JP2017146296A - Method and apparatus for evaluating surface property of hot-dip galvanized steel sheet, and method for manufacturing hot-dip galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for evaluating surface properties of a hot-dip galvanized steel sheet, capable of accurately, quantitatively evaluating the level of rippled surface defect of the hot-dip galvanized steel sheet without being limited to specific manufacturing conditions.SOLUTION: The method and apparatus for evaluating surface properties of a hot-dip galvanized steel sheet, capable of evaluating the level of rippled surface defect of the hot-dip galvanized steel sheet comprises the steps of: calculating an undulation curve showing an undulation shape in the width direction of the hot-dip galvanized steel sheet by applying a phase compensation filter to a cross sectional curve showing a cross sectional shape in the width direction of the hot-dip galvanized steel sheet (the step S3); and evaluating the level of rippled surface defect of the hot-dip galvanized steel sheet using the average length of undulation elements constituting the undulation curve as an evaluation index.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface property evaluation method for a hot dip galvanized steel sheet, a surface property evaluation apparatus for a hot dip galvanized steel sheet, and a method for producing a hot dip galvanized steel sheet.

  Generally, in the manufacturing process of a hot dip galvanized steel sheet, after passing the steel sheet through a pot containing hot dip galvanizing, the thickness of the hot dip galvanizing adhered to the steel sheet surface is made uniform by wiping the steel sheet surface. In such a hot dip galvanized steel sheet manufacturing process, unevenness in the thickness of the hot dip galvanizing occurs during the wiping process and the subsequent solidification process of the hot dip galvanizing. (Also called). In product manufacturing and manufacturing process development, it is necessary to evaluate the degree of a bath defect. From such a background, Patent Document 1 proposes a method for evaluating the degree of a bath defect visually in three stages of ◯, Δ, and X. Patent Document 2 proposes a method of measuring several points on the surface roughness Ra of a hot-dip galvanized steel sheet and quantitatively evaluating the degree of the hot water defect based on the standard deviation.

JP-A-10-226863 Japanese Patent No. 3278607

  However, according to the method described in Patent Document 1, since the degree of the bath defect is visually evaluated, the evaluation results vary depending on the evaluator's subjectivity. On the other hand, the evaluation method based on the standard deviation of the surface roughness Ra described in Patent Document 2 is based on an example under specific manufacturing conditions, and the presence or absence of a temper rolling process, a chemical conversion process, and a roll roughness. It may not be effective under other manufacturing conditions such as differences in degrees. For this reason, when the manufacturing conditions are changed, the degree of the hot water defect cannot be accurately evaluated, and as a result, it becomes difficult to manufacture the hot-dip galvanized steel sheet with a high yield.

  The present invention has been made in view of the above-mentioned problems, and the object thereof is not limited to specific manufacturing conditions, and the degree of the sag defect of the hot-dip galvanized steel sheet can be accurately and quantitatively evaluated. An object of the present invention is to provide a surface property evaluation method and a surface property evaluation apparatus for a hot dip galvanized steel sheet. Moreover, the other object of this invention is to provide the manufacturing method of the hot dip galvanized steel plate which can manufacture a hot dip galvanized steel plate with a sufficient yield.

  The surface property evaluation method for a hot dip galvanized steel sheet according to the present invention is a method for evaluating the surface property of a hot dip galvanized steel sheet, which evaluates the degree of the hot water defect of the hot dip galvanized steel sheet, By applying a phase compensation filter to the cross-sectional curve indicating the cross-sectional shape, a waviness curve indicating the waviness shape in the width direction of the hot-dip galvanized steel sheet is calculated, and the average length of the waviness elements constituting the waviness curve The method includes a step of evaluating the degree of the hot-dip defect of the hot-dip galvanized steel sheet using as an evaluation index.

  The surface property evaluation method for a hot dip galvanized steel sheet according to the present invention is the above invention, wherein the waviness curve is extracted at a plurality of longitudinal positions of the hot dip galvanized steel sheet, and the evaluation index calculated from each waviness curve The average value or the maximum value is used to evaluate the degree of the dip in the hot dip galvanized steel sheet.

