Preparation method of metallographic small sample for observing phase change of high-temperature structure

Abstract

The invention relates to a preparation method of a metallographic small sample for observing phase change of a high-temperature structure, which specifically comprises the following steps of: cutting a metallographic sample by using a linear cutting method; 120 # waterproof abrasive paper, 400 # waterproof abrasive paper, 800 # waterproof abrasive paper and 1200 # waterproof abrasive paper are adopted for wet grinding with water; polishing for the third time; and taking out the polished sample, putting the sample into an ultrasonic absolute ethyl alcohol solution, carrying out oscillation cleaning, contacting and wiping the test surface of the sample by using absorbent cotton containing the absolute ethyl alcohol solution, removing floating ash and electrostatic adsorption on the surface of the sample, and drying by using a blower. According to the preparation method, the specific operation processes of linear cutting, full-surface grinding, secondary scrubbing and drying are stipulated, so that the problem that a small sample is easy to pollute and oxidize in the preparation process is solved, the high-cleanliness metallographic sample meeting the high-temperature vacuum experiment can be simply, rapidly and efficiently prepared, and the success rate of the subsequent high-temperature experiment is greatly increased.

Description

Technical Field

[0001] The present invention belongs to the field of material analysis and testing, and particularly relates to a method for preparing a small metallographic specimen for observing high-temperature tissue phase transformation. Background Art

[0002] With the continuous development of modern technology, in-situ real-time dynamic observation and recording of the microstructure phase transformation experiment of steel materials at high temperatures can be carried out by using various high-temperature detection and analysis equipment, such as high-temperature laser confocal microscopes. Due to its significant advantages of intuitive results and flexible experiments, its application has important guiding significance for product process improvement and research and development. However, due to the equipment characteristics, the experimental samples need to be placed in a vacuum chamber and the temperature needs to be controlled precisely for heating and cooling. Therefore, the samples are required to be of small size, with high quality requirements and no oxidation or pollution on the surface. Compared with the preparation of conventional metallographic samples, the preparation of samples for high-temperature experiments is more difficult and the experimental success rate is low.

[0003] A metallographic grinding and polishing process with the publication number of CN105437050A discloses a metallographic grinding and polishing process, and its steps are as follows: (1) cleaning the surface of the metallographic specimen; (2) grinding the surface of the metallographic specimen; (3) polishing the metallographic specimen; (4) cleaning; The vibration of an ultrasonic cleaning machine is used to clean and polish the metallographic specimen. When cleaning the metallographic specimen, the liquid inside the ultrasonic cleaning machine is industrial purified water, and diamond grinding sand, polishing paste and glycerin are put inside for cleaning. First, degreasing treatment is carried out to avoid affecting the subsequent grinding and polishing processes. A rubber soft bottom is placed at the bottom of the metallographic specimen to avoid scratching the surface during grinding. The metallographic specimen needs to be dried multiple times to avoid oxidation during the operation and ensure that the surface color of the metallographic specimen is uniform without water stains.

[0004] A method for preparing a superalloy metallographic specimen with the publication number of CN112903385A discloses a method for preparing a superalloy metallographic specimen, including: Step 1: Cutting according to the detection requirements and the size of the fixture seat of the automatic grinding and polishing machine to obtain the specimen to be ground and polished; Step 2: Fixing the cut specimen to be ground and polished on the fixture seat of the automatic grinding and polishing machine; Step 3: Setting the grinding and polishing parameters on the automatic grinding and polishing machine; Step 4: Starting the automatic grinding and polishing machine and starting grinding and polishing according to the preset parameters; Step 5: Immediately removing the specimen after grinding and polishing, cleaning and drying the specimen to obtain a metallographic specimen; wherein, in the step 4, the grinding and polishing go through four processes of rough grinding, fine grinding, rough polishing and fine polishing. During the grinding and polishing process, the grinding and polishing disc and the fixture seat rotate in the same direction. The invention adopts the method of rotating the fixture seat and the grinding and polishing disc in the same direction. Through the synergistic effect of the grinding and polishing time and the force value in each link of grinding and polishing, the true morphology of carbides in the superalloy metallographic specimen is shown.

