Welding and heat treatment methods for deep hardened rails and rails

Abstract

This invention discloses a welding and heat treatment method for deep-hardened rails and the rail itself. The method includes: flash welding of the rail, comprising: sequentially performing an electric heating stage and a pressure upsetting stage; wherein, the voltage of the electric heating stage is 300-385V, the average current is 500-800A, and the duration is 80-100s; and heat treatment of the flash-welded rail, comprising: sequentially performing a first cooling stage, a heating stage, a second cooling stage, and a third 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 starting temperature of the second cooling stage is greater than 900℃ and the termination temperature is 600-700℃, and the starting temperature of the third cooling stage is 600-700℃ and the termination temperature is 430-500℃. This invention can improve the internal hardness of the rail head of the flash-welded rail joint, thereby improving the wear resistance and service life of the rail weld joint.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, specifically to a method for welding and heat treatment of deep-hardened rails and the rail itself. 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 welding and heat treatment method for deep-hardened steel rails and a steel rail in order to solve the technical problem of how to improve the hardness of the flash weld joint of steel rails.

[0006] According to one aspect of the present invention, a method for welding and heat treatment of deeply hardened steel rails 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 300-385V, the average current is 500-800A, and the duration is 80-100s;

[0008] The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a second cooling stage, and a third 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 starting temperature of the second cooling stage is greater than 900°C and the termination temperature is 600-700°C, and the starting temperature of the third cooling stage is 600-700°C and the termination temperature is 430-500°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 20-130 kN, and the rail consumption is 8-20 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 100-200s.

[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, with an average heating rate of 2 to 30°C / s.

[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 welding and heat treatment method for deep hardened rails according to an embodiment of the present invention, by improving the relevant parameters of the flash welding process (especially the voltage, current, time, etc. in 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 welding and heat treatment method for deep-hardened steel rails, 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 300-385V, the average current is 500-800A, and the duration is 80-100s;

[0026] The heat treatment of the flash-welded rails includes: a first cooling stage, a heating stage, a second cooling stage, and a third 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 starting temperature of the second cooling stage is greater than 900°C and the termination temperature is 600-700°C, and the starting temperature of the third cooling stage is 600-700°C and the termination temperature is 430-500°C.

[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 by implementing refined staged control and designing reasonable parameters for the post-weld heat treatment process, the internal hardness of the rail head of the flash welded joint can be improved ("internal hardness of the rail head" can refer to the hardness of the internal area of ​​the rail head near the weld zone described below), thereby improving 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 welding and heat treatment method for deeply hardened layer rails to solve this problem.

[0029] In an embodiment of the present invention, by setting the voltage, current and time values ​​as described above, the rail to be welded is heated mainly by short-circuiting the rail under power-on conditions, and by utilizing the heat generated by the contact short-circuit resistance heat and the heat generated by the explosion of a small amount of crossbeam formed between the liquid metal at the end face of the rail to be welded.

[0030] In some embodiments, during the energizing heating stage, the opposing pressure applied to both ends of the rail to be welded is 20–130 kN, and the rail consumption is 8–20 mm. This maintains the simultaneous existence of intermittent short circuits and beam bursts.

[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. 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.

[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 100-200s.

[0033] In embodiments of the present invention, the post-weld heat treatment process mainly includes four stages: a first cooling stage, a heating stage, a second cooling stage, and a third cooling stage. The next stage begins after the previous stage is completed. The starting temperature and / or ending 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 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.

[0037] 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.

