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

Abstract

The embodiment of the invention provides martensitic steel, a preparation method of the martensitic steel, a structural part and terminal equipment. The martensitic steel comprises the following elements in percentage by mass: 7%-9% of Ni, 16%-18% of Co, 5%-8% of Mo, 7%-9% of Cr, 0.1%-0.6% of Nb and 0.03%-0.12% of C, and Fe and other trace elements. Due to the specific elements and the mass ratio of all the elements in the martensitic steel, the martensitic steel can be produced through powder forming technologies such as metal injection forming, and the martensitic steel produced through the powder forming technology can also have high strength and excellent toughness.

Description

[0001] This application claims priority to the Chinese patent application No. 202411105412.1, filed on August 12, 2024, entitled “Maraging Steel and Preparation Method and Application Thereof”, the entire content of which is incorporated herein by reference. TECHNICAL FIELD

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

[0003] With the development of material science, various types of materials are emerging, but the demand for high mechanical performance alloy materials such as steel materials, aluminum alloys, titanium alloys, etc. is still large. Among them, stainless steel is widely used due to its ultra-high strength, high modulus and certain elongation. The current forming methods of stainless steel workpieces generally include traditional profile machining and powder forming technology, but traditional profile machining has great difficulty in producing complex workpieces and is low in efficiency, and the strength of the metal material produced by the powder forming technology is generally lower than that of the material produced by traditional profile machining. Therefore, it is urgent to provide a newly designed steel material that can be produced by powder forming technology and has high strength and excellent toughness. SUMMARY

[0004] The embodiments of the present application provide a maraging steel, a preparation method thereof, a structural member and a terminal device. The specific elements and the mass percentage of each element in the maraging steel make the maraging steel not only be produced by powder forming technology such as metal injection molding, but also have high strength and excellent toughness.

[0005] The first aspect of the embodiments of the present application provides a maraging steel. Based on the total mass of the maraging steel, the maraging steel includes the following mass content 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, 0.03%-0.12% of C; and Fe, other trace elements.

[0006] Based on the special element selection and element content design of the above maraging steel, the steel material can be prepared by powder forming process such as metal injection molding, and the structure of the prepared steel material is mainly high-strength martensite. In addition, the special component design can generate various reinforcing phases and toughening phases during the preparation of the steel material, thereby effectively improving the strength and toughness of the steel material.

[0007] In some embodiments of the present application, the mass percentage of the Co element in the martensitic steel is 16.5%-18%. In this way, the dislocation recovery of the martensitic structure is more inhibited, the dislocation density is improved, the dislocation strengthening effect is more improved, and in addition, the nucleation sites for the above-mentioned various precipitated phase structures can be provided during the aging stage of the preparation of the martensitic steel, the aging strengthening reaction is strongly promoted, and the martensitic steel is endowed with higher tensile strength. Furthermore, the austenite transformation temperature of the martensite can be improved, the tendency of the martensite to transform into austenite is inhibited, the risk of the martensite transforming into austenite is greatly reduced, and the strength of the steel is ensured to be high.

[0008] In some embodiments of the present application, the mass ratio of the Ni element to the Co element is 1:(1.94-2.57). In this way, the martensitic steel with high strength and toughness is more beneficial.

[0009] In some embodiments of the present application, the microstructure of the martensitic steel includes intermetallic compounds (Fe, Co, Ni) x CrMo, and x is 1.5-2.5. The above-mentioned intermetallic compound is beneficial to improving the strength of the martensitic steel.

[0010] In some embodiments of the present application, the mass percentage of the Cr element in the martensitic steel is 7.5%-8.5%. In this way, not only is the CrMo type precipitated phase fully formed, but the risk of the formation of ferrite in the steel is also fully reduced, and the mechanical properties of the martensitic steel are more improved. Furthermore, the corrosion resistance of the martensitic steel is ensured to be better.

[0011] In some embodiments of the present application, the mass ratio of the Cr element to the Mo element is (1-1.6):1. In this way, the performance of the Co element is beneficial to be exerted, and the risk of the mechanical properties of the martensitic steel being negatively affected by the Cr element is reduced.

[0012] In some embodiments of the present application, the microstructure of the martensitic steel includes CrMo type precipitated phases; and the size of the CrMo type precipitated phases is ≤500 nm. The nanoscale size of the CrMo type precipitated phases is better for the strengthening effect of the steel, and is more beneficial to improving the tensile strength of the steel.

[0013] In some embodiments of the present application, the microstructure of the martensitic steel includes FeMo type precipitated phases; and the size of the FeMo type precipitated phases is ≤500 nm. The nanoscale size of the FeMo type precipitated phases is better for the strengthening effect of the steel, and is more beneficial to improving the tensile strength of the steel.

[0014] In some embodiments of this application, the microstructure of the martensitic steel contains dispersed NbC grains; the size of the NbC grains is ≤10μm. The NbC grains can strengthen the matrix and optimize the toughness of the steel.

[0015] In some embodiments of this application, the microstructure of the martensitic steel contains dispersed CrC grains; the size of the CrC grains is ≤10μm. The formation of CrC grains not only strengthens the matrix and optimizes the toughness of the steel, but also effectively inhibits the formation of ferrite by Cr in the matrix and reduces the risk of C having a negative impact on the mechanical properties of the steel.

[0016] In some embodiments of this application, the Ni element accounts for 7%-8.5% of the mass of the martensitic steel. This is more conducive to promoting the formation of reverse austenite in the steel. When the steel is prepared using powder molding processes such as metal injection molding, controlling the mass content of Ni element within the above range is more conducive to the diffusion of Ni element between the martensitic structure and the precipitated phase structure during the aging stage, and the formation of reverse austenite, thereby improving the toughness of the martensitic steel.

[0017] In some embodiments of this application, the microstructure of the martensitic steel contains dispersed reverse-transformed austenite. This further enhances the toughness of the martensitic steel.

[0018] In some embodiments of this application, based on the total mass of the martensitic steel, the mass percentage of Ni is 7%-8.5%, the mass percentage of Co is 16.5%-18%, the mass percentage of Mo is 5.5%-7.5%, the mass percentage of Cr is 7.5%-8.5%, the mass percentage of Nb is 0.2%-0.5%, and the mass percentage of C is 0.05%-0.1%. This is more conducive to obtaining martensitic steel with densely dispersed nanoscale CrMo and FeMo precipitates, dispersed NbC and CrC grains, and high dislocation density. It also facilitates the formation of reverse austenite between the martensitic structure and the precipitate structure, further improving both the tensile strength and elongation at break of the martensitic steel.

