Application of Q345qD steel flux-cored welding wire in overhead internal welding of U-ribs in steel bridges

Abstract

This invention relates to welding technology, specifically the application of a flux-cored welding wire for Q345qD steel in overhead internal welding of U-ribs in steel bridges. The chemical composition of the flux-cored welding wire, by mass percentage, includes: 0.035% ≤ C ≤ 0.06%, 0.4% ≤ Si ≤ 0.61%, 1.29% ≤ Mn ≤ 1.6%, S ≤ 0.0085%, P ≤ 0.017%, with the balance being Fe. The aforementioned flux-cored welding wire for Q345qD steel comprises a flux-cored material and a wire sheath. The chemical composition and mechanical properties of the deposited metal meet the requirements for all-position welding of Q345qD steel, making it particularly suitable for overhead internal welding of U-ribs in Q345qD steel bridges. By using the flux-cored welding wire for Q345qD steel provided by this invention for overhead internal welding of U-ribs in Q345qD steel bridges, the welding quality and efficiency of bridge structures can be further improved, engineering costs reduced, and the overall safety and economy of the project enhanced.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to the application of flux-cored welding wire for Q345qD steel in overhead welding of U-ribs in steel bridges. Background Technology

[0002] As is well known, in actual welding applications, the choice of welding materials must be equally matched with the base material.

[0003] Flux-cored welding wires used for low-strength steels (such as Q345qD) are typically designed to improve the plasticity and toughness of the weld metal, thus meeting the welding requirements of low-strength steels. However, flux-cored welding wires used for high-strength steels require higher strength and hardness. Therefore, using currently available flux-cored welding wires designed for high-strength steels to weld low-strength steels may result in insufficient plasticity and toughness in the weld metal, thereby affecting the quality and performance of the weld joint.

[0004] Furthermore, different types of steel vary in chemical composition, mechanical properties, and heat treatment processes. Therefore, it is necessary to select a suitable flux-cored welding wire to meet specific welding requirements. Using an unsuitable welding wire may lead to metallurgical incompatibility between the weld metal and the base metal, thereby affecting the performance and quality of the weld joint.

[0005] Q345 steel is a high-quality low-alloy structural steel. Due to its good strength and toughness, it is often used in the manufacture of steel structure bridges and other projects that require seismic resistance. Q345 steel includes grades such as Q345qC, Q345qD, and Q345qE. These grades of bridge steel plates are thick steel plates used to manufacture bridge structural components, mainly used in the construction of railway, highway bridges, and cross-sea bridges.

[0006] Q345qD steel plate, with its excellent weldability and low notch sensitivity, is widely used in bridge construction. It can not only withstand the weight of the bridge structure and external loads, but also transfer these forces to the bridge's supporting structure. Furthermore, Q345qD steel exhibits good durability and stability, resisting the effects of various natural factors such as wind, rain, and temperature changes.

[0007] In summary, steel bridges constructed using Q345qD steel exhibit excellent mechanical properties and stability, meeting the requirements of modern bridge engineering for safety, stability, and economy. Currently, Q345qD steel is the most widely used steel plate for constructing railway and highway bridges.

[0008] Due to limitations in past technology, the inner side of the U-ribs of existing steel bridges has not undergone internal welding treatment. This has resulted in cracks originating from the weld root and extending to the top plate being not only hidden but also difficult to repair. Applying internal weld treatment could improve the fatigue performance of the bridge deck in service. By using an in-service bridge internal welding robot to enter the interior of the U-ribs of existing steel bridges and perform internal weld repair work on both sides, the fatigue durability of the bridge deck system can be extended.

