A 550mpa grade high-strength acid electrode and preparation and welding method

Abstract

The application discloses a 550MPa high-strength acid electrode and a preparation and welding method thereof. The electrode comprises an electrode core and a coating covering the surface of the electrode core. The coating comprises the following components in parts by weight: 1-3 parts of microcrystalline fiber, 9-12 parts of medium-carbon ferromanganese, 1-5 parts of baking soda, 0.5-3 parts of ferromolybdenum, 30-40 parts of reduced ilmenite, 4-10 parts of white clay, 5-15 parts of potassium feldspar, 7-12 parts of mica, 10-15 parts of marble, and 0.5-3 parts of silicon-calcium alloy. The electrode is designed by an innovative coating system and reasonable alloy ratio, so that the tensile strength of the electrode is far higher than the current acid electrode standard requirement, the impact performance is good, the coating has better moisture resistance than similar alkaline electrodes, is suitable for field construction operation, and can meet the welding requirement of 550MPa low-carbon steel.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and more specifically, to a 550MPa high-strength acidic welding electrode and its preparation and welding methods. Background Technology

[0002] In infrastructure construction, such as buildings, bridges, railways, and highways, welding of low-carbon steel primarily relies on ordinary 430MPa and 490MPa grade acidic welding electrodes. While these electrodes offer relatively average tensile strength and met past construction needs, future infrastructure projects will require higher strength, larger spans, and more stringent environmental conditions. As a result, 430MPa and 490MPa acidic welding electrodes will be gradually phased out. Currently, some projects have begun using 550MPa grade alkaline welding electrodes to replace acidic electrodes and address the tensile strength issue in welded joints. Although this improves mechanical properties, it significantly increases the difficulty of welding operations. It necessitates rust and oil removal from the base material and joints. Furthermore, alkaline welding electrodes have poor moisture resistance and limited all-position welding performance, severely impacting work efficiency in actual field construction. Therefore, developing new high-strength acidic welding electrodes that significantly reduce the operational requirements for welders while improving the tensile strength of welded joints is a pressing issue that needs to be addressed.

[0003] In view of the above, this application is hereby submitted. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a 550MPa-grade high-strength acidic welding electrode and its preparation and welding method. By improving the composition of the electrode coating, and utilizing the individual components and their synergistic effects, the tensile strength of the welded joint is increased while significantly reducing the operational requirements for welders. This solves the problem that current ordinary acidic and alkaline welding electrodes cannot simultaneously meet mechanical performance requirements and also ensure ease of field construction.

[0005] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a 550MPa grade high-strength acidic welding electrode, comprising a welding core and a coating covering the surface of the welding core, wherein the coating comprises the following components by weight: 1-3 parts microcrystalline fiber, 9-12 parts medium carbon ferromanganese, 1-5 parts sodium bicarbonate, 0.5-3 parts ferromolybdenum, 30-40 parts reduced ilmenite, 4-10 parts white clay, 5-15 parts potassium feldspar, 7-12 parts mica, 10-15 parts marble, and 0.5-3 parts silicon-calcium alloy.

[0006] This invention achieves a tensile strength of ≥550 MPa in the welded joint by rationally controlling the composition and ratio of the flux powder, especially the precise control of the amount of trace alloying elements added. This is far superior to ordinary acidic welding electrodes. Compared with alkaline welding electrodes of the same grade, it has better welding processability, beautiful weld formation, slag shell that can automatically lift and fall off, excellent all-position welding operability, and significantly improved re-arc striking performance. At the same time, the impact performance still meets the relevant standard requirements.

[0007] The main components of reduced ilmenite are TiO2, Fe, and C. This component is one of the most important components of acidic welding electrode coatings. It contains a large amount of TiO2, which can stabilize the arc and form slag to protect the weld in acidic welding electrodes. The optimal protective performance can be obtained by controlling the addition amount between 30% and 50%. However, because this material contains a lot of Fe and C, it has extremely strong reducing properties and will cause a violent redox reaction during welding, resulting in greater spatter. Therefore, its dosage should not be too large.

