A residual stress self-balanced gas shielded welding method without preheating

Abstract

The application discloses a residual stress self-balancing non-preheating gas shield welding method, which is characterized in that a double-sided symmetric welding groove form is designed, and a double-sided symmetric simultaneous welding process with the residual stress self-balancing characteristic is adopted, so that the heat distribution of a molten pool and the residual stress distribution characteristic during base welding of thick-walled high-strength steel are improved, the purpose of double-sided simultaneous welding residual stress self-balancing is achieved, and the welding cold crack defects are avoided under the non-preheating welding condition, the welding quality is ensured, the welding efficiency is improved, the welding cost is reduced, the energy consumption in the welding process is reduced, the energy utilization rate is improved, the carbon emission in the welding process is fundamentally reduced, and the green low-carbon characteristic is achieved.

Description

Technical Field

[0001] This invention relates to preheating-free welding technology, and more specifically, to a preheating-free gas shielded welding method for self-balancing residual stress. Background Technology

[0002] Currently, the mainstream welding methods in various engineering structures such as shipbuilding, pressure vessels and pipelines, machinery and equipment, and transportation are gas metal arc welding and submerged arc welding. These two welding technologies are convenient to operate, have high overall efficiency, and low comprehensive cost. By matching different types of welding materials, they can meet the requirements of joint performance and structural integrity in various service environments, such as conventional static mechanical properties, dynamic fatigue performance, corrosion resistance, and high temperature resistance.

[0003] With the increasing application of high-strength steel, especially in thick-walled applications, cold cracking in welding has become a critical issue affecting weld quality. During the initial root pass welding of thick-walled high-strength steel, the low temperature and rapid cooling of the steel plate easily lead to hardened structures at the weld joint. Furthermore, the high restraint during the initial root pass prevents the release of residual stress, thus contributing to cold cracking in the high-strength steel root pass weld. To avoid this, many industrial sectors currently employ high-temperature preheating before welding to reduce the post-weld cooling rate and its resulting hardening tendency in the high-strength steel weld joint, and to decrease residual stress. While this preheating technology, widely adopted in industry, fundamentally solves the problem of cold cracking in thick high-strength steel plate welding, it increases the complexity of the welding process and overall cost. Simultaneously, regardless of whether oxy-acetylene flame, liquefied natural gas, or induction preheating is used, all methods increase energy consumption and carbon emissions throughout the welding process, which is inconsistent with the current strong advocacy for green, low-carbon, and high-quality development. Therefore, it is necessary to develop universally applicable green and low-carbon welding technologies.

[0004] Currently, the technology for high-efficiency welding of medium and heavy plates is relatively mature. Application No. 201310567567.2 discloses a high-efficiency welding method for single-pass, single-sided, double-sided forming of butt joints in medium and heavy plates. This method employs a composite welding technique using both consumable electrode and non-consumable electrode arcs for the root pass, followed by dual-wire consumable electrode gas shielded welding supplemented with cold wire filler welding for the cover pass. By changing the power supply polarity, extension length, and gas mixture ratio, it achieves spatter-free, high-deposition, and efficient filler welding under large welding parameters. However, as a crucial quality-influencing variable, the cold wire feeding parameters are not quantified, leading to uncertainties in welding quality and limiting its applicability. Application No. 201611144535.1 discloses a high-efficiency welding method using metal-cored flux-cored wire. By using metal-cored wire with a specific flux composition wrapped in thin steel strips, the wire deposition rate is increased, thus achieving high-efficiency welding. However, this technology lacks high energy utilization. Application No. 201710554829.X discloses an efficient welding method for ultra-thick steel plates used in steel structure buildings. Based on multi-layer submerged arc welding, a layer of shredded welding wire is pre-laid between each layer to balance the welding heat distribution, reduce welding stress and deformation, and improve energy utilization and welding efficiency. However, this method, which is equivalent to a cold wire filler effect, cannot achieve quantitative control or precise control and reproducibility of welding quality. Application No. 201010249754.2 discloses a welding method for ultra-thick high-strength hydropower steel. Based on manual welding for the root pass and gas metal arc welding for the fill and cover passes, it employs an asymmetrical double-sided U-shaped bevel to achieve narrow-gap welding. Essentially, the narrow-gap bevel design improves welding efficiency. Application No. 2017106199523.X discloses an efficient welding method for E690 high-strength steel cylinders; Application No. 201710750258.7 discloses an efficient welding method for S460NL high-strength steel flanges; and Application No. 201810927796.3 discloses an efficient welding method for high heat input twin-wire submerged arc welding. All of these are submerged arc welding-based processes used for thick steel plates. Compared with manual welding and semi-automatic welding, the welding efficiency is indeed greatly improved, but they do not have the characteristics of improving energy utilization and reducing carbon emissions. Application No. 200610070181.0 discloses a preheat-free welding process for 800MPa high-strength steel. It mainly uses pulsed gas shielded welding with low-strength solid welding wire or flux-cored welding wire for the root pass, and then uses aluminum silicate plate to cover the weld joint for heat preservation and slow cooling to achieve preheat-free welding of high-strength steel. However, this technology is applicable to a limited range of plate thicknesses and reduces the strength matching of the root pass welding wire, which poses a safety hazard in some front-load applications.Patent application number 200410084699.0 discloses a low yield strength ratio easy-to-weld structural steel thick plate and its production method, and patent application number 200410096795.7 discloses a high tensile strength, high toughness, low yield strength ratio bainitic steel and its production method. Both of them improve the weldability of high-strength steel plates by optimizing the chemical composition and controlling the rolling process during the steel design and manufacturing stage. However, this approach has many limitations in terms of adaptability to subsequent welding manufacturing processes and will increase the overall cost.

