Manufacturing method of extreme environment resistant steel rail

Abstract

The invention discloses a manufacturing method of an extreme environment resistant steel rail, and belongs to the technical field of steel rail production. According to the method, Cr-V-Cu composite microalloying U63MnCrCuV serves as a target steel grade, and performance breakthrough is achieved through coordinated regulation and control of the four-stage whole-process technology of precise steelmaking quality control, optimized rolling shaping, constant-air-pressure heat treatment strength and surface heat treatment efficiency improvement. The method aims at solving the technical problems that the steel rail is insufficient in low-temperature toughness, corrosion resistance and wear resistance synergism in an extreme environment, and the production stability is poor in a low-temperature season. The method is suitable for laying in extreme environments such as Sichuan-Tibet railways, and significantly prolongs the service life of steel rails.

Description

Technical Field

[0001] This invention belongs to the field of rail manufacturing technology, and particularly relates to a method for manufacturing rails resistant to extreme environments. It is suitable for complex environments such as extreme low temperatures of -40℃ and corrosion from high-altitude salt lakes, and is especially suitable for the heavy-load laying requirements of the Sichuan-Tibet Railway and railways in the cold regions of Northeast China. Background Technology

[0002] As railway construction extends to extreme regions such as high latitudes and plateaus, rails must withstand multiple challenges simultaneously, including low-temperature brittle fracture, corrosion, and wear. Existing technologies suffer from three major drawbacks: First, conventional rails, such as U75V, lack sufficient fracture toughness at -40℃. The addition of alloying elements like Cr and Cu can lead to uneven microstructure, making it difficult to achieve a balance between strength and toughness. Second, corrosion-resistant technologies often rely on high-content alloying or single oxide film protection. The former deteriorates weldability, while the latter is prone to cracking and failure, failing to provide long-term protection against corrosive media. Third, online heat treatment often employs variable air pressure or water mist cooling, resulting in poor cooling uniformity and insufficient production stability during low-temperature seasons (-5℃ to -10℃), making it difficult to meet winter supply demands.

[0003] Existing patents such as CN111719083A improve corrosion resistance through high Cr, Cu, and Co content, but significantly reduce weldability; CN246028B9C uses water mist cooling to reduce costs, but has low precision in cooling rate control and is prone to generating harmful microstructures. Therefore, there is an urgent need to develop an innovative technology that balances process stability, performance synergy, and environmental adaptability, and to solve the challenges of rail service in extreme environments through process coupling and parameter optimization. Summary of the Invention

[0004] The purpose of this invention is to provide a method for manufacturing steel rails resistant to extreme environments, which simultaneously improves low-temperature resistance, corrosion resistance, and wear resistance, and solves the problems of "strength versus toughness" and "difficulty in balancing corrosion resistance and wear resistance" in traditional technologies.

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

[0006] This invention discloses a method for manufacturing a steel rail resistant to extreme environments, comprising the following steps:

[0007] (1) Steelmaking process: The steel is pretreated by KR mechanical stirring → top and bottom blowing converter double-slag smelting → LF refining → VD vacuum degassing → large billet continuous casting. During hot metal pretreatment, S ≤ 0.015% and P ≤ 0.12% are controlled. Silicon-calcium-barium alloy + low-carbon ferrosilicon is added for pre-deoxidation during converter tapping, with a final C content of 0.06%–0.08%. LF refining uses a special low-melting-point, high-fluidity refining slag, with a holding time ≥ 50 min, controlling the steel composition by percentage as follows: C 0.55–0.72%, Si 0.35–0.58%, Mn 0.75–1.00%, Cr 0.20–0.50%, Cu 0.20–0.50%, V 0.07~0.12%, P≤0.025%, S≤0.020%; VD vacuum degassing deep vacuum degree≤6kPa, vacuum holding time≥18min, molten steel [H]≤1.8ppm, [O]≤18ppm, [N]≤55ppm; continuous casting adopts 280×380mm cross section, electromagnetic stirring + dynamic light reduction process, billet slow cooling≥48h;

[0008] (2) Rolling process: The continuous casting billet is heated by a walking beam furnace for a total time of ≥3.5h. The preheating temperature is ≤1000℃, the heating section I is ≤1200℃, the heating section II is 1180~1300℃, the soaking section is 1160~1280℃, the initial rolling temperature is 948~958℃, the final rolling temperature is 1100~1152℃, and the rolling is carried out by a 5-stand universal rolling mill. The high-pressure water descaling pressure is ≥18MPa, and the straightening temperature is ≤60℃.

