Method for improving quality of large-sized air pressure welding joint of medium-carbon low-alloy steel rail

Abstract

The present invention discloses a method for improving the quality of large-sized air-pressure welded joints of medium-carbon low-alloy steel rails, which comprises the following steps: heating the to-be-welded part of the rail with an oxygen-acetylene flame until the surface is in a semi-molten state; performing upset welding; performing a forging process, wherein the consumption of the forged rail is 1.5 to 3.0 mm, the forging time is 1.5 to 3.0 s, the average speed is 0.50 to 1.5 mm / s, and the forging pressure is 45 to 60 T; maintaining pressure after flash removal; and performing heat treatment on the welded joint of the rail. By adding a forging process after air-pressure welding, this method obtains high-strength and stable-quality high-quality welded joints of medium-carbon low-alloy steel rails.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a method for improving the quality of large-sized air-pressure welded joints of medium-carbon low-alloy steel rails. Background Art

[0002] The carbon content of pearlitic steel rails is usually 0.70% - 0.84%, the strength range of hot-rolled rails is 880 - 1080 MPa, and the hardness is 260 - 350 HBW; the strength of heat-treated steel rails is 1080 - 1280 MPa, and the hardness is 320 - 400 HB. The main representative steel rail grades are U71Mn, U75V, and U78CrV. This type of steel rail is mainly used for domestic high-speed railways, passenger-cargo mixed transportation, and heavy-haul lines. This type of steel rail has a high carbon content, a relatively high alloy element content, high strength and hardness, and good wear resistance. After welding the joints, normalizing must be carried out to ensure the joint quality. In view of the special natural conditions such as large annual temperature differences and large day-night temperature differences in plateau and alpine regions, higher requirements are put forward for the impact toughness of the steel rails. At present, for railway lines in plateau and alpine regions with large annual and day-night temperature differences and complex line conditions, there is no steel rail that can fully meet its service requirements. Therefore, the tread of the steel rails laid on the extra-long downhill sections in plateau and alpine regions is prone to scuffing martensite structure, resulting in the risk of rail breakage, seriously affecting service safety.

[0003] Therefore, the railway engineering field urgently needs a process method for improving the quality of large-sized air-pressure welded joints of medium-carbon low-alloy steel rails. Summary of the Invention

[0004] The present invention discloses a method for improving the quality of large-sized air-pressure welded joints of medium-carbon low-alloy steel rails, and by adding a forging process after air-pressure welding, a high-strength and stable-quality high-quality medium-carbon low-alloy steel rail welded joint is obtained.

[0005] To solve at least one of the above technical problems, the present invention adopts the following technical solutions:

[0006] According to the present invention, there is provided a method for improving the quality of large-sized air-pressure welded joints of medium-carbon low-alloy steel rails, comprising the following steps:

[0007] Using an oxygen-acetylene flame to heat the part of the steel rail to be welded until the surface is in a semi-molten state;

[0008] Performing upset welding;

[0009] Performing a forging process, wherein the consumption of the forged steel rail is 1.5 - 3.0 mm, the forging time is 1.5 - 3.0 s, the average speed is 0.50 - 1.5 mm / s, and the forging pressure is 45 - 60 T;

[0010] Keeping the pressure after upsetting the flash; and

[0011] Heat-treat the welded joint of the rail.

[0012] According to an embodiment of the present invention, during the process of heating the part to be welded of the rail with an oxygen-acetylene flame, the oxygen flow rate is 80 - 90 L / min, and the acetylene flow rate is 86 - 98 L / min.

[0013] According to an embodiment of the present invention, during the process of performing upset welding, the upset speed is 15 - 18 mm / s, and the upset amount is 30 - 34 mm.

[0014] According to an embodiment of the present invention, during the pressure-holding process, a pressure of 25 - 30 T is applied to the welded joint of the rail for 10 - 15 s.

[0015] According to an embodiment of the present invention, heat-treating the welded joint of the rail includes:

[0016] Wait for the welded joint to cool below 450 °C, reheat and perform normalizing treatment.

