Method for detecting martensitic structure of steel rail

Abstract

The invention provides a method for detecting a martensitic structure of a steel rail. According to the method, the polishing precision of the steel rail sample can be improved and the surface roughness can be reduced by combining electrolytic polishing comprising specific components and mechanical light polishing. Furthermore, according to the method, corrosion is carried out after mechanical polishing, the corrosive liquid comprising an alcohol and nitric acid mixed solution and a picric acid alcohol saturated solution is adopted, rapid display of martensite can be achieved, the overall method is simple in process and easy to operate, and the test efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of metal material testing technology, specifically relating to a method for detecting martensitic structure in steel rails. Background Technology

[0002] Martensitic structures possess high hardness and wear resistance, which are beneficial for improving the fatigue and impact performance of rails. However, excessive martensite can reduce the plasticity and toughness of rails, leading to increased risk of crack initiation and brittle fracture. Therefore, controlling and studying martensitic structures is a crucial issue. Detecting martensitic structures is fundamental to conducting such control and research.

[0003] In existing technologies, the detection of martensitic structure in rails usually adopts the traditional metallographic method: sampling → mounting (if needed) → rough grinding / fine grinding → polishing → nitric acid alcohol (3% or 4%) etching → microscopic observation. The whole process is very time-consuming, and the corrosion contrast of nitric acid alcohol on high carbon rails is low, making it difficult to quickly and accurately distinguish martensitic structure. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for detecting the martensitic structure of steel rails. This method can quickly and accurately detect the martensitic structure of steel rails.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] This invention provides a method for detecting martensitic microstructure in steel rails, comprising the following steps:

[0007] After the rail samples were successively ground, electrolytically polished, mechanically polished and etched, the martensitic structure in the rail samples was detected.

[0008] The electrolyte used in the electropolishing process includes glacial acetic acid, alcohol, perchloric acid, and water.

[0009] The corrosion solution used includes a mixture of alcohol and nitric acid and a saturated solution of picric acid in alcohol.

[0010] The electrolyte, by mass fraction, comprises 90-95% glacial acetic acid, 2-5% ethanol, 3-5% perchloric acid, and 0.5-2% water, preferably comprising 92% glacial acetic acid, 2.8% ethanol, 4.6% perchloric acid, and 0.6% water.

[0011] Preferably, the mass concentration of the perchloric acid is 60-65%.

[0012] Preferably, during the electropolishing process, the current density is 15–20 amps / dm. 2 The voltage is 35-50V.

[0013] Preferably, the alcohol-nitric acid mixture comprises 2-4% nitric acid, 48-49% alcohol, and 48-49% water by mass fraction.

[0014] Preferably, the mass ratio of the alcohol-nitric acid mixture to the saturated picric acid-alcohol solution is (0.5-1):1.

[0015] Preferably, the corrosion time is 7 to 15 seconds.

[0016] Preferably, the rail sample is cold-mounted with phenolic resin and then ground.

[0017] Preferably, the resin liquid used for the phenolic resin cold mounting includes: phenolic resin prepolymer, hexamethylenetetramine, and trimethylaniline.

[0018] Preferably, the resin liquid comprises, by weight, 90-100 parts of phenolic resin prepolymer, 10-25 parts of hexamethylenetetramine, and 1-1.5 parts of trimethylaniline.

[0019] More preferably, the resin liquid also includes talc. The talc is generally added based on the consistency of the prepared solution to adjust it to the desired viscosity.

[0020] Preferably, the rail sample includes, but is not limited to, U75VH rail or U71MnH rail.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention provides a method for detecting martensitic microstructure in steel rails. This method combines electrolytic polishing with light mechanical polishing, which improves the polishing accuracy of rail samples and reduces surface roughness. Furthermore, this invention involves etching after mechanical polishing using an etching solution comprising a mixture of alcohol and nitric acid and a saturated solution of picric acid and alcohol. This facilitates rapid and clear visualization of the martensite structure. The overall method is simple, easy to operate, and improves testing efficiency. Attached Figure Description

[0023] Figure 1 The image shows the metallographic structure of the rail after processing in Example 1.

[0024] Figure 2 This is a metallographic image of the rail after processing, as shown in Comparative Example 1. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a method for detecting martensitic microstructure in steel rails, comprising the following steps:

[0027] After the rail samples were successively ground, electrolytically polished, mechanically polished and etched, the martensitic structure in the rail samples was detected.

