A welding material special for high-aluminum type ferrochrome-aluminum electric heating alloy and a preparation method thereof

Abstract

The application relates to a high-aluminum type iron-chromium-aluminum electric heating alloy special welding material and a preparation method thereof, and belongs to the technical field of welding materials. The embodiment of the application provides the high-aluminum type iron-chromium-aluminum electric heating alloy special welding material, and the chemical components of the welding material are as follows in mass fraction: Cr: 20%-23%, Al: 5.5%-7.0%, Ti: 0.05%-0.60%, Zr: 0.05%-0.30%, Mo: 0.3%-1.0%, Si: 0.2%-0.5%, C: 0.02%-0.08%, rare earth elements: 0.03%-0.12%, P<=0.015%, S<=0.005%, Ni<=0.5%, Mn<=0.5%, and the balance is Fe and inevitable impurities.

Description

Technical Field

[0001] This application relates to the field of welding materials technology, and in particular to a high-alumina iron-chromium-aluminum electrothermal alloy special welding material and its preparation method. Background Technology

[0002] Iron-chromium-aluminum (FeCrAl) electrothermal alloys are an important class of high-resistivity electrothermal materials. With their excellent oxidation resistance, high resistivity and upper limit of operating temperature, they are widely used in industrial electric furnaces, household appliances, thermal management systems for new energy vehicles, electronic ceramic sintering and other fields.

[0003] Aluminum content is a key factor determining the oxidation resistance and upper limit of operating temperature of iron-chromium-aluminum heating alloys. High-aluminum iron-chromium-aluminum heating alloys (such as 0Cr21Al6 and 0Cr23Al6) with aluminum content of 5.3%~6.5% and chromium content of 20%~23% can form a denser and more stable α-Al2O3 oxide film, and have higher oxidation resistance and upper limit of operating temperature than ordinary alloys (aluminum content of 4%~5.3%), and have an irreplaceable position in the field of high-end heating elements. However, while high aluminum content improves the oxidation resistance of the alloy, it also brings more severe welding technology challenges: (1) the severe evaporation and burning loss of aluminum at high welding temperature leads to a serious decrease in the oxidation resistance of the weld; (2) due to the high aluminum content, the pinning effect of aluminum on dislocations in high-aluminum iron-chromium-aluminum alloys is enhanced, but at the same time the driving force for grain growth is also increased. Under welding thermal cycling, the grains in the weld zone and heat-affected zone grow rapidly and uncontrollably, and the grain size can deteriorate from level 6 to 8 of the base material to level 1 to 2. The room temperature impact toughness of the welded joint is extremely low. Summary of the Invention

[0004] This application provides a special welding material for high-alumina iron-chromium-aluminum electrothermal alloys and its preparation method, in order to solve the following technical problem: how to solve the welding problem where the welding material cannot be matched with the welding of high-alumina iron-chromium-aluminum electrothermal alloys. In the first aspect, embodiments of this application provide a high-alumina iron-chromium-aluminum electrothermal alloy special welding material. The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~23%, Al: 5.5%~7.0%, Ti: 0.05%~0.60%, Zr: 0.05%~0.30%, Mo: 0.3%~1.0%, Si: 0.2%~0.5%, C: 0.02%~0.08%, rare earth elements: 0.03%~0.12%, P≤0.015%, S≤0.005%, Ni≤0.5%, Mn≤0.5%, with the balance being Fe and unavoidable impurities.

[0005] Optionally, the chemical composition of the welding material, by mass fraction, is as follows: Cr: 20.5%~22.5%, Al: 6.0%~6.8%, Ti: 0.20%~0.50%, Zr: 0.08%~0.20%, Mo: 0.5%~1.0%, Si: 0.25%~0.40%, C: 0.03%~0.06%, rare earth elements: 0.05%~0.08%, P≤0.015%, S≤0.005%, Ni≤0.5%, Mn≤0.5%, with the balance being Fe and unavoidable impurities.

[0006] Optionally, the rare earth element is at least one of La, Ce, and Y.

[0007] Optionally, the ratio of the sum of the mass fractions of Ti and Zr to the mass fraction of C is (4~8):1.

[0008] Optionally, the welding material meets at least one of the following properties: room temperature tensile strength ≥550MPa, elongation after fracture ≥15%, and grain size ≥6.

[0009] Optionally, the welding material is used to weld a high-alumina iron-chromium-aluminum electrothermal alloy base material, wherein the mass fraction of Al in the high-alumina iron-chromium-aluminum electrothermal alloy base material is 5.3%~6.5%, and the mass fraction of Cr is 20%~23%.

[0010] Optionally, the welding material is wire, and the specifications of the welding material are Φ1.2mm~Φ3.2mm.

[0011] Secondly, this application provides a method for preparing the high-alumina iron-chromium-aluminum electrothermal alloy special welding material described in the first aspect, the method comprising: An electroslag ingot with the aforementioned chemical composition is obtained; The electroslag ingot is subjected to hot rolling, multi-pass cold drawing, and continuous bright annealing in sequence to obtain the finished welding wire.

[0012] Optionally, the total area shrinkage of the multi-pass cold drawing process is ≥80%, and intermediate annealing is performed when the cumulative deformation of the multi-pass cold drawing process reaches 30%~40%. The intermediate annealing temperature is 750℃~850℃ and the holding time is 1h~2h.

