JP2004181531A - Method for producing rare-earth containing alloy flake, alloy flake for rare-earth magnet, alloy powder for rare-earth sintered magnet, rare-earth sintered magnet, alloy powder for bonded magnet and bonded magnet, and evaluation method for metallic structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a rare-earth metal containing alloy thin sheet having the structure excellent in the uniformity by restraining the development of fine R-rich phase zone in the cast R-T-B base alloy block. <P>SOLUTION: A plurality of almost linear recessing and projecting parts are formed on a cast surface and the surface roughness given by almost linear recessing and projecting parts is made to be 3 μm -60 μm by the ten points-average roughness (Rz) and a rotating roll for casting, in which the extending direction of the recessing and projecting parts having ≥ 30% in the almost linear recessing and projecting parts is directed to the direction forming the angle of ≥ 30° to the rotating direction of the roll, is used. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a rare earth-containing alloy flake and a method for producing the same, and more particularly to a method for evaluating a rare earth-containing alloy and a metal structure produced by a strip casting method.

  In recent years, the production of rare earth magnet alloys, especially Nd-Fe-B alloys, has rapidly increased due to their high characteristics, and they are used for HDs (hard disks), MRIs (magnetic resonance imaging), or for various motors. It is used. As rare-earth magnet alloys of this type, those in which a part of Nd is replaced by another rare-earth element such as Pr or Dy, or those in which a part of Fe is replaced by another transition metal such as Co or Ni are usually used. Is generally referred to as an RTB-based alloy, including an Nd-Fe-B-based alloy. Here, R is at least one of rare earth elements including Y. In addition, T is a transition metal in which Fe is essential, and a part of Fe can be replaced by Co or Ni, and Cu, Al, Ti, V, Cr, Ga, Mn, Nb, Ta, Mo, W, Ca, Sn, Zr, Hf, or the like may be added alone or in combination of two or more. B is boron and can be partially substituted with C or N.

  The RTB-based alloy has, as a main phase, a crystal composed of the R2T14B phase, which is a ferromagnetic phase contributing to the magnetizing action, and is a nonmagnetic, rare-earth-enriched low-melting point R (Y-containing rare-earth element including Y). Above)-An alloy in which a rich phase coexists, and since it is an active metal, melting or casting is generally performed in a vacuum or inert gas. Further, in order to produce a sintered magnet from the cast RTB-based alloy ingot by powder metallurgy, the alloy ingot is pulverized to about 3 μm (FSSS: measured by a Fischer subsieve sizer) to obtain an alloy powder. After that, press forming in a magnetic field, sintering in a sintering furnace at a high temperature of about 1000 to 1100 ° C, heat treatment and machining as needed, and then plating to improve corrosion resistance and sintering Usually it is a magnet.

In a sintered magnet made of such an RTB-based alloy, the R-rich phase plays an important role as follows.
(1) It has a low melting point and becomes a liquid phase at the time of sintering, which contributes to increasing the density of the magnet and thus improving the magnetization.
(2) Eliminate irregularities at grain boundaries, reduce nucleation sites in reverse magnetic domains, and increase coercive force.
(3) The main phase is magnetically insulated to increase the coercive force. Therefore, if the dispersion state of the R-rich phase in the formed magnet is poor, local sintering failure and a decrease in magnetism may be caused, so it is important that the R-rich phase is uniformly dispersed in the formed magnet. It becomes. Here, the distribution of the R-rich phase is greatly affected by the structure of the R-T-B-based alloy mass at the time of casting.

  Another problem that occurs in the casting of the RTB-based alloy is that α-Fe is formed in the cast alloy ingot. α-Fe causes deterioration of the pulverizing efficiency when pulverizing the alloy lump, and if it remains in the magnet after sintering, it lowers the magnetic properties of the magnet. Therefore, in the conventional alloy ingot, if necessary, a long time homogenization treatment is performed at a high temperature to eliminate α-Fe.

  In order to solve the problem that α-Fe is generated in the cast RTB-based alloy ingot, as a method of casting the alloy ingot at a higher cooling rate, a strip casting method (hereinafter abbreviated as SC method) is used. Has been developed and used in actual processes. The SC method is a method of rapidly solidifying an alloy by flowing a molten metal on a copper roll whose inside is water-cooled and casting a thin piece of about 0.1 to 1 mm. The precipitation of Fe can be suppressed. Further, since the crystal structure of the alloy lump can be refined, an alloy having a structure in which the R-rich phase is finely dispersed can be generated. As described above, in the alloy cast by the SC method, since the internal R-rich phase is finely dispersed, the dispersibility of the R-rich phase in the magnet after pulverization and sintering is also good, and the The magnetic properties have been successfully improved (for example, see Patent Documents 1 and 2).

  Further, the alloy ingot cast by the SC method has excellent structure homogeneity. The homogeneity of the structure can be compared based on the crystal grain size and the dispersion state of the R-rich phase. In alloy flakes produced by the SC method, chill crystals may be generated on the casting roll side (hereinafter referred to as the mold surface side) of the alloy flakes, but as a whole a moderately fine and homogeneous structure brought about by rapid solidification Can be obtained.

  As described above, in the RTB-based alloy cast by the SC method, since the R-rich phase is finely dispersed and the generation of α-Fe is suppressed, when producing a sintered magnet, The homogeneity of the R-rich phase in the final magnet is enhanced, and the harmful effects of α-Fe on pulverization and magnetism can be prevented. Thus, the RTB-based alloy ingot cast by the SC method has an excellent structure for producing a sintered magnet. However, as the properties of magnets have been improved, it has been increasingly required to improve the homogeneity of the structure of the raw alloy ingot.

For this reason, a technique has been disclosed in which a sintered magnet having good magnet properties is manufactured by setting the area ratio of the chill crystal on the mold surface side of the cast RTB-based alloy to 5% or less. (See, for example, Patent Document 3). Since the chill crystal part becomes a fine powder having a particle size of 1 μm or less in the pulverizing step, it is considered that the particle size distribution of the alloy powder is disturbed and magnetism is deteriorated.
JP-A-5-222488 JP-A-5-295490 JP-A-10-317110

  The present inventor studied the relationship between the structure of the cast RTB-based alloy ingot and the behavior during hydrogen crushing and fine pulverization. As a result, the grain size of the alloy powder for the sintered magnet was made uniform. In order to control, it has been found that controlling the dispersion state of the R-rich phase rather than the crystal grain size of the alloy lump is weight. The volume ratio of the chill crystal in the alloy ingot is actually several percent or less, and the dispersion state of the R-rich phase formed on the mold surface side in the alloy ingot is extremely finer than the adverse effect of the chill crystal. It has been found that the region (fine R-rich phase region) has a greater effect in controlling the particle size of the magnet powder. In other words, even if the number of chill crystals in the RTB-based alloy ingot is reduced depending on the composition of the alloy ingot and the manufacturing conditions, the volume ratio of the fine R-rich phase region may exceed 50% in some cases. It was confirmed that the rich phase region disturbed the particle size distribution of the alloy powder for magnets, and that it was necessary to reduce the fine R rich phase region in order to improve the magnet properties.

The present invention has been made based on the above findings, and an object of the present invention is to form a fine R-rich phase region in a rare earth-containing alloy ingot formed of a cast RTB-based alloy or the like. It is an object of the present invention to provide a method for producing a rare-earth-containing alloy flake capable of effectively suppressing the occurrence of a rare-earth-containing alloy flake, and a rare-earth-containing alloy flake produced by such a production method and having a structure excellent in homogeneity.
Another object is to provide an effective evaluation method for evaluating the metal structure of such a rare earth-containing alloy.

  Previously, the present inventor studied the relationship between the structure of the cast RTB-based alloy ingot and the behavior during hydrogen crushing and fine pulverization, and found that the particle size of the alloy powder for sintered magnets was reduced. It has been found that it is more important to control the dispersion state of the R-rich phase than to the crystal grain size of the alloy lump in order to control uniformly. Then, the casting conditions in the SC method, especially the surface condition of the casting rotary roll, were changed, and the volume ratio at which a fine R-rich phase region was formed in the RTB-based alloy flakes was compared. Then, they found that there was a relationship between the surface roughness of the surface of the alloy flakes on the mold surface side and the volume ratio at which the fine R-rich phase region was formed, and the alloy flake having a fine R-rich phase region of 20% or less and having excellent structure homogeneity. Made possible.

Further, the present inventor has found that by providing a plurality of linear irregularities that form the surface roughness of the casting rotating roll so as to intersect with each other, it is possible to more effectively homogenize the structure. confirmed.
In other words, the fine R-rich phase region can be reduced and the structure can be homogenized by the above method. Further, not only the numerical surface roughness of the rotating roll but also the shape of the unevenness which is the origin of the surface roughness can be controlled. If so, it was confirmed that the tissue can be homogenized more effectively.

