Microhardness testing method and system for carburized gear surface hardness

Abstract

The application discloses a kind of carburizing gear surface hardness microhardness testing method, comprising the following steps: cutting along the section of the gear to be detected carburizing gear and making the metallographic sample of tooth portion;With gear profile line midpoint as origin O, with the tangent of gear profile line at origin O as X axis to 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 carburized gears. Background Technology

[0002] Gear drives offer advantages such as accurate transmission ratios, smooth and reliable transmission, high transmission efficiency, and long service life, making them widely used in the aerospace field. During operation, gear teeth bear contact stress and friction, while the tooth roots bear bending stress and impact stress. Therefore, gears require high surface hardness for friction resistance and high core toughness for impact resistance. Thus, aerospace gears are typically designed and constructed using low-carbon alloy steel. After machining and forming, the tooth surface undergoes carburizing and quenching treatment to obtain a wear-resistant high-carbon martensite surface and a tough low-carbon martensite core. Surface hardness is one of the most important quality indicators for aerospace gears and is the fundamental purpose of heat treatment. Therefore, accurately testing the surface hardness of gears is crucial to ensuring gear product quality.

[0003] Currently, there are no specific hardness testing standards or methods for gears in China. For hardness testing of carburized and quenched gears, GB / T 230 "Metallic Materials - Rockwell Hardness Test Method" is used as a reference. This standard is a general Rockwell hardness test method, and clause 7.5 stipulates that the test force direction must be perpendicular to the test surface of the specimen during the test. However, for spiral bevel gears with curved tooth surfaces, it is difficult to find the highest point of the tooth surface for testing, resulting in low accuracy and large fluctuations in test data. Each gear with a different drawing number requires the design of a dedicated tooling fixture and repeated adjustments to accurately measure the surface hardness value, leading to low testing efficiency and high cost. 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 the surface hardness of carburized gears 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 test method for the surface hardness of carburized gears includes the following steps:

[0007] S1. Cut along the cross section of the carburized gear to be tested, prepare a metallographic sample of the carburized gear teeth to be tested, and polish the metallographic sample to the standard of mirror finish.

[0008] S2. Taking the midpoint of the gear tooth surface profile as the origin O, the tangent to the gear tooth surface profile at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and the line 200 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. This serves as the microhardness value for the surface of the carburized gear 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 500g.

[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, the present invention also provides a microhardness testing system for the surface hardness of carburized gears, comprising:

[0022] The first processing module is used to cut along the cross section of the carburized gear to be tested, prepare a metallographic test sample of the carburized gear teeth, and polish it.

[0023] The second acquisition module is used to select n points as microhardness test points, with the midpoint of the gear tooth surface profile as the origin O, the tangent line of the gear tooth surface profile at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and a line 200 μm away from the origin O and parallel to the X-axis as the baseline. The module measures and records the microhardness values ​​x1, x2, ..., x at each test point. n , n≥3;

[0024] The third calculation module calculates 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 determines whether the data repeatability R is greater than or equal to 5%. If the data repeatability R ≥ 5%, a new microhardness test point is selected on the baseline, and the microhardness value of that 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. This serves as the surface hardness value for the carburized gear 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 test method for the surface hardness of carburized gears.

[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, which solves the problems of large fluctuations, low efficiency and high cost of conventional hardness testing data for carburized bevel gears used in aviation, and provides a reference for surface hardness testing of nitrided and cyanided parts. 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 points 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 gear materials and carburized layer depths, formulate an orthogonal comparison scheme for microhardness testing of carburized gear 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 Orthogonal test scheme for carburized gear specimens

[0038]

[0039] 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 specimen. After grinding and polishing, the surface of the metallographic specimen reached mirror level, with a surface roughness Ra≤0.02. During microscopic testing, a test pressure of 500g was selected. The origin O was taken as the midpoint of the gear tooth profile, the X-axis as the tangent to the gear tooth profile at the origin O, and the Y-axis as the line perpendicular to the X-axis. The test coordinate points are shown in the table below (e.g., ...). Figure 1 and 2 As shown in the figure, each sample was tested with three rows of hardness gradients.

[0040] Table 2 Test Coordinate Points Table

[0041]

[0042] (2) According to the orthogonal experimental design, microhardness test and conventional Rockwell hardness test of cut specimens were performed on the specimens. Data were collected and the average value of the data was calculated. Standard deviation S and data repeatability R;

[0043] Arithmetic mean

[0044] Standard deviation

[0045] Data duplication

[0046] (3) Using GB / T1172-1999 "Conversion Values ​​of Hardness and Strength of Ferrous Metals", the Rockwell hardness test data of conventional cut specimens were converted into Vickers hardness, and compared with the data of microhardness test. The results showed that:

[0047] For carburized gear parts with a carburized layer depth of 0.5–0.9 mm, the hardness data at 0.2 mm obtained by microhardness testing is closest to that obtained by conventional Rockwell hardness testing of cut specimens. The standard deviation and repeatability of the test data are superior to those of the traditional cut specimen hardness testing method.

