Method for displaying original austenite grain boundary of high-temperature-resistant bearing steel
Through the combination of grinding and polishing and electrolytic corrosion, the problem of difficult to show the grain boundary of the original austenite of high-temperature bearing steel is solved, and a clear and complete grain boundary display is achieved. Using the easy-to-get aqueous chromic acid solution, the process is simple and the effect is significant.
Patent Information
- Application Number
- CN202510409971.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-02
- Publication Date
- 2025-07-18
AI Technical Summary
The prior art is difficult to fully display the original austenite grain boundaries of high-temperature bearing steel, and solutions that are difficult to obtain by commonly used corrosion methods are more difficult to obtain.
The method of grinding and polishing treatment combined with muffle furnace heating is adopted. The grain boundary is first made easy to observe through grinding and polishing treatment, and then heated in a muffle furnace, then electrolytic corrosion is performed using aqueous chromic acid solution, and finally observed under a metallographic microscope.
It realizes a clear and complete display of the original austenite grain boundary of high-temperature bearing steel, and the corrosion liquid is a commonly used and easy-to-get aqueous chromic acid solution, with a simple process and good effect.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of metallographic inspection, and particularly relates to a method for revealing the original austenite grain boundaries of high-temperature resistant bearing steel. Background Art
[0002] With the development of the aerospace industry, the need for higher-speed jet engines, gas turbines, aerospace vehicles, etc. has become increasingly urgent. The working temperature of the corresponding equipment bearings is getting higher and higher, reaching 300 °C or even higher. Therefore, high-temperature resistant bearing steel has received extensive attention.
[0003] The high-temperature resistant bearing steels mainly include M50, M50NiL (350 °C), 9Cr18Mo (260 °C), Cr4Mo4V (315 °C), Cr14Mo4 (480 °C), W6Mo5Cr4V2 (480 °C), W9Cr4V2Mo (520 °C), etc. The microstructure of high-temperature resistant bearing steel is composed of martensite, partial carbides and retained austenite, and has high hardness and strength.
[0004] Martensite is transformed from austenite. The refinement of the original austenite grains is the most commonly used and important strengthening method among various strengthening mechanisms, and it is also the only strengthening method that can improve toughness while increasing strength. The grain size of steel directly affects the mechanical properties and fatigue properties of bearing steel. Therefore, the determination and characterization of the original austenite grain size of steel are of great significance for improving its quality; however, the existing means of etching the grain size cannot completely reveal the original austenite grain boundaries, and the solution of individual etching methods is extremely difficult to obtain. Summary of the Invention
[0005] The purpose of the present invention is to propose a method for revealing the original austenite grain boundaries of high-temperature resistant bearing steel, which can effectively reveal the original austenite grain boundaries of high-temperature resistant bearing steel.
[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions: A method for revealing the original austenite grain boundaries of high-temperature resistant bearing steel, comprising the following steps: (1) Cut the high-temperature resistant bearing steel after quenching + tempering according to the standard of GB / T 6394-2017, and then carry out grinding and polishing treatment. The specific operation is as follows: polish the surface to be inspected successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polish it to a mirror surface.
[0007] (2) Place the polished surface of the specimen upwards in a muffle furnace, keep it at 400 °C - 600 °C for 20 - 60 min, and then air-cool it to room temperature.
[0008] (3) Polish the surface to be inspected of the specimen again until it becomes mirror-like, and then perform electrolytic corrosion. The corrosion solution is a 5-15% aqueous chromic acid solution, the corrosion voltage is 20-25V, the current is 3-5A, and the corrosion time is 30-90s.
[0009] (4) After the electrolytic corrosion is completed, rinse the surface to be inspected with water, dry it, and then place it under a metallographic microscope for observation.
