A micro-nitrided austenite-based dual-phase low-density steel and its preparation method

Abstract

This invention provides a micro-nitrided austenitic-based duplex low-density steel and its preparation method. The preparation method includes: batching raw materials according to the chemical composition of the micro-nitrided austenitic-based duplex low-density steel; melting all raw materials using a melting equipment, controlling the nitrogen content within the range of 0.05-0.15%; casting into ingots or continuously cast billets; homogenizing the ingots or continuously cast billets at 1100-1250℃; forging the homogenized billets; hot rolling the forged billets at a temperature range of 1150-850℃; immediately after hot rolling, water quenching and rapid cooling to room temperature; and annealing the water-quenched steel plate at 850-1050℃. This invention utilizes inexpensive nitrogen (N) to combine with the existing Al (Al) element in steel, and through a simple annealing process, can generate a large number of dispersed AlN strengthening phases in situ, achieving low-cost and efficient precipitation strengthening.

Description

Technical Field

[0001] This invention relates to the field of metal material design and preparation technology, and in particular to a micro-nitrided austenitic-based dual-phase low-density steel and its preparation method. Background Technology

[0002] With the increasing demand for lightweight materials in the automotive, aerospace, and other fields, low-density steel (also known as lightweight steel) has attracted widespread attention due to its significantly lower density compared to traditional steel materials. Currently, Fe-Mn-Al-C series low-density steel is a research hotspot. By adding a large amount of Al (usually >5%) to the steel, the material density can be significantly reduced while maintaining good mechanical properties.

[0003] However, existing Fe-Mn-Al-C low-density steels mainly suffer from the following technical problems: 1. The inverse relationship between strength and plasticity: Although adding Al can reduce density and improve plasticity, it is often accompanied by a decrease in strength. Although precipitation strengthening (such as κ-carbides) can improve strength, coarse κ-carbides are prone to becoming crack initiation sources, leading to a sharp decrease in plasticity and making it difficult to achieve a good match between high strength and high plasticity.

[0004] 2. Increased complexity in alloy design: In order to further improve strength, existing technologies often require the addition of expensive microalloying elements such as V, Nb, and Ti to strengthen the alloy by forming carbonitrides. This undoubtedly increases the cost of the alloy and the difficulty of process control.

[0005] 3. Tranquility issues: Austenitic matrices with high Al content are prone to dynamic recrystallization during hot working, with a significant tendency for grain growth, which affects the overall performance of the final product.

[0006] 4. The Harmful Effect of AlN: For a long time, a prevalent technical bias has existed in the steel metallurgy field, namely, that AlN is a harmful inclusion phase. This is because in traditional steel grades (such as aluminum deoxidized steel), if not properly controlled, AlN easily precipitates at grain boundaries in a network, chain, or coarse particle form, severely reducing the hot working properties, toughness, and fatigue life of the steel. Therefore, those skilled in the art usually try their best to avoid or suppress the formation of AlN when designing and preparing high-performance steel materials, and would not consider using it as a strengthening phase. This technical bias severely limits the expansion of the strengthening and toughening pathways of steel materials.

[0007] Therefore, how to develop a low-density steel that is relatively low-cost, simple to process, and can simultaneously achieve high strength and high plasticity is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to provide a micro-nitrided austenitic-based dual-phase low-density steel and its preparation method, aiming to solve the problems of difficulty in balancing strength and plasticity and high strengthening cost of existing Fe-Mn-Al-C system low-density steel, and to break the traditional technical prejudice that AlN is a harmful phase.

[0009] In a first aspect, the present invention provides a micro-nitrided austenitic-based dual-phase low-density steel, the chemical composition of which, by mass percentage, is: C: 0.5-0.8%; Mn: 15-25%; Al: 5-10%; Si: 0.6-1.5%; N: 0.05-0.15%; with the balance being Fe and unavoidable impurities.

[0010] C (0.5-0.8%): The main austenite stabilizing element, which improves strength through interstitial solid solution strengthening. When the content is below 0.5%, the austenite stability is insufficient and the strength is low; when it is above 0.8%, it may lead to decreased weldability and carbide coarsening.

[0011] Mn (15-25%): Expands the austenite phase region, ensuring an austenite-dominant matrix at room temperature. When the content is below 15%, it is difficult to obtain sufficient austenite; when it is above 25%, it does not contribute much to the reduction of density and increases cost and processing difficulty.

