An arc welding electrode suitable for use in ultra-low temperature storage tanks, and a method of manufacture and use thereof

Abstract

The application provides an electric arc welding electrode suitable for an ultralow-temperature storage tank and a preparation method and application thereof, which is composed of a welding core pressure-coated with a medicine powder, wherein the medicine powder is composed of the following components in parts by mass: marble 12-18 parts; potassium carbonate 10-15 parts; sodium fluoride 2-7 parts; fluorite 7-12 parts; aluminum fluoride 3-8 parts; silicon additive 4-9 parts; manganese additive 2-6 parts; molybdenum additive 22-30 parts; niobium additive 8-15 parts; and tungsten additive 4-9 parts. The application has the beneficial effect that the arc stability and concentration can be balanced by reasonably controlling the content of potassium carbonate and sodium fluoride, so that the ultralow-temperature storage tank has good welding process performance in flat welding, vertical welding and overhead welding during alternating current welding, and the welding process is stable.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, and in particular relates to an arc welding electrode suitable for cryogenic storage tanks, its preparation method, and its application. Background Technology

[0002] In recent years, natural gas has received increasing attention as the most important environmentally friendly and clean energy source. LNG (liquefied natural gas at -163℃) has a volume that is 1 / 600th that of its room temperature state. Low-temperature storage and transportation are the most economical methods and the most convenient and effective means to meet peak shaving and power outage requirements.

[0003] As a steel used in large LNG storage tanks at LNG receiving terminals, 9%Ni steel has also begun research on domestic production.

[0004] Welding materials for 9%Ni steel are special Ni-based welding materials. Imported materials have long supply cycles and high prices. Therefore, it is particularly important to study a welding material for 9%Ni steel. Summary of the Invention

[0005] In view of this, the present invention aims to provide an arc welding electrode suitable for cryogenic storage tanks, its preparation method and application, in order to overcome the shortcomings of the prior art.

[0006] The nickel-based welding electrode described in this invention can be used with both AC and DC power, exhibits excellent welding process performance, stable arc, minimal spatter, aesthetically pleasing weld bead formation, and easy slag removal. Its weld metal possesses superior mechanical properties, particularly excellent low-temperature impact toughness, crack resistance, and corrosion resistance at -196℃, meeting the welding requirements for cryogenic storage tanks such as LNG, LEG, liquid nitrogen, or liquid oxygen.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows: An arc welding electrode suitable for cryogenic storage tanks is composed of a core coated with a flux powder. The flux powder comprises the following components in mass fraction: marble 12-18%, potassium carbonate 10-15%, sodium fluoride 2-7%, fluorite 7-12%, aluminum fluoride 3-8%, silicon additive 4-9%, manganese additive 2-6%, molybdenum additive 22-30%, niobium additive 8-15%, and tungsten additive 4-9%.

[0008] Preferably, the chemical composition of the welding core includes the following components by mass fraction: C 0.035-0.06%, Mn 2.2-3.5%, Si≤0.10%, Cr 18.0-20.0%, Ti 0.15-0.50%, Fe 3.0-6.0%, with the balance being Ni and unavoidable impurities, and the sum of the mass fractions of each component is 100%.

[0009] Preferably, the weld metal comprises the following components by mass fraction: C 0.02-0.04%, Mn 2.5-3.5%, Si 0.25-0.40%, Cr 12.5-13.5%, Mo 5.5-6.5%, Nb 1.2-2.0%, W 1.4-2.0%, Cu 0.05-0.10%, Fe 5.0-6.0%, with the balance being Ni and unavoidable impurities, and the sum of the mass fractions of each component being 100%.

[0010] Preferably, the marble contains ≥98.0% CaCO3 by mass, ≤0.020% S by mass, and ≤0.010% P by mass, with particle size requirements of: +40 mesh: 0%, +50 mesh: ≤5%, -200 mesh: ≤40%; where "+" represents above and "-" represents below.

