JP4506123B2 - Rare earth quenching magnet alloy manufacturing method and quenching apparatus - Google Patents

Description

  The present invention relates to a method for producing a rare earth magnet alloy having a fine crystal (nanocrystal) structure and a rapid cooling apparatus.

Nanocomposite magnets are attracting attention as rare earth quenching magnets that are suitably used for bonded magnets. A nanocomposite magnet is a magnet that includes two or more kinds of fine crystal phases and in which a hard magnetic phase and a soft magnetic phase are magnetically coupled. Iron-based rare-earth nanocomposite magnets are theoretically predicted to exhibit higher performance than single-phase magnets with Nd ₂ Fe ₁₄ B phase as the main phase. Nanocomposite magnets with excellent performance have not been mass-produced.

  As a method for producing a rapidly cooled magnet such as a nanocomposite magnet, there are a melt spinning method and a strip casting method, and these conventional techniques are disclosed in Patent Document 1, for example. In the case of producing a quenched magnet by such a conventional technique, first, a quenched alloy in an amorphous state from a molten alloy, or both an amorphous phase and a fine crystalline phase are included by a liquid ultra-quenching method such as a melt spinning method. A quenched alloy is produced. Thereafter, a step of causing crystallization by heating these quenched alloys is performed.

  In the melt spinning method and the strip casting method, the molten alloy is supplied to the surface of the rotating cooling roll, and the heat of the molten alloy is rapidly taken away to be rapidly cooled and solidified. When the molten alloy is rapidly cooled using such a cooling roll, the cooling rate during the rapid cooling is adjusted by controlling the supply rate of the molten alloy and the surface speed of the rapid cooling roll.

  The time that the alloy is in contact with the quench roll is very short. For this reason, the alloy still in a high temperature state (for example, 700-900 degreeC) will be continuously discharged | emitted from the contact area | region with a quenching roll. The alloy in a high temperature state is elongated in a strip shape, and further cools to room temperature while being deprived of heat by the surrounding atmosphere gas (natural cooling).

Conventionally, a nanocomposite magnet having a structure in which the Nd ₂ Fe ₁₄ B phase responsible for hard magnetism and the α-Fe phase and iron-based boride phase responsible for soft magnetism are uniformly and finely dispersed is used to rapidly cool molten alloy having a specific composition. Thus, after preparing a rapidly solidified alloy in which the amorphous phase occupies most of the amorphous phase, the rapidly solidified alloy was heated and crystallized. In this case, if the cooling rate in the rapid cooling process is lowered, a crystal structure in which α-Fe and the like are precipitated is formed in the alloy immediately after the rapid cooling, and the soft magnetic α-Fe and the like are coarsened by the subsequent heat treatment. there were.

However, the present applicant has found that by adding Ti to the alloy composition, the precipitation and growth of α-Fe can be suppressed during the cooling process of the molten alloy, thereby producing a quenched alloy containing a large amount of Nd ₂ Fe ₁₄ B phase. They are found and disclosed in Patent Document 1 and Patent Document 2. The addition of Ti makes it possible to lower the cooling rate in the rapid cooling process, and thus it becomes possible to produce a nanocomposite magnet using a strip casting method with a relatively low cooling rate and excellent mass productivity.

On the other hand, as a technique for controlling the structure of the quenched alloy, the present applicant has disclosed in Patent Document 3 a method for heating or cooling an alloy in a metallic glass state after forming a metallic glass state by quenching the molten alloy. Disclosure.
JP 2002-175908 A WO 02/39465 A1 brochure JP 2001-319821

  In the case of the strip casting method, it is difficult to keep the amount of molten metal supplied to the roll constant per unit time, and if the amount of molten metal supplied per unit time is too large, cooling with the cooling roll becomes insufficient. is there. If the cooling is insufficient, the crystal structure in the quenched alloy becomes coarse even in a composition to which Ti is added, and as a result, it may be difficult to obtain an iron-based rare earth permanent magnet having excellent magnetic properties. Such a problem occurs remarkably when the quenched alloy is deposited in the recovery tank of the apparatus in a state where it is not sufficiently cooled.

  On the other hand, as a result of studying the production of a quenched alloy by the twin roll quenching method, one of the present inventors found that when the roll peripheral speed was increased in order to increase the quenching speed, the quenched ribbon was wound around the roll and the ribbon was stabilized. I couldn't get it. As a result, in order to stably obtain a quenched ribbon, it is necessary to perform quenching at a quenching rate slower than that of strip casting, and as a result, there is a problem that an iron-based rare earth permanent magnet having excellent magnetic properties cannot be obtained. there were.

