A welding wire and a welding method

Abstract

The present application relates to a welding wire and a welding method, and belongs to the field of welding process, solves at least one problem of the mechanical properties of the welding joint, the poor joint quality, the poor welding adaptability / availability and the high cost in the welding process of the light steel, especially the high Al FeMnAlC steel plate in the prior art.A kind of welding wire for welding, the welding wire component includes 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%, the rest is Fe and inevitable impurities.The present application significantly improves the mechanical properties and quality of the welding joint by optimizing the composition of the welding wire, the welding method can still ensure the high quality and mechanical properties of the welding joint while simplifying the operation, reducing the cost and improving the adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding process, in particular to a welding wire and a welding method. BACKGROUND

[0002] With the prevalence of green manufacturing concepts such as weight reduction, energy saving, and carbon emission reduction, FeMnAlC steel has been increasingly valued by the material research field and the industry in recent years due to its low density and good comprehensive performance. Currently, the research on FeMnAlC low-density steel by domestic and foreign scholars mainly focuses on laboratory preparation and performance mechanism, and 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 easy generation of brittle second phase in the welded joint, the easy occurrence of weld composition segregation, and the easy formation of cracks and other defects. These problems make the welded joint of FeMnAlC low-density steel a weak link in the structure. For FeMnAlC low-density steel, as the C and Al contents in the welding material increase or the welding material thickness increases, the above problems become more prominent, and the welding difficulty is greater, and welding cracks and other defects are more likely to occur.

[0004] Due to the above welding difficulties of such steel, the existing welding wire or welding method has one or more of the following problems when applied to weld FeMnAlC low-density steel, especially high-aluminum FeMnAlC steel: poor welding quality, insufficient mechanical properties of the welded joint, expensive welding equipment, and high cost. SUMMARY

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

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] The present application provides a welding wire for 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, Nb meet the requirement: 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1%, [Mo], [W], [V], [Nb] represent the mass percentage (%) of each element.

[0009] Further, the components of the welding wire include, in 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%, the rest being Fe and inevitable impurities.

[0010] Further, the Mo, W, V, Nb also meet: 2.2<([W]+[V]+[Nb]) / [Mo]<2.6.

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

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

[0013] Further, the components of the welding wire also include: Mg≤0.1%, B≤0.1%, Re≤0.1%.

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

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

[0016] The present application also provides a welding method, comprising using the above welding wire to weld the FeMnAlC low-density steel, i.e. the welded piece.

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

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

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

[0020] Further, the welding pass N of the formal welding satisfies: wherein, represents rounding up or down to the nearest integer result; t represents the steel plate thickness of the welding piece, the unit of t is mm and t≥3mm.

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

[0022] (1) The present application 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, Nb), especially when welding FeMnAlC series low-density steel, which can better meet the high-performance requirements in industrial applications;

[0023] 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 C content is further increased (0.6%-1.2%) to improve the strength of the welded joint, and the Al content is appropriately increased to improve the weld uniformity, on the other hand, 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 limit range of these elements), the joint strength and weld uniformity can be improved while ensuring good toughness and plasticity of the welded joint and effectively reducing defects such as cracks and pores; compared with the welding wire disclosed in the prior art, when welding FeMnAlC series low-density steel using the welding wire provided by the present application, the mechanical properties of the welded joint can be significantly improved, especially when applied to welding FeMnAlC series low-density steel welding materials with greater difficulty (such as high Al and C content and / or medium-thick plate), the joint strength can still reach a level of 850Mpa or more, while the toughness and plasticity of the joint can meet the joint mechanical property requirements of such steel plates in industrial applications, such as elongation A5≥20% in tensile test and V-type impact energy KV2≥30J at-84℃.

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

[0025] Specifically, compared with the lower Al content (≤7.0%) in the existing welding wire, the present application improves the weld uniformity by appropriately increasing the Al content (7% < Al ≤ 12%); at the same time, by reasonably adding some key alloying elements (such as Mo, W, V, Nb) and optimizing the content of the elements (such as controlling the upper and lower limit ranges of these elements), the present application can effectively improve the toughness and plasticity of the joint, improve the welding crack resistance, and reduce the defects such as cracks and pores at the welding joint, while ensuring the joint strength and welding quality. Compared with the welding wire disclosed in the prior art, when the welding wire provided by the present application is used to weld FeMnAlC low-density steel, the overall quality of the welding 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 application refines the inclusions of the welding joint by additionally adding key alloying elements (such as Mg, B, Re) in the composition of the welding wire and controlling the content range, thereby improving the toughness and plasticity of the welding joint. This composition optimization not only further improves the mechanical properties of the welding joint, but also enhances the welding crack resistance and reduces defects such as cracks, thereby further improving the quality of the weld.

[0027] (4) In some preferred embodiments, the present application can further improve the mechanical properties of the welding 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 joint strength and toughness, improving the impact resistance at low temperature, further improving the welding crack resistance and reducing defects such as cracks and pores.

