Defect inspection device for alloyed hot dip galvanized steel plate and defect inspection method for alloyed hot dip galvanized steel plate

Abstract

To provide a defect inspection device for an alloyed hot dip galvanized steel plate and a defect inspection method for an alloyed hot dip galvanized steel plate that can discriminatingly detect a non-plating part and a scale-remaining pattern part of an alloyed hot dip galvanized steel plate.SOLUTION: A defect inspection device for an alloyed hot dip galvanized steel plate comprises: lighting means for lighting the surface of a steel plate; imaging means arranged on the opposite side from the lighting means with respect to he normal to he steel plate, and imaging a lit part on the steel plate; image processing means for processing an image signal obtained by the imaging means to extract a defect form on a surface of the steel plate; and defect determination means for classifying extracted defect forms into non-plating and other forms.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a defect inspection device for a galvannealed steel sheet and a defect inspection method for a galvannealed steel sheet. [Background technology]

[0002] Galvannealed (GA) steel sheets are widely used as surface-treated steel sheets for automobiles. Patent Document 1 discloses a technique for detecting minute defects on the surface of GA steel sheets by photographing backward-diffused light. This technique detects minute defects on the surface by positioning a camera on the same side as the light source with respect to the normal to the surface to be inspected and optimizing the angle of incidence of the illumination light on the surface to be inspected and the light-receiving angle of the camera.

[0003] Furthermore, Patent Document 2 discloses a technique for detecting defects by capturing specularly reflected light that has passed through a polarizing filter. Specifically, this technique involves placing a camera on the opposite side of the light source with respect to the normal to the surface to be inspected, and detecting surface defects by separating the reflected light using a polarizing filter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6822494 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-221495 Summary of the Invention [Problem to be solved by the invention]

[0005] One type of surface defect in GA steel sheets is uncoated areas. Because no zinc coating is present in these uncoated areas, exposing the surface of the steel substrate, the surface is a flat iron oxide layer. Furthermore, a unique pattern known as a scale pattern can appear on the surface of GA steel sheets. This occurs when hot-dip galvanizing is performed with scale remaining locally on the steel sheet surface. The zinc coating layer in the scale pattern area becomes thicker than normal areas because the locally remaining scale promotes the alloying reaction of the zinc coating on the steel sheet surface directly below the pattern area. Therefore, when the steel sheet is temper-rolled, the surface of the scale pattern area is rolled more strongly than the surrounding area, resulting in a flat surface.

[0006] In the method described in Patent Document 1, the uncoated and scale patterns on GA steel sheets are detected as darker than the formation because both have flat surfaces, resulting in weaker backscattered light intensity than specularly reflected light, making them difficult to distinguish. In the method described in Patent Document 2, both have flat surfaces and similar polarization characteristics, resulting in both uncoated and scale patterns being detected as brighter than the formation. For this reason, conventional methods have had difficulty distinguishing between uncoated and scale patterns on GA steel sheets with similar surface morphologies. However, since the scale pattern areas are zinc-plated to the required amount, they pose no problem from the perspective of corrosion resistance and are deemed shippable depending on the required surface quality and specifications. Therefore, a technology for distinguishing between uncoated and scale patterns has been demanded.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a defect inspection device for a galvannealed steel sheet and a defect inspection method for a galvannealed steel sheet that are capable of detecting uncoated portions and scale-remaining pattern portions of a galvannealed steel sheet by distinguishing them from the formation. [Means for solving the problem]

[0008] (1) The defect inspection device for galvannealed steel sheet according to the present invention is an illumination means for illuminating the surface of the steel plate; an imaging means that is disposed on the opposite side of the steel plate from the lighting means with respect to a normal line of the steel plate, and that images an illuminated portion on the steel plate; an image processing means for processing the image signal obtained by the imaging means to extract a defect form on the surface of the steel sheet; a defect determination means for classifying the extracted defect forms into non-plating forms and other forms; Equipped with.

[0009] (2) Furthermore, the defect inspection device for galvannealed steel sheet according to the present invention is the defect inspection device for galvannealed steel sheet according to the above (1), the lighting means is arranged so that the angle of incidence of light emitted from the lighting means with respect to the surface of the steel plate is between 5 degrees and 15 degrees with respect to the normal direction of the steel plate, The imaging means is disposed so that the angle of light received by the imaging means is between 35 degrees and 45 degrees on the opposite side to the lighting means with respect to the normal to the steel plate.

