A method for manufacturing a low-cost rail for high-altitude regions

Abstract

The application discloses a kind of low-cost high-altitude area railway rail manufacturing method, and chemical composition includes: C 0.60%‑0.65%, Si 0.40%‑0.60%, Mn 0.50%‑0.80%, Cr 0.20%‑0.30%, P≤0.025%, S≤0.020%, the balance is Fe and impurities by mass fraction;Its manufacturing method includes: smelting;Continuous casting;Rolling;Two-stage heat treatment;Straightening.The purpose of the present application is to eliminate Cu, Ni noble metal elements, the lower limit of Mn content is reduced to 0.50%, using 150 tons converter as smelting core equipment, by optimizing component ratio and two-stage heat treatment process, the performance of rail is completely benchmarked U63MnCrCuH, while greatly reducing alloy cost, without modifying production line, mass production can be realized.

Description

Technical Field

[0001] This invention belongs to the field of rail manufacturing technology, and in particular relates to a low-cost method for manufacturing rails for railways in high-altitude areas. Background Technology

[0002] Railways in high-altitude areas have stringent requirements for the low-temperature toughness, fatigue resistance, and residual stress control of rails. Currently, the mainstream U63MnCrCuH rail contains precious metals such as Cu and Ni, resulting in high raw material procurement and production costs. Meanwhile, the No. 2 line of the rail beam plant, as a dedicated rail production line, is equipped with core equipment such as a 150-ton converter and dedicated coolers in zones 1-14, and has fixed production process specifications. Existing improvement plans are mostly not adapted to the characteristics and specifications of this production line's equipment, leading to difficulties in process implementation and hindering the full utilization of the production line's efficiency.

[0003] In existing technologies, manganese (Mn) is a core strengthening element for rails. Excessive Mn content can lead to segregation in the cast billet, while insufficient Mn content fails to guarantee strength. Traditional solutions struggle to balance the relationship between Mn content and performance. Furthermore, most solutions do not utilize the 150-ton converter compatible with the No. 2 line of the rail beam plant, resulting in mismatched smelting parameters and a lack of heat treatment processes tailored to the cooling machine's zoning characteristics. This leads to significant fluctuations in rail performance, preventing the rails from consistently achieving the performance levels of U63MnCrCuH. Additionally, some solutions require modifications to production line equipment, increasing investment costs and failing to meet the demands of low-cost mass production. Therefore, developing a low-cost high-altitude rail that eliminates precious metal elements, lowers the lower limit of Mn content, and is compatible with the 150-ton converter and the entire process specifications of the No. 2 line of the rail beam plant has become an urgent industry need. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost method for manufacturing railway rails in high-altitude areas. The core of this method is to remove Cu and Ni precious metal elements, reduce the lower limit of Mn content to 0.50%, use a 150-ton converter as the core smelting equipment, and optimize the composition ratio and two-stage heat treatment process to make the rail performance fully comparable to U63MnCrCuH, while significantly reducing alloy costs. Mass production can be achieved without modifying the production line.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a low-cost method for manufacturing railway rails for high-altitude areas. The chemical composition, by mass fraction, includes: C 0.60%-0.65%, Si 0.40%-0.60%, Mn 0.50%-0.80%, Cr 0.20%-0.30%, P≤0.025%, S≤0.020%, with the balance being Fe and impurities. The mechanical properties of the rail are comparable to those of U63MnCrCuH rails, meeting the following requirements: tensile strength ≥880MPa, yield strength ≥720MPa, impact toughness at -40℃ ≥50J / cm², elongation after fracture ≥17%, residual stress ≤110MPa, and fatigue life (10... 7 Second, stress ratio R=0.1) ≥345MPa

[0007] Its manufacturing methods include:

[0008] (1) Smelting: The converter tapping temperature is 1600-1630℃. When tapping, silicon manganese alloy and silicon ferroalloy are added in proportion for pre-deoxidation. The tapping time is controlled at 8-10min. Double slag blocking is used with slag blocking balls and slag blocking cones. The amount of slag carried in is ≤3kg / t. The LF refining temperature is 1530-1560℃. The slag basicity is controlled at 2.8-3.2. Argon bottom blowing and stirring is carried out for 15-20min. Cr ferroalloy is added in batches to optimize the composition. The final molten steel has [H]≤2.0ppm and [O]≤35ppm.

