2000 MPa-grade high-plasticity layered structure steel and preparation method thereof

Abstract

The invention relates to the technical field of alloys, and discloses 2000MPa-grade high-plasticity layered structure steel and a preparation method thereof. The 2000MPa-grade high-plasticity layered structure steel comprises the following chemical components in percentage by weight: 0.3%-0.5% of C, 6%-10% of Mn, 0.2%-0.7% of V, 0.05%-0.15% of Nb, 0.2%-1% of Al, 0.3%-1% of Si and the balance of Fe. The structure of the original austenite is in a lamellar shape, and the length-width ratio of crystal grains of the original austenite is smaller than 1.5 on the transverse-rolling direction plane. The microstructure comprises martensite laths and retained austenite, the martensite laths are arranged in order relative to the rolling direction, and the volume fraction of the retained austenite is 15%-40%. According to the rolling direction and transverse performance of the steel, the yield strength is larger than 1500 MPa, the tensile strength is larger than 2000 MPa, and the uniform ductility is larger than 15%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alloys, and particularly relates to a 2000MPa-grade high-plasticity lamellar structure steel and a preparation method thereof. BACKGROUND

[0002] Ultra-high strength steel is an important structural material in the fields of aerospace, automobile, deep sea and engineering machinery. Developing ultra-high strength steel with high strength (tensile strength exceeding 2000MPa) and high plasticity (elongation exceeding 10%) is the goal of continuous exploration and pursuit in recent years.

[0003] The strength and plasticity of ultra-high strength steel can be improved by alloying methods, such as adding more Ni, Cr, Mo, etc., or phase regulation methods, such as introducing metastable austenite. However, when the tensile strength exceeds 2000MPa, the plasticity improvement effect is poor, and the uniform elongation of most 2000MPa steel materials is less than 10%. The 2000MPa ultra-high strength steel also has problems such as high alloy cost.

[0004] At present, the 2000MPa steel material has poor strength and elongation in the transverse direction (TD) relative to the rolling direction (RD). The introduction of lamellar structure can improve the strength and plasticity of the steel material, but it will further increase the difference between the transverse and longitudinal performance and significantly worsen the transverse performance. For example, in 2020, the document "Making ultrastrong steel tough by grain-boundary delamination" obtained a tensile strength of 2144MPa in the RD direction, and a uniform elongation of 19.0%, but the tensile strength of the TD direction was 2048MPa, and the elongation after fracture was less than 10%. SUMMARY

[0005] The present application aims to at least solve one of the technical problems in the related art.

[0006] Therefore, the first aspect of the present application provides a 2000MPa-grade high-plasticity lamellar structure steel.

[0007] The second aspect of the present application provides a preparation method of a 2000MPa-grade high-plasticity lamellar structure steel.

[0008] Therefore, according to a first aspect of the present application, a 2000MPa grade high plasticity lamellar structure steel is provided, which comprises, in percentage by weight: C: 0.3%-0.5%, Mn: 6%-10%, V: 0.2%-0.7%, Nb: 0.05%-0.15%, Al: 0.2%-1%, Si: 0.3%-1%, and the rest is Fe and inevitable impurities, wherein 0.5%≤Al+Si≤2%; the original austenite of the 2000MPa grade high plasticity lamellar structure steel has a lamellar structure, and the aspect ratio of the grains of the original austenite in the transverse-rolling direction plane is less than 1.5; the microstructure of the 2000MPa grade high plasticity lamellar structure steel is a lamellar complex phase structure, which comprises martensite laths and residual austenite, the martensite laths are orderly arranged relative to the rolling direction, and the volume fraction of the residual austenite is 15%-40%.

[0009] In a possible implementation, the angle between the long axis direction of the martensite laths and the rolling direction is 30°-50°, so that the martensite laths are orderly arranged relative to the rolling direction.

[0010] In a possible implementation, the rolling direction performance of the 2000MPa grade high plasticity lamellar structure steel is: the yield strength is greater than 1500MPa, the tensile strength is greater than 2000MPa, and the uniform elongation is greater than 15%; the transverse direction performance is: the yield strength is greater than 1500MPa, the tensile strength is greater than 2000MPa, and the uniform elongation is greater than 15%.

[0011] According to a second aspect of the present application, a preparation method of a 2000MPa grade high plasticity lamellar structure steel is provided, which is used for preparing the 2000MPa grade high plasticity lamellar structure steel as described above, and comprises the following steps: preparing an austenitized metal; performing controlled rolling on the austenitized metal to obtain a hot state metal; wherein the total reduction rate of the controlled rolling is greater than 80%, the controlled rolling comprises a rough rolling stage and a finish rolling stage, in the rough rolling stage, the austenitized metal is subjected to rough rolling for 3-5 passes; in the finish rolling stage, the austenitized metal after rough rolling is subjected to finish rolling for 5-6 passes, and the finish rolling temperature is 750°C-850°C; performing a staged cooling treatment on the hot state metal to obtain a deep cold state metal; and performing a tempering and partitioning treatment on the deep cold state metal to obtain the 2000MPa grade high plasticity lamellar structure steel.

