Method for improving performance of flash welded joint of R350HT export rail

Abstract

The present application belongs to the field of rail welding, and particularly relates to a method for improving the performance of a flash-welded joint of R350HT export rail, which comprises the following steps: S1, welding treatment of the R350HT export rail; S2, cooling treatment of the welded joint of the rail, wherein the cooling treatment comprises cooling each of different regions divided with reference to a fusion line, and the joint does not need to be subjected to normalizing heat treatment after cooling. The method adopted by the present application greatly improves the performance of the flash-welded joint of the R350HT export rail, such as the absence of abnormal martensite structure and the hardness of the joint, so that the joint structure performance better meets the requirements of the European standard EN 14587-2:2024, and the service performance and running safety of the flash-welded joint are improved.

Description

Technical Field

[0001] This invention belongs to the field of rail welding, specifically relating to a method for improving the performance of flash welded joints of R350HT export rails. Background Technology

[0002] Global rail transportation is constantly advancing with economic and technological development, moving towards higher speeds, heavier loads, and greater comfort and safety, placing increasingly higher demands on steel rails. R350HT rails are high-performance heat-treated pearlitic rails under European standards, widely used in high-speed, heavy-load, and mixed passenger and freight mainlines. They possess extremely high strength and wear resistance and are widely used in overseas markets. However, after undergoing welding thermal cycles, the flash weld joints of these rails exhibit phenomena such as grain coarsening, abnormal martensite structure, element segregation, and localized lamellar pearlite spheroidization. This leads to a significant decrease in the performance of the weld joint, seriously affecting the rail's lifespan and operational safety.

[0003] In China, post-weld normalizing heat treatment of welded joints can effectively improve their microstructure and properties. However, international standards do not allow normalizing heat treatment for flash welded joints of rails, only permitting post-weld air quenching. European standards impose limits on both the maximum and minimum hardness values. The temperature gradient distribution during welding inevitably leads to the presence of lamellar pearlite spheroidization regions in the welded joint, i.e., softened zones. The hardness in these regions decreases significantly, making soft zone control a key challenge. Simultaneously, the high welding temperature causes grain coarsening, which also reduces the overall performance of the joint. High cooling rates can refine the lamellar spacing, thereby improving the joint's hardness and other properties. However, abnormal martensitic structures due to elemental segregation are prone to appear near the weld, thus requiring the joint cooling rate to be moderate, especially given the high carbon and manganese content of R350HT rails. Therefore, the coordinated control of the microstructure and hardness of flash welded joints of R350HT export rails, which cannot undergo post-weld normalizing heat treatment, is a key challenge.

[0004] Chinese patent CN202411969254.4 discloses a fixed flash welding process for high-strength heat-treated steel rails containing trace alloying elements (R350HT). The process includes preparing the steel material for the rails, whose chemical composition must meet industrial production requirements. Specifically, its chemical composition by mass percentage is: C 0.76–0.80; Si 0.50–0.58; Mn 1.0–1.20; P ≤ 0.020; S ≤ 0.025; Cr 0.10–0.15; V 0.01–0.03; the remainder being Fe, for a total mass fraction of 1%. 00%; Rails are produced through smelting, continuous casting, slow cooling of billets, rolling, and heat treatment using the above components. The continuous casting billet size is 280mm × 380mm, and the rolling cross-section is 60E1. Specific steps include: rust removal from the rail ends and adjacent areas of the 60E1 rails; using roller supports to adjust the pre-camber; flash welding using a GAAS80 / 580 fixed flash welding machine; temperature-controlled cooling of the joints after welding; post-weld heat treatment of the welded joints using a split-type induction coil; and marking of each welded joint after heat treatment. This process can meet the requirements of heavy-haul railways for the smoothness of rail joints, improve the risk of fracture caused by "saddle-shaped" wear or abnormal microstructure of the joint due to excessive hardness difference between the base material and the joint in the welding area during the service of high-hardness rails on the line, and ensure that both high-hardness rails and joints meet the service requirements of heavy-haul railways and the safety of line operation. However, this process is only suitable for fixed welding in the factory and cannot be adapted to the on-site mobile welding conditions of overseas lines. It cannot fully meet the requirements of the complete set of European standard projects for exported rails. In addition, although this process can eliminate martensite, the improvement in the softened zone is small and the hardness of the heat-affected zone decreases significantly. It is difficult to simultaneously meet the two high standards of eliminating martensite and high hardness.

