Production method of steel rail with high strength and high impact toughness
By using a medium-carbon, high-silicon, and high-manganese composition formula and a segmented tempering process, the problem of insufficient toughness and strength of rails in heavy-load and urban rail transit was solved, achieving simultaneous improvement in high impact toughness, tensile strength, and plasticity. The welded joint performance is stable, and production costs are reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA BAOTOU STEEL UNION
- Filing Date
- 2026-03-12
- Publication Date
- 2026-05-15
AI Technical Summary
Existing steel rails suffer from insufficient impact toughness, strength, and plasticity in heavy-load and urban rail transit applications, especially at welded joints where they are prone to failure. Furthermore, traditional methods increase production costs or sacrifice wear resistance.
By adopting a medium-carbon, high-silicon, and high-manganese composition formula and a segmented tempering process, and through processes such as smelting, hot rolling, heat treatment, and welding pretreatment, the microstructure is precisely controlled to be fine pearlite, thereby improving the comprehensive mechanical properties of the rail.
It achieves simultaneous improvement in the high impact toughness, tensile strength and plasticity of rails, stable performance of welded joints, reduced production costs, and adapts to the safety requirements of complex working conditions.
Smart Images
Figure CN122038880A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of rail technology for rail transit, and particularly relates to a method for producing high-strength, high-impact-toughness rails; it is especially suitable for heavy-haul railways, urban rail transit and other scenarios that have high requirements for impact toughness, strength, plasticity and wear resistance. Background Technology
[0002] As the core load-bearing component of rail transit, rails must withstand the periodic rolling and impact loads of train wheels and rails for a long time, while also facing the installation requirements of on-site welding and splicing. Their comprehensive mechanical properties (impact toughness, strength, plasticity, and hardness) directly determine the safety of train operation and the cost of operation and maintenance. The mainstream grade of existing rails is U71Mn, which adopts a high carbon and high manganese composition design (C: 0.65%-0.75%, Mn: 1.10%-1.40%). The wear resistance is improved by quenching the rail head. However, this type of rail has obvious performance shortcomings: the microstructure is mainly pearlite, the impact toughness is usually only 30-40 J / cm², the tensile strength is about 1100-1200 MPa, and the elongation after fracture is ≤10%. When heavy-load trains pass frequently, the rail head is prone to peeling and spalling. In the scenario of frequent start and stop of urban rail transit, fatigue cracks are easily generated due to insufficient plasticity. In mountainous lines with steep gradients, the concentrated impact load can easily lead to brittle fracture of the rail. Moreover, the traditional rail welded joints have poor toughness (impact toughness ≤35 J / cm²), and the tensile strength and plasticity are significantly reduced, making them a high-risk part of the line failure.
[0003] In existing technologies, improving the toughness of steel often requires the addition of precious alloys such as chromium and nickel, leading to a significant increase in production costs; or simply reducing carbon content to improve plasticity, but at the expense of the essential wear resistance and strength of the rail, making it difficult to achieve the synergistic optimization of "high toughness, high strength, high plasticity, and high wear resistance". How to simultaneously improve impact toughness, strength, and plasticity by controlling the microstructure (such as obtaining fine pearlite) through compositional and process innovation without introducing precious alloys and ensuring wear resistance, while solving the problem of matching high-toughness components with welding performance, and developing high-performance rails suitable for complex working conditions, has become a pressing technical bottleneck in this field. Summary of the Invention
[0004] The purpose of this invention is to provide a production method for high-strength, high-impact-toughness steel rails. By innovatively designing a "medium-carbon, high-silicon, high-manganese" composition formula and a "segmented tempering" process, the microstructure is precisely controlled to be fine pearlite, simultaneously improving impact toughness, tensile strength, elongation, and hardness. This solves the technical problems of unbalanced comprehensive mechanical properties and easy failure of welded joints in existing steel rails, while ensuring production cost advantages and meeting the safe operation requirements of rail transit under complex working conditions.
[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0006] This invention discloses a method for producing high-strength, high-impact-toughness steel rails, comprising the following steps:
[0007] (1) Smelting and casting: The converter smelting process is adopted, the purity of the molten steel is strictly controlled, and the harmful impurity elements P and S are controlled within the range specified in claim 1. Homogeneous steel billets are obtained through continuous casting process. The cooling rate during continuous casting is controlled at 1.5-2.5℃ / s to avoid component segregation and internal porosity defects.
