A modified smelting flux, its preparation method and application

Abstract

This invention relates to the field of welding technology, specifically to a modified smelting flux, its preparation method, and its application. The modified smelting flux is composed of the following components by mass percentage: CaF2 50%~80%, TiO2 10%~30%, SiO2 10%~25%, B2O3 0.1%~3%, and Y2O3 0.5%~2%. Using this modified smelting flux, even when welding high-carbon ship plate steel, the resulting weld exhibits excellent low-temperature impact toughness, a beautiful weld shape, and is free of porosity and crack defects, while also demonstrating good arc stability during welding. This invention also provides a method for preparing the modified smelting flux and its application in high-heat welding of ship plate steel.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a modified smelting flux, its preparation method, and its application. Background Technology

[0002] Ship plate steel refers to high-strength, high-toughness steel used in ship hull structures. Due to its excellent comprehensive mechanical properties and good weldability, it is widely used in the construction of critical load-bearing structures such as large ships and offshore engineering platforms. The carbon content in ship plate steel is typically no higher than 0.18 wt.%. However, in actual production and applications, to meet higher strength requirements or due to process fluctuations, the carbon content in some batches of ship plate steel is at a higher level, for example, greater than 0.07 wt.%, or even close to the upper limit of 0.18 wt.%.

[0003] As carbon content increases, the weldability of steel faces significant challenges. Higher carbon content significantly increases the hardening tendency of the weld metal, leading to increased hardness, decreased toughness, especially low-temperature toughness, and an increased risk of cold cracking. Therefore, traditional welding processes and fluxes are insufficient to guarantee that welded joints of high-carbon ship plate steel, particularly the weld metal, simultaneously achieve high strength, excellent low-temperature impact toughness, and stable welding process performance.

[0004] Currently, various flux systems exist in the market for welding ship plate steel. For example, CaF2-SiO2 fluxes are common alkaline or neutral fluxes, but they may lead to insufficient weld toughness under high heat input. CaF2-TiO2 fluxes, by introducing TiO2, can effectively promote the formation of acicular ferrite inside the weld, thereby refining the grains and improving toughness. However, relying solely on TiO2 has limited optimization effects, and its role may be weakened in high-alkalinity fluxes, and it also has a certain impact on the stability of the welding arc. Although existing research has explored these binary or ternary systems, no comprehensive solution has been proposed that can systematically resolve the contradictions between strength, toughness, and processability in welding high-carbon ship plate steel.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] To address the issues of decreased toughness, cold cracking, and arc instability in weld metal when welding high-carbon ship plate steel (e.g., greater than 0.07 wt.%, or even close to the upper limit of 0.18 wt.%) using conventional fluxes, the primary objective of this invention is to provide a modified smelting flux. Using this modified smelting flux, even when welding high-carbon ship plate steel, the resulting weld exhibits excellent low-temperature impact toughness, a beautiful weld shape, and is free of porosity and crack defects, while also demonstrating good arc stability during the welding process.

[0007] The second objective of this invention is to provide a method for preparing modified smelting flux, which has the advantages of simple operation, short process flow and suitability for mass production.

[0008] A third objective of this invention is to provide the application of modified smelting flux in high heat input welding of ship plate steel.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The present invention first provides a modified smelting flux, which is made of the following components by mass percentage: CaF2 50%~80%, TiO2 10%~30%, SiO2 10%~25%, B2O3 0.1%~3%, and Y2O3 0.5%~2%.

[0010] Furthermore, the average width of the original austenite grains in the weld formed after welding the ship plate steel with the modified smelting flux is ≤90μm.

[0011] Furthermore, the weld formed after welding ship plate steel using the modified smelting flux has a low-temperature impact energy of -40℃ ≥34J.

[0012] Furthermore, the volume fraction of acicular ferrite in the weld formed after welding ship plate steel using the modified smelting flux is ≥50%.

[0013] Furthermore, the particle size of the modified smelting flux is 8 mesh to 40 mesh.

[0014] The present invention also provides a method for preparing modified smelting flux, comprising the following steps: mixing CaF2, TiO2, SiO2, B2O3 and Y2O3 and then smelting them to obtain a melt; quenching the melt in water to obtain a quenched material; and calcining the quenched material to obtain the modified smelting flux.

[0015] Furthermore, the melting temperature is 1350℃~1400℃, and the melting holding time is 20min~1h.

[0016] Furthermore, the calcination temperature is 650℃~800℃, and the calcination holding time is 1h~3h.

[0017] This invention also provides the application of modified smelting flux in high heat input welding of ship plate steel.

[0018] Furthermore, the high heat input welding is a series dual-wire submerged arc welding.

[0019] Furthermore, the lead wire of the series dual-wire submerged arc welding uses direct current, the welding current of the direct current is 750A~900A, and the welding voltage of the direct current is 25V~40V.

[0020] Furthermore, the rear wire of the series dual-wire submerged arc welding uses alternating current, the welding current of which is 550A~750A, and the welding voltage of which is 25V~45V.

[0021] Furthermore, the wire spacing of the tandem twin-wire submerged arc welding is 20mm~30mm.

[0022] Furthermore, the wire elongation of the tandem twin-wire submerged arc welding is 20mm~30mm.

[0023] Furthermore, the heat input energy of the high heat input welding is 35kJ / cm to 80kJ / cm.

[0024] Furthermore, the welding speed of the high heat input welding is 400 mm / min to 650 mm / min.

[0025] Furthermore, during the high heat input welding process, the stacking height of the modified molten flux is 20mm~40mm.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Using the modified smelting flux provided by the present invention, even when welding high carbon content ship plate steel, the weld formed has excellent low temperature impact toughness, and the weld is beautiful in shape, free of porosity and crack defects, with good arc stability during welding, and good slag removal performance.

