JP2011203201A - Metal defect detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal defect detection method capable of highlighting defect through etching treatment of the inspection surface of a metal sample, while when detection of the defect is carried out by imaging the inspection surface with an imaging device, brightness of non-defect parts on the imagery of inspection surface is made to be homogenized and brightened, leading clear defection of defect part.SOLUTION: An inspection surface 2 of a metal sample 1 is polished unidirectionally, by etching treatment of the metal sample 1, defect in metal material is highlighted, linearly continuous light sources or a light source (a linear light source 4) a plurality of point light source arranged linearly are used as irradiating light source, a linearly direction 17 of the linear light source 4 and the polished direction 11 are presumed to be a same direction, the inspection surface 2 is irradiated by the linear light source 4 from a perpendicular direction to the polished direction 11, and the inspection surface 2 is imaged by an imaging device 3. Thereby, brightness of the non-defect parts in the inspection imaged imageries is to be homogenized and brightened, making the defect part 6 to be detectable clearly.

Description

  The present invention relates to a method for detecting a defect appearing on an inspection surface of a metal sample.

  Detection and evaluation of defects such as cracks and segregation in metal materials, particularly steel slabs and slabs, are indispensable for quality control of slabs and optimization and operation management of slab manufacturing processes. Conventionally, a sulfur printing method or an etch printing method has been used as a quality evaluation method inside a metal material. In any case, a sample is cut out from the metal material, the cross section of the metal material is polished as an inspection surface, and evaluation is performed.

  In the sulfur printing method, an aqueous sulfuric acid solution is immersed in a transfer printing paper containing silver bromide and attached to an inspection surface, and the segregation state of sulfur in a sample appears on the printing paper. The center segregation and internal cracks of the slab are evaluated by utilizing the property that sulfur segregates at the center segregation and cracks of the slab. The sulfur printing method cannot be applied to ultra-low sulfur steels having a low sulfur concentration, which are used for materials having a high sulfur concentration in metal materials.

  The etch print method uses the property that elements are segregated at the center segregation and cracks on the inspection surface. The inspection surface is etched to reveal the element segregation, and the sample is coated with petroleum jelly and then re-polished. This is a technique for visualizing segregation and cracking, and can also be used for materials having a low sulfur concentration.

  With the recent improvement in quality and purity of metal materials, there has been a demand for higher accuracy in detecting defects in metal materials. Regarding the sulfur printing method, there is a problem in the stable supply of photographic paper to be used, and the sulfur printing method cannot be applied to extremely low-sulfur steel in the first place. The etch printing method requires several hours for the entire operation, and speeding up of defect detection is required.

  A method is known in which an inspection surface of a metal material is etched and then the inspection surface is directly imaged by an imaging device such as a camera and recorded as an image. When the inspection surface is etched (macro-corrosion) and the inspection surface is imaged with an imaging device, the brightness of the defect portion and the defect-free portion is low because the lightness of the defect-free portion is low. There is a problem that the contrast is small. On the other hand, Patent Document 1 discloses a method of imaging by irradiating illumination light at an incident angle of 50 ° to 70 ° from both sides with respect to the imaging position of the inspection surface. “As shown in FIG. 1B, set so that the polishing eyes are parallel to the installation direction of the reflecting mirrors 5 and 6”. Illumination light is applied to the position from both sides in the polishing direction (FIG. 1B). Thereby, the size and degree of the segregation part of the metal material can be clearly determined.

JP-A-7-306161

  In the method specifically disclosed in Patent Document 1, a camera using a CCD linear sensor or the like is employed as an imaging device. According to FIG. 1, the imaging range is a linear range that is long in a direction perpendicular to the polishing direction. Illumination light is irradiated from both sides of the linear imaging range using reflecting mirrors. Therefore, in order to image the entire inspection surface, it is necessary to perform imaging while moving the linear imaging range. If the method described in Patent Document 1 is expanded and the entire inspection surface is to be imaged at once, it is necessary to irradiate illumination light from a position away from the inspection surface. In this case, the light reflected from the non-defect portion on the inspection surface toward the imaging device is not uniform depending on the location, and the brightness contrast between the defect portion and the non-defect portion is small in the portion where the reflected light from the non-defect portion is small. There is a problem that the defect detection accuracy is insufficient.

