A welding wire for low-density steel welding and a welding method thereof

Abstract

The present application relates to a kind of welding wire for low-density steel welding and its welding method, belong to welding process field, solve at least one problem of the welding joint mechanical property insufficient, joint quality poor, welding adaptability / accessibility relatively poor, cost higher in the welding process of low-density steel, especially high Al series Fe-Mn-Al-C steel plate in prior art.There is the component of the welding wire including: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, Mg≤0.1%, B≤0.1%, Re≤0.1%, the rest is Fe and inevitable impurities by mass percentage.The present application significantly improves the mechanical properties and quality of the welded joint by optimizing the composition of the welding wire, the welding method can still ensure the high quality and mechanical properties of the welded joint while simplifying the operation, reducing the cost and improving the adaptability.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a welding wire for welding low-density steel and a welding method thereof. Background Technology

[0002] Low-density steel, also known as lightweight steel, is a new type of material typically made by adding a certain mass fraction of Al to medium- or high-manganese steel to achieve lightweighting and excellent mechanical properties. FeMnAlC-based low-density steel has attracted attention from materials research and industry due to its low density and high strength, showing potential applications, especially in automotive manufacturing. Generally, it can be divided into two categories based on Al content: low-Al (Al ≤ 3%) FeMnAlC steel and high-Al (3% < Al ≤ 12%) FeMnAlC steel. As a novel material, the weldability of FeMnAlC-based low-density steel is one of the important indicators for its industrial production. However, recent research on FeMnAlC-based low-density steel has mainly focused on microstructure control and strengthening mechanisms, while research on its weldability is scarce.

[0003] According to existing literature, FeMnAlC low-density steel presents numerous welding challenges due to its alloy composition. These challenges primarily include the formation of brittle second phases at the weld joint, elemental segregation in the weld zone, and susceptibility to cracking. These difficulties result in insufficient mechanical properties and a high susceptibility to welding defects, particularly when the C and / or Al content in the welding material is high or the material thickness is increased. When welding FeMnAlC low-density steel, especially high-alumina FeMnAlC steel in medium and thick plates, existing welding wires and techniques often face challenges, such as substandard weld quality, insufficient mechanical properties of the weld joint, high cost of welding equipment, and poor weldability. These factors limit the widespread application of this type of steel in industrial production. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to provide a welding wire for welding low-density steel and a welding method thereof, in order 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 porosity; (3) expensive welding equipment, poor welding adaptability / accessibility, and high cost.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention provides a welding wire for welding low-density steel, applicable to FeMnAlC series low-density steel. The composition of the welding wire by mass percentage includes: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, Mg≤0.1%, B≤0.1%, Re≤0.1%, with the remainder being Fe and unavoidable impurities.

[0007] Furthermore, 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.

[0008] Furthermore, the composition of the welding wire by mass percentage includes: 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%, with the remainder being 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 composition of the welding wire also includes: Mo≤1.0%, W≤0.5%, V≤0.5%, and Nb≤0.5%.

[0011] Furthermore, the Mo, W, V and Nb also satisfy: 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] Where [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, including using TIG welding process to weld FeMnAlC series low-density steel, i.e., the workpiece, with the above-mentioned welding wire; the main steps of the welding include: first performing a root pass welding, and then performing the final weld.

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

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

[0018] The process parameters for the root pass welding include: welding current of 160-170A; the process parameters for the final pass welding include: welding current of 170-205A.

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

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

[0021] (1) By optimizing the composition of the welding wire, especially by increasing the content of C and Al and rationally adding key alloying elements (such as Mg, B and Re), the mechanical properties of the welded joint are significantly improved. In particular, when welding high-alumina FeMnAlC low-density steel medium and thick plates, it can better meet the high performance requirements in industrial applications.

[0022] Specifically, from the perspective of welding wire composition design, this invention, on the one hand, improves the weld joint strength by further increasing the C content (0.6%-1.2%) compared to the low C content (≤0.3%) in existing welding wires, and appropriately increases the Al content to improve weld uniformity. On the other hand, through the rational 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 joint strength and weld uniformity while ensuring that the weld joint has good toughness and plasticity and effectively reducing cracks. Defects such as porosity are eliminated. Compared with the welding wires disclosed in the prior art, the welding wire provided by this invention can significantly improve the mechanical properties of the welded joint when welding FeMnAlC low-density steel. In particular, when applied to medium and thick plates of high-alumina FeMnAlC low-density steel which are more difficult to weld, the joint strength can still reach 880 MPa or above. At the same time, the toughness and plasticity of the joint can fully meet the mechanical property requirements of such steel plates in industrial applications, such as elongation A5≥20% in tensile tests and V-type impact energy KV2≥30J at -84℃.

[0023] (2) By optimizing the composition of the welding wire, especially by appropriately increasing the Al content and rationally adding key alloying elements (such as Mg, B, Re), the present invention significantly improves the quality of the welded joint and effectively reduces defects such as cracks and porosity.