[0012] Al (5-10%): A key element for reducing density; for every 1% increase in Al, the density decreases by approximately 1.3%. Simultaneously, Al improves the oxidation resistance of steel. Below 5%, the density reduction is not significant; above 10%, the alloy becomes more brittle and its hot workability deteriorates.

[0013] Si (0.6-1.5%): A deoxidizing element that also has a certain solid solution strengthening effect. Within this range, it can improve the strength and toughness of steel.

[0014] Nitrogen (0.05-0.15%): The core element. Nitrogen acts as a strong austenite stabilizer and has a very strong affinity for Al. Under specific composition and processing conditions, Nitrogen reacts in situ with Al in the matrix to generate dispersed submicron-sized AlN particles. These fine, uniformly distributed AlN particles, acting as a second-phase reinforcing phase, effectively hinder dislocation movement, resulting in significant precipitation strengthening, and their damage to plasticity is far less than that of coarse κ-carbides.

[0015] Fe and impurities: Balance. Unavoidable impurities such as P and S should be controlled at low levels.

[0016] In some embodiments, the microstructure of the micronitrided austenitic-based dual-phase low-density steel is an austenitic-based dual-phase structure, wherein the volume fraction of the austenitic phase is 50-70%, and in-situ self-generated submicron or nano-sized AlN reinforcing phase particles are dispersed on the austenitic matrix.

[0017] In some embodiments, the AlN strengthening phase particles are generated by the in-situ reaction of N with Al in steel, and produce precipitation strengthening effect on the matrix in a dispersed distribution form.

[0018] Secondly, the present invention provides a method for preparing micro-nitrided austenite-based duplex low-density steel, used to prepare the micro-nitrided austenite-based duplex low-density steel as described above, the preparation method comprising: Step S1: Prepare the raw materials according to the chemical composition of micro-nitrided austenitic dual-phase low-density steel, and melt all the raw materials using smelting equipment. Control the nitrogen content within the range of 0.05-0.15% by adding nitriding alloy or bottom blowing nitrogen, and cast it into ingots or continuous casting billets. Step S2: Homogenize the ingot or continuously cast billet at 1100-1250℃ for 1-3 hours. Step S3: Forge the homogenized billet at a forging temperature of 950-1200℃, with a cumulative deformation of 30-60%. Step S4: Hot-roll the forged billet at a temperature range of 1150-850℃, with a cumulative deformation of 60-90%; Step S5: Immediately after hot rolling, perform water quenching and rapidly cool to room temperature; Step S6: Anneal the water-quenched steel plate at 850-1050℃ for 10-60 minutes to obtain micro-nitrided austenitic dual-phase low-density steel.

[0019] In some embodiments, in step 1, the smelting equipment is any one of a vacuum induction furnace, a non-vacuum induction furnace, an electric furnace, or a converter.

[0020] In some embodiments, in step 1, the nitride alloy includes at least one of manganese nitride, Fe-Mn-N master alloy, or Fe-Cr-N master alloy.

[0021] In some embodiments, in step 3, the forging is followed by air cooling or water quenching to room temperature.

[0022] In some embodiments, in step 3, the forging is performed using a multi-directional forging method.

[0023] In some embodiments, in step 4, the hot-rolled billet is a forged billet or a directly used continuous casting billet.

[0024] In some embodiments, in step 5, water quenching is used to suppress the precipitation of excessive high-temperature ferrite and grain growth, thereby obtaining a supersaturated austenitic matrix.

[0025] In some embodiments, in step 6, the annealing process causes AlN strengthening phase particles to be dispersed and precipitated on the austenitic matrix, and the austenite content and grain size in the matrix are adjusted to finally obtain a duplex structure with an austenite volume fraction of 50-70%.

[0026] Compared with the prior art, the present invention has the following advantages: 1. Low cost and high strength: Unlike adding precious metal elements such as V, Nb, and Ti, this invention utilizes inexpensive N element to combine with Al element already present in steel. Through a simple annealing process, a large number of dispersed AlN strengthening phases can be generated in situ, achieving low-cost and efficient precipitation strengthening.

