An in-situ self-generated Al2O3 reinforced composite low-density steel and its hot deformation method

Abstract

The application discloses an in-situ self-grown Al2O3 reinforced composite low-density steel and a hot deformation method thereof. The in-situ self-grown Al2O3 reinforced composite low-density steel comprises a steel matrix and Al2O3 reinforcing phases distributed in the steel matrix. The chemical components of the in-situ self-grown Al2O3 reinforced composite low-density steel are as follows in percentage by mass: Al2O3 is 2-5.5%, Al is 9-11%, Cu is 1.5-2.5%, C is 0.1-0.3%, and the balance is Fe and inevitable impurities. The grain size of ferrite in the steel matrix is in a bimodal distribution structure, and the average grain size is 20-60 mu m. The application can obtain the composite low-density steel which is synergistically reinforced by fine delta-ferrite matrix and small Al2O3 reinforcing phase particles, so that the microstructure and comprehensive mechanical properties of the composite low-density steel are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of steel-based composite materials technology, and more specifically, to an in-situ self-generated Al2O3 reinforced composite low-density steel and its hot deformation method. Background Technology

[0002] With increasing global demands for energy conservation, emission reduction, and sustainable development, the need for lightweight, high-performance structural materials in aerospace, transportation, and other fields is becoming increasingly urgent. Steel, due to its mature production processes, low cost, and excellent comprehensive performance, dominates structural applications. Therefore, developing lightweight steel materials with high specific strength (strength / density) has become one of the current hot topics in materials science research. Currently, the most common method for reducing steel density is to add a certain amount of Al. For every 1 wt.% of Al added, the steel density can be reduced by 1.3%. However, the introduction of large amounts of Al also brings a series of problems. High-aluminum low-density steel, while reducing density, suffers from low elastic modulus, coarse grains, a pure δ-ferrite matrix, and insufficient strength-plasticity balance. Utilizing in-situ self-generated reactions to generate dispersed Al2O3 particles in the steel matrix can effectively improve the material's elastic modulus and strength. However, due to defects in the as-cast structure and coarse δ-ferrite grains in the matrix, the material's plasticity is poor, limiting its engineering applications.

[0003] Chinese Patent Publication No. CN119571201A discloses an in-situ self-generated Al2O3-reinforced low-density steel matrix composite material and its preparation method. The in-situ self-generated Al2O3-reinforced low-density steel matrix composite material includes a steel matrix and an Al2O3 reinforcing phase distributed in the steel matrix. The steel matrix is ​​high-alumina steel. The Al2O3 reinforcing phase is generated by the in-situ reaction between oxygen in the molten metal oxide salt and aluminum in the high-alumina steel melt during the smelting process. The volume percentage of the Al2O3 reinforcing phase in the steel matrix is ​​10-20%. Although this technology generates the Al2O3 reinforcing phase in the steel matrix through in-situ reaction and achieves preliminary metallurgical bonding between the reinforcing phase and the matrix, the resulting as-cast composite material still inevitably has typical as-cast structural defects, such as coarse dendritic structure, significant component segregation, and defects such as pores, shrinkage cavities, and microcracks caused by rapid solidification. This results in uneven distribution of the Al2O3 reinforcing phase in the matrix, enrichment of the reinforcing phase in local areas, and unstable interfacial bonding quality. In addition, the high-density residual stress and unresolved dislocation structures formed during the as-cast solidification process often lead to lower overall mechanical properties of the material and greater fluctuations.

[0004] As mentioned above, the technical route of generating dispersed Al2O3 particles in a steel matrix through in-situ self-generation faces a key process challenge in industrial application: how to optimize its coarse and brittle as-cast microstructure. Since the low-density steel matrix is ​​pure δ-ferrite, no phase transformation occurs during cooling, rendering the traditional steel grain refinement mechanism of "phase transformation-induced crystallization" ineffective. Therefore, achieving significant grain refinement in the absence of phase transformation becomes a major challenge. Existing technologies often rely on single hot deformation (such as rolling or forging) or subsequent heat treatment; however, these methods have limitations: single hot deformation may break up coarse grains, but it is difficult to achieve a uniform distribution of reinforcing phase particles, and the deformed microstructure has high energy storage, leading to unstable performance without appropriate heat treatment; while single heat treatment has limited grain refinement effect on materials without phase transformation and cannot effectively improve as-cast defects. Therefore, existing processes often compromise on one aspect while failing to achieve the three objectives of "uniformly dispersed particle distribution," "significantly refined matrix grains," and "synergistic improvement of strength and plasticity."

[0005] In conclusion, developing a novel hot deformation method that can effectively coordinate Al2O3 particle distribution, refine ferrite grains, and ultimately achieve excellent comprehensive mechanical properties is of vital importance for promoting the application of in-situ self-generated Al2O3-reinforced low-density steel from the laboratory to engineering applications. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an in-situ self-generated Al2O3 reinforced composite low-density steel and its hot deformation method, which can obtain a composite low-density steel with a fine δ-ferrite matrix and fine Al2O3 reinforcing phase particles synergistically reinforced, thereby significantly improving its microstructure and comprehensive mechanical properties.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides an in-situ self-generated Al2O3 reinforced composite low-density steel, comprising a steel matrix and an Al2O3 reinforcing phase distributed in the steel matrix, wherein the chemical composition of the in-situ self-generated Al2O3 reinforced composite low-density steel is as follows by mass percentage: Al2O3: 2~5.5%, Al: 9~11%, Cu: 1.5~2.5%, C: 0.1~0.3%, with the balance being Fe and unavoidable impurities;

[0009] The ferrite grain size in the steel matrix exhibits a bimodal distribution structure, with an average grain size of 20~60μm.

[0010] Preferably, the average grain size of the Al2O3 reinforcing phase is 1.5~3μm.

[0011] Preferably, the tensile strength σ of the in-situ self-generated Al2O3 reinforced composite low-density steel is... b The yield strength is 1000~1200 MPa. 0.2 The strength is 800~900 MPa, and the elongation after fracture δ is 15~25%.

[0012] A second aspect of the present invention provides a hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel as described in the first aspect of the present invention, comprising the following steps:

[0013] S1, the in-situ self-generated Al2O3 reinforced composite low-density steel ingot is homogenized and then transferred to room temperature circulating water for cooling.