[0010] (3) Furthermore, the defect inspection device for galvannealed steel sheet according to the present invention is the defect inspection device for galvannealed steel sheet according to (1) or (2), The defect determining means determines whether the defect-like feature is a defect, an acceptable feature, or a normal part based on the difference between the brightness of the measurement point and the brightness of the formation.

[0011] (4) Furthermore, the defect inspection device for galvannealed steel sheet according to the present invention is the defect inspection device for galvannealed steel sheet according to the above (3), Among the defect-like forms, defects are unplated areas, and acceptable forms are scale residue patterns.

[0012] (5) A defect inspection method for a galvannealed steel sheet according to the present invention includes: an illumination step of illuminating the surface of the steel plate with an illumination means; an imaging step of imaging an illuminated portion on the steel plate by an imaging means disposed on an opposite side of the steel plate from the illumination means with respect to a normal line of the steel plate; an image processing step in which an image signal obtained in the imaging step is processed by an image processing means to extract a defect-like form on the surface of the steel sheet; a defect determination step in which the extracted defect forms are classified into non-plating forms and other forms by a defect determination means; Includes.

[0013] (6) Furthermore, the method for inspecting defects in a galvannealed steel sheet according to the present invention is the method for inspecting defects in a galvannealed steel sheet according to the above (5), The defect determination step determines whether the defect-like feature is a defect, an acceptable feature, or a normal part based on the difference between the brightness of the measurement point and the brightness of the formation.

[0014] (7) Furthermore, the method for inspecting defects in a galvannealed steel sheet according to the present invention is the method for inspecting defects in a galvannealed steel sheet according to the above (6), further comprising: Among the defect-like forms, defects are unplated areas, and acceptable forms are scale residue patterns.

[0015] (8) Furthermore, the method for inspecting defects in a galvannealed steel sheet according to the present invention is the method for inspecting defects in a galvannealed steel sheet according to the above (6) or (7), further comprising: The defect determination step identifies the defect type of the defect-like form based on at least one of the area of ​​the defect-like form, the image brightness of the defect-like form, and the shape of the defect-like form.

[0016] (9) Furthermore, the method for inspecting defects in a galvannealed steel sheet according to the present invention is the method for inspecting defects in a galvannealed steel sheet according to the above (8), further comprising: In the defect determination step, the defect type of the defect form is determined to be unplated when any one or more of the following (1) to (3) is satisfied: (1) The area of ​​the defect is 0.05 mm 2 Over 5.0mm 2 The following is the result. (2) The image brightness of the defect-like feature is lower than that of the texture portion. (3) The aspect ratio of the defect-like morphology is 0.8 or more and 1.2 or less. [Effects of the Invention]

[0017] According to the defect inspection device for galvannealed steel sheet and the defect inspection method for galvannealed steel sheet of the present invention, it is possible to distinguish and detect uncoated areas and scale pattern areas of a galvannealed steel sheet from the formation, thereby avoiding overdetection in which an acceptable scale pattern is mistaken for a harmful uncoated area, and enabling efficient surface inspection. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a defect inspection device for a galvannealed steel sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing the detection of unplated areas and the brightness of the remaining scale pattern when the light-receiving angle of the imaging means is changed in the defect inspection device for galvannealed steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A defect inspection device for a galvannealed steel sheet and a defect inspection method for a galvannealed steel sheet according to an embodiment of the present invention will be described with reference to the drawings.

[0020] The inventors focused on the fact that both the unplated surface and the surface of the scale pattern are flat, and inferred that when the surface is flat, the amount of light is greater in forward diffuse reflection on the side opposite to the light source than in backward diffuse reflection on the same side as the light source with respect to the normal to the steel sheet surface, making it easier to see the difference between the light reflected from the unplated surface and the light reflected from the scale pattern.

[0021] Therefore, the inventors investigated the angular dependency of the intensity (brightness) of forward diffused light. They found that the angular dependency of the intensity of diffusely reflected light from the surface of an unplated surface differs from the angular dependency of the intensity of diffusely reflected light from the surface of a scale remaining pattern. As a result, they found the conditions under which the unplated surface, the scale remaining pattern, and the formation can be distinguished. The present invention was completed based on the above findings, and its details are described below.

