Tungsten-containing hollow axle for high-speed train with speed ≥400 km / h and production method thereof

Abstract

The application discloses a tungsten-containing hollow axle for high-speed rail with a speed of more than or equal to 400 kilometers per hour and a production method thereof, and belongs to the technical field of high-speed rail axles. The tungsten-containing hollow axle contains C, Si, Mn, W, V, Al and N in the composition and satisfies G0=14C+17Mn+3Si+16V+12W>=21 and K=-28C-6Si+2Mn+20W-2V>=-3.6. The scheme realizes preparation of the axle with fatigue strength of more than 500 MPa, surface hardness of more than or equal to 600 HV and surface residual compressive stress of more than -810 MPa, and the axle has good rigidity and is suitable for manufacturing the hollow axle for high-speed rail with a speed of more than or equal to 400 kilometers per hour.

Description

Technical Field

[0001] This invention belongs to the field of high-speed rail axle technology, specifically relating to a tungsten-containing hollow axle for high-speed rail with a speed of ≥400 km / h and its manufacturing method. Background Technology

[0002] Heavy-haul and high-speed are the two major development directions for railway vehicles. High-speed rail, as a typical representative of high-speed rail, marks the most advanced level of China's rail transit industry. Lightweight technology for high-speed rail car bodies is of great significance for improving train operating efficiency and energy conservation, and is also one of the current hot topics in high-speed rail technology research and development.

[0003] The axle is an ultra-large, stepped, axisymmetric component that forms a wheelset with the wheels via an interference fit. It bears the entire weight of the vehicle and is one of the three key components of railway vehicles. As the heaviest single moving part, reducing the axle's weight is a crucial means of achieving lightweighting of high-speed train bodies, leading to the development of hollow axles. However, due to the reduced wall thickness, hollow axles not only require higher material strength and toughness than solid axles, but also need sufficient rigidity. Otherwise, insufficient rigidity can cause axle deformation, affecting vehicle operation safety and causing significant losses.

[0004] Currently, commonly used materials for high-speed rail axle steel include EA1N, EA4T, S38C, DZ1, and DZ2. However, materials such as EA1N and S38C have relatively low strength, while materials such as EA4T, DZ1, and DZ2 have relatively low low-temperature toughness, making them unsuitable for use in cold and high-altitude regions. With the continuous increase in the speed and lightweight requirements of high-speed rail, the need to develop axle materials with high strength, toughness, rigidity, and fatigue life is becoming increasingly urgent. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h and its manufacturing method. It achieves the preparation of axles with fatigue strength exceeding 500 MPa, surface hardness ≥600 HV, and surface residual compressive stress exceeding -810 MPa. It has good rigidity and is suitable for manufacturing hollow axles for high-speed trains with a speed of ≥400 km / h.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h. The tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h comprises the following chemical composition by mass percentage: C 0.42%~0.48%, Si 0.20%~0.40%, Mn 0.50%~0.60%, P trace~0.012%, S trace~0.008%, W 0.40%~0.60%, V 0.020~0.040%, Ni≤0.30%, Cr≤0.30%, Mo≤0.30%, Al 0.025%~0.040%, Cu≤0.20%, N 0.0040%~0.0080%, TO≤0.0010%, with the remainder being Fe and other unavoidable impurities.

[0008] The chemical composition satisfies:

[0009] G0=14C+17Mn+3Si+16V+12W, G0≥21;

[0010] K=-28C-6Si+2Mn+20W-2V, K ≥-3.6;

[0011] In the above formula, the value of each component is taken as its content in steel × 100.

[0012] The metallographic structure of the tungsten-containing hollow axle used in high-speed trains with a speed of ≥400 km / h is martensite.

[0013] The tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h has a fatigue strength exceeding 500 MPa, a surface hardness exceeding 600 HV, and a surface residual compressive stress exceeding -810 MPa. Compared with the axle sample without laser quenching, the fatigue strength is increased by more than 70%, and it has good rigidity. It is suitable for manufacturing hollow axles for high-speed trains with a speed of ≥400 km / h.

[0014] The present invention also provides a method for producing tungsten-containing hollow axles for high-speed trains with a speed of ≥400 km / h. The method includes the following steps: forging axle blanks → rough turning of the blank axle → machining of the axle end face → heat treatment → machining of the axle center through hole and finish turning of the outer diameter → grinding of the axle surface → flaw detection → laser quenching → grinding of the outer diameter.

[0015] Furthermore, the heat treatment is normalizing treatment, and the normalizing treatment method is as follows: heat the axle to 900~940℃, keep it at that temperature for 6~8 hours, and then air cool it to below 200℃.

