JP4586556B2 - Surface layer property measurement method, surface layer defect determination method using the same, and metal strip manufacturing method - Google Patents

Description

  The present invention relates to a surface layer property measuring method for detecting an abnormal part including defects such as non-metallic inclusions existing on the surface layer of a metal specimen, a surface layer defect determining method using the same, and a method for producing a metal strip. is there.

  Due to the sophistication of the quality level required for metal products in recent years, there is an increasing demand for metal strips, particularly steel strips, which have few harmful defects such as surface defects. Examples of such steel strips include cold-rolled steel plates and plated steel plates for automobiles and cans. In cold-rolled steel sheets used for automobiles, surface defects may occur due to non-metallic inclusions mixed in the steel at the steel making stage, etc., and even if this surface defect is painted, it can be confirmed with the naked eye Some of them are serious problems in appearance.

  For example, the plated steel sheet for automobiles is manufactured through a steelmaking process, a hot rolling process, a pickling process, a cold rolling process, a plating process, and the like, and further becomes a member for an automobile through a pressing process and a painting process. As one of the serious defects in plated steel sheets for automobiles obtained through these manufacturing processes, there are surface defects generally called hege, sliver, and scratches. In automobiles that are final products, these surface defects are other healthy parts. And apparently differ from each other, which causes the problem of deteriorating the appearance. Furthermore, if the degree of surface defects becomes extremely severe, the press machine may be damaged during press molding.

  The above-mentioned surface defects including heges and the like are generated in the non-magnetic metal inclusions generated in the steel making process, or enter the steel material of the oxide on the entering side of the steel making process and the hot rolling process (before hot rolling). It is said that the origin is on the upper process side in the whole manufacturing process, such as when there is a cause of contamination. And this surface defect becomes obvious by passing through hot rolling, cold rolling, a plating process, and a process.

  In contrast to the above, in order to reduce surface defects and produce high-quality products, it is necessary to detect the surface defects at the earliest possible stage of the entire process, and to take the optimum measures according to the results. It is.

As such a technique, Patent Document 1 discloses a defect detection step for detecting a defect candidate by performing AC excitation and detecting a change in AC magnetic flux, a removal target determination step for determining a defect candidate as a removal target, and defect removal. A method of manufacturing a cold-rolled or plated steel strip for manufacturing and a method of manufacturing a plated steel strip are described. Specifically, in the defect detection step, a reference signal synchronized with the signal from the magnetization power supply is prepared, and the detection signal is synchronously detected with this reference signal, thereby obtaining the output of the defect signal, and in the removal target determination step If the output of the defect signal is greater than or equal to the threshold value, it is determined as a defect.
JP 2003-236613 A

  However, the method described in Patent Document 1 determines that the detected signal strength is equal to or higher than a threshold value as a defect. This is based on the knowledge that the intensity of the detection signal correlates with the volume (size) of the abnormal part, and the part where the abnormal part exceeds the predetermined volume, that is, the part where the abnormal part exceeds the predetermined volume It is determined that the defect is a harmful defect at the time of inspection, or is determined to be manifest as a harmful defect from the process after the inspection through the final process until it becomes a product. However, in practice, for example, shallow defects close to the surface become harmless parts in the rolling process such as cold rolling after the inspection, and on the contrary, abnormal parts that are too deep, even if cold rolled, are the final In some cases, it does not become harmful because it does not manifest to the surface until the process. As described above, in consideration of processing in the processes after the inspection, not only the volume of the abnormal part but also the influence of the depth of the abnormal part is affected. Therefore, the signal intensity corresponding to the volume of the abnormal part disclosed in Patent Document 1 The defects determined based on the above and the defects that become harmful in the post-inspection process did not exactly match. And since the judgment index of whether the abnormal part detected in this way becomes a harmful defect in the subsequent process is incomplete, the part that becomes a harmful defect in the process after the inspection is overlooked, and its early response However, there is a problem in that the yield is reduced when a defect that requires a defect is not dealt with, or when a defect that does not need to be dealt with as an overdetection is dealt with.

  The present invention has been made in view of such circumstances, and by accurately detecting and discriminating defects that are harmful after the processes after inspection (for example, after cold rolling and plating processes), the defects to be dealt with. A surface layer property measuring method, a surface layer defect determining method using the same, and a metal strip manufacturing method capable of accurately responding to the above and preventing a decrease in yield and producing a high quality product The purpose is to provide.

