Welding and heat treatment method for deep hardened layer steel rail and steel rail

Abstract

A welding and heat treatment method for a deep hardened layer steel rail, comprising: carrying out flash welding on a steel rail, by sequentially carrying out an ohmic heating stage and a pressing and upsetting stage, where the voltage is 300-385V, the average current is 500-800A, and the duration time is 80-100s in the ohmic heating stage; and carrying out heat treatment on the steel rail that has undergone flash welding, by sequentially carrying out a first cooling stage, a heating stage, a second cooling stage, and a third cooling stage, where the final temperature is 25-100°C in the first cooling stage, the final temperature is 800-1100°C in the heating stage, the initial temperature is greater than 900°C and the final temperature is 600-700°C in the second cooling stage, and the initial temperature is 600-700°C and the final temperature is 430-500°C in the third cooling stage. Further disclosed is a steel rail prepared by employing the described method. According to the described method, the internal hardness of the railhead of the steel rail at the flash welding joint can be improved, thus improving the wear resistance and the service life of the welding joint of the steel rail.

Description

Welding and heat treatment method of deep hardened layer rail and rail Technical Field

[0001] The invention relates to the technical field of rail welding, and in particular to a welding and heat treatment method for a deep hardened layer rail and the rail. Background Art

[0002] Rails, as the most crucial component of railway lines, face high axle loads and high-frequency service environments, placing higher demands on their performance. This is primarily reflected in wear resistance and fatigue performance. Research has shown that, without considering other factors such as wheel-rail matching and wear media, higher hardness results in better wear resistance. Therefore, hardness is often used as a primary indicator of a material's wear resistance. The hardness of rail base material is primarily characterized by tread hardness and cross-section hardness, while the hardness of rail joints is primarily characterized by tread hardness and longitudinal section hardness.

[0003] Currently, the mainstream rail welding method is flash welding. This resistance welding method utilizes the resistance of current passing through tiny contact points on the rail ends and the heat generated by the arc to heat the rail ends to be welded. After a suitable time, pressure is applied to the joint to securely bond the entire surface of the rails simultaneously. Its high degree of automation and consistent welding quality make it the primary method used for on-site welding in seamless railway construction both domestically and internationally. Flash welding is primarily categorized into fixed and mobile types based on the production method. Fixed flash welding typically involves the welding equipment being stationary within a factory, often referred to as factory welding or base welding. Fixed flash welding typically involves directly short-circuiting the rails and heating them using resistance heat. This heating process is accompanied by minimal or no flash. Currently, the most widely used mobile flash welders in China and abroad are the K950 and YGH-1200TH. The K950 mobile flash welder guarantees high quality and a long service life for the welding head.

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

[0005] Summary of the Invention

[0006] The main purpose of the present invention is to provide a welding and heat treatment method for a deep hardened layer rail and the rail, so as to solve the technical problem of how to improve the hardness of the rail flash weld joint.

[0007] According to one aspect of the present invention, a method for welding and heat treating a deep hardened layer rail is provided, comprising:

[0008] Flash welding of rails includes: sequentially performing an electric heating stage and a pressurized 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;

[0009] The flash-welded rails are heat-treated, comprising: a first cooling stage, a heating stage, a second cooling stage, and a third cooling stage, wherein the first cooling stage ends at a temperature of 25 to 100° C., the heating stage ends at a temperature of 800 to 1100° C., the second cooling stage starts at a temperature greater than 900° C. and ends at a temperature of 600 to 700° C., and the third cooling stage starts at a temperature of 600 to 700° C. and ends at a temperature of 430 to 500° C.

[0010] According to one embodiment of the present invention, during the power-on 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.

[0011] According to one embodiment of the present invention, the flash welding of the rail further comprises: performing a nodule pushing stage after the pressurizing and upsetting stage, and the time from the end of the pressurizing and upsetting stage to the complete end of the nodule pushing stage is 5 to 10 seconds.

