High-strength steel and preparation method thereof

Abstract

The high-strength steel comprises a base plate, and the base plate is prepared from, by mass, 0.18%-0.26% of C, 0.50%-1.60% of Si, 2.00%-2.80% of Mn, 0.035%-1.100% of Al, smaller than or equal to 0.020% of P, smaller than or equal to 0.010% of S, 0.010%-0.040% of Nb, 0.010%-0.040% of Ti and the balance Fe and inevitable impurities. The base plate comprises the following microscopic structures in percentage by volume: 60.0%-75.0% of bainite, 15.0%-30.0% of tempered martensite, 5.0%-10.0% of retained austenite and 0.1%-10.0% of ferrite; the grain size of the bainite is less than or equal to 5.0 microns, the grain size of the tempered martensite is less than or equal to 3.0 microns, the grain size of the retained austenite is less than or equal to 0.8 microns, and the grain size of the ferrite is less than or equal to 3.0 microns.

Description

Technical Field

[0001] The present application belongs to the technical field of steel manufacturing, and in particular relates to a high-strength steel and a preparation method thereof. Background Art

[0002] As the requirements for automobile energy conservation, emission reduction and safety become increasingly stringent, the body structure of the white car has placed higher requirements on the strength and formability of high-strength steel.

[0003] The high-strength steel used in related art for vehicle-in-white body structural parts suffers from low elongation, making it difficult to meet the requirements for manufacturing structural parts with large drawing requirements; low local formability, making it difficult to meet the requirements for manufacturing complex structural parts with high requirements for hole expansion, flanging, and bending angles; or excessively high Si content, resulting in poor surface quality and weldability. As a result, the comprehensive performance of the high-strength steel in related art, including strength, formability, surface quality, and weldability, cannot meet the increasingly stringent requirements for the strength and formability of high-strength steel.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the Invention

[0005] The present application aims to at least partially address the technical problem in the related art that the comprehensive performance of high-strength steel cannot meet the increasingly high requirements for strength and formability of high-strength steel. To this end, the present application provides a high-strength steel and a method for preparing the same.

[0006] The embodiments of the present disclosure provide a high-strength steel, comprising a substrate, wherein the substrate comprises the following components in percentage by mass:

[0007] C: 0.18% to 0.26%, Si: 0.50% to 1.60%, Mn: 2.00% to 2.80%, Al: 0.035% to 1.100%, P ≤ 0.020%, S ≤ 0.010%, Nb: 0.010% to 0.040%, Ti: 0.010% to 0.040%, the balance being Fe and unavoidable impurities;

[0008] The substrate includes the following volume percentages of microstructure:

[0009] Bainite: 60.0% to 75.0%, tempered martensite: 15.0% to 30.0%, retained austenite: 5.0% to 10.0%, and ferrite: 0.1% to 10.0%;

[0010] The grain size of the bainite is less than or equal to 5.0 μm, the grain size of the tempered martensite is less than or equal to 3.0 μm, the grain size of the retained austenite is less than or equal to 0.8 μm, and the grain size of the ferrite is less than or equal to 3.0 μm.

[0011] In some embodiments, the substrate includes the following components in weight percentages:

[0012] C: 0.21%~0.24%, Si: 0.90%~1.60%, Mn: 2.40%~2.70%, Al: 0.400%~0.700%, P≤0.020%, S≤0.010%, Nb: 0.010%~0.030%, Ti: 0.010%~0.030%, and the balance is Fe and inevitable impurities.

[0013] In some embodiments, the yield strength of the high-strength steel is greater than or equal to 850 MPa, the tensile strength of the high-strength steel is greater than or equal to 1190 MPa, the elongation of the high-strength steel is greater than or equal to 13.0%, and the hole expansion rate of the high-strength steel is greater than or equal to 40.0%.

[0014] In some embodiments, the yield strength of the high-strength steel is less than or equal to 1050 MPa, and the tensile strength of the high-strength steel is less than or equal to 1290 MPa.

[0015] In some embodiments, the high-strength steel further includes a nickel-rich layer formed on at least one side of the substrate.

[0016] In some embodiments, the high-strength steel further includes a galvanized layer, and the galvanized layer is disposed on the surface of the nickel-rich layer.

[0017] The present disclosure also provides a method for preparing the high-strength steel, which comprises the following steps:

[0018] a smelting step, providing the components of the substrate and smelting them to obtain a casting;

[0019] Hot rolling step, hot rolling the ingot to obtain a hot-rolled plate, wherein the initial hot rolling temperature of the hot rolling process is 1200° C. to 1250° C., and the final hot rolling temperature of the hot rolling process is 880° C. to 930° C.;

[0020] a coiling step of coiling the hot-rolled plate to obtain a coiled plate, wherein the coiling temperature of the coiling process is 880° C. to 930° C.;

[0021] A pickling step of pickling the coiled plate to obtain a pickled plate;

[0022] a cold rolling step of cold rolling the pickled sheet to obtain a cold rolled sheet; and

[0023] The annealing step is to anneal the cold-rolled sheet to obtain the substrate, and the annealing process includes the following stages:

[0024] In a first annealing stage, the cold-rolled sheet is heated to a first annealing temperature at a first heating rate and maintained at the first annealing temperature for a first annealing time;

[0025] In the second annealing stage, the heated cold-rolled sheet is heated to a second annealing temperature at a second heating rate and maintained at the second annealing temperature for a second annealing time;

[0026] In the slow cooling stage, the soaked cold-rolled sheet is slowly cooled to a slow cooling temperature;

[0027] In the rapid cooling stage, the cold-rolled sheet after slow cooling is rapidly cooled to a rapid cooling temperature; and

[0028] In the aging stage, the cold-rolled sheet after rapid cooling is subjected to aging treatment to obtain the substrate.

[0029] In some embodiments, in the cold rolling step, the reduction ratio of the cold rolling treatment is 40% to 60%.

[0030] In some embodiments, the first annealing temperature is greater than the temperature at which austenite begins to transform and less than the temperature at which austenite is completely transformed; the second annealing temperature is greater than the temperature at which austenite is completely transformed; and the aging temperature is less than the temperature at which tempered martensite begins to transform.

