Flux core for high manganese steel, welding wire, application and deposited metal

Abstract

The invention provides a flux core for high manganese steel, a welding wire, application and deposited metal. The flux core comprises the following components: 32.0 to 45.0 wt% of metal manganese, 18.0 to 32.0 wt% of nickel powder, 6.0 to 12.0 wt% of aluminum powder, 0.7 to 1.5 wt% of graphite, 4.0 to 8.0 wt% of nitrided ferrochrome, 2.0 to 2.5 wt% of chromium carbide, 1.5 to 3.5 wt% of rare earth ferrosilicon, 1.0 to 2.5 wt% of nickel-magnesium alloy, 1.0 to 2.0 wt% of aluminum-magnesium alloy, 5.0 to 8.0 wt% of rutile, 3.0 to 5.0 wt% of potassium feldspar and 0.5 to 2.5 wt% of zirconium quartz. According to the flux-cored wire, Mn, C, Ni, Cr and other alloy elements are reasonably matched, a certain amount of Al element is added, the stacking fault energy is improved, the Mn content is reduced on the premise that the weld joint structure and low-temperature toughness are ensured, the problems that an existing flux-cored wire is large in welding smoke and serious in manganese steam are effectively solved, and the low-harm and efficient welding requirements of high manganese steel are met.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and more specifically, to a flux core for high manganese steel, welding wire and its application, and deposited metal. Background Technology

[0002] With increasing global emphasis on energy conservation and environmental protection, liquefied natural gas (LNG), as an important clean energy source, has attracted particular attention regarding its storage technology. 9% Ni steel, due to its excellent toughness and high strength at extremely low temperatures and the fact that it can be safely used without post-weld stress-relieving heat treatment, has become a primary material for manufacturing large LNG storage tanks. However, it suffers from relatively high prices and construction costs.

[0003] High-manganese austenitic low-temperature steel employs a manganese-for-nickel technology, using a higher manganese content to control austenite stability. This significantly reduces material costs while ensuring low-temperature strength and toughness, and it has been gradually used in the manufacture of large land-based LNG storage tanks and marine fuel tanks. To meet welding performance and processability requirements, related flux-cored welding wires have been developed.

[0004] For example, Chinese patent CN109623199A discloses a metal-cored flux-cored welding wire for gas metal arc welding of ultra-low temperature high-manganese steel. The chemical composition of the metal-cored wire is: 20-25 wt% electrolytic manganese, 1-3 wt% manganese-silicon alloy, 3-8 wt% nickel powder, 2-6 wt% low-carbon ferrochrome, 2-4 wt% tungsten powder, 0.1-2.0% wt% potassium feldspar, and the balance being iron powder. Chinese patent CN117324828A discloses a small-diameter flux-cored welding wire for high-manganese low-temperature steel used in LNG storage tanks. The chemical composition of the flux-cored wire is: 6-10% rutile, 4-8% zircon sand, 1-3% alumina, 1-3% feldspar, 1.5-4% sodium fluoride, 55-60% electrolytic manganese, 1-2% molybdenum powder, 3-6% nickel powder, 10-14% chromium carbide, 1-4% ferrosilicon, and the balance being iron powder. Chinese patent CN113547255A discloses a flux-cored welding wire for ultra-low temperature high-manganese steel suitable for all-position welding. The chemical composition of the flux core is: 2-6% marble, 2-6% potassium titanate, 0.5-2.5% sodium fluoride, 60-70% metallic manganese, 6-8% metallic chromium, 4-8% ferrochrome nitride, 8-12% nickel powder, 2-6% molybdenum powder, 1-2% ferrovanadium, 1-2% copper powder, 0.2-0.4% bismuth oxide, 0.5-1.5% graphite, and the balance being iron powder. However, due to the manganese content exceeding 20 wt%, the above-mentioned design results in high manganese vapor production during welding, making welding fumes and manganese vapor problems more prominent and a significant bottleneck for the large-scale application of high-manganese steel. Summary of the Invention

[0005] The problem solved by this invention is that existing flux-cored welding wires for high manganese steel have problems such as large amounts of smoke and dust and serious manganese vapor during the welding process, which makes it difficult to meet the requirements of low-hazard and high-efficiency welding of high manganese steel.

