Flux-cored wire for dissimilar welding of high-strength weathering resistant steel and ordinary steel and application of flux-cored wire

Abstract

The invention relates to the field of welding materials, in particular to a flux-cored wire for dissimilar welding of high-strength weathering resistant steel and ordinary steel and application of the flux-cored wire. The welding powder for the flux-cored wire comprises the following components in percentage by weight: 2.00 + / -0.20% of rare earth silver core-shell powder; 7.05 + / -0.53% of niobium-vanadium composite powder; 29.97 + / -1.91% of nickel-based alloy powder; 0.79 + / -0.11% of molybdenum powder; 1.00 + / -0.12% of titanium boron alloy powder; 10.00 + / -2.82% of a slag former; and the balance of iron powder. A welding seam formed by the flux-cored wire between high-strength weathering steel and ordinary steel has high low-temperature impact energy, the standard impact energy of a fusion zone at the temperature of-40 DEG C is larger than or equal to 115 J, and the flux-cored wire can still absorb high energy without brittle fracture in an extremely low-temperature environment; the corrosion potential difference of a fusion area between the welding seam and the high-strength weathering steel is smaller than or equal to 20 mV, galvanic corrosion is not prone to occurring in the humid corrosion environment containing salt mist and the like, and the overall corrosion resistance of the connector is guaranteed; and the hardness gradient of a fusion region between the alloy and a base material is less than or equal to 150HV / mm, so that the risk of crack initiation and expansion is reduced.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and in particular to a flux-cored welding wire for dissimilar welding of high-strength weather-resistant steel and ordinary steel, and its application. Background Technology

[0002] In steel structure bridge engineering, to meet the requirements of special environments such as high altitude and cold conditions, high-strength weathering steel is used in key components. This not only achieves structural lightweighting, but the dense rust layer formed on its surface also significantly reduces the corrosion rate in harsh environments. Meanwhile, secondary components such as railings and connecting plates, which are subjected to less stress and are far from corrosive environments, can be made of ordinary steel. Therefore, dissimilar steel welding technology, combining high-strength weathering steel and ordinary carbon steel, is frequently used in steel structure bridge engineering.

[0003] However, dissimilar welding of high-strength weathering steel and ordinary steel still faces three major challenges: First, due to the large strength difference between high-strength weathering steel and ordinary steel, welded joints are prone to severe stress gradient distortion under service loads. The stress concentration factor in the fusion zone is higher than that of homogeneous joints, and the low-temperature impact energy is generally low, far below the requirements of the base material, easily leading to low-temperature brittle fracture. For example, in 2018, Li Shengshen, in his study "Research on the Microstructure and Properties of Welded Joints of High-Strength and High-Weathering Steel for Heavy-Duty Trains," explained that through experiments with different heat inputs, it was found that the impact energy of high-strength weathering steel welded joints at -20℃ and -40℃ showed a trend of first increasing and then decreasing with heat input, with a maximum impact energy of only 98J. Moreover, the hardness of the heat-affected zone increased significantly, forming a stress concentration zone. In 2016, Wang Xin, in his study "Research on the Strength and Toughness of B-HARD360 High-Strength Wear-Resistant Steel GMAW 'Low-Strength Matching' Welded Joints," explained that experiments showed that the impact energy at -40℃ varied with heat input, with a maximum of only 98J. Furthermore, the hardness of the weld zone first increased and then decreased, forming a stress concentration zone with a hardness gradient of over -150HV / mm.

[0004] Secondly, traditional welding materials, due to insufficient corrosion-resistant alloying elements, have a weld corrosion resistance index far lower than that of high-strength weathering steel. This leads to the preferential formation of intergranular corrosion grooves at the fusion line, resulting in a corrosion rate much higher than that of high-strength weathering steel. For example, in 2017, Huang Chen, Huang Feng, Liu Jing, and other authors, in their paper "Corrosion Resistance Analysis of Welded Joints of A710 High-Strength Weathering Steel," clarified that the uneven microstructure of the weld zone and heat-affected zone leads to the formation of micro-galvanic corrosion cells. The weld / heat-affected zone acts as the anode, and the base metal as the cathode, resulting in a significantly higher average corrosion rate of the welded joint compared to the base metal.

[0005] Finally, welding thermal cycling triggers carbon migration: carbon atoms diffuse from the ordinary steel side to the high-carbon weathering steel side, forming an alternating structure of "decarburized soft band" and "carburized hard band" at the fusion line. This results in large hardness fluctuations, becoming a preferred path for crack initiation. For example, in 2002, Zhang Xinbao, in his "Research on the Weldability of Dissimilar Steels for Superheated Tubes in Power Plant Boilers," elucidated that carbon migration from the pearlitic heat-resistant steel side to the austenitic weld side leads to a softening zone on the pearlitic side and a hardening zone (M23C6 carbide precipitation) inside the weld. The increased hardness gradient makes it easier for creep cracks to form in the softening zone and propagate into the hardening zone, forming a preferred path for crack initiation.

