JP7080737B2 - Ultrasonic flaw detection method - Google Patents

Description

The present invention relates to an ultrasonic flaw detection method that is used in an ultrasonic flaw detector to detect defects in an inspected object by ultrasonic waves.

Conventionally, an ultrasonic flaw detector has been used for non-destructive inspection of defects such as scratches, cracks, joint defects and inclusions in an object to be inspected. Especially in the steel industry, ultrasonic flaw detectors are used for quality control on production lines. This ultrasonic flaw detector is an ultrasonic flaw detector that transmits a first ultrasonic wave to the object to be inspected and receives a second ultrasonic wave coming from the object to be inspected based on the transmitted first ultrasonic wave. (Probe for ultrasonic flaw detection) is provided, and the presence or absence of the defect, its position, its size (size), and the like are detected by analyzing the received second ultrasonic wave.

For example, Non-Patent Document 1 discloses a specific method, and discloses that an intervening portion in steel of 20 μm or more can be detected by ultrasonic flaw detection at a high frequency of 50 to 125 MHz.

Yoshiyuki Kato et al., "Development of Evaluation Technique for Inclusions in Steel by High Frequency Ultrasonic Fracture Detection", Sanyo Technical Report Vol. 7 (2000) No. 1

By the way, in such ultrasonic flaw detection, it is usually necessary to prepare in advance such as heat-treating the object to be inspected in advance and polishing the surface flat. Appropriate heat treatment in this advance preparation makes it possible to arrange the crystal grains in an appropriate state and reduce tissue noise. As described above, it takes time and effort to prepare in advance such as heat treatment and surface polishing, it is difficult to continuously and automatically inspect the inspected object, and it is also difficult to inspect many inspected objects.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ultrasonic flaw detection method capable of reducing the labor and time of advance preparation.

As a result of various studies, the present inventor has found that the above object can be achieved by the following invention. That is, the ultrasonic flaw detection method according to one aspect of the present invention is an ultrasonic flaw detector such that ultrasonic flaw detection is performed from the side surface of the short side of the object to be inspected in a state where the cross section is processed to be flatter than before processing. The step A for setting and the step B for performing ultrasonic flaw detection by injecting ultrasonic waves from the side surface of the short side in the state set in the step A are provided, and the crystal grains of the object to be inspected are flat. Therefore, it is oriented along the long side direction of the object to be inspected. Preferably, in the above-mentioned ultrasonic flaw detection method, the object to be inspected is made flatter in cross section than before processing by a cold rolling method using a roller or a die drawing method using a drawing die having a rectangular cross section. A step of processing the inspected object is further provided.

In the ultrasonic flaw detection method, ultrasonic waves are usually reflected not only by defects but also by grain boundaries. The reflected ultrasonic waves due to the grain boundaries become so-called tissue noise or forest noise with respect to the reflected ultrasonic waves due to defects. In the ultrasonic flaw detection method, the object to be inspected is processed to be flatter in cross section than before processing. Therefore, it is considered that the crystal grains in the inspected object are also flattened, and the crystal grains in the inspected object are oriented along the long side direction. In particular, in cold rolling using a roller or a die drawing method using a drawing die having a rectangular cross section, the crystal grains have a characteristic of being oriented in the long axis method (long side direction). Therefore, it is considered that the noise is reduced when the ultrasonic wave is incident from the side surface of the short side of the flat object to be inspected as compared with the case where the ultrasonic wave is incident from the side surface of the long side thereof. In the ultrasonic flaw detection method, since ultrasonic waves are incident from the side surface of the short side, the noise can be reduced, and ultrasonic flaw detection can be performed without performing the above-mentioned heat treatment, surface polishing, or other preliminary preparations. Therefore, the ultrasonic flaw detection method does not require advance preparation, and the labor and time of the advance preparation can be reduced. As a result, the ultrasonic flaw detection method can continuously and automatically inspect the inspected object on the production line, and can inspect more inspected objects.

In another aspect, in the above-mentioned ultrasonic flaw detection method, the ratio of the length of the long side to the length of the short side in the cross section of the object to be inspected is 2 or more (length of long side / short side). Length ≧ 2), further includes a C step of processing the object to be inspected. Preferably, in the ultrasonic flaw detection method described above, in the step C, the ratio of the length of the long side to the length of the short side in the cross section of the object to be inspected is 2.3 or more (the length of the long side). The length of the side / short side ≧ 2.3), the object to be inspected is processed.

