Low-carbon low-alloy welding wire and preparation and welding method thereof

Abstract

The invention relates to a low-carbon low-alloy welding wire and a preparation and welding method thereof, belongs to the technical field of welding materials, and solves the problems that when an existing welding wire is used for welding high-strength materials, the defects of hot cracks, air holes, coarse crystallization and the like are easily generated, the strength and low-temperature toughness of weld metal are insufficient, and the performance matching performance with base metal is poor. The invention provides a low-carbon and low-alloy welding wire. The welding wire is prepared from the following components in percentage by mass: 0.04 to 0.08 percent of C, 0.30 to 0.50 percent of Si, 1.6 to 2.0 percent of Mn, 0.15 to 0.35 percent of Cr, 3.5 to 4.0 percent of Ni, 0.008 to 0.01 percent of Cu, 0.007 to 0.01 percent of Mo, 0.0005 to 0.001 percent of V, 0.02 to 0.07 percent of Ti and 0.01 to 0.018 percent of Al. According to the welding wire, through component design, the mechanical property and low-temperature toughness of a welding joint are remarkably improved, and the welding wire is particularly suitable for welding of P690QL2 steel; and a matched welding method is combined for use, so that the welding performance is better.

Description

Technical Field

[0001] The invention relates to the technical field of welding materials, and in particular to a low-carbon low-alloy welding wire and a preparation method and welding method thereof. Background Art

[0002] As the global demand for storage and transportation of liquefied carbon dioxide continues to increase, cryogenic and high-pressure storage tanks have become key equipment. However, the materials currently used for liquefied carbon dioxide storage tanks are mostly steels with relatively low yield strength, such as 07MnNiMoVDR (yield strength 490MPa) and 15MnNbR (yield strength 370MPa). Although these materials can meet the needs of ordinary cryogenic storage tanks, they often show shortcomings under high-pressure and low-temperature extreme conditions such as liquefied carbon dioxide storage tanks, such as limited strength and unsatisfactory impact resistance, which makes it difficult for the tank's load-bearing capacity and safety to reach the optimal state.

[0003] In order to achieve a higher storage capacity per unit volume of storage tanks, it is inevitable to use materials with higher strength levels. 690MPa-grade high-strength low-temperature steel P690QL2 has become one of the ideal materials for the manufacture of liquefied carbon dioxide storage tanks due to its excellent low-temperature toughness and high strength performance. The use of P690QL2 steel can effectively reduce the wall thickness of the storage tank and reduce the weight of the structure, thereby improving the storage efficiency and economic benefits of the storage tank without increasing the cost. In addition, the use of this high-strength material gives the storage tank a higher safety margin when facing high-pressure conditions.

[0004] However, the technical challenges of P690QL2 steel in the welding process are significant. Due to the high strength characteristics of this material, defects such as thermal cracks, pores, and coarse graining are easily generated during welding, which will affect the toughness and mechanical properties of the welded joint, especially the impact resistance in low temperature environments. The low-temperature toughness and impact resistance of the weld metal formed by existing welding wires are poor, which is difficult to meet the special needs of liquefied carbon dioxide storage tanks. Summary of the invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a low-carbon, low-alloy welding wire and a preparation and welding method thereof, so as to solve the problems that the existing welding wire is prone to produce defects such as thermal cracks, pores, coarse graining, etc. when used for welding high-strength materials, and the strength and low-temperature toughness of the weld metal are insufficient, and the performance matching with the parent material is poor.

[0006] The invention provides a low-carbon low-alloy welding wire. The components in the welding wire are calculated by mass percentage as follows: C 0.04-0.08%, Si 0.30-0.50%, Mn 1.6-2.0%, Cr 0.15-0.35%, Ni 3.5-4.0%, Cu 0.008-0.01%, Mo 0.007-0.01%, V 0.0005-0.001%, Ti 0.02-0.07%, and Al 0.01-0.018%.

[0007] Preferably, the components in the welding wire are calculated by mass percentage as follows: C 0.04-0.06%, Si 0.35-0.45%, Mn 1.75-1.85%, Cr 0.25-0.30%, Ni 3.6-3.8%, Cu 0.008-0.01%, Mo 0.007-0.01%, V 0.0005-0.001%, Ti 0.04-0.06%, and Al 0.013-0.015%.

[0008] More preferably, the components in the welding wire are calculated by mass percentage as follows: C: 0.051%, Si 0.39%, Mn 1.81%, Cr 0.28%, Ni 3.77%, Cu 0.0097%, Mo 0.0092%, V 0.0006%, Ti 0.055%, Al 0.013%.

