JPH0249660B2 - HENTAIRYORITSUNOSOKUTEIHOHO - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention detects electromagnetic changes that occur during the structural transformation of metal materials such as steel, for example, from an austenite phase to a ferrite phase, or vice versa. The present invention relates to a method for measuring the transformation rate of an object (metallic material).

[Conventional technology]

Conventionally, methods for measuring the transformation rate of metal materials such as steel include methods that use radiation, direct current magnetic field methods that use direct current magnetic fields, or detect electromagnetic changes that occur during the transformation process of the specimen as changes in impedance. method is known.

The method of measuring the transformation rate using radiation is a method that takes advantage of the fact that the X-ray diffraction angle changes due to the change in the lattice constant associated with the change from austenite to ferrite. Because of the difficulty, information on only the surface layer (several tens of micrometers below the surface) can be obtained, or when the specimen is a hot-rolled steel strip, for example, the specimen may be violently displaced vertically during measurement ( However, the disadvantage is that the transformation rate cannot be measured with high accuracy under such conditions.

In addition, the DC magnetic field method is a method in which a DC magnetic field is applied to the specimen and the magnetic field is measured using a Hall element, but there is significant nonlinearity between the transformation rate and the measured value, and the When becomes a ferromagnetic material,
Since the DC magnetic field flows only to the surface layer of the object, there is a drawback that it is possible to measure only the starting point of transformation or the vicinity thereof.

Next, a conventional method for measuring the rate of transformation, which uses a coil to detect electromagnetic changes during the transformation process of a subject, similar to the present invention, will be described in detail. As a method for measuring the rate of transformation of this kind, there is a method of measuring the rate of transformation configured as shown in FIG.

In FIG. 1, reference numeral 1 denotes an oscillator that outputs a sine wave current of a frequency appropriate for measuring the amount of transformation of a subject. Reference numeral 2 is a subject, and the amount of metamorphosis is to be measured.

A detection coil 3 is placed close to the upper part of the subject 2 and functions as a sensor for detecting the amount of metamorphosis. A bridge circuit 4 detects a change in impedance of the detection coil 3. 5 is a signal processing device that changes the detection signal of the bridge circuit 4 into a form that is easy to use. The operation of this conventional transformation amount measuring device will be explained below.

A detection coil 3 is placed near a plate-shaped subject 2, and a continuous sinusoidal current generated by an oscillator 1 is passed through the detection coil 3. Thus, an eddy current is generated on the surface of the subject 2, and the apparent impedance of the coil changes. The magnitude of the eddy current that affects this coil impedance is determined by the material of the object 2 (magnetic permeability, conductivity, distance between the sensor and the object 2),
Others). When the specimen 2 is undergoing transformation from austenite to ferrite, the ratio of ferrite to austenite in the specimen 2 increases, so the magnetic permeability changes significantly. As a result, the eddy current flowing on the surface of the subject 2 changes, and the impedance of the detection coil 3 placed near the subject 2 changes. The change in impedance in this detection coil 3 is
A bridge circuit 4 following the detection coil 3 detects the detection signal, a signal processing device 5 changes the detection signal into an easily usable form, and the display unit 6 displays the detected signal.

The above-mentioned conventional technology that uses a coil to detect electromagnetic changes during the metamorphosis process of the object 2 is configured as described above, so it can not only detect changes in magnetic permeability of a plate-shaped object, but also detect other changes. The distance between the subject and the detection coil must therefore be kept constant. Furthermore, since there is significant nonlinearity between the sensor output and the rate of transformation of the subject, although the rate of transformation at or near the start point of metamorphosis can be measured, the rate from the start point to the end point of metamorphosis can be measured. It is not possible to measure the rate of metamorphosis. This conventional technology has various problems as described above.

[Problem to be solved by the invention]

The present invention solves the above-mentioned problems in the prior art, and even when the distance between the object and the sensor changes, for example when the object moves up and down (flapping) violently, such as a steel strip during hot rolling. A method for measuring the transformation amount rate that can measure the transformation amount rate of a specimen with high accuracy and also measure the transformation amount rate from the start point to the end point of the transformation over a wide range of plate thicknesses of the specimen. It was made with the purpose of providing.

