Small-size flux-cored wire for high-manganese cryogenic steel of LNG storage tank

Abstract

The application belongs to the technical field of welding materials, and particularly relates to a small-size flux-cored wire for LNG storage tank high-manganese low-temperature steel, which comprises a steel belt sheath and a flux core, and the steel belt sheath comprises the following chemical components in percentage by mass: C: 0.02-0.04%, Si: 0.005-0.01%, Mn: 0.25-0.45%, S: ≤0.005%, P: ≤0.005%, Ti: 0.05-0.1%, B: 0.005-0.01%, Ce: 0.03-0.08%, and the balance is Fe and inevitable impurities. The small-size flux-cored wire for LNG storage tank high-manganese low-temperature steel provided by the application can reach more than 55% by adjusting the composition of the steel belt, controlling the C, Si and Mn proportion, adding trace amounts of Ti, B and Ce, and improving the uniform elongation of the steel belt, so that the target of drawing the small-size welding wire under the super-high filling rate can be achieved, and excellent mechanical properties and process performance can be ensured.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, specifically relating to a small-specification flux-cored welding wire for high-manganese low-temperature steel used in LNG storage tanks. Background Technology

[0002] With the rapid development of the LNG (liquefied natural gas) industry, the demand for cryogenic materials for LNG storage and transportation is increasing. To balance service performance and manufacturing costs, high-manganese cryogenic steel with a Mn content of 22.5%–25.5% has attracted attention. This steel uses Mn to replace Ni and adds appropriate amounts of C, Cr, Cu, N, and other elements, achieving good microstructural stability and low-temperature toughness while controlling costs, thus showing broad application prospects.

[0003] In recent years, flux-cored wire gas shielded welding has seen rapid development in LNG projects. In particular, when using fine wire (0.8-1.4mm) welding, it can effectively reduce or avoid problems such as spatter, poor weld formation, and hard arc. It has advantages such as high deposition efficiency, less welding spatter, excellent weld joint quality, beautiful weld formation, low overall cost, and suitability for all-position automatic welding. At the same time, the composition is highly adjustable, and the flux composition can be easily designed and proportioned according to different performance requirements, making the composition more flexible.

[0004] Due to the high alloy content (over 35%) in the weld metal of high-manganese cryogenic steel, current patented technologies typically employ a co-alloying transition between steel strip and metal powder to ensure adequate alloy transition. However, the presence of alloying elements in the steel strip severely impacts the wire drawing and diameter reduction, making it impossible to draw into small-diameter wires. The flux filling rate is generally 25-35%, with the entire alloy transition being metal powder, leaving no space for slagging agents, which significantly affects the welding process performance of the wire. Currently, there are no small-diameter, ultra-high filler flux-cored welding wires suitable for high-manganese cryogenic steel used in LNG storage tanks on the market, which will be one of the bottlenecks in the practical application of welding high-manganese cryogenic steel for LNG storage tanks. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a small-specification flux-cored welding wire for high-manganese low-temperature steel for LNG storage tanks. By adjusting the composition of the steel strip, the uniform elongation of the steel strip is improved, and it is possible to draw it into a small-specification welding wire under ultra-high filling rate, with excellent comprehensive mechanical properties and welding process performance.

[0006] To achieve the above objectives, the technical solution of the present invention is a small-specification flux-cored welding wire for high-manganese low-temperature steel used in LNG storage tanks, comprising a steel strip sheath and a flux core. The steel strip sheath comprises the following chemical composition by mass percentage: C: 0.02-0.04%, Si: 0.005-0.01%, Mn: 0.25-0.45%, S≤0.005%, P≤0.005%, Ti: 0.05-0.1%, B: 0.005-0.01%, Ce: 0.03-0.08%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, the components of the core and the mass percentage of each component in the core are as follows: rutile 6-10%, zircon sand 4-8%, alumina 1-3%, feldspar 1-3%, sodium fluoride 1.5-4%, electrolytic manganese 55-60%, molybdenum powder 1-2%, nickel powder 3-6%, chromium carbide 10-14%, ferrosilicon 1-4%, and the balance being iron powder.

[0008] Furthermore, the thickness × width of the steel strip outer sheath is 0.40 × 14 mm to 0.50 × 14 mm, and the diameter of the flux-cored welding wire is 0.8 mm to 1.4 mm.

[0009] Furthermore, the mass of the flux core accounts for 35%-45% of the total mass of the flux-cored welding wire.

