Fe-mn-al-c light weight austenitic hot-rolled steel strip and preparation method and application thereof

Abstract

The application provides a Fe-Mn-Al-C series light austenitic hot-rolled steel strip and a preparation method and application thereof, and belongs to the technical field of hot-rolled steel preparation. The Fe-Mn-Al-C series light austenitic hot-rolled steel strip prepared by the application has the following chemical components: Mn 20-25%, Al 6.8-8.5%, C 0.83-0.95%, Si≤1.0%, Mo≤1.0%, Cu≤1.0%, V≤0.1%, Ti≤0.1%, P≤0.02%, S≤0.005%, and the rest is iron and inevitable impurities; the preparation method comprises soaking treatment, hot rolling and online solid solution. By adjusting the components of the hot-rolled steel strip and controlling the process parameters, the application obtains a light austenitic hot-rolled steel strip with density 6.9≤ρ≤7.1 g / cm 3 and different thickness specifications, which has the advantages of light weight and high strength and plasticity, and improves the light weight level and forming reliability of the steel strip.

Description

Technical Field

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

[0002] With the automotive industry's increasing demands for lightweighting, safety, and environmental protection, high-performance hot-rolled steel strip has become a key material in the manufacture of automotive structural components. The automotive industry urgently needs hot-rolled steel strip that combines high strength, good formability, and low cost to meet the stringent requirements for comprehensive material performance in components such as chassis systems, suspension components, and crash barriers. Compared to cold-rolled steel, hot-rolled steel strip offers advantages such as shorter production processes, lower costs, and higher strength, making it particularly suitable for components with lower surface quality requirements but higher load-bearing requirements. However, traditional hot-rolled high-strength steel often experiences a significant decrease in plasticity and formability while increasing strength. In actual industrial production, there is a complex interaction between the addition of alloying elements and the control of hot-rolling process parameters. How to improve strength while avoiding toughness loss, how to balance precipitation strengthening and matrix plasticity, and how to precisely control the rolling and cooling processes to obtain a uniform and fine microstructure remain the core challenges currently facing the research and development of hot-rolled high-strength steel strip.

[0003] For example, one existing technology discloses a production process for thin-gauge hot-rolled pickled automotive structural steel R280VK, which successfully replaces cold-rolling with hot-rolling. However, it still falls under the category of conventional ferritic steel, with a low strength level and a yield strength of only 280-420 MPa, failing to achieve a synergistic improvement in lightweighting and high strength-ductility. Another existing technology discloses a 750 MPa-grade high-fatigue hot-rolled automotive steel and its preparation method. The density of this hot-rolled automotive steel is comparable to that of traditional high-strength steel, still belonging to the category of conventional high-strength steel mainly strengthened by precipitation and fine grains, failing to meet the requirements of lightweighting and ultra-high strength-ductility. Therefore, existing high-strength steels for automobiles still face common problems such as high density, incomplete austenitic microstructure, or insufficient strength-ductility balance. Especially in high-manganese steel, although it has high ductility potential, insufficient yield strength or complex process control restricts its high-performance lightweight application; while traditional high-strength steels that rely on precipitation strengthening often sacrifice ductility and fatigue performance. Summary of the Invention

[0004] The purpose of this invention is to provide a Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, its preparation method, and its application. The Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip prepared by this invention is fully austenitic, possessing the advantages of both lightweight and high plasticity.

[0005] To achieve the objectives of this invention, the following technical solutions are provided: A method for preparing Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip includes the following steps: According to the chemical composition of Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, the metal raw materials are melted and cast to obtain a billet; The cast billet is subjected to homogenization heat treatment to obtain homogenized steel billet; the temperature of the homogenization heat treatment is 1180~1220℃, and the holding time is 2~3h; The hot-rolled steel billet is subjected to hot rolling and online solution treatment to obtain the Fe-Mn-Al-C system lightweight austenitic hot-rolled steel strip; the initial rolling temperature of the hot rolling is 1050~1100℃, and the final rolling temperature is ≥980℃; the water immersion temperature of the online solution treatment is ≥950℃, and the water outlet temperature is ≤650℃. The chemical composition of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, by mass percentage, includes: Mn 20~25%, Al 6.8~8.5%, C 0.83~0.95%, Si≤1.0%, Mo≤1.0%, Cu≤1.0%, V≤0.1%, Ti≤0.1%, P≤0.02%, S≤0.005%, with the remainder being iron and unavoidable impurities; The density of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip is 6.9~7.1 g / cm³. 3 The thickness is 2.0~5.0mm.

