JP4835341B2 - Ultrasonic flaw detection method - Google Patents

Description

The present invention relates to an ultrasonic flaw detection method , and more particularly to an ultrasonic flaw detection method suitable for flaw detection of a material whose crystal grain size is relatively small in the surface layer portion and relatively large in the inner quality portion.

  In a billet or the like for rolling, the crystal grain size is generally uniform from the cross-sectional surface layer portion (hereinafter simply referred to as the surface layer portion) to the cross-section internal portion (hereinafter simply referred to as the internal portion), and its diameter is small. Conventionally, ultrasonic flaw detection for such materials uses a probe equipped with a flat-type transmitter / receiver transducer to transmit a substantially parallel ultrasonic beam in the cross section of the material, thereby causing defects such as internal cracks in the material. The ultrasonic waves reflected by the laser beam are received and the presence / absence of a defect is determined from the waveform of the received ultrasonic waves.

  In this case, the transmitter / receiver transducer cannot detect flaws on the material surface layer on the side where the transducer is provided due to the influence of ultrasonic reflection on the surface of the material (dead zone), so it occurs on the material surface layer on the opposite side of the transducer. The reflected wave was received to determine the presence or absence of a defect in the surface layer of the material.

In Patent Document 1, a plurality of transducers are provided on the surface of a material so that the ultrasonic beam axes of these transducers are focused at one point inside the material, and the reflected waves of the ultrasonic waves emitted from one transducer are reflected. There is shown an ultrasonic flaw detection method in which a defect inside a material is detected by sequentially receiving with other vibrators and synthesizing received ultrasonic waves.
JP-A-2005-233874

  By the way, in the billet for rolling, the crystal grain size may gradually increase from the surface layer portion toward the inner quality portion depending on the steel type. For such a material with a rough inner part, the attenuation in the inner part is increased, and therefore it is necessary to use a transmission / reception vibrator having a vibrating surface made spherical and focusing the transmitted ultrasonic wave at one point. .

  However, increasing the transducer size of the transmitter / receiver transducer in order to improve the focusing effect increases the dead zone, and the ultrasonic attenuation at the inner part is large, resulting in the material surface layer on the opposite side of the transducer. It is difficult to receive the reflected wave, and there is a problem that flaws cannot be detected over the entire cross section of the material.

Therefore, the present invention solves such problems, and enables flaw detection in the entire cross section of a material whose crystal grain size is relatively small in the surface layer portion and relatively large in the inner quality portion. An object of the present invention is to provide an ultrasonic flaw detection method .

In order to achieve the above object, the ultrasonic flaw detection method of the present invention is an ultrasonic flaw detection method for flaw detection of a material having a crystal grain size that is relatively small in the surface layer portion and relatively large in the inner quality portion. The ultrasonic beam axis of the transmitting transducer and the ultrasonic beam axis of the receiving transducer intersect each other in the surface layer portion to detect a flaw in the surface layer portion from the waveform of the received ultrasonic wave, and the ultrasonic beam of the transmitting / receiving transducer the ratio in the ultrasonic frequency of the flaw detecting There line, and the transmission and reception transducers of the ultrasonic the transmission oscillator and receiving transducer frequency in the inner quality portion from the waveform of the received ultrasonic wave is focused at the inner membrane portion And make it relatively low.

In the present invention , since the transmission transducer and the reception transducer have the ultrasonic beam axes intersecting each other in the surface layer portion of the material, the ultrasonic wave output from the transmission transducer generates a dead zone due to reflection on the material surface. Without being reflected by the defect in the surface layer portion, it is input to the receiving vibrator. Thereby, the defect which arose in the surface layer part is detected reliably. In addition, the ultrasonic wave output from the transmitter / receiver transducer that focuses the ultrasonic beam in the inner part of the material is reflected by the defect in the inner part without being attenuated by the inner part and is input to the transmitter / receiver again. To do. Thereby, the defect which arose in the internal quality part is detected reliably. Further, in the present invention, the attenuation of the ultrasonic wave at the inner part having a relatively large crystal grain size is minimized.

  In addition, the code | symbol in the said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

As described above, according to the ultrasonic flaw detection method of the present invention, the flaw detection in the entire cross section is good for a material having a relatively small crystal grain size distribution in the surface layer portion and a relatively large distribution in the inner quality portion. Can be done.

   FIG. 1 shows a state in which the probes 1 and 2 are positioned with respect to a billet M for rolling, which is a material. On the upper surface Ma of the billet M having a long rectangular parallelepiped shape having a cross section of 155 to 160 squares. Two kinds of probes 1 and 2 for the inner part and the surface part are disposed adjacent to each other. The inner part probe 1 is composed of a single transmission / reception transducer 11 that outputs ultrasonic waves in the billet depth direction below and receives the reflected waves. On the other hand, the surface layer probe 2 is composed of a transmission transducer 21 and a reception transducer 22 that are formed in a divided manner. The transmission transducer 21 outputs ultrasonic waves in the billet depth direction, and the reception transducer 22 Receive reflected waves. The probes 1 and 2 are moved in the billet longitudinal direction while being reciprocated in the billet width direction as indicated by arrows in the figure, and are scanned over the entire upper surface Ma of the billet M. The probes 1 and 2 are connected to signal processors 31 and 32, respectively. The signal processors 31 and 32 output transmission signals to the probes 1 and 2, and the probes 1 and 2, respectively. The received signal is input, and the presence or absence of a defect such as a crack in the billet M is determined from the signal waveform. Such adjacent arrangement can improve the operability at the time of flaw detection. In addition, the surface layer part on the surface (billet) side where the probe is installed can be directly inspected, and the accuracy of the flaw detection is improved compared to the case where the surface layer part on the opposite surface is inspected by passing ultrasonic waves through the billet. Can be made.

