A welding process for extra-high voltage iron tower

Abstract

The application discloses a welding process for an extra-high voltage iron tower, which comprises the following steps: 1) welding preparation: the welding areas of first large-size angle steels and second large-size angle steels to be welded are mechanically polished and chemically cleaned to remove surface oxide scales, oil stains and rust, and a symmetrical X-shaped groove design is adopted; 2) preheating and magnetic field arrangement: integral preheating is carried out by adopting a medium-frequency induction heating mode, and a pulse magnetic field generator is arranged at 5mm-15mm above the welding seam; 3) root welding layer welding: hot wire TIG welding is adopted to carry out root welding; 4) filler layer and cover layer welding: pulse MAG welding process is adopted to carry out multi-pass and multi-layer filling and cover welding; 5) post-welding heat treatment: heat treatment is immediately carried out on the welding seam and the heat affected zone; and 6) post-welding treatment: ultrasonic impact treatment is carried out on the welding seam. Through the above method, the welding process for the extra-high voltage iron tower can solve the problems existing in the production of the extra-high voltage transmission iron tower by adopting a conventional welding process.

Description

Technical Field

[0001] This invention relates to the field of welding ultra-high voltage transmission towers, and in particular to a welding process for ultra-high voltage transmission towers. Background Technology

[0002] As the backbone of the power grid, ultra-high voltage transmission towers bear enormous tensile, compressive, bending and torsional loads, and especially need to withstand dynamic loads such as wind vibration, icing and earthquakes.

[0003] With voltage levels increasing to 1000kV and above, high-strength, large-specification angle steel such as Q420 and Q460 (flange width ≥200mm, thickness 16-32mm) is widely used as the main material for iron towers. This type of steel has a high carbon equivalent (CE≥0.45%) and is highly sensitive to cold cracking during welding.

[0004] Existing conventional welding processes (such as manual arc welding, ordinary welding) Gas shielded welding and submerged arc welding have the following prominent problems: 1. Large residual stress and uneven distribution: Large-size angle steel has high rigidity, and multi-layer and multi-pass welding generates extremely high welding residual stress (often exceeding 60% of the yield strength of the base material), which leads to a decrease in the fatigue resistance of the joint and increases the risk of brittle fracture of the tower in low-temperature environment. 2. Deterioration of performance in the heat-affected zone: Grain growth is severe in the coarse-grained zone, and brittle and hard phases such as martensite are formed, resulting in a significant decrease in impact toughness at -40℃, which does not meet the service requirements of UHV towers in frigid regions. 3. Welding deformation is difficult to control: The asymmetrical cross-section of the angle steel leads to significant welding angle deformation and torsional deformation, making it difficult to straighten the finished product and affecting the overall assembly accuracy of the tower; 4. Root incomplete fusion and porosity defects: Under large blunt edges and large gap bevels, the root weld layer has poor penetration, which easily leads to incomplete fusion, concavity and porosity, becoming fatigue crack initiation points. Summary of the Invention

[0005] The main technical problem solved by this invention is to provide a welding process for ultra-high voltage (UHV) transmission towers, which can solve the problems existing when using conventional welding processes to produce UHV transmission towers.

[0006] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is to provide a welding process for ultra-high voltage transmission towers, comprising the following steps: 1) Pre-welding preparation: Mechanically grind and chemically clean the welding areas of the first and second largest angle steels to be welded to remove surface oxide scale, oil and rust, and adopt a symmetrical X-shaped bevel design with a bevel angle of 50°-70°, a blunt edge height of 1.0mm-2.5mm, and a gap of 2.0mm-4.0mm. 2) Preheating and magnetic field arrangement: Fix the first and second large-size angle steels after step 1) on the welding fixture, preheat the whole by medium frequency induction heating, and arrange the pulse magnetic field generator 5mm-15mm directly above the weld. 3) Root weld layer welding: The first and second large-size angle steels, which were fixed on the welding fixture in step 2), are root welded using hot wire TIG welding; 4) Welding of filler layer and cover layer: The first and second largest angle steels after root welding in step 3) are welded using pulsed MAG welding process to perform multi-pass, multi-layer filler and cover welding. 5) Post-weld heat treatment: Immediately after the weld and heat-affected zone are completed in step 4), the heat treatment temperature is 200℃-300℃, the holding time is 1h-2h, and then the weld is slowly cooled to room temperature at a cooling rate of ≤100℃ / h. 6) Post-weld treatment: The weld after heat treatment in step 5) is subjected to ultrasonic impact treatment. The impact frequency is 20kHz, the diameter of the impact needle is 3mm-5mm, and the treatment speed is 200mm / min-400mm / min, covering the entire weld and its heat-affected zone.

