Fe-Ni-Nb low-stress welding wire for dissimilar steel, preparation method and welding method

Abstract

The embodiment of the invention provides a Fe-Ni-Nb low-stress welding wire for dissimilar steel, a preparation method and a welding method, the Fe-Ni-Nb low-stress welding wire comprises powder and a welding skin, the powder comprises the following components in percentage by mass: 35.0-40.0% of Ni, 35.0-40.0% of Nb, 2.0-4.0% of Al, 2.0-4.0% of Ti, 0.5-2.0% of V, 0.5-2.0% of B and the balance of Fe, and the sum of the mass percentages of the components is 100%. A welding seam obtained by the welding wire is good in toughness matching, the joint stress is lower than that of a traditional welding wire, and the long-term service requirement is met.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, specifically to a Fe-Ni-Nb low-stress welding wire for dissimilar steels, its preparation method, and its welding method. Background Technology

[0002] With the continuous development of the power industry, power plant equipment is facing increasingly harsh operating environments, including higher operating temperatures, pressures, and complex chemical media. In this context, a single type of steel cannot simultaneously meet all performance requirements. For example, in boiler and steam piping systems, components near the combustion zone need excellent high-temperature strength and oxidation resistance, while other parts may have higher requirements for toughness, machinability, or corrosion resistance. Therefore, combining steels with different performance characteristics has become an inevitable choice for optimizing the overall performance of equipment. Through dissimilar steel welding structures, different parts of the equipment can be adapted to their specific operating conditions, thereby improving overall service performance.

[0003] The stable operation of power plant equipment is directly related to the reliability of the power system. However, the 12Cr1MoV / T91 dissimilar steel joints widely used in thermal power boilers frequently fail. The root cause of the failure lies in the significant differences in the microstructure and properties of the two materials: 12Cr1MoV is mainly ferrite-pearlite, characterized by low strength but good toughness; while T91 is a martensitic steel with high strength but poor toughness. Currently, there is a lack of welding materials that are perfectly compatible with T91, leading to significant stress concentration and mechanical property incompatibility in the joint area, thus causing early failure.

[0004] To address this issue, this invention develops a special Fe-Ni-Nb welding wire suitable for welding dissimilar steels 12Cr1MoV and T91. Through scientific alloy composition design, a martensite and austenite dual-phase structure is formed in the weld area, effectively alleviating stress concentration in the joint and significantly reducing the risk of cracking under long-term high-temperature and high-pressure service conditions, thereby improving the service life and reliability of the joint. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art, and provides a Fe-Ni-Nb low-stress welding wire for dissimilar steels, a preparation method thereof, and a welding method thereof.

[0006] In a first aspect, embodiments of the present invention provide a Fe-Ni-Nb low-stress welding wire for dissimilar steels, comprising flux powder and welding scale; wherein... The powder comprises the following components by mass percentage: Ni 35.0~40.0%, Nb 35.0~40.0%, Al 2.0~4.0%, Ti 2.0~4.0%, V 0.5~2.0%, B 0.5~2.0%, and the remainder is Fe. The sum of the mass percentages of the above components is 100%.

[0007] Furthermore, the powder comprises the following components by mass percentage: Ni 37%, Nb 37%, Al 3%, Ti 3%, V 1.3%, B 1.3%, and the remainder is Fe, with the sum of the mass percentages of the above components being 100%.

[0008] Furthermore, the purity of each raw material component alloy powder in the powder is ≥99.9%.

[0009] Furthermore, the particle size of the metal powder in the welding wire is 100-200 mesh.

[0010] Furthermore, the weld skin is made of 430 steel strip, with a thickness of 0.4 mm and a width of 7 mm.

[0011] Furthermore, the filler content of the welding wire is controlled at 18-20%.

[0012] Secondly, embodiments of the present invention provide a method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels, comprising the following steps: Step 1: Weigh out the following components by mass percentage: Ni 35.0~40.0%, Nb 35.0~40.0%, Al 2.0~4.0%, Ti 2.0~4.0%, V 0.5~2.0%, B 0.5~2.0%, with the remainder being Fe. The sum of the mass percentages of the above components should be 100%. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at a temperature of 200~230℃ for 1~3 hours to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1~3 hours. Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip; Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm; Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0013] Furthermore, the diameter of the first drawing die is 2.6 mm.

