Ultralow-density Fe-Mn-Al-C steel and preparation method thereof
Ultra-low density Fe-Mn-Al-C steel was prepared by gradient solution treatment and rapid forging process, which solved the problem of low-density high-strength materials in the aerospace field and achieved comprehensive performance of high strength and high elongation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-06
- Publication Date
- 2026-04-07
AI Technical Summary
Existing technologies struggle to provide low-density, high-strength structural materials for the aerospace field. Traditional high-strength steels and titanium alloys suffer from high density, high cost, or processing difficulties. Existing low-density steels have insufficient aluminum content or inadequate carbide reinforcing phases, limiting strength improvement.
A gradient solution treatment combined with rapid forging and radial forging processes is adopted. Through a reasonable chemical composition design, including C: 1.35%-1.60%, Mn: 33.5%-36.0%, Al: 12.5%-15.5%, with the balance being Fe, smelting, casting, rapid forging, and radial forging are carried out to form fine equiaxed austenite grains and uniform κ-carbides.
Fe-Mn-Al-C steel with a density of 6.09-6.25 g/cm3, yield strength of 780-860 MPa, tensile strength of 960-1020 MPa, elongation of 30%-40%, and specific strength of 155-165 MPa·cm3/g was obtained, which is significantly better than existing high-strength steel, aerospace aluminum alloy and titanium alloy.
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Figure CN121802126A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of metal material preparation technology, specifically, to an ultra-low density Fe-Mn-Al-C steel and its preparation method. Background Technology
[0002] The rapid development of the aerospace industry has driven the development of structural materials towards lower cost, lighter weight, and higher specific strength. Although traditional high-strength steel and titanium alloys meet the mechanical performance requirements, they still have many drawbacks. For example, the excessive density of high-strength steel leads to excessively heavy structural components, increasing operating costs; while titanium alloys are limited by high cost and difficulties in subsequent processing. In recent years, low-density steel (density 6.6-7.5 g / cm³) has become increasingly popular. 3 While research and development of ultra-low density high-strength steel has made some progress in the lightweighting of structural components, its specific strength is still difficult to match that of titanium alloys and aerospace aluminum alloys. Therefore, the development of ultra-low density high-strength steel is urgently needed.
[0003] Although the existing Fe-25Mn-8Al-0.8C steel achieves a low density (6.7 g / cm³), it is still a significant advancement in the field. 3 However, its low aluminum content leads to insufficient matrix strength and the failure to construct an effective precipitated strengthening phase. Existing technology also involves reducing the density of low-density steel to 6.6 g / cm³ by adding 2% Cu. 3 However, the introduction of precious metal elements significantly increases the preparation cost. Existing technologies have also prepared austenitic + ferrite dual-phase low-density steel, but its excessively high ferrite volume fraction (>30%) limits the improvement in strength. The above-mentioned existing technical solutions generally have three common defects: (1) the aluminum content is controlled within the range of 5-10%, and the lightweighting effect is not significant; (2) the particle size of the carbide strengthening phase is >50nm; (3) the single-stage solid solution treatment causes severe oxidation of the grain boundaries. Therefore, the existing technical solutions cannot well meet the development needs of structural materials used in the aerospace field. Summary of the Invention
[0004] To solve the above-mentioned technical problems, this application provides a method for preparing ultra-low density Fe-Mn-Al-C steel, comprising the following steps: S1, obtaining an Fe-Mn-Al-C billet, and performing gradient solution treatment on the Fe-Mn-Al-C billet to obtain a solution-treated billet; the gradient solution treatment includes a first solution treatment and a second solution treatment, and the composition of the Fe-Mn-Al-C billet, by mass percentage, includes: C: 1.35%-1.60%, Mn: 33.5%-36.0%, Al: 12.5%-15.5%, with the balance being Fe and unavoidable impurities; S2, performing rapid forging and radial forging on the solution-treated billet to obtain Fe-Mn-Al-C steel, wherein the density of the Fe-Mn-Al-C steel is 6.09-6.25 g / cm³. 3 .
[0005] As a preferred embodiment of the preparation method of ultra-low density Fe-Mn-Al-C steel described in this application, before step S1, the method further includes preparing raw materials according to the composition of the Fe-Mn-Al-C billet, adding them sequentially to the furnace cavity of a vacuum induction melting furnace for smelting, and holding the molten steel at a constant temperature for 20-30 minutes after the raw materials are completely melted. The steel is then cast using a water glass sand mold with a refractory coating on the inner wall. After casting, the billet is not demolded and is air-cooled to room temperature. After the mold is opened, the Fe-Mn-Al-C billet is obtained. The smelting temperature is 1550-1600℃, and the casting temperature is 1350-1450℃.
[0006] As a preferred embodiment of the preparation method of ultra-low density Fe-Mn-Al-C steel described in this application, in step S1, the first solution treatment method is as follows: the Fe-Mn-Al-C billet is heated to a furnace temperature of 1150-1250℃ for 3-6 hours, and the cooling method is water cooling, to obtain the first solution-treated billet.
