A method for improving the wear resistance of the softened zone of a flash welded rail joint

Abstract

The present application relates to the field of steel rail welding, in particular to a method for improving the wear performance of the softened zone of a steel rail flash welded joint, which comprises the following steps: using a heating device to heat the area of the steel rail flash welded joint, the starting temperature of the heating process is less than 300 DEG C, and the terminal temperature is 800 DEG C-1000 DEG C; after heating to the terminal temperature, the heating device is removed immediately, and a cooling device is used to accelerate the cooling of the local area of the heated steel rail flash welded joint, the average cooling speed of the accelerated cooling is 5 DEG C / s-35 DEG C / s, and the terminal temperature of the accelerated cooling is 200 DEG C-400 DEG C. The average hardness of the softened zone of the steel rail flash welded joint treated by the method is improved by more than 95% compared with the post-weld air-cooled joint, the unilateral softened zone width of the joint is less than 5 mm, and the wear performance of the softened zone of the steel rail flash welded joint is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of rail welding, and more specifically, to a method for improving the wear performance of the softened zone of a flash welded joint in rails. Background Technology

[0002] In recent years, with the continuous increase in heavy-haul railway freight volume, axle load, and maximum single-train load, the wear and damage problems of rails and their welded joints have become increasingly serious. Whether aluminothermic welding or flash welding is used, the welded joint after heat-affected zone treatment, especially the softened zone, has a lower surface hardness than the base material. Its tensile strength, hardness, fatigue strength, and other mechanical properties are also reduced compared to the base material. Under high-volume conditions, the softened zone of the welded joint wears faster, with severe collapse, and the joint life is shorter than that of the rail base material. Studies have shown that fatigue wear caused by impact wear and rolling contact in the softened zone of the welded joint is a significant cause of welded joint damage.

[0003] The softened zone of a flash welded rail joint refers to the area where the hardness of the weld joint is significantly lower than that of the base material. Unlike the austenitized region where the hardness is lower than the base material, the metal in the softened zone does not undergo austenitic transformation during heating. Its temperature range is usually within the annealing range in metal heat treatment, hence the softened zone is sometimes called the annealing zone. Since rail material typically exhibits a granular pearlitic structure after annealing, the softened zone is also called the spheroidizing annealing zone. Generally, the tensile and impact properties of the softened zone are poor, making it a weak point in the rail joint. Because rail welding mainly involves localized heating of the rail ends, a transition zone always exists between the heated part and the unheated base material. The area with lower hardness in this transition zone is the softened zone. The softened zone is a persistent area in rail welded joints and cannot be completely eliminated.

[0004] Regarding rail joint wear, numerous studies have shown that, in addition to measures such as proper lubrication, damage grinding, and profile grinding, while strategies like altering the wheel-rail friction coefficient, improving wheel-rail contact, and eliminating early damage to the rail surface are effective, enhancing the strength and toughness of the softened zone of the joint remains one of the most effective means of improving wear resistance. Simultaneously, reducing the width of the softened zone of the rail joint is also a beneficial way to improve its wear resistance. Therefore, reducing accelerated wear in the softened zone of welded joints and extending the service life of rail welded joints has become an important direction urgently requiring research. Summary of the Invention

[0005] In view of this, the present invention provides a method for improving the wear resistance of the softened zone of a rail flash welded joint. The method mainly includes two main processes: heating and cooling the area of ​​the rail flash welded joint, which can solve the problem of low wear resistance of the softened zone of the existing welded joint.

[0006] The present invention provides a method for improving the wear performance of the softened zone of a flash welded joint in rails, comprising the following steps: A heating device is used to heat the area of ​​the flash welded joint of the rail. The initial temperature of the heating process is less than 300℃ and the final temperature is 800℃~1000℃. After heating to the termination temperature, the heating device is immediately removed, and a cooling device is used to accelerate the cooling of the local area of ​​the heated rail flash weld joint. The average cooling rate of the accelerated cooling is 5℃ / s to 35℃ / s, and the termination temperature of the accelerated cooling is 200℃ to 400℃.