[0007] The beneficial effects of this invention are as follows: This invention provides a welding process for ultra-high voltage iron towers. This process can not only significantly reduce the residual stress level of large-specification angle steel welded joints and avoid stress corrosion cracking and fatigue failure, but also refine the grain structure of the weld metal and heat-affected zone, improve the low-temperature impact toughness at -40℃, and minimize the angular deformation and torsional deformation of the angle steel by controlling the stress-strain state during the welding process, ensuring full penetration of the root weld layer of thick-walled large bevel, and eliminating root incomplete fusion and porosity defects. Detailed Implementation

[0008] The preferred embodiments of the present invention will now be described in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0009] A welding process for ultra-high voltage transmission towers includes the following steps: 1) Pre-welding preparation: Mechanically grind and chemically clean the welding areas of the first and second largest angle steels to be welded to remove surface oxide scale, oil and rust, and adopt a symmetrical X-shaped bevel design with a bevel angle of 50°-70°, a blunt edge height of 1.0mm-2.5mm and a gap of 2.0mm-4.0mm.

[0010] 2) Preheating and magnetic field arrangement: Fix the first and second large-size angle steels after step 1) on the welding fixture, and preheat the whole by medium frequency induction heating to 120℃-180℃. The preheating range is 150mm-250mm on both sides of the weld.

[0011] A pulsed magnetic field generator is placed 5mm-15mm directly above the weld. The frequency of the pulsed magnetic field generated by the generator is 10Hz-50Hz, the peak magnetic induction intensity is 20mT-80mT, the magnetic field direction is perpendicular to the weld length direction and parallel to the welding plate plane, the number of coil turns of the pulsed magnetic field generator is 100-300, the excitation current is 10A-30A, the pulse duty cycle is 30%-60%, and the pulsed magnetic field forms an angle of 80°-100° with the welding direction. This magnetic field direction is perpendicular to the welding current direction, which can generate the maximum Lorentz force component, so that the molten pool forms a vortex motion, optimizes the grain refinement effect, and avoids arc blow. The 100-300 coil turns ensure the magnetic field strength and uniformity.

[0012] 3) Root weld: The first and second largest angle steels, fixed on the welding fixture in step 2), are root welded using hot-wire TIG (tungsten inert gas) welding. The welding current is 140A-200A, the arc voltage is 12V-16V, the welding speed is 80mm / min-120mm / min, the hot-wire current is 30A-50A, the shielding gas is pure argon, and the gas flow rate is 15L / min-20L / min. During the welding process, the pulsed magnetic field in step 2) is continuously applied. Hot-wire TIG welding can improve the deposition efficiency and precisely control the heat input to ensure full penetration of the root without burn-through.

[0013] The tungsten electrode diameter for hot-wire TIG welding is 2.4mm-3.2mm, the tungsten electrode extension length is 3mm-6mm, the arc length control coefficient is 1.0-1.2, and the root weld thickness is 3mm-5mm, which provides a good base for the subsequent filler layer and avoids root defects.