[0014] Thirdly, embodiments of the present invention provide a method for welding dissimilar steels, using the Fe-Ni-Nb low-stress welding wire for dissimilar steels described above, the welding method comprising the following steps: Asymmetrical V-grooves are made between 12Cr1MoV and T91 dissimilar steels, with the T91 side angle being 40~45° and the 12Cr1MoV side angle being 30~35°. The passivation thickness is 1.0~1.5mm, and the assembly gap is 0~1.5mm. Before welding, the T91 side is hammered to a depth of 0.1~0.5mm. The hammering needle is 2~5mm in size and made of T91 material. After the hammering is completed, the low-stress welding wire is used to butt weld 12Cr1MoV and T91 dissimilar steels. The welding current is 180~260A and the welding voltage is 20~30V.

[0015] Compared with existing technologies, the Fe-Ni-Nb low-stress welding wire for dissimilar steels proposed in this invention, along with its preparation and welding methods, effectively solves the stress concentration problem in butt joints of 12Cr1MoV and T91 dissimilar steels, addressing the challenge of early failure. This invention utilizes solid solution strengthening of Ni, Nb, and Cr elements combined with precipitation strengthening of Al, Ti, and Nb elements to synergistically improve the strength and toughness of the weld metal. The precipitation strengthening in this invention is also a composite precipitate phase, including Ti, Al, and Ni reacting to form a certain amount of γ' strengthening phase, Ni and Nb reacting to generate a certain amount of Ni3Nb, and Fe and B reacting to generate a Fe-B hard phase. The resulting weld exhibits excellent strength and toughness. Before welding, the T91 side bevel is hammered, effectively refining the martensite grains at T91. During subsequent welding, these broken grains directly serve as heterogeneous nucleation sites, further refining the grains and improving weld toughness. The welding wire provided by this invention has a simple preparation process. The obtained welding wire has a wide welding process window and is suitable for both TIG and MIG welding methods, making it easy to implement and apply in engineering sites. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A schematic diagram showing the bevel dimensions for butt welding of 12Cr1MoV and T91 dissimilar steels. Figure 2 A schematic diagram showing the welding sequence of 12Cr1MoV and T91 dissimilar steels; Figure 3 Metallographic structure of butt weld between 12Cr1MoV and T91 dissimilar steel prepared using Implementation Case 2. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Unless otherwise specifically stated, the technical or scientific terms used in the embodiments of this invention should be understood in their ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains. The terms "comprising" or "including," as used in the embodiments of this invention, do not limit the shapes, numbers, steps, actions, operations, components, elements, and / or groups thereof mentioned, nor do they exclude the appearance or addition of one or more other different shapes, numbers, steps, actions, operations, components, elements, and / or groups thereof, or the inclusion of these.

[0020] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale, and techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail; however, where appropriate, the illustrated techniques, methods, and apparatus should be considered part of the specification. In all the examples shown and discussed herein, any other specific example may have different values. It should be noted that similar symbols and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0021] In the description of the embodiments of the present invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In the embodiments of the present invention, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in the embodiments of the present invention, as well as the features of different embodiments or examples.

[0022] This invention relates to a low-stress Fe-Ni-Nb welding wire for dissimilar steels, comprising flux powder and welding scale. The flux powder comprises the following components by mass percentage: Ni 35.0~40.0%, Nb 35.0~40.0%, Al 2.0~4.0%, Ti 2.0~4.0%, V 0.5~2.0%, B 0.5~2.0%, and the remainder is Fe. The sum of the mass percentages of the above components is 100%.

[0023] In some embodiments, the purity of each raw material component alloy powder in the pharmaceutical powder is ≥99.9%.

[0024] In some embodiments, the particle size of the metal powder in the welding wire is 100~200 mesh.

[0025] In some embodiments, the weld skin is 430 steel strip with a thickness of 0.4 mm and a width of 7 mm.