In such an ultrasonic flaw detection method, since the ratio of the length of the long side to the length of the short side in the cross section of the object to be inspected is 2 or more, the crystal grains can be oriented with a sufficiently flat structure, and the noise can be detected. Can be reduced.

In another aspect, in the above-mentioned ultrasonic flaw detection method, the step A sets the ultrasonic flaw detector by a high-frequency vertical method.

As described above, it is considered that the flat crystal grains are oriented along the long side direction. Since the above ultrasonic flaw detection method uses a high-frequency vertical flaw detection method (vertical flaw detection method), it is possible to focus ultrasonic waves in the object to be inspected with high accuracy by incident from an appropriate distance using an appropriate acoustic lens. It is possible to obtain reflected ultrasonic waves from defects in the object to be inspected.

In another aspect, in the above-mentioned ultrasonic flaw detection method, the length of the short side is three times or more the wavelength of the ultrasonic wave in the object to be inspected in the short side direction along the short side. The flat surface is further provided with a D step of processing the side surface of the short side.

Such an ultrasonic flaw detection method has a plane with a length of three times or more the wavelength of the ultrasonic wave in the object to be inspected in the short side direction along the short side, so that the high frequency vertical method can be more easily performed. realizable.

The ultrasonic flaw detection method according to the present invention can reduce the labor and time of advance preparation.

It is a figure which shows the schematic structure of the die wire drawing apparatus which uses the ultrasonic flaw detection method in an embodiment. It is a figure for demonstrating the cross section of the steel wire after the 1st to 7th passes in the die wire drawing apparatus. It is a figure for demonstrating the ultrasonic flaw detection method in this embodiment. As an example, it is a figure for demonstrating the sample after flattening a steel wire and the flaw detection result thereof. As an example, it is a figure for demonstrating a sample in a steel wire of a circular cross section before flattening, and the flaw detection result thereof. It is a figure for demonstrating the action effect of the ultrasonic flaw detection method in an embodiment. It is a figure which shows the result of the ultrasonic flaw detection of one Example for a sample containing a defect. It is a figure for demonstrating a modified form.

Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. It should be noted that the configurations with the same reference numerals in the respective drawings indicate the same configurations, and the description thereof will be omitted as appropriate. In the present specification, when they are generically referred to, they are indicated by reference numerals without subscripts, and when they refer to individual configurations, they are indicated by reference numerals with subscripts.

FIG. 1 is a diagram showing a schematic configuration of a die wire drawing device using the ultrasonic flaw detection method in the embodiment. FIG. 2 is a diagram for explaining a cross section of a steel wire after the first to seventh passes in the die wire drawing device. 2A to 2G are micrographs of cross sections of the steel wire after polishing, FIG. 2A shows after the first pass (after drawing with the first drawing die # 1), and FIG. 2B. Shows after the second pass (after drawing with the second drawing die # 2), FIG. 2C shows after the third pass (after drawing with the third drawing die # 3), and FIG. 2D shows. Shows after the 4th pass (after drawing with the 4th drawing die # 4), and FIG. 2E shows after the 5th pass (after drawing with the 5th drawing die # 5), FIG. 2F. Shows after the 6th pass (after drawing with the 6th drawing die # 6), and FIG. 2G shows after the 7th pass (after drawing with the 7th drawing die # 7). FIG. 3 is a diagram for explaining the ultrasonic flaw detection method in the present embodiment.

The ultrasonic flaw detection method in the present embodiment is, for example, a cold rolling method using a roller or a die wire drawing method using a drawing die having a rectangular cross section, in a state where the cross section is processed to be flatter than before processing. This is a method of inspecting a linear inspected object WK on a production line using an ultrasonic flaw detector. Here, the case where the steel wire is drawn flat by the die drawing method will be described, but the case where the steel wire is rolled flat by the cold rolling method can also be described in the same manner. Further, the object to be inspected is not limited to the steel wire, but may be another metal (including an alloy).

The wire drawing processing device S by the die wire drawing method includes a plurality of wire drawing dies DS (DS-1 to DS-7) and a plurality of pairs of drive rollers RL (RL-1 to RL-7).

