Steel with high product of strength and elongation, high specific strength and low density and preparation method thereof

Abstract

The invention discloses steel with high product of strength and elongation, high specific strength and low density and a preparation method thereof. The steel is composed of 0.85%-1.15% of C, 9.5%-12% of Mn, 8.5%-11.5% of Al, 2.5%-3.5% of Ni, 2%-3% of Cr, 0.3%-0.5% of V, smaller than or equal to 0.005% of S, smaller than or equal to 0.008% of P, iron and inevitable impurities. The preparation method comprises the working procedures of smelting, casting, forging, hot rolling, cold rolling and recrystallization annealing. Through the collaborative design of high C, medium Mn and high Al, Cr inhibits grain boundary carbide segregation, Ni promotes formation of a B2 ordered phase, V microalloying promotes precipitation of a VC precipitated phase, and a multi-scale layered structure composed of strip-shaped delta ferrite, an equiaxial (Fe, Ni) Al type B2 phase, austenite and a nano VC precipitated phase is formed. And in the recrystallization annealing process, regulation and control of a multi-scale layered structure and synergistic strengthening of an equiaxed (Fe, Ni) Al type B2 phase and a VC nano precipitated phase are achieved through the processes of rapid heating, short-time heat preservation and rapid cooling. According to the invention, the balance bottleneck of strength-plasticity-density of low-density steel is broken through, and a high-performance material solution is provided for light weight of automobiles.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and in particular relates to a high-strength-plasticity, high-specific strength, low-density steel and a preparation method thereof. Background Art

[0002] As a core strategy for addressing energy crises and environmental challenges, automotive lightweighting technology has consistently faced the challenge of balancing high strength with low density. Traditional lightweighting approaches have primarily focused on two types of materials: first, third-generation advanced high-strength steels, such as QP steel and MS steel, can increase tensile strength to 1200 MPa, but their elongation after fracture is typically less than 15%, making them susceptible to springback cracking during cold stamping. Furthermore, their density is typically higher than 7.8 g / cm³, limiting their potential for lightweighting. Second, the use of lightweight materials such as aluminum alloys and magnesium alloys can significantly reduce density, but they suffer from poor formability, insufficient collision energy absorption, and high costs.

[0003] In this context, the development of new metal materials with high strength, low density and excellent formability has become a key path to breaking through the bottleneck of the automotive lightweighting industry. By increasing the proportion of Mn and Al in steel and constructing a composition system with Fe, Mn, Al and C as the core elements, the density of steel can be effectively reduced to below 7.3g / cm³. At the same time, the introduction of Al-containing precipitates into the material provides additional precipitation strengthening and solid solution strengthening for the material, which helps to improve the strength-plasticity matching and has become an important development direction of lightweighting technology. However, the following defects are common in existing technologies: increasing the Al content in steel can easily lead to the precipitation of brittle κ carbides, deteriorating the plasticity of the material and increasing the risk of processing cracking; in addition, the technological evolution of existing low-density steels has always faced the difficult problem of balancing strength, plasticity and density, making it difficult to achieve both high strength-plasticity product and high specific strength.

[0004] Patent CN108396244A discloses a cold-rolled medium-manganese, high-aluminum, low-density steel and its preparation method. The alloy composition, by weight, is as follows: C: 1.20-1.30%, Mn: 10.7-11.3%, Al: 9.5-10%, P ≤ 0.005%, S ≤ 0.003%, with the remainder being Fe and unavoidable impurities. The structure is austenite + ferrite + kappa carbide. The precipitation strengthening effect of kappa carbide gives the low-density steel a high tensile strength of 1300 MPa. However, the elongation is less than 20%, and the strength-ductility product is low, making it more difficult to stamp and form automotive parts, increasing manufacturing costs.

[0005] Patent CN106756567A discloses a method for producing a hot-rolled, low-density steel with a strength-ductility product of 40 GPa·%. The alloy composition, by weight, is as follows: 0.6%-1.0% C, 8%-12% Mn, 7%-11% Al, 0.01%-0.2% V, P ≤ 0.003%, S ≤ 0.002%, with the remainder being Fe and unavoidable impurities. The structure is austenite + ferrite. While this simple production process achieves a strength-ductility product of 40 GPa·%, the tensile strength is less than 1 GPa, resulting in a low specific strength, making it difficult to meet the safety requirements for automotive collision energy-absorbing components. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a high-strength-plasticity, high-specific strength, low-density steel and a preparation method thereof.

