Method for improving abrasion performance of softening area of flash welding joint of steel rail

Abstract

The invention relates to the field of steel rail welding, in particular to a method for improving the abrasion performance of a softening area of a steel rail flash welding joint, which comprises the following steps: heating the area of the steel rail flash welding joint by using a heating device with the initial temperature of less than 300 DEG C and the final temperature of 800-1000 DEG C in the heating process; after the steel rail is heated to the final temperature, the heating device is moved away immediately, a cooling device is adopted for conducting accelerated cooling on the local area of the heated steel rail flash welding joint, the average cooling speed of accelerated cooling is 5 DEG C / s-35 DEG C / s, and the final temperature of accelerated cooling is 200 DEG C-400 DEG C. The average hardness of the softening area of the steel rail flash welding joint treated through the method is improved by 95% or above compared with that of a welded air cooling joint, the width of the softening area on the single side of the joint is 5 mm or below, and the abrasion performance of the softening area of the steel rail flash welding joint is greatly improved.

Description

Technical Field

[0001] The invention relates to the field of rail welding, and in particular to a method for improving the wear performance of a softening zone of a rail flash welding joint. Background Art

[0002] In recent years, with the continuous increase in heavy-duty railway transportation volume, axle load and maximum load of a single train, the wear and damage problems of rails and their welded joints have become increasingly serious. Whether it is thermite welding or flash welding, the hardness of the welded joints after the heat of welding, especially the rail surface hardness in the softened zone of the joints, is lower than that of the parent material, and its tensile strength, hardness, fatigue strength and other mechanical properties are also lower than those of the parent material. When used under high-volume conditions, the softened zone of the welded joint wears faster, the collapse is very serious, and the joint life is lower than that of the rail parent material. Studies have shown that fatigue wear caused by impact wear and rolling contact in the softened zone of the welded joint is an important cause of damage to the welded joint.

[0003] The softening zone of the rail flash weld joint refers to the area where the hardness of the weld joint is significantly lower than that of the base material. Unlike the austenitization area of ​​the joint where the hardness is lower than that of the base material, the metal in the softening zone does not undergo austenite transformation during the heating process, and its temperature range is usually in the annealing range of metal heat treatment, so the softening zone is sometimes called the annealing zone. Since the rail material usually presents a granular pearlite structure after annealing, the softening zone is also called the spheroidizing annealing zone. In general, the tensile and impact properties of the joint softening zone are poor, which is the weak link of the rail joint. Because rail welding mainly heats the end of the rail locally, there is always a transition zone between the heated part and the unheated base material. The area with lower hardness in the transition zone is the softening zone. The softening zone is an area that always exists in the rail weld joint and cannot be completely eliminated.

[0004] In terms of rail joint wear, a large number of studies have shown that in addition to taking reasonable lubrication, damage grinding, profile grinding and other measures, changing the wheel-rail friction coefficient, improving the wheel-rail contact relationship and eliminating early damage on the rail surface are effective, but improving the strength and toughness of the joint softening zone is still one of the most effective means to improve wear resistance. At the same time, reducing the width of the softening zone of the rail joint is also a favorable way to improve the wear resistance of the joint. Therefore, reducing the accelerated wear of the softening zone of the welded joint and extending the life of the rail welded joint have become important directions that need to be studied urgently. Summary of the invention

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

[0006] A method for improving the wear performance of the softened zone of a rail flash welding joint provided by the present invention includes the following steps: Use a heating device to heat the rail flash welding joint area. The starting temperature during the heating process is less than 300°C, and the ending temperature is 800°C - 1000°C; After heating to the ending temperature, immediately remove the heating device, and use a cooling device to rapidly cool the local area of the heated rail flash welding joint. The average cooling rate of the rapid cooling is 5°C / s - 35°C / s, and the ending temperature of the rapid cooling is 200°C - 400°C.

