Flux-cored wire and use thereof

Abstract

The invention discloses a flux-cored wire for welding a low-temperature alloy steel plate and application of the flux-cored wire. Deposited metal formed after welding of the flux-cored wire comprises the following chemical components in percentage by weight: 15-25% of Cr, 9-15% of Ni, 1-6% of Mn and less than or equal to 0.06% of C; and the ratio of the Creq to the Nieq is 1.5 to 2.0. The flux-cored wire has excellent all-position welding performance, the technical requirement for operators is low, and the complexity of on-site construction can be simplified. In addition, the flux-cored wire can be welded through a single-face welding and double-face forming process, so that the welding process is simpler, construction is convenient, and the defect rate is low. And when the flux-cored wire is used for welding the low-temperature alloy steel plate, deposited metal formed by melting the flux-cored wire has excellent strength performance and low-temperature toughness, and the crack sensitivity is low.

Description

Technical Field

[0001] This application relates to the field of flux-cored welding wire, and particularly to flux-cored welding wire for welding low-temperature alloy steel plates and its applications. Background Technology

[0002] 5Ni steel plates and other low-temperature alloy steel plates are important types of nickel-based steels, characterized by high strength, high toughness, and excellent weldability. They are suitable for manufacturing storage tanks for transporting and storing liquefied ethane, ethylene, etc., as well as for manufacturing equipment such as cryogenic pressure vessels. By using suitable welding wires or electrodes, these steel plates can be joined to form the required shapes to obtain storage tank devices that meet the requirements. Summary of the Invention

[0003] This application provides a flux-cored welding wire. The deposited metal formed after the flux-cored welding wire melts has high crack resistance, tensile strength and low-temperature impact resistance, which can meet the requirements of storage tank equipment.

[0004] This application provides a flux-cored welding wire in a first aspect, wherein the flux-cored welding wire is configured such that the chemical composition of the deposited metal formed after welding comprises, by weight percentage: Cr: 15-25%, Ni: 9-15%, Mn: 1-6%, C ≤ 0.06%; and the ratio of Creq to Niq is 1.5-2.0, wherein:

[0005] Nieq=wt%Ni+wt%Co+0.5·wt%Mn+0.3·wt%Cu+25·wt%N+30·wt%C

[0006] Creq=wt%Cr+2·wt%Si+1.5·wt%Mo+5·wt%V+5.5·wt%Al+1.75·wt%Nb+

[0007] 1.5 wt% Ti + 0.75 wt% W.

[0008] According to the first aspect above, the chemical composition of the deposited metal further includes, by weight percentage: Si ≤ 0.9%, W ≤ 2%, Mo: 1.5-4%, and the balance Fe.

[0009] According to the first aspect above, the chemical composition of the deposited metal further includes, by weight percentage: P≤0.015%, S≤0.015%, Ti≤0.3%, N≤0.2%, Al≤0.1%, Cu≤0.1%.

[0010] According to the first aspect above, the room temperature microstructure of the deposited metal is a mixed microstructure of austenite and ferrite.

[0011] According to the first aspect above, the flux-cored welding wire is used for welding low-temperature alloy steel plates.

[0012] According to the first aspect above, the flux-cored welding wire is welded in a protective gas atmosphere, wherein the protective gas is a mixture of 100% CO2 by volume or 75-85% argon and the balance CO2.

[0013] According to the first aspect above, the wire diameter of the flux-cored welding wire is 1.2mm, 1.4mm or 1.6mm.

[0014] According to the first aspect above, the flux-cored welding wire includes a shell and a flux core, wherein the shell has a lumen, and the flux core is housed within the lumen. The shell is made of stainless steel, and its chemical composition by weight percentage includes: C≤0.04%, Mn≤2.0%, Si≤0.75%, P≤0.02%, S≤0.02%, Cr: 16~20%, Ni: 8~14%, Mo: 0~3%, Cu≤0.75%, N≤0.10%.

[0015] According to the first aspect above, the filling amount of the flux core is 20-30% by weight, and the flux core composition includes alloying raw materials, deoxidizers, arc stabilizers and slag-forming agents, and the flux core composition is configured such that the deposited metal has the chemical composition as described in claim 1.

