High-strength corrosion-resistant iron-chromium-aluminum alloy and method for producing same

Abstract

The application provides a high-strength corrosion-resistant iron-chromium-aluminum alloy and a preparation method thereof, relates to the technical field of iron-chromium-aluminum alloys, and the alloy contains Cr 19-25%, Al 8.5-11%, Nb 0.3-0.8%, Ti 0.1-0.4% and Si 0.2-0.6% by mass percent, and the rest is Fe and limited impurities. The alloy is formed with dispersion strengthening phases by the composite addition of Nb and Ti, and the oxidation resistance is improved by optimizing the Cr / Al ratio. The preparation method comprises raw material pretreatment, vacuum melting + refining, directional solidification, homogenization annealing, hot working and solid solution + aging heat treatment, and the process parameters are precisely controllable. The Cr / Al ratio is optimized, and Nb and Ti are added to solve the problem that the strength and corrosion resistance are difficult to be coordinated. Meanwhile, homogenization annealing is added in the process, and the parameters of directional solidification and heat treatment are optimized to eliminate segregation and internal stress, so that the performance of the prepared iron-chromium-aluminum alloy is superior to that of conventional iron-chromium-aluminum alloys, and the alloy is suitable for high-end scenes and has high stability.

Description

Technical Field

[0001] This invention relates to the field of iron-chromium-aluminum alloy technology, and in particular to a high-strength, corrosion-resistant iron-chromium-aluminum alloy and its preparation method. Background Technology

[0002] Iron-chromium-aluminum alloys are widely used in electric heating elements, high-temperature structural components, and chemical corrosion-resistant equipment due to their excellent high-temperature oxidation resistance, good electrical properties, and cost advantages. Current iron-chromium-aluminum alloy compositions are mostly concentrated in a basic ratio of 12-18% Cr and 4-8% Al. While this meets the requirements for conventional high-temperature applications, it suffers from two major drawbacks: First, it is difficult to simultaneously improve strength and corrosion resistance. When corrosive ions such as Cl⁻ and SO₄²⁻ are present in the environment, or during long-term service at high temperatures (above 800℃), the surface oxide film is prone to peeling off, leading to a sharp decline in corrosion resistance. Second, the manufacturing process is prone to grain coarsening, compositional segregation, and inclusion defects, resulting in a room-temperature tensile strength generally below 600 MPa, making it unsuitable for high-end applications requiring higher structural strength (such as aero-engine exhaust systems and deep-sea corrosion-resistant components).

[0003] In existing improvement schemes, simply increasing the Cr and Al content will lead to increased alloy brittleness and greater difficulty in processing and forming; adding a single rare earth element can improve the adhesion of the oxide film, but its effect on strength improvement is limited; the preparation process mostly adopts conventional electric arc melting + forging, lacks targeted grain refinement and composition homogenization control, and it is difficult to solve the segregation problem.

[0004] Therefore, this application develops an iron-chromium-aluminum alloy with a reasonable composition design, controllable preparation process, and the ability to simultaneously achieve high strength and excellent corrosion resistance. Summary of the Invention

[0005] The purpose of this invention is to address the problems in existing improved solutions, such as the fact that simply increasing the Cr and Al content leads to increased alloy brittleness and greater difficulty in processing and forming; the fact that adding a single rare earth element can improve the adhesion of the oxide film, but has limited effect on improving strength; and the fact that the preparation process mostly adopts conventional electric arc melting + forging, lacking targeted grain refinement and composition homogenization control, making it difficult to solve the segregation problem. Therefore, this invention proposes a high-strength corrosion-resistant iron-chromium-aluminum alloy and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a high-strength, corrosion-resistant iron-chromium-aluminum alloy, the chemical composition of which, by mass percentage, includes: Cr 19-25%, Al 8.5-11%, Nb 0.3-0.8%, Ti 0.1-0.4%, Si 0.2-0.6%, C ≤ 0.05%, P ≤ 0.02%, S ≤ 0.01%, with the remainder being Fe and unavoidable impurities; among the unavoidable impurities, Mn ≤ 0.3%, Cu ≤ 0.2%, Ni ≤ 0.2%, the content of a single impurity ≤ 0.1%, and the total impurity content ≤ 0.8%; the alloy has a room temperature tensile strength ≥ 750 MPa, a corrosion resistance time ≥ 1000 h in a 5% NaCl salt spray environment, an oxidation weight gain ≤ 0.8 g / m² after continuous oxidation in air at 900℃ for 1000 h, and an oxide film adhesion of Grade 1.

