Laser ultrasonic flaw detection apparatus, laser ultrasonic flaw detection method, continuous casting equipment, continuous casting method, method for manufacturing objects, and method for quality control of objects.

Abstract

To accurately identify the direction and location of defects present on the surface of a relatively moving object. [Solution] The system includes a transmitting / receiving unit that excites surface waves by irradiating the surface of a relatively moving object with a laser and receives multiple reflected surface waves over time, and a calculation unit that uses the reflected waves received by the transmitting / receiving unit to detect defects on the surface of the object. The transmitting / receiving unit excites surface waves in two opposite directions by irradiating with a laser whose irradiation area has a linear shape, such that the longitudinal direction of the irradiation area is at an angle with respect to the direction of movement of the object. The calculation unit includes an extraction unit that extracts signals with an intensity of a predetermined level or higher from the multiple reflected waves as multiple defect signals and generates a flaw detection image showing the change in the intensity of the multiple defect signals with respect to the reception time of the multiple reflected waves and the movement time of the object, and a determination unit that uses the flaw detection image to determine whether the defect is in the region approaching or moving away from the laser irradiation position.

Description

Technical Field

[0001] The present invention relates to a laser ultrasonic flaw detector, a laser ultrasonic flaw detection method, a continuous casting facility, a continuous casting method, a method for manufacturing an object, and a method for quality control of an object.

Background Art

[0002] As a method for inspecting defects existing on the surface layer of an object, there is an ultrasonic flaw detection method. This method uses ultrasonic waves (hereinafter referred to as surface waves) that propagate on the surface of the object. A laser ultrasonic flaw detection method that uses a laser as a means for exciting surface waves is known. In the laser ultrasonic flaw detection method, a laser is irradiated on the surface of the object, and by generating a thermal expansion or ablation effect, surface waves are excited on the surface of the object. The excited surface waves propagate through the surface layer of the object, and flaw detection is performed by measuring the surface waves reflected by the defects with a laser interferometer.

[0003] The laser ultrasonic flaw detection method can be used to inspect high-temperature objects, etc., because ultrasonic waves can be transmitted and received non-contact with respect to the object. However, generally, the shape of the laser irradiation region is point-like, and since surface waves propagate omnidirectionally from the point-like irradiation region, it is difficult to specify the direction and position of the defect only from the propagation time of the surface waves. On the other hand, knowing in which direction and position a defect exists with respect to the laser irradiation region is necessary for specifying the cause of the defect and performing defect removal work.

[0004] From such a background, Patent Document 1 proposes a method for specifying the position of a defect when performing flaw detection using a laser ultrasonic flaw detection method. Specifically, the method described in Patent Document 1 utilizes that ultrasonic waves in the longitudinal wave mode and the transverse wave mode excited by a laser have directivity in a specific direction, and specifies the position of the defect by scanning the laser irradiation point around the position of the defect.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-81858 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, since longitudinal and transverse ultrasonic waves propagate within the material, the method described in Patent Document 1 makes it difficult to determine the direction and location of defects when they are on the surface rather than inside the material. Furthermore, detecting surface defects requires exciting surface waves using a laser, but Patent Document 1 does not disclose or suggest a method for determining the direction and location of defects using surface waves. Moreover, scanning the laser irradiation point complicates the overall configuration of the apparatus, including the drive unit, and requires multiple laser irradiations to determine the direction and location of the defect, thus increasing the time required for flaw detection.

[0007] The present invention has been made to solve the above problems, and its objective is to provide a laser ultrasonic flaw detection apparatus and a laser ultrasonic flaw detection method that can accurately identify the direction and location of defects present on the surface of a relatively moving object with a simple apparatus configuration. Another objective of the present invention is to provide a continuous casting apparatus and a continuous casting method that can accurately identify the direction and location of defects present on the surface of a continuously cast steel billet with a simple apparatus configuration. Yet another objective of the present invention is to provide a method for manufacturing an object and a quality control method that can produce an object with a high yield. [Means for solving the problem]

[0008] [1] The laser ultrasonic flaw detection apparatus according to the present invention comprises a transmitting and receiving unit that excites surface waves by irradiating a laser onto the surface of a relatively moving object and receives a plurality of reflected waves of the surface waves over time, and a calculation unit that uses the reflected waves received by the transmitting and receiving unit to detect defects on the surface of the object, wherein the transmitting and receiving unit excites surface waves in two opposite directions by irradiating a laser with a linear irradiation area such that the longitudinal direction of the irradiation area is at an angle with respect to the direction of movement of the object, and the calculation unit extracts signals with an intensity of a predetermined level or higher from the plurality of reflected waves as a plurality of defect signals, and uses the extracted plurality of defect signals to generate a flaw detection image showing the change in the intensity of the plurality of defect signals with respect to the reception time of the plurality of reflected waves and the movement time of the object, and uses the flaw detection image to determine whether the defect is in the region approaching or moving away from the laser irradiation position.

[0009] [2] In the laser ultrasonic flaw detection apparatus according to the present invention, the determination unit performs aperture synthesis processing on the plurality of defect signals using two types of delay time groups that emphasize defects present in each of the two directions, thereby determining whether the defect is in the region approaching the laser irradiation position or the region moving away from it.

[0010] [3] The laser ultrasonic flaw detection method according to the present invention includes a transmission and reception step of exciting a surface wave by irradiating the surface of a relatively moving object with a laser and receiving a plurality of reflected waves of the surface wave over time, and a calculation step of detecting a defect on the surface of the object using the reflected waves received in the transmission and reception step, wherein the transmission and reception step is performed by irradiating a laser having a linear irradiation area shape such that the longitudinal direction of the irradiation area is at an angle with respect to the direction of movement of the object, thereby exciting a surface wave in two directions opposite to each other, the calculation step includes an extraction step of extracting signals of a predetermined intensity or higher from the plurality of reflected waves as a plurality of defect signals, and using the extracted plurality of defect signals to generate a flaw detection image showing the change in the intensity of the plurality of defect signals with respect to the reception time of the plurality of reflected waves and the movement time of the object, and a determination step of using the flaw detection image to determine whether the defect is in the region approaching or moving away from the laser irradiation position.

[0011] [4] The continuous casting equipment according to the present invention comprises a continuous casting apparatus for continuously casting steel billets, and a laser ultrasonic flaw detection apparatus as described in [1] or [2] above for inspecting defects on the surface of the steel billets continuously cast by the continuous casting apparatus.

[0012] [5] The continuous casting method according to the present invention includes a continuous casting step of continuously casting a steel billet and an inspection step of inspecting defects on the surface of the steel billet continuously cast in the continuous casting step using the laser ultrasonic flaw detection method described in [3] above.

