Welding wire for welding low-density steel and welding method thereof

Abstract

The invention relates to a welding wire for welding low-density steel and a welding method of the welding wire, and belongs to the field of welding processes. The invention aims to solve at least one problem that a welding process of a high-Al-series Fe-Mn-Al-C steel medium-thickness plate is insufficient in mechanical property of a welding joint, poor in joint quality, poor in welding adaptability / accessibility and high in cost, in particular to a welding process of a high-Al-series Fe-Mn-Al-C steel medium-thickness plate. The welding wire comprises, by mass, 0.6% < = C < = 1.2%, 25% < = Mn < = 35%, 7% < Al < = 12%, Mg < = 0.1%, B < = 0.1%, Re < = 0.1% 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 for low-density steel welding and a welding method thereof. Background Art

[0002] Low-density steel, also known as lightweight steel, is usually a new type of material that adds a certain mass fraction of Al elements to medium and high manganese steel to achieve lightweight and excellent mechanical properties. FeMnAlC-based low-density steel has attracted attention in the field of material research and industry due to its low density and high strength, especially in the fields of automobile manufacturing, showing potential application prospects. Generally, it can be divided into two categories according to the Al content, namely low Al-based (Al≤3%) FeMnAlC steel and high Al-based (3%<Al≤12%) FeMnAlC steel. As a new type of material, the welding performance of FeMnAlC-based low-density steel is one of the important indicators to measure whether it can enter industrial production. However, in recent years, research on FeMnAlC-based low-density steel has mainly focused on organizational regulation and strengthening and toughening mechanisms, while research on its welding performance is rare.

[0003] According to existing literature reports, FeMnAlC low-density steel has many welding difficulties due to its alloy element combination. These welding difficulties mainly include the easy generation of brittle second phases at the welded joints, the easy occurrence of element segregation in the weld zone, and the easy occurrence of cracks. These welding difficulties cause the problems of insufficient mechanical properties of welded joints and easy occurrence of welding defects, especially when the C and / or Al content in the welding materials of FeMnAlC low-density steel is high or the thickness of the welding materials increases. Such problems are more prominent. When welding FeMnAlC low-density steel, especially high-aluminum FeMnAlC steel medium and thick plates, existing welding wires and welding technologies often face challenges, such as substandard welding quality, insufficient mechanical properties of welded joints, high cost of required welding equipment or poor welding accessibility. These factors limit the widespread application of such steels in industrial production. Summary of the invention

[0004] In view of the above analysis, the present invention aims to provide a welding wire for low-density steel welding and a welding method thereof, so as to solve at least one of the following problems existing in the welding process of low-density steel, especially high-Al 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.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The invention provides a welding wire for low-density steel welding, 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%, Mg≤0.1%, B≤0.1%, Re≤0.1%, and the rest are Fe and unavoidable impurities;

[0007] And 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.

[0008] Furthermore, 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%, and the rest are Fe and unavoidable impurities.

[0009] Furthermore, the Mg, B, and Re also satisfy: 0.5<([B]+[Mg]) / [Re]<2.1, and / or, 0.8<[B] / [Mg]<1.6.

[0010] Furthermore, the welding wire also comprises the following components: Mo≤1.0%, W≤0.5%, V≤0.5%, and Nb≤0.5%.

[0011] Furthermore, the Mo, W, V and Nb also satisfy the following: 2.2<([W]+[V]+[Nb]) / [Mo]<2.6, where [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element.

[0012] Furthermore, W, V, and Nb also have the following relationship: [W]: [V]: [Nb] = (0.9-1.1): (0.9-1.1): (0.9-1.1).

[0013] Furthermore, the C, B, Mg, Re, Mo, W, V, and Nb also satisfy: γ = 2.5×([Mg]+[B]+[Re])+0.3×[Mo]+0.4×([W]+[V]+[Nb]) and 0.8γ<[C]<1.2γ;

[0014] Here, [C], [Mg], [B], [Re], [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element.

[0015] The present invention also provides a welding method, which includes adopting TIG welding technology to weld FeMnAlC low-density steel, i.e. weldment, with the above-mentioned welding wire; the main steps of welding include: first performing base welding and then performing formal welding.

