JP7600041B2 - Metal fatigue evaluation method - Google Patents

Description

The present invention relates to a metal fatigue evaluation method that uses a diffraction ring to evaluate the degree of metal fatigue.

Evaluating the degree of metal fatigue is important and desirable because damage to equipment due to metal fatigue can lead to abrupt process shutdowns and accidents. A technology for evaluating the degree of metal fatigue is disclosed, for example, in Patent Document 1.

In this patent document, X-ray diffraction is performed on fatigued areas identified by observing the corroded areas due to the structural change to martensite, and the amount of change in the half-width of martensite and the amount of change in retained austenite are measured, and the degree of fatigue is calculated from the measurement results.

Generally, when the periodicity of a crystal is high, strong diffracted waves (Bragg reflected waves) are generated in a direction defined by the periodic interval and periodic direction. On the other hand, metal fatigue generates dislocations in the metal crystal, disrupting the periodicity of the metal crystal lattice. This causes the Bragg reflected waves to spread in the reflection direction, resulting in a change in the half-width of the diffracted waves (spread from the peak position). Therefore, it is presumed that the degree of metal fatigue can be evaluated by evaluating the half-width of the diffracted waves due to Bragg reflection in the crystal lattice, as in Patent Document 1.

JP 2009-41993 A

Metal fatigue is generally evaluated every few years and may be evaluated based on changes over time. However, metal fatigue evaluation is not only performed in laboratories with a well-equipped evaluation environment, but is also preferably performed on-site. In such cases, there is a risk that the evaluation environments may differ, which may call into question the reliability of the evaluation results.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a metal fatigue evaluation method that can obtain more reliable evaluation results.

After extensive investigation, the inventors have found that the above object can be achieved by the present invention described below. That is, a metal fatigue evaluation method according to one aspect of the present invention is a method for determining an evaluation index that represents the degree of metal fatigue in a metal evaluation object, and includes a data acquisition step of acquiring diffraction ring data that represents a diffraction ring formed by irradiating the evaluation object with a beam that has a diffracting property, and an index processing step of determining the evaluation index based on the diffraction ring data acquired in the data acquisition step, in which the beam is irradiated at an incident angle of 0 degrees or more and 65 degrees or less, and the beam is irradiated so that there are 3,000 or less crystal grains within the irradiation area of the beam, or the spot diameter of the beam is 3 mm or less.

In this metal fatigue evaluation method, when obtaining diffraction ring data, the beam is irradiated at an incident angle of 0 degrees or more and 65 degrees or less, and the number of crystal grains present within the irradiation area of the beam is 3,000 or less, or the spot diameter of the beam is 3 mm or less. This makes it possible to obtain diffraction ring data in a more appropriate evaluation environment (evaluation conditions), resulting in more reliable evaluation results.

As described below, as metal fatigue progresses, the number of crystal grains increases due to the refinement of the crystal grains (cell organization) accompanying dislocation proliferation, but the number of crystal grains in the claims is the number before the increase due to the progression of metal fatigue.

In another aspect, in the above-mentioned metal fatigue evaluation method, the evaluation index is a uniformity index that represents the degree of uniformity of the peak intensity in the diffraction ring.

When the metal being evaluated is in its initial state, the number of crystal grains in the X-ray irradiated area is insufficient, resulting in a spotty diffraction ring; however, as metal fatigue progresses, the number of crystal grains increases due to the refinement of crystal grains (cell organization) accompanying dislocation proliferation, and the diffraction ring becomes uniform. The above metal fatigue evaluation method determines a uniformity index that indicates the degree of uniformity of the peak intensity in the diffraction ring based on the diffraction ring data as an evaluation index that indicates the degree of metal fatigue, allowing for a more appropriate evaluation of the degree of metal fatigue.

In another aspect, in the metal fatigue evaluation method described above, the uniformity index is the standard deviation in the peak intensity distribution of the diffraction ring with respect to the azimuth angle, or the standard deviation in the half-width distribution with respect to the azimuth angle.

This makes it possible to provide a metal fatigue evaluation device that determines the standard deviation in the peak intensity distribution of the diffraction ring with respect to the azimuth angle, or the standard deviation in the half-width distribution with respect to the azimuth angle, as the uniformity index, i.e., the evaluation index.

