Method for post-weld heat treatment of dissimilar steel rails for field low temperature construction environments

Abstract

The application discloses a post-welding heat treatment method for dissimilar steel rail in field low-temperature construction environment, which comprises five stages: the surface temperature of the rail joint formed by welding is 700-900 DEG C, the rail joint is naturally cooled in the field low-temperature construction environment, the surface temperature of the rail joint is reduced to 400-450 DEG C, the surface temperature of the rail joint is reduced to 320-380 DEG C under the second cooling speed, the rail joint is heated in the whole section in the form of heat compensation, the surface of the rail joint is heated to 850-890 DEG C, the rail joint is cooled to 350-380 DEG C under the fourth cooling speed, and the rail joint is cooled to 180-220 DEG C under the fifth cooling speed. The application can improve the tread hardness of the rail reduced due to welding, avoid the abnormal martensite structure generated in the process of welding and post-welding heat treatment, improve the impact toughness of the rail joint, and ensure the service performance of the dissimilar rail joint and the railway operation safety.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, and in particular to a method for post-weld heat treatment of dissimilar rails used in low-temperature field construction environments. Background Technology

[0002] Currently, the carbon content of railway rails used both domestically and internationally is mainly concentrated between 0.7% and 1.1%, with a fully pearlitic microstructure or a microstructure consisting of pearlite plus a small amount of proeutectoid ferrite or proeutectoid cementite. These rails typically require a strength of no less than 880 MPa and good wear resistance. However, for harsh sections with special natural conditions such as cold regions and large annual and diurnal temperature variations, new requirements are placed on the impact toughness and resistance to contact fatigue damage of the rails. U71Mn hot-rolled rails, widely used on railway lines, have a U-shaped impact toughness of 25-30 J at room temperature (20-30℃), but this drops to only 5-8 J at -40℃, indicating a significant decrease in impact toughness. Under these circumstances, medium-low carbon hypoeutectoid rails with a carbon content of 0.50-0.65%, moderate strength and hardness, and higher impact toughness and better resistance to contact fatigue damage have emerged. However, similar to other pearlitic rails, these rails also suffer from problems such as poor impact toughness and low hardness across the entire weld joint after welding. Therefore, post-weld heat treatment of the rail joint becomes the most effective means of restoring the mechanical properties of the rail that have been reduced due to welding.

[0003] Conventional rail welding heat treatment normalizing equipment is bulky and cannot be used on railway construction sites. While the oxygen-acetylene flame normalizing equipment commonly used on railway construction sites can perform rail welding normalizing, the quality of flame heating is affected by the oxygen-acetylene flow ratio and the operator's skill level, making it impossible to quantitatively and precisely control the heating and cooling process of rail welding post-weld heat treatment. This results in unstable joint performance produced by flame normalizing. For rail welding and post-weld heat treatment operations in low-temperature outdoor environments, controlling the abnormal martensitic structure of rail joints caused by rapid cooling in low-temperature environments, as well as controlling joint hardness and impact toughness, becomes an urgent technical problem to be solved. Due to the low temperature in the field, rail joints are prone to fatigue damage and fracture during service due to the martensite formed during welding and post-weld heat treatment. At the same time, the performance regulation of rail joints after post-weld heat treatment in low-temperature environments is also a technical problem that needs to be solved. Especially when welding rails with different strength grades together, the welding of dissimilar rail joints and the subsequent synergistic improvement of microstructure and performance through post-weld heat treatment are issues that need to be considered. Considering that the welding quality of rails determines whether seamless tracks can withstand the test of railway operation, and even the safety of train operation, there is a need in the existing technology to improve the welding and post-weld heat treatment technologies for rails of different strength grades and materials.

[0004] Therefore, existing technologies still need improvement. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a post-weld heat treatment method for dissimilar rails used in low-temperature field construction environments, thereby resolving the technical issue that existing post-weld heat treatment methods for dissimilar rails in low-temperature field construction environments cannot meet the requirements.

[0006] To address the aforementioned technical problems, some embodiments of the present invention disclose a post-weld heat treatment method for dissimilar rails used in low-temperature field construction environments, comprising:

[0007] The first stage: The welded rail joints with a surface temperature of 700-900°C are naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the welded joints to 400-450°C.

[0008] Second stage: Reduce the surface temperature of the welded joint to 320-380℃ at the second cooling rate;

[0009] The third stage: The rail joint is heated across the entire cross section using thermal compensation, and the surface of the welded joint is heated to 850-890℃.

[0010] Fourth stage: Cool the rail joint to 350-380℃ at the fourth cooling rate;

[0011] Fifth stage: Cool the rail joint to 180-220°C at the fifth cooling rate.

[0012] In some embodiments,

[0013] The second cooling rate is 0.8–1.2 °C / s;

[0014] The fourth cooling rate is 2.0–4.0 °C / s;

[0015] The fifth cooling rate is 0.8–1.2 °C / s.

[0016] In some embodiments, the cooling rate of the first stage is 3.5–8.0 °C / s.

[0017] In some embodiments, a sixth stage is also included: placing the rail joint in a low-temperature outdoor environment for natural cooling treatment, allowing the joint to cool naturally to the ambient temperature.

[0018] In some embodiments, during the second, third, fourth, and fifth stages, the rail joint is placed inside the conformal temperature control device;

[0019] The conformal temperature control device is a split conformal temperature control device, which includes two insulated shells hinged together and multiple rows of small-sized ceramic heating elements arranged on the inner wall of the insulated shells. The two insulated shells form an inner cavity adapted to the welded joint of dissimilar steel rails.

[0020] In some embodiments, multiple rows of parallel circular track-type ceramic heating elements are uniformly fixed to the inner wall of the insulation shell. Furthermore, the number of circular track-type ceramic heating elements covering the rail head region is smaller, more numerous, and denser than the track-type ceramic heating elements covering the rail web and rail bottom regions.

[0021] In some embodiments, during the first stage, the ambient temperature of the outdoor low-temperature construction environment is 1–15°C.

[0022] In some embodiments, the rail joint is made using moving flash welding, with the upsetting amount maintained at 13.5-15.5 mm and a heat input of 7.0-9.3 MJ used during welding.

[0023] In some embodiments, the welded joint of dissimilar rails is formed by welding hypoeutectoid pearlitic rails and eutectoid pearlitic rails;

[0024] The hypoeutectoid pearlitic rail base material comprises: 0.50–0.65% C, 0.40–0.70% Si, 0.55–0.8% Mn, 0.20–0.40% Cr, 0.15–0.45% Cu, 0.05–0.25% Ni, 0.02–0.08% V, with the balance being Fe and unavoidable impurities;

[0025] The eutectoid pearlitic rail base material comprises: 0.73–0.82% C, 0.50–0.80% Si, 0.70–1.0% Mn, 0.30–0.50% Cr, 0.06–0.10% V, with the balance being Fe and unavoidable impurities.

[0026] In some embodiments, the hypoeutectoid pearlitic rail base material has a tensile strength of 1000-1200 MPa at room temperature, an elongation of 14.5-18.5%, a room temperature U-shaped impact energy of 30-50 J at the rail head, and a room temperature U-shaped impact energy of 20-30 J at the rail web and rail base.

[0027] The eutectoid pearlitic rail base material has a tensile strength of 1300-1380 MPa at room temperature, an elongation of 11.0-13.0%, a room temperature U-shaped impact energy of 12-16 J for the rail head, and a room temperature U-shaped impact energy of 10-14 J for the rail web and rail base.