[0008] (2) Hot rolling: The billet is heated to 1100-1200℃ and held for 2-3 hours to eliminate the internal stress of the billet. Then it is formed into a rail section by multiple passes of controlled rolling. The final rolling temperature is controlled at 850-900℃. After the final rolling, it is air-cooled to 950-1000℃ to obtain a uniform and fine austenitic structure, which lays the foundation for the improvement of subsequent heat treatment performance.
[0009] (3) Heat treatment process: ① Quenching treatment: Online continuous quenching is adopted to rapidly cool the key stress-bearing parts such as rail head and rail web to 280-320℃, with a cooling rate of 15-20℃ / s; ② Segmented tempering: At a heating rate of 5-8℃ / min, it is first held at 300-350℃ for 1.5 hours to eliminate quenching stress, and then heated to 480-520℃ and held for 2 hours to promote the transformation of fine pearlite structure. It is then cooled to room temperature in the furnace to ensure the uniformity of structure and the stability of mechanical properties.
[0010] (4) Welding pretreatment: Grind and remove rust from the welding area at both ends of the rail, remove surface oxide scale and impurities, and then use induction preheating treatment. The preheating temperature is controlled at 200-250℃, and the preheating range is 50mm on both sides of the welding end. The temperature is maintained for 10-15 minutes. The mechanical properties of the welded joint meet the following requirements: impact toughness ≥45 J / cm², tensile strength ≥1200 MPa, elongation after fracture ≥10%, and microstructure is fine pearlite + a small amount of dispersed carbides.
[0011] (5) Finished product processing: The rails are surface-polished and ultrasonically tested to ensure that there are no cracks, inclusions, or air holes, and finally the finished rails are obtained.
[0012] The chemical composition of the rail, by mass percentage, is as follows: C: 0.58%-0.63%, Si: 1.20%-1.80%, Mn: 0.80%-1.10%, P≤0.025%, S≤0.020%, with the remainder being Fe and unavoidable impurities. The microstructure of the rail is mainly fine pearlite, and its mechanical properties meet the following requirements: impact toughness ≥55 J / cm², tensile strength ≥1280 MPa, yield strength ≥1150 MPa, elongation after fracture ≥12%, and rail head hardness HRC 55-58.
[0013] Furthermore, the chemical composition contains 1.40%-1.60% Si and 0.90%-1.00% Mn. Through the synergistic effect of silicon and manganese elements, the elasticity, toughness and weldability of the rail are balanced. The corresponding mechanical properties are optimized as follows: impact toughness ≥58 J / cm², tensile strength ≥1300 MPa, and elongation after fracture ≥13%.
[0014] Furthermore, in step (2), the hot rolling process adopts multi-pass controlled rolling and cooling technology, with the reduction amount of each pass gradually increasing to ensure the accuracy of the rail cross-section dimensions and the density of the structure, providing structural guarantee for obtaining a uniform fine pearlite structure after subsequent heat treatment.
[0015] Furthermore, in step (3), the heating rate of the segmented tempering is strictly controlled at 5-8℃ / min to avoid the stress concentration caused by the sudden temperature rise, further improve the uniformity of the mechanical properties of the rail, and make the tensile strength fluctuation range of the whole section ≤50MPa and the HRC hardness fluctuation ≤2.
[0016] Furthermore, the chemical composition of the rail, by mass percentage, is: C: 0.58%, Si: 1.40%, Mn: 0.90%, P: 0.020%, S: 0.015%, with the remainder being Fe and unavoidable impurities.
[0017] Furthermore, the chemical composition of the rail, by mass percentage, is: C: 0.61%, Si: 1.60%, Mn: 1.00%, P: 0.022%, S: 0.018%, with the remainder being Fe and unavoidable impurities.
[0018] Furthermore, the chemical composition of the rail, by mass percentage, is: C: 0.63%, Si: 1.20%, Mn: 1.10%, P: 0.025%, S: 0.016%, with the remainder being Fe and unavoidable impurities.
