A Low-Carbon Austenitic Stainless Steel Welding Wire, Its Application and Welding Method

Abstract

This invention discloses a low-carbon austenitic stainless steel welding wire, its application, and welding method, belonging to the field of welding materials technology. The chemical composition of the welding wire (wt.%) is: C: 0.005-0.029%, Cr: 17.0-21.0%, Ni: 12.5-14.5%, Mo: 2.2-3.0%, Si: 0.2-0.7%, Mn: 1.00-2.20%, N: 0.09-0.25%, Cu≤0.10%, Co≤0.06%, P≤0.02%, S≤0.02%, with the balance being iron and unavoidable impurities. The welding wire of this invention is suitable for welding austenitic stainless steel components used in high-temperature environments such as nuclear power, thermal power, and petrochemical plants. The welding process is stable, with minimal spatter and good process performance. Welding with the low-carbon austenitic stainless steel welding wire of this invention in high-temperature environments can yield welds with excellent crack resistance and high-temperature microstructural stability, meeting the requirements of high-temperature, long-term service environments.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, specifically to a low-carbon austenitic stainless steel welding wire for high-temperature environments (usable in the temperature range of room temperature to 600°C, preferably in the range of 450-600°C) and its application. This welding wire is used for welding components that are used for a long time in high-temperature environments such as nuclear power, thermal power, and petrochemical industries. Background Technology

[0002] Austenitic stainless steel is widely used in the manufacture of high-temperature service components in the energy and petrochemical industries due to its excellent high-temperature mechanical properties, corrosion resistance, and weldability. Welding is a major hot working process in component manufacturing, indispensable from component manufacturing at the main equipment manufacturer to on-site assembly. Some critical components have large structural dimensions and compact, complex designs, resulting in complex welding processes and a large amount of welding work. During the service life of these components, the structural materials are subjected to extremely harsh conditions under high-temperature and high-corrosion environments. Furthermore, some critical components cannot be replaced during their service life. Welded joints typically consist of two parts: the base metal and the weld metal. The performance of the joint depends not only on the properties and weldability of the base metal but also, crucially, on the properties of the weld metal, which in turn depends on the welding materials. From the service experience of large welded structures in China's energy and petrochemical sectors, welded joints are weak links prone to early aging. Based on these factors, engineering design places high demands on the performance of welding materials used in critical high-temperature service components to ensure the safety and reliability of component service. Therefore, research on the microstructure and long-term stability of weld metals is a key aspect of developing welding materials for high-temperature environments.

[0003] The performance of existing austenitic stainless steel welding consumables, especially their high-temperature creep resistance, still lags behind that of the base metal. Under prolonged high-temperature conditions, they are prone to failure at the weld seam, affecting the overall lifespan of the welded components. Furthermore, the maximum service temperature for existing low-carbon austenitic stainless steel welding consumables is 425℃, rendering them unusable at temperatures above this level. Improving the high-temperature performance of austenitic stainless steel welds remains a challenge. While carbon (C) and nitrogen (N) act as interstitial atoms in austenitic stainless steel, their solid solution in the matrix causes lattice distortion, potentially increasing the steel's strength. However, C and N are strong austenitizing elements; excessively high content can lead to pure austenitic welds, which are prone to hot cracking under high restraint conditions. Additionally, when the C content in austenitic stainless steel welds is high, carbides (MnO2) can form during long-term high-temperature service. 23The precipitation of C6 (carbon dioxide) can lead to the growth of carbides at high temperatures, reducing the material's high-temperature performance and resistance to intergranular corrosion. In contrast, nitrogen (N) has a higher solid solubility in the austenitic matrix than carbon (C), resulting in better solid solution strengthening. Furthermore, N inhibits carbide precipitation, eliminating the adverse effects of carbides and improving the material's high-temperature performance. However, studies have found that excessively high N content can cause welding defects such as porosity and slag inclusions in the weld metal, negatively impacting the long-term high-temperature performance of the weld joint. There is currently no unified standard for the content of elements like N and C that significantly affect weld microstructure. Research worldwide on improving the high-temperature microstructure stability of austenitic stainless steel welding materials is relatively limited. Research should focus on designing austenitic stainless steel welding materials with excellent high-temperature performance suitable for long-term high-temperature service environments and applicable to various fields such as energy (thermal power, nuclear power, etc.) and petrochemicals. Summary of the Invention

