Method for prolonging the service life of rail head of flash welded rail joint and rail

Abstract

This invention discloses a method and a rail for extending the service life of a flash-welded rail head. The method includes: flash welding the rail, comprising sequentially performing an electric heating stage and a pressure upsetting stage; wherein the voltage of the electric heating stage is 340-410V, the average current is 50-300A, and the duration is 150-300s; and heat treatment of the flash-welded rail, comprising sequentially performing a first cooling stage, a heating stage, a heat preservation stage, and a second cooling stage, wherein the termination temperature of the first cooling stage is 25-100℃, the termination temperature of the heating stage is 800-1100℃, the temperature range maintained in the heat preservation stage is 800-950℃, and the starting temperature of the second cooling stage is greater than or equal to 800℃ and the termination temperature is 420-480℃. This invention can improve the internal hardness of the flash-welded rail head, thereby improving the wear resistance and service life of the rail welded head.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, specifically to a method for extending the service life of a rail head in a flash welded rail and a rail. Background Technology

[0002] As the most important structural component of railway lines, rails face high axle loads and frequent service environments, placing higher demands on their performance. This is primarily reflected in their wear resistance and fatigue resistance. Studies show that, without considering wheel-rail matching, abrasive media, and other factors, higher hardness generally corresponds to better wear resistance. Therefore, hardness is typically used as one of the main indicators for evaluating a material's wear resistance. The methods for characterizing the hardness of the rail base material are mainly tread hardness and cross-sectional hardness, while the methods for characterizing rail joints are mainly tread hardness and longitudinal section hardness.

[0003] Currently, the mainstream welding method for rails is flash welding. Flash welding utilizes the resistance of the electric current passing through the small contact points on the rail end contact surface and the heat generated by the electric arc to heat the rail end to be welded. After an appropriate time, pressure is applied to the joint, causing the entire area of ​​the rail mating surfaces to be firmly bonded simultaneously. This resistance welding method boasts a high degree of automation and stable welding quality, making it the primary method for on-site welding of seamless railway tracks both domestically and internationally. Based on its production method, it is mainly divided into two types: fixed flash welding and mobile flash welding. Fixed flash welding typically involves fixing the welding equipment inside a factory building, hence it is also commonly referred to as factory welding or base welding. Fixed flash welding usually involves directly short-circuiting the rail and heating it using resistance heat; the heating process does not (or minimally) involve flashing. Currently, the most widely used mobile flash welding machines domestically and internationally are the K950 and YGH-1200TH models. The K950 mobile flash welding machine ensures high quality and long service life of the welding head.

[0004] Improving the hardness of the flash weld joints of rails to enhance their wear resistance and fatigue performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The main objective of this invention is to provide a method and a rail for extending the service life of a flash welded rail head, in order to solve the technical problem of how to improve the hardness of a flash welded rail head.

[0006] According to one aspect of the present invention, a method for extending the service life of a rail head in a flash welded rail joint is provided, comprising:

[0007] Flash welding of the rails includes: sequentially performing an electric heating stage and a pressure upsetting stage; wherein, the voltage of the electric heating stage is 340-410V, the average current is 50-300A, and the duration is 150-300s;

[0008] The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a heat preservation stage, and a second cooling stage in sequence. The termination temperature of the first cooling stage is 25-100°C, the termination temperature of the heating stage is 800-1100°C, the temperature range maintained during the heat preservation stage is 800-950°C, and the starting temperature of the second cooling stage is greater than or equal to 800°C and the termination temperature is 420-480°C.

[0009] According to one embodiment of the present invention, during the electric heating stage, the opposing pressure applied to both ends of the rail to be welded is 80-160 kN, and the rail consumption is 10-35 mm.

[0010] According to one embodiment of the present invention, the flash welding of the rail further includes: performing a slug pushing stage after the pressure upsetting stage, and the time from the end of the pressure upsetting stage to the complete end of the slug pushing stage is 5 to 10 seconds.

[0011] According to one embodiment of the present invention, during the entire flash welding process, the temperature in the area between the two steel rails and the end face to be welded is 900-1650°C for a duration of 180-350 seconds.

[0012] According to one embodiment of the present invention, the average cooling rate of the first cooling stage is 5 to 10 °C / s.

