A method of producing a pearlitic rail containing vanadium

Abstract

The application discloses a pearlite rail production method containing vanadium elements, which comprises the following steps: hot metal pretreatment and smelting: hot metal is pretreated by desulfurization; refining and micro alloying; continuous casting forming; casting blank heating and soaking; controlled rolling and controlled cooling rolling; isothermal spheroidizing and shaping treatment; the chemical composition of the rail is composed of the following components in mass fraction: C 0.82%-1.05%, Si 0.25%-0.48%, Mn 0.70%-1.00%, V 0.06%-0.18%, Cr 0.20%-0.45%, Cu≤0.20%, P≤0.020%, S≤0.012%, Als 0.02%-0.06%. The application aims to realize synergistic effect of vanadium element dispersion strengthening and pearlite structure refinement, completely eliminate net cementite, simultaneously optimize the production process, reduce vanadium element burning loss, and guarantee stable and controllable rail performance.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and in particular relates to a method for producing pearlitic steel rails containing vanadium. Background Technology

[0002] Heavy-haul railways impose stringent requirements on the strength, wear resistance, and fatigue life of rails. Hypereutectoid steel, with a carbon content exceeding 0.77%, possesses natural advantages in high hardness and wear resistance, making it a preferred material for heavy-haul rails. However, during the traditional production process of hypereutectoid rails, network cementite easily precipitates at grain boundaries, leading to insufficient rail toughness and poor fatigue resistance. This results in problems such as railhead spalling and cracking during service, significantly shortening the service life. Currently, existing hypereutectoid rails often improve performance by adding chromium and manganese, but this fails to achieve a balanced match between strength and toughness. Some vanadium-containing rails are predominantly eutectoid, where the dispersion strengthening effect of vanadium is not fully utilized. Furthermore, insufficient precision in controlled rolling and cooling during production processes fails to effectively suppress network cementite, resulting in rail wear resistance and fatigue life that cannot meet the demands of heavy-haul railways with an annual transport volume exceeding 500 million tons. Simultaneously, existing production processes are lengthy, with high vanadium burn-off rates, low composition control precision, and high production costs, hindering large-scale promotion.

[0003] Vanadium, often referred to as "the MSG of modern industry," can refine grains and achieve precipitation strengthening when added to steel. This significantly enhances the strength and hardness of steel while optimizing its ductility and toughness. Simultaneously, it improves the hardenability of steel, allowing for uniform hardening after heat treatment and comprehensively upgrading its overall performance. Currently, vanadium microalloyed steel is widely used in products such as thick plates, hot-rolled strips, long profiles, and seamless steel pipes, demonstrating remarkable performance improvements and significant market value. Therefore, developing a vanadium-containing hypereutectoid rail that fully utilizes the strengthening effect of vanadium, lacks a network of cementite, and exhibits excellent strength-toughness balance, along with a suitable low-cost, high-precision production method, is of significant practical importance for improving the domestic production level of heavy-duty rails and reducing maintenance costs. Summary of the Invention

[0004] To address the technical pain points of existing hypereutectoid rails, such as the easy formation of network cementite, poor toughness and fatigue resistance, low vanadium utilization rate and insufficient composition control precision, as well as complex production processes and high costs, the present invention aims to provide a method for producing vanadium-containing pearlitic rails. This method achieves synergistic effects of vanadium dispersion strengthening and pearlite microstructure refinement, completely eliminates network cementite, optimizes the production process, reduces vanadium burn-off, and ensures stable and controllable rail performance.

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

[0006] This invention discloses a method for producing vanadium-containing pearlitic steel rails, comprising the following steps:

[0007] (1) Hot metal pretreatment and smelting: Hot metal is pretreated by desulfurization and the sulfur content is controlled to be ≤0.008% before it is smelted in a converter. The final control is to have a C content of 0.75%~0.98% and a temperature of 1620~1650℃. Silicon manganese alloy and ferrochrome alloy are added simultaneously during tapping.

