Rare earth magnet and method for producing the same

Abstract

To provide a rare earth magnet capable of improving both residual magnetization and coercive force.SOLUTION: The rare earth magnet of the present invention comprises a main phase and a grain boundary phase present around the main phase, wherein the overall composition in terms of atomic ratio is: Formula R1xT (100-x-y-z) (B (1-s) Cs) yMz (where R1 is one or more elements selected from the group consisting of Nd, Ce, La, Pr, Gd, Tb, Dy, and Ho, T is one or more elements selected from the group consisting of Fe, Co, and Ni, M is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn and an inevitable impurity element, and 12.0 ≤ x ≤ 20.0, 5.00 ≤ y ≤ 20.0, 0 ≤ z ≤ 2.0, and 0.07 ≤ s ≤ 0.17). Wherein the main phase is a R2Fe14B type (where R is a rare-earth element). FIG. 1 is a schematic cross-sectional view of an embodiment of the present invention.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rare earth magnet and a method for manufacturing the same, and more particularly to an RTB rare earth magnet (where R is a rare earth element, T is a transition metal element, and B is boron) and a method for manufacturing the same. [Background technology]

[0002] The RTB rare earth magnet has a main phase and a grain boundary phase surrounding the main phase. The main phase is R2Fe 14 This is a magnetic phase with a B-type crystal structure. RTB rare earth magnets are often used in motors because this main phase allows them to achieve high remanence.

[0003] Various attempts have been made to improve the magnetic properties of RTB rare earth magnets, and one known example is a magnet that attempts to improve magnetic properties by substituting a portion of the boron (B) with carbon (C). For example, a Nd-Fe-B magnet is known that is manufactured by hot plastic working using 40% or less by weight of powder of waste materials with a carbon content of 0.2% or less by weight (Patent Document 1). Another example is an anisotropic permanent magnet containing rare earth elements, iron or a mixture of iron and cobalt, carbon, and boron, which has a tetragonal crystalline phase, RE2™. 14 C X B 1-X A magnet is known that contains a main phase of fine, flat particles aligned by hot working, where RE is one or more rare earth elements, TM is iron or a mixture of iron and cobalt, and X is 0.2 to 1.0 (Patent Document 2). Furthermore, an RTB-based permanent magnet is known that contains at least C and Ga in addition to R, T, and B, and satisfies 0.14≦[C] / ([B]+[C])≦0.30 (where [B] is the B content (at %) and [C] is the C content (at %)) (Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-100524 [Patent Document 2] Japanese Patent Application Publication No. 5-152119 [Patent Document 3] Japanese Patent Application Publication No. 2017-157834 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional RTB rare earth magnets in which part of the B is replaced with C, the effect of improving the coercive force can be obtained by replacing part of the B with C. However, replacing B with C improves the anisotropy field, but also reduces the saturation magnetization of the main phase, which can result in a decrease in remanence.

[0006] The present invention has been made in view of the above circumstances, and its object is to provide a rare earth magnet that can improve both remanence and coercivity, and a method for manufacturing the same. [Means for solving the problem]

[0007] In order to solve the above problems, the rare earth magnet of the present invention comprises a main phase and a grain boundary phase surrounding the main phase, and has an overall composition in atomic ratios represented by the formula R 1 x T (100-x-y-z) (B (1-s) C s ) y M z (However, R 1 is one or more elements selected from the group consisting of Nd, Ce, La, Pr, Gd, Tb, Dy, and Ho; T is one or more elements selected from the group consisting of Fe, Co, and Ni; M is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, and unavoidable impurity elements, and 12.0≦x≦20.0, 5.00≦y≦20.0, 0≦z≦2.0, and 0.07≦s≦0.17. 14 It is characterized by having a B-type (where R is a rare earth element) crystal structure.

[0008] Furthermore, the method for producing a rare earth magnet of the present invention is the method for producing the rare earth magnet described above, and further comprises the step of forming a rare earth magnet having a main phase and a grain boundary phase existing around the main phase, the entire composition in atomic ratio being expressed by the above-mentioned formula R 1 x T (100-x-y-z) (B (1-s) C s ) y M z and the main phase is the above-mentioned R2Fe 14 The method is characterized by comprising the steps of: preparing a sintered body having a B-type crystal structure; and subjecting the sintered body to hot plastic processing to produce a hot plastic processed body having anisotropy. [Effects of the Invention]

[0009] According to the present invention, it is possible to improve both the residual magnetization and the coercive force. [Brief explanation of the drawings]

[0010] [Figure 1] 1(a) and 1(b) are a schematic perspective view and a schematic diagram of a cross-sectional structure of a rare earth magnet according to one embodiment, respectively. [Figure 2] 1(a) to 1(d) are schematic cross-sectional views showing the steps of a method for producing a rare earth magnet according to one embodiment. [Figure 3A] 1 is a graph showing the change in ΔBr versus the ratio s of the atomic ratio of C to the total atomic ratio of B and C for magnets in each group: a group of magnets in which C has been added to an Nd-Fe-B based base material, a group of magnets in which part of the B in an Nd-Fe-B based base material has been substituted with C, and a group of magnets in which part of the B in a Nd-reduced base material has been substituted with C. [Figure 3B] 1 is a graph showing the change in ΔHc versus the ratio s of the atomic ratio of C to the total atomic ratio of B and C for magnets in each group: a group of magnets in which C has been added to an Nd-Fe-B based base material, a group of magnets in which part of the B in an Nd-Fe-B based base material has been substituted with C, and a group of magnets in which part of the B in a Nd-reduced base material has been substituted with C. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the rare earth magnet and the method for manufacturing the same according to the present invention will be described. First, a rare earth magnet and a method for manufacturing the same according to one embodiment will be described. Figures 1(a) and 1(b) are a schematic perspective view and a schematic diagram of the cross-sectional structure of a rare earth magnet according to one embodiment, respectively. Figures 2(a) to 2(d) are schematic cross-sectional views showing the steps of a method for manufacturing a rare earth magnet according to one embodiment.

