WO2017081879A1 - 鋼材の表面特性評価方法 - Google Patents
鋼材の表面特性評価方法 Download PDFInfo
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- WO2017081879A1 WO2017081879A1 PCT/JP2016/066922 JP2016066922W WO2017081879A1 WO 2017081879 A1 WO2017081879 A1 WO 2017081879A1 JP 2016066922 W JP2016066922 W JP 2016066922W WO 2017081879 A1 WO2017081879 A1 WO 2017081879A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/023—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance where the material is placed in the field of a coil
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/023—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance where the material is placed in the field of a coil
- G01N27/025—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance where the material is placed in the field of a coil a current being generated within the material by induction
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/80—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating mechanical hardness, e.g. by investigating saturation or remanence of ferromagnetic material
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
- G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
- G01N27/9046—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents by analysing electrical signals
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/20—Metals
- G01N33/204—Structure thereof, e.g. crystal structure
- G01N33/2045—Defects
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
- C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
- C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
- G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
Definitions
- the present invention relates to a method for evaluating the residual stress of a steel material subjected to surface modification treatment.
- Patent Document 1 A method for measuring the fatigue strength of a steel material is disclosed in Patent Document 1.
- Patent Document 1 the depth at which a predetermined compressive residual stress of a steel material subjected to shot peening exhibits a peak value is evaluated.
- the evaluation method disclosed in Patent Document 1 it is necessary to set measurement conditions for each measurement object and surface modification treatment condition. Therefore, accurate evaluation cannot be performed due to variations such as individual differences in materials.
- Patent Document 2 Another method for measuring the fatigue strength of steel is disclosed in Patent Document 2.
- the output voltage value of the detection coil is changed while sequentially changing the penetration depth (permeability) of the magnetic flux on the steel material surface by sequentially changing the frequency of the excitation current flowing through the excitation coil brought into contact with the steel material.
- the distribution of compressive residual stress of the steel material is calculated.
- the output voltage value of the detection coil includes a voltage component due to a change in magnetic permeability and a voltage component due to the impedance of the detection coil itself. Therefore, when the impedance characteristics of the detection coil itself change due to changes in the surrounding environment (temperature, noise, etc.), the reliability of the measured value decreases.
- the excitation coil in this measuring apparatus needs to be designed in consideration of a phenomenon (lift-off phenomenon) in which the detection signal changes depending on the distance from the steel material, but no disclosure is made from this viewpoint.
- the measuring device of Patent Document 2 cannot accurately evaluate the compressive residual stress of the steel material.
- an object is to provide a surface property evaluation method capable of accurately evaluating the residual stress of a steel material subjected to surface modification treatment in consideration of the distribution in the depth direction.
- One aspect of the present invention is a surface property evaluation method for evaluating a residual stress of a steel material subjected to a surface modification treatment.
- This surface property evaluation method includes the following steps (1) to (6). These steps may be performed separately or two or more may be performed simultaneously.
- a surface characteristic evaluation apparatus including an oscillator including an AC power source and a frequency variable circuit, a detector connected to a transmitter and including a coil, and a measuring instrument connected to the frequency variable circuit and the detector. Preparation process to prepare.
- a subject placement step in which the subject is placed so that the alternating current magnetism excited by the coil penetrates into the subject using the steel material subjected to the surface modification treatment as the subject.
- the strain generated inside by the surface modification treatment is detected by allowing the AC material excited by the coil to permeate the steel material.
- the distribution of the strain in the depth direction can be detected by continuously changing the frequency of the alternating current applied to the coil.
- the impedance Z 1 the signal corresponding to the impedance of the coil and the S / N ratio (S: evaluation voltage, N: noise from other than the evaluation voltage) can be increased, thereby improving the evaluation accuracy. be able to.
- the residual stress of the steel material subjected to the surface modification treatment can be accurately evaluated in consideration of the depth direction.
- the method may further include a reference impedance measurement step of measuring the reference impedance Z 0 in advance for each frequency using the steel material before the surface modification treatment as an object.
- the ratio between the reference impedance Z 0 and the impedance Z 1 may be calculated for each frequency, and the residual stress of the steel material subjected to the surface modification treatment may be evaluated based on the calculated value group.
- the inductive reactance X 1 is calculated for each frequency using the impedance Z 1, and the residual stress of the steel material subjected to the surface modification treatment is evaluated based on the inductive reactance X 1. May be.
