Microhardness testing method and system for carbonitrided spline surface hardness

Abstract

The application discloses a kind of carbonitriding spline surface hardness microhardness testing methods, comprising the following steps: cutting along the section of carbonitriding spline to be detected to prepare the metallographic sample of tooth part;With spline tooth surface midpoint as origin O, with spline tooth surface midpoint profile line as X axis, establish coordinate system and determine reference line, select multiple test points on reference line, test and record the microhardness value of each test point;Calculate average, standard deviation, data repeatability;Judge whether data repeatability is greater than or equal to 5%, when data repeatability >=5%, select new test point on reference line, and record the microhardness value of the test point and calculate data repeatability R, until data repeatability R >=5%, otherwise, average is used as final microhardness value.The application has the advantages of accurate data detection and high efficiency.

Description

Technical Field

[0001] This invention relates to the field of hardness testing methods, and more particularly to a microhardness testing method and system for the surface hardness of carbonitrided splines. Background Technology

[0002] Spline drives consist of a pair of internal and external splines, offering advantages such as large contact area, high load-bearing capacity, and good centering performance. They are widely used in aerospace applications. The spline surfaces used in aerospace transmissions must withstand high speeds, heavy loads, and high-frequency dynamic alternating loads, necessitating surface strengthening to meet these requirements.

[0003] Carbonitriding is a chemical heat treatment process that simultaneously introduces carbon and nitrogen elements into the surface of steel parts to improve surface hardness. It is commonly used for internal and external spline parts with shallow diffusion layers (the diffusion layer depth is usually ≤0.5mm). For carbonitriding, surface hardness is a core quality control indicator. However, there is currently no specific hardness testing standard or method for carbonitriding splines in China. When testing the hardness of carbonitriding splines, GB / T 230 "Metallic Materials - Rockwell Hardness Test Method" is referenced. However, aerospace spline parts are usually quite small, with spline tooth width generally less than 5mm. Therefore, it is difficult to process conventional surface hardness samples, resulting in a high scrap rate. This is especially true for internal spline parts, where the spline teeth are inside the part, making it difficult to accurately test the surface hardness of internal splines. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a microhardness testing method and system for carbonitriding spline surface hardness that is accurate and efficient in data detection.

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

[0006] A microhardness testing method for the surface hardness of carbonitrided splines includes the following steps:

[0007] S1. Cut along the cross section of the carbonitrided spline to be tested, prepare a metallographic sample of the carbonitrided spline to be tested, and polish it until the metallographic sample reaches the mirror surface standard.

[0008] S2. Taking the midpoint of the spline tooth profile as the origin O, the tangent to the spline tooth profile at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and the line 100 μm away from the origin O and parallel to the X-axis as the baseline, select n points on the baseline as microhardness test points, test and record the microhardness values ​​x1, x2...x at each test point. n , n≥3;

[0009] S3. Calculate the average value of the microhardness values ​​based on the recorded microhardness values ​​at each test point. Standard deviation S, data repeatability R;

[0010] S4. Determine if the data repeatability R is greater than or equal to 5%. If the data repeatability R ≥ 5%, continue to select new microhardness test points on the baseline and record the microhardness value of the test point. Repeat step S3. Otherwise, use the average value of the test points. As the microhardness value of the carbonitrided spline surface to be tested.

[0011] As a further improvement to the above technical solution:

[0012] In step S3, the average value

[0013] Standard deviation

[0014] Data duplication

[0015] In step S1, the polished surface of the metallographic sample reaches the mirror standard, with a surface roughness Ra≤0.02.

[0016] In step S1, the surface of the polished metallographic sample is free of grinding burn layer.

[0017] In step S2, a microhardness tester is used to test the microhardness value at each test point.

[0018] In step S2, the test pressure at each test point is 200g.

[0019] In step S2, the distance between each test point is at least 200 μm.

[0020] Step S4 also includes averaging the test points. Convert to any one of the following hardness values: HRC, HRA, HR15N, or HB.

[0021] As a general inventive concept, this invention also provides a microhardness testing system for the surface hardness of carbonitrided splines, comprising:

[0022] The first processing module is used to cut along the cross section of the carbonitrided spline to be tested, prepare the metallographic sample of the carbonitrided spline to be tested, and polish the metallographic sample to achieve the mirror surface standard.