[0004] To address the issue that existing austenitic stainless steel welding wires have relatively low high-temperature performance compared to their base materials, the present invention aims to provide a low-carbon austenitic stainless steel welding wire for high-temperature environments. This welding wire is suitable for welding key high-temperature structural components in fields such as energy (thermal power, nuclear power, etc.) and petrochemicals.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A low-carbon austenitic stainless steel welding wire for high-temperature environments has the following chemical composition by weight percentage:

[0007] C: 0.005-0.029%, Cr: 17.0-21.0%, Ni: 12.5-14.5%, Mo: 2.2-3.0%, Si: 0.2-0.7%, Mn: 1.00-2.20%, N: 0.09-0.25%, Cu≤0.10%, Co≤0.06%, P≤0.02%, S≤0.02%, balance being iron and unavoidable impurities.

[0008] Furthermore, the preferred carbon content in the welding wire is 0.005-0.02% or 0.02-0.029%.

[0009] Furthermore, the Cr content in the welding wire is preferably 17.0-17.9%, or 17.9-20.1%, or 20.1-21.0%.

[0010] Furthermore, the Ni content in the welding wire is preferably 12.5-13.6%, or 13.6-14.5%.

[0011] Furthermore, the Mo content in the welding wire is preferably 2.20-2.61%, or 2.61-2.80%, or 2.80-3.00%.

[0012] Furthermore, the Si content in the welding wire is preferably 0.2-0.29%, or 0.29-0.50%, or 0.50-0.70%.

[0013] Furthermore, the Mn content in the welding wire is preferably 1.00-1.39%, or 1.39-1.80%, or 1.80-2.20%.

[0014] Furthermore, the preferred N content in the welding wire is 0.09-0.15%, or 0.15-0.20%, or 0.20-0.25%.

[0015] Furthermore, the Cu content in the welding wire is preferably Cu≤0.05%, or Cu≤0.02%, or Cu≤0.01%.

[0016] Furthermore, the Co content in the welding wire is preferably Co ≤ 0.03%, or Co ≤ 0.02%, or Co ≤ 0.01%.

[0017] Furthermore, the phosphorus (P) content in the welding wire is preferably P ≤ 0.01% or P ≤ 0.005%.

[0018] Furthermore, the sulfur content in the welding wire is preferably S≤0.01% or S≤0.005%.

[0019] The reasons for identifying the above chemical components are as follows:

[0020] In the fusion welding process of austenitic stainless steel, excessive structural restraint can easily lead to hot cracking. To prevent cracking during welding, it is generally desirable for a certain amount of δ-ferrite to form in the weld microstructure. Furthermore, the formation and coarsening of carbides and intermetallic compounds within the weld during long-term high-temperature service are significant factors deteriorating the high-temperature performance of the weld. Reducing the carbon (C) content can significantly reduce carbide formation and coarsening, but reducing C content increases the amount of δ-ferrite formation, which in turn promotes the formation of intermetallic compounds. Nitrogen (N), an austenite-forming element, can inhibit δ-ferrite formation. In austenitic stainless steel welds, increasing the N content while reducing the C content can reduce carbide formation during long-term high-temperature service, simultaneously inhibiting the increase in δ-ferrite caused by C reduction, and thus suppressing the formation of intermetallic compounds during long-term high-temperature service, which is beneficial for improving the high-temperature microstructure stability of the weld. Simultaneously, the increased susceptibility to welding hot cracking caused by a decrease in δ-ferrite content in austenitic stainless steel welds can be controlled by adjusting the content of sulfur (S) and phosphorus (P) impurities within the weld. Therefore, the contents of C, N, S, and P should be rationally configured. In this application, C: 0.005-0.029%, preferably 0.005-0.02%, or 0.02-0.029%; C≤0.01%; N: 0.09-0.25%, preferably 0.09-0.15%, or 0.15-0.20%, or 0.20-0.25%; P≤0.02%, preferably P≤0.01%, or P≤0.005%; S≤0.02%, preferably S≤0.01%, or S≤0.005%.

