RTB-based sintered magnet and methods for its production

Abstract

RTB-based sintered magnet with: R: 27.5 to 34.0 mass%, where R is at least one of the rare earth elements, and necessarily includes Nd and a heavy rare earth element RH, where RH is at least one of Dy, Tb, Gd and Ho, RH: 2 to 10 mass%, B: 0.89 to 0.95 mass%, Ti: 0.1 to 0.2 mass%, Ga: 0.3 to 0.7 mass%, Cu: 0.07 to 0.50 wt%, Al: 0.05 to 0.50 mass%, M: 0 to 0.3 mass%, where M is Nb and / or Zr, Remainder T and unavoidable impurities, where T is a transition metal element and necessarily includes Fe, satisfying the following inequalities (1), (2) and (3): [T] − 72.3 ([B] − 0.45 [Ti]) > 0 ([T] − 72.3 ([B] − 0.45 [Ti])) / 55.85 < 13 [Ga] / 69.72 [ Ga ] ≥ [ Cu ] where [T] is the content of T, expressed in mass%, [B] is the content of B, expressed in mass%, [Ti] is the content of Ti, expressed in mass%, [Ga] is the content of Ga, expressed in mass%, and [Cu] is the content of Cu, expressed in mass%.

Description

Technical field

[0001] The present disclosure relates to an RTB-based sintered magnet and a method for its manufacture. State of the art

[0002] An RTB-based sintered magnet (R is composed of a light rare earth element RL and a heavy rare earth element RH, RL is at least one of Nd and Pr and necessarily includes Nd, RH is at least one of Dy, Tb, Gd and Ho, and T is a transition metal element and necessarily includes Fe) is known as the highest-performing magnet among permanent magnets and is used in various motors such as voice-coil motors (VCM) of hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), and motors for industrial equipment, household appliances, and the like.

[0003] The RTB-based sintered magnet is mainly composed of a main phase made of an R2T 14B-compound, and a grain boundary phase located in the grain boundary region of this main phase. The R2T 14 B-compound as the main phase is a ferromagnetic material with high saturation magnetization and magnetic field anisotropy, and represents the basis of the properties of RTB-based sintered magnets.

[0004] The RTB-based sintered magnet has a coercivity H cJ (hereinafter sometimes simply referred to as "H") cJ (referred to as “), which is reduced at high temperatures, leading to irreversible thermal demagnetization. For this reason, the RTB-based sintered magnet must have a high H cJ especially if it is to be used for motors of electric vehicles.

[0005] It is known that H cJ is improved when RL, which is in R of an R2T 14The B-compound is contained as the main phase, in which RTB-based sintered magnets are partially replaced by RH. With increasing content of substituting RH, H cJ improved.

[0006] However, if RL in the R2T 14 When a B-compound is substituted with RH, H cJ of the RTB-based sintered magnet improved, while remanence (residual magnetic flux density B) r ; hereinafter sometimes simply referred to as "B" r “” is decreasing. Dy, in particular, has several problems, including unreliable supply and large price fluctuations due to small deposits and a limited area where the deposits are located, and the like. For this reason, there is a need to H cJ to improve without using RH as far as possible (by reducing its content as far as possible).

[0007] Patent document 1 mentions that the B content is limited to a relatively small specific range, compared to a conventionally used RTB-based alloy, while at least one element selected from Al, Ga and Cu is included as the metallic element M to provide an R2T 17 -phase to form, which ensures that a sufficient volume fraction of a transition metal-rich phase (R6T) is present. 13 M) is formed, using the R2T 17 -phase as raw material, enabling the production of a high-coercivity RTB-based rare-earth sintered magnet while reducing the Dy content. Patent document 2 discloses a rare-earth alloy containing 28.0-35.0 wt% rare-earth elements, 0.8 to 1.5 wt% B, up to 8.0 wt% of one or more elements selected from Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ta, W, Al, Ga, C, Ge, Sn, Pb, Mg and Ca, and the remainder Fe. State-of-the-art documents, patent documents Patent document 1: WO 2013 / 008756 A1 Patent document 2: JP 2008-264 875 A Disclosure of the invention; Task of the invention

[0008] As mentioned above, RTB-based sintered magnets are mostly used in motors. Therefore, improving the magnetic properties of RTB-based sintered magnets can either result in increased motor performance or reduced size. Thus, it is very effective to... r and H cJ to improve. However, there is a need to improve the square ratio H. k / H cJ (hereinafter sometimes simply referred to as "H") k / H cJ “” is designated) along with these properties to increase. A low H k / H cJThis leads to a reduction in the critical demagnetizing field strength, thus creating the problem that demagnetization occurs easily. Therefore, an RTB-based sintered magnet is needed, which has a high B r and high H cJ as well as high H k / H cJ exhibits. In the field of RTB-based sintered magnets, H k , a parameter measured to obtain the square ratio, usually a value on the H-axis in a graph of an I (magnetizing strength)-H (magnetic field strength) curve, at a point in the second quadrant where I equals 0.9 B r The square ratio is defined as the value (H). k / H cJ ), which is obtained by dividing H k by H cJ as obtained in the demagnetization curve mentioned above.

[0009] A sintered magnet with the composition mentioned in patent document 1, wherein the content of B is set lower than in the standard RTB-based sintered magnet (is set lower than the content of B in the stoichiometric ratio of an R2T 14 B-type compound) and Ga is added, a higher B can be achieved. r and higher H cJ to reach. However, the problem arose that H k / H cJ compared to a standard RTB-based sintered magnet, the B content was reduced (the stoichiometric ratio of an R2T is higher). 14B-type compound). For example, as shown in Tables 4 to 6 of Patent Document 1, the square ratio (Sq, or “squareness” in Patent Document 1) is approximately 90%, and when a heavy rare-earth element RH (Dy) is included, the square ratio is often at the 80% level, so it would be difficult to consider this level as high. Although Patent Document 1 itself does not mention a definition of the square ratio, JP 2007-119882 A of the same applicant, which is cited in Patent Document 1 as a prior art document, mentions the square ratio as “value expressed by percent, which is obtained by dividing a value of an external magnetic field in which magnetization accounts for 90% of saturation magnetization by iHc,” so the definition of the square ratio in Patent Document 1 is considered to be the same.In other words, the definition of the square ratio in patent document 1 is considered to be the same definition that is commonly used.

