RTB rare earth magnet and its manufacturing method

Abstract

To provide an R-T-B rare earth magnet and a manufacturing method thereof that suppress the decrease in residual magnetization when the R-T-B rare earth magnet contains a light rare earth element while improving coercive force.SOLUTION: An R-T-B rare earth magnet 100 according to the present disclosure includes a main phase 10 and a grain boundary phase 20 having an R2T14B type crystal structure. An average particle size of the main phase 10 is 1.0 to 10.0 μm. The main phase 10 has a core portion 12 and a shell portion 14. The total content of cerium, lanthanum, yttrium, and scandium is higher in the core portion 12 than in the shell portion 14. The total content of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium is higher in the shell portion 14 than in the core portion 12. The R-T-B rare earth magnet 100 contains 0.05 to 0.50 atom% of carbon. The content of carbon is higher in the grain boundary phase 20 than in the main phase 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an RTB rare earth magnet and a method for producing the same. [Background technology]

[0002] An RTB rare earth magnet (where R is a rare earth element, T is at least one of Fe and Co, and B is boron) comprises a main phase and a grain boundary phase surrounding the main phase. 14 This is a magnetic phase with a B-type crystal structure. This main phase provides high remanence. However, in RTB rare earth magnets, magnetization reversal easily occurs between the main phases, reducing coercivity. Therefore, various methods for improving coercivity have been attempted.

[0003] For example, in Patent Document 1, the main phase is R2T 14 The RTB rare earth magnet disclosed has a B-type crystal structure, an average grain size of the main phase of 0.8 to 2.8 μm, a boron content of 0.71 to 0.86 mass% or less, a carbon content of 0.13 to 0.34 mass% or less, a gallium content of 0.40 to 1.80 mass% or less, and a range of 0.14≦[C] / ([B]+[C])≦0.30 ([B] is the boron content in atomic %, and [C] is the carbon content in atomic %).

[0004] Furthermore, Patent Document 1 discloses that by reducing the boron content and adjusting the balance between the boron content and the carbon content, a thick grain boundary phase is formed, magnetically separating the main phases, and improving the coercive force, even when the grain size of the main phase is small. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-157834 Summary of the Invention [Problem to be solved by the invention]

[0006] The RTB rare earth magnet disclosed in Patent Document 1 contains a relatively large amount of carbon, which does not contribute to the development of magnetism, and therefore although it contributes to improving the coercive force, it inevitably reduces the remanence.

[0007] Among RTB rare earth magnets, the most common, offering an excellent balance between performance and price, are Nd-Fe-B rare earth magnets (neodymium magnets). As a result, Nd-Fe-B rare earth magnets are rapidly becoming more popular, leading to a sharp increase in the amount of Nd used, and it is possible that in the future, Nd usage will exceed production. For this reason, attempts are being made to replace some of the Nd with light rare earth elements such as Ce, La, Y, and Sc.

[0008] However, since substituting a portion of the Nd with a light rare earth element reduces remanence and coercivity, various measures are taken to use light rare earth elements to avoid practical problems. For this reason, when an RTB rare earth magnet contains a light rare earth element, adding a relatively large amount of carbon with the intention of improving coercivity, as in the RTB rare earth magnet disclosed in Patent Document 1, results in a serious decrease in remanence.

[0009] The present disclosure aims to solve the above-mentioned problems. That is, the present disclosure has an object to provide an RTB rare earth magnet and a method for manufacturing the same that can suppress a decrease in remanence and enjoy improved coercivity when the RTB rare earth magnet contains a light rare earth element. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to achieve the above object and have completed the RTB rare earth magnet and its manufacturing method of the present disclosure. The RTB rare earth magnet and its manufacturing method of the present disclosure include the following aspects. <1> An RTB rare earth magnet in which R is a rare earth element, T is at least one of Fe and Co, and B is boron, R2T 14 A main phase having a B-type crystal structure, and Grain boundary phase present around the main phase Equipped with The average grain size of the main phase is 1.0 to 10.0 μm, the main phase has a core portion and a shell portion present around the core portion, the total content of cerium, lanthanum, yttrium, and scandium is higher in the core portion than in the shell portion; the total content of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium is higher in the shell portion than in the core portion, The RTB rare earth magnet contains 0.05 to 0.50 atomic % of carbon, and The content ratio of the carbon is higher in the grain boundary phase than in the main phase. RTB rare earth magnet. <2> The RTB rare earth magnet according to <1>, wherein the shell portion has a higher carbon content than the core portion. <3> The RTB rare earth magnet according to <1> or <2>, wherein in the shell portion, when the carbon content [C] and the boron content [B] are expressed in atomic % relative to all constituent elements of the shell portion, [C] is 0.25 to 0.75 atomic %, and [C] / ([C]+[B]) is 0.04 to 0.10. <4> The RTB rare earth magnet according to <1> or <2>, wherein the main phase has an average grain size of 4.0 to 10.0 μm. (5) Diffusion and penetration of the modifier into the rare earth magnet precursor; Including, The rare earth magnet precursor essentially contains one or more elements selected from the group consisting of cerium, lanthanum, yttrium, and scandium as rare earth elements, and R2T 14 The alloy comprises a main phase having a B-type crystal structure and a grain boundary phase present around the main phase, and the main phase has an average grain size of 1.0 to 10.0 μm, The modifier contains 90 to 95 atomic % of one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium, and 5 to 10 atomic % of carbon, and A method for producing an RTB rare earth magnet, comprising diffusing and infiltrating 1.0 to 5.0 moles of the modifier into 100 moles of the rare earth magnet precursor. <6> The method for producing an RTB rare earth magnet according to <5>, wherein the modifier further contains 5 atomic % or less of an element other than a rare earth element that is alloyed with one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium. <7> The method for producing an RTB rare earth magnet according to <5> or <6>, wherein the main phase has an average grain size of 4.0 to 10.0 μm. [Effects of the Invention]

[0011] According to the present disclosure, by increasing the carbon content in the grain boundary phase compared to the main phase, the carbon content in the entire RTB rare earth magnet can be reduced, thereby providing an RTB rare earth magnet that, when containing a light rare earth element, can enjoy improved coercivity while suppressing a decrease in remanence.