[0007] In some embodiments, the microstructure of the rail is pearlite material; in the chemical composition of the rail, the mass fraction of C element is 0.35% - 1.20%, the mass fraction of Si element is 0.10% - 1.20%, the mass fraction of Mn element is 0.60% - 1.40%, the mass fraction of Cr element does not exceed 0.25%, the mass fraction of V element does not exceed 0.20%, the mass fractions of P and S elements do not exceed 0.040%, the mass fraction of Al element does not exceed 0.004%, and the rest is iron and inevitable impurities.

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

[0009] In some embodiments, the heating device is an electric induction coil imitating the rail profile. The distance between the electric induction coil imitating the rail profile and the rail surface is 5 mm - 50 mm, and the heating area covers the entire welding joint area.

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

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

[0012] In some embodiments, the local area of the rail flash welding joint is the transition area between the heated area and the unheated base metal during the heating process. When heated to the ending temperature, the temperature of the local area of the rail flash welding joint is 400°C - 600°C.

[0013] In some embodiments, the cooling device is a contact type heat conduction device imitating the rail profile. The cooling device is a hollow structure, and heat exchange is carried out through a cooling medium inside. Its contact surface with the rail is coupled with a flexible heat conduction material.

[0014] In some embodiments, the cooling device includes a first cooling portion that contacts the top surface of the rail head, and a second cooling portion that contacts the fillet and the side surface of the rail head. The thicknesses of the first cooling portion and the second cooling portion are 15 mm to 30 mm, and the lengths in the extending direction of the rail are 20 mm to 40 mm.

[0015] In some embodiments, the flash welding process includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid burr pushing. During the welding process, the temperatures of the two sides of the rail at a distance of 0 mm to 25 mm from the end face of the rail to be welded are 900 °C to 1800 °C, and the welding duration is 50 s to 300 s.

[0016] The beneficial effects of the present invention are as follows: By adopting the processes of heating and accelerated cooling for the flash welded joint of the rail, the average hardness of the softened zone of the welded joint is increased by more than 95% compared with the traditional air-cooled joint after welding. This increase in hardness can effectively enhance the wear resistance of the welded joint and reduce the failures caused by impact and fatigue wear. Moreover, the width of the unilateral softened zone of the welded joint processed by this method can be controlled within 5 mm, making the overall performance of the welded joint more uniform and reducing the stress concentration and wear risk caused by local softening. The heating and cooling processes can improve the microstructure of the welded joint, making it more uniform and closer to the microstructure of the base material, thus significantly extending the service life of the rail during service. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other embodiments can also be obtained based on these drawings.

[0018] Figure 1 It is a top view of the schematic diagram of the heating and cooling area of the flash welded joint of the rail provided by an embodiment of the present invention; Figure 2 It is a side view of the heating and cooling area of the flash welded joint of the rail. Detailed Description of the Embodiments

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the following further elaborates on the embodiments of the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0020] It should be noted that all the expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two entities or parameters with the same name but different identities. It can be seen that "first" and "second" are only for the convenience of expression and should not be construed as a limitation on the embodiments of the present invention. This will not be elaborated one by one in the subsequent embodiments.

[0021] The present invention provides a method for improving the wear performance of the softened zone of a rail flash welding joint, comprising the following steps: Use a heating device to heat the rail flash welding joint area, where the starting temperature of the heating process is less than 300 °C and the ending temperature is 800 °C - 1000 °C; After heating to the ending temperature, immediately remove the heating device and use a cooling device to rapidly cool the local area of the heated rail flash welding joint. The average cooling rate of the rapid cooling is 5 °C / s - 35 °C / s, and the ending temperature of the rapid cooling is 200 °C - 400 °C.

[0022] Compared with the prior art, the present invention adopts a process of heating and rapid cooling for the rail flash welding joint. The average hardness of the softened zone of the welding joint is increased by more than 95% compared with the traditional post-weld air-cooled joint. This increase in hardness can effectively enhance the wear resistance of the welding joint and reduce failures caused by impact and fatigue wear. Moreover, the width of the unilateral softened zone of the welding joint after being treated by this method can be controlled within 5 mm, making the overall performance of the welding joint more uniform and reducing the stress concentration and wear risk caused by local softening. The heating and cooling processes can improve the microstructure of the welding joint, making it more uniform and closer to the microstructure of the base material, thus significantly extending the service life of the rail during service.