- the inductive reactance that is the Y-axis component of the impedance (imaginary component of the complex impedance) and performing the evaluation based on this inductive reactance, only the magnetic permeability of the subject can be evaluated. As a result, the accuracy of evaluation is improved.
- the penetration depth of the AC magnetism is converted from the frequency of the AC current by the following formula, and the residual stress in the depth direction of the steel material subjected to the surface modification treatment based on the converted penetration depth is calculated. Distribution may be evaluated. It is possible to accurately grasp and evaluate the distribution in the depth direction of strain.
- the calculation value group may be plotted on a coordinate system having the following coordinate axes A and B. It is possible to visually grasp the distribution of strain inside the steel material caused by the surface modification treatment.
- Coordinate axis A The ratio of the reference impedance Z 0 measured using the steel material before the surface modification treatment as the specimen and the impedance Z 1 measured using the steel material after the surface modification treatment as the specimen.
- Coordinate axis B indicates a frequency.
- the step of evaluating the residual stress based on one or a plurality of calculation values including a trajectory of a graph of the calculation value group plotted on the coordinate system having the coordinate axes A and B and an extreme value of the trajectory. Further, the residual stress of the steel material subjected to the surface treatment may be evaluated. The evaluation of the residual stress can be performed from both the aspect of the distribution of strain inside the steel material generated by the surface modification treatment and the value of the calculated value at the extreme depth.
- the quality of the surface modification process may be determined by comparing one or a plurality of calculated values including extreme values with a preset threshold value in the evaluation step. Whether or not the surface modification treatment is properly performed can be determined in consideration of the depth direction.
- a surface property evaluation method capable of accurately evaluating the residual stress of the steel material subjected to the surface modification treatment in consideration of the depth direction.
- the degree of the surface modification treatment applied to the steel material can be accurately evaluated in consideration of the distribution in the depth direction.
- the surface property evaluation apparatus 1 includes an oscillator 10, a detector 20, and a measuring instrument 30.
- the oscillator 10 includes an AC power supply 11 and a frequency variable circuit 12.
- the frequency variable circuit 12 is connected to the AC power supply 11 and can change the frequency of the AC current output from the AC power supply 11.
- the detector 20 includes a coil 21.
- One end side (point A) of the coil 21 is connected to the AC power supply 11, and an AC current output from the AC power supply 11 is supplied.
- a circuit symbol in a broken line indicating the coil 21 in FIG. 1 indicates an electric equivalent circuit of the coil 21.
- the measuring instrument 30 includes an amplification circuit 31, an absolute value circuit 32, a low pass filter (LPF) 33, an I / V conversion circuit 34, an absolute value circuit 35, an LPF 36, a control means 37, and a display 38. Further, a storage means is provided in the control means 37 or in an area not shown. Specifically, the control means 37 can be constituted by a microprocessor, an interface circuit, a memory, and a program (not shown) for operating these.
- the amplifier circuit 31 is connected to points A and B which are both ends of the coil 21.
- the signal of the potential difference between the points A and B is input to the amplifier circuit 31 and amplified.
- This amplified signal is full-wave rectified by the absolute value circuit 32 and then converted into direct current by the LPF 33. This converted signal is input to the control means 37.
- the I / V conversion circuit 34 is connected to the other end side (point B) of the coil 21.
- a signal indicating the current value of the current flowing through the coil 21 is input to the I / V conversion circuit 34 and converted into a signal indicating a potential difference. Then, after full-wave rectification by the absolute value circuit 35, it is converted into direct current by the LPF 36. This converted signal is input to the control means 37.
- the control means 37 is connected to the frequency variable circuit 12, the LPF 33, and the LPF 36, and receives the frequency of the alternating current applied to the coil 21 and the signal that has passed through the LPFs 33 and 36 corresponding to this frequency. Calculations are performed based on these input signals, and the surface characteristics of the subject are evaluated based on the calculation results.
- the frequency of the alternating current may be changed manually, or the frequency may be changed automatically by providing the control means 37 with a function for causing the frequency variable circuit 12 to output a signal for continuously changing the frequency. Good. In the present embodiment, the latter is used.
- the display unit 38 displays or warns the evaluation result by the control means 37.
- S01 Preparation step The above-described steel material (untreated product) before the surface property evaluation apparatus 1 and the SP treatment are prepared.