[0005] In view of the above, there is an urgent need to develop a high-strength steel welding technology without preheating that can balance residual stress. This technology can improve the heat distribution of the molten pool and the characteristics of residual stress during the root pass welding of thick-walled high-strength steel, and achieve the goal of self-balancing of residual stress in double-sided welding. This will prevent cold cracking in welding under preheating conditions, ensure welding quality, improve welding efficiency, and reduce welding costs. Summary of the Invention

[0006] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a self-balancing residual stress gas-shielded welding method. By designing a double-sided symmetrical welding groove and employing a double-sided symmetrical simultaneous welding process with residual stress self-balancing characteristics, the heat distribution of the molten pool and the distribution of welding residual stress during the root pass welding of thick-walled high-strength steel are improved. This achieves the goal of self-balancing residual stress during double-sided simultaneous welding, thereby avoiding welding cold cracking defects under preheating welding conditions, ensuring welding quality, improving welding efficiency, reducing welding costs, reducing energy consumption during the welding process, improving energy utilization, and fundamentally reducing carbon emissions during the welding process, exhibiting green and low-carbon characteristics.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a self-balancing gas shielded welding method for residual stress without preheating, comprising the following steps:

[0009] S1, Welding bevel design: The welding joint of the workpiece to be welded is processed into a double-sided symmetrical welding bevel; the blunt edge length F of the double-sided symmetrical welding bevel satisfies the following formula: F=k×d; where F is the blunt edge length of the double-sided symmetrical welding bevel, in mm; k is the welding wire diameter coefficient, dimensionless, and the value range of k is 2~5; d is the diameter of the gas metal arc shielded solid welding wire used for welding, in mm;

[0010] S2, No preheating welding: After the parts to be welded are positioned and assembled, they are welded by gas shielded welding without preheating. During the root pass welding, the starting welding torch and the following welding torch are started on both sides of the welding bevel of the parts to be welded to perform double-sided symmetrical welding simultaneously.

[0011] Preferably, in step S1,

[0012] When the welding joint of the workpiece to be welded is a butt joint, the bevel angle α of the double-sided symmetrical welding groove is 50 to 80°, and in the calculation formula of the blunt edge length F of the double-sided symmetrical welding groove, the value range of the welding wire diameter coefficient k is 2.5 to 5.

[0013] Preferably, in step S1,

[0014] When the welded joint of the workpiece to be welded is a full penetration corner joint, the bevel angle α of the double-sided symmetrical welding groove is 30 to 50°, and in the calculation formula of the blunt edge length F of the double-sided symmetrical welding groove, the value range of the welding wire diameter coefficient k is 2 to 4.

[0015] Preferably, in step S2, before the positioning assembly, mechanical or chemical cleaning methods are used to remove contaminants from the welding bevel of the workpiece to be welded and from at least 50 mm on both sides.

[0016] Preferably, in step S2, when the parts to be welded are positioned and assembled, the assembly gap of the parts to be welded does not exceed 0.5 mm.

