R-T-B series sintered magnets

Abstract

The present invention provides an R-T-B sintered magnet that hardly uses heavy rare earth elements RH and has a high coercive force H even at a high temperature (e.g., 100 °C). cJ The R-T-B sintered magnet contains: R: 28.5% by mass or more and 33.0% by mass or less (R is at least one of rare earth elements and contains at least one of Nd and Pr); B: 0.85% by mass or more and 0.91% by mass or less; Ga: 0.35% by mass or more and 0.75% by mass or less; Cu: 0.05% by mass or more and 0.50% by mass or less; Mn: 0.03% by mass or more and 0.15% by mass or less; T: 61.5% by mass or more and 70.0% by mass or less (T is Fe or Fe and Co, and 90% or more of T is Fe), satisfying formula (1): 14[B] / 10.8 < [T] / 55.85, ([B] is the content of B expressed in mass%, and [T] is the content of T expressed in mass%).

Description

Technical Field

[0001] The present invention relates to an R-T-B system sintered magnet. Background Art

[0002] The R-T-B system sintered magnet (R is at least one of rare earth elements, containing at least one of Nd and Pr; T is Fe or Fe and Co, and more than 90% by mass of T is Fe) is composed of a main phase containing a compound having an R2T 14 B-type crystal structure and a grain boundary phase located at the grain boundary portion of the main phase, and is known as a magnet having the highest performance among permanent magnets.

[0003] Therefore, it is used in various motors such as voice coil motors (VCM) of hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and various applications such as home appliances.

[0004] With such an expansion of applications, for example, when used in a motor for an electric vehicle, it may be exposed to a high temperature of about 100 °C, and thus it is required to be able to operate stably even at high temperatures.

[0005] However, the R-T-B system sintered magnet has a problem that the coercive force H cJ (hereinafter sometimes simply referred to as "H cJ ") decreases at high temperatures, and irreversible thermal demagnetization occurs. For example, when an R-T-B system sintered magnet is used in a motor for an electric vehicle, H cJ may decrease due to use at high temperatures, and stable operation of the motor may not be achieved. Therefore, there is a need for an R-T-B system sintered magnet having a high H cJ even at high temperatures.

[0006] In order to increase H cJ , currently, a heavy rare earth element RH (mainly Dy) is added to the R-T-B system sintered magnet, but there is a problem that the residual magnetic flux density B r (hereinafter sometimes simply referred to as "B r ") decreases. Moreover, due to limited production areas of Dy and other reasons, there are problems of unstable supply and large price fluctuations. Therefore, there is a need for a technology that can increase H cJ of the R-T-B system sintered magnet without using heavy rare earth elements RH such as Dy as much as possible.

[0007] As such a technology, for example, Patent Document 1 discloses a technology that generates an R2T 17 phase by reducing the content of B compared with a general R-T-B system sintered magnet and containing one or more metal elements M selected from Al, Ga, and Cu, and sufficiently ensuring the R2T 17The volume fraction of the rich transition metal phase (R-T-Ga phase) formed from the raw materials is used to suppress the content of Dy, and an R-T-B sintered magnet with high coercivity can be obtained.

[0008] Prior art documents

[0009] Patent documents

[0010] Patent Document 1: International Publication No. WO2013 / 008756 Summary of the invention

[0011] Technical problem to be solved by the invention

[0012] However, although the H of the R-T-B sintered magnet described in Patent Document 1 is improved, it is not sufficient to meet the requirements in recent years. cJ Therefore, the present invention provides an R-T-B sintered magnet that does not use heavy rare earth elements RH as much as possible and has high coercivity H even at high temperatures (e.g., 100 °C).

[0013] For this reason, the present invention provides an R-T-B sintered magnet that does not use heavy rare earth elements RH as much as possible and has high coercivity H even at high temperatures (e.g., 100 °C). cJ of the R-T-B sintered magnet.