[0008] Microcrystalline fibers are mainly composed of organic matter, which is crucial for the arc blowing force and re-ignition of welding electrodes, especially in AC welding applications. It prevents arc interruption and, by appropriately increasing the blowing force, facilitates all-position welding. The total amount added to the electrode coating should be controlled below 3%. This improves its AC welding process performance while preventing excessive carbon from causing porosity in the weld. Because the weld pool temperature is very high, carbon has a strong reducing ability and can react violently with oxides in the molten pool, increasing spatter and generating CO and CO2. If these are not removed promptly, porosity can easily occur.

[0009] Baking soda's main component is NaHCO3. It begins to decompose at around 80℃ and is almost completely decomposed above 200℃, producing CO2 and Na2CO3. Above 1000℃, it further decomposes into Na2O and CO2. Utilizing this property, adding Na2O to this welding electrode can provide gas protection during the early stages of flux melting, preventing oxidation of the weld by air. During the molten pool formation stage, Na2O can enter the weld, increasing the slag basicity and thus improving impact toughness. This is a core material for ensuring the impact performance of high-tensile-strength acidic welding electrodes; it is an excellent inorganic material that provides gas protection and increases weld basicity. Furthermore, the sodium ion has an extremely low ionization potential, readily ionizing at high arc temperatures, maintaining arc conductivity and improving arc stability. However, adding too much Na2O to the electrode flux can lead to severe moisture absorption, and excessively high basicity is detrimental to weld formation. Therefore, through trial and error, it has been found that adding 2%-5% Na2O to the flux yields the best results.

[0010] Medium-carbon ferromanganese mainly consists of Mn and Fe. Mn is an important deoxidizer and also a crucial alloying agent for weld metal, significantly influencing its strength and toughness. Mn can lower the austenite-ferrite transformation temperature and promote the formation of acicular ferrite (AF), thereby improving the low-temperature impact resistance of the weld. However, excessive addition can increase tensile strength but decrease impact resistance. In this welding electrode, through a reasonable composition and ratio design, and the combined action of the flux and core material, the Mn to Si ratio in the weld metal is achieved to approximately 2:1. This results in stronger deoxidation by Si before solidification of the weld pool and stronger deoxidation by Mn in the later stages of weld pool solidification. Furthermore, Mn can combine with impurity element S to form MnS, reducing impurities and purifying the weld metal.

[0011] Ferromolybdenum, mainly composed of Mo and Fe, is a key trace metal additive that can significantly improve the strength, toughness, heat resistance, and corrosion resistance of welded joints. However, due to the large amount of carbon present in the welded joint of this electrode, the amount added should not be too high; otherwise, the formation of a large amount of MoC will greatly reduce the impact performance. The total amount added to the electrode coating should be controlled within 3%.

[0012] The main components of white clay and potassium feldspar are SiO2, Al2O3, K2O, and Na2O. When present in molten slag, they are repelled to the surface due to their low bond energy, reducing the surface tension of the slag and thus improving its fluidity. A lower proportion in the flux coating can result in finer droplet particles, leading to a smoother slag wall transition in welding. However, excessive addition slows down the solidification rate of the slag, causing molten iron and slag to flow downwards during vertical and overhead welding.

[0013] The main component of mica is KMg3(AlSi3O) 10 F2 primarily functions as a slag-forming agent in the weld, protecting the weld metal from oxidation in the air and resulting in a high-quality metallic luster and weld formation. However, excessive addition should be avoided to prevent the introduction of too many silicates and aluminates, which could negatively impact arc stability. Furthermore, this material significantly enhances the strength of the electrode coating, making it crucial for ensuring normal electrode production.

