A method for revealing original austenite grain boundaries of high-temperature bearing steel

Abstract

The application discloses a high-temperature bearing steel original austenite grain boundary display method, which comprises the following steps: (1) performing grinding and polishing treatment on a to-be-observed surface of a sample; (2) performing primary corrosion on the to-be-observed surface by using a nitric acid alcohol solution, and the corrosion time is 1-3 minutes; (3) slightly polishing the to-be-observed surface of the sample corroded in the step 2; (4) performing secondary corrosion on the to-be-observed surface of the sample, and a corrosion agent is prepared from a nitric acid alcohol solution, a ferric chloride alcohol solution and a copper sulfate alcohol solution, and the corrosion time is 1-3 minutes; (5) slightly polishing the to-be-observed surface of the sample corroded in the step 4; and (6) placing the to-be-observed surface of the sample in a 5%-10% nitric acid alcohol solution for third corrosion, and the corrosion time is 0.5-1 minute. The method can effectively display the high-temperature bearing steel original austenite grain boundary, and has the advantages of easy acquisition of the corrosion agent, convenient preparation, simple operation process and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallography, and particularly relates to a high-temperature bearing steel original austenite grain boundary display method. BACKGROUND

[0002] The aero-engine is a power device of an aircraft and represents the forefront of cutting-edge engineering technology. The main shaft bearing of the aero-engine needs to withstand severe vibration stress, bending torque and harsh lubrication conditions under high temperature and high speed conditions, and the cracking of the bearing will have a disastrous consequence on the integrity of the aero-engine. With the development of the aero-engine towards the direction of high thrust-to-weight ratio, high reliability, high durability, low oil consumption rate and low cost, the working conditions of the main shaft bearing as a key component of the aero-engine become more severe, and the bearing steel needs to have sufficient hardness, strength and dimensional stability when operating in a high-temperature environment.

[0003] GCr4Mo4V is the most widely used high-temperature bearing steel for the main shaft bearing of the aero-engine in China, and is widely used for machining the ring and rolling body of the main shaft bearing of the aero-engine below 316℃. The refinement degree and uniformity of the grain structure directly determine the service performance and stability, so the determination and characterization of the original austenite grain size of the high-temperature bearing steel GCr4Mo4V are of great significance to improve the quality of the bearing steel.

[0004] According to the national standard GB / T 38886-2020 of the high-temperature bearing steel, the austenite grain size of the steel is sampled, etched and graded according to the provisions of GB / T 6394, and the method for displaying the original austenite grain boundary includes cementite display method, ferrite display method, oxidation display method, fine pearlite display method and martensite grain direct etching method.

[0005] (1) Cementite display method

[0006] The cementite display method is mainly used for carbon steel and alloy steel with a carbon content of ≤0.25%. First, a cementation layer is formed by cementation, and a certain heat treatment means is adopted to precipitate a cementite network at the austenite grain boundary. Then, 3% to 4% nitric acid alcohol solution or 50% picric acid solution is used to etch the cementite network.

[0007] (2) Ferrite display method

[0008] The ferrite display method is used for carbon steel and alloy steel with a carbon content of 0.25% to 0.6%. A clear ferrite network is precipitated at the austenite grain boundary by heat treatment, and 3% to 4% nitric acid alcohol solution or 5% picric acid alcohol solution is used to etch the cementite network.

[0009] (3) Oxidation display method

[0010] Primarily targeting carbon steel and alloy steel with a content of 0.25% to 0.6%, the steel is heated in an oxidizing atmosphere to cause oxidation at the grain boundaries, followed by etching with a 15% hydrochloric acid ethanol solution.

[0011] (4) Fine pearlite display method

[0012] Primarily targeting eutectoid steel, an incompletely hardened zone is formed by using quenching or gradient quenching processes. The original austenite grains will consist of a small amount of fine pearlite surrounding martensite. Then, 3%–4% nitric acid alcohol solution or 5% picric acid alcohol solution is used for etching, thereby revealing the original austenite grain boundaries.

