Method for determining residual stress of curved surface of bearing ring

Abstract

The invention relates to a method for determining bearing ring curved surface residual stress, and belongs to the technical field of bearing part residual stress detection. The method for determining the residual stress of the curved surface of the bearing ring comprises the following steps: calculating a strain value according to the expansion and contraction amount of the to-be-measured curved surface of the to-be-measured bearing ring in the circumferential direction before and after heat treatment; calculating and determining the residual stress of the to-be-measured curved surface based on the corresponding relationship between the stress and the strain; the material of the bearing ring to be detected is GCr15; the temperature of the heat treatment is 500 DEG C; the martensite microstructure of the bearing ring to be detected is 2-3 grades, and the Rockwell hardness of the bearing ring to be detected is 58-62. The method for determining the residual stress of the curved surface of the bearing ring has the advantages of being easy to operate and high in result accuracy.

Description

Technical Field

[0001] The invention relates to a method for determining residual stress of a bearing ring curved surface, and belongs to the technical field of residual stress detection of bearing parts. Background Art

[0002] As we all know, the detection and evaluation of residual stress in bearing parts has always been a concern of the bearing industry. GCr15 material is widely used in bearing manufacturing due to its high and uniform hardness after quenching and tempering, high wear resistance, high fatigue resistance, good hot workability and good comprehensive performance. With the continuous improvement of bearing processing capabilities and levels, people pay more and more attention to the common technical issues related to bearings manufactured with GCr15 materials, especially the processing control and evaluation of residual stress on the working surface of bearings.

[0003] At present, residual stress measurement methods are mainly divided into two categories: mechanical methods and non-destructive testing methods. Among them, most non-destructive testing methods belong to physical methods, and their basic principles are as follows: based on the basic premise that residual stress will cause changes in a certain physical quantity of the material, by establishing the relationship between the physical quantity and the residual stress, the residual stress is calculated by measuring the physical quantity. Destructive testing refers to removing a part of the workpiece being measured by mechanical processing, and the local residual stress is released to produce corresponding strain and displacement. The corresponding strain and displacement can be used to determine the residual stress, and then the original residual stress of the workpiece can be inferred based on relevant mechanical principles.

[0004] In the actual detection process, bearing processing companies usually use X-ray diffraction to detect surface residual stress, considering the accuracy and reliability of the test results. This method is relatively accurate and is also a method recognized by the industry. However, X-ray diffraction equipment is expensive, the detection area and depth are small, and it is difficult to measure stress on the inner and outer surfaces of smaller parts and working surfaces with larger curvature. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the residual stress of the curved surface of a bearing ring, which can solve the problem of high price when the X-ray diffraction method is currently used to detect the residual stress of the curved surface of a bearing ring.

[0006] In order to achieve the above objectives, the technical solution adopted by the method for determining the residual stress of the curved surface of the bearing ring of the present invention is: A method for determining residual stress of a curved surface of a bearing ring comprises the following steps: calculating a strain value according to the amount of expansion and contraction of the curved surface of the bearing ring to be tested in the circumferential direction before and after heat treatment; calculating and determining the residual stress of the curved surface to be tested based on the corresponding relationship between stress and strain; the material of the bearing ring to be tested is GCr15; the temperature of the heat treatment is 500°C; the martensitic microstructure of the bearing ring to be tested is level 2-3, and the Rockwell hardness of the bearing ring to be tested is 58-62; the residual stress calculation formula is as follows:

[0007] Among them, σ is the residual stress, the unit is MPa; ε is the strain value; E is the elastic modulus, the unit is MPa.

[0008] The method for determining the residual stress of the curved surface of a bearing ring of the present invention measures the strain value of the curved surface to be tested of the bearing ring to be tested with a martensitic microstructure of level 2 to 3 and a Rockwell hardness of 58 to 62 before and after heat treatment, and calculates and determines the residual stress of the curved surface to be tested based on the corresponding relationship between stress and strain. The method has the advantages of simple operation and high result accuracy.

[0009] Preferably, the roughness of the curved surface to be measured is Ra≤6.4.

[0010] Preferably, the roughness of the curved surface to be measured is Ra≤1.6.