[0027] 2. Excellent strength and plasticity matching: Nano- / submicron-sized AlN particles are uniformly distributed in the austenitic matrix and ferrite, providing a significant strengthening effect without severely tearing the matrix like coarse carbides. This achieves a significant increase in strength while maintaining excellent plasticity.

[0028] 3. Simple process and easy to control: The preparation method of the present invention makes full use of conventional heat processing and heat treatment equipment, without the need for complex process flow or special equipment modification, and is easy to realize large-scale industrial production.

[0029] 4. Good structural stability: Fine AlN particles can pin grain boundaries, effectively inhibiting the growth of austenite grains at high temperatures, which is conducive to obtaining a fine-grained structure and further improving strength and plasticity. Attached Figure Description

[0030] Figure 1 The fracture microstructure of the micronitrided austenite-based dual-phase low-density steel prepared in Example 1 is shown in the diagram. Figure 2 The image shows a comparison of the stress-strain curves of the micro-nitrided austenitic-based dual-phase low-density steel prepared in Example 1 and Comparative Example 1.

[0031] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but does not exclude other elements or objects.

[0033] Example 1 Composition (mass percentage): C 0.65%, Mn 20%, Al 10%, Si 1.0%, N 0.06%, balance Fe.

[0034] Step S1: Prepare the raw materials according to the chemical composition of micro-nitrided austenitic dual-phase low-density steel, and melt it in a vacuum induction melting furnace. Add manganese nitride master alloy to adjust the nitrogen content to 0.06%, and cast it into an ingot.

[0035] Step S2: Homogenize the ingot or continuously cast billet at 1200℃ and hold for 2 hours.

[0036] Step S3: Forge the homogenized billet using an air hammer for multi-directional forging. The initial forging temperature is 1150℃, the final forging temperature is 950℃, the cumulative deformation is 50%, and the billet is air-cooled to room temperature after forging.

[0037] Step S4: Reheat the forging billet to 1150℃, start rolling at 1100℃, finish rolling at 900℃, with a total deformation of 80%, and roll it into a 5mm thick plate.

[0038] Step S5: Immediately after hot rolling, quench in water to room temperature.

[0039] Step S6: Anneal the water-quenched steel plate at 950℃ for 15 minutes, and then water-cool it to room temperature.

[0040] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: density 6.68 g / cm³. 3 It has a yield strength of 756 MPa, a tensile strength of 1010 MPa, and an elongation of 31%. The microstructure contains 60% austenite by volume, with submicron-sized AlN particles dispersed in the matrix.

[0041] Example 2 This embodiment is basically the same as Embodiment 1, except that the composition is adjusted to: C 0.5%, Mn 15%, Al 5%, Si 0.6%, N 0.05%, with the balance being Fe.

[0042] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: density 6.90 g / cm³. 3 Yield strength 652 MPa, tensile strength 905 MPa, elongation 28%, austenite volume fraction 50%.

[0043] Example 3 This embodiment is basically the same as Embodiment 1, except that the composition is adjusted to: C 0.8%, Mn 25%, Al 10%, Si 1.5%, N 0.15%, with the balance being Fe.

[0044] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: density 6.68 g / cm³. 3 Yield strength 812 MPa, tensile strength 1115 MPa, elongation 25%, austenite volume fraction 70%.

[0045] Example 4 This embodiment is basically the same as Embodiment 1, except that the homogenization temperature in step S2 is adjusted to 1100℃ and the heat preservation time is adjusted to 3 hours.

[0046] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3 Yield strength 735 MPa, tensile strength 985 MPa, elongation 30%, austenite volume fraction 58%.

[0047] Example 5 This embodiment is basically the same as Embodiment 1, except that the homogenization temperature in step S2 is adjusted to 1250℃ and the heat preservation time is adjusted to 1 hour.

[0048] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3 Yield strength 748 MPa, tensile strength 1005 MPa, elongation 30%, austenite volume fraction 62%.

[0049] Example 6 This embodiment is basically the same as Embodiment 1, except that the initial forging temperature in step S3 is adjusted to 1200℃, the final forging temperature is adjusted to 900℃, and the deformation amount is 30%.

[0050] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3 Yield strength 725 MPa, tensile strength 975 MPa, elongation 29%, austenite volume fraction 59%.

[0051] Example 7 This embodiment is basically the same as Embodiment 1, except that the initial forging temperature in step S3 is adjusted to 1150℃, the final forging temperature is adjusted to 950℃, and the deformation amount is 60%.

