Special welding material for iron-chromium-aluminum electric heating alloy and preparation method thereof

Abstract

The application relates to a welding material special for iron-chromium-aluminum electric heating alloy and a preparation method thereof, and belongs to the technical field of welding materials. The chemical components of the welding material are as follows in terms of mass fraction: Cr: 20%-24%, Al: 4.5%-5.5%, Ni: 2.0%-6.0%, Mn: 0.5%-2.0%, Nb: 0.1%-0.5%, Si: 0.2%-0.5%, C<=0.020%, rare earth elements: 0.02%-0.10%, P<=0.015%, S<=0.005%, 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 special welding material for iron-chromium-aluminum electrothermal alloy and its preparation method. Background Technology

[0002] Iron-chromium-aluminum (FeCrAl) heating alloys are an important class of high-resistance heating materials, possessing excellent high-temperature oxidation resistance, high resistivity, and good economic efficiency. They are widely used in industrial electric furnaces, household appliances, thermal management systems for new energy vehicles, and electronic ceramic sintering. With the continuous expansion of product applications and the sustained increase in service temperatures, the demand for welding of FeCrAl heating alloy elements is increasing. Welding quality directly determines the service life and operational safety of the heating alloy elements.

[0003] However, iron-chromium-aluminum electrothermal alloys maintain a completely body-centered cubic (BCC) single-phase ferrite structure from room temperature to melting point, lacking a solid-state phase transformation mechanism. Under the action of welding thermal cycling, the weld zone and heat-affected zone experience rapid grain growth due to high temperatures. During the post-weld cooling process, the coarsened grains cannot be refined through solid-state phase transformation, resulting in a significant reduction in the plasticity of the welded joint and making it extremely prone to brittle fracture. Summary of the Invention

[0004] This application provides a special welding material for iron-chromium-aluminum electrothermal alloys and its preparation method to solve the following technical problem: how to develop a special welding material that can solve the problems of grain coarsening and embrittlement in iron-chromium-aluminum electrothermal alloy welded joints. In the first aspect, embodiments of this application provide a special welding material for iron-chromium-aluminum electrothermal alloys. The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~24%, Al: 4.5%~5.5%, Ni: 2.0%~6.0%, Mn: 0.5%~2.0%, Nb: 0.1%~0.5%, Si: 0.2%~0.5%, C≤0.020%, rare earth elements: 0.02%~0.10%, P≤0.015%, S≤0.005%, with the balance being Fe and unavoidable impurities.

[0005] Optionally, the chemical composition of the welding material, by mass fraction, is as follows: Cr: 21%~23%, Al: 4.8%~5.3%, Ni: 3.0%~5.0%, Mn: 0.8%~1.5%, Nb: 0.15%~0.35%, Si: 0.2%~0.5%, C≤0.020%, rare earth elements: 0.02%~0.10%, P≤0.015%, S≤0.005%, with the balance being Fe and unavoidable impurities.

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

[0007] Optionally, the welding material is used to weld an iron-chromium-aluminum electric heating alloy base material, wherein the mass fraction of Al in the iron-chromium-aluminum electric heating alloy base material is 4.0%~5.3% and the mass fraction of Cr is 21%~23%.

[0008] Optionally, the weld metal formed by welding the welding material has a dual-phase microstructure, which includes a ferrite matrix and an austenite second phase, wherein the volume fraction of the austenite second phase is 15% to 50% of the total volume of the weld metal.

[0009] Optionally, the welding material meets at least one of the following properties: room temperature tensile strength ≥500MPa, elongation after fracture ≥20%, and grain size ≥6.

[0010] Secondly, this application provides a method for preparing the iron-chromium-aluminum electrothermal alloy special welding material described in the first aspect, the method comprising: The raw materials with the aforementioned chemical composition are subjected to vacuum induction melting to obtain molten steel; The molten steel is cast into electrode rods; Using a CaF2-Al2O3-CaO ternary slag system, the electrode rod was used as a consumable electrode for electroslag remelting to obtain an electroslag ingot. The electroslag ingot is heated to 1050℃~1150℃ and then hot-rolled, and the final rolling temperature is controlled to be ≥800℃ to obtain hot-rolled wire rod. The hot-rolled wire rod is subjected to multiple cold drawing processes, and intermediate annealing is performed when the cumulative deformation reaches 30%~40% to eliminate work hardening, so as to obtain welding wire that meets the target specifications. The welding wire is subjected to continuous bright annealing under a protective atmosphere to obtain the finished welding wire.

[0011] Optionally, the vacuum degree of the vacuum induction melting is ≤10Pa, the temperature of the vacuum induction melting is 1550℃~1650℃, and the time of the vacuum induction melting is 20min~40min.

[0012] Optionally, in the multi-pass cold drawing process, the surface shrinkage rate of each cold drawing process is 15%~25%, and the total surface shrinkage rate is ≥80%; the intermediate annealing temperature is 750℃~850℃, and the intermediate annealing holding time is 1h~2h.

