A high ductility low density steel and a method of making the same

Abstract

This invention relates to the field of low-density steel technology, specifically to a high-ductility low-density steel and its preparation method, comprising the following steps: Weighing of raw materials: The chemical composition, by mass percentage, is: C: 0.30~0.45%, Mn: 0.50~3.50%, Al: 4.0~6.0%, Si: 0.20~1.0%, Ti: 0.01~0.3%, Nb: 0.005~0.1%, P≤0.02%, S≤0.01%, N≤0.01%, with the remainder being Fe. The process steps of this invention are clear, and the parameter ranges are reasonable. Vacuum melting, ultrasonic modification, hot-cold rolling, and two-stage annealing are all mature industrial technologies, requiring no special equipment. Production costs are controllable, making it suitable for mass production. It can be widely used in lightweight structural components in the automotive, aerospace, and other fields, possessing significant industrial application value and market prospects.

Description

Technical Field

[0001] This invention relates to the field of low-density steel technology, specifically to a high-ductility low-density steel and its preparation method. Background Technology

[0002] With the automotive industry trending towards lightweight and low-emission designs, replacing traditional steel with high-strength, lightweight materials is one of the core approaches to achieving structural weight reduction. Low-density steel, due to its significant reduction in density through the addition of lightweight elements such as Al while maintaining high strength, has become a research hotspot for next-generation lightweight structural materials. However, existing low-density steel products struggle to balance low density, ductility, and strength, and their poor corrosion resistance limits their usability. Therefore, this invention provides further improvements to these products. Summary of the Invention

[0003] In view of the deficiencies of the prior art, the purpose of this invention is to provide a high-ductility, low-density steel and its preparation method, so as to solve the problems mentioned in the background art.

[0004] The present invention solves the technical problem by adopting the following technical solution:

[0005] This invention provides a method for preparing high-ductility, low-density steel, comprising the following steps:

[0006] Step 1, weighing the raw materials: The chemical composition by mass percentage is as follows: C: 0.30~0.45%, Mn: 0.50~3.50%, Al: 4.0~6.0%, Si: 0.20~1.0%, Ti: 0.01~0.3%, Nb: 0.005~0.1%, P≤0.02%, S≤0.01%, N≤0.01%, with the remainder being Fe.

[0007] Composition design principles: C content is controlled at 0.30~0.45%, which can form a solid solution with Fe to strengthen the matrix and promote carbide precipitation, thus improving strength; Mn content is 0.50~3.50%, which can improve the hardenability of steel, inhibit the formation of brittle phases, and improve ductility; Al, as a core lightweight element, a content of 4.0~6.0% can significantly reduce the material density, and at the same time form dispersed intermetallic compounds with Fe to achieve precipitation strengthening; Si: 0.20~1.0% can deoxidize and remove impurities, improve the fluidity of molten steel, and optimize casting quality; Ti and Nb work synergistically to form fine carbonitrides, hindering grain growth, refining the microstructure, and simultaneously improving strength and ductility; Strict control of P, S, and N content can avoid the formation of brittle inclusions (such as FeS, AlN) and prevent a decrease in material toughness.

[0008] Step 2, Melting, Casting and Ultrasonic Modification: Place the above raw materials in a vacuum induction melting furnace and melt them completely under inert gas protection (melting temperature 1550~1650℃, holding for 30~60min to ensure uniform composition). Then, use sand casting or metal mold casting to form the casting. After the casting cools to room temperature, put it into a sufficient amount of ultrasonic liquid for ultrasonic treatment. The ultrasonic power is 350-400W and the ultrasonic time is 1h. After the ultrasonic treatment, take the casting out of the ultrasonic liquid, filter to remove the ultrasonic liquid residue adhering to the surface, and dry it at 80~100℃ for 2~3h to obtain the ultrasonically improved casting.

[0009] Step 3, hot-cold rolling and homogenization: The ultrasonically improved casting is subjected to hot-cold rolling in sequence, and finally homogenization is performed to obtain high-ductility low-density steel.