[0009] (2) Continuous casting: The cooling water volume of the crystallizer is 0.8-1.0 m³ / h, the vibration frequency is 100-120 times / min, the amplitude is 8-10 mm, the casting speed is 0.85-1.05 m / min, the secondary cooling adopts air mist cooling, the cooling intensity is 1.2-1.4 L / kg, the cross-sectional size of the billet is strictly controlled to be 320 mm × 280 mm, and after exiting the crystallizer, the special heat preservation cover of the production line is used to naturally cover and preserve the heat to avoid the surface temperature of the billet dropping too quickly;

[0010] (3) Rolling: The billet is heated to 1180-1220℃ at a rate of ≤150℃ / h and held for 4-4.5h. The heating furnace is divided into three sections for temperature control: preheating section, heating section and soaking section. The temperature difference between each section is ≤30℃. The billet is rolled in 10-13 passes by a universal rolling mill. The reduction per pass is 9%-12% according to the standard of the production line. The final rolling temperature is 840-870℃. The temperature is monitored in real time by the online temperature measuring instrument of the production line during the rolling process. The temperature deviation is ≤±5℃.

[0011] (4) Two-stage heat treatment: The first stage is graded controlled cooling. In the cooling machine, the air pressure in zones 1-10 is 0.4-0.6MPa, the cooling rate is 3-4.5℃ / s, and the temperature is cooled to 580-620℃. In zones 11-14, the air pressure is switched to 0.15-0.25MPa, the cooling rate is 1.5-2.2℃ / s, and the temperature is cooled to 380-420℃. The fan frequency in each zone of the cooling machine is adjusted according to the preset parameters of the production line. The second stage isothermal stabilization treatment is to send the rail into the continuous isothermal furnace of the production line and keep it at 380-420℃ for 1.5-2h. During the heat preservation process, the temperature uniformity in the furnace is ≤±3℃.

[0012] (5) Straightening: Straightening is carried out at a temperature of 380-420℃ after isothermal treatment, with a straightening pressure of 280-320MPa, a straightening speed of 1.2-1.6m / min, and a straightening amount of 0.3-0.5mm per pass. The displacement sensor of the straightening machine provides real-time feedback and adjustment to ensure that the straightness deviation of the rail is ≤0.5mm / m.

[0013] Furthermore, it also includes (6) finishing inspection: mechanical grinding to remove surface defects, defect depth ≤ 0.3 mm, roughness Ra ≤ 6.5 μm; using a laser diameter gauge on the production line to detect key dimensions, deviation ≤ ± 0.3 mm / m; using an ultrasonic flaw detector on the production line for full-length flaw detection, detection sensitivity ≥ 40 dB, with no internal defects.

[0014] Furthermore, in step (1), the purity of the Cr-iron alloy is ≥98%, and the silicon-manganese alloy contains 65%-70% Mn and 18%-22% Si.

[0015] Furthermore, in step (4), the cooling machine in zones 1-10 operates according to the independent air control program of the No. 2 line of the rail beam plant, with a wind speed deviation of ≤0.05MPa in each zone; the production line matching flow guiding device is activated in zones 11-14 to ensure uniform cooling of the rail cross section and a temperature difference of ≤15℃, which fully matches the characteristics of the production line cooling machine equipment.

[0016] Furthermore, the composition of the rail is: C 0.63%, Mn 0.55%, Cr 0.25%.

[0017] Further, rolling: According to the production line rolling specifications, the billet is heated to 1200℃ at a rate of 130℃ / h and held in a walking beam furnace for 4.2h. The temperatures of the preheating section, heating section, and soaking section of the furnace are controlled at 950℃, 1180℃, and 1200℃ respectively, with a temperature difference of ≤25℃ between each section. After exiting the furnace, the billet enters the universal rolling mill and undergoes 12 passes of rolling. The reduction per pass is allocated according to the production line standard as follows: 9% for passes 1-3, 11% for passes 4-9, and 10% for passes 10-12. The final rolling temperature is stabilized at 855℃ through real-time monitoring by the online temperature measuring instrument on the production line.

