JPH0146027B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an ultrasonic flaw detection method for effectively detecting internal defects including subcutaneous defects on the surface of a square steel piece. (Prior art) Conventionally, an ultrasonic vertical flaw detection method has been applied to detect internal defects in square steel pieces.
As shown in the figure, the ultrasonic wave S emitted from the probe 1 to the square steel piece 2 produces a reflected echo S ₁ on the incident surface and a reflected echo B ₁ on the bottom surface, which has the drawback of creating a dead zone near the surface. Therefore, in order to eliminate the above-mentioned drawbacks, ultrasonic waves are transmitted from the outer circumferential surface of the square steel piece to the square steel piece by tilting it laterally with respect to the normal line of the surface, and the ultrasonic waves are received by the square steel piece adjacent to the ultrasonic incident surface. Detect internal defects near the subcutaneous part of the piece. A so-called oblique flaw detection method is known (see, for example, Japanese Patent Laid-Open No. 126761/1983). When using this angle flaw detection method, as shown in Fig. 12, the reflected echo from the incident surface of the ultrasonic wave S is
Although a considerable amount of S ₁ remains, since the reflected echo S ₂ from the side surface of the square steel piece 2 travels downward, a dead zone due to the reflected echo does not occur on the side surface. Therefore, by using the angle angle flaw detection method and setting the side surface adjacent to the entrance plane as the flaw detection area, it becomes possible to detect flaws from the surface to the inside of the square steel piece 2 without a dead zone. On the other hand, in order to perform online flaw detection over the entire length of a square steel piece, it is necessary to scan the ultrasonic beam at high speed. In this case, scanning methods can be roughly divided into mechanical scanning and electronic scanning.
The electronic scanning method is far more advantageous in terms of high-speed scanning, directivity, defect position estimation accuracy, etc. Even in the case of electronic scanning, there are further electronic linear scanning and electronic sector scanning (for example,
(See JP-A-52-84884 and JP-A-53-140879). The probe used for the electronic scanning is called an electronic scanning array type probe, and as shown in FIG.
It is constructed by arranging a large number of transducer elements 3 in a line on the plane of a base 4, and applying a coating 5 to the surface thereof. The ultrasonic beam from the probe is controlled by adjusting the timing of wave transmission and reception of each element 3 using a delay time control circuit. For example, if the delay time is not set as shown in Figure 14,
The ultrasonic beam S forms a wavefront equivalent to the wavefront from a single large-diameter transducer, but if this delay time is set appropriately, the beam S can be tilted as shown in Figure 14a, or It is possible to freely form a wavefront that narrows the beam S as shown in b, or narrows and tilts the beam S as shown in FIG. 14c. The characteristics of electronic linear or sector scanning, in which such a probe is electronically scanned and the ultrasonic beam is translated or swung onto the incident surface, are summarized as follows. (i) High-speed scanning ability High-speed scanning is easier than mechanical scanning. (ii) Sharp directivity Since an electronic scanning probe operates many transducer elements simultaneously, it has sharp directivity, which is the same as a large-diameter transducer as a whole. (iii) Electron focusing As mentioned above, electronic scanning probes can be used for flaw detection by narrowing the beam and increasing resolution, similar to concave vibrators and lensed vibrators, by giving a predetermined delay time to the transmitted and received signals. enable. Since this focal length can be set arbitrarily, by converging the beam on the flaw detection area in the material, the accuracy of detecting minute defects can be improved, and at the same time, the accuracy of estimating the defect position is also improved. For reference, Fig. 15 shows the relationship between the ultrasonic beam diameter during flaw detection of a square steel piece and the S/N for a φ2 horizontal hole. (iv) Since the ultrasonic beam can be scanned with the probe fixed, a wide flaw detection area can be obtained with one probe. Next, a case where electronic linear scanning is performed using an electronically scanned array type probe having such characteristics and a case where electronic sector scanning is performed will be compared and explained. First, in the case of electronic linear scanning, the probe 1
18a, b, c.
As shown in FIG. 2, while the ultrasonic beam S is moved parallel to the incident surface, the surface layer side of the adjacent side surface is detected for flaws. An example of the scanning circuit required in this case is as shown in FIG. That is, for example, if a linear array probe with a total number of elements of 64 is set as one set of 16 elements,
The probe 1 and the transceiver 6 are connected to the delay circuit 7 described above.
In addition, connect via reed relay circuit 8, shift the transmitting and receiving elements sequentially with a changeover switch,
It scans the ultrasound beam. On the other hand, in the case of electronic sector scanning, the probe 1 is also set in a predetermined state and the probes shown in FIG.