- S02 First arrangement process (unprocessed product) An untreated product is set in the detector 20 as an object.
- the method of setting the subject is not particularly limited as long as the alternating magnetism permeates into the subject when the magnet 21 is excited in the next step.
- the untreated product is set so that the center of the circular cross section of the coil 21 and the entire untreated product are located inside the coil 21.
- the magnitude of the magnetic flux that combines the demagnetizing field and the AC magnetism varies depending on the magnitude of the residual stress that indicates the degree of surface modification treatment. That is, depending on the magnitude of the residual stress, a signal indicating the electrical characteristics of the coil when an alternating current flows through the coil (a signal indicating the potential difference between the coils (between AB) and a signal indicating the current value after flowing through the coil) ) Will change.
- a signal input to the control means 37 through the amplifier circuit 31-absolute value circuit 32-LPF33 and a signal input to the control means 37 through the I / V conversion circuit 34-absolute value circuit 35-LPF36 Then, the control unit 37 calculates the impedance Z 0 at that frequency.
- the depth at which AC magnetism penetrates the subject depends on the frequency of the AC current. Therefore, as a first frequency changing step, the frequency of the alternating current output from the alternating current power supply 11 is changed by the control means 37. While changing the frequency of the alternating current, as a first detection step, a signal indicating the electrical characteristics of the alternating current is detected for each frequency, and the impedance Z 0 of the coil 21 is calculated from this signal and stored in the storage means.
- S04 Surface modification treatment step After untreated products are taken out from the detector 20, compressive residual stress is applied by SP treatment to obtain the above-described steel material (surface modified products) subjected to the surface modification treatment.
- step S05 Measuring process of surface-modified product
- the steel material (surface-modified product) that has been subjected to the surface modification process in step S04 is set in the detector 20 as a second specimen arrangement process.
- the second eddy current generation step executes a second frequency changing step, and the second detection step, to calculate the impedance Z 1 of the coil 21 for each frequency.
- the frequency in this step is the same as that in step S03. Since the above-mentioned demagnetizing field varies depending on the magnitude of the compressive residual stress indicating the degree of the surface modification treatment, the degree of the surface modification treatment of the subject is evaluated by evaluating the electrical characteristics of the alternating current flowing through the coil. be able to.
- the depth from the steel surface is calculated from the frequency, and this may be used as the horizontal axis.
- the relationship between the frequency and the depth from the steel surface can be calculated from the calibration curve by creating a calibration curve indicating the relationship between the frequency and the depth from the steel surface from (Equation 2).
- the correction coefficient k in (Equation 2) indicates the shape (for example, the volume of the subject) and properties (for example, presence or absence of heat treatment as a previous stage) and SP processing conditions (for example, shot particle diameter, hardness, injection) This value fluctuates under the influence of time, injection pressure, etc., and is calculated in advance by experiments.
- control means 37 determines the quality of the surface modification treatment. Although the determination method is illustrated below, it is not limited to this method.
- a threshold group and an allowable range for determining whether or not the SP processing is properly performed A plurality of steel materials (non-defective products) that have been properly subjected to SP treatment and steel materials (defective products) that are unsatisfactory in SP treatment are measured by the operations of the above-described steps S01 to S04, and the impedance ratio is determined based on this measurement. And the threshold value group and the tolerance
- ⁇ ⁇ Compare this threshold group with the value of the calculation value group. For example, several points are selected (for example, 6 points) at a frequency at which the locus of the graph of the calculation value group in which the impedance ratio is calculated is an extreme value and any frequency in the vicinity thereof, and the impedance ratio at the selected frequency is set as a threshold value. Compare each. At this time, if all the compared values are within the allowable range of the threshold, it is determined that “SP processing is properly performed”, and if even one point deviates from the threshold range, “SP processing is inappropriate. Is determined.
- Another determination method is “determining whether a graph indicating a calculation value group (a graph indicating a relationship between a frequency or a depth from a steel surface and an impedance ratio) is within an allowable range of a similar graph indicated by a threshold group. And “determining whether or not the extreme value of the graph of the impedance ratio is within the allowable range of the extreme value in the threshold value group”. If both are within the allowable range of the threshold group, it is determined that “SP processing is properly performed”, and if both are outside the allowable range of the threshold group, it is determined that “SP processing is inappropriate”.
