JP7251158B2 - Evaluation method of raw material alloy for rare earth magnet, apparatus for evaluating raw material alloy for rare earth magnet, and manufacturing method of rare earth magnet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating raw material alloys for rare earth magnets, an evaluation apparatus for raw material alloys for rare earth magnets, and a method for manufacturing rare earth magnets.

Rare earth magnets are used in various motors and the like because they have excellent magnetic properties and, in particular, high coercive force can be obtained. Rare earth magnets are usually manufactured using powder obtained by pulverizing a raw material alloy having a predetermined composition.

Such a raw material alloy has a columnar structure including a main phase and a rare earth-rich phase. Since the rare earth-rich phase becomes the grain boundary phase in the rare earth magnet, an increase in the ratio of the rare earth-rich phase adversely affects the magnetic properties of the rare earth magnet.

Moreover, the raw material alloy may contain a structure called a chill crystal. Chill crystals are a fine granular structure, not a columnar structure. When a rare earth magnet is produced using a raw material alloy containing chill crystals, magnetic properties such as coercive force and squareness ratio of the rare earth magnet tend to deteriorate due to the chill crystals.

Therefore, it is important to evaluate the ratio of the structure contained in the raw material alloy. Patent Document 1 discloses a method for evaluating a region (fine R-rich phase) in which the R-rich phase is extremely finer than other regions and is present randomly.

JP-A-2008-58323

In the method disclosed in Patent Document 1, an R-rich phase is identified on a microscopic image of an alloy cross-sectional structure, and the R-rich phase is evaluated by the circularity when approximated to a circle and the area of the R-rich phase. and determines whether or not the R-rich phase is a fine R-rich phase.

However, with such an evaluation method, it is difficult to accurately calculate the area of the fine R-rich phase when the quality of the image is poor. In addition, image quality also depends on the skill of the observer. Therefore, there is a problem that such a measurement method cannot accurately evaluate the structure in the raw material alloy.

The present invention has been made in view of such circumstances, and provides a method for evaluating raw material alloys for rare earth magnets, an apparatus for evaluating raw material alloys for rare earth magnets, and an evaluation method for rare earth magnets using the evaluation method, which can evaluate the structure in the raw material alloys. The object is to provide a manufacturing method.

To achieve the above objects, aspects of the present invention are:
[1] an image acquiring step of acquiring a cross-sectional image of a raw material alloy for a rare earth magnet having a main phase and a rare earth rich phase;
an image processing step of extracting a main phase, a rare earth-rich phase, and a chill crystal by performing image processing based on the luminance value of each pixel constituting the cross-sectional image;
an evaluation step of evaluating a raw material alloy for a rare earth magnet based on at least the extracted chill crystals,
In the image processing step, each pixel is classified into a first group corresponding to the main phase, a second group corresponding to the rare earth rich phase, and a third group corresponding to the chill crystal, based on the luminance value of each pixel constituting the cross-sectional image. A grouping step of grouping into groups;
An extraction step of extracting a main phase, a rare earth-rich phase and chill crystals from cross-sectional images based on the first group, the second group and the third group.

[2] The method for evaluating raw material alloys for rare earth magnets according to [1], wherein the image processing step includes a binarization step of binarizing the third group and groups other than the third group.

[3] The method for evaluating a raw material alloy for a rare earth magnet according to [2], wherein the image processing step includes a median filtering step of performing median filtering on the image after the binarization step.

[4] In the image processing step, pixels belonging to the third group are removed as noise from the image after the median filtering step in regions other than the rapidly solidified region of the raw material alloy for rare earth magnets and the region near the rapidly solidified region. The method for evaluating a raw material alloy for rare earth magnets according to [3], which includes a first noise removal step for removing noise.

[5] In the image processing step, the image after the median filtering step belongs to the third group included in a predetermined number of pixels continuous along the direction orthogonal to the thickness direction of the raw material alloy for rare earth magnets. The method for evaluating a raw material alloy for rare earth magnets according to [3], which includes a second noise removal step of removing pixels as noise when the number of pixels is less than a predetermined threshold.

[6] In the image processing step, in the image after the first noise removal step, the number of pixels belonging to the third group included in a predetermined number of consecutive pixels along the direction perpendicular to the thickness direction of the raw material alloy for rare earth magnets. is less than a predetermined threshold, the method for evaluating a raw material alloy for a rare earth magnet according to [4], which includes a second noise removal step of removing the pixel as noise.

