JP6104161B2 - Surface characteristic evaluation apparatus and surface characteristic evaluation method - Google Patents

Description

  The present invention relates to a surface characteristic evaluation apparatus and a surface characteristic evaluation method, and more particularly to a surface characteristic evaluation apparatus and a surface characteristic evaluation method for evaluating surface characteristics such as residual stress and hardness of an object to be inspected.

Steel products such as gears and shafts used for automobile parts are subjected to surface treatment such as heat treatment, surface hardening by nitriding treatment, shot peening treatment, etc. to improve wear resistance and fatigue strength. .
Conventionally, evaluation of surface characteristics such as residual stress and hardness after surface treatment of these products has been performed by sampling destructive inspection. For this reason, there are problems that all products cannot be inspected directly, and that the inspected product cannot be used because of destructive inspection.

  Therefore, there is an increasing demand for development of an apparatus capable of nondestructively inspecting the surface characteristics of products. As such an apparatus, for example, in Patent Document 1, an AC signal is input to a test circuit having a coil disposed above the shot peening processing surface while changing the frequency, and the frequency response characteristic of the impedance in the test circuit. A non-destructive inspection device for shot peening treatment surfaces that inspects the state of occurrence of residual stress in an inspection object is disclosed.

JP 2008-2773 A

  However, in the inspection apparatus in which the coil having the open magnetic circuit structure is disposed above the shot peening processing surface as in the above-described technique, the detection sensitivity is large because the magnetic attenuation and leakage between the inspection target and the sensor are large. In addition, there is a problem that the reproducibility of the measured value is lowered. In addition, since the method of obtaining the frequency response characteristics of the impedance by inputting an AC signal while changing the frequency is used, the penetration depth of the magnetism into the object to be inspected changes, and the surface characteristics having a distribution in the depth direction are accurately determined. There was a problem that could not be grasped.

  Accordingly, the present invention provides a surface property evaluation apparatus and a surface property evaluation method that can accurately and non-destructively evaluate the surface properties of an object to be inspected that have undergone surface treatment such as heat treatment, nitriding treatment, and shot peening treatment. The purpose is to do.

In order to achieve the above-described object, the present invention is a surface property evaluation apparatus for evaluating the surface property of a test object, which is a steel material subjected to shot peening treatment, a core made of a magnetic material, and a core wound around the core. A magnetic sensor for detecting the magnetic characteristics of the surface of the object to be inspected, power supply means for supplying AC power of a single frequency to the coil of the magnetic sensor, and AC power is supplied. The magnetic detection signal is input from the coil, and the magnetic detection signal is synchronously detected by a carrier wave having the same frequency as the AC power supplied to the coil, so that the magnetic characteristics of the surface of the inspection target detected by the magnetic sensor are obtained. a signal detecting means for detect the surface characteristic signal corresponding storage means for storing a value that indicates the relationship between the predetermined surface characteristic signal and the surface characteristics of the object to be inspected, in the storage means And憶value, based on a single surface characteristics signals thus detected in the signal detecting means by supplying the AC power of single frequency, the surface characteristic calculating means for calculating the surface characteristics of the object to be inspected The power supply means supplies alternating current power of a certain frequency to the coil of the magnetic sensor so that the core of the magnetic sensor is excited and forms a closed magnetic circuit with the surface of the object to be inspected. The core of the magnetic sensor is an E-shaped core in which a coil is wound around a central leg.

According to the present invention configured as described above, the magnetic characteristics of the surface of the inspection target are detected by the magnetic sensor supplied with AC power by the power supply means, and the inspection target detected by the magnetic sensor in the signal detection means A surface characteristic signal corresponding to the magnetic characteristic of the surface of the surface is detected, and the surface characteristic calculation means detects the surface characteristic value stored in the storage means and the value indicating the relationship between the surface characteristics of the object to be inspected and the surface Based on the characteristic signal, the surface characteristic of the object to be inspected can be calculated.
In the magnetic sensor, since the core forms a closed magnetic circuit with the surface of the inspection target, it is possible to prevent magnetic attenuation and leakage between the inspection target and the magnetic sensor. As a result, the strength of the surface characteristic signal can be increased, and the detection sensitivity of the magnetic characteristic by the magnetic sensor can be improved, so that the surface characteristic of the object to be inspected can be evaluated with high accuracy in a non-destructive manner.
In addition, by supplying AC power of a certain frequency to the coil, the surface characteristics of the object to be inspected are evaluated, so that the magnetic penetration depth into the object to be inspected can be made constant. The surface characteristics having the distribution can also be accurately grasped.
Further, the core of the magnetic sensor is formed in an E-shaped core in which a coil is wound around a central leg, and the coil is sandwiched between the cores, so that magnetic leakage can be effectively suppressed. And it is easy to form a closed magnetic circuit.
Here, “calculating surface characteristics” means not only calculating absolute values such as residual stress and hardness, but also calculating whether or not the surface characteristic signal is within a predetermined range with respect to a reference value. It is a concept including the case of evaluating surface characteristics.

