Stranded low-temperature phase change welding wire and preparation and welding method thereof

Abstract

The invention relates to the technical field of high-strength steel material welding, in particular to a stranded low-temperature phase change welding wire and a preparation and welding method thereof. A stranded structure formed by the center wire and the peripheral wires is adopted, the chemical component proportion of the whole welding wire is accurately controlled by changing the number, the diameter and the combination mode of the center wire and the peripheral wires, particularly, the chromium content is controlled to be 9%-12%, and the nickel content is controlled to be 8%-11%; the martensite phase transformation starting temperature of weld metal is accurately set in an ideal interval from 200 DEG C to room temperature, beneficial pressure stress is actively generated by utilizing martensite phase transformation of the weld metal in the specific temperature interval, inherent welding residual tensile stress is counteracted, and active and in-situ regulation and control of the welding residual stress are achieved; in addition, a magnetic field unit is applied in the martensite phase transformation process, and the regulation and control effect of the residual stress is further improved.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel welding technology, and in particular to a twisted-strand low-temperature phase change welding wire with active stress regulation, and its preparation and welding method. Background Technology

[0002] Low-alloy high-strength steels, such as pipeline steel X80, bridge steel Q345qD, and marine steel EH36, are widely used in oil and gas pipelines, engineering machinery, and shipbuilding due to their high strength, high toughness, and good weldability. Welding is a major manufacturing process for these steel structures, and the quality of their joints directly affects the safety and service life of the overall structure.

[0003] Currently, the materials used for welding low-alloy high-strength steel are mainly solid welding wire, flux-cored welding wire, and technologies developed to improve efficiency such as hot-wire TIG and oscillating welding. Traditional solid welding wire has poor flexibility in composition adjustment, making it difficult to precisely control the phase transformation behavior of the weld. While flux-cored welding wire has adjustable composition, its manufacturing process is complex, its wire feeding stability is poor, and its design focuses primarily on conventional mechanical properties, lacking a systematic product design for actively controlling residual stress through phase transformation. To improve welding quality, existing technologies have introduced magnetic field-assisted processes, acting on the molten pool, arc, or the welding wire itself during the high-temperature welding stage. The main goal is to improve the stability of the welding process and the quality of weld formation; this type of magnetic field technology essentially belongs to welding process control. Neither traditional welding materials nor existing magnetic field-assisted processes have fundamentally changed the unfavorable stress state of the weld joint, which is dominated by residual tensile stress. For the solid-state phase transformation behavior that occurs in the low-temperature range after welding, and how to actively and in-situ utilize this phase transformation to generate beneficial compressive stress and precisely control the final residual stress field through a combination of material design and external field intervention, existing technologies have not yet provided effective solutions. Summary of the Invention

[0004] In view of this, the present invention proposes a stranded low-temperature phase change welding wire and its preparation and welding method. The stranded low-temperature phase change welding wire of the present invention combines the advantages of adjustable composition of flux-cored welding wire and good wire feeding performance of solid welding wire. Through a unique stranded structure design and precise alloy element ratio, the martensitic phase transformation point (Ms point) of the weld metal is preset in a low-temperature range. During the welding cooling process, the weld metal undergoes a martensitic phase transformation within the stated temperature range. Utilizing the phase transformation volume expansion effect, beneficial compressive residual stress is actively generated inside the weld joint, thereby offsetting the inherent welding residual tensile stress. Furthermore, a magnetic field is applied during the low-temperature martensitic phase transformation of the weld to regulate the process of the martensitic low-temperature phase transformation, thereby synergistically achieving a superior residual stress control effect.

[0005] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a stranded low-temperature phase change welding wire, the welding wire comprising a central wire and peripheral wires, the peripheral wires being spirally wound around the periphery of the central wire to form the main body of the welding wire; the peripheral wires comprising chromium wire and nickel wire, and the central wire comprising iron-manganese based welding wire.

[0006] Based on the above technical solutions, the preferred method is to use chromium accounting for 9-12%, nickel accounting for 8-11%, carbon accounting for ≤0.3%, manganese accounting for 1-2%, and the remainder being iron and impurities, based on a total mass percentage of 100%.

