a high H content even at high temperatures _cJ I.e. higher H at room temperature _cJ 。

It is known that if R is replaced by heavy rare earth elements (mainly Dy, Tb) ₂ T ₁₄ Light rare earth elements (mainly Nd, Pr) in B type compound phase, then H _cJ And (4) improving. However, although H _cJ Is increased but due to R ₂ T ₁₄ The saturation magnetization of the B-type compound phase decreases, so that a residual magnetic flux density B exists _r (hereinafter, abbreviated as "B _r ") decrease such problems.

Patent document 1 describes supplying a heavy rare earth element such as Dy to the surface of a sintered magnet of an R-T-B alloy and diffusing the heavy rare earth element RH into the interior of the sintered magnet. In the method described in patent document 1, Dy is diffused from the surface to the inside of the R-T-B sintered magnet, and is enriched only in H for improvement _cJ Effective outer shell of main phase crystal grain, and B can be suppressed _r And a high H is obtained _cJ 。

Patent document 2 describes that the composition and thickness of a grain boundary phase in an R-T-B sintered magnet can be controlled and the H content can be increased by bringing an R-Ga-Cu alloy having a specific composition into contact with the surface of an R-T-B sintered body and performing heat treatment _cJ 。

Documents of the prior art

Patent document

Patent document 1: international publication No. 2007/102391

Patent document 2: international publication No. 2016/133071

Disclosure of Invention

Technical problems to be solved by the invention

However, in recent years, particularly in motors for electric vehicles and the like, it has been demanded to obtain a composition which can reduce the amount of expensive heavy rare earth elements and which can also reduce the amount of B _r And H _cJ Is more excellent in balance (suppression of B) _r Is high and H is high _cJ R-T-B sintered magnet of (1).

Various embodiments of the present invention provide a method for reducing the amount of heavy rare earth elements used and B _r And H _cJ A method for producing an R-T-B sintered magnet having an excellent balance.

Technical solution for solving technical problem

In an exemplary embodiment, a method for producing an R-T-B sintered magnet according to the present invention includes: a step for preparing an R-T-B-based sintered magnet material (wherein R is a rare earth element and must contain at least 1 type selected from Nd, Pr, and Ce, and T is at least 1 type selected from Fe, Co, Al, Mn, and Si and must contain Fe.); and a diffusion step of adhering at least a part of an RL-RH-C-M alloy (RL is at least 1 of light rare earth elements and necessarily contains at least 1 of Nd, Pr and Ce, RH is at least 1 of Tb, Dy and Ho, C is carbon, M is at least 1 of Cu, Ga, Fe, Co, Ni, Al, Ag, Zn, Si and Sn) to at least a part of the surface of the R-T-B sintered magnet material, and heating the R-T-B sintered magnet material at a temperature of 700 ℃ to 1100 ℃ in a vacuum or inert gas atmosphere, wherein the molar ratio [ T ]/[ B ] of the R-T-B sintered magnet material to B is greater than 14.0 and 15.0 or less, the RL content in the RL-RH-C-M alloy is 50 mass% to 95 mass%, and the RH content is 45 mass% to 45 mass% (including 0%), the content of C is 0.10 to 0.50 mass%, and the content of M is 4 to 49.9 mass%.

In one embodiment, the molar ratio [ T ]/[ B ] of T to B in the R-T-B based sintered magnet raw material is greater than 14.0 and 15.0 or less.

Effects of the invention

According to the embodiment of the present invention, it is possible to provide a compound B which is reduced in the amount of heavy rare earth elements used _r And H _cJ A method for producing an R-T-B sintered magnet having an excellent balance.

Drawings

Fig. 1A is an enlarged and schematic sectional view showing a part of an R-T-B system sintered magnet.

Fig. 1B is a further enlarged and schematically representative cross-sectional view within the dashed rectangular area of fig. 1A.

FIG. 2 is a flowchart showing an example of the steps in the method for producing an R-T-B sintered magnet according to the present invention.

Description of the symbols

12: comprising R ₂ T ₁₄ The main phase of the compound B; 14: a grain boundary phase; 14 a: two grain boundary phases; 14 b: grain boundary triple point.