[0023] In some embodiments, the microstructure of the rail is pearlite material; in the chemical composition of the rail, the mass fraction of C element is 0.35% - 1.20%, the mass fraction of Si element is 0.10% - 1.20%, the mass fraction of Mn element is 0.60% - 1.40%, the mass fraction of Cr element does not exceed 0.25%, the mass fraction of V element does not exceed 0.20%, the mass fractions of P and S elements do not exceed 0.040%, the mass fraction of Al element does not exceed 0.004%, and the rest is iron and inevitable impurities. By reasonably controlling the microstructure and chemical composition of the rail, the present application can significantly improve the hardness, wear resistance and fatigue resistance of the rail welding joint, while avoiding problems such as brittleness or overheat sensitivity caused by improper composition, thereby extending the service life of the rail and improving its service performance.

[0024] In some embodiments, the flash welding joint area of the rail includes a fusion line, a heat affected zone, and a base metal zone. The fusion line is the area formed after the materials at both ends of the rail melt and re-solidify during the welding process, ensuring the physical connection of both ends of the rail. The width of the fusion line is 0.5 mm to 2.0 mm. The heat affected zone is the area that is affected by heat but not melted during the welding process, located on both sides of the fusion line. The width of each heat affected zone is 5.0 mm to 30.0 mm. The base metal zone is the area that is not affected by heat during the welding process, 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.

[0025] In some embodiments, the heating device is an electric induction coil imitating the profile of the rail, which heats the flash welding joint area of the rail by using the principle of electromagnetic induction. The distance between the electric induction coil imitating the profile of the rail and the rail surface is 5 mm to 50 mm, and the heating area covers the entire welding joint area, including the fusion line, the heat affected zone, and the base metal zone. This design can achieve rapid and efficient heating while ensuring the uniformity of the temperature distribution.

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

[0027] In some embodiments, the heating device controls the temperature rise rate of the flash welding joint area of the rail to be 1.0 °C / s to 20.0 °C / s, so as to effectively refine the grains in the welding joint area, reduce the residual stress of the welding joint, and ensure a more uniform temperature distribution across the entire cross-section of the welding joint.

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

[0029] In some embodiments, the cooling device is a contact type heat conduction device imitating the profile of the rail, which cools the entire head area of the rail on both sides of the fusion line of the flash welding joint of the rail, including the rail top surface, the rail head fillet, and the rail head side surface, so as to achieve rapid cooling and reduce the residence time of the welding joint at high temperature. The cooling device is a hollow structure, and heat exchange is carried out through a cooling medium inside. Its contact surface with the rail is coupled with a flexible heat conduction material. Specifically, cooling medium inlets and outlets are provided on the cooling device to allow the cooling medium to circulate inside the device. This circulation system can continuously remove the heat of the welding joint, ensuring the stability and efficiency of the cooling process.

[0030] In some embodiments, the cooling device includes a first cooling portion that contacts the top surface of the rail head, and a second cooling portion that contacts the fillet and the side surface of the rail head, which can achieve precise cooling of the key parts of the welded joint. The thickness d of the first cooling portion and the second cooling portion is 15 mm to 30 mm, the length b along the extending direction of the rail is 20 mm to 40 mm, and the width c = the width of the rail head + 2d. The dimensional parameters of the cooling device (such as the thickness d, the length b, and the width c) can be adjusted according to the specific shape of the rail to ensure that the cooling device can closely fit the surface of the rail. This design improves the versatility and adaptability of the cooling device and is applicable to various types of rails. As Figure 1 shown, when cooling the same flash welded joint of the rail, two cooling devices are used for cooling simultaneously. By the simultaneous action of the two cooling devices, the cooling efficiency can be significantly improved, and the uniformity of the cooling process can be ensured at the same time.

