Accelerated cooling defect inspection device and inspection method

Abstract

The present invention provides an apparatus and method for inspecting the surface material of a steel plate, which can accurately and quickly inspect the material of a steel plate using eddy currents. In one embodiment, the apparatus for inspecting the surface material of a steel plate, which generates eddy currents in the steel plate to determine the surface material of the steel plate, includes: an eddy current inspector arranged facing the steel plate; and a frame to which the eddy current inspector is fixed; wherein the eddy current inspector includes a coil unit arranged to form an AC magnetic field in only one direction; an AC power supply unit connected to the coil; a sensor unit connected to the coil; and a material determination unit connected to the sensor unit to determine the material of the steel plate based on a measurement signal obtained via the sensor unit.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for inspecting the surface material of a steel plate. [Background technology]

[0002] A common hardness measurement method is a destructive method in which a specific load is applied to a surface portion of a test object and the hardness strength is measured according to the shape of the surface. This method calculates the hardness value by measuring the shape of the destructed portion. However, since commonly used steel plates have lengths of several meters to several tens of meters and widths of several meters, it is practically impossible to measure the hardness of the entire surface of such steel plates using conventional methods.

[0003] As disclosed in Patent Documents 1 and 2, a technology has been developed to measure the characteristics of a steel sheet by generating eddy currents in the steel sheet via a coil to which an AC power source is applied without contact, but the accuracy is insufficient and there is a problem in that the plate-shaped material cannot be measured quickly and accurately. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-227421 [Patent Document 2] International Publication No. 2018 / 010743 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is intended to solve the problems of the prior art, and aims to provide a steel plate surface material inspection device and method that can accurately and quickly inspect the material of a steel plate using eddy currents. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides the following steel plate surface material inspection device and method.

[0007] In one embodiment, the present invention provides a steel plate surface material inspection device that generates eddy currents in a steel plate to determine the surface material of the steel plate, comprising: an eddy current inspector arranged facing the steel plate; and a frame to which the eddy current inspector is fixed; the eddy current inspector including a coil unit arranged to generate an AC magnetic field in only one direction; an AC power supply unit connected to the coil; a sensor unit connected to the coil; and a material determination unit connected to the sensor unit and that determines the material of the steel plate based on a measurement signal obtained via the sensor unit.

[0008] In this case, the steel plate may be a rolled steel plate, and the one direction may be the rolling direction of the steel plate.

[0009] In one embodiment, the AC power supply unit can supply a current of 0.5 kHz to 10 kHz to the coil, and the eddy current inspection device further includes a yoke unit shaped like a "C", "U", or "V", with both ends facing the steel material, and the coil unit can be wound around the center of the yoke unit.

[0010] In one embodiment, both ends of the yoke portion may be arranged perpendicular to the rolling direction of the steel plate.

[0011] In one embodiment, the inspection device may further include a demagnetizing unit disposed in front of the eddy current inspection device to demagnetize the steel plate being moved to the eddy current inspection device.

[0012] In one embodiment, the material determination unit may determine the material by taking into account the distance between the steel plate and the sensor unit, and the eddy current tester may further include a lift-off compensation unit connected to the coil to measure a lift-off compensation value and provide the lift-off compensation value to the material determination unit.

[0013] In one embodiment, the lift-off compensator measures a Q factor when a resonant frequency of a current frequency provided by the AC power supply is provided, and provides the Q factor to the material determiner. The material determiner can determine the material of the material based on a signal obtained by converting a measurement signal of the sensor using the measurement value of the lift-off compensator as a compensation coefficient.

[0014] In one embodiment, the eddy current tester further includes a distance measuring device provided on the frame and capable of measuring a distance, and a measurement value of the distance measuring device is provided to the material determining unit, and the material determining unit can determine the material of the steel plate in consideration of the distance measurement value.