[0012] In a possible implementation, the rough rolling stage adopts transverse rolling, the rough rolling temperature is 850°C-1200°C, and the total reduction rate is 45%-55%; the finish rolling stage adopts rolling direction rolling, the finish rolling temperature is 750°C-880°C, and the total reduction rate is 20%-40%.

[0013] In one possible implementation, during the roughing stage, the first 1 to 3 transverse rolling passes are performed at 850°C to 1200°C, and the subsequent 2 transverse rolling passes are performed at 850°C to 880°C, with a total reduction of 25% to 35% for the subsequent 2 transverse rolling passes. The deformation during the roughing stage includes deformation in the fully recrystallized austenite region and deformation in the non-recrystallized austenite region, with a total deformation of 20% to 40% in the non-recrystallized austenite region.

[0014] In one possible implementation, the roughing stage has a roughing temperature of 850°C to 1200°C and a total reduction of 45% to 55%; the finishing stage has a finishing temperature of 750°C to 880°C and a total reduction of 40% to 45%; and both the roughing and finishing stages involve alternating transverse and axial rolling, ensuring that the total deformation of the non-recrystallized austenite region is greater than 40%.

[0015] In one possible implementation, the step of performing graded cooling treatment on the hot-rolled metal to obtain cryogenic metal includes: air-cooling the hot-rolled metal to obtain a metal microstructure comprising 40% to 80% retained austenite and 20% to 60% martensite laths by volume; and cryogenically cooling the air-cooled metal to obtain the cryogenic metal, wherein the microstructure of the cryogenic metal comprises 15% to 40% retained austenite and 60% to 85% martensite laths by volume.

[0016] In one possible implementation, the step of tempering and partitioning the cryogenic metal to obtain a 2000MPa grade high-plasticity layered structure steel includes: tempering and partitioning the cryogenic metal at a temperature of 200°C to 400°C for 10 to 120 minutes, and then air-cooling it to room temperature to obtain the 2000MPa grade high-plasticity layered structure steel.

[0017] In one possible implementation, the steps for preparing the austenitic metal include: preparing raw materials according to the aforementioned chemical composition and proportion of the 2000MPa grade high-plasticity layered structure steel; smelting the raw materials to obtain a cast metal, wherein the cast metal is a cast billet or steel ingot; heating the cast metal to a complete austenitizing temperature of 1100°C to 1200°C and holding it at that temperature for 2 to 3 hours to obtain the austenitic metal.

[0018] The 2000MPa grade high-plasticity layered structural steel and its preparation method provided in this application can achieve at least the following technical effects: In this application, the chemical composition of the 2000MPa grade high-plasticity layered structural steel, by weight percentage, includes: C: 0.3%~0.5%, Mn: 6%~10%, V: 0.2%~0.7%, Nb: 0.05%~0.15%, Al: 0.2%~1%, Si: 0.3%~1%, with the remainder being Fe and unavoidable impurities, of which 0.5%≤Al+Si≤2%. In terms of composition design, a low-cost Fe-C-Si-Al-Mn-V low alloy is adopted, with Mn: 6%~10%. Compared with maraging steel and nano-bainitic steel in related technologies, no expensive alloying elements such as Co and Ni are added, and the carbon content is low, which makes the raw material cost of the 2000MPa grade high-plasticity layered structural steel low and the welding performance good. The original austenite in 2000MPa grade high-plasticity layered structural steel is lamellar. In the transverse-rolling plane (i.e., the rolling surface), the aspect ratio of the original austenite grains is less than 1.5, improving the anisotropy of the steel and achieving excellent transverse and rolling properties. Furthermore, the microstructure of 2000MPa grade high-plasticity layered structural steel is a layered multiphase structure, including martensitic laths and retained austenite. The martensitic laths are arranged in an ordered manner relative to the rolling direction, and the volume fraction of retained austenite is 15% to 40%. This allows 2000MPa grade high-plasticity layered structural steel to simultaneously achieve high strength and high elongation in both the rolling direction (RD) and transverse direction (TD). Specifically, the rolling (RD) properties are: yield strength greater than 1500 MPa, tensile strength greater than 2000 MPa, and uniform elongation greater than 15%; the transverse (TD) properties are: yield strength greater than 1500 MPa, tensile strength greater than 2000 MPa, and uniform elongation greater than 15%.