Detailed Description

First, the basic structure of the R-T-B sintered magnet of the present invention will be described. The R-T-B sintered magnet has a structure in which powder particles of a raw material alloy are bonded by sintering, and is composed of a sintered magnet containing mainly R ₂ T ₁₄ The main phase of the B compound particles and a grain boundary phase located at a grain boundary portion of the main phase.

Fig. 1A is an enlarged and schematic sectional view showing a part of an R-T-B system sintered magnet, and fig. 1B is a further enlarged and schematic sectional view showing a region within a dotted rectangular region of fig. 1A. In fig. 1A, an arrow having a length of 5 μm is shown as an example as a reference length indicating the size for reference. As shown in FIG. 1A and FIG. 1B, the R-T-B system sintered magnet is composed of a sintered magnet mainly containing R ₂ T ₁₄ A main phase 12 of the B compound and a grain boundary phase 14 located at a grain boundary portion of the main phase 12. Further, as shown in FIG. 1B, the grain boundary phase 14 includes 2R ₂ T ₁₄ Two-grain boundary phase 14a and 3R adjacent to B compound grain (crystal grain) ₂ T ₁₄ Crystals of adjacent particles of the B compoundAnd a triple point 14 b. The typical main phase crystal grain size is 3 μm or more and 10 μm or less in terms of the average value of equivalent circle diameters of the magnet cross section. R as the main phase 12 ₂ T ₁₄ The B compound is a ferromagnetic material having high saturation magnetization and an anisotropic magnetic field. Therefore, in the R-T-B sintered magnet, R as the main phase 12 is increased ₂ T ₁₄ The presence ratio of the compound B can be increased _r . To increase R ₂ T ₁₄ The B compound is present in such a ratio that the amount of R, the amount of T and the amount of B in the raw material alloy are close to R ₂ T ₁₄ The stoichiometric ratio of B compound (R: T: B: 2: 14: 1) was determined. Wherein R can be replaced by C ₂ T ₁₄ Part of B of the B compound.

In addition, it is known that R as a main phase is substituted with a heavy rare earth element such as Dy, Tb or Ho ₂ T ₁₄ Part of R in the B compound can reduce saturation magnetization and increase the anisotropy field of the main phase. In particular, the main phase shell in contact with the two-particle grain boundary easily becomes the starting point of magnetization reversal, and therefore, the heavy rare earth diffusion technique in which the heavy rare earth element can be preferentially substituted in the main phase shell can be used, and a decrease in saturation magnetization can be suppressed, and high H can be efficiently obtained _cJ 。

On the other hand, it is known that a high H content can be obtained by controlling the magnetic properties of the two-grain boundary phase 14a _cJ . Specifically, by reducing the concentration of the magnetic element (Fe, Co, Ni, or the like) in the two-particle grain boundary phase, the two-particle grain boundary phase can be made close to nonmagnetic, and the magnetic bonding between the main phases can be weakened to suppress magnetization reversal.

As a result of studies by the present inventors, it has been found that the method described in patent document 2 can reduce the amount of heavy rare earth elements used and can obtain a high H content _cJ R-T-B sintered magnet of (1), B may be caused by diffusion _r Is reduced. Consider this B _r The reason for this is that the R amount (in particular, RL) near the magnet surface becomes larger due to diffusion, and the volume ratio of the main phase near the magnet surface is lowered. Based on these findings, the inventors of the present invention conducted further studiesAs a result, it was found that C in a narrow specific range is diffused from the surface of the R-T-B sintered magnet material to the inside of the magnet material through the grain boundary together with RL and M in specific ranges, and a decrease in the volume ratio of the main phase in the vicinity of the surface of the magnet can be suppressed. Thereby, B can be suppressed _r The amount of heavy rare earth elements used can be reduced due to the decrease caused by diffusion, and B can be obtained _r And H _cJ The R-T-B sintered magnet has an excellent balance. This is considered to be because Fe and RL introduced by diffusion, which are present in the grain boundaries near the magnet surface, form a main phase with C (C that can be substituted with B) introduced by diffusion.