[0007] Based on the above technical solutions, preferably, the chromium content of the chromium wire is ≥99.0wt%, and the nickel content of the nickel wire is ≥99.5wt%.

[0008] The composition and content of each element are designed in a coordinated manner to control the martensitic transformation initiation temperature (Ms point) of the weld metal formed by the welding wire within the range of 200℃ to room temperature (about 30℃). This is the foundation and key to ensuring that the weld metal can undergo martensitic transformation within this temperature range during the subsequent welding cooling process. Then, by utilizing its phase transformation volume expansion effect, beneficial compressive residual stress is actively generated inside the weld joint, thereby offsetting the inherent welding residual tensile stress.

[0009] Manganese (Mn) is entirely supplied by the center wire of the iron-manganese based solid welding wire. The content of chromium (Cr) and nickel (Ni) is precisely controlled by adjusting the number of chromium and nickel wires and their diameter ratio with the center wire. The content of Cr and Ni also affects the toughness and strength of the weld. Too high a Cr and Ni content will lead to a decrease in weld toughness, while too low a content will cause the weld to fail to reach the strength of the base material or even increase brittleness and cracks.

[0010] Based on the above technical solutions, preferably, the martensitic phase transformation initiation temperature of the welding wire is in the range of 200~30℃.

[0011] Secondly, a method for preparing the stranded low-temperature phase change welding wire as described above is provided, comprising the following steps: S1, perform surface cleaning and drying on the center and outer wires that meet the requirements; S2 is formed by spirally winding the outer wires around the center wire as the core.

[0012] Based on the above technical solutions, preferably, in step S1, the center wire includes a low-carbon steel welding wire with a diameter of 1.00~1.60mm; the outer wire includes 3~6 welding wires, preferably, the outer wire includes 4 welding wires, and the diameter of a single welding wire is 0.25~0.4mm.

[0013] Based on the above technical solution, a further preferred embodiment is that the center wire is selected from iron-manganese based welding wire with a diameter of 1.2 mm, the outer wire is selected from two chromium wires and a nickel wire with a single wire diameter of 0.3 mm, and the diameter of the center wire is 4 times the diameter of a single outer wire.

[0014] Based on the above technical solutions, preferably, a precision wire cutting machine is used to cut each wire into rolls of uniform length. All the cut wires are then immersed in acetone (analytical grade) and ultrasonically cleaned to thoroughly remove surface grease, drawing lubricant, and other contaminants. Subsequently, they are rinsed with anhydrous ethanol and thoroughly dried in a nitrogen atmosphere drying oven at 50°C.

[0015] Based on the above technical solutions, preferably, in step S2, the twist angle of the outer wire spirally wound around the outer periphery of the central wire is 20~30° and the twist pitch is 7~18mm.

[0016] Based on the above technical solutions, a further preferred embodiment is that the twist angle is 25° and the twist pitch is 11mm.

[0017] However, the stranded welding wire with its special central matrix and peripheral alloy in this invention is prone to uneven melting during welding, leading to Ms point fluctuations and localized burn-off of alloying elements. Therefore, to overcome this problem, this invention achieves lower heat input by controlling the wire feed speed and welding voltage during welding, thereby mitigating the burn-off and evaporation of alloying elements. The wire feed speed (Ws) directly determines the welding current (I) and deposition rate, while the welding voltage (V) determines the arc length and energy distribution. When Ws and V are within a suitable range and properly matched, the arc is stable, and the central wire and peripheral thin wires can achieve near-synchronous melting. At this time, high-melting-point alloying elements such as chromium and nickel can fully integrate into the iron-based molten droplet, achieving premixing before entering the molten pool, greatly reducing Ms point fluctuations caused by compositional inhomogeneity. S Point fluctuations and localized burn-off of alloying elements.

[0018] Thirdly, a welding method for the stranded low-temperature phase change welding wire as described above is provided. Preferably, the wire feeding speed during welding is 8.0~12.0m / min and the welding voltage is 25.6~28.8V.

