Nickel-based flux-cored wire for LNG storage tank and preparation method and application thereof

Abstract

The application discloses a nickel-based flux-cored wire for LNG storage tanks and a preparation method and application thereof, and belongs to the technical field of welding material flux-cored wires, and solves the problem that the mechanical properties and toughness of a weld after welding of an existing welding wire used for welding 9Ni steel plates are not matched with the 9Ni steel, thereby leading to low service life of the storage tank. The nickel-based flux-cored wire comprises a core and a cladding layer cladded outside the core; the cladding layer comprises, in percentage by mass, C: 0.015%, Cr: 14.5%-20.0%, S: 0.04%, P: 0.04%, and the balance of Ni and inevitable impurities; and the core comprises, in percentage by mass, Co: 0.5%-2.5%, Cr: 13.0%-18.0%, Si: 0.15%, Al: 0.01%-0.03%, Mn: 0.001%-0.02%, Mo: 15%-17%, W: 10%-20%, Fe: 10%-15%, and the balance of Ni and inevitable impurities.

Description

Technical Field

[0001] This invention relates to the field of flux-cored welding wire technology, and particularly to a nickel-based flux-cored welding wire for LNG storage tanks, its preparation method, and its application. Background Technology

[0002] LNG is the cleanest and most efficient fossil fuel in the world today, and many countries have listed it as their preferred fuel. LNG is a flammable and explosive hazardous material, typically stored at -162°C. At this temperature, natural gas liquefies and is stored in LNG tanks. Due to its flammable and explosive nature, special attention must be paid to safety during storage and transportation. With the continuous increase in demand for LNG, domestically produced LNG storage tanks are developing towards larger capacity, higher parameters, and higher requirements. These new development directions also place higher demands on the performance of LNG tank welds.

[0003] Among nickel-based cryogenic steels, 9Ni steel is the only medium-alloy low-carbon martensitic cryogenic steel that can serve under cryogenic conditions. Even at -196℃, its impact absorption energy can reach 200-300J, making it the material with the best toughness under cryogenic conditions. The chemical composition of 9Ni steel is: Ni: 8.5-9.5%, C: <0.13%, Si: 0.15-0.30%, Mn: 0.3%-0.90%, S≤0.02%, P≤0.035%, Mo:≤0.1%, V≤0.01%. Its mechanical properties are: tensile strength TS: 680-820MPa, yield strength YS≥570MPa, elongation A≥20%. Currently, 9Ni steel is widely used in the manufacture of LNG carriers, LNG storage tanks, and LNG pipelines, among other LNG infrastructure. With the continuous improvement of 9Ni steel plate production technology in my country, the composition and performance of 9Ni steel plates are becoming increasingly superior.

[0004] The mechanical properties and toughness of the weld seam produced by the welding wire used for welding 9Ni steel plates do not match those of 9Ni steel, which prevents the storage tank from fully utilizing the excellent properties of the base material, resulting in a short service life of the storage tank. Summary of the Invention

[0005] In view of the above, the present invention aims to provide a nickel-based flux-cored welding wire for LNG storage tanks, its preparation method and application, to solve the problem that the mechanical properties and toughness of the weld after welding with existing welding wires used for welding 9Ni steel plates do not match those of 9Ni steel, resulting in a short service life of the storage tank.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides an austenitic submerged arc welding nickel-based flux-cored wire for LNG storage tanks, characterized in that the nickel-based flux-cored wire comprises a flux core and a coating layer covering the outside of the flux core; the coating layer comprises, by mass percentage: C<0.015%, Cr: 14.5%-20.0%, S<0.04%, P<0.04%, with the balance being Ni and unavoidable impurities;

[0008] The core contains, by mass percentage: Co: 0.5%-2.5%, Cr: 13.0%-18.0%, Si < 0.15%, Al: 0.01%-0.03%, Mn: 0.001%-0.02%, Mo: 15%-17%, W: 10%-20%, Fe: 10%-15%, with the balance being Ni and unavoidable impurities.

[0009] Optionally, the core comprises: Co: 1.45%-2.5%, Cr: 13.0%-18.0%, Si < 0.15%, Al: 0.015%-0.03%, Mn: 0.0086%-0.02%, Mo: 15%-17%, W: 10%-20%, Fe: 10%-15%, with the balance being Ni and unavoidable impurities.