  In order to solve the above-mentioned problems, the present inventors measure the depth position of the abnormal part existing in the surface layer part, and based on the information, accurately determine whether the abnormal part is harmful in the process after the measurement. In order to determine, the following knowledge was obtained.

  Each position on the surface of the metal object is AC magnetized, the AC magnetic flux from each position of the metal object is measured, and a region showing a signal different from the normal part is extracted from the AC magnetic flux as an abnormal part. At this time, in addition to the signal intensity, phase information of a signal having depth information where an abnormal portion exists is also measured, and defect determination may be performed using the signal intensity and the phase information. However, the region showing a signal different from the normal part is detected almost corresponding to the size of the abnormal part having a different property from the normal part (for example, the region when viewed from the surface). The signal state is not uniform, and the signal changes at a location within the region. Therefore, when determining whether or not the defect is a harmful defect in the process after the measurement, the determination result may be different if the location of the signal serving as the representative value used for the determination is different even in the same region.

  Therefore, in predicting and judging whether the abnormal part becomes a harmful defect in the process after the measurement, the size and depth of the abnormal part are determined from the signal intensity and the distribution of the phase information in the region indicating the abnormal signal. It is important to predict the position distribution and determine whether it becomes a harmful defect. In particular, it is necessary to select an index (representative value) representing the phase distribution in the abnormal region.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

[1] AC normal magnetization of a metal object, and based on signal intensity and phase obtained by detecting an alternating magnetic flux change from the object at a plurality of positions of the object, In the surface layer property measurement method for detecting different abnormal parts ,
A method for measuring a surface layer property, comprising: detecting the abnormal portion using a value obtained by performing weighted averaging of the phases obtained at the plurality of positions with the signal intensity obtained at the same position as the phase .

[2] [1] of the abnormality of the detected metal object with a surface layer portion texture measuring method according to, surface defects and judging the portion to be detrimental in the subsequent measurement of the superficial layer properties Judgment method.

[ 3 ] A surface layer property measuring step for measuring the property of the surface layer of the metal strip,
Of the abnormal portion of the metal strip detected in the surface layer property measurement step, including a surface layer defect determination step for determining a harmful part in the step after the surface layer property measurement step,
In the surface layer property measuring step, the surface layer property measuring method described in [1] is used.

  In addition, the surface layer defect in this invention exists in a metal belt | band | zone, and in the post process, for example, it becomes manifest as an equivalent defect cracked at the time of a press, and includes a surface defect.

  According to the present invention, it is possible to accurately discriminate a site that becomes a harmful defect in each process (cold rolling and plating process) after the measurement and its processing at an early process stage. And by discovering the part that causes the defect at an early stage, it becomes possible to resolve the cause of the defect early, remove the defective part at an early stage, and the like, which greatly contributes to the improvement of the product yield. It is also possible to produce a high-quality metal strip with few defects.

  The present invention will be described in detail below as an example applied to surface layer property measurement and its defect determination in a steel sheet manufacturing process. FIG. 1 is a schematic diagram showing the configuration of the surface layer property measuring apparatus according to the first embodiment of the present invention. In FIG. 1, the steel plate 1 has an abnormal portion 2 that is minute in the width direction and long in the length direction (direction perpendicular to the paper surface). The magnetizer 4 and the magnetic sensor 9 are arranged to face each other with the steel plate 1 interposed therebetween. Then, an alternating current is supplied to the coil of the magnetizer 4 by the magnetization power source 3 so that the vicinity of the surface of the steel plate 1 is intensively magnetized. In FIG. 1, magnetization is performed such that the magnetic flux is formed in the width direction of the steel sheet 1, but the abnormal portion that can be a defect extends long in the length direction (rolling direction), and the abnormal portion having such a shape In order to facilitate detection, it is preferable to perform such magnetization as much as possible.

  The magnetic flux generated between the two magnetic poles by the magnetizer 4 passes near the surface of the steel plate 1. In this case, since the abnormal portion 2 exists in the steel plate 1, the magnetic flux is blocked by the abnormal portion 2, and a large amount of magnetic flux leaks to the outside of the steel plate 1, and the change is detected by the magnetic sensor 9.

