Welding process of pure silver-low alloy steel composite plate for electronic-grade reduction furnace bell jar

Abstract

The invention discloses a welding process of a pure silver-low alloy steel composite plate for an electronic-grade reduction furnace bell jar. The process sequentially comprises the steps of groove machining, specifically, a base layer is machined into a Y-shaped groove, and a groove is formed in a composite layer; bottoming, filling and covering the low alloy steel base layer; carrying out nondestructive testing on the base layer; bottoming the pure silver composite layer, and filling the cover surface; and nondestructive testing of the whole weld joint is realized. And according to different material characteristics of the base layer and the composite layer, corresponding welding methods and welding process parameters are selected for welding. The method is simple and convenient to operate, the polishing procedure is reduced, the labor intensity is reduced, meanwhile, the defects such as air holes are reduced, the weld joint performance and the welding stability are guaranteed, the welding quality is improved, a base layer and a composite layer can be subjected to 100% RT detection II-level qualification and 100% PT detection I-level qualification according to NB / T47013, and a guarantee is provided for safe use of equipment.

Description

Technical Field

[0001] The invention relates to the technical field of welding technology, in particular to a welding process for a pure silver-low alloy steel composite plate for an electronic grade reduction furnace bell. Background Art

[0002] The bell-type reduction furnace is the core equipment of the improved Siemens method polysilicon production process. During operation, the high-temperature silicon core will continuously emit near-infrared electromagnetic waves with a central wavelength of 2~2.3μm. The inner wall of the bell of a conventional stainless steel reduction furnace has a low near-infrared reflectivity and exhibits a high absorption performance for infrared electromagnetic waves. The radiation energy emitted by the silicon core is absorbed by the inner wall of the bell of the reduction furnace and converted into low-grade heat energy, resulting in energy loss accounting for more than 60% of the total energy input of the reduction furnace.

[0003] Silver metal has a near-infrared reflectivity of over 90%. Using a silver-steel composite plate of a certain thickness as the inner tube of the bell jar can reflect most of the infrared waves from the silicon core and store the energy in the reduction furnace, thereby reducing energy input. This not only reduces the production cost of polysilicon, but also improves the purity of polysilicon for the production of electronic-grade polysilicon.

[0004] At present, the inner cylinder of the bell jar of the domestic electronic-grade reduction furnace generally adopts pure silver-austenitic stainless steel composite plate. Prior art application number: CN202210695657.9 discloses a welding method of silver-steel composite plate, including: processing of welding groove of silver-steel composite plate; welding of base layer of silver-steel composite plate: assembling the groove of silver-steel composite plate to ensure that the silver layer side is flush, and the gap between the groove joint surface of silver-steel composite plate is 2-4mm; welding of base layer of silver-steel composite plate, base layer of silver-steel composite plate filling layer, and base layer of silver-steel composite plate cap layer are carried out in sequence; grinding and non-destructive testing of the back of the weld of base layer of silver-steel composite plate; welding of silver layer of silver-steel composite plate; non-destructive testing of silver layer of silver-steel composite plate, and the silver layer weld is qualified according to NB / T47013.5-2015 100% PT qualified level I test. The basic defect is that it uses the traditional groove processing method to process the base welding end of the silver-steel composite plate into an outer groove, and the silver layer welding end of the silver-steel composite plate is processed into an outer groove. The traditional groove welding is easy to cause welding deformation. For large-type reduction furnaces, it is more difficult to provide back inflation protection and deformation control when the inner tube of the pure silver-austenitic stainless steel composite plate is bottomed, and as the furnace size increases, the economic efficiency of austenitic stainless steel as a base material is poor.

[0005] Secondly, the welding of pure silver-austenitic stainless steel composite plates is difficult. When welding the stainless steel base layer, the back needs to be inflated for protection, otherwise it will oxidize. In addition, the linear expansion coefficient of stainless steel is large, and the weld shrinks a lot after welding. In addition, the thermal conductivity of silver is high, and a high heat input is required during welding. Oxygen has a large solubility in liquid silver. During the cooling process after welding, liquid silver turns into a solid state, and the solubility of oxygen in silver decreases rapidly. The precipitated oxygen remains between the dendrites and cannot escape, which easily produces pores, resulting in the entire weld joint quality not meeting the standard.