[0010] Secondly, the present invention also provides a method for preparing a nickel-based flux-cored welding wire, which includes the following steps:

[0011] Step 1: Weigh each component of the core according to the formula, dry them, mix them evenly, and obtain the core powder;

[0012] Step 2: Weigh the components that make up the coating layer according to the proportions and make them into nickel-chromium alloy strips;

[0013] Step 3: Roll the nickel-chromium alloy strip into a "U-shaped groove";

[0014] Step 4: Fill the "U-shaped groove" with the flux-cored powder from Step 1, seal it, and pull it to reduce its diameter to obtain the flux-cored welding wire.

[0015] Optionally, in step 1, the filling rate of the "U-shaped groove" in the core powder is 20%-30%.

[0016] Optionally, in step 1, the drying temperature is 100-150℃ and the drying time is 2-4 hours.

[0017] Optionally, in step 1, the particle size of the core powder is 80-200 mesh.

[0018] Optionally, step 2 further includes: subjecting the prepared nickel-chromium alloy strip to ultrasonic cleaning and hot air drying in sequence.

[0019] Optionally, in step 4, the diameter of the flux-cored wire is 2-3 mm.

[0020] Optionally, the diameter of the flux-cored welding wire is 2.4-2.6 mm.

[0021] Thirdly, the present invention also provides an application of the above-mentioned nickel-based flux-cored welding wire or the nickel-based flux-cored welding wire prepared by the above-mentioned preparation method in welding LNG storage tanks.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] a) This invention controls the proportion of harmful phases in the weld metal by optimizing the composition and content of the cladding layer and the flux core. Specifically, the harmful phase is TCP (topologically close-packed phase). By taking SEM images and statistically analyzing the precipitated phases, the area fraction of the precipitated phase was reduced to 0.73%, thereby improving the toughness of the weld metal. As a result, after welding LNG storage tanks with the welding wire of this invention, the weld cladding metal at -196°C exhibits low-temperature impact toughness, high tensile strength, and yield strength comparable to 9Ni steel. This allows the excellent properties of the base material to be fully utilized when applied to LNG storage tanks, extending the service life to 50 years.

[0024] b) After welding LNG storage tanks with the welding wire of the present invention, the tensile strength of the weld is 724-748MPa, the impact energy of the weld at -196℃ is 85-93J, the yield strength is 362-384MPa, and the temperature range is characterized by full ductile fracture without ductile-brittle transition. Its KV2 impact energy is greater than 243J. The data in Table 2 have all met the service requirements of the national standard for welded joints for LNG storage tanks.

[0025] c) In the preparation method of the flux core of the present invention, by controlling the filling rate of the flux core to 20%-30%, the content of weld elements can be guaranteed, and the difficulty of rolling and drawing can be reduced.

[0026] d) The raw materials for this invention are widely available, inexpensive, and the preparation method is simple and easy to implement. The welding wire obtained using the preparation method of this invention will reduce the production cost of LNG storage tanks by more than 30%, resulting in significant economic benefits.

[0027] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0028] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0029] Figure 1 This is a scanning electron microscope image of the weld seam in an embodiment of the present invention. Detailed Implementation

[0030] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0031] This invention provides an austenitic submerged arc welding nickel-based flux-cored wire for LNG storage tanks, comprising a flux core and a cladding layer covering the flux core. The cladding layer is a nickel-chromium alloy strip, and by mass percentage, the cladding layer comprises: C<0.015%, Cr: 14.5%-20.0%, S<0.04%, P<0.04%, with the balance being Ni and unavoidable impurities.

[0032] The core contains, by mass percentage: Co: 1.45%-2.5%, Cr: 13.0%-18.0%, Si < 0.15%, Al: 0.015%-0.03%, Mn: 0.0086%-0.02%, Mo: 15%-17%, W: 10%-20%, Fe: 10%-15%, with the balance being Ni and unavoidable impurities.