  When the output is guided to the synchronous detector 7a and the waveform of the magnetizing power source 3 is synchronously detected with a signal whose phase is shifted to an appropriate value by the phase shifter 5 as a reference signal, a signal corresponding to the size of the abnormal portion 2 is obtained. can get. This output is guided to the signal level discriminator 8 and compared with a predetermined threshold value, so that the level of the abnormal portion 2 is discriminated.

  Next, the result obtained by the signal level discriminator 8 is guided to the phase distribution calculator 10. On the other hand, as signal processing of another system, synchronous detection is performed by the synchronous detector 7b and a signal that is 90 degrees phase shifted by the 90-degree phase shifter 12 with respect to the signal based on the above-described synchronous detection. In the phase distribution calculator 10, the phase is calculated based on the output signal of the signal level discriminator 8 and the output of the synchronous detector 7b.

  The result obtained by the phase distribution calculator 10 is sent to the defect manifestation determination device 11, and here, by combining the phase distribution of the signal and the defect signal intensity level, the process after the measurement or finally manifests It is determined whether or not it becomes a defect.

  Although FIG. 1 shows an example in which one magnetic sensor is installed, a plurality of sensors are provided in the width direction, and a result obtained by processing by a phase detector and a signal level discriminator provided for each sensor is a phase distribution calculator. It is also possible to send to 10. In this way, phase distribution information in the width direction of the steel sheet 1 can be obtained by arranging the phases calculated for each sensor. In addition, since the steel plate moves in the direction perpendicular to the paper surface, the phase distribution in the length direction of the steel plate 1 can be obtained by arranging the phases with respect to time by the phase distribution calculator 10.

  In the present invention, the width direction of a magnetic metal specimen (for example, a steel plate) means a direction perpendicular to the rolling direction of the magnetic metal specimen unless otherwise specified.

  FIG. 2 is a schematic diagram showing the configuration of the surface layer property measuring apparatus according to the second embodiment of the present invention. In FIG. 2, the same components as those shown in FIG. 1 described above may be denoted by the same reference numerals and the description thereof may be omitted. The steel plate 1 has an abnormal portion 2 that is minute in the width direction and long in the length direction (direction perpendicular to the paper surface). As the surface layer property measuring device, a magnet (hereinafter referred to as an E-shaped coil) 13 using an E-shaped core as a magnetizer and a magnetic sensor is used. The yoke of the E-shaped coil 13 has three leg portions 13a, 13b, 13c, facing the steel plate 1 so that each is substantially perpendicular to the surface of the steel plate 1 and aligned in the width direction of the steel plate 1. Is provided.

  The coil wound around the central leg 13a is supplied with an alternating current from the magnetizing power source 3 and magnetized. A coil is also wound around the leg portions 13b and 13c on both sides, and used as a magnetic sensor. The magnetic flux generated by the coil of the leg portion 13a passes through the vicinity of the surface of the steel plate 1, returns to the leg portion 13a through the leg portions 13b and 13c on both sides.

  At that time, if the abnormal part 2 is present at the position as shown in FIG. The magnetic flux density of the magnetic flux passing through 13b is smaller than the magnetic flux density of the magnetic flux passing through the leg portion 13c. Therefore, the voltage induced in the coil wound around the leg portion 13b is smaller than the voltage induced in the coil wound around the leg portion 13c, and if both are input to the differential amplifier 6, the difference between the two is handled. Is output.

  When the output is guided to the synchronous detector 7a and the waveform of the magnetizing power source 3 is synchronously detected by using the signal whose phase is shifted to an appropriate value by the phase shifter 5 as a reference signal, a signal corresponding to the size of the abnormal portion 2 is obtained. can get. This output is guided to the signal level discriminator 8 and compared with a predetermined threshold value, so that the level of the abnormal portion 2 is discriminated.

  Next, the result obtained by the signal level discriminator 8 is guided to the phase distribution calculator 10. On the other hand, as signal processing of another system, synchronous detection is performed by the synchronous detector 7b and a signal that is 90 degrees phase shifted by the 90-degree phase shifter 12 with respect to the signal based on the above-described synchronous detection. In the phase distribution calculator 10, the phase is calculated based on the output signal of the signal level discriminator 8 and the output of the synchronous detector 7b.

  The result obtained by the phase distribution calculator 10 is sent to the defect manifestation determination device 11, where it is determined whether or not the surface defect is finally manifested by combining the signal phase distribution and the defect signal intensity level. Do.