[0018] Furthermore, a two-stage heat treatment process is employed: the air pressure in zones 1-10 of the cooling machine is set to 0.5 MPa, the cooling rate is 3.8℃ / s, and the temperature is cooled to 600℃; the air pressure in zones 11-14 is switched to 0.2 MPa, the cooling rate is 1.8℃ / s, and the temperature is cooled to 400℃. The fan frequency in each zone is adjusted according to the preset parameters of the production line to ensure uniform airflow. Subsequently, the steel rail is fed into the continuous isothermal furnace of the production line and held at 400℃ for 1.8 hours, with the temperature uniformity inside the furnace controlled within ±2℃.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] This invention achieves three core breakthroughs by eliminating Cu and Ni precious metal elements, reducing the lower limit of Mn content to 0.50%, and utilizing a 150-ton converter adapted to the entire production process of the No. 2 line at the rail beam plant: First, significantly reduced costs, decreasing by 22%-26% compared to U63MnCrCuH rails, resulting in savings in both raw materials and production energy consumption; second, strong process adaptability, fully complying with the No. 2 line regulations of the rail beam plant, requiring no modification to existing equipment, lowering the production threshold, and enabling rapid industrial-scale mass production; third, stable and reliable performance, with core indicators such as tensile strength and low-temperature toughness fully matching those of U63MnCrCuH rails, and residual stress controlled below 110MPa, suitable for the harsh service environment of plateau railways. This invention balances economic and practical value, and has extremely broad prospects for promotion. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 Manufacturing process flow diagram adapted to this invention;

[0023] Figure 2 This is a schematic diagram of the rail heat treatment process of the present invention;

[0024] Figure 3 This is a graph showing the relationship between air pressure and cooling rate of the coolers in zones 1-14 of the heat treatment line.

[0025] Figure 4 This is a comparison of the microstructure of the rail of this invention and the U63MnCrCuH rail;

[0026] Figure 5 This is a schematic diagram of the residual stress distribution in the rail of the present invention. Detailed Implementation

[0027] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-cost railway rail for high-altitude areas and its manufacturing method. The core of the invention is to remove Cu and Ni precious metal elements, reduce the lower limit of Mn content to 0.50%, use a 150-ton converter as the core smelting equipment, strictly follow the production process regulations of the No. 2 line of the rail beam plant throughout the entire process, and optimize the composition ratio and two-stage heat treatment process to make the rail performance fully comparable to U63MnCrCuH, while significantly reducing alloy costs. Mass production can be achieved without modifying the production line.

[0028] Low-cost railway rails for high-altitude areas

[0029] This steel rail eliminates Cu and Ni precious metal elements, completely eliminating the cost of precious metal raw materials. The core optimization is to reduce the Mn content range to 0.50%-0.80%. This lower limit avoids the problem of insufficient strengthening caused by excessively low Mn content, while also reducing the risk of Mn segregation and raw material consumption costs. The C content is precisely controlled at 0.60%-0.65%, balancing the structural strength and wear resistance of the rail; the Cr content is maintained at 0.20%-0.30%, effectively improving the hardness and wear resistance of the rail; and 0.40%-0.60% Si element plays a solid solution strengthening role, compensating for the performance loss caused by low Mn content.

[0030] Strict control of P≤0.025% and S≤0.020% reduces the damage of harmful impurities to the rail matrix and avoids the formation of crack sources. The raw materials used in this composition system are all industrial-grade conventional alloys that meet the standards of the No. 2 line of the rail beam factory. The cost is 22%-26% lower than that of U63MnCrCuH rails, and the mechanical properties fully meet the standards, with tensile strength ≥1080MPa, impact toughness at -40℃ ≥20J / cm², and residual stress ≤120MPa. It can be used stably for a long time in high-altitude areas above 3000m.

[0031] Manufacturing method

[0032] This manufacturing method is based entirely on the existing equipment and procedures of the No. 2 line of the rail beam plant. The core of the method is a 150-ton converter. The parameters of each process are precisely matched to the characteristics of the production line, and no additional equipment modifications are required.

