Fe-mn-al-c light weight austenitic steel, and preparation method and application thereof

Abstract

The application provides a Fe-Mn-Al-C series light-weight austenitic steel and a preparation method and application thereof, and belongs to the technical field of metallurgical materials. The Fe-Mn-Al-C series light-weight austenitic steel plate and the manufacturing method thereof significantly improve the strength through a twinning and dislocation mechanism; the alloy composition is designed through regulation and control; a multi-stage thermal mechanical treatment strategy is adopted; the compression ratio and the rolling temperature are adjusted through on-line solid solution process; high-density dislocations and twins are introduced into the austenitic matrix; and the strengthening effect of nanoscale precipitates is combined, so that the synergistic improvement of high strength, high toughness and light weight is realized. The application is suitable for the light-weight austenitic steel plate with a medium-thickness specification of 14-35 mm and the manufacturing method thereof.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, specifically relating to a Fe-Mn-Al-C lightweight austenitic steel, its preparation method, and its application. Background Technology

[0002] In the process of socio-economic development, the massive consumption of energy has led to numerous environmental problems. To solve these problems, two common approaches are adopted: first, replacing traditional fuels with clean energy; and second, reducing the weight of transportation equipment to decrease fuel consumption and pollution. Therefore, lightweighting of transportation equipment has become a future development trend. Fe-Mn-Al-C lightweight steel is a new type of material that has emerged under these circumstances. It reduces the density of steel by adding the lightweight element Al, and then obtains a single austenitic structure and improves the strength of the steel by adding austenite-stabilizing elements Mn and C. It is a high-performance new steel with broad application prospects. However, due to the large addition of Al and C, it is prone to forming brittle phases within a certain temperature range. κ -carbide.

[0003] One existing technology provides a method for preparing Fe-Mn-Al-C series low-density thin-gauge steel plates with a yield strength ≥1000MPa, but its low-temperature impact strength and high toughness are insufficient. Another existing technology provides a method for preparing low-density medium plates with a yield strength of 460MPa, but its strength and lightweight effect are insufficient. Therefore, it is necessary to solve the problem of "easy precipitation" in existing Fe-Mn-Al-C series lightweight austenitic steel plates. κ - Carbides cause defects such as deterioration of toughness, insufficient low-temperature impact performance and poor synergy with lightweighting. Summary of the Invention

[0004] The purpose of this invention is to provide a Fe-Mn-Al-C lightweight austenitic steel, its preparation method, and its applications. The Fe-Mn-Al-C lightweight austenitic steel provided by this invention is less prone to precipitation. κ - Carbides combine low density, high and low temperature impact strength, and high toughness.

[0005] To achieve the objectives of this invention, the following technical solutions are provided: A Fe-Mn-Al-C series lightweight austenitic steel, wherein the Fe-Mn-Al-C series lightweight austenitic steel comprises the following elements in mass percentage: Mn 28~32%, Al 8.60~9.20%, C 0.90~1.05%, Si ≤0.50%, P ≤0.010%, S≤0.005%, Cr ≤0.50%, Ni ≤0.30%, Mo ≤0.30%, Nb ≤0.10%, O ≤20ppm, N ≤50ppm, H ≤5ppm, with the remainder being Fe and unavoidable impurities; The mass ratio of Mn to Al is 3.04~3.72; the mass ratio of Mn to C is 26.67~35.56; and the mass ratio of Al to C is 8.19~10.22. The microstructure of the lightweight austenitic steel is a single-phase austenitic matrix, with κ-carbides, deformation twins and dislocations dispersed in the single-phase austenitic matrix.

[0006] Preferably, the mass ratio of Mn to Al in the lightweight austenitic steel is 3.47 to 3.72; the mass ratio of Mn to C is 30.02 to 35.56; and the mass ratio of Al to C is 9.05 to 10.22.

[0007] Preferably, the twinning integral of the Fe-Mn-Al-C lightweight austenitic steel is 10-30%, and the dislocation density is 8.3 × 10⁻⁶. 14 ~6.6×10 15 m -2 .

[0008] This invention also provides a method for preparing the Fe-Mn-Al-C lightweight austenitic steel described in the above technical solution, comprising the following steps: According to the elemental composition of Fe-Mn-Al-C lightweight austenitic steel described in the above technical solution, the metal raw materials are smelted and cast to obtain steel billets; The steel billet is heated for heat treatment to obtain a heat-treated steel billet; The hot-rolled steel billet is then hot-rolled to obtain a hot-rolled steel billet; The hot-rolled steel billet is subjected to solution treatment to obtain the Fe-Mn-Al-C series lightweight austenitic steel.

[0009] Preferably, the heat treatment method is a gradient heating, which includes the following steps in sequence: 500~550℃, holding for 60~80min; 1000~1050℃, holding for 30~60min; 1150~1200℃, holding for 100~150min; 1200~1210℃, holding for 20~30min.

[0010] Preferably, the initial rolling temperature of the hot rolling is 1040~1150℃, and the final rolling temperature is 940~970℃; the hot rolling is a multi-pass hot rolling deformation, with 9~12 rolling passes and a cumulative deformation of 75~90%.

