Welding rod for 43kg grade weathering steel and its application

Abstract

This invention provides a 43 kg grade weathering steel welding electrode, comprising a core and a coating wrapped around the core. The coating comprises the following components by mass percentage: 30-40% marble, 20-30% fluorite, 3-7% sodium fluoride, 1-3% zircon sand, 3-7% rutile, 2-4% quartz, 2-4% 45# atomized ferrosilicon, 1.5-3% metallic manganese, 1.4-2.5% nickel-magnesium alloy, 0.7-1.5% metallic chromium, 0.6-1.2% copper powder, 0-1.5% silicon-zirconium iron, 0.3-0.7% boron trioxide, 0-1% soda ash, 0-1% CMC, with the balance being iron powder. This welding electrode transfers appropriate amounts of Ni, Cr, Cu, and Si elements to the weld metal through its coating, giving the weld metal excellent weather resistance, with a weather resistance index (I) greater than 6.5. Simultaneously, by adjusting the coating composition, the content of C, Mn, Si, and other alloying elements in the weld metal is controlled, ensuring a tensile strength of 430–550 MPa and a low-temperature impact absorption energy of over 47 J at -20°C, exhibiting stable mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, specifically relating to a 43 kg class welding electrode for weathering steel and its application. Background Technology

[0002] Weathering steel, due to its resistance to atmospheric corrosion, is increasingly being used in bridges, automobiles, railway vehicles, and other industries. It offers advantages such as reduced weight, lower maintenance costs, and improved construction efficiency. Currently, ordinary steel bridges primarily rely on painting to address rust, but painting costs and subsequent maintenance are high. Therefore, weathering steel for bridges has seen widespread development both domestically and internationally, and the development of matching welding materials is becoming increasingly urgent.

[0003] Currently, there are few types of corrosion-resistant steel welding electrodes on the market, and their mechanical properties are unstable, with inconsistent weather resistance. According to AWSD1.5, the corrosion resistance index I of the weld metal should not be lower than 6.0, but there is very little research on the weather resistance performance of welding electrodes for weather-resistant steel with a tensile strength of 43 kg. Summary of the Invention

[0004] The purpose of this invention is to provide a 43 kg class welding electrode for weathering steel, which can at least solve some of the defects existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A 43 kg grade weathering steel welding electrode includes a core and a coating wrapped around the surface of the core. The coating comprises the following components by mass percentage: 30-40% marble, 20-30% fluorite, 3-7% sodium fluoride, 1-3% zircon sand, 3-7% rutile, 2-4% quartz, 2-4% 45# atomized ferrosilicon, 1.5-3% metallic manganese, 1.4-2.5% nickel-magnesium alloy, 0.7-1.5% metallic chromium, 0.6-1.2% copper powder, 0-1.5% silicon-zirconium iron, 0.3-0.7% boron trioxide, 0-1% soda ash, 0-1% CMC, with the balance being iron powder.

[0007] Furthermore, the sum of the amounts of rutile, quartz, and zircon sand added to the coating is 6-11% of the weight of the coating.

[0008] Furthermore, the sum of the amounts of soda ash and CMC added to the coating accounts for 1% of the weight of the coating.

[0009] Furthermore, the weld metal deposited on the aforementioned 43 kg grade weathering steel welding electrode contains the following chemical composition by mass percentage: C: 0.02–0.06%, Mn: 0.4–0.7%, Si: 0.15–0.40%, S≤0.015%, P≤0.015%, Ni: 0.4–0.65%, Cr: 0.25–0.5%, Cu: 0.2–0.4%.

[0010] Specifically, the coating comprises the following components by mass percentage: 30% marble, 20% fluorite, 7% sodium fluoride, 1% zircon sand, 3% rutile, 2% quartz, 2% 45# atomized ferrosilicon, 1.5% manganese, 2.5% nickel-magnesium alloy, 1.5% chromium, 1.2% copper powder, 1% silicon-zirconium-iron, 0.7% boron trioxide, 1% soda ash, and the balance being iron powder.

