JPH05203503A - Apparatus for measuring residual stress distribution of steel - Google Patents

Abstract

PURPOSE:To measure the distribution of compression residual stress in the direction of the depth of the machined surface of shotpeened steel. CONSTITUTION:A magnetic core 210 is applied on steel 1 having compressed residual stress. An exciting coil 211 is wound arc the magnetic core 210 and forms the magnetic path. A detecting coil 212 is wound around the magnetic core 210 and outputs the voltage signal corresponding to the compression residual stress at the surface part of the steel 1 based on the electromagnetic induction caused by the exciting current. An oscillator 231 makes high-frequency AC as the exciting current flow through the exciting coil 211. A viriable- frequency timing circuit 238 changes the frequency of the current. A correcting circuit 234 corrects the voltage signal, which is detected by the detecting coil 212, in response to the frequency of the exciting current. This apparatus is constituted of arithmetic unit these parts and an arithmetic unit 235. The residual austenite in the steel 1 is shotpeened and induction transformed. Thus, martensite is obtained. The compression residual stress is increased, and permeability is changed. Therefore, the compression residual stress is grasped with the voltage value of the detecting coil 212.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring residual stress distribution of steel materials. This measuring device can be applied, for example, when measuring the compressive residual stress in the case where shot peening is performed on steel materials used for parts such as gears and axles.

[0002]

2. Description of the Related Art Conventionally, Japanese Unexamined Patent Publication No. 48-43954 discloses a nondestructive sorting apparatus for steel materials. This sorting device utilizes the fact that there is a certain relationship between the hardness of steel and coercive force, and sets the hardness to the desired stage to be sorted, and sets the coercive force corresponding to the hardness of each sorting limit. After saturation excitation of the steel material, demagnetize to the coercive force corresponding to the hardness of the selection limit, detect the positive or negative of the magnetic flux density in each demagnetized state, and determine whether the magnetic flux density is positive or negative. The steel material is selected to have a hardness at a desired stage depending on the number of the steel sheets.

Further, conventionally, a device for measuring the residual stress of the induction hardening shaft by magnetism is known. This measuring device uses two sensors in which an exciting coil and a detecting coil are wound around a U-shaped magnetic core made of laminated silicon steel plates, and the residual stress as a reference obtained by the X-ray stress measuring device is used. The value is compared with the output obtained by abutting each sensor on the axle in the axial direction and the circumferential direction, and the residual stress of the axle is obtained. There is also known a device which uses a magnetic anisotropy sensor in which the above two sensors are combined at right angles to each other and simultaneously detects outputs in the axial direction and the circumferential direction (Non-destructive inspection Vol. 35, No. 2 ( 62.2.2
0)).

However, each of the above-mentioned conventional techniques focuses on the change in coercive force due to tension and compression in the axial direction and the circumferential direction, that is, in the perpendicular direction, the main stress difference and the magnetic permeability in the main stress direction. The fact that there is a proportional relationship with the difference between the two was utilized, and the applicable range was limited to the measurement when the stress state was anisotropic. Therefore, in such a technique, when the shot peening process in which the stress state is isotropic is performed, there is no difference in the magnetic permeability in the perpendicular direction, and it is impossible to accurately measure the residual stress. ..

Further, in the apparatus disclosed in Japanese Patent Laid-Open No. 48-43954, first, a direct current is used to magnetically saturate the steel material, and thereafter the magnetic field is increased in the direction opposite to the magnetic field when the magnetic saturation is reached. Thus, the coercive force at which the magnetization becomes 0 is measured. Therefore, in this apparatus, it is necessary to add a magnetic field for reaching magnetic saturation and a magnetic field for zero magnetization to the steel material to be measured, and it is difficult to apply it to a production line because of poor operability.