[0026] In some embodiments, the filler content of the flux-cored wire is controlled at 18-20%.

[0027] The functions and roles of the main alloy components in the welding wire of this invention are as follows: (1) The main alloying element in the cladding metal of the welding wire is Fe: 12Cr1MoV and T91 base metals are both mainly Fe. Therefore, the welding wire is designed with Fe as the main element to meet the requirements of welding metallurgical connection with the base metals on both sides. In addition, the main alloying element of the welding wire is the same as that of the base metal, and their coefficients of thermal expansion are also close, so the residual stress is not easy to concentrate during welding, thus meeting the original intention of the design of this invention.

[0028] (2) The main alloying element of the welding wire cladding metal is Ni: Ni-based alloys have a face-centered cubic (fcc) structure and good plasticity and toughness. During welding, Ni dissolves in the Fe matrix, which can significantly improve the plasticity and toughness of the matrix. When dissimilar steels are welded, stress concentration is difficult to avoid; if the weld area has excellent plasticity and toughness, the residual stress can be released through plastic deformation, thereby reducing the overall stress peak and alleviating the stress concentration. In addition, Ni-based alloys also exhibit excellent high-temperature oxidation resistance, which can meet the requirements of high-temperature service environments; its high-temperature strength is also outstanding, and it can maintain stable strength performance even above 500℃, ensuring the safe service of components under high-temperature conditions. Therefore, designing welding wire alloy systems with Ni as the matrix can meet the basic service requirements of materials under complex working conditions.

[0029] (3) The cladding metal of the welding wire contains a certain amount of Cr element: Cr mainly enters the cladding metal through the 430 weld skin. The addition of Cr in the Fe matrix has two main functions. On the one hand, it acts as a solid solution strengthening element to improve the strength of the Fe matrix; on the other hand, Cr can improve the Fe matrix's resistance to high-temperature oxides. By forming a dense Cr2O3 protective layer, Cr can significantly improve the high-temperature performance of Fe-based alloys, thereby ensuring their service requirements at high temperatures. Cr is a ferrite-forming element, which can help the weld to form a part of the ferrite structure, thereby meeting the microstructure matching with the 12Cr1MoV side. In addition, the presence of Cr in the weld also meets the composition matching with the T91 side, inhibiting the diffusion of Cr due to concentration differences at high temperatures, thereby ensuring the mechanical properties of the fusion line on the T91 side.

[0030] (4) The welding wire cladding metal contains a certain amount of Nb: In complex iron-based alloys containing Ni, Cr, Ti, Al, and B, Nb plays a key role mainly through microalloying. Its core function is to form stable carbonitrides (such as NbC and NbN). These compounds can effectively pin grain boundaries at high temperatures and inhibit austenite grain growth, thereby improving the strength and toughness of the alloy by refining the grains. In addition, during hot working or tempering, the dispersed nano-sized NbC particles will produce a significant precipitation strengthening effect, further improving the strength and hardness of the alloy. Another important characteristic of Nb is that it can significantly increase the recrystallization temperature of the alloy, enabling it to maintain a fine-grained structure and creep resistance at high temperatures (such as above 500℃), ensuring its thermal strength. In this alloy system, Nb has an important synergistic effect with elements such as Ti and Al: Ti and Nb together form composite carbides to enhance precipitation strengthening and grain refinement; while Nb can also dissolve into the γ' phase (Ni3Al) formed by Al, improving the stability and anti-coarsening ability of this strengthening phase.

