Novel underwater wet welding flux-cored wire and preparation method thereof

Abstract

The invention provides a novel underwater wet welding flux-cored wire and a preparation method thereof. The flux-cored wire comprises a metal sheath and a flux core, the flux core is prepared by sintering a flux core base material and a flux core additive; the flux core base material comprises the following raw materials in percentage by mass: 20-40% of rutile, 15-35% of fluoride, 2-7% of titanate, 3-10% of aluminum powder, 5-15% of manganese powder and 10-15% of composite nano metal oxide; the composite nano metal oxide at least comprises the following raw materials: nano aluminum oxide, nano zirconium dioxide, nano yttrium oxide, nano cerium oxide and nano lanthanum oxide; and the flux-cored additive is linear aliphatic epoxy resin. The specific mixed nano metal oxide powder is added into the flux-cored wire, grain refinement is achieved, a quenched martensite structure is reduced, the mechanical property of a weld joint is improved, meanwhile, the specific epoxy resin and the flux-cored base material are mixed, filled and sintered, a proper amount of carbon element is introduced while all raw material components of the flux-cored wire are dispersed uniformly and stably, and the welding quality of the flux-cored wire is improved. And metal is prevented from being oxidized in the welding process.

Description

Technical Field

[0001] The present application relates to a novel underwater wet welding flux-cored wire and a preparation method thereof, belonging to the technical field of welding materials. Background Art

[0002] With the deepening of ocean development, a large number of marine engineering projects have begun construction. However, the harsh ocean environment results in a large amount of marine equipment being damaged and requiring repair each year. Due to the special characteristics of the marine environment, both marine engineering construction and marine engineering equipment repair require the support of underwater welding or underwater additive repair technology. Currently, existing underwater welding and underwater additive repair technologies are mainly divided into three categories: underwater wet welding, local dry welding, and dry welding. Compared with the other two technologies, underwater wet welding has simpler equipment, easier operation, and a wider range of applications, making it widely used for underwater in-situ repair and welding. Existing materials used in underwater wet welding mainly include underwater special welding rods and self-shielded flux-cored wire. The former is used for manual arc welding performed by divers underwater. However, it has certain limitations due to low welding efficiency and the welding quality is greatly affected by the welder. The latter is characterized by continuous production and continuous use. Combined with underwater welding robots, it can achieve continuous automated underwater welding operations, with high welding efficiency and welding quality, and is an important future development direction.

[0003] Flux-cored welding wire, also known as powder-cored welding wire or tubular welding wire, is a filamentary welding material with a tubular cross-section composed of internal flux powder and external metal coating. Flux-cored welding wire has the characteristics of continuous production and continuous use, and the composition of its internal flux powder can be specifically designed and adjusted according to the different usage conditions and expected effects. Therefore, it has been widely used in high-temperature resistant materials, wear-resistant materials, high-strength materials, wear-resistant materials and even some extreme environments (such as underwater welding).

[0004] Currently, underwater wet welding primarily occurs within the arc bubble. Due to the high thermal conductivity of the water environment, the base metal and the molten pool cool rapidly. This rapid cooling of the base metal creates a large temperature gradient at the base of the molten pool, leading to the formation of numerous coarse columnar crystals at the weld root and significantly reducing the weld's mechanical properties.

[0005] Chinese invention patent CN113681196A - A flux-cored wire for underwater submerged arc welding of low-carbon steel, its preparation method and application, achieves grain refinement by directly adding nano-alumina particles. Other existing technologies for adding nano-metal oxides to onshore welding wires generally use direct mixing, surface coating, and other methods. However, these filling methods have certain drawbacks. In actual applications, due to the large size difference between nanomaterials and other materials, aggregation and stratification are easily generated in the welding wire, affecting the distribution of components in the flux-cored wire and preventing the different components of the flux core from being evenly distributed in the flux-cored wire. In addition, rapid cooling of the molten pool will easily lead to the formation of hardened martensite structure in the weld zone, which increases the proportion of martensite in the weld structure and further reduces the toughness of the weld. Summary of the Invention

[0006] To solve the above problems, the present application proposes a new type of underwater wet welding flux-cored wire and its preparation method. By adding specific mixed nano-metal oxide powder to the flux-cored wire, grain refinement is achieved, coarse columnar crystals are reduced, hardened martensite structure is reduced, and the mechanical properties of the weld are improved. At the same time, a specific epoxy resin is mixed with the flux-cored base material for filling and sintering to achieve uniform and stable dispersion of the raw material components of the flux-cored wire. At the same time, an appropriate amount of carbon element is introduced to protect the metal from oxidation during the welding process, thereby further enhancing the comprehensive mechanical properties of the weld.