  The present invention has been made in view of such various points, and the object of the present invention is that even if a quenching method having a relatively low quenching rate such as a strip casting method or a twin-roll quenching method is used, the magnetic property is finally obtained. An object of the present invention is to provide a method for producing a rare earth quenched magnet alloy and a quenching apparatus that can obtain a nanocrystalline magnet having excellent characteristics.

  A method of manufacturing a rare earth quenched magnet alloy according to the present invention includes a first quenching step for rapidly cooling a molten metal of a rare earth alloy, and an alloy whose temperature starts to be lowered by the first quenching step is brought into contact with a cooling medium. The second rapid cooling step further includes a step of bringing the alloy into contact with the inner wall of the drum while rotating the cooling drum functioning as the cooling medium.

  In a preferred embodiment, the method includes the step of further quenching the alloy by bringing the alloy that has been crystallized before the second quenching step into contact with the inner wall of the cooling drum, thereby suppressing grain growth of the crystal phase. .

  In a preferred embodiment, the second rapid cooling step includes a step of pulverizing the alloy by rotating the cooling drum.

  In a preferred embodiment, the second rapid cooling step includes a step of pressing the alloy against the inner wall of the cooling drum by a centrifugal force generated by the rotation of the cooling drum.

  In a preferred embodiment, after the first quenching step, the alloy moves through the atmosphere without contacting other members until the second quenching step is started.

  In a preferred embodiment, the first rapid cooling step includes a step of bringing the molten metal of the rare earth alloy into contact with the surface of a rotating cooling roll.

  In a preferred embodiment, the time until the alloy comes into contact with the inner wall of the cooling drum after being separated from the surface of the cooling roll is adjusted to 0.2 seconds or less.

  In a preferred embodiment, the first quenching step includes a step of quenching the melt of the rare earth alloy by a gas atomizing method.

In a preferred embodiment, the crystal phase developed by crystallization by the first quenching step is a hard magnetic phase having an Nd ₂ Fe ₁₄ B type crystal structure.

  In a preferred embodiment, the temperature of the alloy when the alloy is brought into contact with the inner wall of the cooling drum in the second quenching step is set in a range of 500 ° C. or higher and 1000 ° C. or lower.

  The method for producing a rare earth magnet according to the present invention includes a step of producing a rare earth quenched magnet alloy by any one of the methods for producing a rare earth quenched magnet alloy and a step of performing a heat treatment on the rare earth quenched magnet alloy.

  In a preferred embodiment, a nanocrystalline magnet structure is completed by performing the heat treatment.

  In a preferred embodiment, the nanocrystalline magnet structure is a nanocomposite magnet structure in which a hard magnetic phase and a soft magnetic phase are magnetically coupled.

  The quenching apparatus of the present invention is a quenching apparatus comprising a first quenching means for quenching a molten metal of a rare earth alloy, and a second quenching means for contacting an alloy whose temperature starts to be lowered by the first quenching means, The second quenching means includes a cooling drum that is rotatably supported and a drive unit that rotates the cooling drum, and the alloy is brought into contact with an inner wall of the rotating cooling drum in a quenching process. Therefore, the arrangement relationship between the first quenching means and the second quenching means is defined.

  In a preferred embodiment, at least an inner wall of the cooling drum is formed of carbon steel, W, Fe, Cu, Mo, Be, Al, and / or an alloy thereof.

  In a preferred embodiment, the driving machine rotates the cooling drum so that the alloy can be pressed against the inner wall of the cooling drum by a centrifugal force generated by the rotation of the cooling drum.

  In a preferred embodiment, the cooling drum includes a crushing mechanism that crushes the alloy.

  In a preferred embodiment, the first quenching means is a rotating cooling roll.

  In a preferred embodiment, the first quenching means and the second quenching are performed so that the time until the alloy comes into contact with the inner wall of the cooling drum after being separated from the surface of the cooling roll is 0.2 seconds or less. An arrangement relationship with means is defined.