In another aspect, in the metal fatigue evaluation method described above, the evaluation index is the result of dividing the standard deviation in the peak intensity distribution of the diffraction ring with respect to the azimuth angle by the average value of the peak intensity distribution in the diffraction ring, or the result of dividing the standard deviation in the half-width distribution with respect to the azimuth angle by the average value of the half-width distribution in the diffraction ring.

This metal fatigue evaluation method divides the standard deviation by the average value, thereby reducing the impact of variations in the beam irradiation time on the evaluation index.

The metal fatigue evaluation method of the present invention can obtain more reliable evaluation results.

1 is a block diagram showing a configuration of a metal fatigue evaluation device in an embodiment. FIG. 2 is a block diagram showing a configuration of an example of a data acquisition unit in the metal fatigue evaluation device. 10 is a diagram for explaining the state of change in the diffraction ring accompanying the progression of metal fatigue. FIG. FIG. 1 shows an example of a diffraction ring, the distribution of peak intensities versus azimuth angle of said diffraction ring, their average value and their standard deviation. 11A and 11B are diagrams for explaining the influence of the incident angle of a beam on an evaluation index. 11A and 11B are diagrams for explaining the influence of a beam spot diameter on an evaluation index. 11 is a diagram for explaining the influence of the beam irradiation time on the evaluation index. FIG. 4 is a flowchart showing an operation of the metal fatigue evaluation device.

One or more embodiments of the present invention will be described below with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. Note that components with the same reference numerals in each drawing are the same components, and their description will be omitted as appropriate. In this specification, when referring to a general term, a reference numeral without a subscript is used, and when referring to an individual component, a reference numeral with a subscript is used.

The metal fatigue evaluation method in the embodiment is a method for obtaining an evaluation index that represents the degree of metal fatigue in a metal evaluation object. This metal fatigue evaluation method includes a data acquisition step of obtaining diffraction ring data that represents a diffraction ring formed by irradiating the evaluation object with a beam that has a diffracting property, and an index processing step of obtaining the evaluation index based on the diffraction ring data obtained in the data acquisition step. In the data acquisition step, the beam is irradiated at an incident angle of 0 degrees or more and 65 degrees or less, and the beam is irradiated so that there are 3000 or less crystal grains in the irradiation area of the beam, or the spot diameter of the beam is 3 mm or less. Such a metal fatigue evaluation method will be described in more detail below.

1 is a block diagram showing the configuration of a metal fatigue evaluation device in an embodiment. FIG. 2 is a block diagram showing the configuration of an example of a data acquisition unit in the metal fatigue evaluation device. FIG. 2A shows the overall configuration, and FIG. 2B shows the relationship between the imaging unit 15 and the evaluation object Ob. FIG. 3 is a diagram for explaining the state of change in the diffraction ring with the progression of metal fatigue. FIG. 4 is a diagram showing, as an example, a diffraction ring, a peak intensity distribution with respect to the azimuth angle of the diffraction ring, its average value, and its standard deviation. FIG. 4A shows a diffraction ring, and FIG. 4B shows a peak intensity distribution (distribution of peak intensity at each position in the circumferential direction of the diffraction ring) with respect to the azimuth angle α in the diffraction ring shown in FIG. 4A, its average value μ, and its standard deviation σ. The horizontal axis of FIG. 4B is the azimuth angle α [deg] from 0° to 360°, and the vertical axis is the peak value of the diffraction intensity (Diffraction Intensity [counts]).

The metal fatigue evaluation device D in the embodiment includes, for example, a data acquisition unit 1, a control processing unit 2, a memory unit 3, an input unit 4, an output unit 5, and an interface unit (IF unit) 6, as shown in FIG. 1.

The data acquisition unit 1 is connected to the control processing unit 2, and is a device that acquires diffraction ring data representing a diffraction ring formed by irradiating a metal (including alloy) evaluation object with a beam having a diffracting property according to the control of the control processing unit 2. More specifically, for example, in this embodiment, the data acquisition unit 1 includes an irradiation unit that irradiates the beam, and an imaging unit that images a diffraction ring formed by irradiating the evaluation object with the beam by the irradiation unit, and generates diffraction ring data representing the diffraction ring.

More specifically, as shown in FIG. 2, the data acquisition unit 1 includes a high-voltage power supply 11, a cooling unit 12, a control unit 13, an X-ray irradiation unit 14, and an imaging unit 15. The high-voltage power supply 11 is a device that supplies a high voltage for accelerating the electron beam to the X-ray irradiation unit 14. The cooling unit 12 is a device that cools the X-ray irradiation unit 14. The control unit 13 is a device that controls the operation of the entire data acquisition unit 1. The control unit 13 may also be used as a control unit 21 (described later) that is functionally configured in the control processing unit 2.

