Method for residual stress improvement of railway wheels

Abstract

The application discloses a residual stress improvement method for a railway wheel, and specifically as follows: determining vibration parameters of a vibration aging treatment, including exciting force, exciting time and exciting frequency of different tread depths, and then performing the vibration aging treatment on the wheel. The residual stress improvement method based on the vibration aging treatment improves the production efficiency of the wheel, and compared with a wheel treated by a traditional quenching + tempering process, the wheel treated by the vibration aging treatment can effectively reduce the residual stress of the wheel, the shrinkage value of the wheel flame cutting is reduced by about 30%, and the mechanical properties and the contact fatigue properties can be improved.

Description

Technical Field

[0001] This invention belongs to the field of wheel manufacturing technology, and more specifically, this invention relates to a method for improving residual stress in railway wheels. Background Technology

[0002] Residual stress is a crucial indicator of train wheel quality, and major international wheel standards all have clear regulations regarding the residual stress within wheel products. Residual stress generated during heat treatment significantly impacts wheel performance. European standard EN13262 requires a shrinkage value greater than 1mm, while American standard AAR M-107 / M-208 only requires compressive stress within a depth of 25.7mm. Domestic CL65 and CL70 wheels, as well as Russian standard GOST 10791, require a shrinkage of 1-5mm. Wheels produced using a normal quenching and tempering process have a flame cutting shrinkage value of less than 5mm. However, recently, some wheels, after tempering to reduce residual stress, have shown flame cutting shrinkage exceeding 5mm, failing to meet the requirements.

[0003] Invention Patent: A heat treatment method and wheel for improving residual stress in wheels, Authorization Announcement No.: CN113088667B, Authorization Announcement Date: 2022-03-11. This invention provides a heat treatment method and wheel for improving residual stress in wheels. The heat treatment method includes: air cooling of the wheel spokes during quenching; simultaneous water cooling of both the tread and outer rim surfaces of the wheel rim; and then tempering. This method can control the residual stress of the wheel within the range required by the EN13262 standard, enabling both new and worn wheels to pass the thermodynamic property evaluation certification in one go.

[0004] The technical defects of the above-mentioned technical solution are: 1) Compared with the conventional tread cooling heat treatment method, it adds both spoke cooling and outer rim cooling at the same time, making it difficult to coordinate between cooling systems and unsuitable for mass industrial production; 2) The wheel is placed horizontally for cooling, and the tread and outer surface are cooled at the same time, which can easily cause the outer surface to cool too fast, increase the depth of abnormal structure, and is not conducive to optimizing residual stress; 3) Tempering after quenching improves the magnitude of residual stress, which increases energy consumption and is detrimental to the environment. Summary of the Invention

[0005] This invention provides a method for improving residual stress in railway wheels, aiming to address the aforementioned problems.

[0006] This invention is implemented as follows: a method for improving residual stress in railway wheels, the method being as follows:

[0007] The vibration parameters for vibration aging treatment are determined, including the excitation force, excitation time, and excitation frequency at different tread depths, and then the wheels are subjected to vibration aging treatment.

[0008] Furthermore, the tensile strength Rm at 20mm below the wheel tread is tested to see if it exceeds the set tensile strength threshold. If the test result is yes, the wheel is subjected to vibration aging treatment based on the vibration parameters, followed by tempering treatment. If the test result is no, the wheel is subjected to vibration aging treatment based on the vibration parameters.

[0009] Furthermore, the excitation force at different depths beneath the tread surface;

[0010] F=a·σ1·s

[0011] Where a is the excitation coefficient, which is proportional to the quenching time t1; σ1 is the initial excitation stress at the corresponding depth below the tread surface; and s is the unit area of ​​the excitation point.

[0012] The specific formula for calculating the initial excitation stress σ1 is as follows:

[0013]

[0014] Among them, Rp 0.2 Rm represents the wheel yield strength at the corresponding depth below the tread, b represents the wheel tensile strength at the corresponding depth below the tread, and σ represents the stress coefficient, ranging from 1.5 to 2.0. min This represents the initial minimum residual compressive stress at the depth corresponding to the tread surface.

