A soft magnetic steel plate for a high-speed maglev train guide rail and a production method thereof

Abstract

This invention discloses a soft magnetic steel plate for high-speed maglev train guide rails and its production method, belonging to the field of structural steel manufacturing technology for railway tracks. The soft magnetic steel plate comprises the following components by mass percentage: C: 0.040-0.070%, Si: 1.20-1.70%, Mn: 0.35-0.70%, P≤0.015%, S≤0.002%, Ni: 0.40-1.00%, Cu: 0.20-0.50%, N≤60ppm, H≤2ppm, with the remainder being Fe and unavoidable impurities. The sum of the percentages of the above components is 100%. The production method includes low-temperature heating, high-temperature controlled rolling, controlled cooling, and normalizing processes. This production method is simple, low-cost, and easy to scale up, and the produced soft magnetic steel plate can simultaneously possess excellent low-temperature toughness and good magnetic properties.

Description

Technical Field

[0001] This invention relates to a steel plate and its production method, specifically to a soft magnetic steel plate for high-speed maglev train guide rails and its production method, belonging to the field of structural steel manufacturing technology for railway tracks. Background Technology

[0002] Maglev trains are a highly competitive contactless ground transportation mode in the 21st century, boasting advantages such as high safety, ultra-high speed, excellent passenger comfort, and environmental compatibility. After more than 30 years of research and development, maglev train technology has resulted in commercially operational maglev transportation systems, represented by Germany's TR08, Japan's MLX01, and HSST-100. In 2009, Germany's new TR09 maglev train achieved a top speed of 550 km / h during testing; in 2015, Japan set a world record of 603 km / h for manned operation on its Yamanashi maglev test line. my country has made significant breakthroughs in key technologies such as levitation and guidance, and has entered the test line construction and trial operation phase; meanwhile, the Shanghai Maglev Line project, using German TR08 technology, has been operating for many years since 2003. Currently, CRRC Qingdao Sifang Co., Ltd. has successfully developed a high-speed maglev train test line with a speed of 600 km / h.

[0003] As a new generation of high-speed ground transportation, maglev trains place extremely high demands on the material properties of key structural components such as tracks. Among these, the guide rail plates, used to guide the train, need to be made of soft magnetic steel with both excellent magnetic and mechanical properties. Ideally, the soft magnetic steel plates for the guide rails must not only possess high magnetic induction intensity and high resistivity to reduce eddy current losses, but also excellent low-temperature toughness to ensure the structural safety of the train during winter operation in frigid regions such as northern China.

[0004] Existing technologies for developing such soft magnetic steel sheets typically employ a process route of hot rolling followed by normalizing. However, these technologies have significant drawbacks: First, the low-temperature toughness is insufficient. The high-performance soft magnetic steel for maglev trains, patent CN1169993C, is produced by water cooling after rough rolling and finishing rolling, and normalizing and air cooling at 950℃. Its low-temperature impact performance test temperature is only 0℃, with an impact strength of 125-154J. The impact test temperature is relatively high, which is difficult to meet the safety redundancy requirements of high-speed maglev trains in environments with temperatures of -25℃ or even lower. It cannot meet the stringent requirements for safe operation in all weather conditions in cold regions such as northern China, and there are potential safety hazards. Secondly, there is the difficulty in achieving the process. To improve magnetic properties, a high silicon (Si) content composition design is adopted. For example, patent CN113416901B describes a high magnetic induction weather-resistant soft magnetic steel with excellent low-temperature toughness and its production method. This design mainly uses ultra-high C: 0.015~0.028%, high Si: 2.18~2.85%, ultra-low P≤0.0010%, and S≤0.0010% to obtain high magnetic induction intensity and good low-temperature toughness. However, this method has a high Si content, which will deteriorate the weldability of the steel plate and bring difficulties to the subsequent guide rail manufacturing. The pursuit of ultra-low P, S and other impurity content leads to a long smelting cycle, high production difficulty, and is not conducive to cost control and industrial mass production. Then, the process control is not precise and the cooling process after rolling is relatively rough. For example, natural air cooling is used, which makes it difficult to ensure the uniformity of the microstructure and properties of the entire cross section of the thick steel plate. This may lead to the formation of unexpected hard and brittle microstructure inside, affecting the stability of the overall performance. Finally, there is the contradiction between performance and cost. In pursuit of excellent magnetic properties and low-temperature toughness, high-temperature normalizing processes with temperatures exceeding 930℃ are adopted, such as the patent CN113832410B "A High-Performance Soft Magnetic Structural Steel Plate and Its Manufacturing Method". This process involves rough rolling + finish rolling followed by water cooling and normalizing at 930-950℃ with air cooling. While the -20℃ impact resistance is improved to 87-151J, it is still insufficient for use in cold regions below -20℃. Furthermore, the normalizing temperature of 930-950℃ is quite high. This high-temperature treatment not only leads to huge energy consumption but also places stringent requirements on the performance of the heat treatment furnace, necessitating a special heat treatment furnace. This significantly increases production costs, weakens the product's market competitiveness, and hinders large-scale promotion and application. In addition, the soft magnetic steel plate and its manufacturing method in patent CN118726840A achieve a high magnetic induction intensity by fusing scrap iron into an alloy and adding 1.0 to 7.0 wt% Si and 0.1 to 1.0 wt% Cu. However, the steel plate produced is only 0.03 to 0.15 mm thick, which is too thin to be used on the guide rails of maglev trains.