[0022] (Device configuration) As shown in FIG. 1, the defect inspection device 1 includes an illumination means 11, an imaging means 12, and an information processing device 13.

[0023] The lighting means 11 projects light onto the surface of the galvannealed steel sheet (hereinafter also simply referred to as "steel sheet") S to illuminate it, and for example, a projector can be used. The type of this projector is not particularly limited, and for example, halogen lighting, metal halide lighting, fluorescent lighting, LED lighting, xenon strobe lighting, etc., which are used in conventional surface defect inspections, can be used.

[0024] The lighting means 11 is arranged so that the incident angle (illumination angle) θ1 of the light emitted from the lighting means 11 with respect to the surface of the steel plate S is an angle of 5 degrees or more and 15 degrees or less with respect to the normal direction of the steel plate S. Details of the installation angle of this lighting means 11 will be described later.

[0025] The imaging means 12 captures an image of light reflected from the surface of the steel sheet S (illuminated portion on the steel sheet S), and may be, for example, an imaging device such as a CCD area sensor camera or a CCD line sensor camera. The spatial resolution of this imaging device may be set, for example, as follows: For example, when detecting non-plating defects of about φ1.0 mm, the spatial resolution of the imaging device is preferably 0.5 mm or less. Furthermore, when detecting minute non-plating defects of φ0.5 mm or less, the spatial resolution of the imaging device is preferably 0.2 mm or less.

[0026] The imaging means 12 is disposed on the opposite side of the illumination means 11 with respect to the normal to the steel sheet S. The imaging means 12 is disposed so that the light-receiving angle θ2 of the light received by the imaging means 12 is an angle of 35 degrees or more and 45 degrees or less with respect to the normal to the steel sheet S on the opposite side of the illumination means 11. The installation angle of the imaging means 12 will be described in detail later.

[0027] The information processing device 13 is configured by, for example, a personal computer, a workstation, etc. The information processing device 13 has as its main components a processor such as a CPU (Central Processing Unit), and a memory (main storage unit) such as a RAM (Random Access Memory) and a ROM (Read Only Memory), etc. The information processing device 13 also functions as an image processing means and a defect determination means.

[0028] The image processing means performs threshold processing on the image signal transmitted from the imaging means 12 to extract the defect-like form on the surface of the steel sheet S.

[0029] The defect determination means classifies the defect-like features extracted by the image processing means into bare spots and other features. That is, the defect determination means determines whether the defect-like feature is a defect (bare spot), an acceptable feature (scale pattern), or a normal part (neither bare spot nor scale pattern) based on the difference between the brightness of the measurement point and the brightness of the formation.

[0030] The defect determination means may also identify the defect type of the defect based on at least one of the area of ​​the defect, the image brightness of the defect, and the shape of the defect, where the "defect type" is, for example, a non-plating, a point defect, a linear defect, a scratch, a scab, a foreign matter defect, a dross defect, a scale remaining pattern, etc.

[0031] Furthermore, as will be described later, the defect determining means determines that the defect type of the defective form is unplated when any one or more of the following (1) to (3) is satisfied: (1) The area of ​​the defect is 0.05 mm2 Over 5.0mm 2 The following is the result. (2) The image brightness of the defect-like feature is lower than that of the texture portion. (3) The aspect ratio of the defect-like morphology is 0.8 or more and 1.2 or less.

[0032] 1 shows an example in which one information processing device 13 functions as both the image processing means and the defect determination means, but the image processing means and the defect determination means may each be configured as independent devices. In this case, the image processing means may be a computer or the like similar to the image processing means used in conventional surface defect inspection devices. Furthermore, the defect determination means may be a computer or the like that stores defect determination logic in advance.

[0033] (Arrangement of lighting means and imaging means) Next, the arrangement of the lighting means 11 (projector) and the imaging means 12 (imager) will be described. In the defect inspection device 1, as shown in Fig. 1, the imaging means 12 is arranged on the opposite side of the lighting means 11 with respect to the normal to the steel sheet S. Furthermore, the incident angle θ1 of the lighting means 11 is set to an angle of 5 degrees or more and 15 degrees or less with respect to the normal direction of the steel sheet S, and the light-receiving angle θ2 of the imaging means 12 is set to an angle of 35 degrees or more and 45 degrees or less with respect to the normal direction of the steel sheet S. The basis for setting these angles will be explained below.