[0012] According to one embodiment of the present invention, during the entire flash welding process, the temperature of the rails on both sides within a region 0 to 25 mm from the end face to be welded is 900 to 1650° C., and the duration is 100 to 200 seconds.

[0013] According to one embodiment of the present invention, the average cooling rate in the first cooling stage is 5-10° C. / s.

[0014] According to one embodiment of the present invention, during the heating stage, the rail head top surface, rail head side surface and rail head lower jaw near the weld area of ​​the rail joint are heated, with an average heating rate of 2-30° C. / s.

[0015] According to one embodiment of the present invention, in the second cooling stage, the rail head top surface is cooled at an accelerated rate of 25-40° C. / s.

[0016] According to one embodiment of the present invention, in the third cooling stage: the rail head top surface, rail head side surface and rail head lower jaw are cooled at an accelerated rate, the average cooling rate of the rail head top surface is 20-35°C / s, and the average cooling rate of the rail head side surface and rail head lower jaw is 5-15°C / s.

[0017] According to one embodiment of the present invention, the steel rail to be welded is a high-strength head-hardened pearlite rail, and the mass fraction of the C element in the main chemical composition of the steel rail is 0.74% to 0.86%, the mass fraction of the Si element is 0.10% to 0.60%, the mass fraction of the Mn element is 0.75% to 1.25%, the mass fractions of the P element and the S element are both no more than 0.020%, the mass fraction of the Cr element is no more than 0.30%, and the mass fraction of the V element is no more than 0.01%; the tensile strength of the steel rail at the gauge angle is at least 1172 MPa, and the hardness at a depth of 25 mm from the outer profile surface of the rail head is greater than or equal to 370 HB.

[0018] According to another aspect of the present invention, a rail is provided that is manufactured using the method described above, wherein the hardness of an inner region of the rail head near the weld of the rail is 95% to 110% of the hardness of the inner region of the rail head of the rail base material, and the area proportion of pearlite in the microstructure of the inner region of the rail head near the weld of the rail is greater than or equal to 97%, wherein the inner region of the rail head is an area at a depth of 0 to 25 mm from the surface of the rail head.

[0019] In the welding and heat treatment method of the deep-hardened layer rail according to an embodiment of the present invention, by improving the relevant parameters of the flash welding process (especially the voltage, current, time and other parameters in the power-on 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 rail flash weld joint can be improved, thereby improving the wear resistance and service life of the rail weld joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] FIG1 is a schematic diagram showing an inner region of a rail head near a weld zone according to an embodiment of the present invention;

[0022] FIG2 shows another schematic diagram of the inner region of the rail head near the weld zone according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0024] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. Subsequent embodiments will not explain this one by one.

[0025] The present invention provides a method for welding and heat treating a deep hardened layer rail, comprising:

[0026] Flash welding of rails includes: sequentially performing an electric heating stage and a pressurized 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;

[0027] The flash-welded rails are heat-treated, comprising: a first cooling stage, a heating stage, a second cooling stage, and a third cooling stage, wherein the first cooling stage ends at a temperature of 25 to 100° C., the heating stage ends at a temperature of 800 to 1100° C., the second cooling stage starts at a temperature greater than 900° C. and ends at a temperature of 600 to 700° C., and the third cooling stage starts at a temperature of 600 to 700° C. and ends at a temperature of 430 to 500° C.

[0028] In an embodiment of the present invention, by improving the relevant parameters of the flash welding process (especially the voltage, current, time and other parameters in the power-on 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 rail flash welded joint can be improved ("the internal hardness of the rail head of the welded joint" may 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.