[0028] According to the present invention, after the rail sample is subjected to the above-described treatments in sequence, the martensitic structure can be quickly and accurately displayed during testing. The rail sample includes, but is not limited to, U75VH rails or U71MnH rails.

[0029] In some embodiments of the present invention, it is preferable to pretreat the rail sample before performing the above-mentioned grinding, electrolytic polishing, mechanical polishing and corrosion operations.

[0030] The pretreatment includes: taking a metallographic sample of the rail to be tested, ultrasonically cleaning it with acetone to remove oil stains, spraying it with alcohol, drying it with cold air, drying it in an oven (to prevent moisture from affecting curing), and cold mounting it with phenolic resin.

[0031] In this invention, the phenolic resin cold mounting method facilitates grinding and is also very effective for detecting carburized layers.

[0032] In some embodiments of the present invention, the resin liquid used for the phenolic resin cold mounting comprises: phenolic resin prepolymer type 2130, hexamethylenetetramine, trimethylaniline, and talc. The resin liquid comprises, by weight, 90-100 parts of phenolic resin prepolymer, 10-25 parts of hexamethylenetetramine, and 1-1.5 parts of trimethylaniline. The 90-100 parts can be 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 parts, etc.; the 10-25 parts can be 10, 12, 15, 18, 20, 22, or 25 parts, etc.; and the 1-1.5 parts can be 1, 1.1, 1.2, 1.3, 1.4, or 1.5 parts, etc.

[0033] The aforementioned phenolic resin prepolymers, such as type 2130, can be purchased commercially. By adding hexamethylenetetramine, trimethylaniline, and talc, a cold-mounting resin solution is formed. In this solution, phenolic resin prepolymer type 2130 serves as the mounting matrix material, hexamethylenetetramine as the curing agent, trimethylaniline as the curing accelerator, and talc as the functional filler. Cold mounting can meet the testing needs of small, irregularly shaped, and other special samples. Furthermore, it is highly effective for detecting certain types of carbonized layers.

[0034] Specifically, the phenolic resin cold mounting operation is as follows: after weighing the phenolic resin prepolymer, hexamethylenetetramine, and trimethylaniline according to the proportion, first premix the hexamethylenetetramine and trimethylaniline, stir evenly, and let stand for 10-30 minutes to ensure full dissolution. After pouring in the phenolic resin prepolymer, add an appropriate amount of talc powder in batches and stir until uniform. Finally, slowly pour the obtained resin liquid into the mold, cover the metallographic sample of the rail to be tested, put it into a vacuum drying oven, remove air bubbles, and demold after curing for at least 24 hours.

[0035] It should be noted that during the resin injection process, the inspection surface of the rail metallographic specimen faces bottom. After the resin is injected, it will not cover the bottom inspection surface, or there may be a small amount of liquid on the inspection surface. Generally, after the rail metallographic specimen has cured, the inspection surface is ground to expose the metal at the bottom of the specimen using grinding or other methods.

[0036] After the above-mentioned phenolic resin cold mounting is completed, mechanical grinding is performed according to the present invention.

[0037] In this invention, the mechanical grinding is used in the coarse grinding stage. Generally, mechanical grinding is performed using sandpaper, and specifically, the mechanical grinding includes the following steps:

[0038] Mechanical grinding was performed sequentially using 180# → 400# → 800# → 1200# sandpaper, with each subsequent grinding pass perpendicular to the previous one. After mechanical grinding, the sample was rinsed with water, dehydrated with alcohol, and then dried with an air blower.

[0039] After the mechanical grinding described above is completed, electropolishing is performed according to the present invention. This electropolishing is used for the initial polishing of the test surface, which can improve the microstructure of the sample test surface.

[0040] The electrolyte used in the electropolishing process includes glacial acetic acid, alcohol (anhydrous ethanol, analytical grade), perchloric acid, and water, preferably distilled water. In some embodiments of the present invention, the electrolyte, by mass fraction, comprises 90-95% (which can be 90%, 91%, 92%, 93%, 94%, 95%, etc.), 2-5% alcohol (which can be 2%, 3%, 4%, 5%, etc.), 3-5% perchloric acid (which can be 3%, 3.5%, 4%, 4.5%, or 5%, etc.), and 0.5-2% water (which can be 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, or 2%, etc.). The mass concentration of the perchloric acid is 60-65%, such as 60%, 61%, 62%, 63%, 64%, or 65%, etc.

