Martensitic steel and preparation method thereof, structural member of electronic equipment and electronic equipment

Abstract

The invention provides martensitic steel and a preparation method thereof, a structural part of electronic equipment and the electronic equipment. The preparation method of the martensitic steel comprises the steps that a steel billet is provided; carrying out hot isostatic pressing treatment; carrying out solution treatment; and cyclic phase change treatment is conducted, and the martensite steel is obtained. The martensitic steel prepared through the preparation method of the martensitic steel has the small grain size and the high yield strength, tensile strength and ductility.

Description

Technical Field

[0001] The present application relates to the field of electronics, and in particular to a martensitic steel material and a preparation method thereof, a structural component of an electronic device, and the electronic device. Background Art

[0002] With the continuous development of electronic devices, the materials used in their structural components are becoming increasingly diverse. Steel, with its low price and reliable performance, has become one of the most widely used materials in the world. Martensitic steel, with its high strength and hardness, is widely used in the structural components of electronic devices. However, the strength and toughness of martensitic steels in related technologies still need to be further improved. Summary of the Invention

[0003] The embodiment of the present application provides a method for preparing a martensitic steel, wherein the prepared martensitic steel has a smaller grain size, higher yield strength, tensile strength and elongation.

[0004] In a first aspect, an embodiment of the present application provides a method for preparing a martensitic steel, the method comprising:

[0005] Provide steel billets;

[0006] Perform hot isostatic pressing;

[0007] performing a solution treatment; and

[0008] The cyclic phase transformation treatment is carried out to obtain martensitic steel.

[0009] In a second aspect, an embodiment of the present application provides a martensitic steel, which is prepared using the method for preparing martensitic steel described in the embodiment of the present application.

[0010] In a third aspect, an embodiment of the present application provides a martensitic steel, wherein the average grain size of the martensitic steel is in a range of 20 μm to 60 μm.

[0011] In a fourth aspect, an embodiment of the present application provides a structural component of an electronic device, wherein the structural component of the electronic device is manufactured by the preparation method of the martensitic steel described in the first aspect, and the structural component of the electronic device includes the martensitic steel described in the second and third aspects.

[0012] In a fifth aspect, an embodiment of the present application provides an electronic device, which includes the structural components of the electronic device described in the fourth aspect.

[0013] The preparation method of the martensitic steel of the embodiment of the present application sequentially performs hot isostatic pressing, solution treatment and cyclic phase transformation treatment on the steel. During the hot isostatic pressing process, the local plastic deformation and grain refinement pore area of ​​the steel billet preferentially undergoes plastic deformation under high pressure, resulting in an increase in dislocation density, activating the dynamic recrystallization process, and the deformation difference between the pore and the dense area produces a strain gradient, which promotes non-uniform recrystallization, resulting in the grain size around the pore being smaller than that in other areas; after the pore is eliminated and closed, the physical barrier that originally hindered the migration of the grain boundary is reduced, but in the HIP high pressure environment (such as argon medium), the pressure itself becomes a new inhibitory factor, offsetting the coarsening risk caused by the disappearance of the barrier; after the pore is eliminated, the atomic diffusion path is smoother, promoting the uniform distribution of elements at the grain boundary, and reducing the abnormal grain growth caused by local component segregation; thus, after the steel billet is subjected to hot isostatic pressing, the density of the steel billet can be significantly improved, the porosity can be reduced, and the grain size can be reduced. In addition, the hot isostatic pressing (HIP) steel billet is then subjected to a solution treatment, which allows the impurity phases in the HIP steel billet to be reintegrated into the iron matrix, forming a uniform supersaturated solid solution. The solution-treated steel billet is then subjected to a cyclic phase transformation treatment. During the cyclic phase transformation process, the increased high dislocation density is inherited by the reverse-transformed austenite through phase transformation cold work hardening, further increasing the dislocation density of the reverse-transformed austenite, providing storage energy for recrystallization and increasing the driving force for recrystallization. With the fragmentation of the structure and the increase in dislocation density, the internal storage energy of the structure increases compared to that after the solution treatment. As the number of cyclic phase transformation recrystallization increases, the internal storage energy of the structure also shows an increasing trend. After multiple cyclic phase transformation treatments, the grain size of the martensitic steel is greatly reduced, the yield strength and tensile strength of the martensitic steel are increased, and the plasticity and elongation of the martensitic steel are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 1 is a flow chart of a method for preparing martensitic steel according to an embodiment of the present application.

[0016] Figure 2 It is a schematic flow chart of a method for preparing a steel billet according to an embodiment of the present application.

[0017] Figure 3 FIG. 4 is a graph showing temperature and time of a cyclic phase change process according to an embodiment of the present application.

[0018] Figure 4It is a schematic flow chart of a method for preparing martensitic steel according to another embodiment of the present application.

[0019] Figure 5 It is a schematic flow chart of a method for preparing martensitic steel according to another embodiment of the present application.

[0020] Figure 6 This is a metallographic corrosion picture of the steel billet in Example 1.

[0021] Figure 7 This is a metallographic image of a steel billet that has only been polished and not corroded.

[0022] Figure 8 This is the porosity distribution diagram of the steel billet calculated using the porosity calculation software of the metallographic microscope.

[0023] Figure 9 This is a metallographic corrosion picture of the first intermediate product of Example 1 (i.e., the steel billet after hot isostatic pressing).

[0024] Figure 10 This is the metallographic image of the first intermediate product after only polishing and no corrosion.

[0025] Figure 11 This is the porosity distribution diagram of the first intermediate product calculated using the porosity calculation software of the metallographic microscope.

[0026] Figure 12 This is a metallographic corrosion picture of the second intermediate product of Example 1 (i.e., the steel billet after solid solution treatment).

[0027] Figure 13 This is a metallographic corrosion picture of the third intermediate product of Example 1 (i.e., the steel billet after cyclic phase transformation treatment).

[0028] Figure 14 Schematic diagram of the structure of the electronic device according to one embodiment of the present application.

[0029] Figure 15 It is a flow chart of a method for preparing a structural component of an electronic device according to an embodiment of the present application.

[0030] Figure 16 3 is a structural diagram of an electronic device according to an embodiment of the present application, wherein the foldable middle frame is in a folded state.

[0031] Figure 17 yes Figure 16 Enlarged view of the dotted box I in the middle.

[0032] Figure 18 It is a structural diagram of an electronic device according to an embodiment of the present application, wherein the foldable middle frame is in a flattened state.

[0033] Figure 19 This is a circuit block diagram of an electronic device according to an embodiment of the present application.

[0034] Description of reference numerals:

[0035] 400-Structural parts / rotating shaft of electronic equipment, 500-Electronic equipment, 510-Flexible display, 520-Foldable middle frame, 521-First middle frame, 522-Second middle frame, 530-Processor, 540-Memory, 550-Camera module. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0038] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0039] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0040] With the continuous development of electronic devices, the materials used in their structural components are becoming increasingly diverse. Steel, with its low price and reliable performance, has become one of the most widely used materials in the world. Martensitic steel, with its high strength and hardness, is widely used in the structural components of electronic devices. However, the strength and toughness of martensitic steels in related technologies still need to be further improved.

[0041] Ultra-high-strength steel (UHSS) is a type of alloy steel used to manufacture structural components in electronic equipment subjected to high stresses. Generally boasting a yield strength greater than 1180 MPa and a tensile strength greater than 1380 MPa, this type of steel exhibits sufficient toughness, a high specific strength and yield ratio, and good weldability and formability. Ultra-high-strength steel is typically classified based on its degree of alloying and microstructure, primarily into three categories: low-alloy, medium-alloy, and high-alloy. The high-alloy category further includes maraging steel and precipitation-hardening stainless steel.

[0042] Ultra-high-strength steels can be categorized as martensitic or non-martensitic, depending on their dominant strengthening mechanism and microstructure. Non-martensitic ultra-high-strength steels include bainitic steels, duplex steels, and precipitation-hardening steels.

[0043] Metal Powder Injection Molding (MIM) is a near-net-shape forming process. Conventional heat treatment methods for ultra-high-strength MIM parts enhance material strength through phase transformation strengthening or precipitation aging. However, the structure of MIM parts is relatively complex, and deformation strengthening cannot be used to refine the material grain size, as this would destroy the final form of the part. Furthermore, during the sintering densification process, the maximum sintering temperature is generally at the end of the austenite transformation to ensure the highest possible density of the part after sintering. Sintering at this temperature will cause the grain size to grow rapidly, resulting in a decrease in material performance.

[0044] Figure 1 1 is a flow chart of a method for preparing martensitic steel according to an embodiment of the present application.

[0045] See Figure 1 The present invention provides a method for preparing a martensitic steel material, the method comprising:

[0046] S101, providing steel billets;

[0047] S102, performing hot isostatic pressing;

[0048] Hot Isostatic Pressing (HIP) is an advanced material processing technology that simultaneously applies high temperature and high pressure (isotropic pressure) to the material to eliminate internal defects, increase density and improve mechanical properties.

[0049] S103, performing solution treatment; and

[0050] Solution treatment refers to a heat treatment process in which an alloy is heated to a high temperature single-phase region and maintained at a constant temperature to allow the excess phase to fully dissolve into the solid solution and then rapidly cooled to obtain a supersaturated solid solution.

[0051] S104, performing cyclic phase transformation treatment to obtain martensitic steel.

[0052] "Cyclic phase transformation treatment" refers to a method in which a material undergoes multiple solid solution phase transformation cycles. "Multiple" means greater than or equal to two cycles.

[0053] Martensite is the name of a structure in ferrous metals, consisting of a supersaturated solid solution of carbon in α-Fe. Martensite exhibits high strength and Vickers hardness. Austenite is a lamellar microstructure in steel, typically a nonmagnetic solid solution of a small amount of carbon in γ-Fe. Austenite exhibits excellent plasticity, low strength, and a certain degree of toughness.