[0013] Optionally, during the continuous bright annealing process, the annealing temperature is 750℃~900℃, and the annealing speed is 5m / min~15m / min; the protective atmosphere during the continuous bright annealing process is decomposed ammonia or pure hydrogen.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a special welding material for iron-chromium-aluminum electric heating alloy. The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~24%, Al: 4.5%~5.5%, Ni: 2.0%~6.0%, Mn: 0.5%~2.0%, Nb: 0.1%~0.5%, Si: 0.2%~0.5%, C≤0.020%, rare earth elements: 0.02%~0.10%, P≤0.015%, S≤0.005%, with the balance being Fe and unavoidable impurities. This application introduces nickel and manganese as austenite-forming elements into the welding material. Utilizing the austenite phase expansion effect of these two elements, the weld metal spontaneously forms a two-phase microstructure with ferrite as the matrix and austenite as the second phase during solidification and cooling. The austenite phase forms continuous or semi-continuous physical barriers at the ferrite grain boundaries, effectively hindering grain boundary migration during welding thermal cycling through interfacial pinning effects. Simultaneously, the excellent face-centered cubic crystal structure of the austenite phase itself provides synergistic toughening through crack deflection, crack passivation, and crack bridging mechanisms, thus fundamentally solving the room-temperature embrittlement problem caused by coarse grains. Building upon this, this application further introduces niobium, utilizing the niobium carbide and Laves phase nanoprecipitates formed during solidification. These niobium act as additional barriers pinning grain boundaries and dislocations, and as non-uniform nucleation sites for the austenite phase, lowering its nucleation energy barrier and promoting the dispersed distribution of austenite, thereby further enhancing the grain refinement effect. Furthermore, this application sets the aluminum content of the welding material to a level higher than that of the base metal. The excess aluminum in the welding material offsets the inevitable evaporation loss of aluminum due to high vapor pressure at high welding temperatures, ensuring that the residual aluminum content in the weld metal after burn-out remains at a concentration comparable to that of the base metal. This maintains the integrity of the Al2O3 oxide film and its high-temperature oxidation resistance. Simultaneously, rare earth elements purify grain boundaries by segregating and pinning low-melting-point impurities, combine with oxygen and sulfur to modify inclusions, and accumulate at the oxide film-metal interface to inhibit oxide film peeling. Together with the oxidation-resistant effects of chromium and aluminum, they form a multi-layered protective network. This application precisely controls the austenite phase volume fraction within the range of 15% to 50%, ensuring that the ferrite matrix always dominates. This guarantees that the thermal expansion coefficients of the welding material and the base metal are at the same level, completely eliminating the risk of interfacial thermal stress cracking caused by differences in physical properties during dissimilar metal welding. 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 special welding material for iron-chromium-aluminum electrothermal alloys, 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 special welding material for iron-chromium-aluminum electrothermal alloys. The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~24%, Al: 4.5%~5.5%, Ni: 2.0%~6.0%, Mn: 0.5%~2.0%, Nb: 0.1%~0.5%, Si: 0.2%~0.5%, C≤0.020%, rare earth elements: 0.02%~0.10%, P≤0.015%, S≤0.005%, with the balance being Fe and unavoidable impurities.

[0021] The combination of nickel (2.0%~6.0% by mass) and manganese (0.5%~2.0% by mass) results in a total mass fraction of 2.5%~8.0%. Nickel, as the main austenite-forming element, dominates the nucleation and growth of the austenite phase, while manganese, as an auxiliary austenite-forming element, enhances the austenitization effect of nickel. Together, they enable the weld metal to form a second austenite phase with a volume fraction of 15%~50% during solidification and cooling, achieving the grain boundary pinning effect of the two-phase structure.

[0022] During welding, the molten pool temperature can reach over 1500℃. Aluminum has a high vapor pressure at high temperatures, and aluminum atoms easily evaporate from the molten pool surface, resulting in a lower aluminum content in the weld metal compared to the original aluminum content of the welding material. Typically, the burn-off is 10% to 30% of the base metal's aluminum content. If the aluminum content of the welding material is the same as that of the base metal, the aluminum content of the weld metal after welding will be lower than that of the base metal. This leads to insufficient continuity and density of the alumina film formed on the weld metal surface, making the weld metal a weak point in the welded joint's oxidation resistance. Consequently, the welded joint's oxidation resistance life under high-temperature service conditions is lower than that of the base metal. In this application, the aluminum content of the welding material is designed to be 4.5% to 5.5%, which is higher than the target welded joint's aluminum content of approximately 4.0% to 5.0%. During welding, the higher aluminum content in the welding material provides a sufficient supply of aluminum. After this portion of aluminum evaporates and burns off during welding, the residual aluminum content in the weld metal can still be maintained within the range of the target welded joint's aluminum content. This aluminum content compensation design ensures that the final aluminum content of the weld metal after undergoing welding thermal cycling and aluminum burn-off is comparable to that of the base metal. This guarantees the formation of a protective oxide film on the weld metal surface that is as dense and continuous as that of the base metal, matching the high-temperature oxidation resistance of the weld metal to that of the base metal and avoiding the problem of preferential oxidation of the weld due to aluminum burn-off. Secondly, the combined use of 20%–24% chromium and 4.5%–5.5% aluminum by mass allows the weld metal to form a composite oxide film under high-temperature service conditions, possessing both the high density of alumina and the excellent adhesion of a chromium-rich oxide film. This composite oxide film offers superior oxidation protection compared to a single chromium oxide film or a single aluminum oxide film.