[0014] S2, the homogenized ingot is heated to 900~1100℃ for high-temperature hot deformation treatment, and the cumulative deformation is controlled to be 50~70%;

[0015] S3 involves solution treatment of the ingot after high-temperature heat deformation, followed by air cooling to room temperature.

[0016] S4 involves heating the solution-treated ingot to 350~550℃ for medium-temperature hot deformation treatment, controlling the cumulative deformation to 20~30%, and finally forming an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal ferrite grain size distribution.

[0017] Preferably, in step S1, the in-situ self-generated Al2O3 reinforced composite low-density steel ingot includes a steel matrix and an Al2O3 reinforcing phase distributed in the steel matrix. The chemical composition of the ingot is as follows by mass percentage: Al2O3: 2~5.5%, Al: 9~11%, Cu: 1.5~2.5%, C: 0.1~0.3%, with the balance being Fe and unavoidable impurities.

[0018] Preferably, in step S1, the equipment used for homogenization is a muffle furnace, the homogenization temperature is 1000~1150℃, and the holding time is 1~3h.

[0019] Preferably, in step S2, the deformation method of the high-temperature hot deformation treatment is multi-directional forging, with a single-pass deformation amount of 5~10% and a strain rate of 0.1~10 s. -1 After each pressing, keep warm at 900~1100℃ for 3~5 minutes.

[0020] Preferably, in step S3, the equipment used for the solution treatment is a vacuum heat treatment furnace, the solution treatment temperature is 650~750℃, and the solution treatment time is 0.5~1h.

[0021] Preferably, in step S4, the deformation method of the medium-temperature hot deformation treatment is multi-directional forging, with a single-pass deformation amount of 5~10% and a strain rate of 0.1~10 s. -1 After each pressing, keep warm at 350~550℃ for 3~5 minutes.

[0022] The in-situ self-generated Al2O3 reinforced composite low-density steel and its hot deformation method provided by this invention have the following beneficial effects:

[0023] 1. This invention breaks through the limitations of traditional single hot processing or heat treatment, creatively combining the four stages of "homogenization treatment", "high temperature hot deformation", "solution treatment" and "medium and low temperature hot deformation" in an orderly manner. This design is not a simple superposition of steps, but constitutes a logically rigorous whole. First, internal stress and segregation are eliminated through high temperature treatment, then defect healing and microstructure fragmentation are achieved through large deformation, then the matrix and reinforcing phase are stabilized through solid solution, and finally, grain refinement and performance improvement are achieved through the fine interaction between dislocations and particles at low temperature, forming a synergistic reinforcement effect.

[0024] 2. This invention discloses a novel mechanism for refining ferrite grains using "medium-low temperature deformation + particle pinning". Addressing the global challenge of refining grains in low-density steel matrices without phase transformation, the core innovation of this invention lies in introducing a crucial medium-low temperature deformation step. This step, through plastic deformation in the temperature range of 350~550℃, actively induces high-density dislocations and utilizes dispersed Al2O3 particles as strong pinning points to effectively hinder dislocation movement, thereby strongly promoting dynamic recovery and the formation of subgrain boundaries. Ultimately, without phase transformation, it successfully transforms coarse cast ferrite grains into a structure with a bimodal grain size distribution, achieving significant microstructural refinement.

[0025] 3. This invention achieves the unified goal of "macroscopic defect healing", "microstructure refinement" and "reinforcing phase distribution control". Existing technologies often struggle to simultaneously address issues such as as-cast macroscopic defects, coarse grains, and reinforcing phase agglomeration. This invention achieves this by precisely dividing and connecting multiple stages of heat treatment processes: high-temperature large deformation primarily addresses the macroscopic defect healing problem; subsequent solution treatment and medium-low temperature hot deformation work synergistically at the microscale, simultaneously refining the matrix grains and achieving uniform distribution of reinforcing phase particles. Thus, multiple key microstructural challenges restricting the application of this material are solved in a single process, resulting in a leapfrog improvement in the material's overall performance.

[0026] 4. This invention, through an integrated multi-stage hot deformation process, synergistically solves several key bottleneck problems in the engineering application of in-situ self-generated Al2O3-reinforced low-density steel, significantly improving the comprehensive mechanical properties of the material, achieving a good match between strength and plasticity, and meeting the safety requirements of engineering structural materials. It effectively optimizes the microstructure, healing macroscopic defects such as as-cast shrinkage cavities and porosity, and significantly refines the coarse δ-ferrite grains (average 950 μm) to 20~60 μm, while ensuring the uniform and dispersed distribution of Al2O3 reinforcing phase particles, laying a solid microscopic foundation for performance improvement. The method of this invention is stable and has industrialization potential, with clearly defined process parameters. The equipment used (such as muffle furnaces and forging equipment) are all common industrial equipment. Through multi-pass, multi-directional deformation control, the cracking risk of high-alloy materials during processing is reduced, providing a feasible path for the stable preparation of large-size, high-performance composite low-density steel. Attached Figure Description

[0027] Figure 1 This is a schematic flowchart of the hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel according to the present invention.

[0028] Figure 2 This is a metallographic image of the in-situ self-generated Al2O3 reinforced composite low-density steel prepared in Example 1 of this invention;

[0029] Figure 3 This is an engineering stress-strain curve of the in-situ self-generated Al2O3 reinforced composite low-density steel prepared in Example 1 of this invention;

[0030] Figure 4 The image shows the microstructure of the as-cast composite low-density steel sample prepared in Comparative Example 1.

[0031] Figure 5 This is the engineering stress-strain curve of the composite low-density steel as-cast sample prepared in Comparative Example 1. Detailed Implementation

[0032] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] The applicant of this invention proposed an in-situ self-generated Al2O3-reinforced low-density steel-based composite material and its preparation method in Chinese Patent Publication No. CN119571201A. However, composite materials obtained under as-cast conditions may still have potential limitations in terms of reinforcing phase distribution, matrix structure, and overall properties due to the inherent characteristics of the solidification process. It is difficult to simultaneously achieve the triple goals of "uniform and dispersed particle distribution," "significantly refined matrix grains," and "synergistic improvement in strength and plasticity" by relying solely on the casting process. This invention, by introducing a controlled deformation process, can further regulate the reinforcing phase distribution, promote dynamic recrystallization, eliminate defects, and optimize the interface structure, thereby promoting the synergistic achievement of the above-mentioned key performance indicators.