[0033] The following details the function and dosage selection of the components contained in this invention:

[0034] Cr: The addition of Cr is mainly used to improve the corrosion resistance of weld metal and stabilize the austenitic phase. The outer layer acts as a conductive layer, melting the welding wire to form the weld metal. In nickel-based alloys, the equilibrium distribution coefficient of Cr is greater than 1. When the Cr content exceeds 12%, it can significantly improve the alloy's resistance to intergranular stress corrosion, especially in oxidizing environments such as sulfuric acid. Cr has a stronger affinity for O than Fe, therefore, a stable (Fe,Cr)₂O₃ oxide film can form on the surface of Cr-containing stainless steel, effectively preventing the outward diffusion of metallic elements and the inward diffusion of harmful elements such as O, N, and S, thus protecting the alloy from corrosion. Furthermore, Cr has a strong affinity for C, forming various carbides (such as C...). 23The continuous or discontinuous precipitation of carbides (C6, Cr3C2, and Cr7C3) at grain boundaries can hinder grain boundary movement and improve the high-temperature ductility of the material. However, the precipitation of grain boundary carbides can also lead to the formation of Cr-depleted regions near the grain boundaries, reducing the corrosion resistance of the alloy. Furthermore, when carbides precipitate continuously at grain boundaries, they can become pathways for crack propagation. Although increasing the Cr content can alleviate corrosion problems caused by Cr-depleted regions, in alloys containing C and N, excessive Cr can reduce the thermal conductivity of the weld, potentially leading to cracking, deformation, and localized melting at the weld edge. Therefore, this invention limits the Cr content in the cladding layer to 14.5%–20% and the Cr content in the flux core to 13%–18%.

[0035] Mo: The main function of Mo is to strengthen the matrix through solid solution. At the same time, this welding wire increases the Mo content to 15% to 17%, which can effectively improve the corrosion performance caused by Mo segregation.

[0036] The main role of Fe is to enhance the strength and hardness of the weld metal and improve the impact toughness of the weld.

[0037] The role of silicon (Si) is to improve the fluidity of the weld metal and to work with manganese (Mn) for deoxidation. However, excessive Si content can enhance the stability of harmful phases in the weld metal, promote the formation of the Laves phase, and reduce the strength and toughness of the weld metal. Therefore, the Si content must be strictly controlled below 0.15%.

[0038] Al and Mn: Mn promotes austenite formation, and its addition improves weld toughness, slightly enhancing weld hardness and strength. Mn inhibits porosity in the weld, acting as a deoxidizer. If the deoxidation products of Mn do not float to the surface of the weld pool in time, they may act as nucleating agents, helping to refine grains. Al also has a deoxidizing effect and can optimize weld appearance and improve weld toughness. However, excessive Al and Mn can lead to excessive oxide inclusions in the weld, reducing its toughness and plasticity, and may even become the initiation point for cracks. When the Al and Mn content is too low, the deoxidizing effect cannot be fully utilized, and coarse oxides are prone to appear in the weld. Therefore, this invention limits the flux core content to 0.0086 ≤ Mn ≤ 0.02% and 0.01 ≤ Al ≤ 0.03%.

[0039] Co: Co plays a role in solid solution strengthening, improving the strength and toughness of the weld metal, and also reducing interdendritic segregation and inhibiting TCP phase precipitation. However, excessive Co content will result in excessively high weld strength and reduced toughness, while insufficient Co content will lead to inadequate weld strength. Therefore, this invention limits the Co content in the flux core to 1.45%-2.5%.

[0040] C, S, P: In this invention, C, S, and P are harmful elements, and the lower the content, the better.

[0041] W: The role of W in high-temperature nickel-based alloys is that it dissolves in the matrix γ-phase and γ'-phase, with an equilibrium distribution coefficient greater than 1. Since the diameter of a W atom is about 10% larger than that of a Ni atom, its solubility in nickel-based alloys at 1000℃ can reach 38%. W atoms in the nickel-based alloy matrix can cause significant lattice expansion, forming a large long-range stress field, hindering dislocation movement and thus increasing the strength of the matrix. However, excessive W content can lead to excessively high weld metal hardness and reduced plastic deformation capacity. This invention limits the W content in the flux core to 10%–20%.

[0042] Specifically, the microstructure of the aforementioned welding wire is austenitic.

[0043] The design concept of the welding wire of this invention is to control the proportion of harmful phases in the weld metal by optimizing the composition and content of the cladding layer and the flux core. Specifically, the harmful phase is TCP (topologically close-packed phase). By taking SEM images and statistically analyzing the precipitated phases, the area fraction of the precipitated phase was reduced to 0.73%, thereby improving the toughness of the weld metal. As a result, after welding LNG storage tanks with the welding wire of this invention, the weld metal at the weld joint exhibits low-temperature impact toughness, high tensile strength, and yield strength at -196℃, comparable to 9Ni steel. This allows the excellent properties of the base material to be fully utilized when applied to LNG storage tanks, extending the service life to 50 years.