[0021] Cr is one of the essential elements for the resistance of austenitic stainless steel to high-temperature oxidation and corrosion. Cr can improve the oxidation resistance and corrosion resistance of materials. Cr dissolved in the matrix plays a role in solid solution strengthening and improves the hot strength of steel. However, excessive Cr content in steel will promote the formation of high-temperature δ-ferrite and lead to coarsening of the corresponding carbide precipitates, thus having adverse effects. In this application, Cr is 17.0-21.0%, preferably 17.0-17.9%, or 17.9-20.1%, or 20.1-21.0%.

[0022] Ni is an austenitizing element. Increasing the Ni content in austenitic stainless steel can inhibit the formation of high-temperature δ-ferrite. Ni added to steel not only makes it resistant to acids but also to alkalis, and it has corrosion resistance to the atmosphere and salt. Nickel is one of the important elements in stainless acid-resistant steel. At the same time, Ni can also improve the weldability and high-temperature resistance of stainless steel. In addition, under the influence of irradiation, Ni is also an important source of helium formation. In this application, Ni is 12.5-14.5%, preferably 12.5-13.6%, or 13.6-14.5%.

[0023] Mo can improve the corrosion resistance of stainless steel, especially its resistance to acidic environments and chloride ions. Mo can also improve the tensile strength and thermal stability of stainless steel. However, excessive Mo content will promote the formation of δ-ferrite. Therefore, its upper and lower limits should be limited. In this application, Mo is 2.2-3.0%, preferably 2.20-2.61%, or 2.61-2.80%, or 2.80-3.00%.

[0024] Si is an essential alloying element in stainless steel. Si can effectively improve the corrosion resistance of steel by increasing the electrode potential of the base metal and reducing the number of microcells. Si can also effectively improve the passivation ability of iron and form a dense oxide film on the surface of steel, thus improving the corrosion resistance of steel. Si can also improve the resistance of austenitic steel to carburization at high temperatures. However, excessive Si content drastically increases the tendency to form hot cracks during welding and hot embrittlement. Therefore, the Si content should be reasonably selected within a certain range. In this application, Si is 0.2-0.7%, preferably 0.2-0.29%, or 0.29-0.50%, or 0.50-0.70%.

[0025] Mn is an austenitizing element. Increasing the Mn content in austenitic stainless steel can inhibit the formation of δ-ferrite. Furthermore, Mn is a good deoxidizer and desulfurizer, exhibiting strong substitutional solid solution strengthening in steel. However, Mn also significantly impairs the plasticity of steel; the higher the substitutional solid solution content, the lower the plastic strain. Appropriate Mn addition can ensure high strength while maintaining high low-temperature impact toughness and strong crack resistance. Therefore, the Mn content should be strictly controlled. In this application, Mn is 1.00-2.20%, preferably 1.00-1.39%, or 1.39-1.80%, or 1.80-2.20%.

[0026] Sulfur (S) and phosphorus (P) are harmful impurities in steel, mostly introduced during steelmaking from raw materials, and should be minimized. During welding, inadequate beveling can also increase S content. Excessive P content increases the tendency for cold cracking, while excessive S content increases the tendency for hot cracking. Therefore, the S and P content in the welding wire's chemical composition should be strictly controlled. In this application, S ≤ 0.02%, preferably S ≤ 0.01%, or S ≤ 0.005%; P ≤ 0.02%, preferably P ≤ 0.01%, or P ≤ 0.005%.

