Method for improving service 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 service performance of a softening area of a steel rail flash welding joint. The method comprises the steps that a steel rail flash welding joint area cooled to a certain temperature after welding is subjected to secondary heating, the heating process comprises a common heating stage and a special heating stage, and in the common heating stage, a single heating device is adopted for heating the whole section of a steel rail flash welding joint; in the special heating stage, an auxiliary heating device is adopted for conducting auxiliary heating on rail heads in specific areas at the two ends of a single heating device; and after the steel rail flash welding joint area is heated to the preset temperature, the single heating device and the auxiliary heating device are moved away immediately, and a cooling device is adopted for conducting accelerated cooling on the steel rail flash welding joint local area heated to the preset temperature. According to the steel rail flash welding joint treated through the method, the hardness, toughness and plasticity of the softening area of the welding joint can be remarkably improved, and the service performance of the softening area of the steel rail flash welding joint is improved.

Description

Technical Field

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

[0002] In recent years, with the rapid development of railway transportation, especially the continuous increase in the transportation volume, axle load and maximum load of a single train of heavy-duty railways, the wear and damage of rails and their welded joints have become increasingly serious. Whether it is thermite welding or flash welding, the hardness of the rail surface of the welded joint, especially the softened zone of the joint, is lower than that of the parent material under the influence of welding heat, and its tensile strength, hardness, fatigue strength and other mechanical properties are all reduced. Under high-volume conditions, the softened zone of the welded joint wears faster, and the collapse phenomenon is very serious, resulting in the joint life being lower than that of the rail parent material.

[0003] Studies have shown that the collapse of the softening zone of the weld joint, impact wear, and fatigue wear caused by rolling contact are important causes of weld joint damage. 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. The metal in this area does not undergo austenite transformation during the heating process, but is in the annealing range of heat treatment, so it is also called the annealing zone or spheroidizing annealing zone. Since rail welding mainly involves local heating of the rail end, 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 existence of the softening zone makes the tensile and impact properties of the weld joint poor, becoming the weak link of the rail joint.

[0004] At present, rail welding mainly adopts two methods: flash welding and thermite welding. The comprehensive mechanical properties of thermite welded joints are significantly lower than those of the parent material, and the weld strength and rail service life can usually only reach one-third to three-quarters of the parent material. Rail flash welding is completed by a mobile flash welding machine, which has a high degree of automation, stable process, and excellent welding quality. Its welded joints are dense forging structures, and the mechanical properties are close to those of the rail parent material. It is currently the most practical method for rail welding, with the highest welding precision and the best welding quality. However, even with flash welding, the performance of the softening zone of the welded joint still cannot meet the needs of large-volume and heavy-load railways.

[0005] To solve the above problems, the prior art has adopted a post-weld heat treatment process to improve the performance of the welded joint by reheating austenitization and controlling cooling. For example, the use of medium-frequency induction heating and air jet cooling processes can improve the rail surface hardness and toughness and plasticity of the welded joint. However, the prior art still has shortcomings, especially in reducing the width of the softening zone and improving the comprehensive service performance of the softening zone, which still needs to be further optimized. Based on this, the prior art still needs to be improved. Summary of the invention

[0006] In view of this, the present invention aims to provide a method for improving the service performance of the softening zone of a rail flash weld joint. By optimizing the heating and cooling processes, the width of the joint softening zone is greatly reduced, and the comprehensive service performance of the softening zone is significantly improved. This can at least solve the technical problem of the low service performance of the softening zone of the existing rail flash weld joint.

[0007] A method for improving the service performance of a softening zone of a rail flash welded joint proposed by the present invention comprises: The flash welded rail joints cooled to a certain temperature after welding are heated again, and the heating process includes a normal heating stage and a special heating stage. In the normal heating stage, a single heating device is used to heat the entire section of the flash welded rail joint; in the special heating stage, a single heating device is continued to be used to heat the entire section of the flash welded rail joint, and an auxiliary heating device is used to perform auxiliary heating on the rail heads at both ends of the area covered by the single heating device; After the rail flash weld joint is heated to a preset temperature, the single heating device and the auxiliary heating device are immediately removed, and a cooling device is used to accelerate cooling of the local areas of the rail flash weld joint heated to the preset temperature on both sides of the fusion line.

