Ferromagnetic Steel Plate U-Shaped Defect Detection Method

Abstract

A ferromagnetic steel plate U-shaped defect detection method, comprising the following steps: S1, applying an excitation signal; S2, finding the defect position range; S3, performing a long scan; S4, performing a wide scan; S5, extracting the required values; S6, calculating the U-shaped defect length L, the maximum defect depth H, and the defect width W.

Description

Technical Field

[0001] The present invention relates to the technical field of non-destructive testing of ferromagnetic steel plate materials, and particularly relates to a method for detecting U-shaped defects of ferromagnetic steel plates. Background Art

[0002] With the development of economy and industrialization, due to its good mechanical properties, corrosion resistance and processing characteristics, ferromagnetic steel plates can be applied to welding and other processing and forming technologies, and are used in various fields, so the demand is increasing continuously. However, during the production, manufacturing, storage, transportation, and processing of ferromagnetic steel plates, U-shaped defects may occur on their surfaces or near the surfaces for various reasons. For example, if the steel used to manufacture ferromagnetic steel plates has defects such as uneven chemical composition, the manufactured ferromagnetic steel plates will have U-shaped defects; if ferromagnetic steel plates are exposed to humid, high-temperature and other environments that may cause corrosion for a long time during storage, corrosion may occur on the surfaces of ferromagnetic steel plates, resulting in U-shaped defects; if ferromagnetic steel plates are mechanically damaged such as being collided and scratched during transportation and use, it may also cause U-shaped defects to appear on the surfaces of ferromagnetic steel plates; if there are process problems such as uneven heating and too fast rolling speed during the processing and manufacturing of ferromagnetic steel plates, it may also cause U-shaped defects to occur on the surfaces or near the surfaces of ferromagnetic steel plates. Therefore, in order to effectively repair the U-shaped defects on the surfaces or near the surfaces of ferromagnetic steel plates, an effective method for non-destructively detecting the U-shaped defect information on the surfaces or near the surfaces of ferromagnetic steel plates is urgently needed. Summary of the Invention

[0003] In view of this, it is necessary to provide a method for detecting U-shaped defects of ferromagnetic steel plates.

[0004] A method for detecting U-shaped defects of ferromagnetic steel plates includes the following steps:

[0005] S1. Applying an excitation signal:

[0006] Applying an excitation signal with a predetermined frequency and intensity to the excitation coil;

[0007] S2. Finding the defect position range:

[0008] Scanning on the metal workpiece to be tested to find the position range of U-shaped defects, and determining the length and width directions of the U-shaped defects;

[0009] S3. Scanning along the length:

[0010] Along the length direction of the U-shaped defect, scanning every m 1 and recording the voltage values detected by the detection coil at each interval until the entire defect position range is scanned;

[0011] S4. Scanning along the width:

[0012] Along the width direction of the U-shaped defect, every m intervals 2 Perform scanning, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is scanned;

[0013] S5. Extract the required values:

[0014] Among the voltage values obtained in the long scan, extract the interval distance x between the starting voltage mutation point and the voltage peak; among the voltage values obtained in the width scan, extract the voltage peak y and the interval distance z between the starting voltage mutation point and the voltage peak;

[0015] S6. Calculate the length L, maximum defect depth H, and defect width W of the U-shaped defect:

[0016] According to the functional relationship between the length L of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance x between the starting voltage mutation point and the voltage peak in the long scan, obtain the length L of the U-shaped defect of the metal workpiece to be measured;

[0017] According to the functional relationship between the maximum defect depth H of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the voltage peak y in the width scan, obtain the maximum defect depth H of the U-shaped defect of the metal workpiece to be measured;

[0018] According to the functional relationship between the width W of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance z between the starting voltage mutation point and the voltage peak in the width scan, obtain the width W of the U-shaped defect of the metal workpiece to be measured.

[0019] Preferably, in step S6, the functional relationship between the length L of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance x between the starting voltage mutation point and the voltage peak in the long scan is L(x) = a 1 x + b 1 x 2 -c 1 x 3 .

[0020] Preferably, in step S6, the functional relationship between the maximum defect depth H of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the voltage peak y in the width scan is H(y) = a 2 -b 2 y + c 2 y 2 .

