A flux and a method for double wire submerged arc welding of stainless steel

Abstract

The application provides a welding flux and a double-wire submerged-arc welding method for stainless steel, and relates to the technical field of stainless steel welding. 2 10%-20%; calcium-magnesium-manganese mixture 50%-70%; K2S 0.01%-0.035%; KH2PO 4 0.02%-0.04%; binder 15%-45%; the calcium-magnesium-manganese mixture is composed of CaF2, CaO, MgO and MnO; the mass ratio of the mixture of CaF2 and the three oxides CaO, MgO and MnO is (23-26):(39-42); the binder is any one of vaseline, paraffin oil, mineral oil or acrylic resin solution. The welding flux can be simultaneously adapted to direct current and alternating current through the selection and proportion adjustment of the substances, has good deslagging performance, is not prone to generating pores, and improves the high-temperature wettability of the welding flux, so that the welding flux can be more adapted to high-speed welding.

Description

Technical Field

[0001] This invention relates to the field of stainless steel welding technology, and more particularly to a flux, its application, and a method for twin-wire submerged arc welding of stainless steel. Background Technology

[0002] Based on the current technological status of stainless steel welding, traditional submerged arc welding fluxes have significant limitations when dealing with high-alloy materials such as austenitic stainless steel. On the one hand, although conventional fluorine-alkali fluxes have good deoxidation capabilities, they are prone to slag removal difficulties due to insufficient slag viscosity during high-speed twin-wire welding, and slag residues are easily left on the weld surface, increasing subsequent cleaning costs. On the other hand, existing fluxes generally adopt a cautious approach to the application of sulfur and phosphorus elements, as excessive addition may cause hot cracking or embrittlement, especially under high heat input conditions.

[0003] The twin-wire submerged arc welding process places stringent requirements on the metallurgical stability of the flux. Existing formulations are prone to arc instability and increased porosity defects at welding speeds exceeding 550 mm / min, making them unsuitable for modern high-efficiency welding demands. Especially for thick stainless steel structures (such as chemical containers and pipelines), traditional methods require multi-layer, multi-pass welding, resulting in low efficiency and a significant risk of grain coarsening in the heat-affected zone. Furthermore, existing twin-wire submerged arc welding processes are complex, have poor applicability, and are limited in practical applications.

[0004] Therefore, there is an urgent need to develop a new flux system that, while ensuring the metallurgical quality of the weld, also takes into account the adaptability to high-speed welding, the self-removal of slag, and the controllability of trace elements, so as to break through the technical bottleneck of high-efficiency welding of stainless steel.

[0005] Therefore, this invention is proposed. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a flux that, through the selection and adjustment of materials and proportions, enables the flux to adapt to both direct current and alternating current; it exhibits good slag removal performance, is less prone to porosity, and improves the high-temperature wettability of the flux, making it more suitable for high-speed welding.

[0007] The present invention also provides the application of flux in twin-wire submerged arc welding of stainless steel.

[0008] This invention also provides a method for using flux in double-wire submerged arc welding of stainless steel. This method has a simple process flow and a significantly improved preparation efficiency compared to single-wire submerged arc welding, which greatly improves welding speed and production efficiency.

[0009] To achieve the objectives of this invention, a flux is provided, which, by weight percentage, is mainly made from the following raw materials:

[0010] SiO2 10%-20%;

[0011] Calcium, magnesium, and manganese mixture 50%-70%;

[0012] K2S 0.01%-0.035%;

[0013] KH2PO4 0.02%-0.04%;

[0014] Li2CO3 0.5% - 1.5%;

[0015] La2O3 0.1% - 0.5%;

[0016] Adhesive 15%-45%;

[0017] The calcium-magnesium-manganese mixture is composed of CaF2, CaO, MgO, and MnO.

[0018] The mass ratio of CaF2 to the three oxides CaO, MgO and MnO is (23-26):(39-42).

[0019] The flux has an alkalinity index of 2.0–2.6, a particle size distribution of ≥60% of particles with a size of 0.2–0.45 mm, and a slag viscosity of 0.3–0.8 Pa·s at 1300℃.

[0020] The adhesive is any one of petrolatum, paraffin oil, mineral oil, or acrylic resin solution.