[0007] To achieve this technical purpose, the present invention adopts the following scheme: In the first aspect, the present invention provides a high-strength-plasticity product, high specific strength, and low-density steel. The chemical composition and mass percentage of the high-strength-plasticity product, high specific strength, and low-density steel are: C: 0.85-1.15%, Mn: 9.5-12.0%, Al: 8.5-11.5%, Ni: 2.5-3.5%, Cr: 2.0-3.0%, V: 0.3-0.5%, S≤0.005%, P≤0.008%, and the rest are Fe and unavoidable impurities.

[0008] Furthermore, the yield strength of high strength-plasticity product, high specific strength, and low density steel is ≥1060MPa, the tensile strength is ≥1300MPa, the elongation is ≥38.0%, the density is 6.63~6.78g / cm³, the strength-plasticity product is ≥50GPa•%, and the specific strength is ≥195MPa / (g / cm³).

[0009] Furthermore, the microstructure of the finished steel product with high strength-ductility product, high specific strength and low density consists of banded delta ferrite, equiaxed (Fe, Ni)Al type B2 phase, austenite, and VC nano-precipitates dispersed in the matrix.

[0010] Furthermore, in the high-strength-ductility, high-specific strength, and low-density steel, the banded δ-ferrite accounts for 15-20%, with an average band width of 1.5-2.5 μm; the equiaxed (Fe, Ni)Al-type B2 phase accounts for 5-10%, with a grain size of ≤1.5 μm; the austenite accounts for 70-80%, with a grain size of 6-8 μm; and the nano-scale VC precipitate phase has an average particle size of ≤80 nm.

[0011] In a second aspect, the present invention provides a method for preparing high-strength-ductility-product, high-specific strength, and low-density steel, comprising smelting, casting, forging, hot rolling, cold rolling, and recrystallization annealing steps, specifically: According to the chemical composition of the high-strength-plasticity, high-specific-strength, low-density steel of the present invention, the steel is smelted and cast into an ingot, and the ingot is forged into a rectangular billet; The hot rolling process parameters are controlled as follows: the rectangular billet is heated to a temperature of 1180-1220°C, the holding time is 1.5-2.5h, the starting rolling temperature is 1140-1180°C, the finishing rolling temperature is 880-920°C, the hot rolling reduction ratio is 85-93%, and the hot rolling is cooled to room temperature with water. The thickness of the hot rolled plate is 4.0-5.5mm. The cold rolling process parameters are controlled as follows: the cold rolling reduction rate is 60-75%, and the cold rolled plate thickness is 1.0-2.0 mm; The parameters of the recrystallization annealing process are controlled as follows: the heating rate is 80-100°C / s, the annealing temperature is 950-1050°C, the holding time is 60-300s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0012] The functions of the main elements in the chemical composition of the high-strength-ductility, high-specific strength, low-density steel of the present invention are as follows: C: As a core strengthening element, it improves the matrix strength through the interstitial solid solution mechanism; the C element also regulates the stability of austenite, increasing its stacking fault energy to the critical threshold that inhibits deformation-induced martensitic phase transformation, ensuring that the material does not undergo brittle transformation during plastic deformation, and achieving coordinated optimization of strength and toughness. The C content of the present invention ranges from 0.85 to 1.15%.

[0013] Mn: As an austenite-forming element, it increases the stability of austenite at room temperature, improving the plasticity and workability of steel. Mn also reduces the tendency of carbon segregation at the ferrite-austenite phase boundary, alleviating the risk of interfacial embrittlement. The Mn content of the present invention ranges from 9.5% to 12.0%.

[0014] Al: It primarily reduces material density, lowering the steel's density to below 6.8g / cm³ through atomic substitution. It also acts as a strong ferrite-forming element, promoting the formation of delta-ferrite. Delta-ferrite precipitates at high temperatures, distributing itself within the matrix as strips with an average width of 1.5 to 2.5μm. Its high orientational continuity regulates strain distribution, improving the material's strength-ductility ratio and energy absorption efficiency. The Al content in this invention ranges from 8.5% to 11.5%.