[0024] Specifically, compared to the relatively low Al content (≤7.0%) in existing welding wires, this invention improves weld uniformity by appropriately increasing the Al content (7% < Al ≤ 12%). Simultaneously, by rationally adding key alloying elements (such as Mg, B, and Re) and optimizing the composition (e.g., controlling the upper and lower limits of these elements), this invention can improve the toughness and plasticity of the weld joint while ensuring joint strength and welding quality. This is achieved through refining inclusions, refining grains, and purifying grain boundaries. Improved toughness and plasticity enhance weld crack resistance and reduce defects such as cracks and porosity at the weld joint. Compared to welding wires disclosed in the prior art, when using the welding wire provided by this invention to weld FeMnAlC low-density steel, the overall quality of the weld joint is better, exhibiting improved weld crack resistance and weld uniformity, with fewer defects such as cracks and porosity.

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

[0026] (4) In some preferred embodiments, the present invention can further improve the mechanical properties of the welded joint and the weld quality 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 their relative proportions; for example, further improving the joint strength and toughness, improving the impact resistance at low temperatures, further improving the welding crack resistance and reducing defects such as cracks and porosity.

[0027] (5) When applied to FeMnAlC series low-density steel, the welding method provided by the present invention has significant advantages over the prior art, such as: ease of 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 still ensure the high quality and mechanical properties of the welded joint while simplifying operation, reducing costs and improving adaptability, providing an efficient and economical new option for welding FeMnAlC series low-density steel.

[0028] (6) Based on the special composition design of the welding wire in this invention, the welding method of this invention eliminates the traditional heat treatment process (such as preheating before welding and slow cooling after welding), making the welding steps more simplified.

[0029] (7) In some preferred embodiments, the welding method of the present invention can optimize the microstructure of the weld by optimizing and controlling some key parameters during the welding process (e.g., welding current, welding passes), 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.

[0030] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0031] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0032] Figure 1 This is an enlarged metallographic image of the welded joint obtained in Embodiment 1 of the present invention;

[0033] Figure 2 This is a low-magnification morphology image of the welded joint obtained in Embodiment 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 Implementation

[0035] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form 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 intended to limit the scope of the present invention.

[0036] In recent years, a few researchers have attempted to apply some common welding processes (such as laser welding, resistance spot welding, electron beam welding, and friction stir welding) to welding low-Al FeMnAlC steel. However, these existing methods have significant drawbacks in practical applications. For example, laser welding has a rapid cooling rate and a large weld penetration. During rapid heating and solidification, it is easy to generate large internal stresses and porosity in the weld joint, thus affecting the quality of the weld joint. In resistance spot welding, the weld point becomes a weak zone, which is prone to brittle fracture. After electron beam welding, due to the rapid supercooling and cooling rate during the welding process, the austenite structure of the entire weld exists in the form of columnar crystals with preferred orientation. These columnar crystals grow and aggregate perpendicular to the fusion line towards the center of the weld, eventually forming a clear dividing line in the center of the weld, which leads to poor fracture ductility of the weld joint. Friction stir welding lacks welding flexibility, the wear of the weld joint is relatively large, the cost is high, and the hardening effect in the stir zone affects the welding performance.

[0037] The inventors of this invention comprehensively considered the characteristics of FeMnAlC low-density steel, especially high-alumina FeMnAlC steel, in welding. These steels contain relatively high levels of Mn and Al, making them prone to significant deformation and overheating during welding. Therefore, they believed that welding processes with lower heat input should be selected whenever possible. Compared to other joining methods, tungsten inert gas welding (TIG) does not have the problem of electrode metal transition, has a simple arc phenomenon, is easy to operate, and has good adaptability, making it suitable for welding FeMnAlC low-density steel. However, for FeMnAlC 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 costs, or poor adaptability / accessibility that are prone to occur when welding such lightweight steels.

[0038] Based on this, in a first aspect, the present invention provides a welding wire for welding low-density steel, applicable to FeMnAlC series low-density steel. The composition of the welding wire, by mass percentage, includes: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, Mg≤0.1%, B≤0.1%, Re≤0.1%, with the remainder being 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.

[0039] Compared with existing technologies, this invention significantly improves the mechanical properties of welded joints by optimizing the welding wire composition, particularly by increasing the C and Al content and rationally adding key alloying elements (such as Mg, B, and Re). This is especially beneficial when welding medium-thick plates of high-alumina FeMnAlC low-density steel, better meeting the high-performance requirements of industrial applications. Specifically, from the perspective of welding wire composition design, this invention, on the one hand, increases the welded joint strength by further increasing the C content (0.6%-1.2%) compared to the relatively low C content (≤0.3%) in existing welding wires, and appropriately increases the Al content to improve weld uniformity. On the other hand, it optimizes the composition by rationally adding key alloying elements (such as Mg, B, and Re). (Such as controlling the upper and lower limits of these elements) can improve the joint strength and weld uniformity while ensuring that the welded joint has good toughness and plasticity and effectively reduces defects such as cracks and porosity. Compared with the welding wires disclosed in the prior art, when using the welding wire provided by this invention to weld FeMnAlC low-density steel, the mechanical properties of the welded joint can be significantly improved. In particular, when applied to medium and thick plates of high-alumina FeMnAlC low-density steel which are more difficult to weld, the joint strength can still reach 880 MPa and above. At the same time, the toughness and plasticity of the joint can fully meet the mechanical property requirements of such steel plates in industrial applications, such as elongation A5≥20% and V-type impact energy KV2≥30J at -84℃ in the tensile test.

