Method for improving rail head wear resistance of rail welded joint and rail

Abstract

The application discloses a method for improving the wear resistance of a rail head of a rail welded joint and a rail, and the method comprises the following steps: flash welding the rail, including: sequentially performing an electric heating stage and a press forging stage; wherein the voltage of the electric heating stage is 90%-100% of the total input voltage, the current is 40-80 kA, the number of short-circuit contacts is 6-14, the duration of each time is 4-6 s, and the interval is 0.5-2 s; and heat treating the rail after the flash welding, including: sequentially performing a first cooling stage, a heating stage, a holding stage, a second cooling stage and a third cooling stage; wherein the end temperature of the first cooling stage is 25-100 DEG C, the end temperature of the heating stage is 800-1100 DEG C, the temperature interval of the holding stage is 800-900 DEG C, the start temperature of the second cooling stage is greater than 900 DEG C and the end temperature is 600-700 DEG C, and the start temperature of the third cooling stage is 600-700 DEG C and the end temperature is 430-500 DEG C. The application can improve the wear resistance 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 wear resistance of the rail head in rail welding 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 pressing technical problem that 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 wear resistance of welded rail heads, thereby solving the technical problem of how to improve the hardness of flash welded rail heads.

[0006] According to one aspect of the present invention, a method for improving the wear resistance of the rail head of a welded rail joint is provided, comprising:

[0007] Flash welding of rails includes: sequentially performing an electric heating stage and a pressure upsetting stage; wherein, the voltage of the electric heating stage is 90% to 100% of the total input voltage, the current is 40 to 80 kA, the number of short-circuit contacts is 6 to 14, the duration of each contact is 4 to 6 seconds, and the interval is 0.5 to 2 seconds.

[0008] The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a holding stage, a second cooling stage, and a third cooling stage in sequence. The end temperature of the first cooling stage is 25-100℃, the end temperature of the heating stage is 800-1100℃, the temperature range of the holding stage is 800-900℃, the starting temperature of the second cooling stage is greater than 900℃ and the end temperature is 600-700℃, and the starting temperature of the third cooling stage is 600-700℃ and the end temperature is 430-500℃.

[0009] According to one embodiment of the present invention, during the energizing heating stage, the opposing pressure applied to both ends of the rail to be welded is 300-500 kN.

[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 10 to 20 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 50-250 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 near the weld zone of the rail joint are heated at an average heating rate of 2 to 30°C / s; and / or during the heat preservation 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 zone of the rail joint are heat preserved for a duration of 50 to 200s.

[0014] According to one embodiment of the present invention, in the second cooling stage, the top surface of the rail head is accelerated to cool, with an average cooling rate of 25-40°C / s.

[0015] According to one embodiment of the present invention, in the third cooling stage: the top surface of the rail head, the side surface of the rail head, and the lower jaw of the rail head are acceleratedly cooled, with the average cooling rate of the top surface of the rail head being 20-35°C / s and the average cooling rate of the side surface of the rail head and the lower jaw of the rail head being 5-15°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 improving the wear resistance of rail head welded joints according to embodiments of the present invention, by improving the relevant parameters of the flash welding process (especially the voltage, current, number of short-circuit contacts, duration, interval, etc. during the electric heating stage) and by finely controlling the post-weld heat treatment process in stages 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. 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 wear resistance of rail heads in rail welded joints, comprising:

[0025] Flash welding of rails includes: sequentially performing an electric heating stage and a pressure upsetting stage; wherein, the voltage of the electric heating stage is 90% to 100% of the total input voltage, the current is 40 to 80 kA, the number of short-circuit contacts is 6 to 14, the duration of each contact is 4 to 6 seconds, and the interval is 0.5 to 2 seconds.

[0026] The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a holding stage, a second cooling stage, and a third cooling stage in sequence. The end temperature of the first cooling stage is 25-100℃, the end temperature of the heating stage is 800-1100℃, the temperature range of the holding stage is 800-900℃, the starting temperature of the second cooling stage is greater than 900℃ and the end temperature is 600-700℃, and the starting temperature of the third cooling stage is 600-700℃ and the end temperature is 430-500℃.

