Superplastic austenite-based dual-phase lightweight steel and preparation method thereof

Abstract

The invention relates to superplastic austenite-based dual-phase light steel and a preparation method thereof, belongs to the technical field of light steel, and solves one of the problems of low elongation, poor structure stability and low industrial efficiency of high-aluminum light steel in high-strain-rate superplastic forming in the prior art. The superplastic austenite-based dual-phase light steel comprises the following components in percentage by mass: 0.3%-0.35% of C, 28.0%-36.0% of Mn, 7.0%-9.0% of Al, 0.8%-1.0% of Nb, 0.8%-1.0% of V, 0.8%-1.0% of Mo, 0.8%-1.0% of W, less than 0.03% of P, less than 0.01% of S and the balance of Fe. And the balance of Fe and inevitable trace impurities. The austenite-based dual-phase light steel prepared by the invention has good superplasticity.

Description

Technical Field

[0001] This invention relates to the field of lightweight steel technology, and in particular to a superplastic austenitic-based dual-phase lightweight steel and its preparation method. Background Technology

[0002] Fe-Mn-Al-C lightweight steel has advantages such as low cost, high specific strength, and low density, and is widely used in aerospace and transportation fields, thus attracting widespread attention.

[0003] Superplasticity refers to the phenomenon where materials with stable, fine grains exhibit elongation exceeding 100% at low strain rates and temperatures above 0.5 Tm (thermodynamic melting temperature). In contrast, typical steel materials elongate only 30%–60% at room temperature. Superplastic materials are suitable for manufacturing parts with complex shapes requiring large deformations, offering advantages such as reduced manufacturing costs, simplified processing, and elimination of defects during machining. Currently, superplastic materials are widely used in many industrial production fields.

[0004] Currently, research on the superplasticity of lightweight steel mainly focuses on low-aluminum (Al < 6%) compositions. While these systems can achieve some superplasticity at low strain rates, their performance is limited at high strain rates (e.g., ≥ 10⁻²). s -1) The elongation rate decreases significantly, making it impossible to balance forming efficiency and performance. For high-aluminum lightweight steels with higher aluminum content (Al>6%) and greater potential for lightweighting, their superplastic behavior at high strain rates has not been systematically studied, and there is a lack of corresponding composition design and process support, which limits the application of such materials in practical superplastic forming.

[0005] Furthermore, existing high-alumina lightweight steels are prone to problems such as abnormal precipitation of κ-carbides and grain coarsening during high-temperature deformation, affecting microstructure stability and superplasticity. Therefore, developing a high-alumina austenitic-based dual-phase lightweight steel that still exhibits excellent superplasticity at high strain rates and is suitable for efficient forming has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a superplastic austenitic-based dual-phase lightweight steel and its preparation method, at least to solve one of the following problems existing in existing lightweight steel: 1. The slow strain rate of existing lightweight steel plastic forming hinders industrial efficiency; 2. Existing high-alumina lightweight steel has low elongation in high-strain-rate superplastic forming; 3. Existing high-alumina lightweight steel has poor microstructure stability in high-strain-rate superplastic forming.

[0007] The objective of this invention is mainly achieved through the following technical solutions:

[0008] This invention provides a superplastic austenitic-based dual-phase lightweight steel, the composition of which, by mass percentage, comprises: C 0.3%-0.35%, Mn 28.0%-36.0%, Al 7.0%-9.0%, Nb 0.8%-1.0%, V 0.8%-1.0%, Mo 0.8%-1.0%, W 0.8%-1.0%, P < 0.03%, S < 0.01%; the balance being Fe and unavoidable trace impurities.

[0009] Furthermore, the ratio of Mn content to Al content satisfies: 3.5 ≤ Mn / Al ≤ 4.5;

[0010] The ratio of the C content to the sum of the Nb, V, Mo, and W contents satisfies the following condition: 0.07 ≤ C / (Nb+V+Mo+W) ≤ 0.09.

[0011] Furthermore, the microstructure of the austenitic dual-phase lightweight steel includes an austenitic matrix and banded ferrite structures uniformly distributed on the austenitic matrix, with no κ-carbide precipitation and an average grain size of less than 10 μm.

[0012] This invention also provides a method for preparing superplastic austenitic-based duplex lightweight steel, which includes the following steps:

[0013] S1: Prepare the raw materials according to the chemical composition ratio of light steel, and then perform vacuum induction melting and casting to obtain steel ingots;

[0014] S2: Reheat the steel ingot to the forging temperature, hold it at that temperature, and then forge it. Air cool or stack cool the forging billet to room temperature to obtain the forging billet.

[0015] S3: The forging billet is reheated and then hot-rolled in multiple passes to the target thickness. After rolling, it is water-cooled to room temperature to obtain a hot-rolled plate.

[0016] S4: The hot-rolled plate is cold-rolled in multiple passes to the target thickness to obtain austenitic dual-phase lightweight steel cold-rolled plate.

[0017] Furthermore, in step S1, the vacuum degree of the vacuum induction melting is ≤5×10-2P. a The casting temperature is 1500-1550℃.

[0018] Furthermore, in step S2, the initial forging temperature is 1050-1100℃, the holding time is 1-3h, and the final forging temperature is ≥850℃.

[0019] Furthermore, in step S3, the heating temperature is 1000℃-1100℃, and the holding time is 30-60min.

[0020] Furthermore, in step S3, the hot rolling temperature is 950℃-1050℃, and the total hot rolling reduction rate is 70%-85%.

[0021] Furthermore, in step S3, the water cooling rate is ≥20℃ / s.

[0022] Furthermore, in step S4, the total reduction rate of the cold rolling is 75%-85%.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] 1. The superplastic austenitic-based dual-phase lightweight steel of the present invention, by adopting a medium-high C, high Al, and high Mn content in its composition, and preferably with a synergistic relationship of 3.5≤Mn / Al≤4.5 and C / (Nb+V+Mo+W)≤0.09, obtains a dual-phase steel composition system with austenitic matrix. At the same time, it ensures that elements such as Nb, V, Mo, and W can completely fix the carbon in the steel, fundamentally inhibiting the precipitation of κ-carbides, solving the problem of poor microstructure stability of existing high-aluminum lightweight steel, and laying a compositional foundation for obtaining stable superplasticity.