[0021] Preferably, in step S6, the functional relationship between the width W of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance z between the starting voltage mutation point and the voltage peak in the width scan is W(z) = a 3+b 3 z - c 3 z 2 +d 3 z 3 。

[0022] Preferably, in step S2, the specific steps of scanning to find the defect position range are as follows:

[0023] Using an orthogonal axial eddy current probe, scan along two directions of a "cross", respectively on the surface of the metal workpiece to be tested, and in the two directions, from the position of the starting voltage mutation point obtained from the detection coil to the position range where the voltage mutation ends, and extend m outward at the starting and ending positions, which is the defect position range; among them, the direction with a larger distance between the starting voltage mutation point and the voltage peak is the defect length direction, and the direction with a smaller distance between the starting voltage mutation point and the voltage peak is the defect width direction.

[0024] Preferably, the functional relationship L(x) = a 1 x + b 1 x 2 -c 1 x 3 , between the U-shaped defect length L of the material of the metal workpiece to be tested pre-fitted and calibrated, and the interval distance x between the starting voltage mutation point and the voltage peak along the long scan, and the functional relationship H(y) = a 2 -b 2 y + c 2 y 2 , between the maximum defect depth H and the voltage peak y along the width scan, and the functional relationship W(z) = a 3 +b 3 z - c 3 z 2 +d 3 z 3 , are measured respectively by the following steps:

[0025] S61. Make specimens:

[0026] Use ferromagnetic materials of the same material as the metal workpiece to be tested to make specimens T 1 、T 2 、T 3 , and on the specimens T 1 、T 2 、T 3 , a U-shaped defect with known defect information is made respectively, and their defect lengths are L 1 、L 2 、L 3 , and the maximum defect depths are H 1 、H2 and H 3 , the defect widths are W 1 , W 2 , and W 3 ;

[0027] S62. Apply an excitation signal:

[0028] Apply an excitation signal with the same frequency and intensity as in step S1 to the excitation coil;

[0029] S63. Longitudinal scan:

[0030] For specimens T 1 , T 2 , and T 3 , scan along the defect length direction at intervals of m 1 respectively, and record the voltage values detected by the detection coil at each interval until the entire defect position range is scanned;

[0031] S64. Transverse scan:

[0032] For specimens T 1 , T 2 , and T 3 , scan along the defect width direction at intervals of m 2 respectively, and record the voltage values detected by the detection coil at each interval until the entire defect position range is scanned;

[0033] S65. Extract required values:

[0034] For specimens T 1 , T 2 , and T 3 , extract the interval distance x 1 , x 2 , and x 3 between the starting voltage mutation point and the voltage peak value from the voltage values obtained in the longitudinal scan; extract the voltage peak value y 1 , y 2 , and y 3 from the voltage values obtained in the transverse scan, as well as the interval distance z 1 , z 2 , and z 3 ;

[0035] S66. Fit and calibrate the functional relationship:

[0036] According to the known defect lengths L 1 , L 2 , and L 3 of specimens T 1 , L 2 , and L3 , the maximum defect depth H 1 , H 2 , H 3 , the defect width W 1 , W 2 , W 3 , and those obtained in step S65, the respective interval distances x between the starting voltage mutation point and the voltage peak in the long scan 1 , x 2 , x 3 , the voltage peak y in the width scan 1 , y 2 , y 3 , the interval distance z between the starting voltage mutation point and the voltage peak in the width scan 1 , z 2 , z 3 , respectively fit and calibrate the functional relationship between the defect length L and the interval distance x between the starting voltage mutation point and the voltage peak in the long scan as L(x)=a 1 x + b 1 x 2 - c 1 x 3 , the maximum defect depth H, and the functional relationship between the voltage peak y in the width scan as H(y)=a 2 - b 2 y + c 2 y 2 , the defect width W, and the functional relationship between the interval distance z between the starting voltage mutation point and the voltage peak in the width scan as W(z)=a 3 + b 3 z - c 3 z 2 + d 3 z 3 .

[0037] Preferably, the m 1 is 0.5 - 5 mm.

[0038] Preferably, the m 2 is 0.5 - 1 mm.

[0039] Preferably, the m is 5 - 10 mm.