[0041] The present invention preferably uses an electrolyte comprising glacial acetic acid and perchloric acid because: glacial acetic acid is stable and has weak corrosive properties, thus the corrosion is more thorough and uniform; perchloric acid is a strong acid with fast reaction, and adding a small amount of perchloric acid can improve efficiency and make it more corrosive. If either component is replaced with other acidic reagents or either component is missing, it will lead to adverse results such as reduced surface polishing quality.

[0042] In some embodiments of the present invention, it is preferred to prepare glacial acetic acid, alcohol, perchloric acid, and water in a specific ratio. First, the glacial acetic acid, distilled water, and alcohol are mixed. Then, the container containing the mixture is placed in cold water, and perchloric acid is added very slowly. The rate of perchloric acid addition should ensure that the temperature inside the mixing container does not exceed 13°C. After preparation, the mixture is allowed to stand for 24 hours to ensure homogenization, resulting in a more thorough effect. During electrolytic polishing, the current density is preferably controlled at 15–20 amps / dm. 2 For example, it could be 15 amps / decimeter. 2 16 amps / decimeter 2 17 amps / decimeter 2 18 amps / decimeter 2 19 A / dm² or 20 A / dm², preferably 19 A / dm². 2 The voltage is controlled between 35 and 50V, such as 35V, 37V, 40V, 42V, 45V, 47V or 50V, with 47V being the preferred value.

[0043] By controlling the current density and voltage within the above-mentioned range, the present invention can achieve optimal polishing quality.

[0044] In this invention, during the electrolytic polishing process, the machine is stopped when the scratches on the observation surface (i.e., the test surface) of the rail sample disappear and a mirror-like gloss appears. The rail sample is then immediately immersed in flowing cold water for 5-10 seconds to terminate the residual electrolytic reaction on the surface. Then, a gradient cleaning is performed: first, ultrasonic cleaning is performed with an alkaline solution, preferably sodium bicarbonate solution, for 5-10 seconds (to remove acidic substances adsorbed on the surface), followed by rinsing with flowing cold water, then rinsing with alcohol to remove water, and finally drying.

[0045] The above 5 to 10 seconds can be 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, or 10 seconds, etc.

[0046] After the electrolytic polishing is completed, mechanical polishing is performed according to the present invention. The mechanical polishing is a light mechanical polishing, the purpose of which is to eliminate protruding inclusions and make the rail sample flatter.

[0047] In some embodiments of the present invention, it is preferred to set the grinding disc speed to 300–1000 rpm, spray an appropriate amount of polishing liquid onto the grinding disc, and begin polishing from the outer edge of the grinding disc. Gently press the rail sample by hand, and after 20–30 seconds, move the sample to a distance of 3–4 cm from the center of the grinding disc. Gently press and rotate the sample to continue polishing for 10–15 seconds. Then rinse the polished surface with running cold water and wipe it dry. Furthermore, add water to the grinding disc every approximately 8–10 seconds during polishing to prevent the polishing cloth and polished surface from drying out and affecting the polishing effect. Furthermore, the roughness of the grinding disc should be ≤2.5 μm.

[0048] This invention combines electropolishing and light mechanical polishing to improve the polishing accuracy of rail samples, reduce surface roughness, and improve surface microstructure.

[0049] After the above mechanical polishing is completed, etching is preferably performed according to the present invention.

[0050] In this invention, the etching solution used for corrosion comprises an alcohol-nitric acid mixture and a picric acid-alcohol saturated solution. The alcohol-nitric acid mixture comprises, by mass fraction, 2-4% nitric acid, 48-49% alcohol (anhydrous ethanol, analytical grade), and 48-49% water. The mass ratio of the alcohol-nitric acid mixture to the picric acid-alcohol saturated solution is (0.5-1):1, such as 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1, etc.

[0051] The aforementioned 2-4% can be 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, or 4%, etc.

[0052] The aforementioned 48-49% can be 48%, 48.1%, 48.2%, 48.3%, 48.4%, 48.5%, 48.6%, 48.7%, 48.8%, 48.9%, or 49%, etc.