[0010] The object of the present invention is to provide an RTB-based sintered magnet with high B r and high H cJ and with high H k / H cJ to propose a method for its production, whereby no RH is used as far as possible (by reducing the content as far as possible). Means of solving the problem

[0011] An RTB-based sintered magnet according to a first aspect of the present invention comprises: R (R is at least one rare earth element, and necessarily includes Nd and one heavy rare earth element RH (at least one of Dy, Tb, Gd and Ho)): 27.5 to 34.0 mass%, RH: 2 to 10 mass%, B: 0.89 to 0.95 mass%, Ti: 0.1 to 0.2 mass%, Ga: 0.3 to 0.7 mass%, Cu: 0.07 to 0.50 wt%, Al: 0.05 to 0.50 mass%, M (M is Nb and / or Zr): 0 to 0.3 mass%, Residual T (T is a transition metal element and necessarily includes Fe), and unavoidable impurities, satisfying the following inequalities (1), (2) and (3): [T]−72.3([B]−0.45[Ti])>0 ([T]−72.3([B]−0.45[Ti])) / 55.85<13[Ga] / 69.72 [Ga]≥[Cu] where [T] is the content of T, expressed in mass %, [B] is the content of B, expressed in mass %, [Ti] is the content of Ti, expressed in mass%, [Ga] is the content of Ga, expressed in mass%, and [Cu] is the content of Cu, expressed in mass%.

[0012] An RTB-based sintered magnet according to the second aspect of the present invention is the RTB-based sintered magnet according to the first aspect, which further comprises: Ti: 0.1 mass% or more and less than 0.15 mass%.

[0013] A method for producing an RTB-based sintered magnet according to the third aspect of the present invention is a method for producing the RTB-based sintered magnet according to the first or second aspect, wherein the method comprises: One step in the production of one or more types of main alloy powder and one or more types of additional alloy powder; a step of mixing one or more grades of additional alloy powder in 0.5 wt% or more and 20 wt% or less below 100 wt% of a mixed alloy powder after mixing, to obtain the mixed alloy powder from the one or more grades of the main alloy powder and the one or more grades of the additional alloy powder; a forming step of shaping the mixed alloy powder to obtain a shaped body; a sintering step of the sintering of the molded body to obtain a sintered body; and a heat treatment step of subjecting the sintered body to a heat treatment; wherein one or more varieties of the main alloy powder have a composition that includes: R: 27.5 to 34.0 mass%, RH: 2 to 10 mass%, B: 0.89 to 0.97 mass%, Ti: 0 to 0.2 wt% (except 0 wt% if Ti constitutes 0 wt% in one or more grades of the additional alloy powder), Ga: 0 to 0.4 mass%, Cu: 0.07 to 0.50 wt%, Al: 0.05 to 0.50 mass%, Residual T and unavoidable impurities, and wherein one or more types of the additional alloy powder have a composition that includes: R1 (R1 is at least one of the rare earth elements other than the heavy rare earth element RH, and necessarily includes Nd): 32 to 66 mass%, B: 0.3 to 0.9 mass%, Ti: 0 to 4 wt% (except 0 wt% if Ti constitutes 0 wt% in one or more grades of the main alloy powder), Ga: 0.7 to 12 mass%, Cu: 0 to 4 mass%, Al: 0 to 10 mass%, Residual T and unavoidable impurities, the composition satisfying the following inequality (4): [T]≤72.4[B]

[0014] A method for producing an RTB-based sintered magnet according to a fourth aspect of the present invention is the method for producing an RTB-based sintered magnet according to the third aspect, wherein one or more grades of main alloy powder are obtained by a strip casting process. Effect of the invention

[0015] According to the present invention, it is possible to produce an RTB-based sintered magnet with high B r and high H cJ and with high H k / H cJ to manufacture it, as far as possible without using RH, and to specify a method for its manufacture. Description of the embodiments

[0016] The inventors of the present invention have investigated and found that when the composition of a sintered magnet is adjusted to a composition in which a boride of Ti is formed during the manufacturing process by using Ti in a specific range, the content of B obtained by subtracting the B consumed in the formation of the boride of Ti from the total B content of the RTB-based sintered magnet, in other words, the content of B remaining without forming a boride with Ti (hereinafter sometimes referred to as the "effective B content" or "B content") eff“ is set lower than the total B content of the standard RTB-based sintered magnet (is set lower than the B content in the stoichiometric ratio of an R2T 14 B-type compound) and Ga is added, it is possible to create a high B-type RTB-based sintered magnet. r and high H cJ and with high H k / H cJ to obtain.

[0017] There are still unclear points regarding the reason why the RTB-based sintered magnet according to the embodiment of the invention has a high B r and high H cJ and a high H k / H cJ exhibits. A description of a mechanism is given, based on the inventors' previous knowledge of the present invention. It should be noted that the following description of the mechanism is not intended to limit the scope of the present invention.

[0018] As mentioned in patent document 1, if the B content is set lower than in the standard RTB-based sintered magnet (set lower than the B content in the stoichiometric ratio of an R2T 14 When B-type ratio) and Ga are added, a transition metal-rich phase (RT-Ga phase) is formed, making it possible to achieve a higher H cJ to obtain. However, as a result of the investigations of the inventors of the present invention, it was found that the RT-Ga phase sometimes also exhibits weak magnetism and, when the RT-Ga phase is excessively present at the grain boundaries of the RTB-based sintered magnet, in particular at the grain boundaries existing between two main phases (hereinafter sometimes referred to as "grain boundaries between two grains"), which are the main influence on H k / H cJ is viewed, H k / H cJis reduced. There is a need to form the RT-Ga phase to reduce high H k / H cJ to achieve this, but the amount produced must be regulated.