In the present invention, it is preferable that the preset value indicating the relationship between the surface characteristic signal and the surface property of the inspection target is a calibration curve indicating the correspondence between the surface characteristic signal and the inspection target.
According to the present invention thus configured, the surface characteristics of the object to be inspected (for example, the thickness of the nitrided layer when the nitriding treatment is performed, the depth of the compressive residual stress when the shot peening treatment is performed, etc.) Can be calculated.

In the present invention, it is preferable that the value indicating the relationship between the preset surface characteristic signal and the surface characteristic of the object to be inspected is a reference value indicating the surface characteristic signal in a reference sample having a predetermined surface characteristic.
According to the present invention configured as described above, the quality of the inspected object is determined by calculating the difference between the measured surface characteristic signal and the reference value (for example, the thickness of the nitride layer when nitriding is performed) And whether or not the depth of compressive residual stress when the shot peening process is performed is sufficient.

In this invention, Preferably, the core of a magnetic sensor can contact along the surface shape of to-be-inspected object.
According to the present invention configured as described above, since the core of the magnetic sensor can be contacted along the surface shape of the object to be inspected, the core to be in contact with the surface of the object to be inspected can be magnetically coupled to the object to be inspected. Magnetic attenuation and leakage with the sensor can be prevented. Thereby, the intensity | strength of a surface characteristic signal can be increased and the detection sensitivity of the magnetic characteristic by a magnetic sensor can be improved.

In the present invention, preferably, the core of the magnetic sensor can be arranged such that the distance between the core and the surface of the object to be inspected is 3.0 mm or less.
According to the present invention configured as described above, when the detection signal of the magnetic characteristic detected by the magnetic sensor is strong, such as when the inspection target is a ferromagnetic material, the core and the surface of the inspection target Since the magnetic sensor and the surface of the object to be inspected can form a closed magnetic path, and a sufficiently strong magnetic detection signal can be obtained. The surface characteristics of the object can be evaluated accurately with non-destructiveness.

In the present invention, preferably, the core of the magnetic sensor can be arranged such that the distance between the core and the surface of the object to be inspected is 0.3 mm or less.
According to the present invention configured as described above, since the distance between the core and the surface of the object to be inspected can be arranged to be 0.3 mm or less, the object to be inspected having a weak magnetic property detection signal is measured. Even in this case, the surface characteristics of the object to be inspected can be evaluated with high accuracy in a nondestructive manner.

In the present invention, preferably, the core of the magnetic sensor is formed of a ferromagnetic material.
According to the present invention configured as described above, since the core of the magnetic sensor is formed of a ferromagnetic material, the magnetic flux density inside the core can be increased, and the S / N ratio (S: to the object to be inspected). (Magnetic penetration, N: leakage magnetism) can be increased, so that the detection sensitivity of the magnetic characteristics by the magnetic sensor can be improved.

In order to achieve the above-described object, the present invention is a surface property evaluation apparatus for evaluating the surface property of a test object that is a steel material subjected to shot peening treatment, and a core made of a magnetic material, and the core A magnetic sensor for detecting the magnetic characteristics of the surface of the object to be inspected, power supply means for supplying AC power of a single frequency to the coil of the magnetic sensor, and AC power A magnetic detection signal is input from the supplied coil, and this magnetic detection signal is synchronously detected by a carrier wave having the same frequency as the AC power supplied to the coil, whereby the surface magnetism detected by the magnetic sensor is detected. a signal detecting means for the surface characteristic signal to detect in accordance with the characteristics, a storage means for storing a value indicating a preset surface characteristic signal and relationship between the surface characteristics of the object to be inspected, the storage Surface properties based the value stored in the stage, on the single surface characteristics signals thus detected in the signal detecting means by supplying the AC power of single frequency to calculate the surface characteristics of the object to be inspected And a power supply means for supplying AC power of a constant frequency to the coil of the magnetic sensor, thereby exciting the core of the magnetic sensor and forming a closed magnetic circuit with the surface of the object to be inspected. The magnetic sensor core includes a cylindrical part around which a coil is wound, and a circular pipe part that is disposed so as to surround the cylindrical part and whose one end is closed by a base part. It is arranged at the axial center of the pipe part, and one end of the cylindrical part is connected to the base part of the circular pipe part.
According to the present invention configured as described above, since the coil is surrounded by the core, magnetic leakage can be effectively suppressed and a closed magnetic circuit can be easily formed. In addition, the core is easy to manufacture and low cost.

