Method for improving contact wear resistance of rail by adjusting pearlite interlamellar spacing

Abstract

The application discloses a method for improving the contact wear resistance of a rail by refining the pearlite lamellar spacing to 260-320 nm through a staged temperature control isothermal heat treatment process combined with micro stress induction, thereby significantly improving the wear resistance and fatigue resistance while ensuring high strength. The rolling contact wear test results under a load of 20-40 N show that the Brinell hardness of the rail sample prepared by the process is increased by about 16%, the average friction coefficient is reduced by 9.8%, the wear volume is reduced by about 24.5%, and the crack initiation life is increased by about 1.4 times. The method has stable process, accurate control, is suitable for batch manufacturing of U75V heavy load and high speed rail, and has a wide industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of rail technology, and particularly relates to a method for improving the contact wear resistance of rails by adjusting the spacing of pearlite lamellars. Background Technology

[0002] With the rapid development of railway transportation systems towards higher speeds and heavier loads, the wheel-rail contact stress is constantly increasing. The surface material of the rail is subjected to high-frequency alternating shear stress, making it prone to failure behaviors such as abrasive wear, fatigue cracks, spalling, and oxidative wear. In recent years, the main research direction for rail steel has focused on improving the contact damage resistance of the pearlitic microstructure through heat treatment or microalloying.

[0003] U75V steel, a typical rail steel for heavy-haul railways in my country, is primarily composed of refined pearlite. Studies have shown that the interlamellar spacing of pearlite is a key structural parameter determining wear resistance, strength, and fatigue performance. Many researchers have pointed out that lowering the isothermal temperature can effectively reduce the interlamellar spacing of U75V steel, significantly decreasing the coefficient of friction and wear rate, resulting in higher wear resistance.

[0004] In summary, controlling the pearlite lamellar spacing and lamellar orientation consistency is a key technical approach to improving the contact wear resistance of U75V rails. However, in existing technologies, the isothermal temperature is mostly above 600℃, the lamellar spacing is generally greater than 450 nm, resulting in coarse microstructure and insufficient crack resistance; furthermore, a systematic control method for U75V steel has not been developed. Therefore, a new comprehensive process is proposed to achieve synergistic optimization of pearlite lamellar refinement and orderly cementite distribution in the medium-low temperature range, in order to achieve U75V rail steel with high strength, high wear resistance, and high stability. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the contact wear resistance of rails by increasing the spacing between pearlite lamellars. By combining graded isothermal heat treatment with micro-stress induction, the pearlite lamellars are refined and evenly distributed, thereby achieving a comprehensive improvement in the hardness, wear resistance, and contact fatigue resistance of U75V rail steel. The innovative aspects of this method include: (1) Temperature precision control mechanism: reducing the traditional isothermal temperature of 630℃ to 510–580℃ to achieve a lamellar spacing of 260–320 nm; (2) Micro-stress induction orientation mechanism: applying 0.2–0.5 MPa axial compressive stress during the phase transformation process to promote consistent orientation of cementite lamellars; (3) Multi-parameter matching mechanism: achieving microstructure homogenization by controlling the cooling rate, holding time, and stress coupling; (4) Performance synergy mechanism: balancing strength and toughness to reduce the fatigue crack propagation rate by more than 20%.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing, comprising the following steps:

[0008] (1) Heat the U75V steel rail to 900℃±5℃ and hold for 30 min to obtain a uniform austenitic structure;

[0009] (2) Cool to 510-580℃ at 15-25℃ / min and hold for 10-20 min to achieve the isothermal transformation of austenite to pearlite;

[0010] (3) Apply axial compressive stress of 0.2-0.5 MPa (preferably 0.3 MPa) during the isothermal stage to promote the orderly arrangement of cementite layers;

[0011] (4) Remove and air cool to room temperature to obtain a refined microstructure with an average pearlite lamellar spacing of 260-320 nm and a cementite thickness of less than 100 nm.

[0012] Furthermore, the chemical composition of the U75V rail by mass percentage is as follows: C 0.70-0.80%, Mn 0.75-1.05%, Si 0.50-0.80%, V 0.08-0.10%, P≤0.03%, S≤0.03%; the remainder is Fe and impurities.

[0013] Furthermore, after heat treatment, the Brinell hardness is 250–265 HBW, the yield strength is not less than 980 MPa, and the coefficient of friction is ≤0.42.

[0014] Furthermore, its wear volume was reduced by more than 20% compared to the sample treated at 630℃ under conventional heat treatment, and the average length of fatigue cracks was reduced by 25%.

[0015] Furthermore, by refining the pearlite lamellar spacing and optimizing the cementite orientation, the service life of rails can be increased by more than 15%.

[0016] Furthermore, the chemical composition of the U75V rail by mass percentage is: C 0.75%, Mn 0.95%, Si 0.65%, V 0.09%, P≤0.002%, S≤0.002%, with the remainder being Fe and impurities.

[0017] Furthermore, the treated U75V rail exhibits: continuous and consistent distribution of cementite lamellae, tight bonding at the ferrite / cementite interface, and a uniform "white layer" hardened band on the surface.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] This method employs a staged, temperature-controlled isothermal heat treatment process combined with micro-stress induction to refine the pearlite lamellar spacing to 260–320 nm, thereby significantly improving wear resistance and fatigue resistance while maintaining high strength. Rolling contact wear tests under loads of 20–40 N show that rail samples prepared using this method exhibit an approximately 16% increase in Brinell hardness, a 9.8% reduction in the average coefficient of friction, an approximately 24.5% reduction in wear volume, and an approximately 1.4-fold increase in crack initiation life. This method is stable, precisely controlled, and suitable for the mass production of U75V heavy-duty and high-speed railway rails, demonstrating broad prospects for industrial application. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 This relates to the relationship between hardness and interlamellar spacing.

