Manufacturing method for RTB sintered magnets

Abstract

A method for producing an R-T-B-based sintered magnet according to the present disclosure comprises a sintering step for sintering a shaped product of R-T-B-based alloy powder. This sintering step includes: a first stage step for heating the shaped product at a first sintering temperature T1 to prepare a first stage sintered body; a cooling step for lowering the temperature of the first stage sintered body to a cooling temperature T0; and a second stage step for heating the first stage sintered body at a second sintering temperature T2 to prepare a second stage sintered body. The first sintering temperature T1 and the second sintering temperature T2 are higher than 900°C, and the cooling temperature T0 is 900°C or lower. A first sintering time t1 for which the first sintering temperature T1 is maintained in the first stage step is shorter than a second sintering time t2 for which the second sintering temperature T2 is maintained in the second stage step.

Description

[Technical Field]

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

[0002] RTB sintered magnets (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one transition metal and must contain Fe, and B is boron) are classified into RFe 14 It consists of a main phase of a compound with a B-type crystal structure, a grain boundary phase located at the grain boundaries of this main phase, and a compound phase formed by the influence of trace additive elements and impurities. RTB-based sintered magnets have a high residual magnetic flux density B r (Hereafter, simply "B r ") and high coercive force H cJ (Hereafter, simply "H cJ "), and are known as the highest performing permanent magnets. For this reason, they are used in a wide variety of applications, including voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and various other motors, as well as home appliances. RTB sintered magnets contribute to energy conservation and reduced environmental impact by making various motors smaller and lighter.

[0003] Such RTB sintered magnets are manufactured through steps such as preparing alloy powder, press-molding the alloy powder to form a compact, and sintering the compact.

[0004] Patent Document 1 discloses an example of such an RTB based sintered magnet. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 008756 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the development of RTB sintered magnet materials and improvements in manufacturing methods have led to the development of H cJ and squareness ratio (H k / H cJ ) has been increasing, but it may unexpectedly decrease due to variations in composition and manufacturing conditions. cJ and H k / H cJ It has been found that the decrease in % is particularly noticeable when the composition ratio of B (boron) contained in the RTB based sintered magnet is low, as described in Patent Document 1.

[0007] An embodiment of the present disclosure provides a method for producing an RTB based sintered magnet that can solve these problems. [Means for solving the problem]

[0008] In an exemplary embodiment, the method for producing an RTB sintered magnet according to the present disclosure includes a sintering step of sintering a compact of RTB alloy powder, the sintering step including a first-stage step of heating the compact to a first sintering temperature T1 to produce a first-stage sintered body, a cooling step of lowering the temperature of the first-stage sintered body to a cooling temperature T0, and a second-stage step of heating the first-stage sintered body to a second sintering temperature T2 to produce a second-stage sintered body. The first sintering temperature T1 and the second sintering temperature T2 are above 900°C, and the cooling temperature T0 is 900°C or less. The first sintering time t1, during which the temperature is maintained at the first sintering temperature T1 in the first stage, is shorter than the second sintering time t2, during which the temperature is maintained at the second sintering temperature T2 in the second stage.

[0009] In one embodiment, the first sintering temperature T1 and the second sintering temperature T2 are 1000°C or higher and 1100°C or lower.

[0010] In one embodiment, the first sintering temperature T1 is equal to or higher than 1040°C and lower than 1080°C, and the second sintering temperature T2 is equal to or higher than 1020°C and lower than 1060°C.

[0011] In one embodiment, the first sintering time t1 is 30 minutes or more and 2 hours or less, and the second sintering time t2 is 1 hour or more and 15 hours or less.

[0012] In one embodiment, the first sintering time t1 is equal to or less than half the second sintering time t2.

[0013] In one embodiment, the cooling temperature T0 is 700°C or higher and 900°C or lower.