[0011] Specifically, the coating comprises the following components by mass percentage: 35% marble, 30% fluorite, 3% sodium fluoride, 3% zircon sand, 3% rutile, 4% quartz, 3% 45# atomized ferrosilicon, 2.5% metallic manganese, 2.2% nickel-magnesium alloy, 0.7% metallic chromium, 0.6% copper powder, 1.5% silicon-zirconium-iron, 0.3% boron trioxide, 0.5% soda ash, 0.5% CMC, with the balance being iron powder.

[0012] Specifically, the coating comprises the following components by mass percentage: 40% marble, 30% fluorite, 3% sodium fluoride, 1% zircon sand, 7% rutile, 3% quartz, 45# atomized ferrosilicon, 3% manganese, 1.4% nickel-magnesium alloy, 0.9% chromium, 1% copper powder, 0.3% boron trioxide, 1% CMC, with the balance being iron powder.

[0013] Furthermore, the diameter of the welding core is 4mm, and the outer diameter of the welding core after being coated with flux is 6.5 to 6.6mm.

[0014] The welding electrode for 43 kg grade weathering steel provided by this invention has a welding current of 160-170 A and a welding voltage of 23-25 ​​V.

[0015] The design principle of the coating formulation for the 43 kg-class weathering steel welding electrode of this invention is as follows:

[0016] Marble, as a slag-forming and gas-generating agent, increases the gas blowing force and depth of penetration by decomposing into CO2. However, the CaO formed during decomposition is a highly alkaline substance with a high melting point. Too much CaO will affect the fluidity and surface tension of the slag, which is not only detrimental to weld formation but also increases the size of the molten droplets, leading to horseshoe-shaped welds during vertical welding and deteriorating the welding process. In particular, the electrode coating thickness provided by this invention is greater than that of ordinary products, requiring further control of the high-melting-point CaO content, while ensuring good compatibility with the dilute slag substances in the coating formulation. On the other hand, too little marble content results in excessively low alkalinity and insufficient slag-forming dosage, which will have a certain impact on the mechanical and technological properties of the weld. Therefore, controlling the marble content to 30-40% in this invention can achieve better mechanical and technological properties.

[0017] Fluorite: As a slag thinner, it can significantly reduce the melting point of the coating and improve the fluidity of the slag. However, excessive amounts can lead to arc instability and slag separation from both sides of the weld, affecting weld formation. It needs to be properly matched with the fluorite in the coating. The electrode provided by this invention controls its content to 20-30% from the perspectives of arc stability and slag fluidity.

[0018] Sodium fluoride: fluoride dehydrogenates, dilutes slag, and can replace part of the fluorite in the coating. The difference between sodium fluoride and fluorite is that adding an appropriate amount helps stabilize the arc, but it should not exceed 7%, otherwise the characteristic of F destroying ionization and affecting arc stability will disappear.

[0019] Zircon sand: An appropriate amount of zircon sand can improve the slag removal effect of the weld, making the weld surface clean and the edges neat. Generally, 1-3% is added.

[0020] Quartz: Reduces the surface tension of molten iron in the molten pool, refines molten droplets, reduces spatter, improves slag coverage, and reacts with alkaline substances in the coating to form compounds with relatively low melting points, thus lowering the melting point of the slag and improving fluidity. However, if the amount added is small, these effects are not significant. Quartz is an acidic substance and forms a long slag; if the amount added is too large, the slag solidification temperature range is wide, which is not conducive to all-position welding, and the slag becomes glassy, ​​which is not conducive to slag removal. Therefore, the welding electrode provided by this invention controls the amount of quartz added to be between 2% and 4%.