[0028] (5) The welding method provided by the present application exhibits significant advantages when applied to FeMnAlC low-density steel compared to the prior art, such as: ease of operation, economy, good welding adaptability / availability, and at the same time, thanks to the special composition design of the welding wire in the present application, the welding method of the present application can still ensure the high quality and mechanical properties of the welding joint while simplifying the operation, reducing the cost and improving the adaptability, 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 application can optimize the microstructure of the weld, improve the strength, toughness and plasticity of the welding joint, further improve the quality and mechanical properties of the welding joint, and achieve an optimized balance of welding performance, efficiency and cost by optimizing and controlling some key parameters in the welding process (such as welding current, voltage, speed, and welding passes).

[0030] The technical solutions in the present application can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the following description, and some advantages will become apparent from the description, or will be understood by those skilled in the art through implementation of the present application. The objects and other advantages of the present application can be realized and obtained by the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this application. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0032] Figure 1 The enlarged metallographic structure diagram of the welding joint obtained in the embodiment 1 of the present application;

[0033] Figure 2 The enlarged metallographic structure diagram of the welding joint obtained in the comparative example 4;

[0034] Figure 3 The macroscopic appearance diagram of the welding joint obtained in the embodiment 1 of the present application;

[0035] Figure 4 The macroscopic appearance diagram of the welding joint obtained in the comparative example 4. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present application will be described in detail below with reference to the drawings, wherein the drawings constitute a part of this application and are used to explain the principles of the embodiments of the present application, but are not used to limit the scope of the present application.

[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, friction stir welding) to weld low Al-based FeMnAlC steel, but these existing methods have obvious drawbacks in practical application. For example, the cooling speed is very fast during the laser welding process, and the weld penetration is large, which is easy to produce large internal stress and porosity in the welding joint during the rapid heating and solidification process, thereby affecting the quality of the welding joint; the welding spot of the resistance spot welding becomes a weak area, which is easy to appear brittle fracture phenomenon; after the electron beam welding, the undercooling degree and the cooling rate are fast during the welding process, and the entire weld austenite organization exists in the form of columnar crystals with preferred orientation, these columnar crystals grow and gather perpendicularly to the fusion line to the center of the weld, finally making the weld form a clear boundary line in the center, which leads to poor fracture ductility of the welding joint; the friction stir welding lacks flexibility of welding, the wear of the welding joint is relatively large, the cost is high, and the hardening effect appears in the stirring area, which affects the welding performance.

[0038] The inventors of the present application comprehensively consider the characteristics of FeMnAlC low-density steel, especially high-aluminum FeMnAlC steel in welding. The steel contains more Mn and Al elements, and is prone to generate large deformation and obvious overheating phenomenon during welding. It is considered that a welding process with smaller line energy should be selected as much as possible during welding. Compared with other connection methods, tungsten inert gas 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 low-density steel. However, for FeMnAlC low-density steel, especially when the C content and / or Al content and / or welding material thickness is large, there is currently no suitable welding wire and welding method that can effectively solve the problems of joint mechanical property deficiency, poor weld quality, high welding cost, poor adaptability / availability of such lightweight steel during welding.

[0039] Therefore, in a first aspect, the present application provides a welding wire for welding 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; and the Mo, W, V, and Nb satisfy the requirement: 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1%, wherein [Mo], [W], [V], and [Nb] represent the mass percentage (%) of each element.

[0040] Compared with the prior art, the welding wire provided by the present application can significantly improve the mechanical properties of the welded joint by optimizing the composition of the welding wire, in particular, by increasing the content of C and Al and reasonably adding key alloying elements (such as Mo, W, V and Nb), and can better meet the high performance requirements in industrial applications, in particular, when welding FeMnAlC low-density steel. Specifically, from the perspective of the composition design of the welding wire, on the one hand, compared with the lower content of C (≤0.3%) in the existing welding wire, the content of C is further increased (0.6%-1.2%) to improve the strength of the welded joint, and the content of Al is appropriately increased to improve the weld uniformity, on the other hand, by reasonably adding some key alloying elements (such as Mo, W, V and Nb) and optimizing the content of the elements (such as controlling the upper and lower limit ranges of these elements), the strength of the joint and the weld uniformity can be improved, while the toughness and plasticity of the welded joint are ensured, and the defects such as cracks and pores are effectively reduced. Compared with the welding wire disclosed in the prior art, when the welding wire provided by the present application is used to weld FeMnAlC low-density steel, the mechanical properties of the welded joint can be significantly improved, in particular, when the welding wire is applied to weld Fe-Mn-Al-C low-density steel which is more difficult to weld, such as high Al and C content and / or medium-thick plate, the joint strength can still reach a level of 850 MPa or above, while the toughness and plasticity of the joint can meet the requirements of the joint mechanical properties of such steel plates in industrial applications, such as elongation A5≥20% in the tensile test and V-type impact energy KV2≥30 J at-84 ℃.