[0014] Technical solution for solving the technical problem

[0015] In the exemplified embodiment, the R-T-B sintered magnet of the present invention contains:

[0016] R: 28.5 mass% or more and 33.0 mass% or less (R is at least one of rare earth elements, containing at least one of Nd and Pr);

[0017] B: 0.85 mass% or more and 0.91 mass% or less;

[0018] Ga: 0.35 mass% or more and 0.75 mass% or less;

[0019] Cu: 0.05 mass% or more and 0.50 mass% or less;

[0020] Mn: 0.03 mass% or more and 0.15 mass% or less;

[0021] T: 61.5 mass% or more and 70.0 mass% or less (T is Fe or Fe and Co, and 90 mass% or more of T is Fe),

[0022] The R-T-B sintered magnet satisfies the following formula (1):

[0023] 14[B] / 10.8 < [T] / 55.85 (1),

[0024] ([B] is the content of B expressed in mass%, and [T] is the content of T expressed in mass%).

[0025] In one embodiment, the above R-T-B series sintered magnet does not contain heavy rare earth elements (except inevitable impurities), and at 100 °C, H cJ ≥ 880 kA / m, and at 22.5 °C, B r ≥ 1.32 T.

[0026] In one embodiment, the above R-T-B series sintered magnet contains 1.0 mass% or less of Tb, and at 100 °C, H cJ ≥ 880 + 168[Tb] kA / m, and at 22.5 °C, B r ≥ 1.32 - 0.024[Tb] T, ([Tb] represents the content of Tb in mass%).

[0027] Effects of the Invention

[0028] According to the embodiments of the present invention, it is possible to provide an R-T-B series sintered magnet that uses as little heavy rare earth element RH as possible and has a high coercive force H at high temperatures (e.g., 100 °C). cJ Description of the Drawings

[0029] Figure 1 It is an explanatory diagram showing the relationship between the Mn amount and H at 100 °C for No. 1 to 10 of Experimental Example 1. cJ Detailed Embodiments

[0030] The inventors of the present invention conducted in-depth research and found that by further containing Mn within a specific range in an R-T-B series sintered magnet having specific contents of R, B, Ga, and Cu, particularly having an extremely narrow specific range of B content, it is possible to have a high H even at high temperatures. cJ This is considered to be because by further containing Mn in an R-T-B series sintered magnet with the B amount within the specific composition range of the present invention, the temperature coefficient can be improved.

[0031] [R-T-B Series Sintered Magnet]

[0032] The R-T-B series sintered magnet of the present invention contains:

[0033] R: 28.5 mass% or more and 33.0 mass% or less (R is at least one of rare earth elements, containing at least one of Nd and Pr);

[0034] B: 0.85 mass% or more and 0.91 mass% or less;

[0035] Ga: 0.35 mass% or more and 0.75 mass% or less;

[0036] Cu: 0.05 mass% or more and 0.50 mass% or less;

[0037] Mn: 0.03 mass% or more and 0.15 mass% or less;

[0038] T: 61.5 mass% or more and 70.0 mass% or less (T is Fe or Fe and Co, and 90 mass% or more of T is Fe),

[0039] This R-T-B series sintered magnet satisfies the following formula (1):

[0040] 14[B] / 10.8 < [T] / 55.85 (1)

[0041] ([B] is the content of B expressed in mass%, and [T] is the content of T expressed in mass%).

[0042] Next, each component will be described in detail.

[0043] (R: 28.5 - 33.0 mass%)

[0044] R is at least one of the rare earth elements and contains at least one of Nd and Pr. The content of R is 28.5 - 33.0 mass%. When the content of R is less than 28.5 mass%, densification during sintering may become difficult. When it exceeds 33.0 mass%, the main phase ratio decreases, and B r may decrease. The content of R is preferably 29.5 - 32.5 mass%. When R is within this range, a higher B r .

[0045] (B: 0.85 - 0.91 mass%)

[0046] The content of B is 0.85 - 0.91 mass%. By making the R-T-B series sintered magnet contain B within the scope of the present invention and further contain Mn within a specific scope described later, the temperature coefficient is improved, and a high H can be obtained even at high temperatures cJ . Therefore, when the content of B is less than 0.85 mass% or exceeds 0.91 mass%, a high H cannot be obtained at high temperatures cJ . Among them, a part of B can be replaced by C.

