JP2002014081A - Method and device for measuring hardness penetration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for measuring hardness penetration that can directly measure the depth of the quench hardening layer of a steel material quickly and nondestructively, has high measurement accuracy and reliability, and moreover can be constituted inexpensively. SOLUTION: In this method for measuring hardness penetration, where the depth of the quench hardening layer of the steel material is measured nondestructively, a steel material 10 is magnetized in a direction along the surface by a low-frequency AC magnetic field which is generated by an excitation coil 1, an induction magnetic filed, that is induced by an eddy current generated by the magnetization, is detected by a detection coil 2, the output voltage of the detection coil is compared with the correlation data between the depth of the already known quench hardening layer of the same type of steel material and an output voltage, thus calculating the depth of the quench hardening layer of the target steel material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quenching depth measuring method and apparatus, and more particularly to a quenching depth measuring method and apparatus for non-destructively measuring the depth of a hardened layer of steel. It is.

[0002]

2. Description of the Related Art Induction hardened steel is often used for many equipment parts including automobile parts. For induction hardened steel, it is essential to evaluate the depth of the hardened layer to ensure strength. For this depth measurement, non-destructive measurement methods such as the ultrasonic method and the eddy current method have been studied.However, due to the low measurement accuracy and reliability, they have not yet become widespread. The mainstream method is to partially cut a steel material and measure the cross-sectional strength with various hardness meters such as a Vickers hardness meter. However, this method requires a lot of measurement time, requires a sample material, and has a problem that 100% inspection is impossible in principle.

The principle of measuring the depth of a hardened hardened layer by the eddy current method is that when a steel material is magnetized by a low-frequency AC magnetic field generated by an exciting coil, the magnetization lag characteristic of the steel material changes depending on the depth of the hardened layer. It is a thing that utilizes that.
In other words, the steel material is magnetized in the direction along the surface by the low-frequency AC magnetic field generated by the excitation coil, the induced magnetic field induced by the eddy current generated by the magnet is detected by the detection coil, and the peak value of the excitation current waveform and This utilizes a phenomenon in which the phase angle (magnetization delay) between the peak values of the integral waveform (magnetic flux waveform) of the output voltage of the detection coil changes depending on the depth of the hardened layer. However, since the phase angle shows a maximum at a certain depth of the hardened layer, the depth of the hardened layer cannot be uniquely determined only by the value of the phase angle.

On the other hand, martensite after quenching steel,
Both the initial magnetization curve and the conductivity of the original structure cause a difference.In the case of induction hardened materials, these differences are caused by the change in the output voltage amplitude of the detection coil placed on the steel surface with the change in quenching depth under a low-frequency AC magnetic field. Causes a change in the value. Since the output voltage of the detection coil has a characteristic that monotonously decreases as the depth of the hardened layer increases, conventionally, the output voltage of the detection coil is used for identification of the phase angle, and the value of the phase angle is conventionally used. Thus, the depth of the hardened layer was determined.

[0005]

The present inventors have repeated experiments and numerical analysis in order to find out the cause of poor measurement accuracy in the conventional eddy current method especially when the quenching depth is deep. As a result, it was confirmed that the phase angle showed a larger change as the exciting current increased at any frequency, and that the phase angle showed a peak at a quenching depth at any frequency. It has been confirmed that the quenching depth at which the peak value of the phase angle appears becomes shallower. Next, an analysis was performed to confirm whether the change in the phase angle with respect to the quenching depth was significantly affected by the magnetization curve of the original structure, martensite, or conductivity. As a result, when a difference is given to the conductivity, the phase angle change does not show a large difference with respect to the change in the quenching depth, but when the conductivity is fixed and the difference is given to the magnetization curve, a large phase angle change occurs. Was confirmed to occur. At the same time, it was confirmed that a peak value of the phase angle appeared at a certain quenching depth. From the above, it was confirmed that the change in the phase angle with respect to the induction hardening depth was greatly affected by the difference in the magnetization curve between the original structure and the martensite portion (hardened layer).

[0006] The relative permeability, magnetic flux density and eddy current density distribution inside the steel material were analyzed while keeping the frequency and the exciting current constant. As a result, since the relative magnetic permeability appeared lower in the quenched region than in the original structure, it was confirmed that the magnetic flux density distribution inside the steel material was concentrated in the original structure having higher magnetic permeability. on the other hand,
The eddy current density distribution shows the highest value in the steel surface layer, the gradient of the eddy current density distribution in the quenched region is smaller than that in the original structure region, and the peak value of the eddy current in the steel surface layer has a deeper quenching depth It was also confirmed that the tendency to decrease was shown.