[0010] Furthermore, the rutile is 98° rutile, wherein the mass percentage of TiO2 is ≥98%, S≤0.01%, and P≤0.01%; the mass percentage of C in the chromium carbide is 12-14%, and the mass percentage of Cr is 82-86%; the mass percentage of Si in the ferrosilicon is 44-49%, and the alumina is α-alumina calcined at 1200℃-1400℃.

[0011] Furthermore, the particle size of the core component is 120–180 μm.

[0012] Preferably, the steel strip sheath comprises the following chemical composition by mass percentage: C: 0.02%, Si: 0.01%, Mn: 0.45%, S: 0.005%, P: 0.0038%, Ti: 0.08%, B: 0.005%, Ce: 0.065%, with the balance being Fe and unavoidable impurities; the thickness × width of the steel strip sheath is 0.40 × 14 mm; the composition of the flux core and the mass percentage of each component in the flux core are as follows: rutile 8%, zircon sand 4%, alumina 2%, feldspar 3%, sodium fluoride 4%, electrolytic manganese 55%, molybdenum powder 1.5%, nickel powder 6%, chromium carbide 13%, ferrosilicon 2%, with the balance being iron powder; the mass of the flux core accounts for 45% of the total mass of the flux-cored welding wire.

[0013] Preferably, the steel strip sheath comprises the following chemical composition by mass percentage: C: 0.04%, Si: 0.007%, Mn: 0.35%, S: 0.0043%, P: 0.005%, Ti: 0.05%, B: 0.0082%, Ce: 0.08%, with the balance being Fe and unavoidable impurities; the thickness × width of the steel strip sheath is 0.50 × 14 mm; the composition of the flux core and the mass percentage of each component in the flux core are as follows: rutile 10%, zircon sand 8%, alumina 1%, feldspar 1%, sodium fluoride 3%, electrolytic manganese 60%, molybdenum powder 1%, nickel powder 3%, chromium carbide 10%, ferrosilicon 1%, with the balance being iron powder; the mass of the flux core accounts for 35% of the total mass of the flux-cored welding wire.

[0014] Preferably, the steel strip sheath comprises the following chemical composition by mass percentage: C: 0.03%, Si: 0.005%, Mn: 0.25%, S: 0.0041%, P: 0.0044%, Ti: 0.1%, B: 0.01%, Ce: 0.03%, with the balance being Fe and unavoidable impurities; the thickness × width of the steel strip sheath is 0.45 × 14 mm; the composition of the flux core and the mass percentage of each component in the flux core are as follows: rutile 6%, zircon sand 5%, alumina 3%, feldspar 2%, sodium fluoride 1.5%, electrolytic manganese 58%, molybdenum powder 2%, nickel powder 4%, chromium carbide 14%, ferrosilicon 4%, with the balance being iron powder; the mass of the flux core accounts for 40% of the total mass of the flux-cored welding wire.

[0015] Furthermore, the welding conditions for the flux-cored welding wire are as follows: the shielding gas is a mixture of [80% Ar + 20% CO2], the welding current is 160-220A, the welding voltage is 24-30V, and the interpass temperature is ≤100℃.

[0016] The design principle of the small-specification flux-cored welding wire for high-manganese cryogenic steel LNG storage tanks of the present invention is as follows:

[0017] The small-diameter flux-cored welding wire for high-manganese cryogenic steel used in LNG storage tanks of this invention has a diameter of 0.8mm to 1.4mm. The steel strip outer skin has a low C, Si, S, and P content, and an appropriate amount of Mn is added. By controlling the C, Si, and Mn ratio, the uniform elongation of the steel strip outer skin is improved, and the yield strength is reduced. At the same time, trace amounts of Ti, B, and Ce are added to promote the formation of the TiB8Ce phase, forming nanoscale TiB2 and CeB6 ceramic phase particles. This changes the morphology of ferrite from needle-like to equiaxed blocky, and the size becomes smaller. Secondly, it reduces the contact area between the crystal nucleus and impurities, reduces the inclusion level, and ensures the uniformity of the material structure. With a uniform elongation of ≥55% for the steel strip outer skin of this invention, the goal of drawing small-diameter flux-cored welding wire under ultra-high filler ratio can be achieved.