[0033] (1) Smelting: The 150-ton converter fully conforms to the smelting regulations of the No. 2 line of the rail beam plant. The tapping temperature, time, and slag blocking method are all implemented according to the production line standards. The slag basicity, stirring time, and alloy addition sequence of the LF refining strictly follow the "deoxidation-alloying" process of the production line to ensure the purity and uniformity of the molten steel and meet the requirements of subsequent processes.

[0034] (2) Continuous casting: The arc-shaped continuous casting machine with a radius of 12.5m of the No. 2 line of the rail beam plant is adopted. The crystallizer parameters, casting speed and secondary cooling method are all adjusted according to the preset program of the production line. The special heat preservation cover ensures the quality of the billet and avoids cracks caused by excessive temperature drop. It is fully compatible with the continuous casting rhythm of the production line.

[0035] (3) Rolling: The production line uses a walking beam furnace and a universal rolling mill. The three-stage temperature control of the furnace, the reduction of each rolling pass, and the monitoring of the final rolling temperature all follow the rolling specifications of the No. 2 line of the rail beam plant. The temperature is precisely controlled by an online temperature measuring instrument to ensure that the rolled parts have a uniform structure, laying a good foundation for subsequent heat treatment.

[0036] (4) Two-stage heat treatment: The core is adapted to the cooling machine and continuous isothermal furnace in zones 1-14 of the No. 2 line of the rail beam plant. The cooling machine in zones 1-10 uses high air pressure to quickly cool down and refine the pearlite lamellar spacing, while the cooling machine in zones 11-14 uses low air pressure to slowly cool down and avoid internal stress. The frequency of the fans in each zone is adjusted according to the production line parameters. The subsequent isothermal treatment is carried out in the continuous isothermal furnace of the production line. The holding temperature and time are strictly matched with the production line equipment capacity to further homogenize the structure and reduce residual stress.

[0037] (5) Straightening and finishing inspection: The production line uses an 8-roll straightener. The straightening parameters are set according to the hot straightening standard of the production line. The displacement sensor is adjusted in real time to ensure straightness. The grinding standard, size detection and flaw detection process of the finishing inspection all follow the finished product inspection procedure to ensure that the product meets the production line's factory standards.

[0038] Quality control standards

[0039] A quality control standard fully adapted to the production system was established, conforming to the TB / T 2344.1-2020 basic standard and production line-specific inspection specifications. Chemical composition testing utilizes a direct-reading spectrometer on the production line, with sampling locations and testing frequencies following production line procedures. Mechanical property testing is completed in a dedicated laboratory on the production line, simulating a high-altitude environment to ensure test results closely reflect actual service conditions. Residual stress and non-destructive testing utilize existing equipment and processes on the production line, streamlining redundant steps to reduce testing costs while ensuring quality, thus adapting to the needs of large-scale mass production.

[0040] Example

[0041] Raw material and equipment preparation

[0042] The main raw materials are low-impurity industrial molten iron (P≤0.015%, S≤0.010%) and carbon steel scrap (P≤0.020%, S≤0.015%) that meet the standards of the No. 2 line of the rail beam plant. The raw material sources are stable and meet the smelting requirements of the 150-ton converter; the alloy raw materials are conventional ferrosilicon manganese alloys with Mn 65%-70% and Si 18%-22%, industrial-grade Cr ferroalloys with a purity of ≥98%, and ferrosilicon alloys with a purity of ≥99%, which fully meet the raw material procurement standards of the production line and do not require additional procurement of special alloys; the slag-making raw materials are ordinary lime with CaO≥88% and fluorite with CaF2≥85%, which meet the slag-making requirements of the LF refining furnace of the production line.

[0043] The core equipment completely uses the existing equipment of the No. 2 line of the rail beam plant, including a 150-ton converter (the accuracy of the tapping temperature control is ±8°C), a 2500kVA LF refining furnace, a 12.5m radius arc continuous caster, a walking beam heating furnace, a universal rolling mill, a 1-14 zone cooling machine, a continuous isothermal furnace, an 8-roll straightening machine, and inspection equipment such as a direct reading spectrometer, a universal material testing machine, a laser diameter gauge, and an ultrasonic flaw detector supporting the production line, without the need to add any special equipment.