[0011] Preferably, the solution treatment method is water quenching; the water inlet temperature is 920~950℃, and the water outlet temperature is ≤250℃.

[0012] Preferably, the operation time from the end of hot rolling to solution treatment is 15-20 seconds.

[0013] The present invention also provides the application of the Fe-Mn-Al-C lightweight austenitic steel described in the above technical solution or the Fe-Mn-Al-C lightweight austenitic steel prepared by the above technical solution preparation method in automobile, ship and submarine structural components or high-speed train bodies.

[0014] This invention provides a Fe-Mn-Al-C series lightweight austenitic steel, which comprises the following elements in mass percentage: Mn 28~32%, Al 8.60~9.20%, C 0.90~1.05%, Si ≤0.50%, P≤0.010%, S ≤0.005%, Cr ≤0.50%, Ni ≤0.30%, Mo ≤0.30%, Nb ≤0.10%, O ≤20ppm, N≤50ppm, H ≤5ppm, with the remainder being Fe and unavoidable impurities; the mass ratio of Mn to Al is 3.04~3.72; the mass ratio of Mn to C is 26.67~35.56; and the mass ratio of Al to C is 8.19~10.22. This invention significantly reduces the density of austenitic steel by optimizing alloy design and introducing high levels of Mn and Al into the austenitic matrix. Simultaneously, it utilizes the solid solution strengthening effect of C to further enhance low-temperature impact strength. The key element mass ratios are controlled as follows: Mn / Al = 3.04~3.72, Mn / C = 26.67~35.56, and Al / C = 8.19~10.22. This ratio design stabilizes the austenitic matrix structure and provides thermodynamic and kinetic conditions for the formation of high-density defects.

[0015] This invention also provides a method for preparing Fe-Mn-Al-C lightweight austenitic steel. This invention employs a multi-stage thermomechanical treatment strategy, using controlled rolling and cooling, and online solution treatment processes to adjust the compression ratio and rolling temperature, introducing high-density dislocations and twins into the austenitic steel. The resulting lightweight austenitic steel plate exhibits significant microstructural characteristics: a twin integral of 10%–30%, and a dislocation density as high as 8.3 × 10⁻⁶. 14 ~6.6×10 15 m -2High-density dislocations and twins constitute the core of the strengthening mechanism. During stress, twin boundaries can hinder dislocation movement through dislocation cutting and dislocation pile-up, while the interaction between high-density dislocations further enhances the suppression effect on the slip system through dislocation entanglement and pinning. The results of the embodiments of this invention show that the yield strength of lightweight austenitic steel is increased to 600~900 MPa, and the tensile strength reaches 850~1050 MPa. Simultaneously, this steel plate also possesses excellent comprehensive properties: density ≤6.8 g / cm³. 3 It meets the requirements for lightweighting; the elongation is maintained at 30%~50%, and the impact energy is ≥80 J in the low temperature range of -40℃ to -196℃, achieving synergistic optimization of strength, toughness and lightweighting.

[0016] The Fe-Mn-Al-C lightweight austenitic steel provided by this invention not only possesses excellent strength-toughness matching but also exhibits good formability and fatigue resistance, making it widely applicable in automotive lightweighting, ship and submarine structural components, and other fields with stringent material performance requirements. The preparation method of this invention achieves a synergistic improvement in both high strength and high toughness while ensuring material lightweighting, providing a new technical approach for the design and development of advanced lightweight materials. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a line graph showing the process parameter control of the gradient heating heat treatment method according to an embodiment of the present invention; Figures 2-5 Line graph showing the control parameters for the coordinated regulation of process, microstructure, and properties of lightweight austenitic steel plates; Figure 6 Online solution-treated XRD images of lightweight steel plates with different compositions undergoing temperature-controlled rolling processes at both high and low temperatures. Figure 7 Temperature-controlled rolling of lightweight steel plates with different compositions under both high-temperature and low-temperature processes - online solution-treated OM microstructure; Figure 8 Average grain size of online solid solution microstructure during temperature-controlled rolling of lightweight steel plates with different compositions under both high-temperature and low-temperature processes; Figure 9 Online TEM and SAED images of the microstructure and structure of lightweight steel plates with different compositions during rolling; Figure 10Dislocation density in online solid solution state during rolling of lightweight steel plates with different compositions. Detailed Implementation

[0019] This invention provides a Fe-Mn-Al-C series lightweight austenitic steel, wherein the Fe-Mn-Al-C series lightweight austenitic steel comprises the following elements in mass percentage: Mn 28~32%, Al 8.60~9.20%, C 0.90~1.05%, Si ≤0.50%, P≤0.010%, S ≤0.005%, Cr ≤0.50%, Ni ≤0.30%, Mo ≤0.30%, Nb ≤0.10%, O ≤20ppm, N≤50ppm, H ≤5ppm, with the remainder being Fe and unavoidable impurities; The mass ratio of Mn to Al is 3.04~3.72; the mass ratio of Mn to C is 26.67~35.56; and the mass ratio of Al to C is 8.19~10.22. The microstructure of the lightweight austenitic steel is a single-phase austenitic matrix, with κ-carbides, deformation twins and dislocations dispersed in the single-phase austenitic matrix.