[0005] Therefore, developing a method for producing soft magnetic steel sheets that can ensure excellent low-temperature toughness and magnetic properties while taking into account production costs, process feasibility, and the needs of large-scale production is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a soft magnetic steel plate for high-speed magnetic levitation train guide rails and its production method. The production method is simple, low-cost, and easy to scale up, and the produced soft magnetic steel plate can simultaneously have excellent low-temperature toughness and good magnetic properties.

[0007] To address the above technical problems, this invention provides a soft magnetic steel plate for high-speed maglev train guide rails, comprising the following components by mass percentage: C: 0.040–0.070%, Si: 1.20–1.70%, Mn: 0.35–0.70%, P≤0.015%, S≤0.002%, Ni: 0.40–1.00%, Cu: 0.20–0.50%, N≤60ppm, H≤2ppm, with the remainder being Fe and unavoidable impurities, and the sum of the percentages of the above components being 100%.

[0008] The technical solution further defined in this invention is: Furthermore, the aforementioned soft magnetic steel plate for high-speed maglev train guide rails comprises the following components by mass percentage: C: 0.065%, Si: 1.25%, Mn: 0.70%, P: 0.011%, S: 0.002%, Ni: 0.95%, Cu: 0.25%, N: 45ppm, H: 1.5ppm, with the remainder being Fe and unavoidable impurities, and the sum of the percentages of the above components is 100%.

[0009] The aforementioned soft magnetic steel plate for high-speed maglev train guide rails comprises the following components by mass percentage: C: 0.045%, Si: 1.65%, Mn: 0.40%, P: 0.010%, S: 0.001%, Ni: 0.65%, Cu: 0.45%, N: 50ppm, H: 1ppm, with the remainder being Fe and unavoidable impurities. The sum of the percentages of the above components is 100%.

[0010] In the aforementioned soft magnetic steel plate used for the guide rail of high-speed maglev train, the thickness of the soft magnetic steel plate is 16-32mm.

