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

Abstract

The application discloses a high-rigidity 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 high-rigidity hollow axle contains C, Si, Mn, Cr, Ni, Mo, Nb, Co and Al, and satisfies G0=14C+17Mn+7.2Cr+9Ni+15Mo+3Si+11Nb+12Co>=32 and K=-28C-6Si+2Mn+10Mo+18Ni+3Cr+20Nb+17Co>=7. The scheme realizes preparation of the axle with fatigue strength of more than 720 MPa, surface hardness of more than or equal to 650 HV and surface residual compressive stress of more than -810 MPa, and the axle has good rigidity and is suitable for manufacturing the high-speed rail hollow axle 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 high-rigidity 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 high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h and its manufacturing method. It realizes the preparation of axles with fatigue strength exceeding 720 MPa, surface hardness ≥650 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 high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h, comprising the following chemical composition by mass percentage: C: 0.32~0.38%, Si: 0.15~0.25%, Mn: 0.40~0.60%, P≤0.010%, S≤0.008%, Cr: 1.40~1.60%, Ni: 0.40~0.48%, Mo: 0.12~0.18%, Nb: 0.020~0.030%, Co: 0.20~0.28%, Cu≤0.10%, Al: 0.020~0.038%, with the remainder being Fe and other unavoidable impurities;

[0008] The chemical composition satisfies:

[0009] G0=14C+17Mn+7.2Cr+9Ni+15Mo+3Si+11Nb+12Co, G0≥32;

[0010] K=-28C-6Si+2Mn+10Mo+18Ni+3Cr+20Nb+17Co, K ≥7;

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

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

[0013] The high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h has a fatigue strength exceeding 720 MPa, a surface hardness exceeding 650 HV, and a surface residual compressive stress exceeding -810 MPa.

[0014] This invention also provides a method for producing high-rigidity hollow axles for high-speed trains with speeds ≥ 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 hardening → grinding of the outer diameter; the heat treatment includes normalizing, quenching and high-temperature tempering.

[0015] The normalizing method is as follows: heat the axle to 910~940℃, keep it at that temperature for 4~6 hours, and then air cool it to below 300℃.

[0016] The quenching method is as follows: heat to 890~930℃, hold for 3~5 hours, and then water cool to below 80℃.

[0017] The high-temperature tempering method is as follows: heat to 580~650℃, hold for 7~9 hours, and then air cool to below 80℃.

[0018] The metallographic structure of the heat-treated axle is tempered sorbite. The tensile strength of the heat-treated axle is ≥860MPa, the yield strength is ≥720MPa, and the elongation A is ≥23%.

[0019] After being normalized, quenched, and tempered, the steel is machined into hollow axles with a central through-hole diameter of φ60mm to φ120mm.

[0020] In the laser quenching step, the entire length of the axle is laser quenched, the hardened layer depth H is 1.4~2.0mm, the laser output power is 3000~8000W, the laser scanning speed is 400~1000mm / min, and the laser overlap rate is controlled between 20% and 28%.

[0021] 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 5~6mm.

[0022] Since the material of the axle steel, the diameter of the central through hole, and the laser hardening depth all affect the stiffness of high-speed rail axles, the chemical composition ratio, the diameter D of the central through hole, and the hardened layer depth H of the high-rigidity hollow axles for high-speed rail with a speed ≥ 400 km / h should meet the following requirements, based on the degree of influence:

[0023] 47≤G= G0+28H-0.3D≤74.

[0024] G is the comprehensive stiffness index, which is used to characterize the stiffness of hollow axles of high-speed trains with a speed of ≥400 km / h. In the calculation, the numerical parts of the element percentage content, laser hardening depth, and central through hole diameter are directly used.

[0025] The functions and control of each component in the high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h provided by this invention are as follows:

[0026] Carbon (C): Carbon is the cheapest strengthening element in steel. Each 0.1% increase in dissolved C can increase strength by approximately 450 MPa. C forms precipitates with alloying elements in steel, resulting in precipitation strengthening. C significantly improves hardenability, enabling large-sized axles to achieve a martensitic structure. However, as its content increases, plasticity and toughness decrease; therefore, the C content is controlled between 0.32% and 0.38%.