[0028] The room temperature impact energy range of the rail head weld of dissimilar rail joints in the welded state is 15-19 J, and the room temperature impact energy range of the rail web and rail base weld is 8-13 J. By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0029] This invention provides a post-weld heat treatment method for dissimilar rails used in low-temperature field construction environments. Through comprehensive control of the rail welding process and post-weld heat treatment, it effectively improves the joint hardness and impact toughness, while avoiding the formation of martensitic abnormal structures in the heat-affected zone. The dissimilar rail welded joints obtained using this invention show no martensitic or other abnormal structures across the entire cross-section at room temperature (20–30°C), and the average hardness of the longitudinal section reaches 90–93% of the corresponding base material hardness. At room temperature, the average impact energy of the rail head weld in the normalized joint reaches 26–34 J, and the average impact energy of the rail web and rail base welds reaches 19–25 J. Under low-temperature testing conditions of -20°C, the average impact energy of the rail head weld in the normalized joint reaches 17–23 J, and the impact energy of the rail web and rail base welds ranges from 12–18 J, contributing to ensuring railway operation safety. This invention can improve the "saddle-shaped" wear of rail welded joints caused by low hardness in the welded area during rail service. There are no abnormal structures such as martensite in the heat-affected zone of rail welding, and the joint has good toughness, which helps to ensure the safety of railway operation. Attached Figure Description

[0030] 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.

[0031] Figure 1 This is a schematic diagram of the sampling location of the impact test specimen of the welded joint of a dissimilar rail for post-weld heat treatment in a low-temperature field construction environment, as disclosed in some embodiments of the present invention.

[0032] Figure 2 This is a schematic diagram of the hardness test location of the longitudinal section of the rail joint, which is disclosed in some embodiments of the present invention as a method for post-weld heat treatment of dissimilar rails used in low-temperature construction environments in the field.

[0033] Figure 3 This is a schematic diagram of the metallographic specimen cutting position for a method of post-weld heat treatment of dissimilar rails in low-temperature field construction environments disclosed in some embodiments of the present invention.

[0034] Figure 4This is a schematic diagram showing the distribution of electric heating elements at the rail head of a contour temperature control device for a method of post-weld heat treatment of dissimilar rails in low-temperature field construction environments, as disclosed in some embodiments of the present invention.

[0035] Figure 5 This is a schematic diagram of a contour-following temperature control device for a post-weld heat treatment method for dissimilar rails used in low-temperature field construction environments, as disclosed in some embodiments of the present invention.

[0036] Figure 6 The image shows the metallographic structure of the weld heat-affected zone in Example 1.

[0037] Figure 7 The image shows the metallographic structure of the weld heat-affected zone in Example 2.

[0038] Figure 8 The metallographic structure of the weld heat-affected zone in Comparative Example 1 is shown.

[0039] Figure 9 The metallographic structure of the weld heat-affected zone in Comparative Example 3 is shown.

[0040] Figure 10 The metallographic structure of the weld heat-affected zone in Comparative Example 4 is shown.

[0041] Figure 11 The image shows the metallographic structure of the weld heat-affected zone in Comparative Example 5.

[0042] Explanation of reference numerals in the attached figures:

[0043] Figure 2 In the diagram, points a and c represent the base material area of ​​the rail, point b represents the heat-affected zone of the welded joint, point d represents the rail head tread, and point e represents the center of the weld.

[0044] Figure 3 In the diagram, d represents the heat-affected zone, and c represents the weld.

[0045] Figure 4 In the diagram, A1 / A2 / B1 / B2 are terminal blocks, C is a circular track-type ceramic heating element at the rail web, D is a rotating shaft, E is a retaining ring, F is the outer casing of the device, G is an asbestos insulation layer, and H is the weld centerline of the device's geometric centerline corresponding to the weld joint of the rail.

[0046] Figure 5 In the diagram, A3 is the rail head tread heating area, B3 is the rail head side heating area, C3 is the rail head lower jaw heating area, D3 is the circular track-type ceramic heating element, and E3 is the rail joint rail head weld positioning line. Detailed Implementation

[0047] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0048] In the embodiments and comparative examples of the present invention, such as Figure 1 As shown, the impact toughness at the rail head, rail web, and rail base of the welded rail joint is the average value of the room temperature impact energy of the impact specimens at the rail head, rail web, and rail base of the welded rail joint. Specifically, the impact toughness at the rail head of the welded joint is the average impact energy of the corresponding specimens #1 to #4; the impact toughness at the rail web of the welded joint is the average impact energy of the corresponding specimens #5 to #8; and the impact toughness at the rail base of the welded joint is the average impact energy of the corresponding specimens #9 to #14. Figure 2 In the diagram, points a and c represent the base material area of ​​the rail, point b represents the heat-affected zone of the welded joint, point d represents the rail head tread, and point e represents the center of the weld. Figure 3 In the diagram, d represents the heat-affected zone, and c represents the weld.

[0049] It should be noted that the post-weld heat treatment device for rails involved in this invention is fixed with the center of the rail head weld (weld positioning line) as the boundary. For example... Figure 4 As shown, terminals A1 and A2 form a circuit and provide full-section controlled heating for the left half of the device (rail welded joint); terminals B1 and B2 form a circuit and provide full-section controlled heating for the right half of the device (rail welded joint).

[0050] It should be noted that the heating capacity (heating rate and heating temperature) of the left and right halves of the contouring device is the same during the heat treatment process. The ceramic heating elements in the rail head area of ​​the contouring device are more densely distributed and smaller in size, resulting in a higher heating temperature. In contrast, the ceramic heating elements in the rail waist and bottom areas of the contouring device are larger in size and sparser in distribution than in the rail head area, thus the heating temperature in the rail waist and bottom areas is slightly lower than that in the rail head area.

[0051] During rail welding, the brittle martensite structure formed in the weld and heat-affected zone directly affects the service life of the rail and can even endanger railway safety. In rail welding production, improper welding processes and post-weld cooling control often lead to the formation of large-sized martensite in the heat-affected zone. The formation of large-sized martensite inevitably involves rapid expansion of the local volume, resulting in microcracks within the martensite. These microcracks directly affect the service life of the rail joint and can even endanger railway operation safety. It should be noted that the reheating austenitization process accompanying post-weld heat treatment can eliminate the martensite formed during welding, but it cannot eliminate the microcracks within the martensite. That is, once large-sized martensite forms, its harmful effects on fatigue fracture and impact toughness of the rail joint cannot be completely removed by subsequent post-weld heat treatment. Therefore, to ensure the service performance of welded rail joints, it is necessary to avoid the formation of harmful martensite structures during rail welding and post-weld heat treatment. Currently, my country's existing railway rail welding standard TB / T 1632.2-2014 stipulates that the microstructure of rail joint welds and heat-affected zones should be mainly pearlite, with a small amount of ferrite allowed, but harmful structures such as martensite or bainite should not be present. Welding ash spots are another major cause of drop hammer, fatigue, and tensile fractures in rail joints.

[0052] During rail welding, it is crucial to strictly control the welding heat input to prevent excessively low heat input from causing rapid post-weld cooling and the formation of martensitic structures. This is especially important in low-temperature outdoor construction environments, where the cooling rate of the welded rail is often too rapid (far exceeding the critical cooling rate for martensitic transformation). Without post-weld cooling control, harmful martensitic structures will form inside the joint. Therefore, in low-temperature outdoor construction environments, a high heat input is typically required for rail welding to prevent the formation of martensitic structures due to excessively rapid cooling. Simultaneously, performance control of welded rail joints also requires appropriate upsetting to effectively eliminate potential weld defects such as weld ash spots and slag inclusions, reducing their impact on the mechanical properties of the rail joint. Compared to the base metal, the mechanical properties of rail joints inevitably decline to varying degrees due to the flash welding thermal cycle. Currently, post-weld heat treatment is the most effective means of improving the microstructure and mechanical properties of rail joints. Post-weld heat treatment significantly affects the joint's impact toughness and hardness. In addition, it should be noted that the high-temperature dwell time after rail welding can be controlled by adjusting the heat input. Generally, a higher welding heat input is accompanied by a significant extension of the high-temperature dwell time.

[0053] Some embodiments of the present invention disclose a post-weld heat treatment method for dissimilar rails used in low-temperature field construction environments, comprising the following steps:

[0054] Flash welding of dissimilar rails was carried out using a welding upsetting amount of 13.5–15.5 mm and a welding heat input of 7.0–9.3 MJ.

[0055] The welded rail joints with a surface temperature of 700-900℃ are naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the welded joints to 400-450℃. The cooling rate during this stage is 3.5-8.0℃ / s.

[0056] The rail profile temperature control device is used to slowly cool the rail joint in the profile temperature control device by means of heat compensation. The cooling rate in this stage is 0.8 to 1.2℃ / s, so that the surface temperature of the welded joint is reduced to 320 to 380℃.