  In FIG. 2, one E-type coil is installed as a magnetic sensor. In order to obtain a two-dimensional distribution of the signal phase in the length direction and width direction of the steel plate, the width direction and length of the steel plate 1 described above are used. The sensor may be traversed in the direction, a plurality of sensors may be arranged in the width direction of the steel plate 1, and the sensor may be traversed in the length direction of the steel plate 1, or a plurality of sensors may be arranged in the length direction of the steel plate 1. The traverse may be performed in the width direction of the steel plate 1, or a plurality of sensors may be arranged in the width direction and the length direction of the steel plate 1 to obtain a two-dimensional distribution of signals in the length direction and the width direction of the steel plate. In either case, the steel plate may be moved instead of traversing the sensor.

  In addition, when using a plurality of sensors as described above, each sensor has a differential amplifier, a phase detector, and a signal level discriminator, and the output results of the signal level discriminators for each sensor are collected into a phase distribution calculator. A method of calculating the distribution of the feed phase can be considered, but the output of multiple sensors may be combined between any of the differential amplifier, phase detector, and signal level discriminator by electrical or mechanical switching. .

  In this embodiment, an E-type sensor is used, but other magnetic detection methods such as a combination of a U-shaped coil and a detection sensor using a Hall element may be used.

  As described above, in the present invention, the generated magnetic flux passes through the vicinity of the surface of the steel sheet, so that not only the surface defects at that time are measured, but also the surface layer properties that are not manifested as surface defects ( Hereinafter, the potential defect portion) is also measured. That is, in the present invention, not only the surface of the steel strip but also the abnormal portion of the surface layer portion is the object of measurement.

  Therefore, in the present invention, it is possible to predict the possibility that an abnormal portion (potential defect) that has not been manifested as a surface defect or a surface layer defect at the time of measurement will be manifested in a subsequent process, that is, finally. it can. In this case, the accuracy of prediction can be improved by accumulating past data.

  In addition, in the present invention, the defect finally manifested is expected to be manifested (detrimental) in the manufacturing process up to the shipment in the process after the measurement among the parts that showed signals different from the normal part at the time of measurement. In addition to the surface layer properties, the surface layer properties that are expected to be manifested (detrimental) during processing steps in final consumption, that is, press working in the consumer after shipment, are included.

  FIG. 3 is a diagram showing the relationship between the signal intensity and signal phase of the abnormal portion of the pickled steel sheet detected by the surface layer property measuring apparatus shown in FIG. 2, and the rolling direction at the time of manufacturing the steel sheet. In this experiment, the experimental conditions were an excitation frequency of 750 kHz and a lift-off of 1 mm. On the other hand, cold rolling is performed on a plurality of pickled steel sheets including abnormal parts with a length shorter than 5 mm in the rolling direction to form cold-rolled steel sheets, and the actual cold-rolled steel sheets are actually measured using a surface defect meter. The surface defects were investigated and the data was collected. As a result, data was obtained that the phase range of the abnormal portion measured by the surface layer property measuring device corresponding to the defects that finally became apparent after cold rolling was 40 to 80 degrees.

  Based on the above, from FIG. 3 (FIG. 3 is a diagram showing a one-dimensional distribution in the length direction), the phase at the point where the signal intensity has been maximum conventionally used is used as a representative value of the phase of the abnormal portion. In this case, the typical value of the phase is 33 degrees. The phase range of 40 degrees to 80 degrees of the defect that is finally manifested is outside the range of 40 degrees to 80 degrees.

  On the other hand, the entire abnormal portion detected in FIG. 3 is almost included in the phase range of 40 degrees to 80 degrees, which is supposed to be finally manifested as a defect, and the signal intensity of the portion is also increased. You can see that When this steel plate was cold-rolled, this abnormal portion became apparent as a surface defect. For example, when taking a weighted average based on the signal intensity based on Equation 1 described below and taking a weighted average, it becomes 61 degrees, and in the pickling stage of defects that became apparent after cold rolling in the above experiment. It falls within the range of the abnormal part phase (40 degrees to 80 degrees) shorter than 5 mm. As described above, when the length of the abnormal portion is as long as 5 mm or more, it is preferable to set a numerical value representative of the phase of the entire abnormal portion by weighted averaging, and an appropriate result can be obtained. In addition, even if the abnormal part is as short as 5 mm or less, the abnormal part is short, so even if the weighted average is taken, the phase of the peak is almost the same, but the method of taking the weighted average is also effective, so distinguish by length The weighted average processing may be performed on all abnormal parts. Here, the weighted average W is expressed by Equation 1 when the signal intensity is Ai and the phase is θi. The subscript i is a signal detection position (in the example of FIG. 3, it is a one-dimensional coordinate in the length direction, but it is a coordinate in a two-dimensional position when measured in the length direction and width direction).

