A method for artificial detection of phase organization content of a dual-phase steel

Abstract

The present application relates to the field of metal material analysis, and particularly relates to a dual-phase steel phase organization content artificial detection method, metallographic sample preparation; sample corrosion; image acquisition: using a metallographic microscope to randomly select 3-5 fields of view on a detection surface under 100-200 times magnification to take microstructure photos; phase organization content measurement: superimposing a 9*9 dot matrix grid on the microstructure photo, adjusting the grid to make the grid and the phase organization deformation direction form an about 30 degree angle, carrying out organization point counting, and calculating each phase volume percentage. The present application has the following advantages: using conventional metallographic sample preparation equipment, without relying on expensive image analysis systems or complex equipment such as electron backscatter diffraction, reducing the hardware threshold and daily maintenance cost of detection, and being suitable for various enterprise laboratories and on-site quality control; the optimized corrosion process can stably and clearly display the ferrite and austenite two-phase boundary, avoiding the problems of complex preparation and unstable display effect of the traditional coloring corrosion method.

Description

Technical Field

[0001] This invention relates to the field of metallic material analysis, and in particular to a method for artificially detecting the content of dual-phase steel phase microstructure. Background Technology

[0002] Duplex stainless steel stands out due to its superior comprehensive performance, combining the high strength and excellent corrosion resistance of ferritic stainless steel with the good toughness and weldability of austenitic stainless steel. Therefore, it has found wide and important applications in many key fields such as shipbuilding and marine engineering, deep-sea oil extraction, chemical equipment, and building structures. In recent years, global production of duplex stainless steel has maintained a continuous growth trend. With increasing awareness of resource conservation, energy efficiency, and environmental protection, steel materials are steadily developing towards high performance and low cost, while also being given higher expectations for possessing multiple excellent properties. The multi-functionality of single materials has become the core development trend of the next generation of steel materials, which also means that the application ratio of duplex stainless steel will further expand significantly in the future.

[0003] With the increasing trend towards multifunctional materials and their expanding applications, the demand for large-scale industrial production is urgent. The phase content and distribution directly determine product performance and safety, requiring efficient testing methods to control quality during production. However, existing research-based testing technologies such as image analysis software for automatic identification and electron backscatter diffraction (EBSD) are costly and complex to operate, making them unsuitable for rapid on-site testing and batch quality control, thus hindering industrial expansion. Therefore, the expanded production and widespread application of duplex stainless steel urgently require convenient and reliable manual testing methods to provide technical support, ensuring product quality and application safety. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the manual detection of duplex stainless steel phase content, solving the problems of strong equipment dependence, complex operation procedures, high detection costs, and poor applicability in actual production in existing duplex stainless steel phase content detection methods. By optimizing the metallographic sample preparation process, standardizing the corrosion operation procedure, and organically combining it with the precise manual point counting method, a simple, economical, efficient, and reliable manual detection system is constructed. This system not only meets the actual needs of on-site testing and batch quality control, but also effectively lowers the technical threshold for detection, significantly improves detection efficiency and accuracy, and provides practical and feasible technical support for the research and development optimization, production quality control, and performance evaluation of duplex stainless steel.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for manually detecting the content of dual-phase steel phase microstructure includes: S1. Metallographic sample preparation: The test surface of the sample is polished by sanding it with sandpaper ranging from 120 grit to 800 grit in sequence, and then finely polished to make the test surface bright and smooth. S2, Corrosion Sample: Immerse the polished sample test surface in the etching solution for 5-30 seconds, then rinse, soak in hot water, wipe with anhydrous alcohol and blow dry. S3, Image Acquisition: Using a metallurgical microscope at 100-200x magnification, select representative locations on the surface being examined and take microscopic images of the tissue at 3-5 consecutive fields of view. The actual area of ​​each field of view should be no less than 0.5 mm². 2 ; S4. Phase structure content measurement: Superimpose a square grid with at least 100 intersecting points onto the micrograph. Adjust the grid so that it forms an angle of approximately 25-35° with the direction of phase deformation. Count the number of points and calculate the volume percentage of each phase. 1 point is counted if the point completely falls within the phase region, 0.5 points are counted if it crosses a phase region, and 0 points are counted if it does not fall within the phase region.

[0006] In S1, fine polishing uses diamond polishing compound, and the polishing time is 2 to 5 minutes.

[0007] In S2, rinsing is done with running clean water for 10-30 seconds.

[0008] In S2, the hot water immersion temperature is 80~100℃.

[0009] In S2, the corrosive solution is a mixed solution of nitric acid and hydrochloric acid in a volume ratio of 1:2~3.

[0010] In S3, the image acquisition magnification is 100x.

[0011] In S4, the total number of points in the lattice grid is 100, and each phase in each phase structure covers an average of 2 to 3 points.