[0014] 4) Welding of the filler and capping layers: The first and second largest angle steels, after root welding in step 3), are subjected to multi-pass, multi-layer filler and capping welding using pulsed MAG (gas metal arc welding) technology. The welding current is 220A-300A, the pulse frequency is 2Hz-5Hz, the arc voltage is 24V-30V, the welding speed is 250mm / min-400mm / min, and the shielding gas is 80% Ar + 20% Ar by volume. The mixed gas has a flow rate of 18L / min-25L / min, the interpass temperature is controlled at 100℃-180℃, the oscillation width of each weld does not exceed 8 times the diameter of the welding wire, and the pulsed magnetic field in step 2) is continuously applied during the welding process.

[0015] The pulsed MAG welding adopts a unified adjustment mode, with a peak current of 350A-450A, a base current of 80A-150A, a pulse width of 2ms-5ms, and a solid core welding wire with a diameter of 1.2mm or 1.6mm and a wire extension length of 15mm-20mm. The unified adjustment mode simplifies the operation, and the 1.2mm or 1.6mm solid core welding wire matches the 220A-300A welding current in this step, ensuring deposition efficiency and controllability of the weld pool.

[0016] When performing multi-pass, multi-layer welding, the overlap between adjacent weld passes is 30%-50%, and the crater of the previous weld must be completely covered by the subsequent weld. The welding sequence is to weld from the back of the angle steel to the tip of the leg. Reasonable overlap avoids incomplete fusion between layers. The specific welding sequence utilizes the asymmetric constraint of the angle steel to make the subsequent weld pass produce a tempering heat treatment effect on the previous weld pass, and control the deformation direction, significantly reducing the angular deformation of the angle steel flange.

[0017] 5) Post-weld heat treatment: Immediately after the weld and heat-affected zone are completed in step 4), the heat treatment temperature is 200℃-300℃, the holding time is 1h-2h, and then the weld is slowly cooled to room temperature at a cooling rate of ≤100℃ / h.

[0018] Heat treatment uses resistance heating strips or medium-frequency induction heating coils, with a heating width of 100mm-200mm on each side of the weld center. During the heat treatment process, an auxiliary low-frequency alternating magnetic field with a frequency of 1Hz-5Hz and a magnetic induction intensity of 5mT-15mT is applied to promote the homogenization of residual stress.

[0019] This low-frequency alternating magnetic field does not cause stirring of the molten pool, but rather causes periodic movement of the magnetic domains inside the ferromagnetic material, generating micro-regional thermal and vibrational effects, accelerating hydrogen diffusion and homogenizing residual stress, thus making stress release more complete and uniform.

[0020] 6) Post-weld treatment: The weld after heat treatment in step 5) is subjected to ultrasonic impact treatment. The impact frequency is 20kHz, the diameter of the impact needle is 3mm-5mm, and the treatment speed is 200mm / min-400mm / min, covering the entire weld and its heat-affected zone.

[0021] After ultrasonic impact treatment, the welds undergo non-destructive testing, including ultrasonic testing and magnetic particle testing, to ensure zero defects upon leaving the factory, thus guaranteeing the safety of the tower from the testing end.

[0022] Example 1 A welding process for ultra-high voltage transmission towers, using Q420 steel as the base material with a thickness of 20mm, includes the following steps: 1) Pre-welding preparation: Mechanical grinding and chemical cleaning are performed on the welding areas of the first and second largest angle steels to be welded to remove surface oxide scale, oil and rust. A symmetrical X-shaped bevel design is adopted with a bevel angle of 60°, a blunt edge height of 1.5mm and a gap of 3.0mm.

[0023] 2) Preheating and magnetic field arrangement: Fix the first and second large-size angle steels after step 1) on the welding fixture, and preheat them as a whole using medium frequency induction heating to 140°C. The preheating range is 200mm on each side of the weld.

[0024] A pulsed magnetic field generator is placed 10 mm directly above the weld. The frequency of the pulsed magnetic field generated by the magnetic field generator is 30 Hz, the peak magnetic induction intensity is 50 mT, the magnetic field direction is perpendicular to the length of the weld and parallel to the plane of the welding plate, the number of coil turns of the pulsed magnetic field generator is 200, the excitation current is 15 A, the pulse duty cycle is 45%, and the pulsed magnetic field forms a 90° angle with the welding direction.