[0014] In one embodiment, the composition of the alloy powder includes 28% by mass or more and 35% by mass or less of R, 0.8% by mass or more and 1.20% by mass or less of B, and 61.5% by mass or more of T, where [B] is the content of B in mass% and [T] is the content of T in mass% and satisfies 14[B] / 10.8<[T] / 55.85. [Effects of the Invention]

[0015] According to embodiments of the present disclosure, good H cJ and H k / H cJ It is therefore possible to provide a method for producing an RTB based sintered magnet that can achieve the above. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a flow chart showing the sintering process in the present disclosure. [Figure 2] FIG. 2 is a diagram schematically showing an example of a temperature profile of the object to be heat treated (the compact and the sintered body) in the sintering step of this embodiment. [Figure 3] FIG. 3 is a diagram schematically showing another example of the temperature profile of the object to be heat treated (the compact and the sintered body) in the sintering step of this embodiment. [Figure 4]FIG. 4 is a diagram schematically showing yet another example of the temperature profile of the object to be heat treated (the compact and the sintered body) in the sintering step of this embodiment. [Figure 5] FIG. 5 is a diagram schematically showing yet another example of the temperature profile of the object to be heat treated (the compact and the sintered body) in the sintering step of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of a method for producing an RTB based sintered magnet according to the present disclosure will be described.

[0018] In the RTB based sintered magnet according to this embodiment, R is a rare earth element and always includes at least one selected from the group consisting of Nd, Pr, and Ce, and T is at least one transition metal and always includes Fe.

[0019] The RTB based sintered magnet of this embodiment is produced as shown in FIG. A first-stage process (S10) of heating the compact to a first sintering temperature T1 to prepare a first-stage sintered compact; A cooling step (S20) of lowering the temperature of the first-stage sintered body to a cooling temperature T0; A second-stage process (S30) of heating the first-stage sintered body to a second sintering temperature T2 to prepare a second-stage sintered body; Includes.

[0020] Here, the first sintering temperature T1 and the second sintering temperature T2 are above 900° C., and the cooling temperature T0 is equal to or lower than 900° C. In the first stage process, the first sintering time t1 during which the material is held at the first sintering temperature T1 is shorter than the second sintering time t2 during which the material is held at the second sintering temperature T2 in the second stage process.

[0021] RTB sintered magnets are made of NdFe 14It is composed of B-phase (ferromagnetic) crystal grains and intermetallic compounds such as boron (B)-rich and Nd-rich phases located at the grain boundaries of the main phase crystal grains. The sintering reaction proceeds through the formation of a liquid phase involving these phases contained in the powder particles that make up the compact. When the amount of liquid phase is insufficient, the densification reaction does not occur, but as the amount of liquid phase increases with increasing temperature, the densification reaction progresses rapidly. During the sintering process, some of the intermetallic compounds within the powder particles melt, creating a liquid phase that modifies the surfaces of the main phase crystal grains or reduces oxides, thereby promoting particle bonding and densification.

[0022] According to the inventor's investigation, H cJ and H k / H cJ The H content can unexpectedly decrease due to variations in the alloy powder composition and manufacturing conditions. It was also found that this phenomenon is more pronounced when the B content of the RTB-based sintered magnet is low. Since it is difficult to avoid variations in the alloy powder composition and manufacturing conditions, it is difficult to achieve good H content even if the alloy powder composition and manufacturing conditions vary. cJ and H k / H cJ It is required to achieve a good H cJ and H k / H cJTo achieve this, it is necessary to densify the alloy to the desired density and create a uniform structure during sintering. To achieve a densified and uniform crystal structure even when there are variations in the alloy powder composition and manufacturing conditions, the sintering time has traditionally been set to a long time (e.g., 25 hours). However, this lengthens the sintering process and reduces mass productivity. If the sintering temperature is increased to prevent this deterioration in mass productivity, abnormal grain growth may occur, potentially resulting in a rapid deterioration in magnetic properties. Therefore, sintering must be performed to prevent abnormal grain growth. The inventors' research has revealed that the optimal sintering conditions for achieving densification and a uniform structure differ for each material. Based on this knowledge, further research has revealed that a densified and uniform crystal structure can be achieved by sintering for a relatively short time (first stage) to promote densification, followed by cooling to a predetermined temperature and further sintering (second stage) even when there are variations in the alloy powder composition and manufacturing conditions. This allows for a good H sintering process without a long sintering time. cJ and H k / H cJ It is possible to provide a sintered magnet.

[0023] In the field of RTB sintered magnets, H k / H cJ H is one of the parameters that defines k is determined as follows: the strength of magnetization is "J" and the residual magnetization is "J r (=B r ) and the magnetic field strength is "H", in the second quadrant of the JH curve, J is 0.9 × J. r The H axis reading at the position where the value of this H k H of the demagnetization curve cJ The value divided by H k / H cJ =H k (kA / m) / H cJ (kA / m) x 100(%) is defined as the squareness ratio.