[0012] In S4, the lattice grid is arranged in a square pattern. A point is counted as 1 if it falls completely into the phase structure region, 0.5 if it crosses the phase region, and 0 if it does not fall into the phase structure region.

[0013] In S4, the volume percentage of each phase includes the volume percentage of the austenite phase.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. It adopts conventional metallographic sample preparation equipment, without relying on expensive image analysis systems or complex equipment such as electron backscatter diffraction, reducing the hardware threshold and daily maintenance costs of detection, and is suitable for various enterprise laboratories and on-site quality control. 2. The optimized etching process can stably and clearly display the boundary between ferrite and austenite phases, avoiding the problems of complex preparation and unstable display effect of traditional color etching method. Combined with the grid point counting method at a specific angle (about 30°), it effectively reduces the counting deviation caused by the orientation of the structure and improves the accuracy of manual statistical measurement of phase content. 3. The entire testing process is clearly defined and short-lived (from sample preparation to measurement can be completed in a short time). It does not require complex data processing software, has strong versatility and adaptability, and is conducive to rapid organizational evaluation on the production site or in the laboratory, providing timely and reliable data support for production process adjustment and quality control. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of grid measurement. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0017] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0018] Example 1 A method for manually detecting the content of dual-phase steel phase microstructure includes: S1. Metallographic sample preparation: Select duplex stainless steel samples, determine the locations of their transverse and longitudinal test surfaces, and cut and sample them. After sampling, the sample is fixed on the grinding disc, and the test surface is ground from coarse to fine using a series of sandpapers, from 120 grit to 800 grit. After grinding, the test surface is finely polished using a diamond polishing agent with a particle size of 2.5 microns. The polishing time is controlled at 3 minutes until the test surface presents a bright, smooth, and scratch-free mirror effect.

[0019] S2, Corrosion Sample: The polished sample surface was completely immersed in a 1:3 volume ratio of nitric acid and hydrochloric acid in an etching solution for 12 seconds. The sample was then quickly removed and rinsed under running water for about 30 seconds to thoroughly remove any residual corrosive liquid. Next, the sample was immersed in hot water at about 100°C for a short time to further clean the surface; Finally, gently wipe the test surface with a cotton ball soaked in anhydrous alcohol to remove water stains, and then dry it with a hairdryer on the cool setting to ensure that the surface is clean and dry so that the microstructure can be clearly seen.

[0020] S3, Image Acquisition: The etched sample was placed on the stage of a metallographic optical microscope. Using a 100x objective lens, five representative microscopic tissue fields were randomly selected on the sample testing surface. Clear digital photographs of the microstructures were taken and saved as the image basis for subsequent quantitative analysis.

[0021] S4. Phase structure content measurement: The measurement was performed using a manual point counting method. First, prepare a transparent square grid consisting of 9×9 straight lines, which will form 10×10 intersection points on the image; The measurement grid is placed at a 30° angle to the deformation direction of the phase structure, and then superimposed on the five microstructure images obtained in step S3. Count the number of grid intersections that fall within the austenitic phase region in each photograph. Count 1 point for completely falling within the phase region, 0.5 points for crossing phase regions, and 0 points for not falling within the phase region.

[0022] The point counts for the 5 photos are as follows: 52 points, 55 points, 51.5 points, 53 points, and 54 points. The average number of austenite phase points is calculated to be: (52+55+51.5+53+54)÷5=53.1 points; Since the total number of mesh points is 100, the volume percentage of austenite phase is: (53.1 ÷ 100) × 100% = 53.1% See the diagram of the measurement method. Figure 1 .

[0023] Example 2 A method for manually detecting the content of dual-phase steel phase microstructure includes: S1. Metallographic sample preparation: Select duplex stainless steel samples, determine the locations of their transverse and longitudinal test surfaces, and cut and sample them. After sampling, the sample is fixed on the grinding disc, and the test surface is ground from coarse to fine using a series of sandpapers, from 120 grit to 800 grit. After grinding, the test surface is finely polished using a diamond polishing agent with a particle size of 2.5 microns. The polishing time is controlled at 4 minutes until the test surface presents a bright, smooth, and scratch-free mirror effect.

[0024] S2, Corrosion Sample: The test surface of the finely polished sample was completely immersed in a 1:3 volume ratio of nitric acid and hydrochloric acid in an etching solution for 20 seconds to more clearly show the microstructure boundary between the ferrite and austenite phases. The sample was then quickly removed and rinsed under running water for about 30 seconds to thoroughly remove any residual corrosive liquid. Next, the sample was immersed in hot water at about 80°C for a short time to further clean the surface; Finally, gently wipe the test surface with a cotton ball soaked in anhydrous alcohol to remove water stains, and then dry it with a hairdryer on the cool setting to ensure that the surface is clean and dry so that the microstructure can be clearly seen.