[0013] [6] A method for manufacturing an object according to the present invention includes a manufacturing step of manufacturing an object and an inspection step of inspecting defects on the surface of the object manufactured in the manufacturing step using the laser ultrasonic flaw detection method described in [3] above.

[0014] [7] The method for quality control of an object according to the present invention includes an inspection step of inspecting defects on the surface of an object using the laser ultrasonic flaw detection method described in [3] above, and a determination step of determining whether the object meets predetermined standards based on the inspection results of the inspection step. [Effects of the Invention]

[0015] The laser ultrasonic flaw detection apparatus and laser ultrasonic flaw detection method according to the present invention allow for the accurate identification of the direction and location of defects present on the surface of a relatively moving object with a simple apparatus configuration. Furthermore, the continuous casting equipment and continuous casting method according to the present invention allow for the accurate identification of the direction and location of defects present on the surface of a continuously cast steel billet with a simple apparatus configuration. In addition, the manufacturing method and quality control method for objects according to the present invention allow for the manufacturing of objects with a high yield. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a schematic diagram illustrating the principle of laser ultrasonic flaw detection. [Figure 2] Figure 2 shows an example of a received signal. [Figure 3] Figure 3 is a schematic diagram showing how transmitted waves propagate from a point-shaped irradiation area. [Figure 4] Figure 4 is a schematic diagram showing how transmitted waves propagate from a point-shaped irradiation area. [Figure 5] Figure 5 is a schematic diagram showing how transmitted waves propagate from a linear irradiation area. [Figure 6] Figure 6 shows the relationship between the location of a defect and the change in the received signal as the object moves. [Figure 7] Figure 7 shows the relationship between the location of a defect and the change in the received signal as the object moves. [Figure 8] Figure 8 is a block diagram showing the configuration of a laser ultrasonic flaw detection apparatus, which is a first embodiment of the present invention. [Figure 9]FIG. 9 is a flowchart showing the flow of ultrasonic flaw detection processing according to the first embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing an example of a flaw detection image and a defect image. [Figure 11] FIG. 11 is a diagram showing an example of a defect image. [Figure 12] FIG. 12 is a diagram showing an example of a defect image. [Figure 13] FIG. 13 is a diagram showing the direction and position of a defect with respect to a linear irradiation region. [Figure 14] FIG. 14 is a diagram for explaining a method of determining the direction and position of a defect using the aperture synthesis method. [Figure 15] FIG. 15 is a diagram for explaining the configuration of a laser ultrasonic flaw detector according to the second embodiment of the present invention. [Figure 16] FIG. 16 is a diagram for explaining the configuration of a laser ultrasonic flaw detector according to the third embodiment of the present invention. [Figure 17] FIG. 17 is a diagram for explaining the configuration of a laser ultrasonic flaw detector according to the fourth embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

[0017] When detecting a defect existing on the surface layer of an object using ultrasonic waves, it is common to use surface waves. Surface waves can be excited by irradiating the surface of the object with a high-energy laser such as a pulsed laser. As shown in FIG. 1, the laser ultrasonic flaw detection method utilizing this phenomenon irradiates the surface of the object S with a laser from the laser unit 11 to excite a transmitted wave TW which is a surface wave, and receives the transmitted wave TW reflected by the defect D as a reflected wave RW by the transmitting and receiving unit 10, thereby detecting the defect D existing on the surface layer. An example of the voltage signal received by the transmitting and receiving unit 10 at that time is shown in FIG. 2. As shown in FIG. 2, the transmitted wave TW is received immediately after the laser irradiation time (receiving time = 0). On the other hand, the reflected wave RW is received with a delay from the laser irradiation time and in a state where the intensity is lower than that of the transmitted wave TW.

[0018] In this type of laser ultrasonic testing method, when a laser with a point-shaped irradiation area is irradiated onto the surface of an object S, the transmitted wave TW propagates in all directions from the point-shaped irradiation area 11a, as shown in Figure 3. Figure 3 shows the state when the laser is irradiated onto the side of the object S. Furthermore, when detecting defects using the laser ultrasonic testing method, a defect is determined to exist when the intensity of the reflected wave RW exceeds a predetermined threshold within a predetermined reception time range. However, as described above, when a laser with a point-shaped irradiation area is irradiated, the transmitted wave TW propagates in all directions from the point-shaped irradiation area 11a. Therefore, when a laser with a point-shaped irradiation area is irradiated, the presence or absence of a defect can be determined, but it is not possible to specify the direction or position of the defect relative to the point-shaped irradiation area 11a.

[0019] For example, as shown in Figure 3, if there are defects A1 to A4 at the four corners of the side surface of an object S, and a laser with a point-shaped irradiation area is shone near the center of the side surface of the object S, the transmitted wave TW will be excited in a concentric circle around the laser irradiation position. In the example shown in Figure 3, defect A1 is located in the upper left of the point-shaped irradiation area 11a, defect A2 in the upper right, defect A3 in the lower left, and defect A4 in the lower right, and the distance from the point-shaped irradiation area 11a to each defect is assumed to be the same. When the transmitted wave TW is excited, the reflected waves RW from defects A1 to A4 are received by a receiver also located near the center of the side surface of the object S. However, since the reception time of the reflected waves RW from each defect is approximately the same, it is not possible to determine where the reflected waves TW came from, in other words, the direction and location of the defects.

[0020] Therefore, in this invention, the shape of the laser irradiation area that excites the transmitting wave TW is linear rather than point-shaped, and a transmitting wave TW having directionality in two opposite directions perpendicular to the linear irradiation area is excited. Then, in this invention, the direction and position of the defect relative to the linear irradiation area are determined by utilizing the fact that multiple reflected waves RW obtained by multiple transmissions and receptions of ultrasonic waves and the defect move with the object S over time. Specifically, in this invention, the laser is irradiated such that the longitudinal direction of the linear irradiation area is oblique (at an angle, excluding 0 degrees and 90 degrees) to the direction of movement of the object S. Then, by focusing on the fact that the pattern of change in the reception time of the reflected wave RW accompanying the movement of the object changes depending on which of the two opposite directions the defect is located on, the direction and position of the defect relative to the laser irradiation position are determined. Note that the shape of the laser irradiation area is not limited to linear; it may be a shape other than linear, such as a rectangle, as long as a longitudinal direction and a short direction can be defined.