[7] The image processing step has a first noise removal step of removing pixels belonging to the third group as noise in a region other than the rapidly solidified region of the raw material alloy for rare earth magnet and the region near the rapidly solidified region [ 1] or [2] is a method for evaluating a raw material alloy for a rare earth magnet.

[8] The method for evaluating a raw material alloy for a rare earth magnet according to any one of [1] to [7], including an image generating step of generating an image in which a mark indicating chill crystals is superimposed on the cross-sectional image.

[9] in the image generating step, generating an image in which the first color is superimposed on the main phase, the second color is superimposed on the rare earth-rich phase, and the third color is superimposed on the chill crystal;
The third color is an intermediate color between the first color and the second color, which is the evaluation method for raw material alloys for rare earth magnets described in [8].

[10] image acquisition means for acquiring a cross-sectional image of a raw material alloy for a rare earth magnet having a main phase and a rare earth rich phase;
image processing means for extracting a main phase, a rare earth rich phase, and a chill crystal by image processing based on the luminance value of each pixel constituting the cross-sectional image;
evaluation means for evaluating the raw material alloy for rare earth magnets based on at least the extracted chill crystals,
The image processing means includes grouping means for grouping each pixel into a first group corresponding to the main phase, a second group corresponding to the rare earth rich phase, and a third group corresponding to the chill crystal;
Extraction means for extracting a main phase, a rare earth-rich phase, and chill crystals from cross-sectional images based on the first group, the second group, and the third group.

[11] A step of evaluating a raw material alloy for a rare earth magnet having a main phase and a rare earth rich phase by the evaluation method according to any one of [1] to [9];
a step of adjusting manufacturing conditions for the raw material alloy for rare earth magnets based on the results of evaluating the raw material alloy for rare earth magnets;
a step of producing a raw material alloy for a rare earth magnet based on the adjusted production conditions;
and a step of manufacturing a rare earth magnet using the manufactured raw material alloy for a rare earth magnet.

ADVANTAGE OF THE INVENTION According to this invention, the evaluation method of the raw material alloy for rare earth magnets which can evaluate the structure|tissue in a raw material alloy correctly, the evaluation apparatus of the raw material alloy for rare earth magnets, and the manufacturing method of the rare earth magnet using the said evaluation method are provided. be able to.

FIG. 1 is a flow chart of a method for evaluating a raw material alloy for a rare earth magnet according to this embodiment. FIG. 2 is a cross-sectional image of the obtained raw material alloy for rare earth magnets. FIG. 3A is a cross-sectional image before clustering processing, and FIG. 3B is a cross-sectional image after clustering processing. FIG. 4 is an image obtained by binarizing the cross-sectional image after the clustering process. FIG. 5 is an image obtained by subjecting the binarized image to median filter processing. FIG. 6 is an image obtained by subjecting the median filtered image to the first noise removal process. FIG. 7 is an image obtained by subjecting the median-filtered image to the second noise removal process. FIG. 8 is an image obtained by performing the second noise removal process on the image that has been subjected to the median filter process and the first noise removal process. FIG. 9 is an image in which chill crystals extracted in the method for evaluating a raw material alloy for a rare earth magnet according to this embodiment are superimposed on a cross-sectional image. FIG. 10 is a schematic configuration diagram of an evaluation apparatus for raw material alloys for rare earth magnets according to this embodiment. FIG. 11 is an image obtained by subjecting the binarized image to the first noise removal process.

Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. Rare earth magnet 1.1 Raw material alloy for rare earth magnet 2. Evaluation method of raw material alloy for rare earth magnet 2.1 Image acquisition process 2.2 Image processing process 2.2.1 Grouping process 2.2.2 Binarization process 2.2.3 First noise removal process 2.2 .4 Second noise removal process 2.2.5 Extraction process 2.3 Evaluation process 2.4 Image display process3. Equipment for evaluating raw material alloys for rare earth magnets4. 4. Method for manufacturing rare earth magnets; 6. Effects of this embodiment. Modification

(1. Rare earth magnet)
First, rare earth magnets manufactured using raw material alloys evaluated by the method according to the present embodiment will be described.

A rare earth magnet is a magnet comprising a ferromagnetic compound having a rare earth element and an iron group element. Rare earth magnets have a high coercive force due to the magnetocrystalline anisotropy of this ferromagnetic compound.

A neodymium magnet etc. are illustrated as a rare-earth magnet. In this embodiment, an RTB-based magnet represented by a neodymium magnet will be described. Also, in this embodiment, the rare earth magnet may be a sintered magnet or a bonded magnet.

