Martensitic steel and preparation method therefor, structural member, and terminal device

Abstract

Embodiments of the present application provide a martensitic steel and a preparation method therefor, a structural member, and a terminal device. The martensitic steel provided in the embodiments of the present application comprises the Ni element, the Co element, the Mo element, the Nb element, the C element, the Fe element and other trace elements; on the basis of the total mass of the martensitic steel, the mass fraction of the Ni element is 14%-16%, the mass fraction of the Co element is 16%-18%, the mass fraction of the Mo element is 7%-10%, the mass fraction of the Nb element is 0.1%-0.6%, and the mass fraction of the C element is 0.003%-0.1%. On the basis of the element selection of the martensitic steel and the design of the content of each element, the martensitic steel can be prepared by means of a powder molding process such as metal injection molding, and the martensitic steel prepared by means of the described process can have high strength, good toughness, and a preset shape.

Description

Martensitic steel, preparation method thereof, structural member and terminal device

[0001] The present application claims priority to the Chinese patent application No. 202411105676.7, filed on August 12, 2024, entitled "Martensitic Steel, Preparation Method Thereof and Application", and the Chinese patent application No. 202411369076.1, filed on September 27, 2024, entitled "Martensitic Steel, Preparation Method Thereof, Structural Member and Terminal Device", the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of metal materials, in particular to a martensitic steel, a preparation method thereof, a structural member and a terminal device. BACKGROUND

[0003] At present, the market demand for high-performance alloy materials is large, especially for steel materials with ultra-high strength and good toughness. At present, the above-mentioned steel materials can generally only be prepared by traditional profile processing. The above-mentioned process has great difficulty in producing high-precision complex structure workpieces, low production efficiency and low yield, which limits the commercial application of the above-mentioned steel materials. At present, high-precision metal workpieces with complex structures can be directly prepared by using powder forming processes such as metal injection molding, but due to process limitations, the strength of the steel material prepared by using the above-mentioned process is generally lower than that of the steel material prepared by traditional profile processing, or the powder forming process cannot be used at all. Therefore, it is urgent to provide a steel material that can be produced by using a powder forming technology, and the produced steel material can have high strength and good toughness. SUMMARY

[0004] The embodiments of the present application provide a martensitic steel, a preparation method thereof, a structural member and a terminal device. The martensitic steel provided by the embodiments of the present application can be prepared by using a powder forming process such as metal injection molding, and the martensitic steel prepared by the above-mentioned process can have high strength and good toughness.

[0005] The first aspect of the embodiments of the present application provides a martensitic steel. Based on the total mass of the martensitic steel, the martensitic steel includes the following mass content of each element:

[0006] 14%-16% of Ni, 16%-18% of Co, 7%-10% of Mo, 0.1%-0.6% of Nb, 0.003%-0.1% of C, and Fe, other trace elements.

[0007] By special element selection and mass ratio between elements, the above-mentioned steel can be prepared by powder forming process such as metal injection molding, and the structure of the prepared steel is mainly high-strength martensite. In addition, special component design can generate various reinforcing phases and toughening phases during the preparation of the steel, thereby effectively improving the strength and toughness of the steel.

[0008] In some embodiments of the present application, the mass percentage of Ni element in the martensitic steel is 14.5%-15.5%. In this way, it is more conducive for Ni element to fully form Ni3Mo precipitated phase with Mo element to better improve the strength of the steel; it is also conducive to promoting the formation of appropriate amount of reverse transformation austenite in the steel, so that the comprehensive mechanical properties of the martensitic steel are more excellent.

[0009] In some embodiments of the present application, the mass percentage of Mo element in the martensitic steel is 7.5%-9%. In this way, it is conducive to the formation of Ni3Mo precipitated strengthening mechanism and FeMo type precipitated strengthening mechanism, and also conducive to improving the distribution density of Ni3Mo precipitated phase and FeMo type precipitated phase, and reducing the size of Ni3Mo precipitated phase and FeMo type precipitated phase.

[0010] In some embodiments of the present application, the mass ratio of Ni element to Mo element is ≤2:1. Controlling the mass ratio of the two elements within the above range is more conducive to taking into account the strength and toughness of the martensitic steel, and further optimizing the comprehensive mechanical properties of the martensitic steel.

[0011] In some embodiments of the present application, the Ni3Mo precipitated phase is dispersed in the organizational structure of the martensitic steel; the size of the Ni3Mo precipitated phase is ≤500nm. The nanoscale size of the Ni3Mo precipitated phase has better strengthening effect on the steel, and especially the high-density nanoscale Ni3Mo precipitated phase is more conducive to improving the tensile strength of the steel.

[0012] In some embodiments of the present application, the FeMo type precipitated phase is dispersed in the organizational structure of the martensitic steel; the size of the FeMo type precipitated phase is ≤500nm. The nanoscale size of the FeMo type precipitated phase has better strengthening effect on the steel.

[0013] In some embodiments of the present application, the mass percentage of Co element in the martensitic steel is 16.5%-18%. In this way, it is more conducive to taking into account the strength and toughness of the steel.

[0014] In some embodiments of the present application, the mass percentage of Nb element in the martensitic steel is 0.2%-0.4%. In this way, it is not only conducive to more fully combining with C element, but also conducive to reducing the size of the generated NbC grains, thereby strengthening the matrix strength and optimizing the toughness of the steel.

[0015] In some embodiments of the present application, the microstructure of the martensitic steel is dispersed with NbC grains; the size of the NbC grains is ≤10 μm. The small-sized NbC grains have a better strengthening effect on the matrix, and are more conducive to improving the tensile strength of the martensitic steel.

[0016] In some embodiments of the present application, the microstructure of the martensitic steel is dispersed with reverted austenite.

[0017] In some embodiments of the present application, the martensitic steel further comprises an Al element, and the mass percentage of the Al element in the martensitic steel is ≤1%. In this way, the strength of the steel can be further improved without excessively sacrificing the toughness of the steel.

[0018] In some embodiments of the present application, the other trace elements include one or more of N element, Re element, Cu element, Ti element, S element, P element, H element, Zr element, Mg element, Ta element, Ca element, V element and Zn element; and the mass percentage of the other trace elements in the martensitic steel is ≤1%. When the above-mentioned other trace elements are contained and the mass content thereof is controlled within the above-mentioned range, the martensitic steel can be endowed or improved with other properties without causing obvious negative effects on the mechanical properties of the martensitic steel.