[0029] In some embodiments, the rails to be welded are high-strength, head-hardened pearlite rails. The rails' primary chemical composition includes a mass fraction of C ranging from 0.74% to 0.86%, a mass fraction of Si ranging from 0.10% to 0.60%, a mass fraction of Mn ranging from 0.75% to 1.25%, a mass fraction of each of P and S not exceeding 0.020%, a mass fraction of Cr not exceeding 0.30%, and a mass fraction of V not exceeding 0.01%. The rails exhibit a tensile strength of at least 1172 MPa at a gauge angle 12.7 mm from the rail head tread and side surfaces, respectively, and a hardness of 370 HB or greater at a depth of 25 mm from the rail head outer profile surface. Prior art flash welds of high-strength, head-hardened pearlite rails suffer from low wear resistance and a short service life. The present invention provides a method for welding and heat treating a deep-hardened rail to address this problem.

[0030] In an embodiment of the present invention, by setting the voltage, current and time values ​​as described above, during the power-on heating stage, the rails to be welded are mainly heated by short-circuiting the rails in the power-on state, and utilizing the heat generated by the short-circuit resistance heat and the heat generated by the explosion of a small amount of lintel formed between the liquid metal end faces of the rails to be welded.

[0031] In some embodiments, during the power-on 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, thereby maintaining the state of intermittent short circuit and lintel explosion coexisting.

[0032] In some embodiments, the flash welding of the rails further includes a bump-pushing stage after the pressurized upsetting stage. This bump-pushing stage improves the weld surface appearance and weld quality. An integrated rail-shaped bump-pushing mechanism can be used for this purpose. In some embodiments, the time from the pressurized upsetting stage to the complete completion of the bump-pushing stage is 5 to 10 seconds, thereby ensuring joint quality and the effectiveness of subsequent post-weld heat treatment.

[0033] In some embodiments, the flash welding process mainly includes four stages: electrode clamping, power heating, pressurized top forging, and rapid nodule pushing. During the entire flash welding process, the temperature in the area of ​​0 to 25 mm from the end face of the rails on both sides to be welded is 900 to 1650°C, and the duration is 100 to 200 seconds.

[0034] In the embodiments of the present invention, the post-weld heat treatment process primarily includes four stages: a first cooling stage, a heating stage, a second cooling stage, and a third cooling stage. Each stage is followed by the next. The starting and / or ending temperatures for each stage are defined above.

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

[0036] In some embodiments, during the heating stage, dedicated equipment may be used to heat the rail head top surface, rail head side surface, and rail head lower jaw near the weld area of ​​the rail joint, with an average heating rate of 2-30°C / s.

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

[0038] In some embodiments, during the third cooling stage, dedicated equipment may be used to accelerate the cooling of the rail head top surface, rail head side surfaces, and rail head lower jaw, with an average cooling rate of 20-35°C / s for the rail head top surface, and an average cooling rate of 5-15°C / s for the rail head side surfaces and rail head lower jaw.

[0039] The primary function of heat treatment is to eliminate internal stress in the weld joint, refine the austenite grains, homogenize the structure, and improve the joint strength and hardness. In addition to the basic functions of heat treatment described above, the heat treatment method employed in this invention also improves the internal hardness of the rail head in the deep-hardened rail flash weld. 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 each region across the entire rail cross-section varies, the cooling rates of each region under natural cooling conditions vary. To prevent martensite, bainite, and other microstructural transformations from occurring during the first cooling stage, the cooling rate during the first cooling stage must be controlled to 5-10°C / s. The final cooling temperature during the first cooling stage must be controlled to 25-100°C to ensure that both the surface and core of the rail joint are completely transformed into pearlite. The primary function of the heating stage is to cause the joint region, which has undergone a complete pearlite transformation and cooled to 25-100°C, to re-transform into austenite. To ensure uniform temperature across the joint interior and exterior, as well as across the entire cross-section, the temperature rise rate during the heating stage must be controlled to 2-30°C / s. The purpose of the second cooling stage, following the heating phase, is to rapidly cool the rail head and tread area, increasing the degree of undercooling and strengthening the driving force for the transformation of austenite to the low-temperature microstructure. Therefore, the cooling rate during the second cooling stage must be controlled to an average of 25-40°C / s, and the termination temperature of the rapid cooling stage must be at the starting temperature of the austenite to low-temperature microstructure transformation. Therefore, to achieve this, the starting temperature of the second cooling stage must be greater than 900°C and the termination temperature must be between 600 and 700°C. The primary function of the third cooling stage is to completely transform the undercooled austenite into pearlite, thereby refining the spacing between austenite grains and pearlite lamellae. Furthermore, to refine the microstructure and increase hardness in the core of the joint rail head, which is farther from the tread, the cooling intensity must be increased simultaneously on the side surfaces and the lower jaw of the rail head. Therefore, accelerated cooling is required on the top, side surfaces, and lower jaw of the rail head. After the second cooling stage, the joint temperature of the rail head top surface has dropped to a lower range. In addition, with the supplementary cooling of the rail head side and rail head 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, it is necessary to control the average cooling rate of the rail head top surface to 20-35℃ / s, the average cooling rate of the rail head side and rail head jaw to 5-15℃ / s, and the termination temperature to 430-500℃.