  In the present invention, after the rapid cooling in the first rapid cooling process, the rapid cooling in the second rapid cooling process using the cooling drum is performed. For this reason, in the process of rapidly cooling and solidifying the molten alloy, the alloy can be efficiently quenched in the temperature range where the crystallization reaction proceeds at the highest speed, and the crystallization process can be optimally controlled. As a result, even if the quenching rate in the first quenching process is relatively decreased and crystallization starts in the first quenching process, the second quenching process is performed on the alloy in the initial state of crystallization, thereby Since coarsening of the grains can be suppressed, a high-performance rare-earth quenching magnet alloy can be stably produced even if a quenching apparatus having a relatively low quenching rate and excellent mass productivity is used.

  In the method for producing a rare earth quenched magnet alloy according to the present invention, a first quenching step of rapidly cooling the molten metal of the rare earth alloy, and an alloy whose temperature starts to be lowered by the first quenching step is brought into contact with the “cooling medium”. And a second quenching step for further quenching. In the present invention, when performing the second rapid cooling step, the alloy is brought into contact with the inner wall of the cooling drum while rotating the cooling drum functioning as a cooling medium. Since the alloy is pressed against the inner wall of the drum by centrifugal force, efficient heat removal is possible.

In a preferred embodiment of the present invention, the first quenching step is performed to lower the temperature of the molten alloy, so that crystallization starts during or after the first quenching step. In the 2 quenching step, it is brought into contact with the inner wall of the cooling drum and further quenched to suppress grain growth of the crystal phase. “Start of crystallization” in the specification of the present application means that the number density of crystal phases in the alloy reaches a range of 2 × 10 ²¹ m ⁻³ to 10 ²⁷ m ⁻³ . Since heat generation starts to occur due to the start of crystallization, the second rapid cooling step is preferably performed before or after the start of crystallization.

  In the present invention, since the initial quenching step for changing the state of the alloy from the liquid phase to the solid phase and the subsequent quenching step are performed separately, the degree of freedom in designing the cooling process is improved. For this reason, after the rapid cooling process as in the prior art, it is possible to stably form a fine quenched structure composed of a desired constituent phase as compared with the case of performing cooling by natural heat dissipation mediated by atmospheric gas.

Hereinafter, the basic concept of the present invention will be described with reference to FIGS. Here, a nanocomposite magnet in which a hard magnetic phase composed of an Nd ₂ Fe ₁₄ B type compound and a soft magnetic phase such as α-Fe or boride are mixed in the same structure will be described as an example of the rare earth quenched magnet alloy.

  FIG. 1 is a graph showing changes in alloy temperature with time when a molten alloy is rapidly cooled and its state is changed from a liquid phase to a solid phase. The vertical axis of the graph indicates the alloy temperature, and the horizontal axis indicates the elapsed time (logarithmic display) from the contact between the molten alloy and the quenching roll.

  In the graph of FIG. 1, the cooling paths 1 to 3 and the generation regions of the crystal phases A to C are schematically shown. When the two-stage quenching according to the present invention is performed, the molten alloy changes from the liquid phase to the solid phase via the cooling path 1 and solidifies. The first quenching step in this example is performed by bringing the molten alloy into contact with the surface of the cooling roll. The starting point of the cooling path 1 corresponds to the time when the molten alloy comes into contact with the surface of the cooling roll in the first quenching step, and the point a on the cooling path corresponds to the time when the alloy leaves the surface of the cooling roll.

  The alloy temperature drops in a very short time in contact with the chill roll. In the example shown in FIG. 1, it is assumed that the nucleus of the crystal phase A is generated in the state at the point a of the cooling path 1 (hereinafter referred to as “state a”). The structure of the alloy in this state a is shown in FIG.

When producing an alloy for a nanocomposite magnet including an Nd ₂ Fe ₁₄ B type compound as a hard magnetic phase, the crystal phase A is, for example, an Nd ₂ Fe ₁₄ B type compound. In this case, the small white dots shown in FIG. 2A schematically show the nucleus of crystal growth of the Nd ₂ Fe ₁₄ B type compound. The Nd ₂ Fe ₁₄ B type compound (= crystalline phase A) grows around these nuclei. Actually, the precipitation / growth of the crystal phase A may start earlier or later than the time indicated by the point a of the cooling path. Here, for the sake of simplicity, the present invention will be described on the assumption that most crystallization starts when the alloy leaves the cooling means (cooling roll) for the first quenching step.