[0007] Preferably, the chemical composition, by mass percentage, is: Cr 21-23%, Al 9-10%, Nb 0.5-0.7%, Ti 0.2-0.3%, Si 0.3-0.5%, C ≤0.03%, with the remainder being Fe and unavoidable impurities; the alloy has a room temperature tensile strength ≥800MPa, a corrosion resistance time ≥1100h in a 5% NaCl salt spray environment, and an oxidation weight gain ≤0.7g / m² after continuous oxidation in air at 900℃ for 1000h.

[0008] Preferably, among the unavoidable impurities, Mn≤0.3%, Cu≤0.2%, Ni≤0.2%, the content of a single impurity≤0.1%, and the total impurity content≤0.8%.

[0009] A method for preparing an iron-chromium-aluminum alloy includes the following steps: S1. Raw material pretreatment: Weigh industrial pure iron, ferrochrome alloy, aluminum ingot, ferroniobium alloy, ferrotitanium alloy, and ferrosilicon alloy according to the chemical composition ratio, remove surface oil and oxide scale, and crush to a particle size of 20-50mm. S2. Vacuum melting: Add the pretreated raw materials to a vacuum induction melting furnace, evacuate to a vacuum degree ≤5Pa, heat to 1520-1580℃, hold for 30-60min, and during this period, introduce argon gas with a purity ≥99.99% and stir 2-3 times, each time for 5-8min, with an argon gas flow rate of 0.5-1.0L / min to remove slag from the surface of the molten pool. S3. Refining treatment: Add Ca-Si alloy to the molten pool for refining. The amount added is 0.1-0.3% of the total mass of the raw materials. Hold for 15-20 minutes and then let stand for 10-15 minutes. S4. Directional solidification: The refined alloy liquid is poured into a graphite mold preheated to 800-900℃. The inner wall of the mold is coated with a boron nitride release agent with a thickness of 0.5-1.0mm. The directional solidification process is adopted, and the cooling rate is controlled at 5-15℃ / s to obtain the alloy ingot. S5. Hot working: Heat the alloy ingot to 950-1050℃, hold for 2-3 hours and then forge it. The forging deformation is 40-60%. Then air cool it to room temperature. S6. Heat treatment: The forged alloy is subjected to solution treatment and aging treatment in sequence. The solution treatment temperature is 1050-1150℃, and the holding temperature is 2-4h. The alloy is then water-quenched and cooled at a rate of ≥50℃ / min. The aging temperature is 700-800℃, and the holding temperature is 6-10h. The heating rate is 5-10℃ / min. The alloy is then cooled to room temperature in the furnace to obtain the finished alloy.

[0010] Preferably, the argon gas purity in the vacuum melting is ≥99.99%, and the argon gas flow rate during stirring is 0.5-1.0 L / min.

[0011] Furthermore, setting the argon purity to ≥99.99% is to prevent impurities such as O2 and N2 in the argon from reacting with the molten alloy to form inclusions such as Al2O3 and CrN. When the argon purity is below 99.99%, the inclusion content in the alloy increases by 2-3 times, leading to a decrease in tensile strength of ≥30MPa. The argon flow rate of 0.5-1.0L / min was determined through fluid dynamics simulation. If the flow rate is too low, the molten pool cannot be effectively stirred, resulting in a compositional uniformity deviation of ≥2%; if the flow rate is too high, it will cause molten pool splashing, resulting in compositional loss.