[0007] As a preferred embodiment of the preparation method of ultra-low density Fe-Mn-Al-C steel described in this application, in step S1, the second solution treatment method is as follows: the first solution casting billet is heated to a furnace temperature of 1000-1100℃ for 4-8 hours, and the cooling method is air cooling to obtain the solution casting billet.
[0008] As a preferred embodiment of the preparation method of ultra-low density Fe-Mn-Al-C steel described in this application, in step S2, the initial forging temperature of the rapid forging is 1140-1190℃, the final forging temperature of the rapid forging is 1060-1110℃, the forging ratio of the rapid forging is 4-6, and the impact frequency of the rapid forging is 150-220 times / min.
[0009] As a preferred embodiment of the preparation method of ultra-low density Fe-Mn-Al-C steel described in this application, in step S2, the initial forging temperature of the radial forging is 1050-1100℃, the final forging temperature of the radial forging is 970-1020℃, the forging ratio of the radial forging is 3-4, the impact frequency of the radial forging is 80-120 times / min, and the cooling method of the radial forging is air cooling.
[0010] This application also provides an ultra-low density Fe-Mn-Al-C steel, which is prepared using the above-described method for preparing ultra-low density Fe-Mn-Al-C steel.
[0011] As a preferred embodiment of the ultra-low density Fe-Mn-Al-C steel described in this application, the microstructure of the Fe-Mn-Al-C steel comprises 85-92 vol% austenite and 15-8 vol% ferrite.
[0012] As a preferred embodiment of the ultra-low density Fe-Mn-Al-C steel described in this application, the austenite further includes precipitated phases, including κ-carbides.
[0013] As a preferred embodiment of the ultra-low density Fe-Mn-Al-C steel described in this application, the Fe-Mn-Al-C steel has a yield strength of 780-860 MPa, a tensile strength of 960-1020 MPa, an elongation of 30%-40%, and a specific strength of 155-165 MPa·cm² at room temperature. 3 / g.
[0014] The beneficial effects of this application are as follows: This application proposes an ultra-low density Fe-Mn-Al-C steel and its preparation method, which employs rapid forging: the process is carried out using a rapid forging machine. The rapid forging machine is characterized by high striking frequency, small deformation per pass, and fast deformation speed.
[0015] The following effects can be achieved: **Outer edge grain refinement:** The high-frequency, rapid impact causes a rapid rise in the temperature of the billet's outer edge. The accumulated distortion from deformation quickly triggers static recrystallization (SRX), transforming the coarse as-cast structure at the outer edge into fine recrystallized grains. **Core structure control:** Due to the small reduction per forging cycle and limited deformation penetration depth, the core temperature is lower, and the degree of deformation is smaller. Therefore, the core grains do not grow and remain relatively fine, preparing for subsequent radial forging. **Purpose:** To initially break down the as-cast structure, providing a billet with a suitable temperature gradient and pre-improved structure for subsequent radial forging, avoiding the risk of cracking due to poor core plasticity during direct radial forging.
[0016] Radial forging is employed: immediately following rapid forging, the still-hot billet is quickly fed into a radial forging mill. The radial forging mill uses multiple hammers to forge symmetrically and at high speed from the radial direction, resulting in strong deformation penetration and extremely high strain rate.
[0017] The following effects can be achieved: Extreme refinement of the outer edge: The extremely high strain rate causes the outer edge material to heat up rapidly, resulting in dynamic recrystallization and the formation of extremely fine equiaxed austenite grains. Intense deformation and refinement of the core: The powerful penetrating deformation capability of radial forging causes the core to also undergo intense plastic deformation. This refines the original grains and generates high-density dislocations, providing numerous nucleation sites for κ-carbide precipitation. Controlled κ-carbide precipitation: Air cooling, rather than water cooling, is used after radial forging. During air cooling, the defects (dislocations, vacancies, etc.) introduced by the intense plastic deformation promote the uniform and dispersed precipitation of κ-carbide in the matrix as granules or short rods, avoiding discontinuous precipitation at grain boundaries, thereby simultaneously improving both strength and plasticity.
[0018] Advantages of the combined process: "Rapid forging + radial forging" creates a gradient deformation and recrystallization from the surface inwards, ultimately achieving an ideal microstructure of fine equiaxed grains on the outer edge, refined grains in the core, and uniformly dispersed κ-carbides throughout. This is unattainable with traditional forging or single forging processes. Through reasonable chemical composition and process design, employing smelting, billet casting, gradient solution treatment, and rapid forging + radial forging processes, ultra-low density Fe-Mn-Al-C steel is obtained. The microstructure of Fe-Mn-Al-C steel includes 85-92 vol% austenite and 15-8 vol% ferrite, with precipitates including κ-carbides within the austenite. The density of the ultra-low density Fe-Mn-Al-C steel at room temperature is 6.09-6.25 g / cm³. 3 The yield strength is 780-860 MPa, the tensile strength is 960-1020 MPa, and the elongation is 30%-40%. This application's ultra-low density Fe-Mn-Al-C steel, through groundbreaking alloy composition design and innovative preparation process, achieves excellent elongation and yield strength while maintaining low density, with a specific strength (155-165 MPa·cm). 3 / g) is significantly superior to existing high-strength steel (approximately 100 MPa·cm). 3 / g), aviation aluminum alloy (approximately 110MPa·cm) 3 / g) and titanium alloy (approximately 120 MPa·cm) 3 / g), providing a brand-new material solution for resolving the contradiction of "lightweight and high strength" in structural components used in the aerospace field. Attached Figure Description
[0019] 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, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0020] Figure 1 This is a SEM image of the Fe-Mn-Al-C steel of Example 1 of this application; Figure 2 This is a TEM image of the Fe-Mn-Al-C steel of Example 1 of this application; Figure 3 This is a SEM image of the Fe-Mn-Al-C steel of Comparative Example 1 of this application.
