Method for increasing the hardness of the rail head inside a flash welded rail joint and rail

Abstract

This invention discloses a method for improving the internal hardness of the rail head in a flash-welded rail joint, and a rail itself. 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: accelerated cooling of 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 zone of the rail joint, wherein the initial temperature of the accelerated cooling is greater than 700℃, the termination temperature is 430℃-500℃, and the average cooling rate is 5-35℃ / s. This invention can improve the internal hardness of the rail head in a flash-welded rail joint, thereby improving the wear resistance and service life of the rail welded joint.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, specifically to a method for improving the internal hardness of the rail head in a flash welded rail and a rail thereof. 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 improving the internal hardness of a flash welded rail head, thereby solving 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 improving the internal hardness of the 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] Heat treatment of the rails that have undergone flash welding includes: accelerated cooling of 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 zone of the rail joint. The initial temperature of the accelerated cooling is greater than 700°C, the termination temperature is 430°C to 500°C, and the average cooling rate is 5 to 35°C / s.

[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 voltage of the heating phase is 400V, the average current is 200A, and the duration is 150s; the starting temperature of the accelerated cooling is 710℃, the ending temperature is 480℃, and the average cooling rate is 25℃ / s.

[0013] According to one embodiment of the present invention, the voltage of the heating phase is 400V, the average current is 210A, and the duration is 200s; the starting temperature of the accelerated cooling is 770℃, the ending temperature is 490℃, and the average cooling rate is 30℃ / s.

[0014] According to one embodiment of the present invention, the voltage of the heating phase is 340V, the average current is 50A, and the duration is 150s; the termination temperature of the accelerated cooling is 430℃, and the average cooling rate is 5℃ / s.

[0015] According to one embodiment of the present invention, the voltage of the heating phase is 410V, the average current is 300A, and the duration is 300s; the termination temperature of the accelerated cooling is 500℃, and the average cooling rate is 35℃ / 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 improving the internal hardness of the rail head of a flash welded rail head according to an embodiment of the present invention, the internal hardness of the rail head of the flash welded rail head can be improved by improving the relevant parameters of the flash welding process (especially the voltage, current, time, etc. during the electric heating stage) and the relevant parameters of the post-weld heat treatment process, thereby improving the wear resistance and service life of the rail welded head. 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 names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0024] This invention proposes a method for improving the internal hardness of the rail head in a flash welded rail joint, comprising:

[0025] 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;

[0026] Heat treatment of rails that have undergone flash welding includes: using specialized equipment to accelerate cooling of 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. The initial temperature of the accelerated cooling is greater than 700℃, the termination temperature is 430℃~500℃, and the average cooling rate is 5~35℃ / s.

[0027] In embodiments 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 the relevant parameters of the post-weld heat treatment process, the internal hardness of the rail head of the flash welded joint can be increased, thereby improving the wear resistance and service life of the rail welded joint.

[0028] 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's strength and hardness. In addition to the basic functions of heat treatment mentioned above, 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. After rail welding, the microstructure of the joint at the high-temperature stage is austenitic. As the rail joint cools, the austenitic microstructure undergoes transformations at different temperature stages and cooling rates, including austenite to pearlite, martensite, and bainite. Martensite and bainite are harmful structures in pearlitic rails, significantly reducing the joint's service performance and affecting train operation safety. When austenite is cooled at a rate greater than the critical cooling rate of the rail material to below the temperature at which bainite and martensite begin to transform, harmful structures such as martensite or bainite will appear inside the joint. Therefore, it is necessary to control the termination temperature to 430℃~500℃ and the average cooling rate to 5~35℃ / s. Meanwhile, in order to ensure that the hardness of the joint in the core of the rail head is improved, the austenite needs to have a sufficiently high degree of supercooling at a sufficiently high temperature. Therefore, the starting temperature of accelerated cooling is greater than 700℃, and accelerated cooling is carried out on 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.

[0029] The temperature of the rail joint and the rate of cooling / heating directly affect the phase transformation process of the metallic material. This invention defines the synergistic effect of all time, current, voltage, and pressure in the welding process, as well as all heating temperature, cooling / heating rate, and cooling termination temperature in the heat treatment process, to achieve the desired performance of the rail weld joint.

[0030] 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% by mass), Si (0.10%–0.60% by mass), Mn (0.75%–1.25% by mass), P and S (both not exceeding 0.020% by mass), Cr (not exceeding 0.30% by mass), and V (not exceeding 0.01% by mass). 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 improve the internal hardness of the rail head in flash-welded joints to solve this problem.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] This invention also proposes a rail prepared using the method described above. Through this method, 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).

