JP2020085888A - Crystal structure evaluation method and crystal structure evaluation device - Google Patents

Abstract

To provide a crystal structure evaluation method and a crystal structure evaluation device each of which allows for evaluation of non-uniformity in a crystal structure using ultrasonic waves, even when a portion having the non-uniformity in the crystal structure exists in only a part of whole material including crystal grains.SOLUTION: A crystal structure evaluation method comprises: a measuring step of causing a ultrasonic wave U to enter a material S to be inspected formed of a material including crystal grains S3, from a plurality of incidence points P on a surface, measuring intensity of a scattered wave U3 detected as scattering intensity, for every incidence point P; a statistical processing step of organizing the number of incidence points P for which prescribed scattering intensity can be acquired in the measuring step, as a function of scattering intensity, for generating a scattering intensity function; and an evaluation step of determining that, as a peak width of the scattering intensity function acquired in the statistical processing step is larger, non-uniformity of a crystal structure in the material S to be inspected is higher. There is also provided the crystal structure evaluation device comprising an ultrasonic inspection device 11 executing such a crystal structure evaluation method.SELECTED DRAWING: Figure 3

Description

The present invention relates to a crystal structure evaluation method and a crystal structure evaluation device, and more particularly, to a crystal structure evaluation method and a crystal structure evaluation device for evaluating the nonuniformity of the crystal structure of a material using ultrasonic waves.

In a material including crystal grains, such as a metal material, it is important to determine the state of the crystal structure by inspection in order to secure desired material characteristics. Ultrasonic inspection is used as a method of nondestructively determining the state of crystal grains.

For example, Patent Document 1 discloses a method for determining the anisotropy of crystal grains using ultrasonic waves. Here, ultrasonic waves are oscillated in the material to be measured, the reflected waves within a predetermined time range are extracted from the reflected waves received, and the frequency analysis of the extracted reflected waves is performed. It is determined whether or not the crystal grains of the material to be measured are deformed based on the ratio of the total value of the reflected wave power of a predetermined frequency or more to the value. Utilizing the fact that the anisotropy of the crystal grains inside the material to be measured causes the distortion of harmonics and waveforms, and the anisotropy of the crystal grains occurs when the above ratio exceeds a certain value. It is determined that there is.

JP, 2013-257146, A

By using ultrasonic waves as in the determination method disclosed in Patent Document 1, the state of crystal grains such as anisotropy can be determined. However, in the method of analyzing the reflected wave in a single measurement like the method of Patent Document 1, it is only possible to detect the state as an average of the material structure existing in the region through which the ultrasonic wave passes, and the crystal structure When a region where the state of <1> has changed nonuniformly exists locally, it is difficult to detect the presence of such a region. For example, in the method of Patent Document 1, if the entire crystal grains contained in the structure have high anisotropy, the anisotropy can be detected, but the crystal grain with low anisotropy Even if a crystal grain with high anisotropy is locally generated in the inside, it is difficult to detect the existence of such a crystal grain with high anisotropy.

In the case of materials such as metals, even if most of the crystal grains in the structure are well aligned in characteristics such as grain size and anisotropy, most of the crystal grains are similar in grain size and anisotropy. Regions with different values may locally occur, resulting in uneven tissue. Such local texture non-uniformity can significantly affect the properties of the material. Further, when a uniform structure composed of fine crystal grains is required, high accuracy is also required for quality assurance. Therefore, a method capable of non-destructively detecting the local nonuniformity of the crystal structure is desired.

The problem to be solved by the present invention is that, in a material containing crystal grains, even if a site having nonuniformity in the crystal structure exists only in a part of the entire material, the It is an object of the present invention to provide a crystal structure evaluation method and a crystal structure evaluation device capable of evaluating uniformity.

In order to solve the above-mentioned problems, the crystal structure evaluation method according to the present invention is a scattered wave detected by injecting ultrasonic waves from a plurality of incident points on the surface of a material to be inspected made of a material containing crystal grains. , The measurement step of measuring each of the incident points as the scattering intensity, and the number of the incident points for which a predetermined scattering intensity is obtained in the measuring step is arranged as a function of the scattering intensity to obtain the scattering intensity. A statistical processing step of creating a function, and an evaluation step of considering that the larger the peak width of the scattering intensity function obtained in the statistical processing step is, the higher the heterogeneity of the crystal structure in the inspected material is. It is a thing.

Here, in the evaluation step, as the nonuniformity of the crystal structure, it is preferable to evaluate nonuniformity in at least one of a grain size, a component composition, and anisotropy of crystal grains in the material to be inspected.

In the measuring step, in the reflection direction of the incident ultrasonic wave, the intensity of the ultrasonic signal is measured as a function of time, and the reflected wave reflected on the surface of the inspection target material and the bottom surface facing the surface are measured. The scattering intensity may be obtained by integrating the intensity of the ultrasonic signal observed in the time between the reflected wave and the reflected wave. In this case, in the evaluation step, it may be considered that the larger the scattering intensity of the median of the peaks of the scattering intensity function, the larger the average grain size of the crystal grains. In the measuring step, the ultrasonic signal measured as a function of time may be subjected to frequency analysis, and the scattering intensity may be obtained based on a signal having the same frequency as the incident ultrasonic wave. Further, in the measuring step, an ultrasonic inspection device that performs generation and detection of ultrasonic waves moves around the inspection target material relative to the inspection target material, so that the plurality of incident points are detected. On the other hand, it is preferable that the ultrasonic wave is incident and detected.

The material to be inspected is a bar material, and in the measuring step, at least 180° along the circumferential direction of the bar material, and at least a part of the area along the longitudinal direction of the bar material, It is advisable to set a plurality of incident points.

In the evaluation step, the crystal structure may be evaluated to be non-uniform when the peak width is larger than a predetermined threshold value.

In the evaluation step, the scattering intensity function may be separated into a plurality of peaks having different median scattering intensities. In this case, in the evaluation step, the scattering intensity function may be separated into two peaks, a main peak and a sub-peak having a peak height smaller than that of the main peak. Further, with the mode of the scattering intensity function as the center, a symmetrical copy of the scattering intensity function on the side with a small distribution width is defined as the main peak, and the contribution of the main peak is removed from the scattering intensity function. It is preferable that the sub-peak is one. Then, the sub-peaks are weighted by the distance from the mode of the scattering intensity function and integrated, and the larger the obtained integrated value, the higher the heterogeneity of the crystal structure may be evaluated.

A crystal structure evaluation apparatus according to the present invention includes an ultrasonic inspection apparatus that generates and detects ultrasonic waves, and executes a crystal structure evaluation method as described above on a material to be inspected made of a material containing crystal grains. It is a thing.

Here, it is preferable that the crystallographic structure evaluation apparatus further includes an exerciser that moves the ultrasonic inspection apparatus relative to the material to be inspected.

In the crystal structure evaluation method according to the above-mentioned invention, ultrasonic waves are incident on a material to be inspected made of a material containing crystal grains from a plurality of incident points on the surface, and the scattering intensity is measured for each incident point. At this time, if the nonuniformity of the crystal structure contributing to the scattering is low (the uniformity is high), the dispersion of the scattering intensity obtained at each incident point becomes small. On the other hand, when the nonuniformity of the crystal structure that contributes to scattering is high, the obtained scattering intensity varies greatly depending on the incident point. Therefore, the higher the nonuniformity of the crystal structure, the larger the peak width in the scattering intensity function in which the number of incident points at which a predetermined scattering intensity is obtained is arranged as a function of the scattering intensity. In this way, by paying attention to the peak width of the scattering intensity function obtained by measuring the scattering intensity at a large number of incident points, the site having non-uniformity in the crystal structure is a part of the entire material. Even when it exists only in the non-uniformity of the crystal structure, it can be evaluated from the result of the measurement using the ultrasonic wave. At this time, the measurement result can be simply crystallized by a simple statistical process for collecting the number of incident points at which a predetermined scattering intensity is obtained, without performing a complicated calculation process or simulation for the measurement result. It can correspond to the heterogeneity of the organization.

Here, in the evaluation step, when the nonuniformity of the crystal structure is evaluated as the nonuniformity in at least one of the grain size, the component composition, and the anisotropy of the crystal grain in the inspected material, Since the grain size, component composition, and anisotropy of the crystal grains in the material all have characteristics that have a great influence on the ultrasonic scattering intensity, the peak width of the scattering intensity function obtained by ultrasonic measurement is Using as an index, it is possible to sensitively detect nonuniformity in these characteristics.

In the measurement process, the intensity of the ultrasonic signal is measured as a function of time in the reflected direction of the incident ultrasonic wave, and the reflected wave reflected on the surface of the material to be inspected and the reflection wave reflected on the bottom surface facing the surface are measured. When calculating the scattering intensity by integrating the intensity of the ultrasonic signal observed at the time between waves, distinguish it from the reflected wave reflected on the surface or bottom of the inspected material, and The acoustic signal can be detected and a scatter intensity function can be created.

