Method for improving strength of gas shielded welding joint

Abstract

The invention relates to the technical field of strength of gas shield welding joints, in particular to a method for improving the strength of a gas shield welding joint, steel plate welding is completed in the mode of folding back welding at the plate seam position of two steel plates, a lining is arranged below the welding position of the two steel plates, and a welding groove is formed in the position, at the plate seam position of the two steel plates, of the lining. The welding starting position is on the steel plate on one side, welding is conducted in the plate seam direction, welding is conducted on the steel plate on the other side across the plate seam, the distances between welding pools passing through plate seam gaps in the plate seam turning-back process are the same, and welding seam forced water cooling points are arranged at the positions, 10-30 mm away from the welding pools, behind the welding pools. The method has the beneficial effects that the problem that the joint strength is reduced due to softening generated in a heat affected zone in the gas shielded welding process of high-strength steel is solved, the strength of a weld joint softening zone is improved, and the joint strength is larger than that of base metal.

Description

Technical Field

[0001] This invention relates to the field of gas-shielded welded joint strength technology, and in particular to a method for improving the strength of gas-shielded welded joints. Background Technology

[0002] Gas shielded welding (GSW) is widely used in industrial production due to its high welding efficiency, ease of operation, and excellent weld quality. In hot continuous rolling production, GSW is used to weld the ends of two hot-rolled steel coils together in a single pass to form a continuous steel strip. As the strength of steel plates increases, the strength requirements for welded joints also increase. Generally, replacing the welding wire with one of the same strength is sufficient to meet the strength requirements of the welded joint. However, in the heat-affected zone (HAZ) of the welded steel plate, due to the influence of the welding thermal cycle, a softening zone appears. The strength of this softened zone is relatively low, becoming the weakest point of the welded joint. Because the weld is straight, the softened zone of the welded joint is also distributed in a straight line parallel to the weld. After the strip is welded, under the tension of the strip and the bending of the rollers, the insufficient strength of the softened zone leads to cracks that rapidly propagate along the softened zone, causing joint failure. Therefore, improving the strength of the softened zone of the weld joint is a key factor in improving the strength of GSW joints of high-strength steel.

[0003] Chinese invention patent CN1708593A, entitled "Method for Improving the Toughness of the Heat-Affected Zone in Welded Joints of Steel," strengthens the heat-affected zone and obtains high-strength welded joints through shot peening hardening treatment using ultrasonic vibration or ultrasonically vibrating steel balls. However, while shot peening has a significant impact on the heat-affected zone on the weld surface, it has a smaller impact on the weld core and little effect on improving the strength of the weld joint. Post-weld processing is required, making it unsuitable for mass production applications.

[0004] Chinese invention patent CN102107313A, entitled "An Online Process for Improving the Performance of the Welded Heat-Affected Zone," uses compressed air sprayed behind the welding arc and immediately followed by insulation cotton to slowly cool the weld, aiming to reduce or eliminate cracks in the welded heat-affected zone. While this patented post-weld compressed air cooling method is effective in reducing the welded heat-affected zone, its effectiveness on hot-rolled plates is limited, as it cannot cool the steel to the core. It requires additional equipment and complex processes to improve weld performance, making it difficult and costly to implement. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a method for improving the strength of gas shielded welded joints. The method employs a reciprocating welding technique at the seam of two steel plates to enhance the strength of the welded joint, thereby solving the problem of reduced joint strength caused by softening in the heat-affected zone during the gas shielded welding process of high-strength steel.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A method for improving the strength of gas-shielded welded joints, wherein the steel plates are welded by a reverse welding method at the seam of the two plates, the specific method is as follows: a. A pad is placed below the welding position of the two steel plates. The pad has a welding groove at the joint of the two steel plates. The groove width e: 2mm~5mm, the groove depth h: 1mm~2mm, the groove length n> the joint length, and the pad is cooled by water. b. The welding starts on one side of the steel plate and is welded towards the seam. Welding is then performed across the seam to the other side of the steel plate. The spacing of the weld pool is the same when it passes through the gap between the seams during the seam return process. The spacing L is 5-7 mm and the peak value A is 9-12 mm. The weld pool is continuously welded in the direction of the seam, and the heat-affected zone exhibits non-linear fluctuations. c. A forced water cooling point is set behind the weld pool, at a distance of 10mm to 30mm from the weld pool, and the water cooling zone covers the entire weld joint.

[0007] Furthermore, the welding path for the reversible welding includes an oblique triangle path, a sine wave path, or an equilateral triangle path.