[0019] Welding using this process yields high-quality welds with uniform composition (Cr and Ni content fluctuations < ±0.5%), stable MS points, and significant residual compressive stress. If Ws is below 8.0 m / min, the weld filler is insufficient, and the content of the outer wire decreases due to inevitable burn-off. If Ws is above 12.0 m / min, the heat input is too high, and the higher the welding current, the higher the arc voltage, which leads to large droplet repulsion transition, causing welding spatter, overall transitional burn-off of alloying elements, and weakening the low-temperature phase transformation effect.

[0020] Based on the above technical solutions, a further preferred embodiment is that the wire feeding speed during welding is 10.00 m / min and the welding voltage is 27.2 V.

[0021] Based on the above technical solutions, preferably, the welding also includes a magnetic field application unit step. After welding is completed, the weld begins to cool. When the weld temperature cools to below the martensitic phase transformation start temperature, an external pulsed magnetic field is applied to the weld metal.

[0022] The magnetic field application unit in this invention is an optimized component that works in synergy with the welding wire. Its function is to enhance and optimize the low-temperature martensitic phase transformation process. The core mechanism is as follows: a pulsed magnetic field induces eddy currents in the conductive weld pool and the solid phase transformation metal, generating strong Lorentz forces and magnetization energy. This energy promotes phase transformation nucleation, refines the phase transformation microstructure, and harmonizes the stress field. The introduction of the magnetic field promotes the nucleation and growth of martensite, thereby increasing its content and further improving the uniformity and magnitude of the stress field.

[0023] Based on the above technical solutions, preferably, the magnetic field induction intensity range of the magnetic field is 0.1~1.5T; more preferably, the magnetic field induction intensity range is 0.5T.

[0024] The twisted-strand low-temperature phase change welding wire with active stress regulation of this invention has the following advantages over existing technologies: This invention employs a stranded structure consisting of a central wire and peripheral wires, and precisely controls the overall chemical composition of the welding wire, particularly controlling the chromium (Cr) content to 9%–12% and the nickel (Ni) content to 8%–11%. This allows the martensitic transformation initiation temperature (Ms point) of the weld metal to be precisely set within the ideal range of 200°C to room temperature. During the cooling process to room temperature after welding, the weld metal undergoes a martensitic transformation within this specific temperature range. Utilizing the volume expansion effect, beneficial compressive stress is actively generated within the weld joint, effectively counteracting the inherent residual tensile stress. This not only significantly reduces the risk of component deformation and cracking but also eliminates the need for complex post-heat treatment, achieving active, in-situ control of residual welding stress. This invention also integrates the specific stranding process of the welding wire with magnetic field-assisted welding, forming a complete residual stress control solution. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the main structure of the stranded welding wire of the present invention; Figure 2 This is a flow chart of the stranded welding wire preparation process of the present invention; Figure 3 This is a schematic diagram of the external pulsed magnetic field assisted welding of the present invention; Figure 4 This is a schematic diagram of the cross-section of the stranded welding wire prepared in Embodiment 1 of the present invention; Figure 5 This is a data graph showing the reduction in longitudinal tensile stress in the weld seam produced by the stranded welding wire prepared in Example 1 of the present invention. Figure 6 A data graph showing the reduction in transverse tensile stress in the weld seam welded using stranded welding wire prepared in Example 1 of the present invention; Figure 7 This is a schematic diagram of the cross-section of the stranded welding wire prepared in Example 4 of the present invention; Figure 8 This is a SEM microstructure image of the weld metal sample in Example 8 of the present invention without an applied magnetic field. Figure 9 This is a SEM microstructure image of the weld metal sample when a magnetic field is applied in Example 8 of the present invention. Figure 10 The images show actual photographs of the stranded welding wire of this invention and a diagram of the welding process. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 Preparation of a stranded low-temperature phase change welding wire that can reduce residual stress.

[0029] 1. Select commercially available Fe-based wire, Ni wire (Ni content ≥ 99.5%), and Cr wire (Cr content ≥ 99.0%) as raw materials, and use a precision wire cutting machine to cut each wire into rolls of uniform length.

[0030] 2. Immerse all the slit filaments in acetone (analytical grade) and perform ultrasonic cleaning to thoroughly remove surface grease, drawing lubricant, and other contaminants. Then rinse with anhydrous ethanol and dry thoroughly in a nitrogen atmosphere drying oven at 50°C.