[0025] 2. This invention, through precise composition design and a "hot rolling + large deformation cold rolling" manufacturing process, obtains a banded austenite-ferrite dual-phase microstructure with strong rolling orientation. This microstructure has fine grains (<10μm) and stores high-density deformation energy. This high-energy, orientationd cold-rolled microstructure allows the steel plate to rapidly induce extensive static and dynamic recrystallization during subsequent high-temperature tensile (superplastic deformation) processes. After high-temperature tensile testing, the dual-phase structure in the deformed microstructure of the lightweight steel of this invention has completely transformed into equiaxed and uniformly fine austenite and ferrite grains without obvious rolling orientation. This equiaxed ultrafine grain structure, which forms and stabilizes in real time during deformation, greatly promotes the superplastic deformation mechanism dominated by grain boundary slip, thereby enabling the prepared lightweight steel to exhibit excellent high-strain-rate superplasticity at higher strain rates (e.g., 10⁻²). s It still exhibits excellent superplasticity under -1) conditions, with an elongation after fracture far exceeding 100%.

[0026] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 This is a schematic diagram of a non-standard dog-bone-shaped tensile specimen of superplastic austenitic-based dual-phase lightweight steel in Example 1.

[0029] Figure 2 The image shows the cold-rolled metallographic structure of the superplastic austenitic-based dual-phase lightweight steel of Example 1.

[0030] Figure 3 The equilibrium phase diagram of the superplastic austenitic-based dual-phase lightweight steel of Example 1;

[0031] Figure 4 The stress-strain curves of the superplastic austenitic-based duplex lightweight steel in Example 1 are obtained from tensile tests at 800°C and different strain rates.

[0032] Figure 5 This is a frequency distribution diagram of grain size at different strain rates in the superplastic austenitic dual-phase lightweight steel of Example 1 at 800℃.

[0033] Figure 6 The volume fraction of the two phases after tensile tests at 800°C and different strain rates on the superplastic austenitic-based dual-phase lightweight steel of Example 1 is shown.

[0034] Figure 7 Example 1: Superplastic austenitic-based duplex lightweight steel at different temperatures and 10... -2 s -1 Stress-strain curves from strain rate tensile tests;

[0035] Figure 8 Example 1 is a superplastic austenitic-based dual-phase lightweight steel at 700℃-900℃, 10 -2 s -1 Metallographic structure after strain rate stretching. Detailed Implementation

[0036] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of this application and are used to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0037] This invention provides a superplastic austenitic-based dual-phase lightweight steel, the composition of which, by mass percentage, comprises: C 0.3%-0.35%, Mn 28.0%-36.0%, Al 7.0%-9.0%, Nb 0.8%-1.0%, V 0.8%-1.0%, Mo 0.8%-1.0%, W 0.8%-1.0%, P < 0.03%, S < 0.01%; the balance being Fe and unavoidable trace impurities.

[0038] Preferably, the ratio of Mn content to Al content satisfies: 3.5 ≤ Mn / Al ≤ 4.5;

[0039] The ratio of the C content to the sum of the Nb, V, Mo, and W contents satisfies the following condition: 0.07 ≤ C / (Nb+V+Mo+W) ≤ 0.09.

[0040] The following details the function and dosage selection of the components contained in this invention:

[0041] Carbon (C) is a strong austenite stabilizing element, crucial for maintaining the austenitic properties of the matrix and preventing harmful phase transformations over a wide temperature range. An appropriate amount of C can stabilize austenite and combine with strong carbide-forming elements (Nb, V, etc.). If the C content is low, the austenite stability is insufficient, and there is not enough stable carbides to completely fix the carbon atoms, potentially leading to the precipitation of κ-carbides during subsequent heat treatment or deformation. If the C content is too high, it exceeds the complete fixation capacity of elements such as Nb, V, Mo, and W, and the excess carbon will participate in the formation of κ-carbides, impairing the purity and properties of the microstructure. Therefore, the C content in this invention is controlled at 0.3-0.35%.

[0042] Mn: Mn is an austenite forming and stabilizing element, ensuring that the matrix of steel remains face-centered cubic austenite within the room temperature and even the superplastic deformation temperature range (0.5-0.8Tm, where Tm is the absolute melting point). The grain boundaries of face-centered cubic austenite are usually large-angle grain boundaries with high stacking fault energy, which are more prone to grain boundary slip and diffusion than the grain boundaries of body-centered cubic ferrite. This is a prerequisite for achieving superplasticity. The manganese content directly affects the stacking fault energy of austenite. If the Mn content is insufficient, the austenite phase region will be too narrow, making it difficult to obtain the ideal two-phase structure at high temperatures, and the stability of the austenite matrix will be insufficient. Excessive Mn will cause lightweight steel to easily form the β-Mn brittle phase, which will significantly reduce the toughness of the material. Therefore, the Mn content in this invention is controlled at 28.0%-36.0%.

[0043] Al: Aluminum is a core element for achieving lightweighting and participates in the regulation of dual-phase microstructure as a ferrite stabilizing element. Insufficient Al content results in limited reduction in material density and makes it difficult to form a sufficient volume fraction of ferrite phase at high temperatures to constitute an ideal dual-phase structure conducive to grain boundary slip. Excessive Al content leads to an excessive amount of ferrite phase, which may impair the microstructure stability and deformation compatibility at high temperatures. Therefore, the Al content in this invention is controlled at 7.0-9.0%.

[0044] Nb, V, Mo, and W: These four elements are all strong carbide-forming elements, with a carbide-forming ability far exceeding that of Fe, Mn, and Al. In this invention, these four elements preferentially combine with carbon in steel to form stable, fine MC-type carbides (such as NbC and VC). These carbides are very stable at high temperatures. By controlling the content of these four elements and ensuring that their total amount matches the carbon content, the carbon in the steel can be thermodynamically completely consumed (fixed), thereby completely eliminating the driving force for the precipitation of κ-carbides. If the content of any one of these elements is too low, the overall "carbon fixation" ability will be insufficient, and the precipitation of κ-carbides cannot be completely suppressed. If the content is too high, it may lead to increased costs and limited additional performance improvement. Therefore, the content of these four elements in this invention is controlled at 0.8-1.0%.

[0045] Preferably, the ratio of Mn content to Al content satisfies: 3.5≤Mn / Al≤4.5; this allows for precise control of the volume ratio of austenite to ferrite within the superplastic deformation temperature range, which is beneficial for obtaining a high strain rate superplastic microstructure.

[0046] The ratio of the C content to the sum of the Nb, V, Mo, and W contents satisfies: 0.07 ≤ C / (Nb+V+Mo+W) ≤ 0.09. This ensures that the total Nb, V, Mo, and W contents are sufficient to completely "fix" all the carbon in the steel, thereby ensuring that no κ-carbide precipitation occurs in the microstructure.

[0047] Preferably, the present invention provides a superplastic austenitic-based dual-phase lightweight steel, the composition of which, by mass percentage, comprises: C 0.3%-0.33%, Mn 30.5%-35.0%, Al 7.2%-8.5%, Nb 0.8%-1.0%, V 0.8%-1.0%, Mo 0.8%-1.0%, W 0.8%-1.0%, P < 0.03%, S < 0.01%; the balance being Fe and unavoidable trace impurities.