[0006]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention As a result of earnest research on changes in the characteristics of steel products when residual stress is generated, the present inventor has found that the retained austenite structure of steel products undergoes work-induced transformation due to working and martensite. Since it becomes a structure, the magnetic permeability of the steel material changes due to this, and it was found that there is a correlation between the change value of this magnetic permeability and the compressive residual stress, and the following measurement method was developed (this application Sometimes unknown). That is, the pre-processing magnetic permeability detection step of detecting the magnetic permeability of the steel material having a retained austenite structure before processing, the post-processing magnetic permeability detection step of detecting the magnetic permeability of the steel material after processing, and the detected pre-processing magnetic permeability. And a calculation step of calculating the compressive residual stress from the change value of the magnetic permeability after processing.

The present invention has been made as a part of such development, and an object of the present invention is to provide a measuring apparatus for residual stress distribution of steel material capable of measuring residual stress distribution in the depth direction of steel material.

[0008]

According to the present invention, there is provided a device for measuring a residual stress distribution of a steel material, comprising: a magnetic core applied to a steel material having permeability and a built-in residual stress; and a surface layer of the steel material wound around the magnetic core. Having an exciting coil that forms a magnetic path connecting the core and the magnetic core, and a detection coil that is wound around the magnetic core and outputs a voltage signal according to the residual stress of the steel material by electromagnetic induction accompanying the exciting current of the exciting coil And a current supply unit capable of changing a frequency of a high-frequency alternating current as an exciting current in the exciting coil of the sensor, and a correcting unit correcting the voltage signal detected by the detecting coil according to the frequency of the exciting current. By applying exciting currents having different frequencies to the exciting coil, the voltage signal obtained by the detecting coil is corrected by the correcting unit, and the residual stress distribution in the depth direction of the steel material is measured. That.

Assuming that the frequency of the exciting current flowing through the exciting coil is f and its period is t, the period t becomes smaller when the frequency f is larger because of the relation of t = 1 / f. Therefore, from the equation V = −N · (dΦ / dt) in the following equation (1), the period t
When becomes smaller, the temporal displacement of the magnetic flux in the magnetic path increases, so that the voltage signal value V of the detection coil is output high due to the electromagnetic induction phenomenon that cancels the temporal variation of the magnetic flux. Therefore, it is necessary to correct the output voltage value V of the detection coil according to the frequency of the exciting current. Therefore, in the device of the present invention, the relationship between the frequency f and the output voltage value V is measured in advance, and the voltage signal value V of the detection coil is corrected according to the frequency f based on the relationship. The correction unit can be configured using, for example, a memory such as a RAM or a ROM that stores the above relationship.

[0010]

When a high-frequency alternating current is passed through the exciting coil as an exciting current, the magnetic flux in the magnetic path changes with time. Therefore, the electromagnetic induction causes an eddy current in the structure of the steel material. Further, a high frequency magnetic field is generated by this eddy current. This is measured by the detection coil as a change in impedance and thus as a change in the output voltage value. Here, since the magnetic permeability varies depending on the structure of the steel material (such as martensite phase and austenite phase), the output voltage value of the detection coil changes depending on the structure of the steel material. Here, since the structural ratio of the steel material changes depending on the degree of work-induced transformation, the degree of residual stress can be grasped from the output voltage value of the detection coil.

When the frequency of the exciting current flowing through the exciting coil is changed, the penetration depth of the magnetic flux on the surface of the steel material changes. Therefore, if the frequency of the exciting current is changed, a voltage signal corresponding to the depth from the surface of the steel material will be output from the detection coil. At this time, the voltage signal of the detection coil fluctuates according to the frequency of the exciting current, so the correction unit corrects it.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. (Steel Material) Steel material 1 used in this example is before carburizing and carburizing carburized steel and performing shot peening, and has a martensite structure of about 70 to 80% in area ratio and about 20 to 30.
% Retained austenite structure.