[0016] Further, no preheating is performed before welding and no heat treatment is performed after welding; and / or,

[0017] The thickness of the weldment t≥3mm, the number of welding passes N of the formal welding ≥5; and / or,

[0018] The process parameters of the base welding include: the welding current is 160-170A; the process parameters of the formal welding include: the welding current is 170-205A.

[0019] Furthermore, the room temperature tensile strength Rm of the welded joint obtained by the welding method is ≥880MPa, the room temperature elongation after fracture A5 is ≥20%, and the V-type impact energy KV2 is ≥30J at -84°C.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] (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 Mg, B, and Re), especially when welding medium and thick plates of high-aluminum FeMnAlC low-density steel, which can better meet the high performance requirements in industrial applications;

[0022] Specifically, from the perspective of welding wire composition design, the present invention, on the one hand, improves the strength of the weld 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 Mg, B, Re) 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 weld joint has good toughness and plasticity and effectively reduces cracks. , pores and other defects; 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 medium and thick plates of high-aluminum FeMnAlC low-density steel that are more difficult to weld, the joint strength can still reach a level of 880Mpa and above, and the toughness and plasticity of the joint can fully meet the mechanical property requirements for the joints of such steel plates in industrial applications, such as the elongation A5 ≥ 20% and the V-type impact energy KV2 ≥ 30J at -84°C in the tensile test.

[0023] (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 Mg, B, and Re);

[0024] 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 improve the toughness and plasticity of the weld joint by refining the inclusions in the weld joint, refining the grains, purifying the grain boundaries, etc. while ensuring the joint strength and welding quality through the reasonable addition of some key alloy elements (such as Mg, B, Re) and the optimization of the component content (such as controlling the upper and lower limits of these elements). The improvement of toughness and plasticity can improve the welding crack resistance and reduce defects such as cracks and pores at the weld 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 weld joint is better, such as showing better welding crack resistance and weld uniformity, and fewer defects such as cracks and pores.

[0025] (3) In some preferred embodiments, the present invention further improves the toughness of the welded joint by adding additional key alloying elements (such as Mo, W, V, Nb) to the welding wire composition and controlling the content range, and refines the welding structure through large atom dragging and forming MC carbides. This composition optimization not only further improves the mechanical properties of the welded joint, but also enhances the welding crack resistance, reduces defects such as cracks, and thus further improves the quality of the weld.

[0026] (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 (such as Mg, B, Re, Mo, W, V, Nb) 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.

[0027] (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; 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, providing a new efficient and economical choice for the welding of FeMnAlC low-density steel.

[0028] (6) Based on 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 (such as preheating before welding and slow cooling after welding), making the welding steps simpler.

[0029] (7) 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, 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 a low-magnification morphology image of the welded joint obtained in Example 1 of the present invention;

[0034] Figure 3 This is a low-magnification morphology image of the welded joint obtained in Comparative Example 2. DETAILED DESCRIPTION

[0035] 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.

[0036] 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.

[0037] 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 or poor adaptability / accessibility that are prone to occur during welding of such lightweight steels.

[0038] Based on this, in the first aspect, the present invention provides a welding wire for low-density steel welding, which is applied to FeMnAlC low-density steel. The components of the welding wire include, in mass percentage: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, Mg≤0.1%, B≤0.1%, Re≤0.1%, and the rest are Fe and unavoidable impurities; and the Mg, B, and Re meet the requirements: 0.09%≤[B]+[Mg]+[Re]≤0.21%, and [Mg], [B], and [Re] represent the mass percentage (%) of each element.

[0039] 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 Mg, B, Re), especially when welding medium and thick plates of high-aluminum FeMnAlC low-density steel, it can better meet the high performance requirements in industrial applications; specifically, from the perspective of welding wire composition design, on the one hand, compared with the lower C content (≤0.3%) in the existing welding wire, the welding joint strength is improved by further increasing the C content (0.6%-1.2%), and the weld uniformity is improved by appropriately increasing the Al content; on the other hand, by reasonably adding some key alloying elements (such as Mg, B, Re) and optimizing 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 reduce 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 high-aluminum FeMnAlC low-density steel medium and thick plates that are more difficult to weld, the joint strength can still reach a level of 880Mpa and above, and the toughness and plasticity of the joint can fully meet the joint mechanical property requirements for such steel plates in industrial applications, such as the elongation A5 ≥ 20% and the V-type impact energy KV2 ≥ 30J at -84°C in the tensile test.