[0011] This invention also designs a method for producing soft magnetic steel plates for high-speed maglev train guide rails. The production process includes: low-temperature heating, high-temperature controlled rolling, controlled cooling, and normalizing processes, specifically: (1) The steel billet is heated to a temperature of 1150℃~1230℃, preferably 1150℃~1220℃. Low-temperature heating is used to ensure the solid solution of the alloy and avoid grain coarsening on the surface of the steel billet. This ensures that the grains in the thickness direction of the steel billet are relatively uniform. The optimization principle is that the lower limit of the temperature of 1150℃ ensures that the carbides and various alloying elements in the steel can be fully dissolved into the austenite to form a uniform solid solution, which provides an ideal initial structure for subsequent rolling. The upper limit of the temperature of 1230℃ is to prevent the austenite grains from becoming excessively coarsened and to avoid the final product from having a decrease in toughness due to coarse grains. This step lays the foundation for obtaining a fine-grained structure in the future. (2) After the steel billet has been heated at low temperature, it is cooled and then hot rolled at a rolling temperature of 950℃~960℃. The final rolling temperature is 930℃~940℃. Through high temperature and high reduction rate, the deformation of the steel billet penetrates into the core, and more distortion zones are formed, providing more nucleation points for microstructure transformation. Optimization principle: Rolling at such a high temperature range (the austenite recrystallization region) is designed to utilize the excellent plasticity of austenite at high temperatures. A large reduction rate allows deformation to fully penetrate the core of the steel plate, especially for thicker plates. This is crucial for eliminating internal defects in the cast billet and achieving uniform microstructure across the entire cross-section. Simultaneously, high-temperature deformation can create more dislocations, subgrain boundaries, and other distortion regions within the austenite grains. These regions become preferential nucleation sites during subsequent phase transformations, promoting the formation of fine, dispersed ferrite grains. (3) The rolled steel plate is subjected to controlled cooling at a cooling rate of 1-3℃ / s, with the steel plate's red-hot temperature reaching 650℃-720℃. The purpose of this cooling system is twofold: firstly, to promote the full transformation of austenite to ferrite through a relatively gentle cooling rate and to inhibit the formation of harmful Widmanstätten structures; and secondly, to avoid the formation of brittle martensite or bainite and other non-equilibrium structures on the surface or subsurface of the steel plate due to excessively rapid cooling. By controlling the red-hot temperature and cooling rate in a coordinated manner, the phase transformation process is precisely controlled, which is a key step in obtaining a uniform fine-grained structure. (4) The steel plate after controlled cooling is subjected to heating and normalizing treatment. The normalizing temperature of the steel plate is 790℃~830℃, and the heating time is 2min / m. Based on the thickness of the steel plate, compared with the existing technology of high-temperature normalizing above 930℃, the principle of low-temperature normalizing is that the ferrite-pearlite structure is re-austenitized at a lower temperature, which can effectively inhibit the re-growth of austenite grains. In the subsequent air cooling process, due to the fineness of the austenite grains, they can be transformed into even finer ferrite grains, such as... Figure 2-4 As shown, this step is the final optimization of the microstructure of the steel plate. By further refining the grains, the ductile-brittle transition temperature of the steel is significantly reduced, thereby greatly improving its low-temperature impact toughness and solving the defect of insufficient low-temperature performance in the background technology.

[0012] Furthermore, in the aforementioned production method of soft magnetic steel plates for high-speed maglev train guide rails, the steel billet subjected to low-temperature heating treatment is obtained by refining molten steel through LF and RH processes.

[0013] Technical advantages: The molten steel of this invention is processed using existing ladle refining furnace (LF) and vacuum circulating degassing (RH) technologies. LF (Ladle Furnace) is used to precisely adjust the chemical composition and temperature of the molten steel, while RH (Ruhrstahl-Heraeus) is used to efficiently remove harmful gases such as hydrogen and nitrogen from the molten steel, improving the purity of the steel. The refined molten steel is used to prepare steel billets. Through ladle refining technology, the chemical composition of the molten steel can be precisely controlled, and harmful gaseous impurities such as hydrogen and nitrogen can be effectively removed from the steel, improving the purity of the steel. This is crucial for ensuring the final low-temperature toughness and magnetic properties of the steel plate, and also ensures that the composition of the steel plate meets the aforementioned characteristic requirements.

[0014] In the aforementioned production method of soft magnetic steel plate for high-speed maglev train guide rail, the heating temperature in step (1) is 1220℃, the initial rolling temperature in step (2) is 960℃, the final rolling temperature is 930℃, the controlled cooling temperature is 700~720℃, and the normalizing temperature is 800±10℃.

[0015] In the aforementioned production method of soft magnetic steel plate for high-speed maglev train guide rail, the heating temperature in step (1) is 1150℃, the initial rolling temperature of high-temperature rolling is 952℃, the final rolling temperature is 940℃, the controlled cooling temperature is 650~670℃, and the normalizing temperature is 820±10℃.

[0016] In the aforementioned production method of soft magnetic steel plate for high-speed maglev train guide rail, the soft magnetic steel plate has a yield strength ≥275 MPa, tensile strength 430-550 MPa, elongation ≥27%, impact strength at -25℃ ≥150 J, resistivity ≥0.36 μΩ·m, and B300 ≥0.60 T and B5000 ≥1.60 T.