[0014] Marble's main component is CaCO3, and its primary functions are slag formation, gas generation, arc stabilization, and increasing slag basicity. It also exhibits good desulfurization capabilities and indirect dephosphorization effects. The CO2 decomposed during welding reduces weld oxidation and nitriding, and lowers the content of diffusible hydrogen. Furthermore, when used in conjunction with other carbonates with different decomposition temperatures, these carbonates enter the molten pool before complete decomposition, absorbing heat from the pool, rapidly lowering the slag temperature, increasing slag viscosity, and accelerating slag solidification, which is beneficial for all-position welding.

[0015] Silicon-calcium alloy, mainly composed of Si, Ca, and a small amount of Al, possesses extremely strong deoxidizing and desulfurizing capabilities, effectively purifying oxidizing inclusions in the weld. Its deoxidation product is low-melting-point CaO·SiO2 (calcium silicate), which, compared to SiO2 generated by ferrosilicon, floats more easily into the slag, reducing silicate inclusions. Simultaneously, Ca has a strong desulfurizing effect, reducing the tendency for hot cracking. Silicon can dissolve into the matrix (ferrite), bringing a small amount of solid solution strengthening and thus improving the tensile strength of the weld. However, silicon-calcium alloy itself has a high basicity and cannot be added in excessive amounts; otherwise, it easily produces a large amount of spatter and a cloudy molten pool in acidic welding electrodes. Therefore, the optimal addition amount in this welding electrode is controlled within 3%.

[0016] In one specific embodiment, the welding core comprises the following components by weight percentage: 0.02%-0.2% carbon, 0.1%-0.4% manganese, 0.01%-0.03% silicon, 99.5%-99.9% iron, with the balance being unavoidable impurities.

[0017] In one specific embodiment, the coating comprises the following components by weight: 1.4-1.8 parts microcrystalline fiber, 10.5-12.0 parts medium-carbon ferromanganese, 3-4 parts sodium bicarbonate, 1-2 parts ferromolybdenum, 34-38.5 parts reduced ilmenite, 7-9 parts white clay, 11.2-11.8 parts potassium feldspar, 8.0-10.5 parts mica, 12.5-14 parts marble, and 1.5-2.5 parts silicon-calcium alloy; the core comprises the following components by weight percentage: 0.05%-0.1% carbon, 0.3%-0.35% manganese, 0.03% silicon, and 99.555%-99.559% iron, with the balance being unavoidable impurities.

[0018] In one specific embodiment, the coating comprises the following components by weight: 1.5 parts microcrystalline fiber, 11.0 parts medium-carbon ferromanganese, 3.5 parts sodium bicarbonate, 1.4 parts ferromolybdenum, 38.0 parts reduced ilmenite, 8.5 parts white clay, 11.5 parts feldspar, 9.0 parts mica, 13.5 parts marble, and 2.1 parts silicon-calcium alloy; the core comprises the following components by weight percentage: 0.05% carbon, 0.35% manganese, 0.03% silicon, and 99.555% iron, with the balance being unavoidable impurities.

[0019] In one specific embodiment, the coating comprises the following components by weight: 1.6 parts microcrystalline fiber, 11.2 parts medium-carbon ferromanganese, 3.4 parts sodium bicarbonate, 1.4 parts ferromolybdenum, 37.8 parts reduced ilmenite, 8.0 parts white clay, 11.7 parts feldspar, 9.3 parts mica, 13.5 parts marble, and 2.1 parts silicon-calcium alloy; the core comprises the following components by weight percentage: 0.1% carbon, 0.3% manganese, 0.03% silicon, and 99.559% iron, with the balance being unavoidable impurities.

[0020] In one specific embodiment, the composition includes 1.5 parts microcrystalline fiber, 11.2 parts medium-carbon ferromanganese, 3.8 parts sodium bicarbonate, 1.1 parts ferromolybdenum, 37.2 parts reduced ilmenite, 8.8 parts white clay, 11.5 parts feldspar, 9.5 parts mica, 13.0 parts marble, and 2.4 parts silicon-calcium alloy; the welding core comprises the following weight percentage components: 0.1% carbon, 0.3% manganese, 0.03% silicon, and 99.556% iron, with the balance being unavoidable impurities.