[0044] After welding LNG storage tanks using the welding wire of this invention, the tensile strength of the weld is 724-748 MPa, the impact energy of the weld at -196℃ is 85-93 J, the yield strength is 362-384 MPa, and the fracture is fully ductile within the temperature range without ductile-brittle transition. Its KV2 impact energy is greater than 243 J, all of which meet the service requirements of welded joints for LNG storage tanks in the national standard.

[0045] The coating layer of this invention is a nickel-chromium alloy, which has a wide availability of raw materials, low cost, and is easy to process. The core component of this invention also has the advantages of wide availability of raw materials and low cost.

[0046] The present invention also provides a method for preparing the above-mentioned welding wire, comprising the following steps:

[0047] Step 1: Weigh each component of the core according to the formula, dry them, mix them evenly, and obtain the core powder;

[0048] Step 2: Weigh the components that make up the coating layer according to the proportions and make them into nickel-chromium alloy strips;

[0049] Step 3: Roll the nickel-chromium alloy strip into a "U-shaped groove";

[0050] Step 4: Fill the "U-shaped groove" with the flux-cored powder from Step 1, seal it, and pull it to reduce its diameter to obtain the flux-cored welding wire.

[0051] Specifically, in step 1, the drying temperature is 100–150℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, or 150℃. The drying time is 2–4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0052] In step 1, the particle size of the core powder is 80-200 mesh.

[0053] Step 2 also includes: subjecting the prepared nickel-chromium alloy strip to ultrasonic cleaning and hot air drying in sequence.

[0054] Specifically, in step 3, a flux-cored wire forming device is used to roll the nickel-chromium alloy strip into a "U-shaped groove" using forming rollers.

[0055] Specifically, in step 4, a tracked powder adding device is used to add the core powder to the "U-shaped groove" with a filling rate of 20%-30%, for example, 20%, 22%, 25%, 28%, or 30%.

[0056] It should be noted that if the filling rate is too high, it will increase the difficulty of rolling and drawing, and may even cause the steel strip to fail to contain the flux powder, resulting in flux powder leakage, serious waste, and affecting the smooth progress of rolling. If the filling rate is too low, the content of weld elements cannot be guaranteed. The filling rate of the flux core in this invention is controlled at 20%-30%, which can both guarantee the content of weld elements and reduce the difficulty of rolling and drawing.

[0057] Furthermore, large fluctuations in the filler ratio can lead to uneven composition of the deposited metal during welding, resulting in unstable performance. Therefore, this invention controls the filler ratio to 20%-30%, with fluctuations of only 10%.

[0058] In addition, in step 4, a flux-cored wire forming device is used to seal the wire, resulting in a thicker wire. After drawing and reducing the diameter, the final flux-cored wire is obtained.

[0059] In step 4, the diameter of the flux-cored welding wire is 2-3mm, for example, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, or 3mm.

[0060] The welding wire prepared by the method proposed in this invention can significantly reduce costs and improve the economic efficiency of welding materials. Specifically, the welding wire prepared by the method of this invention will reduce the production cost of LNG storage tanks by more than 30%, resulting in significant economic benefits.

[0061] The welding wire and its preparation method of the present invention will be described in detail below with reference to specific embodiments.

[0062] Example 1

[0063] This embodiment provides a submerged arc welding nickel-based flux-cored wire for welding LNG storage tanks, comprising an inner metallic flux-cored powder and an outer nickel-chromium alloy strip serving as a coating. The outer nickel-chromium alloy strip has a size of 0.5mm × 16mm, and its composition and weight percentage content are: Cr = 16.95%, S = 0.0004%, P = 0.002%, C = 0.002%, Ni balance, with the total amount of each component being 100%. The composition and weight percentage content of the inner flux-cored powder are as follows: Cr = 17.5%, S = 0.0004%, P = 0.004%, Al = 0.026%, Mn = 0.012%, Co = 1.53%, Ni balance. The particle size of the flux-cored powder is controlled between 80 and 200 mesh, the flux filling rate is 24%, and the diameter of the prepared flux-cored welding wire is 2.4mm. The specific steps are as follows:

[0064] Step (1): Place the metal core powder in a drying oven for drying (100℃, 4h), and mechanically mix the treated core powder to obtain a uniformly mixed core powder.