[0057] The rail joint is heated across its entire cross-section using a heat-compensated method within the conformal temperature control device. After the surface of the welded joint is heated to 850–890°C, a cooling mode is initiated, causing the rail joint to cool to 350–380°C at a cooling rate of 2.0–4.0°C / s. Subsequently, the rail joint is cooled to 180–220°C at a cooling rate of 0.8–1.2°C / s, thereby completing the heat treatment of the welded joint.

[0058] Remove the contour-following temperature control device and place the rail joint in a low-temperature outdoor environment for natural cooling, allowing the joint to cool naturally to the ambient temperature.

[0059] This invention utilizes a mobile flash welding machine for rails, employing a welding upsetting depth of 13.5-15.5 mm and a heat input of 7.0-9.3 MJ to perform flash welding of dissimilar rails. If the upsetting depth is less than 13.5 mm, large weld ash spots and non-metallic inclusions may not be removed in time, reducing the weld's impact toughness. If the upsetting depth is greater than 15.5 mm, excessive high-temperature metal may be removed, forming a cold joint and reducing the weld's impact toughness. Controlling the welding heat input to 7.0-9.3 MJ ensures that the welded rail joint does not cool too quickly due to the low ambient temperature in low-temperature field construction environments, preventing the formation of martensite in the heat-affected zone of the welded rail and effectively avoiding the formation of large ash spot defects. Under low-temperature field construction conditions of 1-15℃, the rail joints cool down quickly after welding. When the welding heat input is below 7.0MJ, randomly distributed point-like martensite will appear in the heat-affected zone of the rail weld. When the welding heat input is above 9.3MJ, large-sized gray spots may appear at the weld, affecting the impact toughness and service safety of the joint.

[0060] To avoid the formation of harmful martensitic structures in the heat-affected zone (HAZ) during rail welding and post-weld heat treatment, cooling can be controlled artificially to keep the cooling rate during welding and post-weld heat treatment below the critical martensitic transformation rate of the rail steel. Alternatively, a cooling rate higher than the critical martensitic transformation rate can be used to control the final cooling temperature of the rapid cooling phase of welding and post-weld heat treatment above the Ms initiation temperature of the rail steel's martensitic transformation, followed by cooling to ambient temperature at a rate lower than the critical martensitic transformation rate. During rail welding and post-weld heat treatment, to improve the hardness and toughness of the welded area, accelerated cooling methods (such as using compressed air as a cooling medium) are typically employed to achieve a pearlitic structure with fine lamellar spacing in the weld HAZ.

[0061] Due to differences in hardenability, the critical cooling rate for martensitic transformation of the hypoeutectoid pearlitic rail steel involved in this invention is 1.8–2.5 °C / s, and the martensitic transformation initiation temperature is 255–300 °C. In contrast, the critical cooling rate for martensitic transformation of the eutectoid pearlitic rail steel involved in this invention is 1.3–1.7 °C / s, and the martensitic transformation initiation temperature is 210–250 °C. When improving the strength, hardness, and toughness of dissimilar rail joints through post-weld accelerated cooling, for the same performance improvement ratio, the required cooling rate / intensity for hypoeutectoid pearlitic rails is higher than that for eutectoid pearlitic rails.

[0062] When rail welding is carried out at room temperature (20-30℃), the rails cool naturally after welding (air cooling), and harmful martensite structures do not form in the heat-affected zone due to excessively rapid cooling. However, when working in low-temperature outdoor environments (1-15℃), the ambient temperature causes extremely rapid cooling during rail welding and post-weld heat treatment (cooling rates can reach 3.5-8.0℃ / s), creating conditions conducive to martensite formation. Therefore, when performing rail welding and post-weld heat treatment in low-temperature outdoor environments, special attention must be paid to the formation of abnormal martensite structures; that is, the rail welding and post-weld heat treatment processes must be strictly controlled.

[0063] This invention relates to a dissimilar rail welded joint formed by welding hypoeutectoid pearlitic steel rails and eutectoid pearlitic steel rails with a specification of 60 kg / m. The welded joint comprises a region ranging from 70 to 110 mm in length, including the weld seam and the heat-affected zone, with the weld seam located at the center of this region. In this invention, "room temperature or normal temperature" refers to a temperature ranging from 20 to 30°C, and "low-temperature field construction environment" refers to a temperature ranging from 1 to 15°C.

[0064] The hypoeutectoid pearlitic rail steel involved in this invention has a critical cooling rate for martensitic transformation of 1.8–2.5 °C / s and a martensitic transformation initiation temperature of 255–300 °C. The eutectoid pearlitic rail steel involved has a critical cooling rate for martensitic transformation of 1.3–1.7 °C / s and a martensitic transformation initiation temperature of 210–250 °C. For the post-weld heat treatment of dissimilar rail welded joints composed of hypoeutectoid pearlitic and eutectoid pearlitic rails, to improve the mechanical properties of the weld heat-affected zone and avoid the formation of harmful martensite due to excessively rapid cooling during heat treatment, the rapid cooling stage is performed at a cooling rate higher than the critical cooling rate for martensitic transformation of the rail steel. Simultaneously, the final cooling temperature is controlled above the Ms temperature of the rail steel's martensitic transformation, i.e., the final cooling temperature of the post-weld heat treatment is controlled above 300 °C. Meanwhile, considering the unavoidable component segregation during the alloying process of rail steel and the welding construction in low-temperature outdoor environments, in order to avoid the generation of martensite during the post-weld heat treatment, the final cooling temperature of the rapid cooling stage of the post-weld heat treatment of rail steel is controlled above 50°C of the martensite transformation Ms temperature of rail steel.

[0065] It should be noted that post-weld heat treatment of rails is a heat treatment process without heat preservation. Once the rail joint is heated to the set temperature, the heating process ends, and the cooling phase begins immediately. Compared to the rail web and rail base, the rail head, due to its greater thickness, exhibits a significant heating lag during heat treatment. When using a traditional medium-frequency induction normalizing unit for post-weld heat treatment of rail welded joints, the rail head temperature is significantly lower than that of the rail web and rail base when they are heated to the set temperature. To achieve a matching of impact toughness between the rail head and the rail web and rail base of the rail welded joint, the heating temperature of the rail welded joint area needs to be appropriately increased, ensuring sufficient austenitization of the rail head area without causing a decrease in the mechanical properties of the rail head area due to overheating. In this invention, by rationally arranging the size, number, and distribution distance of the ceramic heating elements embedded in the split-type device, the temperature difference between the rail head and the rail web and rail base areas is eliminated, allowing the rail head, rail web, and rail base of the rail joint to reach the same heating temperature at the same time.

[0066] In this invention, the normalizing heat treatment typically refers to a process where the metal workpiece is heated to 30-50°C above Ac3 (the final temperature at which ferrite transforms into austenite during heating) using conventional methods, held at that temperature for a period of time, then removed from the furnace and allowed to cool naturally in air, or by spraying, or by spraying compressed air. However, the post-weld normalizing heat treatment of rail joints differs from the heat treatment process typically used for small-sized workpieces. Because the length of the welded rail sample can reach hundreds of meters, it is impossible to hold the welded rail joint at the target temperature (above the austenitizing temperature) for an extended period after reaching the target temperature. It should be noted that due to differences in heat conduction and surface energy loss, the core temperature of the rail joint is typically more than 50°C higher than the surface temperature during normalizing. Furthermore, considering the coarsening of austenite grains and the resulting deterioration in joint performance caused by excessively high normalizing temperatures, the preferred normalizing temperature in this invention is 850-890°C.