[0013] According to one embodiment of the present invention, during the heating stage, the top surface of the rail head, the side surface of the rail head, and the lower jaw of the rail head in the weld zone of the rail joint are heated, with an average temperature rise rate of 2 to 30°C / s.

[0014] According to one embodiment of the present invention, during the heat preservation stage, the top surface of the rail head and the lower jaw of the rail head near the weld joint are heat-preserved for 50 to 200 seconds.

[0015] According to one embodiment of the present invention, in the second cooling stage, the top surface and side surface of the rail head are accelerated cooled, with the average cooling rate of the top surface of the rail head being 30-40°C / s and the average cooling rate of the side surface of the rail head being 15-25°C / s.

[0016] According to one embodiment of the present invention, the rail to be welded is a high-strength head-hardened pearlitic steel rail. The main chemical composition of the rail has the following mass fractions: C is 0.74% to 0.86%, Si is 0.10% to 0.60%, Mn is 0.75% to 1.25%, P and S are both less than 0.020%, Cr is less than 0.30%, and V is less than 0.01%. The rail has a tensile strength of at least 1172 MPa at the gauge angle and a hardness of greater than or equal to 370 HB at a depth of 25 mm from the outer surface of the rail head.

[0017] According to another aspect of the present invention, a rail prepared by the method described above is provided, wherein the hardness of the rail head interior region near the weld zone is 95% to 110% of the hardness of the rail head interior region of the rail base material, and the area ratio of pearlite in the microstructure of the rail head interior region near the weld zone is greater than or equal to 97%, wherein the rail head interior region is a region with a depth of 0 to 25 mm from the rail head surface.

[0018] In the method for extending the service life of a rail head in a flash welded joint according to an embodiment of the present invention, by improving the relevant parameters of the flash welding process (especially the voltage, current, time, etc. during the electric heating stage) and by implementing refined staged control and designing reasonable parameters for the post-weld heat treatment process, the internal hardness of the rail head in the flash welded joint can be improved, thereby enhancing the wear resistance and service life of the rail welded joint. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram showing the internal region of the rail head near the weld zone according to an embodiment of the present invention;

[0021] Figure 2 Another schematic diagram of the rail head interior region near the weld zone according to an embodiment of the present invention is shown. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0023] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different identities. Therefore, "first" is used to indicate that...

[0024] The term "second" is used for convenience only and should not be construed as a limitation on the embodiments of the present invention. Subsequent embodiments will not elaborate on this point.

[0025] This invention proposes a method for extending the service life of rail heads in flash welded rail joints, characterized by comprising:

[0026] Flash welding of the rails includes: sequentially performing an electric heating stage and a pressure upsetting stage; wherein, the voltage of the electric heating stage is 340-410V, the average current is 50-300A, and the duration is 150-300s;

[0027] The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a heat preservation stage, and a second cooling stage in sequence. The termination temperature of the first cooling stage is 25-100°C, the termination temperature of the heating stage is 800-1100°C, the temperature range maintained during the heat preservation stage is 800-950°C, and the starting temperature of the second cooling stage is greater than or equal to 800°C and the termination temperature is 420-480°C.

[0028] In embodiments of the present invention, by improving relevant parameters of the flash welding process (especially parameters such as voltage, current, and time during the electric heating stage) and by implementing refined, phased control of the post-weld heat treatment process and designing reasonable parameters, the internal hardness of the rail head of the flash welded joint can be improved, thereby enhancing the wear resistance and service life of the rail welded joint.

[0029] In some embodiments, the rail to be welded is a high-strength head-hardened pearlitic steel rail. The main chemical composition of the rail contains C (0.74%–0.86%), Si (0.10%–0.60%), Mn (0.75%–1.25%), P and S (both not exceeding 0.020%), Cr (not exceeding 0.30%), and V (not exceeding 0.01%). The tensile strength at a gauge angle of 12.7 mm from both the rail head tread and side is at least 1172 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is greater than or equal to 370 HB. Existing high-strength head-hardened pearlitic steel rail flash welded joints have low wear resistance and short service life. This invention provides a method to extend the service life of the rail head of a flash welded rail joint to solve this problem.

