Method for evaluating the anti-stripping performance of a surface hardening layer of a wheel rail material

Abstract

The application provides an evaluation method for the anti-peeling performance of a surface hardening layer of a wheel-rail material, and relates to the technical field of performance evaluation of a railway wheel-rail material.The evaluation method comprises the following steps: preparing a rail material sample and a wheel material sample; performing surface hardening treatment on the rail material sample and the wheel material sample respectively, and forming a hardening layer on the surface of the rail material sample and the surface of the wheel material sample; performing a pair grinding test on the rail material sample after surface hardening and the wheel material sample after surface hardening; measuring cracks generated in the hardening layer after the pair grinding test, and evaluating the anti-peeling performance of the hardening layer according to the measured data.The evaluation method for the anti-peeling performance of the surface hardening layer of the wheel-rail material can uniformly evaluate the anti-peeling performance of the surface hardening layer of different wheel-rail materials.

Description

Technical Field

[0001] This invention relates to the field of railway wheel and rail material performance evaluation technology, and in particular to a method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials. Background Technology

[0002] In the field of railway wheel and rail materials, improving the surface hardness of wheel and rail materials is the most common way to improve their wear resistance. Specifically, a surface-hardened layer can be obtained through methods such as work hardening, fine-grained strengthening, dispersion strengthening, second-phase strengthening, and heat treatment strengthening (e.g., quenching, carburizing, nitriding, and metallizing). While the surface-hardened layer can effectively improve the wear resistance of wheel and rail materials, in practical applications, problems such as poor toughness and plasticity of the surface-hardened layer and poor compatibility with the base material can lead to fatigue damage, eventually developing into spalling. For example, the wheel-rail scratching process forms a brittle and hard martensitic structure, which has high hardness and good wear resistance, equivalent to a surface-hardened layer. However, it is highly prone to crack initiation, leading to fatigue damage on the wheel and rail tread and threatening the safe service life of wheel and rail components.

[0003] Therefore, for the surface hardened layer of wheel and rail materials, it is necessary not only to examine its hardening performance but also to evaluate its peel resistance. However, there are many existing preparation methods for surface hardened layers, and the subsequent performance evaluation of the hardened layer also has different focuses. In the current standards and technical conditions related to wheel and rail materials, there are no test methods and evaluation standards for the peel resistance of the surface hardened layer of wheel and rail materials.

[0004] In view of this, based on years of experience in production and design in this and related fields, the inventor has developed a method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials through repeated experiments, in order to solve the problems existing in the prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials, which can uniformly evaluate the anti-peeling performance of the surface hardened layer of different wheel and rail materials.

[0006] To achieve the above objectives, this invention proposes a method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials, characterized in that the evaluation method includes:

[0007] Prepare rail material samples and wheel material samples;

[0008] The rail material sample and the wheel material sample are subjected to surface hardening treatment respectively to form a hardened layer on the surface of the rail material sample and the wheel material sample.

[0009] A grinding test was conducted on the surface-hardened rail material sample and the surface-hardened wheel material sample.

[0010] The cracks generated in the hardened layer after the grinding test were measured, and the anti-peeling performance of the hardened layer was evaluated based on the measured data.

[0011] Compared with the prior art, the present invention has the following features and advantages:

[0012] The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials proposed in this invention can compare the anti-peeling performance of surface hardened layers formed by different surface hardening processes for the same wheel and rail material; and it can also use different wheel and rail materials to prepare surface hardened layers for the same surface hardening process, thereby selecting and optimizing wheel and rail materials suitable for surface hardening.

[0013] The evaluation method for the anti-peeling performance of the surface hardened layer of wheel and rail materials proposed in this invention can be applied to different wheel and rail materials and different surface hardening processes, thus forming a unified and effective evaluation method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials. It is more universal and more suitable for widespread use. Attached Figure Description

[0014] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. Those skilled in the art, guided by the teachings of this invention, can select various possible shapes and proportions to implement the invention according to specific circumstances.