[0024] Next, examples of the above steps S10, S20, and S30 will be described in more detail with reference to Figures 2 to 5. These figures are graphs with time on the horizontal axis and temperature on the vertical axis, and schematically show examples of the temperature profile of the objects to be heat-treated (green bodies and sintered bodies) during the sintering process. The temperature of the objects to be treated is measured using a thermometer such as a thermocouple installed in the sintering apparatus (sintering furnace). The actual temperature of the green body or sintered body does not need to strictly match the reading (temperature measurement value) shown by the thermometer in the sintering furnace; a deviation of ±5°C or less between the two is acceptable.

[0025] First, let us refer to FIG. 2. In FIG. 2, the thick solid line indicates the relationship between temperature and time. The time is the elapsed time from the start of the sintering process. The elapsed time is measured in hours, for example, but may also be measured in minutes or seconds. As mentioned above, the temperature is a thermometer measurement value, but is substantially equal to the set temperature specified by the temperature control program. The thick solid line in the figure is composed of straight line segments, but the actual temperature or the set temperature may fluctuate in a curved manner.

[0026] In the example of Figure 2, the temperature of the object to be processed (molded body) increases linearly and monotonically from room temperature to the first sintering temperature T1, and the temperature increase rate is constant. However, the temperature increase rate does not need to be constant, and there may be a period during which the temperature increase rate becomes zero. In order to volatilize the lubricant, hydrogen (during hydrogen pulverization), and oil agents such as slurry contained in the molded body, the molded body may be held at a temperature of, for example, about 200°C for 1 hour to 10 hours.

[0027] The graph in the figure includes horizontal lines representing temperatures of 900°C and 1000°C. In a preferred embodiment, the first sintering temperature T1 and the second sintering temperature T2 are both 1000°C or higher and 1100°C or lower. In the example of FIG. 2, the first sintering temperature T1 is higher than the second sintering temperature T2, but as shown in FIG. 3, the first sintering temperature T1 and the second sintering temperature T2 may be equal to each other. In a preferred embodiment, the first sintering temperature T1 is, for example, 1040°C or higher and lower than 1080°C, and the second sintering temperature T2 is, for example, 1020°C or higher and lower than 1060°C.

[0028] In one embodiment, the first sintering time t1 is 30 minutes or more and 2 hours or less, and the second sintering time t2 is 1 hour or more and 15 hours or less. cJ and H k / H cJ To provide a sintered magnet of this type, the first sintering time t1 is preferably 30 minutes or more and 1 hour or less, and the second sintering time t2 is preferably 1 hour or more and 8 hours or less. In particular, when the first sintering temperature T1 is higher than the second sintering temperature T2 as shown in Fig. 2, it is preferable to set the first sintering time t1 shorter than the second sintering time t2. In this case, for example, it is preferable that the first sintering time t1 be half or less of the second sintering time t2.

[0029] In this embodiment, a cooling step (S20) is carried out between the first step (S10) and the second step (S30) to lower the temperature of the first-stage sintered body to a cooling temperature T0. In this disclosure, the time t0 during which the temperature of the object to be treated (first-stage sintered body) is 900°C or lower during the cooling step is defined as the "cooling time." Therefore, this cooling time t0 includes the temperature drop period from 900°C to the cooling temperature T0 during the temperature drop from the first sintering time t1, and the transition time from the cooling temperature T0 to 900°C during the temperature rise from the cooling temperature T0. It is preferable that there is a difference of 50°C or more between the first sintering temperature T1 and the cooling temperature T0. In other words, it is preferable that the cooling temperature T0 is a temperature lower than the first sintering temperature T1 by 50°C or more. By making T0 50°C or more lower than T1, it is possible to reliably obtain a good H. cJ and H k / H cJ It is possible to provide a sintered magnet.

[0030] The cooling rate may be lower than that shown in Fig. 2, as shown in Fig. 4, for example. However, experiments by the inventors have shown that the magnetic properties do not depend much on the cooling rate. Therefore, from the viewpoint of shortening the time required for the sintering step and improving mass productivity, the cooling rate is preferably 3°C / min or higher, and more preferably 20°C / min or higher.