[0025] 3) Root weld layer welding: The first and second largest angle steels, which are fixed on the welding fixture in step 2), are root welded using hot wire TIG welding process. The welding current is 160A, the arc voltage is 14V, the welding speed is 100mm / min, the hot wire current is 40A, the shielding gas is pure argon, and the gas flow rate is 18L / min. The pulsed magnetic field in step 2) is continuously applied during the welding process.

[0026] The tungsten electrode diameter for hot-wire TIG welding is 2.4 mm, the tungsten electrode extension length is 4 mm, the arc length control coefficient is 1.1, and the root weld thickness is 4 mm.

[0027] 4) Welding of the filler and capping layers: The first and second largest angle steels, after root welding in step 3), are subjected to multi-pass, multi-layer filler and capping welding using pulsed MAG welding. The welding current is 260A, the pulse frequency is 4Hz, the arc voltage is 26V, the welding speed is 320mm / min, and the shielding gas is 80% Ar + 20% Ar by volume. The mixed gas has a flow rate of 22 L / min, the interpass temperature is controlled at 120℃-150℃, the oscillation width of each weld does not exceed 8 times the diameter of the welding wire, and the pulsed magnetic field in step 2) is continuously applied during the welding process.

[0028] The pulsed MAG welding adopts a single-mode adjustment, with a peak current of 400A, a base current of 120A, a pulse width of 3ms, and a solid core wire with a diameter of 1.2mm and a wire extension length of 18mm. When welding multiple passes and multiple layers, the overlap between adjacent weld passes is 40%, and the crater of the previous weld must be completely covered by the next weld. The welding sequence is to weld pass by pass from the back of the angle steel towards the tip.

[0029] 5) Post-weld heat treatment: Immediately after the weld and heat-affected zone are completed in step 4), the heat treatment temperature is 250℃ and the holding time is 1.5h, and then the weld is slowly cooled to room temperature at a cooling rate of 80℃ / h.

[0030] Heat treatment is performed using resistance heating strips or medium-frequency induction heating coils, with a heating width of 150mm on each side of the weld center. An auxiliary low-frequency alternating magnetic field with a frequency of 2Hz and a magnetic induction intensity of 10mT is applied during the heat treatment process to promote the homogenization of residual stress.

[0031] 6) Post-weld treatment: The weld after heat treatment in step 5) is subjected to ultrasonic impact treatment. The impact frequency is 20kHz, the diameter of the impact needle is 4mm, the treatment speed is 300mm / min, and the entire weld and its heat-affected zone are covered.

[0032] Example 2 A welding process for ultra-high voltage transmission towers, using Q460 steel as the base material with a thickness of 16mm, includes the following steps: 1) Pre-welding preparation: Mechanical grinding and chemical cleaning are performed on the welding areas of the first and second largest angle steels to be welded to remove surface oxide scale, oil and rust. A symmetrical X-shaped bevel design is adopted with a bevel angle of 50°, a blunt edge height of 1.0mm and a gap of 2.0mm.

[0033] 2) Preheating and magnetic field arrangement: Fix the first and second large-size angle steels after step 1) on the welding fixture, and preheat them as a whole using medium frequency induction heating to 150°C. The preheating range is 150mm on each side of the weld.

[0034] A pulsed magnetic field generator is placed 8mm directly above the weld. The frequency of the pulsed magnetic field generated by the magnetic field generator is 45Hz, the peak magnetic induction intensity is 30mT, the magnetic field direction is perpendicular to the length of the weld and parallel to the plane of the welding plate, the number of coil turns of the pulsed magnetic field generator is 150, the excitation current is 12A, the pulse duty cycle is 35%, and the pulsed magnetic field forms a 90° angle with the welding direction.