  In the present invention, as in this example, even when the nuclei of the crystal phase A are generated by the first quenching step of the molten alloy, after the crystallization starts, the cooling of the alloy is not allowed to be allowed to cool freely. 2 Take the heat of the alloy positively by performing the quenching process. For this reason, even when the crystal phase A is growing, the alloy temperature is lowered, and quickly passes through the generation temperature region of the crystal phase B (cooling path 1 in FIG. 1). As a result, in the final state b-1, as shown in FIG. 2 (b-1), a microstructure in which the fine crystal phase A and the crystal phase B are dispersed is obtained, and the excellent characteristics of the nanocomposite magnet are obtained. It will be possible to make the most of it.

  Next, the case where it cools via the cooling path 2 of FIG. 1 is demonstrated. In this example, the second quenching process is not performed after the first quenching process. As a result, due to the heat of crystallization reaction released at the start of crystallization of the crystal phase A, the alloy temperature does not decrease rapidly, but follows the cooling path 2 shown in FIG. 1, and the crystal phase A precipitates and grows. Longer stay time in easy areas. For this reason, the remelting and growth process of the crystal nucleus proceeds, and the crystallization of the crystal phase B starts after the generation of the crystal phase A is completed. For this reason, in the final state B-2, as shown in FIG. 2B-2, a structure in which the crystal phase A is coarsened is obtained.

  Next, the case where it cools via the cooling path | route 3 of FIG. 1 is demonstrated. Also in this case, the second quenching step is not performed after the first quenching step, but in this example, the amount of heat of crystallization reaction released with the start of crystallization of the crystal phase A is large, and the alloy temperature temporarily rises. To do. Therefore, the nucleus of the crystal phase A is remelted, and an undesired crystal phase C (phase unnecessary for the nanocomposite magnet) is generated. After the crystal phase C is thus formed, the crystal phase A and the crystal phase B grow in this order. Therefore, in the final state B-3, as shown in FIG. 2 (b-3), the presence of the crystal phase C changes the composition of the remaining portion, and the crystal phase A and the crystal phase B is not sufficiently formed, and a nanocomposite magnet structure in which crystal phase A and crystal phase B are magnetically coupled cannot be obtained.

  As described above, in the cooling paths 2 and 3, the second quenching step is not executed, and the temperature drop of the alloy after the point a on the cooling example path is caused by free cooling. On the other hand, in the present invention, after the crystallization starts in the course of cooling, the second quenching step is performed, and further the alloy is quenched to suppress the growth of the crystal phase in the cooling process.

  In the example shown in FIG. 1, crystallization has already started at the time of starting the second quenching step, but crystallization of the alloy may be started after starting the second quenching step. Depending on the composition of the alloy and the conditions of the first quenching step, the alloy may not be cooled to a temperature at which crystallization begins before the second quenching step is started. Even in such a case, since the growth of the crystal phase can be effectively suppressed by performing the second quenching step, a fine quenching structure can be stably formed.

  In the present specification, “free cooling” means that the alloy ribbon that is separated from the surface of the cooling part of a quenching means such as a quenching roll is deprived of heat through the atmospheric gas, and is thereby cooled naturally. This means that the alloy loses heat by radiative cooling. In addition, “quick cooling” means that the alloy gas takes heat at a rate faster than the rate at which the atmosphere gas takes heat from the alloy by “free cooling”, and the alloy temperature is lowered at a cooling rate faster than the cooling rate by free cooling. It means that In the present invention, there may be a period during which the alloy flies in the air after the first quenching process until the second quenching process is started. This period is a period existing between the first quenching process and the second quenching process, and corresponds to a very short free cooling period.

  In the present invention, an important point as the role of the second quenching step is that when crystallization starts in the alloy and heat of crystallization reaction is generated, the heat is quickly taken away, so that the crystal growth during the cooling is performed. It is in suppressing appropriately.

  Patent Document 3 discloses a technique for controlling the temperature of the metallic glass after the first quenching process but before the start of crystallization in the alloy, but deprives the heat generated by the crystallization heat generation. Therefore, it is not taught to suppress crystal growth.

  Hereinafter, a quenching device suitable for performing quenching controlled in this way will be described.

[Manufacturing equipment]
FIG. 3 is a diagram showing a configuration example of an apparatus that can be suitably used in the method for producing a rare earth quenched magnet alloy according to the present invention. The apparatus shown in the figure includes a tapping part provided with a nozzle for discharging the molten alloy 1, a quenching roll 4 for applying a first quenching process to the molten alloy 1 discharged from the tapping part, and a thinning from the quenching roll 4. A cooling drum 6 for performing a second quenching process on the alloy 5 extending in a band shape and a drive motor 7 for rotating the cooling drum 6 are provided. A high-frequency coil 2 is wound around the hot water supply portion, and by supplying high-frequency power to the high-frequency coil 2, the raw material alloy can be melted.