[0044] The specific manufacturing process (strictly following the procedures of the No. 2 line of the rail beam plant)

[0045] (1) Smelting: According to the smelting procedures of the 150-ton converter of the No. 2 line of the rail beam plant, 100t of molten iron and 50t of steel scrap are added to the converter. The top-bottom combined blowing process is adopted, the oxygen supply intensity is 3.9m³ / (t·min), the blowing time is 16-18min, the tapping temperature is accurately controlled at 1615°C, the tapping time is 9min, and a double slag-blocking method of slag-blocking balls + slag-blocking cones is used, with the slag carry-over amount ≤2.8kg / t; 3.2t of ferrosilicon manganese alloy and 50kg of ferrosilicon alloy are added for preliminary deoxidation during tapping; the molten steel is transferred to the LF refining furnace, heated to 1540°C, 1.2t of lime and 0.09t of fluorite are added, the slag alkalinity is adjusted to 3.0, 60kg of Cr ferroalloy is added in batches, and the argon bottom blowing stirring is started for 18min. Finally, the molten steel has [H] 1.8ppm and [O] 32ppm, and the composition meets the core requirements of C 0.63%, Mn 0.55%, and Cr 0.25%.

[0046] (2) Continuous casting: Following the continuous casting procedures of the No. 2 line of the rail beam plant, the cooling water volume of the mold is adjusted to 0.9m³ / h, the vibration frequency is 110 times / min, the amplitude is 9mm, the molten steel temperature in the tundish is maintained at 1510°C, the casting speed is set at 0.95m / min, and the secondary cooling uses aerosol cooling with a cooling intensity of 1.3L / kg; after the billet exits the continuous caster, it is cut into a fixed length of 12m according to the production line standard, immediately covered with a special thermal insulation cover of the production line, and naturally insulated to below 750°C before being transferred to the walking beam heating furnace.

[0047] (3) Rolling: According to the rolling procedure of the production line, the billet is heated to 1200℃ at a rate of 130℃ / h and held in the walking beam furnace for 4.2h. The temperatures of the preheating section, heating section and soaking section of the furnace are controlled at 950℃, 1180℃ and 1200℃ respectively, and the temperature difference between each section is ≤25℃. After the billet exits the furnace, it enters the universal rolling mill and is rolled in 12 passes. The reduction per pass is allocated according to the standard of the production line as 9% for passes 1-3, 11% for passes 4-9 and 10% for passes 10-12. The final rolling temperature is stabilized at 855℃ by real-time monitoring through the online temperature measuring instrument of the production line.

[0048] (4) Two-stage heat treatment: strictly adapt to the cooling machine specifications of the No. 2 line of the rail beam plant. The air pressure of the cooling machine in zones 1-10 is set to 0.5MPa, the cooling rate is 3.8℃ / s, and the temperature is cooled to 600℃. The air pressure in zones 11-14 is switched to 0.2MPa, the cooling rate is 1.8℃ / s, and the temperature is cooled to 400℃. The frequency of the fans in each zone is adjusted according to the preset parameters of the production line to ensure uniform air speed. Then the rails are sent into the continuous isothermal furnace of the production line and kept at 400℃ for 1.8h. The temperature uniformity in the furnace is controlled within ±2℃.

[0049] (5) Straightening: The No. 2 line of the rail beam factory uses an 8-roller straightening machine to perform hot straightening at 400℃. The straightening pressure is set to 300MPa, the straightening speed is 1.4m / min, and the straightening amount per pass is 0.4mm. The straightening machine is adjusted in real time by feedback from the displacement sensor. After straightening, the straightness deviation of the rail is ≤0.4mm / m. The residual stress test shows 105MPa at the head and 100MPa at the waist, which meets the standard requirements.

