JPS6029900B2 - Method and device for detecting strength deterioration due to martensitic transformation of stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and a detection device for detecting strength deterioration due to martensitic transformation of stainless steel.

In recent years, austenitic stainless steel has been mainly used for piping systems of low-temperature equipment and nuclear power equipment, such as those used in the liquefied natural gas industry.

This material undergoes martensitic transformation through processing, but
It is also known that a similar change can occur simply by being placed in a specific atmosphere, causing destruction from that part. The reason for this is that chromium precipitates at phase boundaries during transformation, and this is eroded in a corrosive environment, forming microcracks that lead to fracture, or It is conceivable that destruction may occur. These phenomena are closely related to the amount of martensitic phase produced, and it is extremely important to precisely measure the amount of transformation. The amount of transformation of martensite is measured by transmission electron microscopy or X-ray diffraction, but with the former method it is difficult to subject the material to be measured in its original form. However, with the latter method, it is not easy to quantify the martensitic phase.

Furthermore, it has the disadvantage that it is almost impossible to measure when the precipitated phase is minute. For this reason, there is a strong demand from various quarters for a method and apparatus that can easily measure on-site the deterioration of materials in industrial facilities due to aging. The present inventor completed the present invention by paying attention to the fact that the martensitic phase exhibits ferromagnetic properties.

Therefore, an object of the present invention is to provide a method and apparatus for detecting a martensitic phase that is much easier to obtain and provides higher sensitivity than conventional measuring methods.

According to the invention, the windings are wound oppositely to each other on the detection coil.
A strength deterioration detection method using martensitic transformation is characterized in that the alternating current magnetic field formed by exciting a pair of coils is balanced, and the output appearing in the detection coil is detected by bringing the object to be measured close to this balanced magnetic field. provided.

When an object to be measured is brought close to the balanced magnetic field, a current proportional to the magnetic permeability of the object flows through the detection coil, and by detecting the difference between this AC phase and the phase of the AC flowing through the excitation coil, the object to be measured is detected. The amount of martensite in the specimen is measured, and based on this, the state of strength deterioration of the lever material can be determined. Also,
According to the present invention, excitation coils having mutually opposite phases are wound around the detection coil so that the output of the highly permeable rod around which the detection coil is zero is zero. There is provided an apparatus for detecting strength deterioration based on the amount of martensitic transformation, characterized in that a terminal is connected to an alternating current source, and a terminal of the detection coil is connected to a phase detection mechanism. Next, preferred embodiments of the present invention will be explained according to the drawings.

In FIGS. 1 and 2, reference numeral 1 indicates a twill member having high magnetic permeability such as permalloy, super permalloy, or European iron, and a detection coil 3 is placed between two flange members 2 attached thereon. is wound many times, and both terminals thereof are connected to a phase detection and amplification mechanism 4. A tube body 5 having a high magnetic yield similar to that of the shank member 1 is placed on the detection coil 3. This tube serves as a magnetic shield against external noise signals. Excitation coils 8 and 9 are connected to both ends of this tube body 5 via insulating bobbins 6 and 7, respectively.
is being rolled around. The excitation coils have opposite phases to each other, and one end of each is directly connected, and one end of the excitation coil is connected to a power amplifier. The input side terminal of this amplifier is connected to an oscillator 1, and on the other hand, this oscillator 11 is wired to send a reference signal to the phase detection amplification mechanism 4. The excitation coils 8, 9 wound on the tube 5 which holds the detection coil inside are wound in opposite directions, preferably with the same number of turns, so that the excitation current of the excitation coils 8, 9 causes a drop in the detection coil. The alternating magnetic fields generated by the sensor cancel each other out, so that the output of the detection coil becomes zero.
However, even if the excitation coil has a different number of turns, the magnetic field can be balanced by moving the position of the detection coil 3 in the tube, and by providing a mutual inductance adjustment member at one end of the detection coil, the magnetic field can be balanced. It is also possible to provide it so as to compensate for the uniform magnetic field. The number of turns of the excitation coil is chosen to match the output impedance of the power amplifier 10. The detection coil preferably has a large number of turns, but in relation to the excitation coil it has more than 5 times the number of turns, particularly preferably in the range from 10 to 10,000 turns. Oscillator 11 Although not particularly limited, 10Hz to 100KHz
, preferably one that oscillates at a frequency of 40 Hz to 10,000 Hz is used. The phase detection amplifier 11 may be of a type that can detect the difference between the phase of the current flowing therein and the phase of the current flowing from the oscillator 11 due to the loss of the balance system of the detection coil, and is preferably a locking type. In-amp can be used. In order to measure the amount of martensite in the object to be measured 12 using the measuring device configured as described above, the high magnetic permeability shield member 1 wound around the detection coil 3 is used.
When the exposed end of the detection coil is brought close to the object to be measured 12, a magnetic field passing through the object to be measured is formed, which disturbs the balance of the magnetic field of the detection coil and generates a current.