[0007] According to one aspect of the present application, a novel underwater wet welding flux-cored wire is provided, comprising a metal sheath and a flux core; the flux core is prepared by sintering a flux core base material and a flux core additive; The core base material comprises the following raw materials in percentage by mass: 20-40% rutile, 15-35% fluoride, 2-7% titanate, 3-10% aluminum powder, 5-15% manganese powder, and 10-15% composite nano-metal oxide; the composite nano-metal oxide comprises at least the following raw materials: nano-alumina, nano-zirconium dioxide, nano-yttrium oxide, nano-cerium oxide, and nano-lanthanum oxide; The core additive is a linear aliphatic epoxy resin, specifically DER732.

[0008] First, by adding different types of nanometal oxides in specific proportions and utilizing their nano-effect as heterogeneous nucleating agents during the solidification process of the molten pool, the high specific surface area and surface activity of each component provide a large number of nucleation sites for crystallization within the molten pool and reduce the nucleation barrier. This results in the formation of a large number of dispersed, fine, spherical composite inclusions in the weld, enhancing the nucleation ability of acicular ferrite and resulting in a large amount of evenly distributed acicular ferrite in the weld structure, thereby improving the weld toughness and strength. Furthermore, the composite nanometal oxides possess high strength and high elastic modulus, effectively preventing dislocation motion and improving weld structure strength.

[0009] Grain refinement of the weld structure is achieved through the combined action of multiple nano-metal oxides. Nano-alumina can effectively inhibit grain growth, promote the stability of the weld pool, and reduce the occurrence of thermal cracks. The low-proportion addition of zirconium dioxide can significantly improve the material's thermal shock resistance and crack resistance, and enhance the toughness of the weld joint. Nano-yttrium oxide is used in combination with oxides such as alumina and zirconium oxide, which not only enhances the material's oxidation resistance and corrosion resistance, but also improves the microstructure of the weld area. At the same time, the addition of cerium oxide and lanthanum oxide can provide better antioxidant effects, especially for underwater welding, which can improve the thermal stability and corrosion resistance of the weld joint and prevent oxidation defects in the weld.

[0010] At the same time, the inventors continued to study and found that although the problem of coarse columnar crystals in welds can be solved to a certain extent through formula research and development and design alone, the size difference between nanomaterials and other materials is too large, and aggregation and stratification are prone to occur when the welding wire is produced. The distribution of components in the flux-cored welding wire is uneven, the improvement of the comprehensive mechanical properties of the weld is limited, and the martensite in the weld structure is large, and the weld toughness is reduced.

[0011] Furthermore, the present application adopts linear aliphatic epoxy resin as a core additive. On the one hand, its high viscosity characteristics can make the different components in the core fully dispersed and maintain uniform and stable. On the other hand, by utilizing the thermal decomposition characteristics of the linear aliphatic epoxy resin, the linear aliphatic epoxy resin matrix undergoes thermal decomposition during the sintering process to produce network solid carbon, CO2 and H2O, of which CO2 and H2O escape, while the network solid carbon remains in the welding wire. The residual network carbon can ensure that the components of the welding wire are evenly distributed, solving the problem of easy aggregation and stratification of nanomaterials. In addition, the residual carbon can also react with free oxygen elements during the welding process, reducing the oxidation of the molten metal and enhancing the mechanical properties of the weld.

[0012] Optionally, the core base material includes the following raw materials in percentage by mass: Rutile 20~40%, fluoride 15~35%, titanate 2%~7%, aluminum powder 3%~10%, manganese powder 5%~15%, nano-alumina 2%~7%, nano-zirconium dioxide 0.5%~3%, nano-yttrium oxide 3%~10%, nano-cerium oxide 2%~7%, and the rest is nano-lanthanum oxide.

[0013] Specifically, the physicochemical parameters of each raw material are as follows: rutile 80-100 mesh, fluoride 100-200 mesh, aluminum powder 80-120 mesh, manganese powder 80-120 mesh, nano-alumina 20-80nm, nano-zirconium dioxide 10-30nm, nano-yttrium oxide 20-50nm, nano-cerium oxide 15-40nm, and nano-lanthanum oxide 10-25nm.