[0008] In some embodiments, the starting temperature of the entire heating process is less than 300° C., and the ending temperature of the entire heating process is 900° C. to 1100° C. The preset temperature is the ending temperature of the entire heating process.

[0009] In some embodiments, the starting temperature of the common heating stage is less than 300° C., the ending temperature of the common heating stage is 500° C. to 600° C., and the duration is ≤100 s.

[0010] In some embodiments, in the special heating stage, the temperature difference between the starting temperature of the auxiliary heating device and the ending temperature of the ordinary heating stage is ≤ 20°C, until the ending temperature of the entire heating process is reached and the heating process is terminated.

[0011] In some embodiments, a single heating device uses an electric induction coil that simulates the profile of a rail, and the distance between the electric induction coil that simulates the profile of a rail and the surface of the rail is 5mm to 50mm, and the heating area covers the entire weld joint area. The length of the heating device along the extension direction of the rail is 60mm to 150mm; in the ordinary heating stage, the single heating device controls the temperature rise rate of the entire section of the rail flash weld joint to be 1.0℃ / s to 20.0℃ / s.

[0012] In some embodiments, in the special heating stage, the areas assisted by the auxiliary heating device are located at both ends of the welding joint area and are the rail head working area including the rail top surface, the rail head fillet and the rail head side surface.

[0013] In some embodiments, the length of the auxiliary heating device along the extension direction of the rail is 20 mm to 30 mm, the center line of the area covered by the auxiliary heating device coincides with the edge covered by the single heating device, and the duration of the auxiliary heating is less than 40 s.

[0014] In some embodiments, 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.

[0015] In some embodiments, the local area cooled by the cooling device includes a transition area between the heated area during the heating process and the unheated joint base material area. When heated to the termination temperature of the entire heating process, the temperature of the local area is 400°C to 600°C.

[0016] In some embodiments, the cooling device is a contact heat-conducting device that imitates the profile of a rail. The cooling device is a hollow structure, and heat exchange is performed inside through a cooling medium. The contact surface between the cooling device and the rail is coupled with a flexible heat-conducting material.

[0017] In some embodiments, the cooling device includes a first cooling part in contact with the top surface of the rail head, 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.

[0018] The beneficial effects of the present invention are as follows: the present invention reheats and accelerates the cooling of the rail flash weld joint that has been cooled to a certain temperature after welding, thereby significantly improving the hardness and toughness and plasticity of the softening zone of the weld joint, reducing the collapse phenomenon of the weld joint, and improving the service performance of the softening zone of the rail flash weld joint. The optimized heat treatment process can effectively improve the microstructure of the weld joint, reduce the appearance of unfavorable structures such as martensite, thereby improving the overall performance of the weld joint and extending the service life of the weld joint. The width of the softening zone on one side of the rail flash weld joint treated by the above method can be controlled below 5 mm, which is significantly reduced compared to the traditional process. The average hardness of the softening zone is increased by more than 95% compared to the air-cooled joint after welding, which is close to the hardness level of the parent material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A schematic front view of the heating and cooling areas of a rail flash welding joint provided by an embodiment of the present invention; Figure 2 A left schematic diagram of the heating and cooling areas of a rail flash weld joint provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0022] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. The subsequent embodiments will not explain this one by one.

[0023] A method for improving the service performance of a softening zone of a rail flash welded joint provided by the present invention comprises: The rail flash weld joint that has been cooled to a certain temperature (such as below 300°C) after welding is subjected to secondary heating. The heating process includes a normal heating stage and a special heating stage. In the normal heating stage, a single heating device is used to heat the entire cross-section of the rail flash weld joint. In the special heating stage, a single heating device continues to be used to heat the entire cross-section of the rail flash weld joint, and an auxiliary heating device is used to auxiliary heat the rail heads at both ends of the area covered by the single heating device, so as to further optimize the heating effect, make the heating more precise, and avoid local overheating or underheating. Preferably, the auxiliary heating device mainly adopts non-contact heating, such as flame, laser, etc.