[0031] In some embodiments, flash welding mainly refers to the method of heating the rail parts to be welded by resistance heat until reaching a predetermined temperature, and then quickly applying upsetting force to achieve atomic bonding between the rails. The flash welding process includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid burr removal. During the welding process, the temperatures of the two sides of the rail at 0 mm to 25 mm from the end face of the rail to be welded are 900 °C to 1800 °C, and the welding duration is 50 s to 300 s. Specifically, in the electrode clamping stage: through electrode clamping, it can be ensured that the ends of the rails to be welded remain stable during the welding process, avoiding welding defects caused by vibration or displacement. In the energized heating stage: heating the rail ends to 900 °C to 1800 °C and controlling the time within 50 s to 300 s can make the rail ends reach sufficient plasticity, providing good conditions for subsequent upsetting. In the pressure upsetting stage: applying upsetting force at high temperature to cause plastic deformation of the rail ends and achieve atomic bonding to form a firm welded joint. In the rapid burr removal stage: after welding is completed, removing the excess burrs through rapid burr removal to ensure the surface of the welded joint is flat, reducing stress concentration points, and improving the fatigue performance of the welded joint.

[0032] The following will further illustrate the method for improving the wear performance of the softened zone of the rail flash welded joint provided by this application in combination with specific embodiments: Embodiment 1 In this embodiment, the mass fraction of C element in the pearlite material rail used is 0.80%, the mass fraction of Si element is 1.20%, the mass fraction of Mn element is 1.10%, the mass fraction of Cr element is 0.12%, the mass fraction of V element is 0.05%, the mass fractions of P and S elements are both 0.005%, and the mass fraction of Al element is 0.001%. The flash welding process mainly includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid tumor pushing. The duration of the entire welding process is 130 s. After the welding process is completed and the joint is cooled to below 300 °C, an electric induction coil imitating the rail profile is used to perform secondary heating on the flash welding joint area of the rail. The distance between the profiling induction coil and the rail surface is 5 mm, and the heating area covers the entire welding joint area. Its length a along the rail extension direction is 60 mm. The temperature rise rate of the flash welding joint area of the rail during the heating process is 1.0 °C / s. When the heating temperature reaches 800 °C, the heating device is immediately removed, and a contact thermal conduction device imitating the rail profile is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the rail, including the rail top surface, rail head fillet, and rail head side surface. The length b of the cooling device along the rail extension direction is 20 mm, and the thickness d is 15 mm; the average cooling rate of the accelerated cooling is 5 °C / s. When the temperature of the rail joint drops to 200 °C, the joint is left to cool naturally in the air. The average hardness of the softened area of the flash welding joint of the rail treated by this method is increased by 97% compared with the joint cooled in air after welding. The width of the unilateral softened area of the joint is 4 mm, which greatly improves the wear performance of the softened area of the flash welding joint of the rail.

[0033] Example 2 In this embodiment, the mass fraction of C element in the pearlitic steel rail used is 0.80%, the mass fraction of Si element is 1.20%, the mass fraction of Mn element is 1.10%, the mass fraction of Cr element is 0.12%, the mass fraction of V element is 0.05%, the mass fractions of P and S elements are both 0.005%, and the mass fraction of Al element is 0.001%. The flash welding process mainly includes four stages: electrode clamping, electric heating, pressure upsetting, and rapid burr pushing. The duration of the entire welding process is 130 s. After the welding process is completed and the joint is cooled to below 300 °C, an electric induction coil with a profile similar to that of the steel rail is used to perform secondary heating on the flash welding joint area of the steel rail. The distance between the profiling induction coil and the steel rail surface is 50 mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the steel rail is 150 mm. The temperature rise rate in the flash welding joint area of the steel rail during the heating process is 20.0 °C / s. When the heating temperature reaches 1000 °C, the heating device is immediately removed, and a contact heat conduction device with a profile similar to that of the steel rail is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the steel rail, including the rail top surface, rail head fillet, and rail head side surface. The length b of the cooling device along the extension direction of the steel rail is 40 mm, and the thickness d is 30 mm; the average cooling rate of the accelerated cooling is 35 °C / s. When the temperature of the steel rail joint drops to 400 °C, the joint is left to cool naturally in the air. The average hardness of the softened area of the flash welded joint of the steel rail treated by this method is increased by 98% compared with the joint cooled in air after welding. The width of the single-sided softened area of the joint is 3 mm, which greatly improves the wear performance of the softened area of the flash welded joint of the steel rail.