[0052] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3 Yield strength 768 MPa, tensile strength 1025 MPa, elongation 31%, austenite volume fraction 61%.

[0053] Example 8 This embodiment is basically the same as Embodiment 1, except that the initial rolling temperature in step S4 is adjusted to 1000℃, the final rolling temperature is adjusted to 850℃, and the total deformation is 60%.

[0054] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3 Yield strength 715 MPa, tensile strength 965 MPa, elongation 29%, austenite volume fraction 57%.

[0055] Example 9 This embodiment is basically the same as Embodiment 1, except that the initial rolling temperature in step S4 is 1150℃, the final rolling temperature is 900℃, and the total deformation is 90%.

[0056] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3 Yield strength 775 MPa, tensile strength 1035 MPa, elongation 30%, austenite volume fraction 63%.

[0057] Example 10 This embodiment is basically the same as Embodiment 1, except that the annealing temperature in step S6 is adjusted to 850°C and the holding time is adjusted to 10 minutes.

[0058] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3Yield strength 785 MPa, tensile strength 1060 MPa, elongation 26%, austenite volume fraction 50%.

[0059] Example 11 This embodiment is basically the same as Embodiment 1, except that the annealing temperature in step S6 is adjusted to 1050℃ and the holding time is adjusted to 20 minutes.

[0060] The properties of the obtained micro-nitrided austenitic-based dual-phase low-density steel were tested: Density 6.68 g / cm³ 3 Yield strength 705 MPa, tensile strength 955 MPa, elongation 33%, austenite volume fraction 70%.

[0061] Comparative Example 1 This comparative example is basically the same as Example 1, except that the N content is adjusted to 0.002%.

[0062] Test result: Density 6.68 g / cm³ 3 Yield strength 610 MPa, tensile strength 868 MPa, elongation 34%, austenite volume fraction 65%, no AlN strengthening phase.

[0063] Comparative Example 2 This comparative example is basically the same as Example 1, except that the N content is adjusted to 0.25%.

[0064] Test result: Density 6.68 g / cm³ 3 Yield strength 705 MPa, tensile strength 955 MPa, elongation 17%, austenite volume fraction 55%, AlN particle coarsening.

[0065] Comparative Example 3 This comparative example is basically the same as Example 1, except that the C content is adjusted to 0.3%.

[0066] Test result: Density 6.68 g / cm³ 3 Yield strength 540 MPa, tensile strength 785 MPa, elongation 31%, austenite volume fraction 40%.

[0067] Comparative Example 4 This comparative example is basically the same as Example 1, except that the C content is adjusted to 1.0%.

[0068] Test result: Density 6.68 g / cm³ 3 Yield strength 815 MPa, tensile strength 1120 MPa, elongation 17%, austenite volume fraction 72%.

[0069] Comparative Example 5 This comparative example is basically the same as Example 1, except that the Mn content is adjusted to 10%.

[0070] Test result: Density 6.68 g / cm³ 3 Yield strength 495 MPa, tensile strength 740 MPa, elongation 19%, austenite volume fraction 35%.

[0071] Comparative Example 6 This comparative example is basically the same as Example 1, except that the Al content is adjusted to 3%.

[0072] Test result: Density 7.15 g / cm³ 3 Yield strength 655 MPa, tensile strength 910 MPa, elongation 28%, austenite volume fraction 70.2%.

[0073] Comparative Example 7 This comparative example is basically the same as Example 1, except that step S2 homogenization is omitted, i.e., the ingot is directly forged.

[0074] Test result: Density 6.68 g / cm³ 3 Yield strength 640 MPa, tensile strength 870 MPa, elongation 21%, austenite volume fraction 55%.

[0075] Comparative Example 8 This comparative example is basically the same as Example 1, except that the homogenization temperature in step S2 is adjusted to 1000℃ and kept at that temperature for 2 hours.

[0076] Test result: Density 6.68 g / cm³ 3 Yield strength 675 MPa, tensile strength 895 MPa, elongation 23%, austenite volume fraction 56%.

[0077] Comparative Example 9 This comparative example is basically the same as Example 1, except that forging is omitted, that is, it is directly hot rolled after homogenization.

[0078] Test result: Density 6.68 g / cm³ 3 Yield strength 695 MPa, tensile strength 915 MPa, elongation 24%, austenite volume fraction 57%.