  In the above invention, the method for evaluating the surface properties of a hot-dip galvanized steel sheet according to the present invention is a two-dimensional first method having a cutoff value larger than the cutoff value of the phase compensation filter for the two-dimensional image including the cross-sectional curve. By applying a two-phase compensation filter, an average value or maximum value of the uneven height on the surface of the hot dip galvanized steel sheet is calculated, and the hot dip galvanizing is performed based on the calculated average value or maximum value of the uneven height. The method includes the step of evaluating the degree of the hot water defect of the steel sheet.

  In the above invention, the surface property evaluation method for a hot dip galvanized steel sheet according to the present invention measures the uneven shape of the surface of the hot dip galvanized steel sheet, and a height equal to or higher than a predetermined first height threshold is a predetermined first area. The total of the convex defect portion having a continuous area that is equal to or greater than the threshold value and the concave defect portion having a height that is equal to or less than the predetermined second height threshold value that is smaller than the first height threshold value and that has a continuous area equal to or greater than the predetermined second area threshold value Calculating each area from the measurement result of the concave and convex shape, calculating a ratio of the sum of the total area of the convex defect portion and the total area of the concave defect portion in the inspection region as an uneven defect portion area ratio; The brightness of the surface of the hot dip galvanized steel sheet is measured, the inspection area is divided into a plurality of small areas, the average brightness of the surface in each small area is calculated from the measurement result of the brightness, and the average in the adjacent small areas Small area where the difference in brightness is greater than or equal to a predetermined value Extracting a certain small region as a luminance defect portion, calculating a ratio of the total area of the luminance defect portion in the inspection region as a luminance defect portion area ratio, and the uneven defect portion area ratio and the luminance defect portion area ratio, And a step of performing grade evaluation of the unevenness defect in the inspection region using an evaluation index obtained by linearly combining.

  The surface property evaluation apparatus for hot dip galvanized steel sheet according to the present invention is a surface property evaluation apparatus for hot dip galvanized steel sheet, which evaluates the degree of hot water defects in the hot dip galvanized steel sheet, in the width direction of the hot dip galvanized steel sheet. Means for calculating a waviness curve indicating the waviness shape in the width direction of the hot-dip galvanized steel sheet by applying a phase compensation filter to the cross-sectional curve showing the cross-sectional shape, and the average of the waviness elements constituting the waviness curve And a means for calculating a length as an evaluation index when evaluating the degree of the hot water defect of the hot-dip galvanized steel sheet.

  The manufacturing method of the hot dip galvanized steel sheet according to the present invention is based on controlling the manufacturing conditions based on the degree of the hot dip in the hot dip galvanized steel sheet evaluated by the surface property evaluation method of the hot dip galvanized steel sheet according to the present invention. The method includes a step of manufacturing a hot dip galvanized steel sheet.

  According to the surface property evaluation method and the surface property evaluation apparatus for hot dip galvanized steel sheet according to the present invention, the degree of the sag defect of the hot dip galvanized steel sheet is accurately and quantitatively evaluated without being limited to specific manufacturing conditions. it can. Moreover, according to the manufacturing method of the hot dip galvanized steel plate which concerns on this invention, a hot dip galvanized steel plate can be manufactured with a sufficient yield.

FIG. 1 is a flowchart showing a flow of a surface property evaluation method for a hot-dip galvanized steel sheet according to the first embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the length of the undulation element. FIG. 3 is a diagram showing an example of a two-dimensional image of the surface of the hot dip galvanized steel sheet. FIG. 4 is a diagram showing an example of a cross-sectional curve of a hot-dip galvanized steel sheet. FIG. 5 is a diagram showing a waviness curve obtained from the cross-sectional curve shown in FIG. FIG. 6 is a diagram showing the relationship between the evaluation index of the example of the present invention and the rating of the degree of the bath defect given visually. FIG. 7 is a diagram showing the relationship between the evaluation index of the comparative example and the rating of the degree of the bath defect given visually. FIG. 8 is a flowchart showing the flow of the surface property evaluation method for hot-dip galvanized steel sheet according to the second embodiment of the present invention. FIG. 9 is a diagram showing the relationship between the maximum value of the average length of the swell element and the rating of the degree of the bath defect given visually. FIG. 10 is a diagram showing a relationship between the maximum value of the unevenness height and the rating of the degree of the bathing defect given visually. FIG. 11 is a diagram showing the relationship between the average value of the unevenness height and the rating of the degree of the bath defect given visually. FIG. 12 is a flowchart showing the flow of the surface property evaluation method for hot-dip galvanized steel sheet according to the third embodiment of the present invention. FIG. 13 is a diagram showing the relationship between the area ratio of the concavo-convex defect portion and the rating of the degree of the concavo-convex defect given visually. FIG. 14 is a diagram for explaining a method of extracting a luminance defect portion. FIG. 15 is a diagram showing the relationship between the luminance defect area ratio and the rating of the degree of unevenness visually imparted. FIG. 16 is a diagram showing the relationship between the evaluation index and the score of the degree of the unevenness defect given visually.

