Welding wire for welding and welding method

Abstract

The invention relates to a welding wire for welding and a welding method, belongs to the field of welding processes, and solves at least one of the problems of insufficient mechanical property of a welding joint, poor joint quality, poorer welding adaptability / accessibility and higher cost in the welding process of light steel, particularly a high-Al-series FeMnAlC steel medium-thickness plate in the prior art. The welding wire comprises, by mass, 0.6% < = C < = 1.2%, 25% < = Mn < = 35%, 7% < Al < = 12%, 0.3% < = Mo < = 0.9%, W < = 0.5%, 0.1% < V < = 0.5%, 0.1% < Nb < = 0.5% and the balance Fe and inevitable impurities. By optimizing the components of the welding wire, the mechanical property and the quality of the welding joint are remarkably improved, and the welding method can still ensure the high quality and the mechanical property of the welding joint while simplifying the operation, reducing the cost and improving the adaptability.

Description

Technical Field

[0001] The invention relates to the technical field of welding technology, and in particular to a welding wire and a welding method. Background Art

[0002] With the prevalence of green manufacturing concepts such as "weight reduction, energy saving, and carbon emission reduction", FeMnAlC steel has low density and good comprehensive performance, and has been increasingly valued in the field of material research and industry in recent years. At present, domestic and foreign scholars' research on FeMnAlC low-density steel mainly focuses on laboratory preparation and performance mechanism, but there is little research on subsequent process performance, especially the welding process performance of FeMnAlC low-density steel.

[0003] According to existing literature reports, FeMnAlC low-density steel faces some challenges in the welding process due to its alloy element combination. These challenges mainly include the formation of brittle second phases in welded joints, segregation of weld components, and cracks. These problems make the welded joints of FeMnAlC low-density steels a weak link in the structure. For FeMnAlC low-density steels, as the C and Al content in the welding materials increases or the thickness of the welding materials increases, the above problems become more prominent, welding becomes more difficult, and defects such as welding cracks are more likely to occur.

[0004] Due to the above-mentioned welding difficulties of this type of steel, the existing welding wires or welding methods, when used to weld FeMnAlC low-density steels, especially high-aluminum FeMnAlC steels, have one or more problems including poor welding quality, insufficient mechanical properties of welded joints, expensive equipment and high costs. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a welding wire and a welding method to solve at least one of the following problems existing in the welding process of lightweight steel, especially high Al-based FeMnAlC steel medium and thick plates in the prior art: (1) insufficient mechanical properties of the welded joint; (2) poor quality of the welded joint, such as the presence of cracks and pores; (3) expensive welding equipment, poor welding adaptability / accessibility, and high cost.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The invention provides a welding wire, which is applied to FeMnAlC low-density steel. The components of the welding wire include, by mass percentage: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, 0.3%≤Mo≤0.9%, W≤0.5%, 0.1%<V≤0.5%, 0.1%<Nb≤0.5%, and the rest is Fe and unavoidable impurities;

[0008] And the Mo, W, V, and Nb meet the requirement: 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1%, where [Mo], [W], [V], and [Nb] represent the mass percentage (%) of each element.

[0009] Furthermore, the components of the welding wire include, by mass percentage, 0.6%≤C≤1.2%, 25%≤Mn≤35%, 8%≤Al≤10%, 0.4%≤Mo≤0.6%, 0.3%≤W≤0.5%, 0.3%≤V≤0.5%, 0.3%≤Nb≤0.5%, and the rest are Fe and unavoidable impurities.

[0010] Furthermore, the Mo, W, V, and Nb also satisfy the following relationship: 2.2<([W]+[V]+[Nb]) / [Mo]<2.6.

[0011] Furthermore, the C, Mo, W, V, and Nb also satisfy: α=0.5×[Mo]+0.6×([W]+[V]+[Nb]) and 0.8α<[C]<1.2α;

[0012] Here, [C], [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element.

[0013] Furthermore, the welding wire also comprises the following components: Mg≤0.1%, B≤0.1%, and Re≤0.1%.

[0014] Furthermore, the Mg, B, and Re satisfy the requirement: 0.09%≤[B]+[Mg]+[Re]≤0.21%, where [Mg], [B], and [Re] represent the mass percentage (%) of each element.

[0015] Furthermore, the Mg, B, and Re also meet the requirement: 0.5<([B]+[Mg]) / [Re]<2.1.

[0016] The present invention also provides a welding method, comprising welding FeMnAlC low-density steel, i.e., weldment, using the above-mentioned welding wire;

[0017] The main steps of the welding method include: using TIG welding technology under inert gas protection, first performing base welding, then performing formal welding, and immediately tapping the weld to release stress after the weld is solidified.

[0018] Further, the process parameters of the base welding include: welding current is 160-170A; and / or,

[0019] The process parameters of the formal welding include: welding voltage of 15-19V, welding current of 170-205A, and welding speed of 14-19cm / min.

[0020] Furthermore, the welding pass N of the formal welding satisfies: in, It indicates rounding up or down to the nearest integer result; t indicates the steel plate thickness of the weldment, the unit of t is mm and t≥3mm.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] (1) The present invention significantly improves the mechanical properties of the welded joint by optimizing the composition of the welding wire, especially increasing the C and Al contents and rationally adding key alloying elements (such as Mo, W, V, and Nb), especially when welding FeMnAlC low-density steel, which can better meet the high performance requirements in industrial applications;

[0023] Specifically, from the perspective of welding wire composition design, the present invention, on the one hand, improves the strength of the welded joint by further increasing the C content (0.6%-1.2%) compared to the lower C content (≤0.3%) in the existing welding wire, and appropriately increases the Al content to improve the weld uniformity. On the other hand, through the reasonable addition of some key alloying elements (such as Mo, W, V, Nb) and the optimization of the composition content (such as controlling the upper and lower limits of these elements), it is possible to improve the joint strength and weld uniformity while ensuring that the welded joint has good toughness and plasticity and effectively reduces defects such as cracks and pores. Compared with the welding wire disclosed in the prior art, when the welding wire provided by the present invention is used to weld FeMnAlC low-density steel, the mechanical properties of the welded joint can be significantly improved, especially when it is used for FeMnAlC low-density steel welding materials with greater welding difficulty (such as high Al and C content and / or medium and thick plates), the joint strength can still reach a level of 850Mpa and above, and the toughness and plasticity of the joint can meet the mechanical property requirements for the joint of such steel plates in industrial applications, such as elongation A5 ≥ 20% and V-type impact energy KV2 ≥ 30J at -84°C in the tensile test.