[0022] Figure 2 This relates the average friction coefficient to the interlamellar spacing.

[0023] Figure 3 This relates the wear volume to the interlamellar spacing.

[0024] Figure 4 This represents the relationship between the average crack length and the interlamellar spacing. Detailed Implementation

[0025] (1) Material composition: U75V rail steel (C 0.75%, Mn 0.95%, Si 0.65%, V 0.09%, P 0.002%, S 0.002%, the remainder being Fe and impurities) was selected, and the billet was wire-cut into 25 mm × 15 mm × 10 mm samples.

[0026] (2) Heat treatment process: Heat to 900℃±5℃ and hold for 30min to obtain uniform austenite; cool to the target temperature (510℃, 540℃, 580℃) at 20℃ / min and hold for 15min; apply 0.3 MPa axial compressive stress during the isothermal process; take out and air cool to room temperature.

[0027] (3) Microstructure analysis: SEM and EBSD were used to analyze the interlamellar spacing and orientation angle distribution. The results showed that the interlamellar spacing increased from 265 nm to 315 nm with the increase of isothermal temperature, and the uniformity of lamellar orientation improved by about 12%.

[0028] (4) Performance test: Using a rolling contact friction tester, with loads of 20, 30, and 40 N, frequency of 4 Hz, and friction time of 1800 s, the friction coefficient and wear volume were measured.

[0029] (5) Data processing and evaluation: Determine the depth and volume of wear marks and compare them with those of conventional process samples (630℃).

[0030] Three groups of samples were selected for comparative experiments. The specific experimental parameters are shown in Table 1.

[0031] Table 1 Comparative test parameters

[0032] Sample number Isothermal temperature (°C) Interlayer spacing (nm) Hardness (HBW) Average coefficient of friction Wear volume (×10⁻³ mm³) Average crack length (µm) A (This invention) 520 265 263 0.38 2.12 78 B (Medium-temperature control) 560 295 256 0.41 2.34 94 C (Standard temperature 630℃) 630 490 224 0.44 2.83 115

[0033] analyze Figures 1-4 As shown in Table 1, the hardness of sample A increased by 17.4%; the coefficient of friction decreased by 13.6%; the wear volume decreased by 25.1%; and the average crack length decreased by 32.2%, indicating a significant improvement in fatigue crack propagation resistance.

[0034] Microstructural observation revealed that cementite lamellars in sample A were continuously distributed and uniformly oriented, with a tight bond at the ferrite / cementite interface. A uniform "white layer" hardened band, approximately 4.5 µm thick, formed on the surface, effectively dispersing contact stress. Fatigue wear was mainly characterized by shallow grooved abrasive wear, without obvious spalling pits.

[0035] The overall results show that the combined process of isothermal temperature control and micro-stress induction proposed in this invention can effectively refine pearlite lamellae, improve the contact wear resistance of U75V rails, and provide a new approach for extending the service life of rail steel.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing, characterized in that, Includes the following steps: (1) Heat the U75V steel rail to 900℃±5℃ and hold for 30 min to obtain a uniform austenitic structure; (2) Cool to 510-580℃ at 15-25℃ / min and hold for 10-20 min to achieve the isothermal transformation of austenite to pearlite; (3) Apply axial compressive stress of 0.2-0.5 MPa during the isothermal stage to promote the orderly arrangement of cementite layers; (4) Remove and air cool to room temperature to obtain a refined microstructure with an average pearlite lamellar spacing of 260-320 nm and a cementite thickness of less than 100 nm.

2. The method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing according to claim 1, characterized in that, The chemical composition of the U75V steel rail by mass percentage is as follows: C 0.70-0.80%, Mn 0.75-1.05%, Si 0.50-0.80%, V 0.08-0.10%, P≤0.03%, S≤0.03%; the remainder is Fe and impurities.

3. The method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing according to claim 1, characterized in that, After heat treatment, the Brinell hardness is 250–265 HBW, the yield strength is not less than 980 MPa, and the coefficient of friction is ≤0.

42.

4. The method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing according to claim 1, characterized in that, Its wear volume is reduced by more than 20% compared with the sample that was conventionally heat-treated at 630℃, and the average length of fatigue cracks is reduced by 25%.

5. The method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing according to claim 1, characterized in that, By refining the pearlite lamellar spacing and optimizing the cementite orientation, the service life of rails can be increased by more than 15%.

6. The method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing according to claim 1, characterized in that, The chemical composition of the U75V rail by mass percentage is: C 0.75%, Mn 0.95%, Si 0.65%, V 0.09%, P≤0.002%, S≤0.002%, with the remainder being Fe and impurities.

7. The method for improving the contact wear resistance of rails by adjusting the pearlite lamellar spacing according to claim 6, characterized in that, The treated U75V rail has a continuous distribution of cementite lamellae with consistent orientation, and a tight bond between the ferrite / cementite interface; a uniform "white layer" hardened band is formed on the surface.

Images