[0025] S3, Image Acquisition: The etched sample was placed on the stage of a metallographic optical microscope. Using a 200x objective lens, five representative microscopic tissue fields were randomly selected on the sample testing surface. Clear digital photographs of the microstructures were taken and saved as the image basis for subsequent quantitative analysis.

[0026] S4. Phase structure content measurement: The measurement was performed using a manual point counting method. First, prepare a transparent square grid consisting of 9×9 straight lines (i.e., the grid spacing is equal). This grid can be superimposed on the image to form a 10×10 grid with a total of 100 intersection points. The measurement grid is placed at a 30° angle to the deformation direction of the phase structure, and then superimposed on the five microstructure images obtained in step S3. For each photograph, count the number of grid intersections falling into the ferrite and austenite phase regions; The statistical results for 5 photos are shown below: Photo 1: Ferrite phase 48 points, austenite phase 52 points; Photo 2: Ferrite phase 49 points, austenite phase 51 points; Photo 3: 46 ferrite phase points, 54 austenite phase points; Photo 4: Ferrite phase 47 points, austenite phase 53 points; Photo 5: Ferrite phase at point 45, austenite phase at point 55; Calculate the average number of points in the ferrite phase: (48+49+46+47+45)÷5=47(48+49+46+47+45)÷5=47 points; Calculate the average number of points in the austenite phase: (52+51+54+53+55)÷5=53(52+51+54+53+55)÷5=53 points; Since the total number of grid points is 100, therefore: The volume percentage of ferrite phase is: (47÷100)×100%=47%; The volume percentage of austenite phase is: (53÷100)×100%=53%.

[0027] Measurement results are shown Figure 1 .

[0028] This invention employs conventional metallographic sample preparation equipment, eliminating the need for expensive image analysis systems or complex equipment such as electron backscatter diffraction, thus lowering the hardware threshold and daily maintenance costs for testing. It is suitable for various enterprise laboratories and on-site quality control. The optimized etching process can stably and clearly display the boundary between ferrite and austenite phases, avoiding the problems of complex preparation and unstable display effects in traditional color etching methods. Combined with a grid point counting method at a specific angle (approximately 30°), it effectively reduces counting deviations caused by microstructure orientation, improving the accuracy of manual statistical analysis of phase content measurement. The entire detection process is clearly defined and time-efficient (from sample preparation to measurement can be completed in a short time), requiring no complex data processing software. It has strong versatility and adaptability, facilitating rapid microstructure evaluation in production sites or laboratories, and providing timely and reliable data support for production process adjustments and quality control.

Claims

1. A method for artificially detecting the content of dual-phase steel phase microstructure, characterized in that, include: S1. Metallographic sample preparation: The test surface of the sample is polished by sanding it with sandpaper ranging from 120 grit to 800 grit in sequence, and then finely polished to make the test surface bright and smooth. S2, Corrosion Sample: Immerse the polished sample test surface in the etching solution for 5-30 seconds, then rinse, soak in hot water, wipe with anhydrous alcohol and blow dry. S3, Image Acquisition: Using a metallurgical microscope at a magnification of 100 to 200, take microscopic tissue photographs of 3 to 5 consecutive fields of view on the test surface, with each field of view having an actual area of ​​not less than 0.5 mm2. S4. Phase structure content measurement: Superimpose a square grid with no less than 100 intersecting points onto the micrograph, adjust the grid so that it forms an angle of 25° to 35° with the direction of phase deformation, count the tissue points, and calculate the volume percentage of each phase.

2. The method for artificially detecting the content of dual-phase steel phase microstructure according to claim 1, characterized in that, Polishing time is 2-5 minutes, rinsing is done with running water for 10-30 seconds, and hot water immersion temperature is 80-100℃.

3. The method for artificially detecting the content of dual-phase steel phase microstructure according to claim 1, characterized in that, In S2, the corrosive solution is a mixed solution of nitric acid and hydrochloric acid prepared in a volume ratio of 1:2~3.

4. The method for artificially detecting the content of dual-phase steel phase microstructure according to claim 1, characterized in that, In S3, the image acquisition magnification factor is 100 times.

5. The method for artificially detecting the content of dual-phase steel phase microstructure according to claim 1, characterized in that, In S4, the total number of points in the lattice grid is 100, and each phase in each phase organization covers an average of 2 to 3 points.

6. The method for artificially detecting the content of dual-phase steel phase microstructure according to claim 1, characterized in that, In S4, the dot grid is arranged in a square pattern, with 1 point counting as completely falling into the phase organization region, 0.5 points counting as crossing the phase region, and 0 points counting as not falling into the phase organization region.

7. The method for artificially detecting the content of dual-phase steel phase microstructure according to claim 1, characterized in that, In S4, the volume percentage of each phase includes the volume percentage of the austenite phase.

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