[0034] The inventors have conducted extensive research into an optical arrangement that can detect unplated areas with a high signal-to-noise ratio and separate the brightness polarity of the unplated areas from the remaining scale pattern, i.e., the angle of incidence θ1 of the illumination means 11 and the angle of reception θ2 of the imaging means 12.

[0035] As a result, it was found that when the light-receiving angle θ2 of the imaging means 12 is increased, there are regions where the brightness polarity of the bare metal and the scale remaining pattern, i.e., the polarity of whether they are bright or dark relative to the formation, differs. Furthermore, it was found that when the light-receiving angle θ2 is increased, the brightness values ​​show a mountain-like distribution, and the height of the peak of the distribution and the brightness values ​​at the base differ between the bare metal and the scale remaining pattern.

[0036] Furthermore, it was found that increasing the incident angle θ1 narrows the region in which the signal polarities of the bare spot and the scale remaining pattern differ. Based on the above findings, the inventors have concluded that an apparatus configuration in which the illumination means 11 is arranged at a small incident angle θ1 and the imaging means 12 is arranged on the opposite side of the illumination means 11 with respect to the normal to the steel sheet S is suitable for inspecting bare spot defects.

[0037] By configuring it in this way, the unplated portion has a lower brightness than the background portion, while the scale remaining pattern appears as a bright spot with a high brightness, so the signal polarities of the unplated portion and the scale remaining pattern are different, making it easy to separate the two.

[0038] Fig. 2 is a graph showing the detection of bare spots and the brightness of the scale pattern when the light-receiving angle θ2 of the imaging means 12 is changed, with the horizontal axis representing the light-receiving angle θ2 of the imaging means 12 and the vertical axis representing the image brightness of the defect. From Fig. 2, it can be seen that an angle of 35° to 45° is suitable for the light-receiving angle θ2. As described above, a first aspect of the defect determination means of this embodiment determines whether the bare spot is bare, a scale pattern, or a formation by utilizing the fact that the brightness of the bare spot, the scale pattern, and the formation are different.

[0039] Next, as a second aspect of the defect determination means of this embodiment, a function for identifying and determining various defect types from defect shapes will be described. Surface defects extracted by the image processing means include not only highly harmful non-plating but also minor point defects and linear defects, which are less harmful. Therefore, the inventors recognized the importance of providing the defect determination means with the function for separating non-plating from these minor defects, and conducted extensive research into methods for classifying non-plating from other defects. As a result, it was found that non-plating has the following characteristics (1) to (3). In the following description, defects other than non-plating include, for example, point defects, linear defects, scratches, scuffs, foreign matter defects, dross defects, and scale residue patterns.

[0040] A scab is a defect caused by foreign matter trapped during the casting process. Therefore, the scab is elongated parallel to the rolling direction. Furthermore, because the scab area contains foreign matter, it is more convex than normal areas, and is rolled more aggressively than normal areas in the temper rolling process that follows the hot-dip galvanizing process. As a result, the surface shape of the scab area becomes flat.

[0041] Foreign object defects are defects caused by foreign objects adhering to the base steel or the surface after galvanization. In most cases, foreign object defects occur when foreign objects, such as hydraulic oil or grease used in the production line, drip onto the steel sheet. As a result, the foreign object defect is nearly perfectly round. Whether the foreign object adheres to the steel sheet before or after hot-dip galvanization, the surface shape of the foreign object defect area is highly irregular. If the foreign object adheres before galvanization, the alloying reaction of the hot-dip galvanization is inhibited, resulting in large irregularities on the surface of the foreign object defect area. Furthermore, if the foreign object adheres after galvanization, the surface irregularities of the foreign object defect area are large, reflecting the irregularities of the foreign object itself.

[0042] Dross defects are caused by zinc oxide lumps that form on the surface of the molten zinc bath during the hot-dip galvanizing process, or by zinc lumps that form when the amount of zinc applied to the steel sheet is reduced. As a result, dross defects have a shape that is close to a perfect circle. Because zinc oxide lumps or zinc lumps adhere to the steel sheet surface, they are rolled more aggressively than normal areas in the temper rolling process, resulting in a flat surface shape.

