JP2006284428A - Method and device for detecting inclusion with nonlinear ultrasonic wave - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic inspection method and device for more accurately determining existence of an inclusion. <P>SOLUTION: An ultrasonic transmitting piece 18a and an ultrasonic receiving piece 18b are arranged so as to face one side surface of an investigated object 16, ultrasonic pulse wave is radiated towards the investigated object 16, the reflected wave is processed, and it is determined whether or not reflected wave from an internal defect of the investigated object 16 is included. When the reflected wave from the internal defect is included, ultrasonic burst wave is radiated from the ultrasonic transmitting piece 16b, and the reflected wave is processed, ratio of second harmonic amplitude of the reflected wave amplitude to ultrasonic burst incident wave amplitude is obtained. When a linear relation exists between the input voltage and the ratio of the second harmonic amplitude to the incident wave amplitude, it is determined that there is an inclusion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic flaw detection method and apparatus for detecting an inclusion in a steel material by transmitting an ultrasonic wave into the steel material.

Japanese Laid-Open Patent Publication No. 2002-323481 discloses an ultrasonic flaw detection method and apparatus for discriminating non-metallic inclusions from non-flat voids such as a substantially spherical shape and flat non-crimped voids. ing. In the ultrasonic flaw detector disclosed in the publication, an ultrasonic focused beam is transmitted to a test material, a reflected wave from a foreign substance in the test material is extracted based on the received reflected wave, and the reflected wave of the reflected wave is extracted. In the ultrasonic flaw detection method that inspects foreign matter by measuring the amplitude, the amplitude of the reflected wave from the foreign matter in the test material is measured by multiple ultrasonic focused beams with different beam diameters at the position in the depth direction where the foreign matter exists. The type of the foreign matter is discriminated by taking the difference.
JP 2002-323481 A

  Steel slabs should be produced as homogeneously as possible, but it is impossible to completely unify the grain size, and even if they do not contain non-metallic inclusions, they have certain inhomogeneities. is doing. When ultrasonic testing is performed on inhomogeneous materials, the observed waveform includes not only the response from inclusions to be detected, but also noise and grain boundaries based on inhomogeneities existing in the material at the same time. Scattering noise at is included. In the apparatus and method disclosed in the above publication, there is a problem that a significant signal is lost in such noise and the inclusion cannot be detected.

If the noise characteristics are examined and the noise can be removed from the response waveform, it is considered that the accuracy of the ultrasonic flaw detection test is improved.
Therefore, the present invention enables an ultrasonic flaw detection method and apparatus to accurately determine the presence / absence of inclusions by separating noise contained in an ultrasonic wave reflected toward an object to be inspected, for example, a steel slab. The purpose is to be.

  The present invention described in claim 1 includes: (a) a step of arranging an ultrasonic transmitter and an ultrasonic receiver so as to face one side of an inspection object; and (b) an ultrasonic burst wave from the ultrasonic transmitter. Transmitting to the inspection object, (c) receiving an ultrasonic burst wave reflected from the inspection object by the ultrasonic receiver, and (d) a signal transmitted from the ultrasonic receiver. To obtain the ratio of the amplitude of the second harmonic of the reflected ultrasonic burst wave to the incident wave amplitude; and (e) changing the input voltage applied to the ultrasonic transmitter; and f) repeating the steps (b) to (e) to correlate the change in the input voltage with the change in the ratio of the second harmonic amplitude to the incident wave amplitude. The gist is an ultrasonic flaw detection method for detecting an object.

  According to a fourth aspect of the present invention, in the ultrasonic flaw detector, a means for fixing the inspection object, and an ultrasonic transmitter for transmitting an ultrasonic burst wave positioned so as to face one surface of the inspection object; An ultrasonic receiver for receiving an ultrasonic burst wave that is positioned so as to face the one surface of the inspection object and reflected from the inspection object; and a signal transmitted from the ultrasonic receiver; Signal processing means for obtaining a ratio of the amplitude of the second harmonic of the reflected ultrasonic burst wave to the amplitude of the incident wave, a change in input voltage applied to the ultrasonic transmitter, and a second harmonic with respect to the incident wave amplitude The gist of the present invention is an ultrasonic flaw detection apparatus for detecting inclusions included in an inspection object having a means for associating with a change in the ratio of wave amplitudes.