The plurality of wire drawing dice DS are arranged on the flat surface of the base BS at predetermined intervals. In the present embodiment, in order to process a steel wire WK having a circular cross section into a steel wire WK having a flat cross section by drawing with seven passes, a plurality of wire drawing dies DS are seven first to first. The seventh wire drawing die DS-1 (# 1) to DS-7 (# 7) is provided. These 1st to 7th wire drawing dice DS-1 (# 1) to DS-7 (# 7) are arranged on the base BS in this order with a predetermined interval, respectively, and Table 1 As shown in, gradually (gradually in the order of the path) from the upstream side to the downstream side, the opening cross section of the die changes from a circular shape to a flat shape, and the size (cross-sectional area) becomes smaller. It is formed. The specifications of the first to seventh wire drawing dice DS-1 (# 1) to DS-7 (# 7) are as shown in Table 1 as an example.

Each of the plurality of pairs of drive rollers RL is a device that includes a pair of rollers, holds the steel wire WK between the pair of rollers, and draws the steel wire WK by rotating the pair of rollers. In the present embodiment, the number of the plurality of pairs of drive roller RLs is the number corresponding to the plurality of wire drawing die DSs, and is arranged in the subsequent stage of each of the plurality of wire drawing die DSs. In the example shown in FIG. 1, the plurality of pairs of drive rollers RL include seven pairs of first to seventh drive rollers RL-1 to RL-7. Each of the first to seventh drive rollers RL-1 to RL-7 is arranged in the rear stage (each downstream side) of each of the first to seventh wire drawing dice DS-1 to DS-7. The number of wire drawing dice DS is not limited to 7, and may be arbitrary, and the number of a pair of drive roller RLs is not limited to 7, and may be arbitrary. The number of pairs of drive rollers RL may be the same as or different from the number of wire drawing dice DS.

In FIG. 1, the second to sixth wire drawing dice DS-2 (# 2) to DS-6 (# 6) and a pair of second to sixth drive rollers RL-2 to RL-6 are shown. Is omitted.

In the wire drawing machine S having such a configuration, the steel wire WK is unwound from a winding reel (not shown) around which the steel wire WK to be machined is wound, and the first wire drawing die DS-1 (#). It is inserted through 1) and inserted into the second wire drawing die DS-2 (# 2) of the next pass (next stage) via the pair of first drive rollers RL-1, and the pair of second drive rollers. It is inserted into the third wire drawing die DS-3 (# 3) of the next pass (next stage) via RL-1. After that, similarly, the die DS for wire drawing in the next stage is sequentially inserted through the pair of drive rollers RL in the previous stage, and finally, after processing through the pair of seventh drive rollers RL-7. The steel wire WK is pulled out. As shown in FIGS. 2A to 2G, for example, the steel wire WK is used for each wire drawing every time it passes through the first to seventh wire drawing dies DS-1 (# 1) to DS-7 (# 7). The dies DS-1 (# 1) to DS-7 (# 7) are processed so that the cross section changes from a circular shape to a flat shape and the size (cross-sectional area) is reduced. Then, the processed steel wire WK is wound on a take-up reel (not shown).

Then, in the present embodiment, after such processing, processing is performed by a commonly used ultrasonic flaw detector at a predetermined position PS between the final die DS-7 (# 7) and the drive roller RL-7. The later steel wire WK is ultrasonically detected. The material to be inspected (steel wire WK in this embodiment) that is generally die-drawn is vibrating or rotating to some extent. In ultrasonic flaw detection, it is not desirable that the relative position of the material to be inspected and the ultrasonic flaw detector PB change, and vibration or rotation of the material to be inspected causes the relative position to change. A large tension acts on the steel wire WK of the material to be inspected between the final die DS-7 and the drive roller RL-7, which causes the least vibration in this process and is the optimum location for ultrasonic flaw detection. ..

More specifically, in the present embodiment, as shown in FIG. 3, first, the short side of the inspected object WK (steel wire WK in the present embodiment) in a state where the cross section is processed to be flatter than before processing. A high-frequency ultrasonic flaw detector Pb is set at an appropriate distance from the surface of the steel wire WK of the inspected object in a vertical flaw detection method arrangement so as to perform ultrasonic flaw detection from the side surface SS.