[0021] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0022] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0023] This application provides a method for preparing ultra-low density Fe-Mn-Al-C steel, comprising the following steps: S1. Obtain Fe-Mn-Al-C billet, and perform gradient solution treatment on the Fe-Mn-Al-C billet to obtain a solution-treated billet; the gradient solution treatment includes a first solution treatment and a second solution treatment. Before step S1, the process includes preparing raw materials according to the composition of the Fe-Mn-Al-C billet, adding them sequentially to the furnace cavity of a vacuum induction melting furnace for smelting, and holding the molten steel at a constant temperature for 20-30 minutes after the raw materials are completely melted. The steel is then cast using a water glass sand mold with a refractory coating on the inner wall. After casting, the billet is not demolded and is air-cooled to room temperature. After the mold is opened, the Fe-Mn-Al-C billet is obtained. The smelting temperature is 1550-1600℃, and the casting temperature is 1350-1450℃. The raw materials include a carbon raiser, electrolytic manganese, aluminum granules, and pure iron. The smelting process also includes: laying the carbon raiser at the bottom, then layering electrolytic manganese and aluminum granules in the middle, adding pure iron and electrolytic manganese on top, evacuating to 500 mbar and preheating, and then smelting.
[0024] Specifically, the smelting temperature can be any one or a range between any two of, for example, 1550℃, 1560℃, 1570℃, 1580℃, 1590℃, and 1600℃; the holding time of the molten steel can be any one or a range between any two of, for example, 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min, 29min, and 30min.
[0025] The casting temperature can be any one of, or a range between, 1350°C, 1360°C, 1370°C, 1380°C, 1390°C, 1400°C, 1410°C, 1420°C, 1430°C, 1440°C, and 1450°C.
[0026] The first solution treatment method is as follows: the Fe-Mn-Al-C billet is placed in the furnace at a temperature of 1150-1250℃ for 3-6 hours and cooled by water to obtain the first solution-treated billet. Specifically, the holding temperature of the first solid solution can be any one or a range between any two of, for example, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, and 1250℃; and the holding time of the first solid solution can be any one or a range between any two of, for example, 3h, 4h, 5h, and 6h.
[0027] The second solution treatment method is as follows: the first solution casting billet is heated to a furnace temperature of 1000-1100℃ for 4-8 hours, and then cooled by air cooling to obtain the solution casting billet. Specifically, the holding temperature of the second solid solution can be any one or a range between any two of, for example, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, and 1100℃; and the holding time of the second solid solution can be any one or a range between any two of, for example, 4h, 5h, 6h, 7h, and 8h.
[0028] S2. The solid solution cast billet is subjected to rapid forging and radial forging to obtain Fe-Mn-Al-C steel.
[0029] The composition of the Fe-Mn-Al billet, by mass percentage, includes: C: 1.35%-1.60%, Mn: 33.5%-36.0%, Al: 12.5%-15.5%, with the balance being Fe and unavoidable impurities; The Fe-Mn-Al-C steel designed in this application is a high-manganese austenitic steel, and achieves ultra-low density and high strength through the addition of high aluminum and high carbon; the reasons for the roles and ranges of each element are as follows: Carbon (C: 1.35%-1.60%): Mechanism of action: Carbon is the most critical interstitial solid solution strengthening element in this case, and it is also a necessary element for the formation of κ-carbide [(Fe,Mn)3AlC]; the dispersed precipitation of κ-carbide can produce a significant precipitation strengthening effect, greatly improving the strength of steel; Reason for the range: When the C content is below 1.35%, it is insufficient to form a sufficient volume fraction of κ-carbides, resulting in the strength not reaching the expected target; while when it is above 1.60%, coarse cementite (θ-Fe3C) or other brittle carbides are easily precipitated continuously at the grain boundaries during casting and heat treatment, which seriously deteriorates the plasticity and toughness of the steel; this range is the key to ensuring a balance between high strength and high elongation. Manganese (Mn: 33.5%-36.0%): Mechanism of action: Manganese is an austenite stabilizing element. High Mn content can significantly reduce stacking fault