[0012] As shown in FIGS. 1(a) and 1(b), the rare earth magnet M according to one embodiment comprises main phase crystal grains 2 and grain boundary phases 4 present around the crystal grains 2, as is clear from the cross-sectional structure Mc. The overall composition of the rare earth magnet M in atomic ratio (molar ratio) [atomic %] is expressed by the formula R 1 x T (100-x-y-z) (B (1-s) C s ) y M z In this specification, the overall composition of a rare earth magnet in terms of atomic ratio means the overall composition including the crystal grains of the main phase and the grain boundary phase. 1 is an essential component and, together with T and B, forms the main phase (R2Fe 14 B phase). 1is one or more elements selected from the group consisting of Nd (neodymium), Ce (cerium), La (lanthanum), Pr (praseodymium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), and Ho (holmium). T (transition metal element) is a major component constituting the main phase and is one or more elements selected from the group consisting of Fe (iron), Co (cobalt), and Ni (nickel). B (boron) constitutes the main phase and affects the proportions of the main phase and grain boundary phase. C (carbon) substitutes a portion of B. M is an element that can be contained within a range that does not impair magnetic properties and is one or more elements selected from the group consisting of Ga (gallium), Al (aluminum), Cu (copper), Au (gold), Ag (silver), Zn (zinc), In (indium), and Mn (manganese), as well as unavoidable impurity elements. In this specification, the term "unavoidable impurity elements" refers to impurity elements that cannot be avoided, such as impurity elements in raw materials, impurity elements mixed in during manufacturing (including elements that are contained to an extent that does not affect magnetic properties), or impurity elements that are difficult to avoid due to significant cost increases, etc. Furthermore, the following relationships are satisfied: 12.0≦x≦20.0, 5.00≦y≦20.0, 0≦z≦2.0, and 0.07≦s≦0.17. x is R 1 where y is the total atomic ratio of B and C; z is the atomic ratio of M; and s is the ratio [-] of the atomic ratio of C to the total atomic ratio of B and C.

[0013] The crystal grain 2 (main phase) of rare earth magnet M is R2Fe 14 A magnetic phase (referred to herein as "RFe") having a B-type (where R is a rare earth element) crystal structure. 14 In this specification, the rare earth elements consist of 17 elements: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The average grain size of the crystal grains 2 is less than 1.0 μm.

[0014] In one embodiment of the method for producing a rare earth magnet M, first, the overall composition in atomic ratio is determined by the above formula R 1 x T (100-x-y-z) (B (1-s) Cs ) y M z Next, as shown in Figure 2(a), a liquid quenching method is used to produce a magnetic ribbon (quenched ribbon) S by spraying the molten metal L from a nozzle N onto the surface of a rotating cooling roll R in a liquid quenching device Da.

[0015] Next, the magnetic ribbon S is pulverized to obtain magnetic flake powder P, and as shown in Figure 2(b), the magnetic flake powder P is pressure sintered in a high-frequency sintering device Db to produce a sintered body B containing crystal grains (main phase) and a grain boundary phase existing around the crystal grains. The crystal grains of the sintered body B are composed of R2Fe 14 The sintered body B is in the B phase. Next, as shown in FIG. 2(c), the sintered body B is hot-plastically processed in a pressure device Dc to produce a hot-plastically processed body W with anisotropy. Next, as shown in FIG. 2(d), the hot-plastically processed body W is subjected to optimized heat treatment in a heat treatment furnace Dd. In this manner, a rare earth magnet M is produced.

[0016] In rare earth magnet M according to one embodiment, a portion of B is substituted with C, so that the ratio s of the atomic ratio of C to the total atomic ratio of B and C is 0.07 or more and 0.17 or less (0.07≦s≦0.17). This means that, unlike conventional magnets that differ from rare earth magnet M in that B is not substituted with C or the ratio s of the atomic ratio of C to the total atomic ratio of B and C is less than 0.07, because the ratio s of the atomic ratio of C to the total atomic ratio of B and C is 0.07 or more, C enters the grain boundary phase during the process of producing sintered body B, lowering the melting point of the grain boundary phase and sufficiently improving its wettability. As a result, in the process of producing an anisotropic hot-processed body W by hot-processing the sintered body B, the crystal grains (main phase) tend to orient so that their easy axis coincides with the stress direction, accompanied by anisotropic grain growth and grain boundary sliding perpendicular to the easy axis. The enhanced wettability of the grain boundary phase facilitates the orientation of the crystal grains. Therefore, the enhanced orientation of the crystal grains (main phase) in the hot-processed body W also enhances the orientation of the crystal grains (main phase) in the rare-earth magnet M. For these and other reasons, the remanence of the rare-earth magnet M can be improved. Furthermore, by ensuring that the ratio s of the atomic ratio of C to the total atomic ratio of B and C is 0.07 or greater, the anisotropy field (Ha) of the main phase can be improved. Furthermore, the inclusion of C in the grain boundary phase components enhances wettability with the main phase, improving the coverage of the main phase and promoting magnetic isolation, thereby improving the coercivity of the rare-earth magnet M.