In order to achieve the above-described object, the present invention provides a surface property evaluation method for evaluating the surface property of a test object that is a steel material subjected to shot peening treatment, and includes a core made of a magnetic material, and a core wound around the core. A magnetic sensor for detecting the magnetic characteristics of the surface of the object to be inspected, and supplying a single frequency AC power to the coil of the magnetic sensor, thereby providing a core for the magnetic sensor. Energizing and forming a closed magnetic circuit with the surface of the object to be inspected, and inputting a magnetic detection signal from a coil to which AC power is supplied, and this magnetic detection signal is a carrier wave having the same frequency as the AC power supplied to the coil by by synchronous detection, the a step of detect a surface characteristic signal corresponding to the magnetic properties of the detected object to be inspected on the surface by the magnetic sensor, and the surface characteristics signal set in advance A step of storing a value that indicates the relationship between the surface characteristics of査subject, and the stored relationship, a single detected in the step of detecting a surface characteristic signal by supplying the AC power of single frequency based on the surface characteristics signal, characterized in that have a, a step of calculating the surface characteristics of the object to be inspected, the core of the magnetic sensor is an E-shaped core coil in the center of the leg portion is wound It is said.

It is a block diagram which shows the surface characteristic evaluation apparatus by embodiment of this invention. It is explanatory drawing which shows the magnetic sensor of the surface characteristic evaluation apparatus by embodiment of this invention. It is a perspective view which shows the some modification of the magnetic sensor of the surface characteristic evaluation apparatus by embodiment of this invention, respectively. It is a diagram which shows distribution of the depth direction of the residual stress in the steel materials which performed the shot peening process in Example 1 of this invention. It is a diagram which shows distribution of the depth direction of the amount of retained austenite in the steel materials which performed the shot peening process in Example 1 of this invention. It is a diagram which shows the relationship between the hardness in Example 2 of this invention, and the voltage value of a surface characteristic signal. It is a diagram which shows the relationship between the thickness of the nitride layer in Example 4 of this invention, and the voltage value of a surface characteristic signal.

  Hereinafter, a surface property evaluation apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, a surface property evaluation apparatus 1 according to an embodiment of the present invention detects a magnetic property such as a permeability change and an inverse magnetostriction effect on a surface to be inspected and outputs a magnetic detection signal. And power supply means 20 for supplying AC power to the magnetic sensor 10, and signal detection for extracting and detecting a surface characteristic signal corresponding to the magnetic characteristic of the surface of the inspection object from the magnetic detection signal detected by the magnetic sensor 10 Means 21, surface characteristic calculation means 22 for calculating the surface characteristics of the object to be inspected such as residual stress and hardness based on the surface characteristic signal obtained by the signal detection means 21, and a preset surface characteristic signal A value indicating the relationship between the surface characteristics detected by the signal detection means, specifically, a calibration curve indicating the relationship between the surface characteristics signal and the surface characteristics, and surface characteristics such as hardness and residual stress are known. Storage means 23 for storing the previously acquired surface characteristic signal (reference value) using a reference sample, and a. Further, a display screen 24 for displaying the surface characteristics calculated by the surface characteristic calculation means 22 and a display means 24 such as an audio output device are provided.
The surface property evaluation apparatus 1 can include other components such as an amplifier.

  Here, “surface characteristics” means characteristics near the surface of the object to be inspected and up to a predetermined depth affected by the surface treatment, and “surface magnetic characteristics” means magnetism excited by the magnetic sensor 10. Shows the magnetic characteristics of the region up to a predetermined depth of the object to be inspected, which is detected through penetration.

  The signal detector 21 synchronously detects the magnetic detection signal output from the magnetic sensor 10, and extracts a surface characteristic signal corresponding to the magnetic characteristic of the surface of the inspection target from the detection output of the synchronous detector 21a. And a low-pass filter 21b.

  The magnetic sensor 10 has a shape capable of forming a closed magnetic path by the magnetic sensor 10 and the surface of the inspection target. Here, a magnetic sensor having an E-shaped core will be described as an example of such a magnetic sensor. The E-shaped core is easy to manufacture and low cost.