[0030] In an embodiment of the present invention, by setting the voltage, current and time values ​​as described above, the steel rail to be welded is heated mainly by short-circuiting the rail under power-on conditions and utilizing the heat generated by the continuous beam explosion formed between the liquid metals on the end face of the steel rail.

[0031] In some embodiments, during the energizing heating stage, the opposing pressure applied to both ends of the rail to be welded is 80–160 kN, and the rail consumption is 10–35 mm. This maintains the continuous and stable operation of the blasting of the lintel.

[0032] In some embodiments, the flash welding of the rail further includes a spur removal stage after the upsetting stage. Spur removal improves the weld surface appearance and weld quality. An integrated profile rail spur removal mechanism can be used. In some embodiments, the time from the end of the upsetting stage to the complete end of the spur removal stage is 5–10 seconds, thereby ensuring joint quality and the effectiveness of subsequent post-weld heat treatment.

[0033] In some embodiments, the flash welding process mainly includes four stages: electrode clamping, electric heating, pressure upsetting, and rapid spheroid pushing. During the entire flash welding process, the temperature in the area between the two steel rails and the end face to be welded is 900-1650℃, and the duration is 180-350s.

[0034] In embodiments of the present invention, the post-weld heat treatment process mainly includes four stages: a first cooling stage, a heating stage, a holding stage, and a second cooling stage. The next stage begins after the previous stage is completed. The starting temperature, ending temperature, and / or holding temperature of each stage are defined above.

[0035] In some embodiments, the average cooling rate of the first cooling stage is 5 to 10 °C / s.

[0036] In some embodiments, during the heating stage, specialized equipment can be used to heat the top surface of the rail head, the side surface of the rail head, and the lower jaw of the rail head in the weld zone of the rail joint, with an average temperature rise rate of 2 to 30°C / s.

[0037] In some embodiments, during the heat preservation stage, specialized equipment can be used to heat the top surface of the rail head near the weld zone and the lower jaw of the rail head, with a heat preservation time of 50 to 200 seconds.

[0038] In some embodiments, during the second cooling stage, specialized equipment can be used to accelerate the cooling of the top and side surfaces of the rail head, with an average cooling rate of 30–40 °C / s for the top surface and 15–25 °C / s for the side surfaces.

[0039] The main function of heat treatment is to eliminate internal stress in the welded joint, refine austenite grains, homogenize the microstructure, and improve the joint strength and hardness. In addition to the basic functions of heat treatment, the heat treatment method used in this invention can also improve the internal hardness of the rail head of the flash welded joint of a deeply hardened rail. The starting temperature of the first cooling stage of the heat treatment process is the temperature at the end of the welding process. Because the thickness of different regions across the entire rail cross-section is different, the cooling rates of different regions under natural cooling conditions are also different. To prevent martensitic and bainitic phase transformations from occurring during the first cooling stage, the cooling rate of the first cooling stage needs to be controlled at 5–10 °C / s; the cooling termination temperature of the first cooling stage needs to be controlled at 25–100 °C to ensure that the surface and core of the rail joint are completely transformed into pearlite. The main function of the heating stage is to allow the joint regions that have undergone complete pearlitic phase transformation at 25–100 °C to re-transform into austenite. To ensure uniform temperature between the inside and outside of the joint and across all regions of the cross-section, the temperature rise rate of the heating stage needs to be controlled at 2–30 °C / s. After heating to the expected temperature, the joint is insulated to further ensure uniform temperature across the entire rail section. Excessive insulation temperature or time will widen the heat-affected zone of the joint; insufficient insulation temperature or time will fail to achieve uniform heating. Therefore, the insulation time for the rail head top surface, side surface, and lower jaw near the weld joint is 50–200 seconds, with a temperature range of 800–950℃. The second cooling stage aims to rapidly cool the rail head tread area, increasing the supercooling and enhancing the phase transformation driving force of austenite to a lower-temperature microstructure. This ensures that all supercooled austenite transforms into pearlite, refining the austenite grains and pearlite lamellar spacing. Therefore, the starting temperature of the second cooling stage must be greater than or equal to 800℃, and the ending temperature must be 420–480℃. To refine the microstructure and increase the hardness of the core layer of the rail head, which is farther from the tread surface, it is necessary to simultaneously enhance the cooling intensity of the rail head sides and the lower jaw. To supplement the cooling of the rail head sides and lower jaw, the air cooling intensity of the rail head top surface can be appropriately reduced to avoid harmful phase transformation processes such as martensite and bainite formation. Therefore, accelerated cooling is applied to the rail head top surface and sides, with an average cooling rate of 30–40°C / s for the rail head top surface and 15–25°C / s for the rail head sides.

