JP5633404B2 - Metal structure measurement method and metal structure measurement apparatus - Google Patents

Description

  The present invention relates to a metal structure measuring method and a metal structure measuring apparatus for measuring a fine structure inside a steel material using ultrasonic waves.

  Since microstructures such as crystal grain size and fine precipitates of metal materials affect material properties such as tensile strength, a microstructure evaluation technique has been conventionally demanded. On the other hand, for example, the microstructure can be evaluated by microscopic observation. However, since much labor is required for cutting out the test piece and polishing the observation surface, a non-destructive microstructure evaluation technique is strongly desired. Against such a background, Patent Document 1 proposes a method for measuring the crystal grain size non-destructively using ultrasonic waves.

International Publication No. 2007/148655

  By the way, the factors affecting the material properties of the metal material include not only the crystal grain size but also the fine structure of fine grains such as fine precipitates smaller than the crystal grains existing in the crystal grains or in the crystal grain boundaries. However, according to the technique described in Patent Document 1, only the crystal grain size can be measured. For this reason, provision of the technique which can measure the fine structure inside a to-be-measured material was anticipated.

  This invention is made | formed in view of the above, Comprising: It aims at providing the metal structure measuring method and metal structure measuring apparatus which can measure the fine structure inside steel materials by nondestructive using an ultrasonic wave.

  In order to solve the above-described problems and achieve the object, a metallographic measurement method according to the present invention transmits ultrasonic waves from an ultrasonic probe to a metal as a material to be measured, and generates backscattered waves from the inside. It is a metallographic measurement method for measuring fine grains different from crystal grains in a material to be measured, or fine structure and crystal grains by measuring, and the center wavelength at the measurement target part of the ultrasonic wave to be transmitted is A measurement step of measuring a backscattered wave using an ultrasonic wave that is 5 times or less the average grain size of crystal grains and 5 or more times the average grain size of fine grains; and a crystal from the measured backscattered wave From the extraction step of removing the backscattered wave component due to the particles and extracting the backscattered wave component due to the fine particles, and from the backscattered wave component due to the extracted fine particles, the volume density, number density, and average particle size of the fine particles At least one of Characterized in that it comprises a, an evaluation step of obtaining a.

  Further, in the metallographic structure measurement method according to the present invention, in the above invention, the extraction step performs a frequency analysis on the measured backscattered wave, and removes a backscattered wave component due to a crystal grain independent of the frequency, thereby reducing the frequency. The method includes a step of extracting a backscattered wave component due to fine particles depending on.

  In the metal structure measurement method according to the present invention as set forth in the invention described above, the extraction step transmits an ultrasonic wave having a center wavelength at a measured portion that is 5 times or more the average particle diameter of the crystal grains, The method includes the step of specifying a backscattered wave component due to the crystal grains by measuring the average grain size of the grains.

  In addition, the metallographic structure measurement apparatus according to the present invention transmits ultrasonic waves from an ultrasonic probe to a metal as a material to be measured, and measures a backscattered wave from the inside to measure the crystal grains in the material to be measured. Is a metallographic measurement device that measures different fine grains, or fine structures and crystal grains, and the center wavelength of the ultrasonic wave to be measured is 5 times or less the average grain size of the crystal grains And measuring means for measuring backscattered waves using ultrasonic waves that are 5 times or more the average particle diameter of the fine grains, and removing backscattered wave components due to crystal grains from the measured backscattered waves, Extraction means for extracting a backscattered wave component, and evaluation means for obtaining at least one of volume density, number density, and average particle diameter of the fine particles from the extracted backscattered wave component of the fine particles. It is characterized by

  ADVANTAGE OF THE INVENTION According to this invention, the fine structure inside steel materials can be measured nondestructively using an ultrasonic wave.

FIG. 1 is a block diagram schematically showing a configuration of a metallographic measurement apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart showing an ultrasonic measurement processing procedure according to the embodiment of the present invention. FIG. 3 is a flowchart showing a detailed example 1 of step S3 in FIG. FIG. 4 is a flowchart showing a detailed example 2 of step S3 in FIG. FIG. 5 is a flowchart showing a detailed example 3 of step S3 in FIG. FIG. 6 is a diagram illustrating a configuration of a simulation model according to the embodiment of the present invention. FIG. 7 is a diagram illustrating a waveform of a transmission signal in the simulation using the model of FIG. FIG. 8 is an explanatory diagram of a procedure for acquiring a backscattered wave for case 1 of the simulation model of FIG. FIG. 9 is a diagram showing the scattering coefficient for each frequency obtained as a result of simulation by the model of FIG. FIG. 10 is a diagram illustrating an evaluation value obtained from the result of FIG. 9 and an evaluation value according to a comparative example.