[0015] Alternatively, the present invention provides a method for determining the surface quality of a steel sheet by generating eddy currents to determine the quality of the rolled steel sheet, the method comprising: a magnetic field forming step of forming an AC magnetic field only in the rolling direction of the rolled steel sheet via a coil; a signal measuring step of measuring a signal via a sensor connected to the coil; and a material determining step of determining the quality of the steel sheet at a measurement location based on the signal obtained in the signal measuring step.

[0016] In one embodiment of the present invention, the AC magnetic field can be generated by a current having a frequency of 0.5 to 10 kHz.

[0017] In one embodiment, the sensor can measure an impedance signal of a coil, and the material determining step can determine the material by taking into account the distance between the steel plate and the sensor.

[0018] In one embodiment, the method for determining the surface material of a steel sheet further includes a lift-off compensation value measuring step of measuring a lift-off compensation value through a lift-off compensation unit connected to the coil, and the material determining step may determine the material of the steel sheet from a signal obtained by converting the measurement signal of the sensor using the compensation value of the lift-off compensation unit as a compensation coefficient.

[0019] In one embodiment, in the step of measuring the lift-off compensation value, the lift-off compensator may measure a Q factor when a resonant frequency of a current frequency provided by the AC power source is provided. [Effects of the Invention]

[0020] With the above-described configuration, the present invention can provide a steel plate surface material inspection device and method that can accurately and quickly inspect the material quality of a steel plate via eddy currents. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a conceptual diagram of steel plate material inspection using eddy currents. [Figure 2] This is a BH curve diagram for different materials. [Figure 3] FIG. 2 is a schematic diagram of the eddy current tester shown in FIG. [Figure 4] 4 is a graph showing the relationship between the measurement signal and hardness obtained by the eddy current tester of FIG. 3. [Figure 5] 1 is a schematic diagram of an inspection device according to a first embodiment of the present invention. [Figure 6] FIG. 2 is a schematic plan view of the eddy current tester shown in FIG. [Figure 7] FIG. 2 is a schematic side view of the eddy current tester shown in FIG. [Figure 8] 1 is a graph of the actual hardness along the length of the steel plate. [Figure 9] 6 is a graph of a measurement signal obtained by the eddy current tester of FIG. 5. [Figure 10] 6 is a graph showing the relationship between the measurement signal and hardness measured by the inspection device of FIG. 5. [Figure 11] FIG. 4 is a schematic diagram of an inspection device according to a second embodiment of the present invention. [Figure 12] FIG. 12 is a schematic plan view of the inspection device of FIG. [Figure 13] 12 is a graph showing a measurement signal along the length direction of the steel plate by the inspection device of FIG. 11. [Figure 14] FIG. 10 is a schematic diagram of an inspection device according to a third embodiment of the present invention. [Figure 15] FIG. 15 is a schematic diagram showing a measurement method of the eddy current tester of FIG. [Figure 16] 15 is a graph showing a signal measured by the sensor unit of FIG. 14. [Figure 17] 15 is a graph of a signal measured by the lift-off compensation unit of FIG. 14. [Figure 18] 18 is a final signal graph obtained by compensating the measurement signal of FIG. 16 with the lift-off compensation signal of FIG. 17. [Figure 19] 19 is a graph showing the measured signal of FIG. 16 together with the final signal graph of FIG. 18. [Figure 20] 19 is a graph showing the relationship between the final signal and hardness in FIG. 18. [Figure 21] FIG. 10 is a schematic diagram of an inspection device according to a fourth embodiment. [Figure 22] 1 is a flowchart of an inspection method according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

[0023] Plates can be used as oil and gas pipelines, and in such cases, they require rigidity and sour resistance to prevent problems caused by substances passing through them. Thermo-Mechanical Control Process Steel (TMPC steel) is usually used to make plates with rigidity and sour resistance.

[0024] In such thick plates, if the hardness of the plate is higher (250Hv) than the standard hardness of 200Hv, the high-hardness area may react with H2S under high pressure, causing cracks and destroying the pipe, resulting in hydrogen-inducible cracking (HIC). This is also disclosed in "DNV-OS-F101 (Submarine Pipeline System)" and "API 5L Specification for Line Pipe."

