Verification method for judging cooling uniformity of ultrafast cooling based on oxide skin color

Abstract

The invention discloses a verification method for judging cooling uniformity of ultrafast cooling based on oxide skin color, which comprises the following steps of: (1) cutting a metallographic sample from a steel plate sample with black spot morphology, and respectively occupying half areas of black spot oxide skin and normal oxide skin on the surface of the sample; (2) after the sample is cleaned and dried, respectively measuring the roughness of the black spot oxide skin and the grey white oxide skin on the surface by using a laser confocal microscope; (3) grinding and polishing the section of the sample, corroding the section with a 4% nitric acid-alcohol solution for 5s, and analyzing a near-surface metallographic structure; (4) the surface roughness value of the black spots is more than 0.1 mu m greater than that of the grey oxide skin, and the corresponding martensite of the black spot structure is more; and (5) verifying the feasibility of judging the cooling uniformity of the plate surface according to the color of the surface oxide skin according to an analysis result. The method has the advantages that the cooling uniformity of the ultra-fast cooling system is quickly and accurately judged through the color of the oxide skin, the non-uniform cooling area of the ultra-fast cooling system is locked and adjusted in time, and black spots on the surface of a steel plate can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-fast cooling system processes, and in particular relates to a verification method for judging ultra-fast cooling uniformity based on oxide scale color. Background Art

[0002] The ultra-fast cooling system can achieve high cooling intensity and cooling uniformity through the high-pressure jet impact heat exchange mechanism, which plays a key role in the cooling control and structural performance optimization of medium and thick plates. However, since the high-density nozzles usually used in ultra-fast cooling systems have a small aperture, they are prone to clogging during use, which will cause uneven cooling. At present, in this case, the infrared temperature distribution diagram after the steel plate enters the water can be used to judge whether the cooling is uniform, but this method is not very sensitive. When the cooling uniformity of the plate surface is above 15°C, this method can be used to judge, but when the cooling uniformity is below 10°C, it cannot be judged whether the cooling is uniform. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems of low accuracy and low sensitivity in the existing ultra-fast cooling uniformity judgment. It provides a verification method for judging the ultra-fast cooling uniformity based on the color of the oxide scale. The cooling uniformity of the ultra-fast cooling system can be quickly and accurately judged by the color of the oxide scale, and the area of ​​uneven ultra-fast cooling can be timely locked. The nozzle or ultra-fast cooling manifold in the area can be adjusted, which is beneficial to improving the black spots on the surface of the steel plate and improving product quality.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: A verification method for judging ultrafast cooling uniformity based on oxide scale color, comprising the following steps: (1) Sample preparation: Take a steel plate sample with black spots. The black spots are darker than the normal spots and are black. The oxide scale at the normal location is grayish white. Cut a metallographic sample, and the area of ​​the black spots and oxide scale on the surface of the sample is half each. (2) Roughness analysis: The sample was placed in anhydrous ethanol and ultrasonic cleaning was used to remove the oil on the surface. After the sample was dried with a hair dryer, the roughness of the black spot oxide scale and the gray-white oxide scale on the surface was measured using a laser confocal microscope. (3) Metallographic analysis: The cross section of the metallographic specimen was polished, where the cross section was the surface corresponding to the black oxide scale and the gray oxide scale. After polishing, the cross section was etched with 4% nitric acid-alcohol solution for 5 seconds. The upper surface of the cross section corresponding to the black oxide scale and the gray oxide scale was photographed using a laser confocal microscope. (4) Analysis data: The surface roughness of the black oxide scale is greater than that of the gray oxide scale by more than 0.1 μm, and the martensite content of the metallographic structure corresponding to the cross section of the black oxide scale is greater than that of the gray oxide scale; (5) According to the analysis results of the metallographic samples, the black spot oxide scale has a large roughness and a high martensite content, which verifies that high cooling intensity will cause the oxide scale to turn black. For hot-rolled and controlled-cooled steel plates, the cooling uniformity of the plate surface can be judged based on the color of the surface oxide scale.

