High-carbon nitrogen-containing stainless steel flux-cored wire for very low temperature steel

Abstract

The application discloses a high-carbon nitrogen-containing stainless steel flux-cored wire for extremely low-temperature steel, which comprises a sheath and a core filled in the sheath. The cladding metal obtained by surfacing with the flux-cored wire comprises the following components in percentage by weight: C 0.08-0.25%, Si 0.2-1.0%, Mn 4.0-9.0%, 15%≤Ni≤20%, Cr 18-22%, Mo 2.5-5.0%, P≤0.01%, S≤0.01%, N 0.1-0.3%, 0≤Cu≤1%, the balance of Fe and inevitable impurities. The core comprises 10-70% of metal and metal compounds, 4.5-25% of slag forming agents, 0.3-1% of alkali metal oxide arc stabilizers and 0.6-2% of functional regulators, and the balance of iron powder. The flux-cored wire for extremely low-temperature steel is suitable for all-position welding of various low-temperature steels, and the obtained cladding metal has excellent strength and extremely low-temperature toughness.

Description

Technical Field

[0001] This invention belongs to the field of flux-cored welding wire technology, specifically relating to a high-carbon nitrogen-containing stainless steel flux-cored welding wire for ultra-low temperature steel. Background Technology

[0002] With continuous industrialization and technological development, the use of refrigerants for storage at temperatures ranging from -30°C to -196°C is increasing. Therefore, nickel alloy low-temperature steels (3.5-9%), Invar, austenitic stainless steel, and high-manganese steel are used as base materials. Typically, nickel-based welding materials are used for welding these structures, or the same material is used when welding high-manganese steel. However, nickel-based welding materials are 20-100 times more expensive per kilogram than the iron-based welding materials previously used in shipbuilding and offshore platforms, resulting in numerous problems in terms of cost and usage. Furthermore, the same material welding materials used for welding high-manganese steel release large amounts of manganese vapor during the welding process due to their high manganese (Mn) content of approximately 25%, posing a serious safety hazard to workers. Therefore, it is necessary to develop a low-cost, high-safety iron-based welding material suitable for extremely low-temperature environments down to -196°C. Summary of the Invention

[0003] The purpose of this invention is to provide a high-carbon nitrogen-containing stainless steel flux-cored welding wire for ultra-low temperature steel. This welding wire has excellent all-position welding operability under arc welding, and can obtain cladding metal with excellent strength and ultra-low temperature toughness.

[0004] This invention provides a flux-cored welding wire for high-carbon, nitrogen-containing stainless steel used in ultra-low temperature welding. The flux-cored welding wire of this invention, after surfacing welding, forms a cladding metal with a specific chemical composition. This composition directly determines the strength, ultra-low temperature toughness, and crack resistance of the weld joint. Therefore, this invention limits the content of the main chemical elements in the cladding metal as follows (by mass percentage): Carbon (C): 0.08~0.25% Silicon (Si): 0.2~1.0% Manganese (Mn): 4.0~9.0% Nickel (Ni): 15~20% Chromium (Cr): 18~22% Molybdenum (Mo): 2.5~5.0% Phosphorus (P) and sulfur (S): both below 0.01% Nitrogen (N): 0.1~0.3% Copper (Cu): 0~1% (excluding 0%) Residual iron (Fe) and unavoidable impurities; Furthermore, the above components must satisfy the relationship 1:0.20%. <C+N<0.55%。

[0005] Among the above-mentioned cladding metal components:

[0006] Carbon (C) is an effective solid solution strengthening element. This invention strictly limits its range to 0.08–0.25%. Below 0.08%, it cannot provide sufficient strength; while above 0.25%, it forms excessive carbides, severely impairing extremely low temperature toughness and crack resistance. Within this range, C can effectively improve strength without significantly compromising toughness.

[0007] Silicon (Si), as an element that enhances deoxidation and wettability, exhibits several drawbacks. When its content is below 0.2%, insufficient deoxidation capacity and decreased droplet wettability occur. Conversely, when its content exceeds 1.0%, it promotes the formation of brittle phases, leading to reduced weld toughness. Therefore, in this invention, the Si content is limited to 0.2% to 1.0%.

[0008] Manganese (Mn) is a key element for maintaining the low-temperature stable austenite phase. Compared to nickel, it is a much lower-cost austenite stabilizing element. In this invention, Mn is primarily used to replace a portion of the nickel to maintain a sufficient amount of austenite in the weld. In addition, it also acts as a deoxidizer. Therefore, to achieve these effects, the Mn content needs to be at least 4.0%. However, a content exceeding 9.0% will lead to a sharp decrease in toughness and elongation, as well as increased susceptibility to cracking and the generation of large amounts of welding fumes. Therefore, in this invention, the Mn content is preferably limited to 4.0% to 9.0%.

