A post-weld heat treatment method for rails in a low-temperature environment

Abstract

The present invention discloses a post-weld heat treatment method for rails in a low-temperature environment. The method comprises naturally cooling a dissimilar rail weld joint formed by welding, having a surface temperature of 920-1050°C, to reduce the surface temperature to 470-570°C; slowly cooling the joint with thermal compensation using a contoured temperature control device, reducing the surface temperature of the weld joint to 340-390°C at a second cooling rate; heating the entire cross-section of the rail joint within the contoured temperature control device with thermal compensation, heating the weld joint surface to 910-940°C; cooling the rail joint to 385-420°C at a fourth cooling rate, and finally cooling the rail joint to 150-170°C at a fifth cooling rate. This method can improve the tread hardness of the rail, which is reduced by welding, and avoid the formation of abnormal martensitic structures during welding and post-weld heat treatment. It also improves the impact toughness of the rail joint, ensuring the service performance of the dissimilar rail weld joint and railway operation safety.

Description

Technical Field

[0001] The present invention relates to the technical field of rail welding, and in particular to a post-weld heat treatment method for rails in a low-temperature environment. Background Art

[0002] At present, the carbon content of railway rails at home and abroad is mainly concentrated in the range of 0.7-1.1%, with a full pearlite structure or a structure of pearlite + a small amount of proeutectoid ferrite or proeutectoid cementite. The rail strength is usually required to be no less than 880MPa and have good wear resistance. Compared with eutectoid rails, hypereutectoid rails have higher strength, hardness and wear resistance due to their higher carbon content, but the toughness and ductility of the rails are significantly lower than those of eutectoid rails. Similar to other pearlite rails, this type of rail also has problems in welding applications, such as poor impact toughness and low hardness of the full cross-section of the joint after welding. Therefore, post-weld heat treatment of the rail joints has become the most effective means to restore the mechanical properties of the rails that have been reduced by welding.

[0003] Conventional rail post-weld heat treatment (PWHT) normalizing equipment is bulky and impractical for use at railway construction sites. While the oxygen-acetylene flame normalizing equipment commonly used at railway construction sites can perform PWHT, its flame heating quality is affected by the oxygen-acetylene flow ratio and the operator's skill level. This makes it difficult to precisely and quantitatively control the heating and cooling processes during PWHT, leading to unstable joint performance during flame normalizing. When performing rail welding and PWHT operations in low-temperature environments, controlling the abnormal martensite structure in rail joints caused by rapid cooling at low temperatures, as well as controlling joint hardness and impact toughness, poses a pressing technical challenge. Due to the low ambient temperatures, rail joints are susceptible to fatigue damage and fracture during service due to the martensite formed during welding and PWHT. Furthermore, controlling the PWHT performance of rail joints in low-temperature environments is a critical technical challenge. In particular, when welding rails of different strength grades together, the welding of these dissimilar rail joints and the subsequent PWHT to achieve synergistic improvements in microstructure and performance require consideration. Considering that the welding quality of rails determines whether seamless lines can withstand the test of railway operation and even the driving safety, there is a need in the existing technology to improve the welding and post-weld heat treatment technology of rails with different strength grades and different materials.

[0004] Based on this, the existing technology still needs to be improved. Summary of the Invention

[0005] To solve the above technical problems, an embodiment of the present invention proposes a post-weld heat treatment method for rails in a low-temperature environment to solve the technical problems existing in the prior art in welding and post-weld heat treatment of rails of different strength grades and materials.

[0006] To solve the above technical problems, some embodiments of the present invention disclose a method for post-weld heat treatment of rails in a low-temperature environment, comprising:

[0007] The first stage: The dissimilar rail welded joints with a surface temperature of 920-1050°C are naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the welded joints to 470-570°C.

[0008] The second stage: the rail joint is slowly cooled in the temperature control device in a heat-compensated manner, and the surface temperature of the welded joint is reduced to 340-390°C at the second cooling rate;

[0009] The third stage: heating the entire cross-section of the rail joint in a thermal compensation manner in the profiling temperature control device, heating the surface of the welded joint to 910-940°C;

[0010] The fourth stage: cool the rail joint to 385-420℃ at the fourth cooling rate.

[0011] The fifth stage: cooling the rail joint to 150-170° C. at the fifth cooling rate.

[0012] In some embodiments, the second cooling rate is 1.0-2.0°C / s;

[0013] The fourth cooling rate is 2.0-4.0°C / s;

[0014] The fifth cooling rate is 0.6-0.9°C / s.

[0015] In some embodiments, in the first stage, the field construction environment temperature is -10 to 0°C;

[0016] And / or, the cooling rate in the first stage is 8.5-12.5°C / s.

[0017] In some embodiments, a sixth stage is further included: placing the rail joint in a low-temperature outdoor environment for natural cooling, so that the joint is naturally cooled to the ambient temperature.

[0018] In some embodiments, the contoured temperature control device is a split-type contoured temperature control device, comprising two hingedly connected thermal insulation shells and multiple rows of small-sized ceramic heating plates arranged on the inner walls of the thermal insulation shells, and the two thermal insulation shells form an inner cavity adapted to the welded joints of dissimilar rails.

[0019] In some embodiments, multiple rows of parallel arranged disc-shaped track-type ceramic electric heaters are evenly fixed on the inner wall of the thermal insulation shell, and the number of the disc-shaped track-type ceramic electric heaters covering the rail head area is smaller in size, more numerous, and denser than the track-type ceramic electric heaters covering the rail waist and rail bottom areas.

[0020] In some embodiments, in the third stage, the heating temperature of the rail waist and rail bottom in the contoured temperature control device is 20-25° C. higher than the heating temperature of the rail head.

[0021] In some embodiments, the rail joint is welded using moving flash welding, with the upset amount maintained at 11.0-14.0 mm and a heat input of 10.0-13.0 MJ during welding.

[0022] In some embodiments, the dissimilar rail weld joint is formed by welding a eutectoid pearlite rail and a hypereutectoid pearlite rail;

[0023] The eutectoid pearlite 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, and the balance is Fe and unavoidable impurities;

[0024] The hypereutectoid pearlite rail base material contains: 0.90-0.99% C, 0.94-1.02% Si, 0.48-0.56% Mn, 0.22-0.25% Cr, 0.06-0.10% V, and the balance is Fe and unavoidable impurities.

[0025] In some embodiments, the tensile strength of the eutectoid pearlite rail base material at room temperature is 1300-1380 MPa, and the elongation is 11.0-13.0%; the room temperature U-shaped impact energy of the rail head is 12-16 J, and the room temperature U-shaped impact energy of the rail waist and rail bottom is in the range of 10-14 J;

[0026] The tensile strength of the hypereutectoid pearlite rail base material at room temperature is 1400-1450 MPa, and the elongation is 8.8-11.2%. The room temperature U-shaped impact energy of the rail head is 10-14 J, and the room temperature U-shaped impact energy of the rail waist and rail bottom is in the range of 9-12 J.

[0027] The room temperature impact energy of the rail head weld of the dissimilar rail joint in the welded state ranges from 8 to 12 J, and the room temperature impact energy of the rail waist and rail bottom welds ranges from 6 to 9 J.