[0043] (1) Because a non-plating defect is harmful when its area is within a specific range, it can be determined whether it is a non-plating defect or not by its size (area). For example, if the non-plating defect is a very small defect whose area is smaller than a predetermined lower limit S1, it can be considered harmless. Furthermore, because non-plating defect cannot become extremely large due to its generation mechanism, a defect whose area exceeds a predetermined upper limit S2 can be determined to be a defect other than a non-plating defect, such as a scab or foreign matter defect, and a defect whose area is between S1 and S2 can be determined to be a non-plating defect.

[0044] The specific values ​​of the lower limit value S1 of the area and the upper limit value S2 of the area depend on the hot-dip galvanizing line to which this embodiment is applied and the strictness of the defect inspection. For example, S1=0.05 mm 2 , S2=5.0mm 2 It can be set as follows.

[0045] (2) Because the image brightness of a non-plating is lower than a specific threshold, a defect-like feature having a brightness equal to or greater than the specific threshold can be determined to be a defect-like feature other than a non-plating. When inspected using the optical arrangement described above (incident angle θ1 = 5° to 15°, receiving angle θ2 = 35° to 45°), a non-plating is detected as a dark defect, i.e., a defect with a lower brightness than the formation portion.

[0046] Then, when the image brightness of non-plating and other defects was checked, it was found that the image brightness of non-plating was below a specific threshold, and the image brightness of defects other than non-plating, such as scale patterns, scabs, and dross defects, was above this threshold.

[0047] That is, defects with an image brightness equal to or greater than this predetermined value can be determined to be defects other than non-plating, such as scale patterns, scabs, or dross defects, and defects with an image brightness less than the predetermined value can be determined to be non-plating. The image brightness of a defect represents the peak brightness value of the defective portion, i.e., the minimum brightness value among the pixels forming the defective portion. In addition to the peak brightness value, the image brightness of a defect may also be, for example, the average brightness value of the defective portion. In addition, multiple thresholds may be set to distinguish between non-plating and defects other than non-plating, in order to avoid the influence of image noise.

[0048] (3) When the shape of the defect shape was investigated, it was found that the unplated parts had a shape close to a perfect circle. On the other hand, it was found that defects with low circularity, such as vertically elongated defects or horizontally elongated defects, were defects other than unplated parts, such as scratches or scale patterns. Therefore, whether a defective part is an unplated part can be determined using image feature quantities that represent the shape of the defect, such as circularity, out-of-roundness, or aspect ratio.

[0049] Circularity is the ratio of the perimeter of a circle with the same area to the perimeter of the actual shape. Circularity is the difference in the radii of two concentric geometric circles when a circular object is sandwiched between them and the gap between the two circles is at its smallest. The aspect ratio is the ratio of the length and width of the defect.

[0050] When the aspect ratio is used as an image feature quantity that represents the shape of a defect, it is possible to determine and separate defects such that the value is around 1.0 (for example, 0.8 to 1.2) as unplated defects and other values ​​as other defects.

[0051] Based on the findings of (1) to (3) above, in a second aspect of the defect determination means of this embodiment, whether or not a defect is unplated is determined based on at least one of the area of ​​the defect-like feature, the image brightness of the defect-like feature, and the shape of the defect-like feature. This enables the defect determination means to determine whether or not a defect is unplated in the steel sheet S, separately from other minor defects.

[0052] According to the defect inspection device for galvannealed steel sheet and the defect inspection method for galvannealed steel sheet of the above-described embodiments, it is possible to distinguish and detect uncoated portions and scale pattern portions of a galvannealed steel sheet from the formation. This makes it possible to avoid overdetection, in which an allowable scale pattern is mistaken for a harmful uncoated portion, and enables efficient surface inspection.

[0053] (Example) An example of a defect inspection device for a galvannealed steel sheet and a defect inspection method for a galvannealed steel sheet according to the present invention will be described below.

[0054] In this example, a cut sheet sample of galvannealed steel sheet, on which the uncoated and scale patterns had been confirmed in advance, was subjected to a defect detection process using a defect detection device equipped with the optical system shown in Fig. 1. In this case, the incident angle θ1 of the lighting means was set to 10 degrees, and the light-receiving angle θ2 of the photographing means was set to 40 degrees.