[0013] Optionally, during the continuous brightening process, the annealing temperature is 750℃~900℃, and the annealing speed is 5m / min~15m / min.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a high-alumina iron-chromium-aluminum electrothermal alloy special welding material. The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~23%, Al: 5.5%~7.0%, Ti: 0.05%~0.60%, Zr: 0.05%~0.30%, Mo: 0.3%~1.0%, Si: 0.2%~0.5%, C: 0.02%~0.08%, rare earth elements: 0.03%~0.12%, P≤0.015%, S≤0.005%, Ni≤0.5%, Mn≤0.5%, with the balance being Fe and unavoidable impurities. This application sets the aluminum content in the welding material to 5.5%~7.0%, higher than the aluminum content of the base metal. Through the principle of mass balance, the higher aluminum content directly compensates for aluminum evaporation loss during welding, ensuring that the aluminum content of the weld after welding remains at the same level as the base metal. Simultaneously, titanium and zirconium, as strong aluminum-affinity elements, preferentially combine with oxygen in the molten pool to form titanium oxide and zirconium oxide protective films, reducing the partial pressure of aluminum in the molten pool and thus inhibiting aluminum evaporation into the gas phase. This, combined with the high aluminum compensation, forms a dual aluminum protection mechanism. During the solidification and cooling process of the weld metal, the introduced titanium, zirconium, and carbon elements undergo in-situ precipitation reactions to generate nano-sized titanium carbide (TiC) and zirconium carbide (ZrC) carbides, as well as Fe2(Ti,Zr) type Laves phases. These nano-precipitates are densely distributed at the ferrite grain boundaries, generating strong pinning forces through the Zener pinning principle. When the pinning force exceeds the driving force for grain growth, grain boundary migration is effectively suppressed, resulting in refined grain size in the weld zone. Simultaneously, the carbon content is controlled at 0.02%~0.08%. This design ensures sufficient formation of nano-carbide while preventing embrittlement caused by the segregation of free carbon at grain boundaries. Molybdenum provides strength through solid solution strengthening, while rare earth elements purify grain boundaries by segregating at grain boundaries and combining with phosphorus and sulfur to form high-melting-point compounds. They also improve the density and adhesion of the oxide film by embedding into the α-Al₂O₃ oxide film lattice. The restrictions of nickel content ≤0.5% and manganese content ≤0.5% ensure that the weld metal does not introduce austenite-forming elements and maintains a completely ferrite single-phase structure, making the thermal expansion coefficient of the weld metal similar to that of the base metal. Complete consistency eliminates the risk of interfacial thermal stress cracking. The above components work synergistically within the same welding material system, enabling the special welding material for high-alumina iron-chromium-aluminum electric heating alloys to simultaneously achieve effective maintenance of the aluminum content in the weld metal, significant refinement of the grains in the weld and heat-affected zone, and phase structure and thermal expansion properties that are completely matched with the base material when welding high-alumina iron-chromium-aluminum electric heating alloy base materials with an aluminum content of 5.3%~6.5% and a chromium content of 20%~23%. This comprehensively solves the technical difficulties in welding high-alumina iron-chromium-aluminum electric heating alloy base materials. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart illustrating a method for preparing a high-alumina iron-chromium-aluminum electrothermal alloy welding material, as provided in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0020] In the first aspect, embodiments of this application provide a high-alumina iron-chromium-aluminum electrothermal alloy special welding material. The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~23%, Al: 5.5%~7.0%, Ti: 0.05%~0.60%, Zr: 0.05%~0.30%, Mo: 0.3%~1.0%, Si: 0.2%~0.5%, C: 0.02%~0.08%, rare earth elements: 0.03%~0.12%, P≤0.015%, S≤0.005%, Ni≤0.5%, Mn≤0.5%, with the balance being Fe and unavoidable impurities.

[0021] Fe (iron) is the base element of welding materials. Using iron as the base element ensures that the coefficient of thermal expansion of the weld metal is consistent with that of the high-alumina iron-chromium-aluminum heating alloy base material. Iron, together with chromium and aluminum, constitutes the Fe-Cr-Al ternary alloy system. At high temperatures, this system relies on the selective oxidation of aluminum to form a dense α-Al2O3 oxide film, giving the heating alloy excellent high-temperature oxidation resistance.

[0022] The mass fraction of Cr (chromium) is 20%~23%, matching the chromium content of the base metal in high-alumina iron-chromium-aluminum electric heating alloys. The main role of Cr in welding materials is to strengthen the ferrite matrix through solid solution, improving the oxidation and corrosion resistance of the welding material. When the mass fraction of Cr is below 20%, the oxidation resistance of the welding material and weld metal decreases, and oxidation weight gain accelerates during high-temperature service. When the mass fraction of Cr is above 23%, it promotes the precipitation of the σ phase. The σ phase is a brittle intermetallic compound, and its precipitation in the ferrite matrix significantly reduces the room-temperature plasticity and toughness of the weld metal.

