Manufacturing method for RTB sintered magnets

Abstract

To provide a method for producing an R-T-B based sintered magnet capable of improving productivity while reducing the contend of RH and maintaining a high Hcj and a high Hk / Hci.SOLUTION: There is provided a method for producing an R-T-B based sintered magnet which comprises: a step of preparing a main alloy powder; a step of preparing an oxide powder containing 15 mass% or more and 40 mass% or less of O and 60 mass% or more and 85 mass% or less of M (M is at least one selected from the group consisting of Zn, Mg, Ca, Sn, Cd, Sb, As and Hg); a step of preparing a mixed powder; and a step of producing a sintered body, in which the mixing amount of an oxide powder to the whole mixed powder is 0.03 mass% or more and 0.55 mass% or less and the oxygen content is 500 ppm or more and 3500 ppm or less, which is an amount obtained by increasing the content of O in the mixed powder to the oxygen content of the main alloy powder by 300 ppm or more and 2000 ppm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing an RTB based sintered magnet. [Background technology]

[0002] R2T 14 RTB sintered magnets (R is at least one rare earth element and always includes Nd, and T is at least one transition metal element and always includes Fe) with a B-type compound as the main phase are known as the highest performance magnets among permanent magnets, and are used in a wide variety of applications such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and other motors, as well as in home appliances.

[0003] RTB sintered magnets have a coercive force H cJ (Hereafter, simply "H cJ ") decreases, and irreversible thermal demagnetization occurs. Therefore, especially when used in electric vehicle motors, high H cJ To maintain the H cJ is required.

[0004] Conventionally, H cJ To improve the residual magnetic flux density B r (Hereinafter, simply "B r For this reason, in recent years, heavy rare earth elements have been diffused from the surface to the inside of RTB sintered magnets to concentrate the heavy rare earth elements in the outer periphery of the main phase crystal grains, thereby improving the B r While suppressing the decline of cJ A method has been adopted to obtain

[0005] However, Dy has problems such as unstable supply and price fluctuations due to limited production areas. For this reason, the amount of heavy rare earth elements such as Dy used is minimized to maximize the H content of RTB sintered magnets.cJ There is a demand for technologies that can improve this.

[0006] Patent Document 1 describes a method for producing an R2T alloy by lowering the B content compared to conventional RTB alloys and adding one or more metal elements M selected from Al, Ga, and Cu. 17 The R2T 17 Transition metal-rich phase (R6T 13 By ensuring a sufficient volume fraction of M, the content of Dy can be suppressed while cJ It is described that an RTB rare earth sintered magnet with high mechanical properties can be obtained.

[0007] As mentioned above, RTB sintered magnets are most commonly used in motors, and H is particularly important in electric vehicle motors to ensure high temperature stability. cJ It is very effective to improve the squareness ratio Hk / H cJ (Hereafter, simply Hk / H cJ (sometimes called "high-frequency") must also be high. cJ If H is low, it will cause the problem of demagnetization. cJ and has a high Hk / H cJ In the field of RTB sintered magnets, the ratio Hk / H cJ The parameter Hk measured to determine this is the value in the second quadrant of the J (magnetization strength)-H (magnetic field strength) curve, where J is 0.9 × J. r (J r is the remanent magnetization, J r =B r The H-axis reading at the position where the value of Hk is reached is used. cJ Divided by (Hk / H cJ =Hk(kA / m) / H cJ (kA / m) × 100(%) is defined as the squareness ratio. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2013 / 008756 Summary of the Invention [Problem to be solved by the invention]

[0009] The RTB rare earth magnet described in Patent Document 1 has a high H cJ However, the general RTB sintered magnet (R2T 14 Compared with B-type compounds, which have a higher B content than the stoichiometric ratio, k / H cJ However, there was a problem in that the range of appropriate sintering temperatures (appropriate temperature range) for obtaining this was narrow, resulting in poor productivity.