[0006] Traditional welding materials cannot simultaneously address the strength transition, corrosion resistance matching, and crack resistance requirements between high-strength weather-resistant steel and ordinary steel. Once the low-temperature toughness, corrosion resistance index, or hardness gradient of the fusion zone becomes uncontrolled, dissimilar steel welded joints will quickly become high-risk points for both fracture and corrosion, making the weld a bottleneck in the durability of steel structure bridges. CN112453756A achieves a high-strength and high-toughness match in the weld metal by optimizing the powder composition (e.g., 20%-40% TiO2, 1.0%~3.0% rare earth alloys), particularly emphasizing an impact energy ≥120J at -40℃, suitable for welding 55kg-class low-carbon steel and low-alloy steel; however, the composition design focuses on improving single material properties and lacks synergistic optimization of multiple properties. Therefore, developing a new welding material that can simultaneously solve the problems of strength transition, corrosion resistance matching, and crack resistance is of great significance for improving the durability and safety of steel structure bridges. Summary of the Invention

[0007] This invention provides a flux-cored welding wire and its welding powder for dissimilar welding of high-strength weathering steel and ordinary steel, in order to solve the problem that traditional welding materials cannot simultaneously meet the requirements of strength transition, corrosion resistance matching and crack resistance between high-strength weathering steel and ordinary steel.

[0008] In a first aspect, the present invention provides a welding powder for flux-cored welding wire, the welding powder comprising, by weight percentage: Rare earth silver core-shell powder 2.00±0.20%; Niobium-vanadium composite powder: 7.05±0.53%; Nickel-based alloy powder 29.97±1.91%; Molybdenum powder 0.79±0.11%; Titanium-boron alloy powder 1.00±0.12%; Slag-forming agent 10.00±2.82%; The remainder consists of iron powder and unavoidable impurities; in: The rare earth silver core-shell powder is composed of rare earth silver core-shell particles. The rare earth silver core-shell particles have a core-shell structure. The core is composed of rare earth oxides composed of nano-cerium oxide and nano-lanthanum oxide in a weight ratio of (2~3):1. The shell is silver, and the shell accounts for 60%~80% of the total mass of the core-shell structure. The niobium-vanadium composite powder is composed of niobium powder and vanadium powder in a weight ratio of (2~4):1, and the purity of both niobium powder and vanadium powder is not less than 99.5%. In the titanium-boron alloy powder, the weight ratio of Ti to B is (3~5):1, wherein the total mass fraction of Ti and B is not less than 99.0%, and the remainder is unavoidable impurities; The nickel-based alloy powder comprises, by weight percentage: Cr 7.5%~8.5%, Cu 4.5%~5.5%, Mn 1.8%~2.2%, C≤0.10%, Si≤1.0%, P≤0.020%, S≤0.020%, with the balance being Ni and unavoidable impurities.

[0009] In conjunction with the first aspect of the invention, some embodiments include: The rare earth silver core-shell particles have a particle size of 8-12 μm and a shell thickness of 1.0-2.0 μm; and / or, The niobium-vanadium composite powder has a particle size of 10-15 μm; and / or, The molybdenum powder has a particle size of 1~5 μm; and / or, The titanium-boron alloy powder has a particle size of 10~20 μm; and / or, The nickel-based alloy powder has a particle size of 10~20 μm; and / or, The slag-forming agent has a particle size of 10~30μm; and / or, The iron powder has a particle size of 5~15μm.

[0010] In conjunction with the first aspect of the present invention, in some embodiments: the rare earth oxide is composed of nano-cerium oxide and nano-lanthanum oxide in a weight ratio of (2~3):1.

[0011] In conjunction with the first aspect of the present invention, in some embodiments: the slag-forming agent is composed of calcium fluoride and zirconium silicate in a weight ratio of (1.3~1.6):1, wherein the purity of calcium fluoride is ≥98% and the purity of zirconium silicate is ≥99%.

[0012] In conjunction with the first aspect of the present invention, in some embodiments: the method for preparing the rare earth silver core-shell powder includes: Surface modification of rare earth oxide particles by amination; Chemical silver plating was performed on amination-modified rare earth oxide particles. The silver-plated particles are washed and dried to obtain rare earth silver core-shell powder.

[0013] Secondly, the present invention provides a flux-cored welding wire, which is composed of the welding powder used for flux-cored welding wire and a metal outer sheath wrapped around the welding powder.

[0014] In conjunction with the second aspect of the present invention, in some embodiments: the flux-cored welding wire is used for carbon dioxide gas shielded welding of the interface between high-strength weather-resistant steel and ordinary steel.

[0015] In conjunction with the second aspect of the present invention, in some embodiments: the weld formed by the flux-cored welding wire between high-strength weathering steel and ordinary steel satisfies at least one of the following performance indicators: (i) The standard impact energy at -40°C in the fusion zone is 115~125J; (ii) The corrosion potential difference in the fusion zone between the weld and the high-strength weathering steel is 17.0~19.5mV; (iii) The hardness gradient of the fusion zone is 120~146HV / mm.

[0016] In conjunction with the second aspect of the present invention, in some embodiments: the weight percentage of welding powder in the flux-cored welding wire is 40% to 60%.

[0017] Thirdly, the present invention provides a dissimilar welding method for high-strength weather-resistant steel and ordinary steel, wherein the above-mentioned flux-cored welding wire is used for carbon dioxide gas shielded welding, the carbon dioxide gas is 80%Ar+20%CO2, the gas flow rate is 25L / min, and a weld is formed between the interface of high-strength weather-resistant steel and ordinary steel.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The flux-cored welding wire provided by this invention forms a weld between high-strength weathering steel and ordinary steel with high low-temperature impact energy: -40℃ impact energy ≥115J. It can still absorb high energy without brittle fracture in extreme low-temperature environments, meeting the service requirements of cold regions.