As shown in b and c, the ultrasonic beam S is swung toward the incident surface and the surface layer side of the lower half of the adjacent side surface is detected for flaws. An example of the scanning circuit required in this case is shown in FIG. That is, for example, the total number of divided elements is 32
By connecting the probes 1 and the transmitter/receiver 6 in a one-to-one correspondence via a delay circuit 7, and sequentially changing the delay time setting of the delay circuit 7, the inclination angle of the ultrasonic beam can be adjusted. This is done by changing the beam and scanning by swinging the beam. (Problems to be Solved by the Invention) The electronic linear scanning has the following drawbacks. (i) Since the transmitting and receiving elements are sequentially shifted, the total number of elements increases and the overall transducer diameter increases. (ii) A large number of relays are required for switching, and the lifespan of these relays is short. (iii) Since the transmitter/receiver elements are sequentially shifted, there is no one-to-one correspondence between the transmitter/receiver (T/R unit) and the element, making it difficult to adjust sensitivity variations. (iv) Since the amount of movement of the incident point of the ultrasonic beam is large, the refraction angle changes due to the influence of the surface unevenness of the square steel piece, and the defect position estimation accuracy deteriorates. On the other hand, in the case of electronic sector scanning, as shown in FIG. 16, there is a problem in that by swinging the ultrasonic beam S, the point of incidence on the incident surface of the square steel piece 2 is shifted. That is, in both electronic linear scanning and electronic sector scanning, there is a problem in that the point of incidence on the incident surface of the rectangular steel piece shifts, resulting in variations in detection accuracy due to unevenness on the incident surface. . In other words, if the incident surface is uniform and flat over the entire surface, detection accuracy will not be affected even if the incident point moves sequentially, but in the case of a square piece of steel, the condition of the surface may vary between the center and both sides. There was a problem in that it was not possible to detect flaws with the same accuracy over the entire surface unless the accuracy was corrected depending on the position of the incident point because of the difference in the degree of unevenness and unevenness (flatness). SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a flaw detection method for a rectangular steel piece that can perform highly accurate detection regardless of the state of the entrance surface. (Means for Solving the Problems) In order to achieve the above object, the present invention takes the following measures. That is, the present invention is characterized by a longitudinal wave angle flaw detection method using an electronically scanned array type probe, in which the probe is moved from the surface of a square steel piece in a plane perpendicular to the axial direction of the piece. By setting the probe at a predetermined distance and at a predetermined angle with respect to the material surface, and scanning the probe using a combination of electronic sector scanning and electronic linear scanning, the incident point on the material surface is made approximately constant. The purpose of this method is to detect flaws in the interior of the square steel piece and the surface layer on the side surface adjacent to the entrance surface. (Function) The basic principle of the present invention is to detect the inside of a square steel piece and the side surface adjacent to the incident surface by this longitudinal wave oblique angle flaw detection method. Therefore, the use of longitudinal waves for ultrasonic waves and the flaw detection area by longitudinal wave oblique angle flaw detection will be explained. First, the reason for using longitudinal waves is as follows. In other words, when a transverse wave is used in the oblique flaw detection method, the second
As can be seen from the figure, the reciprocating pass rate is small when the refraction angle is 34° or less, and when detecting flaws in the refraction angle range of 30° to 40°, due to slight errors in the shape of the entrance surface and the setting of the incidence angle. It is possible that the round-trip passage rate changes dramatically, and that if a refraction angle in the range of 50° to 65° is used, where the round-trip passage rate does not fluctuate much, the lower part of the side surface adjacent to the entrance surface, which is the geometrical flaw detection area, cannot be detected. There are drawbacks. On the other hand, when longitudinal waves are used, there is an advantage that fluctuations in the round-trip pass rate due to changes in the refraction angle are relatively small and continuous, and longitudinal waves are introduced from this point. Next, we will explain the effective detection area when sector scanning is performed using the longitudinal wave oblique angle flaw detection method.As the refraction angle increases, it will be affected by transverse waves (see Figure 2), and the reception of side reflection echoes will Since the S/N ratio near the side surface decreases, the refraction angle is limited to a maximum of about 50°. That is, the flaw detection area is limited to the surface layer side of the lower half of the side surface of the square steel piece 2, as shown in FIG. Next, a method for setting the probe will be explained. In an electronically scanned array type probe, the transducer element spacing d required to prevent the generation of grating ropes is d<λ/1+1sinθ, where the maximum inclination angle of the ultrasound beam S is ± _θ0 . ₀ 1 λ: Expressed by the wavelength in the ultrasonic propagation medium. Therefore, in order to increase the inclination angle of the ultrasonic beam S, the element spacing d must be decreased when λ is constant (Fig. 4a,
(b shows the relationship between element width and maximum beam inclination angle θ ₀ ). That is, the element width needs to be made small. The following two methods for setting the probe can be proposed using this characteristic. (i) One method is to position the probe at a predetermined distance from the surface of the square steel piece in a plane perpendicular to the axial direction of the piece, and set the probe horizontally to the plane of incidence.
