Electromagnetic treatment method for rail welding seam strengthening and destressing

Abstract

The invention discloses an electromagnetic treatment method for rail welding seam strengthening and destressing, and relates to the technical field of rail welding. The electromagnetic treatment method comprises the processes of preheating, smelting, pouring, cooling and destressing, and a low-frequency alternating magnetic field is applied in the whole process of preheating, smelting, pouring, cooling and destressing. The method comprises the specific steps that electromagnetic preheating is conducted on a welding position and a mold, metal ingredients are smelted, the metal ingredients are stirred, the metal ingredients are poured into the mold, the mold is disassembled, and electromagnetic destressing treatment is conducted on a welding seam. Strength and destressing treatment is conducted on the welding seam through the magnetic field generator, the problems of stress concentration, slag inclusion, composition segregation and the like existing in an existing thermit welding process and a flash welding process can be effectively solved, the mechanical property of the welding seam is remarkably improved, and the service life is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, and in particular to an electromagnetic treatment method for strengthening and stress-relieving rail welds. Background Technology

[0002] In the process of railway track construction and operation and maintenance, rail welding is the core process to achieve seamless track laying and ensure track smoothness and stability. It is directly related to railway operation safety, passenger comfort and rail service life. At present, the industry generally uses aluminothermic welding and flash welding as the main technologies for track welding. However, both aluminothermic welding and flash welding have problems in actual use. First, the problems of aluminothermic welding are: (1) Preheating before welding requires gas, and gas cylinders need to be carried during operation, which poses a safety hazard during transportation and use; (2) Molten iron is melted by chemical reaction between aluminum powder and iron oxide, which generates a lot of heat and dust, polluting the environment; (3) The temperature of molten iron is not accurately controlled. Too high a temperature will cause coarse particles, and too low a temperature will cause inclusions; (4) After the molten iron melts, it sinks into the weld by its own density, and lighter reaction impurities float to the surface, inevitably carrying impurities to sink; (5) When the molten iron solidifies, it is easy to produce defects such as sand holes, sand inclusions, inclusions, pores and shrinkage; (6) The structure is uneven during solidification. (7) During aluminothermic welding, the flux is greatly affected by environmental factors, especially humidity and temperature. (8) Since the aluminothermic flux is quantitatively prepared according to the size of the weld, welding cannot be performed when the weld size changes, otherwise the rail may be scrapped. (9) Adjusting the weld size is complicated, wasting time and labor. Secondly, the problems of flash welding process are: (1) The equipment is complex, bulky, difficult to operate, and has high power (generally above 200Kw), resulting in high energy consumption. (2) It is subject to many restrictions on the construction site conditions (such as power supply and site layout). (3) The molten metal splashes during the welding process, causing pollution and safety hazards. (4) Since the temperature of the molten metal is not easy to control, the heat-affected zone (HAZ) is large and the temperature is too high, which easily leads to oxidation and decarburization. Summary of the Invention

[0003] In view of the problems of numerous weld defects, low connection strength, large residual stress, and frequent maintenance required by the current welding methods, the present invention provides an electromagnetic treatment method for strengthening and stress-relieving track welds.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An electromagnetic treatment method for strengthening and stress-relieving rail welds includes preheating, melting, casting, cooling, and stress relief processes, with a low-frequency alternating magnetic field applied throughout these processes. Specific steps include: S1, installing a mold and a magnetic field generator at the welding site, with the magnetic field generator electromagnetically preheating both the welding site and the mold; S2, filling an induction furnace with a metal mixture identical to the rail base material, adjusting the furnace's frequency range to between 20Hz and 50Hz, and its power range to between 20kW and 30kW, melting the metal mixture to a temperature range between 1400℃ and 1600℃; S3, adjusting the induction furnace's frequency range to between 5Hz and 15Hz, and the duration to between 30s and 120s, electromagnetically stirring the metal mixture within the furnace. S4. After pouring the molten metal into the mold, adjust the frequency range of the magnetic field generator to between 5Hz and 15Hz, and the magnetic induction intensity range to between 1T and 1.5T. S5. After the temperature of the metal mixture decreases to between 850℃ and 950℃, disassemble the mold. S6. Adjust the frequency range of the magnetic field generator to between 15Hz and 30Hz, and the magnetic induction intensity range to between 0.5T and 1.0T, so that the temperature of the metal mixture remains between 850℃ and 950℃ for at least 180 seconds. S7. Adjust the frequency of the magnetic field generator to 5Hz, and the magnetic induction intensity range to between 1T and 1.5T, until the temperature of the metal mixture decreases to 400℃. Then, maintain this temperature at 400℃ for at least 2 minutes, and then turn off the magnetic field generator.