[0009] (3) Constant air pressure online heat treatment process: The rail inlet temperature is 770~784℃, and constant air pressure spray cooling is adopted at 7~12KPa. All 12 sets of spray units are fully open, the roller speed is 1.2m / s, the quenching time is 110-125s (preferred quenching time is 118s), the average cooling rate is 2.3~2.5℃ / s, the outlet temperature is 490~510℃, and the return temperature is 530~570℃; the cooling is divided into a rapid cooling stage with a cooling rate ≥5℃ / s, a pearlite transformation stage with a cooling rate of 1.2~1.7℃ / s, and an isothermal transformation stage with a cooling rate of 0.94~1.7℃ / s;

[0010] (4) Surface heat treatment process: The surface induction hardening process is adopted, with an induction coil frequency of 15-20kHz, a heating temperature of 860-880℃, a holding time of 8-12s, and then water mist cooling to below 200℃ to form a 0.3-0.5mm surface hardened layer.

[0011] Furthermore, it also includes: (5) Post-processing: after being cooled by a stepping cold bed, straightened by a small deformation flat and vertical composite, tested by ultrasonic testing, and processed by sawing and drilling, it is collected and stored.

[0012] Furthermore, the reduction of the No. 2 roller of the horizontal straightener is 12-14 mm.

[0013] Further, step (1) hot acid low magnification inspection of continuous casting billet: central porosity ≤ 0.5 grade, central crack ≤ 0.5 grade, no shrinkage cavities, intermediate cracks and subcutaneous bubbles, non-metallic inclusions coarse series ≤ 2.0 grade, fine series ≤ 2.0 grade.

[0014] Furthermore, in step (3), the temperature uniformity error of the cross-section of constant wind pressure cooling is ≤3℃ to avoid the formation of abnormal structures such as bainite.

[0015] Furthermore, after surface induction hardening in step (4), the surface is tempered at a low temperature of 200-220℃ for 20-30 minutes to eliminate residual stress in the hardened layer and achieve a surface hardness ≥400HBW.

[0016] Furthermore, the properties of the finished rails are as follows: tensile strength ≥1100MPa, elongation ≥14%, and fracture toughness (KIC) at -40℃ ≥40MPa·m. 1 / 2 The decarburized layer depth is ≤0.5mm, the seawater corrosion rate is ≤0.05mm / a, and the wear resistance is more than 35% higher than that of U75V rails.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] The core innovation of this invention lies in the synergistic process of constant wind pressure staged cooling and surface induction hardening, which breaks through the performance bottleneck of traditional single processes:

[0019] Innovative composition: It adopts a Cr-V-Cu composite microalloying system, where V element refines grains and strengthens through precipitation, while Cr-Cu provides corrosion protection, thus avoiding the deterioration of weldability caused by high alloy content;

[0020] Process synergy: Constant air pressure cooling ensures the uniformity of the fine pearlite structure in the matrix, and subsequent surface induction hardening forms a dense hardened layer, achieving the dual guarantee of "strong and tough matrix + wear-resistant and corrosion-resistant surface".

[0021] Environmental adaptability: Optimize the parameter matching of induction heating and constant air pressure cooling to achieve stable production in low-temperature seasons of -10℃, breaking the production limitations of low-temperature seasons.

[0022] Specific effects:

[0023] 1. Performance Synergistic Breakthrough: Through the synergistic process of Cr-V-Cu composite microalloying and constant wind pressure-surface heat treatment, the low temperature resistance, corrosion resistance and wear resistance are improved simultaneously, solving the problems of "strength and toughness contradiction" and "difficulty in balancing corrosion resistance and wear resistance" in traditional technologies;

[0024] 2. Innovative and efficient process: Constant air pressure cooling simplifies the heat treatment control process, surface induction hardening utilizes rolling residual heat to reduce energy consumption, low-temperature tempering eliminates residual stress, and the overall process has high stability, enabling stable production in low-temperature seasons down to -10℃, with a product qualification rate of ≥98%.

[0025] 3. Significant application value: The product is suitable for railway laying in extreme environments such as the Sichuan-Tibet Railway and the cold regions of Northeast China. Its service life is more than twice that of conventional rails, which greatly reduces replacement and maintenance costs. It provides a reliable material solution for railway construction in extreme environments and has significant economic value and social benefits.

[0026] 4. Product performance advantages

[0027] Low temperature resistance: fracture toughness KIC ≥ 40 MPa·m at -40℃ 1 / 2 It is more than 35% better than conventional rails and can resist the risk of brittle fracture at extreme low temperatures;

[0028] Corrosion resistance: The surface hardening layer and Cr-Cu composite passivation film provide dual protection, with a seawater corrosion rate of ≤0.05mm / a, making it suitable for corrosive environments such as high-altitude salt lakes and coastal areas.

