JPH02253152A - Method and device for flaw detection - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a flaw detection method and a flaw detection apparatus for detecting flaws by detecting leakage magnetic flux of a material to be flaw-tested using a magneto-optic effect element.

[Conventional technology]

Conventionally, methods for detecting surface flaws in ferromagnetic materials include the magnetic particle flaw detection method, in which the material to be flawed is magnetized, magnetic particles are attracted to the leakage magnetic flux caused by the defect, and visually detected, or the leakage magnetic field is detected using a Hall element,
A leakage magnetic flux flaw detection method that electrically detects flaws using a coil or the like is widely used.

However, although the former method has low resolution, it is excellent in quantifying defect depth. On the other hand, the latter method has a problem in that it is difficult to detect defects smaller than the size of a Hall element or the like.

As a countermeasure to this problem, magneto-optical flaw detection, which detects a magnetic field using a magneto-optic effect element, has attracted attention in recent years. In this magneto-optical flaw detection method, when a leakage magnetic field from a defect is applied to a magneto-optic effect element, the polarization plane of linearly polarized light that passes through the magneto-optic effect element is proportional to the magnitude of the component of the magnetic field that is parallel to the light. This method uses the so-called Faraday effect.

Figure 7 shows the conventional magneto-optical flaw detection method (0, L, Fitzpa
tric;11th World Conf, on
NDT, 1985 Vol, 1, p186) is a schematic diagram showing the flaw detection state. A detection head 16 for detecting leakage magnetic flux is placed on the surface of the ferromagnetic material M to be tested, and an analyzer 19 is provided on which the reflected light from the detection head 16 enters.

The detection head 16 has magneto-optical effect elements 16b and 16c formed on both the front and back sides of a transparent substrate 16a, a reflective film 16d formed on the lower surface facing the material M to be detected, and a bias magnetizing coil surrounding the substrate 16a. 16e is wound.

When detecting a defect Ma in the material M to be tested, the detection head 16 is placed on the surface of the material M to be tested while applying a magnetic field to the material M to be tested.
The detection head 16 projects linearly polarized light PL onto the magneto-optic effect element 16c from the upper surface side of the detection head 16.

The projected light PL is transmitted through the magneto-optic effect element 16c and the substrate 16a.
, passes through the magneto-optic effect element 16b, is reflected by the reflective film 16d, and returns to the magneto-optic effect element 16b.

After passing through the substrate 16a and the magneto-optic effect element 16c, the light reaches the analyzer 19 and is observed through the analyzer 19.

When a flaw exists in the material M to be detected and leakage magnetic flux is generated, the leakage magnetic field due to this is applied to the magneto-optic effect element 16b16c, and the magneto-optic effect element 1 to which this leakage magnetic field is applied is applied.
The plane of polarization of the linearly polarized light PL transmitted through 6b and 16c rotates in accordance with the strength of the applied magnetic field, and the amount of light passing through the analyzer 19 changes in accordance with the leakage magnetic field. By capturing the flaws, the presence or absence of flaws in the material M to be detected can be detected.

The magneto-optic effect elements 16b and 16c have rectangular (hysteresis) magnetic characteristics as shown in FIG.

Due to this square magnetic characteristic, the magneto-optic effect elements 16b, 16
The magnetic field H applied to the magneto-optic effect elements 16b and 16c
Until it reaches the coercive force + HC that it has, its polarization plane rotation angle θ is 1 θ. is maintained.

Therefore, if a bias magnetic field H8 having an amplitude smaller than the coercive force Hc is applied to the magneto-optic effect elements 16b and 16c, when a leakage magnetic field ΔH is generated due to a defect in the material M to be tested, it will be added to the bias magnetic field Ho. When the coercive force of the magneto-optic effect element 16c reaches +Hc, the polarity of the polarization plane rotation angle θ changes to +θ0. Thereby, the defect M3 of the material M to be tested is detected. However, even if the leakage magnetic field ΔH becomes larger than Hc-H, the polarization plane rotation angle θ1 remains θ. Since it remains unchanged and does not change, it is not possible to quantitatively evaluate the leakage magnetic field, that is, the defect, and it is only used to inspect the presence or absence of the defect M8 in the material M to be detected.