[0009] Nickel (Ni) is a key austenite stabilizing element for ensuring extremely low-temperature toughness. This invention employs a nickel content of 15.0% to 20.0% to ensure a single austenitic structure even at ultra-high strength, thus guaranteeing excellent low-temperature toughness in the cladding metal. A nickel content below 15.0% is insufficient to suppress martensitic transformation, resulting in insufficient toughness and a tendency for brittle cracking; a content exceeding 20.0% offers limited improvement in toughness, reduces slag space, significantly increases costs, and diminishes the benefit of toughness enhancement, potentially increasing the tendency for hot cracking. Therefore, 15% < Ni ≤ 20% is preferred.

[0010] Chromium (Cr) ensures the corrosion resistance of the cladding metal and enhances its strength through solid solution strengthening. In this invention, the Cr content ranges from 18.0% to 22.0%, ensuring good pitting corrosion resistance and matching the high Ni content. Below 18%, the cladding metal has low strength and poor corrosion resistance; above 22%, it promotes intermetallic phase precipitation, impairing toughness and crack resistance.

[0011] Molybdenum (Mo) can significantly improve the strength of the cladding metal while ensuring its corrosion resistance. Furthermore, it exhibits a good synergistic effect with other components in this invention, further guaranteeing the high strength of the cladding metal. When the molybdenum content is below 2.5%, the weld's pitting corrosion resistance and strength are insufficient; exceeding 5.0% easily leads to the formation of intermetallic compounds in the cladding metal structure, creating harmful phases, increasing the brittleness of the cladding metal, and causing a decrease in toughness and weldability. Therefore, the Mo content in this invention ranges from 2.5% to 5.0%.

[0012] Copper (Cu) can further optimize the microstructure, improve plasticity and low-temperature toughness while ensuring the corrosion resistance of the cladding metal. Simultaneously, it exhibits good synergistic effects with other components in the system, stabilizing the austenitic microstructure and enhancing the overall mechanical properties of the cladding metal. Trace amounts of copper are beneficial for refining grains, improving low-temperature toughness, and enhancing resistance to localized corrosion; however, amounts exceeding 1% can easily lead to the precipitation of copper-rich harmful phases in the cladding metal, significantly reducing low-temperature impact toughness and deteriorating the welding wire's process performance and weld crack resistance. In this invention, the Cu content is preferably above 0.15% and below 1%.

[0013] Phosphorus (P) and sulfur (S) are both harmful components. Therefore, the content of both P and S should be controlled below 0.01%.

[0014] Nitrogen (N) enhances the strength of weld metal and is also a strong austenitizing element. Too low a nitrogen content results in insufficient strength, while too high a nitrogen content leads to the formation of nitrides, reducing toughness. Therefore, the nitrogen content in this invention is limited to 0.10–0.30%. Furthermore, the total carbon and nitrogen content is controlled to 0.20%–0.55% to fully leverage the synergistic strengthening effect of carbon and nitrogen, avoid the formation of harmful phases, and adapt to extremely low-temperature service conditions. This allows the cladding metal to maintain extremely high impact toughness at -196°C while possessing ultra-high strength.

[0015] To obtain the aforementioned cladding metal composition and ensure excellent welding performance of the welding wire in all welding positions (flat, vertical, horizontal, and overhead), this invention designs the flux core composition of the flux-cored welding wire as follows:

[0016] This invention provides a high-carbon nitrogen-containing stainless steel flux-cored welding wire for ultra-low temperature steel welding in all positions. It uses stainless steel strip as the outer sheath and the flux filling rate is 24-26%. The flux contains, by mass percentage: 10-70% metal and metal compounds, 4.5-25% slag-forming agent, 0.3-1% alkali metal oxide arc stabilizer, 0.6-2% functional modifier, and the balance iron powder.

[0017] The metals and metal compounds include elemental metal powders such as nickel powder, chromium powder, molybdenum powder, manganese powder, and copper powder, as well as metal compounds such as metal carbides and metal nitrides; preferably, the metals and metal compounds include: 9-22.5% manganese powder, 0-16% nickel powder, 0-6% chromium powder, 3.5-10% molybdenum powder, 0.5-3% copper powder, 0-7% chromium carbide powder, and 1-10% chromium nitride powder.

[0018] Slag-forming agent: B2O3 0.5~1.2%, Na2TiO3 1.0~3.0%, and at least one of SiO2, TiO2 and ZrO2 3.0~21.0%.