[0019] In some embodiments of the present application, the other trace elements include Cu element. The Cu element can improve the toughness of the steel.

[0020] In some embodiments of the present application, the tensile strength of the martensitic steel is ≥2200 MPa, and the elongation at break of the martensitic steel is ≥3%.

[0021] The second aspect of the present application provides a preparation method of a martensitic steel, comprising:

[0022] Preparation of metal particles, the metal particles include the following mass percentage of each element: 7%-9% of Ni, 16%-18% of Co, 5%-8% of Mo, 7%-9% of Cr, 0.1%-0.6% of Nb, 0.08%-0.15% of C; and Fe;

[0023] Mixing the metal particles with a binder to obtain a feedstock;

[0024] Injection molding of the feedstock to obtain a blank;

[0025] The blank is sequentially subjected to debinding, sintering and heat treatment to obtain a martensitic steel with a preset shape.

[0026] The above preparation method is based on the MIM forming process, so that a martensitic steel workpiece with complex structure and high precision can be prepared, and the production cost is low and the production efficiency is high, which is suitable for large-scale industrial production.

[0027] In some embodiments of the present application, the holding temperature of the sintering is 1220-1380℃, and the holding time is 1-8h. In this way, the combination of Nb and C in the raw material is facilitated, and nucleation sites are provided for the precipitation of Ni3Mo phase and FeMo type phase in the subsequent aging process.

[0028] In some embodiments of the present application, the heat treatment comprises solid solution treatment and aging treatment performed in sequence; the holding temperature of the solid solution treatment is 900-1100℃, and the holding time is 0.5-6h; the holding temperature of the aging treatment is 480-580℃, and the holding time is 0.5-8h. In this way, a martensitic steel with better comprehensive performance is obtained.

[0029] The third aspect of the embodiments of the present application provides a structural member comprising the martensitic steel provided by the first aspect of the embodiments of the present application, or a preset shape of the martensitic steel prepared according to the preparation method of the martensitic steel provided by the second aspect of the embodiments of the present application.

[0030] In some embodiments of the present application, the structural member comprises but is not limited to a hinge of a foldable electronic device, a part of an aerospace device.

[0031] The fourth aspect of the embodiments of the present application provides a terminal device comprising the structural member provided by the third aspect of the embodiments of the present application, or the martensitic steel provided by the first aspect of the embodiments of the present application, or a preset shape of the martensitic steel prepared according to the preparation method of the martensitic steel provided by the second aspect of the embodiments of the present application. The terminal device has high quality reliability and strong market competitiveness.

[0032] In some embodiments of the present application, the terminal device comprises but is not limited to a mobile phone, a tablet computer, a notebook computer, a smart watch, and a new energy vehicle. BRIEF DESCRIPTION OF DRAWINGS

[0033] The element distribution diagrams of different elements of the martensitic steel prepared in Example 1 are summarized in FIG. 1. DETAILED DESCRIPTION

[0034] At present, with the development of material science, various high-mechanical-property materials are emerging, such as composite materials and various alloy materials. However, the demand for high-mechanical-property alloy materials in the market is still large. The application scenarios of high-mechanical-property alloy materials include but are not limited to hinges, shafts or other load-bearing components in foldable terminal devices, and parts in aerospace devices. The above-mentioned parts generally have complex structures and high precision requirements. At present, stainless steel materials are widely used in the above-mentioned scenarios due to their ultra-high strength, high modulus and certain elongation.

[0035] In the related art, stainless steel is generally processed by traditional profile processing or powder forming technology. The traditional profile processing is to shape the blocky material by subtractive manufacturing, and the shaping methods include but are not limited to cutting, boring, drilling and grinding. In order to realize the complex structure of the parts and meet the high precision requirement, the industry usually adopts computerized numerical control (CNC) precision machining, which is strict in process and relatively low in production efficiency, and the product yield needs to be improved. The powder forming technology can realize the direct forming of complex and fine structure, which includes but is not limited to metal injection molding process (MIM), powder metallurgy (PM), 3D printing, etc. Among them, the application of MIM process is the most widely used. The process flow mainly includes mixing metal powder particles with binder, heating, and then injecting into the mold cavity by injection machine. The solidified workpiece is then subjected to degreasing, sintering, heat treatment (generally including solid solution treatment and aging treatment) and other processes to obtain finished workpiece. Compared with other processes, MIM not only can prepare high-precision complex structure workpiece, but also has low production cost and high production efficiency, which is beneficial to the application of alloy materials in the above-mentioned scenes. However, due to the difference between MIM technology and traditional forming process, the chemical composition design of high-strength steel in the related art makes it impossible to be prepared by MIM forming process. For example, in the related art, traditional process casting can use Ni3Ti precipitation system to strengthen martensitic steel, but in the MIM process, Ti element is more likely to combine with C element and O element, which reduces the Ni3Ti precipitation effect, not only wastes raw materials, but also damages the strength and toughness of the steel in the form of inclusions. In addition, for the steel that can be prepared by MIM forming process, the strength of the steel prepared by MIM forming process is generally lower than that of the steel prepared by traditional processing under the condition that the chemical components are completely the same. In the face of rapid product replacement, the existing MIM steel cannot meet the reliability requirements of the product, which will seriously limit the development and application of MIM materials.

[0036] In order to better understand the technical solutions of the present application, the following explanations are provided for some key terms involved in the present application:

[0037] Martensite: a microstructure structure of steel and iron with high hardness and low plasticity, which is a supersaturated solid solution of carbon in a-Fe, and is relatively stable at low temperature (room temperature and below room temperature), providing hardness to the material. The three-dimensional organization form of martensite is usually plate or lath, but it is usually needle-shaped in metallographic microscope observation (two-dimensional).

[0038] Austenite: A microstructure of steel with high plasticity and toughness, which is stable at high temperature and provides plasticity to the material as a whole.

[0039] Reverse austenite: Austenite obtained after heating the material to austenite transformation temperature after the preparation of the material.

[0040] Ferrite: Ferrite is a interstitial solid solution in which carbon is dissolved in α-Fe.

[0041] Metal injection molding: A powder metallurgy molding technique in which metal particles and a binder are mixed and injected into a mold to form a blank, and the binder is completely removed and the blank is densified in the subsequent sintering process.

[0042] Injection: The process of injecting heated and softened metal and binder mixed particles (industry commonly referred to as "feedstock") into a mold to shape by means of an injection molding machine.