[0041] Compared with the prior art, the welding wire provided by the present application can significantly improve the mechanical properties of the welded joint by optimizing the composition of the welding wire, in particular, by increasing the content of C and Al and reasonably adding key alloying elements (such as Mo, W, V and Nb), and can better meet the high performance requirements in industrial applications, in particular, when welding FeMnAlC low-density steel. Specifically, from the perspective of the composition design of the welding wire, on the one hand, compared with the lower content of C (≤0.3%) in the existing welding wire, the content of C is further increased (0.6%-1.2%) to improve the strength of the welded joint, and the content of Al is appropriately increased to improve the weld uniformity, on the other hand, by reasonably adding some key alloying elements (such as Mo, W, V and Nb) and optimizing the content of the elements (such as controlling the upper and lower limit ranges of these elements), the strength of the joint and the weld uniformity can be improved, while the toughness and plasticity of the welded joint are ensured, and the defects such as cracks and pores are effectively reduced. Compared with the welding wire disclosed in the prior art, when the welding wire provided by the present application is used to weld FeMnAlC low-density steel, the mechanical properties of the welded joint can be significantly improved, in particular, when the welding wire is applied to weld Fe-Mn-Al-C low-density steel which is more difficult to weld, such as high Al and C content and / or medium-thick plate, the joint strength can still reach a level of 850 MPa or above, while the toughness and plasticity of the joint can meet the requirements of the joint mechanical properties of such steel plates in industrial applications, such as elongation A5≥20% in the tensile test and V-type impact energy KV2≥30 J at-84 ℃.

[0042] Therefore, the welding wire provided by the present application can fully meet the welding needs of the FeMnAlC low-density steel, and is especially suitable for high-Al FeMnAlC steel medium-thick plates, and significantly improves the tensile property and plastic toughness of the welding joint of the light-weight steel, and especially can optimize the microstructure of the fusion zone, effectively reduces the cold crack and hot crack sensitivity during welding, and significantly improves the welding quality.

[0043] Specifically, the chemical component design of the welding wire in the present application mainly includes:

[0044] C: As an interstitial atom in steel, C is very important for improving the strength of the steel. Too high C content aggregation will cause excessive precipitation of kappa-carbide in austenite, especially large particles of kappa-carbide will be formed after welding, thereby seriously deteriorating the welding performance. In addition, high carbon content is also easy to combine with oxygen to form pores. Therefore, the present application limits the C content to be within 0.6-1.2%. Exemplarily, the C content is 0.7%, 0.8%, 0.9%, 1.0%, 1.1%.

[0045] Mn: Mn is an austenite forming and stabilizing element, which can expand the austenite phase region and reduce the critical quenching speed of the steel. However, too high Mn content will make the light-weight steel prone to form brittle beta-Mn phase, which will greatly reduce the toughness of the material. However, in order to ensure that the matrix structure of the steel in the present application is austenite structure, the Mn content should not be less than 25%. Therefore, the present application limits the Mn content to be 25%-35%. Exemplarily, the Mn content is 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 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, Al element has a high liquid diffusion rate during welding, which can promote the mixing and interdiffusion of welding materials, and help to form a uniform weld. Too much aluminum content will reduce the strength and toughness of the welding joint, and increase the hot crack sensitivity of the welding joint; at the same time, too low Al content will result in insufficient strength of the welding joint, and the present application limits the Al content to meet 7% < Al ≤ 12%. Exemplarily, the Al content is 8%, 9%, 10%, 11%.

[0047] In the welding wire applied to FeMnAlC low-density steel welding, increasing the carbon (C) and aluminum (Al) content can indeed bring the benefits as described above (for example, higher C content can improve the strength, and higher Al content can improve the weld uniformity), but at the same time, it also brings 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 at the welding joint, and cracks are prone to occur during welding; when the aluminum content is high, brittle phases such as aluminum carbide are prone to be formed with other elements in the steel, which will reduce the toughness of the welding joint and increase the risk of cracks.

[0048] To solve and balance the above welding challenges, the present application can make the welded joint have good plasticity and toughness, including toughness and plasticity performance at room temperature and low temperature environment, while taking some benefits brought by high C and Al content (such as improving strength and weld uniformity), thereby improving welding crack resistance, reducing welding defects such as cracks, and thus improving welding quality, by adding Mo, W, V, Nb alloying elements and controlling their content in a suitable range.

[0049] Mo, W, Nb, V: The addition of a small amount of Mo, W, Nb, V can refine the welding structure through large atomic drag and form MC carbides, thereby improving the toughness of the material. They can form stable carbides (MC type) with carbon, which can play a role in refining the grain and stabilizing the austenite during welding, thereby improving the mechanical properties of the welded joint. However, a large amount of addition will increase the risk of precipitation of large particle carbides, which are easy to become the starting point of cracks and reduce the toughness of the material, so it is required that 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%, [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, V can be better realized 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 cost of the material; wherein, the requirement 1.3%≤[Mo]+[W]+[V]+[Nb]≤2.1% can effectively suppress the embrittlement of the welded joint caused by the precipitation of the second phase such as κ-carbide at the welded joint during welding.