[0023] In the embodiments of this application, niobium preferentially combines with carbon in the welding material to form fine niobium carbide (NbC) particles, thereby suppressing harmful chromium-rich carbides (MnC) by consuming free carbon. 23Niobium (C6 type) precipitates at grain boundaries, preventing grain boundary weakening and the consumption of effective chromium content in the matrix. During weld metal solidification, niobium promotes the precipitation of the Laves phase (Fe2Nb) at grain boundaries and within grains. These nanoscale Laves phase precipitates, acting as second-phase particles, pin dislocations and grain boundaries, synergistically inhibiting ferrite grain growth with the austenite second phase. During weld cooling, niobium-containing precipitates act as non-uniform nucleation sites for the austenite phase, promoting the dispersed distribution of the austenite second phase at grain boundaries and within grains. When the niobium mass fraction is below 0.1%, the amount of niobium carbide and Laves phase formed is insufficient, resulting in insignificant precipitation strengthening and grain boundary pinning effects, failing to effectively inhibit ferrite grain growth. When the niobium mass fraction is above 0.5%, the number and size of Laves phase precipitates are excessive, and the large Laves phase particles become preferential sites for crack initiation, thus impairing the toughness and plasticity of the weld metal. By controlling the niobium mass fraction within the range of 0.1% to 0.5%, toughness damage caused by precipitate coarsening can be avoided while ensuring sufficient precipitation strengthening and grain boundary pinning effect.

[0024] In iron-chromium-aluminum alloys, carbon combines with chromium to form chromium-rich carbides. When the carbon content exceeds 0.020%, the precipitated chromium-rich carbides accumulate at grain boundaries, leading to grain boundary embrittlement, reducing the toughness and crack resistance of welded joints. Simultaneously, they deplete chromium in the matrix, weakening the effective chromium content and thus impairing high-temperature oxidation resistance. Controlling the carbon mass fraction to no more than 0.020% can prevent the harmful precipitation of chromium-rich carbides and ensure grain boundary bonding and the effective chromium content of the matrix.

[0025] In this embodiment, the main functions of rare earth elements are: purifying grain boundaries, removing low-melting-point impurities at grain boundaries, and improving grain boundary bonding; forming high-melting-point rare earth oxides and rare earth sulfides with oxygen and sulfur, thus acting as deoxidizers, desulfurizers, and removes modified inclusions; and improving the density and adhesion of the oxide layer on the weld metal surface, thereby enhancing the high-temperature oxidation resistance of the weld joint. When the mass fraction of rare earth elements is less than 0.02%, the grain boundary purification, deoxidation, desulfurization, and oxide layer modification effects of rare earth elements are insufficient, and their effect on improving the toughness and oxidation resistance of the weld metal cannot be fully realized. When the mass fraction of rare earth elements is greater than 0.10%, excessive rare earth elements accumulate at grain boundaries, forming brittle rare earth compounds, which reduces grain boundary bonding. At the same time, excessive rare earth elements increase the amount of non-metallic inclusions in the molten steel, reducing the purity of the weld metal. By controlling the mass fraction of rare earth elements within the range of 0.02% to 0.10%, it is possible to ensure that rare earth elements fully exert their functions in the three aspects mentioned above, while avoiding problems such as grain boundary weakening and purity reduction caused by excessive rare earth elements.

[0026] Phosphorus (P) and sulfur (S) are strictly restricted harmful impurity elements in this application. In the welding materials of this application, the mass fraction of phosphorus is controlled at an extremely low level of no more than 0.015% and the mass fraction of sulfur is controlled at no more than 0.005%.

[0027] Fe is a matrix element, and the specific content / range of Fe can be obtained through the upper and lower limit formulas of the component, that is: The sum of the percentages of all components in a composition shall be equal to 100%, and the content ranges of several components shall meet the following conditions: the upper limit of a certain component + the lower limit of other components ≤ 100; the lower limit of a certain component + the upper limit of other components ≥ 100.

[0028] In some embodiments, the chemical composition of the welding material, by mass fraction, is: Cr: 21%~23%, Al: 4.8%~5.3%, Ni: 3.0%~5.0%, Mn: 0.8%~1.5%, Nb: 0.15%~0.35%, Si: 0.2%~0.5%, C≤0.020%, rare earth elements: 0.02%~0.10%, P≤0.015%, S≤0.005%, with the balance being Fe and unavoidable impurities.

[0029] In some embodiments, the rare earth element is at least one of La, Ce, Y, and Hf.

[0030] In this embodiment, the rare earth element is at least one of lanthanum, cerium, yttrium, and hafnium. In practice, the choice can be made based on different performance priorities and cost considerations. Whether used alone or in combination, the total mass fraction of rare earth elements is maintained within the range of 0.02% to 0.10%, ensuring that while leveraging the combined effects of rare earth elements in grain boundary purification, deoxidation, desulfurization, and oxide layer modification, problems such as grain boundary weakening and increased inclusions caused by excessively high total rare earth element content are avoided.

[0031] In some embodiments, the welding material is used to weld an iron-chromium-aluminum electric heating alloy base material, wherein the mass fraction of Al in the iron-chromium-aluminum electric heating alloy base material is 4.0% to 5.3%, and the mass fraction of Cr is 21% to 23%.

[0032] Iron-chromium-aluminum (FeCrA) heating alloys can be classified into various grades and types based on their aluminum and chromium content. Different base metal compositions require different welding material compositions. FeCrA base metals with an Al mass fraction of 4.0%–5.3% and a Cr mass fraction of 21%–23% belong to the high-temperature grade within the FeCrA series. These alloys can operate at temperatures up to 1200℃–1400℃ and are mainly used in heating alloy products requiring high-temperature oxidation resistance. The welding materials provided in this application are specifically designed for welding the aforementioned FeCrA base metals, avoiding misleading use of unsuitable base metals.

[0033] In some embodiments, the weld metal formed by welding the welding material has a dual-phase microstructure, which includes a ferrite matrix and an austenite second phase, wherein the volume fraction of the austenite second phase is 15% to 50% of the total volume of the weld metal.