[0010] Preferably, the ultrasonic fluid is prepared by:

[0011] S01: Preparation of the functional agent; 3-5 parts of calcium sulfate whiskers, 2-5 parts of silicon carbide, and 1-2 parts of boron nitride are placed in a sintering furnace and sintered for 1 hour at a sintering temperature of 210-220℃. After sintering, the mixture is allowed to cool naturally to room temperature to obtain the functional agent. Calcium sulfate whiskers can improve the dispersion stability of the ultrasonic fluid. Silicon carbide and boron nitride have high hardness and high wear resistance, which can be used to micro-grind the surface of the casting during the ultrasonic process, remove oxide scale, and promote ultrasonic energy transfer, thus refining the internal structure of the casting.

[0012] S02: Preparation of β-cyclodextrin solution and graphene-β-cyclodextrin combined solution; First, sodium silicate solution, β-cyclodextrin, and sodium alginate were placed in a stirred tank at a weight ratio of (5-8):2:(1-3) and stirred at 300-500 r / min for 20-30 min at room temperature until homogeneous to obtain β-cyclodextrin solution; then, modified graphene and β-cyclodextrin solution were placed in a high-speed mixer at a weight ratio of (3-5):7 and stirred for 30-40 min to obtain graphene-β-cyclodextrin combined solution. β-cyclodextrin has a unique cavity structure that can encapsulate modified graphene and prevent its aggregation. Sodium alginate can improve the viscosity and adhesion of the system, and sodium silicate solution can enhance the compatibility between the ultrasonic fluid and the surface of the casting.

[0013] S03: Preparation of hydroxyapatite solution; 3-5 parts by weight of hydroxyapatite, 2-4 parts by weight of nanocellulose, and 5-8 parts by weight of sodium citrate solution are placed in a stirred tank and stirred at room temperature for 30 min. Then, 1-2 parts by weight of silane coupling agent KH550 are added, and the mixture is stirred at 50-60℃ and 400-600 r / min for 1 h. After thorough stirring, the mixture is cooled to room temperature to obtain hydroxyapatite solution. Hydroxyapatite can improve the corrosion resistance of materials, nanocellulose enhances the dispersibility of ultrasonic fluid, sodium citrate solution acts as a chelating agent to promote the synergistic effect of various components, and silane coupling agent KH550 can improve the compatibility of hydroxyapatite with graphene system.

[0014] S04: Preparation of ultrasonic fluid; Hydroxyapatite solution and graphene-β-cyclodextrin combined solution are placed in a stirring vessel at a weight ratio of 5:(8-11) and stirred at room temperature for 40-60 min to obtain the modified body; The modified body and functional agent are placed in a ball mill at a weight ratio of (11-15):4, and the ball milling speed is 1000-1500 r / min for 2 h. After the ball milling is completed, the mixture is passed through a 200-mesh sieve to remove large particulate impurities and obtain ultrasonic fluid.

[0015] Preferably, the sodium citrate solution has a mass fraction of 10-15%; the sodium silicate solution has a mass fraction of 8-12%.

[0016] Preferably, the modified graphene is prepared as follows: 5-8 parts of graphene, 2-3 parts of calcined talc powder, and 1-2 parts of lanthanum oxide are placed in a mixer and premixed for 15-20 minutes. Then, 5-8 parts of urea solution are added and stirred until evenly dispersed. Next, 1-2 parts of sodium lignosulfonate solution are added, and the mixture is stirred for 1 hour at a stirring temperature of 55-60℃ and a stirring speed of 550-750 r / min. After stirring, the mixture is repeatedly washed with deionized water until the filtrate is neutral. After filtration, the filter cake is dried at 100-120℃ for 4-6 hours to obtain the modified graphene. Calcined talc powder can improve the dispersibility of graphene, lanthanum oxide can introduce rare earth elements and optimize the casting structure, and the synergistic effect of urea solution and sodium lignosulfonate solution can form a modified layer on the graphene surface, enhancing its compatibility with other components of the ultrasonic fluid.

[0017] Preferably, the sodium lignosulfonate solution has a mass fraction of 8-12%; the urea solution has a mass fraction of 2-5%.