[0012] Furthermore, according to the present disclosure, when a modifier containing rare earth elements other than light rare earth elements is diffused and infiltrated into a rare earth magnet precursor containing light rare earth elements, a predetermined proportion of carbon is added to the modifier. The carbon content in the modifier is set within a range that contributes to improving coercivity in the modifier and does not excessively reduce the content of rare earth elements other than light rare earth elements. This makes it possible to provide a method for producing an RTB rare earth magnet that can enjoy improved coercivity while suppressing a decrease in remanence, even when the RTB rare earth magnet contains light rare earth elements. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is an explanatory diagram schematically illustrating an example of an RTB rare earth magnet according to the present disclosure. [Figure 2] FIG. 2 is a graph showing the relationship between the content (molar ratio) of C in the modifier and the coercive force for each sample. [Figure 3] FIG. 3 is a graph in which the graph of FIG. 2 is stratified by the content ratio (molar ratio) of Nd in the modifier. [Figure 4] FIG. 4 is a graph showing the relationship between the Cu content (molar ratio) and the C content (molar ratio) in the modifier for each sample. [Figure 5] FIG. 5 is an explanatory diagram showing the results of line analysis of the vicinity of the interface between the main phase and the grain boundary phase in Example 2, performed using STEM-EDX. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the RTB rare earth magnet and its manufacturing method according to the present disclosure will be described in detail. Note that the RTB rare earth magnet and its manufacturing method according to the present disclosure are not limited to the embodiments described below.

[0015] Without being bound by theory, the present inventors will explain their findings regarding why RTB rare earth magnets containing light rare earth elements can enjoy improved coercivity while suppressing a decrease in remanence.

[0016] In RTB rare earth magnets, the inclusion of light rare earth elements reduces remanence and coercivity. RTB rare earth magnets have higher remanence than other permanent magnets, so even if the inclusion of light rare earth elements reduces remanence, the reduction in coercivity can be compensated for and the magnet can often be used without any problems in practice. However, when an RTB rare earth magnet contains light rare earth elements, even if the coercivity is improved by adding carbon, as in the rare earth magnet disclosed in Patent Document 1, a further reduction in remanence can pose a practical problem.

[0017] When an RTB rare earth magnet contains a light rare earth element, a modifier containing a rare earth element other than the light rare earth element is diffused and infiltrated into the rare earth magnet precursor containing the light rare earth element to compensate for the coercivity. The modifier diffuses and infiltrates into the grain boundary phase surrounding the main phase and further into the outer periphery of the main phase. During this process, the light rare earth element is exchanged with the rare earth element other than the light rare earth element at the outer periphery of the main phase, and the main phase forms a core portion and a shell portion. As a result, the core portion contains a higher proportion of the light rare earth element than the shell portion, and the shell portion contains a higher proportion of the rare earth element other than the light rare earth element than the core portion. This results in improved coercivity when the same amount of light rare earth element is used compared to an RTB rare earth magnet obtained by simply replacing the rare earth element other than the light rare earth element with the light rare earth element and blending the raw materials, thereby compensating for the decrease in coercivity that occurs when using a light rare earth element.

[0018] Therefore, the present inventors have discovered that when a modifier containing a predetermined proportion of carbon in addition to rare earth elements other than light rare earth elements is diffused and infiltrated into a rare earth magnet precursor containing light rare earth elements, the coercivity is further improved while suppressing the decrease in remanence. This is thought to be because the modifier diffuses and infiltrates through the grain boundary phase present around the main phase, allowing the amount of carbon to be increased in the outer surface region and / or the region near the outer surface of the main phase and reduced in the internal region of the main phase. The present inventors have also discovered that when the carbon content in the modifier exceeds a predetermined range, the content of elements that improve coercivity, i.e., rare earth elements other than light rare earth elements, in the modifier decreases, resulting in a decrease in coercivity.

[0019] That is, by adding carbon to the modifier within a range that does not excessively reduce the coercivity-enhancing elements in the modifier and then diffusing and infiltrating the modifier, sufficient carbon is present in the areas necessary for increasing coercivity, while minimizing the presence of carbon in areas that do not contribute to increasing coercivity, thereby reducing the carbon content of the rare earth magnet as a whole.The present inventors have discovered that this makes it possible to enjoy improved coercivity while suppressing a decrease in remanence.

[0020] Based on these findings, the constituent elements of the RTB rare earth magnet and the method for producing the same according to the present disclosure will now be described.

[0021] <RTB rare earth magnet> First, the constituent elements of the RTB rare earth magnet of the present disclosure will be explained using the drawings. FIG. 1 is an explanatory diagram that schematically shows an example of an RTB rare earth magnet of the present disclosure. The RTB rare earth magnet 100 of the present disclosure comprises a main phase 10 and a grain boundary phase 20. The grain boundary phase 20 exists around the main phase 10. The main phase 10 is an R2T 14 It has a B-type crystal structure. 14 The phase with B-type crystal structure is called "R2T 14 This is sometimes referred to as "phase B." Main phase 10 has a core portion 12 and a shell portion 14. Shell portion 14 is present around core portion 12. Below, the composition of RTB rare earth magnet 100 of the present disclosure, main phase 10, and grain boundary phase 20 will be described. Furthermore, with regard to main phase 10, the core portion 12 and shell portion 14 will be described.

[0022] <composition> The RTB rare earth magnet of the present disclosure contains 0.05 to 0.50 atomic % of carbon relative to the entire RTB rare earth magnet, in addition to the basic components R, T, and B. R is a rare earth element, T is at least one of Fe and Co, and B is boron.

[0023] When the carbon content is 0.05 atomic % or more, 0.10 atomic % or more, 0.15 atomic % or more, or 0.20 atomic % or more, the coercivity can be improved. On the other hand, when the carbon content is 0.50 atomic % or less, 0.49 atomic % or less, 0.48 atomic % or less, 0.47 atomic % or less, 0.46 atomic % or less, 0.45 atomic % or less, 0.44 atomic % or less, 0.43 atomic % or less, 0.42 atomic % or less, 0.41 atomic % or less, 0.40 atomic % or less, or 0.39 atomic % or less, the decrease in remanence can be suppressed. Furthermore, the presence of an excess of carbon can prevent a relative decrease in the content of rare earth elements, which contribute to the improvement of coercivity.

