Manufacturing method for RTB sintered magnets

Abstract

To suppress decreases in coercive force HcJ and squareness ratio Hk / HcJ due to variations in manufacturing conditions.SOLUTION: A method for manufacturing an R-T-B based sintered magnet includes: a step of preparing a compact of alloy powder including a rare earth element; a sintering step of sintering the compact to produce a sintered body; a first heat treatment step of heat-treating the sintered body at a first temperature of 300°C or higher and less than 400°C for 30 minutes or more and 900 minutes or less in a heat treatment furnace; and a second heat treatment step of heat-treating the sintered body at a second temperature of 400°C or higher and 500°C or lower for 30 minutes or more and 900 minutes or less in the heat treatment furnace. A difference between the first temperature and the second temperature is 50°C or more.SELECTED DRAWING: Figure 2

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-performance permanent magnets. For this reason, RTB sintered magnets are used in a variety of motors in fields including electric vehicles (EVs, HVs, and PHVs) and other automotive applications, renewable energy applications such as wind power generation, home appliances, and industrial applications. RTB sintered magnets are essential materials for making these motors smaller, lighter, more efficient, and more energy-efficient (improving energy efficiency). RTB sintered magnets are also used in the drive motors of electric vehicles, and the replacement of internal combustion engines with electric vehicles contributes to the prevention of global warming by reducing greenhouse gases such as carbon dioxide (fuel and exhaust gas emissions). In this way, RTB sintered magnets are making a significant contribution to the realization of a clean energy society.

[0003] Such RTB sintered magnets are manufactured through steps such as preparing alloy powder, press-molding the alloy powder to produce a powder compact, and sintering the powder 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 However, there are cases where it unexpectedly decreases due to variations in manufacturing conditions. cJ and squareness ratio H k / H cJ It was found that the variation in depends on the heat treatment method performed after the sintering process.

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

[0008] In an exemplary embodiment, a method for producing an RTB based sintered magnet according to the present disclosure includes the steps of preparing a compact of alloy powder containing a rare earth element, sintering the compact to produce a sintered body, a first heat treatment step of heat-treating the sintered body in a heat treatment furnace at a first temperature of at least 300°C but less than 400°C for at least 30 minutes but not more than 900 minutes, and a second heat treatment step of heat-treating the sintered body in the heat treatment furnace at a second temperature of at least 400°C but not more than 500°C for at least 30 minutes but not more than 900 minutes, the difference between the first temperature and the second temperature being at least 50°C. The alloy powder has a composition containing R (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce), T (T is at least one selected from the group consisting of Fe, Co, Al, Mn, and Si and must contain Fe), B, and at least one selected from the group consisting of Cu, Ga, Ni, Ag, Zn, and Sn, and the molar ratio of T to B, [T] / [B], is greater than 14.0.

[0009] In one embodiment, the first temperature is less than 390°C, and the second temperature is 460°C or higher.

[0010] In one embodiment, the rate of temperature rise from the first temperature to the second temperature is 0.5° C. / min or more and 30° C. / min or less. [Effects of the Invention]

[0011] According to an embodiment of the present disclosure, H is obtained by a heat treatment process performed after the sintering process. cJ and squareness ratio H k / H cJ This makes it possible to suppress variations in the magnet size and to stably produce high-performance RTB-based sintered magnets. [Brief explanation of the drawings]

[0012] [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 a heat treatment furnace in the low-temperature heat treatment step of this embodiment. [Figure 3] FIG. 3 is a diagram showing a typical example of a temperature profile of a heat treatment furnace in a conventional low-temperature heat treatment process. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of a method for producing an RTB based sintered magnet according to the present disclosure will be described.

[0014] 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.

[0015] The RTB based sintered magnet of this embodiment is produced as shown in FIG. A step (S10) of preparing a compact of alloy powder containing a rare earth element; a sintering step (S20) of sintering the compact to produce a sintered body; a first heat treatment step (S30) of heat treating the sintered body in a heat treatment furnace at a first temperature of 300°C or higher and lower than 400°C for 30 minutes or longer and 900 minutes or shorter; a second heat treatment step (S40) of heat treating the sintered body in a heat treatment furnace at a second temperature of 400°C or higher and 500°C or lower for 30 minutes or higher and 900 minutes or lower; Includes:

[0016] Here, the difference between the first temperature and the second temperature is 50°C or more. Hereinafter, the first heat treatment step (S30) and the second heat treatment step (S40) may be collectively referred to as the "low-temperature heat treatment step" or the "two-stage low-temperature heat treatment step." The term "low temperature" means a temperature that is sufficiently lower than the heat treatment temperature (e.g., 950°C or higher and 1100°C or lower) in the sintering step (S20).