[0015] Figure 1 This is a flowchart of the method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials proposed in this invention;

[0016] Figure 2a This is a schematic diagram (I) of the double-disc grinding experiment in this invention;

[0017] Figure 2b This is a schematic diagram (II) of the double-disc grinding experiment in this invention;

[0018] Figure 3a This is a practical appearance drawing of the main sample after the grinding experiment of this invention;

[0019] Figure 3b This is a schematic diagram of the damage development of the main sample after the grinding experiment of this invention;

[0020] Figure 4a This is a schematic diagram showing that the cracks did not penetrate into the matrix after the grinding experiment of the present invention;

[0021] Figure 4b This is a schematic diagram showing the crack penetrating into the matrix after the grinding experiment of the present invention.

[0022] Explanation of reference numerals in the attached figures:

[0023] 10. Main sample;

[0024] 20. Accompanying test sample. Detailed Implementation

[0025] The details of the present invention can be more clearly understood by referring to the accompanying drawings and the description of specific embodiments. However, the specific embodiments of the present invention described herein are for illustrative purposes only and should not be construed as limiting the invention in any way. Under the teachings of this invention, those skilled in the art can conceive of any possible modifications based on the invention, and these should all be considered to fall within the scope of the invention.

[0026] like Figures 1 to 4b As shown, this invention proposes a method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials, comprising:

[0027] Prepare rail material samples and wheel material samples;

[0028] Surface hardening treatment was performed on the rail material sample and the wheel material sample respectively to form a hardened layer on the surface of the rail material sample and the wheel material sample.

[0029] A grinding test was conducted on surface-hardened rail material samples and surface-hardened wheel material samples.

[0030] The cracks generated in the hardened layer after the grinding test were measured, and the anti-peeling performance of the hardened layer was evaluated based on the measured data.

[0031] The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials proposed in this invention can compare the anti-peeling performance of surface hardened layers formed by different surface hardening processes for the same wheel and rail material; and it can also use different wheel and rail materials to prepare surface hardened layers for the same surface hardening process, thereby selecting and optimizing wheel and rail materials suitable for surface hardening.

[0032] The evaluation method for the anti-peeling performance of the surface hardened layer of wheel and rail materials proposed in this invention can be applied to different wheel and rail materials and different surface hardening processes, thus forming a unified and effective evaluation method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials. It is more universal and more suitable for widespread use.

[0033] In one optional embodiment of the present invention, the wheel material sample is cut 5 to 15 mm below the center tread of the actual wheel.

[0034] In an optional embodiment of the present invention, the rail material sample is cut 5 to 15 mm below the center tread of the actual rail.

[0035] In an optional embodiment of the present invention, the surface of the rail material sample and / or wheel material sample is hardened by laser quenching process.

[0036] In an optional example of this implementation, a JSY-6000 laser is used to prepare a laser-hardened layer on the surface of the sample (rail material sample and / or wheel material sample), and the laser hardening power is selected as 1200W.

[0037] Furthermore, the specimens (rail material specimens and / or wheel material specimens) are mounted on a chuck, which rotates the rail material specimens and / or wheel material specimens at a speed of 7 r / min.

[0038] Preferably, in order to prevent the laser quenching strips from overlapping and forming secondary quenching, the laser is turned on after the chuck rotates for 5 seconds; the laser is turned off after 2 seconds of laser quenching, forming a strip-shaped hardened layer of 3 / 4 circumference on the surface of the sample (rail material sample and / or wheel material sample). At the same time, Ar gas protection is used throughout the process to avoid surface oxidation.

[0039] In another optional embodiment of the present invention, the surface hardened layer can also be obtained by methods such as work hardening, grain refinement strengthening, dispersion strengthening, second phase strengthening, and heat treatment strengthening (such as quenching, carburizing, nitriding, and metallizing).

[0040] In an optional embodiment of the present invention, a wheel-rail dual-disc grinding tester is used to conduct a grinding test, which can carry out rolling contact fatigue tests on different surface hardened structures and obtain different degrees of peeling and spalling results.

[0041] In one optional example of this implementation, such as Figure 2a , Figure 2b As shown, the rail material sample is used as the main sample 10, and the wheel material sample is used as the auxiliary sample 20.

[0042] In an optional example, both the main specimen 10 and the auxiliary specimen 20 are annular in shape. The outer edge of the main specimen 10 is cut with a boss. During the grinding test, the boss of the main specimen 10 is ground against the outer edge of the auxiliary specimen to increase the contact stress between the main specimen and the auxiliary specimen.