[0040] Compared with existing technologies, this invention significantly improves the quality of welded joints and effectively reduces defects such as cracks and porosity by optimizing the welding wire composition, particularly by appropriately increasing the Al content and rationally adding key alloying elements (such as Mg, B, and Re). Specifically, compared with the relatively low Al content (≤7.0%) in existing welding wires, this invention improves weld uniformity by appropriately increasing the Al content (7% < Al ≤ 12%). Simultaneously, by rationally adding key alloying elements (such as Mg, B, and Re) and optimizing the composition (e.g., controlling the upper and lower limits of these elements), this invention can improve the toughness and plasticity of the welded joint while ensuring joint strength and welding quality. This is achieved by refining inclusions, refining grains, and purifying grain boundaries. Improved toughness and plasticity enhance weld crack resistance and reduce defects such as cracks and porosity at the weld joint. Compared with welding wires disclosed in existing technologies, when using the welding wire provided by this invention to weld FeMnAlC low-density steel, the overall quality of the welded joint is better, exhibiting better weld crack resistance and weld uniformity, and fewer defects such as cracks and porosity.

[0041] Therefore, the welding wire provided by this invention can fully meet the welding needs of FeMnAlC low-density steel, and is especially suitable for medium and thick plates of high Al FeMnAlC steel. It significantly improves the tensile strength and plastic toughness of the welded joints of such lightweight steels. In particular, it can optimize the microstructure of the fusion zone and effectively reduce the sensitivity to cold and hot cracking during welding, thereby significantly improving the welding quality.

[0042] Specifically, the chemical composition design of the welding wire in this invention is mainly based on:

[0043] Carbon (C): As an interstitial atom in steel, carbon is crucial for improving its strength. Excessive carbon content leads to excessive precipitation of κ-carbides in austenite, especially after welding, resulting in large κ-carbide particles that severely degrade weldability. Furthermore, high carbon content readily combines with oxygen to form porosity. Therefore, this invention limits the carbon content to 0.6-1.2%. Exemplary examples include carbon contents of 0.7%, 0.8%, 0.9%, 1.0%, and 1.1%.

[0044] Mn: Mn is an austenite-forming and stabilizing element that can expand the austenite phase region and reduce the critical quenching rate of steel. However, excessively high Mn content leads to the formation of the brittle β-Mn phase in lightweight steel, significantly reducing the material's toughness. To ensure that the matrix structure of the steel of this invention is austenitic, the Mn content needs to be no less than 25%. Therefore, this invention limits the Mn content to 25%–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 crucial for ensuring the quality and performance of the weld. Simultaneously, Al has a high liquid diffusion rate during welding, promoting the mixing and cross-diffusion of welding materials and contributing to the formation of a uniform weld. Excessive Al content reduces the strength and toughness of the weld joint and increases its susceptibility to hot cracking; conversely, insufficient Al content leads to inadequate weld joint strength. This invention limits the Al content to 7% < Al ≤ 12%. Exemplarily, Al contents are 8%, 9%, 10%, and 11%.

[0046] In welding wires used for welding low-density FeMnAlC steels, increasing the carbon (C) and aluminum (Al) content does indeed bring the benefits mentioned above (e.g., higher C content can increase strength, and higher Al content can improve weld uniformity), but it also comes with some welding challenges. Higher C and Al content increases the difficulty of welding. For example, high carbon content reduces the plasticity and toughness of the weld joint, making it more prone to cracking during welding; when the aluminum content is high, it is easy to form brittle phases, such as aluminum carbides, with other elements in the steel, which reduces the toughness of the weld joint and increases the risk of cracking.

[0047] To address and balance the aforementioned welding challenges, this invention adds trace amounts of Mg, B, and Re alloying elements and controls their content within a suitable range. This allows the welded joint to possess good plasticity and toughness, including ductility and toughness at both room and low temperatures, while taking advantage of the benefits of high C and Al content (such as increased strength and weld uniformity). This improves weld crack resistance, reduces welding defects such as cracks, and ultimately enhances weld quality.

[0048] Mg, B, and Re: The addition of trace amounts of Mg, B, and Re can refine inclusions in the weld joint, thereby improving its toughness and plasticity. Excessive addition, however, increases the number and size of inclusions, affecting the mechanical properties of the joint. Therefore, B ≤ 0.1%, Mg ≤ 0.1%, and rare earth Re ≤ 0.1%. Simultaneously, the Mg, B, and Re content must meet the requirement: 0.09% ≤ [B] + [Mg] + [Re] ≤ 0.21%, where [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 Mg, B, and Re, their synergistic effects can be better utilized to ensure that they significantly improve the toughness, plasticity, and welding quality of the welded joint while maintaining its high strength, without significantly increasing material costs. For example, controlling the total content of Mg, B, and Re within a suitable range (0.09%-0.21%) can more effectively inhibit the precipitation of harmful phases (such as κ-carbides) during welding, reduce the embrittlement of the welded joint, and improve its crack resistance.

[0049] In some embodiments, 0.01% ≤ Mg ≤ 0.1%; exemplaryly, the Mg content is 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or 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%, or 0.065%.

[0050] In some embodiments, 0.01% ≤ B ≤ 0.1%; for example, the B content is 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or 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%, or 0.065%.

[0051] In some embodiments, 0.01% ≤ Re ≤ 0.1%; for example, the Re content is 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or 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%, or 0.065%.

