Treatment method for improving rolling contact fatigue resistance of high and cold railway steel rail

Abstract

The invention discloses a treatment method for improving rolling contact fatigue resistance of a high and cold railway steel rail, and belongs to the technical field of steel rail preparation. The treatment method for improving the rolling contact fatigue resistance of the high-cold railway steel rail comprises the following steps that the high-cold railway steel rail is placed in a vacuum environment where a magnetic field is applied to be subjected to subzero treatment. The treatment method can greatly improve the rolling contact fatigue performance of the steel rail for the high and cold railway, is low in cost, can be used for repairing steel rails of different rail types, steel rail turnouts and joints, prolongs the service life, and provides technical support for prolonging the service life of the steel rail for the high and cold railway.

Description

Technical Field

[0001] The invention relates to the technical field of rail preparation, and in particular to a processing method for improving the rolling contact fatigue resistance of high-cold railway rails. Background Art

[0002] The alpine regions have complex geological conditions and climatic characteristics such as high cold and humidity, seasonal frozen soil, regional uneven severe snow and wind, intermittent geothermal, fragile and sensitive ecological environment, etc., with huge temperature difference between winter and summer, and strong cold and frost weathering. Therefore, the service environment of alpine railways is very complex, and extreme service conditions pose new challenges to rails, especially the rail switches and joints of railway rails in alpine regions, which face more arduous challenges. Among them, the Sichuan-Tibet Railway, which has the most complex and severe operating conditions, has a large number of long and steep slopes along the road and a harsh service environment, which puts more stringent requirements on the fatigue resistance, low-temperature plasticity and toughness of rails. With the increase in railway operation speed and transportation volume in alpine regions, the loads borne by rails have become more complex, rail damage has become more serious, the life of rail switches and joints is extremely short, and the service time of rails is much shorter than that of other regions. The shorter rail life is directly reflected in the maintenance cycle. Compared with other regions, rails in alpine regions need to be inspected more frequently, such as rail switches and joints, whose inspection cycle has been calculated on a daily basis. At present, rail grinding machines are mainly used for rail repair. However, in high-cold areas, rail grinding machines are often faced with various extreme weather conditions and cannot perform normal work. The complex terrain also makes normal rail repair work more difficult. For high-cold areas, rail repair requires a lot of maintenance manpower, which has become a key issue affecting and restricting the maintenance of engineering equipment. Therefore, it is of great significance to fully consider the characteristics and actual conditions of high-cold areas, develop advanced rail life extension technology, and formulate a more complete life extension plan for railway operations in high-cold areas. Summary of the invention

[0003] The purpose of the present invention is to provide a processing method for improving the rolling contact fatigue resistance of high-cold railway rails, so as to solve the problems existing in the above-mentioned prior art.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is a method for improving the rolling contact fatigue resistance of high-cold railway rails, comprising the following steps:

[0006] The high-altitude railway rails are placed in a vacuum environment with an applied magnetic field for deep freezing treatment, and then naturally heated to room temperature to complete the primary treatment of the rails.

[0007] Furthermore, the treatment method also includes the steps of repeatedly placing the material in a vacuum environment with a magnetic field applied for cryogenic treatment, and then naturally heating the material to room temperature.

[0008] Furthermore, the number of repetitions is 1 to 10 times, and the specific number of repetitions depends on the cryogenic medium used, the degree of rail damage and cost considerations.

[0009] Furthermore, the treatment method further comprises performing a tempering treatment after the cryogenic treatment (the tempering treatment is an optional process, and whether to perform the tempering treatment can be determined according to factors such as the actual use conditions of the rail and the conditions of the tempering treatment).

[0010] Furthermore, the tempering treatment temperature is 250-500° C., and the holding time is 60-360 min.

[0011] Furthermore, the magnetic field is an alternating magnetic field, and the current intensity is 100-150A.

[0012] Furthermore, the cryogenic treatment includes using a cooling medium to reduce the temperature of the high-cold railway rails to -150 to -200°C.

[0013] Furthermore, the cooling medium includes liquid nitrogen, liquid helium or dry ice, and the selection of the cooling medium depends on the material of the rail, processing requirements and cost considerations.

[0014] Furthermore, the cryogenic treatment time is 3 to 10 hours, and the specific optimal time varies depending on the material of the rail and the cooling medium used.