[0067] In this invention, to avoid the formation of martensite after rail welding in low-temperature field construction environments, after the rail welding protrusion is completed and the temperature drops to 400-450℃, a split-type conformal temperature control device is used to fully cover the rail head, web, and base of the rail joint to slow down the post-weld cooling rate. Simultaneously, within the split-type device, thermal compensation is used to cool the rail joint to 320-380℃ at a rate of 0.8-1.2℃ / s, followed by subsequent heat treatment. It should be noted that thermal compensation is achieved using embedded ceramic heating elements within the split-type device to regulate the cooling rate at this stage. If the cooling rate is below 0.8℃ / s, the excessively slow cooling will take too long and affect subsequent rail welding production. If the cooling rate is above 1.2℃ / s, since the critical cooling rate for martensitic transformation of rail steel is 1.3℃ / s, an excessively high cooling rate may lead to the formation of martensite during the continuous cooling process after welding, affecting the service safety of the rail joint. Therefore, in this invention, during the post-flash welding cooling stage of the rail joint, the joint is cooled at a rate of 0.8–1.2 °C / s using a heat-compensated method in a split-type device to prevent the formation of martensite in the heat-affected zone of the rail weld. In the subsequent heat treatment process, the rail joint surface is heated to 850–890 °C in the split-type device. Then, a cooling mode is initiated, cooling the rail joint to 350–380 °C in the device at a rate of 2.0–4.0 °C / s, followed by further cooling to 180–220 °C at a rate of 0.8–1.2 °C / s, thus completing the heat treatment of the welded joint. After heat treatment, the contour-following temperature control device is removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing the joint to cool naturally to ambient temperature. In this invention, the cooling rate of the rail joint after normalizing is controlled at 2.0 to 4.0 °C / s, which is higher than the critical cooling rate of the rail steel for martensitic transformation of 1.8 to 2.5 °C / s. This is to refine the pearlite lamellar spacing by accelerating the cooling of the supercooled austenite and improve the mechanical properties of the pearlite structure in the weld area.

[0068] In this invention, the final cooling temperature after the rapid cooling stage is 350–380°C, which is more than 50°C higher than the martensitic transformation start temperature of the rail steel (255–300°C). This helps to avoid the formation of martensitic structure during the rapid cooling process of heat treatment. After this cooling stage, the rail joint is cooled to 180–220°C at a cooling rate of 0.8–1.2°C / s using a contour-following temperature control device for thermal compensation. Subsequently, the power supply to the split-type device is stopped and the device is removed, allowing the joint to cool to the ambient temperature of 1–15°C under the influence of the outdoor environment.

[0069] It should be noted that when the surface temperature of the rail joint reaches 350–380℃, the core of the rail joint is more than 50℃ higher than the surface, meaning the core temperature is above 400–430℃. At this point, both the surface and core of the rail joint have completed the pearlitic transformation. Subsequent cooling of the rail joint at a rate lower than the critical cooling rate for martensitic transformation will not produce martensitic structure.

[0070] It should be noted that the process of reducing the joint surface temperature from 400-450℃ to 320-380℃ after the rail welding and pushing-out process, and the process of reducing the temperature from 850-890℃ to 180-220℃ after normalizing, are both achieved through thermal compensation within the contour-following temperature control device. This device contains densely arranged small, circular, track-type ceramic heating elements that fit closely to the rail surface, achieving excellent heat conduction. The combined action of multiple rows of parallel circular, track-type ceramic heating elements enables the thermal compensation process of the rail joint.

[0071] Figure 4 In this diagram, A3 is the rail head tread heating area, B3 is the rail head side heating area, C3 is the rail head lower jaw heating area, D3 is a circular tracked ceramic heating element, E3 is the rail joint rail head weld positioning line, A1 / A2 / B1 / B2 are terminals, C is the circular tracked ceramic heating element at the rail web, D is the rotating shaft, E is the fixing shackle, F is the device housing, G is the asbestos insulation layer, and H is the device's geometric center line corresponding to the weld center line of the rail weld joint. It should be noted that the rail post-weld heat treatment device of this invention is fixed with the center of the rail head weld (weld positioning line) of the rail weld joint as the boundary. Terminals A1 and A2 form a circuit and provide full-section controlled heating for the left half of the device (rail weld joint); terminals B1 and B2 form a circuit and provide full-section controlled heating for the right half of the device (rail weld joint). It should be noted that the heating capacity (heating rate and heating temperature) of the left and right halves of the contouring device is the same during heat treatment. The ceramic heating elements in the rail head area of ​​the contouring device are more densely distributed and smaller in size, resulting in a higher heating temperature. Conversely, the ceramic heating elements in the rail web and rail bottom areas are larger and more sparsely distributed than in the rail head area. By rationally arranging the size, quantity, and distribution distance of the embedded ceramic heating elements in the split-type device, the temperature difference between the rail head, rail web, and rail bottom areas is eliminated, ensuring that the rail head, rail web, and rail bottom of the rail joint reach the same heating temperature at the same time.

[0072] Figure 5The layout of the heating areas for the rail head, rail web, and rail bottom in the illustrated split-type contour temperature control device is similar. Because the rail head is thicker and heat transfer is slower, the number of circular, track-type ceramic heating elements covering the rail head is greater, denser, and has a smaller diameter than those in the rail web and rail bottom areas, ensuring sufficient heating of the rail head portion of the rail joint. Furthermore, the size and density of the circular, track-type heating elements distributed on both sides of the split-type device are identical. By rationally arranging the size, number, and distribution distance of the embedded ceramic heating elements within the split-type device, the temperature difference between the rail head, rail web, and rail bottom areas is eliminated, allowing the rail head, rail web, and rail bottom of the rail joint to reach the same heating temperature at the same time.

[0073] like Figure 5 The illustrated split-type contour-following temperature control device boasts advantages such as compactness, flexibility, and low cost, facilitating on-site construction. It can be powered by a 380V diesel generator or 220V AC mains, with a rated power of 10kW. The device uses commercial LCD-style circular tracked ceramic heating elements as the heat source. The rail head area of ​​the split-type device uses circular tracked ceramic heating elements with a diameter of φ5mm and a thickness of 5mm, while the rail web and bottom areas use circular tracked ceramic heating elements with a diameter of φ8mm and a thickness of 5mm. Equipped with asbestos insulation and a steel structure shell, it forms a rail contour-following split-type heater, facilitating assembly and disassembly, and suitable for localized heating of rail welded joints. The actual dimensions of the heating device, as well as the specifications and distribution of the heaters, can be adjusted and modified according to the actual profile of the rail. In the device design, multiple rows of parallel, circular, track-type ceramic heating elements are uniformly fixed inside the device, which has a profile similar to a steel rail. This ensures the heating elements evenly cover and fully adhere to the rail surface, achieving good heat conduction during heating. This device is used to achieve thermal compensation and normalizing heating of the rail joint. During the experiment, a temperature controller was used to control the heating temperature. The operating temperature range of this split-type device is 400–1000℃, and the device can rotate a maximum of 180° around its axis.

[0074] This invention refers to the standard TB / T 1632.2-2014 "Rail Welding Part 2: Flash Welding" to machine rail joints into longitudinal section hardness test specimens, and performs longitudinal section Rockwell hardness testing on the joints at a position 5mm below the tread surface. The test points are symmetrically arranged to the left and right sides with the weld as the center, and the test point spacing is 5mm. The Rockwell hardness method is performed according to GB / T230.1-2009, using the HRC scale. Hp represents the average hardness of the rail base material, and Hj represents the average hardness of the joint. The position where the joint hardness is lower than 0.9Hp indicates the softening area.

[0075] Example 1

[0076] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled, with the rail base material having a tensile strength of 1000MPa, an elongation of 18.5%, a room temperature U-shaped impact energy of 50J for the rail head, and a room temperature U-shaped impact energy of 30J for the rail web and rail base. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.50% C, 0.40% Si, 0.55% Mn, 0.20% Cr, 0.15% Cu, 0.05% Ni, 0.02% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1300MPa, the elongation is 13.0%, the room temperature U-shaped impact energy of the rail head is 16J, and the room temperature U-shaped impact energy of the rail web and rail base is 14J. The chemical composition of rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, 0.06% V, with the balance being Fe and unavoidable impurities.

[0077] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 7.0 MJ. The actual weld upsetting depth was maintained at 13.5 mm. The welded rail joint, with a surface temperature of 700℃, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 450℃. [Further details are needed for accurate translation.] Figure 5 The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate during this stage is 1.2℃ / s, reducing the surface temperature of the welded joint to 380℃. The rail joint is heated across its entire cross-section using thermal compensation, raising the joint surface to 890℃. It is then cooled to 380℃ at a rate of 4.0℃ / s, followed by a further cooling to 220℃ at a rate of 1.2℃ / s, thus completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to the ambient temperature of 1℃. This completes the welding and post-weld heat treatment process for dissimilar rails.