[0031] 3. Using a laser diameter gauge, select 10 points at equal intervals along the length of each wire to measure the diameter, calculate the average and standard deviation, and record the precise original diameter. Perform room temperature tensile tests using a universal testing machine, referring to national standards, to determine the tensile strength and elongation after fracture of each individual wire. Quantitatively analyze the chemical composition of the wire using spark direct-reading spectroscopy to ensure it meets the preset targets. Summarize and enter the measured data on the original diameter, tensile strength, elongation, and chemical composition of each individual wire.

[0032] 4. Select one 1.20 mm diameter iron-manganese based welding wire (model ER50-6), two 0.3 mm diameter pure chromium wires, and two 0.3 mm diameter pure nickel wires from the basic database. The ratio of the center wire diameter to the outer wire diameter (1.2 mm & 0.3 mm) is designed to ensure a balance between sufficient center matrix volume and the number of outer alloy wires, and is determined through the following calculations: The center wire is selected from commercially available iron-manganese based welding wire (ER50-6), and its composition is shown in Table 1.

[0033] Table 1. Chemical elemental composition (%) of ER50-6

[0034] Based on the content of each element in Table 1 (average values ​​for C, Si, and Mn), the Fe content is calculated as: (100 - 0.105 - 0.975 - 1.625 - 0.025 - 0.025 - 0.15 - 0.15 - 0.5 - 0.15 - 0.03)% = 96.265%.

[0035] The relative atomic masses of Fe are approximately 56, Cr approximately 52, Ni approximately 59, and Mn approximately 55. Let the radius of the central wire be *a*, and the radius of the outer wire be *b*. Both the central and outer wires can be considered as homogeneous alloy wires. The content ratio of each element can then be expressed by the surface mass of the cross-section. To simplify the calculations, within the allowable error range, we only consider iron, chromium, nickel, and manganese in the central and outer wires, resulting in: Total surface mass:

[0036] Cr surface quality:

[0037] Ni surface quality:

[0038] The percentage of Cr in the total welding wire is: w1 = m2 / M = 9%-12%. The percentage of Ni in the total welding wire content is: w2 = m3 / M = 8%-11%. The calculation yields: 3.953 ≤ a / b ≤ 4.149, which rounds up to a / b = 4.

[0039] 5. Using the 1.20 mm diameter iron-manganese-based welding wire as the center, strands of pure chromium wire (0.3 mm diameter), pure nickel wire (0.3 mm diameter), pure chromium wire (0.3 mm diameter), and pure nickel wire (0.3 mm diameter) are sequentially twisted clockwise at a 25° winding angle. This stranded wire is loaded into the wire feeding reel of the stranding machine as the main body of the stranded wire. The equipment is started, and the spindle speed and traction wheel feed speed of the stranding machine are set according to the target twist pitch L=11 mm. Under constant tension control, the center wire and the four outer wires are synchronously and continuously stranded to form the low-temperature phase change stranded welding wire. The composition of the low-temperature phase change stranded welding wire is shown in Table 2 below.

[0040] Table 2

[0041] The key design feature of this embodiment is that, in order to achieve an overall Cr content of 9% and Ni content of 10% in the welding wire, and to ensure uniform composition after melting, a stranded configuration of "1 thick center wire + 4 thin outer wires" was selected (see cross-sectional diagram). Figure 4 (As shown). Calculations show that the center wire (ER50-6) provides the main Fe and Mn matrix, while two pure Cr wires and two pure Ni wires serve as sources of alloying elements. The 4-fold ratio of the center wire diameter to the outer wire diameter (1.2 mm & 0.3 mm) is designed to ensure a balance between sufficient center matrix volume and the number of outer alloy wires.

[0042] Example 2 Preparation of a stranded low-temperature phase change welding wire that can reduce residual stress.

[0043] The preparation method of this embodiment is basically the same as that of Example 1, except that: 4. In the basic database, there is one 1.20 mm diameter iron-manganese based welding wire (model ER50-6), two 0.28 mm diameter pure chromium wires, and two 0.28 mm diameter pure nickel wires, which are the center wire and outer wire of the stranded low-temperature phase change welding wire, respectively.