[0013] (5) Direct etching of martensitic grains

[0014] For carbon steel and alloy steel with a carbon content of less than 1%, a method of full quenching to generate martensite structure is adopted, and a reagent prepared with 1g picric acid, 5ml hydrochloric acid and 95ml ethanol is used to etch the original austenite grains.

[0015] Based on the above summary of all the methods for revealing the original austenite grain boundaries, it is not difficult to find that for hypereutectoid alloy steels with a carbon content of around 0.8%, such as high-temperature bearing steel, the only suitable method currently available is the direct etching method of martensite grains. However, the etchant contains picric acid, which is a chemical currently under public security control, making procurement relatively difficult and limiting the application of this method for revealing the original austenite grain boundaries. Therefore, it is essential to find a simple, practical method suitable for revealing the austenite grain boundaries of high-temperature bearing steel. Summary of the Invention

[0016] The technical problem to be solved by the present invention is to provide a method for revealing the original austenite grain boundaries of high-temperature bearing steel, which can effectively reveal the original austenite grain boundaries of high-temperature bearing steel. The etchant is easy to obtain and prepare, and the operation process is simple.

[0017] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0018] A method for revealing the original austenite grain boundaries in high-temperature bearing steel includes the following steps:

[0019] Step 1: Polish the surface of the high-temperature bearing steel sample to be observed.

[0020] Step 2: Use a 5% to 10% nitric acid alcohol solution to perform initial etching on the surface of the sample to be observed for 1 to 3 minutes. Rinse with water and air dry.

[0021] Step 3: Lightly polish the surface of the sample to be observed after step 2 on a polishing machine at a speed of 100-300 rpm for 1-3 minutes;

[0022] Step 4: A second corrosion is performed on the observed surface of the sample after slight polishing in step 3, and the corrosion agent is prepared by mixing 5%-10% nitric acid alcohol solution, iron chloride alcohol saturated solution and copper sulfate alcohol saturated solution in a volume ratio of 3-5:1-2:1-2, and the corrosion time is 1-3 minutes; after being washed with water and dried in air;

[0023] Step 5: The observed surface of the sample corroded in step 4 is slightly polished on a polishing machine at a speed of 100-300 revolutions per minute for 1-3 minutes;

[0024] Step 6: The observed surface of the sample after slight polishing in step 5 is placed in 5%-10% nitric acid alcohol solution for a third corrosion, and the corrosion time is 0.5-1 minute; after being washed with water and dried in air, the sample is observed under a microscope.

[0025] The high-temperature bearing steel sample in step 1 of the application needs to meet the technical index requirements of GB / T 38886-2020 High-Temperature Bearing Steel, and is treated according to the sampling and heat treatment system specified in clause 6.7 of the standard.

[0026] The grinding and polishing treatment in step 1 of the application is specifically operated as follows: the observed surface of the sample is polished on sandpaper with mesh sizes of 180, 400, 800, 1000 and 1200 in sequence, and then polished on a polishing machine at a speed of 300-900 revolutions per minute for 3-5 minutes.

[0027] The high-temperature bearing steel in the application is GCr4Mo4V for a main shaft bearing of an aero-engine, and the chemical composition and mass percentage thereof are as follows: C: 0.75%-0.85%, Mn≤0.35%, Si≤0.35%, Cr: 3.75%-4.25%, Mo: 4%-4.5%, V: 0.9%-1.1%, W≤0.25%, P≤0.025%, S≤0.015%, Ni≤0.25%, Cu≤0.20%, Co≤0.25%, and the balance is Fe and unavoidable impurities.

[0028] The high-temperature bearing steel treated by the method provided by the application can weaken the confusion of the martensite structure to the original austenite grain boundary, and clearly display the original austenite grain boundary, thereby preparing for further development of grain size rating.