[0040] The temperature of the rail joint and the speed of cooling / heating directly affect the phase transformation process of the metal material. All heating temperatures, cooling / heating rates and cooling end temperatures in the above process defined by the present invention work together to achieve the above-mentioned heat treatment effect.

[0041] The present invention also provides a rail manufactured using the method described above, wherein the hardness of the inner region of the rail head near the weld zone of the rail is 95% to 110% of the hardness of the inner region of the rail head of the rail base material, and the pearlite area in the microstructure of the inner region of the rail head near the weld zone of the rail is greater than or equal to 97%. Referring to Figures 1 and 2, the near-weld zone (also called the near-fusion line zone) can be a heat-affected zone 1 to 10 mm from each side of the fusion line; the inner region of the rail head can be an area 0 to 25 mm deep from the rail head surface (which can include: the top surface of the rail head, the gauge angle, the two 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 profile surface of the rail head).

[0042] In summary, the present invention mainly addresses the technical problems of reduced wear resistance and short service life of flash welded joints of high-strength rail head hardened pearlite rails, and provides a welding and heat treatment method for deep-hardened layer rails. The method includes two main processes: welding and post-weld heat treatment. The present invention improves the parameters and steps of these two main processes, which can significantly increase the hardness of the flash welded joints of high-strength rail head hardened pearlite rails, thereby improving wear resistance and service life.

[0043] The following describes the specific examples and comparative examples.

[0044] Example 1

[0045] The main chemical composition of the steel rails used in this embodiment includes a mass fraction of 0.76% C, 0.55% Si, 1.15% Mn, 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 the gauge angle, 12.7 mm from the rail head tread and side surfaces, is 1252 MPa, and the hardness at a depth of 25 mm from the rail head outer profile surface is ≥ 375 HB. The welding process consists of two main steps: welding and post-weld heat treatment. The welding method is rail flash welding, and the welding process consists of four stages: electrode clamping, electrical heating, pressurized forging, and rapid nodule 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°C to 1650°C, and the welding duration lasts for 130 seconds. The heating phase of the welding process primarily involves short-circuiting the rails while energized. The rails are heated using both the heat from the short-circuit resistance and the heat generated by the small lintel explosion between the liquid metal ends of the rails. The voltage during the heating phase is 300V, the average current is 500A, and the duration is 100s. During this heating phase, a pressure of 130kN is applied to both ends of the rails, resulting in a rail consumption of 15mm. The rapid nodule removal phase of the welding process utilizes an integrated, contoured rail nodule removal mechanism. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, a 10s delay is maintained from the end of upsetting to the completion of nodule removal. Post-weld heat treatment is performed after welding. Post-weld heat treatment consists of four phases: first-stage cooling, heating, second-stage cooling, and third-stage cooling. Each phase progresses to the next upon completion of the previous one. The average cooling rate of the first cooling stage of the post-weld heat treatment process is 8°C / s, and the cooling end temperature is 50°C. In the heating stage of the post-weld heat treatment process, special equipment is used to heat the top surface, side surfaces and lower jaw of the rail head near the weld area of ​​the rail joint. The average temperature rise rate of the heating process is 13°C / s, and the heating stage end temperature is 1000°C. In the second cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface of the rail head. The starting temperature of the accelerated cooling is greater than 900°C, the average cooling rate of the accelerated cooling of the top surface of the rail head is 35°C / s, and the end temperature of the accelerated cooling is 700°C. In the third cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface, side surfaces and lower jaw of the rail head. The starting temperature of the accelerated cooling is 700°C, the average cooling rate of the accelerated cooling of the top surface of the rail head is 35°C / s, the average cooling rate of the accelerated cooling of the side surfaces and lower jaw of the rail head is 15°C / s, and the end temperature of the accelerated cooling is 500°C. The longitudinal section hardness test was carried out at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was inspected in accordance with BS EN14587.The results show that the ratio of the internal hardness of the rail head near the fusion line area to the hardness of the rail base material at the same position in the high-strength rail head hardened pearlite rail flash weld formed by this method is 98%, and the pearlite area in the microstructure accounts for ≥98%.