[0031] In some embodiments, the annealing step satisfies any one or more of the following annealing conditions:

[0032] The first heating rate is 2°C / s to 5°C / s, the first annealing temperature is 725°C to 735°C, and the first annealing time is 1.0 min to 2.0 min;

[0033] The second heating rate is 0.5°C / s to 3.0°C / s, the second annealing temperature is 850°C to 900°C, and the second annealing time is 1.2 min to 2.5 min;

[0034] The slow cooling temperature is 720°C to 780°C;

[0035] The rapid cooling temperature is 250°C to 300°C;

[0036] The aging temperature of the aging treatment is 300° C. to 400° C., and the aging time of the aging treatment is 0.5 min to 2.0 min.

[0037] In some embodiments, after the cold rolling step and before the annealing step, the preparation method further comprises the following steps:

[0038] a nickel plating step of plating the cold-rolled sheet to obtain a nickel-plated layer;

[0039] Wherein, before the annealing step, the thickness of the nickel plating layer is 400 mg / m 2 ~1000 mg / m 2 ; After the annealing step, the nickel-plated layer is converted into a nickel-rich layer.

[0040] In some embodiments, after the annealing step, the preparation method further comprises the following steps:

[0041] The galvanizing step is to galvanize the substrate to obtain a galvanized layer. The galvanizing temperature of the galvanizing treatment is 440° C. to 460° C., and the galvanizing belt speed of the galvanizing treatment is 70 m / min to 100 m / min.

[0042] The embodiments of the present application have at least the following beneficial effects:

[0043] The substrate of the high-strength steel is processed through a specific process to impart a specific microstructure, resulting in high strength and excellent formability. Furthermore, while maintaining high strength and formability, the high-strength steel has a low Si content, ensuring good surface quality and excellent weldability. This results in high overall performance for the high-strength steel, enabling it to better meet the increasingly demanding performance requirements for high-strength steel used in vehicle-in-white (VW) body structural components. Furthermore, the LME sensitivity of this high-strength steel is significantly lower than that of other high-strength steels of the same strength level. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application, a brief introduction will be given below to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0045] Figure 1 A photograph showing the microstructure of the high-strength steel in the embodiment of the present application is shown;

[0046] Figure 2 A schematic flow chart of a method for preparing high-strength steel in an embodiment of the present application is shown;

[0047] Figure 3 A schematic flow chart of a method for preparing high-strength steel in another embodiment of the present application is shown;

[0048] Figure 4 A process schematic diagram of the annealing step in the method for preparing high-strength steel in an embodiment of the present application is shown;

[0049] Among them, Ac1 is the temperature at which austenite begins to transform, Ac3 is the temperature at which austenite completes the transformation, and Ms is the temperature at which tempered martensite begins to transform. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0051] In addition, this application may repeat reference numbers and / or reference letters in different examples. This repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed. In addition, this application provides examples of various specific processes and materials, but those of ordinary skill in the art will recognize the application of other processes and / or the use of other materials.

[0052] The present application is described below with reference to specific embodiments and with reference to the accompanying drawings:

[0053] As the requirements for automobile energy conservation, emission reduction and safety become increasingly stringent, the body structure of white vehicles places higher demands on the strength and formability of high-strength steel.

[0054] In the related art, the comprehensive performance of high-strength steel used for body structural parts of white vehicles, including strength, formability, surface quality and welding performance, cannot meet the increasingly higher requirements for the strength and formability of high-strength steel.

[0055] Related dual-phase steel (DP) suffers from low elongation and poor formability, making it difficult to meet the requirements for manufacturing structural parts requiring high draw loads. For example, Chinese patent application CN 111455285A discloses a low-cost, easily produced, cold-rolled DP steel with a tensile strength of 980 MPa and a production method. The cold-rolled DP steel's microstructure primarily consists of ferrite and martensite, achieving a tensile strength of 980 MPa and an elongation after fracture (A80) of less than 15%, indicating relatively low elongation.

[0056] While the elongation of related high-ductility dual-phase steels (DH) and transformation-induced plasticity steels (TRIP) is somewhat superior to that of DP steel, their local formability is relatively low, making it difficult to meet the requirements for the fabrication of complex structural parts with high requirements for hole expansion, flanging, and bending angles. For example, Chinese patent application CN 114480957A discloses a 980 MPa hot-dip galvanized dual-phase steel with excellent formability and a method for manufacturing the same. This hot-dip galvanized dual-phase steel is a DH steel with a microstructure primarily composed of ferrite, bainite, martensite, and a small amount of austenite. It has a tensile strength of 980 MPa and an elongation (A80) of 15% to 17%. Although the elongation after fracture A80 of this hot-dip galvanized duplex steel has been improved, the martensite in its microstructure appears to be fresh martensite at room temperature. Those skilled in the art will appreciate that the presence of fresh martensite is detrimental to local formability. The presence of a large amount of fresh martensite in this hot-dip galvanized duplex steel significantly deteriorates its hole expansion and bending performance, making it difficult to meet the requirements for the preparation of complex structural parts with high requirements for hole expansion, flanging, and bending angles.

[0057] The microstructure of the related quenching and partitioning steel (QP) is mainly composed of tempered martensite, ferrite and a small amount of retained austenite. It uses the quenching and partitioning process to obtain a large amount of tempered martensite and an appropriate amount of retained austenite in the microstructure, which can achieve high elongation while also ensuring its hole expansion and bending performance. However, the Si content in QP steel is too high, which can easily lead to deterioration of the surface quality of QP steel. What is worse is that the excessive Si content will have a significant negative impact on the welding performance of QP steel, resulting in excessive sensitivity to liquid metal embrittlement (LME) of QP steel, which is prone to LME cracks, poor welding performance, and cannot meet the welding quality requirements of structural parts.

[0058] In response to the defects of the above-mentioned high-strength steel in the related art, the embodiments of the present disclosure provide a high-strength steel, which includes a substrate. The substrate includes the following components in percentage by mass:

[0059] C: 0.18% to 0.26%, Si: 0.50% to 1.60%, Mn: 2.00% to 2.80%, Al: 0.035% to 1.100%, P ≤ 0.020%, S ≤ 0.010%, Nb: 0.010% to 0.040%, Ti: 0.010% to 0.040%, the balance being Fe and unavoidable impurities;

[0060] The substrate includes the following volume percentages of microstructure:

[0061] Bainite: 60.0% to 75.0%, tempered martensite: 15.0% to 30.0%, retained austenite: 5.0% to 10.0%, and ferrite: 0.1% to 10.0%;

[0062] The grain size of bainite is less than or equal to 5.0 μm, the grain size of tempered martensite is less than or equal to 3.0 μm, the grain size of retained austenite is less than or equal to 0.8 μm, and the grain size of ferrite is less than or equal to 3.0 μm.