In one example, the high frequency ultrasonic probe PB is inspected so that its axis is always perpendicular to the side surface SS of the short side of the line WK of the inspected material and at a constant distance from its surface. It is held by a copying mechanism that automatically follows the steel wire WK of the material. More specifically, the dynamic friction of Teflon (registered trademark) or the like that is pressed against the side surface SS of the short side of the steel wire WK of the inspected material by a spring mechanism and is always in sliding contact with the steel wire WK of the inspected material. A contact member with a sliding surface made of a material with a small coefficient, and an automatic copying mechanism that keeps a constant distance while maintaining a constant distance while following the same contact member as the contact member and keeping it perpendicular to the steel wire WK of the material to be inspected. The ultrasonic probe Pb is held.

The ultrasonic flaw detector (ultrasonic flaw detector probe) Pb is connected to the ultrasonic flaw detector body (not shown) via a cable, and ultrasonic waves are input to and from the WK to be inspected via the contact catalyst WC. The contact catalyst WC, which is attached to the tip of the ultrasonic flaw detector main body 11 and the ultrasonic flaw detector main body 11, is formed in a columnar shape between the ultrasonic flaw detector main body 11 and the object WK to be inspected. It is provided with a substantially cylindrical nozzle 12. The contact catalyst WC may be appropriately selected, and in this embodiment, for example, water. The ultrasonic flaw detector main body is connected to the ultrasonic flaw detector Pb via the cable, and the ultrasonic flaw detector Pb is transmitted to the ultrasonic flaw detector Pb via the cable to transmit an electric signal. The tentacle Pb is made to transmit the first ultrasonic signal (transmitted ultrasonic signal) to the inspected object WK, and the second ultrasonic signal coming from the inspected object WK received by the ultrasonic flaw detector Pb. It is a device that images a defect of an inspected object WK as an ultrasonic image based on a received signal of an electric signal generated by an ultrasonic flaw detector Pb according to (received ultrasonic signal).

The high-frequency vertical method (vertical flaw detection method) is a method in which ultrasonic waves are incident perpendicularly to the flaw detection surface (side surface SS of the short side in the present embodiment) of the object to be inspected WK.

Then, in the set state in which the ultrasonic flaw detector Pb is set, ultrasonic flaw detection is executed while flowing water of the contact catalyst WC using the nozzle 12. The result of ultrasonic flaw detection by such an ultrasonic flaw detection method is shown in FIG. 4 as an example.

FIG. 4 is a diagram for explaining a sample after flattening a steel wire and a flaw detection result thereof, as an example. FIG. 4A shows the result of ultrasonic flaw detection from the side surface of the long side of the first steel wire WK-1 having a flat cross section, and FIG. 4B shows the result of ultrasonic flaw detection from the side surface of the short side of the first steel wire WK-1 having a flat cross section. The results are shown, FIG. 4C is a diagram for explaining the first sample SP-1 cut out from the first steel wire WK-1, and FIG. 4D is a diagram for explaining the first sample SP-1 for ultrasonic flaw detection. It is a figure for demonstrating the incident direction (the flaw detection direction) of the ultrasonic wave incident on -1. FIG. 5 is a diagram for explaining a sample and a flaw detection result thereof in a steel wire having a circular cross section before flattening, as an example. FIG. 5A shows the result of ultrasonic flaw detection from one of two surfaces orthogonal to each other in the second steel wire WK-2 having a circular cross section before being processed into the first steel wire WK-1 having a flat cross section. 5B shows the result of ultrasonic flaw detection from the other side of the two surfaces, and FIG. 5C is a diagram for explaining the second sample SP-2 cut out from the second steel wire WK-2. FIG. 5D is a diagram for explaining the incident direction (damage detection direction) of the ultrasonic wave incident on the second sample SP-2 for ultrasonic wave detection. FIG. 6 is a diagram for explaining the action and effect of the ultrasonic flaw detection method in the embodiment. FIG. 6A shows a case where ultrasonic flaw detection is performed by a high-frequency vertical method (vertical flaw detection method) from the side surface of a short side of a flat subject to be inspected as in the present embodiment, and FIG. 6B shows a case where the flat subject is to be inspected for comparison. The case where ultrasonic flaw detection is performed by the high frequency vertical method (vertical flaw detection method) from the side surface of the long side of an object is shown. FIG. 7 is a diagram showing the results of ultrasonic flaw detection of one example for a sample containing defects. FIG. 7A shows the result of ultrasonic flaw detection in the range of 1 mm × 1 mm, and FIG. 7B shows the signal waveform of the received signal at the place where the defect exists. The horizontal axis of FIG. 7B is the distance (depth) from the incident surface, and the vertical axis thereof is the signal level (reception intensity) of the received signal.