[0017] Preferably, in step S2, when the welding joint of the workpiece to be welded is a butt joint,

[0018] The relative misalignment of the butt joint after positioning and assembly is less than 1 / 3 of the thickness of the workpiece to be welded, and less than 5mm.

[0019] After the butt joint is positioned and assembled, for every 1mm increase in the relative misalignment, the blunt edge length F calculated according to the formula F=k×d decreases by 1mm accordingly.

[0020] Preferably, in step S2, when the welding joint of the workpiece to be welded is a butt joint, during the root pass welding process, a gap distance D is provided between the starting welding torch and the following welding torch, and the gap distance D satisfies the following formula:

[0021]

[0022] In the formula, D is the distance between the starting welding torch and the following welding torch, in mm, and D≥10mm;

[0023] P cm The cold cracking sensitivity index of the workpiece to be welded is dimensionless.

[0024] t represents the thickness of the workpiece to be welded, in mm;

[0025] d represents the diameter of the gas metal arc shielded solid welding wire used for butt welding, in mm.

[0026] Preferably, in step S2, when the welding joint of the workpiece to be welded is a butt joint, during the root pass welding process, the welding current I of the initial welding torch is... 起 The welding voltage is 140-450A. 起 The voltage ranges from 15 to 38 V, and the welding speed is V. 起 The flow rate is 160–500 mm / min, using direct pull welding or oscillating welding, with a shielding gas flow rate of 15–40 L / min, and no preheating is required throughout the welding process;

[0027] The welding current I following the welding torch 跟 =(1.0~1.5)I 起 Welding voltage U 跟 The voltage is 16-39V. The welding speed of the following welding torch is the same as that of the starting welding torch. Straight pull welding or oscillating welding is used. The flow rate of the shielding gas is 15-40L / min. There is no preheating throughout the welding process.

[0028] Preferably, in step S2, when the weld joint of the workpiece to be welded is a full penetration corner joint, during the root pass welding process, a gap distance D is provided between the starting welding torch and the following welding torch, and the gap distance D satisfies the following formula:

[0029]

[0030] In the formula, D is the distance between the starting welding torch and the following welding torch, in mm, and D is at least 0;

[0031] P cm The cold cracking sensitivity index of the workpiece to be welded is dimensionless.

[0032] t represents the thickness of the workpiece to be welded, in mm;

[0033] d represents the diameter of the gas metal arc shielded solid welding wire used for full penetration corner joint welding, in mm.

[0034] Preferably, in step S2, the welding current I of the starting welding torch... 起 The welding voltage is 160–480A. 起 The voltage ranges from 15 to 38 V, and the welding speed is V. 起 The flow rate is 140–450 mm / min, using direct pull welding or oscillating welding, with a shielding gas flow rate of 15–40 L / min, and no preheating is required throughout the welding process;

[0035] The welding current I following the welding torch 跟 =(1.0~1.5)I 起 Welding voltage U 跟The voltage is 19-40V. The welding speed of the following welding torch is the same as that of the starting welding torch. Straight pull welding or oscillating welding is used. The flow rate of the shielding gas is 15-40L / min. There is no preheating during the entire welding process.

[0036] The self-balancing residual stress gas shielded welding method provided by this invention has the following advantages:

[0037] 1. The residual stress self-balancing gas shielded welding method of the present invention, particularly for butt joints and corner joints (including T-joints and cross joints) that are based on gas metal arc welding and can be operated in the horizontal welding position, improves the heat distribution of the molten pool and the distribution of welding residual stress during the root pass welding of thick-walled high-strength steel by a specific double-sided symmetrical groove design and optimization of double-sided symmetrical welding process parameters with self-balancing welding residual stress characteristics. This achieves the purpose of self-balancing of residual stress in double-sided welding, thereby avoiding welding cold cracks under preheating welding conditions, ensuring welding quality, improving welding efficiency, and reducing welding costs.

[0038] 2. The residual stress self-balancing gas shielded welding method of the present invention reduces energy consumption in the welding process and improves energy utilization by welding with large blunt edges and large penetration depth on both sides without preheating before welding. It fundamentally reduces carbon emissions in the manufacturing and welding process and has green and low-carbon characteristics.