[0016] According to the first aspect above, the alloying raw materials include at least one of chromium (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), silicon (Si), ferrotungsten (W-Fe), ferrochrome (Cr-Fe), ferronickel (Ni-Fe), ferromolybdenum (Mo-Fe), ferrosilicon (Si-Fe), ferromanganese silicon (Mn-Si-Fe), and ferromanganese (Mn-Fe).

[0017] According to the first aspect above, the deoxidizer includes at least one of titanium (Ti), aluminum (Al), magnesium (Mg), aluminum-magnesium alloy (Al-Mg), silicon (Si), manganese (Mn), ferrotitanium (Ti-Fe), ferroaluminum (Al-Fe), ferrosilicon (Si-Fe), ferromanganese (Mn-Fe), ferrochrome (Cr-Fe), ferromanganese silicon (Mn-Si-Fe), ferrosilicon silicon (Si-Zr-Fe), and ferrocalcite silicon (Si-Ca-Fe).

[0018] According to the first aspect above, the arc stabilizer includes at least one selected from TiO2, Na2O, K2O, FeO, Fe2O3, SiO2, CaO, ZrO2, and MnO.

[0019] According to the first aspect above, the slag-forming agent includes at least one selected from TiO2, ZrO2, Fe2O3, Al2O3, MgO, CaO, SiO2, Bi2O3, MnO, BaF2, NaF, K2SiF6, Na3AlF6, CaF2, and MgF2.

[0020] According to the first aspect above, the chemical composition of the core comprises, by weight percentage: Ti: 25-35%, Cr: 10-30%, Ni: 0-20%, Mo: 0-10%, Mn: 3-25%, W: 0-7%, Si: 4-15%, Mg: 0-3%, Al: 1-5%, Ca: 0.3-3%, F: 0.3-2%, K: 0.3-3%, Na: 0.3-3%, Zr: 0.5-4%, Bi: 0.05-0.5%, C: 0.03-0.2%, and the balance Fe.

[0021] This application provides, in a second aspect, the use of the flux-cored welding wire according to any one of the first aspects for welding 5Ni steel plates or 3.5Ni steel plates.

[0022] Other features, advantages, and embodiments of this application may be set forth or become apparent upon consideration of the following detailed description, accompanying drawings, and claims. Furthermore, it should be understood that the foregoing summary and the following detailed description are exemplary and intended to provide further explanation, without limiting the scope of the claimed application. It should also be understood that although specific component arrangements are disclosed and shown in these exemplary embodiments, other arrangements may also be within the scope of this application. However, the detailed description and specific examples only indicate preferred embodiments of this application. Various changes and modifications within the spirit and scope of this application will become apparent to those skilled in the art through this detailed description. Attached Figure Description

[0023] Figure 1A This is a schematic diagram of the structure of the flux-cored welding wire of this application;

[0024] Figure 1B for Figure 1A A cross-sectional view of the Chinese medicine core welding wire;

[0025] Figure 2A For use Figure 1A A schematic diagram of a fillet welding process using a Chinese medicine core welding wire;

[0026] Figure 2B For use Figure 1A A schematic diagram of the structure for butt welding of Chinese medicine core welding wire. Detailed Implementation

[0027] Various specific embodiments of this application will now be described with reference to the accompanying drawings, which form part of this specification. It should be understood that although terms indicating direction, such as "front," "rear," "upper," "lower," "left," "right," "top," "bottom," "inner," and "outer," are used herein to describe various exemplary structural parts and elements, their use is merely for illustrative purposes and is based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed in this application can be arranged in different orientations, these terms indicating direction are illustrative only and should not be considered limiting.

[0028] In this application, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0029] Liquefied gases such as ethane and ethylene have very low temperatures, reaching around -105°C. Therefore, storage and transportation tanks must possess excellent cryogenic toughness (construction standards generally require impact toughness testing at -110°C and -125°C) to prevent breakage in the event of an impact. Furthermore, when cryogenic ethylene or similar substances are loaded (or unloaded) into the storage tank, the tank contracts (or expands) instantaneously due to cooling (or heating), generating significant thermal stress. To resist this thermal stress, the storage tank needs excellent strength and plasticity to prevent cracking. Therefore, these tanks are typically manufactured using cryogenic alloy steels such as 5Ni steel. During tank construction, cracks at weld seams should be minimized to improve production efficiency and ensure the tank is robust, durable, and resistant to breakage and potential hazards.