[0010] The inventive principle of the technical solution of the present invention lies in: Perform grain boundary weakening treatment on the same polished surface. First, polish the surface to be observed into a mirror surface by grinding and polishing, and then heat it in a muffle furnace to weaken the grain boundaries, making the grain boundaries more easily corroded; after polishing the mirror surface again, perform electrolysis using a chromic acid electrolyte, and after rinsing and drying, the clear and complete grain boundary distribution can be observed under the microscope.
[0011] The beneficial technical effects of the present invention are: The method of the present invention can effectively reveal the complete original austenite grain boundaries, solving the problem that ordinary corrosion cannot completely reveal the original austenite or cannot reveal the original austenite. The corrosion solution used in the method of the present invention is an aqueous chromic acid solution, which is a commonly used and easily obtainable chemical reagent and is not subject to control.
[0012] The entire process of the method of the present invention is relatively simple, and the revealing effect is good. Description of the Drawings
[0013] Figure 1 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Example 1; Figure 2 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Example 2; Figure 3 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Example 3; Figure 4 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Example 4; Figure 5 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Example 5; Figure 6 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Comparative Example 1; Figure 7 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Comparative Example 2; Figure 8 It is a metallographic photograph (500 times) of the original austenite grain boundaries in Comparative Example 3. Detailed Embodiments
[0014] The technical solution of the present invention will be further described in detail below through embodiments. Example 1
[0015] The high-temperature resistant bearing steel in this example is M50-NiL, and the method for revealing the original austenite grain boundaries includes the following steps: (1) Cut the quenched and tempered M50-NiL specimen according to the standard of GB / T 6394-2017, and then polish the surface to be inspected of the specimen. The specific operation is as follows: polish the surface to be inspected of the specimen successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polish it on a polishing machine at a speed of 600 revolutions per minute until it becomes a mirror surface.
[0016] (2) Place the polished surface of the specimen upward in a muffle furnace, keep it at 400 °C for 60 min, and then air-cool it to room temperature.
[0017] (3) Polish the surface to be inspected of the specimen to a mirror surface again, and then put it into an electrolytic corrosion device for corrosion treatment. The corrosion solution is an 8% chromic acid aqueous solution, the corrosion voltage is 20 V, the current is 5 A, and the corrosion time is 90 s.
[0018] (4) After the electrolytic corrosion is completed, rinse the surface to be inspected with water, dry it, and then place it under a metallographic microscope for observation. The results are as Figure 1 shown; it can be seen from Figure 1 that the obtained original austenite grain boundaries are clear and complete. Example 2
[0019] The high-temperature resistant bearing steel in this example is M50-NiL, and the method for revealing the original austenite grain boundaries includes the following steps: (1) Cut the quenched and tempered M50-NiL specimen according to the standard of GB / T 6394-2017, and then polish the surface to be inspected of the specimen. The specific operation is as follows: polish the surface to be inspected of the specimen successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polish it on a polishing machine at a speed of 600 revolutions per minute until it becomes a mirror surface.
[0020] (2) Place the polished surface of the specimen upward in a muffle furnace, keep it at 450 °C for 50 min, and then air-cool it to room temperature.
[0021] (3) Polish the surface to be inspected of the specimen to a mirror surface again, and then put it into an electrolytic corrosion device for corrosion treatment. The corrosion solution is a 12% chromic acid aqueous solution, the corrosion voltage is 23 V, the current is 4 A, and the corrosion time is 60 s.
[0022] (4) After the electrolytic corrosion is completed, rinse the surface to be inspected with water, dry it, and then place it under a metallographic microscope for observation. The results are as Figure 2 shown; it can be seen from Figure 2It can be seen that the obtained prior austenite grain boundaries are clear and complete. Example 3
[0023] In this example, the high-temperature resistant bearing steel is M50, and the method for revealing the prior austenite grain boundaries includes the following steps: (1) Cut the quenched and tempered M50 specimen according to the standard of GB / T 6394-2017, and then perform grinding and polishing on the surface to be inspected of the specimen. The specific operation is as follows: Grind the surface to be inspected of the specimen successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polish it to a mirror surface on a polishing machine at a speed of 650 revolutions per minute.