[0020] In this invention, the Fe-Mn-Al-C lightweight austenitic steel comprises 28-32% Mn, which can be 29%, 30%, or 31% in specific embodiments. In this invention, Mn serves as a key stabilizing element in the austenitic matrix, reducing stacking fault energy and expanding... γ Phase region and suppression κ The tendency of carbides to precipitate at grain boundaries provides a thermodynamic basis for obtaining a uniform and stable austenitic microstructure. Their solid solution in the austenitic lattice can significantly enhance matrix strength and work hardening ability, promote the formation of multi-level twins and high-density dislocation structures during deformation, thereby synergistically optimizing the strength-ductility balance of the material. However, excessively high Mn content increases the difficulty of hot working and adversely affects weldability, corrosion resistance, and production costs. Therefore, precisely controlling the Mn content within the range of 28-32% can effectively balance austenitic microstructure stability, excellent comprehensive mechanical properties, and the feasibility of industrial manufacturing.

[0021] In this invention, the Fe-Mn-Al-C lightweight austenitic steel comprises 8.60-9.20% Al, which can be 8.70%, 8.80%, 8.90%, or 9.10% in specific embodiments. In this invention, Al, as a key alloying design element, plays a multi-dimensional role in the fully austenitic lightweight steel. It significantly reduces material density by replacing iron atoms to induce lattice distortion, making it a core contributing element for achieving lightweighting. Simultaneously, Al can increase stacking fault energy, regulate austenite stability, and help maintain microstructural stability during deformation. Furthermore, Al improves matrix strength through solid solution strengthening, and its dense oxide film on the surface can improve the material's high-temperature oxidation resistance and serve as a major source of corrosion resistance and its underlying mechanism. However, excessively high Al content will promote short-range ordered structures and even... κ The precipitation of brittle phases severely impairs the toughness and ductility of materials; it also increases the viscosity of molten steel and enhances the deformation resistance during hot working. Therefore, precisely controlling the Al content within the range of 8.60% to 9.20% can synergistically optimize lightweighting, austenite stability, and overall mechanical properties.

[0022] In this invention, the Fe-Mn-Al-C lightweight austenitic steel comprises 0.90~1.05% C, which can be 0.95%, 1.00%, 1.03%, or 1.04% in specific embodiments. In this invention, C, as a key interstitial alloying element, plays a multi-scale regulatory role in the fully austenitic lightweight steel. It provides a core guarantee for obtaining a room-temperature fully austenitic microstructure by significantly reducing stacking fault energy, improving the stability of the austenitic phase, and expanding its thermodynamic existence range. Simultaneously, C interstitial solid solution can produce a strong strengthening effect, significantly improving the matrix strength and work hardening capacity. During deformation, C promotes nanotwin formation and delays dynamic recovery, synergistically improving uniform elongation and tensile strength. However, excessively high C content will exacerbate the tendency for brittle κ phase precipitation at grain boundaries, reducing plasticity and toughness; it also increases the risk of macroscopic segregation, deteriorates the compositional uniformity of continuously cast billets, and increases hot cracking sensitivity during hot rolling due to the reduced solidus temperature. Therefore, by precisely controlling the C content within the range of 0.90~1.05%, the optimal balance between austenitic stability, high strength-high plasticity matching, and good processing performance can be achieved.

[0023] In this invention, the Fe-Mn-Al-C lightweight austenitic steel comprises Si ≤0.50%, preferably 0.10~0.45%, and in specific embodiments, it can be 0.15%, 0.23%, or 0.32%. In this invention, Si is used as an auxiliary alloying element, effectively improving the matrix strength through solid solution strengthening, and can, to a certain extent, suppress… κThe tendency for carbide precipitation is observed. However, excessively high Si content will worsen the high-temperature plasticity during hot rolling, exacerbate the adhesion of surface iron oxide scale, and hinder surface quality control of hot-rolled plates. Therefore, its content is limited to ≤0.50% to balance strength and processing performance.

[0024] In this invention, the Fe-Mn-Al-C lightweight austenitic steel contains P ≤0.010%, preferably 0.003~0.008%, and in specific embodiments, it can be 0.005% or 0.007%. P, as a common residual element in this invention, can impair the plasticity of the weld heat-affected zone, increase weld crack susceptibility, and adversely affect corrosion resistance. Therefore, in lightweight high-alloy steel, it must be strictly limited as a harmful impurity, with its content controlled below ≤0.010% to ensure the material's toughness, weldability, and overall service performance.

[0025] In this invention, the Fe-Mn-Al-C lightweight austenitic steel contains sulfur (S) ≤0.005%, preferably 0.001~0.003%, and in specific embodiments, it can be 0.002%. S, as a harmful impurity element in steel, often combines with Mn to form ductile MnS inclusions. During hot rolling, these inclusions extend along the rolling direction, becoming microcrack initiation sources and propagation channels, significantly reducing the material's transverse toughness, fatigue performance, and forming limit. Furthermore, S deteriorates weldability, increases hot cracking tendency, and impairs corrosion resistance. Therefore, in lightweight steel, S must be strictly controlled as a harmful element, with its content limited to ≤0.005% to ensure high purity, excellent toughness, and service reliability of the material.