[0016] After the normalizing treatment, the axle has a tensile strength ≥630MPa, a yield strength ≥350MPa, and an elongation A ≥27%.

[0017] After the normalizing treatment, the metallographic structure of the axle consists of ferrite and pearlite.

[0018] In the laser quenching step, the entire length of the axle is laser quenched, the hardened layer depth is 1.6~2.0mm, the laser output power is 4000~8000W, the laser scanning speed is 300~400mm / min, and the laser overlap rate is controlled between 20% and 28%.

[0019] In the laser quenching step, a rectangular laser spot is used for laser quenching, with the length of the rectangular laser spot controlled at 15~25mm and the width controlled at 3~5mm.

[0020] The central through hole diameter of the tungsten-containing hollow axle used for high-speed trains with a speed of ≥400 km / h is φ30mm ~φ60mm, and it is machined after heat treatment.

[0021] The comprehensive stiffness index G of the tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h conforms to the following with respect to the chemical composition ratio, the diameter D of the central through hole, and the hardened layer depth H: G=G0+30H-0.4D, 46≤ G ≤72, where the unit of D is mm.

[0022] The functions and control of each component in the tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h provided by this invention are as follows:

[0023] C: C is the cheapest strengthening element in steel. C forms precipitates with alloying elements in steel, resulting in precipitation strengthening. C can significantly improve hardenability, enabling large-sized axles to acquire a martensitic structure. However, as its content increases, plasticity and toughness decrease, so the C content is controlled between 0.42% and 0.48%.

[0024] Si: Si is an effective solid solution strengthening element in steel. It also acts as a deoxidizer during steelmaking. However, Si tends to segregate at austenite grain boundaries, reducing grain boundary bonding and causing brittleness. Furthermore, Si easily causes elemental segregation in steel. Therefore, the Si content is controlled between 0.20% and 0.40%.

[0025] Mn: Mn can play a solid solution strengthening role. As an austenite stabilizing element, Mn can significantly improve the hardenability of steel. Mn can significantly improve the stiffness of steel, and the combination of Mn and S can prevent hot brittleness caused by S. However, excessive Mn will reduce the plasticity of steel. Therefore, the Mn content should be controlled between 0.50% and 0.60%.

[0026] W: W is a strong carbide-forming element. The carbides formed can pin grain boundaries during high-temperature austenitization, preventing grain growth and thus improving the strength and toughness of the material. The W content is controlled at 0.40%~0.60%.

[0027] Al: Al is a strong deoxidizing element and also improves the oxidation resistance of steel. However, with the increase of Al content, the amount of coarse carbonitride inclusions increases. The Al content should be controlled between 0.025% and 0.035%.

[0028] TO and N: TO forms oxide inclusions in steel, and TO should be controlled to ≤0.0010%; N can form compounds with Al and other materials, refining the grains. A reasonable Al / N ratio has a significant effect on grain refinement, while excessive N can form continuous casting defects such as bubbles. Therefore, the N content should be controlled between 0.0040% and 0.0080%.

[0029] To ensure sufficient stiffness in the axle, the alloying elements affecting stiffness need to be properly matched. Carbon (C) significantly improves stiffness, with a stiffness influence factor of 14. Mn (Mn) is also a major element in improving stiffness, and its substitution effect is stronger and more significant, with a stiffness influence factor of 17. V (Volume) also has a significant impact on stiffness, with a stiffness influence factor of 16. W (Welfare) improves the stiffness of steel through carbides, with a stiffness influence factor of 12. Based on the contribution of each alloying element to stiffness, the stiffness coefficient G0 should meet the following requirements:

[0030] G0=14C+17Mn+3Si+16V+12W≥21.

[0031] A relentless pursuit of high strength and stiffness often leads to a deterioration in the toughness of steel. To ensure high toughness, the proportions of various alloying elements must be carefully controlled. While C, Si, and V can improve stiffness to varying degrees, they are detrimental to toughness. Based on the influence of each alloying element on toughness, the toughness coefficient K should meet the following requirements:

[0032] K=-28C-6Si+2Mn+20W-2V≥-3.6.