[0019] In some embodiments of this application, based on the total mass of the martensitic steel, the mass percentage of the other trace elements in the martensitic steel is ≤1%; the other trace elements include one or more of Ti, P, S, N, O, H, Mn and Si.

[0020] In some embodiments of this application, based on the total mass of the martensitic steel, the mass percentages of Ti, P, S, N, O, Mn, and Si are ≤0.3%, ≤0.003%, ≤0.05%, ≤0.02%, ≤0.02%, ≤0.005%, ≤1%, and ≤1%, respectively. When other trace elements are present and their mass content is controlled within the above ranges, other properties of the martensitic steel can be imparted or improved without significantly negatively impacting its strength and toughness.

[0021] In some embodiments of this application, the martensitic steel further includes Al, with the mass percentage of Al in the martensitic steel being ≤1%. Adding an appropriate amount of Al can improve the strength of the martensitic steel while slightly sacrificing its toughness.

[0022] In some embodiments of this application, the tensile strength of the martensitic steel is ≥2300MPa and the elongation at break is ≥4%.

[0023] The second aspect of this application provides a method for preparing martensitic steel, comprising:

[0024] Prepare metal particles comprising the following elements by mass percentage: 7%-9% Ni, 16%-18% Co, 5%-8% Mo, 7%-9% Cr, 0.1%-0.6% Nb, 0.008%-0.15% C; and Fe;

[0025] The metal particles are mixed with a binder to obtain a feedstock;

[0026] The feed material is injection molded to obtain a blank;

[0027] The blank is subjected to degreasing, sintering and heat treatment in sequence to obtain martensitic steel of a preset shape.

[0028] The above preparation method is based on the MIM forming process, which can produce martensitic steel workpieces with complex structures and high precision. Moreover, it has low production cost and high production efficiency, and is suitable for large-scale industrial production.

[0029] In some embodiments of this application, the sintering holding temperature is 1220℃-1380℃, and the holding time is 1h-8h. This facilitates the combination of Nb and C elements in the raw materials and provides nucleation sites for the precipitation of CrMo and FeMo phases during the subsequent aging process.

[0030] In some embodiments of this application, the heat treatment includes a solution treatment and an aging treatment performed sequentially; the solution treatment is held at a temperature of 900℃-1100℃ for a duration of 0.5h-6h; the aging treatment is held at a temperature of 480℃-580℃ for a duration of 0.5h-8h. This method facilitates the production of martensitic steel with superior overall performance.

[0031] A third aspect of this application provides a structural component, including martensitic steel as provided in the first aspect of this application, or martensitic steel of a predetermined shape prepared according to the method for preparing martensitic steel as provided in the second aspect of this application.

[0032] In some embodiments of this application, the aforementioned structural components include, but are not limited to, hinges for foldable electronic devices and components for aerospace equipment.

[0033] A fourth aspect of this application provides a terminal device, including the structural components provided in the third aspect of this application, or including martensitic steel provided in the first aspect of this application, or including martensitic steel of a preset shape prepared according to the method for preparing martensitic steel provided in the second aspect of this application. This terminal device has high reliability and strong market competitiveness.

[0034] In some embodiments of this application, the aforementioned terminal devices include, but are not limited to, mobile phones, tablet computers, laptop computers, smartwatches, and new energy vehicles. Attached Figure Description

[0035] Figure 1A The results of ATP (Atom Probe Tomography) testing of the martensitic steel prepared in Example 1 are shown below.

[0036] Figure 1B for Figure 1A The atomic concentrations of Fe, Cr, and Mo in the corresponding regions change with the test depth. Detailed Implementation

[0037] Currently, with the development of materials science, various high-mechanical-performance materials are emerging in large numbers, such as composite materials and various alloy materials; however, the market demand for high-mechanical-performance alloy materials remains significant. Applications of high-mechanical-performance alloy materials include, but are not limited to, hinges, pivots, or other load-bearing components in foldable terminal devices, and parts in aerospace equipment. These components generally have complex structures and require high precision. Currently, stainless steel is widely used in these applications due to its ultra-high strength, high modulus, and certain elongation.

[0038] In related technologies, stainless steel is generally processed using traditional profile manufacturing or powder forming techniques. Traditional profile manufacturing involves shaping block materials through subtractive manufacturing, including but not limited to cutting, boring, drilling, and grinding. To achieve complex structures and meet high precision requirements, the industry typically employs Computerized Numerical Control (CNC) precision machining, which is demanding, has relatively low production efficiency, and its product yield needs improvement. Powder forming technology, on the other hand, can directly form complex and intricate structures. This includes, but is not limited to, Metal Injection Molding (MIM), Powder Metallurgy (PM), and 3D printing. MIM is the most widely used process. Its flow mainly involves mixing metal powder particles with a binder, heating the mixture, and then injecting it into a mold cavity using an injection molding machine. After solidification, the workpiece undergoes debinding, sintering, and heat treatment (generally including solution treatment and aging treatment) to obtain the finished product. Compared to other processes, MIM (Metal Injection Molding) can not only produce high-precision, complex-structured workpieces, but also boasts low production costs and high efficiency, facilitating the application of alloy materials in the aforementioned scenarios. However, due to differences in process operations between MIM technology and traditional forming processes, the chemical composition design of high-strength steels in related technologies makes them unsuitable for MIM forming. For example, in traditional casting processes, Ni3Ti precipitation can be used to strengthen martensitic steel, but in the MIM process, Ti readily combines with C and O elements, resulting in reduced Ni3Ti precipitation. This not only wastes raw materials but also impairs the strength and toughness of the steel through inclusions. Furthermore, for steels that can be produced using MIM forming, even with identical chemical compositions, the strength of MIM-formed steel is generally lower than that of steel produced through traditional processing. Faced with rapid product iterations, existing MIM steels cannot meet product reliability requirements, severely limiting the development and application of MIM materials.

[0039] To better understand the technical solution of this application, the following explanations are provided for some key terms involved in this application:

[0040] Martensite: A hard but low-plasticity microstructure in steel. It is a supersaturated solid solution of carbon in α-Fe. It is relatively stable at low temperatures (room temperature and below room temperature), providing hardness to the material. The three-dimensional morphology of martensite is usually plate-like or lath-like, but in metallographic microscopy (two-dimensional), it usually appears as needle-shaped.

