JPH0380258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses image processing to determine the grain size of crystals and
The present invention relates to a particle size and second phase fraction measuring device capable of measuring phase fraction.

Conventionally, ferrite grain size, austenite grain size,
To measure the second phase fraction, etc., a comparison method has been widely used in which a standard sample of known particle size number is compared with the target metal structure. However, in the above-mentioned comparative method, rough measurements can be made due to differences in shape and distribution between the sample to be measured and the standard sample, but accurate measurements are not possible.

Accurate values can also be obtained by taking a microscopic photograph of the sample to be measured and measuring the area of individual grains and second phase components using a replanimeter that traces the grain boundaries artificially. Although this method requires a lot of effort, it yields few results and is inefficient. The second phase component refers to a portion other than ferrite or austenite, such as pearlite.

FIG. 1 is a diagram showing the configuration of a conventional automatic image analysis device capable of measuring particle size and second phase fraction.
In Fig. 1, a microscopic photograph of the sample or a microscopic image of the sample is input into the analyzer using a surface scanning image input device such as a television camera, and after being binarized as it is, the particle size and secondary The phase fraction is being measured. However, when the above-mentioned automatic analysis equipment reveals the grain boundaries of a sample due to nital corrosion, it is not possible to correctly identify grain boundaries with thin corrosion or polishing scratches, resulting in problems with measurement accuracy and reliability. There was a problem. The main reason for this is that the original image is binarized as is. That is, when inputting an image to an analysis device, a considerable amount of grain boundary information is already lost or noise is mixed in, so if the image is binarized and analyzed as it is, problems will remain in the measured values.

The purpose of the present invention is to solve the above-mentioned problems and measure the grain size and second phase fraction of crystals with high accuracy and reproducibility by performing image processing such as emphasizing line elements and connecting grain boundaries. It is intended to provide a possible particle size and second phase fraction measuring device.

The particle size and second phase fraction measuring device of the present invention includes:
A microscope for observing metallographic structures, an imaging device connected to this microscope that captures images of metallographic structures and outputs analog image information, and converts the analog image information from this imaging device into gray-level digital image information. Analog/digital converter and this analog/digital converter
An image processing section that emphasizes grain boundary areas by applying line element extraction filter processing to the digital image information converted by the digital conversion section, and an image obtained from the image processing section that is compared with a preset threshold value. Therefore, linear parts are extracted from the binarized image of the second phase part and grain boundary part from the metallographic image and used as grain boundaries, and the parts where the grain boundaries are not closed among the extracted grain boundary parts are An arithmetic processing unit that calculates image information corrected by extending the linear portion so that all grain boundaries are closed; and a calculation processing unit that calculates the grain boundary position and second phase in the image information obtained by the arithmetic processing unit. The apparatus is characterized by comprising a quantitative processing section that measures the particle size and the second phase fraction from the coordinates of the position.

FIG. 2 is a diagram showing an embodiment of the particle size and second phase fraction measuring device of the present invention. In FIG. 2, the structure of the measurement sample revealed with a nital corrosive solution or a picric acid corrosive solution is read out as optical image information by an imager 2 connected to a microscope 1, and sent to an A/D converter 3. Supplied. A/D
The optical image information supplied to the converter 3 is converted into digital image information in which one screen consists of, for example, 512×512 pixels, and each pixel has 64 or more gray tones, preferably 256 gray tones. Here, the gray tone level is the absolute value of the gray tone from black to white in the image, and is 256
Gray tone is the tone between black and white divided into 256 equal parts, with black being 0 and white being 255. The digital image information is stored in a gray tone image memory consisting of a frame memory provided in the line element emphasis processing section 4.

Next, the line element enhancement processing section 4 performs line element enhancement processing on the image stored in the gray tone image memory based on the following principle. First, for each pixel of the image stored in the gray image memory, a line element emphasis filter shown in FIG. 3 is created, which consists of, for example, 5×5 pixels in the vicinity of that pixel, and
The averages A ₁ to _{A 4} of the gray level values of pixels located on straight lines in four directions passing through the center pixel as shown below and the total average value Aa of the pixels in the filter are calculated.
Note that a _ij in FIG. 3 represents the gray tone level of each pixel.

A ₁ = 1/5 (a ₃₁ + a ₃₂ + a ₃₃ + a ₃₄ + a ₃₅ ) A ₂ = 1/5 (a ₁₃ + a ₂₃ + a ₃₃ + a ₄₃ + a ₅₃ ) A ₃ = 1/5 (a ₁₁ + a ₂₂ + a ₃₃ + a ₄₄ + a ₅₅ ) A ₄ = 1/5 (a ₅₁ + a ₄₂ + a ₃₃ + a ₂₄ + a ₁₅ ) A _a = 1/25 ( ₅ 〓 ⁱ⁼¹ ₅ 〓 ^j=1 a _ij ) Next, the obtained A ₁ ~ Extract the minimum value Amin from A ₅ , compare this minimum value Amin and the total average value Aa, and if the difference is greater than a preset threshold, select the minimum value Amin, and if it is smaller, use the total average value. Give Aa as the new gray level of the target pixel. If the above-described operation is performed on all pixels of the gray-tone image memory, image information in which line elements are emphasized can be obtained. Note that this processing involves addition and division of digital values and comparison of magnitudes, and from the viewpoint of processing speed and the repetition of similar processing, it is desirable to configure it with a dedicated electronic circuit.

The image information with the line elements emphasized by the method described above is supplied to the binarization processing unit 5, where it is binarized using a preset threshold value, and only the grain boundary portion and the second phase portion are removed. Extract. The image information after the binarization process is stored in a binarized image memory consisting of a frame memory provided in the arithmetic processing section 6. Each pixel in the binarized image memory has a grain boundary area and a second
The phase portion is stored as 1, and the other portions of the crystal are stored as 0.