[0019] As a result of the investigations of the inventors of the present invention, it was also found that if the content of B of the standard RTB-based sintered magnet (the content of B is greater than in the stoichiometric ratio of an R2T 14B-type compound), the RT-Ga phase is not readily formed, and the Ti boride is not readily formed in the raw material stage, but is readily formed during subsequent sintering and / or heat treatment. Therefore, it is concluded that the B content is adjusted to match the B content of a standard RTB-based sintering magnet, and Ti is added in a specific quantity, thus enabling the RT-Ga phase to form primarily during sintering and / or heat treatment (the Ti boride is formed during sintering and / or heat treatment, thus reducing the B content). eff(The B content is set lower than the total B content in a standard RTB-based sintered magnet) and suppresses the formation of the RT-Ga phase in the raw material stage. Therefore, it is possible to suppress the formation of the RT-Ga phase compared to the case where the B content is initially set lower than the B content of a standard RTB-based sintered magnet, thus enabling the production of a high-B RTB-based sintered magnet. r and high H cJ and with high H k / H cJ to obtain. [RTB-based sintered magnet]

[0020] One embodiment according to the present invention relates to an RTB-based sintered magnet comprising: R (R is at least one of the rare earth elements, and necessarily includes Nd and a heavy rare earth element RH (at least one of Dy, Tb, Gd and Ho)): 27.5 to 34.0 mass%, RH: 2 to 10 mass%, B: 0.89 to 0.95 mass%, Ti: 0.1 to 0.2 mass%, Ga: 0.3 to 0.7 mass%, Cu: 0.07 to 0.50 wt%, Al: 0.05 to 0.50 mass%, M (M is Nb and / or Zr): 0 to 0.3 mass%, Residual T (T is a transition metal element and necessarily contains Fe), and unavoidable impurities, satisfying the following inequalities (1), (2) and (3): [T]−72.3([B]−0.45[Ti])>0 ([T]−72.3([B]−0.45[Ti])) / 55.85<13[Ga] / 69.72 [Ga]≥[Cu] where [T] is the content of T, expressed in mass%, [B] is the content of B, expressed in mass%, [Ti] is the content of Ti, expressed in mass%, [Ga] is the content of Ga, expressed in mass%, and [Cu] is the content of Cu, expressed in mass%.

[0021] R is at least one of the rare-earth elements and necessarily includes Nd and a heavy rare-earth element RH (at least one of Dy, Tb, Gd, and Ho). The R content is in the range of 27.5 to 34.0 wt%. If the R content is lower than 27.5 wt%, an insufficiently liquid phase can be formed during sintering, so the sintered magnet cannot be made sufficiently dense. Conversely, if the R content exceeds 34.0 wt%, the proportion of the main phase can decrease, and a high B density cannot be achieved. r The RH content is 2 to 10% by mass of the total RTB-based sintered magnet. If the RH content is lower than 2% by mass, no high H can be obtained. cJ can be obtained, and if the content exceeds 10% by mass, B can r It may be reduced. The "RH content" refers to the RH content contained in R above. The "RH content" is, in fact, contained within the "R content".

[0022] The B content ranges from 0.89 to 0.95% by mass. If the B content is lower than 0.89% by mass, B r It may be reduced, and if the content exceeds 0.95% by mass, no high H can be present. cJ This occurs because too little RT-Ga phase is formed. B may be partially replaced by C.

[0023] The titanium content is in the range of 0.1 to 0.2% by mass. The titanium boride is formed by including titanium, and the B content is eff is set lower than the total content of the standard RTB-based sintered magnet by satisfying inequality (1) mentioned below, thus making it possible to produce a high H RTB-based sintered magnet k / H cJ to obtain. If the Ti content is lower than 0.1% by mass, no high H can be obtained. k / H cJare obtained, and if the Ti content exceeds 0.2 mass%, unnecessary Ti may be present, leading to a reduction in B. r The titanium content is preferably 0.1% by mass or more and less than 0.15% by mass. A higher percentage is possible. r to obtain.

[0024] The Ga content is in the range of 0.3 to 0.7 wt%. Each of the B and Ti contents is adjusted to the aforementioned range, and the inequalities (1), (2) and (3) mentioned below are satisfied, and Ga is present in an amount of 0.3 to 0.7 wt% to form the RT-Ga phase located at the grain size limit of the main phase, thus enabling a high B r and high H cJ to obtain. If the Ga content is lower than 0.3% by mass, no high H can be obtained. cJThis occurs because too small an amount of the RT-Ga phase is formed. If the content exceeds 0.7 wt%, the amount of RT-Ga phase formed can become too large, resulting in unnecessary Ga and a reduction in B. r This leads to the RT-Ga phase typically being an Nd6Fe phase. 13 Ga connection. The R6T 13 Ga compound exhibits a La6Co 11 Ga3-type crystal structure. The R6T 13 Depending on its condition, a Ga compound is sometimes an R6T. 13-δ Ga 1+δ -compound. When Cu, Al and Si are included in the RTB-based sintered magnet, the compound is sometimes R6T. 13-δ (Ga 1-x-y-z Cu x Al y Si z ) 1+δ .

[0025] The copper content ranges from 0.07 to 0.50% by mass. If the copper content is lower than 0.07% by mass, high hydrogen cannot be produced. cJ can be obtained, and if the content exceeds 0.50% by mass, B can rbe reduced.

[0026] Al may also be present in the usual amounts (0.05% by mass or more and 0.5% by mass or less). H cJ The quality can be improved by including Al. The manufacturing process typically results in 0.05% or more of Al as unavoidable impurities, and the total amount (the amount of Al present as an unavoidable impurity and the amount of Al intentionally added) may be 0.50% or less.

[0027] It is generally known that abnormal grain growth of crystal grains during sintering is suppressed by the inclusion of Nb and / or Zr in the RTB-based sintering magnet. In the present invention, Nb and / or Zr can also be present in a total amount of 0.3% by mass or less (that is, at least one of Nb and Zr can be present, and the total amount of Nb and Zr is 0.3% by mass or less). If the total amount of Nb and / or Zr exceeds 0.3% by mass, the volume fraction of the main phase may be reduced by the presence of unnecessary Nb and / or Zr, leading to a reduction in B. r leads.