[0026] In this invention, the twinning integral of the Fe-Mn-Al-C lightweight austenitic steel is 10-30%, and the dislocation density is 8.3 × 10⁻⁶. 14 ~6.6×10 15 m -2 .

[0027] In this invention, the mass ratio of Mn to Al in the Fe-Mn-Al-C lightweight austenitic steel is 3.47~3.72; the mass ratio of Mn to C is 30.02~35.56; and the mass ratio of Al to C is 9.05~10.22. This invention controls the Mn / Al ratio to be 3.04~3.72 to regulate stacking fault energy and suppress dislocation degree recovery; the Mn / C ratio to be 26.67~35.56 optimizes carbon solid solution and strengthens dislocation pinning; and the Al / C ratio to be 8.19~10.22 refines grains, promotes twin nucleation, and further enhances toughness.

[0028] In this invention, the Fe-Mn-Al-C lightweight austenitic steel has a yield strength of 600~900 MPa, a tensile strength of 850~1050 MPa, and a density ≤6.8 g / cm³. 3 The elongation is 30%~50%, and the impact energy in the range of -40℃~-196℃ is ≥80 J. This invention also provides a method for preparing the Fe-Mn-Al-C lightweight austenitic steel described in the above technical solution, comprising the following steps: According to the elemental composition of Fe-Mn-Al-C lightweight austenitic steel described in the above technical solution, the metal raw materials are smelted and cast to obtain steel billets; The steel billet is heated for heat treatment to obtain a heat-treated steel billet; The hot-rolled steel billet is then hot-rolled to obtain a hot-rolled steel billet; The hot-rolled steel billet is subjected to solution treatment to obtain the Fe-Mn-Al-C series lightweight austenitic steel.

[0029] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0030] In this invention, the heat treatment method is a gradient heating, sequentially including: 500~550℃, holding for 60~80 min; 1000~1050℃, holding for 30~60 min; 1150~1200℃, holding for 100~150 min; 1200~1210℃, holding for 20~30 min; in a specific embodiment, it can be 513℃, holding for 60~80 min; 1010℃, holding for 32 min; 1193℃, holding for 100~80 min. min; 1207℃, hold for 26 min; the present invention does not have a special limitation on the heating rate of each stage; in a specific embodiment, the heating rate from 500~550℃ to 1000~1050℃ is 10~12℃ / min; the heating rate from 1000~1050℃ to 1150~1200℃ is 4~6℃ / min; the heating rate from 1150~1200℃ to 1200~1210℃ is 4~6℃ / min.

[0031] In this invention, the initial rolling temperature of the hot rolling is 1040~1150℃, and in specific embodiments it can be 1050, 1100, 1120℃, 1130℃, 1135℃, 1140℃ or 1145℃; the final rolling temperature is 940~970℃, and in specific embodiments it can be 944, 953 or 969℃; the hot rolling is a multi-pass hot rolling deformation, with 9~12 rolling passes and a cumulative deformation of 75~90%, and in specific embodiments it can be 78%, 80%, 82%, 85% or 88%.

[0032] In this invention, the solution treatment is water quenching; the water immersion temperature is 920~950℃, and in specific embodiments it can be 923, 929, 933 or 950℃; the water outlet temperature is ≤250℃, preferably 220~240℃, and in specific embodiments it can be 223, 228 or 230℃.

[0033] In this invention, the operation time from the end of hot rolling to solution treatment is 15-20 seconds, and in specific embodiments it can be 16, 17, 18, or 19 seconds. By controlling the final rolling temperature (940-970℃) and the water immersion temperature (920-950℃) within a specific process window, this invention promotes austenite recrystallization to form a uniform fine-grained structure. The rapid cooling of 15-20 seconds effectively suppresses κ-carbide precipitation, while simultaneously increasing the twin nucleation rate (volume fraction 10%-30%) and dislocation density (8.3 × 10⁻⁶). 14 ~6.6×10 15 m -2 Through the synergistic strengthening mechanism of the two, a low material density (≤6.8 g / cm³) was achieved. 3 Synergistic optimization of high strength (yield strength 600~900MPa, tensile strength 850~1050MPa), high toughness (impact energy ≥80J at -40℃~-196℃) and good plasticity (elongation 30%~50%).

[0034] The present invention also provides the application of the Fe-Mn-Al-C lightweight austenitic steel described in the above technical solution or the Fe-Mn-Al-C lightweight austenitic steel prepared by the preparation method described in the above technical solution in automobile, ship and submarine structural components or high-speed train bodies.

[0035] To further illustrate the present invention, the Fe-Mn-Al-C lightweight austenitic steel, its preparation method, and its application provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1 Steel billet preparation: The alloy composition was prepared according to the following mass percentages: Mn: 29.63%, Al: 8.74%, C: 0.95%, Si: 0.32%, P: 0.008%, S: 0.003%, Cr: 0.25%, Ni: 0.15%, Mo: 0.12%, Nb: 0.092%, [O]: 15ppm, [N]: 35ppm, [H]: 3ppm, with the remainder being Fe and unavoidable impurities. The mass ratios of key elements were Mn / Al = 3.39, Mn / C = 31.19, and Al / C = 9.20. The raw materials were melted in a vacuum induction furnace according to the above proportions and then cast into steel billets with a thickness of 120mm.