In the RTB magnet, R indicates a rare earth element, T indicates a transition metal element containing iron, and B indicates boron. Also, the RTB magnet has main phase grains made of the R ₂ T ₁₄ B compound and grain boundary phases. The grain boundary phase consists of various phases, including a phase with a higher rare earth concentration than the main phase.

It is believed that the existence of the grain boundary phase around the main phase grains exhibiting ferromagnetism cuts the exchange coupling between the main phase grains and increases the coercive force of the RTB magnet.

(1.1 Raw material alloy for rare earth magnet)
Rare earth magnets are manufactured using raw material alloys for rare earth magnets. A raw material alloy for a rare earth magnet can be produced by a known method. In this embodiment, the raw material alloy for rare earth magnets is produced by the strip casting method.

In the strip casting method, a raw material alloy for a rare earth magnet in the form of ribbons or flakes is obtained by supplying a molten metal obtained by melting individual metals constituting the raw material alloy onto a cooled rotating roll and quenching the molten metal. .

The raw material alloy for rare earth magnets produced by the strip casting method has a fine structure. Typically, the structure is a columnar structure, and a rare earth-rich phase, which is a phase with a high rare earth concentration, extends between main phases responsible for ferromagnetism. In other words, the main phase and the rare earth-rich phase are stacked in a predetermined direction.

As the ratio of the rare earth rich phase increases, the coercive force of the rare earth magnet tends to decrease. Therefore, it is important to evaluate the proportion of the main phase and the proportion of the rare earth-rich phase.

Also, the structure in the raw material alloy produced by the strip casting method may contain chill crystals. Chill crystals are fine granular structures that occur on the side of the molten metal that comes into contact with the rotating roll. Since chill crystals have a magnetically isotropic structure compared to the main phase, the magnetic properties of the rare earth magnet tend to deteriorate when the proportion of chill crystals contained in the material alloy increases. In addition, since the chill crystal region becomes fine grains when the material alloy is pulverized, the particle size distribution of the obtained powder deviates from the desired particle size distribution.

Therefore, in the method for evaluating raw material alloys for rare earth magnets, which will be described later, the main phase, rare earth rich phase, and chill crystals are extracted, and the ratio of these phases is calculated and evaluated.

(2. Evaluation method of raw material alloy for rare earth magnet)
The evaluation method of the raw material alloy for rare earth magnets according to the present embodiment is a method of evaluating the alloy structure appearing in the cross section of the raw material alloy. A method for evaluating a raw material alloy for a rare earth magnet according to this embodiment will be described with reference to the flowchart shown in FIG.

(2.1 Image Acquisition Step: S10)
In the image acquisition step, an image of the raw material alloy for rare earth magnets to be evaluated is acquired. The image is a cross-sectional image of the raw material alloy. Also, this cross-sectional image is an image reflecting the composition information of the raw material alloy. An image reflecting composition information refers to an image in which a difference in composition appears as a difference in the image. Specifically, it is an image in which the difference in composition appears as the difference in brightness.

Examples of such images include images observed by electron microscopes such as SEMs (scanning electron microscopes), TEMs (transmission electron microscopes), and STEMs (scanning transmission electron microscopes). Since the number of electrons (backscattered electrons) reflected by colliding an electron beam with the sample depends on the atomic number and the crystal structure, the cross-sectional image is preferably a backscattered electron image in this embodiment.

The cross-sectional image may be an image that can extract the main phase, the rare earth-rich phase, and the chill crystals. That is, even if the quality of the image is poor and it is difficult to distinguish chill crystals from the rare earth-rich phase by the method disclosed in the above-mentioned Patent Document 1, according to the method described later, the main phase, the rare earth Rich phases and chilled crystals can be accurately distinguished and extracted.

In addition, in the cross-sectional image, the entire material alloy appears in the thickness direction of the material alloy (the direction from the surface in contact with the roll to the surface (free surface) that did not contact the roll), and the width direction of the material alloy ( In the direction orthogonal to the thickness direction), it is preferable that the material alloy is exposed over the length of the thickness or more. An example of the acquired cross-sectional image is shown in FIG. FIG. 2 is a cross-sectional image of the starting alloy produced by the strip casting method. In FIG. 2, the roll surface side is on the left side and the free surface side is on the right side. 2 is the thickness direction (TD) of the raw material alloy 50 for rare earth magnets, and the vertical direction in FIG. 2 is the width direction (WD) of the raw material alloy 50 for rare earth magnets.