[0048] Preferably, the ratio of Mn content to Al content satisfies: 3.59 ≤ Mn / Al ≤ 4.4;

[0049] The ratio of the C content to the sum of the Nb, V, Mo, and W contents satisfies the following condition: 0.083 ≤ C / (Nb+V+Mo+W) ≤ 0.089.

[0050] This invention also provides a method for preparing the above-mentioned superplastic austenitic-based duplex lightweight steel, comprising:

[0051] S1: Prepare the raw materials according to the chemical composition ratio of light steel, and then perform vacuum induction melting and casting to obtain steel ingots;

[0052] Specifically, the vacuum degree of the vacuum induction melting is ≤5×10-2P. a High vacuum can effectively remove gas from furnace charge and furnace chamber, promote the volatilization of volatile impurity elements, and reduce the gas content and harmful impurities in steel. However, excessively high vacuum will significantly increase equipment costs and time, while excessively low vacuum will result in insufficient degassing effect. Once the furnace charge has completely melted, control the melt temperature at 1550-1600℃ (exemplary, 1560℃, 1570℃, 1580℃, 1590℃), and maintain this temperature for refining for 10-15 minutes (exemplary, 11 minutes, 12 minutes, 13 minutes, 14 minutes). During refining, use electromagnetic stirring to ensure uniform melt composition and temperature. This temperature range ensures that all high-melting-point alloying elements (such as Nb, V, Mo, W) are fully dissolved, and allows for sufficient metallurgical reactions between carbon and alloying elements, promoting the early formation and uniform distribution of stable carbides (such as NbC, VC), which is beneficial for achieving "complete carbon fixation" in subsequent processes. If the temperature is too low, high-melting-point elements may not dissolve sufficiently, resulting in compositional segregation; if the temperature is too high, it will exacerbate furnace lining erosion and increase the risk of impurity introduction. After refining, the molten steel is poured into a steel ingot mold preheated to 200-300℃ (exemplary, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃). The casting temperature is controlled at 1500-1550℃ (exemplary, 1510℃, 1520℃, 1530℃, 1540℃). The appropriate mold temperature can prevent the molten steel from splashing or solidifying too quickly in the mold due to excessive temperature difference, and ensure the surface quality of the steel ingot and the uniformity of the internal solidification structure. The casting temperature in the range of 1500-1550℃ can ensure that the molten steel has good fluidity, so that the molten steel with uniform composition fills the mold, and can also avoid abnormally large grains and severe central shrinkage cavities caused by excessive temperature. The cooling method is to let it cool to room temperature in the mold.

[0053] S2: Reheat the steel ingot to the forging temperature, hold it at that temperature, and then forge it. Air cool or stack cool the forging billet to room temperature to obtain the forging billet.

[0054] Specifically, the steel ingot is reheated to a forging temperature of 1050-1100℃ (exemplary, 1055℃, 1060℃, 1065℃, 1070℃, 1075℃, 1080℃, 1085℃, 1090℃, 1095℃), held at that temperature for 1-3 hours (exemplary, 1.5 hours, 2 hours, 2.5 hours), and forged into a steel billet with a predetermined cross-sectional area. This temperature range is higher than the complete austenitization temperature of the lightweight steel, ensuring that the steel ingot is transformed into a single austenitic phase, providing a highly ductile microstructure for subsequent forging. At the same time, the high temperature promotes the full diffusion of alloying elements. If the temperature is below 1050℃, austenitization may be incomplete, and residual as-cast segregated structures or undissolved phases will worsen hot working plasticity, and insufficient element diffusion motives will result in poor homogenization. If the temperature is above 1100℃, although diffusion is faster, the grains will become significantly coarser (austenite grain growth), and the oxidation and decarburization of the ingot surface will be aggravated, reducing yield and surface quality. Maintaining the temperature at high temperature for a sufficient time allows elements in the steel (especially Mn, Al, Nb, V, etc.) to achieve a uniform distribution in both macroscopic and microscopic scales through diffusion, reducing or eliminating dendritic segregation generated during ingot solidification. If the holding time is too short, homogenization will be insufficient, and residual segregation will lead to uneven subsequent microstructure and properties. If the holding time is too long, the homogenization benefits are no longer significant, and efficiency will be reduced due to continuous grain growth and increased energy consumption. After the heat preservation is completed, forging should be carried out immediately. The initial forging temperature is 1050℃-1100℃ (i.e., the heat preservation temperature). The initial forging temperature is consistent with the heating temperature, which is conducive to the implementation of large deformation. The final forging temperature is ≥850℃ (exemplary, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃). If the final forging temperature is lower than 850℃, the material may enter part of the two-phase region or even the lower temperature region. At this time, the deformation resistance increases sharply, recrystallization is insufficient, which can easily lead to work hardening, internal stress accumulation, and even cracks. Through the synergistic effect of process parameters in this high-temperature forging step, the original coarse as-cast structure is broken and deformed, providing favorable nucleation sites for sufficient austenite recrystallization and grain refinement during subsequent hot rolling heating. The forging process also welds together defects such as porosity inside the ingot and fully releases the residual stress of the ingot, ultimately obtaining a forged billet with a dense structure, relatively uniform composition, and good stress state.

[0055] S3: The forging billet is reheated and then hot-rolled in multiple passes to the target thickness. After rolling, it is water-cooled to room temperature to obtain a hot-rolled plate.

[0056] Specifically, the heating temperature is 1000℃-1100℃ (exemplary, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃), the holding time is 30-60min (exemplary, 35min, 40min, 45min, 50min, 55min), followed by heating at 950℃-1050℃ (exemplary, 960℃, 970℃, 980℃, 990℃, 1000℃). The plate is hot-rolled to the target thickness in multiple passes within a temperature range of 1010℃, 1020℃, 1030℃, and 1040℃, with the total reduction rate controlled at 70%-85% (exemplary, 72%, 74%, 75%, 77%, 78%, 80%, 82%, and 84%). After rolling, the plate is immediately water-cooled to room temperature at a cooling rate of not less than 20℃ / s (exemplary, 22℃ / s, 24℃ / s, 25℃ / s, 26℃ / s, 28℃ / s, and 30℃ / s) to obtain a hot-rolled plate.