[0043] Preferably, the boss is cut only on the main specimen 10, and the boss does not need to be cut on the auxiliary specimen 20.

[0044] In one optional example, the main sample 10 is annular with an outer radius of 30 mm, an inner radius of 15 mm, a boss width of 5 mm, a boss height of 3 mm, and the boss is arranged around the outer edge along the center line of the outer edge of the main sample; the auxiliary sample 20 is annular with a width of 20 mm.

[0045] Depending on the surface hardening process, the width of the boss can be adjusted appropriately to facilitate the preparation of the surface hardened layer. It should be noted that changes in the boss width do not affect the analysis of the test results, but the magnitude of the vertical load needs to be updated accordingly.

[0046] In another optional example of this implementation, the wheel material is used as the main specimen and the rail material is used as the secondary specimen.

[0047] In an optional embodiment of the present invention, the test parameters for the grinding test include at least contact stress, slip, medium, and termination rotation speed, and the selection of the above test parameters is matched with the flaking pattern of the phase change white layer.

[0048] Different surface hardening processes may result in different degrees of hardening, microstructure characteristics, and development patterns. Therefore, the termination rotation speed among the four key test parameters mentioned above needs to be adjusted flexibly.

[0049] In one optional example of this implementation, the contact stress includes at least the contact stress under high-speed railway conditions and the contact stress under conventional railway conditions, to take into account the two types of trains corresponding to the two operating conditions of high-speed railway and conventional railway.

[0050] Furthermore, it is agreed that the wheel-rail contact stress corresponding to the 17t axle load EMU is 1150MPa; and the wheel-rail contact stress corresponding to the 23t axle load locomotive is 1550MPa.

[0051] In an optional example of this implementation, the contact stress is calculated according to the Hertzian contact theory formula, then,

[0052]

[0053] In the formula, p0 is the contact stress, F is the vertical load applied to the specimen, L is the width of the specimen; ν1 is the Poisson's ratio of the main specimen, ν2 is the Poisson's ratio of the secondary specimen; E1 is the elastic modulus of the main specimen, E2 is the elastic modulus of the secondary specimen, ρ1 is the radius of curvature of the main specimen, and ρ2 is the radius of curvature of the secondary specimen.

[0054] The above formula can be applied to different loading capacities and different sample sizes, further expanding the universality of the evaluation method for the anti-peeling performance of the surface hardened layer of wheel and rail materials proposed in this invention.

[0055] Preferably, for rail steel and wheel steel, ν1=ν2=0.3, E1=E2=206GPa.

[0056] In this embodiment, the greater the slip difference between the main sample and the auxiliary sample, the greater the surface tangential force, and the faster the crack initiation and propagation. However, the wear rate also increases sharply. This embodiment focuses on the anti-peeling performance of the hardened layer and needs to reduce the interference of wear on crack propagation.

[0057] Furthermore, a slip of 1% is more appropriate.

[0058] In this embodiment, during the grinding test, no medium is selected between the main sample and the auxiliary sample; instead, a dry grinding state is used to match the actual working conditions.

[0059] It should be noted that during the grinding test, grease or liquid media can be added between the main sample and the auxiliary sample to generate an oil wedge effect, which can accelerate crack development. However, in actual working conditions, wheel-rail contact is mainly dry friction.

[0060] In this embodiment, the termination speed is also a key test parameter in the grinding test. The selection of the termination speed must ensure the measurability and comparability of the test data while improving test efficiency. When the termination speed is different, the appearance of the hardened layer will also be different after the test, such as... Figure 4a As shown, the appearance of the hardened layer after 100,000, 500,000, and 1,100,000 rotations can be seen. As the number of rotations increases, cracks gradually emerge from the starting end, and the number of cracks in the circumferential length direction gradually increases.

[0061] Preferably, after multiple comparative experiments, 500,000 revolutions was selected as the termination revolution.

[0062] In an optional embodiment of the present invention, evaluating the peel resistance of the hardened layer based on the measured data includes: characterizing the peeled-off area of ​​the hardened layer based on the measured data, and evaluating the peel resistance of the surface hardened layer based on the characterization results.

[0063] In this embodiment, the measurement data is the measurement data of the crack at the boss of the main specimen.