[0010] Accordingly, an object of the present disclosure is to provide a method for producing an RTB sintered magnet that can improve productivity while reducing the content of heavy rare earth elements (RH) and maintaining high HcJ and high Hk / HcJ. [Means for solving the problem]

[0011] A method for producing an RTB based sintered magnet according to the present disclosure, in a non-limiting embodiment, is a method for producing an RTB based sintered magnet, comprising the steps of: R: 28.5 mass % or more and 33.0 mass % or less (R is at least one rare earth element, and is at least one selected from the group consisting of Nd, Pr, and Ce); B: 0.85 mass % or more and 0.95 mass % or less; Ga: 0.2 mass % or more and 1.0 mass % or less; Cu: 0.05 mass % or more and 0.50 mass % or less; % or less by mass, T: 61.5 mass% or more and 70.0 mass% or less (T is Fe or Fe and Co, and the content of Fe in the total amount of T is 90 mass% or more), and O: 100 ppm or more and 1500 ppm or less, wherein the content (mass%) of T is [T] and the content (mass%) of B is [B], the formula [T] / 55.85>14×[B] / 10.8 is satisfied; and O: 15 mass% or more and 40 mass% or less. The method includes the steps of: preparing an oxide powder containing 60 mass % or more and 85 mass % or less of M (M is at least one selected from the group consisting of Zn, Mg, Ca, Sn, Cd, Sb, AS, and Hg); preparing a mixed powder by mixing the main alloy powder with the oxide powder; and producing a sintered body of the mixed powder, wherein the mixed powder preparation step has a mixed amount of the oxide powder of 0.03 mass % or more and 0.55 mass % or less with respect to the total mixed powder, and the oxygen content of the mixed powder is increased by 300 ppm or more and 2000 ppm or less relative to the oxygen content of the main alloy powder, resulting in an RTB sintered magnet with an oxygen content of 500 ppm or more and 3500 ppm or less. In one embodiment, M in the oxide powder is at least one selected from the group consisting of Zn, Mg, and Ca. Effect of the Invention

[0012] According to an embodiment of the present invention, it is possible to provide a method for producing an RTB based sintered magnet that can improve productivity while reducing the RH content and maintaining high HcJ and high Hk / HcJ. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] As a result of investigations, the present inventors have found that, in an RTB alloy powder having a lower B content than that of a normal RTB alloy powder as described in Patent Document 1, a specific element including oxygen and an oxide powder having a specific composition range are added in a specific amount, thereby achieving a high H k / H cJ It was found that the range of suitable sintering temperatures (suitable temperature range) for obtaining high H can be expanded. cJ and high H k / H cJ It is therefore possible to produce RTB based sintered magnets with improved productivity while maintaining the above properties. On the other hand, as shown in the examples described later, when oxygen is introduced in the manufacturing process (for example, the crushing process or the molding process) without using oxide powder, the same effect as that of the present disclosure cannot be obtained. This is considered to be because the process of generating the liquid phase during sintering is different between the case where oxygen is introduced using oxide powder and the case where oxygen is introduced by the manufacturing process. This will be described in detail below. It is considered that the amount of the phase mainly composed of unoxidized rare earth in the main alloy powder greatly affects the generation of the liquid phase during the temperature rise process during sintering. When oxygen is introduced in the manufacturing process, the main alloy powder is oxidized, and the amount of the phase mainly composed of unoxidized rare earth in the main alloy powder decreases. It is considered that if sintering is performed after molding using the oxidized main alloy powder, the liquid phase is unlikely to be generated during the temperature rise process during sintering. On the other hand, when the oxide powder of the present disclosure is used, the oxidation of the main alloy powder is suppressed until the main alloy powder reduces the oxide phase in the oxide powder. Therefore, the amount of the phase mainly composed of unoxidized rare earth in the main alloy powder does not decrease for a certain period of time during the temperature rise process, and the generation of the liquid phase is unlikely to be inhibited during the temperature rise process during sintering. Therefore, it is believed that a sufficient liquid phase is generated during the temperature rise process during sintering. In this way, it is believed that the addition of oxide powder generates a sufficient liquid phase during the temperature rise process during sintering, and then oxygen is introduced from the oxide powder, which greatly expands the range of appropriate sintering temperatures. In addition, by adding a specific amount of oxide powder consisting of specific elements containing oxygen and specific composition ranges as disclosed herein, these elements are unlikely to remain in the sintered magnet and do not have a negative effect on the sintered magnet as impurities, so that it is possible to reduce the RH content while maintaining a high H cJ and high H k / H cJ can be obtained. In addition, the high H k / H cJ The appropriate sintering temperature range to obtain H cJ More than 1400kA / m was obtained, and H k / H cJ The range in which 85% or more of the sintering temperature can be obtained can be used as the sintering temperature range.