[0044] 5. Centered on the 1.20 mm diameter iron-manganese-based welding wire, strands of pure chromium wire (0.28 mm diameter), pure nickel wire (0.28 mm diameter), pure chromium wire (0.28 mm diameter), and pure nickel wire (0.28 mm diameter) are sequentially twisted clockwise at a 25° winding angle. This stranded welding wire is loaded into the wire feeding reel of the stranding machine. The equipment is started, and the spindle speed and traction wheel feed speed of the stranding machine are set according to the target twist pitch L=10 mm. Under constant tension control, the center wire and the four outer wires are synchronously and continuously twisted together to form the low-temperature phase change stranded welding wire.

[0045] Example 3 Preparation of a stranded low-temperature phase change welding wire that can reduce residual stress.

[0046] The preparation method of this embodiment is basically the same as that of Example 1, except that: 4. In the basic database, there is one 1.10 mm diameter iron-manganese based welding wire (model ER50-6), two 0.29 mm diameter pure chromium wires, and two 0.29 mm diameter pure nickel wires, which are the center wire and outer wire of the stranded low-temperature phase change welding wire, respectively.

[0047] 5. Centered on the 1.10 mm diameter iron-manganese-based welding wire, a pure chromium wire with a diameter of 0.29 mm, a pure nickel wire with a diameter of 0.29 mm, a pure chromium wire with a diameter of 0.29 mm, and a pure nickel wire with a diameter of 0.33 mm are sequentially twisted clockwise at a winding angle of 25°. This stranded welding wire is loaded into the wire feeding reel of the stranding machine. The equipment is started, and the spindle speed and traction wheel feed speed of the stranding machine are set according to the target twist pitch L=9.6 mm. Under constant tension control, the center wire and the four outer wires are synchronously and continuously twisted together to form the low-temperature phase change stranded welding wire.

[0048] Comparative Example 1 Preparation of a stranded low-temperature phase change welding wire that can reduce residual stress.

[0049] The preparation method of this embodiment is basically the same as that of Example 1, except that: 4. In the basic database, there is one 1.20 mm diameter iron-manganese based welding wire (model ER50-6), two 0.24 mm diameter pure chromium wires, and two 0.24 mm diameter pure nickel wires, which are the center wire and outer wire of the stranded low-temperature phase change welding wire, respectively.

[0050] 5. Centered on the 1.20 mm diameter iron-manganese-based welding wire, strands of pure chromium wire, pure nickel wire, pure chromium wire, and pure nickel wire with a diameter of 0.24 mm are sequentially twisted clockwise at a winding angle of 25°. These strands are loaded into the wire feeding reel of the stranding machine as the main body of the stranded welding wire. The equipment is started, and the spindle speed and traction wheel feed speed of the stranding machine are set according to the target twist pitch L=9.7 mm. Under constant tension control, the central wire and the four outer wires are synchronously and continuously stranded to form the low-temperature phase change stranded welding wire 1.

[0051] Comparative Example 2 Preparation of a stranded low-temperature phase change welding wire that can reduce residual stress.

[0052] The preparation method of this embodiment is basically the same as that of Example 1, except that: 4. In the basic database, there is one 1.20 mm diameter iron-manganese based welding wire (model ER50-6), three 0.30 mm diameter pure chromium wires, and two 0.32 mm diameter pure nickel wires, which are the center and outer wires of the stranded low-temperature phase change welding wire.

[0053] 5. Centered on the 1.20 mm diameter iron-manganese-based welding wire, strands of pure chromium wire (0.30 mm diameter), pure nickel wire (0.32 mm diameter), pure chromium wire (0.30 mm diameter), pure nickel wire (0.32 mm diameter), and pure chromium wire (0.30 mm diameter) are sequentially twisted clockwise at a 25° winding angle. This stranded welding wire is loaded into the wire feeding reel of the stranding machine. The equipment is started, and the spindle speed and traction wheel feed speed of the stranding machine are set according to the target twist pitch L = 10.2 mm. Under constant tension control, the center wire and the five outer wires are synchronously and continuously twisted together to form the low-temperature phase change stranded welding wire 2.