[0015] Furthermore, the high-altitude and cold-weather railway rails are rails with a total cumulative passing mass of 5 to 50 Mt.

[0016] During the railway operation, the rail will generate large internal stress, which is very likely to induce dimensional instability and crack expansion. Cryogenic treatment helps to eliminate the internal residual stress of the rail, effectively reduce the possibility of deformation and cracking of the rail, maintain the dimensional stability of the rail, improve the rail's resistance to plastic deformation, strength, toughness, wear resistance, corrosion resistance and fatigue resistance, and extend the service life of the rail. In addition, cryogenic treatment is simple to operate, pollution-free, and low-cost, which meets the requirements of modern industry for environmental protection and economic benefits.

[0017] Mechanism of the present invention:

[0018] The treatment method of the present invention (subjecting to deep cryogenic treatment in a vacuum environment with a magnetic field applied) can eliminate the internal residual stress of the rail, significantly improve the hardness, wear resistance, fatigue resistance, corrosion resistance, etc. of the rail, and effectively reduce the possibility of deformation and cracking of the rail.

[0019] The present invention discloses the following technical effects:

[0020] (1) The treatment method of the present invention can greatly improve the rolling contact fatigue performance of steel rails for high-cold railways with low cost. It can be used to repair rails of different rail types and rail switches and joints to extend their service life, providing technical support for extending the service life of steel rails for high-cold railways.

[0021] (2) The treatment method of the present invention can repair the strength and toughness of the rails, improve the rails' resistance to plastic deformation, strength, toughness, wear resistance, corrosion resistance and fatigue resistance, reduce the risk of deformation and cracking of the rails, ensure that the repaired rails are better adapted to the service environment in high-altitude cold areas, and make the rails have more stable wear resistance and fatigue resistance.

[0022] (3) The treatment method of the present invention fully considers the characteristics and actual conditions of the high-cold regions, and selectively introduces the tempering treatment step according to actual needs, and the specific number of treatments for the rails (the number of times the rails are placed in a vacuum environment with a magnetic field applied for deep cold treatment) can be flexibly adjusted. In addition, the treatment method of the present invention is obtained by comprehensively considering multiple factors such as the material properties of the rails, the effects to be achieved by the treatment, and cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 is a schematic diagram of a rail specimen;

[0025] Figure 2 is a schematic diagram of the ER8 wheel steel specimen;

[0026] Figure 3 is the wear rate diagram of rail specimens obtained under different treatment methods;

[0027] Figure 4 The friction coefficient diagram of rail samples obtained under different treatment methods;

[0028] Figure 5 The microstructure and morphology of the friction cross section of rail samples obtained by different treatment methods after low-temperature rolling-sliding contact test;

[0029] Figure 6 The internal residual stress diagram of rail samples obtained by different treatment methods after low-temperature rolling-sliding contact test;

[0030] Figure 7SEM images of the friction surfaces of rail samples obtained under different treatment methods after low-temperature rolling-sliding contact tests. DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] The “parts” described in the following examples are all “parts by weight”.

[0037] Example 1

[0038] A treatment method for improving the rolling contact fatigue resistance of high-cold railway rails:

[0039] (1) The Golmud section of the Qinghai-Tibet Railway is located in the heart of the Qinghai-Tibet Plateau. A section of rail (U71MnG rail) with a total passing mass of 10 Mt was taken from the rail joint on site. Three rail samples of the same type were prepared at the same depth of the rail (see Figure 1, the dimensions in the figure are in mm), marked as 1# rail sample, 2# rail sample and 3# rail sample.

[0040] (2) No. 1 rail sample: no treatment is done to obtain an untreated rail sample;

[0041] 2# Rail sample: placed in a vacuum (vacuum degree 10 3 The rails were cryogenically treated in a 400-degree Pa (cryogenic medium: liquid nitrogen, holding time: 5 h, temperature: -196 °C) environment, and then naturally heated to room temperature. The above treatment process was repeated once to obtain the treated rail specimens.