(Measuring Device) A measuring device 2 is shown in FIG. The measuring device 2 includes a sensor 21 that is in contact with the machined surface 11 of the steel material 1, and a measuring instrument 23 connected to the sensor 21. As shown in FIG. 1, the sensor 21 includes a U-shaped magnetic core 210 formed by stacking silicon steel sheets in the thickness direction, and an exciting coil wound around the magnetic core 210 and supplied with a high-frequency alternating current. 211, and a detection coil 212 wound around the magnetic core 210 and outputting a voltage value by an electromagnetic induction phenomenon based on a magnetic field change. The magnetic core 210 is formed so that its tip portion surely contacts the machined surface 11 of the steel material 1. The measuring instrument 23 includes an oscillator 231 as shown in FIG.
A frequency variable timing circuit 238 for changing the frequency of the high frequency alternating current oscillated from the oscillator 231, an amplifier 232 connected to the oscillator 231 for supplying an alternating current to the exciting coil 211, and an output voltage value of the detection coil 212 is amplified. An amplifier 233, a correction circuit 234 that corrects the output voltage value amplified by the amplifier 233, and a correction circuit 23.
4 is connected to the arithmetic unit 235, a display device 236 connected to the arithmetic unit 235, and a memory 237 connected to the correction circuit 234. Here, the oscillator 231, the frequency variable timing circuit 238, and the amplifier 232 form a current supply unit. In addition, the correction circuit 234 and the memory 2
37 and 37 constitute a correction unit.

(Process for detecting magnetic permeability before processing) As shown in FIG. 1, first, a sensor 21 is provided on the processed surface 11 of the steel material 1 before shot.
Abut. As a result, the machined surface 11 of the steel material 1 has a depth h.
_A magnetic flux is generated within the range of _n . The measuring device 23 detects the voltage value (voltage value before processing; V ₀ ) of the detection coil 212. The pre-working voltage value (V ₀ ) has the following correlation with the pre-working permeability (μ ₀ ) of the steel material 1.

That is, the exciting coil 211 of the sensor 21.
When a high-frequency alternating current is applied to, a loop-shaped magnetic path that connects the machined surface 11 of the steel material 1 and the magnetic core 210 is formed. At this time, as shown in FIG. 1, a magnetic flux (Φ) is generated at a depth hn of about 100 μm from the surface of the processed surface 11. Since the magnetic permeability of the magnetic core 210 is known, the amount of magnetic flux (Φ) generated is basically determined by the magnitude of the magnetic permeability (μ) at the depth hn of the processed surface 11.

That is, the voltage value (V) electromagnetically induced in the detection coil 212 by the temporal change amount of the magnetic flux (Φ).
Is basically obtained based on the following equation (1). V = −N · (dΦ / dt) (N is the number of coil turns of the detection coil 212, t is time) (1) Equation (1) Before processing on the display device 236 of the measuring instrument 23 under the above correlation. The voltage value (V ₀ ) is displayed. On the other hand, the maximum compressive residual stress (hereinafter referred to as compressive residual stress (Rs ₀ )) of the steel material 1 having this pre-processing voltage value (V ₀ ) is obtained in advance from the X-ray stress measuring device. The X-ray stress measuring device measures strain of the lattice plane due to compressive residual stress by X-ray diffraction.

(Process of detecting magnetic permeability after processing) Next, the steel material 1
A predetermined shot process is applied to the processed surface 11 of. Then, as shown in FIG. 1, the sensor 21 is attached to the machined surface 11 of the steel material 1.
Abut. As a result, the measuring device 23 detects the voltage value of the sensor 21 (post-processing voltage value; V ₁ ) as in the pre-processing magnetic permeability detection step described above. This processed voltage value (V ₁ ) also has a correlation with the processed magnetic permeability (μ ₁ ). In this way, the processed voltage value (V ₁ ) is displayed on the display device 236. The compressive residual stress (Rs ₁ ) of the steel material 1 having this post-working voltage value (V ₁ ) is obtained from an X-ray stress measuring device or the like.

Then, in a plurality of shot treatment stages, the above-mentioned post-working permeability detection step is similarly performed, and each compressive residual stress (Rs _{2 to} Rs ₄ ) of each steel material 1 is obtained by an X-ray stress measuring device or the like. Keep it. (Calculation process) Voltage values (V _{0 to} V) after processing in the steel material 1
₄ ) and each compressive residual stress (Rs _{0 to} Rs ₄ ) are shown in FIG. The characteristics shown in FIG. 2 are stored in the memory 237.