[0019] 2. The corrosion potential difference between the flux-cored welding wire provided by this invention and the weld formed between high-strength weather-resistant steel and ordinary steel is ≤20mV. It is not easy to cause galvanic corrosion in humid, salt spray and other corrosive environments, thus ensuring the overall corrosion resistance of the joint.

[0020] 3. The flux-cored welding wire provided by this invention forms a weld seam between high-strength weather-resistant steel and ordinary steel, with a hardness gradient of ≤150HV / mm between the weld seam and the base material, reducing the risk of crack initiation and propagation. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0022] Figure 1 : A schematic diagram of the structure of the flux-cored welding wire provided by the present invention; wherein, 1 represents welding powder, 2 represents metal outer sheath, and 3 represents seam.

[0023] Figure 2 Transmission electron microscopy image of the grain boundary region of the weld formed between high-strength weathering steel and ordinary steel using the flux-cored welding wire prepared in Example 1 (resolution: 10 nm).

[0024] Figure 3 High-resolution transmission electron microscopy image (resolution: 2 nm) of the grain boundary region of the weld formed between high-strength weathering steel and ordinary steel using the flux-cored welding wire prepared in Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] In this article, "powder" refers to small particles with a particle size in the micrometer range; molybdenum powder, iron powder, niobium powder, vanadium powder, and silver are all pure metals; nickel-based alloy powder and titanium-boron alloy powder are powders made of alloys; niobium-vanadium composite powder is a mixture of niobium powder and vanadium powder.

[0027] In this article, "base material" refers to the metallic material being welded; "weld" refers to the solid connection formed after the base material and / or filler material are melted at high temperature and then cooled and solidified during the welding process; "welded joint" refers to the integral structure formed by connecting two or more workpieces together through welding, which consists of three parts: the weld, the fusion zone, and the heat-affected zone. The "fusion zone" is the transition area between the weld and the base material, where the base metal partially melts and mixes with the weld metal, significantly affecting the weld strength; the "heat-affected zone" is the area where the base material, though not melted due to the high temperature of welding, undergoes changes in its microstructure or properties, and its extent and degree of property change are closely related to the welding process (such as temperature and cooling rate).

[0028] The significant strength difference between high-strength weathering steel and ordinary steel means that when welded together, the high-strength weathering steel hardly deforms under stress, while the ordinary steel deforms severely. This asymmetrical deformation leads to extremely high stress concentration in the weld and fusion zone. Low temperatures drastically reduce the material's plastic deformation capacity, preventing stress concentration from being relieved through plastic deformation. High stress directly acts on the grain boundaries, second-phase particles, or defects in the weld metal, becoming a driving force for crack initiation. This results in rapid crack propagation under impact loads, reduced impact energy, and a significantly increased tendency for brittle fracture. The high carbon content (0.05%~0.16%) in high-strength weathering steel is mismatched with the Mn / S ratio in ordinary steel. During welding thermal cycles, carbon atoms diffuse from the ordinary steel side to the high-strength weathering steel side, forming an alternating structure of soft decarburized and hard carburized layers near the fusion line. The large hardness fluctuations in this region induce stress concentration, becoming a preferred path for crack initiation. The above reasons make the weld between high-strength weathering steel and ordinary steel a bottleneck in the durability of steel structure bridges. To address the problem that traditional welding materials cannot simultaneously meet the requirements for strength transition, corrosion resistance matching, and crack resistance between high-strength weathering steel and ordinary steel, this invention provides a flux-cored welding wire for dissimilar welding of high-strength weathering steel and ordinary steel, and its application.

[0029] This invention provides a welding powder for flux-cored welding wire, wherein the welding powder comprises, by weight percentage: Rare earth silver core-shell powder 2.00±0.20%; Niobium-vanadium composite powder: 7.05±0.53%; Nickel-based alloy powder 29.97±1.91%; Molybdenum powder 0.79±0.11%; Titanium-boron alloy powder 1.00±0.12%; Slag-forming agent 10.00±2.82%; The remainder consists of iron powder and unavoidable impurities; in: The rare earth silver core-shell powder is composed of rare earth silver core-shell particles. The rare earth silver core-shell particles have a core-shell structure. The core is composed of rare earth oxides composed of nano-cerium oxide and nano-lanthanum oxide in a weight ratio of (2~3):1. The shell is silver, and the shell accounts for 60%~80% of the total mass of the core-shell structure. The niobium-vanadium composite powder is composed of niobium powder and vanadium powder in a weight ratio of (2~4):1, and the purity of both niobium powder and vanadium powder is not less than 99.5%. In the titanium-boron alloy powder, the weight ratio of Ti to B is (3~5):1, wherein the total mass fraction of Ti and B is not less than 99.0%, and the remainder is unavoidable impurities; The nickel-based alloy powder comprises, by weight percentage: Cr 7.5%~8.5%, Cu 4.5%~5.5%, Mn 1.8%~2.2%, C≤0.10%, Si≤1.0%, P≤0.020%, S≤0.020%, with the balance being Ni and unavoidable impurities.