  In the present invention, when the inspection surface of a metal sample is etched to reveal a defect and the defect is detected by imaging the inspection surface with an imaging device, the brightness of the non-defect portion in the inspection surface captured image is uniform and bright. It is an object of the present invention to provide a metal defect detection method capable of clearly detecting a defect portion.

That is, the gist of the present invention is as follows.
(1) The inspection surface 2 of the metal sample 1 is polished in one direction using a polishing means having a roughness of No. 100 to No. 1000 specified in JIS R6252, and the metal sample 1 is subjected to an etching treatment to cause the A light source (hereinafter collectively referred to as “linear light source 4”) in which a defect appears and a linearly continuous light source 4a or a plurality of point light sources 4b is linearly arranged is prepared. In a linearly arranged light source, the distance between adjacent point light sources is 30% or less of the length in the polishing direction of the metal sample inspection surface 2 (hereinafter referred to as “sample polishing direction length 15”). When a line perpendicular to the polishing direction is drawn from both ends in the polishing direction of the inspection surface 2 (hereinafter referred to as “both-end perpendicular line 16”), the linear light source emits the two right-angle lines at both ends. Occupies at least 60% of the area between the two right angles When a plane perpendicular to the polishing direction 11 including an arbitrary point on the linear light source 4 is drawn in an area of at least 60% between the lines 16, the linear light source 4 and an arbitrary surface on the inspection surface are drawn on the surface. The angle θ ₂ between the line connecting the points and the normal of the inspection surface ₂ is
15 ° ≦ θ ₂ ≦ 80 °
The minimum distance Lmin between the linear light source 4 and the inspection surface 2 is set to 1000 mm or less, and an imaging device 3 that images the inspection surface 2 is disposed, and the light from the linear light source 4 is applied to the inspection surface 2. A method for detecting a defect in a metal, wherein the inspection surface 2 is imaged by the imaging device 3 while irradiating.
(2) The angle θ ₁ between the linear direction 17 of the linear light source 4 and the polishing direction 11 of the inspection surface 2 is
| Θ ₁ | ≦ 35 °
The metal defect detection method according to the above (1), characterized in that:
(3) The angle θ ₃ formed by the line connecting the imaging device 3 and an arbitrary point on the inspection surface with the normal of the inspection surface is
θ ₃ ≦ 60 °
The metal defect detection method according to the above (1) or (2), characterized in that:

  The present invention is a method for detecting defects appearing on the inspection surface of a metal sample, polishing the inspection surface of the metal sample in one direction, and performing an etching process on the metal sample to reveal defects in the metal sample, By inspecting the inspection surface from a predetermined arrangement position using a linearly continuous light source or a light source (linear light source) in which a plurality of point light sources are linearly arranged, and imaging the inspection surface by an imaging device, the inspection surface The brightness of the non-defect portion in the captured image can be made uniform and bright, and the defect portion can be detected clearly.

It is a perspective conceptual diagram which shows the defect detection method of this invention, When (a) uses the linear continuous light source as a linear light source, (b) arrange | positions several point light sources linearly as a linear light source This is the case. It is a top view which shows the defect detection method of this invention. It is a figure which shows the defect detection method of this invention, (a) is a perspective view, (b) is a front view. It is a perspective conceptual diagram which shows the defect detection method of this invention. It is a perspective conceptual diagram which shows the defect detection method of this invention. It is a perspective conceptual diagram which shows the defect detection method of this invention. (A) is sectional drawing which shows the condition where irradiation light reflects, (b) is a figure which shows the condition of the polishing eye in a test | inspection surface. It is a perspective view which shows the reflective condition of irradiated light, (a) is a case where it irradiates from a direction parallel to a grinding | polishing direction, (b) is a case where it irradiates from a direction orthogonal to a grinding | polishing direction. It is a perspective conceptual diagram which shows the case where a point light source is used. It is a perspective conceptual diagram explaining the Example of this invention. It is a top view explaining the Example of this invention.

  Etching is performed after polishing the inspection surface to reveal the defective portion. As for the defect portion, for example, the crack portion forms a recess, and the segregation portion causes formation of a recess due to corrosion or darkening of the segregation portion (for example, blackening). As shown in FIG. 7A, when the inspection surface 2 is irradiated with the illumination light 12, the defect portion 6 is a concave portion or a dark color portion, and therefore the upward reflected light 13 is reduced. If the reflected light 13 upward from the non-defect portion 7 other than the defect portion is large and uniform, the defect portion 6 is recognized as a dark portion (black portion) as a captured image.