[0054] The preparation method of the martensitic steel of the embodiment of the present application sequentially performs hot isostatic pressing, solution treatment and cyclic phase transformation treatment on the steel. During the hot isostatic pressing process, the local plastic deformation and grain refinement of the steel billet pore area preferentially undergoes plastic deformation under high pressure, resulting in an increase in dislocation density and activation of the dynamic recrystallization process. The deformation difference between the pore and the dense area produces a strain gradient, which promotes non-uniform recrystallization and causes the grain size around the pore to be smaller than that in other areas. After the pore is eliminated,

[0055] After the pores are closed, the physical barriers that previously hindered grain boundary migration are reduced. However, in the HIP high-pressure environment (such as argon medium), the pressure itself becomes a new inhibitor, offsetting the risk of coarsening caused by the disappearance of the barriers. After the pores are eliminated, the atomic diffusion path is smoother, promoting the uniform distribution of elements at the grain boundaries and reducing abnormal grain growth caused by local component segregation. As a result, after the hot isostatic pressing treatment, the density of the steel billet can be significantly improved, the porosity can be reduced, and the grain size can be reduced. In addition, the steel billet after hot isostatic pressing is then subjected to solid solution treatment, which allows the impurity phase in the hot isostatic pressing steel billet to be reintegrated into the iron matrix, forming a uniform supersaturated solid solution. The steel billet after solution treatment is then subjected to cyclic phase transformation treatment. During the cyclic phase transformation process, the increased high dislocation density is inherited to the reverse transformed austenite through phase transformation cold work hardening, which further increases the dislocation density of the reverse transformed austenite, provides storage energy for recrystallization, and increases the driving force for recrystallization. With the fragmentation of the structure and the increase of dislocation density, the internal storage energy of the structure increases compared with that after solution treatment. With the increase of the number of cyclic phase transformation recrystallizations, the internal storage energy of the structure also shows an increasing trend. After multiple cyclic phase transformation treatments, the grain size of the obtained martensitic steel is greatly reduced, the yield strength and tensile strength of the martensitic steel are improved, and the plasticity and elongation of the martensitic steel are improved.

[0056] Figure 2 It is a schematic flow chart of a method for preparing a steel billet according to an embodiment of the present application.

[0057] See Figure 2 In some embodiments, in S101, providing a steel billet includes:

[0058] S1011, provides alloy steel powder;

[0059] Optionally, the alloy steel powder may be, but is not limited to, 18Ni maraging steel alloy steel powder.

[0060] In a specific embodiment, the alloy steel powder comprises, by mass fraction, 16% to 19% nickel (Ni), 7.5% to 11.5% cobalt (Co), 5.0% to 7.0% molybdenum (Mo), 0.2% to 0.8% vanadium (V), ≤0.5% chromium (Cr), and ≤0.020% carbon (C).

[0061] ≤0.4% oxygen (O), ≤0.020% sulfur (S), ≤0.1% manganese (Mn), ≤0.5% silicon (Si), and the balance iron (Fe).

[0062] In the embodiments of the present application, when a numerical value range from a to b is involved, unless otherwise specified, it means that the numerical value can be any numerical value between a and b, including the endpoint numerical value a and the endpoint numerical value b.

[0063] In another specific embodiment, the alloy steel powder includes, by mass fraction, 16% to 20% nickel (Ni), 15.1% to 19% cobalt (Co), 5.5% to 8.5% molybdenum (Mo), 0.2% to 0.8% vanadium (V), 0.1% to 1.0% chromium (Cr), ≤0.020% carbon (C), 0.1% to 1% oxygen (O), ≤0.02% sulfur (S), ≤0.1% manganese (Mn), ≤0.5% silicon (Si), and the balance iron (Fe).

[0064] In another specific embodiment, the alloy steel powder includes, by mass fraction, 16% to 19% Ni, 7.5% to 11.5% Co, 5% to 7% Mo, 0.2% to 0.8% V, 0.1% to 1% Cr, less than or equal to 0.025% C, 0.0215% to 0.3% O, and the balance Fe.

[0065] In another specific embodiment, the alloy steel powder includes, by mass fraction, 15% to 20% nickel, 11% to 12.5% ​​cobalt, 4.5% to 5.5% molybdenum, 0.2% to 0.5% titanium, less than 0.1% carbon, less than or equal to 0.4% impurity elements, and the balance iron.

[0066] Optionally, the D10 particle size of the alloy steel powder is in the range of D10≤5μm. Further, the D10 particle size of the alloy steel powder is in the range of 1μm≤D10≤5μm. Still further, the D10 particle size of the alloy steel powder is in the range of 2μm≤D10≤4μm. Still further, the D10 particle size of the alloy steel powder is in the range of 2.5μm≤D10≤3.5μm. Specifically, the D10 particle size of the alloy steel powder may be, but is not limited to, 1μm, 1.3μm, 1.5μm, 1.8μm, 2μm, 2.3μm, 2.5μm, 2.8μm, 3μm, 3.3μm, 3.5μm, 3.8μm, 4μm, 4.3μm, 4.5μm, 4.8μm, 5μm, etc.

[0067] “D10” refers to the particle size at which the cumulative volume distribution of particles is 10%, that is, the volume content of particles smaller than this particle size accounts for 10% of all particles.

[0068] Optionally, the D50 particle size of the alloy steel powder is in the range of 7.5 μm ≤ D50 ≤ 9.5 μm. Specifically, the D50 particle size of the alloy steel powder may be, but is not limited to, 7.5 μm, 7.8 μm, 8 μm, 8.3 μm, 8.5 μm, 8.8 μm, 9 μm, 9.3 μm, 9.5 μm, etc.

[0069] “D50” refers to the particle size at which the cumulative volume distribution of particles is 50%, that is, the volume content of particles smaller than this particle size accounts for 50% of all particles.

[0070] Optionally, the D90 particle size of the alloy steel powder is in the range of 17 μm ≤ D90 ≤ 23 μm. Specifically, the D90 particle size of the alloy steel powder may be, but is not limited to, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, etc.

[0071] “D90” refers to the particle size at which the cumulative volume distribution of particles is 90%, that is, the volume content of particles smaller than this particle size accounts for 90% of all particles.

[0072] S1012, mixing the alloy steel powder with a binder, and performing injection molding to obtain a first blank;

[0073] Alternatively, the adhesive may be, but is not limited to, polyoxymethylene.

[0074] Optionally, the alloy steel powder and the binder are mixed and kneaded to obtain a feed material, which is then placed in an injection molding machine for injection molding to obtain a first blank.

[0075] S1013, degreasing the first blank to obtain a second blank; and

[0076] Alternatively, the first blank is placed in a degreasing furnace filled with nitric acid or oxalic acid to remove the binder in the first blank. Nitric acid or oxalic acid can react with polyoxymethylene, and the generated products (such as gas) are carried out by nitrogen, thereby achieving the purpose of removing polyoxymethylene in the first blank.

[0077] S1014, sintering the second blank to obtain a steel billet.

[0078] Optionally, the sintering is performed using a Hengpu two-temperature zone graphite furnace.

[0079] Optionally, the sintering includes a first sub-sintering, a second sub-sintering and a third sub-sintering; the sintering of the second blank to obtain a steel billet includes: (1) placing the second blank in a negative pressure and nitrogen atmosphere, performing a first sub-sintering at a temperature of 370°C to 610°C (for example, 370°C, 400°C, 430°C, 450°C, 480°C, 500°C, 530°C, 550°C, 580°C, 610°C, etc.), and holding the blank for 40 min to 120 min (for example, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min); (2) placing the second blank under negative pressure at a temperature of 610°C to 920°C (for example, 610°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, etc.); (3) placing the steel sheet in a nitrogen atmosphere at a temperature of 920°C to 1380°C (for example, 920°C, 950°C, 1000°C, 1050°C, 1100°C, 1250°C, 1300°C, 1350°C, 1375°C, 1380°C, etc.) and carrying out a third sub-sintering at a temperature of 40min to 120min (for example, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, 120min) to obtain a steel billet.

[0080] Optionally, the steel billet is a martensite-based ultra-high strength steel billet, and the grain size of the steel billet is in the range of 150 μm to 300 μm. Specifically, the grain size of the steel billet may be, but is not limited to, 150 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm, etc.

[0081] Optionally, the steel billet is a martensite-based ultra-high strength steel billet, and the density of the steel billet is 7.94 g / cm 3 .

[0082] In some embodiments, in S102, the hot isostatic pressing process includes:

[0083] The steel billet is placed under a pressure ranging from 120 MPa to 180 MPa for hot isostatic pressing, wherein the temperature of the hot isostatic pressing is greater than the austenite transformation end point temperature of the steel billet.

[0084] It should be noted that when the billet is heated to the austenite transformation temperature (i.e., Ac1), austenite begins to form in the billet, that is, pearlite (a eutectoid structure of ferrite + cementite) begins to transform into austenite. The temperature continues to rise to the austenite transformation end point temperature (also known as the austenite complete formation temperature, i.e., Ac3), the temperature at which ferrite completely dissolves and transforms into austenite. The temperature of hot isostatic pressing treatment is greater than Ac3.

[0085] For ease of description, the following description refers to the hot isostatically pressed steel billet as the first intermediate product, and the solution-treated steel billet as the second intermediate product. In other words, the hot isostatically pressed steel billet yields the first intermediate product, while the solution-treated steel billet yields the second intermediate product.

[0086] Alternatively, the hot isostatic pressing treatment can be carried out using a HIP furnace from Gangyan Haopu.

[0087] Specifically, the hot isostatic pressing pressure can be, but is not limited to, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, etc. If the hot isostatic pressing pressure is too low, the density of the hot isostatically pressed steel billet (i.e., the first intermediate product) will be insufficient, with excessive internal defects and excessive porosity. If the hot isostatic pressing pressure is too high, grain boundary defects will be caused, the grain size will grow, and the plasticity of the final martensitic steel will be reduced. In addition, if the hot isostatic pressing pressure is too high, the requirements for the hot isostatic pressing furnace will increase, and the hot isostatic pressing furnace may even be unable to withstand it, thereby increasing the production cost of the martensitic steel.