[0043] Debinding: The process of removing most of the binder from the injection-molded blank by one or more processes such as catalysis, heating, dissolution, etc. before sintering.

[0044] Sintering: The process of making powder bodies densify and recrystallize by heating to give the molecules or atoms in the solid sufficient energy to migrate, causing the particles to bond and produce strength.

[0045] Solution: That is, solution treatment, refers to the process of obtaining a metastable supersaturated solid solution single-phase structure when the solid solution is solidified, and the equilibrium transformation is inhibited.

[0046] Aging: That is, aging treatment, refers to the heat treatment process in which the alloy workpiece is subjected to solution treatment, quenched from high temperature or deformed by cold working to a certain extent, and then placed at a higher temperature or room temperature to maintain its shape, size, and performance changes over time.

[0047] Tensile strength: The maximum stress value that the material can withstand before breaking in a tensile test, with units of MPa.

[0048] Elongation at break: The percentage of the length of the sample after elongation to the original length in a tensile test.

[0049] The embodiments of the present application provide a martensitic steel, based on the total mass of the above martensitic steel, the martensitic steel includes the following mass content of each element:

[0050] 14%-16% of Ni, 16%-18% of Co, 7%-10% of Mo, 0.1%-0.6% of Nb, 0.003%-0.1% of C; and Fe, other trace elements.

[0051] The martensitic steel provided in the embodiments of the present application can form a microstructure mainly of martensite with high strength, and is beneficial to the formation of various strengthening mechanisms and the formation of toughening phases, thereby effectively improving the strength and toughness of the steel, so that the steel exhibits high tensile strength and high elongation at break.

[0052] Specifically, in the chemical environment of the martensitic steel in the embodiments of the present application, the mass content of Ni element (nickel element) is controlled in the range of 14%-16%, which is beneficial to the reaction with Mo element (molybdenum element) to form Ni3Mo precipitates to improve the strength of the steel, and is beneficial to the formation of reverted austenite in the microstructure to improve the toughness of the steel. For example, the mass content of Ni element in the martensitic steel can be 14.0%, 14.1%, 14.2%, 14.3%, 14.4%, 14.5%, 14.6%, 14.7%, 14.8%, 14.9%, 15.0%, 15.1%, 15.2%, 15.3%, 15.4%, 15.5%, 15.6%, 15.7%, 15.8%, 15.9%, or 16.0%.

[0053] A higher content of Mo element is easy to react with Ni element to form the above-mentioned Ni3Mo precipitates, and is also beneficial to the formation of FeMo-type precipitates in the preparation process of the steel, thereby effectively improving the strength of the steel. It should be noted that in the embodiments of the present application, the FeMo-type precipitates refer to precipitates formed by Fe element and Mo element, and do not mean that the stoichiometric ratio of Fe element and Mo element is 1:1; in some specific embodiments, the stoichiometric ratio of Fe element and Mo element in the FeMo-type precipitates can be 2:1 or 1:1, or (1-2):1, and the chemical formula thereof can be Fe2Mo, FeMo, etc. For example, the mass content of Mo element in the martensitic steel can be 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9.0%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, 9.6%, 9.7%, 9.8%, 9.9%, or 10.0%.

[0054] A higher amount of Co element (cobalt element) is beneficial to be dissolved in the matrix during the preparation of the steel material to improve the strength of the steel material, and can delay the dislocation recovery in the microstructure to improve the dislocation density to strengthen the dislocation strengthening effect. For example, the mass percentage of Co element can be 16.0%, 16.1%, 16.2%, 16.3%, 16.4%, 16.5%, 16.6%, 16.7%, 16.8%, 16.9%, 17.0%, 17.1%, 17.2%, 17.3%, 17.4%, 17.5%, 17.6%, 17.7%, 17.8%, 17.9%, 18.0%.

[0055] It can be understood that C element (carbon element) is one of the necessary component elements of the steel material, but C element has a greater negative impact on the mechanical properties of the martensitic steel, for example, combined with Mo element or Fe element during the preparation of the steel material, and disturbs the microstructure of the steel material. The introduction of 0.1%-0.6% mass content of Nb element is beneficial to react with C element to form NbC grains under high temperature environment during the preparation of the steel material, which not only can reduce the risk of mechanical performance damage caused by C element disturbing the microstructure of the steel material, form NbC grain strengthening, and further improve the strength of the steel material; but also can expand the process window of sintering during the preparation of the steel material (for example, expand the temperature interval of sintering), reduce the control difficulty of MIM process; and a certain mass content of Nb element can also reduce the problem of excessive residual carbon caused by low clean sintering of MIM process. For example, the mass content of Nb element in the martensitic steel can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, etc. For example, the mass content of C element in the martensitic steel can be 0.003%, 0.005%, 0.008%, 0.01%, 0.02%, 0.025%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%.

[0056] In the embodiments of the present application, the mass percentage of Fe element (iron element) in the martensitic steel is 54.3%-62.897%. Specifically, the mass percentage of Fe element in the martensitic steel can be 54.3%, 54.5%, 55%, 55.5%, 55.5%, 56%, 56.5%, 56.9%, 57%, 58%, 59%, 60%, 61%, 61.2%, 61.3%, 62%, 62.2%, 62.5%, 62.8%, 62.85%, 62.87%, 62.88%, 62.89%, etc.

[0057] In some embodiments of the present application, the other trace elements include inevitable impurities introduced by raw materials during the preparation of the martensitic steel, and can further include elements intentionally added to improve other properties of the martensitic steel; for example, N element, Re element, Cu element, Ti element, Zr element, Mg element, Ta element, Ca element, V element and Zn element. The above other properties may, for example, be corrosion resistance, oxidation resistance, welding performance, etc. In some embodiments of the present application, the sum of the mass percentage of the other trace elements in the martensitic steel is ≤1%. Specifically, the mass percentage of the other trace elements in the martensitic steel may, for example, be 0.003%, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0058] In some embodiments of the present application, the martensitic steel includes the following mass contents of each element based on the total mass of the martensitic steel: 14%-16% of Ni element, 16%-18% of Co element, 7%-10% of Mo element, 0.1%-0.6% of Nb element, 0.003%-0.1% of C element, 54.3%-62.897% of Fe element, and other trace elements, the sum of the mass percentage of the other trace elements in the martensitic steel being ≤1%. In some specific embodiments, the martensitic steel includes the following mass contents of each element: 14%-16% of Ni element, 16%-18% of Co element, 7%-10% of Mo element, 0.1%-0.6% of Nb element, 0.003%-0.1% of C element, the sum of the mass percentage of the other trace elements being ≤1%, and the balance being Fe element.