  When the metal material is cut into a metal sample and the cross section, which is the inspection surface of the metal sample, is polished, polishing marks are formed parallel to the polishing direction. That is, when the roughness is measured in a direction parallel to the polishing direction, the roughness is small, and when the roughness is measured in a direction perpendicular to the polishing direction, the roughness is large. Then, polishing marks parallel to the polishing direction when the polishing machine comes into contact lastly appear. When a cross section of a large metal material such as a slab is used as the inspection surface, as shown in FIG. 7B, the polishing direction 11 is different for each small area of the inspection surface, and the direction having various polishing eye directions is small. The areas are arranged like a mosaic.

When illuminating the inspection surface obliquely from above the inspection surface, the irradiation light 12 irradiated from the direction parallel to the polishing direction 11 as shown in FIG. The regular reflection component 13a having the same reflection angle is relatively strong, and the irregular reflection component 13b reflected in all directions tends to be relatively small. Therefore, among the arbitrary points on the inspection surface, at the point P ₁ where the specular reflection direction coincides with the imaging device direction, the non-defective part in the captured image shines brightly, and the regular reflection direction does not coincide with the imaging device direction. _{For 2} (most area of the inspection surface), a captured image with non-uniform brightness over the entire screen is obtained in which the brightness of the non-defect portion is low. If the brightness of the non-defect portion is low, the contrast with the defect portion is small and the defect detection accuracy is low.

  On the other hand, the irradiation light 12 irradiated from the direction perpendicular to the polishing direction 11 as shown in FIG. 8B among the irradiation light irradiated obliquely above the inspection surface when reflected on the inspection surface, There is a tendency that the regular reflection component 13a is relatively small and the irregular reflection component 13b is relatively large. Therefore, in any part of the inspection surface, the non-defect portion has a property that the brightness is high and the brightness is uniform due to relatively strong irregular reflection light.

  Therefore, if the light source is arranged so that the polishing direction 11 is one direction on the inspection surface 2 and the irradiation light 12 irradiates the inspection surface from a direction perpendicular to the polishing direction 11, the non-defective portion of the entire inspection surface is placed on the imaging device. Since irregularly reflected light is incident, the non-defect portion has a high brightness as a whole and the brightness is kept uniform. Therefore, the brightness contrast with the defect portion having a low brightness is increased, and the defect detection accuracy can be increased. . Here, the direction of polishing is set to one direction, in addition to the case where the entire inspection surface is the same direction, the angle may be changed as long as it is slightly. For example, an arc having a large curvature radius may be drawn in the polishing eye. In this case, the change in the polishing direction may be about 15 ° or less in the inspection surface. More preferably, it is 10 ° or less.

  In the present invention, a method of polishing the inspection surface for increasing the diffuse reflection (diffuse reflection) component from the non-defect portion on the inspection surface and improving the detection accuracy of the defect portion will be described. When the inspection surface is polished in one direction, there is a preferable range for the arithmetic average roughness Ra of the inspection surface in a direction perpendicular to the polishing direction. The arithmetic average roughness Ra is measured by a method defined in JIS B0601 and JIS B0633. If the Ra is too small, the diffuse reflection (diffuse reflection) component in the non-defect portion is small, and the component reflected in the diffuse reflection (diffuse reflection) component toward the imaging device is also small, so that the detection accuracy of the defective portion is low. In the present invention, if the Ra is 0.1 μm or more, the diffuse reflection (irregular reflection) component can be sufficiently increased. On the other hand, if the Ra is too large, it becomes difficult to distinguish between a non-defect portion and a defect portion, and the detection accuracy of the defect portion is low. In the present invention, when the Ra is 50 μm or less, the non-defective portion and the defective portion can be distinguished well. In order to set the arithmetic average roughness Ra of the inspection surface in a direction perpendicular to the polishing direction to 0.1 μm or more, the inspection surface is polished using polishing means having a roughness of 1000 or less as defined in JIS R6252. Just do it. Further, in order to set the Ra to 50 μm or less, polishing may be performed using a polishing means having the roughness of 100 or more. As the polishing means, any of polishing paper, polishing cloth, and polishing material may be used.