[0030] The inventors of this application have discovered that when welding 5Ni steel plates using ordinary flux-cored welding wire, the deposited metal formed by the melting of the flux-cored wire is prone to cracking during solidification, or exhibits problems such as poor tensile strength (less than 570 MPa) or poor low-temperature impact toughness (less than 34 J). Therefore, it often fails to meet the performance requirements of storage tanks for transporting and storing liquefied ethane and ethylene made of 5Ni steel plates. Furthermore, the inventors of this application have found that in large-scale commercial applications, the varying welding skill levels of workers exacerbate these problems. Additionally, surface defects (such as undercut and surface porosity) and internal defects (such as lack of fusion, slag inclusions, and internal porosity) in the weld are easily encountered, leading to decreased construction efficiency, increased costs, and potential quality issues.

[0031] This application provides a flux-cored welding wire that exhibits excellent all-position welding performance, requires less technical expertise from operators, and simplifies on-site construction. Furthermore, this flux-cored welding wire can utilize a single-sided welding with double-sided forming process, making the welding process simpler, easier to apply, and resulting in a low defect rate. In some construction environments, this flux-cored welding wire can also be used in conjunction with automated welding carriages or robotic arms to achieve more efficient automated welding.

[0032] Furthermore, when welding 5Ni steel plates using the flux-cored wire of this application, the deposited metal formed by the melting of the flux-cored wire not only has excellent strength properties and low-temperature toughness (i.e., low-temperature impact properties), but also has low crack sensitivity.

[0033] Figure 1A This is a schematic diagram of the structure of a flux-cored wire according to an embodiment of this application. Figure 1B for Figure 1A A cross-sectional view of the Chinese herbal medicine core welding wire. Figure 1A and Figure 1B As shown, the flux-cored welding wire 100 includes a shell 101 and a flux core 102. The shell 101 is tubular and has an internal cavity 110. The flux core 102 is housed within the cavity 110 and fills the cavity 110 axially along the shell 101. As an example, the diameter of the flux-cored welding wire 100 is 1.2 mm. Depending on the application, the diameter of the flux-cored welding wire 100 can also be 1.4 mm or 1.6 mm. It is understood that although the shell in this embodiment is cylindrical, the shell in other embodiments can be elliptical, square, polygonal, or any other suitable shape.

[0034] Figure 2A and Figure 2B For use Figure 1A A schematic diagram of the welding joint in the welding of traditional Chinese medicine core wire. Figure 2A A schematic diagram of the fillet weld structure is shown. Figure 2B A schematic diagram of a butt weld is shown. (Example) Figure 2A As shown, the first workpiece 211 and the second workpiece 212 are 5Ni steel plates. The first workpiece 211 and the second workpiece 212 are welded using flux-cored welding wire 100 to form a fillet weld 216.

[0035] In this embodiment, the fillet weld 216 is located at the horizontal position 2F. In other embodiments, the flux-cored welding wire of this application can also be used for welding at other positions (horizontal position 1F, vertical position 3F, and overhead position 4F) according to specific welding process requirements, to obtain corresponding high-quality welds.

[0036] like Figure 2BAs shown, the third workpiece 213 and the fourth workpiece 214 are 5Ni steel plates. The third workpiece 213 and the fourth workpiece 214 are welded using flux-cored welding wire 100 to form a butt weld 217. In this embodiment, a ceramic backing 210 is provided below the third workpiece 213 and the fourth workpiece 214. During the welding process, the operator, with the assistance of the ceramic backing 210, performs single-sided welding and double-sided forming of the butt weld 217. This single-sided welding and double-sided forming process avoids defects at the root of the butt weld 217, thus avoiding the need for reverse cleaning of the root of the butt weld 217 and welding from the reverse side, thereby greatly improving welding quality and efficiency.

[0037] In this embodiment, the butt weld 217 is located in the horizontal position 1G. In other embodiments, the flux-cored welding wire of this application can also be used for welding in other positions (horizontal position 2G, vertical position 3G, and overhead position 4G) according to specific welding process requirements, to obtain corresponding high-quality welds, and all of them can achieve single-sided welding and double-sided forming with the assistance of ceramic backing.