[0015] Ni: helps to suppress the abnormal growth of δ ferrite grains during high temperature annealing, and improves the uniformity and refinement of the structure. In addition, Ni and Al have a tendency to form an ordered B2 phase at high temperature. The generated equiaxed (Fe, Ni) Al type B2 structure has a regular and ordered arrangement, which increases the difficulty of dislocation cross-slip and enhances the ability to disperse stress within the grain, thereby improving the yield strength. The equiaxed (Fe, Ni) Al type B2 phase exists as a strengthening phase in the multiphase structure of the present invention, and synergistically improves the strength-plastic coordination and deformation uniformity of the steel with austenite and δ ferrite. The Ni content of the present invention is in the range of 2.5 to 3.5%.

[0016] Cr: It increases the solubility of carbon in austenite, thereby reducing the driving force for carbide precipitation, inhibiting the precipitation of kappa carbides at austenite grain boundaries, and preventing a decrease in the material's plasticity. Cr also improves the corrosion resistance of low-density steel. The Cr content of the present invention is in the range of 2.0 to 3.0%.

[0017] V: The V element combines with carbon atoms to form a VC precipitate with a particle size of ≤80 nm. VC exhibits excellent thermal stability and high interfacial bonding strength, allowing it to disperse and precipitate within the matrix, enhancing the material's precipitation strengthening effect. The VC precipitate effectively pins grain and phase boundaries, inhibiting grain growth and microstructure coarsening while hindering the preferential growth of brittle kappa carbides, thereby optimizing the steel's plasticity and plastic performance. The V content in this invention is controlled within a range of 0.3-0.5%.

[0018] Compared with the existing technology, the beneficial effects of adopting the above technical solution are: The present invention achieves synergistic optimization of composition through a matching design of high C, medium Mn, and high Al, combined with microalloying of Ni, Cr, and V, to form a multi-phase organization of banded δ ferrite, equiaxed (Fe, Ni) Al-type B2 phase, austenite, and a multi-scale layered structure composed of VC nano-precipitates. Austenite can dissolve a large number of C atoms, improving the matrix strength through the interstitial solid solution mechanism. The banded δ ferrite forms a layered framework on the microscale and is periodically distributed in the austenite. It can withstand large strains without being easily broken during deformation, thereby improving the overall toughness of the material; the equiaxed (Fe, Ni) Al-type B2 phase precipitates at the submicron scale, improving the yield strength through the fine grain strengthening mechanism, while the uniform distribution along the austenite grain boundaries can promote uniform stress dispersion and enhance the material's stable plastic deformation ability; the VC nano-scale precipitates further hinder dislocation movement and achieve a precipitation strengthening effect. This multiscale layered structure establishes a coordinated distribution and interface regulation mechanism between the reinforcement phase and the matrix at the micro-submicro-nanoscale, enhancing the material's adaptability to local stress concentration and non-uniform plastic deformation, resulting in excellent strength and plasticity. High-reduction hot rolling refines the delta-ferrite bands and austenite grains. Water cooling to room temperature after final rolling inhibits the precipitation of brittle phases and prevents grain coarsening, improving microstructural uniformity. Cold rolling ensures an increased dislocation density within the low-density steel, providing sufficient driving force for recrystallization during the annealing phase. The recrystallization annealing process utilizes a rapid heating-short-holding-rapid cooling process, enabling higher heating and cooling rates. While promoting the formation of equiaxed (Fe,Ni)Al-type B2 phases and VC nanoprecipitates, it inhibits the coarsening of the VC precipitates and the growth of the B2 phase grains, enhancing the refinement and microstructural compatibility of the multiscale layered structure.

[0019] In summary, the present invention constructs a multi-scale layered structure through the collaborative innovation of composition design and preparation process, achieving multiple goals of multiphase distribution, microstructure refinement, precipitation phase optimization and brittleness suppression, breaking through the process bottleneck of traditional low-density steel that is difficult to balance strength, plasticity and density, and providing an efficient, stable and high-performance material preparation solution for lightweighting of automobiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a microstructure diagram of the high-strength-ductility, high-specific strength, and low-density steel in Example 1 of the present invention.

[0021] Figure 2 It is the VC nano-precipitated phase in the high-strength-ductility, high-specific strength, and low-density steel in Example 1 of the present invention.

[0022] Figure 3 This is the microstructure diagram of the steel in Comparative Example 1 of the present invention.

[0023] Figure 4This is the microstructure diagram of the steel in Comparative Example 2 of the present invention.