[0059] In some embodiments of the present application, inductively coupled plasma technology (inductively coupled plasma, ICP) can be used, for example, Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), to test the presence and mass content of each of the above elements in the martensitic steel.

[0060] In some embodiments of the present application, the mass percentage of the Ni element in the martensitic steel is 14.5%-15.5%. In this way, when the martensitic steel is prepared using the MIM forming process, it is more conducive for the Ni element to form Ni3Mo precipitated phases with the Mo element during the aging treatment stage, so as to better improve the strength of the steel. In addition, it is also conducive to promoting the formation of reverted austenite in the steel, and the distribution density of the reverted austenite can be controlled within a more suitable range, so that the overall mechanical properties of the martensitic steel are more optimal.

[0061] In some embodiments of the present application, the martensitic steel has dispersed reverted austenite in the microstructure. In some specific embodiments, the martensitic steel has reverted austenite between the martensite microstructure and the Ni3Mo precipitates. The martensitic steel with the above microstructure is easier to prepare and has better toughness. In the embodiments of the present application, the reverted austenite with a non-triangular cross-section can be observed under a metallographic microscope, and the reverted austenite is dispersed in the grains and between the lamellas.

[0062] In some embodiments of the present application, the mass percentage of Mo in the martensitic steel is 7.5%-9%. Controlling the mass content of Mo within the above range is conducive to the formation of the Ni3Mo precipitation strengthening mechanism and the FeMo type precipitation strengthening mechanism, and is also conducive to improving the distribution density of the Ni3Mo precipitates and the FeMo type precipitates and reducing the size of the Ni3Mo precipitates and the FeMo type precipitates.

[0063] In some embodiments of the present application, the mass ratio of Ni to Mo is ≤2:1. In some specific embodiments, the mass ratio of Ni to Mo is (1.6-1.9):1. Controlling the mass ratio of Ni to Mo within the above range is more conducive to balancing the strength and toughness of the martensitic steel and further optimizing the comprehensive mechanical properties of the martensitic steel. Specifically, the mass ratio of Ni to Mo may, for example, be 2:1, 1.95:1, 1.9:1, 1.85:1, 1.8:1, 1.75:1, 1.7:1, 1.65:1, 1.6:1, etc.

[0064] In some embodiments of the present application, the martensitic steel has dispersed Ni3Mo precipitates in the microstructure. In some specific embodiments, the size of the above Ni3Mo precipitates is ≤500 nm. In the embodiments of the present application, the existence and size of the Ni3Mo precipitates can be characterized by using the atom probe tomography (APT) technique, or the size of the Ni3Mo precipitates can be tested by using a high-magnification scanning electron microscope (SEM), for example, an SEM with a magnification of more than 10,000 times. The nanoscale Ni3Mo precipitates have a better strengthening effect on the steel, and especially, high-density nanoscale Ni3Mo precipitates are more conducive to improving the tensile strength of the steel. Specifically, the size of the Ni3Mo precipitates may, for example, be 20 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, or ≤20 nm, etc.

[0065] In some embodiments of the present application, the microstructure of the martensitic steel is dispersed with FeMo type precipitates; the size of the FeMo type precipitates is ≤500 nm. In the embodiments of the present application, APT can be used to characterize the existence and size of the FeMo type precipitates, or high-magnification SEM can be used to test the size of the FeMo type precipitates. Similarly, the nanoscale FeMo type precipitates have better strengthening effect on the steel, and especially, the high-density nanoscale FeMo type precipitates are more conducive to improving the tensile strength of the steel. Specifically, the size of the FeMo type precipitates can be, for example, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, or ≤20 nm, etc.

[0066] In some embodiments of the present application, the mass percentage of Co in the martensitic steel is 16.5%-18%. During the preparation of the martensitic steel, Co generally does not form compounds with other metal elements in the system, but is solid-solved in the matrix. Controlling the mass content of Co within the above range is more conducive to inhibiting the dislocation recovery of the martensitic microstructure, improving the dislocation density, and more conducive to improving the dislocation strengthening effect; in addition, it can also provide nucleation sites for the above-mentioned precipitate microstructure during the aging stage, strongly promote the aging strengthening reaction, and give the martensitic steel higher tensile strength. Furthermore, it can also improve the austenite transformation temperature (Ms) of the martensite, inhibit the tendency of the martensite to transform into austenite, reduce the risk of the martensite transforming into austenite, and help to ensure that the steel has high strength.

[0067] In some embodiments of the present application, the mass percentage of Nb element in the martensitic steel is 0.2%-0.4%. Nb element is a strong carbide forming element. In the chemical environment of the martensitic steel of the embodiments of the present application, Nb element can react with C element and Mo element and Fe element to generate NbC grains at high temperature. Further controlling the content of Nb element in the above range not only helps to combine C element more sufficiently, but also helps to reduce the size of the generated NbC grains, thereby strengthening the matrix strength and optimizing the toughness of the steel. In some embodiments of the present application, the microstructure of the martensitic steel is dispersed with NbC grains. In some embodiments of the present application, the size of the NbC grains is ≤10 μm. In some specific embodiments, the size of the NbC grains is ≤2 μm, for example, 1 μm-2 μm. The small-sized NbC grains have a better strengthening effect on the matrix and are more conducive to improving the tensile strength of the martensitic steel. Specifically, the size of the NbC grains can be, for example, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm. In the embodiments of the present application, APT can be used to characterize the existence and size of the NbC grains, or high-magnification SEM can be used to test the size of the NbC grains.

[0068] In some embodiments of the present application, the martensitic steel includes the following mass content of each element based on the total mass of the martensitic steel: 14.5%-15.5% of Ni element, 7.5%-9% of Mo element, 16.5%-18% of Co element, 0.2%-0.4% of Nb element, 0.003%-0.1% of C element, 56%-61.297% of Fe element, and ≤1% of other trace elements. In this way, it is more conducive to obtaining a martensitic steel with high strength and high toughness.