[0041] Austenite: A microstructure in steel with high plasticity and toughness. It is relatively stable at high temperatures and provides plasticity to the material as a whole.

[0042] Reverse austenite: Austenite obtained by reheating martensite to the austenite transformation temperature during the steel manufacturing process.

[0043] Ferrite: Ferrite is an interstitial solid solution of carbon dissolved in α-Fe.

[0044] Metal injection molding: a molding technology in which metal particles are mixed with a binder and injected into a mold to form a preform, and the binder is completely removed and the preform is densified during the subsequent sintering process.

[0045] Injection: The process of using an injection molding machine to inject heated and softened metal and binder mixed particles (commonly referred to in the industry as "feed") into a mold for shaping.

[0046] Debinding: The process of removing most of the binder from the injection-molded blank through one or more processes such as catalysis, heating, and dissolution before sintering.

[0047] Sintering: The process of heating a solid to give molecules or atoms enough energy to migrate, causing the powder to bond together, gain strength, and undergo densification and recrystallization.

[0048] Solid solution: also known as solid solution treatment, refers to the process in which the equilibrium transition of a solid solution is suppressed during solidification, resulting in a metastable, supersaturated solid solution single-phase structure.

[0049] Aging: also known as aging treatment, refers to the heat treatment process in which alloy workpieces, after solution treatment, high-temperature quenching or a certain degree of cold working deformation, are placed at a relatively high temperature or room temperature to maintain their shape, size, and properties over time.

[0050] Tensile strength: The maximum stress a material can withstand before fracture in a tensile test, expressed in MPa.

[0051] Elongation at break: In a tensile test of a material, the percentage of the length the specimen elongates after fracture compared to its original length.

[0052] This application provides a martensitic steel, which, based on the total mass of the martensitic steel, comprises the following elements in the following mass contents: 7%-9% Ni, 16%-18% Co, 5%-8% Mo, 7%-9% Cr, 0.1%-0.6% Nb, 0.03%-0.12% C; and Fe, and other trace elements.

[0053] In this embodiment, the special selection and content design of the steel elements enable the steel to be manufactured using the MIM forming process, and the resulting steel structure is mainly composed of high-strength martensite. Furthermore, the special composition design allows for the generation of various reinforcing and toughening phases during the steel manufacturing process, thereby effectively improving the strength and toughness of the steel.

[0054] Specifically, in the embodiments of this application, the mass content of Mo (molybdenum) in the martensitic steel is 5%-8%. This facilitates the reaction with Cr and Mo during the steel preparation process, generating intermetallic compounds in the microstructure and further promoting the expression of CrMo-type and FeMo-type precipitates to enhance the strength of the steel. It should be noted that in the embodiments of this application, CrMo-type precipitates refer to precipitates formed by Cr and Mo, and do not necessarily mean that the stoichiometric ratio of Cr and Mo is 1:1; in some specific embodiments, the stoichiometric ratio of Cr and Mo in the CrMo-type precipitates is 1:1 or approximately 1:1. Similarly, FeMo-type precipitates refer to precipitates formed by Fe and Mo, and do not necessarily mean that the stoichiometric ratio of Fe and Mo is 1:1; in some specific embodiments, the stoichiometric ratio of Fe and Mo in the FeMo-type precipitates can be 2:1, 1:1, or (1-2):1, and its chemical formula can be, for example, Fe2Mo, FeMo, etc. Controlling the Cr content within the range of 7%-9% not only facilitates the full formation of CrMo-type precipitates and increases their distribution density, but also results in smaller CrMo-type precipitates, thus improving the tensile strength of the steel. Furthermore, it effectively enhances the corrosion resistance of martensitic steel. For example, the Mo content in martensitic steel can be 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, or 8.0%.

[0055] For example, the mass content of Cr (chromium) in 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%, etc. If the mass content of Cr is too low (less than 7%), it is not conducive to the formation of CrMo type precipitates; if the mass content of Cr is too high (greater than 9%), it will crowd out the share of other elements and form ferrite in the matrix, which will have a negative impact on the mechanical properties of the steel.

[0056] In related technologies, to obtain high-strength martensitic steel, the mass content of carbon (C) is generally controlled to be below 0.03% to avoid the carbon element disrupting the strengthening mechanism of the steel and increasing its brittleness. In this embodiment, the mass content of carbon in the martensitic steel is controlled within the range of 0.03%-0.12%, and niobium (Nb) is introduced. This facilitates the formation of NbC grains during steel preparation, strengthening the steel matrix, while simultaneously hindering the influence of carbon on the nucleation of precipitated phases, weakening or even eliminating the damage of carbon to the strengthening mechanism, reducing the risk of carbon dissolved in the matrix affecting the toughness of the steel, and expanding the sintering process window during steel preparation (e.g., expanding the sintering temperature range), thus reducing the control difficulty of the MIM process. Furthermore, a specific mass content of Nb can also reduce the problem of excessive residual carbon caused by the low-cleanliness sintering of the MIM process, and also helps to control the mass content of carbon within the range of 0.03%-0.12%. Furthermore, an excess of Cr relative to Mo can react with C to form CrC grains, further strengthening the steel and reducing or even eliminating the negative impact of C on the matrix. For example, the mass content of Nb in martensitic steel can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, etc. For example, the mass content of C in martensitic steel can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%.

[0057] The high content of Co element (cobalt element) is beneficial for its solid solution in the matrix during the preparation of steel and the formation of solid solution strengthening. The solid solution of Co element can delay the dislocation recovery of the steel matrix and improve the dislocation strengthening effect. In addition, in the chemical environment of the steel in the embodiments of this application, Co element can also promote the formation of CrMo type precipitates and FeMo type precipitates in the steel, especially the formation of the above-mentioned small-sized precipitates, thereby improving the strengthening effect. For example, the mass percentage of Co in martensitic steel 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%, etc.

[0058] A higher Ni (nickel) content promotes the formation of reverse-transformed austenite during steel production, thereby improving the steel's toughness, specifically manifested as higher elongation at break. For example, the Ni content in 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%, or 9.0%.

[0059] In this embodiment of the application, based on the mass content of martensitic steel, the mass content of Fe element (iron element) is 54.28%-64.87%. Specifically, the mass content of Fe element can be, for example, 54.3%, 54.5%, 54.8%, 55.0%, 55.2%, 55.5%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 64.5%, 64.6%, 64.8%, 64.5%, etc.