[0027] In embodiments of the present invention, by improving relevant parameters of the flash welding process (especially parameters such as voltage, current, number of short-circuit contacts, duration, and interval 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.

[0028] 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 improve the wear resistance of the rail head of the welded rail joint to solve this problem.

[0029] In embodiments of the present invention, by setting the voltage, current, number of short-circuit contacts, duration, and interval value as described above, the steel rail is heated mainly by resistance heat generated when the steel rail to be welded is intermittently short-circuited during the energized heating phase.

[0030] In some embodiments, during the energizing heating phase, a counter-pressure of 300–500 kN is applied to both ends of the rail to be welded. This ensures good contact between the two ends of the rail to be welded.

[0031] 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. A split-type profile rail spur removal mechanism (comprising four parts corresponding to the rail head, left and right rail webs, and rail base) can be used for spur removal. In some embodiments, the time from the end of the upsetting stage to the complete end of the spur removal stage is 10–20 seconds, thereby ensuring joint quality and the effectiveness of subsequent post-weld heat treatment.

[0032] 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 50-250s.

[0033] In embodiments of the present invention, the post-weld heat treatment process mainly includes five stages: a first cooling stage, a heating stage, a holding stage, a second cooling stage, and a third 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.

[0034] In some embodiments, the average cooling rate of the first cooling stage is 5 to 10 °C / s.

[0035] 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 near the weld joint, with an average heating rate of 2 to 30°C / s.

[0036] In some embodiments, during the heat preservation 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 area near the weld of the rail joint, for a heat preservation time of 50 to 200 seconds.

[0037] In some embodiments, during the second cooling stage, specialized equipment can be used to accelerate the cooling of the top surface of the rail head, with an average cooling rate of 25–40 °C / s.

[0038] In some embodiments, during the third cooling stage, specialized equipment can be used to accelerate the cooling of the top surface, side surface, and lower jaw of the rail head. The average cooling rate of the top surface of the rail head is 20–35 °C / s, and the average cooling rate of the side surface and lower jaw of the rail head is 5–15 °C / s.

[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 top surface, sides, and lower jaw of the rail head near the weld joint is 50–200 seconds, with a temperature range of 800–900℃. 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 structure. Therefore, the cooling rate in the second cooling stage must be controlled at an average cooling rate of 25–40℃ / s, and the termination temperature of the rapid cooling in the second cooling stage should be the starting temperature of the austenite transformation to a lower-temperature structure. To achieve these effects, the starting temperature of the second cooling stage must be greater than 900℃, and the termination temperature must be 600–700℃. The main function of the third cooling stage is to transform all the supercooled austenite structure into pearlite structure, thereby refining the austenite grains and the interlamellar spacing of pearlite. Simultaneously, to refine the core structure of the rail head, which is farther from the tread surface, and to increase its hardness, the cooling intensity of the rail head sides and lower jaw needs to be strengthened. Therefore, accelerated cooling is required for the top surface, sides, and lower jaw of the rail head. After the second cooling stage, the joint temperature of the rail head top surface has already decreased to a relatively low range. With the supplementary cooling from the 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. Therefore, the average cooling rate of the rail head top surface needs to be controlled at 20–35℃ / s, the average cooling rate of the sides and lower jaw at 5–15℃ / s, and the termination temperature at 430–500℃.

