Large-scale gas pressure welding process for medium-carbon low-alloy steel rails

Abstract

The application discloses a medium-carbon low-alloy steel rail and a large-scale gas pressure welding process method. The medium-carbon low-alloy steel rail contains components with mass fractions as follows: C: 0.50%-0.63%, Si: 0.30%-0.60%, Mn: 0.55%-0.80%, Cr+Ni+Cu+V: 0.30%-1.0%, P and S: less than or equal to 0.025%, and the balance of Fe and inevitable impurities. The method comprises the following steps: using an oxygen-acetylene flame to heat a to-be-welded part of the steel rail, and closing the gas when the surface temperature of the to-be-welded part of the steel rail reaches 1200-1300 DEG C; performing upset welding; performing pressure maintaining and nodule pushing; and performing forced air cooling on a high-temperature joint after welding. The method optimizes the chemical composition of the alloy, and performs forced air cooling after gas pressure welding, so that a high-quality medium-carbon low-alloy steel rail welding joint with high strength and stable quality is obtained.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and specifically relates to a large-scale gas pressure welding process for medium carbon low alloy steel rails. Background Technology

[0002] Pearlitic steel rails typically have a carbon content of 0.70%–0.84%, with hot-rolled rails having a strength range of 880–1080 MPa and a hardness of 260–350 HBW. Heat-treated rails have a strength of 1080–1280 MPa and a hardness of 320–400 HB, with representative grades including U71Mn, U75V, and U78CrV. These rails are mainly used in domestic high-speed railways, mixed passenger and freight lines, and heavy-haul lines. They have high carbon content, high alloy element content, high strength and hardness, and good wear resistance. Normalizing is essential after welding to ensure joint quality. For high-altitude and frigid regions with large annual and diurnal temperature variations, higher requirements are placed on the impact toughness of the rails. Currently, no single type of rail can fully meet the service requirements of railway lines in high-altitude and frigid regions with large annual and diurnal temperature variations and complex track conditions. Therefore, the rail treads laid on extremely long downhill sections in high-altitude and cold regions are prone to abrasion of martensite structure, which can lead to rail breakage and seriously affect the safety of railway service.

[0003] To ensure the joint toughness meets standard requirements, existing high-carbon steel rails must be reheated and normalized after welding. Reheating consumes a large amount of fuel gas, resulting in high overall costs.

[0004] Therefore, the railway engineering field urgently needs a rail welding method that is low in cost and has good overall weld performance. Summary of the Invention

[0005] This invention discloses a large-scale gas pressure welding process for medium carbon low alloy steel rails. By optimizing the alloy chemical composition and subjecting the welded rails to forced air cooling after gas pressure welding, a high-strength, high-quality, and stable medium carbon low alloy steel rail welded joint is obtained.

[0006] To solve at least one of the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] According to the present invention, a large-scale gas pressure welding process for medium-carbon low-alloy steel rails is provided. The medium-carbon low-alloy steel rails contain the following components by mass fraction: C: 0.50%–0.63%, Si: 0.30%–0.60%, Mn: 0.55%–0.80%, Cr+Ni+Cu+V: 0.30%–1.0%, P, S ≤ 0.025%, with the balance being Fe and unavoidable impurities. The method includes the following steps:

[0008] Use an oxy-acetylene flame to heat the area of ​​the rail to be welded, and turn off the gas when the surface temperature of the rail to be welded reaches 1200-1300℃.

[0009] Perform upsetting welding;

[0010] Perform pressure holding and tumor pushing; and

[0011] Forced air cooling is applied to the high-temperature joint after welding.

[0012] According to one embodiment of the present invention, during the heating of the section of the rail to be welded, the heater oscillates by 15 to 20 mm.

[0013] According to one embodiment of the present invention, during the upsetting welding process, the upsetting amount is 33-36 mm.

[0014] According to one embodiment of the present invention, performing pressure holding and tumor pushing includes:

[0015] After upsetting and welding, the pressure holding, slugging, and secondary pressure holding are performed sequentially.

[0016] According to one embodiment of the present invention, during a single pressure holding process, a pressure of 51-55T is applied to the welded joint of the rail for 3-5 seconds.

[0017] According to one embodiment of the present invention, during the secondary pressure holding process, a pressure of 15-20T is applied to the welded joint of the rail for 5-10 seconds.

[0018] According to one embodiment of the present invention, during the air-jet cooling process, the air-jet pressure is 0.3 to 0.4 MPa.