[0030] In this welding powder, the rare earth silver core-shell powder has a core-shell composite structure. The core is composed of rare earth oxides, which, as the main functional component, are primarily responsible for addressing the toughness of the weld and the purification of the molten pool. Specifically, during the welding metallurgical process, it adsorbs at grain boundaries to form fine rare earth compounds, which enhance low-temperature toughness by reducing grain boundary energy and increasing grain boundary bonding strength, and improves weld quality by purifying impurities in the molten pool. The shell is a dense silver layer, which acts as both a functional enhancer and a protective agent, physically isolating the rare earth oxide core from external oxygen and moisture. It ensures chemical stability while also taking into account welding process stability. On the other hand, it acts as a "hydrogen trap" by strongly adsorbing hydrogen atoms and catalyzes the combination of hydrogen atoms into hydrogen molecules at high arc temperatures, thus effectively reducing the risk of hydrogen-induced cracking. The two are not independent but rather an organic whole with complementary functions and synergistic effects. The core-shell synergy ensures that the weld metal can maintain excellent toughness at low temperatures and can still absorb high energy (impact energy ≥115J) at -40°C, achieving the integration of "toughness enhancement" and "hydrogen-induced crack control".

[0031] In this welding powder, Nb and V in the niobium-vanadium composite powder are both strong carbide-forming elements, which can form fine NbC and VC carbides, forming a gradient strength transition zone in the fusion zone, reducing the stress concentration factor in the fusion zone, and smoothly transitioning the strength from high-strength weathering steel to ordinary steel.

[0032] In this welding powder, Cr in the nickel-based alloy powder forms a protective oxide film, Cu improves corrosion resistance, and Mn improves the continuity of the corrosion-resistant layer, so that the corrosion potential difference between the weld and the high-strength weathering steel is ≤20mV, preventing galvanic corrosion and allowing the weld to corrode synchronously with the high-strength weathering steel in a humid, salt spray environment.

[0033] In this welding powder, Ti and B in the titanium-boron alloy powder form TiB2 fine particles, which act as grain refiners, refining the grain size of the weld metal, reducing the hardness gradient in the fusion zone, reducing grain boundary defects, and lowering the probability of crack initiation.

[0034] In this welding powder, the Mo in the molybdenum powder forms carbides such as Mo2C, which improves the strength and hardness of the weld and matches the strength of high-strength weather-resistant steel; the slag-forming agent forms stable slag, protects the molten pool, reduces porosity and inclusions, and improves the quality of the weld.

[0035] In this welding powder, iron powder serves as the main component of the weld metal, providing basic mechanical properties and working synergistically with other components to form a complete weld metal structure.

[0036] The weld formed by the synergistic action of the above components has a high low-temperature impact energy: the impact energy of the fusion zone at -40℃ is ≥115J, indicating that the weld can still absorb high energy without brittle fracture in extreme low-temperature environments.

[0037] In some embodiments of the present invention: the particle size of the rare earth silver core-shell particles is 8~12 μm, and the thickness of the shell is 1.0~2.0 μm. This particle size range ensures that the rare earth silver core-shell particles are uniformly distributed in the molten pool during welding, while maintaining the integrity of their core-shell structure. Particle size that is too small (<8 μm) may cause premature failure of the core-shell structure at high temperatures, resulting in the loss of the low-temperature toughness-enhancing effect of rare earth oxides; particle size that is too large (>12 μm) may lead to uneven particle distribution, reducing low-temperature impact performance. This particle size range allows the rare earth silver core-shell particles to effectively exert the synergistic effect of "the rare earth oxides in the core improving toughness, and the shell preventing rare earth oxidation" in the molten pool, achieving a low-temperature performance of ≥115J impact energy at -40℃.

[0038] In some embodiments of the present invention, the particle size of the niobium-vanadium composite powder is 10-15 μm. This particle size range allows niobium and vanadium to be uniformly distributed in the molten pool, forming a fine reinforcing phase. If the particle size is too small (<10 μm), the niobium and vanadium may melt prematurely, forming a coarse reinforcing phase and reducing the strength transition effect; if the particle size is too large (>15 μm), the niobium and vanadium may be unevenly distributed, failing to effectively achieve a strength gradient transition. This particle size range ensures that the niobium-vanadium composite powder can form a smooth strength transition zone with the base material, reducing stress concentration in the fusion zone and achieving strength matching.

[0039] In some embodiments of the present invention, the particle size of the molybdenum powder is 1~5 μm. This particle size range is beneficial for the uniform diffusion of nickel-based alloying elements in the molten pool, forming a uniform corrosion-resistant layer. A finer particle size (1~5 μm) allows molybdenum to melt quickly and distribute uniformly in the molten pool. Too small a particle size (<1 μm) may cause molybdenum to melt prematurely, failing to effectively exert its strengthening effect; too large a particle size (>5 μm) may lead to uneven molybdenum distribution, affecting the strengthening effect. This particle size range ensures that molybdenum can effectively strengthen the weld metal, improving strength and hardness, while avoiding uneven strengthening caused by excessively large particle sizes.

[0040] In some embodiments of the present invention, the particle size of the titanium-boron alloy powder is 10-20 μm. This particle size range allows titanium and boron to be uniformly distributed in the molten pool, forming a fine grain refiner. Too small a particle size (<10 μm) may lead to excessive grain refinement, affecting weld strength; too large a particle size (>20 μm) may result in poor grain refinement, increasing the risk of cracking. This particle size range allows the titanium-boron alloy powder to effectively refine the grains, reduce the hardness gradient in the fusion zone to ≤150 HV / mm, and reduce crack initiation.