[0006] In view of the above, it is necessary to propose a welding process of pure silver-low alloy steel composite plate for electronic grade reduction furnace bell to solve the above problems. Summary of the invention

[0007] The object of the present invention is to overcome the defects in the prior art and provide a welding process for a pure silver-low alloy steel composite plate for an electronic grade reduction furnace bell.

[0008] To achieve the above object, the technical solution of the present invention is as follows: A welding process of a pure silver-low alloy steel composite plate for an electronic grade reduction furnace bell comprises the following steps: Step 1, groove processing: Process the welding parts of the pure silver-low alloy steel composite plate to form a Y-shaped groove of the base layer and a groove of the composite layer, and clean the groove. When grooving the composite layer, all the composite layers within the length range will be removed, and the base layer will also be grooved to a depth of 1-1.2mm.

[0009] Step 2, welding of low alloy steel base layer: base layer welding from the composite layer side, single-sided welding and double-sided forming, that is, welding from one side of the composite layer, the front and back surfaces of the weld are both qualified; then fill the two layers on the base layer side with welding to form a base filling layer; then fill the base layer with welding to form a base cover layer; when welding, the welding method is not restricted, and a variety of welding methods can be selected, such as manual arc welding, submerged arc welding, gas shielded welding and other methods.

[0010] Step 3: Non-destructive testing: Perform non-destructive testing on the base layer.

[0011] Step 4, pure silver composite welding: preheat the composite groove and both sides before welding; the preheating in this application is for silver layer welding, and it is difficult for silver to fuse with silver. If the parent material is not preheated or preheated in place, the molten pool formed on the parent material after the silver welding wire is melted by the welding gun cannot be spread, and the shape will become similar to a small metal ball. Silver has excellent thermal conductivity, and not preheating will also cause the silver layer parent material to fail to melt, affecting normal welding. Preheating can reduce the cooling rate, help reduce the hardening tendency, and thus reduce the risk of cold cracks. By controlling the cooling rate of the metal, the microstructure of the weld can be improved, and its toughness and fatigue resistance can be improved. Uniform preheating can help control thermal deformation during welding and make the geometry of the final product more accurate. Preheating helps to promote the escape of gases (such as oxygen) in the welding molten pool and reduce the formation of pores. Although preheating itself will increase a certain amount of preparation time, it can improve production efficiency overall by reducing the need for subsequent processing steps (such as post-weld heat treatment) and reducing defect rework. After the preheating temperature is reached, a layer of bottom welding is performed on the composite side to form a composite base layer, and then a layer of composite filling cover and a composite cover surface layer are formed by welding.

[0012] Step 5: Non-destructive testing: Perform non-destructive testing on the composite layer.

[0013] The pure silver-low alloy steel composite plate has a pure silver composite layer thickness of ≥2.5 mm and a low alloy steel base layer thickness of ≥20 mm.

[0014] Furthermore, the Y-shaped groove of the base layer described in step 1 has a blunt edge of 0-2 mm and a single-side angle of 25-30°. The length of the single-side groove of the composite layer is 3-3.2 mm and the angle is 25-30°.

[0015] Further, in step 2, the tungsten inert gas welding current is 100-140A, the voltage is 14-16V, the speed is 5-10cm / min, the welding torch shielding gas is 99.99% argon, the gas flow rate is 12-20L / min, and no back shielding gas is required. The welding current of the arc welding is 140-170A, the voltage is 23-27V, and the speed is 6-12cm / min. The submerged arc welding current is 450-550A, the voltage is 32-38V, and the speed is 35-45cm / min. The interpass temperature is controlled to be ≤300℃ during welding.

[0016] Specifically, the present invention uses tungsten inert gas arc welding to prime the base layer, and the welding gun is welded on the composite side to ensure that the weld surface facing the composite side is smoothly formed, which can avoid grinding before subsequent welding of the composite layer, simplify the steps, and reduce labor intensity. According to the above, when the base layer is primed from the composite side, the front of the weld is the side facing the composite side, so that before the composite side is welded, the flatness of the bottom of the groove can be better, and the step of grinding the weld to be flat can be omitted; the argon arc welding wire model used is ER50-6 (W49A36), the specification is φ2.0mm, and one layer is welded, that is, the base layer. Since the composite plate base used in the present invention is low alloy steel, compared with the commonly used stainless steel, it does not require back protection and inflation, and its welding deformation is also small, which can effectively ensure the quality of the weld.