  In the illustrated apparatus, after the first quenching process is quenched by heat removal by the quenching roll 4, the second quenching process is quenched by heat removal by the cooling drum 6. That is, in this embodiment, the cooling drum 6 functions as a “cooling medium”.

  In the quenching apparatus of the present embodiment shown in the figure, a melt spinning apparatus by a single roll method is adopted as the first quenching means for executing the first quenching process, but the first quenching means of the present invention is used as this. It is not limited. For example, various liquid quenching apparatuses such as a twin roll quenching apparatus, a strip casting apparatus, a gas atomizing apparatus, a centrifugal atomizing apparatus, and a water atomizing apparatus can be suitably employed.

  The cooling drum 6 is rotatably supported and is rotated by the drive motor 7, and the rotation speed is arbitrarily adjusted within a predetermined range. According to the rapid cooling device of the present embodiment, the rotational speed of the cooling drum 6 can be adjusted independently without being limited by the rotational speed of the cooling roll 4, so that the degree of freedom in designing the cooling profile is greatly improved.

  Furthermore, according to the present invention, the alloy 5 can be pressed against the inner wall of the drum by utilizing the centrifugal force of the cooling drum 6, so that the heat removal from the alloy 5 by the inner wall of the drum can be effectively performed. When the cooling is performed by the single roll method as in the primary cooling, the contact time between the surface of the cooling roll 4 and the alloy 5 (alloy molten metal 1) is short, but by using the cooling drum 6, the alloy 5 and The contact time with the drum inner wall can be lengthened.

  The temperature of the alloy 5 when contacting the inner wall of the cooling drum 6 is appropriately selected depending on the alloy composition. Specifically, in the case of an Nd—Fe—B type quenched alloy magnet, it may be brought into contact with the inner wall of the cooling drum 6 when the temperature of the quenched alloy is 500 ° C. to 1000 ° C.

  At least the inner wall portion of the cooling drum 6 is made of tungsten (W), iron (Fe), copper (Cu), molybdenum (Mo), beryllium (Be), aluminum (Al) from the viewpoint of thermal conductivity and durability. ) And / or an alloy thereof. In order to stably cool the alloy, it is preferable to use a material having a thermal conductivity of 100 W / mK or more (copper, copper alloy, W, Mo, Be). The surface of the inner wall of the drum 6 is preferably plated with a single layer / multilayer of Cr, Ni, or an alloy thereof. Even when the drum 6 is made of a material having a relatively low melting point and hardness such as Cu, the strength of the inner wall of the drum can be increased by plating with Cr, etc., and the inner wall surface can be melted or deteriorated during the rapid cooling process. It becomes possible to suppress.

  As described above, in a preferred embodiment of the present invention, the second quenching step is performed on an alloy that has started to crystallize during the rapid cooling in the first quenching step or an alloy that has started to be crystallized immediately after the first quenching step. Is quenched to suppress undesired growth of the crystal phase. If the second quenching step is not performed, the crystal phase grows and leads to a final deterioration of the magnet characteristics. According to a preferred embodiment of the present invention, such a crystal phase grows. Therefore, it is possible to produce a quenched alloy that can exhibit excellent magnet characteristics. In order to perform the second rapid cooling process accurately after starting the crystallization, it is necessary to start the second rapid cooling process without missing the timing when the decreasing alloy temperature enters the predetermined range. In a preferred embodiment, the timing at which the alloy leaving the quenching roll 4 flies through the atmosphere and contacts the inner wall of the cooling drum 6 is appropriately adjusted, for example, 0.002 to 0 after the alloy leaves the quenching roll 4. It is possible to reach the inner wall of the cooling drum 6 within a range of 2 seconds. Making this period shorter than 0.002 seconds is difficult due to the design of the apparatus because the quenching roll 4 and the cooling drum 6 are too close. On the other hand, if the time is longer than 0.2 seconds, the cooling rate after the first quenching process becomes too low, so that a phase other than the target crystal phase is precipitated, or the target crystal phase is coarsened and good magnetic properties are obtained. It becomes difficult to obtain characteristics. From these viewpoints, the period is preferably set in the range of 0.002 to 0.2 seconds. Moreover, in order to enhance the effect of the second quenching step, it is more preferable to set the period in the range of 0.005 to 0.02 seconds.