[0034] Example 3 In this embodiment, the pearlitic steel rail used has a mass fraction of C element of 0.80%, a mass fraction of Si element of 1.20%, a mass fraction of Mn element of 1.10%, a mass fraction of Cr element of 0.12%, a mass fraction of V element of 0.05%, mass fractions of P and S elements both of 0.005%, and a mass fraction of Al element of 0.001%. The flash welding process mainly includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid burr pushing. The duration of the entire welding process is 130 s. After the welding process is completed and the joint is cooled to below 300 °C, a secondary heating is performed on the flash welding joint area of the steel rail using an electric induction coil imitating the rail profile. The distance between the profiling induction coil and the rail surface is 45 mm, and the heating area covers the entire welding joint area, with its longitudinal dimension a on the steel rail being 100 mm. The temperature rise rate in the flash welding joint area of the steel rail during the heating process is 15.0 °C / s. When the heating temperature reaches 900 °C, the heating device is immediately removed, and a contact heat conduction device imitating the rail profile is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the steel rail, including the rail top surface, rail head fillet, and rail head side surface. The length b along the rail extension direction is 30 mm, and the thickness d is 20 mm; the average cooling rate of the accelerated cooling is 25 °C / s. When the temperature of the rail joint drops to 300 °C, the joint is left to cool naturally in the air. The average hardness of the softened area of the flash welding joint of the steel rail treated by this method is increased by 98% compared to the joint cooled in air after welding, and the width of the unilateral softened area of the joint is 3 mm, significantly improving the wear performance of the softened area of the flash welding joint of the steel rail.

[0035] Example 4 In this embodiment, the mass fraction of C element in the pearlite material rail used is 0.80%, the mass fraction of Si element is 1.20%, the mass fraction of Mn element is 1.10%, the mass fraction of Cr element is 0.12%, the mass fraction of V element is 0.05%, the mass fractions of P and S elements are both 0.005%, and the mass fraction of Al element is 0.001%. The flash welding process mainly includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid tumor pushing. The duration of the entire welding process is 130 s. After the welding process is completed and the joint is cooled to below 300 °C, an electric induction coil imitating the rail profile is used to perform secondary heating on the flash welding joint area of the rail. The distance between the profiling induction coil and the rail surface is 5 mm, and the heating area covers the entire welding joint area, with its longitudinal dimension a on the rail being 60 mm. The temperature rise rate in the flash welding joint area of the rail during the heating process is 1.0 °C / s. When the heating temperature reaches 800 °C, the heating device is immediately removed, and a contact thermal conduction device imitating the rail profile is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the rail, including the rail top surface, rail head fillet, and rail head side surface. The external dimension b of the cooling device is 40 mm, and the dimension d is 30 mm; the average cooling rate of the accelerated cooling is 35 °C / s. When the temperature of the rail joint drops to 400 °C, the joint is left to cool naturally in the air. The average hardness of the softened zone of the flash welded joint of the rail treated by this method is increased by 99% compared to the joint cooled in air after welding, and the width of the unilateral softened zone of the joint is 2 mm, significantly improving the wear performance of the softened zone of the flash welded joint of the rail.