The X-ray irradiation unit 14 includes an X-ray generator that generates X-rays by colliding an electron beam with a target, and an X-ray irradiation tube that irradiates the generated X-rays as a thin X-ray beam to the evaluation object Ob. The X-ray generator is, for example, an X-ray tube (vacuum tube) that accelerates an electron beam with high voltage and causes it to collide with an anode to generate CrKα characteristic X-rays. The X-ray irradiation tube is, for example, a pinhole collimator that narrows the generated X-rays into a thin parallel beam and irradiates it.

Here, an example will be described in which X-rays are used as a beam (diffracted light) that has the property of diffracting toward the evaluation object Ob, but beams that have the property of diffraction are not limited to X-rays and include electromagnetic waves (including visible light, ultraviolet light, and gamma rays), neutron beams, electron beams, etc.

The imaging unit 15 is a device that images a diffraction ring formed by irradiating the evaluation object Ob with a beam by the X-ray irradiation unit 14, and generates diffraction ring data representing the diffraction ring. The imaging unit 15 is configured, for example, with a so-called imaging plate. This imaging plate utilizes the phenomenon of photostimulable fluorescence. In general, a film coated with a photostimulable phosphor is exposed to X-rays, and the amount of fluorescence generated by irradiating the exposed film with laser light is measured. The fluorescence emits light with an amount corresponding to the amount of exposure to X-rays, so an X-ray image can be obtained by measuring the amount of light emitted.

The conditions (evaluation conditions, evaluation environment) for acquiring diffraction ring data using such a data acquisition unit 1 will be described later.

Returning to FIG. 1, the input unit 4 is connected to the control processing unit 2 and is a device that inputs various commands, such as a command to start the evaluation, and various data required for operating the metal fatigue evaluation device D, such as the name of the evaluation target to be evaluated by the metal fatigue evaluation device D (e.g., serial number, etc.), to the metal fatigue evaluation device D, and is, for example, a plurality of input switches, a keyboard, a mouse, etc., each assigned with a specific function. The output unit 5 is connected to the control processing unit 2 and is a device that outputs commands and data input from the input unit 4, diffraction rings represented by the diffraction ring data acquired by the data acquisition unit 1, and evaluation indices calculated by the metal fatigue evaluation device D, in accordance with the control of the control processing unit 2, and is, for example, a display device such as a CRT display, LCD (liquid crystal display device), or organic EL display, or a printing device such as a printer.

The IF unit 6 is connected to the control processing unit 2 and is a circuit that inputs and outputs data to and from, for example, an external device according to the control of the control processing unit 2, such as an interface circuit for RS-232C, which is a serial communication method, an interface circuit using the Bluetooth (registered trademark) standard, and an interface circuit using the USB standard. The IF unit 6 may also be a communication interface circuit that transmits and receives communication signals to and from an external device, such as a data communication card or a communication interface circuit conforming to the IEEE 802.11 standard.

The memory unit 3 is connected to the control processing unit 2 and is a circuit that stores various predetermined programs and various predetermined data according to the control of the control processing unit 2. The various predetermined programs include, for example, a control processing program, which includes a control program that controls each of the parts 1, 3 to 6 of the metal fatigue evaluation device D according to the function of each part, and an index processing program that determines an evaluation index that represents the degree of metal fatigue based on the diffraction ring data acquired by the data acquisition unit 1. The various predetermined data include data necessary to execute each of these programs, such as the diffraction ring data. Such a memory unit 3 includes, for example, a ROM (Read Only Memory) that is a non-volatile memory element, an EEPROM (Electrically Erasable Programmable Read Only Memory) that is a rewritable non-volatile memory element, and the like. The storage unit 3 includes a RAM (Random Access Memory) that serves as a so-called working memory for the control processing unit 2, which stores data generated during execution of the specified program. The storage unit 3 may also include a hard disk device capable of storing large amounts of data in order to store relatively large amounts of learning data.

The control processing unit 2 is a circuit that controls each of the units 1, 3 to 6 of the metal fatigue evaluation device D according to the function of each unit, and determines an evaluation index that represents the degree of metal fatigue in the evaluation target. The control processing unit 2 is configured, for example, with a CPU (Central Processing Unit) and its peripheral circuits. In the control processing unit 2, a control unit 21 and an index processing unit 22 are functionally configured by executing the control processing program.