[0021] If the object moves and the transmitting / receiving unit 10 is fixed, the defect also moves relative to the laser irradiation position. However, in this invention, the transmitted wave TW propagates obliquely to the direction of movement of the object. Therefore, even if the directivity is narrowed to two opposite directions, the defect moves with the object, and thus the defect will eventually pass through the propagation region of the transmitted wave TW. Consequently, there is no need to scan the laser. Furthermore, by reading the pattern of change in the reception time of the reflected wave RW in response to changes in the positional relationship between the defect position and the laser irradiation position from the reflected waves acquired multiple times, the direction and location of the defect relative to the laser irradiation position can be identified. Specifically, by calculating the reception time of the reflected wave and confirming whether the reception time becomes faster or slower as the object moves, the direction in which the defect exists relative to the laser irradiation position can be identified.

[0022] The present invention will be described in more detail below.

[0023] Generally, as shown in Figure 4, when a laser with a point-shaped irradiation area 11a is irradiated onto the side surface of an object S and a transmitted wave TW is excited, the transmitted wave TW propagates in all directions from the point-shaped irradiation area 11a. In contrast, the inventors of the present invention have conceived that by making the laser irradiation area a linear irradiation area 11b, as shown in Figure 5, and irradiating the laser obliquely to the direction of movement of the object S, it is possible to excite a transmitted wave TW that has directionality in two opposite directions. In the example shown in Figure 5, the transmitted wave TW is excited in two regions, R1 and R4, and the transmitted wave TW propagates to the locations of defects A1 and A4, while it hardly propagates to the locations of defects A2 and A3. In other words, a transmitted wave TW with directionality in the two directions in which defects A1 and A4 exist is excited. Therefore, by repeatedly transmitting and receiving surface waves as the object S moves, it is possible to acquire only the reflected waves RW from defects A1 and A2 multiple times.

[0024] Here, as shown in Figure 6(a), the position of defect A1 changes in the order of positions t1 to t5 relative to the laser irradiation position as the object S moves. Also, defect A1 is located on the upper left side of the linear irradiation area 11b and is in a position that approaches the linear irradiation area 11b as the object S moves. Therefore, as the object S moves, the distance between defect A1 and the linear irradiation area 11b decreases in the order of positions t1 to t5, and as shown in Figure 6(b), the reception time of the reflected wave RW from defect A1 becomes shorter in the order of positions t5 to t1.

[0025] Furthermore, the intensity of the reflected wave RW increases as the defect is located closer to being perpendicular to the linear irradiation region 11b. This is because the transmitted wave TW, excited and propagating in each minute region within the linear irradiation region 11b, overlaps and reinforces at positions equal to the distance from each minute region, i.e., on the central axis of the linear irradiation region 11b. As a result, the reflected wave RW from defect A1 is received multiple times, with its intensity changing as the object S moves. Also, as shown in Figure 6(b), the intensity of the reflected wave from defect A1 gradually increases, reaching a maximum at position t3, which is a position passing through the central axis of the linear irradiation region 11b, and then gradually decreasing.

[0026] In contrast, as shown in Figure 7(a), the position of defect A4 changes in the order of positions t1 to t5 relative to the laser irradiation position as the object S moves. Furthermore, defect A4 is located on the lower right side of the linear irradiation area 11b and is located away from the linear irradiation area 11b. Therefore, as the object S moves, the distance between defect A4 and the linear irradiation area 11b increases in the order of positions t1 to t5, and as shown in Figure 7(b), the reception time of the reflected wave TW from defect A4 decreases in the order of positions t1 to t5. Also, as shown in Figure 7(b), the intensity of the reflected wave from defect A4 gradually increases, reaching a maximum at position t3, which is the position passing through the central axis of the linear irradiation area 11b, and then gradually decreasing.

[0027] In this way, by transmitting and receiving the transmitted wave TW as the object moves, multiple reflected waves can be acquired, as shown in Figures 6(b) and 7(b), with the vertical axis representing amplitude and the horizontal axis representing reception time. Then, by arranging the acquired multiple reflected waves in order of the object's movement time and converting the amplitude to a brightness value, a brightness image (hereinafter referred to as a flaw detection image) can be obtained, with the vertical axis representing the reception time of the reflected wave and the horizontal axis representing the movement time. The flaw detection image shows how the intensity of the reflected wave from the defect changes as the object moves. Therefore, by determining from the flaw detection image whether the reception time of the reflected wave from the defect is getting faster or slower as the object S moves, it is possible to visually determine whether the location of the defect is in a region approaching or moving away from the linear illumination region 11b. Note that the flaw detection image includes not only the reflected wave from the defect but also noise signals with low reflection intensity. Therefore, only pixels with a brightness value of a predetermined value or higher relative to the brightness of the reflected wave may be extracted and shown as a flaw detection image (see Figures 11 and 12 described later).

[0028] As described above, in this invention, a laser having a linear irradiation area 11b is irradiated onto the surface of an object S such that the longitudinal direction of the irradiation area is oblique to the direction of movement of the object, thereby exciting a transmitted wave TW that is directional in two opposite directions. Then, based on the difference in the pattern of change of the reception time of the reflected wave RW accompanying the movement of the object S, depending on which of the two opposite directions the defect is located in, the position and direction of the defect relative to the linear irradiation area 11b is determined. With this configuration, when detecting defects on the surface of an object S using laser ultrasonic testing, it is possible to accurately determine in which direction and position the defect is located relative to the laser irradiation position. Furthermore, it is possible to simultaneously detect defects in two opposite directions, and since it utilizes the movement of the object, laser scanning is unnecessary, and the device configuration can be made simpler.

[0029] The configurations of the laser ultrasonic flaw detection apparatus according to the first to fourth embodiments of the present invention will be described below with reference to the drawings.

[0030] [First Embodiment] Figure 8 is a block diagram showing the configuration of a laser ultrasonic flaw detection apparatus according to the first embodiment of the present invention. As shown in Figure 8, the laser ultrasonic flaw detection apparatus 1 according to the first embodiment of the present invention comprises a transmitting / receiving unit 10, a calculation unit 20, a storage unit 30, and a display unit 40.

[0031] The transmitting / receiving unit 10 comprises a laser unit 11 and a receiving unit 12. The laser unit 11 excites a transmitted wave TW by irradiating the surface of a moving object S with a laser. A continuous wave laser or a pulsed laser can be used as the laser. It is preferable to use a pulsed laser because a strong transmitted wave TW can be excited by concentrating the energy for a short time, and the temporal separation of the reflected wave RW from defects becomes easier. The laser beam is widened in one direction by using a cylindrical lens, and the irradiation area is irradiated in a linear shape.

[0032] To improve the directivity of the transmitted wave TW, it is preferable for the longitudinal length of the linear irradiation area 11b to be long. On the other hand, if the longitudinal length is made too long, the energy per unit area within the linear irradiation area 11b will be low, and insufficient energy will be obtained to cause ablation or thermal expansion, making it impossible to excite the transmitted wave TW. For this reason, the longitudinal length should be appropriately selected from within the range of 10 to 100 mm, depending on the energy of the laser. Furthermore, the transverse length should be kept short, to a few mm or less, in order to improve the directivity of the transmitted wave TW.