[0031] Also, if the cooling temperature T0 is 900°C or lower, it may be in the range of 700°C or higher and 900°C or lower, or as shown in FIG. 5, it may be at room temperature level. From the viewpoint of shortening the time required for the cooling process and improving mass productivity, the cooling temperature T0 can be set, for example, within the range of 800°C or higher and 900°C or lower.

[0032] <R-T-B sintered magnet> R is a rare earth element and necessarily contains at least one selected from the group consisting of Nd, Pr, and Ce. Preferably, a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, Nd-Pr-Dy-Tb is used.

[0033] Among R, Dy and Tb are particularly effective in improving H cJ In addition to the above elements, other rare earth elements such as La may be contained, and mischmetal or didymium can also be used. Also, R may not be a pure element and may contain unavoidably-occurring impurities in the manufacturing process within an industrially available range. The content is, for example, 27 mass% or more and 35 mass% or less. Preferably, the R content of the R-T-B sintered magnet is 31 mass% or less (27 mass% or more and 31 mass% or less, preferably 29 mass% or more and 3l mass% or less). By setting the R content of the R-T-B sintered magnet to 31 mass% or less and the oxygen content to 400 ppm or more and less than 4000 ppm (preferably 400 ppm or more and 2500 ppm or less, more preferably 400 ppm or more and 2000 ppm or less), the generation of oxidized R is reduced. Therefore, higher magnetic properties can be obtained.

[0034] [[ID=第十九]]T contains iron (including the case where T consists substantially of iron), and up to 50% of it by mass ratio may be replaced with cobalt (Co) (including the case where T consists substantially of iron and cobalt). Co is effective in improving temperature characteristics and corrosion resistance, and the alloy powder may contain up to 10 mass% of Co. The content of T may occupy the remainder of R and B or R, B, and M described later.

[0035] The content of B may be a known content, and for example, a preferred range is 0.8% by mass to 1.2% by mass. If it is less than 0.9% by mass, high H cJ If it exceeds 1.2 mass%, B may not be obtained. r In addition, a part of B can be substituted with C (carbon).

[0036] In addition to the above elements, H cJ To improve the properties, an M element can be added. The M element is one or more elements selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. The amount of M element added is preferably 5.0 mass% or less. If it exceeds 5.0 mass%, Br may decrease. Inevitable impurities are also acceptable.

[0037] The N (nitrogen) content in the RTB sintered magnet is preferably 50 ppm or more and 600 ppm or less. By pulverizing the magnet so that the N (nitrogen) content is 50 ppm or more and 600 ppm or less, it is possible to improve pulverizability while suppressing deterioration of magnetic properties due to nitriding. The nitrogen content is more preferably 50 ppm or more and 400 ppm or less, and most preferably 100 ppm or more and 300 ppm or less. This is because it is possible to further improve pulverizability while suppressing deterioration of magnetic properties due to nitriding. Furthermore, the C (carbon) content in the RTB sintered magnet is preferably 50 ppm or more and 1300 ppm or less.

[0038] An example of the composition of the RTB based sintered magnet according to this embodiment is shown below. R: 28% by mass or more and 35% by mass or less, B: 0.8% by mass or more and 1.2% by mass or less, When T contains 61.5 mass% or more, [B] is the content of B expressed in mass%, and [T] is the content of T expressed in mass%, 14[B] / 10.8<[T] / 55.85 Equation 1 Satisfy.

[0039] By satisfying the relationship 1: 14[B] / 10.8<[T] / 55.85, the B content is lower than that of typical RTB sintered magnets. Typical RTB sintered magnets contain R2T, 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, [T] / 55.85 (atomic weight of Fe) is less than 14[B] / 10.8 (atomic weight of B).

[0040] <(1) Example of a process for preparing coarsely pulverized powder of alloy for RTB sintered magnets> In this embodiment, the step of preparing a coarsely pulverized powder of an alloy for an RTB based sintered magnet can include a step of preparing an alloy for an RTB based sintered magnet and a step of coarsely pulverizing this alloy by, for example, a hydrogen pulverization method.

[0041] The following is an example of a method for producing an alloy for an RTB based sintered magnet.