[0027] Co has a large neutron absorption cross section, which can easily cause Co-containing materials to fail under neutron irradiation. Moreover, the half-life of the radioactive isotope 60Co is as long as 5.26 years. Its impact will increase with the increase of reactor operating time. It not only introduces radioactivity into the equipment and components inside the reactor, but also makes the pipelines, pumps, valves and other equipment in the primary loop system radioactive. This will bring many difficulties to the maintenance of nuclear reactor equipment and components and waste disposal, and may even endanger personal safety. Therefore, the Co content should be strictly limited. In this application, Co ≤ 0.06%, preferably Co ≤ 0.03%, or Co ≤ 0.02%, or Co ≤ 0.01%.

[0028] Under irradiation, Cu forms a Cu-rich precipitate phase, which is a major mechanism causing embrittlement of nuclear power steel. Therefore, the Cu content should be strictly limited. In this application, Cu ≤ 0.10%, preferably Cu ≤ 0.05%, or Cu ≤ 0.02%, or Cu ≤ 0.01%.

[0029] The low-carbon austenitic stainless steel welding wire for high-temperature environments of this invention can be produced by vacuum induction furnace smelting or by electric furnace smelting and ladle refining, as long as the final chemical composition of the welding wire meets the above requirements.

[0030] The welding wire of this invention is applied to the welding of key high-temperature structural components in the fields of energy (thermal power, nuclear power, etc.) and petrochemicals. The welding process is as follows: take a Φ1.2mm welding wire, use TIG welding, and the joint type is butt joint. The welding parameters are: welding current 150-250A, arc voltage 10-15V, DC positive polarity, welding speed 0.05-0.20m / min, arc protection using high-purity argon gas with a purity ≥99.995%, argon gas flow rate 12-30L / min; weld the test piece using a multi-layer, multi-pass deposition method, and the interpass temperature during the welding process is ≤150℃.

[0031] The room temperature tensile property requirement for the weld metal of this invention is: yield strength Rp 0.2 ≥220MPa, tensile strength R m ≥525MPa, elongation A≥30%; room temperature impact energy KV2≥90J in the weld state; room temperature impact energy KV2≥25J in the accelerated aging state at 750℃×100h; high temperature tensile properties of weld metal: 550℃: Rp 0.2 ≥107MPa, R m ≥374MPa; Weld metal microstructure requirements: The δ ferrite number (FN value) in the weld metal in the as-welded state is between 0.5 and 3.9.

[0032] The welding wire of this invention is suitable for welding austenitic stainless steel components used in high-temperature environments such as nuclear power, thermal power, and petrochemical industries. The welding process is stable, with minimal spatter and good process performance. Welding with the low-carbon austenitic stainless steel welding wire of this invention in high-temperature environments can produce welds with excellent crack resistance and high-temperature microstructural stability, meeting the requirements of long-term high-temperature service environments.

[0033] The present invention has the following advantages:

[0034] 1. The low-carbon austenitic stainless steel welding wire for high-temperature environments of this invention possesses excellent high-temperature mechanical properties, high strength and toughness, high high-temperature microstructural stability, and excellent resistance to radiation swelling. It can be used for welding key high-temperature structural components in energy (thermal power, nuclear power, etc.), petrochemical, and other fields. The welding wire of this invention contains 0.05-0.029% C, which inhibits the formation and coarsening tendency of carbides during long-term high-temperature service. The addition of 0.09-0.25% N compensates for the strength reduction caused by the lower C content and reduces the δ-ferrite content. While ensuring that the austenitic stainless steel weld has low welding hot cracking sensitivity, it improves the high-temperature microstructural stability of the weld, which is crucial for the safety of austenitic stainless steel welds during long-term high-temperature service.