[0021] In one specific embodiment, the medium-carbon ferromanganese has a content of Mn ≥ 75% and Si ≤ 2.5%; the ferromolybdenum has a content of Mo ≥ 55.0% and C ≤ 0.2%.

[0022] In one specific embodiment, TiO2 ≥ 56.0%; the white mud has SiO2 ≥ 59.0% and Al2O3 ≥ 17.0%.

[0023] In one specific embodiment, the potassium feldspar has the following composition: SiO2 ≥ 62.0%, Al2O3 ≥ 16.0%, K2O + Na2O ≥ 12.0%; and the mica has the following composition: SiO2 ≥ 45.0%, Al2O3 ≥ 22.0%, K2O + Na2O ≥ 7.0%.

[0024] In one specific embodiment, the marble has a CaCO3 content of ≥96.0%; the silicon-calcium alloy has a Ca content of 25%-32% and a Si content of 50%-65%.

[0025] Secondly, the present invention provides a method for preparing the 550MPa-grade high-strength acidic welding electrode, comprising the following steps: (1) Add each component of the medicine powder to the mixer according to the proportion, stir and mix evenly, then add potassium sodium water glass with a modulus of 2.6, a viscosity of 39Be' and a weight percentage of 19.0%-22.0% to mix and adjust the powder to obtain the mixed medicine powder; (2) Place the powder and the core (the mixed powder accounts for 22% to 32% of the total weight of the welding rod, and the core accounts for 68% to 78% of the total weight of the welding rod) in a welding rod coating press, and after coating and pressing, the welding rod is a welding rod with the core coated with powder; (3) The product is baked at low temperature of 70℃-130℃, high temperature of 140℃-190℃, printed, and packaged in sequence.

[0026] Thirdly, the present invention provides a welding method for welding 550MPa grade low carbon steel, using the 550MPa grade high-strength acidic welding rod described in the claim for welding, and the welding parameters are: welding current 140-210A, arc voltage 20-30V, and welding pass temperature 90-130℃.

[0027] This invention utilizes the aforementioned welding rods to weld 550MPa grade low-carbon steel, achieving weld metal with higher tensile strength than ordinary acid welding rods. It also yields good tensile strength at room temperature and mechanical properties meeting relevant standards. The tensile strength of the weld metal is 550 MPa-620 MPa, and the impact energy (Akv) of the weld metal at 0℃ is 80 J-110 J.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The present invention provides a 550MPa grade high-strength acidic welding electrode and its preparation and welding method. By rationally controlling the composition and ratio of the flux powder, especially the precise control of the amount of trace alloying elements added, the tensile strength of the welded joint of the electrode is ≥550 MPa, which is much higher than that of ordinary acidic welding electrodes, while the impact performance still meets the relevant standard requirements. 2. The present invention provides a 550MPa high-strength acidic welding electrode and its preparation and welding method. The 550MPa high-strength acidic welding electrode has better welding processability compared with the same level of basic welding electrode. The weld formation is beautiful, the slag shell can automatically lift and fall off, the all-position welding operation is excellent, and the re-arc striking performance is greatly improved. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0030] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0031] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] Performance parameters of each component raw material in the drug coating Overall requirements: particle size 30-200 mesh, moisture content ≤5%, S≤0.02%, P≤0.02%; Medium carbon ferromanganese (Mn≥75%, Si≤2.5%); Potassium feldspar (SiO2≥62.0%, Al2O3≥16.0%, K2O+Na2O≥12.0%). Mica (SiO2≥45.0%, Al2O3≥22.0%, K2O+Na2O≥7.0%) White clay (SiO2≥59.0%, Al2O3≥17.0%); Reduced ilmenite (TiO2≥56.0%); marble (CaCO3≥96.0%). Ferromolybdenum (Mo≥55.0%, C≤0.2%); Calcium-silicon alloy (Ca:25%-32%, Si:50%-65%).