[0040] The temperature of the rail joint and the rate of cooling / heating directly affect the phase transformation process of the metallic material. The present invention defines a process in which all heating temperatures, cooling / heating rates, and cooling termination temperatures work synergistically to achieve the heat treatment effect described above.

[0041] This invention also proposes a rail prepared using the method described above, wherein the hardness of the rail head interior region near the weld zone is 95% to 110% of the hardness of the rail head interior region of the rail base material, and the pearlite area ratio in the microstructure of the rail head interior region near the weld zone is greater than or equal to 97%. (Reference) Figure 1 and Figure 2 The near-weld zone (also called the near-fusion line zone) can be the heat-affected zone 1 to 10 mm away from both sides of the fusion line; the internal area of ​​the rail head can be the area 0 to 25 mm away from the surface of the rail head (which may include: the top surface of the rail head, the gauge angle, both sides of the rail head, and the area at the lower jaw of the rail head with a depth of 0 to 25 mm from the outer surface of the rail head).

[0042] In summary, this invention mainly addresses the technical problems of reduced wear resistance and short service life of flash welded joints of high-strength hardened pearlitic steel rails. It provides a method to extend the service life of the rail head of a flash welded joint. This method includes two main processes: welding and post-weld heat treatment. This invention improves the parameters and steps of these two main processes, which can significantly increase the hardness of the flash welded joint of high-strength hardened pearlitic steel rails, thereby improving wear resistance and service life.

[0043] The following description is based on specific embodiments and comparative examples.

[0044] Example 1

[0045] In this embodiment, the main chemical composition of the test rails contained C at a mass fraction of 0.74%, Si at 0.60%, Mn at 0.75%, P and S at no more than 0.020%, Cr at no more than 0.30%, and V at no more than 0.01%. The minimum tensile strength at a gauge angle of 12.7 mm from both the rail head tread and side surface was 1200 MPa, and the minimum hardness at a depth of 25 mm from the outer surface of the rail head was 375 HB. The welding process included two main steps: welding and post-weld heat treatment. The welding method was flash welding, which consisted of four stages: electrode clamping, electric heating, pressure upsetting, and rapid sulphur pushing. Throughout the welding process, the temperature of the rails on both sides, from 0 mm to 25 mm from the end face to be welded, ranged from 900℃ to 1650℃ for 200 seconds. During the heating phase of the welding process, the rails to be welded are short-circuited under energized conditions, and the heat generated by the continuous bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the continuous bursting is 380V, the average current is 80A, and the duration is 150s. During the continuous bursting of the heating phase, the opposing pressure applied to both ends of the rails to be welded is 100kN, and the rail consumption is 25mm. The rapid push-up phase of the welding process uses an integrated contoured rail push-up mechanism. To ensure the joint quality and the effect of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 7s. After welding, post-weld heat treatment is performed, which mainly includes four stages: first-stage cooling, heating, holding, and second-stage cooling. The next stage begins after the previous stage is completed. The average cooling rate of the first cooling stage in the post-weld heat treatment process is 8℃ / s, and the cooling termination temperature is 80℃. In the heating stage, specialized equipment is used to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during heating is 10℃ / s, and the heating termination temperature is 1000℃. In the heat preservation stage, specialized equipment is used to preserve the top surface and lower jaw of the rail head near the weld joint, maintaining a temperature of 900℃ for 100s. In the second cooling stage, specialized equipment is used to accelerate the cooling of the top surface of the rail head. The accelerated cooling start temperature is 900℃, the average cooling rate of the top surface is 35℃ / s, the average cooling rate of the sides is 15℃ / s, and the accelerated cooling termination temperature is 460℃. The longitudinal section hardness test was performed at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was examined in accordance with BS EN14587.The results show that the high-strength rail head hardened pearlitic rail flash weld joint formed by this method has a rail head internal hardness ratio of 98% to that of the rail base material at the same location in the near fusion line area, and the area ratio of pearlitic microstructure is ≥97%.