energy and promote mechanical twinning (TWIP effect), thereby providing continuous work hardening ability during deformation and ensuring high elongation; at the same time, Mn is also one of the constituent elements of κ-carbides; Reasons for the range of values: When the Mn content is insufficient (<33.5%), it is impossible to stabilize the all-austenitic structure at room temperature, which will lead to harmful martensitic phase transformation or excessive ferrite phase, reducing plasticity and work hardening ability; when it is too high (>36.0%), the gain on mechanical properties is no longer obvious, and it will increase costs, aggravate the segregation of the billet, and be detrimental to quality control. Aluminum (Al: 12.5%-15.5%): Mechanism of action: Aluminum is the core element for achieving ultra-low density. Al has a light atomic mass, effectively reducing the density of steel (density decreases by approximately 1.5% for every 1% increase in Al); simultaneously, Al is a ferrite-forming element, combining with carbon to form κ-carbides, providing strengthening. Appropriate amounts of Al can also improve the oxidation and corrosion resistance of steel. Reason for the range: With an Al content below 12.5%, the density reduction effect is insufficient, failing to achieve "ultra-low density" (<6.5 g / cm³). 3 The requirement is that when the content is higher than 15.5%, excessive δ-ferrite will be formed, and the precipitation of coarse and brittle β-DO3 (Fe3Al) or FeAl intermetallic compounds will be promoted, which will seriously impair the hot workability and room temperature plasticity of steel. Iron (Fe): Balance, the matrix of the alloy; Specifically, the mass percentage of C in the Fe-Mn-Al-C steel can be, for example, 1.35%, 1.36%, 1.37%, 1.38%, 1.39%, 1.40%, 1.41%, 1.42%, 1.43%, 1.44%, 1.45%, 1.46%, 1.47%, 1.48%, 1.49%, 1.50%, 1.51%, 1.52%, 1.53%, 1.54%, 1.55%, 1 The mass percentage of Mn in the Fe-Mn-Al-C steel can be, for example, any one or a range between any two of the following: 0.56%, 1.57%, 1.58%, 1.59%, 1.60%; the mass percentage of Mn in the Fe-Mn-Al-C steel can be, for example, any one or a range between any two of the following: 33.5%, 33.6%, 33.7%, 33.8%, 33.9%, 34.0%, 34.1%, 34.2%, 34.3%, 34.4%, 34.5%, 34.6%, 34.7%, 34.8%, 34.9%, 35.0%, 35.1%, 35.2%, 35.3%, 35.4%, 35.5%, 35.6%, 35.7%, 35.8%, 35.9%, 36.0%; the mass percentage of Al in the Fe-Mn-Al-C steel can be, for example, 12.5%, 12.6%, 12.7%, 12.8%, 12.9%, 13.0%, 13.1%, 13%; The range of any one or any two of the following: 0.2%, 13.3%, 13.4%, 13.5%, 13.6%, 13.7%, 13.8%, 13.9%, 14.0%, 14.1%, 14.2%, 14.3%, 14.4%, 14.5%, 14.6%, 14.7%, 14.8%, 14.9%, 15.0%, 15.1%, 15.2%, 15.3%, 15.4%, and 15.5%.
[0030] The initial forging temperature of the rapid forging is 1140-1190℃, the final forging temperature of the rapid forging is 1060-1110℃, the forging ratio of the rapid forging is 4-6, and the striking frequency of the rapid forging is 150-220 times / min. Specifically, the initial forging temperature of the rapid forging can be, for example, any one or a range between any two of 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, and 1190℃; the final forging temperature of the rapid forging can be, for example, any one or a range between any two of 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, and 1110℃; and the forging ratio of the rapid forging can be, for example, any one or a range between any two of 4, 5, and 6. The initial forging temperature of the radial forging is 1050-1100℃, the final forging temperature of the radial forging is 970-1020℃, the forging ratio of the radial forging is 3-4, the impact frequency of the radial forging is 80-120 times / min, and the cooling method of the radial forging is air cooling. Specifically, the initial forging temperature of the radial forging can be any one or a range between any two of, for example, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, and 1100℃; the final forging temperature of the radial forging can be any one or a range between any two of, 970℃, 980℃, 990℃, 1000℃, 1010℃, and 1020℃.
[0031] The density of the Fe-Mn-Al-C steel is 6.09-6.25 g / cm³. 3 The microstructure of the Fe-Mn-Al-C steel comprises 85-92 vol% austenite and 15-8 vol% ferrite, wherein the austenite further comprises precipitates, including κ-carbides.
[0032] The Fe-Mn-Al-C steel has a yield strength of 780-860 MPa, a tensile strength of 960-1020 MPa, an elongation of 30%-40%, and a specific strength of 155-165 MPa·cm at room temperature. 3 / g.
[0033] The technical solution of this application will be further described below with reference to specific embodiments.