[0036] 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 improve the internal hardness of the rail head of the flash welded joint. This method includes two main processes: welding and post-weld heat treatment. This invention improves the parameters 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.

[0037] The following description is based on specific embodiments and comparative examples.

[0038] Example 1

[0039] In this embodiment, the main chemical composition of the rail material contains 0.78% carbon, 0.50% silicon, and 0.89% manganese. The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) is 1175 MPa to 1210 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is 370 HB to 385 HB. The 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 removal. The entire welding process lasts 180 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous beam explosion formed between the liquid metal at the rail ends. The voltage during the continuous beam explosion is 400V, the average current is 200A, and the duration is 150s. During heating, the opposing pressure applied to both ends of the rails is 100kN, and the rail consumption is 15mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 5s. After welding, specialized equipment is used to accelerate cooling the top surface, sides, and lower jaw of the rail head near the weld joint. The initial cooling temperature for the top surface, sides, and lower jaw of the rail head is approximately 710℃, the average cooling rate during accelerated cooling is 25℃ / s, and the final accelerated cooling temperature is 480℃. Longitudinal section hardness tests were conducted at 5mm and 25mm below the tread surface of the joint according to AS1085.20 standard, and the microstructure of the joint was examined according to BS EN14587. The results show that the high-strength, hardened pearlitic rail flash welded joint formed using this method has an internal hardness near the fusion line zone of the rail head that is 98%–90% higher than that of the rail base material at the same location, and the pearlitic area ratio in the microstructure is ≥98%.

[0040] Example 2

[0041] In this embodiment, the main chemical composition of the rail material contains 0.81% carbon (C), 0.58% silicon (Si), and 0.88% manganese (Mn). The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) is 1259 MPa to 1380 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is 390 HB to 420 HB. The 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 removal. The entire welding process lasts 280 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous bursting of the molten metal between the rail ends. The voltage during this continuous bursting is 400V, the average current is 210A, and the duration is 200s. During heating, the opposing pressure applied to both ends of the rails is 120kN, and the rail consumption is 23mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 8s. After welding, specialized equipment is used to accelerate cooling of the rail head top surface, side surface, and lower jaw near the weld joint. The initial cooling temperature for the rail head top surface, side surface, and lower jaw is approximately 770℃, the average cooling rate during accelerated cooling is 30℃ / s, and the final accelerated cooling temperature is 490℃. Longitudinal section hardness tests were conducted at 5mm and 25mm below the tread surface of the joint according to AS1085.20 standard, and the microstructure of the joint was examined according to BS EN14587. The results show that the high-strength, hardened pearlitic rail flash welded joint formed using this method exhibits a hardness ratio of 98%–100% between the rail head internal hardness near the fusion line and the hardness of the rail base material at the same location, with a pearlitic microstructure area ratio of approximately 99%.

[0042] Example 3

[0043] In this embodiment, the main chemical composition of the rail material contains 0.81% carbon, 0.58% silicon, and 0.88% manganese. The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) is 1259 MPa to 1380 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is 390 HB to 420 HB. The 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 removal. The entire welding process lasts 180 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous beam explosion formed between the liquid metal at the rail ends. The voltage during the continuous beam explosion is 340V, the average current is 50A, and the duration is 150s. During heating, the opposing pressure applied to both ends of the rails is 80kN, and the rail consumption is 10mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 5s. After welding, specialized equipment is used to accelerate cooling of the rail head top surface, side surface, and lower jaw near the weld joint. The initial cooling temperature of the rail head top surface, side surface, and lower jaw is >700℃, the average cooling rate during accelerated cooling is 5℃ / s, and the final accelerated cooling temperature is 430℃. Longitudinal section hardness tests were conducted at 5mm and 25mm below the tread surface of the joint according to AS1085.20 standard, and the microstructure of the joint was examined according to BS EN14587. The results show that the high-strength, hardened pearlitic rail flash welded joint formed using this method exhibits a hardness ratio of 95%–96% between the rail head interior hardness near the fusion line and the hardness of the rail base material at the same location, with a pearlitic microstructure area ratio of approximately 99%.