[0052] In some preferred embodiments, the welding wire comprises, 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%, with the remainder being Fe and unavoidable impurities.

[0053] Preferably, in the welding wire provided by the present invention, the Mg, B, and Re also satisfy the following condition: 0.5 < ([B] + [Mg]) / [Re] < 2.1, where [Mg], [B], and [Re] represent the mass percentage (%) of each element. Through relatively systematic research and theoretical analysis, the inventors believe that the amount of boron (B), magnesium (Mg), and rhenium (Re) added and their relative proportions are crucial. When the amount of these three elements added meets the following specific ratio condition, namely 0.5 < ([B] + [Mg]) / [Re] < 2.1, the synergistic effect between these elements can be maximized. This optimized element ratio strategy is beneficial in addressing the challenges to welding toughness and quality caused by increased C and Al content. In this way, not only can the toughness and plasticity of the welded joint be improved, but the best balance of material cost-effectiveness can also be achieved while ensuring the quality and high strength of the welded joint. Specifically, boron (B) in 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. When rare earth element Re is added to the welding wire in trace amounts, it can refine the grains, purify the grain boundaries, and improve the overall performance of the weld metal. Optimal welding performance can be obtained when the ratio of the total amount of boron (B) and magnesium (Mg) to rare earth element Re is between 0.5 and 2.1, because this ratio can balance the hardness, toughness, and processability of the weld metal. Excessive boron (B) and magnesium (Mg) can lead to brittle weld metal, while excessive rare earth element Re can directly affect the formability of the weld joint.

[0054] Preferably, in the welding wire provided by the present invention, the Mg, B, and Re further satisfy the following condition: 0.8 < [B] / [Mg] < 1.6, where [Mg] and [B] represent the mass percentage (%) of each element. For example, [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 and Mg elements, as well as B and Mg with other elements, further improving the toughness, plasticity, and crack resistance of the welded joint, as well as improving the welding quality and ensuring the high strength of the joint.

[0055] In one embodiment, when the welding wire is composed of C, Mn, Al, B, Mg, Re, and Fe, wherein C, B, Mg, and Re further satisfy: β = 5 × ([Mg] + [B]) + 3 × [Re] and 0.8β < [C] < 1.2β; where [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 addressing the challenges in weld toughness and quality caused by high carbon (C) and high aluminum (Al) content. In this way, while improving weld 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 welding wire of the present invention further comprises: Mo ≤ 1.0%, W ≤ 0.5%, V ≤ 0.5%, and Nb ≤ 0.5%. By adding key alloying elements (such as Mo, W, V, and Nb) to the welding wire composition and controlling their content range, the present invention helps to refine the weld microstructure, thereby further improving the toughness and plasticity of the weld joint. This composition optimization not only further improves the mechanical properties of the weld joint but also enhances the weld crack resistance and reduces defects such as cracks, thereby further improving the quality of the weld.

[0057] In embodiments of the present invention, the design basis for the additional addition of key alloying elements (such as Mo, W, Nb, V) to the welding wire composition mainly includes:

[0058] Mo, W, Nb, V: The addition of small amounts of Mo, W, Nb, and V can refine the weld microstructure through large atom dragging and the formation of MC carbides, thereby improving the toughness of the material. They can form stable carbides (MC type) with carbon, which can refine grains and stabilize austenite during welding, thus improving the mechanical properties of the weld joint. However, excessive addition increases the risk of large carbide precipitation, which can easily become crack initiation points and reduce the toughness of the material. Therefore, it is required that the welding wire contain Mo ≤ 1.0%, W ≤ 0.5%, V ≤ 0.5%, and Nb ≤ 0.5%.

[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 among Mo, W, Nb, and V can be better realized to ensure that they significantly improve the toughness and plasticity of the weld joint and the welding quality, while guaranteeing the high strength of the weld joint, without significantly increasing the material cost; among them, the requirement of 1.3% ≤ [Mo] + [W] + [V] + [Nb] ≤ 2.1% can effectively suppress the embrittlement of the weld joint caused by the precipitation of second phases such as κ-carbides in the weld joint area during the welding process.

[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%, or 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%, or 0.48%.

[0062] In some embodiments, the V content is 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or 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%, or 0.48%.

[0063] In some embodiments, the Nb content is 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or 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%, or 0.48%.

[0064] In some embodiments, the welding wire comprises, 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%, with the remainder being Fe and unavoidable impurities.

[0065] In some preferred embodiments, the welding wire comprises, 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%, with the remainder being Fe and unavoidable impurities.

[0066] When the welding wire provided by the present invention also contains alloying elements Mo, W, Nb, and V, preferably, the Mo, W, V, and Nb also satisfy: 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 amount of molybdenum (Mo), tungsten (W), vanadium (V), and niobium (Nb) added and their relative proportions are also important. When the amount of these four elements added meets the following specific ratio condition, namely 2.2 < ([W] + [V] + [Nb]) / [Mo] < 2.6, the synergistic effect between these elements can be maximized. This optimized element ratio strategy has a positive effect on solving the challenges of welding toughness and quality caused by increasing C and Al content. In this way, not only can the precipitation of second phases (such as κappa carbides) be effectively reduced or suppressed, and the element segregation phenomenon be reduced, 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-effectiveness can be achieved while ensuring the quality and high strength of the welded joint.