[0024] The composition of the RTB rare earth magnet of the present disclosure can be expressed, for example, by the molar ratio formula (R 2 (1-x) R 1 x ) y T (100-y-z-v) B z M 1 v ·(R 3 (1-p-q) C p M 2 q ) s It may be expressed as, but is not limited to,

[0025] In the above formula, R 1 is one or more elements selected from the group consisting of Ce, La, Y, and Sc. Ce is cerium, La is lanthanum, Y is yttrium, and Sc is scandium. R 2 and R 3 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho. Nd is neodymium, Pr is praseodymium, Gd is gadolinium, Tb is terbium, Dy is dysprosium, and Ho is holmium. T is either Fe or Co. Fe is iron, and Co is cobalt. B is boron. M 1is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, as well as unavoidable impurity elements. Ga is gallium, Al is aluminum, Cu is copper, Au is gold, Ag is silver, Zn is zinc, In is indium, and Mn is manganese. C is carbon. M 2 is R 3 These are elements other than rare earth elements that are alloyed with the alloy, and unavoidable impurity elements.

[0026] In this specification, unless otherwise specified, the rare earth elements are 17 elements: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Sc is scandium, Y is yttrium, La is lanthanum, Ce is cerium, Pr is praseodymium, Nd is neodymium, Pm is promethium, Sm is samarium, Eu is europium, Gd is gadolinium, Tb is terbium, Dy is dysprosium, Ho is holmium, Er is erbium, Tm is thulium, Yb is ytterbium, and Lu is lutetium.

[0027] In addition, unless otherwise specified in the specification, Sc, Y, La, and Ce are light rare earth elements. Pr, Nd, Pm, Sm, Eu, and Gd are medium rare earth elements. Tb, Dy, Ho, Er, Tm, Yb, and Lu are heavy rare earth elements. In general, heavy rare earth elements are highly rare, while light rare earth elements are less rare. The rarity of medium rare earth elements is between that of heavy rare earth elements and light rare earth elements.

[0028] In the above composition formula, R 2 (1-x) R 1 x is R 2 and R 1 The molar ratio of R to the total is (1-x). 2 There exists x in R 1 Similarly, in the above equation, R 3 (1-p-q) C p M 2 q is R 3, C, and M 3 The molar ratio of R to the total of (1-pq) 3 There exists a C of p, and there exists an M of q. 3 means that there is

[0029] In the above composition formula, (R 2 (1-x) R 1 x ) y Fe (100-y-z-v) B z M 1 v is derived from rare earth magnet precursors. 3 (1-p-q) C p M 2 q is derived from the modifier. The RTB rare earth magnet of the present disclosure is obtained by diffusing and infiltrating s moles of modifier into 100 moles of rare earth magnet precursor. After diffusing and infiltrating the modifier into the rare earth magnet precursor, the RTB rare earth magnet of the present disclosure has (100+s) moles. The composition formula above represents this, and R 1 and R 2 The total is y moles, T is (100-yzv) moles, B is z moles, and M 1 is v moles, and the sum of these is y moles + (100-yzv) moles + z moles + v moles = 100 moles. And R 3 , C, and M 2 The sum is s moles.

[0030] The constituent elements of the RTB rare earth magnet of the present disclosure, represented by the composition formula above, will now be described.

[0031] <R 1 〉 R 1 is an essential component of the RTB rare earth magnet of the present disclosure. 1 is one or more elements selected from the group consisting of Ce, La, Y, and Sc. 1 R belongs to the light rare earth elements and contributes to reducing the amount of medium and heavy rare earth elements used, which are rarer than light rare earth elements. 1is the main phase (R2T 14 B phase). R near the surface of the main phase 1 At least a part of the R in the modifier 3 By substituting R, the main phase can have a core portion and a shell portion. 1 Cerium and lanthanum are preferred as the modifiers because cerium, which exists in both trivalent and tetravalent forms, is relatively less stable, and lanthanum has a larger ionic radius than other rare earth elements, and therefore, when the modifier diffuses and penetrates into the grain boundary phase, cerium and / or lanthanum near the surface of the main phase are particularly likely to be expelled into the grain boundary phase.

[0032] <R 2 〉 R 2 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho, and belongs to the rare earth elements other than the light rare earth elements. Nd, Pr, and Gd belong to the medium rare earth elements, and Tb, Dy, and Ho belong to the heavy rare earth elements. That is, R 2 R belongs to the middle rare earth elements and / or heavy rare earth elements. In the rare earth magnet of the present disclosure, from the viewpoint of the balance between performance and price, it is preferable to increase the content ratio of Nd and Pr, and it is even more preferable to increase the content ratio of Nd. 1 When Nd and Pr coexist, didymium may be used as the R 2 are the constituent elements of the main phase.

[0033] <R 1 and R 2 Molar ratio of In the RTB rare earth magnet of the present disclosure, R 1 and R 2 is an element derived from rare earth magnet precursors. 1 and R 2 The molar ratio of x to R is 1 exists and R of (1-x) 2 The RTB rare earth magnet of the present disclosure may satisfy the condition 0.1≦x≦1.0. 1 This means that it is mandatory.

[0034] R present near the surface of the main phase 1 However, the modified material R 3 Since the shell part is formed by substitution with R 1 is present even in a small amount. When x is 0.1 or more, the formation of the shell portion becomes substantially recognizable. From the viewpoint of the formation of the shell portion, x may be 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, or 1.0. When x is 1.0, R 1 and R 2 For the total amount of R 1 This means that

[0035] R2Fe 14 In the B phase (main phase), when rare earth elements other than light rare earth elements are contained in a larger amount than light rare earth elements, the remanence and coercivity are higher. 1 (light rare earth elements) and R 2 The rare earth elements (rare earth elements other than light rare earth elements) are derived from the rare earth magnet precursor. By diffusing and penetrating the modifier into the rare earth magnet precursor, the R of the rare earth magnet precursor is 1 At least a part of the (light rare earth element) is R of the modifier 3 (rare earth elements other than light rare earth elements) to form the shell portion. When the main phase has a core portion and a shell portion, the remanence and coercivity of the entire rare earth magnet can be improved more efficiently by improving the remanence and coercivity in the shell portion rather than in the core portion. For this reason, the core portion is made entirely of inexpensive R 1 (light rare earth elements), in the shell 1 (light rare earth elements) is R 3 (rare earth elements other than light rare earth elements).