[0040] The above ferromagnetic steel plate U-shaped defect detection method makes U-shaped defects on a specimen with the same material as the metal workpiece to be measured, and scans the U-shaped defects of the specimen to obtain the functional relationship between the length L of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance x between the starting voltage mutation point and the voltage peak value during the long-axis scanning, the maximum defect depth H and the functional relationship between the voltage peak value y during the width-axis scanning, and the defect width W and the interval distance z between the starting voltage mutation point and the voltage peak value during the width-axis scanning; according to the above pre-fitted and calibrated functional relationships, and according to the interval distance x between the starting voltage mutation point and the voltage peak value during the long-axis scanning of the U-shaped defect of the metal workpiece to be measured, the voltage peak value y during the width-axis scanning, and the interval distance z between the starting voltage mutation point and the voltage peak value during the width-axis scanning obtained during the scanning, the defect length L, the maximum defect depth H and the defect width W of the U-shaped defect of the metal workpiece to be measured can be obtained, realizing the effective quantitative detection of the U-shaped defects of the ferromagnetic steel plate, and the operation process is simple. Description of the Drawings

[0041] Figure 1 It is a three-dimensional structural schematic diagram of the orthogonal axial eddy current probe adopted in the present invention.

[0042] Figure 2 It is a schematic diagram of the overall structure of the eddy current detection device adopted in the present invention.

[0043] Figure 3 It is an exploded structural schematic diagram of the orthogonal axial eddy current probe, the long-axis scanning bracket and the width-axis scanning bracket in the present invention.

[0044] Figure 4 It is a schematic diagram of the scanning in the defect length direction in the present invention.

[0045] Figure 5 It is a schematic diagram of the scanning in the defect width direction in the present invention.

[0046] Figure 6 It is for the specimen T 1 The voltage values obtained by the detection coil at each interval during the long-axis scanning of the specimen.

[0047] Figure 7 It is for the specimen T 2 The voltage values obtained by the detection coil at each interval during the long-axis scanning of the specimen.

[0048] Figure 8 It is for the specimen T 3 The voltage values obtained by the detection coil at each interval during the long-axis scanning of the specimen.

[0049] Figure 9 It is for the specimen T 1The voltage values obtained by the detection coil at each interval during the widthwise scan.

[0050] Figure 10 For the test piece T 2 The voltage values obtained by the detection coil at each interval during the widthwise scan.

[0051] Figure 11 For the test piece T 3 The voltage values obtained by the detection coil at each interval during the widthwise scan.

[0052] Figure 12 It is the fitting function curve between the length L of the U-shaped defect of the 45# steel plate and the interval distance x between the starting voltage mutation point and the voltage peak value during the lengthwise scan.

[0053] Figure 13 It is the fitting function curve between the maximum defect depth H of the U-shaped defect of the 45# steel plate and the voltage peak value y during the widthwise scan.

[0054] Figure 14 It is the fitting function curve between the width W of the U-shaped defect of the 45# steel plate and the interval distance z between the starting voltage mutation point and the voltage peak value during the widthwise scan.

[0055] In the figure: Orthogonal axial eddy current probe 1; Excitation coil 10; Detection coil 11; Eddy current detection device 2; Signal generator 20; Power amplifier 21; Scanning auxiliary component 22; Lengthwise scanning bracket 220; Probe fixing part 2200; Handle 2201; Probe fixing groove 2202; Widthwise scanning bracket 221; Probe placement groove 2210; Workpiece placement groove 2211; Observation window 2212; Scanning alignment groove 2213; Signal collector 23; Metal workpiece to be tested 24; Defect 240. Detailed implementation manners

[0056] The following further elaborates in detail on the technical solutions and technical effects of the embodiments of the present invention in combination with the accompanying drawings of the present invention.

[0057] Please refer to Figure 1 , An orthogonal axial eddy current probe 1, comprising: The probe is composed of an excitation coil 10 and a detection coil 11 placed orthogonally to each other; The detection coil 11 is a rectangular coil and is placed perpendicular to the surface of the metal workpiece to be tested; The excitation coil 10 is a racetrack-shaped coil and is axially placed at the center of the detection coil 11.

[0058] In this embodiment, the excitation coil 10 is a racetrack-shaped coil. The two ends of the excitation coil 10 are semi-circular arcs, and the middle part is linear. The semi-circular arc design enables the current to flow more smoothly at both ends of the excitation coil 10 without sudden changes. Compared with the rectangular coil in the prior art, the distance in the width direction of the excitation coil 10 can be further reduced to an ideal state, greatly reducing the field-free hollow region generated by the alternating magnetic field generated by the excitation coil 10 at the center.