  Conventionally, the degree of the dripping defect has been evaluated by the operator visually observing the surface of the hot-dip galvanized steel sheet and expressing the degree of the dripping defect with a plurality of grades. Here, unevenness at intervals of several millimeters or more in the plane direction is seen in the bathing defect, but in the case of a severe bathing defect, the sagging with unevenness with a small period overlaps and becomes a large sagging. From this, the inventors of the present invention focused on the size of the interval between the concaves and convexes, and evaluated the average length of the waviness, thereby quantitatively evaluating the bath defect having a high correlation with the visual evaluation of the operator. I came up with the idea that an index could be obtained.

  The average swell length is defined for one cross-sectional curve. For this reason, in order to quantify the degree of the bath defect with high accuracy, it is necessary to calculate the average waviness length for a plurality of cross-sectional curves and to calculate the average value or the maximum value of the average waviness length. On the other hand, the average length of waviness takes a small value for any cross-section curve in a steel plate without a dripping defect, whereas in a steel plate with a dripping defect, the average waviness depends on the uneven part. There are places where the length takes a large value.

  In addition, as a hot dip galvanized steel plate used for this invention, a hot dip galvanized steel plate, a zinc-aluminum alloy plated steel plate, a zinc-iron alloy plated steel plate, a zinc-magnesium plated steel plate, a zinc-aluminum-magnesium alloy plated steel plate, etc. are used. be able to. In addition, as the hot dip galvanized steel sheet used in the present invention, a steel sheet having a surface treatment film formed on the surface of the hot dip galvanized steel sheet by chemical conversion treatment or the like can also be used.

  Hereinafter, with reference to drawings, the surface property evaluation method of the hot dip galvanized steel sheet which is the 1st-3rd embodiment of the present invention is explained.

[First Embodiment]
First, with reference to FIGS. 1-7, the surface property evaluation method of the hot dip galvanized steel plate which is the 1st Embodiment of this invention is demonstrated.

  FIG. 1 is a flowchart showing a flow of a surface property evaluation method for a hot-dip galvanized steel sheet according to the first embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the length of the undulation element.

  As shown in FIG. 1, in the surface property evaluation method for a hot dip galvanized steel sheet according to the first embodiment of the present invention, first, a hot dip galvanization is performed by using a contact type or non-contact type surface roughness measuring device. A two-dimensional image of the concavo-convex shape of the surface of a steel plate (hereinafter abbreviated as a steel plate) is measured (step S1). Next, after removing the warp component of the steel plate itself from the measured two-dimensional image by shape correction, a plurality of cross-sectional curves in the width direction are extracted from the two-dimensional image (step S2). In addition, it is good to extract the cross-sectional curve of the width direction about 10 per 1 m of length of a steel plate. Moreover, it is desirable that the location where the cross-sectional curve is extracted is a location where there is no defect other than a bath defect.

  Next, a waviness curve indicating the waviness shape in the width direction of the steel sheet is calculated by applying a phase compensation filter (high-pass filter for wavelength) to each extracted cross-sectional curve (step S3). Here, the high-pass filter for the wavelength means a filter that passes a wavelength longer than the cutoff value λc1. The cut-off value λc1 of the phase compensation filter is a value that can sufficiently remove the calculated average roughness Ra of the steel sheet, and may be set within a range of, for example, 0.8 to 2.5 mm. Next, within a predetermined evaluation length range of the undulation curve, a length D of a plurality of undulation elements constituting the undulation curve is calculated, and an average value of the calculated lengths D of the plurality of undulation elements is calculated. The average length WSm of the waviness element is calculated (step S4). In addition, the evaluation length of the undulation curve may be determined based on the average length of the dip defect obtained previously, and it is desirable not to include the end in the width direction of the hot dip galvanized steel sheet. Further, as shown in FIG. 2, the length D of the undulation element is a point where the zero crossing from the positive to the negative of the undulation curve C (start point of the valley) P1 is a point (start of the valley) from the next positive to negative zero crossing. Point) It means the length up to P2, in other words, the length of one wave of swell.