[0027] (2) The modified smelting flux provided by the present invention, B2O3, as an excellent fluxing agent, can significantly reduce the melting point and viscosity of the slag, and improve the fluidity and coverage of the slag; the addition of Y2O3 can not only moderately adjust the slag structure, but also exert its strong deoxidation and desulfurization capabilities, and deeply purify the weld pool; more importantly, trace amounts of boron and rare earth yttrium elements are infiltrated into the weld metal, which can play a role in composite microalloying: on the one hand, appropriate amounts of boron preferentially agglomerate at the austenite grain boundaries, effectively suppressing the nucleation of coarse proeutectoid ferrite, thereby greatly improving the hardenability of the weld; on the other hand, the yttrium elements transitioned by Y2O3 interact with TiO2 to form a large number of fine and dispersed rare earth-titanium composite oxide inclusions in the weld. These rare earth composite particles, as extremely efficient heterogeneous nucleation cores, form a strong synergistic effect with the acicular ferrite induced by TiO2 and the grain boundary inhibition effect of boron, further significantly improving the strength, toughness and low-temperature impact performance of the weld.

[0028] (3) The modified smelting flux provided by the present invention has less boron volatilization after smelting, smaller average austenite grain size in the weld, higher proportion of beneficial acicular ferrite in the weld metal, and lower proportion of harmful side plate ferrite and grain boundary ferrite in the weld metal.

[0029] (4) The modified smelting flux provided by the present invention has good fluorine fixation effect, is environmentally friendly and low cost by adopting a fixed component ratio. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a topographic image of the weld bead obtained after welding in Example 1; Figure 2 This is a cross-sectional macroscopic morphology diagram of the weld obtained after welding in Example 1; Figure 3 This is a topographic image of the weld bead obtained after welding in Example 2; Figure 4 The image shows the metallographic structure of the weld obtained after welding in Example 2. Figure 5 The image shows the fracture morphology of the weld obtained after welding in Example 2. Figure 6 This is a scanning electron microscope image of the microstructure of the weld obtained after welding in Example 4; Figure 7 The image shows the metallographic structure of the weld obtained after welding in Comparative Example 1. Figure 8 The image shows the fracture morphology of the weld obtained after welding in Comparative Example 1. Figure 9 for Figure 8 Enlarged view within the box. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0033] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0034] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0035] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0036] In a first aspect, the present invention provides a modified smelting flux, which is made of the following components by mass percentage: 50%~80% CaF2, 10%~30% TiO2, 10%~25% SiO2, 0.1%~3% B2O3, and 0.5%~2% Y2O3. Adding trace amounts of boron oxide to the flux can achieve effective control of the weld metal microstructure.

[0037] The values ​​for CaF2, by mass percentage, include but are not limited to 50%, 60%, 70%, and 80%, or a range between any two. The values ​​for TiO2, by mass percentage, include but are not limited to 10%, 15%, 20%, 25%, and 30%, or a range between any two. The values ​​for SiO2, by mass percentage, include but are not limited to 10%, 15%, 20%, and 25%, or a range between any two. The values ​​for B2O3, by mass percentage, include but are not limited to 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, and 3%, or a range between any two. The values ​​for Y2O3, by mass percentage, include but are not limited to 0.5%, 1%, 1.5%, 2%, 2.5%, and 2%, or a range between any two.

[0038] Using the modified smelting flux, even when welding high-carbon ship plate steel (e.g., mass fraction greater than 0.07%, or even close to the upper limit of 0.18%), the resulting weld has excellent low-temperature impact toughness, beautiful weld formation, no porosity or crack defects, and good arc stability during welding.

[0039] Among them, ship plate steel refers to high-strength and high-toughness steel used in ship hull structures, such as EH36 grade ship plate steel, EH690 grade ship plate steel, EH550 grade ship plate steel, EH420 grade ship plate steel, etc., but is not limited to these.

[0040] Furthermore, welding using the aforementioned modified smelting flux exhibits excellent slag removal performance and low cost; by employing a fixed component ratio, it achieves good fluorine fixation and is environmentally friendly.

[0041] In some specific embodiments, the slag removal rate of the weld formed after welding the ship plate steel with the modified smelting flux is ≥90%, including but not limited to any one of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100% or any range between two.

[0042] Specifically, this invention improves the weld microstructure of ship plate steel by regulating the slag-metal reaction and alloy transition behavior of modified smelting flux, and enhances the comprehensive mechanical properties and crack resistance of the weld metal by utilizing the nucleation-promoting and phase transformation-regulating characteristics of trace boron elements. From the perspective of microstructure improvement, ship plate steel is prone to volume shrinkage and coarse network ferrite during solidification phase transformation. By regulating the effective reduction transition of boron elements in thermodynamics and the grain boundary segregation behavior in kinetics, the nucleation of high-toughness acicular ferrite is maximized, resulting in a significant improvement in weld strength, toughness, and crack resistance. From the perspective of metallurgical physicochemical properties, the suitable basicity and phase structure formed by the slag during cooling and solidification improve the shrinkage stress inside the slag layer, making it easier for it to automatically peel off from the weld metal surface after welding, and the flux has good slag removal properties. Secondly, the optimized slag viscosity and fluidity are reasonably matched, allowing non-metallic inclusions and gases generated in the weld pool to float smoothly and be effectively absorbed by the slag, avoiding residues in the weld matrix or capture at the interface, thus preventing the formation of inclusions and porosity defects. Finally, a reasonable slag structure regulates the solidification heat transfer rate of the weld pool, delays the transformation process of the original austenite to proeutectoid ferrite, and inhibits the initiation and propagation of cracks during peritectic solidification of marine steel, ultimately achieving the effect of refining grains and comprehensively improving the weld microstructure.

[0043] Therefore, the use of this modified smelting flux can ensure that the weld (or welded joint) obtained after welding has high mechanical properties and meets the requirements of harsh service environments.