[0019] Slag-forming agent: including one or more of SiO2, TiO2, and ZrO2, with a content of 3.0~21.0%; and 0.5~1.2% of B2O3 and 1.0~3.0% of Na2TiO3.

[0020] Arc stabilizers include one or more of Li2O, Na2O, and K2O·nTiO2 (n=1-6).

[0021] Functional modifiers: including 0.6~1.2% Bi2O3, and one or more rare earth compounds selected from CeF3, LaF3, and Y2O3, wherein the content of rare earth compounds independently is 0~0.3%, and the total content is ≤0.8%.

[0022] In the above component system, the ratio of slag-forming agent, arc-stabilizing agent, and functional modifier directly determines the slag coverage, arc stability, and weld pool anti-sagging performance during all-position welding. Therefore, this invention constrains the relationships between the above components using Equation 2 to ensure arc stability, controllable weld pool, and excellent anti-sagging during all-position welding (flat, vertical, horizontal, and overhead), while simultaneously reducing spatter, improving slag removal, and weld formation.

[0023] Relationship 2: 0.88

[0024] Where A = 0.13×(TiO2 + Na2TiO3 + ZrO2 + SiO2 + B2O3), B = arc stabilizer + Bi2O3 + 1.2×(CeF3 + LaF3 + Y2O3). Each component represents its mass percentage in the core.

[0025] ​Furthermore, the core components, by mass percentage, include: rutile powder 3.0-16.0%, quartz powder 0.5-5.0%, zirconium oxide powder 1.0-4.0%, boron oxide powder 0.5-1.2%, sodium titanate powder 1.0-3.0%, arc stabilizer 0.3-1.0%, cerium fluoride powder 0-0.3%, lanthanum fluoride powder 0-0.3%, yttrium oxide powder 0-0.3%, bismuth oxide powder 0.6-1.2%, chromium carbide powder 0-7%, chromium nitride powder 1-10%, manganese metal powder 9-22.5%, nickel powder 0-16%, chromium metal powder 0-6%, molybdenum metal powder 3.5-10%, copper powder 0.5-3%, and iron powder as the balance.

[0026] Further, the chemical composition of the stainless steel strip, by mass percentage, includes: C 0.04~0.08%, Si 0.5~1.0%, Mn 1.5~2.5%, Cr 24~26.5%, Ni 18~22%, S 0.015%, P 0.030%, N 0.12~0.2%, with the balance being iron and unavoidable impurities. Nitrogen-containing 310 series austenitic stainless steel strip is preferred.

[0027] The reasons for defining the function and scope of each raw material in the core of this invention are as follows:

[0028] In the slag system, Si, Ti, and Zr oxides (quartz powder, rutile powder, and zirconium oxide powder) are used to adjust the melting point of the slag, thereby improving the operability of all-position welding. If the total amount of the above oxides added is less than 3.0%, the amount of slag is insufficient, which will lead to a decrease in the coating properties of the slag. Conversely, if the total amount of the above oxides added exceeds 21.0%, slag contamination is likely to occur. Therefore, this invention limits the total content of one or more of SiO2, TiO2, and ZrO2 to 3.0% to 21.0%, and the effect of adding metal oxides is independent of their respective content ratios.

[0029] Boron oxide powder (B2O3) can regulate the high-temperature viscosity and solidification rate of molten slag, thereby improving the slag pool's support and shape during all-position welding. If the B2O3 addition is less than 0.5%, the high-temperature viscosity of the molten slag is too high, resulting in poor molten pool fluidity and making it prone to bulging and poor shape during vertical and overhead welding. If it exceeds 1.2%, the slag melting point is too low and solidification is too slow, easily causing molten pool sagging and flowing, while also increasing the risk of slag inclusions. Therefore, this invention limits the addition amount of B2O3 to 0.5~1.2%, and its addition effect and content range are directly related to the operability of all-position welding.

[0030] Sodium titanate powder (Na2TiO3) promotes the formation of a low-melting-point, highly covert dynamic slag film, thereby improving the sag resistance of the molten pool and the aesthetic appearance of the weld bead during all-position welding. If the Na2TiO3 addition is less than 1.0%, the slag film support is insufficient, and the molten pool is prone to flowing and undercut during vertical and overhead welding. If it exceeds 3.0%, the slag viscosity decreases sharply, making it difficult to peel off the slag shell, causing slag adhesion to the weld surface, and deteriorating arc stability. Therefore, this invention limits its addition to 1.0~3.0% to improve the controllability of the molten pool during all-position welding.