[0054] The low-temperature phase transformation stranded welding wires prepared in Examples 1-3 and Comparative Examples 1-2, as well as the commercially available ER50-6 welding wire from Example 1, were subjected to MIG gas shielded welding on low-alloy high-strength steel plates. The heat input was controlled during the welding process to allow the weld to undergo normal melting and cooling. The wire feed speed (Ws) was controlled at 10.0 m / min, and the welding voltage (V) at 27.2 V to ensure uniform weld composition. S The weld was stable. After welding, the chemical composition, residual stress, and mechanical properties of the weld were analyzed using conventional methods. The results are shown in Table 3.

[0055] Table 3

[0056] In embodiments 1-3 of this invention, the Ms point is precisely controlled within the ideal range of 200°C to room temperature, achieving optimal matching between the phase transformation volume expansion and cooling contraction processes. This generates significant and uniform compressive residual stress, resulting in a prominent effect of actively counteracting welding tensile stress. The performance is significantly improved compared to ordinary commercially available welding wires, especially in embodiment 1, where the longitudinal and transverse tensile stress data of the weld are as follows: Figure 5 and Figure 6 As shown, compared with conventional welding wire, both longitudinal and transverse tensile stresses are significantly reduced. Furthermore, while achieving excellent stress control, it exhibits no tendency to crack, achieving an optimal balance between strength and toughness. However, when the Cr content is below 9% or above 12%, or the Ni content is below 8% or above 11% (as in Comparative Examples 1 or 2), it is impossible to simultaneously achieve the dual goals of generating high-amplitude compressive residual stress from low-temperature phase transformation and maintaining good weld toughness.

[0057] Example 4 Preparation of a stranded low-temperature phase change welding wire that can reduce residual stress.

[0058] The preparation of this embodiment is basically the same as that of Example 1, except that: 4. Select one 1.00 mm diameter iron-manganese based welding wire (model ER50-6), two 0.25 mm diameter pure chromium wires, and two 0.25 mm diameter pure nickel wires from the basic database.

[0059] 5. Using the aforementioned 1.0 mm diameter iron-manganese-based welding wire as the center, sequentially twist together pure chromium wire (0.25 mm diameter), pure nickel wire (0.25 mm diameter), pure chromium wire (0.25 mm diameter), and pure nickel wire (0.25 mm diameter) at a clockwise winding angle of 20°. This stranded welding wire is loaded into the wire feeding reel of the stranding machine. The equipment is started, and the spindle speed and traction wheel feed speed of the stranding machine are set according to the target lay length L = 7 mm. Under constant tension control, the center wire and four outer wires are simultaneously and continuously stranded to form the low-temperature phase change stranded welding wire. The composition of the low-temperature phase change stranded welding wire is the same as in Example 1. Its cross-sectional diagram of the stranded configuration of "1 thick center wire + 4 thin outer wires" is shown below. Figure 7 As shown.

[0060] Example 5 Preparation of a stranded low-temperature phase change welding wire that can reduce residual stress.

[0061] The preparation of this embodiment is basically the same as that of Example 1, except that: 4. From the basic database, select one 1.60 mm diameter iron-manganese based welding wire (model ER50-6), two 0.4 mm diameter pure chromium wires, and two 0.4 mm diameter pure nickel wires. The key design of this embodiment is: to achieve an overall Cr content of approximately 9% and a Ni content of approximately 10% in the welding wire, and to ensure uniform composition after melting, a stranded configuration of "1 thick center wire + 4 thin outer wires" was selected. Through calculation, the center wire (ER50-6) provides the main Fe and Mn matrix, while the two pure Cr wires and two pure Ni wires serve as sources of alloying elements. The 4-fold relationship between the diameters of the center wire and the outer wires (diameter relationship calculation is the same as in Example 1) is designed to ensure a balance between sufficient center matrix and the number of outer alloy wires, thereby achieving the target composition and good stranding processability.