[0019] The above general description and the description below are exemplary and illustrative only and are not intended to limit this application. Attached Figure Description

[0020] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations and drawings do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are shown as similar elements. The drawings are not to be scaled. And wherein: Figure 1 A flowchart illustrating the preparation method of 2000MPa grade high-plasticity layered structural steel provided in this embodiment of the disclosure; Figure 2 The image shows the original austenite morphology of the 2000MPa grade high-plasticity layered steel obtained in Example 1. Figure 2In the diagram, (a) is the original austenite morphology diagram of the RD-TD plane, (b) is the original austenite morphology diagram of the RD-ND plane, and (c) is the original austenite morphology diagram of the TD-ND plane. The dashed area pointed to by arrow S is used to indicate the original austenite grains, the straight line pointed to by arrow L1 is used to indicate the length of the original austenite grains, and the straight line pointed to by arrow L2 is used to indicate the width of the original austenite grains. Figure 3 Rolling direction (RD) tensile engineering stress of the 2000MPa grade high-plasticity layered structure steel obtained in Example 1 Strain curve diagram; Figure 4 Transverse (TD) tensile engineering stress of the 2000MPa grade high-plasticity layered structural steel obtained in Example 1 Strain curve diagram. Detailed Implementation

[0021] To provide a more detailed understanding of the features and technical content of the embodiments of this disclosure, the implementation of the embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this disclosure. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be simplified in their depiction to simplify the drawings.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in the present disclosure can be combined with each other.

[0023] It should be noted that, in the description of the embodiments of this disclosure, the rolling direction refers to the rolling direction (RD). The transverse direction (TD) is perpendicular to RD but lies within the rolling plane. The normal direction (ND) is perpendicular to the rolling plane. The RD-TD plane is the rolling surface, the RD-ND plane is the longitudinal section, and the TD-ND plane is the cross-section.

[0024] This application discloses a 2000MPa grade high-plasticity layered structural steel with the following chemical composition by weight percentage: C: 0.3%~0.5%, Mn: 6%~10%, V: 0.2%~0.7%, Nb: 0.05%~0.15%, Al: 0.2%~1%, Si: 0.3%~1%, with the remainder being Fe and unavoidable impurities. Specifically, 0.5% ≤ Al + Si ≤ 2%, meaning the sum of the Al and Si contents is greater than or equal to 0.5% and less than or equal to 2%. The original austenite in 2000MPa grade high-plasticity layered structural steel is lamellar, with an aspect ratio of less than 1.5 in the transverse-rolling plane. The microstructure of 2000MPa grade high-plasticity layered structural steel is a layered multiphase structure, consisting of martensitic laths and retained austenite. The martensitic laths are arranged in an ordered manner relative to the rolling direction, and the volume fraction of retained austenite ranges from 15% to 40%.

[0025] The chemical composition of the 2000MPa grade high-plasticity layered structural steel, by weight percentage, includes: C: 0.3%~0.5%, Mn: 6%~10%, V: 0.2%~0.7%, Nb: 0.05%~0.15%, Al: 0.2%~1%, Si: 0.3%~1%, with the remainder being Fe and unavoidable impurities, of which 0.5%≤Al+Si≤2%. In terms of composition design, a low-cost Fe-C-Si-Al-Mn-V low alloy is adopted, with Mn: 6%~10%. Compared with maraging steel and nano-bainitic steel in related technologies, it does not add expensive alloying elements such as Co and Ni, and has a low carbon content, which makes the raw material cost of the 2000MPa grade high-plasticity layered structural steel low and its welding performance good.

[0026] The original austenite microstructure of 2000MPa grade high-plasticity layered structural steel is lamellar. In the transverse-rolling plane (i.e., the rolling surface), the aspect ratio of the original austenite grains is less than 1.5, improving the anisotropy of the steel and achieving excellent transverse and rolling properties. Furthermore, the microstructure of 2000MPa grade high-plasticity layered structural steel is a layered multiphase structure, including martensitic laths and retained austenite. The martensitic laths are arranged in an ordered manner relative to the rolling direction, and the volume fraction of retained austenite is 15% to 40%. This allows the 2000MPa grade high-plasticity layered structural steel to simultaneously achieve high strength and high elongation in both the rolling direction (RD) and transverse direction (TD). Specifically, the rolling (RD) properties of 2000MPa grade high-plasticity layered structural steel are: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%. Transverse (TD) properties of 2000MPa grade high-plasticity layered structural steel: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%.

[0027] In this embodiment, the volume fraction of retained austenite of 15% to 40% means that the volume of retained austenite accounts for 15% to 40% of the microstructure volume of the 2000MPa grade high-plasticity layered structural steel.