[0060] In this embodiment, the martensitic structure exhibits micron-sized grains. In some embodiments, the size of the micron-sized grains is ≤100μm, for example, 20μm-50μm. This is more conducive to improving the strength of the steel. In this embodiment, the size of the aforementioned grains can be observed using a metallographic microscope.

[0061] In this application's embodiments, other trace elements include unavoidable impurities introduced during the preparation of martensitic steel due to the raw materials. Further, they may include elements specifically added to improve other properties of martensitic steel, such as Si, Mn, Ti, and N. These other properties may include, for example, corrosion resistance, oxidation resistance, and weldability. In some embodiments of this application, the sum of the mass percentages of other trace elements in the martensitic steel is ≤1%.

[0062] In some embodiments of this application, based on the total mass of the martensitic steel, the martensitic steel comprises the following elements by mass content: 7%-9% Ni, 16%-18% Co, 5%-8% Mo, 7%-9% Cr, 0.1%-0.6% Nb, 0.03%-0.12% C, 54.28%-64.87% Fe, and other trace elements; the sum of the mass content of other trace elements in the martensitic steel is ≤1%. In some specific embodiments, the martensitic steel comprises the following elements by mass content: 7%-9% Ni, 16%-18% Co, 5%-8% Mo, 7%-9% Cr, 0.1%-0.6% Nb, 0.03%-0.12% C, other trace elements with a sum of mass percentage ≤1%, and the balance iron.

[0063] In this embodiment of the application, inductively coupled plasma (ICP) technology, such as inductively coupled plasma-atomic emission spectroscopy (ICP-AES), can be used to test the presence and mass content of the above-mentioned elements in martensitic steel.

[0064] In some embodiments of this application, the mass percentage of Ni in the martensitic steel is 7%-8.5%. This is more conducive to promoting the formation of reverse-transformed austenite in the steel. When the steel is prepared using the MIM forming process, controlling the mass content of Ni within the above range is more conducive to the diffusion of Ni into the martensitic structure and precipitated phase structure during the aging stage, forming reverse-transformed austenite, thereby improving the toughness of the martensitic steel. It is understood that austenite generally includes reverse-transformed austenite and retained austenite. In the embodiments of this application, reverse-transformed austenite with a non-triangular cross-section can be observed under a metallographic microscope, and the reverse-transformed austenite is dispersed within the grains and between the lamellae. To illustrate the difference, the cross-section of retained austenite is generally triangular and it remains on the grain boundaries.

[0065] In some embodiments of this application, the microstructure of the martensitic steel contains dispersed reverse-transformed austenite. In some specific embodiments, reverse-transformed austenite exists between the martensitic microstructure and the precipitated phase microstructure of the martensitic steel. This is more conducive to improving the toughness of the martensitic steel and makes it easier to prepare.

[0066] In some embodiments of this application, the mass content of Co in the martensitic steel is 16.5%-18%. During the preparation of martensitic steel, Co generally does not form compounds with other metallic elements in the system, but rather remains dissolved in the matrix. Controlling the mass content of Co within the above range is more conducive to suppressing dislocation recovery in the martensitic microstructure, increasing its dislocation density, and further enhancing the dislocation strengthening effect. Furthermore, it can provide nucleation sites for the aforementioned precipitated phases during the aging stage, strongly promoting the age-hardening reaction and imparting higher tensile strength to the martensitic steel. Moreover, it can also increase the austenite transformation temperature (Ms) of martensite, suppressing the tendency of martensite to transform into austenite, reducing the risk of a significant transformation of martensite into austenite, and helping to ensure higher strength of the steel.

[0067] Considering that a high Co content can inhibit the formation of reverse-transformed austenite, while a high Ni content can promote the formation of reverse-transformed austenite, and that a martensitic steel with both high strength and toughness is required, in some embodiments of this application, the mass ratio of Ni to Co in the martensitic steel is controlled to be 1:(1.94-2.57). Specifically, the mass ratio of Ni to Co can be, for example, 1:1.94, 1:1.95, 1:2.00, 1:2.05, 1:2.10, 1:2.15, 1:2.20, 1:2.25, 1:2.30, 1:2.35, 1:2.40, 1:2.45, 1:2.50, 1:2.55, etc.

[0068] In some embodiments of this application, the microstructure of martensitic steel includes intermetallic compounds (Fe, Co, Ni). x CrMo, x is 1.5-2.5. The above intermetallic compounds can further exhibit CrMo-type precipitates and FeMo-type precipitates. In some embodiments, (Fe, Co, Ni) x For CrMo, x is 1.8-2.2, and within this range, the closer the value of x is to 2, the better; thus, (Fe, Co, Ni) x CrMo is more stable, which is beneficial to the mechanical properties of martensitic steel. Specifically, the values ​​of x mentioned above can be, for example, 1.5, 1.6, 1.7, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, 2.15, 2.2, 2.3, 2.4, and 2.5.

[0069] In some embodiments of this application, the mass percentage of Cr in the martensitic steel is 7.5%-8.5%. Cr is a strong ferrite stabilizing element. Controlling the mass content of Cr within the above range not only facilitates the full formation of CrMo-type precipitates but also significantly reduces the risk of ferrite formation in the steel, thereby improving the mechanical properties of the martensitic steel. Furthermore, it also ensures superior corrosion resistance of the martensitic steel.

[0070] In some embodiments of this application, the mass ratio of Cr to Mo is (1-1.6):1. This facilitates the utilization of the positive properties of Co and reduces the risk of Cr negatively impacting the mechanical properties of martensitic steel. Specifically, the mass ratio of Cr to Mo can be, for example, 1.00:1, 1.05:1, 1.10:1, 1.15:1, 1.20:1, 1.25:1, 1.30:1, 1.35:1, 1.40:1, 1.45:1, 1.50:1, 1.55:1, 1.60:1, etc.

[0071] In some embodiments of this application, CrMo-type precipitates are dispersed in the microstructure of the martensitic steel; the size of the CrMo-type precipitates is ≤500 nm. In the embodiments of this application, the presence and size of the CrMo-type precipitates can be characterized using atomic probe tomography (APT), or a high-magnification scanning electron microscope (SEM), for example, an SEM with a magnification of 10,000x or higher, can be used to test the size of the CrMo-type precipitates. Nanoscale CrMo-type precipitates have a better strengthening effect on steel, especially high-density nanoscale CrMo-type precipitates, which are more conducive to improving the tensile strength of the steel. Specifically, the size of the CrMo type precipitate can be, for example, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, or ≤20nm, etc.