[0009] In terms of welding, the overhead internal welding of Q345qD steel bridges requires the use of appropriate welding materials and processes to ensure the quality and performance of the weld. Although flux-cored welding wire is a commonly used welding material, the existing flux-cored welding wires on the market are difficult to use in overhead welding positions because the molten pool formed during the welding process deforms and sags under the influence of gravity. This easily leads to problems such as poor weld formation and welding defects. Moreover, the welding process tends to produce more spatter, making it difficult to guarantee the welding quality of the overhead internal welding of Q345qD steel bridges. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides an application of Q345qD steel flux-cored welding wire in overhead welding of U-ribs in steel bridges.

[0011] This invention provides the application of Q345qD steel flux-cored welding wire in overhead internal welding of U-ribs in steel bridges. The chemical composition of the flux-cored welding wire, by mass percentage, includes: 0.035%≤C≤0.06%, 0.4%≤Si≤0.61%, 1.29%≤Mn≤1.6%, S≤0.0085%, P≤0.017%, with the balance being Fe.

[0012] Furthermore, the flux-cored welding wire contains TiO2, SiO2, Al2O3, and NaF, and the specific mass ratio of TiO2, SiO2, Al2O3, and NaF is 36-40:3.5-5.5:1.0-1.6:0.98-2.94. During the welding process, the melting point is maintained within the range of 990-2050℃.

[0013] Furthermore, the flux-cored welding wire also contains magnesium powder, metallic manganese, and silicon-manganese alloy, and the specific mass ratio of magnesium powder, metallic manganese, and silicon-manganese alloy is 3-5:2-4:18-22, which undergo desulfurization and deoxidation reactions in the early, middle, and late stages of the welding process, respectively.

[0014] Furthermore, the mass ratio of silicon to manganese in the silicon-manganese alloy is 17:65.

[0015] Furthermore, the flux-cored welding wire includes a flux-cored material for the welding wire and a welding wire sheath.

[0016] Furthermore, the flux-cored material for the welding wire is filled into the outer sheath of the welding wire at a filling rate of 13.5~15.0%.

[0017] Furthermore, the flux-cored material for the welding wire comprises the following components by mass percentage: rutile 38-42%, feldspar 5-8%, sodium fluoride 1-3%, silicon-manganese alloy 18-22%, metallic manganese 2-4%, magnesium powder 3-6%, and iron powder to make up to 100%.

[0018] Furthermore, the outer sheath of the welding wire is made of low-carbon steel or low-alloy steel.

[0019] Furthermore, the diameter of the flux-cored welding wire is 1.2 mm to 1.4 mm.

[0020] Furthermore, the preparation method of the flux-cored welding wire includes the following steps:

[0021] 1) The components of the flux-cored material for welding wire are dried for the first time, then added to a powder mixer and stirred evenly. The evenly mixed flux-cored material for welding wire is then dried for the second time to obtain a dry powder mixture of flux-cored material for welding wire.

[0022] 2) The steel strip used as the outer sheath of the welding wire is rolled into a U-shaped groove;

[0023] 3) Fill the U-shaped groove with the dry powder mixture of the flux-cored welding wire material;

[0024] 4) Close the U-shaped groove containing the dry powder mixture of the core material, roll it into an O-shape, and then draw it to the diameter of the set welding wire.

[0025] The present invention has the following advantages and effects compared with the prior art:

[0026] This invention relates to the application of Q345qD steel flux-cored welding wire in overhead internal welding of U-ribs in steel bridges. The chemical composition of the flux-cored welding wire, by mass percentage, includes: 0.035%≤C≤0.06%, 0.4%≤Si≤0.61%, 1.29%≤Mn≤1.6%, S≤0.0085%, P≤0.017%, with the balance being Fe. While meeting the engineering requirements for high-strength steel plates, it also meets the requirements for all-position welding of Q345qD steel, making it particularly suitable for overhead internal welding of Q345qD steel bridge U-ribs. The weld metal formed after welding the Q345qD steel flux-cored welding wire provided by this invention in overhead internal welding of U-ribs exhibits the following properties: tensile strength ≥ 545 MPa, yield strength ≥ 450 MPa, elongation after fracture ≥ 24%, and energy absorbed at -20℃ ≥ 34 KV² / J. The flux-cored welding wire for Q345qD steel used in this invention produces slag with high viscosity and high toughness during the overhead welding of the U-rib of a steel bridge. The weld formed is neat and reduces defects. It is also less prone to spatter during welding. This not only ensures the welding quality of the overhead welding of Q345qD steel bridges, but also further improves the welding quality and efficiency of the bridge structure, reduces engineering costs, and enhances the safety and economy of the overall project.