[0031] (5) The welding wire cladding metal contains a certain amount of boron: In complex iron-based alloys containing Ni, Cr, Ti, Al, and Nb, the addition of boron (B), though in trace amounts, plays a crucial role. Its core function is highly concentrated at the grain boundaries: B atoms preferentially aggregate at the grain boundaries, thereby effectively strengthening the grain boundaries and reducing the grain boundary energy. This not only inhibits the migration of grain boundaries and the formation of pores at high temperatures, but more importantly, it can delay the nucleation and growth of precipitates (such as carbides) near the grain boundaries, improving the plasticity of the grain boundaries. This effect significantly improves the hardenability, high-temperature creep resistance, and resistance to creep-fatigue interaction of the alloy, and effectively inhibits the tendency of grain boundary embrittlement under high-temperature aging or stress, which is crucial for preventing intergranular fracture. In this multi-element alloy system, the grain boundary strengthening of B, together with the intragranular precipitation strengthening and grain refinement of Nb and Ti, form a perfect "intragranular-grain boundary" synergistic strengthening. At the same time, the addition of B also helps the stability of the γ' phase strengthening system, in which Al, Ti and Nb participate, at high temperatures.

[0032] (6) The welding wire cladding metal contains a certain amount of Ti and Al: In complex iron-based alloys containing Ni, Cr, Ti, Al, Nb, and B, the elements construct a comprehensive strengthening and toughening system through multi-element synergistic effects. Ti and Nb, as strong carbide-forming elements, together form stable (Ti,Nb)C carbonitrides to strongly pin grain boundaries, achieve grain refinement, and generate dispersed nanoscale precipitates within the grains, providing significant precipitation strengthening effects. At the same time, they can increase the recrystallization temperature of the alloy, jointly ensuring the high-temperature strength and creep resistance of the material. Al and Ti (and some Nb) are the main forming elements of the key precipitation strengthening phase γ' (Ni3(Al, Ti, Nb)), which is the core pillar for the alloy to maintain high strength at high temperatures.

[0033] (8) The welding wire cladding metal contains a certain amount of vanadium (V): Introducing vanadium (V) into an alloy system containing Ni, Cr, Ti, Al, Nb, and B can further optimize the microstructure and overall properties of the alloy. As a strong carbonitride forming element, V plays a core role similar to Nb and Ti, mainly by forming fine V(C,N) precipitates to produce a significant precipitation strengthening effect, further enhancing the alloy strength. More importantly, the dissolution-precipitation behavior of V carbonitrides in the austenitizing temperature range differs from that of NbC and TiC. This multi-scale, staged composite precipitation (such as the first precipitated TiN or NbC serving as heterogeneous nucleation sites for vanadium) can more effectively pin grain boundaries and substructures, producing a superimposed strengthening effect and more precisely suppressing grain growth. During heat treatment, the addition of V helps improve the secondary hardening response and tempering stability of the alloy, enabling the material to maintain high strength and hardness even at higher tempering temperatures. In addition, V can also dissolve in the matrix, providing a certain solid solution strengthening effect. V, Nb, and Ti work together to form a more continuous and stable carbonitride strengthening network from low to high temperature and from the grain interior to the grain boundary. This not only significantly improves the room temperature strength and toughness of the alloy, but also further enhances its high temperature creep resistance and long-term microstructure stability, thereby further optimizing the overall performance of the alloy, especially the strength-toughness balance and thermal strength.

[0034] This invention also provides a method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels, the specific steps of which are as follows: Step 1: Weigh out Ni (35.0~40.0%), Nb (35.0~40.0%), Al (2.0~4.0%), Ti (2.0~4.0%), V (0.5~2.0%), B (0.5~2.0%), and the remainder Fe according to the mass percentage. The sum of the mass percentages of the above components is 100%.

[0035] Step 2: Place the weighed medicinal powder from Step 1 into a vacuum heating furnace and heat it at 200~230℃ for 1~3 hours to remove the water of crystallization. After drying, place the powder into a powder mixer for thorough mixing for 1~3 hours. Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip. The diameter of the first drawing die is 2.6mm.

[0036] Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0037] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0038] This invention also provides a method for welding dissimilar steels using Fe-Ni-Nb low-stress welding wire, and a welding method (such as...) Figure 1 As shown): 12Cr1MoV and T91 dissimilar steels are butt-welded with an asymmetrical V-groove, with the T91 side angle being 40~45° and the 12Cr1MoV side angle being 30~35°. The passivation thickness is 1.0~1.5mm, and the assembly gap is 0~1.5mm. Before welding, the T91 side is hammered to a depth of 0.1~0.5mm, using a 2~5mm hammering needle made of T91 material. After hammering, the welding wire of this invention is used for butt welding of 12Cr1MoV and T91 dissimilar steels. The welding current is 180~260A, and the welding voltage is 20~30V.