[0014] The method for producing an RTB based sintered magnet of the present disclosure includes the steps of preparing a main alloy powder, preparing an oxide powder, preparing a mixed powder, and producing a sintered body. The RTB based sintered magnet of the present disclosure has an oxygen content of 500 ppm or more and 3500 ppm or less. If the oxygen content of an RTB based sintered magnet is less than 500 ppm, the amount of oxygen is too low and the magnet will have a high H k / H cJ The appropriate sintering temperature range for obtaining H may become narrower. If the concentration exceeds 3500 ppm, cJ may decrease, and even higher H k / H cJ However, the range of appropriate sintering temperatures (appropriate temperature range) for obtaining the above properties may become narrower.

[0015] [Preparing main alloy powder] The primary alloy powder of the present disclosure has the following composition: R: 28.5% by mass or more and 33.0% by mass or less B: 0.85% by mass or more and 0.95% by mass or less, Ga: 0.2% by mass or more and 1.0% by mass or less, Cu: 0.05% by mass or more and 0.50% by mass or less, T: 61.5% by mass or more and 70.0% by mass or less, Oxygen (O): 100ppm or more and 1500ppm or less, including Each composition will be described in detail below. (R:28.5~33.0% by mass) In the primary alloy powder of the present disclosure, R is at least one rare earth element selected from the group consisting of Nd, Pr, and Ce, and T is Fe or Fe and Co, with the content of Fe relative to the total amount of T being 90 mass% or more. The content of R is 28.5 to 33.0 mass%. If the content of R is less than 28.5 mass%, it may be difficult to densify during sintering, and if it exceeds 33.0 mass%, the main phase ratio decreases and high B r The content of R is preferably 29.5 to 32.5 mass %. If R is in this range, a higher B r can be obtained. (B:0.85~0.95% by mass) The content of B is 0.85 to 0.95 mass%. When the content of B is less than 0.85 mass%, the R2T 17 Phase is generated and high H cJ If the content exceeds 0.92 mass%, R6T may not be obtained. 13 The amount of M phase produced is too small, resulting in high H cJ The B content is preferably 0.85 to 0.92 mass%. r and high H cJ A part of B can be replaced with C.

[0016] The content of B satisfies the following formula (1). [T] / 55.85>14×[B] / 10.8 By satisfying formula (1), the B content is less than that of a typical RTB sintered magnet. A typical RTB sintered magnet contains R2T, which is the main phase. 14 In addition to the B phase, there is a soft magnetic phase, R2T 17 To prevent the formation of any phase, the composition is set such that [T] / 55.85 (atomic weight of Fe) is less than 14 × [B] / 10.8 (atomic weight of B) ([T] is the Fe content in mass %). Unlike typical RTB based sintered magnets, the RTB based sintered magnet of the present invention is specified by formula (1) such that [T] / 55.85 is greater than 14 × [B] / 10.8. Note that since the main component of T in the RTB based sintered magnet of the present invention is Fe, the atomic weight of Fe is used.

[0017] (Ga:0.2~1.0% by mass) The Ga content is 0.2 to 1.0 mass%. When the Ga content is less than 0.2 mass%, R6T 13 The amount of M phase produced is too small, so R2T 17 The phase cannot be eliminated, and high H cJ If it exceeds 1.0 mass%, unnecessary Ga will be present, and the main phase ratio will decrease, resulting in a decrease in B. rThe Ga content is preferably 0.3 mass % or more and less than 0.7 mass %. This allows for a higher B r and high H cJ can be obtained.