[0027] The flux-cored welding wire for Q345qD steel provided by this invention is mainly designed for use in welding scenarios involving overhead internal welding of Q345qD steel. Given that Q345qD steel has a relatively low strength level and is a common bridge steel, compared to existing flux-cored welding wires, the flux-cored welding wire for Q345qD steel provided by this invention preferentially incorporates quartz, ferrotitanium, ferroboron, and other components. A reasonable proportion of these components in the formulation can achieve the required performance standards. The fewer component types in the Q345qD steel flux-cored welding wire result in better component stability, a simpler manufacturing process, and relatively lower costs, which is beneficial for the product's widespread application. Simultaneously, by increasing the amount of iron powder in the Q345qD steel flux-cored welding wire, the iron content transitioning to the weld increases, thereby improving the deposition efficiency of the Q345qD steel flux-cored welding wire, increasing the fullness of the overhead internal weld, and enhancing the welding performance of the Q345qD steel flux-cored welding wire. Attached Figure Description

[0028] Figure 1 This is a weld bead formation diagram of the flux-cored welding wire for Q345qD steel prepared in Example 1; Detailed Implementation

[0029] Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings and described below. Although the invention will be described in conjunction with exemplary embodiments thereof, it should be understood that this specification is not intended to limit the invention to those exemplary embodiments. On the other hand, the invention is intended to cover not only the exemplary embodiments thereof, but also various alternatives, modifications, equivalents and other embodiments that may be included within the spirit and scope of the invention as defined by the appended claims.

[0030] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The specific structures and functions described in the exemplary embodiments of the present invention are for illustrative purposes only. Embodiments of the present invention can be implemented in various forms, and it should be understood that they should not be construed as limited to the exemplary embodiments described in the exemplary embodiments, but include all modifications, equivalents, or substitutions included within the spirit and scope of the present invention.

[0031] Throughout this specification, the technical terms used are for the purpose of describing various exemplary embodiments only and are not intended to be limiting. It will be further understood that the terms "comprising," "including," "having," etc., when used in the exemplary embodiments, specifically refer to the presence of the stated components, steps, operations, or elements, but do not exclude the presence or addition of one or more other components, steps, operations, or elements.

[0032] The present invention provides the application of Q345qD steel flux-cored welding wire in overhead internal welding of U-ribs in steel bridges. The chemical composition of the flux-cored welding wire, by mass percentage, includes: 0.035%≤C≤0.06%, 0.4%≤Si≤0.61%, 1.29%≤Mn≤1.6%, S≤0.0085%, P≤0.017%, with the balance being Fe.

[0033] Preferably, the flux-cored welding wire contains TiO2, SiO2, Al2O3, and NaF in a mass ratio of 36-40:3.5-5.5:1.0-1.6:0.98-2.94, and the melting point is maintained within the range of 990-2050℃ during the U-rib overhead welding process.

[0034] The components TiO2, SiO2, Al2O3, and NaF are mixed in the above specific proportions. The resulting mixture can ensure that it has a high melting point, can support the molten liquid metal and prevent it from flowing downwards, and can also ensure that the weld seam of the U-rib inner weld is aesthetically pleasing. During the welding process, due to the action of the electric arc, this mixture can release more ionized substances to stabilize the electric arc and ensure the full combustion of the electric arc.