[0046] Example 2

[0047] The main chemical composition of the rails used in this embodiment includes a C mass fraction of 0.86%, a Si mass fraction of 0.10%, a Mn mass fraction of 0.75%, a P mass fraction of no more than 0.020% and a S mass fraction of no more than 0.30%, a Cr mass fraction of no more than 0.01%, and a V mass fraction of no more than 0.01%. The minimum tensile strength at the gauge angle, 12.7 mm from the rail head tread and side surfaces, is 1183 MPa, and the hardness at a depth of 25 mm from the rail head outer profile surface is ≥ 380 HB. The welding process consists of two main steps: welding and post-weld heat treatment. The welding method is rail flash welding, and the welding process consists of four stages: electrode clamping, electrical heating, pressurized forging, and rapid nodule 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°C to 1650°C, and the welding duration lasts for 200 seconds. The heating phase of the welding process primarily involves short-circuiting the rails while energized. The rails are heated using both the heat from the short-circuit resistance and the heat generated by the small lintel explosion between the liquid metal ends of the rails. The voltage during the heating phase is 385V, the average current is 800A, and the duration is 100s. During this heating phase, a 20kN pressure is applied to both ends of the rails, resulting in a rail consumption of 20mm. The rapid nodule removal phase of the welding process utilizes an integrated, contoured rail nodule removal mechanism. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, a 10s delay is maintained from the end of upsetting to the completion of nodule removal. Post-weld heat treatment is performed after welding. The post-weld heat treatment consists of four phases: first-stage cooling, heating, second-stage cooling, and third-stage cooling. Each phase progresses to the next upon completion of the previous one. The average cooling rate of the first cooling stage of the post-weld heat treatment process is 10℃ / s, and the cooling end temperature is 100℃; in the heating stage of the post-weld heat treatment process, special equipment is used to heat the top surface, side surfaces and lower jaw of the rail head near the weld area of ​​the rail joint. The average temperature rise rate of the heating process is 30℃ / s, and the heating stage end temperature is 900℃; in the second cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface of the rail head. The starting temperature of the accelerated cooling is greater than 900℃, the average cooling rate of the accelerated cooling of the top surface of the rail head is 40℃ / s, and the end temperature of the accelerated cooling is 600℃; in the third cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface, side surfaces and lower jaw of the rail head. The starting temperature of the accelerated cooling is 600℃, the average cooling rate of the accelerated cooling of the top surface of the rail head is 20℃ / s, the average cooling rate of the accelerated cooling of the side surfaces and lower jaw of the rail head is 5℃ / s, and the end temperature of the accelerated cooling is 430℃. The longitudinal section hardness test was carried out at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was inspected in accordance with BS EN14587.The results show that the ratio of the internal hardness of the rail head near the fusion line area to the hardness of the rail base material at the same position in the high-strength rail head hardened pearlite rail flash weld formed by this method is 99%, and the area proportion of pearlite in the microstructure is ≥98%.