[0034] Weld metal refers to the metallic portion that constitutes the weld after the welding material melts and mixes with partially molten base metal under the influence of welding heat, and then solidifies upon cooling. The ferrite matrix refers to the ferrite phase in the weld metal that exists with a body-centered cubic (BCC) crystal structure; this phase constitutes the continuous main body of the weld metal's microstructure. The austenite second phase refers to the austenite phase in the weld metal that exists with a face-centered cubic (FCC) crystal structure; this phase is distributed in a discontinuous second-phase form within the ferrite matrix.

[0035] When the volume fraction of the austenite second phase is less than 15%, the amount of austenite second phase is insufficient to form a continuous or semi-continuous distribution at the ferrite grain boundaries. The pinning sites on the grain boundaries are not adequately covered, and the ferrite grain boundaries not pinned by the austenite second phase can still migrate. The grains will still grow significantly during the welding thermal cycle. The grain boundary pinning effect of the dual-phase structure is insufficient. At the same time, the amount of austenite phase required for crack deflection and crack passivation is insufficient, resulting in limited toughening effect.

[0036] When the volume fraction of the austenite second phase exceeds 50%, its proportion in the weld metal becomes excessively high. This disrupts the continuity of the ferrite matrix, causing the overall thermal expansion coefficient of the dual-phase structure to deviate from the intrinsic value of ferrite, shifting towards the austenitic thermal expansion coefficient. Meanwhile, the base metal remains a pure ferrite structure, increasing the difference in thermal expansion coefficients between the weld metal and the base metal. This leads to additional thermal stress at the interface under high-temperature service conditions. Furthermore, the austenite phase carries the risk of transformation into ferrite or precipitation of harmful phases during long-term high-temperature service, resulting in structural degradation. An excessively high austenite proportion exacerbates this degradation, negatively impacting the weld joint's performance. Controlling the volume fraction of the austenite second phase within the range of 15% to 50% ensures sufficient pinning coverage at the ferrite grain boundaries and effective toughening, while avoiding the thermal expansion coefficient mismatch and structural degradation risks associated with an excessively high austenite proportion. This optimizes the beneficial effects of the dual-phase structure on grain refinement and toughness improvement.

[0037] In some embodiments, the welding material satisfies at least one of the following properties: room temperature tensile strength ≥500MPa, elongation after fracture ≥20%, and grain size ≥6.

[0038] The above three performance indicators characterize the overall quality level of welding materials from three dimensions: strength, plasticity, and microstructure refinement. Room temperature tensile strength reflects the welding material's ability to resist tensile fracture, elongation after fracture reflects the welding material's ability to undergo plastic deformation before fracture, and grain size reflects the degree of refinement of the welding material's microstructure.

[0039] Figure 1 This is a schematic flowchart illustrating a method for preparing a special welding material for iron-chromium-aluminum electrothermal alloys, as provided in an embodiment of this application.

[0040] Please see Figure 1 Secondly, this application provides a method for preparing the iron-chromium-aluminum electrothermal alloy special welding material described in the first aspect, the method comprising: S1. The raw materials having the aforementioned chemical composition are subjected to vacuum induction melting to obtain molten steel; S2. Cast the molten steel into an electrode rod; S3. Using a CaF2-Al2O3-CaO ternary slag system, the electrode rod is used as a consumable electrode for electroslag remelting to obtain an electroslag ingot. S4. The electroslag ingot is heated to 1050℃~1150℃ and then hot rolled, and the final rolling temperature is controlled to be ≥800℃ to obtain hot rolled wire rod. S5. The hot-rolled wire rod is subjected to multiple cold drawing processes, and intermediate annealing is performed when the cumulative deformation reaches 30%~40% to eliminate work hardening, so as to obtain welding wire that meets the target specifications. S6. The welding wire is continuously bright annealed under a protective atmosphere to obtain the finished welding wire.

[0041] The raw materials with the chemical composition defined in the first aspect are subjected to vacuum induction melting. The vacuum environment is used as a melting protection condition to isolate the oxidation of the molten metal by external air during the melting process. This allows the actual yield of aluminum and chromium in the molten steel to be maintained at a high level, while significantly reducing the gas content and harmful impurity content in the molten steel. This provides high-purity and precisely composed molten steel raw materials for the subsequent casting of electrode rods.

[0042] Casting refers to the process of pouring molten steel obtained after vacuum induction melting from the crucible of the vacuum induction furnace into a mold for cooling and solidification. An electrode rod is a solid metal billet with a cylindrical cross-section, obtained after casting, and used as a consumable electrode in the electroslag remelting process. The diameter of the electrode rod is Φ100 mm to Φ150 mm, a specification that facilitates clamping operations in the electroslag remelting process while ensuring a suitable melting rate and molten pool stability during electroslag remelting.

[0043] Electroslag remelting is a secondary refining metallurgical process that uses an electrode rod as a consumable electrode. The electrode rod's tip is melted by the resistance heat generated when current passes through the molten slag system. The electrode rod material is then sequentially solidified in a water-cooled crystallizer after being refined by the slag system. This process employs a CaF2-Al2O3-CaO ternary slag system, which refers to a molten slag system composed of calcium fluoride, alumina, and calcium oxide. In the electroslag remelting step, the amount of CaF2-Al2O3-CaO ternary slag system can be 3% to 5% of the electroslag ingot weight, the melting rate can be 3~5 kg / min, and the feeding time can be 5~10 min. The melting rate refers to the melting rate of the consumable electrode during electroslag remelting, i.e., the amount of metal melted and entering the crystallizer per unit time. Feeding refers to the process of gradually reducing the current and melting rate near the end of electroslag remelting, so that the molten metal in the upper metal pool of the crystallizer is replenished by subsequent metal during the solidification shrinkage process, thereby eliminating the shrinkage cavity at the top of the electroslag ingot. After the consumable electrode is refined by electroslag remelting, an electroslag ingot is obtained, with a specification of Φ130~180mm.