  A crushing mechanism for crushing the alloy 5 may be provided inside the cooling drum 6. The structure of the crushing mechanism is not particularly limited. For example, the rotational force of the cooling drum 6 is used by providing one or a plurality of crushing blades 8 on the bottom surface and / or inner wall of the cooling drum 6 as shown in FIG. Thus, the alloy can be pulverized efficiently. When the crushing blade 8 is provided on the bottom surface of the cooling drum 6, the crushing blade 8 may be rotated independently of the rotation of the cooling drum 6, or the crushing blade 8 is not rotated. You may fix with respect to an apparatus. On the other hand, when the crushing blade 8 is rotated, the direction of rotation may coincide with the direction of rotation of the cooling drum 6 or may be set in the opposite direction.

The rotational speed of the cooling drum 6 is preferably set to a speed at which the alloy 5 can come into contact with the inner wall of the drum by centrifugal force, that is, a rotational speed at which centrifugal force> gravity. Specifically, when the drum radius is r (m), it is preferable to set it to 30 r ^1/2 rpm or more. If the drum 5 can be in contact with the inner wall of the drum for a long time against its own weight, efficient heat removal can be realized.

[Production method]
Hereinafter, an embodiment of a method for producing a rare earth quenched magnet alloy according to the present invention will be described.

  In the present embodiment, first, a molten alloy having a desired composition is produced according to the magnet to be finally produced, and the first quenching step is performed using the apparatus shown in FIG. 3 to lower the temperature of the alloy. To initiate crystallization. Thereafter, the second quenching step is performed using the cooling drum 6. The composition of the magnet that can be suitably produced by the production method of the present invention is not particularly limited, but here, a magnet having the following composition is produced.

(Fe _1-m T m) is expressed by _{100-xyzl Q x R y M1} z M2 l. Here, T is one or more elements selected from the group consisting of Co and Ni, Q is one or more elements selected from the group consisting of B, C, O, and N, and R is Y (yttrium) And one or more elements selected from the group consisting of rare earth metals, M1 is one or more elements selected from the group consisting of Ti, Zr, Nb, V, Cr, Ta, and Hf, and M2 is Si And one or more elements selected from the group consisting of Al, Ga, Cu, Ag, Au, Sn, Pb, In, and Bi. The composition ratios (atomic ratios) x, y, z, l, and m are 1 <x ≦ 30 atomic%, 3 ≦ y <20 atomic%, 0.1 ≦ z ≦ 20 atomic%, and 0.1 ≦, respectively. l ≦ 20 atomic%, and 0 ≦ m ≦ 0.5.

In particular, the production method of the present invention includes a hard magnetic phase in which a crystal phase developed by crystallization during the first and second quenching steps and / or after the quenching step has an Nd ₂ Fe ₁₄ B type crystal structure, and an iron or iron group It is particularly preferably employed when it is a boride soft magnetic phase. However, a nanocomposite magnet including other constituent phases or a single-phase magnet has an advantage that a tissue structure containing a desired constituent phase in an appropriate size can be formed.

  In the present embodiment, the cooling roll 4 is rotated so that the roll surface speed of the cooling roll 4 is, for example, 3 m / sec or more and 30 m / sec or less. The rapid cooling is preferably performed in an inert gas atmosphere of 70 kPa or less or in a vacuum. When the atmospheric pressure exceeds 70 kPa, the atmospheric gas is likely to be caught between the surface of the rotating roll and the molten alloy. When such atmospheric gas entrainment occurs, gas pockets are formed on the surface of the alloy strip, uniform quenching is not achieved, and the quenching structure becomes non-uniform, making it difficult to perform quenching stably. A preferable range of the gas pressure when quenching in an inert gas atmosphere is 35 kPa or less, particularly about 1.5 kPa.

  For example, the temperature of the inner wall of the cooling drum 6 is preferably set to a temperature equal to or lower than the lower limit temperature of the generation region of the crystal phase B in FIG. When producing a Nd—Fe—B-based nanocomposite magnet as in this embodiment, it is preferable to maintain the inner wall temperature of the drum 6 at 500 ° C. or lower. This is because when the inner wall temperature of the cooling drum 6 exceeds 500 ° C., heat removal in the second quenching process becomes insufficient, and the growth of the crystal phase may not be sufficiently suppressed.