[0023] The aluminum (Al) content is 5.5%–7.0%, higher than the 5.3%–6.5% aluminum content of the base metal in high-alumina iron-chromium-aluminum heating alloys. The direct purpose of this design is to compensate for the severe evaporation and burn-off of aluminum during welding. In high-alumina iron-chromium-aluminum heating alloys, the molten pool temperature can reach over 1500℃ during welding, resulting in extremely high aluminum vapor pressure and a burn-off rate of 15%–35%. If the aluminum content of the welding material is the same as that of the base metal, the aluminum content in the weld metal will drop to 4.0%–5.0%, severely degrading the oxidation resistance of the weld zone. Increasing the aluminum content of the welding material to 5.5%–7.0% maintains the aluminum content of the weld metal at 5.3%–6.0%, comparable to the base metal, ensuring that the weld zone has matching high-temperature oxidation resistance with the base metal. When the mass fraction of Al is less than 5.5%, the compensation effect is insufficient, and the aluminum content of the weld is lower than that of the base material after welding, making the weld a weak link in oxidation resistance. When the mass fraction of Al is higher than 7.0%, the room temperature plasticity of the welding material itself decreases significantly, making cold drawing and forming difficult, and excessively high aluminum content will exacerbate the processing brittleness during the preparation of the welding material.

[0024] The mass fraction of Ti (titanium) is 0.05%~0.60%, the mass fraction of Zr (zirconium) is 0.05%~0.30%, and the mass fraction of C (carbon) is 0.02%~0.08%. Titanium, zirconium, and carbon constitute the core compositional design feature of this application—a titanium-zirconium-carbon synergistic microalloying system. Both titanium and zirconium are strong carbide-forming elements. Titanium has a stronger bonding ability with carbon than zirconium, but both can form MC-type carbides in a ferrite matrix, namely titanium carbide and zirconium carbide. Titanium carbide and zirconium carbide have a face-centered cubic crystal structure, exhibiting good phase relationship with the ferrite matrix, and can precipitate in situ from the ferrite matrix at nanometer-scale (10~200 nm) during solidification and cooling. These nano-carbide particles are dispersed within and at the grain boundaries of ferrite grains, hindering grain boundary migration by pinning the ferrite grain boundaries, thereby suppressing abnormal grain growth of ferrite grains in the weld metal and heat-affected zone during welding thermal cycles. Meanwhile, titanium and zirconium are also Laves phase-forming elements, forming Fe2(Ti,Zr)-type Laves phase precipitates on the ferrite matrix. These Laves phases also have the effect of pinning grain boundaries and inhibiting grain growth. Titanium carbide, zirconium carbide, and the Fe2(Ti,Zr)-type Laves phase together constitute a dispersion-strengthened structure, which can refine the grain size in the weld zone.

[0025] Besides forming carbides and the Laves phase, titanium and zirconium also inhibit the evaporation and burn-off of aluminum. Both titanium and zirconium are strong aluminum-affinity elements, preferentially reacting with oxygen in the molten pool to form titanium oxide and zirconium oxide, respectively. These oxides form a protective film on the molten pool surface, reducing the partial pressure of aluminum and thus inhibiting its evaporation into the gas phase. The aluminum evaporation inhibition effect of titanium and zirconium, combined with the compensation effect of the high aluminum content in the welding material, forms a dual protective mechanism.

[0026] When the Ti mass fraction is below 0.05%, the amount of titanium carbide and Fe2Ti-type Laves phase generated is insufficient, resulting in insufficient grain boundary pinning points and ineffective grain refinement. When the Ti mass fraction is above 0.60%, excessive titanium promotes the formation of coarse Fe2Ti-type Laves phase, weakening the strengthening effect of nano-precipitates. Furthermore, excessive titanium increases the work hardening rate of the weld material, increasing the difficulty of cold drawing. When the Zr mass fraction is below 0.05%, the contribution of zirconium carbide and Fe2Zr-type Laves phase is insufficient. When the Zr mass fraction is above 0.30%, the strong oxidizing properties of zirconium increase the tendency for oxide inclusions to form in the molten pool, reducing the purity of the weld metal. When the C mass fraction is below 0.02%, the amount of carbide generated is insufficient, resulting in limited precipitation strengthening. When the C mass fraction is above 0.08%, the risk of free carbon segregation at grain boundaries increases significantly, potentially leading to grain boundary embrittlement.

[0027] Mo (Mo) is one of the most effective solid solution strengthening elements in ferritic alloys. When molybdenum atoms dissolve into the ferrite matrix, the difference in atomic size between molybdenum and iron causes lattice distortion, resulting in solid solution strengthening and improving the room temperature tensile strength and high-temperature creep resistance of the weld metal. When the mass fraction of Mo is below 0.3%, the solid solution strengthening effect is insufficient, and the room temperature strength of the weld metal is difficult to reach the requirement of ≥550 MPa. When the mass fraction of Mo is above 1.0%, excessive molybdenum promotes the precipitation of brittle intermetallic compounds such as the σ and χ phases, impairing the plasticity and toughness of the weld metal. Therefore, the mass fraction of Mo is limited to 0.3%~1.0%.