[0014] Specifically, rutile (TiO2) and titanate serve as the main slag-forming agents. During welding, slag is generated to cover the welding area and provide protection for the welding process.

[0015] Within this limited ratio, fluoride, manganese powder, and aluminum powder serve as the primary deoxidizers, reducing the effects of hydrogen and oxygen on the weld process through metallurgical reactions with oxygen and hydrogen. Excessive aluminum powder can negatively impact the mechanical properties of the weld joint, while excessive manganese increases the ionization voltage, hindering arc stability.

[0016] Optionally, the metal sheath is low carbon steel H08A or stainless steel N6 nickel strip.

[0017] Optionally, the linear aliphatic epoxy resin generates network-like solid carbon after sintering, and the residual solid carbon accounts for 2% to 3% of the total mass of the welding wire core component.

[0018] By limiting the amount of solid carbon residue, the raw materials in the welding wire can be evenly dispersed and can fully react with free oxygen. At the same time, the network of solid carbon formed can play a ductile buffering role in the weld, thereby improving the toughness and crack resistance of the weld joint.

[0019] Optionally, the fluoride is composed of CaF2 and LiF, NaF or BaF2, and the mass proportion of each component is CaF2 60%~100%, LiF 0~20%, NaF 0~20% or BaF2 0~30%.

[0020] Optionally, the titanate is one or more of calcium titanate, potassium titanate, sodium titanate and magnesium titanate.

[0021] According to another aspect of the present application, a method for preparing the novel underwater wet welding flux-cored wire is provided, comprising the following steps: (1) Mix the raw materials in the core base material evenly, and then mix and stir with the core additive to form a suspension; (2) The uncured core base material and core additive mixture is filled into the groove after the metal skin is rolled by the extrusion filling method; (3) Before the flux-cored wire is sealed, it is moved into the sintering furnace and sintered under nitrogen protection; (4) After sintering is completed, the flux-cored wire is sealed and cleaned to obtain the novel underwater wet welding flux-cored wire.

[0022] Specifically, the viscosity of the suspension is 3000-8000 mPa·s, and the parameters of the extrusion filling are an extrusion speed of 1.5-2.0 m / min, a filling pressure of 1.5 MPa, and a rolling pressure of 40 MPa.

[0023] Optionally, in step (1), the weight ratio of the core base material to the core auxiliary agent is 1:(1-1.5).

[0024] Optionally, the filling rate in step (2) is 40% to 50%.

[0025] Optionally, in step (3), the sintering temperature is 400-500° C., and the sintering time is 2-3 min.

[0026] The beneficial effects of this application include but are not limited to: 1. The novel underwater wet welding flux-cored wire of this application incorporates composite nano-metal oxides in specific proportions and types. Utilizing the nano-effect of the nano-metal oxides, the wire enhances the nucleation ability of acicular ferrite, resulting in the production of a large amount of evenly dispersed acicular ferrite in the weld, which replaces the hardened martensite structure. This reduces the content of hardened martensite in the weld structure, inhibits grain growth, refines grains, reduces the formation of coarse columnar crystals, and introduces a second phase at the grain boundaries, thereby regulating the weld structure and improving the overall mechanical properties of the weld.

[0027] 2. The novel underwater wet welding flux-cored wire disclosed in this application utilizes a linear aliphatic epoxy resin as a flux-coring additive, leveraging its excellent dispersibility to form a matrix that is bonded to the flux-coring base material. Through an extrusion, filling, and sintering process, while maintaining the original properties of the flux-cored components, this wire eliminates the aggregation and stratification problems caused by size differences between nanomaterials and conventional materials, achieving overall uniformity of composition and ensuring stable welding quality. Furthermore, the wire incorporates carbon to protect the molten metal from oxidation during welding, appropriately increasing the carbon content in the weld and improving the mechanical properties of the weld.

[0028] 3. The novel method for preparing underwater wet welding flux-cored wire disclosed herein utilizes a linear aliphatic epoxy resin as a dispersion matrix, which is mixed with a core base material to form a core-epoxy resin composite. The high viscosity of the linear aliphatic epoxy resin allows for the full dispersion of the various components in the core, maintaining uniformity and stability. Furthermore, the composite is filled and sintered to form a network of solid carbon residues, addressing the problem of nanomaterial aggregation and delamination, and achieving overall uniformity in the distribution of components in the cored wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1This is an SEM picture of the weld using the flux-cored wire 1# of this application; Figure 2 This is the SEM image of the weld using the comparison flux-cored wire 1#; Figure 3 This is the SEM image of the weld using the comparison flux-cored wire 2#. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0032] Example 1 Flux-cored welding wire 1# Flux-cored welding wire #1 consists of a metal sheath and a core. The core is made by sintering a core base material and a core additive. The core base material comprises the following raw materials by weight: 30% rutile, 30% fluoride, 5% titanate, 10% aluminum powder, 10% manganese powder, and 15% composite nanometal oxide. The composite nanometal oxide comprises 5% nanoalumina, 1% nanozirconium dioxide, 3% nanoyttrium oxide, and 5% nanocerium oxide, with the remainder being nanolanthanum oxide. The core additive is a linear aliphatic epoxy resin.