  According to the present invention, the reflected wave is processed by irradiating an ultrasonic burst wave, and by associating the change in the input voltage with the change in the ratio of the second harmonic amplitude of the reflected wave to the incident wave amplitude, When the reflected wave appears to be a reflected wave from an inclusion, it can be determined whether the reflected wave is a defect signal or a noise signal.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, the flaw detection apparatus 10 includes an ultrasonic element 18 that is movably disposed in three orthogonal directions in the water tank 12 by a scanning device 20. The ultrasonic element 18 is arranged so as to face one side surface of, for example, a steel slab 16 as a material to be inspected fixed on the table 14 arranged in the water tank 12, and is arranged in the center portion and radiates an ultrasonic signal. The hydrophone or ultrasonic receiver 18a and the ultrasonic probe or ultrasonic transmitter 18b disposed around the hydrophone or ultrasonic receiver 18a (see FIG. 2). The ultrasonic transmitter 18b has a concave surface so as to focus at a predetermined distance from the end surface of the ultrasonic receiver 18a along the central axis of the ultrasonic receiver 18a.

  The ultrasonic element 18 is connected to a control device 24 having an oscillator (not shown) for the ultrasonic transmitter 18b, and the ultrasonic wave transmitted from the ultrasonic transmitter 18b is the surface of the slab 16. The ultrasonic wave receiver 18 a reflects the internal defect of the slab 16 and the back surface of the slab 16, and the signal received by the ultrasonic receiver 18 a is transmitted to the control device 24. The driving device 22 of the scanning device 20 is also connected to the control device 24, and the positioning of the ultrasonic element 18 is controlled by the control device 24. The control device 24 further monitors a personal computer 26 as signal processing means for processing a signal transmitted to the control device 24 together with position information of the ultrasonic element 18 and a signal received by the control device 24. An oscilloscope 28 is connected.

Hereinafter, the operation of the present embodiment will be described.
Referring to FIG. 3, a steel slab 16 'having a thickness of 60 mm is shown as a typical example of the inspection object 16, and the steel slab 16' has a small hole 16a formed from the back surface of the steel slab 16 'by a drill. And imitate the defects inside the slab.

  The steel slab is a metal member that is generally a molten steel material cast by a continuous casting method, cooled and solidified, and is slag taken into the molten steel at the refining stage, particularly a particle size of about 0.5 to 1 mm. Aluminum oxide (Al2O3) is mixed as inclusions. These inclusions have a very low specific gravity compared to steel, so they float in the steel due to buoyancy when solidification progresses from the steel surface to the inside during the cooling process, and exist at a depth of about 50 mm from the surface of the steel. Often to do. Therefore, the ultrasonic transmitter 18b is arranged so as to face one side arranged on the upper side in the cooling process of the steel slab, and is formed so as to focus on a position about 50 mm deep from the surface of the steel. It is preferable.

  4 to 8 show the results of experiments conducted by irradiating an ultrasonic pulse signal from the ultrasonic transmitter 18b with the experimental apparatus 10 shown in FIG. 1 using the steel slab 16 ′ shown in FIG. 3 as the inspection object 16. FIG. Show. FIG. 4 shows a case of a steel slab 16 ′ not provided with a small hole 16a. FIGS. 3 to 8 show that the steel slab 16 ′ has a depth of 14 mm, a diameter of 0.5 mm, 1 mm, 2 mm, and 3 mm. It is an experimental result at the time of using the member in which the small hole 16a was formed as the test object 16, respectively.

  4 to 8, a defect, that is, the bottom surface of the small hole 16a, is formed between the reflected wave I on the surface of the steel slab 16 'and the reflected wave II on the back surface of the pulse wave irradiated from the ultrasonic transmitter 18b. It will be understood that the reflected wave III appears. In particular, when the diameter of the small hole 16a is increased, the reflected wave III at the defect is increased, and the reflected wave II at the back surface is decreased. This indicates that when the diameter of the small hole 16a is increased, the ultrasonic wave from the ultrasonic transmitter 18b is reflected on the bottom surface of the small hole 16a and cannot reach the back surface of the steel slab 16 '. This is considered to be an effect of forming a concave surface so as to focus on a position at a depth of about 50 mm from the surface of the steel material.

  In the configuration of FIG. 1, since the ultrasonic transmitter 18b irradiates a pulsed ultrasonic signal, the inspection time can be relatively short. In general, air bubbles may be taken into steel slabs in addition to inclusions, but in many cases, the air bubbles are less likely to be crushed in the rolling process after the casting process. However, when inclusions are present in the steel slab, the steel strip may crack in the rolling process, or the product may crack when plastic working is performed at the automobile manufacturer, for example, an automobile manufacturer. .