[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:
[0020] Core component formulation innovation: Breaking through the limitations of traditional high-carbon, low-silicon steel rail components, a "medium-carbon-high-silicon-high-manganese" synergistic formulation system was designed, precisely controlling the proportion of each element to achieve a balance between microstructure and performance.
[0021] Carbon (C): Controlled at 0.58%-0.63%, which is moderately reduced compared to traditional rail steel (0.65%-0.75%). While ensuring the basic hardness and strength of the rail, it significantly reduces the brittleness of the steel, laying the compositional foundation for the formation of fine pearlite structure and the improvement of toughness.
[0022] Silicon (Si): The innovative setting is 1.20%-1.80%, which is much higher than that of traditional rail steel (0.15%-0.35%). By utilizing the solid solution strengthening effect of silicon, the elastic limit, tensile strength and impact toughness of steel are greatly improved. At the same time, the upper limit is strictly controlled to avoid welding embrittlement and processing difficulties.
[0023] Manganese (Mn): Controlled at 0.80%-1.10%, manganese optimizes the hardenability and impact resistance of steel, and forms a synergistic effect with silicon to balance the contradiction between improving toughness and welding performance and plasticity;
[0024] Strictly control the content of P and S impurities (P≤0.025%, S≤0.020%) to avoid crack sensitivity caused by the segregation of impurity elements at grain boundaries, and ensure the overall mechanical property stability and microstructure uniformity of the steel.
[0025] Production process innovation and optimization: Through precise control of process parameters, an ideal microstructure dominated by fine pearlite is obtained, achieving a synergistic improvement in comprehensive mechanical properties.
[0026] Smelting and casting: The converter smelting + continuous casting process is adopted, and the continuous casting cooling rate is precisely controlled (1.5-2.5℃ / s) to reduce component segregation and internal porosity defects, so as to obtain homogeneous steel billets and provide a high-quality raw material base for subsequent processes.
[0027] Hot rolling: Optimize the heating temperature (1100-1200℃) and holding time (2-3 hours), and combine multi-pass controlled rolling and cooling technology to control the final rolling temperature at 850-900℃. After final rolling, air cool to 950-1000℃ to obtain a uniform and fine austenitic structure, creating conditions for the formation of uniform fine pearlite after heat treatment.
[0028] Innovative segmented tempering process: Breaking through the traditional single low-temperature tempering mode for steel rails, a two-stage tempering process of "low-temperature stress relief + medium-temperature toughening" is designed. First, the quenching stress is eliminated by holding at 300-350℃, and then the transformation of fine pearlite is promoted at 480-520℃. This structure has the characteristics of high hardness (ensuring wear resistance), high toughness (resisting impact) and good plasticity (avoiding brittleness), which is the core to achieve a balance of comprehensive performance.
[0029] Welding pretreatment process: In response to the welding characteristics of high silicon content, an innovative combination of "mechanical grinding and rust removal + electric induction preheating" is adopted. Through precise preheating at 200-250℃, the microstructure transformation environment of the weld joint is improved, so that the weld joint obtains a uniform microstructure of fine pearlite + a small amount of dispersed carbides, avoiding weld embrittlement and ensuring that the mechanical properties of the joint meet the standards.
[0030] It has the following outstanding beneficial effects:
[0031] (1) Synergistic breakthrough in comprehensive mechanical properties: Through the synergistic innovation of the "medium carbon-high silicon-high manganese" composition system and segmented tempering process, a microstructure mainly composed of fine pearlite is obtained, achieving simultaneous improvement of multiple performance indicators: impact toughness ≥55 J / cm² (more than 40% higher than traditional rails), tensile strength ≥1280 MPa (8%-16% higher), elongation after fracture ≥12% (more than 20% higher), rail head hardness HRC55-58 (meeting wear resistance requirements), solving the pain point of "unbalance between strength and toughness, and contradiction between plasticity and hardness" in traditional rails;
[0032] (2) Precise balance between impact toughness and wear resistance: The fine structure of the fine pearlite structure and the distribution of dispersed carbides enable the rail to have both excellent impact resistance (able to withstand periodic impact loads under complex working conditions) and high hardness and wear resistance. The risk of rail head peeling and falling off is reduced by more than 60%, and the service life is extended by more than 30% compared with traditional rails.
