A gas shielded flux cored wire for very low temperature and a method for manufacturing the same, and a welding method

Abstract

The application belongs to the field of welding materials, and provides a gas shielded flux-cored wire for extremely low temperature and a preparation method and a welding method thereof. The gas shielded flux-cored wire comprises a nickel-based sheath and a core powder, and the core powder comprises alloying elements such as chromium, molybdenum, niobium, nickel and iron as well as a slagging agent and a deoxidizing agent. The sintering process is used to remove the crystal water of the powder, and the composition is optimized, so that the welding wire still has excellent low-temperature toughness and tensile strength at-196 DEG C. The application is suitable for welding of 06Ni9DR steel for liquefied natural gas storage tanks, has low cost, stable process and good engineering applicability.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, specifically, it relates to a gas-shielded flux-cored welding wire suitable for use in ultra-low temperature environments such as liquefied natural gas storage tanks, as well as its preparation method and welding method. Background Technology

[0002] With the global energy structure shifting towards cleaner energy sources, the liquefied natural gas (LNG) industry is developing rapidly. LNG storage temperatures are approximately -161.5℃, and its storage tanks often use 06Ni9DR steel, which retains excellent low-temperature toughness even at -196℃. Welding is a critical step in tank manufacturing, and the quality of its joints directly determines the safety and reliability of the tank in ultra-low temperature environments.

[0003] Currently, high-performance nickel-based alloy welding materials suitable for cryogenic welding of 06Ni9DR steel, especially gas-shielded flux-cored welding wire (FCAW), still largely rely on imports in the domestic market. Imported welding wires are expensive and have long delivery cycles. Furthermore, existing cryogenic welding wires still have room for improvement in terms of weld metal purity control, low-temperature toughness stability, and welding method performance.

[0004] Therefore, developing a gas-shielded flux-cored welding wire with reasonable cost, good process performance, and high toughness and strength at extremely low temperatures of -196℃, along with its supporting technologies, is of great significance for achieving the domestic substitution of key welding materials.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art, and the purpose is to provide a flux-cored welding wire for gas protection welding that has good mechanical properties, low economic cost and good toughness at -196℃, and is suitable for manufacturing cryogenic liquefied natural gas storage tanks.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned welding wire.

[0008] Another object of the present invention is to provide a welding method using the above-described welding wire.

[0009] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is: a gas-shielded flux-cored wire for extremely low temperature environments, comprising an outer nickel-based metal strip and an inner flux-cored powder, wherein the composition of the flux-cored powder, by mass percentage, includes: Chromium: 45.0%–48.0% Molybdenum: 20.0%–22.0% Niobium: 7.0–8.0%, Iron: 4.0-4.5%, Nickel: 10.0%–13.0% Titanium dioxide: 4.0–6.0%, Silicon dioxide: 1.0–2.0%, Calcium fluoride: 1.0–2.0%, Aluminum oxide: 0-1.0%, Manganese: 0.2-0.5%, Silicon: 0.5%–1.0% Titanium: 0.5-1.0%.

[0010] According to one embodiment of the present invention, the chemical composition of the nickel-based metal strip contains ≤0.02% carbon, ≤0.01% sulfur, ≤0.01% phosphorus, ≥99% nickel, and the remainder is unavoidable impurities.

[0011] According to one embodiment of the present invention, the filling rate of the core powder is 35% to 40%.

[0012] According to one embodiment of the present invention, the particle size range of the core powder is 80 to 200 mesh.

[0013] According to one embodiment of the present invention, the diameter of the welding wire is 1.2 mm.

[0014] The present invention also provides a method for preparing the above-mentioned flux-cored welding wire, characterized by comprising the following steps: 1) Dry the core powder to constant weight; 2) The slag-forming agent is sintered at 720℃ for 2 hours. 3) After sintering, the powder is obtained by ball milling and mixing; 4) After the nickel strip is rolled into shape, it is filled with flux powder and sealed to obtain coarse welding wire; 5) The diameter of the coarse welding wire is reduced to the target diameter through a drawing process.

[0015] According to one embodiment of the present invention, the compression rate is controlled at 10% to 15% during each drawing process.

[0016] The present invention also provides a method for welding 06Ni9DR steel using the above-mentioned flux-cored welding wire, using a mixture of argon and carbon dioxide as the protective medium, with a welding heat input of 10-15 KJ / cm and an interpass temperature ≤100℃.