[0064] In an optional example of this implementation, the measured data includes at least the crack propagation arc length, the deepest crack depth D, and the angle θ between the deepest crack and the horizontal plane.

[0065] In an optional example, such as Figure 4a , Figure 4b As shown, cracks typically have two propagation paths. One propagation path is as follows: Figure 4a As shown, if the crack does not extend into the matrix and the deepest crack extends along the interface between the hardened layer and the matrix, then the angle between the deepest crack and the horizontal plane is fitted along the interface direction; another propagation path is as follows... Figure 4b As shown, if the crack extends into the matrix, the angle between the deepest crack and the horizontal plane is fitted along the direction of the deepest crack's extension.

[0066] In an optional example, characterizing the hardened layer peeling-off region includes calculating the macroscopic area of ​​the surface hardened layer peeling-off region, then...

[0067] S=L×D×A×tanθ (1-2)

[0068] In the formula, S is the macroscopic area of ​​the hardened layer peeled off, L is the crack propagation arc length, D is the deepest crack depth, A is the average amplitude value during the grinding test, and θ is the angle between the deepest crack and the horizontal plane.

[0069] Furthermore, such as Figure 3b As shown, after undergoing a (double-disc) grinding test, the surface of the sample was measured to obtain the crack propagation arc length L.

[0070] Meanwhile, the grinding tester is equipped with an amplitude sensor, which can monitor and record the vibration signal during the test. As the surface peels off and flakes, the roughness and smoothness are affected, and the vibration amplitude increases accordingly. Through data analysis, the average amplitude value A (amplitude) during the last 20,000 revolutions of the test is calculated.

[0071] In one optional example, the anti-scraping performance of the hardened layer is inversely proportional to the macroscopic area S of the hardened layer peeling off. Additionally, L×D represents the maximum area involved in crack propagation, A is an evaluation parameter for the degree of surface spalling, and tanθ is an evaluation parameter for the tendency of the crack to propagate in the depth direction.

[0072] The following is a detailed description of the specific implementation process of the evaluation method for the anti-peeling performance of the surface hardened layer of wheel and rail materials proposed in this invention, with reference to an embodiment:

[0073] I. Determine the research object and clarify whether the object to be evaluated is the surface hardening process or the material.

[0074] When rail steel is used as the main specimen, CL60 or ER8 wheel steel is selected as the secondary specimen; when wheel steel is used as the main specimen, U71Mn or U75V steel is selected as the secondary specimen.

[0075] In this embodiment, the surface hardening layer is prepared by laser quenching. The width of the contact boss in the processing dimensions of the main sample is 5 mm to match the width of the laser quenching and ensure the reliability of the test results.

[0076] At the same time, at least two sets of samples (main sample and auxiliary sample) need to be prepared for repeated testing.

[0077] II. Determine the parameters of the double-disc grinding test machine.

[0078] In this embodiment, as shown in Figure 2, the slip is selected as 1%, the termination speed is selected as 500,000, and the dry grinding state is still used.

[0079] In addition, supplementary test conditions can be provided, namely, setting the test machine to automatically stop when the amplitude reaches 3dB as the termination state. The total number of revolutions recorded at this time can be used as an evaluation index for the average amplitude value A.

[0080] 3. Conduct a double-disc grinding experiment.

[0081] The dual-disc grinding tester is equipped with an amplitude sensor to monitor and record the vibration signal during the test. As surface peeling and spalling occur, the roughness and smoothness are affected, and the vibration amplitude increases accordingly. Through data analysis, the average amplitude value A (amplitude) during the last 20,000 revolutions of the test is calculated.

[0082] IV. Laboratory Microscopic Characterization and Calculation

[0083] The specimens after the grinding test were cut open using wire cutting equipment to prepare two metallographic specimens: cross-section and longitudinal section. After grinding and polishing, they were etched with 4% nitric acid alcohol solution. Microcracks were observed under a metallographic microscope, and the crack propagation arc length L, the deepest crack depth D, and the angle θ between the deepest crack and the horizontal plane were measured.

[0084] Calculate the macroscopic area S of the hardened layer peeled off: S = L × D × A × tanθ, where L and D are in mm, A is in dB, and S is in mm. 2 The smaller the macroscopic area S value of the hardened layer peeled off, the stronger the peel resistance of the hardened layer.