Every time the sensor 21 is brought into contact with another new steel material, the measuring device 23 detects the post-machining voltage value (Vx). The post-machining voltage value (Vx) and the pre-machining voltage value (Vx) are detected.
₀ ) and the amount of change (V ₀ −Vx = ΔV) are obtained, and the compressive residual stress (Rsx) of the steel material is calculated from the amount of change (ΔV) and the correlation shown in FIG. To be done.
By the way, since the work-induced transformation is promoted by the shot peening treatment, the retained austenite on the worked surface 11 is reduced. FIG. 3 shows the relationship between the compressive residual stress measured based on the measuring instrument 23 and the reduction rate of retained austenite. It is understood from FIG. 3 that there is a proportional relationship between the reduction rate of retained austenite and the compressive residual stress. The reason for this is as follows. That is, as shown in FIGS. 4 and 5, when the machined surface 11 of the steel material 1 is shot, the retained austenite undergoes a work-induced transformation, the retained austenite undergoes a martensite transformation, and a volume expansion occurs. A morphology that undergoes plastic deformation with the martensite structure as it is. Here, since the latter form is substantially negligible as a change in magnetic permeability, it is considered that compressive residual stress is applied to the machined surface 11 by the former form.

FIG. 6 shows the relationship between the reduction rate of retained austenite and the voltage value of the sensor 21 (processing voltage value and processing voltage value). It can be seen from FIG. 6 that the voltage value increases as the reduction rate of retained austenite increases.
This is because the austenite structure is paramagnetic and the martensite structure is ferromagnetic, so that the shot changes the retained austenite structure to a martensite structure by shot, and the magnetic permeability increases and the magnetic resistance increases. This is because the magnetic flux decreases, the temporal change amount of the magnetic flux increases, and the voltage value increases.

Further, the relationship between the compressive residual stress measured by the measuring instrument 23 and the voltage value is shown in FIG. It can be seen from FIG. 7 that the compressive residual stress and the voltage value have a proportional relationship. Therefore, the compressive residual stress of the steel material 1 after the shot can be calculated by detecting the voltage value of the steel material 1 before the shot, detecting the voltage value after the shot after that, and obtaining the change amount of these voltage values. Recognize. According to this measuring method, the steel material 1 can be used after the measurement because of the nondestructive test, and the measurement can be performed with good operability and accurately.

FIG. 8 shows the relationship between the amount of retained austenite and the compressive residual stress before the shot. As can be seen from FIG. 8, there is a region where the compressive residual stress is maximized due to the amount of retained austenite before the shot. In the present embodiment, it is preferable that the range of the amount of retained austenite that maximizes the compressive residual stress is the applicable range. Further, as shown in FIG. 9, if the applicable range is represented by the arc height amount which is a standard of the shot condition, it is a range of 0.6 to 0.8 _{mm in} a relatively high strength region.

(Measurement of residual stress distribution) When the frequency f of the exciting current flowing through the exciting coil 211 is different, the magnetic flux penetration depth h in the machined surface 11 of the steel material 11 is caused by the skin effect.
Changes. That is, when the frequency f is large, the magnetic flux penetration depth h in the processed surface 11 is small. Here, when the frequency of the exciting current has a constant value, the compressive residual stress from the surface of the machined surface 11 to the penetration depth h _n should be detected in total as the area S1 indicated by the diagonal lines in FIG. become. However, as is clear from the comparison between FIG. 10A and FIG. 10B, the distribution of the compressive residual stress may be different even if the shaded area, that is, the total value of the compressive residual stress is the same. Therefore, the area S1 shown in FIG.
Even if the area S2 shown in (B) is the same, the stress distribution form shown in FIG. 10 (A) and the stress distribution form shown in FIG. 10 (B) may not be distinguished.