- the determination result of the quality of the surface modification process is output to the display 38.
- the display unit 38 may display only the pass / fail result, or may sound a warning sound when it is determined to be no. Or you may display the above-mentioned graph (The graph which shows the relationship between frequency (or the depth from the surface of steel materials) and the ratio of impedance).
- Shot peening machine manufactured by Shinto Kogyo Co., Ltd. shots with an average particle diameter of 50 ⁇ m to 1000 ⁇ m (both made by Shinto Kogyo Co., Ltd.) toward the chrome molybdenum steel ( ⁇ 40 mm ⁇ 30 mm) that has been carburized and quenched. ), And shot peening treatment was performed by spraying at a spray pressure of 0.3 MPa so that the coverage was 300% (see Table 1). A chromium molybdenum steel subjected to the shot peening treatment was used as a specimen.
- the frequency of AC current (frequency used) was set to 10 kHz to 20 MHz. Moreover, the penetration depth of AC magnetism was calculated from the operating frequency from the calibration curve described above.
- the depth at which the locus of the impedance ratio (Z 1 / Z 0 ) shows the extreme value is about 10 ⁇ m for the subject A, about 25 ⁇ m for the subject B, and about 55 ⁇ m for the subject C.
- FIG. 5 shows the results of measuring the compressive residual stresses of the specimens A to C using an X-ray stress measuring device. It can be seen from FIG. 5 that the depth at which the locus of compressive residual stress shows an extreme value is about 5 to 10 ⁇ m for the subject A, about 20 ⁇ m for the subject B, and about 50 ⁇ m for the subject C. 4 and FIG. 5 are almost correlated with the depth showing the extreme value. Therefore, the surface property evaluation apparatus and the surface property evaluation method of the present embodiment are used to evaluate the degree of the surface modification treatment in consideration of the depth direction. It was suggested that can be done.
- FIG. 6 shows a surface property evaluation apparatus 2 according to another embodiment.
- the measuring instrument 30 in the surface property evaluation apparatus 2 of one embodiment includes an amplifier circuit 31, an A / D conversion circuit 39a, an I / V conversion circuit 34, and an A / D conversion circuit 39b.
- Control means 37 and display 38 are provided.
- the control means 37 includes a storage means 37a. Note that the storage unit 37 a may be provided outside the control unit 37.
- the configurations of the oscillator 10 and the detector 20 are the same as those in the above-described embodiment, and thus the description thereof will be omitted. Here, differences from the embodiment will be mainly described.
- the amplifier circuit 31 is connected to points A and B which are both ends of the coil 21.
- the signal of the potential difference between the points A and B is input to the amplifier circuit 31 and amplified.
- the amplified signal is converted from an analog voltage signal to a digital signal by the A / D conversion circuit 39a.
- the converted digital signal is input to the control means 37.
- the I / V conversion circuit 34 is connected to the other end side (point B) of the coil 21.
- a signal indicating the current value of the current flowing through the coil 21 is input to the I / V conversion circuit 34 and converted into an analog voltage signal.
- the analog voltage signal output from the I / V conversion circuit 34 is converted into a digital signal by the A / D conversion circuit 39 b and input to the control means 37.
- each digital signal input from the amplifier circuit 31 and the I / V conversion circuit 34 is a time-series signal that fluctuates in an alternating manner, but the absolute value circuits 32 and 35 and the LPFs 33 and 36 (see FIG. It is converted into a DC digital signal by a digital operation equivalent to 1).
- the analog voltage AC signal input to each of the A / D conversion circuits 39a and 39b is converted into a digital value proportional to the amplitude of the AC signal in the control means 37. Then, the impedance is calculated based on these digital values.
- the surface property evaluation apparatus 2 is configured to be less susceptible to noise because signal calculation is performed by digital signal processing. Therefore, even when evaluating in an environment in which noise is likely to occur, more accurate evaluation can be performed.
- FIG. 7 shows a surface property evaluation apparatus 3 according to another embodiment.
- a phase detection circuit 301, an absolute value circuit 302, and an LPF 303 are newly added to the measuring instrument 30 of the surface property evaluation apparatus 1 (FIG. 1) of one embodiment. Yes.
- the configurations of the oscillator 10 and the detector 20 are the same as those of the above-described embodiment, the description thereof will be omitted.
- the configuration newly added to the measuring instrument 30 will be mainly described.