[0017] On the other hand, unlike conventional magnets that differ from rare earth magnet M in that the ratio s of the atomic ratio of C to the total atomic ratio of B and C is greater than 0.17, by keeping the ratio s of the atomic ratio of C to the total atomic ratio of B and C at 0.17 or less, the amount of C contained in the crystal grains (main phase) of rare earth magnet M is not excessive, thereby suppressing a decrease in the saturation magnetization of the crystal grains due to the inclusion of C. Furthermore, by preventing excessive C from entering the grain boundary phase of sintered body B during the process of producing sintered body B, it is possible to suppress the segregation of carbon compounds and the like in the grain boundary phase of rare earth magnet M, which would cause the grain boundary phase structure to become inhomogeneous. For these and other reasons, the remanence magnetization of rare earth magnet M can be improved. Furthermore, by keeping the ratio s of the atomic ratio of C to the total atomic ratio of B and C at 0.17 or less, it is possible to suppress the above-mentioned inhomogeneity in the grain boundary phase structure of rare earth magnet M. For these and other reasons, the coercivity of rare earth magnet M can be improved. Therefore, according to the embodiment, it is possible to improve both the remanence and the coercivity. Next, the configuration of the rare earth magnet and the method of manufacturing the same according to the embodiment will be described in further detail.

[0018] The rare earth magnet according to the embodiment comprises a main phase and a grain boundary phase present around the main phase, and the overall composition in atomic ratio [atomic %] is expressed by the above formula R 1 x T (100-x-y-z) (B (1-s) C s ) y M z The main phase is represented by R2Fe 14 There is no particular limitation as long as it is a B phase.

[0019] R 1 From the viewpoint of the balance between magnetic properties and cost, it is preferable that R is one or more elements selected from the group consisting of Nd and Pr. 1 The atomic ratio x of R2Fe 14 When the atomic ratio of R in B is greater than the theoretical composition, the main phase is R2Fe 14 Since it can be stably obtained as B phase, if it is 12.0 or more, a sufficient amount of R2Fe 14From this viewpoint, x may be 12.4 or more, 12.8 or more, 13.0 or more, 13.2 or more, 13.4 or more, or 14.0 or more. On the other hand, if x is 20.0 or less, the grain boundary phase will not be excessive, and from this viewpoint, x may be 19.0 or less, 18.0 or less, 17.0 or less, 16.0 or less, or 15.0 or less. If the total atomic ratio y of B and C is 5.00 or more, a sufficient amount of R2Fe 14 The B phase (main phase) can be formed, and from this viewpoint, y may be 5.2 or more, 5.4 or more, 5.5 or more, 5.7 or more, or 5.8 or more. On the other hand, if y is 20.0 or less, a magnet in which the main phase and grain boundary phase are appropriately present can be obtained, and from this viewpoint, y may be 18.0 or less, 16.0 or less, 14.0 or less, 12.0 or less, 10.0 or less, 8.0 or less, 6.0 or less, or 5.9 or less. The atomic ratio z of M, so long as it is 2.0 or less, does not impair the magnetic properties, and from this viewpoint, it may be 1.5 or less, 1.0 or less, 0.65 or less, 0.6 or less, or 0.5 or less.

[0020] If the atomic ratio s[-] of C to the total atomic ratio of B and C is 0.07 or more, the wettability of the grain boundary phase can be sufficiently improved to improve remanence and coercivity, and from this viewpoint, it may be 0.074 or more, 0.08 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, or 0.16 or more. On the other hand, if s is 0.17 or less, the remanence can be improved by suppressing a decrease in the saturation magnetization of the crystal grains (main phase), and the coercivity can be improved by suppressing the grain boundary phase structure from becoming heterogeneous. From this viewpoint, it may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less.

[0021] The main phase of a rare earth magnet is preferably nanocrystalline. In this specification, "nanocrystalline main phase" means that the average grain size of the main phase is less than 1.0 μm. When the main phase is nanocrystalline, the sintered body is subjected to hot plastic processing to orient the crystal grains (main phase), making it easier to orient the crystal grains and impart anisotropy when producing a hot plastic processed body to produce a rare earth magnet. From this perspective, the average grain size of the main phase may be 0.05 μm or more, 0.10 μm or more, 0.20 μm or more, 0.30 μm or more, 0.40 μm or more, or 0.50 μm or more, or 0.90 μm or less, 0.80 μm or less, 0.70 μm or less, or 0.60 μm or less. In this specification, "average grain size" is measured as follows. In a scanning electron microscope image or a transmission electron microscope image, a certain region is defined when observed from a direction perpendicular to the easy axis of magnetization, and multiple lines are drawn perpendicular to the easy axis of magnetization for the main phase present in this certain region, and the diameter (length) of the main phase is calculated from the distance between the intersecting points within the main phase particle (intersection method). If the cross section of the main phase is close to a circle, it is converted to the diameter equivalent to the projected area circle. If the cross section of the main phase is close to a rectangle, it is converted to a rectangular approximation. The D of the diameter (length) distribution (particle size distribution) obtained in this way is 50 The value is the average particle size.