[0033] (3) Stable and reliable performance of welded joints: Through precise control of silicon content and innovation of welding preheating process, the microstructure of welded joints is fine pearlite + a small amount of dispersed carbides, and the mechanical properties meet the following requirements: impact toughness ≥45 J / cm², tensile strength ≥1200 MPa, elongation after fracture ≥10%, no cracks, inclusions and other defects, fully meeting the requirements of on-site splicing construction, and the risk of joint failure is significantly reduced.
[0034] (4) Significant production cost advantages: No need to add precious alloys such as chromium and nickel, the existing rail production equipment can be used to achieve process adaptation, no need to add special equipment, high production efficiency, controllable raw material costs, and good uniformity of mechanical properties across the entire cross section (tensile strength fluctuation ≤50 MPa, hardness fluctuation ≤HRC2), which has the industrial foundation for large-scale promotion.
[0035] (5) Wide range of applicable scenarios: The ratio of Si and Mn elements and heat treatment parameters can be flexibly adjusted according to the performance focus of different scenarios, making it suitable for various working conditions such as heavy-duty railways (emphasizing high strength and wear resistance), urban rail transit (emphasizing high toughness and impact resistance), and mountain railways (emphasizing high plasticity and brittle fracture resistance), with strong practicality and compatibility. Attached Figure Description
[0036] The present invention will be further described below with reference to the accompanying drawings.
[0037] Figure 1 This is a flowchart of the rail production process of the present invention. The diagram clearly shows the complete process chain of the present invention from smelting and casting to finished product processing, and clarifies the connection logic of each link. The two core innovative processes, "heat treatment (quenching + segmented tempering)" and "welding pretreatment", are highlighted by bold borders, which intuitively demonstrates the feasibility of the technical solution.
[0038] Figure 2This is a comparison chart of the mechanical properties of the rail of the present invention and traditional rails; it adopts the form of a bar chart, with the horizontal axis representing performance indicators (impact toughness, tensile strength, elongation, rail head hardness) and the vertical axis representing the corresponding values (units are J / cm², MPa, %, HRC, respectively), clearly showing the comprehensive advantages of the rail of the present invention in each core mechanical indicator, and the technical effect is intuitive and verifiable.
[0039] Figure 3 This is a schematic diagram of the microstructure of the rail of the present invention (500x magnification); the microstructure consists of fine pearlite + a small amount of dispersed carbides, with a dense and uniform structure and no obvious defects, which directly confirms the effectiveness of the synergistic control of composition and process.
[0040] Figure 4 This is a schematic diagram of the microstructure of the rail welded joint of the present invention (500x magnification). The diagram shows that the microstructure of the welded joint is fine pearlite with a small amount of dispersed carbides. The grains are fine and uniform, and there are no defects such as welding cracks or inclusions, which provides microstructural support for the welded joint to meet the performance standards. Detailed Implementation
[0041] Example 1
[0042] A high-impact toughness steel rail has the following chemical composition by mass percentage: C: 0.58%, Si: 1.40%, Mn: 0.90%, P: 0.020%, S: 0.015%, with the remainder being Fe and unavoidable impurities.
[0043] The production process is as follows:
[0044] (1) Smelting and casting: After smelting in a converter, continuous casting process is adopted, and the cooling rate is controlled at 2.0℃ / s to obtain a homogeneous steel billet without compositional segregation;
[0045] (2) Hot rolling: The steel billet is heated to 1150℃, held for 2.5 hours, and then rolled in multiple passes with a final rolling temperature of 880℃. After final rolling, it is air-cooled to 980℃.
[0046] (3) Heat treatment process: ① Quenching treatment: Online continuous quenching is adopted to rapidly cool the key stress parts of the rail to 300℃ at a cooling rate of 18℃ / s; ② Segmented tempering: The temperature is raised to 320℃ at a heating rate of 6℃ / min, held for 1.5 hours, then heated to 500℃ and held for 2 hours, and then cooled to room temperature in the furnace.