It is considered that various physical phenomena are involved in the cause of the change in the phase angle of the output voltage with respect to the exciting current, but the largest cause is considered to be the eddy current generated inside the steel material. . As a result of analyzing the total amount of eddy current generated inside the steel material for each quenching depth while keeping the frequency and excitation current constant, a peak appears at a certain quenching depth, and the quenching depth corresponding to this peak value has a phase angle peak The quenching depth was almost the same, and the overall tendency of the total eddy current was the same as the phase angle. From this result, it can be understood that the amount of eddy current generated inside the steel material changes with the change in the burn-in depth, and the amount of eddy current is reflected in the phase angle.

Next, the peak value of the integrated waveform (magnetic flux density) of the output voltage with respect to the change in the quenching depth was evaluated. From the analysis results when the quenching depth was changed with the frequency and the excitation current as parameters, as the frequency increased,
Since the skin effect is enhanced, the slope becomes smaller in the region where the quenching depth is deep, but it can be confirmed that the amplitude shows a decreasing tendency in proportion to the depth. This is presumably because, as the quenching depth increases, the region with low magnetic permeability spreads over the steel surface layer, and the peak value of the eddy current concentrated on the steel surface layer decreases.

The conventional eddy current method uses a Lissajous display consisting of two elements, a phase angle and an output voltage amplitude. As a result of verifying the characteristics both analytically and experimentally,
At the same frequency, the amplitude and phase of the overall Lissajous curve increase as the exciting current increases, making it easier to determine the quenching depth.On the other hand, the frequency change is related to the penetration depth of the eddy current. It was found that the higher the height, the easier it was to identify a region with a small quenching depth, but the more difficult it was to identify a deep region. In other words, if the change in phase angle is used, when the quenching depth is deep, it is inevitable that the measurement accuracy is extremely reduced and a result with poor reliability is displayed.

On the other hand, a magnetic material has non-uniformity in magnetic characteristics and causes magnetic noise in an unsaturated magnetization region.
Since it is expected that a large variation occurs in the output voltage of the detection coil, it is hardly possible to measure the quenching depth using only the output voltage of the detection coil.

The present inventors have paid attention to the fact that the output voltage of the detection coil is substantially proportional to the quenching depth, and dared to develop a method of measuring the quenching depth using only the output voltage. To evaluate the variation of the magnetic properties of the site by experiments and to examine the high frequency quenching depth non-destructive inspection method using a low frequency AC magnetic field by numerical analysis considering the non-uniformity of the magnetic properties to complete the present invention It was reached. However, the present invention is capable of directly measuring the depth of a quenched hardened layer of a steel material in a short time and nondestructively, and has a high measurement accuracy, high reliability, and a low cost quenching depth measuring method. And an apparatus therefor.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a quenching depth measuring method for non-destructively measuring the depth of a quenched hardened layer of steel, wherein the method comprises the steps of: The steel material is magnetized in the direction along the surface by the low-frequency AC magnetic field, the induced magnetic field induced by the eddy current generated by the magnet is detected by a detection coil, and the output voltage of the detection coil is converted to the known firing of the same steel material. A quenching depth measurement method was established by calculating the quench hardened layer depth of the target steel by comparing the correlation data between the depth of the hardened layer and the output voltage.

Here, it is preferable to improve the accuracy by detecting the spatial magnetic field generated by the exciting coil by an external magnetic field detecting means and controlling the exciting current so that the spatial magnetic field becomes constant.

The present invention also relates to a quenching depth measuring device for non-destructively measuring the depth of a quenched hardened layer of a steel material, wherein a low-frequency AC magnetic field for magnetizing in a direction along the surface of the steel material is provided. An excitation coil to be generated, a detection coil to detect an induction magnetic field induced by an eddy current generated in the steel material, and correlation data of a known quench hardened layer and output voltage of the same type of steel material are stored in advance, and the detection coil And a calculating means for calculating the depth of the quench hardened layer of the target steel material from the output voltage and the correlation data.

