A kind of electric furnace preheating section U-shaped groove body segmented replacement assembly welding structure and process

Abstract

The application discloses a kind of electric furnace upper preheating section U-shaped groove body segmented replacement assembly welding structure and process, including U-shaped material groove preheating section and U-shaped material groove feeding section, U-shaped transition assembly welding section is equipped between U-shaped material groove preheating section and U-shaped material groove feeding section;U-shaped material groove feeding section side is through inside bevel D and inside bevel B, outside bevel D and outside bevel B horizontal group pair form welding butt joint bevel face angle 60 °, the side with bevel of U-shaped material groove preheating section and the side with bevel of U-shaped transition assembly welding section, through inside bevel A and inside bevel C, outside bevel A and outside bevel C horizontal group pair form welding butt joint bevel face angle 60 °.The above structure and process are implemented, not only safe and easy to operate, welding quality is stable, investment cost is lower, meet the actual demand on site, work efficiency is high, and greatly reduce maintenance cost, reduce downtime loss, provide guarantee for reasonable group production.

Description

Technical Field

[0001] The invention relates to the technical field of repairing parts for production of electric furnace equipment, and in particular to a segmented replacement and assembly welding structure and process for a U-shaped trough body in a preheating section of an electric furnace. Background Art

[0002] The existing converter steelmaking equipment is being replaced by the new ECS scrap preheating continuous charging electric arc furnace technology. This achieves operational flexibility and allows for the selection of charge materials between scrap and molten iron, minimizing environmental impact. The energy-saving steelmaking equipment consists of two sections: a charging section and a preheating section. The feed end of the preheating section is connected to the waste heat recovery and dust removal system piping, and the discharge end is overlapped with the electric furnace port, forming a fully enclosed electric furnace steelmaking process that combines scrap preheating, flue gas purification, and waste heat recovery, including continuous feeding, preheating, melting, and smelting. The preheating section has an arched cross-section smoke hood at the top and a U-shaped water-cooled chute at the bottom. During operation, the scrap in the U-shaped chute is uniformly and continuously moved toward the furnace bath under the action of vibration. The scrap is gradually heated from room temperature to an average temperature of 400-650°C by the combined effects of flue gas waste heat and CO combustion heat, and then enters the furnace bath for rapid melting.

[0003] Since the U-shaped trough is welded together with multiple sections, it is divided into the U-shaped trough feeding section B and the U-shaped trough preheating section A (such as Figure 1 As shown in the figure, the main process is to transport the scrap steel from the feeding section to the preheating section. Because the preheating section trough not only carries a large amount of scrap steel for a long time, but is also affected by the vibration of the bottom bracket, the scrap steel is moved, and the thermal expansion and contraction caused by alternating hot and cold temperatures, the U-shaped trough in the preheating section has cracked and deformed on a large scale. If production continues, it may cause major equipment hazards. The preheating section must be replaced. Since the equipment is imported spare parts, there are problems:

[0004] 1. If the entire U-shaped trough is sent offline for repair or replacement, it will be difficult to disassemble, hoist and transport it, and the production cycle will be long, and it will not meet the needs of continuous production.

[0005] 2. Make the U-shaped trough preheating section A into domestic Q345 spare parts, but the welds of different materials must ensure that there are no cracks, pores and other welding defects in the UT and MT penetration inspections.

[0006] 3. The original U-shaped trough body is made of NM400, which has a large carbon equivalent, large thickness, and high tensile strength, resulting in poor weldability. Therefore, it is necessary to design a segmented replacement and assembly welding device and process for the U-shaped trough body in the preheating section of the electric furnace to carry out on-site segmented replacement. Summary of the Invention