[0057] It should be noted that the heating temperature is 1000℃-1100℃, and the holding time is 30-60 minutes. This heating process aims to fully austenitize the forging billet and ensure that the elements in the steel (especially Mn, Al, Nb, V, etc.) are fully and uniformly diffused, providing a single-phase austenitic structure with uniform composition and good plasticity for hot rolling. If the temperature is below 1000℃, austenitization may be incomplete, and the residual structure will deteriorate the hot rolling plasticity. If the temperature is above 1100℃, the grains will grow abnormally and oxidation will be aggravated. If the holding time is too short, the core of the forging billet will not be able to be heated through and the composition will be uneven. If it is too long, it will lead to low production efficiency and grain coarsening. Rolling within the temperature range of 950℃-1050℃ ensures the material is in the fully recrystallized region, allowing for sufficient dynamic recrystallization and effective refinement of austenite grains. The total reduction rate controls grain refinement and deformation texture; a reduction rate below 70% results in insufficient cumulative deformation energy and limited grain refinement. A reduction rate above 85% places extremely high demands on equipment capabilities and may lead to defects such as edge cracks. After rolling, the plate is immediately water-cooled to room temperature at a rate of at least 20℃ / s to obtain a hot-rolled plate. Rapid cooling (quenching) inhibits the growth of high-temperature austenite grains, preserving the refined grain structure achieved through hot rolling, while simultaneously controlling the precipitation behavior of the second phase. For the high Mn and high Al composition system of the present invention, at this cooling rate, fine banded ferrite can be precipitated from austenite along the rolling direction, thereby forming a two-phase structure of austenite matrix + banded ferrite. At the same time, the high cooling rate strongly inhibits the precipitation and growth of κ-carbides, ensuring the cleanliness of the structure. If the cooling is too slow (such as air cooling), the ferrite morphology will become coarse, and κ-carbides will easily precipitate, which will damage the steel properties.

[0058] S4: The hot-rolled plate is cold-rolled in multiple passes to the target thickness to obtain austenitic dual-phase lightweight steel cold-rolled plate.

[0059] Specifically, multiple cold rolling passes are performed at temperatures ranging from room temperature to 250°C, with a total cold rolling reduction of 75%-85% (exemplary, 76%, 78%, 80%, 82%, 84%).

[0060] Controlling the rolling temperature between room temperature and 250°C ensures that rolling deformation primarily focuses on dislocation accumulation and work hardening, preventing dynamic recrystallization. This promotes the formation of a deformed microstructure with high dislocation density and strong texture, providing sufficient driving force for recrystallization during subsequent superplastic deformation. If the temperature is too high (e.g., >250°C), dynamic recovery or even partial recrystallization may occur, weakening work hardening and energy storage, and affecting the final formation of ultrafine grains. A cold rolling reduction rate of 75%-85% aims to refine the original two-phase microstructure of the hot-rolled plate through strong plastic deformation, introducing high-density dislocations, deformation bands, and texture, thereby forming a fibrous deformed microstructure with strong rolling orientation. If the reduction rate is below 75%, the accumulated strain energy is insufficient, making it difficult for the steel plate to store enough recrystallization driving force, which is detrimental to the formation of a uniform ultrafine grain structure under superplastic conditions. If the reduction rate is above 85%, the plate undergoes severe work hardening, placing stringent demands on the rolling mill's capacity and significantly increasing the risk of edge cracking or strip breakage.

[0061] The obtained austenitic dual-phase lightweight steel was subjected to isothermal superplastic deformation tests:

[0062] Non-standard "dog bone" shaped tensile specimens (such as...) were wire-cut from the prepared austenitic dual-phase lightweight steel (cold-rolled sheet). Figure 1 As shown), the temperature is increased to 800℃ at a rate of 5℃ / s and held for 15 minutes for uniform heating, and then heated at this temperature at a rate of 10... -4 s -1 -10 -1 s -1 The strain rate was determined by isothermal stretching until failure fracture, and the strain rate corresponding to the optimal superplasticity was determined.

[0063] After determining the strain rate corresponding to the optimal superplasticity, the optimal deformation temperature was determined by conducting experiments at different deformation temperatures of 700-900℃ with 50℃ intervals at that strain rate.

[0064] The microstructure of the superplastic austenitic dual-phase lightweight steel prepared by this invention includes an austenitic matrix and banded ferrite structures uniformly distributed on the austenitic matrix, with no κ-carbide precipitation and an average grain size of less than 10 μm.

[0065] The superplastic austenitic-based dual-phase lightweight steel of this invention, through the use of medium-high C, high Al, and high Mn content, and preferably a synergistic relationship of 3.5≤Mn / Al≤4.5 and C / (Nb+V+Mo+W)≤0.09, obtains a dual-phase steel composition system with austenite as the matrix. Simultaneously, it ensures that elements such as Nb, V, Mo, and W can completely fix the carbon in the steel, fundamentally inhibiting the precipitation of κ-carbides. Through a "hot rolling + large deformation cold rolling" process, a banded austenitic-ferrite dual-phase microstructure with strong rolling orientation is obtained. This microstructure has fine grains (<10μm) and stores high-density deformation energy. This high-energy-storage, orientationd cold-rolled microstructure allows the steel sheet to rapidly undergo extensive static and dynamic recrystallization during subsequent high-temperature tensile (superplastic deformation) processes.

[0066] After high-temperature tensile testing, the two-phase structure in the deformed microstructure of the lightweight steel of the present invention has been completely transformed into equiaxed and uniformly fine austenite and ferrite grains without obvious rolling orientation. This equiaxed ultrafine grain structure, which is formed and stabilized in real time during deformation, greatly promotes the superplastic deformation mechanism dominated by grain boundary slip, thereby making the material exhibit excellent high strain rate superplasticity.

[0067] The austenitic-based duplex lightweight steel prepared by this invention exhibits an elongation after fracture ≥500% (e.g., 580-633%) at 800℃ and 10⁻² s⁻¹, and at a constant strain rate (10⁻²). s -1) Under a wide temperature range of 700℃-900℃, the elongation after fracture is >100%.

[0068] Example 1

[0069] This embodiment provides a superplastic austenitic-based dual-phase lightweight steel, the composition of which, by mass percentage, includes: C 0.3%, Mn 35.0%, Al 8.0%, Nb 0.8%, V 0.8%, Mo 1.0%, W 1.0%, P < 0.03%, S < 0.01%; the balance being Fe and unavoidable trace impurities.

[0070] The ratio of Mn content to Al content is 4.375, satisfying the condition: 3.5 ≤ Mn / Al ≤ 4.5;

[0071] The ratio of the C content to the sum of the Nb, V, Mo, and W contents is 0.083, which satisfies the condition: 0.07≤C / (Nb+V+Mo+W)≤0.09.