[0017] According to an embodiment of the present invention, the method further includes:

[0018] Perform the steps of end milling, grinding, rail stretching, and rail alignment before welding.

[0019] According to an embodiment of the present invention, the method further includes:

[0020] Grind the rail head tread and the rail side after heat treatment.

[0021] According to an embodiment of the present invention, the medium-carbon low-alloy steel rail contains 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%, and the balance is Fe and unavoidable impurities.

[0022] By adopting the above technical solutions, the present invention has at least one of the following advantages compared with the prior art:

[0023] 1. The method of the present invention adds a forging process. Under the action of forging pressure, the metal atoms on the end face of the rail to be welded penetrate and diffuse with each other under the action of forging force, forming a connection between metal atoms, and completing crystallization under the action of pressure. The joint forms a forging structure, greatly improving the joint quality;

[0024] 2. By adopting the technical solution of the present invention, the medium-carbon low-alloy steel rail can be successfully welded by gas pressure welding. The internal defects of the rail joint are few, the strength of the welded joint is high, and the quality is stable. Description of the Drawings

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 It is a flowchart of a method for improving the quality of large-sized gas-pressure welded joints of medium-carbon low-alloy steel rails according to the present invention. Detailed implementation manners

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] At present, the main rail welding methods are flash welding (including base flash welding and mobile flash welding), thermite welding and gas-pressure welding, etc. Base flash welding is used for in-plant welding; thermite welding is used for on-site replacement and locking welding and broken rail repair. Thermite welding of rails has high requirements for welding flux and on-site welding technology. Due to difficulties in controlling the welding flux composition and preheating temperature, the weld seam is a cast structure, so the joint quality is not high. The hardness of the thermite weld seam is much lower than that of the base metal, resulting in serious wear of the joint on heavy-haul lines.

[0029] In the rail flash welding method, the joint heating temperature exceeds the melting point of the rail. If the welding heat input, upsetting amount and final burning speed do not match properly, defects such as overburning and gray spots are likely to occur in the joint. It is very difficult for 15 consecutive joints to pass the drop hammer test. To pass the drop hammer test, a large amount of process optimization is usually required. The number of test joints alone is as high as 150 - 500 joints, consuming a large amount of manpower and material resources.

[0030] During the gas-pressure welding process, the rail does not melt, so there is no decarburized layer in the weld seam, which is where gas-pressure welding is superior to flash welding; the gas-pressure welded joint is a forged structure, which is where gas-pressure welding is superior to thermite welding. Theoretically, the strength of the gas-pressure welded joint is not lower than that of flash welding and is superior to thermite welding.

[0031] Figure 1 The flow of a method for improving the quality of large-sized gas-pressure welded joints of medium-carbon low-alloy steel rails according to the present invention is shown. This method is applicable to medium-carbon low-alloy steel rails. The chemical composition of the welded base metal and the weight percentage of each component are preferably: 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%, and the balance is Fe and unavoidable impurities. The method generally may include the following steps:

[0032] Step S1: Heat the part of the steel rail to be welded with an oxygen-acetylene flame until the surface is in a semi-molten state;

[0033] Step S2: Perform upset welding;

[0034] Step S3: Perform a forging process, where the consumption of the forged steel rail is 1.5 - 3.0 mm, the forging time is 1.5 - 3.0 s, the average speed is 0.50 - 1.5 mm / s, and the forging pressure is 45 - 60 T;

[0035] Step S4: Hold the pressure after upsetting the protrusion; and

[0036] Step S5: Perform heat treatment on the welded joint of the steel rail.

[0037] To ensure the quality of the gas pressure welding, steps such as end milling, grinding, rail stretching, and rail alignment can be performed before the gas pressure welding of the steel rail. In the example of the present invention, a special end milling machine can be used to mill the steel rail before welding, and the rust and oxides near the weld are polished until the metal luster is exposed.