[0034] Example 1 This invention provides a 550MPa grade high-strength acidic welding electrode, consisting of a core and a coating covering the surface of the core. The composition and content of the coating are as follows: 1.5 kg of microcrystalline fiber, 11.0 kg of medium-carbon ferromanganese, 3.5 kg of sodium bicarbonate, 1.4 kg of ferromolybdenum, 38.0 kg of reduced ilmenite, 8.5 kg of white clay, 11.5 kg of feldspar, 9.0 kg of mica, 13.5 kg of marble, and 2.1 kg of silicon-calcium alloy were used to obtain a mixed powder.

[0035] The composition of the welding core, by weight, is: 0.07 kg of carbon, 0.35 kg of manganese, 0.03 kg of silicon, 99.50 kg of iron, and unavoidable impurities introduced by the material.

[0036] The preparation method is as follows: Step 1: Add the components of the medicine powder to the mixer, stir and mix evenly, then add potassium sodium water glass with a modulus of 2.6, a viscosity of 39Be', and a weight percentage of 21.0% to mix the powder.

[0037] Step 2: Place the welding core and the mixed powder obtained in Step 1 into a welding electrode coating press. The mixed powder accounts for 27.0% of the total weight of the welding electrode, and the welding core accounts for 73.0% of the total weight of the welding electrode. The coating pressure is 48 MPa - 55 MPa. After coating and molding, the welding electrode has the welding core wrapped in the powder.

[0038] Step 3: Baking at a low temperature of 70-130℃, baking at a high temperature of 140-190℃, printing, and packaging.

[0039] Welding parameters: I=140-210A, U=25-30V, interpass temperature 90-130 (°C).

[0040] According to the requirements of ANSI / AWS B4.0M-2000(R2010) "Standard Method for Testing Mechanical Properties of Welds", the tested weld properties are shown in Tables 1 and 2.

[0041] Table 1 Chemical composition of deposited metal (%) ; Table 2 Mechanical properties of deposited metal .

[0042] Example 2 This invention provides a 550MPa grade high-strength acidic welding electrode, consisting of a core and a coating covering the surface of the core. The composition and content of the coating are as follows: 1.6 kg of microcrystalline fiber, 11.2 kg of medium-carbon ferromanganese, 3.4 kg of sodium bicarbonate, 1.4 kg of ferromolybdenum, 37.8 kg of reduced ilmenite, 8.0 kg of white clay, 11.7 kg of feldspar, 9.3 kg of mica, 13.5 kg of marble, and 2.1 kg of silicon-calcium alloy were used to obtain a mixed powder.

[0043] The composition of the welding core, by weight, is: 0.07 kg of carbon, 0.35 kg of manganese, 0.03 kg of silicon, 99.50 kg of iron, and unavoidable impurities introduced by the material.

[0044] The preparation method is as follows: Step 1: Add the components of the medicine powder to the mixer, stir and mix evenly, then add potassium sodium water glass with a modulus of 2.6, a viscosity of 39Be', and a weight percentage of 20.0% to mix the powder.

[0045] Step 2: Place the welding core and the mixed powder obtained in Step 1 into a welding electrode coating press. The mixed powder accounts for 28.0% of the total weight of the welding electrode, and the welding core accounts for 72.0% of the total weight of the welding electrode. The coating pressure is 48 MPa - 55 MPa. After coating and molding, the welding electrode has the welding core wrapped in the powder.

[0046] Step 3: Baking at a low temperature of 70-130℃, baking at a high temperature of 140-190℃, printing, and packaging.

[0047] Welding parameters: I=140-210A, U=25-30V, interpass temperature 90-130 (°C).