The control unit 21 controls each of the parts 1, 3 to 6 of the metal fatigue evaluation device D according to the function of each part, and is responsible for controlling the entire metal fatigue evaluation device D.

The index processing unit 22 determines an evaluation index that indicates the degree of metal fatigue based on the diffraction ring data acquired by the data acquisition unit 1. The evaluation index may generally be the half-width of the diffraction ring, but in this embodiment, a uniformity index that indicates the degree of uniformity of the peak intensity in the diffraction ring is used.

Figure 3 shows, as an example, the change in the diffraction ring with the progression of metal fatigue. In Figure 3, X-ray diffraction was performed on each sample with fatigue damage of 0% (%), 10% (%), 30% (%), 50% (%), and 100% (%) by a tension-compression cyclic test in which tension and compression were alternately repeated, and the diffraction ring images obtained as a result are shown. A fatigue testing machine with a normal vibration load was used for the tension-compression cyclic test, and the number of cycles at which the sample broke was considered to be a damage degree of 100% (%), and the damage degrees of 0% (%), 10% (%), 30% (%), and 50% (%) are the ratios of the number of cycles to this. As an example, the sample is a steel pipe material of a general standard used for boiler pipes. The upper row of Figure 3 shows the diffraction ring images of each sample that has not been subjected to electrolytic polishing, and the lower row shows the diffraction ring images of each sample that has been subjected to electrolytic polishing. From left to right, the diffraction ring images are of samples with damage levels of 0% (planar), 10% (planar), 30% (planar), 50% (planar), and 100% (planar).

Looking at Figure 3 from left to right, it can be seen that the diffraction rings change from an initial spotty shape in which the peak intensity varies at each circumferential position to a shape in which the peak intensity becomes approximately uniform at each circumferential position as metal fatigue increases. Comparing this change with the results of TEM (transmission electron microscope) observations (not shown), it is inferred that the process in which numerous fine cell structures are formed due to dislocation proliferation accompanying the accumulation of fatigue damage is related to the change in the diffraction rings to become uniform.

In general, when there are a sufficient number of crystal grains in the X-ray irradiation area, a uniform diffraction ring is obtained. The results shown in Figure 3 are presumably due to the fact that in the initial state, the number of crystal grains in the X-ray irradiation area was insufficient, resulting in a spotty diffraction ring shape, but the number of crystal grains increased due to the refinement of the crystal grains (cell organization) associated with dislocation proliferation, which contributed to the uniformity of the diffraction ring. In evaluation methods using X-ray diffraction, including residual stress measurement, it is recommended that the average crystal grain size of the sample be 30 μm or less to avoid a decrease in measurement accuracy. Compared to this guideline, the ferrite grain size in the initial state of the sample in Figure 3 is as large as 50 to 60 μm, which is in the coarse category in terms of X-ray diffraction measurement, and is consistent with the above consideration.

From the above, it can be concluded that the phenomenon of the diffraction ring becoming uniform due to the accumulation of fatigue damage is caused by two factors: first, microstructural refinement due to dislocation proliferation (cell structure formation), and second, a change in the orientation of the microstructural structure. The unevenness of the diffraction ring is considered to be a physical quantity that succinctly represents the change in the microstructural structure, and the uniformity index, which indicates the degree of uniformity of the peak intensity in the diffraction ring, can be used as a new evaluation index to indicate the degree of metal fatigue.

The uniformity index (= an example of an evaluation index) may be, for example, the difference between the maximum peak intensity and the minimum peak intensity with respect to the azimuth angle of the diffraction ring, or the change in the half-width of the peak (for example, the standard deviation in the half-width distribution of the peak with respect to the azimuth angle), but in this embodiment, the standard deviation in the peak intensity distribution of the diffraction ring with respect to the azimuth angle is used as the uniformity index. An example is shown in FIG. 4. FIG. 4A shows a diffraction ring, and FIG. 4B shows the peak intensity distribution (distribution of peak intensity at each position in the circumferential direction of the diffraction ring) with respect to the azimuth angle α in the diffraction ring shown in FIG. 4A, its average value μ, and its standard deviation σ. The horizontal axis of FIG. 4B is the azimuth angle α [deg] from 0° to 360°, and the vertical axis is the peak value of the diffraction intensity (Diffraction Intensity [counts]). As shown in FIG. 4A, the azimuth angle α is the angle from the baseline passing through the center position O of the diffraction ring in the clockwise circumferential direction of the diffraction ring, when the baseline is set as 0°. The evaluation object Ob is STBA21, an example of a steel pipe material of a general standard used for boiler pipes, and electrolytic polishing treatment is performed. The diffraction angle 2θ is 156.396 degrees. When the standard deviation σ as the uniformity index is relatively large, the peak intensity at each position in the circumferential direction of the diffraction ring varies, and metal fatigue is relatively small. On the other hand, when the standard deviation σ is relatively small, the peak intensity at each position in the circumferential direction of the diffraction ring is approximately uniform (the variation is small), and metal fatigue is relatively large.