[0035] 2. In the composition and proportion of the welding wire, this invention fully considers the special characteristics of weld metal under nuclear conditions, which must not only withstand the deterioration effect of high radiation on materials, but also take into account the weld life under high temperature and stress conditions. Considering the nuclear application field, the welding wire of this invention does not add Co and Cu, and reduces the generation of long-lived radioactive isotope 60Co by limiting the content of impurity Co to less than 0.06%, and inhibits the irradiation embrittlement of weld metal by limiting the content of impurity Cu to less than 0.10%.

[0036] 3. This invention provides a solid low-carbon austenitic stainless steel welding wire for high-temperature environments. When welding under inert gas protection, it effectively prevents weld oxidation, reduces inclusions in the weld, and improves weld quality. It effectively avoids slag contamination and quality degradation of the weld during the welding of austenitic stainless steel welding electrodes and flux-cored wires. Experiments show that when using the austenitic stainless steel welding wire of this invention in conjunction with the welding process defined in this invention, spatter is minimal, the process is stable, and the process performance is good. Furthermore, it can obtain weld metal with the required properties, especially good high-temperature performance and microstructural stability.

[0037] 4. Experiments show that the weld metal of the low-carbon austenitic stainless steel welding wire for high-temperature environments of the present invention meets the following performance requirements: Weld metal room temperature performance requirements: Yield strength Rp 0.2 ≥220MPa, tensile strength R m≥525MPa, elongation ≥30%; room temperature impact energy KV2 ≥90J for weld metal in as-welded state; room temperature impact energy KV2 ≥25J for weld metal in accelerated aging state at 750℃×100h; high temperature tensile properties of weld metal: 550℃: Rp 0.2 ≥107MPa, R m ≥374MPa; Weld metal microstructure requirements: The δ ferrite number (FN value) in the weld metal in the as-welded state is between 0.5 and 3.9. Attached Figure Description

[0038] Figure 1 This is the welding joint form of the present invention. Detailed Implementation

[0039] The low-carbon austenitic stainless steel welding wire for high-temperature environments of this invention can be produced by vacuum induction furnace smelting or by electric furnace smelting and ladle refining, as long as the final chemical composition of the welding wire meets the specified welding wire composition; in addition, the entire smelting and processing process of the welding wire is no different from that of ordinary austenitic stainless steel welding wire.

[0040] The following examples and comparative examples all use vacuum induction furnace smelting for production;

[0041] Taking Φ1.2mm welding wire as an example, a multi-layer, multi-pass TIG (automatic tungsten inert gas welding) method was used to prepare the weld metal of the Φ1.2mm welding wire. The base material was 316L austenitic stainless steel, and the joint type was a 20mm thick plate butt weld. The welding parameters were: welding current 150-250A (specifically 180A in this case), arc voltage 10-15V (specifically 11-13V in this case), DC positive polarity, welding speed 0.05-0.20m / min (specifically 0.1m / min in this case), arc protection using high-purity argon gas with a purity ≥99.999%, and argon gas flow rate 12-30L / min (specifically 20L / min in this case); the interpass temperature during the welding process was ≤150℃. Samples were then taken from the weld metal for mechanical property analysis. Of course, the welding process of this application can be adjusted for different welding wire diameters. Example 1:

[0042] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0043] C: 0.022%, Cr: 18.98%, Ni: 13.20%, Mo: 2.64%, Si: 0.45%, Mn: 1.60%, N: 0.21%, P: 0.004%, S: 0.0015%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0044] Example 2:

[0045] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0046] C: 0.005%, Cr: 18.78%, Ni: 13.22%, Mo: 2.61%, Si: 0.43%, Mn: 1.62%, N: 0.19%, P: 0.004%, S: 0.002%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0047] Example 3:

[0048] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0049] C: 0.029%, Cr: 18.90%, Ni: 13.12%, Mo: 2.65%, Si: 0.46%, Mn: 1.58%, N: 0.15%, P: 0.004%, S: 0.0022%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0050] Example 4:

[0051] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0052] C: 0.021%, Cr: 17.0%, Ni: 13.35%, Mo: 2.55%, Si: 0.40%, Mn: 1.68%, N: 0.20%, P: 0.004%, S: 0.0021%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0053] Example 5:

[0054] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0055] C: 0.021%, Cr: 21.0%, Ni: 13.05%, Mo: 2.69%, Si: 0.51%, Mn: 1.49%, N: 0.16%, P: 0.0035%, S: 0.002%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0056] Example 6:

[0057] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0058] C: 0.020%, Cr: 19.05%, Ni: 12.50%, Mo: 2.72%, Si: 0.53%, Mn: 1.72%, N: 0.18%, P: 0.004%, S: 0.0023%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0059] Example 7:

[0060] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0061] C: 0.019%, Cr: 18.87%, Ni: 14.50%, Mo: 2.46%, Si: 0.40%, Mn: 1.54%, N: 0.18%, P: 0.0042%, S: 0.0021%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0062] Example 8:

[0063] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0064] C: 0.022%, Cr: 18.93%, Ni: 13.04%, Mo: 2.20%, Si: 0.43%, Mn: 1.59%, N: 0.19%, P: 0.0038%, S: 0.0024%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0065] Example 9:

[0066] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0067] C: 0.025%, Cr: 18.91%, Ni: 13.32%, Mo: 3.0%, Si: 0.45%, Mn: 1.64%, N: 0.21%, P: 0.004%, S: 0.0022%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0068] Example 10:

[0069] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0070] C: 0.022%, Cr: 18.69%, Ni: 13.17%, Mo: 2.57%, Si: 0.20%, Mn: 1.58%, N: 0.20%, P: 0.0041%, S: 0.0023%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0071] Example 11:

[0072] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0073] C: 0.021%, Cr: 18.73%, Ni: 13.31%, Mo: 2.59%, Si: 0.70%, Mn: 1.64%, N: 0.21%, P: 0.0043%, S: 0.0021%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0074] Example 12:

[0075] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0076] C: 0.021%, Cr: 18.91%, Ni: 12.98%, Mo: 2.56%, Si: 0.47%, Mn: 1.00%, N: 0.20%, P: 0.0039%, S: 0.0020%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0077] Example 13:

[0078] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0079] C: 0.020%, Cr: 18.77%, Ni: 13.18%, Mo: 2.57%, Si: 0.46%, Mn: 2.20%, N: 0.22%, P: 0.0044%, S: 0.0026%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0080] Example 14:

[0081] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0082] C: 0.024%, Cr: 18.92%, Ni: 13.50%, Mo: 2.67%, Si: 0.48%, Mn: 1.61%, N: 0.09%, P: 0.0042%, S: 0.0020%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0083] Example 15:

[0084] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0085] C: 0.021%, Cr: 18.89%, Ni: 13.45%, Mo: 2.58%, Si: 0.47%, Mn: 1.59%, N: 0.25%, P: 0.0043%, S: 0.0022%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0086] Comparative Example 1:

[0087] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0088] C: 0.039%, Cr: 18.99%, Ni: 13.46%, Mo: 2.62%, Si: 0.45%, Mn: 1.53%, N: 0.20%, P: 0.0040%, S: 0.0021%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0089] Comparative Example 2:

[0090] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0091] C: 0.021%, Cr: 18.88%, Ni: 13.21%, Mo: 2.59%, Si: 0.44%, Mn: 1.60%, N: 0.04%, P: 0.0041%, S: 0.0020%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0092] Comparative Example 3:

[0093] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0094] C: 0.023%, Cr: 18.77%, Ni: 13.18%, Mo: 2.65%, Si: 0.41%, Mn: 1.61%, N: 0.31%, P: 0.0040%, S: 0.0022%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0095] Comparative Example 4:

[0096] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0097] C: 0.020%, Cr: 22.11%, Ni: 13.06%, Mo: 2.68%, Si: 0.44%, Mn: 1.58%, N: 0.20%, P: 0.0041%, S: 0.0021%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0098] Comparative Example 5:

[0099] The chemical composition (by weight) of the low-carbon austenitic stainless steel welding wire used in this high-temperature environment is as follows:

[0100] C: 0.024%, Cr: 18.72%, Ni: 14.92%, Mo: 2.64%, Si: 0.45%, Mn: 1.61%, N: 0.22%, P: 0.0042%, S: 0.0020%, Co < 0.01%, Cu < 0.01%, with the remainder being iron and unavoidable impurities.