[0006] To address the aforementioned problems, this invention provides a high-manganese steel core comprising the following components: 32.0–45.0 wt% metallic manganese, 18.0–32.0 wt% nickel powder, 6.0–12.0 wt% aluminum powder, 0.7–1.5 wt% graphite, 4.0–8.0 wt% ferrochromium nitride, 2.0–2.5 wt% chromium carbide, 1.5–3.5 wt% rare earth ferrosilicon, 1.0–2.5 wt% nickel-magnesium alloy, 1.0–2.0 wt% aluminum-magnesium alloy, 5.0–8.0 wt% rutile, 3.0–5.0 wt% potassium feldspar, and 0.5–2.5 wt% zircon.

[0007] This application adopts a Fe-Mn-C-Al composition design based on the existing high-manganese austenitic low-temperature steel composition, increases the C content and adds certain Ni and N elements to improve the stability of the austenitic structure. At the same time, by adding Al elements to adjust the stacking fault energy, the formation of martensite is effectively avoided. Under the premise of ensuring weld structure and low-temperature toughness, the Mn content is significantly reduced.

[0008] The functions of each raw material component in the core are detailed below: Carbon (C): C is an important austenite-forming element in steel, and a certain carbon content is an important factor in ensuring the stability of austenite in weld metal under extremely low temperature impact. When the carbon content is below 0.40%, a small amount of martensite will appear in the weld, and when it exceeds 0.70%, weld porosity defects are prone to occur. Therefore, in this invention, the carbon content is preferably controlled between 0.40% and 0.70%.

[0009] Manganese (Mn): Mn expands the austenite phase region, significantly lowers the martensite transformation temperature, stabilizes the austenite microstructure, and controls the stacking fault energy. This invention employs an appropriate Mn content and adds a certain amount of Al to ensure the alloy has a high stacking fault energy, promotes the TWIP (twin-induced plasticity) effect, and inhibits the martensitic phase transformation in the steel during deformation. Based on experimental results, the Mn content in this invention is controlled between 10.0% and 14.0%.

[0010] Nickel (Ni): Ni is an austenite-forming element and can increase the stacking fault energy of weld metal, improving the low-temperature impact toughness of welded joints. To ensure good ductility and toughness of the weld metal, an appropriate amount of Ni should be added to the composition system. It works synergistically with C, Mn, and N to control the weld microstructure and ensure that the weld metal maintains an austenitic structure at low temperatures. Low Ni content results in martensite formation in the weld, while excessively high Ni content easily leads to hot cracking. Experimental comparisons have determined that the optimal Ni content is 6.0–10.0%.

[0011] Aluminum (Al): Al effectively increases the stacking fault energy of steel, ensuring that the weld metal retains a high stacking fault energy at low temperatures. This promotes the formation of low-temperature deformation twins, improving the strength and ductility of the steel. Choosing an appropriate Al content is crucial for ensuring that the weld metal exhibits deformation twinning at low temperatures and possesses high ductility and toughness. However, excessive Al content leads to the formation of δ-ferrite in the weld microstructure and deteriorates weldability. Therefore, the Al content is set at 1.5–3.5%.

[0012] Silicon (Si): Adding Si can strengthen the weld through solid solution, while also inhibiting cross-slip and promoting planar slip, increasing the number of stacking faults, and promoting twinning deformation. Furthermore, Si plays a role in deoxidation and improving the fluidity of the molten pool during welding. A silicon content below 0.50% leads to insufficient deoxidation and poor weld processability, while a content exceeding 0.90% reduces weld toughness. Therefore, this invention sets the Si content to 0.50–0.90%.