[0017] The beneficial effects of the present invention are: (1) Excellent comprehensive performance: Through the synergistic effect of specific chemical composition design such as C-Si-Ni-Cu and unique "high temperature rolling + low temperature normalizing" process, it is possible to stably produce thick (16~32mm) soft magnetic steel plates with excellent ultra-low temperature toughness (impact energy far exceeds 150J at -25℃), high resistivity (not less than 0.36μΩ·m) and good magnetic properties (B300≥0.60T, B5000≥1.60T), which can meet the requirements of safe operation of high-speed maglev trains in cold regions; The specific chemical composition design is as follows: The appropriate Si content aims to ensure high resistivity and magnetic induction intensity to reduce eddy current losses. The addition of Ni aims to significantly improve the low-temperature toughness of the steel plate. The content of elements such as C and Mn optimizes the magnetic properties while ensuring basic strength. Cu precipitation can provide nucleation cores for nanocrystals, refine the grains, and thus optimize the magnetic properties. At the same time, strictly controlling the content of harmful elements such as P, S, N, and H is a prerequisite for obtaining a high-purity matrix and excellent performance. The composition system of this invention abandons the practice of using ultra-high silicon content to improve magnetism but sacrificing weldability in the prior art, and also avoids the route of significantly increasing smelting costs in pursuit of ultimate purity. Through the reasonable combination of elements such as C, Si, Mn, Ni, and Cu, it ensures excellent magnetic properties and low-temperature toughness while taking into account the strength, plasticity, and weldability of the material, thus providing the possibility for the industrialized and low-cost production of high-performance soft magnetic steel plates.

[0018] The specific functions of the process flow are as follows: Ladle refining furnace (LF) and vacuum circulating degassing (RH) refining: This is a combined refining process. LF refining is mainly used to heat the molten steel, fine-tune its composition, and desulfurize it. RH refining, on the other hand, efficiently removes harmful gases such as hydrogen (H) and nitrogen (N), as well as non-metallic inclusions, from the molten steel by circulating it in a vacuum environment. Hydrogen is the main cause of defects such as white spots and hydrogen embrittlement in steel, while nitrogen can form nitrides that precipitate and deteriorate the toughness of the steel. Through LF+RH refining, the H content is controlled at an extremely low level (e.g., ≤2ppm) and the N content is controlled at ≤60ppm, thus laying a solid metallurgical foundation for subsequent processes to obtain high-toughness and high-density steel plates. The combined refining technology of this invention is used to obtain high-purity molten steel, laying a solid material foundation for the excellent low-temperature toughness and magnetic properties of the final product. Low-temperature heating: The steel billet is heated at a low temperature of 1150℃~1230℃. This temperature range can ensure the full solid solution of alloying elements to prepare for subsequent rolling, and can also avoid excessive coarsening of surface grains due to excessive temperature, which is conducive to obtaining a uniform original structure. High-temperature rolling process: The steel billet, after being heated in the low-temperature heating process, is cooled and then hot-rolled after its temperature drops to the initial rolling temperature of 950℃~960℃. The final rolling temperature is 930℃~940℃. By rolling with a large reduction in a higher temperature range, it is ensured that the deformation can fully penetrate into the core of the thick steel plate, forming more structural distortion bands, providing more nucleation sites for subsequent phase transformation, which is conducive to obtaining a fine and uniform grain structure in the end. Controlled cooling process: The red-hot temperature refers to the temperature at which the surface temperature of the steel plate rises again and turns dark red again due to the conduction of heat from the core to the cooled surface during the controlled cooling process after rolling. In this invention, after the high-temperature rolling process is completed, the steel plate is controlled to cool at a cooling rate of 1 to 3°C / s, and the red-hot temperature of the steel plate is 650°C to 720°C. This is an important process step to control the austenite to ferrite phase transformation process, refine the grains, and avoid the formation of brittle hard structures such as martensite. Through this relatively slow cooling method, the formation of hard and brittle structures such as martensite on or inside the steel plate due to excessively rapid cooling is effectively avoided. Especially for thick steel plates, it can better ensure the uniformity of the structure from the surface to the core, thereby improving the stability of the overall performance and ensuring the uniformity of the structure of the entire cross section of the steel plate. Low-temperature normalizing process: The steel plate, after being cooled by controlled cooling, is reheated to a normalizing temperature of 790℃~830℃ for normalizing treatment. Compared with the high-temperature normalizing above 930℃ commonly used in existing technologies, this lower normalizing temperature significantly reduces energy consumption in the heat treatment process and reduces the requirements for production equipment, thereby reducing the overall manufacturing cost. At the same time, normalizing at a temperature in the two-phase region or near the austenite transformation point can effectively inhibit the growth of austenite grains and promote the formation of finer ferrite grains during the subsequent cooling process. This is a key metallurgical means to improve the low-temperature toughness of steel plates, especially the ultra-low temperature toughness, effectively achieving microstructure recrystallization and obtaining uniform ferrite grains, thereby ensuring excellent magnetic properties and low-temperature toughness. Magnetic flux density (B300 / B5000): This refers to the magnetic flux density (B) exhibited by a soft magnetic material under a specific magnetic field strength (H). B300 and B5000 represent the magnetic flux density values ​​measured at magnetic field strengths of 300 A / m and 5000 A / m, respectively, with the unit being Tesla (T). These two parameters are key indicators for evaluating the magnetic properties of soft magnetic steel sheets. B300 reflects the material's magnetic permeability under a weak magnetic field, while B5000 reflects its saturation magnetization level under a high magnetic field. In summary, the superior performance parameters of the soft magnetic steel plate of this invention are the inevitable result of the synergistic effect of specific production processes and chemical compositions. Specifically, the average longitudinal impact energy of the steel plate at -25℃ is not less than 150J, and the resistivity is not less than 0.36μΩ·m. By directly linking the product's performance indicators with the core manufacturing method of the invention, the problem of not being able to clearly define the product based solely on composition or performance parameters is solved. This ensures that the protected high-performance product truly originates from the creative contribution of this invention, namely the specific "high-temperature rolling + low-temperature normalizing" process. Thus, the product's performance is linked to the specific manufacturing process, ensuring the clarity and stability of the protection scope.