[0024] (2) The present invention significantly improves the quality of the welded joint and effectively reduces defects such as cracks and pores by optimizing the composition of the welding wire, especially appropriately increasing the Al content and rationally adding key alloying elements (such as Mo, W, V, and Nb);

[0025] Specifically, compared with the lower Al content (≤7.0%) in the existing welding wire, the present invention improves the uniformity of the weld by appropriately increasing the Al content (7%<Al≤12%); at the same time, the present invention can ensure the joint strength and welding quality by reasonably adding some key alloy elements (such as Mo, W, V, Nb) and optimizing the content of the components (such as controlling the upper and lower limits of these elements), and can refine the welding structure by dragging large atoms and forming MC carbides, effectively improve the toughness and plasticity of the joint, improve the welding crack resistance, and reduce defects such as cracks and pores at the welding joint. Compared with the welding wire disclosed in the prior art, when the welding wire provided by the present invention is used to weld FeMnAlC low-density steel, the overall quality of the welded joint is better, such as showing better welding crack resistance and weld uniformity, and fewer defects such as cracks and pores.

[0026] (3) In some preferred embodiments, the present invention refines the inclusions of the weld joint and improves the toughness and plasticity of the weld joint by adding additional key alloy elements (such as Mg, B, Re) to the welding wire composition and controlling the content range. This composition optimization not only further improves the mechanical properties of the weld joint, but also enhances the welding crack resistance, reduces defects such as cracks, and thus further improves the quality of the weld.

[0027] (4) In some preferred embodiments, the present invention can further improve the mechanical properties of the weld joint and the quality of the weld by carefully designing and controlling the content of some key alloying elements (Mo, W, V, Nb or Mg, B, Re) in the welding wire and the proportional relationship between them; for example, further improving the strength and toughness of the joint, improving the impact resistance at low temperatures, further improving the crack resistance of the welding and reducing defects such as cracks and pores.

[0028] (5) When the welding method provided by the present invention is applied to FeMnAlC low-density steel, it shows significant advantages compared with the prior art, such as: convenient operation, economy, and good welding adaptability / accessibility. At the same time, thanks to the special composition design of the welding wire in the present invention, the welding method of the present invention can simplify the operation, reduce the cost, and improve the adaptability while still ensuring the high quality and mechanical properties of the welded joint, thereby providing a new efficient and economical choice for the welding of FeMnAlC low-density steel.

[0029] (6) In some preferred embodiments, the welding method of the present invention can optimize the microstructure of the weld, improve the strength, toughness and plasticity of the weld joint, further improve the quality and mechanical properties of the weld joint, and achieve an optimal balance between welding performance, efficiency and cost by optimizing and controlling some key parameters in the welding process (for example, welding current, voltage, speed, and welding passes).

[0030] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0032] Figure 1 This is an enlarged metallographic structure diagram of the welded joint obtained in Example 1 of the present invention;

[0033] Figure 2 This is an enlarged metallographic structure diagram of the welded joint obtained in Comparative Example 4;

[0034] Figure 3 This is a low-magnification morphology image of the welded joint obtained in Example 1 of the present invention;

[0035] Figure 4 This is a low-magnification morphology image of the welded joint obtained in Comparative Example 4. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0037] In recent years, a few researchers have tried to apply some common welding processes (such as laser welding, resistance spot welding, electron beam welding, and stir friction welding) to welding low-Al FeMnAlC steel. However, these existing methods have obvious disadvantages in practical application. For example, the cooling speed of the laser welding process is very fast, and the weld penetration is large. During the rapid heating and solidification process, it is easy to generate large internal stress and pores in the weld joint, thereby affecting the quality of the weld joint; the weld point of the resistance spot welding becomes a weak area and is prone to brittle cracking; after electron beam welding, due to the supercooling and fast cooling rate during the welding process, the austenite structure of the entire weld exists in the form of columnar crystals with preferential orientation. These columnar crystals grow and aggregate perpendicular to the fusion line toward the center of the weld, and finally form an obvious dividing line in the center of the weld, which leads to poor fracture ductility of the weld joint; stir friction welding lacks welding flexibility, the wear of the weld joint is relatively large, the cost is high, and the stirring zone will have a hardening effect and affect the welding performance.

[0038] The inventors of the present invention comprehensively consider the characteristics of FeMnAlC series low-density steel, especially high-aluminum FeMnAlC steel in welding, which contains more Mn and Al elements, and is prone to large deformation and obvious overheating during welding. It is believed that a welding process with a smaller line energy should be selected as much as possible during welding. Compared with other connection methods, tungsten inert gas shielded welding (TIG) does not have the problem of electrode metal transition, the arc phenomenon is simple, the welding process is easy to operate, and the adaptability is good, which is suitable for the welding of FeMnAlC series low-density steel; however, for FeMnAlC series low-density steel, especially when the C content and / or Al content and / or the thickness of the welding material are large, there is currently no suitable welding wire and welding method that can effectively solve the problems of insufficient joint mechanical properties, poor weld quality, high welding cost, and poor adaptability / accessibility that are prone to occur during welding of such lightweight steels.

[0039] Based on this, in the first aspect, the present invention provides a welding wire, which is applied to FeMnAlC low-density steel, and the components of the welding wire include, in mass percentage: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, 0.3%≤Mo≤0.9%, W≤0.5%, 0.1%<V≤0.5%, 0.1%<Nb≤0.5%, and the rest are Fe and unavoidable impurities; and the Mo, W, V, and Nb meet the requirements: 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1%, and [Mo], [W], [V], and [Nb] represent the mass percentage (%) of each element.

[0040] Compared with the prior art, the present invention significantly improves the mechanical properties of the welded joint by optimizing the welding wire composition, especially increasing the C and Al contents and reasonably adding key alloying elements (such as Mo, W, V, and Nb), and can better meet the high performance requirements in industrial applications when welding FeMnAlC low-density steel. Specifically, from the perspective of welding wire composition design, the present invention, on the one hand, improves the strength of the welded joint by further increasing the C content (0.6%-1.2%) compared to the lower C content (≤0.3%) in the existing welding wire, and appropriately increases the Al content to improve the uniformity of the weld. On the other hand, by reasonably adding some key alloying elements (such as Mo, W, V, and Nb) and optimizing the composition content (such as controlling these elements), the present invention can significantly improve the mechanical properties of the welded joint. The upper and lower limits of the elements are within the range of the upper and lower limits of the elements, which can improve the joint strength and weld uniformity while ensuring that the welded joint has good toughness and plasticity and effectively reduces defects such as cracks and pores; compared with the welding wire disclosed in the prior art, when the welding wire provided by the present invention is used to weld FeMnAlC low-density steel, the mechanical properties of the welded joint can be significantly improved, especially when it is applied to Fe-Mn-Al-C low-density steel welding materials with greater welding difficulty, such as high Al and C content and / or medium and thick plates, the joint strength can still reach a level of 850Mpa and above, and the toughness and plasticity of the joint can meet the joint mechanical property requirements for such steel plates in industrial applications, such as elongation A5≥20% and V-type impact energy KV2≥30J at -84°C in the tensile test.