  As shown in FIG. 2, the magnetic sensor 10 includes an E-shaped core 11 made of a magnetic material and a coil 12. The core 11 includes a central leg portion 11a, leg portions 11b and 11c disposed on both sides of the leg portion 11a, and a base portion 11d disposed to face the surface 30a of the inspection target 30. Yes. One end of each of the leg portions 11a, 11b, and 11c is connected to the base portion 11d. The core 11 is erected so as to be E-shaped from the base portion 11d toward the surface 30a. The coil 12 is wound around the leg portion 11a.

  Here, the core 11 is preferably formed of a ferromagnetic material. In this case, the magnetic flux density inside the core 11 can be increased, and the S / N ratio (S: magnetism penetrating into the steel material, N: leakage magnetism) can be increased, so that the detection sensitivity of the magnetic characteristics by the magnetic sensor 10 can be improved. Examples of the ferromagnetic material include iron, supermalloy, permalloy, silicon steel, ferrite (Mn—Zn series, Ni—Zn series), carbonyl iron dust, molybdenum permalloy, Sendust, and the like.

  The magnetic sensor 10 is formed so that the tip portions of the leg portions 11a, 11b, and 11c can come into contact with the surface 30a of the inspection target 30. For example, when the inspection target 30 is a flat plate, the legs 11a, 11b, and 11c are formed so that the tip ends thereof are on the same plane.

  Next, a method for evaluating the surface property of the inspection object by the surface property evaluation apparatus 1 will be described. Here, a steel material in which the compound layer 30b is formed in the vicinity of the surface 30a by nitriding will be described as an example of the inspection target 30.

  First, the magnetic sensor 10 is arranged so that the legs 11a, 11b, and 11c are in contact with the surface 30a of the inspection target 30. The “contact” in the present embodiment includes a case where at least one of the legs 11a, 11b, and 11c is in contact with the surface 30a of the inspection target 30 (for example, the shape of the surface 30a and the magnetic field). When the entire leg portions 11a, 11b, 11c are not in close contact with the surface 30a due to manufacturing errors of the sensor 10, etc.).

  By disposing the magnetic sensor 10 so as to be in contact with the surface 30 a of the inspection target 30, it is possible to prevent magnetic attenuation and leakage between the inspection target 30 and the magnetic sensor 10. Thereby, the intensity | strength of a surface characteristic signal can be increased and the detection sensitivity of the magnetic characteristic by the magnetic sensor 10 can be improved.

  If the magnetic sensor 10 and the surface (compound layer 30b) of the test object 30 form a closed magnetic circuit and a sufficiently strong magnetic detection signal can be obtained, the magnetic sensor 10 is brought into contact with the surface 30a of the test object 30. It does not have to be. Here, the distance between the magnetic sensor 10 and the surface of the inspection object 30 is desirably 3.0 mm or less, and more desirably 0.3 mm or less. In the case of a material having a weak magnetic detection signal, it is desirable that the distance be 0.3 mm or less in order to obtain a sufficient magnetic detection signal intensity. When the object 30 to be inspected is made of a material having a strong magnetic detection signal such as a ferromagnetic material, the magnetic sensor 10 can obtain a sufficient magnetic detection signal intensity, so that the distance is set to 3.0 mm or less. Can do.

  Note that the arrangement direction of the magnetic sensor 10 with respect to the inspection object 30 may be changed in accordance with the shape of the inspection object 30. Specifically, when the object 30 to be inspected is a curved surface, for example, as shown in FIG. 3D described later, when the object 30 to be inspected has a cylindrical shape, the magnetic sensor 10 is placed in the longitudinal direction of the columnar shape. It is good to arrange along.

By making the distance between the magnetic sensor 10 and the surface of the object 30 to be inspected the same as the distance when the calibration curve or the reference value is acquired, the fluctuation error of the surface characteristic signal due to lift-off can be eliminated.
By performing the non-contact evaluation, for example, measurement can be performed without stopping the object to be inspected 30 while it is being conveyed, so that the time required for inspection can be shortened.

  Next, when AC power of a predetermined frequency is supplied to the coil 12 by the power supply means 20, an AC magnetic field H is generated in the core 11, and magnetism is generated to a predetermined depth of the compound layer 30b of the test object 30 according to the frequency. The closed magnetic circuit is formed by the region that penetrates and reaches the predetermined depths of the legs 11a and 11c and the compound layer 30b of the test object 30.

  Since the alternating magnetic field H linked to the coil 12 changes according to the magnetic property of the compound layer 30b through which the magnetism penetrates, the coil 12 can detect the magnetic property according to the property (surface property) of the compound layer 30b. it can. The coil 12 outputs a change in magnetic quantity generated based on the magnetic permeability and the inverse magnetostriction effect according to the surface characteristics to the signal detection means 21 as a magnetic detection signal.