[0012] Preferably, the mold material for directional solidification is graphite, and the inner wall of the mold is coated with a boron nitride release agent with a thickness of 0.5-1.0 mm.

[0013] Furthermore, graphite molds are chosen because they have high temperature resistance and moderate thermal conductivity, which can match the cooling rate requirements of directional solidification. A boron nitride release agent thickness of 0.5-1.0 mm avoids problems such as poor release effect when too thin, easy adhesion of mold debris to the ingot surface, and impaired heat transfer between the mold and the molten alloy when too thick, leading to fluctuations in cooling rate and uneven ingot grain size.

[0014] Preferably, after obtaining the alloy ingot in step 4 and before hot working in step 5, a homogenization annealing treatment is added to the ingot: the ingot is heated to 850-900℃, held for 4-6 hours, with a heating rate of 3-5℃ / min, and then cooled to room temperature in the furnace before hot working.

[0015] Furthermore, a cooling rate of ≥50℃ / min after solution treatment can quickly overcome the precipitation temperature range of the strengthening phase and obtain a supersaturated solid solution. The aging temperature of 700-800℃ and holding time of 6-10h are determined based on thermodynamic calculations. This temperature range allows the strengthening phases Fe3Nb and TiC to precipitate uniformly at their optimal size, avoiding problems such as affecting the strengthening effect or causing internal stress due to excessively rapid heating, which could lead to alloy cracking.

[0016] Preferably, the cooling rate after solution treatment in heat treatment is ≥50℃ / min, and the heating rate of aging treatment is 5-10℃ / min.

[0017] Furthermore, adding a homogenization annealing treatment before hot working of the ingot can promote the diffusion of alloying elements through high-temperature holding, eliminate micro-composition segregation of the ingot after directional solidification, and release the internal thermal stress of the ingot. The annealing temperature of 850-900℃ is lower than the recrystallization temperature of the alloy (950℃), which can avoid coarse grains in the ingot; holding at high temperature for 4-6 hours can ensure sufficient element diffusion, and the heating rate of 3-5℃ / min can reduce the internal stress caused by the temperature gradient.

[0018] Compared with the prior art, the advantages and positive effects of the present invention are as follows: In this invention, the pain point of difficulty in achieving a balance between strength and corrosion resistance is solved by optimizing the Cr and Al ratio and adding Nb and Ti in combination. At the same time, the process is improved by adding homogenization annealing, optimizing directional solidification and heat treatment parameters, and eliminating segregation and internal stress. As a result, the prepared iron-chromium-aluminum alloy has comprehensively surpassed the performance of conventional iron-chromium-aluminum alloys, making it suitable for high-end applications and exhibiting strong stability. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation process of the iron-chromium-aluminum alloy in this application. Detailed Implementation

[0020] Example 1, such as Figure 1As shown, a high-strength, corrosion-resistant iron-chromium-aluminum alloy, by mass percentage, comprises: Cr 19-25%, Al 8.5-11%, Nb 0.3-0.8%, Ti 0.1-0.4%, Si 0.2-0.6%, C ≤ 0.05%, P ≤ 0.02%, S ≤ 0.01%, with the remainder being Fe and unavoidable impurities; among the unavoidable impurities, Mn ≤ 0.3%, Cu ≤ 0.2%, Ni ≤ 0.2%, with individual impurity content ≤ 0.1% and total impurity content ≤ 0.8%; the alloy exhibits a room temperature tensile strength ≥ 750 MPa, corrosion resistance in a 5% NaCl salt spray environment ≥ 1000 h, and a corrosion resistance after continuous oxidation in air at 900℃ for 1000 h. The oxidation weight gain is ≤0.8g / m², and the oxide film adhesion reaches Grade 1. The chemical composition, by mass percentage, is: Cr 21-23%, Al 9-10%, Nb 0.5-0.7%, Ti 0.2-0.3%, Si 0.3-0.5%, C ≤0.03%, with the remainder being Fe and unavoidable impurities. The alloy has a room temperature tensile strength ≥800MPa, corrosion resistance time in a 5% NaCl salt spray environment ≥1100h, and an oxidation weight gain ≤0.7g / m² after continuous oxidation in air at 900℃ for 1000h. Among the unavoidable impurities, Mn ≤0.3%, Cu ≤0.2%, Ni ≤0.2%, with the content of a single impurity ≤0.1% and the total impurity content ≤0.8%.