[0034] This invention utilizes a heat treatment method of "homogenization treatment - high-temperature hot deformation - solution treatment - medium-temperature hot deformation" to achieve the healing of as-cast segregation and defects, uniform dispersion of Al2O3 particles, and significant refinement of the ferrite matrix. Ultimately, it yields a composite low-density steel with synergistic reinforcement from a finer δ-ferrite matrix and fine Al2O3 reinforcing phase particles, thereby significantly improving its microstructure and overall mechanical properties. This invention provides an in-situ self-generated Al2O3-reinforced composite low-density steel, comprising a steel matrix and an Al2O3 reinforcing phase distributed within the steel matrix. The chemical composition of the in-situ self-generated Al2O3-reinforced composite low-density steel, by mass percentage, is as follows: Al2O3: 2~5.5%, Al: 9~11%, Cu: 1.5~2.5%, C: 0.1~0.3%, with the balance being Fe and unavoidable impurities. The ferrite grain size in the steel matrix exhibits a bimodal distribution structure, with an average grain size of 20~60 μm. Ferrite has a bimodal grain size distribution structure, which can provide effective grain boundary strengthening and deformation coordination through the fine grain region, while the relatively coarse grain region undertakes plastic deformation and strain distribution, thereby achieving a synergistic improvement in strength and plasticity.

[0035] In the aforementioned in-situ self-generated Al2O3 reinforced composite low-density steel, the average size of the Al2O3 reinforcing phase is 1.5~3 μm.

[0036] Based on the synergistic effect of ferrite with a bimodal grain size distribution and fine Al2O3 reinforcing phase, the tensile strength σ of this in-situ self-generated Al2O3 reinforced composite low-density steel is increased. b The yield strength is 1000~1200 MPa. 0.2 The strength is 800~900MPa, and the elongation after fracture δ is 15~25%.

[0037] Combination Figure 1 As shown, the present invention also provides a hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel, which adopts a multi-stage coupled hot deformation method, specifically including the following steps:

[0038] S1, the in-situ self-generated Al2O3 reinforced composite low-density steel ingot is homogenized and then transferred to room temperature circulating water for cooling.

[0039] The in-situ self-generated Al2O3 reinforced composite low-density steel ingot used in this step is an in-situ self-generated Al2O3 reinforced low-density steel matrix composite material prepared by the method mentioned in Chinese Patent Publication No. CN119571201A. This in-situ self-generated Al2O3 reinforced composite low-density steel ingot includes a steel matrix and an Al2O3 reinforcing phase distributed in the steel matrix. The steel matrix is ​​high-alumina steel. The Al2O3 reinforcing phase is generated by the in-situ reaction between oxygen element in the molten metal oxide salt and aluminum element in the high-alumina steel melt during the smelting process. The chemical composition of the ingot is as follows by mass percentage: Al2O3: 2~5.5%, Al: 9~11%, Cu: 1.5~2.5%, C: 0.1~0.3%, with the balance being Fe and unavoidable impurities.

[0040] In this step, the in-situ self-generated Al2O3 reinforced composite low-density steel ingot undergoes homogenization treatment to eliminate segregation and internal stress in the as-cast structure and promote full diffusion of elements. The homogenization treatment is performed in a muffle furnace at a temperature of 1000–1150℃ for 1–3 hours. As low-density steel is a non-transformation steel, homogenization at this temperature promotes the diffusion of Al elements in the matrix, thereby reducing segregation.

[0041] In this step, the homogenization treatment temperature is set to 1000~1150℃. If the temperature is below 1000℃, the diffusion motive force of atoms is insufficient, making it difficult to eliminate segregation, resulting in uneven microstructure and affecting subsequent processing performance. If the temperature is above 1150℃, it may cause grain coarsening or local melting, affecting the mechanical properties of the material. The holding time is set to 1~3h because if the holding time is too short (less than 1h), it will lead to uneven diffusion and segregation residue. If the time is too long (more than 3h), it may lead to energy waste and excessive microstructure coarsening.

[0042] S2, the homogenized ingot is heated to 900~1100℃ for high-temperature hot deformation treatment, and the cumulative deformation is controlled to be 50~70%;

[0043] This step is a high-temperature hot deformation process. High-temperature deformation aims to refine grains and improve microstructure uniformity through plastic deformation. The deformation method is multi-directional forging, with a cumulative deformation of 50-70%, a single-pass deformation of 5-10%, a hot deformation temperature of 900-1100℃, and a strain rate of 0.1-10 s⁻¹. -1After each pressing, the material is held at 900~1100℃ for 3~5 minutes to prevent a sudden increase in deformation resistance due to ingot temperature drop. The hot deformation temperature is set at 900~1100℃, which matches the high-temperature plasticity range of δ-ferrite, avoiding deformation cracking, while ensuring the activation energy required for dynamic recrystallization. If the temperature is too low (below 900℃), the material's deformation resistance will increase, easily leading to cracking or work hardening; if the temperature is too high (above 1100℃), it may cause excessive dynamic recrystallization or grain growth, which is not conducive to microstructure control. The cumulative deformation is controlled at 50-70% to heal defects such as shrinkage cavities and porosity in the as-cast state. Simultaneously, dynamic recovery and partial dynamic recrystallization initially refine the coarse grains of δ-ferrite, and the in-situ self-generated Al2O3 further detaches from the agglomeration zone under shear stress, achieving initial dispersion within the steel matrix. If the cumulative deformation is too small (below 50%), it is insufficient to break the as-cast structure, and the improvement effect is not significant. If the cumulative deformation is too large (above 70%), it may introduce too many defects or lead to shape control issues. The single-pass deformation is set at 5-10% because if the single-pass deformation is too small (below 5%), the high-temperature hot deformation efficiency is low and the refinement effect is poor; if the single-pass deformation is too large (above 10%), it easily causes local stress concentration and cracking. The high-temperature hot deformation strain rate is set at 0.1-10 s⁻¹. -1 This is conducive to the full healing of defects and can inhibit the growth of Al2O3. Under high temperature hot deformation, if the strain rate is too low (below 0.1 s⁻¹), the production efficiency will be low and the recrystallization process may be insufficient. If the strain rate is too high (above 10 s⁻¹), it may lead to the accumulation of deformation heat, causing temperature runaway or uneven structure.