The present invention has been made based on the knowledge obtained by the previous research and the subsequent research, and further improved the irregular shape of the surface of the casting rotary roll to obtain the cast R-T- Method for producing a rare-earth-containing alloy flake having a structure excellent in homogeneity by effectively suppressing the formation of a fine R-rich phase region in a B-based alloy ingot, and homogeneity of distribution of an R-rich phase in a magnet The present invention provides a rare-earth sintered magnet having high magnet characteristics and excellent magnet properties.
Further, the present inventor has established a metallographic evaluation method for measuring the distance between R-rich phases in a cast rare earth magnet alloy and measuring the fine R-rich phase to determine the distribution state of the R-rich phase.

That is, the present invention
(1) In a method for producing a rare earth-containing alloy flake by a strip casting method, a plurality of substantially linear irregularities are formed on a casting surface, and the surface roughness provided by the substantially linear irregularities is a ten-point average roughness (Rz). )), A casting roll is used in which the direction of extension of at least 30% of the substantially linear irregularities forms a direction at an angle of at least 30 ° with the roll rotation direction. A method for producing a rare earth-containing alloy flake.
(2) It is characterized in that a casting rotary roll is used in which the extending direction of 30% or more of the plurality of substantially linear irregularities is a direction forming an angle of 45 ° or more with the roll rotating direction ( 1) A method for producing a rare earth-containing alloy flake.
(3) A casting rotating roll is used in which the extending direction of 50% or more of the plurality of substantially linear irregularities is a direction forming an angle of 30 ° or more with the roll rotating direction ( 1) A method for producing a rare earth-containing alloy flake.
(4) A casting rotating roll is used in which the extending direction of 50% or more of the plurality of substantially linear irregularities is a direction that forms an angle of 45 ° or more with the roll rotating direction ( The method for producing a rare earth-containing alloy flake according to any one of 1) to (3).
(5) When producing a rare earth-containing alloy flake by a strip casting method, an RTB system used for a rare earth magnet (where R is at least one of the rare earth elements including Y, and T is essential for Fe) Wherein the transition metal and B are boron.) The method for producing a rare earth-containing alloy flake according to any one of (1) to (4), characterized by producing a rare earth-containing alloy flake made of an alloy.
(6) An alloy flake for a rare earth magnet, produced by the production method according to (5), wherein the volume ratio of the fine R-rich phase region in the alloy is 20% or less.
(7) An alloy powder for a rare-earth sintered magnet produced by subjecting the alloy flake for a rare-earth magnet produced by the method according to (5) to a hydrogen disintegration step, followed by jet milling.
(8) A rare earth sintered magnet produced from the alloy powder for a rare earth magnet according to (7) by a powder metallurgy method.
(9) An alloy powder for a bonded magnet manufactured by the HDDR method using the alloy flake for a rare earth magnet manufactured by the method according to (5).
(10) A bonded magnet produced using the alloy powder for a bonded magnet according to (9).

(11) The microstructure of the cross section of the RTB-based magnet alloy is captured as a digital image, a straight line having a length (L) substantially parallel to the solidified surface of the alloy is drawn on the microstructure image, and R _{The two} phases are determined from the difference in luminance between the ₂ T ₁₄ B main phase and the R-rich phase, and the luminance on the straight line changes from the luminance determined as the R ₂ T ₁₄ B main phase to the luminance determined as the R-rich phase. A metal structure evaluation method for an RTB-based magnet alloy in which a value (L / N) obtained by dividing the length of a straight line (L) by the number of times (N) is evaluated as an R-rich phase interval (r).
(12) The average value and the standard deviation of the R-rich phase interval are calculated from the R-rich phase interval obtained from each straight line by using a plurality of the straight lines, and the RTB-based magnet alloy according to (11) is calculated. Metal structure evaluation method.
(13) The microstructure of the RTB-based magnet alloy cross section is divided into a digital image and the microstructure image by cells having an appropriate area, and the R ₂ T ₁₄ B main phase and the R-rich are determined from the difference in luminance in each cell. R-T which determines both phases of each phase and measures the shape, size and number of individual R-rich phases present in each cell to determine whether or not each cell is a fine R-rich phase region -Method for evaluating metal structure of B-based magnet alloy (14) As the shape of the R-rich phase, any one or more of roundness, aspect ratio, and rectangular aspect ratio of the structure is used. -A metallographic structure evaluation method for a TB alloy.
(15) A cell in which the R-rich phase has a roundness of 1.0 to 1.4 and has an area of 5 square micrometers or less and 20 or more R-rich phases in 100 square micrometers. The metal structure evaluation method for an RTB-based alloy according to (14), wherein the portion is determined to be a fine R-rich phase region.

(16) A cell part in which 20 or more R-rich phases having an aspect ratio of 1.0 to 5.0 and an area of 5 square micrometers or less are included in 100 square micrometers. Is determined to be a fine R-rich phase region.
(17) A portion in which 100 or more square micrometers contain 20 or more R-rich phases having a square aspect ratio of 1.0 to 5.0 and an area of 5 square micrometers or less. Is determined to be a fine R-rich phase region.
(18) The cells dividing the microstructure image are divided into grid cells by equally spaced straight lines substantially parallel to the solidified surface of the alloy and equally spaced straight lines substantially perpendicular to the solidified surface of the alloy. If the cell determined to be a fine R-rich phase region by the metallographic evaluation method according to any one of (1) to (17) is discontinuous in a direction perpendicular to the solidification surface of the alloy, The metal structure evaluation method for an RTB-based alloy according to (13), wherein all cells from the cell farthest from the solidified surface to the solidified surface are determined to be a fine R-rich phase region.
(19) The cells dividing the microstructure image are divided into grid cells by equally spaced straight lines substantially parallel to the solidified surface of the alloy and equally spaced straight lines substantially perpendicular to the solidified surface of the alloy. 13) When a cell determined to be a fine R-rich phase region by the metal structure evaluation method according to any one of (17) to (17) is discontinuous in a direction perpendicular to a solidified surface of the alloy, From the cells determined to be the fine R-rich phase region, all cells from the two or more continuous cells farthest from the solidified surface to the solidified surface are determined to be the fine R-rich phase region, and the two or more continuous cells are determined to be the fine R-rich phase region. The method of evaluating a metal structure of an RTB-based alloy according to (13), wherein all cells existing alone in the free surface direction are determined not to be in the fine R-rich phase region.
(20) The total area of cells determined to be a fine R-rich phase region by the metallographic evaluation method according to any one of (13) to (19) was divided by the total area of all measured cells. A method for evaluating the structure of an RTB-based alloy in which a value is an area ratio of a fine R-rich phase region. (21) The method for evaluating a metal structure of an RTB-based magnet alloy according to (11) or (13), wherein the digital image is a reflected electron beam image of a scanning electron microscope.
(22) The metallographic structure evaluation method of the RTB-based magnet alloy according to (11) or (13), wherein a threshold is provided for the difference in luminance to determine the R ₂ T ₁₄ B main phase and the R-rich phase. .
It is.

ADVANTAGE OF THE INVENTION According to the manufacturing method of the rare-earth-containing alloy flake of this invention, the volume ratio of a fine R-rich area | region is small, and the homogeneity of the dispersion state of the R-rich phase in an alloy is more favorable than the conventional SC material. Thin sections can be produced with good reproducibility. As a result, the sintered magnet manufactured from the obtained alloy flakes and the bonded magnet manufactured by the HDDR method exhibit superior magnet characteristics as compared with conventional magnets.
Further, according to the metal structure evaluation method of the present invention, it is possible to objectively determine the crystallization and distribution state of the R-rich phase, and it is easy to obtain a rare earth magnet alloy exhibiting an optimum metal structure for each application. There are advantages.

FIG. 1 shows a backscattered electron image when a cross section of a thin section of an Nd—Fe—B alloy (Nd: 31.5 mass%) cast by a conventional SC method is observed with a scanning electron microscope (SEM). In FIG. 1, the left side is the mold surface side, and the right side is the free surface side.
In FIG. 1, the white portion is the Nd-rich phase (the R-rich phase is called Nd-rich phase because R is Nd), and the free surface side (opposite to the casting surface side) from the center of the alloy flake. Side surface), it forms a lamella-like pool in the thickness direction or forms a small pool with a directional shape as if the lamella were divided. However, a region in which the Nd-rich phase is extremely fine and randomly present than other portions is generated on the mold surface side, and the present inventors show that the region is a fine R-rich phase region (R Is also referred to as a fine Nd-rich phase region when the main component is Nd). This fine R-rich phase region usually starts from the mold surface side and extends toward the center. On the other hand, a portion where the fine R-rich phase region does not exist from the center to the free surface side is referred to as a normal portion here.