[0063] The high-strength steel proposed in the embodiments of the present disclosure has a substrate having a specific microstructure through a specific process, thereby enabling the high-strength steel to have high strength and excellent formability. At the same time, while ensuring high strength and good formability, the high-strength steel has a low Si content in its components, which can ensure good surface quality and excellent welding performance of the high-strength steel. As a result, the high-strength steel has high overall performance and can better meet the increasingly high performance requirements of high-strength steel for white vehicle body structural parts. In addition, the LME sensitivity of this high-strength steel is significantly lower than that of other types of high-strength steel of the same strength level.

[0064] The high-strength steel proposed in the embodiments of the present disclosure is a phase transformation-induced plasticity bainitic ferrite steel and can be applied to automobile body structural parts and engineering structural parts.

[0065] As an optional embodiment, the substrate includes the following components in mass percentages:

[0066] C: 0.21%~0.24%, Si: 0.9%~1.6%, Mn: 2.4%~2.7%, Al: 0.400%~0.700%, P≤0.020%, S≤0.010%, Nb: 0.010%~0.030%, Ti: 0.010%~0.030%, and the balance is Fe and inevitable impurities.

[0067] As an optional implementation, the yield strength of the high-strength steel is greater than or equal to 850 MPa, the tensile strength of the high-strength steel is greater than or equal to 1190 MPa, the elongation of the high-strength steel is greater than or equal to 13.0%, and the hole expansion rate of the high-strength steel is greater than or equal to 40.0%.

[0068] In some embodiments of the present disclosure, the yield strength of the high-strength steel is greater than or equal to 850 MPa, and the tensile strength is greater than or equal to 1190 MPa, that is, the tensile strength of the high-strength steel reaches 1200 MPa level, which has higher strength, enabling the high-strength steel to meet the higher strength requirements of vehicle body structural parts; at the same time, the elongation of the high-strength steel is greater than or equal to 13.0%, and the hole expansion rate is greater than or equal to 40.0%, that is, the formability and local formability of the high-strength steel are good, which enables the high-strength steel to meet the preparation requirements of structural parts with a large drawing amount, and can meet the preparation requirements of complex structural parts with high requirements for hole expansion flanging and bending angles.

[0069] As an optional implementation, the yield strength of the high-strength steel is less than or equal to 1050 MPa, and the tensile strength of the high-strength steel is less than or equal to 1290 MPa.

[0070] As an optional embodiment, the high-strength steel further includes a nickel-rich layer formed on at least one side of the substrate. In some embodiments of the present disclosure, a nickel-plated layer is optionally formed on the substrate before the annealing step. This allows the nickel-plated layer to diffuse inwardly toward the substrate during the annealing step, forming a nickel-rich layer with the side portions of the substrate that acts as a barrier, thereby preventing liquid metal from penetrating into the substrate, thereby reducing the LME sensitivity of the high-strength steel.

[0071] As an optional embodiment, the high-strength steel further includes a galvanized layer, and the galvanized layer is provided on the surface of the nickel-rich layer.

[0072] In some embodiments of the present disclosure, a galvanized layer is provided on the surface of the nickel-rich layer, and the galvanized layer is located at the outermost layer of the high-strength steel. The galvanized layer can improve the corrosion resistance of the high-strength steel.

[0073] The present disclosure also provides a method for preparing the high-strength steel. Figure 2 As shown, the preparation method comprises the following steps:

[0074] Smelting step S100, providing components of the substrate and smelting to obtain a casting;

[0075] Hot rolling step S200, hot rolling the ingot to obtain a hot-rolled plate, wherein the initial hot rolling temperature of the hot rolling process is 1200°C to 1250°C, and the final hot rolling temperature of the hot rolling process is 880°C to 930°C;

[0076] Coiling step S300, coiling the hot-rolled plate to obtain a coiled plate, wherein the coiling temperature of the coiling process is 880°C to 930°C;

[0077] Pickling step S400, pickling the coiled plate to obtain a pickled plate;

[0078] Cold rolling step S500, cold rolling the pickled sheet to obtain a cold rolled sheet; and

[0079] Annealing step S700, annealing the cold rolled sheet to obtain a substrate, such as Figure 4 As shown, the annealing process includes the following stages:

[0080] In the first annealing stage, the cold-rolled sheet is heated to a first annealing temperature at a first heating rate and maintained at the first annealing temperature for a first annealing time;

[0081] In the second annealing stage, the heated cold-rolled sheet is heated to a second annealing temperature at a second heating rate and maintained at the second annealing temperature for a second annealing time;

[0082] In the slow cooling stage, the soaked cold-rolled sheet is slowly cooled to the slow cooling temperature;

[0083] In the rapid cooling stage, the cold-rolled sheet is rapidly cooled to the rapid cooling temperature after slow cooling; and

[0084] In the aging stage, the cold-rolled sheet after rapid cooling is subjected to aging treatment to obtain a base plate.

[0085] The method for preparing the high-strength steel proposed in the embodiments of the present disclosure, by controlling the composition of the substrate and the conditions of each preparation step, can promote the formation of a substrate having a specific limiting structure, thereby making the high-strength steel having the substrate have high strength and excellent formability. At the same time, while ensuring high strength and good formability, the high-strength steel has a low Si content in its components, which can ensure good surface quality and excellent welding performance of the high-strength steel. As a result, the high-strength steel has high overall performance and can better meet the increasingly high performance requirements of high-strength steel for white car body structural parts. In addition, the LME sensitivity of the high-strength steel is significantly lower than that of other types of high-strength steel of the same strength level.

[0086] In some embodiments of the present disclosure, optionally, in the smelting step S100, the components of the substrate are put into a converter or an electric furnace, and after smelting in the converter or the electric furnace, continuous casting can be used to obtain a cast ingot.

[0087] In some embodiments of the present disclosure, optionally, in the hot rolling step S200, the ingot can be removed from the surface defects and then placed in a heating furnace, where the ingot is heated to an initial hot rolling temperature of 1200°C to 1250°C. The heated ingot is then taken out of the furnace and subjected to rough rolling and hot rolling in sequence until the desired thickness is reached, while ensuring that the final rolling temperature of the hot rolling treatment is 880°C to 930°C.

[0088] In the hot rolling step S200, the ingot is heated to an initial hot rolling temperature of 1200°C to 1250°C to homogenize the ingot's microstructure and allow the microalloying elements to dissolve. If the initial hot rolling temperature of the ingot exceeds 1250°C, it may cause abnormal grain growth in the ingot, hindering grain size control in the microstructure. If the initial hot rolling temperature of the ingot is lower than 1200°C, it may result in inhomogeneous microstructure and / or insufficient microalloying elements dissolving in the ingot, affecting the final microstructure.