  Next, the average value or the maximum value of the average length WSm of the undulation element calculated from each undulation curve is calculated (step S5), and the average value or the maximum value of the calculated average length WSm of the undulation element is used as an evaluation index. As an evaluation, the degree of hot water defects in the steel sheet is evaluated. Specifically, the smaller the average value or the maximum value of the average length WSm of the swell element, the smaller the hot water defect and the better the surface property. The average value or the maximum value of the average length WSm of the undulation element can take a large value within the measurement range of the undulation curve C. ) Is suppressed to 5 points (inferior), so an upper limit value (for example, 15) may be set to the average value or the maximum value of the average length WSm of the swell elements.

[Example 1]
In this example, for 40 hot-dip galvanized steel sheet samples manufactured by changing the manufacturing conditions (with or without temper rolling treatment and chemical conversion treatment) in a continuous hot dip galvanizing facility, the degree of the sag defect is shown as an example of the present invention. And it evaluated using the comparative example. In the comparative example, the average value (arithmetic average waviness) of the absolute value of the height is calculated for a plurality of waviness curves obtained by the same processing as the present invention, and the average value of the arithmetic average waviness obtained from each waviness curve is calculated. It was used as an evaluation index Wa for a bath defect. The evaluation length lr of the undulation curve was 44.2 mm. In addition, for each sample, a hot water scoring score was given visually in increments of 0.5 points from 0 points (good) to 5 points (poor). Moreover, in the present Example, the uneven | corrugated shape of the surface was measured about the range of about 30 mm x 40 mm using the non-contact-type optical surface roughness measuring apparatus (the Keyence Corporation make, VR-3000). The cut-off value λc1 of the phase compensation filter was 0.8 mm. A two-dimensional image of the measured surface irregularities is shown in FIG. 4 shows a cross-sectional curve along the line segment L shown in FIG. 3, and FIG. 5 shows a waviness curve obtained from the cross-sectional curve shown in FIG. In addition, since the influence of shape correction remained in the edge part (hatch area | region shown in FIG. 4, 5) of the width direction of a hot dip galvanized steel plate, it excluded from the process target range.

FIG. 6 is a diagram showing the relationship between the maximum value (unit: mm) of the average length WSm of the swell elements obtained by the example of the present invention and the hot water score. FIG. 7 is a diagram showing the relationship between the evaluation index Wa (unit: μm) obtained by the comparative example and the hot water score. As apparent from the comparison between FIG. 6 and FIG. 7, the maximum value of the average length WSm of the swell element obtained by the example of the present invention is higher than the evaluation index Wa obtained by the comparative example. Correlation with anyone's score is deep. Specifically, in the example of the present invention shown in FIG. 6, the square value (decision coefficient) R ² of the correlation coefficient R was 0.80, whereas in the comparative example shown in FIG. ² was 0.37. From the above, according to the example of the present invention, it is possible to accurately and quantitatively evaluate the degree of the sag defect in the hot-dip galvanized steel sheet without being limited to specific manufacturing conditions without performing visual evaluation. Was confirmed. Moreover, a hot dip galvanized steel sheet can be manufactured with a sufficient yield by manufacturing a hot dip galvanized steel sheet by controlling manufacturing conditions based on the degree of the hot-dip defect of the hot dip galvanized steel sheet evaluated by the example of this invention.

[Second Embodiment]
Next, with reference to FIGS. 8-11, the surface property evaluation method of the hot dip galvanized steel plate which is the 2nd Embodiment of this invention is demonstrated.

  A mild bath defect has the feature that the dripping is single-shot, and the difference in unevenness is small due to undulation in a large cycle. For this reason, it may not be possible to evaluate a slight bathing defect with high accuracy by evaluating only the average length WSm of the waviness element. Therefore, the inventors of the present invention considered that it is necessary to extract the uneven height of the single-shot dripping that occurs in order to subdivide and evaluate this mild dripping defect. Then, the inventors of the present invention apply a phase compensation filter (high-pass filter for wavelength) having a large cutoff value (several mm or more) different from that for evaluating a severe bath defect, thereby increasing the unevenness. It was found that the evaluation with the direction parameter was effective for the evaluation of mild bath defects, and the evaluation index was highly correlated with the bath score.