[0028] The remainder is T (T is a transition metal element and necessarily includes Fe), and inequalities (1) and (2) mentioned below are satisfied. Fe preferably constitutes 90% or more of T by mass. Other transition metal elements besides Fe include, for example, Co. The degree of substitution (as content) of Co preferably constitutes 2.5% or less of the total T by mass. It is not preferred that the degree of substitution of Co constitutes more than 10% of the total T, due to a reduction in B. rThe RTB-based sintered magnet of the present embodiment may contain impurities such as Cr, Mn, Si, La, Ce, Sm, Ca, Mg, and the like, which are unavoidable impurities in a didymium alloy (Nd-Pr), electrolytic iron, ferroboron, and the like. Examples of unavoidable impurities from the manufacturing process include O (oxygen), N (nitrogen), C (carbon), and the like. The sintered magnet may also contain small amounts of V, Ni, Mo, Hf, Ta, W, and the like.

[0029] The present embodiment satisfies inequality (1), inequality (2), and inequality (3). By satisfying inequality (1), the content of B is eff lower than the B content of the standard RTB-based sintered magnet (lower than the B content at the stoichiometric ratio of an R2T 14B-type compound). In the present embodiment, a boride is formed by the addition of Ti (typically TiB2). Therefore, the B content (B content) eff ), which is obtained by subtracting the content of B consumed by TiB2 ([Ti] / 47.867 (atomic weight of Ti) × 2) from the total content of B ([B] / 10.811 (atomic weight of B)) of the RTB-based sintered magnet, [B] - 0.45[Ti] in inequality (1). In the present embodiment, the content of B eff set lower than the B content at the stoichiometric ratio of an R2T 14 B-type compound. That is, the setting is determined by inequality (1) such that [Fe] / 55.85 (atomic weight of Fe) is set higher than [B eff] / 10.811) × 14, i.e., (([B]-0.45[Ti]) / 10.811)× 14 ([ ] denotes the content of the element in parentheses, expressed as mass %, and, for example, [Fe] denotes the content of Fe, expressed as mass %. The determination is further determined by inequality (2), such that the composition of the remaining Fe ([T] - 72.3([B] - 0.45[Ti])) is less than 13[Ga] / 69.72 (atomic weight of Ga) to form the RT-Ga phase (typically the compound Nd6Fe). 13 Ga) to form without the R2Fe 17 -phase to form, which, due to the remaining Fe, results in a significant reduction in H cJ This causes. If the composition does not satisfy inequalities (1) and (2), a reduction H may occur. cJ occur, so that no high H k / H cJ will be received. [T]−72.3([B]−0.45[Ti])>0 ([T]−72.3([B]−0.45[Ti])) / 55.85<13[Ga] / 69.72

[0030] Furthermore, the present embodiment satisfies inequality (3). [Ga]≥[Cu]

[0031] In the present embodiment of the invention, the Ga content is set higher than, or equal to, the Cu content. If the Ga content is lower than the Cu content, the amount of RT-Ga phase formed decreases because there is too little Ga in the grain boundary phase at the grain boundary region, leading to a significant reduction in H cJ leads to the result that no high H k / H cJ is obtained. Preferably, [Ga] ≥ 1.5[Cu]. Within the above range, a higher H is acceptable. cJ will be obtained. [Method for manufacturing the RTB-based sintered magnet]

[0032] The RTB-based sintered magnet of the present embodiment can be manufactured by a known manufacturing process and is produced using a main alloy powder and an additional alloy powder according to the present embodiment, which is described below as a preferred aspect. This is because such a higher H cJ and H k / H cJ An example of a method for manufacturing an RTB-based sintered magnet of the present embodiment is now described. The method for manufacturing an RTB-based sintered magnet includes a step for obtaining an alloy powder, a forming step, a sintering step, and a heat treatment step. Each of the steps is described below. (1) Step of obtaining alloy powder

[0033] A single type of alloy powder (single alloy powder) can be used as an alloy powder. A so-called two-alloy process for obtaining an alloy powder (mixed alloy powder) by mixing two or more alloy powders can be used to obtain an alloy powder with the composition of the present invention according to a known process. An alloy powder with the composition of the present embodiment can be obtained according to a known process. It is particularly preferred to use a strip casting process among the known processes. When the two-alloy process is used, the main alloy powder is preferably obtained by using at least the strip casting process. This is because the formation of a titanium boride in the crude state can be further suppressed in this way.

[0034] In the case of single-element alloy powder, metals or alloys of the respective elements are produced to yield the aforementioned composition, and a flaky alloy is manufactured from these by a strip casting process. The resulting flaky alloy is subjected to hydrogen milling to obtain a coarse powder with a particle size of 1.0 mm or less. Next, the coarse powder is finely pulverized by a jet mill to obtain a fine powder (alloy powder) with a particle size D50 (value measured by laser diffraction using an airflow dispersion method (median size on a volume basis)) of 3 to 7 µm. A known lubricant can be added to the coarse powder as a pulverizing aid before jet mill pulverization, or to an alloy powder during and after jet mill pulverization.

[0035] When a mixed alloy powder is used, one or more grades of main alloy powder and one or more grades of additional alloy powder are first produced according to a preferred aspect, as described below. Then, one or more grades of additional alloy powder are mixed with the one or more grades of main alloy powder in a specific ratio to obtain a mixed alloy powder. Metals or alloys of the respective elements are produced such that, from the one or more grades of main alloy powder and the one or more grades of additional alloy powder, they yield the compositions specified in more detail below. In the same manner as with the single alloy powder mentioned above, flake alloys are produced by a strip casting process, and then the flake alloys are subjected to hydrogen milling to obtain coarse-grained powders.The resulting main alloy powders (coarse-grained powder of the main alloy powder) and additional alloy powders (coarse-grained powder of the additional alloy powders) are placed in a V-type mixer and mixed to obtain a blended alloy powder. If the coarse-grained powders have been mixed in this way at this stage, the resulting blended alloy powder is then fine-pulverized using a jet mill to obtain a fine-grained powder, thus yielding a blended alloy powder. Alternatively, the main alloy powder and the additional alloy powder can each be fine-pulverized in a jet mill to obtain fine-grained powders, which are then mixed to obtain the blended alloy powder.When a large quantity of the additional alloy powder is mixed, and because ignition can easily occur during fine pulverization, the main alloy powder and the additional alloy powder are preferably finely pulverized after mixing. The main alloy powder and the additional alloy powder have a composition within the range specified in more detail below. Several grades of main alloy powder and additional alloy powder may be used. In this case, the main alloy powder and the additional alloy powder have a composition within the range specified in more detail below. [Main alloy powder]

[0036] A primary alloy powder, from a preferred perspective, has a composition that includes: R: 27.5 to 34.0 mass%, RH: 2 to 10 mass%, B: 0.89 to 0.97 mass%, Ti: 0 to 0.2 wt% (except 0 wt% if Ti constitutes 0 wt% in one or more grades of the additional alloy powder), Ga: 0 to 0.4 mass%, Cu: 0.07 to 0.50 wt%, Al: 0.05 to 0.50 mass%, Residual T, and unavoidable impurities.