[0009] The present invention also provides a method for preparing the welding wire, which specifically comprises the following steps:

[0010] S21 ultra-pure smelting: Preliminary weighing and mixing of raw materials according to the preset formula, using double smelting technology, firstly melting in an electric arc furnace, then refining in an induction furnace, to obtain alloy liquid with a preset composition, and then pouring and cooling to obtain ingots;

[0011] S22 forging and rolling: forging is carried out by using a gradual cooling technology, and then rolling is performed after forging to obtain welding wire rods;

[0012] S23 Bright Drawing: Add lubricant and draw the wire rod to obtain low carbon low alloy welding wire.

[0013] Furthermore, in the refining process in step S21, the temperature is controlled at 1600-1700° C. for 1.5-3 hours; and the vacuum degree is maintained at at least 10^-3 Torr.

[0014] Furthermore, the specific operation of the forging process in step S22 is: first, the alloy is heated to 850-1050°C by preheating, and then forging is performed at an initial forging temperature of 1150-1250°C, and the temperature is controlled by a gradual cooling technique; after forging, the alloy is slowly cooled, and the final cooling temperature is ≥900°C; and the pressure applied for each forging in the forging process is ≥120MPa.

[0015] Furthermore, the specific operations and parameters of the rolling process in step S22 are:

[0016] Rough rolling stage: first, heat the billet to 1100-1150℃, the reduction of each rough rolling is between 25% and 35%, and the cooling rate is 40-60℃ / h;

[0017] Finishing rolling stage: the temperature is maintained between 850 and 900°C, the reduction amount of each finishing rolling should be controlled between 10% and 15%, and the cooling rate is controlled at 10 to 20°C / h.

[0018] Furthermore, the drawing speed in the drawing process in step S23 is 5 to 10 m / min.

[0019] Furthermore, step S23 also includes step S24 of surface wiping and cleaning: firstly mechanically wiping the low-carbon low-alloy welding wire, and then ultrasonically cleaning it to remove microscopic impurities.

[0020] The present invention also provides a welding method for the welding wire, in which the welding wire is used to weld the workpiece in a protective gas having a volume ratio of 95% argon gas + 5% carbon dioxide, using a metal active gas shielded welding process.

[0021] Further, the specific welding process is as follows:

[0022] S1: Open the groove according to the material and specifications of the welded parts;

[0023] S2: MAG welding is used to weld layers one by one. The welding direction is adjusted after each layer is welded. The welding directions of adjacent layers are opposite, while the welding directions of the same layer are the same.

[0024] S3: After welding is completed, post-weld treatment is performed.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] 1. The present invention adopts a new type of low-carbon low-alloy welding wire for welding, and the formed weld has good matching with high-strength steel (especially P690QL2 steel), and has excellent mechanical properties and low-temperature toughness.

[0027] The compatibility of the new low-carbon low-alloy welding wire used in the present invention with P690QL2 steel is mainly reflected in the following aspects:

[0028] Component compatibility: The chemical composition of the welding wire has good compatibility with the chemical composition of P690QL2 steel. For example, the high content of Ni and Mo in the welding wire forms a good combination with the corresponding elements of the base material, improves the bonding strength of the interface between the weld and the base material, and reduces the interface defects caused by chemical mismatch. Matching of thermal expansion coefficient: The thermal expansion coefficient of the welding wire is close to that of P690QL2 steel, which can reduce residual stress during the cooling process after welding and reduce the risk of cracks in the weld area. Matching of mechanical properties: The yield strength (Rp0.2) of P690QL2 steel is ≥690MPa, and the tensile strength (Rm) is 770-940MPa. The yield strength (≥792MPa) and tensile strength (≥894MPa) of the joint formed after welding by the welding method of the present invention match the strength of the base material, thereby ensuring the load-bearing capacity of the weld area in actual use.

[0029] Excellent mechanical properties of weld metal:

[0030] The role of Ni (nickel): The Ni content in the welding wire is 3.5%-4.0%, which forms fine and uniform acicular ferrite and bainite structures in the weld, improving the strength and low-temperature toughness of the weld metal. Ni also reduces grain boundary segregation and enhances the impact resistance of the weld. The role of Mo (molybdenum): The Mo content is 0.007%-0.01%, which can effectively prevent the grain growth of the weld structure, improve the toughness in low-temperature environments, and enhance the wear resistance and corrosion resistance of the weld. The role of Ti (titanium): The Ti content is 0.02%-0.07%, which can refine the weld grains, form a uniform fine-grained structure, and improve the mechanical properties and toughness of the joint. The role of Mn (manganese): The Mn content is 1.6%-2.0%, which can effectively improve the strength and toughness of the weld metal, and reduce the thermal crack sensitivity of the weld by combining with S (sulfur) to form MnS inclusions. Function of Al (aluminum): The Al content is 0.01%-0.018%, which has the effect of deoxidation and grain refinement, and improves the toughness and impact resistance of the weld.