[0024] After the rail flash weld joint is heated to a preset temperature, the single heating device and the auxiliary heating device are immediately removed, and a cooling device is used to accelerate the cooling of the local areas on both sides of the fusion line of the rail flash weld joint heated to the preset temperature, so as to effectively refine the grain size of the weld joint and improve the organizational structure.

[0025] In the present application, the rail flash weld joint includes a fusion line, a heat-affected zone and a parent material zone. Among them, the rail flash weld joint is centered on the fusion line. The fusion line is the area formed by the melting and re-solidification of the materials at both ends of the rail during the welding process, which ensures the physical connection between the two ends of the rail. The width of the fusion line is 0.5mm to 2.0mm. The heat-affected zone is the area that is affected by heat but not melted during the welding process. It is located on both sides of the fusion line. The width of the heat-affected zone on each side is 5.0mm to 30.0mm. The parent material zone is the area that is not affected by heat during the welding process. It is located on the side of the heat-affected zone away from the fusion line. The width of the parent material zone on each side is 5.0mm to 20.0mm.

[0026] In the present application, 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.

[0027] Flash welding mainly refers to a method of using resistance heat to heat the part of the rail to be welded until it reaches a predetermined temperature, and then quickly applying a forging force to achieve atomic bonding between the rails. 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 of the rails 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. Specifically, the electrode clamping stage: through electrode clamping, it can ensure that the end of the rail to be welded remains stable during the welding process to avoid welding defects caused by vibration or displacement. The power heating stage: the end of the rail is heated to 900℃ to 1800℃, and the time is controlled at 50s to 300s, which can make the end of the rail reach sufficient plasticity and provide good conditions for subsequent forging. The pressure forging stage: the forging force is applied at high temperature to cause plastic deformation of the rail end and achieve atomic bonding to form a firm welded joint. Rapid nodule removal stage: After welding is completed, excess weld nodules are removed by rapid nodule removal to ensure a smooth surface of the weld joint, reduce stress concentration points, and improve fatigue performance of the weld joint.

[0028] Compared with the prior art, the present application reheats and accelerates the cooling of the rail flash weld joint that has been cooled to a certain temperature after welding, thereby significantly improving the hardness and toughness of the softening zone of the weld joint and reducing the collapse of the weld joint. The optimized heat treatment process can effectively improve the microstructure of the weld joint and reduce the appearance of unfavorable structures such as martensite, thereby improving the overall performance of the weld joint and extending the service life of the weld joint. The width of the softening zone on one side of the rail flash weld joint treated by the above method can be controlled below 5 mm, which is significantly reduced compared to the traditional process. The average hardness of the softening zone is increased by more than 95% compared to the air-cooled joint after welding, which is close to the hardness level of the parent material.

[0029] In some embodiments, the starting temperature of the entire heating process is less than 300°C, and the ending temperature of the entire heating process is 900°C to 1100°C; the preset temperature is the ending temperature of the entire heating process. The low starting temperature (less than 300°C) of the present application ensures that the weld joint is in a relatively low temperature state before heating, avoiding thermal stress concentration caused by excessive temperature difference. The ending temperature is set at 900°C to 1100°C so that the metal in the weld joint area reaches the austenitizing temperature, thereby improving its microstructure through subsequent cooling processes. By precisely controlling the heating termination temperature, the grain size can be effectively refined, the hardness and toughness of the weld joint can be improved, and its performance can be close to that of the parent material. At the same time, coarse grains or overheated structures caused by excessively high temperatures are avoided, thereby improving the comprehensive mechanical properties of the weld joint.

[0030] In some embodiments, the starting temperature of the ordinary heating stage is less than 300°C, the ending temperature of the ordinary heating stage is 500°C to 600°C, and the duration is ≤100s, which is intended to quickly increase the overall temperature of the weld joint and provide a basic temperature for the subsequent special heating stage. This rapid heating method can reduce the width of the heat-affected zone while avoiding the adverse effects of long-term high temperature on the properties of the parent material. Through rapid heating, the width of the softening zone of the weld joint can be effectively reduced while improving the hardness and strength of the weld joint.