[0040] 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 Mg, B, Re), 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 improve the toughness and plasticity of the welded joint by refining the welded joint inclusions, refining the grains, purifying the grain boundaries, etc. while ensuring the joint strength and welding quality through the reasonable addition of some key alloying elements (such as Mg, B, Re) and the optimization of the component content (such as controlling the upper and lower limits of these elements). The improvement of toughness and plasticity can improve the welding crack resistance and reduce defects such as cracks and pores at the welded 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.

[0041] 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.

[0042] Specifically, the chemical composition design basis of the welding wire in the present invention mainly includes:

[0043] 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%.

[0044] 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%.

[0045] 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%.

[0046] 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.

[0047] In order to solve and balance the above-mentioned welding challenges, the present invention adds trace amounts of Mg, B, and Re alloying elements and controls their contents within an appropriate range. This can make the welded joint have good plasticity and toughness, including toughness-plastic properties at room and low temperatures, while utilizing some of the benefits brought by high C and Al contents (such as improving strength and weld uniformity). This can further enhance the welding crack resistance, reduce welding defects such as cracks, and thus improve the welding quality.

[0048] Mg, B, Re: Trace additions of Mg, B, and 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 the size of the particles, affecting the mechanical properties of the joint. Therefore, B≤0.1%, Mg≤0.1%, and rare earth Re≤0.1% are required. At the same time, the Mg, B, and Re meet the requirements: 0.09%≤[B]+[Mg]+[Re]≤0.21%, [Mg], [B], and [Re] represent the mass percentage (%) of each element. By 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.

[0049] 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%.

[0050] 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%.

[0051] 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%.

[0052] 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%, and the rest is Fe and unavoidable impurities.

[0053] Preferably, in the welding wire provided by the present invention, the Mg, B, and Re also satisfy: 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 condition, 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.

[0054] Preferably, in the welding wire provided by the present invention, the Mg, B, and Re also satisfy: 0.8<[B] / [Mg]<1.6, [Mg], [B] represent the mass percentage (%) of each element. Exemplarily, [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.

[0055] In one embodiment, when the components of the welding wire are composed of C, Mn, Al, B, Mg, Re and Fe, wherein C, B, Mg, and Re also satisfy: β = 5×([Mg]+[B])+3×[Re] and 0.8β<[C]<1.2β; wherein [C], [Mg], [B], and [Re] represent the mass percentage (%) of each element. More preferably, 0.9β<[C]<1.1β For welding wires of this alloy system, 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 improving welding quality and strength, the positive effects of B, Mg, and Re on refining inclusions in the weld joint can be maximized, thereby improving the toughness and plasticity of the weld joint, while achieving the best balance of cost-effectiveness.

[0056] In some preferred embodiments, the components of the welding wire of the present invention further include: Mo≤1.0%, W≤0.5%, V≤0.5%, Nb≤0.5%. The present invention is beneficial to refine the welding structure by adding key alloy elements (such as Mo, W, V, Nb) to the welding wire composition and controlling the content range, thereby further improving the toughness and plasticity of the welded joint. This composition optimization not only further improves the mechanical properties of the welded joint, but also enhances the welding crack resistance, reduces defects such as cracks, and thus further improves the quality of the weld.

[0057] In the embodiment of the present invention, the chemical composition design basis of additionally adding key alloy elements (such as Mo, W, Nb, V) to the welding wire composition mainly includes:

[0058] 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, Mo≤1.0%, W≤0.5%, V≤0.5%, and Nb≤0.5% are required in the welding wire.

[0059] In some preferred embodiments, key alloying elements (such as Mo, W, Nb, and V) are additionally added to the welding wire composition to meet the following requirements: 0.3%≤Mo≤0.9%, W≤0.5%, 0.1%<V≤0.5%, 0.1%<Nb≤0.5%, and 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1%. By further 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; wherein, 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 at the welded joint during welding.