[0017] The alloy powder according to the embodiment of the present disclosure has a composition containing R, T, B, and at least one element selected from the group consisting of Cu, Ga, Ni, Ag, Zn, and Sn, and the molar ratio of T to B, [T] / [B], is greater than 14.0. Here, R is a rare earth element and always contains at least one element selected from the group consisting of Nd, Pr, and Ce. T is Fe, Co, It is at least one selected from the group consisting of Al, Mn, and Si, and always contains Fe.

[0018] RTB sintered magnets are made of NdFe 14 It 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 proceeds. During the sintering process, some of the intermetallic compounds in the powder particles melt, creating a liquid phase that modifies the surface of the main phase crystal grains or reduces oxides, thereby promoting particle bonding and densification.

[0019] In addition, by adding various elements to the raw materials or diffusing them from the outside to the inside of the sintered body, the grain boundaries of the sintered body can be modified, and H cJ and squareness ratio H k / H cJ For example, the grain boundaries are modified to increase the H cJ and squareness ratio H k / H cJ The success or failure of improving H depends on the type and amount of compound phases present at the grain boundaries, which are affected by the conditions of the low-temperature heat treatment process performed after the sintering process. cJ and squareness ratio H k / H cJIt has been found that this phenomenon can occur significantly when the molar ratio of T to B in an RTB-based sintered magnet, [T] / [B], exceeds 14.0 and when elements such as Cu and Ga are added to modify the grain boundaries. The condition of a T molar ratio [T] / [B] exceeding 14.0 is due to the fact that the main phase (R2T 14 This shows that the amount of B is relatively small compared to the amount of T used to form the B compound. By reducing the amount of B to a lower level than that of a typical RTB-based sintered magnet and adding elements such as Cu and Ga, a high H cJ However, as mentioned above, the low-temperature heat treatment process performed after the sintering process can cJ and squareness ratio H k / H cJ Furthermore, as a result of intensive research by the present inventors, there was a problem that H cJ and squareness ratio H k / H cJ It was found that the reason for the variation in temperature distribution of the sintered body varies depending on the position of the sintered body in the heat treatment furnace during the low-temperature heat treatment process.

[0020] In the manufacturing method of the present disclosure, the low-temperature heat treatment process performed after the sintering process is devised to improve the uniformity of the temperature distribution in the heat treatment furnace, thereby achieving high H cJ and squareness ratio H k / H cJ This problem can be solved by expanding the heat treatment temperature range in which the above-mentioned high H can be achieved. Specifically, in the first heat treatment step (S30), the sintered body is heat treated at a first temperature of 300°C or higher but lower than 400°C for 30 minutes or longer but 900 minutes or shorter, thereby increasing the uniformity of the temperature distribution of the sintered body in the heat treatment furnace. cJ and squareness ratio H k / H cJ The temperature of the low-temperature heat treatment required to increase the H of the sintered body is 400°C or higher. Therefore, at the first temperature of 300°C or higher but lower than 400°C in the first heat treatment step (S30), various reactions that may occur in the sintered body due to the low-temperature heat treatment are suppressed and hardly proceed. For this reason, the first heat treatment step (S30) is performed to prevent the H of the sintered body from being generated. cJand squareness ratio H k / H cJ The temperature in the first heat treatment step (S30) is preferably 350°C or higher and lower than 400°C. cJ and squareness ratio H k / H cJ In the second heat treatment step (S40), which is the original low-temperature heat treatment for increasing the temperature, the sintered body is heat-treated at a second temperature of 400°C or higher and 500°C or lower for 30 minutes or longer and 900 minutes or shorter. This causes the various effects required in the low-temperature heat treatment step to be exerted on the sintered body, resulting in the formation of H cJ and squareness ratio H k / H cJ It becomes possible to increase the value of