[0028] The main role of silicon (Si) in welding materials is as a deoxidizer and an auxiliary element for enhancing high-temperature oxidation resistance. Silicon has a strong affinity for oxygen, and during smelting and welding, it can consume dissolved oxygen in the molten pool, reducing the consumption of aluminum through oxidation. Simultaneously, silicon can promote the densification of the α-Al₂O₃ oxide film during high-temperature oxidation, improving the high-temperature oxidation resistance of the weld metal. When the mass fraction of Si is below 0.2%, the deoxidation and oxide film densification effects are not significant; when the mass fraction of Si is above 0.5%, excessive silicon reduces the plasticity of the ferrite matrix, and the brittle transition temperature of the weld metal increases with excessive silicon content. Therefore, the silicon content is limited to 0.2%~0.5%.

[0029] Rare earth elements play multiple beneficial roles in welding materials. Firstly, they purify grain boundaries. Rare earth atoms, concentrated at grain boundaries, can form high-melting-point compounds with low-melting-point impurities (such as phosphorus, sulfur, lead, and tin) at the grain boundaries, removing these impurities and improving grain boundary bonding. Secondly, rare earth elements form high-melting-point rare earth oxides and sulfides with oxygen and sulfur. These compounds act as heterogeneous nucleation sites in the molten pool, refining the solidification structure. Thirdly, rare earth elements improve the density and adhesion of the α-Al₂O₃ oxide film on the weld metal surface. Rare earth ions embedded in the oxide film lattice reduce growth stress and peeling tendency, enhancing the long-term oxidation resistance of the weld joint in high-temperature service environments. When the mass fraction of rare earth elements is below 0.03%, the above-mentioned effects are insufficient; when the mass fraction of rare earth elements is above 0.12%, excessive rare earth elements will form too many rare earth oxide inclusions, which will reduce the purity and plasticity of the weld metal. Therefore, the mass fraction of rare earth elements is limited to 0.03%~0.12%.

[0030] Phosphorus (P) and sulfur (S) are the most harmful impurity elements in iron-chromium-aluminum welding materials. Phosphorus segregates at ferrite grain boundaries, significantly reducing grain boundary bonding and inducing temper brittleness or embrittlement of the weld heat-affected zone. Sulfur forms a low-melting-point FeS eutectic with iron (melting point only about 988℃). At the high welding temperature, the FeS eutectic is distributed along the grain boundaries, leading to a sharp increase in the susceptibility to welding hot cracking. Strictly controlling the mass fraction of phosphorus to ≤0.015% and the mass fraction of sulfur to ≤0.005% aims to eliminate grain boundary weakening factors, ensure that the weld joint does not develop hot cracks during post-weld cooling, and guarantee that the room temperature plasticity and toughness meet the application requirements.

[0031] Ni (nickel) and Mn (manganese) are austenite-forming elements. High nickel and manganese content in welding materials can induce austenitic phase transformation in the weld metal, resulting in a ferrite + austenite dual-phase structure rather than a completely ferrite single-phase structure. This application limits the mass fraction of nickel to ≤0.5% and the mass fraction of manganese to ≤0.5% to ensure that the weld metal maintains a completely ferrite single-phase structure, perfectly consistent with the phase structure of the high-alumina iron-chromium-aluminum heating alloy base material. This completely ferrite single-phase structure ensures a high degree of consistency in the coefficients of thermal expansion between the welding material and the base material, eliminating the risk of interfacial thermal stress cracking caused by differences in thermal expansion coefficients.

[0032] In some embodiments, the chemical composition of the welding material, by mass fraction, is: Cr: 20.5%~22.5%, Al: 6.0%~6.8%, Ti: 0.20%~0.50%, Zr: 0.08%~0.20%, Mo: 0.5%~1.0%, Si: 0.25%~0.40%, C: 0.03%~0.06%, rare earth elements: 0.05%~0.08%, P≤0.015%, S≤0.005%, Ni≤0.5%, Mn≤0.5%, with the balance being Fe and unavoidable impurities.

[0033] In some embodiments, the rare earth element is at least one of La, Ce, and Y.

[0034] La (lanthanum), Ce (cerium), and Y (yttrium) are all rare earth elements. These three elements perform similar core functions in welding materials, achieving the basic goals of purifying grain boundaries, removing inclusions, and improving oxide film performance. They each have similar technical effects and can be substituted for one another. The economics of different rare earth elements vary significantly, with cerium being the cheapest, followed by lanthanum, and yttrium the most expensive. This application allows for the selection of at least one, providing flexibility in welding material production based on cost and performance requirements. In certain applications, the combined use of two or three rare earth elements may produce synergistic effects. For example, the combined addition of lanthanum and cerium shows superior effects in purifying grain boundaries and refining grains compared to adding either element alone, while the combined addition of yttrium and cerium has complementary advantages in improving the anti-scraping properties of the oxide film.

[0035] In some implementations, the ratio of the sum of the mass fractions of Ti and Zr to the mass fraction of C is (4~8):1.

[0036] The setting of this ratio directly serves the in-situ formation and dispersion of nano-sized titanium carbide, zirconium carbide, and Fe2(Ti,Zr) type Laves phase in the weld metal of the welding material. Titanium and zirconium, as strong carbide-forming elements, preferentially combine with carbon to form nano-sized titanium carbide and zirconium carbide particles; simultaneously, some titanium and zirconium that do not form carbides further combine with iron to form the Fe2(Ti,Zr) type Laves phase. These two precipitated phases together exert a pinning effect on ferrite grain boundaries, hindering grain boundary migration during welding thermal cycling and achieving grain refinement. At the same time, titanium and zirconium preferentially combine with oxygen in the molten pool to form stable oxides, reducing the partial pressure of aluminum and effectively suppressing the evaporation and burn-off of aluminum in the high-alumina iron-chromium-aluminum heating alloy base material at high welding temperatures.