[0025] Therefore, it is necessary to accurately determine the hardness of the subsurface portion of a thick plate to prevent potential defects. In particular, an accident in a raw material transport pipeline can cause serious complex problems, such as human and material losses as well as environmental pollution. Therefore, accurate measurement of the hardness of the entire area of ​​a high-strength, highly corrosion-resistant steel thick plate is required. The present invention provides a method for accurately measuring the hardness of a high-strength, highly corrosion-resistant steel thick plate.

[0026] Hereinafter, a steel plate material inspection device capable of accurately measuring the hardness of thick plates will be described mainly with reference to an embodiment.

[0027] Figure 1 shows a conceptual diagram of steel plate material inspection using eddy currents. When an AC magnetic field is applied to steel plate S, the target material, with AC power source 2 connected to coil 1, eddy currents are generated in the steel plate S, and the eddy currents generated in the steel plate S can be detected by coil 1. As can be seen from the BH curve diagram for each material in Figure 2, the magnetic permeability varies depending on the material, so the material of the steel plate can be identified through the detected signal.

[0028] FIG. 3 shows a schematic plan view of the eddy current tester shown in FIG. 1, and FIG. 4 shows a graph of the measurement signal and hardness obtained by the eddy current tester of FIG.

[0029] As shown in Figure 3, Coil 1 is wound around the vertical direction of steel sheet S, so an AC magnetic field is formed in the radial direction around Coil 1. As can be seen from the graph in Figure 4, which compares the signal measured by Coil 1 with the actual hardness, the signal strength cannot be correlated with the actual hardness, which means that accurate measurements cannot be made in actual measurements.

[0030] The inventors of the present invention have confirmed that most steel plates, especially thick plates, are rolled materials, and that the rolling process makes the rolled material anisotropic, which affects the signal. In particular, as can be seen from the dotted line area in Figure 3, they have confirmed that the signal is distorted when the rolling direction Rd intersects with the magnetic field direction. Based on this, they have devised the steel plate material inspection device of the present invention.

[0031] FIG. 5 shows a schematic diagram of an inspection device according to a first embodiment of the present invention, FIG. 6 shows a schematic plan view of the eddy current inspection device shown in FIG. 1, and FIG. 7 shows a schematic side view of the eddy current inspection device shown in FIG. 1.

[0032] 5, the inspection apparatus according to the present invention includes an eddy current inspection device 100 disposed facing a steel sheet S and a frame to which the eddy current inspection device 100 is fixed. The eddy current inspection device 100 includes a coil unit 101 disposed to generate an AC magnetic field in only one direction, an AC power supply unit 102 connected to the coil, a sensor unit 110 connected to the coil, and a material determination unit 120 connected to the sensor unit 110 and determining the material of the steel sheet based on a measurement signal obtained through the sensor unit 110. In this embodiment, the eddy current inspection device 100 is fixed and inspects the material or hardness of the entire area of ​​the steel sheet S while the steel sheet S moves, but the present invention is not limited thereto. The steel sheet S can also be inspected while the steel sheet S is fixed or while the eddy current inspection device 100 is moved along with the movement of the steel sheet S.

[0033] The eddy current tester 100 includes a yoke 103 around which a coil 101 is wound, and both ends of the yoke 103 are disposed facing the steel material. As shown in Fig. 6, both ends of the yoke 103 are disposed perpendicular to the rolling direction Rd of the steel sheet S, and the coil 101 is wound around the center of the yoke 103 to form a magnetic field in the rolling direction Rd.

[0034] When rolling, the structure elongates in the rolling direction, increasing anisotropy. When a magnetic field is applied in the rolling direction, i.e., in the direction in which the structure elongates, the signal change due to eddy currents increases, making it possible to accurately determine the material quality.