[0005] Therefore, how to simultaneously eliminate abnormal martensitic structure in rail joints and significantly improve joint hardness and other properties, so that the joint structure and properties can better meet the requirements of European standard EN 14587-2:2024, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the main objective of this invention is to provide a method for improving the performance of flash welded joints of R350HT export rails. By coordinating the control of the welding process and the post-weld cooling process of the joint in different regions and segments, the flash welded joints of R350HT export rails exhibit significantly improved properties such as the absence of abnormal martensitic structures and joint hardness. This allows the joint's microstructure and properties to better meet the requirements of European standard EN 14587-2:2024, thereby improving the service performance and traffic safety of the flash welded joints.

[0007] According to one aspect of the present invention, a method for improving the performance of flash welded joints of R350HT export rails is provided, the method comprising the following steps: S1. Welding is performed on the R350HT export rails. S2. Cool the welded rail joint. The cooling process includes cooling different areas defined by the reference fusion line. No normalizing heat treatment is required after cooling.

[0008] According to one embodiment of the present invention, in step S1, the R350HT export rail is a pearlitic steel rail, and the mass fraction of each element in the pearlitic steel rail is as follows: The mass fraction of element C is 0.72%–0.78%; The mass fraction of silicon is 0.30% to 0.58%. The mass fraction of Mn is 0.70%–1.20%; The mass fraction of element V is ≤0.030%; The mass fraction of Cr element is ≤0.15%; The mass fraction of sulfur (S) is ≤0.020%; The balance is Fe and unavoidable impurities.

[0009] According to an embodiment of the present invention, in step S1, the welding process adopts moving flash welding, which includes four stages in sequence: flash leveling stage, preheating stage, sintering stage and upsetting stage. The voltage of the flashover phase is 360–450V, and the time is 10–40s; The voltage during the preheating stage is 290–400V, and the time is 40–100s. The voltage during the burning stage is 350–440V, and the time is 15–50s. The upsetting amount during the upsetting stage is 9–18 mm.

[0010] According to one embodiment of the present invention, in step S2, the area corresponding to the cooling treatment includes a first cooling area and a second cooling area, which are separated by a baffle, and the first cooling area and the second cooling area are cooled synchronously.

[0011] According to one embodiment of the present invention, the first cooling region includes a region centered on the fusion line, and the first cooling region employs continuous natural cooling; The second cooling zone includes the areas on both sides of the first cooling zone. The second cooling zone is continuously cooled in three stages. After reaching the target temperature of each stage, it switches to the next stage. The first and second stages use air jet cooling, and the third stage uses natural cooling. The first stage uses air jet cooling with a constant air pressure P1 to a temperature T1, and the second stage uses air jet cooling with a constant air pressure P2 to a temperature T2, where P1 > P2.

[0012] According to one embodiment of the present invention, for an R350HT export rail with a specification of 60kg / m, the width of the first cooling zone is 15-30mm; The width of the second cooling zone is 50-100 mm.

[0013] According to one embodiment of the present invention, in the second cooling zone, P1 is 0.3 to 0.6 MPa, and T1 is 590 to 610°C; The P2 is 0.1 to 0.4 MPa, and the T2 is 410 to 500 °C.

[0014] According to one embodiment of the present invention, in the second cooling zone, the vertical distance between the air jet surface of the air jet box and the tread surface of the rail joint is 10-60 mm.

[0015] According to one embodiment of the present invention, the baffle is a split structure, comprising left and right parts, and the baffle is detachably assembled to the outside of the rail head of the rail joint.

[0016] According to one embodiment of the present invention, the outer profile of the baffle is rectangular, and the inner profile is adapted to the rail head profile of the rail joint.

[0017] By adopting the above technical solution, the present invention has the following advantages compared with the prior art: This invention achieves significant improvements in properties such as the absence of martensitic abnormalities and joint hardness in the flash welded joint of R350HT export rails through coordinated control of the welding process and the post-weld cooling process of the joint in different regions and segments. This results in the joint's microstructure and properties better meeting the requirements of European standard EN 14587-2:2024, thereby improving the service performance and traffic safety of the flash welded joint. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a method for improving the performance of flash welded joints of R350HT export rails according to an embodiment of the present invention; Figure 2 This is a front view of a zoned cooling system according to an embodiment of the present invention; Figure 3 This is a left view of a zoned cooling system according to an embodiment of the present invention.

