Nondestructive testing method for thickness of oxide scale on surface of thin-gauge strip steel

Abstract

The invention discloses a nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge strip steel, and belongs to the technical field of metal material surface detection.The nondestructive testing method comprises the steps that S1, plate shearing and carbon powder composite sample preparation are conducted, specifically, firstly, the thin-gauge strip steel is cut through a plate shearing machine to obtain a strip steel sample, then the strip steel sample and carbon powder are mixed, and finally hot inlaying treatment is conducted; s2, multi-angle progressive grinding and polishing are conducted, and in the grinding and polishing process, the sample is rotated by 20 + / -5 degrees every time the abrasive paper is replaced; s3, gray scale and depth-of-field two-parameter analysis: firstly, based on the gray scale difference among the carbon powder, the strip steel substrate and the oxide layer, carrying out regional distinguishing on the carbon powder, the strip steel substrate and the oxide layer; acquiring depth-of-field parameters for different areas; and finally, obtaining the thickness of the oxide layer according to the difference value of the three depth-of-field parameters. Through the synergistic effect of the sample preparation technology, the grinding and polishing technology and two-parameter analysis, the detection precision is improved, and meanwhile the detection efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface detection of metal materials, and particularly relates to a non-destructive detection method for the thickness of mill scale on the surface of thin-gauge strip steel. Background Art

[0002] In the field of surface detection of metal materials, there have always been many difficulties in detecting the thickness of mill scale on the surface of thin-gauge strip steel. Traditional detection methods have obvious defects: mechanical cutting and grinding problems: when detecting 1.5 - 6 mm thin-gauge strip steel, the traditional mechanical cutting / grinding method will generate large vibrations, resulting in the shedding of mill scale on the strip steel surface, making subsequent detection unable to be carried out accurately. Insufficient embedding process: the existing embedding process is difficult to effectively protect micron-level oxide layers (such as 5 μm), and it is easy to damage the oxide layer during the embedding process. Difficulties in microscopic observation: when using a microscope for observation, due to the lack of a comparison reference, there are great difficulties in determining the boundary of mill scale and positioning, affecting the accuracy of measurement. Pickling risk: when using the pickling method, if the pickling time is not properly controlled, it will cause corrosion of the strip steel substrate, thus seriously affecting the measurement result of the mill scale thickness. Summary of the Invention

[0003] Aiming at the problems existing in the prior art, the present invention provides a non-destructive detection method for the thickness of mill scale on the surface of thin-gauge strip steel, which synergistically acts from three aspects: sample preparation technology, grinding and polishing process, and dual-parameter analysis, not only improving the detection accuracy but also improving the detection efficiency.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A non-destructive detection method for the thickness of mill scale on the surface of thin-gauge strip steel, comprising:

[0006] S1. Sample preparation by combining shearing and carbon powder, specifically including: first, cutting the thin-gauge strip steel with a shearing machine to obtain a strip steel sample, then mixing the strip steel sample and carbon powder in a volume ratio of 1:3, and finally performing hot embedding treatment;

[0007] S2. Progressive grinding and polishing at multiple angles. During the grinding and polishing process, every time the sandpaper is changed, the sample is rotated by 20° ± 5°;

[0008] S3. Dual-parameter analysis of gray level and depth of field. First, based on the gray level differences among carbon powder, strip steel substrate, and oxide layer, the three are regionally distinguished; then, for different regions, the depth of field parameters are obtained; finally, according to the differences in the three depth of field parameters, the thickness of the oxide layer is obtained.

[0009] Preferably, the particle size of the carbon powder is 200 mesh to 400 mesh.

[0010] Preferably, the hot inlay treatment is controlled at 120°C to 150°C, and the hot pressing time is 8 minutes to 10 minutes.

[0011] Preferably, during the grinding and polishing process, the specimen is rotated 20° each time the sandpaper is changed.

[0012] Preferably, the control pressure of the shearing machine is not greater than 5 MPa.

[0013] Preferably, the size of the strip specimen is 50 mm × 50 mm.