[0041] Compared with the prior art, the present invention significantly improves the quality of the welded joint by optimizing the welding wire composition, especially appropriately increasing the Al content and reasonably adding key alloying elements (such as Mo, W, V, Nb), and effectively reduces defects such as cracks and pores; specifically, compared with the lower Al content (≤7.0%) in the existing welding wire, the present invention improves the weld uniformity by appropriately increasing the Al content (7%<Al≤12%); at the same time, the present invention can ensure the joint strength and welding quality by reasonably adding some key alloying elements (such as Mo, W, V, Nb) and optimizing the composition content (such as controlling the upper and lower limits of these elements), and can effectively improve the toughness and plasticity of the joint, improve the welding crack resistance, and reduce defects such as cracks and pores at the welded joint by dragging large atoms and forming MC carbides. Compared with the welding wire disclosed in the prior art, when the welding wire provided by the present invention is used to weld FeMnAlC low-density steel, the overall quality of the welded joint is better, such as showing better welding crack resistance and weld uniformity, and fewer defects such as cracks and pores.

[0042] It can be seen that the welding wire provided by the present invention can fully meet the welding needs of FeMnAlC low-density steel, and is particularly suitable for medium and thick plates of high-Al FeMnAlC steel, which significantly improves the tensile properties and plastic toughness of the welded joints of such lightweight steels, and can especially optimize the microstructure of the fusion zone, effectively reduce the sensitivity to cold cracks and hot cracks during welding, thereby significantly improving the welding quality.

[0043] Specifically, the chemical composition design basis of the welding wire in the present invention mainly includes:

[0044] C: As an interstitial atom in steel, it is very important for improving the strength of steel. Excessive C content will lead to excessive precipitation of κ-carbide in austenite, especially large particles of κ-carbide will be formed after welding, which will seriously deteriorate the welding performance. In addition, high carbon content is also easy to combine with oxygen to form pores. Therefore, the present invention limits the C content to 0.6-1.2%. Exemplarily, the C content is 0.7%, 0.8%, 0.9%, 1.0%, and 1.1%.

[0045] Mn: Mn is an austenite forming and stabilizing element, which can expand the austenite phase region and reduce the critical quenching rate of steel. However, too high a Mn content causes lightweight steel to easily form a β-Mn brittle phase, which greatly reduces the toughness of the material. However, in order to ensure that the matrix structure of the steel of the present invention is an austenite structure, the Mn content must be no less than 25%. Therefore, the present invention limits the Mn content to 25% to 35%. Exemplarily, the Mn content is 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, and 34%.

[0046] Al: Al is an important deoxidizer in the welding process, which is very important for ensuring the quality and performance of the weld. At the same time, the Al element has a high liquid diffusion rate during the welding process, which can promote the mixing and cross-diffusion of welding materials and help form a uniform weld. Excessive aluminum content will reduce the strength and toughness of the weld joint and increase the thermal crack sensitivity of the weld joint; at the same time, too low Al content will lead to insufficient strength of the weld joint. The present invention limits the Al content to 7%<Al≤12%. Exemplarily, the Al content is 8%, 9%, 10%, and 11%.

[0047] In welding wires used for welding FeMnAlC low-density steel, increasing the carbon (C) and aluminum (Al) content can indeed bring the benefits mentioned above (for example, higher C content can improve strength, and higher Al content can improve weld uniformity), but it is also accompanied by some welding challenges. Higher C and Al content will increase the difficulty of welding. For example, high carbon content will reduce the plasticity and toughness of the weld joint, and it is easy to crack during welding; when the aluminum content is high, it is easy to form brittle phases with other elements in the steel, such as aluminum carbide, which will reduce the toughness of the weld joint and increase the risk of cracks.

[0048] In order to solve and balance the above-mentioned welding challenges, the present invention adds Mo, W, V, and Nb alloy elements and controls their content within an appropriate range. While utilizing some benefits brought by high C and Al contents (such as improving strength and weld uniformity), the welded joint can have good plasticity and toughness, including toughness-plastic properties at room and low temperature environments, thereby improving welding crack resistance, reducing welding defects such as cracks, and thus improving welding quality.

[0049] Mo, W, Nb, V: The addition of a small amount of Mo, W, Nb, and V can refine the welding structure by dragging large atoms and forming MC carbides, thereby improving the toughness of the material. They can form stable carbides (MC type) with carbon, which can refine the grains and stabilize austenite during welding, thereby improving the mechanical properties of the welded joint. However, adding a large amount will increase the risk of precipitation of large-particle carbides, which can easily become the starting point of cracks and reduce the toughness of the material. Therefore, it is required that 0.3%≤Mo≤0.9%, W≤0.5%, 0.1%<V≤0.5%, 0.1%<Nb≤0.5% in the welding wire, and 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1%, [Mo], [W], [V], [Nb] represent the mass percentage (%) of each element. By controlling and optimizing the content of these elements, the synergistic effect between Mo, W, Nb, and V can be better achieved to ensure that they significantly improve the toughness and plasticity of the welded joint and the welding quality while ensuring the high strength of the welded joint without significantly increasing the material cost; among them, the requirement of 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1% can effectively inhibit the embrittlement of the welded joint caused by the precipitation of the second phase such as κ-carbide in the welded joint during welding.

[0050] In some embodiments, the Mo content is 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%. Preferably, 0.4%≤Mo≤0.6%.

[0051] In some embodiments, the W content is 0.05%, 0.10%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%. Preferably, 0.3%≤W≤0.5%, for example, the W content is 0.32%, 0.34%, 0.36%, 0.38%, 0.40%, 0.42%, 0.44%, 0.46%, 0.48%.

[0052] In some embodiments, the V content is 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%. Preferably, 0.3%≤V≤0.5%, for example, the V content is 0.32%, 0.34%, 0.36%, 0.38%, 0.40%, 0.42%, 0.44%, 0.46%, 0.48%.

[0053] In some embodiments, the Nb content is 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%. Preferably, 0.3%≤Nb≤0.5%, for example, the Nb content is 0.32%, 0.34%, 0.36%, 0.38%, 0.40%, 0.42%, 0.44%, 0.46%, 0.48%.

[0054] In some preferred embodiments, the components of the welding wire include, by mass percentage: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 8%≤Al≤10%, 0.4%≤Mo≤0.6%, 0.3%≤W≤0.5%, 0.3%≤V≤0.5%, 0.3%≤Nb≤0.5%, and the rest is Fe and unavoidable impurities.

[0055] Preferably, in the welding wire provided by the present invention, the Mo, W, V, and Nb also satisfy the following relationship: 2.2<([W]+[V]+[Nb]) / [Mo]<2.6, where [Mo], [W], [V], and [Nb] represent the mass percentage (%) of each element. After relatively systematic research and theoretical analysis, the inventors believe that the addition amount of molybdenum (Mo), tungsten (W), vanadium (V) and niobium (Nb) and their mutual proportions are also very important. When the addition amount of these four elements meets the following specific ratio conditions, namely 2.2<([W]+[V]+[Nb]) / [Mo]<2.6, the synergistic effect between these elements can be maximized; this preferred element ratio strategy is very effective in solving the challenges of welding toughness and quality caused by increasing the C and Al content. In this way, it can not only effectively reduce or inhibit the precipitation of the second phase (such as κappa carbide) and reduce the element segregation phenomenon, thereby improving the toughness and plasticity of the welded joint and reducing welding defects (such as cracks), but also achieve the best balance of material cost-effectiveness while ensuring the quality and high strength of the welded joint.