  Regarding the relationship between the surface characteristics and the magnetic characteristics, for example, when the surface is cured or a compound layer is formed, the magnetic permeability decreases. When compressive residual stress is applied by shot peening or the like, the magnetic permeability decreases due to the inverse magnetostrictive effect. When the magnetic permeability decreases, the amount of magnetism in the magnetic circuit decreases, so the strength of the magnetic detection signal decreases.

  The frequency of the AC power is appropriately set according to the material of the object 30 to be inspected, the characteristics to be evaluated, the depth to be evaluated, and the like. For example, it can set so that magnetism may penetrate | infiltrate intensively with respect to the depth of 100-200 micrometers from the outermost layer surface of steel materials.

The signal detection means 21 detects a surface characteristic signal corresponding to the magnetic characteristic of the surface 30 a of the test object 30 (magnetic characteristic characteristic of the compound layer 30 b) as a voltage signal from the magnetic detection signal input from the magnetic sensor 10.
The magnetic detection signal input from the magnetic sensor 10 is input to the synchronous detector 21a, and the synchronous detector 21a detects the carrier wave having the same frequency as the AC power supplied to the coil 12 by the power supply means 20. The detection output of the synchronous detector 21a is output to the low-pass filter 21b. The low-pass filter 21b extracts a surface characteristic signal corresponding to the magnetic characteristic of the surface 30a of the inspection object 30 from the detection output as a voltage signal, and surface characteristic calculation means 22 to output.

  The surface characteristic calculation means 22 calculates the surface characteristics of the inspection object 30 such as residual stress and hardness based on the signal obtained by the signal detection means 21. The surface characteristic calculation unit 22 can calculate the hardness, the residual stress value, and the like based on the calibration curve stored in the storage unit 23 as the relationship between the voltage and the surface characteristic. Here, when only the voltage value of the surface characteristic signal is sufficient as a value for managing the surface characteristic of the inspection object 30, the calculation of the surface characteristic by the calibration curve may not be performed.

  The surface property calculation means 22 may be able to make a pass / fail determination based on whether or not the calculated surface property is within a predetermined range.

  Further, the quality determination may be performed based on a difference value between a surface characteristic signal (reference value) of a reference sample showing a predetermined surface characteristic and a measured surface characteristic signal. In this case, first, a reference sample showing a predetermined surface characteristic is prepared, a surface characteristic signal is measured in advance, and stored in the storage means 23 as a reference value. The surface characteristic calculation unit 22 calculates a difference value between the reference value and the measured surface characteristic signal, and determines whether the surface characteristic signal is within a predetermined range.

  For example, when it is desired to manage the hardness of the surface of the inspection object 30 to H ± α, a reference value is set using a sample of hardness H as a reference sample, and a difference value of a surface characteristic signal corresponding to α is set as a threshold value. When the calculated difference value exceeds the threshold value, it can be determined as defective.

  The surface characteristics and determination results calculated by the surface characteristic calculation means 22 are output to the display means 24, and the display means 24 displays the surface characteristics and determination results by a screen, audio output, or the like. For example, values of surface characteristics such as hardness and residual stress can be displayed. Also, only the voltage value of the surface characteristic signal can be displayed.

  When the surface characteristic calculation means 22 performs pass / fail determination of an object to be inspected, it is possible to display a warning of a defect by a warning sound or a warning lamp.

  According to the surface characteristic evaluation apparatus 1, a closed magnetic path is formed by the magnetic sensor 10 and the region from the surface 30 a of the inspection target 30 to a predetermined depth, and therefore, the magnetism between the inspection target 30 and the magnetic sensor 10 is formed. Attenuation and leakage can be prevented. As a result, the strength of the surface characteristic signal can be increased, and the detection sensitivity of the magnetic characteristic by the magnetic sensor 10 can be improved, so that the surface characteristic of the object to be inspected 30 can be evaluated nondestructively with high accuracy. .

  Further, during inspection, the surface characteristics of the inspection object 30 are evaluated by supplying AC power of a constant frequency to the coil 12, so that the penetration depth of the magnetism into the inspection object 30 is constant. Therefore, it is possible to accurately grasp the surface characteristics having a distribution in the depth direction. Thereby, the thickness of the nitride layer can be evaluated.

  In this embodiment, the surface property evaluation of the steel material in which the compound layer 30b is formed by nitriding as the object to be inspected 30 has been described. Can do.