[0015] Furthermore, when the value of b is 2.0, it is checked whether the initial excitation stress σ1 satisfies the constraint condition σ1+σ min >Rp 0.2 If σ1 < 0.5Rm, the excitation force corresponding to the current initial excitation stress σ1 will be output. If it is not satisfied, the value of b will be gradually reduced until an initial excitation stress σ1 that satisfies the constraint conditions is found. If the calculated initial excitation stress σ1 still cannot satisfy the constraint conditions after the value of b is reduced to 1.5, the wheel will only be tempered and not subjected to vibration aging treatment.

[0016] Furthermore, the excitation time t can satisfy the following condition:

[0017] t = a1 × B1 + a2 × B2;

[0018] F / t = a3, 1.0 ≤ a3 ≤ 1.9;

[0019] 6.0≤a1+a2≤9.0, and 3.0≤a1≤6.3, 2.5≤a2≤5.5;

[0020] In the formula, F is the excitation force, B1 is the rim thickness, B2 is the rim height, a1 and a2 represent the rim thickness coefficient and rim height coefficient, respectively, and a3 is the Ft coefficient.

[0021] Furthermore, the excitation frequency is the minimum natural frequency of the wheel.

[0022] Furthermore, wheels of the same specifications and materials are subjected to a natural frequency test.

[0023] Furthermore, the vibration aging treatment process for wheels is as follows:

[0024] After quenching, the wheel is horizontally fixed on a circular vibration platform. Vibrators are evenly distributed around the bottom of the vibration platform along the circumference, and the vibrators are located at the corresponding depth below the tread. The vibrators are in contact with the vibration platform through elastic support pads. The vibrators perform vibration aging treatment on the wheel fixed on the vibration platform based on the above-mentioned excitation force, excitation frequency and excitation time.

[0025] Furthermore, the process of obtaining the natural frequency of the wheel is as follows:

[0026] n striking points are evenly arranged circumferentially at 1 / 2 of the wheel rim thickness, and m vibration accelerometers are evenly arranged circumferentially at 1 / 2 of the outer side of the hub and rim.

[0027] After quenching, the wheel is in a free suspension state. The hammer strikes once at each impact point, and each impact point generates an excitation signal V1. The corresponding m vibration accelerometers generate m induction signals. The excitation signal V1 and its corresponding response signal V2 are collected by a multi-channel data logger and transmitted to the BK Connect software. The BK Connect software outputs the natural frequency of the wheel.

[0028] The vibration aging-based method for improving residual stress in wheels provided by this invention improves wheel production efficiency. Compared with wheels produced by traditional quenching and tempering processes, vibration aging-treated wheels can effectively reduce residual stress, reduce the flame cutting shrinkage value of wheels by about 30%, and improve mechanical properties and contact fatigue performance. Attached Figure Description

[0029] Figure 1 A flowchart of a method for improving residual stress in railway wheels provided in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the distribution of the exciter provided in an embodiment of the present invention;

[0031] Figure 3 A comparison chart of residual stress shrinkage values ​​provided in an embodiment of the present invention;

[0032] Figure 4 A comparison diagram of residual stress peak values ​​using the ultrasonic method provided in an embodiment of the present invention. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0034] Figure 1 This is a flowchart of a method for improving residual stress in railway wheels provided by an embodiment of the present invention. The method specifically includes the following steps:

[0035] S1. After the wheel quenching is completed, the natural frequency of the wheel is determined by experiment.

[0036] The natural frequency of a wheel is generally related to its specifications and material. Therefore, for wheels of the same specifications and material, only one fixed-frequency test is needed. The method for determining the natural frequency of a wheel in this embodiment of the invention is as follows:

[0037] A hammer is installed at 1 / 2 the thickness of the wheel rim. n striking points are evenly arranged along the circumference at 1 / 2 the thickness of the wheel rim, with equal intervals between each striking point. If 4 striking points are arranged, the interval between each striking point is 90°. The hammer used is a BK8206 hammer.

[0038] m vibration accelerometers are evenly arranged circumferentially at 1 / 2 of the outer side of the hub and rim to receive the response signal corresponding to each hammer strike. Each strike has an excitation signal V1 and m response signals V2. The value of m is generally 16. The vibration accelerometers are BK 4508 accelerometer sensors.