[0056] Preferably, the W, V, and Nb have the following relationship: [W]: [V]: [Nb] = (0.9-1.1): (0.9-1.1): (0.9-1.1). More preferably, [W]: [V]: [Nb] = (0.95-1.05): (0.95-1.05): (0.95-1.05). By precisely controlling the ratio of W, V, and Nb, it is beneficial to maximize the synergistic effect of W, V, and Nb elements and W, V, and Nb with other elements, further improve the toughness and crack resistance of the welded joint, improve the quality of the weld and ensure the high strength of the welded joint. For example, [W]: [V]: [Nb] = 1:1:1.

[0057] In some preferred embodiments, in the welding wire provided by the present invention, the C, Mo, W, V, and Nb also satisfy: α = 0.5×[Mo] + 0.6×([W] + [V] + [Nb]) and 0.8α<[C]<1.2α; wherein [C], [Mo], [W], [V], and [Nb] represent the mass percentage (%) of each element. More preferably, 0.9α<[C]<1.1α. This preferred element ratio strategy is very effective in solving the challenges of welding toughness and quality caused by high carbon (C) and high aluminum (Al) content. In this way, while improving the welding quality and strength, it is possible to maximize the role of Mo, W, V, and Nb in refining the welding structure through large atomic drag and the formation of MC carbides, while effectively reducing or inhibiting the precipitation of the second phase (such as κappa carbide) and the phenomenon of element segregation, thereby improving the toughness and plasticity of the welded joint, while achieving the best balance of cost-effectiveness.

[0058] In some preferred embodiments, the composition of the welding wire in the present invention further includes: Mg≤0.1%, B≤0.1%, Re≤0.1%. The present invention refines the inclusions of the weld joint and improves the toughness and plasticity of the weld joint by adding additional key alloy elements (such as Mg, B, Re) to the welding wire composition and controlling the content range. This composition optimization not only further improves the mechanical properties of the weld joint, but also enhances the crack resistance of the weld, reduces defects such as cracks, and thus further improves the quality of the weld.

[0059] It should be noted that the chemical composition design basis for adding additional key alloy elements (such as Mg, B, Re) to the welding wire composition mainly includes:

[0060] Mg, B, Re: Trace addition of Mg, B, Re can refine the inclusions in the weld joint, thereby improving the toughness and plasticity of the weld joint. Excessive addition will increase the number of inclusions and increase the particle size. Therefore, B≤0.1%, Mg≤0.1% and rare earth Re≤0.1% are required.

[0061] In some embodiments, 0.01%≤Mg≤0.1%; illustratively, the Mg content is 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%. Preferably, 0.03%≤Mg≤0.07%, for example, the Mg content is 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, 0.06%, 0.065%.

[0062] In some embodiments, 0.01%≤B≤0.1%; illustratively, the B content is 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%. Preferably, 0.03%≤B≤0.07%, for example, the B content is 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, 0.06%, 0.065%.

[0063] In some embodiments, 0.01%≤Re≤0.1%; illustratively, the Re content is 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%. Preferably, 0.03%≤Re≤0.07%, for example, the Re content is 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, 0.06%, 0.065%.

[0064] In some embodiments, the components of the welding wire include, by mass percentage: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 8%≤Al≤10%, 0.01%≤Mg≤0.1%, 0.01%≤B≤0.1%, 0.01%≤Re≤0.1%, 0.4%≤Mo≤0.6%, 0.3%≤W≤0.5%, 0.3%≤V≤0.5%, 0.3%≤Nb≤0.5%, and the rest is Fe and unavoidable impurities.

[0065] In some preferred embodiments, the components of the welding wire include, by mass percentage: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 8%≤Al≤10%, 0.03%≤Mg≤0.07%, 0.03%≤B≤0.07%, 0.03%≤Re≤0.07%, 0.4%≤Mo≤0.6%, 0.3%≤W≤0.5%, 0.3%≤V≤0.5%, 0.3%≤Nb≤0.5%, and the rest is Fe and unavoidable impurities.

[0066] When the welding wire provided by the present invention also adds Mg, B, and Re alloy elements, preferably, the Mg, B, and Re meet the requirements: 0.09% ≤ [B] + [Mg] + [Re] ≤ 0.21%, [Mg], [B], [Re] represent the mass percentage (%) of each element. By further controlling and optimizing the upper and lower limits of the sum of the contents of the three elements Mg, B, and Re, the synergistic effect between them can be better exerted to ensure that they significantly improve the toughness and plasticity of the welded joint and the welding quality while ensuring the high strength of the welded joint without significantly increasing the material cost; for example, controlling the total content of these elements Mg, B, and Re within a suitable range (0.09%-0.21%) can more effectively inhibit the precipitation of harmful phases (such as κ-carbide) during welding, reduce the embrittlement of the welded joint, and improve the crack resistance of the welded joint.

[0067] When the welding wire provided by the present invention also adds Mg, B, and Re alloy elements, it is further preferred that the Mg, B, and Re also meet the requirements: 0.5<([B]+[Mg]) / [Re]<2.1, [Mg], [B], [Re] represent the mass percentage (%) of each element. After relatively systematic research and theoretical analysis, the inventors believe that the addition amount of boron (B), magnesium (Mg) and rhenium (Re) and their mutual proportions are crucial. When the addition amount of the three elements meets the following specific proportion conditions, that is, 0.5<([B]+[Mg]) / [Re]<2.1, the synergistic effect between these elements can be maximized; this optimized element ratio strategy is beneficial for solving the challenges of welding toughness and quality caused by increasing the C and Al content. In this way, not only the toughness and plasticity of the welded joint can be improved, but also the best balance of material cost-effectiveness can be achieved while ensuring the quality and high strength of the welded joint. Specifically, boron (B) is used in welding wire to form borides or boron carbides with high hardness and good thermal stability. These hard phases can significantly improve the hardness and wear resistance of weld metal. When rare earth element Re is added to welding wire in trace amounts, it can refine grains, purify grain boundaries and improve the comprehensive performance of weld metal. When the ratio of the total amount of boron (B) and magnesium (Mg) to the rare earth element Re is between 0.5 and 2.1, the best welding performance can be obtained, because this ratio can balance the hardness, toughness and processability of weld metal. Too much boron (B) and magnesium (Mg) will cause the weld metal to become brittle, while too much rare earth element Re will easily directly affect the formability of the weld joint.