[0033] The linear irradiation area 11b is positioned such that its longitudinal direction is oblique to the direction of movement of the object S. That is, the angle of the longitudinal direction with respect to the direction of movement of the object S is greater than 0 degrees and less than 90 degrees. It is preferable to set the angle of the longitudinal direction with respect to the direction of movement of the object S within the range of 20 to 70 degrees in order to facilitate the separation of reflected waves RW. The angle of the longitudinal direction with respect to the direction of movement of the object S can be changed by adjusting the rotation direction of the cylindrical lens.

[0034] Depending on the extent possible, the transmitting and receiving unit 10 may be configured to arrange multiple transmitting and receiving units 10 in a direction perpendicular to the direction of movement of the object S, or the intensity of the transmitted wave TW may be increased.

[0035] The receiving unit 12 is composed of a laser interferometer that receives ultrasonic waves in a non-contact manner. The receiving unit 12 may also receive ultrasonic waves in a manner that contacts the object S. The receiving unit 12 receives the transmitted wave TW excited by the laser unit 11 and the reflected wave RW that is reflected by a defect from the transmitted wave TW, and inputs electrical signals indicating the intensity and reception time of the received transmitted wave TW and reflected wave RW to the calculation unit 20. In this embodiment, the same device as the laser unit 11 for exciting the transmitted wave TW is used as the laser unit of the laser interferometer that constitutes the receiving unit 12. Of course, the laser unit 11 for exciting the transmitted wave TW and the laser unit that constitutes the receiving unit 12 may be separate units.

[0036] The calculation unit 20 is composed of a calculation processing unit such as a CPU and functions as a measurement control unit 21, a signal acquisition unit 22, an extraction unit 23, and a determination unit 24 by executing a computer program stored in a storage device such as a memory unit 30. The functions of the measurement control unit 21, the signal acquisition unit 22, the extraction unit 23, and the determination unit 24 will be described later.

[0037] The memory unit 30 is composed of a non-volatile memory device and includes a signal storage unit 31 and a signal processing condition storage unit 32. The signal storage unit 31 stores data of defective signals, which will be described later. The signal processing condition storage unit 32 stores signal processing setting information (signal processing conditions), such as the cropping range of the defective image, the delay time and blending width of the aperture blending process.

[0038] The display unit 40 is composed of a display output device such as a liquid crystal display and displays various information such as flaw detection results generated by the calculation unit 20.

[0039] The laser ultrasonic flaw detection apparatus 1, having this configuration, identifies the direction and location of defects present on the surface of a moving object S by performing the ultrasonic flaw detection process described below. The operation of the laser ultrasonic flaw detection apparatus 1 when performing this ultrasonic flaw detection process will be explained below with reference to the flowchart shown in Figure 9.

[0040] [Ultrasonic flaw detection] Figure 9 is a flowchart showing the flow of ultrasonic flaw detection processing according to the first embodiment of the present invention. The flowchart shown in Figure 9 starts when an execution command for ultrasonic flaw detection processing is input to the laser ultrasonic flaw detection device 1, and the ultrasonic flaw detection processing (hereinafter abbreviated as flaw detection processing) proceeds to step S1. At the stage before the start of flaw detection processing, (a) flaw detection conditions such as the laser irradiation frequency, irradiation angle, and shape of the irradiation area and the moving speed of the object S by the laser unit 11, and (b) information regarding the defect signal extraction range such as the threshold for extracting defect signals, the number of waveforms and the time range are set in the laser ultrasonic flaw detection device 1.

[0041] In step S1, the measurement control unit 21 controls the laser irradiation period, irradiation range, irradiation angle, and focal length of the laser unit 11 to irradiate the surface of the object S with a laser having a linear irradiation area 11b, thereby exciting the surface of the object S with a transmitted wave TW. At this time, the measurement control unit 21 controls the irradiation direction of the laser so that the longitudinal direction of the linear irradiation area 11b is oblique to the direction of movement of the object S. The laser irradiation range, irradiation angle, and focal length can be changed by adjusting the rotation angle of the cylindrical lens in the laser unit 11 and the distance between the lenses using an electric actuator or the like. With this, the process of step S1 is completed, and the flaw detection process proceeds to step S2.

[0042] In step S2, the measurement control unit 21 first receives the surface waves (transmitted wave TW and reflected wave RW) by controlling the receiving unit 12. Next, the measurement control unit 21 inputs an analog electrical signal indicating the intensity of the received surface waves to the signal acquisition unit 22. The signal acquisition unit 22 then converts the analog electrical signal indicating the intensity of the surface waves input from the receiving unit 12 into a digital electrical signal, and stores the digital electrical signal indicating the intensity of the surface waves as a defect signal in the signal storage unit 31. At this time, the signal acquisition unit 22 also associates information regarding the reception time of the surface waves and the moving speed of the object S during the reception time with the defect signal and stores it in the signal storage unit 31. A large transmitted wave TW is received immediately after the laser is irradiated, but the transmitted wave TW is the transmitted ultrasonic wave itself. For this reason, the signal acquisition unit 22 does not use the transmitted wave TW in subsequent processing, and performs subsequent processing on the smaller reflected wave RW that is received after the transmitted wave TW. With this, the processing of step S2 is completed, and the flaw detection process proceeds to step S3.

[0043] In step S3, the extraction unit 23 extracts multiple defect signal data points with an intensity above a predetermined threshold from the defect signal data stored in the signal storage unit 31. In this process, the extraction unit 23 extracts a predetermined number of defect signal data points with an intensity above the predetermined threshold from a predetermined time range set before the start of the flaw detection process. For example, in the example shown in Figure 6(b), the extraction unit 23 extracts five reflected waves RW with an intensity above a predetermined threshold from the reception time of the transmitted wave TW within a predetermined time range. The extraction unit 23 then arranges the extracted defect signals in order of the object's movement time, as shown in Figure 10, and converts the amplitude to a brightness value, thereby generating a brightness image with the vertical axis representing reception time and the horizontal axis representing movement time as a flaw detection image. This completes the process in step S3, and the flaw detection process proceeds to step S4.

[0044] In step S4, the determination unit 24 performs signal processing on the defect images in the flaw detection image generated in step S3, and uses the results of the signal processing to identify the direction and position of the defect relative to the linear illumination area 11b. In the example shown in Figure 10, multiple defect images appear in the flaw detection image, but some of them are circled. In this example, it can be seen that as the object S moves, the reception time of defect image 1 becomes shorter and the reception time of defect image 2 becomes longer. Therefore, since defect image 1 is moving in the direction of approaching the linear illumination area 11b, it can be determined that the defect corresponding to defect image 1 is located to the upper left of the linear illumination area 11b, similar to defect A1 shown in Figure 6(a). In contrast, since defect image 2 is moving in the direction of moving away from the linear illumination area 11b, it can be determined that the defect corresponding to defect image 2 is located to the lower right of the linear illumination area 11b, similar to defect A4 shown in Figure 7(a).