[Heat treatment]
The quenched alloy solidified through the two-stage quenching process is preferably subjected to heat treatment using a known heat treatment apparatus for the purpose of improving magnetic properties. This heat treatment may be performed after coarsely pulverizing the quenched alloy. By this heat treatment, all or part of the amorphous phase can be crystallized to further improve the magnet characteristics.

  When producing a nanocomposite magnet having the above composition, the quenched alloy is preferably heat-treated at a temperature of 500 ° C. to 900 ° C. in a vacuum or in an inert gas atmosphere such as argon gas. By such heat treatment, crystallization of the amorphous phase remaining in the rapidly cooled alloy can be advanced, and an iron-based rare earth permanent magnet having more excellent magnetic properties can be obtained.

[Crystal structure]
When producing a nanocomposite magnet having the above composition, the metal structure of the obtained alloy is a mixture of a soft magnetic phase of iron or iron-based boride and a hard magnetic phase having an R ₂ Fe ₁₄ B type crystal structure, It has a nanocomposite structure in which these phases are magnetically coupled by exchange interaction. The average crystal grain size of the soft magnetic phase and the hard magnetic phase are both 1 nm or more and 100 nm or less, and in particular, the average crystal grain size of the soft magnetic phase is as small as 30 nm or less. In the most preferred form, the soft magnetic phase forms a film-like layer having a thickness of about 5 nm and surrounds the hard magnetic phase. Such a structure is suitably formed when Ti is added.

  When manufacturing Sm—Co-based or Sm—Fe-based rare-earth quenched magnets, a suitable nanocrystalline structure may be formed using a raw material alloy suitable for each magnet. It can be said that the production method of the present invention exhibits a remarkable effect particularly when a target magnet constituent phase is generated by a peritectic reaction.

  The nanocrystalline magnet manufactured by the method described above can be applied to various apparatuses in various modes. Hereinafter, a method for producing a bonded magnet using a nanocrystalline magnet powder produced by the production method of the present invention will be briefly described.

  First, a compound is prepared by adding a binder made of an epoxy resin and an additive to the powder of the nanocrystalline magnet and kneading. Next, after the compound is press-molded in an orientation magnetic field by a molding apparatus, a final bonded magnet can be obtained through a heat curing step, a cleaning step, a coating step, an inspection step, and a magnetization step. This bonded magnet is suitably used for various motors and actuators.

The preferred embodiments of the present invention have been described above mainly using a nanocomposite magnet including a soft magnetic phase such as iron or iron-based boride and an R ₂ Fe ₁₄ B type hard magnetic phase as an example. The manufacturing method can also be applied to nanocrystal magnets of other material systems. In the present invention, by performing the cooling process in two stages, it becomes possible to produce a nanocrystalline microstructure that is difficult to obtain by only the first quenching process with good reproducibility. Even nanocrystalline magnets contained as a single phase can be used. In particular, in order to obtain a uniform nanocrystal structure by the conventional melt spinning method, it is necessary to set the rotational peripheral speed of the cooling roll high. However, according to the manufacturing method of the present invention, the cooling speed in the first quenching step Even if it is set to be relatively low, effective cooling can be performed in the second quenching step, so that a desired nanocrystalline structure can be obtained. This also has the advantage of making it possible to reduce the size of the chill roll device used in the first quenching step.

  FIG. 4 shows the time variation of the alloy temperature when the first-stage quenching process and the two-stage quenching process are performed when the cooling rate (primary cooling rate) in the first quenching process is relatively high and low. Yes. In FIG. 4, the horizontal axis indicates the cooling time on a linear scale. In the graph of FIG. 1, since the horizontal axis is a log scale, the time required for the first quenching process seems to be long, but actually, the time for the second quenching process is relatively long as shown in FIG. For this reason, if effective secondary cooling by the cooling drum is not performed, the alloy will experience a temperature state far higher than room temperature for a long period of time, resulting in coarsening of the nanocrystal structure or as desired. There is a possibility that no phase is precipitated and coarsened. According to the present invention, such inconvenience can be appropriately avoided, and finally a nanocrystalline magnet exhibiting excellent magnet characteristics can be produced with good reproducibility.