Therefore, the measurement of the compressive residual stress distribution in the depth direction of the machined surface 11 of the steel material 1 is performed as follows. That is, the compressive residual stress generation layer due to shot peening is generally set to have a depth of about 300 μm from the surface, and it is necessary for the magnetic flux to penetrate into that range. Therefore, the inventor has a frequency of the exciting current of 1 KHz to 1 MH.
I thought that the range of z was appropriate. Therefore, in this embodiment, as shown in FIG.
By the frequency variable timing circuit 238 shown in FIG.
The frequency of the exciting current from 31 is changed within the range of 1 KHz to 1 MHz. Specifically, the frequency starts from 1 MHz and gradually decreases to 1 KHz (f ₁ , f ₂ , f ₃ ,
f ₄ ~). Here, in FIG. 11, the penetration depth of the magnetic flux in the processed surface 11 at the frequency f ₁ is h ₁ . Also,
The penetration depth of the magnetic flux at the frequency f ₂ of the exciting current is h ₂ . The penetration depth of the magnetic flux at the frequency f ₃ is h ₃ .

Then, each frequency (f
The compressive residual stress of the machined surface 11 at ₁ , f ₂ , f ₃ , f ₄ to) is measured. At this time, the exciting current cycle t = 1 / f
From the relationship, the larger the frequency f, the smaller the cycle t.
Therefore, from the above formula (1) of V = −N · (dΦ / dt), when the frequency of the exciting current flowing through the exciting coil 211 becomes high, the voltage value V of the detecting coil 212 tends to be output high. , It is necessary to correct the output voltage value according to the frequency. Therefore, in the present embodiment, the exciting coil 2
The relationship between the frequency of the exciting current flowing through 11 and the output voltage value of the detection coil 212 is measured in advance, and the measured value is stored in the memory 23.
7, and the output voltage value is corrected by the correction circuit 234 according to the value of the frequency used.

By the way, the output voltage value of the detection coil 212 measured at the frequency f ₂ of the exciting current is basically as shown in FIG.
It is represented by a hatched range in (A), which corresponds to the total value F2 of the compressive residual stress from the surface of the processed surface 11 to the depth h ₂ . The output voltage value measured at the frequency f ₃ is basically represented by the shaded area in FIG. 11B, which is the total value of the compressive residual stress from the surface of the processed surface 11 to the depth h _3. Corresponds to F3. Further, the output voltage value measured at the frequency f ₄ is basically represented by the shaded area in FIG. 11C, which is the total value of the compressive residual stress from the surface of the processed surface 11 to the depth h _4. Corresponds to F4. Therefore, machined surface 1
In order to know the compressive residual stress at a certain depth position h ₄ from 1, it is necessary to subtract the compressive residual stress F3 from the surface to the depth h ₃ from the compressive residual stress F 4 from the surface to the depth h _4. is there. In the device of this example shown in FIG.
To achieve this. Since the compressive residual stress at each depth position can be measured by changing the frequency in this way, the distribution of the compressive residual stress in the depth direction can be measured as shown in FIG. 11 (D).

If the compressive residual stress distribution in the depth direction is measured in the post-processing magnetic permeability detecting step, the distribution of the compressive residual stress in the depth direction after shot peening can be measured. If the compressive residual stress distribution is measured in the pre-processing magnetic permeability detecting step, the distribution of the compressive residual stress in the depth direction before shot peening can be measured.

(Application Example) FIG. 12 shows an application example of the device of the present invention. In this example, as shown in FIG. 12, the gear part 100 as a steel material has a bevel gear part 110 as a processing surface and a shaft part 120. The gear part 100 is made by carburizing and quenching carburized steel, and its structure is basically composed of about 80% martensite structure and about 20% retained austenite structure. In this example, the two sensors 21 are the bevel gears 1
10 and shaft 120 respectively. In this example, as shown in FIG. 13, the magnetic core 210 of the sensor 21 for the bevel gear portion has a bevel gear portion 1 of which each tip portion is a gear component 100.
It is formed substantially symmetrically so as to almost certainly contact the bottom 116 of the tooth groove of 10, and the side wall of each tip portion is made of ceramic or the like to concentrate the magnetic flux at each tip portion and improve wear resistance. A coating layer 210a made of is laminated.