[0045] Alternatively, only areas with high brightness can be extracted from the flaw detection image and used as a defect image, as shown in Figure 11, to determine the location of the defect. In the example shown in Figure 11, the dashed line DL represents defect image 1 shown in Figure 10, and the solid line SL represents defect image 2 shown in Figure 10. Furthermore, when defect images DL and SL as shown in Figure 12 are obtained, the direction and location of the defect can be determined based on the reception times of the locations D1 and D2 where the brightness of defect images DL and SL is maximum. In this example, the reception time at location D1 decreases with the movement of the object S, and the reception time at location D2 increases with the movement of the object S. Therefore, it can be determined that location D1 is located to the upper left of the linear illumination area 11b, and location D2 is located to the lower right of the linear illumination area 11b. In addition, as shown in Figures 13(a) and (b), by considering the position of the linear illumination area 11b, the reception position 12a, the reception times of locations D1 and D2, and the speed of sound in the object S, the detailed locations of locations D1 and D2 can also be determined as shown in Figure 13. Basically, the magnitude of the defect signal is maximum when a defect exists in the direction of the central axis of the linear irradiation area 11b. Therefore, by determining the reception time of the defect signal at this time from the defect image, the distance between the defect and the transmitting / receiving unit can be determined, and thus the location of the defect can be identified. With this, the process of step S4 is completed, and the flaw detection process proceeds to the process of step S5.

[0046] In step S5, the determination unit 24 displays information regarding the direction and location of defects in the linear irradiation area 11b identified in step S4 on the display unit 40 in the form of a two-dimensional color map or a binarized image. This completes step S5, and the series of flaw detection processes is finished.

[0047] [Open-aperture synthesis method] In the process of step S4 described above, the determination unit 24 may use the aperture synthesis method to determine the direction and position of the defect relative to the linear irradiation area 11b. The aperture synthesis method allows for the utilization of all received defect signals, thus enabling a more accurate calculation of the defect's location. A method for determining the direction of a defect using the aperture synthesis method will be described below with reference to Figure 14.

[0048] As shown in Figure 14, as the object S moves, the location of the defect changes in the order of positions t1 to t5, and surface waves are transmitted and received and defect signals are acquired at each position, with position t3 located on the central axis α of the linear irradiation region 11b. Furthermore, the central axis α is perpendicular to the line of the linear irradiation region 11b, and the central axis α passes through the longitudinal center of the linear irradiation region 11b. Let L1 be the distance between the linear irradiation region 11b and position t1, L1' be the distance between the defect signal reception position 12a and position t1, L3 be the distance between the linear irradiation region 11b and position t3, and L3' be the distance between the defect signal reception position 12a and position t3. At this time, if the speed of sound of the surface wave is V, the reception times T1 and T3 of the reflected waves from the defects at positions t1 and t3 can be calculated using the following equations (1) and (2).

[0049]

number

[0050]

number

[0051] Furthermore, the delay in the reception time of the defective signal at position t1 (hereinafter referred to as the delay time), Δt1, with the reception time of the defective signal at position t3 on the central axis α as the reference time, can be calculated using the following formula (3).

[0052]

number

[0053] This delay time is calculated for positions t2, t4, and t5 as well as position t3. The four defect signals at positions t1, t2, t4, and t5 are then multiplied by the delay times Δt1, Δt2, Δt4, and Δt5 in order, and these are added to the defect signal at position t3 and averaged. As a result, reflected waves from defects passing through the thickness-direction positions of the object S are amplified, while reflected waves from defects passing through other thickness-direction positions are weakened. Therefore, even if a defect passes through a position opposite to the thickness-direction position X in the linear irradiation area 11b, the delay times will not be the same, and the signals will cancel each other out.

[0054] Therefore, by using a delay time group assuming defect A1 located on the upper left side of the linear irradiation region 11b, and another delay time group assuming defect A4 located on the lower right side of the linear irradiation region 11b, aperture synthesis processing can be performed on the defect signal to obtain two types of aperture-synthesized images. Here, the image obtained by performing aperture synthesis processing using the delay time pattern assuming defect A1 is called aperture-synthesized image 1, and the image obtained by performing aperture synthesis using the delay time pattern assuming defect A4 is called aperture-synthesized image 2.

[0055] At this time, if a defect image appears in aperture composite image 1, it can be determined to be defect A1, and if a defect image appears in aperture composite image 2, it can be determined to be defect A4. Furthermore, by applying a delay time group to each position in the thickness direction, based on the reception time of the defect signal, the position in the thickness direction can also be identified more clearly.

[0056] [Second Embodiment] Since surface waves excited by a laser propagate while attenuating, the amplitude of the reflected signal from defects located far from the laser transmission / reception point becomes small, which can make it difficult to detect defects. Therefore, when performing flaw detection over a wide area, it is advisable to transmit and receive laser signals at multiple locations along a direction perpendicular to the relative direction of movement to perform flaw detection over the entire area. Examples of methods for transmitting and receiving laser signals at multiple locations along a direction perpendicular to the relative direction of movement include installing multiple transmission / reception units along the vertical direction, or moving the transmission / reception unit along the vertical direction to transmit and receive laser signals at each location. The second embodiment of the present invention, a laser ultrasonic flaw detection apparatus, transmits and receives laser signals at multiple locations along a direction perpendicular to the relative direction of movement by installing multiple transmission / reception units along the vertical direction. The configuration of the second embodiment of the present invention, a laser ultrasonic flaw detection apparatus, will be described below with reference to Figure 15.

[0057] Figure 15 is a diagram illustrating the configuration of a laser ultrasonic flaw detection apparatus according to a second embodiment of the present invention. As shown in Figure 15, in this embodiment, the relative direction of movement refers to the direction of movement in the figure, that is, the direction in which the object S moves horizontally from left to right in the drawing. The direction perpendicular to the direction of movement refers to the vertical direction from top to bottom in the drawing, and corresponds to the thickness direction of the object S. As in the first embodiment, the laser is irradiated onto the side surface of the object S.