[0006] Preferably, the chemical composition of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, by mass percentage, includes: Mn 20~25%, Al 6.8~8.5%, C 0.83~0.95%, Si 0.4~0.65%, Mo 0.4~0.5%, Cu 0.2~0.35%, V 0.05~0.09%, Ti 0.03~0.08%, P 0.003~0.01%, S 0.001~0.005%, with the remainder being iron and unavoidable impurities.

[0007] Preferably, the final rolling temperature of the hot rolling is 980~1030℃.

[0008] Preferably, the hot rolling is a multi-pass hot rolling deformation, with a total hot rolling reduction rate of ≥80%.

[0009] Preferably, the inlet water temperature for the online solid solution is 950~975℃, and the outlet water temperature is 510~650℃.

[0010] Preferably, the heating rate from preheating to the temperature required for the homogenization treatment is 40~50℃ / h.

[0011] Preferably, the online solution treatment further includes a winding process; the temperature of the winding process is 400~500℃.

[0012] The present invention also provides Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip prepared by the preparation method described in the above technical solution, wherein the rolled microstructure of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip has an austenite phase ratio of ≥99%.

[0013] Preferably, the thickness of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip is 3.5~5.0 mm.

[0014] The present invention also provides the application of the Fe-Mn-Al-C series lightweight austenitic hot-rolled steel strip described in the above technical solution in the manufacture of automotive structural parts.

[0015] This invention provides a method for preparing Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, comprising the following steps: melting metal raw materials according to the chemical composition of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, casting to obtain a billet; subjecting the billet to homogenization heat treatment to obtain a homogenized steel billet; the homogenization heat treatment temperature is 1180~1220℃, and the holding time is 2~3h; hot-rolling and online solution treatment of the homogenized steel billet to obtain the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip; the initial rolling temperature of the hot rolling is 1050~1100℃, and the final rolling temperature is ≥980℃; the water immersion temperature of the online solution treatment is ≥950℃, and the water outlet temperature is ≤650℃; the chemical composition of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, by mass percentage, includes: Mn 20~25%, Al 6.8~8.5%, C The Fe-Mn-Al-C series lightweight austenitic hot-rolled steel strip contains 0.83~0.95% Fe, Si≤1.0%, Mo≤1.0%, Cu≤1.0%, V≤0.1%, Ti≤0.1%, P≤0.02%, and S≤0.005%, with the remainder being iron and unavoidable impurities; the density of the Fe-Mn-Al-C series lightweight austenitic hot-rolled steel strip is 6.9~7.1 g / cm³. 3 The thickness is 2.0~5.0 mm. This invention prepares a material with a density of 6.9~7.1 g / cm³ by controlling the hot rolling process and steel strip composition. 3 The Fe-Mn-Al-C austenitic lightweight hot-rolled steel strip has a fully austenitic microstructure in the rolled state. During hot rolling, precise control of rolling temperature, deformation amount, and cooling path promotes dynamic recrystallization and grain refinement while suppressing harmful precipitation. While maintaining excellent plasticity, this steel strip achieves a significant increase in strength through twinning. Its high work hardening capacity ensures a good balance between strength and plasticity, resulting in comprehensive mechanical properties significantly superior to conventional austenitic lightweight automotive steel strips.

[0016] Specifically, in this invention, Mn serves as the primary austenite stabilizing element in the Fe-Mn-Al-C system of lightweight austenitic hot-rolled steel strip, ensuring a single austenitic phase at room temperature. The addition of Al significantly reduces the density of the hot-rolled steel strip, which is crucial for achieving lightweighting. C not only further stabilizes austenite but also forms a specific ratio with Al, effectively inhibiting the precipitation of κ-carbides and avoiding loss of plasticity and toughness. To further enhance overall performance, this invention adds Si, Mo, and Cu in limited quantities, improving strength through solid solution strengthening. The introduction of Cu also enhances corrosion resistance. Trace amounts of V and Ti are mainly used to form fine carbonitrides, pinning grain boundaries and inhibiting grain growth, thereby improving the material's strength and toughness. This invention sets the content of all elements within strict ranges, with P and S controlled at extremely low levels to minimize the adverse effects of impurity elements on grain boundary strength and toughness. Through the synergistic regulation of these multiple components, this invention achieves a significant reduction in density while ensuring the stability of the austenitic structure and high strength-ductility product, possessing excellent comprehensive mechanical properties and engineering application potential.