However, in this case, the width of each element of the probe is made smaller and the number of divisions is increased. A feature of this set method is that since the maximum beam inclination angle is large, it is possible to detect flaws on both sides adjacent to the entrance surface. (ii) The other method is to place the probe at a predetermined distance from the surface of the square steel piece in a plane perpendicular to the axis of the piece, and place the probe at the center of incidence for sector scanning with respect to the incidence plane. This is a method of setting it by tilting it by an angle. The feature of this setting method is that the absolute value of the beam inclination angle becomes small, so
The maximum delay time can be small. Also, since the absolute value of the beam inclination angle becomes smaller,
The number of element divisions of the probe may be large. Next, scanning by combining electronic linear scanning with electronic sector scanning will be explained. In the case of only electronic sector scanning, as shown in FIG. 1, by swinging the ultrasonic beam S, the point of incidence on the incident surface of the square steel piece 2 is shifted. Therefore, in the present invention, linear scanning is combined with sector scanning. As shown in FIG. Therefore, the defect position estimation accuracy can be improved. (Example) Hereinafter, an example of the present invention will be described. 5 and 6 show the arrangement of the probe 1 with respect to the square steel piece 2. FIG. First, in the case of the example shown in FIG. 5, one probe 1 is arranged parallel to each surface of the square steel piece 2. That is, one probe 1 detects flaws in the lower half of both sides of the rectangular steel piece 2 adjacent to the entrance plane as shown in the figure, and four probes 1 detect the entire surface layer of the rectangular steel piece 2. It is. On the other hand, in the case of the example shown in FIG. 6, two probes 1 are arranged at a predetermined angle to each surface of the square steel piece 2. That is, in this case, one probe 1 is used to detect the lower half of one side of the square steel piece 2 adjacent to the entrance plane as shown in the figure, and a total of eight probes 1 are used to detect the entire length surface layer of the square steel piece 2. It is used to detect flaws. In either arrangement, high-speed flaw detection can be performed online over the entire surface layer of a square steel piece. Then, by scanning the probe 1 with a combination of electronic sector scanning and electronic linear scanning, the incident point on the material surface is determined as shown in Fig. 1 a, b, and c.
As shown in the figure, the flaws are detected at a constant temperature. By keeping the incident point approximately constant, the angle of refraction becomes constant without being affected by the surface unevenness of the square steel piece 1.
Defect position estimation accuracy is made uniform over the entire surface. Next, a process for identifying surface defects in square steel pieces will be explained. According to the above-described angle flaw detection method using electronic linear scanning of the present invention, internal defects including surface subcutaneous flaws can be detected with high precision over the entire surface of a target square steel piece at high speed. By the way, when the surface layer of a square steel piece is flaw-detected, not only surface subcutaneous defects but also surface flaws are detected at the same time, and the flaw detection results also include information detected by surface flaw detection. However, surface defects can be removed by chipping or grinding in the billet processing process, and do not pose a problem during secondary processing of the product. Therefore, internal defects that do not include surface defects (of course, surface defects It is necessary to detect only subcutaneous defects (including subcutaneous defects). Therefore, in order to detect internal defects, it is sufficient to subtract the results of surface defect detection from the results of ultrasonic angle inspection from the inside of the square steel piece described above. The table below shows each surface defect detection method along with its detection ability.