[0038] The fillet weld 216 and butt weld 217 include deposited metal obtained from the melting of flux-cored wire 100. In various embodiments of this application, the deposited metal obtained by various welding methods exhibits excellent mechanical properties such as strength and low-temperature toughness, and low crack sensitivity, resulting in welds with good strength. This demonstrates that the flux-cored wire of this application has excellent all-position welding performance. It is understood that although the workpieces in this embodiment are 5Ni steel plates, the deposited metal obtained when the flux-cored wire of this application is used to weld other low-temperature alloy steel plates, such as 3.5Ni steel plates, also exhibits similar properties.

[0039] Based on the chemical composition of the outer shell and the flux core of the flux-cored wire, a weld metal with a specific chemical composition can be obtained. By controlling the chemical composition of the weld metal, it is possible to give the weld metal better mechanical properties.

[0040] In this application, the chemical composition of the deposited metal, by weight percentage, includes:

[0041] Cr: 15-25%, Ni: 9-15%, Mn: 1-6%, C ≤ 0.06%. The ratio of Creq to Niq is 1.5-2.0, where:

[0042] Nieq=wt%Ni+wt%Co+0.5·wt%Mn+0.3·wt%Cu+25·wt%N+30·wt%C

[0043] Creq=wt%Cr+2·wt%Si+1.5·wt%Mo+5·wt%V+5.5·wt%Al+1.75·wt%Nb+

[0044] 1.5 wt% Ti + 0.75 wt% W.

[0045] In some embodiments, the chemical composition of the deposited metal further includes, by weight percentage:

[0046] Si ≤ 0.9%, W ≤ 2%, Mo: 1.5–4%, and the balance Fe.

[0047] In some embodiments, the chemical composition of the deposited metal further includes, by weight percentage:

[0048] P≤0.015%, S≤0.015%, Ti≤0.3%, N≤0.2%, Al≤0.1%, Cu≤0.1%.

[0049] The room temperature microstructure of the weld metal formed using the flux-cored wire of this application is a mixed austenitic and ferrite dual-phase microstructure, making it particularly suitable for welding low-temperature alloy steel plates. This is achieved by controlling the Cr equivalent (i.e., Cr...). eq ) and Ni equivalent (i.e. Ni eq By controlling the ratio of Cr, Ni, Mn, and C, and by controlling the percentage content of Cr, Ni, Mn, and C, the deposited metal according to this application can possess excellent strength properties, such as yield strength and tensile strength, as well as good low-temperature impact resistance. Because the deposited metal formed by the flux-cored wire of this application has good strength properties such as yield strength and tensile strength, the crack resistance of the deposited metal will also be good.

[0050] The inventors of this application discovered that Cr eq and Ni eq The ratio of Cr to Cr in the weld metal typically determines the macroscopic room temperature microstructure of the weld metal. Generally, when the Cr content of the weld metal is higher than that of the weld metal... eq and Ni eq When the ratio of Cr to austenite is between 1.5 and 2.0, the microstructure of the weld metal consists of ferrite and austenite. When the microstructure of the weld metal includes both ferrite and austenite, the weld metal exhibits not only high tensile strength but also good crack resistance. The inventors of this application have discovered that by controlling the Cr content of the weld metal... eq and Ni eq The ratio is in the range of 1.5 to 2.0, so that the weld metal is ferrite and austenite. At the same time, by controlling the percentage content of Mn, Ni, Cr and C, the weld metal can have low crack sensitivity and high tensile strength and yield strength, while having sufficient low temperature impact performance.

[0051] To ensure the deposited metal achieves the aforementioned content after welding, the outer shell and flux core of the flux-cored wire are configured with corresponding compositions. As an example, by weight percentage, the outer shell comprises 70-80% of the flux-cored wire, and the flux core comprises 20-30%. The outer shell is made of stainless steel, for example, AISI 316L stainless steel, and its chemical composition by weight percentage includes: C≤0.04%, Mn≤2.0%, Si≤0.75%, P≤0.02%, S≤0.02%, Cr: 16-20%, Ni: 8-14%, Mo: 0-3%, Cu≤0.75%, N≤0.10%.

