A special welding electrode for high-strength steel restraint parts with high plasticity, toughness, and low magnetic permeability.

Abstract

This invention relates to the field of welding materials technology, and more particularly to a special welding electrode for high-strength steel with large restraints and high ductility and low magnetic permeability. The electrode has a weld metal chemical composition by mass percentage as follows: C: 0.04–0.12%, Mn: 1.5–4.0%, Si: 0.70–1.40%, S≤0.020%, P≤0.025%, Ni: 10.0–14.0%, Cr: 22.0–27.0%, Mo≤0.50%, V≤0.30%, Ti≤0.30%, with the balance being Fe and impurities; the weld metal has a microstructure of austenite and ferrite, with a ferrite content of 5–20%. A special welding electrode for high-strength steel with high plasticity, toughness, and low magnetic permeability has the advantages of good welding processability, improved arc stiffness, which can greatly suppress magnetic blow, reduce spatter, reduce electrode heating, facilitate operation, improve the corrosion resistance of the deposited metal, and ensure the safety of rigid joints of important high-strength steel structures.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and in particular to a special welding electrode for high-strength steel with high plasticity, toughness, and low magnetic permeability, specifically for large restraint parts. Background Technology

[0002] Fillet welds for open-hole welded components in large-scale deep-sea pressure-resistant structures are characterized by high structural constraint, high sensitivity to welding cracks, and limited welding space. To ensure structural performance and welding quality, high-strength, high-ductility, alkaline low-hydrogen austenitic welding materials are typically selected. However, these austenitic welding materials have poor operability in vertical and overhead welding positions, especially in the root weld. Due to factors such as magnetic blow and spatial position, welding defects (mainly incomplete fusion and porosity) are often unavoidable, sometimes requiring rework, directly affecting welding efficiency and joint quality. Therefore, there is an urgent need to develop a root pass welding electrode with good welding processability to match existing austenitic welding materials for welding pressure-resistant structures. However, rigid joints in high-strength steel structures are more prone to magnetic blow during welding, and the difficulty in controlling process stability is significantly increased.

[0003] Currently, methods to prevent arc blow during welding of large rigid joints mainly involve process and material approaches. For example, Chinese invention patent CN1431079A discloses a technique for eliminating arc blow of austenitic welding electrodes using permanent magnets. This involves measuring the magnetic field near the bevel using a Tesla meter, and then using a neodymium iron boron permanent magnet to demagnetize the electrode to below 2 mT. However, methods like this patent have non-adjustable magnetic field strength, and the high temperatures during welding can easily demagnetize the permanent magnet. Shipyards face limitations in flexibility and safety, particularly in welding complex rigid joints in confined spaces. Using austenitic welding materials results in significant spatter during welding due to short-circuit transfer, leading to instability. Furthermore, the high resistance of the austenitic core makes it prone to overheating, causing the flux coating to crack and peel off, rendering the latter half of the electrode unusable. In terms of performance, the strength and toughness of pure austenitic welds are also difficult to achieve at high levels. Summary of the Invention

[0004] In view of this, the present invention aims to provide a special welding electrode for high-strength steel with large restraint parts, characterized by high ductility, toughness, and low magnetic permeability. It employs a specific weld metal composition design, precisely proportioning alloying elements and controlling the balance between carbon and alloying elements. The weld metal microstructure is controlled to be austenitic and ferrite, with a low ferrite content. Addressing the pain points of traditional pure austenitic welding cores—high resistance, easy overheating, and easy coating detachment—a targeted dual-phase welding core design is implemented, optimizing the coating formula and solving the problems of unadjustable magnetic field strength and the tendency for permanent magnets to demagnetize due to high temperatures during welding. Shipyards lack flexibility and safety in this application, particularly unsuitable for welding complex rigid joints in confined spaces. Using austenitic welding materials results in significant spatter during welding due to short-circuit transition, leading to welding instability. Furthermore, the high resistance of the austenitic welding core causes it to overheat during welding, leading to coating cracking and detachment, rendering the latter half of the electrode unusable. In terms of performance, pure austenitic welds also struggle to achieve high levels of strength and toughness.