  In the hydrogen crushing step of the RTB-based alloy flakes during the production of the sintered magnet, hydrogen is absorbed from the R-rich phase and expands into brittle hydride. Therefore, in hydrogen crushing, fine cracks are introduced into the alloy along the R-rich phase or starting from the R-rich phase. In the subsequent pulverization step, the alloy is broken by a large number of fine cracks generated by hydrogen pulverization, so that the finer the dispersion of the R-rich phase in the alloy, the finer the particle size after the fine pulverization. Therefore, the fine R-rich phase region has a strong tendency to crack more finely than the normal part. For example, in an alloy powder manufactured from the normal part, the average particle size is about 3 μm as measured by FSSS (Fisher subsieve sizer). On the other hand, the alloy powder produced from the fine R-rich phase region contains a high proportion of fine powder of 1 μm or less, so that the particle size distribution after the fine pulverization is widened.

  JP-A-09-170055 discloses that the dispersion state of the R-rich phase in an RTB-based alloy can be controlled by controlling the cooling rate after solidification of the molten metal during casting or by heat treatment. It is described in Japanese Unexamined Patent Publication No. Hei 10-36949. However, the cooling rate after solidification or the behavior of the change of the R-rich phase inside the fine R-rich phase region due to the heat treatment is difficult to control, unlike the normal part, and the dispersion of the R-rich phase is unlikely to be coarse and remains fine. It is.

The volume ratio of the fine R-rich phase region can be measured by the following method. FIG. 3 is a reflected electron beam image of the same field of view as that of FIG. 1, but a line is drawn at the boundary between the fine R-rich phase region and the normal part. The boundary between the two regions can be easily determined from the dispersion state of the R-rich phase, and the area ratio of the fine R-rich phase region can be calculated. The area ratio in the cross section of the field of view corresponds to the volume ratio in the alloy. In addition, if an image analysis device is used, it is possible to quickly and univocally obtain the value.
This point will be described later in detail as a metal structure evaluation method, and an outline thereof will be described here.
The shape, size, and density of the R-rich phase in the fine R-rich phase region are different from those of the normal portion. That is, if the density of the fine and nearly spherical R-rich phase has a certain level or more, it can be determined that the R-rich phase region is a fine R-rich phase region. The threshold varies depending on the alloy composition and the image quality of the reflected electron beam image used for image analysis. However, the present inventors have found that for each R-rich phase, the density of the R-rich phase having a roundness of 1 to 1.4 and an area of 5 square microns or less is 20 per 100 square microns. If there is a portion that does not correspond to the standard on the mold surface side of the portion or the portion corresponding to the standard, the portion including the portion is judged to be a fine R-rich phase region, and the reproducibility is improved. And a fine R-rich phase region can be measured. Here, the roundness is a value obtained by dividing (the square of the perimeter) of the target figure by (4π × area), and becomes 1 in a circle, and increases as the shape becomes elongated.
Furthermore, it was confirmed that the volume fraction of the fine R-rich phase region calculated in this way could well explain the characteristics of the alloy structure, the particle size distribution after the fine pulverization, and the effect on the magnetic properties of the sintered magnet. ing.
In the measurement of the volume ratio of the fine R-rich phase region, the change in the amount of the fine R-rich phase region is large between flakes or within the same flake, even if the alloy flakes are simultaneously cast. Therefore, the volume fraction of the fine R-rich phase region of the entire alloy can be calculated by measuring about 5 to 10 or more flakes and taking the average.

FIG. 2 shows a reflected electron beam image of a cross section of the RTB-based alloy flake (Nd 31.5% by mass) of the present invention. In FIG. 2, the left side is the mold surface side, and the right side is the free surface side. A feature of the alloy flake manufacturing method of the present invention is that, in the method for manufacturing a rare earth-containing alloy flake by a strip casting method, the surface roughness of a casting roll is provided by a plurality of linear irregularities formed on the casting surface. Most of them use a casting rotating roll which has an angle of not less than a certain angle with respect to the rotating direction of the casting roll. The alloy flake shown in FIG. 2 was produced using a casting roll having the casting surface of the above configuration and having a surface roughness of 3.5 μm. As shown in FIG. 2, no fine R-rich phase region exists on the mold surface side (left side in FIG. 2), and the dispersion state of the R-rich phase is extremely uniform from the mold surface to the free surface.
On the other hand, the alloy flake of FIG. 1 was produced using a casting rotary roll in which linear irregularities were formed on the casting surface so as to extend substantially parallel to the roll rotation direction, and the surface roughness of the casting surface was reduced. The thickness is almost the same as 3.3 μm, but the volume ratio of the fine R-rich phase region on the left side of the drawing is larger than that of the alloy flake shown in FIG.

The relationship between the direction of the linear irregularities on the surface of the casting roll and the fine R-rich phase region of the alloy flake in the strip casting method can be explained as follows.
When the surface of the casting roll is smooth and has good wettability with the molten alloy, heat transfer from the molten metal to the mold is extremely good (heat transfer coefficient is large), and the mold surface of the alloy is excessively rapidly cooled. You. It is considered that the fine R-rich phase region tends to be generated when the heat transfer coefficient between the mold and the molten metal is large and the mold surface of the alloy is excessively rapidly cooled.

  On the other hand, when fine irregularities are formed on the surface of the casting roll, the surface roughness of the casting roll becomes large. Then, due to its own viscosity, the molten alloy cannot completely enter into the fine irregularities on the surface of the rotary casting roll, causing a non-contact portion, and the heat transfer coefficient decreases. As a result, it is considered that the mold surface side of the alloy is not excessively rapidly cooled, and the generation of the fine R-rich phase region can be suppressed.

  Here, if attention is further paid to the shape of the unevenness, when the shape is linear, each of the contact portion and the non-contact portion between the molten metal and the roll tends to exist continuously along the linear unevenness. Therefore, the internal structure also tends to have continuity along the irregularities. In this case, when a fine R-rich phase region is generated in a certain linear uneven portion for some reason, the probability that a fine R-rich phase region is generated over the entire linear portion becomes extremely high.

However, even with the same linear unevenness, the extending direction of the unevenness is in a direction intersecting with the rotating direction of the casting rotary roll, like the casting rotary roll applied to the manufacturing method of the present invention. When formed, it was confirmed that the continuity of the internal structure of the alloy flake along the extending direction of the unevenness can be reduced, and the generation of the fine R-rich phase region can be suppressed.
The relationship between the direction of the linear irregularities formed on the casting surface and the internal structure formed on the alloy flake is considered as follows. That is, when the extending direction of the unevenness is parallel or nearly parallel to the rotating direction of the rotating roll, when the molten metal contacts the rotating roll surface and enters the gap of the unevenness, the atmosphere gas in the recessed portion is pushed out in the rotating direction. As a result, the contact area between the rotating roll surface and the molten metal increases.
On the other hand, when the extending direction of the unevenness is set to the direction intersecting the roll rotation direction, the atmosphere gas in the concave portion of the rotating roll surface tends to be trapped by the molten metal as the angle between the two increases. And the excessive contact between the roll surface and the molten metal can be suppressed. Therefore, even if the surface roughness of the casting surface is the same, the generation of the fine R-rich phase region tends to be suppressed as the angle between the extending direction of the linear unevenness and the roll rotation direction increases. . In addition, since the continuity of the internal structure along the extending direction of the unevenness is also lower than when the rotation direction and the extending direction of the unevenness match, even if a fine R-rich phase region is generated, it can be expanded. Sex is reduced.

In the present invention, the surface roughness of the casting roll is 3 μm or more and 60 μm or less in ten-point average roughness (Rz), and the surface roughness of the casting surface is provided by a plurality of substantially linear irregularities formed on the casting surface. A casting rotary roll, wherein at least 30% of the substantially linear unevenness extends in a direction forming an angle of 30 ° or more with the roll rotation direction. .
Preferably, 30% or more of the linear projections and depressions are formed so as to extend in a direction forming an angle of 45 ° or more with the roll rotation direction, or 50% or more of the linear projections and depressions. A casting roll is used in which the irregularities extend in a direction forming an angle of 30 ° or more with the roll rotation direction.
More preferably, a casting rotating roll is used in which 50% or more of the linear irregularities extend in a direction forming an angle of 45 ° or more with the roll rotating direction.
Here, the angle between the direction in which the unevenness extends and the roll rotating direction in the present invention is 0 ° when the extending direction of the unevenness is parallel to the roll rotating direction, and the extending direction of the unevenness is parallel to the roll width direction. Is defined as 90 °.
As a result, even when the surface roughness is smaller than when the linear irregularities are parallel to the roll rotation direction, the effect of homogenizing the structure by reducing the fine R-rich phase can be obtained. This makes it possible to reduce the amount of cutting when adjusting the roll surface and increase the life of the casting roll. In addition, since it is hard to be affected by the difference in surface roughness, it is possible to simplify the management standard of the roll surface state.