Next, the present invention is characterized in that a linearly continuous light source 4a or a light source in which a plurality of point light sources 4b are linearly arranged (collectively, a linear light source 4) is used as a light source of irradiation light. In the case where the irradiation light source is a simple point light source, even if the light source is arranged in a direction perpendicular to the polishing direction, there are the following problems. That is, in FIG. 9, a plane F ₁ including the point light source 5 and the imaging device 3 and perpendicular to the inspection surface 2 is considered. On the line 21 where the surface F ₁ and the inspection surface 2 intersect, the brightness of the non-defect portion 7 is high in any part. However, the lightness of the non-defect portion is lowered as shown below for the other portions on the inspection surface. On the inspection surface, when an arbitrary point P ₃ deviating from the line 21 is irradiated with light from the point light source 5 obliquely above in a direction perpendicular to or close to the polishing direction 11, the diffuse reflection component is relatively large. However, the irregular reflection component tends to increase in the direction along the normal of the inspection surface passing through the point P ₃ and the surface F ₃ including the point light source 5, and the irregular reflection component toward the direction away from the surface F _3. Less. Therefore, if the direction of the imaging device 3 is arranged in a direction away from the surface F ₃ like the point P ₃ , the brightness of the non-defective part is observed near the point P ₃ when viewed from the imaging device 3. It is.

In the present invention, as shown in FIG. 1, a linear light source 4a (FIG. 1 (a)) or a light source (FIG. 1 (b)) in which a plurality of point light sources 4b are linearly arranged (generically referred to). This problem was solved by using “linear light source 4”) as the light source. In the case of the linear light source 4, when considering the surface F ₄ including the normal of the inspection surface passing through an arbitrary point P ₄ on the inspection surface and an appropriate portion (4c in this case) on the linear light source, The imaging device 3 exists at a position where the angle is not greatly separated from the surface F ₄ or the surface F _4. When viewed from the imaging device 3, the diffuse reflection component from the point P ₄ on the inspection surface is sufficient. Can be received with strength. As a result, the brightness of the non-defect portion is kept high and uniform for all points on the inspection surface.

Here, as shown in FIG. 2, a line perpendicular to the polishing direction 11 passing through both ends 14 in the polishing direction of the inspection surface 2 when viewed from above is referred to as “a right-angle line 16 at both ends”. In order to exhibit the above effects using the linear light source 4, the area 18 occupied by the linear light source is between the two right-angled lines (the length is equal to the sample polishing direction length 15). It is necessary to occupy as wide an area as possible. When the linear direction of the linear light source 4 coincides with the polishing direction 11 as shown in FIG. 2A, the linear direction of the linear light source 4 is an angle with respect to the polishing direction 11 as shown in FIG. The same applies to any of the cases having. In the present invention, the area 18 occupied by the linear light source occupies an area that is at least 60% of the distance between the two right-angled lines, so that the reflected light from the inspection surface to the imaging device can be maintained with high brightness and uniformity. Can do. Hereinafter, the area of the linear light source that occupies the distance between the two right-angle lines is also referred to as “light source cover ratio C _R (%)”. More preferably, the light source cover ratio _CR is 70% or more. More preferably, it is 80% or more.

  The linear light source 4 is preferably a linear light source 4a as shown in FIG. For example, a straight tube fluorescent lamp corresponds to such a light source. Even if they are not continuous, a light source in which a plurality of point light sources 4b are linearly arranged as shown in FIG. 1B can be used. However, in this case, if the distance between the adjacent point light sources is too long, it becomes difficult to uniformly hold the reflected light from the inspection surface when viewed from the imaging device. In the present invention, if the distance between adjacent point light sources is 30% or less of the polishing direction length (sample polishing direction length 15) of the inspection surface of the metal sample, the brightness from the inspection surface can be kept uniform. it can. It is more preferable if the distance between adjacent point light sources is 15% or less of the sample polishing direction length 15. A light source in which a large number of LEDs are linearly arranged at short intervals can be suitably used.