[0031] In some embodiments, during the special heating stage, the temperature difference between the starting temperature of the auxiliary heating device and the end temperature of the ordinary heating stage is ≤20°C, until the end temperature of the entire heating process is reached and terminated, so as to avoid overheating or underheating of local areas and ensure the uniformity and stability of the heating process. Through the precise heating of the auxiliary heating device, the microstructure of the welded joint at the rail head can be further refined, and its hardness and toughness can be improved. At the same time, the uniform heating process can reduce the residual stress of the welded joint, improve its fatigue resistance and the service performance of the joint softening zone.

[0032] In some embodiments, a single heating device uses an electric induction coil that simulates the profile of a rail, and uses the principle of electromagnetic induction to heat the entire cross-section of the rail flash weld joint. The distance between the electric induction coil that simulates the profile of a rail and the surface of the rail is 5mm to 50mm, and the heating area covers the entire weld joint area, including the fusion line, heat-affected zone and parent material area during the welding process. This design can achieve fast and efficient heating while ensuring the uniformity of temperature distribution. The length a of the heating device along the extension direction of the rail is 60mm to 150mm. In the normal heating stage, the single heating device controls the temperature rise rate of the entire cross-section of the rail flash weld joint to be 1.0℃ / s to 20.0℃ / s, so as to effectively refine the grains in the weld joint area, reduce the residual stress of the weld joint, and ensure that the temperature distribution of the entire cross-section of the weld joint is more uniform.

[0033] In some embodiments, during the special heating stage, the areas assisted by the auxiliary heating device are located at both ends of the weld joint area and are the rail head working area including the rail top surface, rail head fillet and rail head side. Since the rail head area is the contact area with the wheel after the rail is on the railway, the hardness of the rail head area is higher than that of the non-wheel contact area such as the rail waist and rail bottom area, and a higher hardness is required. The rail waist and rail bottom areas are mainly used for support and require higher toughness. The purpose of improving toughness can be achieved through ordinary heating, so only the rail head area needs to be assisted with heating.

[0034] In some embodiments, the length e of the auxiliary heating device along the extension direction of the rail is 20 mm to 30 mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the single heating device, so as to effectively compensate for the temperature non-uniformity that may exist in the ordinary heating stage, and can concentrate on heating the key working area of ​​the rail head to ensure the temperature consistency of the entire weld joint area. The duration of auxiliary heating is less than 40s, so as to effectively reduce the width of the heat affected zone (HAZ). Short-term high-temperature heating can avoid excessive heat diffusion, thereby reducing the performance degradation caused by coarse grains in the heat affected zone.

[0035] In some embodiments, 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. Accelerated cooling can quickly reduce the temperature of the weld joint and promote grain refinement. The fine grain structure can significantly improve the hardness, toughness and fatigue resistance of the weld joint.

[0036] In some embodiments, the local area of ​​the rail flash weld joint cooled by the cooling device includes a transition area between the heated area during the heating process and the unheated joint parent metal area, wherein the width of the joint parent metal area on each side described in the present application is 5.0 mm to 20.0 mm. When heated to the termination temperature of the entire heating process, the temperature of the local area of ​​the rail flash weld joint is 400°C to 600°C.

[0037] In some embodiments, the cooling device is a contact heat conduction device that imitates the profile of a rail, and uses heat conduction to cool the entire rail head area on both sides of the fusion line of the rail flash weld joint, including the rail top surface, rail head fillet and rail head side, so as to achieve rapid cooling and reduce the residence time of the weld joint at high temperature. The cooling device is a hollow structure, and heat exchange is carried out through a cooling medium inside. The cooling device and the contact surface of the rail are coupled with a flexible heat conductive material. Specifically, the cooling device is provided with a cooling medium inlet and outlet to allow the cooling medium to circulate inside the device. This circulation system can continuously take away the heat of the weld joint and ensure the stability and efficiency of the cooling process.

