550MPa-grade flux-cored wire matched with nuclear power and preparation method of 550MPa-grade flux-cored wire

Abstract

The invention discloses a 550MPa-grade flux-cored wire for nuclear power matching and a preparation method of the 550MPa-grade flux-cored wire, and belongs to the technical field of welding materials. The flux-cored wire is composed of a steel sheath and a flux core, wherein the flux core comprises the following components in parts by weight: 2.0 to 5.0 parts of natural rutile, 0.1 to 0.5 part of 75 ferrosilicon powder, 0.1 to 0.4 part of sodium titanate, 0.1 to 0.4 part of magnesium powder, 0.2 to 0.5 part of fluoride, 1 to 4 parts of ferromanganese powder, 0.1 to 0.6 part of nickel powder, 0.2 to 0.5 part of potassium feldspar, 0.1 to 0.6 part of zircon sand, 0.8 to 1.8 parts of iron powder, 0.5 to 1.0 part of manganese-silicon alloy, and 0.3 to 0.8 part of ferromolybdenum; after the flux-cored wire is used for welding, the performance of deposited metal is greatly improved, the flux-cored wire has high strength, good low-temperature impact toughness and high-temperature resistance, the welding process performance is good, electric arcs are stable, splashing is small, and formed weld joints are attractive.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, specifically to a 550MPa grade flux-cored welding wire for nuclear power applications and its preparation method. Background Technology

[0002] With the development of nuclear power technology in my country, the fourth generation of nuclear power technology has made a new breakthrough based on the third generation of nuclear power technology—the breakthrough of high-temperature gas-cooled reactor.

[0003] The CNNC CX project originated from the nuclear power project built by CNNC in Xin'an Town, Haiyang City, Shandong Province. This project, built upon the success of the Shidaowan High-Temperature Gas-Cooled Reactor (HTGR) demonstration project, is the first engineering project for the industrial application of HTGRs. This project plays a crucial role in optimizing the energy structure, ensuring energy supply security, and contributing to the achievement of "dual-carbon" goals. During welding for the CX project, the base material is high-strength 550MPa grade steel, requiring matching welding materials. However, currently, there are no flux-cored welding wires available on the market specifically designed for 550MPa grade nuclear power steel.

[0004] Flux-cored welding wire is a tubular welding wire in which flux powder is wrapped in a metal sheath and made by drawing process. It is a very important welding material. However, the existing flux-cored welding wire has low tensile strength of the weld metal and cannot meet the high strength requirements. In addition, it lacks low temperature impact toughness and the overall performance of the weld is poor, which cannot meet the needs of the current CX project. Summary of the Invention

[0005] This invention aims to solve the technical problems of low strength of welded cladding metal, insufficient low-temperature impact toughness, and poor overall weld performance of existing flux-cored welding wires. The purpose is to provide a 550MPa grade flux-cored welding wire for nuclear power applications and its preparation method. The performance of the welded metal after welding is greatly improved, with high strength, good low-temperature impact toughness and high-temperature resistance, as well as good welding process performance, stable arc, less spatter, and beautiful weld formation.

[0006] The present invention is achieved through the following technical solution.

[0007] The first objective of this invention is to provide a 550MPa grade flux-cored welding wire for nuclear power applications, comprising a steel outer sheath and a flux core, wherein the flux core comprises the following components in parts by weight:

[0008] Natural rutile 2.0-5.0 parts, 75% ferrosilicon powder 0.1-0.5 parts, sodium titanate 0.1-0.4 parts, magnesium powder 0.1-0.4 parts, fluoride 0.2-0.5 parts, manganese iron powder 1-4 parts, nickel powder 0.1-0.6 parts, potassium feldspar 0.2-0.5 parts, zircon sand 0.1-0.6 parts, iron powder 0.8-1.8 parts, manganese silicon alloy 0.5-1.0 parts, ferromolybdenum 0.3-0.8 parts.

[0009] The technical principle of this invention is as follows:

[0010] The present invention adds nickel powder to the formula to improve the mechanical properties of the material, mainly to improve the low-temperature impact toughness.

[0011] This invention adds 75% ferrosilicon powder to the formula: silicon is an important deoxidizer and also an important alloying agent for weld metal. Adding silicon to the weld can increase the number of acicular ferrite in the weld metal. Ferrosilicon can react with oxygen in the deposited metal to generate silicon dioxide (SiO2), which effectively removes oxygen from the metal, reduces oxide inclusions, and improves weld quality.

[0012] This invention incorporates natural rutile into the formula: its main chemical component is titanium dioxide (TiO2), which mainly acts as an arc stabilizer and slag-forming agent to ensure a stable arc and fine weld formation.