As shown in FIG. 2, the method for producing an R-T-B sintered magnet according to the present invention includes a step S10 of preparing a raw material for the R-T-B sintered magnet and a step S20 of preparing an RL-RH-C-M alloy. The sequence of the step S10 of preparing the R-T-B sintered magnet material and the step S20 of preparing the RL-RH-C-M alloy is arbitrary.

The method for producing an R-T-B sintered magnet according to the present invention further includes a diffusion step S30 of adhering at least a part of an RL-RH-C-M alloy to at least a part of the surface of the R-TB sintered magnet material and heating the resultant magnet at a temperature of 700 ℃ to 1100 ℃ in a vacuum or an inert gas atmosphere, as shown in FIG. 2.

In the present invention, the R-T-B sintered magnet before and during the diffusion step is referred to as "R-T-B sintered magnet raw material", and the R-T-B sintered magnet after the diffusion step is referred to as "R-T-B sintered magnet".

(step of preparing R-T-B based sintered magnet Material)

In the R-T-B-based sintered magnet raw material, R is a rare earth element and must contain at least 1 kind selected from Nd, Pr, and Ce, and T is at least 1 kind selected from Fe, Co, Al, Mn, and Si and must contain Fe. The content of R is, for example, 27 mass% or more and 35 mass% or less of the total R-T-B sintered magnet material. The content of Fe relative to the total T is preferably 80 mass% or more.

When R is less than 27 mass%, the liquid cannot be sufficiently formed in the sintering processPhase, it may be difficult to sufficiently densify the sintered body. On the other hand, when R is more than 35 mass%, grain growth occurs during sintering, and H is contained _cJ The possibility of a drop. R is preferably 28% by mass or more and 33% by mass or less.

The R-T-B sintered magnet material has, for example, the following composition ranges.

Comprises the following components:

R：27～35mass％、

B：0.80～1.20mass％、

Ga：0～1.0mass％、

x: 0 to 2 mass% (X is at least one of Cu, Nb and Zr),

T: 60 mass% or more.

Preferably, in the R-T-B sintered magnet material, the molar ratio of T to B [ T [ ]]/[B]Greater than 14.0 and not more than 15.0. Higher H can be obtained _cJ . [ T ] in the present invention]/[B]Is obtained by summing up values obtained by dividing an analysis value (mass%) of each element (at least 1 selected from the group consisting of Fe, Co, Al, Mn and Si, T necessarily containing Fe, and the content of Fe being 80 mass% or more with respect to the total T) constituting T by atomic weights of the elements [ T]Analysis value (mass%) of B divided by atomic weight of B [ B]The ratio of. Molar ratio [ T]/[B]The condition of more than 14.0 indicates that the main phase (R) is formed ₂ T ₁₄ Compound B) the amount of T used is relatively small. Molar ratio [ T]/[B]More preferably from 14.3 to 15.0. Can further obtain high H _cJ . The content of B is preferably 0.9 mass% or more and less than 1.0 mass% of the total R-T-B sintered body.

The R-T-B sintered magnet material can be prepared by using a general production method for R-T-B sintered magnets represented by Nd-Fe-B sintered magnets. As an example, a raw material alloy produced by a strip casting method or the like is pulverized to a particle diameter D using a jet mill or the like ₅₀ After the thickness is 2.0 to 5.0 μm, the sintered body can be prepared by molding in a magnetic field and sintering at 900 to 1100 ℃. By crushing to a particle size D ₅₀ Has a magnetic characteristic of 2.0 to 5 μm and can be obtainedAnd (4) sex. Preferred particle diameter D ₅₀ Is 2.5 to 4.0 μm. In addition to suppressing deterioration of productivity, it is possible to reduce the precious RH and obtain an R-T-B sintered magnet having a better Br-HcJ balance. In addition, D is ₅₀ The particle size is a particle size in which the cumulative particle size distribution (volume basis) from the small diameter side in the particle size distribution obtained by the laser diffraction method using the air flow dispersion method is 50%. In addition, D ₅₀ For example, a particle size distribution measuring apparatus "HELOS" manufactured by Sympatec can be used&RODOS "dispersion pressure: 4bar, measurement Range: r2, measurement mode: measurement was performed under HRLD conditions.