[0020] In the diagram, 1-rail joint, 2-first cooling zone, 3-fusion line, 4-second cooling zone, 5-baffle, 6-air spray box. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0022] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0023] like Figure 1 As shown, an embodiment of the present invention provides a method for improving the performance of flash welded joints of R350HT export rails, comprising the following steps: S1. Welding is performed on the R350HT export rails. S2. Cool the welded rail joint 1. The cooling process includes cooling different areas defined by the reference fusion line 3. No normalizing heat treatment is required after cooling.

[0024] In step S1, the R350HT export rail is a pearlitic rail, whose microstructure is mainly pearlitic. In the pearlitic rail, the mass fraction of each element is as follows: C 0.72%~0.78%; Si 0.30%~0.58%; Mn 0.70%~1.20%; V ≤0.030%; Cr ≤0.15%; S ≤0.020%; the balance is Fe and unavoidable impurities. This composition ratio can balance the hardenability and plasticity of the rail to a certain extent, avoid excessive segregation of primary carbon and manganese in the base material, and reduce the risk of martensite precipitation after welding.

[0025] In step S1, the welding process employs moving flash welding, which consists of four stages: flash leveling, preheating, melting, and upsetting. The flash leveling stage uses a voltage of 360–450V for 10–40 seconds. Since the rail is at room temperature at this stage, a higher voltage is required to remove impurities and unevenness from the weld end face, resulting in a good weld end face. The preheating stage uses a voltage of 290–400V for 40–100 seconds, which is relatively lower than the flash leveling stage. The melting stage uses a voltage of 350–440V for 15–50 seconds. The upsetting stage involves an upsetting amount of 9–18 mm. After the melting stage, the rail is brought close to the contact point at a suitable speed and force is applied to obtain a high-quality welded joint with atomic bonding.

[0026] like Figure 2 , Figure 3 As shown, in step S2, the areas corresponding to the cooling treatment include a first cooling area 2 and a second cooling area 4. The first cooling area 2 and the second cooling area 4 are separated by a baffle 5, and the first cooling area 2 and the second cooling area 4 are cooled synchronously. For R350HT export rails with a specification of 60kg / m, the first cooling zone 2 includes an area centered on the fusion line 3 (width 15-30mm). The first cooling zone 2 adopts continuous natural cooling without any other treatment. The second cooling zone 4 includes the areas on both sides of the first cooling zone 2 (width 50-100mm). The second cooling zone 4 is continuously cooled in three stages. After reaching the target temperature of each stage, it switches to the next stage. The first and second stages both use air spray cooling, and the third stage uses natural cooling. In the first stage, air spray cooling is carried out at a constant air pressure P1 to a temperature T1 (P1 is 0.3-0.6MPa, preferably 0.45-0.5MPa, T1 is 590-610℃). In the second stage, air spray cooling is carried out at a constant air pressure P2 to a temperature T2 (P2 is 0.1-0.4MPa, preferably 0.18-0.25MPa, T2 is 410-500℃), where P1 > P2. In the second cooling zone 4, air is sprayed only on the rail head and the side of the rail head. The cooling air is compressed air at room temperature. The vertical distance between the spray surface of the air spray box 6 and the tread surface of the rail joint 1 is 10-60mm.

[0027] The above-mentioned segmented and controlled post-weld cooling process for joints includes: natural cooling of the weld, grain growth zone, and fine grain zone; and segmented air-jet cooling of the spheroidized zone. This process not only ensures that no martensite structure appears near the weld, but also effectively controls the width of the softened zone, reduces the spheroidization rate of the softened zone, and ultimately improves the overall performance of the joint.

[0028] The baffle 5 is a split structure, consisting of two parts, left and right. The baffle 5 is detachably mounted on the outside of the rail head of the rail joint 1. After welding, the baffle 5 is immediately placed on the rail head during cooling, and the second cooling area 4 is cooled by air jets. The baffle 5 separates the first cooling area 2 and the second cooling area 4, preventing the air jets from the second cooling area 4 from affecting the first cooling area 2. The outer profile of the baffle 5 is rectangular, and its inner profile matches the rail head profile of the rail joint 1.

[0029] The following are specific embodiments and their specific process parameters of the method for improving the performance of flash welded joints of R350HT export rails according to the present invention. The microstructure and performance analysis of the welded joints obtained in each embodiment are based on standard EN 14587-2:2024.