[0007] In some embodiments, the microstructure of the rail is pearlitic; in the chemical composition of the rail, the mass fraction of C is 0.35% to 1.20%, the mass fraction of Si is 0.10% to 1.20%, the mass fraction of Mn is 0.60% to 1.40%, the mass fraction of Cr does not exceed 0.25%, the mass fraction of V does not exceed 0.20%, the mass fractions of P and S both do not exceed 0.040%, the mass fraction of Al does not exceed 0.004%, and the remainder is iron and unavoidable impurities.

[0008] In some embodiments, the flash welded joint area of ​​the rail includes a fusion line, a heat-affected zone, and a base material area. The fusion line has a width of 0.5 mm to 2.0 mm, the heat-affected zone is located on both sides of the fusion line, and the width of the heat-affected zone on each side is 5.0 mm to 30.0 mm. The base material area is located on the side of the heat-affected zone away from the fusion line, and the width of the base material area is 5.0 mm to 20.0 mm.

[0009] In some embodiments, the heating device is an induction coil with a profile similar to a steel rail, the distance between the induction coil and the surface of the steel rail is 5mm to 50mm, and the heating area covers the entire weld joint area.

[0010] In some embodiments, the length of the heating device along the extension direction of the rail is 60mm to 150mm.

[0011] In some embodiments, the heating device controls the temperature rise rate of the rail flash weld joint area to be 1.0℃ / s to 20.0℃ / s.

[0012] In some embodiments, the local area of ​​the flash welded joint of the rail is a transition area between the heated area and the unheated base material during the heating process. When the temperature reaches the termination temperature, the temperature of the local area of ​​the flash welded joint of the rail is 400°C to 600°C.

[0013] In some embodiments, the cooling device is a contact-type heat-conducting device that mimics the profile of a steel rail. The cooling device has a hollow structure, and heat exchange is carried out inside through a cooling medium. Its contact surface with the steel rail is coupled with a flexible heat-conducting material.

[0014] In some embodiments, the cooling device includes a first cooling section that contacts the top surface of the rail head and a second cooling section that contacts the rounded corners and side surfaces of the rail head. The thickness of the first cooling section and the second cooling section is 15 mm to 30 mm, and the length along the rail extension direction is 20 mm to 40 mm.

[0015] In some embodiments, the flash welding process includes four stages: electrode clamping, electric heating, pressure upsetting, and rapid spheroid pushing. During the welding process, the temperature of the rails on both sides, which are 0mm to 25mm away from the end face of the rail to be welded, is 900℃ to 1800℃, and the welding duration is 50s to 300s.

[0016] The beneficial effects of this invention are as follows: By employing a heating and accelerated cooling process on the flash welded joint of the rail, the average hardness of the softened zone of the weld joint is increased by more than 95% compared to traditional post-weld air-cooled joints. This increased hardness effectively enhances the wear resistance of the weld joint and reduces failures caused by impact and fatigue wear. Furthermore, the width of the softened zone on one side of the weld joint treated by this method can be controlled within 5mm, resulting in more uniform overall performance of the weld joint and reducing the risk of stress concentration and wear due to localized softening. The heating and cooling process improves the microstructure of the weld joint, making it more uniform and closer to the microstructure of the base material, thus significantly extending the service life of the rail during operation. Attached Figure Description

[0017] 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 embodiments can be obtained based on these drawings without creative effort.

[0018] Figure 1 A top view of the heating and cooling zone of a flash welded joint for rails provided in one embodiment of the present invention; Figure 2 Side view of the heating and cooling zone of a flash weld joint on a rail. Detailed Implementation

[0019] 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.

[0020] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0021] This invention provides a method for improving the wear performance of the softened zone of a flash welded joint in rails, comprising the following steps: A heating device is used to heat the area of ​​the flash welded joint of the rail. The initial temperature of the heating process is less than 300℃ and the final temperature is 800℃~1000℃. After heating to the termination temperature, the heating device is immediately removed, and a cooling device is used to accelerate the cooling of the local area of ​​the heated rail flash weld joint. The average cooling rate of the accelerated cooling is 5℃ / s to 35℃ / s, and the termination temperature of the accelerated cooling is 200℃ to 400℃.