[0036] Example 5 In this embodiment, the pearlitic steel rail used has a mass fraction of C element of 0.80%, a mass fraction of Si element of 1.20%, a mass fraction of Mn element of 1.10%, a mass fraction of Cr element of 0.12%, a mass fraction of V element of 0.05%, mass fractions of P and S elements both of 0.005%, and a mass fraction of Al element of 0.001%. The flash welding process mainly includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid burr pushing. The duration of the entire welding process is 130 s. After the welding process is completed and the joint is cooled to below 300 °C, an electric induction coil imitating the rail profile is used to perform secondary heating on the flash welding joint area of the rail. The distance between the profiling induction coil and the rail surface is 50 mm, and the heating area covers the entire welding joint area, and its length a along the rail extension direction is 150 mm. The temperature rise rate of the flash welding joint area of the rail during the heating process is 20.0 °C / s. When the heating temperature reaches 1000 °C, the heating device is immediately removed, and a contact heat conduction device imitating the rail profile is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the rail, including the rail top surface, the rail head fillet, and the rail head side surface. The length b of the cooling device along the rail extension direction is 20 mm, and the thickness d is 15 mm; the average cooling rate of the accelerated cooling is 5 °C / s. When the temperature of the rail joint drops to 200 °C, the joint is placed in the air for natural cooling. The average hardness of the softened area of the flash welding joint of the rail treated by this method is increased by 98% compared with the joint cooled in air after welding, and the width of the unilateral softened area of the joint is 4 mm, greatly improving the wear performance of the softened area of the flash welding joint of the rail.

[0037] Example 6 In this embodiment, the mass fraction of C element in the pearlite material steel rail used is 1.20%, the mass fraction of Si element is 1.20%, the mass fraction of Mn element is 0.60%, the mass fraction of Cr element is 0.012%, the mass fraction of V element is 0.009%, the mass fractions of P and S elements are both 0.010%, and the mass fraction of Al element is 0.001%. The flash welding process mainly includes four stages: electrode clamping, electric heating, pressure upsetting, and rapid tumor pushing. The duration of the entire welding process is 200 s. After the welding process is completed and the joint is cooled to below 300 °C, an electric induction coil imitating the rail profile is used to perform secondary heating on the flash welding joint area of the rail. The distance between the profiling induction coil and the rail surface is 45 mm, and the heating area covers the entire welding joint area. Its length a along the rail extension direction is 100 mm. The temperature rise rate in the flash welding joint area of the rail during the heating process is 15.0 °C / s. When the heating temperature reaches 900 °C, the heating device is immediately removed, and a contact heat conduction device imitating the rail profile is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the rail, 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 30 mm, and the thickness d is 20 mm; the average cooling rate of the accelerated cooling is 25 °C / s. When the temperature of the rail joint drops to 300 °C, the joint is placed in the air for natural cooling. The average hardness of the softened area of the flash welded joint of the rail treated by this method is increased by 98% compared with the joint cooled in air after welding. The width of the single-sided softened area of the joint is 3 mm, which greatly improves the wear performance of the softened area of the flash welded joint of the rail.

[0038] Comparative Example 1 In this comparative example, the mass fraction of C element in the pearlite material steel rail used is 0.80%, the mass fraction of Si element is 1.20%, the mass fraction of Mn element is 1.10%, the mass fraction of Cr element is 0.12%, the mass fraction of V element is 0.05%, the mass fractions of P and S elements are both 0.005%, and the mass fraction of Al element is 0.001%. The flash welding process mainly includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid burr pushing. The duration of the entire welding process is 130 s. After the welding process is completed and the joint is cooled to below 300 °C, an electric induction coil imitating the rail profile is used to perform secondary heating on the flash welding joint area of the steel rail. The distance between the profiling induction coil and the rail surface is 4 mm, and the heating area covers the entire welding joint area. Its length a along the rail extension direction is 50 mm. The temperature rise rate in the flash welding joint area of the steel rail during the heating process is 0.8 °C / s. When the heating temperature reaches 700 °C, the heating device is immediately removed, and a contact thermal conduction device imitating the rail profile is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the steel rail, 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 10 mm, and the thickness d is 10 mm; the average cooling rate of the accelerated cooling is 4 °C / s. When the temperature of the steel rail joint drops to 100 °C, the joint is placed in the air for natural cooling. The average hardness of the softened area of the flash welding joint of the steel rail treated by this method is only increased by 40% compared with the joint cooled in air after welding. The width of the unilateral softened area of the joint is 25 mm, which cannot meet the use requirements.