- the phase detection circuit 301 is connected to the other end side (point B) of the AC power supply 11 and the coil 21.
- a signal indicating the phase difference of the current flowing through the coil 21 with respect to the voltage applied by the AC power supply 11 is output from the phase detection circuit 301, and full-wave rectified by the absolute value circuit 302, and then converted into DC by the LPF 303.
- This converted signal is input to the control means 37. That is, a voltage signal proportional to the phase difference between the voltage applied to the coil 21 and the current flowing through the coil 21 is input to the control means 37.
- an impedance Z 0 when an unprocessed product is used as a subject is calculated.
- a phase difference ⁇ 0 when an unprocessed product is used as a subject is calculated from a signal input from the LPF 303.
- the impedance Z 1 and the phase difference ⁇ 1 when the surface-modified product is used as a specimen are similarly calculated, and the inductive reactance X 1 is calculated for each frequency.
- the ratio (X 1 / X 0 ) of the inductive reactance X 1 (surface modified product) to the inductive reactance X 0 (untreated product) described above is determined by the control means 37 for each frequency. Calculate.
- the ratio of inductive reactance as the evaluation of the surface characteristics, only the magnetic permeability of the subject can be evaluated. Inductive reactance is small compared to impedance, but it has excellent sensitivity to changes in electrical characteristics. In particular, when a precise evaluation is necessary, a higher-accuracy evaluation can be performed by evaluating the induction reactance ratio.
- the inductive reactance may be calculated by analog signal processing as in the present embodiment, or may be calculated by digital signal processing in the control means 37 using the circuit of FIG.
- a digital operation equivalent to the phase detection circuit 301, the absolute value circuit 302, and the LPF 303 in the circuit of FIG. 7 is executed inside the control means 37 and guided based on the obtained phase difference ( ⁇ 0 , ⁇ 1 ).
- Reactance (X 0 , X 1 ) is calculated. That is, the control unit 37 performs the following calculations a to c.
- Phase difference between a digital signal obtained by A / D converting the voltage between both ends of the coil by the A / D conversion circuit 39a and a digital signal obtained by A / D converting the signal of the current flowing through the coil by the A / D conversion circuit 39b ( ⁇ 0 , ⁇ 1 ) are calculated by the control means 37.