[0059] Further, referring to Figure 1 , the detection coil 11 is a square coil. In this embodiment, the detection coil 11 is set as a square coil. Compared with the rectangular coil, the four sides of the square coil are of equal length and the side length is more uniform, further improving the sensitivity of the detection coil 11 to magnetic field changes.

[0060] Further, referring to Figure 1 , the inner distance in the width direction of the excitation coil 10 is less than or equal to 1 mm. This setting in this embodiment greatly reduces the field-free hollow region generated by the alternating magnetic field generated by the excitation coil 10 at the center.

[0061] Further, the excitation coil 10 is formed by winding 800 turns of enameled copper wire with a diameter of 0.1 mm.

[0062] Further, the detection coil 11 is formed by winding 400 turns of enameled copper wire with a diameter of 0.1 mm.

[0063] Please refer to Figure 2 and Figure 3 , the eddy current detection device 2 provided by the present invention containing the above-mentioned orthogonal axial eddy current probe includes: a signal generator 20, a power amplifier 21, an orthogonal axial eddy current probe 1, a scanning auxiliary component 22, and a signal collector 23; the input end of the power amplifier 21 is electrically connected to the signal generator 20, and the output end of the power amplifier 21 is electrically connected to the excitation coil 10 of the orthogonal axial eddy current probe 1; the input end of the signal collector 23 is electrically connected to the detection coil 11 of the orthogonal eddy current detection probe 1; the orthogonal axial eddy current probe 1 is placed on the scanning auxiliary component 22.

[0064] In this embodiment, the signal collector 23 collects the changes in the original magnetic field around the detection coil 11 caused by the secondary magnetic field generated by the eddy current. The collected signal can be a voltage signal, and the signal collector 23 can be a device for collecting voltage, such as an oscilloscope. The scanning auxiliary component 22 is used to assist the operator in operating the orthogonal axial eddy current probe 1 during detection.

[0065] Further, referring to Figure 3 and Figure 4 , the scanning auxiliary component 22 includes: a long scanning bracket 220 and a wide scanning bracket 221.

[0066] Further, referring to Figure 3 , the long-axis scanning bracket 220 includes: a probe fixing part 2200 and a handle 2201; the probe fixing part 2200 is in the shape of a cuboid; a probe fixing groove 2202 is formed in the center of the probe fixing part 2200; the shape and size of the probe fixing groove 2202 match the shape and size of the orthogonal axial eddy current probe 1; the handle 2201 is in the shape of a long strip, one end of the handle 2201 is fixedly connected to the lower end of the probe fixing part 2200, and the other end of the handle 2201 extends in a direction parallel to and away from the probe fixing part 2200. In this embodiment, the probe fixing part 2200 is used to fix the orthogonal axial eddy current probe 1.

[0067] Further, referring to Figure 3 , the width-axis scanning bracket 221 is in the shape of a cuboid; a probe placement groove 2210, a workpiece placement groove 2211, an observation window 2212, and a scanning alignment groove 2213 are formed in the width-axis scanning bracket 221; the probe placement groove 2210 is located at the central part of the width-axis scanning bracket 221, the probe placement groove 2210 penetrates the upper and lower end faces of the width-axis scanning bracket 221, and the shape and size of the probe placement groove 2210 match the shape and size of the long-axis scanning bracket 220; the workpiece placement groove 2211 is formed in the bottom end face of the width-axis scanning bracket 221; the workpiece placement groove 2211 penetrates the left and right end faces of the width-axis scanning bracket 221; the observation window 2212 is formed directly above the top of the probe placement groove 2210, and the observation window 2212 penetrates the upper and lower end faces of the width-axis scanning bracket 221; the scanning alignment groove 2213 is linear and is formed in the upper end face of the width-axis scanning bracket 221; the scanning alignment groove 2213 is located at the central part in the left and right directions of the observation window 2212.

[0068] In this embodiment, the probe placement groove 2210 is used to place the long-axis scanning bracket 220 installed with the orthogonal axial eddy current probe 1, and the long-axis scanning bracket 220 and the probe placement groove 2210 are in an interference fit to fix the lift-off value height of the orthogonal axial eddy current probe 1 from the surface of the metal workpiece 24 to be measured; the observation window 2212 is used to assist the operator in observing the metal workpiece during measurement, and the scanning alignment groove 2213 is used to assist the operator in aligning the scanning lines marked on the metal workpiece 24 to be measured.