[0005] Furthermore, in S1, during electromagnetic preheating, the frequency range of the magnetic field generator is between 30Hz and 50Hz, preheating the temperature of the area to be welded and the mold to a temperature range between 500°C and 600°C.

[0006] Furthermore, in S2, the furnace liner inside the induction furnace is made of graphite material, and the maximum capacity for metal batching is 6 kg.

[0007] Furthermore, in S4, the pouring time ranges from 3 to 5 seconds.

[0008] Furthermore, in S4, after the metal material is poured into the mold, the frequency of the magnetic field generator is adjusted after 120 seconds.

[0009] Furthermore, in S6, the duration ranges from 180s to 300s.

[0010] The beneficial effects of the present invention are as follows: The present invention uses a magnetic field generator to perform electromagnetic treatment on the track weld, thereby strengthening and relieving the track weld. Compared with the existing aluminothermic welding process and flash welding process, it has the following advantages: (1) It can significantly improve the mechanical properties of the weld. The electromagnetic field treatment can promote the refinement of the weld metal grains and the homogenization of the structure, thereby enhancing the tensile strength, impact toughness and fatigue life of the weld, effectively extending the service life of the track and reducing maintenance costs; (2) By applying an alternating magnetic field of specific frequency and intensity to the track weld during the welding process, it can effectively stimulate the microscopic movement of the atomic structure inside the metal, thereby promoting the uniform release of residual stress, significantly reducing the residual stress in the weld area, eliminating the stress concentration problem, and significantly reducing the risk of cracking or fatigue failure after welding; (3) Electromagnetic treatment is a non-contact, green and low-energy-consumption means of strengthening the weld. It is achieved by relying solely on the conversion of electromagnetic energy. It is not only highly safe and will not cause secondary damage to the track structure or the surrounding environment, but also the equipment is portable and suitable for large-area track maintenance operation scenarios. Attached Figure Description

[0011] Figure 1 The diagram shown is a flowchart of one embodiment of the present invention. Detailed Implementation

[0012] This invention discloses an electromagnetic treatment method for strengthening and stress-relieving rail welds. The embodiments of this invention are described in detail below with reference to the accompanying drawings.

[0013] like Figure 1 As shown, an electromagnetic treatment method for strengthening and stress-relieving rail welds includes preheating, melting, casting, cooling, and stress-relieving processes. A low-frequency alternating magnetic field is applied throughout these processes. Specific steps include: First, a mold and a magnetic field generator are installed at the welding point of two adjacent rails. The direction of the magnetic field generated by the generator is perpendicular to the welding point. Then, the magnetic field generator is powered on, and its frequency is adjusted to between 30Hz and 50Hz. Electromagnetic preheating is performed simultaneously on the welding point and the mold, bringing their temperatures to between 500℃ and 600℃. Finally, the power to the magnetic field generator is disconnected.

[0014] The second step involves connecting the induction furnace to a power source and filling the furnace chamber with a metal mixture identical to the base material of the steel rail. The frequency of the induction furnace is then adjusted to between 20Hz and 50Hz, and the power to between 20kW and 30kW, rapidly melting the metal mixture to a temperature between 1400℃ and 1600℃. In this embodiment, the furnace chamber is a graphite crucible, and the maximum capacity of the furnace chamber relative to the metal mixture is 6kg.

[0015] The third step involves adjusting the frequency range of the induction furnace to between 5Hz and 15Hz, and the duration to between 30s and 120s, to electromagnetically stir the metal ingredients inside the furnace. In this embodiment, electromagnetic stirring not only avoids contamination of the metal ingredients by the stirring material itself at high temperatures, but also reduces the temperature gradient, promoting the formation of isocrystalline structures.

[0016] The fourth step involves connecting the magnetic field generator to the power supply and adjusting its frequency range to between 5Hz and 15Hz. The molten metal is then poured into the mold over a time of 3 to 5 seconds to prevent solidification. After pouring for 120 seconds, the frequency of the magnetic field generator is adjusted back to 5Hz, with the magnetic induction intensity ranging from 1T to 1.5T. At this point, the metal gradually begins to solidify. In this embodiment, not only is slow cooling achieved, reducing the temperature gradient and delaying solidification, thus preventing the formation of columnar crystals between the molten metal and the mold, but the electromagnetic stirring effect also helps to create an isocrystalline structure, improving mechanical properties and increasing the weld strength between the weld and the base material.

[0017] Fifth, once the temperature of the metal material has dropped to between 850°C and 950°C, the mold is disassembled from the weld seam.

[0018] The sixth step is to adjust the frequency range of the magnetic field generator to between 15 Hz and 30 Hz, and the magnetic induction intensity range to between 0.5 T and 1.0 T, so that the temperature range of the metal material is between 850 ℃ and 950 ℃, and the duration range is between 180 s and 300 s. This is used to reduce residual stress in the weld and avoid local stress concentration problems.