[Means to solve the problem]

The present invention is characterized by providing a transmitting coil and a receiving coil located opposite to each other with the subject in between,
This is a method of measuring the rate of metamorphosis of a subject from an electric signal generated in a receiving coil by supplying an alternating current to the transmitting coil, and the relationship between the magnitude of the output signal and the rate of metamorphosis is determined from the initial stage of metamorphosis of the subject. During linear changes, measurement is performed by supplying a continuous wave alternating current to the transmitting coil, and even before the transformation of the object progresses and the relationship between the logarithm of the output signal and the transformation amount rate becomes non-linear. The purpose is to perform measurements by switching to pulsed alternating current and supplying it to the transmitting coil.

The present invention will be explained in detail below.

FIG. 2 shows the configuration of an apparatus for carrying out the method for measuring the transformation rate of the present invention.

In FIG. 2, 21 is a transmitting coil. 2
Reference numeral 2 denotes a receiving coil, which is arranged at a position opposite to the transmitting coil 21 with the plate-shaped subject 23 in between. Reference numeral 24 denotes an oscillator, which generates in the transmitting coil 21 a continuous alternating current, such as a sine wave alternating current, or a pulse wave current suitable for measuring the rate of transformation of the subject 23. In the present invention, continuous alternating current, such as sinusoidal alternating current and pulsed alternating current, is collectively referred to as alternating current.

25 is a pulse signal-continuous signal switching device;
26 is a power amplifier which supplies power to a pulsed current or continuous alternating current, such as a sine wave alternating current. 27 is an amplifier and tuned amplifier, which amplifies the voltage generated in the receiving coil 22.

The amplifier and tuned amplifier 27 are switched by a switching device 25.

28 is a signal processing circuit that processes the received signal. The signal processing circuit 28 is a circuit for separating the received transmission signal and wraparound signal and replacing them with a reference value of a predetermined transformation amount rate. 29 is a display section that displays the signal from the signal processing circuit 28.

Next, the operation of the apparatus shown in FIG. 2 will be explained.

In the present invention, a continuous alternating current, for example, a sinusoidal alternating current, is supplied to the transmitting coil 21 at the beginning of the metamorphosis of the subject 23, and when the metamorphosis has progressed to a certain extent, the pulse signal/continuous signal switching device 25 The current supplied to the transmitting coil 21 is switched from a continuous alternating current, such as a sinusoidal alternating current, to a pulsed alternating current.

When a continuous alternating current, for example a sinusoidal alternating current, is supplied to the transmitting coil 21, an eddy current is generated on the surface of the plate-shaped object 23. This eddy current
3 and propagates downward in the thickness direction of the receiving coil 2.
Create a high-frequency magnetic field around 2. This change in magnetic field induces a voltage across the receiving coil 22. The voltage induced in the receiver 22 is approximately given by the following equation.

V=V ₀ · exp (−√d) ... (1) where: Frequency μ: Magnetic permeability σ: Conductivity d: Thickness of the object 23.

As the transformation of the object 23 progresses, austenite changes to ferrite, and the magnetic permeability of the object 23 increases in accordance with the ratio of ferrite to the total amount (austenite + ferrite). The magnetic permeability of austenite and ferrite, where the ratio of ferrite to the total amount is K,
When the conductivities are μ ₁ , μ ₂ , σ ₁ , and σ _{2 ,} respectively, the induced voltage generated across the receiving coil 22 is V=V ₀・exp(−√ _{1 1} (1−K) d −√ _{2 2} Kd) ...(2) Here, K: Ferrite/(Austenite +
ferrite). Here, K corresponds to the metamorphosis rate,
Since the values other than K are known, the desired transformation rate can be determined by measuring the induced voltage.

Thus, the basic principle of the present invention follows (2).

However, in equation (2), there is no term representing the distance (interval) between the sensor and the plate-shaped object 23, and the induced voltage is determined by the distance (interval) between the sensor and the plate-shaped object 23.
The rate of transformation obtained by the induced voltage is not affected by the distance (spacing) between the sensor and the plate-shaped object 23. That is, even if the plate-shaped object 23 causes "flapping" between the transmitting coil and the receiving coil, the accuracy of measuring the rate of transformation will not be reduced.

Furthermore, if we take the logarithm of equation (2), since the magnetic permeability of ferrite is sufficiently larger than that of austenite, the logarithm of the induced voltage is linear with the transformation rate K as shown in equation (3). Become.