[0036] <R 1 and R 2 Total content ratio of In the above composition formula, R 1 and R 2The total content ratio of these is represented by y, and may satisfy 12.0≦y≦20.0, where the value of y corresponds to the content ratio (atomic %) relative to the rare earth magnet precursor.

[0037] If y is 12.0 or more, the rare earth magnet precursor does not contain a large amount of αFe phase, and a sufficient amount of the main phase (R2T 14 From this viewpoint, y may be 12.4 or more, 12.8 or more, or 13.2 or more. On the other hand, if y is 20.0 or less, the grain boundary phase will not become excessive. From this viewpoint, y may be 19.0 or less, 18.0 or less, or 17.0 or less.

[0038] B is the main phase (R2T 14 B phase) and affects the proportions of the main phase and grain boundary phase. The B content is represented by z in the above formula. The value of z corresponds to the content (atomic %) relative to the rare earth magnet precursor. If z is 20.0 or less, an RTB rare earth magnet can be obtained in which the main phase and grain boundary phase are appropriately present. From this perspective, z may be 18.0 or less, 16.0 or less, 14.0 or less, 12.0 or less, 10.0 or less, or 8.0 or less. On the other hand, if z is 5.0 or more, 6.0 or more, or 7.0, Th2Zn 17 and / or Th2Ni 17 It is unlikely that a large amount of phases with the R2T type crystal structure will occur. 14 The formation of B phase is rarely inhibited.

[0039] <M 1 〉 M 1 M can be contained within a range that does not impair the properties of the RTB rare earth magnet of the present disclosure. 1may contain unavoidable impurity elements. In this specification, unavoidable impurity elements refer to impurity elements contained in the raw materials of rare earth magnets, or impurity elements mixed in during the manufacturing process, which cannot be avoided, or which would result in a significant increase in manufacturing costs if avoided. Impurity elements mixed in during the manufacturing process include elements that are included for manufacturing reasons, to the extent that they do not affect the magnetic properties. In addition, unavoidable impurity elements include R 1 and R 2 The rare earth elements include rare earth elements other than those selected as above that are inevitably mixed in for the reasons described above.

[0040] Elements that can be contained within a range that does not impair the effects of the RTB rare earth magnet and the manufacturing method thereof of the present disclosure include Ga, Al, Cu, Au, Ag, Zn, In, and Mn. 1 As long as these elements are present in amounts below the upper limit of the content ratio, they do not substantially affect the magnetic properties. Therefore, these elements may be treated as unavoidable impurity elements. 1 As a result, it may contain unavoidable impurity elements.

[0041] In the above equation, M 1 The content ratio of is represented by v. The value of v corresponds to the content ratio (atomic %) relative to the rare earth magnet precursor. If the value of v is 2.0 or less, the magnetic properties of the RTB rare earth magnet of the present disclosure will not be impaired. From this perspective, v may be 1.5 or less, 1.0 or less, or 0.5 or less.

[0042] M 1 Since it is impossible to completely eliminate Ga, Al, Cu, Au, Ag, Zn, In, and Mn as well as unavoidable impurity elements, there is no practical problem even if the lower limit of v is 0.05, 0.1, or 0.2.

[0043] <T> T is the R 1 , R 2 , B, and M1 The content ratio of T is expressed as (100-yzv). When y, z, and v are within the ranges explained above, a main phase and a grain boundary phase existing around the main phase are obtained.

[0044] T is at least one of Fe and Co. 14 From the viewpoint of the stability of the B phase, T is more preferably Fe.

[0045] <R 3 〉 R 3 is an element derived from the modifier. The modifier diffuses and penetrates into the rare earth magnet precursor through the grain boundary phase. When the modifier diffuses and penetrates into the grain boundary phase, R near the surface of the main phase 1 At least a part of the R 3 to form the shell portion.

[0046] R 3 is one or more elements selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho, and belongs to the rare earth elements other than the light rare earth elements (medium rare earth elements and heavy rare earth elements). 1 At least a part of the (light rare earth element) is R of the modifier 3 (rare earth elements other than light rare earth elements), increasing the concentration of rare earth elements other than light rare earth elements in the shell portion. As a result, the remanence and coercivity of the RTB rare earth magnet of the present disclosure are improved.

[0047] <C> C is an element derived from the modifier. The modifier diffuses and penetrates into the rare earth magnet precursor through the grain boundary phase. This allows a large amount of C (carbon) to be present in the outer surface region and / or the region near the outer surface of the main phase, contributing to an improvement in coercivity.

[0048] As described above, the RTB rare earth magnet of the present disclosure contains 0.05 to 0.50 atomic percent of C. In the composition formula above, the C content (atomic percent) is {(p×s) / (100+s)}×100, and therefore satisfies 0.05≦{(p×q) / (100+q)}×100≦0.50.

[0049] <M 2 〉 M 2 is R 3 These are elements other than rare earth elements that are alloyed with M and unavoidable impurity elements. 2 is R 3 (1-p-q) C p M 2 q The melting point of the modifier having the composition represented by R 3 Elements other than rare earth elements and unavoidable impurity elements that lower the melting point of M 2 Examples of the impurity elements include one or more elements selected from the group consisting of Cu, Al, Co, and Fe, with Cu being particularly preferred. In this specification, the term "unavoidable impurity elements" refers to impurity elements contained in the raw materials of rare earth magnets, or impurity elements mixed in during the manufacturing process, which cannot be avoided, or which would result in a significant increase in manufacturing costs if avoided. Impurity elements mixed in during the manufacturing process include elements that are included for manufacturing reasons, but to the extent that they do not affect the magnetic properties. The unavoidable impurity elements also include R 3 The rare earth elements include rare earth elements other than those selected as above that are inevitably mixed in for the reasons described above.

[0050] M 2 (Except for rare earth elements as unavoidable impurities) do not contribute to the development of magnetism and cause a decrease in remanence. Therefore, if the diffusion and penetration of the modifier is ensured, M 2 The content of M in the modifier is preferably as low as possible. 2 The content ratio of will be explained next.