[0072] Prepared by the following steps:

[0073] S1: Prepare the raw materials according to the chemical composition ratio of light steel, and then perform vacuum induction melting and casting to obtain steel ingots;

[0074] The vacuum degree of vacuum induction smelting is 2×10⁻²P. a Once the furnace charge has completely melted, the melt temperature is controlled at 1580℃ and refined for 12 minutes. During the refining process, electromagnetic stirring is used to ensure uniform melt composition and temperature. After refining, the molten steel is poured into a steel ingot mold preheated to 250℃, with a casting temperature of 1550℃.

[0075] S2: Reheat the steel ingot to the forging temperature, hold it at that temperature, and then forge it. Air cool or stack cool the forging billet to room temperature to obtain the forging billet.

[0076] Specifically, the steel ingot is reheated to the forging temperature of 1080℃, held for 2 hours, the initial forging temperature is 1080℃ (i.e., the holding temperature), and the final forging temperature is 900℃.

[0077] S3: The forging billet is reheated and then hot-rolled in multiple passes to the target thickness. After rolling, it is water-cooled to room temperature to obtain a hot-rolled plate.

[0078] The heating temperature is 1050℃, the holding time is 35min, and then six hot rolling passes are performed in the temperature range of 1000℃. The billet is successively reduced from 22mm to 19mm, 16mm, 13mm, 10mm, 7mm until the target thickness of 5mm, with a total reduction rate of 77%. After rolling, the plate is immediately water-cooled to room temperature at a cooling rate of 25℃ / s to obtain the hot-rolled plate.

[0079] S4: The hot-rolled plate is cold-rolled in multiple passes to the target thickness to obtain austenitic dual-phase lightweight steel cold-rolled plate.

[0080] Multiple cold rolling passes were performed at 200℃, with a total cold rolling reduction rate of 80%, to reduce the thickness of the 5mm hot-rolled plate to the target thickness of 1mm, thus obtaining austenitic dual-phase lightweight steel cold-rolled sheet.

[0081] The microstructure of the austenitic dual-phase lightweight cold-rolled steel sheet obtained in this embodiment is as follows: Figure 1 The microstructure exhibits a dual-phase structure of fine banded austenite and ferrite, with austenite as the matrix and banded ferrite as the distribution. The average grain size is 4.3 μm, and there is a clear rolling orientation.

[0082] The superplastic austenitic dual-phase lightweight steel obtained in this embodiment was subjected to an isothermal superplastic deformation test:

[0083] The superplastic austenitic dual-phase lightweight steel (cold-rolled sheet) prepared in this embodiment was used to cut non-standard "dog bone" shaped tensile specimens (such as...). Figure 2 As shown), superplastic deformation tests were conducted at different temperatures and strain rates to determine the optimal deformation temperature and the strain rate corresponding to the optimal superplasticity. Specifically:

[0084] Heat to 700℃-900℃ at a rate of 5℃ / s and hold for 15 minutes to ensure uniform heating. Within this temperature range, maintain a constant temperature of 10℃ / s. -4 s -1 -10 -1 s -1 The properties of superplastic austenitic-based duplex lightweight steel under constant strain rate tension until failure fracture are shown in Table 1-1; 700℃-900℃, 1×10 -3 s -1 The properties of superplastic austenitic-based dual-phase lightweight steel at strain rates are shown in Table 1-2; 700℃-900℃, 1×10 -2 s -1 The properties of superplastic austenitic-based dual-phase lightweight steel at strain rates are shown in Tables 1-3; 700℃-900℃, 1×10 -1 s -1 The properties of superplastic austenitic dual-phase lightweight steel under strain rate are shown in Table 1-4.

[0085] Table 1-1 700℃-900℃, 1×10 -4 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0086] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -4 s -1 ]]> 700℃ 34 39 78.5 <![CDATA[10 -4 s -1 ]]> 750℃ 66 83 170 <![CDATA[10 -4 s -1 ]]> 800℃ 14 17 203.5 <![CDATA[10 -4 s -1 ]]> 850℃ 9 13 121.5 <![CDATA[10 -4 s -1 ]]> 900℃ 16 21 120.5

[0087] Table 1-2 700℃-900℃, 1×10 -3 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0088] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -3 s -1 ]]> 700℃ 125 142 280.5 <![CDATA[10 -3 s -1 ]]> 750℃ 39 60 428 <![CDATA[10 -3 s -1 ]]> 800℃ 78 86 457.5 <![CDATA[10 -3 s -1 ]]> 850℃ 20 30 412 <![CDATA[10 -3 s -1 ]]> 900℃ 40 45 196.5

[0089] Table 1-3 700℃-900℃, 1×10 -2 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0090] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -2 s -1 ]]> 700℃ 173 273 406 <![CDATA[10 -2 s -1 ]]> 750℃ 97 144 400 <![CDATA[10 -2 s -1 ]]> 800℃ 58 83 633 <![CDATA[10 -2 s -1 ]]> 850℃ 58 72 407.5 <![CDATA[10 -2 s -1 ]]> 900℃ 65 79 263.5

[0091] Table 1-4 700℃-900℃, 1×10 -1 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0092] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -1 s -1 ]]> 700℃ 398 540 134.5 <![CDATA[10 -1 s -1 ]]> 750℃ 181 268 156 <![CDATA[10 -1 s -1 ]]> 800℃ 141 208 167.5 <![CDATA[10 -1 s -1 ]]> 850℃ 140 165 132.5 <![CDATA[10 -1 s -1 ]]> 900℃ 124 146 79.5

[0093] As can be seen from Tables 1-1 to 1-4, the austenitic-based duplex lightweight steel of this embodiment has a strength of 10... -4 s -1 ~10-1 s -1 Good superplasticity was achieved at all strain rates, with elongation mostly exceeding 100%. Regardless of the strain rate, the superplastic elongation reached its optimum at 800℃, while the elongation was consistently around 10% when comparing strain rates longitudinally. -2 s -1 The optimal strain rate elongation is obtained by coupling two conditions, which shows that the austenitic-based duplex lightweight steel in this embodiment exhibits optimal elongation at 800℃ and 10℃. -2 s -1 It has the best superplastic properties.

[0094] Example 2

[0095] This embodiment provides a superplastic austenitic-based dual-phase lightweight steel, the composition of which, by mass percentage, includes: C 0.31%, Mn 30.5%, Al 8.5%, Nb 0.9%, V 0.9%, Mo 0.9%, W 0.9%, P < 0.03%, S < 0.01%; the balance being Fe and unavoidable trace impurities.

[0096] The ratio of Mn content to Al content is 3.59, satisfying the condition: 3.5 ≤ Mn / Al ≤ 4.5;

[0097] The ratio of the C content to the sum of the Nb, V, Mo, and W contents is 0.086, which satisfies the condition: 0.07≤C / (Nb+V+Mo+W)≤0.09.