[0039] After quenching, the wheel is in a free suspension state. The hammer strikes once at each striking point, and each striking point generates an excitation signal V1. The corresponding m vibration accelerometers generate m induction signals.

[0040] The excitation signal V1 and its corresponding response signal V2 are acquired by a multi-channel data logger and then transmitted to the BKConnect software. The BK Connect software outputs the natural frequency of the wheel. The multi-channel data logger used is the BK 8404 multi-channel data logger.

[0041] S2. Determine the vibration parameters for vibration aging treatment, including: excitation force, excitation time and excitation frequency at different tread depths, and then perform vibration aging treatment on the wheel.

[0042] The test checks whether the tensile strength Rm at 20mm below the wheel tread exceeds the set tensile strength threshold. If the test result is yes, the wheel is subjected to vibration aging treatment based on the vibration parameters, followed by tempering treatment. If the test result is no, the wheel is subjected to vibration aging treatment based on the vibration parameters.

[0043] In this embodiment of the invention, the methods for determining the excitation force, excitation time, and excitation frequency in the vibration aging treatment are as follows:

[0044] (1) Excitation frequency;

[0045] When a periodic external force is applied to the vibrator, a resonance response is induced, causing the parts to produce alternating motions with specific amplitude and periodicity. This exceeds the material's yield limit, resulting in minute plastic deformation and gradual slippage of dislocations within the grains, thereby reducing or eliminating residual stress. Empirically, when the vibrator's excitation frequency equals a lower-order natural frequency, a smaller excitation force can achieve a larger amplitude vibration with a more uniform distribution. This not only reduces energy consumption but also allows for the generation of sufficient vibration amplitude with minimal excitation force. Therefore, the minimum natural frequency of the current wheel is used as the excitation frequency of the vibrator.

[0046] (2) Excitation force at different tread depths;

[0047] The specific formula for calculating the excitation force is as follows:

[0048] F=a·σ1·s (1)

[0049] Where 'a' is the excitation coefficient, which is proportional to the quenching time 't1', a = t1 / 100, where 't1' is in seconds; 'σ1' is the initial excitation stress at the corresponding depth below the tread surface, in MPa; and 's' is the unit area of ​​the excitation point, in mm. 2 .

[0050] The specific formula for calculating the initial excitation stress is as follows:

[0051]

[0052] Among them, Rp 0.2 Rm represents the wheel yield strength at the corresponding depth below the tread, in MPa; b represents the wheel tensile strength at the corresponding depth below the tread, in MPa; b is the stress coefficient, ranging from 1.5 to 2.0; σ min The initial minimum residual compressive stress at the depth corresponding to the tread surface is obtained by ultrasonic residual stress testing method, and the residual stress depth and magnitude in the rim area are measured in MPa. 880MPa is a correction value obtained by simulation calculation and verification by a large number of experiments. It is applicable to wheels with single-sided quenching of the rim and without tempering treatment.

[0053] When the value of b is generally 2.0, the initial excitation stress σ1 calculated by formula (2) does not satisfy the constraint condition σ1+σ min >Rp 0.2If σ1 < 0.5Rm, the value of b is gradually reduced until the initial excitation stress σ1 that meets the constraint conditions is found. If the calculated initial excitation stress σ1 still cannot meet the constraint conditions when the value of b is reduced to 1.5, it indicates that the residual stress of this batch of wheels is relatively small. Conventional tempering is sufficient, and vibration aging treatment is not required. If vibration aging treatment is performed, the residual compressive stress of the wheel will be too small, which is detrimental to the service of the wheel.

[0054] When the tensile strength Rm at 20mm below the wheel tread exceeds the set tensile strength threshold, the vibration stress applied to the wheel is relatively small, the change in residual stress inside the wheel is limited, and the stress reduction rate is low. At this point, simple vibration aging treatment is no longer sufficient to meet the residual stress control requirements. Conventional tempering treatment is necessary after vibration aging treatment because, according to ultrasonic residual stress test results, the residual compressive stress at 20mm below the tread is the largest and is the main factor causing the residual stress to exceed the standard. The excitation stress σ1 and the initial residual stress σ1 calculated above are... min The sum of these stresses can exceed the wheel's yield strength, causing plastic deformation and internal dislocation slippage, which reduces residual stress, while not exceeding the wheel's tensile strength, thus preventing the wheel from breaking.