[0051] <R3 , C, and M 2 Molar ratio of R 3 , C, and M 2 is R 3 (1-p-q) C p M 2 q These are elements that constitute a modifier having a composition represented by the formula:

[0052] p is the molar ratio of C (carbon) in the modifier. If p is 0.05 or more, the melting point of the modifier is lowered, allowing the modifier to diffuse and penetrate into the rare earth magnet precursor, contributing to an improvement in coercivity. From this perspective, p may be 0.06 or more or 0.07 or more. On the other hand, if p is 0.10 or less, the R that contributes to an improvement in coercivity is reduced. 3 The content ratio of C does not decrease. Furthermore, excessive C can be prevented from diffusing into the rare earth magnet precursor, and as a result, a decrease in remanence can be prevented. From these viewpoints, p may be 0.09 or less or 0.08 or less. For example, when p is 0.05 to 0.10, the content ratio of C (carbon) in the entire modifier is 5 to 10 atomic %.

[0053] q is the M in the modifier 2 When q is 0.05 or less, the decrease in remanence does not pose a practical problem. From this point of view, q may be 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less, or may be 0. For example, when q is 0.05 or less, the ratio of M to the entire modifier is 2 is 5 atomic % or less.

[0054] R in the modified material 3 The molar ratio of C and M 2 is the remainder of the equation, expressed as (1-pq).

[0055] <Molar Ratio of Elements Derived from Rare Earth Magnet Precursor and Elements Derived from Modifier> In the above composition formula, this means that the modifier is present in an amount of s moles per 100 moles of rare earth magnet precursor.

[0056] If s is 1.0 or more, the R of the main phase of the rare earth magnet precursor 1 At least a part of the (light rare earth element) is 3 (rare earth elements other than light rare earth elements), forming a shell portion. As a result, the remanence and coercivity of the rare earth magnet of the present disclosure are improved. Furthermore, C (carbon) is present in large amounts in the outer peripheral surface region and / or the region near the outer peripheral surface of the main phase, further improving coercivity. From this perspective, s may be 2.0 or greater, or 3.0 or greater. On the other hand, if s is 5.0 or less, excess C (carbon) will not reduce remanence. From this perspective, s may be 4.0 or less, or 3.0 or less.

[0057] Next, the main phase and the grain boundary phase will be described, including the core and shell portions of the main phase.

[0058] <Main phase> The main phase is R2T 14 It has a B-type crystal structure. 14 The term "B type" is used because the main phase (crystal structure) may contain elements other than R, T, and B in substitutional and / or interstitial forms.

[0059] The average grain size of the main phase is 1.0 to 10.0 μm. The modifier used to obtain the rare earth magnet of the present disclosure has a relatively high melting point. When the average grain size of the main phase is 1.0 μm or more, coarsening of the main phase can be substantially avoided even when the modifier is diffused and infiltrated. From this perspective, the average grain size of the main phase may be 1.1 μm or more, 1.3 μm or more, 1.5 μm or more, 2.0 μm or more, 2.5 μm or more, 3.0 μm or more, 3.5 μm or more, 4.0 μm or more, 4.5 μm or more, 5.0 μm or more, or 5.5 μm or more. When the average grain size of the main phase is 10.0 μm or less, the desired remanence and / or coercivity are not reduced due to the grain size of the main phase. From this perspective, the average grain size of the main phase may be 9.0 μm or less, 8.0 μm or less, 7.0 μm or less, or 6.0 μm or less. The average grain size of the main phase hardly changes before and after the diffusion and penetration of the modifier.

[0060] When carbon is added without using a modifier, as in Patent Document 1, it is considered necessary for the average grain size of the main phase to be 2.8 μm or less to improve coercivity. To obtain the RTB rare earth magnet of the present disclosure, the modifier is diffused and infiltrated, thereby causing a large amount of C (carbon) to be present in the outer peripheral surface region and / or the region near the outer peripheral surface of the main phase. Therefore, even if the average grain size of the main phase is relatively large, the coercivity is improved. From this perspective, the average grain size of the main phase may be 4.0 μm or more, 4.1 μm or more, 4.2 μm or more, 4.3 μm or more, 4.4 μm or more, 4.5 μm or more, or 4.6 μm or more.

[0061] The "average grain size" refers to the average maximum length of the main phase. The "average maximum length" refers to the average maximum length of each main phase within a defined region in a scanning electron microscope image or transmission electron microscope image. For example, if the cross section of the main phase is elliptical, the length of its major axis is the maximum length. For example, if the cross section of the main phase is rectangular, the length of the longer diagonal is the maximum length. Furthermore, since the main phase of the rare earth magnet of the present disclosure has a core portion and a shell portion, the maximum length of the main phase is the maximum length including the shell portion. For example, in the example shown in Figure 1, the maximum length of the main phase 10 is the length indicated by L.

[0062] <Core and shell> The main phase of the RTB rare earth magnet of the present disclosure has a core portion and a shell portion. The shell portion surrounds the core portion.

[0063] Increasing the remanence and coercivity of the entire rare earth magnet can be achieved by increasing the remanence and coercivity in the shell portion rather than in the core portion. In the RTB rare earth magnet of the present disclosure, the light rare earth elements in the rare earth magnet precursor are discharged from the shell portion to the grain boundary phase due to the diffusion and penetration of the modifier, and the rare earth elements other than the light rare earth elements in the modifier are diffused and penetrated from the grain boundary phase into the shell portion, which is advantageous for improving the remanence and coercivity.

[0064] The rare earth magnet precursor for obtaining the rare earth magnet of the present disclosure essentially contains one or more elements selected from the group consisting of cerium, lanthanum, yttrium, and scandium as rare earth elements. Therefore, in the RTB rare earth magnet of the present disclosure, the total content of cerium, lanthanum, yttrium, and scandium is higher in the core than in the shell. For example, if the RTB rare earth magnet of the present disclosure contains cerium and lanthanum but does not contain yttrium and scandium, the total content of cerium, lanthanum, yttrium, and scandium is the total content of cerium and lanthanum. The total content ratio of cerium, lanthanum, yttrium, and scandium in the core portion may be, for example, 1.1 times or more, 1.3 times or more, or 1.5 times or more, and may be 10.0 times or less, 9.0 times or less, 8.0 times or less, 7.0 times or less, 6.0 times or less, 5.0 times or less, 4.5 times or less, 4.0 times or less, 3.0 times or less, or 2.0 times or less, of the total content ratio of cerium, lanthanum, yttrium, and scandium in the shell portion.