[0031] The arc stabilizer of this invention uses alkali metal oxides. Alkali metal oxides can reduce the ionization potential of the welding arc, thereby helping the arc to ignite smoothly and maintaining arc stability during welding. Specifically, this invention includes one or more of lithium oxide (Li₂O), sodium oxide (Na₂O), and potassium titanate (K₂O·nTiO₂). In the flux core, the total amount of this arc stabilizer is controlled between 0.3% and 1.0%. When the addition amount reaches 0.3%, it can achieve the effect of stabilizing the arc; however, if the addition amount exceeds 1.0%, due to the high vapor pressure characteristics of alkali metal oxides, a large amount of smoke will be generated during welding, which will not only affect the operator's visibility but may also increase the environmental burden. Therefore, limiting the addition amount to the range of 0.3% to 1.0% is a reasonable choice that balances arc stabilization effect and low smoke generation. The arc stabilization effect of this invention mainly depends on the total amount of alkali metal oxides added, and is independent of the specific content ratio between the components.

[0032] The main function of adding Bi2O3 in this invention is to reduce the surface tension of the molten droplets, making them finer and the transition more uniform. This suppresses molten pool sagging and reduces spatter during all-position welding. This invention limits the addition amount to 0.6%–1.2%. If the Bi2O3 addition is below 0.6%, the droplets are too coarse, and the anti-sagging effect is not significant; if it is above 1.2%, the arc stability deteriorates, the molten pool flows too quickly, easily leading to flow and undercut, while also increasing costs and potentially introducing excess impurities into the weld. Therefore, the Bi2O3 content in this invention directly determines the smoothness of droplet transition and the anti-sagging ability during all-position welding.

[0033] In the present invention, one or more rare earth fluorides or oxides selected from cerium fluoride (CeF₃), lanthanum fluoride (LaF₃) and yttrium oxide (Y₂O₃) are added, which aims to purify grain boundaries and refine grains, thereby improving the toughness and crack resistance of welds at extremely low temperatures, and also improving the slag detachability of molten slag. It should be noted that the addition amount of each rare earth compound should not exceed 0.3%, and the total content should not exceed 0.8%. Exceeding this range easily leads to unstable arc, slag inclusion in welds and increased cost. If no rare earth compound is added, the purity of the weld is insufficient, and the impact toughness at extremely low temperatures will decrease significantly. Therefore, the present invention selects one or more rare earth compounds according to actual needs, and balances the weld toughness and slag detachability during all-position welding by adjusting the addition amount thereof.

[0034] In the flux-cored wire with a stainless steel sheath filled with flux core according to the present invention, the ratio of austenite-forming elements to ferrite-forming elements in the deposited metal directly determines the matching of strength and toughness at extremely low temperatures. When the composition of alloy elements is controlled within the range required by the present invention, and the welding wire satisfies the above relational expression 1 (0.20% < C+N < 0.55%), the phase composition and grain boundary state of the deposited metal can be accurately regulated, ensuring that while the deposited metal achieves ultra-high strength of 720 MPa or above, it still maintains an excellent impact energy of more than 70 J in the extremely low temperature environment of -196°C, avoids low-temperature brittle fracture or insufficient strength caused by microstructure imbalance, and achieves the ultimate balance of strength and toughness under extremely low temperature working conditions.

[0035] In the flux-cored component system of the present invention, the ratio of slag-forming components to arc-stabilizing and function-regulating components directly determines the slag coverage, arc stability and molten pool anti-sagging performance during all-position welding. In the present invention, when the flux-cored powder satisfies the above relational expression 2, the melting point, viscosity and dynamic slag supporting capacity of the molten slag can be collaboratively optimized, ensuring that the arc is stable, the molten pool is controllable, and the anti-sagging performance is excellent during all-position welding in flat, vertical, horizontal and overhead positions, while reducing spatter, improving slag detachability and weld forming, and achieving good welding processability and excellent weld performance of the welding wire for extremely low temperatures.

[0036] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0037] 1. This invention controls the total C+N content between 0.20% and 0.55%, and combines this with a relatively high Ni content of 15% to 20%, a Cr content of 18% to 22%, and a Mo content of 2.5% to 5.0%, ensuring that the cladding metal obtains a stable austenitic structure while achieving ultra-high strength exceeding 720 MPa. Most importantly, by precisely controlling Equation 1, the total carbon and nitrogen content is adjusted to 0.20% to 0.55%, fully leveraging the synergistic strengthening effect of carbon and nitrogen, avoiding the formation of harmful phases, and adapting to extremely low temperature service conditions. This allows the cladding metal to maintain extremely high impact toughness even at -196℃ while possessing ultra-high strength.