[0021] Furthermore, SiO2 18%;

[0022] Calcium, magnesium, and manganese mixture: 64.67%;

[0023] K2S 0.02%;

[0024] KH2PO4 0.03%;

[0025] Li2CO3 1.0%;

[0026] La2O 30.3%;

[0027] Adhesive 15.98%;

[0028] The flux has an alkalinity index of 2.4, a particle size distribution of 70% of particles ranging from 0.2 to 0.45 mm, and a slag viscosity of 0.5 Pa·s at 1300 °C.

[0029] Furthermore, the mass ratio of the mixture of CaF2 and the three oxides CaO, MgO, and MnO is 25:40.

[0030] Furthermore, the mass ratio of the three oxides CaO, MgO, and MnO is 2:1:1.

[0031] The present invention also provides the application of flux in twin-wire submerged arc welding of stainless steel.

[0032] The present invention also provides a method for twin-wire submerged arc welding of stainless steel, comprising the following steps:

[0033] S1. Thoroughly remove impurities from at least 30mm of the bevel until the metallic luster is exposed;

[0034] S2. Spot welding is performed on a single stainless steel welding wire under the flux layer, followed by root pass welding on the single stainless steel welding wire.

[0035] S3. Then, filler or capping welding is performed on the single stainless steel welding wire under the flux layer.

[0036] S4. Finally, use two stainless steel welding wires for high-speed filler welding.

[0037] Furthermore, the welding speed of the high-speed filler welding in step S4 is 600 mm / min-700 mm / min.

[0038] Furthermore, the welding speed of the high-speed filler weld is 650 mm / min.

[0039] Furthermore, the two stainless steel welding wires adopt a cooperative welding mode of front wire and rear wire, with the front wire using DC pulse current and the rear wire using AC square wave current.

[0040] Furthermore, the peak current of the DC pulse current is 700A-750A, the base current is 300A-350A, and the frequency is 80Hz-120Hz; the effective value of the AC square wave current is 550A-600A, and the AC balance ratio is 30%-40% EP.

[0041] Furthermore, the peak current of the DC pulse current is 700A, the base current is 350A, and the frequency is 100Hz; the effective value of the square wave current is 600A, and the AC balance ratio is 35%EP.

[0042] Furthermore, the heat input for the high-speed filler welding is 40-42 KJ / min.

[0043] Furthermore, the heat input for the high-speed filler welding is 41 KJ / min.

[0044] Furthermore, the welding speed for filler or capping welding in step S3 is 550 mm / min to 600 mm / min.

[0045] Furthermore, the welding speed for filler or capping welding in step S3 is 580 mm / min.

[0046] Furthermore, the flux should be dried at 300-350℃ for 1.5-2 hours before use, and kept warm at 110-120℃ until ready for use.

[0047] Furthermore, in step S2, the welding rate for the root pass using a single stainless steel welding wire is 400-450 mm / min.

[0048] The present invention has the following technical effects:

[0049] (1) This flux can effectively avoid the difficulty of slag removal caused by insufficient slag viscosity during high-speed twin-wire welding. It has good slag removal performance, reduces the slag residue on the weld surface, and reduces cleaning costs. At the same time, this flux can adapt to both DC and AC power. It is not prone to porosity and improves the high-temperature wettability of the flux, making it more suitable for high-speed welding and compatible with twin-wire submerged arc welding process, effectively improving welding efficiency.

[0050] (2) The method of double-wire submerged arc welding of stainless steel used in this invention has a simple process flow and a significantly improved preparation efficiency compared with single-wire submerged arc welding, which greatly improves the welding speed and production efficiency. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0052] In a first aspect, the present invention provides a flux, which, by mass percentage, is mainly made from the following raw materials:

[0053] SiO2 10%-20%;

[0054] Calcium, magnesium, and manganese mixture 50%-70%;

[0055] K2S 0.01%-0.035%

[0056] KH2PO4 0.02%-0.04%;

[0057] Li2CO3 0.5% - 1.5%;

[0058] La2O3 0.1% - 0.5%;

[0059] Adhesive 15%-45%;

[0060] The calcium-magnesium-manganese mixture is composed of CaF2, CaO, MgO, and MnO.