[0035] Furthermore, the flux-cored welding wire also contains magnesium powder, metallic manganese, and a silicon-manganese alloy in a mass ratio of 3-5:2-4:18-22, preferably with a silicon to manganese mass ratio of 17:65 in the silicon-manganese alloy. These components sequentially undergo desulfurization and deoxidation reactions in the early, middle, and late stages of the U-rib internal welding process, acting at their respective melting points to thoroughly remove oxide inclusions from the weld, ensuring the purity of the weld metal. Simultaneously, the alloy transition is sufficient, guaranteeing the high toughness of the weld metal.

[0036] In the preparation of the Q345qD steel flux-cored welding wire of the present invention, the flux-cored material is preferably prepared according to the following composition by mass percentage: rutile 38-42%, feldspar 5-8%, sodium fluoride 1-3%, silicon-manganese alloy 18-22%, metallic manganese 2-4%, magnesium powder 3-6%, and iron powder to make up to 100%. The flux-cored material is wrapped around the welding wire sheath; the flux-cored material is filled into the welding wire sheath at a filling rate of 13.5-15.0%. The welding wire sheath is made of low-carbon steel or low-alloy steel; the diameter of the flux-cored welding wire is 1.2 mm to 1.4 mm.

[0037] The flux-cored material for welding wire provided by this invention has the following functions for each component constituting the flux-cored welding wire for Q345qD steel:

[0038] Rutile: Its main functions are slag formation and arc stabilization. The main component of rutile is TiO2, which can adjust the solidification rate of molten slag, improve droplet transition, and enhance arc stability.

[0039] Feldspar: Its main function is to stabilize the arc. Feldspar contains high levels of K₂O and Na₂O, which helps stabilize the welding arc and contributes to the stability of the welding process. Because the high melting point components in feldspar may affect the viscosity and slag removal properties of the slag, the amount of feldspar added needs to be properly controlled to adjust the properties of the slag.

[0040] Sodium fluoride: Its main functions are to improve weld quality and increase welding efficiency. Sodium fluoride can form an antioxidant protective layer during the welding process, effectively protecting the weld area, reducing the generation of oxidation and impurities, and improving the uniformity and strength of the weld, thereby improving weld quality. Sodium fluoride can also improve the stability of the electric arc, promote the formation and continuation of the arc, and lower the melting temperature, thereby increasing welding speed and efficiency.

[0041] Silicon-manganese alloy: The main function of silicon (Si) is to refine carbide grains and improve the strength of the matrix. An appropriate amount of silicon content helps improve welding quality, but too low a silicon content may lead to oxide porosity and burn-off of alloying elements; manganese (Mn), as an important element for desulfurization and deoxidation, mainly functions to refine austenite grains, eliminate non-metallic inclusions, and improve the toughness of the weld overlay alloy.

[0042] Metallic manganese: Its main functions are to improve hardness and toughness, enhancing the durability of welding wire; it can also adjust the composition of the molten pool, making the welding process more stable. As a deoxidizer, metallic manganese can also react with sulfur to form manganese sulfide, thereby reducing the tendency of welds to hot cracking caused by sulfur.

[0043] Magnesium powder: used as a reducing agent or additive to improve welding performance.

[0044] Iron powder: Its main function is to enhance the fluidity and permeability of welding materials, allowing molten metal to flow into the weld joint more quickly and ensuring weld quality. Iron powder can also accelerate the reduction process of iron oxides, which helps in the removal of oxides.

[0045] Welding with flux-cored wire made from Q345qD steel containing the above-mentioned components results in aesthetically pleasing weld formations that are easy to remove slag; the welded joint exhibits excellent mechanical properties and high toughness.

[0046] Unless otherwise stated, all the following embodiments are prepared according to the following methods:

[0047] 1) The components of the flux-cored material for welding wire are dried for the first time, then added to a powder mixer and stirred evenly. The evenly mixed flux-cored material for welding wire is then dried a second time to obtain a dry powder mixture of flux-cored material for welding wire.