[0098] Prepared by the following steps:

[0099] S1: The ingredients are batched according to the chemical composition ratio of the light steel, and the batched ingredients are vacuum induction melted and cast to obtain steel ingots. The specific parameters are the same as in Example 1.

[0100] S2: Reheat the steel ingot to the forging temperature, hold it at that temperature, and then forge it. Air cool or stack cool the forging billet to room temperature to obtain the forging billet.

[0101] Specifically, the steel ingot is reheated to the forging temperature of 1070℃, held for 2 hours, the initial forging temperature is 1070℃ (i.e., the holding temperature), and the final forging temperature is 890℃.

[0102] S3: The forging billet is reheated and then hot-rolled in multiple passes to the target thickness. After rolling, it is water-cooled to room temperature to obtain a hot-rolled plate.

[0103] The heating temperature is 1040℃, the holding time is 40min, and then five hot rolling passes are performed in the temperature range of 990℃. The billet is successively reduced from 20mm to 18mm, 15mm, 12mm, 9mm until the target thickness of 5mm. The total reduction rate is 75%. After rolling, the plate is immediately water-cooled to room temperature at a cooling rate of 22℃ / s to obtain the hot-rolled plate.

[0104] S4: The hot-rolled plate is cold-rolled in multiple passes to the target thickness to obtain austenitic dual-phase lightweight steel cold-rolled plate.

[0105] Multiple cold rolling passes were performed at 180℃, with a total cold rolling reduction rate of 78%, to reduce the thickness of the 5mm hot-rolled plate to the target thickness of 1mm, thus obtaining austenitic dual-phase lightweight steel cold-rolled sheet.

[0106] The superplastic austenitic dual-phase lightweight steel obtained in this embodiment was subjected to an isothermal superplastic deformation test:

[0107] The superplastic austenitic dual-phase lightweight steel (cold-rolled sheet) prepared in this embodiment was used to cut non-standard "dog bone" shaped tensile specimens (such as...). Figure 1 As shown), superplastic deformation tests were conducted at different temperatures and strain rates to determine the optimal deformation temperature and the strain rate corresponding to the optimal superplasticity. Specifically:

[0108] Heat to 700℃-900℃ at a rate of 5℃ / s and hold for 15 minutes to ensure uniform heating. Within this temperature range, maintain a constant temperature of 10℃ / s. -4 s -1 -10 -1 s -1 The properties of superplastic austenitic-based duplex lightweight steel under constant strain rate tension until failure fracture are shown in Table 2-1; 700℃-900℃, 1×10 -3 s -1 The properties of superplastic austenitic-based dual-phase lightweight steel at strain rates are shown in Table 2-2; 700℃-900℃, 1×10 -2 s -1 The properties of superplastic austenitic-based dual-phase lightweight steel at strain rates are shown in Table 2-3; 700℃-900℃, 1×10 -1 s -1 The properties of superplastic austenitic dual-phase lightweight steel under strain rate are shown in Table 2-4.

[0109] Table 2-1 700℃-900℃, 1×10 -4 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0110] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -4 s -1 ]]> 700℃ 42 48 82 <![CDATA[10 -4 s -1 ]]> 750℃ 72 90 195 <![CDATA[10 -4 s -1 ]]> 800℃ 19 23 245 <![CDATA[10 -4 s -1 ]]> 850℃ 13 19 155 <![CDATA[10 -4 s -1 ]]> 900℃ 21 28 140

[0111] Table 2-2 700℃-900℃, 1×10 -3 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0112] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -3 s -1 ]]> 700℃ 130 150 310 <![CDATA[10 -3 s -1 ]]> 750℃ 48 70 480 <![CDATA[10 -3 s -1 ]]> 800℃ 82 92 510 <![CDATA[10 -3 s -1 ]]> 850℃ 26 37 460 <![CDATA[10 -3 s -1 ]]> 900℃ 44 50 220

[0113] Table 2-3 700℃-900℃, 1×10 -2 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0114] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -2 s -1 ]]> 700℃ 180 280 425 <![CDATA[10 -2 s -1 ]]> 750℃ 110 160 418 <![CDATA[10 -2 s -1 ]]> 800℃ 68 95 580 <![CDATA[10 -2 s -1 ]]> 850℃ 68 84 430 <![CDATA[10 -2 s -1 ]]> 900℃ 75 90 285

[0115] Table 2-4 700℃-900℃, 1×10 -1 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0116] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -1 s -1 ]]> 700℃ 410 555 145 <![CDATA[10 -1 s -1 ]]> 750℃ 200 290 165 <![CDATA[10 -1 s -1 ]]> 800℃ 155 230 180 <![CDATA[10 -1 s -1 ]]> 850℃ 152 185 140 <![CDATA[10 -1 s -1 ]]> 900℃ 138 160 88

[0117] As shown in Tables 2-1 to 2-4, the austenitic-based duplex lightweight steel in this embodiment is subjected to temperatures of 800℃ and 10℃. -2 s -1 It has the best superplastic properties.

[0118] Example 3

[0119] This embodiment provides a superplastic austenitic-based dual-phase lightweight steel, the composition of which, by mass percentage, includes: C 0.33%, Mn 31.7%, Al 7.2%, Nb 1.0%, V 1.0%, Mo 0.85%, W 0.85%, P < 0.03%, S < 0.01%; the balance being Fe and unavoidable trace impurities.

[0120] The ratio of Mn content to Al content is 4.40, satisfying the condition: 3.5 ≤ Mn / Al ≤ 4.5;

[0121] The ratio of the C content to the sum of the Nb, V, Mo, and W contents is 0.089, satisfying the condition: 0.07≤C / (Nb+V+Mo+W)≤0.09.

[0122] Prepared by the following steps:

[0123] S1: The ingredients are batched according to the chemical composition ratio of the light steel, and the batched ingredients are vacuum induction melted and cast to obtain steel ingots. The specific parameters are the same as in Example 1.

[0124] S2: Reheat the steel ingot to the forging temperature, hold it at that temperature, and then forge it. Air cool or stack cool the forging billet to room temperature to obtain the forging billet.

[0125] Specifically, the steel ingot is reheated to the forging temperature of 1060℃, held for 2.5 hours, the initial forging temperature is 1060℃ (i.e., the holding temperature), and the final forging temperature is 880℃.

[0126] S3: The forging billet is reheated and then hot-rolled in multiple passes to the target thickness. After rolling, it is water-cooled to room temperature to obtain a hot-rolled plate.

[0127] The heating temperature is 1020℃, the holding time is 50min, and then six passes of hot rolling are carried out in the temperature range of 970℃. The billet is successively reduced from 22mm to 19mm, 16mm, 13mm, 10mm, 8mm, 6mm until the target thickness of 5mm. The total reduction rate is 80%. After rolling, the plate is immediately water-cooled to room temperature at a cooling rate of 30℃ / s to obtain the hot-rolled plate.