  In addition, an arbitrary region is determined from design matters or empirical matters with reference to the position where the signal intensity is maximum in the abnormal portion region, and an average of phases at points included in the region is taken. Also good. Moreover, although Formula 1 is a formula when the position is measured by discrete sampling, a result similar to the above can be obtained even in the case of a continuous measurement result. The weighted average W in this case is expressed by Equation 2 when the signal intensity is A (x) and the phase is θ (x). Note that x represents the position of the abnormal part signal. (In the example of FIG. 3, it is a one-dimensional coordinate in the length direction, but when measured in the length direction and the width direction, it is a coordinate of a two-dimensional position.)

  Furthermore, for example, a numerical value representing the phase of the entire abnormal part based on the signal strength, such as using the square of the signal strength, or setting the weight to 1 only when the signal strength is greater than or equal to a certain threshold, and 0 otherwise. It is also possible to determine.

  Furthermore, based on the signal strength, the weight is set to 1 at points up to 3 points in the order of strong signal strength, and the weight at other points is set to 0. That is, the average of the phases up to 3 points in the order of strong signal strength. A value can also be obtained. In this case, when applied to the abnormal part of FIG. 3, it is 58 degrees, and it can be seen that the numerical value representing the phase of the whole abnormal part is an appropriate numerical value.

  As described above, in the present invention, the surface layer abnormal portion of the metal specimen is obtained based on the phase and the signal intensity obtained by AC magnetizing the metal specimen and detecting the change of the AC magnetic flux generated due to the defect. Further, by combining these phase distribution and defect signal intensity level, it is determined whether or not the detected abnormal part is a defect that finally becomes apparent.

That is, in the present invention, first, an output whose output Y with respect to the first reference signal exceeds a threshold value is temporarily determined as an abnormal part. Next, prepare a second reference signal that is shifted 90 degrees from the first reference signal in advance, perform synchronous detection, output Y for the first reference signal and the second reference for the abnormal part Using the output X for the signal, the phase θ is determined as θ = tan ⁻¹ (Y / X). Defect manifestation is determined by a combination of the phase θ and the reference signal output Y.

  As described above, the above-described surface layer property measuring method and surface layer defect determining method can be used when manufacturing a steel sheet.

  Specifically, for example, after hot rolling, the surface layer property measuring device of FIG. 2 is installed in the pickling line before cold rolling, and surface layer property measurement is performed on the hot-rolled steel sheet. It is discriminated whether or not the detected abnormal part becomes apparent as a defect after the cold rolling process or the zinc plating process. Next, the abnormal part finally determined to be manifested is removed, for example, in the pickling stage, and the steel sheet from which the abnormal part has been removed is subjected to cold rolling or further plating, and is subjected to cold rolling steel sheet or plating. It becomes a steel plate. This cold-rolled steel sheet or plated steel sheet is a high-quality steel sheet with very few surface defects as a result of the removal of defective portions. As described above, the method of the present invention measures the properties of the surface layer portion, predicts and determines the defects that will be manifested in the subsequent steps, and determines the harmful portions, so that defects that are not manifested on the surface at the time of property measurement are determined. Can also be detected. And by discovering the cause of the defect at an early stage, it becomes possible to resolve the cause of the defect early and to remove the defective part at an early stage, and it is possible to manufacture a cold-rolled or plated steel sheet with a high yield.

  In the above, the surface layer property measuring device was installed in the pickling line, and after the hot rolling and before the cold rolling, the surface layer portion was measured to make the prediction of the defect manifestation. The timing for performing the prediction determination is not particularly limited. However, 1) It is necessary to uniform the shape and properties of the partially removed steel strip by rolling so as not to cause defects on the contrary. It is better to do it before hot rolling. On the other hand, 2) Ease of detection (it is easier to detect when the plate shape is good and the plate thickness is reduced and the abnormal part is as close as possible to the surface), and the accuracy of detection (the abnormal part due to rolling) In the process of deformation, detection is performed at a stage as close to the final product as possible so that the severity can be evaluated more accurately. For the above reasons, it is preferable to carry out after hot rolling and before cold rolling.