[0017] The welding rod model used is E5015, with a specification of φ4.0mm, and welding is performed from the base side. Two layers, namely the base filling layer, are welded. When welding the base filling layer, there is no need to re-grind and trim the weld. Since the base filling layer is welded with the same material as the base base layer, when the base filling layer is welded by arc welding, the unevenness of the back of the base layer has a remelting effect during welding, so that both sides of the base base layer do not need to be ground and trimmed, thereby simplifying the welding steps. If the existing general welding steps are used first, such as direct base welding from the base side, the back of the weld is facing the composite side, which will be very uneven, so there is an additional step of grinding and flattening before the composite layer is welded.

[0018] The submerged arc welding wire and flux model are H10Mn2+HJ431 (S49A2MS-SU34), the welding wire specification is φ4.0mm, the flux particle size is 8-40 mesh, and the base and cover layers are welded.

[0019] Furthermore, the non-destructive testing in step three is carried out by performing 100% RT testing on the base weld according to NB / T47013.2, and passing level II, and then performing 100% PT testing on both surfaces of the base weld according to NB / T47013.5, and passing level I.

[0020] Furthermore, before welding the composite base layer in step 4, the temperature within 100mm on both sides of the composite groove needs to be preheated to 120°C. Specifically, when welding the composite base layer, the shielding gas used by the welding gun is a helium-argon mixture (volume fraction is 50%+50%, gas purity is 99.999%), the gas flow rate is 12-20 L / min, the welding current is 160-190A, the voltage is 15-18V, and the welding speed is 10-15cm / min. When welding the composite filling and capping layers, the shielding gas used by the welding gun is high-purity helium (gas purity is 99.999%), the gas flow rate is 15-25L / min, the welding current is 170-200A, the voltage is 19-21V, and the welding speed is 10-15cm / min. During welding, the interpass temperature is controlled to be ≤200℃. During the welding process, the shielding gas of the drag hood is high-purity argon (gas purity is 99.999%), and the gas flow rate is 15-25L / min.

[0021] Specifically, the argon arc welding wire used is Ag99.99 with a specification of φ2.0mm. The above-mentioned preheating uses a crawler heating device fixed on the base side, and the preheating temperature is measured on the silver layer using a contact thermocouple thermometer. When welding each layer, the two sides are welded first, and then the middle. The swing arc stays for a while on the parent material side to extend the cooling time of the weld, ensure that oxygen escapes in time, and avoid the formation of pores. As mentioned above, silver has excellent thermal conductivity, and the swing arc stays for a while on the parent material side of the silver layer. There are the following effects: 1. The arc heat generated by the welding gun can better melt the metal on the parent material side to ensure good bonding with the weld metal; 2. The welding gun stays for a while so that the arc continues to heat the molten pool, slowing down the solidification of the molten pool, allowing enough time for oxygen to escape, and avoiding the formation of pores.

[0022] In the existing common silver-steel composite plate welding technology, the silver layer groove is opened relatively small, and the argon arc welding single layer single pass can fill it without arc swing. Because there is basically no RT detection requirement for the silver layer, only surface PT is required, and the tiny pores in the weld are often not taken seriously. In this application, this welding technique can effectively avoid the generation of pores and pass RT detection.

[0023] The shielding gas used in the welding gun during the double-layer bottom welding of the present invention is a helium-argon mixed gas with a mass fraction of 50%+50%, which not only avoids the problem that the molten pool cannot be spread and the molding is poor when high-purity argon is used alone as the welding gun shielding gas, but also avoids the problem that the ionization energy of the silver layer metal is too high when high-purity helium is used alone as the welding gun shielding gas, and the silver layer metal is diluted by the base layer. When the double-layer filling and covering is performed, since there is already a layer of silver layer for the bottom welding, there is no dilution problem, so the welding gun uses high-purity helium as the shielding gas alone, which can improve the welding efficiency and the weld formation is also more beautiful. High-purity argon is introduced into the drag hood to isolate the air and prevent the weld from being oxidized.