  Embodiments of a metallographic measurement method and a metallographic measurement apparatus according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a block diagram schematically showing a configuration of a metallographic measurement apparatus according to an embodiment of the present invention. As shown in FIG. 1, the metallographic measurement apparatus 10 includes an ultrasonic probe 1, an ultrasonic transmission unit 2, an ultrasonic reception unit 3, a scattered wave component extraction unit 4, an evaluation value calculation unit 5, A control unit (not shown).

  The ultrasonic probe 1 includes an ultrasonic transmission unit 2 and an ultrasonic reception unit 3. The ultrasonic transmission unit 2 transmits ultrasonic waves from the ultrasonic probe 1 for non-destructively measuring a metal microstructure as a material to be measured. In addition, the ultrasonic receiving unit 3 receives the backscattered wave (measurement signal) from the measurement target portion of the transmitted ultrasonic wave by the ultrasonic probe 1. The ultrasonic transmitter 2 and the ultrasonic receiver 3 may be attached to the same ultrasonic probe 1 or may be attached to separate ultrasonic probes 1. The ultrasonic probe 1 may be realized by a single transducer or an array transducer.

  The scattered wave component extraction unit 4 extracts a back scattered wave component due to fine particles from the measurement signal. Moreover, the evaluation value calculation part 5 calculates the evaluation value of a fine grain from the backscattered wave component by the extracted fine grain. The control unit is realized using a memory that stores a processing program and the like and a CPU that executes the processing program, and controls each component of the metallographic measurement apparatus 10.

  Here, with reference to the flowchart shown in FIG. 2, the metal structure measurement processing procedure by the metal structure measuring apparatus 10 will be described. The flowchart shown in FIG. 2 is started at the timing when the operator inputs a metallographic measurement instruction to the measurement target, and the metallographic measurement process proceeds to step S1.

In the process of step S1, the ultrasonic transmission unit 2 irradiates the measurement target unit with ultrasonic waves, and the control unit acquires information on transmission signals such as the wavelength λ and the intensity A ₀ in the measurement unit of the transmission ultrasonic waves. To do. Thereby, the process of step S1 is completed, and the metallographic measurement process proceeds to the process of step S2.

  In the present invention, when the crystal grain size (diameter of crystal grains) is D and the fine grain size (diameter of fine grains) is d, the wavelength λ in the measurement target portion of the ultrasonic wave used for measurement is as follows. The wavelength of the transmission ultrasonic wave is determined so as to satisfy the following equation.

  However, since the above equation (1) is satisfied in a normal case, it is sufficient to satisfy the equation (2).

  Here, λ is the wavelength of the ultrasonic wave at the part to be measured, which is different from the wavelength at the time of transmission of the ultrasonic wave, due to factors such as the difference in sound speed and the frequency dependence of attenuation along the path to the part to be measured. Change. In addition, since broadband ultrasonic waves are used for measurement, ultrasonic waves of various wavelengths are synthesized, and the center wavelength is assumed to be λ. In the case where the ultrasonic wave for each wavelength can be separated by performing frequency analysis after being received by the measured part, the separated wavelength corresponds to λ.

  The ultrasonic transmission direction may be inclined at a predetermined angle with respect to the surface of the material to be measured, as shown in FIG. By tilting in this way, the degree of reception of reflection from the surface of the material to be measured can be reduced. Further, although a transverse wave is generated in the measurement target part, the transverse wave has a shorter wavelength than the longitudinal wave, and can easily satisfy the above formula (2). However, a method of transmitting ultrasonic waves perpendicular to the surface of the material to be measured is also applicable to the present invention.

  Further, here, the ultrasonic beam is focused so that only a specific region (measurement portion) of the material to be measured is strongly irradiated with the ultrasonic wave. Even when the microstructure of the material to be measured varies from region to region, the microstructure of a specific region can be measured by the present invention. However, a method that does not focus the ultrasonic beam is also applicable to the present invention.