[0039] Comparative Example 2 In this comparative example, the mass fraction of C element in the pearlite material steel rail used is 0.80%, the mass fraction of Si element is 1.20%, the mass fraction of Mn element is 1.10%, the mass fraction of Cr element is 0.12%, the mass fraction of V element is 0.05%, the mass fractions of P and S elements are both 0.005%, and the mass fraction of Al element is 0.001%. The flash welding process mainly includes four stages: electrode clamping, energized heating, pressure upsetting, and rapid flash removal. The duration of the entire welding process is 130 s. After the welding process is completed and the joint is cooled to below 300 °C, an electric induction coil imitating the rail profile is used to perform secondary heating on the flash welding joint area of the steel rail. The distance between the profiling induction coil and the rail surface is 60 mm, the heating area covers the entire welding joint area, and its length a along the rail extension direction is 160 mm. The temperature rise rate in the flash welding joint area of the steel rail during the heating process is 25 °C / s. When the heating temperature reaches 1100 °C, the heating device is immediately removed, and a contact thermal conduction device imitating the rail profile is used to accelerate the cooling of the entire rail head area on both sides of the fusion line of the flash welding joint of the steel rail, including the rail top surface, rail head fillet, and rail head side surface. The length b of the cooling device along the rail extension direction is 50 mm, and the thickness d is 32 mm; the average cooling rate of the accelerated cooling is 40 °C / s. When the temperature of the steel rail joint drops to 500 °C, the joint is placed in the air for natural cooling. The average hardness of the softened area of the flash welding joint of the steel rail treated by this method is only increased by 50% compared with the joint cooled in air after welding, and the width of the single-sided softened area of the joint is 30 mm, which cannot meet the use requirements.

[0040] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope recorded in this specification.

[0041] The above-described embodiments merely represent several implementation manners of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for improving the wear performance of the softening zone of a rail flash welded joint, characterized in that: The method comprises the following steps: A heating device is used to heat the rail flash welding joint area, the starting temperature of the heating process is less than 300°C, and the ending temperature is 800°C to 1000°C; After heating to the termination temperature, the heating device is immediately removed, and a cooling device is used to accelerate cooling of the local area of ​​the heated rail flash welding joint. The average cooling rate of the accelerated cooling is 5°C / s to 35°C / s, and the termination temperature of the accelerated cooling is 200°C to 400°C.

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

3. The method according to claim 1, characterized in that: The rail flash welding joint area includes a fusion line, a heat-affected zone and a parent material area, wherein the welding joint area is centered on the fusion line, the width of the fusion line is 0.5mm to 2.0mm, the heat-affected zone is on both sides of the fusion line, and the width of the heat-affected zone on each side is 5.0mm to 30.0mm, and the parent material area is on the side of the heat-affected zone away from the fusion line, and the width of the parent material area is 5.0mm to 20.0mm.

4. The method according to claim 3, characterized in that: The heating device is an electric induction coil imitating the profile of a rail, the distance between the electric induction coil imitating the profile of a rail and the surface of the rail is 5mm to 50mm, and the heating area covers the entire welding joint area.

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

6. The method according to claim 4, characterized in that: The heating device controls the temperature rise rate of the rail flash welding joint area to be 1.0°C / s to 20.0°C / s.

7. The method according to claim 3, characterized in that: The local area of ​​the rail flash weld joint 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 weld joint is 400°C to 600°C.

8. The method according to claim 1, characterized in that: The cooling device is a contact heat-conducting device imitating the profile of a steel rail. The cooling device is a hollow structure, and heat exchange is performed inside through a cooling medium. The contact surface of the cooling device and the steel rail is coupled by a flexible heat-conducting material.

9. The method according to claim 8, characterized in that: The cooling device includes a first cooling part in contact with the top surface of the rail head of the rail, and a second cooling part in contact with the rail head fillet and the side surface of the rail head. The thickness of the first cooling part and the second cooling part is 15mm to 30mm, and the length along the extension direction of the rail is 20mm to 40mm.

10. The method according to claim 1, characterized in that: The flash welding process includes four stages: electrode clamping, power heating, pressure forging and rapid nodule pushing. During the welding process, the temperature of the rails on both sides 0mm to 25mm away from the end face of the rail to be welded is 900°C to 1800°C, and the welding duration is 50s to 300s.

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