[0005] To address the aforementioned problems, this invention provides a special welding electrode for high-strength steel with high plasticity, toughness, and low magnetic permeability, comprising a welding core and a flux coating covering the outside of the welding core;

[0006] The chemical composition of the deposited metal of the welding electrode, by mass percentage, is as follows: C: 0.04–0.12%, Mn: 1.5–4.0%, Si: 0.70–1.40%, S≤0.020%, P≤0.025%, Ni: 10.0–14.0%, Cr: 22.0–27.0%, Mo≤0.50%, V≤0.30%, Ti≤0.30%, with the balance being Fe and impurities;

[0007] The microstructure of the deposited metal is austenite and ferrite, with a ferrite content of 5-20%.

[0008] Furthermore, the welding core is an austenitic and ferritic dual-phase welding core;

[0009] The chemical composition by mass percentage is as follows: C: 0.07–0.13%, Mn: 1.00–3.00%, Si: 0.30–1.80%, S≤0.015%, P≤0.02%, Ni: 11.00–15.00%, Cr: 22.00–28.50%, Mo: 0–0.5%, V: 0–0.5%, Ti: 0.2–1.50%, N: 0–0.3%, with the balance being Fe and impurities.

[0010] Furthermore, the coating comprises the following raw materials: marble: 36-40%, fluorite: 37-42%, quartz: 2-5%, titanium dioxide: 4-6%, ferrotitanium: 1-3%, metallic manganese: 5-9%, ferrosilicon: 3-9%, soda ash: 0-2%, bentonite: 0.5-3.5%, and solid water glass: 0.5-1.5%.

[0011] Furthermore, the Cr alloy equivalent Cr eq ≥20%;

[0012] Ni alloy equivalent Ni eq Greater than or equal to 12%.

[0013] Furthermore, the coating contains soda ash, CMC, and special baked mica as plasticizers, as well as bentonite and solid water glass.

[0014] Furthermore, the welding electrode uses pure sodium silicate as the coating binder.

[0015] Furthermore, the raw materials for the coating are mixed and then pressed onto the welding core.

[0016] Furthermore, the diameter of the electrode coating die is 6.3 mm, and the powder coating pressure is maintained at 100 kgf / cm². 2 above.

[0017] Furthermore, the baking process after the welding electrode is prepared is as follows:

[0018] The first baking was carried out at 100℃ for 8 hours.

[0019] The second baking was carried out at 360℃ for 2 hours.

[0020] Furthermore, the mechanical properties of the deposited metal satisfy the following: yield strength Rp0.2≥410MPa, tensile strength Rm≥650MPa, elongation A≥35%, reduction of area Z≥55%, and room temperature impact energy KV2≥90J.

[0021] Compared with existing technologies, the high-strength steel welding electrode with high plasticity, toughness, and low magnetic permeability described in this invention has the following advantages:

[0022] The advantages of this technical solution are that the welding electrode prepared by this invention has good welding processability, improves arc stiffness, can greatly suppress magnetic blow, reduce spatter, weaken the heating phenomenon of welding electrode, is easy to operate, improves the corrosion resistance of the deposited metal, and ensures the safety of rigid nodes of high-strength steel in important structures. Attached Figure Description

[0023] Figure 1Line graph showing the ranges of Creq and Nieq of the electrode deposited metal as described in the embodiments of this application;

[0024] Figure 2 Images showing the weld structure and processability after welding with the electrode as described in the embodiments of this application. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] In this invention, the terms "first," "second," "upper," and "lower," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "upper," or "lower" may explicitly or implicitly include at least one of those features. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. Where the technical solutions of the embodiments can be combined, they are all within the scope of protection claimed by this invention.

[0027] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, a special welding electrode for high-strength steel with high ductility, toughness, and low magnetic permeability is provided, and the deposited metal design includes the following schemes:

[0029] (1) In order to ensure strength and avoid damage to corrosion resistance, the C content should be controlled below 0.12%, and V, Ti and a small amount of N should be added. At the same time, the corrosion resistance and intergranular corrosion resistance are improved to a certain extent.

[0030] (2) Al, Cu, W, As, S, and P are impurity elements that need to be avoided. After the welding is completed, the composition of the weld metal should be as follows.

[0031] (3) The target microstructure is austenite + ferrite (1-20%), so the approximate range of each alloy is determined according to the Schaeffler diagram.

[0032] It is the equivalent of Cr alloy. ;

[0033] Ni eq Ni alloy equivalent, .

[0034] visible Figure 1 Cr in the corresponding region eq and Ni eqRange. To avoid the formation of martensite, Cr is usually... eq It should not be less than 20%, Ni eq It should not be lower than 12%.