In this case, in the evaluation step, the larger the central value of the scattering intensity function, the larger the scattering intensity of the crystal grains, the larger the average grain size of the crystal grains. By utilizing the increase, not only the non-uniformity of the crystal structure but also the average grain size of the crystal grains can be evaluated based on the scattering intensity function obtained by ultrasonic measurement.

In the measuring step, the ultrasonic signal measured as a function of time is subjected to frequency analysis, and based on the signal of the same frequency as the incident ultrasonic wave, according to the mode of obtaining the scattered intensity, the scattered wave is equal to the incident ultrasonic wave. Since it is strongly observed at the same frequency, the scattered wave is detected with high sensitivity and in distinction from the contributions of other components by obtaining the scattering intensity from the signal of that frequency, and it is possible to accurately detect the nonuniformity of the crystal structure. It becomes easy to match.

Further, in the measurement process, an ultrasonic inspection device that generates and detects ultrasonic waves moves around the inspection target material relative to the inspection target material, so When performing sound wave incidence and detection, an ultrasonic inspection device that has been conventionally used as a flaw detector is used to perform ultrasonic wave incidence and detection at multiple incident points, and the unevenness of the crystal structure is observed. It becomes possible to evaluate the sex.

The material to be inspected is made of a bar material, and in the measuring step, a plurality of incident points are set so as to extend over at least 180° along the circumferential direction of the bar material and over at least a part of the region along the longitudinal direction of the bar material. In the case of setting, it is possible to inspect whether or not there is a region where the crystal structure is non-uniform in the range over the entire cross section of the rod and the predetermined region in the longitudinal direction.

In the evaluation step, when the peak width is larger than a predetermined threshold, when the crystal structure is evaluated to be non-uniform, the peak width of the scattering intensity function corresponding to the upper limit of the allowable non-uniformity is set. By setting the threshold as a threshold value, even if there is no information on the detailed correspondence between the peak width of the scattering intensity function and the nonuniformity of the crystal structure, the material to be inspected containing the nonuniformity which is not allowed is included in the crystal structure. Can be found and removed.

Further, in the evaluation step, in the case of separating the scattering intensity function into a plurality of peaks having different median scattering intensities, when a plurality of different crystal structures such as crystal grain sizes are mixed, those crystals It is possible to obtain the information on the state of the crystal structure by analyzing the scattering intensity function by separating the contribution for each type of the structure.

In this case, in the evaluation step, according to the mode in which the scattering intensity function is separated into two peaks, that is, the main peak and the sub-peak whose peak height is smaller than that of the main peak, the scattering intensity function can be obtained by a simple analysis. Can be separated. In this form, the main peak is associated with a highly uniform region occupying most of the crystal structure, and the sub-peak is associated with a non-uniform crystal structure mixed in the highly uniform crystal structure. Can be attached.

Furthermore, with the mode of the scattering intensity function at the center, a symmetrical copy of the scattering intensity function on the side with a smaller distribution width is used as the main peak, and the one obtained by removing the contribution of the main peak from the scattering intensity function is the sub-peak. According to this mode, the contributions of the main peak and the sub-peak can be separated by a particularly simple analysis.

Then, the sub-peak is weighted and integrated by the distance from the mode of the scattering intensity function, and the larger the obtained integral value is, the higher the heterogeneity of the crystal structure is, the higher the crystallinity of the crystal structure is. Quantitative evaluation of the degree of tissue heterogeneity can be easily performed.

In the crystal structure evaluation apparatus according to the above-mentioned invention, the ultrasonic inspection apparatus can detect the signal including the contribution of scattering by injecting the ultrasonic wave to each incident point on the material to be inspected. Then, by performing the crystal structure evaluation method according to the above-mentioned invention based on the obtained scattering intensity, it is possible to easily evaluate the nonuniformity of the crystal structure of the material to be inspected. The ultrasonic inspection device is widely used as a flaw detection device and the like, and such a device can be diverted to construct a crystal structure evaluation device.

Here, when the crystallographic structure evaluation apparatus further includes an exercise device that moves the ultrasonic inspection apparatus relative to the material to be inspected, a common ultrasonic inspection apparatus is used to detect the material on the material to be inspected. Measurements can be performed at a plurality of incident points to evaluate the nonuniformity of the crystal structure.

It is a figure which shows the structure of the crystal structure evaluation apparatus concerning one Embodiment of this invention. An example of a data group obtained by the crystal structure evaluation apparatus is shown. It is a figure explaining the behavior of the ultrasonic wave in a to-be-inspected material, (a) is the whole to-be-inspected material, (b) has shown the enlarged view of a structure. It is an example of the ultrasonic signal detected by the ultrasonic inspection apparatus. When the crystal grain size is large, (a) an SEM image of the crystal structure, (b) behavior of ultrasonic waves, and (c) an example of obtained ultrasonic signals are shown. In the case where the crystal grain size is small, (a) an SEM image of the crystal structure, (b) an ultrasonic behavior, and (c) an example of the obtained ultrasonic signal are shown. It is a figure which shows typically the example of a crystal structure with the path|route of an ultrasonic wave, and the scattered wave obtained, (a) is a uniform and fine structure, (b) is a non-uniform and fine structure containing a coarse crystal grain, (C) shows a non-uniform/fine structure containing particularly fine crystal grains, and (d) shows a uniform/coarse structure. It is a figure explaining the correspondence between a scattering intensity function and the state of a crystal structure, (a) explains creation of a scattering intensity function, (b) is a peak width of a scattering intensity function, a median, and a crystal structure. It shows the relationship of the states. It is a figure explaining the separation into two peaks of a scattering intensity function. (A) shows a left-right asymmetrical scattering intensity function before separation, and (b) also shows two separated peaks. It is a figure explaining contribution of a sub-peak when the degree of non-uniformity of crystal structure changes. (A) shows the scattering intensity function together with the separated sub-peaks in the case where the crystal structure has high homogeneity and (b) shows the case where a partially non-uniform structure is generated. The change in the scattering intensity function obtained when the heat treatment temperature is changed for the Ti-based alloy is shown, (a) shows the scattering intensity function itself, and (b) shows the standard deviation in the scattering intensity function. .. The change in the scattering intensity function obtained when the forging ratio is changed is shown for the Ti-based alloy. It is a figure which shows the relationship between the variation of the pixel in a SEM image, and a nonuniformity evaluation value. In the figure, the sample number corresponding to each plot point is also displayed.

The crystal structure evaluation method and the crystal structure evaluation apparatus according to the embodiment of the present invention will be described below. The crystal structure evaluation method according to one embodiment of the present invention is a method for evaluating the non-uniformity of the crystal structure of a material to be inspected made of a material containing crystal grains, and the crystal according to one embodiment of the present invention It can be performed using a tissue evaluation device.

[Crystal structure evaluation device]
First, a crystal structure evaluation apparatus according to an embodiment of the present invention will be described. FIG. 1 shows an outline of a crystal structure evaluation apparatus 1 according to this embodiment.

The crystal structure evaluation apparatus 1 includes an ultrasonic inspection apparatus 11, a motion apparatus 12, and a calculation/control apparatus 13, and with respect to the inspection material S, the crystal structure of the inspection material S is determined. Evaluate non-uniformity.

First, the inspected material S to be inspected in the present crystal structure evaluation apparatus 1 may be any material as long as it is made of a material containing crystal grains, such as a polycrystalline material, and the material and shape are not limited. Not something. The material may be either a metal or a nonmetal, or may include both of them, but in the following, it is mainly assumed that the material is a metal material. Above all, the data shown as an example is obtained for the inspected material S made of a titanium-based alloy. Titanium-based alloys are metals that can form α-phase and β-phase, and the state of the formed phase easily changes depending on the conditions of heat treatment and forging. It is important to assess the condition of. Among them, in the α+β type alloy made of a titanium-based alloy, the α-phase crystal grains and the β-phase crystal grains coexist stably, and the evaluation of the crystal structure becomes particularly important. The crystal structure evaluation apparatus 1 of the present invention can be preferably used to evaluate the state of the crystal structure of iron-based alloys as well as two-phase SUS alloys. As the shape of the material S to be inspected, in the following, it is assumed that a bar, particularly a round bar is targeted.

The ultrasonic inspection device 11 is a device that generates ultrasonic waves, makes them incident on an object, and detects ultrasonic waves reflected or scattered by the object. Here, the ultrasonic inspection apparatus 11 applies a pulse to a point of incidence P set on the surface of the material S to be inspected mounted on the exerciser 12 from a position distant from the surface of the material S to be inspected substantially perpendicularly. The ultrasonic wave U having a circular shape is irradiated and made incident on the material to be inspected. Then, in the reflection direction of the ultrasonic wave U, the ultrasonic signal returned by being reflected or scattered by the material S to be inspected is detected. The ultrasonic inspection device 11 of this type is generally used as an ultrasonic probe in a flaw detection device that detects a flaw in a material, and in the present embodiment, such an ultrasonic probe is used as an ultrasonic probe. It can be used as the inspection device 11. As the frequency of the ultrasonic wave U generated by the ultrasonic inspection device 11, a frequency used in a general ultrasonic probe can be applied, but from the viewpoint of increasing the intensity of scattering by crystal grains, 1 It is preferable to use a frequency of about 30 MHz. Further, more specifically, as a relationship between the average crystal grain size d of the material and the wavelength λ of the ultrasonic wave, under the condition that the relationship of (1/30)λ<d<(1/3)λ is satisfied, The inspection according to the embodiment can be preferably applied, and it is preferable to select a frequency that satisfies the condition.