[0017] According to one embodiment of the present invention, the welding current is 200-240A and the welding voltage is 26-30V.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: a) The flux-cored welding wire of the present invention improves the solid solution strengthening effect and grain boundary strength of the alloy by precisely controlling the content of individual elements such as Cr, Mo, Nb, Fe, Mn, Si, and Ti in the alloy; and reduces the content of inclusions in the alloy by precisely controlling the content of O, N, S, and P during the processing, thereby improving the purity, plasticity, and fatigue performance of the alloy.

[0019] b) The flux-cored welding wire of the present invention reduces the crystal water in the powder by adding a sintering process of slag-forming agent before powder mixing, which is beneficial to reduce the generation of gas in the subsequent welding process.

[0020] c) The flux-cored welding wire of this invention can be used for welding 06Ni9DR steel in liquefied natural gas storage tanks in an environment of -196 ℃. Its properties are as follows: Example 1: Room temperature tensile properties: tensile strength R m =721 MPa, yield strength Rp 0.2 =451 MPa, elongation after fracture A=36.8%, reduction of area Z=36%, low temperature impact performance at -196℃: energy absorbed KV2=75 J; Example 2: Room temperature tensile properties: tensile strength R m =716.5 MPa, yield strength Rp 0.2 =437 MPa, elongation after fracture A=43%, reduction of area Z=42%, low temperature impact performance at -196℃: absorbed energy KV2=75 J.

[0021] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0022] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 These are macroscopic views of the weld metal in Embodiments 1-2 of the present invention; Figure 2 These are microstructure diagrams of the weld metal in Examples 1-2 of the present invention; Figure 3 The fracture morphology of the fiber region of the tensile specimens of the weld metal in Examples 1-2 of this invention is shown in high magnification SEM. Figure 4The fracture morphology of the fused metal impact specimens in Examples 1-2 of this invention is shown.

[0023] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] The inventors discovered through in-depth research that people's demand for liquefied natural gas is increasing. However, the development of nickel-based welding materials for liquefied natural gas storage tanks in my country lags far behind that of steel materials for liquefied natural gas storage tanks. This situation has become a bottleneck in my country's current development, greatly restricting the development of the liquefied natural gas industry.

[0028] This invention provides a flux-cored welding wire for gas shielded welding of 06Ni9DR steel in cryogenic liquefied natural gas storage tanks, its preparation method, and welding method. The specific implementation scheme is as follows: The welding wire consists of flux-cored powder and an outer nickel metal strip that serves as a coating. The flux-cored powder is controlled within the following range by weight percentage: Alloying elements: Cr: 45.0~48.0%, Mo: 20.0~22.0%, Nb: 7.0~8.0%, Fe: 4.0~4.5%, Ni: 10.0~13.0%; Slag-forming agent: TiO2: 4.0~6.0%, SiO2: 1.0~2.0%, CaF2: 1.0~2.0%, Al2O3: 0~1.0%; Deoxidizer / alloying element Mn: 0.2~0.5%, Si: 0.5~1.0%, Ti: 0.5~1.0%.

[0029] The sum of the mass percentages of the above components is 100%.

[0030] This welding wire controls the range of the above alloying elements, thereby controlling the proportion of harmful phases in the weld metal and achieving the goal of improving the toughness of the weld metal.

[0031] Furthermore, compared to imported welding wire, the welding wire prepared by the method proposed in this invention can significantly reduce costs, thereby improving the economic efficiency of welding materials. Welding tests on the welding wire have demonstrated that the impact toughness and tensile strength of the weld metal both meet the application requirements.

[0032] The following details the function and dosage selection of the components contained in this invention: Cr: The addition of Cr mainly optimizes mechanical properties through interstitial and substitutional solid solutions when dissolved in the austenitic matrix in the form of solute atoms. This enhances the matrix's resistance to deformation while maintaining good ductility. Besides its strengthening effect, Cr's unique passivation effect effectively suppresses grain boundary corrosion sensitivity, exhibiting unique resistance to stress corrosion cracking, especially in sulfur-containing environments. It is important to note that when the Cr concentration exceeds a critical value, it will cause a decrease in thermal conductivity, leading to thermal stress concentration during welding thermal cycling and increasing the tendency for solidification crack formation. Simultaneously, the selective precipitation of Cr23C6 type carbides at grain boundaries can induce chromium depletion at grain boundaries, resulting in a decrease in localized corrosion resistance. Therefore, in this invention, the Cr content in the flux core powder is controlled at 45.0% to 48.0%.