[0048] Example 3

[0049] The main chemical composition of the rails used in this example includes a C mass fraction of 0.80%, a Si mass fraction of 0.50%, a Mn mass fraction of 1.20%, a P mass fraction of no more than 0.020% for each of the S elements, a Cr mass fraction of no more than 0.30%, and a V mass fraction of no more than 0.01%. The minimum tensile strength at the gauge angle, 12.7 mm from the rail head tread and side surfaces, is 1302 MPa, and the hardness at a depth of 25 mm from the rail head outer profile surface is ≥ 389 HB. The welding process consists of two main steps: welding and post-weld heat treatment. The welding method is rail flash welding, and the welding process consists of four main stages: electrode clamping, electrical heating, pressurized upsetting, and rapid nodule removal. Throughout the welding process, the rail temperature on both sides, 0 mm to 25 mm from the end face of the rail to be welded, ranges from 900°C to 1650°C, and the duration is 150 seconds. The heating phase of the welding process primarily involves short-circuiting the rails while energized. The rails are heated using both the heat from the short-circuit resistance and the heat generated by the small lintel explosion between the liquid metal ends of the rails. The voltage during the heating phase is 375V, the average current is 600A, and the duration is 90s. During this heating phase, a 100kN pressure is applied to both ends of the rails, resulting in a rail consumption of 13mm. The rapid nodule removal phase of the welding process utilizes an integrated, contoured rail nodule removal mechanism. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, the time from the end of upsetting to the completion of nodule removal is 8s. Post-weld heat treatment is performed after welding. The post-weld heat treatment consists of four phases: first-stage cooling, heating, second-stage cooling, and third-stage cooling. Each phase progresses to the next upon completion of the previous one. The average cooling rate of the first cooling stage of the post-weld heat treatment process is 8°C / s, and the cooling end temperature is 75°C; in the heating stage of the post-weld heat treatment process, special equipment is used to heat the top surface, side surfaces and lower jaw of the rail head near the weld area of ​​the rail joint. The average temperature rise rate of the heating process is 15°C / s, and the heating stage end temperature is 1100°C; in the second cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface of the rail head. The starting temperature of the accelerated cooling is greater than 900°C, the average cooling rate of the accelerated cooling of the top surface of the rail head is 30°C / s, and the end temperature of the accelerated cooling is 650°C; in the third cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface, side surfaces and lower jaw of the rail head. The starting temperature of the accelerated cooling is 650°C, the average cooling rate of the accelerated cooling of the top surface of the rail head is 30°C / s, the average cooling rate of the accelerated cooling of the side surfaces and lower jaw of the rail head is 12°C / s, and the end temperature of the accelerated cooling is 460°C. The longitudinal section hardness test was carried out at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was inspected in accordance with BS EN14587.The results show that the ratio of the hardness of the rail head near the fusion line area to the hardness of the rail base material at the same position in the high-strength rail head hardened pearlite flash welded joint formed by this method is 98%, and the pearlite area in the microstructure accounts for ≥99%.