[0038] 2. This invention ensures arc stability, molten pool control, and strong slag film support during welding in all positions (flat, vertical, horizontal, and overhead) by precisely matching the slag-forming agent to a composite system of rutile, quartz, zirconium oxide, boron oxide, and sodium titanate, and combining it with a lithium, sodium, and potassium composite arc stabilizer. Most importantly, by introducing bismuth oxide to synergistically regulate droplet transition behavior and molten pool fluidity, and precisely controlling Equation 2 between 0.88 and 1.75, it balances arc stability, slag fluidity, and anti-sagging ability, resulting in welding wire that does not drip, does not undercut, has minimal spatter, smooth slag removal, and produces aesthetically pleasing welds in all positions, truly achieving excellent process performance for unobstructed welding in all positions.

[0039] 3. The flux-cored welding wire of the present invention can be used for welding a variety of ultra-low temperature structural materials such as 9% Ni steel, high manganese steel and austenitic stainless steel, and has good base material adaptability, which can reduce the complexity of welding material management and use on construction site.

[0040] 4. This invention uses manganese to replace part of the expensive nickel element, controlling the Ni content in the cladding metal to 15-20%. Compared with traditional nickel-based welding materials (Ni content is usually ≥55%), the amount of nickel used is reduced by more than 60%, which significantly reduces material costs while ensuring performance and has high economic efficiency. Detailed Implementation

[0041] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0042] Unless otherwise specified, the raw materials used in the following embodiments of the present invention are all commercially available or prepared using conventional smelting / drawing processes. The purity of the core raw material powders in the following embodiments of the present invention is all above 99%.

[0043] The arc stabilizers used in the following embodiments of the present invention are all composed of Li2O, Na2O, and K2O·4TiO2 in a mass ratio of 1:3:5.

[0044] The stainless steel strip used in the following embodiments of the present invention is a nitrogen-containing 310 series austenitic (hereinafter referred to as 310N) stainless steel strip, whose chemical composition by mass percentage includes: carbon 0.08%; silicon 0.75%; manganese 2%; chromium 24%; nickel 20%; sulfur 0.015%; phosphorus 0.030%; nitrogen 0.15%; the balance being iron and unavoidable impurities. Example 1

[0045] A high-carbon, nitrogen-containing stainless steel flux-cored welding wire suitable for ultra-low temperature steel is disclosed. Its structure consists of an iron sheet and a flux core. The iron sheet is a 310N stainless steel strip with a thickness of 0.4 mm. The flux core, by weight percentage, comprises: 16% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 1% chromium nitride (CrN) powder, 22.5% manganese powder, 10% molybdenum powder, 0.5% copper powder, and the balance being iron powder. All components are passed through an 80-mesh standard sieve, and the weighed powders are mixed evenly for later use.

[0046] The preparation method of the stainless steel flux-cored welding wire is as follows:

[0047] (1) Roll the stainless steel strip into a U-shape, add the formula amount of core powder into the U-shaped groove, the average particle size of the core powder is about 100 mesh;

[0048] (2) The U-shaped groove is rolled into an O-shaped steel pipe, and the filling rate of the core powder in the O-shaped steel pipe is 25%;

[0049] (3) The O-shaped steel pipe is rolled by 6 sets of 30 rollers, drawn by 1 sizing die, and annealed by a welding wire to produce Φ2.0mm stainless steel flux-cored welding wire; after 10 drawing processes and surface mechanical cleaning, it is made into Φ1.2 stainless steel flux-cored welding wire. Example 2

[0050] A high-carbon, nitrogen-containing stainless steel flux-cored welding wire suitable for ultra-low temperature steel has a structure consisting of an iron sheet and a flux core. The iron sheet is a 310N stainless steel strip with a thickness of 0.4 mm. The flux core, by weight percentage, comprises the following: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide (Cr3C2) powder, 5% chromium nitride (CrN) powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Example 3

[0051] A high-carbon, nitrogen-containing stainless steel flux-cored welding wire suitable for ultra-low temperature steel has a structure consisting of an iron sheet and a flux core. The iron sheet is a 310N stainless steel strip with a thickness of 0.4 mm. The flux core is composed of the following by weight percentage: 12% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 2% ferrosilicon powder, 7% chromium carbide (Cr3C2) powder, 10% chromium nitride (CrN) powder, 9% manganese powder, 11% nickel powder, 6% metallic chromium powder, 5.5% molybdenum powder, 3% copper powder, and the balance being iron powder. Comparative Example 1

[0052] Similar to Example 2, except that the C content is increased in this comparative example. The specific core powder composition, by mass percentage, is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 16% chromium carbide powder, 5% chromium nitride powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 2

[0053] Similar to Example 2, except that no slag-forming agent was used in this comparative example. The composition of the core in this comparative example, by mass percentage, is as follows: 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 3