[0065] Step (2): The nickel metal strip that serves to coat the flux-cored powder is subjected to ultrasonic cleaning and hot air drying processes. Using a flux-cored wire forming equipment, the processed nickel metal strip is rolled into a "U-shaped groove" using forming rollers; using a tracked powder feeding device, the flux-cored metal powder obtained in the previous step (1) is added to the "U-shaped groove" according to the flux-cored filling rate requirements; finally, the wire is rolled and sealed by the flux-cored wire forming equipment to obtain a thicker wire.

[0066] Step (3): The coarser welding wire prepared in step (2) is reduced to a diameter of 2.4 mm by a flux-cored welding wire drawing device.

[0067] Step (4): The flux-cored wire prepared in step (3) was subjected to a welding test. The chemical composition of the cladding metal is shown in Table 1. The performance of the cladding metal was tested, and the results are shown in Table 2.

[0068] Example 2

[0069] This embodiment provides another type of submerged arc welding nickel-based flux-cored wire for welding LNG storage tanks, comprising an inner metallic flux-cored powder and an outer nickel-chromium alloy strip that acts as a coating. The outer nickel-chromium alloy strip has a size of 0.5mm × 16mm, and its composition and weight percentage content are: Cr = 17.91%, S = 0.0004%, P = 0.004%, C = 0.001%, Ni balance, with the total amount of each component being 100%. The composition and weight percentage content of the inner flux-cored powder are as follows: Cr = 16.53%, S = 0.0004%, P = 0.004%, Al = 0.025%, Mn = 0.0086%, Co = 1.66%, Ni balance. The particle size of the flux-cored powder is controlled between 80 and 200 mesh, the flux filling rate is 25%, and the diameter of the prepared flux-cored welding wire is 2.4mm. The specific steps are as follows:

[0070] Step (1): Place the metal core powder in a drying oven for drying (150℃, 2h), and mechanically mix the treated core powder to obtain a uniformly mixed core powder.

[0071] Step (2): The nickel metal strip that serves to coat the flux-cored powder is subjected to ultrasonic cleaning and hot air drying processes. Using a flux-cored wire forming equipment, the processed nickel metal strip is rolled into a "U-shaped groove" using forming rollers; using a tracked powder feeding device, the flux-cored metal powder obtained in the previous step (1) is added to the "U-shaped groove" according to the flux-cored filling rate requirements; finally, the wire is rolled and sealed by the flux-cored wire forming equipment to obtain a thicker wire.

[0072] Step (3): The coarser welding wire prepared in step (2) is reduced to a diameter of 2.6 mm by a flux-cored welding wire drawing device.

[0073] Step (4): The flux-cored wire prepared in step (3) was subjected to a welding test. The chemical composition of the cladding metal is shown in Table 1. The performance of the cladding metal was tested, and the results are shown in Table 2.

[0074] Example 3

[0075] This embodiment provides a submerged arc welding nickel-based flux-cored wire for welding LNG storage tanks, comprising an inner metallic flux-cored powder and an outer nickel-chromium alloy strip for coating. The outer nickel-chromium alloy strip has a size of 0.5mm × 16mm, and its composition and weight percentage content are: Cr = 18.95%, S = 0.0004%, P = 0.0004%, C = 0.002%, Ni balance, with the total amount of each component being 100%. The composition and weight percentage content of the inner flux-cored powder are as follows: Cr = 15.13%, S = 0.004%, P = 0.0027%, Al = 0.015%, Mn = 0.012%, Co = 1.45%, Ni balance. The particle size of the flux-cored powder is controlled between 80 and 200 mesh, the flux filling rate is 26%, and the diameter of the prepared flux-cored welding wire is 2.4mm. The specific steps are as follows:

[0076] Step (1): Place the metal core powder in a drying oven for drying (120℃, 3h), and mechanically mix the treated core powder to obtain a uniformly mixed core powder.

[0077] Step (2): The nickel metal strip that serves to coat the flux-cored powder is subjected to ultrasonic cleaning and hot air drying processes. Using a flux-cored wire forming equipment, the processed nickel metal strip is rolled into a "U-shaped groove" using forming rollers; using a tracked powder feeding device, the flux-cored metal powder obtained in the previous step (1) is added to the "U-shaped groove" according to the flux-cored filling rate requirements; finally, the wire is rolled and sealed by the flux-cored wire forming equipment to obtain a thicker wire.