[0021] Rutile: Adding an appropriate amount of rutile to an alkaline slag system can improve arc stability, refine molten droplets, and lower the melting point of the coating. As a short slag material, the addition of rutile can improve the performance of vertical welding. However, because it reduces the basicity of the slag and avoids excessive Ti alloy in the weld, thus increasing weld strength beyond the standards required by this invention, it should not be added in excess, otherwise it will affect the mechanical properties of the weld. Based on comprehensive research, the rutile content in the electrode formulation provided by this invention is controlled at 3-7%.

[0022] Preferably, the sum of the amounts of rutile, quartz, and zircon sand is controlled at 6-11%, which can achieve better slag performance in terms of slag fluidity, melting point, and slag removal.

[0023] 45# atomized ferrosilicon: Si in 45# atomized ferrosilicon is an important deoxidizer, which can reduce the oxygen content of weld metal, improve low-temperature impact toughness, and regulate the fluidity of molten iron. In weathering steel, Si helps to refine oxides in the rust layer, thereby reducing the overall corrosion rate of weathering steel. If the amount added is too low, it will lead to insufficient deoxidation, and the low-temperature impact toughness and weld weathering index will not meet the requirements. If the amount added is too high, it will cause the weld strength to exceed the standard. Therefore, in this invention, the content of 45# atomized ferrosilicon is controlled at 2-4%.

[0024] Metallic manganese: As a deoxidizer, it reduces the oxygen content of the weld metal, increasing its strength and crack resistance. The weld tensile strength of this invention has certain requirements, and its content should be strictly controlled to ensure the achievement of the required strength. However, the beneficial effect of Mn on impact toughness weakens as the Mn content decreases, and the impact toughness may even fail to meet the standard requirements. Therefore, the Mn content should be controlled within a suitable range to balance strength and low-temperature impact toughness. In this invention, when the Mn content is below 1.5%, insufficient deoxidation will result in insufficient weld metal strength and low-temperature impact toughness. When the Mn content exceeds 3%, the weld strength will be excessively high.

[0025] Nickel-magnesium alloys: Mg in nickel-magnesium alloys acts as a strong deoxidizer, and the deoxidation products are alkaline substances that can improve impact toughness. If the amount added is too small, the ability to improve low-temperature impact toughness and deoxidation is insufficient, and other substances need to be used for deoxidation and toughening. If the amount added is too large, the deoxidation products contain magnesium oxides, which raises the melting point of the slag and accelerates the solidification rate, which is not conducive to the removal of weld gas and will also cause poor vertical weld formation. Therefore, its content should be controlled. Mg is easily oxidized in air, is not easy to store, and poses an explosion hazard. The formation of nickel-magnesium alloys with Ni can solve the problem of magnesium's easy oxidation.

[0026] The strength requirement of the welding material of this invention is within a certain range. The C and Mn content in the weld should be controlled to ensure that the strength does not exceed the standard. However, low levels of the aforementioned nickel and magnesium alloy elements can lead to the precipitation of coarse proeutectoid ferrite, which has an adverse effect on impact toughness. Therefore, the addition of Ni can improve the impact toughness of the weld and also has a certain effect on improving the strength. However, when the Ni content is low, it is detrimental to the impact toughness of the weld and the weather resistance index I is low. When the Ni content is high, the influence of Mg content on the welding process should be considered. Therefore, in this invention, the nickel and magnesium alloy content is controlled between 1.4% and 2.5%.

[0027] Metallic chromium (Cr): Metallic chromium (Cr) is a common alloying element in weathering steel. Cr can form a dense oxide film on the steel surface, increasing the electrode potential, producing a passivation effect, and improving the steel's corrosion resistance. This effect is particularly pronounced when added to steel simultaneously with copper (Cu). When the amount of metallic chromium added is less than 0.7%, the above effects are not obvious, and the weathering index (I) is low. When the amount of metallic chromium added exceeds 1.5%, it will increase the weld strength beyond the required range.