[0007] The purpose of the present invention is to provide a segmented replacement and assembly welding structure and process for the U-shaped trough body of the preheating section of an electric furnace, which is used for the repaired U-shaped trough body of the preheating section. It not only has low investment cost, convenient on-site operation and maintenance, and short repair time, but also the metallurgically bonded welding layer is suitable for periodic use. A manual angle grinder is used to grind the surface of all group welds flush with the trough surface, ensuring the original arcs on both sides of the U-shaped trough body, restoring the drawing size and accuracy of the U-shaped trough body, and passing the on-site actual sample inspection and acceptance to fully meet the overall U-shaped trough body operation requirements, so as to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A segmented replacement and assembly welding structure for a U-shaped trough in a preheating section of an electric furnace comprises a U-shaped trough preheating section made of Q345 and a U-shaped trough feeding section originally made of NM400; a U-shaped transition assembly welding section made of low-strength Q235 material is provided between the U-shaped trough preheating section and the U-shaped trough feeding section; an inner groove A and an outer groove A are machined on one side of the pair welding of the U-shaped trough preheating section; an inner groove B and an outer groove B are machined on one side of the pair welding of the U-shaped trough feeding section; the U-shaped transition assembly welding section is formed by cutting and bending 50mm steel plates, and inner grooves C, inner groove D, outer groove C and outer groove D are machined on both sides of the pair welding.

[0010] Preferably, a U-shaped transition assembly welding section is installed on one side of the U-shaped trough feeding section, and the inner groove D and the inner groove B, the outer groove D and the outer groove B are horizontally paired to form a welding butt groove surface angle of 60°, and the side of the U-shaped trough preheating section with a groove and the side of the U-shaped transition assembly welding section with a groove are horizontally paired through the inner groove A and the inner groove C, the outer groove A and the outer groove C to form a welding butt groove surface angle of 60°.

[0011] The present invention provides another technical solution: a segmented replacement and assembly welding process for a U-shaped trough body in a preheating section of an electric furnace, comprising the following steps: first assembling a U-shaped transition assembly welding section made of low-strength Q235 material - then assembling a U-shaped material trough preheating section made of Q345 material - forming an X-groove - preheating the inner groove D and inner groove B, outer groove D and outer groove B of the dissimilar steel before welding - welding the inner groove D and inner groove B, outer groove D and outer groove B symmetrically in the bottom layer welding order, and directly welding the inner groove A and inner groove C, outer groove A and outer groove C of the high-strength steel symmetrically - hammering the weld surface - confirming defects - controlling the interlayer temperature - the filling and covering welding order is the same as the bottom layer - the covering layer is higher than the base material and has a smooth transition - the inner groove D and inner groove B, outer groove D and outer groove B of the dissimilar steel are heat treated after welding - manual grinding - inspection and acceptance - delivery for use.

[0012] Preferably, the process also includes the following steps before welding:

[0013] S1: Welding equipment: HT400D digitally controlled inverter manual argon arc welding machine combined with DC welding machine, overall NM400 wear-resistant plate welding layer: welding rod φ3.2mm, φ4.0mm, welding materials: E5015 and J857Cr;

[0014] S2: Heating device: Preheating: oxygen-acetylene flame preheating, post-weld heat treatment: electric heating;

[0015] S3: Auxiliary facilities: angle grinder, file, hammer, flat shovel, mask, sample, thermometer, magnifying glass, thermal insulation cotton;

[0016] S4: Weldment materials: NM400 wear-resistant plate, Q345 plate, Q235 plate;

[0017] S5: Requirements for surfacing welding before welding: clean the surface of the groove from water, paint, rust, oil, and welding slag. Do not strike the arc directly on the groove surface. Use an arc-starting plate.

[0018] S6: Welding position: single-sided V-groove, all-position welding;

[0019] S7: Welding requirements: All weld layers must be free of any welding defects and fused to the parent material.

[0020] Preferably, after the U-shaped trough preheating section, the U-shaped transition assembly welding section and the U-shaped trough feeding section are assembled and fixed, the welding sequence is as follows:

[0021] S1: First, perform symmetrical welding of the bottom layers of the inner groove D and inner groove B, and the outer groove D and outer groove B of the dissimilar steel;

[0022] S2: Then perform direct symmetrical welding of the inner groove A and inner groove C of the strength steel, and the outer groove A and outer groove C.

[0023] Preferably, in S1, the preheating is carried out by using an oxygen-acetylene flame to heat 50-100 mm on both sides of the groove to 100-130°C, and a temperature measuring gun is used to verify the temperature on both sides of the weld. After the temperature is reached, an HT400D digitally controlled inverter manual combined DC welding machine is used, a low-strength E5015 welding rod, and a φ3.2mm arc starting plate are used to start the bottom layer welding, and the weld surface is hammered.