[0068] When Mg, B, and Re alloy elements are also added to the welding wire provided by the present invention, it is further preferred that the C, Mo, W, V, Nb, B, Mg, and Re also satisfy: γ = 2.5×([Mg]+[B]+[Re])+0.3×[Mo]+0.4×([W]+[V]+[Nb]) and 0.8γ<[C]<1.2γ; wherein [C], [Mo], [W], [V], [Nb], [Mg], [B], and [Re] represent the mass percentage (%) of each element. More preferably, 0.9γ<[C]<1.1γ. This optimized element ratio strategy has a positive effect on solving the challenges of welding toughness and quality caused by high carbon (C) and high aluminum (Al) content. In this way, while ensuring welding quality and high strength, the role of B, Mg, and Re in refining weld joint inclusions and the role of Mo, W, V, and Nb in refining the weld structure through large atom dragging and forming MC carbides can be maximized, while effectively reducing or inhibiting the precipitation of the second phase (such as κappa carbide) and element segregation, thereby significantly improving the toughness and plasticity of the weld joint and achieving the best balance between improving weld joint performance and controlling costs.

[0069] When Mg, B, and Re alloy elements are further added to the welding wire provided by the present invention, it is further preferred that the B and Mg have the following relationship: 0.8<[B] / [Mg]<1.6; illustratively, [B] / [Mg]=0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5. More preferably, 0.9<[B] / [Mg]<1.2. By precisely controlling the ratio of B and Mg, it is beneficial to maximize the synergistic effect of B, Mg elements and B, Mg and other elements, further improve the toughness and crack resistance of the welded joint, and improve the welding quality and ensure the high strength of the joint.

[0070] In addition, the welding wire provided by the present invention has the advantages of high strength and high toughness, which means that during the welding process, the welding wire is more durable and not easy to break or deform. Specifically, after the welding wire described in the embodiment of the present invention is solution treated, the tensile strength is ≥950MPa, and the impact energy KV2 at -84°C is ≥100J. The temperature of the solution treatment is 1000-1100°C, and the time is 0.5-2h. Exemplarily, the temperature of the solution treatment is 1050°C, and the time is 1.0h, 1.5h.

[0071] It should be noted that the welding wire provided by the present invention can be applied to FeMnAlC series low-density steel, that is, weldments, and is particularly suitable for welding medium and thick plates of high-aluminum series FeMnAlC low-density steel.

[0072] In the chemical formula mentioned in the present invention, the number after each element represents the mass percentage of the element in the material. Fe is the main element in steel, and the specific content is not marked.

[0073] In a second aspect, the present invention further provides a welding method, comprising welding a FeMnAlC-based low-density steel, i.e., a weldment, using the welding wire as described in the first aspect; illustratively, the weldment is a steel plate.

[0074] The main steps of the welding method include: using TIG welding technology under inert gas protection, first performing base welding, then performing formal welding, and immediately tapping the weld to release stress after the weld is solidified.

[0075] The welding method provided by the present invention, when applied to FeMnAlC low-density steel, shows significant advantages compared with the prior art, such as: convenient operation, economy, and good welding adaptability / accessibility. At the same time, thanks to the special composition design of the welding wire in the present invention, the welding method of the present invention can simplify the operation, reduce the cost, and improve the adaptability while still ensuring the high quality and mechanical properties of the welded joint, thereby providing a new efficient and economical option for the welding of FeMnAlC low-density steel.

[0076] Specifically, before the base welding, the surface to be welded of the weldment is beveled, and the surface to be welded of the weldment and the welding wire are cleaned before welding. The cleaning before welding includes: grinding the weldment, removing rust, oil and dust from the surface of the weldment and the welding wire, avoiding the influence of rust or oil on the surface of the weldment and the welding wire on the weld, so as to reduce or avoid welding defects.

[0077] In some embodiments, the groove is a V-shaped groove with an angle of 60° to 80°. Exemplarily, the groove angle is 65°, 70°, or 75°.

[0078] In some embodiments, the weldment is a medium-thick plate, and the thickness of the medium-thick plate is 3 mm to 20 mm; illustratively, the thickness of the medium-thick plate is 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, and 18 mm.

[0079] In some embodiments, the diameter of the welding wire is 0.5 mm to 3.2 mm. For example, the diameter of the welding wire is 0.6 mm, 1.0 mm, 1.6 mm, 2.0 mm, 2.4 mm, or 2.8 mm.

[0080] Furthermore, after cleaning, a base welding is performed first, which mainly includes: a base welding pass is first performed on the weldment at the root of the groove on the back of the joint to effectively avoid the corner deformation and burn-through phenomenon that may occur when the weldment is directly welded.

[0081] It can be understood that since welding stress and weld deformation are mainly caused by the shortening of the weld after welding, appropriately extending and lengthening the weld can compensate for the shortening, thereby reducing welding stress and deformation; therefore, after welding is completed, tapping the weld immediately after each solidification of the filler metal at the weld joint can appropriately extend the weld and reduce stress and deformation.

[0082] In some preferred embodiments, the process parameters of the formal welding include: welding voltage of 15-19V, welding current of 170-205A, and welding speed of 14-19cm / min. When using the TIG process to weld FeMnAlC low-density steel, selecting appropriate welding parameters is also important for ensuring the stability of the welding process and the quality of the weld. The inventors have found that for the welding wire with special components provided by the present invention (i.e., the welding wire as described in the first aspect), by selecting the above-mentioned welding parameters that have a synergistic effect and match the welding wire described in the present invention, it is helpful to better ensure the stability of the welding process and the excellent quality of the weld, reduce the generation of welding defects such as cracks and pores, and thus provide a more solid process foundation for manufacturing a strong and durable weld joint.

[0083] Specifically, by using the above preferred current (170-205A), a suitable heat input can be obtained, which can have a good effect on the penetration of the welding wire in the weld area, especially when welding medium and thick plates. The suitable heat input can improve the deposition efficiency, increase production efficiency, allow slag inclusions and pores to have enough time to overflow the weld, and promote the crystallization process, reduce residual stress and deformation during the welding process, and make the weld more uniform, dense and defect-free. However, if the heat input is too high, the temperature in the welding area will be too high, the alloy elements will be severely burned, and the grains of the weld and HAZ will be coarse, which will deteriorate the joint performance. Therefore, in combination with the special components of the welding wire provided by the present invention, the preferred welding current is 170A-205A.

[0084] Exemplarily, in the formal welding, the welding voltage is 16V, 17V, 18V; the welding current is 175A, 180A, 185A, 190A, 195A, 200A; and the welding speed is 15cm / min, 16cm / min, 17cm / min, 18cm / min.

[0085] Further preferably, the process parameters of the formal welding include: welding voltage of 17-19V, welding current of 195-205A, and welding speed of 16-19cm / min, so as to achieve an optimal balance between welding quality and mechanical properties and welding efficiency.

[0086] In some preferred embodiments, the process parameters of the base welding include: a welding voltage of 14-17V and a welding current of 160-170A. When base welding, excessive welding heat input will cause the solidification speed of the molten pool to be lower than the crack initiation speed of the solidification crack, so the welding current cannot be too large, and it is appropriate to use a formal welding current lower than the overall current. When welding, the current and voltage match.

[0087] In some embodiments, during TIG welding, the distance between the welding gun tip and the surface of the weldment is 5 mm to 15 mm, and the welding gun has an inclination angle of 5° to 15°, which helps to better ensure the welding quality and the mechanical properties of the welded joint. For example, the distance between the welding gun tip and the surface of the weldment is 7 mm, 9 mm, 11 mm, and 13 mm; the inclination angle of the welding gun is 7°, 9°, 11°, and 13°.