[0022] Compared with existing technologies, this invention, through a heating and accelerated cooling process on the flash welded joint of rails, increases the average hardness of the softened zone of the weld joint by more than 95% compared with traditional post-weld air-cooled joints. This increased hardness effectively enhances the wear resistance of the weld joint and reduces failures caused by impact and fatigue wear. Furthermore, the width of the softened zone on one side of the weld joint treated by this method can be controlled within 5mm, resulting in more uniform overall performance of the weld joint and reducing the risk of stress concentration and wear due to localized softening. The heating and cooling process improves the microstructure of the weld joint, making it more uniform and closer to the microstructure of the base material, thus significantly extending the service life of the rail during operation.

[0023] In some embodiments, the microstructure of the rail is pearlitic; the chemical composition of the rail contains 0.35%–1.20% C, 0.10%–1.20% Si, 0.60%–1.40% Mn, no more than 0.25% Cr, no more than 0.20% V, no more than 0.040% P and S, no more than 0.004% Al, with the remainder being iron and unavoidable impurities. This application, by rationally controlling the microstructure and chemical composition of the rail, can significantly improve the hardness, wear resistance, and fatigue resistance of the rail welded joints, while avoiding problems such as brittleness or overheating sensitivity caused by improper composition, thereby extending the service life of the rail and improving its service performance.

[0024] In some embodiments, the flash welded joint area of ​​the rail includes a fusion line, a heat-affected zone (HAZ), and a base metal area. The fusion line is the area formed by the resolidification of the materials at both ends of the rail during welding, ensuring the physical connection between the two ends. The width of the fusion line is 0.5 mm to 2.0 mm. The HAZ is the area affected by heat during welding but not melted, located on both sides of the fusion line, with a width of 5.0 mm to 30.0 mm on each side. The base metal area is the area not affected by heat during welding, located on the side of the HAZ furthest from the fusion line, with a width of 5.0 mm to 20.0 mm.

[0025] In some embodiments, the heating device is an induction coil shaped like a steel rail, which heats the flash weld joint area of ​​the rail using the principle of electromagnetic induction. The induction coil, shaped like a steel rail, is 5mm to 50mm away from the rail surface, and the heating area covers the entire weld joint area, including the fusion line, heat-affected zone, and base material area. This design enables rapid and efficient heating while ensuring uniform temperature distribution.

[0026] In some embodiments, the length 'a' of the heating device along the extension direction of the rail is 60 mm to 150 mm. The length of the heating device determines the range of the weld joint area it can cover. By setting the length to 60 mm to 150 mm, it can be ensured that the entire weld joint area (including the fusion line, heat-affected zone, and part of the base material area) is heated uniformly.

[0027] In some embodiments, the heating device controls the temperature rise rate of the flash welded joint area of ​​the rail to be 1.0℃ / s to 20.0℃ / s, so as to effectively refine the grains in the welded joint area, reduce the residual stress of the welded joint, and ensure that the temperature distribution of the entire cross section of the welded joint is more uniform.

[0028] In some embodiments, the local area of ​​the rail flash welded joint cooled by the cooling device is a transition area between the heated area and the unheated base material area during the heating process. When heated to the termination temperature, the temperature of the local area of ​​the rail flash welded joint is 400°C to 600°C.

[0029] In some embodiments, the cooling device is a contact-type heat-conducting device that mimics the profile of a rail. It utilizes heat conduction to cool both sides of the fusion line of the flash welded joint, including the entire rail head area, including the rail top surface, rail head fillet, and rail head side, thereby achieving rapid cooling and reducing the time the welded joint remains at high temperatures. The cooling device has a hollow structure, with heat exchange occurring internally through a cooling medium. It is coupled to the rail contact surface using a flexible thermally conductive material. Specifically, the cooling device is equipped with cooling medium inlets and outlets to allow the cooling medium to circulate within the device. This circulation system continuously removes heat from the welded joint, ensuring the stability and efficiency of the cooling process.