[0062] 5. Using the 1.60 mm diameter iron-manganese-based welding wire as the center, strands of pure chromium wire, pure nickel wire, pure chromium wire, and pure nickel wire with a diameter of 0.4 mm are sequentially twisted clockwise at a winding angle of 20°. These strands are loaded into the wire feeding reel of the stranding machine as the main body of the stranded welding wire. The equipment is started, and the spindle speed and traction wheel feed speed of the stranding machine are set according to the target twist pitch L=18 mm. Under constant tension control, the center wire and the four outer wires are synchronously and continuously stranded to form the low-temperature phase change stranded welding wire. The composition of the low-temperature phase change stranded welding wire is the same as in Example 1.

[0063] Example 6 Using the stranded low-temperature phase change welding wire prepared in Example 1, MIG gas shielded welding was performed on a low-alloy high-strength steel plate. The wire feed speed (Ws) was controlled at 8.0 m / min, and the welding voltage (V) was controlled at 25.6V.

[0064] Example 7 Using the stranded low-temperature phase change welding wire prepared in Example 1, MIG gas shielded welding was performed on a low-alloy high-strength steel plate. The wire feed speed (Ws) was controlled at 12.0 m / min, and the welding voltage (V) was controlled at 28.8V.

[0065] Comparative Example 3 Using the stranded low-temperature phase change welding wire prepared in Example 1, MIG gas shielded welding was performed on a low-alloy high-strength steel plate. The wire feed speed (Ws) was controlled at 7.0 m / min, and the welding voltage (V) was controlled at 24.5V.

[0066] Comparative Example 4 Using the stranded low-temperature phase change welding wire prepared in Example 1, MIG gas shielded welding was performed on a low-alloy high-strength steel plate. The wire feed speed (Ws) was controlled at 13.0 m / min, and the welding voltage (V) was controlled at 29.5V.

[0067] The weld properties obtained from Examples 6-7 and Comparative Examples 3-4 were tested, and the results are shown in Table 4.

[0068] Table 4

[0069] As shown in Table 4, within the range of wire feed speed of 8.0–12.0 m / min and welding voltage of 25.6–28.8 V (Examples 6 and 7), the martensitic transformation initiation temperature (Ms point) of the weld metal stabilized at 180–200 °C, the longitudinal residual tensile stress of the weld was significantly reduced (≤+318 MPa), and even compressive stress (-25 MPa) appeared in the transverse direction, indicating that the welding residual stress was effectively and actively controlled.

[0070] When the wire feeding speed is below 8.0 m / min (Comparative Example 3) or above 12.0 m / min (Comparative Example 4), the weld composition fluctuates more, the Ms point shifts, the stress control effect decreases significantly, and even high residual tensile stress appears, verifying the importance of welding process parameters in achieving the effect of the present invention.

[0071] Example 8 A comparative experiment on welding with and without a magnetic field applied.

[0072] Using the stranded low-temperature phase change welding wire prepared in Example 1, MIG gas shielded welding was performed on low-alloy high-strength steel plates. Heat input was controlled during the welding process to ensure the weld underwent normal melting and cooling. To clearly distinguish between the inherent function of the welding wire and the optimization effect of the magnetic field assistance, the following two sets of experiments were conducted.

[0073] Experimental Group: An external pulsed magnetic field was applied during the cooling process after welding. MIG gas shielded welding was performed on low-alloy high-strength steel plates. Heat input was controlled during the welding process to allow the weld to undergo normal melting and cooling. The wire feed speed (Ws) was controlled at 10.0 m / min, and the welding voltage (V) at 27.2 V. After the welding arc extinguished, the weld began to cool. The weld temperature was monitored or predicted in real time using an infrared thermometer or a prediction model based on welding parameters. When the weld temperature cooled to below its Ms point (200°C) until room temperature, the magnetic field application unit was activated, with a magnetic induction intensity of 0.5 T, a pulsed magnetic field, a frequency of 5 Hz, and a duty cycle of 50%. The excitation coils of the magnetic field application unit were symmetrically arranged on both sides of the weld to ensure uniform magnetic field coverage of the entire weld area. The magnetic field was applied continuously from below the Ms point until the weld temperature dropped to room temperature.