[0035] For Ni eq The C and N contents are relatively low, so Ni and Mn are the main contributors. To avoid poor weld fluidity and hot cracking caused by high Mn content, and considering the difficulty of core preparation and austenite stability, Ni is the main component, with appropriate Mn added to improve the ultimate tensile strength. To ensure a certain strength for the austenitic steel, the target C content is designed to be between 0.04% and 0.12%, and the tendency for intergranular corrosion is reduced by adding certain amounts of V and Ti. However, excessive Ti can easily lead to the precipitation of brittle phases, and excessive V can easily lead to the formation of σ phase, reducing toughness.

[0036] For Cr eq Because the tensile strength of austenitic welds is often low, to ensure sufficient weld reinforcement in critical areas, a high Cr content is required in the weld to form stainless steel. Referring to the relationship between Cr content and the corrosion potential of structural steel, the Cr content in the weld metal typically needs to be no less than 19%. Based on the target Cr content... eq The calculation range is relatively wide, depending on the actual Ni. eq Its content can be between 22% and 27%. Furthermore, austenitic welds typically have poor fluidity, requiring an appropriate increase in the Si content of the deposited metal, depending on the target Cr content. eq The Si content is calculated to be between 0.5% and 2%. A small amount of Mo can improve the strength and pitting corrosion resistance of austenitic steel and can consume C, thus avoiding increased susceptibility to intergranular corrosion. However, excessive Mo can easily lead to the formation of Laves and μ phases, and together with Cr, it promotes the formation of σ phase, affecting toughness. Therefore, the content is limited to within 0.5%.

[0037] The target content of the deposited metal is shown in Table 1.

[0038] Table 1

[0039]

[0040] At this point, the ferrite content in the weld can be guaranteed to be between 5% and 20%, thus achieving higher mechanical properties and weldability.

[0041] Regarding the core electrode design, since the electrode's deposited metal alloy is mainly transferred through the core electrode, a higher alloy content is required. Furthermore, considering the high thermal expansion and high resistivity of pure austenitic core electrodes, an austenitic + ferrite dual-phase core electrode is proposed. Details are as follows:

[0042] (1) The electrode deposited metal mainly relies on the core alloy for transition. In addition, in order to reduce electromagnetic force, an austenitic core system is proposed. The design has a high Mn and Ni content, mainly transitioning from the core. In addition, considering the difficulty of drawing high Mn core, the austenitic alloy is mainly Ni, and a certain amount of Mn is added to save Ni.

[0043] (2) Cr is mainly transferred from the core, and the alloy yield can reach more than 90%. Therefore, the Cr content in the core is close to the design value of the deposited metal.

[0044] (3) To prevent excessive resistance of the welding electrode during welding, which could lead to overheating and damage to the flux coating and affect the welding process, a small amount of ferrite is introduced into the core material by adding Cr, V, Ti, etc., based on the Schaeffler diagram. This measure also ensures that a small amount of ferrite is present in the weld, which helps to suppress hot cracking and grain growth, and improves strength and toughness.

[0045] Based on the target composition range of the deposited metal, the core composition is designed by combining the transition coefficient of the core alloy and the Ti, Mn, and Si content in the coating.

[0046] (4) S, P, Al, Cu, W and As are impurity elements that need to be avoided. Therefore, it is necessary to control the impurity content of the welding core from the source.

[0047] The final core design is shown in Table 2.

[0048] Table 2

[0049]

[0050] In terms of coating design, the main considerations are the electrode coating processability, and alloying elements such as Ti, Mn, and Si are added to the coating to promote deoxidation and ensure the alloy content in the deposited metal.

[0051] (1) In order to improve the processability of the welding electrode and the slag formation, the ratio of marble / fluorite in the coating was adjusted, and a large amount of quartz powder was added to the coating of the welding electrode.

[0052] (2) A variety of plasticizers, such as soda ash, CMC and special baked mica, are used in combination to improve the density and pressure coating performance of the coating. Bentonite and solid water glass are also added to improve the pressure coating processability.

[0053] (3) Pure Na water glass is used to replace the K-Na water glass in the original formula.

[0054] Meanwhile, in order to improve the problems of low slag content and poor slag coverage of the coating, and to increase the density and weight coefficient of the coating, the diameter of the electrode coating die was changed from 6.1mm to 6.3mm, and the powder coating pressure was kept above 100kgf / cm2.

[0055] The added metals such as Mn, ferrotitanium, and ferrosilicon, in addition to deoxidation, also serve as transition alloying elements, depending on the composition of the target deposited metal and the selection of the welding core.