[0053] It should be noted that the combination of nitric acid alcohol solution and picric acid alcohol solution in the above-mentioned etching solution can effectively reveal martensite structure. If either component is missing or replaced with another acidic solution, it may result in adverse consequences such as the martensite not being visible.

[0054] In this invention, the corrosion time is 7 to 15 seconds, such as 7 seconds, 8 seconds, 9 seconds, 10 seconds, 11 seconds, 12 seconds, 13 seconds, 14 seconds, or 15 seconds.

[0055] In some embodiments of the present invention, after the above-mentioned corrosion is completed, the rail sample is preferably rinsed with running water for 3 to 5 seconds, then immediately dehydrated with alcohol, dried, and observed with a metallographic microscope to detect the martensitic structure in the rail sample.

[0056] Tests have shown that the method provided by this invention can quickly and accurately detect martensitic structure in rail samples, laying the foundation for the control and research of martensitic structure downstream.

[0057] To further illustrate the present invention, the following embodiments provide a detailed description. The phenolic resin prepolymer used in the following embodiments of the present invention is phenolic resin prepolymer type 2130.

[0058] Example 1

[0059] This embodiment performs metallographic testing on U75VH steel rails, and the steps are as follows:

[0060] (1) Sample pretreatment. The sample is ultrasonically cleaned with acetone to remove oil stains → sprayed with alcohol → dried with cold air → dried in an oven (to prevent moisture from affecting curing) → cold mounting with phenolic resin. The steps of cold mounting with phenolic resin are as follows: weigh 100 parts of phenolic resin prepolymer 2130, 18 parts of hexamethylenetetramine, and 1 part of trimethylaniline according to the proportion; first, premix the hexamethylenetetramine and trimethylaniline, stir evenly and let stand for 15 minutes, then pour in the phenolic resin prepolymer and add an appropriate amount of talc powder and stir until uniform. Finally, slowly pour the resin liquid into the mold, cover the sample, put it in a vacuum drying oven, vacuum to eliminate air bubbles, and demold immediately after curing for 24 hours.

[0061] (2) Mechanical grinding. After curing, the sample was mechanically ground sequentially using 180#→400#→800#→1200# sandpaper. During manual grinding, the next grinding mark was perpendicular to the previous grinding mark. After mechanical grinding, the sample was rinsed with water, dehydrated with alcohol, and dried with a blower.

[0062] (3) Electropolishing. Prepare the electrolyte: 92 wt% glacial acetic acid, 0.6 wt% distilled water, 2.8 wt% alcohol, and 4.6 wt% perchloric acid (60-65% by mass). Perform electropolishing using an electropolishing machine, controlling the current density at 19 A / dm. 2 The voltage is controlled at 47V. When the scratches on the sample observation surface disappear and a mirror-like gloss appears, stop the machine and immediately immerse the sample in running cold water for 5 seconds to terminate the residual electrolytic reaction on the surface. Then perform gradient cleaning: first clean with sodium bicarbonate solution for 7 seconds (to remove acidic substances adsorbed on the surface), then rinse with running cold water, rinse with alcohol to dehydrate, and finally blow dry.

[0063] (4) Light mechanical polishing. Set the grinding wheel speed to 800 rpm, spray an appropriate amount of polishing liquid onto the grinding wheel, and start polishing from the outer edge of the grinding wheel. Gently press the sample with your hand. After 25 seconds, move the sample to a position 3 cm away from the center of the grinding wheel, gently press and rotate the sample to continue polishing for 12 seconds. Then rinse the polished surface with running cold water and wipe it dry. Furthermore, add water to the grinding wheel approximately every 10 seconds during polishing. The roughness of the grinding wheel is 2.5 μm.

[0064] (5) Acid etching. Preparation of etching solution: 3wt% nitric acid + 48.5wt% ethanol + 48.5wt% distilled water. Then, add a saturated picric acid-ethanol solution to the mixture of nitric acid, ethanol, and distilled water at a ratio of 1:1 (mass ratio). Etching time: 11s.

[0065] (6) Observation. After acid etching, rinse with running water for 3-5 seconds, immediately dehydrate with alcohol, blow dry, and observe immediately with a metallographic microscope. The results are as follows: Figure 1 As shown.

