JPS59116541A - Method for detecting flaw of square steel piece by using both electronic sector scanning and electronic linear scanning - Google Patents

Abstract

PURPOSE:To make it possible to detect flaws on the entire surface layer of a square steel piece at a high speed on line without no flaw scanning area, by using an electronic scanning array type probe, performing longitudinal wave flaw detection at a slant angle, inputting an ultrasonic wave beam at the central part of the incident surface, and performing both electronic sector scanning and electronic linear scanning. CONSTITUTION:In an electronic scanning array type probe, many vibrating elements 3 are aligned on a plane of a substrate 4. A coating 5 is applied on the surface thereof. The control of an ultrasonic wave beam is performed by adjusting the timing of the sent and received waves of each element 3 by a delay time control circuit. When electronic linear scanning is performed, the probe 1 is set at a specified state, the beam S is moved on the incident surface in parallel, and the side of the surface layer of the neighboring side surface is scanned for flaws. Meanwhile, when electronic sector scanning is performed, the probe is set at the specified state, the ultrasonic wave beam S is swung with respect to the incident angle, and the side of the surface layer of the lower half of the neighboring side surface is scanned for flaws. By combining those operations, both the electronic sector scanning and the electronic linear scanning are performed.

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to enable flaw detection related to an ultrasonic flaw detection method for effectively detecting internal defects including subsurface defects of a square steel piece.

In recent years, in the secondary processing stage of wire rods and steel bars, process omissions have been promoted with the aim of saving labor, energy, and reducing costs.
, processing conditions for wire rods and steel bars are becoming increasingly severe. As a result, processing cracks during cold forging and wire breakage during wire drawing due to minute inclusions existing inside wire rods and steel bars have become a problem, and as a countermeasure, removal of inclusions during the ironmaking and steelmaking stages has become a problem. In addition to out-of-furnace refining technology to prevent contamination, the establishment of inspection technology to detect the presence or absence of fine inclusions has become essential from the perspective of quality assurance.

As an inspection technique for this purpose, an ultrasonic flaw detection method is known for steel bar products, in which the bar is rotated or a probe is rotated around the bar while a focused ultrasonic beam is directed into the material. Similar flaw detection methods cannot be applied to wire products due to their small diameters, and it is currently impossible to perform flaw detection with equipment over the entire circumference and length of the final coiled product.

Incidentally, the problematic inclusions in wire rods and steel bars are present from the material stage, so detecting inclusions at the stage of rectangular steel pieces guarantees the internal quality of the product. In the case of wire rods, ultrasonic flaw detection inside square steel pieces is used as a substitute for flaw detection inside the product. By introducing internal flaw detection into this intermediate process, defective pieces of steel can be removed in advance, and compared to flaw detection at the product stage, the length of the tested material is shorter and the flaw detection process is more efficient. However, in order to ensure its reliability, it is required to exhibit high detection accuracy even for minute inclusions.

Conventionally, as an ultrasonic flaw detection method for square steel pieces, a vertical flaw detection method using a two-piece probe is known.

However, this method has a major problem in that, although defects existing inside can be detected, defects existing beneath the surface of the square steel slab cannot be detected. In other words, when actually processing square steel pieces into products, inclusions that cause problems such as processing cracks are often present under the surface skin, and it is highly desirable to establish a flaw detection method that detects internal defects including under the surface skin. This is because

In view of these technical issues, the present invention has developed a new ultrasonic flaw detection method that can effectively detect internal defects, including subsurface defects, in square steel pieces. It is made of square steel pieces.

In summary, the ultrasonic flaw detection method according to the present invention is constructed by combining the following technical means.

a. Performing longitudinal wave angle flaw detection on a square steel piece using an electronically scanned array probe.

b. The probe shall be fixed at a predetermined angle to the material surface at a position a predetermined distance from the material surface within a plane perpendicular to the axial direction of the square steel piece.

By inputting the C0 ultrasonic beam from the center of the incident surface and scanning the electron sector + linearly, 1, (D, ”
Detect flaws on the surface layer of the side surface.

The flaw detection means according to the present invention described above will be explained in detail below.

First, the introduction of the angle angle flaw detection method in the present invention will be explained.