[0011] Preferably, the heat treatment time is 2 hours.

[0012] Preferably, the curved surface to be measured is the inner diameter, outer diameter or raceway of the bearing ring to be measured.

[0013] Preferably, the curved surface to be measured is the inner diameter of the bearing ring to be measured, and the expansion and contraction in the circumferential direction is determined by measuring the diameter change of the inner diameter; the curved surface to be measured is the outer diameter of the bearing ring to be measured, and the expansion and contraction in the circumferential direction is determined by measuring the diameter change of the outer diameter; the curved surface to be measured is the raceway of the bearing ring to be measured, and the expansion and contraction in the circumferential direction is determined by measuring the diameter change of the raceway.

[0014] Preferably, the calculation formula of the strain value is:

[0015] in, is the dimensional parameter of the tested surface of the bearing ring before heat treatment, in mm; is the dimensional parameter of the tested surface of the bearing ring after heat treatment, in mm; ε is the strain value.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention subjects the bearing ring made of GCr15 to a heat treatment at 500°C, and at the same time controls the martensitic microstructure of the bearing ring before the heat treatment to level 2~3 and the Rockwell hardness to 58~62. The residual stress of the surface to be measured of the bearing ring can be determined more accurately through the relationship between the strain and stress obtained by calculating the circumferential expansion and contraction of the surface to be measured of the bearing ring before and after the heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a picture of the appearance of the bearing ring to be tested in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The method for determining the residual stress of the curved surface of a bearing ring of the present invention is a pioneering invention. In view of the problems that the X-ray diffraction method is expensive and difficult to measure the inner and outer surfaces of small-sized parts and working surfaces with large curvature when determining the residual stress of the curved surface of a bearing ring, the present invention detects the strain value of the curved surface to be measured before and after heat treatment, and uses the corresponding relationship between stress and strain to calculate and determine the residual stress of the curved surface to be measured.

[0019] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0020] Example 1 The method for determining the residual stress on the curved surface of the bearing ring of this embodiment is as follows: Figure 1 The bearing ring shown is made of GCr15 as the bearing ring to be tested. The bearing ring includes a quenching and tempering heat treatment step during processing. The bearing ring has no elliptical deformation, warping or other special shapes as a whole. The outer diameter of the bearing ring is used as the curved surface to be tested, and the following steps are specifically included: (1) According to the method in standard GB / T34891-2017, the microstructure of the bearing ring to be tested is analyzed and the martensitic microstructure grade of the bearing ring to be tested is determined; the Rockwell hardness HRC of the bearing ring to be tested is tested according to the method in standard GB / T230.1-2009; the roughness of the surface to be tested of the bearing ring to be tested is tested according to the method in standard JB / T 7051-2006; the test results are as follows: the martensitic microstructure grade of the bearing ring to be tested is level 3, the Rockwell hardness is 61.7HRC, and the roughness Ra of the surface to be tested is 0.18μm.

[0021] (2) The measurement accuracy of the five-axis coordinate measuring machine and the temperature accuracy of the box-type resistance furnace are calibrated to ensure the stability and accuracy of the measurement results. The measurement accuracy of the five-axis coordinate measuring machine is 1.0 μm, and the temperature accuracy of the box-type resistance furnace is 0.1 °C. The test temperature range of the box-type resistance furnace is from room temperature to 1000 °C. The box-type resistance furnace is equipped with a temperature sensor.

[0022] (3) Use a five-axis coordinate measuring machine to measure the outer diameter of the bearing ring to be tested At the same time, determine the position of the initial origin O of the measurement, and record the relevant parameters of the instrument during the detection. The outer diameter measured in this embodiment is the diameter The measurement result is 110.0214mm.

[0023] (4) Place the bearing ring to be tested horizontally in the center of the box-type resistance furnace, heat the bearing ring to be tested to 500°C with the furnace, and keep it warm for 2 hours. After the insulation is completed, cool the bearing ring to room temperature with the furnace.

[0024] (5) Place the bearing ring to be tested, which has been cooled in the furnace, on the five-axis coordinate measuring machine again, and measure the outer diameter of the bearing ring to be tested under the instrument-related parameters in step (3) and the position of the initial origin O. The outer diameter measured in this embodiment is The measurement result is 110.2128mm.