[0018] (Cu:0.05~0.50% by mass) The Cu content is 0.05 to 0.50 mass%. If the Cu content is less than 0.05 mass%, the high H cJ If it exceeds 0.50 mass%, the sintering property may deteriorate and a high H cJ C

[0019] (T:61.5~70.0% by mass) T is Fe or Fe and Co, and the Fe content in the whole of T is 90 mass% or more. The inclusion of Co can improve corrosion resistance, but if the amount of Co substituted exceeds 10 mass% of Fe, high B r The T content is 61.5 mass% or more and 70.0 mass% or less. If the T content is less than 61.5 mass%, the B r If it exceeds 70.0 mass%, H cJ may decrease. In addition to the above elements, the main alloy powder may contain one or more other elements (elements intentionally added other than unavoidable impurities). For example, such elements may include Al, Ag, Zn, In, Sn, Ti, Ge, Y, H, F, P, S, V, Ni, Mo, Hf, Ta, W, Nb, Zr, etc. .child Such elements may be contained in a total amount of, for example, about 2.0 mass%. cJ It is quite possible to obtain an RTB based sintered magnet having the above properties.

[0020] (Oxygen (O): 100 ppm or more and 1500 ppm or less) The oxygen content is 100ppm to 1500ppm. If the oxygen content is less than 100ppm, productivity may be significantly reduced, and if it exceeds 1500ppm, HcJ may decrease.

[0021] Next, a method for producing the main alloy powder of the present disclosure will be described. The main alloy powder can be produced by a known method. For example, metals or alloys of the respective elements are prepared so as to have the above composition, and flakes of the alloy are obtained by strip casting or the like. The obtained flake-like alloy is subjected to hydrogen pulverization to obtain a coarsely pulverized powder having a size of, for example, 1.0 mm or less. Next, the coarsely pulverized powder is finely pulverized by a jet mill or the like to obtain a particle size D 50 A finely pulverized powder (alloy powder) having a median diameter (value obtained by laser diffraction method using air flow dispersion method) of 2 to 7 μm is obtained. A known lubricant may be used as an auxiliary agent for the coarsely pulverized powder before the jet mill pulverization, and for the alloy powder during and after the jet mill pulverization.

[0022] [Preparing oxide powder] The oxide powder of the present disclosure has the following composition: O: 15% by mass or more and 40% by mass or less, M: 60% by mass or more and 85% by mass or less (M is at least one selected from the group consisting of Zn, Mg, Ca, Sn, Cd, Sb, AS, and Hg). The oxide powder may be any known oxide containing Zn, Mg, Ca, Sn, Cd, Sb, As, or Hg. (O:15~40% by mass) The O (oxygen) content is 15% by mass or more and 40% by mass or less. If the O content is less than 15% by mass, the mixed ratio of the oxide powder increases, and the M element may remain as an impurity after sintering, while if it exceeds 40% by mass, the mixed ratio of the oxide powder decreases, and a sufficient effect may not be obtained. (M: 60~85% by mass) M is at least one element selected from the group consisting of Zn, Mg, Ca, Sn, Cd, Sb, As, and Hg. These elements are easily evaporated during sintering and are unlikely to remain in the sintered magnet. Therefore, these elements are unlikely to adversely affect the magnet as impurities, and the RH content can be reduced while maintaining high H cJ and high H k / H cJ The M element is preferably at least one selected from the group consisting of Zn, Mg, and Ca.

[0023] [Preparing mixed alloys] The main alloy powder and the oxide powder thus prepared are mixed to obtain a mixed powder. The main alloy powder and the oxide powder may be mixed in a known mixer such as a V-type mixer.

[0024] The main alloy powder and the additive alloy powder are mixed so that the amount of oxide powder mixed with respect to the entire mixed powder is 0.03 mass% or more and 0.55 mass% or less. If the amount of oxide powder mixed with respect to the entire mixed powder is less than 0.03 mass%, high H k / H cJ It may not be possible to widen the range of appropriate sintering temperatures (appropriate temperature range) for obtaining Br, and if it exceeds 0.55 mass %, Br may decrease. Furthermore, the amount of the oxide powder mixed with respect to the entire mixed powder is an amount that increases the O content of the mixed powder by 300 ppm to 2000 ppm with respect to the oxygen content of the main alloy powder. In other words, the amount of the oxide powder mixed with respect to the entire mixed powder is an amount that increases the oxygen content of the mixed alloy powder obtained by mixing the oxide powder with the main alloy powder by 300 ppm to 2000 ppm with respect to the main alloy powder. If the amount of the oxide powder mixed increases by less than 300 ppm, the amount of oxygen added by the oxide powder is too small, resulting in high H k / H cJ It may not be possible to widen the range of appropriate sintering temperatures (appropriate temperature range) to obtain H. cJ may decrease.