[0033] Because axles are ultra-large, stepped, axisymmetric parts with large dimensions, and the aforementioned axle steel contains relatively few alloying elements, overall quenching and tempering would result in poor hardenability, leading to poor uniformity of the final axle microstructure, significant differences in surface and core microstructure, and extremely low cost-effectiveness. Surface laser hardening would only slightly improve the axle's fatigue performance. The present invention provides a method for producing tungsten-containing hollow axles for high-speed trains with speeds ≥400 km / h, which involves only overall normalizing pretreatment of the axle to obtain a fine-grained, uniform ferrite + pearlite microstructure. This microstructure readily yields uniform austenite during subsequent heating, which transforms into uniform martensite after laser hardening, thus forming a high-hardness hardened layer on the axle surface and significantly improving its fatigue performance.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The axle of this invention, after normalizing pretreatment, obtains a fine and uniform ferrite + pearlite structure. After laser quenching, it transforms into a uniform martensite structure, thereby forming a high-hardness hardened layer with a surface hardness ≥600HV on the axle surface. The surface hardness and strength are greatly improved, enhancing the resistance to plastic distortion of the sample surface. At the same time, residual compressive stress is formed on the axle surface, with the near-surface residual compressive stress exceeding -810MPa, which greatly reduces the effective tensile stress borne by the sample surface and significantly improves the durability limit stress of the surface layer. In addition, due to the high phase transformation temperature during laser quenching, the austenite nucleation rate is large and does not have sufficient time to grow, resulting in the actual grain size of the austenite in the hardened layer being much finer than the grain size of the matrix. The grain size of the surface layer is significantly refined, all of which contribute to improving fatigue performance. The fatigue strength is ≥500MPa, exhibiting excellent fatigue resistance, which is significantly better than that of the same material without laser quenching. After laser quenching, the fatigue strength of the axle increases by more than 71%. Because the larger the diameter of the central through hole of the hollow axle, the greater the impact on the stiffness of the finished axle, in order to ensure that the hollow axle has sufficient stiffness, this invention adjusts the alloy composition and laser quenching depth to achieve effective control of the stiffness of the hollow axle of high-speed trains with a speed of ≥400 km / h.

[0036] The tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h provided by this invention has a fatigue strength of over 500 MPa, a surface hardness of ≥600 HV, and a surface residual compressive stress of over -810 MPa. Compared with the same material axle that has not been laser hardened, the fatigue strength of the axle is increased by more than 71%, and it also has good rigidity. It is suitable for manufacturing hollow axles for high-speed trains with a speed of ≥400 km / h. Detailed Implementation

[0037] This invention provides a tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h. The tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h comprises the following chemical composition by mass percentage: C 0.42%~0.48%, Si 0.20%~0.40%, Mn 0.50%~0.60%, P trace~0.012%, S trace~0.008%, W 0.40%~0.60%, V 0.020~0.040%, Ni≤0.30%, Cr≤0.30%, Mo≤0.30%, Al 0.025%~0.040%, Cu≤0.20%, N 0.0040%~0.0080%, TO≤0.0010%, with the remainder being Fe and other unavoidable impurities.

[0038] The chemical composition satisfies:

[0039] G0=14C+17Mn+3Si+16V+12W, G0≥21;

[0040] K=-28C-6Si+2Mn+20W-2V, K ≥-3.6;

[0041] In the above formula, the value of each component is taken as its content in steel × 100.

[0042] The production method of the tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h includes the following steps: axle blank forging → rough turning of the blank axle → axle end face machining → normalizing treatment → machining of the axle center through hole and finish turning of the outer circle → axle surface grinding → flaw detection → laser quenching → outer circle grinding.

[0043] Furthermore, the normalizing treatment method is as follows: heat the axle to 900~940℃, keep it at that temperature for 6~8 hours, and then air cool it to below 200℃.

[0044] In the laser quenching step, the entire length of the axle is laser quenched, the hardened layer depth H is 1.6~2.0mm, the laser output power is 4000~8000W, the laser scanning speed is 300~400mm / min, and the laser overlap rate is controlled between 20% and 28%.

[0045] In the laser quenching step, a rectangular laser spot is used for laser quenching, with the length of the rectangular laser spot controlled at 15~25mm and the width controlled at 3~5mm.

[0046] The present invention will now be described in detail with reference to the embodiments.

[0047] The composition and weight percentage of the hollow axles in each embodiment and comparative example are shown in Table 1.

[0048] Table 1

[0049]

[0050] The normalizing process parameters for the hollow axles in each embodiment and comparative example are shown in Table 2.

[0051] Table 2

[0052]

[0053] The mechanical properties of the hollow axles in each embodiment and comparative example after normalizing heat treatment are shown in Table 3.

[0054] Table 3 Mechanical properties of the examples and comparative examples

[0055]

[0056] The laser quenching process parameters for the hollow axles in each embodiment and comparative example are shown in Table 4, wherein Comparative Example 1 does not undergo laser quenching.