[0052] The flux core includes alloying materials, deoxidizers, arc stabilizers, and slag-forming agents. It should be understood that although some components are listed for specific purposes, in reality, each component can be used for more than one purpose in the welding process.

[0053] While metallic raw materials can act on the welding process in other ways (e.g., as arc stabilizers and / or slag-forming agents and / or deoxidizers), generally these alloying raw materials are substantially incorporated (e.g., more than 90%) into the deposited metal to influence the properties of the weld and surrounding workpiece (e.g., strength, ductility, corrosion resistance, etc.). Alloying raw materials generally include pure metals or alloying raw materials, and in some embodiments, the alloying raw materials include at least one of chromium (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), silicon (Si), ferrotungsten (W-Fe), ferrochrome (Cr-Fe), ferronickel (Ni-Fe), ferromolybdenum (Mo-Fe), ferrosilicon (Si-Fe), ferromanganese silicon (Mn-Si-Fe), and ferromanganese (Mn-Fe).

[0054] While deoxidizers can act on welding processes in other ways (e.g., as alloying and / or arc stabilizers and / or slag-forming agents), these deoxidizer components are typically selected to strongly bind with oxygen to block (e.g., restrict or prevent) oxygen atoms from remaining in the weld pool and weaken the deposited metal. In some embodiments, the deoxidizer includes at least one of titanium (Ti), aluminum (Al), magnesium (Mg), aluminum-magnesium alloy (Al-Mg), silicon (Si), manganese (Mn), ferrotitanium (Ti-Fe), ferroaluminum (Al-Fe), ferrosilicon (Si-Fe), ferromanganese (Mn-Fe), ferrochrome (Cr-Fe), ferromanganese-silicon (Mn-Si-Fe), ferrosilicon (Si-Zr-Fe), and ferrocalcite (Si-Ca-Fe).

[0055] While arc-stabilizing components can act on welding processes in other ways (e.g., as alloying and / or slag-forming and / or deoxidizing agents), arc stabilizers typically provide a substance to the easily ionized arc, thereby achieving a more consistent and / or controllable arc on the workpiece surface. Arc-stabilizing components generally include metal oxides or other easily ionized metal compounds, and in some embodiments, they include at least one of TiO2, Na2O, K2O, FeO, Fe2O3, SiO2, CaO, ZrO2, and MnO.

[0056] Slag-forming agents are typically used to form slag from molten flux cores, providing good mechanical protection and metallurgical treatment. The components of slag-forming agents generally include metal oxides or metal fluorides. In some embodiments, the slag-forming agent includes at least one of TiO2, ZrO2, Fe2O3, Al2O3, MgO, CaO, SiO2, Bi2O3, MnO, BaF2, NaF, K2SiF6, Na3AlF6, CaF2, and MgF2.

[0057] In some embodiments of this application, the flux-cored wire is welded in a shielding gas atmosphere. As an example, the shielding gas is 100% CO2 gas by volume or an argon-rich mixture of 75-85% argon gas and the balance CO2. Those skilled in the art will understand that in some embodiments, by adjusting the composition range of the flux core, for example, by adjusting the slagging agent content range, welding can also be performed in an atmosphere without a shielding gas.

[0058] Those skilled in the art will understand that by coordinating the design of the outer shell composition, the core composition, and the core dosage, nearly identical weld metal results can be obtained. Using the same core composition with different outer shell compositions and / or different core dosages may yield significantly different weld metal results. The core composition should be designed with the goal of obtaining the desired weld metal, taking into account the specific outer shell composition, dimensions, and core dosage. In some embodiments, the chemical composition of the core, by weight percentage (C is from combustion analysis, the remainder from XRF elemental analysis, total 100%), includes: Ti: 25-35%, Cr: 10-30%, Ni: 0-20%, Mo: 0-10%, Mn: 3-25%, W: 0-7%, Si: 4-15%, Mg: 0-3%, Al: 1-5%, Ca: 0.3-3%, F: 0.3-2%, K: 0.3-3%, Na: 0.3-3%, Zr: 0.5-4%, Bi: 0.05-0.5%, C: 0.03-0.2%, and the balance Fe. In some embodiments, the core also includes other elements such as P, S, V, Nb, Cu, Se, Sn, Co, and N.