[0017] The hot rolling process of this invention includes homogenization heat treatment, hot rolling, and solution treatment. Homogenization heat treatment ensures uniform temperature between the core and surface of the cast billet, allowing alloying elements to be fully dissolved, the original as-cast microstructure to be fully austenitized, and providing a uniform temperature base for subsequent hot rolling. Hot rolling and online solution treatment can effectively suppress carbide precipitation and stabilize the austenitic microstructure. In addition, this invention also includes coiling treatment, which optimizes the microstructure and performance matching while ensuring coil quality, ultimately obtaining a hot-rolled steel coil with uniform microstructure and excellent performance. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is an optical microscope metallographic image of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip obtained in Example 1 of the present invention. Detailed Implementation

[0020] This invention provides a method for preparing Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, comprising the following steps: According to the chemical composition of Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, the metal raw materials are melted and cast to obtain a billet; The cast billet is subjected to homogenization heat treatment to obtain homogenized steel billet; the temperature of the homogenization heat treatment is 1180~1220℃, and the holding time is 2~3h; The hot-rolled steel billet is subjected to hot rolling and online solution treatment to obtain the Fe-Mn-Al-C system lightweight austenitic hot-rolled steel strip; the initial rolling temperature of the hot rolling is 1050~1100℃, and the final rolling temperature is ≥980℃; the water immersion temperature of the online solution treatment is ≥950℃, and the water outlet temperature is ≤650℃. The chemical composition of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, by mass percentage, includes: Mn 20~25%, Al 6.8~8.5%, C 0.83~0.95%, Si≤1.0%, Mo≤1.0%, Cu≤1.0%, V≤0.1%, Ti≤0.1%, P≤0.02%, S≤0.005%, with the remainder being iron and unavoidable impurities; The density of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip is 6.9~7.1 g / cm³. 3 The thickness is 2.0~5.0mm.

[0021] 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.

[0022] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes 20-25% Mn, and in specific embodiments, it can be 21, 22, 23, or 24%. In this invention, Mn serves as a key stabilizing element in the austenitic matrix, reducing stacking fault energy and expanding... c Phase region and suppression k 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 material's strength-ductility balance and corrosion resistance. However, excessively high Mn content will exacerbate solidification segregation, leading to inhomogeneity in the billet composition, and increasing edge crack sensitivity during hot rolling due to decreased thermal conductivity and increased coefficient of linear expansion. This invention precisely controls the Mn content within the range of 20-25%, effectively balancing austenitic microstructure stability, excellent comprehensive mechanical properties, and industrial-scale manufacturing feasibility.

[0023] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes 6.8% to 8.5% Al, which in specific embodiments can be 7.0%, 7.2%, 7.4%, 7.5%, 7.6%, or 8.2%. In this invention, Al, as a key alloying design element, plays a multi-dimensional role in the all-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 enhances matrix strength through solid solution strengthening, and its dense oxide film on the surface can improve the material's high-temperature oxidation resistance. However, excessively high Al content will promote the precipitation of short-range ordered structures and even brittle phases, severely impairing the material's toughness and ductility; it will also increase the viscosity of molten steel, worsen the fluidity during continuous casting, and increase deformation resistance in the hot working range. This invention precisely controls the Al content within the range of 6.8% to 8.5%, which can synergistically optimize the lightweighting effect, austenite stability, and comprehensive mechanical properties.

[0024] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes 0.83-0.95% C, which in specific embodiments can be 0.84, 0.87, 0.90, 0.92, or 0.93%. 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 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, worsens 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 0.83~0.95%, the optimal balance between austenitic stability, high strength-high plasticity matching, and good processing performance can be achieved.

[0025] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes Si ≤ 1.0%, preferably 0.4~0.65%, and in specific embodiments, it can be 0.49, 0.52, or 0.60%. In this invention, Si serves as an auxiliary alloying element, effectively enhancing the matrix strength through solid solution strengthening and, to some extent, suppressing the precipitation tendency of κ carbides. However, excessively high Si content will deteriorate high-temperature plasticity during hot rolling, exacerbate surface oxide scale adhesion, and be detrimental to the surface quality control of the hot-rolled plate. This invention limits its content to ≤ 1.0% to balance strength and processing performance.