In the present embodiment, a digital image of the cross section may be obtained as the cross-sectional image, or an image obtained by converting the analog image of the cross section into a digital image may be obtained as the cross-sectional image. The device may convert the analog image of the cross section into a digital image to obtain the cross section image. It is sufficient that the pixels forming the acquired cross-sectional image have at least luminance information.

(2.2 Image processing step: S20)
The acquired cross-sectional image is subjected to image processing. In the image processing step, the cross-sectional image is image-processed based on the luminance values of the pixels forming the cross-sectional image. The steps included in the image processing steps are described below.

(2.2.1 Grouping step: S21)
In the grouping step, each pixel is grouped so as to belong to one of the main phase, the rare earth-rich phase, and the chill crystal based on the luminance value of the pixels forming the cross-sectional image. In addition, when a background that does not constitute the raw material alloy appears in the cross-sectional image, the pixels may be grouped so that the background belongs to the main phase, the rare earth-rich phase, and the chill crystal in addition to the background. Alternatively, after extracting the background in advance and removing the background, grouping may be performed so that each pixel belongs to one of the main phase, the rare earth-rich phase, and the chill crystal.

Note that when the cross-sectional image contains color information, grayscale conversion is performed to convert the color information into luminance information.

Further, when noise is present in the acquired cross-sectional images, it is preferable to perform smoothing processing on the cross-sectional images before grouping to reduce the noise, as shown in FIG. A known filter may be used for the smoothing process. In this embodiment, a Gaussian filter, a bilateral filter, and the like are exemplified.

In this embodiment, the grouping is performed by clustering the brightness values of the pixels forming the cross-sectional image. FIG. 3A shows a cross-sectional image before clustering processing.

For example, by setting the number of clusters to 4 and clustering the brightness values, each brightness value finally belongs to one of the four clusters.

As described above, the composition information is reflected in the luminance value of the cross-sectional image, and the luminance value of the pixel corresponding to the rare-earth-rich phase is usually higher than the luminance value of the pixel corresponding to the main phase. This is because the rare earth-rich phase contains more rare earth elements with a large atomic number than the main phase.

In chill crystals, fine rare earth-rich phases are dispersed in the main phase. It indicates the intermediate value between the brightness value of the pixel to be used.

Furthermore, the background in the cross-sectional image is the area where the material alloy does not exist. Therefore, since reflected electrons are not detected from the background, the luminance value of pixels corresponding to the background is almost zero.

Therefore, the set of pixels belonging to the cluster with the lowest luminance value, that is, the cluster whose luminance value is approximately 0, is the group corresponding to the background. The set of pixels belonging to the cluster with the second lowest luminance value is the first group corresponding to the main phase. A set of pixels belonging to the cluster with the third lowest luminance value (the cluster with the second highest luminance value) is the third group corresponding to the chill crystal. The set of pixels belonging to the cluster with the highest luminance value is the second group corresponding to the rare earth rich phase. As described above, the pixels indicating the material alloy are distributed to any one of the first group, the second group and the third group.

FIG. 3B shows a cross-sectional image after clustering processing. In FIG. 3B , the white area indicates the second group 62 , the light gray area indicates the third group 63 , and the dark gray area indicates the first group 61 . Comparing FIG. 3(A) and FIG. 3(B), it can be seen that each region is clearly distinguished in FIG. 3(B).

A known method may be adopted as a clustering method. In this embodiment, the Kmeans method is adopted. First, each luminance value is randomly assigned to each cluster. A brightness value corresponding to the center of gravity of each cluster is calculated, and the cluster to which each brightness value is assigned is changed to a cluster having a center of gravity closest to each brightness value. If the cluster after change is different from the assigned cluster, the center of gravity of each cluster is calculated again, and the cluster of each luminance value is changed. The clustering process ends when the cluster of each luminance value is not changed. In this embodiment, since the number of clusters to be set is known in advance, the Kmeans method is suitable as a clustering method.

Moreover, it is preferable to further perform image processing on the image after the clustering processing in order to increase the extraction accuracy of each region. For example, as described above, the luminance value of the pixel corresponding to the chill crystal indicates an intermediate value between the luminance value of the pixel corresponding to the rare earth-rich phase and the luminance value of the pixel corresponding to the main phase. Therefore, in an image after clustering processing, there is a possibility that some of the pixels grouped into the third group corresponding to chill crystals should be grouped into the first group or the second group. In other words, the third group after clustering may contain noise. Therefore, in order to improve the accuracy of extracting chill crystals, it is preferable to perform further image processing on the image after the clustering process to remove noise.