[0059] As specific examples, the chemical composition of the flux-cored wires in Examples 1-24 was analyzed by the C combustion method, and the rest by XRF elemental analysis. The weight percentage (wt%) of the main components, based on a total of 100, is shown in Table 1.

[0060] Table 1. XRF composition of flux-cored tubular welding wires (unit: wt%)

[0061]

[0062]

[0063] The chemical composition (wt%) of the weld metal A1-A24 obtained by using flux-cored welding wires with embodiments 1-24 of this application under 100% CO2 gas protection, according to ABS classification society specifications, is shown in Table 2:

[0064] Table 2 Chemical composition of the deposited metal (unit: wt%)

[0065]

[0066]

[0067] Yield strength and elongation tests were conducted on weld metals A1-A24 according to the mechanical property test of the full weld metal. Tensile strength tests were conducted on weld metals A1-A24 according to ISO 6892-1 and ASTM E8. Low-temperature impact tests were conducted on weld metals A1-A23 according to ASTM E23. The test results are shown in Table 3.

[0068] Table 3 Mechanical properties of the deposited metal

[0069]

[0070] As shown in Table 3, the yield strength of the deposited metals A1-A24 is at least greater than 390 MPa, the tensile strength is at least greater than 570 MPa, the elongation is at least greater than 25%, and the impact energy at -125℃ and -140℃ is at least greater than 34 J. Therefore, the deposited metal of the flux-cored welding wire in this application, after melting, not only meets the requirements for pressure vessels in terms of low-temperature impact resistance but also possesses excellent yield strength and tensile strength, indicating good crack resistance.

[0071] Although this application uses 5Ni steel as an example of the welding application of the flux-cored wire of this application, it should be understood that the flux-cored wire of this application is also applicable to other welding applications that require high and low temperature impact performance and mechanical strength, such as 3.5Ni steel, which is also a low temperature alloy steel.

[0072] The flux-cored welding wire of this application welds in a shielding gas atmosphere, which can be 100% CO2 gas by volume or an argon-rich mixture of 75-85% argon gas and the balance CO2. Furthermore, the flux-cored welding wire of this application exhibits excellent all-position welding performance, requires less technical expertise from operators, and simplifies on-site construction. It can also utilize a single-sided welding with double-sided forming process, making the welding process simpler, easier to construct, and resulting in a low defect rate. In some construction environments, the flux-cored welding wire of this application can also be used in conjunction with automated welding carriages or robotic arms to achieve more efficient automated welding.

[0073] Furthermore, when using the flux-cored welding wire of this application to weld 5Ni steel plates or 3.5Ni steel plates, the deposited metal formed by the melting of the flux-cored welding wire not only has excellent strength properties and low-temperature toughness (i.e., low-temperature impact properties), but also has low crack sensitivity.

[0074] Although this disclosure has been described in conjunction with examples of the embodiments outlined above, various alternatives, modifications, variations, improvements, and / or substantially equivalents, whether known or currently or soon to be foreseen, will likely be apparent to those skilled in the art. Furthermore, the technical effects and / or technical problems described herein are exemplary and not limiting; therefore, the disclosures herein may be used to solve other technical problems and have other technical effects and / or can solve other technical problems. Accordingly, the examples of embodiments of this disclosure as set forth above are intended to be illustrative and not limiting. Various changes may be made without departing from the spirit or scope of this disclosure. Therefore, this disclosure is intended to include all known or previously developed alternatives, modifications, variations, improvements, and / or substantially equivalents.

Claims

1. A flux-cored welding wire, Its features are: The flux-cored welding wire is configured such that the chemical composition of the deposited metal formed after welding comprises, by weight percentage: Cr: 15-25%, Ni: 9-15%, Mn: 1-6%, C ≤ 0.06%; and The ratio of Creq to Nieq is 1.5 to 2.0, wherein: Ni eq =wt%Ni+wt%Co+0.5·wt%Mn+0.3·wt%Cu+25·wt%N+30·wt%C Cr eq =wt%Cr+2·wt%Si+1.5·wt%Mo+5·wt%V+5.5·wt%Al+1.75·wt%Nb+1.5·wt%Ti+0.75·wt%W。 2. The flux-cored welding wire according to claim 1, characterized in that: The chemical composition of the deposited metal, by weight percentage, also includes: Si ≤ 0.9%, W ≤ 2%, Mo: 1.5–4%, and the balance Fe.