[0042] First, an alloy ingot can be obtained by ingot casting, in which a metal or alloy previously prepared to have the above-mentioned composition is melted and poured into a mold. Alternatively, alloy flakes can be produced by a rapid cooling method, such as strip casting or centrifugal casting, in which the molten metal is brought into contact with a single roll, twin rolls, rotating disk, or rotating cylindrical mold, and then solidified into a thinner alloy than the alloy produced by the ingot method.

[0043] In the embodiments of the present disclosure, materials produced by either the ingot method or the quenching method can be used, but production by a quenching method such as strip casting is preferred. The thickness of quenched alloys produced by the quenching method is typically in the range of 0.03 mm to 1 mm and in the form of flakes. The molten alloy begins to solidify from the surface that contacts the chill roll (the roll contact surface), and crystals grow columnarly from the roll contact surface in the thickness direction. Compared to alloys (ingot alloys) produced by conventional ingot casting (mold casting), quenched alloys are cooled in a shorter time, resulting in a finer structure and smaller crystal grain size. Furthermore, the grain boundary area is larger. Because the R-rich phase spreads widely within the grain boundaries, the quenching method provides excellent dispersibility of the R-rich phase. Therefore, fracture at the grain boundaries is more likely to occur when using hydrogen pulverization. By hydrogen pulverizing the quenched alloy, the size (average particle size) of the hydrogen pulverized powder (coarsely pulverized powder) can be reduced to, for example, 1.0 mm or less, preferably 10 μm to 500 μm.

[0044] <(2) Example of a process for obtaining fine powder> In the process of obtaining a fine powder in this embodiment, the coarsely pulverized powder is supplied to a jet mill device whose pulverization chamber is filled with an inert gas, and the coarsely pulverized powder is pulverized to obtain a fine powder. In this process, for example, a fine powder (RTB-based alloy powder) having an average particle size of 2.0 μm to 4.5 μm can be obtained. The process of obtaining such a fine powder can be carried out, for example, using a jet mill pulverization system.

[0045] The increase in oxygen content of the RTB sintered magnet due to the steps after pulverization (mainly the steps of producing a sintered body from the fine powder) is preferably 50 ppm to 300 ppm, and more preferably 50 ppm to 200 ppm. To achieve this, it is preferable to perform wet pressing in a magnetic field or magnetic pressing in an inert gas atmosphere, as described below, and then sinter the resulting compact. The average particle size of the fine powder obtained in the step of obtaining the fine powder is preferably 2.0 μm to 3.5 μm. Reducing the average particle size makes it possible to improve the magnetic properties.

[0046] <(3) Example of a process for producing a compact of fine powder> In the process of producing a compact, it is preferable to form the compact by pressing in an inert gas atmosphere or wet pressing from the viewpoint of suppressing oxidation when pressing in a magnetic field. In particular, wet pressing coats the surfaces of the particles constituting the compact with a dispersant such as an oil, suppressing contact with oxygen and water vapor in the atmosphere. This prevents or suppresses oxidation of the particles by the atmosphere before, during, or after the pressing process.

[0047] When wet pressing in a magnetic field is performed, a slurry is prepared by mixing a dispersion medium with fine powder, and the slurry is supplied to a cavity in a mold of a wet pressing device and press-molded in a magnetic field.

[0048] ·Dispersion medium The dispersion medium is a liquid in which the alloy powder can be dispersed to obtain a slurry.

[0049] Preferred dispersion media used in the present disclosure include mineral oils and synthetic oils. While the type of mineral oil or synthetic oil is not limited, if the kinematic viscosity at room temperature exceeds 10 cSt, the increased viscosity may strengthen the bonding strength between the alloy powders, adversely affecting the orientation of the alloy powder during wet compaction in a magnetic field. For this reason, the kinematic viscosity of the mineral oil or synthetic oil at room temperature is preferably 10 cSt or less. Furthermore, if the distillation point of the mineral oil or synthetic oil exceeds 400°C, deoiling after obtaining a compact becomes difficult, resulting in increased residual carbon in the sintered compact and possibly degrading the magnetic properties. Therefore, the distillation point of the mineral oil or synthetic oil is preferably 400°C or less. Vegetable oil may also be used as the dispersion media. Vegetable oil refers to oil extracted from plants, and the type of plant is not limited to a specific plant.

