A method for etching the prior austenite grain size of a high carbon pearlitic rail

Abstract

This invention discloses a corrosion method for high-carbon pearlitic steel rails with a pre-austenite grain size. The sample test surface is polished, and during corrosion, the polished surface is completely immersed in the corrosive agent, taking care not to touch the bottom of the container to avoid affecting the corrosion effect. The corroded surface is observed periodically during corrosion. Once the corroded surface exhibits a uniform dark gray frosted state, it is removed, rinsed, and dried. Finally, excess corrosion layer is lightly polished on a polishing machine before observation. The corrosive agent includes hydrochloric acid, acetic acid, ferric chloride, benzalkonium bromide, shampoo, and deionized water. The purpose of this invention is to provide a corrosion method for high-carbon pearlitic steel rails with a pre-austenite grain size that can clearly display the pre-austenite grain boundaries, solving the problem of difficult corrosion of pre-austenite grains. Furthermore, the reagents used are stable, safe, and easy to store.

Description

Technical Field

[0001] This invention belongs to the field of metallographic testing technology, and particularly relates to a corrosion method for high-carbon pearlitic steel rails with original austenitic grain size. Background Technology

[0002] High-carbon pearlitic steel rails are commonly used in heavy-haul freight lines, and their mechanical properties are important indicators for evaluating service performance. The original austenite grain size is an important characteristic reflecting the mechanical properties of a material, significantly affecting the strength, plasticity, and toughness of steel. However, revealing the original austenite grain boundaries has always been a challenge.

[0003] Currently available methods for revealing the original austenite grain boundaries, besides direct etching, include oxidation methods, all of which require reheating the sample to a high temperature. This reheating process is not only cumbersome and complex, requiring additional heating equipment, but it can also affect the microstructure, causing inaccuracies in grain size measurements. Direct etching has traditionally used picric acid solution, which has proven effective. However, due to its toxicity and explosiveness, picric acid is now strictly controlled and difficult to obtain. Therefore, there is an urgent need to find a corrosive agent and etching method that can solve the existing problems. Summary of the Invention

[0004] The purpose of this invention is to provide a corrosion method for high-carbon pearlitic steel rails with original austenite grain size, which can clearly display the original austenite grain boundaries of high-carbon pearlitic steel rails, solve the problem of difficult corrosion of original austenite grain size, and the reagents used are stable, safe and easy to store.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a corrosion method for high-carbon pearlitic steel rails with original austenitic grain size. The test surface of the sample is ground and polished. During corrosion, the polished surface is completely immersed in the corrosive agent. Care should be taken not to touch the bottom of the container to avoid affecting the corrosion effect. During the corrosion process, the sample is taken out and observed at any time. When the corrosion surface shows a uniform dark gray frosted state, it is taken out, rinsed and dried. Finally, the excess corrosion layer is removed by lightly polishing on a polishing machine before observation.

[0007] The corrosive agents include hydrochloric acid, acetic acid, ferric chloride, benzalkonium bromide, shampoo, and deionized water.

[0008] Furthermore, the proportions of each component in the corrosive agent are as follows: 3-7g ferric chloride: 10-20ml hydrochloric acid: 100-120ml deionized water: 10-20ml glacial acetic acid: approximately 2-3ml benzalkonium bromide solution: ≤0.2ml shampoo.

[0009] Furthermore, the concentration of the hydrochloric acid is 36%.

[0010] Furthermore, the benzalkonium bromide content is 25-30 g / L.

[0011] Furthermore, the preparation process of the corrosive agent is as follows: ferric chloride is added to deionized water, followed by hydrochloric acid and acetic acid. Benzalkonium bromide and shampoo are added together at the end of the preparation of the corrosive agent or added in proportion each time the corrosive agent is used, and then mixed evenly.

[0012] Furthermore, the etchant is used at room temperature and the etching time is 3-5 minutes.

[0013] Furthermore, the samples are U75VH and U71MnH.

[0014] Furthermore, the acetic acid is glacial acetic acid.

[0015] The roles and mechanisms of the various components of the corrosive agent in this invention:

[0016] In this invention, deionized water is used as the solvent, ferric chloride and hydrochloric acid are used as oxidants, and glacial acetic acid is used to fine-tune the pH of the corrosive agent. Benzalkonium bromide is a cationic surfactant that can exist stably in an acidic environment and delays the corrosion of the substrate by the corrosive agent. The addition of shampoo can inhibit the appearance of dense pitting corrosion on the corroded surface. However, since its main component is anionic surfactant, adding too much will neutralize the cationic surfactant in the corrosive agent. At the same time, it is not easy to exist stably in an acidic environment. Therefore, the amount added must be strictly controlled, otherwise its inhibitory effect will be weakened.

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

[0018] This invention solves the problem of difficult corrosion of the original austenitic grains in high-carbon pearlitic rail steel. It requires no heating or oxidative heat treatment, uses safe and readily available raw materials for the etchant, effectively reducing costs. The corrosion process is simple, exhibits good corrosion effect on the original austenitic grain boundaries, and minimizes interference between the microstructure and the grain boundaries. This grain-specific etchant and corrosion method are simple, highly operable, and easy to promote and apply. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 The image shows the morphology of U75VH steel rail material. The left image is the morphology after corrosion with 4% nitric acid alcohol at 100x magnification, and the right image is the morphology after corrosion with 4% nitric acid alcohol at 200x magnification.