[0101] Table 1. Results of as-welded room temperature tensile and impact properties of the examples and comparative examples.

[0102]

[0103]

[0104] Table 2. Tensile property test results at 550℃ for the Examples and Comparative Examples

[0105]

[0106]

[0107] Table 3. Room temperature impact properties of weld metals aged at 750℃ for 100h in Examples and Comparative Examples

[0108]

[0109] Table 4. Weld FN values ​​for the Examples and Comparative Examples

[0110]

[0111]

[0112] The welding test conditions for the above embodiments and comparative examples are shown in Table 5, and the types of welded joints used are as follows: Figure 1 As shown.

[0113] Table 5 Welding test conditions

[0114]

[0115] The performance design requirements of this invention for the weld metal of low-carbon austenitic stainless steel welding wire for high-temperature environments are as follows:

[0116] Room temperature performance requirements for weld metal: Yield strength Rp 0.2 ≥220MPa, tensile strength R m ≥525MPa, elongation ≥30%; room temperature impact energy KV2 ≥90J for weld metal in as-welded state; room temperature impact energy KV2 ≥25J for weld metal in accelerated aging state at 750℃×100h; high temperature tensile properties of weld metal: 550℃: Rp 0.2 ≥107MPa, R m ≥374MPa; Weld metal microstructure requirements: The δ-ferrite number (FN value) in the weld metal in the as-welded state is between 0.5 and 3.9. The standard for room temperature tensile properties is GB / T2652-2008, the standard for high temperature tensile properties is GB / T 228.2-2015, the standard for room temperature impact properties is GB / T2650-2008, and the standard for δ-ferrite number is GB / T 1954-2008.

[0117] As can be seen from Examples 1-15, Comparative Examples 1-5, and Table 1-4:

[0118] The chemical composition of the welding wire designed using this invention, as shown in Examples 1-15, is within the scope of the technical solution of this invention, and the weld metal meets the performance design requirements of this invention. In Comparative Example 1, the C content of the welding wire is 0.039%, which is outside the scope of the technical solution of this invention (C: 0.005-0.029%). Increased C content will decrease the number of δ-ferrite, resulting in a δ-ferrite number (FN value) of 0.02 in the weld metal, which does not meet the design requirements of this invention (FN value: 0.5-3.9). In Comparative Example 2, the N content of the welding wire is 0.04%, which is outside the scope of the technical solution of this invention (N: 0.09-0.25%). Decreased N content will increase the number of δ-ferrite, resulting in a δ-ferrite number (FN value) of 4.81 in the weld metal, which is... The design requirements of this invention (FN value: 0.5-3.9) are not met, and δ-ferrite decomposes to form intermetallic compounds during high-temperature aging, thus deteriorating the impact performance of the weld metal. Therefore, the δ-ferrite number is high, resulting in a room temperature impact energy of 19J for the weld metal aged at 750℃×100h, which does not meet the design requirements of this invention (750℃×100h accelerated aging state weld metal room temperature impact energy KV2≥25J). In Comparative Example 3, the N content of the welding wire is 0.31%, which is not within the range of the technical solution of this invention (N: 0.09-0.25%). Increasing the N content will reduce the impact performance of the weld metal. The number of δ-ferrite particles resulted in a δ-ferrite particle number (FN value) of 0.05 in the weld metal, which does not meet the design requirements of this invention (FN value: 0.5-3.9). In Comparative Example 4, the Cr content of the welding wire was 22.11%, which is outside the scope of the technical solution of this invention (Cr: 17.0-21.0%). The increased Cr content will increase the δ-ferrite particle number, resulting in a δ-ferrite particle number (FN value) of 5.21 in the weld metal, which also does not meet the design requirements of this invention (FN value: 0.5-3.9). Moreover, δ-ferrite particles will decompose during high-temperature aging to form intermetallic compounds, thus deteriorating the weld metal's impact resistance. Due to the high δ-ferrite number, the room temperature impact energy of the weld metal aged at 750℃ for 100h is 17J, which does not meet the design requirements of this invention (room temperature impact energy KV2 ≥ 25J for weld metal aged at 750℃ for 100h). In Comparative Example 5, the Ni content of the welding wire is 14.92%, which is not within the scope of the technical solution of this invention (Ni: 12.5-14.5%). The increase in Ni content will reduce the δ-ferrite number, resulting in a δ-ferrite number (FN value) of 0.0 in the weld metal, which does not meet the design requirements of this invention (FN value: 0.5~3.9).