[0048] According to the requirements of ANSI / AWS B4.0M-2000(R2010) "Standard Method for Testing Mechanical Properties of Welds", the tested weld properties are shown in Tables 3 and 4.

[0049] Table 3 Chemical composition of deposited metal (%) ; Table 4 Mechanical properties of deposited metal .

[0050] Example 3 This invention provides a 550MPa grade high-strength acidic welding electrode, consisting of a core and a coating covering the surface of the core. The composition and content of the coating are as follows: 1.5 kg of microcrystalline fiber, 11.2 kg of medium-carbon ferromanganese, 3.8 kg of sodium bicarbonate, 1.1 kg of ferromolybdenum, 37.2 kg of reduced ilmenite, 8.8 kg of white clay, 11.5 kg of feldspar, 9.5 kg of mica, 13.0 kg of marble, and 2.4 kg of silicon-calcium alloy were used to obtain a mixed powder.

[0051] The composition of the welding core, by weight, is: 0.11 kg of carbon, 0.33 kg of manganese, 0.02 kg of silicon, 99.50 kg of iron, and unavoidable impurities introduced by the material.

[0052] The preparation method is as follows: Step 1: Add the components of the medicine powder to the mixer, stir and mix evenly, then add potassium sodium water glass with a modulus of 2.6, a viscosity of 39Be', and a weight percentage of 21.0% to mix the powder.

[0053] Step 2: Place the welding core and the mixed powder obtained in Step 1 into a welding electrode coating press. The mixed powder accounts for 29.0% of the total weight of the welding electrode, and the welding core accounts for 71.0% of the total weight of the welding electrode. The coating pressure is 48 MPa - 55 MPa. After coating and molding, the welding electrode has a welding core wrapped with the powder.

[0054] Step 3: Baking at a low temperature of 70-130℃, baking at a high temperature of 140-190℃, printing, and packaging.

[0055] Welding parameters: I=140-210A, U=25-30V, interpass temperature 90-130 (°C).

[0056] According to the requirements of ANSI / AWS B4.0M-2000(R2010) "Standard Method for Testing Mechanical Properties of Welds", the tested weld properties are shown in Tables 5 and 6.

[0057] Table 5 Chemical composition of deposited metal (%) ; Table 6 Mechanical properties of deposited metal .

[0058] Comparative Example 1 In the comparative example of this invention, welding was performed using an existing acidic welding electrode of the same type, J502. The composition and content of the coating were as follows: 1.2 kg of microcrystalline fiber, 9.8 kg of medium-carbon ferromanganese, 3.2 kg of wood flour, 0.5 kg of ferromolybdenum, 49.5 kg of reduced ilmenite, 8.2 kg of white clay, 6.3 kg of feldspar, 8.5 kg of mica, 11.0 kg of marble, and 1.8 kg of manganese silicon alloy; thus, a mixed coating powder was obtained.

[0059] The composition of the welding core, by weight, is: 0.08 kg of carbon, 0.35 kg of manganese, 0.04 kg of silicon, 99.50 kg of iron, and unavoidable impurities introduced by the material.

[0060] The preparation method is as follows: Step 1: Add the components of the medicine powder to the mixer, stir and mix evenly, then add potassium sodium water glass with a modulus of 2.6, a viscosity of 37.5Be', and a weight percentage of 20.0% to mix the powder.

[0061] Step 2: Place the welding core and the mixed powder obtained in Step 1 into a welding electrode coating press. The mixed powder accounts for 31.0% of the total weight of the welding electrode, and the welding core accounts for 69.0% of the total weight of the welding electrode. The coating pressure is 48 MPa - 55 MPa. After coating and molding, the welding electrode has a welding core wrapped with the powder.

[0062] Step 3: Baking at a low temperature of 70-130℃, baking at a high temperature of 140-190℃, printing, and packaging.

[0063] Welding parameters: I=140-210A, U=25-30V, interpass temperature 90-130 (°C).