[0056] The final determined components of the drug coating are shown in Table 3.

[0057] Table 3

[0058]

[0059] As a specific example, the drug coating formulation shown in Table 4 below is used:

[0060] Table 4

[0061]

[0062] The components of the core are shown in Table 5 below:

[0063] Table 5

[0064]

[0065] The above-described electrode coating method uses a 6.3mm diameter powder coating mold. After coating, the electrode is baked at 100℃ for 8 hours, followed by baking at 360℃ for 2 hours. Test welding of the deposited metal was conducted, and the mechanical properties were tested, showing that the performance requirements were met. The mechanical properties of the electrode deposited metal are shown in Table 6 below.

[0066] Table 6

[0067]

[0068] The weld microstructure and processability of the welding electrodes prepared according to the above method are as follows: Figure 2 As shown in the figure, the welding electrodes prepared by the method of this application have good welding processability, high arc stiffness, and can not only greatly suppress magnetic blow, but also significantly reduce spatter compared with ordinary austenitic welding electrodes. The electrode heating phenomenon is significantly improved, and the operability is very good. The weld metal contains 1-20% δ-ferrite. Its mechanical properties are shown in Table 7 below.

[0069] Table 7

[0070]

[0071] It is evident that it not only has higher strength, but also has an elongation of about 25% compared to typical high-strength austenitic welding electrodes, and a room temperature KV2 of about 80J.

[0072] The deposited metal also has good corrosion resistance, with no obvious tendency for intergranular corrosion and a very low corrosion rate, which can ensure the safety of rigid nodes of high-strength steel in important structures.

[0073] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A special welding electrode for high-strength steel with high ductility, toughness, and low magnetic permeability, characterized in that, Includes the welding core and the flux coating covering the outside of the welding core; The chemical composition of the deposited metal of the welding electrode, by mass percentage, is as follows: C: 0.04–0.12%, Mn: 1.5–4.0%, Si: 0.70–1.40%, S≤0.020%, P≤0.025%, Ni: 10.0–14.0%, Cr: 22.0–27.0%, Mo≤0.50%, V≤0.30%, Ti≤0.30%, with the balance being Fe and impurities; The microstructure of the deposited metal is austenite and ferrite, with a ferrite content of 5-20%.

2. The special welding electrode according to claim 1, characterized in that, The welding core is an austenitic and ferritic duplex welding core; The chemical composition by mass percentage is as follows: C: 0.07–0.13%, Mn: 1.00–3.00%, Si: 0.30–1.80%, S≤0.015%, P≤0.02%, Ni: 11.00–15.00%, Cr: 22.00–28.50%, Mo: 0–0.5%, V: 0–0.5%, Ti: 0.2–1.50%, N: 0–0.3%, with the balance being Fe and impurities.

3. The special welding electrode according to claim 1, characterized in that, The coating comprises the following raw materials: marble: 36-40%, fluorite: 37-42%, quartz: 2-5%, titanium dioxide: 4-6%, ferrotitanium: 1-3%, metallic manganese: 5-9%, ferrosilicon: 3-9%, soda ash: 0-2%, bentonite: 0.5-3.5%, and solid water glass: 0.5-1.5%.

4. The special welding electrode according to claim 1, characterized in that, Cr alloy equivalent Cr eq ≥20%; Ni alloy equivalent Ni eq Greater than or equal to 12%.

5. The special welding electrode according to any one of claims 1 to 3, characterized in that, The coating contains soda ash, CMC, and special baked mica as plasticizers, as well as bentonite and solid water glass.

6. The special welding electrode according to claim 4, characterized in that, The welding electrode uses pure sodium silicate as the coating binder.

7. The special welding electrode according to claim 5, characterized in that, The raw materials for the coating are mixed and then pressed onto the welding core.

8. The special welding electrode according to claim 6, characterized in that, The diameter of the electrode coating die is 6.3 mm, and the powder coating pressure is maintained above 100 kgf / cm².

9. The special welding electrode according to claim 6, characterized in that, The baking process after the welding electrode is prepared is as follows: The first baking was carried out at 100℃ for 8 hours. The second baking was carried out at 360℃ for 2 hours.

10. The special welding electrode according to claim 1, characterized in that, The mechanical properties of the deposited metal meet the following requirements: yield strength Rp0.2≥410MPa, tensile strength Rm≥650MPa, elongation A≥35%, reduction of area Z≥55%, and room temperature impact energy KV2≥90J.

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