  In the process of step S2, the ultrasonic receiver 3 receives the backscattered wave (measurement signal) from the measurement target portion of the transmitted ultrasonic wave by the ultrasonic probe 1, and the frequency, intensity, etc. of the measurement signal are received. Get information. Thereby, the process at step S2 is completed, and the metallographic measurement process proceeds to the process at step S3.

Here, the backscattered wave is a superposition of the reflected waves from the minute reflectors, and can be specified by considering the reflections from the individual reflectors. According to the following literature 1, if the distance from the transducer of the ultrasonic transmitter 2 to the spherical reflector is x, the radius of the spherical reflector is r, and the intensity of the ultrasonic wave irradiated to the reflector is A ₀ , backscattering is performed. It is known that the wave reflection intensity A satisfies the following equation.

    [Reference 1] Ultrasonic flaw test 2001 edition, Japan Nondestructive Inspection Association

In general, when the speed of sound is c, the following formula is established between the frequency f and the wavelength λ.

  In the present invention, based on the above formulas (3) and (4), in step S1, the wavelength λ at the measurement target portion of the ultrasonic wave used for measurement is set to satisfy the formulas (1) and (2). Were determined.

Then, the intensity A ₁ of the back scattered wave from the crystal grains and the intensity A ₂ of the back scattered wave from the fine grains can be expressed by the following equations.

ただし、Ｃ_１は、結晶粒と測定条件によって決まる定数であって、（Ｄ／ｘ）に比例する。またＣ_２は、微細粒と測定条件によって決まる定数であって、（ｄ^３／ｘ）に比例する。

However, C ₁ is a constant determined by the crystal grains and measuring conditions, is proportional to (D / x). C ₂ is a constant determined by fine grains and measurement conditions, and is proportional to (d ³ / x).

In this case, the wave intensity A _total measured as a backscattered wave is represented by the sum of A ₁ and A ₂ and satisfies the following expression.

  In the process of step S3, the scattered wave component extraction unit 4 performs a process of extracting the back scattered wave component due to the fine particles of the back scattered wave based on the information of the measurement signal and the above formulas (6) to (8). . As can be seen from the above equation (8), the backscattered wave component due to the crystal grains of the backscattered wave does not depend on the frequency f, and the backscattered wave component due to the fine particles of the backscattered wave depends on the frequency f. Therefore, the process of extracting the backscattered wave component due to the fine particles of the backscattered wave is nothing but the process of extracting the component depending on the frequency f. The process of extracting the backscattered wave component due to the fine particles from the backscattered wave in step S3 can be variously realized as illustrated below.

(Example 1)
FIG. 3 is a flowchart of Example 1 detailing the process of extracting the backscattered wave component due to the fine particles from the backscattered wave in step S3. In the process of step S311, based on the information of the transmission signal acquired in the step S1, the process of acquiring the intensity A ₀ of each frequency f by performing frequency analysis. Next, in the process of step S312, based on the information of the backscattered wave acquired in step S2, the frequency analysis is performed to acquire the intensity A _total for each frequency f. Next, in the process of step S313, based on the result of step S311 and step S312, the performed processing for obtaining scattering coefficient for each frequency _{f (A total / A 0)} . Then, in the processing in step S314, the based on the equation (8), it performs a process of calculating a _{C 2.} Thereby, the process which extracts the backscattered wave component by the fine grain of step S3 is completed, and a metal structure measurement process transfers to the process of step S4.

In addition, based on the scattering coefficient (A _total / A ₀ ) for each frequency f acquired in the process of step S313, it is also possible to calculate C ₁ using equation (8). Thereby, the backscattered wave component by a crystal grain is extracted.

(Example 2)
FIG. 4 is a flowchart of Example 2 detailing the process of extracting the backscattered wave component due to the fine particles from the backscattered wave in step S3. In the process of step S321, a process of measuring the crystal grain size D is performed. For example, the crystal grain size D is measured by applying the method described in Patent Document 1. Then, the processing in step S322, performs processing for calculating a _{C 1} based on the crystal grain size D measured in step S321. Next, in the process of step S323, the intensity _{A 0} of the transmission signal obtained in step S1, based on the _{C 1} calculated in step S322, the rear of acquiring the _{A 1} from the equation (6), obtained in step S2 By subtracting A ₁ from the scattered wave intensity A _total, a process for obtaining the intensity A ₂ of the back scattered wave due to the fine particles is performed. In the process of step S323, it is not necessary to perform frequency analysis. Then, in the processing in step S324, based on the equation (7), it performs a process of calculating a _{C 2.} Thereby, the process which extracts the backscattered wave component by the fine grain of step S3 is completed, and a metal structure measurement process transfers to the process of step S4.