[0037] If the ratio is less than 4:1, then carbon is in excess relative to titanium and zirconium. The carbon cannot be fully combined to form beneficial nanoscale titanium carbide and zirconium carbide. The excess carbon will agglomerate at grain boundaries in a free form, causing grain boundary embrittlement, or forming coarse M-shaped particles. 23 C6-type carbides impair the toughness and ductility of weld metal, or form carbides with other alloying elements that negatively affect mechanical properties. If the ratio is higher than 8:1, then titanium and zirconium are in excess relative to carbon. Although some of them will form Fe2(Ti,Zr) type Laves phases to play a grain boundary pinning role, the excessive titanium and zirconium elements, after dissolving in the matrix, lead to excessive strengthening and reduced ductility, or form excessive coarse Laves phases at the grain boundaries, weakening the grain boundary bonding force.

[0038] In some embodiments, the welding material satisfies at least one of the following properties: room temperature tensile strength ≥550MPa, elongation after fracture ≥15%, and grain size ≥6.

[0039] These three performance indicators quantify the quality of welding materials from three dimensions: mechanical strength, plasticity, and microstructure refinement. They also concretely reflect the technical effects achieved by the present application's technical solution in terms of composition design and preparation process. Tensile strength is the maximum engineering stress a material can withstand in a room temperature tensile test, reflecting the welding material's ability to resist tensile fracture. Elongation after fracture is the amount of plastic deformation after fracture in a room temperature tensile test, reflecting the welding material's ability to resist brittle fracture. Grain size is an indicator characterizing the grain size in polycrystalline materials; a larger grain size level indicates finer grains.

[0040] In some embodiments, the welding material is used to weld a high-alumina iron-chromium-aluminum electrothermal alloy base material, wherein the mass fraction of Al in the high-alumina iron-chromium-aluminum electrothermal alloy base material is 5.3%~6.5% and the mass fraction of Cr is 20%~23%.

[0041] This application clearly defines the applicable objects and scope of the welding materials in this application, and directly reflects the matching between the welding material composition design and the base material composition. The iron-chromium-aluminum electric heating alloy base material, with an aluminum mass fraction of 5.3%~6.5% and a chromium mass fraction of 20%~23%, belongs to the high-aluminum type in the iron-chromium-aluminum electric heating alloy series, and holds an irreplaceable position in high-end electric heating elements in fields such as industrial electric furnaces, household appliances, new energy vehicle thermal management systems, and electronic ceramic sintering.

[0042] In some embodiments, the welding material is wire with a specification of Φ1.2mm to Φ3.2mm.

[0043] The wire diameter range of Φ1.2mm to Φ3.2mm covers commonly used wire diameters in welding high-alumina iron-chromium-aluminum heating alloys. Specifically, Φ1.2mm and Φ1.6mm are suitable for welding thin plates (thickness 1.0mm to 2.5mm). The smaller wire diameter matches the lower welding heat input, allowing for precise control of weld formation and reducing grain growth in the heat-affected zone. Φ2.0mm and Φ2.4mm are suitable for welding medium-thick plates (thickness 2.5mm to 4.5mm). This range offers an optimal balance between wire feeding performance and melting efficiency, making it the most commonly used range in practical applications. Φ3.2mm is suitable for welding thick plates (thickness 4.5mm to 6.0mm). The larger diameter wire ensures sufficient filler metal, improving welding efficiency.

[0044] This specification range offers good compatibility with various welding methods. Φ1.2mm and Φ1.6mm specifications are primarily suitable for both manual and automatic tungsten inert gas (TIG) welding; the fine wire is easy to handle manually and offers high feeding accuracy automatically. Φ2.0mm and larger specifications are mainly suitable for gas metal arc welding (GMAW) and automatic TIG welding; the larger diameter wire is fed smoothly by the wire feed wheel, making it suitable for mechanized welding operations.

[0045] Figure 1 This is a schematic flowchart illustrating a method for preparing a high-alumina iron-chromium-aluminum electrothermal alloy welding material, as provided in an embodiment of this application.

[0046] Please see Figure 1 Secondly, this application provides a method for preparing the high-alumina iron-chromium-aluminum electrothermal alloy special welding material described in the first aspect, the method comprising: S1. Obtain an electroslag ingot having the aforementioned chemical composition; S2. The electroslag ingot is subjected to hot rolling, multi-pass cold drawing and continuous bright annealing in sequence to obtain the finished welding wire.

[0047] The process of obtaining electroslag ingots involves two closely linked smelting stages: vacuum induction melting and electroslag remelting. Vacuum induction melting is conducted under vacuum conditions. The vacuum environment effectively reduces the solubility of gaseous elements in the molten pool, promoting the escape of hydrogen, oxygen, and nitrogen from the melt, achieving deep degassing. Simultaneously, the vacuum condition prevents reactive elements such as aluminum, titanium, and rare earth elements from being oxidized and burned off by oxygen in the air during the melting process, ensuring precise control of the alloy composition. Electroslag remelting uses the electrode rod obtained from vacuum induction melting as a consumable electrode, undergoing secondary refining under slag protection. The molten slag pool has a washing effect on the molten metal droplets, effectively adsorbing and removing non-metallic inclusions from the metal, reducing the inclusion content to extremely low levels. The directional solidification conditions of electroslag remelting improve the solidification structure of the ingot, reducing casting defects such as shrinkage cavities, porosity, and compositional segregation, resulting in an electroslag ingot with a dense macrostructure and a uniform microstructure.