[0031] In summary, the welding wire design and process control in the present invention (process control is conducive to better exerting the performance of the component welding wire) ensure the high matching between the weld and the P690QL2 steel, thereby forming a high-strength, high-toughness welded joint, which meets the use requirements of liquefied carbon dioxide storage tanks under high pressure and low temperature extreme environments. The yield strength of the welded joint formed by the welding method is ≥792MPa, the tensile strength is ≥894MPa, and the elongation is ≥13.5%; the average absorbed energy of the -60℃ impact test is ≥130.4J, and the joint hardness is 315~367HV.

[0032] 2. The welding method provided by the present invention innovatively uses 95% argon + 5% carbon dioxide shielding gas instead of the traditional 80% argon + 20% carbon dioxide. This gas ratio significantly reduces the formation of pores and inclusions, improves the weld metal structure, and makes the weld joint have higher strength and low-temperature toughness by increasing the penetration and stability of the welding zone.

[0033] 3. The welding method provided by the present invention is not prone to cracks during the welding process. During the welding process, the welding direction is adjusted after each weld pass is completed to avoid the concentration and cumulative effect of thermal stress caused by continuous welding, thereby effectively reducing the risk of welding cracks.

[0034] 4. The welding method provided by the present invention adopts a slow cooling method to control the cooling rate after welding. Compared with post-weld heat treatment, the present invention can prevent the weld structure from becoming brittle and ensure the excellent toughness of the weld joint under low temperature conditions.

[0035] 5. The welding method provided by the invention has simple process, low cost, excellent comprehensive performance of the welded joint, and is suitable for large-scale promotion.

[0036] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0038] Figure 1 This is a metallographic photograph of the weld metal in Example 1;

[0039] Figure 2 This is a metallographic photograph of the weld metal in Comparative Example 1;

[0040] Figure 3 This is a photo of the weld morphology in Example 1. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0042] The invention provides a low-carbon low-alloy welding wire. The components in the welding wire are calculated by mass percentage as follows: C 0.04-0.08%, Si 0.30-0.50%, Mn 1.6-2.0%, Cr 0.15-0.35%, Ni 3.5-4.0%, Cu 0.008-0.01%, Mo 0.007-0.01%, V 0.0005-0.001%, Ti 0.02-0.07%, and Al 0.01-0.018%.

[0043] Preferably, the components in the welding wire are calculated by mass percentage as follows: C 0.04-0.06%, Si 0.35-0.45%, Mn 1.75-1.85%, Cr 0.25-0.30%, Ni 3.6-3.8%, Cu 0.008-0.01%, Mo 0.007-0.01%, V 0.0005-0.001%, Ti 0.04-0.06%, and Al 0.013-0.015%.

[0044] More preferably, the components in the welding wire are calculated by mass percentage as follows: C: 0.051%, Si 0.39%, Mn 1.81%, Cr 0.28%, Ni 3.77%, Cu 0.0097%, Mo 0.0092%, V 0.0006%, Ti 0.055%, Al 0.013%.

[0045] C (Carbon, 0.04-0.08%): Carbon is an important element to enhance the strength of the weld. With an appropriate amount of carbon content, a trace amount of carbides can be formed in the weld metal to enhance its hardness and strength. Controlling the carbon content within this range can not only ensure the strength of the weld, but also avoid brittleness and crack tendency caused by excessive carbon content.

[0046] Si (silicon, 0.30-0.50%): As a deoxidizer, silicon can effectively remove oxygen from the molten pool during welding and improve the purity of the weld metal. In addition, an appropriate amount of silicon helps to improve the tensile strength and plasticity of the weld.

[0047] Mn (manganese, 1.6-2.0%): Manganese has a good desulfurization effect and can form MnS inclusions with sulfur, reducing the embrittlement effect of sulfur on the weld metal and significantly reducing the risk of welding hot cracks. High content of manganese can also improve the strength and toughness of the weld, especially in low temperature environment.

[0048] Cr (chromium, 0.15-0.35%): The addition of chromium can enhance the corrosion resistance of the weld metal. At the same time, during the welding cooling process, chromium helps to form a stable ferrite structure, thereby improving the oxidation resistance and toughness of the weld.