[0041] In some embodiments of the present invention, the particle size of the nickel-based alloy powder is 10-20 μm. Too small a particle size (<10 μm) may cause premature precipitation of nickel-based alloying elements, affecting the continuity of the corrosion-resistant layer; too large a particle size (>20 μm) may lead to uneven distribution of corrosion-resistant elements, reducing the corrosion resistance effect. This particle size range allows the nickel-based alloy powder to effectively provide corrosion-resistant elements such as Cr, Cu, and Mn, achieving a corrosion resistance performance where the corrosion potential difference between the weld and the high-strength weathering steel is ≤20 mV.

[0042] In some embodiments of the present invention, the particle size of the slag-forming agent is 10~30 μm. This wide particle size range (10~30 μm) allows the slag-forming agent to form suitable slag in the molten pool. Too small a particle size (<10 μm) may result in excessively fine slag that is difficult to float, increasing porosity; too large a particle size (>30 μm) may result in coarse slag that cannot effectively cover the molten pool, affecting pool protection. This particle size range ensures that the slag-forming agent can effectively control the molten pool, reduce porosity and inclusions, and improve weld quality.

[0043] In some embodiments of the present invention, the particle size of the iron powder is 5~15 μm. This particle size range allows the iron powder to melt uniformly in the molten pool, providing a stable metal matrix. Too small a particle size (<5 μm) may cause the iron powder to melt prematurely, affecting the stability of the molten pool; too large a particle size (>15 μm) may cause incomplete melting of the iron powder, affecting weld formation. This particle size range ensures that the iron powder, as a base metal component, is uniformly distributed, forming a stable weld metal matrix.

[0044] In some embodiments of the present invention, the rare earth oxide is composed of nano-cerium oxide and nano-lanthanum oxide in a weight ratio of (2~3):1.

[0045] In some embodiments of the present invention, the slag-forming agent is composed of calcium fluoride and zirconium silicate in a weight ratio of (1.3~1.6):1. Calcium fluoride has a low melting point (1360℃), which can effectively lower the melting point of the slag and improve its fluidity; zirconium silicate has a high melting point (2270℃), which can improve the stability of the slag and prevent premature solidification. The (1.3~1.6):1 ratio of calcium fluoride and zirconium silicate can form a slag with appropriate melting point, fluidity, and stability.

[0046] In some embodiments of the present invention, the preparation method of the rare earth silver core-shell powder includes: Surface modification of rare earth oxide particles by amination; Chemical silver plating was performed on amination-modified rare earth oxide particles. The silver-plated particles are washed and dried to obtain rare earth silver core-shell powder.

[0047] Introducing amino groups onto the surface of rare earth oxide particles can improve their adhesion to the silver layer; depositing a silver layer on the surface of aminated rare earth particles to form a shell can prevent the rare earth oxides from oxidizing at the high temperature of welding.

[0048] The flux-cored welding wire provided by this invention consists of the aforementioned welding powder and a metal sheath surrounding the welding powder. The working principle of the flux-cored welding wire is that the wire is melted by arc heating, while the welding powder undergoes a chemical reaction at high temperature, forming protective slag and gas to protect the molten pool from air pollution. Simultaneously, specific alloying elements are added to the weld to improve its performance. The flux-cored welding wire using the aforementioned welding powder can form durable welds between high-strength weather-resistant steel and ordinary steel.

[0049] In some embodiments of the present invention, the flux-cored welding wire is welded using carbon dioxide gas shielded welding. The principle of welding with carbon dioxide gas shielded welding using flux-cored welding wire is as follows: Under the protection of carbon dioxide gas, the welding powder inside the flux-cored welding wire works synergistically at the high temperature of the electric arc: the slag-forming agent and carbon dioxide gas form a double protection, preventing oxidation of the molten pool; each component melts and reacts according to its particle size gradient; niobium-vanadium composite powder achieves strength transition; rare earth silver core-shell powder improves low-temperature toughness; nickel-based alloy powder ensures corrosion resistance matching; titanium-boron alloy powder reduces the hardness gradient in the fusion zone; molybdenum powder strengthens the weld; and iron powder provides the basic metallic composition. This synergistic effect enables the weld to achieve ideal levels in key properties such as strength transition, corrosion resistance matching, and crack resistance, breaking through the "low-temperature toughness-corrosion resistance" seesaw effect, solving the technical difficulties in dissimilar welding of high-strength weathering steel and ordinary steel, and making carbon dioxide gas shielded welding a reliable welding method suitable for this scenario.

[0050] In some embodiments of the present invention, the weld formed by the flux-cored welding wire between high-strength weathering steel and ordinary steel satisfies at least one of the following performance indicators: (i) The standard impact energy of the fusion zone at -40℃ is 115~125J; the weld can still absorb high energy in extreme low temperature environments, avoiding brittle fracture, and is suitable for bridges in cold regions. (ii) The corrosion potential difference in the fusion zone between the weld and the high-strength weathering steel is 17.0~19.5mV; The weld and high-strength weather-resistant steel corrode simultaneously in the corrosive environment, avoiding galvanic corrosion and improving corrosion resistance; (iii) The hardness gradient of the fusion zone is 120~146HV / mm; the hardness transition between the weld and the base material is smooth, reducing the risk of cracking and improving fatigue resistance.