Although the conventional SC method contained alloy flakes having a homogeneous structure as shown in FIG. 2 to some extent, flakes containing a large amount of fine R-rich phase regions as shown in FIG. 1 are also generated at the same time. As a result, there was a problem in the homogeneity of the structure throughout the alloy. Such variations in the alloy structure produced by the conventional SC method are considered to be caused by subtle differences in the contact state between the roll surface and the melt, such as the surface state of the casting roll, the supply state of the melt, and the atmosphere. Can be The unevenness of a suitable size on the surface of the rotary casting roll suppresses excessive heat transfer when the molten metal solidifies, and can suppress the generation of the fine R-rich phase region with good reproducibility. Furthermore, in the present invention, the extension direction of the linear irregularities on the roll surface is formed at an angle with respect to the rotation direction of the casting rotary roll, thereby enhancing the effect of suppressing generation of the fine R-rich phase region. Thus, the effect can be obtained even with a relatively small surface roughness. As a result, the yield of alloy flakes having a homogeneous structure as shown in FIG. 2 can be further increased.
In addition, the linear unevenness of the present invention is not necessarily required to be continuous, and may be intermittent. Further, it may be curved or linear. Usually, pure copper or a copper alloy is preferable as a roll material. The present invention is also possible when a coating is applied to the casting surface layer.

Further, details of the present invention will be described.
(1) Strip casting method The present invention relates to a rare-earth-containing alloy flake. Here, casting of an RTB-based alloy by a strip casting method will be described.
FIG. 4 shows a schematic view of an apparatus for casting by the strip casting method. Usually, the RTB-based alloy is melted using the refractory crucible 1 in a vacuum or an inert gas atmosphere due to its active properties. After the melt of the melted alloy is held at 1350-1500 ° C. for a predetermined period of time, the casting rotating roll 3 whose inside is water-cooled through a tundish 2 provided with a rectifying mechanism and a slag removing mechanism as necessary. Supplied to The supply speed of the molten metal and the number of rotations of the rotating roll are appropriately controlled in accordance with the required alloy thickness. Generally, the rotation speed of the rotating roll is about 0.5 to 3 m / s in terms of peripheral speed. Copper or a copper alloy is suitable for the material of the casting roll because of its good thermal conductivity and easy availability. Depending on the material of the rotating roll and the surface condition of the roll, metal easily adheres to the surface of the casting rotating roll, so if a cleaning device is installed as necessary, the quality of the R-T-B alloy is stable. I do. The alloy 4 solidified on the rotating roll separates from the roll on the opposite side of the tundish and is collected in the collection container 5. By providing a heating and cooling mechanism in this collection container, the state of the R-rich phase structure in the normal part can be controlled.

  The thickness of the alloy flake produced by the production method according to the present invention is preferably 0.1 mm or more and 0.5 mm or less. If the thickness of the alloy flakes is less than 0.1 mm, the solidification rate will increase excessively, the crystal grain size will be too fine, and it will be close to the finely pulverized grain size in the magnetizing process, so the magnet orientation rate and magnetization will decrease. There is a problem of inviting. On the other hand, if the thickness of the alloy flake is larger than 0.5 mm, problems such as a decrease in the dispersibility of the R-rich phase due to a decrease in the solidification rate and precipitation of α-Fe are caused.

(2) Surface Roughness of Casting Surface of Rotating Roll for Casting In the present invention, when casting an RTB-based magnet alloy by a strip casting method, the surface roughness of the casting surface of the rotating roll for casting is reduced to 10%. The point average roughness (Rz) is 3 μm or more and 60 μm or less.
Here, the surface roughness is measured under the conditions shown in JIS B 0601 “Definition and Display of Surface Roughness”, and the ten-point average roughness (Rz) is also defined therein. Specifically, first, a curve (roughness curve) obtained by removing a surface undulation component longer than a predetermined wavelength by a phase-compensating high-pass filter or the like from a cut (cross-sectional curve) obtained by cutting a plane perpendicular to the measurement surface. Ask. From the roughness curve, a reference length is extracted in the direction of the average line, and from the average line of the extracted portion, the average value of the absolute values of the altitudes (Yp) of the highest to fifth peaks and the lowest value The sum of the absolute values of the altitudes (Yv) of the valley bottoms from the valley bottom to the fifth is called ten-point average roughness (Rz). For measurement parameters such as the reference length, standard values for the surface roughness are specified in the JIS.
The surface roughness may vary greatly and should be measured at least at five points and the average value should be used.

(3) The shape of the unevenness of the roll casting surface The surface roughness is mainly brought about by a plurality of linear unevennesses formed on the roll surface. Are formed so as to extend in a direction at an angle. Specifically, 30% or more of the linear unevenness has an angle of 30 ° or more from the roll rotation direction. Preferably, 30% or more of the linear unevenness has an angle of 45 ° or more from the roll rotation direction, or 50% or more of the linear unevenness has an angle of 30 ° or more from the roll rotation direction. Is to have. More preferably, 50% or more of the linear unevenness has an angle of 45 ° or more from the roll rotation direction.
When the extending direction of the linear irregularities is parallel or nearly parallel to the rotation direction, when the molten metal comes into contact with the roll surface and enters into the gap of the surface irregularities, it becomes easier to push out the atmosphere gas in the concave portion, and the roll surface And the contact area increases. However, as the angle between the direction in which the unevenness extends and the rotation direction increases, the tendency of the atmosphere gas in the recesses to be trapped by the molten metal increases, so that excessive contact with the roll surface can be suppressed.
Therefore, even if the surface roughness is the same, as the angle between the extending direction of the linear unevenness and the roll rotation direction increases, or the linear unevenness has such a large angle with the roll rotation direction. As the number increases, the generation of fine R-rich phase regions is suppressed. In addition, since the continuity of the structure in the uneven direction is also lower than when the rotation direction and the extending direction of the unevenness coincide with each other, even if a fine R-rich phase region is generated, the possibility of expansion is low.

A plurality of linear irregularities formed on the casting surface have an angle of 30 ° or more from the roll rotation direction, whereby at least 30% of the linear irregularities effectively suppress the fine R-rich region described above. Can be. If it is less than 30%, the effect is small.
The linear unevenness on the surface of the casting rotary roll according to the present invention is not necessarily required to be continuous, and may be intermittent. Further, it may be curved or linear.
Such linear irregularities may be caused by a device having a rotating polishing paper, a rotating wire brush, or a belt polishing device in which the polishing paper moves linearly, even in a polishing direction and a roll rotation direction. It can be formed by giving an angle to.

In the present invention, the homogenization effect of the structure can be obtained even if the surface roughness is relatively small due to the effect of the linear unevenness extending at an angle to the rotation direction of the casting roll.
However, when the surface roughness is 3 μm or less, the effect of the unevenness of the surface of the casting roll cannot be obtained, and the heat transfer coefficient is large due to good contact with the molten metal. As a result, a fine R-rich phase region is easily generated in the alloy.
On the other hand, when the surface roughness of the casting rotary roll exceeds 60 μm, the alloy flakes bite into the roll surface, making it difficult for the alloy flakes to peel off, which may cause troubles such as breaking the tundish. Therefore, the surface roughness of the casting rotary roll is 60 μm or less.

(4) Volume ratio of fine R-rich phase region in alloy When manufacturing an RTB-based alloy by the production method of the present invention, the volume ratio of the fine R-rich phase region in the alloy should be 20% or less. Is preferred. As a result, the particle size distribution of the alloy powder after the pulverization in the process of the sintered magnet becomes narrow and uniform, so that a homogeneous sintered magnet having no variation in characteristics can be obtained.

(5) Manufacturing method of alloy powder for rare earth sintered magnet and rare earth sintered magnet From a rare earth-containing alloy flake made of an RTB-based alloy used as a raw material for a magnet cast according to the present invention, pulverization, molding, Through the sintering step, an anisotropic sintered magnet with high characteristics can be manufactured.

The pulverization of the alloy flake is usually performed in the order of hydrogen pulverization and fine pulverization, and an alloy powder of about 3 μm (FSSS) is produced.
Here, the hydrogen disintegration is divided into a pre-process hydrogen storage process and a post-process dehydrogenation process. In the hydrogen storage step, hydrogen is stored mainly in the R-rich phase of the alloy flakes in a hydrogen gas atmosphere at a pressure of 266 hPa to 0.3 MPa · G, and the R-rich phase is formed by the R-hydride generated at this time. Utilizing the volume expansion, the alloy flake itself is finely divided or innumerable fine cracks are generated. This hydrogen storage is carried out at a temperature in the range of room temperature to about 600 ° C. In order to increase the volume expansion of the R-rich phase and efficiently split it, the pressure of the hydrogen gas atmosphere should be increased and the room temperature to about 100 ° C. It is preferable to carry out within the range. The preferred processing time is one hour or more. Since the R-hydride produced in this hydrogen storage step is unstable in the atmosphere and easily oxidized, after the hydrogen storage treatment, dehydration is performed by holding the alloy flakes in a vacuum at about 200 to 600 ° C. and 1.33 hPa or less. It is preferable to perform elementary treatment. By this treatment, it is possible to change to R-hydride which is stable in the atmosphere. The preferred treatment time of the dehydrogenation treatment is 30 minutes or more. When atmosphere control for preventing oxidation is performed in each step from hydrogen storage to sintering, dehydrogenation treatment can be omitted.

