JP4289074B2 - Steel strip manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a steel strip having excellent surface layer properties with few defects that are manifested in any process from the production process to the final consumption process.

  Due to the sophistication of the quality level required for metal products in recent years, there is an increasing demand for steel strips with few harmful defects such as surface defects. For example, there are cold rolled steel sheets and plated steel sheets for automobiles and cans. As a specific example, in cold-rolled steel sheets used for automobiles, surface defects may occur due to non-metallic inclusions or the like mixed in the steel at the steel making stage or the like. Some of them can be confirmed with the naked eye even after painting, which can be a big problem in appearance.

  Another example is a plated steel sheet for automobiles. 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. One of the serious defects in plated steel sheets for automobiles is a surface defect commonly called hege, sliver, or scratches, and in the final product automobile, the defective part looks distinctly different from other healthy parts, and it impairs the appearance. If it causes problems or becomes extremely severe, it will cause damage such as damage to the press machine during press molding.

  These surface defects (such as scabs) are caused by non-magnetic metal inclusions generated in the steel making process, or the oxides enter the steel material on the steel making process and hot rolling process entry side (before hot rolling). It is said that the origin is on the upper process side in the entire manufacturing process, such as when there is a cause of contamination. And it becomes obvious as the above-mentioned surface defect through hot rolling, cold rolling, and plating treatment.

  In order to reduce defects as in the above example and manufacture high-quality products, the defective parts are detected as early as possible in the entire process, and appropriate measures are taken according to the results. A production method that can be used is necessary.

Therefore, as a technique corresponding to the above-described example (cold rolled steel sheet for automobiles), as an example of detecting a surface defect that has already become apparent, for example, it is disclosed in Japanese Patent Application Laid-Open No. 61-219403. There is something like that. It detects the position and size of surface flaws of the steel strip after pickling treatment in a continuous pickling line outlet side of the hot rolled strip, in a continuous cold rolling line, hands steel strip in the rolling mill entry side scratches The removal is performed. In the embodiment, a surface defect detection device is provided as a detection unit on the exit side of the pickling line, and a brush / roll containing abrasive grains is provided as a defect removal unit on the entry side of the continuous cold rolling line.

Similarly, as a technique applicable to the former example (cold rolled steel sheet), Patent Document 2 Japanese Patent Application Laid-Open No. 2001-191206 discloses that surface scratches such as bald scratches generated on a steel sheet are removed by cutting, A method for erasing the processing marks by rolling has been proposed.
Japanese Patent Laid-Open No. 61-219403 JP 2001-191206 A

The following problems exist in the prior art.
In the prior art described in Patent Documents 1 and 2 described above, only surface defects that have already become apparent at the inspection stage and are clearly a quality problem (hazardous defect) are targeted.

  On the other hand, for example, according to our detailed investigation on surface defects (such as the above-mentioned heges) in the latter example (plated steel sheet for automobiles), some of these surface defects include the hot-rolled sheet or pickling sheet stage. Then, the abnormal part is not manifested, that is, it does not appear on the surface, or only a part is exposed, so that there is a harmless part at that stage. These become obvious after cold rolling, plating, or pressing after surface layer scale removal by pickling.

  A surface defect that becomes apparent after plating can be detected by a surface defect inspection apparatus after plating. However, even if the presence or absence of a defect is found at that stage, it is difficult to remove the defect part and make it harmless as in the prior art because it is close to the final process in terms of steel strip production. Further, other means that can be taken are limited depending on the inspection result. In addition, since the time for the inspection process has elapsed since the process in the upper process such as the steelmaking process that caused the surface defect, there is a restriction in terms of feedback to the manufacturing conditions of the upper process.

  For the reasons described above, it is necessary to determine whether or not the surface defects become after the plating before the surface defects become apparent after the plating process, but this is not possible with the prior art.

The present invention was made in view of such circumstances, and in each process (hot pickling, cold rolling, heat treatment, plating, surface treatment such as enamel, press molding, coating, etc.) leading to final consumption after hot rolling, It is possible to take appropriate manufacturing measures even for abnormal parts that have not been revealed, and there are few defects in each process leading to final consumption, or excellent surface layer properties that do not hinder manufacturing even if there are defects It aims at providing the manufacturing method of a steel strip.

The invention according to claim 1 of the present invention is a steel strip manufacturing method for manufacturing a steel strip and further a surface-treated steel strip by at least hot rolling the steel, and after hot rolling, the following (1) to (3 ) And the following steps (4) and (5) before the steel strip shipping process.
(1) Surface layer property measurement process for measuring the properties of the surface layer of the steel strip
(2) Using the results of the surface layer measurement, a defect revealing prediction process for predicting whether or not the measurement part will appear as a surface defect in the subsequent manufacturing process or processing
(3) Manufacturing process and condition determination process for determining the manufacturing process and manufacturing conditions according to the obtained prediction results
(4) Surface texture measurement process that measures only the surface texture of steel strips
(5) Display target determining step for determining a display target part from parts predicted to be manifested as defects

  The invention according to claim 2 of the present invention is a steel strip manufacturing method for manufacturing a steel strip and further a surface-treated steel strip by at least hot rolling the steel, and after hot rolling, the following (1) to (3 ) (1) Surface layer property measuring step for measuring the surface layer property of the steel strip, (2) Using the results of this surface layer measurement, in the subsequent manufacturing process or processing Defect revealing prediction step for predicting whether or not the measurement part is manifested as a surface defect, (3) Manufacturing process / condition determining step for determining a manufacturing process and manufacturing conditions according to the obtained prediction result, The prediction process includes information on steel strip production conditions, targets, actual results, production conditions scheduled for subsequent processes, product specifications, applications, and inspection specifications. Steel strip characterized by using one or more of them It is a manufacturing method.

  The invention according to claim 3 of the present invention is a steel strip manufacturing method for manufacturing a steel strip and further a surface-treated steel strip by at least hot rolling the steel, and after hot rolling, the following (1) to (3 ) (1) Surface layer property measuring step for measuring the surface layer property of the steel strip, (2) Using the results of this surface layer measurement, in the subsequent manufacturing process or processing Defect revealing prediction process for predicting whether or not the measurement part is manifested as a surface defect, (3) Manufacturing process / condition determining process for determining the manufacturing process and manufacturing conditions according to the obtained prediction result, the manufacturing process The condition determining step is a method for manufacturing a steel strip characterized in that one or more of product specifications, applications, and destinations are determined or changed based on the prediction result of the defect manifestation prediction step.

