Fe-mn-al-v-c super-high-strength austenitic low-density steel and method for manufacturing the same

Abstract

The application relates to a Fe-Mn-Al-V-C ultrahigh-strength austenitic low-density steel and a preparation method thereof, and belongs to the technical field of metal materials. The chemical composition of the steel is as follows: C 1.2-1.8 wt%, Mn 22-30 wt%, Al 8-10 wt%, V 0.2-1.5 wt%, Nb <=0.1 wt%, and the rest is Fe and inevitable impurities. The method comprises the following steps: sequentially performing solid solution treatment, cold rolling deformation, subsequent annealing and aging treatment on the Fe-Mn-Al-V-C austenitic low-density steel, so that dislocation strengthening, fine-grain strengthening, second-phase strengthening and back stress hardening are combined in the structure, the strengthening effects are mutually strengthened, and the strength is significantly improved. The yield strength of the steel reaches 1500 MPa, the tensile strength reaches 1800 MPa, the high-strength level is realized, meanwhile, the elongation is kept above 15%, and the density is 6.6-6.9 g / cm 3 .

Description

Technical Field

[0001] This invention relates to an ultra-high strength austenitic low-density steel of Fe-Mn-Al-VC and its preparation method, belonging to the field of metal materials technology. Background Technology

[0002] Fe-Mn-Al-C austenitic low-density steel, with its combination of high strength, high plasticity, and low density, is an ideal energy-saving and environmentally friendly structural material for the future automotive industry. Austenitic low-density steel primarily achieves high strength and thus high specific strength through (Fe,Mn)3AlC type nanoscale κ-carbide precipitation strengthening. However, the strength improvement brought about by aging treatment alone to precipitate κ-carbides is limited, and over-aging can lead to the enrichment of κ-carbides at grain boundaries and the precipitation of coarse κ-carbides within the grains, thereby significantly reducing the steel's plasticity.

[0003] Currently, to further improve the strength of materials, researchers mostly adopt measures such as alloying or deformation strengthening. V, as one of the most effective strengthening alloying elements in steel, increases the yield strength by about 70 MPa for every 0.1% added, with minimal impact on plasticity and toughness. However, its application in high-manganese austenitic low-density steel is rarely reported. One reported Fe-20Mn-9Al-1.2C-1V low-density steel, after cold rolling with a 20% deformation and annealing at 900℃ for 2 minutes, forms V4C3 with κ-carbides, DO3, and other precipitates to improve strength. This steel achieves a yield strength of 1200 MPa and a tensile strength of 1320 MPa. However, compared to conventional austenitic low-density steel, its yield and tensile strength improvements are not significant, and its plasticity is only 12%. For its application in lightweight automotive structural components, its overall mechanical properties still have considerable room for improvement. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide an ultra-high strength austenitic low-density steel of Fe-Mn-Al-VC and its preparation method. The Fe-Mn-Al-VC steel plate after solution treatment is cold rolled and deformed, then annealed within a certain temperature range, and then aged. This results in a microstructure that combines fine grain strengthening, second phase strengthening, and dislocation strengthening. During the treatment process, the precipitated phase, dislocations, and grain boundaries interact, which enhances the strengthening effect of each strengthening mechanism, significantly improves the material strength, and maintains a certain degree of plasticity.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel, wherein the chemical composition and its mass percentage, based on the total mass of the steel as 100%, are as follows: C 1.2-1.8wt%, Al 8-10wt%, Mn 22-30wt%, V 0.2-1.5wt%, Nb≤0.1wt%, with the remainder being Fe and unavoidable impurities;

[0007] The method steps include:

[0008] (1) Solution treatment: The cast and hot-rolled steel plates are kept at 950-1100℃ for 1-3 hours and then water-cooled to obtain Fe-Mn-Al-VC steel plates after solution treatment.