[0050] In some embodiments, the Mo content is 0.4%, 0.5%, 0.6%, 0.7%, 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, in 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 inevitable impurities.

[0055] Preferably, the welding wire provided by the present application satisfies the following condition: 2.2<([W]+[V]+[Nb]) / [Mo]<2.6, where [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element. Through systematic research and theoretical analysis, the inventors believe that the addition amount and mutual ratio of molybdenum (Mo), tungsten (W), vanadium (V) and niobium (Nb) are also important. When the addition amount of these four elements satisfies the following specific ratio condition, i.e. 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 for solving the challenges of welding toughness and quality caused by the increase of C and Al content. In this way, not only can the second phase (such as kappa carbide) precipitation and element segregation phenomenon be effectively reduced or inhibited, thereby improving the toughness and plasticity of the welded joint and reducing welding defects (such as cracks), but also the best balance of material cost efficiency can be achieved on the premise of ensuring the quality and high strength of the welded joint.

[0056] Preferably, the W, V, 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, Nb, the synergistic effect of W, V, Nb elements and W, V, Nb and other elements is maximized, further improving the toughness and plasticity of the welded joint and the crack resistance, and improving the weld quality and ensuring the high strength of the welded joint. Exemplarily, [W]: [V]: [Nb] = 1:1:1.

[0057] In some preferred embodiments, the C, Mo, W, V, Nb in the welding wire provided by the present application also satisfy: a = 0.5 x [Mo] + 0.6 x ([W] + [V] + [Nb]) and 0.8a < [C] < 1.2a; wherein [C], [Mo], [W], [V] and [Nb] represent the mass percentage (%) of each element. More preferably, 0.9a < [C] < 1.1a. This preferred element ratio strategy is very effective in solving the challenges in welding toughness and quality caused by high carbon (C) and high aluminum (Al) content. In this way, the effects of maximizing Mo, W, V, Nb on refining the welding structure through large atomic drag and forming MC carbide, effectively reducing or inhibiting the precipitation of secondary phases (such as kappa carbide) and element segregation, thereby improving the toughness and plasticity of the welded joint, can be achieved while achieving the best balance of cost effectiveness.

[0058] In some preferred embodiments, the components of the welding wire in the present application also include: Mg ≤ 0.1%, B ≤ 0.1%, Re ≤ 0.1%. By adding key alloying elements (such as Mg, B, Re) to the composition of the welding wire and controlling their content range, the present application refines the inclusions of the welded joint and improves 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 crack resistance of the welding, reduces defects such as cracks, and further improves the quality of the weld.

[0059] It should be noted that the chemical composition design of the additional key alloying elements (such as Mg, B, Re) in the composition of the welding wire mainly includes:

[0060] Mg, B, Re: The addition of trace amounts of Mg, B, Re can refine the inclusions of the welded joint, thereby improving the toughness and plasticity of the welded joint. Excessive addition will cause an increase in the number and size of inclusions. 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, in mass percent: 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%, the balance being Fe and unavoidable impurities.

[0065] In some preferred embodiments, the components of the welding wire include, in mass percent: 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%, the balance being Fe and unavoidable impurities.

[0066] When the Mg, B, Re alloying elements are further added in the welding wire provided by the present application, preferably, the Mg, B, Re satisfy the requirement: 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 Mg, B, Re three elements, the synergistic effect between them can be better played to ensure that they can significantly improve the toughness and plasticity of the welding joint and the welding quality while ensuring the high strength of the welding joint, without significantly increasing the material cost; for example, controlling the total content of Mg, B, Re elements 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 welding joint, and improve the crack resistance of the welding joint.

[0067] When the Mg, B, Re alloying elements are further added in the welding wire provided by the present application, further preferably, the Mg, B, Re also satisfy the requirement: 0.5≤([B]+[Mg]) / [Re]≤2.1, [Mg], [B], [Re] represent the mass percentage (%) of each element. Through more systematic research and theoretical analysis, the inventors believe that the addition amount and mutual ratio of boron (B), magnesium (Mg) and rhenium (Re) are crucial, when the addition amount of the three elements satisfies the following specific ratio condition, i.e. 0.5≤([B]+[Mg]) / [Re]≤2.1, the synergistic effect between these elements can be maximized; this optimized element ratio strategy has beneficial effects on solving the challenges in welding toughness and quality caused by increasing the content of C and Al, in this way, not only the toughness and plasticity of the welding joint can be improved, but also the best balance of material cost benefit can be achieved on the premise of ensuring the quality and high strength of the welding joint. Specifically, boron (B) in the welding wire is used to form borides or borocarbides with high hardness and good thermal stability, these hard phases can significantly improve the hardness and wear resistance of the weld metal, and the rare earth element Re can refine the grain, purify the grain boundary and improve the comprehensive performance of the weld metal when added in trace amounts in the welding wire; 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 the weld metal. Too much boron (B) and magnesium (Mg) will make the weld metal brittle, and too much rare earth element Re will directly affect the formability of the welding joint.

