JPH02210257A - Method for detecting surface layer flaw of square steel billet - Google Patents

Abstract

PURPOSE:To securely find the position of a defect by setting a flaw detection area by a vertical method from the surface layer area of the square steel billet whose defect is to be detected and further setting a flaw detection area by an oblique method. CONSTITUTION:An internal defect in the surface area T(ABCD) within a range of specific depth from the surface of the square steel billet 2 is detected by ultrasonic flaw detection. For the purpose, ultrasonic probes S1 - S3, S5, and S6 are arranged outside an area-side surface 2a facing the area T and outside both flanks 2b and 2c of the steel billet 2 adjoining the end part of the area T only in a flaw detection angle area to detect the internal defect by the straight method or oblique method. Here, it is estimated that defects which are not detected by the probes S1 - S3 and detected by the probes S5 and S6 are in the area T and defects detected by the probes S1 - S3 are all inside the area T.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an ultrasonic flaw detection method, and more particularly to a method for detecting surface defects in a square steel billet, which makes it possible to easily detect surface defects in a square steel billet.

[Conventional technology]

The square steel pieces are further processed to make them into products, but
If there are minute inclusions inside this square steel piece, processing cracks or wire breaks often occur during the secondary processing stage due to the presence of the inclusions. As a measure to prevent the occurrence of such defects, it is necessary to establish inspection technology to detect the presence of minute inclusions, as well as extra-furnace semen technology to remove inclusions and prevent inclusions from entering the ironmaking and steelmaking stages. It is essential. By the way, inclusions that have a negative effect on materials such as square steel slabs are present from the material stage, so if these inclusions can be detected at the stage of the material before secondary processing, it will be possible to improve the quality of the product after secondary processing. It becomes possible to guarantee internal quality.

However, detection of internal defects (hereinafter referred to as defects) in square steel slabs, which is a material such as this, has conventionally been carried out by ultrasonic flaw detection, but these inclusions are detected in Table I of square steel slabs.
Since they often occur in the O region, it is difficult to reliably detect defects based on these inclusions living in this back area using the vertical method. If there is a defect in the vicinity of the surface on which the surface (abbreviated as ``)'' is placed or the surface opposite to that surface, there will be a reflected echo, which is the reflected ultrasonic wave reflected by these surfaces, and a reflected ultrasonic wave reflected by this defect. The reason is that it is difficult to determine whether the detected echoes are reflected by the surface or by the defect due to the proximity of the defective echoes. The so-called bevel method, in which a probe is arranged at an angle with respect to the surface of a square steel piece, has been introduced.

As such an oblique angle method using ultrasonic waves, a technique disclosed in Jikai Publication No. 129852 of 1983 is well known.

The bevel method, which uses this ultrasonic wave to detect defects in each steel piece, is shown in Figure 2, which is an explanatory diagram of the probe arrangement in the ultrasonic bevel method.
To explain this based on Figure 3 (A), which is an explanatory diagram of its action, and Figure 3 (B), which is an explanatory diagram of the echo situation, as shown in Figure 2, 4 probes (S,
), (S, (Sl), (S4) are perpendicular to the center position in the width direction of the square steel piece (2), and as they are further away from the center of the width direction of the square steel piece (2) Said square steel piece (2
) is arranged so as to be inclined with respect to the upper surface.

Therefore, these probes (S,), (S2), (S,),
The position of the defect is evaluated by emitting ultrasonic waves from (S4) toward the bottom side of the square steel piece (2) and detecting the reflected ultrasonic waves, so-called echoes, which are reflected back.
Among the echoes detected in this way, in addition to defective echoes, there are transmission echoes that are emitted from the transmitter and reflected back, and top surface echoes (T[ ) and bottom echoes reflected from the bottom surface, it is necessary to determine the cause of the echo based on the time difference at the time of detection and evaluate the internal defect.

In other words, as shown in Figure 3 (a) and (b),
When there are defects F, , F inside the square steel piece (2),
Defect echoes CP+), (Pg) reflected by these defects F, , F, will be detected, but these defects Fl, F! The position of is evaluated as follows.

That is, the time from when the surface echo (TI) reflected on the upper surface of this square steel piece (2) is detected until the defect echo (p+), <pg) reflected by the defects Fl and Ft is detected. Then, the distance 2 from the top surface of this square steel piece (2) to this defect is determined by the following formula: 1 = (1/2) ・C・LF.

In addition, in the above formula, C written in English is a square steel piece (
2) Shows the sound speed of ultrasound propagating inside.

However, for example, if these defects F+1Fg and Fg are located at the same distance from the probe (S,), the ultrasonic beam emitted from the probe (S4) may penetrate inside the square steel piece (2). If the refraction angle at the time of incidence is θ and the distance from the side surface of the square steel piece (2) to the ultrasonic beam incident position is D, then the depth d from this side surface to these defects F6 and F8 is calculated by the following formula, d -D-(1/2) = Muy-C-srn θ
There was a problem in that the depth d from this side surface to the defect position could not be determined.