[0009] (2) Cold rolling: The steel plate is rolled and deformed at room temperature, with a rolling reduction of ≥40%, to obtain a rolled plate;

[0010] (3) Heat treatment: First, the rolled plate is annealed: at a temperature of 700-880℃, it is held for 0.5-6h and then cooled to room temperature in water; then it is aged: at a temperature of 450-600℃, it is held for 1-6h and then cooled to room temperature to obtain a Fe-Mn-Al-VC ultra-high strength austenitic low-density steel.

[0011] Preferably, the mass fraction of C is 1.4 to 1.8 wt%.

[0012] Preferably, the mass fraction of V is 0.5–1.2 wt%.

[0013] Preferably, the chemical composition and its mass percentage, based on the total mass of the steel (100%), are as follows: C 1.4–1.8 wt%, Al 8–10 wt%, Mn 22–30 wt%, V 0.5–1.2 wt%, Nb ≤ 0.1 wt%, with the remainder being Fe and unavoidable impurities.

[0014] Preferably, in step (1), the cast and hot-rolled steel plate is prepared by the following method: weighing and selecting raw materials according to the mass percentage of chemical composition, vacuum melting and remelting the raw materials, then holding them at a temperature of 1200±50℃ for 2~15h for homogenization treatment, and finally hot rolling, with an initial rolling temperature of 1100~1150℃ and a final rolling temperature ≥950℃, and cooling to room temperature to obtain the cast and hot-rolled steel plate.

[0015] Preferably, during smelting, raw materials are weighed and selected according to the mass percentage of chemical composition, and vacuum melting is carried out: the raw materials are loaded into the furnace, and the vacuum degree is evacuated to <50Pa. After heating until the raw materials are completely melted and no bubbles overflow from the surface of the molten pool, the material is refined at a vacuum degree <1Pa and a temperature of 1600-1700℃ for 0.5-2 hours. After sufficient deoxidation, alloying is carried out under argon protection, and then the material is poured and cooled under vacuum to obtain a steel ingot. Then, remelting is carried out: the steel ingot is placed in the furnace, protected by argon, with a pressure of 100-150Pa, and heated until completely melted. After holding at this temperature for 2-5 hours, the remelted steel ingot is obtained.

[0016] Preferably, in step (1), the solution treatment temperature is 1000-1050℃ and the holding time is 1-2h.

[0017] Preferably, in step (2), the rolling reduction is 55% to 72%.

[0018] Preferably, in step (3), the annealing temperature is 750-850℃ and the holding time is 1-2h.

[0019] Preferably, in step (3), the aging treatment is carried out at a temperature of 500-550°C for 1-3 hours.

[0020] Preferably, in step (3), during the aging process, the cooling method is water cooling or air cooling.

[0021] The Fe-Mn-Al-VC ultra-high strength austenitic low-density steel of the present invention is prepared by the above method.

[0022] Beneficial effects:

[0023] (1) This invention provides an ultra-high strength austenitic low-density steel of Fe-Mn-Al-VC and its preparation method. The method involves sequentially performing solution treatment, cold rolling deformation, and subsequent annealing and aging treatments on the Fe-Mn-Al-VC austenitic low-density steel, resulting in a composite microstructure of fine grain strengthening, second-phase strengthening, and dislocation strengthening, with their strengthening effects mutually reinforcing each other, thus significantly improving the strength. Specifically, the large deformation during cold rolling introduces high-density dislocations into the solution-treated steel plate, promoting the dispersed precipitation and recrystallization of nano-VC particles during subsequent annealing. The fine carbides precipitated in the early stages of annealing hinder dislocation recovery, delaying complete recrystallization and retaining some of the dislocation strengthening effect. Furthermore, during the incomplete recrystallization process in annealing, the fine carbides precipitated earlier pin the grain boundaries, significantly refining the grain size and enhancing the fine grain strengthening effect. Furthermore, the annealing temperature must be strictly controlled during the annealing process. When the annealing temperature is below 700℃, the matrix recrystallization is incomplete, with more than 80% of the grains being deformed banded grains. Simultaneously, a large number of micron-sized incoherent VC particles precipitate at the grain boundaries, resulting in poor plasticity and toughness. However, when the annealing temperature exceeds 880℃, the matrix recrystallization tends to be complete, with more than 90% being equiaxed recrystallized grains. The precipitation of VC particles within the grains is also significantly reduced. Although plasticity is greatly improved, the increase in strength is not significant. Only annealing at 700–880℃ can an austenitic matrix with heterogeneous bimodal grain size and dislocation gradient distribution be obtained. The back stress hardening formed by this structure during stress also enhances the material's strength. In summary, by combining multiple strengthening mechanisms, the yield strength of the steel is significantly increased to over 1.5 GPa.