[0023] The second acquisition module is used to select n points as microhardness test points, with the midpoint of the spline tooth surface contour line as the origin O, the tangent line of the spline tooth surface contour line at the origin O as the X-axis, the straight line perpendicular to the X-axis as the Y-axis, and a straight line 100μm away from the origin O and parallel to the X-axis as the baseline. The module tests and records the microhardness values ​​x1, x2...x at each test point. n , n≥3;

[0024] The third calculation module is used to calculate the average value of the microhardness values ​​based on the recorded microhardness values ​​at each test point. Standard deviation S, data repeatability R;

[0025] The fourth judgment module is used to determine whether the data repeatability R is greater than or equal to 5%. When the data repeatability R ≥ 5%, a new microhardness test point is selected on the baseline, and the microhardness value of the test point is recorded. The data is then returned to the third calculation module for processing. Otherwise, the average value of the test points is used. As the surface hardness value of the carbonitrided spline to be tested.

[0026] As a general inventive concept, the present invention also provides a computer-readable storage medium storing a computer program programmed or configured to perform the aforementioned microhardness testing method for the surface hardness of carbonitrided splines.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] High testing accuracy: Metallographic specimens are ground on both sides of a grinding machine, resulting in high flatness and reducing the impact of specimen tilt. After polishing, the specimen surface is mirror-like, with clear and accurate indentation edges and corners, and high data repeatability.

[0029] High testing efficiency: Surface hardness testing can be performed simultaneously with effective hardened layer depth testing, reducing sample clamping time. At the same time, the indentation edges are clear and accurate. The equipment can automatically calculate the readings and convert the hardness according to the GB / T1172-1999 standard "Conversion Values ​​of Hardness and Strength of Ferrous Metals", which greatly improves testing efficiency.

[0030] The present invention has a reasonable process technology. Conventional surface hardness testing samples for carbonitrided splines used in aviation are difficult to process, have a high scrap rate, and cannot guarantee the accuracy of hardness testing. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the test points for the orthogonal experimental scheme of this invention.

[0032] Figure 2 This is a schematic diagram of the coordinate axes of the test area in this invention.

[0033] Figure 3 This is a flowchart of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.

[0035] The technical concept of this invention is as follows:

[0036] (1) Based on the different materials of the spline parts, formulate a comparative scheme for microhardness testing of carbonitrided spline surface hardness, and determine the sample, load and test coordinates used for microhardness testing according to GB / T4342-91 "Metallic Micro Vickers Hardness Test Method".

[0037] Table 1 Test Scheme for Spline Carbonitriding Specimens

[0038]

[0039]

[0040] The above materials are basically common aerospace spline materials. The carbonitriding layer depth ranges approximately from 0.1 to 0.55 mm. According to HB5493-1991 "Method for Determining the Depth of Carburizing and Carbonitriding Layers in Aerospace Steel Parts," a micro Vickers hardness tester (model FM-910) was used to test the microhardness gradient on the metallographic samples. After grinding and polishing, the surface of the metallographic samples reached mirror finish, with a surface roughness Ra ≤ 0.02. The test pressure was 200 g. The origin O was set at the midpoint of the spline tooth profile, the X-axis was the tangent to the spline tooth profile at the origin O, and the Y-axis was the line perpendicular to the X-axis. The test coordinates are shown in the table below. Figure 1 As shown, each sample was tested with three rows of hardness gradients.

[0041] Table 2. Test Coordinate Points

[0042]

[0043] (2) Perform microhardness testing and conventional Rockwell hardness testing on the samples, collect data, and calculate the average value of the data. Standard deviation S and data repeatability R;

[0044] Arithmetic mean

[0045] Standard deviation

[0046] Data duplication

[0047] (3) The average value A of the microhardness test data was converted using the GB / T1172-1999 standard "Conversion Values ​​of Hardness and Strength of Ferrous Metals". Depending on the design drawing requirements, it was converted into different hardness scales such as HRC, HRA, HR15N, and HB. This data was then used as the surface hardness sample for the part. The results showed:

[0048] Six groups of carbonitriding samples were tested. The microhardness at coordinate A2 was close to that of the cut sample. Therefore, it can be considered that during the cyanidation of the shallow infiltration layer, the microhardness at 100μm can replace the hardness of the cut sample as the surface hardness of the part. Moreover, the standard deviation and repeatability of the microhardness test method are much smaller than those of the cut sample test method, which proves that the test method is more stable and the data is more accurate.