[0033] The metal sheath is low-carbon H08A steel. The linear aliphatic epoxy resin produces a network of solid carbon after sintering, with the residual solid carbon accounting for 2% of the total weight of the welding wire. The fluoride is composed of CaF2 and LiF, with the weight ratio of each component being CaF2 80% and LiF 20%. The titanate is calcium titanate.

[0034] The preparation method comprises the following steps: (1) Mix the raw materials in the core base material evenly, and then mix and stir with the core additive to form a suspension; (2) The uncured core base material and core additive mixture is filled into the groove after the metal skin is rolled by the extrusion filling method; (3) Before the flux-cored wire is sealed, it is moved into the sintering furnace and sintered under nitrogen protection; (4) After sintering is completed, the flux-cored wire is sealed and cleaned to obtain the new underwater wet welding flux-cored wire 1#.

[0035] In step (1), the weight ratio of the core base material to the core auxiliary agent is 1:1.5; the filling rate in step (2) is 45%; and the sintering temperature in step (3) is 450° C. and the sintering time is 3 minutes.

[0036] Example 2 Flux-cored welding wire 2# Flux-cored welding wire #2 consists of a metal sheath and a core. The core is made by sintering a core base material and a core additive. The core base material comprises the following raw materials by weight: 40% rutile, 20% fluoride, 7% titanate, 10% aluminum powder, 13% manganese powder, and 10% composite nanometal oxides. The composite nanometal oxides include 3% nanoalumina, 1% nanozirconium dioxide, 3% nanoyttrium oxide, 2% nanocerium oxide, and the remainder is nanolanthanum oxide. The core additive is a linear aliphatic epoxy resin.

[0037] The metal sheath is low-carbon H08A steel. The linear aliphatic epoxy resin produces a network of solid carbon after sintering, with the residual solid carbon accounting for 3% of the total weight of the welding wire. The fluoride is composed of CaF2 and NaF, with the weight ratio of each component being CaF2 80% and NaF 20%. The titanate is potassium titanate.

[0038] The preparation method comprises the following steps: (1) Mix the raw materials in the core base material evenly, and then mix and stir with the core additive to form a suspension; (2) The uncured core base material and core additive mixture is filled into the groove after the metal skin is rolled by the extrusion filling method; (3) Before the flux-cored wire is sealed, it is moved into the sintering furnace and sintered under nitrogen protection; (4) After sintering is completed, the flux-cored wire is sealed and cleaned to obtain the new underwater wet welding flux-cored wire 2#.

[0039] In step (1), the weight ratio of the core base material to the core auxiliary agent is 1:1; the filling rate in step (2) is 40%; and the sintering temperature in step (3) is 400° C. and the sintering time is 3 minutes.

[0040] Example 3 Flux-cored welding wire 3# Flux-cored welding wire #3 consists of a metal sheath and a core. The core is made by sintering a core base material and a core additive. The core base material comprises the following raw materials by weight: 30% rutile, 30% fluoride, 5% titanate, 10% aluminum powder, 10% manganese powder, and 15% composite nanometal oxides. The composite nanometal oxides include 3% nanoalumina, 2% nanozirconium dioxide, 4% nanoyttrium oxide, and 4% nanocerium oxide, with the remainder being nanolanthanum oxide. The core additive is a linear aliphatic epoxy resin.

[0041] The metal sheath is stainless steel N6 nickel strip. The linear aliphatic epoxy resin produces a network of solid carbon after sintering, with the residual solid carbon accounting for 2% of the total welding wire mass. The fluoride is composed of CaF2 and BaF2, with the weight ratio of each component being CaF2 70% and BaF2 30%. The titanate is magnesium titanate.