  Here, an example of the crystal grain size distribution in the cross section of the billet M, which is the object to be inspected according to the present invention, is shown by a line X in FIG. Line X shows the grain size distribution of ferritic stainless steel (JIS SUS430). In such a steel type, the crystal grains cannot be refined by heat treatment, so the surface layer portion is only slightly refined by rolling. It is. As is apparent from the figure, the billet M has a crystal grain size that gradually increases from about 0.2 mm to 1.6 mm or more in the depth direction from the surface in the cross section. On the other hand, as shown by the line Y in FIG. 2, in the conventional general billet, the crystal grain size is almost uniform from the surface to the inside in the cross section, and the diameter is also as small as 0.1 mm or less. The line Y indicates the crystal grain size distribution of chromium molybdenum steel (JIS SCM435).

  Here, in the present embodiment, as shown in FIG. 3, the shape of the vibration surface 11 a of the transmitting / receiving transducer 11 of the inner probe 1 is a circular concave spherical surface having a radius of curvature of 200 mm facing downward, and In order to increase the focusing effect, the vibration surface size is increased to 40 mm in diameter. And since the crystal grain size is large in the inner part of the billet M as described above, the frequency of the transmitted ultrasonic wave is set to a relatively low frequency of 1 MHz in order to avoid attenuation of the output ultrasonic wave, and in addition, the wave number of 1.5 to The flaw detection resolution is improved as 2 broadband waves. Thereby, the ultrasonic wave output from the transmission / reception transducer 11 is focused from the upper surface (front surface) Ma of the billet M to a point h (80 mm in this embodiment), and flaw detection of the billet internal part 30 to 140 mm below the surface. It can be performed. Here, the frequency of the transmitted ultrasonic wave is preferably in the range of 0.7 to 2.0 MHz, and the vibration surface size is preferably in the range of 30 to 40 mm in diameter. Moreover, it is preferable to use a composite type vibrator that can transmit and receive high-intensity ultrasonic waves. Table 1 shows the details of the specifications of such an inner part probe 1.

  The vibration surfaces 21a and 22a of the transmitting transducer 21 and the receiving transducer 22 of the surface layer probe 2 are 10 mm and 15 mm rectangles, respectively, and have a radius of curvature of 150 mm in the short side direction as shown in FIG. As shown in FIG. 4 (2), it is a concave surface facing downward with a radius of curvature of 200 mm in the long side direction. 4 (1) and 4 (2) are views of the vibration surfaces 21a and 22a as viewed from the side direction different by 90 degrees. The frequency of the ultrasonic wave used in the probe 2 is relatively high, 2 MHz, and in addition, the flaw detection resolution is further improved as a broadband wave having a wave number of 1.5-2. The transmission transducer 21 and the reception transducer 22 intersect each other with the ultrasonic beam axes Ax and Ay as shown in FIG. The range R is generated, and the flaw detection of the billet surface layer portion 2 to 30 mm below the surface can be performed. Here, the frequency of the transmitted ultrasonic wave is preferably in the range of 2.0 to 5.0 MHz. Table 1 shows details of the specifications of the surface layer probe 2. The transducer inclination angle shown in Table 1 is an angle provided for two transducers in order to bring the cross axis range closer to the probe side as described above. In the present embodiment, the vibrator inclination angle θ is set to 7.2 ° as shown in FIG.

  The reception signals obtained by the ultrasonic probes 1 and 2 are schematically shown in FIGS. 5 (1) and 5 (2). FIG. 5 (1) shows the received signal of the inner part probe 1, and its waveform causes signal peaks P1 and P2 due to reflected waves on the front and back surfaces of the billet M and a defect in the billet inner part. If there is, a signal peak P3 due to the reflected wave at the defect is generated between these signal peaks P1 and P2. Note that a so-called dead zone Zd that generates a signal peak due to a surface reflection wave is relatively widened by relatively increasing the vibrator size.

  FIG. 5 (2) shows the received signal of the probe 2 for the surface layer, and the waveform thereof is a defect in the billet surface layer where the dead zone Zd is in the received signal of the probe 1 for the inner part. In some cases, the signal peak P4 is generated by the reflected wave at the defect. In this manner, flaw detection from the surface layer portion to the inner quality portion of the billet M having a crystal grain size relatively small in the surface layer portion and relatively large in the inner quality portion can be performed. Then, the inside of the billet M can be completely detected by inverting the billet M as appropriate and scanning the probe with different side surfaces as the upper surface.

It is a perspective view of the billet which located the probe which shows one embodiment of the present invention. It is a graph which shows the crystal grain size distribution of a billet cross section. It is a schematic side view which shows the ultrasonic beam of the probe for internal parts. It is a schematic side view which shows the ultrasonic beam of the probe for surface layer parts. It is a figure which shows the signal waveform of a probe.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface layer probe, 11 ... Transmission / reception vibrator, 2 ... Inner part probe, 21 ... Transmission vibrator, 22 ... Reception vibrator, Ax, Ay ... Beam axis, M ... Billet (material) .

Claims (1)

An ultrasonic flaw detection method for flaw detection of a material having a relatively small crystal grain size in a surface layer portion and a relatively large distribution in an inner quality portion, wherein the ultrasonic beam axis of a transmission transducer and the ultrasonic beam of a reception transducer In the surface layer portion, the axes intersect each other to detect flaws in the surface layer portion from the waveform of the received ultrasonic wave, and the ultrasonic beam of the transmission / reception transducer is focused in the inner part to detect the internal wave from the waveform of the received ultrasonic wave. ultrasonic flaw detection method have rows flaw detection, and characterized in that the ultrasonic frequency of the transceiver transducer was relatively lower than the ultrasonic frequency of the transmission oscillator and the receiving transducer in the quality unit.

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