[0049] Ni (nickel, 3.5-4.0%): Nickel is an important element for enhancing the low-temperature toughness and strength of welds, and has significant performance advantages in low-temperature environments. The addition of nickel can also refine the weld structure, reduce grain boundary segregation, and improve the plasticity and impact properties of the weld.

[0050] Cu (copper, 0.008-0.01%): trace copper can enhance the crack resistance of weld metal and help improve the corrosion resistance of weld. The copper content is controlled within a lower range to prevent it from forming harmful low melting point phases during high temperature welding.

[0051] Mo (Molybdenum, 0.007-0.01%): The addition of Mo can refine the grains and enhance the strength and wear resistance of the weld. At the same time, Mo can also reduce the grain growth phenomenon at high temperatures, thereby improving the thermal stability of the weld.

[0052] V (vanadium, 0.0005-0.001%): trace vanadium can significantly refine the weld structure and improve the yield strength and impact resistance of the weld metal. Vanadium can also combine with carbon to form vanadium carbide, further improving the strength and toughness of the weld.

[0053] Ti (titanium, 0.02-0.07%): Titanium is an efficient grain refining element that can significantly improve the low-temperature impact performance of the weld. Titanium can also combine with oxygen to form TiO2 during the welding process, further improving the crack resistance of the weld metal.

[0054] Al (aluminum, 0.01-0.018%): Aluminum is an important deoxidizing element that can improve the purity of weld metal and refine grains. Trace amounts of aluminum can also stabilize the weld structure and enhance the toughness and impact resistance of the weld.

[0055] Synergy:

[0056] Organization optimization: The interaction between Ni, Mo and Ti in the welding wire can promote the formation of acicular ferrite and bainite in the weld, thereby improving the strength and toughness of the weld. Improved crack resistance: The synergistic effect of Mn, V and Cr can significantly reduce the tendency of thermal cracks and pores during welding, making the weld denser and more uniform. Low-temperature performance: Ni, Ti and Al jointly optimize the microstructure of the weld, giving the weld better impact resistance in low-temperature environments. Grain refinement: Ti and V can form stable carbides or nitrides during welding, effectively refining the weld metal grains and improving the overall performance of the weld. Corrosion resistance: The synergistic effect of Cr and Cu can significantly enhance the corrosion resistance of the weld metal in harsh environments.

[0057] Through the precise control and synergistic effect of the above elements, the welding wire can form uniform and fine ferrite and bainite structures during the welding process, so that the weld metal has high strength, high toughness and excellent low-temperature properties, meeting the use requirements of P690QL2 steel under extreme working conditions.

[0058] The present invention also provides a method for preparing the welding wire, which specifically comprises the following steps:

[0059] S21 ultra-pure smelting: Preliminary weighing and mixing of raw materials according to the preset formula, using double smelting technology, firstly melting in an electric arc furnace, then refining in an induction furnace, to obtain alloy liquid with a preset composition, and then pouring and cooling to obtain ingots;

[0060] S22 forging and rolling: forging is carried out by using a gradual cooling technology, and then rolling is performed after forging to obtain welding wire rods;

[0061] S23 Bright Drawing: Add lubricant and draw the wire rod to obtain low carbon low alloy welding wire.

[0062] Specifically, the preparation method of the welding wire adopts ultra-pure smelting technology, strictly controls the content of impurity elements (such as P, S), and reduces the intrusion of gas elements (H, O, N) through vacuum melting and refining deoxidation process to ensure the purity of the welding wire. At the same time, alloy elements (such as C, Ni, Mn, Ti, Mo, etc.) are accurately added according to the designed proportion to achieve component homogenization, further improving the low-temperature toughness and crack resistance of the welding wire. The grains are refined through forging, rolling and bright drawing processes, and combined with surface pickling and cleaning treatments, it is ensured that the surface of the welding wire is free of impurities and pollutants, providing an excellent material basis for high-strength welding.

[0063] Furthermore, in the refining process in step S21, the temperature is controlled at 1600-1700° C. and maintained for 1.5-3 hours to ensure that impurities are fully floated out; the vacuum degree is maintained at at least 10^-3 Torr to avoid oxidation of components or mixing of gas impurities.

[0064] Furthermore, the specific operation of the forging process in step S22 is: firstly, preheating the alloy to 850-1050°C, then forging at an initial forging temperature of 1150-1250°C, and applying a gradual cooling technique for temperature control; after forging, slowly cooling, with a final cooling temperature ≥900°C.