(Other Example) Another example of the device of the present invention is shown in FIGS.
It shows in FIG. That is, the gear component 1 shown in FIG. 13 described above.
The dimension S1 of the valley portion 115 of the tooth portion of 00 is 4 to 5 mm, for example.
When the magnetic core 210 is small or less, the magnetic core 210 does not enter the trough 115, and the tip of the magnetic core 210 is fixed to the tooth bottom 116.
May be difficult or impossible to contact.
Further, when the residual stress is measured using the sensor 21 in a mass production line, the number of times of measurement is extremely large (for example, tens of thousands times / month), and the number of times of contact with the tip of the magnetic core 210 is extremely large, and wear occurs. Therefore, there is a considerable possibility that the measured value may change due to wear. In this case, the sensor 21 must be replaced, and the sensor 21 must be calibrated each time.

In this point, the apparatus according to another example shown in FIGS. 14 to 20 uses a large number of U-shaped thin plates 271 made of silicon steel plate with varying length L2 as shown in FIG. The magnetic core 270 (thickness S2 = 9 to 10 mm) is configured by laminating a large number of 271 in the thickness direction. One thin plate 2
The thickness of 71 can be appropriately selected, but is usually 0.1 to 0.1.
It is about 5 mm. Here, as can be understood from FIG. 18, the thin plate 271a having the longest length L2 is arranged in the central region T1 in the thickness direction T of the magnetic core 270, and the thin plates 271b, 271c, 271d to 271i ... Are sequentially arranged toward the outer side in the thickness direction T, so that the tip of the magnetic core 270 is set in a tapered shape toward the tip thereof.

Then, as shown in FIG. 16, the exciting coil 211 and the detecting coil 212 are wound around the magnetic core 270 a predetermined number of times. Further, of the magnetic core 270, the exciting coil 21
The portion around which 1 and the detection coil 212 are wound is hermetically fixed to the sensor case 21a made of hard resin. With the engaged portion 21c of the sensor case 21a engaged with the engaged portion 21e of the sensor guide 21b made of a hard resin, the sensor guide 21b is detachably attached to the sensor case 21a by a bolt, whereby the sensor 21 is It is configured.

Here, as shown in FIG. 16, the sensor guide 21b has a bifurcated leg 21k. Tip 2 of leg 21k
1i protrudes from the tip of the magnetic core 270 by a dimension ΔL4. The value of ΔL4 is set to about 0.2 to 0.5 mm in this example. The tip portion 21i of the sensor guide 21b may be made of a non-magnetic material having a good wear resistance, such as ceramics.

In this example, at the time of measurement, as shown in FIG. 19, the tip 21i of the sensor guide 21b of the sensor 21 is measured.
To the tooth bottom 116 (S3 = 4-5 mm) of the gear part 100. In this case, since the tip end of the sensor guide 21b projects by ΔL4, the tip end of the magnetic core 270 is maintained in a non-contact state without directly contacting the gear component 100, and therefore the tip end of the magnetic core 270 is not worn. To be prevented.
Here, the characteristic line M1 in FIG. 20 schematically shows the relationship between the dimension ΔL4 and the detection voltage of the detection coil 211. Dimension ΔL4
As indicated by the characteristic line M1, the detection voltage slightly decreases as the dimension ΔL4 increases under the influence of the magnetic permeability of the air gap corresponding to, but if the amount of ΔL4 is kept small and constant,
It can be measured sufficiently. Further, the correction unit can correct the amount corresponding to the decrease in the detected voltage.

In this example, as described above, the tip of the magnetic core 270 is set to have a shape that tapers toward the tip thereof. It is possible to measure even in such a narrow measurement region as described above, and it is applicable to various kinds of gear parts 100. Further, in this example, the sensor guide 21b is used as it is used.
If the tip end 21i of the leg 21k of the above is worn, only the sensor guide 21b may be replaced with a new one.