[0037] Steel billet heating: according to Figure 1 The resulting steel billet was heat-treated by gradient heating as shown.

[0038] Hot rolling process: After heat treatment, hot rolling is carried out. The initial rolling temperature is 1120℃, and the final rolling temperature is as shown in Table 1. Figure 2 The rolling process is set to 10 passes, with a cumulative deformation of 85% and a final rolling thickness of 20mm.

[0039] Solution treatment process: Within 18 seconds after final rolling, the billet is sent to the cooling device, and the water inlet temperature is as per Table 1 and... Figures 2-5 Set and control the outlet water temperature to 220℃ to complete online solid solution treatment.

[0040] Table 1. Parameter settings for coordinated control of process, microstructure, and properties of Fe-Mn-Al-C lightweight austenitic steel.

[0041] As shown in Table 1, the present invention employs a multi-stage thermomechanical treatment strategy, which involves controlled rolling and cooling, online solution treatment, and adjustment of compression ratio and rolling temperature to introduce high-density dislocations and twins into the material. Through the twinning and dislocation mechanism, high-strength lightweight austenitic steel plates are obtained.

[0042] Specifically, the coordinated control of final rolling temperature and water immersion temperature is the core of achieving the balance of "strength-toughness-plasticity". Its essence is the directional evolution of microstructure. Under low-temperature final rolling ≤900℃ and low water immersion temperature ≤880℃, austenite recrystallization is insufficient, and dislocations accumulate in large quantities in the non-recrystallized regions, with a dislocation density reaching 8.3×10. 14 ~6.6×10 15 m -2 Furthermore, localized stress concentration easily induces microcracks. The atomic diffusion rate is low in this temperature range, resulting in a small amount of... κ Carbides tend to segregate at grain boundaries, further deteriorating low-temperature toughness. When the final rolling temperature reaches 940~970℃ and the water immersion temperature reaches 920~950℃, the high temperature provides sufficient driving force for austenite recrystallization, forming uniform fine-grained austenite. At the same time, rapid cooling for 15~20s inhibits the diffusion of Al and C atoms, completely avoiding... κ - Carbide precipitation and twin nucleation rate are significantly improved under this process, with twin integral increasing from ≤10% to 22%~30%. High-density twins of 10%~30% not only hinder dislocation movement through twin boundaries to maintain tensile strength of 932~1019MPa, but also absorb crack propagation energy through twin interfaces, greatly improving low-temperature toughness. The optimal process windows are 940~970℃ for final rolling and 920~940℃ for water immersion, corresponding to impact energy exceeding 200J (-40℃) and 160J (-84℃), fully meeting the stringent requirements of transportation equipment for low-temperature toughness.

[0043] Example 2 The proportions of Mb, Al, and C in the steel billet were set according to the mass percentages in Table 2. The proportions of other elements were: Si: 0.32%, P: 0.008%, S: 0.003%, Cr: 0.25%, Ni: 0.15%, Mo: 0.12%, [O]: 15ppm, [N]: 35ppm, [H]: 3ppm, and the remainder being Fe and unavoidable impurities. The theoretical density was designed. The raw materials were melted in a vacuum induction furnace according to the following proportions and then cast into steel billets with a thickness of 120mm.

[0044] Steel billet heating: according to Figure 1 The resulting steel billet was heat-treated by gradient heating as shown.

[0045] Hot rolling process: After heat treatment, hot rolling is carried out. The initial rolling temperature is 1120℃, the final rolling temperature is set according to Table 3, the rolling passes are 10, the cumulative deformation is 85%, and the final rolling thickness is 20mm.

[0046] Solution treatment process: Within 18 seconds after final rolling, the billet is sent into the cooling device. The water inlet temperature is set according to Table 3, and the water outlet temperature is controlled at 220℃ to complete the online solution treatment.

[0047] Table 2 Synergistic Regulation of Composition, Microstructure, and Properties of Lightweight Austenitic Steel Plates

[0048] As shown in Table 2, the increase in Al and C content from Q1 (Al 8.60%, C 0.95%) to Q3 (Al 9.50%, C 1.05%) increased the theoretical density from 6.87 g / cm³. 3 Reduced to 6.77 g / cm³ 3 This achieves a lightweight upgrade, but the Al / C ratio increases from 9.05 (Q1) to 9.05 (Q3, calculated value 9.50 / 1.05≈9.05), approaching the upper limit (8.19~10.22), while the Mn / Al ratio decreases from 3.37 (Q1) to 3.05 (Q3), approaching the lower limit (3.04~3.72), and the stacking fault energy decreases accordingly to 20 mJ / m. 2 The critical value is κ - Carbide precipitation provides thermodynamic conditions.

[0049] Table 3 Actual process parameters for temperature-controlled rolling and online solution treatment of lightweight austenitic steel plates.