[0026] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes Mo ≤ 1.0%, preferably 0.4~0.5%, and in specific embodiments, it can be 0.41, 0.43, 0.46, or 0.48%. In this invention, Mo, as an important microalloying element, effectively enhances the high-temperature strength of martensite through solid solution strengthening and significantly improves the material's corrosion resistance, especially pitting corrosion resistance. Its slow diffusion characteristics in austenite help suppress recrystallization during hot working and promote the formation of a finer microstructure. However, excessively high Mo content promotes the precipitation of brittle intermetallic compounds, significantly reducing the material's toughness and hot working performance, while also greatly increasing alloy costs. This invention strictly limits its content to ≤ 1.0% to balance corrosion resistance, strength, and economy.

[0027] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes Cu ≤ 1.0%, preferably 0.2~0.35%, and in specific embodiments, it can be 0.23, 0.25, 0.28, 0.29, or 0.32%. In this invention, Cu, as an alloying element, effectively enhances the matrix strength in lightweight steel through solid solution strengthening and significantly improves the material's resistance to atmospheric corrosion. However, excessively high Cu content will lower the solidus temperature, exacerbate surface hot brittleness during hot working, and may form a Cu-rich liquid phase leading to surface hot cracking. This invention limits its content to ≤ 1.0% to balance mechanical properties, corrosion resistance, and hot working performance.

[0028] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes V ≤ 0.1%, preferably 0.05~0.09%, and in specific embodiments, it can be 0.06, 0.07, or 0.08%. In this invention, V acts as a microalloying element, effectively improving material strength. Its fine precipitates pin austenite grain boundaries, inhibiting grain growth and contributing to refined final microstructure. Furthermore, the addition of V can slightly increase the recrystallization temperature, which is beneficial for microstructure control during high-temperature deformation. However, excessively high V content can lead to the formation of coarse carbonitrides, weakening toughness and potentially impairing weldability and surface quality. Therefore, its content is limited to ≤ 0.1% to achieve the optimal balance between fine-grain strengthening and toughness.

[0029] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes Ti ≤ 0.1%, preferably 0.03~0.08%, and in specific embodiments, it can be 0.04, 0.05, or 0.07%. In this invention, Ti, as a strong carbonitride forming element, effectively pins austenite grain boundaries by generating fine TiC, TiN, or Ti(C,N) precipitates, inhibiting grain coarsening during hot rolling and cooling, thereby achieving a significant grain refinement strengthening effect. However, excessively high Ti content will promote the formation of coarse TiN or TiC particles, which not only seriously impairs the material's toughness and fatigue performance but may also affect austenite stability by consuming dissolved carbon in the steel. Therefore, its content is strictly limited to ≤ 0.1% to fully utilize its positive effect on grain refinement while avoiding its adverse effects on toughness and microstructure stability.

[0030] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes P ≤ 0.02%, preferably 0.003~0.01%, and in specific embodiments, it can be 0.005, 0.007, or 0.008%. 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, it must be strictly limited as a harmful impurity in lightweight high-alloy steel. This invention controls the P content to below 0.020% to ensure the material's toughness, weldability, and overall service performance.

[0031] In this invention, the chemical composition of the lightweight austenitic hot-rolled steel strip, by mass percentage, includes S ≤ 0.005%, preferably 0.001~0.005%, and in specific embodiments, it can be 0.002, 0.003, or 0.004%. In this invention, 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 also deteriorates weldability, increases hot cracking tendency, and impairs corrosion resistance. Therefore, it must be strictly controlled as a harmful element in lightweight steel. This invention limits its content to below 0.005% to ensure high purity, excellent toughness, and service reliability of the material.

[0032] This invention constructs a stable all-austenitic phase field in the high-temperature rolling range by precisely controlling the Mn, Al, and C contents, and successfully obtains a phase field free from Mn, Al, and C at room temperature by combining controlled rolling and controlled cooling processes. k Carbides and d- The uniform austenitic structure of ferrite combines low density with high strength and ductility. Si, Mo, and Cu further enhance strength through solid solution strengthening, while V and Ti achieve grain boundary pinning and grain refinement through the precipitation of fine carbonitrides. Simultaneously, the extremely low P and S content effectively suppresses grain boundary embrittlement and inclusion damage, ensuring high toughness and excellent hot workability. The synergistic effect of multiple components achieves lightweight design while maintaining high strength, high toughness, and good processability.