[0029] Wear resistance: Surface hardness ≥400HBW, fine pearlite matrix combined with surface reinforcement, wear resistance is improved by more than 35% compared with conventional steel rails, and service life is extended by more than 100%.

[0030] Process stability: Stable production can be carried out in low temperature seasons of -10℃, with a product qualification rate of ≥98%, meeting the supply needs of railway construction in winter, and reducing energy consumption by 15% compared with traditional processes. Attached Figure Description

[0031] The present invention will be further described below with reference to the accompanying drawings.

[0032] Figure 1 The continuous cooling transformation (CCT) curve for U63MnCrCuV steel is shown. This curve serves as the basis for process parameter design. The constant air pressure cooling path controls the cooling rate at 2.3–2.5℃ / s to ensure that the microstructure of the rail matrix is ​​mainly composed of fine pearlite, without the formation of abnormal structures such as bainite and martensite, thus ensuring the synergistic effect of strength and toughness in the matrix.

[0033] Figure 2 This is a manufacturing process that combines heat treatment with other technologies.

[0034] Figure 3 This is a schematic diagram of the microstructure and hardness distribution of a steel rail cross section.

[0035] Figure 4 Micrograph of the surface hardened layer in the example (magnified 500x). Detailed Implementation

[0036] A method for manufacturing steel rails resistant to extreme environments:

[0037] (1) Steelmaking process: High cleanliness and low segregation control

[0038] The combined process of "dual-slag smelting - refining and fine-tuning - vacuum degassing - dynamic light-pressure continuous casting" aims to reduce the content of harmful elements and gases and improve the purity of molten steel. LF refining uses a special low-melting-point, high-fluidity refining slag to efficiently remove inclusions; VD vacuum degassing extends the vacuum holding time to over 18 minutes, controlling [H] below 1.8 ppm to avoid white spot defects; continuous casting employs electromagnetic stirring + dynamic light-pressure technology, significantly reducing center segregation of the billet, with center porosity ≤0.5 grade, laying the foundation for subsequent performance improvements.

[0039] (2) Rolling process: precise temperature control and forming control

[0040] The heating furnace adopts a four-stage temperature control system to avoid overheating and burning of the billet. The temperature of the soaking zone is kept stable at 1160-1280℃ to ensure uniform and refined austenite grains. During the universal rolling process, the high-pressure water descaling pressure is ≥18MPa to thoroughly remove iron oxide scale. The final rolling temperature is controlled at 1100-1152℃ to balance dimensional accuracy and surface quality.

[0041] (3) Constant air pressure - surface heat treatment synergistic process (core innovation)

[0042] Constant air pressure staged cooling: Based on the CCT curve of U63MnCrCuV steel (see...) Figure 1 The design employs a three-stage cooling system, with a constant air pressure of 7–12 kPa to ensure cross-sectional cooling uniformity error ≤3°C, avoiding the bainite transformation range, promoting the formation of fine pearlite structure, and ensuring the strength and toughness of the matrix.

[0043] Surface induction hardening: High-frequency induction heating technology is used to quickly heat the surface of the rail to 860-880℃ for austenitization. After a short period of heat preservation, water mist cooling is performed to form a 0.3-0.5mm mixed hardened layer of martensite and fine pearlite. The hardened layer is metallurgically bonded to the substrate, effectively blocking corrosive media and improving surface hardness.

[0044] Low-temperature tempering: After quenching, the product is tempered at a low temperature of 200-220℃ to eliminate residual stress in the hardened layer, prevent cracking during use, and retain the high hardness of the hardened layer.

[0045] (4) Post-processing: Low-stress straightening

[0046] The small deformation horizontal and vertical composite straightening technology is adopted to control the reduction of the No. 2 roller of the horizontal straightening machine to 12-14mm and the total reduction of the upper roller to ≤35mm, thereby reducing the residual stress of the rail and avoiding cracking of the surface hardened layer during the straightening process.

[0047] The present invention will be further described below with reference to specific embodiments.

[0048] Example 1

[0049] 1. Steelmaking process: After hot metal pretreatment, S = 0.012% and P = 0.11%; after converter tapping, C = 0.07% and Mn = 0.10%; after LF refining and holding for 55 min, the chemical composition of the molten steel by mass percentage is adjusted to C = 0.65%, Si = 0.45%, Mn = 0.85%, Cr = 0.35%, Cu = 0.30%, V = 0.09%, P = 0.018%, and S = 0.012%; after VD vacuum degassing and holding for 20 min, [H] = 1.5 ppm and [O] = 15 ppm; the continuous casting billet cross section is 280×380 mm, the electromagnetic stirring current is 300 A, and the slow cooling time is 48 h, with a central porosity grade of 0.3.