[0021] Reference Figure 1 As shown, a method for preparing a high-strength, corrosion-resistant iron-chromium-aluminum alloy includes the following steps: S1. Raw material pretreatment: Weigh industrial pure iron, ferrochrome alloy, aluminum ingot, ferroniobium alloy, ferrotitanium alloy, and ferrosilicon alloy according to the chemical composition ratio, remove surface oil and oxide scale, and crush to a particle size of 20-50mm. S2. Vacuum melting: Add the pretreated raw materials to a vacuum induction melting furnace, evacuate to a vacuum degree ≤5Pa, heat to 1520-1580℃, hold for 30-60min, and during this period, introduce argon gas with a purity ≥99.99% and stir 2-3 times, each time for 5-8min, with an argon gas flow rate of 0.5-1.0L / min to remove slag from the surface of the molten pool. S3. Refining treatment: Add Ca-Si alloy to the molten pool for refining. The amount added is 0.1-0.3% of the total mass of the raw materials. Hold for 15-20 minutes and then let stand for 10-15 minutes. S4. Directional solidification: The refined alloy liquid is poured into a graphite mold preheated to 800-900℃. The inner wall of the mold is coated with a boron nitride release agent with a thickness of 0.5-1.0mm. The directional solidification process is adopted, and the cooling rate is controlled at 5-15℃ / s to obtain the alloy ingot. S5. Hot working: Heat the alloy ingot to 950-1050℃, hold for 2-3 hours and then forge it. The forging deformation is 40-60%. Then air cool it to room temperature. S6. Heat treatment: The forged alloy is subjected to solution treatment and aging treatment in sequence. The solution treatment temperature is 1050-1150℃, and the holding temperature is 2-4h. The alloy is then water-quenched and cooled at a rate of ≥50℃ / min. The aging temperature is 700-800℃, and the holding temperature is 6-10h. The heating rate is 5-10℃ / min. The alloy is then cooled to room temperature in the furnace to obtain the finished alloy.

[0022] Reference Figure 1 As shown in this embodiment: the argon purity in vacuum melting is ≥99.99%, and the argon flow rate during stirring is 0.5-1.0 L / min. Setting the argon purity to ≥99.99% is to prevent impurities such as O2 and N2 in the argon from reacting with the alloy liquid to generate inclusions such as Al2O3 and CrN. When the argon purity is lower than 99.99%, the inclusion content in the alloy will increase by 2-3 times, leading to a decrease in tensile strength of ≥30 MPa. The argon flow rate of 0.5-1.0 L / min was determined through fluid dynamics simulation. If the flow rate is too low, the molten pool cannot be effectively stirred, resulting in a compositional uniformity deviation of ≥2%; if the flow rate is too high, it will cause molten pool splashing, resulting in compositional loss. Reference Figure 1 As shown in this embodiment: the mold material for directional solidification is graphite, and the inner wall of the mold is coated with a boron nitride release agent with a thickness of 0.5-1.0 mm. Furthermore, the graphite mold is chosen because it has strong high-temperature resistance and a moderate thermal conductivity, which matches the cooling rate requirements of directional solidification. The 0.5-1.0 mm thickness of the boron nitride release agent avoids the problems of poor release effect when too thin, easy adhesion of mold debris to the ingot surface, and excessive thickness affecting heat transfer between the mold and the molten alloy, leading to fluctuations in cooling rate and uneven ingot grain size. Reference Figure 1 As shown in this embodiment: after obtaining the alloy ingot in step 4 and before hot working in step 5, a homogenization annealing treatment is added to the ingot: the ingot is heated to 850-900℃, held for 4-6 hours, with a heating rate of 3-5℃ / min, and then cooled to room temperature in the furnace before hot working. Furthermore, the cooling rate after solution treatment is ≥50℃ / min, which can quickly cross the precipitation temperature range of the strengthening phase and obtain a supersaturated solid solution. The aging temperature of 700-800℃ and the holding time of 6-10 hours are determined based on thermodynamic calculations. This temperature range allows the strengthening phases Fe3Nb and TiC to precipitate uniformly at the optimal size, avoiding problems such as affecting the strengthening effect or causing internal stress due to excessively rapid heating, which could lead to alloy cracking. Reference Figure 1As shown in this embodiment: the cooling rate after solution treatment in heat treatment is ≥50℃ / min, and the heating rate of aging treatment is 5-10℃ / min. Furthermore, a homogenization annealing treatment is added before hot working of the ingot. This can promote the diffusion of alloying elements through high-temperature holding, eliminate the micro-composition segregation of the ingot after directional solidification (such as local enrichment or depletion of Cr and Al), and release the thermal stress inside the ingot. The annealing temperature of 850-900℃ is lower than the recrystallization temperature of the alloy (950℃), which can avoid coarse grains in the ingot; holding for 4-6 hours can ensure sufficient element diffusion, and the heating rate of 3-5℃ / min can reduce the internal stress caused by the temperature gradient.