[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 primarily 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 wear resistance of the rail head of the 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, significantly increasing the hardness of the flash welded joint of high-strength hardened pearlitic steel rails, thereby enhancing 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 rail has a carbon content of 0.74%, a silicon content of 0.10%, and a manganese content of 0.75%. The minimum tensile strength at the gauge angle 12.7 mm from both the rail head tread and the side surface is 1172 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is ≥370 HB. The welding method is flash welding, and the welding process mainly consists of four stages: electrode clamping, energizing and heating, pressure upsetting, and rapid stub removal. Throughout the welding process, the temperature of the rails on both sides, 0 mm to 25 mm from the end face of the rail to be welded, ranges from 900℃ to 1650℃ for 250 seconds. The heating stage during welding is mainly achieved by resistance heating of the rails through intermittent short-circuit contact under energized conditions. During intermittent short-circuit contact, the voltage is 100% of the total input voltage, the current is 80kA, and the number of short-circuit contacts is 14, each lasting 6 seconds with a 2-second interval. During the intermittent short-circuit contact in the heating phase, the opposing pressure applied to both ends of the rail to be welded is 300kN. The rapid push-up stage in the welding process is characterized by a split-type contoured rail push-up mechanism, consisting of four parts: rail head, left and right rail webs, and rail base. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 10 seconds. After welding, a five-stage post-weld heat treatment process is performed: first-stage cooling, heating, heat preservation, second-stage cooling, and third-stage cooling. The next stage begins after the previous stage is completed. The first cooling stage has an average cooling rate of 10℃ / s and a cooling termination temperature of 100℃. The heating stage uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint, with an average temperature rise rate of 2℃ / s and a heating termination temperature of 900℃. The heat preservation stage uses specialized equipment to maintain the temperature of the top surface, sides, and lower jaw of the rail head near the weld joint at 900℃ for 50 seconds. The second cooling stage uses specialized equipment... The rail head top surface underwent accelerated cooling, with an initial temperature of 900℃, an average cooling rate of 40℃ / s, and a termination temperature of 700℃. The third cooling stage employed specialized equipment to accelerate cooling the rail head top surface, sides, and lower jaw. This accelerated cooling also began at 700℃, with an average cooling rate of 35℃ / s for the top surface, 15℃ / s for the sides and lower jaw, and a termination temperature of 430℃. Longitudinal section hardness tests were performed at 5mm and 25mm below the joint tread surface according to AS1085.20 standard, and microstructure examination was conducted according to BS EN14587. The results showed that the hardness of the rail head interior near the fusion line was 97% of the hardness of the rail base material at the same location, and the pearlite area ratio in the microstructure was ≥98%.

[0046] Example 2

[0047] In this embodiment, the main chemical composition of the test rail has a carbon content of 0.86%, a silicon content of 0.60%, and a manganese content of 1.25%. The minimum tensile strength at the gauge angle 12.7 mm from both the rail head tread and the side surface is 1372 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is ≥390 HB. The welding method is flash welding, and the welding process mainly consists of four stages: electrode clamping, energizing, 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 of the rail to be welded, ranges from 900℃ to 1650℃ for 150 seconds. The heating stage during welding is mainly achieved by resistance heating of the rails through intermittent short-circuit contact under energized conditions. During intermittent short-circuit contact, the voltage is 90% of the total input voltage, the current is 40kA, and the number of short-circuit contacts is 8, each lasting 4 seconds with a 0.5-second interval. During the intermittent short-circuit contact in the heating phase, the opposing pressure applied to both ends of the rail to be welded is 500kN. The rapid push-up stage in the welding process is characterized by a split-type contoured rail push-up mechanism, consisting of four parts: rail head, left and right rail webs, and rail base. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 10 seconds. After welding, a five-stage post-weld heat treatment process is performed: first-stage cooling, heating, heat preservation, second-stage cooling, and third-stage cooling. The next stage begins after the previous stage is completed. The first cooling stage has an average cooling rate of 5℃ / s and a cooling termination temperature of 25℃. The heating stage uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint, with an average temperature rise rate of 30℃ / s and a heating termination temperature of 1100℃. The heat preservation stage uses specialized equipment to maintain the temperature of the top surface, sides, and lower jaw of the rail head near the weld joint at 890℃ for 200 seconds. The second cooling stage uses specialized equipment... The equipment performs accelerated cooling on the top surface of the rail head. The initial accelerated cooling temperature is 800℃, the average cooling rate is 25℃ / s, and the final accelerated cooling temperature is 600℃. In the third cooling stage, specialized equipment is used to accelerate cooling on the top surface, sides, and lower jaw of the rail head. The initial accelerated cooling temperature is 600℃, the average cooling rate on the top surface is 20℃ / s, and the average cooling rate on the sides and lower jaw is 5℃ / s. The final accelerated cooling temperature is 500℃. Longitudinal section hardness tests were performed at 5mm and 25mm below the joint tread surface according to AS1085.20 standard, and microstructure examination of the joint was performed according to BS EN14587. The results show that the hardness of the rail head interior near the fusion line is 110% higher than that of the rail base material at the same location, and the pearlite area ratio in the microstructure is ≥97%.