[0019] According to one embodiment of the present invention, the air jetting is stopped when the welded joint cools to 410°C to 460°C.

[0020] According to one embodiment of the present invention, the method further includes:

[0021] Before welding, perform end milling and grinding, rail pulling, and rail alignment.

[0022] According to one embodiment of the present invention, the method further includes:

[0023] After air cooling, the rail head tread and rail side are ground.

[0024] By adopting the above technical solution, the present invention has at least one of the following advantages compared with the prior art:

[0025] 1. The large-scale gas pressure welding process for medium carbon low alloy steel rails according to the present invention simplifies the post-weld heat treatment process of the joint, saves the oxygen and acetylene required for reheating the joint, and greatly reduces the cost.

[0026] 2. According to the present invention, the average tensile strength Rm of the large gas pressure welded joint of carbon low alloy steel rail is ≥910MPa, the average hardness of the joint longitudinal section reaches more than 90% of the hardness of the rail base material, the width of the softened zone of the joint is <20mm, and the average U-shaped impact energy of the joint weld is ≥13J. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A flowchart of the medium carbon low alloy steel rail and large gas pressure welding process according to the present invention;

[0029] Figure 2 The location of the longitudinal section hardness test point is shown, which is 3-5 mm below the rail head tread of the rail welded joint.

[0030] Figure 3 The sampling location of the metallographic specimen of the rail head tread surface of the rail welded joint is shown.

[0031] Figure 4 The hardness curve of the longitudinal section of the gas pressure welded joint in Example 1 is shown.

[0032] Figure 5 The sampling locations and number of samples for the impact test of gas pressure welded joints are shown.

[0033] Figure 6 The longitudinal section hardness curve of the gas pressure welded joint in Comparative Example 1 is shown. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Currently, there are three main methods for rail welding: flash welding (including base flash welding and moving flash welding), aluminothermic welding, and gas pressure welding. Base flash welding is used for in-plant welding; aluminothermic welding is used for on-site replacement and locking welding, as well as for rail break repair. Aluminothermic welding of rails has high requirements for flux and on-site welding process. Due to the difficulty in controlling the flux composition and preheating temperature, the weld has a cast structure, resulting in poor joint quality. The hardness of the aluminothermic weld is much lower than that of the base material, leading to severe joint wear on heavy-load lines.

[0036] The flash welding method for rails involves heating the joint to a temperature exceeding the melting point of the rail. Improper matching of welding heat input, upsetting amount, and final burning rate can easily lead to defects such as overburning and ash spots in the joint. It is extremely difficult for 15 consecutive joints to pass the drop hammer test. In order to pass the drop hammer test, a lot of process optimization is usually required, with the number of test joints reaching as high as 150-500, which consumes a lot of manpower and resources.

[0037] During gas pressure welding, the rail does not melt, resulting in no decarburized layer in the weld, which is an advantage of gas pressure welding over flash welding. Furthermore, the weld joint produced by gas pressure welding has a forged structure, which is an advantage over aluminothermic welding. Theoretically, the strength of a gas pressure weld joint is no less than that of a flash weld and superior to that of an aluminothermic weld.

[0038] The preferred chemical composition and weight percentage of each component of the medium-carbon low-alloy steel rail according to this application are as follows: C: 0.50%–0.63%, Si: 0.30%–0.60%, Mn: 0.55%–0.80%, Cr+Ni+Cu+V: 0.30%–1.0%, P, S ≤ 0.025%, with the balance being Fe and unavoidable impurities. This medium-carbon low-alloy steel rail has a lower carbon content and lower alloy element content than pearlitic steel rails, exhibiting better plasticity and toughness.

[0039] Figure 1 A flow chart of a large-scale gas pressure welding process applicable to the aforementioned medium-carbon low-alloy steel rails is shown. The method generally includes the following steps:

[0040] Step S1: Use an oxy-acetylene flame to heat the area of ​​the rail to be welded. Turn off the gas when the surface temperature of the area to be welded on the rail reaches 1200-1300°C.

[0041] Step S2: Perform upsetting welding;

[0042] Step S3, perform pressure holding and tumor pushing; and

[0043] Step S4: Forced air cooling is applied to the high-temperature joint after welding.

[0044] To ensure the quality of gas pressure welding, end milling, grinding, rail pulling, and rail alignment can be performed before gas pressure welding of the rails. In the example of this invention, a special end milling machine can be used to mill the rails before welding, and rust and oxides near the weld joint can be ground clean until the metal luster is exposed.