[0088] Optionally, the hot isostatic pressing time ranges from 0.5h to 3h. Specifically, the hot isostatic pressing time can be, but is not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, etc. If the hot isostatic pressing time is too short, the density of the hot isostatically pressed steel billet (i.e., the first intermediate product) will be insufficient, with excessive internal defects and excessive porosity. If the hot isostatic pressing time is too long, grain boundary defects will be caused, the grain size will grow, and the plasticity of the final martensitic steel will be reduced.

[0089] Optionally, during hot isostatic pressing, the heating rate is 1°C / min to 5°C / min. Specifically, during hot isostatic pressing, the heating rate can be, but is not limited to, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, etc. If the heating rate is too fast, the temperature at various locations within the hot isostatic pressing furnace may become uneven; if the heating rate is too slow, production costs may increase.

[0090] In this embodiment, hot isostatic pressing is performed on the steel billet at the end point temperature of austenite transformation, so that the first intermediate product obtained can be denser, that is, the degree of densification is higher and the porosity is smaller, and plastic deformation under high temperature and high pressure will cause recrystallization, making the grain size smaller, which is beneficial to improving the tensile strength, yield strength and elongation of the final martensitic steel, that is, improving the strength and plasticity of the martensitic steel.

[0091] In some embodiments, the steel billet is a martensite-based ultra-high strength steel billet, the hot isostatic pressing temperature ranges from 1100° C. to 1150° C., and the hot isostatic pressing pressure ranges from 150 MPa to 170 MPa.

[0092] Specifically, the HIP temperature may be, but is not limited to, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, etc. If the HIP temperature is too low, the steel billet (i.e., the first intermediate product) after HIP will be insufficiently dense, have excessive internal defects, and have excessive porosity. If the HIP temperature is too high, grain boundary defects will occur, the grain size will grow, and the plasticity of the resulting martensitic steel will be reduced. In addition, if the HIP temperature is too high, the requirements for the HIP furnace will increase, which will increase the production cost of the martensitic steel.

[0093] Specifically, the hot isostatic pressing pressure can be, but is not limited to, 150 MPa, 155 MPa, 160 MPa, 165 MPa, 170 MPa, etc. If the hot isostatic pressing pressure is too low, the steel billet (i.e., the first intermediate product) after hot isostatic pressing will not be dense enough, will have too many internal defects, and will have too much porosity. If the hot isostatic pressing pressure is too high, it will cause grain boundary defects, increase the grain size, and reduce the plasticity of the final martensitic steel. In addition, if the hot isostatic pressing pressure is too high, the requirements for the hot isostatic pressing furnace will increase, and the hot isostatic pressing furnace may even be unable to withstand it, increasing the production cost of the martensitic steel.

[0094] In this embodiment, the steel billet is a martensitic ultra-high strength steel billet, the temperature of the hot isostatic pressing is in the range of 1100°C to 1150°C, and the pressure of the hot isostatic pressing is in the range of 150 MPa to 170 MPa. This can make the obtained first intermediate product denser, that is, the degree of densification is higher, the porosity is smaller, and the grain size is smaller, which is beneficial to improving the tensile strength, yield strength and elongation of the final martensitic steel, that is, improving the strength and plasticity of the martensitic steel.

[0095] Optionally, the steel billet is a martensitic ultra-high strength steel billet, and the density of the hot isostatically pressed steel billet (i.e., the first intermediate product) is 8.10 g / cm 3 .

[0096] In some embodiments, the steel billet is a martensitic ultra-high-strength steel billet, and the average grain size of the steel billet after hot isostatic pressing is less than or equal to 160 μm. That is, the average grain size of the first intermediate product is less than or equal to 160 μm. Specifically, the grain size of the first intermediate product may be, but is not limited to, less than or equal to 160 μm, less than or equal to 150 μm, less than or equal to 140 μm, less than or equal to 130 μm, less than or equal to 120 μm, less than or equal to 110 μm, less than or equal to 100 μm, less than or equal to 90 μm, etc.

[0097] In some embodiments, in S103 , the temperature of the solution treatment is 50° C. to 250° C. higher than the austenite transformation end point temperature of the steel billet.

[0098] It can be understood that the difference between the solution treatment temperature and the austenite transformation end point temperature of the steel billet is in the range of 50°C to 250°C.

[0099] Specifically, the difference between the temperature of the solution treatment and the austenite transformation end point temperature of the steel billet can be but is not limited to 50°C, 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 250°C, etc.

[0100] If the difference between the solution treatment temperature and the austenite transformation end point temperature of the steel billet is too small, the impurity phases in the first intermediate product will not be fully integrated into the iron matrix, and the resulting second intermediate product (i.e., the steel billet after solution treatment) will not form a uniform supersaturated solid solution. In other words, the solid solution is incomplete, and the impurity phases are present in the second intermediate product. If the difference between the solution treatment temperature and the austenite transformation end point temperature of the steel billet is too large, the grain size of the second intermediate product obtained after solution treatment is likely to be too large, which is not conducive to improving the tensile strength, yield strength, and elongation of the resulting martensitic steel.

[0101] In this embodiment, the steel billet is solution treated at a temperature 50°C to 250°C above the austenite transformation end point temperature, which can better ensure that the impurity phase in the first intermediate product can be reintegrated into the iron matrix, ensure that the impurity phase is completely dissolved, and the obtained second intermediate product can form a uniform supersaturated solid solution.

[0102] In some embodiments, in S103, the steel billet is a martensite-based ultra-high strength steel billet, and the solution treatment includes:

[0103] The solution treatment is carried out at a temperature ranging from 980°C to 1050°C.

[0104] Specifically, the temperature of the solution treatment may be, but is not limited to, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, etc.

[0105] If the solution treatment temperature is too low, the impurity phases in the first intermediate product will not be fully integrated into the iron matrix, and the resulting second intermediate product (i.e., the steel billet after solution treatment) will not form a uniform supersaturated solid solution. In other words, the solid solution is incomplete, and the impurity phases will be present in the second intermediate product. If the solution treatment temperature is too high, the grain size of the second intermediate product obtained after solution treatment will be too large, which is not conducive to improving the tensile strength, yield strength, and elongation of the resulting martensitic steel.

[0106] Optionally, the solution treatment time ranges from 30 minutes to 120 minutes. The solution treatment time may be, but is not limited to, 30 minutes, 45 minutes, 60 minutes, 75 minutes, 90 minutes, 115 minutes, 120 minutes, etc. If the solution treatment time is too short, the solid solution is incomplete, and the second intermediate product is likely to contain impurity phases. If the solution treatment time is too long, the grain size of the obtained second intermediate product is likely to be too large, which is not conducive to improving the tensile strength, yield strength, and elongation of the resulting martensitic steel.

[0107] In some embodiments, in S104, the cyclic phase change treatment includes at least two phase change treatments, and the at least two phase change treatments include a first phase change treatment, and the temperature of the first phase change treatment is 30° C. to 100° C. lower than the temperature of the solution treatment.

[0108] The cyclic phase transformation of maraging steel begins with austenite transformation at the solid solution temperature, and then completes the full martensite transformation below the martensite transformation end temperature. The repeated changes between austenite and martensite in the material cause recrystallization, thereby refining the grain size.

[0109] Optionally, the cyclic phase transformation treatment may include, but is not limited to, two-phase transformation treatment, three-phase transformation treatment, four-phase transformation treatment, five-phase transformation treatment, etc. The number of cyclic phase transformation treatments is determined until the grain size does not grow. The number of cyclic phase transformation treatments is mainly based on the grain size of the material and the degree of grain size refinement caused by the cyclic phase transformation. When the cyclic phase transformation reaches a certain level, the grain size will not decrease further. Conversely, the degree of grain refinement will be less than the degree of grain size growth caused by the temperature increase. At the same time, the cyclic phase transformation temperature must be above the end point of the austenite transformation.

[0110] It can be understood that the difference between the temperature of the solution treatment and the temperature of the first phase transformation treatment ranges from 30°C to 100°C.

[0111] Specifically, the temperature of the first phase transformation treatment may be, but is not limited to, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc., lower than the temperature of the solution treatment. If the temperature of the first phase transformation treatment is much lower than the temperature of the solution treatment, the temperature of the first phase transformation treatment is too low, the driving force for recrystallization of the second intermediate product is insufficient, recrystallization is difficult, and it is not conducive to reducing the grain size. If the temperature of the first phase transformation treatment is too low than the temperature of the solution treatment, the temperature of the first phase transformation treatment is too high, the grain size is likely to grow, and the grain size refinement effect is not obvious.

[0112] In this embodiment, the temperature of the first phase transformation treatment (i.e., the temperature of the first phase transformation of the cyclic phase transformation treatment) is lower than the temperature of the solution treatment. This can better prevent the grain size from growing, which is beneficial to the phase transformation, making the grain size of the obtained martensitic steel smaller, and is beneficial to improving the tensile strength, yield strength and elongation of the martensitic steel.

[0113] In some embodiments, the temperatures of the at least two phase change treatments decrease sequentially.

[0114] It can be understood that the temperature of each phase change treatment is lower than the temperature of the previous phase change treatment, that is, the cyclic phase change treatment is a variable temperature cyclic phase change treatment.

[0115] Exemplarily, the cyclic phase change treatment includes a first phase change treatment and a second phase change treatment. The first phase change treatment is performed first and then the second phase change treatment. The temperature of the first phase change treatment is higher than the temperature of the second phase change treatment.

[0116] As another example, the cyclic phase change treatment includes a first phase change treatment, a second phase change treatment and a third phase change treatment. The first phase change treatment, the second phase change treatment and the third phase change treatment are performed sequentially, and the temperature of the first phase change treatment is higher than the temperature of the second phase change treatment, and the temperature of the second phase change treatment is higher than the temperature of the third phase change treatment.

[0117] As another example, the cyclic phase change treatment includes a first phase change treatment, a second phase change treatment, a third phase change treatment and a fourth phase change treatment, and the first phase change treatment, the second phase change treatment, the third phase change treatment and the fourth phase change treatment are performed in sequence, then the temperature of the first phase change treatment is higher than the temperature of the second phase change treatment, the temperature of the second phase change treatment is greater than the temperature of the third phase change treatment, and the temperature of the third phase change treatment is greater than the temperature of the fourth phase change treatment.