[0024] Figure 5 This is the microstructure diagram of the steel in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0025] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0026] The present invention provides a high-strength-ductility, high-specific strength, low-density steel and a preparation method thereof, which includes smelting, casting, forging, hot rolling, cold rolling, and recrystallization annealing processes, specifically carried out in the following steps. Example 1

[0027] According to the chemical composition of the high-strength-plasticity, high-specific strength, and low-density steel of the present invention, smelting, casting, and forging are performed into rectangular billets, and the chemical composition thereof is as follows in terms of mass percentage: C: 0.96%, Mn: 11.0%, Al: 11.0%, Ni: 3.2%, Cr: 2.3%, V: 0.35%, S: 0.003%, P: 0.006%, and the remainder is Fe and unavoidable impurities.

[0028] Hot rolling process parameter control: heating temperature is 1190℃, holding time is 2h, starting rolling temperature is 1150℃, finishing rolling temperature is 880℃, hot rolling reduction rate is 88%, water cooling to room temperature after hot rolling, hot rolled plate thickness is 5.1mm; Cold rolling process parameter control: cold rolling reduction rate is 65%, cold rolled plate thickness is 1.8mm; The parameters of the recrystallization annealing process are as follows: the heating rate is 95°C / s, the annealing temperature is 1000°C, the holding time is 180s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0029] The high strength-ductility, high specific strength, and low density steel prepared in this embodiment has a multi-scale layered structure. Figure 1 and Figure 2 The microstructure consists of 17% banded delta ferrite (average band width 2.5 μm), 10% equiaxed (Fe, Ni) Al type B2 phase (average grain size 1.1 μm), 73% austenite (average grain size 7.0 μm), and the average grain size of VC precipitation phase is 80 nm.

[0030] The high-strength-ductility product, high specific strength, and low-density steel prepared in this embodiment has a yield strength of 1068 MPa, a tensile strength of 1300 MPa, an elongation of 38.7%, a density of 6.67 g / cm³, a strength-ductility product of 50.3 GPa·%, and a specific strength of 195 MPa / (g / cm³). Example 2

[0031] According to the chemical composition of the high-strength-plasticity, high-specific strength, and low-density steel of the present invention, smelting, casting, and forging are performed into rectangular billets, and the chemical composition thereof is as follows in terms of mass percentage: C: 1.05%, Mn: 10.0%, Al: 8.5%, Ni: 3.5%, Cr: 3.0%, V: 0.35%, S: 0.003%, P: 0.007%, and the remainder is Fe and unavoidable impurities.

[0032] Hot rolling process parameter control: heating temperature is 1180℃, holding time is 2.5h, starting rolling temperature is 1140℃, finishing rolling temperature is 900℃, hot rolling reduction rate is 85%, water cooling to room temperature after hot rolling, and hot rolled plate thickness is 5.5mm.

[0033] Cold rolling process parameter control: cold rolling reduction rate is 64%, and cold rolled plate thickness is 2.0 mm.

[0034] The parameters of the recrystallization annealing process are as follows: the heating rate is 90°C / s, the annealing temperature is 970°C, the holding time is 90s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0035] The high-strength-ductility, high-specific strength, and low-density steel prepared in this embodiment has a multi-scale layered structure. The microstructure consists of 16% banded δ-ferrite (average band width 2.3 μm), 5% equiaxed (Fe, Ni)Al-type B2 phase (average grain size 1.5 μm), and 79% austenite (average grain size 8.0 μm). The average particle size of the VC precipitate phase is 77 nm.

[0036] The high-strength-ductility product, high specific strength, and low-density steel prepared in this embodiment has a yield strength of 1073 MPa, a tensile strength of 1337 MPa, an elongation of 38.4%, a density of 6.78 g / cm³, a strength-ductility product of 51.3 GPa·%, and a specific strength of 197 MPa / (g / cm³). Example 3

[0037] According to the chemical composition of the high-strength-plasticity, high-specific strength, and low-density steel of the present invention, smelting, casting, and forging are performed into rectangular billets, and the chemical composition thereof is as follows in terms of mass percentage: C: 0.88%, Mn: 12.0%, Al: 11.5%, Ni: 2.6%, Cr: 2.2%, V: 0.50%, S: 0.005%, P: 0.008%, and the remainder is Fe and unavoidable impurities.

[0038] Hot rolling process parameter control: heating temperature is 1180℃, holding time is 1.5h, starting rolling temperature is 1140℃, finishing rolling temperature is 880℃, hot rolling reduction rate is 90%, water cooling to room temperature after hot rolling, and hot rolled plate thickness is 4.5mm.