[0024] (2) Place the polished surface of the specimen upward in a muffle furnace, keep it at 500 °C for 45 min, and then air-cool it to room temperature.
[0025] (3) Polish the surface to be inspected of the specimen to a mirror surface again, and then put it into an electrolytic corrosion device for corrosion treatment. The corrosion solution is 10% chromic acid aqueous solution, the corrosion voltage is 25 V, the current is 3 A, and the corrosion time is 70 s.
[0026] (4) After the electrolytic corrosion is completed, rinse the surface to be inspected with water, dry it, and then place it under a metallographic microscope for observation. The results are as Figure 3 shown; It can be seen from Figure 3 that the obtained prior austenite grain boundaries are clear and complete. Example 4
[0027] In this example, the high-temperature resistant bearing steel is Cr4Mo4V, and the method for revealing the prior austenite grain boundaries includes the following steps: (1) Cut the quenched and tempered Cr4Mo4V specimen according to the standard of GB / T 6394-2017, and then perform grinding and polishing on the surface to be inspected of the specimen. The specific operation is as follows: Grind the surface to be inspected of the specimen successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polish it to a mirror surface on a polishing machine at a speed of 700 revolutions per minute.
[0028] (2) Place the polished surface of the specimen upward in a muffle furnace, keep it at 550 °C for 35 min, and then air-cool it to room temperature.
[0029] (3) Polish the surface to be inspected of the specimen to a mirror surface again, and then put it into an electrolytic corrosion device for corrosion treatment. The corrosion solution is 5% chromic acid aqueous solution, the corrosion voltage is 24 V, the current is 3 A, and the corrosion time is 80 s.
[0030] (4) After the electrolytic corrosion is completed, rinse the surface to be inspected with water, dry it, and then place it under a metallographic microscope for observation. The results are as Figure 4 shown; It can be seen from Figure 4It can be seen that the obtained prior austenite grain boundaries are clear and complete. Example 5
[0031] The high-temperature resistant bearing steel in this example is Cr14Mo4V, and the method for revealing its prior austenite grain boundaries includes the following steps: (1) Cut the quenched and tempered Cr14Mo4V sample according to the standard of GB / T 6394-2017, and then perform grinding and polishing on the surface to be inspected of the sample. The specific operation is as follows: Grind the surface to be inspected of the sample successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polish it on a polishing machine at a speed of 700 revolutions per minute until it becomes a mirror surface.
[0032] (2) Place the polished surface of the sample upward in a muffle furnace, keep it at 600 °C for 30 min, and then air-cool it to room temperature.
[0033] (3) Polish the surface to be inspected of the sample to a mirror surface again, and then put it into an electrolytic corrosion device for corrosion treatment. The corrosion solution is 15% chromic acid aqueous solution, the corrosion voltage is 23 V, the current is 4 A, and the corrosion time is 75 s.
[0034] (4) After the electrolytic corrosion is completed, rinse the surface to be inspected with water, dry it, and then place it under a metallographic microscope for observation. The results are as Figure 5 shown; It can be seen from Figure 5 that the obtained prior austenite grain boundaries are clear and complete.
[0035] Comparative Example 1
[0036] In this comparative example, a nitric acid alcohol solution is used to reveal the prior austenite grain boundaries of the high-temperature resistant bearing steel M50-NiL. The specific operation is as follows: (1) Cut the quenched and tempered M50-NiL sample according to the standard of GB / T 6394-2017, and then perform grinding and polishing on the surface to be inspected of the sample. The specific operation is as follows: Grind the surface to be inspected of the sample successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polish it on a polishing machine at a speed of 600 revolutions per minute until it becomes a mirror surface.
[0037] (2) Immerse the polished sample in a 4% nitric acid alcohol solution for corrosion, and the corrosion time is 3 min.