[0018] Preferably, the specific operation steps of the hot-cold rolling process are as follows:

[0019] Hot rolling: The ultrasonically modified casting is placed in a heating furnace and heated to 900~1100℃, held for 1~2 hours to ensure full austenitization of the casting structure; a multi-pass hot rolling process is adopted, with a single pass reduction of ≤25% and a total reduction of 60~85%; the final hot rolling temperature is controlled at 800~850℃ to avoid the structure becoming brittle due to excessively low final temperature; after hot rolling, it is air-cooled to room temperature to obtain the hot-rolled plate;

[0020] Cold rolling: After grinding the surface of the hot-rolled plate to remove the oxide scale, it is subjected to multiple cold rolling passes. The reduction in a single pass is ≤20%, and the total reduction is 50~75%. The ambient temperature is controlled at 20~30℃ during the cold rolling process to avoid excessive cold rolling deformation that could cause the material to crack, thus obtaining a cold-rolled plate.

[0021] Preferably, the specific steps of the homogenization treatment are as follows: the cold-rolled sheet is placed in an annealing furnace and subjected to two-stage annealing under the protection of an inert gas (argon or nitrogen); the first stage annealing temperature is 920~980℃, and the holding time is 3~10min, so that the deformed structure generated during the cold rolling process can be fully recrystallized and the grains can be refined; the second stage annealing temperature is 580~630℃, and the holding time is 10~30min, so as to promote the dispersion and precipitation of carbides, eliminate internal stress, and improve the ductility of the material; finally, the material is cooled to room temperature in the furnace to obtain high-ductility low-density steel.

[0022] The present invention also provides a high-ductility low-density steel prepared by the above preparation method. The low-density steel has a density of 6.5~6.8 g / cm³, a tensile strength ≥650MPa, an elongation ≥20%, a Brinell hardness ≥200HBW, and a corrosion rate ≤0.03mm / a in a neutral salt spray test (5% NaCl solution, 35℃). It possesses excellent comprehensive mechanical properties and corrosion resistance stability.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention synergistically optimizes alloy composition and preparation process to achieve a balance between "low density, high strength, and high ductility": by precisely controlling the content of main elements such as Al, C, and Mn, and coordinating with Ti and Nb microalloying, the formation of brittle phases is suppressed. At the same time, customized ultrasonic liquid modification, multi-pass hot-cold rolling, and two-stage homogenization treatment are used to refine the grain structure, eliminate casting defects and internal stress, and prepare low-density steel with an elongation of ≥20%, tensile strength of ≥650MPa, and density as low as 6.5g / cm³, which is superior to existing similar products in terms of comprehensive performance. Customized ultrasonic fluid enhances casting quality and corrosion resistance: The ultrasonic fluid of this invention, through the synergistic combination of functional agents, modified graphene-β-cyclodextrin linkage liquid, and hydroxyapatite liquid, not only removes oxide scale from the casting surface under ultrasonic action but also penetrates into the micropores of the casting to fill defects, while forming a dense protective layer on the casting surface. The synergistic effect of modified graphene and hydroxyapatite significantly improves the material's corrosion resistance, with a neutral salt spray corrosion rate ≤0.03mm / a. High process stability and easy mass production: The process steps of this invention are clear, and the parameter ranges are reasonable. Vacuum melting, ultrasonic modification, hot-cold rolling, and two-stage annealing are all mature industrial technologies, requiring no special equipment. Production costs are controllable, making it suitable for mass production. It can be widely used in lightweight structural parts fields such as automobiles and aerospace, and has significant industrial application value and market prospects. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This embodiment describes a method for preparing high-ductility, low-density steel, comprising the following steps:

[0027] Step 1, Weighing the raw materials: The chemical composition by mass percentage is as follows: C: 0.30~0.45%, Mn: 0.50~3.50%, Al: 4.0~6.0%, Si: 0.20~1.0%, Ti: 0.01~0.3%, Nb: 0.005~0.1%, P≤0.02%, S≤0.01%, N≤0.01%, with the remainder being Fe;

[0028] Step 2: Melt the above raw materials completely, then cast them into a shape to obtain a casting; place the casting into a sufficient amount of ultrasonic liquid for ultrasonic treatment; after ultrasonic treatment, filter and dry to obtain an ultrasonically improved casting.

[0029] Step three involves ultrasonically improved hot-cold rolling of the cast material, followed by homogenization treatment to obtain low-density steel.

[0030] In this embodiment, the ultrasonic power for ultrasonic treatment is 350-400W, and the ultrasonic treatment lasts for 1 hour.