  FIG. 8 is a flowchart showing the flow of the surface property evaluation method for hot-dip galvanized steel sheet according to the second embodiment of the present invention. Note that the processing contents of steps S11 to S15 shown in FIG. 8 are the same as the processing contents of steps S1 to S5 shown in FIG. 1, so only the processing after step S6 will be described below.

  As shown in FIG. 8, in the surface texture evaluation method for hot-dip galvanized steel sheet according to the second embodiment of the present invention, after the processing in step S15 is completed, shape correction is performed from the two-dimensional image measured in step S11. The warping component of the steel plate itself is removed. The shape correction method for removing the warp component is desirably the same as the method used in step S12, including the conditions. This is because the warpage of the steel sheet is the same because the measurement object is the same hot-dip galvanized steel sheet. As a result, the cross-sectional curve in the width direction obtained in step S12 is included in the two-dimensional image from which the warp component has been removed. Next, a two-dimensional phase compensation filter (high-pass filter for wavelength) having a cutoff value different from the phase compensation filter used in the process of step S12 for the two-dimensional image from which the warp component has been removed. ) Is applied (step S16). Specifically, in the process of step S16, a two-dimensional phase compensation filter having a cutoff value λc2 larger than the cutoff value λc1 of the phase compensation filter used in the process of step S13 is used. Specifically, the cut-off value λc2 is preferably about twice the cut-off value λc1, and is preferably set within a range of 2.5 to 10.0 mm.

  And, the average value or maximum value of the two-dimensional unevenness height of the steel sheet surface is calculated from the curve obtained by applying a two-dimensional phase compensation filter with a cutoff value λc2 for a plurality of cross-sectional curves, Using the calculated average value or maximum value of the unevenness height as an evaluation index, the degree of the bath defect of the steel sheet is evaluated (step S17). Thereby, the precision of the quantification of a mild bath defect (for example, the range of the hot bath score 0 to 0.5) can be increased. In addition, the definition of the average value of the concavo-convex height conforms to the two-dimensional arithmetic average roughness Sa shown in the following formula (1) specified in the ISO standard, and the definition of the maximum value of the concavo-convex height is specified in the ISO standard. Only the cut-off value to be used is different according to the two-dimensional maximum height Sz shown in the following formula (2). Here, in the formula (1), the parameter A indicates the evaluation range, and in the formulas (1) and (2), the parameter Z (x, y) indicates the two-dimensional uneven height. Further, there is a relationship represented by the following mathematical formula (3) between the evaluation range A and x, y.

However, maxZ (x, y) and min | Z (x, y) | are values for the evaluation range A.

[Example 2]
As described above, the accuracy of quantification may not be high with respect to mild hot water defects only by the surface property evaluation method of the hot-dip galvanized steel sheet according to the first embodiment of the present invention. For this reason, in this case, the average value or the maximum value of the uneven height obtained by the processing of steps S16 and S17 shown in FIG. 8 is used as a supplement to the evaluation index. In the present embodiment, the degree of the hot water defect is determined for another 10 hot dip galvanized steel sheet samples (hot water score 0 to 0.5) manufactured by changing the manufacturing conditions in a continuous hot dip galvanizing facility. It evaluated using the example and the comparative example. The cutoff value λc2 of the phase compensation filter was 5.0 mm. On the other hand, the cutoff value λc1 of the phase compensation filter in the comparative example was set to 0.8 mm, which is the same as that in the first embodiment. Similarly, since the influence of the shape correction remains on the end of the hot dip galvanized steel sheet, it was excluded from the processing target range. The evaluation range A was an area of 49.9 mm in the width direction and 34.1 mm in the longitudinal direction.