[0065] The modifier for obtaining the rare earth magnet of the present disclosure contains one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium. Therefore, in the RTB rare earth magnet of the present disclosure, the total content of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium is higher in the shell than in the core. For example, if the RTB rare earth magnet of the present disclosure contains neodymium and praseodymium but does not contain gadolinium, terbium, dysprosium, or holmium, the total content of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium is the total content of neodymium and praseodymium. The total content ratio of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium in the shell portion may be, for example, 1.1 times or more, 1.3 times or more, or 1.5 times or more, and may be 10.0 times or less, 9.0 times or less, 8.0 times or less, 7.0 times or less, 6.0 times or less, 5.0 times or less, 4.5 times or less, 4.0 times or less, 3.0 times or less, or 2.0 times or less, of the total content ratio of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium in the core portion.

[0066] Since the modifier contains carbon, some of the carbon that has diffused and penetrated into the grain boundary phase is present in the outer surface region and / or the region near the outer surface of the main phase. 14 It is believed that some of the boron in the modifier (phase B) is replaced by carbon. It is also believed that the carbon in the modifier diffuses and penetrates into the shell portion but does not diffuse into the core portion. Therefore, the carbon content is higher in the shell portion than in the core portion.

[0067] Furthermore, the degree to which boron is substituted by carbon in the shell portion is expressed by the carbon content [C] (atomic %) relative to all the constituent elements of the shell portion, and the substitution rate. The substitution rate can be expressed as [C] / ([C]+[B]). As mentioned above, [C] is the carbon content (atomic %) in the shell portion relative to all the constituent elements of the shell portion. [B] is the boron content (atomic %) in the shell portion relative to all the constituent elements of the shell portion.

[0068] [C] is determined by STEM-EDX analysis of the shell part. [B] is determined by the main phase (R2T 14 The boron content in the theoretical composition of the alloy (phase B) is 5.88 atomic %, and the value of [C] (atomic %) is subtracted to obtain the boron content.

[0069] When [C] is 0.25 atomic % or more, 0.30 atomic % or more, or 0.35 atomic % or more, the coercivity can be improved by carbon, while when [C] is 0.50 atomic % or less, 0.45 atomic % or less, or 0.40 atomic % or less, the decrease in remanence can be suppressed.

[0070] When [C] / ([C]+[B]) is 0.04 or more, 0.05 or more, or 0.06 or more, the carbon improves the coercivity. On the other hand, when [C] / ([C]+[B]) is 0.10 or less, 0.09 or less, 0.08 or less, or 0.07 or less, the decrease in remanence can be suppressed.

[0071] <Grain boundary phase> The grain boundary phase exists around the main phase. 14 Various phases other than the B phase are mixed in. Some of these phases have an incomplete crystal structure. For this reason, it is difficult to express the grain boundary phase in terms of its crystal structure. However, its composition is such that, prior to the diffusion and penetration of the rare earth magnet precursor, i.e., the main phase (R2T), is present throughout the grain boundary phase. 14 The grain boundary phase has a higher content of rare earth elements than the grain boundary phase (B phase). For this reason, the grain boundary phase is sometimes called the "R-rich phase," "rare earth element-rich phase," or "rare earth-rich phase."

[0072] The modifier diffuses through the grain boundary phase, and the content of rare earth elements in the grain boundary phase increases after the modifier diffuses. Furthermore, carbon is present in the grain boundary phase due to the modifier diffuses.

[0073] A portion of the carbon that has diffused and penetrated into the grain boundary phase further diffuses and penetrates into the outer peripheral surface region and / or the outer peripheral surface-near region of the main phase, but most of the carbon that has diffused and penetrated into the grain boundary phase remains in the grain boundary phase. As a result, the carbon content in the grain boundary phase is higher than that in the main phase. The carbon content in the grain boundary phase may be, for example, 1.1 times or more, 1.3 times or more, or 1.5 times or more, or may be 30 times or less, 25 times or less, 20 times or less, 15 times or less, 10 times or less, 9.0 times or less, 8.0 times or less, 7.0 times or less, 6.0 times or less, 5.0 times or less, 4.0 times or less, 3.0 times or less, or 2.0 times or less of the carbon content in the main phase.

[0074] 《Manufacturing method》 Next, a method for producing the RTB rare earth magnet of the present disclosure will be described.

[0075] The method for producing an RTB rare earth magnet according to the present disclosure includes diffusing and infiltrating a modifier into a rare earth magnet precursor. The rare earth magnet precursor and the modifier will be described below.

[0076] <Rare earth magnet precursor> The rare earth magnet precursor essentially contains one or more elements selected from the group consisting of cerium, lanthanum, yttrium, and scandium as rare earth elements. The composition of the rare earth magnet precursor is, for example, as described above, represented by the composition formula (R 2 (1-x) R 1 x ) y T (100-y-z-v) B z M 1 v It may be expressed as, but is not limited to,

[0077] The rare earth magnet precursor comprises a main phase and a grain boundary phase. The main phase is R2T 14It has a B-type crystal structure. The grain boundary phase exists around the main phase. The average grain size of the main phase is 1.0 to 10 μm.

[0078] Regarding the rare earth magnet precursor, the composition, main phase, and grain boundary phase are as explained in "<RTB Rare Earth Magnet>".

[0079] The rare earth magnet precursor can be prepared by a known method for producing a rare earth sintered magnet, which means a magnet obtained by high-temperature, pressureless sintering of a magnetic powder having a micron-sized main phase.

[0080] The rare earth magnet precursor may be prepared, for example, as follows, but is not limited to this.