[0031] The method for preparing the ultrasonic fluid in this embodiment is as follows:

[0032] S01: Preparation of functional agents;

[0033] 3-5 parts of calcium sulfate whiskers, 2-5 parts of silicon carbide and 1-2 parts of boron nitride are blended and sintered for 1 hour at a sintering temperature of 210-220℃. After sintering, the functional agent is obtained.

[0034] S02: The modified graphene and β-cyclodextrin solution are mixed evenly at a weight ratio of (3-5):7 to obtain a graphene-β-cyclodextrin conjugate.

[0035] Sodium silicate solution, β-cyclodextrin and sodium alginate were mixed evenly in a weight ratio of (5-8):2:(1-3) to obtain β-cyclodextrin solution;

[0036] S03: Mix 3-5 parts by weight of hydroxyapatite, 2-4 parts of nanocellulose and 5-8 parts of sodium citrate solution evenly, then add 1-2 parts of silane coupling agent KH550 and stir thoroughly to obtain hydroxyapatite solution.

[0037] S04: The hydroxyapatite liquid and the graphene-β-cyclodextrin mixture are stirred thoroughly at a weight ratio of 5:(8-11) to obtain the improved body. The improved body and the functional agent are ball-milled at a weight ratio of (11-15):4. After ball milling, the ultrasonic liquid is obtained.

[0038] In this embodiment, the sodium citrate solution has a mass fraction of 10-15%; the ball milling speed is 1000-1500 r / min, and the ball milling time is 2 h.

[0039] The method for preparing the modified graphene in this embodiment is as follows:

[0040] 5-8 parts graphene, 2-3 parts calcined talc powder and 1-2 parts lanthanum oxide were mixed and added to 5-8 parts urea solution, followed by 1-2 parts sodium lignosulfonate solution. The mixture was stirred, washed with water, filtered, and dried to obtain modified graphene.

[0041] In this embodiment, the sodium lignosulfonate solution has a mass fraction of 8-12%, and the urea solution has a mass fraction of 2-5%.

[0042] In this embodiment, the stirring speed is 550-750 r / min, the stirring time is 1 hour, and the stirring temperature is 55-60℃.

[0043] The specific operation steps of the hot-cold rolling process in this embodiment are as follows:

[0044] Hot rolling: The billet is heated to 900~1100℃ and held for 1~2 hours. Multi-pass hot rolling is adopted, with a single pass reduction of ≤25% and a total reduction of 60~85%. The final hot rolling temperature is controlled at 800~850℃. Then it is air-cooled to room temperature to obtain hot-rolled plate.

[0045] Cold rolling: Hot-rolled plates are subjected to multiple cold rolling passes, with a single pass reduction of ≤20% and a total reduction of 50~75%.

[0046] The specific steps of the homogenization process in this embodiment are as follows:

[0047] Two-stage annealing is carried out under inert gas protection: the first stage annealing temperature is 920~980℃, and the holding temperature is 3~10min to allow the cold-rolled structure to recrystallize fully; the second stage annealing temperature is 580~630℃, and the holding temperature is 10~30min, and finally the furnace is cooled to room temperature.

[0048] This embodiment describes a method for preparing high-ductility low-density steel, specifically low-density steel.

[0049] Example 1

[0050] A method for preparing high-ductility, low-density steel includes the following steps:

[0051] Step 1, Weighing raw materials: Weigh the raw materials according to the following mass percentages: C: 0.35%, Mn: 2.0%, Al: 5.0%, Si: 0.6%, Ti: 0.15%, Nb: 0.05%, P: 0.015%, S: 0.008%, N: 0.009%, with the remainder being Fe. The total mass of the raw materials is 10 kg.

[0052] Step 2, Melting, Casting and Ultrasonic Modification: The above raw materials are placed in a vacuum induction melting furnace, protected by argon gas, heated to 1600℃, and held for 45 minutes. After complete melting, the metal mold is used for casting to obtain the casting body. After the casting body cools to room temperature, it is placed in a sufficient amount of ultrasonic liquid and ultrasonically treated for 1 hour at an ultrasonic power of 380W. After ultrasonic treatment, the residual ultrasonic liquid on the surface is removed by filtration, and the casting body is dried at 90℃ for 2.5 hours to obtain the ultrasonically improved casting body.