[0039] 3. The residual stress self-balancing gas shielded welding method of the present invention can be applied to various industrial fields related to welding of high-strength steel thick plate structures. Without the need to fundamentally change the mainstream welding process methods at the product manufacturing end, it is based on gas metal arc welding and adopts a double-sided symmetrical simultaneous root pass welding technology with residual stress self-balancing characteristics. Under the condition of no preheating, it can avoid the problem of cold cracking in the welding of thick-walled high-strength steel. It provides a green, low-carbon, low-cost, and high-efficiency solution for welding of high-strength steel structures, showing significant technical and cost advantages and has broad application value.

[0040] 4. The residual stress self-balancing gas shielded welding method of the present invention is designed for high-strength steel butt joints and corner joints. Based on the current mainstream gas metal arc welding process for structural components manufacturing in the industrial field, it does not require any revolutionary changes to the welding process technology. By utilizing the self-balancing and partial elimination mechanism of residual stress during simultaneous welding of both sides symmetrically, it can achieve preheating welding of the root pass weld, which has the highest sensitivity to cold cracking. It is easy to operate, has a short implementation cycle, and low overall cost, and has direct engineering application value and guiding significance.

[0041] 5. The residual stress self-balancing gas shielded welding method of the present invention adopts the double-sided simultaneous symmetrical root pass welding technology, which can significantly improve the welding penetration depth within the same welding process range. Therefore, the filler amount can be reduced by increasing the bevel blunt edge size in the welding structure design, which ultimately improves the welding efficiency and reduces the overall welding manufacturing cost.

[0042] 6. The residual stress self-balancing gas shielded welding method of the present invention significantly improves the energy utilization rate of the molten pool, reduces the consumption of primary energy, and fundamentally reduces carbon emissions in the manufacturing and welding process, thus exhibiting green and low-carbon characteristics. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the double-sided symmetrical bevel form of the butt joint in the self-balancing residual stress gas shielded welding method of the present invention.

[0044] Figure 2 This is a schematic diagram of the double-sided symmetrical bevel form of the corner joint in the self-balancing residual stress gas shielded welding method of the present invention.

[0045] Figure 3 This is a schematic diagram of the root pass welding of the butt joint in the self-balancing residual stress gas shielded welding method of the present invention.

[0046] Figure 4 This is a schematic diagram of the root pass welding of a corner joint in the self-balancing residual stress gas shielded welding method of the present invention. Detailed Implementation

[0047] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0048] This invention provides a self-balancing residual stress gas shielded welding method without preheating. Based on gas metal arc welding (GMAW) for butt joints and corner joints (including T-joints and cross joints) manufactured in horizontal welding positions, this method avoids cold cracking in thick-walled high-strength steel welding without preheating by utilizing the mechanism of residual stress self-balancing and partial elimination during simultaneous symmetrical welding. Simultaneously, it fully utilizes the residual heat in the welding area to increase the penetration depth of the root pass, improving energy utilization and overall welding efficiency. Key technical points of this invention include: specific double-sided symmetrical bevel design, pre-weld preparation and assembly, design and optimization of GMAW process parameters for simultaneous symmetrical welding with self-balancing residual stress, and preheating-free welding and joint quality inspection for butt and corner joints.

[0049] The present invention provides a self-balancing residual stress gas shielded welding method without preheating, comprising the following steps:

[0050] S1, Welding bevel design: The welding joint of the workpiece to be welded is processed into a double-sided symmetrical welding bevel; the blunt edge length F of the double-sided symmetrical welding bevel satisfies the following formula: F=k×d; where F is the blunt edge length of the double-sided symmetrical welding bevel, in mm; k is the welding wire diameter coefficient, dimensionless, and the value range of k is 2~5; d is the diameter of the gas metal arc shielded solid welding wire used for welding, in mm;

[0051] Specifically, based on the structural characteristics and design requirements of different industrial sectors, the first step is to design a double-sided symmetrical welding bevel. Considering the rapid cooling rate of steel plates at room temperature during the first root pass welding, especially for high-strength steel, this leads to a significant hardening tendency. Furthermore, the high restraint stress during the root pass welding prevents the release of residual welding stress, resulting in a high tendency for cold cracking. Therefore, for both butt joints and corner joints, a double-sided symmetrical bevel is adopted. This allows for the mutual elimination of residual welding stress during simultaneous double-sided root pass welding, achieving a self-balancing characteristic of residual stress and significantly reducing the tendency for cold cracking without preheating. Furthermore, simultaneous double-sided symmetrical root pass welding increases the energy utilization rate of the welding area, thereby increasing the actual weld penetration. Therefore, the blunt edge dimension of the double-sided symmetrical weld bevel is larger than that under conventional asymmetric welding conditions, and is positively correlated with the diameter of the welding wire used, i.e., F = k × d, where F is the blunt edge length of the double-sided symmetrical weld bevel in mm; k is the welding wire diameter coefficient, dimensionless, with a value ranging from 2 to 5; and d is the diameter of the gas metal arc shielded solid welding wire used in the welding process in mm. The value of k here needs to be determined based on the diameter d of the welding wire used in the welding process and the weld joint. When the weld joint is a butt joint, the larger the welding wire diameter d, the larger the value of k; when the weld joint is a full penetration fillet joint, the larger the welding wire diameter d, the larger the value of k.