[0045] In step S1, during the heating of the rail section to be welded using an oxy-acetylene flame, the heater oscillation amplitude is preferably 15–20 mm. In gas pressure welding, heating and upsetting are closely related. During heating, as the temperature rises, the rail absorbs heat, increasing the vibrational energy of atoms and thus increasing the amplitude, leading to a rapid acceleration of diffusion. A portable infrared thermometer and accompanying software are used to monitor the temperature during heating. The gas is shut off when the surface temperature of the rail section to be welded reaches 1200–1300°C, and upsetting welding is then performed.

[0046] During the upsetting welding process in step S2, the upsetting amount is controlled to be 33-36mm.

[0047] The pressure holding and push-off process in step S3 may further include: performing a first pressure holding, push-off, and a second pressure holding sequentially after upsetting welding. Specifically, during the first pressure holding process, a pressure of 51-55T is applied to the welded joint of the rail for 3-5 seconds; during the second pressure holding process, a pressure of 15-20T is applied to the welded joint of the rail for 5-10 seconds.

[0048] In step S4, the joint is directly subjected to forced air cooling using a jetting device at high post-weld temperature to increase joint hardness and reduce the width of the softened zone. Preferably, the high-temperature joint after welding is subjected to forced air cooling at a pressure of 0.3–0.4 MPa, and the air cooling is stopped when the joint cools to 410°C–460°C.

[0049] After the joint has cooled to room temperature, the gas pressure welded joint can be ground. The grinding surfaces are the rail head tread and the side of the rail. The grinding contour should maintain the original rail head profile as much as possible. All weld beads below the rail web must be ground clean, and the remaining weld beads should be rounded off from the base material.

[0050] The following are specific embodiments of the medium-carbon low-alloy steel rail and the large-scale gas pressure welding process method according to the present invention. The embodiments of the present invention use a GPW-1200 fully automatic CNC large-scale gas pressure rail welding machine configured on a YHGQ-1200 rail welding vehicle to weld medium-carbon low-alloy steel rails. Before welding, various welding parameters (heater oscillation frequency, heating time, gas flow rate, etc.) are input. During the welding process, no operator intervention is required; the entire process is automatically controlled through PLC programming, and the welding process curve is automatically recorded.

[0051] Example 1

[0052] In this embodiment, the medium-carbon low-alloy steel rails used contain the following components by mass fraction: C: 0.50%, Si: 0.6%, Mn: 0.8%, Cr+Ni+Cu+V: 0.8%, P, S≤0.025%, with the balance being Fe and unavoidable impurities.

[0053] The weld section of the rail is heated within a certain range using an oxy-acetylene flame. During heating, the heater oscillates at a rate of 15mm. A portable infrared thermometer and accompanying software monitor the temperature during the heating process. The gas is shut off when the surface temperature of the rail section to be welded reaches 1250℃, and upsetting welding is then performed. The upsetting welding process parameters are: upsetting amount 33.5mm; after upsetting, a first pressure holding of 51T for 3 seconds; during the first pressure holding, the weld bead is pushed out; followed by a second pressure holding of 15T for 5 seconds. Immediately after the second pressure holding, a dedicated air jet device is used to force-cool the high-temperature weld joint at a pressure of 0.35MPa. Air jetting is stopped when the joint cools to 450℃. After the joint cools to room temperature, the gas-pressure welded joint is ground. The ground surfaces are the rail head tread and the rail side. The grinding contour should maintain the original rail head shape as much as possible. All weld beads below the rail web must be ground clean, and the remaining weld beads should transition smoothly with the base material using a rounded transition.

[0054] Reference to the polished joint Figure 2 The sampling method shown is as follows: a) is the heat-affected zone of the rail weld, b) is the rail head tread of the rail joint, and c) is the weld center. The joint is machined into longitudinal hardness test specimens, and longitudinal hardness tests of the rail welded joints are carried out according to the rail welding standard TB / T1632.4-2014.

[0055] Example 1: Longitudinal hardness curve as shown Figure 4 As shown. The longitudinal hardness H of the rail joint. J / H P The value reaches 0.93, and the width of the softened zone on the left and right sides of the joint is ≤15mm.