[0028] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0029] The present invention provides a post-weld heat treatment method for rails in a low-temperature environment, which can effectively improve the hardness and impact toughness of the joint, while avoiding the formation of abnormal martensite structures in the heat-affected zone of the joint. The dissimilar rail welded joint obtained by the welding method of the present invention has no abnormal structures such as martensite in the entire cross-section at room temperature (20-30°C), and the average hardness of the longitudinal section of the joint reaches 91-93% of the hardness of the corresponding parent material. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 14-19J, and the average impact energy of the rail waist and rail bottom welds reaches 11-15J; under low-temperature test conditions of -20°C, the average impact energy of the rail head weld of the normalized joint reaches 11-16J, and the impact energy of the rail waist and rail bottom welds ranges from 9-13J, which helps to ensure the safety of railway operation. The present invention can improve the tread hardness of the rails reduced by welding, and avoid the abnormal martensite structure generated by welding and post-weld heat treatment processes. At the same time, it can also improve the impact toughness of the rail joint, ensuring the service performance of the dissimilar rail welded joint and the safety of railway operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 A schematic diagram of the sampling positions of impact test specimens for rail weld joints in a method for post-weld heat treatment of rails in a low-temperature environment disclosed in some embodiments of the present invention;

[0032] Figure 2 A schematic diagram of a hardness inspection position of a longitudinal section of a rail joint in a method for post-weld heat treatment of a rail in a low-temperature environment disclosed in some embodiments of the present invention;

[0033] Figure 3 A schematic diagram of the location for cutting metallographic samples in a method for post-weld heat treatment of rails in a low-temperature environment disclosed in some embodiments of the present invention;

[0034] Figure 4 A schematic diagram of the distribution of electric heating plates at the rail head portion of a contour temperature control device for a post-weld heat treatment method for a low-temperature rail according to some embodiments of the present invention;

[0035] Figure 5 A schematic structural diagram of a contour-based temperature control device for a post-weld heat treatment method for rails in a low-temperature environment disclosed in some embodiments of the present invention;

[0036] Figure 6 This is the metallographic structure diagram of the welding heat affected zone of Example 1;

[0037] Figure 7 This is the metallographic structure diagram of the welding heat affected zone of Example 2;

[0038] Figure 8 This is the metallographic structure diagram of the welding heat affected zone of Comparative Example 1;

[0039] Figure 9 This is the metallographic structure diagram of the welding heat affected zone of Comparative Example 3;

[0040] Figure 10 This is the metallographic structure diagram of the heat-affected zone of welding of Comparative Example 4;

[0041] Figure 11 This is the metallographic structure diagram of the heat-affected zone of welding of Comparative Example 5;

[0042] Figure 12 This is the metallographic structure diagram of the welding heat affected zone of comparative example 6.

[0043] Description of reference numerals:

[0044] Figure 2 In the figure, a and c are the rail base material areas, b is the heat affected zone of the weld joint, d is the rail head tread, and e is the weld center.

[0045] Figure 3 In the figure, d is the heat affected zone and c is the weld.

[0046] Figure 4 In the figure, A1 / A2 / B1 / B2 are terminal blocks, C is the circular crawler-type ceramic electric heater at the rail waist, D is the rotating shaft, E is the fixed clamping ring, F is the device casing, G is the asbestos insulation layer, and H is the geometric center line of the device corresponding to the weld center line of the rail weld joint.

[0047] Figure 5 In the figure, A3 is the rail head tread heating area, B3 is the rail head side heating area, C3 is the rail head jaw heating area, D3 is the circular crawler ceramic electric heater, and E3 is the rail joint rail head weld positioning line. DETAILED DESCRIPTION

[0048] The embodiments of the present disclosure are described in further detail below with reference to the accompanying drawings and examples.

[0049] In the examples and comparative examples of the present invention, Figure 1As shown in the figure, the impact toughness of the rail head, rail waist, and rail bottom of the rail welded joint is the average impact energy of the impact specimens at the rail head, rail waist, and rail bottom of the rail welded joint at room temperature. Among them, the impact toughness of the rail head of the welded joint is the average impact energy of the corresponding 1# to 4# specimens, the impact toughness of the rail waist of the welded joint is the average impact energy of the corresponding 5# to 8# specimens, and the impact toughness of the rail bottom of the welded joint is the average impact energy of the corresponding 9# to 14# specimens. Figure 2 In the figure, a and c are the rail base material areas, b is the heat affected zone of the weld joint, d is the rail head tread, and e is the weld center. Figure 3 In the figure, d is the heat affected zone and c is the weld.

[0050] It should be noted that if Figure 4 As shown, the rail post-weld heat treatment device of the present invention is fixed with the center of the weld seam of the rail head of the rail weld joint (weld seam positioning line) as the boundary. The A1 terminal and the A2 terminal form a circuit and perform full-section controlled heating on the left half of the device (rail weld joint); the B1 terminal and the B2 terminal form a circuit and perform full-section controlled heating on the right half of the device (rail weld joint). During the heat treatment process, the heating capacity (heating rate, heating temperature) of the left and right halves of the profiling device are the same. The ceramic electric heating plates in the rail head area of ​​the profiling device are more densely distributed and smaller in size, resulting in a higher heating temperature. However, the ceramic electric heating plates in the waist and rail base areas of the profiling device are larger in size and more sparsely distributed than in the rail head area of ​​the profiling device, resulting in a slightly lower heating temperature in the waist and rail base areas of the profiling device than in the rail head area of ​​the profiling device.

[0051] During rail welding, the brittle martensite structure produced in the weld and heat-affected zone is directly related to the service life of the rail and may even endanger driving safety. During rail welding production, large-scale martensite is often formed in the heat-affected zone due to improper welding technology and post-weld cooling control. The formation of large-scale martensite is inevitably accompanied by a rapid expansion of the volume of the local area, leading to the formation of microcracks within the martensite. These microcracks will directly affect the service life of the rail joint and even endanger railway operation safety. It should be noted that the reheating austenitization process accompanying the post-weld heat treatment of the rail can eliminate the martensite formed during welding, but it cannot eliminate the microcracks within the martensite. In other words, once large-scale martensite is formed, the damage it causes to the fatigue fracture and impact toughness of the rail joint cannot be completely removed by subsequent post-weld heat treatment. Therefore, in order to ensure the service performance of rail welded joints, it is necessary to avoid the formation of harmful martensite structure during rail welding and post-weld heat treatment. my country's current railway industry rail welding standard, TB / T 1632.2-2014, stipulates that the microstructure of rail joint welds and heat-affected zones should be primarily pearlite, with a small amount of ferrite permitted. Unfavorable microstructures such as martensite or bainite should be avoided. Welding speckling is another major cause of drop-weight, fatigue, and tensile fractures in rail joints.

[0052] During rail welding, the heat input must be strictly controlled to avoid rapid cooling of the joint after welding due to excessively low heat input, which can lead to the formation of martensitic structures. Especially in low-temperature field construction environments, the cooling rate of the rail after welding is too rapid (far exceeding the critical cooling rate for martensitic transformation of rail steel). Failure to control post-weld cooling will lead to the formation of harmful martensitic structures within the joint. Therefore, in low-temperature field construction environments, high heat input is usually required for rail welding to avoid the formation of martensitic structures due to the rapid cooling rate in the low-temperature construction environment.

[0053] It should be noted that to avoid welding defects such as gray spots and slag inclusions, low welding heat input is usually accompanied by a relatively low amount of upsetting, while high heat input is usually accompanied by a relatively high amount of upsetting to reduce the impact of welding defects on the mechanical properties of the rail joint. Compared with the parent material, the mechanical properties of the rail joint inevitably decline to varying degrees due to the thermal cycle of flash welding. Currently, post-weld heat treatment is the most effective means to improve the microstructure and mechanical properties of rail joints. Post-weld heat treatment of the joint will have a significant impact on the impact toughness, hardness, and other properties of the joint.

[0054] Some embodiments of the present invention disclose a method for post-weld heat treatment of rails in a low-temperature environment, comprising the following steps:

[0055] Flash welding of dissimilar rails is performed using a weld upset of 11.0-14.0 mm and a weld heat input of 10.0-13.0 MJ;

[0056] The rail welded joints, which had a surface temperature of 920-1050°C, were naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the welded joints by 470-570°C. The cooling rate during this stage was 8.5-12.5°C / s.

[0057] A rail profiling temperature control device is used to slowly cool the rail joint in a heat-compensated manner within the profiling temperature control device. The cooling rate in this stage is 1.0-2.0°C / s, reducing the surface temperature of the weld joint to 340-390°C.

[0058] The entire cross-section of the rail joint is heated in a thermally compensated manner in the profiling temperature control device. After the surface of the welded joint is heated to 910-940°C, a cooling mode is started to cool the rail joint to 385-420°C at a cooling rate of 2.0-4.0°C / s. Then, the rail joint is cooled to 150-170°C at a cooling rate of 0.6-0.9°C / s, thereby completing the heat treatment of the welded joint.

[0059] The contoured temperature control device is removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling, so that the joint is naturally cooled to the ambient temperature.