- Impedances (Z 0 , Z 1 ) are calculated from the digital signals input via the A / D conversion circuits 39a, 39b by the operation described with reference to FIG.
- Inductive reactance (X 0 , X 1 ) is calculated using the “phase difference” and “impedance” calculated in a and b above.
- the evaluation of the degree of shot peening treatment when the steel material that has been carburized and quenched is subjected to shot peening treatment has been described.
- the surface property evaluation apparatus and the surface property evaluation method of the present invention can also evaluate when various heat treatments are performed as the surface modification treatment.
- evaluation of the steel material which performed only the shot peening process can also be performed.
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Abstract
Description
(1)交流電源及び周波数可変回路を備えた発振器と、発信器に接続され、コイルを備えた検出器と、周波数可変回路及び検出器に接続された計測器と、を含む表面特性評価装置を準備する準備工程。
(2)表面改質処理を施した鋼材を被検体として、コイルにより励起された交流磁気が被検体の内部に浸透するように該被検体を配置する被検体配置工程。
(3)交流電源を作動させることにより、コイルに交流磁気を励起させ、この交流磁気を被検体の内部に浸透させて、被検体に渦電流を発生させる渦電流生成工程。
(4)周波数可変回路によって交流電流の周波数を連続的に変更することにより、被検体への交流磁気の浸透深さを連続的に変更させる周波数変更工程。
(5)コイル両端の間の電位差及びコイルを流れる電流値を検出して、インピーダンスZ1を周波数毎に算出するインピーダンス算出工程。
(6)インピーダンスZ1に基づいて被検体の残留応力を評価する評価工程。
座標軸A:表面改質処理を施す前の鋼材を被検体として測定した基準インピーダンスZ0と表面改質処理を施した後の鋼材を被検体として測定したインピーダンスZ1の比を示す。
座標軸B:周波数を示す。
一実施形態の表面特性評価装置1は、発振器10、検出器20、計測器30、を備えている。
次に、本実施形態の表面特性評価装置1を用いて、被検体の表面特性を評価する方法について説明する。以下では、表面改質処理としてショットピーニング処理(以降、SP処理と記載)を選択し、表面改質処理の程度としてSP処理を施した鋼材の圧縮残留応力を評価した場合について説明する。
表面特性評価装置1及びSP処理を施す前の前述の鋼材(未処理品)を準備する。本実施形態では、φ40mm×30mmのクロムモリブデン鋼(JIS G4053に規定されるSCM420H)を、浸炭焼き入れしたものを準備した。
被検体として未処理品を検出器20にセットする。次の工程でコイル21に交流磁気を励起させた際にこの交流磁気が被検体の内部に浸透しさえすれば、被検体をセットする方法は特に限定されない。本実施形態では、未処理品をコイル21の円形断面中心で、且つ未処理品全体がコイル21の内部に位置するようにセットする。被検体をこのようにセットすることで、材料に起因する被検体内部の深さ方向に直行する方向のバラツキを軽減することができるので、測定精度を向上させることができる。
第1の渦電流生成工程として、制御手段37より交流電源11より出力される交流電流の周波数を制御する信号を周波数可変回路12に出力すると共に、交流電源11を作動させる。交流電源11の作動により、コイル21には交流磁気が励起される(図2を参照)。コイル21の内周側には被検体がセットされているので、この交流磁気が被検体に浸透する。交流磁気の浸透により被検体の表面には渦電流が発生する。渦電流により、交流磁気に対する反磁界が生じる。この時、残留応力の大きさによって透磁率が変わる。したがって、この反磁界と交流磁気とを合わせた磁束の大きさは、表面改質処理の程度を示す残留応力の大きさによって異なる。即ち、残留応力の大きさによって、交流電流がコイルに流れる際のコイルの電気特性を示す信号(コイル間(A-B間)の電位差を示す信号及びコイルを流れた後の電流値を示す信号)が変化する。増幅回路31-絶対値回路32-LPF33を通って制御手段37に入力された信号と、I/V変換回路34-絶対値回路35-LPF36を通って制御手段37に入力された信号と、から、制御手段37によりその周波数におけるインピーダンスZ0を算出する。
また、交流磁気が被検体に浸透する深さは、交流電流の周波数に依存する。従って、第1の周波数変更工程として、交流電源11より出力される交流電流の周波数を制御手段37により変化させる。交流電流の周波数を変化させながら、第1の検出工程として、各々の周波数毎に交流電流の電気的特性を示す信号を検出し、この信号からコイル21のインピーダンスZ0を算出して記憶手段に記憶する。
未処理品を検出器20より取り出した後、SP処理により圧縮残留応力の付与を行い、表面改質処理を施した前述の鋼材(表面改質処理品)を得る。