[Problem to be solved by the invention]

As mentioned above, when a magneto-optic effect element is applied to leakage magnetic flux flaw detection, (1) until the applied magnetic field to the magneto-optic effect element on which the leakage magnetic field is superimposed reaches the coercive force of the magneto-optic effect element or more, the polarized light is The polarity of the surface rotation angle does not change and the detection sensitivity is low.

(2) Since the magneto-optic effect element has square magnetic characteristics,
There is a problem in that it is not possible to quantitatively evaluate defects in the material being tested.

Therefore, this is a major obstacle to further improving the quality of steel materials through flaw detection.

In view of such problems, it is an object of the present invention to provide a flaw detection method and a flaw detection apparatus that can detect defects in a material to be flaw-detected with high sensitivity and quantitatively using a magneto-optic effect element.

[Means to solve the problem]

A first aspect of the present invention is a flaw detection method for detecting defects in a material to be tested using a magneto-optic effect element, in which an alternating current magnetic field having an amplitude larger than a coercive force of the magneto-optic effect element is applied to the magneto-optic effect element, so that the polarization plane of the flaw detection method is It is characterized by detecting defects from the phase or time width of a rectangular wave corresponding to a change in polarity of the rotation angle.

A second invention provides a flaw detection apparatus for detecting defects in a material to be flaw-detected using a magneto-optic effect element, including a magnetizer that applies an alternating current magnetic field to the magneto-optical effect element with an amplitude larger than a coercive force thereof; The present invention is characterized in that it includes a phase difference measuring circuit that measures a phase difference between a rectangular wave synchronized with and a rectangular wave corresponding to a polarity change of the rotation angle of the polarization plane of the magneto-optic effect element.

A third aspect of the present invention provides a flaw detection apparatus that uses a magneto-optic effect element to detect defects in a material to be tested, including a magnetizer that applies an alternating magnetic field to the magneto-optical element with an amplitude larger than a coercive force thereof; The present invention is characterized by comprising a time width difference measuring circuit that measures the difference between the time width of a rectangular wave synchronized with the time width of the rectangular wave and the time width of the rectangular wave corresponding to the polarity change of the rotation angle of the polarization plane of the magneto-optic effect element.

A fourth invention is a flaw detection method for detecting defects in a material to be tested using a magneto-optic effect element, in which the magneto-optic effect element includes:
It is characterized in that an alternating magnetic field having an amplitude larger than the coercive force of the magnet is applied, a magnetizing current at a point in time when the alternating magnetic field exceeds the coercive force is determined, and defects are detected from the magnetizing current.

A fifth invention is a flaw detection apparatus for detecting defects in a material to be tested using a magneto-optic effect element, in which the magneto-optic effect element includes:
A magnetizer that provides an alternating magnetic field with an amplitude larger than the coercive force it has, and a magnetizing current measuring circuit that measures the magnetizing current output by the magnetizer at the time when the alternating magnetic field exceeds the coercive force of the magneto-optic effect element. It is characterized by

[Effect]

In the first invention, an alternating magnetic field having an amplitude greater than the coercive force of the magneto-optic effect element is applied to the magneto-optic effect element. When the alternating magnetic field reaches the coercive force, the polarity of the polarization plane rotation angle changes.

When the AC magnetic field is amplitude-modulated by a leakage magnetic field generated by a defect in the material to be tested, the phase or time width of the rectangular wave corresponding to a change in the rotation angle of the plane of polarization changes depending on the defect in the material to be tested.

In the second invention, the magnetizer applies an alternating magnetic field to the magneto-optic effect element with an amplitude greater than its coercive force. When the alternating magnetic field reaches coercive force, the rotation angle of the plane of polarization changes.

The phase difference measurement circuit determines the phase difference between a rectangular wave related to the alternating magnetic field and a rectangular wave related to a change in the polarization plane rotation angle. The phase difference changes depending on the defects in the material being tested.