[0035] In this case, the yoke portion 103, when viewed from the side, is "C" or "U" shaped as shown in Fig. 7(a), or may be "U" shaped as shown in Fig. 7(b), or may be "V" shaped. In other words, as long as the coil portion 101 can generate a magnetic field along the rolling direction of the steel sheet S, it may have other shapes.

[0036] The AC power supply unit 102 is connected to the coil unit 101 and supplies AC power of a predetermined frequency to the coil unit 101. The AC power supply unit 102 supplies AC power in the range of 0.5 to 10 kHz so that the material of the surface of the steel sheet S, such as hardness and microstructure, can be determined.

[0037] The sensor unit 110 is connected to the coil unit 101 and measures a signal from the coil unit 101. The signal measured by the sensor unit 110 is supplied to a material determination unit 120 connected to the sensor unit 110. The sensor unit 110 can measure and provide an impedance signal from the coil unit 101.

[0038] The material determination unit 120 determines the material, for example, hardness, based on the level of the signal measured by the sensor unit 110. Since the level of the signal measured by the sensor unit 110 correlates with the material, the material of the corresponding part can be determined based on the signal level.

[0039] The material determination unit 120 is connected to a display unit 130, which displays the determination of the material determination unit 120, that is, the signal analysis content, to the user.

[0040] FIG. 8 shows a graph of the actual hardness along the length of the steel sheet S, FIG. 9 shows a graph of the measurement signal measured by the inspection device of FIG. 5, and FIG. 10 is a graph showing the relationship between the measurement signal obtained by the eddy current inspection device of FIG. 5 and the actual hardness.

[0041] FIG. 8 shows the measured hardness, i.e., the actual hardness, of the actual steel plate S used in the experiment, measured using a general hardness measurement method (for example, applying a specific load to the surface of the object to be measured as described in the background art and measuring the hardness intensity according to its shape).

[0042] Figure 9 is a graph of a measurement signal measured by the inspection device of Figure 5, and it can be seen that it shows the same tendency as the actual hardness graph of Figure 8. This can be seen in Figure 10, and it can be seen that the signal level of the sensor unit 110 measured in the first embodiment has a correlation with hardness, and therefore, when the material determination unit 120 determines hardness according to the signal level of the sensor unit 110, it can be seen that an accurate hardness determination is possible.

[0043] 11 and 12 show a second embodiment of the present invention. The inspection apparatus of the second embodiment includes an eddy current inspection device 100 and a demagnetization unit 200. The eddy current inspection device 100 is the same as the eddy current inspection device 100 of the first embodiment, so a detailed description thereof will be omitted to avoid duplication.

[0044] In the case of ordinary rolled materials, the plate may be moved for rolling, and in this case, it is moved by an overhead crane equipped with an electromagnet. When the steel plate S is moved by the electromagnet, residual magnetism remains in the steel plate S, and this residual magnetism acts as a disturbance to the signal measurement of the sensor unit 110.

[0045] In the second embodiment, in order to remove such disturbance factors, a demagnetization unit 200 is included, which is positioned in front of the eddy current inspection device 100, i.e., so that the steel sheet S is inspected by the eddy current inspection device 100 after passing through the demagnetization unit 200.

[0046] Meanwhile, in the second embodiment, the eddy current inspection devices 100 are fixed to a frame F, and a plurality of devices are arranged in two rows along the width direction of the steel sheet S. The first row of eddy current inspection devices 100 and the second row of eddy current inspection devices 100 are arranged offset from each other in the width direction of the steel sheet S, so that the entire area of ​​the steel sheet S can be inspected at once.

[0047] Figure 13 shows a graph of the measurement signal along the length of the steel sheet using the inspection device of Figure 11. As can be seen from the graph of the signal level according to the length when the demagnetizing unit 200 is in operation and when it is not in operation for the same steel sheet S, it can be seen that when the demagnetizing unit 200 is in operation, the signal changes less rapidly, making it possible to measure the signal level accurately.