[0044] S3 involves solution treatment of the ingot after high-temperature heat deformation, followed by air cooling to room temperature.

[0045] This step is a solution treatment process. The equipment used for solution treatment is a vacuum heat treatment furnace. The solution treatment temperature is 650~750℃, and the solution treatment time is 0.5~1h. This step allows Al to fully dissolve in the ferrite matrix and stabilize the Al2O3 reinforcing phase, eliminates residual stress from hot deformation, and further homogenizes the microstructure, thereby obtaining a supersaturated solid solution structure and stabilizing the particle distribution of the Al2O3 reinforcing phase.

[0046] S4 involves heating the solution-treated ingot to 350~550℃ for medium-temperature hot deformation treatment, controlling the cumulative deformation to 20~30%, and finally forming an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal ferrite grain size distribution.

[0047] This step is a medium-temperature hot deformation treatment process. Through the dynamic recrystallization effect in the medium temperature range, the δ-ferrite structure is further refined. At the same time, the entanglement of contact dislocations and Al2O3 promotes the greater dispersion of Al2O3, making the interface between the Al2O3 reinforcing phase and the steel matrix tightly bonded.

[0048] The deformation method for the medium-temperature hot deformation treatment in this step is multi-directional forging, with a hot deformation temperature of 350~550 ℃, a cumulative deformation of 20~30%, a single-pass deformation of 5~10%, and a strain rate of 0.1~10 s. -1 Medium-temperature hot deformation is mainly used to adjust dislocation structure and control precipitation behavior to further improve mechanical properties. The hot deformation temperature is set at 350~550℃ because this temperature range can activate dislocation movement and induce dynamic recrystallization, while avoiding low-temperature embrittlement of the matrix. If the hot deformation temperature is too low (below 350℃), the material will have poor plasticity, high deformation resistance, and be prone to brittle cracking. If the hot deformation temperature is too high (above 550℃), it may enter the high-temperature deformation range, losing the advantages of medium-temperature deformation in controlling dislocations and precipitation. The cumulative deformation amount is set at 20~30% because if the cumulative deformation amount is too small (below 20%), dynamic recrystallization will be insufficient, limiting its effect on improving the microstructure. If the cumulative deformation amount is too large (above 30%), it is easy to cause local aggregation of Al2O3, which may lead to overwork hardening or decreased toughness. Setting the single-pass deformation amount to 5-10% allows for precise control of grain refinement and prevents excessive grain growth. This single-pass deformation amount is based on the material deformation characteristics at medium temperatures; too small a single-pass deformation amount (below 5%) results in low deformation efficiency, while too large a single-pass deformation amount (above 10%) easily leads to cracking. Setting the strain rate to 0.1-10 s⁻¹ facilitates sufficient dynamic recrystallization, thereby refining the microstructure. If the strain rate is too low (below 0.1 s⁻¹), the recovery process may dominate, weakening the deformation effect; if the strain rate is too high (above 10 s⁻¹), it may cause adiabatic heating, affecting microstructural stability.

[0049] This invention solves the problems of poor healing effect of casting defects, easy agglomeration of reinforcing phases, incomplete elimination of element segregation, limited grain refinement, and imbalance of strength and plasticity in the prior art through the above-mentioned heat treatment process of "homogenization treatment + high temperature hot deformation + solution treatment + medium temperature hot deformation". It also makes the cast ferrite grains in the steel matrix significantly refined and improves the performance of in-situ self-generated Al2O3 reinforced composite low-density steel, forming a synergistic reinforcement effect.

[0050] The in-situ self-generated Al2O3 reinforced composite low-density steel obtained after the above heat treatment exhibits a bimodal ferrite grain size distribution in its matrix, with an average grain size of 20–60 μm. The average grain size of the Al2O3 reinforcing phase is 1.5–3 μm. The tensile strength σ of this in-situ self-generated Al2O3 reinforced composite low-density steel is [not specified in the original text]. b The yield strength is 1000~1200 MPa. 0.2 The strength is 800~900 MPa, and the elongation after fracture δ is 15~25%.

[0051] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are merely illustrative of one aspect of the invention and are not intended to limit its scope. The invention can be employed under various conditions as long as it does not depart from its spirit and achieves its objectives.

[0052] The in-situ self-generated Al2O3 reinforced composite low-density steel ingots used in the following examples and comparative examples were prepared using the method mentioned in Chinese Patent Publication No. CN119571201A. The in-situ self-generated Al2O3 reinforced low-density steel matrix composite material includes a steel matrix and an Al2O3 reinforcing phase. The specific composition of the ingot is shown in Table 1.

[0053] Example 1

[0054] Referring to Table 2, the hot deformation method of the in-situ self-generated Al2O3 reinforced composite low-density steel in this embodiment is as follows:

[0055] In-situ self-generated Al2O3-reinforced composite low-density steel ingots underwent homogenization heat treatment in a muffle furnace, with the temperature increased to 1150℃ at a rate of 10℃ / min and held for 1.5 h. After holding, the ingots were transferred to ambient temperature circulating water for cooling. The homogenized ingots were then subjected to high-temperature hot deformation. First, they were reheated to 1000℃ at a heating rate of 10℃ / min and held for 1 h to ensure uniform temperature throughout the ingot. Then, multi-directional forging was performed using a 2000t hydraulic forging machine, with a cumulative deformation of 70% and a single-pass reduction of 10%. The forging direction was X→Y→Z→X, with one X→Y→Z cycle constituting one pass, completed in 7 passes. After each pass, the ingot was held for 5 min to prevent a sudden increase in deformation resistance due to temperature drop. During forging, a lubricant was applied to the ingot surface to prevent adhesion to the mold, and the hot deformation strain rate was controlled at 0.1 s⁻¹. -1To prevent localized stress concentration and cracking, and to initially heal defects such as shrinkage cavities and porosity in the ingot, the ingot, after high-temperature hot deformation, is placed in a vacuum heat treatment furnace for solution treatment. The temperature is raised to 650℃ at a heating rate of 5℃ / min and held for 0.5h. After holding, it is cooled to room temperature by air cooling, allowing Al to dissolve in the ferrite matrix and stabilize the dispersed phase. The solution-treated ingot is then subjected to medium-temperature hot deformation at 350℃ using a multi-directional forging method. The cumulative deformation is 30%, the single-pass reduction is 10%, and the strain rate is controlled at 0.1 s⁻¹. -1 The forging direction is X→Y→Z→X, and one X→Y→Z cycle is one pass. It is completed in 3 passes. After each pass is pressed down, it is held at a temperature for 5 minutes. Through the interaction between induced dislocations and dispersed Al2O3 reinforcing phase particles, the ferrite in the steel matrix is ​​significantly refined. Finally, an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal ferrite grain size distribution structure is obtained. Its properties are shown in Table 3.