[0039] Cold rolling process parameter control: cold rolling reduction rate is 72%, and the cold rolled plate thickness is 1.3mm.

[0040] The parameters of the recrystallization annealing process are as follows: the heating rate is 80°C / s, the annealing temperature is 990°C, the holding time is 300s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0041] The high-strength-ductility, high-specific strength, and low-density steel prepared in this embodiment has a multi-scale layered structure. The microstructure consists of 18% banded δ-ferrite (average band width 1.5 μm), 7% equiaxed (Fe, Ni)Al-type B2 phase (average grain size 1.3 μm), and 75% austenite (average grain size 6.8 μm). The average particle size of the VC precipitate phase is 68 nm.

[0042] The high-strength-plasticity product, high specific strength, and low-density steel prepared in this embodiment has a yield strength of 1064 MPa, a tensile strength of 1328 MPa, an elongation of 39.3%, a density of 6.63 g / cm³, a strength-plasticity product of 52.2 GPa·%, and a specific strength of 200 MPa / (g / cm³). Example 4

[0043] According to the chemical composition of the high-strength-plasticity, high-specific strength, and low-density steel of the present invention, smelting, casting, and forging are performed into rectangular billets, and the chemical composition thereof is as follows in terms of mass percentage: C: 0.85%, Mn: 9.5%, Al: 8.5%, Ni: 2.5%, Cr: 2.0%, V: 0.33%, S: 0.004%, P: 0.008%, and the remainder is Fe and unavoidable impurities.

[0044] Hot rolling process parameter control: heating temperature is 1210℃, holding time is 2.5h, starting rolling temperature is 1170℃, finishing rolling temperature is 880℃, hot rolling reduction rate is 85%, water cooling to room temperature after hot rolling, and hot rolled plate thickness is 4.8mm.

[0045] Cold rolling process parameter control: cold rolling reduction rate is 60%, and the cold rolled plate thickness is 1.9 mm.

[0046] The parameters of the recrystallization annealing process are as follows: the heating rate is 100°C / s, the annealing temperature is 950°C, the holding time is 60s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0047] The high-strength-ductility, high-specific strength, and low-density steel prepared in this embodiment has a multi-scale layered structure. The microstructure consists of 15% banded δ-ferrite (average band width 2.5 μm), 5% equiaxed (Fe, Ni)Al-type B2 phase (average grain size 1.2 μm), and 80% austenite (average grain size 6.0 μm). The average particle size of the VC precipitate phase is 79 nm.

[0048] The high-strength-plasticity product, high specific strength, and low-density steel prepared in this embodiment has a yield strength of 1060 MPa, a tensile strength of 1317 MPa, an elongation of 40.1%, a density of 6.75 g / cm³, a strength-plasticity product of 52.8 GPa·%, and a specific strength of 195 MPa / (g / cm³). Example 5

[0049] According to the chemical composition of the high-strength-plasticity, high-specific strength, and low-density steel of the present invention, smelting, casting, and forging are performed into rectangular billets, and the chemical composition thereof is as follows in terms of mass percentage: C: 1.15%, Mn: 12.0%, Al: 10.0%, Ni: 2.7%, Cr: 2.5%, V: 0.40%, S: 0.005%, P: 0.005%, and the remainder is Fe and unavoidable impurities.

[0050] Hot rolling process parameter control: heating temperature is 1200℃, holding time is 2h, starting rolling temperature is 1160℃, finishing rolling temperature is 920℃, hot rolling reduction rate is 90%, water cooling after hot rolling, hot rolled plate thickness is 4.5mm; Cold rolling process parameter control: cold rolling reduction rate is 70%, cold rolled plate thickness is 1.4mm; The parameters of the recrystallization annealing process are as follows: the heating rate is 85°C / s, the annealing temperature is 980°C, the holding time is 200s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0051] The high-strength-ductility, high-specific strength, and low-density steel prepared in this embodiment has a multi-scale layered structure. The microstructure consists of 18% banded δ-ferrite (average band width 2.0 μm), 8% equiaxed (Fe, Ni)Al-type B2 phase (average grain size 1.1 μm), and 74% austenite (average grain size 7.5 μm). The average particle size of the VC precipitate phase is 75 nm.