[0061] The mass ratio of CaF2 to the three oxides CaO, MgO and MnO is (23-26):(39-42).

[0062] The flux has an alkalinity index of 2.0–2.6, a particle size distribution of ≥60% of particles with a size of 0.2–0.45 mm, and a slag viscosity of 0.3–0.8 Pa·s at 1300℃.

[0063] The adhesive is any one of petrolatum, paraffin oil, mineral oil, or acrylic resin solution.

[0064] In this invention, SiO2 forms the slag, providing suitable viscosity and coverage, while a calcium-magnesium-manganese mixture serves as the main flux and deoxidizer. The CaF2 contained in the flux decomposes due to the high temperatures generated during welding, producing F... - Ions, F - Ions can dissolve the Cr2O3 oxide film on stainless steel and improve the fluidity of the molten pool. When CaF2 is in excess, it will cause the slag to be too thin, while when its content is insufficient, it will result in a weak deoxidation ability. Under the control of this ratio, the viscosity of the slag can be effectively maintained.

[0065] Existing fluxes generally avoid adding sulfur (S) or phosphorus (P) because improper control of their addition can easily lead to cracking and embrittlement of stainless steel. In this invention, trace amounts of K₂S and KH₂PO₄ are added. S is a surface-active element. In a high-temperature molten pool, S preferentially accumulates on the surface of the liquid metal, effectively reducing the surface tension. With reduced surface tension, the liquid welding wire metal spreads more easily on the base metal surface, much like water droplets quickly spreading on a dish with detergent. This significantly improves weld formation, increasing weld width, penetration depth, and weld reinforcement uniformity. P also has surface-active properties, helping to improve metal fluidity. Furthermore, P oxides (P₂O₅) can form low-melting-point composite compounds with other compounds, adjusting the viscosity and melting point of the slag to some extent, ensuring good coverage and separation even during rapid cooling.

[0066] Because this application uses a twin-wire submerged arc welding process, and welding is performed at high speed, the molten pool exists for an extremely short time. If the flux wettability is poor, the molten pool metal may not have enough time to spread and fuse before solidifying, resulting in poor weld formation and defects such as undercut and humped weld beads. The addition of trace amounts of sulfur (S) and phosphorus (P) can improve the flux wettability, thus solving this key problem under high-speed welding.

[0067] In practical applications, the amounts of phosphorus (P) and sulfur (S) need to be controlled to avoid excessive addition. S and Fe form a low-melting-point eutectic, Fe-FeS (melting point approximately 989℃). These low-melting-point liquid films accumulate on the austenite grain boundaries during the later stages of weld solidification. When the weld is subjected to shrinkage stress during cooling, these fragile liquid grain boundaries cannot withstand the stress, leading to intergranular hot cracking. Simultaneously, excessive sulfide inclusions can cleave the metal matrix, significantly reducing the weld's impact toughness and plasticity, and may also become the initiation point for pitting corrosion. P, on the other hand, has a severe tendency to segregate in steel, dissolving in ferrite and greatly increasing the steel's brittle-crust transition temperature. This means the weld becomes very brittle at room temperature, with a sharp decrease in impact toughness. P also forms a low-melting-point eutectic, Fe-Fe3P, increasing the weld's susceptibility to hot cracking.

[0068] S and P are typical harmful impurities in welding, and their content must be controlled at extremely low levels. One of the key innovations of this invention lies in finding a "critical point"—that is, being able to utilize their positive effect of improving wettability while ensuring that they do not cause the negative effects of cracking and embrittlement through extremely low addition amounts.