Even if the linear light source 4 is prepared and arranged so that the linear light source occupies an area of 60% or more between the right-angle lines at both ends, the irradiation angle from the linear light source to an arbitrary point on the inspection surface is too large. If it is too small, good defect detection cannot be performed. Here, as shown in FIG. 3A, when a surface F ₅ including an arbitrary point 4c on the linear light source and perpendicular to the polishing direction 11 is drawn, the linear light source 4 and the inspection are inspected on the surface F _5. The angle θ ₂ between the line connecting arbitrary points on the surface and the normal of the inspection surface is set. When θ ₂ is too small, that is, when the irradiation light 12 is irradiated from a direction perpendicular to the inspection surface 2, if the defect portion is a recess and the depth of the recess is small, the defect is reflected from the defect portion in the direction of the imaging device. The reflected light toward the surface increases, and as a result, the lightness of the defective portion increases, so that the difference in lightness between the defective portion and the non-defective portion decreases, and the detection accuracy of the defective portion decreases. If θ ₂ is 15 ° or more, defect detection can be performed without causing such a problem. On the other hand, when θ ₂ is too large, that is, when the irradiation surface 12 is irradiated with the irradiation light 12 from a low angle, the component reflected in the direction of the imaging device in the diffuse reflection (diffuse reflection) component from the non-defect portion on the inspection surface is small. Thus, since the brightness of the non-defect portion is insufficient, the difference in brightness between the defect portion and the non-defect portion is small, and the detection accuracy of the defect portion is reduced. If θ ₂ is 80 ° or less, defect detection can be performed without causing such a problem. Therefore, in the present invention, when a surface that includes an arbitrary point on the linear light source and is perpendicular to the polishing direction is drawn, the line connecting the linear light source and the arbitrary point on the inspection surface is the inspection surface method. The angle θ _{2 made} with the line is
15 ° ≦ θ ₂ ≦ 80 °
And FIG. 3B is a view as seen from a direction perpendicular to the polishing direction 11 of the inspection surface. In order for θ ₂ to maintain the above relationship at any point on the inspection surface where the surface F ₅ and the inspection surface intersect, the position of the linear light source at the position where the surface F ₅ intersects is shown in FIG. It is necessary to exist in the area indicated by hatching in (b). It is preferable to dispose the linear light sources in both the left and right areas shown by hatching in FIG. 3B because the uniformity of the brightness on the inspection surface is improved. However, the linear light sources are applied only to either the left or right area. Even when they are arranged, sufficiently uniform brightness can be obtained for defect inspection.

On the other hand, it is not necessary until θ ₂ holds the above relationship in all light sources on the linear light source. It is only necessary that the position of the light source on the linear light source has the above θ ₂ relationship in an area of at least 60% between the two right angle lines.

In FIG. 4, if the shortest distance Lmin between the linear light source 4 and the inspection surface 2 is too long, the output of the light source must be increased, and the overall size of the defect detection device becomes too large. If Lmin is 1000 mm or less, defect detection can be performed without causing such a problem. On the other hand, when the shortest distance Lmin between the linear light source 4 and the inspection surface 2 is too close, the component that reflects toward the imaging device in the diffuse reflection (diffuse reflection) component in the non-defect portion of the inspection surface close to the linear light source 4 The brightness of the portion near the light source in the inspection surface becomes high and unevenness in brightness may occur, but Lmin may be more than half of the length perpendicular to the polishing direction on the inspection surface of the metal sample. If it is long, such a problem does not occur and it is preferable. For example, if the length in the direction perpendicular to the polishing direction on the inspection surface of the metal sample is 100 mm, Lmin is preferably 50 mm or more. Usually, the occurrence of this problem can be avoided when θ ₂ has the above-described relationship.

  As described above, the inspection surface of the metal sample is polished in one direction using a polishing means having a predetermined roughness, and defects in the metal sample are revealed by an etching process. 4 and an imaging device 3 that images the inspection surface 2 are disposed, and the inspection surface 2 is imaged by the imaging device 3 while irradiating the inspection surface 2 with light from the linear light source 4. Thereby, the brightness of the non-defect portion 7 on the inspection surface 2 is bright and uniform, the brightness of the defect portion 6 is dark, and as a result, the brightness difference between the defect portion 6 and the non-defect portion 7 is clarified. It is possible to capture an image that can be detected satisfactorily.

  As the imaging device 3, any film camera or digital camera can be used as long as the imaging device can image the inspection surface. It is preferable to use an imaging device using a semiconductor imaging device or the like because captured image data can be taken into an image processing device and image analysis of a defective portion can be performed.

  Next, a preferred arrangement form of the linear light source 4 and the imaging device 3 of the present invention will be described.