[0019] Step 7: Adjust the frequency of the magnetic field generator to 5Hz, with the magnetic induction intensity ranging from 1T to 1.5T, until the temperature of the metal material drops to 400℃. Then, maintain the temperature at 400℃ for at least 2 minutes before turning off the magnetic field generator and allowing the weld to cool naturally to room temperature.

[0020] The present invention will be further described below with reference to an embodiment in actual production. In this embodiment, a container plate made of 16Mn material is used as a welding workpiece for welding. The weld is a straight seam with a width of 10mm, a thickness of 20mm, a length of 300mm, and a width of 100mm.

[0021] The first step is to connect the magnetic field generator to the power supply, adjust the frequency of the magnetic field generator to 50Hz and the power to 30kW, and electromagnetically preheat the material to be welded and the mold. The user uses an infrared thermometer to measure whether the temperature of the material to be welded is between 530℃ and 550℃. If the temperature is between 530℃ and 550℃, then disconnect the power supply of the magnetic field generator.

[0022] The second step is to turn on the power to the induction furnace, put the material of the same material as the material to be welded into the furnace chamber of the induction furnace, heat the material to melt it, raise the temperature to between 1560℃ and 1600℃, and continue for 60 seconds.

[0023] The third step is to adjust the frequency of the induction furnace to 10Hz and the magnetic induction intensity to 0.5T, and to electromagnetically stir the molten material for 120 seconds.

[0024] Fourth step: Disconnect the power supply of the induction furnace and connect the power supply of the magnetic field generator. Quickly pour the molten material in the furnace into the mold within a time range of 3 to 5 seconds. Then adjust the frequency of the magnetic field generator to 5 Hz, the magnetic induction intensity to 1.0 T, and the duration to 120 seconds.

[0025] Fifth, the molten material begins to solidify. When the material temperature drops to between 850°C and 950°C, adjust the frequency of the magnetic field generator to 15Hz and the magnetic induction intensity to 1.0T, and maintain this for 5 minutes. Then, adjust the frequency of the magnetic field generator to 5Hz and the magnetic induction intensity to 1.0T, and maintain this for 5 minutes. After that, disassemble the mold. When the material temperature drops to 400°C and is maintained at 400°C for at least 2 minutes, disconnect the power supply to the magnetic field generator and allow the material to cool naturally to room temperature, thereby obtaining a welded workpiece with electromagnetic treatment.

[0026] Step 6: Repeat the above steps, except that without electromagnetic treatment, obtain a welded workpiece without electromagnetic treatment using the traditional welding method.

[0027] The seventh step involves processing the welded workpieces with and without electromagnetic treatment separately, and preparing three samples for each type of workpiece for testing.

[0028] Step 8: Mark the prepared samples, take samples from each sample, and conduct comparative tests on residual stress and tensile strength. Use a MagStress5c Barkhausen gravitational stress analyzer to detect the residual stress of the weld and a universal tensile testing machine to detect the tensile strength of the weld. The results are shown in Tables 1 and 2.

[0029] Table 1 Comparison of residual stress between those without electromagnetic treatment and those with electromagnetic treatment .

[0030] Table 2 Comparison of tensile strength between those without electromagnetic treatment and those with electromagnetic treatment .

[0031] As shown in Tables 1 and 2, the residual stress of the welded workpiece with electromagnetic treatment is significantly reduced by 52% compared to that without electromagnetic treatment; the tensile strength of the welded workpiece with electromagnetic treatment is significantly increased by 29% compared to that without electromagnetic treatment.

[0032] The invention will be further described below with reference to another embodiment in actual production. In this embodiment, 40Cr round steel is used as the welding workpiece. The dimensions of the welding workpiece are 30mm in diameter and 70mm in length, and there are 12 pieces in total. They are welded in pairs to form 6 groups. Straight seams are required, and the weld width is 10mm. The base material is 40Cr with auxiliary materials. First, 3 groups are taken out and machined on a lathe. The welding surface is ground and rusted. Then, the weld seam of the material to be welded is clamped in a mold for later use.

[0033] The first step is to connect the magnetic field generator to the power supply, adjust the frequency of the magnetic field generator to 50Hz and the power to 30kW, and electromagnetically preheat the material to be welded and the mold. The user uses an infrared thermometer to measure whether the temperature of the material to be welded is within the temperature range of 550℃ to 570℃.

[0034] The second step is to disconnect the power supply to the magnetic field generator, then connect the power supply to the induction furnace, and adjust the frequency of the induction furnace to 50Hz and the power to 30kW, melting the metal material to 1400℃ for 60 seconds.