[0039] This invention relates to a Fe-Ni-Nb low-stress welding wire for dissimilar steels, its preparation method, and welding method. The welding wire, combined with the hammering treatment of the joint, effectively solves the stress concentration problem in butt joints of 12Cr1MoV and T91 dissimilar steels, addressing the challenge of early failure. This invention utilizes solid solution strengthening of Ni, Nb, and Cr elements, along with precipitation strengthening of Al, Ti, and Nb elements, to synergistically improve the strength and toughness of the weld metal. The precipitation strengthening in this invention is also a composite precipitate phase, including the reaction of Ti and Al with Ni to form a certain amount of γ' strengthening phase, the reaction of Ni and Nb to generate a certain amount of Ni3Nb, and the reaction of Fe and B to generate a Fe-B hard phase. The resulting weld exhibits excellent strength and toughness. Before welding, the T91 side bevel is hammered, effectively refining the martensite grains at T91. During subsequent welding, these broken grains directly serve as heterogeneous nucleation sites, thereby refining the grains and improving weld toughness. The welding wire provided by this invention has a simple preparation process. The obtained welding wire has a wide welding process window and is suitable for both TIG and MIG welding methods, making it easy to implement and apply in engineering sites.

[0040] The following will describe in detail the preparation method of the Fe-Ni-Nb low-stress welding wire for dissimilar steels according to the present invention through several specific embodiments.

[0041] Example 1 A method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels includes the following steps: Step 1: Weigh out Ni 35.0%, Nb 35.0%, Al 2.0%, Ti 2.0%, V 0.5%, B 0.5%, and the remainder Fe according to their respective mass percentages. The sum of the mass percentages of the above components is 100%.

[0042] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace and heat it at 200℃ for 1 hour to remove the water of crystallization from the powder. After drying, place the powder into a powder mixer for thorough mixing for 1 hour.

[0043] Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip. The diameter of the first drawing die is 2.6mm.

[0044] Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0045] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0046] Welding of 12Cr1MoV and T91 dissimilar steels was performed using the welding wire prepared in Example 1. The welding method (e.g.) Figure 1 As shown): 12Cr1MoV and T91 dissimilar steels are butt-welded with an asymmetrical V-groove, with the T91 side angle at 40° and the 12Cr1MoV side angle at 30°, a passivation thickness of 1.0 mm, and an assembly gap of 0~1.5 mm; before welding, the T91 side is hammered to a depth of 0.1 mm, using a 2 mm hammering needle made of T91 material; after hammering, the welding wire of this invention is used for butt welding of 12Cr1MoV and T91 dissimilar steels, with a welding current of 180 A and a welding voltage of 20 V.

[0047] The mechanical properties and residual stress of the welded 12Cr1MoV and T91 dissimilar steel joints were tested, and the test results are as follows: (1) Full-thickness compact tensile specimens were prepared. The tensile results showed that the joint strength was 541 MPa, the fracture area was the heat-affected zone of the 12Cr1MoV base material, and the elongation after fracture was 36.7%.

[0048] (2) The results of the joint residual stress test showed that the peak residual stress of the joint was on the T91 side, and the stress was 374 MPa; compared with the joint obtained by welding with existing welding wire, the stress was reduced by 10%.

[0049] Example 2 A method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels includes the following steps: Step 1: Weigh out Ni 40.0%, Nb 40.0%, Al 4.0%, Ti 4.0%, V 2.0%, B 2.0%, and the remainder Fe according to their respective mass percentages. The sum of the mass percentages of the above components is 100%.

[0050] Step 2: Place the weighed medicine powder from Step 1 into a vacuum heating furnace and heat it at 230℃ for 3 hours to remove the water of crystallization from the medicine powder; place the dried medicine powder into a powder mixer for thorough mixing for 3 hours.

[0051] Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip. The diameter of the first drawing die is 2.6mm.