  The invention according to claim 4 of the present invention is the method of manufacturing a steel strip according to claim 1, wherein the defect revealing prediction step is a manufacturing condition and a target of the steel strip until prediction is performed as information for prediction. The steel strip manufacturing method is characterized by using one or more kinds of information on the actual conditions, manufacturing conditions scheduled in the subsequent processes, product specifications, uses, and inspection specifications.

  The invention according to claim 5 of the present invention is the method of manufacturing a steel strip according to any one of claims 1, 2, and 4, wherein the manufacturing process / condition determining process is a defect revealing prediction. One or more of product specifications, applications, and destinations are determined or changed based on the process prediction results.

The invention according to claim 6 of the present invention is the method for producing a steel strip according to any one of claims 1 to 5, wherein after the hot rolling and before the cold rolling, the following (6) And a method for producing a steel strip, comprising the steps described in (7), followed by cold rolling.
(6) Removal target surface layer determination step for determining a surface layer portion to be removed from the portions predicted to be manifested as defects
(7) Partial removal step of removing the region including the surface layer portion to be removed by the partial removal means

  The invention according to claim 7 of the present invention is the method of manufacturing a steel strip according to any one of claims 1 to 6, wherein the defect manifestation prediction step relates to a distribution in a depth direction of the surface layer portion. The steel strip manufacturing method is characterized in that the prediction is performed using information.

  The invention according to claim 8 of the present invention is the method of manufacturing a steel strip according to any one of claims 1 to 7, wherein the surface layer portion property measuring step includes alternating current magnetization of the surface portion of the steel strip measurement surface. At the same time, the method of manufacturing a steel strip is characterized in that the property of the surface layer portion of the steel strip is measured by measuring the change in the alternating magnetic flux generated due to the property of the surface layer portion.

  The invention according to claim 9 of the present invention is the method of manufacturing a steel strip according to any one of claims 1 to 8, wherein the surface layer property measuring step includes AC magnetizing the steel strip, The change of the alternating magnetic flux generated due to the properties of the steel strip is detected by two or more magnetic sensors provided with the magnetic flux arranged in the width direction of the steel strip, and the surface layer of the steel strip based on the difference signal in the width direction of the detection signal It is the manufacturing method of the steel strip characterized by measuring the property of a part.

  The invention according to claim 10 of the present invention is the method of manufacturing a steel strip according to any one of claims 1 to 9, wherein the surface layer property measuring step is performed by using an E-shaped ferromagnetic material. The leg portions of the books are arranged facing the steel strip surface and arranged in the width direction of the steel strip, and an alternating current is applied to the primary coil wound around the central leg portion to excite the steel strip. The steel strip manufacturing method is characterized in that the property of the surface layer portion of the steel strip is measured based on the difference in voltage induced in the secondary coil wound around each of the two outer leg portions.

  The invention according to an eleventh aspect of the present invention is the method of manufacturing a steel strip according to any one of the first to ninth aspects, wherein the surface layer property measuring step includes winding a coil around a leg portion. The comb-shaped ferromagnet legs are arranged side by side in the width direction of the steel strip so as to face the steel strip surface, and the selection of the three adjacent leg sets is switched while changing over time. Among the legs of the book, an alternating current is applied to the primary coil wound around the central leg to excite it, and the voltage induced in the secondary coil wound around each of the two outer legs A method of manufacturing a steel strip characterized by measuring properties of a surface layer portion of the steel strip based on a difference signal.

  According to a twelfth aspect of the present invention, in the steel strip manufacturing method according to any one of the first to eleventh aspects, the surface layer property measuring step includes a DC magnetization level of excitation of the steel strip. The steel strip manufacturing method is characterized in that the surface layer property is measured in a state of substantially close to zero and the frequency of AC magnetization is in the range of 100 kHz to 10 MHz.

  In each process leading to the final consumption, the range to be measured in order to determine whether or not the measurement part is manifested as a defect is limited to the surface layer part. Therefore, it is preferable to concentrate the magnetic flux on the surface layer part as much as possible. For that purpose, it is appropriate that the penetration depth of the magnetic flux (the depth at which the magnetic flux density becomes 1 / e of the surface) be about 50 μm or less.

  In the case of steel, when the direct current magnetization is close to 0, the frequency is preferably 100 kHz or more. In addition, from the standpoint of noise stability and in order to prevent the penetration depth from becoming too shallow, the frequency of AC magnetization is set to 10 MHz or less. Therefore, in the present invention, the frequency of AC magnetization is in the range of 100 kHz to 10 MHz. The frequency of AC magnetization is preferably 1 MHz or less.

Note that by applying DC magnetization to AC magnetic flux, the differential permeability can be lowered, and the penetration depth can be increased compared to the case where DC magnetization is not applied even when the same excitation frequency is used. Therefore, it is also possible to control the DC magnetization level in order to realize a plurality of penetration depth measurement conditions.

As described above, according to the present invention, by measuring the properties of the surface layer portion after hot rolling in the steel strip manufacturing process, it is not manifested in the measurement stage, and the final consumption thereafter is reached. By predicting the part that will be manifested in any of the above steps and taking appropriate measures such as removing the part including the part, we can efficiently manufacture high-quality steel strips with few defects. be able to. Steel strips are particularly effective not only for pickled steel strips and cold-rolled steel strips, but particularly for surface-treated steel strips such as plated steel strips where defects are likely to be manifested by the treatment.

  Implementation of the invention will be described with reference to FIGS. As illustrated in FIG. 10, processes after the prediction process and manufacturing conditions are determined. Alternatively, a part that is predicted to become apparent in the future as a defect is partially removed before cold rolling. The defect revealing prediction step in FIG. 10 is performed by the surface layer property measuring device 13 and the defect revealing predicting device 15 as shown in FIG.

  The term “characteristic” as used herein refers to the presence / absence, type, and spatial distribution of an abnormal part different from other healthy parts. In addition, the “abnormal part different from other healthy parts” specifically, for example, biting into the base steel layer of the scale, non-metallic inclusions, large irregularities at the boundary between the scale and the base steel layer, There are crystal grain sizes, portions with different grain properties, and uneven components.

First, the manufacturing process for measuring the properties of the surface layer portion of the steel strip and the selection of the location will be described.
When removing the abnormal part partially, it is necessary to prepare the shape and properties of the steel strip uniformly in subsequent processes such as rolling so as not to cause defects due to property changes caused by the removal. For this reason, it is better to remove the abnormal portion of the surface layer as upstream as possible, at least before cold rolling.