[0065] Specifically, the gradual cooling technology ensures the uniformity of the alloy's structure and grain refinement in different temperature ranges by carefully controlling the cooling rate during forging and rolling. The forging process first preheats the alloy to 850-1050°C, and then forges it at an initial forging temperature of 1150-1250°C, using the gradual cooling technology for temperature control. In the initial stage, a slower cooling rate (30-50°C / h) is used to ensure the plasticity of the alloy and avoid cracks; the cooling rate is further reduced in the medium and low temperature stages (20-40°C / h and 10-20°C / h) to prevent grain coarsening and internal stress concentration. After forging, the alloy should not be cooled quickly immediately, but should be cooled slowly until about 900°C. During this process, direct exposure to the air should be avoided to prevent stress concentration or cracks caused by excessively high or low temperatures. To ensure the uniformity of the material, cooling should be carried out in a controlled environment as much as possible to avoid stress unevenness caused by environmental differences.

[0066] Specifically, in the forging process, each forging application pressure is ≥120MPa to ensure the uniformity and density of the material.

[0067] Furthermore, the specific operations and parameters of the rolling process in step S22 are:

[0068] Rough rolling stage: first, heat the billet to 1100-1150°C, the reduction of each rough rolling is between 25% and 35%, and the cooling rate is 40-60°C / h;

[0069] Finishing rolling stage: the temperature is maintained between 850 and 900°C, the reduction amount of each finishing rolling should be controlled between 10% and 15%, and the cooling rate is controlled at 10 to 20°C / h.

[0070] Specifically, the rolling process begins after forging is completed. In the rough rolling stage, the billet is first heated to 1100-1150°C for preliminary deformation and gradual thinning. During this process, the reduction of each rough rolling should be controlled between 25% and 35%, and the cooling rate is 40-60°C / h to prevent surface cracks caused by excessive cooling. The temperature control in the finishing stage is relatively strict, requiring the temperature to be maintained between 850 and 900°C, and the cooling rate to be controlled at 10-20°C / h to ensure grain refinement and uniform structure. During the finishing process, the reduction of each finishing rolling should be controlled between 10% and 15% to maintain the surface quality of the alloy and optimize the mechanical properties. After rolling, the alloy should continue to be cooled evenly to avoid internal stress or cracks caused by excessive temperature difference, and finally obtain high-quality and uniformly structured alloy materials. Through this optimized step-by-step cooling method, problems such as cracks, grain coarsening and internal stress concentration caused by excessive cooling can be effectively avoided, and the mechanical properties and structural uniformity of the alloy can be improved.

[0071] Furthermore, the drawing speed in the drawing process in step S23 is 5 to 10 m / min to ensure the stability of the material during the drawing process. Lubricants are added during the drawing process to reduce friction and improve surface finish. A synthetic lubricant with stable performance is selected from common commercial lubricants that are suitable for high temperature and high tension conditions.

[0072] Furthermore, step S23 also includes step S24 of surface wiping and cleaning: firstly mechanically wiping the low-carbon low-alloy welding wire, and then ultrasonically cleaning it to remove microscopic impurities.

[0073] Furthermore, highly absorbent microfiber cloth is used for mechanical wiping to improve cleaning efficiency. Ultrasonic cleaning is performed after mechanical wiping to remove microscopic impurities. The ultrasonic frequency is 35 to 45 kHz, and the cleaning time is 10 to 20 minutes to completely remove all attached impurities.

[0074] Furthermore, after the welding wire is prepared, vacuum annealing technology is used to reduce the diffusible hydrogen content to prevent the occurrence of cold cracks, and the welding wire is stored in a dry or vacuum environment to ensure the long-term stability of the welding wire. The welding wire prepared by this method has high strength, high toughness and low impurity content, which can meet the use requirements of high-pressure and low-temperature equipment such as liquefied carbon dioxide storage tanks, and effectively improve the purity, impact resistance and structural reliability of the weld.

[0075] Specifically, the welding wire is stored in a vacuum before welding to prevent oxidation from affecting the welding quality.

[0076] The present invention also provides a welding method for the welding wire, in which the welding wire is used to weld the workpiece in a protective gas having a volume ratio of 95% argon gas + 5% carbon dioxide, using a metal active gas shielded welding process.

[0077] Further, the specific welding process is as follows:

[0078] S1: According to the material and specifications of the welded parts, grooves are opened according to implementation needs and relevant standards;

[0079] S2: MAG welding is used to weld layers one by one. The welding direction is adjusted after each layer is welded. The welding directions of adjacent layers are opposite, while the welding directions of the same layer are the same.

[0080] S3: After welding is completed, post-weld treatment is performed.