[0078] Step (3): The coarser welding wire prepared in step (2) is reduced to a diameter of 2.2 mm by a flux-cored welding wire drawing device.

[0079] Step (4): The flux-cored wire prepared in step (3) was subjected to a welding test. The chemical composition of the cladding metal is shown in Table 1. The performance of the cladding metal was tested, and the results are shown in Table 2.

[0080] Table 1. Chemical composition of the cladding metal of the welding wire in the examples (mass percentage, %)

[0081] C Si Mn P S Cr Ni Mo Co Fe W Example 1 0.0058 0.12 0.49 0.004 0.0024 13.30 56.72 16.03 1.33 8.635 3.37 Example 2 0.012 0.080 0.40 0.0027 0.0077 12.80 58.27 15.40 1.67 8.007 3.40 Example 3 0.014 0.13 0.53 0.0043 0.0023 12.00 56.79 14.08 1.60 8.975 2.96

[0082] The welding method was submerged arc welding (SAW), using ZT-MNi276 flux. The flux baking temperature was 300℃ for 2 hours, and the welding equipment was a Dimension 1250 welding machine. The welding current was 280-290A, the welding voltage was 25-30V, the heat input was 14.3KJ / cm, the interpass temperature was ≤100℃, and the welding speed was 34cm / min. The base material was 20mm thick 9Ni steel, with a 30° bevel on one side. 9Ni steel was used as a backing plate for cladding tests.

[0083] The chemical composition of the cladding metal of the welding wire, in mass percentage, includes: C: 0.0058%-0.014%, Si: 0.080%-0.13%, Mn: 0.40%-0.53%, P: 0.0027%-0.0043%, S: 0.0023%-0.0077%, Cr: 12.00%-13.30%, Ni: 56.72%-58.27%, Mo: 14.08%-16.03%, Co: 1.33%-1.67%, Fe: 8.007%-8.975%, W: 2.96%-3.40%.

[0084] Observation revealed that the weld formation quality of Examples 1-3 was good, with no hot cracks, obvious spatter, holes, undercut, or other poor forming defects on the surface. The welded test plates were cut using wire cutting and fabricated into standard specimens for mechanical property testing.

[0085] Figure 1 This is a scanning electron microscope image of the weld seam in Embodiment 3 of the present invention. Figure 1 In the image, the darker-colored particles represent columnar austenite matrix crystals, while the lighter-colored particles represent harmful phases distributed in the intergranular spaces of the austenite matrix. It is evident that the number of harmful phases is relatively small.

[0086] Impact tests were conducted according to GB / T 2650-2022: Three impact specimens were taken, a V-notch was made at the center of the weld, and the impact test was carried out at -196℃ to measure the impact energy.

[0087] According to GB / T 2652-2022, longitudinal tensile test of cladding metal was carried out: two tensile specimens were taken and tensile test was carried out at room temperature to measure the yield strength and tensile strength of cladding metal.

[0088] Table 2 Performance test results of the embodiments

[0089] Tensile strength (MPa) Yield strength (Rp0.2 / MPa) <![CDATA[Impact value (J -196℃ ) <!-- 6 -->]]> Example 1 736、737 378、366 88、85、93 Example 2 724、736 375、380 86、87、89 Example 3 748、727 362、384 88、86、92

[0090] As shown in Table 2, after welding LNG storage tanks using the welding wire of the present invention, the tensile strength of the weld is 724-748 MPa, the impact energy of the weld at -196℃ is 85-93 J, the yield strength is 362-384 MPa, and the fracture is fully ductile within the temperature range without ductile-brittle transition. Its KV2 impact energy is greater than 243 J. The data in Table 2 all meet the service requirements of the welded joints for LNG storage tanks in the national standard.

[0091] This invention controls the proportion of harmful phases in the weld metal by optimizing the composition and content of the cladding layer and the flux core. Specifically, the harmful phase is TCP (topologically close-packed phase). By taking SEM images and statistically analyzing the precipitated phases, the area fraction of the precipitated phase was reduced to 0.73%, thereby improving the toughness of the weld metal. As a result, when LNG storage tanks are welded using the welding wire of this invention, the weld cladding metal exhibits low-temperature impact toughness, high tensile strength, and yield strength at -196°C, comparable to 9Ni steel. This allows the excellent properties of the base material to be fully utilized when applied to LNG storage tanks, extending the service life to 50 years.