In addition, in the manufacturing process / condition determination process, not only feedforward to such a lower process but also the so-called next production timing (manufacturing chance) and the production lot of the steel strip produced in the next production lot. Information for determining a change in manufacturing conditions or a process change including feedback to the manufacturing conditions is output. In this way, by predicting whether a defect in the subsequent future next step becomes apparent, it is also possible to Ru determine the production conditions of the steel strip to be produced therefrom (for feedback).

  For example, when considering the feedback of manufacturing conditions to a process that has caused the cause of an abnormal part, such as a steelmaking process, it is desirable to measure the properties of the surface layer part as close to the upper process as possible. Therefore, it is desirable to measure the properties of the surface layer portion, which must be performed prior to the removal of the abnormal portion of the surface layer, at least before cold rolling.

On the other hand, for the following reasons, it is desirable to measure the properties of the surface layer portion as downstream as possible, at least after the hot rolling step.
1) When detecting minute abnormal parts,
(a) To prevent the detection performance from deteriorating due to the occurrence of noise due to surface irregularities,
(b) When detecting the sensor close to the surface of the steel strip, make sure that the detection performance does not deteriorate due to fluctuations in the distance (lift-off) between the sensor and the steel strip.
(c) To prevent the sensor and steel strip from coming into contact with each other due to lift-off fluctuation, the sensor will be damaged, and the steel strip will not be damaged.
The plate shape needs to be good for the reasons (a), (b), and (c).

In this regard, the plate shape tends to be better on the lower process side, and the shape becomes more stable on the lower process side by applying tension or the like. Other,
2) It is easier to detect when the sheet thickness is reduced due to rolling and the abnormal part is present as close as possible from the surface.
3) While the abnormal part is deformed by rolling, the severity can be evaluated more accurately by detecting it as close to the final product as possible.

  For the reasons described above, when removing the abnormal portion of the surface layer portion, it is preferable to install a surface layer property measuring device and a partial removing device after the hot rolling and before the cold rolling. Further, when selecting other manufacturing conditions, it is necessary to determine the installation position in consideration of the above-mentioned matters regarding the installation position for each case.

For example, when it is necessary to determine the plate thickness as a manufacturing condition based on the surface layer property measurement result, the surface layer property measurement needs to be performed before cold rolling. Also, for example, predict whether or not surface defects will appear after plating in the plated steel sheet, and place markings so that they will not be used in subsequent processes in areas where defects are expected to appear after pressing, or in the longitudinal direction of the steel strip In the case where measures that can be implemented even after plating are performed, such as by cutting off a region where defects are likely to occur, it may be possible to measure the properties of the surface layer after plating near the end use form.

In addition, regarding the selection of the installation position of the surface layer property measuring apparatus, there are the following in addition to the reasons described above.
1) For detecting and removing abnormal parts, it is desirable that the amount of fluttering of the steel sheet is small.
2) The line speed should not be too fast for detecting and removing abnormal parts. The exit side of the hot rolling line is very fast and is generally unsuitable.
3) Since removal generates chips and the like, it is desirable to have equipment that can be easily washed and dried, or to be easily installed.

  Regarding 1) above, specifically, a) it is desirable to apply a leveler, and b) it is desirable to apply a strong tension, so the surface opposite the inspection surface of the steel strip after the leveler is rolled with a roll. It is preferable to install a surface layer property measuring device at a supported position. In addition, for the reasons 2) and 3) above, it is better if it can be installed on the side of the pickling line (just before the pickling tank). Also in the surface layer property abnormal part removing apparatus, it is preferable to provide it at the same position as the surface layer property measuring apparatus for the same reason.

In addition, if the inspection is performed in a place where the unit tension of the steel strip is 0.3 kgf / mm ² or more, the steel strip becomes flat, so that it is possible to perform an accurate inspection without being affected by the distortion of the steel plate. .

After the measurement of the surface layer properties, the prediction of whether or not it will manifest as a defect in the subsequent processes is not only the measurement results of the surface layer properties, but the actual manufacturing conditions until the surface layer property measurement, the subsequent More accurate by taking into account closely related items such as manufacturing conditions scheduled for the process and product specifications (including steel strip customers, usage patterns at the final consumption stage, etc.) Will be expensive. Specifically, the steel type, heat treatment conditions, rolling conditions, types of plating, other various conditions of the steel strip production line, press conditions, coating conditions, final use form, and the like.

The defect or defect candidate is classified into three as shown in FIG.
(1) Hazardous defect A: Defect newly generated in the process after measuring the surface layer properties of the prediction device
(2) Hazardous defect B: Measured site that was measured with the surface layer property measuring device and was predicted to be manifested as a defect in the subsequent process among the sites detected as signals
(3) Normal part: Measurement site that is predicted not to appear after surface layer property measurement Normally, harmful defects are subjected to surface inspection by a surface defect meter or human visual inspection in the final process, and the above-mentioned (1) Both (2) are targeted for detection.

  For example, when these harmful defects have a very high degree of harm, all the places of the defective parts are cut and excised. In addition, when the degree of harm is moderate to mild, the number of defects existing in one coil as a unit of shipment of the steel strip or for every unit of length of the steel strip (for example, 500 m or 1000 m) is acceptable. The defect part is appropriately cut and excised so as to fit in the inside, and the work of adjusting the inside of one coil of the steel strip or the defect per unit length is performed.

  In addition, if the number of defects does not fall within the allowable range, the delivery destination or application is changed and the product grade is lowered before shipment. Therefore, these operations not only reduce the yield of defects, but also need to be transported to a dedicated inspection line or cutting line in order to perform cutting and excision work, and there is a problem that enormous costs are required. Further, there is a cost for performing a wasteful process such as performing a plating process on a steel strip that has too many defects and cannot be shipped.

These problems are due to the fact that the presence or absence of defects cannot be grasped in advance. In particular, these defects are mainly treated as serious defects due to abnormal operations in the steelmaking process or hot rolling process. Will occur. This is equivalent to the harmful defect B shown in FIG. 12, that is, the surface defect that has been manifested after the surface layer property measurement, when it is detected by the surface layer property measuring apparatus installed after hot rolling and before cold rolling. Therefore, if the existence of the hazardous defect B can be known before the final process, the planned process route after the next process (next process → next process → next next process → ... → shipment → ... → Steel strip distribution route that leads to customer use, etc.), or change the destination of customer users who deliver as final products, or change manufacturing conditions. .

  As a result, if it is predicted at least before the steel strip is inserted into the final process, the manufacturing process route will not perform unnecessary processes or removal of defects until the conventional final product is completed. Thus, not only the yield of products can be improved, but also the manufacturing cost can be reduced.