[0024] (2) This invention provides an Fe-Mn-Al-VC ultra-high strength austenitic low-density steel with a density of 6.6-6.9 g / cm³. 3 With a yield strength exceeding 1500MPa, a tensile strength exceeding 1800MPa, and an elongation of over 15%, it achieves ultra-high strength while maintaining high plasticity.

[0025] (3) The composition design of this invention is based on the following:

[0026] The main role of carbon (C) is to participate in the precipitation strengthening of κ-carbide ((Fe,Mn)3AlC) and MC (M=V) carbide, thereby improving the strength of steel. C is also an important solid solution strengthening element, which can promote austenite formation and reduce density. If the C content is too low, the dispersion precipitation of VC and κ-carbide will be insufficient, and the significant strength improvement effect will not be achieved. As the C content increases, the strength of steel can be greatly improved, but excessively high C content will lead to a significant decrease in the weldability of steel, and an increase in cold brittleness and aging sensitivity. Therefore, the C content of the present invention is 1.2% to 1.8%, more preferably 1.4% to 1.8%.

[0027] Mn is an austenite stabilizing element, and its main function is to promote the austenitization of the matrix. Austenitic microstructure allows steel to maintain a high work hardening rate and improves plasticity; however, high Mn content can lead to the formation of brittle β-Mn phases, increasing the tendency for cracking during rapid heating and cooling. Conversely, excessively low Mn content can result in the formation of ferrite phases, reducing ductility. Therefore, the Mn content in this invention is 22%–30%.

[0028] The density of Al is 2.7 g / cm³. 3 Al is a major element that reduces the density of steel, and it also promotes the formation of κ-carbides as a component element. Too low an Al content will result in insufficient formation of κ-carbides, while too high an Al content will promote ferrite formation, reducing the strength and plasticity of the steel. Therefore, the Al content in this invention is 8% to 10%.

[0029] Nitrogen (Nb) can combine with carbon atoms to form stable MC-type carbides. During steel casting and hot rolling, it can nucleate and pin grain boundaries, refining the grains and thus inhibiting precipitation and growth. Furthermore, Nb is often added as a microalloying element in combination with V, resulting in finer and more dispersed carbides, effectively avoiding ductility loss caused by coarsening of precipitates. However, the effect is not significant when the Nb content is too high, reaching saturation. Therefore, the Nb content in this invention is ≤0.1%.

[0030] The addition of volatile organic compounds (V) promotes the precipitation of VC nanoparticles within the grains. However, excessively high V content leads to larger VC particles, significantly reducing the strengthening effect and deteriorating ductility, while also greatly increasing costs. Conversely, excessively low V content results in VC carbides that cannot disperse and precipitate in the matrix, resulting in insignificant strengthening effects. Therefore, the V content in this invention is 0.2%–1.5%, more preferably 0.5%–1.2%. Attached Figure Description

[0031] Figure 1 This is an optical microscope (OM) image of the Fe-Mn-Al-VC low-density steel after annealing treatment as described in Example 5.

[0032] Figure 2 The diagram shows the dislocation average orientation difference (KAM) of the Fe-Mn-Al-VC low-density steel after annealing treatment as described in Example 5.

[0033] Figure 3 This is a bright-field transmission electron microscope (BF-TEM) image of the Fe-Mn-Al-VC low-density steel after secondary aging as described in Example 5.