[0013] Chromium (Cr): Chromium has a strengthening effect in high-manganese steel, and a certain amount of chromium can improve the corrosion resistance of welds. However, when the chromium content is high, chromium-based carbides such as (FeCr)3C are formed, leading to a decrease in toughness. Based on experimental results, this invention determines the chromium content to be 1.0–2.0%.

[0014] Nitrogen (N): N is a solid solution strengthening element, and its content is best limited to below 0.3 wt%. If the N content exceeds 0.3 wt%, the low-temperature impact toughness will decrease, and porosity defects will easily occur. Therefore, it is not advisable to have an excessively high N content. Based on the results of comparative experiments, the suitable range of N content is determined to be 0.10–0.20%.

[0015] In other words, in this invention, graphite, metallic manganese, nickel powder, and aluminum powder respectively transition C, Mn, Ni, and Al alloying elements to ensure that the composition of the deposited metal is within the set range; ferrochrome nitride, chromium carbide, and rare earth ferrosilicon transition Cr, N, Si, and other elements, and also provide C; nickel-magnesium alloy and aluminum-magnesium alloy, as strong reducing agents, mainly have a deoxidizing effect, reducing the oxidation of metallic manganese, while adjusting the basicity of the weld slag, and also assisting in the transition of Ni and Al elements; zircon, rutile, and potassium feldspar mainly act as slag-forming agents, while also stabilizing the arc, reducing welding spatter, and improving weld bead formation; rare earth ferrosilicon transitions rare earth elements, which mostly exist in the form of internal adsorption at grain boundaries, reducing the interfacial energy of the grain boundaries and hindering the growth of carbides along the grain boundaries. At the same time, rare earth elements can form high-melting-point rare earth sulfides with sulfur, which purify the weld metal and inhibit the precipitation of carbides at the grain boundaries.

[0016] Preferably, the high-manganese steel core is composed of the following components: 34.0–45.0 wt% metallic manganese, 20.0–24.5 wt% nickel powder, 6.5–12.0 wt% aluminum powder, 1.0–1.5 wt% graphite, 4.0–7.5 wt% ferrochromium nitride, 2.2–2.5 wt% chromium carbide, 2.0–3.3 wt% rare earth ferrosilicon, 1.2–2.5 wt% nickel-magnesium alloy, 1.2–2.0 wt% aluminum-magnesium alloy, 7.3–8.0 wt% rutile, 3.5–5.0 wt% potassium feldspar, and 0.5–2.0 wt% zircon.

[0017] The present invention also provides a welding wire for high manganese steel, the welding wire comprising a steel strip and the aforementioned flux core, wherein the flux core is filled in the steel strip and its weight is 25% to 35% of the weight of the welding wire. As an example of the present invention, the steel strip is a low-carbon steel strip, such as ordinary SPCC carbon steel strip, and the high manganese steel is a high-manganese austenitic steel with a manganese content of 22-25%.

[0018] Preferably, the filling rate of the flux core is 31% to 33%. Preferably, the diameter of the welding wire is φ1.20mm to φ2.40mm.

[0019] The present invention also discloses the application of the above-mentioned high-manganese steel welding wire in the preparation of LNG storage tanks.

[0020] This invention also discloses a weld metal for welding high-manganese steel, formed using the aforementioned high-manganese steel welding wire. The chemical composition of the weld metal includes Mn, Ni, and Al, with their contents expressed as Mn%, Ni%, and Al%, respectively. and The shielding gas used in the welding process is CO2.

[0021] Preferably, the chemical composition of the weld metal includes: C 0.40–0.70 wt%, Mn 10.0–14.0 wt%, Si 0.50–0.90 wt%, Cr 1.0–2.0 wt%, Ni 6.0–10.0 wt%, Al 1.5–3.5 wt%, N 0.10–0.20 wt%, S ≤ 0.010 wt%, and P ≤ 0.012 wt%. Preferably, the chemical composition of the weld metal includes: C 0.40–0.70 wt%, Mn 10.0–14.0 wt%, Si 0.50–0.90 wt%, Cr 1.0–2.0 wt%, Ni 6.0–10.0 wt%, Al 1.5–3.5 wt%, N 0.10–0.20 wt%, S ≤ 0.010 wt%, P ≤ 0.012 wt%, with the balance being Fe.