[0118] The temperature and time curve of cyclic phase change treatment is as follows Figure 3 shown.

[0119] In this embodiment, during the temperature-dependent cyclic phase transformation, the increased high dislocation density is inherited by the reverse-transformed austenite through phase transformation cold work hardening, further increasing the dislocation density of the reverse-transformed austenite, providing storage energy for recrystallization and increasing the driving force for recrystallization. With the fragmentation of the structure and the increase in dislocation density, the internal storage energy of the structure increases compared to that after solution treatment. As the number of temperature-dependent cyclic phase transformation recrystallization cycles increases, the internal storage energy of the structure also shows an increasing trend. After a single phase transformation and recrystallization treatment, the alloy's driving force for recrystallization increases. That is, when the phase transformation and recrystallization treatment is repeated, lowering the treatment temperature can still achieve complete recrystallization. If the previous recrystallization temperature is continued, the recrystallized grains will tend to increase. That is, during multiple cyclic α'-γ (martensite-austenite) phase transformations, when the dislocation density increases to a certain level, gradually lowering the phase transformation temperature of the α'-γ transformation is beneficial for suppressing the growth rate of the crystal nucleus. A temperature-dependent cyclic phase transformation with decreasing temperatures (i.e., the temperatures of the at least two phase transformation treatments decrease sequentially) can effectively refine grain size, with significantly better results than isothermal cyclic phase transformation. Furthermore, using linear martensite (i.e., lath-like martensite) as the starting microstructure for cyclic phase transformation can increase the nucleation rate and produce finer recrystallized grains. It can be understood that the temperatures of the at least two phase transformation treatments decrease sequentially, which can more effectively refine grain size and prevent excessive grain growth.

[0120] In some embodiments, the temperature of each phase change treatment is 30° C. to 100° C. lower than the temperature of the previous phase change treatment.

[0121] Specifically, the temperature of each phase change treatment may be, but is not limited to, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc. lower than the temperature of the previous phase change treatment.

[0122] If the temperature of each phase change treatment may be, but is not limited to, much lower than the temperature of the previous phase change treatment, the temperature of the phase change treatment is too low, the driving force for recrystallization is insufficient, recrystallization is difficult, and it is not conducive to reducing the grain size; if the temperature of each phase change treatment may be, but is not limited to, much lower than the temperature of the previous phase change treatment, the temperature of the phase change treatment is too high, the grain size is easy to grow, and the grain size refinement effect is not obvious.

[0123] Exemplarily, the cyclic phase change includes a first phase change treatment and a second phase change treatment, the first phase change treatment is performed first and then the second phase change treatment, and the temperature of the first phase change treatment is 30° C. to 100° C. higher than the temperature of the second phase change treatment.

[0124] As another example, the cyclic phase change includes a first phase change treatment, a second phase change treatment and a third phase change treatment, and the first phase change treatment, the second phase change treatment and the third phase change treatment are performed sequentially. The temperature of the first phase change treatment is 30°C to 100°C higher than the temperature of the second phase change treatment, and the temperature of the second phase change treatment is 30°C to 100°C higher than the temperature of the third phase change treatment.

[0125] As another example, the cyclic phase change includes a first phase change treatment, a second phase change treatment, a third phase change treatment and a fourth phase change treatment, and the first phase change treatment, the second phase change treatment, the third phase change treatment and the fourth phase change treatment are performed sequentially, then the temperature of the first phase change treatment is 30°C to 100°C higher than the temperature of the second phase change treatment, the temperature of the second phase change treatment is 30°C to 100°C higher than the temperature of the third phase change treatment, and the temperature of the third phase change treatment is 30°C to 100°C higher than the temperature of the fourth phase change treatment.

[0126] In some embodiments, in the at least two phase change treatments, the duration of a single phase change treatment ranges from 15 minutes to 2 hours.

[0127] It can be understood that the holding time of a single phase change treatment ranges from 15 minutes to 2 hours.

[0128] Specifically, the time for a single phase change treatment can be, but is not limited to, 15 min, 20 min, 30 min, 45 min, 60 min, 75 min, 90 min, 105 min, 120 min, etc.

[0129] If the single phase transformation treatment time is too short, the temperature in the furnace will be uneven. In addition, the second intermediate product will not fully recrystallize (or the structure will not be fully transformed), which is not conducive to reducing the grain size. If the single phase transformation treatment time is too long, the grain size will tend to grow, and the grain size refinement effect will not be obvious.

[0130] In some embodiments, the steel billet is a martensite-based ultra-high strength steel billet, and the at least two phase transformation treatments include a first phase transformation treatment and a second phase transformation treatment;

[0131] The first phase change treatment includes: placing the device at a temperature of 910° C. to 980° C. for heat preservation, and then cooling the device;

[0132] The second phase change treatment includes: keeping the temperature at 850° C. to 920° C. and then cooling.

[0133] Specifically, the temperature of the first phase transformation treatment may be, but is not limited to, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, etc. If the temperature of the first phase transformation treatment is too low, the driving force for recrystallization is insufficient, making recrystallization difficult and hindering grain size reduction. If the temperature of the first phase transformation treatment is too high, the grain size tends to grow, and the grain refinement effect is not significant.

[0134] Optionally, after the first phase change treatment is completed, liquid nitrogen is used to quickly cool the mixture to -196°C, and the liquid nitrogen insulation time ranges from 1 hour to 3 hours (for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.).

[0135] Specifically, the temperature of the second phase transformation treatment may be, but is not limited to, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, etc. If the temperature of the second phase transformation treatment is too low, the driving force for recrystallization is insufficient, making recrystallization difficult and hindering grain size reduction. If the temperature of the second phase transformation treatment is too high, the grain size tends to grow, and the grain refinement effect is not significant.

[0136] Optionally, after the second phase change treatment is completed, rapid cooling to room temperature is adopted.

[0137] Optionally, after the second phase change treatment is completed, the liquid nitrogen can be used to quickly cool the mixture to room temperature.

[0138] In this embodiment, the grain size of the obtained martensitic steel can be well refined through two phase transformation treatments, so that the obtained martensitic steel has better tensile strength, yield strength and elongation.

[0139] In some embodiments, the steel billet is a martensite-based ultra-high strength steel billet, and the at least two phase transformation treatments include a first phase transformation treatment, a second phase transformation treatment, and a third phase transformation treatment;

[0140] The first phase change treatment includes: placing the device at a temperature of 910° C. to 980° C. for heat preservation, and then cooling the device;

[0141] The second phase change treatment includes: placing the device at a temperature of 850° C. to 920° C. for heat preservation, and then cooling the device;

[0142] The third phase change treatment includes: keeping the temperature at 790° C. to 860° C. and then cooling.

[0143] For detailed descriptions of other aspects of the first phase change process and the second phase change process, please refer to the description of the corresponding parts of the above embodiments, which will not be repeated here.

[0144] Specifically, the temperature of the third phase transformation treatment may be, but is not limited to, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, etc. If the temperature of the third phase transformation treatment is too low, the driving force for recrystallization is insufficient, making recrystallization difficult and unfavorable for reducing grain size. If the temperature of the third phase transformation treatment is too high, the grain size tends to grow, and the grain refinement effect is not obvious.

[0145] Optionally, after the third phase change treatment is completed, rapid cooling to room temperature is adopted.

[0146] Optionally, after the third phase change treatment is completed, the liquid nitrogen can be used to quickly cool the mixture to room temperature.

[0147] In this embodiment, the grain size of the produced martensitic steel can be better refined through the three-phase transformation treatment, so that the produced martensitic steel has better tensile strength, yield strength and elongation.

[0148] In one example, the steel billet is maraging steel, and the cyclic phase transformation treatment includes: keeping it at 950°C for 30 minutes, and rapidly cooling it to -196°C using liquid nitrogen (first phase transformation treatment), and keeping it in liquid nitrogen for 2 hours; keeping it at 890°C for 30 minutes, and rapidly cooling it to room temperature (second phase transformation treatment); keeping it at 790°C for 30 minutes, and rapidly cooling it to room temperature (third phase transformation treatment).

[0149] In some embodiments, the steel billet is a martensitic ultra-high strength steel billet, and the average grain size of the martensitic steel is in a range of 20 μm to 60 μm.

[0150] It can be understood that the average grain size of the second intermediate product after the cyclic phase change process ranges from 20 μm to 60 μm.

[0151] It should be noted that the average grain size in the embodiment of the present application is the average grain size of any area (e.g. 1 mm 2 , 0.5mm 2 The grain sizes of multiple grains in the area are measured and the average value is calculated.

[0152] In some embodiments, more than 70% (eg, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 100%, etc.) of the martensitic steel has a grain size between 20 μm and 60 μm.

[0153] Specifically, the average grain size of the martensitic steel may be, but is not limited to, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, 53 μm, 55 μm, 58 μm, 60 μm, etc.

[0154] The smaller the average grain size of a martensitic steel, the more it reduces porosity, increases density, and improves tensile strength, yield strength, and elongation. However, if the average grain size is too small, more cyclic phase transformation processes are required, significantly increasing the production cost and even making it impossible to manufacture. If the average grain size is too large, the tensile strength, yield strength, and elongation of the martensitic steel will be reduced.

[0155] Figure 4 It is a schematic flow chart of a method for preparing martensitic steel according to another embodiment of the present application.

[0156] See Figure 4 The present invention provides a method for preparing a martensitic steel material, the method comprising:

[0157] S201, providing steel billets;

[0158] S202, performing hot isostatic pressing on the steel billet to obtain a first intermediate product;

[0159] S203, performing a solution treatment on the first intermediate product to obtain a second intermediate product;

[0160] S204, performing a cyclic phase change process on the second intermediate product to obtain a third intermediate product; and

[0161] For detailed description of other aspects of S201 to S204, please refer to the description of the corresponding parts of the above embodiment, which will not be repeated here.

[0162] S205, performing deep cryogenic treatment on the third intermediate product to obtain martensitic steel.

[0163] Optionally, the third intermediate product is rapidly cooled to a temperature below the martensitic transformation end point by water cooling or other quenching processes and then kept warm, so as to transform the material of the third intermediate product into a fully martensitic structure.