[0005] A preparation method of a GCr15 high-temperature laser confocal in-situ dynamic observation sample with the publication number CN111811904A. The specific steps of the preparation method include: sample cutting, grinding with rosin adhesion, cleaning, polishing, polishing with silica sol, and sampling by dissolving in carbon tetrachloride. The invention avoids the problem of local blackening caused by corrosion with nitric acid alcohol, and the surface is clean and pollution-free. The prepared sample is used for high-temperature laser confocal in-situ observation, and the thickness and fineness of the cementite lamellae are clearly visible. For high-temperature laser confocal experiments, it is a reliable method that can clearly display the microstructure for dynamic observation. However, in the sample preparation process, multiple solvents are required for steps such as grinding with rosin adhesion, polishing with silica sol, and sampling by dissolving in carbon tetrachloride, and the preparation process is relatively complicated and takes a relatively long time.

[0006] A metallographic sample preparation method for preventing impurities from being generated during the preparation process with the publication number CN116481881A. The metallographic sample preparation method includes the following steps: S1. Cutting and embedding; S2. Rough grinding; S3. Fine grinding; S4. Polishing preparation: Immerse the polishing cloth in 75wt% absolute ethanol and perform ultrasonic cleaning. After cleaning, take it out and blow it to semi-dry with a hair dryer; S5. Rough polishing: Lay the semi-dry polishing cloth flat on the polishing machine, apply diamond polishing paste, and polish until only scratches remain. Add distilled water during the polishing process; S6. Re-cleaning: Immerse the polishing cloth in 75wt% absolute ethanol and perform ultrasonic cleaning. After cleaning, take it out and blow it to completely dry with a hair dryer; S7. Fine polishing: The polishing force is lighter than that in the rough polishing in S5, and continuously add distilled water until the polishing shows a mirror surface; S8. Corrosion and observation.

[0007] The above-mentioned metallographic sample preparation method of the prior art is more suitable for the inspection of metallographic samples at room temperature, and the quality requirements for its detection surface are relatively low. The metallographic samples prepared by this method are prone to oxidation and other situations during high-temperature experiments, and the success rate is relatively low. Different from the observation of the microstructure of traditional room-temperature corrosion samples, the samples used in high-temperature experiments are mostly small samples, which need to be assisted by clamping tools. Also, because they need to be placed in a vacuum environment in the sample chamber for heating experiments, the quality requirements for sample preparation are relatively high. Therefore, it is necessary to invent a metallographic preparation method that can solve problems such as easy contamination and easy oxidation of small samples during the preparation process, so as to ensure that the sample has no high-temperature oxidation during the subsequent observation of high-temperature tissue phase change experiments, can obtain a clear observation and detection effect, and obtain accurate experimental data. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing small metallographic specimens for observing high-temperature microstructure phase transitions. The sample preparation steps include specific operations such as wire cutting, full-surface grinding, secondary scrubbing, and drying to address the problem of small specimens being easily contaminated and oxidized during preparation. This allows for the simple, rapid, and efficient preparation of highly clean metallographic specimens suitable for high-temperature vacuum experiments, greatly improving the success rate of subsequent high-temperature experiments. This is an advanced and effective method for preparing small specimens for high-temperature experiments. This method promotes the widespread application of high-temperature microstructure phase transition experiments in the development of steel products and improves testing and scientific research capabilities.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] High-temperature microstructural phase transformation refers to the process by which the internal microstructure of steel undergoes phase transformation (such as austenitization) through atomic diffusion and crystal structure reconstruction when heated above the critical temperature. A method for preparing small metallographic specimens for observing high-temperature microstructural phase transformations includes wire cutting, full-surface grinding, secondary scrubbing, and drying. The specific method is as follows:

[0011] 1) Cutting the sample: Use the wire cutting method to cut a smaller metallographic sample according to the experimental requirements. The side length of the sample is generally less than 10mm; put it into the corresponding fixture according to the shape of the sample and lock it.

[0012] 2) Grinding: 120 # , 400 # The whole surface of the sample is polished with water sandpaper in sequence until the oxide layer on the surface of the sample is cut away without any cracks and the sample is bright in metal color, which can reduce the pollution of non-test surface during high temperature heating. Then the test surface is polished with 120 # , 400 # , 800 # , 1200 # Use wet sandpaper and add water to wet grind until the scratches on the surface of the sample are consistent in direction and even in depth.