[0048] 2) The steel strip used as the outer sheath of the welding wire is rolled into a U-shaped groove;

[0049] 3) Fill the U-shaped groove with the dry powder mixture of the flux-cored welding wire material;

[0050] 4) Close the U-shaped groove containing the dry powder mixture of the core material, roll it into an O-shape, and then draw it to the diameter of the set welding wire.

[0051] It should be noted that, as a preferred embodiment of the flux-cored welding wire for Q345qD steel provided by this invention, the rutile in the flux-cored component contains more than 98% TiO2, and its impurity S and P content is very low; the feldspar is anhydrous feldspar that has been baked; the mass ratio of silicon to manganese in the silicon-manganese alloy is 17:65, and the magnesium powder is in atomized spherical form. Using a flux-cored welding wire for Q345qD steel that meets the above component requirements can ensure its welding process performance and mechanical properties. Example 1

[0052] A flux-cored material for welding wire comprises the following components by weight percentage:

[0053] Rutile: 38%, Feldspar: 5%, Sodium fluoride: 2%, Silicon-manganese alloy: 20%, Metallic manganese: 3%, Magnesium powder: 4%, and the remainder is iron powder to bring the total to 100%.

[0054] A flux-cored welding wire for Q345qD steel comprises the aforementioned flux-cored material and a low-carbon steel strip for the outer sheath.

[0055] Example 2

[0056] A flux-cored material for welding wire comprises the following components by weight percentage:

[0057] Rutile: 40%, Feldspar: 6%, Sodium fluoride: 1%, Silicon-manganese alloy: 18%, Metallic manganese: 4%, Magnesium powder: 5%, and the remainder is iron powder to bring the total to 100%.

[0058] A flux-cored welding wire for Q345qD steel comprises the aforementioned flux-cored material and a low-carbon steel strip for the outer sheath. Example 3

[0059] A flux-cored material for welding wire comprises the following components by weight percentage:

[0060] Rutile: 42%, Feldspar: 8%, Sodium fluoride: 1%, Silicon-manganese alloy: 22%, Metallic manganese: 2%, Magnesium powder: 3%, The remainder is iron powder to make up 100%.

[0061] A flux-cored welding wire for Q345qD steel comprises the aforementioned flux-cored material and a low-carbon steel strip for the outer sheath. Example 4

[0062] A flux-cored material for welding wire comprises the following components by weight percentage:

[0063] Rutile: 39%, Feldspar: 7%, Sodium fluoride: 3%, Silicon-manganese alloy: 19%, Metallic manganese: 2%, Magnesium powder: 3%, and the remainder is iron powder to bring the total to 100%.

[0064] A flux-cored welding wire for Q345qD steel comprises the aforementioned flux-cored material and a low-carbon steel strip for the outer sheath.

[0065] Example 5

[0066] A flux-cored material for welding wire comprises the following components by weight percentage:

[0067] Rutile: 38%, Feldspar: 5%, Sodium fluoride: 2%, Silicon-manganese alloy: 18%, Metallic manganese: 3%, Magnesium powder: 6%, and the remainder is iron powder to bring the total to 100%.

[0068] A flux-cored welding wire for Q345qD steel comprises the aforementioned flux-cored material and a low-carbon steel strip for the outer sheath.

[0069] Example 6

[0070] A flux-cored material for welding wire comprises the following components by weight percentage:

[0071] Rutile: 39%, Feldspar: 6%, Sodium fluoride: 3%, Silicon-manganese alloy: 21%, Metallic manganese: 2%, Magnesium powder: 6%, and the remainder is iron powder to bring the total to 100%.

[0072] A flux-cored welding wire for Q345qD steel comprises the aforementioned flux-cored material and a low-carbon steel strip for the outer sheath.

[0073] Example 7

[0074] A flux-cored material for welding wire comprises the following components by weight percentage:

[0075] Rutile: 41%, Feldspar: 7%, Sodium fluoride: 2%, Silicon-manganese alloy: 21%, Metallic manganese: 4%, Magnesium powder: 4%, and the remainder is iron powder to bring the total to 100%.