[0029] The design idea of the present application is: the normal polishing and polishing surface is corroded three times and slightly polished, wherein the first corrosion uses 5%-10% nitric acid alcohol solution with relatively high concentration, the purpose is to corrode the original austenite grain boundary and martensite structure at the same time, but the corrosion degree of the original austenite grain boundary is relatively heavy, and the corrosion of the martensite structure is weakened after slight polishing; the second corrosion uses 5%-10% nitric acid alcohol solution, saturated iron chloride alcohol solution and saturated copper sulfate alcohol solution prepared according to the volume ratio of 3-5:1-2:1-2, the purpose is to deepen the corrosion intensity of the original austenite grain boundary, and the martensite structure is inevitably corroded again in this process, so the corrosion depth of the martensite structure is weakened by the second slight polishing; after two times of corrosion and slight polishing, the corrosion depth of the original austenite grain boundary is weakened compared with the second corrosion, but it is strengthened compared with the corrosion depth after the first corrosion, so the third corrosion and slight polishing are further adopted, which uses 5%-10% nitric acid alcohol solution with high concentration, but the corrosion time is greatly shortened, the purpose is to avoid the martensite structure being corroded too much, and after the third slight polishing, the corrosion depth of the martensite structure is very weak or even eliminated, and the original austenite grain boundary is retained.

[0030] The etchant used in the present application is composed of nitric acid, alcohol, ferric chloride, copper sulfate and other chemical reagents, which are common and easy to obtain chemical reagents, not limited by public security, the reagent preparation process is simple, the operation steps are clear, the corrosion steps and slight polishing links proposed significantly improve the corrosion contrast of the original austenite grain boundary, and the corrosion depth of the martensite structure is weak or even almost completely eliminated. Compared with the traditional method, the method has outstanding advantages in terms of simplicity, implementation effect and the like. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The metallographic photo of the original austenite grain boundary of example 1 (500 times);

[0032] Figure 2 The metallographic photo of the original austenite grain boundary of example 2 (500 times);

[0033] Figure 3 The metallographic photo of the original austenite grain boundary of example 3 (500 times);

[0034] Figure 4 The metallographic photo of the original austenite grain boundary of example 4 (500 times);

[0035] Figure 5 The metallographic photo of the original austenite grain boundary of example 5 (500 times);

[0036] Figure 6Metallographic photo of original austenite grain boundary (500 times) for Example 6;

[0037] Figure 7 Metallographic photo of original austenite grain boundary (500 times) for Example 7;

[0038] Figure 8 Metallographic photo of original austenite grain boundary (500 times) for Example 8;

[0039] Figure 9 Metallographic photo of original austenite grain boundary (500 times) for Example 9;

[0040] Figure 10 Metallographic photo of original austenite grain boundary (500 times) for Example 10; Embodiment

[0041] The application will be further described in detail below with specific examples.

[0042] The original blank of the high-temperature bearing steel used in the example is a φ300mm x 700mm specification GCr4Mo4V vacuum consumable ingot smelted under the same process condition of double vacuum (vacuum induction + vacuum consumable), which is prepared into a φ12mm specification hot-rolled straight bar after forging breakdown, bar hot rolling and other links. The chemical composition is shown in Table 1, and each technical index meets the technical index requirements of GB / T 38886-2020 “High-temperature bearing steel”. Example 1

[0043] First, the φ12mm specification GCr4Mo4V hot-rolled straight bar is sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 “High-temperature bearing steel” and is treated by oil quenching at 1090℃, and then the following steps are performed:

[0044] (1) The observation surface is polished on 180 mesh, 400 mesh, 800 mesh, 1000 mesh and 1200 mesh sandpaper in turn, and then polished on a polishing machine at a speed of 300 revolutions / minute for 3 minutes;

[0045] (2) The observation surface is placed in a 5% nitric acid alcohol solution for initial etching, and the etching time is 1 minute. After rinsing with water and air drying, the observation surface is slightly polished on a polishing machine at a speed of 100 revolutions / minute for 1 minute;