The control processing unit 2, memory unit 3, input unit 4, output unit 5, and IF unit 6 can be configured, for example, by a desktop, notebook, tablet, or other type of computer. If the data acquisition unit 1 is an interface circuit or a communication interface circuit, the IF unit 6 can also be used as the data acquisition unit 1, so the metal fatigue evaluation device D, including the data acquisition unit 1, can be configured by a computer.

Next, the evaluation conditions (evaluation environment) will be described. FIG. 5 is a diagram for explaining the influence of the incident angle of the beam on the evaluation index. The horizontal axis of FIG. 5 is the degree of damage, and the vertical axis is the rate of change of the standard deviation of the peak intensity distribution in the diffraction ring (the rate of change of the non-uniformity of the peak intensity). FIG. 6 is a diagram for explaining the influence of the spot diameter of the beam on the evaluation index. FIG. 6A shows a case where the average spot diameter is 1.7 to 3 [mm], and FIG. 6B shows a case where the average spot diameter is limited to less than 2 [mm]. The horizontal axis of FIG. 6A and FIG. 6B is the degree of damage, and the vertical axis of each is the division result σ/μ obtained by dividing the standard deviation σ of the peak intensity distribution in the diffraction ring with respect to the azimuth angle by the average value μ of the peak intensity distribution in the diffraction ring. FIG. 7 is a diagram for explaining the influence of the irradiation time of the beam on the evaluation index. FIG. 7A shows a case where the evaluation index (uniformity index) is the standard deviation of the peak intensity distribution in the diffraction ring with respect to the azimuth angle, and FIG. 7B shows a case where the evaluation index is the result of dividing the standard deviation of the peak intensity distribution in the diffraction ring with respect to the azimuth angle by the average value of the peak intensity distribution in the diffraction ring. The horizontal axis of FIG. 7A is the degree of damage, and the vertical axis is the standard deviation. The horizontal axis of FIG. 7B is the degree of damage, and the vertical axis is the result of the division.

The diffraction ring changes depending on the incidence angle _Ψ0 , the spot diameter, the distance L from the evaluation object, and the irradiation time of the beam. Therefore, the half-value width of the diffraction ring or the uniformity index of the diffraction ring (for example, the standard deviation of the peak intensity distribution or the standard deviation of the half-value width distribution) as an evaluation index may be affected by these. The spot diameter is determined by the collimator diameter, the distance L from the evaluation object, and the incidence angle _Ψ0 . Therefore, the evaluation conditions are defined by the incidence angle _Ψ0 , the collimator diameter, the distance L from the evaluation object Ob, and the irradiation time of the beam.