[0030] In some embodiments, the cooling device includes a first cooling section that contacts the top surface of the rail head and a second cooling section that contacts the rail head fillet and side surface, enabling precise cooling of critical parts of the welded joint. The thickness d of the first and second cooling sections is 15mm–30mm, the length b along the rail extension direction is 20mm–40mm, and the width c = the width of the rail head + 2d. The dimensional parameters of the cooling device (such as thickness d, length b, and width c) can be adjusted according to the specific shape of the rail to ensure a tight fit between the cooling device and the rail surface. This design improves the versatility and adaptability of the cooling device, making it suitable for various rail types. Figure 1 As shown, when cooling the same flash welded joint of a rail, two cooling devices are used simultaneously. By having two cooling devices work together, the cooling efficiency can be significantly improved, while ensuring the uniformity of the cooling process.

[0031] In some embodiments, flash welding mainly refers to a method of heating the rail section to be welded using resistance heating until a predetermined temperature is reached, and then rapidly applying upsetting force to achieve atomic bonding between the rail sections. The flash welding process includes four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. During the welding process, the temperature of the rail sections 0mm to 25mm from the end face of the rail to be welded is 900℃ to 1800℃, and the welding duration is 50s to 300s. Specifically, in the electrode clamping stage: electrode clamping ensures that the end of the rail to be welded remains stable during the welding process, avoiding welding defects caused by vibration or displacement. In the electric heating stage: heating the rail end to 900℃ to 1800℃ for 50s to 300s allows the rail end to achieve sufficient plasticity, providing good conditions for subsequent upsetting. In the pressure upsetting stage: applying upsetting force at high temperature causes plastic deformation of the rail end and achieves atomic bonding, forming a strong welded joint. Rapid weld bead removal stage: After welding is completed, excess weld beads are removed by rapid weld bead removal to ensure a smooth surface of the weld joint, reduce stress concentration points, and improve the fatigue performance of the weld joint.

[0032] The method for improving the wear performance of the softened zone of the flash welded joint of rail provided in this application will be further explained below with reference to specific embodiments: Example 1 In this embodiment, the pearlitic steel rail has a C element mass fraction of 0.80%, a Si element mass fraction of 1.20%, a Mn element mass fraction of 1.10%, a Cr element mass fraction of 0.12%, a V element mass fraction of 0.05%, a P element mass fraction of 0.005%, a S element mass fraction of 0.005%, and an Al element mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasts for 130 seconds. After the welding process is completed and the joint cools to below 300°C, an induction coil with a profile similar to the rail is used to reheat the flash welded joint area of ​​the rail. The distance between the induction coil and the rail surface is 5 mm, and the heating area covers the entire welded joint area, with a length 'a' of 60 mm along the rail's extension direction. The temperature rise rate of the flash welded joint area of ​​the rail during the heating process is 1.0°C / s. Once the heating temperature reaches 800℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a rail, is used to accelerate cooling of both sides of the fusion line of the flash-welded rail joint, including the entire rail head area, including the rail top surface, rail head fillet, and rail head side. The length (b) of the cooling device along the rail extension direction is 20mm, and the thickness (d) is 15mm; the average cooling rate is 5℃ / s. When the rail joint temperature drops to 200℃, the joint is left to cool naturally in air. The average hardness of the softened zone of the flash-welded rail joint treated using this method is 97% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 4mm, significantly improving the wear performance of the softened zone of the flash-welded rail joint.