[0060] The present invention utilizes a mobile flash welder for rails, adopts a welding upset amount of 11.0-14.0mm, and a heat input of 10.0-13.0MJ to carry out flash welding of dissimilar rails. If the upset amount is lower than 11.0mm, it is easy to cause large-sized weld gray spots, welding non-metallic inclusions, etc. to not be discharged in time, reducing the impact toughness of the weld. If the welding upset amount is higher than 14.0mm, it is easy to cause excessive discharge of high-temperature metal, forming a cold joint, and reducing the impact toughness of the weld. The welding heat input is controlled at 10.0-13.0MJ in order to ensure that in a low-temperature field construction environment, the rail joint after welding will not cool too quickly due to the low ambient temperature, thereby avoiding the appearance of martensite in the heat-affected zone of the rail weld in the welded state, and at the same time effectively avoiding the formation of large-sized gray spot defects. Under low-temperature field construction conditions of -10 to 0°C, due to the rapid cooling of the rail joint after welding, when the welding heat input is lower than 10.0 MJ, randomly distributed point-like martensite will appear in the rail welding heat-affected zone; when the welding heat input is higher than 13.0 MJ, large-sized gray spots may appear at the weld, affecting the impact toughness and service safety of the joint.

[0061] To avoid the formation of harmful martensitic structure in the heat-affected zone (HAZ) during rail welding and post-weld heat treatment (PWHT), the cooling rate during welding and PWHT can be controlled manually to be lower than the critical cooling rate for martensitic transformation of the rail steel. Alternatively, the final cooling temperature during the rapid cooling phase of welding and PWHT can be controlled to be above the martensitic transformation Ms start temperature of the rail steel at a cooling rate higher than the critical cooling rate for martensitic transformation of the rail steel, and then the rail steel can be cooled to ambient temperature at a cooling rate lower than the critical cooling rate for martensitic transformation of the rail steel. During rail welding and PWHT, accelerated cooling (such as the injection of a cooling medium such as compressed air) is often used to improve the hardness and toughness of the weld area, so that the HAZ obtains a pearlite structure with finer interlamellar spacing. Furthermore, it should be noted that the high-temperature dwell time after rail welding can be controlled by adjusting the heat input. High welding heat input is generally accompanied by a significant increase in the high-temperature dwell time.

[0062] Due to differences in hardenability, the critical cooling rate for martensitic transformation of the eutectoid pearlite rail steel involved in the present invention is 1.3-1.7°C / s, and the martensitic transformation start temperature is 215-245°C. In contrast, the critical cooling rate for martensitic transformation of the hypereutectoid pearlite rail steel involved in the present invention is between 1.0-1.2°C / s, and the martensitic transformation start temperature is 190-210°C. When improving the strength, hardness, and toughness of dissimilar rail joints through accelerated post-weld cooling, the cooling rate / cooling intensity required for the eutectoid pearlite rail is higher than that required for the hypereutectoid pearlite rail, when the performance improvement ratio is the same.

[0063] When rail welding is performed at room temperature (20-30°C), the rails cool naturally with the environment after welding (air cooling), and the heat-affected zone of the rail weld will not form harmful martensite due to excessive cooling speed. However, when working in the field at low temperatures (-10-0°C), the ambient temperature causes the rails to cool extremely quickly during welding and post-weld heat treatment (the cooling rate can reach 8.5-12.5°C / s), creating conditions for the formation of martensite. Therefore, when performing rail welding and post-weld heat treatment in the field at low temperatures, special attention should be paid to the formation of abnormal martensite structure, that is, the rail welding and post-weld heat treatment processes should be strictly controlled.

[0064] The present invention forms a dissimilar rail weld joint by welding a 60 kg / m eutectoid pearlite rail to a hypereutectoid pearlite rail. The weld joint encompasses an area ranging from 70 to 110 mm in length, including the weld and heat-affected zone, with the center of this area defining the weld. In this invention, "room temperature or normal temperature" refers to a temperature between 20°C and 30°C, and "low-temperature field construction environment" refers to a temperature between -10°C and 0°C.

[0065] The critical cooling rate for martensitic transformation of the eutectoid pearlite rail steel involved in the present invention is 1.3-1.7°C / s, and the martensitic transformation start temperature is 215-245°C. The critical cooling rate for martensitic transformation of the hypereutectoid pearlite rail steel involved in the present invention is 1.0-1.2°C / s, and the martensitic transformation start temperature is 190-210°C. For the post-weld heat treatment of dissimilar rail welds composed of eutectoid pearlite and hypereutectoid pearlite 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 the heat treatment process, the rapid cooling stage is performed at a cooling rate higher than the critical cooling rate for martensitic transformation of the rail steel, and the final cooling temperature is controlled above the martensitic transformation temperature, Ms, of the rail steel. That is, the final cooling temperature of the post-weld heat treatment is controlled above 245°C. Furthermore, taking into account the inevitable compositional segregation during the rail steel alloying process and the relatively rapid cooling rate during construction in a low-temperature field environment, and the significantly higher cooling rate in the ambient environment after rail welding than in the profiling device after post-weld heat treatment, in order to avoid the formation of brittle and hard martensitic structures during rail welding and post-weld heat treatment, the present invention controls the final cooling temperature during the rapid cooling stage after rail welding to be above the martensitic transformation temperature of the rail steel, i.e., 470-570°C; and controls the final cooling temperature during the rapid cooling stage of post-weld heat treatment to be above the martensitic transformation temperature of the rail steel, i.e., 385-420°C.

[0066] It should be pointed out that the post-weld heating treatment of rails is a heat treatment process without insulation. After the rail joint is heated to the set temperature, the heating process ends and the cooling stage begins. Compared with the rail waist and rail bottom, the rail head has a significant heating lag during the heat treatment process due to its larger thickness. During the post-weld heat treatment of rail welded joints using a traditional medium-frequency induction normalizing unit, when the rail waist and rail bottom are heated to the set temperature, the rail head temperature is significantly lower than that of the rail waist and rail bottom. In order to achieve the impact toughness matching of the rail head with the rail waist and rail bottom of the rail welded joint, it is necessary to appropriately increase the heating temperature of the rail welded joint area, while ensuring that the rail head area of ​​the welded joint is fully austenitized without causing a decrease in the mechanical properties of the joint rail head area due to overheating of the tissue. In the present invention, by rationally arranging the size, number and distribution distance of the ceramic electric heaters embedded in the split device, the heating temperature difference between the rail head and the rail waist and rail bottom areas is eliminated, so that the rail head, rail waist and rail bottom of the rail joint reach the same heating temperature at the same time.

[0067] In the present invention, the normalizing heat treatment generally refers to a heat treatment process in which a metal workpiece is heated to 30 to 50°C above Ac3 (the final temperature at which ferrite transforms to austenite during heating) in a conventional manner, and after keeping the temperature for a period of time, the metal workpiece is removed from the furnace and cooled naturally in the air, or sprayed, or cooled with compressed air. However, the post-weld normalizing heat treatment of rail joints is different from the heat treatment process usually used for small-sized workpieces. Since the length of the sample after rail welding can be as long as hundreds of meters, it is impossible to keep the normalizing heat treatment of rail welded joints warm for a long time after reaching the target temperature (temperature above the austenitizing temperature). It should be pointed out that due to differences in heat conduction and surface energy loss, the core temperature of the rail joint is usually more than 50°C higher than the surface temperature during the normalizing heating process. At the same time, considering the coarsening of austenite grains and the subsequent deterioration of joint performance caused by excessively high normalizing temperatures, as well as the faster cooling rate during construction in outdoor low-temperature environments, the preferred normalizing heating temperature of the present invention is 910-940°C, and the actual rail core temperature can reach 950-990°C.

[0068] In the present invention, to prevent the formation of martensite after rail welding in low-temperature field construction environments, after the rail welding is completed and the temperature drops to 470-570°C, a split-type contoured temperature control device is used to fully cover the rail head, rail web, and rail foot of the rail joint to slow the post-weld cooling rate of the rail joint. Simultaneously, the split-type device uses thermal compensation to cool the rail joint to 340-390°C at a cooling rate of 1.0-2.0°C / s, followed by subsequent heat treatment. It should be noted that ceramic heaters embedded in the split-type device are used for thermal compensation to regulate the cooling rate during this stage. The rail joint cooling rate is controlled at 1.0-2.0°C / s, and the final cooling temperature is controlled at 100°C above the Ms temperature of the two rail steels. This effectively prevents the formation of martensite in the heat-affected zone (HAZ) caused by improper post-weld cooling control and element enrichment in the micro-region.