[0044] Example 4

[0045] In this embodiment, the main chemical composition of the rail material contains 0.78% carbon, 0.50% silicon, and 0.89% manganese. The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) is 1175 MPa to 1210 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is 370 HB to 385 HB. The 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 removal. The entire welding process lasts 350 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous bursting of the molten metal between the rail ends. The voltage during this continuous bursting is 410V, the average current is 300A, and the duration is 300s. The opposing pressure applied to both ends of the rails during heating is 160kN, and the rail consumption is 35mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 10s. After welding, specialized equipment is used to accelerate cooling of the rail head top surface, side surface, and lower jaw near the weld joint. The initial cooling temperature of the rail head top surface, side surface, and lower jaw is >700℃, the average cooling rate during accelerated cooling is 35℃ / s, and the final accelerated cooling temperature is 500℃. Longitudinal section hardness tests were conducted at 5mm and 25mm below the tread surface of the joint according to AS1085.20 standard, and the microstructure of the joint was examined according to BS EN14587. The results show that the high-strength, hardened pearlitic rail flash welded joint formed using this method exhibits a hardness ratio of 100%–110% between the rail head internal hardness near the fusion line and the hardness of the rail base material at the same location, with a pearlitic microstructure area ratio of approximately 99%.

[0046] Comparative Example 1

[0047] The main chemical composition of the rail material used in this comparative example contains 0.78% carbon, 0.50% silicon, and 0.89% manganese. The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) is 1175 MPa–1210 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is 370 HB–385 HB. The 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 push-off. The entire welding process lasts 100 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous bursting of the molten metal between the rail ends. The voltage during this continuous bursting is 320V, the average current is 40A, and the duration is 80s. During heating, the opposing pressure applied to both ends of the rails is 50kN, and the rail consumption is 9mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 10s. After welding, specialized equipment is used to accelerate cooling of the rail head top surface, side surface, and lower jaw near the weld joint. The initial cooling temperature for the rail head top surface, side surface, and lower jaw is approximately 500℃, the average cooling rate during accelerated cooling is 40℃ / s, and the final accelerated cooling temperature is 410℃. The longitudinal section hardness of the joint was tested at 5mm and 25mm below the tread surface according to AS1085.20 standard, and the microstructure of the joint was examined according to BS EN14587. The results show that the high-strength railhead hardened pearlitic rail flash weld joint formed by this method has a hardness ratio of 90% to that of the rail base material in the near fusion line zone, and the pearlite area ratio of the microstructure is ≥90%. A large amount of abnormal martensite structure was detected, which does not meet the usage requirements.

[0048] Comparative Example 2

[0049] The main chemical composition of the rail material used in this comparative example contains 0.81% carbon (C), 0.58% silicon (Si), and 0.88% manganese (Mn). The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) ranges from 1259 MPa to 1380 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head ranges from 390 HB to 420 HB. The 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 push-off. The entire welding process lasts for 400 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous bursting of the molten metal between the rail ends. The voltage during this continuous bursting is 420V, the average current is 310A, and the duration is 350s. The opposing pressure applied to both ends of the rails during heating is 180kN, and the rail consumption is 45mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 11s. After welding, specialized equipment is used to accelerate cooling of the rail head top surface, side surface, and lower jaw near the weld joint. The initial cooling temperature for the rail head top surface, side surface, and lower jaw is 700℃, the average cooling rate during accelerated cooling is 50℃ / s, and the final accelerated cooling temperature is 400℃. Longitudinal section hardness tests were conducted at 5mm and 25mm below the tread surface of the joint according to AS1085.20 standard, and microstructure inspection was performed on the joint according to BS EN14587. The results show that the high-strength railhead-hardened pearlitic rail flash weld joint formed using this method has a railhead internal hardness near the fusion line zone that is 105%–115% higher than the hardness of the rail base material at the same location. The pearlite area ratio in the microstructure is ≥87%, and a large amount of abnormal martensitic structure was detected, which does not meet the usage requirements.