The luminance value of the pixel corresponding to the boundary portion between the main phase and the rare-earth-rich phase may indicate an intermediate value between the luminance value of the pixel corresponding to the rare-earth-rich phase and the luminance value of the pixel corresponding to the main phase. Therefore, there is a possibility that the pixels corresponding to the boundary portion between the main phase and the rare earth-rich phase are grouped into the third group corresponding to the chill crystal.

In addition, chill crystals are likely to occur in regions where molten metal is rapidly solidified. That is, since the regions where chill crystals are present are biased, the third group corresponding to chill crystals may include pixels located in regions where chill crystals are less likely to occur. Such pixels often exist as isolated pixels from other regions.

(2.2.2 Binarization processing step: S22)
In order to remove noise, it is sufficient to determine whether or not a pixel is a chill crystal. divided into groups corresponding to areas of That is, a predetermined value is assigned to the luminance value of the pixels belonging to the third group, and the predetermined luminance value assigned to the third group is assigned to the luminance values of the pixels belonging to the first group, the second group, and the group corresponding to the background. A binarization process that assigns a luminance value different from the

Specifically, when the luminance value varies between 0 and 255, the luminance value of the pixels belonging to the third group is set to 255, and the luminance values of the pixels belonging to the first group, the second group, and the group corresponding to the background are is set to 0. By doing so, in the binarized image, the area corresponding to the third group is displayed as white, and the areas other than the third group (the first group, the second group, and the group corresponding to the background) are displayed in white. ) are displayed as black. FIG. 4 shows an image after binarization processing. The image shown in FIG. 4 is an image obtained by subjecting the image shown in FIG. 2 to clustering processing and then binarization processing. In FIG. 4, the white area is the third group 63, and the black area is the group 64 other than the third group.

By converting the image after the clustering process into a binarized image indicating whether or not the pixel belongs to the third group, noise can be removed with high accuracy in the process described later.

(2.2.3 Median filter processing step: S23)
In this embodiment, median filter processing is performed on an image after clustering processing as processing for removing noise corresponding to the boundary portion between the main phase and the rare earth-rich phase.

In median filtering, first, for each pixel that constitutes an image, a matrix of a predetermined number (for example, 3×3) is assumed centering on the pixel, and the median value of the luminance value distribution of all pixels in the matrix is A luminance value indicating (median value) is calculated. Then, the calculated brightness value is replaced with the brightness value of the pixel located at the center of the matrix. This operation is performed for all pixels.

In this embodiment, the median filtering process is performed on the binarized image, so it is a majority process. That is, when the number of pixels belonging to the third group is greater than the number of pixels belonging to groups other than the third group in the matrix, the pixel located in the center of the matrix is considered to be the pixel belonging to the third group. Become. On the other hand, if the number of pixels belonging to the third group is less than the number of pixels belonging to groups other than the third group in the matrix, the pixel located in the center of the matrix belongs to the groups other than the third group. It becomes the belonging pixel.

FIG. 5 shows an image after median filtering. The image shown in FIG. 5 is an image obtained by subjecting the image shown in FIG. 4 to median filter processing. Comparing FIG. 5 and FIG. 4, it can be seen that the upper portion of the region on the roll surface side is occupied by the third group 63 corresponding to the chill crystals, and the region on the free surface side has almost no third group 63. I understand.

By performing such processing, it is possible to accurately remove noise corresponding to the boundary portion between the main phase and the rare-earth-rich phase included in the third group.

(2.2.4 First noise removal step: S24)
In the present embodiment, a first noise removal step and a second noise removal step are exemplified as processing for removing isolated pixels as noise. First, the first noise removal step will be described.

When the raw material alloy is produced by the strip casting method, the molten metal is rapidly cooled in contact with the roll surface, so chill crystals are likely to occur on the surface in contact with the roll surface and in the vicinity thereof. To put it the other way around, the probability of the presence of chill crystals decreases sharply as the film progresses in the thickness direction from the surface in contact with the roll surface.

Therefore, it is assumed that chill crystals do not exist in regions where the possibility of the presence of chill crystals is low, and processing is performed to remove all pixels belonging to the third group in the regions. can be removed as noise.

Specifically, in the cross-sectional image, a region up to a predetermined length in the thickness direction from the roll surface side is defined as a region where chill crystals exist, and pixels belonging to the third group existing in other regions are removed as noise. good. It is preferable that the predetermined length is, for example, 1/2 or less of the length in the thickness direction.

FIG. 6 shows an image after the first noise removal process. The image shown in FIG. 6 is an image obtained by subjecting the image shown in FIG. 5 to the first noise removal process. In FIG. 6, a region up to 1/2 of the thickness T of the material alloy is extracted from the roll surface side toward the thickness direction, and the third group 63 existing in the other region is removed as noise.