[0078] according to Figure 1 The sampling location shown indicates that the rail joint obtained in this embodiment after post-weld heat treatment was machined into Charpy U-shaped impact specimens, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown conforms to GB / T13298-2015 "Methods for Examination of Microstructure of Metals".

[0079] Metallographic structure of rail joint metallographic specimens was examined by etching with 3% nitric acid alcohol solution and observing the metallographic structure of rail joints using a Leica MeF3 optical microscope.

[0080] The results show that for dissimilar rail normalized joints obtained by the post-weld heat treatment construction method of the present invention, such as Figure 6 As shown, no martensite structure was observed in the heat-affected zones on either side of the rail joint weld. Specifically, the weld microstructure consisted of pearlite and intergranular proeutectoid ferrite; the heat-affected zone on the hypoeutectoid rail side of the rail joint consisted of pearlite and a small amount of proeutectoid ferrite; and the heat-affected zone on the eutectoid rail side consisted entirely of pearlite. The average room temperature impact energy of the rail head weld after flash welding and air cooling (in the welded state) was 19 J, and the average room temperature impact energy of the welds at the rail web and rail base was 13 J. The average longitudinal section hardness of the normalized joint using this invention reached 90% of the hardness of the base material. At room temperature, the average impact energy of the rail head weld of the normalized joint reached 34 J, and the average impact energy of the rail web and rail base welds reached 25 J; under a low-temperature test condition of -20℃, the average impact energy of the rail head weld of the normalized joint reached 23 J, and the impact energy of the rail web and rail base welds ranged from 18 J, meeting the various indicators required for rail welded joints in low-temperature environments and contributing to ensuring railway operation safety.

[0081] Example 2

[0082] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled, with the tensile strength of the rail base material being 1200MPa, the elongation being 14.5%, the room temperature U-shaped impact energy of the rail head being 30J, and the room temperature U-shaped impact energy of the rail web and rail base being 20J. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.65% C, 0.70% Si, 0.80% Mn, 0.40% Cr, 0.45% Cu, 0.25% Ni, 0.08% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1380MPa, the elongation is 11.0%, the room temperature U-shaped impact energy of the rail head is 12J, and the room temperature U-shaped impact energy of the rail web and rail base is 10J. The chemical composition of rail steel that yields the desired microstructure and mechanical properties must meet the following conditions: 0.82% C, 0.80% Si, 1.0% Mn, 0.50% Cr, 0.10% V, with the balance being Fe and unavoidable impurities.

[0083] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 9.3 MJ. The actual weld upsetting depth was maintained at 15.5 mm. The welded rail joint, with a surface temperature of 900℃, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 400℃. [Further details are needed for accurate translation.] Figure 5 The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate during this stage is 0.8℃ / s, reducing the surface temperature of the welded joint to 320℃. The rail joint is then heated across its entire cross-section using thermal compensation, raising the joint surface to 850℃. The joint is then cooled to 350℃ at a rate of 2.0℃ / s, followed by a further cooling to 220℃ at a rate of 0.8℃ / s, thus completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to an ambient temperature of 15℃. This completes the welding and post-weld heat treatment process for dissimilar rails.

[0084] according to Figure 1 The sampling location shown indicates that the rail joint obtained in this embodiment after post-weld heat treatment was machined into Charpy U-shaped impact specimens, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown conforms to GB / T13298-2015 "Methods for Examination of Microstructure of Metals".

[0085] Metallographic structure of rail joint metallographic specimens was examined by etching with 3% nitric acid alcohol solution and observing the metallographic structure of rail joints using a Leica MeF3 optical microscope.

[0086] The results show that for dissimilar rail normalized joints obtained by the post-weld heat treatment construction method of the present invention, such as Figure 7As shown, no martensite structure was observed in the heat-affected zones on either side of the rail joint weld. Specifically, the weld microstructure consisted of pearlite and intergranular proeutectoid ferrite; the heat-affected zone on the hypoeutectoid rail side of the rail joint consisted of pearlite and a small amount of proeutectoid ferrite; and the heat-affected zone on the eutectoid rail side consisted entirely of pearlite. The average room temperature impact energy of the rail head weld after flash welding and air cooling (in the welded state) was 15 J, and the average room temperature impact energy of the welds at the rail web and rail base was 8 J. The average longitudinal section hardness of the normalized joint using this invention reached 93% of the hardness of the base material. At room temperature, the average impact energy of the rail head weld of the normalized joint reached 26 J, and the average impact energy of the rail web and rail base welds reached 19 J; under a low-temperature test condition of -20℃, the average impact energy of the rail head weld of the normalized joint reached 17 J, and the impact energy of the rail web and rail base welds ranged from 12 J, meeting the various indicators required for rail welded joints in low-temperature environments and contributing to ensuring railway operation safety.

[0087] Example 3

[0088] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled. The tensile strength of the rail base material was 1150MPa, the elongation was 17.0%, the room temperature U-shaped impact energy of the rail head was 45J, and the room temperature U-shaped impact energy of the rail web and rail base was 27J. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.62% C, 0.63% Si, 0.70% Mn, 0.35% Cr, 0.40% Cu, 0.22% Ni, 0.05% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1350MPa, the elongation is 12.0%, the room temperature U-shaped impact energy of the rail head is 14.5J, and the room temperature U-shaped impact energy of the rail web and rail base is 12.5J. The chemical composition of rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.78% C, 0.70% Si, 0.90% Mn, 0.40% Cr, 0.09% V, with the balance being Fe and unavoidable impurities.

[0089] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 8.8 MJ. The actual weld upsetting depth was maintained at 14.5 mm. The welded rail joint, with a surface temperature of 850°C, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 430°C. [Further details regarding the process are needed for accurate translation.] Figure 5The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate during this stage is 1.0℃ / s, reducing the surface temperature of the welded joint to 360℃. The rail joint is then heated across its entire cross-section using thermal compensation, raising the joint surface to 875℃. The joint is then cooled to 365℃ at a rate of 2.5℃ / s, followed by a further cooling to 210℃ at a rate of 1.0℃ / s, thus completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to an ambient temperature of 3℃. This completes the welding and post-weld heat treatment process for dissimilar rails.

[0090] according to Figure 1 The sampling location shown indicates that the rail joint obtained in this embodiment after post-weld heat treatment was machined into Charpy U-shaped impact specimens, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0091] The results show that for dissimilar rail normalized joints obtained by the post-weld heat treatment construction method of this invention, the metallographic structure test results are consistent with those of... Figure 6 and Figure 7 Consistent with the results, no martensite structure was observed in the heat-affected zones on either side of the rail joint weld. Specifically, the weld microstructure consisted of pearlite and intergranular proeutectoid ferrite; the heat-affected zone on the hypoeutectoid rail side of the rail joint consisted of pearlite and a small amount of proeutectoid ferrite; and the heat-affected zone on the eutectoid rail side consisted entirely of pearlite. The average room temperature impact energy of the rail head weld after flash welding and air cooling (in the welded state) was 17 J, and the average room temperature impact energy of the welds at the rail web and rail base was 11 J. The average longitudinal section hardness of the normalized joint using this invention reached 92% of the base metal hardness. At room temperature, the average impact energy of the rail head weld of the normalized joint reached 31 J, and the average impact energy of the rail web and rail base welds reached 21 J; under a low-temperature test condition of -20℃, the average impact energy of the rail head weld of the normalized joint reached 19 J, and the impact energy of the rail web and rail base welds ranged within 15 J, meeting the various indicators required for rail welded joints in low-temperature environments and contributing to ensuring railway operation safety.