[0052] Figure 1 , Figure 2 These are double-sided symmetrical welding groove forms for butt joints and full penetration corner joints that can be used for welding parts without preheating.

[0053] Combination Figure 1As shown, when the welded joint is a butt joint, the bevel angle α of the double-sided symmetrical weld bevel is 50 to 80°. In the calculation formula of the blunt edge length F of the double-sided symmetrical weld bevel, the value range of the welding wire diameter coefficient k is 2.5 to 5, that is, F = (2.5 to 5) × d. Generally, the diameter d of the gas metal arc shielded solid welding wire used for butt joints is 1.6 mm, 1.2 mm, 1.0 mm, and 0.9 mm. Therefore, the upper limit boundary of the welding wire diameter is d = 1.6 mm, and at this time F = 8 mm.

[0054] Combination Figure 2 As shown, when the welded joint is a full penetration type corner joint, the bevel angle α of the double-sided symmetrical welding groove is 30 to 50°. In the calculation formula of the blunt edge length F of the double-sided symmetrical welding groove, the value range of the welding wire diameter coefficient k is 2 to 4, that is, F = (2 to 4) × d. Generally, the diameter d of the gas metal arc shielded solid welding wire used for full penetration type corner joints is 1.6 mm, 1.2 mm, 1.0 mm, and 0.9 mm. Therefore, the upper limit boundary of the welding wire diameter is d = 1.6 mm, and at this time F = 6.4 mm.

[0055] For non-full penetration corner joints, they are generally not used as positive load-bearing nodes, and there are no explicit restrictions on the bevel angle α and the blunt edge length F.

[0056] S2, No preheating welding: After the parts to be welded are positioned and assembled, they are welded by gas shielded welding without preheating. During the root pass welding, the starting welding torch and the following welding torch are started on both sides of the welding bevel of the parts to be welded to perform double-sided symmetrical welding simultaneously.

[0057] Pre-welding preparation and assembly: After the welding bevel of the parts to be welded is processed, pre-welding preparation is required, which involves cleaning the welding area. Mechanical or chemical cleaning methods can be used to thoroughly remove rust, moisture, oil, and other contaminants that may affect welding quality from the surface of the welding bevel and at least 50mm on both sides, in order to avoid unnecessary welding defects during the welding process. Then, the parts to be welded are positioned and assembled. Whether it is a butt joint or a full-penetration corner joint, the assembly gap should not exceed 0.5mm. In particular, to ensure the penetration depth and the quality of the root pass, the following restrictions are imposed on the relative misalignment caused during the assembly of butt joints: the relative misalignment after butt joint assembly should be less than 1 / 3 of the thickness of the parts to be welded, and less than 5mm. For every 1mm increase in misalignment, the blunt edge dimension calculated according to the relationship between the blunt edge dimension F (mm) and the welding wire diameter d (mm) F = (2.5~5) × d should be reduced by 1mm accordingly.

[0058] For welding without preheating, the assembled parts to be welded are placed in a horizontal welding position, and gas shielded welding is used to weld the parts without preheating. During the root pass welding, the starting and following welding torches are activated simultaneously on both sides of the weld bevel of the parts to be welded, performing symmetrical welding on both sides. The welding process for butt joints and corner joints needs to be determined according to the actual situation.

[0059] For butt joints, place the assembled parts to be welded in the horizontal welding position, such as... Figure 3 As shown; during the root pass welding process, the initial welding torch and the follow-up welding torch are started simultaneously on both sides of the weld groove of the workpiece to be welded, performing double-sided symmetrical welding; according to the cold cracking sensitivity index P of the workpiece to be welded. cm (Dimensionless) and the thickness t (in mm) of the parts to be welded vary. A certain interval D is set between the starting welding torch and the following welding torch. That is, the starting welding torch completes the root pass welding at interval D (in mm) before the following welding torch starts welding on the other side, and then both welding operations proceed simultaneously. This fully utilizes the heat from the initial weld pool to increase the penetration depth of the following weld, improving the blunt edge penetration and welding efficiency. It also quickly balances and eliminates residual stress and joint hardening caused by the initial weld bead, minimizing the occurrence of cold cracks in high-strength steel welding.