  Here, referring to FIG. 9, the bonding rigidity between the parent phase of the steel material and the nonmetallic inclusion is different between the compression phase and the tension (diluted) phase, and the tension side is lower than the compression side. Since the propagation speed of ultrasonic waves is proportional to the square root of Young's modulus, the propagation speed is higher in the compression phase than in the tensile phase. Therefore, by irradiating a burst wave from the transmitter 18b toward the inspection object 16, a waveform is generated after the burst wave is incident on the inspection object 16 and reflected by the inclusion, and this distortion is a harmonic. It is possible to quantify with the amplitude of (a wave having a frequency that is an integer multiple of 2 or more of the incident wave frequency) (see FIG. 10). Therefore, the presence or absence of non-metallic inclusions can be determined by obtaining the ratio of the harmonic component of the reflected wave to the incident wave amplitude, particularly the amplitude of the second harmonic.

The relationship of nonlinear stress strain is given by the following equation.
σ = E _1ε + E _2ε ² (E ₂ : negative) (1)
The solution of the one-dimensional wave equation of the elastic body according to the equation (1) is given by the following equation.

here,
u: Displacement A ₁ : Incident wave amplitude E ₁ : Steel Young's modulus E ₂ : Nonmetallic inclusion Young's modulus i: Imaginary unit k: Wave number (2π / λ (wavelength))
x: distance ω: 2πf (frequency)
It is.

で表される。
従って、入射波振幅に対する二次高調波振幅の比は以下の式にて得られる。

If the amplitude of the second harmonic component is A2,

It is represented by
Therefore, the ratio of the second harmonic amplitude to the incident wave amplitude is obtained by the following equation.

  From equation (4), it is understood that the ratio of the second harmonic amplitude to the incident wave amplitude is proportional to the incident amplitude, the propagation distance x, and the square of the wave number. Note that there is anisotropy in elastic modulus due to the difference in crystal orientation between the steel crystal grains, but there is no difference in rigidity between the tensile phase and the compression phase at the interface between the steel crystal grains and the crystal grains. The harmonics that can be detected with are not excited. In addition, since there is no difference in rigidity between the tensile phase and the compression phase even at the interface between the steel crystal grains and the bubbles, the harmonics that can be detected by the measuring device are not excited. Therefore, it is possible to determine whether the internal defect of the inspection object 16 is caused by bubbles or inclusions by obtaining harmonics, particularly second harmonics, of the reflected wave of the incident ultrasonic burst wave.

  However, the reflected wave received by the ultrasonic receiver includes a reflected wave (noise signal) unrelated to the reflected wave from the inclusion, in addition to the reflected wave (defect signal) from the inclusion. The noise signal is generated due to various causes such as noise based on inhomogeneity existing in the material and scattering noise at the crystal grain boundary. The present invention mainly aims to separate the noise signal from the defect signal. It is said.

Hereinafter, a method for separating a noise signal and a defect signal will be described with reference to FIGS.
FIG. 11 shows a sample slab used in the experiment. The sample slab 30 has a columnar lower part 32 and an upper part 34 joined to the lower part 32 by a joining surface 36, and 0.8 mm, 0.7 mm, 0.6 mm, 0 as inclusions on the joining surface 34. Small balls 38 made of four alumina-based materials having a diameter of .5 mm are arranged. The upper part 34 includes a cylindrical part 34a having the same diameter as that of the lower part 32 and a conical part 34b that is connected to the upper surface of the cylindrical part 34a and spreads upward. Irradiated.

In the experiment, the input voltage Vi applied to the ultrasonic transmitter was changed, and the ratio A ₂ / A ₁ of the _second harmonic amplitude to the incident wave amplitude was measured by the method described above. Figure 12 is a graph showing the measurement result, the vertical axis is a value obtained by percentage of A ₂ / A _1, the horizontal axis is the percentage value of the input voltage V _i with respect to the maximum input voltage Vmax. In FIG. 12, an example of a measurement location other than the spherical inclusion shown in FIG. 11B is shown as a measurement location A. In the graph of FIG. 12, a signal from a 0.8 mm small sphere is indicated by a solid line, a signal from a 0.7 mm small sphere is indicated by a broken line, and a signal from a 0.6 mm small sphere is indicated by a one-dot chain line. The signal from a small sphere with a diameter of 0.5 mm is indicated by a two-dot chain line. The dotted line indicates A ₂ / A ₁ when the small sphere 38 is removed and the ultrasonic burst wave is irradiated.