[0047] In addition, the content of B satisfies the following formula (1):

[0048] 14[B] / 10.8 < [T] / 55.85 (1).

[0049] By satisfying formula (1), the content of B is less than that of a general R-T-B series sintered magnet. In a general R-T-B series sintered magnet, in order to have R2T as the main phase 14No soft magnetic R2T phase is formed outside the B phase, resulting in a composition where [T] / 55.85 (atomic weight of Fe) is less than 14[B] / 10.8 (atomic weight of B) ([T] represents the content of T in mass %). Different from general R-T-B sintered magnets, the R-T-B sintered magnet of the present invention is defined by formula (1) such that [T] / 55.85 is greater than 14[B] / 10.8. Here, since the main component of T in the R-T-B sintered magnet of the present invention is Fe, the atomic weight of Fe is used. 17 The phase composition is such that [T] / 55.85 (atomic weight of Fe) is less than 14[B] / 10.8 (atomic weight of B) ([T] represents the content of T in mass %). Different from general R-T-B sintered magnets, the R-T-B sintered magnet of the present invention is defined by formula (1) such that [T] / 55.85 is greater than 14[B] / 10.8. Here, since the main component of T in the R-T-B sintered magnet of the present invention is Fe, the atomic weight of Fe is used.

[0050] (Ga: 0.35 - 0.75 mass%)

[0051] The content of Ga is 0.35 - 0.75 mass%. When the content of Ga is less than 0.35 mass%, the temperature coefficient cannot be improved, and high H cannot be obtained at high temperatures. cJ In addition, the amount of R-T-Ga phase formed decreases, and it is impossible to make the R2T 17 phase disappear, and it may be impossible to obtain high H at room temperature. cJ When the content of Ga exceeds 0.75 mass%, due to the presence of unnecessary Ga, the main phase ratio decreases, and B r may decrease.

[0052] (Cu: 0.05 - 0.50 mass%)

[0053] The content of Cu is 0.05 - 0.50 mass%. When the content of Cu is less than 0.05 mass%, it may be impossible to obtain high H at room temperature and high temperatures. cJ When it exceeds 0.50 mass%, the sinterability deteriorates, and it may be impossible to obtain high H at room temperature and high temperatures. cJ .

[0054] (Mn: 0.03 - 0.15 mass%)

[0055] The content of Mn is 0.03 - 0.15 mass%. By restricting the content of B within the above range and further containing 0.03 - 0.15 mass% of Mn, the temperature coefficient is improved, and high H can be obtained at high temperatures. cJ When the content of Mn is less than 0.03 mass%, the temperature coefficient cannot be improved, and high H cannot be obtained at high temperatures. cJ . In addition, when it exceeds 0.15 mass%, B r may decrease. (T: 61.5 mass% - 70.0 mass%)

[0056] T is Fe or Fe and Co, and more than 90 mass% of T is Fe. By containing Co, the corrosion resistance can be improved, but when the replacement amount of Co exceeds 10 mass% of T, it may be impossible to obtain high Br The content of T is 61.5% by mass or more and 70.0% by mass or less, and satisfies the above formula (1). When the content of T is less than 61.5% by mass, B r may be significantly reduced. Preferably, T is the remainder.

[0057] The R-T-B-based sintered magnet of the present invention may also contain Cr, Mn, Si, La, Ce, Sm, Ca, Mg, etc. that are usually contained as inevitable impurities in neodymium praseodymium alloy (Nd-Pr), electrolytic iron, iron boron alloy, etc. In addition, as inevitable impurities in the manufacturing process, O (oxygen), N (nitrogen), C (carbon), Al, etc. can be exemplified. In addition, the R-T-B-based sintered magnet of the present invention may contain one or more other elements (elements intentionally added in addition to inevitable impurities). For example, as such elements, a small amount (about 0.1% by mass each) of Ag, Zn, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, etc. can be contained. In addition, the elements listed as the above inevitable elements may also be intentionally added. Such elements can be contained in an amount of about 1.0% by mass in total. If it is this level, there is a sufficient possibility of obtaining an R-T-B-based sintered magnet having a high H cJ at high temperatures.