[0048] 14 is a schematic diagram of a third embodiment of the present invention. Similar to the second embodiment, the inspection apparatus of the third embodiment includes a demagnetization unit 200 and an eddy current inspection device 100. The eddy current inspection device 100 includes a coil unit 101 arranged to generate an AC magnetic field in only one direction; an AC power supply unit 102 connected to the coil; a sensor unit 110 connected to the coil; a lift-off compensation unit 140 connected to the coil; a material determination unit 120 connected to the sensor unit 110 and the lift-off compensation unit 140 and determining the material quality of the steel sheet based on a measurement signal obtained via the sensor unit 110 and the lift-off compensation unit 140; and a display unit 130 displaying the analysis results of the material determination unit 120.

[0049] In this embodiment, the eddy current inspection device 100 may further include a yoke around which a coil 101 is wound, and the yoke may be the same as that in the first embodiment. In the third embodiment, the coil 101 also forms a magnetic field in the rolling direction Rd.

[0050] The AC power supply unit 102 is connected to the coil unit 101 and supplies AC power of a predetermined frequency to the coil unit 101. The AC power supply unit 102 supplies AC power in the range of 0.5 to 10 kHz so that the material of the surface of the steel sheet S, such as hardness and microstructure, can be determined.

[0051] TMPC steel undergoes accelerated cooling, but if the amount of cooling water becomes uneven and concentrates in a specific area during accelerated cooling, the surface of that area may become highly hard. This high-hardness surface layer can induce hydrogen-organic cracks as mentioned above, and the 0.5 to 10 kHz range can detect high-hardness areas that occur for various reasons, and can detect high-hardness defects that occur during accelerated cooling.

[0052] In addition, in the present invention, after forming a magnetic field in one direction, the detection depth is expanded by detecting at a lower frequency range than conventional methods, and high hardness areas that occur on the surface for various reasons can be detected.

[0053] The sensor unit 110 is connected to the coil unit 101 and measures a signal from the coil unit 101. The signal measured by the sensor unit 110 is supplied to a material determination unit 120 connected to the sensor unit 110. The sensor unit 110 can measure and provide an impedance signal from the coil unit 101.

[0054] The lift-off compensation unit 140 is connected to the coil unit 101 and is a compensation unit that is changed by lift-off. coefficient For example, the lift-off compensation unit 140 measures a Q factor when the resonant frequency of the current frequency provided by the AC power supply unit 102 is provided to the coil unit 101. Since the Q factor varies depending on the lift-off, measuring the Q factor provides a compensation coefficient that can compensate for the lift-off.

[0055] The material determination unit 120 obtains a final signal by combining the level of the signal measured by the sensor unit 110 with the compensation coefficient provided by the lift-off compensation unit 140, and determines the material, for example, hardness, based on the final signal. The level of the signal measured by the sensor unit 110 is correlated with the material, and the compensation coefficient is related to lift-off. The final signal obtained by combining these two factors takes into account the distance between the eddy current inspection device 100 and the steel sheet S, allowing for accurate material determination.

[0056] The material determination unit 120 is connected to a display unit 130, which displays the determination of the material determination unit 120, that is, the signal analysis content, to the user.

[0057] 16 to 19 show graphs of signals obtained by the third embodiment. FIG. 16 shows a graph of the signal measured by the sensor unit 110 of the third embodiment, FIG. 17 shows a graph of the lift-off compensation coefficient measured by the lift-off unit 140 of the third embodiment, FIG. 18 shows a graph of the final signal obtained by combining the measurement signal of FIG. 16 and the measurement signal of FIG. 17, and FIG. 19 shows the final signal ( 18 ) and the measurement signal of the sensor unit 110 (Fig. 16 ) is also shown in the graph.

[0058] As shown in FIG. 19, a comparison between the final signal obtained by combining the lift-off compensation coefficient of the lift-off compensator 140 with the measurement signal of the sensor unit 110 and the measurement signal measured by the sensor unit 110 can be confirmed.