  Further, as described above, even if the signal level of the surface layer measuring device is the same, if the shipment and use as the final product change, what is predicted as the harmful defect B in FIG. It becomes different whether it becomes what is expected to be harmless defect C. That is, tolerance is different even for the same defect depending on whether it is a molten-plated steel sheet, an electric-plated steel sheet, a cold-rolled steel sheet, an automobile, or an electrical product. For example, it may be difficult to see defects existing on the original steel plate under plating, or it may be easier to see, or it may be easier to see depending on the press shape and painting conditions at the customer site. On the contrary, it may be difficult to see.

  Therefore, the area of the harmful defect B in FIG. 12 becomes wider or narrower depending on conditions. In addition, in the determination of the prediction device, not only is it determined at each detected part, but also the entire predicted defect existing in one coil or unit length, for example, predicted The determination is made in consideration of the distribution of the degree and number of defects, the density of defects, and the like.

  As shown in FIG. 9, these pieces of information are provided to the defect revealing prediction device 15 by the manufacturing information holding device 16 (generally, a process computer or the like is used as a host computer) and the association database 17. The manufacturing information storage device 16 has information on manufacturing conditions such as the coil number of the steel strip whose surface layer property is to be measured, the type, the steel type indicating the component characteristics, the inspection conditions, the customer and the specification application, etc. corresponding to each steel strip. And this information is transmitted to the defect revealing prediction devices 15a and 15b until the surface layer property measurement is started or the defect revealing prediction process is started. The defect revealing prediction devices 15a and 15b are based on the surface layer property detection signals of the surface layer property measuring devices 13a and 13b, the steel strip information from the manufacturing information holding device 16, and the information in the association database 17. Each part of the steel strip is checked for surface defects in the final line included in the steel strip information.

  For example, in the case of surface defects that are manifested after plating in a plated steel strip, the type of plating (melt plating / electroplating, alloyed hot dipping (GA ) / Simple molten plating (GI), single layer plating / double layer plating), whether or not surface defects are manifested after plating differs. In addition, regarding the defects that are manifested when the plated steel strip is pressed, the same difference is caused because the surface square (sliding) property varies depending on the type of plating.

  Therefore, in order to judge these differences, each signal of the surface layer property measuring devices 13a and 13b, for example, the size (length, width, thickness), shape, and depth of the abnormal portion exceeding a predetermined threshold value A feature value such as a position is associated with a grade indicating the type and / or degree of a surface defect that is finally manifested in each process and detected by a surface defect meter or human visual inspection. It is necessary to keep. In this information, the correspondence between the surface layer property measuring device signal and the surface defects detected in each manufacturing process (for example, manufacturing lines such as continuous annealing, continuous hot dip galvanizing, and continuous electrogalvanizing) is tabulated. And stored in the association database 17 as a file.

  In addition, this database performs surface inspection in each manufacturing process after measurement with the surface layer property measuring devices 13a and 13b, and if the results in each manufacturing process can be collected, the results are manufactured as a host computer. The information is input to the process computer of the information holding device 16 as inspection information, and then transmitted and stored in the association database 17. In addition, the measurement results of the revealing prediction apparatuses 13 a and 13 b are also transmitted to the association database 17 via the manufacturing information holding apparatus 16 and stored. The result of the surface layer property measuring device and the result of the surface inspection of each process are associating the steel strip with the coil number etc. of the steel strip, and the position in the steel strip is not only the direction of conveyance but also by rolling The association is performed in consideration of the reduction ratio.

  The measurement signals of the surface layer property measuring devices 13a and 13b and the surface inspection result are sequentially stored, and the correspondence table is updated. The data of the surface inspection result is not limited to the process in which the steel strip is finally inspected, but when inspecting in the intermediate process up to the final stage, the data is also input and a correspondence table is created. And based on this table, the logic of the prediction determination of defect actualization prediction apparatus 15a, 15b is produced. Alternatively, determination logic may be created by inputting table data into a logic automatic generation tool such as a neural network.

  Further, the defect revealing prediction device 15 determines which manufacturing process the steel strip to be predicted is satisfactory, and selects a process route. This prediction result is transmitted to the manufacturing information holding device 16, and the subsequent process route of the steel strip is changed. At this time, even if the customer and the specification application are not determined in advance for one steel strip, a plurality of varieties and customers that are candidates based on the manufacturing conditions prior to the defect revealing prediction devices 15a and 15b, for example, the steel types. The distribution route of the steel strip may be selected after the prediction determination result according to the prediction determination result from the specification application. Thus, according to the present invention, the distribution route and the like can be made flexible.

  FIG. 13 and FIG. 14 show an example of a process for determining a manufacturing process / manufacturing condition according to the prediction result. Here, as shown in FIG. 13, surface layer property measurement is performed, and defect manifestation prediction under the condition of product type 1 is performed. The measurement result is compared with the association table stored in the association database 17 to predict and determine whether the surface layer property is applicable to the product type 1. The determination of pass / fail is made not only for each surface layer property measurement site, for example, but also based on one coil of steel strip or the number of manifest defects per unit length. For example, even if the number of manifestation defects is one, if the degree is predicted to be heavy, it will be rejected. If the degree is moderate to light, the number in one coil or unit length will be rejected. For example, when the number exceeds five, a process of determining that it is unacceptable is performed. If it passes, manufacture under the conditions of product type 1. In the case of failure, it is predicted whether the surface layer property is applicable to the condition of product type 2 or whether or not the defect is obvious.

  Thereafter, the prediction result is determined in the same manner, and if the result is acceptable, the production is performed under the condition of the product type 2, and if the result is unacceptable, the process is sequentially performed, such as predicting the occurrence of defects in the next product type. In this way, the product specifications are changed according to the prediction result, and the manufacturing process and manufacturing conditions are determined accordingly. Such judgment logic is set to judge from product types with strict standards (product type with strict standards is set to product type 1), and if it does not apply to all product type standards, it becomes a product. It is regarded as scrap that cannot be obtained.

  As a specific example, as a result of measuring surface properties, it is predicted that sufficient quality can be secured when the subsequent manufacturing process is performed as an alloyed hot-dip galvanized steel sheet used as a high-grade automobile outer plate. In such a case, a predetermined production such as rolling to an appropriate thickness as an automobile outer plate is performed. As a result of the prediction, if it is predicted that it is unsuitable as an automotive outer sheet alloyed hot-dip galvanized steel sheet, but can be used as a general building material, change the delivery destination, The manufacturing conditions and product specifications (including the destination) after the next process are determined, such as rolling to a plate thickness corresponding to that and making a plated steel sheet that is not alloyed.