In the third invention, the magnetizer applies an alternating magnetic field to the magneto-optic effect element with an amplitude greater than its coercive force. When the alternating magnetic field reaches coercive force, the rotation angle of the plane of polarization changes. The time width difference measurement circuit determines a time width difference between a time width of a rectangular wave related to an alternating magnetic field and a time width of a rectangular wave related to a change in a polarization plane rotation angle. The time width difference changes depending on the defect in the material to be detected.

In the fourth invention, an alternating magnetic field having an amplitude greater than the coercive force of the magneto-optic effect element is applied to the magneto-optic effect element. When the alternating magnetic field whose amplitude is modulated by the leakage magnetic field reaches the coercive force, a difference occurs between the magnetizing current that generates the alternating magnetic field and the current that generates the alternating magnetic field equal to the coercive force. The current difference changes depending on the defects in the material being tested.

In the fifth invention, the magnetizer applies an alternating magnetic field to the magneto-optic effect element with an amplitude greater than its coercive force.

The magnetizing current measuring circuit measures the magnetizing current output by the magnetizer at the time when the alternating magnetic field whose amplitude is modulated by the leakage magnetic field exceeds the coercive force. The measured magnetizing current changes depending on the defects in the material being tested.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

FIG. 1 is a schematic diagram showing a flaw detection state by the flaw detection method according to the first invention. For example, the detection head 1 is arranged close to the surface of a material M to be detected, which is made of steel and has a defect M2. The detection head 1 has a magneto-optic effect element 1 on the side of the material M to be tested.
It has a. The magneto-optic effect element 1a is made of a ferromagnetic material such as YIG (Y3PesO+z) that exhibits the Faraday effect. The magneto-optic effect element 1a includes an AC bias excitation coil 1 that applies an AC bias magnetic field to the magneto-optic effect element 1a.
b is wound around the magneto-optic effect element 1a. A reflective film 1c is provided on the side of the material M to be tested of the magneto-optic effect element 1a. In addition, approaching the material M to be tested, a material magnetizer 2 equipped with an excitation coil 3 and having a U-shaped side surface is applied with a magnetic field perpendicular to the extending direction of the defect M3 on the material M to be tested. The material magnetizer 2 is arranged to straddle the detection head 1 in the radial direction.

Linearly polarized light PL is projected from a light source (not shown) onto the magneto-optic effect element 1a of the detection head 1, passes through the magneto-optic effect element 1a, is reflected by the reflective film IC, and passes through the magneto-optic effect element 1a again. The light enters a photodetector 5 via an analyzer 4.

In such a magneto-optic effect element 1a, the plane of polarization of linearly polarized light passing through the magneto-optic effect element 1a rotates in relation to the intensity of the magnetic field applied to the magneto-optic effect element 1a.

The polarization plane rotation angle θ is given by the following equation (1).

θ,=VH#...(1) However, ■: Herde's constant (proportionality constant) H: Magnetic field strength β; Transmission distance Also, the magneto-optic effect element 1a has a rectangular shape (
hysteresis) has magnetic properties.

Now, a method for detecting defects in a material to be tested using such testing conditions will be explained with reference to FIG. 2.

FIG. 2 is an explanatory diagram showing the relationship between the rectangular magnetic characteristics of the magneto-optic effect element, the alternating current bias magnetic field H9, and the polarization plane rotation angle θ. When linearly polarized light PL is projected from a light source (not shown) onto the magneto-optic effect element 1a, the light is transmitted to the reflection film I
The light is reflected by C, passes through the analyzer 4, and enters the photodetector 5. On the other hand, the AC bias excitation coil 1b is energized to provide an AC bias magnetic field H9 having an amplitude greater than the coercive force He of the magneto-optic effect element 1a, as shown in FIG. Also, the excitation coil 3 has an AC bias excitation coil 1.
A current of the same phase as the current applied to b is applied to the material M to be tested.
A predetermined alternating current magnetic field is applied to the

Then, leakage magnetic flux will be generated in relation to the M defects at the position where the defect M8 is present in the material M to be tested.