The exercise device 12 moves the inspection object S with respect to the ultrasonic inspection device 11. Here, the exercise device 12 is configured as a trapezoidal device that can perform an axial rotation R and a translational movement T. The material S to be inspected is placed on the upper surface of the exercise device 12. When the material S to be inspected has a rod shape (columnar shape) such as a round bar, the material S to be inspected is placed upright on the upper surface of the exercise device 12 at one of the end faces. The exercise device 12 can rotate the material S to be inspected with respect to the ultrasonic inspection device 11 by performing the axial rotation R. It is preferable that the exercise device 12 is capable of rotating the inspected material S axially over the entire circumference. Further, the exercise device 12 can move the material S to be inspected in the translation direction with respect to the ultrasonic inspection device 11 by performing the translational movement T. When the rod-shaped inspected material S is erected on the upper surface of the exercise device 12, the translational movement T is to move the inspected material S along the longitudinal direction.

The calculation/control device 13 is a device that controls the ultrasonic inspection device 11 and the exercise device 12 and analyzes the data obtained by the ultrasonic inspection device 11 by calculation, and is configured by, for example, a computer. You can Specifically, the arithmetic/control device 13 controls the ultrasonic measurement by the ultrasonic inspection device 11 and the movement of the inspected material S by the exercise device 12. Then, an ultrasonic signal output from the ultrasonic inspection apparatus 11 is input as an electric signal corresponding to the detected ultrasonic intensity, and the ultrasonic signal is analyzed. The content of the analysis will be described in detail later as a crystal structure evaluation method, but the scattering intensity is extracted from the obtained ultrasonic signal, and a statistical analysis based on the scattering intensity is performed to determine the crystal structure. Evaluate non-uniformity.

In order to evaluate the non-uniformity of the crystal structure of the material S to be inspected, the arithmetic/control device 13 drives the axial rotation R and the translational motion T of the motion device 12 when performing ultrasonic measurement. The rotational position and translational position of the material S to be inspected so that the ultrasonic wave U can be incident from the ultrasonic inspection apparatus 11 to a certain one incident point P set on the surface (side surface) of the material S to be inspected. Adjust and stop. Then, the ultrasonic inspection apparatus 11 is controlled so that the ultrasonic waves U are made to enter the inside of the inspection object S from the incident point P substantially vertically, and the ultrasonic waves reflected by the inspection object S are received. To detect. At this time, an ultrasonic signal indicating the intensity of the detected ultrasonic wave is input to and stored in the arithmetic/control device 13 in the form of a function of time.

When the measurement is completed for one incident point P, the arithmetic/control device 13 drives the axis rotation R of the exercise device 12 so that the ultrasonic wave U can be incident on another one incident point P. The material S to be inspected is rotated and stopped. Then, the same measurement as that performed on the incident point P is performed to acquire the ultrasonic signal. When the same measurement is performed on the incident points P set on the entire circumference of the material S to be inspected at a predetermined angular interval such as an interval of 1°, the arithmetic/control device 13 then causes the movement device 12 to translate. Drive movement T. Then, the same measurement is repeated while rotating at a predetermined angle interval. In this way, the measurement is repeated along the longitudinal direction of the inspection target material S at predetermined length intervals such as 0.5 mm at predetermined angle intervals with respect to the entire circumference. As a result, ultrasonic signals are acquired for a large number of incident points P set on the entire surface (side surface) of the inspection object S at predetermined angular intervals and length intervals. As many ultrasonic signals as the number of incident points P are acquired, and as shown in FIG. 2, a data group composed of the same number of ultrasonic signals as the number of incident points P is formed. In FIG. 2, each graph represents the ultrasonic wave intensity detected at one incident point P as a function of time. The analysis described below is performed on such a data group.

In the crystal structure evaluation apparatus 1 described above, the ultrasonic inspection apparatus 11 is fixed, and the inspected material S is moved by the movement device 12 to measure the plurality of incident points P. If the device 11 can be moved relative to the inspection material S, the configuration is not limited to such a configuration, the inspection material S is fixed, and the exercise device 12 is moved around the inspection material S. It may be one. The ultrasonic inspection apparatus 11 is relatively moved with respect to the material S to be inspected in both the circumferential direction and the translational direction, so that one ultrasonic inspection apparatus 11 is used to perform measurement on a large number of incident points P. be able to. Alternatively, if the ultrasonic inspection apparatus 11 is arranged so as to surround the entire circumference of the material S to be inspected like an inspection apparatus having a large number of channels, the ultrasonic inspection apparatus 11 is set to the entire circumference of the material S to be inspected without performing a rotational movement. Measurement can be performed at once for the incident point P.

Further, in the crystal structure evaluation apparatus 1 described above, the ultrasonic wave U which is vertically incident on the material S to be inspected is detected in the reflection direction, but the transmitted wave may be detected in the transmission direction. Good. Further, the incident direction of the ultrasonic waves U does not have to be the vertical direction, and may be, for example, an oblique direction.

As described above, the ultrasonic inspection apparatus 11 is also used for flaw detection in the material, and the crystallographic structure evaluation apparatus 1 according to this embodiment can also be used as a flaw detection apparatus. That is, when the crystal structure evaluation apparatus 1 is used to evaluate the nonuniformity of the crystal structure of the material S to be inspected, the material S to be inspected can be detected at the same time or as an independent step.

[Crystal structure evaluation method]
Next, a method for performing the crystal structure evaluation method according to the embodiment of the present invention using the crystal structure evaluation apparatus 1 as described above to evaluate the non-uniformity of the crystal structure of the inspection target material S will be described. ..

(Crystal structure state and ultrasonic scattering)
Before describing each step in the crystal structure evaluation method, the relationship between the state of the crystal structure and the scattering of ultrasonic waves will be described.

FIG. 3A schematically shows the behavior of the ultrasonic waves U incident on the material S to be inspected. Further, FIG. 3B shows an enlarged view of the internal structure of the material S to be inspected. FIG. 4 shows an example of an ultrasonic signal obtained by the ultrasonic inspection device 11. The ultrasonic signals shown in FIG. 4 and FIGS. 5(c) and 6(c), which will be described later, are obtained by extracting a component having the same frequency as the fundamental wave of the incident ultrasonic wave U by frequency analysis.

As shown in FIG. 3A, most of the incident ultrasonic wave U is reflected by the surface S1 of the inspection object S and becomes a surface reflected wave U1. The surface reflected wave U1 is detected with a very large amplitude at the beginning of the time when the ultrasonic signal is detected, as indicated by the component A1 in FIG. In the material S to be inspected, most of the ultrasonic waves U reaching the bottom surface S2 facing the surface S1 are reflected by the bottom surface S2 and become bottom surface reflected waves U2. The bottom surface reflected wave U2 is detected with a relatively large amplitude at the end of the time when the ultrasonic signal is detected, as indicated by the component A2 in FIG.

In the ultrasonic signal, as shown as a component A3 in FIG. 4, in addition to the component A1 due to the surface reflected wave U1 and the component A2 due to the bottom reflected wave U2, a signal with a small amplitude is generated in the time domain between them. Observed continuously for a long time. The component A3 corresponds to the scattered wave U3 generated by the ultrasonic wave U being scattered inside the inspection object S.

As shown in FIG. 3B, which is an enlarged view of a region indicated by a broken line in FIG. 3A, a large number of crystal grains S3 are contained in the metal material forming the material S to be inspected. include. The outer edge of the crystal grain S3 is a crystal grain boundary S4. The ultrasonic wave U incident on the crystal structure is scattered at the crystal grain boundary S4. The size of the crystal grain S3 in the polycrystalline metal material is typically in the order of submicron to micron, and the contribution of backscattering (Rayleigh scattering) is large in the scattering of the ultrasonic wave U. At least a part of the scattered wave U3 generated at the crystal grain boundary S4 reaches the ultrasonic inspection apparatus 11 and is detected. The scattered wave U3 reaching the ultrasonic inspection device 11 becomes a component A3 observed in the time between the surface reflected wave U1 and the bottom surface reflected wave U2 in the ultrasonic signal. Scattering by the crystal grain boundaries S4 occurs over the entire path from the surface S1 to the bottom surface S2 of the inspected material S, so that the signal component A3 due to the scattered wave U3 is observed for a long time.