[0034] Example 1 Prepare the raw materials according to the composition of the Fe-Mn-Al-C billet. Following the alloy layering process: place the carburizing agent at the bottom, then layer electrolytic manganese and aluminum granules in the middle, and finally add pure iron and electrolytic manganese on top. Place the billet in a vacuum induction melting furnace, evacuate to 500 mbar, and preheat. Then smelt at 1580℃. After the raw materials are completely melted, hold the molten steel at that temperature for 25 minutes. After smelting, use a water glass sand mold with a refractory coating on the inner wall for casting at 1400℃. After casting, do not demold and allow to air cool to room temperature. After opening the mold, the Fe-Mn-Al-C billet is obtained. The composition of the Fe-Mn-Al billet, by mass percentage, includes: C: 1.50%, Mn: 35.0%, Al: 13.0%, with the balance being Fe and unavoidable impurities. A gradient solution treatment process is performed on the Fe-Mn-Al-C billet to obtain a solution-treated billet; the gradient solution treatment includes a first solution treatment and a second solution treatment. The first solution treatment method involves placing the Fe-Mn-Al-C billet into the furnace at a temperature of 1200℃ for 4 hours, followed by water cooling to obtain the first solution-treated billet. The second solution treatment method involves placing the first solution-treated billet into the furnace at a temperature of 1050℃ for 6 hours, followed by air cooling to obtain the solution-treated billet. Fe-Mn-Al-C steel is obtained by rapid forging and radial forging of solution-treated billets; The forging temperature for quick forging is 1160℃, the final forging temperature is 1080℃, the forging ratio is 5, and the impact frequency is 180 times / min; the forging temperature for radial forging is 1070℃, the final forging temperature is 990℃, the forging ratio is 4, the impact frequency is 100 times / min, and the cooling method for radial forging is air cooling.
[0035] The Fe-Mn-Al-C steel prepared in Example 1 was tested, and the results showed that: Please refer to [link / reference needed]. Figure 1 and Figure 2 , Figure 1 This is a SEM image of the Fe-Mn-Al-C steel of Example 1 of this application; Figure 2 This is a TEM image of the Fe-Mn-Al-C steel of Example 1 of this application; Figure 1 Combination Figure 2 This indicates that the microstructure of Fe-Mn-Al-C steel includes austenite, ferrite, and κ-carbide particles; The microstructure of Fe-Mn-Al-C steel consists of 92 vol% austenite and 8 vol% ferrite. The austenite also includes high-density κ-carbide particles. The density of Fe-Mn-Al-C steel is 6.25 g / cm³. 3 The yield strength is 825 MPa, the tensile strength is 995 MPa, the elongation after fracture is 38%, and the specific strength is 159.2 MPa·cm. 3 / g.
[0036] Example 2 Prepare the raw materials according to the composition of the Fe-Mn-Al-C billet. Following the alloy layering process: place the carburizing agent at the bottom, then layer electrolytic manganese and aluminum granules in the middle, and finally add pure iron and electrolytic manganese on top. Place the billet in a vacuum induction melting furnace, evacuate to 500 mbar, and preheat. Then smelt at 1580℃. After the raw materials are completely melted, hold the molten steel at that temperature for 25 minutes. After smelting, use a water glass sand mold with a refractory coating on the inner wall for casting at 1400℃. After casting, do not demold and allow to air cool to room temperature. After opening the mold, the Fe-Mn-Al-C billet is obtained. The composition of the Fe-Mn-Al billet, by mass percentage, includes: C: 1.35%, Mn: 33.5%, Al: 15.5%, with the balance being Fe and unavoidable impurities. A gradient solution treatment process is performed on the Fe-Mn-Al-C billet to obtain a solution-treated billet; the gradient solution treatment includes a first solution treatment and a second solution treatment. The first solution treatment method involves placing the Fe-Mn-Al-C billet into the furnace at a temperature of 1150℃ for 6 hours, followed by water cooling to obtain the first solution-treated billet. The second solution treatment method involves placing the first solution-treated billet into the furnace at a temperature of 1000℃ for 8 hours, followed by air cooling to obtain the solution-treated billet. Fe-Mn-Al-C steel is obtained by rapid forging and radial forging of solution-treated billets; The forging temperature for quick forging is 1140℃, the final forging temperature is 1060℃, the forging ratio is 4, and the impact frequency is 150 times / min; the forging temperature for radial forging is 1050℃, the final forging temperature is 970℃, the forging ratio is 3, the impact frequency is 80 times / min, and the cooling method for radial forging is air cooling.
[0037] The Fe-Mn-Al-C steel prepared in Example 2 was tested, and the results showed that the matrix structure of the Fe-Mn-Al-C steel consisted of 85 vol% austenite and 15 vol% ferrite. The austenite also included high-density κ-carbide particles, and the density of the Fe-Mn-Al-C steel was 6.09 g / cm³. 3 The yield strength is 780 MPa, the tensile strength is 967 MPa, the elongation after fracture is 30%, and the specific strength is 158.8 MPa·cm. 3 / g.