Here, an external magnetic field detecting means for detecting a spatial magnetic field generated by the exciting coil is provided near the exciting coil, and the spatial magnetic field detected by the external magnetic field detecting means is kept constant. It is preferable to control the exciting current so that

Further, the exciting coil is wound around one contact core of a U-shaped yoke having a pair of parallel contact cores to be brought into contact with the surface of the steel material, and the detection coil is wound around the other contact core. It is preferable that a measuring probe having the external magnetic field detecting means disposed between the tip ends of the contact cores is used.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

The quenching depth measuring apparatus of the present invention is a quenching depth measuring apparatus for non-destructively measuring the depth of a quenched hardened layer of a steel material, and has a low quenching depth for magnetizing in a direction along the surface of the steel material. An excitation coil for generating a high-frequency alternating magnetic field, a detection coil for detecting an induction magnetic field induced by an eddy current generated in a steel material, and a correlation data between a known quench hardened layer of the same type of steel material and an output voltage are stored in advance. Computing means for calculating the depth of the quench hardened layer of the target steel from the output voltage of the detection coil and the correlation data. Further, an external magnetic field detecting means for detecting a spatial magnetic field generated by the exciting coil is provided near the exciting coil, and the external magnetic field is excited so that the spatial magnetic field detected by the external magnetic field detecting means becomes constant. It controls the current.

In this embodiment, a steel material of S45C is used, and this steel material is subjected to induction hardening. First, the electrical conductivity and initial magnetization characteristic change accompanying the hardness change due to quenching were evaluated, and the non-uniformity of the quenched steel material magnetic characteristics was measured.

(Evaluation of Martensite Hardness of S45C Steel) FIG. 1 shows a cylindrical steel material (φ80 mm × 150 mm) hardened by induction hardening to a depth of 1, 2, or 3 mm.
1 shows a martensite hardness distribution of This shows a hardness result measured by a Vickers hardness tester at a pitch of 0.25 mm from the surface by cutting an induction hardened steel into a slice. Generally, the quenching depth is Hv450. From this result, it can be understood that in the case of induction hardening of S45C, the hardness of the martensite portion is maintained at about Hv700 from the surface, and thereafter, the hardness rapidly decreases and reaches the hardness Hv245 of the original structure. For example, when the quenching depth is 3 mm, Hv700 is maintained from the surface to a depth of about 2 mm, and thereafter, the hardness is rapidly attenuated for about 1.5 mm, and Hv245 is maintained from the depth of 3.5 mm to the surface. I understand.

(Evaluation of Conductivity at Each Hardness) Based on the above results, in this embodiment, the hardness of the quenched region is Hv700, and the attenuation region from the quenched region to the original structure region is Hv57.
Assuming 0 and Hv430, a total of three steel materials (09 × 210 mm) in which all steel materials were subjected to through-hardening were prepared. Further, in order to simulate the original microstructure region, a steel material (Hv245) in which a steel material having the same shape was annealed was prepared. Next, the conductivity of each of these four steel materials was measured by a double bridge low resistance measurement circuit. The measurement result,
The conductivity of Hv245 steel is 4.98 × 10 ⁶ S /
m, Hv430: 4.00 × 10 ⁶ S / m, Hv57
At 0, 3.97 × 10 ⁶ S / m, at Hv700, 3.7.
It was 4 × 10 ⁶ S / m. As the hardness increases, the conductivity shows a decreasing tendency. For example, in the case of a hardness Hv700 steel, the conductivity is reduced by about 25% as compared with the original structure steel.

(Evaluation of Magnetic Characteristics and Magnetic Noise at Each Hardness) Next, the magnetic characteristics and magnetic noise at each hardness were evaluated. In order to evaluate the variation of the initial magnetization characteristics and the magnetic characteristics of the S45C steel material at each hardness, a magnetic characteristic measuring device using a variable magnetic pole interval electromagnet as an exciting device was developed. This device has a structure in which a test steel material is sandwiched by a yoke material without any gap and magnetized uniformly. Magnetic flux density B from coil directly wound on test steel (B coil: 200 turns)
Was measured, and the spatial magnetic field H was measured by a hole probe vertically arranged between the magnetic poles.