[0052] Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0053] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0054] The welding wire prepared in Example 2 was used to weld 12Cr1MoV and T91 dissimilar steels. The welding method (e.g.) Figure 1 As shown): 12Cr1MoV and T91 dissimilar steels are butt-welded with an asymmetrical V-groove, with the T91 side angle at 45° and the 12Cr1MoV side angle at 35°, a passivation thickness of 1.5mm, and a mating gap of 1.5mm. Before welding, the T91 side is hammered to a depth of 0.5mm using a 5mm hammering needle made of T91 material. After hammering, the welding wire of this invention is used for butt welding of 12Cr1MoV and T91 dissimilar steels, with a welding current of 260A and a welding voltage of 30V.

[0055] The mechanical properties and residual stress of the welded 12Cr1MoV and T91 dissimilar steel joints were tested, and the test results are as follows: (1) Full-thickness compact tensile specimens were prepared. The tensile results showed that the joint strength was 543 MPa, the fracture area was the heat-affected zone of the 12Cr1MoV base material, and the elongation after fracture was 36.1%.

[0056] (2) The results of the joint residual stress test show that the peak residual stress of the joint is on the T91 side, and the stress is 370MPa. The stress obtained by welding the joint using the existing welding wire is 462MPa, which is 19.9% ​​lower than that of the existing welding wire.

[0057] Figure 3 The image shows the metallographic structure of the butt weld between 12Cr1MoV and T91 dissimilar steel prepared using Example 2. As can be seen from the image, the weld is predominantly cellular dendritic in morphology with a fine microstructure, indicating that the hammering was effective. No cracks, porosity, or other defects were observed.

[0058] Example 3 A method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels includes the following steps: Step 1: Weigh out Ni 37.0%, Nb 37.0%, Al 3.0%, Ti 3.0%, V 1.3%, B 1.3%, and the remainder Fe according to their respective mass percentages. The sum of the mass percentages of the above components is 100%.

[0059] Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at 215℃ for 2 hours to remove the water of crystallization from the powder. After drying, place the powder into a powder mixer for thorough mixing for 2 hours.

[0060] Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip. The diameter of the first drawing die is 2.6mm.

[0061] Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0062] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0063] The welding wire prepared in Example 3 was used to weld 12Cr1MoV and T91 dissimilar steels. The welding method (e.g.) Figure 1 As shown): 12Cr1MoV and T91 dissimilar steels are butt-welded with an asymmetrical V-groove, with the T91 side angle being 43° and the 12Cr1MoV side angle being 33°. The passivation thickness is 1.3mm, and the assembly gap is 0~1.5mm. Before welding, the T91 side is hammered to a depth of 0.3mm using a 3.5mm hammering needle made of T91 material. After hammering, the welding wire of this invention is used for butt welding of 12Cr1MoV and T91 dissimilar steels. The welding current is 220A and the welding voltage is 25V.

[0064] The mechanical properties and residual stress of the welded 12Cr1MoV and T91 dissimilar steel joints were tested, and the test results are as follows: (1) Full-thickness compact tensile specimens were prepared. The tensile results showed that the joint strength was 545 MPa, the fracture area was the heat-affected zone of the 12Cr1MoV base material, and the elongation after fracture was 35.0%.

[0065] (2) The results of the joint residual stress test show that the peak residual stress of the joint is on the T91 side, and the stress is 360MPa. The stress obtained by welding the joint using the existing welding wire is 462MPa, which is 22.0% lower than that of the existing welding wire.

[0066] Example 4 A method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels includes the following steps: Step 1: Weigh out Ni 36.0%, Nb 36.0%, Al 2.5%, Ti 2.5%, V 0.6%, B 0.6%, and the remainder Fe according to their respective mass percentages. The sum of the mass percentages of the above components is 100%.

[0067] Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at 210℃ for 1.2 hours to remove the water of crystallization from the powder. After drying, place the powder into a powder mixer for thorough mixing for 1.2 hours.

[0068] Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip. The diameter of the first drawing die is 2.6mm.