[0054] Similar to Example 2, except that no arc stabilizer was used in this comparative example. The core in this comparative example, by mass percentage, consists of the following: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 4

[0055] Similar to Example 2, except that rare earth components were not used in this comparative example. The core material in this comparative example, by mass percentage, consists of the following: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 5

[0056] Similar to Example 2, except that bismuth oxide was not used in this comparative example. The core in this comparative example, by mass percentage, consists of: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 6

[0057] Similar to Example 2, except that the nitrogen content is increased. The composition of the medicinal core in this comparative example, by mass percentage, is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 15% chromium nitride powder, 16% manganese powder, 8% nickel powder, 8.5% molybdenum powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 7

[0058] Same as Example 2, except that Ni is in excess. The composition of the core in this comparative example by mass percentage is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 36% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 8

[0059] Same as Example 2, except that Mn is in excess. The composition of the medicinal core in this comparative example, by mass percentage, is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 7% chromium nitride powder, 37.5% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and iron powder balance. Comparative Example 9

[0060] Same as Example 2, except that Mo is in excess. The composition of the core material in this comparative example by mass percentage is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 17% molybdenum powder, 3% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 10

[0061] Same as Example 2, except that Cr is in excess. The composition of the medicinal core in this comparative example by mass percentage is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 17.5% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 11

[0062] Same as Example 2, except that Cu is in excess. The composition of the core material in this comparative example by mass percentage is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, 5% copper powder, and the balance being iron powder. Comparative Example 12

[0063] Similar to Example 2, except that copper powder is not added. The composition of the medicinal core in this comparative example by weight percentage is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 3% chromium carbide powder, 5% chromium nitride powder, 16% manganese powder, 16% nickel powder, 8.5% molybdenum powder, 3% metallic chromium powder, and the balance being iron powder. Comparative Example 13

[0064] This comparative example uses commercially available 316L stainless steel strip. The chemical composition of the commercially available 316L stainless steel strip, by mass percentage, includes: carbon 0.039%; silicon 0.45%; manganese 1.47%; chromium 16.96%; nickel 9.88%; molybdenum 2.12%; sulfur 0.001%; ​​phosphorus 0.037%; nitrogen 0.10%; the balance being iron and unavoidable impurities. To ensure the Ni content of the cladding metal, the amount of nickel powder in the flux core was increased, and the slagging agent was adjusted for compatibility. The core is composed of the following components by weight percentage: 1% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 18% manganese powder, 48% nickel powder, 4% molybdenum powder, 18.5% metallic chromium powder, 1.5% copper powder, and the balance being iron powder. Comparative Example 14

[0065] This comparative example uses commercially available 316L steel strip with a filler ratio of 25%. Its core composition by weight percentage is as follows: 10% rutile powder, 2.5% quartz powder, 1.5% zirconium oxide powder, 0.6% boron oxide powder, 2.0% sodium titanate powder, 1% arc stabilizer, 0.6% bismuth oxide powder, 0.1% cerium fluoride, 0.1% lanthanum fluoride, 0.1% yttrium oxide, 6% chromium carbide powder, 5% chromium nitride powder, 18% manganese powder, 13% nickel powder, 4% molybdenum powder, 9.5% metallic chromium powder, 1.5% copper powder, and the balance being iron powder.

[0066] Performance testing

[0067] Five layers of 9% Ni steel base material were deposited using the flux-cored welding wires obtained in the embodiments and comparative examples of this invention. Each layer consisted of three passes, with a deposit thickness of 15 mm. Deposition was carried out under a mixed shielding gas (80% Ar2 + 20% CO2). Welding parameters were: welding current 210~250A, welding voltage 27~30V, gas flow rate 16~20L / min, and welding speed 5~8mm / s. After the deposit was completed, the properties of the weld cladding metal were tested. Each group underwent 10 parallel tests, and the average value was taken. The results are shown in Table 2. The composition of the weld cladding metal was sampled and analyzed. For elemental composition analysis, the weld was first ground downwards for 2 mm along its surface before elemental composition analysis. The analysis results are shown in Table 3.

[0068] Tensile strength and elongation after fracture were tested according to GB / T 228-2021 standard. Impact energy at -196℃ was tested according to GB / T 229-2020 standard. Splashing rate and slag removal rate were tested according to GB / T 25776-2010, and slag removal performance was rated. Crack resistance was tested according to GB / T41107.2-2021 (Self-Constrained Hot Crack Test). The crack resistance evaluation standard adopted the MSI(TT) quantitative assessment: MSI(TT) = Total length of all cracks / Characteristic length of effective cross-section of the specimen.