[0068] When the Mg, B, Re alloying elements are further added in the welding wire provided by the present application, it is further preferred that the C, Mo, W, V, Nb, B, Mg, Re satisfy: γ = 2.5 x ([Mg] + [B] + [Re]) + 0.3 x [Mo] + 0.4 x ([W] + [V] + [Nb]) and 0.8γ < [C] < 1.2γ; wherein [C], [Mo], [W], [V], [Nb], [Mg], [B], [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 in welding toughness and quality caused by high carbon (C) and high aluminum (Al) content. In this way, the B, Mg, Re can be maximized to refine the inclusions of the welding joint, and the Mo, W, V, Nb can be maximized to refine the welding structure through large atomic drag and form MC carbides, while effectively reducing or inhibiting the precipitation of secondary phases (such as kappa carbides) and element segregation, thereby significantly improving the toughness and plasticity of the welding joint, achieving the best balance between improving the performance of the welding joint and controlling the cost.

[0069] When the Mg, B, Re alloying elements are further added in the welding wire provided by the present application, it is further preferred that the B, Mg satisfy the following relationship: 0.8 < [B] / [Mg] < 1.6; and 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, the synergistic effect of B, Mg elements and B, Mg with other elements can be maximized, further improving the toughness and plasticity of the welding joint, and improving the welding quality and ensuring the high strength of the joint.

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

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

[0072] In the chemical formula mentioned in the present application, 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 application also provides a welding method, which comprises welding a FeMnAlC low-density steel welding piece by using the welding wire according to the first aspect; and the welding piece is exemplarily a steel plate.

[0074] The main steps of the welding method include: firstly, performing a backing welding under inert gas protection by using a TIG welding process, and then performing a formal welding, and immediately performing a knock on the welding seam to release stress after the welding seam is completely solidified.

[0075] The welding method provided by the present application has significant advantages when applied to FeMnAlC low-density steel compared to the prior art, such as: convenient operation, economy, good welding adaptability / reachability, and at the same time, due to the special component design of the welding wire in the present application, the welding method of the present application can still ensure the high quality and mechanical properties of the welded joint while simplifying the operation, reducing the cost and improving the adaptability, thereby providing a new efficient and economical choice for the welding of FeMnAlC low-density steel.

[0076] Specifically, before the backing welding, the welding surface of the welding piece is subjected to a groove opening treatment, and the welding surface of the welding piece and the welding wire are subjected to a pre-welding cleaning. The pre-welding cleaning includes: polishing the welding piece, and removing rust, oil stains and dust from the surface of the welding piece and the welding wire, so as to avoid the influence of rust or oil stains on the surface of the welding piece and the welding wire on the welding seam, thereby reducing or avoiding 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°, 75°.

[0078] In some embodiments, the welding piece is a medium plate, and the thickness of the medium plate is 3 mm to 20 mm. Exemplarily, the thickness of the medium plate is 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm or 18 mm.

[0079] In some embodiments, the diameter of the welding wire is 0.5 mm to 3.2 mm. Exemplarily, 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] Further, after the cleaning is completed, the backing welding is performed first, which mainly includes: performing a backing welding on the joint back groove root of the welding piece, so as to effectively avoid the angle deformation and burning phenomenon of the welding piece directly and completely welded.

[0081] It can be understood that since the welding stress and the deformation of the weld are mainly caused by the shortening of the weld after welding, the appropriate extension of the weld can compensate for the shortening, thereby reducing the welding stress and the deformation; therefore, after the welding is completed, the filler metal at the joint of the welded part is immediately knocked after each solidification, so as to appropriately extend the weld, reduce the stress and the deformation.

[0082] In some preferred embodiments, the process parameters of the formal welding include that the welding voltage is 15-19 V, the welding current is 170-205 A, and the welding speed is 14-19 cm / min. When the FeMnAlC low-density steel is welded by using the TIG process, it is also important to select appropriate welding parameters to ensure the stability of the welding process and the weld quality. The inventors have found that, by selecting the above-mentioned welding parameters which have a synergistic effect and are matched with the welding wire provided in the present application (i.e., the welding wire as described in the first aspect), 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 basis for manufacturing a welded joint which is both strong and durable.

[0083] Specifically, by using the above-mentioned preferred current (170-205 A), a suitable heat input amount can be obtained, which can have a better effect on the penetration of the welding wire in the weld zone, especially when thick plate welding is performed. A suitable heat input amount can improve the deposition efficiency, increase the production efficiency, allow the slag and pores to overflow the weld in time, promote the crystallization process, reduce the residual stress and deformation in the weld process, make the weld more uniform, dense and defect-free. However, if the heat input amount is too high, the temperature in the welding area will be too high, the alloying elements will be severely burned, the grain size of the weld and HAZ will be coarse, and the joint performance will be deteriorated. Therefore, in combination with the special components of the welding wire provided in the present application, the welding current is preferably 170 A-205 A.