[0088] It should be noted that, thanks to the special composition design of the welding wire in the present invention, the welding method of the present invention omits the traditional heat treatment process, that is, no preheating is performed before welding and no heat treatment is performed after welding. Therefore, after welding, the obtained weldment is placed in a room temperature environment for cooling, and the weldment is obtained after complete cooling. The welding method provided by the present invention is based on a carefully designed welding wire composition, and can achieve excellent welding effects without the need for traditional preheating before welding and post-weld heat treatment. For example, the reasonable addition of some key alloying elements to the welding wire and the control of the content of each element are helpful to form a fine microstructure during the welding process, and effectively reduce or inhibit the precipitation of the second phase (such as κappa carbide) and reduce the phenomenon of element segregation, so that good joint toughness and crack resistance can be maintained, and welding stress can be reduced without heat treatment.

[0089] When welding FeMnAlC low-density steel, especially high-aluminum FeMnAlC low-density steel, welding cracks are easily generated because this material is very sensitive to welding thermal cycles. Especially in the welding process of medium and thick plates, the thermal gradient is large, the welding stress increases, and welding defects are easily caused. In order to solve this problem, the present invention adopts a multi-pass welding process.

[0090] Preferably, the welding pass N of the formal welding satisfies: in, Indicates the result of rounding up or down to the nearest integer; t represents the steel plate thickness of the weldment, in mm, and t≥3mm. The use of welding passes that meet the above conditions can not only effectively reduce the thermal gradient and reduce the risk of welding defects, but also ensure the welding quality while taking into account production efficiency and economy. When the above conditions are not met, for example: if there are too many welding passes, the grains in the heat-affected zone will be coarse, the toughness of the joint will be reduced, and the deformation and residual stress in the welding area will be increased, as well as the risk of reheat cracks.

[0091] In some embodiments, when the thickness of the weldment is 3 mm-20 mm, the number of welding passes for formal welding is preferably 5-8 passes.

[0092] In some embodiments, when the thickness of the weldment is 12 mm to 20 mm, the number of passes of the formal welding is 7 to 8. For example, when the thickness of the weldment is 12 mm, The value is rounded up or down to the nearest integer, which is 2 or 3 respectively, and the welding pass N is 7 or 8.

[0093] In some embodiments, in the welding method provided by the present invention, the inert gas is argon gas with a purity higher than 99.99% to prevent oxidation of more active elements in the weldment and welding wire during welding. Further, the gas flow rate of the inert gas is 10-16L / min. Exemplarily, the gas flow rate is 11L / min, 12L / min, 13L / min, 14L / min, 15L / min. More preferably, the gas flow rate of the inert gas is 12-16L / min. For welding wires containing alloying elements such as Al, Mo, W, V, and Nb, the use of high-purity argon gas and appropriate gas flow rates can reduce the evaporation and oxidation of these elements during welding, thereby maintaining the chemical composition and properties of the weld metal, helping to further improve the welding quality and reduce welding defects. It should be noted that excessive gas flow rates will lead to a decrease in the protection effect and excessive cooling of the weld, thereby affecting the weld formation and performance.

[0094] Based on the welding wire and the welding method of the present invention, the obtained welding joint has a room temperature tensile strength Rm≥850MPa, a room temperature elongation after fracture A5≥20%, and a V-type impact energy KV2≥30J at -84°C.

[0095] For FeMnAlC-based low-density steels, the difficulty of welding (such as low joint toughness and easy cracking) limits the development of this type of lightweight steel materials (especially when the aluminum and carbon content in this type of material is high and / or the material is thick) towards high strength and lightweight in practical applications. Since welded joints often become weak points in the structure, it is particularly important to ensure high-quality and high-strength and toughness connections between such lightweight steels. Based on the welding wire and welding method provided by the present invention, the welding performance of such lightweight steel materials can be effectively improved, and while achieving a higher strength and reliable connection, the plasticity and toughness of the welded joints can be significantly improved, and the welding quality can be improved, which is of great significance for the widespread promotion of such lightweight steel materials in industrial applications.

[0096] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and comparative examples.

[0097] Example 1

[0098] This embodiment provides a welding wire, the general chemical formula of which is Fe-30Mn-8Al-1.2C-0.9Mo-0.1W-0.2V-0.2Nb (referred to as welding wire 1), and the diameter of the welding wire is 1.6 mm.

[0099] This embodiment also provides a welding method, comprising welding a weldment using the welding wire (welding wire 1) as described above, wherein the weldment is a steel plate with a thickness of 12 mm, and the chemical formula of the weldment is Fe-30Mn-8Al-0.9C;

[0100] The main steps of the welding method include:

[0101] S0, open the groove first, then clean before welding:

[0102] The groove cutting comprises: using a wire cutting machine to cut a V-shaped groove on the weldment butt joint, wherein the angle of the V-shaped groove is 80°;

[0103] The pre-welding cleaning includes: grinding the periphery of the to-be-welded area of ​​the weldment with a grinder until the periphery of the to-be-welded area is bright; degreasing the surface of the weldment and the welding wire 1 with ethanol;

[0104] S1. Welding: TIG welding process is used. First, the base welding is performed, and then the formal welding is performed. After the weld is solidified, the weld is immediately tapped with a tool hammer. The vibration generated by the tool hammer releases the stress of the weld. No heat treatment is required after welding. It is directly placed in room temperature for cooling. After complete cooling, the welded part can be obtained.

[0105] In the base welding, the welding current is 170A and the welding voltage is 15V;

[0106] In the formal welding, the welding current is 200A, the welding voltage is 19V, the welding passes are 8 times, and the welding speed is 18cm / min.

[0107] In both the base welding and the main welding, argon gas with a purity higher than 99.99% is used as the protective gas, and the flow rate of the inert gas, namely argon gas, is 12 L / min.

[0108] Example 2

[0109] The difference between this embodiment and embodiment 1 is that the general chemical formula of the welding wire is Fe-30Mn-8Al-1.2C-0.4Mo-0.4W-0.4V-0.4Nb (referred to as welding wire 2); the remaining parameters and steps of the welding method are similar to those of embodiment 1.

[0110] Example 3

[0111] The difference between this embodiment and embodiment 1 is that the general chemical formula of the welding wire is Fe-30Mn-8Al-1.2C-0.5Mo-0.4W-0.4V-0.4Nb (referred to as welding wire 3); the remaining parameters and steps of the welding method are similar to those of embodiment 1.

[0112] Example 4

[0113] The difference between this embodiment and embodiment 1 is that the general chemical formula of the welding wire is Fe-30Mn-8Al-1.2C-0.6Mo-0.5W-0.5V-0.4Nb (referred to as welding wire 4); the remaining parameters and steps of the welding method are similar to those of embodiment 1.