[0038] During the process of Step S1 using an oxygen-acetylene flame to heat the part of the steel rail to be welded, the oxygen flow rate is preferably 80 - 90 L / min, and the acetylene flow rate is preferably 86 - 98 L / min. During the gas pressure welding process, heating and upsetting are closely related. During heating, as the temperature rises, the steel rail absorbs heat, increasing the vibrational energy of atoms, the amplitude increases, resulting in a sharp acceleration of diffusion. When the surface temperature is about 1350 °C, the surface of the steel rail is in a semi-molten state, and the inside of the steel rail also reaches the welding temperature. At this time, the gas is turned off for welding and upsetting.

[0039] During the upset welding process of Step S2, control the upsetting speed to be 15 - 18 mm / s and the upsetting amount to be 30 - 34 mm.

[0040] The forging process of Step S3 enables the metal atoms on the end face of the steel rail to be welded to penetrate and diffuse with each other under the action of the forging pressure, forming a connection between metal atoms, and completing crystallization under pressure. The joint forms a forged structure, greatly improving the joint quality.

[0041] During the pressure holding process of Step S4, a pressure of 25 - 30 T can be applied to the welded joint of the steel rail for 10 - 15 s.

[0042] The heat treatment in Step S5 can include normalizing treatment, that is, waiting for the welded joint to cool below 450 °C, reheating and performing normalizing treatment. Subsequently, cooling is performed by air spraying.

[0043] The rails can be ground after normalizing. The ground surfaces are the rail head tread and rail sides. The grinding profile should try to keep the original rail head profile. All weld nodules below the rail waist must be ground clean, and the rest of the weld nodules should transition to a circular arc with the parent material.

[0044] The following is a specific embodiment of the method for improving the quality of large gas pressure welded joints of medium carbon low alloy rails according to the present invention.

[0045] Example 1

[0046] In this embodiment, the medium carbon low alloy rail contains the following components by mass fraction: C: 0.60%, Si: 0.45%, Mn: 0.72%, Cr+Ni+Cu+V: 0.80%, P, S≤0.025%, and the remainder is Fe and unavoidable impurities.

[0047] The part of the rail to be welded is heated with an oxygen-acetylene flame. The oxygen flow rate is 83L / min and the acetylene flow rate is 87L / min. During the heating process, a portable infrared thermometer and supporting software are used to monitor the temperature. When the surface temperature of the rail head to be welded is 1350℃ and the surface is semi-molten, the gas is turned off and welding and upsetting are carried out. The upsetting welding process parameters are: upsetting speed 16.1mm / s, upsetting amount 31.2mm, and the forging process is added after the upsetting is completed. The rail consumption in the forging process is 1.5mm, the forging time is 1.5s, the average speed is 1.0mm / s, and the forging pressure is 45T. Under the action of the forging pressure, the metal atoms on the end face of the rail to be welded penetrate and diffuse each other under the action of the forging force, forming a connection between the metal atoms, and completing the crystallization under the action of pressure. The joint forms a forging structure, which greatly improves the quality of the joint. After the forging is completed, the convex is pushed and the pressure is maintained. The pressure is 25.8T and the pressure is maintained for 15s.

[0048] After the pressure is maintained, the gas pressure welded joint is cooled to below 400℃. After the welded joint is completely transformed into pearlite + a small amount of proeutectoid ferrite, the rail is reheated for normalization to avoid coarse grains in the joint after normalization. The rail is ground after normalization. The ground surface is the rail head tread and the side of the rail. The grinding profile should try to keep the original rail head profile. The weld nodules below the rail waist must be completely ground clean, and the rest of the weld nodules should transition to the parent material arc.

[0049] The pneumatic welded joint obtained in this embodiment was subjected to a drop hammer test on a rail welded joint according to the current rail welding standard of China's railway industry, TB / T1632.4-2014. During the drop hammer test on a rail welded joint, the hammer head hits the weld area of the rail joint. The mass of the hammer head used is 1000 kg, and the free fall height is 3.1 m. The results show that the pneumatic welded joint obtained in this embodiment was continuously dropped by the hammer twice, and the joint deflection after the drop hammer was 23.5 mm.