[0069] In some embodiments of the present application, the tensile strength of the martensitic steel is ≥ 2200 MPa, and the elongation at break of the martensitic steel is ≥ 3%. In the embodiments of the present application, the tensile strength and the elongation at break of the martensitic steel are tested according to GB / T 228.1-2021 "Metallic Materials-Tensile Testing-Part 1: Method of Test at Room Temperature". It should be noted that the martensitic steel prepared by using the MIM forming technology can achieve the above strength and toughness, and the martensitic steel of the above composition prepared by using the traditional profile processing has better tensile strength and toughness. Specifically, the tensile strength of the martensitic steel can be, for example, 2200 MPa, 2220 MPa, 2250 MPa, 2280 MPa, 2300 MPa, 2320 MPa, 2350 MPa, 2380 MPa, 2400 MPa, 2420 MPa, 2450 MPa, etc.; the elongation at break of the martensitic steel can be, for example, 3%, 3.5%, 4%, 4.2%, 4.5%, 4.8%, 5.0%, 5.2%, 5.5%, 5.8%, 6.0%, 6.2%, 6.5%, 6.8%, 7.0%, etc.

[0070] In some embodiments of the present application, the other trace elements include, but are not limited to, one or more of N element (nitrogen element), Re element (rhenium element), Cu element (copper element), Ti element (titanium element), S element (sulfur element), P element (phosphorus element), H element (hydrogen element), Zr element (zirconium element), Mg element (magnesium element), Ta element (tantalum element), Ca element (calcium element), V element (vanadium element), and Zn element (zinc element). In the embodiments of the present application, the sum of the mass fractions of the other trace elements in the martensitic steel is controlled to be ≤ 1%. When the above other trace elements are contained in the martensitic steel and the mass content thereof is controlled within the above range, the martensitic steel can be endowed or improved with other properties without significantly negatively affecting the mechanical properties of the martensitic steel. For example, a small amount of Ti element can improve the oxidation resistance of the steel, but the mass fraction of Ti element is controlled to be ≤ 0.3% to avoid the reaction of a large amount of Ti element with O element to generate titanium oxide, which affects the mechanical properties of the steel; a small amount of V element can help to improve the fatigue strength of the steel, etc.

[0071] When the application scene of the steel material requires higher toughness and looser strength, Cu element can be introduced into the martensitic steel of the embodiments of the present application. In some embodiments of the present application, the other trace elements include Cu element. In some specific embodiments, the martensitic steel includes Cu element, and the mass percentage of Cu element in the martensitic steel is ≤1%. In this way, the martensitic steel can maintain its tensile strength within a certain level and has better toughness. For example, the tensile strength of the martensitic steel is ≥2100 MPa, and the elongation at break is ≥6.5%. Specifically, the mass percentage of Cu element in the martensitic steel may, for example, be 0.003%, 0.005%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0072] Considering that in some scenarios in the actual application process of the martensitic steel, the strength requirement of the steel material is higher and the toughness demand is lower. In some embodiments of the present application, the martensitic steel further includes Al element; the mass percentage of Al element in the martensitic steel is ≤1%. The appropriate addition of Al element can further improve the strength of the martensitic steel at the cost of slightly losing the toughness of the martensitic steel. For example, the tensile strength of the martensitic steel is ≥2400 MPa, and the elongation at break is ≥2.3%. Specifically, the mass percentage of Al element in the martensitic steel may, for example, be 0.003%, 0.005%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0073] It should be noted that the martensitic steel provided in the present application can be a martensitic steel material of any shape; for example, the martensitic steel may, for example, be a strip material, a plate material, or a workpiece with a certain structural shape, but is not limited thereto.

[0074] The embodiments of the present application also provide a preparation method of a martensitic steel, which can be used to prepare the aforementioned martensitic steel; the preparation method comprises:

[0075] S1, preparing metal particles, the metal particles comprising the following mass percentage of each element: 14%-16% of Ni, 16%-18% of Co, 7%-10% of Mo, 0.1%-0.6% of Nb, 0.003%-0.1% of C; and Fe; in the preparation of the martensitic steel, the mass content of the elements of Ni, Co, Mo, Nb and Fe basically does not change. In addition, since the raw material of the steel may contain some O elements (oxygen elements), the oxygen elements can be removed in the preparation process (for example, sintering) of the steel. In some embodiments of the present application, the oxygen content of the metal particles is controlled to be ≤0.5wt%; in some specific embodiments, the oxygen content of the metal particles is controlled to be ≤0.3wt%. In this way, the oxygen content of the final martensitic steel can be controlled in a lower range; for example, the oxygen content of the martensitic steel is ≤0.02wt%. It can be understood that other trace elements in the martensitic steel of the embodiments of the present application include unavoidable impurity elements, or further include intentionally added trace elements. When the martensitic steel to be prepared contains the above intentionally added trace elements, especially intentionally added metal trace elements, the raw material of the metal particles also needs to add the above metal trace elements according to the mass content to be prepared.

[0076] S2, mixing the above metal particles with a binder to obtain a feedstock;

[0077] S3, injection molding the above feedstock to obtain a blank;

[0078] S4, sequentially performing debinding, sintering and heat treatment on the above blank to obtain a martensitic steel with a preset shape.

[0079] The above preparation method is based on the MIM forming process, so that a martensitic steel workpiece with complex structure and high precision can be prepared, and the production cost is low, the production efficiency is high, and it is suitable for large-scale industrial production. It can be understood that those skilled in the art can also use traditional profile processing methods to prepare the aforementioned martensitic steel provided in the embodiments of the present application, which is not limited by the present application.

[0080] In some embodiments of the present application, the metal particles in step S1 can be prepared by atomization. In some specific embodiments, the particle size D10 of the metal particles is less than or equal to 4.5 microns, the particle size D50 is between 5 microns and 14 microns, and the particle size D90 is less than or equal to 35 microns. Controlling the particle size of the metal particles within the above range can improve the uniformity of the structure of the final martensitic steel and reduce the size of the structure, thereby improving the strength and toughness of the prepared martensitic steel. Specifically, in step S1, the particle size D10 of the metal particles can be, for example, 1.0 micron, 1.5 microns, 2.0 microns, 2.5 microns, 3.0 microns, 3.5 microns, 4.0 microns, 4.5 microns, etc., the particle size D50 can be, for example, 5 microns, 6 microns, 7 microns, 8 microns, 9 microns, 10 microns, 11 microns, 12 microns, 13 microns, 14 microns, etc., and the particle size D90 can be, for example, 20 microns, 21 microns, 22 microns, 23 microns, 24 microns, 25 microns, 26 microns, 27 microns, 28 microns, 29 microns, 30 microns, 31 microns, 32 microns, 33 microns, 34 microns, 35 microns, etc. In the embodiments of the present application, a laser particle size analyzer can be used to test the particle size distribution of the metal particles. In the embodiments of the present application, the raw material used to prepare the metal particles can be, for example, a single element or an alloy of the above-mentioned elements, or a mixture of a single element and an alloy, and the mass ratio of the elements in the metal particles can be controlled within the above range, which is not limited in the present application.