[0089] In the hot rolling step S200, by setting the hot rolling finishing temperature to 880°C to 930°C, the hot-rolled plate obtained in the hot rolling step S200 can be guaranteed to have a good hot-rolled microstructure. If the hot rolling finishing temperature exceeds 930°C, the grains in the hot-rolled plate may become coarse, which is not conducive to grain size control in the microstructure. If the hot rolling finishing temperature is lower than 880°C, warp mixing may occur in the hot-rolled plate, and the hot-rolled plate may not form a good hot-rolled microstructure.

[0090] In some embodiments of the present disclosure, optionally, the initial hot rolling temperature of the hot rolling process may be 1200° C., 1205° C., 1210° C., 1215° C., 1220° C., 1225° C., 1230° C., 1235° C., 1240° C., 1245° C., or 1250° C. Optionally, the final hot rolling temperature may be 880° C., 885° C., 890° C., 895° C., 900° C., 905° C., 910° C., 915° C., 920° C., 925° C., or 930° C.

[0091] In some embodiments of the present disclosure, optionally, in the coiling step S300, the hot-rolled plate is coiled to obtain a coiled plate. During the coiling process, the hot-rolled plate can be kept at a coiling temperature of 880°C to 930°C.

[0092] In the coiling step S300, the coiling temperature is set to 880°C to 930°C. This is done by comprehensively considering the impact of the coiled sheet obtained from the coiling process on the load of the cold rolling mill and the surface quality of the finished cold-rolled sheet coil in the cold rolling step S500. This ensures that the cold rolling process in the cold rolling step S500 can be made relatively easy to reduce the load of the cold rolling mill, while also not negatively affecting the surface quality of the finished cold-rolled sheet coil. If the coiling temperature exceeds 930°C, the surface quality of the finished cold-rolled sheet coil in the cold rolling step S500 will be reduced. If the coiling temperature is lower than 880°C, the cold rolling process in the cold rolling step S500 will be more difficult, increasing the load of the cold rolling mill and making the cold rolling process more difficult.

[0093] In some embodiments of the present disclosure, optionally, in the pickling step S400, the coiled plate may be immersed in an acidic aqueous solution for pickling treatment to remove oxide and other films on the surface of the coiled plate to obtain a pickled plate with a clean surface.

[0094] In the pickling step S400 , the acidic aqueous solution may be any one or more aqueous solutions of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, and hydrofluoric acid.

[0095] In some embodiments of the present disclosure, optionally, in the cold rolling step S500, the pickled plate is placed in a cold rolling mill for cold rolling treatment, and the pickled plate is rolled to a preset thickness by the cold rolling mill to obtain a cold rolled plate.

[0096] In the cold rolling step S500, the thickness of the cold rolled sheet can be set to 0.7 mm to 2.5 mm. Alternatively, the thickness of the cold rolled sheet can be 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, or 2.5 mm.

[0097] In some embodiments of the present disclosure, in the annealing step S700, a stepwise heating process may be used for annealing, and the annealing process may include a first annealing stage, a second annealing stage, a slow cooling stage, a rapid cooling stage, and an aging stage. Through the staged annealing process, the microstructure of the resulting substrate can be adjusted, and the elongation of the high-strength steel can be improved by achieving a specific microstructure composition.

[0098] In the first annealing stage, the cold-rolled sheet is heated at a first heating rate to a first annealing temperature and held at the first annealing temperature for a first annealing time. During the first annealing stage, a small amount of reversed austenite with a high carbon content is initially obtained, laying the foundation for obtaining a larger amount of more stable retained austenite.

[0099] In the second annealing stage, the heated cold-rolled sheet is heated to a second annealing temperature at a second heating rate and held at the second annealing temperature for a second annealing time. In the second annealing stage, the room temperature microstructure after annealing can be adjusted so that the room temperature microstructure (microstructure) after annealing includes relatively more bainite and tempered martensite and relatively less retained austenite and ferrite.

[0100] In the slow cooling stage, the soaked cold rolled sheet can be slowly cooled in a slow cooling pit and then slowly cooled to the slow cooling temperature after a certain slow cooling time. In the slow cooling stage, the ferrite content can be adjusted by slow cooling.

[0101] In the rapid cooling stage, the cold-rolled sheet, after slow cooling, can be rapidly cooled by a cooling medium. After a certain rapid cooling time, it can be rapidly cooled to the rapid cooling temperature. In the aging stage, the cold-rolled sheet after rapid cooling is aged to obtain a substrate. During the rapid cooling and aging stages, the transformation of the two-phase microstructure can be promoted.

[0102] As an optional embodiment, optionally, in the cold rolling step S500, the reduction ratio of the cold rolling treatment is 40% to 60%.

[0103] In some embodiments of the present disclosure, in the cold rolling step S500, the pickled plate can be placed in a cold rolling mill and cold rolled at a reduction rate of 40% to 60%, and the pickled plate can be rolled to a preset thickness by the cold rolling mill to obtain a cold rolled plate.

[0104] In the cold rolling step S500, the cold rolling reduction is controlled to be between 40% and 60%. This allows the cold-rolled sheet to obtain a relatively fine microstructure, ensuring that the high-strength steel ultimately produced has a high yield strength. This also prevents excessive load on the cold rolling mill, which is detrimental to the control of the cold-rolled sheet's shape. If the cold rolling reduction exceeds 60%, this can easily lead to excessive load on the cold rolling mill, increasing the difficulty of cold rolling and detrimental to the control of the cold-rolled sheet's shape. If the cold rolling reduction is less than 40%, the low reduction is detrimental to obtaining a relatively fine microstructure in the cold-rolled sheet, resulting in a low yield strength of the ultimately produced high-strength steel, which cannot meet the strength requirements of automotive body structural parts.

[0105] In some embodiments of the present disclosure, optionally, the reduction ratio of the cold rolling process is 40%, 45%, 50%, 55%, or 60%.

[0106] As an optional embodiment, the first annealing temperature is greater than the temperature at which austenite begins to transform and less than the temperature at which austenite is completely transformed; the second annealing temperature is greater than the temperature at which austenite is completely transformed; and the aging temperature is less than the temperature at which tempered martensite begins to transform.