By performing such processing, it is possible to easily remove noise in a region where the possibility of the presence of chill crystals is low.

(2.2.5 Second noise removal step: S25)
Next, the second noise removal step will be explained. In the second noise removal step, in the cross-sectional image, when a predetermined number of pixels that are continuous along the direction orthogonal to the thickness direction of the raw material alloy include pixels belonging to the third group, the number of pixels belonging to the third group is a predetermined number. If it is less than the threshold of , the pixel is removed as noise.

The predetermined number of pixels is preferably P+1 pixels, for example, where P is the number of pixels corresponding to the grain size to be pulverized. Also, the predetermined threshold is preferably 0.9×P/2 or less.

By performing such processing, it is possible to accurately remove noise that exists in isolation.

FIG. 7 shows an image after the second noise removal process. The image shown in FIG. 7 is an image obtained by subjecting the image shown in FIG. 5 to the second noise removal process. Comparing FIG. 7 and FIG. 5, it can be seen that in FIG. 7, the pixels belonging to the third group 63 that are isolated in the area on the free surface side in FIG. 5 are removed as noise.

Furthermore, the noise removal processing described above may be combined. For example, after performing the median filtering process and the first noise removal process on the image after the clustering process, the second noise removal process may be further performed. FIG. 8 shows an image subjected to the second noise removal process of the image (FIG. 6) subjected to the median filter process and the first noise removal process.

(2.2.6 Extraction step: S26)
In this embodiment, the main phase, rare earth-rich phase, and chill crystals are extracted based on the first, second, and third groups obtained by performing the above-described processing on the clustering-processed image. By performing the above image processing, the main phase, rare earth-rich phase, and chill crystals can be distinguished with high accuracy.

(2.3 Evaluation step: S30)
In the cross-sectional image after the image processing, the region occupied by the material alloy other than the background is specified as any one of the main phase, the rare earth-rich phase, and the chill crystal. Therefore, the proportions of the main phase, the rare earth-rich phase, and the chill crystals in the material alloy are calculated, and the material alloy is evaluated based on the calculated results. Also, the raw material alloy may be evaluated based on the distribution state of the main phase, rare earth-rich phase, and chill crystals.

For example, by calculating the ratio of chill crystals, it is possible to evaluate the effect on the particle size distribution of the powder obtained by pulverizing the material alloy. As a result, the magnetic properties of the rare earth magnet can be controlled.

(2.4 Image generation step: S40)
In this embodiment, the results obtained in the above image processing steps are displayed on the cross-sectional image. Specifically, as shown in FIG. 9, an image is generated by superimposing and displaying a region 53 extracted as a chill crystal after the image processing on the cross-sectional image before the image processing by filling with a predetermined color. In the generated image, the chill crystal region can be visually recognized easily, so that it is easy to visually understand the distribution state of the chill crystal on the cross-sectional image.

On the cross-sectional image, the region extracted as the main phase is filled with the first color, the region extracted as the rare earth rich phase is filled with the second color, and the region extracted as the chill crystal is filled with the first color and the second color. If the third color, which is an intermediate color between the two colors, is used for superimposition display, the distribution state of the main phase, the rare-earth-rich phase, and the chill crystals can be visually understood.

In addition, visual evaluation such as the distribution state of chill crystals based on the superimposed image may be added to the evaluation performed in the above evaluation process. The image to be superimposed may be a cross-sectional image before image processing or a cross-sectional image after image processing.

(3. Equipment for evaluating raw material alloys for rare earth magnets)
FIG. 10 is a schematic diagram showing a configuration example of a raw material alloy evaluation apparatus for rare earth magnets according to the present embodiment. As shown in FIG. 7, the raw material alloy evaluation apparatus 1 for rare earth magnets has a processing unit 10, a display unit 20, a storage unit 30, and an operation unit 40, and is composed of a known computer.

In this embodiment, the processing unit 10 has an image acquisition unit 11 , an image processing unit 12 , an evaluation unit 13 and an image generation unit 14 .

The image acquisition unit 11 acquires a cross-sectional image of the raw material alloy for rare earth magnets. When the cross-sectional image is an analog image, it cooperates with the image processing unit 12 to convert the cross-sectional image into a digital image.

The acquired cross-sectional image is sent to the image processing unit 12 . In this embodiment, the image processing section 12 has a grouping section 122 and an extraction section 127 . Grouping 122 performs the clustering process described above and groups each pixel constituting the cross-sectional image. The extraction unit 127 extracts the main phase, rare earth rich phase, chill crystals, and background based on the grouped results.