[0044] Hot rolling is a process in which electroslag ingots are heated to a high temperature and then plastically deformed. This process breaks down the coarse columnar and dendritic structures of the cast electroslag ingots through high-temperature plastic deformation and transforms them into fine equiaxed crystal structures. Simultaneously, the large cross-sectional dimensions of the electroslag ingots are rolled into small cross-sectional wire rods suitable for cold drawing. In this process, the electroslag ingots are loaded into a heating furnace (charging temperature ≤400℃), and the overall temperature of the ingots is uniformly raised to the range of 1050℃ to 1150℃ and held for a certain time (1~2 hours) to homogenize the internal and external temperatures. The heated electroslag ingots are then subjected to multi-pass rolling deformation on a rolling mill. The final rolling temperature refers to the instantaneous temperature of the hot-rolled wire rod at the end of the last rolling pass. Controlling the final rolling temperature to ≥800℃ ensures that hot rolling is completed above the recrystallization temperature, avoiding work hardening caused by deformation in the low-temperature region. After heating and hot rolling, the electroslag ingots are obtained as hot-rolled wire rods with diameters ranging from Φ8 mm to Φ12 mm.

[0045] Cold drawing refers to a cold deformation process in which metal wire rods are forcibly drawn through drawing dies with cross-sectional dimensions smaller than the original cross-section of the wire rod at room temperature, thereby reducing the cross-section and increasing the length of the wire rod. Multi-pass cold drawing refers to passing hot-rolled wire rods sequentially through multiple drawing dies with progressively smaller diameters. Each pass through a drawing die constitutes one cold drawing pass, and the hot-rolled wire rod is processed to the target specification through multiple passes of progressive diameter reduction. In this application's embodiment, the diameter of the hot-rolled wire rod is gradually reduced from Φ8 mm to Φ12 mm to the target specifications (Φ1.2 mm, Φ1.6 mm, Φ2.0 mm, Φ2.4 mm, or Φ3.2 mm) through multi-pass cold drawing. Cumulative deformation refers to the percentage of the cumulative reduction in cross-sectional area achieved after multiple cold drawing passes, starting from the initial state of the hot-rolled wire rod, relative to the initial cross-sectional area of ​​the hot-rolled wire rod. In the multi-pass cold drawing process, whenever the cumulative section reduction rate, calculated from the initial section of the hot-rolled wire rod, reaches the range of 30% to 40%, an intermediate annealing treatment is performed on the wire rod during cold drawing.

[0046] Continuous bright annealing is a process in which cold-drawn welding wire to the target specification is continuously passed through a heating furnace under a protective atmosphere for annealing heat treatment. This process eliminates the residual stress generated during the multiple cold drawing processes of the welding wire, and allows the deformed structure in the work-hardened state after cold drawing to be transformed into a uniform and fine equiaxed crystal structure through recrystallization. At the same time, the protective atmosphere prevents the surface oxidation of the welding wire during the high-temperature annealing process, so that the finished welding wire obtains a bright and oxidation-free surface quality.

[0047] In some embodiments, the vacuum degree of the vacuum induction melting is ≤10Pa, the temperature of the vacuum induction melting is 1550℃~1650℃, and the time of the vacuum induction melting is 20min~40min.

[0048] Vacuum induction melting is a smelting method that uses the eddy current heating effect generated by an induced electromagnetic field to melt metal raw materials in a vacuum environment. The core function of vacuum induction melting is that melting under vacuum conditions can reduce the partial pressure of oxygen and other active gases in the melting space, thereby effectively preventing the oxidation and burn-off of active elements (especially aluminum and chromium) in the alloy at high temperatures. At the same time, the vacuum environment removes dissolved gases such as hydrogen and nitrogen, as well as low-melting-point harmful impurities, to extremely low levels, resulting in high-purity molten steel.

[0049] Setting the upper limit of vacuum to 10Pa is a reasonable balance point within the economical operating range of industrial vacuum equipment, which can ensure the deoxidation and degassing effect while avoiding the excessive pursuit of ultra-high vacuum that would lead to a sharp increase in equipment investment and operating costs.

[0050] The temperature of vacuum induction melting provides the necessary thermodynamic driving force for the deoxidation and degassing reactions in the molten steel, allowing alloying elements (especially high-melting-point alloying elements such as niobium and chromium) to fully dissolve and uniformly distribute in the molten steel. Simultaneously, the reduced viscosity of the molten steel allows suspended non-metallic inclusions to gain sufficient kinetic energy to float to the surface and be removed. In this embodiment, the refining temperature is controlled within the range of 1550℃ to 1650℃. This ensures that the high-melting-point alloying elements are fully dissolved and homogenized, while keeping the evaporation and burn-off of aluminum within an acceptable industrial range, and reducing the adverse effects of furnace lining erosion on the purity of the molten steel.

[0051] The vacuum induction melting time refers to the time that molten steel remains within the refining temperature range of 1550℃ to 1650℃ after reaching this temperature. The vacuum induction melting time provides sufficient kinetic time for the deoxidation and degassing reactions of the molten steel, the homogenization of alloying element diffusion, and the flotation and removal of inclusions. In this application, the refining time is controlled within the range of 20 to 40 minutes. This ensures sufficient deoxidation and degassing, as well as composition homogenization, while keeping the cumulative evaporation loss of aluminum within the design compensation range, and also takes into account smelting production efficiency.