[0024] Preferably, the welding sequence of the filling and cover layers is the same as that of the bottom layer, specifically: high-strength steel welding rod J857Cr is used for symmetrical welding of the inner groove D and inner groove B, and the outer groove D and outer groove B of the dissimilar steel to ensure sufficient wear resistance in the connection area. During welding, the two sides pause slowly and the transition of the rod in the middle is fast. After the weld is completed, the surface is hammered immediately, and the interlayer temperature is controlled to be not less than 100°C. Then a small crescent-shaped rod movement method is used. The cover surface of the weld layer is higher than the base material, which is convenient for manual grinding and smooth transition with the base material. The inner groove A and inner groove C of the high-strength steel, and the outer groove A and outer groove C are directly welded symmetrically with E5015, and the welding method is the same as the dissimilar steel groove welding.

[0025] Preferably, after the high-temperature weld is completed, the inner groove D and inner groove B, outer groove D and outer groove B welds of the dissimilar steel are locally heated to 500-600℃ for stress relief treatment, kept at a constant temperature for 1 hour and then slowly cooled to room temperature with 150-170℃ insulation cotton wrapping; the welds are then tested by UT and MT penetrant testing to ensure no cracks and pore defects, and the welds are precisely ground with a manual angle grinder to ensure a smooth transition between the welds and the U-shaped trough base material, and compared with a previously produced sample that meets the requirements, and the tolerance size is restored before delivery for use.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention provides a segmented replacement and assembly welding structure and process for the U-shaped trough body in the preheating section of an electric furnace. Combined with the welding working conditions of high-strength steel groups made of dissimilar materials, the invention uses low-strength Q235 material to make the U-shaped transition assembly welding section, which meets the transition welding between the original NM400 U-shaped trough body and the U-shaped trough preheating section made of domestic spare parts made of Q345, thereby realizing on-site heating, temperature control and insulation capabilities to meet the overall group welding quality requirements of the welding process.

[0028] 2. The present invention provides a segmented replacement and assembly welding structure and process for the U-shaped trough body of the preheating section of an electric furnace. Not only does it have low investment costs, convenient on-site operation and maintenance, and short repair time, but the segmented replacement of the large preheating section feed U-shaped trough body can be welded through transition tooling, and all welds can be metallurgically bonded and meet periodic use.

[0029] 3. The present invention provides a segmented replacement and assembly welding structure and process for the U-shaped trough body in the preheating section of an electric furnace. A manual angle grinder is used to grind the surface of all the welds flush with the surface of the trough body, ensuring the original arcs on both sides of the inside and outside of the U-shaped trough body, restoring the size and accuracy of the U-shaped trough body on the drawing, and passing the on-site actual sample inspection and acceptance to fully meet the overall U-shaped trough body operation requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is an axonometric drawing of the overall structure of the present invention;

[0031] Figure 2 It is a schematic diagram of the overall structure of the present invention;

[0032] Figure 3 It is an exploded view of the overall structure of the present invention.

[0033] In the figure: 1. Inner groove A; 2. Inner groove C; 3. Inner groove D; 4. Inner groove B; 5. Outer groove A; 6. Outer groove C; 7. Outer groove D; 8. Outer groove B; 9. U-shaped trough preheating section; 10. U-shaped trough feeding section; 11. U-shaped transition assembly welding section. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] See also Figure 1-3 In an embodiment of the present invention, a segmented replacement and assembly welding structure of a U-shaped trough body in a preheating section of an electric furnace is provided, comprising a U-shaped trough preheating section 9 made of Q345 and a U-shaped trough feeding section 10 originally made of NM400. A U-shaped transition assembly welding section 11 made of low-strength Q235 material is provided between the U-shaped trough preheating section 9 and the U-shaped trough feeding section 10; an inner groove A1 and an outer groove A5 are machined on one side of the group welding of the U-shaped trough preheating section 9; an inner groove B4 and an outer groove B8 are machined on one side of the group welding of the U-shaped trough feeding section 10; the U-shaped transition assembly welding section 11 is formed by cutting and bending 50mm steel plates, and inner grooves C2, inner groove D3, outer grooves C6 and outer grooves D7 are machined on both sides of the group welding.