[0059] 20, it can be seen that the correlation between the actual hardness and the final signal is improved by receiving the compensation signal from the lift-off compensator 140 and combining it with the signal from the sensor unit 110, which confirms that the accuracy of material determination is improved by the lift-off compensator 140. In contrast, referring to FIG. 19, it can be seen that the measurement signal before compensation has a different pattern from the final signal, which reduces the accuracy of material determination.

[0060] 21 shows a fourth embodiment of the present invention. The inspection apparatus in the fourth embodiment includes a demagnetization unit 200 and an eddy current inspection device 100, similar to the third embodiment. The eddy current inspection device 100 includes a coil unit 101 fixed to a frame and arranged to generate an AC magnetic field in only one direction; an AC power supply unit 102 connected to the coil; a sensor unit 110 connected to the coil; a lift-off compensation unit 140 provided on the frame; a material determination unit 120 connected to the sensor unit 110 and the lift-off compensation unit 140 and determining the material of the steel sheet based on measurement signals obtained through the sensor unit 110 and the lift-off compensation unit 140; and a display unit 130 displaying the analysis results of the material determination unit 120.

[0061] The fourth embodiment is the same as the third embodiment except for the lift-off compensation unit 140, so only the lift-off compensation unit 140 will be described, and the remaining parts will be omitted to avoid duplication with the description of the third embodiment.

[0062] In the fourth embodiment, unlike the third embodiment, the lift-off compensation unit 140 is not connected to the coil unit 101 but is provided separately. That is, the lift-off compensation unit 140 is fixed / provided to a frame, measures the distance between the steel sheet S and the eddy current inspection device 100, and provides the measured value to the material determination unit 120. The lift-off compensation unit 140 may be various distance measurement means, such as a laser distance meter or a physical distance meter. The distance obtained by the lift-off compensation unit 140 is provided to the material determination unit 120 using a compensation coefficient to compensate for the measurement signal obtained from the sensor unit 110. For example, if the distance between the steel sheet S and the eddy current inspection device 100 increases, the signal measured by the sensor unit 110 is amplified.

[0063] FIG. 22 shows a flow chart of the inspection method of the present invention.

[0064] As shown in FIG. 22, the inspection method according to the present invention includes a demagnetization step (S100) for removing residual magnetization of a rolled material; a magnetic field forming step (S110) for forming an AC magnetic field only in the rolling direction of the rolled steel sheet using a coil; a signal measuring step (S120) for measuring a signal using a sensor connected to the coil; and a material determining step (S130) for determining the material of the steel sheet at a measurement location based on the signal obtained in the signal measuring step.

[0065] In the demagnetization step (S100), residual magnetization is removed through a demagnetization unit, and the steel sheet S is returned to the origin of the BH curve.

[0066] The magnetic field forming step (S110) is formed by supplying a current having a frequency of 0.5 to 10 kHz to a coil via an AC power source. It is preferable that the coil is wound around the rolling direction so that a magnetic field is formed only in the rolling direction of the steel sheet.

[0067] In the signal measuring step (S120), an impedance signal changed by the eddy current is measured via a sensor connected to the coil.

[0068] In the material determination step (S130), the material of the measurement part is determined based on the relationship between the measurement signal measured in the signal measurement step (S130) and the material. At this time, the material may be the surface phase or hardness of the steel sheet.

[0069] Meanwhile, the inspection method according to the present invention can also determine the material by taking into consideration the distance between the steel sheet and the sensor. inspection The method further includes a lift-off compensation value measuring step of measuring a lift-off compensation value through a lift-off compensation unit connected to the coil, and the material determining step may determine the material of the steel sheet from a signal obtained by converting the measurement signal of the sensor using the compensation value of the lift-off compensation unit as a compensation coefficient.