[0058] The R-T-B-based sintered magnet having the composition according to the above-described embodiment of the present invention can be manufactured, for example, by the following manufacturing method, which includes the following steps: a step of producing a rapidly quenched alloy; a molding step of molding the above alloy powder to obtain a molded body; a sintering step of sintering the molded body to obtain a sintered body; and a heat treatment step of performing heat treatment on the sintered body. [Manufacturing method of R-T-B-based sintered magnet]

[0059] Next, each step will be described.

[0060] (Step of producing alloy powder)

[0061] Prepare metals or alloys (melting raw materials) of each element so that the R-T-B-based sintered magnet has the above specific composition, and produce a thin raw material alloy by a strip casting method or the like. Next, coarsely pulverize the thin raw material alloy by hydrogen crushing or the like to prepare a coarsely pulverized powder having an average particle size of 1.0 mm or less. Next, finely pulverize the coarsely pulverized powder in an inert gas using a jet mill or the like to obtain, for example, a finely pulverized powder (raw material alloy powder) having a particle size D 50 of 3 to 5 μm. As an auxiliary agent, a known lubricant can be added to the coarsely pulverized powder before jet mill pulverization, the alloy powder during jet mill pulverization, and the alloy powder after jet mill pulverization.

[0062] (Forming process)

[0063] The obtained raw material powder is used for forming in a magnetic field to obtain a formed body. Regarding the forming in a magnetic field, any known magnetic field forming method can be adopted, including a dry forming method in which the dried alloy powder is inserted into the cavity of the mold and then formed while applying a magnetic field, and a wet forming method in which a slurry is injected into the cavity of the mold and then formed while discharging the dispersion medium of the slurry.

[0064] (Sintering process)

[0065] The sintered body (sintered magnet) is obtained by sintering the formed body. The sintering of the formed body can be carried out by a known method. In addition, in order to prevent oxidation caused by the atmosphere during sintering, it is preferably sintered in a vacuum atmosphere or in an inert gas. The inert gas is preferably an inert gas such as helium or argon.

[0066] (Heat treatment process)

[0067] The obtained sintered magnet is preferably heat-treated for the purpose of improving magnetic properties. The heat treatment temperature, heat treatment time, etc. can be based on known conditions. For example, heat treatment (one-stage heat treatment) can be carried out only at a relatively low temperature (above 400°C and below 600°C), or heat treatment can be carried out at a relatively high temperature (above 700°C and below the sintering temperature (for example, below 1050°C)) and then at a relatively low temperature (above 400°C and below 600°C) (two-stage heat treatment). As preferred conditions, heat treatment can be carried out at 730°C or above and 1020°C or below for about 5 minutes to 500 minutes, followed by cooling (after cooling to room temperature, or after cooling to above 440°C and below 550°C), and then heat treatment at 440°C or above and 550°C or below for about 5 minutes to 500 minutes. Regarding the heat treatment atmosphere, it is preferably carried out in a vacuum atmosphere or an inert gas (helium, argon, etc.).

[0068] For the purpose of making the final product shape, etc., machining such as grinding can be carried out on the obtained sintered magnet. In this case, the heat treatment can be carried out either before or after the machining. Furthermore, the obtained sintered magnet can be subjected to surface treatment. The surface treatment can be a known surface treatment, or surface treatment such as Al evaporation, Ni electroplating, resin coating, etc. can be carried out.

[0069] Examples

[0070] The present invention will be further described in detail by way of examples, but the present invention is not limited to these examples.