[0050] Example 2

[0051] In this embodiment, the medium-carbon low-alloy steel rail used contains the following components by mass fraction: C: 0.63%, Si: 0.30%, Mn: 0.55%, Cr + Ni + Cu + V: 0.45%, P, S ≤ 0.025%, and the balance is Fe and inevitable impurities.

[0052] Heat the part of the rail to be welded with an oxygen-acetylene flame. During heating, the oxygen flow rate is 86 L / min and the acetylene flow rate is 90 L / min. During the heating process, use a portable infrared thermometer and supporting software for temperature monitoring. When the surface temperature of the rail head to be welded reaches 1350 °C and the surface has shown a semi-molten state, turn off the gas and perform welding and upsetting. The upset welding process parameters are: upsetting speed 17.1 mm / s, upsetting amount 32 mm. After upsetting is completed, add a forging process. The consumption of the rail in the forging process is 3 mm, the forging time is 3 s, the average speed is 1.0 mm / s, and the forging pressure is 60 T. Under the action of the forging pressure, the metal atoms on the end face of the rail to be welded penetrate and diffuse with each other under the action of the forging force, forming a connection between metal atoms, and completing crystallization under the action of pressure. The joint forms a forged structure, greatly improving the joint quality. After forging is completed, perform upset bulge removal and hold pressure. The holding pressure is 26 T and the holding time is 10 s.

[0053] After holding pressure is completed, when the gas pressure welded joint of the rail cools below 420 °C and all the welded joints are transformed into pearlite + a small amount of proeutectoid ferrite, then reheat the rail for normalizing to avoid grain coarsening of the joint after normalizing. After the rail is normalized, perform grinding. The grinding surfaces are the running surface of the rail head and the side surface of the rail. The grinding profile should try to maintain the original profile of the rail head as much as possible. The weld beads below the rail web must be completely ground off, and the weld beads in the remaining parts are transitioned to the base metal in an arc shape.

[0054] Perform a drop hammer test on the gas pressure welded joint of the rail in this embodiment. The mass of the hammer head is 1000 kg, the drop height is 3.1 m, and the rail does not break after 2 drops. The maximum deflection is 25.0 mm, and the joint quality is high.

[0055] Example 3

[0056] In this embodiment, the medium-carbon low-alloy steel rail used contains the following components by mass fraction: C: 0.50%, Si: 0.60%, Mn: 0.80%, Cr + Ni + Cu + V: 1.0%, P, S ≤ 0.025%, and the balance is Fe and inevitable impurities.

[0057] The part of the rail to be welded is heated with an oxygen-acetylene flame. The oxygen flow rate is 80L / min and the acetylene flow rate is 86L / min. During the heating process, a portable infrared thermometer and supporting software are used to monitor the temperature. When the surface temperature of the rail head to be welded is 1350℃ and the surface is semi-molten, the gas is turned off and welding and upsetting are performed. The upsetting welding process parameters are: upsetting speed 15.1mm / s, upsetting amount 30mm, and a forging process is added after the upsetting is completed. The rail consumption in the forging process is 2mm, the forging time is 2s, the average speed is 1.0mm / s, and the forging pressure is 50T. Under the action of the forging pressure, the metal atoms on the end face of the rail to be welded penetrate and diffuse each other under the action of the forging force, forming a connection between the metal atoms, and completing crystallization under the action of pressure. The joint forms a forged structure, which greatly improves the quality of the joint. After the forging is completed, the convex is pushed and the pressure is maintained, and the pressure is maintained at 25T and the pressure is maintained for 15s.

[0058] After the pressure is maintained, the gas pressure welded joint is cooled to below 450℃. After the welded joint is completely transformed into pearlite + a small amount of proeutectoid ferrite, the rail is reheated for normalization to avoid coarse grains in the joint after normalization. The rail is ground after normalization. The ground surface is the rail head tread and the side of the rail. The grinding profile should try to keep the original rail head profile. The weld nodules below the rail waist must be completely ground clean, and the rest of the weld nodules should transition to the arc of the parent material.