[0048] Comparative Example 1

[0049] The test rails used in this comparative example have the following main chemical compositions: C (0.74%), Si (0.60%), and Mn (0.75%). The minimum tensile strength at the gauge angle (12.7 mm from the rail head tread and side) is 1172 MPa, and the minimum hardness at a depth of 25 mm from the outer surface of the rail head is 370 HB. The welding method is flash welding, and the welding process mainly consists of four stages: electrode clamping, energizing, 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) ranges from 900℃ to 1650℃ for 50 seconds. The heating stage during welding is mainly achieved by resistance heating of the rails through intermittent short-circuit contact under energized conditions. During intermittent short-circuit contact, the voltage is 90% of the total input voltage, the current is 40kA, and the number of short-circuit contacts is 5, each lasting 3 seconds with a 0.4-second interval. During the intermittent short-circuit contact in the heating phase, the opposing pressure applied to both ends of the rail to be welded is 200kN. The rapid push-up stage in the welding process is characterized by a split-type contoured rail push-up mechanism, consisting of four parts: rail head, left and right rail webs, and rail base. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 30 seconds. After welding, a five-stage post-weld heat treatment process is performed: first-stage cooling, heating, heat preservation, second-stage cooling, and third-stage cooling. The next stage begins after the previous stage is completed. The first cooling stage has an average cooling rate of 4℃ / s and a cooling termination temperature of 100℃. The heating stage uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint, with an average temperature rise rate of 35℃ / s and a heating termination temperature of 800℃. The heat preservation stage uses specialized equipment to maintain the temperature of the top surface, sides, and lower jaw of the rail head near the weld joint at 800℃ for 30 seconds. The second cooling stage uses specialized equipment... The equipment performs accelerated cooling on the top surface of the rail head. The initial accelerated cooling temperature is 800℃, the average cooling rate during accelerated cooling of the top surface is 35℃ / s, and the final accelerated cooling temperature is 710℃. In the third cooling stage, specialized equipment is used to accelerate cooling of the top surface, sides, and lower jaw of the rail head. The initial accelerated cooling temperature is 710℃, the average cooling rate during accelerated cooling of the top surface is 25℃ / s, the average cooling rate during accelerated cooling of the sides and lower jaw is 2℃ / s, and the final accelerated cooling temperature is 410℃. Longitudinal section hardness tests are performed at 5mm and 25mm below the joint tread surface according to AS1085.20 standard, and microstructure inspection of the joint is performed according to BS EN14587.The results show that the ratio of the internal hardness of the rail head near the fusion line zone of the rail joint to the hardness of the rail base material at the same location is 88%, and the area ratio of pearlite in the microstructure is ≥93%. The joint exhibits severe collapse and does not meet the requirements.