[0044] Flux composition is one of the key factors affecting welding quality. A good flux needs to have a suitable melting point and viscosity, and provide excellent mechanical protection and metallurgical control for the weld. This invention, by using specific amounts of CaF2, TiO2, SiO2, B2O3, and Y2O3, achieves excellent slag removal performance and ensures that the slag has suitable viscosity and fluidity during high-temperature welding; the weld formation is good, with no pitting or porosity defects on the surface, significantly refined microstructure grains, and excellent low-temperature impact toughness. In particular, this invention uses TiO2 to transition Ti element to the weld metal, utilizing oxide metallurgy principles to form fine titanium-containing oxide nuclei in the weld, inducing the nucleation of highly tough acicular ferrite. More importantly, the introduction of Y2O3 deeply purifies the weld pool and removes modified non-metallic inclusions. The trace transition of rare earth Y element not only effectively deoxidizes and desulfurizes, but also synergistically forms fine, dispersed rare earth-titanium composite oxides with Ti, significantly improving the density and efficiency of heterogeneous nucleation particles. The high content of CaF2, in synergy with SiO2, effectively regulates the basicity and structure of the slag system, optimizing the physical encapsulation of the weld metal by the slag while ensuring arc stability. Furthermore, the precise transition of boron into the weld via B2O3 effectively segregates at the proto-austenite grain boundaries, suppressing the formation of coarse proeutectoid ferrite. Combined with the strong pinning effect of rare earth compounds on grain boundaries, the synergistic effect of B-Ti-Y elements further refines the weld microstructure, ultimately achieving a comprehensive enhancement of the overall performance of ship plate steel welds.

[0045] More specifically, in the modified smelting flux of the present invention: CaF2, as a diluent and a strong slag-forming substance, mainly plays a role in adjusting the basicity of the slag, reducing viscosity, and enhancing metallurgical protection. The F2 groups released from CaF2 in the high-temperature melt structure... - It can effectively break the silicate network skeleton, significantly reduce the high-temperature viscosity of the slag, and increase its fluidity. Furthermore, CaF2 can react with hydrogen in the welding metallurgical reaction to generate gases that escape, effectively reducing the hydrogen content of the weld and minimizing porosity and cold cracking defects. In this invention, the amount of CaF2 added is appropriate. Excessive CaF2 addition, while improving fluidity, leads to the volatilization of a large amount of fluorides, deteriorating the welding operating environment and drastically reducing arc stability; conversely, insufficient CaF2 content results in insufficient slag basicity and excessively high high-temperature viscosity, hindering the upward escape of bubbles and inclusions in the molten pool, leading to difficulty in slag removal and deterioration of weld surface quality.

[0046] TiO2 is an amphoteric, slightly acidic substance that primarily functions to stabilize the electric arc, improve slag removal, and provide nucleation sites for oxide metallurgy. In the high-temperature melt structure, TiO2 can reduce the high-temperature viscosity of the slag and improve its wettability on the weld surface. Furthermore, TiO2 can introduce Ti and O elements into the weld pool. Appropriate amounts of Ti combined with O will form fine, dispersed titanium-containing composite oxide inclusions in the weld. These inclusions can serve as efficient nucleation sites, inducing the formation of high-toughness acicular ferrite. In this invention, the amount of TiO2 added is appropriate. Excessive TiO2 addition significantly increases the oxidizing properties of the slag, leading to severe burn-off of alloying elements in the weld and resulting in large inclusions, which in turn reduces the low-temperature impact toughness of the weld metal. Conversely, insufficient TiO2 content leads to poor arc combustion stability and insufficient effective nucleation sites in the weld, failing to leverage the role of oxide metallurgy in strengthening and toughening marine steel.

[0047] SiO2 is an acidic substance that primarily functions to form slag, regulate the viscosity and flowability of flux, and improve formability. In the high-temperature melt structure, SiO2 acts as a network skeleton, significantly increasing the high-temperature viscosity and surface tension of the slag. It combines with CaF2 to form a suitable slag system structure. Furthermore, SiO2 can introduce Si into the weld pool; an appropriate amount of Si can improve the tensile strength and hardness of the weld. In this invention, the amount of SiO2 added is appropriate. Excessive SiO2 leads to high high-temperature flux viscosity, hindering gas escape during welding and resulting in numerous porosity defects. It also causes severe Si and O accumulation in the weld, reducing the mechanical properties of the weld metal. Conversely, insufficient SiO2 content results in insufficient support of the slag network skeleton, deterioration of the weld form, poor arc stability, and a tendency for arc breakage.

[0048] Borosilicate (B₂O₃) is an acidic oxide that primarily functions to regulate the physicochemical properties of slag, achieve microalloying, and refine the weld microstructure. In the high-temperature melt structure, B₂O₃ effectively disrupts the complex silicate network framework, significantly reducing the high-temperature viscosity and melting point of the slag. Furthermore, B₂O₃ can introduce trace amounts of boron (B) into the weld pool. Appropriate amounts of B preferentially segregate at the proto-austenite grain boundaries, effectively inhibiting the nucleation of coarse proeutectoid ferrite during weld solidification, thereby significantly improving the strength and toughness of the weld. In this invention, the amount of B₂O₃ added is appropriate. Excessive B₂O₃ will lead to excessive dissolved boron content in the weld, increasing the susceptibility to welding hot cracking, and will also result in excessively low slag viscosity, affecting weld formation. Conversely, insufficient B₂O₃ will fail to provide enough boron for microstructure regulation, making it difficult to achieve the goals of grain refinement and improved weld microstructure.