[0019] (2) Low production cost and simple process: The low temperature normalizing process (790℃~830℃) adopted in this invention significantly reduces the energy consumption of the heat treatment process compared with the high temperature normalizing above 930℃ adopted in the prior art. It also has low requirements for production equipment and can be produced using the existing conventional rolling and heat treatment equipment of steel enterprises. No special investment is required, and the cost advantage is obvious, which is conducive to large-scale industrial production.

[0020] (3) Uniform and stable microstructure: By precisely controlling each step of heating, high-temperature rolling and controlled cooling, this invention effectively achieves the homogenization of the microstructure from the surface to the core of the thick steel plate, and obtains a microstructure dominated by fine and uniform ferrite, thereby ensuring the overall stability and reliability of the steel plate.

[0021] (4) Suitable for industrial mass production: The composition design of this invention avoids the welding difficulties caused by high Si and the smelting difficulties caused by ultrapure steel. The process parameter window is reasonable and the control is stable. It solves the contradiction between high performance, high cost and production difficulty in the existing technology and provides a feasible mass production solution for the steel for the guide rail of high-speed maglev train with a speed of 600 km / h. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart illustrating the production method of soft magnetic steel plates for high-speed magnetic levitation train guide rails according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the metallographic structure near the surface of a 32mm thick soft magnetic steel according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the metallographic structure at 1 / 4 of the thickness of the 32mm thick soft magnetic steel in an embodiment of the present invention; Figure 4 This is a schematic diagram of the metallographic structure at 1 / 2 of the thickness of the 32mm thick soft magnetic steel in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without innovative effort are within the scope of protection of this application.

[0025] This embodiment provides a method for producing soft magnetic steel plates for high-speed maglev train guide rails, which solves the technical problem that existing technologies struggle to balance excellent ultra-low temperature toughness, good magnetic properties, and low-cost industrial production when producing such steel plates. This invention achieves a significant improvement in comprehensive performance through the synergistic effect of specific chemical composition design and a unique "high-temperature rolling + low-temperature normalizing" process. The method first obtains a steel billet with a specific chemical composition through refining, and then sequentially heats, rolls at high temperature, controls cooling, and normalizes the billet to finally obtain a finished soft magnetic steel plate that meets stringent performance requirements. Example 1

[0026] This embodiment provides a soft magnetic steel plate for a high-speed maglev train guide rail, with a thickness of 16mm. Its chemical composition and mass percentage are shown in Table 1.