[0072] In some embodiments of this application, FeMo-type precipitates are dispersed in the microstructure of the martensitic steel; the size of the FeMo-type precipitates is ≤500nm. In the embodiments of this application, APT can be used to characterize the presence and size of the FeMo-type precipitates, or high-magnification SEM can be used to test the size of the FeMo-type precipitates. Similarly, nanoscale FeMo-type precipitates have a better strengthening effect on steel, especially high-density nanoscale FeMo-type precipitates, which are more conducive to improving the tensile strength of steel. Specifically, the size of the FeMo-type precipitates can be, for example, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, or ≤20nm, etc.

[0073] Nitrogen (Nb) is a strong carbide-forming element. During steelmaking, under high-temperature conditions, Nb preferentially reacts with C, rather than Cr and Fe, to form NbC. In some embodiments of this application, the microstructure of the martensitic steel contains dispersed NbC grains. These NbC grains strengthen the matrix and improve the toughness of the steel. Given the elemental composition of the martensitic steel in the embodiments of this application, the presence of NbC grains can increase the tensile strength of the martensitic steel by approximately 100 MPa. In some embodiments of this 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. Smaller NbC grains provide better strengthening of the matrix and are more conducive to improving the tensile strength of the martensitic steel. Specifically, the size of 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, or 10 μm. In the embodiments of this application, APT can be used to characterize the presence and size of NbC grains, or high-magnification SEM can be used to test the size of NbC grains.

[0074] In some embodiments of this application, CrC grains are dispersed in the microstructure of the martensitic steel. The formation of CrC grains not only strengthens the matrix and optimizes the toughness of the steel, but also effectively inhibits the formation of ferrite by Cr in the matrix and reduces the risk of negative impact of C on the mechanical properties of the steel. In some embodiments of this application, the size of the CrC grains is ≤10μm. Smaller CrC grains have a better strengthening effect on the matrix and are more conducive to improving the tensile strength of martensitic steel. Specifically, the size of the CrC grains can be, for example, 1μm, 1.2μm, 1.5μm, 1.8μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm. In the embodiments of this application, APT can be used to characterize the presence and size of CrC grains, or high-magnification SEM can be used to test the size of the CrC grains.

[0075] In some embodiments of this application, based on the total mass of the martensitic steel, the mass percentage of Ni is 7%-8.5%, the mass percentage of Co is 16.5%-18%, the mass percentage of Mo is 5.5%-7.5%, the mass percentage of Cr is 7.5%-8.5%, the mass percentage of Nb is 0.2%-0.5%, and the mass percentage of C is 0.05%-0.1%. In this case, the mass content of Fe can be, for example, 55.9%-63.25%. This is more conducive to obtaining martensitic steel with densely dispersed nanoscale CrMo and FeMo precipitates, dispersed NbC and CrC grains, and high dislocation density, while controlling the martensite grain size within the range of 10μm-20μm; simultaneously, it facilitates the formation of reverse austenite between the martensite and precipitate structures in the martensitic steel, further improving both the tensile strength and elongation at break of the martensitic steel.

[0076] In some embodiments of this application, the aforementioned other trace elements include, but are not limited to, one or more of Ti (titanium), P (phosphorus), S (sulfur), N (nitrogen), O (oxygen), H (hydrogen), Mn (manganese), and Si (silicon). In some specific embodiments, based on the total mass of the martensitic steel, the mass percentage of Ti is ≤0.3%, the mass percentage of P is ≤0.003%, the mass percentage of S is ≤0.05%, the mass percentage of N is ≤0.02%, the mass percentage of O is ≤0.02%, the mass percentage of H is ≤0.005%, the mass percentage of Mn is ≤1%, and the mass percentage of Si is ≤1%; furthermore, the sum of the mass percentages of other trace elements in the martensitic steel is ≤1%. Specifically, the mass content of other trace elements in martensitic steel can be, for example, 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. When these other trace elements are present and their mass content is controlled within the above ranges, they can impart or enhance other properties of martensitic steel without significantly negatively impacting its strength and toughness. For example, silicon (Si) can improve the oxidation resistance and wear resistance of martensitic steel; manganese (Mn) can deoxidize and desulfurize, improving the purity of martensitic steel and preventing hot brittleness. Those skilled in the art can select the appropriate element based on actual production conditions and application needs.

[0077] Considering that in some practical applications of martensitic steel, higher strength is required while lower toughness is needed, some embodiments of this application further include Al (Al) in the martensitic steel; the mass percentage of Al in the martensitic steel is ≤1%. Adding an appropriate amount of Al can further improve the strength of the martensitic steel while slightly sacrificing its toughness. Specifically, the mass percentage of Al in the martensitic steel can be, for example, 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.

[0078] In some embodiments of this application, the tensile strength of the martensitic steel is ≥2300 MPa, and / or the elongation at break is ≥4%. In some specific embodiments, the tensile strength of the martensitic steel is ≥2300 MPa, and the elongation at break is ≥4%. It should be noted that the above-mentioned strength and toughness can be achieved when the martensitic steel is produced using MIM forming technology. However, if the above-mentioned martensitic steel with the above-mentioned composition is obtained using conventional profile processing, its tensile strength and toughness performance are even better. In the embodiments of this application, the tensile strength and elongation at break of the martensitic steel are tested in accordance with GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test method at room temperature".

[0079] It should be noted that the martensitic steel provided in this application can be martensitic steel material of any shape; for example, martensitic steel can be strip material, plate, or workpiece with a certain structural shape, but is not limited to these.

[0080] This application also provides a method for preparing martensitic steel, which can be used to prepare the aforementioned martensitic steel; the preparation method includes:

[0081] S1. Preparation of metal particles, wherein the metal particles comprise the following elements by mass percentage: 7%-9% Ni, 16%-18% Co, 5%-8% Mo, 7%-9% Cr, 0.1%-0.6% Nb, 0.008%-0.15% C; and Fe; In this embodiment of the application, during the preparation of martensitic steel, the mass contents of Ni, Co, Mo, Cr, Nb, and Fe remain essentially unchanged, but the C content will change. In other words, the mass content of carbon (C) in the metal particles may not be equal to the mass content of non-metallic elements such as C in the final martensitic steel. Therefore, in the embodiments of this application, the mass content of C in the metal particles is controlled to be 0.008%-0.15%, specifically, for example, 0.008%, 0.009%, 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, etc. Furthermore, since the raw materials of steel may contain some oxygen (O), this oxygen can be removed during the steel preparation process (e.g., sintering). In some embodiments of this 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%. This allows the oxygen content of the final martensitic steel to be controlled within a low range; for example, the oxygen content of the martensitic steel is ≤0.02wt%. It is understood that other trace elements in the martensitic steel of this application include unavoidable impurity elements, or further include intentionally added trace elements. When the martensitic steel to be prepared contains the aforementioned intentionally added trace elements, especially intentionally added metallic trace elements, the raw material of the metal particles also needs to have the aforementioned metallic trace elements added according to the mass content to be prepared.