[0064] According to the requirements of ANSI / AWS B4.0M-2000(R2010) "Standard Method for Testing Mechanical Properties of Welds", the tested weld properties are shown in Tables 7 and 8.

[0065] Table 7 Chemical composition of the deposited metal (%) ; Table 8 Mechanical properties of deposited metal .

[0066] As can be seen from the data in the table above, the tensile strength of the weld of similar acidic welding electrodes is around 500 MPa, which is far lower than the 550 MPa high tensile strength welding electrode of this invention.

[0067] Comparative Example 2 The difference between this comparative example and the embodiment is that the composition of the welding electrode powder used in the welding is different. This comparative example includes: 1.5 kg of microcrystalline fiber, 9.2 kg of medium carbon ferromanganese, 3.8 kg of wood flour, 3.1 kg of ferromolybdenum, 39.2 kg of reduced ilmenite, 8.8 kg of white clay, 12.5 kg of feldspar, 9.5 kg of mica, 11.0 kg of marble, and 1.4 kg of high carbon ferrochrome; thus, a mixed powder is obtained.

[0068] According to the requirements of ANSI / AWS B4.0M-2000(R2010) "Standard Method for Testing Mechanical Properties of Welds", the tested weld properties are shown in Tables 9 and 10.

[0069] Table 9 Chemical composition of the deposited metal (%) ; Table 10 Mechanical Properties of Deposited Metal .

[0070] This comparative example replaced baking soda with wood flour and removed the calcium silicon alloy. As shown in the table above, although the tensile strength of the weld can still reach over 550 MPa, the impact performance is significantly reduced and cannot meet the requirements of actual construction. This is because the addition of baking soda and the calcium silicon alloy introduces appropriate amounts of Si and Ca elements during the welding process. These elements have extremely strong deoxidizing and desulfurizing capabilities, which can greatly purify oxidizing inclusions in the weld. Oxide inclusions are crack initiation points and significantly reduce room temperature and low temperature impact toughness. Without the addition of these two materials, the low-temperature impact toughness of high tensile strength acidic welding electrodes cannot meet the standard requirements.

[0071] Comparative Example 3 The difference between this comparative example and Example 1 is that the composition of the welding electrode powder used in the welding is different. This comparative example includes: 1.5 kg of microcrystalline fiber, 11.0 kg of medium carbon ferromanganese, 6.5 kg of sodium bicarbonate, 1.4 kg of ferromolybdenum, 38.0 kg of reduced ilmenite, 8.5 kg of white clay, 11.5 kg of feldspar, 9.0 kg of mica, 10.5 kg of marble, and 2.1 kg of silicon-calcium alloy; thus, a mixed powder is obtained.

[0072] According to the requirements of ANSI / AWS B4.0M-2000(R2010) "Standard Method for Testing Mechanical Properties of Welds", the tested weld properties are shown in Tables 11 and 12.

[0073] Table 11 Chemical composition of deposited metal (%) ; Table 12 Mechanical Properties of Deposited Metal .

[0074] This comparative example increased the baking soda content to 6.5% while reducing the marble content to 10.5%. As shown in the table above, although the tensile strength of the weld can reach over 550 MPa, the impact performance is unstable, with a minimum value of only 24 J, which cannot meet the requirements of actual construction. This is because excessive baking soda addition (≥5%) causes the welding to release a large amount of CO and water vapor in a short time. Furthermore, reducing the marble content in acidic welding rods thickens the slag, trapping air bubbles inside the molten pool. This increases the resistance to bubble buoyancy, making it difficult for the bubbles to escape from the weld and easily forming localized CO or hydrogen pores. Porosity is a stress concentration source, and the impact specimen is prone to brittle fracture along the pores, significantly reducing the local impact energy.