Since 1n(V/V ₀ )=−(√ _{1 1} (1−K)d +√ _{2 2} Kd)μ ₂ ≫μ ₁ , approximately, 1n(V/V ₀ )=−√ _{2 2} Kd...(3) becomes. However, if the thickness d of the metal plate material that is the object 23 is large and the transformation has progressed sufficiently, the induced voltage V generated by the transmitted signal 30 will be The specimen 23 is buried by the induced voltage Vε generated by the signal 31 that goes around the specimen 23.

Therefore, in the present invention, as shown in FIG. 4, a continuous alternating current, such as a sinusoidal alternating current, is supplied to the transmitting coil in the region where equation (3) holds, and a pulsed alternating current is supplied in other regions. It uses electric current.

To explain this point in detail, first, if the current supplied to the transmitting coil is a continuous alternating current, for example, a sinusoidal alternating current, the accuracy of measuring the transformation rate of the subject 23 can be made to a higher level. However, as mentioned above, when the thickness d of the specimen 23 is large and the transformation is progressing (in Fig. 4, the nonlinear part to the right of the solid line indicating "measurement by continuous method")
The induced voltage V generated by the transmitted signal 30 is buried by the induced voltage Vε generated by the signal 31 (see FIG. 3) that goes around the object 23, making it impossible to measure the transformation rate. . However, when the transformation rate is measured by supplying pulsed AC current to the transmitting coil 21, the true signal (induced voltage V generated by the transmitted signal 30) and the signal 31 (third (see figure), it becomes possible to separate the induced voltage Vε generated by the method (see figure), and the transformation rate can also be measured in the nonlinear portion to the right of the solid line indicating "measurement by the continuous method" in FIG.

However, when measuring the transformation rate by supplying pulsed alternating current to the transmitting coil 21, the included frequencies are not necessarily single. Therefore, the received signal is the sum of a group of frequencies centered around the intended frequency, and the continuous method using a single frequency (method of measuring the transformation rate by supplying a continuous alternating current, such as a sine wave alternating current, to a transmitting coil) Compared to this, the measurement accuracy is essentially lower. Therefore, in the present invention, parts that can be measured by the continuous method (the solid linear part in Figure 4) are measured by the continuous method, and parts that cannot be measured by the continuous method are measured by the pulse method, which can be measured although the accuracy is lower. I try to measure it by. This ensures a wide measurement range.

When carrying out the present invention, in order to determine the timing to switch from the continuous method to the pulse method, first obtain the _diagram in FIG _. V) Determine _Linit and set this value l _o
(V) When the measured output value l _o (V) becomes smaller than _Linit , switch from the continuous method to the pulse method.

Next, the operation using the pulse method will be explained.

When a pulse wave alternating current is passed through the transmitting coil 21,
Eddy currents are generated on the surface of the plate-shaped object 23. This eddy current propagates downward in the thickness direction of the subject 23 and creates a pulsed magnetic field around the receiving coil 22. Due to this change in magnetic field, the receiving coil 22
A voltage is induced across the . When the pulse current I is defined by the following formula, approximately I=I ₀ (t) (nT≦t<nT+t ₀ ) =0 (nT+t ₀ ≦t<(n+1)T) where n=0, 1, 2, 3... Assuming the center frequency, the induced voltage V is given by: V=K∂/∂t(I ₀ (t−Δt)exp)−√d.

The propagation time Δt is: Δt=√4×d Here, μ: Magnetic permeability: Frequency σ: Conductivity d: Thickness of the object The transmission speed v is approximated as v=√4. The transmission speed v of this eddy current is
=1kHZ, μ=150×4μ×10 ^-7 H/m, σ=8×
When 10 ⁶ v/m and d=3 mm, it is about 3 m/s,
The traveling speed of the electromagnetic waves is 3×10 ⁸ m/s, which is very low compared to the traveling speed of the loop signal.

The present invention takes advantage of this fact. That is, since the signal passing through the object 23 is delayed by Δt compared to the signal going around the object, the signal passing through the object 23 and the signal coming around the object are separated. becomes possible.

FIG. 5 shows an example of the shape of the transmitted pulse and the shape of the received pulse as the metamorphosis of the subject 23 progresses.
5. FIG. 1 shows the transmitted waveform, and 2, 3, 4, and 5 show the received pulse waveforms when the transformation rate is 0%, 20%, 40%, and 80%. Among these, the wrap-around component is included within 1 ms from the start of the pulse waveform. The true signal (transmission signal) is included in peaks 2, 3, 4, and 5 that are shifted in time. In Nos. 2 and 3, the position of this peak and the wraparound signal almost overlap, but the wraparound signal cannot be observed because the true signal (transmitted signal) is sufficiently large.