[0051] In some embodiments of the present invention: the weight percentage of welding powder in the flux-cored welding wire is 40% to 60%. When the welding powder content is in the range of 40% to 60%, the arc stability of the flux-cored welding wire is optimal, the welding process is smooth, and the spatter rate is low.

[0052] The dissimilar welding method for high-strength weather-resistant steel and ordinary steel provided by the present invention uses the above-mentioned flux-cored welding wire for carbon dioxide gas shielded welding. The carbon dioxide gas is 80%Ar+20%CO2, and the gas flow rate is 25L / min, forming a weld between the interface of high-strength weather-resistant steel and ordinary steel.

[0053] In some embodiments of the present invention, the high-strength weathering steel is Q700NH high-strength weathering steel, and the ordinary steel is Q355B ordinary steel. The strength difference between Q700NH high-strength weathering steel and Q355B ordinary steel exceeds 300MPa, which places higher demands on the low-temperature toughness of the welding materials.

[0054] The technical solution of the present invention will be described in detail below through specific embodiments: The rare earth silver core-shell powder used in the following examples was prepared according to CN107096915A. The specific preparation steps are as follows: (1) Weigh nano-cerium oxide (CeO2) powder and nano-lanthanum oxide (La2O3) powder at a weight ratio of 3:2, mix them, and add them to deionized water containing 0.1% (w / v) sodium hexametaphosphate (as a dispersant) to prepare a suspension with a solid content of 5%. Under ice-water bath, sonicate (power 600W, on for 2s, off for 1s) for 1 h to obtain a uniformly dispersed rare earth oxide suspension for later use.

[0055] (2) Take 100 mL of the suspension obtained in step (1) and add it dropwise to 100 mL of 7.5% (v / v) 3-aminopropyltriethoxysilane (APTES) anhydrous ethanol solution (adjust the pH to 5.0 with acetic acid). Stir the mixture magnetically at 60 °C for 4 h, centrifuge (8000~12000 rpm, 15~20 min), wash three times with anhydrous ethanol to remove unreacted APTES, and dry the resulting solid under vacuum at 60 °C for 2 h to obtain aminated rare earth oxide powder for later use.

[0056] (3) Add all the modified rare earth oxides obtained in step (2) to the mixed solution (composed of 1.0 g silver nitrate, 200 mL deionized water and 300 mL polyvinylpyrrolidone (PVP)) and ultrasonically disperse for 15 min to obtain solution A; Separately dissolve 0.8 g of sodium borohydride (NaBH4) in 100 mL of deionized water, and adjust the pH to 8.5 with 10 wt% sodium hydroxide solution to obtain solution B; Liquid B was added to liquid A droplet at a rate of 5 mL / min using a peristaltic pump. During the reaction, the mixture was continuously stirred with ultrasound (ultrasound power 300±50W, frequency 40kHz) and stirred for 12 h. The reaction progress was monitored by taking intermediate samples (every 2 h). Immediately after the reaction was completed, 0.1% PVP (relative to the solution volume) was added as an Ag particle dispersant, and the mixture was centrifuged (10000~14000 rpm, 20~30 min) to obtain surface-activated rare earth oxides.

[0057] (4) The surface-activated rare earth oxides obtained in step (3) are transferred into the electroless silver plating solution. The reaction temperature is controlled at 8℃ and pH at 8.5. The reaction is ultrasonically stirred for 25 min. [The composition of the electroless silver plating solution is: silver nitrate (AgNO3, concentration 4.0 g / L), potassium sodium tartrate (NaKC4H4O6, concentration 5.0 g / L), glucose (C6H4O6)] 12 [O6 (concentration 12.5 g / L) and water]. After the reaction was completed, the mixture was centrifuged (12000~15000 rpm, 25~35 min), washed three times with deionized water, and dried under vacuum at 60℃ for 2 h to obtain rare earth silver core-shell powder.

[0058] The particle size of rare earth silver core-shell powder is 8~12 μm, the shell accounts for 60%~80% of the total mass of the core-shell structure, and the silver thickness is 1.0~2.0 μm.

[0059] The raw material information used in the following examples is as follows: The niobium-vanadium composite powder is composed of niobium powder and vanadium powder in a weight ratio of 3:1, with a particle size of 10~15 μm, and the purity of both niobium powder and vanadium powder is not less than 99.5%. The mass percentages of each element in the nickel-based alloy powder are approximately: Ni 85%, Cr 8%, Cu 5%, Mn 2%, C ≤ 0.10%, Si ≤ 1.0%, P ≤ 0.020%, S ≤ 0.020%, and the particle size is 10~20 μm.

[0060] In the titanium-boron alloy powder, the weight ratio of Ti to B is 4:1, and the total mass fraction of Ti and B is not less than 99.0%, with the remainder being unavoidable impurities with a particle size of 10~20 μm. The slag-forming agent is composed of calcium fluoride (purity ≥98%) and zirconium silicate (purity ≥99%) in a weight ratio of 3:2, with a particle size of 10~30μm; The particle size of molybdenum powder is 1~5 μm; The particle size of the iron powder is 5~15μm; The metal outer sheath is made of low-carbon steel strip with a carbon content of ≤0.05%.

[0061] Example 1. Preparation of solder powder Prepare the raw materials according to Table 3 and mix them into welding powder.