[0055] The tensile strength threshold mentioned above is generally taken as 1150MPa. If the tensile strength Rm at 20mm below the wheel tread is lower than the set tensile strength threshold, then vibration aging treatment of the quenched wheel is sufficient to improve the residual stress.

[0056] (3) Excitation time

[0057] In vibration aging treatment, dislocations undergo movement, multiplication, re-movement, and re-multiplication before finally stabilizing, which requires a certain amount of time. Different materials and heat treatment processes for wheels result in different required vibration aging excitation times. The excitation time t (in seconds) must satisfy the following:

[0058] t = a1 × B1 + a2 × B2;

[0059] F / t = a3, 1.0 ≤ a3 ≤ 1.9;

[0060] 6.0≤a1+a2≤9.0, and 3.0≤a1≤6.3, 2.5≤a2≤5.5;

[0061] In the formula, F is the excitation force in N, B1 is the rim thickness in mm, B2 is the rim height in mm, a1 and a2 represent the rim thickness coefficient and rim height coefficient respectively, and a3 is the Ft coefficient, which limits the excitation time t. On the one hand, it can avoid the excitation time being too long, which would adversely affect the fatigue life of the wheel; on the other hand, it can avoid the excitation time being too short, which would not achieve the vibration aging treatment effect.

[0062] In this embodiment of the invention, the quenched wheel is horizontally fixed on a circular vibration platform. Vibrators are evenly distributed circumferentially at the bottom of the platform, with each vibrator positioned at a depth corresponding to the tread surface. The vibrators are in contact with the vibration platform via elastic support pads. For example, six vibrators are arranged circumferentially at the bottom of the platform, as shown in the diagram. Figure 2 As shown, the vibrator performs vibration aging treatment on the wheel fixed on the vibration platform based on the excitation force, excitation frequency, and excitation time. Wheels from the same production batch use the same vibration parameters during vibration aging treatment. In this embodiment of the invention, the vibrator is a spectrum harmonic vibration aging instrument.

[0063] In this embodiment of the invention, since resonance can allow the material to acquire greater kinetic energy, the low-order natural frequency of the wheel is selected as the frequency of the excitation load. This allows for the acquisition of the maximum dynamic stress in the material with the minimum excitation force. Simulation calculations and experimental verification analysis show that when the low-order natural frequency of the wheel is above 100Hz, vibration aging treatment is more effective in eliminating residual stress. However, it places higher demands on the aging equipment, is prone to exciter damage, generates significant noise, and may also cause fatigue damage in parts of the rim. Therefore, when the low-order natural frequency of the wheel exceeds 100Hz, vibration aging treatment is not suitable for reducing residual stress. Instead, optimization should be performed on the spoke shape, size, rim thickness, and heat treatment process.

[0064] The following is in conjunction with the appendix Figure 1-3 The present invention will be described in detail in Examples 1-3. In the examples, the spectrum harmonic vibration aging instrument is a commercially available device that can meet the requirements of excitation frequency of 10Hz to 500Hz and excitation force of 0 to 25KN. For wheels of the same batch produced with the same materials and processes, it is only necessary to randomly select one wheel to determine the vibration aging process, and then the process can be applied to this batch of wheels.

[0065] The chemical composition mass fraction of the wheel steel in the examples and comparative examples is shown in Table 1. The wheel material and specifications of the examples and corresponding comparative examples are consistent. The wheels in the examples and comparative examples are all made by electric furnace smelting, LF+RH refining and vacuum degassing, and then directly continuous casting. The round billet is cut into ingots and heated and rolled to form wheels of different wheel types with a diameter of 957mm.