[0069] The working principle and process of the eddy current detection device in the specific embodiment of the present invention are as follows:

[0070] First step, install the orthogonal axial eddy current probe 1 in the probe fixing groove 2202 on the long-axis scanning bracket 220, and place it parallel to the metal workpiece 24 to be measured at a lift-off value h.

[0071] Step 2: Turn on the signal generator 20. After the alternating excitation signal generated by the signal generator 20 is amplified by the power amplifier 21, it is applied to the excitation coil 10. Observe through the signal collector 23 whether there is a signal generated in the detection coil 11. If no signal is generated, check the connection of the circuit until a signal is output from the detection coil 11.

[0072] Step 3: Further observe whether the waveform of the signal output by the detection coil 11 is basically similar to the waveform of the signal applied to the excitation coil 10. If not, check whether the wiring of the excitation coil 10 is properly connected until it is ensured that the excitation coil 10 receives the alternating excitation signal applied by the signal generator 20.

[0073] Step 4: Use the longitudinal scanning bracket 220 to scan the surface of the metal workpiece 24 to be measured in two directions of length and width to determine the position range of the defect 240.

[0074] Step 5: Refer to Figure 4 , within the determined position range of the defect 240, along the length direction of the defect 240, make marking lines on the metal workpiece 24 to be measured every 0.5 - 5 mm, and move the longitudinal scanning bracket 220 to scan the defect until the orthogonal axial eddy current probe 1 completely sweeps across the defect 240.

[0075] Step 6: Install the longitudinal scanning bracket 220 in the probe placement groove 2210 of the transverse scanning bracket 221, and keep the lift-off value h between the excitation coil 10 of the orthogonal axial eddy current probe 1 and the upper surface of the metal workpiece 24 to be measured.

[0076] Step 5: Refer to Figure 5 , along the width direction, make marking lines on the metal workpiece 24 to be measured every 0.5 - 1 mm, then place the metal workpiece 24 to be measured in the workpiece placement groove 2211 along the width direction, hold the handle 2201, and move the transverse scanning bracket 221 to scan the defect 240 along the width direction until the orthogonal axial eddy current probe 1 completely sweeps across the defect 240.

[0077] Step 6: During the above scanning process, record the information obtained by the signal collector 23 and analyze the information to obtain the defect 240 information of the metal workpiece 24 to be measured.

[0078] The ferromagnetic steel plate U-shaped defect detection method provided by the specific embodiment of the present invention specifically includes the following two stages:

[0079] Stage 1: Function relationship fitting and calibration stage, including the following steps:

[0080] S11: Fabricate a specimen:

[0081] Make a specimen T using a ferromagnetic material with the same material as the metal workpiece to be measured. 1 , T 2 , T 3 , in this invention, taking 45# steel plate as an example, specimen T 1 , T 2 , T 3 is respectively made with a U-shaped defect with known defect information, and their defect lengths are L 1 = 28 mm, L 2 = 24 mm, L 3 = 29 mm, and the maximum defect depths are H 1 = 2 mm, H 2 = 1 mm, H 3 = 3 mm, and the defect widths are W 1 = 2 mm, W 2 = 2.2 mm, W 3 = 1.9 mm;

[0082] S12. Apply an excitation signal:

[0083] Apply an excitation signal with a frequency of 100 Hz and a voltage intensity of 6 V to the excitation coil;

[0084] S13. Longitudinal scan:

[0085] For specimen T 1 , along the defect length direction, scan every m 1＝ 4.5 mm, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is scanned. The scan results are shown in Figure 6 ;

[0086] For specimen T 2 , along the defect length direction, scan every m 1＝ 5 mm, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is scanned. The scan results are shown in Figure 7 ;

[0087] For specimen T 3 , along the defect length direction, scan every m 1＝ 4 mm, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is scanned. The scan results are shown in Figure 8 ;

[0088] S14. Width scan:

[0089] For specimen T 1 , along the defect width direction, scan every m 2Scan at intervals of 1.5 mm, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is scanned. The scan results are shown in Figure 9 as shown;

[0090] For specimen T 2 , scan at intervals of m 2 = 1 mm along the width direction of the defect, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is scanned. The scan results are shown in Figure 10 as shown;

[0091] For specimen T 3 , scan at intervals of m 2 = 1 mm along the width direction of the defect, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is scanned. The scan results are shown in Figure 11 as shown;

[0092] S15. Extract the required values:

[0093] For specimens T 1 , T 2 , T 3 , respectively extract the interval distance x 1＝ = 12.5 mm, x 2 = 10 mm, x 3 = 14 mm between the starting voltage mutation point and the voltage peak in the voltage values obtained from the long scan; extract the voltage peak y 1 = 0.13466 mV, y 2 = 0.13066 mV, y 3 = 0.13542 mV, and the interval distance z 1 = 2.5 mm, z 2 = 3.5 mm, z 3 = 2 mm;

[0094] S16. Fit the calibration function relationship:

[0095] According to the known defect lengths L 1 , L 2 , L 3 of specimens T 1 = 28 mm, L 2 = 24 mm, L 3 = 29 mm, the maximum defect depth H 1 = 2 mm, H 2 = 1 mm, H 3 = 3 mm, and the defect width W 1 = 2 mm, W2 = 2.2 mm, W 3 = 1.9 mm, and the interval distance x between the starting voltage mutation point and the voltage peak value in the long scan obtained in step S15 1＝ 12.5 mm, x 2 = 10 mm, x 3 = 14 mm, the voltage peak value y in the width scan 1 = 0.13466 mV, y 2 = 0.13066 mV, y 3 = 0.13542 mV, the interval distance z between the starting voltage mutation point and the voltage peak value in the width scan 1 = 2.5 mm, z 2 = 3.5 mm, z 3 = 2 mm, respectively fitting and calibrating the U-shaped defects of 45# steel plate:

[0096] The function curve between the defect length L and the interval distance x between the starting voltage mutation point and the voltage peak value in the long scan, see Figure 12 as shown, the functional relationship is L(x) = a 1 x + b 1 x 2 -c 1 x 3 , where a 1 = 1.52817, b 1 = 0.2081, c 1 = 0.0121;

[0097] The fitting function curve between the maximum defect depth H and the voltage peak value y in the width scan, see Figure 13 as shown, the functional relationship is H(y) = a 2 -b 2 y + c 2 y 2 , where, a 2 = 448.03194, b 2 = 6705.360 74, c 2 = 25138.702197;

[0098] The fitting function curve between the defect width W and the interval distance z between the starting voltage mutation point and the voltage peak value in the width scan, see Figure 14 as shown, the functional relationship is W(z) = a 3 +b 3 z - c 3 z 2 +d 3 z 3 , where, a 3 = 1.777636×10-15 , b 3 = 0.68667, c 3 = 0.074, d 3 = 0.00253.

[0099] Stage 2: The measurement and evaluation stage of the U-shaped defect of the metal workpiece to be measured, including the following steps:

[0100] S1. Apply an excitation signal:

[0101] Apply an excitation signal with the same predetermined frequency and voltage intensity as in Stage 1 to the excitation coil;

[0102] S2. Find the defect position range:

[0103] Scan the 45# steel plate of the metal workpiece to be measured to find the position range of the U-shaped defect, and determine the length and width directions of the U-shaped defect. The specific steps are as follows:

[0104] Use an orthogonal axial eddy current probe to scan the surface of the metal workpiece to be measured along two directions of a "cross", and in both directions, from the position of the starting voltage mutation point obtained from the detection coil to the position range where the voltage mutation ends, and extend m outward at the starting and ending positions, which is the defect position range; among them, the direction with a larger distance between the starting voltage mutation point and the voltage peak is the defect length direction, and the direction with a smaller distance between the starting voltage mutation point and the voltage peak is the defect width direction; the m is 5 - 10 mm;

[0105] S3. Scan along the length:

[0106] Along the length direction of the U-shaped defect, scan every m 1 and record the voltage value detected by the detection coil at each interval until the entire defect position range is scanned; the m 1 is 0.5 - 5 mm;

[0107] S4. Scan along the width:

[0108] Along the width direction of the U-shaped defect, scan every m 2 and record the voltage value detected by the detection coil at each interval until the entire defect position range is scanned; the m 2 is 0.5 - 1 mm;

[0109] S5. Extract the required values:

[0110] Among the voltage values obtained in the scan along the length, extract the interval distance x between the starting voltage mutation point and the voltage peak; among the voltage values obtained in the scan along the width, extract the voltage peak y and the interval distance z between the starting voltage mutation point and the voltage peak;

[0111] S6. Calculate the length L, maximum defect depth H, and defect width W of the U-shaped defect:

[0112] According to the function relationship L(x) = a 1 x + b 1 x 2 -c 1 x 3 between the length L of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance x between the starting voltage mutation point and the voltage peak value during the longitudinal scan, where a 1 = 1.52817, b 1 = 0.2081, c 1 = 0.0121, to obtain the length L of the U-shaped defect of the metal workpiece to be measured;

[0113] According to the function relationship H(y) = a 2 -b 2 y + c 2 y 2 between the maximum defect depth H of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the voltage peak value y during the widthwise scan, where a 2 = 448.03194, b 2 = 6705.36074, c 2 = 25138.702197, to obtain the maximum defect depth H of the U-shaped defect of the metal workpiece to be measured;

[0114] According to the function relationship W(z) = a 3 +b 3 z - c 3 z 2 +d 3 z 3 between the width W of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance z between the starting voltage mutation point and the voltage peak value during the widthwise scan, where a 3 = 1.777636×10 -15 , b 3 = 0.68667, c 3 = 0.074, d 3 = 0.00253, to obtain the width W of the U-shaped defect of the metal workpiece to be measured.

[0115] The above ferromagnetic steel plate U-shaped defect detection method makes U-shaped defects on a specimen with the same material as the metal workpiece to be measured, and scans the U-shaped defects of the specimen to obtain the function relationship between the length L of the U-shaped defect of the material to which the metal workpiece to be measured belongs, which is pre-fitted and calibrated, and the interval distance x between the starting voltage mutation point and the voltage peak value during the long-axis scan, the function relationship between the maximum defect depth H and the voltage peak value y during the width-axis scan, and the function relationship between the defect width W and the interval distance z between the starting voltage mutation point and the voltage peak value during the width-axis scan; according to the above pre-fitted and calibrated function relationships, and based on the interval distance x between the starting voltage mutation point and the voltage peak value during the long-axis scan, the voltage peak value y during the width-axis scan, and the interval distance z between the starting voltage mutation point and the voltage peak value during the width-axis scan obtained during the scan of the U-shaped defect of the metal workpiece to be measured, the defect length L, the maximum defect depth H, and the defect width W of the U-shaped defect of the metal workpiece to be measured can be obtained, realizing the effective quantitative detection of the U-shaped defects of the ferromagnetic steel plate, and the operation process is simple.

[0116] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A method for detecting U-shaped defects in ferromagnetic steel plates, characterized in that, it includes the following steps: S1. Apply an excitation signal: Apply an excitation signal with a predetermined frequency and intensity to the excitation coil; S2. Find the defect position range: Use an orthogonal axial eddy current probe to scan the surface of the metal workpiece to be measured along two directions of a "plus" cross, find the position range of the U-shaped defect, and determine the length and width directions of the U-shaped defect; S3. Scan along the length: Along the length direction of the U-shaped defect, every m intervals 1 Perform scanning, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is completely scanned; S4. Scan along the width: Along the width direction of the U-shaped defect, every m intervals 2 Perform scanning, and at each interval, record the voltage value detected by the detection coil until the entire defect position range is completely scanned; S5. Extract the required values: Among the voltage values obtained during the scan along the length, extract the interval distance x between the starting voltage mutation point and the voltage peak; among the voltage values obtained during the scan along the width, extract the voltage peak y and the interval distance z between the starting voltage mutation point and the voltage peak; S6. Calculate the U-shaped defect length L, the maximum defect depth H, and the defect width W: According to the functional relationship L(x)=a 1 x + b 1 x 2 -c 1 x 3 between the length L of the U-shaped defect of the metal workpiece to be measured belonging to the pre-fitted and calibrated material and the interval distance x between the starting voltage mutation point and the voltage peak during the long scan, the length L of the U-shaped defect of the metal workpiece to be measured is obtained; According to the functional relationship H(y)=a 2 -b 2 y + c 2 y 2 , between the maximum defect depth H of the U-shaped defect of the metal workpiece to be measured belonging to the pre-fitted and calibrated material and the peak value y of the scanning voltage along the width, the maximum defect depth H of the U-shaped defect of the metal workpiece to be measured is obtained; According to the functional relationship W(z)=a 3 +b 3 z - c 3 z 2 +d 3 z 3 between the width W of the U-shaped defect of the material to be measured of the metal workpiece to be measured that has been pre-fitted and calibrated, and the interval distance z between the starting voltage mutation point and the voltage peak value during the width scanning, the width W of the U-shaped defect of the metal workpiece to be measured is obtained.