[0033] Mo: The main function of Mo is the same as that of Cr, optimizing mechanical properties through a dual mechanism of interstitial solid solution and substitutional solid solution. However, excessive Mo promotes the formation of topologically close-packed phases (such as the σ phase) and the Laves phase. The dispersed distribution of these brittle intermetallic compounds can severely weaken the ductility of the material and also cause stress concentration at the phase interface, reducing the overall toughness of the weld microstructure. Therefore, in this invention, the Mo content in the flux core powder is controlled at 20.0~22.0%.

[0034] Nb: The main function of Nb is to prevent carbide precipitation and improve the crack resistance of the weld. Therefore, in this invention, the Nb content in the flux core powder is controlled at 7.0~8.0%.

[0035] Fe: The main function of Fe is to enhance the strength and hardness of the weld metal through solid solution strengthening, and to improve the impact toughness of the weld. Therefore, in this invention, the Fe content in the flux core powder is controlled at 4.0~4.5%.

[0036] Ni: As a core element for regulating austenite phase transformation, Ni plays a significant role in the microstructure of weld metal. This element also improves the corrosion resistance of weld metal, especially in non-oxidizing corrosive media containing Cl ions, significantly enhancing the material's environmental adaptability through the stabilizing effect of a surface passivation film. Therefore, in this invention, the Ni content in the flux-cored powder is controlled at 10.0~13.0%.

[0037] TiO2: The main function of TiO2 is as a primary slag-forming agent, ensuring excellent arc stability, weld bead formation, and slag removal. Meanwhile, a higher Cr content may require more TiO2 to maintain process performance. Therefore, in this invention, the TiO2 content in the flux core powder is controlled at 4.0~6.0%.

[0038] SiO2: The main function of SiO2 is to adjust the fluidity and viscosity of the slag. Therefore, in this invention, the SiO2 content in the core powder is controlled at 1.0~2.0%.

[0039] CaF2: The main function of CaF2 is to remove hydrogen and prevent weld cracks. Therefore, in this invention, the CaF2 content in the flux core powder is controlled at 1.0~2.0%.

[0040] Al2O3: The main function of Al2O3 is to fine-tune the properties of the slag. Therefore, in this invention, the Al2O3 content in the core powder is controlled at 0~1.0%.

[0041] Mn: The role of Mn is to promote austenite formation. The addition of Mn can also improve weld toughness and slightly enhance weld hardness and strength. Mn also acts as a deoxidizer; if the deoxidation products of Mn do not have time to float to the surface of the weld pool, they may act as nucleating agents, helping to refine grains. Therefore, in this invention, the Mn content in the flux core powder is controlled at 0.2~0.5%.

[0042] Ti: Ti acts as a powerful deoxidizer and can improve weld performance. Therefore, in this invention, the Ti content in the flux core powder is controlled at 0.5~1.0%.

[0043] This invention also provides a method for preparing nickel-based flux-cored welding wire and a corresponding welding method, including: (1) Place the core powder in a drying oven for drying. Adjust the drying temperature and time, and compare the weight of the powder before and after drying in real time. When the weight of the powder remains unchanged, the drying is complete. Thoroughly mix the dry core powder and sinter it. Through solid-phase reaction, particle surface softening, and local melting, the powder is sintered into blocks to remove the water of crystallization in the core powder. Too high a sintering temperature will cause the core powder to fail. Strictly control the sintering temperature at 720℃ and the holding time for 2 hours. Since the sintered core powder is coarse-grained or blocky, it needs to be ball-milled for 15 minutes to obtain core powder with good particle size. Place the core powder in a powder mixer for mixing. The mixing time is 30 minutes. Too short a mixing time will result in uneven mixing, while too long a mixing time will cause the core powder to deform and affect the flowability of the powder.

[0044] (2) The nickel metal strip coated with the flux-cored powder is formed into a "U-shaped groove" through shaping and three rolling processes. The flux-cored powder is then uniformly filled into the "U-shaped groove" of the nickel metal strip according to the corresponding filling ratio using a powder feeding device. Finally, the nickel metal strip is sealed to obtain a thicker flux-cored welding wire.