[0128] S4: The hot-rolled plate is cold-rolled in multiple passes to the target thickness to obtain austenitic dual-phase lightweight steel cold-rolled plate.

[0129] Multiple cold rolling passes were performed at room temperature, with a total cold rolling reduction rate of 82%, to reduce the thickness of the 5mm hot-rolled plate to the target thickness of 1mm, thus obtaining austenitic dual-phase lightweight steel cold-rolled sheet.

[0130] The superplastic austenitic dual-phase lightweight steel obtained in this embodiment was subjected to an isothermal superplastic deformation test:

[0131] The superplastic austenitic dual-phase lightweight steel (cold-rolled sheet) prepared in this embodiment was used to cut non-standard "dog bone" shaped tensile specimens (such as...). Figure 1 As shown), superplastic deformation tests were conducted at different temperatures and strain rates to determine the optimal deformation temperature and the strain rate corresponding to the optimal superplasticity. Specifically:

[0132] Heat to 700℃-900℃ at a rate of 5℃ / s and hold for 15 minutes to ensure uniform heating. Within this temperature range, maintain a constant temperature of 10℃ / s. -4 s -1 -10 -1 s -1 The properties of superplastic austenitic-based duplex lightweight steel under constant strain rate tension until failure fracture are shown in Table 3-1; 700℃-900℃, 1×10 -3 s -1 The properties of superplastic austenitic-based dual-phase lightweight steel at strain rates are shown in Table 3-2; 700℃-900℃, 1×10 -2 s -1 The properties of superplastic austenitic-based dual-phase lightweight steel at strain rates are shown in Table 3-3; 700℃-900℃, 1×10 -1 s -1 The properties of superplastic austenitic dual-phase lightweight steel under strain rate are shown in Table 3-4.

[0133] Table 3-1 700℃-900℃, 1×10 -4 s -1Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0134] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -4 s -1 ]]> 700℃ 36 42 88 <![CDATA[10 -4 s -1 ]]> 750℃ 65 82 205 <![CDATA[10 -4 s -1 ]]> 800℃ 16 20 255 <![CDATA[10 -4 s -1 ]]> 850℃ 11 17 160 <![CDATA[10 -4 s -1 ]]> 900℃ 19 25 145

[0135] Table 3-2 700℃-900℃, 1×10 -3 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0136] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -3 s -1 ]]> 700℃ 120 140 335 <![CDATA[10 -3 s -1 ]]> 750℃ 42 62 495 <![CDATA[10 -3 s -1 ]]> 800℃ 75 85 530 <![CDATA[10 -3 s -1 ]]> 850℃ 22 33 475 <![CDATA[10 -3 s -1 ]]> 900℃ 40 46 235

[0137] Table 3-3 700℃-900℃, 1×10 -2 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0138] strain rate Deformation temperature Yield strength / MPa Tensile strength / MPa Elongation after fracture / % <![CDATA[10 -2 s -1 ]]> 700℃ 168 265 440 <![CDATA[10 -2 s -1 ]]> 750℃ 102 150 435 <![CDATA[10 -2 s -1 ]]> 800℃ 61 88 605 <![CDATA[10 -2 s -1 ]]> 850℃ 61 78 440 <![CDATA[10 -2 s -1 ]]> 900℃ 70 85 295

[0139] Table 3-4 700℃-900℃, 1×10 -1 s -1 Performance of the superplastic austenitic-based dual-phase lightweight steel in Example 1 at strain rates

[0140]

[0141]

[0142] As shown in Tables 3-1 to 3-4, the austenitic-based duplex lightweight steel of this embodiment is subjected to temperatures of 800℃ and 10℃. -2 s -1 It has the best superplastic properties.

[0143] Comparative Example 1

[0144] This comparative example provides an austenitic-based dual-phase lightweight steel whose composition, by mass percentage, comprises: C 0.40%, Mn 25.0%, Al 10.0%, Nb 1.0%, V 1.0%, Mo 0.8%, W 0.8%, P < 0.03%, S < 0.01%; the balance being Fe and unavoidable trace impurities.

[0145] The ratio of Mn content to Al content is 2.5, which does not satisfy the condition: 3.5≤Mn / Al≤4.5;

[0146] The ratio of the C content to the sum of the Nb, V, Mo, and W contents is 0.11, which does not satisfy the condition: 0.07≤C / (Nb+V+Mo+W)≤0.09.

[0147] The preparation method and process parameters are the same as in Example 1.

[0148] The superplastic austenitic duplex lightweight steel obtained in this comparative example was subjected to an isothermal superplastic deformation test, and the specific test procedure was the same as in Example 1. The conclusion was that the superplastic austenitic duplex lightweight steel in this comparative example exhibited good superplastic deformation at 800℃ and 10℃. -2 s -1 Its elongation after fracture is 85%, its yield strength is 120 MPa, and its tensile strength is 150 MPa.

[0149] Comparative Example 2

[0150] This comparative example provides an austenitic-based duplex lightweight steel with the same composition and content as Example 1, and a similar preparation method as Example 1, except that:

[0151] In S2, the heating / initial forging temperature is set to 1200℃; the final forging temperature is set to 750℃.

[0152] In S3, air cooling is used after hot rolling, with a cooling rate of approximately 5°C / s.

[0153] In S4, the cold rolling reduction rate is set to 60%.

[0154] The superplastic austenitic duplex lightweight steel obtained in this comparative example was subjected to an isothermal superplastic deformation test, and the specific test procedure was the same as in Example 1. The conclusion was that the superplastic austenitic duplex lightweight steel in this comparative example exhibited good superplastic deformation at 800℃ and 10℃. -2 s -1 Its elongation after fracture is 180%, its yield strength is 180 MPa, and its tensile strength is 220 MPa.

[0155] Comparative Example 3

[0156] This comparative example provides an austenitic-based duplex lightweight steel whose composition, by mass percentage, comprises: C 0.09%, Mn 36.0%, Al 6.0%, Nb 0.8%, V 0.14%, Mo 0.4%, W 0.6%, P 0.01%, S 0.005%; the balance being Fe and unavoidable trace impurities.

[0157] The ratio of Mn content to Al content is 6, which does not satisfy the condition: 3.5 ≤ Mn / Al ≤ 4.5;

[0158] The ratio of the C content to the sum of the Nb, V, Mo, and W contents is 0.046, which does not satisfy the condition: 0.07≤C / (Nb+V+Mo+W)≤0.09.