In order to explain the change due to flattening, first, a test was carried out on a steel wire WK having a circular cross section before flattening. As an example, as shown in FIG. 5C, a rectangular parallelepiped second sample SP-2 having a diameter of 2.5 mm × 2.5 mm is cut out from a second steel wire WK-2 having a circular cross section with a diameter of φ5.5 mm before flattening. , Each surface is polished to eliminate the influence of surface irregularities. Then, as shown in FIG. 5D, with respect to the second sample SP-2, one first B side surface SF-1B is set as an XY plane, and the other second B side surface SF-1B orthogonal to the first B side surface SF-1B-. When an XYZ Cartesian coordinate system with 2B as the ZX plane is set, ultrasonic flaw detection is performed from the Z direction DR1 on the first B side surface SF-1B of the second sample SP-2 by the vertical flaw detection method, and the result is shown in the figure. Shown in 5A, and on the second B side surface SF-2B of the second sample SP-2, ultrasonic flaw detection was performed from the Y direction DR2 by the vertical flaw detection method, and the result is shown in FIG. 5B. In FIGS. 4A and 4B and FIGS. 5A and 5B, the sensitivity of the ultrasonic flaw detection is adjusted so that the echo level (reflected wave intensity) from the flat bottom hole having a diameter of 50 μm, which is a reference artificial defect, is 80%. Signals with signal levels below 20% in the device are cut and not displayed. As can be seen by comparing the results of the ultrasonic flaw detection shown in FIGS. 5A and 5B with each other, these results are not so different and are substantially equivalent, and therefore, the crystal grains of the second steel wire WK-2 are not so different. Therefore, the so-called tissue noise is almost the same regardless of which direction in the circumferential direction the ultrasonic flaw detection is performed by the vertical flaw detection method.

Next, a test was carried out on a steel wire having a flat cross section obtained by processing such a steel wire having a circular cross section into a flat shape. In this test, first, the ratio of the length of the long side to the length of the short side in the cross section of the steel wire WK as the object to be inspected is 2 or more (length of long side / length of short side ≧). 2) In one example, the steel wire WK is processed so that the ratio is 2.3 or more (long side length / short side length ≧ 2.3), and the long side is about 6 mm, which is short. A first steel wire WK-1 having a flat cross section with a side of about 2.6 mm was created (6 / 2.6 = about 2.3). As shown in FIG. 4C, a first sample SP-1 having a rectangular parallelepiped of 2.5 mm × 3.0 mm was cut out from the first steel wire WK-1, and each surface was polished to eliminate the influence of surface irregularities. ing. Then, as shown in FIG. 4D, with respect to the first sample SP-1, the first A side surface SF-1A, which was the side surface of the long side before being cut into a rectangular parallelepiped, is set as the XY plane and the side surface of the short side. When an XYZ Cartesian coordinate system with the second A side surface SF-2A as the ZX plane is set, ultrasonic flaw detection is performed on the first A side surface of the first sample SP-1 from the Z direction DR1 by a vertical flaw detection method. The results are shown in FIG. 4A, and ultrasonic flaw detection was performed on the second A side surface SF-2A of the first sample SP-1 from the Y direction DR2 by the vertical flaw detection method, and the results are shown in FIG. 4B. .. As can be seen from FIG. 4A, when ultrasonic flaw detection is performed from the side surface of the long side (corresponding to the side surface SF-1A of the first A) by the vertical flaw detection method with respect to the first steel wire WK-1 having a flat cross section, so-called tissue noise is high. As can be seen from FIG. 4B, when ultrasonic flaw detection is performed from the side surface of the short side (corresponding to the second A side surface SF-2A) with respect to the first steel wire WK-1 having a flat cross section, such tissue noise is observed. Has been reduced. Comparing the results of ultrasonic flaw detection shown in FIG. 4B with the results of ultrasonic flaw detection shown in FIGS. 5A and 5B, the tissue noise in the result of ultrasonic flaw detection shown in FIG. 4B is shown in FIGS. 5A and 5B. It is reduced to less than 1/2 of the tissue noise in each result of the ultrasonic flaw detection shown.