[0011] The potassium carbonate contains K2CO3 with a mass content ≥96.0%, S with a mass content ≤0.050%, and P with a mass content ≤0.050%. The particle size requirements are: -50 mesh: ≥99.0%, -100 mesh: ≥98.0%; where "+" represents above and "-" represents below.

[0012] The sodium fluoride contains NaF mass content ≥ 98.0%, H2O mass content ≤ 0.30%, C mass content ≤ 0.060%, and S mass content ≤ 0.015%. The particle size requirements are: -80 mesh: = 100%, -100 mesh: ≥ 95%, -300 mesh: ≤ 30%; where "+" represents above and "-" represents below.

[0013] The fluorite contains ≥96.0% CaF2, ≤0.010% S, and ≤0.010% P. The particle size requirements are: +50 mesh: 0%, +60 mesh: ≤1%, -200 mesh: ≤70%; where "+" represents above and "-" represents below.

[0014] The aluminum fluoride contains F with a mass content ≥61.0%, Na with a mass content ≤0.50%, Al with a mass content ≥31.0%, S with a mass content ≤0.050%, P2O5 with a mass content ≤0.040%, and H2O with a mass content ≤0.40%. The particle size requirements are: -80 mesh: =100%, +120 mesh: ≤10%; where "+" represents above and "-" represents below.

[0015] Preferably, the silicon additive is one or more of 75# ferrosilicon, rare earth ferrosilicon, silicon carbide, and silicon-manganese alloy; the manganese additive is one or more of electrolytic manganese, silicon-manganese alloy, and high-carbon ferromanganese; the molybdenum additive is one or two of metallic molybdenum and ferromolybdenum; the niobium additive is one or two of metallic niobium and ferroniobium; and the tungsten additive is one or more of metallic tungsten, ferrotungsten, tungsten carbide, and silicon-ferrotungsten.

[0016] Preferably, the binder used is potassium sodium silicate with a modulus M of 3.00-3.10 and a concentration Beº of 40-45.

[0017] Preferably, the coating rate of the flux (the proportion of flux to the total mass of the welding electrode) is 40%-45%; Preferably, the diameter of the welding core is 3.2-4.0 mm.

[0018] This invention also provides a method for preparing an arc welding electrode suitable for LNG cryogenic storage tanks as described above. The electrode is coated and then subjected to an air-drying and baking process. The air-drying process is: natural air-drying for 12 hours. The baking process consists of 4 steps: 80℃ for 1 hour; 150℃ for 1 hour; 260℃ for 1 hour; and 380℃-400℃ for 2 hours.

[0019] The present invention also provides a method for welding using an arc welding electrode suitable for cryogenic storage tanks as described above, wherein the welding process parameters are: voltage 22V-28V, current 70A-130A, AC / DC dual-use.

[0020] This invention also provides the application of an arc welding electrode suitable for cryogenic storage tanks as described above, or an electrode prepared by the method described above, in the welding of cryogenic storage tanks such as LNG, LEG, liquid nitrogen, or liquid oxygen.

[0021] The present invention also provides the application of an arc welding electrode suitable for cryogenic storage tanks as described above, or an electrode prepared by the method described above, in the welding of 9% Ni steel.

[0022] Preferably, the product is used at an ambient temperature of -163°C after welding.

[0023] The function of each component: Marble, primarily composed of CaCO3 with a melting point of 2572℃, plays a crucial role in welding by desulfurizing, dephosphorizing, stabilizing the arc, decomposing CO2 to protect the weld from oxidation and nitriding, and creating short slag, thus facilitating directional welding. Under the influence of an electric arc, the following reactions occur: Desulfurization: CaCO3→CaO+ CO2 FeS + CaO → CaS + FeO FeO + Mn → MnO + Fe Dephosphorization: 3CaO + P₂O₅ → Ca₃P₂O₈ 4CaO + P₂O₅ → Ca₄P₂O₉ 2Fe₂P + 5FeO + 3CaO → Ca₃P₂O₈ + 9Fe 2Fe₂P + 5FeO + 4CaO → Ca₄P₂O₉ + 9Fe This achieves the effect of desulfurization and dephosphorization.