[0042] 3# rail sample: placed in a vacuum (vacuum degree 10 3 The sample was cryogenically treated in a 400-degree Pa (376-degree C) environment (the cryogenic medium was liquid nitrogen, the holding time was 5 h, and the temperature was -196 °C), and then naturally heated to room temperature. The above treatment process was repeated once. Finally, the sample was placed in a heat treatment furnace and heated to 350 °C at a heating rate of 50 °C / h. After holding for 80 min, the temperature was cooled to room temperature at a cooling rate of 40 °C / h to complete the tempering treatment and obtain the tempered rail sample.

[0043] Effect Example 1

[0044] (1) Take three ER8 wheel steel specimens (see Figure 2 , the dimensions in the figure are in mm) and the three rail samples in step (2) of Example 1 were ultrasonically cleaned with acetone for 5 minutes, and their weights were weighed 7 times respectively, and data were collected.

[0045] The treated rail sample (2# rail sample), the tempered rail sample (3# rail sample), and the untreated rail sample (1# rail sample) were respectively subjected to low-temperature rolling-sliding contact experiments with the ER8 wheel steel sample in a rolling contact tester. The number of experimental cycles was set to 5×10 5 The experimental environment temperature was -40℃, simulating the actual operation conditions of high-altitude and cold railways.

[0046] After the rolling-sliding contact experiment, the rails and wheels were taken out and ultrasonically cleaned with acetone for 5 min, respectively. Then, they were weighed 7 times, data was collected, wear loss was calculated, and wear rate was analyzed. The results are shown in Figure 3 .

[0047] The wear rate directly reflects the wear resistance of the wheel and rail materials. Under the same use conditions, the wear rate of materials with good wear resistance will be relatively small. Therefore, by analyzing the wheel and rail wear rate, the wear resistance of the material can be evaluated and a basis for material selection and improvement can be provided.

[0048] from Figure 3 It can be seen that under the same number of cycles, the average wear rate of the untreated rail samples on the grinding wheels is about 18.897ug / r, and the average wear rate of the treated rail samples on the grinding wheels is about 18.884ug / r, and there is no significant difference between the two; the average wear rate of the rail samples after tempering treatment on the grinding wheels is about 19.112ug / r, which is significantly higher than the former two.

[0049] The average wear rate of the untreated rail samples is about 4.282ug / r, the average wear rate of the treated rail samples is about 1.860ug / r, and the average wear rate of the tempered rail samples is about 1.013ug / r. The average wear rate of the untreated rail samples is about three times that of the treated rail samples, and the wear rate of the tempered rail samples is less than that of the treated rail samples.

[0050] It can be seen that the wear resistance of the treated rail sample is significantly better than that of the untreated rail sample, while the wear on the wheel is almost unchanged; the wear resistance of the tempered rail sample is better than that of the treated rail sample. The treatment method of the present invention can significantly improve the wear resistance of the rail sample, and the tempering post-treatment process can be selectively added according to the actual situation. The tempering treatment can further improve the wear resistance of the rail on the basis of the pre-treatment, but this will slightly increase the wear of the wheel.

[0051] (2) The wheel-rail friction data were obtained by the rolling contact test machine, and the friction coefficients of the untreated rail sample (uncryogenically treated rail) and the treated rail sample (cryogenically treated rail) in step (2) of Example 1 were analyzed. The results are shown in Figure 4 .

[0052] In actual working conditions, the friction coefficient between the wheel and rail is an important factor affecting the friction and traction between the wheel and rail.

[0053] from Figure 4 It can be seen that the friction coefficient of the treated rail sample is slightly higher than that of the untreated rail sample in the first half of the cycle number, indicating that the treated rail sample has greater traction, which makes the power more effectively transmitted to the wheel; when the cycle time gradually increases, the friction coefficient of the treated rail sample gradually decreases and is less than that of the untreated rail sample, indicating that the wear between the wheel and rail of the treated rail sample is less than that of the untreated rail sample, and its adhesion and resistance are significantly reduced. The above results show that the rolling contact fatigue performance of the treated rail sample is significantly better than that of the untreated rail sample.

[0054] (3) The untreated rail sample (uncryogenically treated rail) and the treated rail sample (cryogenically treated rail) prepared in step (2) of Example 1 after the low-temperature rolling-sliding contact test were cut from the tread of the rail, and the cross section was polished and then corroded with a corrosive liquid to observe its metallographic image, that is, to analyze the microstructure and morphology of the rolling-sliding friction cross section of the specimen. The results are shown in FIG. Figure 5 .