  The RTB-based alloy flakes produced by the strip casting method of the present invention are characterized in that the R-rich phase is uniformly dispersed. The preferred average value of the interval of the R-rich phase depends on the pulverized particle size in the magnet manufacturing process, but is generally from 3 μm to 8 μm. In hydrogen cracking, cracks are introduced along the R-rich phase or starting from the R-rich phase. Therefore, the effect of the R-rich phase uniformly and finely dispersed in the alloy can be maximized by crushing hydrogen and then finely pulverizing, and the alloy powder having a very narrow particle size distribution can be efficiently produced. It is possible to produce. When a sintered magnet is manufactured without performing the hydrogen crushing step, the characteristics of the manufactured sintered magnet are inferior. (M. Sagawa et al. Proceeding of the 5th International Conference on Advanced Materials, Beinging China (1999))

Fine pulverization refers to pulverizing an RTB-based alloy flake to about 3 μm (FSSS). As a pulverizing device for fine pulverization, a jet mill device is most suitable because of high productivity and a narrow particle size distribution. By using the alloy flakes having a small fine R-rich phase region of the present invention, an alloy powder having a narrow particle size distribution can be produced with high efficiency and high stability.
The atmosphere during the pulverization is an inert gas atmosphere such as an argon gas or a nitrogen gas. 2% by mass or less, preferably 1% by mass or less of oxygen may be mixed into these inert gases. Thereby, the pulverization efficiency is improved, and the oxygen concentration of the pulverized alloy powder can be set to 1000 to 10000 ppm, and the alloy powder can be appropriately stabilized. At the same time, abnormal growth of crystal grains when sintering the magnet can be suppressed.

  When the above alloy powder is molded in a magnetic field, the powder is lubricated with zinc stearate or the like to reduce the friction between the alloy powder and the inner wall of the mold and to reduce the friction between the powder and improve the orientation. It is preferable to add an agent. A preferable addition amount is 0.01 to 1% by mass. The lubricant may be added before or after the pulverization, but it is preferable that the lubricant is sufficiently mixed using an V-type blender or the like in an inert gas atmosphere such as an argon gas or a nitrogen gas before molding in a magnetic field.

The alloy powder pulverized to about 3 μm (FSSS) is press-molded by a molding machine in a magnetic field. The mold is made by combining a magnetic material and a non-magnetic material in consideration of the direction of the magnetic field in the cavity. The molding pressure is preferably 0.5 to 2 t / cm2. The magnetic field in the cavity during molding is preferably 5 to 20 kOe. The atmosphere at the time of molding is preferably an inert gas atmosphere such as an argon gas or a nitrogen gas. However, in the case of the above-mentioned oxidation-resistant powder, it can be performed in the air.
Molding can also be performed by cold isostatic pressing (CIP) or pseudo isostatic pressing (RIP: Rubber Isostatic Press) using a rubber mold. CIP and RIP are hydrostatically compressed, so that the orientation is not disturbed at the time of molding, the orientation ratio can be increased as compared with the die molding, and the maximum magnetic energy product can be increased.

Sintering of the molded body is performed at 1000 to 1100 ° C. The sintering atmosphere is preferably an argon gas atmosphere or a vacuum atmosphere of 1.33 × 10 −2 hPa or less. The holding time at the sintering temperature is preferably 1 hour or more. During sintering, it is necessary to remove as much as possible the lubricant contained in the molded body and the hydrogen contained in the alloy powder before reaching the sintering temperature. A preferable condition for removing the lubricant is to maintain the lubricant at 300 to 500 ° C. for 30 minutes or more in a vacuum of 1.33 × 10 −2 hPa or less or in a reduced Ar flow atmosphere. Further, a preferable condition for removing hydrogen is to hold at 700 to 900 ° C. for 30 minutes or more in a vacuum of 1.33 × 10 −2 hPa or less.

  After the sintering is completed, heat treatment can be performed at 500 to 650 ° C. as needed to improve the coercive force of the sintered magnet. A preferable atmosphere in this case is an argon gas atmosphere or a vacuum atmosphere, and a preferable holding time is 30 minutes or more.

  In addition, the R-T-B based alloy flakes for rare earth magnets produced by the production method of the present invention, in which the generation of the fine R-rich region is suppressed, can be suitably used for producing bonded magnets in addition to sintered magnets. it can. Hereinafter, a case where a bonded magnet is manufactured from alloy flakes manufactured by the method for manufacturing alloy flakes for rare earth magnets of the present invention will be described.

  The RTB-based alloy flake of the present invention is first heat-treated as necessary. The purpose of the heat treatment is to remove α-Fe from the alloy and to coarsen the crystal grains. To prepare an alloy powder for the production of a bonded magnet, an HDDR (Hydrogenation Disposition Decomposition Recombination) process is performed. However, α-Fe present in the alloy cannot be erased in the HDDR process and causes a decrease in magnetism. It becomes. Therefore, α-Fe needs to be erased before performing the HDDR process.

  The average particle size of the alloy powder for the bonded magnet is 50 to 300 μm, which is much larger than that of the alloy powder for the sintered magnet. In the HDDR method, the crystal orientation of the original alloy coincides with the orientation of the recombined submicron crystal grains with a certain distribution. Therefore, if two or more crystal grains having different crystal orientations in the alloy flakes of the raw material are included in one bonded magnet alloy powder, the alloy powder will include a region in which the crystal orientation is greatly different, The orientation ratio of the magnet decreases, and the maximum magnetic energy product decreases. To avoid this, the crystal grain size in the alloy flakes is preferably larger. In an alloy cast by a rapid solidification method such as a strip cast method, the crystal grain size tends to be relatively small. Therefore, the coarsening of the crystal grains by heat treatment is effective for improving the magnet properties.

  There are many reports on a method for producing an alloy powder for a bonded magnet by the HDDR method (for example, T. Takeshita et al, Proc. 10th Int. Works on RE magnets and their application, Kyoto, Vol. 1989, Vol. 1989). ). The production of the alloy powder by the HDDR method is performed as follows.

  When the raw RTB alloy flakes are heated in a hydrogen atmosphere, the magnetic phase R2T14B phase is decomposed into three phases of α-Fe, RH2, and Fe2B at about 700 to 850 ° C. Next, when the atmosphere is switched to an inert gas atmosphere or a vacuum atmosphere at the same temperature to remove hydrogen, the decomposed phase is recombined with the R2T14B phase having a submicron crystal grain size. At this time, if the composition of the alloy and the processing conditions are appropriately controlled, the axis of easy magnetization of each recombined R2T14B phase (R2T14B phase C axis) becomes substantially parallel to the C axis of the R2T14B phase in the raw material alloy before decomposition. An anisotropic magnet powder in which the directions of the axes of easy magnetization of the fine crystal grains are uniform can be obtained.

  The alloy that has been subjected to the HDDR treatment may be pulverized to about 50 to 300 μm to obtain an alloy powder, and then mixed with a resin and subjected to compression molding, injection molding, or the like to form a bonded magnet.

  The fine R-rich phase region has a strong tendency to be pulverized during the HDDR treatment as in the above-described hydrogen crushing treatment. The properties of the magnetic powder according to the HDDR method decrease as the particle size decreases. Therefore, the RTB-based alloy of the present invention in which the generation of the fine R-rich phase is suppressed can be suitably used for the production of the magnetic powder for the bonded magnet in the HDDR process.

Recently, it has been reported that the homogeneity of the structure is improved by adjusting the surface roughness of the roll outer peripheral surface to a certain range of Sm / Ra and Sm in the production of rare earth alloys (Japanese Patent Application Laid-Open No. 2002-59245, JP-A-9-1296). However, they are intended to suppress a change in the structure in the width direction of the strip and to prevent a decrease in cooling rate at the end of the strip. Further, the shape of the unevenness that causes the surface roughness is not particularly defined.
On the other hand, the present invention is intended to suppress the structural change in the thickness direction of the alloy flakes, that is, from the roll surface side to the free surface side, and to homogenize the structure, and introduce a fine R-rich phase region as a measure of homogeneity. However, the specific volume ratio is clearly shown, and is completely different from JP-A-2002-59245 or JP-A-9-1296.
In Japanese Patent Application Laid-Open No. 4-28457, the roughness of the roll surface is set to 0.05 to 1.5 [mu] m in Ra to reduce the variation in crystal grain size. However, it relates to the rapid quenching with a large roll speed, and it is confirmed that the surface roughness of the casting roll of the present invention is higher than that of the casting roll surface, although the measurement standard is different.