[0053] The preparation method of the ultrasonic fluid is as follows:

[0054] S01: Preparation of functional agent: Take 4 parts of calcium sulfate whiskers, 3.5 parts of silicon carbide and 1.5 parts of boron nitride, put them into a sintering furnace, and sinter them at 215°C for 1 hour. After cooling, the functional agent is obtained.

[0055] S02: Preparation of β-cyclodextrin solution: Take 6.5 parts of 10% sodium silicate solution, 2 parts of β-cyclodextrin and 2 parts of sodium alginate, stir at 350 r / min for 25 min at room temperature to obtain β-cyclodextrin solution; Take 4 parts of modified graphene and 7 parts of β-cyclodextrin solution, stir at high speed for 35 min to obtain graphene-β-cyclodextrin combined solution;

[0056] S03: Preparation of hydroxyapatite solution: Take 4 parts of hydroxyapatite, 3 parts of nanocellulose and 6.5 parts of sodium citrate solution with a mass fraction of 12%, stir at room temperature for 30 min, add 1.5 parts of silane coupling agent KH550, stir at 500 r / min for 1 h at 55℃, and obtain hydroxyapatite solution after cooling.

[0057] S04: Preparation of ultrasonic fluid: Take 5 parts of hydroxyapatite liquid and 9.5 parts of graphene-β-cyclodextrin combined liquid, stir at room temperature for 50 min to obtain the modified body; take 13 parts of the modified body and 4 parts of functional agent, put them into a ball mill, ball mill at 1200 r / min for 2 h, and pass through a 200 mesh sieve to obtain ultrasonic fluid.

[0058] The modified graphene was prepared as follows: 6.5 parts graphene, 2.5 parts calcined talc powder and 1.5 parts lanthanum oxide were premixed for 18 min, 6.5 parts of 3.5% urea solution were added and stirred to disperse evenly; then 1.5 parts of 10% sodium lignosulfonate solution were added and stirred at 650 r / min for 1 h at 58 °C; the filtrate was washed with water until neutral, filtered and dried at 110 °C for 5 h to obtain modified graphene.

[0059] Step 3, Hot-Cold Rolling and Homogenization Treatment:

[0060] Hot rolling: The ultrasonically improved casting is placed in a heating furnace, heated to 1000℃, and held for 1.5 hours; five passes of hot rolling are used, with single pass reductions of 20%, 22%, 20%, 18%, and 15%, respectively, for a total reduction of 75%. The final hot rolling temperature is 820℃, and the hot-rolled plate is air-cooled to room temperature to obtain the hot-rolled plate.

[0061] Cold rolling: The surface of the hot-rolled plate is ground to remove the oxide scale, and then cold-rolled in 4 passes with a single pass reduction of 18%, 16%, 15%, and 14%, respectively, for a total reduction of 63%. The cold-rolled plate is obtained by cold rolling at room temperature.

[0062] Homogenization treatment: The cold-rolled sheet is placed in an annealing furnace and protected with nitrogen gas. It undergoes two-stage annealing: the first stage is held at 950℃ for 6 minutes, and the second stage is held at 600℃ for 20 minutes. The sheet is then cooled to room temperature in the furnace to obtain high-ductility, low-density steel.

[0063] Example 2

[0064] A method for preparing high-ductility, low-density steel differs from Example 1 in that:

[0065] Raw material composition (mass percentage): C: 0.30%, Mn: 0.50%, Al: 4.0%, Si: 0.20%, Ti: 0.01%, Nb: 0.005%, P: 0.02%, S: 0.01%, N: 0.01%, balance Fe;

[0066] The ultrasonic power was 350W, and the SO4 ball milling speed in the ultrasonic fluid preparation was 1000r / min.

[0067] Hot rolling temperature 900℃, holding time 1 hour, total reduction 60%, final temperature 800℃; cold rolling total reduction 50%;

[0068] Homogenization treatment: First stage: 920℃ for 3 min, second stage: 580℃ for 10 min.