It is known that the scattering intensity of ultrasonic waves at crystal grain boundaries is proportional to the sixth power of the grain size of crystal grains. That is, as shown in the scanning electron microscope image (SEM) image in FIG. 5A, when the grain size of the crystal grain S3 is large as a whole, as shown in FIG. Strong scattering occurs. Then, as shown in FIG. 5C, in the ultrasonic signal detected by the ultrasonic inspection device 11, the intensity of the component A3 due to the scattered wave U3 increases. On the other hand, as shown in the SEM image of FIG. 6A, when the grain size of the crystal grain S3 is small as a whole, the scattering at the crystal grain boundary S4 becomes weak as shown in FIG. 6B. FIG. 6B shows a form in which almost no scattering occurs. Then, as shown in FIG. 6C, in the ultrasonic signal detected by the ultrasonic inspection device 11, the intensity of the component A3 due to the scattered wave U3 becomes small. As described above, the grain size of the crystal grains S3 forming the crystal structure is reflected on the scattering intensity of ultrasonic waves, and the scattering intensity increases as the grain size increases.

FIG. 7 shows four structures having different crystal grain size uniformity and different crystal grain size. In addition, here, each crystal grain is enlarged and displayed rather than actual. As described above, when fine crystals are uniformly generated (uniform/fine structure) as shown in FIG. 7A, a small scattering intensity is observed, and as shown in FIG. When coarse crystals are uniformly generated (uniform/coarse structure), a large scattering intensity is observed.

Consider a case where ultrasonic waves U are respectively incident on the material S to be inspected from different incident points P (incident points P1 and P2 in the figure) to perform signal detection. In the uniform and fine structure of FIG. 7A, regardless of the incident point P, small crystal grains S3 having a uniform grain size are distributed in the path through which the ultrasonic waves U pass. Therefore, as schematically showing the signal intensity of the scattered wave U3 at the end of the path of the ultrasonic waves in the figure, regardless of the incident point P, a scattering intensity as small as the same is observed. On the other hand, in the uniform/coarse structure of FIG. 7D, large crystal grains S3 having a uniform grain size are distributed in the path through which the ultrasonic waves U pass, regardless of the incident point P. Therefore, regardless of the incident point P, an equally large scattering intensity is observed. Thus, when the particle size is highly uniform (low inhomogeneity), the scattering intensity does not change significantly between the incident points P, and the scattering intensity that reflects the particle size is obtained regardless of the incident point P. Be done. As a result, the scattering intensity does not vary greatly between the incident points P.

On the other hand, in FIG. 7B, a coarse and fine crystal grain M1 (indicated by diagonal lines) is nonuniformly formed in the microstructure of the fine crystal grain S3. There is. Further, in FIG. 7C, in the structure composed of the minute crystal grains S3, the crystal grains M2 finer than the crystal grains S3 (indicated by diagonal lines) are nonuniformly generated. Tissue is formed. For example, in a titanium-based alloy, when the formation of a coarse α phase or the segregation of the β phase occurs in the structure that consists mostly of fine crystals of the α phase, such a non-uniform/fine structure may occur. Can be formed.

As shown in FIGS. 7B and 7C, when the ultrasonic waves U are incident on different inhomogeneous/fine tissues from different incident points P, the ultrasonic waves U pass through the incident points P. The grain size distribution of the grains present in the pathway may vary. For example, in FIG. 7B, the ultrasonic wave U incident from the incident point P1 in the figure passes only through the region where the fine crystal grains S3 are generated, and therefore does not cause strong scattering in the path. .. On the other hand, the ultrasonic wave U incident from the incident point P2 passes through the region where the coarse crystal grains M1 are generated on the way. Therefore, there is a portion where the ultrasonic waves are strongly scattered in the passage. Therefore, when the ultrasonic wave U is incident from the incident point P set at each position on the surface of the inspected material S and the scattering intensity is measured, the fine crystal grains S3 are generated as in the case where the ultrasonic wave U is incident from the incident point P1. In the case where the ultrasonic wave U passes through the region generated by only the ultrasonic wave U, the scattering intensity becomes small, and the ultrasonic wave U passes through the region generated by the coarse crystal grain M1 as in the case where the ultrasonic wave U is incident from the incident point P2. The scattering intensity becomes large. As a result, the scattering intensity changes depending on the incident point P, and the variation in the scattering intensity between the incident points P increases.

On the other hand, in FIG. 7(c), the ultrasonic wave U incident from the incident point P2 in the figure passes through the region where the particularly small crystal grains M2 are generated. Therefore, there is a portion in the passing path where the ultrasonic waves hardly scatter (or weakly). Therefore, when the ultrasonic wave U is incident from the incident point P set at each position on the surface of the inspection target material S and the scattering intensity is measured, as in the case where the ultrasonic wave U is incident from the incident point P2, particularly fine crystal grains When the ultrasonic wave U passes through the region generated by M2, the scattering intensity is smaller than when the ultrasonic wave U does not pass through the region generated by the minute crystal grain M2, as in the case of incidence from the incident point P1. As described above, even when the minute crystal grains M2 are mixed, the scattering intensity changes depending on the incident point P, and the scattering intensity varies between the incident points P as in the case where the coarse crystal grains M2 are mixed. The variation becomes large.

As described above, the variation in the scattering intensity depending on the incident point P reflects the nonuniformity of the crystal grain size in the structure. Therefore, in order to quantitatively analyze the nonuniformity of the particle size, statistical analysis is performed on the scattering intensity obtained at each incident point P. Specifically, as shown in FIG. 8A, the number of incident points P at which a predetermined scattering intensity is obtained is arranged as a function of the scattering intensity to create a scattering intensity function. In FIG. 8A, the horizontal axis indicates the scattering intensity, and the vertical axis indicates the number of data, that is, the number of incident points P at which the predetermined scattering intensity is observed. Each of the data points indicated by circles corresponds to each incident point P, and in the illustrated form, for example, there are 16 incident points P at which the scattering intensity “6” was observed. It is shown.

When the uniformity of the grain size in the crystal structure is high (the nonuniformity is low) and the variation of the scattering intensity obtained for each incident point P is small, the scattering intensity function as shown in FIG. , The data points should be concentrated in a region of narrow scattering intensity, giving narrow peaks. On the other hand, when the non-uniformity of the particle size is high and the dispersion of the scattering intensity obtained for each incident point P is large, the data points are spread over a wide scattering intensity in the scattering intensity function and the width is wide. Should give a big peak of. That is, in the scattering intensity function, the peak width has a high correlation with the nonuniformity of the crystal structure, and it can be evaluated that the larger the peak width, the higher the nonuniformity of the crystal structure.

Further, as described above, the larger the grain size of the entire crystal structure, the larger the scattering intensity, and therefore the data points should be distributed in the region where the scattering intensity is large. Therefore, the scattering intensity at the median value (peak top) of the peak of the scattering intensity function shows a high correlation with the average value of the grain size, and the larger the scattering intensity at the median value, the larger the average grain size in the crystal structure. It can be evaluated that it has become. In this way, in the scattering intensity function created by statistically analyzing the scattering intensity obtained for each incident point P, the scattering intensity of the peak width and the median value is focused to determine the grain size distribution of the crystal structure. Both non-uniformity and average particle size can be evaluated.

FIG. 8B schematically shows the scattering intensity function obtained for each crystal structure shown in FIG. First, for the uniform/fine structure shown in FIG. 7A, a scattering intensity function with a small peak width is obtained, reflecting the high uniformity of the grain size. In addition, the scattering intensity of the median value of the peaks becomes small corresponding to the small average particle size. Also for the uniform/coarse structure shown in FIG. 7D, a scattering intensity function with a small peak width is obtained, as in the case of the uniform/fine structure, reflecting the high uniformity of the grain size. On the other hand, the scattering intensity at the median of the peaks is increased corresponding to the large average particle size.

For the nonuniform/fine structure shown in FIGS. 7B and 7C, a scattering intensity function having a large peak width is obtained, reflecting the high nonuniformity of the particle size. In addition, although there are some coarse grains and particularly fine crystal grains, the number of them is small, reflecting the fact that the average grain size is small, and the scattering intensity of the median peak is small. Become. That is, since the average grain size is the same in the case of the uniform/fine structure of FIG. 7A and the case of the uneven/fine structure of FIGS. 7B and 7C, the center of the peak Although the scattering intensities of the values are almost the same, the peak width becomes wider in the case of the nonuniform/fine structure due to the difference in the nonuniformity of the particle size.

So far, the relationship between the peak width of the scattering intensity function and the non-uniformity of the crystal structure has been described, focusing on the non-uniformity in the grain size distribution as the non-uniformity of the crystal structure. However, not only the grain size but also the peak width of the scattering intensity function can be used as an index having a correlation with the non-uniformity in the distribution of the characteristics of the crystal grain S3. It can be evaluated that the nonuniformity is high. That is, it can be considered that the larger the peak width of the scattering intensity function, the larger the variation in the characteristics among the large number of crystal grains S3 forming the crystal structure.