[0028] In this embodiment, the microstructure of the 2000MPa grade high-plasticity layered structural steel is a layered multiphase structure, which can be understood as an alternating arrangement of martensite laths and retained austenite lamellae. The performance is improved through this layered multiphase structure, enabling the 2000MPa grade high-plasticity layered structural steel to exhibit similar and excellent mechanical properties in both the transverse and rolling directions.

[0029] In this embodiment, the microstructure of 2000MPa grade high-plasticity layered structural steel is controlled by “material simplification design” to obtain high-quality layered structural steel with excellent microstructure properties in both RD and TD directions in a high-efficiency and low-cost manner.

[0030] In some embodiments, the angle between the long axis direction of the martensitic lath and the rolling direction is 30° to 50°, so that the martensitic lath is arranged in an orderly manner relative to the rolling direction.

[0031] Specifically, by using a layered multiphase structure and an angle of 30° to 50° between the long axis of the martensite lath and the rolling direction, the martensite laths can be arranged in an orderly manner relative to the rolling direction. This results in a topologically ordered distribution of the martensite laths, meaning that the martensite laths are arranged regularly and orderly in geometric space. This promotes the slippage of dislocations along the lath interface, thereby increasing the mean free path of dislocations and achieving a high strength-plastic bond.

[0032] In some embodiments, the rolling properties of 2000MPa grade high-plasticity layered structural steel are: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%. The transverse properties of 2000MPa grade high-plasticity layered structural steel are: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%.

[0033] The 2000MPa grade high-plasticity layered structural steel of this embodiment exhibits excellent transverse and rolling (rolling direction can refer to longitudinal) properties, and can be applied to special engineering fields with extremely high requirements for strength and plasticity.

[0034] Combination Figure 1 As shown in the embodiments of this disclosure, a method for preparing 2000MPa grade high-plasticity layered structural steel is also provided. This method, used to prepare the aforementioned 2000MPa grade high-plasticity layered structural steel, includes the following steps: S1. Preparation of austenitic metals.

[0035] By preparing austenitic metal, a microstructure with uniform composition and excellent plasticity is provided, which provides the basic structure for subsequent controlled rolling, graded cooling treatment and tempering and partitioning treatment.

[0036] In some embodiments, the step of preparing austenitic metal includes: preparing raw materials according to the aforementioned chemical composition and proportion of 2000MPa grade high-ductility layered structural steel; smelting the raw materials to obtain cast metal, which is a cast billet or steel ingot; heating the cast metal to a complete austenitizing temperature of 1100°C to 1200°C and holding it at that temperature for 2 to 3 hours to obtain austenitic metal.

[0037] In this process, raw materials are prepared according to the aforementioned chemical composition and proportions of 2000MPa grade high-plasticity layered structural steel to provide suitable raw materials for the preparation of 2000MPa grade high-plasticity layered structural steel. The raw materials are smelted to obtain cast metal, which can be either a cast billet or a steel ingot, thus homogenizing the material composition. The cast metal is heated to the complete austenitizing temperature of 1100℃ to 1200℃ and held for 2 to 3 hours to obtain austenitized metal, refining the grains, improving plasticity, and facilitating subsequent hot working.

[0038] S2. Control rolling of austenitic metal to obtain hot-rolled metal; wherein, the total reduction ratio of controlled rolling is greater than 80%, and controlled rolling includes rough rolling stage and finish rolling stage. In the rough rolling stage, the austenitic metal is rough rolled 3 to 5 times; in the finish rolling stage, the rough rolled austenitic metal is finish rolled 5 to 6 times, and the final rolling temperature is 750℃ to 850℃.

[0039] By controlling the total rolling reduction ratio to be greater than 80%, greater plastic deformation is achieved, optimizing the grain refinement effect. Through 3 to 5 passes of rough rolling of the austenitic metal in the rough rolling stage, and 5 to 6 passes of finish rolling of the rough-rolled austenitic metal in the finish rolling stage, with a final rolling temperature of 750℃ to 850℃, deformation can be carried out within the non-recrystallized austenite region, improving strength and plasticity, and enhancing properties in different directions.

[0040] In some embodiments, the roughing stage employs transverse rolling, with a roughing temperature of 850°C to 1200°C and a total reduction of 45% to 55%. The finishing stage employs directional rolling, with a finishing temperature of 750°C to 880°C and a total reduction of 20% to 40%.

[0041] The roughing stage employs transverse rolling, i.e., widening rolling. The roughing temperature is 850℃ to 1200℃, with a total reduction of 45% to 55%, achieving efficient widening and initial microstructure refinement. The finishing stage uses directional rolling, with a finishing temperature of 750℃ to 880℃ and a total reduction of 20% to 40%, significantly improving strength and achieving excellent plasticity and toughness.