[0050] Slurry preparation The obtained alloy powder is mixed with a dispersion medium to obtain a slurry.

[0051] The mixing ratio of the alloy powder and the dispersion medium is not particularly limited, but the concentration of the alloy powder in the slurry is preferably 70% or more (i.e., 70% by mass or more) in terms of mass ratio. 3 This is because a flow rate of 1 / sec allows the alloy powder to be efficiently supplied into the cavity and excellent magnetic properties to be obtained. The concentration of the alloy powder in the slurry is preferably 90% or less by mass. The method for mixing the alloy powder and the dispersion medium is not particularly limited. The alloy powder and the dispersion medium may be prepared separately, and then weighed and mixed in predetermined amounts. Alternatively, when dry-pulverizing coarsely pulverized powder using a jet mill or the like to obtain alloy powder, a container containing the dispersion medium may be placed at the alloy powder outlet of the jet mill or other grinding device, and the pulverized alloy powder may be directly recovered in the dispersion medium in the container to obtain a slurry. In this case, the container is preferably also filled with a nitrogen and / or argon gas atmosphere, and the obtained alloy powder is directly recovered in the dispersion medium without being exposed to the air to form a slurry. Furthermore, it is also possible to wet-pulverize the coarsely pulverized powder in the dispersion medium using a vibrating mill, ball mill, attritor, or the like to obtain a slurry consisting of the alloy powder and the dispersion medium.

[0052] The slurry thus obtained is molded in a known wet press to obtain a molded body having a predetermined size and shape, which is then sintered to obtain a sintered body.

[0053] <(4) Example of sintering process> Next, the compact is sintered to obtain a sintered body. A first-stage process (S10) of heating the compact to a first sintering temperature T1 to prepare a first-stage sintered compact; A cooling step (S20) of lowering the temperature of the first-stage sintered body to a cooling temperature T0; A second-stage process (S30) of heating the first-stage sintered body to a second sintering temperature T2 to prepare a second-stage sintered body; Includes:

[0054] The compact may be sintered in vacuum or using an inert gas such as helium or argon.

[0055] The sintered body thus obtained is preferably subjected to a heat treatment. Heat treatment can improve the magnetic properties. Known conditions, such as the heat treatment temperature and time, can be used. For example, the sintered body is heat-treated by heating it for one hour or more at a temperature equal to or lower than the first sintering temperature T1 and the first sintering temperature T2 (for example, 400°C to 800°C). The RTB-based sintered magnet thus obtained is then subjected to grinding and polishing, surface treatment, and magnetization as necessary to produce the final RTB-based sintered magnet.

[0056] In a preferred embodiment, the method for producing an RTB-based sintered magnet of the present disclosure includes 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 interior. Diffusing the heavy rare-earth element RH from the surface to the interior of the sintered body can efficiently increase the coercive force. [Example]

[0057] The present disclosure will be explained in more detail by way of examples, but the present disclosure is not limited thereto.

[0058] Experimental Example 1 Each element was weighed and strip-cast to obtain a flake-shaped alloy so that the RTB-based sintered magnet had the composition shown in Table 1, No. 1. The alloy was then subjected to hydrogen embrittlement in a pressurized hydrogen atmosphere, followed by a dehydrogenation treatment in which the alloy was heated and cooled in a vacuum, to obtain a coarsely pulverized powder. The coarsely pulverized powder was then pulverized using an airflow pulverizer (jet mill) to obtain a D 50 The alloy powder obtained was 3.6 μm in size.

[0059] 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 a compact. 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.

[0060] The resulting compacts were sintered under the conditions shown in Table 2. Nos. 1-4 in Table 2 were obtained by heating the compact, prepared to have the composition of No. 1 in Table 1, at a first sintering temperature T1 of 1,050°C for a first sintering time t1 of 0.5 hours (30 minutes) to produce a first sintered body (first stage). The temperature of the first sintered body was then rapidly cooled (at 10°C / min or faster) to a cooling temperature T0 of room temperature (approximately 30°C). The cooled first sintered body was then heated at a second sintering temperature of 1,040°C for a second sintering time t2 of 4 hours to produce a second sintered body (second stage). Other Nos. are described similarly. Note that Nos. 1-1 to 1-3, which are comparative examples, were sintered only once. The sintered RTB sintered magnets (Nos. 1-1 to 1-9) were obtained by heat treating the sintered RTB sintered magnets by holding them at 900°C for two hours, cooling to room temperature, and then holding them at 500°C for two hours, followed by cooling to room temperature.