[0069] During the subsequent heat treatment process, the surface of the rail head of the rail joint is heated to 910-940°C in the split device. Then the cooling mode is started, and the rail joint is cooled to 385-420°C at a cooling rate of 2.0-4.0°C / s in the device, and then the rail joint is cooled to 150-170°C at a cooling rate of 0.6-0.9°C / s, and the heat treatment of the welded joint is completed. After the heat treatment is completed, the contoured temperature control device is removed, and the rail joint is placed in a low-temperature outdoor environment for natural cooling treatment, and the joint is allowed to cool naturally to ambient temperature. In the present invention, the cooling rate of the rail joint after normalizing heating is controlled at 2.0-4.0°C / s, which is higher than the critical cooling rate of 1.3-1.7°C / s for martensite transformation of eutectoid pearlite rail steel, so as to refine the pearlite lamellar spacing by accelerating the cooling of supercooled austenite and improve the mechanical properties of the pearlite structure in the welding area.

[0070] The final cooling temperature after the rapid cooling stage in the present invention is 385-420°C, which is more than 100°C higher than the martensitic transformation start temperature of 215-245°C for eutectoid pearlite rail steel. This helps prevent the formation of martensitic structure during the rapid cooling process. After this cooling stage, the rail joint is cooled to 150-170°C at a cooling rate of 0.6-0.9°C / s using thermal compensation by a contoured temperature control device. The split device is then powered off and removed, allowing the joint to cool to an ambient temperature of -10-0°C in the field.

[0071] It should be noted that when the surface temperature of the rail joint reaches 385-420°C and the core of the rail joint is more than 50°C higher than the surface, that is, the core temperature is between 435-470°C, at which point the pearlite transformation has been completed on both the surface and the core of the rail joint. Subsequent cooling of the rail joint at a rate lower than the critical cooling rate for martensitic transformation of the rail steel will not produce martensitic structure.

[0072] It should be noted that after the rail welding process is complete, the process of reducing the joint surface temperature from 920-1050°C to 470-570°C, and after normalizing, the temperature is reduced from 910-940°C to 150-170°C. Both are achieved through thermal compensation within the contoured temperature control device. This device is equipped with densely packed small, disc-shaped, crawler-type ceramic heaters that adhere closely to the rail surface, ensuring good heat conduction. The combined action of multiple parallel rows of disc-shaped, crawler-type ceramic heaters achieves thermal compensation of the rail joint.

[0073] Figure 4A3 is the rail head tread heating area, B3 is the rail head side heating area, C3 is the rail head jaw heating area, D3 is a circular crawler-type ceramic electric heater, E3 is the rail joint rail head weld positioning line, A1 / A2 / B1 / B2 are terminal posts, C is a circular crawler-type ceramic electric heater at the rail waist, D is the rotating shaft, E is a fixed clamp, F is the device shell, G is the asbestos insulation layer, and H is the device 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 involved in the present invention is fixed with the center of the rail head weld of the rail weld joint (weld positioning line) as the boundary. The A1 terminal and the A2 terminal form a circuit and perform full-section controlled heating on the left half of the device (rail weld joint); the B1 terminal and the B2 terminal form a circuit and perform full-section controlled heating on the right half of the device (rail weld joint). It should be noted that during the heat treatment process, the heating capacity (heating rate and heating temperature) of the left and right halves of the profiling device are the same. The ceramic heaters in the rail head area of ​​the profiling device are densely distributed and smaller in size, resulting in higher heating temperatures. However, the ceramic heaters in the waist and rail foot areas of the profiling device are larger and more sparsely distributed than in the rail head. By rationally arranging the size, number, and spacing of the ceramic heaters embedded in the split device, the heating temperature differences between the rail head, waist, and rail foot areas are eliminated, ensuring that the rail joint head, waist, and rail foot reach the same heating temperature at the same time.

[0074] Figure 5 The layout of the rail head, rail web, and rail base heating areas of the split-type contoured temperature control device shown is similar. Because the rail head is thicker and heat transfer is slower, the number and density of the circular, track-mounted ceramic heaters covering the rail head are greater than those in the rail web and rail base, and the heaters are smaller in diameter to ensure adequate heating of the rail joint head. Furthermore, the size and density of the circular, track-mounted heaters on the left and right sides of the split-type device are identical. By rationally arranging the size, number, and spacing of the ceramic heaters within the split-type device, temperature differences between the rail head, rail web, and rail base are eliminated, ensuring that the rail joint head, rail web, and rail base reach the same heating temperature at the same time.

[0075] like Figure 5 The split-type contoured temperature control device shown in the figure is compact, flexible, and low-cost, making it easy to construct on site. It can be powered by a 380V diesel generator or 220V AC mains electricity, with a rated power of 10kW. The device uses a commercial LCD disc-shaped crawler ceramic heater as the heat source. The split-type contoured temperature control device uses a diameter of The thickness of the disc-shaped crawler type ceramic electric heater is 5mm, while the diameter of the split device rail waist and rail bottom area is The 5mm-thick, circular, track-mounted ceramic heaters are constructed with asbestos insulation and a steel casing to create a rail-shaped split-type heater. This allows for easy assembly and disassembly, making it 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 based on the actual rail profile. During the device design process, multiple rows of parallel, circular, track-mounted ceramic heaters were evenly fixed to the inside of a device with a rail-like profile. This ensures that the heaters evenly cover the rail surface and adhere closely to it, ensuring good heat conduction during heating. This device is used to achieve thermal compensation and normalizing heating of rail joints. During testing, a temperature controller was used to control the heating temperature. The split-type device has an operating temperature range of 200-1100°C and can rotate up to 180° around its axis.

[0076] The present invention refers to the TB / T 1632.2-2014 "Rail Welding Part 2: Flash Welding" standard to machine a rail joint into a longitudinal section hardness specimen, and conducts a longitudinal section Rockwell hardness test on the joint at a position 5 mm below the tread. The measuring points are symmetrically arranged on the left and right sides with the weld as the center, and the measuring points are spaced 5 mm apart. The Rockwell hardness method is carried out in accordance with the provisions of GB / T230.1-2009, using the HRC scale. Hp represents the average hardness of the rail base material, Hj represents the average hardness of the joint, and the position where the joint hardness is lower than 0.9 Hp represents the softening area.

[0077] Example 1

[0078] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with the rail base material exhibiting a tensile strength of 1300 MPa and an elongation of 13.0%. The rail head exhibits a room temperature U-shaped impact energy of 16 J, while the rail web and rail base exhibit a room temperature U-shaped impact energy of 14 J. The rail steel's chemical composition, which achieves these microstructures and mechanical properties, must meet the following requirements: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, and 0.06% V, with the remainder being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with the rail head exhibiting a tensile strength of 1400 MPa and an elongation of 11.2%. The rail head exhibits a room temperature U-shaped impact energy of 14 J, while the rail web and rail base exhibits a room temperature U-shaped impact energy of 12 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.90% C, 0.94% Si, 0.48% Mn, 0.22% Cr, 0.06% V, and the balance being Fe and unavoidable impurities.

[0079] Rail flash welding was carried out using a mobile rail flash welder with a heat input of 10.0 MJ. The actual welding upset was maintained at 11.0 mm. The rail weld joint with a surface temperature of 920°C was naturally cooled in a low-temperature field construction environment until the surface temperature of the weld joint dropped to 470°C. Figure 5 The split-type contoured temperature control device shown provides thermal compensation for the rail joint head, rail web, and rail foot. The cooling rate during this stage is 1.0°C / s, reducing the surface temperature of the welded joint to 340°C. The rail joint is heated across its entire cross-section to 940°C, after which it is cooled at a rate of 4.0°C / s to 385°C. The joint is then cooled at a rate of 0.9°C / s to 170°C, completing the heat treatment of the welded joint. The contoured temperature control device is 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 -10°C, completing the welding and post-weld heat treatment process for the dissimilar rails.