[0024] Potassium carbonate, whose main component is K2CO3, has a melting point of 800℃. Its main function in the welding process is to stabilize the arc and can also decompose CO2 to protect the weld from oxidation and nitriding.

[0025] Sodium fluoride, whose main component is NaF, has a melting point of 993℃. During the welding process, it can increase the stiffness and penetration of the electric arc, allowing the base material and welding material to fully fuse and prevent welding defects. On the other hand, it can reduce the welding temperature and increase the fluidity of the molten pool during the welding process, thereby improving welding efficiency.

[0026] Fluorite, primarily composed of CaF2, has a melting point of 1357℃. In the welding process, it plays a role in desulfurization, combining with hydrogen (H) to form HF which volatilizes, reducing the tendency for hydrogen white spots and enhancing weld plasticity. On the other hand, it effectively improves slag fluidity, reduces slag viscosity, and enhances impact toughness. Under the influence of an electric arc, the following reactions occur: Combined with H: CaF₂ + H₂O → CaO + 2HF CaF2 + 2H → Ca + 2HF 2CaF2 + 3SiO2 → 2CaSiO3 + SiF4 (This reaction can also optimize the process performance of welding electrodes and reduce spatter) SiF4 + H → SiF + 3HF Desulfurization: CaF₂ + [S] → CaS + 2[F] This achieves the effect of dehydrogenation and desulfurization.

[0027] Aluminum fluoride, whose main components are F and Al, plays a role in the welding process by adjusting the viscosity, acidity and alkalinity and surface tension of the slag, lowering the melting point of the slag, improving fluidity, improving slag removal, and making the weld bead look better; reducing the porosity sensitivity of the weld, reducing the diffusible hydrogen content of the weld metal, and improving the impact toughness of the weld metal.

[0028] C is one of the main elements in weld metal. To a certain extent, it can improve the strength of weld metal, but excessive content can affect the welding process performance.

[0029] Mn is the main element for strengthening, desulfurization, and deoxidation. It can expand the austenite region, but its content should not be too high, as excessive content will lead to a decrease in the toughness of the weld metal.

[0030] As a deoxidizing element, silicon reacts with oxygen to form SiO2, thus playing a deoxidizing role. Silicon is also a key element for improving welding process performance. Appropriate addition of silicon can improve the processing performance of welding materials to a certain extent.

[0031] Cr is a ferrite-forming element that can lower the phase transformation temperature of microstructures and has a certain solid solution strengthening effect, which can improve the hardenability of welds. Furthermore, Cr is a corrosion-resistant element, which can give the weld a certain degree of corrosion resistance after welding.

[0032] Mo promotes the formation of acicular ferrite, which greatly improves the overall mechanical properties and low-temperature toughness of the weld. However, excessive Mo content will produce strong solid solution strengthening and reduce the impact toughness of the weld metal.

[0033] Ni is an austenite stabilizing element that can improve the low-temperature impact toughness of weld metal. With the increase of Ni content, the microstructure of high-strength steel welds changes from a predominantly lath bainite and martensite microstructure to a mixed microstructure of finer lath martensite and bainite, resulting in increased weld strength while maintaining good low-temperature toughness.

[0034] The addition of W element can maintain the wear resistance of the weld, as well as its long-term strength and hardness at high temperatures.

[0035] The addition of Cu can improve the corrosion resistance of materials and increase the strength of welds to a certain extent.

[0036] Nib is a major stabilizing element. Due to its relatively large atomic radius, Nib is less prone to ionization and decomposition, resulting in Ni3Nb precipitates that provide precipitation strengthening, which is beneficial to the microstructure and properties. Nib can also refine the microstructure, strengthen the weld metal, and improve the mechanical properties of the weld.