[0092] Comparative Example 1

[0093] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled, with the tensile strength of the rail base material being 1200MPa, the elongation being 14.5%, the room temperature U-shaped impact energy of the rail head being 30J, and the room temperature U-shaped impact energy of the rail web and rail base being 20J. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.65% C, 0.70% Si, 0.80% Mn, 0.40% Cr, 0.45% Cu, 0.25% Ni, 0.08% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1380MPa, the elongation is 11.0%, the room temperature U-shaped impact energy of the rail head is 12J, and the room temperature U-shaped impact energy of the rail web and rail base is 10J. The chemical composition of rail steel that yields the desired microstructure and mechanical properties must meet the following conditions: 0.82% C, 0.80% Si, 1.0% Mn, 0.50% Cr, 0.10% V, with the balance being Fe and unavoidable impurities.

[0094] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 9.3 MJ. The actual weld upsetting depth was maintained at 15.5 mm. The welded rail joint, with a surface temperature of 900℃, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 400℃. [Further details are needed for accurate translation.] Figure 5 The split-type contour-following temperature control device shown performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate at this stage is 0.8℃ / s, reducing the surface temperature of the welded joint to 320℃. The rail joint is heated across its entire cross-section using thermal compensation, raising the joint surface to 850℃. Then, the joint is cooled to ambient temperature (15℃) at a rate of 2.0℃ / s, thus completing the welding and post-weld heat treatment process for dissimilar rails.

[0095] according to Figure 1 The sampling locations shown were used to machine the untreated rail joints obtained in this comparative example into Charpy U-shaped impact specimens, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0096] The results show that for rail joints obtained without using the post-weld heat treatment construction method of this invention, such as Figure 8 As shown, a small amount of martensite appears in the heat-affected zone on the hypoeutectoid rail side of the rail joint, while the amount of martensite in the heat-affected zone on the eutectoid rail side is significantly increased. The average room temperature impact energy of the rail head weld after flash welding and air cooling (in the as-welded state) is 16J, and the average room temperature impact energy of the weld at the rail web and rail base is 10J. Under the low-temperature test condition of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 17J, and the impact energy of the weld at the rail web and rail base is in the range of 13J. The results show that the weld impact energy is good, but brittle and hard martensite structure appears in the heat-affected zone of the rail weld on both sides of the weld, which is not conducive to railway operation safety.

[0097] Comparative Example 2

[0098] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled, with the rail base material having a tensile strength of 1000MPa, an elongation of 18.5%, a room temperature U-shaped impact energy of 50J for the rail head, and a room temperature U-shaped impact energy of 30J for the rail web and rail base. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.50% C, 0.40% Si, 0.55% Mn, 0.20% Cr, 0.15% Cu, 0.05% Ni, 0.02% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1300MPa, the elongation is 13.0%, the room temperature U-shaped impact energy of the rail head is 16J, and the room temperature U-shaped impact energy of the rail web and rail base is 14J. The chemical composition of rail steel that yields this microstructure and mechanical properties must meet the following conditions: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, 0.06% V, with the balance being Fe and unavoidable impurities.

[0099] Using a mobile flash welding machine, flash welding of rails was carried out with a heat input of 7.0 MJ. The actual weld upsetting amount was maintained at 13.5 mm. After the rails were welded, no heat treatment was applied to the joint; instead, the joint was allowed to cool naturally to ambient temperature in the low-temperature field construction environment. In other words, the welded rail joint with a surface temperature of 700℃ was allowed to cool naturally to 1℃ in the low-temperature field construction environment, thus completing the welding process of dissimilar rails.

[0100] according to Figure 1The sampling locations shown were used to machine Charpy U-shaped impact specimens from the post-weld heat-treated rail joints obtained in this comparative example, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0101] The results show that for rail normalized joints obtained without using the post-weld heat treatment construction method of this invention, the metallographic structure test results are similar to those of... Figure 8 Similarly, a significant amount of martensite was observed in the heat-affected zones on both sides of the rail joint weld, resulting in poor impact toughness. At room temperature, the average impact energy of the rail head weld in the normalized joint reached 18J, while the impact energy of the rail web and rail bottom welds ranged from 15J. Under low-temperature testing conditions of -20℃, the average impact energy of the rail head weld in the normalized joint reached 15J, while the impact energy of the rail web and rail bottom welds ranged from 10J. The presence of a large amount of martensite and the poor impact toughness of the joint are detrimental to railway operation safety.

[0102] Comparative Example 3

[0103] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled, with the rail base material having a tensile strength of 1000MPa, an elongation of 18.5%, a room temperature U-shaped impact energy of 50J for the rail head, and a room temperature U-shaped impact energy of 30J for the rail web and rail base. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.50% C, 0.40% Si, 0.55% Mn, 0.20% Cr, 0.15% Cu, 0.05% Ni, 0.02% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1300MPa, the elongation is 13.0%, the room temperature U-shaped impact energy of the rail head is 16J, and the room temperature U-shaped impact energy of the rail web and rail base is 14J. The chemical composition of rail steel that yields this microstructure and mechanical properties must meet the following conditions: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, 0.06% V, with the balance being Fe and unavoidable impurities.

[0104] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 7.0 MJ. The actual weld upsetting depth was maintained at 13.5 mm. The welded rail joint, with a surface temperature of 700℃, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 450℃. [Further details are needed for accurate translation.] Figure 5 The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate at this stage is 1.2℃ / s, reducing the surface temperature of the welded joint to 380℃. The rail joint is then heated across its entire cross-section using thermal compensation, raising the surface temperature to 890℃. The joint is then cooled to 240℃ at a rate of 4.0℃ / s, followed by a further cooling at 1.2℃ / s to 220℃, completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to the ambient temperature of 1℃. This completes the welding and post-weld heat treatment process for dissimilar rails.

[0105] according to Figure 1 The sampling locations shown were used to machine Charpy U-shaped impact specimens from the post-weld heat-treated rail joints obtained in this comparative example, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0106] The results show that for rail normalized joints obtained without using the post-weld heat treatment construction method of this invention, the metallographic structure test results are as follows: Figure 9A small amount of martensite appeared in the heat-affected zones on both sides of the rail joint weld. The average room temperature impact energy of the rail head weld after flash welding and air cooling (in the as-welded state) was 19 J, and the average room temperature impact energy of the welds at the rail web and rail base was 13 J. The average longitudinal section hardness of the normalized joint obtained using this comparative example reached 95% of the hardness of the base metal. Because the final cooling temperature of the rapid cooling stage of the post-weld heat treatment of this joint was 240℃, which is lower than the martensitic transformation start temperature of hypoeutectoid pearlitic rail steel (255-300℃) and within the martensitic transformation start temperature of eutectoid pearlitic rail steel (210-250℃), martensite formed in the heat-affected zones on both sides of the rail weld, resulting in poor impact toughness of the joint. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 18J, and the impact energy of the rail web and rail bottom welds ranges from 13J; under the low temperature test condition of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 14J, and the impact energy of the rail web and rail bottom welds ranges from 8J. The joint has poor impact toughness and the presence of martensitic structure, which is not conducive to railway operation safety.

[0107] Comparative Example 4

[0108] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled, with the rail base material having a tensile strength of 1000MPa, an elongation of 18.5%, a room temperature U-shaped impact energy of 50J for the rail head, and a room temperature U-shaped impact energy of 30J for the rail web and rail base. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.50% C, 0.40% Si, 0.55% Mn, 0.20% Cr, 0.15% Cu, 0.05% Ni, 0.02% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1300MPa, the elongation is 13.0%, the room temperature U-shaped impact energy of the rail head is 16J, and the room temperature U-shaped impact energy of the rail web and rail base is 14J. The chemical composition of rail steel that yields this microstructure and mechanical properties must meet the following conditions: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, 0.06% V, with the balance being Fe and unavoidable impurities.

[0109] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 7.0 MJ. The actual weld upsetting depth was maintained at 13.5 mm. The welded rail joint, with a surface temperature of 700℃, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 450℃. [Further details are needed for accurate translation.] Figure 5The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate at this stage is 1.2℃ / s, reducing the surface temperature of the welded joint to 380℃. The rail joint is then heated across its entire cross-section using thermal compensation, raising the surface temperature to 890℃. The joint is then cooled to 280℃ at a rate of 4.0℃ / s, followed by a further cooling at 1.2℃ / s to 220℃, completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to 1℃, thus completing the welding and post-weld heat treatment process for dissimilar rails.