[0008] (2) Refining and microalloying: The molten steel is transferred to the LF refining furnace and heated to 1630~1660℃. It is then kept warm and deoxidized. Then, ferrovanadium alloy is added to complete microalloying. The V element is precisely controlled to meet the standard and is evenly distributed. After refining, the molten steel is allowed to stand for 15~25 minutes to ensure that the inclusions float to the surface. The cleanliness of the molten steel meets the DS class inclusion ≤1.0 level.

[0009] (3) Continuous casting: Continuous casting is carried out using protective casting process. The crystallizer vibration frequency is 120~180 times / min, the cooling water volume is 220~280L / min, the casting speed is controlled at 0.8~1.2m / min, the billet cross section is 280mm×380mm, the billet center segregation grade is ≤1.0, and there are no shrinkage cavities, porosity and crack defects.

[0010] (4) Heating and homogenizing the billet: The qualified billet is sent into the walking beam furnace and heated to 1080~1160℃. It is homogenized in sections for a total time of 90~150min to ensure that the temperature inside and outside the billet is uniform, the vanadium element is fully dissolved in the austenite, and the original cementite is completely dissolved.

[0011] (5) Controlled rolling and controlled cooling: A two-stage controlled rolling process is adopted. The temperature of the roughing stage is 980~1050℃, with 3~5 passes, a cumulative reduction rate of ≥65%, and a single pass reduction rate of 18%~25%; the temperature of the finishing stage is 860~920℃, with 6~8 passes, a cumulative reduction rate of ≥82%, and a final rolling speed of 6~9m / s; after finishing rolling, online controlled cooling is immediately started, and the temperature is cooled to 630~690℃ at a cooling rate of 40~70℃ / s, and held for 10~20min to inhibit the precipitation of network cementite;

[0012] (6) Isothermal spheroidization and shaping treatment: After controlled cooling, the rail is sent into an isothermal furnace and isothermally held at 570~620℃ for 25~45min to promote the spheroidization and refinement of cementite and the dispersion and precipitation of vanadium carbides; then it is cooled to room temperature at a cooling rate of 25~40℃ / s, and then the rail is straightened and cut to length. The length is 25~100m. After straightening, the straightness of the rail is ≤0.3mm / m.

[0013] (7) Finished product inspection: The appearance, dimensions, mechanical properties and structure of the rails are inspected, and they are put into storage after passing the inspection;

[0014] The rail is made of hypereutectoid steel and contains vanadium as a strengthening element. Its chemical composition by mass fraction is as follows: C 0.82%~1.05%, Si 0.25%~0.48%, Mn 0.70%~1.00%, V 0.06%~0.18%, Cr 0.20%~0.45%, Cu≤0.20%, P≤0.020%, S≤0.012%, Als 0.02%~0.06%, with the balance being Fe and unavoidable trace impurities.

[0015] Furthermore, the room temperature microstructure of this rail consists of refined pearlite and dispersed vanadium carbides, without network cementite.

[0016] Furthermore, in step (2), the amount of vanadium-iron alloy added is calculated as 1.05 to 1.10 times the target V content of the rail, to avoid vanadium element burn-off leading to substandard composition.

[0017] Furthermore, in step (5), the online cooling system adopts an air mist cooling method to precisely control the cooling rate of the rail head, rail web, and rail bottom, ensuring that the structure and performance of each part of the rail are uniform.

[0018] Furthermore, after the isothermal insulation is completed in step (6), the surface of the rail needs to be shot blasted to remove the iron oxide scale, and the surface roughness Ra≤12.5μm.

[0019] Furthermore, the pearlitic steel rail, by mass fraction, has the following chemical composition: C 0.82%, Si 0.32%, Mn 0.82%, V 0.10%, Cr 0.28%, Cu 0.15%, P 0.016%, S 0.009%, Als 0.035%, with the balance being Fe and unavoidable impurities.