  By changing the frequency of the AC power supplied to the coil 12 by the power supply means 20, the magnetic penetration depth can be changed. Since the magnetic penetration depth becomes shallower as the frequency is higher, the surface characteristics of the shallow region from the surface can be evaluated. By changing the frequency of the AC power in this way, the distribution of residual stress in the depth direction, the thickness of the compound layer, and the like can be evaluated.

  Next, a modified example of the magnetic sensor will be described with reference to FIG. In the above-described embodiment, the magnetic sensor including the E-shaped core 11 is used. However, the present invention is not limited to this, and a closed magnetic circuit is formed by the magnetic sensor and a region from the surface of the inspection target to a predetermined depth. Can be used, a magnetic sensor having variously shaped cores can be used.

  As shown in FIG. 3 (A), a cylindrical part 41a around which a coil 42 is wound, and a circular pipe part 41b arranged so as to surround the cylindrical part 41a and closed at one end by a base part 41c are provided. It is possible to use the magnetic sensor 40 in which the portion 41a is arranged at the axial center of the circular tube portion 41b and one end of the cylindrical portion 41a is connected to the base portion of the circular tube portion 41b. According to the magnetic sensor 40, since the entire circumference of the coil 42 is surrounded by the circular tube portion 41b, magnetic leakage can be effectively suppressed, and a closed magnetic circuit is easily formed.

  Further, a magnetic sensor 50 in which a coil 52 is wound around a U-shaped core 51 as shown in FIG. 3B, a magnetic sensor 60 in which a coil 62 is wound around an L-shaped core 61 as shown in FIG. Can also be used.

  Further, as shown in FIG. 3D, a magnetic sensor 10 using a core 11 configured such that the shapes of the legs 11a, 11b, and 11c can be brought into contact with the shape of the object to be inspected 30 can be used. .

Next, the effect of the surface property evaluation apparatus according to the above-described embodiment of the present invention will be described.
(1) According to the surface characteristic evaluation apparatus 1 according to the present embodiment, a closed magnetic path is formed by the magnetic sensor 10 and the region from the surface 30a of the inspection target 30 to a predetermined depth. 10 can be prevented from being attenuated or leaked. As a result, the strength of the surface characteristic signal can be increased, and the detection sensitivity of the magnetic characteristic by the magnetic sensor 10 can be improved, so that the surface characteristic of the object to be inspected 30 can be evaluated nondestructively with high accuracy. .
Further, since the surface characteristics of the inspection object 30 are evaluated by supplying AC power of a constant frequency to the coil 12, the depth of magnetic penetration into the inspection object 30 can be made constant. Surface characteristics having a distribution in the vertical direction can also be accurately grasped.

(2) By disposing the core 11 of the magnetic sensor 10 so as to be in contact with the surface 30a of the inspection target 30, magnetic attenuation and leakage between the inspection target 30 and the magnetic sensor 10 can be prevented. . Thereby, the intensity | strength of a surface characteristic signal can be increased and the detection sensitivity of the magnetic characteristic by the magnetic sensor 10 can be improved. In addition, the fluctuation error of the surface characteristic signal due to lift-off can be eliminated.

(3) When the inspection object is a ferromagnetic material, the core 11 of the magnetic sensor 10 is not in contact with the inspection object 30 and the distance between the core 11 and the surface 30a of the inspection object 30 is 3. When the magnetic sensor 10 is arranged to be 0 mm or less, a closed magnetic circuit is formed by the magnetic sensor 10 and the surface of the object 30 to be inspected, and a sufficiently strong magnetic detection signal can be obtained. Non-destructive and accurate evaluation is possible. Even when measuring an object to be inspected with a weak magnetic detection signal, the surface characteristics of the object to be inspected can be made nondestructive by arranging the core and the surface of the object to be inspected so that the distance between them is 0.3 mm or less. It can be evaluated with high accuracy.
In addition, by performing the non-contact evaluation, for example, it is possible to perform measurement without stopping the object to be inspected 30 while conveying the object to be inspected, so that the time required for inspection can be shortened.

(4) When the core 11 is formed of a ferromagnetic material such as ferrite, the magnetic flux density inside the core 11 can be increased, and the S / N ratio (S: magnetism penetrating the steel material, N: leakage magnetism) is increased. The detection sensitivity of the magnetic characteristics by the magnetic sensor 10 can be improved.

  Examples of surface property measurement using the surface property evaluation apparatus of the present invention are shown below.

Example 1
In this example, the residual stress on the surface of the steel material subjected to the shot peening treatment was evaluated.