[0058] A laser ultrasonic flaw detection apparatus, which is a second embodiment of the present invention, performs flaw detection in the direction of the thickness W of an object S using three transmitting and receiving units 10. The thickness W is much longer in the vertical direction than the area that can be inspected by a single transmitting and receiving unit 10. Hereinafter, the three linear irradiation areas will be referred to as 11b-11, 11b-12, and 11b-13 from the top of the drawing, and the three receiving positions will be referred to as 12a-11, 12a-12, and 12a-13 from the top of the drawing. The areas inspected by transmission and reception between the linear irradiation area 11b-11 and receiving position 12a-11 will be referred to as regions R111 and R411. Similarly, the areas inspected by transmission and reception between the linear irradiation area 11b-12 and receiving position 12a-12 will be referred to as regions R112 and R412. Similarly, regions R113 and R413 are defined as regions R113 and R413, respectively, where defects are detected by transmission and reception at the linear irradiation region 11b-13 and the receiving position 12a-13. Furthermore, regions R111, R112, and R113 are defined as regions where defects move closer to the irradiation position due to the relative movement of the object S, and regions R411, R412, and R413 are defined as regions where defects move away from the irradiation position due to the relative movement of the object S.

[0059] Furthermore, the length in the thickness direction of the object S that can be inspected in regions R111 and R411 is defined as the thickness W1 of regions R111 and R411. Similarly, the thickness of regions R112 and R412 is defined as thickness W2, and the thickness of regions R113 and R413 is defined as thickness W3. In other words, the thicknesses that can be inspected in regions R111 and R411, regions R112 and R412, and regions R113 and R413 are represented by thicknesses W1, W2, and W3, respectively. Three transmitting and receiving units 10 are then arranged so that the linear irradiation regions 11b-11 to 11b-13 or receiving positions 12a-11 to 12a-13 are roughly aligned in a straight line in the thickness W direction of the object S.

[0060] The sizes of regions R111, R112, R113, R411, R412, and R413 are determined by the directivity and / or attenuation of the excited surface wave, the size of the defect to be detected, etc. The entire thickness W can be inspected by moving the object S relative to the transmitting / receiving unit 10 in the direction of movement shown in the figure. If it is to inspect the thickness W without any gaps, the transmitting / receiving points are arranged so that the thicknesses W1, W2, and W3 of each region partially overlap, so that the thickness W of the object S is smaller than the sum of the thicknesses W1, W2, and W3 of each region.

[0061] Furthermore, if transmission and reception are performed simultaneously in each region, surface waves propagating from another transmission source may be received, overlapping with the defect signal and interfering with defect detection. For example, if surface waves transmitted from a linear irradiation region 11b-12 are received at receiving positions 12a-11, it will interfere with defect detection in both the linear irradiation region 11b-11 and receiving position 12a-11. For this reason, it is preferable to transmit and receive lasers in each region at different times, for example, between the linear irradiation region 11b-11 and receiving position 12a-11, the linear irradiation region 11b-12 and receiving position 12a-12, and the linear irradiation region 11b-13 and receiving position 12a-13.

[0062] The actual flaw detection that follows can be carried out according to the flowchart shown in Figure 9. In this case, since the laser irradiation and the reception of the reflected wave can be performed at different times, the processes from step S3 onwards in the flowchart shown in Figure 9 can also be performed simultaneously. Furthermore, when aperture synthesis is applied to this embodiment, first, the defect signals obtained by transmission and reception between the linear irradiation area 11b-11 and the reception position 12a-11 are subjected to aperture synthesis processing using two types of delay time groups. This results in an aperture synthesis image in which defects passing through region R111 are emphasized and an aperture synthesis image in which defects passing through region R411 are emphasized. Similarly, by performing aperture synthesis processing on the defect signals obtained by transmission and reception between the linear irradiation area 11b-12 and the reception position 12a-12, and between the linear irradiation area 11b-13 and the reception position 12a-13, aperture synthesis images in which defects passing through regions R112, R412, R113, and R413 are emphasized are obtained.

[0063] Through the above procedure, six aperture composite images are obtained from the defect signals acquired at the three transmission and reception points. Based on the obtained aperture composite images, the defect location is identified for each transmission and reception point. The same two delay time groups can be applied to the defect signals at the three locations. That is, the same delay time group can be applied to regions R111, R112, and R113, and the other delay time group can be applied to regions R411, R412, and R413. The reflected signals from defects passing through regions R111, R112, and R113 are enhanced by the delay time that assumes the defect is approaching the irradiation position. The reflected signals from defects passing through regions R411, R412, and R413 are enhanced by the delay time that assumes the defect is moving away from the irradiation position. Based on the obtained aperture composite images, the defect location can be identified.

[0064] [Third Embodiment] As shown in Figure 5, in this invention, the regions R1 and R4, where a pair of transmitted waves propagate in two directions, become the inspectionable region. In this embodiment, a method for more precisely defining this inspectionable region will be described. In the inspectionable region, it is preferable to obtain a reflected signal from the defect to be detected with sufficient intensity. Therefore, considering the attenuation and directivity due to the propagation of the excited surface wave, the inspectionable regions R1 and R4 can be represented as shown in Figure 16(a). Here, in ultrasonic testing, the vicinity of the sound source is called the near-field and is well known to be a region with a complex sound pressure distribution. In other words, the vicinity of the linear irradiation region 11b and the receiving position 12a is basically considered unsuitable for inspection. Furthermore, for defects near the receiving position 12a, the reception times of the reflected wave from the defect and the transmitted wave propagating directly from the linear irradiation region 11b are close, making it difficult to separate the transmitted wave and the reflected wave. In addition, when a surface wave for transmission is excited by a laser, unwanted shock waves are often excited at the same time. If the reception times of unwanted shock waves and reflected waves from defects overlap, it becomes difficult to extract the defect signal from the reflected waves.

[0065] Therefore, it is preferable to exclude from the inspection area regions where reflected waves from defects and transmitted waves are likely to overlap, and / or regions where unwanted shock waves and reflected waves are likely to overlap. Specifically, these are the concentric neighbor regions N11 and N14 centered on the linear irradiation region 11b and the receiving position 12a. Schematic representations of the neighbor regions N11 and N14 are shown in Figure 16(b). The concept of neighbor regions N11 and N14 is as follows: Although it depends on the material and temperature of the object, the velocity of unwanted shock waves is generally considerably smaller than the velocity of reflected waves. For example, in the case of a high-temperature cast slab, the velocity of the shock wave can be about 1 / 10 of the velocity of the surface wave. A schematic diagram of the received signal is shown in Figure 16(e). Assume that the transmitted wave TW transmitted from the linear irradiation region 11b, the unwanted shock wave SW, and the reflected wave RW reflected from the defect are received at the receiving position 12a. Let QT, QS, and QR be the reception times for the transmitted wave TW, the unwanted shock wave SW, and the reflected wave RW, respectively. Let d be the distance between the linear irradiation area 11b and the receiving position 12a, d1 be the distance between the linear irradiation area 11b and the defect, d2 be the distance between the receiving position 12a and the defect, and Vtw and Vsw be the speeds of sound for the transmitted wave TW and the shock wave SW, respectively. Then the reception time QT for the transmitted wave TW, the reception time QS for the shock wave SW, and the reception time QR for the reflected wave RW are expressed by the following equations (4) to (6).