[0049] (4) Based on the test data above, it was determined that the microhardness value measured at 0.1 μm vertically downwards from the high center surface of the spline tooth using a 200g load can be used as the surface hardness data for the carbonitriding layer. The standard deviation and repeatability of the test data obtained by this method are superior to those of the traditional hardness test method using cut specimens.

[0050] Example 1:

[0051] A certain aero-engine gear requires carbonitriding heat treatment for its internal splines. After heat treatment, the internal splines are required to be inspected according to the HB5013-1996 "Inspection Categories of Heat-Treated Parts" standard for Class II parts, including the depth of carbonitriding, metallographic structure, surface hardness, core hardness, and mechanical properties. The surface hardness of the internal splines must be ≥88HR15N.

[0052] like Figure 3 As shown, a microhardness testing method for the surface hardness of carbonitrided splines includes the following steps:

[0053] (1) Select the parts that were scrapped due to the machining dimensions in the previous batch as test materials and carry out carbonitriding quenching heat treatment together with the remaining parts.

[0054] (2) Use a cutting machine to cut metallographic test samples of the internal spline along the cross section of the sample. During the cutting process, take measures to ensure that the surface condition of the sample is not affected by high temperature.

[0055] (3) Grind the sample with metallographic sandpaper and polish the sample with diamond polishing liquid. The sample surface reaches the mirror standard, the surface roughness Ra≤0.02, and the sample edge must not be rounded.

[0056] (4) Use metallographic etchant (4% nitric acid alcohol solution) to etch the sample, perform metallographic testing on the sample, observe the metallographic structure of the carburized layer, ensure that there is no grinding burn layer on the sample cross section, and repolish the sample cross section after the metallographic testing is completed.

[0057] (5) Use a microhardness tester to test the microhardness of the sample. Before testing, use a standard hardness block to calibrate the hardness tester.

[0058] (6) The test pressure is 200g. The test position is selected at the middle of the spline tooth height. The origin O is the intersection of the spline tooth height center axis and the spline tooth profile. The origin O is the midpoint of the spline tooth profile. The X-axis is the tangent of the spline tooth profile at the origin O. The Y-axis is the straight line perpendicular to the X-axis. The baseline is a straight line 100μm away from the origin O and parallel to the X-axis. n points are selected on the baseline as microhardness test points. The microhardness values ​​x1, x2...x at each test point are tested and recorded. n , n≥3;

[0059] In this embodiment, the test depth was 100 μm, and the Vickers hardness values ​​were measured at 3 points. The lateral interval between the three points was 200 μm. The test coordinates are shown in the table below:

[0060]

[0061] (7) The test data is shown in the table below.

[0062]

[0063] The repeatability R of the test data is less than 1%, indicating that the test data of this method is stable and has small fluctuations, meeting the requirements of GB / T4342-91 "Metallic materials - Micro Vickers hardness test method".

[0064] (8) The average value of the microhardness test data was calculated using the GB / T1172-1999 standard "Conversion Values ​​of Hardness and Strength of Ferrous Metals". The conversion is performed, and the converted data values ​​are as follows:

[0065] Test site Average Vickers hardness (HV) Rockwell hardness conversion value (HR15N) Carbonitriding sample 702 90.6

[0066] (9) The test results show that the surface hardness of the internal spline is ≥88HR15N.

[0067] This invention also provides a microhardness testing system for the surface hardness of carbonitrided splines, comprising:

[0068] The first processing module is used to cut along the cross section of the carbonitrided spline to be tested, prepare the metallographic sample of the carbonitrided spline to be tested, and polish the metallographic sample to achieve the mirror surface standard.