Explaining with a schematic diagram, when a steel wire WK having a circular cross section is processed flat, the crystal grain CG in the steel wire WK is deformed flat as shown schematically in FIGS. 6A and 6B, and the grain CG is formed. It is considered that the flat shapes are aligned and oriented so that the side surface of the long side (the side surface of the long side of the crystal grain) is parallel to the side surface of the long side (the side surface of the long side of the steel wire) in the steel wire WK. In particular, in cold rolling using a roller or a die drawing method using a drawing die having a rectangular cross section, the crystal grain CG has a characteristic of being oriented in the long axis method (long side direction). As a result, as shown in FIG. 6B, when the crystal grain CG is viewed from the side surface of the long side of the steel wire WK, the size (cross-sectional area of the surface having the incident direction of the ultrasonic wave as the normal) seems to be relatively large. As shown in FIG. 6A, when the crystal grain CG is viewed from the side surface of the short side of the steel wire WK, the size seems to be relatively small. Therefore, as shown in FIG. 4 above, ultrasonic flaw detection from the side surface of the long side of the steel wire WK increases so-called tissue noise, while ultrasonic flaw detection from the side surface of the short side of the steel wire WK results in such flaws. Tissue noise can be reduced. In particular, in the example shown in FIG. 4, since the ratio of the length of the long side to the length of the short side in the cross section of the steel wire WK as the object to be inspected is 2 or more, the crystal grains can be oriented with a sufficiently flat structure. , The tissue noise can be reduced.

Therefore, as shown in FIG. 6, when an inclusion Ob is present in the steel wire WK, ultrasonic flaw detection by the ultrasonic flaw detector Pb from the side surface of the long side of the steel wire WK by the ultrasonic flaw detector method is so-called. Since the structure noise is high, it is difficult to detect the inclusions Ob, but when ultrasonic flaw detection is performed by the ultrasonic flaw detector Pb from the side surface of the short side of the steel wire WK by the vertical flaw detector method, so-called tissue noise can be reduced. The inclusion Ob becomes easy to detect.

The results of ultrasonic flaw detection by the vertical flaw detector method with the ultrasonic flaw detector Pb from the side surface of the short side of the sample of one example are shown in FIG. 7, and FIG. 7A shows an image of inclusions Ob. Can be seen well. When this sample was polished and observed under a microscope, the presence of inclusions Ob was confirmed at the position of the image of inclusions Ob shown in FIG. 7A. As an example of creating the image of FIG. 7A, FIG. 7B shows a received signal at a position where an inclusion Ob is detected during scanning of the ultrasonic flaw detector Pb, and is shown in FIG. 7B. The peak CHf on the left side of the paper surface is a signal due to ultrasonic waves reflected on the incident surface of ultrasonic waves, and the peak CHb on the right side of the paper surface in FIG. 7B is a signal due to ultrasonic waves reflected on the back surface facing the incident surface. , The peak CHs in the meantime are ultrasonic signals reflected by the inclusions Ob.

In another embodiment, while continuously drawing a steel wire WK having a diameter of φ5.5 mm at 30 m / min, an echo from a 50 μm flat bottom hole is generated using a point-focused 75 MHz ultrasonic flaw detector. Continuous flaw detection was performed with a sensitivity of 80%. The repetition frequency in this case is 10 kHz, and high-speed flaw detection of about 3.0 kg per hour is possible when calculated from the flaw detection region per pulse calculated from the half-value width of the point-focused ultrasonic flaw detector. It became.