[0069] Example 3

[0070] A method for preparing high-ductility, low-density steel differs from Example 1 in that:

[0071] Raw material composition (mass percentage): C: 0.45%, Mn: 3.50%, Al: 6.0%, Si: 1.0%, Ti: 0.3%, Nb: 0.1%, P: 0.01%, S: 0.005%, N: 0.008%, the remainder being Fe;

[0072] The ultrasonic power was 400W, and the SO4 ball milling speed in the ultrasonic fluid preparation was 1500r / min.

[0073] Hot rolling temperature 1100℃, holding temperature for 2 hours, total reduction 85%, final temperature 850℃; cold rolling total reduction 75%;

[0074] Homogenization treatment: First stage: 980℃ for 10 min, second stage: 630℃ for 30 min.

[0075] Comparative Example 1

[0076] A method for preparing low-density steel differs from Example 1 in that the ultrasonic modification step is omitted, while the remaining process parameters are the same as in Example 1.

[0077] Comparative Example 2

[0078] A method for preparing low-density steel differs from Example 1 in that: the ultrasonic fluid is replaced with deionized water, while the other process parameters are the same as in Example 1.

[0079] Comparative Example 3

[0080] A method for preparing low-density steel differs from Example 1 in that the homogenization treatment uses single-stage annealing (holding at 700℃ for 30 min), while the remaining process parameters are the same as in Example 1.

[0081] Comparative Example 4

[0082] A method for preparing low-density steel differs from Example 1 in that: no modified graphene is added in the preparation of the ultrasonic fluid; only β-cyclodextrin fluid is used instead of graphene-β-cyclodextrin linkage fluid, while the remaining process parameters are the same as in Example 1.

[0083] Comparative Example 5

[0084] A method for preparing low-density steel differs from Example 1 in that: the hydroxyapatite liquid is omitted in the preparation of the ultrasonic liquid, and only the graphene-β-cyclodextrin linkage liquid and the functional agent are ball-milled to prepare the ultrasonic liquid, while the remaining process parameters are the same as in Example 1.

[0085] Comparative Example 6

[0086] A method for preparing low-density steel differs from Example 1 in that the functional agent in the ultrasonic fluid preparation is not sintered, but calcium sulfate whiskers, silicon carbide, boron nitride and the modifier are directly ball-milled, and the remaining process parameters are the same as in Example 1.

[0087] Performance testing

[0088] The low-density steels prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests according to the following standards: density was determined by the water displacement method; tensile strength and elongation were determined according to GB / T 228.1-2010 "Metallic materials, tensile testing—Part 1: Tests at room temperature"; corrosion resistance was determined by the neutral salt spray test (GB / T 10125-2021) for 240 hours, and the corrosion rate was calculated. The test results are shown in the table below.

[0089]

[0090] The test results above show that the low-density steels prepared in Examples 1-3 of this invention all possess excellent comprehensive properties, with a density controlled at 6.5~6.8 g / cm³, tensile strength ≥650 MPa, elongation ≥20%, and corrosion rate ≤0.03 mm / a. In contrast, Comparative Examples 1-3, due to omitting ultrasonic modification, replacing the ultrasonic fluid, or using single-stage annealing, exhibited significantly reduced performance, particularly a poorer synergy between ductility and strength. The newly added Comparative Examples 4-6 further validated the key roles of each component of the ultrasonic fluid and the preparation process.

[0091] Comparative Example 4, without modified graphene, resulted in insufficient dispersibility and strengthening effect of the ultrasonic fluid, with tensile strength and elongation decreasing by 11.1% and 26.4% respectively compared to Example 1.

[0092] Comparative Example 5, which omitted hydroxyapatite solution, showed a significant deterioration in corrosion resistance, with the corrosion rate increasing by 86.4%, while its mechanical properties also declined simultaneously.

[0093] In Comparative Example 6, the functional agent was not sintered, resulting in weakened component synergy and an inability to effectively refine the casting microstructure, leading to overall performance degradation. These results fully demonstrate the rationality of the composition and preparation process design of the ultrasonic fluid of this invention. Only through the synergistic effect of each component can the optimal improvement of the material's overall performance be achieved, further highlighting the superiority of the present invention.