The image processing unit 12 may have a smoothing processing unit 121 that performs smoothing processing on the acquired image before performing the clustering processing, if necessary. In addition, the image processing unit 12 applies, as necessary, the binarization processing unit 123 that performs the above-described binarization processing, the median filtering unit 124 that performs median filtering, and the first noise removal to the image after the clustering processing. A first noise removal processing unit 125 that performs processing and a second noise removal processing unit 126 that performs second noise removal processing may be provided.

Based on the extracted main phase, rare earth-rich phase, and chill crystals, the evaluation unit 13 calculates the ratio of these regions in the raw material alloy to evaluate the raw material alloy.

The image generation unit 14 generates an image in which at least one selected from the main phase, the rare earth-rich phase, and the chill crystal calculated by the image processing unit 12 is superimposed on the cross-sectional image with a visible mark (filled in). . The generated image is displayed by the display unit 20 .

The display unit 20 is not particularly limited as long as it has a function of displaying an acquired cross-sectional image, an image processed by the processing unit 10, an evaluation result, and the like, and a known monitor may be used.

The storage unit 30 stores programs for executing functions in the processing unit 10, and the programs are started when various functions are executed. In addition, it is possible to store acquired images and the like. In addition, it may have external storage means such as a memory card.

The operation unit 40 has a function of externally inputting commands to the processing unit 10 and the like. A touch panel or the like in which the display unit 20 and the operation unit 40 are integrated may be used.

(4. Method for producing rare earth magnet)
The method of manufacturing the rare earth magnet according to the present embodiment can adopt a known method other than evaluating the raw material alloy by the method of evaluating the raw material alloy for the rare earth magnet described above and feeding back the result.

The raw material alloy for rare earth magnets can be produced by the method described above. The ratio of chilled crystals, the ratio of rare earth-rich phases, etc., of the raw material alloy for rare earth magnets thus produced are calculated by the evaluation method described above, and then evaluated.

As a result of the evaluation, for example, when the ratio of chill crystals is large, the evaluation result can be fed back to the manufacturing conditions of the raw material alloy to adjust the manufacturing conditions of the raw material alloy.

Subsequently, based on the adjusted manufacturing conditions, the raw material alloy is manufactured and pulverized, and the pulverized raw material alloy is used to produce a rare earth magnet. At this time, since the manufacturing conditions of the raw material alloy are adjusted based on the evaluation results of the raw material alloy, the magnetic properties of the rare earth magnet to be manufactured do not deteriorate, and the initially planned magnetic properties can be exhibited.

(5. Effect in this embodiment)
In this embodiment, the main phase, the rare earth-rich phase, and the chill crystal can be accurately distinguished and extracted from the cross-sectional image of the raw material alloy for rare earth magnets. Therefore, it is possible to accurately calculate the ratio of chill crystals in the raw material alloy, so that the raw material alloy for rare earth magnets can be evaluated from various aspects, and the evaluation results can be fed back to the manufacturing process.

As a result, the manufacturing conditions for the rare earth magnet can be optimized according to the evaluation results, so that the magnetic properties of the rare earth magnet to be manufactured are not degraded.

(6. Modification)
In the above-described embodiment, the image after the binarization process is median filtered and then subjected to the first noise removal process. Chill crystals may be extracted by performing the first noise removal process on the image (FIG. 4) after the smoothing process. In the binarized image, the third group may contain many boundary portions between the main phase and the rare earth-rich phase. However, the proportion of the boundary portion in the chill crystal is small. Therefore, this method can also accurately evaluate the ratio of chill crystals.

Further, in the above-described embodiment, clusters of pixels belonging to the background are calculated in the clustering process, but the pixels belonging to the background may be removed in advance before the clustering process. The background is a region that is not the raw material alloy in the cross-sectional image, and can be easily distinguished from the raw material alloy, so it can be removed before the clustering process.

By doing so, the number of clusters is reduced, so the time required for the clustering process is shortened.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to the above embodiments, and may be modified in various ways within the scope of the present invention.