[0049] Y₂O₃ is an alkaline rare earth oxide that primarily functions to purify the weld pool, remove non-metallic inclusions, and refine the weld microstructure. In the high-temperature melt structure, Y₂O₃ can dissociate free oxygen ions, effectively disrupting the complex silicate network framework, moderately adjusting slag basicity, and improving the high-temperature fluidity of the slag. Furthermore, Y₂O₃ can introduce trace amounts of Y into the weld pool. Appropriate amounts of Y, with its strong deoxidizing and desulfurizing capabilities, form fine, dispersed high-melting-point rare earth compounds (such as yttrium oxysulfide) in the weld pool. These inclusions can serve as effective heterogeneous nucleation sites for high-toughness acicular ferrite, while significantly pinning the original austenite grain boundaries to inhibit grain growth, thereby significantly improving the strength and toughness of the weld metal. In this invention, the amount of Y₂O₃ added is appropriate. When the amount of Y2O3 added is too high, it will lead to an excessive amount of rare earth elements transitioning into the weld and agglomerating to form coarse rare earth inclusion clusters, which will reduce the low-temperature impact toughness of the weld. At the same time, due to its extremely high melting point, it will also cause the high-temperature viscosity of the slag to increase sharply, resulting in difficulty in slag removal and deterioration of the weld surface formation. When the Y2O3 content is too low, it cannot provide enough Y elements for molten pool purification and inclusion deterioration, making it difficult to form effective nucleation particles with a sufficient density, thus failing to achieve the purpose of refining grains and improving weld microstructure.

[0050] In some specific embodiments, the average width of the original austenite grains in the weld formed after welding ship plate steel with the modified flux is ≤90μm, including but not limited to point values ​​or ranges between any two of 90μm, 89μm, 88μm, 87μm, 86μm, 85μm, 83μm, 81μm, 80μm, and 75μm. The size of the original austenite grains refers to the original grain boundary size corresponding to the austenite grains formed during the high-temperature welding stage after cooling transformation; for columnar original austenite grains in the weld, their size is usually characterized by the average width perpendicular to the long axis. An average width of ≤90μm for the original austenite grains indicates fine and uniform grains, strong resistance to welding coarsening, and that the grains are not prone to coarsening after welding thermal cycling.

[0051] In some specific embodiments, the weld formed after welding ship plate steel using the modified fusion flux has a low-temperature impact energy of ≥34J at -40℃, including but not limited to a point value or a range between any two of 34J, 38J, 40J, 44J, 49J, 53J, 58J, 60J, 63J, 68J, and 70J. The modified fusion flux provided by this invention exhibits excellent low-temperature impact toughness.

[0052] In some specific embodiments, the volume fraction of acicular ferrite in the weld formed after welding ship plate steel with the modified smelting flux is ≥50%, including but not limited to any one of 50%, 52%, 55%, 56%, 58%, 60%, 62%, and 65%, or any range between two values. A high proportion of acicular ferrite in the weld microstructure can significantly improve the low-temperature impact toughness and overall mechanical properties of the weld metal.

[0053] In some specific embodiments, the mass fraction of carbon in the ship plate steel is 0.07% to 0.20%, for example, 0.08%, 0.10%, 0.12%, 0.13%, 0.15% or 0.18%.

[0054] In some specific embodiments, the volume fraction of grain boundary ferrite in the weld formed after welding ship plate steel with the modified smelting flux is ≤38%, including but not limited to any one of 38%, 36%, 35%, 33%, 31%, 30%, 28%, 25%, 20%, or any range between two of them.

[0055] In some specific embodiments, the volume fraction of ferrite in the side strips of the weld formed after welding the ship plate steel with the modified smelting flux is ≤15%, including but not limited to any one of 15%, 14%, 13%, 12%, 11%, 10%, 8%, 5%, or any range between two of them.

[0056] This invention fully utilizes the synergistic modification effect of CaF2, SiO2, TiO2, B2O3 and Y2O3 to specifically address the welding challenges of high-carbon ship plate steel, exhibiting a good weld metal microstructure ratio and excellent low-temperature toughness.

[0057] In some specific embodiments, the absolute value of the difference between the mass fraction of B2O3 in the mixed material obtained after mixing and the mass fraction of B2O3 in the modified smelting flux obtained after calcination is ≤0.3%. The modified smelting flux provided by the present invention exhibits minimal changes in composition before and after smelting, with a high yield and stable composition of the core component B2O3.

[0058] In some specific embodiments, the particle size (referring to the particle size distribution range) of the modified molten flux is 8 mesh to 40 mesh, that is, within the range of 8 mesh to 40 mesh, including but not limited to the point value of any one of 8 mesh, 10 mesh, 15 mesh, 20 mesh, 25 mesh, 30 mesh, 35 mesh, and 40 mesh, or the range between any two, such as 8 mesh to 35 mesh, 20 mesh to 35 mesh, etc. Using the modified molten flux with the above particle size increases the interfacial reaction area between the slag and the weld metal, promotes the efficient transition of boron and titanium elements, and does not cause blockage by floating air bubbles and non-metallic inclusions in the weld pool, thereby ensuring sufficient metallurgical reactivity and excellent weld formation.

[0059] Secondly, the present invention provides a method for preparing modified smelting flux, comprising the following steps: According to the target ratio of modified smelting flux, weigh CaF2, TiO2, SiO2, B2O3 and Y2O3 and mix them evenly, then smelt them to obtain a molten liquid.

[0060] The melt is then water-quenched at room temperature (e.g., 10℃~30℃) to obtain quenched material.

[0061] The quenched material is then roasted and cooled to obtain the modified smelting flux. The purpose of roasting is to remove residual crucible carbon powder and moisture from the quenched material.

[0062] This method has the advantages of simple operation, short process flow, high production efficiency and suitability for mass production.

[0063] In some specific embodiments, the melting temperature is 1350℃~1400℃, including but not limited to any one of 1350℃, 1360℃, 1380℃, and 1400℃, or a range between any two. By controlling the melting temperature to ≤1400℃, this invention can prevent the volatilization of B2O3 and the escape of gases such as CaF2.

[0064] In some specific embodiments, the holding time for melting is 20 min to 1 h, including but not limited to any one of 20 min, 30 min, 40 min, 50 min, and 1 h, or any range between two of them. This can effectively suppress the volatilization of boron oxide.

[0065] In some specific embodiments, the roasting temperature is 650℃~800℃, including but not limited to any one of 650℃, 670℃, 700℃, 730℃, 750℃, 780℃, 800℃ or any range between two of them.

[0066] In some specific embodiments, the calcination holding time is 1h to 3h, including but not limited to any one of 1h, 1.5h, 2h, 2.5h, and 3h, or any range between two of them.