[0061] The composition of the obtained RTB sintered magnet is shown in Table 1. Note that the sum of the individual compositions and the amounts of oxygen and carbon in Table 1 does not equal 100 mass%. This is because impurity elements other than those listed in the table are included. The same applies to the other tables. Furthermore, if formula 1 is satisfied, it is marked with "○", and if it is not, it is marked with "×". The RTB sintered magnet was machined to prepare a sample measuring 7 mm in length, 7 mm in width, and 7 mm in thickness, which was measured with a BH tracer to determine the magnetic properties. Furthermore, 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 of the H axis is read as H k and H of the demagnetization curve cJ This H k The ratio H k / H cJ , H k (kA / m) / H cJ The results were calculated as (kA / m) × 100 (%). The results are shown in Table 3.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] As shown in Table 3, the present invention example cJ ≧1646kA / m and H k / H cJ ≧90.1%, which is better than the comparative example. cJ and H k / H cJ Furthermore, in the comparative examples (Nos. 1-1 to 1-3), when the sintering temperature was changed to 1030°C to 1050°C, H cJ In contrast, the magnetic properties of the inventive examples were significantly reduced (No. 1-1) and coarse grains were generated (No. 1-3). This means that variations in manufacturing conditions can lead to unexpected deterioration of the magnetic properties. cJ and H k / H cJ Furthermore, the difference in sintering time is only about 0.5 hours compared to the comparative example, which is almost the same. Therefore, the present invention example can produce good H without long sintering time. cJ and H k / H cJ The RTB-based sintered magnets having the above properties have been obtained.

[0066] Experimental Example 2 Compacts were produced in the same manner as in Experimental Example 1, except that each element was weighed out so as to obtain the compositions Nos. 2 to 4 in Table 4. The resulting compacts were sintered under the conditions shown in Table 5. The sintered RTB based sintered magnets were subjected to heat treatment in the same manner as in Experimental Example 1, to obtain RTB based sintered magnets (Nos. 2-1 to 2-6).

[0067] The compositions of the obtained RTB sintered magnets are shown in Table 4. As shown in Tables 4 and 5, Nos. 2-1 and 2-2 correspond to the composition of No. 2 in Table 4, Nos. 2-3 and 2-4 correspond to the composition of No. 3 in Table 4, and Nos. 2-5 and 2-6 correspond to the composition of No. 4 in Table 4. The magnetic properties and H k / H cJ The results are shown in Table 6.

[0068] [Table 4]

[0069] [Table 5]

[0070] [Table 6]

[0071] As shown in Table 6, the examples of the present invention exhibited good H properties compared to the comparative examples (comparing No. 2-1 with No. 2-2, No. 2-3 with No. 2-4, and No. 2-5 with No. 2-6). cJ and H k / H cJ The RTB-based sintered magnets having the above properties have been obtained.

[0072] Experimental Example 3 A compact was produced in the same manner as in Experimental Example 1, except that each element was weighed to obtain the composition No. 5 in Table 7. The resulting compact was sintered under the conditions shown in Table 8. The composition of the resulting RTB-based sintered magnet is shown in Table 7. The resulting RTB-based sintered magnet was subjected to a diffusion process. Specifically, an atomized powder (106 μm or less) containing 0.3 mass% Nd, 76.4 mass% Pr, 13.4 mass% Tb, 4.7 mass% Cu, and 5.2 mass% Ga was prepared. Next, an adhesive containing sugar alcohols was applied to the entire surface of the RTB-based sintered magnet by dipping. The atomized powder was attached to the adhesive-coated RTB-based sintered magnet in an amount of 2 mass% relative to the mass of the RTB-based sintered magnet. Next, the atomized powder and the RTB-based sintered magnet were heated in a heat treatment furnace at 920°C for 10 hours to carry out a diffusion process, and then cooled. Thereafter, a heat treatment was carried out in a heat treatment furnace at 480°C for 3 hours. The obtained diffused RTB sintered magnet was subjected to the same procedures as in Experimental Example 1 to measure the magnetic properties and H k / H cJ The results are shown in Table 9.