[0042] In this embodiment, the original austenite structure is controlled by transverse rolling and lateral rolling to obtain excellent lateral and lateral properties at the same time.

[0043] In some embodiments, during the roughing stage, the first 1 to 3 transverse rolling passes are performed at 850°C to 1200°C, and the subsequent 2 transverse rolling passes are performed at 850°C to 880°C, with a total reduction of 25% to 35% for the subsequent 2 transverse rolling passes, and the deformation during the roughing stage includes deformation in the fully recrystallized austenite region and deformation in the non-recrystallized austenite region, with a total deformation of 20% to 40% in the non-recrystallized austenite region.

[0044] In this process, the first three transverse rolling passes are performed at 850°C to 1200°C, and the subsequent two transverse rolling passes are performed at 850°C to 880°C. The total reduction rate of the subsequent two transverse rolling passes is 25% to 35%. This ensures that the deformation during the roughing stage includes deformation in the fully recrystallized austenite region and deformation in the non-recrystallized austenite region. The total deformation in the non-recrystallized austenite region is 20% to 40%, thereby improving strength and plasticity, and enhancing properties in different directions. Through the transverse and lateral rolling processes of this embodiment, it is possible to achieve the following properties for 2000MPa grade high-plasticity layered structural steel in both the rolling and transverse directions: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%.

[0045] In some embodiments, during the roughing stage, the roughing temperature is 850°C to 1200°C, and the total reduction is 45% to 55%. During the finishing stage, the finishing temperature is 750°C to 880°C, and the total reduction is 40% to 45%. Furthermore, both the roughing and finishing stages involve alternating transverse and axial rolling, and the total deformation of the non-recrystallized austenite region is greater than 40%.

[0046] In the roughing and finishing stages, alternating rolling is performed in both the transverse and rolling directions. Specifically, after each rolling pass, the austenitized metal plane is rotated 90° and rolling continues, ensuring that the total deformation of the non-recrystallized austenite region is greater than 40%. This helps to achieve the following performance requirements for 2000MPa grade high-plasticity layered structural steel in both the rolling and transverse directions: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%.

[0047] In other words, controlled rolling of austenitic metals can effectively improve the performance of 2000MPa grade high-plasticity layered structural steel in both the rolling and transverse directions through the following two methods.

[0048] The first method is as follows: The roughing stage uses transverse rolling. The deformation in the roughing stage includes deformation in the fully recrystallized austenite region and deformation in the non-recrystallized austenite region, with the total deformation in the non-recrystallized austenite region being 20% ​​to 40%. The finishing stage uses directional rolling, with a finishing temperature of 750℃ to 880℃ and a final rolling temperature of 750℃ to 850℃. The total reduction rate in the finishing stage is 20% to 40%.

[0049] The second method is to perform alternating transverse and directional rolling in both the roughing and finishing stages, and to ensure that the total deformation of the non-recrystallized austenite region is greater than 40%, with a final rolling temperature of 750℃ to 850℃.

[0050] S3. Perform graded cooling treatment on the hot-rolled metal to obtain cryogenic metal.

[0051] By performing graded cooling treatment on hot-rolled metal, a synergistic improvement in ultra-high strength and high plasticity can be achieved.

[0052] In some embodiments, the step of performing graded cooling treatment on hot-rolled metal to obtain cryogenic metal includes: air-cooling the hot-rolled metal to obtain a metal microstructure comprising 40% to 80% retained austenite and 20% to 60% martensite laths by volume; and then subjecting the air-cooled metal to cryogenic treatment to obtain cryogenic metal, wherein the cryogenic metal microstructure comprises 15% to 40% retained austenite and 60% to 85% martensite laths by volume.

[0053] In this embodiment, the initial distribution of the microstructure and the stabilization of austenite are achieved by air cooling the hot-rolled metal, so that the resulting metal microstructure includes 40% to 80% retained austenite and 20% to 60% martensite laths by volume.

[0054] By subjecting air-cooled metal to cryogenic treatment, the martensite lath content is increased and the martensite structure is refined, so that the microstructure of the cryogenic metal includes 15% to 40% retained austenite and 60% to 85% martensite laths by volume.

[0055] S4. Tempering and partitioning treatment is performed on the cryogenic metal to obtain a 2000MPa grade high-plasticity layered structural steel.

[0056] By tempering and partitioning the cryogenic metal, carbon partitioning is promoted, the stability of the retained austenite is enhanced, and the retained austenite undergoes a continuous transformation-induced plasticity (TRIP) effect during deformation, providing high work hardening and further increasing the strength and plasticity of the steel.