[0022] Compared with the prior art, the flux core, welding wire and deposited metal described in the embodiments of the present invention have the following beneficial effects: (1) The welding wire adopts the comprehensive effect of multiple elements such as C, Mn, Al and Ni, and achieves the stability control of austenitic structure on the basis of reducing manganese content. The manganese content is reduced to below 14%, which greatly reduces the pollution of manganese vapor during welding; (2) The welding wire is further reduced by adding nickel-magnesium alloy and aluminum-magnesium alloy strong reducing agents to reduce the oxidation and volatilization of manganese, which further reduces the generation of manganese vapor; (3) The weld metal formed has excellent toughness at low temperature, and KV2 at -196℃ is above 60J. Detailed Implementation

[0023] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Without conflict, the technical features of the embodiments of the present invention can be combined with each other.

[0024] 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 manganese content of 22.5%–25.5% has attracted attention. This steel uses manganese to replace nickel 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. High-manganese steel is used to manufacture LNG tanks via welding, requiring matching welding wire. The high manganese content of existing flux-cored welding wires for high-manganese steel leads to significant problems with fumes and manganese vapor during welding.

[0025] To address this, Chinese Patent CN116352312A discloses a gas-shielded flux-cored welding wire for high-manganese austenitic low-temperature steel. It uses steel strip with high manganese content, which reduces the filling rate of flux powder. However, the steel strip contains 26-28 wt% manganese, and manganese fumes are still quite severe during the welding process. Chinese Patent CN113414518A discloses a low-dust multi-purpose high-manganese steel flux-cored welding wire and its preparation process. It uses titanium dioxide to coat the manganese particles, which can reduce the dense yellow fumes generated during the welding process to a certain extent. However, since the flux powder contains 60-70 wt% manganese powder, a large amount of manganese vapor is still formed. At the same time, the addition of high titanium dioxide causes slag modification and affects the welding processability. Chinese Patent CN114799430A discloses a welding method for low-temperature high-manganese steel butt joints, which uses nickel-based welding materials such as ENiCrMo-6 welding rods and ERNiCrMo-4 welding wire to build up a transition layer to reduce welding manganese fumes. However, this method suffers from drawbacks such as high welding cost and low efficiency. Therefore, the applicant proposes the following technical solution: Example 1

[0026] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by weight percentage, comprises the following components: 40.0% manganese, 21.0% nickel powder, 12.0% aluminum powder, 1.0% graphite, 7.5% ferrochrome nitride, 2.2% chromium carbide, 2.0% rare earth ferrosilicon, 1.2% nickel-magnesium alloy, 1.8% aluminum-magnesium alloy, 7.3% rutile, 3.5% potassium feldspar, and 0.5% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 31%. Example 2

[0027] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by weight percentage, comprises the following components: 45.0% manganese, 24.5% nickel powder, 6.5% aluminum powder, 1.2% graphite, 4.0% ferrochrome nitride, 2.5% chromium carbide, 2.5% rare earth ferrosilicon, 2.0% nickel-magnesium alloy, 1.2% aluminum-magnesium alloy, 5.5% rutile, 4.1% potassium feldspar, and 1.0% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 32%. Example 3

[0028] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by mass percentage, comprises the following components: 34.0% manganese, 20.0% nickel powder, 12.0% aluminum powder, 1.5% graphite, 7.5% ferrochrome nitride, 2.2% chromium carbide, 3.3% rare earth ferrosilicon, 2.5% nickel-magnesium alloy, 2.0% aluminum-magnesium alloy, 8.0% rutile, 5.0% potassium feldspar, and 2.0% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 33%. Comparative Example 1