[0057] Table 4

[0058]

[0059] Table 5 compares the fatigue strength, surface hardness, maximum residual compressive stress, and stiffness coefficient of the hollow axles in Examples 1-5, 2, 3, and 4 after laser quenching treatment. The fatigue strength test was conducted according to GB / T 4337 "Metallic Materials - Fatigue Testing - Rotational Bending Method", the surface hardness test was conducted according to GB / T 4340.1-2024 "Metallic Materials - Vickers Hardness Testing - Part 1: Test Methods", and the maximum residual compressive stress test was conducted according to GB / T 7704-2017 "Non-destructive Testing - X-ray Stress Measurement Method".

[0060] Table 5

[0061]

[0062] As can be seen, after laser quenching, the fatigue cycle count in each embodiment is 1×10⁻⁶. 8 The fatigue strength is ≥500MPa, the surface hardness is ≥600HV, and the surface residual compressive stress exceeds -810MPa. Compared with the fatigue strength (292MPa) of the axle sample in Comparative Example 1 without laser quenching, these figures are increased by 73%, 75%, and 77%, respectively. Compared with Comparative Example 4, all embodiments show improved fatigue strength and impact toughness while maintaining stiffness. In summary, all embodiments not only possess good fatigue strength and impact toughness but also good overall stiffness, making them suitable for manufacturing hollow axles for high-speed trains with speeds ≥400 km / h.

[0063] In Comparative Example 2, the contents of C, Si, and Mn were too high, the content of W was too low, and the normalizing temperature and holding time were also low. Although the same laser quenching process as in Example 1 was used, the fatigue strength was reduced by 155 MPa compared to Comparative Example 1, and the stiffness was also reduced.

[0064] The difference between Comparative Example 3 and Comparative Example 2 is that the stiffness of the axle will further decrease after the diameter of the central through hole of the axle in Comparative Example 3 is increased.

[0065] The above detailed description of a tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h and its production method is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, changes and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h, characterized in that, The tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h comprises the following chemical composition by mass percentage: C 0.42%~0.48%, Si 0.20%~0.40%, Mn 0.50%~0.60%, P trace~0.012%, S trace~0.008%, W 0.40%~0.60%, V 0.020~0.040%, Ni≤0.30%, Cr≤0.30%, Mo≤0.30%, Al 0.025%~0.040%, Cu≤0.20%, N 0.0040%~0.0080%, TO≤0.0010%, with the remainder being Fe and other unavoidable impurities; The chemical composition satisfies: G0=14C+17Mn+3Si+16V+12W, G0≥21; K=-28C-6Si+2Mn+20W-2V, K ≥-3.

6.

2. The tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h as described in claim 1, characterized in that, The metallographic structure of the tungsten-containing hollow axle used in high-speed trains with a speed of ≥400 km / h is martensite.

3. The tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h as described in claim 1, characterized in that, The tungsten-containing hollow axles used in high-speed trains with a speed of ≥400 km / h have a fatigue strength exceeding 500 MPa, a surface hardness exceeding 600 HV, and a surface residual compressive stress exceeding -810 MPa.

4. The method for producing tungsten-containing hollow axles for high-speed trains with a speed of ≥400 km / h as described in any one of claims 1-3, characterized in that, The production method includes the following steps: forging of axle blank → rough turning of blank axle → machining of axle end face → heat treatment → machining of axle center through hole and finish turning of outer diameter → grinding of axle surface → flaw detection → laser quenching → grinding of outer diameter.

5. The production method according to claim 4, characterized in that, The heat treatment is normalizing treatment, and the normalizing treatment method is as follows: heat the axle to 900~940℃, keep it at that temperature for 6~8 hours, and then air cool it to below 200℃.

6. The production method according to claim 5, characterized in that, After the normalizing treatment, the axle has a tensile strength ≥630MPa, a yield strength ≥350MPa, and an elongation A ≥27%.

7. The production method according to claim 5, characterized in that, After the normalizing treatment, the metallographic structure of the axle consists of ferrite and pearlite.

8. The production method according to claim 4, characterized in that, In the laser quenching step, the entire length of the axle is laser quenched, the hardened layer depth H is 1.6~2.0mm, the laser output power is 4000~8000W, the laser scanning speed is 300~400mm / min, and the laser overlap rate is controlled between 20% and 28%.

9. The production method according to claim 4, characterized in that, In the laser quenching step, a rectangular laser spot is used for laser quenching, with the length of the rectangular laser spot controlled at 15~25mm and the width controlled at 3~5mm.

10. The production method according to claim 4, characterized in that, The comprehensive stiffness index G of the tungsten-containing hollow axle for high-speed trains with a speed of ≥400 km / h conforms to the following with respect to the chemical composition ratio, the diameter D of the central through hole, and the hardened layer depth H: G=G0+30H-0.4D, 46≤G≤72, where D is in mm.

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