[0037] The rhodium content ranges from 27.5 to 34.0 wt%. If the rhodium content is less than 27.5 wt%, insufficient liquid phase can be formed during the sintering process, resulting in an insufficient density of the sintered magnet. However, if the rhodium content exceeds 34.0 wt%, the proportion of the main phase in the resulting RTB-based sintered magnet may be reduced, thus preventing a high B-value. r The RH content is 2 to 10% by mass of the total main alloy powder. If the RH content is less than 2% by mass, no high H can be obtained. cJin the RTB-based sintered magnet ultimately obtained. However, if the content exceeds 10% by mass, B r be reduced.

[0038] The B content ranges from 0.89 to 0.97% by mass. If the B content is less than 0.89% by mass, B r in the RTB-based sintered magnet ultimately obtained. However, if the content exceeds 0.97% by mass, no high H can be achieved. cJ This occurs because too little RT-Ga phase is formed. B may be partially replaced by C.

[0039] The titanium content ranges from 0 to 0.2% by mass. If the titanium content exceeds 0.2% by mass, excess titanium may be present, leading to a reduction in B. rof the RTB-based sintered magnet ultimately obtained. If Ti is not included in the main alloy powder, it is included in an additional alloy powder, so that the Ti content in the RTB-based sintered magnet ultimately obtained falls in the range of 0.1 to 0.2 wt%.

[0040] The Ga content ranges from 0 to 0.4% by mass. If the Ga content exceeds 0.4% by mass, excess Ga may be present, leading to a reduction in B. r in the RTB-based sintered magnet ultimately obtained. If Ga is not included in the main alloy powder, it is present in an additional alloy powder in a range of 0.7 to 12 wt%, so that the Ga content in the RTB-based sintered magnet ultimately obtained falls into a range of 0.3 to 0.7 wt%.

[0041] The copper content ranges from 0.07 to 0.50% by mass. If the copper content is less than 0.07% by mass, high hydrogen cannot be produced. cJ in the RTB-based sintered magnet ultimately obtained. However, if the content exceeds 0.50 mass%, B r be reduced.

[0042] Al (0.05% by mass or more and 0.5% by mass or less) may also be present to the extent that it is normally present. H cJ The quality may be improved by the presence of aluminum. The manufacturing process typically results in 0.05% or more of aluminum as unavoidable impurities, and the total amount (the amount of aluminum present as unavoidable impurities and the amount of intentionally added aluminum) may be 0.5% or less.

[0043] The Ga content in the main alloy powder is lower than that in the additional alloy powder. The formation of the RT-Ga phase in the main alloy powder can be suppressed by reducing the Ga content in the main alloy powder. [Additional alloy powder]

[0044] An additional alloy powder, from a preferred perspective, has a composition that includes: R1 (R1 is at least one rare earth element other than a heavy rare earth element RH, and necessarily includes Nd): 32 to 66 mass%, B: 0.3 to 0.9 mass%, Ti: 0 to 4 wt% (except 0 wt% if Ti constitutes 0 wt% in one or more main alloy powders), Ga: 0.7 to 12 mass%, Cu: 0 to 4 mass%, Al: 0 to 10 mass%, Residual T, and unavoidable impurities, the composition satisfying the following inequality (4). [T]≤72.4[B]

[0045] With the above composition, the additional alloy powder has a composition in which the contents of R and B are relative to those of the stoichiometric R2T. 14 B-composition is higher. Therefore, the formation of the RT-Ga phase can be suppressed.

[0046] R1 is at least one of the rare earth elements, excluding the heavy rare earth elements RH, and necessarily includes Nd. The heavy rare earth element RH is not present in the additional alloying powder. If the heavy rare earth element RH is present in the additional alloying powder, it cannot be present in the main phase, so that H cJ and B rIt cannot be improved because unnecessary heavy rare earth element RH is present at a grain boundary. The RH content ranges from 32 to 66 wt%. If the RH content is less than 32 wt%, a high-grade H cannot be produced in the resulting RTB-based sintered magnet. cJ If the content exceeds 66% by mass, the problem of oxidation arises due to the excessive amount of r, which causes a deterioration of the magnetic properties, and the risk of ignition, leading to production problems.

[0047] The B content ranges from 0.3 to 0.9 wt%. If the B content is less than 0.3 wt%, the RT-Ga phase can easily form because the B content is too small for the stoichiometric R²T reaction. 14 B composition. However, if the content exceeds 0.9 mass%, the B content is higher compared to the stoichiometric R2T. 14B composition is large, and therefore the R1T4 B4 phase can be easily formed.

[0048] The titanium content ranges from 0 to 4 wt%. If the titanium content exceeds 4 wt%, coarse and fine pulverization become difficult, leading to production problems. If the additional alloy powder does not contain titanium, the main alloy powder contains it in such a quantity that the titanium content in the resulting RTB-based sintered magnet falls into the range of 0.1 to 0.2 wt%.

[0049] The Ga content ranges from 0.7 to 12% by mass. If the Ga content is less than 0.7% by mass, high H cannot be produced. cJThis is because an insufficient amount of the RT-Ga phase is formed in the resulting RTB-based sintered magnet. However, if the content exceeds 12 wt%, Ga can be deposited, which is why no RTB-based sintered magnet with high H is possible. cJ will be received.