[0027] See Figure 1 As shown, the production method of the soft magnetic steel plate for the guide rail of the high-speed maglev train includes the following specific steps: S100, Refined Processing Initial molten steel is obtained through existing smelting processes. The molten steel is then refined to obtain a steel billet with the chemical composition shown in Table 1. This steel billet is a 260mm cross-section casting billet. LF and RH refining technologies are used during smelting to ensure that the gaseous H content of the steel plate is 0.5ppm and the N content is 40ppm. S200, Low-temperature heating The steel billet is heated to 1220℃ in a heating furnace and held at that temperature for 260 minutes; S300, high temperature rolling After heating, high-temperature rolling is carried out, with the initial rolling temperature controlled at 960℃. After multiple rolling passes, the final rolling temperature is controlled at 930℃, and finally a 16mm thick steel plate is obtained. S400, Cooling After rolling, the steel plate immediately enters the controlled cooling process. By adjusting the cooling water flow rate, the red-hot temperature of the steel plate is controlled between 700 and 720°C, and the cooling rate is 2.5°C / s. S500, Normalizing The cooled steel plate is sent into a heat treatment furnace for low-temperature normalizing. The normalizing temperature is set at 790℃, and the holding time is 32 minutes according to the calculation formula of 2min / mm. S600, Inspection After normalizing, the steel plate is cooled to room temperature in the air and then inspected as a finished product.

[0028] The performance of the 16mm thick soft magnetic steel plate prepared by the above method was tested, and the results are shown in Table 2. Its room temperature yield strength is 420MPa, tensile strength is 525MPa, and elongation after fracture is 35%, showing good strength and toughness matching. More importantly, according to GB / T 229-2020 standard, the longitudinal impact energy of the three groups of Charpy V-notch impact test specimens at -25℃ is 315J, 219J, and 317J, respectively, with an average value of 283.7J, far exceeding the design requirement of 150J. In addition, its resistivity is 0.361μΩ·m, and the magnetic induction intensities B300 and B5000 at magnetic field strengths of 300A / m and 5000A / m are 0.663T and 1.671T, respectively. The above data fully demonstrate the effectiveness and superiority of the method of the present invention in manufacturing high-performance soft magnetic steel plates. Example 2

[0029] This embodiment provides a soft magnetic steel plate for a high-speed maglev train guide rail, with a thickness of 32mm. Its chemical composition and mass percentage are shown in Table 1.

[0030] See Figure 1 As shown, the production method of the soft magnetic steel plate for the guide rail of the high-speed maglev train includes the following specific steps: S100, Refined Processing Initial molten steel is obtained through existing smelting processes. The molten steel is then refined to obtain a steel billet with the chemical composition shown in Table 1. The steel billet is a 260mm cross-section casting billet. During smelting, LF and RH refining technologies are used to ensure that the gaseous H content of the steel plate is 0.6ppm and the N content is 46ppm. S200, Low-temperature heating The steel billet is heated to 1150°C in a heating furnace and held at that temperature for 268 minutes; S300, high temperature rolling After heating, high-temperature rolling is carried out, with the initial rolling temperature controlled at 952℃ and the final rolling temperature controlled at 945℃, finally obtaining a 32mm thick steel plate. S400, Cooling After rolling, the steel plate immediately enters the controlled cooling process. By adjusting the cooling water flow rate, the red-hot temperature of the steel plate is controlled between 650 and 670°C, and the cooling rate is 1.5°C / s. S500, Normalizing The cooled steel plate is sent into a heat treatment furnace for low-temperature normalizing. The normalizing temperature is set at 830℃. According to the calculation formula of 2min / mm, the holding time is 64 minutes. S600, Inspection After normalizing, the steel plate is cooled to room temperature in the air and then inspected as a finished product.

