JPS58626B2 - Method for detecting internal defects in steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting internal defects in steel, particularly pipe-shaped or bi-plate-shaped internal defects in continuous casting pieces, blooming rolled steel pieces, hot rolled steel products, etc.

In the steel manufacturing process, defects inside slabs, slabs, and steel materials (hereinafter collectively referred to as steel materials), such as center cracks in continuous casting slabs, mechanical pipes in blooming-rolled slabs, or bipolar defects in thick steel plates, are detected in the steel manufacturing process. There may be quite large defects in the

If the steel material is in a cold state, the presence or absence and distribution of such defects can be easily detected by ultrasonic flaw detection.

However, rather than detecting the above-mentioned defects after the steel material has cooled to a cold state, it is preferable to detect the defects after casting so that the defective parts can be removed during the cutting process that follows casting or rolling. Alternatively, it is necessary to detect it in a hot state after rolling.

However, with current ultrasonic flaw detection, it is difficult to detect flaws at high temperatures.

The purpose of the present invention is to determine the presence or absence and distribution of internal defects in steel materials, such as relatively large defects such as pipe-shaped or two-plate defects, and which almost completely block the propagation of sound waves. The purpose is to provide a method of detection.

The gist of the present invention for achieving this object is to provide a striking element made of a magnetic metal body, a striking signal generation circuit connected to the striking element and generating a striking signal at the moment the striking element contacts a test material, and an electromagnetic striker. Using a sonic inspection device equipped with a type sonic receiver, a striking sound is generated by hitting one or more points on one side of the material to be inspected with a striker, and then the other side of the material to be inspected is A sound wave propagated at a point corresponding to the impact point is received by an electromagnetic sound wave receiver, and the sound wave reaches the point where the impact signal from the impact signal generation circuit is the starting point and the sound wave reception signal from the electromagnetic sound wave receiver is the end point. A method for detecting internal defects in steel, characterized in that an internal defect in a test object is detected by measuring time and comparing the measured sound wave arrival time with a known sound wave arrival time determined by the thickness of the test object. be.

An embodiment of the method of the present invention will be described below with reference to the drawings.

Fig. 1 shows the propagation state of sound waves in a good part with no defects inside the material to be inspected, Fig. 2 shows the propagation state of sound waves in a defective part, and Fig. 3 shows the impact signal and the sound wave reception signal. It is a diagram.

In FIG. 1, when one surface of a material 1 to be tested is struck with a striker 2, a sound wave 3 is generated in the material 1 to be tested.

The sound waves 3 propagate in a spherical shape centered on the point of impact, but the sound waves 3 received by the receiver 4 pass through the shortest distance.

This striking element 2 is made of a magnetic metal material, and is connected with, for example, a battery 5, a resistor 6, and a contact member 7 so as to generate a striking signal the moment the object 1 is struck with the striking element 2. The striker 2 functions as a switch, and the moment the striker 2 contacts the surface of the test material 1, the circuit is closed so that a striking signal can be taken out from both ends of the resistor 6.

As shown in FIG. 2, when a defect 8 exists on the line connecting the striker 2 and the receiver 4, the sound wave 3 propagates around the defect 8 by the shortest distance and is received by the receiver 4.

FIG. 3 shows each signal.

Signal A is a striking signal, and the rising point of this signal A becomes the starting point for measuring the sound wave arrival time.

Signal B is the sound wave reception signal in the good part, and is τ.

is the sound wave arrival time. Signal C is a sound wave reception signal when it has bypassed defect 8, and τx is the sound wave arrival time in this case.

The difference (τx−τ0) between the sound wave arrival time τx in the defective part and the sound wave arrival time τ0 in the good part is the time required for the sound wave 3 to bypass the defect.

As shown in FIG. 2, when the defect 8 exists on the line connecting the striker 2 and the receiver 4, the thickness of the material to be inspected is t, the depth from the surface of the material to be inspected to the defect 8 is d, and the striker 2 The material thickness t is 300 m so that the shortest distance from the line connecting the receiver 4 and the edge of the defect 8
Below about m, even if the position d of the defect in the thickness direction of the material to be inspected changes, the propagation distance of the sound wave does not change that much.