[0030] Example 1 In this embodiment, the R350HT steel rail used has a C element mass fraction of 0.77%, a Si element mass fraction of 0.58%, a Mn element mass fraction of 0.98%, a Cr element mass fraction of 0.09%, a V element mass fraction ≤0.006%, and a S element mass fraction ≤0.006%. Welding is performed using a mobile flash welding machine. The flash leveling stage voltage is 375V for 30s, the preheating stage voltage is 331V for 83s, and the burn-in stage voltage is 365V for 23s, with an upsetting amount of 13mm. After welding, post-weld cooling is performed in sections. Immediately after welding, a baffle 5 is placed, and the area around the fusion line 3 with a width of 20mm centered on the fusion line 3 is allowed to cool naturally without any other treatment. The natural cooling zone and the air-jet cooling zone are separated by baffle 5. Both air-jet cooling zones are 50mm wide, with an air jet distance of 35mm from the rail head. First, the air-jet cooling zone is cooled to 600℃ using an air jet pressure of 0.50MPa, then cooled to 410℃ using an air jet pressure of 0.2MPa before the air jet is stopped. Analysis of the microstructure and properties of the welded joint shows that there is no martensitic structure. Except for fusion line 3, the hardness of the joint remains within the range of +30HV30 and -20HV30 of the base metal hardness, indicating a significant improvement in hardness performance. Other joint microstructure and property tests also meet the standard requirements.

[0031] Example 2 In this embodiment, the R350HT steel rail used has a C element mass fraction of 0.77%, a Si element mass fraction of 0.58%, a Mn element mass fraction of 0.98%, a Cr element mass fraction of 0.09%, a V element mass fraction ≤0.006%, and a S element mass fraction ≤0.006%. Welding is performed using a mobile flash welding machine. The flash leveling stage voltage is 375V for 30s, the preheating stage voltage is 331V for 83s, and the burn-in stage voltage is 365V for 23s, with an upsetting amount of 13mm. After welding, post-weld cooling is performed in sections. Immediately after welding, baffle 5 is placed, and the area around the fusion line 3 with a width of 15mm centered on the fusion line 3 is allowed to cool naturally without any other treatment. The natural cooling zone and the air-jet cooling zone are separated by baffle 5. Both air-jet cooling zones are 50mm wide, with an air jet distance of 35mm from the rail head. First, the air-jet cooling zone is cooled to 600℃ using an air jet pressure of 0.50MPa, then cooled to 410℃ using an air jet pressure of 0.2MPa before the air jet is stopped. Analysis of the microstructure and properties of the welded joint shows no martensitic structure. Except for fusion line 3, the hardness of the joint remains within the range of +40HV30 and -20HV30 of the base metal hardness. The microstructure and properties of other joints also meet the standard requirements.

[0032] Example 3 In this embodiment, the R350HT steel rail used has a C element mass fraction of 0.77%, a Si element mass fraction of 0.58%, a Mn element mass fraction of 0.98%, a Cr element mass fraction of 0.09%, a V element mass fraction ≤0.006%, and a S element mass fraction ≤0.006%. Welding is performed using a mobile flash welding machine. The flash leveling stage voltage is 375V for 30s, the preheating stage voltage is 331V for 90s, and the burn-in stage voltage is 360V for 20s, with an upsetting amount of 13mm. After welding, post-weld cooling is performed in sections. Immediately after welding, baffle 5 is placed, and the area around the fusion line 3 with a width of 20mm centered on the fusion line 3 is allowed to cool naturally without any other treatment. The natural cooling zone and the air-jet cooling zone are separated by baffle 5. Both air-jet cooling zones are 60mm wide, with a jet distance of 30mm from the rail head. First, the air-jet cooling zone is cooled to 600℃ using a jet pressure of 0.45MPa, then cooled to 410℃ using a jet pressure of 0.18MPa before the jet cooling stops. Analysis of the microstructure and properties of the welded joint shows no martensitic structure. Except for fusion line 3, the hardness of the joint remains within the range of +35HV30 and -20HV30 of the base metal hardness. Other joint microstructure and property tests also meet the standard requirements.