[0056] After the longitudinal hardness test is completed, refer to Figure 3 The sampling method shown is based on GB / T13298-2015 "Metallic Microstructure Examination Method" for metallographic examination of rail joint metallographic specimens. Point c is the weld center, and point d is the sampling location for the rail head tread metallographic specimen of the rail welded joint. The rail joint metallographic specimens were etched using a 3% nitric acid alcohol solution, and the metallographic structure was observed using a Leica MeF3 optical microscope. The results show that for medium-carbon low-alloy steel rail welded joints treated according to this invention, at a magnification of 100X, the joint microstructure consists of pearlite plus a small amount of proeutectoid ferrite, and no martensite was observed in the heat-affected zone of the joint.

[0057] Example 2

[0058] In this embodiment, the medium-carbon low-alloy steel rails used contain the following components by mass fraction: C: 0.63%, Si: 0.3%, Mn: 0.55%, Cr+Ni+Cu+V: 0.3%, P, S≤0.025%, with the balance being Fe and unavoidable impurities.

[0059] Heat a certain range of the cross-section of the rail welded by an oxygen-acetylene flame. During heating, the swing amplitude of the heater is 20 mm. During the heating process, use a portable infrared thermometer and supporting software for temperature monitoring. When the surface temperature of the rail at the welding position reaches 1300 °C, turn off the gas and perform upset welding. The upset welding process parameters are as follows: the upset amount is 35 mm. After upsetting, perform the first pressure holding. The pressure holding pressure is 55 T, and the pressure holding time is 5 s. During the first pressure holding, push the weld bead, and then perform the second pressure holding. The pressure holding pressure is 20 T, and the pressure holding time is 10 s. After the second pressure holding is completed, immediately use a special air-blowing device to forcibly air-blow and cool the high-temperature joint after welding. The air-blowing pressure is 0.35 MPa. Stop air-blowing when the joint cools to 460 °C. After the joint cools to room temperature, grind the gas-pressure welded joint. The grinding surface is the tread of the rail head and the side of the rail. The grinding profile should尽量保持原钢轨轨头廓形, and the weld beads below the rail web must be completely ground off. The weld beads in the remaining parts are transitioned to the base metal in an arc shape.

[0060] Conduct a drop-weight test on the rail welded joint according to the rail welding standard 《TB / T1632.4 - 2014》. During the drop-weight test of the rail welded joint, the hammer head impacts the weld area of the rail joint. For a 60 kg / m rail, the mass of the hammer head is 1000 kg, the drop height is 3.1 m, and it is qualified if it does not break in 2 times, or the drop height is 5.2 m and it does not break in 1 time.

[0061] Conduct a drop-weight test on the gas-pressure welded joint obtained in Example 2 according to the current Chinese railway industry rail welding standard 《TB / T1632.4 - 2014》. During the drop-weight test of the rail welded joint, the hammer head impacts the weld area of the rail joint. The mass of the used hammer head is 1000 kg, and the free-fall height is 3.1 m.

[0062] The results show that: for the gas-pressure welded joint obtained in Example 2, it does not break in 2 times of drop-weight, and the deflection of the joint after drop-weight is 36 mm.

[0063] Example 3

[0064] In this embodiment, the medium-carbon low-alloy steel rail used contains the following components by mass fraction: C: 0.55%, Si: 0.53%, Mn: 0.7%, Cr + Ni + Cu + V: 1.0%, P, S ≤ 0.025%, and the balance is Fe and unavoidable impurities.

[0065] The cross-section within a certain range of the rail weld is heated with an oxygen-acetylene flame. During heating, the swinging amplitude of the heater is 18 mm. During the heating process, a portable infrared thermometer and supporting software are used for temperature monitoring. When the surface temperature of the rail at the welding position reaches 1280 °C, the gas is turned off and upset welding is carried out. The upset welding process parameters are as follows: the upset amount is 34.3 mm. After upsetting, the first pressure holding is carried out, the pressure holding pressure is 53 T, and the pressure holding time is 5 s. During the first pressure holding, the flash is pushed, and the second pressure holding is carried out, the pressure holding pressure is 18 T, and the pressure holding time is 6 s. Immediately after the second pressure holding is completed, a special air-blowing device is used to forcibly air-blow and cool the high-temperature joint after welding. The air-blowing pressure is 0.4 MPa. The air-blowing stops when the joint cools to 430 °C. After the joint cools to room temperature, the gas-pressure welded joint is polished. The polished surfaces are the tread of the rail head and the side of the rail. The polished profile should尽量 maintain the original profile of the rail head. The flash below the rail web must be completely polished, and the flash in the remaining part is transitioned to the base metal in a circular arc shape.