[0069] This invention also incorporates Li₂CO₃ and La₂O₃. Lithium has extremely low ionization energy and can rapidly ionize at high arc temperatures, providing abundant charged particles and greatly enhancing arc stability and penetration. This is particularly important for high-speed twin-wire welding, effectively resisting electromagnetic interference between the two wires and arc drift caused by high-speed welding. Rare earth elements are extremely strong deoxidizers and desulfurizers, further purifying the weld metal, refining its solidification structure, and breaking down coarse columnar crystals, thereby significantly improving the low-temperature impact toughness of the weld. Simultaneously, they reduce the O and S content in the steel to extremely low levels, fundamentally and significantly reducing hot cracking sensitivity and porosity. They also control the morphology of sulfides, forming a good balance with the sulfur element in this invention. However, the dosage of both elements needs to be controlled during use. Excessive La₂O₃ can form large rare earth inclusions, which can impair toughness; excessive Li₂CO₃ will reduce viscosity, worsen coverage, and decrease slag removal. The above two substances can be effective with trace amounts, and they also have a synergistic effect. La2O3 purifies the weld metal, reducing the root causes of porosity and hot cracking, and creates a "cleaner" metallurgical environment for Li2CO3 to stabilize the arc and achieve high-speed welding. This results in welds that are not only highly efficient but also have excellent internal toughness. Li2CO3 stabilizes the arc, ensuring the smooth progress of the high-speed welding process. A stable arc and molten pool allow the metallurgical purification effect of La2O3 to occur evenly and fully, avoiding problems such as uneven metallurgical reaction and inclusion aggregation caused by arc instability, resulting in a synergistic effect of 1+1>2.

[0070] In some embodiments, SiO2 is 18%;

[0071] Calcium, magnesium, and manganese mixture: 64.67%;

[0072] K2S 0.02%;

[0073] KH2PO4 0.03%;

[0074] Li2CO3 1.0%;

[0075] La2O 30.3%;

[0076] Adhesive 16.95%;

[0077] The flux has an alkalinity index of 2.4, a particle size distribution of 70% of particles ranging from 0.2 to 0.45 mm, and a slag viscosity of 0.5 Pa·s at 1300 °C.

[0078] This ratio is the optimal ratio. The flux prepared under this ratio can not only adapt to high-speed welding of two wires, but also has good slag self-removal properties, reducing cleaning costs, and can also adapt to DC and AC hybrid welding modes.

[0079] This alkalinity range, capable of accommodating the introduced Li₂CO₃ and La₂O₃, reflects the characteristics of high-alkalinity fluxes, matching their excellent metallurgical purification capabilities (desulfurization and dephosphorization). Simultaneously, the slag viscosity is sufficient to accommodate its viscosity-reducing effect, ensuring the flux maintains adequate fluidity during high-speed welding, facilitating gas escape and weld formation. A particle size distribution with 0.2–0.45 mm particles comprising 70% ensures arc stability and flux layer permeability.

[0080] In some embodiments, the mass ratio of the CaF2 to the mixture of CaO, MgO, and MnO oxides is 25:40.

[0081] In some embodiments, the mass ratio of the three oxides CaO, MgO, and MnO is 2:1:1.

[0082] The control of the CaF2 and oxide ratio is the backbone of the entire flux design. CaF2 itself is a double-edged sword; too little results in insufficient deoxidizing ability, while too much leads to an overly thin slag that cannot cover the molten pool like water, causing unstable arc, spatter, and difficulty in slag removal. These oxides are the core of high-basicity fluxes. They provide O2... 2- CaF2 ions possess strong desulfurization and dephosphorization capabilities, purifying weld metal and improving its toughness. They also enhance the viscosity and short slag characteristics of the slag. Maintaining a CaF2 to alkaline oxide ratio of (23-26):(39-42) essentially achieves an optimal balance between "oxide film removal capability" and "slag viscosity." This ratio ensures sufficient CaF2 to decompose the oxide film, guaranteeing weld fusion quality. Simultaneously, it provides enough alkaline oxides to "neutralize" the diluting effect of CaF2, resulting in a suitable viscosity for the slag at the high temperatures of high-speed welding—effectively covering the molten pool and arc while automatically lifting and detaching after cooling due to the significant difference in expansion coefficients with the metal.

[0083] CaO is the main source of high alkalinity and has the strongest desulfurization and dephosphorization capabilities. However, when it exists alone, the resulting slag has a high melting point and high viscosity, making it too "viscous," which is not conducive to gas escape and weld formation.

[0084] MgO itself is also a basic oxide. It can improve the short slag characteristics of molten slag and refine the slag particles to a certain extent, making the slag shell after slag removal more brittle and falling off in small pieces rather than in a whole piece. However, too much MgO will increase the melting point of the molten slag.