[0035] 3) Root weld layer welding: The first and second largest angle steels, which are fixed on the welding fixture in step 2), are root welded using hot wire TIG welding process. The welding current is 145A, the arc voltage is 13V, the welding speed is 110mm / min, the hot wire current is 35A, the shielding gas is pure argon, and the gas flow rate is 16L / min. The pulsed magnetic field in step 2) is continuously applied during the welding process.

[0036] The tungsten electrode diameter for hot-wire TIG welding is 2.4 mm, the tungsten electrode extension length is 3 mm, the arc length control coefficient is 1.05, and the root weld thickness is 3.5 mm.

[0037] 4) Welding of the filler and capping layers: The first and second largest angle steels, after root welding in step 3), are subjected to multi-pass, multi-layer filler and capping welding using pulsed MAG welding. The welding current is 230A, the pulse frequency is 5Hz, the arc voltage is 24V, the welding speed is 380mm / min, and the shielding gas is 80% Ar + 20% Ar by volume. The mixed gas has a flow rate of 20 L / min, the interpass temperature is controlled at 100℃-130℃, the oscillation width of each weld does not exceed 8 times the diameter of the welding wire, and the pulsed magnetic field in step 2) is continuously applied during the welding process.

[0038] The pulsed MAG welding adopts a single-mode adjustment, with a peak current of 360A, a base current of 90A, a pulse width of 2.5ms, and a solid wire with a diameter of 1.2mm and a wire extension length of 15mm. When welding multiple passes and multiple layers, the overlap between adjacent weld passes is 30%, and the crater of the previous weld must be completely covered by the next weld. The welding sequence is to weld pass by pass from the back of the angle steel towards the tip.

[0039] 5) Post-weld heat treatment: Immediately after the weld and heat-affected zone are completed in step 4), the heat treatment temperature is 220℃ and the holding time is 1h, and then the weld is slowly cooled to room temperature at a cooling rate of 60℃ / h.

[0040] The heat treatment uses a resistance heating strip or a medium-frequency induction heating coil, with a heating width of 100mm on each side of the weld center. An auxiliary low-frequency alternating magnetic field with a frequency of 1Hz and a magnetic induction intensity of 5mT is applied during the heat treatment process to promote the homogenization of residual stress.

[0041] 6) Post-weld treatment: The weld after heat treatment in step 5) is subjected to ultrasonic impact treatment. The impact frequency is 20kHz, the diameter of the impact needle is 3mm, the treatment speed is 380mm / min, and the entire weld and its heat-affected zone are covered.

[0042] Example 3 A welding process for ultra-high voltage transmission towers, using Q420 steel as the base material with a thickness of 32mm, includes the following steps: 1) Pre-welding preparation: Mechanically grind and chemically clean the welding areas of the first and second largest angle steels to be welded to remove surface oxide scale, oil and rust, and adopt a symmetrical X-shaped bevel design with a bevel angle of 70°, a blunt edge height of 2.5mm and a gap of 4.0mm.

[0043] 2) Preheating and magnetic field arrangement: Fix the first and second large-size angle steels after step 1) on the welding fixture, and preheat them as a whole using medium frequency induction heating to 170°C. The preheating range is 200mm on each side of the weld.

[0044] A pulsed magnetic field generator is placed 12mm directly above the weld. The frequency of the pulsed magnetic field generated by the magnetic field generator is 15Hz, the peak magnetic induction intensity is 70mT, the magnetic field direction is perpendicular to the length of the weld and parallel to the plane of the welding plate, the number of coil turns of the pulsed magnetic field generator is 280, the excitation current is 25A, the pulse duty cycle is 55%, and the pulsed magnetic field forms a 90° angle with the welding direction.

[0045] 3) Root weld layer welding: The first and second largest angle steels, which are fixed on the welding fixture in step 2), are root welded using hot wire TIG welding. The welding current is 190A, the arc voltage is 15V, the welding speed is 85mm / min, the hot wire current is 50A, the shielding gas is pure argon, and the gas flow rate is 20L / min. The pulsed magnetic field in step 2) is continuously applied during the welding process.