工程S04において表面改質処理を行った鋼材(表面改質処理品)を、第2の被検体配置工程として、検出器20にセットする。次に、工程S03と同様な、第2の渦電流生成工程、第2の周波数変更工程、及び第2の検出工程を実行し、周波数毎のコイル21のインピーダンスZ1を算出する。この工程における周波数は工程S03と同じ周波数とする。先述の反磁界は、表面改質処理の程度を示す圧縮残留応力の大きさによって異なるので、コイルを流れる交流電流の電気特性を評価することで、被検体の表面改質処理の程度を評価することができる。
インピーダンスZ0に対するインピーダンスZ1の比(Z1/Z0)を、制御手段37によって周波数毎に演算し、演算値群を得る。表面特性の評価としてインピーダンスの比(Z1/Z0)を用いることで、測定環境の変化(温度や湿度等)による電圧のドリフトを軽減することができる。また、表面改質処理による被検体の電磁気特性変化のみを抽出できるので、表面特性の評価の精度が向上する。
表面改質処理の良否の判定結果を、表示器38に出力する。表示器38では、良否結果のみ表示してもよいし、否と判定した際に警告音を発するようにしてもよい。または、先述のグラフ(周波数(又は鋼材の表面からの深さ)とインピーダンスの比との関係を示すグラフ)を表示してもよい。
別の実施形態の表面特性評価装置2を図6に示す。本実施形態の表面特性評価装置2は、一実施形態の表面特性評価装置2における計測器30は、増幅回路31、A/D変換回路39a、I/V変換回路34、A/D変換回路39b、制御手段37、表示器38を備えている。また、制御手段37には、記憶手段37aが内蔵されている。なお、記憶手段37aは、制御手段37の外部に設けられていても良い。また、発振器10及び検出器20の構成は、上述した一実施形態と同様であるため説明を省略し、ここでは、一実施形態と異なる点を中心に説明する。
別の実施形態の表面特性評価装置3を図7に示す。本実施形態の表面特性評価装置3においては、一実施形態の表面特性評価装置1(図1)の計測器30に、位相検波回路301、絶対値回路302、及びLPF303が、新たに加えられている。また、発振器10及び検出器20の構成は、上述した一実施形態と同様であるため説明を省略し、ここでは、計測器30に新たに加えられた構成を中心に説明する。
a)コイル両端の間の電圧をA/D変換回路39aによりA/D変換したデジタル信号と、コイルを流れる電流の信号をA/D変換回路39bによりA/D変換したデジタル信号の位相差(α0、α1)を、制御手段37により算出する。
b)A/D変換回路39a、39bを介して入力された各デジタル信号から、図6に基づいて説明した演算によりインピーダンス(Z0、Z1)を算出する。
c)上記a、bで算出された「位相差」及び「インピーダンス」を用いて、誘導リアクダンス(X0、X1)を算出する。
2 別の実施形態の表面特性評価装置(変更例1)
3 別の実施形態の表面特性評価装置(変更例2)
10 発振器
11 交流電源
12 周波数可変回路
20 検出器
21 コイル
30 計測器
31 増幅回路
32 絶対値回路
33 LPF
34 I/V変換回路
35 絶対値回路
36 LPF
37 制御手段
38 表示器
39a A/D変換回路
39b A/D変換回路
301 位相検波回路
302 絶対値回路
303 LPF
Claims (7)
- 表面改質処理を施した鋼材の残留応力を評価する表面特性評価方法であって、
交流電源及び周波数可変回路を備えた発振器と、前記発信器に接続され、コイルを備えた検出器と、前記周波数可変回路及び前記検出器に接続された計測器と、を含む表面特性評価装置を準備する準備工程と、
前記表面改質処理を施した鋼材を被検体として、前記コイルにより励起された交流磁気が前記被検体の内部に浸透するように該被検体を配置する被検体配置工程と、
前記交流電源を作動させることにより、前記コイルに交流磁気を励起させ、この交流磁気を前記被検体の内部に浸透させて、該被検体に渦電流を発生させる渦電流生成工程と、
前記周波数可変回路によって前記交流電流の周波数を連続的に変更することにより、前記被検体への前記交流磁気の浸透深さを連続的に変更させる周波数変更工程と、
前記コイル両端の間の電位差及び前記コイルを流れる電流値を検出してインピーダンスZ1を周波数毎に算出するインピーダンス算出工程と、
前記インピーダンスZ1に基づいて前記被検体の残留応力を評価する評価工程と、
を備えることを特徴とする表面特性評価方法。 - 更に、表面改質処理を施す前の鋼材を被検体として周波数毎に基準インピーダンスZ0を予め測定する基準インピーダンス測定工程を備え、前記評価工程においては、前記基準インピーダンスZ0と前記インピーダンスZ1との比を周波数毎に演算し、この演算値群に基づいて前記表面改質処理を施した鋼材の残留応力を評価することを特徴とする請求項1に記載の表面特性評価方法。
- 前記評価工程においては、前記インピーダンスZ1を用いて周波数毎に誘導リアクタンスX1を算出し、これらの誘導リアクタンスX1に基づいて前記表面改質処理を施した鋼材の残留応力を評価することを特徴とする請求項1に記載の表面特性評価方法。
- 前記評価工程において、更に、前記基準インピーダンスZ0と前記インピーダンスZ1の比、及び周波数を夫々座標軸とする座標系上に、前記比の演算値群をプロットすることを特徴とする請求項2乃至請求項4のいずれか1項に記載の表面特性評価方法。
- 前記評価工程において、更に、前記座標系上にプロットされた前記演算値群のグラフの軌跡及びこの軌跡の極値を含む1又は複数の前記演算値に基づいて前記表面改質処理を施した鋼材の残留応力を評価することを特徴とする請求項5に記載の表面特性評価方法。
- 前記評価工程において、更に、前記極値を含む1又は複数の演算値を予め設定された1又は複数の閾値と比較することにより、表面改質処理の良否を判定することを特徴とする請求項6に記載の表面特性評価方法。
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