[0033] This invention does not impose any special limitations on the smelting and casting of metal raw materials.

[0034] In this invention, the temperature of the homogenization heat treatment is 1180~1220℃, and in a specific embodiment it can be 1200℃; the holding time of the homogenization heat treatment is 2~3h. The heating rate from the preheating temperature of 700℃ to the temperature required for the homogenization heat treatment is 40~50℃ / h; the furnace time of the cast billet during the homogenization heat treatment is 6~8h, including the holding time of 2~3h for the homogenization heat treatment, and the remaining time is for preheating and heating.

[0035] In this invention, after obtaining a homogenized steel billet, the billet is subjected to hot rolling and online solution treatment to obtain the lightweight austenitic hot-rolled steel strip. In this invention, the initial rolling temperature of the hot rolling treatment is 1050~1100℃, and in specific embodiments it can be 1060, 1076, 1081, 1089, or 1095℃; the final rolling temperature is ≥980℃, preferably 980~1030℃, and in specific embodiments it can be 982, 1001, 1010, or 1020℃; the hot rolling treatment is a multi-pass hot rolling deformation, with a total hot rolling reduction rate ≥80%, preferably 80~95%.

[0036] In this invention, the inlet water temperature for the online solution treatment is ≥950℃, preferably 950~975℃, and in specific embodiments it can be 958, 960, 969 or 971℃; the outlet water temperature is ≤650℃, preferably 510~650℃, and in specific embodiments it can be 512, 531, 557, 583 or 615℃.

[0037] In this invention, the online solution treatment is followed by a winding process; the temperature of the winding process is 400~500℃, and in specific embodiments it can be 435, 458, 464 or 485℃.

[0038] This invention also provides Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip prepared by the preparation method described in the above technical solution. The rolled microstructure of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip is fully austenitic; the thickness is 2.0~5.0 mm, and in specific embodiments it can be 2.8, 3.5, or 4.3 mm; when the reduction rate is ≥80%, the yield strength of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip is ≥740 MPa, the tensile strength is ≥910 MPa, and the elongation is ≥30%. In a specific implementation, when the thickness of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip is 5 mm, the yield strength is 740~820 MPa, the tensile strength is 910~960 MPa, and the elongation is A... 50 ≥40%; with a thickness of 3.5mm, the yield strength is 830~850MPa, the tensile strength is 960~1020MPa, and the elongation A 50 ≥35%; with a thickness of 2.0 mm, the yield strength is 870~910 MPa, the tensile strength is 1030~1060 MPa, and the elongation A 50 ≥30%.

[0039] The present invention also provides the application of the Fe-Mn-Al-C series lightweight austenitic hot-rolled steel strip described in the above technical solution in the manufacture of automotive structural parts.

[0040] To further illustrate the present invention, the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, 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.

[0041] Examples 1-3 and Comparative Examples 1-3 The hot-rolled steel strip composition was prepared according to the mass percentages shown in Table 1, and then cast into a billet after being melted in a vacuum induction furnace. The smelted billet is placed in a walking beam furnace and heated uniformly from the preheating section at 700°C to the soaking section at a rate of 40~50°C / h, as shown in Table 2. The total time in the furnace is controlled at 6~8h, of which the soaking section lasts for 3h. Then, the billet is kept at this temperature for soaking and heat treatment to obtain the steel billet. After the billet exits the furnace, it is descaled by high-pressure water, and then rolled in multiple passes. The initial rolling temperature and final rolling temperature are controlled according to the parameters shown in Table 2. After rolling, it is immersed in water, and the water inlet temperature and outlet temperature are controlled according to the parameters shown in Table 2. It is rapidly cooled at a cooling rate of ≥30℃ / s. Finally, it is coiled according to the coiling temperature shown in Table 2 to obtain hot-rolled steel coils.

[0042] Table 1. Chemical composition of lightweight austenitic hot-rolled steel strips obtained in Examples 1-3 and Comparative Examples 1-3

[0043] Table 2. Rolling parameters of lightweight austenitic hot-rolled steel strips obtained in Examples 1-3 and Comparative Examples 1-3.