The characteristic of the crystal grain S3 of interest is not particularly limited as long as it is a characteristic in which the scattering intensity of the ultrasonic wave changes due to the difference in the characteristic, but as the characteristic that greatly affects the scattering intensity of the ultrasonic wave, In addition to the diameter, component composition and anisotropy can be mentioned. If there is nonuniformity in at least one of particle size, component composition, and anisotropy, the nonuniformity may be reflected in the peak width of the scattering intensity obtained by ultrasonic measurement. There is.

The nonuniformity in the component composition may be the presence or absence of the mixture of crystal grains S3 having different component compositions. For example, in an alloy structure in which most of the crystal grains S3 have a uniform component composition, crystal grains S3 made of alloys having different component compositions or crystal grains S3 made of non-metals are When a part is generated, the non-uniformity in the component composition becomes high. Since the scattering factor for ultrasonic waves differs depending on the component composition of the crystal grain S3, the higher the nonuniformity in the component composition, the wider the peak width of the scattering intensity function.

The non-uniformity in anisotropy includes whether or not the shape of each crystal grain S3 has the same degree of anisotropy, and the orientation direction of the crystal grain S3 having a highly anisotropic shape is determined by It is possible to cite whether or not they are available. For example, when crystal grains S3 having a low anisotropy shape are partially generated in most crystal grains S3 having a high anisotropy shape, or when each crystal grain S3 has anisotropy. Although it has a high shape, most of the crystal grains S3 having the same orientation direction have some non-uniformity in anisotropy when some crystal grains S3 having different orientation directions are generated. Become. Since the scattering factor for ultrasonic waves differs depending on the specific shape and arrangement direction of the crystal grains S3, the higher the nonuniformity in the anisotropy of the shape and orientation, the wider the peak width of the scattering intensity function.

(Each step of the crystal structure evaluation method)
Next, in the crystal structure evaluation method according to the embodiment of the present invention, each process executed by utilizing the correlation between the scattering intensity function and the state of the crystal structure as described above will be described. In the evaluation method according to this embodiment, the measurement process, the statistical processing process, and the evaluation process are performed in this order.

(1) Measuring Process In the measuring process, the intensity (scattering intensity) of the scattered wave U3 detected by the ultrasonic waves U being incident from a plurality of incident points P set on the surface (side surface) of the material S to be inspected, Measurement is performed for each incident point P. In the measurement process, first, as described above with respect to the crystal structure evaluation apparatus 1, the arithmetic/control device 13 controls the exercise device 12 and the ultrasonic inspection device 11 to determine a predetermined angular interval and length interval. Then, the ultrasonic wave U is incident on each of the plurality of incident points P set on the surface of the inspection object S, and the ultrasonic signal is acquired. By the measurement, a data group as shown in FIG. 2 is obtained.

Here, on the surface of the material S to be inspected, the range in which the incident point P is set and the measurement is performed is a region in the material S to be inspected in which a crystal structure different from the surrounding may be nonuniformly generated. Any setting may be used as long as the ultrasonic wave U incident from any of the incident points P can reach a region having a sufficiently larger volume. From the viewpoint of sufficiently inspecting whether or not a region having a non-uniform crystal structure is generated in the entire inspected material S, the ultrasonic wave U is made to reach almost the entire inspected material S. Therefore, it is preferable to provide a range for setting the incident point P. When the material S to be inspected is a rod-shaped material, the incident point P may be set over the entire circumference in the circumferential direction and at least a part of the area along the longitudinal direction, preferably the entire area. The incident point P does not necessarily have to be set over the entire circumference, and if it is set over at least 180°, it is possible to inspect the tissue over the entire cross section. In particular, when the material S to be inspected has a shape that is mirror-symmetrical with respect to the central axis such as a round bar, it is sufficient to set the incident point P over 180° (half circumference).

Ultrasonic measurement is sequentially performed on each of the set incident points P, and if a data group as shown in FIG. 2 is obtained, then the supersonic waves obtained for each incident point P forming the data group are obtained. The scattering intensity is extracted for each of the sound wave signals. The scattering intensity is an amount indicating the intensity of the scattered wave U3 generated inside the inspection object S.

At this time, first, frequency analysis is performed on each ultrasonic signal recorded as a temporal change in ultrasonic intensity, and a signal of a specific frequency used for subsequent analysis is extracted. For example, a short-time Fourier transform (STFT) may be performed on each ultrasonic signal to extract a temporal change with respect to a component having the same frequency as the fundamental wave of the incident ultrasonic wave U. The graphs shown in FIG. 4, FIG. 5(c), and FIG. 6(c) are obtained by extracting the time change of the component of the same frequency as the fundamental wave by the STFT.

As described above, as shown in FIG. 4, the component A1 having a large amplitude observed in the initial stage of the ultrasonic signal is due to the surface reflected wave U1, and the component A2 having a relatively large amplitude observed in the final stage. Is due to the bottom surface reflected wave U2. The component A3 having a small amplitude observed between the components A1 and A2 is due to the scattered wave U3. Therefore, the evaluation area G is set at the time between the components A1 and A2 so that the influence of the signals of the surface reflected wave U1 and the bottom surface reflected wave U2 can be sufficiently excluded, and the scattered area U3 is set in the evaluation area G. The strength of the ultrasonic signal may be evaluated.

The intensity of the scattered wave U3 can be evaluated by the energy of the scattered wave U3, for example. Since the energy of ultrasonic waves is proportional to the square of the amplitude, the value of the square of the amplitude can be integrated in the set evaluation region G to obtain the intensity of the scattered wave U3, that is, the scattered intensity. The calculation/control device 13 stores the value of the scattering intensity obtained by such integration in association with the incident point P. Not only the energy but also an amount having a positive correlation with the intensity of the scattered wave U3 can be used for the analysis as the scattered intensity. For example, in the evaluation area G, the integral of the absolute value of the amplitude can be used as the scattering intensity.

In this way, if the scattering intensity can be extracted from the ultrasonic signal obtained at a certain incident point P, the arithmetic/control device 13 can obtain a plurality of incident points P as shown in FIG. Similar processing is performed on each of the ultrasonic signals forming the obtained data group to extract and store the scattering intensity. Note that, here, the processing for extracting the scattered intensity is performed on the signal of the same frequency component as the fundamental frequency extracted by the frequency analysis by the STFT, but this is because the scattered wave U3 is at the fundamental frequency. This is because it is most strongly observed, and it is easy to secure detection sensitivity and distinguish it from the contribution of other phenomena. However, the method of processing the ultrasonic signal is not limited to the above as long as the method can extract the scattered intensity with sufficient accuracy. For example, when the contribution of the scattered wave U3 is sufficiently large, the frequency analysis is omitted, and the scattered intensity is extracted by performing integration or the like on the time-varying signal of the total intensity of the detected ultrasonic waves. May be. Alternatively, the scattering intensity may be extracted from a signal of a frequency other than the fundamental frequency obtained by frequency analysis. Further, when performing frequency analysis, the specific method is not limited to STFT, and for example, fast Fourier transform (FFT) can also be used.

(2) Statistical processing step In the statistical processing step, statistical processing is performed based on the information of the scattering intensity obtained in association with each incident point P in the above measurement step, and a scattering intensity function is created.

The generation of the scattering intensity function is performed by determining the number of incident points P at which a predetermined scattering intensity is obtained, as described above with reference to FIG. 8A for the state of the crystal structure and the scattering of ultrasonic waves. It is done by organizing as a function of scattering intensity. At this time, the values of the scattering intensity may be divided into fixed intervals, and the number of incident points P at which the scattering intensity is obtained in each division may be totaled.

At this time, the data points for all incident points P set on the surface of the inspection object S may be put together into one scattering intensity function, but the surface area of the inspection object S is divided into a plurality of parts, A plurality of scattering intensity functions may be created by organizing the data points for each. Then, the nonuniformity of the crystal structure can be evaluated for each part of the inspection target material S. For example, when the material S to be inspected is a rod-shaped material such as a round bar, the material S to be inspected is divided into a plurality of portions having a predetermined length along the longitudinal direction, and each portion is The data point corresponding to the incident point P set on the entire circumference over the predetermined length can be arranged to create the scattering intensity function of that portion. Then, it is possible to evaluate the non-uniformity of the crystal structure within each site for each site.

(3) Evaluation Step In the evaluation step, the nonuniformity of the crystal structure of the material S to be inspected is evaluated using the scattering intensity function obtained in the statistical processing step.

As described above with reference to FIGS. 7 and 8B, the state of the crystal structure and the scattering of ultrasonic waves are obtained by statistically processing the scattering intensity obtained for each incident point P. The peak width of the scattering intensity function has a high correlation with the nonuniformity of the crystal structure, and it can be considered that the larger the peak width, the higher the nonuniformity of the crystal structure. Therefore, in the evaluation step, the peak width of the scattering intensity function is obtained, and it is evaluated that the larger the width, the higher the nonuniformity of the crystal structure.