[0014] Preferably, the thickness range of the thin-gauge strip is 1.5 mm to 6 mm.

[0015] Preferably, in S3, when the difference in image gray values is greater than or equal to 15%, it is determined as the scale region, and the boundary of the oxide layer is marked.

[0016] Compared with the prior art, the advantages and positive effects of the present application are:

[0017] The present invention synergistically acts from three aspects: sample preparation technology, grinding and polishing process, and dual-parameter analysis, not only improving the detection accuracy but also improving the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is an image after inlaying in the preferred embodiment of the present application;

[0020] Figure 2 It is a schematic diagram of the scale layer under the microscope in the preferred embodiment of the present application;

[0021] Figure 3 It is a schematic diagram of the substrate layer under the microscope in the preferred embodiment of the present application;

[0022] Figure 4 It is a schematic diagram of the toner layer under the microscope in the preferred embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention described and illustrated herein generally can be arranged and designed in a variety of different configurations. Therefore, the detailed description of the embodiments of the present invention provided herein is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0025] Please refer to Figures 1 to 4 , a non-destructive testing method for the thickness of scale on the surface of thin-gauge strip steel, including:

[0026] S1. Sample preparation by combining shearing and carbon powder: Specifically, first use a shearing machine to cut the thin-gauge strip steel to obtain a strip steel sample, then mix the strip steel sample and carbon powder in a volume ratio of 1:3, and finally perform hot embedding treatment;

[0027] S2. Progressive grinding and polishing from multiple angles. During the grinding and polishing process, rotate the sample 20° ± 5° every time the sandpaper is changed;

[0028] S3. Dual-parameter analysis of gray level and depth of field: First, based on the gray level differences among carbon powder, strip steel matrix, and oxide layer, distinguish the three regions; then, for different regions, obtain the depth of field parameters; finally, according to the differences in the three depth of field parameters, obtain the thickness of the oxide layer. Specifically:

[0029] 3.1 Utilization of gray level differences

[0030] Optical properties of materials: Different materials (carbon powder - black, strip steel matrix - gray, oxide layer - white) have different reflectivities to light, resulting in significant differences in gray level values in the image. For example: The oxide layer (white) has a high reflectivity, and the gray level value is close to 255 (8-bit image); the strip steel matrix (gray) has a medium gray level value; the carbon powder (black) has a low reflectivity, and the gray level value is close to 0.

[0031] Layer boundary recognition: Determine the boundaries of each layer through grayscale threshold segmentation (Otsu algorithm) or edge detection (Canny algorithm), and calculate the pixel width between layers.

[0032] 3.2 Calibration function of depth of field parameters

[0033] Challenge of surface unevenness: The surface of the oxide layer may be uneven, resulting in defocus in some areas during microscope imaging and affecting the accuracy of grayscale analysis.

[0034] Principle of depth of field compensation: The depth of field of the microscope determines the longitudinal range of clear imaging. If the surface exceeds the depth of field, the image will be blurred.

[0035] Infer the surface height change through multi-focus imaging (focus stack technology) or known depth of field parameters, combined with the clarity evaluation function, and correct the thickness measurement.

[0036] 3.3 Structure of the thickness calculation model

[0037] The thickness model is a multi-module system, usually including the following core components:

[0038] Image acquisition module: A high-resolution camera or confocal microscope captures the surface topography, ensuring that the pixel resolution reaches the micron level.

[0039] Preprocessing module: Noise reduction (Gaussian filtering or median filtering);

[0040] Contrast enhancement (histogram equalization).

[0041] Grayscale analysis module: Threshold segmentation: Divide the toner, matrix, and oxide layer regions;

[0042] Pixel - physical size conversion: According to the microscope calibration parameters (such as each pixel corresponding to 0.1μm), convert the pixel width between layers into the actual thickness.

[0043] Depth of field calibration module: Focal plane analysis: Calculate the surface height distribution through multi-focal plane images or depth of field parameters;

[0044] Geometric correction: Perform thickness compensation on inclined or undulating areas (such as trigonometric function correction or three-dimensional topography reconstruction).