[0022] The grain boundary phase of rare earth magnets is R2Fe 14 This includes phases with an unclear crystal structure, including phases with a crystal structure other than type B. Without being bound by theory, the term "ill-defined phase" refers to a phase in which at least a portion of the phase has an incomplete crystal structure and is present irregularly, or a phase in which at least a portion of the phase is amorphous and hardly exhibits any appearance of a crystal structure.

[0023] As rare earth magnets, 1 The amount of Nd, which is the most expensive, has been reduced, and instead R 1 Among these, Nd-saving magnets using inexpensive elements are preferred, and among them, R 1 The atomic ratio of Nd to the total [atomic %] is 0 to 99, and R 1The balance of the Nd-saving magnet is preferably an element that is less expensive than Nd, and in particular, for example, R 1 is Nd, Ce, La, and Pr, and R 1 The atomic ratio of Nd to the total [atomic %] is 0 to 98, and R 1 The atomic ratio of Ce to the sum of R is 1 or more and 99 or less, 1 The atomic ratio of La to the sum of R is 1 or more and 99 or less, 1 and the remainder Pr are preferred. If the atomic ratio of Nd is reduced to, for example, the upper limit or lower of the above range, the degree of orientation of the crystal grains (main phase) may decrease, so the effect of improving the degree of orientation by substituting a portion of B with C becomes more effective. On the other hand, by setting the atomic ratio of Nd to, for example, the lower limit or higher of the above range, the effect of decreasing the saturation magnetization and degree of orientation of the crystal grains due to the reduction of Nd can be suppressed.

[0024] The manufacturing method according to the embodiment is a method for manufacturing a rare earth magnet according to the embodiment, which comprises a main phase and a grain boundary phase present around the main phase, and the overall composition in atomic ratio is represented by the formula R which is the same as the overall composition in atomic ratio of the rare earth magnet according to the embodiment. 1 x T (100-x-y-z) (B (1-s) C s ) y M z The main phase is represented by R2Fe 14 There are no particular limitations on the method as long as it includes the steps of preparing a sintered body that is a B phase and subjecting the sintered body to hot plastic processing to produce a hot plastic processed body that has been given anisotropy.

[0025] The process for preparing a sintered body is not particularly limited, but may include, for example, a process having a step of preparing a molten alloy, a step of producing a magnetic ribbon by rapidly cooling the molten alloy, and a step of producing a sintered body by pressure sintering the magnetic ribbon or magnetic flakes obtained by pulverizing the magnetic ribbon, as in one embodiment.

[0026] The step of preparing a molten metal is usually carried out by preparing a molten metal having an overall composition in atomic ratio according to the formula R1 x T (100-x-y-z) (B (1-s) C s ) y M z However, it may also be a process of preparing a molten alloy having a composition that takes into account the amount of elements that may be consumed in subsequent processes. The process of preparing a molten alloy may be, for example, a process of preparing a molten alloy by melting an alloy ingot, optionally together with additives, in an inert gas atmosphere (e.g., N (nitrogen) gas, Ar (argon) gas) or the like.

[0027] For example, the molten metal is cooled to 5 × 10 5 5x10 or more 7 A step of cooling at a rate of °C / sec or less is preferred, because a magnetic ribbon having a nanocrystalline main phase can be suitably produced. The step of quenching the molten metal may be a step of quenching the molten metal using a liquid quenching method. The quenching atmosphere is preferably, for example, an inert gas atmosphere.

[0028] The process of pressure sintering the magnetic ribbon or magnetic flake is not particularly limited as long as the main phase does not become coarse so as to obtain the desired magnetic properties. For example, a process in which the pressure sintering temperature is 470°C to 750°C, the pressure sintering pressure is 50 MPa to 600 MPa, and the pressure sintering time is 5 minutes to 150 minutes is preferred. This is because a sintered body having a nanocrystalline main phase can be suitably obtained. Furthermore, from the viewpoint of suppressing coarsening of the main phase, a process in which the sintered body is quickly cooled after pressure sintering is preferred. The pressure sintering atmosphere is preferably, for example, an inert gas atmosphere.

[0029] The process for producing a hot plastically worked body is not particularly limited as long as it can impart anisotropy to the hot plastically worked body. For example, a process in which the hot plastically worked temperature is 740°C to 780°C, the strain rate is 0.01 / s to 1 / s, and the plastically worked ratio is 50% to 80% is preferred. This is because it sufficiently promotes the crystal orientation of the sintered body, imparts sufficient anisotropy to the hot plastically worked body, and suppresses coarsening of the nanocrystalline main phase. The plastically worked ratio is calculated, for example, as [(thickness of the sample before compression - thickness of the sample after compression) x 100 / thickness of the sample before compression] [%]. Furthermore, from the viewpoint of suppressing coarsening of the main phase, a process in which the hot plastically worked body is rapidly cooled after hot plastically worked is preferred. For example, an inert gas atmosphere is preferred as the hot plastically worked atmosphere.