[0060] In some embodiments, the Mo content is 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%. Preferably, 0.4%≤Mo≤0.6%.

[0061] 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%.

[0062] 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%.

[0063] 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%.

[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 further adds alloy elements Mo, W, Nb and V, preferably, the Mo, W, V and Nb also satisfy the following: 2.2<([W]+[V]+[Nb]) / [Mo]<2.6, [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 amounts of molybdenum (Mo), tungsten (W), vanadium (V) and niobium (Nb) and their mutual proportions are also very important. When the addition amounts of these four elements meet 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 has a positive effect on 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.

[0067] When the welding wire provided by the present invention also adds Mo, W, Nb, and V alloy elements, 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, and improve the quality of the weld and ensure the high strength of the welded joint. For example, [W]: [V]: [Nb] = 1:1:1.

[0068] When the welding wire provided by the present invention also adds Mo, W, Nb, and V alloy elements, preferably, the C, B, Mg, Re, Mo, W, V, and Nb also satisfy: γ = 2.5×([Mg]+[B]+[Re])+0.3×[Mo]+0.4×([W]+[V]+[Nb]) and 0.8γ<[C]<1.2γ; wherein [C], [Mg], [B], [Re], [Mo], [W], [V], and [Nb] 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] 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.

[0070] 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.

[0071] 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.

[0072] In a second aspect, the present invention further provides a welding method, comprising using a TIG welding process to weld a FeMnAlC low-density steel, i.e., a weldment, using the welding wire as described in the first aspect; the main steps of the welding include: first performing a base weld and then performing a formal weld. Exemplarily, the weldment is a steel plate.

[0073] Compared with the prior art, the welding method provided by the present invention, when applied to FeMnAlC low-density steel, shows significant advantages over the prior art, such as: convenient operation, economy, and good welding adaptability / accessibility; 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 costs, and improve adaptability while still ensuring the quality and mechanical properties of the welded joint, providing a new efficient and economical choice for the welding of FeMnAlC low-density steel. Based on 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 (such as preheating before welding and slow cooling after welding), making the welding steps more simplified.

[0074] Preferably, during formal welding, after the weld has solidified, the weld is immediately tapped to release stress.

[0075] 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.

[0076] 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°.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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°.

[0087] 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 excellent welding effects can be achieved without the need for traditional preheating before welding and heat treatment after welding. For example, the reasonable addition of some key trace 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 still be maintained, and welding stress can be reduced without heat treatment.

[0088] 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.

[0089] 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.

[0090] In some embodiments, the thickness of the weldment t≥3 mm, and the number of welding passes N of the formal welding is ≥5.

[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 B, Mg, and Re, 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 thereof of the present invention, the room temperature tensile strength Rm of the welding joint is ≥880MPa, the room temperature elongation after fracture A5 is ≥20%, and the V-type impact energy KV2 is ≥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 higher strength and lower density, 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-25Mn-8Al-0.60C-0.01Mg-0.01B-0.07Re (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 70°;

[0103] 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;

[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 205A, the welding voltage is 19V, the welding passes are 8 times, and the welding speed is 19cm / min.

[0107] In both the base welding and the main welding, argon gas with a purity higher than 99.99% is used as the shielding gas, and the flow rate of the inert gas, namely argon gas, is 16 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-25Mn-8Al-0.60C-0.02Mg-0.02B-0.09Re (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-25Mn-8Al-0.60C-0.07Mg-0.07B-0.06Re (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-25Mn-8Al-0.60C-0.03Mg-0.03B-0.10Re (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-25Mn-8Al-0.60C-0.04Mg-0.04B-0.07Re (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 14 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 4; 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 5 is that in the welding method, the argon gas flow rate is 9 L / min; the other parameters and steps of the welding method are similar to those of embodiment 5.

[0128] Example 12

[0129] The difference between this embodiment and embodiment 1 is that the general chemical formula of the welding wire is Fe-25Mn-8Al-0.60C-0.01Mg-0.01B-0.07Re-0.9Mo-0.1W-0.2V-0.2Nb; the remaining parameters and steps of the welding method are similar to those of embodiment 1.