[0046] (3) The observation surface is etched again in a newly prepared etchant, which is prepared by mixing 5% nitric acid alcohol solution, iron chloride alcohol saturated solution and copper sulfate alcohol saturated solution at a volume ratio of 3:1:1. The etching time is 1 minute. After rinsing with water and air drying, the observation surface is slightly polished on a polishing machine at a speed of 100 revolutions / minute for 1 minute;

[0047] (4) Again, the surface to be observed is placed in a 5% nitric acid alcohol solution for corrosion, with a corrosion time of 0.5 minutes, followed by water rinsing and air drying.

[0048] The surface to be observed is observed under an optical microscope, and the original austenite grain boundary is clearly shown, as shown in FIG. 1. Figure 1 Example 2

[0049] First, the φ12mm GCr4Mo4V hot-rolled straight bar is sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 “High-temperature bearing steel” and is treated by oil quenching at 1090°C, and then the following steps are performed:

[0050] (1) The surface to be observed is polished on 180-mesh, 400-mesh, 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence, and then polished on a polishing machine at a speed of 900 revolutions per minute for 5 minutes;

[0051] (2) The surface to be observed is initially corroded in a 10% nitric acid alcohol solution, with a corrosion time of 3 minutes, and then rinsed with water and air dried, and then slightly polished on a polishing machine at a speed of 300 revolutions per minute for 3 minutes;

[0052] (3) The surface to be observed is again corroded in a newly prepared etchant, which is prepared by mixing a 10% nitric acid alcohol solution, a saturated iron chloride alcohol solution, and a saturated copper sulfate alcohol solution in a volume ratio of 5:2:2, with a corrosion time of 3 minutes, and then rinsed with water and air dried, and then slightly polished on a polishing machine at a speed of 300 revolutions per minute for 3 minutes;

[0053] (4) The surface to be observed is again corroded in a 10% nitric acid alcohol solution, with a corrosion time of 1 minute, and then rinsed with water and air dried.

[0054] The surface to be observed is observed under an optical microscope, and the original austenite grain boundary is clearly shown, as shown in FIG. 1. Figure 2 Example 3

[0055] First, the φ12mm GCr4Mo4V hot-rolled straight bar is sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 “High-temperature bearing steel” and is treated by oil quenching at 1090°C, and then the following steps are performed:

[0056] ​​(1) The surface to be observed is polished on 180 mesh, 400 mesh, 800 mesh, 1000 mesh, and 1200 mesh sandpaper in turn, and then polished on a polishing machine at a speed of 400 rpm for 4 minutes;

[0057] (2) The surface to be observed is placed in a 6% nitric acid alcohol solution for initial etching, with an etching time of 2 minutes. After rinsing with water and air drying, the surface is lightly polished on a polishing machine at a speed of 200 rpm for 2 minutes;

[0058] (3) The surface to be observed is again placed in a newly prepared etchant for etching, the etchant being prepared from a 6% nitric acid alcohol solution, an iron chloride alcohol saturated solution, and a copper sulfate alcohol saturated solution in a volume ratio of 4:1:2. The etching time is 2 minutes. After rinsing with water and air drying, the surface is lightly polished on a polishing machine at a speed of 200 rpm for 2 minutes;

[0059] (4) The surface to be observed is again placed in a 6% nitric acid alcohol solution for etching, with an etching time of 0.8 minutes. Then the surface is rinsed with water and air dried.