[0066]

number

[0067]

number

[0068]

number

[0069] In this case, if the reflected wave RW overlaps with the transmitted wave TW or the shock wave SW, that is, if the reception time QR of the reflected wave RW approaches the reception time QT of the transmitted wave TW or the reception time QS of the shock wave SW, then flaw detection becomes difficult. To prevent this, it is advisable to define the flaw detection area as the range that satisfies the conditions shown in equation (7) or equation (8) below.

[0070]

number

[0071]

number

[0072] As mentioned above, the vicinity of the linear irradiation area 11b and the receiving position 12a is basically unsuitable for flaw detection. Therefore, it is preferable to exclude the area that does not satisfy equation (7) or equation (8) from the flaw detection area as the nearby area N11 or nearby area N14. In this case, shortening the distance d between the linear irradiation area 11b and the receiving position 12a will reduce the nearby areas N11 and N41, and as a result, the flaw detection area can be widened. For example, if Vtw = 3000 m / s and Vsw = 300 m / s, and d = 10 mm, the area that can be inspected will be the range that satisfies d1 + d2 > 100 mm. If d = 2 mm, the area that can be inspected will be the range that satisfies d1 + d2 > 20 mm, allowing for flaw detection over a wider area. It is preferable to use the area R121 obtained by excluding the predetermined nearby area N11 from area R1 based on the above considerations as the flaw detection area. Similarly, it is preferable to define the inspection area as region R421, which is obtained by excluding a predetermined neighboring region N14 from region R4 based on the above considerations. Figure 16(b) shows an example of regions R121 and R421.

[0073] Furthermore, in this embodiment, as described above, the location of a defect is identified based on whether the defect in the object S moves closer to or further away from the receiving position 12a as the object S moves relative to the object S. For this reason, it is preferable that the defect signal from the defect is received multiple times with sufficient strength. In other words, in the inspection areas R121 and R421 in Figure 16(b), the defect signal is received multiple times as the defect moves from the left side to the right side of the paper in Figure 16(b). Here, as shown in Figure 16(c), it is assumed that the two defects D3 and D4 each follow two different paths. The path followed by defect D3 is called path 1, and the other path followed by defect D4 is called path 2. Furthermore, path 1 is assumed to be on the upper side of the paper relative to area R121, and path 2 is assumed to be on the lower side of the paper relative to area R121 than path 1.

[0074] When defect D3 travels along path 1, the distance it travels through the inspectable area R121 is short. On the other hand, when defect D4 travels along path 2, the distance it travels through the inspectable area R121 is long. As can be seen from Figure 16(c), the number of transmissions and receptions that occur while a defect is passing through the inspectable area varies depending on the length of the distance it travels through the inspectable area. In other words, in areas where the distance traveled through the inspectable area is short, it becomes difficult to determine the location of the defect. Therefore, it is preferable to exclude such areas from the inspectable area, designating them as areas with short paths (△).

[0075] The concepts for the short path regions △11, Δ12 and regions △41, Δ42 are determined by considering the physical properties of the object S, the performance of the laser ultrasonic flaw detection device used, the relative movement speed between the object S and the transmitting / receiving unit 10, and the repetition frequency of the transmitted wave TW. For example, let Ftw be the repetition frequency of the transmitted wave TW, Vo be the relative movement speed of the object S with respect to the transmitting / receiving unit 10, and dm be the distance traveled through region R121 of path 2 (see Figure 16(c)). In this case, the number of times M can receive a reflected wave of sufficient intensity from the defect is expressed by the following formula (9).

[0076]

number

[0077] For example, if the process of determining whether or not there is a defect requires receiving 10 or more reflected waves RW, that is, to set M≧10, then if Ftw=20Hz and Vo=20mm / s, then from equation (9), the area in which defects can be detected can be set such that dm≧4mm. The range in which the number of times M can be received in area R121 is less than or equal to a certain value, that is, the area in which the distance dm that the defect D4 passes through area R121 is less than or equal to a certain distance, can be set as the short path areas △11, △12, △42, and △41. Figure 16(d) shows an example of the short path areas △11, △12, △42, and △41. In Figure 16(d), the short path areas within area R121 are represented as Δ11, Δ12, and within area R421, the short path areas are represented as Δ41, Δ42.

[0078] Furthermore, it is preferable to use region R122 as the inspection area by excluding regions △11 and △12, which have predetermined short paths according to the above considerations, from region R121. Similarly, it is preferable to use region R422 as the inspection area by excluding regions △41 and △42, which have predetermined short paths according to the above considerations, from region R421. Figure 16(d) shows an example of regions R122 and R422. The arrangement of the linear irradiation area 11b and the receiving position 12a should be set in advance so that the defect to be detected passes through regions R122 and R422, and then the inspection should be performed.

[0079] The identification of the defect location is carried out according to the flowchart shown in Figure 9 above. Aperture synthesis can also be performed in the same manner as described in the first embodiment. This embodiment makes it possible to perform flaw detection only within a range where the reflected signal can be acquired stably with sufficient intensity, thereby preventing defects from being overlooked and enabling more accurate identification of the defect location.

[0080] [Fourth Embodiment] In the third embodiment, a fourth embodiment will be described in which, in order to perform a wide-area flaw detection using a precisely defined pair of flaw-detectable regions R122, R422, transmission and reception are performed at multiple locations along a direction perpendicular to the relative direction of movement. The same reference numerals are used for parts that are the same as in the first to third embodiments, and detailed descriptions are omitted.

[0081] In the case of only one pair of regions R122 and R422, as shown in Figure 16(d), there is an area near the transmitting / receiving point where flaw detection is not possible. Therefore, in this embodiment, multiple pairs of flaw-detectable regions R122 and R422 are arranged so that the flaw-detectable area of ​​another pair of regions R122 and R422 overlaps with the flaw-detectable area. This allows for flaw detection of the entire thickness W of the object S without any gaps. Specifically, as shown in Figure 17, the transmitting / receiving points are arranged so that regions R131 and R132, R132 and R133, and R133 and R134 have overlapping areas. Similarly, the transmitting / receiving points are arranged so that regions R431 and R432, R432 and R433, and R433 and R434 have overlapping areas. In Figure 17, reference numerals 11b-31, 11b-32, 11b-33, and 11b-34 indicate linear irradiation areas, and reference numerals 12a-31, 12a-32, 12a-33, and 12a-34 indicate receiving positions.