[0052] In some embodiments, during the multi-pass cold drawing process, the surface shrinkage rate of each cold drawing pass is 15%~25%, and the total surface shrinkage rate is ≥80%; the intermediate annealing temperature is 750℃~850℃, and the intermediate annealing holding time is 1h~2h.

[0053] Area reduction ratio refers to the percentage reduction in the cross-sectional area of ​​the wire rod during cold drawing relative to its original cross-sectional area. An area reduction ratio of 15% to 25% per cold drawing pass ensures the feasibility of cold drawing. A reduction ratio below 15% results in low production efficiency and an increase in the number of cold drawing passes, while a reduction ratio above 25% leads to excessive resistance to cold drawing deformation, easily causing surface cracking or breakage of the welding wire. A total area reduction ratio ≥80% means that the cumulative reduction in cross-sectional area across all cold drawing passes, from the initial cross-section of the hot-rolled wire rod to the target cross-section of the welding wire conforming to the target specifications, is no less than 80% of the initial cross-sectional area of ​​the hot-rolled wire rod. A total area reduction ratio ≥80% is a necessary condition for achieving large deformation processing from hot-rolled wire rod to finished welding wire.

[0054] The intermediate annealing temperature of 750℃~850℃ refers to heating the cold-drawn wire rod to a temperature range of 750℃ to 850℃ and holding it therefore during the intermediate annealing process. In this embodiment, the intermediate annealing temperature is 750℃~850℃. This temperature range is higher than the recrystallization temperature of the iron-chromium-aluminum heating alloy, allowing for sufficient recrystallization of the cold-drawn deformation structure, forming fine equiaxed grains. Simultaneously, this temperature range is lower than the temperature for abnormal grain growth, preventing excessive grain coarsening. The intermediate annealing holding time of 1 hour to 2 hours means holding the cold-drawn wire rod at that temperature for 1 to 2 hours. A holding time of 1 hour to 2 hours ensures uniform internal and external temperature of the cold-drawn wire rod and completes sufficient recrystallization. A holding time shorter than 1 hour results in insufficient recrystallization and incomplete elimination of work hardening, while a holding time longer than 2 hours leads to grain coarsening and increased energy consumption. After intermediate annealing, slow furnace cooling is performed to reduce thermal stress during the cooling process.

[0055] In some embodiments, during the continuous bright annealing process, the annealing temperature is 750℃~900℃, and the annealing speed is 5m / min~15m / min; the protective atmosphere during the continuous bright annealing process is decomposed ammonia or pure hydrogen.

[0056] Annealing temperature refers to the temperature set in the heating zone of the continuous bright annealing furnace, i.e., the heat treatment temperature reached by the cold-drawn welding wire to the target specification as it continuously passes through the heating zone. In this embodiment, the annealing temperature is 750℃~900℃, which ensures sufficient recrystallization while preventing abnormal growth of recrystallized grains, resulting in a uniform and fine equiaxed grain structure in the welding wire after continuous bright annealing. Annealing speed refers to the speed at which the cold-drawn welding wire to the target specification continuously passes through the heating zone of the continuous bright annealing furnace, measured in meters per minute. In this embodiment, the annealing speed is 5m / min~15m / min, which ensures sufficient heat treatment time for the welding wire in the heating zone to complete sufficient recrystallization while avoiding grain growth and surface quality degradation caused by excessive dwell time, while also considering production efficiency and energy utilization efficiency.

[0057] A protective atmosphere refers to a gas continuously introduced into the heating and cooling zones of a continuous bright annealing furnace to isolate the welding wire from external air and protect its surface from oxidation during the high-temperature annealing process. In the embodiments of this application, the protective atmosphere is decomposed ammonia or pure hydrogen. Decomposed ammonia is a mixture of liquid ammonia (NH3) and nitrogen (75% by volume) in a high-temperature catalytic decomposition device. Pure hydrogen refers to high-purity hydrogen with a volume fraction of not less than 99.99%.

[0058] 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.

[0059] The room temperature tensile strength and elongation after fracture of the welding consumables were determined according to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Room temperature test method"; the grain size of the welding consumables was determined according to GB / T 6394-2017 "Metallic materials - Determination of average grain size"; the bending test of the welded joint was conducted according to GB / T 2653-2008 "Welded joints - Bending test method"; the volume fraction of the second phase of austenite in the weld zone was quantitatively determined by analyzing metallographic images using image analysis software.

[0060] Example 1 This embodiment provides a special welding material for iron-chromium-aluminum electrothermal alloy, which, by mass fraction, is composed of the following chemical composition: Cr 22.0%, Al 5.3%, Ni 4.0%, Mn 1.0%, Nb 0.25%, Si 0.35%, C 0.012%, rare earth element (Y) 0.05%, P 0.008%, S 0.003%, with the balance being Fe and unavoidable impurities.

[0061] Prepare the special welding material for iron-chromium-aluminum electrothermal alloy according to the following steps: The raw materials, including pure iron, metallic chromium, metallic aluminum, electrolytic nickel, electrolytic manganese, ferroniobium, ferrosilicon, and yttrium alloy, prepared according to the above chemical composition ratio, are loaded into a vacuum induction furnace and smelted under a vacuum of 5 Pa. The refining temperature is controlled at 1600℃ and the refining time is 30 min. The molten steel is then cast into an electrode rod with a diameter of 130 mm.