By the way, when the leakage magnetic flux due to the defect M8 is not acting on the detection head 1, the polarization plane rotation angle θ of the magneto-optic effect element 1a is changed in relation to the AC bias magnetic field Hp shown by the broken line.
The polarity of , changes. That is, until the AC bias magnetic field H exceeds the coercive force +Hc and reaches 1)c, the rotation angle of the plane of polarization is 〇. will be retained. This change in the polarization plane rotation angle θ is caused by the polarity of the polarization plane rotation angle θ changing with the phases t0 and t2 of the alternating current bias magnetic field Hp, as shown in Figure 2, with time t on the horizontal axis. , the period, or time width, of the rectangular wave W1 corresponding to the polarity change is T1.

On the other hand, when leakage magnetic flux due to a defect acts on the detection head 1, the magnetic field due to the leakage magnetic flux is added to the AC bias magnetic field Hp shown by the broken line in FIG. 2(a), and the amplitude is modulated.
An amplitude-modulated alternating current magnetic field HLIJ as shown by the solid line is applied to the magneto-optic effect element 1a. As a result, the rotation angle θ of the polarization plane changes as shown by the solid line in FIG.

The polarity of the rectangular wave W2 changes, and the period, ie, the time width, of the rectangular wave W2 corresponding to the polarity change becomes T2. Therefore, when leakage magnetic flux occurs, the rectangular wave Wl corresponding to the polarity change of the polarization plane rotation angle changes to a rectangular wave W2, its phase advances, and its time width is T1. However, the time width T2 is shorter than that. By the way, since the leakage magnetic flux generated by the defect M8 is proportional to the defect as described above, if the phase or time width of the rectangular waves W, W2 corresponding to the polarity change of the polarization plane rotation angle θ is detected, This means that the defect M can be quantitatively determined.

Further, when an amplitude-modulated alternating current magnetic field HL is generated, the rotation angle θ of the plane of polarization changes regardless of its magnitude, so that the defect M3 in the material M to be detected can always be detected with high sensitivity. Therefore, the accuracy and reliability of flaw detection can be greatly improved.

FIG. 3 is a block diagram of a flaw detection apparatus according to a second invention configured to detect defects in a material to be tested based on the first invention. The detection head 1 includes a magneto-optic effect element 1a provided with a reflective film 1c and an AC bias excitation coil ib.

The linearly polarized light PL projected onto the magneto-optic effect element 1a is reflected by the reflective film 1c, and the light that passes through the magneto-optic effect element 1a enters the photodetector 5 via the analyzer 4. The output of the photodetector 5 is given to a waveform shaper 10, and the output thereof is given to a phase difference measuring device 11. The AC bias excitation coil 1b is excited by the magnetization power supply 12. A current corresponding to the excitation current is applied to the phase shifter 13, and its output is applied to the phase difference measuring device 11.

Next, the flaw detection operation of this flaw detection apparatus will be explained with reference to FIG. An alternating current magnetic field is applied to the material M to be tested by a material magnetizer 2 (see FIG. 1), and an alternating current bias magnetic field having the same phase as that is applied to the magneto-optic effect element 1a.

Then, in the magneto-optic effect element 1a having square magnetic characteristics,
When an AC bias magnetic field Hp having an amplitude larger than the coercive force He of the magneto-optic effect element 1a is applied, the polarity of the polarization plane rotation angle θ of the magneto-optic effect element 1a changes in synchronization with the AC bias magnetic field Hp.

Now, if the leakage magnetic flux due to the defect M in the material M to be tested is not acting on the magneto-optic effect element 1a, the polarization plane rotation angle θ
, a rectangular wave W1 shown by a broken line in FIG. 2(b) is obtained corresponding to the polarity change of . This rectangular wave W1 has a polarization plane rotation angle θ
The time point at which it intersects the straight line indicating F-0 is t. + j2.

However, the leakage magnetic field due to the defect is caused by the magneto-optic effect element 1a.
When the alternating current bias magnetic field Hp is amplitude-modulated by the leakage magnetic field, it becomes an amplitude-modulated alternating current magnetic field HL as shown by the solid line in Fig. 2 ta+, and the polarization plane rotation angle is changed by the alternating current magnetic field Ht. Corresponding to the polarity change of θ, a rectangular wave W2 shown by a solid line in FIG. 2 (bl) is obtained.