Conventionally, as mentioned above, the ultrasonic vertical flaw detection method has been applied to detect internal defects in square steel slabs.In this case, as shown in Figure 1, the square steel slab (2 ) The ultrasonic wave (S) emitted at the surface produces a reflected echo (Sl) at the incident surface and a reflected echo (Bl) at the bottom surface, resulting in a dead zone near the surface. On the other hand, when using the angle angle flaw detection method, as shown in Fig. 2, the reflected echo (Sl) from the incident surface of the ultrasonic wave (S) remains considerably, but the square steel piece (2
) from the side surface (C2) travels downward, so no dead zone is caused by the reflected echoes on the side surface. Therefore, the basic principle is to use the oblique angle flaw detection method, and by setting the side surface adjacent to the entrance surface as the flaw detection area, there is no dead zone from the surface to the inside of the square steel piece (2).

Next, 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 angle flaw detection method, as can be seen from Figure 8, the round-trip passage rate is small at a refraction angle of 84° or less.
When detecting flaws in the refraction angle range of 80° to 40°, the round-trip pass rate changes drastically due to slight errors in the shape of the entrance surface and the settings of the incident angle. When using a range of 100°, there is a disadvantage that the lower part of the side surface adjacent to the entrance surface, which is the geometrically defect detection area, cannot be detected. 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.

To explain the effective detection area when sector scanning is performed using the longitudinal wave oblique angle flaw detection method, the larger the refraction angle, the more influenced by transverse waves (see Figure 8), and the fact that the reception of side reflection echoes Since the S/N near the side surfaces decreases, the refraction angle is limited to a maximum.

In order to perform online flaw detection over the entire length of the target square steel piece using the above-mentioned angle angle flaw detection method, the ultrasonic beam must be scanned at high speed. in this case,
Scanning methods can be roughly divided into mechanical scanning and electronic scanning, but as will be explained later, the latter 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, electronic linear scanning and electronic sector scanning are further compared.

Therefore, the principle of electronic scanning is outlined below.

First, the electronic scanning array type probe, as shown in Figure 5,
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 each element (
3) is performed by adjusting the timing of wave transmission and reception using a delay time control circuit. For example, if the delay time is not set as shown in FIG. 6(I), the ultrasonic beam S forms a wavefront equivalent to the wavefront from a single large-diameter transducer. When set to , Figure 6 (n
It is possible to freely form a wavefront that tilts the beam S as shown in a), constricts it as shown in FIG. 6 (IIb), or constricts and tilts the beam S as shown in FIG. 6 (IIC).

The characteristics of electronic linear or sector scanning, in which such a probe is electronically scanned and the ultrasonic beam is translated or swung on the incident surface, can be summarized as follows.

(1) High-speed scanning performance High-speed scanning is easier than mechanical scanning.

(i) Sharp Directivity Since an electronic scanning probe operates a large number of transducer elements simultaneously, the probe as a whole is the same as a large-diameter transducer and has sharp directivity.

(1) As mentioned above, the electron focusing electronic scanning probe is a flaw detection method that narrows the beam and increases 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, the accuracy of detecting minute defects can be improved by focusing the beam on the flaw detection area in the material, and at the same time, the accuracy of estimating the defect position can also be improved. For reference, the ultrasonic beam diameter during flaw detection of a square steel piece and the S/H for the 02 horizontal hole.
The relationship is shown in Figure 7.

叡) 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, set the probe (1) in a predetermined state, and then
This is a good thing as shown in An example of the scanning circuit required in this case is shown in FIG. That is, for example, if a linear array probe with a total number of 64 elements is set as one set of 16 elements, the probe (1) and the transmitter/receiver (6
) are connected via a reed relay circuit (8) in addition to the delay circuit (7) mentioned above, and the transmitting and receiving elements are sequentially shifted using a changeover switch to scan the ultrasonic beam.

On the other hand, in the case of electronic sector scanning, the probe (1
) in the predetermined state, and as shown in Figure 10 (a), (b)
C) It is something that will cause damage. An example of the scanning circuit required in this case is shown in FIG. That is,
For example, a probe (1) with a total of 82 divided elements and a transmitter/receiver (6) are connected in a one-to-one correspondence via a delay circuit (7), and the delay time is set by the delay circuit (7). By sequentially changing the angle of inclination of the ultrasonic beam, scanning is performed by swinging the beam.