[0050] Table 4 Actual Mechanical Properties of Lightweight Austenitic Steel Plates

[0051] Figure 6XRD images of light steel plates with different compositions undergoing temperature-controlled rolling and online solution treatment under two processes: high temperature and low temperature. Among them, (a) is Q1 high temperature final rolling-into-water; (b) is Q2 high temperature final rolling-into-water; (c) is Q3 high temperature final rolling-into-water; (d) is Q1 low temperature final rolling-into-water; (e) is Q2 low temperature final rolling-into-water; and (f) is Q3 low temperature final rolling-into-water.

[0052] Figure 7 The images show the online solution-treated OM microstructure of lightweight steel plates with different compositions, produced by temperature-controlled rolling and low-temperature processes. Among them, (a) is Q1 high-temperature final rolling-into-water; (b) is Q2 high-temperature final rolling-into-water; (c) is Q3 high-temperature final rolling-into-water; (d) is Q1 low-temperature final rolling-into-water; (e) is Q2 low-temperature final rolling-into-water; and (f) is Q3 low-temperature final rolling-into-water.

[0053] Figure 8 Average grain size of online solid solution microstructure during temperature-controlled rolling of lightweight steel plates with different compositions under both high-temperature and low-temperature processes.

[0054] Figure 9 TEM and SAED images of the microstructure and solid solution state of lightweight steel plates with different compositions during rolling; where (a) is Q1 high temperature final rolling-into-water; (b) is Q2 high temperature final rolling-into-water; (c) is Q3 high temperature final rolling-into-water; (d) is Q1 low temperature final rolling-into-water; (e) is Q2 low temperature final rolling-into-water; and (f) is Q3 low temperature final rolling-into-water.

[0055] As shown in the figure above, the microstructure of the three materials remained unchanged, consisting of austenitic structure with annealed twins. Under high-temperature rolling conditions, both grain and annealed twin sizes increased, and no κ carbide precipitation was observed. This is because κ carbide is a nanoscale precipitate, so its microstructure change is not significant. Under different final rolling temperatures, it can be observed that lowering the final rolling temperature refines the grains, which is one reason for the improved material strength. However, as the final rolling temperature increases, the precipitation of κ carbide decreases, and its morphology changes accordingly, affecting not only the material's strength but also its toughness.

[0056] Specifically, in the embodiments of the present invention (Q1-1, Q1-2, Q2-1), high-temperature final rolling (944~964℃) and high water immersion temperature (921~929℃) are used. The high temperature provides sufficient driving force for austenite recrystallization, forming a fine-grained structure of 11.8~12.8μm. Figure 8 Rapid cooling (immersion in water to ≤250℃) for 15~20s inhibits Al and C atom diffusion (diffusion coefficient decreases exponentially with decreasing temperature), XRD Figure 6 none κ - Carbide diffraction peaks; TEM observation revealed only an austenitic matrix and 20%–25% twinning, with a high dislocation density (3.2 × 10⁻⁶).15 ~3.8×10 15 m -2 ,like Figure 10 The synergistic twin boundaries achieve a balance between strength and toughness, corresponding to Rp0.2 594~622MPa and KV2 171~208J at -40℃ in Table 4; while the comparative examples (Q2-2, Q3-1, Q3-2) have grain coarsening to 13.3~14.5μm due to incomplete recrystallization caused by the final rolling temperature being reduced to 902~927℃ and the water immersion temperature being as low as 874~906℃. Figure 8 Furthermore, the low temperature prolongs the atomic diffusion time, and the enrichment of Al-C in Q3 (Al 9.50%, C 1.05%) induces amplitude-modulated decomposition, precipitating 10~30nm intracrystalline dispersed κ-carbides and 50~100nm coarse κ-carbides at grain boundaries. Figure 9 f), the former increases Rp0.2 to 726~797MPa through dislocation pinning, while the latter becomes a crack initiation source, causing KV2 at -40℃ to drop sharply to 40~81J; Depend on Figure 10 It can be seen that, except for the Q3 low-temperature rolled lightweight steel plate, the matrix structure of lightweight steel plates with different compositions is all austenite. The Q3 low-temperature rolled lightweight steel plate contains a small amount of finely dispersed κ carbides in the matrix, which is consistent with the XRD image results. Comparing Q1 and Q3 lightweight steel plates, combined with TEM microstructure analysis, under high-temperature final rolling conditions, the increase of Al and C elements greatly promotes the precipitation of the second-phase κ carbides, especially the large-sized κ carbides at the grain boundaries, which deteriorates the plasticity and toughness. This is because the κ carbides are produced by amplitude modulation decomposition, that is, the enrichment effect of Al and C elements. The number of dislocations and dislocation lines in lightweight steel plates under high-temperature rolling conditions is much greater than that under low-temperature rolling conditions. This is because during low-temperature rolling, the lightweight steel plates need to undergo a warming treatment after rolling and widening. During the warming treatment, the temperature of the lightweight steel plates is about 1000℃ or higher. At this temperature, the lightweight steel plates will undergo recovery recrystallization behavior, which consumes a certain number of dislocations, thereby improving the strength.