These problems arise from the fact that the number of channels of the probe can be arranged in a practical manner only about 2 to 4, and an ultrasonic beam with a wide directivity angle must be used.

Therefore, in order to improve the above-mentioned drawbacks, Japanese Patent Application Laid-Open No. 59-11 (3541), which was filed by the present applicant, was developed.
This is the technology disclosed in the publication.

An example of this bevel method is explained with reference to FIG. 4, which is an explanatory diagram of the probe arrangement in the ultrasonic bevel method. An array type probe (S+) is tilted on the upper surface side of a square steel piece (2). This 111-inclined probe (S) emits ultrasonic waves, and the presence or absence of defects in the flaw detection area (3), for example, is evaluated based on the reflected echoes.

The echoes detected in this way are similar to the case of the oblique angle method, and include, in addition to defective echoes, transmitted echoes and top surface echoes (TE) reflected from the top surface of the square steel piece (2). The ultrasonic beam emitted from the array type probe (S) can be deflected and focused arbitrarily at high speed, so that defects inside the square steel piece (2) can be detected based on the deflection angle and the focusing angle. position can be easily evaluated.

(Problems to be Solved by the Invention) The bevel method disclosed in JP-A-59-116541 is somewhat useful in detecting defects inside square steel pieces, but From the viewpoint of accuracy, there are still problems as explained below.

In other words, since the square steel piece itself is an intermediate product and not a secondary processed product, the surface shape accuracy of such a square steel piece is better than that of products such as steel bars, wire rods, or plates after secondary processing. do not have.

Therefore, there is a problem in that an error of about several square meters occurs due to the surface shape accuracy of the intermediate product, and this cannot be avoided.

In other words, when wire rods, steel bars, etc., which are rolled from square steel pieces into products, are cold or hot forged by a secondary processing manufacturer, the most problematic problem is This is because this is a surface layer region up to a depth of 4 mm, and it is necessary to accurately evaluate the position of the defect within this surface layer region.

Therefore, an object of the present invention is to provide a surface defect detection method for a square steel piece that can reliably detect defects within a limited surface N'uM range.

(Means for Solving the Problems) The present invention aims to solve the above-mentioned problems by using both the vertical method and the oblique method. The gist of the defect detection method is a surface layer defect detection method for a square steel billet, which detects defects in the table N region in a predetermined depth range below the surface of the square steel billet by ultrasonic testing, A plurality of probes are placed outside the surface of the area to detect defects in the square steel piece using the vertical method, and the defects are detected at the ends of this area on both sides of the square steel piece perpendicular to the surface of the table N area. The probes are placed outside the close position with a limited detection angle range, and the defects in the square steel piece are detected by the bevel method. It is characterized by evaluating defects within the table JffluJl area.

[Effect]

The ultrasonic waves emitted from the probe disposed outside the surface of the area opposite to the area N area on the flaw detection side of the square piece of steel propagate perpendicularly from the surface with a certain spread. The entire side surface layer area is tested by the so-called vertical method. On the other hand, the ultrasonic waves emitted from the ultrasonic probes, which are placed outside the side surfaces of each rope adjacent to the ends of the surface area with a limited detection angle area, also spread to a certain extent. Proceeding in the direction of the side facing the side, defects within the ultrasonic transmission range are detected using the so-called oblique angle method.

Therefore, defects inside the square steel piece are sometimes detected by both probes, and sometimes by one but not by the other, so they are not detected by the vertical probe. Defects detected by the bevel method probe aimed at a limited predetermined surface area are shown in Table F! IH
It can be determined that the defect exists within the JI area.

In addition, defects that are detected by both the vertical method and the oblique method probe, or defects that are not detected by the oblique method probe but are detected by the perpendicular method probe, are Said table r! It is rated as an internal defect rather than the J area.

〔Example〕

An embodiment of the present invention will be described below based on FIG. 1, which is an explanatory diagram of its operation.

That is, the symbols (Sl), (SZ), (S,
), (S4) is Table F for the purpose of flaw detection of square steel piece (2)
l? A group of probes arranged perpendicularly to the surface (2a) on the area side facing the +111 area T to detect defects inside the square steel piece (2) by the so-called vertical method.
) and the spread of the ultrasonic beam, this square steel piece (
2), while arranging only the number that can cover the whole area inside the square steel piece (2), while
b) and (2c) are probes (S,), which are tilted downward with respect to their sides (2bL (2c)) and emit ultrasonic beams toward this table N?J region T, ( S,
) are arranged respectively.