[0073] [Table 7]

[0074] [Table 8]

[0075] [Table 9]

[0076] As shown in Table 9, the examples of the present invention have better H than the comparative examples. cJ and H k / H cJ The RTB-based sintered magnets having the above properties have been obtained. [Industrial Applicability]

[0077] The method for producing an RTB-based sintered magnet according to the present disclosure can be used to produce permanent magnets for a wide variety of applications, including voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EVs, HVs, PHVs), motors for industrial equipment, and other motors, as well as home appliances.

Claims

1. The method includes a sintering step of sintering a compact of an R-T-B type alloy powder (R is a rare earth element and always contains at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one transition metal and always contains Fe, and B is boron), The sintering step comprises: a first-stage process of heating the compact to a first sintering temperature T1 to prepare a first-stage sintered body; a cooling step of lowering the temperature of the first-stage sintered body to a cooling temperature T0; a second stage step of heating the first stage sintered body to a second sintering temperature T2 to prepare a second stage sintered body; Including, the first sintering temperature T1 and the second sintering temperature T2 are greater than 900°C; The cooling temperature T0 is 900°C or less, a first sintering time t1 during which the temperature is maintained at the first sintering temperature T1 in the first stage process is equal to or less than half of a second sintering time t2 during which the temperature is maintained at the second sintering temperature T2 in the second stage process; The method for producing an RTB based sintered magnet, wherein the second sintering time t2 is 1 hour or more and 15 hours or less.

2. 2. The method for producing a sintered RTB based magnet according to claim 1, wherein the first sintering temperature T1 and the second sintering temperature T2 are 1000° C. or higher and 1100° C. or lower.

3. A method for producing a sintered product, comprising a sintering step of sintering a compact of an R-T-B type alloy powder (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr and Ce, T is at least one transition metal and must contain Fe, and B is boron), The sintering step comprises: a first-stage process of heating the compact to a first sintering temperature T1 to prepare a first-stage sintered body; a cooling step of lowering the temperature of the first-stage sintered body to a cooling temperature T0; a second stage step of heating the first stage sintered body to a second sintering temperature T2 to prepare a second stage sintered body; Including, the first sintering temperature T1 and the second sintering temperature T2 are greater than 900°C; The cooling temperature T0 is 900°C or less, a first sintering time t1 during which the temperature is maintained at the first sintering temperature T1 in the first stage process is shorter than a second sintering time t2 during which the temperature is maintained at the second sintering temperature T2 in the second stage process; The first sintering temperature T1 is equal to or higher than 1040°C and lower than 1080°C, The method for producing an RTB based sintered magnet, wherein the second sintering temperature T2 is 1020°C or higher and lower than 1060°C.

4. A method for producing a sintered product, comprising a sintering step of sintering a compact of an R-T-B type alloy powder (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr and Ce, T is at least one transition metal and must contain Fe, and B is boron), The sintering step comprises: a first-stage process of heating the compact to a first sintering temperature T1 to prepare a first-stage sintered body; a cooling step of lowering the temperature of the first-stage sintered body to a cooling temperature T0; a second stage step of heating the first stage sintered body to a second sintering temperature T2 to prepare a second stage sintered body; Including, the first sintering temperature T1 and the second sintering temperature T2 are greater than 900°C; The cooling temperature T0 is 900°C or less, a first sintering time t1 during which the temperature is maintained at the first sintering temperature T1 in the first stage process is shorter than a second sintering time t2 during which the temperature is maintained at the second sintering temperature T2 in the second stage process; The first sintering time t1 is 30 minutes or more and 2 hours or less, The method for producing an RTB based sintered magnet, wherein the second sintering time t2 is 1 hour or more and 15 hours or less.

5. 5. The method for producing a sintered RTB based magnet according to claim 1, wherein the cooling temperature T0 is 700° C. or higher and 900° C. or lower.

6. The alloy powder has a composition including R: 28% by mass or more and 35% by mass or less, B: 0.8% by mass or more and 1.20% by mass or less, and T: 61.5% by mass or more, where [B] is the content of B in mass% and [T] is the content of T in mass% and the ratio is 14[B] / 10.8<[T] / 55.85 6. The method for producing a sintered RTB based magnet according to claim 1, wherein the above-mentioned condition is satisfied.

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