[0038] Example 3 Prepare the raw materials according to the composition of the Fe-Mn-Al-C billet. Following the alloy layering process: place the carburizing agent at the bottom, then layer electrolytic manganese and aluminum granules in the middle, and finally add pure iron and electrolytic manganese on top. Place the billet in a vacuum induction melting furnace, evacuate to 500 mbar, and preheat. Then smelt at 1580℃. After the raw materials are completely melted, hold the molten steel at that temperature for 25 minutes. After smelting, use a water glass sand mold with a refractory coating on the inner wall for casting at 1400℃. After casting, do not demold and allow to air cool to room temperature. After opening the mold, the Fe-Mn-Al-C billet is obtained. The composition of the Fe-Mn-Al billet, by mass percentage, includes: C: 1.55%, Mn: 34.5%, Al: 14.0%, with the balance being Fe and unavoidable impurities. A gradient solution treatment process is performed on the Fe-Mn-Al-C billet to obtain a solution-treated billet; the gradient solution treatment includes a first solution treatment and a second solution treatment. The first solution treatment method involves placing the Fe-Mn-Al-C billet into the furnace at a temperature of 1220℃ for 4.5 hours and then cooling it with water to obtain the first solution-treated billet. The second solution treatment method involves placing the first solution-treated billet into the furnace at a temperature of 1080℃ for 5 hours and then cooling it with air to obtain the solution-treated billet. Fe-Mn-Al-C steel is obtained by rapid forging and radial forging of solution-treated billets; The forging temperature for quick forging is 1190℃, the final forging temperature is 1110℃, the forging ratio is 5.5, and the impact frequency is 220 times / min; the forging temperature for radial forging is 1100℃, the final forging temperature is 1020℃, the forging ratio is 4, the impact frequency is 120 times / min, and the cooling method for radial forging is air cooling.
[0039] The Fe-Mn-Al-C steel prepared in Example 3 was tested, and the results showed that the matrix structure of the Fe-Mn-Al-C steel consisted of 90 vol% austenite and 10 vol% ferrite. The austenite also included high-density κ-carbide particles, and the density of the Fe-Mn-Al-C steel was 6.18 g / cm³. 3 The yield strength is 840 MPa, the tensile strength is 1010 MPa, the elongation after fracture is 35%, and the specific strength is 163.4 MPa·cm. 3 / g.
[0040] Comparative Example 1 The difference from Example 1 is that the Al content in the Fe-Mn-Al-C billet is 10.0%, while the other steps are the same as in Example 1.
[0041] The Fe-Mn-Al-C steel prepared in Comparative Example 1 was tested, and the results showed that: (Please refer to...) Figure 3 , Figure 3 The image shown is a SEM image of the Fe-Mn-Al-C steel of Comparative Example 1 of this application. The matrix structure of the Fe-Mn-Al-C steel consists of 96 vol% austenite and 4 vol% ferrite. The austenite also includes a small amount of κ-carbide particles. Due to the low precipitation of κ-carbide particles, the strength is relatively low. The density of the Fe-Mn-Al-C steel is 6.61 g / cm³. 3 The yield strength is 764 MPa, the tensile strength is 920 MPa, the elongation after fracture is 33%, and the specific strength is 139.2 MPa·cm. 3 / g.
[0042] Comparative Example 2 The difference from Example 1 is that no second solid solution is performed, but all other steps are the same as in Example 1.
[0043] The Fe-Mn-Al-C steel prepared in Comparative Example 2 was tested, and the results showed that the matrix structure of the Fe-Mn-Al-C steel consisted of 70 vol% austenite and 30 vol% ferrite. The austenite also contained some undissolved coarse κ-carbide particles. The coarse undissolved carbides severely deteriorated the mechanical properties of the material. The density of the Fe-Mn-Al-C steel was 6.25 g / cm³. 3 The yield strength is 800 MPa, the tensile strength is 950 MPa, the elongation after fracture is 20%, and the specific strength is 152 MPa·cm. 3 / g.
[0044] Comparative Example 3 The difference from Example 1 is that hot rolling is used instead of fast forging and radial forging of the solution-treated billet to obtain Fe-Mn-Al-C steel. The temperature range and deformation amount of hot rolling are consistent with those of fast forging and radial forging in Example 1. All other steps are the same as in Example 1.
[0045] The Fe-Mn-Al-C steel prepared in Comparative Example 3 was tested, and the results showed that the matrix structure of the Fe-Mn-Al-C steel consisted of 88 vol% austenite and 12 vol% ferrite. Coarse κ-carbide particles precipitated in continuous thin films at the austenite grain boundaries acted as crack initiation sites, severely deteriorating the material's plasticity. The density of the Fe-Mn-Al-C steel was 6.25 g / cm³. 3 The yield strength is 780 MPa, the tensile strength is 930 MPa, the elongation after fracture is 14%, and the specific strength is 148.8 MPa·cm. 3 / g.
[0046] Comparative Example 4 The difference from Example 1 is that only rapid forging is performed, without subsequent radial forging; all other steps are the same as in Example 1.
[0047] The Fe-Mn-Al-C steel prepared in Example 4 was tested, and the results showed that due to the lack of intense radial forging deformation, the core microstructure was insufficiently refined, and κ-carbides mainly precipitated at the outer edge of the austenite and were unevenly distributed. The material properties were as follows: density 6.25 g / cm³. 3 The yield strength is 790 MPa, the tensile strength is 945 MPa, the elongation after fracture is 25%, and the specific strength is 151.2 MPa·cm. 3 / g. Its strength and plasticity are both lower than those of Example 1.