Therefore, the present invention is characterized by performing electronic sector + linear scanning, which is a combination of electronic sector and electronic linear scanning, for the following reasons.

Comparing the above-mentioned electronic linear scanning and electronic sector scanning, the latter can be said to be advantageous in that the following disadvantages mentioned above are overcome.

(1) In the case of electronic linear scanning, since the transmitting and receiving elements are sequentially shifted, the total number of elements increases and the transducer diameter increases as a whole.

(li) A large number of relays are required for switching, and the lifespan of these relays is short.

Transmitter/receiver (T)
/RUnit) and elements do not have a one-to-one correspondence, making it difficult to adjust sensitivity variations.

(IV) Because the amount of movement of the incident point of the ultrasonic beam is large,
The refraction angle changes due to the surface irregularities of the square steel piece, and the accuracy of defect position estimation deteriorates.

However, on the other hand, in the case of electronic sector scanning, as shown in Fig. 12 (CI), there is a problem in that by swinging the ultrasonic beam S, the incident point on the incident surface of the square steel piece (2) is shifted. .

Therefore, in order to solve the above-mentioned problems with electronic sector scanning, we have combined linear scanning.
As shown in Figure 2 [IIaXIIbXIIC], the transmitter/receiver element is shifted according to each beam inclination angle, thereby minimizing the deviation of the incident point, making it less susceptible to the influence of the incident surface than in electronic sector scanning. Adopt a scanning method that improves defect position estimation accuracy.

Next, a probe setting method for performing electronic sector + linear scanning having such characteristics will be explained.

In an electronically scanned array type probe, the transducer element spacing required to prevent the generation of grating lobes is aH1.If the maximum inclination angle of the ultrasound beam (B) is ±θ0, λ: Ultrasonic propagation It is expressed by the wavelength in the 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. 18(a) (1)).
element width and maximum beam inclination angle θ. ). That is, the element width needs to be made small.

The following two methods for setting the probe can be proposed using this characteristic.

(1) 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. The feature of the 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.

(it) 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 axial direction 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. A feature of this set method is that since the absolute value of the beam inclination angle becomes small, the maximum delay time can be shortened. Furthermore, since the absolute value of the beam inclination angle becomes small, the number of element divisions of the probe may be large.

Figures 14 and 15 show the probe (1) for the square steel piece (2).
) is shown below. First, in the case of the example shown in FIG. 14, one probe (1) is arranged parallel to each surface of a square steel piece (2). That is, one probe (1)
As shown in the figure, the lower half of both sides of the square steel piece (2) adjacent to the entrance surface is detected for flaws, and the entire surface layer of the square steel piece (2) is detected using four probes (1). . On the other hand, in the case of the example shown in FIG. 15, 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. The entire length of the rectangular steel slab is inspected for flaws. In either arrangement, high-speed flaw detection can be performed online over the entire surface layer of the steel piece.

Next, a process for identifying surface defects in square steel pieces will be described. According to the above-mentioned oblique flaw detection method using electronic linear scanning of the invention, internal defects including surface skin defects can be detected at high speed and accurately over the entire surface of a target square steel piece. By the way, when the surface layer of a square steel phase 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 the 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 subcutaneous defects) It is necessary to detect only the

Therefore, in order to detect internal defects, it is sufficient to subtract q the result of the surface defect detection from the result of the 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.

As can be seen from the fact that the surface defect detection ability varies depending on the surface defect detection method, the internal defect detection characteristics are determined by 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. 16, but ultrasonic angle flaw detection can eliminate the factors that reduce defect position estimation accuracy. Since the information 1 contains a large amount of information, it has lower reliability than the defect position information (information 2) from surface defect detection, and the error range for estimating the defect position is wide. Therefore, for a surface defect as shown in Figure 17, if information 1 and information 2 are obtained as defect position information indicating that the defect is located at the position of the mark in the figure, if these pieces of information are processed as they are, they will be separated into is determined to be a defect, and Kiyose 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.