[0028] Copper powder (Cu) can improve the corrosion resistance of weathering steel. During the corrosion process, Cu enrichment occurs on the surface of weathering steel, forming a tight CuO interlayer between the corrosion layer and the Cu-rich layer. This interlayer can slow down or prevent the corrosive medium from continuing to penetrate inward. Adding an appropriate amount of Cu to the weld can improve the weathering index of the weld. The Cu content has a significant impact on the weathering index of the weld, and the relationship is not linear; there is a range. Too high or too low a Cu content will cause the weathering index to fail to meet the standard. Therefore, in this invention, the Cu content is controlled between 0.6% and 1.2%.

[0029] Zirconium-zirconium iron: Zirconium (Zr) in ferrosilicon can reduce the oxygen content in the weld as a strong deoxidizing element. At the same time, a small amount of Zr in the weld can improve the weld strength. However, its content should be strictly controlled to avoid the weld strength from exceeding the required range. In this invention, the content of ferrosilicon is controlled at 0 to 1.5%.

[0030] Boron trioxide: A small amount of boron transitions into the weld, which is beneficial to improving the impact toughness of the weld, but its content should be controlled, otherwise it will have the opposite effect.

[0031] Soda ash and CMC (carboxymethyl cellulose): These are beneficial for electrode coating and ensure the appearance quality of the electrode. The sum of the two should be controlled within 1%.

[0032] In addition, this invention controls the content of chemical composition of the deposited metal formed by the welding rod. Specifically, it uses C and Mn to improve the weld strength, but if the C and Mn content is too high, the weld strength will exceed the required range, and if the C and Mn content is too low, the low-temperature impact toughness will be unstable. It also uses Si to improve the weld strength and weather resistance index. If the Si content is too high, the weld strength will exceed the required range, and if the Si content is too low, the weather resistance index will be too low. Furthermore, Ni, Cr, and Cu elements, especially Cu, have a significant impact on the weld weather resistance index. Controlling them within a suitable range ensures both strength and weather resistance index.

[0033] The beneficial effects of this invention are:

[0034] (1) The 43 kg grade weathering steel welding electrode provided by the present invention transfers appropriate amounts of Ni, Cr, Cu and Si elements to the weld metal through the coating, so that the weld metal has excellent weather resistance and its weather resistance index I can be greater than 6.5.

[0035] (2) The 43 kg grade weathering steel welding electrode provided by the present invention controls the content of C, Mn, Si and other alloying elements in the weld metal by adjusting the composition of the coating, ensuring that the tensile strength of the weld metal is 430-550 MPa and the low-temperature impact absorption energy at -20℃ is greater than 47 J, and has stable mechanical properties.

[0036] (3) The 43 kg grade weathering steel welding rod provided by the present invention can be used for all-position welding, with excellent welding process performance, stable arc, and beautiful weld formation. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The 43 kg-grade weathering steel welding electrode in this embodiment consists of a core and a coating covering the surface of the core. The composition of the coating in the corresponding embodiment is shown in Table 1. The iron powder used has a loose bulk density of 270 g / cm³. 3 The electrode contains 270 iron powder; the core diameter is 4mm. When making the electrode, the uniformly mixed coating is evenly pressed onto the core surface according to the manufacturing method of ordinary basic low-hydrogen electrode. The outer diameter of the core after the coating is wrapped is 6.5-6.6mm.

[0039] Table 1: Composition of the drug coating in each example (mass percentage, %)

[0040]

[0041]

[0042] Test plate welding was performed on the three types of welding electrodes prepared using the coatings from the three embodiments described above. The welding current in these embodiments was 160–170 A, and the welding voltage was 23–25 V. The chemical composition, weathering index I, and mechanical properties of the weld metal deposited in each embodiment are shown in Tables 2 and 3. The weathering index I was calculated using the following formula, where the chemical composition is the content of the chemical composition of the weld metal:

[0043] I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.48(%Si)+17.28(%P)-7.29(%Cu)×(%Ni)-9.10(%Ni)×(%P)-33.39(%Cu) 2 .