[0080] according to Figure 1 The rail joints obtained in this example, which had been heat treated after welding, were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test on the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0081] The results show that: for the normalized joints of dissimilar rails obtained by the post-weld heat treatment construction method of the present invention, Figure 6 As shown, no martensite structure appears in the heat-affected zones on both sides of the rail joint weld. Among them, the weld structure is pearlite and intergranular proeutectoid ferrite, and the heat-affected zone structures on both sides of the rail joint are visible pearlite. The average room temperature impact energy of the rail head weld of the obtained flash welding joint after air cooling (in welded state) is 12J, and the average room temperature impact energy of the welds at the rail waist and rail bottom is 9J. The average longitudinal section hardness of the normalized joint using the present invention reaches 93% of the hardness of the parent material. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 19J, and the average impact energy of the rail waist and rail bottom welds reaches 15J; under the low temperature test conditions of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 16J, and the impact energy of the rail waist and rail bottom welds is in the range of 13J, which meets the various indicators required for rail welding joints in low temperature environments and helps to ensure the safety of railway operations.

[0082] Example 2

[0083] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with a tensile strength of 1380 MPa and an elongation of 11.0%. The room temperature U-shaped impact energy of the rail head is 12 J, and the room temperature U-shaped impact energy of the rail web and rail base is 10 J. The chemical composition of the rail steel to achieve these microstructures 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. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with a tensile strength of 1450 MPa and an elongation of 8.8%. The room temperature U-shaped impact energy of the rail head is 10 J, and the room temperature U-shaped impact energy of the rail web and rail base is 9 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.99% C, 1.02% Si, 0.56% Mn, 0.25% Cr, 0.10% V, and the balance being Fe and unavoidable impurities.

[0084] Rail flash welding was carried out using a mobile rail flash welder with a heat input of 13.0 MJ. The actual welding upset was maintained at 14.0 mm. The rail weld joint with a surface temperature of 1050 ° C was naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the weld joint to 570 ° C. Figure 5 The split, contoured temperature control device shown provides thermal compensation for the rail joint head, rail web, and rail foot. The cooling rate during this stage is 2.0°C / s, reducing the surface temperature of the welded joint to 390°C. The rail joint is heated across its entire cross-section to 910°C, after which it is cooled at a rate of 2.0°C / s to 420°C. The joint is then cooled at a rate of 0.6°C / s to 150°C, completing the heat treatment of the welded joint. The contoured temperature control device is 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 0°C, thus completing the welding and post-weld heat treatment process for the dissimilar rails.

[0085] according to Figure 1 The rail joints obtained in this example, which had been heat treated after welding, were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test on the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures"

[0086] The metallographic structure of the rail joint metallographic specimens was inspected and etched with 3% nitric acid alcohol solution. The metallographic structure of the rail joint was observed using a German Leica MeF3 optical microscope.

[0087] The results show that: for the normalized joints of dissimilar rails obtained by the post-weld heat treatment construction method of the present invention, Figure 7 As shown, no martensite structure appears in the heat-affected zones on both sides of the rail joint weld. Among them, the weld structure is pearlite and intergranular proeutectoid ferrite, and the heat-affected zone structures on both sides of the rail joint are visible pearlite. The average room temperature impact energy of the rail head weld of the obtained flash welding joint after air cooling (in welded state) is 8J, and the average room temperature impact energy of the welds at the rail waist and rail bottom is 6J. The average longitudinal section hardness of the normalized joint using the present invention reaches 91% of the hardness of the parent material. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 14J, and the average impact energy of the rail waist and rail bottom welds reaches 11J; under the low temperature test conditions of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 11J, and the impact energy of the rail waist and rail bottom welds is in the range of 9J, which meets the various indicators required for rail welding joints in low temperature environments and helps to ensure the safety of railway operations.

[0088] Example 3

[0089] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with a tensile strength of 1350 MPa and an elongation of 12.0%. The room temperature U-shaped impact energy of the rail head is 14 J, and the room temperature U-shaped impact energy of the rail web and rail base is 12.5 J. The chemical composition of the rail steel to achieve these microstructures and mechanical properties must meet the following conditions: 0.78% C, 0.65% Si, 0.85% Mn, 0.40% Cr, 0.85% V, with the balance being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with a tensile strength of 1430 MPa and an elongation of 9.5%. The room temperature U-shaped impact energy of the rail head is 12 J, and the room temperature U-shaped impact energy of the rail web and rail base is 10.5 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.94% C, 0.97% Si, 0.52% Mn, 0.23% Cr, 0.08% V, and the balance being Fe and unavoidable impurities. Rail flash welding was carried out using a mobile rail flash welder with a heat input of 11.3 MJ. The actual welding upset was maintained at 12.5 mm. The rail weld joint formed by welding with a surface temperature of 980°C was naturally cooled in a low-temperature outdoor construction environment to reduce the surface temperature of the weld joint to 520°C. Figure 5The split, contoured temperature control device shown provides thermal compensation for the rail joint head, rail web, and rail foot. The cooling rate during this stage is 1.3°C / s, reducing the surface temperature of the welded joint to 370°C. The rail joint is heated across its entire cross-section to 930°C, after which it is cooled at a rate of 3.0°C / s to 400°C. The joint is then cooled at a rate of 0.8°C / s to 160°C, completing the heat treatment of the welded joint. The contoured temperature control device is 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 -5°C, completing the welding and post-weld heat treatment of the dissimilar rails.

[0090] according to Figure 1 The rail joints obtained in this example, which had been heat treated after welding, were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test on the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0091] The results show that: for the normalized joint of dissimilar rails obtained by the post-weld heat treatment construction method of the present invention, the metallographic structure test results are the same as those of Figure 6 and Figure 7 The results are consistent, and no martensite structure appears in the heat-affected zone on both sides of the rail joint weld. The weld structure is pearlite and intergranular proeutectoid ferrite, while the heat-affected zone on both sides of the rail joint has visible pearlite.

[0092] The average room temperature impact energy of the rail head weld of the flash welded joint after air cooling (in the welded state) is 10J, and the average room temperature impact energy of the rail waist and rail bottom welds is 8J. The average longitudinal section hardness of the normalized joint using the present invention reaches 92% of the hardness of the parent material. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 16J, and the average impact energy of the rail waist and rail bottom welds reaches 13J. Under low temperature test conditions of -20°C, the average impact energy of the rail head weld of the normalized joint reaches 13J, and the impact energy of the rail waist and rail bottom welds is within 11J, meeting all the indicators required for rail welding joints in low temperature environments and helping to ensure railway operation safety.

[0093] Comparative Example 1

[0094] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with the rail base material exhibiting a tensile strength of 1300 MPa and an elongation of 13.0%. The rail head exhibits a room temperature U-shaped impact energy of 16 J, while the rail web and rail base exhibit a room temperature U-shaped impact energy of 14 J. The rail steel's chemical composition, which achieves these microstructures and mechanical properties, must meet the following requirements: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, and 0.06% V, with the remainder being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with the rail head exhibiting a tensile strength of 1400 MPa and an elongation of 11.2%. The rail head exhibits a room temperature U-shaped impact energy of 14 J, while the rail web and rail base exhibits a room temperature U-shaped impact energy of 12 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.90% C, 0.94% Si, 0.48% Mn, 0.22% Cr, 0.06% V, and the balance being Fe and unavoidable impurities.

[0095] Rail flash welding was carried out using a mobile rail flash welder with a heat input of 10.0 MJ. The actual welding upset was maintained at 11.0 mm. The rail weld joint with a surface temperature of 920°C was naturally cooled in a low-temperature field construction environment until the surface temperature of the weld joint dropped to 470°C. Figure 5 The split, contoured temperature control device shown provides thermal compensation for the rail joint head, rail web, and rail foot. The cooling rate during this stage is 1.0°C / s, reducing the surface temperature of the welded joint to 340°C. The rail joint is heated across its entire cross-section to 940°C, after which it is cooled at a rate of 4.0°C / s to 385°C. The joint is then cooled at a rate of 1.8°C / s to 170°C, completing the heat treatment of the welded joint. The contoured temperature control device is 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 -10°C, completing the welding and post-weld heat treatment process for the dissimilar rails.

