JP2018146567A - Surface quality detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface quality detection method capable of accurately determining surface quality of a hot rolled steel sheet surface after acid cleaning.SOLUTION: The surface quality detection method for detecting surface quality of a hot rolled steel sheet surface after acid cleaning includes the steps of irradiating the hot rolled steel sheet surface with light which is not signal-wavelength light, receiving reflectance from the hot rolled steel sheet surface and determining surface quality on the basis of the reflectance obtained in the light receiving step. In the determination step, the ratio between brightness in a first wavelength range, of the reflectance, and brightness in a second wavelength range different from the first wavelength range is calculated.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a surface property inspection method.

  For example, when manufacturing steel sheets by hot rolling (hot rolling) processing of high-strength steel containing Si, a black skin-like scale made of oxide is formed on the outer surface, and the iron inside the scale A grain boundary oxide may be formed by oxidizing the crystal grain boundary of the surface layer. It is known that such a grain boundary oxide causes deterioration of chemical conversion properties when present in the final product of a high-strength cold-rolled steel sheet.

  The scale and grain boundary oxide layer of a hot-rolled steel sheet (a crystal grain layer around which a grain boundary oxide is formed, which may include a granular material on which an oxide is precipitated) can be removed by pickling. . Therefore, a method for ensuring removal of the scale and the grain boundary oxide by determining the pickling time according to the thickness of the scale and the grain boundary oxide layer has been proposed (Japanese Patent Laid-Open No. 2013-237924). reference).

  Thus, although a method for removing the grain boundary oxide layer from the hot-rolled steel sheet is known, an effective means has been proposed for a method for confirming the presence or absence of residual grain boundary oxide in the steel sheet production line. Not.

JP 2013-237924 A

  In view of the above inconveniences, an object of the present invention is to provide a surface texture inspection method capable of accurately determining the surface texture of the surface of a hot-rolled steel sheet after pickling.

  The invention made in order to solve the above-mentioned problems is a method for inspecting the surface properties of a hot-rolled steel sheet after pickling, the step of irradiating the steel sheet surface with light having a single wavelength, and the reflected light from the steel sheet surface. And determining the surface properties based on the reflected light obtained in the light receiving step, and in the determining step, the first wavelength range of the reflected light in the first wavelength range and the first wavelength range Is characterized by calculating a ratio of luminance in different second wavelength ranges.

  The spectrum of reflected light (luminance profile for each wavelength) when the surface of the steel sheet is irradiated with light that is not a single wavelength varies depending on the surface properties of the steel sheet. For this reason, in the surface texture inspection method, by calculating the ratio of the luminance of the first wavelength range to the luminance of the second wavelength range different from the first wavelength range in the reflected light, the change in the spectrum of the reflected light is calculated. It is possible to digitize and determine the surface properties of the steel sheet relatively easily and accurately.

  In the surface texture inspection method according to the present invention, it is preferable that the upper limit of the first wavelength range and the second wavelength range is 1200 nm or less. Thus, when the upper limit of the first wavelength range and the second wavelength range is 1200 nm or less, when the temperature of the steel plate is high, the surface properties of the steel plate can be more accurately determined without being affected by the thermal radiation of the steel plate. Can be determined.

  In the surface texture inspection method according to the present invention, the first wavelength range may be in a red light wavelength region or a blue light wavelength region. As described above, the first wavelength range is within the red light wavelength range or the blue light wavelength range where the brightness of the reflected light changes relatively greatly depending on the presence or absence of the grain boundary oxide on the steel sheet surface. The removal of an object can be determined more accurately.

  In the surface property inspection method according to the present invention, the second wavelength range may include a red light wavelength, a green light wavelength, and a blue light wavelength. As described above, since the second wavelength range includes the red light wavelength, the green light wavelength, and the blue light wavelength, the luminance value in the wavelength range is relatively stable, so that the surface property of the steel sheet is determined relatively accurately. be able to.

  In the surface property inspection method according to the present invention, one of the first wavelength range and the second wavelength range is in the red light wavelength range, and the other of the first wavelength range and the second wavelength range is in the blue light wavelength range. Also good. As described above, the blue wavelength range in which the first wavelength range and the second wavelength range change relatively greatly as the grain boundary oxide decreases, and the red wavelength in which the blue wavelength range is opposite to the blue wavelength range. By being within the range, the removal of the grain boundary oxide on the steel sheet surface can be detected with high sensitivity.