[0034] Figure 4 The image shows a dark field transmission electron microscope (DF-TEM) image of the Fe-Mn-Al-VC low-density steel after secondary aging as described in Example 5. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments.

[0036] Tensile testing equipment: Electronic universal testing machine, model INSTRON5985.

[0037] The tensile strength test standard in the example is GB / T228-2002; the tensile strength, yield strength and elongation are all measured by the tensile stress-strain curve obtained from the tensile test according to GB / T228-2002.

[0038] According to the chemical composition range of a low-density ultra-high strength steel of the present invention, 7 furnaces of 39 kg alloy ingots were prepared by vacuum induction melting.

[0039] Table 1 shows the chemical composition (mass percentage) of the low-density ultra-high-strength steel described in the examples and comparative examples.

[0040] Table 1

[0041]

[0042]

[0043] Weigh and select raw materials according to the mass percentage of chemical composition in Table 1. Weigh and select raw materials according to the mass percentage of chemical composition and perform vacuum melting: Put the raw materials into the furnace, evacuate to a vacuum degree <50Pa, heat until the raw materials are completely melted and no bubbles overflow from the surface of the molten pool, hold at a vacuum degree <1Pa and a temperature of 1700℃ for 0.5h for refining, fully deoxidize, alloy under argon protection, then cast and cool under vacuum to obtain steel ingots; then remelt: Put the steel ingots into the furnace, purify with argon, pressure of 120Pa, heat until completely melted and hold for 2h to obtain remelted steel ingots; (2) Homogenization treatment: Hold at a temperature of 1200℃ for 2h and cool with the furnace to room temperature; (3) Hot rolling: Hot roll the homogenized steel ingots, with an initial rolling temperature of 1050℃ and a final forging temperature of 950℃, and cool in air to room temperature to obtain Fe-Mn-Al-VC steel plates with a thickness of 24mm.

[0044] Example 1

[0045] A method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel specifically includes the following steps:

[0046] (1) Solution treatment: The steel plate corresponding to No. 1 in Table 1 is kept at 1050℃ for 1 hour and then water-cooled to obtain Fe-Mn-Al-VC steel plate after solution treatment.

[0047] (2) Cold rolling: The Fe-Mn-Al-VC steel plate after solution treatment is rolled in one pass at room temperature with a reduction of 75% to obtain the rolled plate.

[0048] (3) Heat treatment: The rolled plate is first sent to the sample section for processing to obtain a tensile sample blank, and then the tensile sample blank is annealed: at a temperature of 800℃, it is held for 1 hour and cooled to room temperature in water; then it is aged: at a temperature of 500℃, it is held for 3 hours and cooled to room temperature in air to obtain a tensile sample blank of Fe-Mn-Al-VC ultra-high strength austenitic low density steel.

[0049] The OM and EBSD test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 1 show that the austenitic grains after cold rolling and annealing are composed of large unrecrystallized deformed grains and small-sized recrystallized grains. At the same time, the deformed grains have a higher dislocation density, while the recrystallized grains have the opposite.

[0050] TEM test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 1 show that a large number of VC carbide particles (average size less than 15 nm) and κ carbides (average size less than 1 nm) are dispersed in the steel, and a large number of dislocations exist in the matrix.

[0051] Example 2

[0052] A method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel specifically includes the following steps:

[0053] (1) Solution treatment: The steel plate corresponding to No. 2 in Table 1 is kept at 1000℃ for 1 hour and then water-cooled to obtain Fe-Mn-Al-VC steel plate after solution treatment.

[0054] (2) Cold rolling: The Fe-Mn-Al-VC steel plate after solution treatment is rolled in one pass at room temperature with a reduction of 55% to obtain the rolled plate.

[0055] (3) Heat treatment: The rolled plate is first sent to the sample section for processing to obtain a tensile sample blank, and then the tensile sample blank is annealed: at a temperature of 850℃, it is held for 1 hour and cooled to room temperature in water; then it is aged: at a temperature of 550℃, it is held for 1 hour and cooled to room temperature in air to obtain a tensile sample blank of Fe-Mn-Al-VC ultra-high strength austenitic low density steel.