[0067] In some specific embodiments, after roasting, there are also crushing and sieving steps.

[0068] In some specific embodiments, after the crushing and screening, the particle size of the modified smelting flux is 8 mesh to 40 mesh.

[0069] In some specific embodiments, before mixing CaF2, TiO2, SiO2, B2O3, and Y2O3, CaF2, TiO2, SiO2, B2O3, and Y2O3 are dried to remove moisture from each raw material, resulting in dried raw materials. The drying can be performed using any drying equipment and conventional methods commonly used in the art, such as placing the materials in a forced-air drying oven and drying them at 200℃~250℃ for 2h~3.5h.

[0070] In some specific embodiments, before the roasting, the quenched material is placed in a forced-air drying oven at 200℃~250℃ and dried for 2h~3h to completely remove moisture.

[0071] In some specific embodiments, the calcination can be carried out using any sintering equipment commonly used in the art, such as a muffle furnace, but is not limited thereto.

[0072] Thirdly, the present invention provides the application of modified smelting flux in high heat input welding of ship plate steel.

[0073] The modified fusion flux provided by this invention is suitable for high heat input welding of thick plates.

[0074] In some specific implementations, the thickness of the ship plate steel is 23mm to 32mm, including but not limited to any point value or range between any two points of 23mm, 24mm, 25mm, 26mm, 27mm, 28mm, 29mm, 30mm, 31mm, and 32mm.

[0075] In some specific implementations, the high heat input welding is a series twin-wire submerged arc welding.

[0076] In some specific embodiments, the lead wire of the tandem twin-wire submerged arc welding is powered by direct current.

[0077] The welding current of the DC power supply is 750A~900A, including but not limited to any one of 750A, 800A, 810A, 820A, 830A, 840A, 850A, 860A, 870A, and 900A, or the range between any two points.

[0078] The welding voltage of the DC power supply is 25V~40V, including but not limited to any one of 25V, 30V, 31V, 32V, 33V, 34V, 35V, 36V, and 40V, or the range between any two points.

[0079] In some specific embodiments, the rear wire of the series twin-wire submerged arc welding uses alternating current.

[0080] The welding current of the AC power supply is 550A~750A, including but not limited to any one of 550A, 600A, 625A, 650A, 675A, 700A, 725A, and 750A, or the range between any two points.

[0081] The welding voltage of the AC power supply is 25V~45V, including but not limited to any one of 25V, 28V, 29V, 30V, 31V, 32V, 33V, 34V, 35V, 36V, 37V, 38V, 39V, 40V, 41V, 42V, 43V, and 45V, or the range between any two points.

[0082] In some specific embodiments, the wire spacing of the tandem twin-wire submerged arc welding is 20mm~30mm, including but not limited to any point value or range between any two points of 20mm, 22mm, 24mm, 25mm, 26mm, 27mm, 28mm, and 30mm. The wire spacing refers to the distance between the preceding and following wires.

[0083] In some specific embodiments, the wire elongation of the tandem twin-wire submerged arc welding is 20mm~30mm, including but not limited to any point value or range between any two points of 20mm, 22mm, 24mm, 25mm, 26mm, 27mm, 28mm, and 30mm. The wire elongation refers to the length from the tip of the contact tip to the end of the wire during the welding process.

[0084] In some specific embodiments, the heat input of the high heat input welding is 35kJ / cm to 80kJ / cm, including but not limited to any one of 35kJ / cm, 40kJ / cm, 45kJ / cm, 50kJ / cm, 55kJ / cm, 60kJ / cm, 65kJ / cm, 70kJ / cm, 75kJ / cm, and 80kJ / cm, or a range between any two.

[0085] In some specific embodiments, the welding speed of the high heat input welding is 400 mm / min to 650 mm / min, including but not limited to any one of 400 mm / min, 450 mm / min, 500 mm / min, 550 mm / min, 600 mm / min, and 650 mm / min, or the range between any two points.

[0086] In some specific embodiments, during the high heat input welding process, the stacking height of the modified molten flux is 20mm to 40mm, including but not limited to any one of the following values ​​or the range between any two points: 20mm, 22mm, 23mm, 24mm, 25mm, 26mm, 27mm, 28mm, 29mm, 30mm, 31mm, 32mm, 33mm, 34mm, 35mm, 38mm, and 40mm.

[0087] Using the above welding parameters is beneficial to ensure the penetration depth and filling capacity of the front wire while taking into account arc stability, weld formation quality, deposition efficiency and heat input control, thereby obtaining a weld joint with good formation, sufficient fusion and stable microstructure and properties.

[0088] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0089] Example 1 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: CaF2 63.5%, TiO2 20%, SiO2 15%, B2O3 0.5%, and Y2O3 1%.

[0090] The method for preparing the modified smelting flux provided in this embodiment includes the following steps: (1) Place CaF2, TiO2, SiO2, B2O3 and Y2O3 in a drying oven and dry them at 200℃ for 3 hours to remove moisture from the materials and obtain each dried raw material. Weigh out 1.5 kg of each dried raw material according to the above ratio, mix them, stir evenly and put them into a graphite crucible.

[0091] (2) The graphite crucible containing the mixed raw materials obtained in step (1) is placed in the high-temperature constant temperature zone of a high-temperature resistance furnace and melted at 1400℃ for 20 minutes to obtain a molten liquid. The molten liquid is then quickly water-quenched and granulated at room temperature (25℃) to obtain a quenched material. The collected quenched material is placed in a 250℃ forced-air drying oven and dried for 2 hours to completely remove moisture, resulting in a dried water-quenched material.

[0092] (3) The dried water-quenched material obtained in step (2) is placed in a muffle furnace and calcined at 650°C for 3 hours to remove residual crucible carbon powder and moisture from the material, thereby obtaining a semi-finished flux. The semi-finished flux is crushed and sieved to obtain a modified smelting flux with a particle size distribution range of 8 mesh to 35 mesh, wherein the mass fraction of fine particles above 30 mesh does not exceed 10%, and the mass fraction of coarse particles below 10 mesh does not exceed 10%.