[0081] Specifically, the welded parts are preheated before welding, and the preheating temperature is 100-120° C.; the interpass temperature during welding is controlled at 100-120° C. To ensure the temperature consistency during welding, prevent grain coarsening or stress concentration caused by overheating or overcooling in the weld area, and ensure the excellent performance of the welded joint.

[0082] Specifically, the composition of the shielding gas for MAG welding in step S2 is 95% argon + 5% carbon dioxide (volume ratio). As an inert gas, argon can effectively inhibit the oxidation reaction generated during welding, reduce grain boundary inclusions, and improve the purity of the weld metal, thereby improving the low-temperature toughness of the weld. A lower proportion of carbon dioxide provides a certain arc stability while reducing the influence of oxygen content on the organization, forming a fine and uniform grain structure.

[0083] Furthermore, the weld structure with a shielding gas ratio of 95% argon + 5% carbon dioxide is mainly composed of acicular ferrite, side lath ferrite and granular bainite, with uniform tissue distribution and fine grains. A higher proportion of argon as an inert gas can effectively inhibit the oxidation reaction during welding, reduce the oxygen content in the weld metal, and reduce the formation of oxide inclusions at the grain boundaries. This gas ratio promotes a more ideal microstructure transformation process during the cooling process. The high proportion of argon provides a moderate cooling rate, first forming acicular ferrite and side lath ferrite, and then precipitating granular bainite in a lower temperature zone. The moderate cooling rate helps to form a stable bainite phase, ensuring the uniform dispersion and precipitation of carbon in the ferrite, thereby giving the weld a higher strength. The high proportion of bainite and the uniformly distributed ferrite together improve the strength and toughness of the weld, making it show excellent performance in low-temperature impact tests. The fine-grained, multi-phase microstructure effectively disperses stress concentration, reduces the risk of brittle fracture, and significantly improves the overall mechanical properties of the weld joint.

[0084] Specifically, the flow rate of the shielding gas is controlled at 18-22 L / min to ensure that the shielding gas flow rate is stable and evenly covers the welding area. The stable gas flow rate can form a uniform shielding atmosphere and reduce defects caused by air entering the welding area.

[0085] Specifically, the specific process parameters of step S2 are: welding current is 310-340A, welding voltage is 31-33V, welding speed is 40-44cm / min, and heat input is controlled at 14-16KJ / cm.

[0086] The process parameters in step S2 are designed according to the composition of the welding wire and the characteristics of the welding materials to optimize the welding quality and performance. The welding current and voltage directly determine the temperature and penetration of the molten pool, and match the melting characteristics of the alloy components such as Ni, Mn, and Cr in the welding wire to ensure a stable arc and sufficient penetration; the welding speed is controlled at 40-44 cm / min, the cooling rate of the molten pool is optimized, and the fine-grained strengthening elements such as Ti and V in the welding wire are combined to inhibit grain coarsening and improve the quality and toughness of the weld formation. The heat input is controlled within the range of 14-16 KJ / cm, which is a key parameter, which not only meets the needs of fully melting the parent material and the welding wire, but also avoids the problems of grain coarsening and cracking caused by excessively high molten pool temperature. Combined with Ni and Mo in the welding wire composition, this heat input range promotes the formation of fine and uniform ferrite and bainite structures in the weld, significantly improving the low-temperature toughness and impact resistance of the weld. In addition, reasonable heat input and cooling rate reduce welding stress concentration and reduce the probability of cold cracks and hot cracks. Through the optimization of the above parameters, combined with the welding wire composition, the performance advantages of the alloy elements in the welding wire can be fully utilized to form a stable weld structure with excellent strength, toughness and impact resistance. The entire process parameter design can meet the special needs of low-temperature and high-pressure equipment such as liquefied carbon dioxide storage tanks, ensuring the safety and reliability of welded joints in extreme environments.

[0087] Specifically, the post-weld treatment is performed by heat preservation and slow cooling. For example, heat preservation is performed directly after welding for 2 to 6 hours, followed by air cooling; no post-heat treatment is performed after welding, but a slow cooling method is used to control the cooling rate. Slow cooling can prevent the weld from becoming brittle, maintain a relatively fine grain structure, and thus improve the low-temperature toughness of the weld joint.

[0088] Specifically, the welding method is suitable for welding P690QL2 steel.

[0089] Furthermore, the welding method is suitable for the manufacture and maintenance of low-temperature and high-pressure equipment such as liquefied carbon dioxide storage tanks and LNG storage tanks, and is particularly suitable for full-pressure C-type double-ear liquid cargo tanks used in ship transportation.