[0060] Considering different cold cracking sensitivity indices P cm Furthermore, the thickness t of the workpiece to be welded affects the requirements for residual stress self-balancing and elimination, and the interval distance D between the starting welding torch and the following welding torch affects the cold cracking sensitivity index P. cm A quantitative correlation is established between the thickness t of the workpiece to be welded and the diameter d of the welding wire:

[0061]

[0062] In the formula, D is the distance between the starting welding torch and the following welding torch, in mm, and D≥10mm;

[0063] P cm The cold cracking sensitivity index of the workpiece to be welded is dimensionless.

[0064] t represents the thickness of the workpiece to be welded, in mm;

[0065] d represents the diameter of the gas metal arc shielded solid welding wire used for butt welding, in mm.

[0066] Based on the different welding structure manufacturing requirements of various industrial fields and the different diameters (d) of the selected gas-shielded solid welding wire, the following differentiated root pass welding process parameters are adopted for the starting welding torch and the following welding torch:

[0067] For the initial welding torch, the welding current I 起=140~450A, welding voltage U 起 =15~38V, welding speed v 起 =160~500mm / min. Straight pull welding or oscillating welding can be used as needed. The shielding gas used for gas shielded welding can be 100% CO2 or argon-rich mixed gas (including but not limited to commonly used binary and multi-component mixed gases), with a shielding gas flow rate of f = 15~40L / min. No preheating is required throughout the root pass welding process.

[0068] For welding torches, the welding current I... 跟 =(1.0~1.5)I 起 Welding voltage U 跟 Appropriate matching is required while ensuring the stability of the welding process; welding speed v 跟 =v 起 Depending on the requirements, either direct pull welding or oscillating welding can be used. The shielding gas used for gas shielded welding can be 100% CO2 or an argon-rich mixture (including but not limited to commonly used binary and multi-component mixtures), with a flow rate of f = 15–40 L / min. No preheating is required throughout the welding process.

[0069] For full penetration corner joints, place the assembled parts to be welded in the horizontal welding position, such as... Figure 4 As shown; during the root pass welding process, the initial welding torch and the follow-up welding torch are started simultaneously on both sides of the weld groove of the workpiece to be welded, performing double-sided symmetrical welding; according to the cold cracking sensitivity index P of the workpiece to be welded. cm (Dimensionless) and considering the varying thickness t (in mm) of the workpiece to be welded, a certain interval D is set between the starting welding torch and the following welding torch. That is, the starting welding torch first completes the root pass welding at interval D (in mm), then the following welding torch starts welding on the other side, and then both welding operations proceed synchronously. Considering the single-sided V-groove characteristics of the corner joint and its influence on the weld penetration characteristics, the interval D between the starting and following welding torches is related to the cold cracking sensitivity index P. cm A quantitative correlation is established between the thickness t of the workpiece to be welded and the diameter d of the welding wire:

[0070]

[0071] In the formula, D is the distance between the starting welding torch and the following welding torch, in mm, and D is at least 0;

[0072] P cm The cold cracking sensitivity index of the workpiece to be welded is dimensionless.

[0073] t represents the thickness of the workpiece to be welded, in mm;

[0074] d represents the diameter of the gas metal arc shielded solid welding wire used for full penetration corner joint welding, in mm.

[0075] Based on the different welding structure manufacturing requirements of various industrial fields and the different diameters (d) of the selected gas-shielded solid welding wire, the following differentiated root pass welding process parameters are adopted for the starting welding torch and the following welding torch:

[0076] For the initial welding torch, the welding current I 起 =160~480A, welding voltage U 起 =16~38V, welding speed v 起 =140~450mm / min. Straight pull welding or oscillating welding can be used as needed. The shielding gas used for gas shielded welding can be 100% CO2 or argon-rich mixed gas (including but not limited to commonly used binary and multi-component mixed gases), with a shielding gas flow rate of f = 15~40L / min. No preheating is required throughout the welding process.