[0050] 2. Rolling process: Total heating time 240 min, soaking zone temperature 1200~1220℃, initial rolling temperature 952℃, final rolling temperature 1120℃, high-pressure water descaling pressure 20MPa.

[0051] 3. Synergistic Heat Treatment Process: Rapid Cooling Stage: Starting temperature 778℃ (rail inlet temperature), cooling rate 5.2℃ / s, ending temperature 620℃, duration 30.4s; This stage rapidly reduces the rail temperature, creating conditions for pearlite transformation. Pearlite Transformation Stage: Starting temperature 620℃, cooling rate 1.5℃ / s, ending temperature 550℃, duration 46.7s; Precise control of the cooling rate promotes uniform precipitation of fine pearlite. Isothermal Transformation Stage: Starting temperature 550℃, cooling rate 1.3℃ / s, ending temperature 500℃ (rail outlet temperature), duration 38.5s; Stable microstructure transformation ensures the strength and toughness of the matrix.

[0052] 4. Finished product properties: tensile strength 1150MPa, elongation 15%, KIC = 42MPa·m at -40℃ 1 / 2 The surface hardness is 415HBW, the corrosion resistance rate is 0.045mm / a, and the wear resistance improvement rate is 38%. All indicators meet the design requirements.

[0053] Example 2

[0054] Steelmaking process: LF refining and holding for 60 min, the chemical composition of molten steel by mass percentage is: C=0.62%, Si=0.50%, Mn=0.80%, Cr=0.30%, Cu=0.25%, V=0.08%, P=0.020%, S=0.015%; VD vacuum degassing and holding for 18 min, [H]=1.6ppm, [O]=16ppm; the central porosity of the continuously cast billet is grade 0.5.

[0055] Rolling process: total heating time 250 min, soaking zone temperature 1190~1210℃, initial rolling temperature 948℃, final rolling temperature 1110℃.

[0056] Collaborative Processes: Rapid Cooling Stage: Starting temperature 772℃ (rail inlet temperature), cooling rate 5.0℃ / s, ending temperature 617℃, duration 31.0s; rapidly traverses the high-temperature oxidation zone, reducing surface loss. Pearlite Transformation Stage: Starting temperature 617℃, cooling rate 1.4℃ / s, ending temperature 548℃, duration 49.3s; matches the CCT curve of the steel grade to avoid abnormal microstructure formation. Isothermal Transformation Stage: Starting temperature 548℃, cooling rate 1.1℃ / s, ending temperature 495℃ (rail outlet temperature), duration 48.2s; slow cooling improves microstructure stability.

[0057] Finished product properties: tensile strength 1120MPa, elongation 14.5%, KIC = 40.5MPa·m at -40℃ 1 / 2 It has a surface hardness of 405HBW, a corrosion resistance rate of 0.048mm / a, and a wear resistance improvement rate of 35%, meeting the requirements for use in extreme environments.

[0058] Example 3

[0059] Steelmaking process: LF refining and holding for 58 min, the chemical composition of molten steel by mass percentage is: C=0.68%, Si=0.42%, Mn=0.90%, Cr=0.40%, Cu=0.35%, V=0.10%, P=0.016%, S=0.010%; VD vacuum degassing and holding for 22 min, [H]=1.4ppm, [O]=14ppm.

[0060] Rolling process: Total heating time 260 min, soaking zone temperature 1210~1230℃, initial rolling temperature 955℃, final rolling temperature 1130℃.

[0061] Collaborative Processes: Rapid Cooling Stage: Starting temperature 780℃ (rail inlet temperature), cooling rate 5.3℃ / s, ending temperature 622℃, duration 29.8s; efficient cooling, shortening the overall quenching cycle. Pearlite Transformation Stage: Starting temperature 622℃, cooling rate 1.6℃ / s, ending temperature 553℃, duration 43.1s; accelerating the pearlite transformation rate and refining the grains. Isothermal Transformation Stage: Starting temperature 553℃, cooling rate 1.2℃ / s, ending temperature 505℃ (rail outlet temperature), duration 40.0s; ensuring cross-sectional temperature uniformity, error ≤3℃.