  In the present invention, the magnetic metal object is magnetized by the alternating magnetic flux. Therefore, the penetration depth of the magnetic flux is limited by the influence of the skin effect as compared with the case where DC magnetization is used, and it concentrates near the surface layer portion of the magnetic metal object. Therefore, it is possible to efficiently detect only the defects existing on the surface or the surface layer portion.

Moreover, although the steel plate production line was taken up in the description of the embodiment, it goes without saying that the present invention can also be applied to a metal strip production line having the same process as the steel plate using a metal strip such as an aluminum plate or a copper plate.

  The surface layer part property measuring apparatus of FIG. 2 was installed in the pickling line, and the property of the surface layer part was measured with respect to the pickled steel sheet by the method described above. Subsequently, the steel sheet is cold-rolled and galvanized, the obtained plated steel sheet is examined for defects, and whether or not the abnormal part detected in the pickling process is finally manifested as a harmful defect is determined. Examined. The obtained results are shown in FIG. FIG. 4 is a diagram showing the relationship between the three-point average phase and the signal intensity. In FIG. 4, the three-point average phase is the average value of the phases up to three points in descending order of signal intensity.

  From FIG. 4, the presence or absence of manifestation is divided at a certain boundary line, and this boundary line can be expressed by an equation from the signal intensity and the phase, and by using the obtained equation, the final manifestation of the defect It can be seen that the presence or absence of conversion is distributed with high accuracy. That is, it can be seen that whether or not it finally becomes apparent cannot be determined only by the signal intensity, but it becomes possible to predict and determine the defect manifestation only by combining the signal intensity and the phase. This corresponds to the fact that a small phase is present at a shallow position in the pickling stage, and a large phase is present at a deep position, but the shallow and small volume abnormal part is rendered harmless in the rolling process and is deep and volume. It is considered that the abnormal part having a small diameter is too deep and does not become apparent until the final process, and does not become harmful. In addition, even if it is shallow, if there is an abnormal part with a large volume with a large signal intensity, an abnormal part with a large volume even if it is deep and a large volume with a large signal intensity, even if the signal intensity is small and the volume is small, the depth is around 60 degrees. They are thought to manifest as surface defects.

  The method for detecting surface layer defects and the method for determining surface layer defects using the present invention are useful for metal products that have few harmful defects such as surface defects and require an excellent quality level.

It is a schematic diagram which shows the structure of the surface layer property measuring apparatus which is 1st embodiment of this invention. It is a schematic diagram which shows the structure of the surface layer property measuring apparatus which is 2nd embodiment of this invention. It is a figure which shows the relationship between the signal strength of the abnormal part of a pickled steel plate, the phase of a signal, and the rolling direction at the time of steel plate manufacture. It is a figure which shows the relationship between a 3 point average phase and signal strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Abnormal part 3 Magnetization power supply 4 Magnetizer 5 Phase shifter 6 Differential amplifier 7a, 7b Synchronous detector 8 Signal level discriminator 9 Magnetic sensor 10 Phase distribution calculator 11 Defect manifestation determination apparatus 12 90 degree phase shifter 13 E type coil

Claims (3)

Abnormality different from the normal part of the metal object based on the signal intensity and phase obtained by AC magnetizing the metal object and detecting the AC magnetic flux change from the object at a plurality of positions of the object In the surface layer property measuring method for detecting the part ,
A method for measuring a surface layer property, comprising: detecting the abnormal portion using a value obtained by performing weighted averaging of the phases obtained at the plurality of positions with the signal intensity obtained at the same position as the phase . Among the abnormal portion of the metal object detected by the surface layer portion texture measuring method according to claim 1, the surface layer defect determination method characterized by determining the portion to be detrimental in the subsequent measurement of the superficial layer properties. A surface layer property measuring step for measuring the property of the surface part of the metal strip,
Of the abnormal portion of the metal strip detected in the surface layer property measurement step, including a surface layer defect determination step for determining a harmful part in the step after the surface layer property measurement step,
In the said surface layer property measuring process, the surface layer part property measuring method of Claim 1 is used, The manufacturing method of the metal strip characterized by the above-mentioned .