  The ultrasonic wavelength λ ′ at the time of measuring the crystal grain size D is desirably determined so as to satisfy the following formula. In general, the influence of scattering by crystal grains is larger than the influence of scattering by fine grains, and in this case, both the back scattered waves by crystal grains and the back scattered waves by fine grains depend on the frequency (formula (4) Since the influence of scattering by fine grains can be reduced in the entire frequency range, it is convenient for measurement of crystal grains.

(Example 3)
FIG. 5 is a flowchart of Example 3 detailing the process of extracting the backscattered wave component due to the fine particles from the backscattered wave in step S3. This example 3 is applied when the influence of the crystal grain size D on the backscattered wave can be predicted. For example, this can be predicted when manufacturing conditions can be used, or when the crystal grain size of the measurement target is almost constant and measurement is not necessary, and C ₁ or the intensity A _{1 of the} backscattered wave from the crystal grain can be obtained. It is.

Therefore, in the processing in step S331, it performs a process of acquiring the intensity A ₁ of the backscattered waves from the crystal grains. Next, in the process of step S332, subtracts the intensity _{A 0} of the obtained transmission signal on the basis of the _{A 1} obtained in step S331, the _{A 1} from the intensity A _total of backscattered waves acquired in step S2 in step S1 by performs a process of acquiring the intensity a ₂ of the backscattered wave by fine grains. Then, in the processing in step S333, based on the equation (7), it performs a process of calculating a _{C 2.} Thereby, the process which extracts the backscattered wave component by the fine grain of step S3 is completed, and a metal structure measurement process transfers to the process of step S4.

In the process of step S4, the evaluation value calculating unit 5, based on the coefficient C ₂ of the backscattered wave component according to the extracted fine particles, a process of calculating an evaluation value of the fine grains. As the evaluation value, for example, the number of fine particles per unit volume (number density), the volume of fine particles per unit volume (volume density), the particle size of the fine particles, and the like are calculated.

Here, the intensity A ₂ of the backscattered waves from a plurality of fine particle number density is N, it depends on the intensity a ₂ of backscattered waves from each fine particle. It is known that A ₂ is N times a ₂ when the phases of backscattered waves from a plurality of fine grains are aligned. Further, it is known that A ₂ is √N times a ₂ when the phases of backscattered waves from a plurality of fine grains are not aligned.

Therefore, the intensity a ₂ of the backscattered waves from each fine particle because according to the formula (4), the number density N, the intensity A ₂ of the backscattered waves from a plurality of fine particle is the volume density V is phase aligned Is expressed by the following formula.

On the other hand, assuming that the phases are not aligned, A ₂ can be expressed by the following equation.

According to the above equation (11), can be based on the coefficient C ₂ of the backscattered wave component according to the obtained fine particle in the step S3, evaluates the fine particle volume density V. Further, according to the above equation (12), based on C ₂ obtained in step S3, it is possible to evaluate the number density N of fine grains. Further, according to the above formula (13), when the volume density V of the fine particles is known from the addition amount of the fine particle components, the fine particle size (fine particle radius) r is obtained.

  As described above, when the process in step S4 is completed, the control unit appropriately outputs the evaluation result in step S4 to a display or the like (step S5), and the series of metal structure measurement processes is completed.

(Example)
Next, examples corresponding to the above-described embodiment will be described. A metal structure measurement process was simulated using a two-dimensional model having the configuration shown in FIG. As shown in FIG. 6, a single probe for focusing an ultrasonic beam is used as the ultrasonic probe 1, and a sphere having a diameter λ assuming a crystal grain as a measured portion inside a steel as a measured material. A simulation was carried out on a two-dimensional model in which spheres having a diameter of 0.1λ assuming fine grains were arranged inside one. For the following four cases where the reflectance of the crystal grains is 10% and the reflectance of the fine grains is 100% and the arrangement conditions of the fine grains are changed, simulation is performed using commercially available ultrasonic propagation FEM simulation software. Carried out. That is, four fine grains are arranged in Case 1, two fine grains are arranged in Case 2, only fine grains are arranged in Case 3, and no crystal grains are arranged in Case 4.