[0096] according to Figure 1 The rail joint obtained in this comparative example without post-weld heat treatment was machined into a Charpy U-shaped impact specimen at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test of the rail joint impact specimen was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0097] The results show that: for the rail joints obtained without the post-weld heat treatment construction method of the present invention, Figure 8 As shown, a small amount of martensite appears in the heat-affected zone on the eutectoid rail side of the rail joint, while the amount of martensite in the heat-affected zone on the hypereutectoid rail side is significantly increased. The average room temperature impact energy of the rail head weld of the flash welded joint after air cooling (in the as-welded state) is 12J, and the average room temperature impact energy of the welds at the rail waist and rail bottom is 9J. The average longitudinal section hardness of the joint obtained using this comparative example reaches 93% of the hardness of the parent material. At room temperature, the average impact energy of the rail head weld of the normalized joint obtained in this ratio reaches 16J, and the average impact energy of the rail waist and rail bottom welds reaches 13J; under low temperature test conditions of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 12J, and the impact energy of the rail waist and rail bottom welds is in the range of 10J. Judging from the results, the weld impact energy is acceptable, but brittle and hard martensite structure appears in the heat-affected zone of the rails on both sides of the weld, which is not conducive to railway operation safety.

[0098] Comparative Example 2

[0099] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with the rail base material exhibiting a tensile strength of 1300 MPa and an elongation of 13.0%. The rail head exhibits a room temperature U-shaped impact energy of 16 J, while the rail web and rail base exhibit a room temperature U-shaped impact energy of 14 J. The rail steel's chemical composition, which achieves these microstructures and mechanical properties, must meet the following requirements: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, and 0.06% V, with the remainder being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with the rail head exhibiting a tensile strength of 1400 MPa and an elongation of 11.2%. The rail head exhibits a room temperature U-shaped impact energy of 14 J, while the rail web and rail base exhibits a room temperature U-shaped impact energy of 12 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.90% C, 0.94% Si, 0.48% Mn, 0.22% Cr, 0.06% V, and the balance being Fe and unavoidable impurities.

[0100] Rail flash welding was performed using a mobile rail flash welder with a heat input of 10.0 MJ. The actual weld upset was maintained at 11.0 mm. The welded joint, which had a surface temperature of 920°C, was left to cool naturally to ambient temperature in the field's low-temperature construction environment without any heat treatment. This meant that the welded joint, which had a surface temperature of 920°C, was naturally cooled to -5°C in the field's low-temperature construction environment, completing the dissimilar rail welding process.

[0101] according to Figure 1 The rail joints obtained in this comparative example and subjected to post-weld heat treatment were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test of the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0102] The results show that: for the rail normalizing joint obtained without adopting the post-weld heat treatment construction method of the present invention, its metallographic structure inspection results are different from those of Figure 8 Similarly, a significant amount of martensite structure appeared in the heat-affected zones on both sides of the rail joint weld, resulting in poor impact toughness of the joint. The average room temperature impact energy of the rail head weld of the flash welded joint after air cooling (in the welded state) was 8J, and the average room temperature impact energy of the welds at the rail waist and rail bottom was 6J. Due to the presence of high-hardness martensite structure in the heat-affected zone, the average longitudinal section hardness of the joint obtained in this comparative example reached 95% of the hardness of the parent material. At room temperature, the average impact energy of the rail head weld of the joint obtained in this comparative example reached 13J, and the impact energy of the rail waist and rail bottom welds was in the range of 11J; under low-temperature test conditions of -20℃, the average impact energy of the rail head weld of the normalized joint reached 10J, and the impact energy of the rail waist and rail bottom welds was in the range of 7J. The presence of a large amount of martensite structure and the poor impact toughness of the joint are not conducive to railway operation safety.

[0103] Comparative Example 3

[0104] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with a tensile strength of 1350 MPa and an elongation of 12.0%. The room temperature U-shaped impact energy of the rail head is 14 J, and the room temperature U-shaped impact energy of the rail web and rail base is 12.5 J. The chemical composition of the rail steel to achieve these microstructures and mechanical properties must meet the following conditions: 0.78% C, 0.65% Si, 0.85% Mn, 0.40% Cr, 0.85% V, with the balance being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with a tensile strength of 1430 MPa and an elongation of 9.5%. The room temperature U-shaped impact energy of the rail head is 12 J, and the room temperature U-shaped impact energy of the rail web and rail base is 10.5 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.94% C, 0.97% Si, 0.52% Mn, 0.23% Cr, 0.08% V, and the balance being Fe and unavoidable impurities.

[0105] Rail flash welding was carried out using a mobile rail flash welder with a heat input of 11.3 MJ. The actual welding upset was maintained at 12.5 mm. The rail weld joints with a surface temperature of 980 ° C were naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the weld joints to 520 ° C. Figure 5 The split-type contoured temperature control device shown provides thermal compensation for the rail head, rail web, and rail foot of the rail joint. The cooling rate during this stage is 1.3°C / s, reducing the surface temperature of the welded joint to 370°C. The rail joint is heated across its entire cross-section to 890°C, after which it is cooled to 230°C at a rate of 3.0°C / s. The joint is then cooled to 160°C at a rate of 0.8°C / s, completing the heat treatment of the welded joint. The contoured temperature control device is 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 -5°C, thus completing the welding and post-weld heat treatment process of the dissimilar rails.

[0106] according to Figure 1 The rail joints obtained in this comparative example and subjected to post-weld heat treatment were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test of the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0107] The results show that: for the rail normalizing joint obtained without adopting the post-weld heat treatment construction method of the present invention, the metallographic structure inspection results are shown in Figure 9 , a small amount of martensite structure appeared in the heat-affected zone of the eutectoid pearlite rail side of the rail joint weld, while no martensite appeared in the heat-affected zone of the hypereutectoid rail side. The average room temperature impact energy of the rail head weld of the flash welded joint after air cooling (in the welded state) was 10J, and the average room temperature impact energy of the welds at the rail waist and rail bottom was 8J. The average longitudinal section hardness of the joint obtained by this comparative example reached 93% of the hardness of the parent material. Since the final cooling temperature of the rapid cooling stage of the post-weld heat treatment of the joint is 230℃, which is higher than the martensite transformation start temperature of hypereutectoid pearlite rail steel of 190~210℃ and within the martensite transformation start temperature of eutectoid pearlite rail steel of 215~245℃, a small amount of martensite structure appeared in the heat-affected zone on the eutectoid pearlite rail side. At room temperature, the average impact energy of the rail head weld in the normalized joint reaches 14J, and the impact energy of the rail waist and rail bottom welds is in the range of 11J. Under low-temperature test conditions of -20℃, the average impact energy of the rail head weld in the normalized joint reaches 11J, and the impact energy of the rail waist and rail bottom welds is in the range of 9J. The impact toughness of the joint is relatively low and due to the presence of martensitic structure in the heat-affected zone, it is not conducive to railway operation safety.

[0108] Comparative Example 4

[0109] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with a tensile strength of 1350 MPa and an elongation of 12.0%. The room temperature U-shaped impact energy of the rail head is 14 J, and the room temperature U-shaped impact energy of the rail web and rail base is 12.5 J. The chemical composition of the rail steel to achieve these microstructures and mechanical properties must meet the following conditions: 0.78% C, 0.65% Si, 0.85% Mn, 0.40% Cr, 0.85% V, with the balance being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with a tensile strength of 1430 MPa and an elongation of 9.5%. The room temperature U-shaped impact energy of the rail head is 12 J, and the room temperature U-shaped impact energy of the rail web and rail base is 10.5 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.94% C, 0.97% Si, 0.52% Mn, 0.23% Cr, 0.08% V, and the balance being Fe and unavoidable impurities.

[0110] Rail flash welding was carried out using a mobile rail flash welder with a heat input of 11.3 MJ. The actual welding upset was maintained at 12.5 mm. The rail weld joints with a surface temperature of 980 ° C were naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the weld joints to 520 ° C. Figure 5 The split-type contoured temperature control device shown provides thermal compensation for the rail joint head, rail web, and rail foot. The cooling rate during this stage is 1.3°C / s, reducing the surface temperature of the welded joint to 370°C. The rail joint is heated across its entire cross-section to 890°C, after which it is cooled to 200°C at a rate of 3.0°C / s. The joint is then cooled to 160°C at a rate of 0.8°C / s, completing the heat treatment of the welded joint. The contoured temperature control device is 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 -5°C, thus completing the welding and post-weld heat treatment process of the dissimilar rails.