[0159] Prepared by the following method:

[0160] S1: Vacuum induction melting and die casting into billets;

[0161] S2: The billet is heated to 1150℃ and held for 3.6 hours to homogenize it;

[0162] S3: Start forging at 1110℃, finish forging at 860℃, forge into bars of the required specifications, and air cool after forging;

[0163] S4: Perform solution treatment at 1050℃, hold for 120 minutes, and then cool with oil.

[0164] The superplastic austenitic duplex lightweight steel obtained in this comparative example was subjected to an isothermal superplastic deformation test, and the specific test procedure was the same as in Example 1. The conclusion was that the superplastic austenitic duplex lightweight steel in this comparative example exhibited good superplastic deformation at 800℃ and 10℃. -2 s -1 Its elongation after fracture is 160%, its yield strength is 135 MPa, and its tensile strength is 185 MPa.

[0165] Figure 2 The image shows the cold-rolled metallographic structure of the superplastic austenitic-based dual-phase lightweight steel of Example 1. Figure 3 The equilibrium phase diagram of the superplastic austenitic-based dual-phase lightweight steel of Example 1; Figure 4 The stress-strain curves of the superplastic austenitic-based duplex lightweight steel in Example 1 are obtained from tensile tests at 800°C and different strain rates. Figure 5 This is a frequency distribution diagram of grain size at different strain rates in the superplastic austenitic dual-phase lightweight steel of Example 1 at 800℃. Figure 6 The volume fraction of the two phases after tensile tests at 800°C and different strain rates on the superplastic austenitic-based dual-phase lightweight steel of Example 1 is shown. Figure 7 Example 1: Superplastic austenitic-based duplex lightweight steel at different temperatures and 10... -2 s -1 Stress-strain curves from strain rate tensile tests; Figure 8 Example 1: Superplastic austenitic-based duplex lightweight steel at 800°C, 10... -2 s -1 Metallographic images of the austenitic dual-phase lightweight steels of the examples and comparative examples after strain rate stretching at 800℃ and 10℃. Table 4 shows the metallographic structure of the austenitic dual-phase lightweight steels of the examples and comparative examples after strain rate stretching at 800℃ and 10℃. -2 s -1 Performance.

[0166] Table 4 shows the austenitic-based duplex lightweight steels of the examples and comparative examples at 800°C and 10°C. -2 s -1 performance

[0167] condition Yield strength / MPa Tensile strength / MPa Elongation after fracture / % Example 1 <![CDATA[800℃,10 -2 s -1 ]]> 58 83 633 Example 2 <![CDATA[800℃,10 -2 s -1 ]]> 68 95 580 Example 3 <![CDATA[800℃,10 -2 s -1 ]]> 61 88 605 Comparative Example 1 <![CDATA[800℃,10 -2 s -1 ]]> 120 150 85 Comparative Example 2 <![CDATA[800℃,10 -2 s -1 ]]> 180 220 180 Comparative Example 3 <![CDATA[800℃,10 -2 s -1 ]]> 135 185 160

[0168] The austenitic dual-phase lightweight steels prepared in Examples 1-3 all exhibited excellent superplasticity under high strain rate conditions of 800℃ and 10⁻² s⁻¹, with elongation after fracture reaching 633%, 580%, and 605%, respectively, and low deformation resistance (yield strengths of 58 MPa, 68 MPa, and 61 MPa, respectively). The composition of Comparative Example 1 does not meet the requirements of this invention. Although the preparation method and process parameters are the same as those of Example 1, the austenitic duplex lightweight steel prepared therein has a reduced elongation after fracture to 85% under the high strain rate conditions of 800℃ and 10⁻² s⁻¹, while the strength increases. Although the composition of Comparative Example 2 meets the requirements of this invention, several process parameters do not meet the requirements of this invention. The austenitic duplex lightweight steel prepared therein has an elongation after fracture of 180% under the high strain rate conditions of 800℃ and 10⁻² s⁻¹, which is much lower than that of Example 1. Comparative Example 3 uses the "low carbon composition + solution treatment" method. The austenitic duplex lightweight steel prepared therein has an elongation after fracture of 160% under the high strain rate conditions of 800℃ and 10⁻² s⁻¹, which is much lower than that of Example 1.

[0169] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A superplastic austenitic-based dual-phase lightweight steel, characterized in that, The components, by mass percentage, include: C 0.3%-0.35%, Mn 28.0%-36.0%, Al 7.0%-9.0%, Nb 0.8%-1.0%, V 0.8%-1.0%, Mo 0.8%-1.0%, W 0.8%-1.0%, P < 0.03%, S < 0.01%; the balance is Fe and unavoidable trace impurities.

2. The austenitic-based duplex lightweight steel according to claim 1, characterized in that, The ratio of Mn content to Al content satisfies: 3.5 ≤ Mn / Al ≤ 4.5; The ratio of the C content to the sum of the Nb, V, Mo, and W contents satisfies the following condition: 0.07 ≤ C / (Nb+V+Mo+W) ≤ 0.

09.

3. The austenitic-based duplex lightweight steel according to claim 1, characterized in that, The microstructure of the austenitic dual-phase lightweight steel includes an austenitic matrix and banded ferrite uniformly distributed on the austenitic matrix, with no κ-carbide precipitation and an average grain size of less than 10 μm.

4. A method for preparing superplastic austenitic-based duplex lightweight steel, used to prepare the austenitic-based duplex lightweight steel according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Prepare the raw materials according to the chemical composition ratio of light steel, and then perform vacuum induction melting and casting to obtain steel ingots; S2: Reheat the steel ingot to the forging temperature, hold it at that temperature, and then forge it. Air cool or stack cool the forging billet to room temperature to obtain the forging billet. S3: The forging billet is reheated and then hot-rolled in multiple passes to the target thickness. After rolling, it is water-cooled to room temperature to obtain a hot-rolled plate. S4: The hot-rolled plate is cold-rolled in multiple passes to the target thickness to obtain austenitic dual-phase lightweight steel cold-rolled plate.

5. The preparation method according to claim 4, characterized in that, In step S1, the vacuum degree of the vacuum induction melting is ≤5×10-2P. a The casting temperature is 1500-1550℃.

6. The preparation method according to claim 4, characterized in that, In step S2, the initial forging temperature is 1050-1100℃, the holding time is 1-3h, and the final forging temperature is ≥850℃.

7. The preparation method according to claim 4, characterized in that, In step S3, the heating temperature is 1000℃-1100℃, and the holding time is 30-60min.

8. The preparation method according to claim 7, characterized in that, In step S3, the hot rolling temperature is 950℃-1050℃, and the total hot rolling reduction rate is 70%-85%.

9. The preparation method according to claim 8, characterized in that, In step S3, the water cooling rate is ≥20℃ / s.

10. The preparation method according to claim 4, characterized in that, In step S4, the total reduction rate of the cold rolling is 75%-85%.

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