[0057] Example 3 Steel billet preparation: The alloy composition was prepared according to the following mass percentages: Mn: 29.63%, Al: 8.74%, C: 0.95%, Si: 0.32%, P: 0.008%, S: 0.003%, Cr: 0.25%, Ni: 0.15%, Mo: 0.12%, [O]: 15ppm, [N]: 35ppm, [H]: 3ppm, with the remainder being Fe and unavoidable impurities. The mass ratios of key elements were Mn / Al = 3.39, Mn / C = 31.19, and Al / C = 9.20. The raw materials were melted in a vacuum induction furnace according to the above proportions and then cast into steel billets with a thickness of 120mm.

[0058] Steel billet heating: according to Figure 1The resulting steel billet was heat-treated by gradient heating as shown.

[0059] Hot rolling process: After heat treatment, hot rolling is carried out with an initial rolling temperature of 1120℃, a final rolling temperature of 952℃, 10 rolling passes, a cumulative deformation of 85%, and a final rolling thickness of 20mm.

[0060] Solution treatment process: Within 18 seconds after final rolling, the billet is sent into the cooling device with an inlet water temperature of 933℃ and an outlet water temperature of 220℃ to complete the online solution treatment.

[0061] Performance testing: The density of this steel plate is 6.78 g / cm³. 3 Yield strength 636 MPa, tensile strength 963 MPa, elongation 54%, impact energy at -40℃ 254 J, impact energy at -84℃ 191 J, twin integral 28%, dislocation density 5.8 × 10⁻⁶ 15 m -2 No κ-carbide precipitation was observed.

[0062] Example 4 Steel billet preparation: The alloy composition was prepared according to the following mass percentages: Mn: 30.50%, Al: 8.92%, C: 1.02%, Si: 0.41%, P: 0.007%, S: 0.004%, Cr: 0.30%, Ni: 0.20%, Mo: 0.18%, [O]: 18ppm, [N]: 42ppm, [H]: 4ppm, with the remainder being Fe and unavoidable impurities. The mass ratios of the key elements were Mn / Al = 3.42, Mn / C = 30.88, and Al / C = 8.75. The raw materials were melted in a vacuum induction furnace according to the above proportions and then cast into steel billets with a thickness of 130mm.

[0063] Steel billet heating: according to Figure 1 The resulting steel billet was heat-treated by gradient heating as shown.

[0064] Hot rolling process: initial rolling temperature 1135℃, final rolling temperature 949℃, 11 rolling passes, cumulative deformation 82%, final rolling thickness 25mm.

[0065] Solution treatment process: Immerse in water within 16 seconds after final rolling, with an immersion temperature of 929℃ and an outlet temperature of 235℃.

[0066] Performance testing: The density of this steel plate is 6.75 g / cm³. 3 Yield strength 649 MPa, tensile strength 977 MPa, elongation 55%, impact energy at -40℃ 230 J, impact energy at -84℃ 179 J, twin integral 26%, dislocation density 5.8 × 10⁻⁶ 15 m -2 The microstructure consists of uniform fine-grained austenite with twins.

[0067] Comparative Example 1 Steel billet preparation: Same as in Example 1.

[0068] Heating of steel billets: Same as in Example 1.

[0069] Hot rolling process: initial rolling temperature 1120℃, final rolling temperature 884℃, 10 rolling passes, cumulative deformation 85%, final rolling thickness 20mm.

[0070] Solution treatment process: Immerse in water within 18 seconds after final rolling, with an immersion temperature of 863℃ and an outlet temperature of 220℃.

[0071] Performance testing: The density of this steel plate is 6.81 g / cm³. 3 It has a yield strength of 897 MPa, a tensile strength of 1019 MPa, and an elongation of 57%, but its impact energy at -40℃ is only 94 J, and its impact energy at -84℃ is 51 J. It also has a twin integral of 8% and a dislocation density of 8.3 × 10⁻⁶. 14 m -2 A small amount of κ-carbide segregation occurs at the grain boundaries.

[0072] Comparative Example 2 Steel billet preparation: The alloy composition was prepared according to the following mass percentages: Mn: 29.0%, Al: 9.50%, C: 1.05%, Si: 0.35%, P: 0.009%, S: 0.004%, Cr: 0.28%, Ni: 0.22%, Mo: 0.16%, [O]: 16ppm, [N]: 45ppm, [H]: 3ppm, with the remainder being Fe and unavoidable impurities. The mass ratios of the key elements were Mn / Al = 3.05, Mn / C = 27.62, and Al / C = 9.05. The raw materials were melted in a vacuum induction furnace according to the above proportions and then cast into steel billets with a thickness of 120mm.

[0073] Heating of steel billets: Same as in Example 1.

[0074] Hot rolling process: initial rolling temperature 1013℃, final rolling temperature 902℃, 10 rolling passes, cumulative deformation 80%, final rolling thickness 22mm.

[0075] Solution treatment process: Immerse in water within 19 seconds after final rolling, with an immersion temperature of 874℃ and an outlet temperature of 240℃.

[0076] Performance testing: Density 6.77 g / cm³ 3 Yield strength 797 MPa, tensile strength 1004 MPa, elongation 47%, impact energy at -40℃ only 40 J, impact energy at -84℃ 26 J, 10~30 nm dispersed κ-carbides precipitated within the grains and coarse grain boundaries. κ - Carbide, twin integral 12%, dislocation density 3.1 × 10⁻⁶ 15 m-2 .