[0048] Hot rolling is the step of rolling an electroslag ingot into a billet. In the embodiments of this application, the cross-sectional dimensions of the electroslag ingot are typically Φ130~180mm. This size is not suitable for direct cold drawing and must be significantly reduced in cross-section through hot rolling to obtain an intermediate billet suitable for cold drawing. Hot rolling involves heating the electroslag ingot to 1050~1150℃ and holding it at that temperature for 1~2 hours before rolling. The rolling temperature is controlled within the range of 900~1150℃, and the final rolling temperature is ≥800℃. This hot rolling temperature range is above the recrystallization temperature of the iron-chromium-aluminum alloy. Dynamic recrystallization occurs during hot rolling, causing the as-cast structure to break down and refine into an equiaxed grain structure. The diameter of the hot-rolled wire rod obtained after hot rolling is Φ8~12mm. This size eliminates the coarse structure of the as-cast state and provides a suitable billet specification for subsequent cold drawing.

[0049] Multi-pass cold drawing is a process of gradually reducing the diameter of hot-rolled wire rod to the final wire specification. Cold drawing is performed at room temperature, where the metal material is passed through a die with an increasingly smaller cross-section under tensile stress, thus gradually reducing the wire diameter. The reduction of area per pass in cold drawing is controlled between 15% and 25%. This control is to prevent excessive deformation in a single pass, which could lead to rapid work hardening and fracture.

[0050] Continuous bright annealing is the final heat treatment step for welding wire obtained after multiple cold drawing processes. After multiple cold drawing processes, the welding wire is in a cold-deformed state, containing high-density dislocations and residual stress. The grains exhibit a fibrous structure elongated along the deformation direction, lacking an equiaxed crystal structure and exhibiting poor plasticity, making it unsuitable for direct use as a finished product. Continuous bright annealing heats the cold-drawn welding wire to above its recrystallization temperature and holds it at that temperature for a certain time, causing the cold-deformed structure to recover, recrystallize, and the grains to grow, ultimately forming a uniform and fine equiaxed crystal structure. This eliminates residual stress, restores plasticity, and achieves the mechanical properties and surface quality required for use. Continuous bright annealing is carried out in a protective atmosphere (decomposed ammonia or pure hydrogen). The purpose of the protective atmosphere is to prevent oxidation of the welding wire during the high-temperature annealing process, ensuring a bright, oxide-free surface that meets the surface cleanliness requirements for welding applications.

[0051] In some embodiments, the total area shrinkage of the multi-pass cold drawing process is ≥80%, and intermediate annealing is performed when the cumulative deformation of the multi-pass cold drawing process reaches 30%~40%. The intermediate annealing temperature is 750℃~850℃ and the holding time is 1h~2h.

[0052] Reduction of area, also known as cross-sectional reduction rate, refers to the ratio of the reduction in cross-sectional area of ​​a metallic material during tensile or compressive deformation to its original cross-sectional area. In multi-pass cold drawing, the total reduction of area refers to the total reduction ratio from the initial cross-sectional area of ​​the hot-rolled wire rod to the final cross-sectional area of ​​the finished wire. In the embodiments of this application, the limitation of a total reduction of area ≥80% means that the cross-sectional area of ​​the hot-rolled wire rod is reduced to at least 20% of its original cross-sectional area after all cold drawing passes.

[0053] Cumulative deformation refers to the reduction of area accumulated from the start of cold drawing to the current stage during multi-pass cold drawing. When the cumulative deformation reaches 30% to 40%, severe work hardening occurs within the material due to the proliferation and entanglement of numerous dislocations. This manifests as a sharp increase in strength, a significant decrease in plasticity, and a sharp increase in the deformation resistance to further cold drawing. If intermediate annealing is not performed at this point, wire breakage will occur in subsequent passes due to the material's inability to withstand further deformation, leading to processing failure. In the embodiments of this application, the intermediate annealing temperature is 750℃~850℃, and the holding time is 1h~2h. During multi-pass cold drawing, intermediate annealing may need to be performed multiple times. After each intermediate annealing, the plasticity of the material is restored, the dislocation density is significantly reduced, and subsequent cold drawing passes can continue.

[0054] In some embodiments, during the continuous brightening process, the annealing temperature is 750℃~900℃ and the annealing speed is 5m / min~15m / min.

[0055] The annealing temperature in continuous bright annealing refers to the peak temperature reached by the wire in the heating zone of the annealing furnace. This temperature is the thermodynamic driving force for the recovery, recrystallization, and grain growth of the cold-drawn work-hardened wire, directly determining the microstructure and mechanical properties of the wire after annealing. The annealing rate refers to the linear velocity of the wire in the continuous bright annealing furnace. The annealing rate and annealing temperature together determine the residence time of the wire in the high-temperature zone, thus determining whether the recrystallization process can be fully completed. In the embodiments of this application, the annealing temperature is 750℃~900℃, and the annealing rate is 5m / min~15m / min.