[0093] High heat input welding was performed using the modified fused flux prepared in this embodiment. The welding method is as follows: The modified fused flux prepared in this embodiment was dried at 250°C for 2 hours. Using the dried flux and CHWS3 welding wire (H10Mn2 type), a series double-wire submerged arc welding method was used to weld 30mm thick EH36 grade ship plate steel. The carbon content of the EH36 grade ship plate steel was 0.157 wt.%. During the welding process, the welding heat input was 61kJ / cm, the modified fused flux buildup height was 26mm, the welding speed was 550mm / min, the wire spacing was 25mm, and the wire elongation was 25mm. The first wire of the series double-wire submerged arc welding used direct current (DC) with a welding current / voltage of 800A / 30V, and the second wire used alternating current (AC) with a welding current / voltage of 725A / 44V. Observations showed that the arc stability was good during the welding process.

[0094] The weld bead morphology obtained after welding in this embodiment is as follows: Figure 1 As shown, there is no slag adhesion on the weld surface, the slag removal is excellent, and the weld is well protected.

[0095] The macroscopic morphology of the weld section obtained after welding in this embodiment is as follows: Figure 2 As shown, the weld has a beautiful morphology and no defects such as porosity or cracks inside.

[0096] Example 2 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: CaF2 63%, TiO2 20%, SiO2 15%, B2O3 1%, and Y2O3 1%.

[0097] Weigh the materials according to the proportions in this embodiment and prepare the modified smelting flux according to the preparation method in Example 1.

[0098] Welding was performed using the modified molten flux prepared in this embodiment, and the welding method and parameters were the same as in Embodiment 1.

[0099] The weld bead morphology obtained after welding in this embodiment is as follows: Figure 3 As shown, there is no slag adhesion on the weld surface, the slag removal performance is good, and the protection effect on the weld is good.

[0100] The metallographic structure of the weld obtained after welding in this embodiment is as follows: Figure 4 As shown, the weld has fine austenite grains, a high proportion of acicular ferrite, and a low proportion of grain boundary ferrite and side strip ferrite, which indicates excellent impact toughness.

[0101] The microscopic fracture morphology of the weld obtained after welding in this embodiment is as follows: Figure 5 As shown in the figure, the impact fracture morphology of the weld is ductile fracture, with small dimple diameter and high density, which can absorb a large amount of energy released during fracture, effectively preventing sudden fracture during use and avoiding various accidents.

[0102] Example 3 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: CaF2 62.5%, TiO2 20%, SiO2 15%, B2O3 1.5%, and Y2O3 1%.

[0103] Weigh the materials according to the proportions in this embodiment and prepare the modified smelting flux according to the preparation method in Example 1.

[0104] Welding was performed using the modified molten flux prepared in this embodiment, and the welding method and parameters were the same as in Embodiment 1.

[0105] Example 4 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: CaF2 62%, TiO2 20%, SiO2 15%, B2O3 2%, and Y2O3 1%.

[0106] The preparation method of the modified smelting flux provided in this embodiment is basically the same as that in Example 1, except that: in step (1), the drying temperature is 220°C and the drying time is 2.5h, and the sample is weighed according to the proportion of this embodiment; in step (2), the smelting temperature is 1390°C and the smelting holding time is 1h; and in step (3), the calcination temperature is 700°C and the calcination time is 2h.

[0107] High heat input welding was performed using the modified fused flux prepared in this embodiment. The welding method is as follows: The modified fused flux prepared in this embodiment was dried at 260°C for 2 hours. Using the dried flux and CHWS3 welding wire (H10Mn2 type), a series double-wire submerged arc welding method was used to weld 30mm thick EH550 grade ship plate steel. The carbon content of the EH550 grade ship plate steel was 0.16 wt.%. During the welding process, the welding heat input was 60kJ / cm, the modified fused flux buildup height was 28mm, the welding speed was 520mm / min, the wire spacing was 28mm, and the wire elongation was 24mm. The first wire of the series double-wire submerged arc welding used direct current (DC) with a welding current / voltage of 840A / 36V, and the second wire used alternating current (AC) with a welding current / voltage of 780A / 28V.

[0108] The scanning electron microscope image of the microstructure of the weld obtained after welding in this embodiment is shown below. Figure 6 As shown, the weld metal mainly consists of grain boundary ferrite, side strip ferrite, and upright ferrite.

[0109] Example 5 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: CaF2 62%, TiO2 20%, SiO2 15%, B2O3 2%, and Y2O3 1%.

[0110] The preparation method of the modified smelting flux provided in this embodiment is basically the same as that in Example 1, except that: in step (1), the drying temperature is 220°C and the drying time is 2.5h, and the sample is weighed according to the proportion of this embodiment; in step (2), the melting temperature is 1380°C and the melting holding time is 1h; and in step (3), the calcination temperature is 700°C and the calcination time is 1.5h, and the particle size of the modified smelting flux obtained after crushing and sieving is 20 mesh to 35 mesh, wherein the mass fraction of fine particles above 30 mesh does not exceed 20%.

[0111] High heat input welding was performed using the modified fused flux prepared in this embodiment. The welding method is as follows: The modified fused flux prepared in this embodiment was dried at 250°C for 2 hours. Using the dried flux and CHWS3 welding wire (H10Mn2 type), a series double-wire submerged arc welding method was used to weld 30mm thick EH690 grade ship plate steel. The carbon content of the EH690 grade ship plate steel was 0.16 wt.%. During the welding process, the welding heat input was 60kJ / cm, the flux buildup height was 30mm, the welding speed was 550mm / min, the wire spacing was 26mm, and the wire elongation was 26mm. The first wire of the series double-wire submerged arc welding used direct current (DC) with a welding current / voltage of 850A / 35V, and the second wire used alternating current (AC) with a welding current / voltage of 760A / 33V.

[0112] Example 6 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: 68% CaF2, 15% TiO2, 15% SiO2, 1% B2O3, and 1% Y2O3.