(step of preparing RL-RH-C-M alloy)

In the RL-RH-C-M alloy, RL is at least 1 of the light rare earth elements and must contain at least 1 of Nd, Pr and Ce, RH is at least 1 of Tb, Dy and Ho, C is carbon, and M is at least 1 of Cu, Ga, Fe, Co, Ni, Al, Ag, Zn, Si and Sn. The content of RL is 50 to 95 mass% of the total RL-RH-C-M alloy. The light rare earth elements include La, Ce, Pr, Nd, Pm, Sm, Eu, etc. The RH content is 45 mass% or less (including 0 mass%) of the total RL-RH-C-M alloy. That is, RH may not be contained. The content of C is 0.10 mass% to 0.50 mass% of the total RL-RH-C-M alloy. The content of M is 4 to 49.9 mass% of the total RL-RH-C-M alloy. Typical examples of the RL-RH-C-M alloy include TbNdPrCCu alloy, TbNdCePCCu alloy, TbNdPrCCuFe alloy, TbNdCGa alloy, TbNdPrCGaCu alloy, TbNdCGaCuFe alloy, and NdPrbCCCuGaAl alloy. In addition to the above elements, a small amount of an element such as an unavoidable impurity such as Mn, O, or N may be contained.

When RL + RH is less than 50 mass%, RH, C and M are difficult to be introduced into the interior of the R-T-B sintered magnet material and H is present therein _cJ If the reduction rate is more than 95 mass%, the alloy powder becomes very active in the production process of the RL-RH-C-M alloy. As a result, the alloy powder may be significantly oxidized or ignited. Preferably, the RL + RH content is RL-RH-C-M alloyThe amount of the compound is 70 to 80 mass%. Higher H can be obtained _cJ 。

When RH exceeds 45 mass%, the amount of heavy rare earth elements as rare elements cannot be reduced, and B cannot be obtained _r And H _cJ The balance of (A) and (B) is excellent. The RH content is preferably 20 mass% or less of the total RL-RH-C-M alloy. The total content of the RL and the RH in the RL-RH-C-M alloy is preferably 55 mass% or more of the total RL-RH-C-M alloy. Thereby, high HcJ can be obtained. In addition, the RL content (mass%) in the RL-RH-C-M alloy is defined as [ RL ]]And the content of RH is set to [ RH ]]When it is preferable to satisfy [ RL]＞1.5×[RH]The relationship (2) of (c). Thereby, the amount of heavy rare earth elements used can be further reduced, and B can be obtained _r And H _cJ The R-T-B sintered magnet has an excellent balance.

When C is less than 0.10% by mass, there is a possibility that the decrease in the volume ratio of the main phase in the vicinity of the magnet surface cannot be suppressed, and when C is more than 0.50% by mass, H generated from RL and B exists _cJ The possibility of the effect being lowered is increased. The C content is preferably 0.20 to 0.50 mass% of the total RL-RH-C-M alloy. An R-T-B sintered magnet having a better balance between Br and HcJ can be obtained.

When M is less than 4 mass%, RL, B and RH are hardly introduced into the two-grain boundary phase, and H is present _cJ The possibility of insufficient improvement is high, and when the content is more than 49.9 mass%, the contents of RL and B are reduced and H is present _cJ The possibility of not being sufficiently increased. The content of M is preferably 7 to 15 mass% of the total RL-RH-C-M alloy. Higher H can be obtained _cJ . Preferably, M of the RL-RH-C-M alloy contains at least 1 of Cu, Ga and Fe, and when the content of Cu, Ga and Fe in M is 80% or more, a higher H content can be obtained _cJ 。

The method for producing the RL-RH-C-M alloy is not particularly limited. The steel sheet can be produced by a roll quenching method or a casting method. These alloys may be pulverized to prepare alloy powder. The coating composition can also be produced by a known atomization method such as a centrifugal atomization method, a rotary electrode method, a gas atomization method, and a plasma atomization method.