[0164] Optionally, the product is rapidly cooled to -196°C to -180°C (e.g., -180°C, -183°C, -185°C, -188°C, -190°C, -193°C, -196°C) by liquid nitrogen and kept warm for 1h to 3h (e.g., 1h, 1.5h, 2h, 2.5h, 3h, etc.) to ensure that all retained austenite in the third intermediate product is converted into full martensite.

[0165] In this embodiment, the content of lath martensite in the prepared martensitic steel can be better increased by cryogenic treatment, and the tensile strength, yield strength and toughness of the martensitic steel can be better improved.

[0166] The preparation method of the martensitic steel of this embodiment can well refine the grain size of the prepared martensitic steel, so that the prepared martensitic steel has higher density and lower porosity, and the prepared martensitic steel has higher tensile strength, yield strength, modulus and elongation.

[0167] Figure 5 It is a schematic flow chart of a method for preparing martensitic steel according to another embodiment of the present application.

[0168] See Figure 5 The present invention provides a method for preparing a martensitic steel material, the method comprising:

[0169] S301, providing steel billets;

[0170] S302, performing hot isostatic pressing on the steel billet to obtain a first intermediate product;

[0171] S303, performing a solution treatment on the first intermediate product to obtain a second intermediate product;

[0172] S304, performing a cyclic phase change process on the second intermediate product to obtain a third intermediate product;

[0173] S305, performing cryogenic treatment on the third intermediate product to obtain a fourth intermediate product; and

[0174] For detailed descriptions of other aspects of S301 to S305 , please refer to the descriptions of the corresponding parts of the above embodiments, which will not be repeated here.

[0175] S306, performing aging treatment on the fourth intermediate product to obtain martensitic steel.

[0176] Optionally, the fourth intermediate product is placed at a temperature of 470° C. to 510° C. for aging treatment, and the aging treatment time is 3 hours to 5 hours.

[0177] Specifically, the aging treatment temperature may be, but is not limited to, 470°C, 475°C, 480°C, 485°C, 490°C, 495°C, 500°C, 505°C, 510°C, etc. If the aging treatment temperature is too low, the aging process is insufficient, which is not conducive to improving the tensile strength, yield strength, and toughness of the martensitic steel. If the aging treatment temperature is too high, overaging is likely to occur, resulting in excessively large precipitation phases and grain sizes, which is not conducive to improving the tensile strength, yield strength, and toughness of the martensitic steel.

[0178] Specifically, the aging treatment time can be, but is not limited to, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc. If the aging treatment time is too short, the aging is insufficient, which is not conducive to improving the tensile strength, yield strength, and toughness of the martensitic steel. If the aging treatment time is too long, overaging is likely to occur, resulting in excessively large precipitation phases and grain sizes, which is not conducive to improving the tensile strength, yield strength, and toughness of the martensitic steel.

[0179] The method for preparing the martensitic steel of this embodiment can effectively refine the grain size of the resulting martensitic steel, resulting in a higher density, lower porosity, and higher tensile strength, yield strength, modulus, and elongation. Compared to martensitic steels produced by the method for preparing the martensitic steel of this application, which only undergo solid solution, deep cooling, and aging steps after sintering, the tensile strength and yield strength of the martensitic steel produced by the method of this application can be increased by 100 MPa to 300 MPa, and the elongation can be increased by 10% to 30%.

[0180] The embodiment of the present application further provides a martensitic steel, which is prepared using the method for preparing the martensitic steel described in the embodiment of the present application.

[0181] The martensitic steel of this embodiment is prepared by the above-mentioned preparation method of martensitic steel, wherein the preparation method sequentially performs hot isostatic pressing, solution treatment and cyclic phase transformation treatment on the steel. During the hot isostatic pressing process, the local plastic deformation and grain refinement pore area of ​​the steel billet preferentially undergoes plastic deformation under high pressure, resulting in an increase in dislocation density, activating the dynamic recrystallization process, and the deformation difference between the pore and the dense area produces a strain gradient, which promotes non-uniform recrystallization, resulting in a smaller grain size around the pore than in other areas; after the pore is eliminated and closed, the physical barrier that originally hindered grain boundary migration is reduced, but in the HIP high pressure environment (such as argon medium), the pressure itself becomes a new inhibitory factor, offsetting the coarsening risk caused by the disappearance of the barrier; after the pore is eliminated, the atomic diffusion path is smoother, promoting the uniform distribution of elements at the grain boundary, and reducing the abnormal grain growth caused by local component segregation; thus, after the steel billet is subjected to hot isostatic pressing, the density of the steel billet can be significantly improved, the porosity can be reduced, and the grain size can be reduced. In addition, the hot isostatic pressing (HIP) steel billet is then subjected to a solution treatment, which allows the impurity phases in the HIP steel billet to be reintegrated into the iron matrix, forming a uniform supersaturated solid solution. The solution-treated steel billet is then subjected to a cyclic phase transformation treatment. During the cyclic phase transformation process, the increased high dislocation density is inherited by the reverse-transformed austenite through phase transformation cold work hardening, further increasing the dislocation density of the reverse-transformed austenite, providing storage energy for recrystallization and increasing the driving force for recrystallization. With the fragmentation of the structure and the increase in dislocation density, the internal storage energy of the structure increases compared to that after the solution treatment. As the number of cyclic phase transformation recrystallization increases, the internal storage energy of the structure also shows an increasing trend. After multiple cyclic phase transformation treatments, the grain size of the martensitic steel is greatly reduced, the yield strength and tensile strength of the martensitic steel are increased, and the plasticity and elongation of the martensitic steel are improved.

[0182] In some embodiments, the martensitic steel is a steel that can undergo a martensitic phase transformation.

[0183] In some embodiments, the martensitic steel includes, but is not limited to, at least one of martensitic tool steel, martensitic structural steel (quenched and tempered steel), martensitic-based ultra-high strength steel, wear-resistant steel, and bearing steel.

[0184] Optionally, the martensitic-based ultra-high strength steel includes: low alloy martensitic steel, martensitic aging steel, and martensitic stainless steel.

[0185] The martensitic steels of these materials are prepared using the preparation method of the embodiments of the present application, which can better refine the grain size of the martensitic steel, make the porosity of the martensitic steel lower, and the degree of densification higher, which can better improve the tensile strength, yield strength and toughness of the martensitic steel.

[0186] The embodiment of the present application further provides a martensitic steel, wherein the average grain size of the martensitic steel is in a range of 20 μm to 60 μm.

[0187] Specifically, the average grain size of the martensitic steel may be, but is not limited to, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, 53 μm, 55 μm, 58 μm, 60 μm, etc.

[0188] The smaller the average grain size of the martensitic steel, the more conducive it is to reducing the porosity of the martensitic steel, improving the density of the martensitic steel, and the more conducive it is to improving the tensile strength, yield strength and elongation of the martensitic steel. However, if the average grain size of the martensitic steel is too small, more cyclic phase transformation treatments are required, which greatly increases the preparation cost of the martensitic steel and may even be impossible to achieve in terms of technology; if the average grain size of the martensitic steel is too large, the tensile strength, yield strength and elongation of the martensitic steel will be reduced. The martensitic steel of the embodiment of the present application has a lower average grain size, a higher density, and thus has higher tensile strength, yield strength and elongation.

[0189] In some embodiments, the porosity of the martensitic steel is less than or equal to 1%; or, the porosity of the martensitic steel is less than or equal to 0.8%; or, the porosity of the martensitic steel is less than or equal to 0.6%; or, the porosity of the martensitic steel is less than or equal to 0.5%.

[0190] Optionally, the porosity of the martensitic steel may be, but is not limited to, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, etc.

[0191] The martensitic steel of this embodiment has lower porosity, thus having higher density, higher tensile strength, yield strength and elongation.

[0192] In some embodiments, the martensitic steel is a martensitic ultra-high strength steel, and the martensitic ultra-high strength steel satisfies at least one of the following conditions:

[0193] The tensile strength of the martensitic ultra-high strength steel ranges from 2300 MPa to 2600 MPa;

[0194] The yield strength of the martensitic ultra-high strength steel is in the range of 2200 MPa to 2500 MPa;

[0195] The elongation of the martensite-based ultra-high strength steel is in the range of 5% to 8%; and

[0196] The elastic modulus of the martensite-based ultra-high strength steel ranges from 180 GPa to 220 GPa.

[0197] Specifically, the tensile strength of the martensite-based ultra-high strength steel may be, but is not limited to, 2300 MPa, 2330 MPa, 2350 MPa, 2380 MPa, 2400 MPa, 2430 MPa, 2450 MPa, 2480 MPa, 2500 MPa, 2530 MPa, 2550 MPa, 2580 MPa, 2600 MPa, etc.

[0198] Specifically, the yield strength of the martensite-based ultra-high strength steel may be, but is not limited to, 2200 MPa, 2230 MPa, 2250 MPa, 2280 MPa, 2300 MPa, 2330 MPa, 2350 MPa, 2380 MPa, 2400 MPa, 2430 MPa, 2450 MPa, 2480 MPa, 2500 MPa, etc.

[0199] Specifically, the elongation of the martensite-based ultra-high strength steel may be, but is not limited to, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, etc.

[0200] Specifically, the elastic modulus of the martensite-based ultra-high strength steel may be, but is not limited to, 180 GPa, 185 GPa, 190 GPa, 195 GPa, 200 GPa, 205 GPa, 210 GPa, 215 GPa, 220 GPa, etc.

[0201] The martensitic steel of the embodiment of the application has high yield strength, tensile strength, elastic modulus and elongation, and can thus be better applied to structural parts of electronic equipment with high requirements on yield strength, tensile strength and elongation.

[0202] The martensitic steel of the present application is further described below through specific examples.