[0005] Furthermore, in step (1), the size of the metallographic sample is 20*40*full thickness, in mm.

[0006] Furthermore, in the step (1), there is no height difference at the connection between the black oxide scale and the gray oxide scale, and the oxide scales of both are intact and have not fallen off.

[0007] Furthermore, in step (2), the same magnification is selected for the black oxide scale and the gray oxide scale, preferably 200 times.

[0008] Furthermore, in step (3), the metallographic structure is a near-surface structure, which is within 500 μm from the upper surface.

[0009] Furthermore, in step (3), the upper surface of the cross section corresponding to the black spot oxide scale is photographed twice, and the magnifications of the two photographs are 200 times and 500 times respectively.

[0010] Furthermore, in step (3), the upper surface of the cross section corresponding to the gray-white oxide scale is photographed twice, and the magnifications of the two photographs are 200 times and 500 times respectively.

[0011] Furthermore, in step (4), the surface roughness of the black spot oxide scale is 0.1 μm greater than that of the grayish white oxide scale, and the martensite content at the corresponding position is higher.

[0012] Furthermore, in step (5), the location where the black spots are generated is used to locate the area where the ultrafast cooling is uneven, and then the intensity of the cooling is determined based on the color depth of the oxide scale.

[0013] The working principle of the present invention is as follows: When the thermal expansion coefficient of the substrate is greater than that of the oxide scale, the cooling intensity is high, and the substrate shrinks faster than the oxide scale. The oxide scale cracks or peels due to tensile stress, and the roughness increases, resulting in increased diffuse reflection of light, darkening the oxide scale, and forming black spots on the steel plate surface. Conversely, when the cooling intensity is low, the oxide scale is less rough and appears off-white. Therefore, the color of the oxide scale can be used to determine cooling uniformity, and targeted measures can be taken based on the location of the black spots, effectively improving the black spot problem.

[0014] In the technical solution of the present invention, the cooling uniformity of the medium and thick plates subjected to controlled rolling and controlled cooling is judged quickly and accurately according to the mechanism of black spot generation, and the cooling intensity is judged according to the color depth of the oxide scale. Furthermore, according to the location where the black spots are generated, the area of ​​uneven ultra-fast cooling is identified, and the nozzles or ultra-fast cooling manifolds in the area are adjusted, which is beneficial to improving the black spots on the surface of the steel plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a roughness morphology diagram of black spots in the present invention; Figure 2 This is a morphology diagram of black spots on the steel plate surface in the present invention. DETAILED DESCRIPTION Example

[0016] To make the present invention more clear, a verification method for judging the uniformity of ultra-fast cooling based on the color of the oxide scale of the present invention is further described below with reference to the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] The mechanism of black spots is uneven ultra-fast cooling intensity. At the location with high cooling intensity, the oxide scale is easily detached or cracked due to tensile stress, resulting in increased roughness of the oxide scale and greater diffuse reflection of light. The area appears black to the naked eye. Figure 2 At the location with low cooling intensity, the oxide scale is grayish white, forming a color difference on the surface of the steel plate, so the cooling uniformity of ultra-fast cooling can be judged according to the color of the oxide scale.

[0018] In order to verify the feasibility of the above idea, this embodiment provides a verification method for judging the uniformity of ultra-fast cooling based on the color of the oxide scale, which is characterized by: (1) Sample preparation: Take the 30mm thick Q355B with black spots on the surface after hot rolling, controlled rolling and controlled cooling, and cut it into a metallographic sample of 20*40*30mm, with the area of ​​black spot oxide scale and gray-white oxide scale each accounting for half. Ultrasonic cleaning is used to remove the oil stains on the surface.

[0019] (2) Roughness analysis: Roughness was measured using a laser confocal microscope at a magnification of 200 times, see Figure 1 .

[0020] (3) Metallographic analysis: After the sample was polished, it was corroded with 4% nitric acid-alcohol solution for 5 seconds to analyze the near-surface metallographic structure. The near-surface metallographic structure of the black spot oxide scale had a higher martensite content.