Referring to FIG. 12, when an ultrasonic burst wave is irradiated to each of the small spheres 38, the value of A ₂ / A ₁ is approximately proportional to the input voltage Vi, but the small sphere 38 is removed. It is understood that the value of A ₂ / A ₁ is not proportional to the input voltage Vi when the ultrasonic burst wave is irradiated. This is because the incident amplitude A ₁ is proportional to the input voltage V _i , and A ₂ / A ₁ is proportional to the incident amplitude A ₁ from the equation (4).

Therefore, according to the present embodiment, the input voltage is further applied to the portion (defect candidate) obtained by irradiating the ultrasonic pulse wave or the ultrasonic burst wave described above toward the slab to obtain a signal indicating the presence of inclusions. By obtaining the value of A ₂ / A ₁ while changing V _i , the noise signal can be removed, and the presence of inclusions can be detected more accurately.

It is a block diagram which shows an example of the ultrasonic flaw detector by this invention. It is a schematic sectional drawing of an ultrasonic element. It is a schematic diagram which shows the structure of the steel material as a test target object used for experiment. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows the joint rigidity between steel materials and a nonmetallic inclusion. It is a graph which shows the incident wave amplitude contained in the signal from an ultrasonic receiver, and a harmonic. It is the schematic of the sample slab used for experiment, (a) is a side view, (b) is an end view which shows the spherical inclusion arrange | positioned in the joining surface of the lower part of a sample slab. It is a graph which shows an experimental result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Flaw detector 12 Water tank 14 Table 16 Inspection object 18 Ultrasonic element 18a Ultrasonic receiver 18b Ultrasonic transmitter 20 Scanning device 22 Drive device 24 Control device 26 Personal computer 28 Oscilloscope

Claims (9)

(A) arranging the ultrasonic transmitter and the ultrasonic receiver so as to face one surface of the inspection object;
(B) transmitting an ultrasonic burst wave from the ultrasonic transmitter to the inspection object;
(C) receiving an ultrasonic burst wave reflected from the inspection object by the ultrasonic receiver;
(D) processing a signal transmitted from the ultrasonic receiver to obtain a ratio of an amplitude of a second harmonic of the reflected ultrasonic burst wave to an incident wave amplitude;
(E) changing an input voltage applied to the ultrasonic transmitter;
(F) Repeating the steps (b) to (e) to correlate the change in the input voltage with the change in the ratio of the second harmonic amplitude to the incident wave amplitude. Ultrasonic flaw detection method to detect objects.   The ultrasonic flaw detection according to claim 1, further comprising: (g) determining that an inclusion is present when there is a linear relationship between the input voltage and a ratio of the second harmonic amplitude to the incident wave amplitude. Method.   The ultrasonic flaw detection method according to claim 1, wherein the ultrasonic transmitter is disposed concentrically so as to surround the periphery of the ultrasonic receiver. In the ultrasonic flaw detector,
Means for fixing the inspection object;
An ultrasonic transmitter that transmits an ultrasonic burst wave that is positioned so as to face one surface of the inspection object;
An ultrasonic receiver for receiving an ultrasonic burst wave that is positioned so as to face the one surface of the inspection object and reflected from the inspection object;
A signal processing means for processing a signal transmitted from the ultrasonic receiver to obtain a ratio of an amplitude of a second harmonic of the reflected ultrasonic burst wave to an incident wave amplitude;
Means for associating a change in the input voltage applied to the ultrasonic transmitter with a change in the ratio of the second harmonic amplitude to the incident wave amplitude;
An ultrasonic flaw detector for detecting inclusions contained in an inspection object comprising:   5. The ultrasonic flaw detector according to claim 4, further comprising means for determining that an inclusion is present when there is a linear relationship between the input voltage and the ratio of the second harmonic amplitude to the incident wave amplitude.   The ultrasonic flaw detector according to claim 4 or 5, wherein the ultrasonic transmitter is arranged concentrically so as to surround the periphery of the ultrasonic receiver.   The storage device according to any one of claims 4 to 6, further comprising a water storage means for storing water, wherein the inspection object and the ultrasonic element are immersed in the water stored by the water storage means. Ultrasonic flaw detector.   The ultrasonic flaw detection according to any one of claims 4 to 7, wherein the ultrasonic element is provided so as to be movable relative to the inspection target along at least a plane of the inspection target facing each other. apparatus.   The ultrasonic flaw detector according to any one of claims 4 to 8, wherein the inspection object is a steel material obtained by casting a molten steel material, and the ultrasonic element is arranged with the steel material as an inspection object.

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