[0114] Example 5

[0115] The difference between this embodiment and embodiment 1 is that the general chemical formula of the welding wire is Fe-30Mn-8Al-1.2C-0.6Mo-0.5W-0.5V-0.5Nb (referred to as welding wire 5); the remaining parameters and steps of the welding method are similar to those of embodiment 1.

[0116] Example 6

[0117] The difference between this embodiment and embodiment 5 is that in the welding method, the welding current of the formal welding is 210A; the other parameters and steps of the welding method are similar to those of embodiment 5.

[0118] Example 7

[0119] The difference between this embodiment and embodiment 5 is that in the welding method, the welding speed of the formal welding is 13 cm / min; the other parameters and steps of the welding method are similar to those of embodiment 5.

[0120] Example 8

[0121] The difference between this embodiment and embodiment 5 is that in the welding method, the welding speed of the formal welding is 20 cm / min; the other parameters and steps of the welding method are similar to those of embodiment 5.

[0122] Example 9

[0123] The difference between this embodiment and Embodiment 5 is that in the welding method, the number of welding passes of formal welding is 5; the other parameters and steps of the welding method are similar to those of Embodiment 5.

[0124] Example 10

[0125] The difference between this embodiment and Embodiment 5 is that in the welding method, the number of welding passes of formal welding is 9; the remaining parameters and steps of the welding method are similar to those of Embodiment 5.

[0126] Embodiment 11

[0127] The difference between this embodiment and embodiment 1 is that the general chemical formula of the welding wire is Fe-30Mn-8Al-1.2C-0.9Mo-0.1W-0.2V-0.2Nb-0.01Mg-0.01B-0.01Re (referred to as welding wire 11), and the other parameters and steps of the welding method are similar to those of embodiment 1.

[0128] Comparative Example 1

[0129] The difference between this comparative example and Example 1 is that the chemical formula of the welding wire is Fe-25Mn-7Al-0.3C-1.0Mo-1.0W-0.1V-0.1Nb; in the welding method, the welding current of the formal welding is 210A, the welding speed is 12cm / min, the argon gas flow rate is 6L / min, and the remaining steps and parameters are similar to those in Example 1.

[0130] Comparative Example 2

[0131] The difference between this comparative example and Example 1 is that the chemical formula of the welding wire is Fe-30Mn-6Al-0.2C-0.1Mo-0.1W-0.05V-0.05Nb; in the welding method, the welding current of the formal welding is 210A, the welding speed is 12cm / min, the argon gas flow rate is 6L / min, and the remaining steps and parameters are similar to those in Example 1.

[0132] Comparative Example 3

[0133] The difference between this comparative example and Example 1 is that the chemical formula of the welding wire is Fe-35Mn-5Al-0.08C-0.5Mo-0.5W-0.08V-0.08Nb; in the welding method, the welding current of the formal welding is 210A, the welding speed is 12cm / min, the argon gas flow rate is 6L / min, and the remaining steps and parameters are similar to those in Example 1.

[0134] Comparative Example 4

[0135] The difference between this comparative example and Example 1 is that the chemical formula of the welding wire is Fe-30Mn-11Al-0.2C-0.1Mo-0.1W-0.05V-0.05Nb; in the welding method, the welding current of the formal welding is 210A, the welding speed is 12cm / min, the argon gas flow rate is 6L / min, and the remaining steps and parameters are similar to those in Example 1.

[0136] In order to more clearly show the changes in ingredients and process parameters of Examples 1-11 and Comparative Examples 1-4, see Table 1. The performance test results of Examples 1-11 and Comparative Examples 1-4 are shown in Table 2.

[0137] Table 1: Chemical composition and welding process parameters of welding wires in Examples 1-11 and Comparative Examples

[0138]

[0139]

[0140] Table 2: Mechanical properties of welded joints obtained from Examples 1-11 and Comparative Examples of welding wires

[0141]

[0142]

[0143] As can be seen from Table 2, compared with Comparative Examples 1-4, Example 1-10 adopts the alloy composition of the welding wire provided by the present invention (such as adding appropriate amounts of Mo, W, V, Nb, 0.3%≤Mo≤0.9%, W≤0.5%, 0.1%<V≤0.5%, 0.1%<Nb≤0.5%), so the mechanical properties of the welded joints of Example 1-10 are better than those of Comparative Examples 1-4 as a whole, and Example 1-10 significantly improves the strength while ensuring that the impact resistance at low temperature meets the use requirements (≥27J). Further, the comprehensive mechanical properties (such as strength) of Example 1-5 show the general rule of Example 5> Example 4> Example 3> Example 2> Example 1, which shows that based on the alloy composition of the welding wire provided by the present invention, by further controlling the content and proportion of some key elements (such as Mo, W, V, Nb), it is beneficial to further improve the mechanical properties of the weld and reduce welding defects. Furthermore, compared with Example 5, the overall mechanical properties (such as strength) of Examples 6-10 are slightly reduced, which shows that based on the alloy composition of the welding wire provided by the present invention, by selecting the preferred process parameters (such as Example 5), it is beneficial to further improve the mechanical properties of the weld and reduce welding defects. Compared with Example 1, Example 11 further significantly improves the toughness and plasticity of the joint while ensuring high strength due to the additional addition of Mg, B, and Re, such as the elongation A5 (%) and the V-type impact energy KV2 at -84°C are further improved.

[0144] Example 12

[0145] This embodiment provides a welding wire, the general chemical formula of which is Fe-35Mn-10Al-C-0.5Mo-0.2W-0.3V-0.4Nb-0.02Mg-0.04B-0.03Re (referred to as welding wire 12), and the diameter of the welding wire is 1.6 mm.

[0146] This embodiment also provides a welding method, comprising welding a weldment using the welding wire (welding wire 12) as described above, wherein the weldment is a steel plate with a thickness of 12 mm, and the chemical formula of the weldment is Fe-30Mn-8Al-0.9C;

[0147] The main steps of the welding method include:

[0148] S0, open the groove first, then clean before welding:

[0149] The groove cutting comprises: using a wire cutting machine to cut a V-shaped groove on the weldment butt joint, wherein the angle of the V-shaped groove is 60°;

[0150] The pre-welding cleaning includes: grinding the periphery of the welded area of ​​the weldment with a grinder until the periphery of the welded area is bright; and removing oil from the surface of the weldment and the welding wire with ethanol;

[0151] S1. Welding: TIG welding process is used. First, the base welding is performed, and then the formal welding is performed. After the weld is solidified, the weld is immediately tapped with a tool hammer. The vibration generated by the tool hammer releases the stress of the weld. No heat treatment is required after welding. It is directly placed in room temperature for cooling. After complete cooling, the welded part can be obtained.

[0152] In the base welding, the welding current is 170A and the welding voltage is 15V;

[0153] In the formal welding, the welding current is 195A, the welding voltage is 18V, the welding passes are 7 times, and the welding speed is 16cm / min.

[0154] In the base welding and the main welding, argon with a purity higher than 99.99% is used as the protective gas, and the flow rate of the inert gas, namely argon, is 12 L / min.