As described above, in the ultrasonic flaw detection method, ultrasonic waves are usually reflected not only by defects but also by grain boundaries. The reflected ultrasonic waves due to the grain boundaries become so-called tissue noise or forest noise with respect to the reflected ultrasonic waves due to defects. In the ultrasonic flaw detection method of the embodiment, the inspected object WK is processed to be flatter in cross section than before processing. Therefore, it is considered that the crystal grain CG in the inspected object WK is also flattened, and the crystal grain CG in the inspected object WK is oriented along the long side direction. Therefore, it is considered that the noise is reduced when the ultrasonic wave is incident from the side surface of the short side of the flat object WK to be inspected, as compared with the case where the ultrasonic wave is incident from the side surface of the long side thereof. In the ultrasonic flaw detection method, since ultrasonic waves are incident from the side surface of the short side, the noise can be reduced, and ultrasonic flaw detection can be performed without performing the above-mentioned heat treatment, surface polishing, or other preliminary preparations. Therefore, the ultrasonic flaw detection method does not require advance preparation, and the labor and time of the advance preparation can be reduced. As a result, the ultrasonic flaw detection method can continuously and automatically inspect the inspected object WK on the production line, and can inspect more inspected objects WK.

As described above, it is considered that the flat crystal grains CG are oriented along the long side direction. Since the above ultrasonic flaw detection method uses a high-frequency vertical flaw detection method (vertical flaw detection method), ultrasonic waves can be focused in steel with high accuracy by incident from an appropriate distance using an appropriate acoustic lens. Reflected ultrasonic waves can be obtained from defects in the steel.

In the above-described embodiment, after the flattening process and before the ultrasonic flaw detection, the object becomes flat in the short side direction along the short side at a length of three times or more the wavelength of the ultrasonic wave in the WK to be inspected. As described above, the side surface SS on the short side may be machined.

FIG. 8 is a diagram for explaining a modified form. FIG. 8 is an example showing the sound collecting characteristics of the ultrasonic flaw detector, the horizontal axis thereof is each position with respect to the position of the sound axis 0, and the vertical axis thereof is S / N. .. The ultrasonic flaw detector in FIG. 8 has a maximum frequency of 75 MHz, a main frequency of about 50 MHz, a vibrator diameter of φ3 mm, and a focal position of 12.7 mm. The wavelength in the steel is about 0.1 mm. As shown in FIG. 8, the sound collecting characteristic of the ultrasonic flaw detector has a wavelength in the steel, that is, about three times as wide as the wavelength in the WK to be inspected. Therefore, when the side surface SS of the short side is processed so as to be flat at a length of three times or more the wavelength of the ultrasonic wave in the WK to be inspected, the ultrasonic wave is subjected to the high frequency vertical method (vertical flaw detection method). Almost all ultrasonic waves emitted from the flaw detector can more reliably enter from this flat surface. Therefore, such an ultrasonic flaw detection method can more easily realize a high-frequency vertical method.

In order to express the present invention, the present invention has been appropriately and sufficiently described through the embodiments with reference to the drawings described above, but those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that it is possible. Therefore, unless the modified or improved form implemented by a person skilled in the art is at a level that deviates from the scope of rights of the claims stated in the claims, the modified form or the improved form is the scope of rights of the claims. It is interpreted to be included in.

Pb Ultrasonic flaw detector WK Inspected object SS Short side side surface CG Crystal grain Ob inclusions S Die wire drawing device DS (DS-1 to DS-7) Wire drawing die RL (RL-1 to RL-7) ) Pair of drive roller BS base

Claims (4)

Step A, in which the ultrasonic flaw detector is set so that ultrasonic flaw detection is performed from the side surface of the short side of the object to be inspected, which is processed flatter than before processing in the cross section, and
It is provided with a step B in which ultrasonic waves are incident from the side surface of the short side to execute ultrasonic flaw detection in the state set in the step A.
The crystal grains of the inspected object are flat and oriented along the long side direction in the inspected object.
Ultrasonic flaw detection method. A step C for processing the inspected object is further provided so that the ratio of the length of the long side to the length of the short side in the cross section of the inspected object is 2 or more.
The ultrasonic flaw detection method according to claim 1. In step A, the ultrasonic flaw detector is set by the high-frequency vertical method.
The ultrasonic flaw detection method according to claim 1 or 2. In the short side direction along the short side, the D step of processing the side surface of the short side into a plane having a length of the short side at least three times the wavelength of the ultrasonic wave in the inspected object is performed. Further prepare
The ultrasonic flaw detection method according to any one of claims 1 to 3.

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