[0021] After verification by the above method, it was found that the roughness of the black spot oxide scale is 0.1μm or more than that of the gray-white oxide scale, and the corresponding black spot structure has a higher martensite content.

[0022] The present invention uses scale color to determine ultra-rapid cooling uniformity, offering high sensitivity and unaffected by the plate surface's cooling uniformity temperature. This determination can be made directly, regardless of whether the temperature is below 10°C. The present invention uses scale color to quickly and accurately determine the cooling uniformity of the ultra-rapid cooling system. The method of this embodiment demonstrates the feasibility of this determination method, enabling timely identification of areas of ultra-rapid cooling unevenness and adjustments to the nozzles or ultra-rapid cooling manifolds in those areas. This helps improve black spots on the steel plate surface and enhances product quality.

[0023] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A verification method for judging ultrafast cooling uniformity based on scale color, characterized by: (1) Sample preparation: Take a steel plate sample with black spots. The black spots are darker than the normal spots and are black. The oxide scale at the normal location is grayish white. Cut a metallographic sample, and the area of ​​the black spots and oxide scale on the surface of the sample is half each. (2) Roughness analysis: The sample was placed in anhydrous ethanol and ultrasonic cleaning was used to remove the oil on the surface. After the sample was dried with a hair dryer, the roughness of the black spot oxide scale and the gray-white oxide scale on the surface was measured using a laser confocal microscope. (3) Metallographic analysis: The cross section of the metallographic specimen was polished, where the cross section was the surface corresponding to the black oxide scale and the gray oxide scale. After polishing, the cross section was etched with 4% nitric acid-alcohol solution for 5 seconds. The upper surface of the cross section corresponding to the black oxide scale and the gray oxide scale was photographed using a laser confocal microscope. (4) Analysis data: The surface roughness of the black oxide scale is greater than that of the gray oxide scale by more than 0.1 μm, and the martensite content of the metallographic structure corresponding to the cross section of the black oxide scale is greater than that of the gray oxide scale; (5) According to the analysis results of the metallographic samples, the black spot oxide scale has a large roughness and a high martensite content, which verifies that high cooling intensity will cause the oxide scale to turn black. For hot-rolled and controlled-cooled steel plates, the cooling uniformity of the plate surface can be judged based on the color of the surface oxide scale.

2. The method for verifying ultrafast cooling uniformity based on scale color according to claim 1, characterized in that: In the step (1), the size of the metallographic sample is 20*40*full thickness, in mm.

3. The verification method for judging ultrafast cooling uniformity based on scale color according to claim 1 or 2, characterized in that: In the step (1), there is no height difference at the connection between the black oxide scale and the gray oxide scale, and both oxide scales are intact and have not fallen off.

4. The verification method for judging ultra-fast cooling uniformity based on scale color according to claim 1, characterized in that: In the step (2), the same magnification is selected for the black oxide scale and the gray oxide scale, preferably 200 times.

5. The verification method for judging ultrafast cooling uniformity based on scale color according to claim 1, characterized in that: In the step (3), the metallographic structure is a near-surface structure, which is within 500 μm from the upper surface.

6. The method for verifying ultrafast cooling uniformity based on scale color according to claim 1, characterized in that: In the step (3), the upper surface of the cross section corresponding to the black spot oxide scale is photographed twice, and the magnifications of the two photographs are 200 times and 500 times respectively.

7. The method for verifying ultrafast cooling uniformity based on scale color according to claim 6, characterized in that: In the step (3), the upper surface of the cross section corresponding to the gray-white oxide scale is photographed twice, and the magnifications of the two photographs are 200 times and 500 times respectively.

8. The method for verifying ultrafast cooling uniformity based on scale color according to claim 1, characterized in that: In the step (4), the surface roughness of the black oxide scale is 0.1 μm greater than that of the gray oxide scale, and the martensite content at the corresponding position is higher.

9. The verification method for judging ultra-fast cooling uniformity based on scale color according to claim 1, characterized in that: In the step (5), the area where the ultrafast cooling is uneven is identified by the location where the black spots are generated, and the intensity of the cooling is determined based on the color depth of the oxide scale.

Images