[0033] Example 4 In this embodiment, the R350HT steel rail used has a C element mass fraction of 0.77%, a Si element mass fraction of 0.58%, a Mn element mass fraction of 0.98%, a Cr element mass fraction of 0.09%, a V element mass fraction ≤0.006%, and a S element mass fraction ≤0.006%. Welding is performed using a mobile flash welding machine. The flash leveling stage voltage is 375V for 30s, the preheating stage voltage is 331V for 83s, and the burn-in stage voltage is 365V for 23s, with an upsetting amount of 13mm. After welding, post-weld cooling is performed in sections. Immediately after welding, a baffle 5 is placed, and the area around the fusion line 3 with a width of 20mm centered on the fusion line 3 is allowed to cool naturally without any other treatment. The natural cooling zone and the air-jet cooling zone are separated by baffle 5. Both air-jet cooling zones are 50mm wide, with an air jet distance of 30mm from the rail head. First, the air-jet cooling zone is cooled to 600℃ using an air jet pressure of 0.50MPa, then cooled to 410℃ using an air jet pressure of 0.25MPa before the air jet is stopped. Analysis of the microstructure and properties of the welded joint shows no martensitic structure. Except for fusion line 3, the hardness of the joint remains within the range of +45HV30 and -15HV30 of the base metal hardness. The microstructure and properties of other joints also meet the standard requirements.

[0034] Comparative Example 1 In this comparative example, the R350HT steel rail used had a C content of 0.77%, a Si content of 0.58%, a Mn content of 0.98%, a Cr content of 0.09%, a V content ≤0.006%, and a S content ≤0.006%. Welding was performed using a mobile flash welding machine. The flash leveling stage voltage was 375V for 30 seconds, the preheating stage voltage was 331V for 83 seconds, and the burn-in stage voltage was 365V for 23 seconds, with an upsetting amount of 13mm. After welding, the joint was allowed to cool naturally to room temperature. Analysis of the microstructure and properties of the welded joint revealed no martensitic structure. However, excluding the fusion line, four points on the joint (two on each side) had a hardness lower than the base metal hardness -30HV30, which is below the lower limit requirement.

[0035] Comparative Example 2 In this comparative example, the R350HT steel rail used had a C content of 0.77%, a Si content of 0.58%, a Mn content of 0.98%, a Cr content of 0.09%, a V content ≤0.006%, and a S content ≤0.006%. Welding was performed using a mobile flash welding machine. The flash leveling stage voltage was 375V for 30 seconds, the preheating stage voltage was 331V for 83 seconds, and the burn-in stage voltage was 365V for 23 seconds, with an upsetting amount of 15mm. After welding, post-weld cooling was performed in sections. Immediately after welding, a baffle was placed, and the area near the fusion line, centered on the fusion line and 40mm wide, was allowed to cool naturally without any other treatment. The natural cooling zone and the air-jet cooling zone are separated by baffles. Both air-jet cooling zones are 50mm wide, with a jetting distance of 35mm from the rail head. First, the air-jet cooling zone is cooled to 600℃ using a jetting pressure of 0.50MPa, then cooled to 410℃ using a jetting pressure of 0.2MPa before the jetting stops. Analysis of the microstructure and properties of the welded joint shows no martensitic structure. However, excluding the fusion line, four points on the joint (two on each side) have a hardness lower than the base metal hardness of -30HV30, which is below the lower limit requirement.

[0036] Comparative Example 3 In this comparative example, the R350HT steel rail used had a C content of 0.77%, a Si content of 0.58%, a Mn content of 0.98%, a Cr content of 0.09%, a V content ≤0.006%, and a S content ≤0.006%. Welding was performed using a mobile flash welding machine. The flash leveling stage voltage was 375V for 30 seconds, the preheating stage voltage was 331V for 75 seconds, and the burn-in stage voltage was 365V for 28 seconds, with an upsetting amount of 14mm. After welding, post-weld cooling was performed in sections. Immediately after welding, a baffle was placed, and the area near the fusion line, centered on the fusion line and 20mm wide, was allowed to cool naturally without any other treatment. The natural cooling zone and the air-jet cooling zone are separated by baffles. Both air-jet cooling zones are 50mm wide, with an air jet distance of 35mm from the rail head. First, the air-jet cooling zone is cooled to 600℃ using an air jet pressure of 0.50MPa, then cooled to 410℃ using an air jet pressure of 0.2MPa before the air jet is stopped. Analysis of the microstructure and properties of the welded joint shows that the hardness meets the standard requirements, but the joint exhibits a significant amount of martensite.