[0066] The gas-pressure welded joint obtained in Example 3 is subjected to a full-section impact toughness test of the rail welded joint according to the rail welding standard "TB / T 1632.4-2014". The sampling positions and the number of specimens for the impact test of the welded joint are shown in Figure 5 . The standard requires 14 impact specimens, and the average impact value ≥ 6.5 J is qualified.

[0067] The results show that for the gas-pressure welded joint obtained in the example, the average U-shaped impact energy of the entire cross-section of the joint weld is 15.5 J, which is much higher than the standard requirements and helps to ensure the safety of railway operation.

[0068] Example 4

[0069] In this example, the medium-carbon low-alloy steel rail used contains the following components by mass fraction: C: 0.58%, Si: 0.48%, Mn: 0.71%, Cr + Ni + Cu + V: 0.66%, P, S ≤ 0.025%, and the balance is Fe and unavoidable impurities.

[0070] The cross-section within a certain range of the rail weld is heated with an oxygen-acetylene flame. During heating, the swing amplitude of the heater is 18 mm. During the heating process, a portable infrared thermometer and supporting software are used for temperature monitoring. When the surface temperature of the rail at the welding position reaches 1280 °C, the gas is shut off, and upset welding is carried out. The upset welding process parameters are as follows: the upset amount is 33.3 mm. After upsetting, the first pressure holding is carried out, the pressure holding pressure is 52 T, and the pressure holding time is 5 s. During the first pressure holding, the weld bead is pushed, and the second pressure holding is carried out. The pressure holding pressure is 16 T, and the pressure holding time is 10 s. After the second pressure holding is completed, immediately use a special air-blowing device to forcibly air-blow and cool the high-temperature joint after welding. The air-blowing pressure is 0.3 MPa. The air-blowing stops when the joint cools to 450 °C. After the joint cools to room temperature, the gas-pressure welded joint of the rail is polished. The polished surfaces are the running surface of the rail head and the side surface of the rail. The polished contour should尽量保持原钢轨轨头廓形, and the weld beads below the rail web must be completely polished off. The weld beads in the remaining parts are transitioned to the base metal in an arc shape.

[0071] The gas-pressure welded joints obtained in Example 4 are subjected to a tensile test of the rail welded joint according to the rail welding standard "TB / T 1632.1 - 2014". The standard requires 9 tensile specimens, and the average room-temperature tensile strength of the full cross-section ≥ 880 MPa is qualified. The results show that for the gas-pressure welded joints obtained in the example, the average room-temperature tensile strength of the full cross-section of the obtained gas-pressure welded joints is 925 MPa, which helps to ensure the safe operation of the railway.

[0072] Example 5

[0073] In this embodiment, the same steps as in Example 1 are carried out to obtain the welded joint.

[0074] A drop-weight test is carried out on the gas-pressure welded joint of the rail in this embodiment. During the drop-weight test of the rail welded joint, the hammer head impacts the weld area of the rail joint. The mass of the used hammer head is 1000 kg, and the free-fall height is 3.1 m. It is continuously carried out 3 times, and the joint quality is high.

[0075] Example 6

[0076] In this embodiment, the same steps as in Example 1 are carried out to obtain the welded joint.

[0077] A full cross-section impact toughness test of the rail welded joint is carried out on the gas-pressure welded joint of the rail in this embodiment. The average U-notch impact energy of the full cross-section of the joint weld is 17.2 J, which is much higher than the standard requirements and helps to ensure the safe operation of the railway.

[0078] Example 7

[0079] In this embodiment, the same steps as in Example 1 are carried out to obtain the welded joint.

[0080] Tensile tests were conducted on the gas-pressure welded joint of the rail in this embodiment. The average room temperature tensile strength of the entire cross-section of the gas-pressure welded joint was 965 MPa, which helps to ensure the safety of railway operation.

[0081] Example 8

[0082] In this embodiment, the same steps as in Embodiment 2 are performed to obtain the welded joint.

[0083] The rail gas pressure welded joint in this embodiment underwent hardness and metallographic testing. The longitudinal hardness H of the rail joint was... J / H P The microstructure reached 0.95XX, with the width of the softened zone on both sides of the joint ≤15mm. At a magnification of 100X, the joint microstructure consisted of pearlite plus a small amount of proeutectoid ferrite, and no martensite was observed in the heat-affected zone of the joint.