[0077] For welding torches, the welding current I... 跟 =(1.0~1.5)I 起 Welding voltage U 跟 Appropriate matching is required while ensuring the stability of the welding process; welding speed v 跟 =v 起 Depending on the requirements, either direct pull welding or oscillating welding can be used. The shielding gas used for gas shielded welding can be 100% CO2 or an argon-rich mixture (including but not limited to commonly used binary and multi-component mixtures), with a shielding gas flow rate of f = 15–40 L / min. No preheating is required throughout the welding process.

[0078] For subsequent filler and capping welds of butt and corner joints, preheating-free welding is also employed. For high-strength steel welded structures, whether butt or corner joints, the root pass is the most susceptible to cold cracking due to factors such as the inability to release residual stress in time caused by high restraint and the hardening of the base material at low temperatures. By employing the aforementioned techniques to achieve preheating-free root pass welding, the residual heat from the previous weld passes is fully utilized for subsequent filler and capping welds, significantly reducing cold cracking sensitivity. For low-to-medium carbon microalloy steel commonly used in load-bearing industrial structures, the difficulty of preheating-free filler and capping welds is greatly reduced. Generally, there are no special restrictions on the preheating-free filler and capping weld process parameters for both butt and corner joints; the parameters are well-suited to the mainstream welding process parameters used in various industrial fields.

[0079] After welding is completed using the above method, the welded parts are subjected to manual ultrasonic non-destructive testing (UT). The focus is on monitoring whether cold cracking defects occur during the preheating-free welding process, so as to ensure the quality of preheating-free welding with green and low-carbon characteristics.

[0080] The following section provides a further description of the self-balancing residual stress gas shielded welding method of the present invention using specific examples.

[0081] Example

[0082] Q690 structural steel plates with a thickness of 30mm were selected. Following the welding method of this invention, double-sided symmetrical welding bevels were designed and processed for both butt joints and corner joints. The processed welding test plates were cleaned and assembled before welding. Then, double-sided symmetrical simultaneous root pass welding process parameters with residual stress self-balancing characteristics were designed, and preheating-free double-sided symmetrical root pass welding was performed. Based on the self-balancing and elimination mechanism of welding residual stress, cold cracking can be avoided. Subsequently, fillet and cover pass welding was completed according to the welding technology requirements for commonly used structural components. Table 1 shows the bevel design and typical welding process parameters for butt joints in Examples 1-4. Table 2 shows the bevel design and typical welding process parameters for corner joints in Examples 5-8. Theoretically equal-strength welding wires were used, and a mixture of 80% Ar and 20% CO2 was used as the welding shielding gas. For both butt joints and corner joints, all examples yielded welds with good surface formation. Manual ultrasonic non-destructive testing showed no cold cracks inside the welds under preheating conditions.

[0083] Table 1 Bevel type and welding process parameters for butt joints

[0084]

[0085] Table 2. Bevel types and welding process parameters for corner joints

[0086]

[0087] In summary, all embodiments of the present invention employ a larger blunt edge size than conventional techniques, reducing the actual filler volume, eliminating the need for preheating before welding, saving energy consumption, and exhibiting significant green and low-carbon characteristics.

[0088] This invention can be applied to various industrial fields related to welding of high-strength steel thick plate structures. Without requiring a radical change to the mainstream welding process in product manufacturing, it uses gas metal arc welding (GMAW) and employs a double-sided symmetrical simultaneous root pass welding technique with residual stress self-balancing characteristics. This technique avoids the problem of cold cracking in the welding of thick-walled high-strength steel without preheating, providing a green, low-carbon, low-cost, and high-efficiency solution for the welding of high-strength steel structures. It demonstrates significant technical and cost advantages and has broad application value.