[0075] In summary, compared with the prior art, the welding electrode of the present invention has made a significant breakthrough in the tensile strength of the weld seam of acidic welding electrodes, while also taking into account the impact performance; in terms of welding process performance, the weld seam is aesthetically pleasing, the all-position welding operation is excellent, and the welding electrode itself has stronger moisture resistance than alkaline welding electrodes, which meets the requirements for use in field construction environments; it can meet the requirements for welding 550MPa grade low carbon steel in infrastructure construction such as buildings, bridges, railways, and highways.

[0076] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A 550 MPa grade high strength acid type electrode comprising an electrode core and a coating covering the surface of the electrode core, characterized in that, The coating comprises the following components by weight: 1-3 parts microcrystalline fiber, 9-12 parts medium-carbon ferromanganese, 1-5 parts sodium bicarbonate, 0.5-3 parts ferromolybdenum, 30-40 parts reduced ilmenite, 4-10 parts white clay, 5-15 parts potassium feldspar, 7-12 parts mica, 10-15 parts marble, and 0.5-3 parts silicon-calcium alloy.

2. The 550MPa grade high-strength acidic welding electrode according to claim 1, characterized in that, The welding core comprises the following components by weight percentage: carbon 0.02%-0.2%, manganese 0.1%-0.4%, silicon 0.01%-0.03%, iron 99.5%-99.9%, with the balance being impurities.

3. The 550MPa grade high-strength acidic welding electrode according to claim 1, characterized in that, The coating comprises the following components by weight: 1.4-1.8 parts microcrystalline fiber, 10.5-12.0 parts medium-carbon ferromanganese, 3-4 parts sodium bicarbonate, 1-2 parts ferromolybdenum, 34-38.5 parts reduced ilmenite, 7-9 parts white clay, 11.2-11.8 parts potassium feldspar, 8.0-10.5 parts mica, 12.5-14 parts marble, and 1.5-2.5 parts silicon-calcium alloy.

4. The 550MPa grade high-strength acidic welding electrode according to claim 2, characterized in that: The welding core comprises the following components by weight percentage: carbon 0.05%-0.1%, manganese 0.3%-0.35%, silicon 0.03%, iron 99.555%-99.559%, with the balance being impurities.

5. The 550MPa grade high-strength acidic welding electrode according to claim 1, characterized in that, The medium-carbon ferromanganese has a content of Mn ≥ 75% and Si ≤ 2.5%; the ferromolybdenum has a content of Mo ≥ 55.0% and C ≤ 0.2%.

6. The 550MPa grade high-strength acidic welding electrode according to claim 1, characterized in that, The reduced ilmenite has a TiO2 content of ≥56.0%; the white mud has a SiO2 content of ≥59.0% and an Al2O3 content of ≥17.0%.

7. The 550MPa grade high-strength acidic welding electrode according to claim 1, characterized in that, The potassium feldspar has the following composition: SiO2 ≥ 62.0%, Al2O3 ≥ 16.0%, K2O + Na2O ≥ 12.0%; the mica has the following composition: SiO2 ≥ 45.0%, Al2O3 ≥ 22.0%, K2O + Na2O ≥ 7.0%.

8. The 550MPa grade high-strength acidic welding electrode according to claim 1, characterized in that, The marble has a CaCO3 content of ≥96.0%; the silicon-calcium alloy has a Ca content of 25%-32% and a Si content of 50%-65%.

9. A method for preparing a 550MPa grade high-strength acidic welding electrode as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Add the powder of each component to the mixer according to the proportion, stir and mix evenly, then add potassium sodium water glass to mix and adjust the powder to obtain mixed powder; (2) Place the powder and the core material in the electrode coating press, and after coating and pressing, the electrode is a welding rod with the core material coated with powder; (3) Baking at low temperature of 70℃-130℃ and high temperature of 140℃-190℃ in sequence.

10. A welding method for 550MPa grade low carbon steel, characterized in that, Welding is performed using any of the 550MPa grade high-strength acid welding electrodes described in claims 1 to 8, with the following welding parameters: welding current 140-210A, arc voltage 20-30V, and interpass temperature 90-130℃.