[0077] This invention successfully solves the problems of easy κ-carbide precipitation, insufficient low-temperature impact resistance, and poor synergy between strength and lightweight in existing Fe-Mn-Al-C lightweight austenitic steel plates by precisely controlling the alloy composition ratio and multi-stage thermomechanical treatment process. The optimized ratio of key elements Mn / Al = 3.04~3.72, Mn / C = 26.67~35.56, and Al / C = 8.19~10.22 stabilizes the austenitic matrix structure, providing thermodynamic and kinetic conditions for the formation of high-density defects. The process window of a final rolling temperature of 940~970℃ and a water immersion temperature of 920~940℃ promotes austenite recrystallization to form a uniform fine-grained structure. Rapid cooling of 15~20s effectively suppresses κ-carbide precipitation, while simultaneously increasing the twin nucleation rate (volume fraction 10%~30%) and dislocation density (8.3×10⁻⁶). 14 ~6.6×10 15 m -2 Through the synergistic strengthening mechanism of the two, a low material density (≤6.8 g / cm³) was achieved. 3 Synergistic optimization of high strength (yield strength 600~900MPa, tensile strength 850~1050MPa), high toughness (impact energy ≥80J at -40℃ to -196℃) and good plasticity (elongation 30%~50%).

[0078] Compared to existing technologies, the lightweight austenitic steel sheet of this invention maintains excellent overall performance in medium-thickness specifications (14~35mm), and its manufacturing process is simple and controllable, requiring no complex post-processing. Its good formability and fatigue resistance make it promising for applications in fields with stringent material performance requirements, such as automotive lightweighting, ship and submarine structural components, and high-speed train bodies, providing a new technical approach for the design and development of advanced lightweight materials. Further optimization of process parameters can be conducted to explore its performance in a wider range of specifications and under extreme service environments, expanding its application scenarios.

[0079] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A Fe-Mn-Al-C series lightweight austenitic steel, characterized in that, The Fe-Mn-Al-C lightweight austenitic steel comprises the following elements by mass percentage: Mn 28~32%, Al 8.60~9.20%, C 0.90~1.05%, Si ≤0.50%, P ≤0.010%, S ≤0.005%, Cr ≤0.50%, Ni ≤0.30%, Mo ≤0.30%, Nb ≤0.10%, O ≤20ppm, N ≤50ppm, H ≤5ppm, with the remainder being Fe and unavoidable impurities; The mass ratio of Mn to Al is 3.04~3.72; the mass ratio of Mn to C is 26.67~35.56; and the mass ratio of Al to C is 8.19~10.

22. The microstructure of the lightweight austenitic steel is a single-phase austenitic matrix, with κ-carbides, deformation twins and dislocations dispersed in the single-phase austenitic matrix.

2. The Fe-Mn-Al-C lightweight austenitic steel according to claim 1, characterized in that, The mass ratio of Mn to Al in the lightweight austenitic steel is 3.47~3.72; the mass ratio of Mn to C is 30.02~35.56; and the mass ratio of Al to C is 9.05~10.

22.

3. The Fe-Mn-Al-C lightweight austenitic steel according to claim 1 or 2, characterized in that, The twinning integral of the Fe-Mn-Al-C lightweight austenitic steel is 10-30%, and the dislocation density is 8.3 × 10⁻⁶. 14 ~6.6×10 15 m -2 .

4. The method for preparing the Fe-Mn-Al-C lightweight austenitic steel according to any one of claims 1 to 3, characterized in that, Includes the following steps: According to the elemental composition of the Fe-Mn-Al-C lightweight austenitic steel according to any one of claims 1 to 3, the metal raw materials are smelted and cast to obtain a steel billet; The steel billet is heated for heat treatment to obtain a heat-treated steel billet; The hot-rolled steel billet is then hot-rolled to obtain a hot-rolled steel billet; The hot-rolled steel billet is subjected to solution treatment to obtain the Fe-Mn-Al-C series lightweight austenitic steel.

5. The preparation method according to claim 4, characterized in that, The heat treatment method is a gradient heating, which includes the following steps in sequence: 500~550℃, holding for 60~80min; 1000~1050℃, holding for 30~60min; 1150~1200℃, holding for 100~150min; 1200~1210℃, holding for 20~30min.

6. The preparation method according to claim 4, characterized in that, The initial rolling temperature of the hot rolling is 1040~1150℃, and the final rolling temperature is 940~970℃; the hot rolling is a multi-pass hot rolling deformation, with 9~12 rolling passes and a cumulative deformation of 75~90%.

7. The preparation method according to claim 4, characterized in that, The solution treatment method is water quenching; the water inlet temperature is 920~950℃, and the water outlet temperature is ≤250℃.

8. The preparation method according to claim 4, characterized in that, The operation time from the end of hot rolling to solution treatment is 15~20s.

9. The application of the Fe-Mn-Al-C lightweight austenitic steel according to any one of claims 1 to 3 or the Fe-Mn-Al-C lightweight austenitic steel prepared by any one of claims 4 to 8 in automobile, ship and submarine structural components or high-speed train bodies.

Images