[0066] Example 2

[0067] This embodiment performs metallographic testing on U71MnH steel rails, and the steps are as follows:

[0068] (1) Sample pretreatment. The sample was ultrasonically cleaned with acetone to remove oil stains → sprayed with alcohol → dried with cold air → dried in an oven (to prevent moisture from affecting curing) → cold mounting with phenolic resin. The steps of cold mounting with phenolic resin are as follows: weigh 91 parts of phenolic resin prepolymer 2130, 23 parts of hexamethylenetetramine, and 1.5 parts of trimethylaniline according to the proportion; first, premix the hexamethylenetetramine and trimethylaniline, stir evenly and let stand for 23 minutes, then pour in the phenolic resin prepolymer and add an appropriate amount of talc powder in batches and stir until uniform, finally slowly pour the resin liquid into the mold, cover the sample, put it in a vacuum drying oven, vacuum to eliminate air bubbles, and demold after curing for 30 hours.

[0069] (2) Mechanical grinding. After demolding, the sample was mechanically ground in sequence using 180#→400#→800#→1200# sandpaper. During manual grinding, the next grinding mark was perpendicular to the previous grinding mark. After grinding, the sample was rinsed with water, dehydrated with alcohol, and dried with a blower.

[0070] (3) Electrolytic polishing. Prepare the electrolyte: 90 wt% glacial acetic acid, 1 wt% distilled water, 4 wt% alcohol, and 5 wt% perchloric acid (60-65% by mass). Perform electrolytic polishing using an electrolytic polishing apparatus, controlling the current density at 16 A / dm. 2 The voltage is controlled at 40V. When the scratches on the sample observation surface disappear and a mirror-like gloss appears, stop the machine and immediately immerse the sample in running cold water for 7 seconds to terminate the residual electrolytic reaction on the surface. Then perform gradient cleaning: first clean with sodium bicarbonate solution for 5 seconds (to remove acidic substances adsorbed on the surface), then rinse with running cold water, rinse with alcohol to dehydrate, and finally blow dry.

[0071] (4) Light mechanical polishing. Set the grinding wheel speed to 600 rpm, spray an appropriate amount of polishing liquid onto the grinding wheel, and start polishing from the outer edge of the grinding wheel. Gently press the sample with your hand. After 20 seconds, move the sample to a position 3 cm away from the center of the grinding wheel, gently press and rotate the sample to continue polishing for 10 seconds. Then rinse the polished surface with running cold water and wipe it dry. Further, add water to the grinding wheel approximately every 10 seconds during polishing. The roughness of the grinding wheel is 2.5 μm.

[0072] (5) Acid etching. Preparation of etching solution: 2wt% nitric acid + 49wt% ethanol + 49wt% distilled water. Then, add a saturated picric acid-ethanol solution to the mixture of nitric acid, ethanol, and distilled water at a mass ratio of 0.9:1. Etching time: 12s.

[0073] (6) Observation. After acid etching, rinse with running water for 3-5 seconds, immediately dehydrate with alcohol, blow dry and observe with a metallographic microscope. The martensitic structure can be clearly observed.

[0074] Example 3

[0075] This embodiment performs metallographic testing on U75VH steel rails, and the steps are as follows:

[0076] (1) Sample pretreatment. The sample was ultrasonically cleaned with acetone to remove oil stains → sprayed with alcohol → dried with cold air → dried in an oven (to prevent moisture from affecting curing) → cold mounting with phenolic resin. The steps of cold mounting with phenolic resin are as follows: weigh 98 parts of phenolic resin prepolymer 2130, 12 parts of hexamethylenetetramine, and 1.3 parts of trimethylaniline according to the proportion; first, premix the hexamethylenetetramine and trimethylaniline, stir evenly and let stand for 30 minutes, then pour in the phenolic resin prepolymer and add an appropriate amount of talc powder in batches and stir until uniform, finally slowly pour the resin liquid into the mold, cover the sample, put it in a vacuum drying oven, vacuum to eliminate air bubbles, and demold after curing for 40 hours.

[0077] (2) Mechanical grinding. After demolding, the sample was mechanically ground in sequence using 180#→400#→800#→1200# sandpaper. During manual grinding, the next grinding mark was perpendicular to the previous grinding mark. After grinding, the sample was rinsed with water, dehydrated with alcohol, and dried with a blower.