[0069] Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0070] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0071] The welding wire prepared in Example 4 was used to weld 12Cr1MoV and T91 dissimilar steels. The welding method (e.g.) Figure 1 As shown): 12Cr1MoV and T91 dissimilar steels are butt-welded with an asymmetrical V-groove, with the T91 side angle being 41° and the 12Cr1MoV side angle being 31°, a passivation thickness of 1.1mm, and a mating gap of 0.1mm. Before welding, the T91 side is hammered to a depth of 0.2mm, using a 2.1mm hammering needle made of T91 material. After hammering, the welding wire of this invention is used for butt welding of 12Cr1MoV and T91 dissimilar steels, with a welding current of 190A and a welding voltage of 21V.

[0072] The mechanical properties and residual stress of the welded 12Cr1MoV and T91 dissimilar steel joints were tested, and the test results are as follows: (1) Full-thickness compact tensile specimens were prepared. The tensile results showed that the joint strength was 555 MPa, the fracture area was the heat-affected zone of the 12Cr1MoV base material, and the elongation after fracture was 36.2%.

[0073] (2) The results of the joint residual stress test show that the peak residual stress of the joint is on the T91 side, and the stress is 379MPa. The stress obtained by welding the joint using the existing welding wire is 462MPa, which is 17.9% lower than that of the existing welding wire.

[0074] Example 5 A method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels includes the following steps: Step 1: Weigh out Ni 39.0%, Nb 39.0%, Al 3.9%, Ti 3.9%, V 1.9%, B 1.9%, and the remainder Fe according to their respective mass percentages. The sum of the mass percentages of the above components is 100%.

[0075] Step 2: Place the weighed medicine powder from Step 1 into a vacuum heating furnace and heat it at a temperature of 229°C for 2.9 hours to remove the water of crystallization from the medicine powder. After drying, place the medicine powder into a powder mixer for thorough mixing for 2.9 hours.

[0076] Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip. The diameter of the first drawing die is 2.6mm.

[0077] Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0078] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0079] Welding of 12Cr1MoV and T91 dissimilar steels was performed using the welding wire prepared in Example 5. The welding method (e.g.) Figure 1 As shown): 12Cr1MoV and T91 dissimilar steels are butt-welded with an asymmetrical V-groove, with the T91 side angle being 44° and the 12Cr1MoV side angle being 34°, a passivation thickness of 1.4mm, and an assembly gap of 0~1.5mm; before welding, the T91 side is hammered to a depth of 0.4mm, using a 4mm hammering needle made of T91 material; after hammering, the welding wire of this invention is used for butt welding of 12Cr1MoV and T91 dissimilar steels, with a welding current of 250A and a welding voltage of 29V.

[0080] The mechanical properties and residual stress of the welded 12Cr1MoV and T91 dissimilar steel joints were tested, and the test results are as follows: (1) Full-thickness compact tensile specimens were prepared. The tensile results showed that the joint strength was 549 MPa, the fracture area was the heat-affected zone of the 12Cr1MoV base material, and the elongation after fracture was 38.0%.

[0081] (2) The results of the joint residual stress test show that the peak residual stress of the joint is on the T91 side, and the stress is 377MPa. The stress obtained by welding the joint using the existing welding wire is 462MPa, which is 18.3% lower than that of the existing welding wire.

[0082] Example 6 A method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels includes the following steps: Step 1: Weigh out Ni 35.1%, Nb 35.1%, Al 2.1%, Ti 2.1%, V 0.51%, B 0.51%, and the remainder Fe according to their respective mass percentages. The sum of the mass percentages of the above components is 100%.

[0083] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace and heat it at 211℃ for 1.3 hours to remove the water of crystallization from the powder. After drying, place the powder into a powder mixer for thorough mixing for 1.3 hours.

[0084] Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip. The diameter of the first drawing die is 2.6mm.