The output of this detection coil is guided to a phase detection amplifier 4, and phase detection is performed using the alternating current flowing through the excitation coils 8 and 9 as a reference signal. In order to measure an object to be measured, if the object to be measured is brought into direct contact with the shield, it is possible to measure objects with high sensitivity and low magnetic permeability. For this reason, it is preferable to form the tip of the shield in close contact with the surface of the object to be measured. Therefore, the measuring method according to the present invention is an epoch-making method that allows the amount of martensite in the object to be measured to be known instantaneously with high sensitivity just by approaching the object to be measured. Next, examples of the measuring method and measuring device according to the present invention and the conventional X
A comparative example of the amount of martensitic transformation by the line method is shown below.

An excitation coil was wound 300 times in opposite directions around the outside of the permalloy pipe, and an oscillator that supplied an alternating current of 40 z was connected to this.

A measuring device was created by winding a detection coil around a permalloy round bar 4200 times inside a permalloy pipe and connecting both ends of this coil to a lock-in amplifier.The object to be measured was austenitic stainless steel SUS301,30.
Using the heat-rolled and solution-treated material and deep-drawn product of No. 4. The amount of martensitic transformation was first determined by an X-ray method, and then measured by the measuring device described above. The results are shown below. indicates the output of the lock-in amplifier and is on an arbitrary scale.

The sensitivity of this output is extremely high and can be increased by two orders of magnitude beyond the above values. FIG. 3 is a graph showing the above experimental results. There is no linear relationship between the values determined by X-rays and the values determined by the measurement method of the present invention. This is because the martensitic phase detected by Law is 0.0
This is because a martensitic phase of about 0.05 microns can also be detected.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing one embodiment of the martensitic transformation amount measuring device according to the present invention. FIG. 2 is an enlarged longitudinal sectional view of the detection coil and the excitation coil, and FIG. 3 is the output value obtained by the measurement method according to the present invention.
It is a graph showing the relationship between the amount of transformation obtained by the conventional X-ray method. 1... Strongly permeable twill body, 3... Detection coil, 4...
... Phase detection amplifier, 5 ... Strongly permeable tube, 8, 9.
... Excitation coil, 10... Power amplifier, 11... Oscillator, 12... Measured object. Figure 2 Figure 1 Figure 3

Claims (1)

[Claims] 1. On a detection coil into which a rod having strong magnetic permeability is inserted,
The method is characterized in that an alternating current magnetic field formed by exciting a pair of coils wound in opposite phases to each other is balanced, an object to be measured is brought close to this balanced magnetic field, and the output appearing on the detection coil is detected. A method for detecting strength deterioration due to martensitic transformation of stainless steel. 2. The detection method according to claim 1, wherein the phase of the alternating current flowing through the excitation coil and the output current of the detection coil is detected. 3. The detection method according to claim 2, wherein the detection output is amplified. 4. The detection method according to claim 1, wherein the method to be measured is brought into close contact with a member that forms a magnetic field. 5. A detection coil wound around a rod having strong magnetic permeability; An excitation coil wound around the coil in opposite phases to each other so as to balance the output of this coil; connected to the excitation coil. 1. An apparatus for detecting strength deterioration due to martensitic transformation of stainless steel, characterized in that the apparatus comprises an alternating current source and an output detection mechanism connected to the detection coil. 6. Claim 5, wherein the excitation coil is wound around the detection coil via a tube having strong magnetic permeability.
Detection device described in section. 7. The turns ratio of each excitation coil and detection coil is 1:1.
6. The detection device according to claim 5, wherein the detection range is from 0 to 10,000. 8. The detection device according to claim 5, wherein the detection mechanism connected to the detection coil is a phase detection and amplification mechanism. 9. The detection device according to claim 8, wherein the phase detection amplification mechanism is a lock-in amplifier. 10. The detection device according to claim 5, wherein each one terminal of the excitation coil is connected to an oscillator via a power amplifier.