In order to prevent this, information 2 is provided with a certain area, and information 1 that falls within that area is canceled to prevent surface defects from being erroneously detected as internal defects. Information 2 here
This accuracy depends on the accuracy of the information 1, but the accuracy depends on the ultrasonic beam diameter (the thinner the better, i.e., the narrowed state), the shape of the incident surface (if the incident surface is uneven, the apparent cloth angle will be affected). This is largely due to the fact that the incidence point changes less and the plane of incidence is better).In this respect, electronic sector scanning and (electronic sector + linear scanning) are advantageous compared to electronic linear scanning. be.

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 inject the ultrasonic waves from the center of the blood, where the influence of irregularities on the incident surface is thought to be least.

In other words, by doing this, even if the surface of the square steel piece (2) is uneven, as shown in FIG.

Another method is to detect the echo from a part of the corner and calculate its maximum value in order to correct the apparent change in the angle of refraction (So-S) due to the inclination of the incident surface, as shown in Figure 19. The purpose is to find the angle of incidence shown. Then, the slope of the incident plane is calculated from that value.As mentioned above, according to the ultrasonic flaw detection method of the present invention, flaw detection is possible in a certain area from the surface of the steel piece, whereas with the conventional internal flaw detection method, flaw detection is impossible. , it is possible to perform high-speed online flaw detection on the entire surface layer of a square billet without leaving any undetected areas, and it is possible to quickly and accurately detect flaws over the entire length of the surface layer of a square billet, as well as subcutaneously and inside the surface of steel bars and wire rods as products. can provide quality assurance.

Furthermore, since the present invention performs scanning in combination with electronic sector scanning and linear scanning, it has a feature that the defect position estimation accuracy is particularly improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a dead zone according to a conventional vertical flaw detection method. FIG. 2 is a diagram showing a dead zone obtained by the oblique flaw detection method according to the present invention. FIG. 8 is a diagram showing changes in the round-trip passage rate of longitudinal waves and transverse waves depending on the incident angle. FIG. 4 is a diagram showing a flaw detection area by longitudinal wave oblique flaw detection according to the present invention. FIG. 5 is a diagram showing the general structure of an electronically scanned array type probe. Figure 6 CI, l), CIIa) (I
Ib) CUc) is a diagram showing how an ultrasound beam is controlled by an electronically scanned array probe. Figure 7 shows the ultrasonic beam diameter and S/N for 02 horizontal hole during flaw detection of square steel pieces.
FIG. Figure 8 (a) (b) (c)
1 is a diagram conceptually showing how electronic linear scanning is performed on a square piece of steel. FIG. 9 is a diagram showing an example of a circuit configuration for performing electronic linear scanning. Figure 10 (a,) (b) (
C) is a diagram conceptually showing how electronic sector scanning is performed on a square piece of steel. FIG. 11 is a diagram showing an example of a circuit configuration for performing electronic sector scanning. Figure 12 CI), C
IIaXIIbXIIc] is a diagram showing a comparison between electronic sector scanning and electronic sector+linear scanning. 1st
FIG. 8 is a diagram showing the relationship between the transducer element width and the maximum beam inclination angle of an electronic scanning probe. FIG. 14 and FIG. 15 are diagrams showing an example of how the probe is arranged with respect to a square steel piece. FIG. 16 is a diagram showing information processing and detection patterns for surface defect discrimination. FIG. 17 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. 18(a) and 18(b) are diagrams showing the relationship between the influence of irregularities on the incident surface and the incident position of the ultrasonic beam. FIG. 19 is a diagram showing changes in the apparent angle of refraction due to the inclination of the incident surface. (1)...Probe, (2)...Square steel piece, S...Ultrasonic beam. Patent applicant: Kobe Steel, Ltd. S Figure 9, Figure 16I''yI

Claims (1)

[Claims] 1. A longitudinal wave angle flaw detection method using an electronic scanning 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 at a predetermined distance from the material surface. 1. A surface flaw detection method for a square steel piece using a combination of electronic sector and electronic linear scanning, characterized in that the probe is set at a predetermined angle to