[0113] The preparation method of the modified smelting flux provided in this embodiment is basically the same as that in embodiment 1, except that: in step (2), the smelting temperature is 1350℃ and the smelting holding time is 1h.

[0114] High heat input welding was performed using the modified molten flux prepared in this embodiment. The welding method is as follows: The modified molten flux prepared in this embodiment was dried at 280°C for 1.5 hours. The dried flux was then used in conjunction with CHW... S3 welding wire (H10Mn2 type) was used in a tandem twin-wire submerged arc welding method to weld 30mm thick EH36 grade ship plate steel, which contains 0.05% carbon by mass. During welding, the welding heat input was 61kJ / cm², the modified flux buildup height was 32mm, the welding speed was 500mm / min, the wire spacing was 26mm, and the wire elongation was 24mm. The first wire in the tandem twin-wire submerged arc welding used direct current (DC) with a welding current / voltage ratio of 870A / 36V, while the second wire used alternating current (AC) with a welding current / voltage ratio of 625A / 32V.

[0115] Example 7 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: 73% CaF2, 10% TiO2, 15% SiO2, 1% B2O3, and 1% Y2O3.

[0116] Weigh the materials according to the proportions in this embodiment and prepare the modified smelting flux according to the preparation method in Example 1.

[0117] Welding was performed using the modified molten flux prepared in this embodiment, and the welding method and parameters were the same as in Embodiment 1.

[0118] Example 8 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: CaF2 68.5%, TiO2 20%, SiO2 10%, B2O3 1%, and Y2O3 0.5%.

[0119] Weigh the materials according to the proportions in this embodiment and prepare the modified smelting flux according to the preparation method in Example 1.

[0120] Welding was performed using the modified molten flux prepared in this embodiment, and the welding method and parameters were the same as in Embodiment 1.

[0121] Example 9 The modified smelting flux provided in this embodiment is made from the following components by mass percentage: CaF2 57%, TiO2 20%, SiO2 20%, B2O3 1%, and Y2O3 2%.

[0122] Weigh the materials according to the proportions in this embodiment and prepare the modified smelting flux according to the preparation method in Example 1.

[0123] Welding was performed using the modified molten flux prepared in this embodiment, and the welding method and parameters were the same as in Embodiment 1.

[0124] Comparative Example 1 The modified smelting flux provided in this comparative example is made from the following components by mass percentage: 64% CaF2, 20% TiO2, 15% SiO2, and 1% Y2O3. That is, this modified smelting flux does not contain B2O3.

[0125] Weigh the materials according to the proportions in this comparative example and prepare the modified smelting flux according to the preparation method of Example 1.

[0126] Welding was performed using the modified molten flux prepared in this comparative example, and the welding method and parameters were the same as in Example 1.

[0127] The weld metallographic structure obtained after welding in this comparative example is as follows: Figure 7 As shown, the weld has fine austenite grains, a low proportion of acicular ferrite, and a high proportion of grain boundary ferrite and side strip ferrite, which indicates that its impact toughness is relatively poor.

[0128] The microscopic fracture morphology of the weld obtained after the comparative welding is as follows: Figure 8 As shown, Figure 9 for Figure 8 The enlarged view within the box is a microscopic fracture morphology diagram. From Figure 8 and Figure 9 It can be seen that the impact fracture morphology of the weld in Comparative Example 1 is brittle fracture with a large number of river-patterned cleavage surfaces, and poor impact performance.

[0129] Comparative Example 2 The modified smelting flux provided in this comparative example is made from the following components by mass percentage: 64.5% CaF2, 20% TiO2, 15% SiO2, and 0.5% B2O3. That is, this modified smelting flux does not contain Y2O3.

[0130] Weigh the materials according to the proportions in this comparative example and prepare the modified smelting flux according to the preparation method of Example 1.

[0131] Welding was performed using the modified molten flux prepared in this comparative example, and the welding method and parameters were the same as in Example 1.

[0132] Comparative Example 3 The modified smelting flux provided in this comparative example is made from the following components by mass percentage: CaF2 56%, TiO2 20%, SiO2 15%, B2O3 5%, and Y2O3 4%. That is, the content of B2O3 and Y2O3 in this modified smelting flux is too high.

[0133] Weigh the materials according to the proportions in this comparative example and prepare the modified smelting flux according to the preparation method of Example 1.

[0134] Welding was performed using the modified molten flux prepared in this comparative example, and the welding method and parameters were the same as in Example 1.

[0135] Comparative Example 4 The modified smelting flux provided in this comparative example is made from the following components by mass percentage: CaF2 63.5%, TiO2 5%, SiO2 30%, B2O3 0.5%, and Y2O3 1%. That is, the content of SiO2 in this modified smelting flux is too high and the content of TiO2 is too low.

[0136] Weigh the materials according to the proportions in this comparative example and prepare the modified smelting flux according to the preparation method of Example 1.

[0137] Welding was performed using the modified molten flux prepared in this comparative example, and the welding method and parameters were the same as in Example 1.

[0138] Experimental Example The welds obtained after welding in each embodiment and comparative example were tested for the average width of the original austenite grains, the content of acicular ferrite (volume fraction), the content of side strip ferrite (volume fraction), the content of grain boundary ferrite (volume fraction), and the impact energy at -40℃. The test results are shown in Table 1 below.

[0139] The average width of the original austenite grains was measured by taking samples of the weld under an OLYMPUS GX51 metallographic microscope, magnifying them 50 times, and sampling at a specific distance parallel to the fusion line, using the cross-section method.

[0140] The contents of acicular ferrite, side strip ferrite, and grain boundary ferrite (all volume fractions) were obtained by taking samples of the weld under an OLYMPUS GX51 metallographic microscope, taking 200x magnification photographs, and then covering each metallographic photograph with 500 grid points in ImageJ, counting the number of grid points falling on each type of weld microstructure.