[0052] The high-strength-plasticity product, high specific strength, and low-density steel prepared in this embodiment has a yield strength of 1078 MPa, a tensile strength of 1345 MPa, an elongation of 38.0%, a density of 6.68 g / cm³, a strength-plasticity product of 51.1 GPa·%, and a specific strength of 201 MPa / (g / cm³). Example 6

[0053] According to the chemical composition of the high-strength-plasticity, high-specific strength, and low-density steel of the present invention, smelting, casting, and forging are performed into rectangular billets, and the chemical composition thereof is as follows in terms of mass percentage: C: 1.10%, Mn: 10.5%, Al: 9.5%, Ni: 3.4%, Cr: 2.7%, V: 0.3%, S: 0.002%, P: 0.007%, and the remainder is Fe and unavoidable impurities.

[0054] Hot rolling process parameter control: heating temperature is 1220℃, holding time is 2h, starting rolling temperature is 1180℃, finishing rolling temperature is 920℃, hot rolling reduction rate is 93%, water cooling to room temperature after hot rolling, hot rolled plate thickness is 4.2mm.

[0055] Cold rolling process parameter control: cold rolling reduction rate is 67%, and cold rolled plate thickness is 1.4mm.

[0056] The parameters of the recrystallization annealing process are as follows: the heating rate is 100°C / s, the annealing temperature is 1050°C, the holding time is 180s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0057] The high-strength-ductility, high-specific strength, and low-density steel prepared in this embodiment has a multi-scale layered structure. The microstructure consists of 19% banded δ-ferrite (average band width 2.1 μm), 7% equiaxed (Fe, Ni)Al-type B2 phase (average grain size 1.0 μm), and 74% austenite (average grain size 8.0 μm). The average particle size of the VC precipitate phase is 76 nm.

[0058] The high-strength-plasticity product, high specific strength, and low-density steel prepared in this embodiment has a yield strength of 1080 MPa, a tensile strength of 1349 MPa, an elongation of 38.2%, a density of 6.72 g / cm³, a strength-plasticity product of 51.5 GPa·%, and a specific strength of 201 MPa / (g / cm³). Example 7

[0059] According to the chemical composition of the high-strength-plasticity, high-specific strength, and low-density steel of the present invention, smelting, casting, and forging are performed into rectangular billets, and the chemical composition thereof is as follows in terms of mass percentage: C: 1.0%, Mn: 11.5%, Al: 10.0%, Ni: 3.1%, Cr: 2.9%, V: 0.45%, S: 0.002%, P: 0.005%, and the remainder is Fe and unavoidable impurities.

[0060] Hot rolling process parameter control: heating temperature is 1220℃, holding time is 1.5h, starting rolling temperature is 1180℃, finishing rolling temperature is 880℃, hot rolling reduction rate is 93%, water cooling to room temperature after hot rolling, and hot rolled plate thickness is 4.0mm.

[0061] Cold rolling process parameter control: cold rolling reduction rate is 75%, and the cold rolled plate thickness is 1.0 mm.

[0062] The parameters of the recrystallization annealing process are as follows: the heating rate is 85°C / s, the annealing temperature is 1020°C, the holding time is 100s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

[0063] The high-strength-ductility, high-specific strength, and low-density steel prepared in this embodiment has a multi-scale layered structure. The microstructure consists of 20% banded δ-ferrite (average band width 1.9 μm), 10% equiaxed (Fe, Ni)Al-type B2 phase (average grain size 1.1 μm), and 70% austenite (average grain size 6.0 μm). The average particle size of the VC precipitate phase is 68 nm.

[0064] The high-strength-plasticity product, high specific strength, and low-density steel prepared in this embodiment has a yield strength of 1064 MPa, a tensile strength of 1308 MPa, an elongation of 39.3%, a density of 6.70 g / cm³, a strength-plasticity product of 51.4 GPa·%, and a specific strength of 195 MPa / (g / cm³).

[0065] Comparative Example 1 Compared with Example 1, the difference is that the heating rate of the recrystallization annealing process is 5°C / s, and the other components and processes remain the same.

[0066] See also Figure 3 The B2 phase grain size range in the obtained steel microstructure increases to 3-5 μm.

[0067] The steel has a yield strength of 956 MPa, a tensile strength of 1230 MPa, an elongation of 31.4%, a density of 6.67 g / cm³, a strength-ductility product of 38.6 GPa·%, and a specific strength of 184 MPa / (g / cm³).

[0068] Comparative Example 2 Compared with Example 1, the difference is that the annealing temperature of the recrystallization annealing process is 850° C., and the other components and processes remain the same.