[0035] The third step is to adjust the frequency of the induction furnace to 10Hz and the magnetic induction intensity to 0.5T, and to stir the molten metal material for 120 seconds.

[0036] Fourth step, disconnect the power supply of the induction furnace and connect the power supply of the magnetic field generator. Quickly pour the molten material in the furnace into the mold within a time range of 3s to 5s, and adjust the frequency of the magnetic field generator to 5Hz, the magnetic induction intensity to 1.0T, and the maintenance time to 120s.

[0037] Fifth, the molten material begins to solidify. Once the material temperature drops to between 850°C and 950°C, adjust the frequency of the magnetic field generator to 30Hz for 5 minutes, then adjust it to 5Hz for another 5 minutes. Afterward, remove the mold. When the material temperature drops to 400°C and remains at 400°C for at least 2 minutes, disconnect the power to the magnetic field generator and allow the material to cool naturally to room temperature, thus obtaining a welded workpiece with electromagnetic treatment.

[0038] Step 6: Repeat the above steps, except that without electromagnetic treatment, the material is melted and directly poured for welding to obtain the remaining 3 sets of welded workpieces without electromagnetic treatment.

[0039] The seventh step is to mark the welded workpieces with and without electromagnetic treatment and then conduct inspections.

[0040] Step 8: Take samples from the prepared specimens and conduct comparative tests on residual stress and tensile strength. Use a MagStress5c Barkhausen gravitational stress analyzer to detect the residual stress of the weld and a universal tensile testing machine to detect the tensile strength of the weld. The results are shown in Tables 3 and 4.

[0041] Table 3 Comparison of residual stress between those without electromagnetic treatment and those with electromagnetic treatment .

[0042] Table 4 Comparison of tensile strength between those without electromagnetic treatment and those with electromagnetic treatment .

[0043] As shown in Tables 3 and 4, the residual stress of the welded workpiece with electromagnetic treatment is significantly reduced by 64% compared to that without electromagnetic treatment; the tensile strength of the welded workpiece with electromagnetic treatment is significantly increased by 59.8% compared to that without electromagnetic treatment.

[0044] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An electromagnetic treatment method for strengthening and stress-relieving rail welds, characterized in that, The process includes preheating, melting, casting, cooling, and stress relief, with a low-frequency alternating magnetic field applied throughout all stages. Specific steps include: S1. Install the mold and magnetic field generator at the area to be welded. The magnetic field generator performs electromagnetic preheating on the area to be welded and the mold. S2. Fill the induction furnace with metal materials that are the same as the rail base material, adjust the frequency range of the induction furnace to between 20Hz and 50Hz, and the power range to between 20kW and 30kW, and melt the metal materials to a temperature range between 1400℃ and 1600℃. S3. Adjust the frequency range of the induction furnace to between 5Hz and 15Hz, and the duration range to between 30s and 120s, to perform electromagnetic stirring of the metal ingredients in the induction furnace. S4. After pouring the smelted metal into the mold, adjust the frequency range of the magnetic field generator to be between 5Hz and 15Hz, and the magnetic induction intensity range to be between 1T and 1.5T. S5. After the temperature of the metal material has decreased to a temperature range between 850°C and 950°C, disassemble the mold. S6. Adjust the frequency range of the magnetic field generator to be between 15Hz and 30Hz, and the magnetic induction intensity range to be between 0.5T and 1.0T, so that the temperature range of the metal material is between 850℃ and 950℃, and the duration is at least 180s; S7. Adjust the frequency of the magnetic field generator to 5Hz, with the magnetic induction intensity ranging from 1T to 1.5T, until the temperature of the metal material drops to 400℃. Then, maintain the temperature at 400℃ for at least 2 minutes before turning off the magnetic field generator.

2. The electromagnetic treatment method for strengthening and stress-relieving rail welds according to claim 1, characterized in that: In S1, during electromagnetic preheating, the frequency range of the magnetic field generator is between 30Hz and 50Hz, preheating the temperature of the part to be welded and the mold to a temperature range between 500℃ and 600℃.

3. The electromagnetic treatment method for strengthening and stress-relieving rail welds according to claim 1, characterized in that: In S2, the furnace liner inside the induction furnace is made of graphite material, and the maximum capacity for metal batching is 6 kg.

4. The electromagnetic treatment method for strengthening and stress-relieving rail welds according to claim 1, characterized in that: In S4, the pouring time ranges from 3 to 5 seconds.

5. The electromagnetic treatment method for strengthening and stress-relieving rail welds according to claim 1, characterized in that: In S4, after the metal material is poured into the mold, the frequency of the magnetic field generator is adjusted after 120 seconds.

6. The electromagnetic treatment method for strengthening and stress-relieving rail welds according to claim 1, characterized in that: In S6, the duration ranges from 180s to 300s.

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