(diffusion step)

The following diffusion step was performed: at least a part of the prepared RL-RH-C-M alloy is adhered to at least a part of the surface of the R-T-B sintered magnet material prepared as described above, and the resultant material is heated at a temperature of 700 to 1100 ℃ in a vacuum or an inert gas atmosphere. This enables the formation of a liquid phase containing RL, C, (RH) and M from the RL-RH-C-M alloy, which is introduced into the interior of the R-T-B sintered magnet material by diffusion from the surface of the sintered material through the grain boundaries. The amount of the RL-RH-C-M alloy adhering to the R-T-B sintered magnet material is preferably 1% by mass or more and 8% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. Within this range, the amount of heavy rare earth elements used can be reduced more reliably, and a high H content can be obtained _cJ The R-T-B sintered magnet of (1).

When the temperature of heating in the diffusion step is less than 700 ℃, high H cannot be obtained _cJ The possibility of (a). On the other hand, above 1100 deg.C, H is present _cJ The possibility of a substantial decrease. The temperature of heating in the diffusion step is preferably 800 ℃ to 1000 ℃. Can obtain higher H _cJ . In addition, it is preferable that the R-T-B sintered magnet subjected to the diffusion step (700 ℃ C. to 1100 ℃ C.) is cooled from the temperature at which the diffusion step is performed to 300 ℃ at a cooling rate of 15 ℃/min or more. Higher H can be obtained _cJ 。

The diffusion step can be performed by using a known heat treatment apparatus while disposing an RL-RH-C-M alloy having an arbitrary shape on the surface of the R-T-B sintered magnet material. For example, the surface of the R-T-B sintered magnet material may be covered with a powder layer of RL-RH-C-M alloy, and the diffusion step may be performed. For example, a step of applying an adhesive to the surface of the object to be coated and a step of adhering the RL-RH-C-M alloy to the region to which the adhesive is applied can be performed. Examples of the binder include PVA (polyvinyl alcohol), PVB (polyvinyl butyral), PVP (polyvinyl pyrrolidone), and the like. When the binder is an aqueous binder, the R-T-B based sintered magnet material may be preheated before coating. The purpose of preheating is: excess solvent is removed to control adhesion and to allow uniform adhesion of the adhesive. The heating temperature is preferably 60 to 200 ℃. In the case of an organic solvent-based adhesive having high volatility, this step may be omitted. For example, the RL-RH-C-M alloy and the R-T-B sintered magnet material may be adhered to each other by dispersing the RL-RH-C-M alloy in a dispersion medium, applying the resulting slurry to the surface of the R-T-B sintered magnet material, and then evaporating the dispersion medium. Among them, as the dispersion medium, alcohols (ethanol and the like), aldehydes, and ketones can be exemplified.

The position of placement of at least a part of the RL-RH-C-M alloy when it is adhered to at least a part of the R-T-B sintered magnet material is not particularly limited.

(Heat treatment Process)

As shown in fig. 2, the R-T-B sintered magnet subjected to the diffusion step is preferably subjected to a heat treatment in a vacuum or an inert gas atmosphere at a temperature of 400 ℃ to 900 ℃ inclusive and at a temperature lower than the temperature applied in the diffusion step. The heat treatment may be performed a plurality of times. By performing the heat treatment, higher H can be obtained _cJ 。

(R-T-B series sintered magnet)

The R-T-B sintered magnet obtained by the production method of the present invention contains R (R is a rare earth element and must contain at least 1 kind selected from Nd, Pr, and Ce), T (T is at least 1 kind selected from Fe, Co, Al, Mn, and Si and must contain Fe), B, and C, and further contains at least 1 kind selected from Cu, Ga, Ni, Ag, Zn, and Sn.

The R-T-B sintered magnet of the present invention may have the following composition, for example.

Comprises the following steps:

r: 26.8 to 31.5 mass%,

B: 0.90 to 0.97 mass%,

C: 0.08 to 0.30 mass%,

M: 0.05 mass% or more and 1.0 mass% or less (M is at least 1 kind selected from Ga, Cu, Zn and Si),

M1: 0 to 2.0 mass% (M1 represents at least 1 member selected from the group consisting of Al, Ti, V, Cr, Mn, Ni, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb and Bi),

The rest of T (T is Fe or Fe and Co) and unavoidable impurities.