[0069] See also Figure 4 , the austenite in the obtained steel microstructure decomposes, the boundary of δ ferrite becomes blurred, and the multi-scale layered structure morphology disappears.

[0070] The steel has a yield strength of 1403 MPa, a tensile strength of 1527 MPa, an elongation of 5.2%, a density of 6.67 g / cm³, a strength-ductility product of 7.9 GPa·%, and a specific strength of 229 MPa / (g / cm³).

[0071] Comparative Example 3 Compared with Example 1, the difference is that the cooling method of the recrystallization annealing process is air cooling, and the other components and processes remain the same.

[0072] See also Figure 5 , the austenite grains in the obtained steel microstructure grow and κ carbides precipitate along the austenite grain boundaries.

[0073] The steel has a yield strength of 1237 MPa, a tensile strength of 1389 MPa, an elongation of 22.3%, a density of 6.67 g / cm³, a strength-ductility product of 31.0 GPa·%, and a specific strength of 208 MPa / (g / cm³).

[0074] The results of the three comparative examples above demonstrate that, under consistent compositional conditions, recrystallization annealing process parameters play a key role in microstructure control and mechanical properties. Reducing the heating rate to 5°C / s leads to coarsening of the B2 phase grains, reducing the grain refinement strengthening effect. Lowering the annealing temperature to 850°C triggers austenite decomposition, disappearing the multi-scale layered structure and severely degrading plasticity. Switching the cooling method from low-temperature water cooling to air cooling induces austenite grain growth and the precipitation of κ carbides at grain boundaries, disrupting microstructure stability and deformation coordination.

[0075] Finally, it should be noted that the above-listed embodiments are merely preferred embodiments of the present invention. Of course, those skilled in the art may make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should be considered to be within the scope of protection of the present invention.

Claims

1. A high strength-to-ductility, high specific strength, low density steel, characterized in that: The chemical composition and mass percentage of high strength-plasticity, high specific strength and low density steel are: C: 0.85~1.15%, Mn: 9.5~12.0%, Al: 8.5~11.5%, Ni: 2.5~3.5%, Cr: 2.0~3.0%, V: 0.3~0.5%, S≤0.005%, P≤0.008%, and the rest are Fe and unavoidable impurities.

2. The high strength-ductility, high specific strength, low density steel according to claim 1, characterized in that: The yield strength of high-strength-plasticity, high-specific strength, and low-density steel products is ≥1060MPa, the tensile strength is ≥1300MPa, the elongation is ≥38.0%, the density is 6.63~6.78g / cm³, the strength-plasticity product is ≥50GPa•%, and the specific strength is ≥195MPa / (g / cm³).

3. The high strength-ductility, high specific strength, low density steel according to claim 1, characterized in that: The microstructure of the finished steel product with high strength-ductility, high specific strength and low density consists of banded delta ferrite, equiaxed (Fe, Ni)Al type B2 phase, austenite, and VC nano-precipitates dispersed in the matrix.

4. The high strength-ductility, high specific strength, low density steel according to claim 3, characterized in that: The banded delta ferrite accounts for 15-20%, with an average band width of 1.5-2.5 μm; the equiaxed (Fe, Ni)Al type B2 phase accounts for 5-10%, with a grain size of ≤1.5 μm; the austenite accounts for 70-80%, with a grain size of 6-8 μm; the nano-scale VC precipitate phase has an average particle size of ≤80 nm.

5. A method for preparing the high-strength-ductility-product, high-specific strength, low-density steel according to any one of claims 1 to 4, comprising smelting, casting, forging, hot rolling, cold rolling, and recrystallization annealing steps, characterized in that: The hot rolling process parameters are controlled as follows: the rectangular billet is heated to a temperature of 1180-1220°C, the holding time is 1.5-2.5h, the starting rolling temperature is 1140-1180°C, the finishing rolling temperature is 880-920°C, the hot rolling reduction ratio is 85-93%, and the hot rolling is cooled to room temperature with water. The thickness of the hot rolled plate is 4.0-5.5mm. The cold rolling process parameters are controlled as follows: the cold rolling reduction rate is 60-75%, and the cold rolled plate thickness is 1.0-2.0 mm; The parameters of the recrystallization annealing process are controlled as follows: the heating rate is 80-100°C / s, the annealing temperature is 950-1050°C, the holding time is 60-300s, and the cooling method after the recrystallization annealing is low-temperature water cooling with a water temperature of 0-5°C.

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