[0067] When the welding wire provided by this invention also contains Mo, W, Nb, and V alloying 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 improving the toughness, plasticity, and crack resistance of the welded joint, as well as improving the weld quality and ensuring the high strength of the welded joint. For example, [W]:[V]:[Nb] = 1:1:1.

[0068] When the welding wire provided by this invention also contains Mo, W, Nb, and V alloying 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; where [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 effects of B, Mg, and Re on refining inclusions in the weld joint, and the refinement of the weld microstructure by Mo, W, V, and Nb through large atom dragging and the formation of MC carbides, can be maximized. At the same time, the precipitation of second phases (such as κappa carbides) and elemental segregation can be effectively reduced or suppressed, 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] Furthermore, the welding wire provided by this invention possesses the advantages of high strength and high toughness, meaning that it is more robust and durable during welding, and less prone to breakage or deformation. Specifically, in the embodiments of this invention, the welding wire, after solution treatment, has a tensile strength ≥950MPa and an impact energy (KV2) ≥100J at -84℃. The solution treatment temperature is 1000-1100℃, and the time is 0.5-2h. For example, the solution treatment temperature is 1050℃, and the time is 1.0h or 1.5h.

[0070] It should be noted that the welding wire provided by this invention can be applied to FeMnAlC series low-density steel, i.e., welded parts, and is especially suitable for welding medium and thick plates of high-alumina FeMnAlC low-density steel.

[0071] In the general chemical formulas mentioned in this invention, the number following each element represents the mass percentage of that element in the material. Fe is a major element in steel, but its specific content is not specified.

[0072] Secondly, the present invention also provides a welding method, comprising using TIG welding process to weld FeMnAlC-based low-density steel, i.e., the workpiece, with the welding wire as described in the first aspect; the main steps of the welding include: first performing a root pass welding, and then performing the final pass welding. Exemplarily, the workpiece is a steel plate.

[0073] Compared with existing technologies, the welding method provided by this invention exhibits significant advantages when applied to FeMnAlC low-density steel, such as ease of operation, economy, and good weld adaptability / accessibility. Thanks to the special composition design of the welding wire in this invention, the welding method simplifies operation, reduces costs, and improves adaptability while still ensuring the quality and mechanical properties of the weld joint, providing an efficient and economical new option for welding FeMnAlC low-density steel. Based on the special composition design of the welding wire in this invention, the welding method eliminates traditional heat treatment processes (such as preheating before welding and slow cooling after welding), making the welding process even simpler.

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

[0075] Specifically, before the root pass welding, the surface of the workpiece to be welded is beveled, and the surface of the workpiece to be welded and the welding wire are cleaned before welding. The pre-welding cleaning includes: grinding the workpiece, removing rust, oil and dust from the surface of the workpiece and the welding wire, so as to avoid the influence of rust or oil on the weld and reduce or avoid welding defects.

[0076] In some embodiments, the bevel is a V-shaped bevel with an angle of 60° to 80°. For example, the bevel angle is 65°, 70°, or 75°.

[0077] In some embodiments, the weldment is a medium-thick plate with a thickness of 3mm to 20mm; for example, the thickness of the medium-thick plate is 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, or 18mm.

[0078] 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.

[0079] Furthermore, after cleaning, a root pass is first performed, which mainly includes: making a root pass at the root of the bevel on the back of the joint to effectively avoid angular deformation and burn-through that are easily caused by directly welding the entire part.

[0080] It is understandable that since welding stress and weld deformation are mainly caused by the shortening of the weld after welding, the appropriate extension and elongation of the weld can compensate for the shortening, thereby reducing welding stress and deformation. Therefore, after welding, immediately after each solidification of the filler metal at the joint of the workpiece, the weld can be hammered to appropriately extend the weld and reduce stress and deformation.

[0081] In some preferred embodiments, the process parameters for the formal welding include: a welding voltage of 15-19V, a welding current of 170-205A, and a welding speed of 14-19cm / min. When welding FeMnAlC low-density steel using the TIG process, selecting appropriate welding parameters is crucial for ensuring the stability of the welding process and the quality of the weld. The inventors have discovered that, for the welding wire with special composition provided by this invention (i.e., the welding wire described in the first aspect), by selecting the aforementioned synergistic welding parameters that match the welding wire described in this 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 porosity, thereby providing a more solid process foundation for manufacturing welded joints that are both strong and durable.

[0082] Specifically, using the aforementioned preferred current (170-205A) provides a suitable heat input, which effectively promotes wire penetration into the weld zone, particularly noticeable in medium-thick plate welding. A suitable heat input improves deposition efficiency, increases production efficiency, allows sufficient time for slag inclusions and porosity to escape from the weld, and promotes the crystallization process, reducing residual stress and deformation during welding, resulting in a more uniform, dense, and defect-free weld. However, excessive heat input can lead to excessively high temperatures in the welding zone, severe alloy element burn-off, and coarse grains in the weld and HAZ, thus deteriorating joint performance. Therefore, considering the special composition of the welding wire provided by this invention, a welding current of 170A-205A is preferred.

[0083] For example, in the formal welding, the welding voltage is 16V, 17V, or 18V; the welding current is 175A, 180A, 185A, 190A, 195A, or 200A; and the welding speed is 15cm / min, 16cm / min, 17cm / min, or 18cm / min.