[0066] Table 1. Wheel composition (%) for Examples and Comparative Examples

[0067] C Si Mn P S Fe Example 1 0.59 0.27 0.74 0.006 0.008 Remain Example 2 0.62 0.89 0.82 0.010 0.009 Remain Example 3 0.72 0.88 0.82 0.007 0.008 Remain Comparative Example 1 0.59 0.28 0.75 0.008 0.010 Remain Comparative Example 2 0.63 0.75 0.80 0.009 0.006 Remain Comparative Example 3 0.73 0.80 0.82 0.012 0.008 Remain

[0068] Example 1: The rolled blank wheel (wheel type 1, rim thickness B1 of 70mm, rim height B2 of 145mm) was heated to complete austenitization, and then the rim was cooled by water spray for 250s (accelerating the internal metal of the rim to below 550℃ at a cooling rate of 2℃ / s-5℃ / s). An elastic suspension was used to place the wheel in a near-free state. BK4508 accelerometers were arranged on the wheel in 16 equal sections, and connected to a BK 8404 multi-channel data logger. Excitation signals were obtained by striking the wheel at 1 / 2 the rim thickness using a BK8206 hammer at 90° intervals. The accelerometer sensor received the vibration response signal. The excitation and response signals were processed and analyzed using BK Connect software, yielding the low-order frequencies of the wheel as 15Hz, 20Hz, and 25Hz. The wheel of Example 1 was tested using an ultrasonic residual stress analyzer, and the following values ​​were obtained at 10mm below the tread: σ min =260MPa; 20mm below the tread: σ min =320MPa; 30mm below the tread: σ min =280MPa. Place the wheel horizontally and fix it to the vibration platform. Elastic support pads are installed under the vibration platform. Six vibrators are installed on the platform at 60° intervals. The first and fourth vibrators are installed 10-20mm below the tread surface, the second and fifth vibrators are installed 20-30mm below the tread surface, and the third and sixth vibrators are installed 30-40mm below the tread surface. The vibration platform is in contact with the vibrating platform through the elastic support pads. See the diagram for the specific installation positions. Figure 2 As shown. The wheel of Example 1 and the wheel of Comparative Example 1 are made of the same material and have the same quenching process. The tempering treatment of the wheel of Comparative Example 1 only serves to release some residual stress and does not affect the mechanical properties. Therefore, it is believed that the mechanical properties of the wheel of Example 1 without vibration aging treatment are the same as those of the wheel of Comparative Example 1.

[0069] Vibration force at 10mm below the tread surface: And σ1+σ min =447.5 + 260 = 707.5 > Rp 0.2 σ1=447.5<0.5Rm;

[0070] Vibration force at 20mm below the tread surface: And σ1+σ min =414+320=734>Rp 0.2 σ1=414<0.5Rm;

[0071] Vibration force at 30mm below the tread surface: And σ1+σ min =374+280=654>Rp 0.2σ1=374<0.5Rm;

[0072] Excitation time: t=a1×B1+a2×B2=3.5×70+4.2×145=854s, a1+a2=3.5+4.2=7.7, a3=F / t=1100 / 854=1.3;

[0073] The excitation frequency of the vibrator is selected as 15Hz. After the settings are completed, all 6 vibrators will process simultaneously.

[0074] like Figure 3 , Figure 4 As shown, the flame-cut shrinkage values ​​of the wheel in Example 1 and the wheel in Comparative Example 1 are both between 1 and 5 mm. However, the shrinkage value of the wheel prepared in Example 1 is significantly far from the upper limit of 5 mm, with a larger margin. Furthermore, the ultrasonic testing results show that the maximum residual compressive stress at the same location is reduced by more than 30%. The mechanical properties of the wheel in Example 1 are shown in Table 2. Table 2 shows that the strength, hardness, and impact performance of the wheel in Example 1 after vibration aging treatment are slightly higher than those of the wheel in Comparative Example 1. A comparative contact fatigue test was conducted on a computer-controlled rolling contact fatigue test bench. The specimens were 40 mm disc-shaped specimens, all taken from the same location on the rims of the wheels in Comparative Example 1 and Example 1. The test results are shown in Table 3. Table 3 shows that the contact fatigue performance of the wheel in Example 1 is better than that of the wheel in Comparative Example 1. Therefore, it can be seen that the wheel in Example 1, while superior to the wheel in Comparative Example 1 in strength, hardness, impact performance, and contact fatigue performance, has a larger margin in residual stress shrinkage value after flame cutting, and the invention has achieved the expected results.