Generally, the large defects that occur inside the steel material described above often exist within the range of 1/4 to 3/4 of the thickness, so the difference in the propagation distance of the sound wave 3 depending on the position of the defect in the thickness direction is , which can be regarded as the range of measurement error.

Therefore, the position d of the defect 8 in the plate thickness direction is always 1 of the plate thickness t.
/2 position, the propagation distance y of the sound wave 3 is the difference in the arrival time of the sound wave between the y= section and the good section (τx - τ0), where v is the propagation velocity of the sound wave 3, τx - Since τ0=v is known, the arrival time of the sound wave in the good area can be set in advance.Therefore, if you measure the arrival time τ of the sound wave when it is actually received by applying a blow to the test material, the difference can be determined. (τ−τ0)
From this, the presence or absence of the defect 8 and the distance x to the defect edge shown in FIG. 2 can be known.

FIG. 4 shows an example of the relationship between the sound wave arrival time difference (τ-τ0) and the distance x to the defective edge.

In this example, the thickness of the material to be tested is 1.80 mm.

FIG. 5 shows an example of a method for determining the distribution (shape) of internal defects in a steel plate using the above relationships.

FIG. 5 shows a plan view of the material to be tested. As shown in the figure, the sound wave arrival time τ was measured using the method described above at a large number of lattice points as shown in the figure, and the sound wave arrival time difference (τ - τ
Find the distance x for each measurement point from 0), draw a circle with each measurement point as the center and the distance x as a radius, and draw an enclosing line for each time to obtain the defect distribution ( shape) is required.

FIG. 6 is a diagram showing the configuration of a striking device in an embodiment of the present invention.

The striking device includes a heat-resistant outer cylinder 11, a magnetic metal striker 12 built into the outer cylinder 11, an electromagnet 13, and a permanent magnet 15.
and an external magnetization power source 24.

The striking element 12 is normally attracted to the permanent magnet 15 and is on standby at the position shown in the figure.

The permanent magnet 15 is mounted on a magnet mounting plate 16, which is supported by springs 17, 17' and a support rod 18.
It is lowered from the upper part of the outer cylinder 11 by.

Here, the springs 17, 17' are for absorbing the energy returned by the repulsive force of the impactor 12 hitting the surface of the specimen 1.

The support rod 18 is used to maintain a constant position at the moment when the striker 12 is separated from the permanent magnet 15 when the striker 12 is absorbed by the electromagnet 13.

The attraction force of the permanent magnet 15 is set to a level that sufficiently supports the weight of the striker 12 and is not too large compared to the absorbing force of the electromagnet 13.

The electromagnet 13 consists of a solenoid coil mounted on a bobbin 14 made of an insulating material.

Contact rolls 19 and 19' that are in constant contact with the striking element 12 are attached above the bobbin 14 by supports 20 and 20', and a lead wire 21 attached to the contact roll 19 is connected to a striking signal generation circuit 25. connected.

A contact roll 22 is placed on the surface of the material 1 to be tested, and this contact roll 22 is always in contact with the surface of the material 1 to be tested, and a lead wire 23 attached to the contact roll 22 is connected to the impact signal generation circuit 25.

When a current is applied to the electromagnet 3 from the magnetization power supply 24, the striking element 12 separates from the permanent magnet 15 and strikes the surface of the specimen 1.

Then, the impact signal generation circuit 25, the lead wire 21, the contact roll 19, the impactor 12, the test material 1, the contact roll 22,
The lead wire 23 and the signal generating circuit 25 are electrically connected, and a striking signal can be obtained at the moment the striking element 12 contacts the material 1 to be inspected.

The force with which the striker 12 strikes the surface of the test material 1 is determined by the relative positional relationship between the striker 12 and the electromagnet 13, the current flowing through the electromagnet 13, and the number of turns of the coil.

When the test material 1 moves continuously, the striker 12 needs to quickly leave the surface of the test material 1 after impact, and the faster the test material 1 moves, the more the striker 12 and the test material 1 move. Surface contact time should be short.