FIG. 9 is a diagram showing the relationship between the maximum value (unit: mm) of the average length WSm of the undulation element and the hot water score. FIG. 10 is a diagram showing a relationship between the maximum unevenness height value Sz (unit: μm) and the bath score. FIG. 11 is a diagram showing the relationship between the average value Sa (unit: μm) of the unevenness height and the bath score. As apparent from FIGS. 9 to 11, the maximum value Sz or the average value Sa of the uneven height is higher than the maximum value of the average length WSm of the waviness element for the samples having the hot water score 0 to 0.5. The correlation is deeper. Specifically, in the example shown in FIG. 9, while the square value of the correlation coefficient R (coefficient of determination) R ² was 0.04, the coefficient of determination R ² in the example shown in FIG. 10 0. 74, in the example shown in FIG. 10, the determination coefficient R ² was 0.66. As described above, after performing the surface property evaluation method for the hot-dip galvanized steel sheet according to the first embodiment of the present invention, the process of steps S16 and S17 shown in FIG. It was confirmed that the accuracy of evaluation could be improved.

[Third Embodiment]
Finally, with reference to FIGS. 12-16, the surface property evaluation method of the hot dip galvanized steel plate which is the 3rd Embodiment of this invention is demonstrated.

  Even if the dripping defect is good, another irregularity defect may be a problem. Therefore, in the present embodiment, evaluation of a bathing defect and evaluation of another concavo-convex defect are simultaneously performed using another evaluation index. Specifically, the inventors of the present invention have conceived that by using the measured data, an evaluation index for quantifying the degree of the hot water defect and the degree of another uneven defect can be calculated. Here, another irregularity defect to be mainly evaluated is a defect called a dent, and the oxide on the surface of the molten zinc bath is involved in the hot dip galvanizing process, and the portion centering on the oxide becomes uneven. Generated by being plated.

  In addition, the inventors of the present invention have found that the degree of irregularity defects correlates with the area ratio with irregularities exceeding a certain threshold when evaluated visually. However, the inventors of the present invention are not sufficient to evaluate by themselves because the unevenness on the surface becomes small when the temper rolling treatment and the chemical conversion treatment are performed, particularly in the case of a light unevenness defect of a moderate degree. It was found that the difference in brightness caused by the traces of unevenness also needs to be added to the evaluation. Furthermore, the inventors of the present invention have found that a quantitative index of uneven defects having a high correlation with the hot water score can be obtained by linearly combining the uneven defect area ratio and the luminance defect area ratio. did.

  FIG. 12 is a flowchart showing the flow of the surface property evaluation method for hot-dip galvanized steel sheet according to the third embodiment of the present invention. Note that the processing contents of steps S21 to S25 shown in FIG. 12 are the same as the processing contents of steps S1 to S5 shown in FIG. 1, and therefore only the processing after step S26 will be described below.

As shown in FIG. 12, in the surface texture evaluation method for hot dip galvanized steel sheet according to the third embodiment of the present invention, after the process of step S25 is completed, first, the uneven shape on the surface of the steel sheet is measured, A convex defect portion having a height that is equal to or greater than a first height threshold and a height that is less than a predetermined second height threshold that is smaller than the first height threshold. Calculate the total area of concave defects that have a continuous area of two or more area thresholds from the measurement results of the concave and convex shapes, and the ratio of the sum of the total area of convex defects and the total area of concave defects in the inspection area Is calculated as the area ratio of the concavo-convex defect portion (step S26). The first height threshold and the second height threshold are set within a range of ± 1.0 to ± 10.0 μm, and the first area threshold and the second area threshold are set within a range of 0.1 to 100.0 mm ^2. Good.

  Next, the luminance of the surface of the steel plate is measured (step S27), the inspection area is divided into a plurality of small areas, and the average luminance of each small area is calculated from the luminance measurement result. Then, a small area having a small area whose average luminance difference is equal to or larger than a predetermined value in adjacent small areas is extracted as a luminance defect portion, and the ratio of the total area of the luminance defect portion in the inspection area is determined as the luminance defect portion. The area ratio is calculated (step S28). Specifically, when the difference between the maximum value and the minimum value of the average brightness of the small area adjacent to the small area to be evaluated is a predetermined value or more, or the average brightness of the small area to be evaluated and the small area to be evaluated When the difference from the average luminance of the small area adjacent to the pixel is equal to or greater than a predetermined value, the small area to be evaluated is extracted as a luminance defect portion. The size of one side of the small area may be set within a range of 0.1 to 5.0 mm, and the predetermined value may be set within a range of 5 to 50 with respect to a gray scale of 0 to 255. And the grade evaluation of the unevenness | corrugation defect in a test | inspection area | region is performed with the evaluation parameter | index which linearly combined the uneven | corrugated defect part area rate and the brightness | luminance defect part area rate (step S29). Thereby, the evaluation of the level of the bath defect and the evaluation of the level of another uneven defect can be performed simultaneously.