[0033] Example 2 In this embodiment, the pearlitic steel rail has a C element mass fraction of 0.80%, a Si element mass fraction of 1.20%, a Mn element mass fraction of 1.10%, a Cr element mass fraction of 0.12%, a V element mass fraction of 0.05%, a P element mass fraction of 0.005%, a S element mass fraction of 0.005%, and an Al element mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasts for 130 seconds. After the welding process is completed and the joint cools to below 300°C, an induction coil with a profile similar to the rail is used to reheat the flash welded joint area of ​​the rail. The distance between the induction coil and the rail surface is 50 mm, and the heating area covers the entire welded joint area, with a length 'a' of 150 mm along the rail's extension direction. The temperature rise rate of the flash welded joint area of ​​the rail during the heating process is 20.0°C / s. Once the heating temperature reaches 1000℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a rail, is used to accelerate cooling of both sides of the fusion line of the flash-welded rail joint, including the entire rail head area, including the rail top surface, rail head fillet, and rail head side. The length (b) of the cooling device along the rail extension direction is 40mm, and the thickness (d) is 30mm; the average cooling rate is 35℃ / s. When the rail joint temperature drops to 400℃, the joint is placed in air for natural cooling. The average hardness of the softened zone of the flash-welded rail joint treated using this method is 98% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 3mm, significantly improving the wear performance of the softened zone of the flash-welded rail joint.

[0034] Example 3 In this embodiment, the pearlitic steel rail has a C element mass fraction of 0.80%, a Si element mass fraction of 1.20%, a Mn element mass fraction of 1.10%, a Cr element mass fraction of 0.12%, a V element mass fraction of 0.05%, a P element mass fraction of 0.005%, a S element mass fraction of 0.005%, and an Al element mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasts for 130 seconds. After the welding process is completed and the joint cools to below 300°C, an induction coil with a profile similar to the rail is used to reheat the flash welded joint area of ​​the rail. The distance between the induction coil and the rail surface is 45 mm, and the heating area covers the entire welded joint area, with a longitudinal dimension a of 100 mm in the rail. The temperature rise rate of the flash welded joint area of ​​the rail during the heating process is 15.0°C / s. Once the heating temperature reaches 900℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a steel rail, is used to accelerate cooling of both sides of the fusion line of the flash welded joint, including the entire rail head area, including the rail top surface, rail head fillet, and rail head side. The length b along the rail extension direction is 30mm, and the thickness d is 20mm; the average cooling rate is 25℃ / s. When the rail joint temperature drops to 300℃, the joint is left to cool naturally in air. The average hardness of the softened zone of the flash welded joint treated using this method is 98% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 3mm, significantly improving the wear performance of the softened zone of the flash welded joint.

[0035] Example 4 In this embodiment, the pearlitic steel rail has a C element mass fraction of 0.80%, a Si element mass fraction of 1.20%, a Mn element mass fraction of 1.10%, a Cr element mass fraction of 0.12%, a V element mass fraction of 0.05%, a P element mass fraction of 0.005%, a S element mass fraction of 0.005%, and an Al element mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasts for 130 seconds. After the welding process is completed and the joint cools to below 300°C, an induction coil with a profile similar to the rail is used to reheat the flash welded joint area of ​​the rail. The distance between the induction coil and the rail surface is 5 mm, and the heating area covers the entire welded joint area, with a longitudinal dimension a of 60 mm in the rail. The temperature rise rate of the flash welded joint area of ​​the rail during the heating process is 1.0°C / s. Once the heating temperature reaches 800℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a rail, is used to accelerate cooling of both sides of the fusion line of the flash-welded rail joint, including the entire rail head area, including the rail top surface, rail head fillet, and rail head side. The cooling device has external dimensions b = 40mm and d = 30mm; the average cooling rate is 35℃ / s. When the rail joint temperature drops to 400℃, the joint is left to cool naturally in air. The average hardness of the softened zone of the flash-welded rail joint treated using this method is 99% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 2mm, significantly improving the wear performance of the softened zone of the flash-welded rail joint.