[0048] Comparative Example 5 The difference from Example 1 is that rapid forging is omitted, and the solution-treated billet is directly subjected to radial forging. All other steps are the same as in Example 1.
[0049] The Fe-Mn-Al-C steel prepared in Example 5 was tested, and the results showed that, due to the lack of rapid forging pretreatment, the core of the billet had poor plasticity and cracked during radial forging, making it impossible to obtain a complete product. This indicates that the direct radial forging process is not feasible.
[0050] Comparative Example 6 The difference from Example 1 is that the Al content in the Fe-Mn-Al-C billet is 16.0%, while the other steps are the same as in Example 1.
[0051] The Fe-Mn-Al-C steel prepared in Example 6 was tested, and the results showed that the excessively high Al content led to the precipitation of a large number of coarse and brittle intermetallic compounds (Fe3Al), which seriously impaired the hot workability. Severe cracks appeared during the forging process, and the material was extremely brittle at room temperature, making it impossible to conduct effective mechanical property tests.
[0052] As can be seen from the above embodiments and comparative examples: Example 1 combined with Comparative Example 1 shows that when the aluminum content is too low, the density reduction effect of the material is insufficient, and the κ-carbide precipitation of strengthening phase is insufficient, resulting in insufficient strength and plasticity; Example 1 combined with Comparative Example 2 shows that omitting the second-stage solution treatment will cause the κ-carbide to fail to fully dissolve and uniformly disperse and precipitate in the subsequent process, instead forming coarse undissolved carbides, which seriously damages the plasticity of the material, proving that "gradient solution treatment" is crucial for obtaining a uniform microstructure; Example 1 combined with Comparative Example 3 shows that using the traditional hot rolling process to replace the "fast forging + radial forging" combination process of this application will cause the κ-carbide to preferentially precipitate in a continuous film form at the grain boundaries, becoming a crack source. Although the strength is still acceptable, the plasticity deteriorates sharply; Example 1 combined with Comparative Examples 4 and 5 shows that the combination of "fast forging" and "radial forging" has a synergistic effect. Single fast forging (Comparative Example 4) cannot achieve sufficient core refinement and uniform precipitation of κ-carbides, resulting in poor performance; single radial forging (Comparative Example 5) directly leads to process failure due to insufficient plasticity in the core of the cast billet. Only the combination of "fast forging + radial forging" can achieve gradient deformation and microstructure refinement from the surface to the core, obtaining a material with excellent comprehensive performance. Example 1, combined with Comparative Example 6, shows that when the aluminum content is too high, a harmful brittle phase will form, making the material unworkable and completely impractical. Combining the above examples and comparative examples, it is shown that the specific chemical composition range defined in this application, as well as the specific preparation process including "gradient solid solution" and "fast forging + radial forging," are essential for synergistically obtaining the comprehensive excellent performance of "ultra-low density, high strength, and high elongation."
[0053] This application proposes an ultra-low density Fe-Mn-Al-C steel and its preparation method, which employs rapid forging: the process is carried out using a rapid forging machine. The rapid forging machine is characterized by high striking frequency, small deformation per pass, and fast deformation speed.
[0054] The following effects can be achieved: **Outer edge grain refinement:** The high-frequency, rapid impact causes a rapid rise in the temperature of the billet's outer edge. The accumulated distortion from deformation quickly triggers static recrystallization (SRX), transforming the coarse as-cast structure at the outer edge into fine recrystallized grains. **Core structure control:** Due to the small reduction per forging cycle and limited deformation penetration depth, the core temperature is lower, and the degree of deformation is smaller. Therefore, the core grains do not grow and remain relatively fine, preparing for subsequent radial forging. **Purpose:** To initially break down the as-cast structure, providing a billet with a suitable temperature gradient and pre-improved structure for subsequent radial forging, avoiding the risk of cracking due to poor core plasticity during direct radial forging.
[0055] Radial forging is employed: immediately following rapid forging, the still-hot billet is quickly fed into a radial forging mill. The radial forging mill uses multiple hammers to forge symmetrically and at high speed from the radial direction, resulting in strong deformation penetration and extremely high strain rate.
[0056] The following effects can be achieved: Extreme refinement of the outer edge: The extremely high strain rate causes the outer edge material to heat up rapidly, resulting in dynamic recrystallization and the formation of extremely fine equiaxed austenite grains. Intense deformation and refinement of the core: The powerful penetrating deformation capability of radial forging causes the core to also undergo intense plastic deformation. This refines the original grains and generates high-density dislocations, providing numerous nucleation sites for κ-carbide precipitation. Controlled κ-carbide precipitation: Air cooling, rather than water cooling, is used after radial forging. During air cooling, the defects (dislocations, vacancies, etc.) introduced by the intense plastic deformation promote the uniform and dispersed precipitation of κ-carbide in the matrix as granules or short rods, avoiding discontinuous precipitation at grain boundaries, thereby simultaneously improving both strength and plasticity.