[0060] The surface to be observed is observed under an optical microscope, and the original austenite grain boundaries are clearly visible, as shown in Figure 3 . Example 4

[0061] First, φ12mm GCr4Mo4V hot-rolled straight bars are sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 “High Temperature Bearing Steel” and are oil quenched at 1090°C. Then the following steps are performed:

[0062] (1) The surface to be observed is polished on 180 mesh, 400 mesh, 800 mesh, 1000 mesh, and 1200 mesh sandpaper in turn, and then polished on a polishing machine at a speed of 500 rpm for 5 minutes;

[0063] (2) The surface to be observed is placed in a 7% nitric acid alcohol solution for initial etching, with an etching time of 3 minutes. After rinsing with water and air drying, the surface is lightly polished on a polishing machine at a speed of 300 rpm for 2 minutes;

[0064] (3) The surface to be observed is again placed in a newly prepared etchant for etching, the etchant being prepared from a 7% nitric acid alcohol solution, an iron chloride alcohol saturated solution, and a copper sulfate alcohol saturated solution in a volume ratio of 5:1:2. The etching time is 3 minutes. After rinsing with water and air drying, the surface is lightly polished on a polishing machine at a speed of 300 rpm for 2 minutes;

[0065] (4) Again, the surface to be observed is placed in 7% nitric acid alcohol solution for corrosion, the corrosion time is 1 minute, then washed with water and air dried.

[0066] The surface to be observed is observed under an optical microscope, and the original austenite grain boundary is clearly shown, as shown in Figure 4 . Example 5

[0067] First, the φ12mm GCr4Mo4V hot-rolled straight bar is sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 "High-temperature bearing steel" and is treated by oil quenching at 1090℃, and then the following steps are performed:

[0068] (1) The surface to be observed is polished on 180 mesh, 400 mesh, 800 mesh, 1000 mesh and 1200 mesh sandpaper in turn, and then polished on a polishing machine at a speed of 600 rpm for 4 minutes;

[0069] (2) The surface to be observed is first etched in an 8% nitric acid alcohol solution, the etching time is 2 minutes, and then washed with water and air dried, and then slightly polished on a polishing machine at a speed of 100 rpm for 1 minute;

[0070] (3) The surface to be observed is etched again in a newly prepared etchant, which is prepared by mixing 8% nitric acid alcohol solution, iron chloride alcohol saturated solution and copper sulfate alcohol saturated solution in a volume ratio of 3:2:2, the etching time is 2 minutes, and then washed with water and air dried, and then slightly polished on a polishing machine at a speed of 200 rpm for 2 minutes;

[0071] (4) The surface to be observed is etched again in an 8% nitric acid alcohol solution, the etching time is 0.5 minutes, and then washed with water and air dried.

[0072] The surface to be observed is observed under an optical microscope, and the original austenite grain boundary is clearly shown, as shown in Figure 5 . Example 6

[0073] First, the φ12mm GCr4Mo4V hot-rolled straight bar is sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 "High-temperature bearing steel" and is treated by oil quenching at 1090℃, and then the following steps are performed:

[0074] (1) The surface to be observed is polished on 180 mesh, 400 mesh, 800 mesh, 1000 mesh and 1200 mesh sandpaper in turn, and then polished on a polishing machine at a speed of 700 rpm for 4.5 minutes;

[0075] (2) The surface to be observed is placed in a 9% nitric acid alcohol solution for initial etching, with an etching time of 2.5 minutes. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 200 revolutions per minute for 2.5 minutes;

[0076] (3) The surface to be observed is again placed in a newly prepared etchant for etching, with the etchant being prepared from a 9% nitric acid alcohol solution, an iron chloride alcohol saturated solution, and a copper sulfate alcohol saturated solution in a volume ratio of 4:1:1. The etching time is 2.5 minutes. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 200 revolutions per minute for 2.5 minutes;

[0077] (4) The surface to be observed is again placed in a 9% nitric acid alcohol solution for etching, with an etching time of 0.5 minutes. Then, it is rinsed with water and air dried.