[0018] The flux core components of this invention mainly serve as alloy transition and deoxidation slag-forming agents. As can be seen from the above steel strip design principle, the flux core filling rate of this invention can reach 35-45%. While fully meeting the alloy transition requirements, there is a large margin for adding slag-forming agents and other substances that improve welding process performance. The overall mechanical properties and welding process performance are excellent.

[0019] The particle size of the flux core component of this invention is controlled at 120-180 μm, which can improve the flowability of the powder and facilitate powder filling in the production of flux-cored welding wire. Because the particle size has a great influence on the flowability of the powder, when the particle size decreases, the specific surface area of ​​the powder increases, resulting in increased friction, increased adhesion and aggregation of the powder, and poorer flowability. When the particle size increases, the wire is prone to breakage during the production drawing process and there is a lot of spatter during welding.

[0020] Rutile's main component is TiO2, which is used as a slag-forming agent and arc stabilizer. The addition of TiO2 can improve arc stability, optimize wetting conditions, improve slag fluidity and coverage, and improve weld surface quality, ensuring good applicability to all-position welding processes. The 98° rutile added in this invention is of high grade, with high TiO2 content and low content of other impurities, oxides, S, and P, which is beneficial to improving weld quality. When its addition amount is greater than 10%, the slag becomes thicker, the permeability becomes worse, and the weld is prone to indentation or even porosity; when the addition amount is less than 6%, the welding process performance deteriorates.

[0021] Zircon sand's main component is ZrO2, and its primary function is to form slag and adjust its physical properties, improving slag removal. In this invention, the amount of zircon sand added is 4-8%. Too little zircon sand has no effect, while too much can cause large molten droplets to occasionally burst out during welding, and the molten pool will become too large, which is not conducive to all-position welding.

[0022] Alumina has a melting point of 2050℃, which differs significantly from the high-temperature linear expansion coefficient of steel, thus improving slag removal properties. In this invention, α-alumina calcined at 1200℃–1400℃ is selected, exhibiting low water of crystallization content and good moisture resistance. The addition amount is 1–3%. As the content increases, the droplet size decreases, and the melting point and viscosity of the slag increase, which is beneficial for all-position welding performance. However, excessive content can easily lead to the formation of glassy substances with SiO2, MgO, Na2O, K2O, etc., under high-temperature conditions, thereby reducing the permeability of the slag and easily causing indentation defects in the weld.

[0023] Feldspar's main component is SiO2, which is also a major component of slag. It can adjust the slag's melting point and viscosity, increase the arc voltage, refine the molten droplets, reduce welding spatter, improve weld formation, and give the slag good coverage. In this invention, the amount of feldspar added is 1-3%. As the SiO2 content increases, the weld surface becomes brighter, the slag color becomes darker, which is beneficial for slag removal, but at the same time, the low-temperature toughness of the weld gradually decreases.

[0024] Sodium fluoride can lower the eutectic point of slag, reduce its viscosity and surface tension, which is beneficial for improving slag removal and weld surface formation. Sodium fluoride can decompose at high temperatures to form F... - It can be used with H + It combines with highly stable HF to remove hydrogen from the weld and improve resistance to indentation, significantly enhancing the low-temperature toughness of the weld. When its addition exceeds 4%, welding spatter increases and the slag becomes thinner, resulting in poor all-position welding of the welding wire. When the addition is less than 1.5%, the hydrogen removal capacity is insufficient, and porosity and indentation are prone to occur.

[0025] Mn in electrolytic manganese is an element that expands the austenite region and stabilizes the austenite structure. When the Mn content in the weld metal is greater than 20%, a fully austenitic structure can be formed, the low-temperature brittle transition temperature disappears, and the low-temperature impact toughness of the weld metal is improved. Electrolytic manganese can also participate in deoxidation to reduce the oxygen content of the weld metal and increase the strength and crack resistance of the weld metal. The optimal addition amount of electrolytic manganese is 55-60%.

[0026] In molybdenum powder, Mo is dissolved in austenite or exists in the form of strong carbides in the weld to improve the weld strength. Mo can also reduce the solid-liquid coexistence range, which can effectively inhibit the occurrence of hot cracks.

[0027] Ni in nickel powder can lower the low-temperature brittle transition temperature and has a solid solution strengthening effect, which can improve the strength and low-temperature impact toughness of weld metal. Adding an appropriate amount of Ni can also improve its corrosion resistance in saline atmospheres.