First, the effect of the incident angle Ψ ₀ is examined. The evaluation conditions are a collimator diameter φ of 1.0 [mm], a distance L from the evaluation object of 62 [mm], and a beam irradiation time of 33 to 116 [seconds]. Under such evaluation conditions, the other one of the evaluation conditions, the incident angle Ψ _0, is changed in the range of 1 to 65 [degrees], and diffraction ring data is obtained for each case, and the standard deviation σ of the peak intensity distribution in the diffraction ring is obtained as an example of an evaluation index. The result is shown in FIG. 5 as a rate of change. The rate of change of the standard deviation of the peak intensity distribution in the diffraction ring (the rate of change of the non-uniformity of the peak intensity) is obtained by dividing the value of the standard deviation by the value of the damage degree of 0 [%] where there is no fatigue damage. In Fig. 5, the results when the incident angle Ψ ₀ is 1 [degree] are shown by circles, the results when the incident angle Ψ ₀ is 30 [degree] are shown by triangles, the results when the incident angle Ψ ₀ is 45 [degree] are shown by squares, the results when the incident angle Ψ ₀ is 60 [degree] are shown by diamonds, and the results when the incident angle Ψ ₀ is 65 [degree] are shown by circles. As can be seen from Fig. 5, when the incident angle Ψ ₀ is 65 [degree] or less, the change rate can be clearly distinguished between the damage degree of 0 [%] and the damage degree of 10 [%] or more. Even when the incident angle Ψ ₀ is 65 [degree], the damage degree of 0 [%] is about 0.65 times that of 10 [%], and the change rate can be clearly distinguished. In particular, a damage degree of 30% or more is important, but when the incident angle Ψ ₀ is 65 degrees, the damage degree of 0% is about 0.6 times that of 30%, and the change rate can be more clearly distinguished. In the above description, for convenience of implementation, the smallest incident angle Ψ ₀ is 1 degree, but the lower limit of X-ray diffraction is generally 0 degrees. Therefore, it is preferable that the incident angle Ψ ₀ of the beam is 0 degrees or more and 65 degrees or less. When the incident angle Ψ ₀ is 60 degrees or less, the damage degree of 0% is about 0.5 times that of 30%, so it is more preferable that the incident angle Ψ ₀ of the beam is 60 degrees or less, and when the incident angle Ψ ₀ is 45 degrees or less, the change rate becomes smaller as the fatigue damage degree increases, so it is even more preferable that the incident angle Ψ ₀ of the beam is 45 degrees or less.

Next, the spot diameter will be considered. In general, if there are a sufficient number of crystal grains in the X-ray irradiation area, a uniform diffraction ring is obtained. On the other hand, the phenomenon of uniform diffraction rings accompanying the accumulation of metal fatigue is thought to be due to two factors, firstly, the refinement of the structure due to dislocation proliferation (cell structure formation), and secondly, the change in the orientation of the microstructure, as mentioned above. Therefore, in order to capture this change in the microstructure, there is an appropriate irradiation area that matches the crystal grain size. In other words, if there are too many crystal grains in the X-ray irradiation area, a uniform diffraction ring will be obtained regardless of the microstructure structure, which is not preferable. On the other hand, if there are too few crystal grains, the diffraction ring will be discontinuous, which is not preferable. A uniformity index that uses information on the entire diffraction ring reduces the accuracy of metal fatigue evaluation.

The evaluation conditions are that the angle of incidence Ψ ₀ is 45 degrees and the collimator diameter φ is 1.0 mm. Under such evaluation conditions, in order to change the spot diameter, which is another one of the evaluation conditions, diffraction ring data was acquired for each case in which the distance L from the evaluation target was changed in the range of 20 to 93 mm, and as an example of the evaluation index, the division result σ/μ was obtained by dividing the standard deviation σ of the peak intensity distribution in the diffraction ring with respect to the azimuth angle by the average value μ of the peak intensity distribution in the diffraction ring. The result is shown in FIG. 6. The spot diameter was actually measured using photosensitive paper. Note that this division result σ/μ can reduce the influence on the evaluation index due to differences in the irradiation time of the beam, as described later. Diffraction ring data was acquired for each case in which the spot diameter was 1.7 mm, 1.9 mm, 2.1 mm, 2.5 mm, 2.8 mm, and 3 mm, and the evaluation index was obtained. The result is shown in FIG. 6. As shown in Fig. 6A, the division result σ/μ is correlated with the damage level, and when a damage level of 0 [%] is compared with a damage level of 10 [%] or more, the division result σ/μ in the case of a damage level of 0 [%] is about 0.4 to 0.65, while the division result σ/μ in the case of a damage level of 10 [%] is about 0.06 to 0.3, and the division results σ/μ can be clearly distinguished. In particular, when a damage level of 0 [%] is compared with a damage level of 30 [%], the division result σ/μ in the case of a damage level of 30 [%] is about 0.1 to 0.25, and the division result σ/μ can be more clearly distinguished. In this example, the average crystal grain size of the evaluation target was 55 μm, so that the spot diameter of 3 mm can be converted to the number of crystal grains to obtain approximately 3000 (≈2981≈((3/2) ² ×3.14)/((0.055/2) ² ×3.14). Therefore, it is preferable that the number of crystal grains present within the irradiation area of the beam is 3000 or less. On the other hand, when the spot diameter is limited to less than 2 mm, as shown in FIG. 6B, the variation of the division result σ/μ is reduced compared to the case shown in FIG. 6A, and it corresponds more closely to the degree of damage. Therefore, it is more preferable that the spot diameter is less than 2 mm. The spot diameter of 2 mm can be converted to the number of crystal grains to obtain approximately 1324.9 (≈((2/2) ² ×3.14)/((0.055/2) ² × 3.14). Therefore, it is more preferable that the number of crystal grains present within the irradiation area of the beam is 1300 or less.