[0025] [Process for producing sintered bodies of mixed powders] In a preferred embodiment, the step of preparing a sintered body of the mixed powder includes a step of preparing a powder compact from the fine powder by pressing in a magnetic field, and a step of sintering the powder compact. In order to suppress oxidation of the powder other than the oxide powder, it is preferable to form the powder compact by pressing in an inert gas atmosphere or wet pressing in the magnetic field. Next, the compact is sintered to obtain a rare earth sintered magnet body (sintered body). The compact is preferably sintered at a pressure of 0.13 Pa (10 -3 Torr) or less, preferably 0.07 Pa (5.0 x 10 -4 The sintering is carried out at a pressure of 1000 to 1150 Torr or less and at a temperature of 1000 to 1150°C. To prevent oxidation due to sintering, residual gas in the atmosphere may be replaced with an inert gas such as helium or argon. The obtained sintered body is preferably subjected to a heat treatment. The magnetic properties can be improved by the heat treatment. Known conditions can be used for the heat treatment, such as the heat treatment temperature and heat treatment time. The rare earth sintered magnet body thus obtained is subjected to a grinding / polishing process, a surface treatment process, and a magnetization process as necessary to complete the final rare earth sintered magnet. In a preferred embodiment, the method for producing an RTB based sintered magnet of the present disclosure further comprises a diffusion step of diffusing a heavy rare earth element RH (RH is at least one of Tb, Dy, and Ho) from the surface of the sintered body to the inside. Diffusion of the heavy rare earth element RH from the surface to the inside of the sintered body can efficiently increase the coercive force. EXAMPLES

[0026] The present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited thereto. Experimental Example 1 Each element was weighed and cast by strip casting so that the composition of the RTB sintered magnet would be approximately the composition shown in No. 1 of Table 1, to obtain a flake-shaped alloy. The obtained flake-shaped alloy was hydrogen embrittled in a pressurized hydrogen atmosphere, and then subjected to a dehydrogenation treatment in which it was heated to 550°C in a vacuum and cooled, to obtain a coarsely pulverized powder. Next, zinc stearate was added as a lubricant to the obtained coarsely pulverized powder in an amount of 0.04% by mass relative to 100% by mass of the coarsely pulverized powder, and mixed. The mixture was then dry-pulverized in a nitrogen atmosphere using an airflow pulverizer (jet mill device), and the resulting mixture was dried to obtain a D 50 The alloy powder obtained was 4.0 μm in diameter.

[0027] The alloy powder was mixed with 0.4% by mass of lubricant based on 100% by mass of the finely pulverized powder, and then compacted in a magnetic field to obtain multiple compacts. The compacting device used was a so-called perpendicular magnetic field compacting device (horizontal magnetic field compacting device) in which the magnetic field application direction and the pressure direction are perpendicular to each other.

[0028] The obtained molded bodies were sintered to obtain sintered bodies. The sintering temperature was varied between 1000°C and 1100°C in increments of 10°C for the obtained molded bodies, and each was sintered. The obtained sintered bodies were subjected to a heat treatment in which they were held at 800°C for 2 hours, cooled to room temperature, and then held at 500°C for 2 hours, and cooled to room temperature to obtain multiple RTB sintered magnets (No. 1). The contents of the components Nd, Pr, B, Co, Al, Cu, Ga, and Zr in the obtained sintered magnets were measured by ICP atomic emission spectrometry. O (oxygen content) was measured using a gas fusion-infrared absorption method. The results are shown in Table 1 (only one is shown because there was almost no difference in composition between the multiple RTB sintered magnets of No. 1).