[0085] The detailed explanations of the above embodiments are intended only to explain the present invention so as to facilitate a better understanding of the present invention. However, these descriptions should not be construed as limiting the present invention for any reason. In particular, the various features described in different embodiments can be arbitrarily combined with each other to form other embodiments. Unless there is an explicit description to the contrary, these features should be understood to be applicable to any embodiment, and not limited to the described embodiments.

Claims

1. A method for evaluating the peel resistance of the surface hardened layer of wheel and rail materials, characterized in that, The evaluation methods include: Prepare rail material samples and wheel material samples; The rail material sample and the wheel material sample are subjected to surface hardening treatment respectively to form a hardened layer on the surface of the rail material sample and the wheel material sample. A grinding test was conducted on the surface-hardened rail material sample and the surface-hardened wheel material sample. The cracks generated in the hardened layer after the grinding test were measured, and the anti-peeling performance of the hardened layer was evaluated based on the measured data. Evaluating the peel resistance of the hardened layer based on the measured data includes: characterizing the peeled-off area of ​​the hardened layer based on the measured data, and evaluating the peel resistance of the hardened layer based on the characterization results; The measured data includes at least the crack propagation arc length, the deepest crack depth, and the angle between the deepest crack and the horizontal plane; Characterizing the area where the hardened layer has peeled off includes calculating the macroscopic area of ​​the peeled-off area. S=L×D×A×tanθ (1-2) In the formula, S is the macroscopic area of ​​the hardened layer peeled off, L is the crack propagation arc length, D is the deepest crack depth, A is the average amplitude value during the grinding test, and θ is the angle between the deepest crack and the horizontal plane.

2. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 1, characterized in that, The wheel material sample was cut 5-15 mm below the center tread of the actual wheel.

3. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 1, characterized in that, The rail material sample was cut 5-15 mm below the center tread of the actual rail.

4. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 1, characterized in that, The rail material sample and the wheel material sample were surface hardened by laser quenching process.

5. The method for evaluating the peel resistance of the surface hardened layer of wheel and rail materials as described in claim 1, characterized in that, The grinding test was conducted using a wheel-rail dual-disc grinding test machine.

6. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 5, characterized in that, The rail material sample was used as the main sample, and the wheel material sample was used as the auxiliary sample.

7. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 5, characterized in that, The wheel material was used as the main specimen, and the rail material was used as the secondary specimen.

8. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 6 or 7, characterized in that, Both the main sample and the auxiliary sample are disc-shaped. The outer edge of the main sample has a protrusion cut out. During the grinding test, the protrusion of the main sample and the outer edge of the auxiliary sample are ground together.

9. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 8, characterized in that, The boss surrounds the outer edge along the center line of the outer edge.

10. The method for evaluating the peel resistance of the surface hardened layer of wheel and rail materials as described in claim 6 or 7, characterized in that, The test parameters for the grinding test include at least contact stress, slip, medium, and termination speed.

11. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 10, characterized in that, The contact stress includes at least the contact stress under high-speed railway conditions and the contact stress under conventional railway conditions.

12. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 10, characterized in that, The contact stress is calculated according to Hertzian contact theory formulas, then, In the formula, p0 is the contact stress, F is the vertical load applied to the specimen, L is the width of the specimen; ν1 is the Poisson's ratio of the main specimen, ν2 is the Poisson's ratio of the secondary specimen; E1 is the elastic modulus of the main specimen, E2 is the elastic modulus of the secondary specimen, ρ1 is the radius of curvature of the main specimen, and ρ2 is the radius of curvature of the secondary specimen.

13. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 1, characterized in that, If the crack does not extend into the matrix, and the deepest crack extends along the interface between the hardened layer and the matrix, then the angle between the crack and the horizontal plane is fitted along the interface direction; if the crack extends into the matrix, then the angle between the deepest crack and the horizontal plane is fitted along the extension direction of the deepest crack.

14. The method for evaluating the anti-peeling performance of the surface hardened layer of wheel and rail materials as described in claim 1, characterized in that, The peel resistance of the hardened layer is inversely proportional to the macroscopic area of ​​the peeled-off block.

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