[0141] The low-temperature impact toughness (-40℃) test was conducted according to GB / T 2650-2008, using a SANS-ZBC2452-C impact testing machine. Each weld was tested three times for low-temperature impact toughness, and the average value was taken.

[0142] Table 1 Test results for each weld

[0143] As shown in Table 1, the welds obtained in each embodiment exhibit good low-temperature toughness and high acicular ferrite content. In particular, the low-temperature impact energy of Example 2 is 64J, which is far greater than the national standard of 27J (GB / T 5293). (2018), and the content of acicular ferrite is 60%.

[0144] The welds obtained in each comparative example exhibited poor low-temperature toughness and a low volume fraction of acicular ferrite due to the use of unsuitable flux compositions. Specifically, Comparative Example 1, lacking B2O3, suffered from insufficient effective B sources in the weld, making it difficult to adequately suppress the formation of grain boundary ferrite and ferrite sidewalls. Consequently, its acicular ferrite volume fraction and low-temperature toughness were lower than those of Example 1. Comparative Example 2, lacking Y2O3, experienced weakened inclusion degradation and intragranular nucleation regulation, hindering acicular ferrite formation. Consequently, its weld microstructure showed an increase in grain boundary nucleation structures and a decrease in low-temperature toughness. Comparative Example 3, with excessively high B2O3 and Y2O3 content, caused the slag-metal reaction and inclusion evolution during welding to deviate from the optimal range. This, in turn, was detrimental to the formation of fine, dispersed inclusions suitable for acicular ferrite nucleation, leading to a deterioration in the weld microstructure and properties. In Comparative Example 4, the excessively high SiO2 content and the excessively low TiO2 content led to an imbalance in the slag formation and inclusion control of the flux. This was not only detrimental to the low-temperature toughness of the weld, but also weakened the promoting effect on the formation of acicular ferrite. As a result, the volume fraction of acicular ferrite in the weld was low and the low-temperature toughness was poor.

[0145] Furthermore, the average width of the original austenite grains in the welds obtained in each embodiment is relatively small, ranging from 80μm to 90μm, while the average width of the original austenite grains in each comparative example is higher than 100μm.

[0146] This indicates that by controlling the chemical composition of the modified smelting flux, the present invention can achieve rapid cooling of the weld, resulting in a finer weld structure, increasing the proportion of acicular ferrite, and reducing the proportion of side strip ferrite and grain boundary ferrite, thereby playing a role in grain refinement and strengthening, and thus improving the low-temperature impact toughness of the weld metal.

[0147] Combining Table 1 and Figures 1-9 It is known that the modified smelting flux provided by this invention is composed of CaF2, TiO2, SiO2, B2O3, and Y2O3 in a specific ratio, with good metallurgical synergy among the multiple components. On the one hand, it makes the oxygen content and microalloying elements (B, Ti) in the weld after welding more rational, giving the weld good slag removal performance and excellent arc stability and formability. The welding process is stable, and the weld metal composition after welding is accurate, the microstructure is uniform, the surface morphology is smooth, and there are no defects such as porosity, indentation, and cracks, thus ensuring that the weld has excellent comprehensive mechanical properties. On the other hand, the synergistic effect of the specific content of B and Ti can significantly regulate the solidification phase transformation process of marine low-carbon low-alloy steel, greatly increasing the proportion of high-toughness acicular ferrite in the weld, ensuring the excellent mechanical properties of the weld. For both low-carbon and high-carbon ship plate steel, the low-temperature impact toughness of the weld after welding is excellent.

[0148] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can 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 therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A modified smelting flux, characterized in that, It is made from the following components by mass percentage: CaF2 50%~80%, TiO2 10%~30%, SiO2 10%~25%, B2O3 0.1%~3%, and Y2O3 0.5%~2%.

2. The modified smelting flux according to claim 1, characterized in that, The average width of the original austenite grains in the weld formed after welding ship plate steel using the modified smelting flux is ≤90μm.

3. The modified smelting flux according to claim 1, characterized in that, The weld formed by welding ship plate steel using the modified smelting flux has a low-temperature impact energy of -40℃ ≥34J. The volume fraction of acicular ferrite in the weld formed after welding ship plate steel using the modified fusion flux is ≥50%.

4. The modified smelting flux according to claim 1, characterized in that, The particle size of the modified smelting flux is 8 mesh to 40 mesh.

5. The method for preparing the modified smelting flux according to any one of claims 1 to 4, characterized in that, Includes the following steps: CaF2, TiO2, SiO2, B2O3 and Y2O3 are mixed and then smelted to obtain a molten liquid; The molten material is quenched in water to obtain a quenched material. The quenched material is roasted to obtain a modified smelting flux.

6. The method for preparing the modified smelting flux according to claim 5, characterized in that, The melting temperature is 1350℃~1400℃, and the melting holding time is 20min~1h.

7. The method for preparing the modified smelting flux according to claim 5, characterized in that, The roasting temperature is 650℃~800℃, and the roasting holding time is 1h~3h.

8. The application of the modified smelting flux as described in any one of claims 1 to 4 in high heat input welding of ship plate steel.

9. The application of the modified smelting flux according to claim 8 in high heat input welding of ship plate steel, characterized in that, The high heat input welding is a series dual-wire submerged arc welding; The lead wire of the series twin-wire submerged arc welding uses direct current, the welding current of the direct current is 750A~900A, and the welding voltage of the direct current is 25V~40V; The rear wire of the series twin-wire submerged arc welding uses AC power, the AC welding current is 550A~750A, and the AC welding voltage is 25V~45V. The wire spacing of the tandem twin-wire submerged arc welding is 20mm~30mm; The wire elongation of the tandem twin-wire submerged arc welding is 20mm~30mm.

10. The application of the modified smelting flux according to claim 8 in high heat input welding of ship plate steel, characterized in that, The heat input energy of the high heat input welding is 35 kJ / cm to 80 kJ / cm; The welding speed of the high heat input welding is 400 mm / min to 650 mm / min; During the high heat input welding process, the modified molten flux is stacked at a height of 20mm to 40mm.

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