[0069] The second acquisition module is used to select n points as microhardness test points, with the midpoint of the spline tooth surface contour line as the origin O, the tangent line of the spline tooth surface contour line at the origin O as the X-axis, the straight line perpendicular to the X-axis as the Y-axis, and a straight line 100μm away from the origin O and parallel to the X-axis as the baseline. The module tests and records the microhardness values ​​x1, x2...x at each test point. n , n≥3;

[0070] The third calculation module is used to calculate the average value of the microhardness values ​​based on the recorded microhardness values ​​at each test point. Standard deviation S, data repeatability R;

[0071] The fourth judgment module is used to determine whether the data repeatability R is greater than or equal to 5%. When the data repeatability R ≥ 5%, a new microhardness test point is selected on the baseline, and the microhardness value of the test point is recorded. The data is then returned to the third calculation module for processing. Otherwise, the average value of the test points is used. As the surface hardness value of the carbonitrided spline to be tested.

[0072] As a general inventive concept, the present invention also provides a computer-readable storage medium storing a computer program programmed or configured to perform the aforementioned microhardness testing method for the surface hardness of carbonitrided splines.

[0073] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0074] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0075] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0076] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0077] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, should fall within the protection scope of the present invention.

Claims

1. A microhardness testing method for the surface hardness of carbonitrided splines, characterized in that: Includes the following steps: S1. Cut along the cross section of the carbonitrided spline to be tested, prepare a metallographic sample of the carbonitrided spline to be tested, and polish it until the metallographic sample reaches the mirror surface standard. S2. Taking the midpoint of the spline tooth profile as the origin O, the tangent to the spline tooth profile at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and the line 100 μm away from the origin O and parallel to the X-axis as the baseline, select n points on the baseline as microhardness test points, test and record the microhardness values ​​x1, x2...x at each test point. n , n≥3; S3. Calculate the average value of the microhardness values ​​based on the recorded microhardness values ​​at each test point. Standard deviation S, data repeatability R; S4. Determine if the data repeatability R is greater than or equal to 5%. If the data repeatability R ≥ 5%, continue to select new microhardness test points on the baseline and record the microhardness value of the test point. Repeat step S3. Otherwise, use the average value of the test points. As the microhardness value of the carbonitrided spline surface to be tested.

2. The microhardness testing method according to claim 1, characterized in that: In step S3, the average value Standard deviation Data duplication 3. The microhardness testing method according to claim 2, characterized in that: In step S1, the polished surface of the metallographic sample reaches the mirror standard, with a surface roughness Ra≤0.

02.

4. The microhardness testing method according to claim 3, characterized in that: In step S1, the surface of the polished metallographic sample is free of grinding burn layer.

5. The microhardness testing method according to claim 3, characterized in that: In step S2, a microhardness tester is used to test the microhardness value at each test point.

6. The microhardness testing method according to claim 5, characterized in that: In step S2, the test pressure at each test point is 200g.

7. The microhardness testing method according to any one of claims 1 to 6, characterized in that: In step S2, the distance between each test point is at least 200 μm.

8. The microhardness testing method according to any one of claims 1 to 6, characterized in that: Step S4 also includes averaging the test points. Convert to any one of the following hardness values: HRC, HRA, HR15N, or HB.

9. A microhardness testing system for the surface hardness of carbonitrided splines, characterized in that: include: The first processing module is used to cut along the cross section of the carbonitrided spline to be tested, prepare the metallographic sample of the carbonitrided spline to be tested, and polish the metallographic sample to achieve the mirror surface standard. The second acquisition module is used to select n points as microhardness test points, with the midpoint of the spline tooth surface contour line as the origin O, the tangent line of the spline tooth surface contour line at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and a line 100μm away from the origin O and parallel to the X-axis as the baseline. The module tests and records the microhardness values ​​x1, x2...x at each test point. n , n≥3; The third calculation module is used to calculate the average value of the microhardness values ​​based on the recorded microhardness values ​​at each test point. Standard deviation S, data repeatability R; The fourth judgment module is used to determine whether the data repeatability R is greater than or equal to 5%. If the data repeatability R is greater than or equal to 5%, a new microhardness test point is selected on the baseline, and the microhardness value of the test point is recorded. The data is then returned to the third calculation module for processing. Otherwise, the average value of the test points is used. As the surface hardness value of the carbonitrided spline to be tested.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium contains a computer program programmed or configured to perform a microhardness test on the surface hardness of the carbonitrided spline as described in any one of claims 1 to 8.

Images