[0107] In the annealing step S700, by making the first annealing temperature greater than the temperature at which austenite begins to transform and less than the temperature at which austenite is completely transformed, a small amount of reverse transformed austenite with a large carbon content can be obtained in the first annealing stage of the cold-rolled sheet annealing step S700, laying a certain foundation for obtaining more retained austenite with higher stability.

[0108] In the annealing step S700, by making the second annealing temperature greater than the temperature at which austenite is completely transformed, the room temperature structure after annealing can be adjusted and the transformation of austenite can be promoted, so that the room temperature structure (microstructure) after annealing includes relatively more bainite and tempered martensite and relatively less retained austenite and ferrite.

[0109] In the annealing step S700, by making the aging temperature lower than the temperature at which the tempered martensite starts to transform, the austenite formed in the two-phase region can be promoted to transform into tempered martensite and bainite, thereby increasing the content of tempered martensite and bainite in the substrate to a certain extent, while also obtaining a proper amount of retained austenite with moderate stability.

[0110] As an optional embodiment, the annealing step S700 satisfies any one or more of the following annealing conditions: a first heating rate of 2°C / s to 5°C / s, a first annealing temperature of 725°C to 735°C, and a first annealing time of 1.0 min to 2.0 min; a second heating rate of 0.5°C / s to 3.0°C / s, a second annealing temperature of 850°C to 900°C, and a second annealing time of 1.2 min to 2.5 min; a slow cooling temperature of 720°C to 780°C; a rapid cooling temperature of 250°C to 300°C; an aging temperature of 300°C to 400°C, and an aging time of 0.5 min to 2.0 min.

[0111] In some implementations of the present disclosure, the first heating rate can be set at 2°C / s to 5°C / s, the first annealing temperature can be set at 725°C to 735°C, and the first annealing time can be set at 1.0 min to 2.0 min. Under these conditions, the first annealing stage ensures that a small amount of reversed austenite with a high carbon content is obtained in the cold-rolled sheet during this first annealing stage, laying the foundation for obtaining a larger amount of highly stable retained austenite in the subsequent second annealing stage and slow cooling stage. Optionally, the first heating rate may be 2°C / s, 2°C / s, 3°C / s, 4°C / s, or 5°C / s, the first annealing temperature may be 725°C, 726°C, 727°C, 728°C, 729°C, 730°C, 731°C, 732°C, 733°C, 734°C, or 735°C, and the first annealing time may be 1.0 min, 1.1 min, 1.2 min, 1.3 min, 1.4 min, 1.5 min, 1.6 min, 1.7 min, 1.8 min, 1.9 min, or 2.0 min.

[0112] In some embodiments of the present disclosure, the second heating rate can be set to 0.5°C / s to 3.0°C / s, the second annealing temperature can be set to 850°C to 900°C, and the second annealing time can be set to 1.2 min to 2.5 min. During the second annealing stage under these conditions, the room temperature microstructure after annealing can be adjusted so that the room temperature microstructure (microstructure) after annealing includes relatively more bainite and tempered martensite and relatively less retained austenite and ferrite. Optionally, the second heating rate may be 0.5°C / s, 0.7°C / s, 0.8°C / s, 1.0°C / s, 1.1°C / s, 1.3°C / s, 1.5°C / s, 1.7°C / s, 1.8°C / s, 2.0°C / s, 2.1°C / s, 2.3°C / s, 2.5°C / s, 2.7°C / s, 3.0°C / s, the second annealing temperature may be 850°C, 855°C, 860°C, 865°C, 870°C, 875°C, 880°C, 885°C, 900°C, and the second annealing time may be 1.2min, 1.3min, 1.4min, 1.5min, 1.6min, 1.7min, 1.8min, 1.9min, 2.0min, 2.1min, 2.2min, 2.3min, 2.4min, 2.5min.

[0113] In some embodiments of the present disclosure, the slow cooling temperature can be set at 720°C to 780°C. By controlling the slow cooling temperature at 720°C to 780°C, the ferrite content can be adjusted, and the volume percentage of ferrite in the resulting substrate can be controlled to be 0.1% to 10.0%. Alternatively, the slow cooling temperature can be 720°C, 725°C, 730°C, 735°C, 740°C, 745°C, 750°C, 755°C, 760°C, 765°C, 770°C, 775°C, or 780°C.

[0114] In some embodiments of the present disclosure, the rapid cooling temperature may be 250° C. to 300° C. By controlling the rapid cooling temperature to 250° C. to 300° C., a larger amount of primary martensite may be obtained.

[0115] In some embodiments of the present disclosure, the aging temperature can be set to 300°C to 400°C, and the aging time can be set to 0.5 min to 2.0 min. By controlling the aging temperature to 300°C to 400°C and the aging time to 0.5 min to 2.0 min, the primary martensite obtained during the rapid cooling stage can be tempered to improve the formability of the prepared high-strength steel. Furthermore, the diffusion of carbon from the primary martensite into the retained austenite can be promoted, thereby facilitating the formation of retained austenite with good stability.

[0116] In some embodiments of the present disclosure, by controlling the rapid cooling temperature to 250°C to 300°C and the aging temperature to 300°C to 400°C, the austenite formed in the two-phase region can be transformed into tempered martensite and bainite, while obtaining an appropriate amount of retained austenite with moderate stability. The volume percentage of the microstructure in the obtained substrate can then be adjusted so that the microstructure in the substrate includes 60.0% to 75.0% of bainite, 15.0% to 30.0% of tempered martensite, 5.0% to 10.0% of retained austenite, and 0.1% to 10.0% of ferrite.

[0117] In some embodiments of the present disclosure, optionally, the rapid cooling temperature may be 250° C., 255° C., 260° C., 265° C., 270° C., 275° C., 280° C., 285° C., 290° C., 295° C., or 300° C. Optionally, the aging temperature of the aging treatment may be 300° C., 310° C., 320° C., 330° C., 340° C., 350° C., 360° C., 370° C., 380° C., 390° C., or 400° C., and the aging time of the aging treatment may be 0.5 min, 0.6 min, 0.8 min, 0.9 min, 1.0 min, 1.2 min, 1.4 min, 1.5 min, 1.7 min, 1.8 min, or 2.0 min.

[0118] As an optional implementation, Figure 3 As shown, after the cold rolling step S500 and before the annealing step S700, the preparation method further includes the following steps:

[0119] Nickel plating step S600, performing nickel plating on the cold-rolled sheet to obtain a nickel-plated layer;

[0120] Before the annealing step S700, the thickness of the nickel plating layer is 400 mg / m 2 ~1000 mg / m 2 ; After the annealing step S700, the nickel-plated layer is converted into a nickel-rich layer.