  In the surface texture inspection method according to the present invention, in the light receiving step, irregularly reflected light may be received at a position where regular reflected light is not received. Thus, by receiving irregularly reflected light, the surface properties of the steel sheet can be detected with higher sensitivity.

  In the surface property inspection method according to the present invention, in the light receiving step, at least one of an incident angle of light to the steel plate surface in the irradiation step and a reflection angle of reflected light from the steel plate surface in the light receiving step is different. The reflected light may be received, and in the determination step, the surface property may be determined based on the calculated value of the ratio of the two luminances calculated from the two reflected lights.

  Another invention of the present invention is an apparatus for inspecting the surface properties of a hot-rolled steel sheet after pickling, and receives a light source that irradiates light that is not a single wavelength on the surface of the steel sheet and reflected light from the surface of the steel sheet. A light receiver and an arithmetic device that determines surface properties based on the reflected light received by the light receiver, wherein the arithmetic device is different from the first wavelength range of the first wavelength range of the reflected light. The surface texture inspection apparatus is characterized in that a ratio with respect to luminance in the second wavelength range is calculated.

  Since the surface texture inspection apparatus can perform the surface texture inspection method for calculating the ratio of the luminance of the first wavelength range to the luminance of the second wavelength range, the surface texture of the steel sheet is determined relatively accurately. be able to.

  As described above, the surface texture inspection method of the present invention can accurately determine the surface texture on the surface of a hot-rolled steel sheet after pickling.

It is a schematic diagram which shows the structure of the inspection apparatus used for the surface property inspection method which concerns on one Embodiment of this invention. It is a flowchart which shows the procedure of the surface property inspection method which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the inspection apparatus used for the surface property inspection method which concerns on embodiment different from FIG. 1 of this invention. It is a brightness | luminance profile of the light source used for the test of this invention. It is a graph which shows the relationship between the luminance ratio of a different wavelength range and the pickling time which were obtained by the test of this invention. It is a graph which shows the relationship between another luminance ratio obtained by the test of this invention, and pickling time. It is a graph which shows the relationship between the luminance ratio and pickling time in case the incident angle of the light source obtained by another test of this invention differs. It is a graph which shows the relationship between the ratio of the ratio of the brightness | luminance of two incident angles of FIG. 7, and pickling time. It is a graph which shows the change of the ratio of the ratio of the brightness | luminance of two incident angles in an actual steel plate manufacturing line.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[First embodiment]
FIG. 1 shows a configuration of a surface texture inspection apparatus used in a surface texture inspection method according to an embodiment of the present invention. The surface property inspection method is a method for inspecting the surface property of the hot-rolled steel sheet S after pickling.

<Hot rolled steel sheet>
The hot-rolled steel sheet S to be inspected by the surface property inspection method is not particularly limited, but a Si (silicon) -containing high-strength steel sheet from which surface grain boundary oxides are removed by pickling is assumed. The Specific examples of such a Si-containing high-strength steel sheet include Si-high Mn-containing steel containing 1.0% by mass or more of Si and 1.5% by mass or more of Mn (manganese).

  Such a hot-rolled steel sheet S is formed in a long band shape, continuously conveyed in the longitudinal direction by a plurality of conveying rollers, and immersed in an acidic liquid stored in this water tank by passing through the water tank, It is assumed that the surface grain boundary oxide is removed.

  The surface property inspection method includes a light source 1 that irradiates the surface of the hot-rolled steel sheet S with light that is not a single wavelength, and a reflected light of the light irradiated from the light source 1 on the surface of the hot-rolled steel sheet S. It can be performed using a surface property inspection device including a light receiver 2 that acquires a luminance distribution and a calculation device 3 that determines the surface property of the hot-rolled steel sheet S based on the luminance distribution acquired by the light receiver 2.

<Light source>
The light source 1 may be any light source that can irradiate light that is not a single wavelength, but is preferably one that can irradiate white light.

  As such a light source 1, white LED, a fluorescent lamp, a halogen lamp, a xenon lamp etc. can be used, for example.

  The light source 1 includes an optical system that includes, for example, a lens and can irradiate light within a single point or a narrow range so as to improve energy efficiency and make it easy to prevent regular reflection light from entering the light receiver. It is preferable to provide.

<Receiver>
For example, a CCD image sensor or a CMOS image sensor can be used as the light receiver 2.