[0071] [Experimental Example 1]

[0072] Weigh each element in such a way that the composition of the R-T-B system sintered magnet roughly becomes the compositions of Nos. 1 to 12 in Table 1, and perform casting using the strip casting method to produce a rapidly solidified alloy. After hydrogen embrittling the obtained rapidly solidified alloy in a hydrogen-pressurized atmosphere, perform a dehydrogenation treatment of heating to 550 °C in a vacuum and then cooling to obtain a coarsely pulverized powder. Next, to the obtained coarsely pulverized powder, 0.04% by mass of zinc stearate is added as a lubricant with respect to 100% by mass of the coarsely pulverized powder. After mixing, use a jet mill (jet grinding device) to perform dry pulverization in a nitrogen stream to obtain a finely pulverized powder (alloy powder) with a particle size D 50 (median diameter) of 4 μm.

[0073] Mix the obtained alloy powder with a dispersion medium to prepare a slurry. The solvent used is n-dodecane, and methyl octanoate is mixed as a lubricant. The concentration of the slurry is set to 70% by mass of the alloy powder and 30% by mass of the dispersion medium, and the lubricant is 0.16% by mass with respect to 100% by mass of the alloy powder. The above slurry is formed in a magnetic field to obtain a formed body. The magnetic field during forming is a static magnetic field of 0.8 MA / m, and the applied pressure is set to 5 MPa. Among them, as the forming device, a so-called right-angle magnetic field forming device (transverse magnetic field forming device) in which the magnetic field application direction is orthogonal to the pressing direction is used.

[0074] After sintering the obtained formed body in a vacuum at 1000 °C or higher and 1090 °C or lower (the temperature at which sufficient densification occurs through sintering is selected for each sample) for 4 hours, perform rapid cooling to obtain a sintered body. The density of the obtained sintered body is 7.5 Mg / m 3 or more. For the obtained sintered body, perform a heat treatment of holding at 800 °C in a vacuum for 2 hours and then rapidly cooling to room temperature, and then holding at 430 °C or higher and 530 °C or lower (the temperature at which good coercivity can be obtained is selected for each sample) for 2 hours and then cooling to room temperature to obtain an R-T-B system sintered magnet.

[0075] The composition of the obtained R-T-B system sintered magnet is shown in Table 1. Among them, each component (except O, N, and C) in Table 1 is measured using inductively coupled plasma optical emission spectrometry (ICP-OES). In addition, the O (oxygen) content is measured using the gas fusion-infrared absorption method, the N (nitrogen) content is measured using the gas fusion-thermal conductivity method, and the C (carbon) content is measured using the combustion-infrared absorption method.

[0076] The satisfaction of Equation (1) is shown in Table 1. Among them, "○" means that Equation (1) is satisfied, and "×" means that Equation (1) is not satisfied.

[0077] The measurement results of the magnetic properties of the obtained R-T-B system sintered magnet are shown in Table 2. "22.5 °C B" in Table 2 r” and “22.5 °C H cJ ” are the values of B r and H cJ at room temperature (22.5 °C), “100 °C B r ” and “100 °C H cJ ” are the values of B r and H cJ at high temperature (100 °C). The R–T–B system sintered magnet is machined, and the sample is processed into 7 mm × 7 mm × 7 mm. These values of B r , H cJ are measured using a BH tracer. In addition, the temperature coefficient (β: 22.5 to 100 °C) is obtained as described below.

[0078] Temperature coefficient = (H at 100 °C cJ − H at 22.5 °C cJ ) / H at 22.5 °C cJ / (100 °C − 22.5 °C) × 100%

[0079] The smaller the absolute value of the temperature coefficient, the better the temperature coefficient is improved.

[0080] [Table 1]

[0081]

[0082] [Table 2]

[0083]

[0084] As shown in Table 2, the inventive examples (No. 7, 8, 9, 12) that satisfy the composition of the R–T–B system sintered magnet of the present invention have higher H cJ at high temperature (100 °C) compared with the comparative examples (comparative examples outside the composition range of the present invention). In addition, in Experimental Example 1, all the inventive examples do not contain heavy rare earth elements (except inevitable impurities), H cJ ≥ 880 kA / m at 100 °C, and B r ≥ 1.32 T at 22.5 °C, and higher magnetic properties are obtained compared with the comparative examples. In addition, as shown by the temperature coefficients in Table 2, the absolute values of the temperature coefficients of the inventive examples are smaller than those of the comparative examples.