[0062] 2. Flux-cored welding wire (1) Smelting and refining: After mixing raw materials such as iron powder and nickel-based alloy powder, the mixture is melted and refined at 1680℃ and 0.1Pa vacuum for 15 minutes. High-purity argon is introduced, and electrolytic manganese and industrial pure titanium are added. Nickel-magnesium alloy is used for deoxidation, and the steel is tapped at 1635℃ and cast into steel ingots. (2) Forging and rolling: After removing the oxide scale, the steel ingot is forged into a 500mm×500mm×500mm square billet at 1140℃ and air-cooled; the billet is heated to 1100℃ and held for 25 minutes, and then rolled into a wire rod with a diameter of 8mm. (3) Drawing and annealing: After intermediate annealing (air cooling at 680℃ for 20 min), the wire rod is drawn in multiple passes to a diameter of 1.2 mm to obtain flux-cored welding wire.

[0063] 3. Application The obtained flux-cored welding wire was used for vertical welding of fillet welds between high-strength weathering steel (Q700NH, plate thickness 22mm) and ordinary steel (Q355B, plate thickness 22mm). The specific steps are as follows: (1) Preparation before welding: A) Beveling and Cleaning: The test plate uses a V-shaped bevel with dimensions of 60°±5°, a blunt edge of 1.5mm, a root gap of 2mm, and a reverse deformation of 3°~4°. The bevel and the area within ≥50mm on both sides of the bevel are thoroughly cleaned using mechanical grinding (e.g., an angle grinder) to remove oil, moisture, rust, scale, and other impurities until a uniform metallic luster is exposed. After cleaning, it should be wiped with acetone or anhydrous ethanol to further remove any remaining stains.

[0064] B) Environmental Control Welding operations must be carried out under the following environmental conditions: Ambient temperature: not lower than 10℃.

[0065] Relative humidity: not higher than 60%.

[0066] Wind speed: not greater than 2 m / s. A windproof shed must be erected when working outdoors.

[0067] Base material temperature: It must be ensured to be at least 3°C ​​above the ambient dew point temperature to prevent condensation.

[0068] Outdoor work is strictly prohibited in rainy, snowy, or foggy weather or when there is visible moisture on the surface of the substrate.

[0069] C) Assembly and tack welding After the test plates are assembled, tack welding is performed within the bevel. Tack welds should be located at the beginning, end, and middle of the weld (depending on the length of the test plate, the spacing generally should not exceed 300mm). The length of the tack weld should be 30-40mm, and the weld thickness should be 5-6mm. The welding materials, procedures, and welder qualifications used for tack welding should be the same as those for the final welding, ensuring good fusion. After welding, the surface of the tack weld should be carefully inspected to ensure there are no cracks or other defects.

[0070] D) Preheating The test plate must be preheated before welding. Preheating can be done by electric heating or flame heating, and uniform heating should be ensured.

[0071] Preheating temperature: 120~150℃. Preheating range: ≥100mm on both sides of the weld center (i.e., total width ≥200mm or more than twice the plate thickness, whichever is greater).

[0072] Temperature measurement requirements: Use a contact thermometer to measure the temperature 50mm from the center of the bevel on the opposite side of the heating surface to ensure that the temperature in the entire preheating area meets the requirements.

[0073] E) Welding equipment The welding equipment was debugged, and the specific welding process parameters were set according to the recommended values ​​in the JTS Welding 690MPa Grade Welding Wire Technical Manual, as shown in Table 1: Table 1

[0074] (2) Welding: Shielding gas: 80%Ar + 20%CO2; Gas flow rate: 20~25L / min; Gas dew point: ≤-40℃; Welding wire extension length: 14~16mm; Welding wire baking: Welding wire must be baked strictly according to specifications (usually 350℃×1h), and the exposure time after the welding wire is taken out of the heat preservation barrel shall not exceed 3 hours; Welding torch angle: 70°~80° with the workpiece surface; When using left-hand welding (right-hand welding method), maintain a short arc welding. When moving the electrode, you can make slight oscillations or straight movements. Closely observe the size of the molten pool and the formation of the weld in real time. At the same time, the welder must conduct a 100% visual inspection of the weld. If defects such as porosity, slag inclusions, or undercut are found, they should be removed and repaired immediately.

[0075] In addition, key parameters such as actual welding current, voltage, speed, preheating temperature, and interpass temperature for each test plate were recorded and correlated with welding time / weld length.

[0076] Table 2

[0077] (3) Post-weld treatment: After welding is completed, take slow cooling measures immediately, such as wrapping the weld area with insulation cotton (aluminum silicate board) to allow it to cool slowly to room temperature.

[0078] Dimensional inspection: Use a weld leg measuring ruler to check the weld leg dimensions (K value).

[0079] Visual inspection: The weld surface must be free of defects such as cracks, porosity, undercut, and lack of fusion.

[0080] Non-destructive testing (NDT): Ultrasonic testing (UT) is performed on the entire length of the weld in the test plate. The test is usually required to be performed 24 hours or even longer after welding (to prevent delayed cracking).

[0081] (4) Sampling and testing: According to the requirements of GB / T 8110-2020, GB / T 4336-2016, GB / T 2652-2022 and GB / T 2650-2022, samples were taken from the test plate, and the performance test results are shown in Table 3.

[0082] Table 3. Performance test results of the flux-cored welding wires prepared in each embodiment.