[0029] [Table 1] Experimental Example 2

[0030] Each element was weighed and cast by strip casting so that the composition of the main alloy powder would be approximately the composition shown in No. A in Table 2, to obtain a flake-shaped alloy. The obtained flake-shaped alloy was hydrogen embrittled in a pressurized hydrogen atmosphere, and then subjected to a dehydrogenation treatment in which it was heated to 550°C in a vacuum and cooled, to obtain a coarsely pulverized powder. Next, zinc stearate was added as a lubricant to the obtained coarsely pulverized powder in an amount of 0.04 mass% relative to 100 mass% of the coarsely pulverized powder, and mixed, and then dry-pulverized in a nitrogen atmosphere using an airflow pulverizer (jet mill device), to obtain a D 50 An alloy powder having a particle size of 4.0 μm was obtained. The results of the component analysis of the obtained alloy powder are shown in No. A of Table 2. Each component in Table 2 was measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). No. A satisfied the formula 1 of the present disclosure.

[0031] [Table 2]

[0032] Furthermore, an oxide powder was prepared having the composition shown in No. a of Table 3. A known Mg oxide was used as the oxide powder.

[0033] [Table 3]

[0034] A mixed powder was prepared by mixing the main alloy powder and the oxide powder under the conditions shown in Table 4. No. 2 in Table 4 is a mixture of main alloy powder No. A and oxide powder No. a, the mass ratio of the oxide powder to the entire mixed powder is 0.27 mass%, and the mixed amount of the oxide powder is an amount that increases the oxygen content of the mixed powder by 1100 ppm with respect to the oxygen content of the main alloy powder.

[0035] The resulting mixed powder was mixed with 0.4% by mass of lubricant based on 100% by mass of the finely pulverized powder, and then compacted in a magnetic field to obtain multiple compacts. The compacting device used was a so-called perpendicular magnetic field compacting device (horizontal magnetic field compacting device), in which the magnetic field application direction and the pressure direction are perpendicular to each other.

[0036] The resulting molded bodies were sintered at different sintering temperatures in the same manner as in Experimental Example 1, and then heat-treated in the same manner as in Experimental Example 1 to obtain a number of RTB sintered magnets (No. 2). The components of the resulting sintered magnets were measured in the same manner as in Experimental Example 1. The results are shown in Table 5 (only one of the No. 2 RTB sintered magnets is shown, as there was almost no difference in composition between them).

[0037] [Table 4]

[0038] [Table 5]

[0039] The obtained RTB sintered magnets No. 1 (Experimental Example 1) and No. 2 (Experimental Example 2) were machined to prepare samples with a length of 7 mm, a width of 7 mm, and a thickness of 7 mm. r and H cJ In the case of multiple samples of No. 1 and No. 2, H cJ and H k / H cJ Compared with each other, the high H k / H cJ The appropriate sintering temperature range (H cJ More than 1400kA / m was obtained, and H k / H cJ The sintering temperature range in which a sintering efficiency of 85% or more can be obtained was determined. For example, when the appropriate sintering temperature is 1030°C to 1060°C, the sintering temperature range is set to 30°C. In addition, H k / H cJ was calculated as follows: RTB sintered magnets were measured with a BH tracer, and in the second quadrant of the J (magnetization strength)-H (magnetic field strength) curve, J was 0.9×J r (J r is the remanent magnetization, J r =B r) value on the H axis is taken as H k And this H k H of the demagnetization curve cJ Divided by (H k (kA / m) / H cJ (kA / m) × 100(%)) k / H cJ The results are shown in Table 6.

[0040] [Table 6]

[0041] No. 1 in Table 6 is the high H k / H cJ The appropriate sintering temperature range for obtaining H is shown in "Sintering Temperature Range". cJ The minimum and maximum values ​​of "H cJ The width is shown in "B r " shows only one sample because there is almost no difference between samples. The same is true for No. 2.

[0042] As shown in Table 6, comparing No. 1 and No. 2, which have almost the same RTB sintered magnet composition (including almost the same oxygen content), the inventive example has a wider sintering temperature range than the comparative example. Example 3

[0043] Main alloy powders Nos. B to E were prepared in the same manner as in Example 2. The composition results are shown in Table 7. In addition, oxide powders having the compositions shown in Nos. b to d in Table 8 were prepared. The oxide powders used were known oxides of Zn, Ca, and Ni, respectively.