[0031] The performance of the 32mm thick soft magnetic steel plate was tested, and the results are shown in Table 2. Its yield strength was 385MPa, tensile strength was 517MPa, and elongation after fracture was as high as 36%. The longitudinal impact energy of the three groups of samples at -25℃ were 232J, 325J, and 326J, respectively, with an average value of 294.3J. This further proves the significant effect of the method of the present invention in improving low-temperature toughness. Its resistivity was 0.362μΩ·m, and the magnetic induction intensity B300 and B5000 were 0.657T and 1.668T, respectively. The success of this example shows that the method of the present invention has a wide process window, can adapt to the production of products with different thicknesses, and can obtain stable and excellent comprehensive performance.

[0032] Table 1 Chemical composition of steel plates from Examples 1-2 (wt%)

[0033] Table 2. Mechanical properties, resistivity, and magnetic properties of the steel plates from Examples 1-2

[0034] As can be seen from the two specific embodiments above, the average longitudinal impact energy of the soft magnetic steel plate produced by the method of the present invention can be stably much higher than 150J at -25℃. This excellent performance is a direct manifestation of the synergistic effect of the specific chemical composition (especially the addition of Ni) and the unique "high temperature rolling + low temperature normalizing" process adopted in the present invention, which solves the technical problems of insufficient low temperature toughness and safety application risks of existing products.

[0035] Metallographic testing of the soft magnetic steel sheet produced in Example 2 was performed using existing techniques. Please refer to [link to relevant documentation]. Figure 2 , Figure 3 and Figure 4These images respectively demonstrate the metallographic structure of a 32mm thick soft magnetic steel plate prepared according to embodiments of the present invention at near-surface, 1 / 4 of thickness, and 1 / 2 of thickness. As clearly seen in the figure, both the surface and the core exhibit a microstructure composed of fine-sized, regularly shaped, and uniformly distributed ferrite grains with clear and complete grain boundaries. No coarse pearlite clusters or brittle martensite structures were observed. According to the principles of fracture mechanics in metallic materials, grain refinement is the most effective means to improve material toughness and reduce the ductile-brittle transition temperature. Fine grains mean more grain boundaries per unit volume, which effectively hinder crack propagation, thus consuming more fracture energy. This invention generates a large number of nucleation points through high-temperature rolling and inhibits grain growth during subsequent controlled cooling and low-temperature normalizing processes, ultimately obtaining this ideal fine-grained structure. This demonstrates the effectiveness of the "high-temperature rolling" process in controlling the microstructure of thick plates. Therefore, this optimized microstructure significantly reduces the ductile-brittle transition temperature of the steel plate to below -25°C, ensuring that even under extremely cold climatic conditions, the average longitudinal impact energy remains no less than 150J, providing reliable material support for the all-weather safe operation of high-speed maglev trains.

[0036] The soft magnetic steel plate and its production method provided by this invention have broad and clear application prospects in the field of high-speed rail transit, especially in high-speed maglev projects with a speed of 600 km / h. In practical applications, the 16-32 mm thick soft magnetic steel plate manufactured by the method of this invention will be processed into guide rail strips with specific cross-sectional shapes (e.g., F-type) and laid along the maglev line to form part of the train's lateral guidance system.

[0037] When a high-speed maglev train is in operation, the onboard guide electromagnet generates an electromagnetic attraction between itself and the soft magnetic steel guide rail, providing precise lateral guidance and ensuring stable operation along the track centerline at ultra-high speeds. The technical advantages of this invention are fully demonstrated in this scenario. First, its excellent ultra-low temperature toughness is a key factor in ensuring operational safety. In northern China or high-altitude regions, winter track temperatures can easily drop to -20°C or even -25°C. The steel plate of this invention maintains high toughness under such extreme low temperatures, significantly reducing the risk of brittle fracture of the guide rail and providing a fundamental guarantee for safe train operation.

[0038] Secondly, its excellent magnetic properties (high magnetic induction intensity) mean that the guide electromagnet can generate sufficient guiding force with a relatively small excitation current. This not only helps to achieve rapid and precise control of the train's attitude but also reduces the power consumption of the onboard electromagnet system, improving the train's energy efficiency. Furthermore, its high resistivity (≥0.36 μΩ·m) is crucial for suppressing eddy current effects. When the train moves at high speed, the changing magnetic field induces eddy currents in the guide rail. These eddy currents generate resistance in the opposite direction of motion and cause heat generation, resulting in energy loss. The high resistivity of the steel plate in this invention effectively reduces the intensity of eddy currents, thereby reducing energy consumption and unnecessary temperature rise in the guide rail, and improving the overall economic efficiency of the magnetic levitation system.