[0085] MnO effectively lowers the melting point and viscosity of slag, compensating for the viscous tendency introduced by CaO and MgO, thus improving the slag's fluidity at high temperatures and facilitating gas escape and smooth weld surface formation. This combination of the three components in this ratio represents a golden balance of "basicity + fluidity + slag removal," achieving high-basicity purification of the weld while protecting the arc, stabilizing the welding process, and facilitating slag removal after cooling. This precise composition control allows the flux to perfectly match the demanding process requirements of high-speed, high-heat-input twin-wire submerged arc welding, ensuring both metallurgical quality and efficient production.

[0086] Secondly, the present invention also provides the application of flux in twin-wire submerged arc welding of stainless steel.

[0087] Thirdly, the present invention also provides a method for using flux in twin-wire submerged arc welding of stainless steel, characterized by comprising the following steps:

[0088] S1. Thoroughly remove impurities from at least 30mm of the bevel until the metallic luster is exposed;

[0089] S2. Spot welding is performed on a single stainless steel welding wire under the flux layer, followed by root pass welding on the single stainless steel welding wire.

[0090] S3. Then, filler or capping welding is performed on the single stainless steel welding wire under the flux layer.

[0091] S4. Finally, use two stainless steel welding wires for high-speed filler welding.

[0092] This method combines a specialized flux with appropriate heat input to precisely control the viscosity and solidification characteristics of the slag, ensuring excellent slag removal even at welding speeds up to 650 mm / min. The power supply combination of DC pulse and AC square wave greatly enhances arc stability and reduces turbulence; the AC back wire helps agitate the molten pool, facilitating gas escape; trace components in the specialized flux improve high-temperature wettability, making it easier for gas to rise; these three factors work synergistically to fundamentally suppress porosity.

[0093] In some embodiments, the welding speed of the high-speed filler weld in step S4 is 600 mm / min-700 mm / min.

[0094] In some embodiments, the high-speed filler weld has a welding speed of 650 mm / min.

[0095] In some embodiments, the two stainless steel welding wires are used in a coordinated welding mode of front wire and rear wire, with the front wire using DC pulse current and the rear wire using AC square wave current.

[0096] In some embodiments, the peak current of the DC pulse current is 700A-750A, the base current is 300A-350A, and the frequency is 80Hz-120Hz; the effective value of the AC square wave current is 550A-600A, and the AC balance ratio is 30%-40%EP.

[0097] In some embodiments, the peak current of the DC pulse current is 700A, the base current is 350A, and the frequency is 100Hz; the effective value of the square wave current is 600A, and the AC balance ratio is 35%EP.

[0098] In some embodiments, the heat input of the high-speed filler weld is 40-42 KJ / min.

[0099] In some embodiments, the heat input of the high-speed filler weld is 41 KJ / min.

[0100] In some embodiments, the welding speed for filler or capping welds in step S3 is 550 mm / min to 600 mm / min.

[0101] In some embodiments, the welding speed for filler or capping welds in step S3 is 580 mm / min.

[0102] In some embodiments, the flux is dried at 300-350°C for 1.5-2 hours before use and kept warm at 110-120°C until ready for use.

[0103] In some embodiments, the welding rate of the single stainless steel welding wire for root pass welding in step S2 is 400-450 mm / min.

[0104] Digital pulse and AC square wave technologies inherently possess strong anti-interference capabilities, effectively suppressing electromagnetic interference between the two wires. A specialized flux formulation ensures excellent ionization and conductivity in both current modes.

[0105] A "step-by-step acceleration" strategy is adopted, prioritizing stability during the root pass, accelerating the transition passes, and finally achieving ultra-high speed in the fill pass. Simultaneously, the application of pulse technology allows for maintaining a low average heat input even at high deposition rates, perfectly balancing efficiency with the performance requirements of stainless steel joints (corrosion resistance, low deformation). This method features a clear process and well-defined parameters (providing precise ranges and recommended optimal values), reducing the over-reliance on operator experience in traditional twin-wire welding, improving process reliability and repeatability, and making it easier to promote and apply in industrial production.

[0106] The following is a detailed explanation using specific embodiments:

[0107] Example 1

[0108] A flux was prepared by taking 18g of SiO2, 24.87g of CaF2, 19.9g of CaO, 9.95g of MgO, 9.95g of MnO, 0.02g of K2S, 0.03g of KH2PO4, 1g of Li2CO3, 0.3g of La2O3, and 15.98g of acrylic resin solution. The flux was dried at 350℃ for 1.5h and then placed in a 110℃ incubator for later use to prevent moisture absorption.