[0079] Comparative Example 10 This comparative example is basically the same as Example 1, except that step S5 is adjusted: air cooling after hot rolling instead of water quenching.

[0080] Test result: Density 6.68 g / cm³ 3 Yield strength 615 MPa, tensile strength 840 MPa, elongation 25%, austenite volume fraction 48%.

[0081] Comparative Example 11 This comparative example is basically the same as Example 1, except that step S6 annealing is omitted, i.e., it is directly tested after water quenching.

[0082] Test result: Density 6.68 g / cm³ 3 Yield strength 810 MPa, tensile strength 1110 MPa, elongation 14%, austenite volume fraction 72%.

[0083] Comparative Example Twelve This comparative example is basically the same as Example 1, except that the annealing temperature in step S6 is adjusted to 750°C and held for 15 minutes.

[0084] Test result: Density 6.68 g / cm³ 3 Yield strength 705 MPa, tensile strength 955 MPa, elongation 19%, austenite volume fraction 48%.

[0085] Comparative Example Thirteen This comparative example is basically the same as Example 1, except that the annealing temperature in step S6 is adjusted to 1150°C and held for 15 minutes.

[0086] Test result: Density 6.68 g / cm³ 3 Yield strength 595 MPa, tensile strength 845 MPa, elongation 28%, austenite volume fraction 75%.

[0087] Results Analysis: A comparison between Example 1 and Comparative Example 1 shows that, under the same composition and processing conditions, adding 0.06% nitrogen increased the yield strength from 610 MPa to 756 MPa and the tensile strength from 868 MPa to 1010 MPa, representing increases of 146 MPa and 142 MPa respectively. Meanwhile, the elongation only slightly decreased from 34% to 31%, a reduction of only 3 percentage points. This result indicates that the dispersed AlN particles generated through micro-nitriding exert a significant precipitation strengthening effect, while causing far less damage to plasticity than traditional coarse carbides, achieving an excellent effect of significantly increased strength with almost no decrease in plasticity.

[0088] As can be seen from the comparison between Example 1 and Comparative Example 2, when the nitrogen content exceeds 0.05-0.15% and reaches 0.25%, although the tensile strength is still 955 MPa, the elongation drops sharply to 17%, and the austenite volume fraction also drops to 55%. This indicates that excessive nitrogen will cause AlN particles to coarsen, changing from dispersion strengthening to brittle inclusions, which seriously impairs plasticity.

[0089] A comparison of Example 1 with Comparative Examples 3, 4, and 5 shows that when the carbon content is below 0.5%, the austenite stability is insufficient and the strength is low; when the carbon content is above 0.8%, the carbides coarsen and the plasticity decreases; when the manganese content is below 15%, the austenite volume fraction is only 35%, which cannot guarantee a matrix structure dominated by austenite; and when the aluminum content is below 5%, the density is as high as 7.15 g / cm³. 3 The weight reduction effect is not significant.

[0090] Comparisons of Examples 1, 4, 5, 7, and 8 show that a uniform microstructure can be obtained by controlling the homogenization temperature at 1100-1250℃ and the time at 1-3 hours. In Comparative Example 7, omitting homogenization resulted in a yield strength of only 640 MPa and an elongation of only 21%. In Comparative Example 8, the homogenization temperature was too low (1000℃), leading to insufficient diffusion of alloying elements, resulting in lower strength and plasticity compared to Example 1.

[0091] A comparison of Example 1 with Examples 6, 7, and Comparative Example 9 shows that controlling the forging deformation to 30-60% can effectively break down the as-cast microstructure. Comparative Example 9, which skips the forging step and directly hot-rolls, has a yield strength of only 695 MPa and an elongation of only 24%, both significantly lower than Example 1, demonstrating the importance of the forging step for microstructure refinement.

[0092] As can be seen from the comparison between Example 1, Example 8, Example 9, and Comparative Example 10, immediate water quenching after hot rolling is the key to suppressing high-temperature ferrite precipitation and grain growth. Comparative Example 10 uses air cooling instead of water quenching, and the austenite volume fraction is reduced to 48%, with a yield strength of only 615 MPa and a tensile strength of only 840 MPa, which are far lower than those in Example 1.