[0082] S2. Mix the above metal particles with the binder to obtain the feed;

[0083] S3. Inject the above-mentioned feed material into a blank to obtain a blank;

[0084] S4. The above blanks are degreased, sintered and heat-treated in sequence to obtain martensitic steel of the preset shape.

[0085] The above-described preparation method is based on the MIM forming process, which can produce martensitic steel workpieces with complex structures and high precision. Furthermore, it boasts low production costs and high production efficiency, making it suitable for large-scale industrial production. It is 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 this application, and this application does not impose any limitations on this.

[0086] In some embodiments of this application, the metal particles can be prepared by atomization in step S1. In some specific embodiments, the particle size D10 of the metal particles is ≤4.5μm, the particle size D50 is 5μm-14μm, and the particle size D90 is ≤35μm. Controlling the particle size of the metal particles within the above range can improve the uniformity of the structural structure in the final martensitic steel and reduce its size, thereby improving the strength and toughness of the obtained martensitic aging steel. Specifically, in step S1, the particle size D10 of the aforementioned metal particles can be, for example, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, etc.; the particle size D50 can be, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, etc.; and the particle size D90 can be, for example, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, etc. In this embodiment, a laser particle size analyzer can be used to test the particle size distribution of the metal particles. In the embodiments of this application, the raw materials used to prepare metal particles can be, for example, monomers of the above-mentioned elements, alloys, or mixtures of metal monomers and alloys. Those skilled in the art can make selections according to the actual situation, and the mass ratio of each element in the above-mentioned metal particles can be controlled within the above-mentioned range. This application does not impose any restrictions on this.

[0087] In some embodiments of this application, the binder in step S2 can be any binder suitable for the preparation of martensitic steel within the art, such as one or more of polyoxymethylene (POM), ethylene-vinyl acetate copolymer (EVA), polyethylene (PE), CW-based epoxy resin, and sodium alginate (SA), but is not limited thereto. 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 is not limited thereto.

[0088] In this application's embodiments, in step S2, the mixing ratio of metal particles and binder can be any ratio known to those skilled in the art. In some embodiments of this application, the volume ratio of metal particles to binder is 1:(0.15-0.25). This facilitates obtaining feedstock with better forming performance and allows for complete removal of the binder in subsequent processes, resulting in martensitic steel with better overall performance.

[0089] In some embodiments of this application, the above-mentioned feedstock can be prepared using an internal mixer. Specifically, metal particles and binder are mixed at a certain volume ratio and then fed into an internal mixer for mixing to obtain a uniform paste-like feedstock. The paste-like feedstock is then transferred to a granulator, where the screw of the granulator extrudes the gradually cooling paste-like feedstock through a die, and rotating blades cut it to obtain cylindrical particles with a length of 2mm-3mm. The cylindrical particles 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 feedstock preparation in MIM process molding, for example, a temperature of 195°C, a mixing time of 2 hours, and a blade rotation speed of 20 r / min, but are not limited to these.

[0090] In some embodiments of this application, the injection molding process in step S3 can be any process well known to those skilled in the art. In some embodiments, the aforementioned cylindrical granules are fed into an injection molding machine and injection molded under a certain temperature and pressure to obtain a preform. For example, the injection temperature can be 195°C, and the injection pressure can be, for example, 200 MPa, but is not limited thereto.

[0091] In some embodiments of this application, the parameters for degreasing in step S4 can be any degreasing process well-known to those skilled in the art for the preparation of martensitic steel, and this application does not impose any limitations on this. In some embodiments, degreasing is catalytic degreasing. Specifically, fuming nitric acid can be used as the catalyst. In some specific embodiments, the billet is placed in a catalytic degreasing furnace, the temperature is set to 110°C, the fuming nitric acid flow rate is 3.5 g / min, and the degreasing treatment duration is 2 hours, but this is not limited to these methods.

[0092] In some embodiments of this application, the holding temperature for sintering in step S4 is 1220℃-1380℃. It should be noted that the sintering must be carried out under a protective atmosphere, such as argon. It is understood that sintering needs to be carried out in sintering equipment (e.g., a sintering furnace). The holding temperature for sintering refers to the sintering temperature setting of the sintering equipment being 1220℃-1380℃. During sintering, fluctuations in the furnace temperature within ±5℃ of the set temperature are acceptable and will not affect the properties of the resulting martensitic steel. Therefore, during sintering, a furnace temperature of (1220℃-1380℃) ±5℃ is considered within the scope of protection of this application. In some embodiments of this application, the holding time for sintering is 1h-8h. In some specific embodiments, the holding temperature for sintering is 1220℃-1380℃, and the holding time is 1h-8h, resulting in a sintered billet. This facilitates the combination of Nb and C elements in the raw materials, providing nucleation sites for the precipitation of CrMo and FeMo phases during the subsequent aging process. Specifically, the set temperature of the sintering equipment can be, for example, 1220℃, 1250℃, 1280℃, 1300℃, 1320℃, 1350℃, or 1380℃. The holding time for sintering can be, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, or 8h.

[0093] In some embodiments of this application, step S4 includes sequential solution treatment and aging treatment. In some embodiments of this application, the holding temperature for solution treatment is 900℃-1100℃. Similarly, solution treatment needs to be carried out in a heat treatment apparatus. The aforementioned holding temperature for solution treatment refers to setting the temperature of the heat treatment apparatus (e.g., a heat treatment furnace) to 900℃-1100℃. During solution treatment, fluctuations in the furnace temperature within ±5℃ of the set temperature are acceptable and will not affect the properties of the resulting martensitic steel. Therefore, during solution treatment, a furnace temperature of (900℃-1100℃) ±5℃ is considered within the scope of protection of this application. In some embodiments of this application, the holding time for solution treatment is 0.5h-6h. Controlling the solution treatment temperature and holding time within the above range is beneficial for obtaining martensitic steel with superior overall performance. Specifically, during solution treatment, the set temperature of the heat treatment equipment can be, for example, 900℃, 920℃, 950℃, 980℃, 1000℃, 1020℃, 1050℃, 1080℃, 1100℃, etc. Specifically, the holding time for sintering can be, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, etc.