[0024] Furthermore, the non-destructive testing in step five is carried out by performing 100% RT testing on the welds of the composite layer and the base layer according to NB / T47013.2, and passing level II. Then, 100% PT testing is carried out on the surface of the composite layer weld according to NB / T47013.5, and passing level I.

[0025] Furthermore, the cleaning of the groove in step 2 includes removing scale, oil, rust and other debris within 20 mm of the base groove and both sides of the groove to expose the metallic luster and wipe it clean in one direction with anhydrous ethanol; The step 4 also includes cleaning the groove before welding, including brushing with a wire brush to remove impurities, and using anhydrous ethanol to wipe the base material within the groove and within 20 mm on both sides in one direction.

[0026] The advantages and beneficial effects of the present invention are: 1. When welding the base layer of low alloy steel, the argon arc welding gun is operated from the silver composite layer side, which ensures that the surface of the base weld facing the silver composite layer is smooth and beautiful, avoiding the need to grind the base weld combined with it before subsequent welding of the composite layer, reducing labor intensity and simplifying work steps.

[0027] 2. The silver composite layer is welded in multiple layers and multiple passes. Different welding process parameters and welding torch shielding gases are selected for different welding layers. The base layer uses a helium-argon mixed gas with a mass fraction of 50%+50%, which not only avoids the problem of the molten pool being unable to spread and poorly formed, but also avoids the problem of the silver layer metal being diluted by the base layer. The filling and covering layer uses high-purity helium with high ionization energy, which not only ensures the quality of the weld and the beautiful forming, but also improves the welding efficiency. The use of a drag hood to follow the protection prevents the weld from being oxidized.

[0028] 3. The present invention provides a welding process for a pure silver-low alloy steel composite plate for an electronic-grade reduction furnace bell jar, which has good welding quality, beautiful molding, and can pass RT and PT detection. The welding process solves the problems of poor welding quality, poor molding effect, and defects such as pores in the silver layer in the prior art that cannot pass RT detection. In particular, the welding technology problem of pure silver-low alloy steel composite plates with thicker composite layers (≥2mm) is solved, which provides a guarantee for the production and manufacturing of electronic-grade reduction furnace bell jars of pure silver-low alloy steel composite plates, and also provides a guarantee for the safe use of equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of processing parameters of various parts of the groove in the present invention; Figure 2 It is a schematic diagram of the structure of each layer of the welding joint in the present invention; In the figure: 1. Base layer; 2. Base filling layer; 3. Base covering layer; 4. Composite base layer; 5. Composite filling layer; 6. Composite covering layer; 7. Base side; 8. Composite side; 9. Y-shaped groove; 10. Trapezoidal groove; 11. Blunt edge; 12. Groove length. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0031] The welding process described in this embodiment is a welding process for a pure silver-low alloy steel composite plate for an electronic grade reduction furnace bell jar. The silver composite material of the composite plate is IC-Ag99.99 with a thickness of 2.6 mm, and the low alloy steel base material is Q345R with a thickness of 20 mm. The existing reduction furnace silver-steel composite plate is generally a composite pure silver with a base stainless steel. The plate used in the present invention is a composite pure silver with a base of low alloy steel. When the low alloy steel is used as the base to open a Y-shaped groove for welding, the deformation is much smaller than that of stainless steel, and the welding process in the present invention can ensure the composite requirements of the weld.

[0032] The specific steps are as follows: Step 1: Bevel processing: Process the welding part of the pure silver-low alloy steel composite plate to form a Y-shaped bevel of the base layer 9 and a bevel of the composite layer. The processed bevel is as follows: Figure 1 As shown, the blunt edge 11 of the Y-shaped groove 9 of the base layer is 0-2 mm, and the single-side angle is 25-30°. The length 12 of the single-side groove of the multilayer is 3-3.2 mm, and the angle is 25-30°. When the groove is cut, all the multilayers within the length range are removed, and the base layer is also cut 1-1.2 mm deep.

[0033] In the prior art, the grooves on the side of the composite plate made of conventional materials are generally for the convenience of welding the transition layer. After the base layer is welded, the transition layer can be directly welded to the joint surface in the grooves, and then the composite layer is welded to avoid the corrosion-resistant composite layer elements from being diluted. However, in the present invention, the transition layer does not need to be welded, because the melting points of pure silver and low-alloy steel are quite different, and silver has excellent thermal conductivity. When welding the base layer, the silver layer may melt, causing the composite plate to delaminate. The grooves in this embodiment can effectively avoid this situation.