[0057] Advantages of the combined process: "Rapid forging + radial forging" creates a gradient deformation and recrystallization from the surface inwards, ultimately achieving an ideal microstructure of fine equiaxed grains on the outer edge, refined grains in the core, and uniformly dispersed κ-carbides throughout. This is unattainable with traditional forging or single forging processes. Through reasonable chemical composition and process design, employing smelting, billet casting, gradient solution treatment, and rapid forging + radial forging processes, ultra-low density Fe-Mn-Al-C steel is obtained. The microstructure of Fe-Mn-Al-C steel includes 85-92 vol% austenite and 15-8 vol% ferrite, with precipitates including κ-carbides within the austenite. The density of the ultra-low density Fe-Mn-Al-C steel at room temperature is 6.09-6.25 g / cm³. 3The yield strength is 780-860 MPa, the tensile strength is 960-1020 MPa, and the elongation is 30%-40%. This application's ultra-low density Fe-Mn-Al-C steel, through groundbreaking alloy composition design and innovative preparation process, achieves excellent elongation and yield strength while maintaining low density, with a specific strength (155-165 MPa·cm). 3 / g) is significantly superior to existing high-strength steel (approximately 100 MPa·cm). 3 / g), aviation aluminum alloy (approximately 110MPa·cm) 3 / g) and titanium alloy (approximately 120 MPa·cm) 3 / g), providing a brand-new material solution for resolving the contradiction of "lightweight and high strength" in structural components used in the aerospace field.
[0058] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.
Claims
1. A method for preparing ultra-low density Fe-Mn-Al-C steel, characterized in that, Includes the following steps: S1. Obtain an Fe-Mn-Al-C billet, and perform gradient solution treatment on the Fe-Mn-Al-C billet to obtain a solution-treated billet; the gradient solution treatment includes a first solution treatment and a second solution treatment, and the composition of the Fe-Mn-Al-C billet by mass percentage includes: C: 1.35%-1.60%, Mn: 33.5%-36.0%, Al: 12.5%-15.5%, balance being Fe and unavoidable impurities; S2. The solution-treated billet is subjected to rapid forging and radial forging to obtain Fe-Mn-Al-C steel, wherein the density of the Fe-Mn-Al-C steel is 6.09-6.25 g / cm³. 3 .
2. The method for preparing ultra-low density Fe-Mn-Al-C steel according to claim 1, characterized in that, Before step S1, the process includes preparing raw materials according to the composition of the Fe-Mn-Al-C billet, adding them sequentially to the furnace cavity of a vacuum induction melting furnace for smelting, and holding the molten steel at a constant temperature for 20-30 minutes after the raw materials are completely melted. The steel is then cast using a water glass sand mold with a refractory coating on the inner wall. After casting, the billet is not demolded and is air-cooled to room temperature. After the mold is opened, the Fe-Mn-Al-C billet is obtained. The smelting temperature is 1550-1600℃, and the casting temperature is 1350-1450℃.
3. The method for preparing ultra-low density Fe-Mn-Al-C steel according to claim 1, characterized in that, In step S1, the first solution treatment method is as follows: the Fe-Mn-Al-C billet is heated to a temperature of 1150-1250℃ and held for 3-6 hours in a furnace, and then cooled by water to obtain the first solution-treated billet.
4. The method for preparing ultra-low density Fe-Mn-Al-C steel according to claim 3, characterized in that, In step S1, the second solution treatment method is as follows: the first solution casting billet is heated to a furnace temperature of 1000-1100℃ for 4-8 hours, and then cooled by air cooling to obtain the solution casting billet.
5. The method for preparing ultra-low density Fe-Mn-Al-C steel according to claim 1, characterized in that, In step S2, the initial forging temperature of the rapid forging is 1140-1190℃, the final forging temperature of the rapid forging is 1060-1110℃, the forging ratio of the rapid forging is 4-6, and the striking frequency of the rapid forging is 150-220 times / min.
6. The method for preparing ultra-low density Fe-Mn-Al-C steel according to claim 1, characterized in that, In step S2, the initial forging temperature of the radial forging is 1050-1100℃, the final forging temperature of the radial forging is 970-1020℃, the forging ratio of the radial forging is 3-4, the impact frequency of the radial forging is 80-120 times / min, and the cooling method of the radial forging is air cooling.
7. An ultra-low density Fe-Mn-Al-C steel, characterized in that, It is prepared by the method for preparing ultra-low density Fe-Mn-Al-C steel according to any one of claims 1-6.
8. The ultra-low density Fe-Mn-Al-C steel according to claim 7, characterized in that, The microstructure of the Fe-Mn-Al-C steel comprises 85-92 vol% austenite and 15-8 vol% ferrite.
9. The ultra-low density Fe-Mn-Al-C steel according to claim 8, characterized in that, The austenite also includes precipitated phases, which include κ-carbides.
10. The ultra-low density Fe-Mn-Al-C steel according to claim 7, characterized in that, The Fe-Mn-Al-C steel has a yield strength of 780-860 MPa, a tensile strength of 960-1020 MPa, an elongation of 30%-40%, and a specific strength of 155-165 MPa·cm at room temperature. 3 / g.