[0084] More preferably, the process parameters for 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 the optimal balance between welding quality, mechanical properties and welding efficiency.

[0085] In some preferred embodiments, the process parameters for the root pass welding include: a welding voltage of 14-17V and a welding current of 160-170A. During the root pass welding, excessive heat input can cause the molten pool to solidify at a rate lower than the initiation rate of solidification cracks, leading to cracking. Therefore, the welding current should not be too high; it is advisable to use a current lower than the overall welding current. During welding, the current and voltage should be matched.

[0086] In some embodiments, during TIG welding, the distance between the welding torch tip and the workpiece surface is 5mm to 15mm, and the tilt angle of the welding torch is 5° to 15°, which helps to better ensure welding quality and the mechanical properties of the weld joint. For example, the distance between the welding torch tip and the workpiece surface is 7mm, 9mm, 11mm, or 13mm; and the tilt angle of the welding torch is 7°, 9°, 11°, or 13°.

[0087] It should be noted that, thanks to the special composition design of the welding wire in this invention, the welding method of this invention eliminates 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 resulting weldment is placed in a room temperature environment to cool, and the weldment is obtained after complete cooling. The welding method provided by this invention, based on a carefully designed welding wire composition, can achieve excellent welding results without the need for traditional preheating and post-weld heat treatment. For example, the reasonable addition of some key trace alloying elements to the welding wire and the control of the content of each element help to form a fine microstructure during the welding process, and effectively reduce or suppress the precipitation of second phases (such as κappa carbides) and reduce element segregation. Thus, without heat treatment, it can still maintain good joint toughness and crack resistance, as well as reduce welding stress.

[0088] When welding FeMnAlC low-density steel, especially high-alumina FeMnAlC low-density steel, welding cracks are easily generated due to the material's high sensitivity to welding thermal cycles. This is particularly true in the welding of medium and thick plates, where large thermal gradients and increased welding stress can easily lead to welding defects. To address this issue, this invention employs a multi-pass welding process.

[0089] Preferably, the number of welding passes N in the formal welding process satisfies: in, This indicates the result rounded up or down to the nearest integer; t represents the thickness of the steel plate of the weldment, in mm, and t ≥ 3 mm. Using a number of welding passes that meet the above conditions not only effectively reduces the thermal gradient and the risk of welding defects, but also ensures welding quality while maintaining production efficiency and economy. When the above conditions are not met, for example, if there are too many welding passes, it can lead to coarse grains in the heat-affected zone, reduced joint toughness, increased deformation and residual stress in the welded area, and an increased risk of reheat cracking.

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

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

[0092] In some embodiments, when the thickness of the weldment is 12mm-20mm, the number of welding passes in the formal welding is 7-8. For example, when the thickness of the weldment is 12mm... Rounding up or down to the nearest integer results in either 2 or 3, and the number of welding passes N = 7 or 8.

[0093] In some embodiments, the welding method provided by the present invention uses argon gas with a purity higher than 99.99% to prevent oxidation of more reactive elements in the workpiece and welding wire during welding. Further, the gas flow rate of the inert gas is 10-16 L / min. Exemplarily, the gas flow rate is 11 L / min, 12 L / min, 13 L / min, 14 L / min, or 15 L / min. More preferably, the gas flow rate is 12-16 L / min. For welding wires containing alloying elements such as B, Mg, and Re, using high-purity argon gas and an appropriate gas flow rate can reduce the evaporation and oxidation of these elements during welding, thereby maintaining the chemical composition and properties of the weld metal, contributing to further improvement in welding quality and reduction of welding defects. It should be noted that excessively high gas flow rates can lead to a decrease in the protective effect and excessively rapid weld cooling, thus affecting weld formation and performance.

[0094] Based on the welding wire and welding method described in this invention, the room temperature tensile strength Rm of the welded joint is ≥880MPa, the room temperature elongation after fracture A5 is ≥20%, and the V-type impact energy KV2 at -84℃ is ≥30J.

[0095] For FeMnAlC series low-density steels, the difficulty of welding (such as low joint toughness and susceptibility to cracking) limits the development of these lightweight steel materials (especially when the aluminum and carbon content is high and / or the material is thick) towards high strength and lightweight in practical applications. Since welded joints often become weak points in structures, ensuring high-quality and high-strength, high-toughness connections between these lightweight steel materials is particularly important. Based on the welding wire and welding method provided in this invention, the weldability of these lightweight steel materials can be effectively improved, achieving higher strength and lower density while significantly improving the plasticity and toughness of the welded joints, thus enhancing weld quality. This is of great significance for the widespread application of these lightweight steel materials in industry.

[0096] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0097] Example 1

[0098] This embodiment provides a welding wire with the chemical formula Fe-25Mn-8Al-0.60C-0.01Mg-0.01B-0.07Re (referred to as welding wire 1) and a diameter of 1.6mm.

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

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

[0101] S0. First, bevel the groove, then clean it before welding:

[0102] The beveling includes: using a wire cutting machine to cut a V-shaped bevel at the butt joint of the weldment, with the angle of the V-shaped bevel being 70°;

[0103] The pre-welding cleaning includes: using a grinding wheel to grind the outer periphery of the area to be welded on the workpiece until the outer periphery of the area to be welded is bright; and using ethanol to remove oil stains from the surface of the workpiece and the welding wire.