  Further, in addition to making the destination change which is the product type change or the customer change in the determination procedure of FIG. For example, when a product is shipped, the product type and destination may not be changed due to the delivery date. In such a case, as shown in FIG. 14, the surface layer part property measurement is performed, the defect manifestation prediction is made for the product type 1, and the determination is made based on the prediction result. . As a result of measurement, if there is something that must not exist in product type 1, or the number (per unit length) exceeds the allowable number and fails, it exists in the steel strip in the length direction of the steel strip Decide which parts will be rejected.

  Next, the rejected portion of the steel strip is cut and removed, or is ground and made harmless, and the subsequent process is performed as planned. In this way, it is possible to remove the portion where defect manifestation is predicted for the entire width direction and connect only the normal portion, or to render the peripheral portion of the defect manifestation predicted portion harmless and form a normal steel strip. .

  As a specific example, if it is predicted that a defect will occur after plating in a certain region in the longitudinal direction of the steel strip as a result of the prediction on the assumption that the steel plate is manufactured, that region of the steel strip is Can be cut and removed.

The determination method of defect manifestation prediction in the present invention is not limited to the processes of FIGS. 13 and 14, and may be performed in combination, and is not limited to the processes based on FIGS. 13 and 14.

FIG. 8 is a diagram for explaining an example of the embodiment of the present invention. In the pickling line, a surface property measuring device 13 is provided after the entry-side leveler 11, and the defect revealing prediction device 15 is used. It is predicted whether or not the abnormal property portion will be manifested as a defect in a later process, the removal target portion is determined by the surface property abnormal portion removing device 14, and the region including the removal target portion is determined by the partial removal means. It is the figure which showed the manufacturing method to remove. As the surface layer property measuring apparatus, as shown in FIG. 1 to FIG. 6, a device that accurately measures the property of the surface property abnormality portion that is very small in the C cross section and is long in the rolling direction is used. Yes.

The configuration and operation including the components corresponding to the front and back of the steel strip and the surrounding situation will be described in detail. First, the unevenness | corrugation of a board is reduced by the leveler 11 installed in the pickling line entrance side. Thereafter, the surface layer property measuring device 13a (the steel strip front side) is placed on the opposite side of the bridle rolls 12a to 12d across the steel strip 1 at a position where the tension on the plate is large and wound around the large diameter bridle rolls 12a to 12d. ), 13b (for steel strip back side), and surface layer property abnormal part removing device 14a (for steel strip front side), 14b (for steel strip back side) are installed.

In addition, the front side defect actualization prediction apparatus 15a and the back side defect actualization prediction apparatus are set to 15b. In this case, the unit tension of the steel strip at the position where the surface layer property measuring device is installed is preferably 0.3 kgf / mm ² or more in order to suppress fluttering of the plate and reduce lift-off fluctuation. Since the front and back systems are operated separately in principle, the front side will be described below for the sake of simplicity, but the same applies to the back side.

  First, the outline of the basic operations of the surface layer property measuring device 13a, the defect revealing prediction device 15a, and the surface property abnormal portion removing device 14a and the mutual relationship will be described. In evaluating the properties of the surface layer portion, the main points of interest are the size (length in the rolling direction, length in the width direction, thickness), shape, and depth position of the abnormal portion, including the surface layer of the steel sheet. .

  They can be evaluated by using the signal amplitude and phase after synchronous detection and their two-dimensional distribution as measurement result data when a method using AC magnetic flux is adopted as a property measurement method. . The phase includes information on the depth position of the abnormal property portion. Also, since the penetration depth of the magnetic flux from the steel plate surface changes by changing the excitation frequency of the AC magnetic flux, by performing measurement at a plurality of excitation frequencies, the above-mentioned measurement result data shows different properties from other parts. More detailed information on the distribution (thickness, depth position, etc.) in the depth direction of the surface layer portion can be obtained.

The surface layer property measuring device 13a is installed at a position in the line as described above in order to suppress flapping of the plate, lift-off fluctuation due to plate deformation and contact of the steel strip to the sensor. In the surface layer property measuring device 13a, signal values and the like at each measurement point on the steel strip are transmitted to the defect revealing prediction device 15a. As data to be transmitted, for example, when performing surface layer property evaluation using AC magnetic flux in the above-described invention, it is possible to include not only the synchronous detection signal amplitude at each measurement point, but also the synchronous detection phase, The excitation frequency of the alternating magnetic flux is not limited to one type. When a plurality of types are used, the signal value and the synchronous detection phase can be increased by the number of frequencies.

The defect revealing prediction device 15a evaluates the properties of the surface layer portion based on the information from the surface layer property measuring device 13a, and predicts whether or not the property abnormality portion becomes apparent as a defect in the subsequent steps.

  Regarding the property evaluation method for the surface layer portion, an example in the case of performing the surface layer property evaluation using the AC magnetic flux of the above-described invention will be described below. First, based on the data sent from the surface layer property measuring device at each measurement point, for example, regarding a synchronous detection signal amplitude, a certain threshold value is set, and a two-dimensional coordinate point on the steel strip having a signal value exceeding it is abnormal. It is extracted primarily as a part candidate point. Specifically, as shown in FIG. 11, the synchronous detection amplitude A (x, y) and the phase P (x, y) at each point of the two-dimensional coordinates (longitudinal direction x [m], width direction y [m]). ) Collect data.

  Each abnormal part candidate point is recognized for each block (labeling process), and the feature amount (rolling direction length, width direction length, area, etc.), thickness, and synchronous detection phase information of each two-dimensional region are obtained. . Since the synchronous detection phase information is an amount reflecting the position in the depth direction of the signal source, it is evaluated as depth position information by obtaining a conversion coefficient from the phase to the depth in advance.

  As described above, the adjacent abnormality indicating units are recognized as the same group of abnormal units, and it is predicted whether or not they will be manifested as defects in units of the units. For example, when a depth position (which can be estimated from the phase) is shallower than a certain threshold, wider than a certain threshold, and larger than a certain threshold, the synchronous detection amplitude is predicted to be manifested as a defect.

  In addition, when AC excitation is performed at multiple frequencies, when measuring at a higher frequency, the property abnormalities near the surface are emphasized and measured, so the depth is evaluated in more detail. Is possible.