[0050] (6) Finishing inspection: According to the finishing procedure of the production line, the oxide scale and defects on the surface of the rail are removed by mechanical grinding machine. After grinding, the surface defect depth is ≤0.25mm and the roughness Ra is ≤6.3μm. The key dimensions such as rail height and rail head width are inspected along the entire length by the laser diameter measuring instrument of the production line. The dimensional deviation is ≤±0.28mm / m. The chemical composition test is within the set range. The mechanical property test shows that the tensile strength is 895MPa, the impact toughness at -40℃ is 54J / cm², and the fatigue life is 352MPa. The ultrasonic flaw detector of the production line is used for full-length flaw detection. There are no internal defects and it is judged to be qualified.

[0051] Comparison of effects between the examples and the comparative examples

[0052] Examples 1-3 were produced strictly according to the specifications of the No. 2 line of the rail beam factory, with minor adjustments to the Mn content in the core components (0.50%, 0.65%, and 0.80%, respectively). The mechanical properties all stably met the set standards, with impact toughness at -40℃ reaching 50J / cm², 52J / cm², and 55J / cm², respectively, and fatigue life of 345MPa, 348MPa, and 355MPa, respectively, all reaching the performance level of U63MnCrCuH rails.

[0053] Comparative Example 1 is a U63MnCrCuH steel rail containing 0.2%-0.3% Cu and 0.1%-0.2% Ni, smelted using a conventional converter, which is not compatible with the specifications of the No. 2 line of the rail beam plant. Its tensile strength is 880MPa and its impact toughness at -40℃ is 50J / cm², which is comparable to the performance of this invention, but the cost is 22% higher than that of this invention. Comparative Example 2 is a traditional low-Mn steel rail, which does not use a 150-ton converter and two-stage heat treatment. Its tensile strength is only 780MPa and its impact toughness at -40℃ is 35J / cm², which cannot meet the requirements of high-altitude areas, and the process is incompatible with the No. 2 line of the rail beam plant.

[0054] 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 low-cost method for manufacturing railway rails for high-altitude areas, characterized in that: The chemical composition by mass fraction includes: C 0.60%-0.65%, Si 0.40%-0.60%, Mn 0.50%-0.80%, Cr 0.20%-0.30%, P≤0.025%, S≤0.020%, with the balance being Fe and impurities; the mechanical properties of the rail are comparable to those of U63MnCrCuH rail, meeting the following requirements: tensile strength ≥880MPa, yield strength ≥720MPa, impact toughness at -40℃ ≥50J / cm², elongation after fracture ≥17%, residual stress ≤110MPa, and fatigue life (10... 7 Second, stress ratio R=0.1) ≥345MPa Its manufacturing methods include: (1) Smelting: The converter tapping temperature is 1600-1630℃. When tapping, silicon manganese alloy and silicon ferroalloy are added in proportion for pre-deoxidation. The tapping time is controlled at 8-10min. Double slag blocking is used with slag blocking balls and slag blocking cones. The amount of slag carried in is ≤3kg / t. The LF refining temperature is 1530-1560℃. The slag basicity is controlled at 2.8-3.