[0056] Figure 2 This is a microstructure diagram of the in-situ self-generated Al2O3 reinforced composite low-density steel of this embodiment. It can be clearly observed from the figure that the matrix grain size distribution is uniform, the grain boundaries are clear, there are no obvious compositional segregation bands, the Al2O3 reinforcing phase particles are uniformly dispersed in the grains, there is no obvious agglomeration (agglomerated particles account for ≤3%), and the interface with the steel matrix is ​​tightly bonded, there are no interface cracks or voids, the defects such as shrinkage cavities and gas pores remaining in the casting state are completely healed, no pores with a size ≥5μm are observed in the metallographic photographs, and the material density is above 99.8% as tested by the Archimedes method.

[0057] Figure 3 The room temperature tensile curve of the in-situ self-generated Al2O3 reinforced composite low-density steel sample in this embodiment shows that the material has good yield stability.

[0058] As shown in Table 3, the average grain size of ferrite in the steel matrix of this in-situ self-generated Al2O3 reinforced composite low-density steel is 23 μm, the average grain size of the Al2O3 reinforcing phase is 2.6 μm, the yield strength is 873.4 MPa, the tensile strength is 1126.7 MPa, and the elongation after fracture is 15.4%, achieving excellent strength-ductility matching. The elastic modulus of the sample is 207 GPa, indicating that the hindering effect of Al2O3 on dislocations persists and can effectively improve the material's resistance to deformation.

[0059] Example 2

[0060] Referring to Table 2, the hot deformation method of the in-situ self-generated Al2O3 reinforced composite low-density steel in this embodiment is as follows:

[0061] In-situ self-generated Al2O3-reinforced composite low-density steel ingots underwent homogenization heat treatment in a muffle furnace, heating to 1100℃ at a rate of 10℃ / min and holding for 1 hour. After holding, the ingots were transferred to ambient temperature circulating water for cooling. The homogenized ingots were then subjected to high-temperature hot deformation. They were first reheated to 1100℃ at a heating rate of 10℃ / min and held for 1 hour to ensure uniform temperature throughout. Subsequently, multi-directional forging was performed using a 2000t hydraulic forging machine, with a cumulative deformation of 65% and a single-pass reduction of 5%. The forging direction was X→Y→Z→X, with one X→Y→Z cycle constituting one pass, completed in 13 passes. After each pass, the ingot was held for 3 minutes to prevent a sudden increase in deformation resistance due to temperature drop. During forging, a lubricant was applied to the ingot surface to prevent adhesion to the mold, and the strain rate was controlled at 0.1 s². -1 To prevent localized stress concentration and cracking, and to initially heal defects such as shrinkage cavities and porosity in the ingot, the ingot, after high-temperature hot deformation, is placed in a vacuum heat treatment furnace for solution treatment. The temperature is raised to 680℃ at a heating rate of 5℃ / min and held for 1 hour. After holding, it is cooled to room temperature by air cooling, allowing Al to dissolve in the ferrite matrix and stabilize the dispersed phase. The solution-treated ingot is then subjected to medium-temperature hot deformation at 400℃ using a multi-directional forging method. The cumulative deformation is 30%, the single-pass reduction is 5%, and the reduction rate (i.e., deformation rate) is controlled at 0.1 s⁻¹. -1 The forging direction is X→Y→Z→X, and one X→Y→Z cycle is one pass. It is completed in 6 passes. After each pass is pressed down, it is held at a temperature for 4 minutes. Through the interaction between induced dislocations and dispersed Al2O3 reinforcing phase particles, the ferrite in the steel matrix is ​​significantly refined. Finally, an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal ferrite grain size distribution structure is obtained. Its properties are shown in Table 3.

[0062] Example 3

[0063] Referring to Table 2, the hot deformation method of the in-situ self-generated Al2O3 reinforced composite low-density steel in this embodiment is as follows:

[0064] In-situ self-generated Al2O3-reinforced composite low-density steel ingots underwent homogenization heat treatment in a muffle furnace, with the temperature increased to 1080℃ at a rate of 10℃ / min and held for 1 hour. After holding, the ingots were transferred to ambient temperature circulating water for cooling. The homogenized ingots were then subjected to high-temperature hot deformation, reheated to 1100℃, and held to ensure uniform temperature throughout. Multi-directional forging was then performed using a 2000t hydraulic forging machine, with a cumulative deformation of 60% and a single-pass reduction of 6%. The forging direction was X→Y→Z→X, with one X→Y→Z cycle constituting one pass, completed in 10 passes. After each pass, the ingots were held for 4 minutes to prevent a sudden increase in deformation resistance due to temperature drop. Lubricant was applied to the ingot surface during forging to prevent adhesion to the mold, and the reduction rate (i.e., deformation rate) was controlled at 1 second. -1 To prevent localized stress concentration and cracking, and to initially heal defects such as shrinkage cavities and porosity in the ingot, the ingot, after high-temperature hot deformation, is placed in a vacuum heat treatment furnace for solution treatment. The temperature is raised to 720℃ at a heating rate of 5℃ / min and held for 1 hour. After holding, it is cooled to room temperature by air cooling, allowing Al to dissolve in the ferrite matrix and stabilize the dispersed phase. The solution-treated ingot is then subjected to medium-temperature hot deformation at 400℃ using a multi-directional forging method. The cumulative deformation is 30%, the single-pass reduction is 5%, and the reduction rate (i.e., deformation rate) is controlled at 1 second. -1 The forging direction is X→Y→Z→X, and one X→Y→Z cycle is one pass. It is completed in 6 passes. After each pass is pressed down, it is held at a temperature for 4.5 minutes. Through the interaction between induced dislocations and dispersed Al2O3 reinforcing phase particles, the ferrite in the steel matrix is ​​significantly refined. Finally, an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal ferrite grain size distribution structure is obtained. Its properties are shown in Table 3.