[0045] (3) The diameter of the thicker flux-cored welding wire is reduced. By setting a reasonable number of passes, the compression rate of the welding wire is guaranteed to be 10%-15% each time, and finally a flux-cored welding wire for gas shielded welding of 06Ni9DR steel for liquefied natural gas storage tank with a diameter of 1.2mm is obtained.

[0046] Welding tests were conducted using the prepared flux-cored welding wire, and the mechanical properties of the welded joints were measured. The welding method was gas shielded welding (FCAW), with a welding current of 200-240A, a welding voltage of 26-30V, a heat input of 10-15KJ / cm, an interpass temperature ≤100℃, and a welding speed of 32-40cm / min. The base material was 20mm thick 06Ni9DR steel, with a 30° bevel on one side. 06Ni9DR steel was used as a backing plate for cladding tests. Observation of the weld revealed good weld formation quality, with no hot cracks, obvious spatter, holes, undercut, or other poor forming defects. The welded test plates were cut using wire cutting and fabricated into standard specimens for mechanical property testing.

[0047] Impact tests were conducted according to GB / T 2650-2022: three impact samples were taken, a V-notch was made at the center of the weld, and the impact test was carried out at -196℃ to measure the impact energy.

[0048] According to GB / T 2652-2022, longitudinal tensile tests of welds were conducted: two tensile specimens were taken and tensile tests were performed at room temperature to measure the tensile strength of the deposited metal.

[0049] The properties of the deposited metal obtained in the above steps are as follows: Example 1: Room temperature tensile properties: tensile strength Rm = 721 MPa, specified plastic elongation Rp0.2 = 451 MPa, elongation after fracture A = 36.8%, reduction of area Z = 36%, -196 ℃ low temperature impact properties: absorbed energy KV2 = 75 J, shear area SFA = 100%, lateral expansion LE = 1.39 mm; Example 2: Room temperature tensile properties: tensile strength Rm = 716.5 MPa, specified plastic elongation Rp0.2 = 437 MPa, elongation after fracture A = 43%, reduction of area Z = 42%, -196℃ low temperature impact properties: absorbed energy KV2 = 75 J, shear area SFA = 100%, lateral expansion LE = 1.47 mm.

[0050] This invention provides the application of nickel-based flux-cored welding wire in ultra-low temperature environments. The flux-cored welding wire can be used for welding 06Ni9DR steel in liquefied natural gas storage tanks in an environment of -196℃.

[0051] Compared with the prior art, the flux-cored welding wire of the present invention improves the solid solution strengthening effect and grain boundary strength of the alloy by precisely controlling the content of individual elements such as Cr, Mo, Nb, Fe, Mn, Si, and Ti in the alloy; and reduces the content of inclusions in the alloy by precisely controlling the content of O, N, S, and P during the processing, thereby improving the purity, plasticity, and fatigue performance of the alloy.

[0052] The flux-cored welding wire of the present invention reduces the water of crystallization in the powder by adding a sintering process with a slag-forming agent before powder mixing, which helps to reduce the generation of gas during the subsequent welding process.

[0053] The flux-cored welding wire of the present invention produces weld metal with good mechanical properties at both room temperature and ultra-low temperature environments, as follows: Example 1: Room temperature tensile properties: tensile strength R m =721 MPa, specified plastic elongation strength Rp 0.2 =451 MPa, elongation after fracture A=36.8%, reduction of area Z=36%, low temperature impact performance at -196 ℃: absorbed energy KV2=75 J, shear area ratio SFA=100%, lateral expansion value LE=1.39 mm; Example 2: Room temperature tensile properties: tensile strength R m =716.5 MPa, specified plastic elongation strength Rp 0.2 =437MPa, elongation after fracture A=43%, reduction of area Z=42%, low temperature impact performance at -196℃: absorbed energy KV2=75 J, shear area ratio SFA=100%, lateral expansion value LE=1.47 mm.

[0054] The advantages of controlling the alloy composition and preparation method of the present invention are illustrated below with specific embodiments. Embodiments 1-2 of the present invention provide a flux-cored welding wire for gas-shielded welding of 06Ni9DR steel for liquefied natural gas storage tanks and its preparation method.