[0090] Specifically, the weld metal microstructure formed by the welding method is ferrite and bainite, and the relative ratio (volume ratio) of the two is bainite: ferrite = 0.80-0.85: 0.15-0.20, and the grain size is 1.70-1.80 μm. More specifically, it is composed of acicular ferrite, side plate ferrite and granular bainite, with uniform tissue distribution and fine grains. The high proportion of bainite and the uniformly distributed ferrite together improve the strength and toughness of the weld, making it exhibit excellent performance in low-temperature impact tests. The fine-grained, multi-phase microstructure effectively disperses stress concentration, reduces the risk of brittle fracture, and significantly improves the overall mechanical properties of the weld joint.

[0091] Furthermore, the yield strength of the welded joint formed by the welding method is ≥792MPa, the tensile strength is ≥894MPa, and the elongation is ≥13.5%; the average absorbed energy of the -60°C impact test is ≥130.4J, and the joint hardness is 315-367HV.

[0092] Examples and Comparative Examples

[0093] The specific composition of the welding wire of each embodiment and comparative example is shown in Table 1.

[0094] Table 1 Specific composition of welding wire in various embodiments and comparative examples

[0095]

[0096]

[0097] The preparation processes of each embodiment and comparative example are as follows:

[0098] S21 ultra-pure smelting: double melting technology is used, first melting in an arc furnace, then refining in an induction furnace to further reduce the content of phosphorus (P) and sulfur (S). The refining temperature is controlled at 1650℃ for 2 hours, and the vacuum degree is maintained at no less than 10^-3Torr during the refining process.

[0099] S22 Forging and rolling: The process parameters of forging and rolling are shown in Table 2.

[0100] Table 2 Process parameters of forging and rolling

[0101]

[0102]

[0103] S33 bright drawing: Lubricant is added during the drawing process (common commercially available high temperature resistant and high tensile force resistant lubricants can be used, no special requirements), and the drawing speed is controlled at 6-8m / min.

[0104] S34 surface cleaning: Use highly absorbent microfiber cloth for mechanical wiping to improve cleaning efficiency. Perform ultrasonic cleaning after mechanical wiping, with an ultrasonic frequency of 40kHz and a cleaning time of 15 minutes.

[0105] Observation of welding wire morphology:

[0106] After observation and testing, the uniformity of the structure of the welding wire corresponding to the embodiment is significantly better than that of the comparative welding wire, and there is almost no element segregation in the embodiment, while there is slight element segregation in the comparative examples. However, it is worth emphasizing that the performance of the welding wire is mainly determined by the composition design. The preparation process can help improve its performance, but the impact is relatively limited, because the welding wire will actually go through the process of melting and cooling and solidification again during the welding process, and finally form a "new welding seam alloy / metal". The performance of this "new welding seam alloy / metal" plays a decisive role in the final welding performance.

[0107] In other words, the most critical role of the welding wire preparation process is to improve the purity and uniformity of the welding wire as much as possible, remove impurities from it, and thus make the performance of the "new welding alloy / metal" more superior.

[0108] Welding performance test / application example:

[0109] The test plate material is P690QL2 steel plate, with specifications of 500mm long × 150mm wide × 20mm thick. A V-shaped groove is opened along the rolling direction of the test plate, and the groove gap is set to 16mm. The deposited metal welding test is carried out. The specific welding process parameters are shown in Table 3.

[0110] Table 3 Welding process parameters of each embodiment and comparative example

[0111]

[0112]

[0113] The mechanical properties and low-temperature toughness of the welds / welds of each embodiment and comparative example were tested, and the test results are shown in Table 4.

[0114] Table 4 Mechanical properties and low temperature toughness test results of each embodiment and comparative example

[0115]

[0116] In the detailed analysis of the embodiments and the comparative examples, the mechanical properties of the embodiments are significantly better than those of the comparative examples by precisely controlling the chemical composition of the welding wire and the welding process parameters. The embodiments optimize the welding performance by adjusting the proportions of key elements such as carbon, silicon, nickel, and chromium, ensuring high strength and good low-temperature toughness. These adjustments have a direct impact on the microstructure and mechanical properties of the weld. Examples 3 and 5 in particular demonstrate how to refine the grain structure by increasing the carbon and aluminum content, thereby improving the overall performance, especially for applications in extreme environments. It is worth noting that the formula design of the welding wire ensures the lower limit of the welding performance of the welding method, and more preferred welding process parameters help to further give full play to the performance of the welding wire.