[0062] A CaF2-Al2O3-CaO ternary slag system was used, and an electrode rod was used as a consumable electrode for electroslag remelting at a melting rate of 2 kg / min to obtain an electroslag ingot with a specification of Φ180 mm.

[0063] The electroslag ingot is heated to 1100℃ and then hot-rolled. The final rolling temperature is 820℃ to obtain hot-rolled wire rod with a diameter of Φ10mm.

[0064] Hot-rolled wire rod is pickled and then subjected to multiple cold drawing processes. The area shrinkage rate of each cold drawing process is 20%, and the total area shrinkage rate is 85%. When the cumulative deformation reaches 35%, intermediate annealing is performed to eliminate work hardening. The intermediate annealing temperature is 800℃, the holding time is 1.5h, and after intermediate annealing, it is slowly cooled in the furnace to obtain welding wire with a specification of Φ1.6mm.

[0065] The welding wire was subjected to continuous bright annealing under a protective atmosphere of pure hydrogen. The annealing temperature was 820℃, and the annealing rate was 10 m / min, yielding the finished welding wire. The finished welding wire had a room temperature tensile strength of 665 MPa, an elongation after fracture of 24%, and a grain size of 7.0.

[0066] The tungsten inert gas (TIG) welding method was used to weld an iron-chromium-aluminum electrothermal alloy base material with an aluminum content of 5.2% and a chromium content of 22.0% using the welding materials described in this embodiment. The welding parameters were: current 120~140A, voltage 12~14V, welding speed 80~120mm / min, shielding gas was pure argon, and gas flow rate was 12~15L / min.

[0067] The welded joint was tested and found to have the following characteristics: the microstructure of the weld zone is a ferrite-austenite dual-phase structure, with an austenite volume fraction of approximately 30% and a grain size of 5-6; the grain size of the heat-affected zone is 4-5; the room temperature tensile strength of the welded joint is 520 MPa (≥ 85% of the room temperature tensile strength of the base metal); the elongation after fracture is 12%; there are no cracks after bending 180°; the oxidation resistance of the weld and heat-affected zone at 900℃ is comparable to that of the base metal.

[0068] Example 2 This embodiment provides a special welding material for iron-chromium-aluminum electrothermal alloy, which is composed of the following chemical components by mass fraction: Cr 21.5%, Al 4.9%, Ni 3.5%, Mn 1.2%, Nb 0.20%, Si 0.30%, C 0.008%, rare earth element (Y) 0.04%, P 0.010%, S 0.002%, with the balance being Fe and unavoidable impurities.

[0069] The preparation process is the same as in Example 1, and a welding wire with a diameter of Φ2.0mm is obtained after multiple cold drawing processes.

[0070] The welding wire was subjected to continuous bright annealing under a protective atmosphere of pure hydrogen. The annealing temperature was 800℃, and the annealing rate was 10 m / min, resulting in the finished welding wire. The finished welding wire had a room temperature tensile strength of 658 MPa, an elongation after fracture of 26%, and a grain size of 7.0.

[0071] The tungsten inert gas (TIG) welding method was used to weld an iron-chromium-aluminum electrothermal alloy base material with an aluminum content of 5.1% and a chromium content of 21.5% using the welding materials described in this embodiment. The welding parameters were: current 120~140A, voltage 12~14V, welding speed 80~120mm / min, shielding gas was pure argon, and gas flow rate was 12~15L / min.

[0072] The welded joint was tested and found to have the following characteristics: the microstructure of the weld zone is a ferrite-austenite dual-phase structure, with an austenite volume fraction of approximately 28% and a grain size of 5-6; the grain size of the heat-affected zone is 4-5; the room temperature tensile strength of the welded joint is 510 MPa (≥80% of the room temperature tensile strength of the base metal); the elongation after fracture is 14%; there are no cracks after bending 180°; the oxidation resistance of the weld and heat-affected zone at 900℃ is comparable to that of the base metal.

[0073] Example 3 This embodiment provides a special welding material for iron-chromium-aluminum electrothermal alloy, which is composed of the following chemical composition by mass fraction: Cr 23.0%, Al 5.1%, Ni 4.5%, Mn 0.8%, Nb 0.30%, Si 0.40%, C 0.015%, rare earth element (Y) 0.06%, P 0.012%, S 0.004%, with the balance being Fe and unavoidable impurities.

[0074] The preparation process is the same as in Example 1, and a welding wire with a diameter of Φ1.2mm is obtained after multiple cold drawing processes.

[0075] The welding wire was subjected to continuous bright annealing under a protective atmosphere of pure hydrogen. The annealing temperature was 850℃, and the annealing rate was 8 m / min, yielding the finished welding wire. The finished welding wire had a room temperature tensile strength of 672 MPa, an elongation after fracture of 23%, and a grain size of 7.5.

[0076] The tungsten inert gas (TIG) welding method was used to weld an iron-chromium-aluminum electrothermal alloy base material with an aluminum content of 5.3% and a chromium content of 22.5% using the welding materials described in this embodiment. The welding parameters were: current 120~140A, voltage 12~14V, welding speed 80~120mm / min, shielding gas was pure argon, and gas flow rate was 12~15L / min.

[0077] The welded joint was tested and found to have the following characteristics: the microstructure of the weld zone is a ferrite-austenite dual-phase structure, with an austenite volume fraction of approximately 35% and a grain size of 5-6; the grain size of the heat-affected zone is 4-5; the room temperature tensile strength of the welded joint is 540 MPa (≥ 85% of the room temperature tensile strength of the base metal); the elongation after fracture is 11%; there are no cracks after bending 180°; the oxidation resistance of the weld and heat-affected zone at 900℃ is comparable to that of the base metal.