Next, the metallographic evaluation method of the present invention will be described.
The metallographic structure evaluation method of the present invention measures the interval between R-rich phases in a rare-earth magnet alloy and measures the fine R-rich phase region to determine the distribution state of the R-rich phase.
First, a metal structure of a material to be used for evaluation is observed with an electron microscope, and a reflected electron beam image is taken into a computer as a digital image. It is suitable that the digital image has, for example, 1470 vertical pixels × 1960 horizontal pixels × 255 gradations of brightness. The image quality (brightness, contrast) of the image is most important for performing the tissue evaluation.
Thereafter, measurement is performed by operating on the computer screen.

[Measurement of R-rich phase interval]
To measure the distance between the R-rich phase, draw a straight line L ₁ of the length L on a digital image of the reflected electron image as shown in FIG. Since the cast structure having directionality, lines L ₁ is preferably pulled parallel to the solidification surface 10. Then, count the number N of intersections P of the straight line L ₁ and the R-rich phase 12 in the metal structure. Since the R-rich phase is brightly displayed on the screen, a threshold value is set for the brightness, and points at which the points below the threshold value change to points above the threshold value are counted.
Thereafter, a value r obtained by dividing the length L of the straight line by the number N of points crossing the R-rich phase is defined as the interval of the R-rich phase. That is, r = L / N.
The R-rich phase usually extends in a needle shape from the solidified surface toward the free surface, and is finely distributed near the solidified surface as the distance from the solidified surface increases. Naturally, the interval of the R-rich phase also differs depending on the location. Therefore, a plurality of straight lines of length L (L ₁ , L ₂ , L ₃ ,... L _N ) are drawn to obtain a large number of r values. The average value and standard deviation of the intervals can also be obtained, and more accurate tissue evaluation can be performed. It is preferable that a plurality of straight lines (L ₁ , L ₂ , L ₃ ,..., L _N ) used at this time are also drawn in parallel with the solidification surface 10 as shown in FIG.

[Measurement of fine R-rich phase]
Next, measurement of the fine R-rich phase region will be described. The fine R-rich phase is a structure containing a large number of fine and nearly spherical metal structures rich in rare earth elements (R), which are generated by excessive rapid solidification near the solidification surface. The digital image in the vicinity of the solidified surface is divided and divided by a mesh, and the shape, size, and number of R-rich phases contained in each cell are measured, and the form and distribution of the R-rich phase are evaluated. It is determined whether or not the cell is in a fine R-rich phase region.
First, the digital image vertical and horizontal lines (x _{n, y n)} divided into a number of cells divided by mesh of. For example, in FIG. 6, straight lines (y ₁ , y ₂ ,..., Y ₂₀ ) are drawn by dividing the screen into 20 equal parts with a fixed length. On the other hand, the straight line (x ₁ , x ₂ ,..., X ₂₀ ) is drawn by dividing the measurement region into 20 parts because the range of the region to be measured from the solidified surface varies. The cell is divided into a total of 400 cells, and the shape, size, and number of R-rich phases in each cell are measured.
Here, vertical and horizontal lines constituting the mesh (x _{n, y n)} is delimit the grid cell substantially vertical equally spaced straight lines substantially coagulation surface parallel equally spaced straight lines in a coagulation surface Is preferred.

As shown in FIG. 7, since the R-rich phase 12 appears brightly in the matrix of the dark main phase 11 on the digital image, a threshold value is set for the brightness to determine whether each pixel of the digital image is in the R-rich phase. Is determined. As shown in FIG. 6, R-rich phase pixels in each cell divided by a mesh are counted, and the shape, size, and number of R-rich phases are measured.
Next, among the R-rich phases determined from the brightness, the R-rich phases satisfying the following conditions are counted.
Condition 1): The R-rich phase is approximated to a circle, and the R-rich phase whose roundness is 1 or more and 1.4 or less is counted.
Here, the circularity is (perimeter ² ÷ (4π × area)).
Condition 2): Count R-rich phases having an area of 5 square micrometers or less.
Condition 3): Count R-rich phases that satisfy both conditions 1) and 2).

Actually, the shape of the R-rich phase may be closer to a needle or a square than a circle. Therefore, it is also effective to use an aspect ratio or a rectangular aspect ratio instead of the roundness.
For example, when the aspect ratio is used, 20 or more R-rich phases having an R-rich phase aspect ratio of 1.0 to 5.0 and an area of 5 square micrometers or less in 100 square micrometers are used. The included cell portion is determined to be a fine R-rich phase region.
When the quadrangle approximation is used, an R-rich phase having a square aspect ratio of R-rich phase of 1.0 to 5.0 and an area of 5 square micrometers or less is 20 out of 100 square micrometers. The portion containing more than one is determined to be a fine R-rich phase region.
In FIG. 6, the cells in the hatched portions are the cells determined to be the fine R-rich phase region.

[Determination of fine R-rich phase region]
When the count number of the R-rich phase extracted according to the condition 3) is 20 or more in 100 square micrometers, the cell is determined to be a fine R-rich phase region. In this way, it is determined whether or not the 400 cells in FIG. 6 are in the fine R-rich phase region and mapped. _{S 1,} S 2 of the hatched in FIG. 6, · · · _{S n} is the fine R-rich phase region.
For example, in FIG. 6, a portion adjacent to the solidification surface includes a region that does not include a fine and nearly spherical metal structure due to excessive quenching, and such a region is not determined to be a fine R-rich phase region.
However, the fine R-rich phase region is generated only by excessive rapid solidification, and is generated from the cooling roll side. Therefore, if a fine R-rich phase region exists in a portion away from the solidification surface, the solidification surface side should also be a fine R-rich phase region.

One of the determination methods, for example as in the S ₆ from S ₁ shown in FIG. 6, when the cell where it is determined that the fine R-rich phase region is present discontinuously in a direction perpendicular to the solidification surface, solidification surface All cells from the cell furthest away from the solid surface to the solidification surface should be determined to be a fine R-rich phase region. That is, S ₁ ′, S ₂ ′, S ₃ ′, and S ₄ ′ shown in FIG. 6 that are not determined as the fine R-rich phase region are also regarded as the fine R-rich phase regions, and the regions from S ₁ ′ to S ₆ are considered. It is reasonable to use a fine R-rich phase region.
As another determination method, for example as in S ₁₂ from S ₇ shown in FIG. 6, when the cell where it is determined that the fine R-rich phase region is present discontinuously in a direction perpendicular to the solidification surface, Of the cells determined to be the fine R-rich phase region, all the cells from the two or more continuous cells farthest from the solidified surface to the solidified surface are determined to be the fine R-rich phase region, and the two or more cells are determined to be continuous. There is a method of determining that all cells scattered independently in the free surface direction than the cell to be processed are not in the fine R-rich phase region. That is, S ₅ ′ and S ₆ ′, which are not determined to be fine R-rich phase regions in FIG. 6, are regarded as fine R-rich phase regions, and S ₁₁ and S ₁₂ are not regarded as fine R-rich phase regions. According to this, there is an advantage that it is possible to prevent an overestimation of the fine R-rich phase region, particularly in a fine structure containing high-order dendrites of the R-rich phase. Such a structure contains a fine streaked R-rich phase, but a fine higher-order dendrite partially agglomerated and fractured is determined to be a fine R-rich phase region. Is rarely present.

By employing any of the determination methods described above, the range enclosed by the thick line of S _n from S ₁₃ shown in FIG. 6, also comprise a cell which has not determined that even if the fine R-rich phase region, fine R-rich The cells scattered outside the range surrounded by the thick line are not regarded as fine R-rich phase regions.
Further, a value obtained by dividing the total area ΣSn of the cells determined to be the fine R-rich phase region by the total area S of all the measured cells is defined as the area ratio Q of the fine R-rich phase region. That is, Q = ΣSn / S.
In this way, it is possible to evaluate how the fine R-rich phase region is distributed near the solidified surface of the rare earth magnet alloy.
Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

The alloy composition is such that Nd: 31.5 mass%, B: 1.00 mass%, Co: 1.0 mass%, Al: 0.30 mass%, Cu: 0.10 mass%, and the balance iron. Using a alumina crucible, a raw material containing a mixture of neodymium, metal, ferroboron, cobalt, aluminum, copper, and iron is melted in a high-frequency melting furnace in an atmosphere of 1 atm with argon gas, and the molten metal is strip cast. An alloy flake was produced by casting.
The diameter of the casting roll was 300 mm, the material was pure copper, the inside was water-cooled, and the surface roughness of the casting surface was adjusted to 4.0 μm as a ten-point average roughness (Rz). The surface roughness at this time was mainly caused by linear irregularities provided on the casting surface, and 50% or more of the surfaces had an angle of 45 ° or more from the roll rotation direction. The peripheral speed of the roll during casting was 1.0 m / s, and alloy flakes having an average thickness of 0.30 mm were produced.