The moment when this rectangular wave W2 intersects the straight line indicating the polarization plane rotation angle θV-0. J, j21, which is more advanced than the rectangular wave W1 when no leakage magnetic flux is acting. The period of the rectangular wave W1, that is, the time width T1 is equal to the period of the rectangular wave W2.
The period is longer than the time width T2.

The rectangular wave W or W2 obtained in this way is shaped by a waveform shaper 10 to correct the distorted portion, and is then shaped into a phase difference measuring device 1.
Give to 1.

On the other hand, a current similar to the excitation current applied to the AC bias excitation coil 1b is applied from the magnetization power supply 12 to the phase shifter 13.

Thereby, the phase shifter 13 generates a rectangular wave similar to the rectangular wave W that is shifted from the 0 phase of the AC bias current, that is, the AC bias magnetic field Hp, and rises at a phase t0 and falls at a phase t2. It is given to the measuring device 11. Thereby, the phase difference measuring device 11 detects the phase t0 or t of the rectangular wave W or W2 given from the waveform shaper 10. ' and the phase t0 of a rectangular wave similar to the rectangular wave W1 given from the phase shifter 13, 1o-1o or t. -to' (or square wave W,
The phase difference t2-t2') between the phase t2 of the rectangular wave similar to that and the phase t2' of the rectangular wave w2 is measured as the phase difference T.

By the way, the leakage magnetic field of the material M to be tested is the defect M8 of the material M to be tested.
The defect Ma is detected by the phase difference T measured by the phase difference measuring device 11.

In this way, when a leakage magnetic field acts on a magneto-optic effect element, the rotation angle θ of the plane of polarization changes regardless of its magnitude, so defects can be detected with high sensitivity, and defects can also be detected quantitatively from the phase difference. It will be possible.

Now, if an alternating current bias magnetic field H,, having an amplitude sufficiently larger than the coercive force Hc of the magneto-optic effect element 1a is applied to the magneto-optic effect element 1a, and the amplitude modulation due to the leakage magnetic flux is ΔH, then cm〈〈1...・(2) Therefore, ・(3) becomes.

Here, ΔH<<H, so FIG. 4 is a block diagram of a flaw detection apparatus according to a third invention configured to detect defects in a material to be tested based on the first invention.

The outputs of the waveform shaper 10 and the phase shifter 13 are respectively applied to a time width difference measuring device 111, and the other components are similar to the structure of the flaw detection apparatus shown in FIG.

This time width difference measuring device 111 measures the time width T1 or T which is the period of the rectangular wave W or W2 given from the waveform shaper 10.
2 and the time width T1, which is the period of a rectangular wave similar to the rectangular wave W given from the phase shifter 13, is measured.

Therefore, this flaw detection device has a time width T of a rectangular wave similar to the rectangular wave W corresponding to the AC bias magnetic field Hp applied from the phase shifter 13, and an AC amplitude modulated by the leakage magnetic field applied from the waveform shaper 10. The time width difference between the time width TI or Tt of the rectangular wave W1 or W2 corresponding to the magnetic field is measured.

Then, the defect M8 is detected from this time width difference.

Next, the principle of the flaw detection method, which is the fourth invention, is explained in Figures 1 and 5.
This will be explained using figures. FIG. 5 is an explanatory diagram showing the relationship between an alternating current bias magnetic field and its magnetizing current. An AC bias magnetic field having the same phase as the AC magnetic field applied to the material M to be tested is applied to the magneto-optic effect element 1a.

Then, in order to apply an AC bias magnetic field H having a larger amplitude than its coercive force Hc to the magneto-optic effect element 1a, a sinusoidal magnetizing current (2) shown in FIG. 5 (bl) is applied to the AC bias excitation coil 1b. When no leakage magnetic field is generated due to the defect M8 in M, a sinusoidal AC bias magnetic field H is shown by the broken line in FIG. 5+al.

is obtained. And the coercive force +H of the magneto-optic effect element 1a
The magnetizing current to obtain an AC bias magnetic field Hp equal to C (or -Hc) is ■. (or T2).

On the other hand, if a leakage magnetic field is generated due to defect M3,
The AC bias magnetic field Hp is amplitude modulated by the leakage magnetic field, and the AC magnetic field Ht changes in a sinusoidal manner as shown by the solid line in FIG. 1c), the magnetizing current I, ie, the instantaneous value, becomes I0' (or Id).