[0020] Furthermore, the pearlitic steel rail has the following chemical composition by mass fraction: C 0.81%, Si 0.45%, Mn 0.83%, V 0.16%, Cr 0.40%, Cu 0.18%, P 0.015%, S 0.008%, Als 0.05%, with the balance being Fe and unavoidable impurities.

[0021] Furthermore, the pearlitic steel rail, by mass fraction, has the following chemical composition: C 0.83%, Si 0.28%, Mn 0.75%, V 0.08%, Cr 0.23%, Cu 0.12%, P 0.017%, S 0.010%, Als 0.028%, with the balance being Fe and unavoidable impurities.

[0022] This invention achieves precise ingredient ratios and comprehensive process control:

[0023] 1. Precise Composition Design: The hypereutectoid carbon content of 0.82%~1.05% is selected to ensure the basic hardness and wear resistance of the rail; Si and Mn elements are used for solid solution strengthening, and Cr elements are used to refine the grains and improve hardenability; 0.06%~0.18% V element is added to the core, utilizing vanadium and carbon to form stable vanadium carbides, which are dispersed in the microstructure to form dispersion strengthening, while inhibiting the precipitation of cementite network; the content of harmful elements P and S is strictly controlled to improve the purity and toughness of the rail, and Al elements assist in deoxidation to ensure the cleanliness of molten steel.

[0024] 2. Full-process process control: A three-stage smelting process of molten iron pretreatment, converter smelting, and LF refining is adopted to precisely control the amount of ferrovanadium alloy added and reserve the burn-off allowance to ensure that the vanadium element composition meets the standards; in the continuous casting stage, protective casting and precise speed control are adopted to avoid billet segregation and defects; in the heating and soaking stage, vanadium element is fully dissolved to lay the foundation for subsequent precipitation strengthening; two-stage controlled rolling + online gas mist controlled cooling precisely control the rolling temperature and cooling rate to suppress the formation of network cementite; the subsequent isothermal spheroidization treatment promotes the refinement and spheroidization of cementite and the uniform dispersion and precipitation of vanadium carbides, ultimately achieving excellent performance of rail strength and toughness matching.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0026] Compared with the prior art, the present invention has the following key advantages:

[0027] 1. Excellent and balanced performance: Through the synergistic effect of vanadium dispersion strengthening and pearlite refinement, the rail is free of network cementite defects. In Example 2, the tensile strength is ≥1280MPa, the Brinell hardness is 380-385HB, the wear loss is ≤0.12g, and the fatigue life is ≥3.2 million cycles. Compared with traditional hypereutectoid rails, the wear resistance is improved by more than 30% and the fatigue life is improved by more than 25%, which can meet the high-load service requirements of heavy-haul railways and extend the rail replacement cycle.

[0028] 2. High vanadium utilization rate: The amount of ferrovanadium added is accurately calculated according to the burning loss coefficient during the smelting stage, the static setting during the refining stage ensures uniform distribution of vanadium, and the heating and homogenization stage ensures full solidification of vanadium. The process control throughout the process ensures that the vanadium burning loss rate is ≤8%, which is far lower than the burning loss rate of more than 15% in traditional processes, effectively reducing production costs.

[0029] 3. High controllability of production process: The key process parameters such as temperature, rate and time are clearly defined throughout the entire process. Online atomized cooling achieves uniform cooling of all parts of the rail. Isothermal spheroidization treatment ensures stable structure. The performance of finished rails fluctuates little and the pass rate is ≥99.5%, making it suitable for large-scale industrial production.

[0030] 4. Wide adaptability: Finished steel rails can be produced to specific lengths according to demand, taking into account various high-wear scenarios such as heavy-duty freight lines, port railways, and mining railways, without the need for additional process adjustments, making them highly practical. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. All embodiments are exemplary and do not limit the scope of protection of the present invention.

[0032] Example 1

[0033] The vanadium-containing hypereutectoid rail of this embodiment has the following chemical composition by mass fraction: C 0.82%, Si 0.32%, Mn 0.82%, V 0.10%, Cr 0.28%, Cu 0.15%, P 0.016%, S 0.009%, Als 0.035%, with the balance being Fe and unavoidable impurities.