[0203] Example 1

[0204] The martensitic steel of this embodiment is prepared by the following steps:

[0205] (1) preparing a steel billet, comprising:

[0206] (i) providing alloy steel powder (18Ni maraging steel) and a binder (polyoxymethylene) at a volume ratio of binder to alloy steel powder of 40:60, and performing banburying to obtain a feed; wherein the composition of the alloy steel powder, the mass fraction of each element, and the parameters of the alloy steel powder are shown in Table 1 below;

[0207] Table 1 Composition of alloy steel powder and mass fraction of each element, parameters of alloy steel powder

[0208]

[0209] (ii) injecting the feed material into an injection molding machine to obtain a first blank;

[0210] (iii) degreasing the first blank to obtain a second blank; and

[0211] (iv) placing the second blank in a Hengpu two-temperature zone graphite furnace for sintering, the sintering comprising: placing the blank in a negative pressure and nitrogen atmosphere at a temperature of 500°C for a first sub-sintering, with a holding time of 60 minutes; placing the blank under negative pressure at a temperature of 880°C for a second sub-sintering, with a holding time of 90 minutes; and placing the blank in a nitrogen atmosphere at a temperature of 1375°C for a third sub-sintering, with a holding time of 90 minutes, to obtain a steel blank.

[0212] (2) placing the steel billet at a temperature of 1120° C. and a pressure of 160 MPa for hot isostatic pressing for 1 hour to obtain a first intermediate product;

[0213] (3) performing a solution treatment at a temperature of 1010°C for 1 h to obtain a second intermediate product;

[0214] (4) performing a cyclic phase change treatment, wherein the cyclic phase change treatment includes: placing at 950°C for 30 minutes, and rapidly cooling to -196°C using liquid nitrogen (first phase change treatment), and then maintaining the liquid nitrogen treatment for 2 hours; placing at 890°C for 30 minutes, and rapidly cooling to room temperature (second phase change treatment); placing at 790°C for 30 minutes, and rapidly cooling to room temperature (third phase change treatment), to obtain a third intermediate product;

[0215] (5) cryogenic treatment: rapid cooling to -196°C using liquid nitrogen and keeping the temperature for 2 hours to obtain a fourth intermediate product; and

[0216] (6) The steel is placed at 490°C for aging treatment with a holding time of 4 hours to obtain martensitic steel.

[0217] Figure 6 This is a metallographic corrosion picture of the steel billet of Example 1 (taken using a metallographic microscope). Figure 7 This is a metallographic image of a steel billet that has only been polished and not corroded. Figure 8 This is the porosity distribution diagram of the steel billet calculated using the porosity calculation software of the metallographic microscope.

[0218] Depend on Figures 6 to 8It can be seen that the steel billet of Example 1 has a relatively large grain size, which is approximately in the range of 180 μm to 250 μm. The steel billet of Example 1 has a relatively large porosity, which is approximately 4.72%.

[0219] Figure 9 This is a metallographic corrosion picture of the first intermediate product of Example 1 (i.e., the steel billet after hot isostatic pressing). Figure 10 This is the metallographic image of the first intermediate product after only polishing and no corrosion. Figure 11 This is the porosity distribution diagram of the first intermediate product calculated using the porosity calculation software of the metallographic microscope.

[0220] Depend on Figures 9 to 11 It can be seen that after hot isostatic pressing, the grain size of the steel billet of Example 1 becomes smaller, from 150μm to 300μm to 30μm to 80μm. After hot isostatic pressing, the densification degree of the steel billet of Example 1 increases, and the porosity is greatly reduced, from 4.72% to 0.531%.

[0221] Figure 12 This is a metallographic corrosion picture of the second intermediate product of Example 1 (i.e., the steel billet after solid solution treatment). Figure 12 It can be seen that the grain size of the second intermediate product after solution treatment will be further refined.

[0222] Figure 13 This is a metallographic corrosion picture of the third intermediate product of Example 1 (i.e., the steel billet after cyclic phase transformation treatment). Figure 13 It can be seen that the third intermediate product obtained after the cyclic phase change has a smaller grain size, which can be reduced to 20μm to 50μm.

[0223] Example 2

[0224] The martensitic steel of this embodiment is prepared by the following steps:

[0225] (1) preparing a steel billet, comprising:

[0226] (i) providing alloy steel powder (18Ni maraging steel) and a binder (polyoxymethylene) in a volume ratio of binder to alloy steel powder of 40:60, and performing banburying to obtain a feed; wherein the composition of the alloy steel powder, the mass fraction of each element, and the parameters of the alloy steel powder are the same as those in Example 1;

[0227] (ii) injecting the feed material into an injection molding machine to obtain a first blank;

[0228] (iii) degreasing the first blank to obtain a second blank; and

[0229] (iv) placing the second blank in a Hengpu two-temperature zone graphite furnace for sintering, the sintering comprising: placing the blank in a negative pressure and nitrogen atmosphere at a temperature of 500°C for a first sub-sintering, with a holding time of 60 minutes; placing the blank under negative pressure at a temperature of 880°C for a second sub-sintering, with a holding time of 90 minutes; and placing the blank in a nitrogen atmosphere at a temperature of 1375°C for a third sub-sintering, with a holding time of 90 minutes, to obtain a steel blank.

[0230] (2) placing the steel billet at a temperature of 1120° C. and a pressure of 160 MPa for hot isostatic pressing for 1 hour to obtain a first intermediate product;

[0231] (3) performing a solution treatment at a temperature of 1010°C for 1 h to obtain a second intermediate product;

[0232] (4) performing a cyclic phase change treatment, wherein the cyclic phase change treatment includes: placing the product at 950°C for 30 minutes, and rapidly cooling it to -196°C using liquid nitrogen (first phase change treatment), and then maintaining the product with liquid nitrogen for 2 hours; placing the product at 890°C for 30 minutes, and rapidly cooling it to room temperature (second phase change treatment), to obtain a third intermediate product;

[0233] (5) cryogenic treatment: rapid cooling to -196°C using liquid nitrogen and keeping the temperature for 2 hours to obtain a fourth intermediate product; and

[0234] (6) The steel is placed at 490°C for aging treatment with a holding time of 4 hours to obtain martensitic steel.

[0235] Example 3

[0236] The martensitic steel of this embodiment is prepared by the following steps:

[0237] (1) preparing a steel billet, comprising:

[0238] (i) providing alloy steel powder (18Ni maraging steel) and a binder (polyoxymethylene) in a volume ratio of binder to alloy steel powder of 40:60, and performing banburying to obtain a feed; wherein the composition of the alloy steel powder, the mass fraction of each element, and the parameters of the alloy steel powder are the same as those in Example 1;

[0239] (ii) injecting the feed material into an injection molding machine to obtain a first blank;

[0240] (iii) degreasing the first blank to obtain a second blank; and

[0241] (iv) placing the second blank in a Hengpu two-temperature zone graphite furnace for sintering, the sintering comprising: placing the blank in a negative pressure and nitrogen atmosphere at a temperature of 500°C for a first sub-sintering, with a holding time of 60 minutes; placing the blank under negative pressure at a temperature of 880°C for a second sub-sintering, with a holding time of 90 minutes; and placing the blank in a nitrogen atmosphere at a temperature of 1375°C for a third sub-sintering, with a holding time of 90 minutes, to obtain a steel blank.

[0242] (2) placing the steel billet at a temperature of 1120° C. and a pressure of 160 MPa for hot isostatic pressing for 1 hour to obtain a first intermediate product;

[0243] (3) performing a solution treatment at a temperature of 1010°C for 1 h to obtain a second intermediate product;

[0244] (4) performing a cyclic phase change treatment, wherein the cyclic phase change treatment comprises: placing at 950°C for 30 minutes, and rapidly cooling to -196°C using liquid nitrogen (first phase change treatment), and then maintaining the liquid nitrogen treatment for 2 hours; placing at 950°C for 30 minutes, and rapidly cooling to room temperature (second phase change treatment); placing at 950°C for 30 minutes, and rapidly cooling to room temperature (third phase change treatment), to obtain a third intermediate product;

[0245] (5) cryogenic treatment: rapid cooling to -196°C using liquid nitrogen and keeping the temperature for 2 hours to obtain a fourth intermediate product; and

[0246] (6) The steel is placed at 490°C for aging treatment with a holding time of 4 hours to obtain martensitic steel.

[0247] Comparative Example 1

[0248] The martensitic steel of this embodiment is prepared by the following steps:

[0249] (1) preparing a steel billet, comprising:

[0250] (i) providing alloy steel powder (18Ni maraging steel) and a binder (polyoxymethylene) in a volume ratio of binder to alloy steel powder of 40:60, and performing banburying to obtain a feed; wherein the composition of the alloy steel powder, the mass fraction of each element, and the parameters of the alloy steel powder are the same as those in Example 1;

[0251] (ii) injecting the feed material into an injection molding machine to obtain a first blank;

[0252] (iii) degreasing the first blank to obtain a second blank; and

[0253] (iv) placing the second blank in a Hengpu two-temperature zone graphite furnace for sintering, the sintering comprising: placing the blank in a negative pressure and nitrogen atmosphere at a temperature of 500°C for a first sub-sintering, with a holding time of 60 minutes; placing the blank under negative pressure at a temperature of 880°C for a second sub-sintering, with a holding time of 90 minutes; and placing the blank in a nitrogen atmosphere at a temperature of 1375°C for a third sub-sintering, with a holding time of 90 minutes, to obtain a steel blank.

[0254] (2) placing the steel billet at a temperature of 1010°C for solution treatment for 1 hour;

[0255] (3) Cryogenic treatment: Rapid cooling to -196°C using liquid nitrogen and keeping warm for 2 hours; and

[0256] (4) The steel is placed at 490°C for aging treatment with a holding time of 4 hours to obtain martensitic steel.

[0257] Comparative Example 2

[0258] The martensitic steel of this embodiment is prepared by the following steps:

[0259] (1) preparing a steel billet, comprising:

[0260] (i) providing alloy steel powder (18Ni maraging steel) and a binder (polyoxymethylene) in a volume ratio of binder to alloy steel powder of 40:60, and performing banburying to obtain a feed; wherein the composition of the alloy steel powder, the mass fraction of each element, and the parameters of the alloy steel powder are the same as those in Example 1;

[0261] (ii) injecting the feed material into an injection molding machine to obtain a first blank;

[0262] (iii) degreasing the first blank to obtain a second blank; and

[0263] (iv) placing the second blank in a Hengpu two-temperature zone graphite furnace for sintering, the sintering comprising: placing the blank in a negative pressure and nitrogen atmosphere at a temperature of 500°C for a first sub-sintering, with a holding time of 60 minutes; placing the blank under negative pressure at a temperature of 880°C for a second sub-sintering, with a holding time of 90 minutes; and placing the blank in a nitrogen atmosphere at a temperature of 1375°C for a third sub-sintering, with a holding time of 90 minutes, to obtain a steel blank.