  As a specific example of a method of measuring the properties of the surface layer portion of the steel strip after hot rolling and before cold rolling, and predicting whether or not the measurement portion will manifest as a defect before performing the alloying melt plating treatment, There is a method of using the signal amplitude level and phase after synchronous detection. It has been found that an abnormal portion which is at a position shallower than a certain depth from the surface and has a certain size or more and is long in the rolling direction becomes apparent as a surface defect before the plating process.

  Therefore, as a prediction method, as shown in FIG. 16, after obtaining coil information from a manufacturing information storage device such as a host computer, a signal amplitude that exceeds a certain threshold value such that the signal level exceeds or exceeds a predetermined threshold value. Furthermore, there is a property abnormality instruction having a certain length or more in the rolling direction (or considering the width, area, and shape depending on the case), and the range in which the phase corresponds to the abnormal portion depth position. In this case, it is predicted that the surface defects will become apparent after the plating process.

  About the depth position of an abnormal part, since it is rolled in the subsequent process and it becomes easy to become clear, so that it is near the surface (the shallow position), the degree becomes worse. In consideration of such information, a threshold value is set to determine which process can be used. For example, based on the above-mentioned idea, it is determined whether or not it can be used in a production line such as continuous annealing, continuous hot dip galvanizing, and continuous electrogalvanizing within a range of depth positions as shown in FIG.

  Another example of prediction is to investigate in advance what kind of synchronous detection amplitude level the surface defect after plating will have at the pickling stage, and when the synchronous detection amplitude level exceeds a certain threshold. The prediction method itself can be a simple method if it is predicted that a surface defect will occur after plating, and if it is smaller than the threshold, it will not be a surface defect. Note that the threshold and the prediction algorithm are selected according to product specifications such as manufacturing condition targets and results until prediction is performed, manufacturing conditions scheduled thereafter, usage, and inspection specifications.

  The surface property abnormal part removing device 14a is based on the surface layer property abnormal part position (longitudinal direction, width direction, depth direction) to be removed from the defect revealing prediction device 15a, and the surface layer property abnormal part length information. The region including is partially removed by grinding or cutting. In addition, in order to stably remove the surface layer abnormal portion, the surface property abnormal part removing device 14a is also installed at a position in the line where the flapping of the plate and the influence of the plate deformation are small, like the defect candidate portion detecting device 13aA. The entire operation sequence is controlled by a sequencer (not shown).

The steel strip from which the abnormal portion of the surface layer property has been removed undergoes cold rolling and is plated to become a plated steel strip. As described above, as a result of removing the defective portion in the lower step in the pickling step, the plated steel strip has a high quality with very few surface defects.

Hereinafter, some examples of the surface layer property measuring apparatus particularly suitable for use in the present invention will be described. FIG. 1 is a schematic diagram showing the configuration (width direction difference method) of the surface layer property measuring apparatus. The steel sheet 1 has a surface property abnormality portion 2 that is minute in the width direction and long in the length direction (direction perpendicular to the paper surface). An alternating current is supplied to the coil of the magnetizer 4 by the magnetization power source 3 to magnetize the surface layer portion of the steel plate 1 in a concentrated manner. In the figure, magnetization is performed such that the magnetic flux is formed in the width direction of the steel plate 1, but it is preferable to perform such magnetization as much as possible.

  Like the surface defects of the plated steel sheet described above, defects that are manifested in any of the processes up to the final consumption are caused by nonmagnetic metal inclusions generated in the steelmaking process, or the steelmaking process and heat It is said that the origin is on the upper process side in all the manufacturing processes, such as when there is a cause for the occurrence of oxide in the steel material inside the rolling process entry side (before hot rolling). Then, in the step of measuring the properties in the present invention, it is greatly reduced in the C cross section (the cross section when the steel strip is cut in the width direction) and is greatly reduced in the rolling direction by being greatly reduced by hot rolling. It is extended into a long shape. Therefore, in the present invention, in view of the characteristics of such an abnormal part, a method for easily measuring the property of the abnormal part is adopted.

  And the magnetic flux which exists outside the steel plate 1 is detected by the two magnetic sensors 5a and 5b. In this case, since the surface layer property abnormality portion 2 exists under the magnetic sensor 5a, magnetic flux and eddy current are less likely to pass through the surface layer property abnormality portion. As a result, the magnetic sensor 5b detects the magnetic flux detected by the magnetic sensor 5a. More than the detected magnetic flux, the output of the magnetic sensor 5a becomes larger than the output of the magnetic sensor 5b.

Therefore, when these outputs are guided to the differential amplifier 6 and the output is input to the phase detector 7 and phase detection is performed using a signal synchronized with the waveform of the magnetizing power supply 3 (there may be a phase shift), the surface layer property abnormality A signal corresponding to the size of the part 2 is obtained. This output is guided to the surface property abnormal portion level discriminator 8 and compared with a predetermined threshold value, whereby the level of the surface property abnormal portion 2 is determined.

The surface property abnormal portion 2 is very small in the width direction of the steel sheet, but is long in the length direction. Therefore, if magnetization is performed in the width direction of the steel plate, the width of the magnetic path is increased, resulting in a large surface property abnormality. A partial signal is obtained. Also, in the width direction difference method, the surface layer abnormalities are discriminated by the differential signals of the outputs of the two sensors, so noise common to the sensors (such as changes in the permeability of the steel plate) and external noise are canceled out. , It is possible to detect a surface layer abnormal portion having a good S / N ratio.

  In FIG. 2, the outline | summary of the structure (E type sensor system) of a surface layer property measuring apparatus is shown. In the following drawings, the same components as those shown in the previous drawings may be denoted by the same reference numerals and the description thereof may be omitted. In the surface layer property measuring apparatus, an E-type coil 9 is used as a magnetizer and a magnetic sensor. The yoke of the E-shaped coil 9 has three legs 9a, 9b, 9c, 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 9a is supplied with an alternating current from the magnetization power supply 3 and is magnetized. A coil is also wound around the leg portions 9b and 9c on both sides, and is used as a magnetic sensor. The magnetic flux generated by the coil of the leg portion 9a passes through the vicinity of the surface of the steel plate 1 and returns to the leg portion 9a through the leg portions 9b and 9c on both sides.

  At that time, if the surface layer abnormal property portion 2 exists at the position as shown in the figure, the magnetic resistance to the magnetic flux passing through the leg portions 9a and 9b becomes larger than the magnetic resistance to the magnetic flux passing through the leg portions 9a and 9c. The magnetic flux density of the magnetic flux passing through the portion 9b is smaller than the magnetic flux density of the magnetic flux passing through the leg portion 9c. Therefore, the voltage induced in the coil wound around the leg portion 9b is smaller than the voltage induced in the coil wound around the leg portion 9c, and if both are input to the differential amplifier 7, the difference between the two is handled. Is output.