The invention can reduce the use amount of heavy rare earth elements and can obtain B _r And H _cJ The R-T-B sintered magnet has an excellent balance. Therefore, Tb is particularly preferably 5% by mass or less (including 0% by mass), more preferably 1% by mass or less, and still more preferably 0.5% by mass or less of the entire R-T-B sintered magnet.

The R-T-B sintered magnet of the present invention may include a portion where the RH (e.g., Tb) concentration decreases from the surface of the magnet to the inside of the magnet. The R-T-B sintered magnet includes a portion where the RH concentration decreases from the magnet surface toward the inside of the magnet, and means that at least one of the RH is in a state of diffusing from the magnet surface toward the inside of the magnet.

[ examples ]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Experimental example 1

[ Process for preparing R-T-B sintered magnet Material (magnet Material) ]

The elements were weighed according to the composition of the magnet raw material indicated by the symbol 1-A in Table 1, and cast by a strip casting method to obtain a sheet-like raw material alloy having a thickness of 0.2 to 0.4 mm. The obtained sheet-like raw material alloy was subjected to hydrogen pulverization, and then subjected to dehydrogenation treatment in which the sheet-like raw material alloy was heated to 550 ℃ in vacuum and cooled to obtain a roughly pulverized powder. Then, the obtained coarsely pulverized powder was pulverized by an air-flow pulverizer (jet mill) to obtain a particle diameter D ₅₀ A 3 μm fine powder (alloy powder). Wherein the particle diameter D ₅₀ Is a volume center obtained by laser diffraction method of air flow dispersion methodValue (volume-based median particle diameter).

And (3) molding the micro-powder in a magnetic field to obtain a molded body. Among these, the molding device uses a so-called perpendicular magnetic field molding device (transverse magnetic field molding device) in which the magnetic field application direction is orthogonal to the pressing direction.

The obtained compact was sintered in vacuum for 4 hours (for each sample, a temperature at which densification sufficiently occurred by sintering was selected), and then quenched to obtain a magnet raw material. The density of the obtained magnet raw material was 7.5Mg/m ³ The above. The results of the composition of the obtained magnet material are shown in table 1. The components in table 1 were measured by high frequency inductively coupled plasma optical emission spectrometry (ICP-OES). Further, the oxygen content of the magnet material was measured by a gas melting-infrared absorption method, and it was confirmed that all of the oxygen content was about 0.2 mass%. Further, C (carbon content) was measured using a gas analyzer using a combustion-infrared absorption method, and was confirmed to be about 0.1 mass%. "[ T ] in Table 1]/[B]"is a ratio (a/B) of (a) obtained by summing up values obtained by dividing an analysis value (mass%) of each element (here, Fe, Al, Si, Mn) constituting T by an atomic weight of the element, and (B) obtained by dividing an analysis value (mass%) of B by an atomic weight of B. The same applies to all tables below. The total amount of each composition, oxygen amount and carbon amount in table 1 was not 100 mass%. This is because the element contains impurity elements other than those described in the table. The same applies to other tables.

[ Table 1]

[ Process for preparing RL-RH-C-M alloy ]

The elements were weighed based on the composition of the RL-RH-C-M alloy shown by symbols 1-a to 1-e in Table 2, and these raw materials were melted to obtain a ribbon-like or sheet-like alloy by a single-roll super-quenching method (melt spinning method). The obtained alloy was pulverized in an argon atmosphere using a mortar to prepare an RL-RH-C-M alloy. The compositions of the obtained RL-RH-C-M alloys are shown in Table 2.