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

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

[0086] In some preferred embodiments, the process parameters of the backing welding include: a welding voltage of 14-17 V and a welding current of 160-170 A. If the welding heat input is too large during the backing welding, the solidification speed of the molten pool is less than the crack initiation speed of the solidification crack, which leads to cracking. Therefore, the welding current should not be too large, and a lower welding current than the formal welding current is preferably used. During the welding, the current and the voltage are matched.

[0087] In some embodiments, during the TIG welding, the distance between the welding torch head and the surface of the welding piece is 5-15 mm, and the inclination angle of the welding torch is 5-15°, which helps to better ensure the welding quality and the mechanical properties of the welded joint. For example, the distance between the welding torch head and the surface of the welding piece is 7 mm, 9 mm, 11 mm or 13 mm, and the inclination angle of the welding torch is 7°, 9°, 11° or 13°.

[0088] It should be noted that, due to the special component design of the welding wire in the present application, the welding method of the present application eliminates the traditional heat treatment process, i.e., no preheating before welding and no heat treatment after welding. Thus, after welding, the obtained welding piece is cooled in a room temperature environment, and the welded piece is obtained after complete cooling. The welding method provided by the present application is based on the carefully designed component of the welding wire. Without preheating before welding and heat treatment after welding, excellent welding effect can be achieved, for example, reasonable addition of some key alloying elements in the welding wire and control of the content of each element help to form fine microstructure during welding, effectively reduce or inhibit the precipitation of the second phase (such as kappa carbide) and reduce the element segregation phenomenon, so that in the case of eliminating heat treatment, the good joint toughness and crack resistance can still be maintained, and the welding stress is reduced.

[0089] When welding FeMnAlC low-density steel, especially high-aluminum FeMnAlC low-density steel, the material is very sensitive to welding thermal cycle, which is easy to produce welding cracks. In particular, during the welding of medium-thick plates, the thermal gradient is large, the welding stress is increased, and welding defects are easily caused. In order to solve this problem, the present application adopts a multi-pass welding process.

[0090] Preferably, the welding pass number N of the formal welding satisfies: wherein, represents the upward or downward rounding to the nearest integer result; t represents the thickness of the steel plate of the welding piece, in mm, and t≥3 mm. Using the welding pass satisfying the above condition not only effectively reduces the thermal gradient and reduces the risk of welding defects, but also ensures the welding quality while taking into account the production efficiency and economy. When the above condition is not satisfied, for example, if the welding pass is too many, the grains in the heat-affected zone will be coarse, which will reduce the toughness of the joint, and will also increase the deformation and residual stress of the welding area and increase the risk of reheat cracking.

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

[0092] In some embodiments, when the thickness of the welding piece is 12mm-20mm, the number of welding passes for the main welding is 7-8 passes. For example, when the thickness of the welding piece is 12mm, The upward or downward rounding to the nearest integer is 2 or 3, respectively, and the number of welding passes N = 7 or 8.

[0093] In some embodiments, the inert gas used in the welding method provided by the present application is argon with a purity higher than 99.99% to prevent the oxidation of more active elements in the welding piece and welding wire during welding. Further, the gas flow rate of the inert gas is 10-16L / min. For example, the gas flow rate is 11L / min, 12L / min, 13L / min, 14L / min, or 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 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 and helping to further improve the welding quality and reduce welding defects. It should be noted that a too high gas flow rate can lead to a decrease in the protection effect and a too rapid cooling of the weld, thereby affecting the weld formation and properties.

[0094] Based on the welding wire and the welding method thereof provided by the present application, the tensile strength Rm of the obtained welded joint at room temperature is ≥850MPa, the elongation A5 after fracture at room temperature is ≥20%, and the V-type impact energy KV2 at -84℃ is ≥30J.

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

[0096] The technical solutions of the present application are further described in detail below in combination with specific examples and comparative examples.

[0097] Example 1

[0098] The embodiment provides a welding wire, the chemical general formula of the welding wire 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] The embodiment also provides a welding method, which comprises welding a welding piece by using the welding wire (welding wire 1) described above, the welding piece is a steel plate with a thickness of 12 mm, and the chemical general formula of the welding piece is Fe-30Mn-8Al-0.9C.

[0100] The main steps of the welding method comprise the following steps.

[0101] S0, first, groove preparation is performed, and then, pre-welding cleaning is performed.

[0102] The groove preparation comprises the following steps: a V-shaped groove is cut on a butt joint of the welding piece by using a wire cutting machine, and the angle of the V-shaped groove is 80°.

[0103] The pre-welding cleaning comprises the following steps: a grinding machine is used to polish the periphery of a to-be-welded area of the welding piece until the periphery of the to-be-welded area is bright; and ethanol is used to remove oil stains on the surface of the welding piece and the welding wire 1.

[0104] S1, welding: a TIG welding process is used, first, backing welding is performed, then, formal welding is performed, immediately after the welding seam is solidified, the welding seam is tapped by using a tool hammer, and the vibration caused by the tool hammer can release the stress of the welding seam; after welding, the welding piece is directly cooled in a room temperature environment without heat treatment, and the welding piece can be obtained after complete cooling.