[0046] Example 2

[0047] In this embodiment, the main chemical composition of the test rails contains 0.86% C, 0.10% Si, 1.25% Mn, and no more than 0.020% P and S, no more than 0.30% Cr, and no more than 0.01% V. The minimum tensile strength at a gauge angle of 12.7 mm from both the rail head tread and side is 1300 MPa, and the minimum hardness at a depth of 25 mm from the outer surface of the rail head is 385 HB. The welding process includes two main steps: welding and post-weld heat treatment. The welding method is flash welding, which mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid sulphur pushing. Throughout the welding process, the temperature of the rails on both sides, 0 mm to 25 mm from the end face to be welded, ranges from 900℃ to 1650℃ for 180 seconds. During the heating phase of the welding process, the rails to be welded are short-circuited under energized conditions, and the heat generated by the continuous beam explosion formed between the liquid metal at the rail ends is used to heat the rails. The voltage during the continuous beam explosion is 340V, the average current is 50A, and the duration is 150s. During the continuous beam explosion in the heating phase, the opposing pressure applied to both ends of the rails to be welded is 160kN, and the rail consumption is 10mm. The rapid push-up phase of the welding process uses an integrated contoured rail push-up mechanism. To ensure the joint quality and the effect of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 5s to 10s. After welding, post-weld heat treatment is performed, which mainly includes four stages: first-stage cooling, heating, holding, and second-stage cooling. The next stage begins after the previous stage is completed. The average cooling rate of the first cooling stage in the post-weld heat treatment process is 5℃ / s, and the cooling termination temperature is 25℃. In the heating stage, specialized equipment is used to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during heating is 2℃ / s, and the heating termination temperature is 800℃. In the heat preservation stage, specialized equipment is used to preserve the top surface and lower jaw of the rail head near the weld joint at a temperature of 800℃ for 50 seconds. In the second cooling stage, specialized equipment is used to accelerate the cooling of the top surface of the rail head. The initial accelerated cooling temperature is 800℃, the average cooling rate of the top surface is 30℃ / s, the average cooling rate of the sides is 15℃ / s, and the accelerated cooling termination temperature is 480℃. The longitudinal section hardness test was performed at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was examined in accordance with BS EN14587.The results show that the high-strength rail head hardened pearlitic rail flash weld joint formed by this method has a rail head internal hardness ratio of 98% to that of the rail base material at the same location in the near fusion line area, and the area ratio of pearlitic microstructure is ≥98%.

[0048] Example 3

[0049] In this embodiment, the main chemical composition of the test rails contained C at a mass fraction of 0.76%, Si at 0.55%, Mn at 1.05%, P and S at no more than 0.020%, Cr at no more than 0.30%, and V at no more than 0.01%. The minimum tensile strength at a gauge angle of 12.7 mm from both the rail head tread and side surface was 1250 MPa, and the minimum hardness at a depth of 25 mm from the outer surface of the rail head was 390 HB. The welding process included two main steps: welding and post-weld heat treatment. The welding method was flash welding, which consisted of four stages: electrode clamping, electric heating, pressure upsetting, and rapid sulphur pushing. Throughout the welding process, the temperature of the rails on both sides, from 0 mm to 25 mm from the end face to be welded, ranged from 900℃ to 1650℃ for 250 seconds. During the heating phase of the welding process, the rails to be welded are short-circuited under energized conditions, and the heat generated by the continuous bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the continuous bursting is 380V, the average current is 200A, and the duration is 210s. During the continuous bursting of the heating phase, the opposing pressure applied to both ends of the rails to be welded is 100kN, and the rail consumption is 25mm. The rapid push-up phase of the welding process uses an integrated contoured rail push-up mechanism. To ensure the joint quality and the effect of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 10s. After welding, post-weld heat treatment is performed, which mainly includes four stages: first-stage cooling, heating, holding, and second-stage cooling. The next stage begins after the previous stage is completed. The average cooling rate of the first cooling stage in the post-weld heat treatment process is 10℃ / s, and the cooling termination temperature is 80℃. In the heating stage, specialized equipment is used to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during heating is 25℃ / s, and the heating termination temperature is 950℃. In the heat preservation stage, specialized equipment is used to preserve the top surface and lower jaw of the rail head near the weld joint at a temperature of 950℃ for 120 seconds. In the second cooling stage, specialized equipment is used to accelerate the cooling of the top surface of the rail head. The accelerated cooling starting temperature is 950℃, the average cooling rate of the top surface is 35℃ / s, the average cooling rate of the sides is 20℃ / s, and the accelerated cooling termination temperature is 460℃. The longitudinal section hardness test was performed at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was examined in accordance with BS EN14587.The results show that the high-strength rail head hardened pearlitic rail flash weld joint formed by this method has a rail head internal hardness ratio of 99% to that of the rail base material at the same location in the near fusion line area, and the area ratio of pearlitic microstructure is ≥98%.