[0065] Example 4

[0066] Referring to Table 2, the hot deformation method of the in-situ self-generated Al2O3 reinforced composite low-density steel in this embodiment is as follows:

[0067] In-situ self-generated Al2O3-reinforced composite low-density steel ingots underwent homogenization heat treatment in a muffle furnace, with the temperature increased to 1000℃ at a rate of 10℃ / min and held for 3 hours. After holding, the ingots were transferred to ambient temperature circulating water for cooling. The homogenized ingots were then subjected to high-temperature hot deformation. First, they were reheated to 900℃ at a heating rate of 10℃ / min and held for 1 hour to ensure uniform temperature throughout the ingot. Then, multi-directional forging was performed using a 2000t hydraulic forging machine, with a cumulative deformation of 50% and a single-pass reduction of 5%. The forging direction was X→Y→Z→X, with one X→Y→Z cycle constituting one pass, completed in 10 passes. After each pass, the ingot was held for 4 minutes to prevent a sudden increase in deformation resistance due to temperature drop. During the forging process, a lubricant was applied to the ingot surface to prevent adhesion to the mold, and the strain rate was controlled at 0.1s. -1 To prevent localized stress concentration and cracking, and to initially heal defects such as shrinkage cavities and porosity in the ingot, the ingot, after high-temperature hot deformation, is placed in a vacuum heat treatment furnace for solution treatment. The temperature is raised to 750℃ at a heating rate of 5℃ / min and held for 0.5 hours. After holding, it is cooled to room temperature by air cooling, allowing Al to dissolve in the ferrite matrix and stabilize the dispersed phase. The solution-treated ingot is then subjected to medium-temperature hot deformation at 550℃ using a multi-directional forging method. The cumulative deformation is 20%, the single-pass reduction is 5%, and the strain rate is controlled at 10s. -1 The forging direction is X→Y→Z→X, and one X→Y→Z cycle is one pass. It is completed in 4 passes. After each pass is pressed down, it is held at a temperature for 3 minutes. Through the interaction between induced dislocations and dispersed Al2O3 reinforcing phase particles, the ferrite structure in the steel matrix is ​​significantly refined. Finally, an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal distribution of ferrite grain size is obtained. Its properties are shown in Table 3.

[0068] Example 5

[0069] Referring to Table 2, the hot deformation method of the in-situ self-generated Al2O3 reinforced composite low-density steel in this embodiment is as follows:

[0070] In-situ self-generated Al2O3-reinforced composite low-density steel ingots underwent homogenization heat treatment in a muffle furnace, heating to 1130℃ at a rate of 10℃ / min and holding for 2.5 hours. After holding, the ingots were transferred to ambient temperature circulating water for cooling. The homogenized ingots were then subjected to high-temperature hot deformation. They were first reheated to 1100℃ at a heating rate of 10℃ / min and held for 1 hour to ensure uniform temperature throughout. Subsequently, multi-directional forging was performed using a 2000t hydraulic forging machine, with a cumulative deformation of 70% and a single-pass reduction of 10%. The forging direction was X→Y→Z→X, with one X→Y→Z cycle constituting one pass, completed in 7 passes. After each pass reduction, the ingots were held for 5 minutes to prevent a sudden increase in deformation resistance due to temperature drop. During forging, a lubricant was applied to the ingot surface to prevent adhesion to the mold, and the strain rate was controlled at 10s. -1 To prevent localized stress concentration and cracking, and to initially heal defects such as shrinkage cavities and porosity in the ingot, the ingot, after high-temperature hot deformation, is placed in a vacuum heat treatment furnace for solution treatment. The temperature is raised to 710℃ at a heating rate of 5℃ / min and held for 0.5h. After holding, it is cooled to room temperature by air cooling, allowing Al to dissolve in the ferrite matrix and stabilize the dispersed phase. The solution-treated ingot is then subjected to medium-temperature hot deformation at 370℃ using a multi-directional forging method. The cumulative deformation is 30%, the single-pass reduction is 10%, and the strain rate is controlled at 10s. -1 The forging direction is X→Y→Z→X, and one X→Y→Z cycle is one pass. It is completed in 3 passes. After each pass is pressed down, it is held at a temperature for 3.5 minutes. Through the interaction between induced dislocations and dispersed Al2O3 reinforcing phase particles, the ferrite structure in the steel matrix is ​​significantly refined. Finally, an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal distribution of ferrite grain size is obtained. Its properties are shown in Table 3.

[0071] Comparative Example 1

[0072] Referring to Table 2, the hot deformation method of the in-situ self-generated Al2O3 reinforced composite low-density steel in this comparative example is as follows:

[0073] In a muffle furnace, in-situ self-generated Al2O3-reinforced composite low-density steel ingots were homogenized at 1100 °C for 1.5 h and then water-cooled. Subsequently, unidirectional forging (only along the X direction) was performed at 900 °C, with a total deformation of 50% and a single-pass reduction of 25%, completed in two passes. After forging, the ingots were directly air-cooled to room temperature, then held at 600 °C for 4 h before air-cooling to obtain the composite low-density steel.

[0074] Figure 4The image shows the metallographic diagram of the composite low-density steel as-cast sample in this comparative example. As can be seen from the figure, there are a large number of casting defects in the composite low-density steel, such as shrinkage cavities and porosity. The healing rate of defects such as shrinkage cavities and porosity in the sample is less than 60%, and the average grain size is as high as 950 μm.