[0056] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0057] Example 1 This embodiment provides a high-alumina iron-chromium-aluminum electrothermal alloy special welding material, the chemical composition of which, by mass fraction, is: Cr 21.0%, Al 6.3%, Ti 0.15%, Zr 0.12%, Mo 0.8%, Si 0.30%, C 0.04%, rare earth element (Y) 0.06%, P 0.008%, S 0.003%, Ni 0.15%, Mn 0.20%, with the balance being Fe and unavoidable impurities.

[0058] The preparation process of the welding material in this embodiment includes the following steps: S1. Obtain an electroslag ingot with the above chemical composition. Specifically, pure iron, metallic chromium, metallic aluminum, sponge titanium, ferrozirconium, ferromolybdenum, ferrosilicon, cementite, and yttrium rare earth alloy, prepared according to the above component ratio, are charged into a vacuum induction furnace. Vacuum induction melting is performed under a vacuum degree of 5 Pa, the refining temperature is 1620℃, and the refining time is 30 min, casting it into an electrode rod with a diameter of 130 mm. The electrode rod is used as a consumable electrode and electroslag remelted in a crystallizer. The slag system is a CaF2-Al2O3-CaO ternary slag system, obtaining an electroslag ingot with a diameter of 180 mm.

[0059] S2. The electroslag ingot is sequentially hot-rolled, cold-drawn in multiple passes, and continuously bright-annealed to obtain the finished welding wire. Specifically, the electroslag ingot is homogenized and annealed at 1100℃ for 2 hours, then hot-rolled into a Φ10mm hot-rolled wire rod. The hot-rolled wire rod is pickled and descaled, then cold-drawn in multiple passes with a total area reduction ≥80%. When the cumulative deformation reaches 35%, intermediate annealing is performed at 800℃ for 1.5 hours. The wire is then cold-drawn to a finished size of Φ1.6mm. The welding wire obtained after multiple cold-drawing is continuously bright-annealed in a protective atmosphere of decomposed ammonia at 820℃ and 10m / min to eliminate residual stress and obtain an equiaxed grain structure, thus obtaining the finished welding wire.

[0060] The finished welding wire prepared in this embodiment was subjected to performance tests. The room temperature tensile strength and elongation after fracture were determined according to GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test at room temperature". The grain size was determined according to GB / T 6394-2017 "Metallic materials, average grain size determination method". The test results were: room temperature tensile strength 682 MPa, elongation after fracture 16%, and grain size grade 7.

[0061] Welding verification was performed on the welding materials used in this embodiment. A high-alumina iron-chromium-aluminum electrothermal alloy base material with an Al content of 6.0% and a Cr content of 21.5% was welded using the TIG welding method. Welding parameters: current 130~150A, voltage 12~14V, welding speed 80~120mm / min, shielding gas was pure Ar, gas flow rate 12~15L / min.

[0062] The welded joint was tested and found to have the following microstructure: the weld zone consists of a ferrite matrix with dispersed TiC and ZrC nano-precipitates (20-100 nm in size) and Fe2(Ti,Zr) type Laves phase (50-200 nm in size), with a grain size of grade 6; the heat-affected zone has a grain size of grade 5. The welded joint has a room temperature tensile strength of 560 MPa, which is 80% of the room temperature tensile strength of the base metal; the elongation after fracture is 10%; and no cracks were found after bending 180°. The aluminum content of the weld metal was tested to be 5.8%; the oxidation resistance of the weld and heat-affected zone at 1000℃ is comparable to that of the base metal.

[0063] Example 2 This embodiment provides a high-alumina iron-chromium-aluminum electrothermal alloy special welding material, the chemical composition of which, by mass fraction, is: Cr 20.5%, Al 5.8%, Ti 0.13%, Zr 0.10%, Mo 0.6%, Si 0.28%, C 0.035%, rare earth element (Ce) 0.05%, P 0.010%, S 0.002%, Ni 0.10%, Mn 0.15%, with the balance being Fe and unavoidable impurities.

[0064] The difference between the preparation process of the welding material in this embodiment and that in embodiment 1 is that the material is cold-drawn to a diameter of Φ2.0mm in multiple passes and continuously bright annealed at a temperature of 800℃.

[0065] The finished welding wire prepared in this embodiment was subjected to performance testing. The test results were as follows: room temperature tensile strength 668 MPa, elongation after fracture 18%, and grain size grade 7.

[0066] Welding verification was performed on the welding materials used in this embodiment. A high-alumina iron-chromium-aluminum electric heating alloy base material with an Al content of 5.5% and a Cr content of 20.8% was welded using the TIG welding method.

[0067] The welded joint was tested and found to have the following microstructure: the weld zone consists of a ferrite matrix with dispersed TiC and ZrC nano-precipitates (20-100 nm in size) and Fe2(Ti,Zr) type Laves phase (50-200 nm in size), with a grain size of 6.5; the heat-affected zone has a grain size of 5.5. The welded joint has a room temperature tensile strength of 550 MPa, which is 79% of the room temperature tensile strength of the base metal; the elongation after fracture is 12%; and no cracks were found after bending 180°. The aluminum content of the weld metal was tested to be 5.3%; the oxidation resistance of the weld and heat-affected zone at 1000℃ is comparable to that of the base metal.