[0074] The application of the pulsed magnetic field is achieved through an independent control system. This system includes a pulsed magnetic field power supply, an excitation coil, a temperature sensor, and a synchronization controller. The pulsed magnetic field power supply is a high-power pulsed current generator, whose output parameters (intensity 0.1~1.5T, frequency, duty cycle, etc.) are independently adjustable. The excitation coils are symmetrically arranged on both sides of the weld seam, with their input terminals connected to the positive and negative output terminals of the pulsed magnetic field power supply, respectively. The output terminals of the coils are connected to the workpiece grounding terminal, forming an independent electrical circuit. During welding, the welding power supply and welding torch operate; when the temperature sensor detects that the temperature of a certain section of the weld seam has cooled below the Ms point, the synchronization controller sends a command to disconnect the welding power supply output and immediately start the pulsed magnetic field power supply to power the excitation coil until the temperature of that section drops to near room temperature, after which it is shut off.

[0075] Control group: Except for the absence of any magnetic field, all other welding parameters, materials and process conditions were exactly the same as those of the experimental group.

[0076] After welding, the two groups of samples underwent the same microstructure characterization process, and the results are as follows. Figure 8 and Figure 9 As shown. We can see the experimental group ( Figure 9 After applying a magnetic field during the martensitic transformation stage, the martensite laths become finer and more uniformly distributed, indicating that the inherent mechanism of compressive stress generation through low-temperature martensitic transformation in the welding wire of this invention is enhanced under the synergistic effect of an external pulsed magnetic field. The eddy currents and Lorentz forces induced by the magnetic field refine the transformation microstructure and promote the uniform distribution of transformation stress, thus improving the uniformity of the beneficial compressive stress distribution generated by the transformation. This further enhances the overall mechanical properties of the welded joint.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A stranded low-temperature phase change welding wire, characterized in that: The welding wire includes a center wire and an outer wire. The outer wire is spirally wound around the center wire to form the main body of the welding wire. The outer wire includes chromium wire and nickel wire, and the center wire includes iron-manganese-based welding wire.

2. The stranded low-temperature phase change welding wire as described in claim 1, characterized in that: Based on a total mass percentage of 100%, the main body of the welding wire contains 9-12% chromium, 8-11% nickel, ≤0.3% carbon, 1-2% manganese, and the remainder is iron and impurities.

3. The stranded low-temperature phase change welding wire as described in claim 1, characterized in that: The chromium content of the chromium wire is ≥99.0 wt%, and the nickel content of the nickel wire is ≥99.5 wt%.

4. The stranded low-temperature phase change welding wire as described in claim 1, characterized in that: The martensitic phase transformation initiation temperature of the welding wire is in the range of 200~30℃.

5. A method for preparing a stranded low-temperature phase change welding wire as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1, perform surface cleaning and drying on the center and outer wires that meet the requirements; S2 is formed by spirally winding the outer wires around the center wire as the core.

6. The method for preparing the stranded low-temperature phase change welding wire as described in claim 5, characterized in that: In step S1, the center wire includes a low-carbon steel welding wire with a diameter of 1.00~1.60mm; the outer wire includes 3~6 welding wires, each with a diameter of 0.25~0.4mm.

7. The method for preparing the stranded low-temperature phase change welding wire as described in claim 5, characterized in that: In step S2, the twist angle of the outer wire spirally wound around the outer periphery of the central wire is 20~30° and the twist pitch is 7~18mm.

8. A welding method for a stranded low-temperature phase change welding wire as described in any one of claims 1 to 4, characterized in that: The welding wire feed speed during welding is 8.0~12.0m / min, and the welding voltage is 25.6~28.8V.

9. A welding method for the stranded low-temperature phase change welding wire as described in claim 8, characterized in that: The welding process also includes a magnetic field application step. After welding is completed, the weld begins to cool. When the weld temperature cools to below the martensitic transformation initiation temperature, an external pulsed magnetic field is applied to the weld metal.

10. The welding method of the stranded low-temperature phase change welding wire as described in claim 9, characterized in that: The magnetic field induction intensity ranges from 0.1 to 1.5 T.

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