[0110] according to Figure 1 The sampling locations shown were used to machine Charpy U-shaped impact specimens from the post-weld heat-treated rail joints obtained in this comparative example, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0111] The results show that for rail normalized joints obtained without using the post-weld heat treatment construction method of this invention, such as Figure 10 As shown in the metallographic microscope, a small amount of martensite structure appeared in the heat-affected zone of the rail joint. The average room temperature impact energy of the rail head weld after flash welding and air cooling (in the as-welded state) was 19 J, and the average room temperature impact energy of the weld at the rail web and rail base was 13 J. The average longitudinal section hardness of the normalized joint obtained using this comparative example reached 94% of the hardness of the base metal. Because the final cooling temperature of the rapid cooling stage of the post-weld heat treatment of this joint was 280℃, which is within the range of 255-300℃, higher than the martensitic transformation start temperature of 210-250℃ for hypoeutectoid pearlitic rail steel, a small amount of martensite structure was formed in the heat-affected zone on the hypoeutectoid pearlitic rail side of the rail weld. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 17J, and the impact energy of the rail web and rail bottom welds ranges from 13J. Under the low temperature test condition of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 12J, and the impact energy of the rail web and rail bottom welds ranges from 8J. The joint has poor impact toughness and the presence of martensitic structure, which is not conducive to railway operation safety.

[0112] Comparative Example 5

[0113] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled, with the rail base material having a tensile strength of 1000MPa, an elongation of 18.5%, a room temperature U-shaped impact energy of 50J for the rail head, and a room temperature U-shaped impact energy of 30J for the rail web and rail base. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.50% C, 0.40% Si, 0.55% Mn, 0.20% Cr, 0.15% Cu, 0.05% Ni, 0.02% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1300MPa, the elongation is 13.0%, the room temperature U-shaped impact energy of the rail head is 16J, and the room temperature U-shaped impact energy of the rail web and rail base is 14J. The chemical composition of rail steel that yields this microstructure and mechanical properties must meet the following conditions: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, 0.06% V, with the balance being Fe and unavoidable impurities.

[0114] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 12.0 MJ. The actual weld upsetting depth was maintained at 13.5 mm. The welded rail joint, with a surface temperature of 700℃, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 450℃. [Further details are needed for accurate translation.] Figure 5 The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate during this stage is 1.2℃ / s, reducing the surface temperature of the welded joint to 380℃. The rail joint is heated across its entire cross-section using thermal compensation, raising the joint surface to 890℃. It is then cooled to 380℃ at a rate of 4.0℃ / s, followed by a further cooling to 220℃ at a rate of 1.2℃ / s, thus completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to the ambient temperature of 1℃. This completes the welding and post-weld heat treatment process for dissimilar rails.

[0115] according to Figure 1 The sampling locations shown were used to machine Charpy U-shaped impact specimens from the post-weld heat-treated rail joints obtained in this comparative example, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0116] The results show that the metallographic structure of the dissimilar rail normalized joint obtained by the post-weld heat treatment construction method in this comparative example is similar to... Figure 6 The results were consistent, but burnt holes appeared in the heat-affected zone, see details below. Figure 11 Under a metallographic microscope, no martensite was observed in the heat-affected zone (HAZ) of the rail joint. Specifically, the weld microstructure consisted of pearlite and intergranular proeutectoid ferrite; the HAZ on the hypoeutectoid rail side of the rail joint consisted of pearlite and a small amount of proeutectoid ferrite; and the HAZ on the eutectoid rail side consisted entirely of pearlite. The average room temperature impact energy of the rail head weld after flash welding and air cooling (in the as-welded state) was 10 J, while the average room temperature impact energy of the welds at the rail web and rail base was 6 J. The average longitudinal section hardness of the normalized joint using this comparative example reached 90% of the base metal hardness. At room temperature, the average impact energy of the rail head weld in the normalized joint reached 14 J, and the impact energy of the rail web and rail base welds ranged from 11 J; under a low-temperature test condition of -20℃, the average impact energy of the rail head weld in the normalized joint reached 9 J, and the impact energy of the rail web and rail base welds ranged from 5 J. Due to excessive heat input during the flash welding process, burnt holes appeared in the heat-affected zone near the weld, which further led to a significant decrease in the impact performance of the rail joint, which is detrimental to railway operation safety.

[0117] Comparative Example 6

[0118] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled. The tensile strength of the rail base material was 1150MPa, the elongation was 17.0%, the room temperature U-shaped impact energy of the rail head was 45J, and the room temperature U-shaped impact energy of the rail web and rail base was 27J. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.62% C, 0.63% Si, 0.70% Mn, 0.35% Cr, 0.40% Cu, 0.22% Ni, 0.05% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1350MPa, the elongation is 12.0%, the room temperature U-shaped impact energy of the rail head is 14.5J, and the room temperature U-shaped impact energy of the rail web and rail base is 12.5J. The chemical composition of rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.78% C, 0.70% Si, 0.90% Mn, 0.40% Cr, 0.09% V, with the balance being Fe and unavoidable impurities.

[0119] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 8.8 MJ. The actual weld upsetting depth was maintained at 13.0 mm. The welded rail joint, with a surface temperature of 850℃, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 430℃. [Further details are needed for accurate translation.] Figure 5 The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate during this stage is 1.0℃ / s, reducing the surface temperature of the welded joint to 360℃. The rail joint is then heated across its entire cross-section using thermal compensation, raising the joint surface to 875℃. The joint is then cooled to 365℃ at a rate of 2.5℃ / s, followed by a further cooling to 210℃ at a rate of 1.0℃ / s, thus completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to an ambient temperature of 3℃. This completes the welding and post-weld heat treatment process for dissimilar rails.

[0120] according to Figure 1 The sampling locations shown were used to machine Charpy U-shaped impact specimens from the post-weld heat-treated rail joints obtained in this comparative example, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0121] The results show that: for dissimilar rail normalized joints obtained without using the post-weld heat treatment construction method of this invention and Figure 6 The results were completely consistent. Under a metallographic microscope, no martensite structure was observed in the heat-affected zone (HAZ) of the rail joint. Specifically, the weld microstructure consisted of pearlite and intergranular proeutectoid ferrite; the HAZ on the hypoeutectoid rail side of the rail joint consisted of pearlite and a small amount of proeutectoid ferrite; and the HAZ on the eutectoid rail side consisted entirely of pearlite. The average room temperature impact energy of the rail head weld after flash welding and subsequent air cooling (in the as-welded state) was 13 J, while the average room temperature impact energy of the welds at the rail web and rail base was 8 J. The average longitudinal section hardness of the normalized joint obtained using this comparative example reached 92% of the base metal hardness. At room temperature, the average impact energy of the rail head weld of the normalized joint reached 18 J, and the impact energy of the rail web and rail base welds ranged from 15 J; under a low-temperature test condition of -20℃, the average impact energy of the rail head weld of the normalized joint reached 14 J, and the impact energy of the rail web and rail base welds ranged from 11 J. Because the upsetting amount during the flash welding process is low, the weld ash spot defect cannot be removed in time and remains in the weld, which in turn affects the impact performance of the rail joint, causing a significant decrease in the impact performance of the rail joint, which is not conducive to railway operation safety.

[0122] Comparative Example 7

[0123] The room temperature (20-25℃) tensile and impact properties of hypoeutectoid pearlitic rail base material were controlled. The tensile strength of the rail base material was 1150MPa, the elongation was 17.0%, the room temperature U-shaped impact energy of the rail head was 45J, and the room temperature U-shaped impact energy of the rail web and rail base was 27J. The chemical composition of the rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.62% C, 0.63% Si, 0.70% Mn, 0.35% Cr, 0.40% Cu, 0.22% Ni, 0.05% V, with the balance being Fe and unavoidable impurities; the room temperature (20-25℃) tensile and impact properties of the eutectoid pearlitic rail base material must be controlled, wherein the tensile strength of the rail base material is 1350MPa, the elongation is 12.0%, the room temperature U-shaped impact energy of the rail head is 14.5J, and the room temperature U-shaped impact energy of the rail web and rail base is 12.5J. The chemical composition of rail steel to obtain this microstructure and mechanical properties must meet the following conditions: 0.78% C, 0.70% Si, 0.90% Mn, 0.40% Cr, 0.09% V, with the balance being Fe and unavoidable impurities.