[0121] In some embodiments of the present disclosure, after the cold rolling step S500 and before the annealing step S700, the cold-rolled sheet is nickel-plated to obtain a nickel-plated layer; the nickel-plated layer can diffuse toward the inner side of the substrate in the annealing step S70, and the nickel-plated layer can form a nickel-rich layer with a barrier effect together with the side portion of the substrate to prevent liquid metal from penetrating into the inner side of the substrate, thereby reducing the LME sensitivity of the high-strength steel.

[0122] In some embodiments of the present disclosure, before the nickel plating step S600 , the cold-rolled sheet is cleaned to facilitate the nickel plating process.

[0123] In some embodiments of the present disclosure, optionally, the nickel plating layer has a thickness of 400 mg / m2 ~1000 mg / m 2 After annealing, a nickel-rich layer of suitable thickness can be formed to ensure the barrier effect of the nickel-rich layer, thereby improving the effect of blocking the liquid metal from penetrating into the inner side of the substrate, thereby reducing the LME sensitivity of the high-strength steel. Optionally, the nickel plating layer thickness can be 400mg / m 2 , 450mg / m 2 , 500mg / m 2 , 550mg / m 2 , 600mg / m 2 , 650mg / m 2 , 700mg / m 2 , 750mg / m 2 , 800mg / m 2 , 850mg / m 2 , 900mg / m 2 , 950mg / m 2 , 1000mg / m 2 .

[0124] As an optional implementation, Figure 3 As shown, after the annealing step S700, the preparation method further includes the following steps:

[0125] In the galvanizing step S800, the substrate is galvanized to obtain a galvanized layer. The galvanizing temperature of the galvanizing treatment is 440° C. to 460° C., and the galvanizing belt speed of the galvanizing treatment is 70 m / min to 100 m / min.

[0126] In some embodiments of the present disclosure, optionally, a zinc plating layer can be formed on the surface of the nickel-rich layer through the nickel plating step S600, so that the zinc plating layer is located at the outermost layer of the high-strength steel, and the corrosion resistance of the high-strength steel can be improved by the zinc plating layer.

[0127] In some embodiments of the present disclosure, optionally, the galvanizing temperature of the galvanizing process can be 440°C, 445°C, 450°C, 455°C, or 460°C, and the galvanizing belt speed of the galvanizing process can be 70m / min, 75m / min, 80m / min, 85m / min, 90m / min, 95m / min, or 100m / min.

[0128] In this disclosure, unless otherwise defined, all professional terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. For example, the room temperature described in the present invention refers to an indoor temperature of 10 to 35°C. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased on the market or can be prepared by existing methods.

[0129] The high-strength steel and its preparation method disclosed in the present invention will be described in detail below with reference to a number of specific embodiments.

[0130] The high-strength steel of the disclosed embodiment can be used as steel plates for vehicle body structural parts in white, and can also be used as continuously annealed automotive steel.

[0131] Example 1

[0132] Example 1 discloses a method for preparing high-strength steel, such as Figure 3 As shown, the preparation method comprises the following steps:

[0133] Smelting step S100, providing components of the substrate and smelting to obtain a casting;

[0134] Hot rolling step S200, hot rolling the ingot to obtain a hot-rolled plate;

[0135] Coiling step S300, coiling the hot-rolled plate to obtain a coiled plate;

[0136] Pickling step S400, pickling the coiled plate to obtain a pickled plate;

[0137] Cold rolling step S500, cold rolling the pickled sheet to obtain a cold-rolled sheet;

[0138] Nickel plating step S600, performing nickel plating on the cold-rolled sheet to obtain a nickel-plated layer;

[0139] Annealing step S700, annealing the cold-rolled sheet to obtain a substrate, and

[0140] In the galvanizing step S800, the substrate is galvanized to obtain a galvanized layer. The galvanizing temperature of the galvanizing treatment is 440° C. to 460° C., and the galvanizing belt speed of the galvanizing treatment is 70 m / min to 100 m / min.

[0141] Among them, such as Figure 4 As shown, the annealing process includes the following stages:

[0142] In the first annealing stage, the cold-rolled sheet is heated to a first annealing temperature at a first heating rate and maintained at the first annealing temperature for a first annealing time;

[0143] In the second annealing stage, the heated cold-rolled sheet is heated to a second annealing temperature at a second heating rate and maintained at the second annealing temperature for a second annealing time;

[0144] In the slow cooling stage, the soaked cold-rolled sheet is slowly cooled to the slow cooling temperature;

[0145] In the rapid cooling stage, the cold-rolled sheet is rapidly cooled to the rapid cooling temperature after slow cooling; and

[0146] In the aging stage, the cold-rolled sheet after rapid cooling is subjected to aging treatment to obtain a base plate.

[0147] Among them, the components of the substrate / cast billet of Example 1 are shown in Table 1, the control conditions of each preparation step in Example 1 are shown in Table 2, and the physical and chemical properties of the high-strength steel prepared in Example 1 are shown in Table 3.

[0148] Example 1-1 to Example 1-3

[0149] The components of the substrates of Examples 1-1 to 1-3 are the same as those of Example 1. The differences between Examples 1-1 to 1-3 lie in the control conditions of each preparation step. The control conditions of each preparation step of Examples 1-1 to 1-3 are shown in Table 2. The physical and chemical properties of the high-strength steels prepared in Examples 1-1 to 1-3 are shown in Table 3.

[0150] Example 2 to Example 8

[0151] The preparation methods of Examples 2 to 8 were the same as those of Example 1. The difference between Examples 2 to 8 and Example 1 lies in the composition of the substrates, as shown in Table 1. Testing showed that the physical and chemical properties of the high-strength steels produced in Examples 2 to 8 all met the following target performance targets: a yield strength of 850 MPa to 1050 MPa, a tensile strength of 1190 MPa to 1290 MPa, an elongation greater than or equal to 13.0%, and a hole expansion ratio greater than or equal to 40.0%.

[0152] Comparative Example 1

[0153] The components of the substrate of Comparative Example 1 are shown in Table 1. The preparation method of Comparative Example 1 is the same as that of Example 1. The difference between Comparative Example 1 and Example 1 lies in the control conditions of each preparation step.