[0021] It was also found that by dividing the low-temperature heat treatment process into two stages in this way, it is possible to shorten the time required for the low-temperature heat treatment. This is because, when low-temperature heat treatment is performed in a conventional heat treatment furnace with an uneven temperature distribution, there are positions in the heat treatment furnace where the temperature is too high or too low, and the H cJ and squareness ratio H k / H cJ The temperature tends to drop significantly if the temperature setting in the heat treatment furnace deviates from the target value. Therefore, in the conventional low-temperature heat treatment process, it was necessary to narrow the range (margin) of the heat treatment temperature that was the control target and precisely control the heat treatment temperature relative to the target temperature. However, according to the two-stage low-temperature heat treatment process of the present disclosure, H cJ and squareness ratio H k / H cJ Since the value of is unlikely to vary depending on the position in the heat treatment furnace, it is possible to widen the temperature range (margin) around the target temperature. Also, since the second heat treatment step (S40) can be performed in a situation where the temperature variation in the heat treatment furnace is small, even if the heat treatment temperature of the second heat treatment step (S40), i.e., the second temperature, is set to a relatively high temperature (for example, 470°C or higher, or 480°C or higher) within the range of 400°C or higher and 500°C or lower, H cJ and squareness ratio H k / H cJIncreasing the second temperature makes it possible to shorten the time required for the second heat treatment step (S40). These features are suitable for mass production in factories.

[0022] Before the low-temperature heat treatment step, a high-temperature heat treatment step may be performed at a relatively higher temperature (700°C or higher and the sintering temperature or lower) than that of the low-temperature heat treatment step. In particular, when producing an RTB-based sintered magnet in which the molar ratio of T [T] / [B] exceeds 14.0 and elements such as Cu and Ga are added, it is preferable to perform high-temperature heat treatment before the low-temperature heat treatment step (i.e., before the first heat treatment step (S30) and the second heat treatment step (S40)). This more reliably achieves a high H cJ The time for the high-temperature heat treatment step is preferably 30 minutes or more and 900 minutes or less. The term "high temperature" means a temperature that is sufficiently higher than the first heat treatment step (S30) and the second heat treatment step (S40) in the low-temperature heat treatment.

[0023] In the field of RTB sintered magnets, the squareness ratio 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 S30 and S40 will be described in more detail with reference to Figures 2 and 3. These figures are graphs with the horizontal axis representing time and the vertical axis representing temperature, and schematically show examples of the temperature profile (heat pattern) of a heat treatment furnace in a low-temperature heat treatment process. The temperature of the heat treatment furnace is measured by a thermometer such as a thermocouple installed in the heat treatment device. It is preferable that the actual temperature (object temperature) of the sintered body matches the reading (measured temperature value) indicated by the thermometer inside the sintering furnace, but this does not necessarily have to match exactly. A difference of about ±10°C between the two (object temperature) and the measured temperature value inside the sintering furnace is acceptable, and the effects of the present disclosure can be obtained.

[0025] First, let us refer to FIG. 2. FIG. 2 is a diagram schematically illustrating an example of a temperature profile (heat pattern) of a heat treatment furnace in the low-temperature heat treatment process of this embodiment. In FIG. 2, the thick solid line indicates the relationship between temperature and time. Time is the elapsed time from the start of the low-temperature heat treatment process. The elapsed time is measured in hours, for example, but may also be measured in minutes or seconds. The temperature is a measurement value from a thermometer in the heat treatment furnace, but is essentially equal to the set temperature specified by the temperature control program. The thick solid line in the diagram is composed of straight line segments, but the actual temperature or set temperature may fluctuate in a curved manner.

[0026] 2, the "temperature" increases linearly and monotonically from room temperature to the first temperature T1, and the temperature increase rate is constant. However, the temperature increase rate does not have to be constant.

[0027] In the first heat treatment step (S30), heat treatment is performed at a first temperature T1 for a first time t1. This heat treatment may be called "preparatory heating." After the first heat treatment step (S30), The temperature is raised from T1 to a second temperature T2. Then, in the second heat treatment step (S40), heat treatment is performed at the second temperature T2 for a second time t2. Here, the first temperature T1 is equal to or higher than 300°C and lower than 400°C, and the second temperature T2 is equal to or higher than 400°C and lower than 500°C. The difference between the first temperature T1 and the second temperature T2 (T2 - T1) is 50°C or higher. The first time t1 and the second time t2 are each equal to or higher than 30 minutes and lower than 900 minutes.