[0075] Example 2: The rolled blank wheel (wheel type 2, rim thickness B1 of 75mm, rim height B2 of 143mm) was heated to complete austenitization, and then the rim was cooled by water spray for 280s (accelerating the internal metal of the rim to below 550℃ at a cooling rate of 2℃ / s-5℃ / s). An elastic suspension was used to place the wheel in a near-free state. BK4508 accelerometers were arranged on the wheel in 16 equal sections, and connected to a BK 8404 multi-channel data logger. Excitation signals were obtained by striking the wheel at 1 / 2 the rim thickness using a BK8206 hammer at 90° intervals. The accelerometer sensor received the vibration response signal. The excitation and response signals were processed and analyzed using BK Connect software, yielding the low-order frequencies of the wheel as 23Hz, 35Hz, and 46Hz. The wheel of Example 2 was tested using an ultrasonic residual stress analyzer, and the stress at 10mm below the tread was found to be σ. min =255MPa; 20mm below the tread: σ min =300MPa; 30mm below the tread: σ min=282MPa. Place the wheel horizontally and fix it on the vibration platform. Install elastic support pads under the vibration platform. Install six vibrators at 60° intervals on the platform. The first and fourth vibrators are installed 10-20mm below the tread surface, the second and fifth vibrators are installed 20-30mm below the tread surface, and the third and sixth vibrators are installed 30-40mm below the tread surface. See the diagram for specific installation positions. Figure 2 As shown. The wheel of Example 2 is made of the same material and quenching process as the wheel of Comparative Example 2. The tempering treatment of the wheel of Comparative Example 2 only serves to release some residual stress and does not affect the mechanical properties. Therefore, it is believed that the mechanical properties of the wheel of Example 2 without vibration aging treatment are the same as those of the wheel of Comparative Example 2.

[0076] Vibration force at 10mm below the tread surface: And σ1+σ min =507.5 + 255 = 762.5 > Rp 0.2 σ1=507.5<0.5Rm;

[0077] Vibration force at 20mm below the tread surface: And σ1+σ min =458.5 + 300 = 758.5 ​​> Rp 0.2 σ1=458.5<0.5Rm;

[0078] Vibration force at 30mm below the tread surface And σ1+σ min =440.5 + 282 = 722.5 > Rp 0.2 σ1=440.5<0.5Rm;

[0079] Excitation time: t=a1×B1+a2×B2=4.0×75+5.0×143=1015s, and a1+a2=4.0+5.0=9.0, a3=F / t=1400 / 1015=1.4; the excitation frequency of the exciter is selected as 23Hz. After the settings are completed, 6 exciters will process simultaneously. Figure 3 , Figure 4As shown, the flame-cut shrinkage values ​​of the wheel prepared in Example 2 and the wheel in Comparative Example 2 are both between 1 and 5 mm. However, the shrinkage value of the wheel in Example 2 is significantly far from the upper limit of 5 mm, with a larger margin. Furthermore, the ultrasonic test results of the wheel in Example 2 show that the maximum residual compressive stress at the same location is reduced by more than 30%. The mechanical properties of the wheel in Example 2 are shown in Table 2. As can be seen from Table 2, the strength, hardness, and impact performance of the wheel in Example 2 after vibration aging treatment are slightly higher than those of the wheel in Comparative Example 2. A comparative contact fatigue test was conducted on a microcomputer-controlled rolling contact fatigue test bench. The specimens were 40 mm disc-shaped specimens, all taken from the same part of the rim of the wheels in Comparative Example 2 and Example 2. The test results are shown in Table 3. As can be seen from Table 3, the contact fatigue performance of the wheel in Example 2 is better than that of the wheel in Comparative Example 2. Therefore, under the condition that the wheel in Example 2 is superior to the wheel in Comparative Example 2 in terms of strength, hardness, impact performance, and contact fatigue performance, the residual stress shrinkage value of the wheel in Example 2 has a large margin, and the invention has achieved the expected results.