Therefore, when a leakage magnetic field occurs, coercive force + HC (
The AC magnetic field Hp whose amplitude is modulated by the leakage magnetic field at the time when it exceeds the leakage magnetic field (or -Hc) is the sum of the instantaneous value H6 of the AC bias magnetic field and the leakage magnetic field component ΔH (or ΔH'), and the magnetizing current I at that point is ■. ' (or 12').

Therefore, by measuring the magnetizing current I, that is, the instantaneous value at the time when the alternating magnetic field HL exceeds the coercive force Hc, the defect M in the material M to be tested can be detected. Also magnetizing current■
Defect M3 can be quantitatively determined based on .

FIG. 6 is a block diagram of a flaw detection apparatus according to a fifth invention configured to detect defects in a material to be tested based on the fourth invention.

The detection head 1, the photodetector 5, the waveform shaper 10, and the magnetization power source 12 are constructed in the same manner as the flaw detection apparatus shown in FIG. The output of the differentiating circuit 14 and the output of the magnetizing power supply 12 are given to a magnetizing current measuring device 15. The output of the magnetizing current measuring device 15 is given to a computing unit 16.

Next, the flaw detection operation of this flaw detection apparatus will be explained with reference to FIG.

A magnetic field is applied to the material M to be tested by a material magnetizer 2 (see FIG. 1). Further, an AC bias magnetic field H9 having an amplitude larger than the coercive force Hc of the magneto-optic effect element 1 having square magnetic characteristics is applied.

Now, if no leakage magnetic field is generated due to defects in the material M to be tested, the AC bias magnetic field Hp becomes coercive force + Hc (
The magnetizing current I, that is, the instantaneous value at the time when the magnetizing current I (or -HC) exceeds 1° (or I2) is determined as 1° (or I2) as shown in FIG.
be memorized in advance.

Now, the rectangular wave obtained from the photodetector 5 is shaped by the waveform shaper 10 in accordance with the polarity change of the rotation angle of the polarization plane in order to remove the distorted portion. The rectangular wave is given to a differentiating circuit 14 for differentiation. The differentiating circuit 14 outputs a positive trigger pulse when the rectangular wave rises, and outputs a negative trigger pulse when the rectangular wave falls. These positive and negative trigger pulses are given to the magnetizing current measuring device 15 as timing signals when the AC bias magnetic field H0 exceeds the coercive force Hc. Then, the magnetizing current measuring device 15
measures the current applied from the magnetization power source corresponding to the excitation current of the AC bias excitation coil 1b at the timing of the applied trigger pulse, and provides the measured value to the computing unit 16. The arithmetic unit 16 generates a magnetizing current (■) corresponding to the coercive force Hc stored in advance. , lx and the measured magnetizing current I. Then, the defect Ma is detected based on the obtained current difference.

A leakage magnetic field is generated due to the defect M, and the magnetizing current ■ at the time when the amplitude-modulated AC magnetic field HL exceeds the coercive force +Hc is as shown in Fig. 5 (bl).
■It will be 2r.

If the AC bias magnetic field when no leakage magnetic field is generated is H4, and the AC bias magnetic field when a leakage magnetic field is generated is H4', then when the coil shape is circular, ! However, since n: the number of turns of the coil Il: the length of the magnetic path, the leakage magnetic field ΔH2ΔH' is as shown in FIG. 5 fbl. Therefore, the coercive force Hc of the magneto-optic effect element 1a is stored in advance in the arithmetic unit 16, and the above-mentioned (8) and (9)
If the formula is calculated by the calculator 16, the leakage magnetic field ΔI-1ΔH
' can be determined, and defects can be detected from the leakage magnetic field components ΔH and ΔH'.

When a leakage magnetic field occurs due to a defect in this way, the instantaneous value of the magnetizing current, which is the magnetizing current at the point when the amplitude-modulated alternating magnetic field exceeds the coercive force, becomes less than the magnetizing current corresponding to the coercive force. Defects are detected with high precision based on the magnetizing current, and also quantitatively detected according to the magnetizing current.