(Initial Magnetization Characteristics at Each Hardness) The initial magnetization characteristics at each hardness of the S45C steel were measured using the above-described initial magnetization characteristics measuring device. The measured steel material is φ9m
The hardness Hv is applied to all S45C steels of m × 50mm cylindrical shape.
700, Hv570, and Hv430, which were subjected to through-hardening, and four annealed Hv245 steel materials were used. In addition, the coreless hardened material was prepared by heating the entire material to 900 ° C. in an electric furnace and changing the quenching temperature to obtain the respective hardness values. The measurement results are shown in FIGS. 2 (a) and 2 (b). FIG. 2A shows a BH curve, and FIG.
Indicates an H-μr curve. It can be seen that as the hardness increases, the magnetic permeability decreases. For example, when the hardness is Hv700, it can be seen that the maximum relative magnetic permeability is about 65% lower than that of the annealed material.

(Evaluation of Magnetic Noise at Each Hardness) Using the above-described device for measuring initial magnetization characteristics, the nonuniformity of the magnetic characteristics at each hardness was evaluated. The measurement samples were each hardness Hv2
45, Hv430, Hv570, φ9mm of Hv700
It was a cylindrical steel material having a length of 180 mm. The measurement was performed with the same position of the B coil (width 4 mm, 50 turns) and the hole probe, and the B coil and the hole probe were translated in the axial direction of the test steel material at a pitch of 2 mm while the value of the external magnetic field H was kept constant. The magnetic flux density at each point was measured.
The measurement range is ± 20m from the center point in the length direction of the test steel.
m (21 points of 2 mm pitch meter) was measured. The measurement results at each hardness are shown in FIGS. 3, when the external magnetic field H is 300 A / m, the maximum is about 8
%, But when the magnetic field was increased to 500 A / m, it was found to be reduced to about 2%. Next, in the quenched material having a hardness of Hv430 shown in FIG.
/ M, there is a maximum variation of 15%, but 1000A
It was found that increasing the magnetic field to / m reduced it to about 3%. In the quenched material having the hardness Hv570 of FIG. 5, when the external magnetic field H was 500 A / m, the maximum variation was 28%. However, it was found that when the magnetic field was increased to 2000 A / m, the magnetic field became substantially uniform. Finally, the hardness Hv700 of FIG.
It was measured that the quenched material had a maximum of 28% variation when the external magnetic field H was 500 A / m, but became substantially uniform when the magnetic field was increased to 2000 A / m.

From the above results, the annealed material has an external magnetic field H of about 500 A / m, and the Hv430 hardened material has an external magnetic field of 100 A / m.
The variation of the magnetic characteristics is reduced at about 0 A / m, but the variation of the magnetic properties is not reduced unless the magnetized material of hardness Hv570 or more is magnetized to about 2000 A / m.
It has also been found that the variation rate is about 80% at the maximum. It is expected that these variations can cause magnetic noise in magnetic measurements and the like.

(AC Nonlinear Analysis) The present invention is to establish a method for measuring the induction hardening depth in a non-contact or contact manner using a low-frequency AC magnetic field. The measuring probe is
As shown in FIG. 7, the Helmholtz type excitation coils 1, 1
And a detection coil 2 disposed between the two excitation coils 1 and 1, and an external magnetic field detection means 3 disposed inside the detection coil 2. The output voltage obtained from the detection coil 2 when the cylindrical induction hardened material 10 was inserted into the probe was evaluated using an equivalent sine wave AC nonlinear analysis. In FIG. 7, reference numeral 11 denotes an original microstructure of the steel material 10, and reference numeral 12 denotes a hardened hardened layer. Here, the AC excitation frequency is set to 20 in consideration of the penetration depth of the eddy current.
A low frequency of Hz was used. In addition, the effect of the quenching depth on the amplitude of the output voltage was examined by using the measured conductivity and initial magnetization curve of the S45C steel of each hardness described above in the nonlinear analysis.

(Equivalent Sine Wave AC Nonlinear Analysis Method) In this analysis, an axisymmetric finite element method using a magnetic vector potential was used. When a ferromagnetic material is magnetized by alternating current, the magnetic flux waveform is distorted due to nonlinearity. To evaluate this by analysis, it is necessary to solve the problem by a step-by-step method in consideration of nonlinear magnetic characteristics. However, this analysis method requires a lot of calculation time. On the other hand, it has been confirmed that, in the AC excitation, the magnetic flux density is not distorted and can be handled as a sine wave in the unsaturated magnetization region where the magnetic permeability inside the material is up to the maximum magnetic permeability.