After 30 pieces of the obtained alloy flakes were embedded in a resin and polished, a cross section of each alloy flake was taken with a scanning electron microscope (SEM) to take a reflected electron beam image (BEI) at a magnification of 350 times. The photograph was taken as a digital image, and the average R-rich phase interval and the fine R-rich phase region were measured by an image analyzer. Each measurement was specifically calculated by the following method.
First, a method for measuring the R-rich phase interval will be described.
For each cross-sectional structure, straight lines substantially parallel to the alloy surface are drawn at intervals of 10 μm, and the R-rich phase interval is determined for each straight line. At that time, a portion within 10 μm from both surfaces was polished and removed from the analysis. Therefore, it was possible to obtain data of the R-rich phase interval in a number smaller than one tenth to two or three of the thickness for each cross-sectional structure.
The average R-rich phase interval was 4.9 μm as an average value of all the R-rich phase intervals obtained by analyzing each cross-sectional structure.

Next, the variation of the R-rich phase interval was evaluated. Two methods were used to evaluate the variation.
One method was the standard deviation of all R-rich phase intervals used in the calculation of the average R-rich phase interval above, which was 0.78 μm. This represents a variation in micro-R-rich phase spacing inside each slab of the alloy. Here, it is referred to as microstructural change.
In another method, first, an average value of the R-rich phase interval is obtained for each cross-sectional structure. In this example, the average R-rich phase interval is calculated for each of the 30 cross-sectional structures. Since the structure of each slab changes depending on the solidification rate or the cooling rate after solidification, the average R-rich phase interval between the slabs also differs. Therefore, the average of 30 R-rich phase intervals also have some variation, which indicates a macro-scale variation of the R-rich phase interval between the slabs, and is referred to as a macrostructural change. The standard deviation of the mean R-rich phase intervals of the 30 pieces was 0.40 μm.

In the fine R-rich phase region, each cross-sectional structure was divided into 20 × 20 cells by a group of equally spaced straight lines substantially parallel to the surface and a group of equally spaced straight lines perpendicular thereto. For each cell, when the roundness of the R-rich phase existing inside the cell is 1.0 to 1.4 and the area is 5 square micrometers or less, 20 or more cells are included in 100 square micrometers. First, the mesh was defined as a fine R-rich phase region. The fine R-rich phase region was slightly present in the vicinity of the solidified surface, and its volume ratio was 1.7%.
The determination of the fine R-rich phase region was performed by a method in which 20 or more R-rich phases having an aspect of 1.0 to 5.0 and an area of 5 square micrometers or less were included in 100 square micrometers. Of the fine R-rich phase region was 1.9%. Further, a method for forming a fine R-rich phase region by a method in which 20 or more R-rich phases each having a square aspect ratio of 1.0 to 5.0 and an area of 5 square micrometers or less are included in 100 square micrometers. The volume ratio was 1.6%.

(Comparative Example 1)
The raw materials were blended in the same composition as in Example 1, and melting and casting by the SC method were performed in the same manner as in Example 1. However, the surface roughness of the surface of the casting roll was 4.0 μm in terms of ten-point average roughness (Rz), had linear irregularities substantially parallel to the roll rotation direction, and was inclined with respect to the rotation direction. Irregularities were substantially absent.
As a result of evaluating the R-rich phase interval of the obtained alloy flakes in the same manner as in Example 1, the average R-rich phase interval was 5.8 μm, the microstructural change was 1.33 μm, and the macrostructural change was 0.88 μm. Was.
On the other hand, the fine R-rich phase region was evaluated in the same manner as in Example 1. However, not only the solidification surface side but also the internal cells were determined to be the fine R-rich phase region. In addition, since cells determined to be a fine R-rich phase region partially existed discontinuously, all cells from two or more continuous cells farthest from the solidification surface to the solidification surface were removed from the fine R-rich phase region. And the volume ratio was 25%.

(Comparative Example 2)
The raw materials were blended in the same composition as in Example 1, and melting and casting by the SC method were performed in the same manner as in Example 1. However, the surface roughness of the surface of the rotary casting roll was 100 μm in terms of ten-point average roughness (Rz), and the surface roughness was mainly due to linear irregularities imparted to the casting surface as in Example 1. And more than 50% of them had an angle of 45 ° or more from the roll rotation direction.
Then, during the casting, a part of the metal made one round without separating from the roll, came into contact with the tundish, and its front end was broken, so the casting operation was stopped.

Next, an example in which a sintered magnet is manufactured will be described.
The alloy flake obtained in Example 1 was pulverized with hydrogen and pulverized with a jet mill. The condition of the hydrogen storage step, which is a step before the hydrogen disintegration step, was kept at 100% hydrogen atmosphere and 2 atm for 1 hour. The temperature of the metal piece at the start of the hydrogen storage reaction was 25 ° C. The condition of the dehydrogenation step, which is a post-step, was maintained at 500 ° C. for 1 hour in a vacuum of 0.133 hPa. To this powder, 0.07% by mass of zinc stearate powder was added, mixed sufficiently in a 100% nitrogen atmosphere by a V-type blender, and then finely pulverized by a jet mill. The pulverizing atmosphere was a nitrogen atmosphere mixed with 4000 ppm of oxygen. Thereafter, the mixture was again sufficiently mixed in a 100% nitrogen atmosphere by a V-type blender. The obtained powder had an oxygen concentration of 2500 ppm, and from the analysis of the carbon concentration of the powder, it was calculated that the zinc stearate powder mixed with the powder was 0.05% by mass. Further, as a result of measurement with a laser diffraction type particle size distribution analyzer, the average particle size D50 was 5.11 μm, D10 was 1.90 μm, and D90 was 8.60 μm.

  Next, the obtained powder was press-molded in a 100% nitrogen atmosphere using a molding machine in a horizontal magnetic field. The molding pressure was 1.2 t / cm 2, and the magnetic field in the cavity of the mold was 15 kOe. The obtained molded body was kept at 500 ° C. for 1 hour in a vacuum of 1.33 × 10 −5 hPa, and then kept at 800 ° C. for 2 hours in a vacuum of 1.33 × 10 −5 hPa. It was sintered at 1050 ° C. for 2 hours in a vacuum of 33 × 10 −5 hPa. The sintered density was 7.5 g / cm3 or more, which was a sufficiently large density. Further, this sintered body was heat-treated at 560 ° C. for 1 hour in an argon atmosphere to produce a sintered magnet.

  Table 1 shows the results of measuring the magnetic properties of the sintered magnet using a DC BH curve tracer. Table 1 also shows the oxygen concentration and particle size of the fine powder of the raw material of the sintered magnet.

(Comparative Example 3)
The alloy flake obtained in Comparative Example 1 was pulverized in the same manner as in Example 2 to obtain a fine powder.
Further, through the same molding and sintering steps as in Example 2, a sintered magnet was produced.

  Table 1 shows the results of measuring the magnetic properties of the sintered magnet produced in Comparative Example 3 using a direct current BH curve tracer. Table 1 also shows the oxygen concentration and particle size of the fine powder of the raw material for the sintered magnet of Comparative Example 3.

  As shown in Table 1, since D10 is smaller in Comparative Example 3 than in Example 2, it can be seen that the ratio of very fine powder smaller than about 1 μm is large. Such very fine particles are easily oxidized, and the oxygen concentration of the fine powder in Comparative Example 3 is slightly higher than that in Example 2. It is considered that the magnetic properties of the magnet of Comparative Example 3 are lower than those of Example 2 mainly due to an increase in oxygen concentration and inhomogeneity of the crystal structure.

Next, an example in which a bonded magnet is manufactured will be described.
The raw materials were blended such that the alloy composition was 28.5% by mass of Nd, 1.00% by mass of B, 10.0% by mass of Co, 0.5% by mass of Ga, and the balance of iron. Under the conditions, an alloy flake was cast by the SC method.
The obtained alloy flakes were evaluated in the same manner as in Example 1. As a result, the volume ratio of the fine R-rich phase region was 3% or less, and α-Fe was not included.

After holding the above alloy flakes in hydrogen at 1 atm at 820 ° C. for 1 hour, an HDDR process was performed in which the alloy flakes were held at vacuum at the same temperature for 1 hour. The obtained alloy powder was pulverized with a brown mill to 150 μm or less, added with 2.5% by mass of an epoxy resin, and compression-molded by applying a magnetic field of 1.5 T to obtain a bonded magnet. Table 1 shows the magnetic properties of the obtained bonded magnets.
Shown in

(Comparative Example 4)
The raw materials were blended in the same composition as in Example 3, and melting and casting by the SC method were performed in the same manner as in Comparative Example 1. As a result of evaluating the obtained alloy flakes in the same manner as in Example 1, the volume ratio of the fine R-rich phase region was 30%.