[0034] Its production method includes the following steps:

[0035] Pearlitic rail steel with finer interlamellar spacing is obtained by steelmaking, rolling, and heat treatment. The process flow is as follows: desulfurized pretreated molten iron—150t top-and-bottom blowing converter smelting—LF refining—VD vacuum degassing refining—square billet continuous casting (280mm×380mm)—heating—high-pressure water descaling—BD1 rough rolling—BD2 rough rolling—universal rolling mill rolling—online heat treatment—straightening—flaw detection—machining—inspection and warehousing.

[0036] (1) Hot metal pretreatment and smelting: Hot metal is desulfurized to S content of 0.007%, and then smelted in a converter. The final C content is 0.82% and the temperature is 1635℃. When tapping the steel, silicon manganese alloy and ferrochrome alloy are added for pre-alloying.

[0037] (2) Refining and microalloying: The molten steel is heated to 1640℃ in the LF refining furnace, and after holding for deoxidation, vanadium-iron alloy is added at 1.08 times the target content. After refining, it is allowed to stand for 20 minutes. The DS-type inclusions in the molten steel are grade 0.8.

[0038] (3) Continuous casting: The size of the cast billet is 280 mm × 380 mm. The tundish covering agent of the large billet continuous casting machine is calcium-magnesium granules, and the crystallizer uses low-alumina protective slag. The casting process is protected throughout, and the electromagnetic stirring of the crystallizer and the light reduction mode at the end of solidification are turned on simultaneously. The liquidus temperature of the trial rail is 1464℃, and the superheat (ΔT) is controlled at 29℃. The constant casting speed is maintained throughout the process, with a casting speed of 0.65 m / min.

[0039] (4) Heating and homogenization of billet: Heating to 1120℃ in a walking beam furnace and homogenizing for 120 min, with a temperature difference of ≤20℃ between the inside and outside of the billet;

[0040] (5) Controlled rolling and controlled cooling: roughing temperature 1020℃, 4 passes, cumulative reduction 68%; finishing temperature 890℃, 7 passes, cumulative reduction 85%, final rolling speed 7.5m / s; after finishing, air mist controlled cooling, cooling rate 55℃ / s, cooling to 660℃ and holding for 15min;

[0041] (6) Isothermal spheroidization and shaping treatment: isothermal heat treatment at 600℃ for 35 min, cooling to room temperature at a rate of 30℃ / s, straightness after straightening is 0.2 mm / m, and surface roughness Ra after shot blasting is 10.2 μm;

[0042] Example 2

[0043] The vanadium-containing hypereutectoid rail of this embodiment has the following chemical composition by mass fraction: C 0.81%, Si 0.45%, Mn 0.83%, V 0.16%, Cr 0.40%, Cu 0.18%, P 0.015%, S 0.008%, Als 0.05%, with the balance being Fe and unavoidable impurities.

[0044] Its production method includes the following steps:

[0045] (1) Hot metal pretreatment and smelting: Hot metal is desulfurized to S content of 0.006%, and then smelted in a converter. The final C content is 0.92% and the temperature is 1645℃. When tapping the steel, silicon manganese alloy and ferrochrome alloy are added for pre-alloying.

[0046] (2) Refining and microalloying: The molten steel is heated to 1655℃ in the LF refining furnace, and after holding for deoxidation, ferrovanadium alloy is added at 1.10 times the target content. After refining, the molten steel is allowed to stand for 22 minutes, and the DS-type inclusions in the molten steel are grade 0.7.

[0047] (3) Continuous casting: Protective casting continuous casting, crystallizer vibration frequency 170 times / min, cooling water volume 270L / min, casting speed 0.9m / min, billet center segregation grade 0.9, no defects;

[0048] (4) Heating and homogenization of billet: The billet is heated to 1150℃ in a walking beam furnace and homogenized for 140 min. The temperature difference between the inside and outside of the billet is ≤18℃.