[0029] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by mass percentage, comprises the following components: 32.0% manganese, 31.0% nickel powder, 8.0% aluminum powder, 1.5% graphite, 6.8% ferrochrome nitride, 2.3% chromium carbide, 3.0% rare earth ferrosilicon, 2.2% nickel-magnesium alloy, 2.0% aluminum-magnesium alloy, 6.0% rutile, 4.0% potassium feldspar, and 1.2% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 33%. Comparative Example 2

[0030] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by weight percentage, comprises the following components: 37.0% manganese, 20.0% nickel powder, 8.0% aluminum powder, 1.2% graphite, 8.0% ferrochrome nitride, 2.5% chromium carbide, 3.5% rare earth ferrosilicon, 2.5% nickel-magnesium alloy, 1.8% aluminum-magnesium alloy, 8.0% rutile, 5.0% potassium feldspar, and 2.5% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 33%. Comparative Example 3

[0031] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by weight percentage, comprises the following components: 42.0% manganese, 30.0% nickel powder, 4.0% aluminum powder, 1.2% graphite, 6.8% ferrochrome nitride, 2.0% chromium carbide, 2.5% rare earth ferrosilicon, 1.5% nickel-magnesium alloy, 1.0% aluminum-magnesium alloy, 5.5% rutile, 3.0% potassium feldspar, and 0.5% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 33%. Comparative Example 4

[0032] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by weight percentage, comprises the following components: 65.0% manganese, 9.0% nickel powder, 0% aluminum powder, 1.0% graphite, 0% ferrochrome nitride, 2.0% chromium carbide, 2.5% rare earth ferrosilicon, 2.0% nickel-magnesium alloy, 2.0% aluminum-magnesium alloy, 8.0% rutile, 5.0% potassium feldspar, and 3.5% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 33%. Comparative Example 5

[0033] The flux-cored welding wire comprises a steel strip and a flux core filled within the steel strip. The flux core, by mass percentage, comprises the following components: 70.0% manganese, 6.0% nickel powder, 0% aluminum powder, 1.0% graphite, 0% ferrochrome nitride, 2.0% chromium carbide, 2.5% rare earth ferrosilicon, 2.0% nickel-magnesium alloy, 2.0% aluminum-magnesium alloy, 7.5% rutile, 4.0% potassium feldspar, and 3.0% zircon. The flux-cored welding wire has a diameter of 1.2 mm and a filler content of 33%.

[0034] In Examples 1-3 and Comparative Examples 1-5, the same ordinary steel strip was used, and the welding wire was prepared according to the conventional flux-cored welding wire manufacturing process. The formulation composition is shown in Table 1. As can be seen from Table 1, Comparative Examples 1-3 do not satisfy Formula 1 or 2, while Comparative Examples 4-5 are high-manganese flux-cored welding wires with a manganese content greater than 20 wt%.

[0035] Table 1. Formulation composition of flux-cored welding wire

[0036] The flux-cored welding wires prepared in Examples 1-3 and Comparative Examples 1-5 were used to weld test plates according to industry standards. The welding current was (200±10) A, the welding voltage was (27±2) V, and the shielding gas was 100% CO2. The chemical composition and properties of the weld metal were tested, and the results are shown in Table 2-3.

[0037] Table 2 Chemical composition (wt%) of the deposited metal in the examples and comparative examples

[0038] Table 3 Performance test results of the deposited metal in the examples and comparative examples

[0039] As shown in Table 3, the yield strength of the weld metal formed by the flux-cored wires in Examples 1-3 of this application all exceed 440 MPa, and the Charpy impact absorption energy at -196℃ is over 60 J, ensuring a good strength-toughness match. However, the low-temperature impact value of the weld metal formed by the flux-cored wires in Comparative Examples 1-3 is significantly reduced, failing to meet Formula 1 or Formula 2. While the high-manganese flux-cored wires in Comparative Examples 4-5 with a manganese content greater than 20 wt% exhibit acceptable impact toughness, their strength is low, and welding fumes are extremely severe during the welding process.