[0081] In some embodiments of the present application, the binder in step S2 can be any binder suitable for the preparation of martensitic steel in the art, for example, one or more of polyoxymethylene (POM), ethylene-vinyl acetate copolymer (EVA), polyethylene (PE), CW-based epoxy resin, sodium alginate (SA), but not limited to. In some specific embodiments, the binder is a mixture of POM, EVA, PE, CW, and SA; for example, the mass ratio of POM, EVA, PE, CW, and SA is 85:1:5.5:2:1, but not limited to.

[0082] In the embodiments of the present application, the mixing ratio of the metal particles and the binder in step S2 can be any ratio known to those skilled in the art. In some embodiments of the present application, the metal particles and the binder are mixed in a volume ratio of 1:(0.15-0.25). In this way, it is beneficial to obtain a feed with good forming performance, and it is beneficial to completely remove the binder in the subsequent process to obtain a martensitic steel with better overall performance.

[0083] In some embodiments of the present application, the above-mentioned feedstock can be prepared by using an internal mixer. Specifically, the metal particles and the binder are mixed in a certain volume ratio, and then fed into the internal mixer for mixing to obtain a uniform paste-like feedstock. The paste-like feedstock is then moved into a granulator, and the screw of the granulator extrudes the gradually cooled paste-like feedstock through a die head and the rotating blade cuts the extruded material to obtain cylindrical granular feedstock with a length of 2-3 mm. The cylindrical granular feedstock can be directly used for injection molding. In some specific embodiments, the parameters of the internal mixer can be any parameters used in the field for the preparation of feedstock for MIM process molding, for example, the temperature is set to 180-195°C, the mixing time is 2 h, and the blade rotation speed is 20 r / min, but the present application is not limited thereto.

[0084] In some embodiments of the present application, in step S3, the injection molding process can be any process known to those skilled in the art. In some embodiments, the above-mentioned cylindrical granular feedstock is fed into an injection molding machine and molded at a certain temperature and pressure to obtain a green part. For example, the injection temperature can be 195°C, and the injection pressure can be 200 MPa, but the present application is not limited thereto.

[0085] In some embodiments of the present application, in step S4, the parameters of the debinding process can be any debinding process known to those skilled in the art and suitable for the preparation of martensitic steel, and the present application does not limit the debinding process. In some embodiments, the debinding is catalytic debinding. Specifically, fuming nitric acid can be used as a catalyst. In some specific embodiments, the green part is placed in a catalytic debinding furnace, the temperature is set to 110-130°C, the fuming nitric acid is introduced at a rate of 3.5 g / min, and the debinding time is 2 h, but the present application is not limited thereto.

[0086] In some embodiments of the present application, in step S4, the holding temperature of the sintering is 1220-1380°C. It should be noted that the sintering needs to be carried out in a protective atmosphere, for example, argon. It can be understood that the sintering needs to be carried out in a sintering device (for example, a sintering furnace), and the holding temperature of the sintering refers to that the sintering temperature of the sintering device is set to 1220-1380°C, and during the sintering process, the temperature in the furnace fluctuates within ±5°C of the set temperature, which is acceptable and does not affect the performance of the martensitic steel prepared. Therefore, during the sintering process, the temperature in the furnace of the sintering device is (1220-1380°C) ±5°C, which is also considered to be within the protection scope of the present application. In some embodiments of the present application, the holding time of the sintering is 1-8h. In some specific embodiments, the holding temperature of the sintering is 1220-1380°C, and the holding time is 1-8h, to obtain a sintered blank. In this way, it is beneficial to the combination of Nb and C elements in the raw material, and to provide nucleation sites for the subsequent precipitation of Ni3Ti and FeMo type phases during the aging process. Specifically, during the sintering process, the set temperature of the sintering device can be, for example, 1220°C, 1250°C, 1280°C, 1300°C, 1320°C, 1350°C, 1380°C, etc. Specifically, the holding time of the sintering process can be, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0087] In some embodiments of the present application, in step S4, the heat treatment includes solid solution treatment and aging treatment carried out in sequence. In some embodiments of the present application, the holding temperature of the solid solution treatment is 900-1100°C. Similarly, the solid solution treatment needs to be carried out in a heat treatment device, and the holding temperature of the solid solution treatment refers to that the temperature of the heat treatment device (for example, a heat treatment furnace) is set to 900-1100°C, and during the solid solution treatment process, the temperature in the furnace of the heat treatment furnace fluctuates within ±5°C of the set temperature, which is acceptable and does not affect the performance of the martensitic steel prepared. Therefore, during the solid solution treatment, the temperature in the furnace of the heat treatment device is (900-1100°C) ±5°C, which is also considered to be within the protection scope of the present application. In some embodiments of the present application, the holding time of the solid solution treatment is 0.5-6h. Controlling the temperature and holding time of the solid solution treatment within the above range is beneficial to obtain a martensitic steel with better comprehensive performance. Specifically, during the solid solution treatment, the set temperature of the heat treatment device can be, for example, 900°C, 920°C, 950°C, 980°C, 1000°C, 1020°C, 1050°C, 1080°C, 1100°C, etc. Specifically, the holding time of the sintering process can be, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, etc.