[0037] Compared with existing technologies, the arc welding electrode, preparation method, and application of the present invention suitable for cryogenic storage tanks have the following advantages: 1) By properly controlling the particle size of marble, the coating performance of the welding rod can be adjusted, the welding process performance can be improved, and slag removal can be made easier; 2) By properly controlling the content of fluorite and aluminum fluoride, the melting point, viscosity and surface tension of the slag can be adjusted, resulting in a more aesthetically pleasing weld. 3) By reasonably controlling the content of potassium carbonate and sodium fluoride, the stability and concentration of the electric arc can be balanced, ensuring good welding process performance and stable welding process when welding flat, vertical and overhead in AC welding. 4) It can meet the welding requirements of cryogenic storage tanks such as LNG, LEG, liquid nitrogen or liquid oxygen; 5) Use at an ambient temperature of -163℃ after welding. Attached Figure Description

[0038] The accompanying drawings, which form part of this utility model, are used to provide a further understanding of the utility model. The illustrative embodiments of the utility model and their descriptions are used to explain the utility model and do not constitute an undue limitation of the utility model. In the drawings: Figure 1 This is a schematic diagram of the weld seam in Comparative Example 7 as described in the embodiment of this utility model; Figure 2 This is a schematic diagram of the weld seam in Embodiment 2 of this utility model. Detailed Implementation

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0040] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] The present invention will be described in detail below with reference to embodiments.

[0042] After preparing the electrode coating according to the three formulas in Table 1, the powders are mixed evenly, and then potassium sodium water glass with a modulus M of 3.00-3.10 and a concentration Beº of 40-45 is added and mixed well. The powder is then pressed onto the welding core using a hydraulic press. The welding core used is a Ni-Cr-Fe nickel-based alloy welding core with a diameter of 3.2mm, thus obtaining the welding electrode. The electrode is then subjected to an air-drying and baking process. The air-drying process involves natural air drying for 12 hours, followed by a baking process consisting of four steps: 80℃ for 1 hour; 150℃ for 1 hour; 260℃ for 1 hour; and 380℃-400℃ for 2 hours.

[0043] Table 1 Electrode Coating Formulations for 3 Case Studies The coating material described in the examples is as follows: Marble containing ≥98.0% CaCO3, ≤0.020% S, and ≤0.010% P, with particle size requirements of +40 mesh: 0%, +50 mesh: ≤5%, -200 mesh: ≤40%; Potassium carbonate containing ≥96.0% K2CO3, ≤0.050% S, and ≤0.050% P, with particle size requirements of -50 mesh: ≥99.0%, -100 mesh: ≥98.0%; Sodium fluoride containing ≥98.0% NaF, ≤0.30% H2O, ≤0.060% C, and ≤0.015% S, with particle size requirements of -80 mesh: =100%, -100 mesh: ≥95%, -300 mesh: ≤30%; fluorite: CaF2 mass content ≥96.0%, S mass content ≤0.010%, P mass content ≤0.010%, particle size requirements: +50 mesh: 0%, +60 mesh: ≤1%, -200 mesh: ≤70%; aluminum fluoride: F mass content ≥61.0%, Na mass content ≤0.50%, Al mass content ≥31.0%, S mass content ≤0.050%, P2O5 mass content ≤0.040%, H2O mass content ≤0.40%, particle size requirements: -80 mesh: =100%, +120 mesh: ≤10%; where "+" represents above, and "-" represents below. The silicon additive is one or more of 75# ferrosilicon, rare earth ferrosilicon, silicon carbide, and ferrosilicon-manganese alloy; the manganese additive is one or more of electrolytic manganese, ferrosilicon-manganese alloy, and high-carbon ferromanganese; the molybdenum additive is one or two of metallic molybdenum and ferromolybdenum; the niobium additive is one or two of metallic niobium and ferroniobium; and the tungsten additive is one or more of metallic tungsten, ferrotungsten, tungsten carbide, and ferrosilicon-tungsten.

[0044] Welding tests were conducted using 20mm thick 9% Ni steel plates. Welding process parameters: current: 80-100A; pass temperature: 130-150℃; number of passes: 5-7. The chemical composition and mechanical properties of the weld metal are shown in Table 2.