[0028] Next, let us refer to FIG. 3. FIG. 3 is a diagram schematically illustrating an example of a temperature profile (heat pattern) of a heat treatment furnace in a conventional low-temperature heat treatment process. In the example of FIG. 3, the temperature of the heat treatment furnace is raised, for example, from room temperature to a temperature T0 for the low-temperature treatment process. Thereafter, the temperature of the heat treatment furnace is maintained at temperature T0 for a time t0 to perform the low-temperature heat treatment process. During the process of raising the temperature of the heat treatment furnace, the temperature inside the heat treatment furnace is not necessarily uniform and can vary significantly depending on the position. This temperature distribution variation increases as the temperature rise time increases and as the temperature rise rate increases. Therefore, in the example of FIG. 3, at the time when the set temperature of the heat treatment furnace should have reached the target temperature T0, the actual temperature inside the heat treatment furnace is not uniform, with some parts reaching the target temperature T0 and others being higher or lower than temperature T0. It is thought that such temperature variations will decrease as the low-temperature heat treatment process progresses, but when the temperature variations are large, the temperature T0 is 400°C or higher, for example, 450°C, so H cJ and squareness ratio H k / H cJ Various reactions that increase the concentration of hydroxylase occur unevenly.

[0029] However, according to an embodiment of the present disclosure, as shown in Fig. 2, after the step of raising the temperature from room temperature to a first temperature T1, a first heat treatment step (S30) is performed at a first temperature T1 below 400°C before the first heat treatment step (S40), which is essentially a low-temperature heat treatment step, so that the temperature inside the heat treatment furnace, in other words, the temperature variation among the multiple sintered bodies placed in the heat treatment furnace, can be reduced. Furthermore, when the temperature is raised from the first temperature T1 close to 400°C to the second temperature T2 of 400°C or higher, the temperature rise is small, and further temperature variation is unlikely to occur.

[0030] According to experiments by the inventors, it is preferable that the time required to raise the temperature from the first temperature T1 to the second temperature T2 is 5 minutes or more and 30 minutes or less. This time can be appropriately determined depending on the magnitude of T2 - T1. Furthermore, it is preferable that the temperature rise rate from the first temperature T1 to the second temperature T2 is 0.5°C / min or more and 30°C / min or less. In this way, when the second heat treatment step (S40) is started, each sintered body in the heat treatment furnace has reached approximately the same temperature (target temperature), making it possible to appropriately carry out the low-temperature heat treatment in the subsequent second heat treatment step (S40). Therefore, the H of the sintered body finally obtained can be reduced. cJ and squareness ratio H k / H cJ In this case, the variation between sintered bodies and within each sintered body is reduced.

[0031] According to the study by the present inventors, it is preferable that the first temperature is less than 390°C and the second temperature is 460°C or higher. When heat treatment is performed at such temperatures, the first heat treatment step (S30) can be performed for a relatively short time of 30 minutes or more and 90 minutes or less, and the temperature distribution in the heat treatment furnace in the second heat treatment step (S40) can be sufficiently uniform. Furthermore, if the second temperature is 460°C or higher, even if the time for the second heat treatment step (S40) is a relatively short time of 30 minutes or more and 90 minutes or less, H cJ and squareness ratio H k / H cJThe effect of the low-temperature heat treatment of raising [temperature] is fully exerted. The heat treatments in the first heat treatment step (S30) and the second heat treatment step (S40) are preferably carried out in a reduced-pressure atmosphere. This is because it can suppress the sintered body from oxidizing or nitriding during the heat treatment. After the second heat treatment step (S40), the temperature is lowered from the second temperature to, for example, room temperature. At this time, a step of cooling the sintered body at a cooling rate of, for example, 5 °C / min or more can be performed.

[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, Nd-Pr―Ce-Dy, Nd-Pr―Ce-Tb, Nd-Pr-Ce-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 inevitable impurities in the manufacturing process within the range available industrially. The content is, for example, 28 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 31 mass% or less).

[0034] 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 the temperature characteristics and corrosion resistance, and the alloy powder may contain 10 mass% or less 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 can also be within a known content range. For example, 0.9 mass% to 1.2 mass% is a preferable range. If it is less than 0.9 mass%, high HcJ 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, for example, 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 composition of the RTB based sintered magnet in this embodiment contains R (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce), T (T is at least one selected from the group consisting of Fe, Co, Al, Mn, and Si and must contain Fe), B, and at least one selected from the group consisting of Cu, Ga, Ni, Ag, Zn, and Sn, and the molar ratio of T to B, [T] / [B], is greater than 14.0.

[0038] <(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.