[0062] Finished product properties: tensile strength 1180MPa, elongation 15.2%, KIC = 43MPa·m at -40℃ 1 / 2 It has a surface hardness of 425HBW, a corrosion resistance rate of 0.042mm / a, and a wear resistance improvement rate of 40%, which is better than the design standard.

[0063] 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 manufacturing a steel rail resistant to extreme environments, characterized in that: Includes the following steps: (1) Steelmaking process: The steel is pretreated by KR mechanical stirring → top and bottom blowing converter double-slag smelting → LF refining → VD vacuum degassing → large billet continuous casting. During hot metal pretreatment, S ≤ 0.015% and P ≤ 0.12% are controlled. Silicon-calcium-barium alloy + low-carbon ferrosilicon is added for pre-deoxidation during converter tapping, with a final C content of 0.06%–0.08%. LF refining uses a special low-melting-point, high-fluidity refining slag, with a holding time ≥ 50 min, controlling the steel composition by percentage as follows: C 0.55–0.72%, Si 0.35–0.58%, Mn 0.75–1.00%, Cr 0.20–0.50%, Cu 0.20–0.50%, V 0.07~0.12%, P≤0.025%, S≤0.020%; VD vacuum degassing deep vacuum degree≤6kPa, vacuum holding time≥18min, molten steel [H]≤1.8ppm, [O]≤18ppm, [N]≤55ppm; continuous casting adopts 280×380mm cross section, electromagnetic stirring + dynamic light reduction process, billet slow cooling≥48h; (2) Rolling process: The continuous casting billet is heated by a walking beam furnace for a total time of ≥3.5h. The preheating temperature is ≤1000℃, the heating section I is ≤1200℃, the heating section II is 1180~1300℃, the soaking section is 1160~1280℃, the initial rolling temperature is 948~958℃, the final rolling temperature is 1100~1152℃, and the rolling is carried out by a 5-stand universal rolling mill. The high-pressure water descaling pressure is ≥18MPa, and the straightening temperature is ≤60℃. (3) Constant air pressure online heat treatment process: The rail inlet temperature is 770~784℃, and constant air pressure spray cooling is adopted at 7~12KPa. All 12 sets of spray units are fully open, the roller speed is 1.2m / s, the quenching time is 110-125s, the average cooling rate is 2.3~2.5℃ / s, the outlet temperature is 490~510℃, and the return temperature is 530~570℃; the cooling is divided into a rapid cooling stage with a cooling rate ≥5℃ / s, a pearlite transformation stage with a cooling rate of 1.2~1.7℃ / s, and an isothermal transformation stage with a cooling rate of 0.94~1.7℃ / s; (4) Surface heat treatment process: The surface induction hardening process is adopted, with an induction coil frequency of 15-20kHz, a heating temperature of 860-880℃, a holding time of 8-12s, and then water mist cooling to below 200℃ to form a 0.3-0.5mm surface hardened layer.

2. The method for manufacturing extreme environment resistant steel rails according to claim 1, characterized in that: Also includes: (5) Subsequent processing: After being cooled by a stepping bed, straightened by a combination of flat and vertical straightening with small deformation, ultrasonic testing, and combined sawing and drilling, the product is collected and stored.

3. The method for manufacturing extreme environment resistant steel rails according to claim 2, characterized in that: The reduction of the No. 2 roller of the horizontal straightener is 12-14mm.

4. The method for manufacturing a rail resistant to extreme environments according to claim 1, characterized in that: Step (1) Hot acid low magnification inspection of continuous casting billet: central porosity ≤ 0.5 grade, central crack ≤ 0.5 grade, no shrinkage cavities, intermediate cracks and subcutaneous bubbles, non-metallic inclusions coarse series ≤ 2.0 grade, fine series ≤ 2.0 grade.

5. The method for manufacturing a rail resistant to extreme environments according to claim 1, characterized in that: Step (3) Constant air pressure cooling cross-sectional temperature uniformity error ≤3℃, to avoid the formation of abnormal structures such as bainite.

6. The method for manufacturing a rail resistant to extreme environments according to claim 1, characterized in that: Step (4) After surface induction hardening, perform low-temperature tempering at 200-220℃ for 20-30 minutes to eliminate residual stress in the hardened layer and achieve a surface hardness ≥400HBW.

7. The method for manufacturing a rail resistant to extreme environments according to claim 1, characterized in that: Finished rail properties: tensile strength ≥1100MPa, elongation ≥14%, fracture toughness (KIC) at -40℃ ≥40MPa·m 1 / 2, decarburized layer depth ≤0.5mm, seawater corrosion rate ≤0.05mm / a, wear resistance is improved by more than 35% compared with U75V steel rail.

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