[0050] The copper content ranges from 0 to 4% by mass, and the aluminum content ranges from 0 to 10% by mass. If the copper content exceeds 4% by mass or the aluminum content exceeds 10% by mass, B r be reduced.

[0051] The additional alloy powder satisfies inequality (4). The composition in which the content of B is excessive instead of that of T(Fe), based on the stoichiometric R2T 14 The B composition is obtained by satisfying inequality (4). Therefore, the B content is greater than the stoichiometric fraction in R2T. 14B-type compound, which makes it possible to suppress the formation of the RT-Ga phase. [T]≤72.4[B]

[0052] It is possible, by means of the main alloy powder and the additional alloy powder of the present embodiment, to further suppress the formation of the RT-Ga phase compared to the case of production from a single alloy powder, thereby making it possible to achieve higher H cJ and H k / H cJ to reach.

[0053] The main alloy powder mentioned above and the additional alloy powders are mixed in a proportion of the additional alloy powder ranging from 0.5 wt% or more to 20 wt% or less, based on 100 wt% of the mixed alloy powder. The RTB-based sintered magnet produced by adjusting the proportion of the additional alloy powder within the range specified above can achieve a higher H cJThis means that the main alloy powder is one from the aforementioned composition range of the main alloy powder, which constitutes 80% or more by mass and 99.5% or less by mass of the mixed alloy powder after mixing. If two or more grades of a main alloy powder are used, each alloy powder has the aforementioned composition range of the main alloy powder, and the combined quantity of the two or more grades of main alloy powder constitutes 80% or more by mass and 99.5% or less by mass of the mixed alloy powder after mixing. (2) Shaping step

[0054] Using the alloy powder thus obtained (single alloy powder or mixed alloy powder), molding is carried out in a magnetic field to obtain a shaped body. This molding in a magnetic field can be performed according to any known method, including a dry molding process in which a dry alloy powder is filled into a cavity of a mold and then shaped while subjected to a magnetic field, and a wet molding process in which a slurry (containing the alloy powder dispersed therein) is injected into a cavity of a mold and then shaped while the dispersion medium of the slurry is drained off. (3) Sintering step

[0055] The shaped body is sintered to obtain a sintered body. A known method can be used to sinter the shaped body. To avoid oxidation in the atmosphere during sintering, the sintering is preferably carried out in a vacuum atmosphere or under a gas atmosphere. It is preferred to use an inert gas such as helium or argon as the atmospheric gas. (4) Heat treatment step

[0056] The resulting sintered body is preferably subjected to heat treatment to improve its magnetic properties. Known conditions for the heat treatment temperature and duration can be applied. To adjust the size of the sintered magnet, it can be machined, for example, by grinding. In this case, the heat treatment can be performed before or after machining. The sintered magnet can also be surface-treated. The surface treatment can be a known process, and it is possible to perform surface treatments such as aluminum vapor deposition, nickel electroplating, resin coating, and the like.

[0057] Aspects of the present invention are described by means of examples, but the present invention is not limited to these. Example 1

[0058] After weighing out the respective elements to obtain a given composition of an RTB-based sintered magnet as shown in Table 1, alloys were produced by a strip casting process. Each of the alloys thus obtained was coarsely pulverized by a hydrogen milling process to obtain a coarse-grained powder. The coarse-grained powder was then finely pulverized by a jet mill to obtain a fine-grained powder with a particle size D50 (value measured by a laser diffraction method using an airflow dispersion method (median size on a volume basis)) of 4 µm. Zinc stearate was added to the fine-grained powder as a lubricant at a rate of 0.05 parts by mass per 100 parts by mass of the fine-grained powder, followed by mixing and subsequent molding in a magnetic field to obtain a shaped body.The mold used was a so-called transverse magnetic field mold, in which the direction of the applied magnetic field and the pressing direction were perpendicular to each other. The resulting molded part was sintered by holding it in a vacuum for 4 hours at 1050°C to 1090°C according to the specified composition to obtain an RTB-based sintered magnet. The RTB-based sintered magnet had a density of 7.5 Mg / m³. 3or more. The analysis results of the components of the RTB-based sintered magnet thus obtained are shown in Table 1. The respective components in Table 1 were measured by high-frequency induction-coupled plasma emission spectrometry (ICP-OES). O₂ (oxygen content) was measured by a gas fusion infrared absorption method, N₂ (nitrogen content) was measured by a gas fusion thermal conductivity method, and C (carbon content) was measured by a combustion infrared absorption method using a gas analyzer. In Table 1, the value of the total content of Nd, Pr, and Dy is given as TRE (that is, the content of R), and in the cases where inequalities (1) and (2) of the present invention were satisfied, "Pass" was noted, while in the cases where inequalities (1) and (2) of the present invention were not satisfied, "Fail" was noted. The same applies to Table 3.Regarding the content of each component in Table 1, the values ​​of the decimal places following the minimum number of places were omitted. Therefore, the results of the calculations for inequalities (1) and (2) sometimes differ slightly from the values ​​obtained from the numerical values ​​entered in Table 1. For example, with respect to the Ga content of Example No. 1, the digits after the third decimal place were omitted. The same applies to the analysis results for the components listed below in Tables 3, 5, 6, and 8. All samples except for Comparison Example No. 13 in Table 3 and Comparison Example No. 40 in Table 8 satisfied inequality (3) of the present invention.

[0059] The RTB-based sintered magnet obtained after sintering was subjected to a heat treatment consisting of holding for 2 hours at 800°C and cooling to room temperature, followed by aging for 2 hours at 500°C and cooling to room temperature. The sintered magnet obtained after this heat treatment was processed into samples measuring 7 mm length × 7 mm width × 7 mm thickness, and the magnetic properties of each sample were then measured using a BH tracer. The measurement results are shown in Table 2. k / H cJ is H k a value of H (the same applies below) at a point where J has the value of 0.9 × J r (J r is the remanence, J r = B r ) in the second quadrant of a J (magnitude of magnetization) - H (strength of the magnetic field) curve. It is known that H k / H cJ with the RH content being reduced. Therefore, a comparison of H k / H cJExamples were taken where the amount of RH is almost the same. [Table 2] Nr. B r (T) A cJ (kA / m) A k (kA / m) H k / H cJ 1 1,192 2384 2142 0,898 Comparative example 2 1,179 2412 2246 0,931 present invention 3 1,213 2161 1902 0,880 Comparative example 4 1,264 2249 2065 0,918 present invention

[0060] As shown in Table 2, where a comparison was made between samples Nos. 1 and 2 (6.43 wt%) and samples Nos. 3 and 4 (approximately 5 wt%), where the RH (Dy) content is almost the same, a high H k / H cJ obtained in the present invention (samples nos. 2 and 4). Example 2

[0061] In the same manner as in Example 1, an RTB-based sintered magnet was produced, except that the mixing was carried out such that the composition of the RTB-based sintered magnet took on the composition of samples Nos. 5 to 26, as shown in Table 3.