[0069] Table 1. Slag Removal Performance Rating Criteria and Crack Resistance Rating Criteria

[0070]

[0071] Table 2 Mechanical properties and weldability of cladding metal

[0072]

[0073] Table 3 Elemental composition of weld cladding metal (wt%)

[0074]

[0075] The clad metals obtained in Examples 1-3 of this invention have a tensile strength greater than 720 MPa, an elongation after fracture greater than 35%, and a Charpy V-notch impact energy greater than 70 J at -196°C.

[0076] Comparative Example 1 increased the chromium carbide powder content to increase the carbon content in the cladding metal. However, excessively high carbon content easily leads to carbide precipitation, deteriorating corrosion resistance and low-temperature toughness, and significantly increasing the risk of cracking. This was particularly evident in the root pass welding, where numerous cracks and hard inclusions appeared, severely impacting the low-temperature toughness of the cladding metal. Consequently, the weld's impact energy at -196℃ was only 21J, resulting in significantly poorer low-temperature toughness, a crack resistance rating of C, and a spatter rate of 1.42%.

[0077] Comparative Example 2, lacking any slag-forming agents such as rutile, quartz, zirconium oxide, boron oxide, and sodium titanate, and Comparative Example 3, lacking any arc stabilizer, both affected welding performance and failed to achieve stable all-position welding. Comparative Example 4, lacking rare earth compounds such as cerium fluoride, lanthanum fluoride, and yttrium oxide, resulted in a significant decrease in the overall mechanical properties of the cladding metal and a tendency for sharp inclusions, severely impacting its mechanical properties. Simultaneously, arc stability decreased slightly during welding, and the lack of rare earth compounds' ability to regulate slag flowability failed to fully meet the stringent requirements for welding stability under cryogenic conditions. Comparative Example 5, lacking bismuth oxide powder, suffered from a slag removal rating of C and a crack resistance rating of B, a spatter rate of 1.32%, poor slag spreadability, and irregular weld formation. Although the impact energy at -196℃ reached 75J, its welding processability did not meet the requirements for all-position cryogenic welding.

[0078] In Comparative Examples 6 to 12, the content of individual elements such as N, Ni, Mo, Mn, Cr, and Cu exceeded the standard or fell below the lower limit, which could not meet the requirements of ultra-low temperature operating conditions.

[0079] Comparative Example 13 used commercially available 316L steel strip instead of the 310N steel strip of this invention. As shown in Table 3, the C (0.029%) and N (0.082%) in the cladding metal of Comparative Example 13 were both below the lower limit of the required composition. Simultaneously, the C+N ratio was 0.111%, below the lower limit of Equation 1. Since the composition of this steel strip could not fully meet the requirements of this invention, the proportion of rutile had to be reduced to ensure the alloy met the composition range. This resulted in the A / B ratio being below the lower limit of Equation 2, leading to increased spatter, poor formability, and difficulty in slag removal. The tensile strength of Comparative Example 13 was only 577 MPa, and the impact energy at -196℃ was only 68 J. This confirms that the 310N special steel strip is the key substrate for ensuring the cladding metal composition meets the standards, matching the A / B ratio range, and obtaining excellent welding processability and superior low-temperature strength and toughness. Replacing it with conventional 316L steel strip cannot achieve the comprehensive effect expected by this invention.

[0080] In Comparative Example 14, due to the low Ni content in the steel strip, the nickel content in the cladding metal was only about 10%, resulting in an imbalance in the alloy element ratio of the cladding metal. Although the other elements were still within the preferred range, the insufficient nickel content, as a core element for stabilizing austenite and improving toughness and plasticity, directly led to a severe decline in elongation after fracture and impact toughness at -196℃. The overall welding process performance showed no significant fluctuations, and the A / B ratio remained within the standard range, but the strength-toughness match deteriorated significantly. The low nickel content significantly impaired the stability of the austenitic structure and low-temperature impact resistance.

[0081] This invention, by strictly limiting the chemical composition range of the flux-cored welding wire and ensuring that Equation 1 is within the optimal range, ensures both high low-temperature toughness and high strength. As shown in Tables 2 and 3, the impact energy at -196℃ for Examples 1-3 is all above 70J, the tensile strength is above 720MPa, and the elongation is above 35%, achieving an ultimate balance of strength and toughness at extremely low temperatures. Simultaneously, through precise proportioning of the flux-cored slag components, the optimized Equation 2 (0.88...) is ensured...