It is a graph which shows the time change (cooling path | routes 1-3) of the alloy temperature in the case of forming a quenching alloy from a molten alloy. The vertical axis of the graph is temperature, and the horizontal axis is time (Log scale). (A) is a figure which shows typically the alloy structure in the state a, (b-1) is a figure which shows the alloy structure in the state b-1 typically, (b-2) is a state. It is a figure which shows the alloy structure in b-2 typically, (b-3) is a figure which shows the alloy structure in state b-3 typically. It is a figure which shows the structure of the rapid cooling apparatus used suitably by embodiment of this invention. It is a graph which shows the effect by the 2nd cooling process. The vertical axis of the graph is temperature, and the horizontal axis is time (linear scale).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Alloy molten metal 2 High frequency coil 3 Nozzle 4 Quenching roll 5 Quenching alloy 6 Cooling drum 7 Motor 8 Grinding blade

Claims (13)

A first quenching step for quenching the molten rare earth alloy;
A second quenching step in which the alloy whose temperature starts to be lowered by the first quenching step is brought into contact with a cooling medium, thereby further quenching the alloy;
Including
The first quenching step includes a step of bringing the molten rare earth alloy into contact with the surface of a rotating cooling roll,
In the second quenching step, the alloy that has started to be crystallized before the second quenching step is further quenched by rotating the cooling drum functioning as the cooling medium and bringing the alloy into contact with the inner wall of the drum. And a step of suppressing crystal grain growth in the crystal phase,
After the first quenching step, until the second quenching step is started, the alloy moves in the atmosphere without contacting other members, and after the alloy leaves the surface of the cooling roll, A method for producing a rare earth quenched magnet alloy, wherein the time until contact with the inner wall of the cooling drum is adjusted to a range of 0.002 to 0.2 seconds .   The method for producing a rare earth quenched magnet alloy according to claim 1, wherein the second quenching step includes a step of pulverizing the alloy by rotating the cooling drum.   3. The method for producing a rare earth quenched magnet alloy according to claim 1, wherein the second quenching step includes a step of pressing the alloy against the inner wall of the cooling drum by a centrifugal force generated by the rotation of the cooling drum. . The first quenching step, by a gas atomizing method, a manufacturing method of claims 1 to 3 Noise Re earth quenched magnet alloy of crab further comprising the step of quenching a melt of the rare earth alloy. The method for producing a rare earth quenched magnet alloy according to claim 1, wherein the crystal phase is a hard magnetic phase having an Nd ₂ Fe ₁₄ B type crystal structure.   6. The rare earth quenched magnet according to claim 1, wherein a temperature of the alloy when the alloy is brought into contact with an inner wall of the cooling drum in the second quenching step is set in a range of 500 ° C. or more and 1000 ° C. or less. Alloy manufacturing method. Producing a rare earth quenched magnet alloy by the method for producing a rare earth quenched magnet alloy according to any one of claims 1 to 6;
Performing a heat treatment on the rare earth quenched magnet alloy;
A method for producing a rare earth magnet.   The method for producing a rare earth magnet according to claim 7, wherein a nanocrystalline magnet structure is completed by performing the heat treatment.   The method for producing a rare earth magnet according to claim 8, wherein the nanocrystalline magnet structure is a nanocomposite magnet structure in which a hard magnetic phase and a soft magnetic phase are magnetically coupled by an exchange interaction. A quenching device comprising first quenching means for quenching a molten rare earth alloy, and second quenching means for contacting with an alloy whose temperature starts to be lowered by the first quenching means,
The first quenching means is a rotating cooling roll;
The second quenching means includes a cooling drum that is rotatably supported, and a drive unit that rotates the cooling drum.
In the rapid cooling step, the alloy can be brought into contact with the inner wall of the rotating cooling drum, and the time until the alloy comes into contact with the inner wall of the cooling drum after leaving the surface of the cooling roll. A quenching apparatus in which an arrangement relationship between the first quenching means and the second quenching means is defined so as to be in a range of 0.002 to 0.2 seconds .   The quenching device according to claim 10, wherein at least an inner wall of the cooling drum is formed of carbon steel, W, Fe, Cu, Mo, Be, Al, and / or an alloy thereof.   The quenching device according to claim 10 or 11, wherein the driving device rotates the cooling drum so that the alloy can be pressed against the inner wall of the cooling drum by a centrifugal force generated by the rotation of the cooling drum. .   The quenching device according to any one of claims 10 to 12, wherein the cooling drum includes a crushing mechanism that crushes the alloy.

Images