[0062] The RTB-based sintered magnet thus obtained was processed in the same way as in Example 1, and then the magnetic properties were measured in the same way as in Example 1. The results are given in Table 4. [Table 4] No. B r (T) A cJ (kA / m) A k (kA / m) H k / H cJ 5 1,055 3152 2422 0,768 Comparative example 6 1,304 1645 1572 0,956 Comparative example 7 1,311 1931 1785 0,925 present invention 8 1,292 1822 1684 0,924 present invention 9 1,293 1753 1663 0,949 present invention 10 1,226 2082 1973 0,948 Comparative example 11 1,212 2028 1912 0,943 Comparative example 12 1,174 2188 2016 0,921 Comparative example 13 1,234 2038 1767 0,867 Comparative example 14 1,187 2065 1884 0,912 Comparative example 15 1,202 2174 1924 0,885 Comparative example 16 1,204 2019 1785 0,884 Comparative example 17 1,190 2213 2020 0,913 present invention 18 1,217 2206 2016 0,914 present invention 19 1,200 2191 2012 0,918 present invention 20 1,206 2154 1978 0,918 present invention 21 1,206 2100 1978 0,942 present invention 22 1,208 1997 1780 0,891 Comparative example 23 1,184 2227 2087 0,937 Comparative example 24 1,162 2378 2204 0,927 Comparative example 25 1,172 2191 1927 0,880 Comparative example 26 1,178 2404 2203 0,917 present invention

[0063] As shown in Table 4, where a comparison was made between samples Nos. 10 to 22 in which the RH content was almost the same (Dy: about 5.1 to 5.25%), samples Nos. 17 to 21 of the present invention achieved high magnetic properties of B r of 1,190 tons or more, H cJ of 2100 kA / m or more, and H k / H cJof 0.913 or more. However, samples Nos. 10 to 16 and 22, in which B (samples Nos. 10 and 16), Ga (samples Nos. 12, 13, 15 and 22), Cu (sample No. 14), inequality (1) (samples Nos. 10 and 11), or inequality (2) (samples Nos. 13, 15 and 16), which deviated from the scope of the present invention, did not exhibit high magnetic properties of B r of 1,190 tons or more, H cJ of 2100 kA / m or more and H k / H cJ of 0.913 or more. As can be seen from samples Nos. 21 and 22, where the composition is almost the same except that the Ga content differs by 0.11% by mass, no high H cJ This can be achieved if the Ga content is less than 0.3 mass%. . Similarly, the samples nos . 23 to 26, in which the RH content is almost the same (Dy: about 6.5%), of which sample No. 26 of the present invention has higher magnetic properties of a B rof 1.178 T or more, H cJ of 2404 kA / m or more, and H k / H cJ of 0.917 or more, compared to samples Nos. 23 to 25 as reference examples. Example 3

[0064] After weighing the respective elements into the given compositions of a main alloy powder or an additional alloy powder as specified in Table 5, alloys were produced by a strip casting process. The resulting flaky raw material alloy was subjected to hydrogen embrittlement under a hydrogen pressure atmosphere, and a dehydrogenation process was carried out by heating the alloy to 550°C in a vacuum and then cooling, producing a coarse-grained powder. The coarse-grained powder of the additional alloy thus obtained and the coarse-grained powder of the main alloy were placed in a V-type mixer under the conditions specified in Table 6, followed by mixing to obtain a blended alloy powder. For example, sample no.Specimen 30 in Table 6 was produced by using a mixed alloy powder, which was created by mixing an A1 alloy powder (main alloy powder) from Table 5 with a B1 alloy powder (additional alloy powder) to produce an RTB-based sintered magnet, and the proportion of the additional alloy powder in the mixed alloy powder was 5 wt% of 100 wt% of the mixed alloy powder. Similarly, specimens 31 to 33 were produced by using mixed alloy powders in combination in the proportions of the additional alloy powders as specified in Table 6. Then, 0.04 wt% zinc stearate was added as a lubricant and mixed into 100 wt% of the resulting coarse-grained powder, followed by dry pulverization under a stream of nitrogen gas using the gas stream pulverizer (jet mill device), resulting in a finely pulverized powder (as a mixed alloy powder) with a particle size D50 of 4 µm.The resulting mixed alloy powder was subjected to shaping and sintering under the same conditions as in Example 1. The analysis results of the components of the RTB-based sintered magnets thus obtained are given in Table 6. The respective components in Table 6 were measured in the same way as in Example 1. In cases where inequality (4) of the present invention was satisfied, “Pass” was recorded in Table 5. [Table 5] Alloy powder Type of alloy Composition of the alloy powder (mass%) Inequality(4) TRE Nd Pr Dy B Co Al Cu Ga Ti Fe A1 Main alloy powder 31.80 19.76 6.57 5.48 0.93 0.89 0.23 0.22 0.13 0.00 65.80 - A2 Main alloy powder 31.70 19.70 6.54 5.47 0.90 0.90 0.23 0.22 0.13 0.00 65.93 - A3 Main alloy powder 32.02 19.90 6.65 5.47 0.96 0.91 0.10 0.21 0.12 0.14 65.55 - A4 Main alloy powder 32.05 19.90 6.67 5.48 0.89 0.92 0.10 0.21 0.13 0.14 65.57 - B1 additional alloy powder 61.63 46.34 15.28 0.01 0.38 0.90 0.12 0.24 7.34 3.15 26.25 passport B2 additional alloy powder 56.74 42.80 13.91 0.03 0.48 0.88 0.19 0.21 6.82 2.40 32.29 passport B3 additional alloy powder 56.31 42.55 13.75 0.01 0.50 0.87 0.20 0.17 6.91 0.00 35.06 passport