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.​

Claims

1. A high-carbon nitrogen-containing flux-cored welding wire for ultra-low temperature steel, characterized in that, It comprises a stainless steel strip and a flux core filled in the stainless steel strip. The cladding metal formed by surfacing with the flux-cored welding wire comprises the following chemical components by mass percentage: C 0.08~0.25%, Si 0.2~1.0%, Mn 4.0~9.0%, 15%<Ni≤20%, Cr 18~22%, Mo 2.5~5.0%, P≤0.01%, S≤0.01%, N 0.1~0.3%, 0<Cu≤1%, with the balance being Fe and unavoidable impurities; and 0.20%<C+N<0.55%; the flux core filling rate is 24~26%; The chemical components of the stainless steel strip by mass percentage comprise: C 0.04~0.08%, Si 0.5~1.0%, Mn 1.5~2.5%, Cr 24~26.5%, Ni 18~22%, S≤0.015%, P≤0.030%, N 0.12~0.20%, with the balance being Fe and unavoidable impurities; The components of the flux core by mass percentage comprise: 10~70% of metals and metal compounds, 4.5~25% of slag formers, 0.3~1% of arc stabilizers, 0.6~2% of functional regulators, with the balance being iron powder; wherein, said metals comprise one or more of nickel powder, chromium metal powder, molybdenum metal powder, manganese metal powder and copper powder; said metal compounds comprise one or more of metal carbides and metal nitrides; said slag formers comprise one or more of SiO₂, TiO₂ and ZrO₂, as well as B₂O₃ and Na₂TiO₃; said arc stabilizers comprise one or more of Li₂O, Na₂O and K₂O·nTiO₂; said functional regulators comprise Bi₂O₃ and one or more rare earth compounds selected from CeF₃, LaF₃ and Y₂O₃; said slag formers, arc stabilizers and functional regulators satisfy the following relational expression in terms of their mass percentage in the flux core: 0.88<A / B<1.75; wherein, A = 0.13×(TiO₂ + Na₂TiO₃ + ZrO₂ + SiO₂ + B₂O₃), B = arc stabilizer + Bi₂O₃ + 1.2×(CeF₃ + LaF₃ + Y₂O₃).

2. The high-carbon nitrogen-containing flux-cored welding wire for ultra-low temperature steel according to claim 1, characterized in that, The cladding metal comprises the following chemical components by mass percentage: C 0.08~0.25%, Si 0.2~1.0%, Mn 4.0~9.0%, 15%<Ni≤20%, Cr 18~22%, Mo 2.5~5.0%, P≤0.01%, S≤0.01%, N 0.1~0.3%, 0.15%≤Cu≤1%, with the balance being Fe and unavoidable impurities; and 0.20%<C+N<0.55%.

3. The high-carbon nitrogen-containing flux-cored welding wire for ultra-low temperature steel according to claim 1, characterized in that, The components of the flux core by mass percentage comprise: Metals and metal compounds: 9~22.5% of manganese metal powder, 0~16% of nickel powder, 0~6% of chromium metal powder, 3.5~10% of molybdenum metal powder, 0.5~3% of copper powder, 0~7% of chromium carbide powder, 1~10% of chromium nitride powder; Slag-forming agent: B2O3 0.5~1.2%, Na2TiO3 1.0~3.0%, at least one of SiO2, TiO2, and ZrO2 3.0~21.0%; Arc stabilizer: at least one of Li₂O, Na₂O, and K₂O·nTiO₂, 0.3-1%; Functional modifiers: Bi2O3 0.6~1.2%, at least one of CeF3, LaF3, and Y2O3 ≤0.8%; wherein CeF3 0~0.3%, LaF3 0~0.3%, and Y2O3 0~0.3%; Iron powder balance.

4. The high-carbon nitrogen-containing flux-cored welding wire for ultra-low temperature steel according to claim 1, characterized in that, The core components, by mass percentage, include: rutile powder 3.0-16.0%, quartz powder 0.5-5.0%, zirconium oxide powder 1.0-4.0%, boron oxide powder 0.5-1.2%, sodium titanate powder 1.0-3.0%, arc stabilizer 0.3-1.0%, cerium fluoride powder 0-0.3%, lanthanum fluoride powder 0-0.3%, yttrium oxide powder 0-0.3%, bismuth oxide powder 0.6-1.2%, chromium carbide powder 0-7%, chromium nitride powder 1-10%, manganese metal powder 9-22.5%, nickel powder 0-16%, chromium metal powder 0-6%, molybdenum metal powder 3.5-10%, copper powder 0.5-3%, and iron powder as the balance.

5. The high-carbon nitrogen-containing flux-cored welding wire for ultra-low temperature steel according to claim 1, characterized in that, The cladding metal has a tensile strength greater than 720 MPa, an elongation greater than 35%, and a Charpy V-notch impact energy greater than 70 J at -196°C.

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