[0034] Step 2: Welding of low alloy steel base: No preheating is required for base welding. Remove scale, oil, rust and other debris within 20mm on the base groove and both sides of the groove to expose the metallic luster and wipe it clean with anhydrous ethanol in one direction. When assembling, leave a gap of 2-4mm, align it with the silver composite surface as the reference, and then fix it.

[0035] Welding using TIG welding Figure 2The base layer 1 in the base layer is welded by the welding gun on the composite side 8 when the base layer is primed, ensuring that the weld surface toward the composite side 8 is smoothly formed, thereby avoiding the process of performing primer welding from the base side 7 and then grinding and trimming from the composite side 8 in the prior art, which not only ensures the welding quality but also effectively improves the welding efficiency. The welding wire used is ER50-6 (W49A36), the specification is φ2.0mm, the welding current is 130A, the voltage is 15V, the speed is 10cm / min, the welding gun shielding gas is 99.99% argon, the gas flow rate is 20L / min, no back shielding gas is required, and one layer is welded.

[0036] Welding with stick arc welding Figure 2 For the base filling layer 2, the welding rod used is E5015, the specification is φ4.0mm, the welding current is 160A, the voltage is 25V, the speed is 10cm / min, and two layers are welded.

[0037] Welding using submerged arc welding Figure 2 For the base cover layer 3, the welding wire and flux used are H10Mn2+HJ431 (S49A2MS-SU34), the welding wire specification is φ4.0mm, the flux particle size is 8-40 mesh, the welding current is 500A, the voltage is 35V, the speed is 40cm / min, and the welding is three layers.

[0038] In the above welding process, the interpass temperature is controlled to be ≤300℃.

[0039] Step 3: Nondestructive testing: According to NB / T47013.2, the base weld is subjected to 100% RT testing, and the level II is qualified. Then, according to NB / T47013.5, 100% PT testing is carried out on both surfaces of the base weld, and the level I is qualified.

[0040] Step 4: Pure silver composite welding: Before welding, clean the groove with a wire brush to remove impurities, then use anhydrous ethanol to wipe the base material within 20mm of the groove in one direction, and then use a crawler heating device fixed on the base side 7 to preheat the target weld within 100mm on both sides. The preheating temperature is measured on the silver layer using a contact thermocouple thermometer, and welding is started when it reaches 120℃.

[0041] Welding using TIG welding Figure 2 For the composite base layer 4, the welding wire used is Ag99.99, the specification is φ2.0mm, the welding current is 180A, the voltage is 18V, the speed is 10cm / min, the welding gun shielding gas is a helium-argon mixture (volume fraction is 50%+50%, gas purity is 99.999%), the gas flow rate is 20L / min, no back shielding gas is required, the drag hood shielding gas is high-purity argon (gas purity is 99.999%), the gas flow rate is 25L / min, and one layer is welded.

[0042] Welding using TIG welding Figure 2 The composite filling layer 5 and the composite covering layer 6 use Ag99.99 welding wire with a specification of φ2.0mm, a welding current of 200A, a voltage of 20V, a speed of 12cm / min, a welding gun shielding gas of high-purity helium (gas purity of 99.999%), a gas flow rate of 25L / min, no back shielding gas is required, the drag hood shielding gas is high-purity argon (gas purity of 99.999%), a gas flow rate of 25L / min, and two layers are welded.

[0043] In the above welding process, the interpass temperature is controlled at ≤200℃. The two sides are welded first, and then the middle. The arc is slightly paused on the parent material side to extend the cooling time of the weld, ensure that oxygen escapes in time, and avoid the formation of pores.