[0082] If the overlap area is large, the number of required transmitting and receiving locations increases, so it is preferable to keep the overlap area as small as possible. On the other hand, if the surface wave excited by the surface condition of the object becomes small due to the influence of the surface condition, the intensity of the reflected signal from a position far from the transmitting and receiving location will decrease, making it impossible to detect, which may cause missed detections near the overlap area. Therefore, a larger overlap area enables more stable flaw detection. The overlap area is determined considering the simplification of the equipment and the stability of flaw detection. The flaw detection method for the multiple transmitting and receiving units 10 can be performed in the same manner as in the second embodiment.

[0083] The embodiments of the invention made by the present inventors have been described above, but the present invention is not limited by the descriptions and drawings that constitute part of the disclosure of the present invention in this embodiment. For example, in this embodiment, the object S is moved and the transmitting / receiving unit 10 of the laser ultrasonic flaw detection device 1 is fixed, but the object S may be fixed and the transmitting / receiving unit 10 of the laser ultrasonic flaw detection device 1 may be moved. Alternatively, both the object S and the transmitting / receiving unit 10 of the laser ultrasonic flaw detection device 1 may be moved with a speed difference. In either case, it is sufficient that the transmitting / receiving unit 10 can irradiate the surface of the relatively moving object S with a laser. Furthermore, the laser ultrasonic flaw detection device according to the present invention may be applied to an inspection device for a continuous casting facility, and the laser ultrasonic flaw detection device according to the present invention may be used to inspect the surface layers such as the sides, surfaces, and corners of a steel billet continuously cast by a continuous casting facility. Furthermore, the laser ultrasonic flaw detection method according to the present invention may be applied to an inspection method for a continuously cast steel billet, and the laser ultrasonic flaw detection method according to the present invention may be used to inspect the surface layers such as the sides, surfaces, and corners of a steel billet continuously cast by a continuous casting facility. Based on the inspection results, quality control of steel billets can be performed by removing defects such as cracks. Furthermore, the laser ultrasonic testing method according to the present invention may be applied to an inspection step included in the manufacturing method of an object to inspect the surface layers such as the sides, front, and corners of the manufactured object. This allows for the manufacture of objects with a high yield. Moreover, the laser ultrasonic testing method according to the present invention may be applied to a quality control method for objects to inspect the surface layers such as the sides, front, and corners of the object to perform quality control. In the quality control method, based on the inspection results, it is determined whether the manufactured object meets predetermined standards, and the quality of the object is controlled. The "object" referred to here is a metal material that is prone to cracks, chips, and fissures during manufacturing. It is particularly suitable for steel. Thus, all other embodiments, examples, and operational techniques based on this embodiment by those skilled in the art are included in the scope of the present invention. [Explanation of Symbols]

[0084] 10 Transmitter / Receiver 11 Laser section 11a Point-shaped irradiation area Linear irradiation area 11b, 11b-11, 11b-12, 11b-13, 11b-31, 11b-32, 11b-33, 11b-34 12 Receiver Receiving location: 12a, 12a-11, 12a-12, 12a-13, 12a-31, 12a-32, 12a-33, 12a-34 20 Arithmetic section 21 Measurement Control Unit 22 Signal acquisition unit 23 Extraction part 24 Judgment section 30 Storage section 31 Signal storage section 32 Signal Processing Condition Storage Unit 40 Display section A1-A4, D Defect S Object RW reflected wave TW transmission wave

Claims

1. A transmitting and receiving unit that excites a surface wave by irradiating the surface of a relatively moving object with a laser, and receives multiple reflected waves of the surface wave over time, A calculation unit that uses the reflected waves received by the transmitting and receiving unit to detect defects on the surface of the object, Equipped with, The transmitting and receiving unit excites surface waves in two opposing directions by irradiating the object with a laser whose irradiation area has a linear shape, such that the longitudinal direction of the irradiation area is at an angle with respect to the direction of movement of the object. The aforementioned arithmetic unit, An extraction unit extracts signals with an intensity of a predetermined level or higher from the plurality of reflected waves as a plurality of defect signals, and uses the extracted plurality of defect signals to generate a flaw detection image showing the change in the intensity of the plurality of defect signals with respect to the reception time of the plurality of reflected waves and the movement time of the object. A determination unit that uses the aforementioned flaw detection image to determine whether the defect is in the region approaching or moving away from the laser irradiation position, A laser ultrasonic flaw detection device equipped with the following features.

2. The laser ultrasonic flaw detection apparatus according to claim 1, wherein the determination unit determines whether a defect is located in a region approaching or moving away from the laser irradiation position by performing aperture synthesis processing on the plurality of defect signals using two groups of delay times that emphasize defects present in each of the two directions.

3. A transmitting and receiving step in which a laser is irradiated onto the surface of a relatively moving object to excite a surface wave, and multiple reflected waves of the surface wave are received over time, A calculation step in which a defect on the surface of the object is detected using the reflected wave received in the transmission / reception step, Includes, The transmission and reception step involves irradiating the object with a laser whose irradiation area has a linear shape, such that the longitudinal direction of the irradiation area is at an angle with respect to the direction of movement of the object, thereby exciting surface waves in two directions opposite to each other. The calculation step is, Extraction step: Extract signals with an intensity of a predetermined level or higher from the plurality of reflected waves as a plurality of defect signals, and use the extracted plurality of defect signals to generate a flaw detection image showing the change in the intensity of the plurality of defect signals with respect to the reception time of the plurality of reflected waves and the movement time of the object, A determination step of using the aforementioned flaw detection image to determine whether the defect is in the region approaching or moving away from the laser irradiation position, Laser ultrasonic flaw detection method, including

4. A continuous casting apparatus for continuously casting steel billets, A laser ultrasonic flaw detection apparatus according to claim 1 or 2 for inspecting defects on the surface of a steel billet continuously cast by the continuous casting apparatus, A continuous casting facility equipped with the following features.

5. A continuous casting step for continuously casting steel billets, An inspection step for inspecting defects on the surface of a steel billet continuously cast in the continuous casting step, using the laser ultrasonic flaw detection method described in claim 3, A continuous casting method, including the following.

6. Manufacturing steps for producing an object, An inspection step of inspecting defects on the surface of an object manufactured in the manufacturing step using the laser ultrasonic flaw detection method described in claim 3, A method for manufacturing an object, including

7. An inspection step of inspecting defects on the surface of an object using the laser ultrasonic flaw detection method described in claim 3, A determination step, based on the inspection results of the inspection step, determines whether the object meets predetermined criteria, A method for quality control of objects, including the following.

Images