[0130] Comparative Example 1

[0131] The difference between this comparative example and Example 1 is that the general chemical formula of the welding wire is Fe-25Mn-8Al-0.60C-0.15Mg-0.15B-0.15Re; the remaining parameters and steps of the welding method are similar to those of Example 1.

[0132] Comparative Example 2

[0133] The difference between this comparative example and comparative example 1 is that the welding current of the base welding is 140A and the voltage is 12V; the welding current of the formal welding is 150A and the voltage is 13V; the remaining parameters and steps of the welding method are similar to those of comparative example 1.

[0134] Table 1: Chemical composition and welding process parameters of welding wires in Examples 1-12 and Comparative Examples

[0135]

[0136]

[0137] Table 2: Mechanical properties of welded joints obtained from examples 1-12 and comparative example 1 of welding wire

[0138]

[0139] As can be seen from Table 2, compared with Comparative Example 1, due to the use of the alloy composition of the welding wire provided by the present invention (such as adding an appropriate amount of Mg, B, Re, Mg≤0.1%, B≤0.1%, Re≤0.1%), the mechanical properties of the welded joints of Examples 1-11 are better than those of Comparative Example 1 as a whole, and the strength of the weld is significantly improved while maintaining good toughness and plasticity. Further, the comprehensive mechanical properties (such as strength) of Examples 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 controlling the content and proportion of some key elements (such as Mg, B, Re), it is beneficial to further improve the mechanical properties of the weld (strength is improved while ensuring good toughness and plasticity) and reduce welding defects. Further, compared with Example 5, the overall mechanical properties of Examples 6-11 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 (such as strength) and reduce welding defects. Compared with Example 1, Example 12 further adds Mo, W, V and Nb, thereby significantly improving the toughness and plasticity of the joint while ensuring high strength. For example, the elongation A5 (%) and the V-type impact energy KV2 at -84°C are further improved.

[0140] Embodiment 13

[0141] This embodiment provides a welding wire, the general chemical formula of which is Fe-35Mn-10Al-C-0.02Mg-0.04B-0.03Re-0.5Mo-0.2W-0.3V-0.4Nb (referred to as welding wire 13), and the diameter of the welding wire is 1.6 mm.

[0142] This embodiment also provides a welding method, comprising welding a weldment using the welding wire (welding wire 13) 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;

[0143] The main steps of the welding method include:

[0144] S0, open the groove first, then clean before welding:

[0145] 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°;

[0146] 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;

[0147] 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.

[0148] In the base welding, the welding current is 170A and the welding voltage is 15V;

[0149] 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.

[0150] 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.

[0151] Embodiment 14

[0152] The difference between this embodiment and embodiment 13 is that the general chemical formula of the welding wire is Fe-35Mn-10Al-C-0.02Mg-0.04B-0.03Re-0.4Mo-0.3W-0.3V-0.3Nb (referred to as welding wire 14); the remaining parameters and steps of the welding method are similar to those of embodiment 13.

[0153] Embodiment 15

[0154] The difference between this embodiment and embodiment 13 is that the general chemical formula of the welding wire is Fe-35Mn-10Al-C-0.03Mg-0.07B-0.07Re-0.4Mo-0.3W-0.3V-0.3Nb (referred to as welding wire 15); the remaining parameters and steps of the welding method are similar to those of embodiment 13.

[0155] Example 16

[0156] The difference between this embodiment and embodiment 13 is that the general chemical formula of the welding wire is Fe-35Mn-10Al-C-0.07Mg-0.07B-0.07Re-0.4Mo-0.3W-0.3V-0.3Nb (referred to as welding wire 16); the remaining parameters and steps of the welding method are similar to those of embodiment 13.

[0157] Embodiment 17

[0158] The difference between this embodiment and Embodiment 16 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 16.

[0159] Embodiment 18

[0160] The difference between this embodiment and Embodiment 16 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 16.

[0161] Embodiment 19

[0162] The difference between this embodiment and Embodiment 16 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 16.

[0163] Embodiment 20

[0164] The difference between this embodiment and Embodiment 16 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 16.