  Next, using the alloy flake obtained in Comparative Example 4, a bonded magnet was produced in the same manner as in Example 3. Table 1 shows the magnetic properties of the obtained bonded magnet.

  Table 1 shows that the bonded magnets of Example 3 and Comparative Example 4 have excellent magnetic properties of Example 3. In Comparative Example 4, since the volume ratio of the fine R-rich region is high and the amount of relatively fine particles of 50 μm or less after HDDR treatment or pulverization is large, it can be estimated that the magnetism is low.

ADVANTAGE OF THE INVENTION According to the manufacturing method of the rare-earth-containing alloy flake of this invention, the volume ratio of a fine R-rich phase area | region is small, and the homogeneity of the dispersion state of the R-rich phase in an alloy is more favorable than the conventional SC material. Alloy flakes can be manufactured with good reproducibility. As a result, the sintered magnet manufactured from the obtained alloy flakes and the bonded magnet manufactured by the HDDR method exhibit superior magnet characteristics as compared with conventional magnets. Thus, it is very important to contribute to the development of industry through the development of higher performance magnets.
Further, according to the metallographic evaluation method of the present invention, it is extremely easy to more objectively determine a more preferable rare earth magnet, which can greatly contribute to the magnet industry.

It is a figure which shows the cross-sectional structure of the alloy flake for rare earth magnets containing the fine R rich phase manufactured by the conventional SC method. It is a figure showing the section organization of the alloy flakes for rare earth magnets concerning the present invention. FIG. 2 is a diagram in which a line is drawn at a boundary between a fine R-rich region and a normal portion in the sectional structure of FIG. It is a schematic diagram of the casting apparatus of the strip cast method. FIG. 4 is a diagram illustrating a method for measuring an R-rich phase interval. FIG. 3 is a diagram illustrating a method for measuring a fine R-rich phase region. It is a figure explaining the reflected electron beam image of the alloy for rare earth magnets.

Explanation of reference numerals

1 ... refractory crucible, 2 ... tundish, 3 ... rotating roll for casting, 4 ... alloy, 5 ... capture Collection container, 10: solidified surface, 11: main phase, 12: R-rich phase

Claims (22)

  In the method for producing a rare-earth-containing alloy flake by a strip casting method, a plurality of substantially linear irregularities are formed on a casting surface, and the surface roughness given by the substantially linear irregularities is 3 μm in ten-point average roughness (Rz). It is characterized by using a casting rotary roll in which the direction of extension of at least 30% of the substantially linear irregularities is at least 30 ° with respect to the roll rotation direction. Method for producing rare earth-containing alloy flakes.   2. The casting rotating roll according to claim 1, wherein the extending direction of at least 30% of the plurality of substantially linear irregularities is a direction forming an angle of 45 ° or more with the roll rotating direction. Production method of rare earth-containing alloy flakes.   2. The casting roll according to claim 1, wherein at least 50% of the plurality of substantially linear irregularities extend at an angle of 30 [deg.] Or more with the roll rotation direction. Production method of rare earth-containing alloy flakes.   The casting roll according to claim 1, wherein the direction of extension of 50% or more of the plurality of substantially linear irregularities is a direction that forms an angle of 45 ° or more with the roll rotation direction. 4. The method for producing a rare earth-containing alloy flake according to any one of the above items 3.   When producing a rare earth-containing alloy flake by a strip casting method, an RTB system used for a rare earth magnet (where R is at least one kind of rare earth element including Y, and T is a transition which essentially requires Fe The method for producing a rare earth-containing alloy flake according to any one of claims 1 to 4, wherein the metal and B are boron.) A rare earth-containing alloy flake comprising an alloy is produced.   6. An alloy flake for a rare earth magnet, manufactured by the manufacturing method according to claim 5, wherein a volume ratio of a fine R-rich phase region in the alloy is 20% or less.   An alloy powder for a rare-earth sintered magnet produced by subjecting the alloy flake for a rare-earth magnet produced by the method according to claim 5 to a hydrogen disintegration step, followed by jet milling.   A rare earth sintered magnet produced from the alloy powder for a rare earth magnet according to claim 7 by a powder metallurgy method.   An alloy powder for a bonded magnet manufactured by a HDDR method using the alloy flake for a rare earth magnet manufactured by the method according to claim 5.   A bonded magnet produced using the bonded magnet alloy powder according to claim 9. The microstructure of the cross section of the RTB-based magnet alloy is captured as a digital image, a straight line having a length (L) substantially parallel to the solidified surface of the alloy is drawn on the microstructure image, and R ₂ T ₁₄ crossing the straight line is drawn. The two phases are determined from the difference in luminance between the B main phase and the R rich phase, and the number of times that the luminance on the straight line changes from the luminance determined as the R ₂ T ₁₄ B main phase to the luminance determined as the R rich phase ( N), a value (L / N) obtained by dividing the length of the straight line (L) by R as an R-rich phase interval (r). The R-T-B magnet according to claim 11, wherein a plurality of the straight lines are used to calculate an average value and a standard deviation of the R-rich phase interval from the R-rich phase interval obtained from each straight line. Metal structure evaluation method for alloys. The microstructure of the cross section of the RTB-based magnet alloy is divided into a digital image and the microstructure image by cells having an appropriate area, and both the R ₂ T ₁₄ B main phase and the R-rich phase are determined from the difference in luminance in each cell. R is characterized by determining a phase, measuring the shape, size, and number of individual R-rich phases present in each cell to determine whether or not each cell is a fine R-rich phase region. For evaluating the microstructure of a T-B based magnet alloy 14. The metal of the RTB-based alloy according to claim 13, wherein as the shape of the R-rich phase, any one or more of a roundness of a structure, an aspect ratio, and a rectangular aspect ratio is used. Organization evaluation method. The cell part in which 20 or more R-rich phases having a roundness of 1.0 to 1.4 and an area of 5 square micrometers or less are included in 100 square micrometers is finely divided. The method for evaluating a metal structure of an RTB-based alloy according to claim 14, wherein the region is determined to be an R-rich phase region. The cell part in which the aspect ratio of the R-rich phase is 1.0 to 5.0 and the area of the R-rich phase having an area of 5 square micrometers or less is 20 or more in 100 square micrometers is defined as fine R. The method for evaluating a metal structure of an RTB-based alloy according to claim 14, wherein the method is determined to be a rich phase region. The R-rich phase has a square aspect ratio of 1.0 to 5.0 and an area of 5 square micrometers or less. The method for evaluating a metal structure of an RTB-based alloy according to claim 14, wherein the method is determined to be a rich phase region. The cells dividing the microstructure image are divided into grid cells by equally spaced straight lines substantially parallel to the solidified surface of the alloy and equally spaced straight lines substantially perpendicular to the solidified surface of the alloy. Item 18. When the cells determined to be fine R-rich phase regions by the metal structure evaluation method according to any one of Item 17 are discontinuous in a direction perpendicular to the solidification surface of the alloy, the solidification surface of the alloy is 14. The method for evaluating the microstructure of an RTB-based alloy according to claim 13, wherein all cells from a cell farthest from the solid to a solidified surface are determined as a fine R-rich phase region. The cells dividing the microstructure image are divided into grid-like cells by equally spaced straight lines substantially parallel to the solidification surface of the alloy and equally spaced straight lines substantially perpendicular to the solidification surface of the alloy. A cell determined as a fine R-rich phase region by the metal structure evaluation method according to claim 17, wherein the cell is discontinuous in a direction perpendicular to a solidification surface of the alloy, wherein the fine R-rich phase region is discontinuous. Among the cells determined to be phase regions, all cells from the two or more continuous cells farthest from the solidification surface to the solidification surface are determined to be fine R-rich phase regions, and are freer than the two or more continuous cells. 14. The method for evaluating the metallographic structure of an RTB-based alloy according to claim 13, wherein it is determined that all the cells existing alone in the plane direction are not in the fine R-rich phase region. A value obtained by dividing the total area of the cells determined to be the fine R-rich phase region by the metallographic evaluation method according to any one of claims 13 to 19 by the total area of all the cells measured is defined as fine. A method for evaluating the structure of an RTB-based alloy, wherein the area ratio of an R-rich phase region is used. 14. The method for evaluating a metal structure of an RTB-based magnet alloy according to claim 11, wherein the digital image is a reflected electron beam image of a scanning electron microscope. Metal structure of the R-T-B magnet alloy according to claim 11 or claim 13, characterized in that a threshold value is provided to a difference between the luminance discriminating the R _{2 T} 14 _B main phase and R-rich phase Evaluation method.

Images