[0044] [Table 7]

[0045] [Table 8]

[0046] Mixed powders were prepared by mixing the main alloy powder and the oxide powder under the conditions shown in Table 9. Note that No. 6 and No. 8 did not contain any oxide powder (only the main alloy powder).

[0047] The resulting mixed powder and main alloy powder (Nos. 6 and 8) were used to produce a number of compacts in the same manner as in Experimental Example 1. The resulting compacts were sintered at different sintering temperatures in the same manner as in Experimental Example 1, and then heat-treated in the same manner as in Experimental Example 1 to obtain a number of RTB sintered magnets (Nos. 3 to 12). The components of the resulting sintered magnets were measured in the same manner as in Experimental Example 1. The results are shown in Table 11 (since there was almost no difference in composition between the RTB sintered magnets, only one each of Nos. 3 to 12 is shown).

[0048] The obtained RTB sintered magnets No. 3 to No. 12 were machined to prepare samples with a length of 7 mm, a width of 7 mm, and a thickness of 7 mm. r and H cJ Then, a plurality of samples were compared in the same manner as in Example 2 to determine the high H k / H cJ The optimum sintering temperature range for obtaining the above value was determined. The results are shown in Table 11. No. 10 and No. 12 are H cJ Since it was not possible to obtain a value of 1400 kA / m or more, H k / H cJ When 85% or more of cJ The maximum and minimum values ​​are listed.

[0049] [Table 9]

[0050] [Table 10]

[0051] [Table 11]

[0052] As shown in Table 11, when comparing Nos. 3 to 5, 6 and 7, and Nos. 8 and 9, which have similar compositions of RTB sintered magnets, the inventive examples all have a wider sintering temperature range than the comparative examples. No. 5 uses Ni oxide as the oxide powder, but in this case Ni remains in the RTB sintered magnet. And compared to Nos. 3 and 4, the inventive examples, B r and H cJ Furthermore, the oxygen content of the RTB sintered magnet No. 10 is outside the range of the present disclosure. cJ The sintering temperature range is narrow. No. 11, which is outside the range of the main alloy powder and oxide powder mixture, contains too much oxide powder, which causes Ca to remain in the RTB sintered magnet and reduces Br. No. 12, which is outside the range of the R content of the main alloy powder disclosed in this specification, contains too much oxide powder, which causes H cJ The sintering temperature range is also narrow.

Claims

[Claim 1] A method for producing an R-T-B based sintered magnet, comprising the steps of: R: 28.5% by mass or more and 33.0% by mass or less (R is at least one rare earth element selected from the group consisting of Nd, Pr, and Ce); B: 0.85% by mass or more and 0.95% by mass or less, Ga: 0.2% by mass or more and 1.0% by mass or less, Cu: 0.05% by mass or more and 0.50% by mass or less, T: 61.5 mass% or more and 70.0 mass% or less (T is Fe or Fe and Co, and the content of Fe relative to the total content of T is 90 mass% or more), O (mass ratio): 100 ppm or more and 1500 ppm or less, preparing a main alloy powder that satisfies [T] / 55.85>14×[B] / 10.8, where [T] is the content (mass%) of T and [B] is the content (mass%) of B; O: 15% by mass or more and 40% by mass or less, A step of preparing an oxide powder comprising M: 60 mass% or more and 85 mass% or less (M is at least one selected from the group consisting of Zn, Mg, and Ca); preparing a mixed powder by mixing the primary alloy powder and the oxide powder; and preparing a sintered body of the mixed powder. In the step of preparing the mixed powder, the amount of the oxide powder mixed with respect to the entire mixed powder is 0.03 mass% or more and 0.55 mass% or less, and the amount of the oxide powder is an amount that increases the O content of the mixed powder by 300 ppm or more and 2000 ppm or less in mass ratio with respect to the oxygen content of the main alloy powder. A method for producing an RTB based sintered magnet having an oxygen content of 500 ppm or more and 3500 ppm or less by mass ratio.

Images