[Table] As can be seen from the fact that the detection ability of surface defects varies depending on the surface defect detection method, the detection characteristics of internal defects are determined depending on which surface defect detection method is used in combination. As an information processing method for surface defect discrimination, basically information 2 can be subtracted from information 1 as shown in Fig. 7, but ultrasonic angle flaw detection can eliminate the factors that reduce defect position estimation accuracy. Because it contains a lot of
Information 1 is less reliable than the defect position information (information 2) from surface defect detection and has a larger defect position estimation error range. Therefore, when information 1 and information 2 are obtained for a surface defect as shown in Figure 8, assuming that the defect is located at the mark in the figure as defect position information, if these pieces of information are processed as they are, they will be separated into is determined to be a defect, and information 1 is left as internal defect information. In other words, it is considered an internally defective material even though it does not have any internal defects. To prevent this, information 2 is provided with a certain area, and information 1 that falls within that area is canceled, thereby preventing surface defects from being erroneously detected as internal defects. The extent of the area to be given to information 2 here depends on the accuracy of information 1, but this accuracy depends on the ultrasonic beam diameter (the thinner the better, that is, the narrowed state), the shape of the incident surface (if there are irregularities on the incident surface) This is largely due to the fact that the apparent angle of refraction changes, so the smaller the variation in the incident point and the flatter the plane of incidence, the better. ) is advantageous. Therefore, when performing oblique flaw detection using electronic sector + linear scanning, the following two methods can be used in combination to further improve defect position estimation accuracy. One method is to make the ultrasonic waves enter from the center of the surface, where the influence of irregularities on the incident surface is considered to be the least. In other words, by doing this, even if the surface of the square steel piece 2 has irregularities as shown in FIGS. 9a and 9b, it can be approximated to be substantially flat at the center of the surface. Another method is to change the apparent angle of refraction (S ₀ →
In order to correct S), the echoes from the corners are detected and the angle of incidence indicating the maximum value thereof is determined. Then, the slope of the incident surface is calculated from that value, and the incident angle is corrected so that the beam enters the desired flaw detection area. It goes without saying that flaw detection may be performed with either the square steel piece or the detection part moved. (Effects of the Invention) According to the present invention, by scanning a combination of electronic sector scanning and linear scanning, the incident point on the surface of the square steel piece is kept approximately constant, so the influence of unevenness existing on the incident surface is eliminated. Therefore, the defect position can be detected with high accuracy.

[Brief explanation of drawings]

FIGS. 1A, 1B, and 1C are diagrams showing a comparison between electronic sector scanning and electronic sector+linear scanning. FIG. 2 is a diagram showing changes in the round-trip passage rate of longitudinal waves and transverse waves depending on the incident angle. FIG. 3 is a diagram showing a flaw detection area by longitudinal wave angle flaw detection according to the present invention. FIG. 4 is a diagram showing the relationship between the transducer element width and the maximum beam inclination angle of an electronic scanning probe. FIG. 5 and FIG. 6 are diagrams showing the arrangement of the probe with respect to the square steel piece. FIG. 7 is a diagram showing information processing and detection patterns for surface defect discrimination. FIG. 8 is a diagram conceptually showing a process for increasing the reliability of defect position estimation information based on the relationship between defect position information obtained by ultrasonic angle flaw detection and defect position information obtained by surface flaw detection. FIGS. 9a and 9b are diagrams showing the relationship between the influence of irregularities on the incident surface and the incident position of the ultrasonic beam. FIG. 10 is a diagram showing changes in the apparent angle of refraction due to the inclination of the incident surface. FIG. 11 is a diagram showing a dead zone according to the conventional vertical flaw detection method. FIG. 12 is a diagram showing a dead zone obtained by the oblique flaw detection method according to the present invention. FIG. 13 is a diagram showing the general structure of an electronically scanned array type probe. Figure 14 shows a,
b and c are diagrams showing how an ultrasonic beam is controlled by an electronically scanned array probe. FIG. 15 is a diagram showing the relationship between the ultrasonic beam diameter and the S/N for a φ2 horizontal hole during flaw detection of a square steel piece. Figure 16 a, b,
c is a diagram conceptually showing how electronic sector scanning is performed on a rectangular steel piece. FIG. 17 is a diagram showing an example of a circuit configuration for performing electronic linear scanning. 1st
8a, b, and c are diagrams conceptually showing the state of electronic linear scanning on a square steel piece. FIG. 19 is a diagram showing an example of a circuit configuration for performing electronic sector scanning. 1...Probe, 2...Square steel piece, S...Ultrasonic beam.

Claims (1)

[Claims] 1 Longitudinal wave angle flaw detection method using an electronically scanned array type probe, in which the probe is placed at a predetermined distance from the material surface in a plane perpendicular to the axial direction of a square steel piece, and also on the material surface. By setting the probe at a predetermined angle to the rectangular steel piece and scanning the probe by combining electronic sector scanning and electronic linear scanning, the incident point on the material surface is kept approximately constant, and the inside of the rectangular steel piece and the incident surface are A flaw detection method for square steel pieces using a combination of electronic sector and electronic linear scanning, which is characterized by detecting flaws on the surface layer of adjacent side surfaces.