[0076] A flux-cored welding wire for Q345qD steel comprises the aforementioned flux-cored material and a low-carbon steel strip for the outer sheath.

[0077] The flux-cored welding wire for Q345qD steel based on Examples 1-7 was used for overhead internal welding of the U-rib of Q345qD steel bridge, and the experimental results are as follows:

[0078] Table 1 Comparison of Experimental Results for Overhead Welding

[0079] Style Number Weld Forming Appearance quality Existing welding wire Localized sagging and poor weld formation Slag inclusions were present in some areas. Flux-cored welding wire 1 Slight sagging, good weld formation. good Flux-cored welding wire 2 Slight sagging, good weld formation. good Flux-cored welding wire 3 Slight sagging, good weld formation. good Flux-cored welding wire 4 Slight sagging, good weld formation. good Flux-cored welding wire 5 Slight sagging, good weld formation. good Flux-cored welding wire 6 Slight sagging, good weld formation. good Flux-cored welding wire 7 Slight sagging, good weld formation. good

[0080] The comparison of the test results in the table above shows that the viscosity of the molten iron formed by the flux-cored welding wires 1-7 for Q345qD steel of the present invention is increased to varying degrees, which can reduce the phenomenon of molten iron sagging to varying degrees. The shape and appearance of the weld bead are excellent, and there are no welding defects such as slag inclusions in the welded part, effectively improving the forming quality of the supplementary internal weld. Among them, flux-cored welding wire 1 has the outstanding advantages of high viscosity and high toughness, such as... Figure 1As shown, the appearance quality can be maintained during overhead welding, and the overhead welding effect is the best. The main reason is that the flux-cored welding wire for Q345qD steel provided by this invention contains rutile with TiO2 as the main component, feldspar with SiO2 and Al2O3 as the main components, sodium fluoride (NaF), etc. When these components are mixed in the specific proportions of this invention, the resulting mixture can ensure that it has a high melting point, can support the molten liquid metal and prevent it from flowing downwards, and can also ensure a beautiful weld formation. During the welding process, due to the action of the electric arc, this mixture can release more ionized substances to stabilize the arc and ensure the full combustion of the arc. The flux-cored welding wire for Q345qD steel provided by this invention also contains magnesium powder, metallic manganese, and silicon-manganese alloy combination, which have deoxidizing, purifying weld metal and transition alloying properties. Because the melting points of the three substances mentioned above are different, deoxidation is carried out in three stages in sequence during the welding process: early, middle and late stages. This thoroughly removes oxide inclusions in the weld, ensuring the purity of the weld metal. At the same time, the alloy transition is sufficient, ensuring the high toughness of the weld metal.

[0081] Example 8

[0082] This embodiment provides the application of the flux-cored welding wire for Q345qD steel prepared in Examples 1-7 above in the overhead internal welding of the U-rib of Q345qD steel bridge. The welding environment for the overhead internal welding of the U-rib of Q345qD steel bridge was simulated. Flux-cored welding wires for Q345qD steel with diameters of 1.2mm and 1.4mm prepared in Examples 1-7 were welded according to the following process parameters: CO2 shielding gas, overhead welding position, current 200-220A, voltage 22-24V, and welding speed 24-27cm / min.

[0083] It should be noted that in practical applications, this Q345qD steel flux-cored welding wire is used in the overhead welding process of the U-rib of Q345qD steel bridge. The Q345qD steel flux-cored welding wire is carried into the U-rib by an overhead welding robot to perform welding. The welding current is 200-220A, the welding voltage is 20-24V, and the welding speed is 0.25-0.30m / min for overhead welding of the U-rib.