[0030] Preferably, the manufacturing method according to the embodiment further comprises a step of performing an optimization heat treatment on the hot plastically worked body. This is because adjusting the structure of the magnet, particularly the structure of the grain boundary phase, can further improve remanence and coercivity. A preferred example of this step is a step of heat treating the hot plastically worked body at a temperature of 500°C to 700°C for 5 minutes to 200 minutes. This is because the improvement effect is significant. Furthermore, from the viewpoint of suppressing coarsening of the main phase, a step of quickly cooling the hot plastically worked body after the optimization heat treatment is preferred. A preferred heat treatment atmosphere is, for example, an inert gas atmosphere. [Example]

[0031] Hereinafter, the method for producing a rare earth magnet and the rare earth magnet according to the embodiment will be described in more detail with reference to examples and comparative examples.

[0032] 1. Rare earth magnet with C added to Nd-Fe-B base material Below, we will explain examples of rare earth magnets in which C is added to an Nd—Fe—B-based base material (alloy ingot) (Comparative Examples 2 to 4 and Example 1), along with an example of a rare earth magnet in which the Nd—Fe—B-based base material is used as is without adding C (Comparative Example 1).

[0033] [Comparative Example 1] First, predetermined amounts of Nd, Pr, Ga, Al, Cu, B, and Fe were weighed out in a weight ratio (weight %) of 29.03:0.4:0.4:0.08:0.1:1.00:bal. (balance). These predetermined amounts of Nd, Pr, Ga, Al, Cu, B, and Fe were melted in an arc melting furnace to produce an alloy ingot (Nd-Fe-B-based base material). Next, the alloy ingot was melted in a furnace under a reduced pressure atmosphere of Ar gas using high frequency waves to obtain a molten metal at 1400°C.

[0034] Next, as shown in Figure 2(a), a magnetic ribbon (quenched ribbon) was produced by using the liquid quenching method, in which the molten metal was sprayed from a nozzle (diameter: 0.6 mm) onto the surface of a rotating chill roll in a liquid quenching device to rapidly cool the molten metal. The chill roll speed was 25 m / s, and the spray differential pressure was 25 kPa (nozzle pressure: -40 kPa, chamber pressure: -65 kPa).

[0035] Next, the magnetic ribbon was pulverized to obtain magnetic flake powder, which was then pressure-sintered in a high-frequency sintering device to produce a sintered body, as shown in Figure 2(b). The pressure-sintering temperature was 600°C, the pressure was 200 MPa, and the pressure-sintering time was 5 minutes.

[0036] Next, as shown in Figure 2(c), the sintered body was subjected to hot plastic processing in a pressurizing device to produce a hot plastic processed body with anisotropy. The sintered body was heated to the hot plastic processing temperature of 750°C, and then compressed at a strain rate of 0.1 / s with a plastic processing ratio of 75%. Next, as shown in Figure 2(d), the hot plastic processed body was subjected to optimized heat treatment in a heat treatment furnace. The hot plastic processed body was heat treated at 580°C for 180 minutes. This resulted in the production of a rare earth magnet.

[0037] Comparative Example 2 When obtaining the molten metal used to produce the magnetic ribbon, a predetermined amount of carbon was weighed out so that the weight ratio of B in the alloy ingot used in Comparative Example 1 to C in the carbon was 1.00:0.02, and this predetermined amount of carbon was melted together with the alloy ingot used in Comparative Example 1 using high frequency in a furnace in a reduced pressure atmosphere of Ar gas to obtain a molten metal at the same temperature as in Comparative Example 1. Except for this point, a rare earth magnet was produced in the same manner as in Comparative Example 1.

[0038] Comparative Example 3 A rare earth magnet was manufactured in the same manner as in Comparative Example 2, except that when obtaining the molten metal used to produce the magnetic ribbon, a predetermined amount of carbon was melted together with the alloy ingot so that the weight ratio of B in the alloy ingot to C in the carbon was 1.00:0.07.

[0039] [Example 1] A rare earth magnet was manufactured in the same manner as in Comparative Example 2, except that when obtaining the molten metal used to produce the magnetic ribbon, a predetermined amount of carbon was melted together with the alloy ingot so that the weight ratio of B in the alloy ingot to C in the carbon was 1.00:0.1.

[0040] Comparative Example 4 A rare earth magnet was manufactured in the same manner as in Comparative Example 2, except that when obtaining the molten metal used to produce the magnetic ribbon, a predetermined amount of carbon was melted together with the alloy ingot so that the weight ratio of B in the alloy ingot to C in the carbon was 1.00:0.25.

[0041] [Magnet overall composition, average particle size, and magnetic properties] For the rare earth magnets of Comparative Examples 1 to 3, Example 1, and Comparative Example 4, the overall atomic composition and the ratio (s) of the atomic ratio of C to the total atomic ratio of B and C were determined. The contents of Nd, Pr, Ga, Al, Cu, B, and Fe in the rare earth magnets were measured using ICP atomic emission spectroscopy to determine their respective weight ratios. The C content in the rare earth magnets was measured using a carbon-sulfur analyzer ("EMIA-320V2" manufactured by Horiba, Ltd.) to determine its weight ratio. These weight ratios were then converted to atomic ratios to determine the overall atomic composition of the rare earth magnets. The ratio (s) of the atomic ratio of C to the total atomic ratio of B and C in the overall composition was then determined. The average grain size of the main phase of the magnets of Comparative Examples 1 to 3, Example 1, and Comparative Example 4 was measured using scanning electron microscope images, and all were found to be less than 1.0 μm. Furthermore, the magnetic properties of the rare earth magnets of Comparative Examples 1 to 3, Example 1, and Comparative Example 4 were measured. In this case, the remanence Br [T] and coercivity Hc [kA / m] of samples cut from the rare earth magnets were measured at room temperature using a VSM (vibrating sample magnetometer). The maximum value of the magnetic field applied during the measurements was 1900 kA / m. The results are shown in Table 1 below. In Table 1 below, the changes in Br and Hc of the magnets of each example relative to the Br and Hc of the magnet of Comparative Example 1, which did not contain C, are shown as ΔBr [T] and ΔHc [kA / m], respectively. In Table 1 below and Tables 2 and 3 described later, the atomic ratios [atomic %] of each element in the overall composition are rounded to three decimal places.