[0065] The RTB-based sintered magnet thus obtained was processed in the same manner as in Example 1, and then the magnetic properties were measured in the same manner as in Example 1. The results are given in Table 7. [Table 7] No. B r (T) A cJ (kA / m) A k (kA / m) H k / H cJ 30 1.204 2249 2095 0.932 present invention 31 1.215 2191 2018 0.921 present invention 32 1.218 2226 2059 0.925 present invention 33 1.211 2208 2063 0.935 present invention

[0066] As shown in Table 7, samples Nos. 30 to 33, in which an RTB-based sintered magnet is produced using a main alloy powder and an additional alloy powder of the present invention, achieve high H cJ and H k / H cJ compared to sample no. 18 (with a composition almost identical to that of samples nos. 30, 32, and 33) and no. 20 (with a composition almost identical to that of sample no. 31) from Example 2, which were produced from a single alloy with almost the same composition. Samples nos. 31 to 33 (Ti: 0.11 wt% to 0.14 wt%) achieve higher B r than that of sample no. 30 (Ti: 0.16 wt%). Therefore, the Ti content is preferably less than 0.15 wt%. Example 4

[0067] An RTB-based sintered magnet was produced in the same manner as in Example 1, except that the mixing was carried out such that the composition of the RTB-based sintered magnet was that of samples Nos. 34 to 40 specified in Table 8.

[0068] The RTB-based sintered magnet thus obtained was processed in the same manner as in Example 1, and then its magnetic properties were measured in the same manner as in Example 1. The results are given in Table 9. [Table 9] Nr. Br(T) A cJ (kA / m) A k (kA / m) H k / H cJ 34 1,205 2134 2001 0,938 present invention 35 1,202 2179 2045 0,939 present invention 36 1,212 2181 2004 0,919 present invention 37 1,209 2183 2005 0,918 present invention 38 1,206 2154 1979 0,919 present invention 39 1,198 2145 1972 0,919 present invention 40 1,188 1945 1760 0,905 Comparative example

[0069] As shown in Table 9, even when Nb and Zr are present (samples nos. 34 and 35), B exhibits high magnetic properties. r of 1,190T or more, H cJ of 2100 kA / m or more, and H k / H cJof 0.913 or more. As can be seen from samples Nos. 36 to 39, whose composition is almost the same except for the differing Ti content, a high Br is obtained when the Ti content is in the range of 0.1 to 0.15 (samples Nos. 36 to 38). Therefore, the Ti content is preferably 0.1 wt% or more and less than 0.15 wt%. As can be seen from sample No. 40, where inequality (3) ([Ga] ≥ [Cu]) of the present invention differs from the scope of the present invention, when the Ga content is lower than the Cu content, H cJ significantly reduced, so that no high H k / H cJ will be received.

Claims

[1] RTB-based sintered magnet with: R: 27.5 to 34.0 mass%, where R is at least one of the rare earth elements, and necessarily includes Nd and a heavy rare earth element RH, where RH is at least one of Dy, Tb, Gd and Ho, RH: 2 to 10 mass%, B: 0.89 to 0.95 mass%, Ti: 0.1 to 0.2 mass%, Ga: 0.3 to 0.7 mass%, Cu: 0.07 to 0.50 wt%, Al: 0.05 to 0.50 mass%, M: 0 to 0.3 mass%, where M is Nb and / or Zr, Remainder T and unavoidable impurities, where T is a transition metal element and necessarily includes Fe, satisfying the following inequalities (1), (2) and (3): [T]−72.3([B]−0.45[Ti])>0 ([T]−72.3([B]−0.45[Ti])) / 55.85<13[Ga] / 69.72 [Ga]≥[Cu] where [T] is the content of T, expressed in mass%, [B] is the content of B, expressed in mass%, [Ti] is the content of Ti, expressed in mass%, [Ga] is the content of Ga, expressed in mass%, and [Cu] is the content of Cu, expressed in mass%. [2] RTB-based sintered magnet according to claim 1, further comprising: Ti: 0.1 wt% or more and less than 0.15 wt%. [3] Method for producing an RTB-based sintered magnet according to claim 1 or 2, comprising the method: a step of providing one or more types of main alloy powder and one or more types of additional alloy powder; a step of mixing the one or more grades of main alloy powder with the one or more grades of additional alloy powder such that the additional alloy powders constitute 0.5 wt% or more and 20 wt% or less of 100 wt% of a mixed alloy powder after mixing, in order to obtain the mixed alloy powder from one or more grades of main alloy powder and one or more grades of additional alloy powder; a forming step of shaping the mixed alloy powder to obtain a shaped body; a sintering step of the sintering of the molded body to obtain a sintered body; and a heat treatment step of subjecting the sintered body to a heat treatment; wherein one or more types of main alloy powder have a composition that includes: R: 27.5 to 34.0 mass%, RH: 2 to 10 mass%, B: 0.89 to 0.97 mass%, Ti: 0 to 0.2 wt%, except 0 wt% if Ti constitutes 0 wt% in one or more grades of additional alloy powder. Ga: 0 to 0.4 mass%, Cu: 0.07 to 0.50 wt%, Al: 0.05 to 0.50 mass%, Residual T and unavoidable impurities, and which have one or more types of additional alloy powder that include: R1: 32 to 66 mass%, where R1 is at least one of the rare earth elements other than the heavy rare earth elements RH, and necessarily includes Nd. B: 0.3 to 0.9 mass%, Ti: 0 to 4 wt%, except 0 wt% if Ti constitutes 0 wt% in one or more grades of the main alloy powder, Ga: 0.7 to 12 mass%, Cu: 0 to 4 mass%, Al: 0 to 10 mass%, Residual T and unavoidable impurities, the composition satisfying the following inequality (4): [T]≤72.4[B] [4] Method for producing an RTB-based sintered magnet according to claim 3, wherein the one or more grades of main alloy powder are obtained by means of a strip casting process.