[0085] Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0086] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0087] Welding of 12Cr1MoV and T91 dissimilar steels was performed using the welding wire prepared in Example 6. The welding method (e.g.) Figure 1 As shown): 12Cr1MoV and T91 dissimilar steels are butt-welded with an asymmetrical V-groove, with the T91 side angle being 44.5° and the 12Cr1MoV side angle being 34.5°, a passivation thickness of 1.45mm, and a mating gap of 0.9mm. Before welding, the T91 side is hammered to a depth of 0.45mm using a 3.1mm hammering needle made of T91 material. After hammering, the welding wire of this invention is used for butt welding of 12Cr1MoV and T91 dissimilar steels, with a welding current of 185A and a welding voltage of 22V.

[0088] The mechanical properties and residual stress of the welded 12Cr1MoV and T91 dissimilar steel joints were tested, and the test results are as follows: (1) Full-thickness compact tensile specimens were prepared. The tensile results showed that the joint strength was 538 MPa, the fracture area was the heat-affected zone of the 12Cr1MoV base material, and the elongation after fracture was 37.9%.

[0089] (2) The results of the joint residual stress test show that the peak residual stress of the joint is on the T91 side, and the stress is 354 MPa. The stress obtained by welding the joint using the existing welding wire is 462 MPa, which is 23.4% lower than that of the existing welding wire.

[0090] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A low-stress welding wire for dissimilar steels, characterized in that, Includes flux powder and solder coating; among which, The powder comprises the following components by mass percentage: Ni 35.0~40.0%, Nb 35.0~40.0%, Al 2.0~4.0%, Ti 2.0~4.0%, V 0.5~2.0%, B 0.5~2.0%, and the remainder is Fe. The sum of the mass percentages of the above components is 100%.

2. The Fe-Ni-Nb low-stress welding wire for dissimilar steels according to claim 1, characterized in that, The powder comprises the following components by mass percentage: Ni 37%, Nb 37%, Al 3%, Ti 3%, V 1.3%, B 1.3%, and the remainder is Fe, with the sum of the mass percentages of the above components being 100%.

3. The Fe-Ni-Nb low-stress welding wire for dissimilar steels according to claim 1, characterized in that, The purity of each raw material component alloy powder in the powder is ≥99.9%.

4. The Fe-Ni-Nb low-stress welding wire for dissimilar steels according to any one of claims 1 to 3, characterized in that, The particle size of the metal powder in the welding wire is 100~200 mesh.

5. The Fe-Ni-Nb low-stress welding wire for dissimilar steels according to any one of claims 1 to 3, characterized in that, The weld bead is made of 430 steel strip, with a thickness of 0.4 mm and a width of 7 mm.

6. A low-stress welding wire for dissimilar steels according to any one of claims 1 to 3, characterized in that, The filler ratio of the welding wire is controlled at 18-20%.

7. A method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels, characterized in that, Includes the following steps: Step 1: Weigh out the following components by mass percentage: Ni 35.0~40.0%, Nb 35.0~40.0%, Al 2.0~4.0%, Ti 2.0~4.0%, V 0.5~2.0%, B 0.5~2.0%, with the remainder being Fe. The sum of the mass percentages of the above components should be 100%. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at a temperature of 200~230℃ for 1~3 hours to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1~3 hours. Step 3: Use alcohol to remove the grease from the surface of the 430 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 430 steel strip; Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm; Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

8. The method for preparing Fe-Ni-Nb low-stress welding wire for dissimilar steels according to claim 7, characterized in that, The diameter of the first drawing die is 2.6mm.

9. A method for welding dissimilar steels, characterized in that, The welding method using the Fe-Ni-Nb low-stress welding wire for dissimilar steels as described in any one of claims 1 to 6 includes the following steps: Asymmetrical V-grooves are made between 12Cr1MoV and T91 dissimilar steels, with the T91 side angle being 40~45° and the 12Cr1MoV side angle being 30~35°. The passivation thickness is 1.0~1.5mm, and the assembly gap is 0~1.5mm. Before welding, the T91 side is hammered to a depth of 0.1~0.5mm. The hammering needle is 2~5mm in size and made of T91 material. After the hammering is completed, the low-stress welding wire is used to butt weld 12Cr1MoV and T91 dissimilar steels. The welding current is 180~260A and the welding voltage is 20~30V.

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