[0055] In the defect detection process, areas where the intensity of diffuse reflected light was 5% or more lower than the formation were judged to be unplated, and areas where the intensity of diffuse reflected light was 4% or more higher than the formation were judged to be scale remaining patterns. The unplated area detection rate, defined as the ratio of the number of unplated areas judged to be unplated by the defect detection process of the present invention to the number of unplated areas confirmed in advance, was 100%, confirming that this is at a level sufficient for practical use.

[0056] In addition, with regular reflected light where the light-receiving angle θ2 was set to 10 degrees, the same as the incident angle θ1, no significant difference in brightness (light intensity) was observed between the bare metal, the scale remaining pattern, and the formation, and it was not possible to distinguish between the bare metal, the scale remaining pattern, and the formation.

[0057] The defect inspection device and defect inspection method for galvannealed steel sheet according to the present invention have been specifically described above using the detailed description and examples for carrying out the invention, but the gist of the present invention is not limited to these descriptions and should be broadly interpreted based on the claims. Furthermore, various changes and modifications based on these descriptions are also included within the gist of the present invention. [Explanation of symbols]

[0058] 1. Defect inspection equipment 11 Lighting means 12 Imaging means 13 Information processing equipment S steel plate θ1 Incident angle θ2 acceptance angle

Claims

1. an illumination means for illuminating the surface of the steel plate; an imaging means that is disposed on the opposite side of the steel plate from the lighting means with respect to a normal line of the steel plate, and that images an illuminated portion on the steel plate; an image processing means for processing the image signal obtained by the imaging means to extract a defect form on the surface of the steel sheet; a defect determination means for classifying the extracted defect forms into non-plating forms and other forms; A defect inspection device for galvannealed steel sheets.

2. the lighting means is arranged so that the angle of incidence of light emitted from the lighting means with respect to the surface of the steel plate is between 5 degrees and 15 degrees with respect to the normal direction of the steel plate, the imaging means is disposed so that the angle of light received by the imaging means is 35 degrees or more and 45 degrees or less on the opposite side to the lighting means with respect to the normal line of the steel plate. The defect inspection device for galvannealed steel sheet according to claim 1.

3. 3. The defect inspection device for a galvannealed steel sheet according to claim 1 or 2, wherein the defect determination means determines whether the defect form is a defect, an acceptable form, or a normal part based on a difference between the brightness of the measurement point and the brightness of the formation.

4. 4. The defect inspection device for galvannealed steel sheet according to claim 3, wherein the defect among the defect forms is a bare spot, and the allowable form is a scale remaining pattern.

5. an illumination step of illuminating the surface of the steel plate with an illumination means; an imaging step of imaging an illuminated portion on the steel plate by an imaging means disposed on an opposite side of the steel plate from the illumination means with respect to a normal line of the steel plate; an image processing step in which an image signal obtained in the imaging step is processed by an image processing means to extract a defect-like form on the surface of the steel sheet; a defect determination step in which the extracted defect forms are classified into non-plating forms and other forms by a defect determination means; A method for inspecting defects in a galvannealed steel sheet, comprising:

6. 6. The defect inspection method for a galvannealed steel sheet according to claim 5, wherein the defect determination step determines whether the defective form is a defect, an acceptable form, or a normal part based on a difference between the brightness of the measurement point and the brightness of the formation.

7. 7. The method for inspecting defects in a galvannealed steel sheet according to claim 6, wherein the defect among the defect-like forms is a bare spot, and the allowable form is a scale remaining pattern.

8. 8. The defect inspection method for a galvannealed steel sheet according to claim 6 or 7, wherein the defect determination step identifies a defect type of the defect-like form based on at least one of an area of ​​the defect-like form, an image brightness of the defect-like form, and a shape of the defect-like form.

9. 9. The defect inspection method for a galvannealed steel sheet according to claim 8, wherein in the defect determination step, the defect type of the defective form is determined to be uncoated when any one or more of the following (1) to (3) are satisfied: (1) The area of ​​the defect is 0.05 mm ２ Over 5.0 mm ２ The following is the result. (2) The image brightness of the defect-like feature is lower than that of the texture portion. (3) The aspect ratio of the defect-like shape is 0.8 or more and 1.2 or less.

Images