Regarding No. 4, a wraparound signal is first seen, but its shape is distorted due to the true signal (transmission signal). Regarding No. 5, the first signal is the wraparound signal, and the next gentle peak is the true signal (transmission signal). The loop signal and the true signal (transmission signal) are completely separated.

In this way, in the pulse method, in the part where the wraparound signal affects the true signal (transmitted signal),
4 and 5, the true signal (transmitted signal) can be measured separately from the loop signal. A calibration curve is determined in advance using the peak value of this true signal (transmission signal), and the transformation amount rate is determined based on this.

Further, in the case of 2 or 3 where the true signal (transmitted signal) is sufficiently larger than the wraparound signal, the peak value of the true signal (transmitted signal) is used as is. When the peak of this true signal (transmitted signal) begins to separate from the loop signal, the peak value of the separated true signal (transmitted signal) is used.

The wraparound signal is as follows: V=Vε(nT≦t<nT+t ₀ )=0 (nT+t ₀ ≦t<(n+1)T). Therefore, the signal received by the receiving coil 22 is amplified by the amplifier 27, and the signal processing circuit 2
In 8, if attention is paid to only the signal where nT+t ₀ ≦t<(n+1)T, it becomes possible to eliminate the effect of the wraparound signal. In this way, the wrap-around signal and the true signal (transmitted signal) are separated, and the transformation amount rate is calculated based on the magnitude of this true signal (transmitted signal).
It is displayed on the display unit 28.

As described above, in the method for measuring the rate of transformation of a metallic material using alternating current, in a region where the measured value as the output changes linearly to the rate of transformation, the transmitting coil 21 is provided with a continuous alternating current, such as a sine current. A pulse wave alternating current is supplied to the transmitting coil 21, and a pulse wave alternating current is supplied to the transmitting coil 21 in a region where the linearity collapses, that is, in a region where there is an influence of a loop signal.

As another embodiment of the present invention, in the continuous method, the amplitude of the received signal is used as information, but since the phase also has similar information, it is also possible to use the phase to know the metamorphosis rate. good. Regarding the pulse method, in the signal processing circuit 28,
Separates the loop signal and the true signal (transparent signal),
Although the transformation rate was determined based on the magnitude of the true signal (transmission signal), it is also possible to determine the transformation rate by examining the time delay of the true signal (transmission signal).

The power amplifier located immediately before the transmitting coil 21, the tuned amplifier and amplifier located after the receiving coil are not essential components in the configuration of the present invention, and may be omitted in some cases, and the same may be applied. For example, a tuned amplifier may be replaced by a lock-in amplifier.

〔Effect of the invention〕

As described above, the present invention secures measurement accuracy by using a continuous alternating current that uses a frequency preferable to increase measurement accuracy in the early stages of metamorphosis of the subject, and in areas where the continuous method cannot be applied. By using the pulse method, a wide measurement range is ensured.

As described above, the present invention makes it possible to accurately measure the transformation rate of a thick specimen over a wide range from the start point to the end point by switching between the continuous method and the pulse method. The effect that can be achieved is achieved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of a conventional transformation rate measuring device, FIG. 2 is a configuration diagram showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram showing the wrap-around phenomenon.
FIG. 4 is an explanatory diagram showing switching points in measurement by the measurement pulse method using the continuous method, and FIG. 5 is a waveform diagram showing changes in the transmitted pulse and the received pulse as the metamorphosis of the subject progresses. 1: Oscillator, 2: Subject, 3: Detection coil,
4: bridge circuit, 5: signal processing device, 6: display unit.

Claims (1)

[Claims] 1. A method in which a transmitting coil and a receiving coil are provided opposite to each other with a subject in between, and the rate of metamorphosis of the subject is measured from an electric signal generated in the receiving coil by supplying an alternating current to the transmitting coil. From the initial stage of metamorphosis of the subject, while the relationship between the magnitude of the output signal and the rate of metamorphosis changes linearly, measurement is performed by supplying continuous wave alternating current to the transmitting coil, and the metamorphosis of the subject progresses. A method for measuring the rate of transformation, characterized in that before the relationship between the logarithm value of the output signal and the rate of transformation becomes non-linear, the current is switched to a pulsed wave alternating current and supplied to a transmitting coil for measurement.