[0028] In chromium carbide, carbon (C) is an austenitizing element that can form carbides with chromium (Cr) and molybdenum (Mo), thereby increasing the strength of austenitic weld metal. Cr can form a dense oxide film on the steel surface, increasing the electrode potential and producing a passivation effect. Because Cr can partially replace Fe to form ferrochromium hydroxyl oxides, the rust layer exhibits cation selectivity, inhibiting the growth of chloride ions (Cl). － SO4 2- The rust layer penetrates into the substrate surface, thus providing protection. In this invention, the mass percentage of C in chromium carbide is 12-14%, and the mass percentage of Cr is 82-86%. Within this content range, the optimal weld microstructure with C and Cr content can be obtained, resulting in better comprehensive mechanical properties.

[0029] Ferrosilicon, as a alloying agent, also has a deoxidizing effect. Excessive ferrosilicon content increases the acidity and viscosity of the slag, leads to excessively high tensile strength, and reduces the impact toughness of the weld. Conversely, insufficient ferrosilicon content results in weld strength that fails to meet requirements. In this invention, the ferrosilicon contains 44-49% Si by mass, within which good processing and mechanical properties are achieved.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The small-specification flux-cored welding wire for high-manganese low-temperature steel of LNG storage tank provided by the present invention improves the uniform elongation of the steel strip by adjusting the composition of the steel strip, controlling the proportion of C, Si and Mn, and adding trace amounts of Ti, B and Ce, which can reach more than 55%, and can achieve the goal of drawing into small-specification welding wire under ultra-high filling rate.

[0032] (2) The small-diameter flux-cored welding wire for high-manganese low-temperature steel of LNG storage tank provided by the present invention, through adjustment of flux composition and control of particle size, can achieve ultra-high filling rate, add slag-forming agent and other substances to improve welding process performance, and can be drawn into small-diameter welding wire. It has excellent comprehensive mechanical properties and welding process performance. Its deposited metal has tensile strength ≥700MPa, yield strength ≥400MPa, elongation ≥40%, and Akv ≥80J at -196℃. The weld CTOD test characteristic value δm meets the standard requirements (≥0.2mm) and has excellent crack resistance. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The chemical composition and specifications of the steel strip outer sheath of the small-specification flux-cored welding wire for high-manganese low-temperature steel of LNG storage tanks provided in Examples 1-3 of this invention are shown in Table 1. The composition ratio, filling rate and welding wire diameter of the flux core are shown in Table 2. The wires are manufactured using conventional flux-cored welding wire manufacturing processes.

[0035] Table 1. Chemical composition (mass percentage) of the steel strip outer sheath of flux-cored welding wire.

[0036]

[0037] Table 2. Flux core formulation of flux-cored welding wire (mass percentage %)

[0038]

[0039] Mechanical properties of deposited metal and CTOD (crack tip opening displacement) tests were conducted on the flux-cored welding wires prepared using the steel strip outer sheath and flux core of Examples 1-3. During welding, a [80% Ar + 20% CO2] mixture was used as the shielding gas, the welding current was 160–220 A, the welding voltage was 24–30 V, and the interpass temperature was ≤100℃. The mechanical properties of deposited metal of the welding wires of Examples 1-3 are shown in Table 3, and the CTOD test results of the weld are shown in Table 4.

[0040] Table 3 Mechanical properties of deposited metal

[0041] Example Rm / MPa ReL / MPa A / ％ Akv(J) / -196℃ 1 714 525 40 87 95 110 2 718 513 41.5 96 81 105 3 721 508 42.5 90 84 92

[0042] Table 4 Results of CTOD test on weld seams

[0043] Example Test temperature / °C Width / mm Height / mm δm / mm Gap position 1 -165 20.12 40.21 0.51 weld center 2 -165 20.08 40.18 0.50 weld center 3 -165 20.15 40.35 0.52 weld center