  It is preferable that the light receiver 2 is disposed at a position where it does not receive regular reflection light and receives irregular reflection light on the surface of the hot-rolled steel sheet S. Note that “regularly reflected light” means reflected light when the surface of the hot-rolled steel sheet S is flat, and the light irregularly reflected by the fine irregularities on the surface of the hot-rolled steel sheet S is regarded as irregularly reflected light. To do.

<Calculation device>
As the arithmetic unit 3, for example, a computer having a microprocessor, an IC having a dedicated arithmetic circuit, or the like can be used.

  The surface property inspection method performed using the apparatus of FIG. 1, as shown in FIG. 2, a step of irradiating the surface of the hot-rolled steel sheet S with light that is not a single wavelength by the light source 1 <step S1: irradiation step> A process of receiving reflected light from the surface of the hot-rolled steel sheet S with the light receiver 2 <Step S2: light receiving process> and a spectrum of reflected light obtained in the light receiving process by the arithmetic device 3 (distribution of luminance for each wavelength) The step <Step S3: determination step> for determining the surface properties of the hot-rolled steel sheet S is provided.

<Irradiation process>
In the irradiation process of step S1, light is irradiated from the light source 1 to the surface of the hot-rolled steel sheet S. The incident angle of light irradiated from the light source 1 to the hot-rolled steel sheet S (the angle between the optical axis of the light source 1 and the normal line of the hot-rolled steel sheet S) can increase the intensity of incident light and increase the brightness of reflected light. Such a small size is preferable. Specifically, the upper limit of the incident angle of light irradiated from the light source 1 to the hot-rolled steel sheet S is preferably 60 °, and more preferably 45 °. When the incident angle of the light irradiated from the light source 1 to the hot-rolled steel sheet S exceeds the above upper limit, the detection accuracy may be insufficient because the intensity of the reflected light is reduced.

<Light receiving process>
In the light receiving step of step S2, reflected light of light irradiated from the light source 1 onto the surface of the hot-rolled steel sheet S is received by the light receiver 2, and the luminance distribution of the reflected light is measured.

  The light receiving position of the reflected light by the light receiver 2 is preferably a position where the regular reflected light of the light irradiated from the light source 1 onto the surface of the hot-rolled steel sheet S does not enter. Thereby, since the characteristic of the irregular reflection in the surface of the hot-rolled steel sheet S can be grasped in detail, the surface property of the hot-rolled steel sheet S can be detected more accurately.

<Judgment process>
In the determination step of step S3, the luminance of the first wavelength range and the luminance of the second wavelength range different from the first wavelength range are calculated from the reflected light luminance profile acquired in the light receiving step of step S2. Then, the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range is calculated and used as a determination index. That is, in the determination step, the quality of the surface property of the hot-rolled steel sheet S is determined by comparing the ratio with a threshold value. In other words, the surface texture inspection method according to the embodiment of the present invention determines the quality of the surface texture based on a change in the color of the reflected light.

(First wavelength range)
As the first wavelength range, in the reflected light luminance profile, the wavelength range in which the change due to the surface properties of the hot-rolled steel sheet S is relatively large, for example, the area ratio in the diffusely reflected light luminance profile is large depending on the presence or absence of grain boundary oxides. It is preferred to select a wavelength range that varies. Moreover, as for the 1st wavelength range, in order to prevent the error by the heat radiation of the hot-rolled steel sheet S, it is preferable that an upper limit is 1200 nm or less, and it is more preferable that it is 1000 nm or less.

  Specifically, the first wavelength range is in the red light wavelength region (in the region from 580 nm to 800 nm, preferably in the region from 590 nm to 700 nm) or in the blue light wavelength region (from 400 nm to 500 nm). The wavelength range is preferably within the region, more preferably within the region of 430 nm to 460 nm. In addition, the reflected light in the red light wavelength region and the reflected light in the blue light wavelength region have opposite changes with respect to the remaining amount of the grain boundary oxide.

(Second wavelength range)
As said 2nd wavelength range, it is set as the range from which the change rate of the brightness | luminance by the surface property of the hot-rolled steel sheet S differs from the said 1st wavelength range. Thereby, the ratio with respect to the brightness | luminance of the 2nd wavelength range of the brightness | luminance of the 1st wavelength range calculated at a determination process compensates the change of the brightness | luminance of the reflected light whole by the inclination of the hot-rolled steel sheet S, for example, This is a numerical value representing a change in the color of the reflected light. In the second wavelength range, the upper limit is preferably 1200 nm or less and more preferably 1000 nm or less in order to prevent an error due to heat radiation of the hot-rolled steel sheet S, similarly to the first wavelength range. preferable.