[0036] The specific connection method is as follows: first install the U-shaped transition assembly welding section 11 on one side of the U-shaped trough feeding section 10, and form a welding butt groove surface angle of 60° through the inner groove D3 and the inner groove B4, the outer groove D7 and the outer groove B8 horizontally. Then, the side with the groove of the U-shaped trough preheating section 9 and the side with the groove of the U-shaped transition assembly welding section 11 are horizontally paired through the inner groove A1 and the inner groove C2, the outer groove A5 and the outer groove C6 to form a welding butt groove surface angle of 60°. Finally, all are fixed and spot welded to restore the original U-shaped trough body drawing size and accuracy, and then heated and welded.

[0037] In order to further better explain the embodiment of the present invention, a segmented replacement assembly welding process of the U-shaped trough body of the preheating section of the electric furnace is also provided, which includes the following steps: first, a U-shaped transition assembly welding section 11 made of low-strength Q235 material is assembled - then a U-shaped material trough preheating section 9 made of Q345 is assembled - an X groove is formed - the inner groove D3 and the inner groove B4, the outer groove D7 and the outer groove B8 of the dissimilar steel are preheated before welding - the bottom welding sequence is the inner groove D3 and the inner groove B 4. Symmetrical welding of outer groove D7 and outer groove B8; direct symmetrical welding of inner groove A1 and inner groove C2, outer groove A5 and outer groove C6 of strength steel - hammering weld surface - confirm defects - control interlayer temperature - welding sequence of filling and cover is the same as that of base layer - cover layer is higher than base material and has smooth transition - heat treatment of inner groove D3 and inner groove B4, outer groove D7 and outer groove B8 of dissimilar steel after welding - manual grinding - inspection and acceptance - delivery for use.

[0038] Specifically, it also includes the pre-welding preparation process:

[0039] S1: Welding equipment: HT400D digitally controlled inverter manual argon arc welding machine combined with DC welding machine, overall NM400 wear-resistant plate welding layer: welding rod φ3.2mm, φ4.0mm, welding materials: E5015 and J857Cr;

[0040] S2: Heating device: Preheating: oxygen-acetylene flame preheating, post-weld heat treatment: electric heating;

[0041] S3: Auxiliary facilities: angle grinder, file, hammer, flat shovel, mask, sample, thermometer, magnifying glass, thermal insulation cotton;

[0042] S4: Weldment materials: NM400 wear-resistant plate, Q345 plate, Q235 plate;

[0043] S5: Requirements for surfacing welding before welding: clean the surface of the groove from water, paint, rust, oil, and welding slag. Do not strike the arc directly on the groove surface. Use an arc-starting plate.

[0044] S6: Welding position: single-sided V-groove, all-position welding;

[0045] S7: Welding requirements: All weld layers must be free of any welding defects and fused to the parent material.

[0046] The welding process parameters are as follows:

[0047]

[0048] In the above process, Figure 1 As shown: After the U-shaped trough preheating section 9, the U-shaped transition assembly welding section 11 and the U-shaped trough feeding section 10 are assembled and fixed, the welding sequence is as follows:

[0049] S1: First, perform symmetrical welding of the bottom layers of the inner grooves D3 and B4, and the outer grooves D7 and B8 of the dissimilar steel. To ensure welding quality, especially for online welding of NM400 wear-resistant plate, reduce heat input and use a faster welding speed. Short arc welding is recommended, and large lateral swings are prohibited to prevent cracks and other defects. The groove surface must be cleaned of water, paint, rust, oil, welding slag, and other stains. Preheating is performed using an oxygen-acetylene flame to 100-130°C within 50-100mm on both sides of the groove. Because the U-shaped trough body is made of NM400, which has a high carbon equivalent, large thickness, and high tensile strength, a temperature gun must be used to verify the temperature on both sides of the weld. After reaching the temperature, the HT400D digitally controlled inverter manual (argon arc welding machine) combined with a DC welder is used. A low-strength E5015 electrode with a diameter of 3.2mm is used with an arc starter plate to start the bottom layer welding. The weld surface is hammered to confirm that there are no defects.

[0050] S2: Then directly and symmetrically weld the inner groove A1 and inner groove C2 of the strength steel, and the outer groove A5 and outer groove C6.