[0092] Furthermore, the raw materials used in this invention are widely available and inexpensive, and the preparation method is simple and easy to implement. The welding wire obtained using the preparation method of this invention will reduce the production cost of LNG storage tanks by more than 30%, resulting in significant economic benefits.

[0093] The inventors conducted extensive experimental research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0094] Comparative Example 1

[0095] The comparative example is basically the same as Example 3, except that the Co content is 0.1%. The performance of the cladding metal was tested, and the results are shown in Table 3.

[0096] Comparative Example 2

[0097] The comparative example is basically the same as Example 3, except that the Co content is 3%. The performance of the cladding metal was tested, and the results are shown in Table 3.

[0098] Comparative Example 3

[0099] The comparative example is basically the same as Example 3, except that the Cr content in the core is 11%. The performance of the cladding metal was tested, and the results are shown in Table 3.

[0100] Comparative Example 4

[0101] The comparative example is basically the same as Example 3, except that the Cr content in the core is 20%. The performance of the cladding metal was tested, and the results are shown in Table 3.

[0102] Comparative Example 5

[0103] The comparative example is basically the same as Example 3, except that the Mo content in the core is 13%. The performance of the cladding metal was tested, and the results are shown in Table 3.

[0104] Comparative Example 6

[0105] The comparative example is basically the same as Example 3, except that the Mo content in the core is 19%. The performance of the cladding metal was tested, and the results are shown in Table 3.

[0106] Table 3 Comparative Performance Test Results

[0107]

[0108]

[0109] As can be seen from the data in Table 3, an inappropriate element content will affect the strength and / or toughness of the weld, thus proving the advantage of the element content control of the present invention.

[0110] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A nickel-based flux-cored welding wire for austenitic submerged arc welding of LNG storage tanks, characterized in that, The nickel-based flux-cored wire includes a flux core and a cladding layer covering the outside of the flux core; by mass percentage, the cladding layer includes: C<0.015%, Cr: 14.5%-20.0%, S<0.04%, P<0.04%, with the balance being Ni and unavoidable impurities; The core contains, by mass percentage: Co: 0.5%-2.5%, Cr: 13.0%-18.0%, Si < 0.15%, Al: 0.01%-0.03%, Mn: 0.001%-0.02%, Mo: 15%-17%, W: 10%-20%, Fe: 10%-15%, with the balance being Ni and unavoidable impurities.

2. The nickel-based flux-cored welding wire according to claim 1, characterized in that, The core contains: Co: 1.45%-2.5%, Cr: 13.0%-18.0%, Si < 0.15%, Al: 0.015%-0.03%, Mn: 0.0086%-0.02%, Mo: 15%-17%, W: 10%-20%, Fe: 10%-15%, with the balance being Ni and unavoidable impurities.

3. A method for preparing a nickel-based flux-cored welding wire, characterized in that, The method for preparing the nickel-based flux-cored welding wire according to claim 1 or 2 includes the following steps: Step 1: Weigh each component of the core according to the formula, dry them, mix them evenly, and obtain the core powder; Step 2: Weigh the components that make up the coating layer according to the proportions and make them into nickel-chromium alloy strips; Step 3: Roll the nickel-chromium alloy strip into a "U-shaped groove"; Step 4: Fill the "U-shaped groove" with the flux-cored powder from Step 1, seal it, and pull it to reduce its diameter to obtain the flux-cored welding wire.

4. The preparation method according to claim 3, characterized in that, In step 1, the filling rate of the "U-shaped groove" in the core powder is 20%-30%.

5. The preparation method according to claim 3, characterized in that, In step 1, the drying temperature is 100-150℃ and the drying time is 2-4 hours.

6. The preparation method according to claim 3, characterized in that, In step 1, the particle size of the core powder is 80-200 mesh.

7. The preparation method according to claim 3, characterized in that, Step 2 also includes: subjecting the prepared nickel-chromium alloy strip to ultrasonic cleaning and hot air drying in sequence.

8. The preparation method according to claim 3, characterized in that, In step 4, the diameter of the flux-cored welding wire is 2-3 mm.

9. The preparation method according to claim 8, characterized in that, The diameter of the flux-cored welding wire is 2.4-2.6mm.

10. The application of the nickel-based flux-cored welding wire according to claim 1 or 2, or the nickel-based flux-cored welding wire prepared by any one of claims 3-9, in welding LNG storage tanks.

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