[0037] As can be seen from Examples 1-4 and Comparative Examples 1-3, according to the method of the present invention, after welding and segmented post-weld cooling of R350HT export rails, the rail joints have no brittle martensitic structure, the joint hardness is stably controlled within the range of +45HV30 and -20HV30 of the base material, the softening zone is effectively controlled, and all indicators meet the standard of EN14587-2. However, Comparative Examples 1-3, which did not use the method of the present invention, all have obvious defects: Comparative Example 1 only uses overall natural cooling without segmented air spraying reinforcement, and the hardness of many measuring points of the joint is lower than -30HV30 of the base material, failing to meet the standard hardness requirement; Comparative Example 2 sets the width of the natural cooling zone (first cooling zone) at the center of the fusion line to 40mm, exceeding the 15-30mm range limited by the present invention, and there are still many points with unqualified hardness; Comparative Example 3 has an unbalanced welding parameter matching, and the matching cooling method is unable to suppress the martensitic phase transformation, resulting in the formation of a large amount of harmful martensitic structure in the joint. This demonstrates that the present invention, through a synergistic process combining welding and segmented post-weld cooling of the joint, can simultaneously eliminate abnormal martensitic structure in the joint and improve the hardness matching between the joint and the base material. It is compatible with European standard construction constraints that do not allow post-weld induction normalizing on overseas sites, and can stably obtain R350HT export rail welded joints that meet both microstructure and hardness standards.

[0038] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications or equivalent substitutions made to the present invention without departing from the spirit and scope thereof should be covered within the protection scope of the claims of the present invention.

[0039] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of the present invention is limited to these examples; within the framework of the embodiments of the present invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of the present invention should be included within the protection scope of the embodiments of the present invention.

Claims

1. A method for improving the performance of flash welded joints of R350HT export rails, characterized in that, The method includes the following steps: S1. Welding is performed on the R350HT export rails. S2. Cool the welded rail joint (1) by cooling the different areas divided by the reference fusion line (3) and no normalizing heat treatment is required after cooling.

2. The method according to claim 1, characterized in that, In step S1, the R350HT export rail is a pearlitic steel rail, and the mass fraction of each element in the pearlitic steel rail is as follows: The mass fraction of element C is 0.72%–0.78%; The mass fraction of silicon is 0.30% to 0.58%. The mass fraction of Mn is 0.70%–1.20%; The mass fraction of element V is ≤0.030%; The mass fraction of Cr element is ≤0.15%; The mass fraction of sulfur (S) is ≤0.020%; The balance is Fe and unavoidable impurities.

3. The method according to claim 1, characterized in that, In step S1, the welding process adopts moving flash welding, which includes four stages in sequence: flash leveling stage, preheating stage, burning stage and upsetting stage. The voltage of the flashover phase is 360–450V, and the time is 10–40s; The voltage during the preheating stage is 290–400V, and the time is 40–100s. The voltage during the burning stage is 350–440V, and the time is 15–50s. The upsetting amount during the upsetting stage is 9–18 mm.

4. The method according to claim 1, characterized in that, In step S2, the area corresponding to the cooling treatment includes a first cooling area (2) and a second cooling area (4). The first cooling area (2) and the second cooling area (4) are separated by a baffle (5), and the first cooling area (2) and the second cooling area (4) are cooled synchronously.

5. The method according to claim 4, characterized in that, The first cooling zone (2) includes a region centered on the fusion line (3), and the first cooling zone (2) employs continuous natural cooling; The second cooling zone (4) includes the areas on both sides of the first cooling zone (2). The second cooling zone (4) is continuously cooled in three stages. After reaching the target temperature of each stage, it switches to the next stage. The first and second stages both use air spray cooling, and the third stage uses natural cooling. The first stage uses constant air pressure P1 to spray cooling to temperature T1, and the second stage uses constant air pressure P2 to spray cooling to temperature T2, where P1 > P2.

6. The method according to claim 5, characterized in that, For R350HT export rails with a specification of 60kg / m, the width of the first cooling zone (2) is 15-30mm; The width of the second cooling zone (4) is 50-100 mm.

7. The method according to claim 5, characterized in that, In the second cooling zone (4), P1 is 0.3 to 0.6 MPa and T1 is 590 to 610 °C; The P2 is 0.1 to 0.4 MPa, and the T2 is 410 to 500 °C.

8. The method according to claim 5, characterized in that, In the second cooling zone (4), the vertical distance between the air jet surface of the air jet box (6) and the tread surface of the rail joint (1) is 10-60 mm.

9. The method according to claim 4, characterized in that, The baffle (5) is a split structure, consisting of two parts, left and right. The baffle (5) is detachably mounted on the outside of the rail head of the rail joint (1).

10. The method according to claim 4, characterized in that, The outer profile of the baffle (5) is rectangular, and the inner profile is adapted to the rail head profile of the rail joint (1).

Images