[0264] (2) The steel billet is placed at a temperature of 1120°C and a pressure of 160 MPa for hot isostatic pressing for 1 h;

[0265] (3) placing it at a temperature of 1010°C for solution treatment, and the solution treatment time is 1 hour;

[0266] (4) Cryogenic treatment: Rapid cooling to -196°C using liquid nitrogen and keeping warm for 2 hours; and

[0267] (5) The steel is placed at 490°C for aging treatment with a holding time of 4 hours to obtain martensitic steel.

[0268] Comparative Example 3

[0269] The martensitic steel of this embodiment is prepared by the following steps:

[0270] (1) preparing a steel billet, comprising:

[0271] (i) providing alloy steel powder (18Ni maraging steel) and a binder (polyoxymethylene) in a volume ratio of binder to alloy steel powder of 40:60, and performing banburying to obtain a feed; wherein the composition of the alloy steel powder, the mass fraction of each element, and the parameters of the alloy steel powder are the same as those in Example 1;

[0272] (ii) injecting the feed material into an injection molding machine to obtain a first blank;

[0273] (iii) degreasing the first blank to obtain a second blank; and

[0274] (iv) placing the second blank in a Hengpu two-temperature zone graphite furnace for sintering, the sintering comprising: placing the blank in a negative pressure and nitrogen atmosphere at a temperature of 500°C for a first sub-sintering, with a holding time of 60 minutes; placing the blank under negative pressure at a temperature of 880°C for a second sub-sintering, with a holding time of 90 minutes; and placing the blank in a nitrogen atmosphere at a temperature of 1375°C for a third sub-sintering, with a holding time of 90 minutes, to obtain a steel blank.

[0275] (2) placing the steel billet at a temperature of 1010°C for solution treatment for 1 hour;

[0276] (3) performing a cyclic phase change treatment, wherein the cyclic phase change treatment includes: keeping the temperature at 950°C for 30 minutes and rapidly cooling to -196°C using liquid nitrogen (first phase change treatment), and keeping the temperature at liquid nitrogen for 2 hours; keeping the temperature at 890°C for 30 minutes and rapidly cooling to room temperature (second phase change treatment); keeping the temperature at 790°C for 30 minutes and rapidly cooling to room temperature (third phase change treatment);

[0277] (4) Cryogenic treatment: Rapid cooling to -196°C using liquid nitrogen and keeping warm for 2 hours; and

[0278] (5) The steel is placed at 490°C for aging treatment with a holding time of 4 hours to obtain martensitic steel.

[0279] The martensitic steels obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to various performance tests:

[0280] (1) Grain size test: The grain size of each embodiment and comparative example is the average grain size.

[0281] (2) Tensile strength test: measured according to GBT228.1-2010.

[0282] (3) Yield strength test: measured in accordance with GBT228.1-2010.

[0283] (4) Elongation test: measured according to GBT228.1-2010.

[0284] Various performance parameters of the martensitic steels of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2 below.

[0285] Table 2 Performance parameters of martensitic steels of Examples 1 to 3 and Comparative Examples 1 to 3

[0286]

[0287] The test results of Example 1 and Comparative Examples 1 to 3 in Table 2 show that the martensitic steel of Comparative Example 1, prepared by solution treatment, cryogenic treatment, and aging treatment after sintering, resulted in a larger grain size and lower tensile strength, yield strength, modulus, and elongation. The martensitic steel of Comparative Example 2, prepared by hot isostatic pressing after sintering, followed by solution treatment, cryogenic treatment, and aging treatment, significantly reduced grain size compared to the martensitic steel of Comparative Example 1, resulting in improved tensile strength, yield strength, modulus, and elongation, but the magnitude of the improvement was relatively small. When the martensitic steel of Comparative Example 3 was prepared, after sintering, it was sequentially subjected to solid solution treatment, cyclic phase transformation, deep freezing, and aging treatment. Compared with the martensitic steel of Comparative Example 1, the martensitic steel prepared in Comparative Example 3 had a reduced grain size, and its tensile strength, yield strength, modulus, and elongation were all improved, but the improvement was relatively small. When the martensitic steel of Example 1 of the present application was prepared, after sintering, it was sequentially subjected to hot isostatic pressing, solid solution treatment, cyclic phase transformation, deep freezing, and aging treatment. The grain size of the martensitic steel prepared was greatly reduced, and its tensile strength, yield strength, modulus, and elongation were all greatly improved.

[0288] From the test results of Example 1, Example 2, and Example 3, it can be seen that compared with the solution of performing two phase transformation treatments in Example 2, the solution of performing three phase transformation treatments in Example 1 can better reduce the grain size of the martensitic steel and improve the tensile strength, yield strength, modulus, and elongation of the martensitic steel. Compared with the solution of performing three phase transformation treatments at equal temperatures in Example 3, the solution of performing three phase transformation treatments at decreasing temperatures in Example 1 can better reduce the grain size of the martensitic steel and improve the tensile strength, yield strength, and elongation of the martensitic steel. In addition, the preparation process conditions of the martensitic steel have a certain influence on the modulus, but the overall influence is not significant.

[0289] Examples 4 to 18, Comparative Examples 4 to 13

[0290] The difference between each embodiment and comparative example and embodiment 1 is that the conditions of at least one of hot isostatic pressing, solution treatment, and cyclic phase transformation are different. The preparation process conditions of the martensitic steel of each embodiment and comparative example are shown in Table 3 below.

[0291] Table 3 Process conditions of martensitic steels of Example 1, Examples 4 to 18, and Comparative Examples 4 to 13

[0292]

[0293]

[0294] The performance parameters of the martensitic steels of Example 1, Examples 4 to 18, and Comparative Examples 4 to 13 are shown in Table 4 below.

[0295] Table 4 Performance parameters of martensitic steels of Example 1, Examples 4 to 18, and Comparative Examples 4 to 13

[0296]

[0297] From the test results of Example 1, Examples 4 to 5, Comparative Example 4 and Comparative Example 5 in Table 4, it can be seen that, when other conditions remain unchanged, as the temperature of hot isostatic pressing increases, the grain size of the obtained martensitic steel tends to increase as a whole, and the tensile strength, yield strength, modulus and elongation all first gradually increase and then gradually decrease.

[0298] From the test results of Example 1, Examples 6 to 9, and Comparative Examples 6 to 7 in Table 4, it can be seen that with the increase of the temperature of the solution treatment, the grain size of the obtained martensitic steel tends to increase as a whole; the tensile strength and yield strength of the obtained martensitic steel first gradually increase and then gradually decrease; the elongation of the martensitic steel is maintained at a high level, and the modulus of the martensitic steel changes little (mainly determined by the composition).

[0299] From the test data of Examples 1, 10 to 12, Comparative Examples 8 and 9 in Table 4, it can be seen that with the increase in the temperature of the first phase transformation treatment, the grain size of the obtained martensitic steel first gradually decreases and then gradually increases; the tensile strength and yield strength of the obtained martensitic steel first gradually increase and then gradually decrease; the elongation of the obtained martensitic steel is maintained at a high level; and the modulus of the obtained martensitic steel changes little.

[0300] From Example 1, Example 13 to Example 15, and Comparative Example 10 to Comparative Example 11 in Table 4, as the temperature of the second phase transformation treatment increases, the grain size of the obtained martensitic steel first gradually decreases and then gradually increases; the tensile strength of the obtained martensitic steel changes little; the yield strength of the obtained martensitic steel first gradually increases and then gradually decreases; the elongation of the obtained martensitic steel is maintained at a high level; and the modulus of the obtained martensitic steel changes little.

[0301] From Example 1, Example 16 to Example 18, and Comparative Example 12 to Comparative Example 13 in Table 4, as the temperature of the third phase transformation treatment increases, the grain size of the obtained martensitic steel first gradually increases and then gradually decreases; the tensile strength of the obtained martensitic steel gradually decreases; the yield strength of the obtained martensitic steel gradually decreases; the elongation of the obtained martensitic steel gradually decreases; and the modulus of the obtained martensitic steel changes little.

[0302] Figure 14 4 is a schematic structural diagram of a structural component 400 of an electronic device according to an embodiment of the present application.

[0303] See Figure 14 The embodiment of the present application also provides a structural component 400 of an electronic device, wherein the structural component 400 of the electronic device includes the martensitic steel described in the embodiment of the present application, or the structural component 400 of the electronic device is prepared by the preparation method of the martensitic steel described in the embodiment of the present application.

[0304] Optionally, the structural member 400 of the electronic device may be, but is not limited to, a shaft (e.g., a shaft of a foldable electronic device), a housing, a middle frame, a button, a hinge, a gear, or other load-bearing members. In addition, it may also be other structural members that have high requirements for tensile strength, yield strength, and elongation. Figure 14 In the accompanying drawings, the structural component 400 of the electronic device is illustrated by taking a rotating shaft as an example, which should not be understood as a limitation on the structural component 400 of the electronic device of the present application.

[0305] Optionally, the electronic device may be, but is not limited to, a mobile phone, a tablet computer, a laptop computer, a desktop computer, a smart bracelet, a smart watch, an e-reader, a game console, etc.

[0306] Figure 15 4 is a flow chart of a method for preparing a structural component 400 of an electronic device according to an embodiment of the present application.

[0307] See Figure 15 In some embodiments, the method for preparing the structural component 400 of the electronic device of the present application includes:

[0308] S501, providing steel billets;

[0309] S502, performing hot isostatic pressing on the steel billet to obtain a first intermediate product;

[0310] S503, performing a solution treatment on the first intermediate product to obtain a second intermediate product;

[0311] S504, performing a cyclic phase change process on the second intermediate product to obtain a third intermediate product;

[0312] S505, performing cryogenic treatment on the third intermediate product to obtain a fourth intermediate product; and

[0313] S506 , performing aging treatment on the fourth intermediate product to obtain the structural component 400 of the electronic device.