[0050] Comparative Example 3

[0051] The main chemical composition of the rail material used in this comparative example contains 0.81% carbon (C), 0.58% silicon (Si), and 0.88% manganese (Mn). The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) ranges from 1259 MPa to 1380 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head ranges from 390 HB to 420 HB. The 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 removal. The entire welding process lasts for 180 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous beam explosion formed between the liquid metal at the rail ends. The voltage during the continuous beam explosion is 340V, the average current is 50A, and the duration is 150s. During heating, the opposing pressure applied to both ends of the rails is 80kN, and the rail consumption is 10mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 5s. After welding, specialized equipment is used to accelerate cooling of the rail head top surface, side surface, and lower jaw near the weld joint. The initial cooling temperature of the rail head top surface, side surface, and lower jaw is >700℃, the average cooling rate during accelerated cooling is 4℃ / s, and the final accelerated cooling temperature is 580℃. The longitudinal section hardness of the joint was tested at 5mm and 25mm below the tread surface according to AS1085.20 standard, and the microstructure of the joint was examined according to BS EN14587. The results showed that the hardness ratio of the rail head interior near the fusion line zone to the base rail material at the same location was only 78%–85%, indicating severe sag. The pearlite area ratio in the microstructure was ≥99%, which did not meet the usage requirements.

[0052] Comparative Example 4

[0053] The main chemical composition of the rail material used in this comparative example contains 0.78% carbon, 0.50% silicon, and 0.89% manganese. The tensile strength at the gauge angle (12.7 mm from the rail head tread and side) is 1175 MPa–1210 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is 370 HB–385 HB. The 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 push-off. The entire welding process lasts 100 seconds. The welding heating process primarily involves short-circuiting the rails to be welded under energized conditions and utilizing the heat generated by the continuous bursting of the molten metal between the rail ends. The voltage during this continuous bursting is 320V, the average current is 40A, and the duration is 80s. During heating, the opposing pressure applied to both ends of the rails is 50kN, and the rail consumption is 9mm. The rapid push-up stage of the welding process employs an integrated contoured rail push-up mechanism, with the time from the end of upsetting to the complete push-up being 10s. After welding, specialized equipment is used to accelerate cooling of the rail head top surface, side surface, and lower jaw near the weld joint. The initial cooling temperature for the rail head top surface, side surface, and lower jaw is approximately 550℃, the average cooling rate during accelerated cooling is 55℃ / s, and the final accelerated cooling temperature is 400℃. Longitudinal section hardness tests were conducted at 5mm and 25mm below the tread surface of the joint according to AS1085.20 standard, and microstructure examination of the joint was performed according to BS EN14587. The results show that the high-strength, hardened pearlitic rail flash welded joint formed using this method exhibits a hardness ratio of 80%–90% between the rail head interior hardness near the fusion line and the hardness of the rail base material at the same location, indicating significant low collapse. The pearlitic area ratio in the microstructure is ≥97%, failing to meet the usage 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 of improving the hardness of the inside of the rail head of a flash welded rail joint, characterised 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; Heat treatment of the rails that have undergone flash welding includes: accelerated cooling of 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 zone of the rail joint. The initial temperature of the accelerated cooling is greater than 700°C, the termination temperature is 430°C to 500°C, and the average cooling rate is 5 to 35°C / s. The rails to be welded are high-strength railhead hardened pearlitic steel rails, with a tensile strength of at least 1172MPa at the gauge angle and a hardness of greater than or equal to 370HB at a depth of 25mm from the outer surface of the railhead. 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.

2. The method of claim 1, wherein, 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 of claim 1, wherein, 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 of claim 1, wherein, The voltage of the heating phase is 400V, the average current is 200A, and the duration is 150s; the starting temperature of the accelerated cooling is 710℃, the ending temperature is 480℃, and the average cooling rate is 25℃ / s.

5. The method of claim 1, wherein, The voltage of the heating phase is 400V, the average current is 210A, and the duration is 200s; the starting temperature of the accelerated cooling is 770℃, the ending temperature is 490℃, and the average cooling rate is 30℃ / s.

6. The method of claim 1, wherein, The voltage of the heating phase is 340V, the average current is 50A, and the duration is 150s; the termination temperature of the accelerated cooling phase is 430℃, and the average cooling rate is 5℃ / s.

7. The method of claim 1, wherein, The voltage during the heating phase is 410V, the average current is 300A, and the duration is 300s; the termination temperature of the accelerated cooling phase is 500℃, and the average cooling rate is 35℃ / s.

8. The method of claim 1, wherein, The main chemical components of steel rails contain carbon (C) at a mass fraction of 0.74%–0.86%, silicon (Si) at a mass fraction of 0.10%–0.60%, manganese (Mn) at a mass fraction of 0.75%–1.25%, phosphorus (P) and sulfur (S) at a mass fraction of no more than 0.020%, chromium (Cr) at a mass fraction of no more than 0.30%, and v at a mass fraction of no more than 0.01%.

9. A rail produced by the method according to any one of claims 1 to 8, 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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