  FIG. 7 shows the waveform of the transmission signal used in the simulation. FIG. 8 shows the waveform of the measurement signal obtained as a result of simulation for case 1. In addition, the backscattered wave except the reflective component in the surface of a to-be-measured material was acquired by subtracting the measurement signal of case 4 from the measurement signal of case 1.

Next, frequency analysis was performed on the transmission signal and the backscattered wave, and the scattering coefficient A ₀ / A _total for each frequency was calculated for Case 1. The scattering coefficient was calculated in the same manner for Case 2 and Case 3. FIG. 9 shows the scattering coefficient for each frequency calculated for cases 1-3. According to FIG. 9, it can be seen that the case 3 having no fine particles has different frequency dependency from the case 1 and the case 2 in which the fine particles are arranged.

Here, it can be seen that the scattering coefficient α (f) satisfies the following expression from the above expression (8).

By a contrasting and 9 this equation (14), it can be as the evaluation value to obtain the coefficient C _2.

FIG. 10 shows the result of the evaluation value (coefficient C ₂ ) obtained by this example. As a comparative example, the result of extracting the amplitude (intensity A _total ) of the backscattered wave as an evaluation value is shown. According to the comparative example, even when the fine particles of case 3 are not arranged, an evaluation value that cannot be ignored is obtained. This is because scattering due to crystal grains is also evaluated. On the other hand, according to the present Example, it turns out that a fine grain can be evaluated, without receiving the influence of the scattering by a crystal grain.

In the above embodiment, the evaluation value is obtained by comparing the measured value of the scattering coefficient with the equation (14). However, the method of evaluating the fine particles is not limited to this. For example, according to equation (14), since f ² is small and the influence of C ₂ is small at a low frequency, C ₁ is obtained at a low frequency to evaluate a crystal grain, and then C ₂ is obtained at a high frequency. You may make it evaluate a fine grain.

  As described above, according to the present invention, it is possible to measure the fine structure inside the steel material by using ultrasonic waves in a nondestructive manner.

DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 2 Ultrasonic transmission part 3 Ultrasonic reception part 4 Scattered wave component extraction part 5 Evaluation value calculation part 10 Metal structure measuring apparatus

Claims (4)

By transmitting ultrasonic waves from the ultrasonic probe to the metal as the material to be measured and measuring the backscattered waves from the inside, fine grains different from the crystal grains in the material to be measured, or fine structures and crystal grains A metal structure measurement method for measuring,
Backscattering using ultrasonic waves in which the center wavelength of the ultrasonic wave to be transmitted is 5 times or less the average particle size of the crystal grains and 5 times or more the average particle size of the fine grains A measurement step to measure the wave;
An extraction step of removing a backscattered wave component due to crystal grains from the measured backscattered wave, and extracting a backscattered wave component due to fine grains;
From the backscattered wave component by the extracted fine particles, an evaluation step for obtaining at least one of volume density, number density, and average particle size of the fine particles;
A metallographic structure measuring method comprising:   The extraction step includes a step of extracting a backscattered wave component due to frequency-dependent fine grains by performing frequency analysis on the measured backscattered wave and removing a backscattered wave component due to frequency-independent crystal grains. The metallographic measurement method according to claim 1, wherein:   In the extraction step, an ultrasonic wave having a center wavelength at a measured portion that is 5 times or more of the average grain size of the crystal grains is transmitted, and the average grain size of the crystal grains is measured, whereby backscattered waves by the crystal grains are measured. The method for measuring a metallographic structure according to claim 1, further comprising a step of specifying a component. By transmitting ultrasonic waves from the ultrasonic probe to the metal as the material to be measured and measuring the backscattered waves from the inside, fine grains different from the crystal grains in the material to be measured, or fine structures and crystal grains A metallographic measurement device for measuring,
Backscattering using ultrasonic waves in which the center wavelength of the ultrasonic wave to be transmitted is 5 times or less the average particle size of the crystal grains and 5 times or more the average particle size of the fine grains A measuring means for measuring waves;
An extraction means for removing a backscattered wave component due to crystal grains from the measured backscattered wave, and extracting a backscattered wave component due to fine grains;
From the backscattered wave component by the extracted fine particles, evaluation means for obtaining at least one of volume density, number density, and average particle size of the fine particles;
A metallographic structure measuring device comprising:

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