Next, the mode of operation of the flaw detection method when the probe is arranged as described above will be explained below.
), bevel method probe (S, ) placed on the (2c) side
, (S&), defects in the ultrasonic beam propagation region of the square steel piece (2) are detected by these probes (Ss) and (S4). On the other hand, t1114 detected by vertical method probe (Sl)
is a part of the sector shown as al, bl, C2, d in the figure, and the area detected by the vertical probe (S,) is part of the sector shown as Ql % bl, Cps dl. The area detected by the vertical probe (Sl) is a part of the fan shape indicated by al, b2, C1, d, and the area detected by the vertical probe (S4). are parts of the fan shape indicated by a, , b4, C4, and d4.

Furthermore, the open castle flaw detected by the angle probe (SS) is a part of the sector indicated by 8% s b%, C1, d, and by the angle probe (S &). The area to be inspected is a part of the sector ahs' IJh, C6, and dh. In other words, the line connecting C2 and d has arcs a, b, arc am bts arc a3 b3, arc a.

b4, and the arcs c, d, c, d, C2ds, and C4d are set close to the line BC indicating the depth of the surface region T.

Here, the intersection of the above-mentioned circular arc Cm d4 and the lower surface (2d) in the diagram of the square steel piece (2) is the point A, and the circular arc Chd4
The intersection of the arc Cs ds and the arc ca dJ is the point B, the intersection of the arc Cs ds and the arc ca dJ is the 0 point, the arc Cs d, and the square steel piece (
The intersection of 2) with the surface (2d) is point D, lines c, Sd, and line a
Let the intersection with the line C5d and the line bn be the point E, and the intersection with the line C5d and the line bn
The intersection with C4 is set as point F, and A d4 C is detected by angle probes (S, ) and (S&).
Let X be the area surrounded by 8D, and Y be the area surrounded by BCFE detected by vertical probes (S, ), (S8), (Sl), and (S4).
The surface layer fIJl area ABCD of the square steel piece (2) 6, that is, the surface layer area T, can be expressed as: table N area T - area X - area Y.

Therefore, the internal defects (Fl) of each steel piece (2J) detected by the oblique method probes (Ss), (S,) are the same as those detected by the vertical method probes (51), (S8), ( S, ), (S4
), this table Jifil Castle T
On the other hand, the defect (F,) detected by the bevel method probes (S, ), (S4) is detected by the perpendicular method probe (F,). S, ), (S8
), (S3), and (S4), it is determined that there is no defect inside this table MfiJT area'r.

Therefore, with the conventional bevel method, even if a defect exists in a position close to the surface of a square steel piece, it is impossible to evaluate the position of the defect with high precision.However, the ultrasonic flaw detection method of the present invention By this method, it is possible to detect defects existing inside the surface layer T at a predetermined depth of a square steel piece with high accuracy.

In the above, the table N on the - side of the square steel piece (2)? Although we have described the detection of defects that exist only inside the i1 area T, the above-mentioned probe can be used to simultaneously detect defects that exist inside the surface area on all four sides of a square steel billet that is being transported online at the production site. It is sufficient to arrange the child sets at predetermined intervals in the longitudinal direction of the square steel piece, and there is no problem in practical use.

Note that the embodiment described above is only one specific example of the present invention, and therefore the scope of the technical idea of the present invention is not limited by this embodiment.

(Effects of the Invention) According to the surface defect detection method of a square steel piece according to the present invention, the surface area of the square steel piece where defects are to be detected is set by a vertical method, and further by an oblique method. By setting the thickness, it is possible to set the thickness to any desired value, so in the secondary processing stage where square steel pieces are turned into products such as wire rods and steel bars, the internal thickness can be Since the location of the fine inclusions is precisely limited, it is now possible to reliably evaluate the location of the defect.

Therefore, according to the present invention, we have been able to establish an extremely excellent and useful method for detecting surface defects in square steel pieces that can reliably detect defects within the limited surface area of square steel pieces.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the operation in the ultrasonic flaw detection method of the embodiment of the present invention, Fig. 2 is an explanatory diagram of the arrangement of the ultrasonic probe in the ultrasonic bevel method of the conventional example, and Fig. 3 (A). 3(b) is an explanatory diagram of the action in the conventional ultrasonic oblique angle method according to the first example, and FIG.
FIG. 4 is an explanatory diagram of the arrangement of an ultrasonic probe in a second example of the conventional ultrasonic oblique angle method. (S,) ~ (Sh) - Ultrasonic probe, (2) - Square steel piece,
(T) - 11 table i region, (Fl), (pt) - internal defect. Patent applicant Kobe Steel, Ltd.

Claims (1)

[Claims] A surface defect detection method for a square steel piece, which detects internal defects in a surface layer region in a predetermined depth range below the surface of a square steel piece by ultrasonic testing, wherein A plurality of ultrasonic probes are arranged to detect internal defects in the square steel piece using a vertical method, and the defects are detected on both sides of the square steel piece perpendicular to the surface of the surface area at a position close to the end of the area. Ultrasonic probes are placed with a limited flaw detection angle area to detect internal defects in the square steel piece using the bevel method, and based on the presence or absence of internal defects detected by these probes, A surface defect detection method for a square steel piece, characterized by evaluating defects in a square steel piece.