[0013] This invention incorporates ferromolybdenum powder into the formulation: the role of ferromolybdenum in the deposited metal is mainly reflected in improving material properties, specifically as follows:

[0014] (1) Refine grains: After the addition of ferromolybdenum, molybdenum will form stable carbides (such as Mo2C) with carbon, which will hinder grain growth and thus refine the grain structure, making the metal structure more uniform.

[0015] (2) Hardenability: Molybdenum can significantly improve the hardenability of steel, enabling the material to obtain a more uniform microstructure during heat treatment, while enhancing tempering stability and reducing brittleness during high-temperature tempering.

[0016] (3) Enhanced heat resistance and corrosion resistance: Molybdenum can improve the high-temperature strength (creep resistance) and corrosion resistance (such as pitting resistance) of metals, and is especially suitable for high-temperature or corrosive environments such as aerospace and chemical equipment.

[0017] In summary, this invention, through the organic combination of its components, produces weld metal with the following properties after welding: Rm≥573MPa, yield strength≥520MPa, elongation A≥26%, impact energy at -20℃≥98J, and diffusible hydrogen content<5mL / 100g. This effectively improves the overall performance of the weld, solves the problems of insufficient low-temperature toughness of the weld metal and the lack of suitable 550MPa-grade flux-cored welding wire for nuclear power plants, and demonstrates good welding process performance with stable arc, minimal spatter, and aesthetically pleasing weld formation.

[0018] Further, by weight, the core components are: 2.0 parts by weight of natural rutile, 0.1 parts by weight of 75% ferrosilicon powder, 0.1 parts by weight of sodium titanate, 0.1 parts by weight of magnesium powder, 0.2 parts by weight of fluoride, 1 part by weight of ferromanganese powder, 0.1 parts by weight of nickel powder, 0.2 parts by weight of potassium feldspar, 0.1 parts by weight of zircon sand, 0.8 parts by weight of iron powder, 0.5 parts by weight of manganese silicon alloy, and 0.3 parts by weight of ferromolybdenum.

[0019] Further, by weight, the core components are: 3.5 parts by weight of natural rutile, 0.3 parts by weight of 75% ferrosilicon powder, 0.25 parts by weight of sodium titanate, 0.25 parts by weight of magnesium powder, 0.35 parts by weight of fluoride, 2.5 parts by weight of ferromanganese powder, 0.35 parts by weight of nickel powder, 0.35 parts by weight of potassium feldspar, 0.35 parts by weight of zircon sand, 1.3 parts by weight of iron powder, 0.75 parts by weight of manganese silicon alloy, and 0.55 parts by weight of ferromolybdenum.

[0020] Further, by weight, the core components are: 5.0 parts by weight of natural rutile, 0.5 parts by weight of 75% ferrosilicon powder, 0.4 parts by weight of sodium titanate, 0.4 parts by weight of magnesium powder, 0.5 parts by weight of fluoride, 4 parts by weight of ferromanganese powder, 0.6 parts by weight of nickel powder, 0.5 parts by weight of potassium feldspar, 0.6 parts by weight of zircon sand, 1.8 parts by weight of iron powder, 1.0 part by weight of manganese silicon alloy, and 0.8 parts by weight of ferromolybdenum.

[0021] Furthermore, the fluoride is one or more of calcium fluoride, potassium fluorotitanate, and potassium fluoroaluminate.

[0022] Furthermore, the flux core accounts for 10-20% of the weight of the flux-cored welding wire.

[0023] Furthermore, the powder core filling rate inside the steel outer casing is 10-20%.

[0024] Furthermore, the steel outer skin is composed of: C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities.

[0025] Furthermore, the steel outer skin is preferably composed of: C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities.

[0026] The second objective of this invention is to provide a method for preparing a 550MPa grade flux-cored welding wire for nuclear power applications, comprising the following steps:

[0027] After the components of the flux core are mixed evenly according to the formula, the flux core mixture is obtained. The steel strip is placed in the welding wire forming machine, and the flux core mixture is injected into the groove of the steel strip which is laterally bent into a "U" shape. The mixture is then rolled into wire and drawn to ￠1.0-1.6mm to obtain the flux-cored welding wire.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention, through the organic combination of its components, produces a flux-cored welding wire with the following weld metal properties: Rm≥573MPa, yield strength≥520MPa, elongation A≥26%, impact energy at -20℃≥98J, good high-temperature resistance, and diffusible hydrogen content less than 5mL / 100g. This effectively improves the overall performance of the weld and solves the problems of insufficient low-temperature toughness of the weld metal and the lack of suitable 550MPa-grade flux-cored welding wire for nuclear power. Furthermore, the welding process using this flux-cored welding wire exhibits good performance, with a stable arc, minimal spatter, and aesthetically pleasing weld formation. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0030] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other substances not listed may also be included, or that only the listed substances may be included.