[0059] A drop hammer test was performed on the rail pneumatic welded joint in this embodiment. The mass of the hammer head was 1000 kg, the drop hammer height was 3.1 m, and no breakage occurred after the hammer was dropped three times. The maximum deflection was 34.5 mm, and the joint quality was high.

[0060] Example 4

[0061] In this embodiment, the medium carbon low alloy rail contains the following components in mass fraction: C: 0.61%, Si: 0.45%, Mn: 0.76%, Cr+Ni+Cu+V: 0.3%, P, S≤0.025%, and the remainder is Fe and unavoidable impurities.

[0062] The part of the rail to be welded is heated with an oxygen-acetylene flame. The oxygen flow rate is 90L / min and the acetylene flow rate is 98L / min. During the heating process, a portable infrared thermometer and supporting software are used to monitor the temperature. When the surface temperature of the rail head to be welded is 1350℃ and the surface is semi-molten, the gas is turned off and welding and upsetting are performed. The upsetting welding process parameters are: upsetting speed 18mm / s, upsetting amount 34mm, and a forging process is added after the upsetting is completed. The rail consumption in the forging process is 2.5mm, the forging time is 2.5s, the average speed is 1.0mm / s, and the forging pressure is 55T. Under the action of the forging pressure, the metal atoms on the end face of the rail to be welded penetrate and diffuse under the action of the forging force, forming a connection between the metal atoms, and completing the crystallization under the action of pressure. The joint forms a forged structure, which greatly improves the quality of the joint. After the forging is completed, the convex is pushed and the pressure is maintained. The pressure is 30T and the pressure is maintained for 10s.

[0063] After the pressure is maintained, the gas pressure welded joint is cooled to below 450℃. After the welded joint is completely transformed into pearlite + a small amount of proeutectoid ferrite, the rail is reheated for normalization to avoid coarse grains in the joint after normalization. The rail is ground after normalization. The ground surface is the rail head tread and the side of the rail. The grinding profile should try to keep the original rail head profile. The weld nodules below the rail waist must be completely ground clean, and the rest of the weld nodules should transition to the arc of the parent material.

[0064] A drop hammer test was performed on the rail pneumatic welded joint in this embodiment. The mass of the hammer head was 1000 kg, the drop hammer height was 3.1 m, and no breakage occurred after the hammer was dropped three times. The maximum deflection was 33.8 mm, and the joint quality was high.

[0065] Example 5

[0066] In this embodiment, the same steps as in Embodiment 3 are performed to obtain a welded joint.

[0067] The static bending test of the rail gas pressure welding joint in this embodiment is carried out. The test load is 1800KN without breaking, the maximum deflection is 38.2mm without breaking, and the joint quality is high.

[0068] Example 6

[0069] In this embodiment, the same steps as in Embodiment 4 are performed to obtain a welded joint.

[0070] The rail gas pressure welded joint in this embodiment was subjected to a static bending test, with a test load of 1800 KN without break and a maximum deflection of 37.6 mm without break, indicating that the joint quality is high.

[0071] Comparative Example 1

[0072] The rail to be welded is heated with an oxygen-acetylene flame. The oxygen flow rate is 80L / min and the acetylene flow rate is 86L / min. During the heating process, a portable infrared thermometer and supporting software are used to monitor the temperature. When the surface temperature of the rail head to be welded is 1350℃ and the surface is semi-molten, the gas is turned off and welding and upsetting are carried out. The upsetting welding process parameters are: upsetting speed 15.1mm / s, upsetting amount 30mm, and after the upsetting is completed, no additional forging is added, and the convex is directly pushed and pressure is maintained. The pressure is 25T and the pressure holding time is 15s.

[0073] After the pressure is maintained, the gas pressure welded joint is cooled to below 450℃. After the welded joint is completely transformed into pearlite + a small amount of proeutectoid ferrite, the rail is reheated for normalization to avoid coarse grains in the joint after normalization. The rail is ground after normalization. The ground surface is the rail head tread and the side of the rail. The grinding profile should try to keep the original rail head profile. The weld nodules below the rail waist must be completely ground clean, and the rest of the weld nodules should transition to the arc of the parent material.