[0045] Integration and output module: Integrate the grayscale and depth of field data, and output the thickness and error range of each layer.

[0046] The present invention utilizes the instantaneous shearing force generated during the shearing process of a shearing machine to achieve cutting of materials under almost vibration-free conditions. This method significantly reduces the damage to the mill scale on the material surface from the source, thus maintaining the integrity of the material. After the shearing process is completed, the present invention further describes how to process strip specimens. The specific operation is to mix the strip specimens with carbon powder within a specific particle size range, which is between 200 mesh and 400 mesh. The mixing ratio is that the strip specimens and the carbon powder are mixed according to a volume ratio of 1:3. After mixing, the strip specimens will undergo a hot embedding process. During this process, the temperature is precisely controlled between 120°C and 150°C, and the hot pressing time is maintained at 8 to 10 minutes. Through this hot embedding process, the carbon powder not only physically fixes the mill scale tightly on the strip surface, preventing the mill scale from falling off during subsequent processing, but also forms a distinct gray-scale contrast between the black of the carbon powder, the gray of the strip substrate, and the white of the oxide layer. This contrast provides a natural contrast benchmark for subsequent gray-scale analysis, making the analysis process more accurate and efficient.

[0047] The multi-angle progressive grinding and polishing process is an innovative material processing method: during the grinding and polishing process, each time the sandpaper is changed, the operator rotates the specimen by a precise angle, approximately 20°±5°. This meticulous operation step is in sharp contrast to the traditional linear grinding and polishing method. Due to its single-direction grinding and polishing path, the traditional linear grinding and polishing method often causes the grinding and polishing force to concentrate in one direction, which is likely to generate a large lateral stress. The accumulation of lateral stress may damage the oxide layer on the material surface, thus affecting the performance and appearance of the material. However, the multi-angle rotation grinding and polishing method adopted in the present invention effectively distributes the grinding and polishing force evenly on the entire surface of the specimen by changing the grinding and polishing angle. Such an operation can not only ensure the removal of excess material during the grinding and polishing process, but also observe the grinding and polishing effect in real time, thus ensuring that the entire grinding and polishing process is both efficient and safe, without causing any damage to the oxide layer, and ensuring the integrity and quality of the material surface.

[0048] The dual-parameter (gray scale and depth of field) analysis method is a measurement technique that makes full use of the significant gray scale differences existing among the toner (black), the strip steel substrate (gray), and the oxide layer (white). By using high-precision image acquisition equipment, detailed images of the specimen surface can be captured. Subsequently, with the help of professional image analysis software, researchers can construct an accurate thickness calculation model. This model can accurately reflect the thickness differences between different material layers. In addition, this method also combines the depth of field parameter of the microscope to effectively calibrate the errors that may be caused by the unevenness of the oxide layer surface or other factors during the measurement process. In this way, the gray scale-depth of field dual-parameter analysis method can achieve high-precision measurement of the oxide layer thickness, providing important technical support for materials science and industrial applications.

[0049] Core innovation points: Shearing-carbon powder composite sample preparation technology. Shearing instead of cutting: The shearing method is adopted instead of traditional mechanical cutting. This innovation greatly reduces the impact of vibration on the mill scale of the strip steel and effectively avoids the problem of mill scale falling off due to vibration. Carbon powder wrapping and hot embedding: After shearing, the strip steel specimen is directly wrapped with carbon powder for hot embedding treatment. This method not only protects the oxide layer through physical fixation, but also the gray scale contrast formed between the carbon powder, the oxide layer, and the substrate provides great convenience for subsequent analysis. Multi-angle progressive grinding and polishing process: During the grinding and polishing process, every time the sandpaper is changed, the specimen is rotated by 20°±5°. In this way, the grinding and polishing effect can be observed in real time, and at the same time, the lateral stress generated during the grinding and polishing process can be effectively reduced to avoid damage to the oxide layer. Gray scale-depth of field dual-parameter analysis method: Gray scale difference modeling: Based on the obvious gray scale differences among the carbon powder (black), the strip steel substrate (white), and the oxide layer (gray), an accurate thickness calculation category is established. Depth of field parameter calibration: Combining the depth of field parameter of the microscope to calibrate the errors generated during the measurement process to further improve the measurement accuracy.