[0154] Comparative Example 1-1 to Comparative Example 1-8

[0155] The components of the substrates of Comparative Examples 1-1 to 1-8 are the same as those of Comparative Example 1. The difference between Comparative Examples 1-1 to 1-8 lies in the control conditions of each preparation step. The control conditions of each preparation step of Comparative Examples 1-1 to 1-8 are shown in Table 2. The physical and chemical properties of the high-strength steels prepared in Comparative Examples 1-1 to 1-8 are shown in Table 3.

[0156] Comparative Examples 2 to 4

[0157] The preparation methods of Comparative Examples 2 to 4 are the same as those of Comparative Example 1. The differences between Comparative Examples 2 to 4 and Comparative Example 1 lie in the composition of the substrate and the control conditions of each preparation step. The composition of the substrates of Comparative Examples 2 to 4 is shown in Table 1, the control conditions of each preparation step of Comparative Examples 2 to 4 are shown in Table 2, and the physical and chemical properties of the high-strength steels prepared in Comparative Examples 2 to 4 are shown in Table 3.

[0158] Table 1 Composition of substrates / cast billets of Examples and Comparative Examples

[0159]

[0160]

[0161] Table 2 Control conditions of each preparation step of Examples and Comparative Examples

[0162]

[0163] Table 2 continued

[0164]

[0165]

[0166] Table 3 Physical and chemical properties of high strength steel in Examples and Comparative Examples

[0167]

[0168] Table 3 continued

[0169]

[0170] Note: In Table 3, the test method for LME sensitivity adopts the general standard "General-Motors-Rapid LME Test Procedure for Coated Sheet Steels".

[0171] From the control conditions of each preparation step of each embodiment and comparative example in Table 1 to Table 3 and the physical and chemical properties of high-strength steel, it can be seen that:

[0172] The components of Examples 1-1 to 1-3 and the control conditions of each preparation step are all within the scope required by the embodiments of the present disclosure, which can effectively improve the yield strength, tensile strength and elongation after fracture A80 of the high-strength steel produced, and can also achieve a good hole expansion rate and excellent comprehensive mechanical properties; at the same time, it can also have low LME sensitivity and good welding performance. The microstructure of the high-strength steel prepared in Example 1-1 is as follows: Figure 1 As shown, from Figure 1 It can be seen that the grain size of the microstructure of the high-strength steel prepared in Example 1-1 is relatively small and uniform.

[0173] In Comparative Example 1-1, the nickel plating step was not performed, and no nickel-rich layer was formed in the obtained high-strength steel. Although its mechanical properties could reach the level of the embodiment of the present disclosure, its LME sensitivity was high and could not meet the application requirements of vehicle body structural parts, etc.

[0174] In Comparative Example 1-2, although the nickel plating step was performed, the thickness of the nickel plating layer was 200 mg / m 2 , which is much smaller than the 400 mg / m required in the embodiment of the present disclosure. 2 ~1000 mg / m 2 Although comparative examples 1-2 can form a nickel-rich layer in the high-strength steel after annealing, the thickness of the nickel-rich layer formed is much smaller than that achieved in the embodiments of the present disclosure. This has limited effect on reducing LME sensitivity, resulting in a medium LME sensitivity for the resulting high-strength steel, which cannot meet the application requirements of vehicle body structural parts, etc. In comparative examples 1-3, although the annealing step utilizes a step-by-step temperature ramp, the first annealing temperature in the first annealing stage is 750°C, far higher than the 725-735°C required in the embodiments of the present disclosure. This prevents the formation of a small amount of reversed austenite with a high carbon content during the first annealing stage, resulting in the inability to obtain a large amount of highly stable retained austenite in subsequent annealing stages. Consequently, the resulting high-strength steel has an elongation after fracture (A80) of 12.6%, far lower than the A80 of 14.5% or more achieved in the embodiments of the present disclosure.

[0175] In Comparative Examples 1-4, although the annealing step adopts a step-by-step temperature increase process, the first annealing time in the first annealing stage is only 0.5 min, which is shorter than the 1.0 min to 2.0 min required in the embodiments of the present disclosure. Therefore, the amount of reversed austenite with a large carbon content obtained in the first annealing stage is relatively low, resulting in the inability to obtain more and more stable retained austenite in the subsequent annealing stage. As a result, the improvement in the elongation of the obtained high-strength steel is relatively limited, and the elongation after fracture A80 of the obtained high-strength steel can only reach 12.8%.

[0176] In Comparative Examples 1-5, although the annealing step adopts a step-by-step heating process for annealing, the second annealing temperature in the second annealing stage is 840°C, which is lower than the 850°C to 900°C required in the embodiment of the present disclosure, resulting in the inability to obtain relatively more bainite and martensite, and thus the yield strength of the obtained high-strength steel is only 912 MPa, and the tensile strength is only 1165 MPa, which are far lower than the mechanical properties of the high-strength steel obtained in the embodiment of the present disclosure.

[0177] In Comparative Examples 1-6, although the annealing step employed a step-by-step temperature ramp, the rapid cooling stage was performed at a temperature of 241°C, lower than the 250°C to 300°C required by the disclosed embodiments. This resulted in excessive tempered martensite in the microstructure, adversely affecting the tensile strength of the high-strength steel. Consequently, the resulting high-strength steel had a tensile strength of only 1176 MPa.

[0178] In Comparative Examples 1-7, although the annealing step adopts a step-by-step heating process for annealing, the aging temperature in the aging stage is 420°C, which is higher than the aging temperature of 300°C to 400°C required by the embodiments of the present disclosure. As a result, the primary martensite obtained in the rapid cooling stage cannot be tempered, which will significantly increase the yield ratio of the high-strength steel and is not conducive to improving the formability of the high-strength steel. At the same time, it is also impossible to promote the diffusion of the C element from the primary martensite to the residual austenite, which is not conducive to obtaining retained austenite with good stability.

[0179] In Comparative Examples 1-8, although the annealing step adopts a step-by-step heating process for annealing, the aging time in the aging stage is 3.0 min, which is too long compared to the aging time of 0.5 min to 2.0 min in the embodiment of the present disclosure. As a result, the primary martensite obtained in the rapid cooling stage is excessively tempered, and the C element diffuses excessively from the primary martensite to the residual austenite, which leads to insufficient tensile strength of the obtained high-strength steel, which is only 1176 MPa.

[0180] In Comparative Example 2, the preparation method and the control conditions of each preparation step are all within the range required by the embodiments of the present disclosure. However, since the content of component C in the substrate is 0.17%, which is lower than the content range of C in the embodiments of the present disclosure, the yield strength and tensile strength of the high-strength steel finally produced are both low, which cannot meet the application requirements of vehicle body structural parts, etc.