[0104] S1. Welding: The TIG welding process is adopted. First, the root pass is welded, and then the main pass is welded. After the weld has solidified, the weld is immediately tapped with a tool hammer. The vibration generated by the tool hammer releases the stress in the weld. No heat treatment is required after welding. The welded part is placed directly at room temperature to cool. After it has cooled completely, the welded part is obtained.

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

[0106] During the formal welding process, the welding current was 205A, the welding voltage was 19V, the welding passes were 8, and the welding speed was 19cm / min.

[0107] In both the root pass and the final pass, argon gas with a purity higher than 99.99% is used as the protective gas, and the inert gas flow rate is 16 L / min.

[0108] Example 2

[0109] The difference between this embodiment and Embodiment 1 is that the 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 welding method steps are similar to those in Embodiment 1.

[0110] Example 3

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

[0112] Example 4

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

[0114] Example 5

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

[0116] Example 6

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

[0118] Example 7

[0119] The difference between this embodiment and embodiment 5 is that the welding speed of the formal welding is 14 cm / min; the other parameters and welding method steps are similar to those of embodiment 5.

[0120] Example 8

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

[0122] Example 9

[0123] The difference between this embodiment and embodiment 5 is that the welding method described herein involves 4 welding passes in the formal welding process; the remaining parameters and welding method steps are similar to those in embodiment 5.

[0124] Example 10

[0125] The difference between this embodiment and embodiment 5 is that the welding method described herein involves 9 welding passes in the formal welding process; the remaining parameters and welding method steps are similar to those in embodiment 5.

[0126] Example 11

[0127] The difference between this embodiment and embodiment 5 is that the argon flow rate is 9 L / min in the welding method; the other parameters and welding method steps are similar to those in embodiment 5.

[0128] Example 12

[0129] The difference between this embodiment and Embodiment 1 is that the 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 welding method steps are similar to those in Embodiment 1.

[0130] Comparative Example 1

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

[0132] Comparative Example 2

[0133] The difference between this comparative example and Comparative Example 1 is that the welding current for the root pass is 140A and the voltage is 12V; the welding current for the final pass is 150A and the voltage is 13V; the remaining parameters and welding method steps 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 using welding wire

[0138]

[0139] As shown in Table 2, compared to Comparative Example 1, Examples 1-11, due to the use of the alloy composition of the welding wire provided by this invention (e.g., the addition of appropriate amounts of Mg, B, and Re, where Mg ≤ 0.1%, B ≤ 0.1%, and Re ≤ 0.1%), exhibit better overall mechanical properties than Comparative Example 1. While maintaining good toughness and ductility, the weld strength is significantly improved. Furthermore, the overall mechanical properties (e.g., strength) of Examples 1-5 generally follow the pattern of Example 5 > Example 4 > Example 3 > Example 2 > Example 1. This indicates that, based on the alloy composition of the welding wire provided by this invention, controlling the content and proportion of some key elements (e.g., Mg, B, and Re) is beneficial to further improve the mechanical properties of the weld (increasing strength while ensuring good toughness and ductility) and reduce welding defects. Furthermore, compared to Example 5, the overall mechanical properties of Examples 6-11 are slightly lower. This indicates that, based on the alloy composition of the welding wire provided by this invention, selecting preferred process parameters (e.g., Example 5) is beneficial to further improve the mechanical properties (e.g., strength) of the weld and reduce welding defects. Compared to Example 1, Example 12, due to the further addition of Mo, W, V and Nb, significantly improved 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 were both further improved.

[0140] Example 13

[0141] This embodiment provides a welding wire with the chemical formula 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 a diameter of 1.6mm.

[0142] This embodiment also provides a welding method, including welding a workpiece using the welding wire (welding wire 13) as described above, wherein the workpiece is a steel plate with a thickness of 12mm and the chemical formula of the workpiece is Fe-30Mn-8Al-0.9C;

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

[0144] S0. First, bevel the groove, then clean it before welding:

[0145] The beveling includes: using a wire cutting machine to cut a V-shaped bevel at the butt joint of the weldment, with the angle of the V-shaped bevel being 60°;

[0146] The pre-welding cleaning includes: using a grinding wheel to grind the outer periphery of the area to be welded on the workpiece until the outer periphery of the area to be welded is bright; and using ethanol to remove oil stains from the surface of the workpiece and the welding wire.

[0147] S1. Welding: The TIG welding process is adopted. First, the root pass is welded, and then the main pass is welded. After the weld has solidified, the weld is immediately tapped with a tool hammer. The vibration generated by the tool hammer releases the stress in the weld. No heat treatment is required after welding. The welded part is placed directly at room temperature to cool. After it has cooled completely, the welded part is obtained.

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

[0149] During the formal welding process, the welding current was 195A, the welding voltage was 18V, the welding passes were 7, and the welding speed was 16cm / min.

[0150] In both the root pass and the final pass, argon gas with a purity higher than 99.99% is used as the protective gas, and the inert gas flow rate is 12L / min.

[0151] Example 14

[0152] The difference between this embodiment and embodiment 13 is that the 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 welding method steps are similar to those in embodiment 13.