[0050] Comparative Example 1

[0051] The main chemical composition of the steel rails used in this comparative example is that the mass fraction of C is 0.81%, the mass fraction of Si is 0.56%, the mass fraction of Mn is 0.90%, the mass fractions of P and S do not exceed 0.020%, the mass fraction of Cr does not exceed 0.30%, and the mass fraction of V does not exceed 0.01%. The minimum tensile strength at the gauge angle 12.7mm away from the rail head tread and side surface is 1272MPa, and the hardness at a depth of 25mm from the outer surface of the rail head is ≥380HB. The two main processes are welding and post-weld heat treatment. The welding method is rail flash welding, and the welding process mainly consists of four stages: electrode clamping, electric heating, pressure forging, and rapid nodule removal. During the entire welding process, the temperature of the rails on both sides 0mm to 25mm away from the end face of the rail to be welded is 900℃ to 1650℃, and the duration is 250s. The heating phase of the welding process primarily involves short-circuiting the rails while energized. The rails are heated using both the heat from the short-circuit resistance and the heat generated by the small lintel explosion between the liquid metal ends of the rails. The voltage during the heating phase is 390V, the average current is 900A, and the duration is 150s. During this heating phase, a 10kN pressure is applied to both ends of the rails, resulting in a rail consumption of 25mm. The rapid nodule removal phase of the welding process utilizes an integrated, contoured rail nodule removal mechanism. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, a 20s delay is maintained from the end of upsetting to the completion of nodule removal. Post-weld heat treatment is performed after welding. Post-weld heat treatment consists of four phases: first-stage cooling, heating, second-stage cooling, and third-stage cooling, with each phase transitioning to the next. The average cooling rate of the first cooling stage of the post-weld heat treatment process is 2°C / s, and the cooling end temperature is 200°C; in the heating stage of the post-weld heat treatment process, special equipment is used to heat the top surface, side surfaces and lower jaw of the rail head near the weld area of ​​the rail joint. The average temperature rise rate of the heating process is 35°C / s, and the heating stage end temperature is 800°C; in the second cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface of the rail head. The starting temperature of the accelerated cooling is greater than 900°C, the average cooling rate of the accelerated cooling of the top surface of the rail head is 20°C / s, and the end temperature of the accelerated cooling is 500°C; in the third cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface, side surfaces and lower jaw of the rail head. The starting temperature of the accelerated cooling is 500°C, the average cooling rate of the accelerated cooling of the top surface of the rail head is 15°C / s, the average cooling rate of the accelerated cooling of the side surfaces and lower jaw of the rail head is 2°C / s, and the end temperature of the accelerated cooling is 550°C. The longitudinal section hardness test was carried out at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was inspected in accordance with BS EN14587.The results show that the ratio of the internal hardness of the rail head near the fusion line area to the hardness of the rail base material at the same position in the high-strength rail head hardened pearlite rail flash weld formed by this method is 85%, the area proportion of pearlite in the microstructure is ≥96%, and the joint has obvious collapse, which does not meet the requirements.

[0052] Comparative Example 2

[0053] The main chemical composition of the steel rails used in this comparative example includes a mass fraction of 0.84% ​​C, 0.60% Si, 1.15% Mn, 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 the gauge angle, 12.7 mm from 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 welding process consists of two main steps: welding and post-weld heat treatment. The welding method is rail flash welding, and the welding process mainly consists of four stages: electrode clamping, electric heating, pressurized forging, and rapid nodule removal. During the entire 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, is 900°C to 1650°C, and the duration is 90 seconds. The heating phase of the welding process primarily involves short-circuiting the rails while energized. The rails are heated using both the heat from the short-circuit resistance and the heat generated by the small lintel explosion between the liquid metal ends of the rails. The voltage during the heating phase is 300V, the average current is 450A, and the duration is 70s. During this heating phase, a pressure of 140kN is applied to both ends of the rails, resulting in a rail loss of 8mm to 20mm. The rapid nodule removal phase of the welding process utilizes an integrated, contoured rail nodule removal mechanism. To ensure joint quality and the effectiveness of subsequent post-weld heat treatment, the time from the end of upsetting to the completion of nodule removal is 3s. Post-weld heat treatment is performed after welding. Post-weld heat treatment consists of four stages: first-stage cooling, heating, second-stage cooling, and third-stage cooling. Each stage progresses to the next as each stage completes. The average cooling rate of the first cooling stage of the post-weld heat treatment process is 60℃ / s, and the cooling end temperature is 20℃; in the heating stage of the post-weld heat treatment process, special equipment is used to heat the top surface, side surfaces and lower jaw of the rail head near the weld area of ​​the rail joint. The average temperature rise rate of the heating process is 1℃ / s, and the heating stage end temperature is 1200℃; in the second cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface of the rail head. The starting temperature of the accelerated cooling is greater than 900℃, the average cooling rate of the accelerated cooling of the top surface of the rail head is 50℃ / s, and the end temperature of the accelerated cooling is 750℃; in the third cooling stage of the post-weld heat treatment process, special equipment is used to accelerate the cooling of the top surface, side surfaces and lower jaw of the rail head. The starting temperature of the accelerated cooling is 750℃, the average cooling rate of the accelerated cooling of the top surface of the rail head is 40℃ / s, the average cooling rate of the accelerated cooling of the side surfaces and lower jaw of the rail head is 25℃ / s, and the end temperature of the accelerated cooling is 400℃. The longitudinal section hardness test was carried out at 5mm and 25mm below the tread of the joint in accordance with AS1085.20 standard, and the microstructure of the joint was inspected in accordance with BS EN14587.The results show that the ratio of the internal hardness of the rail head near the fusion line area to the hardness of the rail base material at the same position in the high-strength rail head hardened pearlite flash welded joint formed by this method is 130%, the area proportion of pearlite in the microstructure is ≥90%, and the joint has abnormal martensite structure, which does not meet the requirements.