[0027] Si: Si is an effective solid solution strengthening element in steel, improving its stiffness. Si 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 0.15% and 0.25%.

[0028] 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 0.40% and 0.60%.

[0029] Cr: Cr is a carbide-forming element. Cr can improve the hardenability and stiffness of steel, but it easily causes temper brittleness. Cr can improve the oxidation resistance and corrosion resistance of steel, but excessive Cr content will increase the susceptibility to reheat cracking. The Cr content should be controlled between 1.40% and 1.60%.

[0030] Mo: Mo primarily improves the hardenability and tempering stiffness of steel. Mo dissolved in the matrix allows the steel to maintain high stiffness during tempering and reduces the segregation of impurity elements at grain boundaries, thereby improving toughness and reducing temper brittleness. However, adding too much Mo, a precious metal, would lead to excessively high costs. Therefore, Mo is controlled within the range of 0.12% to 0.18%.

[0031] Ni: Ni can form an infinitely miscible solid solution with Fe. It is an austenite stabilizing element, expanding the phase region, increasing the stability of supercooled austenite, shifting the C-curve to the right, and improving the hardenability of steel. Ni can refine the width of martensite laths, increasing strength. Ni significantly lowers the ductile-brittle transition temperature of steel and improves low-temperature toughness. Ni is a precious metal element; excessive addition leads to excessively high costs. The Ni content should be controlled between 0.40% and 0.48%.

[0032] Nb: Nb can dissolve in steel and form compounds with C and N, which strengthen and toughen the steel. Furthermore, Nb can form interfaces with high mismatch angles, increasing crack propagation energy and thus improving fatigue life. Therefore, the Nb content is controlled between 0.020% and 0.030%.

[0033] Co: Co can reduce the aggregation and growth rate of carbides during tempering, improve the tempering stability of martensite, and form a complex with Mo, promoting the dispersed precipitation of intermetallic compounds, thus achieving extremely high strength while maintaining good toughness. The Co content should be controlled at 0.20~0.28%.

[0034] 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 is controlled between 0.020% and 0.038%.

[0035] To ensure sufficient stiffness in the axle, the alloying elements affecting stiffness need to be properly matched. C significantly improves stiffness, with a stiffness influence factor of 14. 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. Mo also has a significant impact on stiffness, with a stiffness influence factor of 15. Cr improves steel stiffness through solid solution and carbides, with a stiffness influence factor of 7.2. Co's composite strengthening effect has 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:

[0036] G0=14C+17Mn+7.2Cr+9Ni+15Mo+3Si+11Nb+12Co≥32.

[0037] 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 and Si 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:

[0038] K=-28C-6Si+2Mn+10Mo+18Ni+3Cr+20Nb+17Co≥7.