  Specifically, the second wavelength range is the blue light wavelength region when the first wavelength range is within the red light wavelength region, and the red light when the first wavelength range is within the blue light wavelength region. It can be in the wavelength region. Thus, by setting one of the first wavelength range and the second wavelength range within the red light wavelength region and the other of the first wavelength range and the second wavelength range within the blue light wavelength region, Since the rate of change of the ratio of the luminance to the luminance in the second wavelength range can be increased, the surface property change of the hot-rolled steel sheet S can be detected with higher sensitivity.

  The second wavelength range may be a range including a red light wavelength, a green light wavelength, and a blue light wavelength. Thus, since the second wavelength range includes the red light wavelength, the green light wavelength, and the blue light wavelength, the brightness of the entire reflected light due to factors other than the surface properties of the hot-rolled steel sheet S, such as the inclination of the hot-rolled steel sheet S, for example. Since the change can be compensated more accurately, the surface properties of the hot-rolled steel sheet S can be more appropriately determined depending on the measurement conditions.

[Second Embodiment]
FIG. 3 shows the configuration of a surface texture inspection apparatus used in a surface texture inspection method according to another embodiment of the present invention. The surface texture inspection apparatus of FIG. 3 is used for inspecting the surface texture of the hot-rolled steel sheet S after pickling, similarly to the surface texture inspection apparatus of FIG.

  The surface texture inspection apparatus receives light reflected from the surface of the hot-rolled steel sheet S by the light source 1 that irradiates the surface of the hot-rolled steel sheet S with light that is not a single wavelength, and receives light reflected from the surface of the hot-rolled steel sheet S for each wavelength. A first light receiver 2a and a second light receiver 2b that acquire a luminance distribution, and an arithmetic device 3a that determines the surface properties of the hot-rolled steel sheet S based on the two luminance distributions acquired by the light receivers 2a and 2b. Is provided.

  The configurations of the light source 1, the light receivers 2a and 2b, and the arithmetic device 3a in the surface texture inspection apparatus in FIG. 3 are the same as those in the surface texture inspection apparatus in FIG. It can be made to be the same as that of the configuration. For this reason, the description which overlaps with the surface property inspection apparatus of FIG. 1 is abbreviate | omitted about the surface property inspection apparatus of FIG.

<Receiver>
The first light receiver 2 a and the second light receiver 2 b receive the irregularly reflected light on the surface of the hot-rolled steel sheet S of the light emitted from the light source 1. The first light receiver 2a and the second light receiver 2b have different reflection angles of the received reflected light. Specifically, the elevation angle of the first light receiver 2a with respect to the surface of the hot rolled steel sheet S viewed from the intersection of the optical axes of the light sources 1 with respect to the surface of the hot rolled steel sheet S is different from the elevation angle of the second light receiver 2b. ing.

  The lower limit of the difference in reflection angle between the first light receiver 2a and the second light receiver 2b is preferably 15 °, and more preferably 20 °. On the other hand, the upper limit of the difference in reflection angle between the first light receiver 2a and the second light receiver 2b is preferably 45 °, more preferably 40 °. When the difference in reflection angle between the first light receiver 2a and the second light receiver 2b is less than the lower limit, the luminance distribution of the reflected light received by the first light receiver 2a and the reflected light received by the second light receiver 2b. If the difference from the luminance distribution is small, there is a possibility that the determination accuracy of the surface property cannot be sufficiently improved. Conversely, when the difference in reflection angle between the first light receiver 2a and the second light receiver 2b exceeds the upper limit, the brightness of the reflected light received by either the first light receiver 2a or the second light receiver 2b is There is a possibility that the accuracy of determining the surface property cannot be sufficiently improved by being small.

<Calculation device>
The arithmetic device 3a first calculates the luminance in the first wavelength range and the first wavelength range from the luminance profile of the reflected light received by the first light receiver 2a and the luminance profile of the reflected light received by the second light receiver 2b. And calculating the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range. Next, the arithmetic device 3a performs an operation using the luminance ratio calculated from the luminance profile of the first light receiver 2a and the luminance ratio calculated from the luminance profile of the second light receiver 2b to perform the grain calculation. A calculated value that monotonously increases or decreases monotonously with respect to the removal rate of the field oxide is derived, and this calculated value is used as an index of the removal rate of the grain boundary oxide on the surface of the hot rolled steel sheet S to determine the surface properties of the hot rolled steel sheet S. judge.