Note that the number of crystal grains converted from this spot diameter is the number before it increases due to the progression of metal fatigue.

On the other hand, for example, the Transactions of the Japan Society of Mechanical Engineers (Series A), Vol. 63, No. 607, discloses the results of measuring residual stress using diffraction rings when using the parallel beam method with a collimator diameter of φ1.0 [mm], and reports that when the crystal grain size is 50 [μm] or less, a continuous diffraction ring is obtained with single-point irradiation, but when it is 100 [μm], it becomes discontinuous. From this, it can be seen that the lower limit of the number of crystal grains is between 100 and 400. Therefore, it is preferable that the number of crystal grains present within the irradiation area of the beam is 400 or more.

Next, the distance L from the evaluation object will be considered. The distance L from the evaluation object affects the radius of the diffraction ring, but does not affect the peak intensity of the diffraction ring. Therefore, the distance L from the evaluation object is adjusted appropriately according to the desired spot diameter. In addition, since the radius of the diffraction ring is proportional to the distance L from the evaluation object, it is set appropriately according to the size of the imaging unit 15 in the data acquisition unit 1.

Next, the beam irradiation time will be considered. The irradiation time affects the diffraction intensity, and in a series of evaluations, the irradiation time is set appropriately so that an appropriate diffraction intensity according to the imaging unit 15 in the data acquisition unit 1 is obtained. When the diffraction intensity is relatively small, the measurement error becomes large, so the irradiation time is made longer, and when the diffraction intensity is relatively large, the irradiation time is made shorter so as not to exceed the rated value of the imaging unit 15.

Metal fatigue, on the other hand, is often evaluated based on deterioration over time, and is generally evaluated at appropriate intervals. This can result in different beam irradiation times, and an evaluation index that can stably evaluate the degree of damage even in such cases is desirable.

The evaluation conditions were an incidence angle Ψ ₀ of 45 degrees, a collimator diameter φ of 1.0 mm, and a distance L from the evaluation target of 65 mm. Under these evaluation conditions, diffraction ring data was obtained and evaluation indices were calculated for each of the other evaluation conditions, ie, the irradiation time, of 4 seconds, 5 seconds, 10 seconds, 30 seconds, and 180 seconds. The results are shown in FIG. 7.

The longer the beam irradiation time, the larger the absolute value of the peak intensity. For this reason, the standard deviation σ of the peak intensity distribution in the diffraction ring, which serves as an evaluation index (uniformity index), varies depending on the beam irradiation time at any damage level, as shown in FIG. 7A. On the other hand, the division result σ/μ obtained by dividing the standard deviation σ of the peak intensity distribution in the diffraction ring by the average value μ of the peak intensity distribution in the diffraction ring reduces the variation due to differences in beam irradiation time at any damage level, as shown in FIG. 7B, and uniquely corresponds to the damage level. Therefore, the non-dimensional division result σ/μ is more preferable as an evaluation index.

Since the half-width is expressed in degrees, the effect of the beam irradiation time on the standard deviation is small, so there is little need to divide by the average value. However, the result of dividing the standard deviation of the half-width distribution in the diffraction ring by the average value of the half-width distribution in the diffraction ring can also be explained in the same way as above.

Next, the operation of this embodiment will be described. Figure 8 is a flowchart showing the operation of the metal fatigue evaluation device.

When the metal fatigue evaluation device D configured in this way is powered on, it initializes the necessary parts and starts its operation. In the control processing unit 2, a control unit 21 and an index processing unit 22 are functionally configured by executing the control processing program.

When the start of evaluation is input, in FIG. 8, first, the metal fatigue evaluation device D acquires diffraction ring data under the above-mentioned evaluation conditions by the data acquisition unit 1, and acquires and stores this diffraction ring data from the data acquisition unit 1 (S1). More specifically, in this embodiment, under the above-mentioned evaluation conditions, the data acquisition unit 1 irradiates the evaluation object Ob with an X-ray beam from the X-ray irradiation unit 14 under the control of the control unit 13, images the diffraction ring with the imaging unit 15 under the control of the control unit 13, and generates diffraction ring data representing the diffraction ring. Then, the data acquisition unit 1 outputs this diffraction ring data to the control processing unit 2.