[0109] S1. Thoroughly remove impurities from at least 30mm of the bevel until a metallic luster is revealed.

[0110] S2. Assemble the cleaned workpieces according to the technical requirements, and strictly control the mating gap and misalignment.

[0111] S3. Under 24V voltage and flux layer, perform spot welding with manual control of welding speed at 180A current, so that the length of spot welding is ≥50mm (55mm in this embodiment) and the spacing is controlled at 300-400mm (350mm in this embodiment). Sufficient strength must be ensured to prevent cracking during subsequent high-speed welding.

[0112] S4. With the power supply reversed, connect 31V and apply 500A current, then perform the root pass welding at a speed of 400mm / min. Use low speed welding during this stage to ensure full penetration and formation.

[0113] S5. After completing the root pass, under the flux layer, with the power supply reversed (DC), apply 33V and 650A current, then perform the cover pass at a welding speed of 580mm / min.

[0114] S6. Subsequently, high-speed filler welding is performed using a combined welding mode of the front wire and the back wire. The front wire uses DC pulse current with a peak current controlled at 700A, a base current controlled at 350A, and a frequency of 100Hz. The back wire uses AC square wave current with an effective current value of 600A and an AC balance ratio of 35%EP. At the same time, the heat input is controlled at 41KJ / min.

[0115] Comparative Example 1

[0116] The same flux, welding wire, and workpiece as those used in Embodiment 1 of the present invention are used.

[0117] Steps S1-S4 are the same as in Example 1. In step S5, after the root pass is completed, under the flux layer, with the power supply reversed, a 33V voltage is applied and a 650A current is supplied. Then, a cover pass is performed at a welding speed of 450mm / min, with multiple passes and multiple layers of welding until the groove is filled.

[0118] Comparative Example 2

[0119] The same flux, welding wire, and workpiece as those used in Embodiment 1 of the present invention are used.

[0120] Steps S1-S3 are exactly the same as those in Embodiment 1 of the present invention.

[0121] Starting with step S4, select the dual DC mode for dual-wire filler soldering. The specific steps are as follows: the front wire is soldered at 700A and 32V; the rear wire is soldered at 550A and 33V. Control the soldering speed at 600mm / min. Due to the dual DC input, the actual heat input is 45kJ / min.

[0122] Comparative Example 3

[0123] The specific operation method is the same as in Example 1, except that the flux is changed, specifically:

[0124] SiO2 18.5g; CaF2 25.5g; CaO 20.5g; MgO 10.25g; MnO 10.25g; Al2O3 10g (used to replace the mass of K2S and KH2PO4 and adjust the viscosity); Vaseline 16.95g.

[0125] Comparative Example 4

[0126] The specific operation method is the same as in Example 1, except that the flux is changed. Specifically, the flux ratio in Example 1 is used, but Li2CO3 and La2O3 are not used.

[0127] Experiment Example 1: Welding Efficiency Comparison Experiment

[0128] Objective: To quantitatively demonstrate the significant advantages of this invention in production efficiency compared to traditional single-wire welding.

[0129] Performance metric: Total welding time required to complete the same filler volume.

[0130] step:

[0131] Prepare three 304 stainless steel test plates with identical dimensions and bevels.

[0132] Welding was performed using the processes of the embodiments of the present invention, Comparative Example 1, and Comparative Example 2, respectively.

[0133] Record key data:

[0134] Filler welding time: Accurately record the total time taken from the start of filling to the completion of the capping.

[0135] The experimental results are shown in Table 1.

[0136] Table 1: Comparison of total welding time between the examples and comparative examples

[0137]

[0138] Experiment Example 2: Comparison Experiment of Comprehensive Weld Performance

[0139] Objective: To comprehensively evaluate the superiority of the present invention in weld quality compared with Comparative Example 2 and Comparative Example 3.

[0140] Performance indicators: slag removal, porosity, non-destructive testing pass rate, mechanical properties (tensile strength, bending performance, impact toughness).