[0038] 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. The purpose of the second cooling stage after the heating stage is to rapidly cool the rail head tread area, increasing the supercooling and enhancing the driving force for the austenite to transform into a lower-temperature microstructure. Therefore, the cooling rate of the second cooling stage must be controlled at an average rate of 25–40 °C / s, and the termination temperature of this rapid cooling stage should be the starting temperature of the austenite to lower-temperature microstructure transformation. To achieve this, the starting temperature of the second cooling stage must be greater than 900 °C, and the termination temperature must be 600–700 °C. The main function of the third cooling stage is to transform all the supercooled austenite microstructure into pearlite microstructure, refining the austenite grains and pearlite lamellar spacing. Simultaneously, to refine the microstructure in the core area of ​​the rail head, which is farther from the tread surface, and to increase 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 top surface of the rail head has been reduced to a low range. With the supplementary cooling of the sides and lower jaw of the rail head, the air cooling intensity of the top surface of the rail head can be appropriately reduced to avoid harmful phase transformation processes such as martensite and bainite. Therefore, it is necessary to control the average cooling rate of the top surface of the rail head to 20-35℃ / s, the average cooling rate of the sides and lower jaw of the rail head to 5-15℃ / s, and the termination temperature to 430-500℃.

[0039] The temperature of the rail joint and the rate of cooling / heating directly affect the phase transformation process of the metallic material. In the process defined in this invention, all heating temperatures, cooling / heating rates, and cooling termination temperatures work synergistically to achieve the heat treatment effect described above.

[0040] 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).

[0041] 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 welding and heat treatment method for deeply hardened steel rails, comprising 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 flash welded joints of high-strength, hardened pearlitic steel rails, thereby improving wear resistance and service life.

[0042] The following description is based on specific embodiments and comparative examples.

[0043] Example 1

[0044] In this embodiment, the main chemical composition of the rails used contains 0.76% C, 0.55% Si, 1.15% Mn, and the mass fractions of P and S both not exceeding 0.020%, 0.30% Cr, and 0.01% V. The minimum tensile strength at the gauge angle 12.7mm from both the rail head tread and side is 1252MPa, and the hardness at a depth of 25mm from the outer surface of the rail head is ≥375HB. The main processes are 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 stub removal. Throughout the welding process, the temperature of the rails on both sides, 0mm to 25mm from the end face to be welded, ranges from 900℃ to 1650℃ for 130s. The heating stage of the welding process mainly involves short-circuiting the rails to be welded under energized conditions. The heat generated by the contact short-circuit resistance and the heat from the small amount of heat generated by the bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the heating stage is 300V, the average current is 500A, and the duration is 100s. During the heating stage, the opposing pressure applied to both ends of the rails is 130kN, and the rail consumption is 15mm. The rapid push-up stage of the welding process uses an integrated contoured rail push-up mechanism. 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 10s. Post-weld heat treatment is performed after welding. Post-weld heat treatment mainly includes four stages: first-stage cooling, heating, second-stage cooling, and third-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 50℃. The heating stage of the post-weld heat treatment process uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during the heating process is 13℃ / s, and the heating termination temperature is 1000℃. The second cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface of the rail head. The accelerated cooling initiation temperature is >900℃, the average cooling rate of the rail head top surface during accelerated cooling is 35℃ / s, and the accelerated cooling termination temperature is 700℃. The third cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface, sides, and lower jaw of the rail head. The accelerated cooling initiation temperature is 700℃, the average cooling rate of the top surface during accelerated cooling is 35℃ / s, the average cooling rate of the sides and lower jaw during accelerated cooling is 15℃ / 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 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%.