For this reason, in this embodiment, a capacitor rechargeable power supply as shown within the dotted line in FIG. 6 is used as the external magnetization power supply 24.

When the electromagnet 13 is energized in this manner, the energization time is determined by the product of the capacitance of the charging capacitor C and the inductance of the coil of the electromagnet 13.

According to this method, the contact time between the striking element 12 and the surface of the material to be tested can be 100 μs to 150 μs.

The sound waves propagating within the test material 1 are received by a non-contact electromagnetic sound wave receiver 4 provided close to the surface of the test material 1 opposite to the surface on which the impact device is provided.

This electromagnetic sound wave receiver 4 is a known sound wave receiver consisting of an electromagnet and a flat coil.

According to the method of the present invention, for example, the shape of a mechanical pipe generated in a blooming slab can be detected after rolling, and information for determining a shearing position in a shearing process can be provided.

That is, mechanical pipes are generated at the head and tail parts of a slab that is bloomed from a steel ingot, and these are cut and removed in the shearing process.

However, the depth and tip position of this mechanical pipe are not necessarily constant for each rolled slab, and furthermore, the slab after rolling is at a high temperature of over 1000°C, so the shape of the mechanical pipe cannot be detected by ultrasonic flaw detection etc. ,
The shearing work begins by cutting near the tip of the mechanical pipe, which an experienced worker would expect, and visually observing the cut surface from the operator's cab.
The reality is that the remaining mechanical pipes are repeatedly cut little by little.

However, the accuracy of visual observation from a distance is extremely poor in this kind of work, resulting in problems such as lower yields due to too many cuts, problems in post-processing due to uncut mechanical pipes, and decreased work efficiency due to the large number of cuts. was there.

According to the method of the present invention, if an electromagnetic sound wave receiver consisting of an electromagnet and a flat coil is used as a receiver, it is possible to receive sound waves without contacting the material to be examined.
Even if the slab is at a high temperature of .degree. C. or higher, the tip position of the mechanical pipe can be detected by the method described above, and the mechanical pipe can be sheared only once, and the mechanical pipe can be cut and removed without leaving any uncut parts or overcutting.

The method of the present invention further provides for crater formation during continuous casting.
It can also be used to detect the position of the tip and to measure whether the inside of a steel ingot has completely solidified after casting.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the propagation state of sound waves inside the material to be inspected, Figure 3 is a diagram showing the impact signal and the sound wave reception signal, and Figure 4 is a diagram showing the difference in arrival time of sound waves and the size of the defect. FIG. 5 is a diagram illustrating a method for determining the distribution of internal defects according to an embodiment of the present invention, and FIG. 6 is a diagram illustrating a configuration of an apparatus according to an embodiment of the present invention. 1... Test material, 2... Striker, 3...
...Sound wave, 4...Receiver, 5...
Battery, 6... Resistor, 7... Contact member,
8...Defect, 11...Outer cylinder, 12...
...Blower, 13...Electromagnet, 15...
...Permanent magnet, 19...Contact roll, 21.
...Lead wire, 22 ...Contact roll, 2
3...Lead wire, 24...Magnetization power supply,
25...Blow signal generation circuit.

Claims (1)

[Claims] 1. A sonic inspection device equipped with a magnetic metal striking element, a striking signal generation circuit connected to the striking element and generating a striking signal at the moment the striking element contacts the test material, and an electromagnetic sonic wave receiver. Using this method, a striking sound is generated by striking one or more points on one surface of the specimen with a striker, and the sound is propagated at a point corresponding to the striking point on the other surface of the specimen. Receive the sound wave with an electromagnetic sound wave receiver, measure the sound wave arrival time starting from the impact signal from the impact signal generation circuit and ending at the sound wave reception signal from the electromagnetic sound wave receiver, and compare the measured sound wave arrival time with the sound wave arrival time. A method for detecting internal defects in steel, characterized by detecting internal defects in a test object by comparing the arrival time of sound waves with a known sound wave arrival time determined by the thickness of the test object.