[0049] (5) Controlled rolling and controlled cooling: roughing temperature 1040℃, 5 passes, cumulative reduction 72%; finishing temperature 910℃, 8 passes, cumulative reduction 88%, final rolling speed 8.2m / s; after finishing, air mist controlled cooling, cooling rate 65℃ / s, cooling to 680℃ and holding for 18min;

[0050] (6) Isothermal spheroidization and shaping treatment: isothermal heat treatment at 610℃ for 30 min, cooling to room temperature at a rate of 38℃ / s, straightness after straightening is 0.25 mm / m, and surface roughness Ra after shot blasting is 9.8 μm;

[0051] Example 3

[0052] The vanadium-containing hypereutectoid rail of this embodiment has the following chemical composition by mass fraction: C 0.83%, Si 0.28%, Mn 0.75%, V 0.08%, Cr 0.23%, Cu 0.12%, P 0.017%, S 0.010%, Als 0.028%, with the balance being Fe and unavoidable impurities.

[0053] Its production method includes the following steps:

[0054] (1) Hot metal pretreatment and smelting: Hot metal is desulfurized to S content of 0.008%, and then smelted in a converter. The final C content is 0.78% and the temperature is 1625℃. When tapping the steel, silicon manganese alloy and ferrochrome alloy are added for pre-alloying.

[0055] (2) Refining and microalloying: The molten steel is heated to 1635℃ in the LF refining furnace, and after holding for deoxidation, vanadium-iron alloy is added at 1.06 times the target content. After refining, it is allowed to stand for 18 minutes. The DS-type inclusions in the molten steel are grade 0.9.

[0056] (3) Continuous casting: Protective casting continuous casting, crystallizer vibration frequency 130 times / min, cooling water volume 230L / min, casting speed 1.1m / min, billet center segregation grade 0.8, no defects;

[0057] (4) Heating and homogenization of billet: Heating to 1090℃ in a walking beam furnace and homogenizing for 100 min, with a temperature difference of ≤22℃ between the inside and outside of the billet;

[0058] (5) Controlled rolling and controlled cooling: roughing temperature 990℃, 3 passes, cumulative reduction 66%; finishing temperature 870℃, 6 passes, cumulative reduction 83%, final rolling speed 6.8m / s; after finishing, air mist controlled cooling, cooling rate 45℃ / s, cooling to 640℃ and holding for 12min;

[0059] (6) Isothermal spheroidization and shaping treatment: isothermal heat treatment at 580℃ for 40 min, cooling to room temperature at a rate of 28℃ / s, straightness after straightening is 0.22 mm / m, and surface roughness Ra after shot blasting is 11.5 μm;

[0060] Finished product test results:

[0061]