[0025] (6) Calculate the residual stress using the diameter test results of the outer diameter of the bearing ring before and after heat treatment; the calculation formula is as follows:

[0026]

[0027] In the formula, is the outer diameter of the bearing ring to be tested before heat treatment, in mm; is the outer diameter of the bearing ring to be tested after heat treatment, in mm; ε is the strain value of the bearing ring to be tested before and after heat treatment; E is the elastic modulus, in MPa; σ is the residual stress, in MPa. In this embodiment, the elastic modulus E=207GPa.

[0028] Example 2 The method for determining the residual stress of the curved surface of a bearing ring of this embodiment uses a bearing ring made of GCr15 as the bearing ring to be tested. The bearing ring includes a heat treatment step of quenching and tempering during processing. The bearing ring as a whole has no elliptical deformation, warping or other special shapes. The raceway of the bearing ring is used as the curved surface to be tested, and specifically includes the following steps: (1) According to the method in standard GB / T34891-2017, the microstructure of the bearing ring to be tested is analyzed and the martensitic microstructure grade of the bearing ring to be tested is determined; the Rockwell hardness HRC of the bearing ring to be tested is tested according to the method in standard GB / T230.1-2009; the roughness of the surface to be tested of the bearing ring to be tested is tested according to the method in standard JB / T 7051-2006; the test results are as follows: the martensitic microstructure grade of the bearing ring to be tested is level 3, the Rockwell hardness is 61.5HRC, and the roughness Ra of the surface to be tested is 0.18μm.

[0029] (2) The measurement accuracy of the five-axis coordinate measuring machine and the temperature accuracy of the box-type resistance furnace are calibrated to ensure the stability and accuracy of the measurement results. The measurement accuracy of the five-axis coordinate measuring machine is 1.0 μm, and the temperature accuracy of the box-type resistance furnace is 0.1 °C. The test temperature range of the box-type resistance furnace is from room temperature to 1000 °C. The box-type resistance furnace is equipped with a temperature sensor.

[0030] (3) Use a five-axis coordinate measuring machine to measure the diameter of the bearing ring raceway to be tested At the same time, the position of the initial origin O of the measurement is determined, and the relevant parameters of the instrument during the detection are recorded. The diameter of the raceway measured in this embodiment is The measurement result is 110.0956mm.

[0031] (4) Place the bearing ring to be tested horizontally in the center of the box-type resistance furnace, heat the bearing ring to be tested to 500°C with the furnace, and keep it warm for 2 hours. After the insulation is completed, cool the bearing ring to room temperature with the furnace.

[0032] (5) Place the bearing ring to be tested, which has been cooled in the furnace, on the five-axis coordinate measuring machine again to measure the diameter of the bearing ring raceway to be tested. The diameter of the raceway measured in this embodiment is The measurement result is 110.2797mm.

[0033] (6) Calculate the residual stress using the test results of the raceway dimension parameters of the bearing ring before and after heat treatment. The calculation formula is as follows:

[0034]

[0035] In the formula, is the outer diameter of the bearing ring to be tested before heat treatment, in mm; is the outer diameter of the bearing ring to be tested after heat treatment, in mm; ε is the strain value of the bearing ring to be tested before and after heat treatment; E is the elastic modulus, in MPa; σ is the residual stress, in MPa. In this embodiment, the elastic modulus E=207GPa.

[0036] Example 3 The difference between the method for determining the residual stress of the bearing ring curved surface of this embodiment and the method for determining the residual stress of the bearing ring curved surface of embodiment 1 is that in step (1) of the method for determining the residual stress of the bearing ring curved surface of this embodiment, the roughness Ra of the surface to be measured is 1.6 μm.

[0037] Example 4 The difference between the method for determining the residual stress of the bearing ring curved surface of this embodiment and the method for determining the residual stress of the bearing ring curved surface of embodiment 1 is that in step (1) of the method for determining the residual stress of the bearing ring curved surface of this embodiment, the roughness Ra of the surface to be measured is 6.4 μm.