[0042] [Table 1]

[0043] As shown in Table 1, the magnet of Example 1, in which the ratio s of the atomic ratio of C to the total atomic ratio of B and C was 0.0826, had both improved Br and Hc without any trade-off, compared to the magnet of Comparative Example 1, in which no C was added. On the other hand, the magnets of Comparative Examples 2, 3, and 4 had a decrease in either Br or Hc, compared to the magnet of Comparative Example 1.

[0044] 2. Rare earth magnets in which some of the B in the Nd-Fe-B matrix is ​​replaced with C Below, examples of rare earth magnets in which part of the B in an Nd—Fe—B base material (alloy ingot) is replaced with C (Examples 2 to 4 and Comparative Example 6) will be described, along with an example of a rare earth magnet in which the Nd—Fe—B base material is used as is without replacing B with C (Comparative Example 5).

[0045] Comparative Example 5 First, predetermined amounts of Nd, Ga, Cu, B, and Fe were weighed out in a weight ratio (weight %) of 30:0.24:0.09:0.97:bal. (balance), and these predetermined amounts of Nd, Ga, Cu, B, and Fe were melted in an arc melting furnace to produce an alloy ingot (Nd-Fe-B-based base material). Next, the alloy ingot was melted by high frequency in a furnace under a reduced pressure atmosphere of Ar gas to obtain a molten metal at 1400°C.

[0046] Next, as shown in Figure 2(a), a magnetic ribbon (quenched ribbon) was produced by using the liquid quenching method, in which the molten metal was sprayed from a nozzle (diameter: 0.6 mm) onto the surface of a rotating chill roll in a liquid quenching device to rapidly cool the molten metal. The chill roll speed was 25 m / s, and the spray differential pressure was 25 kPa (nozzle pressure: -40 kPa, chamber pressure: -65 kPa).

[0047] Next, the magnetic ribbon was pulverized to obtain magnetic flake powder, which was then pressure-sintered in a high-frequency sintering device to produce a sintered body, as shown in Figure 2(b). The pressure-sintering temperature was 600°C, the pressure was 200 MPa, and the pressure-sintering time was 5 minutes.

[0048] Next, as shown in Figure 2(c), the sintered body was subjected to hot plastic processing in a pressurizing device to produce a hot plastic processed body with anisotropy. The sintered body was heated to the hot plastic processing temperature of 760°C, and then compressed at a strain rate of 0.1 / s with a plastic processing ratio of 65%. Next, as shown in Figure 2(d), the hot plastic processed body was subjected to optimized heat treatment in a heat treatment furnace. The hot plastic processed body was heat treated at 600°C for 60 minutes. This resulted in the production of a rare earth magnet.

[0049] [Example 2] When producing the alloy ingot, predetermined amounts of Nd, Ga, Cu, B, C, and Fe were weighed out in a weight ratio [wt %] of Nd, Ga, Cu, B, C, and Fe of 30:0.24:0.09:0.89:0.08:bal. (balance), and these predetermined amounts of Nd, Ga, Cu, B, C, and Fe were melted in an arc melting furnace to produce an alloy ingot in which part of the B in the alloy ingot used in Comparative Example 5 was replaced with C. Except for this point, a rare earth magnet was produced in the same manner as in Comparative Example 5.

[0050] [Example 3] A rare earth magnet was produced in the same manner as in Example 2, except that when producing the alloy ingot, predetermined amounts of B and C were weighed out so that the weight ratio [wt %] of B to C was 0.85:0.12.

[0051] [Example 4] A rare earth magnet was produced in the same manner as in Example 2, except that when producing the alloy ingot, predetermined amounts of B and C were weighed out so that the weight ratio [wt %] of B to C was 0.80:0.17.

[0052] Comparative Example 6 A rare earth magnet was produced in the same manner as in Example 2, except that when producing the alloy ingot, predetermined amounts of B and C were weighed out so that the weight ratio [wt %] of B to C was 0.75:0.22.