[0075] Figure 5 The figure shows the engineering stress-strain curve of the composite low-density steel as-cast sample. The composite low-density steel sample exhibits typical brittle fracture characteristics in the room temperature tensile test. There is no obvious yield plateau in the figure. It fractures before reaching the maximum stress and has extremely low elongation after fracture. This indicates that the macroscopic defects and coarse grains in the as-cast structure severely reduce the compactness and plasticity of the material, making it unable to undergo effective plastic deformation and resulting in extremely poor mechanical properties.

[0076] Comparative Example 2

[0077] This comparative example uses the heat deformation method of Example 1, the difference being that the homogenization treatment temperature is 900°C.

[0078] Comparative Example 3

[0079] This comparative example uses the heat deformation method of Example 1, the difference being that the homogenization treatment temperature is 1200℃.

[0080] Comparative Example 4

[0081] This comparative example uses the heat deformation method of Example 1, the difference being that the high-temperature heat deformation treatment temperature is 800℃.

[0082] Comparative Example 5

[0083] This comparative example uses the heat deformation method of Example 1, the difference being that the high-temperature heat deformation treatment temperature is 1200℃.

[0084] Comparative Example 6

[0085] This comparative example uses the hot deformation method of Example 1, the difference being that the cumulative deformation amount of the high-temperature hot deformation treatment is 40%, and the deformation amount per pass is 4%.

[0086] Comparative Example 7

[0087] This comparative example uses the hot deformation method of Example 1, the difference being that the cumulative deformation amount of the high-temperature hot deformation treatment is 80%, and the deformation amount per pass is 20%.

[0088] Comparative Example 8

[0089] This comparative example uses the heat deformation method of Example 1, the difference being that the solution treatment temperature is 500℃.

[0090] Comparative Example 9

[0091] This comparative example uses the heat deformation method of Example 1, the difference being that the solution treatment temperature is 800℃.

[0092] Comparative Example 10

[0093] This comparative example uses the heat deformation method of Example 1, the difference being that the temperature of the medium-temperature heat deformation treatment is 300°C.

[0094] Comparative Example 11

[0095] This comparative example uses the heat deformation method of Example 1, the difference being that the temperature of the medium-temperature heat deformation treatment is 600℃.

[0096] Comparative Example 12

[0097] This comparative example uses the hot deformation method of Example 1, the difference being that the cumulative deformation amount of the medium-temperature hot deformation treatment is 15%, and the deformation amount per pass is 3%.

[0098] Comparative Example 13

[0099] This comparative example uses the hot deformation method of Example 1, the difference being that the cumulative deformation amount of the medium-temperature hot deformation treatment is 45%, and the deformation amount per pass is 15%.

[0100] Table 1. Composition (wt%) of in-situ self-generated Al2O3 reinforced composite low-density steel ingots

[0101]

[0102] Table 2

[0103]

[0104] Table 3

[0105]

[0106] This invention creatively combines four steps—homogenization treatment, high-temperature hot deformation, solution treatment, and medium-low temperature hot deformation—in an orderly manner. This ensures the successful refinement of the coarse-cast ferrite structure and the uniform distribution of Al2O3 reinforcing phase particles without phase transformation, resulting in in-situ self-generated Al2O3-reinforced composite low-density steel with a bimodal ferrite grain size distribution. As shown in Table 3, the average ferrite grain size in the steel matrix of the in-situ self-generated Al2O3-reinforced composite low-density steel prepared in this embodiment ranges from 20 to 55 μm, and the average size of the Al2O3 reinforcing phase ranges from 1.5 to 3 μm. The tensile strength σ of the in-situ self-generated Al2O3-reinforced composite low-density steel is [not specified in the original text]. b Within the range of 1000~1190MPa, the yield strength σ 0.2Within the range of 800~890 MPa and the elongation after fracture δ within the range of 15~25%, the in-situ self-generated Al2O3 reinforced composite low-density steel prepared in the embodiments of the present invention has a significant refinement effect, exhibiting obvious yield strength and continuous yield behavior, achieving a good match between strength and plasticity, and realizing the unity of the triple goals of "macroscopic defect healing", "microstructure refinement" and "reinforcing phase distribution control".

[0107] Based on Comparative Example 1 and Examples 1-5, it can be seen that the average grain size of ferrite in the as-cast composite low-density steel sample of Comparative Example 1 is 84 μm, the average grain size of the Al2O3 reinforcing phase is 6.8 μm, the tensile strength is only 782.6 MPa, the elongation after fracture is extremely low, only 1.1%, and this composite low-density steel has no yield point, exhibiting brittle fracture. This shows that macroscopic defects and coarse grains in the as-cast microstructure severely reduce the material's density and plasticity, preventing effective plastic deformation and resulting in extremely poor mechanical properties. In contrast, the in-situ self-generated Al2O3-reinforced composite low-density steel obtained by the heat treatment method of this invention exhibits significant yield strength and continuous yield behavior, tensile strength is increased by more than 60%, elongation is increased by an order of magnitude (more than 10%), achieving a good strength-plasticity match. The average grain size of ferrite is refined from 950 μm in the as-cast state to 20~60 μm, with a significant refinement effect, laying the microstructural foundation for performance improvement.

[0108] As can be seen from Examples 1, 2, and 3, when the homogenization temperature is lower than the lower limit of the range of the present invention, the segregation phenomenon in the as-cast structure is difficult to be fully eliminated, the second phase is unevenly distributed, resulting in insufficient microstructure evolution during subsequent hot deformation, and the comprehensive mechanical properties of the material are significantly reduced. When the homogenization temperature is lower than the upper limit of the range of the present invention, abnormal grain growth or coarsening of harmful phases is easily induced, weakening the microstructure stability, which is also not conducive to the improvement of mechanical properties.

[0109] As can be seen from Examples 1, 4, and 5, when the temperature of the high-temperature hot deformation treatment is lower than the lower limit of the range of the present invention, the material's plastic deformation capacity is insufficient, dynamic recovery and dynamic recrystallization are difficult to occur effectively, and the degree of ferrite microstructure refinement is limited; when the temperature of the homogenization treatment is lower than the upper limit of the range of the present invention, the matrix grain boundary migration rate is limited, the ferrite grain growth is suppressed, and the material strength level is relatively high, but due to the limited diffusion and recovery, some defects and residual stresses in the material are difficult to be fully eliminated, resulting in poor material plasticity.