The method for obtaining the peak width of the scattering intensity function is not particularly limited, and the full width at half maximum (FWHM) can be used as the peak width, for example. Alternatively, an amount having a positive correlation with the peak width may be used instead. As shown by the solid line in FIG. 8A, when the scattering intensity function can be approximated to a normal distribution, the standard deviation (σ) can be used for evaluation as an amount corresponding to the peak width.

After estimating the peak width of the scattering intensity function, the degree of nonuniformity in the crystal structure is evaluated based on the peak width. Specifically, it is evaluated that the larger the peak width, the higher the nonuniformity. Here, as the characteristic of the crystal grain S3 in which the non-uniformity is reflected in the peak width of the scattering intensity function, the crystal grain size, the component composition, the anisotropy, etc. can be mentioned. If it is known which of the characteristics that may cause nonuniformity in the material forming the inspection target material S, the peak width of the scattering intensity function is set to the degree of nonuniformity in the characteristics. Can be converted. For example, when unevenness of the crystal grain size is most likely to appear as the unevenness of the crystal structure due to fluctuations in the conditions at the time of manufacturing the material, the peak width of the scattering intensity function is defined as the unevenness in the crystal grain size. Can be converted to a degree.

When evaluating the degree of non-uniformity in the crystal structure based on the peak width of the scattering intensity function, reference data showing the correspondence relationship between the degree of non-uniformity of the crystal structure and the peak width was used in advance tests, etc. If it is collected by, the peak width obtained by the measurement for the inspected material S can be associated with the degree of nonuniformity of the crystal structure. For example, a large number of reference samples prepared in advance under various conditions and having varying degrees of nonuniformity of the crystal grain size are prepared, and the nonuniformity of the crystal structure is observed by SEM observation of the cross section for each of the reference samples. And the peak width of the scattering intensity function should be estimated. Then, the peak width of the scattering intensity function actually obtained for the inspected material S to be inspected is compared with the peak width obtained for each reference sample. If there is a reference sample having a similar peak width, it is possible to evaluate that the material S to be inspected has the same degree of non-uniformity in particle size as the reference sample.

Alternatively, in the process of manufacturing a metal material, when it is determined whether or not each manufactured individual has non-uniform crystal structure that cannot be tolerated from the viewpoint of material properties, etc. It is not necessary to evaluate the degree of non-uniformity of the particle size of the above. In such a case, it is not necessary to collect reference data using a plurality of types of reference samples, one reference sample that is the upper limit of allowable heterogeneity is prepared, and the reference sample is It is sufficient to estimate the peak width of the scattering intensity function as a threshold value in advance. Then, the estimated threshold value may be compared with the peak width of the scattering intensity function actually obtained for the inspection target material S to be inspected. When the obtained peak width is less than or equal to the set threshold value, non-uniformity of the crystal structure at an unacceptable level does not occur, and a crystal structure having sufficiently high uniformity is obtained. Can be evaluated. On the other hand, when the obtained peak width is larger than the threshold value, it is estimated that a crystal structure having an unacceptable level of nonuniformity is generated.

Individuals determined to have a crystal structure having an unacceptable level of nonuniformity in the manufacturing process of the metal material may be excluded from the objects of processing and shipping in the subsequent steps. In addition, the manufacturing apparatus may be inspected, the manufacturing conditions may be reviewed, and measures may be taken so that the uniformity of the crystal structure can be improved in the individual manufactured later.

In the statistical processing step, when the surface of the material S to be inspected is divided into a plurality of parts and a scattering intensity function is created for each part, the nonuniformity of the crystal structure should be evaluated for each part. You can For example, it is possible to determine whether or not a crystalline structure having an unacceptable level of nonuniformity occurs in each part. If an unacceptable level of non-uniformity is found in only some parts along the longitudinal direction of the rod-shaped test material S, it is possible to remove only that part by cutting or the like. You can do it.

As described above, in the crystal structure evaluation method according to the present embodiment, by utilizing the fact that the scattering intensity of ultrasonic waves differs depending on the state of the crystal grains S3, the ultrasonic wave is superposed from a plurality of incident points P on the surface of the inspection object S. Based on the scattering intensity observed when a sound wave is incident, the nonuniformity of the crystal structure can be evaluated easily and nondestructively. The grain size of the crystal grain S3 of the polycrystalline metal material is typically in the submicron to micron order and smaller than the wavelength of ultrasonic waves, but the scattering phenomenon, particularly backscattering, should be used for evaluation. Thus, the nonuniformity in the characteristics of the crystal structure such as the grain size can be detected with high sensitivity.

Unlike the case where the ultrasonic wave is incident on only one point for the inspection or the ultrasonic wave is collectively applied to a wide area for the inspection, the scattering intensity individually measured for a large number of incident points P is used. By statistically analyzing the data of 1., the presence of such a region can be sensitively detected even if the region where the structure becomes nonuniform is a small part in the entire crystal structure. be able to. Further, as shown in FIG. 4 and the like, the intensity of the scattered wave U3 is weaker than the surface reflected wave U1 and the bottom reflected wave U2, but by using statistical processing, the influence of noise can be reduced and A highly accurate analysis can be performed based on the intensity of the wave U3. The influence of noise is further reduced by calculating the scattering intensity, which is the basis of statistical processing, by integration. In this way, by increasing the sensitivity and accuracy of the measurement by reducing the influence of noise, when a large number of individuals are continuously manufactured in the manufacturing process of metal materials, etc. Even if there is a region where the crystal structure is non-uniform in the specified region, such a non-uniform crystal structure can be found with high sensitivity and high accuracy, and the crystal structure that gives the desired material properties. It is possible to accurately select individuals having a uniform value.

In the crystal structure evaluation method according to the present embodiment, the ultrasonic signal obtained for each incident point P is appropriately subjected to frequency analysis and integration, and then statistically processed for the scattering intensity data, Only by evaluating the peak width, it is possible to obtain information regarding the nonuniformity of the crystal structure. It is not necessary to perform a complicated calculation process such as a waveform analysis or a simulation assuming a model of a crystal structure on the detected ultrasonic signal. The inhomogeneity of the crystal structure can be easily evaluated only by simple measurement such as incidence and detection of ultrasonic waves at each incident point P and simple arithmetic processing centered on statistical processing. As a result, even when a large number of individuals are inspected, the inspection of each individual can be completed in a short time.

(4) Other Steps (4-1) Evaluation of Average Crystal Grain Size In the crystal structure evaluation method according to the present embodiment, in the above evaluation step, the crystal grain size difference is determined based on the peak width of the scattering intensity function. The nonuniformity in the crystal structure such as the uniformity is evaluated. In the evaluation step, not only the peak width of the scattering intensity function but also the scattering intensity of the median of the peaks is focused, so that the information on the average grain size of the crystal grains S3 is also combined with the information on the nonuniformity of the crystal structure. ,Obtainable.

As described above, the larger the scattering intensity at the median of the peaks of the scattering intensity function, the larger the average grain size of the crystal grains S3 may be evaluated. By evaluating the nonuniformity of the crystal structure and the average crystal grain size together, for example, the crystal grains S3 having a grain size within a predetermined range that gives desired material characteristics in the manufacturing process of a metal material or the like. Individuals generated with high uniformity can be highly selected.

(4-2) Separation of Scattering Intensity Function into Multiple Components and Quantitative Evaluation of Nonuniformity As described above, in the scattering intensity function, the value of the scattering intensity (horizontal axis) reflects the crystal grain size, The larger the diameter is, the larger the scattering intensity value is, but when a plurality of types of crystal structures having different distribution ranges of the crystal grain size are mixed, the scattering intensity function determines the contribution of the plurality of types of crystal structures. It will be a sum. In this case, the obtained scattering intensity function may have a bilaterally asymmetrical shape. For example, as shown in FIGS. 7B and 7C, in a structure composed of minute crystal grains S3 having high uniformity, the crystal grains M1 larger than the coarse crystal grains M1 or smaller than the fine crystal grains S3 are finer. When the crystal grains M2 are nonuniformly mixed and the area occupied by the mixed crystal grains M1 and M2 is small, the mixed crystal grains M1 and M2 are already described with reference to FIG. The scattering intensity function can be treated as a symmetric function with respect to the peak median value, ignoring the non-uniformity of the scattering intensity function due to However, if the area occupied by the mixed nonuniform crystal grains M1 and M2 is large, the nonuniformity of the scattering intensity function due to the contribution of the crystal grains M1 and M2 may not be negligible. In such a case, in the evaluation step, it is preferable to separate the scattering intensity function into a plurality of peak components having different median scattering intensities.