[0181] In Comparative Example 3, the preparation method and the control conditions of each preparation step are all within the range required by the embodiments of the present disclosure. However, since the Mn content of the constituent components of the substrate is 1.9%, which is lower than the Mn content range in the embodiments of the present disclosure, the yield strength and tensile strength of the high-strength steel finally produced are both low, which cannot meet the application requirements of vehicle body structural parts, etc.

[0182] In Comparative Example 4, the preparation method and the control conditions of each preparation step are all within the range required by the embodiments of the present disclosure. However, since the Si content of the components of the substrate is 1.7%, which is higher than the Si content range of the embodiments of the present disclosure, although the high-strength steel finally produced has high yield strength and tensile strength and excellent elongation after fracture A80, its LME sensitivity is relatively high and cannot better meet the application requirements of vehicle body structural parts, etc.

[0183] In this application, references to "first," "second," and the like are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0184] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0185] In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0186] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and intent of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A high-strength steel, characterized in that: The high-strength steel comprises a substrate, and the substrate comprises the following components in percentage by mass: C: 0.18% to 0.26%, Si: 0.50% to 1.60%, Mn: 2.00% to 2.80%, Al: 0.035% to 1.100%, P ≤ 0.020%, S ≤ 0.010%, Nb: 0.010% to 0.040%, Ti: 0.010% to 0.040%, the balance being Fe and unavoidable impurities; The substrate includes the following volume percentages of microstructure: Bainite: 60.0% to 75.0%, tempered martensite: 15.0% to 30.0%, retained austenite: 5.0% to 10.0%, and ferrite: 0.1% to 10.0%; The grain size of the bainite is less than or equal to 5.0 μm, the grain size of the tempered martensite is less than or equal to 3.0 μm, the grain size of the retained austenite is less than or equal to 0.8 μm, and the grain size of the ferrite is less than or equal to 3.0 μm.

2. The high-strength steel according to claim 1, characterized in that The substrate comprises the following components in percentage by mass: C: 0.21%~0.24%, Si: 0.90%~1.20%, Mn: 2.40%~2.70%, Al: 0.400%~0.700%, P≤0.020%, S≤0.010%, Nb: 0.010%~0.030%, Ti: 0.010%~0.030%, and the balance is Fe and inevitable impurities.

3. The high-strength steel according to claim 1, characterized in that The yield strength of the high-strength steel is greater than or equal to 850 MPa, the tensile strength of the high-strength steel is greater than or equal to 1190 MPa, the elongation of the high-strength steel is greater than or equal to 13.0%, and the hole expansion rate of the high-strength steel is greater than or equal to 40.0%.

4. The high-strength steel according to claim 3, characterized in that The yield strength of the high-strength steel is less than or equal to 1050 MPa, and the tensile strength of the high-strength steel is less than or equal to 1290 MPa.

5. The high-strength steel according to any one of claims 1 to 4, characterized in that: The high-strength steel further includes a nickel-rich layer formed on at least one side of the substrate.

6. The high-strength steel according to claim 5, characterized in that The high-strength steel further includes a galvanized layer, which is arranged on the surface of the nickel-rich layer.

7. A method for preparing high-strength steel according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: a smelting step, providing the components of the substrate and smelting them to obtain a casting; Hot rolling step, hot rolling the ingot to obtain a hot-rolled plate, wherein the initial hot rolling temperature of the hot rolling process is 1200° C. to 1250° C., and the final hot rolling temperature of the hot rolling process is 880° C. to 930° C.; a coiling step of coiling the hot-rolled plate to obtain a coiled plate, wherein the coiling temperature of the coiling process is 880° C. to 930° C.; A pickling step of pickling the coiled plate to obtain a pickled plate; a cold rolling step of cold rolling the pickled sheet to obtain a cold rolled sheet; and The annealing step is to anneal the cold-rolled sheet to obtain the substrate, and the annealing process includes the following stages: In a first annealing stage, the cold-rolled sheet is heated to a first annealing temperature at a first heating rate and maintained at the first annealing temperature for a first annealing time; In the second annealing stage, the heated cold-rolled sheet is heated to a second annealing temperature at a second heating rate and maintained at the second annealing temperature for a second annealing time; In the slow cooling stage, the soaked cold-rolled sheet is slowly cooled to a slow cooling temperature; In the rapid cooling stage, the cold-rolled sheet after slow cooling is rapidly cooled to a rapid cooling temperature; and In the aging stage, the cold-rolled sheet after rapid cooling is subjected to aging treatment to obtain the substrate.

8. The method for preparing high-strength steel according to claim 7, wherein: In the cold rolling step, the reduction ratio of the cold rolling treatment is 40% to 60%.

9. The method for preparing high-strength steel according to claim 7, wherein: The first annealing temperature is greater than the temperature at which austenite begins to transform and less than the temperature at which austenite is completely transformed; the second annealing temperature is greater than the temperature at which austenite is completely transformed; and the aging temperature is less than the temperature at which tempered martensite begins to transform.

10. The method for preparing high-strength steel according to claim 9, wherein: The annealing step satisfies any one or more of the following annealing conditions: The first heating rate is 2°C / s to 5°C / s, the first annealing temperature is 725°C to 735°C, and the first annealing time is 1.0 min to 2.0 min; The second heating rate is 0.5°C / s to 3.0°C / s, the second annealing temperature is 850°C to 900°C, and the second annealing time is 1.2 min to 2.5 min; The slow cooling temperature is 720°C to 780°C; The rapid cooling temperature is 250°C to 300°C; The aging temperature of the aging treatment is 300° C. to 400° C., and the aging time of the aging treatment is 0.5 min to 2.0 min.

11. The method for preparing high-strength steel according to any one of claims 7 to 11, characterized in that: After the cold rolling step and before the annealing step, the preparation method further comprises the following steps: a nickel plating step of plating the cold-rolled sheet to obtain a nickel-plated layer; Wherein, before the annealing step, the thickness of the nickel plating layer is 400 mg / m 2 ~1000 mg / m 2 ; After the annealing step, the nickel-plated layer is converted into a nickel-rich layer.

12. The method for preparing high-strength steel according to claim 11, wherein: After the annealing step, the preparation method further comprises the following steps: The galvanizing step is to galvanize the substrate to obtain a galvanized layer. The galvanizing temperature of the galvanizing treatment is 440° C. to 460° C., and the galvanizing belt speed of the galvanizing treatment is 70 m / min to 100 m / min.

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