[0023] In this specific embodiment, the alloy composition uses an optimized ratio of Cr and Al, which forms a dense and stable oxide film on the alloy surface. This oxide film effectively blocks the intrusion of corrosive media and high-temperature oxidation erosion, thereby improving the alloy's corrosion resistance. The composite addition of Nb and Ti interacts with other elements in the alloy to form fine and uniformly distributed dispersed reinforcing phases. These reinforcing phases can hinder the movement of crystal dislocations, significantly improving the room temperature tensile strength of the alloy and solving the problem of the difficulty in achieving a balance between strength and corrosion resistance in traditional iron-chromium-aluminum alloys. The raw material pretreatment stage removes impurities and oxide layers from the surface of the raw materials through degreasing, descaling, and crushing and screening, ensuring uniform particle size and providing a good foundation for the uniformity of composition during subsequent melting, thus avoiding the introduction of impurities that affect alloy performance. Vacuum melting is carried out in a high-vacuum environment, which reduces the reaction between impurities such as O2 and N2 in the air and the alloy liquid. At the same time, the introduction of high-purity argon gas for stirring ensures that the elements in the molten pool are fully mixed, ensuring the uniformity of the alloy composition and avoiding local enrichment or depletion of components. The invented Ca-Si alloy added during refining possesses strong deoxidation and impurity removal capabilities, further removing harmful impurities and gases from the molten alloy, improving melt purity, and reducing inclusion defects during subsequent forming. Directional solidification, through precise control of the cooling rate, refines alloy grains and reduces inter-grain defects, forming a more regular crystal structure and improving the alloy's mechanical properties and corrosion resistance. Homogenization annealing, by controlling the heating rate and holding time, promotes full diffusion of alloying elements within the ingot, eliminates micro-composition segregation in the ingot after directional solidification, and releases internal thermal stress, providing a more uniform microstructure for subsequent hot working and preventing cracking or deformation during processing. Forging deformation during the hot working stage further refines the grains, increases alloy density, reduces internal porosity and other defects, and improves the alloy's mechanical properties, making the alloy structure more stable. Solution treatment involves heating to a high temperature and holding it there, allowing the alloying elements in the alloy to fully dissolve into the matrix to form a supersaturated solid solution. Subsequent water quenching quickly overcomes the precipitation temperature range of strengthening phases, maintaining the stability of the solid solution and preparing it for subsequent aging treatment. Aging treatment, by controlling the heating rate and holding conditions, causes elements such as Nb and Ti in the supersaturated solid solution to precipitate uniformly in the form of strengthening phases such as Fe3Nb and TiC, and these strengthening phases are distributed in the matrix at optimal sizes, further enhancing the strength of the alloy. The various process steps work together synergistically, optimizing the entire process from composition design to preparation, ultimately resulting in a ferrochromium-aluminum alloy that possesses both high strength and excellent corrosion resistance, meeting the requirements of high-end applications.