Here, in consideration of shortening of calculation time and easiness of analysis, an equivalent sine wave AC nonlinear numerical analysis method was applied as an AC nonlinear analysis method in an unsaturated magnetization region.
This analysis method uses a complex number approximation analysis method (jω method) to approximate a magnetic flux waveform in a material that appears as a distorted waveform in a non-linear AC magnetic field to a sine wave having an equal amplitude. It is an analysis method. The governing equations are shown below.

[0029] _{rot (νrotA) = J o -J} e (1)

DivJ _e = 0 (2)

Here, A, J _o , J _e , and ν are magnetic vector potential, forced current density, damage current density,
The magnetic resistivity. The eddy current density J _e is J _e = jωσA, where ω and σ are angular frequency and conductivity.
This is an analysis method in which the magnetic resistivity ν in equation (1) is set to a non-green shape. In the analysis, steel is treated as an isotropic magnetic material.

(Analysis conditions: quenching region conditions) From the hardness distribution in FIG. 1, in the induction hardening of the S45C steel material, the hardness Hv700 is maintained from the material surface, and then the hardness sharply decreases at a certain depth, and the hardness of the original structure region is reduced. It turns out that it becomes Hv245. However, the quenching hardness is from Hv700 to Hv245.
Although it attenuates rapidly, its middle hardness region is several mm
It can be understood that it exists to some degree. Generally, the induction hardening depth is determined based on the value of Hv450,
The depth of the v700 region is not the quenching depth. Therefore, in this analysis, the intermediate region where the hardness rapidly decreases from the quenched region is higher in hardness than Hv450,
A region less than 700 is Hv570, and an intermediate region having a hardness lower than Hv450 and a hardness higher than Hv245 is Hv.
Assuming v430, the intermediate region where the hardness attenuated from Hv700 to Hv245 was divided into two layers, and evaluation was attempted. Specifically, when the quenching depth is 3 mm, the analysis conditions are Hv700 up to 2 mm from the surface, Hv570 for the layers from 2 mm to 3 mm, and Hv570 for the layers from 3 mm to 3.5 mm.
Assuming that the layers v430 and deeper than that are all layers of Hv245, a non-linear analysis is performed by giving the initial magnetization curve and conductivity of each hardness as initial conditions.

(Analysis Conditions: Initial Magnetization at Each Hardness) A ferromagnetic material such as a steel material has a non-uniform magnetic permeability in the material, and generates magnetic noise in various magnetic measurements. In the present invention, the variation of the magnetic characteristics causing the magnetic noise is shown in FIGS.
In FIG. 6, each hardness was evaluated. Based on this result, the magnetic characteristics were varied for each hardness and analyzed. In the Hv245 region, the initial magnetization curve up to 500 A / m has a maximum of 8%, and in the Hv430 region, it is 1000 A / m.
up to 15%, Hv 570 and H
In the region of v700, the initial magnetization curve up to 2000 A / m was given a magnetic property distribution at random within each divided region of the finite element method within a maximum range of 28%, thereby giving a variation in the initial magnetic permeability. Under the above analysis conditions, when the excitation frequency was kept constant at 20 Hz, the effect of the quenching depth on the amplitude value of the output voltage was evaluated.

(Analysis Results) Based on the hardness distribution shown in FIG. 1, the inside of the steel material was divided into four layers, the quenching depth was set to 3 mm, and an AC nonlinear analysis was performed. The analysis results of the relative magnetic permeability and the magnetic flux density distribution inside the material are shown in FIGS. 8A and 8B, respectively. This is because the spatial magnetic field H between the hardened steel and the probe is 2000
The relative magnetic permeability and magnetic flux density distribution on the z = 0 line at A / m are shown. From the results of the relative magnetic permeability analysis of FIG.
It can be seen that the value of the Hv245 layer is higher than the other three layers, and the surface of this layer is close to the maximum relative magnetic permeability due to the effect of the skin effect, and the variation of the magnetic permeability is also reduced. On the other hand, it can be seen that the relative permeability of the other three layers is extremely lower than that of the Hv245 layer. Therefore, FIG.
In the magnetic flux density distribution, it can be understood that the values are concentrated in the Hv245 layer having high magnetic permeability. Hv480, H
In each of the layers v570 and Hv700, the magnetic permeability varies, but the absolute magnetic permeability is smaller than that in the Hv245 layer, so that there is no large variation as a whole. Next, from the results of the magnetic flux density shown in FIG. 8B, it can be understood that the highest value is obtained in the region where the magnetic permeability is high.
Although the magnetic flux density is proportional to the value of the magnetic permeability, the magnetic flux does not penetrate into the steel due to the effect of the skin effect.Therefore, the magnetic permeability is higher at the center of the steel than at the surface of the steel, but the magnetic flux density is higher at the surface It can be understood that the value is higher than that of the portion and that the variation of the magnetic permeability at the center is hardly affected.