[0056] The OM and EBSD test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 2 show that the austenitic grains after cold rolling and annealing are composed of large unrecrystallized deformed grains and small-sized recrystallized grains. At the same time, the deformed grains have a higher dislocation density, while the recrystallized grains have the opposite.

[0057] TEM test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 2 show that a large number of VC carbide particles (average size less than 15 nm) and κ carbides (average size less than 1 nm) are dispersed in the steel, and a large number of dislocations exist in the matrix.

[0058] Example 3

[0059] A method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel specifically includes the following steps:

[0060] (1) Solution treatment: The steel plate corresponding to No. 3 in Table 1 is kept at 1050℃ for 1 hour and then water-cooled to obtain Fe-Mn-Al-VC steel plate after solution treatment.

[0061] (2) Cold rolling: The Fe-Mn-Al-VC steel plate after solution treatment is rolled in one pass at room temperature with a reduction of 65% to obtain the rolled plate.

[0062] (3) Heat treatment: The rolled plate is first sent to the sample section for processing to obtain a tensile sample blank, and then the tensile sample blank is annealed: at a temperature of 750℃, it is held for 2 hours and cooled to room temperature in water; then it is aged: at a temperature of 550℃, it is held for 2 hours and cooled to room temperature in air to obtain a tensile sample blank of Fe-Mn-Al-VC ultra-high strength austenitic low density steel.

[0063] The OM and EBSD test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 3 show that the austenitic grains after cold rolling and annealing are composed of large unrecrystallized deformed grains and small-sized recrystallized grains. At the same time, the deformed grains have a higher dislocation density, while the recrystallized grains have the opposite.

[0064] TEM test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 3 show that a large number of VC carbide particles (average size less than 15 nm) and κ carbides (average size less than 1 nm) are dispersed in the steel, and a large number of dislocations exist in the matrix.

[0065] Example 4

[0066] A method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel specifically includes the following steps:

[0067] (1) Solution treatment: The steel plate corresponding to No. 4 in Table 1 is kept at 1050℃ for 1 hour and then water-cooled to obtain Fe-Mn-Al-VC steel plate after solution treatment.

[0068] (2) Cold rolling: The Fe-Mn-Al-VC steel plate after solution treatment is rolled in one pass at room temperature with a reduction of 65% to obtain the rolled plate.

[0069] (3) Heat treatment: The rolled plate is first sent to the sample section for processing to obtain a tensile sample blank, and then the tensile sample blank is annealed: at a temperature of 780℃, it is held for 2 hours and cooled to room temperature in water; then it is aged: at a temperature of 550℃, it is held for 2 hours and cooled to room temperature in air to obtain a tensile sample blank of Fe-Mn-Al-VC ultra-high strength austenitic low density steel.

[0070] The OM and EBSD test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 4 show that the austenitic grains after cold rolling and annealing are composed of large unrecrystallized deformed grains and small-sized recrystallized grains. At the same time, the deformed grains have a higher dislocation density, while the recrystallized grains have the opposite.

[0071] TEM test results of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 4 show that a large number of VC carbide particles (average size less than 15 nm) and κ carbides (average size less than 1 nm) are dispersed in the steel, and a large number of dislocations exist in the matrix.

[0072] Example 5

[0073] A method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel specifically includes the following steps:

[0074] (1) Solution treatment: The steel plate corresponding to No. 5 in Table 1 is kept at 1050℃ for 1 hour and then water-cooled to obtain Fe-Mn-Al-VC steel plate after solution treatment.

[0075] (3) Cold rolling: The Fe-Mn-Al-VC steel plate after solution treatment is rolled in one pass at room temperature with a reduction of 60% to obtain the rolled plate.