[0084] It should be noted that, preferably, the chemical composition of the flux-cored welding wire for Q345qD steel provided by the present invention, by mass percentage, includes: 0.035%≤C≤0.06%, 0.4%≤Si≤0.61%, 1.29%≤Mn≤1.6%, S≤0.0085%, P≤0.017%, with the balance being Fe; the flux-cored welding wire for Q345qD steel contains TiO2, SiO2, Al2O3, and NaF, and the specific amounts of TiO2, SiO2, Al2O3, and NaF are as follows: The ratio is 36-40:3.5-5.5:1.0-1.6:0.98-2.94, and the melting point is maintained within the range of 990-2050℃ during welding. The Q345qD steel flux-cored welding wire also contains magnesium powder, metallic manganese, and silicon-manganese alloy, and the specific mass ratio of magnesium powder, metallic manganese, and silicon-manganese alloy is 3-5:2-4:18-22, which undergo desulfurization and deoxidation reactions in the early, middle, and late stages of the welding process, respectively. The mass ratio of silicon to manganese in the silicon-manganese alloy is 17:65.

[0085] Table 2. Mechanical properties of weld metal deposited with flux-cored welding wire for Q345qD steel in Examples 1-7

[0086]

[0087] Note: The specified impact energy value for thin steel plate joints with a thickness of 20mm or less is 27J.

[0088] Table 3 Chemical composition (wt%) of weld metal of Q345qD steel flux-cored welding wire in Examples 1-7

[0089]

[0090] The foregoing description of specific exemplary embodiments of the invention has been presented for purposes of illustration and description. It is not intended to exclude or limit the invention to the precise forms disclosed, and it will be apparent that many modifications and alterations are possible in light of the foregoing teachings. Exemplary embodiments were chosen and described to explain certain principles of the invention and their practical application, so that others skilled in the art can make or utilize various exemplary embodiments of the invention, and their various alternatives and modifications. The purpose is that the scope of the invention will be defined by the appended claims and their equivalents.

[0091] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., means that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples.

Claims

1. The application of Q345qD steel flux-cored welding wire in overhead internal welding of U-ribs in steel bridges, characterized in that... The flux-cored welding wire includes a flux-cored material and a welding wire sheath. The flux-cored material is prepared by comprising the following components in the indicated mass percentages: rutile 38-42%, feldspar 5-8%, sodium fluoride 1-3%, silicon-manganese alloy 18-22%, metallic manganese 2-4%, magnesium powder 3-6%, and iron powder to make up to 100%. The flux-cored welding wire contains TiO2, SiO2, Al2O3, and NaF, and the specific mass ratio of TiO2, SiO2, Al2O3, and NaF is 36-40: 3.5-5.5: 1.0-1.6: 0.98-2.

94.

2. The application according to claim 1, characterized in that, In the flux-cored welding wire, the specific mass ratio of magnesium powder, metallic manganese, and silicon-manganese alloy is 3-5:2-4:18-22.

3. The application according to claim 1, characterized in that, The mass ratio of silicon to manganese in the silicon-manganese alloy is 17:

65.

4. The application according to claim 1, characterized in that, The flux-cored material for the welding wire is filled into the outer sheath of the welding wire at a filling rate of 13.5~15.0%.

5. The application according to claim 1, characterized in that, The outer sheath of the welding wire is made of low-carbon steel or low-alloy steel.

6. The application according to claim 1, characterized in that, The diameter of the flux-cored welding wire is 1.2 mm to 1.4 mm.

7. The application according to claim 1, characterized in that, The preparation method of the flux-cored welding wire includes the following steps: 1) The components of the flux-cored material for welding wire are dried for the first time, then added to a powder mixer and stirred evenly. The evenly mixed flux-cored material for welding wire is then dried for the second time to obtain a dry powder mixture of flux-cored material for welding wire. 2) The steel strip used as the outer sheath of the welding wire is rolled into a U-shaped groove; 3) Fill the U-shaped groove with the dry powder mixture of the flux-cored welding wire material; 4) Close the U-shaped groove containing the dry powder mixture of the flux-cored material for the welding wire, roll it into an O-shape, and then draw it to the diameter of the set welding wire.

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