[0155] Embodiment 13

[0156] The difference between this embodiment and embodiment 12 is that the general chemical formula of the welding wire is Fe-35Mn-10Al-C-0.4Mo-0.3W-0.3V-0.3Nb-0.02Mg-0.04B-0.03Re (referred to as welding wire 13); the remaining parameters and steps of the welding method are similar to those of embodiment 12.

[0157] Embodiment 14

[0158] The difference between this embodiment and embodiment 12 is that the general chemical formula of the welding wire is Fe-35Mn-10Al-C-0.4Mo-0.3W-0.3V-0.3Nb-0.03Mg-0.07B-0.07Re (referred to as welding wire 14); the remaining parameters and steps of the welding method are similar to those of embodiment 12.

[0159] Embodiment 15

[0160] The difference between this embodiment and embodiment 12 is that the general chemical formula of the welding wire is Fe-35Mn-10Al-C-0.4Mo-0.3W-0.3V-0.3Nb-0.07Mg-0.07B-0.07Re (referred to as welding wire 15); the remaining parameters and steps of the welding method are similar to those of embodiment 12.

[0161] Example 16

[0162] The difference between this embodiment and Embodiment 15 is that in the welding method, the welding current of the formal welding is 210A and the welding voltage is 19V; the other parameters and steps of the welding method are similar to those of Embodiment 15.

[0163] Embodiment 17

[0164] The difference between this embodiment and Embodiment 15 is that in the welding method, the welding speed of the formal welding is 15 cm / min; the other parameters and steps of the welding method are similar to those of Embodiment 15.

[0165] Embodiment 18

[0166] The difference between this embodiment and Embodiment 15 is that in the welding method, the welding speed of the formal welding is 20 cm / min; the other parameters and steps of the welding method are similar to those of Embodiment 15.

[0167] Embodiment 19

[0168] The difference between this embodiment and Embodiment 15 is that in the welding method, the number of formal welding passes is 6; the other parameters and steps of the welding method are similar to those of Embodiment 15.

[0169] Embodiment 20

[0170] The difference between this embodiment and Embodiment 15 is that in the welding method, the number of formal welding passes is 9; the other parameters and steps of the welding method are similar to those of Embodiment 15.

[0171] Table 3: Chemical composition and welding process parameters of welding wire in Examples 12-20 of welding wire

[0172]

[0173]

[0174] Table 4: Mechanical properties of welded joints obtained from examples 12-20 of welding wires

[0175]

[0176] As can be seen from Table 4, the comprehensive mechanical properties (such as strength) of Examples 12-15 show the general rule of Example 15> Example 14> Example 13> Example 12, which shows that by further optimizing and controlling the content and proportion of some key elements (such as B, Mg, Re, Mo, W, V, Nb), it is beneficial to further improve the mechanical properties of the weld, such as improving the strength and toughness of the weld and cracking resistance, thereby reducing welding defects. Compared with Example 15, the overall mechanical properties of Examples 16-20 are slightly reduced, which shows that when the composition of the welding wire is constant, by selecting the preferred process parameters (such as Example 15), it is beneficial to further improve the mechanical properties of the weld, including improving the strength and cracking resistance, thereby reducing welding defects.

[0177] In order to verify the quality of the welded joint obtained in the embodiment of the present invention, metallographic testing was performed. First, five different types of metallographic sandpaper were used for manual grinding in sequence, and then the surface of the sample was polished on a polishing machine using diamond polishing paste to make the surface of the sample appear smooth and mirror-like. The polished sample was corroded with a 10% nitric acid alcohol solution for about 1 minute, and then rinsed with a large amount of distilled water and alcohol, and dried with hot air from a hair dryer. Finally, the metallographic structure of the treated sample was observed under an optical microscope.

[0178] The metallographic structures of the welded joints obtained in Example 1 and Comparative Example 4 are shown in Figure 1 and Figure 2 .from Figure 1 It can be seen that the weld area obtained in the embodiment of the present invention is mainly columnar crystals, accompanied by a small amount of fine ferrite, and the organization is uniform, but there are cracks in some parts of the comparative example 4. The macroscopic low-power morphology of the welded joints obtained in Example 1 and Comparative Example 4 is shown in FIG. Figure 3 and Figure 4 ,from Figure 3 It can be seen that the joint obtained in the embodiment of the present invention has good quality and no defects such as cracks and pores. The joint in the comparative example 4 has local cracks (such as Figure 4 (shown in section A).

[0179] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A welding wire, characterized in that: Applicable to FeMnAlC low-density steel, the welding wire comprises the following components by mass percentage: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, 0.3%≤Mo≤0.9%, W≤0.5%, 0.1%<V≤0.5%, 0.1%<Nb≤0.5%, and the rest is Fe and unavoidable impurities; And the Mo, W, V, and Nb meet the requirement: 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1%, where [Mo], [W], [V], and [Nb] represent the mass percentage (%) of each element.

2. The welding wire according to claim 1, characterized in that The components of the welding wire include, by mass percentage, 0.6%≤C≤1.2%, 25%≤Mn≤35%, 8%≤Al≤10%, 0.4%≤Mo≤0.6%, 0.3%≤W≤0.5%, 0.3%≤V≤0.5%, 0.3%≤Nb≤0.5%, and the rest are Fe and unavoidable impurities.

3. The welding wire according to claim 1, characterized in that The Mo, W, V, and Nb also satisfy the following: 2.2<([W]+[V]+[Nb]) / [Mo]<2.

6.

4. The welding wire according to claim 1, characterized in that The C, Mo, W, V, and Nb also satisfy: α = 0.5×[Mo] + 0.6×([W] + [V] + [Nb]) and 0.8α < [C] < 1.2α; Here, [C], [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element.

5. The welding wire according to claim 1, characterized in that The welding wire also includes components of: Mg≤0.1%, B≤0.1%, and Re≤0.1%.

6. The welding wire according to claim 5, characterized in that The Mg, B, and Re meet the requirement: 0.09%≤[B]+[Mg]+[Re]≤0.21%, where [Mg], [B], and [Re] represent the mass percentage (%) of each element.

7. The welding wire according to claim 6, characterized in that The Mg, B and Re also meet the requirement: 0.5<([B]+[Mg]) / [Re]<2.

1.

8. A welding method, characterized in that: The method comprises welding FeMnAlC low-density steel, i.e., weldment, by using the welding wire described in any one of claims 1 to 7; The main steps of the welding method include: using TIG welding technology under inert gas protection, first performing base welding, then performing formal welding, and immediately tapping the weld to release stress after the weld is solidified.

9. The welding method according to claim 8, characterized in that: The process parameters of the base welding include: welding current of 160-170A; and / or, The process parameters of the formal welding include: welding voltage of 15-19V, welding current of 170-205A, and welding speed of 14-19cm / min.

10. The welding method according to claim 8, wherein the welding pass N of the formal welding satisfies: in, It indicates rounding up or down to the nearest integer result; t indicates the steel plate thickness of the weldment, the unit of t is mm and t≥3mm.

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