  As an evaluation sample, a surface-treated material obtained by performing shot peening treatment on the surface of the SCH420H gas carburized material was used. An untreated material that was not subjected to surface treatment was used as a comparative material. The shot peening process was performed using an injection material having a particle diameter of 100 μm and a hardness of Hv 900 to 950 at an injection pressure of 0.2 MPa.

  The residual stress was evaluated by bringing an E-shaped core magnetic sensor into contact with the surface. The core is made of a ferromagnetic Mn—Zn-based ferrite, and is formed by arranging prismatic leg portions of 4 mm × 4 mm × 3 mm at intervals of 3 mm. The alternating current supplied to the coil was 20 kHz and 3.5 mA.

  The voltage of the surface characteristic signal detected by the surface characteristic evaluation apparatus was reduced to 0.71 V for the surface-treated material compared to 0.79 V for the untreated material.

  FIG. 4 shows the distribution of the residual stress in the surface treatment material in the depth direction. The residual stress was measured by an X-ray stress measurement method while polishing the surface treatment material by several μm by electrolytic polishing. As shown in FIG. 5, it can be seen that the surface treated material has a larger compressive residual stress than the untreated material, with a depth of 15 μm as a peak.

  Residual austenite is present in the SCH420H gas carburized material, and the amount of retained austenite decreases because of martensitic transformation by shot peening. FIG. 5 shows the distribution of the retained austenite amount in the depth direction. As shown in FIG. 5, it can be seen that the amount of retained austenite is significantly reduced in the surface-treated material compared to the untreated material.

When compressive residual stress is applied, the change in magnetic properties due to the inverse magnetostriction effect is more dominant than the change in permeability due to the reduction in the amount of retained austenite, and the change in permeability of the entire surface treatment material is reduced. Yes.
The voltage change of the surface characteristic signal corresponds to the permeability change, and it was confirmed that the residual stress can be evaluated with high accuracy by the surface characteristic evaluation apparatus of the present invention.

(Example 2)
In this example, the surface characteristic signal with respect to the hardness of the steel material was evaluated using a steel material (SKS3) whose hardness was changed by heat treatment.

  The hardness was evaluated by bringing an E-shaped core magnetic sensor into contact with the surface. The alternating current supplied to the coil was 20 kHz and 3.5 mA.

  FIG. 6 shows the relationship between the Vickers hardness and the surface characteristic signal voltage (device output). The higher the Vickers hardness, the correspondingly the tendency that the voltage of the surface characteristic signal decreases, and it was confirmed that the surface characteristic evaluation apparatus of the present invention can evaluate the hardness with high accuracy.

(Example 3)
In this example, the effect of bringing the magnetic sensor into contact with the test object was evaluated.

  The evaluation sample and conditions are the same as in Example 1. When the core is not contacted and the distance from the surface of the sample to be evaluated is 1 mm, the surface characteristic signal is 0.2 V and the signal strength is sufficient, but the surface characteristic signal when the core is contacted is It greatly increased to 0.8V. Thus, it was confirmed that the strength of the surface characteristic signal is increased by bringing the core of the magnetic sensor into contact with the detection target, and the detection sensitivity can be improved.

Example 4
In this example, the surface characteristic signal with respect to the thickness of the nitride layer was evaluated using a steel material provided with a nitride layer by nitriding treatment. The steel material (SKD61) was heated at 500 to 600 ° C. in an NH 3 atmosphere to provide a nitride layer having a thickness of 1.5 μm to 10.0 μm.

  The evaluation was performed by bringing an E-shaped core magnetic sensor into contact with the surface. The alternating current supplied to the coil was 20 kHz and 3.5 mA.

  The voltage of the surface characteristic signal detected by the surface characteristic evaluation apparatus increased as the thickness of the nitride layer increased as shown in FIG. Thereby, it was confirmed that the thickness of the nitride layer can be accurately evaluated.