[0036] Example 5 In this embodiment, the pearlitic steel rail has a C element mass fraction of 0.80%, a Si element mass fraction of 1.20%, a Mn element mass fraction of 1.10%, a Cr element mass fraction of 0.12%, a V element mass fraction of 0.05%, a P element mass fraction of 0.005%, a S element mass fraction of 0.005%, and an Al element mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasts for 130 seconds. After the welding process is completed and the joint cools to below 300°C, an induction coil with a profile similar to the rail is used to reheat the flash welded joint area of ​​the rail. The distance between the induction coil and the rail surface is 50 mm, and the heating area covers the entire welded joint area, with a length 'a' of 150 mm along the rail's extension direction. The temperature rise rate of the flash welded joint area of ​​the rail during the heating process is 20.0°C / s. Once the heating temperature reaches 1000℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a rail, is used to accelerate cooling of both sides of the fusion line of the flash-welded rail joint, including the entire rail head area, including the rail top surface, rail head fillet, and rail head side. The length (b) of the cooling device along the rail extension direction is 20mm, and the thickness (d) is 15mm; the average cooling rate is 5℃ / s. When the rail joint temperature drops to 200℃, the joint is left to cool naturally in air. The average hardness of the softened zone of the flash-welded rail joint treated using this method is 98% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 4mm, significantly improving the wear performance of the softened zone of the flash-welded rail joint.

[0037] Example 6 In this embodiment, the pearlitic steel rail has a C element mass fraction of 1.20%, a Si element mass fraction of 1.20%, a Mn element mass fraction of 0.60%, a Cr element mass fraction of 0.012%, a V element mass fraction of 0.009%, a P element mass fraction of 0.010%, a S element mass fraction of 0.010%, and an Al element mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasts for 200 seconds. After the welding process is completed and the joint cools to below 300°C, an induction coil with a profile similar to the rail is used to reheat the flash welded joint area of ​​the rail. The distance between the induction coil and the rail surface is 45 mm, and the heating area covers the entire welded joint area, with a length 'a' of 100 mm along the rail's extension direction. The temperature rise rate of the flash welded joint area of ​​the rail during the heating process is 15.0°C / s. Once the heating temperature reaches 900℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a rail, is used to accelerate cooling of both sides of the fusion line of the flash welded joint, including the rail top surface, rail head fillet, and rail head side. The length (b) of the cooling device along the rail extension direction is 30mm, and the thickness (d) is 20mm; the average cooling rate is 25℃ / s. When the rail joint temperature drops to 300℃, the joint is left to cool naturally in air. The average hardness of the softened zone of the flash welded joint treated using this method is 98% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 3mm, significantly improving the wear performance of the softened zone of the flash welded joint.

[0038] Comparative Example 1 In this comparative example, the pearlitic steel rail used had a C content of 0.80%, a Si content of 1.20%, a Mn content of 1.10%, a Cr content of 0.12%, a V content of 0.05%, a P and S content of 0.005%, and an Al content of 0.001%. The flash welding process mainly consisted of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasted 130 seconds. After the welding process was completed and the joint cooled to below 300°C, a contoured induction coil was used to reheat the flash welded joint area. The induction coil was 4 mm from the rail surface, and the heating area covered the entire welded joint area, with a length 'a' of 50 mm along the rail's extension direction. The temperature rise rate of the flash welded joint area during the heating process was 0.8°C / s. Once the heating temperature reaches 700℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a steel rail, is used to accelerate cooling of both sides of the fusion line of the flash welded joint, including the rail top surface, rail head fillet, and rail head side. The length (b) of the cooling device along the rail extension direction is 10mm, and the thickness (d) is 10mm; the average cooling rate is 4℃ / s. When the rail joint temperature drops to 100℃, the joint is left to cool naturally in air. Using this method, the average hardness of the softened zone of the flash welded joint is only 40% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 25mm, which does not meet the application requirements.