[0038] Example 5 The difference between the method for determining the residual stress of the bearing ring surface of this embodiment and the method for determining the residual stress of the bearing ring surface of embodiment 1 is that in step (1) of the method for determining the residual stress of the bearing ring surface of this embodiment, the microstructure grade of the bearing ring to be tested is grade 2.

[0039] Example 6 The difference between the method for determining the residual stress of the curved surface of the bearing ring of this embodiment and the method for determining the residual stress of the curved surface of the bearing ring of Example 1 is that in step (1) of the method for determining the residual stress of the curved surface of the bearing ring of this embodiment, the Rockwell hardness is 58HRC.

[0040] Comparative Example 1 The method for determining the residual stress of the curved surface of the bearing ring of this comparative example uses a bearing ring made of GCr15 as the bearing ring to be tested. The bearing ring includes a heat treatment step of quenching and tempering during processing. The bearing ring as a whole has no elliptical deformation, warping or other special shapes. The inner diameter of the bearing ring is used as the curved surface to be tested, and specifically includes the following steps: (1) According to the method in standard GB / T34891-2017, the microstructure of the bearing ring to be tested is analyzed and the martensitic microstructure grade of the bearing ring to be tested is determined; the Rockwell hardness HRC of the bearing ring to be tested is tested according to the method in standard GB / T230.1-2009; the roughness of the surface to be tested of the bearing ring to be tested is tested according to the method in standard JB / T 7051-2006; the test results are as follows: the martensitic microstructure grade of the bearing ring to be tested is level 3, the Rockwell hardness is 62.1HRC, and the roughness Ra of the surface to be tested is 0.17μm.

[0041] (2) The measurement accuracy of the five-axis coordinate measuring machine and the temperature accuracy of the box-type resistance furnace are calibrated to ensure the stability and accuracy of the measurement results. The measurement accuracy of the five-axis coordinate measuring machine is 1.0 μm, and the temperature accuracy of the box-type resistance furnace is 0.1 °C. The test temperature range of the box-type resistance furnace is from room temperature to 1000 °C. The box-type resistance furnace is equipped with a temperature sensor.

[0042] (3) Use a five-axis coordinate measuring machine to measure the inner diameter of the bearing ring to be tested At the same time, determine the position of the initial origin O of the measurement and record the relevant parameters of the instrument during the test. The diameter of the inner diameter measured in this comparative example is The measurement result is 110.0113mm.

[0043] (4) Place the bearing ring to be tested horizontally in the center of the box-type resistance furnace, heat the bearing ring to be tested to 500°C with the furnace, and keep it warm for 2 hours. After the insulation is completed, cool the bearing ring to room temperature with the furnace.

[0044] (5) Place the bearing ring to be tested, which has been cooled in the furnace, on the five-axis coordinate measuring machine again to measure the inner diameter of the bearing ring to be tested. The inner diameter measured in this comparative example is The measurement result is 110.1149mm.

[0045] (6) Calculate the residual stress using the inner diameter dimension parameter test results of the bearing ring before and after heat treatment; the calculation formula is as follows:

[0046]

[0047] In the formula, is the outer diameter of the bearing ring to be tested before heat treatment, in mm; is the outer diameter of the bearing ring to be tested after heat treatment, in mm; ε is the strain value of the bearing ring to be tested before and after heat treatment; E is the elastic modulus, in MPa; σ is the residual stress, in MPa. In this comparative example, the elastic modulus E=207GPa.

[0048] Comparative Example 2 The difference between the method for determining the residual stress of the bearing ring surface of this comparative example and the method for determining the residual stress of the bearing ring surface of Example 1 is that in step (1) of the method for determining the residual stress of the bearing ring surface of this comparative example, the microstructure grade of the bearing ring to be tested is grade 4.

[0049] Comparative Example 3 The difference between the method for determining the residual stress of the curved surface of the bearing ring of the comparative example and the method for determining the residual stress of the curved surface of the bearing ring of Example 1 is that in step (1) of the method for determining the residual stress of the curved surface of the bearing ring of the comparative example, the Rockwell hardness is 63HRC.