[0038] In some embodiments, the cooling device includes a first cooling portion in contact with the top surface of the rail head, and a second cooling portion in contact with the fillet and side surfaces of the rail head. The thickness d of the first cooling portion and the second cooling portion is 15 mm to 30 mm, and the length b along the extension direction of the rail is 20 mm to 40 mm. Width c = 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 that the cooling device can fit closely to the surface of the rail. This design improves the versatility and adaptability of the cooling device and is suitable for a variety of rail types. Figure 1 As shown, when cooling the same rail flash weld joint, two cooling devices are used for cooling at the same time. The two cooling devices act at the same time, which can significantly improve the cooling efficiency and ensure the uniformity of the cooling process.

[0039] The method for improving the service performance of the softening zone of the rail flash welded joint provided by the present application will be further described below in conjunction with specific embodiments: Example 1 In this embodiment, the mass fraction of the pearlite rail used is 0.80% for the C element, 1.20% for the Si element, 1.10% for the Mn element, 0.12% for the Cr element, 0.05% for the V element, 0.005% for the P and S elements, and 0.001% for the Al element. The flash welding process mainly consists of four stages: electrode clamping, power-on heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a single electric induction coil imitating the rail profile is used to heat the entire section of the rail flash welding joint in the ordinary stage. The distance between the electric induction coil imitating the rail profile and the surface of the rail is 5mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 60mm, the duration is 80s, and the temperature rise rate is 1.0°C / s. When the temperature of the rail joint is 500℃, the auxiliary heating device is used to perform auxiliary heating on the areas on both sides of the fusion line of the rail flash welding joint (including the rail top surface, rail head fillet and rail head side of the rail head) . The temperature difference between the starting temperature of the auxiliary heating device in the auxiliary heating stage and the end temperature of the ordinary heating stage is 15℃. The length e of the auxiliary heating device along the extension direction of the rail is 20mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the area covered by the single heating device. The duration of the auxiliary heating is 30s. When the heating temperature reaches 900℃, the single heating device and the auxiliary heating device are immediately removed, and the contact heat conduction device imitating the rail profile is used to cool the rail head of the local area of ​​the rail flash welding joint. The length b of the cooling device along the extension direction of the rail is 20mm, the thickness d is 15mm, and the average cooling rate of accelerated cooling is 5℃ / s. When the temperature of the rail joint drops to 200℃, the welded joint is naturally cooled in the air. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 99% compared with the air-cooled joint after welding, and the width of the softening zone on one side of the joint is 2mm, which greatly improves the comprehensive service performance of the softening zone of the rail flash welded joint.

[0040] Example 2 In this embodiment, the mass fraction of the pearlite rail used is 0.80% for the C element, 1.20% for the Si element, 1.10% for the Mn element, 0.12% for the Cr element, 0.05% for the V element, 0.005% for the P and S elements, and 0.001% for the Al element. The flash welding process mainly consists of four stages: electrode clamping, power-on heating, pressurized forging, and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a single electric induction coil imitating the rail profile is used to heat the entire section of the rail flash welding joint in the ordinary stage. The distance between the electric induction coil imitating the rail profile and the rail surface is 50mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 150mm, the duration is 90s, and the temperature rise rate is 20.0°C / s. When the temperature of the rail joint is 600℃, the auxiliary heating device is used to perform auxiliary heating on the areas on both sides of the fusion line of the rail flash welding joint (including the rail top surface, rail head fillet and rail head side of the rail head) . The temperature difference between the starting temperature of the auxiliary heating device in the auxiliary heating stage and the ending temperature in the ordinary heating stage is 15℃. The length e of the auxiliary heating device along the extension direction of the rail is 30mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the area covered by the single heating device. The duration of auxiliary heating is 30s. When the heating temperature reaches 1100℃, the single heating device and the auxiliary heating device are immediately removed, and the contact heat conduction device imitating the rail profile is used to cool the rail head in the local area of ​​the rail flash welding joint. The length b of the cooling device along the extension direction of the rail is 40mm, the thickness d is 30mm, and the average cooling rate of accelerated cooling is 35℃ / s. When the temperature of the rail joint drops to 400℃, the joint is placed in the air for natural cooling. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 98% compared with the air-cooled joint after welding, and the width of the softening zone on one side of the joint is 3mm, which greatly improves the comprehensive service performance of the softening zone of the rail flash welded joint.