[0057] In some embodiments, the step of tempering and partitioning cryogenic metal to obtain 2000MPa grade high-plasticity layered structure steel includes: tempering and partitioning cryogenic metal at a temperature of 200°C to 400°C for 10 min to 120 min, and air-cooling to room temperature to obtain 2000MPa grade high-plasticity layered structure steel.

[0058] By tempering and partitioning cryogenic metal at 200℃ to 400℃ for 10 to 120 minutes and then air-cooling it to room temperature, a 2000MPa grade high-plasticity layered structural steel is obtained. The 2000MPa grade high-plasticity layered structural steel meets the following performance requirements in both the rolling and transverse directions: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%.

[0059] The 2000MPa grade high-plasticity layered structural steel obtained by the preparation method of this disclosure meets the following properties in both the rolling and transverse directions: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%. Specifically, through composition design and simplified process flow, costs are reduced. By controlling the rolling (hot rolling) of the austenitic metal, the properties in both the rolling and transverse directions are improved, achieving property homogenization and obtaining excellent isotropy.

[0060] This disclosure addresses the issue that traditional layered materials are prepared using unidirectional rolling, leading to grain flattening and elongation. Grain sizes are excessively long in the RD direction and significantly shorter in the TD direction. While the elongated structure in the RD direction improves the material's strength and plasticity, the TD direction exhibits very low plasticity, even leading to brittle fracture. This severe anisotropy increases the risk of cracking during forming and application. Furthermore, traditional rolling occurs in the austenite recrystallization region. This disclosure alters the rolling method to achieve a relatively uniform lamellar structure, where grain sizes are similar in both the RD and TD directions. This retains the advantages of the layered structure while maintaining similar microstructures in the transverse and rolling directions (transverse and longitudinal), resulting in excellent isotropy and broadening the applications of high-performance layered steel materials. Moreover, through alloy design and cryogenic treatment, the ratio of martensitic laths to retained austenite is controlled, introducing an appropriate amount of metastable austenite. Furthermore, tempering and fractionation treatment promotes carbon fractionation and enhances the stability of retained austenite, allowing the retained austenite to undergo a continuous transformation-induced plasticity (TRIP) effect during deformation, providing high work hardening and further increasing the strength and plasticity of the steel. This achieves the following rolling (RD) properties for 2000MPa grade high-plasticity layered microstructure steel: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%; and transverse (TD) properties: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%.

[0061] Moreover, the embodiments disclosed herein only employ hot rolling technology, without any cold working methods or additional annealing treatments, etc. The preparation process is simple and efficient, and can be used to prepare large-size, thick-gauge bulk materials.

[0062] Example 1 A 2000MPa grade high-plasticity layered structural steel, the chemical composition of which by weight percentage includes: C: 0.43%, Mn: 7.9%, Al: 0.7%, V: 0.5%, Nb: 0.07%, Si: 0.3%, with the remainder being Fe and unavoidable impurities.

[0063] A method for preparing a 2000MPa grade high-ductility layered structural steel, the preparation process of which includes the following steps: Prepare raw materials according to the chemical composition and proportion of the 2000MPa grade high-plasticity layered structural steel described above.

[0064] The raw materials are smelted and cast into billets or steel ingots (cast metal).

[0065] The billet or steel ingot is fed into a heating furnace and heated to the complete austenitization temperature of 1200℃, and held for 3 hours to obtain austenitized metal.

[0066] The austenitic metal after exiting the furnace is subjected to controlled rolling to obtain hot-rolled metal. During rough rolling, five passes are performed at 900℃ to 1200℃, with a total reduction of 50%. During finish rolling, five passes are performed at 800℃ to 850℃, with a total reduction of 43%, and the final rolling temperature is 800℃. Throughout the rolling process, after each pass, the austenitic metal is rotated 90° in the horizontal plane to achieve alternating transverse and directional rolling.

[0067] The microstructure of the hot-rolled metal after air cooling consists of 70% retained austenite and 30% martensite laths by volume.

[0068] The air-cooled metal was subjected to cryogenic treatment, that is, placed in liquid nitrogen for 15 minutes to obtain cryogenic metal. The microstructure of the cryogenic metal consists of 28% retained austenite and 72% martensite laths by volume.

[0069] The cryogenic metal was tempered and partitioned at 300°C for 15 minutes, and then air-cooled to room temperature to obtain the 2000MPa grade high-plasticity layered structure steel.