[0045] Table 2 Chemical composition and mechanical properties of weld metal (balance: Ni) The above welding tests verified the overall performance of the invention, and the following results were obtained: This invention adjusts the coating performance of welding electrodes by rationally controlling the particle size of marble, improving welding process performance and facilitating slag removal. By rationally controlling the content of fluorite and aluminum fluoride, the melting point, viscosity, and surface tension of the slag can be adjusted, resulting in aesthetically pleasing weld formation. Furthermore, by rationally controlling the content of potassium carbonate and sodium fluoride, the stability and concentration of the arc can be balanced, ensuring good welding process performance and stability during AC welding in flat, vertical, and overhead positions. All three examples meet the welding requirements for cryogenic storage tanks such as LNG, LEG, liquid nitrogen, or liquid oxygen, with Example 2 exhibiting the best match between welding process performance and mechanical properties.

[0046] (a) The electrode production process and welding test are the same as in the example. The formula, chemical composition and mechanical properties of the weld metal are shown in Tables 3 and 4.

[0047] Table 3. Electrode coating formulations for three comparative examples Table 4 Chemical composition and mechanical properties of weld metal (balance: Ni) Compared with Comparative Examples 1, 2 and 3, Example 2 showed a clear molten pool, good slag wettability, more suitable slag viscosity and surface tension, beautiful weld formation after welding, and optimal matching of welding process performance and mechanical properties.

[0048] (ii) The electrode production process and welding test are the same as in the example. The formula, chemical composition and mechanical properties of the weld metal are shown in Tables 5 and 6.

[0049] Table 5. Electrode coating formulations for three comparative examples Table 6 Chemical composition and mechanical properties of weld metal (balance: Ni) Compared to Comparative Examples 4, 5 and 6, Example 2 exhibits a more stable arc with better rigidity and concentration during welding, and the base material and welding material are more fully fused together, with no welding defects such as undercut or lack of fusion. The welding process performance and mechanical properties are optimally matched.

[0050] (iii) The electrode production process and welding test are the same as in the example. The formula, chemical composition and mechanical properties of the weld metal are shown in Table 7 and Table 8.

[0051] Table 7. Coating formulations of two comparative welding electrodes The marble in Comparative Example 7 was required to have a CaCO3 content ≥ 98.0%, a S content ≤ 0.020%, and a P content ≤ 0.010%, with particle size requirements of -40 mesh : = 100% and -60 mesh : 0%. In Example 2, the marble is required to have a CaCO3 content ≥98.0%, an S content ≤0.020%, a P content ≤0.010%, and a particle size requirement of +40 mesh: 0%, +50 mesh: ≤5%, and -200 mesh: ≤40%.

[0052] Table 8 Chemical composition and mechanical properties of weld metal (balance: Ni) As can be seen from the above Comparative Example 7 and Example 2, the particle size of marble can affect subsequent performance parameters.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An arc welding electrode suitable for cryogenic storage tanks, characterized in that: It consists of a welding core coated with a powder, wherein the powder, by weight, is as follows: marble 12-18 parts; potassium carbonate 10-15 parts; sodium fluoride 2-7 parts; fluorite 7-12 parts; aluminum fluoride 3-8 parts; silicon additive 4-9 parts; manganese additive 2-6 parts; molybdenum additive 22-30 parts; niobium additive 8-15 parts; and tungsten additive 4-9 parts. For marble, the mass content of CaCO3 should be ≥98.0%, S ≤0.020%, and P ≤0.010%, with particle size requirements as follows: +40 mesh: 0%, +50 mesh: ≤5%, -200 mesh: ≤40%; for potassium carbonate, the mass content of K2CO3 should be ≥96.0%, S ≤0.050%, and P ≤0.050%, with particle size requirements as follows: -50 mesh: ≥99.0%, -100 mesh: ≥98.0%; for sodium fluoride, the mass content of NaF should be ≥98.0%, H2O ≤0.30%, C ≤0.060%, and S ≤0.015%, with particle size requirement as follows: -80 mesh: 100%. -100 mesh: ≥95%, -300 mesh: ≤30%; fluorite: CaF2 mass content ≥96.0%, S mass content ≤0.010%, P mass content ≤0.010%, particle size requirements: +50 mesh: 0%, +60 mesh: ≤1%, -200 mesh: ≤70%; aluminum fluoride: F mass content ≥61.0%, Na mass content ≤0.50%, Al mass content ≥31.0%, S mass content ≤0.050%, P2O5 mass content ≤0.040%, H2O mass content ≤0.40%, particle size requirements: -80 mesh: =100%, +120 mesh: ≤10%; where "+" represents above, and "-" represents below. The components of the welding core, by mass parts, include: C 0.035-0.06 parts, Mn 2.2-3.5 parts, Si≤0.10 parts, Cr 18.0-20.0 parts, Ti 0.15-0.50 parts, Fe 3.0-6.0 parts, with the balance being Ni.