50... Raw material alloy for rare earth magnet 51... Main phase 52... Rare earth rich phase 53... Chill crystal 61... First group 62... Second group 63... Third group 1... Evaluation apparatus for raw material alloy for rare earth magnet 10... Treatment unit 11 ... image acquisition section 12 ... image processing section 121 ... smoothing processing section 122 ... grouping section 123 ... binarization processing section 124 ... median filter processing section 125 ... first noise removal processing section 126 ... second noise removal processing section 127 ... Extraction unit 13 Evaluation unit 14 Image generation unit 20 Display unit 30 Storage unit 40 Operation unit

Claims (11)

an image acquisition step of acquiring a cross-sectional image of a raw material alloy for a rare earth magnet having a main phase, a rare earth rich phase, and a chill crystal ;
an image processing step of extracting the main phase, the rare earth-rich phase, and the chill crystal by image processing based on the luminance value of each pixel constituting the cross-sectional image;
an evaluation step of evaluating the raw material alloy for a rare earth magnet based on at least the extracted chill crystals;
In the image processing step, each pixel is divided into a first group corresponding to the main phase, a second group corresponding to the rare earth rich phase, and a chill crystal, based on the luminance value of each pixel constituting the cross-sectional image. A grouping step of grouping into corresponding third groups;
An extraction step of extracting the main phase, the rare earth-rich phase and the chill crystal from the cross-sectional image based on the first group, the second group and the third group. 2. The method for evaluating a raw material alloy for rare earth magnets according to claim 1, wherein said image processing step includes a binarization step of binarizing said third group and groups other than said third group. 3. The method for evaluating a raw material alloy for a rare earth magnet according to claim 2, wherein said image processing step includes a median filtering step of performing median filtering on the image after said binarization step. In the image processing step, pixels belonging to the third group are treated as noise in a region other than the rapidly solidified region of the raw material alloy for rare earth magnet and the region near the rapidly solidified region in the image after the median filter processing step. 4. The evaluation method for raw material alloys for rare earth magnets according to claim 3, further comprising a first noise removal step. In the image processing step, for the image after the median filtering step, pixels belonging to the third group included in a predetermined number of pixels continuous along a direction orthogonal to the thickness direction of the raw material alloy for rare earth magnets are processed. 4. The method for evaluating raw material alloys for rare earth magnets according to claim 3, further comprising a second noise removal step of removing pixels as noise when the number is less than a predetermined threshold. In the image processing step, in the image after the first noise removal step, the number of pixels belonging to the third group included in a predetermined number of consecutive pixels along the direction orthogonal to the thickness direction of the raw material alloy for rare earth magnets. 5. The method of evaluating a raw material alloy for a rare earth magnet according to claim 4, further comprising a second noise removal step of removing the pixel as noise when the pixel is less than a predetermined threshold. The image processing step includes a first noise removal step of removing pixels belonging to the third group as noise in regions other than the rapidly solidified region of the raw material alloy for a rare earth magnet and a region in the vicinity of the rapidly solidified region. 3. The method for evaluating the raw material alloy for a rare earth magnet according to 1 or 2. 8. The method for evaluating a raw material alloy for a rare earth magnet according to any one of claims 1 to 7, further comprising an image generating step of generating an image in which the mark indicating the chill crystal is superimposed on the cross-sectional image. In the image generating step, an image is generated in which a first color is superimposed on the main phase, a second color is superimposed on the rare earth-rich phase, and a third color is superimposed on the chill crystal;
9. The method for evaluating a raw material alloy for a rare earth magnet according to claim 8, wherein the third color is a color intermediate between the first color and the second color. an image acquisition means for acquiring a cross-sectional image of a raw material alloy for a rare earth magnet having a main phase, a rare earth rich phase, and a chill crystal ;
image processing means for extracting the main phase, the rare earth-rich phase, and the chill crystal by image processing based on the luminance value of each pixel constituting the cross-sectional image;
evaluation means for evaluating the raw material alloy for a rare earth magnet based on at least the extracted chill crystals;
The image processing means includes grouping means for grouping each pixel into a first group corresponding to the main phase, a second group corresponding to the rare earth rich phase, and a third group corresponding to the chill crystal;
An evaluation apparatus for raw material alloys for rare earth magnets, comprising extracting means for extracting the main phase, the rare earth-rich phase, and the chill crystal from the cross-sectional image based on the first group, the second group, and the third group. a step of evaluating a raw material alloy for a rare earth magnet having a main phase, a rare earth rich phase and a chill crystal by the evaluation method according to any one of claims 1 to 9;
a step of adjusting manufacturing conditions for the raw material alloy for rare earth magnets based on the results of evaluating the raw material alloy for rare earth magnets;
a step of producing a raw material alloy for a rare earth magnet based on the adjusted production conditions;
A method for producing a rare earth magnet, comprising: producing a rare earth magnet using the raw material alloy for a rare earth magnet thus produced.

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