From these results, although the variation in the magnetic characteristics is larger in the quenched region than in the original structure region (see FIGS. 3 to 6), the magnetic flux penetrating into the material is lower due to the lower magnetic permeability. Can be expected to be hardly affected by the variation in the magnetic permeability of the quenched region. In order to clarify this phenomenon, in this analysis, the output at each position when the entire probe was translated at a pitch of 5 mm in the axial direction of the cylindrical steel material (z-axis direction) with the excitation-detection coil interval kept constant. The voltage was determined, and the variation rate of the output voltage due to the non-uniformity of the magnetic characteristics was determined. FIG. 9 shows the results. When the spatial magnetic field H is 100 A / m, the variation rate of the output voltage at each position is about 7%, but it can be understood that the magnetic noise decreases as the value of H increases. From this result, although the magnetic noise of the output voltage is measured due to the non-uniformity of the magnetic characteristics, the variation rate is as small as about several% because the variation of the magnetic permeability of the original structure region is dominant. Measurements showed no major obstacles.

(Comparison with Verification Experiment and Analysis) In the present invention, the probe structure of FIG. 7 was compared with verification experiment and analysis values. With respect to the probe structure of FIG. 7, the exciting current is adjusted in advance, and the value of the spatial magnetic field H is increased to 5000 A / m by the external magnetic field detecting coil 3 installed between the test steel material 10 and the detecting coil 2 of the probe. Also, after confirming that the output voltage waveform obtained from the probe detection coil 2 is in an unsaturated magnetization region where no distortion occurs, the effect of the change in quenching depth on the amplitude value of the output voltage waveform was evaluated. For the experiment, a cylindrical S45C of φ30mm x 150mm
A total of six specimens were prepared from steel, five specimens subjected to induction hardening at a depth of 1, 2, 3, 4, 5 mm from the surface of the steel, and five specimens subjected to a tempering treatment (depth 0 mm). Was done. The experimental and analytical results at H = 500 and 2000 A / m are shown in FIGS. 10 (a) and (b), respectively.

It can be understood that the output voltage shows a decreasing tendency as the quenching depth becomes deeper under any conditions. As can be seen from FIG. 8, the magnetic flux density penetrating into the material is concentrated in the original structure region having high magnetic permeability. Therefore, it is considered that as the quenching depth becomes deeper, the region with low magnetic permeability increases from the material surface, and the original structure region with high magnetic permeability decreases, so that the output voltage decreases. Next, the comparison with the analysis value shows that the analysis value is about 8 at the maximum when H = 2000 A / m.
Although the evaluation was lower by%, H = 500 A / m was able to obtain well-matched results as a whole, indicating the usefulness of the present analysis technique, and at the same time, verifying the effectiveness of the measurement principle of the present invention.

Finally, based on FIG. 11, the structure of a practical probe P capable of measuring the quenching depth only by following the surface of the steel material will be briefly described. FIG. 11A shows the probe P
, (B) is a simplified side view, and (c) is a simplified bottom view. The probe P is configured to wind the exciting coil 1 around one contact core 4A of a U-shaped yoke 4 having a pair of parallel contact cores 4A and 4B to be brought into contact with the surface of a steel material, and to contact the other contact core 4B. And the external magnetic field detecting means 3 is disposed between the distal ends of the contact cores 4A and 4B. Here, as the external magnetic field detecting means 3, a coil, a Hall element, or another known magnetic sensor can be used, and the installation position is not limited to the illustrated position. The only requirement is that a feedback signal for controlling the frequency alternating magnetic field (excitation current) to be constant can be obtained.