[0093] Comparisons of Examples 1, 10, 11, 11, 12, and 13 show that controlling the annealing temperature at 850-1050℃ and the annealing time at 10-60 minutes are crucial for AlN dispersion precipitation and microstructure control. Comparative Example 11, omitting annealing, achieved a tensile strength of 1110 MPa, but its elongation was only 14%, indicating high brittleness. Comparative Example 12 had an excessively low annealing temperature, resulting in insufficient AlN precipitation kinetics and poor strengthening effect. Comparative Example 13 had an excessively high annealing temperature, leading to grain coarsening and AlN particle growth, significantly reducing strength. Example 10, with an austenite volume fraction of 50%, achieved high strength but slightly low plasticity. Example 11, with an austenite volume fraction of 70%, achieved optimal plasticity of 33% but slightly lower strength. Example 1 achieved the best match between a 60% austenite volume fraction, a tensile strength of 1010 MPa, and an elongation of 31%.

[0094] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A micro-nitrided austenitic-based dual-phase low-density steel, characterized in that, By weight percentage, it includes: C: 0.5-0.8%, Mn: 15-25%, Al: 5-10%, Si: 0.6-1.5%, N: 0.05-0.15%, balance being Fe and impurities.

2. The micro-nitrided austenitic-based dual-phase low-density steel according to claim 1, characterized in that, Its microstructure is an austenitic-based dual-phase structure, in which the volume fraction of the austenitic phase is 50-70%, and in-situ self-generated submicron or nano-sized AlN reinforcing phase particles are dispersed on the austenitic matrix.

3. A method for preparing micro-nitrided austenite-based duplex low-density steel, used to prepare the micro-nitrided austenite-based duplex low-density steel as described in any one of claims 1-2, characterized in that, The preparation method includes: Step S1: Prepare the raw materials according to the chemical composition of micro-nitrided austenitic dual-phase low-density steel, and melt all the raw materials using smelting equipment. Control the nitrogen content within the range of 0.05-0.15% by adding nitriding alloy or bottom blowing nitrogen, and cast it into ingots or continuous casting billets. Step S2: Homogenize the ingot or continuously cast billet at 1100-1250℃ for 1-3 hours. Step S3: Forge the homogenized billet at a forging temperature of 950-1200℃, with a cumulative deformation of 30-60%. Step S4: Hot-roll the forged billet at a temperature range of 1150-850℃, with a cumulative deformation of 60-90%; Step S5: Immediately after hot rolling, perform water quenching and rapidly cool to room temperature; Step S6: Anneal the water-quenched steel plate at 850-1050℃ for 10-60 minutes to obtain micro-nitrided austenitic dual-phase low-density steel.

4. The method for preparing a micro-nitrided austenitic-based dual-phase low-density steel according to claim 3, characterized in that, In step 1, the smelting equipment is any one of a vacuum induction furnace, a non-vacuum induction furnace, an electric furnace, or a converter.

5. The method for preparing a micro-nitrided austenitic-based dual-phase low-density steel according to claim 3, characterized in that, In step 1, the nitride alloy includes at least one of manganese nitride, Fe-Mn-N master alloy, or Fe-Cr-N master alloy.

6. The method for preparing a micro-nitrided austenitic-based dual-phase low-density steel according to claim 3, characterized in that, In step 3, the forging is followed by air cooling or water quenching to room temperature.

7. The method for preparing a micro-nitrided austenitic-based dual-phase low-density steel according to claim 3, characterized in that, In step 3, the forging process employs a multi-directional forging method.

8. The method for preparing a micro-nitrided austenitic-based dual-phase low-density steel according to claim 3, characterized in that, In step 4, the hot-rolled billet is either a forged billet or a directly used continuous casting billet.

9. The method for preparing a micro-nitrided austenitic-based dual-phase low-density steel according to claim 3, characterized in that, In step 5, water quenching is used to suppress the precipitation of excessive high-temperature ferrite and grain growth, thereby obtaining a supersaturated austenitic matrix.

10. The method for preparing a micro-nitrided austenitic-based dual-phase low-density steel according to claim 3, characterized in that, In step 6, the annealing process causes AlN strengthening phase particles to be dispersed and precipitated on the austenitic matrix, and adjusts the austenite content and grain size in the matrix structure, ultimately obtaining a duplex structure with an austenite volume fraction of 50-70%.

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