2. Argon bottom blowing and stirring is carried out for 15-20min. Cr ferroalloy is added in batches to optimize the composition. The final molten steel has [H]≤2.0ppm and [O]≤35ppm. (2) Continuous casting: The cooling water volume of the crystallizer is 0.8-1.0 m³ / h, the vibration frequency is 100-120 times / min, the amplitude is 8-10 mm, the casting speed is 0.85-1.05 m / min, the secondary cooling adopts air mist cooling, the cooling intensity is 1.2-1.4 L / kg, the cross-sectional size of the billet is strictly controlled to be 320 mm × 280 mm, and after exiting the crystallizer, the special heat preservation cover of the production line is used to naturally cover and preserve the heat to avoid the surface temperature of the billet dropping too quickly; (3) Rolling: The billet is heated to 1180-1220℃ at a rate of ≤150℃ / h and held for 4-4.5h. The heating furnace is divided into three sections for temperature control: preheating section, heating section and soaking section. The temperature difference between each section is ≤30℃. The billet is rolled in 10-13 passes by a universal rolling mill. The reduction per pass is 9%-12% according to the standard of the production line. The final rolling temperature is 840-870℃. The temperature is monitored in real time by the online temperature measuring instrument of the production line during the rolling process. The temperature deviation is ≤±5℃. (4) Two-stage heat treatment: The first stage is graded controlled cooling. In the first stage, the cooling machine uses a large air pressure of 0.4-0.6MPa and a cooling rate of 3-4.5℃ / s in zones 1-10, cooling to 580-620℃; in the second stage, the cooling machine switches to a small air pressure of 0.15-0.25MPa and a cooling rate of 1.5-2.2℃ / s, cooling to 380-420℃. The fan frequency in each zone of the cooling machine is adjusted according to the preset parameters of the production line. The second stage isothermal stabilization treatment involves sending the rail into the continuous isothermal furnace of the production line and holding it at 380-420℃ for 1.5-2 hours. During the holding process, the temperature uniformity inside the furnace is ≤±3℃. (5) Straightening: Straightening is carried out at a temperature of 380-420℃ after isothermal treatment, with a straightening pressure of 280-320MPa, a straightening speed of 1.2-1.6m / min, and a straightening amount of 0.3-0.5mm per pass. The displacement sensor of the straightening machine provides real-time feedback and adjustment to ensure that the straightness deviation of the rail is ≤0.5mm / m.

2. The method for manufacturing low-cost railway rails for plateau regions according to claim 1, characterized in that: It also includes (6) finishing inspection: mechanical grinding to remove surface defects, defect depth ≤ 0.3 mm, roughness Ra ≤ 6.5 μm; using the production line laser diameter gauge to detect key dimensions, deviation ≤ ± 0.3 mm / m; using the production line ultrasonic flaw detector for full-length flaw detection, detection sensitivity ≥ 40 dB, no internal defects.

3. The method for manufacturing low-cost railway rails for plateau regions according to claim 1, characterized in that: In step (1), the purity of Cr-iron alloy is ≥98%, and the silicon-manganese alloy contains 65%-70% Mn and 18%-22% Si.

4. The method for manufacturing low-cost railway rails for plateau regions according to claim 1, characterized in that: In step (4), the cooling machine in zones 1-10 operates according to the independent air control program of the No. 2 line of the rail beam plant, with a wind speed deviation of ≤0.05MPa in each zone; the production line matching flow guiding device is activated in zones 11-14 to ensure uniform cooling of the rail cross section and a temperature difference of ≤15℃, which fully matches the characteristics of the production line cooling machine equipment.

5. The method for manufacturing low-cost railway rails for plateau regions according to claim 1, characterized in that: The composition of the rail is: C 0.63%, Mn 0.55%, Cr 0.25%.

6. The method for manufacturing low-cost railway rails for plateau regions according to claim 1, characterized in that: Rolling: According to the rolling specifications of the production line, the billet is heated to 1200℃ at a rate of 130℃ / h and held in a walking beam furnace for 4.2h. The temperatures of the preheating section, heating section and soaking section of the furnace are controlled at 950℃, 1180℃ and 1200℃ respectively, with a temperature difference of ≤25℃ between each section. After exiting the furnace, the billet enters the universal rolling mill and is rolled in 12 passes. The reduction per pass is allocated according to the standard of the production line as follows: 9% for passes 1-3, 11% for passes 4-9 and 10% for passes 10-12. The final rolling temperature is stabilized at 855℃ by real-time monitoring through the online temperature measuring instrument of the production line.

7. The method for manufacturing low-cost railway rails for plateau regions according to claim 1, characterized in that: Two-stage heat treatment: The air pressure in zones 1-10 of the cooling machine is set to 0.5MPa, the cooling rate is 3.8℃ / s, and the temperature is cooled to 600℃; the air pressure in zones 11-14 is switched to 0.2MPa, the cooling rate is 1.8℃ / s, and the temperature is cooled to 400℃. The frequency of the fans in each zone is adjusted according to the preset parameters of the production line to ensure uniform air speed. Then the steel rail is sent into the continuous isothermal furnace of the production line and held at 400℃ for 1.8h. The temperature uniformity inside the furnace is controlled within ±2℃.

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