[0041] Example 3 In this embodiment, the mass fraction of the pearlite rail used is 0.80% for the C element, 1.20% for the Si element, 1.10% for the Mn element, 0.12% for the Cr element, 0.05% for the V element, 0.005% for the P and S elements, and 0.001% for the Al element. The flash welding process mainly consists of four stages: electrode clamping, power-on heating, pressurized forging, and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a single electric induction coil imitating the rail profile is used to heat the entire section of the rail flash welding joint in the ordinary stage. The distance between the electric induction coil imitating the rail profile and the surface of the rail is 15mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 100mm, the duration is 80s, and the temperature rise rate is 15.0°C / s. When the temperature of the rail joint is 550℃, the auxiliary heating device is used to perform auxiliary heating on the areas on both sides of the fusion line of the rail flash welding joint (including the rail top surface, rail head fillet and rail head side of the rail head) . The temperature difference between the starting temperature of the auxiliary heating device in the auxiliary heating stage and the ending temperature in the ordinary heating stage is 10℃. The length e of the auxiliary heating device along the extension direction of the rail is 15mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the area covered by the single heating device. The duration of auxiliary heating is 30s. When the heating temperature reaches 1000℃, the single heating device and the auxiliary heating device are immediately removed, and the contact heat conduction device imitating the rail profile is used to cool the rail head in the local area of ​​the rail flash welding joint. The length b of the cooling device along the extension direction of the rail is 30mm, the thickness d is 20mm, and the average cooling rate of accelerated cooling is 30℃ / s. When the temperature of the rail joint drops to 300℃, the joint is placed in the air for natural cooling. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 98% compared with the air-cooled joint after welding, and the width of the softening zone on one side of the joint is 3mm, which greatly improves the comprehensive service performance of the softening zone of the rail flash welded joint.

[0042] Example 4 In this embodiment, the mass fraction of the pearlite rail used is 0.80% for the C element, 1.20% for the Si element, 1.10% for the Mn element, 0.12% for the Cr element, 0.05% for the V element, 0.005% for the P and S elements, and 0.001% for the Al element. The flash welding process mainly consists of four stages: electrode clamping, power-on heating, pressurized upsetting, and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a single electric induction coil imitating the rail profile is used to heat the entire section of the rail flash welding joint in the ordinary stage. The distance between the electric induction coil imitating the rail profile and the surface of the rail is 5mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 60mm, the duration is 80s, and the temperature rise rate is 1.0°C / s. When the temperature of the rail joint is 500℃, the auxiliary heating device is used to perform auxiliary heating on the areas on both sides of the fusion line of the rail flash welding joint (including the rail top surface, rail head fillet and rail head side of the rail head) . The temperature difference between the starting temperature of the auxiliary heating device in the auxiliary heating stage and the ending temperature in the ordinary heating stage is 10℃. The length e of the auxiliary heating device along the extension direction of the rail is 30mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the area covered by the single heating device. The duration of the auxiliary heating is 20s. When the heating temperature reaches 1100℃, the single heating device and the auxiliary heating device are immediately removed, and the contact heat conduction device imitating the rail profile is used to cool the rail head in the local area of ​​the rail flash welding joint. The length b of the cooling device along the extension direction of the rail is 40mm, the thickness d is 30mm, and the average cooling rate of accelerated cooling is 35℃ / s. When the temperature of the rail joint drops to 400℃, the joint is placed in the air for natural cooling. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 99% compared with the air-cooled joint after welding, and the width of the softening zone on one side of the joint is 4mm, which greatly improves the comprehensive service performance of the softening zone of the rail flash welded joint.