[0050] Comparative Example 1

[0051] The main chemical composition of the test rails used in this comparative example includes C at a mass fraction of 0.74%, Si at 0.60%, Mn at 0.75%, P and S at no more than 0.020%, Cr at no more than 0.30%, and V at no more than 0.01%. The minimum tensile strength at a gauge angle of 12.7 mm from both the rail head tread and side surface is 1200 MPa, and the minimum hardness at a depth of 25 mm from the outer surface of the rail head is 375 HB. The welding process includes two main steps: welding and post-weld heat treatment. The welding method is flash welding, and the welding process mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid sulphur pushing. Throughout the welding process, the temperature of the rails on both sides, from 0 mm to 25 mm from the end face to be welded, ranges from 900℃ to 1650℃ for a duration of 400 seconds. During the heating phase of the welding process, the rails to be welded are short-circuited under energized conditions, and the heat generated by the continuous beam explosion formed between the liquid metal at the rail ends is used to heat the rails. The voltage during the continuous beam explosion is 410V, the average current is 350A, and the duration is 350s. During the continuous beam explosion in the heating phase, the opposing pressure applied to both ends of the rails to be welded is 180kN, and the rail consumption is 38mm. The rapid push-up phase of the welding process uses an integrated contoured rail push-up mechanism. To ensure the joint quality and the effect of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 8s. After welding, post-weld heat treatment is performed, which mainly includes four stages: first-stage cooling, heating, holding, and second-stage cooling. The next stage begins after the previous stage is completed. The average cooling rate of the first cooling stage in the post-weld heat treatment process is 10℃ / s, and the cooling termination temperature is 100℃. In the heating stage, specialized equipment is used to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during heating is 1℃ / s, and the heating termination temperature is 1200℃. In the heat preservation stage, specialized equipment is used to preserve the top surface and lower jaw of the rail head near the weld joint, maintaining a temperature range of 900℃ for 300s. In the second cooling stage, specialized equipment is used to accelerate the cooling of the top surface of the rail head. The accelerated cooling starting temperature is 900℃, the average cooling rate of the top surface is 20℃ / s, the average cooling rate of the sides is 10℃ / s, and the accelerated cooling termination temperature is 500℃. The longitudinal section hardness test was performed at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was examined in accordance with BS EN14587.The results show that the high-strength rail head hardened pearlitic rail flash weld joint formed by this method has a hardness ratio of 80% between the rail head interior hardness near the fusion line and the rail base material hardness at the same location, and a pearlitic microstructure area ratio of ≥97%. The joint exhibits severe collapse and does not meet the requirements.