[0013] 3) Polishing: a) Polish the test surface of the sample on a woolen polishing cloth using a metallographic polishing agent with a particle size of 2.5 μm. The polishing time is controlled within 2 to 8 minutes until there are no scratches on the surface.

[0014] b) Use a metallographic polishing agent with a particle size of 1 μm to finely polish the test surface of the sample on a fine-neck polishing cloth. The polishing time is controlled within 2 to 5 minutes until the surface is bright and scratch-free (roughness ≤ 0.025 μm) to prevent the field of view from being affected during high-magnification observation. Pay attention to controlling the time during the polishing process. If the time is too short, the surface polishing agent is likely to have linear residues. If the time is too long, pitting corrosion spots are likely to form.

[0015] c) Polish on a polishing cloth in a deionized water solution containing 50% absolute ethanol (the water solution contains 50% absolute ethanol) for 1 - 2 minutes until there is no visible water stain and no trace left on the surface within about 1 second after the water stain dries quickly to the naked eye. Adding absolute ethanol to the polishing cloth can accelerate the disappearance of the water stain. Pay attention to controlling the time for the water stain to disappear. If it is too short, an oxide film is likely to form on the surface; if it is too long, water spots are likely to remain.

[0016] 4) Two - time cleaning: a) Take out the specimen prepared in step 3) and put it into an ultrasonic absolute ethanol solution for oscillating cleaning for 1 - 3 minutes; b) Pour absolute ethanol solution into a beaker, add a small amount of absorbent cotton, then use tweezers to hold the specimen and gently contact and wipe its test surface with the absorbent cotton suspended in the absolute ethanol solution, or gently contact and wipe the test surface of the specimen with absorbent cotton containing a large amount of absolute ethanol solution to prevent scratches. At the same time, remove the floating dust and electrostatic adsorption on the specimen surface, then dry it with a hair dryer and store it in a specimen box.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] The present invention provides a method for preparing a small metallographic specimen for observing high - temperature tissue phase transformation. In the specimen preparation steps, the specific operation processes of wire - cutting, full - surface grinding, two - time cleaning, and drying are specified, thus solving the problems of easy contamination and easy oxidation of small specimens during the preparation process, and being able to quickly prepare specimens meeting the requirements for high - temperature vacuum experiments, thereby improving the success rate of high - temperature tissue phase transformation experiments, reducing the experimental cost, enhancing the experimental accuracy and efficiency, and better promoting the wide application of high - temperature tissue phase transformation experiments in the process improvement and product R & D of steel materials. And the high - temperature experimental method is widely used in product quality inspection and product R & D work, which has important guiding significance for facilitating production and improving the scientific research level. Brief Description of the Drawings

[0019] Figure 1 is a picture of the high - temperature tissue of a metallographic specimen prepared by the conventional method.

[0020] Figure 2 is a picture of the high - temperature tissue of a metallographic specimen prepared by the method of the present invention. Detailed Embodiments

[0021] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further illustrates the specific embodiments of the present invention in combination with examples. The following examples are used to specifically illustrate the content of the present invention. These examples are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0022] Taking the preparation process of a specimen for a high - temperature laser confocal microscope to observe the high - temperature tissue phase transformation experiment of 20 # steel as an example.

[0023] The specific technical steps and parameters are as follows:

[0024] 1. Sample cutting: Using wire cutting method, cut a metallographic sample of ф7mm×3mm according to the requirements of the experimental equipment; the sample is cylindrical and is placed in a resin fixture.

[0025] 2. Grinding: Use 120 # and 400 # grit water sandpapers to polish all surfaces of the sample in sequence to remove the wire cutting oxide layer on the sample surface until all surfaces are bright white; then further grind the test surface of the sample. Sequentially use 120 # and 400 # , 800 # , 1200 # grit water sandpapers to wet grind the test surface with water. When changing sandpapers during the grinding process, change the grinding direction and keep the test surface horizontal until the scratch directions on the sample surface are consistent and the depths are uniform.