[0039] Comparative Example 2 In this comparative example, the pearlitic steel rail used had a C content of 0.80%, a Si content of 1.20%, a Mn content of 1.10%, a Cr content of 0.12%, a V content of 0.05%, a P and S content of 0.005%, and an Al content of 0.001%. The flash welding process mainly consisted of four stages: electrode clamping, electric heating, pressure upsetting, and rapid stub removal. The entire welding process lasted 130 seconds. After the welding process was completed and the joint cooled to below 300°C, a contoured induction coil was used to reheat the flash welded joint area. The induction coil was 60 mm from the rail surface, and the heating area covered the entire welded joint area, with a length 'a' of 160 mm along the rail's extension direction. The temperature rise rate of the flash welded joint area during the heating process was 25°C / s. Once the heating temperature reaches 1100℃, the heating device is immediately removed. A contact-type heat-conducting device, mimicking the profile of a steel rail, is used to accelerate cooling of both sides of the fusion line of the flash welded joint, including the rail top surface, rail head fillet, and rail head side. The length (b) of the cooling device along the rail extension direction is 50mm, and the thickness (d) is 32mm; the average cooling rate is 40℃ / s. When the rail joint temperature drops to 500℃, the joint is left to cool naturally in air. Using this method, the average hardness of the softened zone of the flash welded joint is only 50% higher than that of the air-cooled joint after welding, and the width of the softened zone on one side of the joint is 30mm, which does not meet the application requirements.

[0040] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0041] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for improving the wear performance of the softened zone of a flash welded joint in rails, characterized in that: The method includes the following steps: A heating device is used to heat the area of ​​the flash welded joint of the rail. The initial temperature of the heating process is less than 300℃ and the final temperature is 800℃~1000℃. After heating to the termination temperature, the heating device is immediately removed, and a cooling device is used to accelerate the cooling of the local area of ​​the heated rail flash weld joint. The average cooling rate of the accelerated cooling is 5℃ / s to 35℃ / s, and the termination temperature of the accelerated cooling is 200℃ to 400℃. The rail flash welded joint area includes a fusion line, a heat-affected zone, and a base material area. The welded joint area is centered on the fusion line, which has a width of 0.5 mm to 2.0 mm. The heat-affected zone is located on both sides of the fusion line, with a width of 5.0 mm to 30.0 mm on each side. The base material area is located on the side of the heat-affected zone away from the fusion line, with a width of 5.0 mm to 20.0 mm. The local area of ​​the flash welded joint of the rail is a transition area between the heated area and the unheated base material area during the heating process. When heated to the termination temperature, the temperature of the local area of ​​the flash welded joint of the rail is 400℃~600℃. The cooling device is a contact-type heat-conducting device that mimics the profile of a steel rail. The cooling device has a hollow structure and heat exchange occurs internally through a cooling medium. The cooling device is coupled to the steel rail contact surface using a flexible heat-conducting material.

2. The method according to claim 1, characterized in that: The microstructure of the rail is pearlitic; in the chemical composition of the rail, the mass fraction of C is 0.35% to 1.20%, the mass fraction of Si is 0.10% to 1.20%, the mass fraction of Mn is 0.60% to 1.40%, the mass fraction of Cr does not exceed 0.25%, the mass fraction of V does not exceed 0.20%, the mass fractions of P and S both do not exceed 0.040%, the mass fraction of Al does not exceed 0.004%, and the remainder is iron and unavoidable impurities.

3. The method according to claim 1, characterized in that: The heating device is an induction coil with a profile similar to a steel rail. The distance between the induction coil and the surface of the steel rail is 5mm to 50mm, and the heating area covers the entire weld joint area.

4. The method according to claim 3, characterized in that: The length of the heating device along the extension direction of the rail is 60mm to 150mm.

5. The method according to claim 3, characterized in that: The heating device controls the temperature rise rate in the flash welded joint area of ​​the rail to be 1.0℃ / s to 20.0℃ / s.

6. The method according to claim 1, characterized in that: The cooling device includes a first cooling section that contacts the top surface of the rail head and a second cooling section that contacts the rounded corners and side surfaces of the rail head. The thickness of the first and second cooling sections is 15mm to 30mm, and their length along the extension direction of the rail is 20mm to 40mm.

7. The method according to claim 1, characterized in that: The flash welding process includes four stages: electrode clamping, electric heating, pressure upsetting, and rapid slugging. During the welding process, the temperature of the rails on both sides, which are 0mm to 25mm away from the end face of the rail to be welded, is 900℃ to 1800℃, and the welding duration is 50s to 300s.

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