[0083] Table 3 (continued)

[0084] Table 3 (continued)

[0085] As shown in Table 3, the flux-cored welding wires provided in Examples 1-18 are used for CO2 gas shielded welding. Due to the protection of rare earth and other microalloying elements, the alloying elements in the weld metal are less lost, effectively ensuring the strength, toughness, and durability of the weld metal. This effectively improves the redox reaction and fluidity of the molten pool, reducing nitrogen and hydrogen porosity, decreasing the number of inclusions, and refining the number of large inclusions. The properties of the weld metal are: yield strength ≥750MPa, corrosion potential difference in the fusion zone ≤20mV, hardness gradient in the fusion zone ≤150HV / mm, and standard impact energy in the fusion zone at -40℃ ≥115J. The potential differences in each zone of the weld joint are not significant, indicating that the weld joint formed by the flux-cored welding wires provided in Examples 1-18 has excellent corrosion resistance when matched with the base metal. The comprehensive performance of the weld meets the welding matching technical conditions such as strength transition, corrosion resistance matching, and crack resistance requirements between high-strength weathering steel and ordinary steel.

[0086] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A welding powder for flux-cored welding wire, characterized in that: The solder powder comprises, by weight percentage: Rare earth silver core-shell powder 2.00±0.20%; Niobium-vanadium composite powder: 7.05±0.53%; Nickel-based alloy powder 29.97±1.91%; Molybdenum powder 0.79±0.11%; Titanium-boron alloy powder 1.00±0.12%; Slag-forming agent 10.00±2.82%; The remainder consists of iron powder and unavoidable impurities; in: The rare earth silver core-shell powder is composed of rare earth silver core-shell particles. The rare earth silver core-shell particles have a core-shell structure. The core is composed of rare earth oxides consisting of nano-cerium oxide and nano-lanthanum oxide in a weight ratio of (2~3):

1. The shell is silver, and the shell accounts for 60%~80% of the total mass of the core-shell structure. The niobium-vanadium composite powder is composed of niobium powder and vanadium powder in a weight ratio of (2~4):1, and the purity of both niobium powder and vanadium powder is not less than 99.5%. In the titanium-boron alloy powder, the weight ratio of Ti to B is (3~5):1, wherein the total mass fraction of Ti and B is not less than 99.0%, and the remainder is unavoidable impurities; The nickel-based alloy powder comprises, by weight percentage: Cr 7.5%~8.5%, Cu 4.5%~5.5%, Mn 1.8%~2.2%, C≤0.10%, Si≤1.0%, P≤0.020%, S≤0.020%, with the balance being Ni and unavoidable impurities.

2. The welding powder for flux-cored welding wire according to claim 1, characterized in that: The rare earth silver core-shell particles have a particle size of 8-12 μm and a shell thickness of 1.0-2.0 μm; and / or, The niobium-vanadium composite powder has a particle size of 10-15 μm; and / or, The molybdenum powder has a particle size of 1~5 μm; and / or, The titanium-boron alloy powder has a particle size of 10~20 μm; and / or, The nickel-based alloy powder has a particle size of 10~20 μm; and / or, The slag-forming agent has a particle size of 10~30μm; and / or, The iron powder has a particle size of 5~15μm.

3. The welding powder for flux-cored welding wire according to claim 1, characterized in that: The rare earth oxide is composed of nano-cerium oxide and nano-lanthanum oxide in a weight ratio of (2~3):

1.

4. The welding powder according to claim 1, characterized in that: The slag-forming agent is composed of calcium fluoride and zirconium silicate in a weight ratio of (1.3~1.6):1, wherein the purity of calcium fluoride is ≥98% and the purity of zirconium silicate is ≥99%.

5. The welding powder for flux-cored welding wire according to claim 1, characterized in that: The preparation method of the rare earth silver core-shell powder includes: Surface modification of rare earth oxide particles by amination; Chemical silver plating was performed on amination-modified rare earth oxide particles. The silver-plated particles are washed and dried to obtain rare earth silver core-shell powder.

6. A flux-cored welding wire, characterized in that, The flux-cored wire is composed of the flux-cored wire as described in any one of claims 1 to 5 and a metal sheath covering the flux-cored wire.

7. The flux-cored welding wire according to claim 6, characterized in that: The flux-cored welding wire is used for carbon dioxide gas shielded welding of the interface between high-strength weather-resistant steel and ordinary steel.

8. The flux-cored welding wire according to claim 6, characterized in that: The weld formed by the flux-cored welding wire between high-strength weather-resistant steel and ordinary steel meets at least one of the following performance indicators: (i) The standard impact energy at -40°C in the fusion zone is 115~125J; (ii) The corrosion potential difference in the fusion zone between the weld and the high-strength weathering steel is 17.0~19.5mV; (iii) The hardness gradient of the fusion zone is 120~146HV / mm.

9. The flux-cored welding wire according to claim 6, characterized in that: The flux-cored welding wire contains 40% to 60% welding powder by weight.

10. A method for dissimilar welding of high-strength weathering steel and ordinary steel, characterized in that: Carbon dioxide gas shielded welding is performed using the flux-cored welding wire as described in any one of claims 6 to 9. The carbon dioxide gas is 80% Ar + 20% CO2, and the gas flow rate is 25 L / min. A weld is formed between the interface of high-strength weather-resistant steel and ordinary steel.

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