[0089] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A self-balancing gas-shielded welding method for residual stress without preheating, characterized in that, Includes the following steps: S1, Welding bevel design, which processes the weld joint of the workpiece to be welded into a double-sided symmetrical welding bevel; the blunt edge length F of the double-sided symmetrical welding bevel satisfies the following formula: In the formula, F is the blunt edge length of the double-sided symmetrical welding groove, in mm; k is the welding wire diameter coefficient, dimensionless, and the value of k ranges from 2 to 5; d is the diameter of the gas metal arc shielded solid welding wire used for welding, in mm. S2, No-preheat welding: After the parts to be welded are positioned and assembled, they are welded using gas shielded welding without preheating. During the root pass welding, the starting welding torch and the following welding torch are activated simultaneously on both sides of the weld bevel of the parts to be welded, performing symmetrical welding on both sides. When the weld joint of the workpiece to be welded is a butt joint, during the root pass welding process, a gap distance D is provided between the starting welding torch and the following welding torch, and the gap distance D satisfies the following formula: ； In the formula, D is the distance between the starting welding torch and the following welding torch, in mm, and D≥10mm; P cm The cold cracking sensitivity index of the workpiece to be welded is dimensionless. t represents the thickness of the workpiece to be welded, in mm; d represents the diameter of the gas metal arc shielded solid welding wire used for butt welding, in mm. When the weld joint of the workpiece to be welded is a full penetration corner joint, during the root pass welding process, a gap distance D is set between the starting welding torch and the following welding torch, and the gap distance D satisfies the following formula: ； In the formula, D is the distance between the starting welding torch and the following welding torch, in mm, and D is at least 0; P cm The cold cracking sensitivity index of the workpiece to be welded is dimensionless. t represents the thickness of the workpiece to be welded, in mm; d represents the diameter of the gas metal arc shielded solid welding wire used for full penetration corner joint welding, in mm.

2. The self-balancing residual stress gas shielded welding method according to claim 1, characterized in that: In step S1 When the welding joint of the workpiece to be welded is a butt joint, the bevel angle α of the double-sided symmetrical welding groove is 50 to 80°, and in the calculation formula of the blunt edge length F of the double-sided symmetrical welding groove, the value range of the welding wire diameter coefficient k is 2.5 to 5.

3. The self-balancing residual stress gas shielded welding method according to claim 1, characterized in that: In step S1 When the welded joint of the workpiece to be welded is a full penetration corner joint, the bevel angle α of the double-sided symmetrical welding groove is 30 to 50°, and in the calculation formula of the blunt edge length F of the double-sided symmetrical welding groove, the value range of the welding wire diameter coefficient k is 2 to 4.

4. The self-balancing residual stress gas shielded welding method according to claim 1, characterized in that: In step S2, before the positioning assembly, mechanical or chemical cleaning methods are used to remove contaminants from the welding bevel of the workpiece to be welded and from at least 50 mm on both sides.

5. The self-balancing residual stress gas shielded welding method according to claim 1, characterized in that: In step S2, when the parts to be welded are positioned and assembled, the assembly gap between the parts to be welded shall not exceed 0.5 mm.

6. The self-balancing residual stress gas shielded welding method according to claim 5, characterized in that: In step S2, when the welding joint of the workpiece to be welded is a butt joint, The relative misalignment of the butt joint after positioning and assembly is less than 1 / 3 of the thickness of the workpiece to be welded, and less than 5mm. After the mating joint is positioned and assembled, for every 1mm increase in the relative misalignment, according to the formula... The calculated blunt edge length F is reduced by 1 mm accordingly.

7. The self-balancing residual stress gas shielded welding method according to claim 1, characterized in that: In step S2, when the welding joint of the workpiece to be welded is a butt joint, during the root pass welding process, the welding current I of the starting welding torch is... 起 The welding voltage is 140-450A. 起 The voltage ranges from 15 to 38 V, and the welding speed is V. 起 The flow rate is 160–500 mm / min, using direct pull welding or oscillating welding, with a shielding gas flow rate of 15–40 L / min, and no preheating is required throughout the welding process; The welding current I following the welding torch 跟 =(1.0~1.5)I 起 Welding voltage U 跟 The voltage is 16-39V. The welding speed of the following welding torch is the same as that of the starting welding torch. Straight pull welding or oscillating welding is used. The flow rate of the shielding gas is 15-40L / min. There is no preheating during the entire welding process.

8. The self-balancing residual stress gas shielded welding method according to claim 1, characterized in that: In step S2, the welding current I of the starting welding torch 起 The welding voltage is 160–480A. 起 The voltage ranges from 15 to 38 V, and the welding speed is V. 起 The flow rate is 140–450 mm / min, using direct pull welding or oscillating welding, with a shielding gas flow rate of 15–40 L / min, and no preheating is required throughout the welding process; The welding current I following the welding torch 跟 =(1.0~1.5)I 起 Welding voltage U 跟 The voltage is 19-40V. The welding speed of the following welding torch is the same as that of the starting welding torch. Straight pull welding or oscillating welding is used. The flow rate of the shielding gas is 15-40L / min. There is no preheating during the entire welding process.

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