[0051] In the above process, the welding sequence of the filling and cover layers is the same as that of the base layer, specifically: high-strength steel welding rod J857Cr is used for symmetrical welding of the inner groove D3 and inner groove B4, and outer groove D7 and outer groove B8 of the dissimilar steel to ensure sufficient wear resistance in the connection area. Because it is a full-position welding rod movement method with short arc operation, the two sides pause slowly and the middle rod movement transition is fast during welding, which is conducive to the fusion of the parent material. After the weld is completed, hammering is performed on the surface immediately to eliminate welding stress and control the interlayer temperature to be not lower than 100°. After ensuring sufficient interlayer temperature, a small crescent-shaped rod movement method is used. The cover surface of the weld layer is higher than the parent material, which is convenient for manual grinding and smooth transition with the parent material. The inner groove A1 and inner groove C2, outer groove A5 and outer groove C6 of the high-strength steel are directly welded with E5015 symmetrically. The welding method is the same as the welding of the inner groove D3 and inner groove B4, outer groove D7 and outer groove B8 of the dissimilar steel.

[0052] In the above process, after the high-temperature weld is completed, the inner groove D3 and inner groove B4, outer groove D7 and outer groove B8 welds of the dissimilar steel are locally heated to 500-600℃ for stress relief treatment. After being kept at a constant temperature for 1 hour, they are wrapped with insulation cotton at 150-170℃ and cooled to room temperature. The welds are then tested by UT and MT penetrant testing to ensure no cracks or pores. A manual angle grinder is used to precisely grind the welds to ensure a smooth transition with the U-shaped trough base material. The welds are then compared with a previously produced sample that meets the requirements, and the tolerance dimensions are restored. The welds are then put into use and the mechanical properties are achieved after a period of operation.

[0053] In summary, the present invention provides a welding structure and process for the segmented replacement and assembly of a U-shaped trough in the preheating section of an electric furnace. This repair method is not only safe and easy to operate, with stable welding quality and low investment costs, meeting actual on-site needs and achieving high efficiency, but also significantly reduces maintenance costs and downtime losses, ensuring optimal production. This welding repair method provides a scientific basis for the welding and repair of other large wear-resistant plates.

[0054] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A U-shaped trough body segmented replacement assembly welding structure for the preheating section of an electric furnace, comprising a U-shaped trough preheating section (9) made of Q345 and a U-shaped trough feeding section (10) originally made of NM400, characterized in that: A U-shaped transition assembly welding section (11) made of low-strength Q235 material is provided between the U-shaped trough preheating section (9) and the U-shaped trough feeding section (10); an inner groove A (1) and an outer groove A (5) are machined on one side of the U-shaped trough preheating section (9); an inner groove B (4) and an outer groove B (8) are machined on one side of the U-shaped trough feeding section (10); the U-shaped transition assembly welding section (11) is formed by cutting and bending 50mm steel plates, and inner groove C (2), inner groove D (3), outer groove C (6) and outer groove D (7) are machined on both sides of the welding.

2. The U-shaped trough segment replacement and assembly welding structure of the upper preheating section of an electric furnace according to claim 1, characterized in that: A U-shaped transition assembly welding section (11) is installed on one side of the U-shaped trough feeding section (10), and a welding butt groove surface angle of 60° is formed by horizontally pairing the inner groove D (3) and the inner groove B (4), and the outer groove D (7) and the outer groove B (8). The side with the groove of the U-shaped trough preheating section (9) and the side with the groove of the U-shaped transition assembly welding section (11) are horizontally paired by the inner groove A (1) and the inner groove C (2), and the outer groove A (5) and the outer groove C (6) to form a welding butt groove surface angle of 60°.

3. A welding process for replacing and assembling a segmented welding structure of a U-shaped trough in a preheating section of an electric furnace as claimed in claim 1 or 2, characterized in that: The following steps are involved: First, assemble the U-shaped transition assembly welding section (11) made of low-strength Q235 material - then assemble the U-shaped trough preheating section (9) made of Q345 material - form the X groove - preheat the inner groove D (3) and inner groove B (4), outer groove D (7) and outer groove B (8) of the dissimilar steel before welding - the bottom welding sequence is symmetrical welding of the inner groove D (3) and inner groove B (4), outer groove D (7) and outer groove B (8), and the inner groove of the strength steel is symmetrical. Side groove A (1) and inner groove C (2), outer groove A (5) and outer groove C (6) are directly welded symmetrically - hammer the weld surface - confirm defects - control the interlayer temperature - the filling and cover welding sequence is the same as the base layer - the cover layer is higher than the base material and has a smooth transition - the inner groove D (3) and inner groove B (4) of the dissimilar steel, outer groove D (7) and outer groove B (8) are heat treated after welding - manually ground - inspection and acceptance - delivery for use.