[0081] The composition of the rare earth magnet precursor is expressed by the formula (R 2 (1-x) R 1 x ) y Fe (100-y-w-z-v) Co w B z M 1 v When the composition of the molten metal is expressed as the main phase (R2T 14 The molten metal is cooled at a rate such that the average particle size of the rare earth magnet precursor (phase B) becomes 1.0 to 10.0 μm, thereby obtaining a magnetic ribbon. Such a cooling rate is, for example, 1 to 1000°C / s. Methods for obtaining magnetic powder at such a cooling rate include, for example, strip casting and book molding. The composition of the molten metal is basically the same as the overall composition of the rare earth magnet precursor, but for elements that may be depleted in the process of producing the rare earth magnet precursor, the amount of depletion may be taken into account.

[0082] The magnetic powder obtained by pulverizing the magnetic ribbon is then compacted. Compaction may be performed in a magnetic field. This allows anisotropy to be imparted to the sintered rare earth magnet. The compacting pressure during compaction may be, for example, 50 MPa or more, 100 MPa or more, 200 MPa or more, or 300 MPa or more, and may be 1000 MPa or less, 800 MPa or less, or 600 MPa or less. The magnetic field applied may be 0.1 T or more, 0.5 T or more, 1 T or more, 1.5 T or more, or 2.0 T or more, and may be 10.0 T or less, 8.0 T or less, 6.0 T or less, or 4.0 T or less. Examples of pulverization methods include coarsely pulverizing the magnetic ribbon and then further pulverizing it using a jet mill or the like. Examples of coarse pulverization methods include using a hammer mill, hydrogen embrittlement of the magnetic ribbon, and combinations thereof.

[0083] The above-mentioned powder compact is pressurelessly sintered to obtain a rare earth magnet precursor. The powder compact is pressurelessly sintered for a long time at a high temperature to increase the density of the sintered compact. The sintering temperature may be, for example, 900°C or higher, 950°C or higher, or 1000°C or higher, and 1100°C or lower, 1050°C or lower, or 1040°C or lower. The sintering time may be, for example, 1 hour or higher, 2 hours or higher, 3 hours or higher, or 4 hours or higher, and 24 hours or lower, 18 hours or lower, 12 hours or lower, or 6 hours or lower. To suppress oxidation of the powder compact during sintering, an inert gas atmosphere is preferred. Examples of inert gas atmospheres include a nitrogen gas atmosphere.

[0084] <Modifier> The modifier contains 90 to 95 atomic % of one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium, and 5 to 10 atomic % of carbon. The modifier may further contain 5 atomic % or less of an element other than a rare earth element that alloys with the one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium. The composition of the modifier can be, for example, represented by the molar composition formula (R 3 (1-p-q) C p M 2q ), but is not limited to this.

[0085] The composition of the modifier is as explained in "<RTB-based rare earth magnet>".

[0086] Examples of methods for preparing modifiers include cooling a molten metal having the modifier composition using a liquid quenching method or a strip casting method to obtain a thin strip or the like. These methods result in little segregation in the modifier because the molten metal is rapidly cooled. Another method for preparing modifiers includes casting a molten metal having the modifier composition into a mold such as a book mold. This method allows for relatively easy production of a large amount of modifier. To reduce the segregation of the modifier, the book mold is preferably made of a material with high thermal conductivity. It is also preferable to subject the cast material to a homogenizing heat treatment to suppress segregation. Another method for preparing modifiers includes charging raw materials for the modifier into a container, arc-melting the raw materials in the container, and cooling the melt to obtain an ingot. This method allows for relatively easy production of the modifier, even when the raw materials have a high melting point. To reduce the segregation of the modifier, it is preferable to subject the ingot to a homogenizing heat treatment.

[0087] <Diffusion and penetration> 1.0 to 5.0 moles of modifier are diffused and infiltrated into 100 moles of rare earth magnet precursor. The ratio of modifier to rare earth magnet precursor is as explained in "<RTB-based rare earth magnet>".

[0088] The modifier is diffused and infiltrated into the rare earth magnet precursor at a temperature equal to or higher than the melting point of the modifier and between 800 and 1000° C. The diffusion and infiltration temperature, as long as it is equal to or higher than the melting point of the modifier, may be 820° C. or higher, 840° C. or higher, 860° C. or higher, 880° C. or higher, 900° C. or higher, 910° C. or higher, 920° C. or higher, 930° C. or higher, 940° C. or higher, or 950° C. or higher, or may be 990° C. or lower, 980° C. or lower, 970° C. or lower, 970° C. or lower, or 960° C. or lower.

[0089] As long as the main phase of the rare earth magnet precursor does not become coarse during the diffusion and infiltration of the modifier, a higher diffusion and infiltration temperature is preferable to form the desired shell portion. A diffusion and infiltration temperature of 1000°C or less, 990°C or less, 980°C or less, 970°C or less, 970°C or less, or 960°C or less can prevent the main phase of the rare earth magnet precursor from becoming coarse.

[0090] Transformation The RTB rare earth magnet and its manufacturing method of the present disclosure can be modified as appropriate within the scope of the claims.

[0091] For example, in the RTB rare earth magnet of the present disclosure, the shell portion may be present around (outside) the core portion. That is, the shell portion may be present directly or indirectly around (outside) the core portion. The shell portion being indirectly present around (outside) the core portion means that there may be an overlapping portion between the core portion and the shell portion. The overlapping portion between the core portion and the shell portion is the transition portion from the core portion to the shell portion.

[0092] Furthermore, with regard to the manufacturing method, for example, the modifier may be diffused and infiltrated into a rare earth magnet precursor, and then cooled to form the RTB rare earth magnet of the present disclosure, or the cooled rare earth magnet may be further heat-treated to form the RTB rare earth magnet of the present disclosure. Without being bound by theory, it is believed that this heat treatment melts part of the grain boundary phase remaining after the modifier has been diffused and infiltrated, without altering (melting) the structure of the main phase, and the molten material solidifies, uniformly coating the main phase and contributing to improving coercivity.

[0093] To obtain the effect of improving the coercive force, the heat treatment temperature is preferably 450° C. or higher, more preferably 475° C. or higher, and even more preferably 500° C. or higher. On the other hand, to avoid alteration of the structure of the main phase, the heat treatment temperature is preferably 600° C. or lower, more preferably 575° C. or lower, and even more preferably 550° C. or lower.