[0070] At this time, in the step of measuring the lift-off compensation value, the lift-off compensator may measure a Q factor when a resonance frequency of a current frequency provided by the AC power supply is provided as a compensation value.

[0071] Although the present invention has been described above with reference to the preferred embodiment, the present invention is not limited to the preferred embodiment and can be modified in various ways. [Explanation of symbols]

[0072] S steel plate F frame 100 eddy current tester 101 coil unit 102 AC power supply section 103 Yoke section 110 Sensor section 120 Material determination section 130 display unit 140 lift-off compensation unit

Claims

1. An accelerated cooling defect inspection device that generates eddy currents in a steel plate to determine defects caused by accelerated cooling of the steel plate, an eddy current inspection device disposed facing the steel plate; and a frame to which the eddy current inspection device is fixed; The eddy current inspection device includes: A "U", "C", "U" or "V" shaped yoke with both ends facing the steel material; a coil portion wound around the center of the yoke portion so as to generate an AC magnetic field in only one direction; an AC power supply unit coupled to the coil unit; a sensor coupled to the coil portion; a material determination unit connected to the sensor and determining the hardness of the steel sheet based on a measurement signal obtained through the sensor; and a lift-off compensation unit connected to the coil unit to measure a lift-off compensation value and provide the lift-off compensation value to the material determination unit; the AC power supply unit supplies a current of 0.5 kHz to 10 kHz to the coil unit, and the sensor measures an impedance signal of the coil; the material determination unit determines the hardness of the defect in consideration of the distance between the steel plate and the sensor; The lift-off compensation unit measures a Q factor when a resonance frequency of the current frequency provided by the AC power supply unit is provided, and provides the Q factor to the material determination unit. The material determination unit determines the hardness of the defect based on a signal obtained by converting a measurement signal of the sensor using the measurement value of the lift-off compensation unit as a compensation coefficient.

2. The steel plate is a rolled steel plate, 2. The defect inspection device using accelerated cooling according to claim 1, wherein the one direction is the rolling direction of the steel plate.

3. 2. The apparatus for inspecting defects by accelerated cooling according to claim 1, wherein both ends of the yoke portion are arranged perpendicular to the rolling direction of the steel plate.

4. 4. The defect inspection device using accelerated cooling according to claim 1, further comprising a demagnetization unit disposed in front of the eddy current inspection device to demagnetize the steel plate being moved to the eddy current inspection device.

5. 4. The defect inspection device using accelerated cooling according to claim 1, wherein a plurality of coil portions are arranged in a row along the width direction of the steel plate so as to continuously inspect the defects in the steel plate.

6. A defect inspection method for accelerated cooling that generates eddy currents to determine defects caused by accelerated cooling of a rolled steel plate, comprising: a magnetic field generation step of generating an AC magnetic field in only one direction through a coil; a signal measuring step of measuring a signal via a sensor coupled to the coil; a material determination step of determining the hardness of the defect in the steel plate at the measurement location based on the signal obtained in the signal measurement step; and a lift-off compensation value measuring step of measuring a lift-off compensation value through a lift-off compensation unit connected to the coil; The coil is wound around the center of a "U", "C", "U" or "V" shaped yoke, both ends of which are positioned toward the steel material, The AC magnetic field is generated by a current having a frequency of 0.5 to 10 kHz, and the sensor measures an impedance signal of a coil. the magnetic field forming step forms an AC magnetic field in only one direction at both ends of the yoke part via the coil and the yoke part; The material determining step determines the material of the steel sheet based on a signal obtained by converting the measurement signal of the sensor using the compensation value of the lift-off compensator as a compensation coefficient, and determines the material based on the distance between the steel sheet and the sensor; In the step of measuring the lift-off compensation value, the lift-off compensator measures a Q factor when a resonance frequency of a current frequency provided by an AC power supply is provided.

7. 7. The method for inspecting defects by accelerated cooling according to claim 6, wherein the one direction is the rolling direction of the rolled steel plate.

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