[0124] Using a mobile flash welding machine for rails, flash welding of rails was carried out with a heat input of 8.8 MJ. The actual weld upsetting depth was maintained at 14.5 mm. The welded rail joint, with a surface temperature of 850°C, was then naturally cooled in a low-temperature field construction environment, reducing the surface temperature of the welded joint to 430°C. [Further details regarding the process are needed for accurate translation.] Figure 5 The illustrated split-type contour-following temperature control device performs thermal compensation on the rail head, web, and base of the rail joint. The cooling rate during this stage is 1.0℃ / s, reducing the surface temperature of the welded joint to 360℃. The rail joint is then heated across its entire cross-section using thermal compensation, raising the joint surface to 820℃. It is then cooled to 365℃ at a rate of 2.5℃ / s, followed by a further cooling to 210℃ at a rate of 1.0℃ / s, thus completing the heat treatment of the welded joint. The contour-following temperature control device is then removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, allowing it to cool naturally to an ambient temperature of 3℃. This completes the welding and post-weld heat treatment process for dissimilar rails.

[0125] according to Figure 1 The sampling locations shown were used to machine Charpy U-shaped impact specimens from the post-weld heat-treated rail joints obtained in this comparative example, with the weld located at the center of the specimen. Impact tests were conducted on the rail joint impact specimens using a SANS ZBC2000 impact testing machine at room temperature (20–30°C). (Refer to...) Figure 2-3 The sampling method shown is to conduct metallographic examination of rail joint metallographic samples according to GB / T13298-2015 "Metallic Microstructure Examination Method". The metallographic samples of rail joint are etched with 3% nitric acid alcohol solution, and the metallographic structure of rail joint is observed with a German Leica MeF3 optical microscope.

[0126] The results show that the metallographic structure of the dissimilar rail normalized joint obtained by the post-weld heat treatment construction method in this comparative example is similar to... Figure 6Consistent with the results, metallographic examination showed that no martensite was present in the heat-affected zone (HAZ) of the rail joint. Specifically, the weld microstructure consisted of pearlite and intergranular proeutectoid ferrite; the HAZ on the hypoeutectoid rail side of the rail joint consisted of pearlite and a small amount of proeutectoid ferrite; and the HAZ on the eutectoid rail side consisted entirely of pearlite. The average room temperature impact energy of the rail head weld after flash welding and subsequent air cooling (in the as-welded state) was 17 J, while the average room temperature impact energy of the welds at the rail web and rail base was 11 J. The average longitudinal section hardness of the normalized joint using this comparative example reached 90% of the base metal hardness. At room temperature, the average impact energy of the rail head weld in the normalized joint reached 22 J, and the impact energy of the rail web and rail base welds ranged from 17 J; under a low-temperature test condition of -20℃, the average impact energy of the rail head weld in the normalized joint reached 15 J, and the impact energy of the rail web and rail base welds ranged from 10 J. Because the heating temperature was too low during the post-weld heat treatment of the joint, the austenitization process of the joint was incomplete. The mechanical properties of the rail normalized joint were not significantly improved compared with the joint in the welded state. In other words, the rail joint that was heat treated at this normalizing temperature (820℃) is not conducive to railway operation safety.

[0127] Comparative Examples 1-3 and 1-7 show that the welding process provided by this invention can effectively reduce the probability of welding ash spots and avoid the formation of martensitic structures in the heat-affected zone of the rail joint. The welding method of this invention can prevent the formation of harmful martensitic structures in the heat-affected zone of the joint. The average hardness of the normalized rail joint at room temperature (20-30℃) reaches 90-93% of the hardness of the base material. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 26-34 J, and the average impact energy of the rail web and rail bottom welds reaches 19-25 J; under low-temperature testing conditions of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 17-23 J, and the impact energy of the rail web and rail bottom welds ranges from 12-18 J, which helps to ensure railway operation safety.

[0128] The embodiments of this disclosure have now been described in detail. To avoid obscuring the concept of this disclosure, some details known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0129] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner.

Claims

1. A method for post-weld heat treatment of dissimilar steel rails used in low-temperature field construction environments, characterized in that, include: The first stage: The welded rail joints with a surface temperature of 700-900°C are naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the welded joints to 400-450°C. Second stage: Reduce the surface temperature of the welded joint to 320-380℃ at the second cooling rate; The third stage: The rail joint is heated across the entire cross section using thermal compensation, and the surface of the welded joint is heated to 850-890℃. Fourth stage: Cool the rail joint to 350-380℃ at the fourth cooling rate; Fifth stage: Cool the rail joint to 180-220°C at the fifth cooling rate; The cooling rate in the first stage is 3.5–8.0 °C / s; The second cooling rate is 0.8–1.2 °C / s; The fourth cooling rate is 2.0–4.0 °C / s; The fifth cooling rate is 0.8–1.2 °C / s; The welded joint of dissimilar steel rails is made by welding hypoeutectoid pearlitic steel rails and eutectoid pearlitic steel rails; The hypoeutectoid pearlitic rail base material comprises: 0.50~0.65% C, 0.40~0.70% Si, 0.55~0.8% Mn, 0.20~0.40% Cr, 0.15~0.45% Cu, 0.05~0.25% Ni, 0.02~0.08% V, with the balance being Fe and unavoidable impurities; The eutectoid pearlitic rail base material comprises: 0.73~0.82% C, 0.50~0.80% Si, 0.70~1.0% Mn, 0.30~0.50% Cr, 0.06~0.10% V, with the balance being Fe and unavoidable impurities.

2. The method for post-weld heat treatment of dissimilar rails used in low-temperature field construction environments according to claim 1, characterized in that, It also includes a sixth stage: placing the rail joint in a low-temperature outdoor environment for natural cooling treatment, allowing the joint to cool naturally to the ambient temperature.

3. The method for post-weld heat treatment of dissimilar rails used in low-temperature field construction environments according to claim 1, characterized in that, During the second, third, fourth and fifth stages, the rail joints are placed inside the conformal temperature control device; The conformal temperature control device is a split conformal temperature control device, which includes two insulated shells hinged together and multiple rows of small-sized ceramic heating elements arranged on the inner wall of the insulated shells. The two insulated shells form an inner cavity adapted to the welded joint of dissimilar steel rails.

4. The method for post-weld heat treatment of dissimilar rails used in low-temperature field construction environments according to claim 3, characterized in that, Multiple rows of parallel circular track-type ceramic heating elements are uniformly fixed to the inner wall of the insulation shell. Furthermore, the number of circular track-type ceramic heating elements covering the rail head area is smaller, more numerous, and denser than the track-type ceramic heating elements covering the rail web and rail bottom areas.

5. The method for post-weld heat treatment of dissimilar rails used in low-temperature field construction environments according to claim 1, characterized in that, In the first stage, the ambient temperature for the outdoor low-temperature construction is 1–15°C.

6. The method for post-weld heat treatment of dissimilar rails used in low-temperature field construction environments according to claim 1, characterized in that, The rail joints are welded using moving flash welding. The upsetting amount is maintained at 13.5-15.5mm during welding, and the heat input is 7.0-9.3MJ.

7. The method for post-weld heat treatment of dissimilar rails used in low-temperature field construction environments according to claim 1, characterized in that, The hypoeutectoid pearlitic rail base material has a tensile strength of 1000~1200MPa at room temperature, an elongation of 14.5-18.5%, a room temperature U-shaped impact energy of 30~50J for the rail head, and a room temperature U-shaped impact energy of 20~30J for the rail web and rail base. The eutectoid pearlitic rail base material has a tensile strength of 1300~1380MPa at room temperature, an elongation of 11.0-13.0%, a room temperature U-shaped impact energy of 12~16J for the rail head, and a room temperature U-shaped impact energy of 10~14J for the rail web and rail base. The room temperature impact energy range of the rail head weld of dissimilar rail joints in the welded state is 15~19J, and the room temperature impact energy range of the rail web and rail bottom weld is 8~13J.

Images