[0314] For detailed description of S501-S506, please refer to the corresponding part of the above embodiment, which will not be repeated here. For detailed description of the composition of the electronic device structural member 400, please refer to the corresponding part of the description of the martensitic steel material, which will not be repeated here.

[0315] Figure 16 3 is a structural diagram of an electronic device 500 according to an embodiment of the present application, wherein the foldable middle frame is in a folded state. Figure 17 yes Figure 16 Enlarged view of the dotted box I in the middle.

[0316] See Figure 16 and Figure 17 , an embodiment of the present application further provides an electronic device 500 , which includes the structural member 400 of the electronic device described in the embodiment of the present application, and the structural member 400 of the electronic device serves as a force-bearing member of the electronic device 500 .

[0317] The electronic device 500 of the embodiment of the present application may be, but is not limited to, a mobile phone, a foldable mobile phone, a tablet computer, a foldable tablet computer, a laptop computer, a desktop computer, a smart bracelet, a smart watch, smart glasses, an e-reader, a game console, or other portable electronic device 500. The electronic device 500 described in this embodiment is only one form of the electronic device 500 to which the structural member 400 of the electronic device is applied. Figure 15The accompanying drawings illustrate an electronic device 500 taking a foldable electronic device as an example, and the structural component 400 of the electronic device taking the hinge 400 of the foldable electronic device as an example. It should not be understood as a limitation on the electronic device 500 provided in the present application, nor should it be understood as a limitation on the structural component 400 of the electronic device provided in each embodiment of the present application.

[0318] For a detailed description of the structural component 400 of the electronic device, please refer to the description of the corresponding part of the above embodiment, which will not be repeated here.

[0319] Figure 18 3 is a schematic structural diagram of an electronic device 500 according to an embodiment of the present application, wherein the foldable middle frame is in a flattened state. Figure 19 4 is a circuit block diagram of an electronic device 500 according to an embodiment of the present application.

[0320] See Figures 16 to 19 In some embodiments, the electronic device 500 is a foldable electronic device, and includes a flexible display 510, a foldable middle frame 520, and a processor 530. The foldable middle frame 520 is used to support the flexible display 510 and drive the flexible display 510 to fold or unfold. The foldable middle frame 520 includes a first middle frame 521, a hinge 400, and a second middle frame 522. The first middle frame 521 and the second middle frame 522 are used to support the non-bendable area of ​​the flexible display 510. The hinge 400 is used to support the bendable area of ​​the flexible display 510. The first middle frame 521 and the second middle frame 522 can rotate relative to the hinge 400 in directions toward or away from each other. The processor 530 is electrically connected to the flexible display 510 and is used to control the display of the flexible display 510. The hinge 400 is a structural component 400 of the electronic device in this embodiment of the application.

[0321] The foldable electronic device of the embodiment of the present application includes at least one of a foldable mobile phone, a foldable tablet computer, a foldable e-reader, a foldable laptop computer, etc.

[0322] It can be understood that the first middle frame 521, the hinge 400 and the second middle frame 522 cooperate with each other to support the flexible display screen 510; the foldable middle frame 520 has a folded state (such as Figure 16 as shown) and flattened state (as shown) Figure 18 As shown), when the foldable middle frame 520 is in a flattened state, the first middle frame 521, the rotating shaft 400 and the second middle frame 522 form a planar structure; when the foldable middle frame 520 is in a folded state, the first middle frame 521 and the second middle frame 522 overlap or stack.

[0323] Optionally, the processor 530 includes one or more general-purpose processors, where a general-purpose processor can be any type of device capable of processing electronic instructions, including a central processing unit (CPU), a microprocessor, a microcontroller, a main processor, a controller, and an ASIC. The processor 530 is used to execute various types of digitally stored instructions, such as software or firmware programs stored in the memory 540, which enables the computing device to provide a wide variety of services.

[0324] In some embodiments, the electronic device 500 of the embodiment of the present application further includes a memory 540. The memory 540 is electrically connected to the processor 530. The memory 540 is used to store program codes required for the processor 530 to run, program codes required for controlling the flexible display 510, and display content of the flexible display 510.

[0325] Optionally, the memory 540 may include a volatile memory, such as a random access memory (RAM); the memory 540 may also include a non-volatile memory (NVM), such as a read-only memory (ROM), a flash memory (FM), a hard disk drive (HDD), or a solid-state drive (SSD). The memory 540 may also include a combination of the aforementioned types of memory 540.

[0326] In some embodiments, the electronic device 500 of the embodiment of the present application further includes a camera module 550, which is electrically connected to the processor 530 and is configured to capture images under the control of the processor 530. Optionally, the camera module 550 can be at least one of a front camera module 550 and a rear camera module 550.

[0327] References to "embodiments" and "implementation methods" in this application mean that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various locations in the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of this application, unless there is a contradiction between them.

[0328] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing a martensitic steel, characterized in that: The preparation method comprises: Provide steel billets; Perform hot isostatic pressing; performing a solution treatment; and The cyclic phase transformation treatment is carried out to obtain martensitic steel.

2. The method for preparing martensitic steel according to claim 1, wherein: The hot isostatic pressing treatment comprises: The steel billet is placed under a pressure ranging from 120 MPa to 180 MPa for hot isostatic pressing, wherein the temperature of the hot isostatic pressing is greater than the austenite transformation end point temperature of the steel billet.

3. The method for preparing martensitic steel according to claim 2, wherein: The steel billet is a martensite-based ultra-high strength steel billet, the hot isostatic pressing temperature ranges from 1100° C. to 1150° C., and the hot isostatic pressing pressure ranges from 150 MPa to 170 MPa.

4. The method for preparing martensitic steel according to claim 1, wherein: The temperature of the solution treatment is 50° C. to 250° C. higher than the austenite transformation end point temperature of the steel slab.

5. The method for preparing martensitic steel according to claim 1, wherein: The steel billet is a martensitic ultra-high strength steel billet, and the solution treatment comprises: The solution treatment is carried out at a temperature ranging from 980°C to 1050°C.

6. The method for preparing a martensitic steel according to any one of claims 1 to 5, characterized in that: The cyclic phase change treatment includes at least two phase change treatments, wherein the at least two phase change treatments include a first phase change treatment, and the temperature of the first phase change treatment is 30° C. to 100° C. lower than the temperature of the solid solution treatment.

7. The method for preparing martensitic steel according to claim 6, characterized in that: The temperatures of the at least two phase change treatments decrease successively.

8. The method for preparing martensitic steel according to claim 6, characterized in that: The temperature of each phase change treatment is 30° C. to 100° C. lower than the temperature of the previous phase change treatment.

9. The method for preparing martensitic steel according to claim 6, characterized in that: In the at least two phase change treatments, the time of a single phase change treatment ranges from 15 minutes to 2 hours.

10. The method for preparing martensitic steel according to claim 6, characterized in that: The steel billet is a martensite-based ultra-high strength steel billet, and the at least two phase transformation treatments further include a second phase transformation treatment; The first phase change treatment includes: placing the device at a temperature of 910° C. to 980° C. for heat preservation, and then cooling the device; The second phase change treatment includes: keeping the temperature at 850° C. to 920° C. and then cooling.

11. The method for preparing martensitic steel according to claim 10, characterized in that: The at least two phase change processes further include a third phase change process; The third phase change treatment includes: keeping the temperature at 790° C. to 860° C. and then cooling.

12. The method for preparing a martensitic steel according to any one of claims 1 to 5 and 7 to 11, characterized in that: After the cyclic phase change treatment, the preparation method further comprises: Perform deep freezing treatment.

13. The method for preparing martensitic steel according to claim 12, characterized in that: After the cyclic phase change treatment, the preparation method further comprises: Carry out aging treatment.

14. The method for preparing a martensitic steel according to any one of claims 1-5, 7-11, and 13, characterized in that: The steel billet is a martensitic ultra-high strength steel billet, The grain size of the steel billet ranges from 150 μm to 300 μm; The average grain size of the steel billet after hot isostatic pressing is less than or equal to 100 μm; The average grain size of the martensitic steel is in a range of 20 μm to 60 μm.

15. A martensitic steel material, characterized in that: The martensitic steel is prepared by the method for preparing the martensitic steel according to any one of claims 1 to 14.

16. The martensitic steel material according to claim 15, characterized in that The martensitic steel material includes at least one of martensitic tool steel, martensitic structural steel, martensitic-based ultra-high strength steel, wear-resistant steel, and bearing steel.

17. A martensitic steel, characterized in that: The average grain size of the martensitic steel is in a range of 20 μm to 60 μm.

18. The martensitic steel material according to claim 17, characterized in that: The porosity of the martensitic steel is less than or equal to 1%; or, the porosity of the martensitic steel is less than or equal to 0.8%; or, the porosity of the martensitic steel is less than or equal to 0.6%; or, the porosity of the martensitic steel is less than or equal to 0.5%.

19. The martensitic steel material according to claim 17 or 18, characterized in that: The martensitic steel is a martensitic ultra-high strength steel, and the martensitic ultra-high strength steel satisfies at least one of the following conditions: The tensile strength of the martensitic ultra-high strength steel ranges from 2300 MPa to 2600 MPa; The yield strength of the martensitic ultra-high strength steel is in the range of 2200 MPa to 2500 MPa; The elongation of the martensite-based ultra-high strength steel is in the range of 5% to 8%; as well as The elastic modulus of the martensite-based ultra-high strength steel ranges from 180 GPa to 220 GPa.

20. A structural component of an electronic device, characterized in that: The structural component of the electronic device is manufactured by the method for preparing the martensitic steel according to any one of claims 1 to 14, and the structural component of the electronic device comprises the martensitic steel according to any one of claims 15 to 19.

21. An electronic device, characterized in that: A structural component of an electronic device comprising the electronic device according to claim 20.

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