[0047] (4) Welding pretreatment: Mechanically grind and remove rust from the welding area at both ends of the rail. After removing the surface oxide scale, use induction preheating to 220°C. The preheating range is 50mm on each side of the welding end, and the temperature is maintained for 12 minutes.
[0048] (5) Finished product processing: The surface of the rail is finely polished and ultrasonically tested to confirm that there are no defects such as cracks, inclusions, or air holes. After that, it is a finished product.
[0049] Performance testing of finished rails: The microstructure is mainly fine pearlite, with an impact toughness of 58 J / cm², tensile strength of 1300 MPa, yield strength of 1180 MPa, elongation after fracture of 13.5%, and rail head hardness of HRC56; the welded joint has an impact toughness of 47 J / cm², tensile strength of 1220 MPa, and elongation after fracture of 10.5%, meeting the requirements for heavy-haul railway use.
[0050] Example 2
[0051] A high-impact toughness steel rail has the following chemical composition by mass percentage: C: 0.61%, Si: 1.60%, Mn: 1.00%, P: 0.022%, S: 0.018%, with the remainder being Fe and unavoidable impurities.
[0052] In the production process, the segmented tempering temperatures were adjusted to 340℃ (first stage) and 510℃ (second stage), while the remaining process parameters were the same as in Example 1.
[0053] Performance testing of finished rails: The microstructure is mainly fine pearlite, with an impact toughness of 62 J / cm², tensile strength of 1330 MPa, yield strength of 1210 MPa, elongation after fracture of 13%, and rail head hardness of HRC57; the welded joint has an impact toughness of 46 J / cm², tensile strength of 1230 MPa, and elongation after fracture of 10.2%, which is suitable for the frequent start-stop conditions of urban rail transit.
[0054] Example 3
[0055] A high-impact toughness steel rail has the following chemical composition by mass percentage: C: 0.63%, Si: 1.20%, Mn: 1.10%, P: 0.025%, S: 0.016%, with the remainder being Fe and unavoidable impurities.
[0056] In the production process, the quenching cooling rate was adjusted to 20℃ / s, and the remaining process parameters were the same as in Example 1.
[0057] Finished rail performance testing: The microstructure is mainly fine pearlite, with an impact toughness of 55 J / cm², tensile strength of 1350 MPa, yield strength of 1230 MPa, elongation after fracture of 12%, and rail head hardness of HRC58; the welded joint has an impact toughness of 48 J / cm², tensile strength of 1250 MPa, and elongation after fracture of 10.8%, making it suitable for complex road conditions in mountainous heavy-haul railways.
[0058] The core innovation of this invention lies in:
[0059] Breaking through the dual limitations of traditional rail composition design and process mode, through the organic combination of "medium carbon-high silicon-high manganese" composition synergistic innovation and "segmented tempering + welding preheating" process innovation, the microstructure is precisely controlled to be fine pearlite, and a three-dimensional balance of impact toughness, tensile strength, elongation and hardness is achieved without adding precious alloys.
[0060] During implementation, parameters can be flexibly adjusted according to the performance focus of specific application scenarios: for heavy-haul railways, the carbon content (0.61%-0.63%) can be appropriately increased to enhance wear resistance and strength; for urban rail transit, the silicon content (1.40%-1.60%) can be appropriately increased to improve resistance to frequent impacts; and for mountain railways, the manganese content (1.00%-1.10%) can be appropriately increased to enhance resistance to bending fatigue and plasticity.
[0061] The equipment and processes not covered in this invention can all adopt conventional technologies in the existing rail production field for rail transit. The process has strong compatibility and good industrial adaptability, and can quickly realize large-scale production and engineering application, which has significant economic value and social benefits.