For example, as shown in FIG. 7B, when a small amount of coarse crystal grains M1 are mixed nonuniformly while the highly uniform fine crystal grains S3 occupy most of the region, As shown in FIG. 9A, the obtained scattering intensity function has a laterally asymmetric distribution in which the distribution width on the high scattering intensity side is larger than the distribution width on the low scattering intensity side. In this case, the asymmetric scattering intensity function can be separated into two peak components as shown in FIG. 9(b). In FIG. 9B, all the components of the scattering intensity function shown in FIG. 9A are separated into two peak components, a main peak shown by a broken line and a sub-peak shown by a thin solid line. The sub-peak has a smaller peak height (value on the vertical axis at the center of the peak) and a higher scattering intensity (value on the horizontal axis) at the center of the peak than the main peak. Of the two peaks thus separated, the main peak can be assigned to a crystal structure having a small crystal grain size and occupying a large region, that is, a microstructure S3 having high uniformity. .. On the other hand, the sub-peak can be assigned to a crystal structure having a large crystal grain size and a narrow occupied area, that is, a structure in which coarse crystal grains M1 are nonuniformly generated. By analyzing each of the main peak and the sub-peak, information on the crystal structure such as the crystal grain size and the nonuniformity of the structure in these two types of structures can be obtained by separating the structures. As shown in FIG. 7C, a crystal grain M2 having a crystal grain size smaller than those of the crystal grains S3 is locally generated in the structure of the crystal grains S3 having high uniformity. In this case, the scattering intensity function has a bilaterally asymmetric distribution in which the distribution width on the low scattering intensity side is larger than the distribution width on the high scattering intensity side. In this case as well, peak separation can be performed in the same manner, and a sub-peak appears on the side of lower scattering intensity than the main peak.

Separation of the scattering intensity function into a plurality of peak components can be performed by a known data analysis method, and for example, a curve fitting method using a plurality of Gaussian functions can be used. However, when the scattering intensity function can be approximated to the superposition of only two peak components of the main peak and the sub-peak, and the contribution of the sub-peak is not excessively large, the peak separation can be performed by a simple method. It can be performed. First, with respect to the mode of the scattering intensity function (the value on the horizontal axis when the value on the vertical axis becomes maximum; indicated by the alternate long and short dash line in FIG. 9A), the scattering on the side with a small distribution width The intensity function, that is, the scattering intensity function on the low scattering intensity side in FIG. 9A, is symmetrically duplicated and is used as the main peak. In other words, the scattering intensity function on the lower scattering intensity side than the mode is folded back to the high scattering intensity side at the mode, and is joined to the scattering intensity function on the low scattering intensity side to obtain the main peak. And Then, a sub-peak is obtained by removing the contribution of the obtained main peak from the entire scattering intensity function, that is, one obtained by subtracting the intensity of the obtained main peak. In this way, the main peak and the sub-peak can be easily separated.

The scattering intensity function may be separated into not only two peak components but also a larger number of peak components. However, when it is possible to separate into two components, a main peak and a sub-peak, the result of peak separation is used. The degree of non-uniformity of the crystal structure can be easily quantified. As an example, FIG. 10 shows the obtained scattering intensity function (thick line) and the sub-peaks (thin line) separated therefrom when the degree of nonuniformity of the crystal structure is different. FIG. 10A shows a case where the crystal structure has high uniformity, and is close to a state in which fine crystal grains S3 are formed with high uniformity as in FIG. 7A. In this case, a scattering intensity function with high symmetry is obtained, and the contribution of the sub-peak is small. On the other hand, FIG. 10B shows the case where there is a region where the crystal structure is locally nonuniform, and as shown in FIG. 7B, fine crystal grains S3 are formed with high uniformity. This corresponds to a state where a large amount of coarse crystal grains M1 that cannot be ignored is partially generated in the region. In this case, a scattering intensity function expanded to the high scattering intensity side is obtained, and the contribution of the sub-peak is large. As described above, the size of the contribution of the sub-peak becomes an index of the degree of non-uniformity of the crystal structure, and the larger the contribution of the sub-peak, the higher the non-uniformity of the crystal structure can be evaluated.

Further, a nonuniformity evaluation value can be introduced as a parameter for quantitatively evaluating the nonuniformity of the crystal structure. The non-uniformity evaluation value can be calculated by weighting the sub-peaks by the distance (distance on the horizontal axis) from the mode of the scattering intensity function (or the median of the main peaks) and integrating. For example, when the value of the scattering intensity is x, the function representing the sub-peak is f(x), and the mode of the scattering intensity function is x=m, the nonuniformity evaluation value is f(x). It is possible to calculate |x−m| as a value integrated over the entire region of x where the sub-peak appears. The non-uniformity evaluation value is weighted by |x−m| which is the distance from the mode. The nonuniformity evaluation value thus obtained becomes larger as the peak height and the peak width of the sub-peak are larger, that is, as the ratio of the region occupied by the nonuniformly generated crystal grains M1 (M2) is larger. In addition, the nonuniformity evaluation value becomes larger as the crystal grain size is far apart between the crystal structure giving the main peak and the crystal structure giving the sub-peak. In other words, the nonuniformity evaluation value increases as the crystal grains M1 (M2) having greatly different grain sizes are generated from the crystal grains S3 forming the highly uniform structure. Therefore, the nonuniformity evaluation value is a good index for quantitatively evaluating the nonuniformity of the crystal structure, and the larger the nonuniformity evaluation value, the higher the nonuniformity of the crystal structure can be evaluated.

(4-3) Material flaw detection Further, since the ultrasonic inspection apparatus 11 provided in the crystal structure evaluation apparatus 1 can be used for material flaw detection, the crystal structure of the material S to be inspected is not uniform. In addition to the evaluation, it is possible to inspect for scratches and defects. Here, the scratches and defects refer to large sizes that are not on the order of crystal grains, generally to sub-millimeters or larger.

If there is a scratch inside the material S to be inspected, in the measurement process, in the ultrasonic signal as shown in FIG. A component due to the reflected wave reflected by the scratch should be observed between the component A1 and the component A2 due to the bottom surface reflected wave U2. When such a component is observed, it can be determined that there is a flaw in the material S to be inspected at a position inside the incident point P. If the evaluation region G is set by removing the signal component derived from the scratch and the scattering intensity is obtained, both the flaw detection and the evaluation of the nonuniformity of the crystal structure can be performed using common data. Further, analysis of the bottom surface reflected wave U2 and analysis of sound velocity, velocity dispersion, attenuation, etc. are performed on the obtained ultrasonic signal, and analysis of various characteristics of the material constituting the inspection object S is also performed. You can go.

Examples of the present invention will be shown below. The present invention is not limited to these examples. Here, the validity of the crystal structure evaluation method according to the above-described embodiment was verified by using a titanium-based alloy as a sample. In addition, the validity of the nonuniformity evaluation value was also verified.

[1] Validity of crystal structure evaluation method [1-1] When heat treatment temperature is changed (test method)
In the test, a titanium-based α+β type alloy (alloy forming an α phase and a β phase) was used as a sample. Specifically, a φ55 mm round bar made of the above alloy was cast, heat-treated at a predetermined temperature for 3 hours, and then air-cooled. The temperature of the heat treatment was changed in five ways within the range of 800°C to 950°C.

A cross section was cut out from the sample heat-treated at each temperature and observed by SEM to observe the state of the structure.

Furthermore, with respect to the sample heat-treated at each temperature, in the same method as described above as the crystal structure evaluation method according to the embodiment of the present invention, the measurement step and the statistical processing step are executed to calculate the scattering intensity function. Created. Then, the standard deviation of the scattering intensity function was obtained. Here, as the ultrasonic waves, a pulse having a frequency of 20 MHz is used, and the incident points are set at intervals of 1° along the entire circumference of the sample and at intervals of 0.2 mm over a region of 50 mm along the longitudinal direction, and the measurement step Was carried out. The obtained ultrasonic signal was subjected to frequency analysis by STFT, and the integral value of energy was calculated for the component of the same frequency as the incident fundamental wave to obtain the scattering intensity.

(result)
It was confirmed by SEM observation that the higher the heat treatment temperature, the more uniformly the α phase and the β phase were generated, and the more uniform the crystal structure was.

FIG. 11A shows the scattering intensity function obtained for the sample that has been subjected to the heat treatment at each temperature. According to this, as the heat treatment temperature rises, the peak moves to the low scattering intensity side. Further, the peak width narrows as the heat treatment temperature rises.

Further, in FIG. 11B, the standard deviation value obtained for each scattering intensity function of FIG. 11A is plotted against the heat treatment temperature. Here, the value of the minimum standard deviation (processing temperature 950° C.) is normalized with 100%, and the value at each heat treatment temperature is shown. According to FIG. 11B, it is more clearly shown that the standard deviation decreases as the heat treatment temperature increases, that is, the peak width of the scattering intensity function narrows.