[0070] The original austenite morphology diagram of the 2000MPa grade high-plasticity layered microstructure steel obtained in Example 1 is shown below. Figure 2 As shown. Among them, Figure 2 (a) is a diagram of the original austenite morphology in the RD-TD plane (rolled surface). Figure 2 (b) is a diagram of the original austenite morphology in the RD-ND plane (longitudinal section). Figure 2 (c) is a diagram of the original austenite morphology in the TD-ND plane (cross-section). It can be seen that the original austenite structure is lamellar. Furthermore, Figure 2 In (a), the dashed area pointed to by arrow S is used to indicate the original austenite grains, the straight line pointed to by arrow L1 is used to indicate the length of the original austenite grains, and the straight line pointed to by arrow L2 is used to indicate the width of the original austenite grains. It can be seen that the aspect ratio of the original austenite grains on the RD-TD plane is approximately 1.2.

[0071] The microstructure of the 2000MPa grade high-plasticity layered structural steel obtained in Example 1 includes 31% retained austenite and 69% martensite laths by volume.

[0072] The 2000MPa grade high-plasticity layered structural steel obtained in Example 1 underwent mechanical property testing, and the following performance indicators were obtained. The rolling direction (RD) tensile curve is shown below. Figure 3 As shown, the rolling (RD) mechanical properties are: yield strength of 1580 MPa, tensile strength of 2011 MPa, and uniform elongation of 19.6%. The transverse (TD) tensile curve is shown below. Figure 4 As shown, the transverse (TD) mechanical properties are: yield strength of 1660 MPa, tensile strength of 2077 MPa, and uniform elongation of 18.2%.

[0073] Example 2: A 2000MPa grade high-plasticity layered structural steel, the chemical composition of which by weight percentage includes: C: 0.39%, Mn: 7.8%, Si: 1%, Al: 0.2%, V: 0.5%, Nb: 0.14%, with the remainder being Fe and unavoidable impurities.

[0074] A method for preparing a 2000MPa grade high-ductility layered structural steel, the preparation process of which includes the following steps: Prepare raw materials according to the chemical composition and proportion of the 2000MPa grade high-plasticity layered structural steel described above.

[0075] The raw materials are smelted and cast into billets or steel ingots (cast metal).

[0076] The billet or steel ingot is fed into a heating furnace and heated to the complete austenitization temperature of 1200℃, and held for 2 hours to obtain austenitized metal.

[0077] The austenitic metal after exiting the furnace is subjected to controlled rolling to obtain hot-rolled metal. Specifically, it is first rolled transversely for 4 passes at 850℃ to 1200℃, with a total reduction of 50%. Among them, the 3rd and 4th transverse rolling passes are rolled at a temperature of 850℃ to 880℃, with a total reduction of 30%. Then, it is rolled longitudinally for 5 passes at 800℃ to 850℃, with a total reduction of 40%, and the final rolling temperature is 800℃.

[0078] The microstructure of the hot-rolled metal after air cooling consists of 55% retained austenite and 45% martensite laths by volume.

[0079] The air-cooled metal is subjected to cryogenic treatment, that is, placed in liquid nitrogen for 20 minutes to obtain cryogenic metal. The microstructure of the cryogenic metal consists of 20% retained austenite and 80% martensite laths by volume.

[0080] The cryogenic metal was tempered and partitioned at 200°C for 60 minutes, and then air-cooled to room temperature to obtain the 2000MPa grade high-plasticity layered structure steel.

[0081] The 2000MPa grade high-plasticity layered structural steel obtained in Example 2 has an aspect ratio of approximately 1.15 for the original austenite grains on the RD-TD plane.

[0082] The microstructure of the 2000MPa grade high-plasticity layered structural steel obtained in Example 2 includes 22% retained austenite and 78% martensite laths by volume.

[0083] The 2000MPa grade high-plasticity layered structural steel obtained in Example 2 was tested for mechanical properties, and the following performance indicators were obtained: Rolling direction (RD) mechanical properties: yield strength 1548MPa, tensile strength 2260MPa, uniform elongation 16.2%. Transverse direction (TD) mechanical properties: yield strength 1610MPa, tensile strength 2310MPa, uniform elongation 15.6%.

[0084] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A 2000MPa grade high-plasticity layered structural steel, characterized in that, The chemical composition, by weight percentage, includes: C: 0.3%~0.5%, Mn: 6%~10%, V: 0.2%~0.7%, Nb: 0.05%~0.15%, Al: 0.2%~1%, Si: 0.3%~1%, with the remainder being Fe and unavoidable impurities, of which 0.5%≤Al+Si≤2%; The original austenite structure of the 2000MPa grade high-plasticity layered structure steel is lamellar, and the aspect ratio of the original austenite grains is less than 1.5 in the transverse-rolling plane. The microstructure of the 2000MPa grade high-plasticity layered structural steel is a layered multiphase structure, including martensitic laths and retained austenite. The martensitic laths are arranged in an orderly manner relative to the rolling direction, and the volume fraction of the retained austenite is 15% to 40%.