[0094] In some embodiments of this application, after solution treatment, the sintered billet is oil-cooled, and then heated for aging treatment. In some embodiments, the sintered billet after solution treatment is oil-cooled to 60°C. In some specific embodiments, ideally, the sintered billet after solution treatment is oil-cooled to room temperature (25°C ± 2°C). In some embodiments of this application, the holding temperature for aging treatment is 480°C-580°C. Similarly, the aging treatment needs to be carried out in a heat treatment device. The holding temperature for aging treatment mentioned above refers to setting the temperature of the heat treatment device (e.g., a heat treatment furnace) to 480°C-580°C. During the aging treatment, fluctuations in the furnace temperature within ±5°C of the set temperature are acceptable and will not affect the properties of the obtained martensitic steel; all such fluctuations are considered within the scope of protection of this application. In some embodiments of this application, the holding time for aging treatment is 0.5h-8h. The sequential deep cryogenic and aging treatments, with the aging temperature and holding time controlled within the aforementioned ranges, facilitate the formation of nanoscale (≤500nm) CrMo and FeMo precipitates, and promote the formation of micron-sized (≤100μm) NbC and CrC grains. Furthermore, it can promote the formation of reverse-transformed austenite to a certain extent, resulting in martensitic steel with superior overall performance. Specifically, the set temperature of the heat treatment equipment during aging can be, for example, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, or 580℃. The holding time for aging can be, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, or 8h.

[0095] In some specific embodiments of this application, step S4 includes sintering, solution treatment, and aging treatment performed sequentially; wherein, the holding temperature for sintering is 1220℃-1380℃, and the holding time is 1h-8h; the holding temperature for solution treatment is 900℃-1100℃, and the holding time is 0.5h-6h; the holding temperature for aging treatment is 480℃-580℃, and the holding time is 0.5h-8h.

[0096] In some embodiments of this application, the martensitic steel prepared by the above preparation method has a tensile strength ≥2300MPa and an elongation at break ≥4%.

[0097] This application also provides a structural component, which includes the martensitic steel provided in this application embodiment, or martensitic steel prepared by the method provided in this application embodiment; or, since the preparation method provided in this application embodiment is a powder molding process, the structural component can be directly prepared using the method provided in this application embodiment. This structural component not only possesses high structural strength and high toughness, but can also be a high-precision complex structural component, and has high production efficiency and high yield, thus having good market prospects. In this application embodiment, the above-mentioned structural component may be, for example, a hinge for a foldable electronic device, a component for aerospace equipment, etc., but is not limited thereto.

[0098] This application also provides a terminal device, including the aforementioned structural components provided in this application embodiment, or including martensitic steel provided in this application embodiment, or including martensitic steel prepared according to the martensitic steel preparation method provided in this application embodiment. This terminal device has high reliability and strong market competitiveness.

[0099] In some embodiments of this application, the aforementioned terminal devices include, but are not limited to, consumer electronic devices such as mobile phones, tablets, laptops, and smartwatches, as well as new energy vehicles. Furthermore, the martensitic steel provided in the embodiments of this application can also be used in other instruments and equipment such as aerospace equipment, or in machine tools.

[0100] The technical solution of this application is further described below with multiple embodiments.

[0101] Example 1

[0102] (1) Preparation of metal particles. The key technical indicators of the metal particles are: D10 is 3.2μm, D50 is 8.2μm, D90 is 17.8μm; carbon content: 0.03wt%; oxygen content: 0.27wt%. In the metal particles, Ni, Co, Mo, Nb, Cr and Fe elements are added according to the mass content of each element in the martensitic steel to be prepared, and are summarized in Table 1.

[0103] (2) Mix the metal particles and binder from step (1) at a certain volume ratio (metal particles / binder = 62 / 38), and then add them to a mixer for mixing (parameters: 195℃, 2h, blade speed 20r / min); then transfer the uniformly mixed paste feed into a granulator. The screw of the granulator extrudes the gradually cooling feed through the die head, and the rotating blade cuts the strip feed into cylindrical feed particles with a length of 2-3mm.

[0104] The binder is composed of POM, EVA, PE, CW, and SA in a mass ratio of 89:1:5:2:1.

[0105] (3) Add the cylindrical feed particles obtained in step (2) into the hopper of the injection molding machine, and perform injection molding under certain temperature and pressure conditions (injection temperature: 195℃, injection pressure: 200MPa) to obtain the blank;

[0106] (4) Place the green blank of the stretched part obtained in step (3) flat on an alumina ceramic plate and put it into a catalytic degreasing furnace for catalytic degreasing at a certain temperature (parameters: temperature set to 110℃, fuming nitric acid flow rate of 3.5g / min, time 2 hours);

[0107] (5) Sintering: The blank after catalytic degreasing in step (4) is placed together with the alumina ceramic sintering plate into the sintering furnace and sintered in Ar (parameters: temperature set to 1360℃, time 3h) to obtain the sintered blank;

[0108] (6) Heat treatment: The sintered billet obtained in step (5) is solution treated in a heat treatment furnace (parameters: temperature set to 980℃, time 2h), oil cooled, and then the solution treated sintered billet is heated to 550℃ and held for 4h to obtain martensitic steel.

[0109] Examples 2-9

[0110] The difference from Example 1 is that the amount of each element added to the metal particles is fine-tuned.

[0111] Comparative Examples 1-4

[0112] The difference from Example 1 is that the amount of each element added to the metal particles is fine-tuned.

[0113] ICP testing was performed on the martensitic steels prepared in each embodiment and comparative example to determine the elemental composition and mass content of each element. The mass percentages of Ni, Co, Mo, Cr, C, and Nb in the martensitic steels of each embodiment and comparative example are summarized in Table 1. It should be noted that other trace elements include Si, Mn, Ti, Al, Zr, V, and unavoidable impurities; the mass percentage of other trace elements in each martensitic steel is ≤1%, with the balance being Fe.