[0039] The following is an example of a method for producing an alloy for an RTB based sintered magnet.

[0040] 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.

[0041] 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.

[0042] <(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 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.

[0043] <(3) Example of a process for producing a compact of fine powder> In a preferred embodiment, the step of producing a sintered body of fine powder includes the steps of producing a powder compact from the fine powder by pressing in a magnetic field and sintering the powder compact. When pressing in a magnetic field, it is preferable to form the powder compact by pressing in an inert gas atmosphere or wet pressing from the viewpoint of suppressing oxidation. The compact is then sintered to obtain a sintered body.

[0044] <(4) Example of sintering process> The compact is then sintered to obtain a rare earth sintered magnet body (sintered body). In the sintering process of this embodiment, the compact is sintered at a temperature of 950°C to 1100°C, and then cooled to room temperature, for example, at a rate of 10°C / min or less. If the sintering temperature is lower than 950°C, the sintered density will be insufficient and a high B r Therefore, the sintering temperature of the compact according to the embodiment of the present invention is 1000°C or higher, and preferably 1020°C or higher. If the sintering temperature exceeds 1100°C, rapid grain growth of the main phase occurs, and a high H cJ and high H k / H cJ Therefore, the sintering temperature for the compact in this embodiment is 1100°C or lower, and preferably 1080°C or lower.

[0045] The compact can be sintered by a known method. The compact is preferably sintered at a pressure of 0.13 Pa (10 -3 Torr) or less, preferably 0.07 Pa (5.0 × 10 -4 To prevent oxidation during sintering, residual gas in the atmosphere may be replaced with an inert gas such as helium or argon.

[0046] <(5) Example of low-temperature heat treatment process> As described with reference to FIG. 3, the low-temperature heat treatment step in this embodiment is as follows: a first heat treatment step (S30) of heat treating the sintered body in a heat treatment furnace at a first temperature of 300°C or higher and lower than 400°C for 30 minutes or longer and 900 minutes or shorter; a second heat treatment step (S40) of heat treating the sintered body in a heat treatment furnace at a second temperature of 400°C or higher and 500°C or lower for 30 minutes or higher and 900 minutes or lower; Includes:

[0047] By performing this two-stage low-temperature heat treatment process, a higher H cJ and high H k / H cJ Thus, an RTB based sintered magnet having the above properties can be obtained with good yield.

[0048] The low-temperature heat treatment step can be carried out using either a continuous furnace or a batch furnace.

[0049] The rare earth sintered magnet body thus obtained is then subjected to grinding and polishing steps, surface treatment steps, and magnetization steps as required to complete the final rare earth sintered magnet.

[0050] 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]

[0051] The present disclosure will be explained in more detail by way of examples, but the present disclosure is not limited thereto.

[0052] Experimental Example 1 A metal or alloy was prepared to achieve the target composition of an RTB-based sintered magnet: 24.0% by mass Nd, 7.0% by mass Pr, 0.89% by mass B, 0.1% by mass Cu, 0.5% by mass Ga, 0.9% by mass Co, and the remainder Fe. Alloy flakes were obtained by strip casting. The obtained alloy flakes were then hydrogen-pulverized to obtain coarsely pulverized powder. The coarsely pulverized powder was then fed to a jet mill and pulverized to obtain a fine powder (alloy powder containing rare earth elements). The fine powder (alloy powder containing rare earth elements) was then compacted in a magnetic field to obtain a compact. A so-called perpendicular magnetic field compacting device (horizontal magnetic field compacting device) was used as the compacting device, in which the magnetic field application direction and the pressure direction are perpendicular to each other.

[0053] Next, the obtained compact was sintered (a temperature sufficient for densification by sintering was selected (approximately 1000°C)) to produce a sintered compact from the compact. Next, the obtained sintered compact was subjected to high-temperature heat treatment. The high-temperature heat treatment was performed at 900°C for 120 minutes. Next, the sintered compact after the high-temperature heat treatment was subjected to low-temperature heat treatment under the conditions shown in Table 1. Condition A in Table 1 corresponds to a first heat treatment step in which the sintered compact was heat-treated in a heat treatment furnace at a first temperature of 380°C for 90 minutes, and a second heat treatment step in which the sintered compact after the first heat treatment was heat-treated in a heat treatment furnace at a second temperature of 460°C for 90 minutes. The difference between the first temperature and the second temperature was 80°C. Conditions B and C are similarly described. The temperature rise rate from the first temperature to the second temperature was 10°C / min. Moreover, conditions D to F were conventional low-temperature heat treatment steps, in which heat treatment was carried out at 460° C. to 490° C. for 180 minutes each.