[0053] [Magnet overall composition, average particle size, and magnetic properties] For the rare earth magnets of Comparative Example 5, Examples 2-4, and Comparative Example 6, the overall atomic composition and the ratio (s) of the atomic ratio of C to the total atomic ratio of B and C were determined. The contents of Nd, Ga, Cu, B, and Fe in the rare earth magnets were measured using ICP atomic emission spectroscopy to determine their respective weight ratios, and the C content in the rare earth magnets was measured using the carbon-sulfur analyzer described above to determine its weight ratio. These weight ratios were then converted to atomic ratios to determine the overall atomic composition of the rare earth magnets. The ratio (s) of the atomic ratio of C to the total atomic ratio of B and C in the overall composition was then determined. The average grain size of the main phase of the magnets of Comparative Example 5, Examples 2-4, and Comparative Example 6 was measured using scanning electron microscope images, and all were found to be less than 1.0 μm. Furthermore, the magnetic properties of the rare earth magnets of Comparative Example 5, Examples 2-4, and Comparative Example 6 were measured. The remanence Br and coercivity Hc were measured in the same manner as above. The results are shown in Table 2 below. In Table 2 below, the changes in Br and Hc of the magnets of each example relative to the Br and Hc of the magnet of Comparative Example 5, in which B was not substituted with C, are shown as ΔBr and ΔHc, respectively.

[0054] [Table 2]

[0055] As shown in Table 2, the magnets of Examples 2 to 4, in which the ratio s of the atomic ratio of C to the total atomic ratio of B and C was 0.0749 to 0.1606, showed both improved Br and Hc without any trade-off, compared to the magnet of Comparative Example 5, in which no B was substituted with C. On the other hand, the magnet of Comparative Example 6 showed decreases in both Br and Hc compared to the magnet of Comparative Example 5.

[0056] 3. Rare earth magnets in which part of the B in the Nd-saving base material is replaced with C Below, we will explain examples of rare earth magnets (Example 5 and Comparative Example 8) in which a Nd-Fe-B-based base material is used, where the amount of expensive Nd is reduced and inexpensive Pr, La, and Ce are used instead, and part of the B in the Nd-reduced base material is replaced with C, along with an example of a rare earth magnet (Comparative Example 7) in which the Nd-reduced base material is used as is without replacing B with C.

[0057] Comparative Example 7 First, predetermined amounts of Nd, Ce, La, Pr, Co, Ga, Cu, B, and Fe were weighed out in a weight ratio (weight %) of 21.85:0.48:1.0:7.25:1.0:0.38:0.1:0.93:bal. (balance). These predetermined amounts of Nd, Ce, La, Pr, Co, Ga, Cu, B, and Fe were melted in an arc melting furnace to produce an alloy ingot (Nd-reduced base metal). Next, the alloy ingot was melted in a furnace under a reduced pressure atmosphere of Ar gas using high frequency waves to obtain a molten metal at 1400°C.

[0058] Next, as shown in Figure 2(a), a magnetic ribbon (quenched ribbon) was produced by using the liquid quenching method, in which the molten metal was sprayed from a nozzle (diameter: 0.6 mm) onto the surface of a rotating chill roll in a liquid quenching device to rapidly cool the molten metal. The chill roll speed was 25 m / s, and the spray differential pressure was 25 kPa (nozzle pressure: -40 kPa, chamber pressure: -65 kPa).

[0059] Next, the magnetic ribbon was pulverized to obtain magnetic flake powder, which was then pressure-sintered in a high-frequency sintering device to produce a sintered body, as shown in Figure 2(b). The pressure-sintering temperature was 600°C, the pressure was 200 MPa, and the pressure-sintering time was 5 minutes.

[0060] Next, as shown in Figure 2(c), the sintered body was subjected to hot plastic processing in a pressurizing device to produce a hot plastic processed body with anisotropy. The sintered body was heated to the hot plastic processing temperature of 760°C, and then compressed at a strain rate of 0.1 / s with a plastic processing ratio of 65%. Next, as shown in Figure 2(d), the hot plastic processed body was subjected to optimized heat treatment in a heat treatment furnace. The hot plastic processed body was heat treated at 650°C for 60 minutes. This resulted in the production of a rare earth magnet.

[0061] [Example 5] When producing the alloy ingot, predetermined amounts of Nd, Ce, La, Pr, Co, Ga, Cu, B, C, and Fe were weighed out in a weight ratio [wt %] of 21.85:0.48:1.0:7.25:1.0:0.38:0.1:0.82:0.11:bal. (balance). These predetermined amounts of Nd, Ce, La, Pr, Co, Ga, Cu, B, C, and Fe were melted in an arc melting furnace to produce an alloy ingot in which part of the B in the alloy ingot used in Comparative Example 7 was replaced with C. Except for this point, a rare earth magnet was produced in the same manner as in Comparative Example 7.

[0062] [Comparative Example 8] A rare earth magnet was produced in the same manner as in Example 5, except that when producing the alloy ingot, predetermined amounts of B and C were weighed out so that the weight ratio [wt %] of B to C was 0.72:0.21.

[0063] [Magnet overall composition, average particle size, and magnetic properties] For the rare earth magnets of Comparative Example 7, Example 5, and Comparative Example 8, the overall atomic composition and the ratio (s) of the atomic ratio of C to the total atomic ratio of B and C were determined. The contents of Nd, Ce, La, Pr, Co, Ga, Cu, B, and Fe in the rare earth magnets were measured using ICP atomic emission spectroscopy to determine their respective weight ratios. The C content in the rare earth magnets was measured using the carbon-sulfur analyzer described above to determine its weight ratio. These weight ratios were then converted to atomic ratios to determine the overall atomic composition of the rare earth magnets. The ratio (s) of the atomic ratio of C to the total atomic ratio of B and C in the overall composition was then determined. The average grain size of the main phase of the magnets of Comparative Example 7, Example 5, and Comparative Example 8 was measured using scanning electron microscope images, and all were found to be less than 1.0 μm. Furthermore, the magnetic properties of the rare earth magnets of Comparative Example 7, Example 5, and Comparative Example 8 were measured. The remanence Br and coercivity Hc were measured in the same manner as above. The results are shown in Table 3. In Table 3, the changes in Br and Hc of the magnets of each example relative to the Br and Hc of the magnet of Comparative Example 7, in which B was not substituted with C, are shown as ΔBr and ΔHc, respectively.