[0026] 3. Polishing: a) Use diamond polishing agent with a particle size specification of 2.5μm to polish the test surface of the sample on a wool polishing cloth, and control the polishing time within 5 minutes until the surface has no scratches and becomes mirror-like; b) Use diamond polishing agent with a particle size specification of 1μm to polish the test surface of the sample on a fine wool polishing cloth, and control the polishing time within about 3 minutes until the surface is bright and has no scratches (roughness ≤0.025μm); c) Polish on a clean polishing cloth containing 50% anhydrous ethanol deionized water solution for about 1 minute until the water trace on the surface of the sample can dry quickly within 1 second and there is no water mark residue after leaving the polishing cloth.

[0027] 4. Two - time cleaning: a) Loosen the sample fixture, take out the polished sample and put it into an ultrasonic anhydrous ethanol solution for oscillating cleaning for about 1 minute; b) Pour anhydrous ethanol solution into a beaker, add a small amount of absorbent cotton, then use tweezers to hold the sample and make its test surface contact and wipe with the absorbent cotton suspended in the anhydrous ethanol solution, dry it with a hair dryer, and put it into a sample box for storage.

[0028] 5. Experimental effect: Put the sample into the heating crucible and then into the sample chamber of the equipment for high - temperature heating experiment. Compared with the samples prepared by other methods after high - temperature experiments, the observation surface of the sample in the experiment is clean and there is no interference, and the change process of the surface microstructure morphology during the phase transformation of the sample can be clearly observed (attached Figure 2 ).

Claims

1. A method for preparing a metallographic small specimen for observing high-temperature tissue phase transformation, characterized in that The specific method is as follows: 1) Cut the specimen: Use wire cutting to cut the metallographic specimen according to the experimental requirements; 2) Grinding: Grind the entire surface of the sample in sequence until there is no wire-cut oxidation layer on the surface of the specimen and it shows a metallic bright color; then successively use 120 # , 400 # , 800 # , 1200 # water sandpapers and wet-grind with water until the scratch directions on the surface of the specimen are consistent and the depths are uniform; 3) Polish: a) Use a metallographic polishing agent to polish the test surface of the specimen until the surface is bright and free of scratches; b) Polish and clean on a polishing cloth with a deionized aqueous solution containing anhydrous ethanol for 1 - 2 minutes until there are no traces after the water dries quickly within 1 second when visible to the naked eye on the surface; 4) Clean twice: a) Take out the specimen prepared in step 3) and put it into an ultrasonic anhydrous ethanol solution for oscillating cleaning for 1 - 3 minutes; b) Then use absorbent cotton soaked in anhydrous ethanol solution to contact and wipe the test surface of the specimen to prevent scratches, and at the same time remove the floating dust and electrostatic adsorption on the specimen surface, and then dry the specimen.

2. The method for preparing a metallographic small specimen for observing high-temperature tissue phase transformation according to claim 1, characterized in that, The side length of the specimen is less than 10 mm.

3. A method for preparing a metallographic small specimen for observing high-temperature tissue phase transformation according to claim 1, characterized in that, The method of using a metallographic polishing agent to polish the test surface of the specimen in step 3) is: First, use a diamond polishing agent with a particle size specification of 2.5 μm to polish the test surface of the specimen on a wool polishing cloth, and control the polishing time within 2 - 8 minutes; Then use a diamond polishing agent with a particle size specification of 1 μm to polish the test surface of the specimen on a fine wool polishing cloth, and control the polishing time within 2 - 5 minutes until the surface is bright and free of scratches.

4. A method for preparing a small metallographic specimen for observing high-temperature tissue phase transformation according to claim 1, characterized in that, In step 3)-b), in the deionized aqueous solution containing anhydrous ethanol, the weight percentage of anhydrous ethanol is 50%, and the roughness of the polished specimen is ≤0.025 μm.

5. A method for preparing a small metallographic specimen for observing high-temperature tissue phase transformation according to claim 1, characterized in that, The specific method of using absorbent cotton soaked in anhydrous ethanol solution to contact and wipe the test surface of the specimen in step 4) is: Pour anhydrous ethanol solution into a beaker, then put absorbent cotton in it, and then use tweezers to hold the specimen and contact and wipe its test surface with the absorbent cotton suspended in the anhydrous ethanol solution.

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