[0117] In contrast, the comparative examples demonstrate the performance limitations under non-optimized conditions. Although comparative examples 1 and 2 use the same basic alloy composition as the examples, they have different shielding gas ratios or increased heat input power, showing how these changes negatively affect the quality and performance of the weld. The poor shielding gas ratio in comparative example 1 leads to a relatively high level of impurities in the weld metal, resulting in reduced mechanical properties; the higher heat input in comparative example 2 leads to overheating of the weld zone, which may cause grain coarsening, which reduces the impact toughness of the weld, indicating the importance of controlling heat input.

[0118] In general, the comparison between the embodiment and the comparative example emphasizes the key role of optimization of reasonable chemical composition and welding process parameters in achieving excellent welding performance. The composition optimization and welding parameter control of the embodiment ensure the high performance of the welded joint, while the performance limitations of the comparative example highlight the necessity and effectiveness of the optimization of welding wire formulation and process parameters. The welded joint formed by the welding method corresponding to the welding wire provided by the present invention has a yield strength of ≥792MPa, a tensile strength of ≥894MPa, and an elongation of ≥13.5%; the average absorbed energy of the -60℃ impact test is ≥130.4J, and the joint hardness is 315~367HV.

[0119] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-carbon low-alloy welding wire, characterized in that: The components in the welding wire are calculated by mass percentage as follows: C 0.04-0.08%, Si 0.30-0.50%, Mn 1.6-2.0%, Cr 0.15-0.35%, Ni 3.5-4.0%, Cu 0.008-0.01%, Mo 0.007-0.01%, V 0.0005-0.001%, Ti 0.02-0.07%, Al 0.01-0.018%.

2. The welding wire according to claim 1, characterized in that The components in the welding wire are calculated by mass percentage as follows: C 0.04-0.06%, Si 0.35-0.45%, Mn 1.75-1.85%, Cr 0.25-0.30%, Ni 3.6-3.8%, Cu 0.008-0.01%, Mo 0.007-0.01%, V 0.0005-0.001%, Ti 0.04-0.06%, Al 0.013-0.015%.

3. The welding wire according to claim 1, characterized in that The components in the welding wire are calculated by mass percentage as follows: C: 0.051%, Si 0.39%, Mn 1.81%, Cr 0.28%, Ni 3.77%, Cu 0.0097%, Mo 0.0092%, V0.0006%, Ti 0.055%, and Al 0.013%.

4. A method for preparing the welding wire according to any one of claims 1 to 3, characterized in that: The specific steps include: S21 ultra-pure smelting: Preliminary weighing and mixing of raw materials according to the preset formula, using double smelting technology, firstly melting in an electric arc furnace, then refining in an induction furnace, to obtain alloy liquid with a preset composition, and then pouring and cooling to obtain ingots; S22 forging and rolling: forging is carried out by using a gradual cooling technology, and then rolling is performed after forging to obtain welding wire rods; S23 Bright Drawing: Add lubricant and draw the wire rod to obtain low carbon low alloy welding wire.

5. The preparation method according to claim 4, characterized in that: In the refining process in step S21, the temperature is controlled at 1600-1700° C. for 1.5-3 hours; the vacuum degree is maintained at at least 10^-3 Torr.

6. The preparation method according to claim 4, characterized in that: The specific operation of the forging process in step S22 is: first, preheat the alloy to 850-1050°C, then forge at an initial forging temperature of 1150-1250°C, and use a gradual cooling technique to control the temperature; slowly cool after forging, and the final cooling temperature is ≥900°C; the pressure applied for each forging in the forging process is ≥120MPa.

7. The preparation method according to claim 4, characterized in that: The specific operations and parameters of the rolling process in step S22 are: Rough rolling stage: first, heat the billet to 1100-1150℃, the reduction of each rough rolling is between 25% and 35%, and the cooling rate is 40-60℃ / h; Finishing rolling stage: the temperature is maintained between 850 and 900°C, the reduction amount of each finishing rolling should be controlled between 10% and 15%, and the cooling rate is controlled at 10 to 20°C / h.

8. The preparation method according to claim 4, characterized in that: The drawing speed in the drawing process in step S23 is 5 to 10 m / min.

9. The preparation method according to claim 4, characterized in that: Step S23 also includes step S24 of surface wiping and cleaning: The low-carbon low-alloy welding wire is firstly mechanically wiped, and then ultrasonically cleaned to remove microscopic impurities.

10. A welding method for the welding wire according to any one of claims 1 to 3 or the welding wire prepared by the preparation method according to any one of claims 4 to 9, characterized in that: In a protective gas with a volume ratio of 95% argon and 5% carbon dioxide, a metal active gas shielded welding process is adopted and the welding wire is used to weld the workpieces to be welded.

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