[0008] Furthermore, the water temperature T at the water cooling point is ≤25℃, and the water flow rate Q is 1L / min~10L / min.

[0009] Furthermore, the thickness B of the steel plate is 2mm to 5mm.

[0010] Furthermore, the gap m between the plates is ≤ 2mm.

[0011] Furthermore, the padding material is made of copper or a copper alloy.

[0012] Furthermore, the padding thickness H is 10mm to 50mm; the width D is 20mm to 60mm.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1) By optimizing the welding process path and combining it with post-weld water cooling, the problem of softening in the heat-affected zone during gas shielded welding of high-strength steel, which leads to a reduction in joint strength, is solved, thus enabling gas shielded welding of high-strength steel plates.

[0014] 2) The dual cooling method combining padding and water cooling achieves rapid cooling of the weld and heat-affected zone, preventing the heat-affected zone from widening and increasing its strength. Simultaneously, the weld metal is forcibly shaped by the concave copper padding, preventing weld leaks and welding defects. This bidirectional forced cooling ensures that the joint strength exceeds that of the base metal, and the weld tensile fracture occurs in the base metal.

[0015] 3) Change the stress concentration characteristics of the heat-affected zone in the entire weld, realize the undulating shape of the heat-affected zone in the welded joint, and realize the joint characteristics of stress dispersion, so as to achieve uneven stress distribution in the heat-affected zone, avoid stress concentration, and improve joint strength.

[0016] 4) The invention is simple in design and easy to implement. The steel plate has good weld penetration, good back-side forming, and the welded joint is not prone to breakage. It has good welding performance, and the two hot-rolled steel coils are firmly welded at the head and tail, with good overall integrity. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the welding process described in this invention.

[0018] Figure 2 This is a schematic diagram of the oblique triangular welding path described in this invention.

[0019] Figure 3 This is a schematic diagram of the equilateral triangular welding path described in this invention.

[0020] Figure 4 This is a schematic diagram of the sinusoidal welding path described in this invention.

[0021] In the diagram: 1. Steel plate; 2. Welded pool; 3. Water cooling point; 4. Lining. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below: like Figures 1-3 As shown, a method for improving the strength of gas-shielded welded joints is described. This method involves welding two steel plates 1 together at their weld seam location using a folding-back welding technique. The folding-back welding path includes an oblique triangular path, a sinusoidal waveform path, or an equilateral triangular path. The purpose of the welding path design is to change the uniform position and concentrated stress distribution of the heat-affected zone (HAZ) along the weld direction. By changing the welding path, the HAZ exhibits an undulating distribution along the welding path, thus altering the concentrated stress distribution within the HAZ throughout the weld and achieving an undulating shape and dispersed stress distribution in the welded joint.

[0023] The specific method is as follows: a. A backing 4 is placed below the welding position of the two steel plates 1. The backing thickness H: 10mm~50mm; the width D: 20mm~60mm. The backing 4 has a welding groove at the seam between the two steel plates 1. The groove width e: 2mm~5mm, the groove depth h: 1mm~2mm, and the groove length n: greater than the weld length. Water is circulated inside the backing 4 for cooling. The function of the backing 4 is to cool the molten weld metal and the steel plate in the weld zone. Simultaneously, the groove forces the weld to form a shape, preventing weld leaks and welding defects. The main reason for the degradation of the heat-affected zone (HAZ) performance is the heat transfer from the molten weld metal to the steel plate 1 through heat conduction, causing deterioration of the HAZ microstructure and reduced performance. The backing 4 on the back of the weld accelerates the cooling capacity of the weld and the steel plate, reduces the HAZ temperature, and increases the cooling rate, thereby reducing the width of the HAZ and increasing its strength. Its concave position corresponds to the weld position, ensuring weld formation.

[0024] b. The welding starts on one side of steel plate 1 and proceeds towards the seam, crossing the seam to the other side of steel plate 1. The weld pool 2 maintains the same spacing (L) as it passes through the seam gap during the seam return process. This spacing ensures a continuous welding effect and a fluctuating heat-affected zone in the seam direction. If the spacing is less than 5mm, the weld pool 2 will exhibit continuous welding characteristics, and the heat-affected zone will not achieve the fluctuating characteristics. When the spacing is greater than or equal to 7mm, unwelded areas will appear in the seam direction, resulting in an unqualified weld.

[0025] Peak value A: 9mm~12mm. A peak value of 9mm~12mm is designed to achieve better weld joint and heat-affected zone (HAZ) undulation effect. A peak value <9mm results in poor HAZ undulation effect. A peak value ≥12mm increases the weld joint width, increases welding material consumption, lengthens welding time, increases welding repetition areas, and results in poor weld appearance. It also reduces the undulation effect of the HAZ, making it closer to a straight line.