4. The welding process for replacing and assembling the U-shaped trough in the upper preheating section of an electric furnace in section by section according to claim 3, characterized in that: Also includes pre-welding preparation steps: S1: Welding equipment: HT400D digitally controlled inverter manual argon arc welding machine combined with DC welding machine, overall NM400 wear-resistant plate welding layer: welding rod φ3.2mm, φ4.0mm, welding materials: E5015 and J857Cr; S2: Heating device: Preheating: oxygen-acetylene flame preheating, post-weld heat treatment: electric heating; S3: Auxiliary facilities: angle grinder, file, hammer, flat shovel, mask, sample, thermometer, magnifying glass, thermal insulation cotton; S4: Weldment materials: NM400 wear-resistant plate, Q345 plate, Q235 plate; S5: Requirements for surfacing welding before welding: clean the surface of the groove from water, paint, rust, oil, and welding slag. Do not strike the arc directly on the groove surface. Use an arc-starting plate. S6: Welding position: single-sided V-groove, all-position welding; S7: Welding requirements: All weld layers must be free of any welding defects and fused to the parent material.

5. The welding process for replacing and assembling the segmented welding structure of the U-shaped trough in the upper preheating section of an electric furnace as claimed in claim 3 is characterized in that: After the U-shaped trough preheating section (9), the U-shaped transition assembly welding section (11) and the U-shaped trough feeding section (10) are assembled and fixed, the welding sequence is as follows: S1: First, perform symmetrical welding of the bottom layers of the inner groove D (3) and inner groove B (4), outer groove D (7) and outer groove B (8) of the dissimilar steel; S2: Then, the inner groove A (1) and the inner groove C (2) of the strength steel, and the outer groove A (5) and the outer groove C (6) are directly and symmetrically welded.

6. The welding process for replacing and assembling the U-shaped trough in the upper preheating section of an electric furnace in section by section according to claim 5 is characterized in that: In S1, oxygen-acetylene flame is used for preheating to 100-130℃ at 50-100mm on both sides of the groove. A temperature measuring gun is used to verify the temperature on both sides of the weld. After the temperature is reached, the HT400D digitally controlled inverter manual combined DC welding machine is used. Low-strength E5015 welding rod and φ3.2mm arc starting plate are used to start bottom welding and hammer the weld surface.

7. The welding process for replacing and assembling the U-shaped trough in the upper preheating section of an electric furnace in section by section as claimed in claim 3 is characterized in that: The welding sequence of filling and covering layer is the same as that of bottom layer, specifically: high strength steel electrode J857Cr is used for symmetrical welding of inner groove D (3) and inner groove B (4), outer groove D (7) and outer groove B (8) of dissimilar steel to ensure sufficient wear resistance of connection area. During welding, the two sides are paused slowly and the transition of the electrode in the middle is fast. After the weld is completed, the surface is hammered immediately and the temperature between layers is controlled to be not less than 100℃. Then a small crescent electrode is used. The cover surface of the weld layer is higher than the base material to facilitate manual grinding and smooth transition with the base material. High strength steel inner groove A (1) and inner groove C (2), outer groove A (5) and outer groove C (6) are directly welded symmetrically with E5015. The welding method is the same as that of dissimilar steel groove welding.

8. The welding process for replacing and assembling the U-shaped trough in the upper preheating section of an electric furnace in sections according to claim 7 is characterized in that: After the high-temperature welds are completed, the inner groove D (3) and inner groove B (4), outer groove D (7) and outer groove B (8) welds of the dissimilar steel are locally heated to 500-600℃ for stress relief treatment. After being kept at a constant temperature for 1 hour, they are wrapped with insulation cotton at 150-170℃ and cooled to room temperature. The welds are then tested by UT and MT penetrant testing to ensure that there are no cracks or pores. The welds are then precisely ground with a manual angle grinder to ensure a smooth transition between the welds and the U-shaped trough base material. The welds are then compared with the previously produced samples to restore the tolerance dimensions and are then delivered for use.

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