[0044] As can be seen from Tables 3 and 4, the deposited metal and weld joint of the small-gauge flux-cored welding wire for high-manganese cryogenic steel of LNG storage tanks provided by this invention have the following comprehensive performance: tensile strength ≥700MPa, yield strength ≥400MPa, elongation ≥40%, Akv ≥80J at -196℃, and the CTOD test characteristic value δm meets the standard requirements (≥0.2mm), which can fully meet the practical application requirements of welding high-manganese cryogenic steel for LNG storage tanks.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A small-gauge flux-cored welding wire for high-manganese cryogenic steel used in LNG storage tanks, comprising a steel strip sheath and a flux core, characterized in that, The outer sheath of the steel strip comprises the following chemical components by mass percentage: C: 0.02-0.04%, Si: 0.005-0.01%, Mn: 0.25-0.45%, S≤0.005%, P≤0.005%, Ti: 0.05-0.1%, B: 0.005-0.01%, Ce: 0.03-0.08%, with the balance being Fe and unavoidable impurities; the composition of the core and the mass percentage of each component in the core are as follows: rutile 6-10%, zircon sand 4-8%, alumina 1-3%, feldspar 1-3%, sodium fluoride 1.5-4%, electrolytic manganese 55-60%, molybdenum powder 1-2%, nickel powder 3-6%, chromium carbide 10-14%, ferrosilicon 1-4%, with the balance being iron powder.

2. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 1, characterized in that: The thickness × width of the steel strip outer sheath is 0.40 × 14 mm to 0.50 × 14 mm, and the diameter of the flux-cored welding wire is 0.8 mm to 1.4 mm.

3. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 2, characterized in that: The mass of the flux core accounts for 35%-45% of the total mass of the flux core welding wire.

4. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 1, characterized in that: The rutile is 98° rutile, wherein the mass percentage of TiO2 is ≥98%, S≤0.01%, and P≤0.01%; the mass percentage of C in the chromium carbide is 12-14%, and the mass percentage of Cr is 82-86%; the mass percentage of Si in the ferrosilicon is 44-49%, and the alumina is α-alumina calcined at 1200℃-1400℃.

5. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 1, characterized in that: The particle size of the core component is 120–180 μm.

6. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 3, characterized in that: The steel strip sheath comprises the following chemical composition by mass percentage: C: 0.02%, Si: 0.01%, Mn: 0.45%, S: 0.005%, P: 0.0038%, Ti: 0.08%, B: 0.005%, Ce: 0.065%, with the balance being Fe and unavoidable impurities; the thickness × width of the steel strip outer sheath is 0.40 × 14 mm; the composition of the flux core and the percentage of each component by mass are as follows: rutile 8%, zircon sand 4%, alumina 2%, feldspar 3%, sodium fluoride 4%, electrolytic manganese 55%, molybdenum powder 1.5%, nickel powder 6%, chromium carbide 13%, ferrosilicon 2%, with the balance being iron powder; the mass of the flux core accounts for 45% of the total mass of the flux-cored welding wire.

7. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 3, characterized in that: The steel strip sheath comprises the following chemical composition by mass percentage: C: 0.04%, Si: 0.007%, Mn: 0.35%, S: 0.0043%, P: 0.005%, Ti: 0.05%, B: 0.0082%, Ce: 0.08%, with the balance being Fe and unavoidable impurities; the thickness × width of the steel strip sheath is 0.50 × 14 mm; the composition of the flux core and the mass percentage of each component in the flux core are as follows: rutile 10%, zircon sand 8%, alumina 1%, feldspar 1%, sodium fluoride 3%, electrolytic manganese 60%, molybdenum powder 1%, nickel powder 3%, chromium carbide 10%, ferrosilicon 1%, with the balance being iron powder; the mass of the flux core accounts for 35% of the total mass of the flux-cored welding wire.

8. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 3, characterized in that: The steel strip sheath comprises the following chemical composition by mass percentage: C: 0.03%, Si: 0.005%, Mn: 0.25%, S: 0.0041%, P: 0.0044%, Ti: 0.1%, B: 0.01%, Ce: 0.03%, with the balance being Fe and unavoidable impurities; the thickness × width of the steel strip sheath is 0.45 × 14 mm; the composition of the flux core and the mass percentage of each component in the flux core are as follows: rutile 6%, zircon sand 5%, alumina 3%, feldspar 2%, sodium fluoride 1.5%, electrolytic manganese 58%, molybdenum powder 2%, nickel powder 4%, chromium carbide 14%, ferrosilicon 4%, with the balance being iron powder; the mass of the flux core accounts for 40% of the total mass of the flux-cored welding wire.

9. The small-diameter flux-cored welding wire for high-manganese cryogenic steel in LNG storage tanks as described in claim 1, characterized in that: The welding conditions for the flux-cored welding wire are as follows: the shielding gas is a mixture of [80%Ar+20%CO2], the welding current is 160-220A, the welding voltage is 24-30V, and the interpass temperature is ≤100℃.

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