[0111] according to Figure 1 The rail joints obtained in this comparative example and subjected to post-weld heat treatment were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test of the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0112] The results show that: for the rail normalizing joint obtained without adopting the post-weld heat treatment construction method of the present invention, the metallographic structure inspection results are shown in Figure 9, a significant amount of martensite appeared in the heat-affected zone of the eutectoid pearlite rail side of the rail joint weld, while the amount of martensite in the heat-affected zone of the hypereutectoid rail side was relatively small. The average room temperature impact energy of the rail head weld of the flash welded joint after air cooling (in the welded state) was 10J, and the average room temperature impact energy of the welds at the rail waist and rail bottom was 8J. The average longitudinal section hardness of the joint obtained by this comparative example reached 95% of the hardness of the parent material. Since the final cooling temperature of the rapid cooling stage of the post-weld heat treatment of the joint is 200℃, which is lower than the martensite transformation start temperature of 215~245℃ for the eutectoid pearlite rail steel and is within the martensite transformation start temperature of 190~210℃ for the hypereutectoid pearlite rail steel, a significant amount of martensite appeared in the heat-affected zone on the eutectoid pearlite rail side, while a small amount of martensite appeared in the heat-affected zone on the hypereutectoid rail side. At room temperature, the average impact energy of the rail head weld in the normalized joint reaches 12J, and the impact energy of the rail waist and rail bottom welds is in the range of 9J. Under low-temperature test conditions of -20℃, the average impact energy of the rail head weld in the normalized joint reaches 10J, and the impact energy of the rail waist and rail bottom welds is in the range of 7J. The impact toughness of the joint is relatively low and due to the presence of martensitic structure in the heat-affected zone, it is not conducive to railway operation safety.

[0113] Comparative Example 5

[0114] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with a tensile strength of 1350 MPa and an elongation of 12.0%. The room temperature U-shaped impact energy of the rail head is 14 J, and the room temperature U-shaped impact energy of the rail web and rail base is 12.5 J. The chemical composition of the rail steel to achieve these microstructures and mechanical properties must meet the following conditions: 0.78% C, 0.65% Si, 0.85% Mn, 0.40% Cr, 0.85% V, with the balance being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with a tensile strength of 1430 MPa and an elongation of 9.5%. The room temperature U-shaped impact energy of the rail head is 12 J, and the room temperature U-shaped impact energy of the rail web and rail base is 10.5 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.94% C, 0.97% Si, 0.52% Mn, 0.23% Cr, 0.08% V, and the balance being Fe and unavoidable impurities.

[0115] Rail flash welding was carried out using a mobile rail flash welder with a heat input of 14.0 MJ. The actual welding upset was maintained at 12.5 mm. The rail weld joints with a surface temperature of 980 ° C were naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the weld joints to 520 ° C. Figure 5The split, contoured temperature control device shown provides thermal compensation for the rail joint head, rail web, and rail foot. The cooling rate during this stage is 1.3°C / s, reducing the surface temperature of the welded joint to 370°C. The rail joint is heated across its entire cross-section to 930°C, after which it is cooled at a rate of 3.0°C / s to 400°C. The joint is then cooled at a rate of 0.8°C / s to 160°C, completing the heat treatment of the welded joint. The contoured temperature control device is 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 -5°C, completing the welding and post-weld heat treatment of the dissimilar rails.

[0116] according to Figure 1 The rail joints obtained in this comparative example and subjected to post-weld heat treatment were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test of the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0117] The results show that: for the normalized joint of dissimilar rails obtained by the post-weld heat treatment construction method of this comparative example, the metallographic structure test results are the same as those of Figure 6 The heat affected zones on both sides of the rail joint are composed of visible pearlite, but burnt holes appear in the heat affected zones. Figure 11 The average room temperature impact energy of the rail head weld obtained by flash welding and air cooling (in the as-welded state) was 10 J, and the average room temperature impact energy of the rail web and rail foot welds was 7 J. The average longitudinal section hardness of the normalized joint obtained using this comparative example reached 91% of the base material hardness.

[0118] At room temperature, the average impact energy of the rail head weld in the normalized joint reached 12 J, while the average impact energy of the rail waist and rail base welds reached 9 J. Under low-temperature testing conditions of -20°C, the average impact energy of the rail head weld in the normalized joint reached 11 J, while the impact energy of the rail waist and rail base welds ranged from 6 J. Due to the excessive heat input during flash welding, burn holes appeared in the heat-affected zone near the weld, further reducing the impact performance of the rail joint and compromising railway operation safety.

[0119] Comparative Example 6

[0120] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with the rail base material exhibiting a tensile strength of 1300 MPa and an elongation of 13.0%. The rail head exhibits a room temperature U-shaped impact energy of 16 J, while the rail web and rail base exhibit a room temperature U-shaped impact energy of 14 J. The rail steel's chemical composition, which achieves these microstructures and mechanical properties, must meet the following requirements: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, and 0.06% V, with the remainder being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with the rail head exhibiting a tensile strength of 1400 MPa and an elongation of 11.2%. The rail head exhibits a room temperature U-shaped impact energy of 14 J, while the rail web and rail base exhibits a room temperature U-shaped impact energy of 12 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.90% C, 0.94% Si, 0.48% Mn, 0.22% Cr, 0.06% V, and the balance being Fe and unavoidable impurities.

[0121] Rail flash welding was performed using a mobile rail flash welder with a heat input of 10.0 MJ. The actual weld upset was maintained at 11.0 mm. The welded joint, which had a surface temperature of 920°C, was left to cool naturally to ambient temperature in the field's low-temperature construction environment without any heat treatment. This meant that the welded joint, which had a surface temperature of 920°C, was naturally cooled to -5°C in the field's low-temperature construction environment, completing the dissimilar rail welding process.

[0122] according to Figure 1 The rail joints obtained in this comparative example and subjected to post-weld heat treatment were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test of the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures"

[0123] The metallographic structure of the rail joint metallographic specimens was inspected and etched with 3% nitric acid alcohol solution. The metallographic structure of the rail joint was observed using a German Leica MeF3 optical microscope.

[0124] The results show that: for the rail normalizing joint obtained without adopting the post-weld heat treatment construction method of the present invention, the metallographic structure inspection results are shown in Figure 12, a significant amount of martensite structure appeared in the heat-affected zones on both sides of the rail joint weld, resulting in poor impact toughness of the joint. The average room temperature impact energy of the rail head weld of the flash welded joint after air cooling (in the welded state) is 8J, and the average room temperature impact energy of the welds at the rail waist and rail bottom is 6J. Due to the presence of high-hardness martensite structure in the heat-affected zone, the average longitudinal section hardness of the joint obtained in this comparative example reaches 95% of the hardness of the parent material. At room temperature, the average impact energy of the rail head weld of the joint obtained in this comparative example reaches 13J, and the impact energy of the rail waist and rail bottom welds is in the range of 11J; under low-temperature test conditions of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 10J, and the impact energy of the rail waist and rail bottom welds is in the range of 7J. The presence of a large amount of martensite structure and the poor impact toughness of the joint are not conducive to railway operation safety.

[0125] Comparative Example 7

[0126] The room temperature (20-25°C) tensile and impact properties of the eutectoid pearlite rail base material are controlled, with the rail base material exhibiting a tensile strength of 1300 MPa and an elongation of 13.0%. The rail head exhibits a room temperature U-shaped impact energy of 16 J, while the rail web and rail base exhibit a room temperature U-shaped impact energy of 14 J. The rail steel's chemical composition, which achieves these microstructures and mechanical properties, must meet the following requirements: 0.73% C, 0.50% Si, 0.70% Mn, 0.30% Cr, and 0.06% V, with the remainder being Fe and unavoidable impurities. The room temperature (20-25°C) tensile and impact properties of the hypereutectoid pearlite rail base material are controlled, with the rail head exhibiting a tensile strength of 1400 MPa and an elongation of 11.2%. The rail head exhibits a room temperature U-shaped impact energy of 14 J, while the rail web and rail base exhibits a room temperature U-shaped impact energy of 12 J. The chemical composition of the rail steel to obtain the microstructure and mechanical properties must meet the following conditions: 0.90% C, 0.94% Si, 0.48% Mn, 0.22% Cr, 0.06% V, and the balance being Fe and unavoidable impurities.