[0043] Example 5 In this embodiment, the mass fraction of the pearlite rail used is 0.80% for the C element, 1.20% for the Si element, 1.10% for the Mn element, 0.12% for the Cr element, 0.05% for the V element, 0.005% for the P and S elements, and 0.001% for the Al element. The flash welding process mainly consists of four stages: electrode clamping, power-on heating, pressurized forging, and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a single electric induction coil imitating the rail profile is used to heat the entire section of the rail flash welding joint in the ordinary stage. The distance between the electric induction coil imitating the rail profile and the surface of the rail is 50mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 150mm, the duration is 80s, and the temperature rise rate is 20.0°C / s. When the temperature of the rail joint is 600℃, the auxiliary heating device is used to perform auxiliary heating on the areas on both sides of the fusion line of the rail flash welding joint (including the rail top surface, rail head fillet and rail head side of the rail head) . The temperature difference between the starting temperature of the auxiliary heating device in the auxiliary heating stage and the ending temperature in the ordinary heating stage is 15℃. The length e of the auxiliary heating device along the extension direction of the rail is 30mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the area covered by the single heating device. The duration of auxiliary heating is 30s. When the heating temperature reaches 1100℃, the single heating device and the auxiliary heating device are immediately removed, and the contact heat conduction device imitating the rail profile is used to cool the rail head in the local area of ​​the rail flash welding joint. The length b of the cooling device along the extension direction of the rail is 20mm, the thickness d is 15mm, and the average cooling rate of accelerated cooling is 5℃ / s. When the temperature of the rail joint drops to 200℃, the joint is placed in the air for natural cooling. The average hardness of the softening zone of the rail flash welded joint treated by this method is increased by 99% compared with the air-cooled joint after welding, and the width of the softening zone on one side of the joint is 4mm, which greatly improves the comprehensive service performance of the softening zone of the rail flash welded joint.

[0044] Comparative Example 1 In this comparative example, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% and a Al mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, power heating, pressurized forging and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a single induction coil imitating the rail profile is used to heat the entire section of the rail flash welding joint in the ordinary stage. The distance between the induction coil imitating the rail profile and the surface of the rail is 3mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 50mm, the duration is 120s, and the temperature rise rate is 0.5°C / s. When the temperature of the rail joint is 400℃, the auxiliary heating device is used to perform auxiliary heating on the areas on both sides of the fusion line of the rail flash welding joint (including the rail top surface, rail head fillet and rail head side of the rail head) . The temperature difference between the starting temperature of the auxiliary heating device in the auxiliary heating stage and the ending temperature in the ordinary heating stage is 25℃. The length e of the auxiliary heating device along the extension direction of the rail is 10mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the area covered by the single heating device. The duration of the auxiliary heating is 50s. When the heating temperature reaches 800℃, the single heating device and the auxiliary heating device are immediately removed, and the contact heat conduction device imitating the rail profile is used to cool the rail head in the local area of ​​the rail flash welding joint. The length b of the cooling device along the extension direction of the rail is 10mm, the thickness d is 10mm, and the average cooling rate of accelerated cooling is 4℃ / s. When the temperature of the rail joint drops to 100℃, the joint is placed in the air for natural cooling. The average hardness of the softening zone of the rail flash welded joint treated by this method is only 30% higher than that of the air-cooled joint after welding. The width of the softening zone on one side of the joint is 22mm, and the joint performance cannot meet the use requirements.