[0042] The preparation method comprises the following steps: (1) Mix the raw materials in the core base material evenly, and then mix and stir with the core additive to form a suspension; (2) The uncured core base material and core additive mixture is filled into the groove after the metal skin is rolled by the extrusion filling method; (3) Before the flux-cored wire is sealed, it is moved into the sintering furnace and sintered under nitrogen protection; (4) After sintering is completed, the flux-cored wire is sealed and cleaned to obtain the new underwater wet welding flux-cored wire 3#.

[0043] In step (1), the weight ratio of the core base material to the core auxiliary agent is 1:1.5; the filling rate in step (2) is 50%; and the sintering temperature in step (3) is 500° C. and the sintering time is 2 minutes.

[0044] Example 4 Flux-cored welding wire 4# Flux-cored welding wire #4 consists of a metal sheath and a core. The core is made by sintering a core base material and a core additive. The core base material comprises the following raw materials by weight: 40% rutile, 30% fluoride, 5% titanate, 10% aluminum powder, 5% manganese powder, and 10% composite nanometal oxides. The composite nanometal oxides include 2% nanoalumina, 2% nanozirconium dioxide, 3% nanoyttrium oxide, 2% nanocerium oxide, and the remainder is nanolanthanum oxide. The core additive is a linear aliphatic epoxy resin.

[0045] The metal sheath is low-carbon H08A steel. After sintering, the linear aliphatic epoxy resin produces a network of solid carbon, with the residual solid carbon accounting for 2% of the total weight of the welding wire. The fluoride is CaF2, and the titanate is sodium titanate.

[0046] The preparation method comprises the following steps: (1) Mix the raw materials in the core base material evenly, and then mix and stir with the core additive to form a suspension; (2) The uncured core base material and core additive mixture is filled into the groove after the metal skin is rolled by the extrusion filling method; (3) Before the flux-cored wire is sealed, it is moved into the sintering furnace and sintered under nitrogen protection; (4) After sintering is completed, the flux-cored wire is sealed and cleaned to obtain the new underwater wet welding flux-cored wire 4#.

[0047] In step (1), the weight ratio of the core base material to the core auxiliary agent is 1:1.5; the filling rate in step (2) is 40%; and the sintering temperature in step (3) is 450° C. and the sintering time is 2 minutes.

[0048] Example 5 Flux-cored welding wire 5# The difference between Example 5 and Example 1 is that the solid carbon residue in the flux-cored welding wire of Example 5 accounts for 5% of the total mass of the welding wire.

[0049] Comparative Example 1: Flux-cored welding wire 1# The difference between Comparative Example 1 and Example 1 is that no composite nano-metal oxide is used in Comparative Example 1.

[0050] Comparative Example 2: Flux-cored welding wire 2# The difference between Comparative Example 2 and Example 1 is that the addition ratio of the composite nano-metal oxide in Comparative Example 2 is 5%.

[0051] Comparative Example 3: Flux-cored welding wire 3# The difference between Comparative Example 3 and Example 1 is that no core additive is used in Comparative Example 3.

[0052] Comparative Example 4: Flux-cored welding wire 4# The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, E-20 epoxy resin is used as the core additive.

[0053] Comparative Example 5: Flux-cored welding wire 5# The difference between Comparative Example 5 and Example 1 is that in the preparation method of Comparative Example 5, the weight ratio of the core base material to the core auxiliary agent in step (1) is 1:3.

[0054] Experimental example Welding experiment: Base material: Q355B low carbon steel plate, groove form: V-groove; welding parameters: current 230A, voltage 30V, welding speed: 100mm / min; wire feeding speed 5.0m / min.

[0055] 1. Weld microstructure analysis The flux-cored welding wire 1# prepared in Example 1 and the comparative flux-cored welding wires 1#-2# prepared in Comparative Examples 1-2 were respectively subjected to conventional welding to obtain welds, and the distribution and content of martensite in the welds were observed and analyzed using a scanning electron microscope (SEM).

[0056] Depend on Figure 1 It can be seen that the martensite content in the final weld of the flux-cored wire 1# prepared by the raw materials and method defined in this application is very small, accounting for 7%, which is less than 10%; Figure 2 It can be seen that the martensite content in the final weld of the comparative flux-cored wire 1# without adding composite nano-metal oxide is relatively high, accounting for 18%; Figure 3 It can be seen that the martensite content in the final weld of the comparative flux-cored wire 2#, which is less than the addition ratio specified by the composite nano-metal oxide in this application, is 12%. Figure 2 It has decreased, but is still greater than 10%.