[0084] Example 9

[0085] In this embodiment, the same steps as in Embodiment 2 are performed to obtain the welded joint.

[0086] A full-section impact toughness test was conducted on the gas-pressure welded joint of the rail in this embodiment. The average U-shaped impact energy of the joint weld section was 18.2 J, which is far higher than the standard requirement and helps to ensure the safety of railway operation.

[0087] Example 10

[0088] In this embodiment, the same steps as in Embodiment 2 are performed to obtain the welded joint.

[0089] Tensile tests were conducted on the gas-pressure welded rail joints in this embodiment. The average room temperature tensile strength of the entire cross-section of the gas-pressure welded joint was 958 MPa, which helps ensure railway operation safety.

[0090] Example 11

[0091] In this embodiment, the same steps as in Embodiment 3 are performed to obtain the welded joint.

[0092] The rail gas pressure welded joint in this embodiment underwent hardness and metallographic testing. The longitudinal hardness H of the rail joint was... J / H P The coefficient reached 0.94, and the width of the softened zone on both sides of the joint was ≤16mm. At a magnification of 100X, the joint microstructure consisted of pearlite plus a small amount of proeutectoid ferrite, and no martensite was observed in the heat-affected zone of the joint.

[0093] Example 12

[0094] In this embodiment, the same steps as in Embodiment 3 are performed to obtain the welded joint.

[0095] A drop hammer test was conducted on the gas pressure welded joint of the rail in this embodiment. During the drop hammer test, the hammer head impacted the weld area of ​​the rail joint. The hammer head used had a mass of 1000 kg, a free fall height of 3.1 m, and was dropped three times without breaking, resulting in a high-quality joint.

[0096] Example 13

[0097] In this embodiment, the same steps as in Embodiment 3 are performed to obtain the welded joint.

[0098] Tensile tests were conducted on the gas-pressure welded rail joints in this embodiment. The average room temperature tensile strength of the entire cross-section of the gas-pressure welded joint was 970 MPa, which helps ensure railway operation safety.

[0099] Example 14

[0100] In this embodiment, the same steps as in Embodiment 4 are performed to obtain the welded joint.

[0101] The rail gas pressure welded joint in this embodiment underwent hardness and metallographic testing. The longitudinal hardness H of the rail joint was... J The HP value reached 0.95, and the width of the softened zone on both sides of the joint was ≤20mm. At a magnification of 100X, the joint microstructure consisted of pearlite with a small amount of proeutectoid ferrite, and no martensite was observed in the heat-affected zone of the joint.

[0102] Example 15

[0103] In this embodiment, the same steps as in Embodiment 4 are performed to obtain the welded joint.

[0104] A drop hammer test was conducted on the gas pressure welded joint of the rail in this embodiment. During the drop hammer test, the hammer head impacted the weld area of ​​the rail joint. The hammer head used had a mass of 1000 kg, a free fall height of 3.1 m, and was dropped three times without breaking, resulting in a high-quality joint.

[0105] Example 16

[0106] In this embodiment, the same steps as in Embodiment 4 are performed to obtain the welded joint.

[0107] A full-section impact toughness test was conducted on the gas-pressure welded joint of the rail in this embodiment. The average U-shaped impact energy of the joint weld section was 17.0 J, which is far higher than the standard requirement and helps to ensure the safety of railway operation.

[0108] Comparative Example 1

[0109] In this embodiment, the medium-carbon low-alloy steel rails used contain the following components by mass fraction: C: 0.53%, Si: 0.35%, Mn: 0.60%, Cr+Ni+Cu+V: 0.40%, P, S≤0.025%, with the balance being Fe and unavoidable impurities.

[0110] The rail section to be welded is heated within a certain range using an oxy-acetylene flame. During heating, the heater oscillates at a rate of 15mm. A portable infrared thermometer and accompanying software monitor the temperature during the heating process. The gas is shut off when the surface temperature of the rail section to be welded reaches 1250℃, and upsetting welding is then performed. The upsetting welding process parameters are: upsetting amount 33.5mm; after upsetting, a first pressure holding of 52T for 3 seconds; during the first pressure holding, the weld bead is pushed out; followed by a second pressure holding of 15T for 5 seconds. No air is blown after the second pressure holding. After the joint cools to room temperature, the gas-pressure welded joint is ground. The ground surfaces are the rail head tread and the rail side. The grinding contour should maintain the original rail head shape as much as possible. All weld beads below the rail web must be ground clean, and the remaining weld beads should transition smoothly with the base material using a rounded transition.