[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 pearlitic steel rails containing vanadium, characterized in that: Includes the following steps: (1) Hot metal pretreatment and smelting: Hot metal is pretreated by desulfurization and the sulfur content is controlled to be ≤0.008% before it is smelted in a converter. The final control is to have a C content of 0.75%~0.98% and a temperature of 1620~1650℃. Silicon manganese alloy and ferrochrome alloy are added simultaneously during tapping. (2) Refining and microalloying: The molten steel is transferred to the LF refining furnace and heated to 1630~1660℃. It is then kept warm and deoxidized. Then, ferrovanadium alloy is added to complete microalloying. The V element is precisely controlled to meet the standard and is evenly distributed. After refining, the molten steel is allowed to stand for 15~25 minutes to ensure that the inclusions float to the surface. The cleanliness of the molten steel meets the DS class inclusion ≤1.0 level. (3) Continuous casting: Continuous casting is carried out using protective casting process. The crystallizer vibration frequency is 120~180 times / min, the cooling water volume is 220~280L / min, the casting speed is controlled at 0.8~1.2m / min, the billet cross section is 280mm×380mm, the billet center segregation grade is ≤1.0, and there are no shrinkage cavities, porosity and crack defects. (4) Heating and homogenizing the billet: The qualified billet is sent into the walking beam furnace and heated to 1080~1160℃. It is homogenized in sections for a total time of 90~150min to ensure that the temperature inside and outside the billet is uniform, the vanadium element is fully dissolved in the austenite, and the original cementite is completely dissolved. (5) Controlled rolling and controlled cooling: A two-stage controlled rolling process is adopted. The temperature of the roughing stage is 980~1050℃, with 3~5 passes, a cumulative reduction rate of ≥65%, and a single pass reduction rate of 18%~25%; the temperature of the finishing stage is 860~920℃, with 6~8 passes, a cumulative reduction rate of ≥82%, and a final rolling speed of 6~9m / s. Immediately after finishing rolling, online controlled cooling is started, and the temperature is cooled to 630-690℃ at a cooling rate of 40-70℃ / s, and held for 10-20 minutes to inhibit the precipitation of network cementite. (6) Isothermal spheroidization and shaping treatment: After controlled cooling, the rail is sent into an isothermal furnace and isothermally held at 570~620℃ for 25~45min to promote the spheroidization and refinement of cementite and the dispersion and precipitation of vanadium carbides; then it is cooled to room temperature at a cooling rate of 25~40℃ / s, and then the rail is straightened and cut to length. The length is 25~100m. After straightening, the straightness of the rail is ≤0.3mm / m. (7) Finished product inspection: The appearance, dimensions, mechanical properties and structure of the rails are inspected, and they are put into storage after passing the inspection; The rail is made of hypereutectoid steel and contains vanadium as a strengthening element. Its chemical composition by mass fraction is as follows: C 0.82%~1.05%, Si 0.25%~0.48%, Mn 0.70%~1.00%, V 0.06%~0.18%, Cr 0.20%~0.45%, Cu≤0.20%, P≤0.020%, S≤0.012%, Als 0.02%~0.06%, with the balance being Fe and unavoidable trace impurities.

2. The method for producing vanadium-containing pearlitic steel rails according to claim 1, characterized in that: The room temperature microstructure of this rail consists of refined pearlite and dispersed vanadium carbides, with no network cementite.

3. The method for producing vanadium-containing pearlitic steel rails according to claim 1, characterized in that: In step (2), the amount of vanadium-iron alloy added is calculated as 1.05 to 1.10 times the target V content of the rail to avoid vanadium burning and resulting in substandard composition.

4. The method for producing vanadium-containing pearlitic steel rails according to claim 1, characterized in that: In step (5), the online cooling system uses a mist cooling method to precisely control the cooling rate of the rail head, rail web, and rail bottom, ensuring that the structure and performance of each part of the rail are uniform.

5. The method for producing vanadium-containing pearlitic steel rails according to claim 1, characterized in that: After the isothermal insulation is completed in step (6), the surface of the rail needs to be shot blasted to remove the iron oxide scale, and the surface roughness Ra≤12.5μm.

6. The method for producing vanadium-containing pearlitic steel rails according to claim 1, characterized in that: The pearlitic steel rail, by mass fraction, has the following chemical composition: C 0.82%, Si 0.32%, Mn 0.82%, V 0.10%, Cr 0.28%, Cu 0.15%, P 0.016%, S 0.009%, Als 0.035%, with the balance being Fe and unavoidable impurities.

7. The method for producing vanadium-containing pearlitic steel rails according to claim 1, characterized in that: The pearlitic steel rail, by mass fraction, has the following chemical composition: C 0.81%, Si 0.45%, Mn 0.83%, V 0.16%, Cr 0.40%, Cu 0.18%, P 0.015%, S 0.008%, Als 0.05%, with the balance being Fe and unavoidable impurities.

8. The method for producing vanadium-containing pearlitic steel rails according to claim 1, characterized in that: The pearlitic steel rail, by mass fraction, has the following chemical composition: C 0.83%, Si 0.28%, Mn 0.75%, V 0.08%, Cr 0.23%, Cu 0.12%, P 0.017%, S 0.010%, Als 0.028%, with the balance being Fe and unavoidable impurities.

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