[0088] In some embodiments of the present application, after the solution treatment, the sintered blank after the solution treatment is oil-cooled, and then the sintered blank after the solution treatment is heated for aging treatment. In some embodiments of the present application, the sintered blank after the solution treatment is oil-cooled to 60℃. In some specific embodiments, the sintered blank after the solution treatment is desirably oil-cooled to room temperature (25℃±2℃). In some embodiments of the present application, the holding temperature of the aging treatment is 480℃-580℃. Similarly, the aging treatment needs to be carried out in a heat treatment device, and the holding temperature of the aging treatment mentioned above refers to that the temperature of the heat treatment device (for example, a heat treatment furnace) is set to 480℃-580℃, and during the aging treatment, the temperature fluctuation of the heat treatment furnace is acceptable within ±5℃ of the set temperature, which does not affect the performance of the prepared martensitic steel, and is all considered to be within the protection scope of the present application. In some embodiments of the present application, the holding time of the aging treatment is 0.5h-8h. The deep cooling and the aging treatment are sequentially carried out, and the temperature and the holding time of the aging treatment are controlled within the above-mentioned ranges, which is beneficial to control the size of the martensitic grains within ≤100μm, and is beneficial to the formation of the nanoscale (size ≤500nm) Ni3Mo precipitated phase and FeMo type precipitated phase, and is beneficial to the generation of the micron-scale size (≤10μm) NbC grains, and can promote the formation of the reversed austenite to a certain extent, which is beneficial to obtain the martensitic steel with more excellent comprehensive performance. Specifically, during the aging treatment, the set temperature of the heat treatment device can be, for example, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, etc. Specifically, the holding time of the aging treatment can be, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0089] In some specific embodiments of the present application, the step S4 comprises sintering, solution treatment and aging treatment sequentially carried out; wherein the holding temperature of the sintering is 1220℃-1380℃, and the holding time is 1h-8h; the holding temperature of the solution treatment is 900℃-1100℃, and the holding time is 0.5h-6h; the holding temperature of the aging treatment is 480℃-580℃, and the holding time is 0.5h-8h. In this way, the microstructure of the finally obtained martensitic steel is more excellent, for example, the size of the martensitic grains is 20μm-50μm, the size of the NbC grains is 1μm-2μm, the size of the Ni3Mo precipitated phase and the FeMo type precipitated phase is ≤500nm, and the Ni3Mo precipitated phase is high-density and dispersedly distributed in the microstructure of the martensitic steel; and it is also beneficial to form the reversed austenite between the martensitic structure and the Ni3Mo precipitated phase.

[0090] In some embodiments of the present application, the martensitic steel prepared by the above preparation method has a tensile strength ≥2200MPa and an elongation at break ≥3%.

[0091] The application further provides a structural member comprising the martensitic steel provided by the application, or a preset shape of the martensitic steel prepared by the preparation method provided by the application; or the structural member can be directly prepared by the preparation method of the martensitic steel provided by the application, because the preparation method provided by the application is a powder forming process. The structural member not only has high structural strength and high toughness, but also can be a high-precision complex structural member, and has high production efficiency, high yield, and good market prospects. In the application, the structural member can be, for example, a hinge of a foldable electronic device, a part of an aerospace device, but is not limited thereto.

[0092] The application further provides a terminal device comprising the aforementioned structural member provided by the application, or comprising the martensitic steel provided by the application, or comprising a preset shape of the martensitic steel prepared by the preparation method provided by the application. The terminal device has high quality reliability and strong market competitiveness.

[0093] In some embodiments of the application, the terminal device includes, but is not limited to, consumer electronic devices such as mobile phones, tablet computers, notebook computers, smart watches, and new energy vehicles. In addition, the martensitic steel provided by the application can also be applied to other instruments and equipment such as aerospace equipment, or mechanical tools.

[0094] The technical solutions of the application are further described in the following embodiments.

[0095] Embodiment 1

[0096] (1) Prepare metal particles, and the key technical indicators of the metal particles are as follows: D10 is 3.2 μm, D50 is 8.2 μm, and D90 is 17.8 μm; the carbon content is 0.03%; the oxygen content is 0.27%, and the mass proportions of Ni elements, Co elements, Mo elements, Nb elements, and Fe elements in the metal particles are added according to the mass contents of the elements of the martensitic steel to be prepared, which are summarized in Table 1.

[0097] (2) Mix the metal particles of step (1) with a binder at a certain volume ratio (metal particles / binder = 62 / 38), and then add a mixing mill (parameters: 195℃, 2h, blade rotation speed 20r / min) for mixing; then move the uniformly mixed paste feed into a granulator, and the screw rod of the granulator extrudes the gradually cooled feed through a die, and the rotating blade cuts the strip-shaped feed into cylindrical feed particles with a length of 2-3mm;

[0098] The binder is POM, EVA, PE, CW, and SA with a mass ratio of 89:1:5:2:1.

[0099] (3) The cylindrical feed particles obtained in step (2) are added to the hopper of an injection molding machine, and injection molding is performed under certain temperature and pressure conditions (injection temperature: 195°C, injection pressure: 200 MPa) to obtain a green part;

[0100] (4) The stretched green part obtained in step (3) is placed on an alumina ceramic plate and placed in a catalytic debinding furnace, and catalytic debinding is performed at a certain temperature (parameters: temperature setting of 110°C, fuming nitric acid flow rate of 3.5 g / min, time of 2 hours);

[0101] (5) Sintering: The green part after catalytic debinding in step (4) is placed in a sintering furnace together with an alumina ceramic support plate, and sintering is performed in an argon atmosphere (parameters: temperature setting of 1360°C, time of 3h) to obtain a sintered part;

[0102] (6) Heat treatment: The sintered part obtained in step (5) is solution treated in a heat treatment furnace (parameters: temperature setting of 910°C, time of 2h), and then oil-cooled to 60°C. Subsequently, the solution-treated sintered part is heated to 580°C and held for 4h to obtain a martensitic steel.

[0103] Examples 2-10

[0104] The difference from Example 1 is that the amount of each element in the fine-tuning metal particles is adjusted.

[0105] Comparative Examples 1-6

[0106] The difference from Example 1 is that the amount of each element in the fine-tuning metal particles is adjusted.

[0107] The martensitic steels prepared in Examples 1-10 and Comparative Examples 1-6 are subjected to ICP testing to determine the elemental composition and mass content of each element in the martensitic steels prepared in each example and comparative example. The mass proportions of Ni, Co, Mo, C, and Nb in the martensitic steels of each example and comparative example are summarized in Table 1. It should be noted that in Examples 1-10, the other trace elements include Si, Mn, Ti, Zr, V, and unavoidable impurity elements, but do not include Al and Cu elements; in the martensitic steels of Examples 1-10 and Comparative Examples 1-6, the mass proportion of other trace elements is ≤1%, and the balance is Fe.

[0108] The tensile strength σ b and the elongation at break A of each martensitic steel are tested according to GB / T 228.1-2021 "Metallic Materials-Tensile Testing-Part 1: Room Temperature Test Methods"; the results are summarized in Table 1.

[0109] Table 1

[0110] To prove the effect of Al element and Cu element among other trace elements, Example 11 and Example 12 are set.

[0111] Example 11

[0112] The difference from Example 1 is that the addition amount of each element in the metal particles is fine-tuned, and Al element is additionally added.