[0046] The tungsten electrode diameter for hot-wire TIG welding is 3.2 mm, the tungsten electrode extension length is 5 mm, the arc length control coefficient is 1.15, and the root weld thickness is 4.5 mm.

[0047] 4) Welding of the filler and capping layers: The first and second largest angle steels, after root welding in step 3), are subjected to multi-pass, multi-layer filler and capping welding using pulsed MAG welding. The welding current is 290A, the pulse frequency is 2.5Hz, the arc voltage is 29V, the welding speed is 270mm / min, and the shielding gas is 80% Ar + 20% Ar by volume. The mixed gas has a flow rate of 24 L / min, the interpass temperature is controlled at 150℃-180℃, the oscillation width of each weld does not exceed 8 times the diameter of the welding wire, and the pulsed magnetic field in step 2) is continuously applied during the welding process.

[0048] The pulsed MAG welding adopts a single-mode adjustment, with a peak current of 440A, a base current of 140A, a pulse width of 4.5ms, and a solid wire with a diameter of 1.6mm and a wire extension length of 20mm. When welding multiple passes and multiple layers, the overlap between adjacent weld passes is 50%, and the crater of the previous weld must be completely covered by the next weld. The welding sequence is to weld pass by pass from the back of the angle steel towards the tip.

[0049] 5) Post-weld heat treatment: Immediately after the weld and heat-affected zone are completed in step 4), heat treatment is performed at a temperature of 280℃ for 2 hours, followed by slow cooling to room temperature at a cooling rate of 100℃ / h.

[0050] Heat treatment is performed using resistance heating strips or medium-frequency induction heating coils, with a heating width of 200mm on each side of the weld center. An auxiliary low-frequency alternating magnetic field with a frequency of 5Hz and a magnetic induction intensity of 15mT is applied during the heat treatment process to promote the homogenization of residual stress.

[0051] 6) Post-weld treatment: The weld after heat treatment in step 5) is subjected to ultrasonic impact treatment. The impact frequency is 20kHz, the diameter of the impact needle is 5mm, the treatment speed is 220mm / min, and the entire weld and its heat-affected zone are covered.

[0052]

[0053] Performance Parameter Comparison Table Compared with existing technologies, the present invention provides a welding process for ultra-high voltage transmission towers. This process combines a symmetrical X-shaped bevel with medium-frequency preheating to reduce the welding temperature gradient. A pulsed magnetic field is applied throughout the welding process. This magnetic field generates a Lorentz force that drives the flow of molten metal in the weld pool and the rotation of the electric arc, refining the grains and interrupting the continuous growth of columnar crystals. At the same time, it promotes the redistribution of the welding stress field. Post-weld heat treatment combined with ultrasonic impact treatment uses high-energy sound waves to induce plastic extension of the weld surface, offsetting the tensile residual stress and converting the residual stress into beneficial compressive stress. Thus, the overall process achieves the comprehensive effects of stress reduction, grain refinement, and defect elimination.

[0054] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A welding process for ultra-high voltage transmission towers, characterized in that, Includes the following steps: 1) Pre-welding preparation: Mechanically grind and chemically clean the welding areas of the first and second largest angle steels to be welded to remove surface oxide scale, oil and rust, and adopt a symmetrical X-shaped bevel design with a bevel angle of 50°-70°, a blunt edge height of 1.0mm-2.5mm, and a gap of 2.0mm-4.0mm. 2) Preheating and magnetic field arrangement: Fix the first and second large-size angle steels after step 1) on the welding fixture, preheat the whole by medium frequency induction heating, and arrange the pulse magnetic field generator 5mm-15mm directly above the weld. 3) Root weld layer welding: The first and second large-size angle steels, which were fixed on the welding fixture in step 2), are root welded using hot wire TIG welding; 4) Welding of filler layer and cover layer: The first and second largest angle steels after root welding in step 3) are welded using pulsed MAG welding process to perform multi-pass, multi-layer filler and cover welding. 5) Post-weld heat treatment: Immediately after the weld and heat-affected zone are completed in step 4), the heat treatment temperature is 200℃-300℃, the holding time is 1h-2h, and then the weld is slowly cooled to room temperature at a cooling rate of ≤100℃ / h. 6) Post-weld treatment: The weld after heat treatment in step 5) is subjected to ultrasonic impact treatment. The impact frequency is 20kHz, the diameter of the impact needle is 3mm-5mm, and the treatment speed is 200mm / min-400mm / min, covering the entire weld and its heat-affected zone.