As the heat treatment is performed at a higher temperature, the scattering intensity of the median of the scattering intensity function becomes smaller and the peak width of the scattering intensity function becomes narrower. Therefore, the average grain size of the crystal grains becomes smaller as the heat treatment temperature increases. It can be interpreted that the nonuniformity of the crystal structure is low, that is, the uniformity is high. This tendency is consistent with the tendency observed in SEM observation. As described above, in the evaluation method according to the embodiment of the present invention, the size of the crystal grain size and the nonuniformity of the crystal structure are evaluated based on the median of the peak and the peak width of the scattering intensity function based on the ultrasonic measurement. The validity of the thing is confirmed.

[1-2] When changing the training ratio (test method)
Here again, an α+β type alloy composed of titanium base was used as a sample. Specifically, the round bar material cast in the same manner as in the above test [1-1] was forged. During forging, the forging ratio was changed in three ways. The training ratio is increased in the order of Samples A, B, and C.

Similar to the above test [1-1], SEM observation and a scattering intensity function based on ultrasonic measurement were performed on the samples of each forging ratio.

(result)
It was confirmed by SEM observation that the larger the wrought ratio, the larger the number of coarse crystal grains and the more nonuniform the crystal grain size.

FIG. 12 shows the scattering intensity function obtained for the samples of each training ratio. According to this, as the training ratio increases in the order of Samples A, B, and C, the peak moves to the high scattering intensity side. In addition, the peak width widens as the training ratio increases.

As the training ratio increases, the median scattering intensity of the scattering intensity function increases, and the peak width of the scattering intensity function widens.As the training ratio increases, the average grain size of the crystal grains increases. It can be interpreted that the heterogeneity of the crystal structure is increasing. This tendency is consistent with the tendency observed in SEM observation. Also from the result of this test [1-2], as in the case of the result of test [1-1], in the evaluation method according to the embodiment of the present invention, the median and peak of the peaks of the scattering intensity function based on the ultrasonic measurement. Based on the width, the validity of evaluating the size of the crystal grain size and the nonuniformity of the crystal structure is confirmed.

Although the structure of the crystal structure and details of the change are different between the case where the heat treatment temperature is changed as in the test [1-1] and the case where the wrought ratio is changed as in the test [1-2]. In each of the tests, it has been confirmed that the larger the crystal grain size, the larger the scattering intensity at the center value of the peak and the wider the peak width in the scattering intensity function. That is, it can be said that the scattering intensity function can be used for evaluating the nonuniformity of the crystal grain size and the crystal structure, regardless of the details of the structure of the crystal structure.

[2] Effectiveness of non-uniformity evaluation value (test method)
Similarly to the above test [1-2], the α+β type alloy made of titanium base was forged with different forging ratios to prepare three kinds of samples having different degrees of nonuniformity of the crystal structure.

By SEM observation, inhomogeneity of the crystal structure increases in the order of sample (1)→(2)→(3) (sample (3) is the highest), and coarse crystal grains are contained in the fine crystal grains. It was confirmed that many of them were mixed.

For each of the samples (1) to (3), a scattering intensity function based on ultrasonic measurement was created in the same manner as in the test [1-1]. Then, each of the obtained scattering intensity functions was separated into a main peak and a sub-peak located on the higher scattering intensity side of the main peak. Then, the sub-peak (f(x)) is weighted by the distance from the mode (m) of the scattering intensity function (f(x)·|x−m|), and the value is calculated over the entire range of the scattering intensity. The nonuniformity evaluation value was obtained by integrating with.

(result)
FIG. 13 shows the relationship between the pixel variation in the SEM image and the obtained nonuniformity evaluation value for each of the samples (1) to (3). The non-uniformity evaluation value is normalized and shown as "1" for the sample (1) having the smallest value. As the evaluation of the pixel variation in the SEM image, after binarizing the SEM image, the moving averages in the vertical and horizontal directions are obtained, and the kurtosis of the histogram of the intensity distribution in the obtained image is calculated as the pixel variation. Is displayed on the horizontal axis of FIG.

According to FIG. 13, a positive correlation is seen between the nonuniformity of the crystal structure and the nonuniformity evaluation value. That is, as the sample (1)→(2)→(3) becomes more inhomogeneous in its crystal structure and the pixel variation in the SEM image becomes larger, the inhomogeneity evaluation obtained from the scattering intensity function is evaluated. The value is increasing. This shows that the nonuniformity evaluation value can be effectively used as a parameter that quantitatively represents the nonuniformity of the crystal structure.

The embodiments of the present invention have been described above. The present invention is not particularly limited to these embodiments, and various modifications can be made. As described above, the crystal structure evaluation apparatus can be configured to detect the transmitted wave in the transmission direction, but the intensity of the transmitted wave becomes smaller as the intensity of the scattered wave becomes higher. Therefore, in this case, in the scattering intensity function created by organizing the number of incident points at which the predetermined transmission intensity was obtained as a function of the transmission intensity, the correspondence between the peak width and the non-uniformity of the crystal grains is: When directly detecting scattered waves in the reflection direction as in the above embodiment, the same procedure can be performed, but the relationship between the average particle size and the scattering intensity of the median of the peaks of the scattering intensity function is reversed, It can be associated that the larger the median strength, the smaller the average grain size of the crystal grains.

1 Crystal Structure Evaluation Device 11 Ultrasonic Inspection Device 12 Exercise Device 13 Calculation/Control Device M1 Coarse Crystal Grain M2 Particularly Fine Crystal Grains P, P1, P2 Incident Point S Inspection Material S1 Surface S2 Bottom S3 Crystal Grain S4 Crystal Grain Field U Incident ultrasonic wave U1 Surface reflected wave U2 Bottom reflected wave U3 Scattered wave

Claims (14)

A measurement step in which ultrasonic waves are incident from a plurality of incident points on the surface of a material to be inspected made of a material containing crystal grains, and the intensity of scattered waves detected is measured as the scattering intensity for each of the incident points. When,
In the measurement step, the number of the incident points for which a predetermined scattering intensity is obtained is arranged as a function of the scattering intensity, and a statistical processing step of creating a scattering intensity function,
The larger the peak width of the scattering intensity function obtained in the statistical processing step, the more inhomogeneity of the crystal structure in the material to be inspected, the evaluation step, and a crystal structure evaluation method, characterized in that . In the evaluation step, as the nonuniformity of the crystal structure, nonuniformity in at least one of a grain size, a component composition, and anisotropy of crystal grains in the inspected material is evaluated. Item 2. The crystal structure evaluation method according to Item 1. In the measuring step, in the reflection direction of the incident ultrasonic wave, the intensity of the ultrasonic signal is measured as a function of time, and the reflected wave reflected on the surface of the inspection target material and the bottom surface facing the surface are measured. The crystal structure evaluation method according to claim 1 or 2, wherein the scattering intensity is obtained by integrating the intensity of the ultrasonic signal observed at a time between the reflected wave and the reflected wave. The crystal structure evaluation method according to claim 3, wherein in the evaluation step, the larger the scattering intensity of the median of the peaks of the scattering intensity function, the larger the average grain size of the crystal grains. 5. In the measuring step, the ultrasonic signal measured as a function of time is subjected to frequency analysis, and the scattering intensity is obtained based on a signal having the same frequency as the incident ultrasonic wave. The crystal structure evaluation method according to any one of 1. In the measuring step, an ultrasonic inspection device that performs generation and detection of ultrasonic waves moves around the inspection material relative to the inspection material, with respect to the plurality of incident points. The crystal structure evaluation method according to any one of claims 1 to 5, wherein the ultrasonic wave is incident and detected. The inspected material is a bar material,
In the measuring step, the plurality of incident points are set so as to extend over at least 180° along the circumferential direction of the rod and at least a part of the region along the longitudinal direction of the rod. The crystal structure evaluation method according to any one of claims 1 to 6. 8. The crystal according to claim 1, wherein in the evaluation step, the crystal structure is evaluated to be non-uniform when the peak width is larger than a predetermined threshold value. Organization evaluation method. 9. The crystal structure evaluation method according to claim 1, wherein in the evaluation step, the scattering intensity function is separated into a plurality of peaks having different median scattering intensities. 10. The crystal structure evaluation according to claim 9, wherein in the evaluation step, the scattering intensity function is separated into two peaks, a main peak and a sub-peak having a peak height smaller than the main peak. Method. With the mode of the scattering intensity function as the center, a symmetrical copy of the scattering intensity function on the side with a small distribution width is used as the main peak, and the contribution of the main peak is removed from the scattering intensity function. The crystal structure evaluation method according to claim 10, wherein the sub-peak is used. The sub-peak is weighted and integrated by the distance from the mode of the scattering intensity function, and the larger the obtained integral value is, the higher the heterogeneity of the crystal structure is evaluated. The crystal structure evaluation method according to claim 10. Equipped with an ultrasonic inspection device that generates and detects ultrasonic waves,
A crystal structure evaluation apparatus, characterized by executing the crystal structure evaluation method according to claim 1 on a material to be inspected made of a material containing crystal grains. The crystal structure evaluation apparatus according to claim 13, further comprising an exerciser that moves the ultrasonic inspection apparatus relative to the material to be inspected.