[0094] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0095] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing high-ductility, low-density steel, characterized in that, Includes the following steps: Step 1, Weighing the raw materials: The chemical composition by mass percentage is as follows: C: 0.30~0.45%, Mn: 0.50~3.50%, Al: 4.0~6.0%, Si: 0.20~1.0%, Ti: 0.01~0.3%, Nb: 0.005~0.1%, P≤0.02%, S≤0.01%, N≤0.01%, with the remainder being Fe; Step 2: Melt the above raw materials completely, then cast them into a shape to obtain a casting; place the casting into a sufficient amount of ultrasonic liquid for ultrasonic treatment; after ultrasonic treatment, filter and dry to obtain an ultrasonically improved casting. Step 3: Ultrasonic-enhanced hot-cold rolling of the cast body, followed by homogenization treatment, yields low-density steel. The method for preparing the ultrasonic fluid is as follows: S01: Preparation of functional agents; 3-5 parts of calcium sulfate whiskers, 2-5 parts of silicon carbide and 1-2 parts of boron nitride were blended and sintered for 1 hour at a sintering temperature of 210-220℃. After sintering, the functional agent was obtained. S02: The modified graphene and β-cyclodextrin solution are mixed evenly at a weight ratio of (3-5):7 to obtain a graphene-β-cyclodextrin conjugate. Sodium silicate solution, β-cyclodextrin, and sodium alginate were mixed evenly at a weight ratio of (5-8):2:(1-3) to obtain a β-cyclodextrin solution; the mass fraction of the sodium silicate solution was 8-12%. S03: Mix 3-5 parts by weight of hydroxyapatite, 2-4 parts of nanocellulose and 5-8 parts of sodium citrate solution evenly, then add 1-2 parts of silane coupling agent KH550 and stir thoroughly to obtain hydroxyapatite solution. The sodium citrate solution has a mass fraction of 10-15%; S04: The hydroxyapatite liquid and the graphene-β-cyclodextrin mixture were stirred thoroughly at a weight ratio of 5:(8-11) to obtain the improved body. The improved body and the functional agent were ball-milled at a weight ratio of (11-15):

4. After ball milling, the ultrasonic liquid was obtained. The method for preparing the modified graphene is as follows: 5-8 parts of graphene, 2-3 parts of calcined talc powder and 1-2 parts of lanthanum oxide were mixed and added to 5-8 parts of urea solution, followed by 1-2 parts of sodium lignosulfonate solution. The mixture was stirred, washed with water, filtered, and dried to obtain modified graphene. The sodium lignosulfonate solution has a mass fraction of 8-12%; the urea solution has a mass fraction of 2-5%.

2. The method for preparing a high-ductility, low-density steel according to claim 1, characterized in that, The ultrasonic power of the ultrasonic treatment is 350-400W, and the ultrasonic treatment lasts for 1 hour.

3. The method for preparing a high-ductility, low-density steel according to claim 1, characterized in that, The ball milling process was carried out at a speed of 1000-1500 r / min for 2 hours.

4. The method for preparing a high-ductility, low-density steel according to claim 1, characterized in that, The stirring speed for the stirring process is 550-750 r / min, the stirring time is 1 h, and the stirring temperature is 55-60℃.

5. The method for preparing a high-ductility, low-density steel according to claim 1, characterized in that, The specific operational steps of the hot-cold rolling process are as follows: Hot rolling: The billet is heated to 900~1100℃ and held for 1~2 hours. Multi-pass hot rolling is adopted, with a single pass reduction of ≤25% and a total reduction of 60~85%. The final hot rolling temperature is controlled at 800~850℃. Then it is air-cooled to room temperature to obtain hot-rolled plate. Cold rolling: Hot-rolled plates are subjected to multiple cold rolling passes, with a single pass reduction of ≤20% and a total reduction of 50~75%.

6. The method for preparing a high-ductility, low-density steel according to claim 1, characterized in that, The specific steps of the homogenization process are as follows: Two-stage annealing is carried out under inert gas protection: the first stage annealing temperature is 920~980℃, and the holding time is 3~10min to allow the cold-rolled structure to recrystallize fully; The second stage of annealing is carried out at a temperature of 580~630℃, held for 10~30 minutes, and finally cooled to room temperature in the furnace.

7. Low-density steel prepared by the method for preparing high-ductility low-density steel according to any one of claims 1-6.

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