[0024] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may utilize the disclosed technical content to make changes or modifications to create equivalent embodiments applicable to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, still fall within the protection scope of the present invention. In the description of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in the present invention can be understood through specific circumstances.

Claims

1. A high-strength, corrosion-resistant iron-chromium-aluminum alloy, characterized in that, The chemical composition, by mass percentage, is: Cr 21-23%, Al 9-10%, Nb 0.5-0.7%, Ti 0.2-0.3%, Si 0.3-0.5%, C ≤ 0.03%, P ≤ 0.02%, S ≤ 0.01%, with the remainder being Fe and unavoidable impurities; the alloy has a room temperature tensile strength ≥ 800 MPa, a corrosion resistance time ≥ 1100 h in a 5% NaCl salt spray environment, and an oxidation weight gain ≤ 0.7 g / m² after continuous oxidation in air at 900℃ for 1000 h.

2. A method for preparing a high-strength, corrosion-resistant iron-chromium-aluminum alloy, characterized in that, The method for preparing the high-strength, corrosion-resistant iron-chromium-aluminum alloy according to claim 1 includes the following steps: S1. Raw material pretreatment: Weigh industrial pure iron, ferrochrome alloy, aluminum ingot, ferroniobium alloy, ferrotitanium alloy, and ferrosilicon alloy according to the chemical composition ratio, remove surface oil and oxide scale, and crush to a particle size of 20-50mm. S2. Vacuum melting: Add the pretreated raw materials to a vacuum induction melting furnace, evacuate to a vacuum degree ≤5Pa, heat to 1520-1580℃, hold for 30-60min, and during this period, introduce argon gas with a purity ≥99.99% and stir 2-3 times, each time for 5-8min, with an argon gas flow rate of 0.5-1.0L / min to remove slag from the surface of the molten pool. S3. Refining treatment: Add Ca-Si alloy to the molten pool for refining. The amount added is 0.1-0.3% of the total mass of the raw materials. Hold for 15-20 minutes and then let stand for 10-15 minutes. S4. Directional solidification: The refined alloy liquid is poured into a graphite mold preheated to 800-900℃. The inner wall of the mold is coated with a boron nitride release agent with a thickness of 0.5-1.0mm. The directional solidification process is adopted, and the cooling rate is controlled at 5-15℃ / s to obtain the alloy ingot. S5. Hot working: Heat the alloy ingot to 950-1050℃, hold for 2-3 hours and then forge it. The forging deformation is 40-60%. Then air cool it to room temperature. S6. Heat treatment: The forged alloy is subjected to solution treatment and aging treatment in sequence. The solution treatment temperature is 1050-1150℃, and the holding temperature is 2-4h. The alloy is then water-quenched and cooled at a rate of ≥50℃ / min. The aging temperature is 700-800℃, and the holding temperature is 6-10h. The heating rate is 5-10℃ / min. The alloy is then cooled to room temperature in the furnace to obtain the finished alloy.

3. The method for preparing the high-strength, corrosion-resistant iron-chromium-aluminum alloy according to claim 2, characterized in that: The argon purity in vacuum melting is ≥99.99%, and the argon flow rate during stirring is 0.5-1.0 L / min.

4. The method for preparing the high-strength, corrosion-resistant iron-chromium-aluminum alloy according to claim 3, characterized in that: After obtaining the alloy ingot in step 4 and before hot working in step 5, a homogenization annealing treatment is added to the ingot: the ingot is heated to 850-900℃, held for 4-6 hours, with a heating rate of 3-5℃ / min, and then cooled to room temperature in the furnace before hot working.

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