[0021] Figure 2 The image shows the morphology of U75VH steel rail material. The left image is the morphology of Example 1 after the corrosion process at 100x magnification, and the right image is the morphology of Example 1 after the corrosion process at 200x magnification.

[0022] Figure 3The image shows the morphology of U71MnH steel rail material. The left image is the morphology after corrosion with 4% nitric acid alcohol at 100x magnification, and the right image is the morphology after corrosion with 4% nitric acid alcohol at 200x magnification.

[0023] Figure 4 The material is U71MnH steel rail. The left image shows the morphology after the corrosion process in Example 2 at 100x magnification, and the right image shows the morphology after the corrosion process in Example 2 at 200x magnification. Detailed Implementation

[0024] Example 1:

[0025] Dissolve 5g of ferric chloride in 105ml of water using ultrasonic heating. Then, add 15ml of hydrochloric acid and 15ml of glacial acetic acid sequentially, stirring thoroughly after each addition to prepare a semi-finished etching agent. When using, take 10ml of the semi-finished etching agent. Since approximately 25-30 drops constitute 1ml of the test dropper, add 4-5 drops of benzalkonium bromide to 10ml of the semi-finished etching agent. The amount of shampoo added should be much less than that of benzalkonium bromide. Use the tip of a glass rod to take a small amount of shampoo and add it to the reagent, stirring until completely dissolved. This will ultimately prepare a crystalline etching agent.

[0026] The sample test surface is first sanded and polished until it reaches a smooth mirror finish. Then, at room temperature, the sample test surface is completely immersed in a grain-gradient etchant for 3-5 minutes. Care is taken to ensure the test surface does not touch the bottom of the container to avoid affecting the etching effect. The etched surface can be observed at any time during the etching process. Once the etched surface exhibits a uniform dark gray frosted appearance, it is removed, rinsed, and dried. Finally, excess etched layer is lightly polished on a polishing machine before observation.

[0027] Example 2:

[0028] Dissolve 6g of ferric chloride in 100ml of water using ultrasonic heating. Then, add 14ml of hydrochloric acid and 15ml of glacial acetic acid sequentially, stirring thoroughly after each addition to prepare a semi-finished etching agent. When using, take 10ml of the semi-finished etching agent. Since approximately 25-30 drops constitute 1ml of the test dropper, add 4-5 drops of benzalkonium bromide to 10ml of the semi-finished etching agent. The amount of shampoo added should be much less than that of benzalkonium bromide. Use the tip of a glass rod to take a small amount of shampoo and add it to the reagent, stirring until completely dissolved. This will ultimately prepare a crystalline etching agent.

[0029] The sample test surface is first sanded and polished until it reaches a smooth mirror finish. Then, at room temperature, the sample test surface is completely immersed in a grain-gradient etchant for 3-5 minutes. Care is taken to ensure the test surface does not touch the bottom of the container to avoid affecting the etching effect. The etched surface can be observed at any time during the etching process. Once the etched surface exhibits a uniform dark gray frosted appearance, it is removed, rinsed, and dried. Finally, excess etched layer is lightly polished on a polishing machine before observation.

[0030] By comparing the corrosion effects of the grain size etchant and 4% nitric acid alcohol in the examples, it can be seen that the grain size etchant and corrosion method of the present invention have a good corrosion effect on the original austenite grain boundaries of high carbon pearlitic steel rail steel.

[0031] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A corrosion method for high-carbon pearlitic steel rails with the original austenitic grain size, characterized in that: Polish the test surface of the sample. When etching, immerse the polished surface completely in the etchant, being careful not to touch the bottom of the container to avoid affecting the etching effect. Take it out and observe the etched surface from time to time during the etching process. When the etched surface shows a uniform dark gray frosted state, take it out, rinse and blow it dry. Finally, lightly polish it on a polishing machine to remove the excess etched layer before observation. The proportions of each component in the corrosive agent are as follows: ferric chloride 3-7g: hydrochloric acid 10-20ml: deionized water 100-120ml: glacial acetic acid 10-20ml: benzalkonium bromide solution 2-3ml: shampoo ≤0.2ml; The concentration of the hydrochloric acid is 36%; The content of benzalkonium bromide is 25-30 g / L.

2. The corrosion method for high-carbon pearlitic steel rails with original austenitic grain size according to claim 1, characterized in that: The preparation process of the etchant is as follows: add ferric chloride to deionized water, followed by hydrochloric acid, glacial acetic acid, benzalkonium bromide and shampoo. These are added together at the end of the preparation process or in proportion each time the etchant is used, and then mixed evenly.

3. The corrosion method for high-carbon pearlitic steel rails with original austenitic grain size according to claim 1, characterized in that: The corrosive agent is used at room temperature, and the corrosion time is 3-5 minutes.

4. The corrosion method for high-carbon pearlitic steel rails with original austenitic grain size according to claim 1, characterized in that: The samples were U75VH and U71MnH.

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