[0039]

The method and apparatus for measuring the quenching depth of the invention described above can directly and non-destructively measure the depth of a quenched hardened layer of a steel material in a short time and have a high measuring accuracy. Therefore, it can be constructed with high reliability and at low cost.
In addition, the magnetic characteristics of each induction hardened steel material for each hardness are obtained, the magnetic noise is analytically evaluated, and the influence of the magnetic noise can be ignored, so that highly accurate measurement can be performed. As the quenching depth increased, the amplitude of the output voltage showed a tendency to decrease in proportion to the depth, and it was confirmed by numerical analysis and verification experiments that the high-frequency quenching depth due to the low-frequency AC magnetic field was detected. It has been proved that the measurement can be performed using only the output voltage of the coil, and that a steel material having a deep quenching depth can be accurately measured. In addition, the hardening depth distribution can be obtained by scanning and measuring the probe along the surface of the steel material.

[Brief description of the drawings]

FIG. 1 is a graph showing a martensite hardness distribution of a cylindrical steel material quenched to a depth of 1, 2, or 3 mm by induction hardening.

FIG. 2 shows initial magnetization characteristics at each hardness, and FIG.
FIG. 3B is a graph of an H-curve, and FIG. 3B is a graph of an H-μr curve.

FIG. 3 is a graph showing a variation in magnetic flux density at each point in the axial direction of a test steel material of Hv245.

FIG. 4 is a graph showing a variation in magnetic flux density at each point in the axial direction of a test steel material of Hv430.

FIG. 5 is a graph showing a variation in magnetic flux density at each point in the axial direction of a test steel material of Hv570.

FIG. 6 is a graph showing a variation in magnetic flux density at each point in the axial direction of a test steel material of Hv700.

FIG. 7 is a perspective view showing a measurement probe including a Helmholtz-type excitation coil and a detection coil, partially cut away;

8A and 8B show analysis results of relative magnetic permeability and magnetic flux density distribution at z = 0 inside the material, where FIG. 8A is a graph of relative magnetic permeability with respect to steel material radius, and FIG. 8B is a graph of magnetic flux density with respect to steel material radius. .

FIG. 9 is a graph showing a variation rate of an output voltage at each position in an axial direction of a cylindrical steel material.

10A and 10B show actual measurement results and theoretical results of test steel materials having different quenching depths subjected to induction hardening, and FIG.
Is a graph when is 500 A / m, and (b) is a graph when the spatial magnetic field H is 2000 A / m.

11A and 11B show a practical probe structure, in which FIG. 11A is a simplified front view, FIG. 11B is a simplified side view, and FIG. 11C is a simplified bottom view.

[Description of Signs] 1 Excitation coil 2 Detection coil 3 External magnetic field detection means (coil) 4 Yoke 4A, 4B Contact core 10 Steel material 11 Original structure 12 Hardened hardened layer

Claims (5)

[Claims] 1. A quenching depth measuring method for non-destructively measuring the depth of a quench hardened layer of a steel material, wherein the steel material is magnetized in a direction along a surface by a low-frequency AC magnetic field generated by an exciting coil. , An induction magnetic field induced by the eddy current generated thereby is detected by a detection coil, and an output voltage of the detection coil is
A quenching depth measuring method, comprising calculating the depth of a quench-hardened layer of a target steel material by comparing the known quench-hardened layer depth of the same type of steel with correlation data of output voltage. 2. A quenching depth measuring method according to claim 1, wherein a spatial magnetic field generated by said exciting coil is detected by an external magnetic field detecting means, and an exciting current is controlled so that the spatial magnetic field is constant. 3. A quenching depth measuring device for non-destructively measuring the depth of a quenched hardened layer of a steel material, wherein the excitation coil generates a low-frequency AC magnetic field for magnetizing in a direction along a surface of the steel material. And, a detection coil for detecting an induction magnetic field induced by an eddy current generated in the steel material, correlation data of the depth and output voltage of a known quenched hardened layer of the same type of steel material is stored in advance, and the output voltage of the detection coil and A quenching depth measuring device comprising: calculating means for calculating the depth of the quench hardened layer of the target steel material from the correlation data. 4. An external magnetic field detecting means for detecting a spatial magnetic field generated by said exciting coil is provided near said exciting coil, and a spatial magnetic field detected by said external magnetic field detecting means becomes constant. 4. The quenching depth measuring apparatus according to claim 3, wherein the exciting current is controlled as described above. 5. The exciting coil is wound around one contact core of a U-shaped yoke having a pair of parallel contact cores to be brought into contact with the steel material surface, and the detection coil is wound around the other contact core. 5. The quenching depth measuring apparatus according to claim 4, wherein a measuring probe having the external magnetic field detecting means disposed between the tips of the contact cores is used.