[0153] Example 15

[0154] The difference between this embodiment and embodiment 13 is that the 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 welding method steps are similar to those in embodiment 13.

[0155] Example 16

[0156] The difference between this embodiment and embodiment 13 is that the 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 welding method steps are similar to those in embodiment 13.

[0157] Example 17

[0158] The difference between this embodiment and embodiment 16 is that the welding current for the formal welding is 210A and the welding voltage is 19V; the remaining parameters and welding method steps are similar to those in embodiment 16.

[0159] Example 18

[0160] The difference between this embodiment and embodiment 16 is that the welding speed of the formal welding is 15cm / min; the other parameters and welding method steps are similar to those of embodiment 16.

[0161] Example 19

[0162] The difference between this embodiment and embodiment 16 is that the welding speed of the formal welding is 20cm / min; the other parameters and welding method steps are similar to those of embodiment 16.

[0163] Example 20

[0164] The difference between this embodiment and embodiment 16 is that the welding method described herein involves 6 welding passes in the formal welding process; the remaining parameters and welding method steps are similar to those in embodiment 16.

[0165] Example 21

[0166] The difference between this embodiment and embodiment 16 is that the welding method described herein involves 9 welding passes in the formal welding process; the remaining parameters and welding method steps are similar to those in embodiment 16.

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

[0168]

[0169]

[0170] Table 4: Mechanical properties of welded joints obtained from Examples 13-21 of the welding wire

[0171]

[0172]

[0173] As shown in Table 4, the overall mechanical properties of Examples 13-16 generally follow the pattern of Example 16 > Example 15 > Example 14 > Example 13. That is, while ensuring good toughness and plasticity, the tensile strength of the welded joint gradually increases. This indicates that by further optimizing and controlling the content and ratio 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 increasing weld strength and crack resistance, thereby reducing welding defects. Furthermore, compared with Example 16, the overall mechanical properties of Examples 17-21 are slightly decreased. This shows that when the welding wire composition is constant, by selecting preferred process parameters (such as Example 16), it is beneficial to further improve the mechanical properties of the weld, including increasing strength and improving crack resistance, thereby reducing welding defects.

[0174] To verify the quality of the welded joint obtained in the embodiments of the present invention, metallographic testing was performed. First, the sample was manually polished sequentially using five different grades of metallographic sandpaper. Then, diamond polishing paste was used on a polishing machine to polish the sample surface until it achieved a smooth, mirror-like finish. After polishing, the sample was etched with a 10% nitric acid-alcohol solution for approximately one minute, followed by thorough rinsing with distilled water and alcohol, and then dried with hot air using a hairdryer. Finally, the metallographic structure of the treated sample was observed using an optical microscope.

[0175] The metallographic structure of the welded joint obtained in Example 1 is shown below. Figure 1 .from Figure 1 It can be seen that the weld zone obtained in the embodiments of the present invention mainly consists of columnar crystals, accompanied by a small amount of fine ferrite, and the microstructure is highly uniform. The macroscopic low-magnification morphology of the welded joints obtained in Example 1 and Comparative Example 2 is shown below. Figure 2 and Figure 3 ,from Figure 2 It can be seen that the joint obtained by the embodiment of the present invention has good quality and is free from defects such as cracks and porosity. However, in Comparative Example 2, the Mg, B, and Re added to the welding wire do not conform to the present invention, and local cracks (such as...) are present. Figure 3 As shown in section A), and due to insufficient welding current, there are local defects of incomplete welding (such as...). Figure 3 (As shown in section B).

[0176] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A welding wire for welding of low-density steel, characterized in that The welding wire is applied to FeMnAlC low-density steel, and the components of the welding wire include, in percentage by mass: 0.6%≤C≤1.2%, 25%≤Mn≤35%, 7%<Al≤12%, 0.01%≤Mg≤0.1%, 0.01%≤B≤0.1%, 0.01%≤Re≤0.1%, and the rest is Fe and inevitable impurities. And the Mg, B and Re satisfy the requirement: 0.09%≤[B]+[Mg]+[Re]≤0.21%, [Mg], [B] and [Re] represent the mass percentage (%) of each element.

2. The welding wire of claim 1, wherein The components of the welding wire include, in percentage by mass: 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 inevitable impurities.

3. The welding wire of claim 1, wherein, The Mg, B and Re also satisfy: 0.5<([B]+[Mg]) / [Re]<2.1, and / or, 0.8<[B] / [Mg]<1.

6.

4. The welding wire of claim 1, wherein, The components of the welding wire also include: Mo≤1.0%, W≤0.5%, V≤0.5%, Nb≤0.5%.

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

6. The welding wire of claim 5, wherein, 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 of claim 5, wherein, 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.

8. A welding method characterized by, The welding method comprises welding a FeMnAlC low-density steel welding piece by using the welding wire according to any one of claims 1-7 by adopting a TIG welding process; and main steps of the welding include: first performing a backing welding, and then performing a formal welding.

9. The welding method of claim 8, wherein, No preheating is performed before the welding, and no heat treatment is performed after the welding; and / or, The thickness of the welding piece t≥3mm, and the welding pass number N of the formal welding≥5; And / or, The process parameters of the backing welding include: a welding current of 160-170A; and the process parameters of the formal welding include: a welding current of 170-205A.

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

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