[0113] Example 12

[0114] The difference from Example 1 is that the addition amount of each element in the metal particles is fine-tuned, and Cu element is particularly added.

[0115] The martensitic steels prepared in Example 11 and Example 12 are subjected to ICP test to determine the mass content of each element; the tensile strength σ b and the elongation at break A of each martensitic steel are tested according to GB / T 228.1-2021 “Metallic Materials-Tensile Testing-Part 1: Method of Test at Room Temperature”; the results are summarized in Table 2.

[0116] It should be noted that in Example 11, the other trace elements include Si element, Mn element, Ti element, Zr element, V element and unavoidable impurity elements, and the mass percentage of other trace elements is ≤0.3%, and the balance is Fe element; and in Example 12, the other trace elements include Si element, Mn element, Ti element, Zr element, V element and unavoidable impurity elements, and the sum of the mass percentage of other trace elements is ≤0.85%, and the balance is Fe element.

[0117] Table 2

[0118] From the data in Table 1, it can be seen that the tensile strength and elongation at break of the martensitic steel prepared in the examples of the present application are both high, indicating that it has high strength and good toughness. When the mass content of Co element is reduced beyond the limit of the present application (Comparative Example 1), the strength of the steel material decreases significantly; when the content of Co element exceeds the limit of the present application (Comparative Example 2), not only the strength of the steel material decreases significantly, but also the toughness is destroyed. When the content of Mo element is reduced, the strength of the steel material also decreases accordingly (Comparative Example 3 and Comparative Example 6).

[0119] Combining the data of the examples in Table 1 and the data in Table 2, it can be found that on the basis of the steel material of the examples, the introduction of Al element can further improve the strength of the steel material; the addition of Cu element can improve the toughness of the steel material, and the tensile strength still maintains within a certain level.

[0120] In addition, the steel material of the embodiment 1 is subjected to the APT probe test, and the atomic distribution of the partial region is shown in Fig. 1. It can be seen from the distribution of each element and the total element in Fig. 1 that the Mo and Ni elements have clusters, and correspond to the positions of the Ni3Mo precipitates.

[0121] It should be understood that the first, second, and various numerical designations referred to herein are only for the convenience of description and do not limit the scope of the present application.

[0122] In the present application, the association relationship of "and / or" between the associated objects means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone, where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0123] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or the like means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0124] In the present application, "-" represents a range value, including the end point values at both ends. For example, the value of a can be 0.5-15, which means that the value of a can be between 0.5 and 15, and includes the end point values 0.5 and 15.

Claims

1. A martensitic steel, characterized in that, The martensitic steel comprises the following mass contents of each element, based on the total mass of the martensitic steel: 14%-16% Ni, 16%-18% Co, 7%-10% Mo, 0.1%-0.6% Nb, 0.003%-0.1% C; and Fe, other trace elements.

2. The martensitic steel according to claim 1, characterized in that, The mass percentage of the Ni element in the martensitic steel is 14.5%-15.5%.

3. The martensitic steel according to claim 1 or 2, characterized in that, The mass percentage of the Mo element in the martensitic steel is 7.5%-9%.

4. Martensitic steel according to any one of claims 1 - 3, characterized in that, The mass ratio of the Ni element to the Mo element is ≤2:

1.

5. The martensitic steel according to any one of claims 1 to 4, characterized in that, The martensitic steel has a Ni3Mo precipitate phase dispersed in the microstructure of the martensitic steel; the size of the Ni3Mo precipitate phase is ≤500 nm.

6. The martensitic steel according to any one of claims 1 to 5, characterized in that, The martensitic steel has a FeMo-type precipitate phase dispersed in the microstructure of the martensitic steel; the size of the FeMo-type precipitate phase is ≤500 nm.

7. The martensitic steel according to any one of claims 1 to 6, characterized in that, The mass percentage of the Co element in the martensitic steel is 16.5%-18%.

8. The martensitic steel according to any one of claims 1 to 7, characterized in that, The mass percentage of the Nb element in the martensitic steel is 0.2%-0.4%.

9. The martensitic steel according to any one of claims 1 to 8, characterized in that, The martensitic steel has NbC grains dispersed in the microstructure of the martensitic steel; the size of the NbC grains is ≤10 μm.

10. The martensitic steel according to any one of claims 1 to 9, characterized in that, The martensitic steel has a reversed austenite dispersed in the microstructure of the martensitic steel.

11. The martensitic steel according to any one of claims 1 to 10, characterized in that, The martensitic steel further comprises an Al element, and the mass percentage of the Al element in the martensitic steel is ≤1%.

12. The martensitic steel according to any one of claims 1 to 11, characterized in that, The other trace elements include one or more of N element, Re element, Cu element, Ti element, S element, P element, H element, Zr element, Mg element, Ta element, Ca element, V element, and Zn element; the mass percentage of the other trace elements in the martensitic steel is ≤1%.

13. The martensitic steel according to claim 12, characterized in that, The other trace elements include the Cu element.

14. The martensitic steel according to any one of claims 1 to 13, characterized in that, The tensile strength of the martensitic steel is ≥2200 MPa, and the elongation at break of the martensitic steel is ≥3%.

15. A method of producing a martensitic steel, characterized in that, Comprising: Preparation of metal particles, the metal particles comprising the following mass percentages of each element: 14%-16% Ni, 16%-18% Co, 7%-10% Mo, 0.1%-0.6% Nb, 0.003%-0.1% C; and Fe; Mixing the metal particles with a binder to obtain a feedstock; Injection molding of the feedstock to obtain a blank; Sequentially performing debinding, sintering, and heat treatment on the blank to obtain a martensitic steel in a preset shape.

16. The method of claim 15, wherein, The holding temperature of the sintering is 1220°C-1380°C, and the holding time is 1h-8h; And / or, The heat treatment comprises sequentially performed solid solution treatment and aging treatment; the holding temperature of the solid solution treatment is 900°C-1100°C, and the holding time is 0.5h-6h; the holding temperature of the aging treatment is 480°C-580°C, and the holding time is 0.5h-8h.

17. A structural member, characterized by Comprising the martensitic steel according to any one of claims 1-14, or a martensitic steel in a preset shape prepared by the preparation method of the martensitic steel according to claim 15 or 16.

18. A terminal device, comprising: A structure according to claim 17, or a martensitic steel according to any one of claims 1 to 14, or a pre-shaped martensitic steel produced according to the method of claim 15 or 16.

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