[0076] (4) Heat treatment: The rolled plate is first sent to the sample section for processing to obtain a tensile sample blank, and then the tensile sample blank is annealed: at a temperature of 790℃, it is held for 2 hours and cooled to room temperature in water; then it is aged: at a temperature of 550℃, it is held for 2 hours and cooled to room temperature in air to obtain a tensile sample blank of Fe-Mn-Al-VC ultra-high strength austenitic low density steel.

[0077] Example 5 describes the OM and EBSD tests of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel. Figure 1 As shown and Figure 2 As shown, the results indicate that the austenite grains after cold rolling and annealing consist of large unrecrystallized deformed grains (40%) and small-sized recrystallized grains (60%). Meanwhile, the deformed grains accumulate a higher dislocation density, while the recrystallized grains show the opposite.

[0078] TEM testing of the Fe-Mn-Al-VC ultra-high strength austenitic low-density steel described in Example 5 is as follows: Figure 3 and Figure 4 As shown, the results indicate that a large number of VC carbide particles (average size less than 15 nm) and κ carbide particles (average size less than 1 nm) are dispersed in the steel, and a large number of dislocations exist in the matrix.

[0079] Comparative Example 1

[0080] A method for preparing Fe-Mn-Al-C austenitic low-density steel specifically includes the following steps:

[0081] (1) Solution treatment: The steel plate corresponding to No. 6 in Table 1 is kept at 1050℃ for 1 hour and then water-cooled to obtain Fe-Mn-Al-C steel plate after solution treatment.

[0082] (2) Cold rolling: The Fe-Mn-Al-C steel plate after solution treatment is rolled in one pass at room temperature with a reduction of 65% to obtain the rolled plate.

[0083] (3) Heat treatment: The rolled plate is first sent to the sample section for processing to obtain a tensile sample blank, and then the tensile sample blank is annealed: at a temperature of 780℃, it is held for 2 hours and cooled to room temperature in water; then it is aged: at a temperature of 550℃, it is held for 2 hours and cooled to room temperature in air to obtain a tensile sample blank of Fe-Mn-Al-C ultra-high strength austenitic low density steel.

[0084] Comparative Example 1 uses the same process as Example 3, but the composition is different. Comparative Example 1 does not contain added element V. During the cold rolling annealing recrystallization process, there is no precipitation of VC particles, nor is there any grain refinement by carbide pinning of grain boundaries. Therefore, the grain refinement strengthening and precipitation strengthening effects are weakened, and the strength is reduced.

[0085] Comparative Example 2

[0086] A method for preparing Fe-Mn-Al-VC austenitic low-density steel specifically includes the following steps:

[0087] (1) Solution treatment: The steel plate corresponding to No. 7 in Table 1 was kept at 1050℃ for 1 hour and then water-cooled to obtain the Fe-Mn-Al-VC steel plate after solution treatment.

[0088] (2) Cold rolling: The Fe-Mn-Al-VC steel plate after solution treatment is rolled in one pass at room temperature with a reduction of 65% to obtain the rolled plate.

[0089] (3) Heat treatment: The rolled plate is first sent to the sample section for processing to obtain a tensile sample blank, and then the tensile sample blank is annealed: at a temperature of 900℃, it is held for 2 hours and cooled to room temperature in water; then it is aged: at a temperature of 550℃, it is held for 2 hours and cooled to room temperature in air to obtain a tensile sample blank of Fe-Mn-Al-VC austenitic low-density steel.

[0090] Comparative Example 2 and Example 3 have the same composition, but different processes. When the annealing temperature of Comparative Example 2 exceeds 880°C, the matrix recrystallization tends to be complete, the dislocation recovery is complete, and more than 90% are equiaxed recrystallized grains. There are no heterogeneous bimodal austenite grains, and the precipitation of VC particles in the grains is significantly reduced. The effects of dislocation strengthening, precipitation strengthening and back stress hardening are all weakened, resulting in a significant reduction in strength under this process.