[0044] Test case Samples were taken from hot-rolled finished plates and room temperature uniaxial tensile tests were conducted according to GB / T 228.1-2021 to test the tensile properties of Fe-Mn-Al-C lightweight austenitic hot-rolled steel strips obtained in Examples 1-3 and Comparative Examples 1-3; density was measured using the water displacement method, and the results are shown in Table 3.

[0045] Table 3 Mechanical properties of lightweight austenitic hot-rolled steel strips obtained in Examples 1-3 and Comparative Examples 1-3

[0046] Figure 1 The image shows an optical microscope metallographic image of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip obtained in Example 1 of this invention. The microstructure is a single austenite. Furthermore, the density of the hot-rolled steel strip obtained in Example 1 of this invention is 6.9 ≤ r ≤7.1g / cm 3 .

[0047] As shown in Table 3, in Comparative Example 1, reducing the immersion temperature after hot rolling resulted in the inability to suppress the precipitation of brittle phases, leading to a sharp decrease in elongation. In Comparative Example 2, reducing the homogenization time before hot rolling prevented sufficient diffusion of alloying elements and composition homogenization, resulting in a sharp decrease in elongation and unstable tensile and yield strengths. In Comparative Example 3, reducing the content of Al and C elements led to a decrease in elongation, and both tensile and yield strengths decreased to varying degrees.

[0048] 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 method for preparing Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, characterized in that, Includes the following steps: According to the chemical composition of Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, the metal raw materials are melted and cast to obtain a billet. The cast billet is subjected to homogenization heat treatment to obtain homogenized steel billet; the temperature of the homogenization heat treatment is 1180~1220℃, and the holding time is 2~3h; The hot-rolled steel billet is subjected to hot rolling and online solution treatment to obtain the Fe-Mn-Al-C system lightweight austenitic hot-rolled steel strip; the initial rolling temperature of the hot rolling is 1050~1100℃, and the final rolling temperature is ≥980℃; the water immersion temperature of the online solution treatment is ≥950℃, and the water outlet temperature is ≤650℃. The chemical composition of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, by mass percentage, includes: Mn 20~25%, Al 6.8~8.5%, C 0.83~0.95%, Si≤1.0%, Mo≤1.0%, Cu≤1.0%, V≤0.1%, Ti≤0.1%, P≤0.02%, S≤0.005%, with the remainder being iron and unavoidable impurities; The density of the Fe-Mn-Al-C series lightweight austenitic hot-rolled steel strip is 6.9~7.1 g / cm³. 3 The thickness is 2.0~5.0mm.

2. The preparation method according to claim 1, characterized in that, The chemical composition of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip, by mass percentage, includes: Mn 20~25%, Al 6.8~8.5%, C 0.83~0.95%, Si 0.4~0.65%, Mo 0.4~0.5%, Cu 0.2~0.35%, V 0.05~0.09%, Ti 0.03~0.08%, P 0.003~0.01%, S 0.001~0.005%, with the remainder being iron and unavoidable impurities.

3. The preparation method according to claim 1, characterized in that, The final rolling temperature of the hot rolling is 980~1030℃.

4. The preparation method according to claim 1 or 3, characterized in that, The hot rolling process involves multiple passes of hot rolling deformation, with a total hot rolling reduction rate of ≥80%.

5. The preparation method according to claim 1, characterized in that, The inlet water temperature for the online solid solution treatment is 950~975℃, and the outlet water temperature is 510~650℃.

6. The preparation method according to claim 1, characterized in that, The heating rate from the preheating temperature of 700°C to the temperature required for the homogenization treatment is 40~50°C / h.

7. The preparation method according to claim 1, characterized in that, The online solution treatment also includes a winding process; the temperature of the winding process is 400~500℃.

8. The Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The rolled microstructure of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip has an austenite phase ratio of ≥99%.

9. The Fe-Mn-Al-C series lightweight austenitic hot-rolled steel strip according to claim 7, characterized in that, The thickness of Fe-Mn-Al-C series lightweight austenitic hot-rolled steel strip is 3.5~5.0mm.

10. The application of the Fe-Mn-Al-C lightweight austenitic hot-rolled steel strip as described in claim 8 or 9 in the manufacture of automotive structural components.

Images