[0078] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: This invention solves the problem of room temperature embrittlement caused by coarse grains when welding iron-chromium-aluminum electrothermal alloys of the same material: In this embodiment, nickel and manganese are introduced into the welding material as austenite forming elements, so that the weld metal forms a two-phase microstructure of ferrite matrix plus austenite second phase. The austenite second phase inhibits ferrite grain boundary migration through the Zener pinning effect. Combined with the synergistic pinning effect of the Laves phase precipitated by niobium and niobium carbide particles, the grain size of the weld zone is refined to level 5-6. Combined with the crack deflection, crack passivation and bridging toughening mechanism of the austenite second phase, the room temperature tensile strength of the weld joint reaches more than 80% of that of the base material and there is no crack when bending 180°.

[0079] This invention addresses the problem of decreased weld oxidation resistance caused by aluminum evaporation and burn-off during welding. The embodiment of this application designs the aluminum content of the welding material to be 4.5%~5.5%, with the portion exceeding the base metal aluminum content (4.0%~5.3%) serving as a burn-off reserve. This reserve is preferentially consumed through evaporation during welding, ensuring that the residual aluminum content of the weld metal after burn-off remains within the range of the base metal aluminum content. This guarantees the formation of a protective oxide film on the weld metal surface that is as dense as that of the base metal, resulting in oxidation resistance of the weld and heat-affected zone at 900℃ comparable to that of the base metal.

[0080] The problem of mismatched thermal expansion coefficients and interface cracking during welding of dissimilar welding materials is eliminated: The welding material provided in this application uses iron-chromium-aluminum as the base material, and the chromium content (20%~24%) and aluminum content (4.5%~5.5%) are highly matched with the base material (Cr 21%~23%, Al 4.0%~5.3%). The welding material and the base material belong to the same iron-chromium-aluminum ferritic alloy system. Both have the same thermal expansion coefficient and the same chromium-aluminum anti-oxidation system in the entire temperature range from room temperature to high temperature, which fundamentally eliminates the risk of interface thermal stress cracking and preferential oxidation of weld caused by dissimilar material systems.

[0081] 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 iron-chromium-aluminum electrothermal alloy, characterized in that, The chemical composition of the welding material, by mass fraction, is as follows: Cr: 20%~24%, Al: 4.5%~5.5%, Ni: 2.0%~6.0%, Mn: 0.5%~2.0%, Nb: 0.1%~0.5%, Si: 0.2%~0.5%, C≤0.020%, rare earth elements: 0.02%~0.10%, P≤0.015%, S≤0.005%, 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: 21%~23%, Al: 4.8%~5.3%, Ni: 3.0%~5.0%, Mn: 0.8%~1.5%, Nb: 0.15%~0.35%, Si: 0.2%~0.5%, C≤0.020%, rare earth elements: 0.02%~0.10%, P≤0.015%, S≤0.005%, 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, Y, and Hf.

4. The welding material according to claim 1, characterized in that, The welding material is used for welding iron-chromium-aluminum electric heating alloy base material, wherein the mass fraction of Al in the iron-chromium-aluminum electric heating alloy base material is 4.0%~5.3% and the mass fraction of Cr is 21%~23%.

5. The welding material according to claim 1, characterized in that, The weld metal formed by welding the welding material has a dual-phase microstructure, which includes a ferrite matrix and an austenite second phase. The volume fraction of the austenite second phase is 15% to 50% of the total volume of the weld metal.

6. The welding material according to claim 1, characterized in that, The welding material shall meet at least one of the following properties: room temperature tensile strength ≥500MPa, elongation after fracture ≥20%, and grain size ≥6.

7. A method for preparing a special welding material for iron-chromium-aluminum electrothermal alloy according to any one of claims 1 to 6, characterized in that, The method includes: The raw materials with the aforementioned chemical composition are subjected to vacuum induction melting to obtain molten steel; The molten steel is cast into electrode rods; Using a CaF2-Al2O3-CaO ternary slag system, the electrode rod was used as a consumable electrode for electroslag remelting to obtain an electroslag ingot. The electroslag ingot is heated to 1050℃~1150℃ and then hot-rolled, and the final rolling temperature is controlled to be ≥800℃ to obtain hot-rolled wire rod. The hot-rolled wire rod is subjected to multiple cold drawing processes, and intermediate annealing is performed when the cumulative deformation reaches 30%~40% to eliminate work hardening, so as to obtain welding wire that meets the target specifications. The welding wire is subjected to continuous bright annealing under a protective atmosphere to obtain the finished welding wire.

8. The method according to claim 7, characterized in that, The vacuum degree of the vacuum induction melting is ≤10Pa, the temperature of the vacuum induction melting is 1550℃~1650℃, and the time of the vacuum induction melting is 20min~40min.

9. The method according to claim 7, characterized in that, In the multi-pass cold drawing process, the surface shrinkage rate of each cold drawing process is 15%~25%, and the total surface shrinkage rate is ≥80%; the intermediate annealing temperature is 750℃~850℃, and the intermediate annealing holding time is 1h~2h.

10. The method according to claim 7, characterized in that, During the continuous bright annealing process, the annealing temperature is 750℃~900℃, and the annealing speed is 5m / min~15m / min; the protective atmosphere during the continuous bright annealing process is decomposed ammonia or pure hydrogen.

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