[0057] 2. Mechanical properties test Welding experiments were conducted on the flux-cored wires obtained in Examples 1-5 and Comparative Examples 1-5, and the weld performance was tested according to GB / T 2652-2022 (Tensile test method for welded joints) and GB / T 229-2007 (Charpy pendulum impact test method for metallic materials). The experimental data are shown in Table 1.

[0058] Table 1 Tensile strength and impact toughness test

[0059] From the above content, it can be seen that the flux-cored welding wire prepared by the method defined in this application has less martensitic structure, high tensile strength, and good low-temperature impact toughness. Among them, the low-temperature impact toughness of flux-cored welding wire 1# is significantly improved compared with the comparative flux-cored welding wires 1#-5#, and the tensile strength is increased by more than 6% compared with the comparative flux-cored welding wire 1#, and the comprehensive mechanical properties are excellent.

[0060] Comparative Example 1 does not use composite nano-metal oxides, and has low tensile strength and poor impact toughness. The proportion of composite nano-metal oxides used in Comparative Example 2 is less than the specified range of this application. The tensile strength is slightly improved compared to Comparative Example 1, but the low-temperature impact toughness is still poor. Comparative Example 3 does not use core additives, and has low tensile strength and greatly reduced low-temperature impact toughness. The reason for this is that the powder inside the core is unevenly dispersed. Comparative Example 4 uses conventional aromatic epoxy resin, has general tensile strength, and low-temperature impact toughness. Comparative Example 5 has reduced tensile strength and poor impact toughness. The reason for this is that the resin is oversaturated with excessive carbon.

[0061] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A new type of underwater wet welding flux-cored wire, characterized in that: It includes a metal outer shell and a core; the core is prepared by sintering a core base material and a core additive; The core base material comprises the following raw materials in percentage by mass: 20-40% rutile, 15-35% fluoride, 2-7% titanate, 3-10% aluminum powder, 5-15% manganese powder, and 10-15% composite nano-metal oxide; the composite nano-metal oxide comprises at least the following raw materials: nano-alumina, nano-zirconium dioxide, nano-yttrium oxide, nano-cerium oxide, and nano-lanthanum oxide; The drug core auxiliary agent is a linear aliphatic epoxy resin.

2. The novel underwater wet welding flux-cored wire according to claim 1 is characterized in that: The core base material includes the following raw materials in percentage by mass: Rutile 20~40%, fluoride 15~35%, titanate 2%~7%, aluminum powder 3%~10%, manganese powder 5%~15%, nano-alumina 2%~7%, nano-zirconium dioxide 0.5%~3%, nano-yttrium oxide 3%~10%, nano-cerium oxide 2%~7%, and the rest is nano-lanthanum oxide.

3. The novel underwater wet welding flux-cored wire according to claim 1, characterized in that: The metal outer skin is low carbon steel H08A or stainless steel N6 nickel strip.

4. The novel underwater wet welding flux-cored wire according to claim 1, characterized in that: The linear aliphatic epoxy resin generates network-like solid carbon after sintering, and the residual solid carbon accounts for 2% to 3% of the total mass of the welding wire.

5. The novel underwater wet welding flux-cored wire according to claim 1, characterized in that: The fluoride is composed of CaF2 and LiF, NaF or BaF2, and the mass proportion of each component is CaF2 60%~100%, LiF 0~20%, NaF 0~20% or BaF20~30%.

6. The novel underwater wet welding flux-cored wire according to claim 1, characterized in that: The titanate is one or more of calcium titanate, potassium titanate, sodium titanate and magnesium titanate.

7. A method for preparing a novel underwater wet welding flux-cored wire according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Mix the raw materials in the core base material evenly, and then mix and stir with the core additive to form a suspension; (2) The uncured core base material and core additive mixture is filled into the groove after the metal skin is rolled by the extrusion filling method; (3) Before the flux-cored wire is sealed, it is moved into the sintering furnace and sintered under nitrogen protection; (4) After sintering is completed, the flux-cored wire is sealed and cleaned to obtain the novel underwater wet welding flux-cored wire.

8. The preparation method according to claim 7, characterized in that In step (1), the weight ratio of the medicine core base material to the medicine core auxiliary agent is 1: (1-1.5).

9. The preparation method according to claim 7, characterized in that The filling rate in step (2) is 40%~50%.

10. The preparation method according to claim 7, characterized in that In step (3), the sintering temperature is 400-500°C, and the sintering time is 2-3 minutes.

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