[0127] Rail flash welding was carried out using a mobile rail flash welder with a heat input of 10.0 MJ. The actual welding upset was maintained at 11.0 mm. The rail weld joint with a surface temperature of 920°C was naturally cooled in a low-temperature field construction environment until the surface temperature of the weld joint dropped to 470°C. Figure 5The split-type contoured temperature control device shown provides thermal compensation for the rail joint head, rail web, and rail foot. The cooling rate during this stage is 1.0°C / s, reducing the surface temperature of the welded joint to 340°C. The rail joint is heated across its entire cross-section to 800°C, then cooled to 385°C at a rate of 4.0°C / s. The joint is then cooled to 170°C at a rate of 0.9°C / s, completing the heat treatment of the welded joint. The contoured temperature control device is 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 -10°C, completing the welding and post-weld heat treatment process for the dissimilar rails.

[0128] according to Figure 1 The rail joints obtained in this comparative example and subjected to post-weld heat treatment were machined into Charpy U-shaped impact specimens at the sampling position shown in the figure, with the weld located at the center of the specimen. The impact test of the rail joint impact specimens was carried out at room temperature (20-30°C) using a SANS ZBC2000 impact testing machine. Figure 2-3 The sampling method shown is to conduct metallographic inspection on the metallographic specimens of the rail joints in accordance with GB / T13298-2015 "Methods for Examination of Metal Microstructures", etch the metallographic specimens of the rail joints with a 3% nitric acid alcohol solution, and observe the metallographic structure of the rail joints with a German Leica MeF3 optical microscope.

[0129] The results show that: for the normalized joint of dissimilar rails obtained by the post-weld heat treatment construction method of this comparative example, the metallographic examination results are the same as those of Figure 6 and Figure 7 The results are consistent, and no martensite structure appears in the heat-affected zone on both sides of the rail joint weld. Among them, the weld structure is pearlite and intergranular proeutectoid ferrite, and the heat-affected zone structure on both sides of the rail joint is visible pearlite. The average room temperature impact energy of the rail head weld of the flash welded joint after air cooling (in welded state) is 12J, and the average room temperature impact energy of the welds at the rail waist and rail bottom is 9J. The average longitudinal section hardness of the normalized joint using this comparative example reaches 88% of the hardness of the parent material. At room temperature, the average impact energy of the rail head weld of the normalized joint reaches 13J, and the average impact energy of the rail waist and rail bottom welds reaches 10J; under low temperature test conditions of -20℃, the average impact energy of the rail head weld of the normalized joint reaches 10J, and the impact energy of the rail waist and rail bottom welds is in the range of 6J. Due to the low heating temperature during the post-weld heat treatment of the joint, the austenitization process of the joint is incomplete, and the mechanical properties of the normalized rail joint are not significantly improved compared to the joint in the welded state. That is, the rail joint heat treated at this normalizing temperature (800℃) is not conducive to railway operation safety.

[0130] By comparing Examples 1-3 and Comparative Examples 1-7, it can be seen that the welding process provided by the present invention can effectively reduce the probability of generating welding gray spots and avoid the appearance of martensite structure in the heat-affected zone of the rail joint. The heterogeneous rail welded joint obtained by the welding method of the present invention has no abnormal structure such as martensite in the entire cross-section at room temperature (20-30°C), and the average hardness of the longitudinal section of the joint reaches 91-93% of the hardness of the corresponding parent material. At room temperature, the average impact energy of the normalized joint rail head weld reaches 14-19J, and the average impact energy of the rail waist and rail bottom welds reaches 11-15J; under the low temperature test conditions of -20°C, the average impact energy of the normalized joint rail head weld reaches 11-16J, and the impact energy of the rail waist and rail bottom welds ranges from 9-13J, which helps to ensure the safety of railway operation.

[0131] Although some specific embodiments of the present disclosure have been described in detail through examples, those skilled in the art will understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Those skilled in the art will understand that the above embodiments may be modified or some technical features may be replaced with equivalents without departing from the scope and spirit of the present disclosure. In particular, as long as there are no structural conflicts, the various technical features mentioned in the various embodiments may be combined in any manner.

Claims

1. A method for heat treatment of rails after welding in a low temperature environment, characterized in that: include: The first stage: The dissimilar rail welded joints with a surface temperature of 920-1050°C are naturally cooled in a low-temperature field construction environment to reduce the surface temperature of the welded joints to 470-570°C. The second stage: the rail joint is slowly cooled in the temperature control device in a heat-compensated manner, and the surface temperature of the welded joint is reduced to 340-390°C at the second cooling rate; The third stage: heating the entire cross-section of the rail joint in a thermal compensation manner in the profiling temperature control device, heating the surface of the welded joint to 910-940°C; The fourth stage: cool the rail joint to 385-420℃ at the fourth cooling rate. The fifth stage: cooling the rail joint to 150-170°C at the fifth cooling rate; The second cooling rate is 1.0-2.0°C / s; The fourth cooling rate is 2.0-4.0°C / s; The fifth cooling rate is 0.6 to 0.9 ° C / s; In the first stage, the field construction environment temperature is -10 to 0°C; The cooling rate in the first stage is 8.5-12.5°C / s; The dissimilar rail welded joint is made by welding eutectoid pearlite rail and hypereutectoid pearlite rail; The eutectoid pearlite 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, and the balance is Fe and unavoidable impurities; The hypereutectoid pearlite rail base material contains: 0.90-0.99% C, 0.94-1.02% Si, 0.48-0.56% Mn, 0.22-0.25% Cr, 0.06-0.10% V, and the balance is Fe and unavoidable impurities.

2. The low temperature environment rail post-weld heat treatment method according to claim 1, characterized in that: The sixth stage is also included: placing the rail joint in a low-temperature outdoor environment for natural cooling, so that the joint is naturally cooled to the ambient temperature.

3. The low temperature environment rail post-weld heat treatment method according to claim 1, characterized in that: The contoured temperature control device is a split-type contoured temperature control device, comprising two hingedly connected heat-insulating shells and multiple rows of small-sized ceramic heating plates arranged on the inner walls of the heat-insulating shells, and the two heat-insulating shells form an inner cavity adapted to the welded joints of dissimilar rails.

4. The low temperature environment rail post-weld heat treatment method according to claim 3, characterized in that: Multiple rows of parallel arranged disc-shaped crawler-type ceramic electric heaters are evenly fixed on the inner wall of the thermal insulation shell, and the number of the disc-shaped crawler-type ceramic electric heaters covering the rail head area is smaller in size, more numerous and denser than the crawler-type ceramic electric heaters covering the rail waist and rail bottom areas.

5. The low temperature environment rail post-weld heat treatment method according to claim 1, characterized in that: In the third stage, the heating temperature of the rail waist and rail bottom in the contour temperature control device is 20~25℃ higher than the heating temperature of the rail head.

6. The low temperature environment rail post-weld heat treatment method according to claim 1, characterized in that: The rail joints are welded by moving flash welding, the upset amount is kept at 11.0-14.0mm, and the heat input is 10.0-13.0MJ during welding.

7. The low temperature environment rail post-weld heat treatment method according to claim 1, characterized in that: The tensile strength of the eutectoid pearlite rail base material at room temperature is 1300-1380 MPa, and the elongation is 11.0-13.0%. The room temperature U-shaped impact energy of the rail head is 12-16 J, and the room temperature U-shaped impact energy of the rail waist and rail bottom is in the range of 10-14 J. The tensile strength of the hypereutectoid pearlite rail base material at room temperature is 1400-1450 MPa, and the elongation is 8.8-11.2%. The room temperature U-shaped impact energy of the rail head is 10-14 J, and the room temperature U-shaped impact energy of the rail waist and rail bottom is in the range of 9-12 J. The room temperature impact energy of the rail head weld of the dissimilar rail joint in the welded state ranges from 8 to 12 J, and the room temperature impact energy of the rail waist and rail bottom welds ranges from 6 to 9 J.

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