[0078] The surface to be observed is observed under an optical microscope, and the original austenite grain boundaries are clearly visible, as shown in FIG. 1. Figure 6 Example 7

[0079] First, φ12mm GCr4Mo4V hot-rolled straight bars are sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 "High-temperature bearing steel" and are treated by oil quenching at 1090°C. Then, the following steps are performed:

[0080] (1) The surface to be observed is polished on 180-mesh, 400-mesh, 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence, and then polished on the polishing machine at a speed of 800 revolutions per minute for 4 minutes;

[0081] (2) The surface to be observed is placed in a 10% nitric acid alcohol solution for initial etching, with an etching time of 1 minute. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 200 revolutions per minute for 1 minute;

[0082] (3) The surface to be observed is again placed in a newly prepared etchant for etching, with the etchant being prepared from a 5% nitric acid alcohol solution, an iron chloride alcohol saturated solution, and a copper sulfate alcohol saturated solution in a volume ratio of 5:1:1. The etching time is 1 minute. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 100 revolutions per minute for 1 minute;

[0083] (4) The surface to be observed is again placed in a 5% nitric acid alcohol solution for etching, with an etching time of 0.5 minutes. Then, it is rinsed with water and air dried.

[0084] ​The observation surface is observed under an optical microscope, and the original austenite grain boundaries are clearly shown, as shown in Figure 7 . Example 8

[0085] First, the φ12mm GCr4Mo4V hot-rolled straight bar is sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 “High-temperature bearing steel” and is treated by oil quenching at 1090°C, and then the following steps are performed:

[0086] (1) The observation surface is polished on 180-mesh, 400-mesh, 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence, and then polished on a polishing machine at a speed of 500 rpm for 3 minutes;

[0087] (2) The observation surface is placed in a 10% nitric acid alcohol solution for initial etching, with an etching time of 1 minute. After rinsing with water and air drying, the surface is lightly polished on a polishing machine at a speed of 100 rpm for 1 minute;

[0088] (3) The observation surface is again placed in a freshly prepared etchant for etching, the etchant being prepared by mixing 5% nitric acid alcohol solution, iron chloride alcohol saturated solution, and copper sulfate alcohol saturated solution in a volume ratio of 5:2:1. The etching time is 1 minute. After rinsing with water and air drying, the surface is lightly polished on a polishing machine at a speed of 100 rpm for 2 minutes;

[0089] (4) The observation surface is again placed in a 10% nitric acid alcohol solution for etching, with an etching time of 0.5 minutes, followed by rinsing with water and air drying.

[0090] The observation surface is observed under an optical microscope, and the original austenite grain boundaries are clearly shown, as shown in Figure 8 . Example 9

[0091] First, the φ12mm GCr4Mo4V hot-rolled straight bar is sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 “High-temperature bearing steel” and is treated by oil quenching at 1090°C, and then the following steps are performed:

[0092] (1) The observation surface is polished on 180-mesh, 400-mesh, 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence, and then polished on a polishing machine at a speed of 300 rpm for 4 minutes;

[0093] (2) The surface to be observed is placed in a 10% nitric acid alcohol solution for initial etching, with an etching time of 1 minute. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 200 rpm for 1 minute;

[0094] (3) The surface to be observed is again placed in a newly prepared etchant for etching, which is prepared by mixing a 10% nitric acid alcohol solution, a saturated iron chloride alcohol solution, and a saturated copper sulfate alcohol solution at a volume ratio of 3:1:1. The etching time is 1 minute. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 100 rpm for 1 minute;

[0095] (4) The surface to be observed is again placed in an 8% nitric acid alcohol solution for etching, with an etching time of 0.5 minutes. Then, it is rinsed with water and air dried.