[0038] (3) After the corrosion is completed, rinse the sample with water, dry it, and then place it under a metallographic microscope for observation. The results are as Figure 6 shown; It can be seen from Figure 6 that the prior austenite grain boundaries are not completely revealed, and some structures appear.
[0039] Comparative Example 2
[0040] In this comparative example, an aqueous picric acid solution was used to reveal the original austenite grain boundaries of high-temperature resistant bearing steel M50-NiL. The specific operation is as follows: (1) The quenched and tempered M50-NiL specimens were cut according to the standard of GB / T 6394-2017, and then the surfaces to be inspected of the specimens were ground and polished. The specific operation was as follows: The surfaces to be inspected of the specimens were ground successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polished on a polishing machine at a speed of 600 revolutions per minute until they became mirror-like.
[0041] (2) The polished specimens were put into a supersaturated aqueous picric acid solution for corrosion, and the corrosion time was 5 min.
[0042] After corrosion, the specimens were rinsed with water, dried, and then placed under a metallographic microscope for observation. The results are as Figure 7 shown; it can be seen from Figure 7 that the original austenite grain boundaries were not completely revealed, and some tissues appeared.
[0043] Comparative Example 3
[0044] In this comparative example, an aqueous FeCl3 solution (5% FeCl3 + 15% HCl + 80% H2O) was used to reveal the original austenite grain boundaries of high-temperature resistant bearing steel M50-NiL. The specific operation is as follows: (1) The quenched and tempered M50-NiL specimens were cut according to the standard of GB / T 6394-2017, and then the surfaces to be inspected of the specimens were ground and polished. The specific operation was as follows: The surfaces to be inspected of the specimens were ground successively on sandpapers with 150 mesh, 300 mesh, 600 mesh, and 1000 mesh, and then polished on a polishing machine at a speed of 600 revolutions per minute until they became mirror-like.
[0045] (2) The polished specimens were put into an aqueous FeCl3 solution (5% FeCl3 + 15% HCl + 80% H2O) for corrosion, and the corrosion time was 3 min.
[0046] (3) After corrosion, the specimens were rinsed with water, dried, and then placed under a metallographic microscope for observation. The results are as Figure 8 shown; it can be seen from Figure 8 that the original austenite grain boundaries were not completely revealed, and some tissues appeared.
[0047] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed as above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content without departing from the technical solution of the present invention. However, as long as it does not depart from the technical solution content of the present invention, any brief modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.
Claims
1. A method for revealing the original austenite grain boundaries of high-temperature resistant bearing steel, characterized in that, It includes the following steps: (1) Specimen cutting and grinding and polishing treatment; (2) Place the polished surface of the specimen facing up in a muffle furnace, keep it at 400°C - 600°C for 20 - 60 minutes, and then air cool it to room temperature; (3) Polish the surface to be inspected of the specimen again until it becomes mirror-like, and then perform electrolytic corrosion; (4) After the electrolytic corrosion is completed, rinse the surface to be inspected with water, dry it, and then place it under a metallographic microscope for observation.
2. A method for revealing the original austenite grain boundaries of a high-temperature resistant bearing steel as claimed in claim 1, characterized in that, The specific operation of the specimen cutting and grinding and polishing treatment is as follows: Cut the high-temperature bearing steel after quenching + tempering according to the GB / T 6394-2017 standard, and then polish the surface to be inspected of the specimen successively on sandpapers with 150 meshes, 300 meshes, 600 meshes, and 1000 meshes, and then polish it until it becomes mirror-like.
3. A method for displaying the original austenite grain boundaries of a high-temperature resistant bearing steel as claimed in claim 1, characterized in that, The corrosion solution for the electrolytic corrosion shown is a 5 - 15% chromic acid aqueous solution.
4. A method for displaying the original austenite grains of a high-temperature resistant bearing steel as shown in claim 1, characterized in that, The corrosion voltage for the electrolytic corrosion shown is 20 - 25V, the current is 3 - 5A, and the corrosion time is 30 - 90s.