[Example 3]
In this example, the degree of irregularity defects was determined for the 23 hot-dip galvanized steel sheet samples produced by changing the production conditions (with or without temper rolling and chemical conversion treatment) in a continuous hot-dip galvanizing facility. And it evaluated using the comparative example. About each sample, the evaluation (unevenness | corrugation rating) of the degree of unevenness | corrugation defect was provided by 0.1 point | interval of 0 point (good) to 5 points (inferior) visually. With respect to the measurement results, a portion where a height of +1.0 μm or more from the reference surface is continuous for an area of 0.56 mm ² or more was defined as a convex defect portion. Further, a portion where a height of −1.0 μm or less from the reference plane is continuous for an area of 0.56 mm ² or more was defined as a concave defect portion. However, in the vicinity of the boundary of the measurement range, the influence of the shape correction may not be completely removed, so it was excluded from the defective part. The area ratio obtained by dividing the sum of the area of the convex defect portion and the area of the concave defect portion by the area of the measurement range excluding the vicinity of the boundary was defined as the uneven defect portion area ratio. Since the upper limit of the concavo-convex rating is suppressed to 5 points, an upper limit is set for the concavo-convex defect area ratio. In this example, the upper limit value was set to 0.148. FIG. 13 shows the relationship between the irregularity defect area ratio (unit:%) and the irregularity score. As shown in FIG. 13, a certain degree of correlation is found between the obtained evaluation index and the unevenness score, but it is not sufficient.

Next, the brightness of the surface of the steel plate was measured. In the non-contact optical surface roughness measuring device (manufactured by Keyence Co., Ltd., VR-3000), it is possible to measure the brightness with an image at the same time as the unevenness measurement, and the measurement result was used. The measurement result was converted to a gray scale of 0 to 255, divided into small areas having a size corresponding to the size of the uneven defect to be extracted, and the average luminance of the small area was calculated. In this example, the size of the small area was about 1.03 mm in length and about 1.03 mm in width. This small area was further measured by dividing it into 44 pixels vertically and 44 pixels horizontally. Next, as shown in FIG. 14, with respect to the small region R ₀ to be evaluated, the maximum value (75 in this example) and the minimum value of the average luminance of 16 surrounding small regions R _n including the small region R _0. A difference of (64 in this example) was calculated, and a portion where the difference exceeded the threshold was determined as a luminance defect portion. In this embodiment, the threshold is set to 10. The above calculation was performed for all the small regions, and the area ratio of the luminance defect portion obtained by dividing the total sum of the areas of the luminance defect portions by the area of the measurement range excluding the vicinity of the boundary was defined as the luminance defect portion area ratio. Similarly, the upper limit is set to 0.402 for the luminance defect area ratio. FIG. 15 shows the relationship between the luminance defect area ratio (unit:%) and the unevenness score. As for the unevenness score, a plurality of persons gave an evaluation of the degree of unevenness defect in increments of 1 point from 0 (good) to 5 (inferior), and took the average value. The fact that the luminance defect area ratio shown in FIG. 15 is vertically divided into two suggests that unevenness defects can be broadly classified into those that appear as luminance defects and those that do not appear.

Finally, the evaluation index is calculated by weighting and summing the uneven defect portion area ratio and the luminance defect portion area ratio. When the uneven defect area ratio is X, the luminance defect area ratio is Y, and the respective weights are a and b, the evaluation index is f = aX + bY. The weight needs to be adjusted according to the target irregularity defect, material, etc., but in the example, a = 18.1 and b = 4.3. The values of a and b can be obtained by linear programming according to the target irregularity defect and material. The relationship between the evaluation index and the unevenness score is shown in the graph of FIG. Compared with FIG. 13 and FIG. 15, it can be seen that the correlation with the concave / convex score is improved by combining them, rather than only the concave / convex defect portion area ratio and the luminance defect portion area ratio. Specifically, in the example shown in FIG. 13, the square value (determination coefficient) R ² of the correlation coefficient R is 0.80, and in the example shown in FIG. 15, the determination coefficient R ² is 0.69. In the example shown in FIG. 16, the determination coefficient R ² was 0.91. From the above, it was confirmed that the accuracy of the quantitative evaluation of the surface property can be improved by adding the evaluation of the degree of unevenness to the evaluation of the degree of the bathing defect.