A thin plate having the same length L2 is formed in the thickness direction T
It is also conceivable to form the tapered magnetic core by obliquely processing the tip portion of the magnetic core after the lamination. In this case, since the thickness of the thin plate is thin, the thin plate may be turned over, or slight processing variations may occur between the thin plates, which affects the measurement accuracy. In this respect, in this example, as described above with reference to FIG. 18, the thin plate 271a having the long length L2 is the magnetic core 27.
The thin plates 271b, 271c, 271d, which are arranged in the central region T1 of 0 in the thickness direction T and whose length L2 is sequentially short, are arranged in order toward the outer side in the thickness direction T, whereby the magnetic core 270 is tapered. Since it is set, it does not need to be cut diagonally. Therefore, turning over the thin plate 271,
It is possible to avoid subtle variations in processing for each thin plate 271.

[0036]

According to the measuring apparatus for residual stress distribution of steel material of the present invention, the residual stress distribution in the depth direction of the steel material can be measured by changing the frequency of the exciting current. Also,
When the tip of the magnetic core is tapered, it can be applied to a narrow measurement area, for example, a measurement area such as the bottom of a gear.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a measuring device.

FIG. 2 is a graph showing the relationship between compressive residual stress and voltage value.

FIG. 3 is a graph showing the relationship between the reduction rate of retained austenite and compressive residual stress.

FIG. 4 is an explanatory view showing the operation of the measuring method of the example.

FIG. 5 is an explanatory diagram showing the operation of the measuring method of the example.

FIG. 6 is a graph showing a relationship between a reduction rate of retained austenite and a voltage value.

FIG. 7 is a graph showing the relationship between compressive residual stress and voltage value.

FIG. 8 is a graph showing the relationship between the amount of retained austenite and the compressive residual stress before the shot.

FIG. 9 is a graph showing the relationship between arc height and compressive residual stress.

10A and 10B are graphs showing distribution forms of compressive residual stress.

11A to 11D are graphs showing distribution forms of compressive residual stress in the depth direction.

FIG. 12 is a side view showing a usage state in an application example.

FIG. 13 is a side view showing a cross section of a part of an essential part in an application example.

FIG. 14 is a front view of a thin plate forming a magnetic core of a measuring apparatus according to another example.

FIG. 15 is a perspective view of a measuring device according to another example.

FIG. 16 is a front view showing a section of a measuring device according to another example.

17 is a cross-sectional view taken along the line W1-W1 of FIG.

FIG. 18 is an enlarged side view of the tip of the magnetic core.

FIG. 19 is a configuration diagram schematically showing a main part of a measuring device according to another example in use.

FIG. 20 is a graph showing the relationship between the amount of protrusion of the sensor guide with respect to the magnetic core and the detected voltage.

[Explanation of symbols]

In the figure, 1 is a steel material, 11 is a machined surface, 2 is a measuring device, 21 is a sensor, 23 is a measuring instrument, 210 is a magnetic core, 211 is an exciting coil, 212 is a detecting coil, 231 is an oscillator, 238 is a frequency variable timing. Circuit 234 is a correction circuit 235
Indicates an arithmetic unit. Further, 271 indicates thin plates 271 and 270, magnetic cores, and 21b indicates a sensor guide.

Claims (1)

[Claims] 1. A magnetic core applied to a steel material having a magnetic permeability and a built-in residual stress, and an exciting coil forming a magnetic path wound around the magnetic core and connecting the surface layer portion of the steel material and the magnetic core. ,
A sensor having a detection coil wound around the magnetic core and outputting a voltage signal according to the residual stress of the steel material by electromagnetic induction accompanying the exciting current of the exciting coil; and a high-frequency wave as an exciting current to the exciting coil of the sensor. The exciting current is composed of a current supply unit that can flow an alternating current and change its frequency, and a correction unit that corrects the voltage signal detected by the detection coil according to the frequency of the exciting current. A residual stress distribution measuring device for steel material, characterized in that the residual stress distribution in the depth direction of the steel material is measured by correcting the voltage signal obtained by flowing through the detector coil by a correction unit.