Claims

1. A welding method for low-carbon austenitic stainless steel welding wire, characterized in that: The chemical composition of this welding wire, by weight percentage, is as follows: C: 0.005-0.029%, Cr: 17.0-17.9%, Ni: 12.5-14.5%, Mo: 2.2-3.0%, Si: 0.2-0.7%, Mn: 1.00-2.20%, N: 0.15-0.25%, Cu≤0.10%, Co≤0.06%, P≤0.01%, S≤0.005%, balance being iron and unavoidable impurities; Furthermore, the number of δ-ferrite in the weld metal in the as-welded state is between 0.5 and 3.9; The high-temperature tensile properties of the weld metal are: 550℃: Rp 0.2 ≥107MPa, R m ≥374MPa; The welding process uses TIG welding, with a butt joint, a welding current of 150-250A, an arc voltage of 10-15V, a current polarity of DC positive polarity, and a welding speed of 0.05-0.20m / min. Welding wire with a specification of Φ1.2mm was selected for the welding process; During the welding process, high-purity argon gas with a purity of ≥99.995% is used for arc protection, with an argon gas flow rate of 12-30L / min.

2. The welding method according to claim 1, characterized in that, The elemental composition of the welding wire is any one or more of the following a-f conditions: a. The C content in the welding wire is further set to C: 0.005-0.02%, or further set to C: 0.02-0.029%; b. The Ni content in the welding wire is further set to Ni: 12.5-13.6%, or further set to Ni: 13.6-14.5%; c. The Mo content in the welding wire is further set to Mo: 2.20-2.61%, or further set to Mo: 2.61-2.80%, or further set to Mo: 2.80-3.00%; d. The Si content in the welding wire is further set to Si: 0.2-0.29%, or further set to Si: 0.29-0.50%, or further set to Si: 0.50-0.70%; e. The Mn content in the welding wire is further set to Mn: 1.00-1.39%, or further set to Mn: 1.39-1.80%, or further set to Mn: 1.80-2.20%; f. The nitrogen content in the welding wire is further set to 0.15-0.20%, or further set to 0.20-0.25% N.

3. The welding method according to claim 1, characterized in that, The elemental composition of the welding wire is any one or more of the following a-c: a. The Cu content in the welding wire is further set to Cu≤0.05%; b. The Co content in the welding wire is further set to Co ≤ 0.03%; c. The phosphorus (P) content in the welding wire is further set to P ≤ 0.005%.

4. The welding method according to claim 1, characterized in that: The specimens were welded using a multi-layer, multi-pass fusion method, with an interpass temperature ≤150℃ during the welding process.

5. The welding method according to claim 1, characterized in that: The properties of the weld metal obtained after welding are as follows: The weld metal properties at room temperature are: yield strength Rp 0.2 ≥220MPa, tensile strength R m ≥525MPa, elongation A≥30%; The room temperature impact energy of the weld metal in the as-welded state is KV2≥90J, and the room temperature impact energy of the accelerated aging state at 750℃×100h is KV2≥25J.

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