  When it is guided to the phase detector 8 and phase detection is performed with a signal synchronized with the waveform of the magnetization power supply 3 (there may be a phase shift), a signal corresponding to the size of the surface layer property abnormality portion 2 is obtained. This output is guided to the surface property abnormal portion level discriminator 8 and compared with a predetermined threshold value, whereby the level of the surface property abnormal portion 2 is determined.

By arranging the E-type sensor system in the width direction as well, a large surface layer property abnormal part signal is obtained for the abnormal part extending in the longitudinal direction of the steel sheet, as in the width direction differential system described above. Further, because of the differential method, changes in magnetic permeability, etc., and external noise are canceled out, and it is possible to detect a surface layer abnormal portion with a high S / N ratio.

FIG. 3 shows a part of the structure (mechanical width scanning method) of the surface layer property measuring apparatus. In this surface layer property measuring apparatus, the steel plate 1 is AC magnetized in the plate width direction by a magnetizing device (not shown). The magnetic sensor 5 is scanned in the plate width direction, and the temporal change in the output is observed. If the surface property abnormal portion 2 exists, the magnetic flux detected at the portion changes, and therefore the output of the magnetic sensor changes. Therefore, the surface property abnormal portion 2 can be detected by signal processing the output of the magnetic sensor 5. When the steel plate 1 is traveling in the length direction, the inspection range becomes a zigzag range. However, if the number of magnetic sensors is increased to shorten the scanning range and increase the scanning speed, the surface layer is longer than a predetermined length. An abnormal property portion can be detected.

FIG. 4 shows a part of the configuration (electronic scanning method) of the surface layer property measuring apparatus. Also in this surface layer property measuring apparatus, the steel plate 1 is AC-magnetized in the plate width direction by a magnetizing device (not shown). In this surface layer property measuring apparatus, a large number of magnetic sensors 5 are arranged in the width direction of the steel plate 1. The output of the magnetic sensor 5 is connected to a scanner, and the output of one magnetic sensor selected in sequence is signal-processed. In this way, scanning equivalent to the mechanical scanning in FIG. 3 can be performed electronically. Since this scanning can be performed at high speed, the length in the longitudinal direction of the surface layer property abnormality portion that can be detected can be shortened.

In this surface layer property measuring apparatus, the output of each magnetic sensor 5 is sequentially processed, and the surface property abnormal portion is not detected from the temporal change, but the outputs of two adjacent magnetic sensors 5 are sequentially detected. The difference between the two magnetic sensors may be input, the difference between the two magnetic sensors may be calculated, and the abnormal surface property portion may be detected by the processing as described above. In this way, it is not necessary to detect the surface layer abnormal portion by temporally processing the signal itself, and it becomes possible to detect the surface layer abnormal portion directly from the difference signal.

FIG. 5 shows a part of the configuration (comb sensor type) of the surface layer part property measuring apparatus. FIG. 5 illustrates the magnetizing device and the magnetic sensor, with the steel plate and the signal processing circuit being omitted. The leg portions of the comb-shaped ferromagnetic body 10 having a comb shape are arranged so as to be substantially perpendicular to the surface of the steel plate and aligned in the width direction of the steel plate. A coil is wound around each leg.

  In order to detect an abnormal surface property using such a detection device, first, as shown in (a), three legs at the left end of the figure are used, and the coil of the leg 10b at the center is used. Is connected to the magnetizing power source 3 to generate an alternating magnetic flux. Then, the magnetic flux is detected by the coils wound around the legs 10a and 10c located on both sides thereof, and the detection signal is guided to the differential amplifier 6. Signal processing is performed in the same manner as shown in FIG. This corresponds to the detection using the three left leg portions of the comb-shaped yoke as the E-shaped coil shown in FIG.

  Next, the electrical path is switched electronically or electrically, and as shown in (b), using the second to fourth legs from the left end, the coil wound around the leg 10c is excited, Magnetic flux is detected by the coils wound around the left and right legs 10b and 10d. Further, as shown in FIG. 3C, the same detection is performed by using the right three leg portions one by one.

Hereinafter, if this is repeated, it corresponds to scanning the detector in the width direction of the steel plate, and scanning can be performed without mechanical movement over a wide range. Switching between the exciting coil and the detection coil may be performed using an electronic switch, or may be performed by a relay or the like.

4 and 5, when sensors and comb-shaped legs are arranged, one or more pairs of sensor rows and comb-shaped ferromagnetic bodies are arranged, and the sensors and comb-shaped legs are staggered. If arranged in a shape, the surface property abnormality portion can be detected without a gap in the width direction. The staggered arrangement may be in two or more rows depending on the shape of the sensor (including the frame portion of the sensor unit). Note that the electronic scanning timing between the sensors that are close to each other in the staggered arrangement is adjusted as necessary so that signals between the sensors do not interfere with each other.

The reason why the waveform as shown in FIG. 6B is obtained is that an elongated surface property abnormality portion having a long side in the rolling direction is scanned in the plate width direction. As shown in FIG. 7 (a), even when the rolling direction elongated surface layer abnormal portion is scanned in the rolling direction, a large signal cannot be obtained as shown in FIG. 6 (b), as shown in FIG. 7 (b). Only a small output is obtained. Therefore, when scanning is performed in the rolling direction, it is difficult to accurately detect the abnormal portion in the rolling direction elongated surface layer.

It is a schematic diagram which shows the structure (width direction difference system) of the surface layer property measuring apparatus of this invention. It is a schematic diagram which shows the structure (E type sensor system) of the surface layer property measuring apparatus of this invention. It is a schematic diagram which shows the structure (width scanning system) of the surface layer property measuring apparatus of this invention. It is a schematic diagram which shows the structure (electronic scanning system) of the surface layer property measuring apparatus of this invention. It is a schematic diagram which shows the structure (comb type sensor system) of the surface layer part property measuring apparatus of this invention. It is a figure which shows the signal waveform of the magnetic sensor of a standard minute surface layer property abnormal part. It is a figure which shows the signal waveform of a magnetic sensor at the time of scanning the rolling direction elongate surface layer property abnormal part in a rolling direction. It is a figure for demonstrating one example of embodiment of this invention. It is a figure which shows the structure of a defect generation | occurrence | production prediction apparatus. It is a figure which shows the basic structural example (outline process). It is a figure which shows the flow of the example of a prediction flow (example using alternating current magnetic flux). It is a figure which shows the relationship between the surface defect actualized in a certain process, and the surface layer part abnormal property part measured in advance. It is a figure which shows the process example (example which determines a product kind and manufacturing conditions) which determines a manufacturing process and manufacturing conditions according to a prediction result. It is a figure which shows the process example (example which determines a process) which determines a manufacturing process and manufacturing conditions according to a prediction result. It is a figure which shows an example estimated with a depth position among prediction results. It is a figure which shows an example of the processing flow of a defect actualization prediction apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel strip 2 Surface layer abnormal part 3 Magnetization power supply 4 Magnetizer 5, 5a, 5b Magnetic sensor 6 Differential amplifier 7 Phase detector 8 Surface layer abnormal part level discriminator 9 E type coils 9a-9c Leg part 10 Comb type strong Magnetic body 10a-10e Leg 11 Leveler 12a-12d Bridle roll 13a, 13b Surface layer property measuring device 14a, 14b Surface layer property abnormal part removing device 15a, 15b Defect revealing prediction device 16 Manufacturing information storage device (process computer etc.)
17 Database for associating surface layer property measurement signals with surface inspection results