[0105] In the backing welding, the welding current is 170 A, and the welding voltage is 15 V.

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

[0107] In the backing welding and the formal welding, argon with a purity higher than 99.99% is used as the protective gas, and the inert gas (i.e., argon) flow is 12 L / min.

[0108] Embodiment 2

[0109] The embodiment is different from the embodiment 1 in that the chemical general 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), and the remaining parameters and the steps of the welding method are similar to those of the embodiment 1.

[0110] Embodiment 3

[0111] The difference between this embodiment and embodiment 1 is that the 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 rest of the parameters and the steps of the welding method are similar to those of embodiment 1.

[0112] Embodiment 4

[0113] The difference between this embodiment and embodiment 1 is that the 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 rest of the parameters and the steps of the welding method are similar to those of embodiment 1.

[0114] Embodiment 5

[0115] The difference between this embodiment and embodiment 1 is that the 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 rest of the parameters and the steps of the welding method are similar to those of embodiment 1.

[0116] Embodiment 6

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

[0118] Embodiment 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 rest of the parameters and the steps of the welding method are similar to those of embodiment 5.

[0120] Embodiment 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 rest of the parameters and the steps of the welding method are similar to those of embodiment 5.

[0122] Embodiment 9

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

[0124] Embodiment 10

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

[0126] Embodiment 11

[0127] The difference between this example and Example 1 is that the 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 rest of the parameters and the steps of the welding method are similar to those of Example 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 210 A, the welding speed is 12 cm / min, and the argon flow rate is 6 L / min, and the rest of the steps and parameters are similar to those of 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 210 A, the welding speed is 12 cm / min, and the argon flow rate is 6 L / min, and the rest of the steps and parameters are similar to those of 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 210 A, the welding speed is 12 cm / min, and the argon flow rate is 6 L / min, and the rest of the steps and parameters are similar to those of 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 210 A, the welding speed is 12 cm / min, and the argon flow rate is 6 L / min, and the rest of the steps and parameters are similar to those of Example 1.

[0136] In order to more clearly show the changes in composition 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 of the welding wire and welding process parameters of the welding wire of Examples 1-11 and Comparative Examples

[0138]

[0139]

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

[0141]

[0142]

[0143] As can be seen from Table 2, compared with Comparative Examples 1-4, the mechanical properties of the welded joints of Examples 1-10 are overall superior to those of Comparative Examples 1-4, because the welding wire provided by the present application is used in Examples 1-10 (for example, appropriate amounts of Mo, W, V, and Nb are added, 0.3%≤Mo≤0.9%, W≤0.5%, 0.1%<V≤0.5%, 0.1%<Nb≤0.5%), and the strength of the welded joints of Examples 1-10 is significantly improved while the impact resistance at low temperature meets the use requirements (≥27 J). Further, the comprehensive mechanical properties (for example, strength) of Example 1-5 show the general rule of Example 5>Example 4>Example 3>Example 2>Example 1, which indicates that based on the alloy composition of the welding wire provided by the present application, by further controlling the content and proportion of some key elements (for example, Mo, W, V, and Nb), the mechanical properties of the welds can be further improved, and the welding defects can be reduced. Further, compared with Example 5, the overall mechanical properties (for example, strength) of Examples 6-10 slightly decrease, which indicates that based on the alloy composition of the welding wire provided by the present application, by selecting the preferred process parameters (for example, Example 5), the mechanical properties of the welds can be further improved, and the welding defects can be reduced. Compared with Example 1, Example 11 further significantly improves the toughness and plasticity of the joints (for example, the elongation A5(%) and the V-type impact energy KV2 at -84℃ are further improved) while ensuring high strength, because Mg, B, and Re are additionally added.

[0144] Example 12

[0145] The present embodiment provides a welding wire, the chemical general formula of the welding wire 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] The embodiment also provides a welding method, which comprises welding a welding piece by using the welding wire as described above (welding wire 12), the welding piece is a steel plate with a thickness of 12 mm, and the chemical general formula of the welding piece is Fe-30Mn-8Al-0.9C;

[0147] The main steps of the welding method comprise the following steps.

[0148] S0, first, groove preparation is performed, and then, pre-welding cleaning is performed.

[0149] The groove preparation comprises the following steps: a V-shaped groove is cut on the butt joint of the welding piece by using a wire cutting machine, and the angle of the V-shaped groove is 60°.

[0150] The pre-welding cleaning comprises the following steps: the outer periphery of the welding area of the welding piece is polished by using a grinding machine until the outer periphery of the welding area is bright, and the surfaces of the welding piece and the welding wire are cleaned by using ethanol.

[0151] S1, welding: TIG welding process is adopted, first, backing welding is performed, then, formal welding is performed, immediately after the welding seam is solidified, the welding seam is tapped by using a tool hammer, and the vibration caused by the tool hammer can release the stress of the welding seam; after welding, the welding piece is directly placed in a room temperature environment for cooling, and the welding piece can be obtained after complete cooling.