[0040] Welding processability was mainly assessed by examining factors such as welding fume emission, resistance to hot cracking, crack rate, and welding spatter, according to the welding processability evaluation items shown in Table 4. Welding tests were conducted on flat plates and in bevels, and the welding processability of the flux-cored welding wires prepared in Examples 1-3 and Comparative Examples 1-5 was evaluated by professional welders. The results are shown in Table 5.

[0041] Table 4 Welding Processability Evaluation Criteria

[0042] Table 5 Welding processability evaluation results

[0043] As shown in Table 5, the flux-cored welding wires of Examples 1-3 of this application exhibit very little or no welding fume and minimal welding spatter during welding, receiving an overall evaluation of A (Excellent). In contrast, the flux-cored welding wires of Comparative Examples 1-3 show high susceptibility to hot cracking during welding, resulting in numerous cracks. The flux-cored welding wires of Comparative Examples 4 and 5 have high manganese content, leading to very severe welding fume and excessive welding spatter, receiving an overall evaluation of D (Poor). It is evident that the flux-cored welding wires prepared using Examples 1-3 of this invention demonstrate significantly superior welding processability, particularly in terms of welding fume and welding spatter levels.

[0044] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A cored wire for high manganese steel, characterized by comprising, The composition comprises the following components: metal manganese 32.0-45.0 wt%, nickel powder 18.0-32.0 wt%, aluminum powder 6.0-12.0 wt%, graphite 0.7-1.5 wt%, chromium iron nitride 4.0-8.0 wt%, chromium carbide 2.0-2.5 wt%, rare earth silicon iron 1.5-3.5 wt%, nickel magnesium alloy 1.0-2.5 wt%, aluminum magnesium alloy 1.0-2.0 wt%, rutile 5.0-8.0 wt%, potassium feldspar 3.0-5.0 wt%, zircon quartz 0.5-2.5 wt%.

2. The high manganese steel cored wire according to claim 1, characterized in that, The composition comprises the following components: metal manganese 32.0-45.0 wt%, nickel powder 18.0-32.0 wt%, aluminum powder 6.0-12.0 wt%, graphite 0.7-1.5 wt%, chromium iron nitride 4.0-8.0 wt%, chromium carbide 2.0-2.5 wt%, rare earth silicon iron 1.5-3.5 wt%, nickel magnesium alloy 1.0-2.5 wt%, aluminum magnesium alloy 1.0-2.0 wt%, rutile 5.0-8.0 wt%, potassium feldspar 3.0-5.0 wt%, zircon quartz 0.5-2.5 wt%.

3. A welding wire for high manganese steel, characterized by, The welding wire comprises a steel strip and the flux core for high manganese steel of claim 1 or 2, the flux core for high manganese steel is filled in the steel strip and the weight is 25%-35% of the weight of the welding wire for high manganese steel.

4. The welding wire for high manganese steel according to claim 3, characterized by The filling rate of the flux core is 31%-33%.

5. The welding wire for high manganese steel according to claim 4, characterized by The diameter of the welding wire for high manganese steel is 1.20-2.40 mm.

6. Use of the welding wire for high manganese steel according to any one of claims 3-5 in the preparation of LNG storage tanks.

7. Deposited metal for welding high manganese steel, characterized in that it comprises The welding wire according to any one of claims 3-5 is used to form a weld, and the chemical composition of the deposited metal includes Mn, Ni, and Al, and the content of Mn, Ni, and Al is represented by Mn%, Ni%, and Al% respectively, wherein and .

8. Deposited metal for welding of high manganese steel according to claim 5, characterized in that, The chemical composition of the deposited metal comprises: C 0.40-0.70 wt%, Mn 10.0-14.0 wt%, Si 0.50-0.90 wt%, Cr 1.0-2.0 wt%, Ni 6.0-10.0 wt%, Al 1.5-3.5 wt%, N 0.10-0.20 wt%, S ≤0.010 wt%, P ≤0.012 wt%.

Images