  The operation for monotonously increasing or monotonically decreasing the grain boundary oxide removal rate using the ratio of the two luminances is not particularly limited, and for example, any of addition, subtraction, multiplication, and division can be used. Further, in order to adjust the luminance gain of the first light receiver 2a and the second light receiver 2b, the ratio of the calculated luminance may be multiplied by a count, or for example, an exponent, a logarithm, or the like may be calculated.

  As described above, the surface texture inspection method performed using the surface texture inspection apparatus of FIG. 3 includes a step of irradiating the surface of the hot-rolled steel sheet S with light having a single wavelength by the light source 1, and hot rolling with the light receivers 2a and 2b. Receiving the reflected light from the surface of the steel sheet S, and determining the surface properties of the hot-rolled steel sheet S based on the spectrum of the two reflected lights obtained in the light receiving process by the arithmetic device 3a, Two reflected lights having different reflection angles of the reflected light from the surface of the hot-rolled steel sheet S are received in the light receiving step, and the first wavelength range calculated from the reflected light received by the first light receiver 2a in the determination step. The hot-rolled steel sheet is calculated by calculating the ratio between the luminance and the luminance in the second wavelength range and the ratio between the luminance in the first wavelength range and the luminance in the second wavelength range calculated from the reflected light received by the second light receiver 2b. The surface property of S is determined.

  In this way, by performing the calculation of the two ratios, it is possible to obtain a calculated value that more accurately reflects the removal rate of the grain boundary oxide. Therefore, by using this calculated value as an index for determination, Even without monitoring, the surface properties of the hot-rolled steel sheet S can be accurately determined.

[Other Embodiments]
The said embodiment does not limit the structure of this invention. Therefore, in the above-described embodiment, the components of each part of the above-described embodiment can be omitted, replaced, or added based on the description and common general knowledge of the present specification, and they are all interpreted as belonging to the scope of the present invention. Should.

  In the surface texture inspection method according to the present invention, the first wavelength range and the second wavelength range may not be continuous wavelength ranges. That is, the first wavelength range and the second wavelength range may include a plurality of wavelength ranges that are not continuous. In addition to the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range, a ratio with the luminance in one or more other wavelength ranges may be added to the index.

  In the surface property inspection method according to the present invention, instead of the light receiver, a light receiving element that can measure the luminance in the second wavelength range and a light receiving element that can measure the luminance in the first wavelength range may be used in combination. As the light receiving element capable of measuring the luminance in such a specific wavelength range, for example, a photodiode having a single wavelength or narrow wavelength filter can be used.

  In the surface texture inspection method according to the present invention, regular reflection light may be received in the light receiving step. In this case, the change in the brightness profile of the reflected light accompanying the removal of the grain boundary oxide on the surface of the steel sheet is generally opposite to the change in the brightness profile of the irregular reflection light described above.

  In the surface property inspection method according to the present invention, the first light receiver and the second light receiver may receive reflected light on the steel plate surface of light irradiated at different incident angles from different light sources. For example, two sensors in which a light source and a light receiver are integrated may be arranged at intervals in the conveyance direction of the steel sheet, and the brightness profiles of the two reflected lights may be acquired at different times.

  In the surface texture inspection method according to the present invention, the determination step may be performed manually without using an arithmetic device.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

<Test 1>
Hot-rolled steel sheets with different pickling times of 30 seconds, 50 seconds, 70 seconds, 90 seconds, 110 seconds, 130 seconds, 150 seconds, 170 seconds, and 200 seconds are irradiated with white light from the light source, and the reflected light is received. The brightness distribution of the reflected light was obtained by receiving the light with the instrument.

  As the hot-rolled steel sheet, a high-strength steel containing 2.0% by mass of Si and rolled up at 660 ° C. after hot rolling was used.

  As the light source, an LED light having a white LED and condensing and irradiating in a dot shape was used. Further, a spectroscope “USB2000 +” manufactured by Ocean Optics was used as the light receiver. The brightness profile of the LED light measured using this spectroscope was as shown in FIG. Note that the luminance in FIG. 4 is normalized by dividing by the peak value.