As shown in FIG. 5, an angle between the linear direction 17 of the linear light source 4 and the polishing direction 11 of the inspection surface 2 is set to θ ₁ . A smaller θ ₁ is preferable because the linear direction 17 of the linear light source 4 and the polishing direction 11 of the inspection surface 2 are nearly parallel, and the brightness viewed from the imaging device 3 is uniform in any part of the inspection surface 2. . And
| Θ ₁ | ≦ 35 °
With this relationship, the uniformity of the brightness on the inspection surface can be sufficiently maintained. Of course, even if it is out of this range and there is some non-uniformity in brightness, it is possible to sufficiently detect defects.

It is preferable that the imaging device 3 is arranged at a position where an image is captured directly above the center of the inspection surface 2 and facing the inspection surface. As shown in FIG. 6, an angle between a line connecting an arbitrary point on the inspection surface and the imaging apparatus and a normal line of the arbitrary point is θ ₃ . If θ ₃ is too large, the diffuse reflection component due to the irradiation light from the linear light source is not sufficient, and the brightness of the non-defect portion on the inspection surface is undesirably lowered. In the present invention, for any part on the inspection surface,
θ ₃ ≦ 60 °
It is preferable to arrange the imaging device 3 so as to maintain the above relationship, since the brightness of the non-defect portion of the inspection surface 2 is uniformly maintained. If an imaging device is arranged directly on the inspection surface from directly above the center of the inspection surface using a camera having a normal focal length, θ ₃ can be set to the above preferable range.

  For etching to reveal defects in metal samples, as a method of generating irregularities in cracks, generating irregularities due to corrosion in segregating parts, or darkening segregated parts (for example, blackening). A commonly used etching method can be employed. For example, an aqueous solution of ammonium persulfate or a method using picric acid and hydrochloric acid is preferably used. In addition, any method may be used as long as the defect portion appears, that is, the appearance of unevenness in the cracked portion, the generation of unevenness due to corrosion in the segregated portion, or the darkening of the segregated portion (for example, blackening). The method may be used.

  A continuous cast slab (width: 1200 mm, thickness: 250 mm) of medium-carbon aluminum killed steel was cut perpendicularly to the length direction to cut out a metal sample 1 having a length direction of 50 mm, and the cut surface was used as an inspection surface 2. The inspection surface was polished by various methods, etched using an aqueous ammonium persulfate solution, and then imaged on the inspection surface under various illumination conditions. As the imaging device, a digital single lens reflex camera (imaging screen size: 22.3 mm × 14.9 mm, effective pixels: about 15.1 million pixels) and a lens (focal length 28 mm) were used. Table 1 shows processing conditions and evaluation results. Numerical values that fall outside the scope of the present invention are underlined.

  As Examples 1-15 and Comparative Examples 1-5, 7-12, as the polishing method of the inspection surface, as shown in FIG. Polishing was performed using For Comparative Example 6, after polishing a portion of 600 mm on one side with a width of 22 mm on one side with the polishing direction 11 as one direction coinciding with the width direction 22 of the slab, the remaining 600 mm on one side was cast into the slab. Polishing was performed using polishing paper with the one direction (thickness direction 23 of the slab) perpendicular to the width direction as the polishing direction 11. The count of the abrasive paper is shown in Table 1.

  As for the light source, for Examples 1 to 13 and Comparative Examples 1 to 11, two straight tube fluorescent lamps each having a length of 630 mm and a rated power consumption of 30 W are provided in each direction, as shown in FIG. A total of four light sources in each direction were used as the linear light sources 4. As a light source in Example 14, two straight tube fluorescent lamps having a length of 630 mm and a bottom angle power consumption of 30 W were used in only one direction. As the light source in Example 15, LEDs with a rated power consumption of 7 W arranged in a straight line at a pitch of 150 mm were used as the point light source 4b, and the linear light source 4 was formed by using nine LEDs in one direction and a total of 18 in two directions. As the light source in Comparative Example 12, two light bulbs with a rated power consumption of 500 W were disposed as point light sources 5 as shown in FIG.