[0039] Finally, the method of this invention enables low-cost, mass production of steel plates with thicknesses ranging from 16 to 32 mm, meeting the structural strength and stiffness requirements of magnetic levitation rails and ensuring that the rails maintain precise geometry and position under immense electromagnetic forces and high-speed aerodynamic loads. In summary, this invention, through an innovative production method, provides a soft magnetic steel plate that meets the requirements of high-speed magnetic levitation rails.

[0040] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A soft magnetic steel plate for a high-speed maglev train guide rail, characterized in that: The composition comprises the following components by mass percentage: C: 0.040–0.070%, Si: 1.20–1.70%, Mn: 0.35–0.70%, P≤0.015%, S≤0.002%, Ni: 0.40–1.00%, Cu: 0.20–0.50%, N≤60ppm, H≤2ppm, with the remainder being Fe and unavoidable impurities. The sum of the percentages of the above components is 100%.

2. The soft magnetic steel plate for high-speed maglev train guide rails according to claim 1, characterized in that: The composition comprises the following components by mass percentage: C: 0.065%, Si: 1.25%, Mn: 0.70%, P: 0.011%, S: 0.002%, Ni: 0.95%, Cu: 0.25%, N: 45ppm, H: 1.5ppm, with the remainder being Fe and unavoidable impurities. The sum of the percentages of the above components is 100%.

3. The soft magnetic steel plate for high-speed maglev train guide rails according to claim 1, characterized in that: The composition comprises the following components by mass percentage: C: 0.045%, Si: 1.65%, Mn: 0.40%, P: 0.010%, S: 0.001%, Ni: 0.65%, Cu: 0.45%, N: 50ppm, H: 1ppm, with the remainder being Fe and unavoidable impurities. The sum of the percentages of the above components is 100%.

4. The soft magnetic steel plate for high-speed maglev train guide rails according to any one of claims 1-3, characterized in that: The thickness of the soft magnetic steel plate is 16-32mm.

5. A method for producing a soft magnetic steel plate for a high-speed maglev train guide rail as described in claim 1, characterized in that: The production process includes: low-temperature heating, high-temperature controlled rolling, controlled cooling, and normalizing processes, specifically: (1) Heat the steel billet to a temperature of 1150℃~1230℃; (2) The steel billet is rolled at high temperature, with an initial rolling temperature of 950℃~960℃ and a final rolling temperature of 930℃~940℃; (3) Controlled cooling is performed on the rolled steel plate, with the steel plate reddening temperature at 650℃~720℃ and the cooling rate at 1~3℃ / s; (4) The steel plate after controlled cooling is normalized. The normalizing temperature of the steel plate is 790℃~830℃ and the heating time is 2min / mm, based on the thickness of the steel plate.

6. The method for producing soft magnetic steel plates for high-speed maglev train guide rails according to claim 5, characterized in that: The steel billet obtained by low-temperature heating treatment is obtained by refining molten steel through LF and RH processes.

7. The method for producing soft magnetic steel plates for high-speed maglev train guide rails according to claim 5, characterized in that: The heating temperature in step (1) is 1220℃, the initial rolling temperature in step (2) is 960℃, the final rolling temperature is 930℃, the controlled cooling temperature is 700~720℃, and the normalizing temperature is 800±10℃.

8. The method for producing soft magnetic steel plates for high-speed maglev train guide rails according to claim 5, characterized in that: In step (1), the heating temperature is 1150℃, the initial rolling temperature of the high-temperature rolling is 952℃, the final rolling temperature is 940℃, the controlled cooling temperature is 650~670℃, and the normalizing temperature is 820±10℃.

9. The method for producing soft magnetic steel plates for high-speed maglev train guide rails according to claim 5, characterized in that: The yield strength of this soft magnetic steel plate is ≥275 MPa, tensile strength is 430-550 MPa, elongation is ≥27%, impact strength at -25℃ is ≥150 J, resistivity is ≥0.36 μΩ·m, and B300 is ≥0.60 T and B5000 is ≥1.60 T.

Images