Next, the metal fatigue evaluation device D uses the index processing unit 22 of the control processing unit 2 to obtain and store the uniformity index as an evaluation index for the evaluation object Ob (S2). More specifically, in this embodiment, the index processing unit 22 obtains the standard deviation σ in the intensity distribution of the diffraction ring for the azimuth angle α as the uniformity index, i.e., the evaluation index. Alternatively, the index processing unit 22 obtains the standard deviation σ in the half-width distribution for the azimuth angle α as the uniformity index (the evaluation index). Alternatively, the index processing unit 22 obtains the division result obtained by dividing the standard deviation in the peak intensity distribution of the diffraction ring for the azimuth angle by the average value of the peak intensity distribution in the diffraction ring as the uniformity index (the evaluation index). Alternatively, the index processing unit 22 obtains the division result obtained by dividing the standard deviation in the half-width distribution for the azimuth angle by the average value of the half-width distribution in the diffraction ring as the uniformity index (the evaluation index).

Then, the metal fatigue evaluation device D causes the control processing unit 2 to output the determined evaluation index from the output unit 5, and ends this process (S3). Note that, if necessary, the evaluation index may be output from the IF unit 6 to an external device.

As described above, in the metal fatigue evaluation method of the embodiment, when obtaining diffraction ring data, the beam is irradiated at an incident angle of 0 degrees or more and 65 degrees or less, and the beam is irradiated so that there are 3,000 or less crystal grains within the irradiation area of the beam, or the spot diameter of the beam is 3 mm or less. This makes it possible to obtain diffraction ring data in a more appropriate evaluation environment (evaluation conditions), and to obtain more reliable evaluation results.

The above metal fatigue evaluation method uses a uniformity index that indicates the degree of uniformity of peak intensity in the diffraction ring based on the diffraction ring data as an evaluation index that indicates the degree of metal fatigue, so that the degree of metal fatigue can be evaluated more appropriately.

When the metal fatigue evaluation method uses the result of dividing the standard deviation by the average value as the evaluation index, the effect of variations in the beam irradiation time on the evaluation index can be reduced.

In order to express the present invention, the present invention has been described above adequately and sufficiently through the embodiments with reference to the drawings. However, it should be recognized that a person skilled in the art can easily modify and/or improve the above-mentioned embodiments. Therefore, unless the modification or improvement implemented by a person skilled in the art is at a level that deviates from the scope of the claims described in the claims, the modification or improvement is interpreted as being included in the scope of the claims.

D Metal fatigue evaluation device 1 Data acquisition unit 2 Control processing unit 11 High voltage power supply 12 Cooling unit 13, 21 Control unit 14 X-ray irradiation unit 15 Imaging unit 22 Index processing unit

Claims (4)

A metal fatigue evaluation method for determining an evaluation index representing a degree of metal fatigue in a metal evaluation object, comprising the steps of:
a data acquisition step of acquiring diffraction ring data representing a diffraction ring formed by irradiating the evaluation object with a beam having a diffractive property;
and an index processing step of determining the evaluation index based on the diffraction ring data acquired in the data acquisition step,
The data acquisition step includes irradiating the sample with the beam at an incident angle of 0 degrees or more and 65 degrees or less, and such that the number of crystal grains present within the irradiation area of the beam is 3,000 or less, or irradiating the sample with the beam at an incident angle of 0 degrees or more and 65 degrees or less, and such that the spot diameter of the beam is 3 mm or less.
Metal fatigue evaluation method. The evaluation index is a uniformity index representing the degree of uniformity of the peak intensity in the diffraction ring.
The metal fatigue evaluation method according to claim 1 . The uniformity index is the standard deviation of the peak intensity distribution of the diffraction ring with respect to the azimuth angle, or the standard deviation of the half-width distribution with respect to the azimuth angle;
The metal fatigue evaluation method according to claim 2 . The evaluation index is a result of dividing a standard deviation in a peak intensity distribution of a diffraction ring with respect to an azimuth angle by an average value of the peak intensity distribution of the diffraction ring, or a result of dividing a standard deviation in a half-width distribution with respect to an azimuth angle by an average value of the half-width distribution of the diffraction ring.
The metal fatigue evaluation method according to claim 1 .

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