[0114] The martensitic steel prepared in Example 1 was subjected to APT probe testing, and the atomic test results of some regions are as follows: Figure 1A As shown, Figure 1B for Figure 1A The atomic concentrations of Fe, Cr, and Mo atoms in the corresponding regions change with the test depth (with 0 nm at the two-phase interface); Figure 1A The X-axis corresponds to Figure 1B Depth within. From Figure 1AClear nanoscale FeMo and CrMo precipitates are visible.

[0115] The tensile strength σ of various martensitic steels was tested according to GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test at room temperature". b The results, including the elongation at break (A), are summarized in Table 1.

[0116] Table 1

[0117]

[0118]

[0119] As can be seen from the data in Table 1, the martensitic steel provided in this application embodiment possesses both high strength and superior toughness. Data from Comparative Examples 1 and 2 show that simply reducing the C element content beyond the range defined in this application significantly reduced both the strength and toughness parameters of the martensitic steel. Data from Comparative Example 3 shows that simply reducing the Co element content beyond the range defined in this application resulted in a significant decrease in both the tensile strength and elongation at break of the martensitic steel, indicating that both the strengthening and toughening systems of the martensitic steel were damaged to varying degrees. Parameters from Comparative Example 4 show that while simultaneously reducing the C and Co element content does not necessarily result in good toughness, it leads to a significant loss in strength; therefore, this steel cannot simultaneously possess both high strength and superior toughness.

[0120] It should be understood that the use of the terms "first," "second," and various numerical designations in this document is merely for descriptive convenience and is not intended to limit the scope of this application.

[0121] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone, where A and B can be singular or plural. The character " / " generally indicates that the related objects before and after it are in an "or" relationship.

[0122] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0123] In this application, "-" indicates a range value, including the endpoint values ​​at both ends. For example, the value of a can be 0.5-15, meaning that the value of a can be between 0.5 and 15, and includes the endpoint values ​​of 0.5 and 15.

Claims

1. A martensitic steel, characterized in that, Based on the total mass of the martensitic steel, the martensitic steel comprises the following elements by mass content: 7%-9% Ni, 16%-18% Co, 5%-8% Mo, 7%-9% Cr, 0.1%-0.6% Nb, 0.03%-0.12% C; and Fe, and other trace elements.

2. The martensitic steel according to claim 1, characterized in that, The Co element accounts for 16.5%-18% of the mass of the martensitic steel.

3. The martensitic steel according to claim 1 or 2, characterized in that, The mass ratio of Ni to Co is 1:(1.94-2.57).

4. The martensitic steel according to any one of claims 1-3, characterized in that, The microstructure of the martensitic steel includes intermetallic compounds (Fe, Co, Ni). x CrMo, x is 1.5-2.

5.

5. The martensitic steel according to any one of claims 1-4, characterized in that, The Cr element accounts for 7.5%-8.5% of the mass of the martensitic steel.

6. The martensitic steel according to any one of claims 1-5, characterized in that, The mass ratio of Cr to Mo is (1-1.6):

1.

7. The martensitic steel according to any one of claims 1-6, characterized in that, The microstructure of the martensitic steel contains CrMo type precipitates dispersed in it; the size of the CrMo type precipitates is ≤500nm.

8. The martensitic steel according to any one of claims 1-7, characterized in that, The microstructure of the martensitic steel contains FeMo type precipitates dispersed in it; the size of the FeMo type precipitates is ≤500nm.

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

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

11. The martensitic steel according to any one of claims 1-10, characterized in that, The Ni element accounts for 7%-8.5% of the mass of the martensitic steel.

12. The martensitic steel according to any one of claims 1-11, characterized in that, The microstructure of the martensitic steel contains dispersed reverse-transformed austenite.

13. The martensitic steel according to any one of claims 1-12, characterized in that, Based on the total mass of the martensitic steel, the mass percentage of Ni is 7%-8.5%, the mass percentage of Co is 16.5%-18%, the mass percentage of Mo is 5.5%-7.5%, the mass percentage of Cr is 7.5%-8.5%, the mass percentage of Nb is 0.2%-0.5%, and the mass percentage of C is 0.05%-0.1%.

14. The martensitic steel according to any one of claims 1-13, characterized in that, Based on the total mass of the martensitic steel, the other trace elements in the martensitic steel have a mass percentage of ≤1%. The other trace elements include one or more of Ti, P, S, N, O, H, Mn, and Si.

15. The martensitic steel according to claim 14, characterized in that, Based on the total mass of the martensitic steel, the mass percentage of Ti is ≤0.3%, the mass percentage of P is ≤0.003%, the mass percentage of S is ≤0.05%, the mass percentage of N is ≤0.02%, the mass percentage of O is ≤0.02%, the mass percentage of H is ≤0.005%, the mass percentage of Mn is ≤1%, and the mass percentage of Si is ≤1%.

16. The martensitic steel according to any one of claims 1-15, characterized in that, The martensitic steel also includes Al, and the mass percentage of Al in the martensitic steel is ≤1%.

17. The martensitic steel according to any one of claims 1-16, characterized in that, The tensile strength of the martensitic steel is ≥2300MPa, and the elongation at break is ≥4%.

18. A method for preparing martensitic steel, characterized in that, include: Prepare metal particles comprising the following elements by mass percentage: 7%-9% Ni, 16%-18% Co, 5%-8% Mo, 7%-9% Cr, 0.1%-0.6% Nb, 0.008%-0.15% C; and Fe; The metal particles are mixed with a binder to obtain a feedstock; The feed material is injection molded to obtain a blank; The blank is subjected to degreasing, sintering and heat treatment in sequence to obtain martensitic steel of a preset shape.

19. The preparation method according to claim 18, characterized in that, The sintering temperature is 1220℃-1380℃, and the holding time is 1h-8h; And / or, The heat treatment includes a solution treatment and an aging treatment performed sequentially; the solution treatment is held at a temperature of 900℃-1100℃ for a duration of 0.5h-6h; the aging treatment is held at a temperature of 480℃-580℃ for a duration of 0.5h-8h.

20. A structural component, characterized in that, Includes martensitic steel according to any one of claims 1-17, or includes martensitic steel of a predetermined shape prepared by the method of preparing martensitic steel according to claim 18 or 19.

21. A terminal device, characterized in that, Includes the structural component according to claim 20, or includes the martensitic steel according to any one of claims 1-17, or includes the martensitic steel of a predetermined shape prepared by the method of preparing martensitic steel according to claim 18 or 19.

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