Claims (12)

In the method of manufacturing a steel strip for producing a steel strip and further a surface-treated steel strip by at least hot rolling the steel, the process described in the following (1) to (3) and the shipment of the steel strip after hot rolling A method for producing a steel strip comprising the following steps (4) and (5) before the step:
(1) Surface layer property measurement process for measuring the properties of the surface layer of the steel strip
(2) Using the results of the surface layer measurement, a defect revealing prediction process for predicting whether or not the measurement part will appear as a surface defect in the subsequent manufacturing process or processing
(3) Manufacturing process and condition determination process for determining the manufacturing process and manufacturing conditions according to the obtained prediction results
(4) Surface texture measurement process that measures only the surface texture of steel strips
(5) Display target determining step for determining a display target part from parts predicted to be manifested as defects In the method for producing a steel strip for producing a steel strip and further a surface-treated steel strip by at least hot rolling the steel, the process according to the following (1) to (3) after hot rolling,
(1) Surface layer property measuring step for measuring the properties of the surface layer of the steel strip,
(2) Using the result of this surface layer measurement, a defect revealing prediction process for predicting whether or not the measurement part is manifested as a surface defect in the subsequent manufacturing process or processing,
(3) Manufacturing process / condition determining process for determining the manufacturing process and manufacturing conditions according to the obtained prediction results,
The defect manifestation prediction process includes steel strip production conditions, targets, actual results, production conditions scheduled for subsequent processes, product specifications, applications, and inspection specifications as prediction information. A method for producing a steel strip, characterized in that one or more of the above-mentioned information are used. In the method for producing a steel strip for producing a steel strip and further a surface-treated steel strip by at least hot rolling the steel, the process according to the following (1) to (3) after hot rolling,
(1) Surface layer property measuring step for measuring the properties of the surface layer of the steel strip,
(2) Using the result of this surface layer measurement, a defect revealing prediction process for predicting whether or not the measurement part is manifested as a surface defect in the subsequent manufacturing process or processing,
(3) Manufacturing process / condition determining process for determining the manufacturing process and manufacturing conditions according to the obtained prediction results,
The manufacturing process / condition determining process determines or changes at least one of product specifications, applications, and destinations based on the prediction result of the defect manifestation prediction process. In the manufacturing method of the steel strip according to claim 1,
The defect manifestation prediction process includes steel strip production conditions, targets, actual results, production conditions scheduled for subsequent processes, product specifications, applications, and inspection specifications as prediction information. A method for producing a steel strip, characterized in that one or more of the above-mentioned information are used. In the manufacturing method of the steel strip of any one of Claim 1, Claim 2, and Claim 4,
The manufacturing process / condition determining process determines or changes at least one of product specifications, applications, and destinations based on the prediction result of the defect manifestation prediction process. In the manufacturing method of the steel strip according to any one of claims 1 to 5,
A method for producing a steel strip comprising the steps described in the following (6) and (7) after hot rolling and before cold rolling, and thereafter performing cold rolling.
(6) Removal target surface layer determination step for determining a surface layer portion to be removed from the portions predicted to be manifested as defects
(7) Partial removal step of removing the region including the surface layer portion to be removed by the partial removal means In the manufacturing method of the steel strip according to any one of claims 1 to 6,
The method of manufacturing a steel strip, wherein the defect revealing prediction step is predicted using information relating to a distribution in a depth direction of a surface layer portion. In the manufacturing method of the steel strip according to any one of claims 1 to 7,
In the surface layer property measuring step, the surface layer portion of the steel strip measurement surface is AC magnetized, and at the same time, the change of the alternating magnetic flux generated due to the property of the surface layer portion is measured to measure the property of the surface layer portion of the steel strip. A method for producing a steel strip characterized by the following. In the manufacturing method of the steel strip according to any one of claims 1 to 8,
In the surface layer property measuring step, the steel strip is AC magnetized, and a change in AC magnetic flux caused by the property of the surface layer portion is detected by two or more magnetic sensors provided with the magnetic flux aligned in the width direction of the steel strip. A method for producing a steel strip, comprising measuring the properties of the surface layer of the steel strip based on a difference signal in the width direction of the detection signal. In the manufacturing method of the steel strip according to any one of claims 1 to 9,
In the surface layer property measurement step, the three legs of the E-shaped ferromagnetic material are arranged facing the steel strip surface and aligned in the width direction of the steel strip, and wound around the center leg. The steel strip is excited by applying an alternating current to the primary coil, and the surface layer of the steel strip is determined based on the voltage difference induced in the secondary coil wound around each of the two outer legs. A method for producing a steel strip characterized by measuring properties. In the manufacturing method of the steel strip according to any one of claims 1 to 9,
In the surface layer property measuring step, the leg portions of the comb-shaped ferromagnetic material in which the coil is wound around the leg portion are arranged side by side in the width direction of the steel strip so as to face the steel strip surface, and adjacent three pieces are arranged. While switching the selection of the leg group in time, among the selected three leg parts, an alternating current is applied to the primary coil wound around the central leg part to excite it, and the outer two A method of manufacturing a steel strip, comprising measuring a property of a surface layer portion of the steel strip based on a differential signal of a voltage induced in a secondary coil wound around each leg portion. In the manufacturing method of the steel strip according to any one of claims 1 to 11,
The surface layer property measuring step is a state in which the DC magnetization level of excitation of the steel strip is substantially close to zero, and the surface layer property is measured in the range of the frequency of AC magnetization from 100 kHz to 10 MHz. Manufacturing method of the belt.

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