[0054] The obtained sintered bodies (samples No. 1 to 6) were subjected to a component analysis, and the results were equivalent to the target composition (the molar ratio of T [T] / [B] was greater than 14.0). Each component was measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). Furthermore, after the sintered bodies (No. 1 to 6) were machined, the properties of each sample (B r and H cJ ) and based on the measurement results, the squareness ratio H k / HcJ H cJ and squareness ratio H k / H cJ The results are shown in Table 2.

[0055] [Table 1]

[0056] [Table 2]

[0057] As shown in Table 2, samples Nos. 1 to 3 under conditions A to C of the present disclosure (the temperature of the second heat treatment step after the first heat treatment was 460°C to 490°C) all exhibited high H cJ and squareness ratio H k / H cJ On the other hand, in the samples Nos. 4 to 6 under the conditions D to F (the temperature of the low-temperature heat treatment step without the first heat treatment was 460°C to 490°C) of the comparative examples, the sample No. 4 (heat treatment temperature was 460°C) had a high H cJ and squareness ratio H k / H cJ However, when the heat treatment temperature was changed to 475°C or 490°C as in Samples No. 5 and 6, H cJ and squareness ratio H k / H cJ From these facts, the manufacturing method of the present disclosure has a high H cJ and squareness ratio H k / H cJ The heat treatment temperature range in which H can be achieved by the heat treatment process can be expanded. cJ and squareness ratio H k / H cJ This makes it possible to suppress variations in the magnet size and to stably manufacture high-performance RTB-based sintered magnets.

[0058] Experimental Example 2 A molded body was obtained in the same manner as in Example 1. Next, the obtained molded body was sintered (a temperature at which sufficient densification by sintering occurs (approximately 1000°C) was selected) to produce a sintered body from the molded body. Next, the obtained sintered body was subjected to high-temperature heat treatment in the same manner as in Example 1. Next, the sintered body after the high-temperature heat treatment was subjected to low-temperature heat treatment under the conditions shown in Table 1. The temperature rise rate from the first temperature to the second temperature was 10°C / min.

[0059] The obtained sintered bodies (samples No. 7 to 10) were subjected to a component analysis, and the results were equivalent to the target composition (the molar ratio of T [T] / [B] was greater than 14.0). The components were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). Furthermore, after machining the sintered bodies (No. 7 to 10), the properties of each sample (B r and H cJ ) and based on the measurement results, the squareness ratio H k / H cJ H cJ and squareness ratio H k / H cJ The results are shown in Table 2.

[0060] [Table 3]

[0061] [Table 4]

[0062] As shown in Table 4, even when the time (30 minutes to 90 minutes) and temperature (380°C and 350°C) of the first heat treatment step were changed under the conditions of the present disclosure, high H cJ and squareness ratio H k / H cJ has been obtained. [Industrial Applicability]

[0063] 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. preparing a compact of alloy powder containing a rare earth element; a sintering step of sintering the compact to produce a sintered body; a first heat treatment step of heat treating the sintered body in a heat treatment furnace at a first temperature of 300°C or higher and lower than 400°C for 30 minutes or longer and 900 minutes or shorter; a second heat treatment step of heat treating the sintered body in the heat treatment furnace at a second temperature of 400°C or higher and 500°C or lower for 30 minutes or higher and 900 minutes or lower; Including, a difference between the first temperature and the second temperature is 50°C or more; The composition of the alloy powder is R (R is a rare earth element and necessarily includes at least one selected from the group consisting of Nd, Pr, and Ce), T (T is at least one selected from the group consisting of Fe, Co, Al, Mn, and Si and necessarily includes Fe), B, and at least one selected from the group consisting of Cu, Ga, Ni, Ag, Zn, and Sn, and the molar ratio of T to B, [T] / [B], is greater than 14.0; A method for producing an RTB based sintered magnet.

2. the first temperature is less than 390°C; The second temperature is 460°C or higher. The method for producing the RTB based sintered magnet according to claim 1.

3. The temperature rise rate from the first temperature to the second temperature is 0.5°C / min or more and 30°C / min or less. The method for producing the RTB based sintered magnet according to claim 1 or 2.

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