[0096] The surface to be observed is observed under an optical microscope, and the original austenite grain boundaries are clearly visible, as shown in Figure 9 . Example 10

[0097] First, φ12mm GCr4Mo4V hot-rolled straight bars are sampled according to the sampling method specified in Article 6.7 of GB / T 38886-2020 "High-temperature bearing steel" and are oil-quenched at 1090°C. Then, the following steps are performed:

[0098] (1) The surface to be observed is polished on 180-mesh, 400-mesh, 800-mesh, 1000-mesh, and 1200-mesh sandpaper in sequence, and then polished on the polishing machine at a speed of 800 rpm for 4.5 minutes;

[0099] (2) The surface to be observed is placed in an 8% nitric acid alcohol solution for initial etching, with an etching time of 2 minutes. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 200 rpm for 2 minutes;

[0100] (3) The surface to be observed is again placed in a newly prepared etchant for etching, which is prepared by mixing a 9% nitric acid alcohol solution, a saturated iron chloride alcohol solution, and a saturated copper sulfate alcohol solution at a volume ratio of 5:1:1. The etching time is 1 minute. After rinsing with water and air drying, light polishing is performed on the polishing machine at a speed of 300 rpm for 2 minutes;

[0101] (4) The surface to be observed is again placed in an 8% nitric acid alcohol solution for etching, with an etching time of 0.6 minutes. Then, it is rinsed with water and air dried.

[0102] The surface to be observed is observed under an optical microscope, and the original austenite grain boundaries are clearly visible, as shown in Figure 10as shown.

[0103] Table 1 Chemical composition and mass fraction (wt%) of high-temperature bearing steel of examples and comparative examples

[0104]

[0105] It can be seen from Examples 1-10 that the original austenite grain boundaries of the GCr4Mo4V high-temperature bearing steel can be clearly presented by the method of the present application, and are not limited by the size of the grain size.

[0106] The above examples are only used to illustrate but not to limit the technical solutions of the present application. Although the present application has been described in detail with reference to the above examples, it should be understood by those skilled in the art that the present application can still be modified or equivalently replaced without departing from the spirit and scope of the present application, and any modification or partial replacement should be covered in the scope of the claims of the present application.

Claims

1. A method for revealing the original austenite grain boundaries in high-temperature bearing steel, characterized in that, The method includes the following steps: Step 1: Polish the surface of the high-temperature bearing steel sample to be observed. Step 2: Use a 5% to 10% nitric acid alcohol solution to perform initial etching on the surface of the sample to be observed for 1 to 3 minutes. Rinse with water and air dry. Step 3: Lightly polish the surface of the sample to be observed after step 2 on a polishing machine at a speed of 100-300 rpm for 1-3 minutes; Step 4: Perform a second etching on the surface of the sample to be observed after slight polishing in Step 3. The etching agent is prepared by mixing 5% to 10% nitric acid alcohol solution, ferric chloride alcohol saturated solution, and copper sulfate alcohol saturated solution in a volume ratio of 3 to 5: 1 to 2: 1 to 2. The etching time is 1 to 3 minutes. After rinsing with water, air dry. Step 5: Lightly polish the surface of the sample to be observed after step 4 on a polishing machine at a speed of 100-300 rpm for 1-3 minutes; Step 6: Place the sample surface to be observed after slight polishing in Step 5 into a 5% to 10% nitric acid alcohol solution for a third etching, with an etching time of 0.5 to 1 minute. Rinse with water, air dry, and then observe under a microscope. The high-temperature bearing steel is GCr4Mo4V for aero-engine main shaft bearings. Its chemical composition and mass percentage are as follows: C: 0.75%~0.85%, Mn≤0.35%, Si≤0.35%, Cr: 3.75%~4.25%, Mo: 4%~4.5%, V: 0.9%~1.1%, W≤0.25%, P≤0.025%, S≤0.015%, Ni≤0.25%, Cu≤0.20%, Co≤0.25%, with the balance being Fe and unavoidable impurities.

2. The method for revealing the original austenite grain boundaries in high-temperature bearing steel as described in claim 1, characterized in that, The polishing process in step 1 is as follows: the surface of the sample to be observed is polished in sequence on sandpaper of 180 grit, 400 grit, 800 grit, 1000 grit and 1200 grit, and then polished on a polishing machine at a speed of 300 to 900 rpm for 3 to 5 minutes.

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