Claims (10)

A surface property evaluation apparatus for evaluating the surface property of a test object that is a steel material subjected to shot peening treatment,
A magnetic sensor comprising a core made of a magnetic material and a coil wound around the core, and detecting magnetic characteristics of the surface of the object to be inspected;
Power supply means for supplying AC power of a single frequency to the coil of the magnetic sensor;
A magnetic detection signal is input from the coil to which AC power is supplied, and this magnetic detection signal is synchronously detected by a carrier wave having the same frequency as that of the AC power supplied to the coil, thereby detecting the target detected by the magnetic sensor. a signal detecting means for detect the surface characteristic signal corresponding to the magnetic properties of the inspected surface,
Storage means for storing a value indicating a relationship between a preset surface characteristic signal and a surface characteristic of an inspection target;
The value stored in the storage means, wherein based on a single surface characteristics signals thus detected in the signal detecting means by supplying the AC power of single frequency, the surface properties of the object to be inspected And a surface property calculation means for calculating,
The power supply means supplies AC power of a certain frequency to the coil of the magnetic sensor, whereby the core of the magnetic sensor is excited and forms a closed magnetic circuit with the surface of the object to be inspected. And
The magnetic sensor core is an E-shaped core in which a coil is wound around a central leg portion. A surface property evaluation apparatus for evaluating the surface property of a test object that is a steel material subjected to shot peening treatment,
A magnetic sensor comprising a core made of a magnetic material and a coil wound around the core, and detecting magnetic characteristics of the surface of the object to be inspected;
Power supply means for supplying AC power of a single frequency to the coil of the magnetic sensor;
A magnetic detection signal is input from the coil to which AC power is supplied, and this magnetic detection signal is synchronously detected by a carrier wave having the same frequency as that of the AC power supplied to the coil, thereby detecting the target detected by the magnetic sensor. a signal detecting means for detect the surface characteristic signal corresponding to the magnetic properties of the inspected surface,
Storage means for storing a value indicating a relationship between a preset surface characteristic signal and a surface characteristic of an inspection target;
The value stored in the storage means, wherein based on a single surface characteristics signals thus detected in the signal detecting means by supplying the AC power of single frequency, the surface properties of the object to be inspected And a surface property calculation means for calculating,
The power supply means supplies AC power of a certain frequency to the coil of the magnetic sensor, whereby the core of the magnetic sensor is excited and forms a closed magnetic circuit with the surface of the object to be inspected. And
The core of the magnetic sensor includes a cylindrical part around which a coil is wound, and a circular pipe part which is disposed so as to surround the cylindrical part and whose one end is closed by a base part, and the cylindrical part is an axis of the circular pipe part The surface characteristic evaluation apparatus is characterized in that one end of the cylindrical part is connected to the base part of the circular pipe part.   3. The surface characteristic according to claim 1, wherein the value indicating the relationship between the preset surface characteristic signal and the surface characteristic of the inspection target is a calibration curve indicating a correspondence relationship between the surface characteristic signal and the inspection target. Evaluation device.   The surface according to claim 1 or 2, wherein the value indicating the relationship between the preset surface characteristic signal and the surface characteristic of the object to be inspected is a reference value indicating a surface characteristic signal in a reference sample having a predetermined surface characteristic. Characteristic evaluation device.   The surface characteristic evaluation apparatus according to claim 1, wherein the core of the magnetic sensor can be contacted along a surface shape of an inspection target.   The surface inspection characteristic evaluation apparatus according to any one of claims 1 to 4, wherein the core of the magnetic sensor can be arranged such that a distance between the core and the surface of the inspection target is 3.0 mm or less.   The surface inspection characteristic evaluation apparatus according to any one of claims 1 to 4, wherein the core of the magnetic sensor can be arranged such that a distance between the core and the surface of the inspection target is 0.3 mm or less.   The surface characteristic evaluation apparatus according to claim 1, wherein the core of the magnetic sensor is formed of a ferromagnetic material.   The surface property evaluation apparatus according to claim 8, wherein the ferromagnetic material is ferrite. A surface property evaluation method for evaluating the surface property of a test object that is a steel material subjected to shot peening treatment,
A step of preparing a magnetic sensor comprising a core made of a magnetic material and a coil wound around the core, and detecting a magnetic characteristic of the surface of the object to be inspected;
Supplying AC power of a single frequency to the coil of the magnetic sensor, thereby exciting the core of the magnetic sensor and forming a closed magnetic circuit with the surface of the object to be inspected;
A magnetic detection signal is input from the coil to which AC power is supplied, and this magnetic detection signal is synchronously detected by a carrier wave having the same frequency as that of the AC power supplied to the coil, thereby detecting the target detected by the magnetic sensor. a step of surface properties signal to detect in accordance with the magnetic properties of the inspected surface,
Storing a value indicating a relationship between a preset surface characteristic signal and a surface characteristic of an inspection target;
This and stored relationship, said single based on a single surface characteristics signal detected in the step of detecting the surface characteristic signal by supplying the AC power frequency, the surface properties of the object to be inspected A calculating step;
Have
The surface property evaluation method according to claim 1, wherein the core of the magnetic sensor is an E-shaped core in which a coil is wound around a central leg.

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