[ Table 2]

[ diffusion step ]

R-T-B sintered magnet material designated by the reference numeral 1-A in Table 1 was cut and machined into a cube of 7.2 mm. times.7.2 mm. Next, a binder containing a sugar alcohol is applied to the entire surface of the R-T-B sintered magnet material by a dipping method. RL-RH-C-M alloy powder was attached to the R-T-B sintered magnet material coated with the binder in an amount of 3 mass% relative to the mass of the R-T-B sintered magnet material. Next, the RL-RH-C-M alloy and the R-T-B sintered magnet material were heated at 900 ℃ for 10 hours in a vacuum heat treatment furnace to perform a diffusion step, and then cooled. Then, the resultant was heat-treated at 470 to 530 ℃ for 3 hours in a vacuum heat-treating furnace, and then cooled.

[ sample evaluation ]

B-H tracer measurement of the R-T-B sintered magnet raw material and the obtained sample (R-T-B sintered magnet after Heat treatment) _r And H _cJ . B of R-T-B sintered magnet _r And H _cJ Measurement results of (2) and B of R-T-B sintered magnet _r Value (B after diffusion) _r ) B minus R-T-B sintered magnet raw material _r Value (B before diffusion) _r ) And the value obtained is taken as Δ B _r And is shown in table 3. The components of the sample were measured by high-frequency inductively coupled plasma optical emission spectrometry (ICP-OES), and the obtained results are shown in table 4. As shown in Table 3, it is understood that in the examples using sample No. 1-1 as the R-T-B sintered magnet material and sample Nos. 1-3 to 1-4 obtained by diffusing the RL-RH-C-M alloy, high H was obtained not only in the diffusion step but also in the diffusion step _cJ And B is _r The reduction is less. Thus obtaining B _r And H _cJ Is excellent in balance (inhibition B) _r Is high and H is high _cJ ) The R-T-B sintered magnet of (1). On the other hand, it is found that in the comparative example of sample No. 1-2 obtained by diffusing the RL-RH-C-M alloy in which the C amount is in the proper range or less, high H was obtained in the diffusion step _cJ But B is _r And is significantly reduced. It is also found that samples Nos. 1-5 and 1-6 obtained by diffusing the RL-RH-C-M alloy in which the C amount is not less than the proper range are comparative examples, although B is _r The decrease was small, but sufficient H was not obtained _cJ 。

[ Table 3]

[ Table 4]

Experimental example 2

[ Process for preparing R-T-B-based sintered magnet Material (magnet Material) ]

The elements were weighed according to the composition of the magnet raw material indicated by the symbols 2-A to 2-B in Table 5, and cast by the strip casting method to obtain a sheet-like raw material alloy having a thickness of 0.2 to 0.4 mm. The obtained sheet-like raw material alloy was subjected to hydrogen pulverization, and then subjected to dehydrogenation treatment in which the sheet-like raw material alloy was heated to 550 ℃ in vacuum and cooled to obtain a roughly pulverized powder. Then, the obtained coarsely pulverized powder was pulverized by an air-flow pulverizer (jet mill apparatus) to obtain a particle diameter D ₅₀ A 3 μm fine powder (alloy powder). Wherein the particle diameter D ₅₀ The volume center value (volume-based median diameter) was obtained by a laser diffraction method using an air-flow dispersion method.

And (3) molding the micro-powder in a magnetic field to obtain a molded body. Among these, the molding device uses a so-called right-angle magnetic field molding device (transverse magnetic field molding device) in which the magnetic field application direction is orthogonal to the pressing direction.

The obtained compact was sintered in vacuum at 1000 ℃ to 1050 ℃ inclusive (for each sample, a temperature selected to sufficiently cause densification by sintering) for 10 hours, and then quenched to obtain a magnet material. The density of the obtained magnet raw material was 7.5Mg/m ³ As described above. The results of the composition of the obtained magnet material are shown in table 5. The components in table 5 were measured by high frequency inductively coupled plasma optical emission spectrometry (ICP-OES). Further, the oxygen content of the magnet material was measured by a gas melting-infrared absorption method, and it was confirmed that all of the oxygen content was about 0.2 mass%. Further, C (carbon content) was measured using a gas analyzer using a combustion-infrared absorption method, and was confirmed to be about 0.1 mass%.