[0055] Example 1 Preparation and application of nickel-based gas-shielded flux-cored welding wire for cryogenic -196℃ liquefied natural gas storage tanks: (1) Place the core powder in a drying oven for drying. Adjust the drying temperature and time, and compare the weight of the powder before and after drying in real time. When the weight of the powder remains unchanged, the drying is complete. Thoroughly mix the dry core powder and sinter it. Through solid-phase reaction, particle surface softening, and local melting, the powder is sintered into blocks to remove the water of crystallization in the core powder. Too high a sintering temperature will cause the core powder to fail. Strictly control the sintering temperature at 720℃ and the holding time for 2 hours. Since the sintered core powder is coarse-grained or blocky, it needs to be ball-milled for 15 minutes to obtain core powder with good particle size. Place the core powder in a powder mixer for mixing. The mixing time is 30 minutes. Too short a mixing time will result in uneven mixing, while too long a mixing time will cause the core powder to deform and affect the flowability of the powder.

[0056] (2) The nickel metal strip coated with the flux-cored powder is formed into a "U-shaped groove" through shaping and three rolling processes. The flux-cored powder is then uniformly filled into the "U-shaped groove" of the nickel metal strip according to the corresponding filling ratio using a powder feeding device. Finally, the nickel metal strip is sealed to obtain a thicker flux-cored welding wire.

[0057] (3) The diameter of the thicker flux-cored welding wire is reduced. By setting a reasonable number of passes, the compression rate of the welding wire is guaranteed to be 10%-15% each time, and finally a flux-cored welding wire for gas shielded welding of 06Ni9DR steel for liquefied natural gas storage tank with a diameter of 1.2mm is obtained.

[0058] Welding tests were conducted using the prepared flux-cored welding wire, and the mechanical properties of the welded joints were measured. The welding method was gas shielded welding (FCAW). The welding current was 200-240A, the welding voltage was 26-30V, the heat input was 10-15KJ / cm, the interpass temperature was ≤100℃, and the welding speed was 32-40cm / min. The base material was 20mm thick 06Ni9DR steel, with a 30° bevel on one side. 06Ni9DR steel was used as a backing plate for cladding tests. Observation of the weld revealed good weld formation quality, with no hot cracks, obvious spatter, holes, undercut, or other poor forming defects on the surface. The welded test plates were cut using wire cutting and fabricated into standard specimens for mechanical property testing.

[0059] Impact tests were conducted according to GB / T 2650-2022: three impact samples were taken, a V-notch was made at the center of the weld, and the impact test was carried out at -196℃ to measure the impact energy.

[0060] According to GB / T 2652-2022, longitudinal tensile tests of welds were conducted: two tensile specimens were taken and tensile tests were performed at room temperature to measure the tensile strength of the deposited metal.

[0061] Example 2 The preparation method in this embodiment is largely the same as that in Example 1, except that the final composition of the deposited metal is different. The composition of the deposited metal in Examples 1-2 is shown in Table 1 below: Table 1. Composition range of deposited metal in Examples 1-2 The room temperature tensile properties test results of the above-mentioned weld metal are shown in Table 2 below: Table 2. Room temperature tensile properties of weld metal from nickel-based welding wires used in liquefied natural gas storage tanks. The results of the cryogenic impact performance tests of the above-mentioned weld metal are shown in Table 3 below: Table 3. Cryogenic Impact Properties of Deposited Metals of Nickel-Based Welding Wires for Liquid Natural Gas Storage Tanks Figure 1 These are macroscopic images of the deposited metal from Examples 1-2. As shown, there are no obvious pores or cracks in the weld. This invention reduces the water of crystallization in the powder by adding a sintering process with a slag-forming agent before powder mixing. This reduces gas generation during subsequent welding, thereby reducing porosity in the weld. During the welding wire preparation process, the content of harmful elements such as sulfur (S) and phosphorus (P) is precisely controlled, as most welding defects are related to excessively high levels of these harmful elements. The S content of the deposited metal in Examples 1-2 is approximately 0.001%, and the P content is less than 0.004%, with no obvious defects found in the macroscopic weld.