The binarized image information is subjected to grain boundary information supplementation processing in the arithmetic processing section 6. In other words, for the image in the binarized image memory, (1) independent non-linear small areas that are not connected to others are removed as signal noise, (2) parts other than ferrite or austenite, such as pearlite, etc. If the part is a linear region, and the linear region is not closed, the evaluation function that is inversely proportional to the square of the distance and proportional to the direction cosine in the direction of the line is maximum at points near the tip of the linear region. By performing the two processes of extending the lines, all grain boundaries can be expressed as closed linear regions.

Hereinafter, the method for detecting connection points and connecting the connection points used in the above-described processing will be described in detail. First, in order to detect the end points of grain boundaries to be replenished,
Connection points are defined for the two cases shown in B. The white circles in the figure are the connection points. In the example shown in FIG. 4A, the end point when the connected pixels are traced is defined as the joining point. In the example shown in Figure 4B, when the connected pixels branch in two directions or in one direction, the protrusion when tracing the connected pixels in each direction is determined by ∠ABC in the figure at a constant angle. A connection point is defined as: Next, the method of connecting bond points is as shown in _FIG. Or ask for F ₂ .

(1) Evaluation function between bonding points A and B (Fig. 5 A) F ₁ = cosθ ₁・cosθ ₂ /L ^2However , when line segments A and B intersect with other grain boundaries,
Let F ₁ =0.

(2) Evaluation function of bonding point A and grain boundary point C (Figure 5B) F ₂ = a・(cos2θ ₃ ) ² /L ² where -π/4≦θ≦π/4, a=1/2 .

Here, find bonding point B and grain boundary point C where the evaluation functions F ₁ and F ₂ are maximum, and if F ₁ ≧ F ₂ , connect bonding point B and bonding point A where the evaluation functions are maximum, and F ₁ < If F ₂ , the maximum grain boundary point C and bonding point A are connected.
By the method described above, an image can be expressed as a linear region in which all regions are closed.

The image information that has been supplemented with grain boundary information by the method described above is supplied to the quantitative processing section 7, which calculates the grain size and second phase fraction from the coordinates of the grain boundary position and second phase position. There is. At this time, to obtain the second phase fraction, line connection processing is not necessary, and the second phase portion extracted by binarization after line element emphasis is
By measuring under the judgment condition that the area is larger than a preset area, the area of only the second phase portion is measured and the ratio to the total area is calculated to determine the second phase fraction. ing.

The actual processing results will be explained below. FIG. 6 is a diagram showing a metallographic image of a ferrite-pearlite structure obtained by corroding a steel material with a nital corrosive solution. FIG. 7 is a diagram showing the processing result of extracting grain boundaries from the metallographic image shown in FIG. 6 by only binarizing using the conventional method. In the example shown in FIG. 7, noise due to grain boundary discontinuities, scratches, rust, etc. can be seen. FIG. 8 is a diagram showing the result of performing binarization processing and line connection processing after line element enhancement on the metallographic image shown in FIG. 6 using the apparatus of the present invention. It is clear that in the example shown in FIG. 8, the crystal grain size can be determined more accurately than in the example shown in FIG. 7 using the conventional apparatus.

In the embodiments described above, image information was obtained by capturing a microscope image with an imaging device, but it is also possible to use other image input devices, and it is also possible to connect a data processing device or the like to the device of the present invention. It is also possible.

As is clear from the detailed explanation above, according to the grain size and second phase fraction measuring device of the present invention, noise caused by polishing scratches, rust, etc. is removed by emphasizing line elements in image information. Furthermore, since grain boundary connection processing is performed on the image signal with emphasis on line elements, it is possible to measure crystal grain size more accurately than with conventional equipment. Measurements of particle size and second phase fraction can be made.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventional automatic image analysis device capable of measuring particle size and second phase fraction, and FIG. 2 is an implementation of the particle size and second phase fraction measuring device of the present invention. A line diagram showing an example; FIG. 3 is a line diagram showing a line emphasis filter; FIG.
Figures A and B are diagrams for explaining the method of connecting bonding points, Figure 6 is a diagram showing a metallographic image of a ferrite-pearlite structure, and Figure 7 is a diagram showing a metallographic image of a ferrite-pearlite structure using a conventional method. Figure 8 is a diagram showing the processing results of extracting grain boundaries only by binarization of It is a figure which shows the result of performing a process. 1... Microscope, 2... Imaging device, 3... A/D conversion section, 4... Image processing section, 5... Binarization processing section,
6... Arithmetic processing section, 7... Quantitative processing section.

Claims (1)

[Claims] 1. A microscope for observing the metallographic structure, an imaging device connected to this microscope that captures the metallographic image and outputs analog image information, and converting the analog image information from this imaging device into gray-level digital image information. an analog/digital converter that performs the conversion, an image processor that emphasizes grain boundary areas by applying line element extraction filter processing to the digital image information converted by the analog/digital converter, and an image obtained from the image processor. A binarization processing unit extracts the second phase part and grain boundary part from the metallographic image by comparing it with a preset threshold value, and a binarization processing unit extracts the linear part from the binarized image. As a grain boundary,
An arithmetic processing unit that calculates corrected image information by extending linear portions of the extracted grain boundary portions where the grain boundaries are not closed, so that all the grain boundaries are in a closed state; A quantitative processing section that measures the particle size and second phase fraction from the coordinates of the grain boundary position and second phase position in the image information obtained by the processing section. rate measuring device.