[0080] Example 3: The rolled blank wheel (wheel type 3, rim thickness B1 of 76mm, rim height B2 of 148mm) was heated to complete austenitization, and then the rim was cooled by water spray for 320s (accelerating the internal metal of the rim to below 550℃ at a cooling rate of 2℃ / s-5℃ / s). An elastic suspension was used to place the wheel in a near-free state. BK4508 accelerometers were arranged on the wheel in 16 equal sections, and connected to a BK 8404 multi-channel data logger. Excitation signals were obtained by striking the wheel at 1 / 2 the rim thickness using a BK8206 hammer at 90° intervals. The accelerometer sensor received the vibration response signal. The excitation and response signals were processed and analyzed using BK Connect software, yielding the low-order frequencies of the wheel as 30Hz, 43Hz, and 65Hz. The wheel of Example 3 was tested using an ultrasonic residual stress analyzer, and the following values ​​were obtained at 10mm below the tread: σ min =252MPa; 20mm below the tread: σ min =296MPa; 30mm below the tread: σ min =271MPa. Place the wheel horizontally and fix it on the vibration platform. Install elastic support pads under the vibration platform. Install six vibrators at 60° intervals on the vibration platform. The first and fourth vibrators are installed 10-20mm below the tread surface, the second and fifth vibrators are installed 20-30mm below the tread surface, and the third and sixth vibrators are installed 30-40mm below the tread surface. See the diagram for specific installation positions. Figure 2As shown. The wheel of Example 3 is made of the same material and quenching process as the wheel of Comparative Example 3. The tempering treatment of the wheel of Comparative Example 3 only serves to release some residual stress and does not affect the mechanical properties. Therefore, it is believed that the mechanical properties of the wheel of Example 3 without vibration aging treatment are the same as those of the wheel of Comparative Example 3.

[0081] Vibration force at 10mm below the tread surface: And σ1+σ min =590+252=842>Rp 0.2 σ1=590<0.5Rm;

[0082] Vibration force at 20mm below the tread surface: And σ1+σ min =560.5 + 296 = 856.5 > Rp 0.2 σ1=560.5<0.5Rm;

[0083] Vibration force at 30mm below the tread surface: And σ1+σ min =504+271=775>Rp 0.2 σ1=504<0.5Rm;

[0084] The excitation time t = a1 × B1 + a2 × B2 = 3.8 × 70 + 5.1 × 145 = 1005.5 s, and a1 + a2 = 3.8 + 5.1 = 8.9, a3 = F / t = 1900 / 1005.5 = 1.9; the excitation frequency of the vibrator is selected as 30 Hz. After the settings are completed, 6 vibrators are used simultaneously. Since the tensile strength Rm at 20 mm below the tread of the wheel in Comparative Example 3 exceeds the threshold of 1150 MPa, the wheel in Example 3 needs to undergo tempering treatment after vibration aging treatment. The tempering temperature is 470-490℃, and the tempering time is ≥4.0 hours. Figure 3 , 4As shown, the flame-cut shrinkage values ​​of the wheel prepared in Example 3 and the wheel in Comparative Example 3 are both between 1 and 5 mm. The shrinkage value of the wheel in Example 3 is significantly lower than the upper limit of 5 mm, indicating a larger margin. Furthermore, the ultrasonic test results of the wheel in Example 3 show that the maximum residual compressive stress at the same location is reduced by more than 30%. The mechanical properties of the wheel in Example 3 are shown in Table 2. Table 2 shows that the strength, hardness, and impact performance of the wheel in Example 3 after vibration aging treatment are slightly higher than those of the wheel in Comparative Example 3. A comparative contact fatigue test was conducted on a microcomputer-controlled rolling contact fatigue test bench. The specimens were 40 mm disc-shaped specimens, all taken from the same location on the rims of the wheels in Comparative Example 3 and Example 3. The test results are shown in Table 3. Table 3 shows that the contact fatigue performance of the wheel in Example 3 is better than that of the wheel in Comparative Example 3. Therefore, it can be seen that the wheel in Example 3, while superior to the wheel in Comparative Example 3 in strength, hardness, impact performance, and contact fatigue performance, has a larger margin in residual stress shrinkage value after flame cutting, and the invention has achieved the expected results.

[0085] The wheels of Comparative Examples 1-3 are made of the same material and quenching process as their corresponding wheels of Examples 1-3. After the comparative example wheels are quenched, they are tempered in a tempering furnace at a temperature of 470-490℃ for a duration of ≥4.0 hours.

[0086] Table 2 Comparison of mechanical performance of wheels in the embodiments and comparative examples

[0087]

[0088]

[0089] Table 3. Contact fatigue resistance of wheels in the examples and comparative cases.