[ Table 5]

[ Process for preparing RL-RH-C-M alloy ]

The elements were weighed based on the composition of the RL-RH-C-M alloy and the composition of the alloy not containing B shown in symbols 2-a to 2-e of Table 6, and these raw materials were melted to obtain a ribbon-like or sheet-like alloy by a single-roll super-quenching method (melt spinning method). The obtained alloy was pulverized in an argon atmosphere using a mortar to prepare an RL-RH-C-M alloy. The compositions of the obtained RL-RH-C-M alloys are shown in Table 6.

[ Table 6]

[ diffusion step ]

R-T-B sintered magnet materials designated by the reference numerals 2-A to 2-B in Table 5 were cut and machined into cubes of 7.2 mm. times.7.2 mm. Next, a binder containing a sugar alcohol is applied to the entire surface of the R-T-B sintered magnet material by a dipping method. An RL-RH-C-M alloy powder at 3 mass% based on the mass of the R-T-B sintered magnet material was adhered to the R-T-B sintered magnet material coated with a binder. Next, the RL-RH-C-M alloy and the R-T-B sintered magnet material were heated at 900 ℃ for 10 hours in a vacuum heat treatment furnace to perform a diffusion step, and then cooled. Then, the resultant was heat-treated at 470 to 530 ℃ for 1 hour in a vacuum heat-treating furnace, and then cooled.

[ sample evaluation ]

B-H tracer measurement of the R-T-B sintered magnet raw material and the obtained sample (R-T-B sintered magnet after Heat treatment) _r And H _cJ . B of R-T-B sintered magnet _r And H _cJ Measurement result of (2) and B of R-T-B sintered magnet _r Value (B after diffusion) _r ) Minus B of R-T-B-based sintered magnet raw material _r Value (B before diffusion) _r ) The value obtained is taken as Δ B _r And is shown in Table 7. As shown in Table 7, it is understood that in the examples using sample Nos. 2-1 and 2-7 as R-T-B sintered magnet materials and sample Nos. 2-3 to 2-5 and 2-9 to 2-10 obtained by diffusing RL-RH-C-M alloy, high H content was obtained not only in the diffusion step but also in the diffusion step _cJ And B is _r The reduction is less. Thus obtaining B _r And H _cJ The R-T-B sintered magnet has an excellent balance. On the other hand, in comparative examples of samples No. 2-2 and No. 2-8 obtained by diffusing the RL-RH-C-M alloy in which the C amount is in the proper range or less, high H content was obtained in the diffusion step _cJ But B is _r The significant decrease was observed in the comparative examples of sample Nos. 2 to 6 and sample Nos. 2 to 11, although B _r The decrease was small, but sufficient H was not obtained _cJ 。

[ Table 7]

Claims

1. A method for manufacturing an R-T-B sintered magnet, comprising:

a step for preparing an R-T-B sintered magnet material, wherein R is a rare earth element and must contain at least 1 kind selected from Nd, Pr, and Ce, and T is at least 1 kind selected from Fe, Co, Al, Mn, and Si and must contain Fe; and

a diffusion step of adhering at least a part of an RL-RH-C-M alloy to at least a part of the surface of the R-T-B sintered magnet material, wherein RL is at least 1 kind of light rare earth element and must include at least 1 kind selected from Nd, Pr and Ce, RH is at least 1 kind selected from Tb, Dy and Ho, C is carbon, M is at least 1 kind selected from Cu, Ga, Fe, Co, Ni, Al, Ag, Zn, Si and Sn, and heating the R-T-B sintered magnet material at a temperature of 700 ℃ to 1100 ℃ in a vacuum or an inert gas atmosphere,

the molar ratio [ T ]/[ B ] of T to B in the R-T-B sintered magnet material is greater than 14.0 and not more than 15.0,

the RL-RH-C-M alloy has a RL content of 50 to 95 mass%, a RH content of 0 to 45 mass%, a C content of 0.10 to 0.50 mass%, and a M content of 4 to 49.9 mass%.

2. The method of manufacturing an R-T-B sintered magnet according to claim 1, wherein: the molar ratio [ T ]/[ B ] of T to B in the R-T-B sintered magnet material is greater than 14.0 and not more than 15.0.