  The light source was arranged so that its optical axis was inclined by 15 ° with respect to the normal line of the hot-rolled steel sheet and the distance in the optical axis direction from the surface of the hot-rolled steel sheet was 500 mm. The light receiver was arranged at a position where the distance in the imaginary line direction from the surface of the hot-rolled steel sheet was 50 mm on the imaginary line inclined further by 1.5 ° in the same direction from the optical axis of the light source.

  About the brightness | luminance profile of the reflected light of each obtained hot-rolled steel plate, the brightness | luminance of the blue range of wavelength 435.46 nm or more and 450.22 nm or less, the brightness | luminance of the green range of wavelength 522.02 nm or more and 536.42 nm or less, respectively, and wavelength 597 The normalized value was derived by calculating the luminance of the red range of .94 nm to 611.999 nm and dividing by the total luminance of the blue range, green range and red range, respectively. That is, the second wavelength of the luminance in the first wavelength range when the blue range, the green range, or the red range is the first wavelength range, and the range obtained by adding the blue range, the green range, and the red range is the second wavelength range. The ratio of the range to the luminance was calculated respectively. The ratios are shown together in Table 1 and plotted in a graph in FIG.

  As shown in FIG. 5, when the blue range or the red range is the first wavelength range, and the range obtained by adding the blue range, the green range, and the red range is the second wavelength range, the second luminance of the first wavelength range is obtained. A correlation was confirmed between the ratio of the wavelength range to the luminance and the pickling time.

  Further, the surface of the hot rolled steel sheet after pickling was observed with a scanning electron microscope, and the degree of removal of the grain boundary oxide layer was confirmed. In the hot-rolled steel sheets with pickling times of 30 seconds and 50 seconds, the grain boundary oxide layer was hardly removed, and the scale remained on the grain boundary oxide layer. Further, in the hot rolled steel sheet with pickling times of 70 seconds and 90 seconds, the grain boundary oxide layer was partially removed, but the grain boundary oxide remained. In the hot-rolled steel sheet having a pickling time of 110 seconds or more, almost all of the grain boundary oxide was removed.

  From this result, when the blue range is the first wavelength range and the range obtained by adding the blue range, the green range, and the red range is the second wavelength range, the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range If it is 0.336 or more, it can be judged that the surface texture of the hot-rolled steel sheet is good with the grain boundary oxide layer sufficiently removed.

  In addition, when the red range is the first wavelength range, and the range obtained by adding the blue range, the green range, and the red range is the second wavelength range, the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range If it is 0.334 or less, it can be judged that the surface texture of the hot-rolled steel sheet is good with the grain boundary oxide layer sufficiently removed.

  In the results of Table 1, the relationship between the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range and the pickling time when the blue range is the first wavelength range and the red range is the second wavelength range. Is shown in FIG. In this case, if the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range is 1.00 or more, the surface property of the hot-rolled steel sheet is good with the grain boundary oxide layer sufficiently removed. Judgment can be made.

<Test 2>
Subsequently, for the same hot-rolled steel sheet as in Test 1, the angle of the light source and the light receiver with respect to the normal direction of the steel sheet surface is changed, the blue range is set as the first wavelength range, and the blue range, the green range, and the red range are added. The ratio of the luminance in the first wavelength range to the luminance in the second wavelength range was calculated with the range as the second wavelength range. Specifically, while maintaining the relative angle between the light source and the light receiver at 1.5 °, the inclination angle (incident angle) of the optical axis of the light source with respect to the normal of the steel plate surface is 75 °, 60 °, 45 °, and The ratio of the luminance in the first wavelength range to the luminance in the second wavelength range was calculated as 15 °. The results are shown in Table 2 and FIG. In addition, when the inclination angle of the light source is set to 15 °, the same data as the blue range of the test 1 is obtained.

  When the incident angle is 15 °, the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range increases substantially monotonically. For this reason, when the incident angle is 15 °, it is considered that the surface properties of the hot-rolled steel sheet can be determined relatively easily. On the other hand, when the incident angle is increased, the ratio of the luminance of the first wavelength range to the luminance of the second wavelength range is reduced by removing the scale, and the removal of the grain boundary oxide is followed by the removal of the first wavelength range. There is a tendency for the ratio of the luminance to the luminance in the second wavelength range to increase again. However, in the actual production of hot-rolled steel sheets, scale removal can be easily discriminated, so the degree of removal of grain boundary oxide in the range of 70 to 140 seconds in pickling time in this test should be confirmed. If you can. For this reason, even when the incident angle is reduced, it is considered that the surface property can be correctly determined at the production site of the hot-rolled steel sheet. However, when the incident angle is set to 75 ° as compared with the case where the incident angle is set to 45 ° and 60 °, the error is increased, and the determination accuracy seems to be lowered. This is considered to be due to the fact that if the incident angle is too large, the total amount of reflected light received by the light receiver is reduced.