[0034] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0035] To address the technical problems of low weld metal strength, insufficient low-temperature impact toughness, and poor overall weld performance in existing flux-cored welding wires, this invention provides a 550MPa grade flux-cored welding wire for nuclear power applications, consisting of a steel outer sheath and a flux core. The flux core comprises the following components in parts by weight:

[0036] Natural rutile 2.0-5.0 parts, 75% ferrosilicon powder 0.1-0.5 parts, sodium titanate 0.1-0.4 parts, magnesium powder 0.1-0.4 parts, fluoride 0.2-0.5 parts, manganese iron powder 1-4 parts, nickel powder 0.1-0.6 parts, potassium feldspar 0.2-0.5 parts, zircon sand 0.1-0.6 parts, iron powder 0.8-1.8 parts, manganese silicon alloy 0.5-1.0 parts, ferromolybdenum 0.3-0.8 parts.

[0037] Preferably, the core composition, by weight, is: 2.0 parts by weight of natural rutile, 0.1 parts by weight of 75% ferrosilicon powder, 0.1 parts by weight of sodium titanate, 0.1 parts by weight of magnesium powder, 0.2 parts by weight of fluoride, 1 part by weight of ferromanganese powder, 0.1 parts by weight of nickel powder, 0.2 parts by weight of potassium feldspar, 0.1 parts by weight of zircon sand, 0.8 parts by weight of iron powder, 0.5 parts by weight of manganese silicon alloy, and 0.3 parts by weight of ferromolybdenum.

[0038] Preferably, the core composition, by weight, is: 3.5 parts by weight of natural rutile, 0.3 parts by weight of 75% ferrosilicon powder, 0.25 parts by weight of sodium titanate, 0.25 parts by weight of magnesium powder, 0.35 parts by weight of fluoride, 2.5 parts by weight of ferromanganese powder, 0.35 parts by weight of nickel powder, 0.35 parts by weight of potassium feldspar, 0.35 parts by weight of zircon sand, 1.3 parts by weight of iron powder, 0.75 parts by weight of manganese silicon alloy, and 0.55 parts by weight of ferromolybdenum.

[0039] Preferably, the core composition, by weight, is: 5.0 parts by weight of natural rutile, 0.5 parts by weight of 75% ferrosilicon powder, 0.4 parts by weight of sodium titanate, 0.4 parts by weight of magnesium powder, 0.5 parts by weight of fluoride, 4 parts by weight of ferromanganese powder, 0.6 parts by weight of nickel powder, 0.5 parts by weight of potassium feldspar, 0.6 parts by weight of zircon sand, 1.8 parts by weight of iron powder, 1.0 part by weight of manganese silicon alloy, and 0.8 parts by weight of ferromolybdenum.

[0040] The fluoride is one or more of calcium fluoride, potassium fluorotitanate, and potassium fluoroaluminate.

[0041] The flux core accounts for 10-20% of the weight of the flux-cored welding wire.

[0042] The filling rate of the powder core inside the steel outer casing is 10-20%.

[0043] The steel outer skin is composed of: C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities.

[0044] Preferably, the steel outer skin is composed of: C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities.

[0045] The above-mentioned method for preparing a 550MPa grade flux-cored welding wire for nuclear power plants includes the following steps:

[0046] After the components of the flux core are mixed evenly according to the formula, the flux core mixture is obtained. The steel strip is placed in the welding wire forming machine, and the flux core mixture is injected into the groove of the steel strip which is laterally bent into a "U" shape. The mixture is then rolled into wire and drawn to ￠1.0-1.6mm to obtain the flux-cored welding wire.