[0039] Because axles are ultra-large, stepped, axisymmetric parts with large dimensions, and the carbon steel contains very few alloying elements, only normalizing treatment results in low overall strength and toughness. If overall quenching and tempering is performed, the poor hardenability of carbon steel leads to poor uniformity of the axle's microstructure, with significant differences in surface and core microstructure and toughness. Surface laser hardening offers limited improvement in fatigue performance, resulting in extremely low cost-effectiveness. The high-rigidity hollow axle for high-speed trains with speeds ≥400 km / h provided in this invention has strong hardenability. After overall normalizing + quenching + high-temperature tempering heat treatment, a relatively uniform tempered sorbite microstructure is obtained. During subsequent heating, uniform austenite is easily obtained, which transforms into uniform martensite after laser hardening, thus forming a high-hardness hardened layer on the axle surface, significantly improving fatigue performance.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The axle of this invention, after pretreatment with "normalizing + quenching + high-temperature tempering," obtains a uniform tempered sorbite structure. During subsequent heating, this readily yields uniform austenite, which, after laser quenching, transforms into a uniform martensite structure. This results in a high-hardness hardened layer with a surface hardness ≥650 HV on the axle surface, significantly improving surface hardness and strength, enhancing the resistance to plastic distortion on the sample surface. Simultaneously, residual compressive stress is formed on the axle surface, with near-surface residual compressive stress exceeding -810 MPa, greatly reducing the effective tensile stress on the sample surface and significantly improving the surface durability limit stress. Furthermore, due to the high phase transformation temperature during laser quenching, the austenite... The high nucleation rate of austenite and insufficient growth time result in a hardened austenite grain size that is much finer than that of the matrix, and the surface grain size is significantly refined. Both of these factors contribute to improved fatigue performance, with a fatigue strength ≥720MPa, which is more than 60% higher than the fatigue strength of the un-laser-quenched train axle sample (451MPa). Since the larger the diameter of the central through hole of the hollow axle, the greater the impact on the stiffness of the finished axle, this invention achieves effective control of the stiffness of the hollow axle of high-speed trains with a speed ≥400 km / h by adjusting the alloy composition and laser quenching depth to ensure that the hollow axle has sufficient stiffness.

[0042] The high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h provided by this invention achieves a fatigue strength of over 720 MPa, a surface hardness of ≥650 HV, and a surface residual compressive stress of over -810 MPa by optimizing the steel composition, combined with heat treatment process and laser quenching, and has good rigidity. It is suitable for manufacturing hollow axles for high-speed trains with a speed of ≥400 km / h. Attached Figure Description

[0043] Figure 1 The metallographic structure of the axle after normalizing in Example 1;

[0044] Figure 2 The metallographic structure of the axle after laser quenching in Example 1. Detailed Implementation

[0045] This invention provides a high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h. The high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h comprises the following chemical composition by mass percentage: C: 0.32~0.38%, Si: 0.15~0.25%, Mn: 0.40~0.60%, P≤0.010%, S≤0.008%, Cr: 1.40~1.60%, Ni: 0.40~0.48%, Mo: 0.12~0.18%, Nb: 0.020~0.030%, Co: 0.20~0.28%, Cu≤0.10%, Al: 0.020~0.038%, with the remainder being Fe and other unavoidable impurities.

[0046] The chemical composition satisfies:

[0047] G0=14×C+17×Mn+7.2×Cr+9×Ni+15×Mo+3×Si+11×Nb+12×Co, G0≥32;

[0048] K = -28×C - 6×Si + 2×Mn + 10×Mo + 18×Ni + 3×Cr + 20×Nb + 17×Co, K ≥ 7. In the above formula, the value of each component is its content in steel × 100.

[0049] The production method of the high-rigidity 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 → heat 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; the heat treatment includes normalizing, quenching and high-temperature tempering.

[0050] The normalizing method is as follows: heat the axle to 910~940℃, keep it at that temperature for 4~6 hours, and then air cool it to below 300℃;

[0051] The quenching method is as follows: heat to 890~930℃, hold for 3~5 hours, and then water cool to below 80℃;

[0052] The high-temperature tempering method is as follows: heat to 580~650℃, hold for 7~9 hours, and then air cool to below 80℃.

[0053] In the laser quenching step, the entire length of the axle is laser quenched, the hardened layer depth H is 1.4~2.0mm, the laser output power is 3000~8000W, the laser scanning speed is 400~1000mm / min, and the laser overlap rate is controlled between 20% and 28%.

[0054] The present invention will now be described in detail with reference to the embodiments.

[0055] The composition and weight percentage of the hollow axles in each embodiment and comparative example are shown in Table 1.

[0056] Table 1

[0057]

[0058] The heat treatment process parameters of the hollow axles in each embodiment and comparative example are shown in Table 2.

[0059] Table 2

[0060]

[0061] The mechanical properties of the hollow axles in each embodiment and comparative example after heat treatment are shown in Table 3.