[0074] A drop hammer test was performed on the rail gas pressure welded joint in this embodiment. The mass of the hammer head was 1000 kg and the drop hammer height was 3.1 m. The joint broke after the third drop hammer test. The joint quality was lower than that of Embodiment 3 in which the forging process was added.

[0075] Comparative Example 2

[0076] The rail to be welded is heated with an oxygen-acetylene flame. The oxygen flow rate is 90L / min and the acetylene flow rate is 98L / min. During the heating process, a portable infrared thermometer and supporting software are used to monitor the temperature. When the surface temperature of the rail head to be welded is 1350℃ and the surface is semi-molten, the gas is turned off and welding and upsetting are carried out. The upsetting welding process parameters are: upsetting speed 18mm / s, upsetting amount 34mm, and after the upsetting is completed, no additional forging is added, and the convex is directly pushed and pressure is maintained, the pressure is 30T, and the pressure holding time is 10s.

[0077] After the pressure is maintained, the gas pressure welded joint is cooled to below 450℃. After the welded joint is completely transformed into pearlite + a small amount of proeutectoid ferrite, the rail is reheated for normalization to avoid coarse grains in the joint after normalization. The rail is ground after normalization. The ground surface is the rail head tread and the side of the rail. The grinding profile should try to keep the original rail head profile. The weld nodules below the rail waist must be completely ground clean, and the rest of the weld nodules should transition to the arc of the parent material.

[0078] The rail gas pressure welded joint in this embodiment was subjected to a static bending test, with a test load of 1727 KN and a maximum deflection of 33.6 mm. The joint strength was lower than that of the embodiment 6 in which a forging process was added.

[0079] Under the forging pressure, the metal atoms on the end faces of the rails to be welded penetrate and diffuse with each other under the action of the forging force, forming a connection between the metal atoms, and completing crystallization under the pressure. The joint forms a forging structure, greatly improving the joint quality. According to the method of the present invention, the welding of medium-carbon low-alloy steel rails can be completed with high quality at a relatively low cost. The joint has high bonding strength and can fully ensure the service performance of the rail welding joint and the safety of railway operation.

[0080] The above embodiments only express the implementation modes of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention shall be subject to the appended claims.

Claims

1. A method for improving the quality of large-sized air-pressure welded joints of medium-carbon low-alloy steel rails, characterized in that, The medium-carbon low-alloy steel rail contains 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%, and the balance is Fe and unavoidable impurities. The method includes the following steps: Use an oxygen-acetylene flame to heat the welding part of the rail until the surface is in a semi-molten state; Perform upset welding; Perform a forging process, where the consumption of the forged rail is 1.5 - 3.0 mm, the forging time is 1.5 - 3.0 s, the average speed is 0.50 - 1.5 mm / s, and the forging pressure is 45 - 60 T; Keep the pressure after upsetting the protrusion; and Perform heat treatment on the welded joint of the rail.

2. The method according to claim 1, characterized in that During the process of using an oxygen-acetylene flame to heat the welding part of the rail, the oxygen flow rate is 80 - 90 L / min, and the acetylene flow rate is 86 - 98 L / min.

3. The method according to claim 1, characterized in that, During the process of performing upset welding, the upsetting speed is 15 - 18 mm / s, and the upsetting amount is 30 - 34 mm.

4. The method according to claim 1, characterized in that During the pressure-holding process, apply a pressure of 25 - 30 T to the welded joint of the rail for 10 - 15 s.

5. The method according to claim 1, wherein The heat treatment of the welded joint of the rail includes: After the welded joint cools below 450 °C, reheat and perform normalizing treatment.

6. The method according to claim 1, wherein The method further includes: Perform the steps of end milling, grinding, rail stretching, and rail alignment before welding.

7. The method according to claim 1, wherein The method further includes: Grind the running surface of the rail head and the side of the rail after heat treatment.

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