[0110] As can be seen from Examples 1, 6, and 7, when the cumulative deformation and single-pass deformation of the high-temperature hot deformation treatment are lower than the lower limit of the scope of the present invention, the internal energy storage of the material is insufficient, making it difficult to drive sufficient dynamic recrystallization, and the ferrite structure refinement effect is not obvious; when the cumulative deformation and single-pass deformation are higher than the lower limit of the scope of the present invention, the local strain of the material is concentrated, which easily induces the formation of defects, which is not conducive to the homogenization of the structure and the stability of the performance.

[0111] As can be seen from Examples 1, 8, and 9, when the solution treatment temperature is below the lower limit of the range of the present invention, the strengthening phase or alloying element is difficult to fully dissolve, the solution strengthening effect is insufficient, and the strength and plasticity of the material are limited, resulting in the deterioration of the overall mechanical properties of the material and grain coarsening. When the solution treatment temperature is above the lower limit of the range of the present invention, excessive grain boundary migration and diffusion behavior can easily lead to coarsening of the matrix grains and instability of the structure, thereby weakening the overall mechanical properties of the material.

[0112] As can be seen from Examples 1, 10, and 11, when the temperature of the medium-temperature heat deformation treatment is lower than the lower limit of the range of the present invention, the material has a greater resistance to deformation, and the recovery and recrystallization processes are limited, resulting in uneven deformation structure; when the temperature of the medium-temperature heat deformation treatment is higher than the lower limit of the range of the present invention, the thermal softening effect is too strong, and the grains are prone to grow, which is not conducive to obtaining a fine and uniform microstructure.

[0113] As can be seen from Examples 1, 12, and 13, when the cumulative deformation and single-pass deformation amount of the hot deformation treatment are lower than the lower limit of the scope of the present invention, the deformation driving force is insufficient, making it difficult to achieve sufficient microstructure control and effectively activate microstructure evolution mechanisms such as dynamic recovery and dynamic recrystallization. The coarse grains and microstructure inhomogeneity left in the casting state are difficult to eliminate, resulting in limited synergistic improvement of material strength and plasticity. When the cumulative deformation and single-pass deformation amount are higher than the lower limit of the scope of the present invention, the degree of internal stress concentration of the material increases, which easily induces defects such as local over-deformation and microcracks, affecting the consistency and stability of the final performance.

[0114] In summary, the heat treatment method of this invention breaks through the limitations of traditional single heat processing or heat treatment, creatively combining the four stages of "homogenization treatment," "high-temperature hot deformation," "solution treatment," and "medium-low temperature hot deformation" in an orderly manner. These four stages form a logically rigorous whole. First, internal stress and segregation are eliminated through high-temperature treatment. Then, defect healing and microstructure fragmentation are achieved through large deformation. Next, the matrix and reinforcing phase are stabilized through solid solution treatment. Finally, at low temperature, the fine interaction between dislocations and particles achieves final grain refinement and performance improvement, forming a synergistic reinforcement effect. This achieves the unity of the three objectives of "macroscopic defect healing," "microstructure refinement," and "reinforcing phase distribution control," ultimately obtaining a composite low-density steel with a fine δ-ferrite matrix and fine Al2O3 reinforcing phase particles, thereby significantly improving its microstructure and comprehensive mechanical properties.

[0115] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. An in-situ self-generated Al2O3 reinforced composite low-density steel, comprising a steel matrix and an Al2O3 reinforcing phase distributed in the steel matrix, characterized in that: The chemical composition of the in-situ self-generated Al2O3 reinforced composite low-density steel is as follows by mass percentage: Al2O3: 2~5.5%, Al: 9~11%, Cu: 1.5~2.5%, C: 0.1~0.3%, with the balance being Fe and unavoidable impurities; The ferrite grain size in the steel matrix exhibits a bimodal distribution structure with an average grain size of 20~60μm. The average size of the Al2O3 reinforcing phase is 1.5~3μm; the Al2O3 reinforcing phase is generated by the in-situ reaction between oxygen element in the molten metal oxide salt and aluminum element in the high-alumina steel melt during the smelting process, and the Al2O3 reinforcing phase is uniformly dispersed in the steel matrix, with the proportion of agglomerated particles of the Al2O3 reinforcing phase ≤3%; The tensile strength σ of the in-situ self-generated Al2O3 reinforced composite low-density steel b The yield strength is 1000~1200MPa. 0.2 The strength is 800~900 MPa, and the elongation after fracture δ is 15~25%.

2. A hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel as described in claim 1, characterized in that: Includes the following steps: S1, the in-situ self-generated Al2O3 reinforced composite low-density steel ingot is homogenized at a temperature of 1000~1150℃, and then transferred to room temperature circulating water for cooling. S2, the homogenized ingot is heated to 900~1100℃ for high-temperature hot deformation treatment. The deformation method is multi-directional forging, with a single-pass deformation amount of 5~10% and a cumulative deformation amount of 50~70%. S3, the ingot after high-temperature hot deformation treatment is subjected to solution treatment at a temperature of 650~750℃, and then air-cooled to room temperature. S4 involves heating the solution-treated ingot to 350~550℃ for medium-temperature hot deformation treatment. The deformation method is multi-directional forging, with a single-pass deformation amount of 5~10% and a cumulative deformation amount of 20~30%, ultimately forming an in-situ self-generated Al2O3 reinforced composite low-density steel with a bimodal ferrite grain size distribution.

3. The hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel according to claim 2, characterized in that: In step S1, the equipment used for homogenization is a muffle furnace, and the holding time is 1~3h.

4. The hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel according to claim 2, characterized in that: In step S2, the strain rate of the high-temperature heat deformation treatment is 0.1~10 s. -1 After each pressing, keep warm at 900~1100℃ for 3~5 minutes.

5. The hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel according to claim 2, characterized in that: In step S3, the equipment used for the solution treatment is a vacuum heat treatment furnace, and the solution treatment time is 0.5~1h.

6. The hot deformation method for in-situ self-generated Al2O3 reinforced composite low-density steel according to claim 2, characterized in that: In step S4, the strain rate of the medium-temperature heat deformation treatment is 0.1~10 s. -1 After each pressing, keep warm at 350~550℃ for 3~5 minutes.

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