[0062] 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 producing high-strength, high-impact-toughness steel rails, characterized in that: Includes the following steps: (1) Smelting and casting: The converter smelting process is adopted, the purity of the molten steel is strictly controlled, and the harmful impurity elements P and S are controlled within the range specified in claim 1. Homogeneous steel billets are obtained through continuous casting process. The cooling rate during continuous casting is controlled at 1.5-2.5℃ / s to avoid component segregation and internal porosity defects. (2) Hot rolling: The billet is heated to 1100-1200℃ and held for 2-3 hours to eliminate the internal stress of the billet. Then it is formed into a rail section by multiple passes of controlled rolling. The final rolling temperature is controlled at 850-900℃. After the final rolling, it is air-cooled to 950-1000℃ to obtain a uniform and fine austenitic structure, which lays the foundation for the improvement of subsequent heat treatment performance. (3) Heat treatment process: ① Quenching treatment: Online continuous quenching is adopted to rapidly cool the key stress-bearing parts such as rail head and rail web to 280-320℃, with a cooling rate of 15-20℃ / s; ② Segmented tempering: At a heating rate of 5-8℃ / min, it is first held at 300-350℃ for 1.5 hours to eliminate quenching stress, and then heated to 480-520℃ and held for 2 hours to promote the transformation of fine pearlite structure. It is then cooled to room temperature in the furnace to ensure the uniformity of structure and the stability of mechanical properties. (4) Welding pretreatment: Grind and remove rust from the welding area at both ends of the rail, remove surface oxide scale and impurities, and then use induction preheating treatment. The preheating temperature is controlled at 200-250℃, and the preheating range is 50mm on both sides of the welding end. The temperature is maintained for 10-15 minutes. The mechanical properties of the welded joint meet the following requirements: impact toughness ≥45 J / cm², tensile strength ≥1200 MPa, elongation after fracture ≥10%, and microstructure is fine pearlite + a small amount of dispersed carbides. (5) Finished product processing: The rails are surface-polished and ultrasonically tested to ensure that there are no cracks, inclusions, or air holes, and finally the finished rails are obtained. The chemical composition of the rail, by mass percentage, is as follows: C: 0.58%-0.63%, Si: 1.20%-1.80%, Mn: 0.80%-1.10%, P≤0.025%, S≤0.020%, with the remainder being Fe and unavoidable impurities. The microstructure of the rail is mainly fine pearlite, and its mechanical properties meet the following requirements: impact toughness ≥55 J / cm², tensile strength ≥1280 MPa, yield strength ≥1150 MPa, elongation after fracture ≥12%, and rail head hardness HRC 55-58.
2. The method for producing high-strength, high-impact-toughness steel rails according to claim 1, characterized in that: The chemical composition contains 1.40%-1.60% Si and 0.90%-1.00% Mn. Through the synergistic effect of silicon and manganese elements, the elasticity, toughness and weldability of the rail are balanced. The corresponding mechanical properties are optimized as follows: impact toughness ≥58 J / cm², tensile strength ≥1300MPa, and elongation after fracture ≥13%.
3. The method for producing high-strength, high-impact-toughness steel rails according to claim 1, characterized in that: In step (2), the hot rolling process adopts multi-pass controlled rolling and cooling technology, with the reduction amount of each pass gradually increasing to ensure the accuracy of the rail cross-section dimensions and the density of the microstructure, providing structural guarantee for obtaining a uniform fine pearlite microstructure after subsequent heat treatment.
4. The method for producing high-strength, high-impact-toughness steel rails according to claim 1, characterized in that: In step (3), the heating rate of the segmented tempering is strictly controlled at 5-8℃ / min to avoid the stress concentration caused by the sudden temperature rise, further improve the uniformity of the mechanical properties of the rail, and make the tensile strength fluctuation range of the whole section ≤50MPa and the HRC hardness fluctuation ≤2.
5. The method for producing high-strength, high-impact-toughness steel rails according to claim 1, characterized in that: The chemical composition of the rail, by mass percentage, is: C: 0.58%, Si: 1.40%, Mn: 0.90%, P: 0.020%, S: 0.015%, with the remainder being Fe and unavoidable impurities.
6. The method for producing high-strength, high-impact-toughness steel rails according to claim 1, characterized in that: The chemical composition of the rail, by mass percentage, is: C: 0.61%, Si: 1.60%, Mn: 1.00%, P: 0.022%, S: 0.018%, with the remainder being Fe and unavoidable impurities.
7. The method for producing high-strength, high-impact-toughness steel rails according to claim 1, characterized in that: The chemical composition of the rail, by mass percentage, is: C: 0.63%, Si: 1.20%, Mn: 1.10%, P: 0.025%, S: 0.016%, with the remainder being Fe and unavoidable impurities.