[0141] step:

[0142] Prepare three sets of test plates and weld them using the processes of the present invention, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

[0143] Slag removal assessment: After welding and cooling, slag is removed by the same welder using a slag removal hammer. The time required for slag removal is recorded, and the degree of slag removal is compared (e.g., automatic lifting, slight adhesion, severe adhesion).

[0144] Visual inspection and non-destructive testing (NDT):

[0145] Visual inspection (VT): Inspect the weld surface for undercut, weld beads, surface porosity, and cracks.

[0146] Radiographic inspection (RT): 100% X-ray inspection of welds, assessing the internal quality of welds according to ISO 10675-1 standard, and recording the quantity and grade of defects such as porosity, slag inclusions, and lack of fusion.

[0147] Penetrant testing (PT): Inspects for minute cracks on the weld surface.

[0148] Mechanical property testing:

[0149] Samples were taken from each group of welds and processed into standard test pieces.

[0150] Tensile test: to determine the tensile strength of the weld metal and to assess whether its strength matches that of the base metal.

[0151] Side bending test (d=3a, 180°): to check the plasticity of the weld and the presence of internal defects.

[0152] Charpy V-notch impact test: Samples are taken from the weld center and heat-affected zone to test their impact energy at room temperature and assess their toughness.

[0153] Evaluation indicators: fusion line shape, fusion depth, presence of incomplete penetration, slag inclusions, and porosity.

[0154] Table 2: Comparison of Comprehensive Weld Performance Experiment Results

[0155]

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A flux, characterized in that, It is mainly produced from the following raw materials by weight percentage: SiO2 10%-20%; Calcium, magnesium, and manganese mixture 50%-70%; K2S 0.01%-0.035%; KH2PO4 0.02%-0.04%; Li2CO3 0.5% - 1.5%; La2O3 0.1% - 0.5%; Adhesive 15%-45%; The calcium-magnesium-manganese mixture is composed of CaF2, CaO, MgO, and MnO. The mass ratio of CaF2 to the three oxides CaO, MgO and MnO is (23-26):(39-42). The adhesive is any one of petrolatum, paraffin oil, mineral oil or acrylic resin solution; The mass ratio of the three oxides CaO, MgO, and MnO is 2:1:

1.

2. The flux according to claim 1, characterized in that, SiO2 18%; Calcium, magnesium, and manganese mixture: 64.67%; K2S 0.02%; KH2PO4 0.03%; Li2CO3 1.0%; La2O 30.3%; Adhesive 15.98%.

3. The flux according to claim 1, characterized in that, The mass ratio of the mixture of CaF2 and the three oxides CaO, MgO and MnO is 25:

40.

4. The application of the flux as described in any one of claims 1-3 in twin-wire submerged arc welding of stainless steel.

5. A method for using flux as described in any one of claims 1-3 for twin-wire submerged arc welding of stainless steel, characterized in that, Includes the following steps: S1. Thoroughly remove impurities from at least 30mm of the bevel until the metallic luster is exposed; S2. Spot welding is performed on a single stainless steel welding wire under the flux layer, followed by root pass welding on the single stainless steel welding wire. S3. Then, filler or capping welding is performed on the single stainless steel welding wire under the flux layer. S4. Finally, use two stainless steel welding wires for high-speed filler welding.

6. The method for using flux in twin-wire submerged arc welding of stainless steel according to claim 5, characterized in that, The welding speed of the high-speed filler welding in step S4 is 600 mm / min to 700 mm / min.

7. The method for using flux in twin-wire submerged arc welding of stainless steel according to claim 5, characterized in that, The S4 step specifically includes: The two stainless steel welding wires are welded in a coordinated manner with a front wire and a rear wire. The front wire uses a DC pulse current and the rear wire uses an AC square wave current.

8. The method for using flux in twin-wire submerged arc welding of stainless steel according to claim 7, characterized in that, The peak current of the DC pulse current is 700A-750A, the base current is 300A-350A, and the frequency is 80Hz-120Hz; the effective value of the AC square wave current is 550A-600A, and the AC balance ratio is 30%-40% EP.

9. The method for using flux in twin-wire submerged arc welding of stainless steel according to claim 5, characterized in that, The heat input for the high-speed filler welding is 40-42 KJ / min.

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