[0048] For carburized gear parts with a carburized layer depth of 0.9–1.3 mm, the hardness data at 0.2 mm obtained by microhardness testing is closest to that obtained by conventional Rockwell hardness testing of cut specimens. The standard deviation and repeatability of the test data are superior to those of the traditional cut specimen hardness testing method.

[0049] For carburized gear parts with a carburized layer depth ≥1.3mm, the hardness data at 0.2mm and 0.3mm obtained by microhardness testing are closest to those obtained by the conventional Rockwell hardness test using cut specimens. Due to the large carburized layer depth, the hardness gradient of the part does not decrease significantly, and the hardness at various depths near the surface is not significantly different. For the purpose of simplifying the testing method, the microhardness at 0.2mm is selected as the surface hardness of the part. The standard deviation and repeatability of the test data are superior to those of the traditional cut specimen hardness test method.

[0050] (4) Based on the test data above, it was determined that the microhardness value measured 0.2 mm vertically downwards from the mid-gear surface using a 500g load can be used as the surface hardness data for carburized gears. 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.

[0051] Example 1:

[0052] A certain aero-engine gear requires carburizing treatment of the teeth and inner bore. After carburizing, the parts must be tested according to the IGC.04.63.120B standard for carburized layer depth, metallographic structure, surface hardness, core hardness, and mechanical properties, with the tooth surface hardness ≥58HRC. The gear part is a spiral bevel gear.

[0053] like Figure 3 As shown, a microhardness test method for the surface hardness of carburized gears includes the following steps:

[0054] (1) Select the parts that were scrapped due to dimensional discrepancies in machining in the previous batch as test materials, and perform carburizing and quenching heat treatment together with the remaining parts.

[0055] (2) Use a cutting machine to cut metallographic test samples along the cross section of the sample, including the toothed part and the inner hole. During the cutting process, take measures to ensure that the surface condition of the sample is not affected by high temperature.

[0056] (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.

[0057] (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.

[0058] (5) Use a microhardness tester to test the microhardness of the sample. Before testing, use a standard hardness block to calibrate the hardness tester.

[0059] (6) The test pressure is 500g. The test position for the tooth sample is located in the middle of the tooth height. The origin O is the midpoint of the gear tooth profile. The X-axis is the tangent line of the gear tooth profile at the origin O. The Y-axis is the line perpendicular to the X-axis. The baseline is a line 200μm 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;

[0060] In this embodiment, the test depth was 200 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:

[0061]

[0062] (7) The test data are shown in the table below.

[0063]

[0064] 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".

[0065] (8) 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". The converted data values ​​are shown in the table below:

[0066] Test site Average Vickers hardness (HV) Rockwell hardness conversion value (HRC) Tooth sample 726 61

[0067] (9) The test results show that the surface hardness of the teeth meets the requirement of ≥58HRC.

[0068] This invention also provides a microhardness testing system for the surface hardness of carburized gears, comprising:

[0069] The first processing module is used to cut along the cross section of the carburized gear to be tested, prepare a metallographic test sample of the carburized gear teeth, and polish it.

[0070] The second acquisition module is used to select n points as microhardness test points, with the midpoint of the gear tooth profile as the origin O, the tangent line of the gear tooth profile at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and a line 200 μm away from the origin O and parallel to the X-axis as the baseline. The module measures and records the microhardness values ​​x1, x2, ..., x at each test point. n , n≥3;

[0071] The third calculation module calculates the average value of the microhardness values ​​based on the recorded microhardness values ​​at each test point. Standard deviation S, data repeatability R;

[0072] The fourth judgment module determines whether the data repeatability R is greater than or equal to 5%. If the data repeatability R ≥ 5%, a new microhardness test point is selected on the baseline, and the microhardness value of that 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. This serves as the surface hardness value for the carburized gear to be tested.

[0073] 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 test method for the surface hardness of carburized gears.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 carburized gears, characterized in that: Includes the following steps: S1. Cut along the cross section of the carburized gear to be tested, prepare a metallographic sample of the carburized gear teeth to be tested, and polish the metallographic sample to the standard of mirror finish. S2. Taking the midpoint of the gear tooth surface profile as the origin O, the tangent to the gear tooth surface profile at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and the line 200 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. This serves as the microhardness value for the surface of the carburized gear 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 500g.

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 carburized gears, characterized in that: include: The first processing module is used to cut along the cross section of the carburized gear to be tested, prepare a metallographic test sample of the carburized gear teeth, and polish it. The second acquisition module is used to select n points as microhardness test points, with the midpoint of the gear tooth surface profile as the origin O, the tangent line of the gear tooth surface profile at the origin O as the X-axis, the line perpendicular to the X-axis as the Y-axis, and a line 200 μm away from the origin O and parallel to the X-axis as the baseline. The module measures and records the microhardness values ​​x1, x2, ..., x at each test point. n , n≥3; The third calculation module calculates 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 determines whether the data repeatability R is greater than or equal to 5%. If the data repeatability R ≥ 5%, a new microhardness test point is selected on the baseline, and the microhardness value of that 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. This serves as the surface hardness value for the carburized gear to be tested.

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

Images