[0050] Comparative Example 2

[0051] The test rails used in this comparative example have the following main chemical compositions: C (0.86%), Si (0.10%), and Mn (1.25%). The minimum tensile strength at a gauge angle of 12.7 mm from both the rail head tread and side surface is 1220 MPa, and the minimum hardness at a depth of 25 mm from the outer surface of the rail head is 380 HB. The welding method is flash welding, and the welding process mainly consists of four stages: electrode clamping, energizing, pressure upsetting, and rapid sulphur push-off. Throughout the welding process, the temperature of the rails on both sides, from 0 mm to 25 mm from the end face, ranges from 900℃ to 1650℃ for 250 seconds. The heating stage during welding is mainly achieved by resistance heating of the rails through intermittent short-circuit contact under energized conditions. During intermittent short-circuit contact, the voltage is 100% of the total input voltage, the current is 90kA, the number of short-circuit contacts is 15, each lasting 7 seconds with a 0.5-second interval; during the intermittent short-circuit contact in the heating phase, the opposing pressure applied to both ends of the rail to be welded is 400kN; the rapid push-up stage in the welding process is characterized by the use of a split-type contoured rail push-up mechanism, consisting of four parts: rail head, left and right rail webs, and rail base. To ensure the joint quality and the effectiveness of subsequent post-weld heat treatment, the time from the end of upsetting to the complete end of push-up is 8 seconds. After welding, a five-stage post-weld heat treatment is performed: first-stage cooling, heating, heat preservation, second-stage cooling, and third-stage cooling. The next stage begins after the previous stage is completed. The first cooling stage has an average cooling rate of 15℃ / s and a cooling termination temperature of 20℃. The heating stage uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint, with an average temperature rise rate of 35℃ / s and a heating termination temperature of 1200℃. The heat preservation stage uses specialized equipment to maintain the temperature of the top surface, sides, and lower jaw of the rail head near the weld joint at 1000℃ for 40 seconds. The second cooling stage uses specialized equipment... The equipment performs accelerated cooling on the top surface of the rail head. The initial accelerated cooling temperature is 900℃, the average cooling rate during accelerated cooling of the top surface is 45℃ / s, and the final accelerated cooling temperature is 800℃. In the third cooling stage, specialized equipment is used to accelerate cooling of the top surface, sides, and lower jaw of the rail head. The initial accelerated cooling temperature is 800℃, the average cooling rate during accelerated cooling of the top surface is 40℃ / s, the average cooling rate during accelerated cooling of the sides and lower jaw is 20℃ / s, and the final accelerated cooling temperature is 500℃. Longitudinal section hardness tests are performed at 5mm and 25mm below the joint tread surface according to AS1085.20 standard, and microstructure inspection of the joint is performed according to BS EN14587.The results show that the hardness of the rail head in the near-fusion line zone of the rail joint is 130% higher than that of the rail base material at the same location, the area ratio of pearlite in the microstructure is ≥90%, and a large amount of martensite structure appears in the joint, which does not meet the requirements.

[0052] 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 improving the wear resistance of welded rail heads, characterized in that, include: Flash welding of rails includes: sequentially performing an electric heating stage and a pressure upsetting stage; wherein, the voltage of the electric heating stage is 90% to 100% of the total input voltage, the current is 40 to 80 kA, the number of short-circuit contacts is 6 to 14, the duration of each contact is 4 to 6 seconds, and the interval is 0.5 to 2 seconds. The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a heat preservation stage, a second cooling stage, and a third cooling stage in sequence. The end temperature of the first cooling stage is 25-100℃, the end temperature of the heating stage is 800-1100℃, the temperature range of the heat preservation stage is 800-900℃, the starting temperature of the second cooling stage is greater than 900℃ and the end temperature is 600-700℃, and the starting temperature of the third cooling stage is 600-700℃ and the end temperature is 430-500℃. The main chemical components of the steel rails include 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%).

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 300-500 kN.

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 10-20 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 50-250s.

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, side surface, and lower jaw of the rail head near the weld zone of the rail joint are heated at an average heating rate of 2–30 °C / s; and / or during the heat preservation stage, the top surface, side surface, and lower jaw of the rail head near the weld zone of the rail joint are heat-preserved for a duration of 50–200 s.

7. The method according to claim 1, characterized in that, In the second cooling stage, the top surface of the rail head is cooled more rapidly, with an average cooling rate of 25–40 °C / s.

8. The method according to claim 1, characterized in that, In the third cooling stage: the top surface, side surface, and lower jaw of the rail head are accelerated for cooling. The average cooling rate of the top surface of the rail head is 20-35℃ / s, and the average cooling rate of the side surface and lower jaw of the rail head is 5-15℃ / s.

9. The method according to claim 1, characterized in that, The rail to be welded is a high-strength head-hardened pearlitic steel rail. The tensile strength at the gauge angle of the rail 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.

10. A rail prepared by the method according to any one of claims 1-9, characterized in that, The hardness of the inner region of the rail head near the weld seam is 95% to 110% of the hardness of the inner region of the rail head of the rail base material. The area ratio of pearlite in the microstructure of the inner region of the rail head near the weld seam is greater than or equal to 97%. The inner region of the rail head is the region with a depth of 0 to 25 mm from the surface of the rail head.

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