[0047] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0048] It should be noted that, unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0049] Example 1

[0050] A method for preparing a 550MPa grade flux-cored welding wire for nuclear power plants: The outer sheath of the welding wire is made of steel strip (width × thickness) 14 × 0.8 mm. Its chemical composition is C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities. Taking the preparation of 100kg of welding wire as an example, in this embodiment, the flux core accounts for 15wt% of the total weight of the welding wire. The components of the flux core are: 2.0kg of natural rutile, 0.1kg of 75% ferrosilicon powder, 0.1kg of sodium titanate, 0.1kg of magnesium powder, 0.2kg of sodium fluoride, 1kg of ferromanganese powder, 0.1kg of nickel powder, 0.2kg of potassium feldspar, 0.1kg of zircon sand, 0.8kg of iron powder, 0.5kg of ferromanganese alloy, and 0.3kg of ferromolybdenum. The components of the flux core are mixed evenly according to the aforementioned mass to form a flux core mixture for later use. The steel strip is placed in the welding wire forming machine, and the flux core mixture to be used is successively injected into the groove of the steel strip which is bent into a "U" shape. Then it is rolled into wire and drawn to Φ1.2mm to obtain the 550MPa grade flux core welding wire for nuclear power.

[0051] The welding parameters in this embodiment are: I=230-250A, U=28-30V, gas flow rate 20L / min, 100%CO2. The chemical composition and mechanical properties of the cladding metal after welding are shown in Table 1 and Table 2.

[0052] Table 1. Chemical composition of deposited metal

[0053] Note: The balance is iron and unavoidable impurities.

[0054] Table 2. Mechanical properties of deposited metal

[0055] Note: The diffusible hydrogen content is 4.1 mL / 100 g.

[0056] Example 2

[0057] The difference between this embodiment and Embodiment 1 is that the content of each component of the powder core is different.

[0058] A method for preparing a 550MPa grade flux-cored welding wire for nuclear power plants: The outer sheath of the welding wire is made of steel strip (width × thickness) 14 × 0.8 mm. Its chemical composition is C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities. Taking the preparation and production of 100kg welding wire as an example, in this embodiment, the flux core accounts for 15wt% of the total weight of the welding wire. The components of the flux core are: 3.5kg natural rutile, 0.3kg 75% ferrosilicon powder, 0.25kg sodium titanate, 0.25kg magnesium powder, 0.35kg sodium fluoride, 2.5kg ferromanganese powder, 0.35kg nickel powder, 0.35kg potassium feldspar, 0.35kg zircon sand, 1.3kg iron powder, 0.75kg silicon manganese alloy, and 0.55kg ferromolybdenum. The components of the flux core are mixed evenly according to the aforementioned mass to form a flux core mixture for later use. The steel strip is placed in the welding wire forming machine, and the flux core mixture to be used is successively injected into the groove of the steel strip which is bent into a "U" shape. Then it is rolled into wire and drawn to Φ1.2mm to obtain the 550MPa grade flux core welding wire for nuclear power.

[0059] The welding parameters in this embodiment are: I=230-250A, U=28-30V, gas flow rate 20L / min, 100%CO2. The chemical composition and mechanical properties of the cladding metal after welding are shown in Tables 3 and 4.

[0060] Table 3. Chemical composition of deposited metal

[0061] Note: The balance is iron and unavoidable impurities.

[0062] Table 4. Mechanical properties of deposited metal

[0063] Note: The diffusible hydrogen content is 4.3 mL / 100g.

[0064] Example 3

[0065] The difference between this embodiment and Embodiment 1 is that the content of each component of the powder core is different.

[0066] A method for preparing a 550MPa grade flux-cored welding wire for nuclear power plants: The outer sheath of the welding wire is made of steel strip (width × thickness) 14 × 0.8 mm. Its chemical composition is C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities. Taking the preparation of 100kg welding wire as an example, in this embodiment, the flux core accounts for 15wt% of the total weight of the welding wire. The components of the flux core are: 5.0kg natural rutile, 0.5kg 75% ferrosilicon powder, 0.4kg sodium titanate, 0.4kg magnesium powder, 0.5kg sodium fluoride, 4kg ferromanganese powder, 0.6kg nickel powder, 0.5kg potassium feldspar, 0.6kg zircon sand, 1.8kg iron powder, 1.0kg ferromanganese alloy, and 0.8kg ferromolybdenum. The components of the flux core are mixed evenly according to the aforementioned mass to form a flux core mixture for later use. The steel strip is placed in the welding wire forming machine, and the flux core mixture to be used is successively injected into the groove of the steel strip which is bent into a "U" shape. Then it is rolled into wire and drawn to Φ1.2mm to obtain the 550MPa grade flux core welding wire for nuclear power.

[0067] The welding parameters for this embodiment are: I=230-250A, U=28-30V, gas flow rate 20L / min, 100%CO2. The chemical composition and mechanical properties of the cladding metal after welding are shown in Tables 5 and 6.

[0068] Table 5. Chemical composition of deposited metal

[0069] Note: Balance consists of iron and unavoidable impurities.

[0070] Table 6. Mechanical Properties of Deposited Metal

[0071] Note: The diffusible hydrogen content is 3.8 mL / 100 g.