[0045] Example 2

[0046] In this embodiment, the main chemical composition of the rails used contains 0.86% C, 0.10% Si, 0.75% Mn, and P and S, with mass fractions not exceeding 0.020%, 0.30% Cr, and 0.01% V. The minimum tensile strength at a gauge angle of 12.7mm from both the rail head tread and side is 1183MPa, and the hardness at a depth of 25mm from the outer surface of the rail head is ≥380HB. The main processes are 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 stub removal. Throughout the welding process, the temperature of the rails on both sides, 0mm to 25mm from the end face to be welded, ranges from 900℃ to 1650℃ for 200s. The heating stage of the welding process mainly involves short-circuiting the rails to be welded under energized conditions. The heat generated by the contact short-circuit resistance and the small amount of heat generated by the bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the heating stage is 385V, the average current is 800A, and the duration is 100s. During the heating stage, the opposing pressure applied to both ends of the rails is 20kN, and the rail consumption is 20mm. The rapid push-up stage of the welding process uses an integrated contoured rail push-up mechanism. 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 10s. Post-weld heat treatment is performed after welding. Post-weld heat treatment mainly includes four stages: first-stage cooling, heating, second-stage cooling, and third-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℃. The heating stage of the post-weld heat treatment process uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during the heating process is 30℃ / s, and the heating termination temperature is 900℃. The second cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface of the rail head. The accelerated cooling initiation temperature is >900℃, the average cooling rate of the rail head top surface during accelerated cooling is 40℃ / s, and the accelerated cooling termination temperature is 600℃. The third cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface, sides, and lower jaw of the rail head. The accelerated cooling initiation temperature is 600℃, the average cooling rate of the top surface during accelerated cooling is 20℃ / s, the average cooling rate of the sides and lower jaw during accelerated cooling is 5℃ / s, and the accelerated cooling termination temperature is 430℃. 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%.

[0047] Example 3

[0048] In this embodiment, the main chemical composition of the rails used contains 0.80% C, 0.50% Si, 1.20% 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 12.7mm from both the rail head tread and side is 1302MPa, and the hardness at a depth of 25mm from the outer surface of the rail head is ≥389HB. The main processes are 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 stub removal. Throughout the welding process, the temperature of the rails on both sides, 0mm to 25mm from the end face to be welded, ranges from 900℃ to 1650℃ for 150s. The heating stage of the welding process mainly involves short-circuiting the rails to be welded under energized conditions. The heat generated by the contact short-circuit resistance and the small amount of heat generated by the bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the heating stage is 375V, the average current is 600A, and the duration is 90s. During the heating stage, the opposing pressure applied to both ends of the rails is 100kN, and the rail consumption is 13mm. The rapid push-up stage of the welding process uses an integrated contoured rail push-up mechanism. 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 8s. Post-weld heat treatment is performed after welding. Post-weld heat treatment mainly includes four stages: first-stage cooling, heating, second-stage cooling, and third-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 75℃. The heating stage of the post-weld heat treatment process uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during the heating process is 15℃ / s, and the heating termination temperature is 1100℃. The second cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface of the rail head. The accelerated cooling initiation temperature is >900℃, the average cooling rate of the rail head top surface during accelerated cooling is 30℃ / s, and the accelerated cooling termination temperature is 650℃. The third cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface, sides, and lower jaw of the rail head. The accelerated cooling initiation temperature is 650℃, the average cooling rate of the top surface during accelerated cooling is 30℃ / s, the average cooling rate of the sides and lower jaw during accelerated cooling is 12℃ / 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 ≥99%.

[0049] Comparative Example 1

[0050] The main chemical composition of the rails used in this comparative example includes C (0.81%), Si (0.56%), Mn (0.90%), P and S (both not exceeding 0.020%), Cr (not exceeding 0.30%), and V (not exceeding 0.01%). The minimum tensile strength at the gauge angle 12.7 mm from both the rail head tread and side is 1272 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is ≥380 HB. The main processes are 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 stub removal. 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 250 seconds. The heating stage of the welding process mainly involves short-circuiting the rails to be welded under energized conditions. The heat generated by the contact short-circuit resistance and the heat from the small amount of heat generated by the bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the heating stage is 390V, the average current is 900A, and the duration is 150s. During the heating stage, the opposing pressure applied to both ends of the rails is 10kN, and the rail consumption is 25mm. The rapid push-up stage of the welding process uses an integrated contoured rail push-up mechanism. 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 20s. Post-weld heat treatment is performed after welding. Post-weld heat treatment mainly includes four stages: first-stage cooling, heating, second-stage cooling, and third-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 2℃ / s, and the cooling termination temperature is 200℃. The heating stage of the post-weld heat treatment process uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld zone of the rail joint. The average temperature rise rate during the heating process is 35℃ / s, and the heating termination temperature is 800℃. The second cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface of the rail head. The accelerated cooling initiation temperature is >900℃, the average cooling rate of the rail head top surface during accelerated cooling is 20℃ / s, and the accelerated cooling termination temperature is 500℃. The third cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface, sides, and lower jaw of the rail head. The accelerated cooling initiation temperature is 500℃, the average cooling rate of the top surface during accelerated cooling is 15℃ / s, the average cooling rate of the sides and lower jaw during accelerated cooling is 2℃ / s, and the accelerated cooling termination temperature is 550℃. 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 85% to that of the rail base material in the near fusion line zone, and the area ratio of pearlitic microstructure is ≥96%. The joint shows obvious collapse and does not meet the requirements.