  In FIG. 8, the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range when the incident angle is 45 ° is divided by the ratio of the luminance in the first wavelength range to the luminance in the second wavelength range when the incident angle is 15 °. The relationship between the calculated value and the pickling time is shown. As shown in this figure, by further calculating two ratios with different incident angles, a calculated value that decreases more smoothly and monotonically according to the pickling time is obtained, and the degree of removal of the grain boundary oxide is more accurately determined. Can be determined. In addition, although description of a specific numerical value is abbreviate | omitted, calculation with a large correlation with the pickling time in any of the case where the ratio of the luminance in the same two incident angles is added, subtracted, and multiplied A value is obtained.

  After pickling equipment on the actual hot-rolled steel plate production line, a set of a light source with an incident angle of 45 ° and a receiver with a reflection angle of 46.5 °, a light source with an incident angle of 15 ° and a receiver with a reflection angle of 16.5 ° And sets the pair to measure the luminance profile of the reflected light, respectively, and the ratio of the luminance of the first wavelength range when the incident angle is 45 ° to the luminance of the second wavelength range of the first wavelength range when the incident angle is 45 °. The calculated value divided by the ratio of the luminance to the luminance in the second wavelength range was continuously calculated.

  The result is shown in FIG. As shown in the figure, the residual grain boundary oxide was confirmed by visual inspection at the end of the measurement period, but the calculated value at this time increased. That is, it was confirmed that it is possible to automatically determine whether or not the grain boundary oxide is properly removed based on the calculated value.

  The surface texture inspection method according to the present invention can be particularly suitably used for confirming the removal of the grain boundary oxide of the hot-rolled steel sheet.

DESCRIPTION OF SYMBOLS 1 Light source 2, 2a, 2b Light receiver 3, 3a Arithmetic device S Hot rolled steel plate

Claims (8)

It is a surface property inspection method for hot-rolled steel sheets after pickling,
Irradiating the steel sheet surface with light that is not a single wavelength;
Receiving reflected light from the steel sheet surface;
And determining the surface properties based on the reflected light obtained in the light receiving step,
The surface property inspection method according to claim 1, wherein, in the determination step, a ratio of the luminance in the first wavelength range of the reflected light to the luminance in the second wavelength range different from the first wavelength range is calculated.   The surface property inspection method according to claim 1, wherein an upper limit of the first wavelength range and the second wavelength range is 1200 nm or less.   The surface property inspection method according to claim 1 or 2, wherein the first wavelength range is in a red light wavelength range or a blue light wavelength range.   The surface property inspection method according to claim 1, wherein the second wavelength range includes a red light wavelength, a green light wavelength, and a blue light wavelength.   3. The surface according to claim 1, wherein one of the first wavelength range and the second wavelength range is in a red light wavelength range, and the other of the first wavelength range and the second wavelength range is in a blue light wavelength range. Property inspection method.   The surface property inspection method according to any one of claims 1 to 5, wherein in the light receiving step, irregularly reflected light is received at a position where regular reflected light is not received. In the light receiving step, two reflected lights that are different in at least one of an incident angle of light on the steel plate surface in the irradiation step and a reflection angle of reflected light from the steel plate surface in the light receiving step are received,
The surface property inspection method according to any one of claims 1 to 6, wherein in the determination step, the surface property is determined based on a calculated value of a ratio of the two luminances calculated from the two reflected lights. An apparatus for inspecting the surface properties of a hot-rolled steel sheet after pickling,
A light source that irradiates the surface of the steel sheet with light that is not a single wavelength;
A light receiver for receiving reflected light from the steel sheet surface;
An arithmetic unit that determines surface properties based on reflected light received by the light receiver, and
The said arithmetic unit calculates the ratio with respect to the brightness | luminance of the 2nd wavelength range different from the said 1st wavelength range of the brightness | luminance of a 1st wavelength range among the said reflected lights, The surface property inspection apparatus characterized by the above-mentioned.

Images