[0094] To avoid oxidation of the RTB rare earth magnet of the present disclosure, the heat treatment is preferably performed in an inert gas atmosphere, including a nitrogen gas atmosphere. Note that the heat treatment after diffusion and infiltration described above is sometimes referred to as the "optimized heat treatment" in this specification. [Example]

[0095] The RTB rare earth magnet and its manufacturing method according to the present disclosure will be explained in more detail below using examples and comparative examples. Note that the RTB rare earth magnet and its manufacturing method according to the present disclosure are not limited to the conditions used in the following examples.

[0096] <Sample preparation> A strip cast material having the composition shown in Table 1 was subjected to hydrogen pulverization and then further pulverized using a jet mill to obtain a magnetic powder. This magnetic powder was molded in a magnetic field to obtain a green compact. This green compact was then pressurelessly sintered at 1,060°C for 4 hours to obtain a sintered body. A modifier having the composition shown in Table 1 was then diffused and infiltrated into this sintered body. The diffusion and infiltration conditions were 950°C and 165 minutes. The sintered body after diffusion and infiltration was then subjected to an optimized heat treatment to obtain samples of Examples 1 to 3 and Comparative Examples 1 to 4. The optimized heat treatment conditions were 500°C and 60 minutes.

[0097] <evaluation> Each sample was cut into 2mm x 2mm x 2mm pieces and its magnetic properties were measured. A vibrating sample magnetometer (VSM) was used for the measurements. The magnetic properties were measured at room temperature. The structure of each sample was observed using an SEM, and the average grain size of the main phase was determined using the method explained in "RTB-based rare earth magnets." EPMA was also used to measure the C concentration in the grain boundary phase. STEM-EDX was also used to perform a compositional analysis of the area near the interface between the main phase and the grain boundary phase.

[0098] The results are shown in Table 1. FIG. 2 is a graph showing the relationship between the C content (molar ratio) in the modifier and the coercive force for each sample. FIG. 3 is a graph in which the graph of FIG. 2 is stratified by the Nd content (molar ratio) in the modifier. FIG. 4 is a graph showing the relationship between the Cu content (molar ratio) and the C content (molar ratio) in the modifier for each sample. FIG. 5 is an explanatory diagram showing the results of line analysis of Example 2 near the interface between the main phase and the grain boundary phase using STEM-EDX.

[0099] [Table 1-1]

[0100] [Table 1-2]

[0101] Table 1 confirms that the samples of Examples 1 to 3 improved their coercivity while suppressing a decrease in remanence. Figures 2 and 3 confirm that an excessive C content in the modifier relatively reduces the Nd (rare earth element other than light rare earth elements) content in the modifier, resulting in a decrease in coercivity. Figure 4 confirms that, within a specified range, the modifier can contain an element (Cu) that lowers the melting point of the rare earth magnet it contains. Figure 5 confirms that carbon that diffused and penetrated into the grain boundary phase diffused all the way to the shell portion of the main phase. Because carbon is not thought to diffuse and penetrate into the core portion of the main phase, the analysis value for the core portion is the baseline.

[0102] The above results confirm the effectiveness of the RTB rare earth magnet and method of manufacturing the same disclosed herein. [Explanation of symbols]

[0103] 10 Main phase 12 Core section 14 Shell part 20 Grain boundary phase 100 RTB rare earth magnet of the present disclosure

Claims

1. A rare earth magnet precursor essentially containing one or more elements selected from the group consisting of cerium, lanthanum, yttrium, and scandium as rare earth elements, having a main phase with an R 2 T 14 B crystal structure and a grain boundary phase present around said main phase, wherein said main phase has an average grain size of 1.0 to 10.0 μm, A modifier containing 90 to 95 atomic % of one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium, and 5 to 10 atomic % of carbon. An R-T-B rare earth magnet obtained by diffusing and infiltrating R is a rare earth element, T is at least one of Fe and Co, and B is boron; R ２ T １４ a main phase having a B-type crystal structure, and Grain boundary phase present around the main phase Equipped with The average grain size of the main phase is 1.0 to 10.0 μm, the main phase has a core portion and a shell portion present around the core portion, the total content of cerium, lanthanum, yttrium, and scandium is higher in the core portion than in the shell portion; the total content of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium is higher in the shell portion than in the core portion, The RTB-based rare earth magnet contains 0.05 to 0.50 atomic % of carbon, and the content ratio of carbon is higher in the grain boundary phase than in the main phase, The carbon content is higher in the shell portion than in the core portion, In the shell portion, when the content ratio of carbon is [C] and the content ratio of boron is [B], in atomic %, relative to all constituent elements of the shell portion, [C] is 0.25 to 0.75 atomic %, and [C] / ([C]+[B]) is 0.04 to 0.

10. RTB rare earth magnet.

2. 2. The RTB system rare earth magnet according to claim 1, wherein the average grain size of the main phase is 4.0 to 10.0 μm.

3. Diffusion-infiltrating the modifier into the rare earth magnet precursor; Including, The rare earth magnet precursor essentially contains one or more elements selected from the group consisting of cerium, lanthanum, yttrium, and scandium as rare earth elements, and R ２ T １４ The alloy comprises a main phase having a B-type crystal structure and a grain boundary phase present around the main phase, and the main phase has an average grain size of 1.0 to 10.0 μm; the modifier contains 90 to 95 atomic % of one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium, and 5 to 10 atomic % of carbon; 1.0 to 5.0 moles of the modifier are diffused and infiltrated into 100 moles of the rare earth magnet precursor; By the diffusion and penetration, a core portion and a shell portion present around the core portion are formed in the main phase, The carbon content is higher in the grain boundary phase than in the main phase, The carbon content is higher in the shell portion than in the core portion. A method for manufacturing an RTB-based rare earth magnet.

4. 4. The method for producing an R-T-B based rare earth magnet according to claim 3, wherein the modifier further contains 5 atomic % or less of an element other than a rare earth element that is alloyed with one or more elements selected from the group consisting of neodymium, praseodymium, gadolinium, terbium, dysprosium, and holmium.

5. 5. The method for producing an RTB based rare earth magnet according to claim 3, wherein the average grain size of the main phase is 4.0 to 10.0 μm.

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