[0078] (3) Electrolytic polishing. Prepare the electrolyte: 93wt% glacial acetic acid, 3wt% distilled water, 1wt% alcohol, and 3wt% perchloric acid (60-65% by mass). Perform electrolytic polishing using an electrolytic polishing apparatus, controlling the current density at 18 A / dm. 2 The voltage is controlled at 38V. When the scratches on the sample observation surface disappear and a mirror-like gloss appears, stop the machine and immediately immerse the sample in running cold water for 8 seconds to terminate the residual electrolytic reaction on the surface. Then perform gradient cleaning: first clean with sodium bicarbonate solution for 10 seconds (to remove acidic substances adsorbed on the surface), then rinse with running cold water, then rinse with alcohol to dehydrate, and finally blow dry.

[0079] (4) Light mechanical polishing. Set the grinding wheel speed to 1000 rpm, spray an appropriate amount of polishing liquid onto the grinding wheel, and start polishing from the outer edge of the grinding wheel. Gently press the sample with your hand. After 30 seconds, move the sample to a position 4 cm away from the center of the grinding wheel, gently press and rotate the sample to continue polishing for 10 seconds. Then rinse the polished surface with running cold water and wipe it dry. Furthermore, add water to the grinding wheel approximately every 8 seconds during polishing. The roughness of the grinding wheel is 2.5 μm.

[0080] (5) Acid etching. Preparation of etching solution: 4wt% nitric acid + 48wt% ethanol + 48wt% distilled water. Then, add a saturated picric acid-ethanol solution to the mixture of nitric acid, ethanol, and distilled water at a mass ratio of 0.7:1. Etching time: 11s.

[0081] (6) Observation. After acid etching, rinse with running water for 3-5 seconds, immediately dehydrate with alcohol, blow dry and observe with a metallographic microscope. The martensitic structure can be clearly observed.

[0082] Comparative Example 1

[0083] Metallographic examination of U75VH was performed using traditional methods. After mechanical grinding with 180#→400#→800#→1200# sandpaper, it was polished with a 2.5μm polishing cloth, etched with a 3% nitric acid-alcohol solution, dehydrated with alcohol, and dried. Immediately afterward, it was observed under a metallographic microscope. The results are as follows: Figure 2 As shown. By Figure 2 As can be seen, the martensite in the figure is not obvious, making it difficult to determine.

[0084] As can be seen from the comparison of the above embodiments and comparative examples, the martensitic structure in the rail sample is more clearly displayed using the method provided by the present invention, indicating that the method of the present invention is more accurate.

[0085] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting martensitic microstructure in steel rails, characterized in that, Includes the following steps: After the rail samples were successively ground, electrolytically polished, mechanically polished and etched, the martensitic structure in the rail samples was detected. The electrolyte used in the electropolishing process includes glacial acetic acid, alcohol, perchloric acid, and water. The corrosion solution used includes a mixture of alcohol and nitric acid and a saturated solution of picric acid in alcohol.

2. The method according to claim 1, characterized in that, The electrolyte, by mass fraction, comprises 90-95% glacial acetic acid, 2-5% ethanol, 3-5% perchloric acid, and 0.5-2% water.

3. The method according to claim 1 or 2, characterized in that, The mass concentration of the perchloric acid is 60-65%.

4. The method according to any one of claims 1 to 3, characterized in that, During the electropolishing process, the current density is 15–20 amps / dm. 2 The voltage is 35-50V.

5. The method according to any one of claims 1 to 4, characterized in that, The alcohol-nitric acid mixture comprises, by mass fraction, 2-4% nitric acid, 48-49% alcohol, and 48-49% water.

6. The method according to any one of claims 1 to 5, characterized in that, The mass ratio of the alcohol-nitric acid mixture to the saturated picric acid-alcohol solution is (0.5–1):

1.

7. The method according to any one of claims 1 to 6, characterized in that, The corrosion time is 7 to 15 seconds.

8. The method according to any one of claims 1 to 7, characterized in that, The rail sample was cold-mounted with phenolic resin and then ground. The resin liquid used for the phenolic resin cold mounting includes: phenolic resin prepolymer, hexamethylenetetramine, and trimethylaniline.

9. The method according to claim 8, characterized in that, The resin liquid comprises, by weight, 90-100 parts of phenolic resin prepolymer, 10-25 parts of hexamethylenetetramine, and 1-1.5 parts of trimethylaniline.

10. The method according to any one of claims 1 to 9, characterized in that, The rail samples include, but are not limited to, U75VH rails or U71MnH rails.

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