[0044] Step 5. Nondestructive testing: According to NB / T47013.2, 100% RT test is carried out on the welds of the composite layer and the base layer, and the level II is qualified. Then, according to NB / T47013.5, 100% PT test is carried out on the surface of the composite layer weld, and the level I is qualified.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. The welding process of pure silver-low alloy steel composite plate for electronic grade reduction furnace bell is characterized in that: The method comprises the following steps: Step 1: Bevel processing: Process the welding parts of the pure silver-low alloy steel composite plate to form a Y-shaped bevel of the base layer and a bevel of the multi-layer groove, and clean the bevel. When the multi-layer groove is cut, all the multi-layers within the length range are removed, and the base layer is also cut to a depth of 1-1.2mm; Step 2: Welding of low alloy steel base layer: welding the base layer from the composite layer side, single-sided welding and double-sided forming; then welding and filling two layers on the base layer side to form a base layer filling layer; then welding and filling on the base layer side to form a base layer cover layer; Step 3: Non-destructive testing: Conduct non-destructive testing on the base layer; Step 4: Pure silver composite welding: Preheat the composite groove and both sides before welding; after the preheating temperature is reached, perform bottom welding on the composite side to form a composite base layer, and then weld to form a composite filling cover and a composite cover surface layer; Step 5: Non-destructive testing: Perform non-destructive testing on the composite layer.

2. The welding process of the pure silver-low alloy steel composite plate for the electronic grade reduction furnace bell according to claim 1 is characterized in that: The Y-shaped groove of the base layer described in step 1 has a blunt edge of 0-2 mm and a single-side angle of 25-30°; the length of the single-side groove of the composite layer is 3-3.2 mm and the angle is 25-30°.

3. The welding process of the pure silver-low alloy steel composite plate for the electronic grade reduction furnace bell according to claim 1 is characterized in that: When welding the base layer in step 2, the welding gun is welded on the composite side to ensure that the weld surface toward the composite side is smoothly formed, and tungsten inert gas arc welding is used for base welding. The welding current is 100-140A, the voltage is 14-16V, the speed is 5-10cm / min, the welding gun shielding gas is 99.99% argon, the gas flow rate is 12-20L / min, and no back shielding gas is required. One layer is welded; The base filling layer is welded by arc welding, the arc welding current is 140-170A, the voltage is 23-27V, the speed is 6-12cm / min, and two layers are welded; When welding the base and cover layers, submerged arc welding is used to fill and cover the surface. The submerged arc welding current is 450-550A, the voltage is 32-38V, and the speed is 35-45cm / min. The remaining layers are welded; the interpass temperature is controlled to be ≤300℃ during welding.

4. The welding process of the pure silver-low alloy steel composite plate for the electronic grade reduction furnace bell according to claim 1 is characterized in that: The damage detection described in step three is to conduct 100% RT inspection on the base weld according to NB / T47013.2, and pass the level II. Then, 100% PT inspection is conducted on both surfaces of the base weld according to NB / T47013.5, and pass the level I.

5. The welding process of the pure silver-low alloy steel composite plate for the electronic grade reduction furnace bell according to claim 1 is characterized in that: Before welding the composite base layer described in step 4, the temperature within 100mm on both sides of the composite groove needs to be preheated to 120°C; when welding the composite base layer, the shielding gas used by the welding gun is a helium-argon mixture with a gas flow rate of 12-20 L / min, a welding current of 160-190A, a voltage of 15-18V, and a welding speed of 10-15cm / min; when welding the composite filling and capping layers, the shielding gas used by the welding gun is high-purity helium with a gas flow rate of 15-25L / min, a welding current of 170-200A, a voltage of 19-21V, and a welding speed of 10-15cm / min; during welding, the interpass temperature is controlled to be ≤200°C, and the shielding gas of the drag hood during welding is high-purity argon with a gas flow rate of 15-25L / min.

6. The welding process of the pure silver-low alloy steel composite plate for the electronic grade reduction furnace bell according to claim 1, characterized in that: The non-destructive testing described in step 5 is to conduct 100% RT testing on the welds of the composite layer and the base layer according to NB / T47013.2, and pass the level II test. Then, 100% PT testing is conducted on the surface of the composite layer weld according to NB / T47013.5, and the level I test is passed.

7. The welding process of the pure silver-low alloy steel composite plate for the electronic grade reduction furnace bell according to claim 1 is characterized in that: Cleaning the groove in step 2 includes removing scale, oil, rust and other debris within 20mm of the base groove and both sides of the groove to expose the metallic luster and wipe it clean with anhydrous ethanol in one direction; The step 4 also includes cleaning the groove before welding, including brushing with a wire brush to remove impurities, and using anhydrous ethanol to wipe the base material within the groove and within 20 mm on both sides in one direction.

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