2. The method for detecting U-shaped defects in ferromagnetic steel plates according to claim 1, characterized in that: In step S2, the specific steps for scanning and finding the defect position range are as follows: Scan the surface of the metal workpiece to be measured respectively. In two directions, from the position of the starting voltage mutation point obtained from the detection coil to the position range where the voltage mutation ends, and extend m outward at the starting and ending positions, which is the defect position range; among them, the direction with a larger distance between the starting voltage mutation point and the voltage peak is the defect length direction, and the direction with a smaller distance between the starting voltage mutation point and the voltage peak is the defect width direction.

3. The method for detecting U-shaped defects in ferromagnetic steel plates according to claim 1 or 2, characterized in that: The functional relationship L(x) = a 1 x + b 1 x 2 - c 1 x 3 between the length L of the U-shaped defect of the material to be measured of the metal workpiece pre-fitted and calibrated in advance and the interval distance x between the starting voltage mutation point and the voltage peak value during the long scan, and the functional relationship H(y) = a 2 - b 2 y + c 2 y 2 between the maximum defect depth H and the voltage peak value y during the width scan, and the functional relationship W(z) = a 3 + b 3 z - c 3 z 2 + d 3 z 3 between the defect width W and the interval distance z between the starting voltage mutation point and the voltage peak value during the width scan are measured respectively by the following steps: S61. Make a specimen: Make a specimen T using a ferromagnetic material with the same material as the metal workpiece to be measured 1 and T 2 and T 3 On the specimen T 1 and T 2 and T 3 make a U-shaped defect with known defect information respectively. Their defect lengths are L 1 and L 2 and L 3 respectively, and the maximum defect depths are H 1 and H 2 and H 3 respectively, and the defect widths are W 1 and W 2 and W 3 ; S62. Apply an excitation signal: Apply an excitation signal with the same frequency and intensity as in step S1 to the excitation coil; S63. Scan along the length: For specimen T 1 、T 2 、T 3 , respectively along the length direction of the defect, scan every m 1 , and at each interval, record the voltage value detected by the detection coil until the entire defect position range is completely scanned; S64. Scan along the width: For the test piece T 1 , T 2 , T 3 , respectively along the width direction of the defect, scan every m 2 , and at each interval, record the voltage value detected by the detection coil until the entire defect position range is completely scanned; S65. Extract the required values: For the test piece T 1 、T 2 、T 3 , respectively extract the interval distance x 1 、x 2 、x 3 between the starting voltage mutation point and the voltage peak value from the voltage values obtained in the long scan; extract the voltage peak value y 1 、y 2 、y 3 , and the interval distance z 1 、z 2 、z 3 between the starting voltage mutation point and the voltage peak value from the voltage values obtained in the wide scan; S66. Fit and calibrate the functional relationship: According to the test piece T 1 、T 2 、T 3 The known defect lengths L 1 、L 2 、L 3 ,the maximum defect depth H 1 、H 2 、H 3 ,the defect width W 1 、W 2 、W 3 ,and those obtained in step S65, their respective interval distances x 1 、x 2 、x 3 between the starting voltage mutation point and the voltage peak in the long scan, the voltage peak y 1 、y 2 、y 3 in the width scan, and the interval distance z 1 、z 2 、z 3 between the starting voltage mutation point and the voltage peak in the width scan. The functional relationship between the calibrated defect length L and the interval distance x between the starting voltage mutation point and the voltage peak in the long scan is fitted as L(x) = a 1 x + b 1 x 2 - c 1 x 3 . The functional relationship between the maximum defect depth H and the voltage peak y in the width scan is H(y) = a 2 - b 2 y + c 2 y 2 . The functional relationship between the defect width W and the interval distance z between the starting voltage mutation point and the voltage peak in the width scan is W(z) = a 3 + b 3 z - c 3 z 2 + d 3 z 3 .

4. The method for detecting U-shaped defects in ferromagnetic steel plates according to claim 1 or 3, characterized in that: The said m 1 is 0.5 - 5 mm.

5. The method for detecting U-shaped defects in ferromagnetic steel plates according to claim 1 or 3, characterized in that: The said m 2 is 0.5 - 1 mm.

6. The method for detecting U-shaped defects in ferromagnetic steel plates according to claim 2, characterized in that: The m is 5 - 10 mm.

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