[0085] In Figure 1 shows the relationship between the content of Mn in No. 1 to 10 and H cJ at 100 °C. Figure 1 The squares (■) of the species are inventive examples, and the triangles (▲) are comparative examples. As Figure 1As shown in No.1 to No.5, when the B content of the R-T-B system sintered magnet is outside the scope of the present invention (the B content in No.1 to No.3 and No.5 is outside the scope, and the formula (1) in No.4 is outside the scope), even if the content of Mn is increased, H at high temperature cJ hardly increases. On the other hand, as shown in No.6 to No.10, if the B content of the R-T-B system sintered magnet is within the scope of the present invention, when the content of Mn exceeds 0.02 mass% (No.6), H at high temperature cJ increases significantly. Among them, in No.10 (Mn: 0.20 mass%), although high H is obtained at high temperature cJ , as shown in Table 2, B r decreases.

[0086] [Experimental Example 2]

[0087] Weighed each element so that the composition of the R-T-B system sintered magnet roughly became the composition of No.13 to No.15 in Table 3. Except for this, the R-T-B system sintered magnet was produced in the same manner as in Experimental Example 1. The components and magnetic properties of the obtained R-T-B system sintered magnet were measured in the same manner as in Experimental Example 1. The respective results are shown in Table 3 and Table 4.

[0088] [Table 3]

[0089]

[0090] [Table 4]

[0091]

[0092] When the R-T-B system sintered magnet contains Tb, corresponding to the content of Tb, B r decreases and H cJ increases. In this case, at 22.5 °C, when containing 1 mass% of Tb, B r decreases by about 0.024 T. In addition, at 100 °C, when containing 1 mass% of Tb, H cJ increases by about 168 kA / m. Therefore, as described above, in the case of the present invention without containing heavy rare earth elements, at 100 °C, H cJ ≥ 880 kA / m, and at 22.5 °C, B r ≥ 1.32 T. Thus, in the case of containing Tb, at 100 °C, H cJ ≥ 880 + 168[Tb] kA / m, and at 22.5 °C, B r ≥ 1.32 - 0.024[Tb] T.

[0093] As shown in Table 3 and Table 4, Nos. 13 to 14 as examples of the present invention contain 1.0% by mass or less of Tb, and at 100 °C, H cJ ≥880 + 168[Tb] kA / m, and at 22.5 °C, B r ≥1.32 - 0.024[Tb] T, all having high magnetic properties. In addition, similar to the examples of the present invention in Experimental Example 1, the absolute values of the temperature coefficients are all small.

Claims

1. A sintered magnet of the R-T-B system, characterized in that, Containing: R: 28.5% by mass or more and 33.0% by mass or less, where R is at least one of rare earth elements and contains at least one of Nd and Pr; B: 0.85% by mass or more and 0.91% by mass or less; Ga: 0.35% by mass or more and 0.75% by mass or less; Cu: 0.05% by mass or more and 0.50% by mass or less; Mn: 0.03% by mass or more and 0.15% by mass or less; T: 61.5% by mass or more and 70.0% by mass or less, where T is Fe or Fe and Co, and 90% by mass or more of T is Fe, The R-T-B system sintered magnet satisfies the following formula (1): [T] / 55.85 - 14[B] / 10.8 ≥ 0.063 (1), where [B] is the content of B expressed in mass%, and [T] is the content of T expressed in mass%.

2. The R-T-B system sintered magnet according to claim 1, characterized in that: Except for inevitable impurities, it does not contain heavy rare earth elements, and at 100 °C, H cJ ≥ 880 kA / m, and at 22.5 °C, B r ≥ 1.32 T.

3. The R-T-B system sintered magnet according to claim 1, characterized in that: containing Tb of 1.0 mass% or less, and at 100 °C, H cJ ≥ 880 + 168 [Tb] kA / m, and at 22.5 °C, B r ≥ 1.32 - 0.024 [Tb] T, where [Tb] is the content of Tb expressed in mass%.

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