[0026] c. A forced water-cooling point 3 is set at a distance of 10mm to 30mm behind the weld pool 2. The purpose is to reduce the continuous increase in the width of the weld heat-affected zone (HAZ). Water cooling rapidly lowers the temperature of the weld joint, achieving rapid cooling and microstructural transformation of the weld and HAZ, thus increasing weld strength and reducing the HAZ width. When the distance of the water-cooling point 3 from the weld pool is less than 10mm, water easily enters the weld pool, causing weld porosity defects. When the distance of the water-cooling point 3 from the weld pool is ≥30mm, the HAZ has already grown in length and width, and the water-cooling effect is severely reduced.

[0027] The water temperature T ≤ 25℃, and the water flow rate Q: 1L / min~10L / min. The water-cooling zone covers the entire weld joint, achieving microstructural transformation of the weld and heat-affected zone. The water temperature primarily cools the weld; excessively high temperatures hinder cooling and prevent the achievement of the desired effect. The water flow rate directly impacts the weld cooling effect. When the flow rate is < 1L / min, the cooling effect is poor, and the back side of steel plate 1 cannot achieve effective cooling. When the water flow rate is ≥ 10L / min, the desired cooling effect of the thick steel plate 1 is achieved; further increasing the flow rate would waste water resources.

[0028] The reserved gap between the plates is to ensure good penetration at the seam during welding. When the gap m > 2mm, welding defects such as weld beads and weld leaks are prone to occur. When the plate thickness B is less than 2.5mm, setting a gap can actually increase the likelihood of weld leaks. Therefore, a gap of 0mm is used when the plate thickness B < 2.5mm, and the gap is appropriately increased when the plate thickness B ≥ 2.5mm. To ensure welding penetration and quality, the gap m is set to 0mm–2mm.

[0029] Example: The conventional straight weld seam welding method used in the comparative example of this invention is used to weld the plate seam. The welding process parameters and welding path of this invention example are shown in Table 1, and the tensile test results of the joint of this invention example are shown in Table 2.

[0030] Table 1 - Welding process parameters and welding paths in embodiments of the present invention: Table 2 - Tensile test results of joints in embodiments of the present invention: As can be seen from the above embodiments, when steel plate 1 is welded by reciprocating welding, the strength of the welded joint basically reaches the strength of the base steel plate 1, which improves the strength of the softened zone of the weld joint, realizes gas shielded welding of high-strength steel plate 1, and the welded joint is not prone to breakage.

[0031] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for improving the strength of gas-shielded welded joints, characterized in that, This method involves welding the steel plates together by folding the weld back at the seam. The specific method is as follows: a. A pad is placed below the welding position of the two steel plates. The pad has a welding groove at the joint of the two steel plates. The groove width e: 2mm~5mm, the groove depth h: 1mm~2mm, the groove length n> the joint length, and the pad is cooled by water. b. The welding starts on one side of the steel plate and is welded towards the seam. Welding is then performed across the seam to the other side of the steel plate. The spacing of the weld pool is the same when it passes through the gap between the seams during the seam return process. The spacing L is 5-7 mm and the peak value A is 9-12 mm. The weld pool is continuously welded in the direction of the seam, and the heat-affected zone exhibits non-linear fluctuations. c. A forced water cooling point is set behind the weld pool, at a distance of 10mm to 30mm from the weld pool, and the water cooling zone covers the entire weld joint.

2. The method for improving the strength of gas-shielded welded joints according to claim 1, characterized in that, The welding path for the reversible welding includes an oblique triangle path, a sine wave path, or an equilateral triangle path.

3. The method for improving the strength of gas-shielded welded joints according to claim 1, characterized in that, The water temperature T at the water cooling point is ≤25℃, and the water flow rate Q is 1L / min~10L / min.

4. The method for improving the strength of gas-shielded welded joints according to claim 1, characterized in that, The thickness B of the steel plate is 2mm to 5mm.

5. A method for improving the strength of a gas-shielded welded joint according to claim 1, characterized in that, The gap between the plates is m≤2mm.

6. The method for improving the strength of gas-shielded welded joints according to claim 1, characterized in that, The padding material is made of copper or a copper alloy.

7. A method for improving the strength of a gas-shielded welded joint according to claim 1, characterized in that, The padding thickness H is 10mm to 50mm; the width D is 20mm to 60mm.

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