[0052] Comparative Example 2

[0053] The main chemical composition of the test rails used in this comparative example includes C (0.86%), Si (0.10%), Mn (1.25%), P and S (both not exceeding 0.020%), Cr (not exceeding 0.30%), and V (not exceeding 0.01%). The minimum tensile strength at a gauge angle of 12.7 mm from both the rail head tread and side surface is 1300 MPa, and the minimum hardness at a depth of 25 mm from the outer surface of the rail head is 385 HB. The welding process includes two main steps: welding and post-weld heat treatment. The welding method is flash welding, which mainly consists of four stages: electrode clamping, electric heating, pressure upsetting, and rapid sulphur pushing. Throughout the welding process, the temperature of the rails on both sides, from 0 mm to 25 mm from the end face to be welded, ranges from 900℃ to 1650℃ for 150 seconds. During the heating phase of the welding process, the rails to be welded are short-circuited under energized conditions, and the heat generated by the continuous bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the continuous bursting is 380V, the average current is 200A, and the duration is 100s. During the continuous bursting of the heating phase, the opposing pressure applied to both ends of the rails to be welded is 70kN, and the rail consumption is 9mm. The rapid push-up phase of the welding process uses an integrated contoured rail push-up mechanism. To ensure the joint quality and the effect of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 8s. After welding, post-weld heat treatment is performed, which mainly includes four stages: first-stage cooling, heating, holding, and second-stage cooling. The next stage begins after the previous stage is completed. The average cooling rate of the first cooling stage in the post-weld heat treatment process is 12℃ / s, and the cooling termination temperature is 20℃. In the heating stage, specialized equipment is used to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during heating is 10℃ / s, and the heating termination temperature is 900℃. In the heat preservation stage, specialized equipment is used to preserve the top surface and lower jaw of the rail head near the weld joint, maintaining a temperature range of 900℃ for 40 seconds. In the second cooling stage, specialized equipment is used to accelerate the cooling of the top surface of the rail head. The accelerated cooling starting temperature is 900℃, the average cooling rate of the top surface is 45℃ / s, the average cooling rate of the sides is 30℃ / s, and the accelerated cooling termination temperature is 400℃. The longitudinal section hardness test was performed at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was examined in accordance with BS EN14587.The results show that the high-strength rail head hardened pearlitic rail flash weld joint formed by this method has a hardness ratio of 1.20% between the rail head interior hardness near the fusion line and the rail base material hardness at the same location, a pearlitic microstructure area ratio of ≥87%, and a large amount of martensite structure in the joint, which does not meet the requirements.

[0054] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for extending the service life of a rail head in a flash welded joint, characterized in that, include: Flash welding of the rails includes: sequentially performing an electric heating stage and a pressure upsetting stage; wherein, the voltage of the electric heating stage is 340-410V, the average current is 50-300A, and the duration is 150-300s; The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a heat preservation stage, and a second cooling stage in sequence. The termination temperature of the first cooling stage is 25-100°C, the termination temperature of the heating stage is 800-1100°C, the temperature range maintained during the heat preservation stage is 800-950°C, and the starting temperature of the second cooling stage is greater than or equal to 800°C and the termination temperature is 420-480°C. During the heat preservation stage, the top surface of the rail head and the lower jaw of the rail head near the weld joint are heat-preserved for 50 to 200 seconds. In the second cooling stage, the top surface and sides of the rail head are accelerated for cooling. The average cooling rate of the top surface of the rail head is 30-40℃ / s, and the average cooling rate of the sides of the rail head is 15-25℃ / s.

2. The method according to claim 1, characterized in that, During the heating phase, the opposing pressure applied to both ends of the rail to be welded is 80-160 kN, and the rail consumption is 10-35 mm.

3. The method according to claim 1, characterized in that, The flash welding of the rails further includes: a push-off stage after the upsetting stage, and the time from the end of the upsetting stage to the complete end of the push-off stage is 5 to 10 seconds.

4. The method according to claim 1, characterized in that, During the entire flash welding process, the temperature in the area 0-25mm away from the end face to be welded on both sides of the rails is 900-1650℃, and the duration is 180-350s.

5. The method according to claim 1, characterized in that, The average cooling rate of the first cooling stage is 5-10℃ / s.

6. The method according to claim 1, characterized in that, During the heating stage, the top surface of the rail head, the side surface of the rail head, and the lower jaw of the rail head near the weld joint are heated, with an average temperature rise rate of 2 to 30°C / s.

7. The method according to claim 1, characterized in that, The rails to be welded are high-strength head-hardened pearlitic steel rails. The main chemical composition of the rails includes C (0.74%–0.86%), Si (0.10%–0.60%), Mn (0.75%–1.25%), P and S (both not exceeding 0.020%), Cr (not exceeding 0.30%), and V (not exceeding 0.01%). The tensile strength at the gauge angle of the rails is at least 1172 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is greater than or equal to 370 HB.

8. A rail prepared using the method described in any one of claims 1-7, characterized in that, The hardness of the rail head interior region near the weld seam is 95% to 110% of the hardness of the rail head interior region of the rail base material. The area ratio of pearlite in the microstructure of the rail head interior region near the weld seam is greater than or equal to 97%. The rail head interior region is the region with a depth of 0 to 25 mm from the rail head surface.

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