In this embodiment, an alternating current magnetic field is applied to the material M to be tested, but similar defects can be detected even if a direct current magnetic field is applied.

〔Effect of the invention〕

As detailed above, the first invention applies an AC bias magnetic field with an amplitude larger than the coercive force of the magneto-optic effect element to the magneto-optic effect element, and based on the phase or time width of the rectangular wave related to the AC bias magnetic field, The second invention is based on the phase difference between the rectangular wave related to the AC bias magnetic field and the rectangular wave corresponding to the rotation angle of the polarization plane. The fourth invention is based on the time width difference with the time width of the rectangular wave corresponding to the rotation angle, the fourth invention is based on the magnetizing current at the time when the AC bias magnetic field exceeds the coercive force of the magneto-optic effect element, and the fifth invention is Based on the difference between the magnetizing current when the bias magnetic field exceeds the coercive force of the magneto-optic effect element and the magnetizing current used to obtain an alternating magnetic field corresponding to the coercive force, defects in the material being tested can be detected with high precision. Can be detected quantitatively.

Therefore, each of the inventions has an excellent effect of significantly improving the accuracy and reliability of quality inspection of materials to be tested such as steel materials.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the flaw detection state by the flaw detection method according to the first invention, FIG. 2 is an explanatory diagram showing the relationship between the rectangular magnetic characteristics of the magneto-optic effect element, the AC bias magnetic field, and the rotation angle of the plane of polarization.
Figure 4 is a block diagram of a deep flaw detection apparatus according to the second invention, Figure 4 is a block diagram of a flaw detection apparatus according to the third invention, and Figure 5 is an AC bias magnetic field and magnetization for explaining the flaw detection method according to the fourth invention. An explanatory diagram showing the relationship between currents, FIG. 6 is a block diagram of the flaw detection device according to the fifth invention, FIG. 7 is a schematic diagram of the flaw detection state by the conventional flaw detection device, and FIG. 8 is a square magnetic field diagram of the magneto-optic effect element. FIG. 3 is a characteristic diagram showing characteristics.

Claims (1)

[Claims] 1. A flaw detection method for detecting defects in a material to be tested using a magneto-optic effect element, comprising: applying an alternating magnetic field having an amplitude larger than a coercive force of the magneto-optic effect element; A flaw detection method characterized by detecting defects from the phase or time width of a rectangular wave corresponding to the polarity change of the rotation angle of the polarization plane. 2. In a flaw detection apparatus that detects defects in a material to be tested using a magneto-optic effect element, a magnetizer that applies an alternating magnetic field to the magneto-optic effect element with an amplitude larger than its coercive force and is synchronized with the alternating magnetic field. A flaw detection apparatus comprising a phase difference measuring circuit that measures a phase difference between a rectangular wave and a rectangular wave corresponding to a polarity change of a polarizer rotation angle of the magneto-optic effect element. 3. In a flaw detection apparatus that detects defects in a material to be tested using a magneto-optic effect element, the magnetizer provides an alternating magnetic field with an amplitude larger than the coercive force of the magneto-optic effect element, and is synchronized with the alternating magnetic field. A flaw detection apparatus comprising a time width difference measuring circuit that measures a difference between a time width of a rectangular wave and a time width of a rectangular wave corresponding to a polarity change of a polarizer rotation angle of the magneto-optic effect element. 4. In a flaw detection method for detecting defects in a material to be tested using a magneto-optic effect element, an alternating current magnetic field having an amplitude larger than a coercive force of the magneto-optic effect element is applied to the magneto-optic effect element, and the alternating current magnetic field Find the magnetizing current at the point when it exceeds the magnetic force,
A flaw detection method characterized by detecting defects from the magnetizing current. 5. In a flaw detection device that detects defects in a material to be tested using a magneto-optic effect element, a magnetizer that applies an alternating magnetic field with an amplitude larger than the coercive force of the magneto-optic effect element to the magneto-optic effect element; A flaw detection apparatus comprising: a magnetizing current measuring circuit that measures a magnetizing current output by the magnetizer at a time when the magnetizing current exceeds the coercive force of an effect element.