2. The welding process for ultra-high voltage transmission towers according to claim 1, characterized in that, In step 2), the entire weld is preheated to 120℃-180℃, and the preheating range is 150mm-250mm on both sides of the weld.

3. The welding process for ultra-high voltage transmission towers according to claim 2, characterized in that, In step 2), the frequency of the pulsed magnetic field generated by the magnetic field generator is 10Hz-50Hz, the peak value of the magnetic induction intensity is 20mT-80mT, the direction of the magnetic field is perpendicular to the length of the weld and parallel to the plane of the welding plate, the number of coil turns of the pulsed magnetic field generator is 100-300, the excitation current is 10A-30A, the pulse duty cycle is 30%-60%, and the pulsed magnetic field forms an angle of 80°-100° with the welding direction.

4. The welding process for ultra-high voltage transmission towers according to claim 1, characterized in that, In step 3), the welding current is 140A-200A, the arc voltage is 12V-16V, the welding speed is 80mm / min-120mm / min, the hot wire current is 30A-50A, the shielding gas is pure argon, and the gas flow rate is 15L / min-20L / min. The pulsed magnetic field in step 2) is continuously applied during the welding process.

5. The welding process for ultra-high voltage transmission towers according to claim 4, characterized in that, In step 3), the diameter of the tungsten electrode in the hot wire TIG welding is 2.4mm-3.2mm, the extension length of the tungsten electrode is 3mm-6mm, the arc length control coefficient is 1.0-1.2, and the root weld layer thickness is 3mm-5mm.

6. The welding process for ultra-high voltage transmission towers according to claim 1, characterized in that, In step 4), the welding current is 220A-300A, the pulse frequency is 2Hz-5Hz, the arc voltage is 24V-30V, the welding speed is 250mm / min-400mm / min, and the shielding gas is 80% Ar + 20% Ar by volume. The mixed gas has a flow rate of 18L / min-25L / min, the interpass temperature is controlled at 100℃-180℃, the oscillation width of each weld does not exceed 8 times the diameter of the welding wire, and the pulsed magnetic field in step 2) is continuously applied during the welding process.

7. The welding process for ultra-high voltage transmission towers according to claim 6, characterized in that, In step 4), the pulsed MAG welding adopts a unified adjustment mode, wherein the peak current is 350A-450A, the base current is 80A-150A, the pulse width is 2ms-5ms, and the welding wire is a solid welding wire with a diameter of 1.2mm or 1.6mm and a welding wire extension length of 15mm-20mm.

8. The welding process for ultra-high voltage transmission towers according to claim 7, characterized in that, In step 4), when performing multi-pass, multi-layer welding, the overlap between adjacent weld passes is 30%-50%, and the arc crater of the previous weld must be completely covered by the next weld. The welding sequence is to weld pass by pass from the back of the angle steel towards the tip.

9. The welding process for ultra-high voltage transmission towers according to claim 1, characterized in that, In step 5), the heat treatment uses a resistance heating strip or a medium-frequency induction heating coil. The heating width is 100mm-200mm on each side of the weld center. An auxiliary low-frequency alternating magnetic field with a frequency of 1Hz-5Hz and a magnetic induction intensity of 5mT-15mT is applied during the heat treatment process to promote the homogenization of residual stress.

10. The welding process for ultra-high voltage transmission towers according to claim 1, characterized in that, After the ultrasonic impact treatment in step 6), the weld is subjected to non-destructive testing, including ultrasonic testing and magnetic particle testing.

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