For each inspection level, the captured image captured by the imaging device 3 was subjected to image analysis, and the number of defects on the inspection surface 2 was counted. Next, normalization was performed using the number of defects detected in Example 3, and the number of defects N _NL under each condition was calculated. From this N _NL , the test status was evaluated according to the following criteria and entered in Table 1.
0.95 ≦ N _NL・ ・ ・ pretty good 0.90 ≦ N _NL <0.95 ・ ・ ・ good 0.85 ≦ N _NL <0.90 ・ ・ ・ good but slightly inferior 0.55 ≦ N _NL <0 .80 ... slightly inferior 0.30 ≦ N _NL <0.55 ... inferior
N _NL <0.30 ... considerably inferior

For Examples 1 to 5 and Comparative Examples 1 to 3, the arrangement direction of the linear light source is shown in FIG. 11B (Example 1) with reference to Example 3 shown in FIGS. 10 (a) and 11 (a). 11 (c) (Comparative Example 1). When FIG. 11 (a) changes angular position of the linear light source relative to (Example 3) θ _4, Example 1 is θ ₄ = -35 °, Comparative Example 1 becomes θ ₄ = -90 °. For each level, the area of the linear light source occupying the distance between the two perpendicular lines is shown in Table 1 as the light source cover ratio C _R (%).

In Examples 6 to 8 and Comparative Examples 4 and 5, the count of the abrasive paper was changed. In Examples 9 and 10 and Comparative Example 8, the arrangement of the linear light sources is the same as that in Example 3, and only Lmin is changed. In Examples 11 and 12, and Comparative Examples 9 and 10, the arrangement of the linear light sources is the same as that in Example 3, and only the angle θ ₂ is changed. In the thirteenth embodiment, the arrangement of the linear light sources is the same as that of the third embodiment, and only the angle θ ₃ related to the imaging device is changed.

  In Table 1, Example 3 serving as a reference is duplicated for each example group for easy comparison.

  In Table 1, it was found that all of the examples of the present invention were in the range of “very good” to “good but slightly inferior”.

  The present invention is not limited to the embodiments specifically described in the above-described embodiments and examples, and can be modified within the scope defined in the claims. For example, The present invention is also applicable to the case of configuring a method for detecting a defective portion in a metal of the present invention, in particular, a steel piece, with high accuracy and speed by combining one or all of the above embodiments, examples and modifications. Is included in the scope of rights.

DESCRIPTION OF SYMBOLS 1 Metal sample 2 Inspection surface 3 Imaging device 4 Linear light source 4a Linear continuous light source 4b Point light source 5 Point light source 6 Defect part 7 Non-defect part 11 Polishing direction 12 Irradiation light 13 Reflected light 13a Regular reflection component 13b Diffuse reflection component 14 Polishing direction both ends 15 Sample polishing direction length 16 Both ends perpendicular line 17 Linear direction 18 Area occupied by linear light source 21 Line 22 Width direction 23 Thickness direction

Claims (3)

The inspection surface of the metal sample is polished in one direction using a polishing means having a roughness of No. 100 to No. 1000 specified in JIS R6252, and the metal sample is etched to reveal defects in the metal sample. ,
A linear light source or a light source in which a plurality of point light sources are arranged in a line (hereinafter collectively referred to as a “linear light source”) is prepared, and the light sources in which the plurality of point light sources are arranged in a line are adjacent. The distance between the matching point light sources is 30% or less of the polishing direction length (hereinafter referred to as “sample polishing direction length”) of the inspection surface of the metal sample,
When the inspection surface is viewed from vertically above and a line perpendicular to the polishing direction is drawn from both ends of the inspection surface in the polishing direction (hereinafter referred to as “both ends perpendicular line”), the linear light source is perpendicular to the two ends. Occupies at least 60% of the area between the lines,
When at least 60% of the area between the two right-angled lines and a plane perpendicular to the polishing direction including any point on the linear light source is drawn on the linear light source and the inspection surface The angle θ ₂ between the line connecting any point of and the normal of the inspection surface is
15 ° ≦ θ ₂ ≦ 80 °
In relation to
The minimum distance Lmin between the linear light source and the inspection surface is 1000 mm or less,
Arranging an imaging device for imaging the inspection surface,
A metal defect detection method, wherein the inspection surface is imaged by the imaging device while irradiating the inspection surface with light from the linear light source. The angle θ ₁ between the linear direction of the linear light source and the polishing direction of the inspection surface is
| Θ ₁ | ≦ 35 °
The metal defect detection method according to claim 1, wherein: An angle θ ₃ formed between a line connecting the imaging device and an arbitrary point on the inspection surface and a normal line of the inspection surface is
θ ₃ ≦ 60 °
The metal defect detection method according to claim 1 or 2, wherein

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