[0090] Contact stress / MPa slip / % Loop count Rotational speed (r / min) Lubricating medium Are you tired? Example 1 900 0.3 <![CDATA[5.5x10 6 ]]> 1500 Oil lubrication no Example 2 920 0.3 <![CDATA[6.5x10 6 ]]> 1500 Oil lubrication no Example 3 1000 0.3 <![CDATA[6.8x10 6 ]]> 1500 Oil lubrication no Comparative Example 1 900 0.3 <![CDATA[5.0x10 6 ]]> 1500 Oil lubrication no Comparative Example 2 890 0.3 <![CDATA[6.5x10 6 ]]> 1500 Oil lubrication no Comparative Example 3 1000 0.3 <![CDATA[6.5x10 6 ]]> 1500 Oil lubrication no

[0091] The present invention has been described by way of example. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A residual stress improvement method for railway wheels, characterized by, The method is as follows: The vibration parameters for vibration aging treatment are determined, including the excitation force, excitation time, and excitation frequency at different tread depths, and then the wheels are subjected to vibration aging treatment. Vibration force at different tread depths; ； in, The excitation coefficient is related to the quenching time. Proportional , This represents the initial excitation stress at the depth below the corresponding tread surface; The area per unit area of ​​the excitation point; Initial excitation stress The specific calculation formula is as follows: ； in, This represents the wheel yield strength at the depth corresponding to the tread surface. To determine the tensile strength of the wheel at the depth below the tread, is the stress coefficient, with a value range of 1.5 to 2.

0.

2. The method for improving residual stress in railway wheels as described in claim 1, characterized in that, Check whether the tensile strength Rm at 20mm below the wheel tread exceeds the set tensile strength threshold. If the test result is yes, then the wheel is subjected to vibration aging treatment based on the vibration parameters, and then tempering treatment is performed. If the test result is no, then the wheel is subjected to vibration aging treatment based on the vibration parameters.

3. The method for improving residual stress in railway wheels as described in claim 1, characterized in that, when The value is set to 2.0 to detect the initial excitation stress. Do the constraints meet? , If satisfied, the current initial excitation stress will be output. If the corresponding excitation force is not satisfied, it should be gradually reduced. The value is calculated until an initial excitation stress that satisfies the constraints is found. ,like After the value is reduced to 1.5, the calculated initial excitation stress If the constraints are still not met, the wheels will only undergo tempering treatment, without vibration aging treatment. This represents the initial minimum residual compressive stress at the depth corresponding to the tread surface.

4. The method for improving residual stress in railway wheels as described in claim 2, characterized in that, Excitation time The following conditions must be met: ； ， ； ,and , ; In the formula, For excitation force, For rim thickness; For the rim height, , These represent the rim thickness coefficient and rim height coefficient, respectively. For Ft coefficients.

5. The method for improving residual stress in railway wheels as described in claim 1, characterized in that, The excitation frequency is the minimum natural frequency of the wheel.

6. The method for improving residual stress in railway wheels as described in claim 5, characterized in that, Wheels of the same specifications and materials are tested for their natural frequency.

7. The method for improving residual stress in railway wheels as described in claim 1, characterized in that, The vibration aging treatment process for wheels is as follows: After quenching, the wheel is horizontally fixed on a circular vibration platform. Vibrators are evenly distributed around the bottom of the vibration platform along the circumference, and the vibrators are located at the corresponding depth below the tread. The vibrators are in contact with the vibration platform through elastic support pads. The vibrators perform vibration aging treatment on the wheel fixed on the vibration platform based on the above-mentioned excitation force, excitation frequency and excitation time.

8. The method for improving residual stress in railway wheels as described in claim 6, characterized in that, The process of obtaining the natural frequency of a wheel is as follows: n striking points are evenly arranged circumferentially at 1 / 2 of the wheel rim thickness, and m vibration accelerometers are evenly arranged circumferentially at 1 / 2 of the outer side of the hub and rim. After quenching, the wheel is in a free suspension state. The hammer strikes once at each impact point, and each impact point generates an excitation signal V1. The corresponding m vibration accelerometers generate m response signals V2. The excitation signal V1 and its corresponding response signal V2 are collected by a multi-channel data logger and transmitted to the BK Connect software. The BK Connect software outputs the natural frequency of the wheel.

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