  The embodiment to which the invention made by the present inventors is applied has been described above, but the present invention is not limited by the description and the drawings that constitute a part of the disclosure of the present invention. For example, a surface quality evaluation apparatus for a hot dip galvanized steel sheet that executes the surface texture evaluation method for a hot dip galvanized steel sheet may be configured by causing a computer to execute each processing step of the surface texture evaluation method for a hot dip galvanized steel sheet. . As described above, other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

  D Length of swell element

Claims (6)

A method for evaluating the surface properties of a hot dip galvanized steel sheet for evaluating the degree of hot water defects in the hot dip galvanized steel sheet,
By applying a phase compensation filter to a cross-sectional curve showing the cross-sectional shape in the width direction of the hot-dip galvanized steel sheet, a waviness curve showing the waviness shape in the width direction of the hot-dip galvanized steel sheet is calculated, and the waviness curve A method for evaluating the surface property of a hot dip galvanized steel sheet, comprising the step of evaluating the degree of a hot dip in the hot dip galvanized steel sheet using the average length of the undulating elements constituting the swell as an evaluation index.   The waviness curve is extracted at a plurality of lengthwise positions of the hot-dip galvanized steel sheet, and the degree of the hot-dip defect of the hot-dip galvanized steel sheet using the average value or the maximum value of the evaluation index calculated from each waviness curve The surface property evaluation method for hot-dip galvanized steel sheets according to claim 1, wherein   By applying a two-dimensional second phase compensation filter having a cutoff value larger than the cutoff value of the phase compensation filter to a two-dimensional image including the cross-sectional curve, the surface of the hot-dip galvanized steel sheet Calculating the average value or the maximum value of the uneven height, and evaluating the degree of the hot-dip defect of the hot-dip galvanized steel sheet based on the calculated average value or maximum value of the uneven height, The surface property evaluation method of the hot dip galvanized steel sheet according to claim 1 or 2. The convex-concave shape of the surface of the hot dip galvanized steel sheet is measured, and the height of a predetermined first height threshold or higher is a continuous area of a predetermined first area threshold or higher and the first height threshold. Calculate the total area of the concave defects where the height below the small predetermined second height threshold is an area equal to or larger than the predetermined second area threshold from the measurement results of the concave and convex shapes, and occupy the inspection area Calculating the ratio of the sum of the total area of the convex defect part and the total area of the concave defect part as the uneven defect part area ratio;
The brightness of the surface of the hot dip galvanized steel sheet is measured, the inspection area is divided into a plurality of small areas, the average brightness of the surface in each small area is calculated from the measurement result of the brightness, and the average in the adjacent small areas Extracting a small area having a small area having a luminance difference equal to or greater than a predetermined value as a luminance defect portion, and calculating a ratio of the total area of the luminance defect portion in the inspection region as a luminance defect portion area ratio;
Performing a grade evaluation of the unevenness defect in the inspection region by an evaluation index that linearly combines the unevenness defect area ratio and the luminance defect area ratio;
The surface property evaluation method for hot-dip galvanized steel sheets according to claim 1 or 2, characterized by comprising: A surface quality evaluation device for hot dip galvanized steel sheet for evaluating the degree of hot water defects in hot dip galvanized steel sheet,
Means for calculating a waviness curve indicating the waviness shape in the width direction of the hot-dip galvanized steel sheet by applying a phase compensation filter to the cross-sectional curve showing the cross-sectional shape in the width direction of the hot-dip galvanized steel sheet;
Means for calculating the average length of the undulation elements constituting the undulation curve as an evaluation index when evaluating the degree of the dip in the hot-dip galvanized steel sheet;
An apparatus for evaluating the surface properties of a hot-dip galvanized steel sheet.   Hot-dip galvanization by controlling manufacturing conditions based on the degree of the hot-dip defect of the hot-dip galvanized steel sheet evaluated by the surface property evaluation method of the hot-dip galvanized steel sheet according to any one of claims 1 to 4. The manufacturing method of the hot dip galvanized steel plate characterized by including the step which manufactures a plated steel plate.