[0064] [Table 3]

[0065] As shown in Table 3, the magnet of Example 5, in which the ratio s of the atomic ratio of C to the total atomic ratio of B and C was 0.1077, had both improved Br and Hc without any trade-off, compared to the magnet of Comparative Example 7, in which no B was substituted with C. On the other hand, the magnet of Comparative Example 8 had a lower Hc than the magnet of Comparative Example 7.

[0066] 4. Evaluation 3A is a graph showing the change in ΔBr versus the ratio s of the atomic ratio of C to the total atomic ratio of B and C for magnets in each group: a group of magnets in which C was added to an Nd-Fe-B based matrix (magnets of Comparative Examples 1 to 3, Example 1, and Comparative Example 4), a group of magnets in which some of the B in the Nd-Fe-B based matrix was substituted with C (magnets of Comparative Example 5, Examples 2 to 4, and Comparative Example 6), and a group of magnets in which some of the B in a Nd-saving matrix was substituted with C (magnets of Comparative Example 7, Example 5, and Comparative Example 8). Meanwhile, FIG. 3B is a graph showing the change in ΔHc versus the ratio s of the atomic ratio of C to the total atomic ratio of B and C for magnets in each group: a group of magnets in which C was added to an Nd-Fe-B based matrix, a group of magnets in which some of the B in the Nd-Fe-B based matrix was substituted with C, and a group of magnets in which some of the B in a Nd-saving matrix was substituted with C.

[0067] 3A and 3B and Tables 1 to 3, it is believed that in magnets in which the ratio s of the atomic ratio of C to the total atomic ratio of B and C is 0.07 or more and 0.17 or less, both Br and Hc are improved without trade-offs, compared to magnets in which the ratio s of the atomic ratio of C to the total atomic ratio of B and C is 0.00. Furthermore, in the group of magnets in which some of the B in the Nd-saving base material is replaced with C, as in the other groups, it is believed that there exists an optimal value for the ratio s of the atomic ratio of C to the total atomic ratio of B and C at which both Br and Hc are improved without trade-offs.

[0068] The above describes in detail the embodiments of the rare earth magnet and its manufacturing method according to the present invention, but the present invention is not limited to the above-described embodiments, and various design modifications can be made within the scope of the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0069] M: Rare earth magnet, 2: Crystal grain (main phase), 4: Grain boundary phase, B: Sintered body, W: Hot plastic processed body

Claims

1. The alloy comprises a main phase and a grain boundary phase present around the main phase, The overall composition in atomic ratio is represented by the formula R １ ｘ T （１００－ｘ－ｙ－ｚ） (B （１－ｓ） C ｓ ) ｙ M ｚ (However, R １ is one or more elements selected from the group consisting of Nd, Ce, La, Pr, Gd, Tb, Dy, and Ho, T is one or more elements selected from the group consisting of Fe, Co, and Ni, M is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, and unavoidable impurity elements, and 12.0≦x≦20.0, 5.00≦y≦20.0, 0≦z≦2.0, and 0.07≦s≦0.17 ) and The main phase is R ２ Fe １４ A rare earth magnet characterized by having a B-type (where R is a rare earth element) crystal structure.

2. 2. The rare earth magnet according to claim 1, wherein the average grain size of the main phase is less than 1.0 μm.

3. 3. The method for producing a rare earth magnet according to claim 1 or 2, The alloy includes a main phase and a grain boundary phase present around the main phase, The overall composition in atomic ratio is represented by the formula R １ ｘ T （１００－ｘ－ｙ－ｚ） (B （１－ｓ） C ｓ ) ｙ M ｚ (However, R １ is one or more elements selected from the group consisting of Nd, Ce, La, Pr, Gd, Tb, Dy, and Ho, T is one or more elements selected from the group consisting of Fe, Co, and Ni, M is one or more elements selected from the group consisting of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, and unavoidable impurity elements, and 12.0≦x≦20.0, 5.00≦y≦20.0, 0≦z≦2.0, and 0.07≦s≦0.17 ) and the main phase is represented by R ２ Fe １４ preparing a sintered body having a B-type crystal structure (where R is a rare earth element); a step of producing a hot plastically worked body having anisotropy by hot plastically working the sintered body; A method for manufacturing a rare earth magnet, comprising:

4. 4. The method for producing a rare earth magnet according to claim 3, wherein in the step of hot plastic working the sintered body, the hot plastic working temperature is 740°C or higher and 780°C or lower, the strain rate is 0.01 / s or higher and 1 / s or lower, and the plastic working rate is 50% or higher and 80% or lower.

5. 4. The method for producing a rare earth magnet according to claim 3, further comprising the step of heat treating the hot plastic worked body at a temperature of 500° C. to 700° C. for a time of 5 minutes to 200 minutes.

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