[0051] Comparative Example 2

[0052] The main chemical composition of the rails used in this comparative example includes C at a mass fraction of 0.84%, Si at 0.60%, Mn at 1.15%, 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 is 1293 MPa, and the hardness at a depth of 25 mm from the outer surface of the rail head is ≥390 HB. The main processes are 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 stub removal. 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 90 seconds. The heating stage of the welding process mainly involves short-circuiting the rails to be welded under energized conditions. The heat generated by the contact short-circuit resistance and the heat from the small amount of heat generated by the bursting of the molten metal between the rail ends is used to heat the rails. The voltage during the heating stage is 300V, the average current is 450A, and the duration is 70s. During the heating stage, the opposing pressure applied to both ends of the rails is 140kN, and the rail consumption is 8mm to 20mm. The rapid push-up stage of the welding process uses an integrated contoured rail push-up mechanism. 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 3s. Post-weld heat treatment is performed after welding. Post-weld heat treatment mainly includes four stages: first-stage cooling, heating, second-stage cooling, and third-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 60℃ / s, and the cooling termination temperature is 20℃. The heating stage of the post-weld heat treatment process uses specialized equipment to heat the top surface, sides, and lower jaw of the rail head near the weld joint. The average temperature rise rate during the heating process is 1℃ / s, and the termination temperature of the heating stage is 1200℃. The second cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface of the rail head. The initial temperature of accelerated cooling is >900℃, the average cooling rate of the top surface during accelerated cooling is 50℃ / s, and the termination temperature of accelerated cooling is 750℃. The third cooling stage of the post-weld heat treatment process uses specialized equipment to accelerate the cooling of the top surface, sides, and lower jaw of the rail head. The initial temperature of accelerated cooling is 750℃, the average cooling rate of the top surface during accelerated cooling is 40℃ / s, the average cooling rate of the sides and lower jaw during accelerated cooling is 25℃ / s, and the termination temperature of accelerated cooling 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 130% 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 ≥90%, and martensitic abnormal structure in the joint, which does not meet the requirements.

[0053] 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 welding and heat treating a deep hardening layer steel rail, characterized by, 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 300-385V, the average current is 500-800A, and the duration is 80-100s; The heat treatment of the flash-welded rails includes: sequentially performing a first cooling stage, a heating stage, a second cooling stage, and a third cooling stage. The termination temperature of the first cooling stage is 25–100°C, the termination temperature of the heating stage is 800–1100°C, the starting temperature of the second cooling stage is greater than 900°C and the termination temperature is 600–700°C, and the starting temperature of the third cooling stage is 600–700°C and the termination temperature is 430–500°C. 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. The average cooling rate in the first cooling stage is 5–10 °C / s; 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, with an average heating rate of 2 to 30°C / s. 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. 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.

2. The method of claim 1, wherein, During the electric heating stage, the opposing pressure applied to both ends of the rail to be welded is 20-130 kN, and the rail consumption is 8-20 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 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 100-200s.

5. The method according to claim 1, characterized in that, 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%.

6. A rail prepared using the method described in any one of claims 1-5, 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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