[0068] Example 3 This embodiment provides a high-alumina iron-chromium-aluminum electrothermal alloy special welding material, the chemical composition of which, by mass fraction, is: Cr 22.0%, Al 6.6%, Ti 0.11%, Zr 0.18%, Mo 1.0%, Si 0.35%, C 0.04%, rare earth element (La) 0.07%, P 0.012%, S 0.004%, Ni 0.20%, Mn 0.25%, with the balance being Fe and unavoidable impurities.

[0069] The difference between the preparation process of the welding material in this embodiment and that in embodiment 1 is that the material is cold-drawn to a diameter of Φ1.2mm in multiple passes and continuously bright annealed at a temperature of 850℃.

[0070] The finished welding wire prepared in this embodiment was subjected to performance testing. The test results were as follows: room temperature tensile strength 668 MPa, elongation after fracture 14%, and grain size grade 7.5.

[0071] Welding verification was performed on the welding materials used in this embodiment. A high-alumina iron-chromium-aluminum electric heating alloy base material with an Al content of 6.3% and a Cr content of 22.0% was welded using the TIG welding method.

[0072] The welded joint was tested and found to have the following microstructure: the weld zone consists of a ferrite matrix with dispersed TiC and ZrC nano-precipitates (20-100 nm in size) and Fe2(Ti,Zr) type Laves phase (50-200 nm in size), with a grain size of 5.5; the heat-affected zone has a grain size of 4.5. The welded joint has a room temperature tensile strength of 580 MPa, which is 82% of the room temperature tensile strength of the base metal; the elongation after fracture is 9%; and no cracks were found after bending 180°. The aluminum content of the weld metal was tested to be 6.4%; the oxidation resistance of the weld and heat-affected zone at 1000℃ is comparable to that of the base metal.

[0073] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: The high-alumina iron-chromium-aluminum electrothermal alloy special welding material and its preparation method provided in this application embodiment, through the precise design of the welding material's chemical composition and the synergistic coordination of the preparation process, simultaneously achieves effective suppression of aluminum element evaporation and burn-off, significant refinement of weld seam and heat-affected zone grains, phase structure and thermal expansion properties that are completely matched with the base material, as well as excellent mechanical properties and high-temperature oxidation resistance of the weld joint in the welding of high-alumina iron-chromium-aluminum electrothermal alloy base material with an aluminum content of 5.3% to 6.5% and a chromium content of 20% to 23%, thus achieving comprehensive technological progress.

[0074] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A special welding material for high-alumina iron-chromium-aluminum electrothermal alloy, characterized in that, The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~23%, Al: 5.5%~7.0%, Ti: 0.05%~0.60%, Zr: 0.05%~0.30%, Mo: 0.3%~1.0%, Si: 0.2%~0.5%, C: 0.02%~0.08%, rare earth elements: 0.03%~0.12%, P≤0.015%, S≤0.005%, Ni≤0.5%, Mn≤0.5%, with the balance being Fe and unavoidable impurities.

2. The welding material according to claim 1, characterized in that, The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20.5%~22.5%, Al: 6.0%~6.8%, Ti: 0.20%~0.50%, Zr: 0.08%~0.20%, Mo: 0.5%~1.0%, Si: 0.25%~0.40%, C: 0.03%~0.06%, rare earth elements: 0.05%~0.08%, P≤0.015%, S≤0.005%, Ni≤0.5%, Mn≤0.5%, with the balance being Fe and unavoidable impurities.

3. The welding material according to claim 1, characterized in that, The rare earth element is at least one of La, Ce, and Y.

4. The welding material according to claim 1, characterized in that, The ratio of the sum of the mass fractions of Ti and Zr to the mass fraction of C is (4~8):

1.

5. The welding material according to claim 1, characterized in that, The welding material meets at least one of the following properties: room temperature tensile strength ≥550MPa, elongation after fracture ≥15%, and grain size ≥6.

6. The welding material according to claim 1, characterized in that, The welding material is used for welding high-alumina iron-chromium-aluminum electric heating alloy base material, wherein the mass fraction of Al in the high-alumina iron-chromium-aluminum electric heating alloy base material is 5.3%~6.5%, and the mass fraction of Cr is 20%~23%.

7. The welding material according to claim 1, characterized in that, The welding material is wire, and the specifications of the welding material are Φ1.2mm~Φ3.2mm.

8. A method for preparing a high-alumina iron-chromium-aluminum electrothermal alloy special welding material according to any one of claims 1 to 7, characterized in that, The method includes: An electroslag ingot with the aforementioned chemical composition is obtained; The electroslag ingot is subjected to hot rolling, multiple cold drawing processes, and continuous bright annealing in sequence to obtain the finished welding wire.

9. The method according to claim 8, characterized in that, The total area shrinkage of the multi-pass cold drawing process is ≥80%. When the cumulative deformation of the multi-pass cold drawing process reaches 30%~40%, intermediate annealing is performed. The temperature of the intermediate annealing treatment is 750℃~850℃, and the holding time is 1h~2h.

10. The method according to claim 8, characterized in that, During the continuous brightening process, the annealing temperature is 750℃~900℃ and the annealing speed is 5m / min~15m / min.

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