[0050] In order to evaluate the error between the residual stress determined in each embodiment and each comparative example and the actual residual stress value, the residual stress of the tested curved surface of the tested bearing ring in each embodiment and each comparative example was measured according to the standard "GB / T 7704-2017 Nondestructive Testing X-ray Stress Measurement Method", and the actual residual stress measurement results were obtained. The calculated residual stress values ​​and the actual measurement results of each embodiment and each comparative example are summarized in Table 1. The error percentage in Table 1 = | calculated residual stress value - actual residual stress measurement result | / actual residual stress measurement result × 100%.

[0051] Table 1 Determination results and actual measurement results of residual stress in each embodiment and each comparative example Determine the method Calculated residual stress value (MPa) Actual measurement results of residual stress (MPa) Error percentage (%) Example 1 -360.1 -370.3 2.75 Example 2 -346.1 -352.7 1.87 Example 3 -323.5 -332.3 2.65 Example 4 -317.7 -329.8 3.67 Example 5 -297.8 -306.2 2.74 Example 6 -316.5 -309.5 2.26 Comparative Example 1 -194.9 -211.3 7.76 Comparative Example 2 -285.4 -339.4 15.91 Comparative Example 3 -327.2 -357.1 8.37 As shown in Table 1, by changing the initial conditions such as the surface roughness, microstructure grade, and surface hardness of the sample to be tested, the residual stress value of the curved surface is calculated using the method of the present invention, and compared with the actual surface residual stress measurement result of the X-ray diffraction method, it can be seen that changing the surface roughness of the sample to be tested has little effect on the measurement result of the residual stress, and when the microstructure grade and surface hardness of the sample to be tested tend to the required upper limit, the deviation between the calculated stress value and the actual measurement result of the diffraction method is large; therefore, the martensitic microstructure of the bearing ring to be tested according to the present invention is level 2~3, the Rockwell hardness of the bearing ring to be tested is 58~62, and the roughness Ra≤6.4μm of the curved surface to be tested, and more preferably the roughness Ra≤1.6μm.

Claims

1. A method for determining residual stress on a bearing ring surface, characterized in that: The following steps are involved: Calculate the strain value according to the expansion and contraction of the tested curved surface of the tested bearing ring in the circumferential direction before and after the heat treatment; Based on the correspondence between stress and strain, the residual stress of the measured surface is calculated and determined; the material of the measured bearing ring is GCr15; the temperature of the heat treatment is 500°C; the martensite microstructure of the measured bearing ring is level 2~3, and the Rockwell hardness of the measured bearing ring is 58~62; the calculation formula of the residual stress is as follows: Among them, σ is the residual stress, the unit is MPa; ε is the strain value; E is the elastic modulus, the unit is MPa.

2. The method for determining the residual stress of the curved surface of a bearing ring according to claim 1, characterized in that: The roughness of the curved surface to be measured is Ra≤6.

4.

3. The method for determining the residual stress of the bearing ring surface according to claim 2, characterized in that: The roughness of the curved surface to be measured is Ra≤1.

6.

4. The method for determining the residual stress of the curved surface of a bearing ring according to claim 1, characterized in that: The heat treatment time is 2h.

5. The method for determining the residual stress of the curved surface of a bearing ring according to claim 1, characterized in that: The curved surface to be measured is the inner diameter, outer diameter or raceway of the bearing ring to be measured.

6. The method for determining the residual stress of the curved surface of a bearing ring according to claim 5, characterized in that: The curved surface to be measured is the inner diameter of the bearing ring to be measured, and the expansion and contraction in the circumferential direction is determined by measuring the diameter change of the inner diameter; the curved surface to be measured is the outer diameter of the bearing ring to be measured, and the expansion and contraction in the circumferential direction is determined by measuring the diameter change of the outer diameter; the curved surface to be measured is the raceway of the bearing ring to be measured, and the expansion and contraction in the circumferential direction is determined by measuring the diameter change of the raceway.

7. The method for determining the residual stress of the curved surface of a bearing ring according to any one of claims 1 to 6, characterized in that: The calculation formula of the strain value is: in, is the dimensional parameter of the tested surface of the bearing ring before heat treatment, in mm; is the dimensional parameter of the tested surface of the bearing ring after heat treatment, in mm; ε is the strain value.

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