2. The 2000MPa grade high-plasticity layered structural steel according to claim 1, characterized in that, The angle between the long axis of the martensitic lath and the rolling direction is 30° to 50°, so that the martensitic lath is arranged in an orderly manner relative to the rolling direction.

3. The 2000MPa grade high-plasticity layered structural steel according to claim 1, characterized in that, The rolling properties of the 2000MPa grade high-plasticity layered structure steel are: yield strength greater than 1500MPa, tensile strength greater than 2000MPa, and uniform elongation greater than 15%. Transverse properties: Yield strength greater than 1500MPa, tensile strength greater than 2000MPa, uniform elongation greater than 15%.

4. A method for preparing a 2000MPa grade high-ductility layered structural steel, characterized in that, The method for preparing 2000MPa grade high-plasticity layered structural steel as described in any one of claims 1 to 3 comprises the following steps: Preparation of austenitic metals; The austenitic metal is subjected to controlled rolling to obtain hot-rolled metal; wherein the total reduction ratio of the controlled rolling is greater than 80%, and the controlled rolling includes a roughing stage and a finishing stage. In the roughing stage, the austenitic metal is subjected to 3 to 5 passes of roughing rolling; in the finishing stage, the rough-rolled austenitic metal is subjected to 5 to 6 passes of finishing rolling, and the final rolling temperature is 750°C to 850°C. The hot-rolled metal is subjected to a graded cooling process to obtain cryogenic metal; The cryogenic metal was subjected to tempering and partitioning treatment to obtain a 2000MPa grade high-plasticity layered structural steel.

5. The method for preparing 2000MPa grade high-plasticity layered structural steel according to claim 4, characterized in that, The roughing stage employs transverse rolling, with a roughing temperature of 850℃ to 1200℃ and a total reduction rate of 45% to 55%. The finishing rolling stage adopts directional rolling, with a finishing rolling temperature of 750°C to 880°C and a total reduction rate of 20% to 40%.

6. The method for preparing 2000MPa grade high-ductility layered structural steel according to claim 5, characterized in that, In the roughing stage, the first 1 to 3 passes of transverse rolling are performed at 850°C to 1200°C, and the subsequent 2 passes of transverse rolling are performed at 850°C to 880°C. The total reduction rate of the subsequent 2 passes of transverse rolling is 25% to 35%, and the deformation in the roughing stage includes deformation in the fully recrystallized austenite region and deformation in the non-recrystallized austenite region, with the total deformation in the non-recrystallized austenite region being 20% ​​to 40%.

7. The method for preparing 2000MPa grade high-ductility layered structural steel according to claim 4, characterized in that, During the roughing stage, the roughing temperature is 850°C to 1200°C, and the total reduction rate is 45% to 55%. During the finishing rolling stage, the finishing rolling temperature is 750°C to 880°C, and the total reduction rate is 40% to 45%. Furthermore, both the roughing and finishing rolling stages involve alternating transverse and directional rolling, ensuring that the total deformation of the non-recrystallized austenite region exceeds 40%.

8. The method for preparing 2000MPa grade high-ductility layered structural steel according to claim 4, characterized in that, The steps of performing graded cooling treatment on the hot-rolled metal to obtain cryogenic metal include: The hot-rolled metal is subjected to air cooling treatment, and the resulting metal microstructure includes 40% to 80% retained austenite and 20% to 60% martensite laths by volume. The air-cooled metal is subjected to cryogenic treatment to obtain the cryogenic metal, wherein the microstructure of the cryogenic metal comprises 15% to 40% retained austenite and 60% to 85% martensite laths by volume.

9. The method for preparing 2000MPa grade high-ductility layered structural steel according to claim 4, characterized in that, The steps for tempering and partitioning the cryogenic metal to obtain 2000MPa grade high-ductility layered structural steel include: The cryogenic metal is tempered and fractionated at a temperature of 200°C to 400°C for 10 to 120 minutes, and then air-cooled to room temperature to obtain the 2000MPa grade high-plasticity layered structure steel.

10. The method for preparing 2000MPa grade high-ductility layered structural steel according to claim 4, characterized in that, The steps for preparing austenitic metals include: Prepare raw materials according to the chemical composition and proportion of the 2000MPa grade high-plasticity layered structure steel as described in claim 1; The raw material is smelted to obtain cast metal, which is either a cast billet or a steel ingot. The as-cast metal is heated to a complete austenitization temperature of 1100°C to 1200°C and held for 2 to 3 hours to obtain the austenitized metal.

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