[0062] Table 3 Mechanical properties of the examples and comparative examples

[0063]

[0064] 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.

[0065] Table 4

[0066]

[0067] 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".

[0068] Table 5

[0069]

[0070] As can be seen, after laser quenching, the fatigue cycle count in each embodiment is 1×10⁻⁶. 8 The fatigue strength is ≥720MPa, surface hardness is ≥650HV, and surface residual compressive stress exceeds -810MPa. Compared with the fatigue strength (451MPa) of the axle sample in Comparative Example 1 without laser quenching, these figures are 60%, 64%, and 67% higher, respectively. Compared with the other examples, Comparative Example 4 is inferior in fatigue strength, impact toughness, and stiffness. In summary, the various examples not only possess good fatigue strength but also good overall stiffness, making them suitable for manufacturing hollow axles for high-speed trains with speeds ≥400 km / h.

[0071] The composition, G0, K values ​​and heat treatment process of Comparative Example 2 do not meet the requirements of this application. Although the same laser quenching process as Example 1 was used, the fatigue strength was reduced by 134 MPa compared with Comparative Example 1, and the stiffness was also reduced.

[0072] 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.

[0073] The above detailed description of a high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h and its manufacturing 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 high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h, characterized in that, The high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h comprises the following chemical composition by mass percentage: C: 0.32~0.38%, Si: 0.15~0.25%, Mn: 0.40~0.60%, P≤0.010%, S≤0.008%, Cr: 1.40~1.60%, Ni: 0.40~0.48%, Mo: 0.12~0.18%, Nb: 0.020~0.030%, Co: 0.20~0.28%, Cu≤0.10%, Al: 0.020~0.038%, with the remainder being Fe and other unavoidable impurities; The chemical composition satisfies: G0=14C+17Mn+7.2Cr+9Ni+15Mo+3Si+11Nb+12Co, G0≥32; K=-28C-6Si+2Mn+10Mo+18Ni+3Cr+20Nb+17Co, K ≥7.

2. The high-rigidity 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 high-rigidity hollow axle used in high-speed trains with a speed of ≥400 km / h is martensite.

3. The high-rigidity hollow axle for high-speed trains with a speed ≥ 400 km / h as described in claim 1 or 2, characterized in that, The high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h has a fatigue strength exceeding 720 MPa, a surface hardness exceeding 650 HV, and a surface residual compressive stress exceeding -810 MPa.

4. The method for producing high-rigidity 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; the heat treatment includes normalizing, quenching and high-temperature tempering.

5. The production method according to claim 4, characterized in that, The normalizing method is as follows: heat the axle to 910~940℃, keep it at that temperature for 4~6 hours, and then air cool it to below 300℃.

6. The production method according to claim 4, characterized in that, The quenching method is as follows: heat the axle to 890~930℃, hold it at that temperature for 3~5 hours, and then cool it with water to below 80℃.

7. The production method according to claim 4, characterized in that, The high-temperature tempering method is as follows: heat the axle to 580~650℃, keep it at that temperature for 7~9 hours, and then air cool it to below 80℃.

8. The production method according to any one of claims 4-7, characterized in that, The metallographic structure of the heat-treated axle is tempered sorbite. The tensile strength of the heat-treated axle is ≥860MPa, the yield strength is ≥720MPa, and the elongation A is ≥23%.

9. The production method according to any one of claims 4-7, characterized in that, In the laser quenching step, the entire length of the axle is laser quenched, the hardened layer depth H is 1.4~2.0mm, the laser output power is 3000~8000W, the laser scanning speed is 400~1000mm / min, and the laser overlap rate is controlled between 20% and 28%.

10. The production method according to any one of claims 4-7, characterized in that, The chemical composition ratio, diameter D of the central through hole, and hardened layer depth H of the high-rigidity hollow axle for high-speed trains with a speed of ≥400 km / h should meet the following requirements: G = G0 + 28H - 0.3D, 47 ≤ G ≤ 74, where G is the comprehensive stiffness index.

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