[0062] Figure 2The images show the low-magnification microstructure of the weld metal in Examples 1-2. The gray precipitates contain Al, Mn, and a high proportion of oxygen, presumably oxides. Since welding is a process of rapid solidification of molten metal, the Al and Mn in the welding wire have a deoxidizing effect and may not be able to be discharged from the weld pool in time, thus remaining in the weld metal in the form of complex oxides. However, the presence of these oxides may lead to a decrease in the mechanical properties of the weld and become crack initiation points under load impact. The bright white precipitates are numerous and rich in Mo because Mo is a key element affecting μ-phase precipitation. The presence of Mo helps the formation of the μ-phase and TCP phase potential energy, significantly increasing the TCP phase precipitation tendency. During μ-phase formation, if the Mo content is insufficient to fill the sites in the precipitates, Cr atoms will replace Mo atoms to occupy the positions, thus continuing to form precipitates. In summary, in this invention, when Cr and Mo are added and dissolved in the austenitic matrix in the form of solute atoms, mechanical properties are optimized through a dual mechanism of interstitial solid solution and substitutional solid solution, improving the matrix's resistance to deformation while maintaining good ductility. Meanwhile, Cr and Mo play important roles in the formation and precipitation of the μ phase, so the composition range of Cr and Mo should be reasonably controlled.

[0063] Figure 3 The high-magnification SEM fracture morphology of the fibrous region in the tensile specimens of the weld metal in Examples 1-2 shows that numerous dimples are present in the fibrous region of the tensile fracture surface of the weld metal, exhibiting obvious ductile fracture characteristics. Second-phase precipitates are present within the dimples. Static toughness is the work consumed per unit volume of material from deformation to fracture during static tension. Cr contributes to the deformation-induced phase transformation from face-centered cubic to body-centered cubic structure during the tensile deformation of nickel-based alloys, resulting in higher static toughness in nickel-based welds with high Cr content. Due to differences in atomic size, Mo exhibits a higher solid solution strengthening effect on austenite than Cr. Furthermore, studies have found that Cr is beneficial for improving the plasticity of nickel-based alloys, while Mo increases their strength.

[0064] Figure 4 The fracture morphology of the weld metal impact specimens from Examples 1-2 shows that both exhibit dense equiaxed dimples. This morphological feature indicates that the material underwent significant plastic deformation during fracture, meaning that the weld metals from Examples 1-2 exhibited ductile fracture. Mo segregation between dendrites leads to an increase in the lattice parameters in the interdendritic region, causing lattice distortion and stacking faults, resulting in increased sliding resistance between atomic layers. This manifests as increased hardness and strength in the interdendritic region, but a decrease in the ability to undergo plastic deformation. Cr atomic diameter is about 0.3% smaller than Ni. The micro-segregation of Cr in the dendrite core does not cause an increase in lattice parameters, but it does increase the deformation capacity of the dendrite core, while slightly decreasing hardness and strength.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A flux-cored gas shielded welding wire for cryogenic environments, characterized in that It includes an outer nickel-based metal strip and an inner core powder, the composition of which, by mass percentage, comprises: Chromium: 45.0%–48.0% Molybdenum: 20.0%–22.0% Niobium: 7.0–8.0%, Iron: 4.0-4.5%, Nickel: 10.0%–13.0% Titanium dioxide: 4.0–6.0%, Silicon dioxide: 1.0–2.0%, Calcium fluoride: 1.0–2.0%, Aluminum oxide: 0-1.0%, Manganese: 0.2-0.5%, Silicon: 0.5%–1.0% Titanium: 0.5%–1.0%; The chemical composition of the nickel-based metal strip is as follows: carbon content ≤0.02%, sulfur ≤0.01%, phosphorus ≤0.01%, and nickel ≥99%.

2. The flux cored welding wire of claim 1, wherein The filling rate of the core powder is 35% to 40%.

3. The flux cored wire of claim 1 wherein, The particle size range of the core powder is 80 to 200 mesh.

4. The flux cored wire of claim 1 wherein, The diameter of the welding wire is 1.2 mm.

5. A method of making the flux-cored wire according to any one of claims 1 to 4, characterized in that, Includes the following steps: 1) Dry the core powder to constant weight; 2) The slag-forming agent is sintered at 720℃ for 2 hours. 3) After sintering, the powder is obtained by ball milling and mixing; 4) After the nickel strip is rolled into shape, it is filled with flux powder and sealed to obtain coarse welding wire; 5) The diameter of the coarse welding wire is reduced to the target diameter through a drawing process.

6. The preparation method according to claim 5, characterized in that, In the drawing process, the compression rate is controlled at 10% to 15% for each step.

7. A method of welding 06Ni9DR steel using the flux-cored wire according to any one of claims 1 to 4, characterized in that, Argon and carbon dioxide mixed gas is used as the protective medium, the welding heat input is 10-15 KJ / cm, and the interpass temperature is ≤100℃.

8. The welding method of claim 7, wherein, The welding current is 200-240A and the welding voltage is 26-30V.

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