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

Claims

1. A method for welding and heat treatment of deep hardened rails, characterized in that: include: Flash welding of the rails includes: sequentially performing an electric heating stage and a pressurized 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 flash-welded rails are heat-treated, including: a first cooling stage, a heating stage, a second cooling stage, and a third cooling stage in sequence, wherein the first cooling stage has an end temperature of 25 to 100°C, the heating stage has an end temperature of 800 to 1100°C, the second cooling stage has a starting temperature greater than 900°C and an end temperature of 600 to 700°C, and the third cooling stage has a starting temperature of 600 to 700°C and an end temperature of 430 to 500°C.

2. The method according to claim 1, characterized in that: During the power-on heating stage, the opposing pressure applied to both ends of the steel rail to be welded is 20-130 kN, and the rail consumption is 8-20 mm.

3. The method according to claim 1, characterized in that The flash welding of the rails further comprises: a nodule pushing stage is performed after the pressurizing and upsetting stage, and the time from the end of the pressurizing and upsetting stage to the complete end of the nodule pushing 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 of ​​0 to 25 mm from the end face of the rails on both sides to be welded is 900 to 1650°C, and the duration is 100 to 200 seconds.

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

6. The method according to claim 1, characterized in that In 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 of the rail joint are heated, and the average heating rate is 2-30° C. / 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 at an accelerated rate, 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 rail head top surface, rail head side surface and rail head lower jaw are cooled at an accelerated rate, the average cooling rate of the rail head top surface is 20-35°C / s, and the average cooling rate of the rail head side surface and rail head lower jaw is 5-15°C / s.

9. The method according to claim 1, characterized in that: The rail to be welded is a high-strength rail head hardened pearlite rail. Among the main chemical components of the rail, the mass fraction of the C element is between 0.74% and 0.86%, the mass fraction of the Si element is between 0.10% and 0.60%, the mass fraction of the Mn element is between 0.75% and 1.25%, the mass fractions of the P element and the S element are both less than 0.020%, the mass fraction of the Cr element is less than 0.30%, and the mass fraction of the V element is less than 0.01%; the tensile strength at the gauge angle of the rail is at least 1172MPa, and the hardness at a depth of 25mm from the outer profile surface of the rail head is greater than or equal to 370HB.

10. A steel rail manufactured by the method according to any one of claims 1 to 9, characterized in that: The hardness of the inner region of the rail head near the weld zone of the rail is 95% to 110% of the hardness of the inner region of the rail head of the rail base material, and the pearlite area accounts for greater than or equal to 97% of the microstructure of the inner region of the rail head near the weld zone of the rail, wherein the inner region of the rail head is an area with a depth of 0 to 25 mm from the surface of the rail head.

Images