[0091] The tensile specimen blanks prepared in Examples 1-5 and Comparative Examples 1-2 were wire-cut and ground into tensile specimens with a cross-sectional dimension of 2×1mm and an original gauge length L0 of 8mm. Mechanical property tests were then conducted, and the results are shown in Table 2. 0.2 σ represents the yield strength. b A represents tensile strength, and A represents elongation.

[0092] Table 2

[0093]

[0094]

[0095] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel, characterized in that: Based on the total mass of the steel (100%), the chemical composition and its mass percentage are as follows: C 1.2~1.8wt%, Al 8~10wt%, Mn 22~30wt%, V 0.2~1.5wt%, Nb≤0.1wt%, with the remainder being Fe and unavoidable impurities; The method steps include: (1) Solution treatment: The cast and hot-rolled steel plates are kept at 950~1100℃ for 1~3h and then water-cooled to obtain Fe-Mn-Al-VC steel plates after solution treatment; (2) Cold rolling: The steel plate is rolled and deformed at room temperature, with a rolling reduction of 55% to 72%, to obtain the rolled plate; (3) Heat treatment: First, the rolled plate is annealed: at a temperature of 750~850℃, it is held for 1~2h and then cooled to room temperature in water; then it is aged: at a temperature of 450~600℃, it is held for 1~6h and then cooled to room temperature to obtain a Fe-Mn-Al-VC ultra-high strength austenitic low density steel. The austenite grains after cold rolling and annealing consist of large unrecrystallized deformed grains and small-sized recrystallized grains. The steel contains a large number of VC carbide particles with an average size of less than 15 nm and κ carbides with an average size of less than 1 nm, and there are a large number of dislocations in the matrix; the density of the steel is 6.6-6.9 g / cm³. 3 The yield strength exceeds 1500MPa, the tensile strength exceeds 1800MPa, and the elongation is above 15%.

2. The method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel as described in claim 1, characterized in that: Based on the total mass of the steel (100%), the chemical composition and its mass percentage are as follows: C 1.4~1.8wt%, Al 8~10wt%, Mn 22~30wt%, V 0.5~1.2wt%, Nb≤0.1wt%, with the remainder being Fe and unavoidable impurities.

3. The method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel as described in claim 1, characterized in that: In step (1), the cast and hot-rolled steel plates are prepared by the following method: raw materials are weighed and selected according to the chemical composition mass percentage, the raw materials are vacuum melted and remelted, then homogenized at a temperature of 1200±50℃ for 2~15h, and finally hot-rolled at an initial rolling temperature of 1100~1150℃ and a final rolling temperature of ≥950℃, and cooled to room temperature to obtain the cast and hot-rolled steel plates.

4. The method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel as described in claim 3, characterized in that: During smelting, raw materials are weighed and selected according to the mass percentage of chemical composition, and vacuum melting is carried out: the raw materials are loaded into the furnace, and the vacuum degree is evacuated to <50Pa. After heating until the raw materials are completely melted and no bubbles overflow from the surface of the molten pool, the material is refined at a vacuum degree <1Pa and a temperature of 1600~1700℃ for 0.5~2h. After sufficient deoxidation, alloying is carried out under argon protection, and then the material is poured and cooled under vacuum to obtain steel ingots. Remelting is then carried out: the steel ingots are placed in the furnace, protected by argon, at a pressure of 100~150Pa, heated to complete melting, and held for 2~5h to obtain remelted steel ingots.

5. The method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel as described in claim 1, characterized in that: In step (1), the solution treatment temperature is 1000~1050℃ and the holding time is 1~2h.

6. The method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel as described in claim 1, characterized in that: In step (3), the aging treatment is carried out at a temperature of 500~550℃ and a holding time of 1~3h.

7. The method for preparing Fe-Mn-Al-VC ultra-high strength austenitic low-density steel as described in claim 6, characterized in that: In step (3), during the aging process, the cooling method is either water cooling or air cooling.

8. A Fe-Mn-Al-VC ultra-high strength austenitic low-density steel, characterized in that: It is prepared by the method described in any one of claims 1 to 7.

Images