[0050] Sampling optimization: A hydraulic shearing machine is used for sampling, controlling the pressure ≤5 MPa, and cutting out a specimen of 50×50 mm to ensure that the burrs on the specimen edge are <0.1 mm. Such a shearing method can minimize the damage to the mill scale on the strip steel surface. Carbon powder embedding process: Mixing according to the volume ratio of carbon powder to specimen of 3:1 and conducting hot pressing treatment at a temperature of 120℃~150℃, with the hot pressing time controlled at 8 - 10 minutes. After this process treatment, the oxide layer can be effectively protected, and at the same time, good gray scale contrast conditions are provided for subsequent analysis. Detection system: Combining image recognition algorithms, when the gray scale value difference of the image ≥15%, it is determined as the mill scale area, realizing the automatic marking of the oxide layer boundary and improving the detection efficiency and accuracy.

[0051] By the method of the present invention, the measurement error of the oxide layer thickness is ≤0.5 μm, while the error of the traditional method is ≥2 μm. Obviously, the accuracy of the present invention has been greatly improved. Efficiency improvement: The sample preparation time is shortened from the original 25 minutes to 8 minutes per piece, greatly improving the detection efficiency. Scope of application: It has been successfully applied to the detection of 1.5-mm ultra-thin strip steel, breaking through the lower limit of 6 mm of the traditional method and expanding the scope of application of the detection. Comparison of the scale-off rate: Through experimental comparison, the scale-off rate of the traditional mechanical cutting / sample grinding method is as high as 80%, while by using the shearing and carbon powder composite sample preparation technology of the present invention, the scale-off rate is reduced to 10%, effectively solving the problem of scale-off. The data is shown in Table 1 below:

[0052] Table 1 shows the scale-off rates corresponding to two different methods

[0053] Scale loss rate Traditional 80％ The method of the present invention 10％

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. A non-destructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip, characterized in that: include: S1, shearing and carbon powder composite sample preparation, specifically comprising: firstly cutting the thin gauge strip steel by a shearing machine to obtain a strip steel sample, then mixing the strip steel sample with carbon powder in a volume ratio of 1:3, and finally performing a hot mounting process; S2, multi-angle progressive grinding and polishing. During the grinding and polishing process, each time the sandpaper is changed, the sample is rotated 20°±5°; S3, grayscale and depth of field dual parameter analysis, first based on the grayscale differences between the carbon powder, strip steel substrate, and oxide layer, the three are divided into regions; then the depth of field parameters are obtained for different regions; finally, the oxide layer thickness is obtained based on the difference between the three depth of field parameters.

2. The nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip according to claim 1 is characterized in that: The particle size of the carbon powder is 200-400 meshes.

3. The nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip according to claim 1 is characterized in that: The heat embedding treatment is controlled at 120° C. to 150° C., and the hot pressing time is 8 minutes to 10 minutes.

4. The nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip according to claim 1 is characterized in that: During the grinding and polishing process, the specimen was rotated 20° each time the sandpaper was changed.

5. The nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip according to claim 1 is characterized in that: The control pressure of the shearing machine shall not exceed 5MPa.

6. The nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip according to claim 1 is characterized in that: The size of the strip steel sample is 50 mm×50 mm.

7. The nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip according to claim 1 is characterized in that: The thickness of the thin-gauge steel strip ranges from 1.5 mm to 6 mm.

8. The nondestructive testing method for the thickness of oxide scale on the surface of thin-gauge steel strip according to claim 1, characterized in that: In S3, when the gray value difference of the image is greater than or equal to 15%, it is determined to be an iron oxide scale area, and the oxide layer boundary is marked.

Images