[0111] Reference to the polished joint Figure 1 The sampling method shown involves machining the joint into longitudinal hardness test specimens, and conducting longitudinal hardness tests on the rail welded joints according to the rail welding standard TB / T1632.4-2014. The standard requires a longitudinal hardness H of the joint. J / H P =0.81

[0112] Comparative Example 1: Longitudinal hardness curve as shown Figure 6 As shown. The longitudinal hardness H of the joint. J / H P =0.81, the entire joint is significantly lower than the base material, and the joint hardness does not meet the standard requirements.

[0113] Comparative Example 2

[0114] In this embodiment, the medium-carbon low-alloy steel rails used contain the following components by mass fraction: C: 0.60%, Si: 0.60%, Mn: 0.70%, Cr+Ni+Cu+V: 0.90%, P, S≤0.025%, with the balance being Fe and unavoidable impurities.

[0115] The weld section of the rail is heated within a certain range using an oxy-acetylene flame. During heating, the heater oscillates at a range of 20mm. A portable infrared thermometer and accompanying software monitor the temperature during the heating process. The gas is shut off when the surface temperature of the rail section to be welded reaches 1290℃, and upsetting welding is then performed. The upsetting welding process parameters are: upsetting amount 34.3mm; after upsetting, a first pressure holding of 55T for 5s is performed; the first pressure holding is followed by shaving of the weld bead, and a second pressure holding of 20T for 10s is performed. Immediately after the second pressure holding, a dedicated air jet device is used to force-cool the high-temperature weld joint at a pressure of 0.45MPa. Air jetting is stopped when the joint cools to 400℃. After the joint cools to room temperature, the gas-pressure welded joint is ground. The ground surfaces are the rail head tread and the rail side. The grinding contour should maintain the original rail head shape as much as possible. All weld beads below the rail web must be ground clean, and the remaining weld beads should transition smoothly with the base material using a rounded transition.

[0116] Refer to after the experiment is completed Figure 3 The sampling method shown was performed according to GB / T13298-2015 "Metallic Microstructure Examination Method" for metallographic examination of rail joint metallographic samples. A 3% nitric acid alcohol solution was used to etch the samples, and a Leica MeF3 optical microscope was used to observe the metallographic structure. The results show that for medium-carbon low-alloy steel rail welded joints treated with this invention, at a magnification of 100X, the joint microstructure consists of pearlite + a small amount of proeutectoid ferrite + a small amount of martensite. This does not meet the standard requirements.

[0117] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A large-scale gas pressure welding process for medium-carbon low-alloy steel rails, characterized in that, The medium-carbon low-alloy steel rail comprises the following components by mass fraction: C: 0.50%–0.63%, Si: 0.30%–0.60%, Mn: 0.55%–0.80%, Cr+Ni+Cu+V: 0.30%–1.0%, P, S≤0.025%, with the balance being Fe and unavoidable impurities. The method includes the following steps: The rail is heated with an oxy-acetylene flame. When the surface temperature of the rail to be welded reaches 1200-1300°C, the gas is turned off. The heater swing amplitude is 15-20mm. Upsetting welding is performed, wherein the upsetting amount is 33-36 mm; The process involves sequentially performing a first pressure holding, a push-off, and a second pressure holding. During the first pressure holding, a pressure of 51-55T is applied to the welded joint of the rail for 3-5 seconds. During the second pressure holding, a pressure of 15-20T is applied to the welded joint of the rail for 5-10 seconds. Forced air cooling is applied to the high-temperature joint after welding, eliminating the need for heat treatment, to obtain a medium-carbon low-alloy steel rail welded joint with an average tensile strength Rm ≥ 910 MPa across the entire cross section, a softening zone width < 20 mm, and an average U-shaped impact energy of ≥ 13 J across the entire weld cross section.

2. The method according to claim 1, characterized in that, During the air-jet cooling process, the air-jet pressure is 0.3 to 0.4 MPa.

3. The method according to claim 2, characterized in that, Stop blowing air when the welded joint cools to 410℃~460℃.

4. The method according to claim 1, characterized in that, The method further includes: Before welding, perform end milling and grinding, rail pulling, and rail alignment.

5. The method according to claim 1, characterized in that, The method further includes: After air cooling, the rail head tread and rail side are ground.

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