[0072] Based on the data from the above embodiments, it can be seen that the present invention, through the organic combination of its components, produces weld metal with the following properties after welding: Rm≥573MPa, yield strength≥520MPa, elongation A≥26%, impact energy at -20℃≥98J, and diffusible hydrogen content<5mL / 100g. This effectively improves the overall performance of the weld, solves the problems of insufficient low-temperature toughness of weld metal and lack of suitable 550MPa flux-cored welding wire for nuclear power, and demonstrates good welding process performance, stable arc, minimal spatter, and aesthetically pleasing weld formation.

[0073] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A 550MPa grade flux-cored welding wire for nuclear power applications, characterized in that, It consists of a steel outer casing and a powder core, wherein the powder core comprises the following components in parts by weight: Natural rutile 2.0-5.0 parts, 75% ferrosilicon powder 0.1-0.5 parts, sodium titanate 0.1-0.4 parts, magnesium powder 0.1-0.4 parts, fluoride 0.2-0.5 parts, manganese iron powder 1-4 parts, nickel powder 0.1-0.6 parts, potassium feldspar 0.2-0.5 parts, zircon sand 0.1-0.6 parts, iron powder 0.8-1.8 parts, manganese silicon alloy 0.5-1.0 parts, ferromolybdenum 0.3-0.8 parts.

2. The 550MPa grade flux-cored welding wire for nuclear power plants according to claim 1, characterized in that, The core components, by weight, are: 2.0 parts natural rutile, 0.1 parts 75% ferrosilicon powder, 0.1 parts sodium titanate, 0.1 parts magnesium powder, 0.2 parts fluoride, 1 part manganese iron powder, 0.1 parts nickel powder, 0.2 parts potassium feldspar, 0.1 parts zircon sand, 0.8 parts iron powder, 0.5 parts manganese silicon alloy, and 0.3 parts ferromolybdenum.

3. The 550MPa grade flux-cored welding wire for nuclear power plants according to claim 1, characterized in that, The core components, by weight, are: 3.5 parts natural rutile, 0.3 parts 75% ferrosilicon powder, 0.25 parts sodium titanate, 0.25 parts magnesium powder, 0.35 parts fluoride, 2.5 parts manganese iron powder, 0.35 parts nickel powder, 0.35 parts potassium feldspar, 0.35 parts zircon sand, 1.3 parts iron powder, 0.75 parts manganese silicon alloy, and 0.55 parts ferromolybdenum.

4. The 550MPa grade flux-cored welding wire for nuclear power plants according to claim 1, characterized in that, The core components, by weight, are: 5.0 parts natural rutile, 0.5 parts 75% ferrosilicon powder, 0.4 parts sodium titanate, 0.4 parts magnesium powder, 0.5 parts fluoride, 4 parts manganese iron powder, 0.6 parts nickel powder, 0.5 parts potassium feldspar, 0.6 parts zircon sand, 1.8 parts iron powder, 1.0 part manganese silicon alloy, and 0.8 parts ferromolybdenum.

5. The 550MPa grade flux-cored welding wire for nuclear power plants according to claim 1, characterized in that, The fluoride is one or more of calcium fluoride, potassium fluorotitanate, and potassium fluoroaluminate.

6. A 550MPa grade flux-cored welding wire for nuclear power plants according to any one of claims 1-5, characterized in that, The flux core accounts for 10-20% of the weight of the flux-cored welding wire.

7. A 550MPa grade flux-cored welding wire for nuclear power plants according to any one of claims 1-5, characterized in that, The filling rate of the powder core inside the steel outer casing is 10-20%.

8. A 550MPa grade flux-cored welding wire for nuclear power plants according to any one of claims 1-5, characterized in that, The steel outer skin is composed of: C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities.

9. A 550MPa grade flux-cored welding wire for nuclear power plants according to claim 8, characterized in that, The steel outer skin is composed of: C 0.030wt%, Mn 0.245wt%, Si 0.01wt%, S 0.008wt%, P 0.010wt%, with the balance being iron and unavoidable impurities.

10. A method for preparing a 550MPa grade flux-cored welding wire for nuclear power plants as described in any one of claims 1-9, characterized in that, Includes the following steps: After the components of the flux core are mixed evenly according to the formula, the flux core mixture is obtained. The steel strip is placed in the welding wire forming machine, and the flux core mixture is injected into the groove of the steel strip which is laterally bent into a "U" shape. The mixture is then rolled into wire and drawn to a fine diameter of 1.0-1.6mm to obtain the flux-cored welding wire.

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