2. The arc welding electrode suitable for cryogenic storage tanks according to claim 1, characterized in that: The silicon additives include one or more of 75# ferrosilicon, rare earth ferrosilicon, silicon carbide, and silicon-manganese alloy; Manganese additives include one or more of electrolytic manganese, ferrosilicon, and high-carbon ferromanganese; The molybdenum additive is one or both of metallic molybdenum and ferromolybdenum; The niobium additive is one or both of metallic niobium and ferroniobium; The tungsten additive is one or more of metallic tungsten, ferrotungsten, tungsten carbide, and ferrosilicon.

3. The arc welding electrode suitable for cryogenic storage tanks according to claim 1, characterized in that: Before applying the powder, add a binder to the powder; The binder used is potassium sodium silicate with a modulus M of 3.00-3.10 and a concentration Beº of 40-45.

4. The arc welding electrode suitable for cryogenic storage tanks according to claim 1, characterized in that: The powder coating rate is 40%-45%.

5. The arc welding electrode suitable for cryogenic storage tanks according to claim 1, characterized in that: The diameter of the welding core is 3.2-4.0mm.

6. The arc welding electrode suitable for cryogenic storage tanks according to claim 1, characterized in that: Welding is performed using welding electrodes, and the weld metal comprises the following components by mass fraction: C 0.02-0.04%, Mn 2.5-3.5%, Si 0.25-0.40%, Cr 12.5-13.5%, Mo 5.5-6.5%, Nb 1.2-2.0%, W 1.4-2.0%, Cu 0.05-0.10%, Fe 5.0-6.0%, with the balance being Ni.

7. The arc welding electrode suitable for cryogenic storage tanks according to claim 1, characterized in that: The welding process parameters are: voltage 22V-28V, current 70A-130A, AC / DC dual-use.

8. A method for preparing an arc welding electrode suitable for cryogenic storage tanks according to any one of claims 1-7, characterized in that: After the powder is stirred evenly, a binder is added to obtain a mixed powder. The core is coated with the mixed powder, and the welding rod is coated with the mixed powder and then air-dried and baked. First stage: Keep warm at 75-85℃ for 1 hour; Second stage: Keep warm at 145-155℃ for 1 hour; Third stage: Keep warm at 255-265℃ for 1 hour; Fourth stage: Keep warm at 380℃-400℃ for 2 hours.

9. A method for preparing an arc welding electrode suitable for cryogenic storage tanks according to claim 8, characterized in that: The air-drying process includes natural air drying, which takes 11-13 hours.

10. A method for preparing an arc welding electrode suitable for cryogenic storage tanks according to claim 8, characterized in that: The baking process includes staged baking.

11. The application of the arc welding electrode suitable for cryogenic storage tanks according to any one of claims 1-7, or the welding electrode prepared by the method of claim 8, in the welding of cryogenic storage tanks, characterized in that, Cryogenic storage tanks include one or more of LNG, LEG, liquid nitrogen, or liquid oxygen, and are used at an ambient temperature of -163°C after welding.

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