[0165] Embodiment 21

[0166] The difference between this embodiment and Embodiment 16 is that in the welding method, the number of formal welding passes is 9; the remaining parameters and steps of the welding method are similar to those of Embodiment 16.

[0167] Table 3: Chemical composition and welding process parameters of welding wire in Examples 13-21 of welding wire

[0168]

[0169]

[0170] Table 4: Mechanical properties of welded joints obtained from examples 13-21 of welding wires

[0171]

[0172]

[0173] As can be seen from Table 4, the comprehensive mechanical properties of Examples 13-16 show the general rule of Example 16> Example 15> Example 14> Example 13, that is, under the condition of ensuring good toughness and plasticity, the tensile strength of the welded joint is gradually improved, 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 cracking resistance of the weld, thereby reducing welding defects. Further, compared with Example 16, the overall mechanical properties of Examples 17-21 are slightly reduced, which shows that when the composition of the welding wire is constant, by selecting the preferred process parameters (such as Example 16), it is beneficial to further improve the mechanical properties of the weld, including improving the strength and cracking resistance, thereby reducing welding defects.

[0174] 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.

[0175] The metallographic structure of the welded joint obtained in Example 1 is shown in Figure 1 .from Figure 1 It can be seen that the weld zone obtained in the embodiment of the present invention is mainly columnar crystals, accompanied by a small amount of fine ferrite, and has good structural uniformity. The macroscopic low-power morphology of the welded joints obtained in Example 1 and Comparative Example 2 is shown in FIG. Figure 2 and Figure 3 ,from Figure 2 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, while in the comparative example 2, since the Mg, B, and Re added to the welding wire components do not conform to the present invention, cracks (such as Figure 3 As shown in the A part of the figure, and because the welding current is too small, there are some unwelded defects (such as Figure 3 (shown in part B in the figure).

[0176] 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 for low-density steel welding, 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%, Mg≤0.1%, B≤0.1%, Re≤0.1%, and the rest is Fe and unavoidable impurities; And 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.

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%, 0.03%≤Mg≤0.07%, 0.03%≤B≤0.07%, 0.03%≤Re≤0.07%, and the rest are Fe and unavoidable impurities.

3. The welding wire according to claim 1, characterized in that The Mg, B, and Re further satisfy: 0.5<([B]+[Mg]) / [Re]<2.1, and / or, 0.8<[B] / [Mg]<1.

6.

4. The welding wire according to claim 1, characterized in that The welding wire also includes components of: Mo≤1.0%, W≤0.5%, V≤0.5%, and Nb≤0.5%.

5. The welding wire according to claim 4, characterized in that The Mo, W, V and Nb also satisfy the following: 2.2<([W]+[V]+[Nb]) / [Mo]<2.6, where [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element.

6. The welding wire according to claim 5, characterized in that The W, V, and Nb also have the following relationship: [W]: [V]: [Nb] = (0.9-1.1): (0.9-1.1): (0.9-1.1).

7. The welding wire according to claim 5, characterized in that The C, B, Mg, Re, Mo, W, V, and Nb also satisfy the following conditions: γ = 2.5×([Mg]+[B]+[Re])+0.3×[Mo]+0.4×([W]+[V]+[Nb]) and 0.8γ<[C]<1.2γ; Here, [C], [Mg], [B], [Re], [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element.

8. A welding method, characterized in that: The method comprises adopting TIG welding process and welding FeMnAlC low-density steel, i.e. weldment, with the welding wire described in any one of claims 1 to 7; the main steps of welding comprise: firstly performing base welding and then performing formal welding.

9. The welding method according to claim 8, characterized in that: No preheating before welding and no heat treatment after welding; and / or, The thickness of the weldment t≥3mm, and the number of welding passes N of the formal welding is ≥5; and / or, The process parameters of the base welding include: the welding current is 160-170A; the process parameters of the formal welding include: the welding current is 170-205A.

10. The welding method according to any one of claims 8 to 9, characterized in that: The room temperature tensile strength Rm of the welded joint obtained by the welding method is ≥880MPa, the room temperature elongation after fracture A5 is ≥20%, and the V-type impact energy KV2 is ≥30J at -84°C.

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