[0055] The wheel-rail plastic deformation layer is a layer of tissue formed by the crystal structure slip and plastic deformation along the rolling direction generated inside the material during the wheel-rail contact process.

[0056] from Figure 5 It can be seen that under the same number of cycles, the thickness of the plastic deformation layer of the treated rail sample is about 153μm, and the thickness of the plastic deformation layer of the untreated rail sample is about 214μm. The plastic deformation degree of the untreated rail sample is more serious, and the plastic rheology is more obvious. It can be seen that the plastic deformation resistance of the treated rail sample is significantly better than that of the untreated rail sample, which also indirectly proves that the wear rate of the treated rail sample is lower than that of the untreated rail sample, because the formation and expansion of the plastic deformation layer is accompanied by material loss and destruction, thereby aggravating the wear of the wheel and rail. In addition, the wheel-rail contact position of the untreated rail sample has obvious fatigue damage spalling because its plastic deformation layer has exceeded 180μm.

[0057] (4) Take the untreated rail sample (without cryogenic treatment) and the treated rail sample (after cryogenic treatment) prepared in step (2) of Example 1 after the low-temperature rolling-sliding contact test, ensure that their surfaces are flat and have no obvious defects, and use X-ray diffraction (XRD) to calculate the magnitude and direction of the residual stress inside the rail. The results are shown in Figure 6 .

[0058] Residual stress inside metal refers to the stress that still exists inside the metal when there is no external load. The residual stress inside the rail sample in the present invention may be due to uneven temperature changes, plastic deformation, etc., resulting in uneven stress distribution inside the sample. Residual stress will have an adverse effect on the performance of the rail, reduce its fatigue strength, and increase the risk of stress corrosion cracking.

[0059] from Figure 6It can be seen that the average residual stress of the treated rail samples in the x direction is about 185.5Mpa, and the average residual stress of the untreated rail samples is about 240.3Mpa, which is significantly higher than the treated rail samples; the average residual stress of the treated rail samples in the y direction is about 202.2Mpa, and the average residual stress of the untreated rail samples is about 249.7Mpa, which is significantly higher than the treated rail samples. It can be seen that deep cryogenic treatment can reduce the residual stress inside the service rails, improve the dimensional stability of the rails in the later use, improve their overall performance, extend the service life of the rails, and reduce the frequency of rail maintenance and replacement.

[0060] (5) The untreated rail samples (without cryogenic treatment) and the treated rail samples (after cryogenic treatment) prepared in step (2) of Example 1 after the low-temperature rolling-sliding contact test were taken to observe the morphology of the friction surface of the rail samples and analyze their friction and wear conditions. The results are shown in FIG. Figure 7 .

[0061] from Figure 7 It can be seen that the wear surface of the untreated rail sample is severely damaged, with relatively serious cracks and obvious peeling; while no obvious cracks, peeling and other damage were found on the wear surface of the treated rail sample. From the perspective of rolling contact fatigue performance, the performance of the treated rail sample is significantly better than that of the untreated sample. This shows that the treatment method of the present invention can significantly improve the wear resistance and fatigue resistance of the rail, so that it can better resist damage and fatigue during rolling contact.

[0062] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the rolling contact fatigue resistance of high-cold railway rails, characterized in that: The following steps are involved: The high-altitude railway rails are placed in a vacuum environment with an applied magnetic field for deep cryogenic treatment.

2. The processing method according to claim 1, characterized in that: The method also includes the step of repeatedly placing the material in a vacuum environment with a magnetic field applied thereto for cryogenic treatment.

3. The processing method according to claim 2, characterized in that: The number of repetitions is 1 to 10 times.

4. The processing method according to claim 2, characterized in that: It also includes tempering treatment after cryogenic treatment.

5. The processing method according to claim 4, characterized in that: The tempering treatment temperature is 250-500° C., and the heat preservation time is 60-360 minutes.

6. The processing method according to claim 1, characterized in that: The magnetic field is an alternating magnetic field, and the current intensity is 100-150A.

7. The processing method according to claim 1, characterized in that: The cryogenic treatment includes using a cooling medium to reduce the temperature of the high-cold railway rails to -150 to -200°C.

8. The processing method according to claim 1, characterized in that: The cryogenic treatment time is 3 to 10 hours.

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