[0044] Table 2: Chemical composition (mass percentage %) and weather resistance index of deposited metal

[0045]

[0046] Table 3: Mechanical Properties of Deposited Metal

[0047]

[0048]

[0049] In summary, the 43 kg-grade weathering steel welding electrode provided by this invention transfers appropriate amounts of Ni, Cr, Cu, and Si elements to the weld metal through the flux coating, giving the weld metal excellent weather resistance, with a weather resistance index I greater than 6.5. Simultaneously, by adjusting the flux coating composition, the content of C, Mn, Si, and other alloying elements in the weld metal is controlled, ensuring a tensile strength of 430–550 MPa and a low-temperature impact absorption energy of greater than 47 J at -20°C, exhibiting stable mechanical properties.

[0050] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A welding electrode for 43 kg grade weathering steel, comprising a core and a coating on the surface of the core, characterized in that, The coating comprises the following components by weight percentage: marble 30-40%, fluorite 20-30%, sodium fluoride 3-7%, zircon sand 1-3%, rutile 3-7%, quartz 2-4%, 45# atomized ferrosilicon 2-4%, metallic manganese 1.5-3%, nickel-magnesium alloy 1.4-2.5%, metallic chromium 0.7-1.5%, copper powder 0.6-1.2%, silicon-zirconium-iron ferrophosphate 0-1.5%, boron trioxide 0.3-0.7%, and soda ash 0-1%. The coating contains 0-1% CMC, with the balance being iron powder. The sum of the amounts of soda ash and CMC added to the coating accounts for 1% of the coating mass. The electrode deposited metal contains the following chemical composition by mass percentage: C: 0.02-0.06%, Mn: 0.4-0.7%, Si: 0.15-0.40%, S≤0.015%, P≤0.015%, Ni: 0.4-0.65%, Cr: 0.25-0.5%, Cu: 0.2-0.4%.

2. The 43 kg class weathering steel welding electrode as described in claim 1, characterized in that, The total amount of rutile, quartz, and zircon sand added to the coating is 6-11% of the weight of the coating.

3. The 43 kg class weathering steel welding electrode as described in claim 1, characterized in that, The coating comprises the following components by mass percentage: 30% marble, 20% fluorite, 7% sodium fluoride, 1% zircon sand, 3% rutile, 2% quartz, 2% 45# atomized ferrosilicon, 1.5% manganese, 2.5% nickel-magnesium alloy, 1.5% chromium, 1.2% copper powder, 1% silicon-zirconium-iron, 0.7% boron trioxide, 1% soda ash, and the balance being iron powder.

4. The 43 kg class weathering steel welding electrode as described in claim 1, characterized in that, The coating comprises the following components by mass percentage: 35% marble, 30% fluorite, 3% sodium fluoride, 3% zircon sand, 3% rutile, 4% quartz, 3% 45# atomized ferrosilicon, 2.5% metallic manganese, 2.2% nickel-magnesium alloy, 0.7% metallic chromium, 0.6% copper powder, 1.5% silicon-zirconium-iron, 0.3% boron trioxide, 0.5% soda ash, 0.5% CMC, with the balance being iron powder.

5. The 43 kg class weathering steel welding electrode as described in claim 1, characterized in that, The coating comprises the following components by mass percentage: 40% marble, 30% fluorite, 3% sodium fluoride, 1% zircon sand, 7% rutile, 3% quartz, 45# atomized ferrosilicon, 3% manganese, 1.4% nickel-magnesium alloy, 0.9% chromium, 1% copper powder, 0.3% boron trioxide, 1% CMC, with the balance being iron powder.

6. The 43 kg class weathering steel welding electrode as described in claim 1, characterized in that, The core diameter is 4mm, and the outer diameter of the core after being coated with flux is 6.5-6.6mm.

7. The application of the 43 kg class weathering steel welding electrode as described in any one of claims 1 to 6, characterized in that, When welding this 43 kg grade weathering steel welding electrode, the welding current is 160-170 A and the welding voltage is 23-25 ​​V.

Images