3. The flux-cored welding wire according to claim 2, characterized in that: The chemical composition of the deposited metal, by weight percentage, also includes: P≤0.015%, S≤0.015%, Ti≤0.3%, N≤0.2%, Al≤0.1%, Cu≤0.1%.

4. The flux-cored welding wire according to claim 1, characterized in that: The room temperature microstructure of the deposited metal is a mixed microstructure of austenite and ferrite.

5. The flux-cored welding wire according to claim 1, characterized in that: The flux-cored welding wire is used for welding low-temperature alloy steel plates.

6. The flux-cored welding wire according to claim 5, characterized in that: The flux-cored welding wire is welded in a protective gas atmosphere, wherein the protective gas is a mixture of 100% CO2 by volume or 75-85% argon and the balance CO2.

7. The flux-cored welding wire according to claim 1, characterized in that: The diameter of the flux-cored welding wire is 1.2mm, 1.4mm or 1.6mm.

8. The flux-cored welding wire according to claim 7, characterized in that: The flux-cored welding wire includes an outer shell and a flux core, wherein the outer shell has a cavity and the flux core is housed in the cavity; The outer casing is made of stainless steel, and its chemical composition by weight percentage includes: C≤0.04%, Mn≤2.0%, Si≤0.75%, P≤0.02%, S≤0.02%, Cr: 16~20%, Ni: 8~14%, Mo: 0~3%, Cu≤0.75%, N≤0.10%.

9. The flux-cored welding wire according to claim 8, characterized in that: The filling amount of the flux core is 20-30% by weight, and the flux core composition includes alloying raw materials, deoxidizers, arc stabilizers and slag-forming agents. The flux core composition is configured such that the deposited metal has the chemical composition as described in claim 1.

10. The flux-cored welding wire according to claim 9, characterized in that: The alloying raw materials include at least one of chromium (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), silicon (Si), ferrotungsten (W-Fe), ferrochrome (Cr-Fe), ferronickel (Ni-Fe), ferromolybdenum (Mo-Fe), ferrosilicon (Si-Fe), ferromanganese silicon (Mn-Si-Fe), and ferromanganese (Mn-Fe).

11. The flux-cored welding wire according to claim 9, characterized in that: The deoxidizer includes at least one of titanium (Ti), aluminum (Al), magnesium (Mg), aluminum-magnesium alloy (Al-Mg), silicon (Si), manganese (Mn), ferrotitanium (Ti-Fe), ferroaluminum (Al-Fe), ferrosilicon (Si-Fe), ferromanganese (Mn-Fe), ferrochrome (Cr-Fe), ferromanganese silicon (Mn-Si-Fe), ferrosilicon silicon (Si-Zr-Fe), and ferrocalcite silicon (Si-Ca-Fe).

12. The flux-cored welding wire according to claim 9, characterized in that: The arc stabilizer includes at least one of TiO2, Na2O, K2O, FeO, Fe2O3, SiO2, CaO, ZrO2, and MnO.

13. The flux-cored welding wire according to claim 9, characterized in that: The slag-forming agent includes at least one of TiO2, ZrO2, Fe2O3, Al2O3, MgO, CaO, SiO2, Bi2O3, MnO, BaF2, NaF, K2SiF6, Na3AlF6, CaF2, and MgF2.

14. The flux-cored welding wire according to claim 9, characterized in that: The chemical composition of the core, by weight percentage, includes: Ti: 25-35%, Cr: 10-30%, Ni: 0-20%, Mo: 0-10%, Mn: 3-25%, W: 0-7%, Si: 4-15%, Mg: 0-3%, Al: 1-5%, Ca: 0.3-3%, F: 0.3-2%, K: 0.3-3%, Na: 0.3-3%, Zr: 0.5-4%, Bi: 0.05-0.5%, C: 0.03-0.2%, and the balance Fe.

15. The use of the flux-cored wire according to any one of claims 1-14 for welding 5Ni steel plates or 3.5Ni steel plates.

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