[0045] Comparative Example 2 In this comparative example, the pearlite rail used has a C mass fraction of 0.80%, a Si mass fraction of 1.20%, a Mn mass fraction of 1.10%, a Cr mass fraction of 0.12%, a V mass fraction of 0.05%, a P mass fraction of 0.005% and a Al mass fraction of 0.001%. The flash welding process mainly consists of four stages: electrode clamping, power heating, pressurized forging and rapid nodule pushing. The duration of the entire welding process is 130s. After the welding process is completed and the joint is cooled to below 300°C, a single induction coil imitating the rail profile is used to heat the entire section of the rail flash welding joint in the ordinary stage. The distance between the induction coil imitating the rail profile and the rail surface is 55mm, and the heating area covers the entire welding joint area. Its length a along the extension direction of the rail is 155mm, the duration is 110s, and the temperature rise rate is 25.0°C / s. When the temperature of the rail joint is 650℃, the auxiliary heating device is used to perform auxiliary heating on the areas on both sides of the fusion line of the rail flash welding joint (including the rail top surface, rail head fillet and rail head side of the rail head) . The temperature difference between the starting temperature of the auxiliary heating device in the auxiliary heating stage and the ending temperature of the ordinary heating stage is 25℃. The length e of the auxiliary heating device along the extension direction of the rail is 35mm, and the center line of the area covered by the auxiliary heating device coincides with the edge of the area covered by the single heating device. The duration of the auxiliary heating is 50s. When the heating temperature reaches 1200℃, the single heating device and the auxiliary heating device are immediately removed, and the contact heat conduction device imitating the rail profile is used to cool the rail head in the local area of ​​the rail flash welding joint. The length b of the cooling device along the extension direction of the rail is 45mm, the thickness d is 35mm, and the average cooling rate of the accelerated cooling is 40℃ / s. When the temperature of the rail joint drops to 500℃, the joint is placed in the air for natural cooling. The average hardness of the softening zone of the rail flash welded joint treated by this method is only 50% higher than that of the air-cooled joint after welding. The width of the softening zone on one side of the joint is 30mm, and the joint performance cannot meet the use requirements.

[0046] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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.

[0047] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, 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 attached claims.

Claims

1. A method for improving the service performance of the softening zone of a rail flash welded joint, characterized in that: include: The flash welded rail joint cooled to a certain temperature after welding is subjected to secondary heating, and the heating process includes a common heating stage and a special heating stage; in the common heating stage, a single heating device is used to heat the entire section of the flash welded rail joint; in the special heating stage, a single heating device is continued to be used to heat the entire section of the flash welded rail joint, and an auxiliary heating device is used to perform auxiliary heating on the rail heads at both ends of the area covered by the single heating device; After the rail flash weld joint is heated to a preset temperature, the single heating device and the auxiliary heating device are immediately removed, and a cooling device is used to accelerate cooling of the local areas of the rail flash weld joint heated to the preset temperature on both sides of the fusion line.

2. The method according to claim 1, characterized in that: The starting temperature of the entire heating process is less than 300° C., and the ending temperature of the entire heating process is 900° C. to 1100° C.; the preset temperature is the ending temperature of the entire heating process.

3. The method according to claim 2, characterized in that: The starting temperature of the common heating stage is less than 300° C., the ending temperature of the common heating stage is 500° C. to 600° C., and the duration is ≤100s.

4. The method according to claim 3, characterized in that: In the special heating stage, the temperature difference between the starting temperature of the auxiliary heating device and the ending temperature of the ordinary heating stage is ≤20°C, until the ending temperature of the entire heating process is reached and the heating process is terminated.

5. The method according to claim 1, characterized in that: The single heating device adopts an electric induction coil that simulates the profile of a rail. The distance between the electric induction coil that simulates 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; the length of the single heating device along the extension direction of the rail is 60mm to 150mm; in the normal heating stage, the single heating device controls the temperature rise rate of the entire cross-section of the rail flash welding joint to be 1.0℃ / s to 20.0℃ / s.

6. The method according to claim 5, characterized in that: In the special heating stage, the area assisted by the auxiliary heating device is located at both ends of the welding joint area, and is the rail head working area including the rail top surface, the rail head fillet and the rail head side surface.

7. The method according to claim 6, characterized in that: The length of the auxiliary heating device along the extension direction of the rail is 20 mm to 30 mm, the center line of the area covered by the auxiliary heating device coincides with the edge covered by the single heating device, and the duration of the auxiliary heating is less than 40 seconds.

8. The method according to claim 1, characterized in that: 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.

9. The method according to claim 1, characterized in that: The local area cooled by the cooling device includes a transition area between the heated area during the heating process and the unheated joint base material area. When heated to the termination temperature of the entire heating process, the temperature of the local area is 400°C to 600°C.

10. 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.

11. The method according to claim 10, 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.

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