[0152] In the backing welding, the welding current is 170 A, and the welding voltage is 15 V.

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

[0154] In the backing welding and the formal welding, argon with a purity higher than 99.99% is used as the protective gas, and the inert gas (i.e., argon) flow is 12 L / min.

[0155] Embodiment 13

[0156] The difference between the embodiment and embodiment 12 is that the chemical general 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), and the remaining parameters and the steps of the welding method are similar to those of embodiment 12.

[0157] Embodiment 14

[0158] The difference between the embodiment and embodiment 12 is that the chemical general 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), and the remaining parameters and the steps of the welding method are similar to those of embodiment 12.

[0159] Example 15

[0160] The difference between this example and Example 12 is that the 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 rest of the parameters and the steps of the welding method are similar to those of Example 12.

[0161] Example 16

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

[0163] Example 17

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

[0165] Example 18

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

[0167] Example 19

[0168] The difference between this example and Example 15 is that in the welding method, the welding pass of the formal welding is 6 passes; the rest of the parameters and the steps of the welding method are similar to those of Example 15.

[0169] Example 20

[0170] The difference between this example and Example 15 is that in the welding method, the welding pass of the formal welding is 9 passes; the rest of the parameters and the steps of the welding method are similar to those of Example 15.

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

[0172]

[0173]

[0174] Table 4: Mechanical properties table of the welded joints obtained in Examples 12-20 of the welding wire

[0175]

[0176] From Table 4, it can be seen that the comprehensive mechanical properties (such as strength) of Examples 12-15 show a general rule of Example 15 > Example 14 > Example 13 > Example 12, thus indicating that by further optimizing and controlling the contents of some key elements (such as B, Mg, Re, Mo, W, V, Nb) and the proportional relationship, the mechanical properties of the weld, such as the strength and toughness and the crack resistance of the weld, can be further improved, thereby reducing welding defects. Compared with Example 15, the overall mechanical properties of Examples 16-20 are slightly decreased, thus indicating that when the composition of the welding wire is certain, by selecting the preferred process parameters (for example, Example 15), the mechanical properties of the weld, including the strength and the crack resistance, can be further improved, thereby reducing welding defects.

[0177] To verify the quality of the welding joints obtained by the embodiments of the present application, metallographic detection is performed. First, five different types of metallographic sandpaper are used for manual grinding in turn, and then the surface of the sample is polished on a polishing machine using diamond polishing paste, so that the sample surface presents a smooth mirror surface. The polished sample is etched with 10% nitric acid alcohol solution, and the treatment time is about 1 minute, then it is washed with a large amount of distilled water and alcohol, and dried by using a hair dryer. Finally, the metallographic structure of the treated sample is observed by an optical microscope.

[0178] The metallographic structure of the welding joint obtained by Example 1 and Comparative Example 4 is shown in Figure 1 and Figure 2 From Figure 1 it can be seen that the weld zone obtained by the embodiments of the present application is mainly columnar crystal, accompanied by a small amount of fine ferrite, and the uniformity of the structure is good, but there are cracks in part of Comparative Example 4. The macro low-magnification morphology of the welding joint obtained by Example 1 and Comparative Example 4 is shown in Figure 3 and Figure 4 From Figure 3 it can be seen that the joint obtained by the embodiments of the present application is of good quality, without cracks, pores and other defects, and there are cracks in part of Comparative Example 4 (as shown in A part of Figure 4 .

[0179] The above description is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements within the technical range disclosed by the present application can be easily thought of by those skilled in the art, which should be covered in the protection scope of the present application.

Claims

1. A welding wire for welding, characterized in that, For use in FeMnAlC low-density steel, the composition of the welding wire by mass percentage includes: 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%, with the remainder being Fe and unavoidable impurities; Furthermore, the Mo, W, V, and Nb satisfy 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 composition of the welding wire by mass percentage includes: 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%, with the remainder being Fe and unavoidable impurities.

3. The welding wire according to claim 1, characterized in that, The Mo, W, V, and Nb also satisfy: 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; Where [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 contains the following components: Mg ≤ 0.1%, B ≤ 0.1%, Re ≤ 0.1%.

6. The welding wire according to claim 5, characterized in that, The Mg, B, and Re content must meet the following 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 satisfy the requirement: 0.5 < ([B] + [Mg]) / [Re] < 2.

1.

8. A welding method, characterized in that, This includes welding FeMnAlC low-density steel, i.e., weldments, using the welding wire described in any one of claims 1-7; The main steps of the welding method include: under inert gas protection, using the TIG welding process, first performing the root pass welding, then performing the final weld, and immediately after the weld has solidified, hammering the weld to release stress.

9. The welding method according to claim 8, characterized in that, The process parameters for the root pass welding include: welding current of 160-170A; and / or, The formal welding process parameters 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 number of welding passes N in the formal weld satisfies: in, This indicates the result of rounding up or down to the nearest integer; t represents the thickness of the steel plate of the weldment, with the unit of t being mm and t≥3mm.

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