Steel, steel structural member, electronic equipment and preparation method of steel structural member

Abstract

The invention provides steel, a steel structural part, electronic equipment and a preparation method of the steel structural part. The steel comprises the following components in percentage by mass: 7%-11% of chromium, 2%-7.5% of nickel, 6%-15% of cobalt, 4%-7% of molybdenum, trace amount-0.4% of oxygen, trace amount-0.35% of carbon and 50%-80% of iron. The steel provided by the invention has relatively high mechanical strength and is not easy to deform, and the risk that the electronic equipment adopting the steel falls off from a high place and is fractured is reduced.

Description

[0001] This application is a divisional application. The application number of the original application is 202110134557.4, and the original application date is January 30, 2021. The entire contents of the original application are incorporated into this application by reference. Technical Field

[0002] The present application relates to the field of steel technology, and in particular to a steel, a steel structure, an electronic device and a method for preparing the steel structure. Background Art

[0003] Currently, electronic devices such as mobile phones, tablets, and computers use a large number of steel structures. For example, the hinge assembly in a folding mobile phone uses steel structures to withstand a certain amount of force and is not easily deformed. However, in traditional technologies, the strength of the steel structures used in the hinge assembly of a folding mobile phone is limited. When the electronic device falls from a height, the steel structures are easily broken, affecting the quality of the electronic device. Summary of the invention

[0004] The present application provides a steel with high structural strength, which reduces the risk of steel breakage during the falling process of electronic equipment using the steel, thereby improving the quality of the electronic equipment. The present application also provides a steel structure, a method for preparing the steel structure, and an electronic equipment including the steel structure.

[0005] In a first aspect, the present application provides a steel. The steel includes the following components in percentage by mass:

[0006] Chromium: 7% to 11%, Nickel: 2% to 7.5%, Cobalt: 6% to 15%, Molybdenum: 4% to 7%, Oxygen: trace to 0.4%, Carbon: trace to 0.35% and Iron: 50% to 80%.

[0007] Chromium plays a decisive role in the corrosion resistance of steel. In the embodiment of the present application, the mass percentage of chromium is less than or equal to 11%, which avoids the formation of ferrite in the steel structure with too high chromium content, resulting in low strength of the steel structure; at the same time, the mass percentage of chromium is greater than or equal to 7%, which avoids the reduction of Ms point of steel due to too low chromium content, inhibits the precipitation of Laves phase, and thus reduces the strength of the steel structure. Laves phase is a chemical formula mainly AB 2 The Laves phase is a second phase in steel. When the second phase is evenly distributed in the matrix phase as fine dispersed particles, it will produce a significant strengthening effect, which is called second phase strengthening.

[0008] Nickel is an important austenite stabilizing element in steel and an important toughening element in steel. In the embodiment of the present application, the mass percentage of nickel is greater than or equal to 2%, which improves the cleavage fracture resistance of the martensite structure in the steel structure and ensures that the steel structure has sufficient toughness; at the same time, the mass percentage of nickel is less than or equal to 7.5%, avoiding the presence of excessive nickel, which inhibits the transformation of austenite into martensite during the quenching process, thereby improving the strength of the steel structure.

[0009] Cobalt promotes the formation of austenite in the process of preparing steel, which is beneficial to improve the toughness of steel structures; at the same time, cobalt can delay the recovery of martensite dislocation substructure, maintain the high dislocation density of martensite laths, and promote the formation of precipitation phase. As an austenite stabilizing element, when its content is too high, it will lead to the formation of stable austenite in the alloy, which cannot be transformed into martensite during quenching, hindering the matrix from obtaining high strength. The cobalt content is defined as 6-15%.

[0010] Molybdenum can promote the formation of strengthening phases, such as Laves phase, molybdenum carbide, etc., thereby increasing the strength of steel structures. At the same time, molybdenum is a ferrite stabilizing element. Too much molybdenum will cause excessive austenite to form in the alloy, which will then transform into stable ferrite, resulting in reduced matrix strength. Its content is defined as 4-7%.

[0011] Carbon is one of the most common elements in steel and is one of the elements that stabilize austenite. At the same time, it can also improve the hardenability of steel. In the Fe-Cr-Ni-Co-Mo system, MC (such as Mo) can also be generated. 2 C.W. 2 C) Carbides, which increase the strength of the matrix. Too much carbon will combine with the chromium in the matrix to form a series of complex carbides, making the structure difficult to control. Therefore, the carbon content is defined as less than or equal to 0.35%.

[0012] In the embodiment of the present application, by limiting the mass percentage of each component in the steel, the steel can be formed by Fe-Co-Ni-Cr-Mo phase, Fe-Co-Cr-Mo phase and carbides (such as Mo 2 C.W. 2 C) Strengthening is achieved so that the steel has both high strength and high toughness, making it less likely to deform or break under high-intensity forces.

[0013] Among them, the mass percentage of each component in the steel is different, and the composition of the strengthening phase is also different, that is, the Fe-Co-Ni-Cr-Mo phase, Fe-Co-Cr-Mo phase or carbide formed is different. The strengthening phase can be but not limited to (Fe, Co, Ni) 17 Cr 8 Mo 18 ,(Fe,Co) 15 Cr8 Mo 4 or(Fe,Co) 16 Cr 8 Mo 18 wait.

[0014] In some embodiments, the steel has a yield strength greater than or equal to 1300 MPa and an elongation greater than or equal to 3%.

[0015] In the embodiments of the present application, the yield strength of the steel is greater than or equal to 1300 MPa, and the elongation is greater than or equal to 3%, so as to reduce the risk of fracture and failure of steel structural parts of electronic equipment using this steel during a fall; at the same time, the strength of the steel is relatively large, and the steel structural parts using this steel do not need to increase the thickness to ensure the reliability of the steel structural parts, which is conducive to the miniaturization of steel structural parts, and thus is conducive to the miniaturization of electronic equipment.

[0016] In some embodiments, the yield strength of the steel is less than or equal to 2000 MPa and the elongation is less than or equal to 12%.

[0017] It is understandable that the greater the yield strength and elongation of the steel, the more difficult the steel preparation method is. In the embodiment of the present application, the yield strength of the steel is less than or equal to 2000Mpa, and the elongation is less than or equal to 12%, which reduces the difficulty of the steel preparation method while ensuring that the steel has strong mechanical strength, thereby helping to reduce the production cost of the steel.

[0018] In some embodiments, the steel further comprises silicon and manganese, wherein the mass percentage of silicon is trace amount to 0.5%, and the mass percentage of manganese is trace amount to 0.5%.

[0019] Silicon can be used as a deoxidizer for molten steel during the preparation of steel powder, and can also increase the fluidity of the molten steel. At the same time, a small amount of silicon is retained in the matrix and can exist in the form of oxide inclusions to improve the strength of the matrix. Its content is defined as trace ~ 0.5%.

[0020] Manganese has the effect of deoxidation and desulfurization in steel. During the preparation of steel powder, it can remove oxygen and sulfur in molten steel. It is also an element that ensures hardenability. Similar to the role of silicon, when the manganese content is too high, it will significantly reduce the toughness of the steel. Therefore, the manganese content is controlled to a trace amount of 0.5% in this application.

[0021] In the embodiment of the present application, the steel structure also includes silicon and manganese, and the mass percentage of silicon or manganese is trace amount to 0.5%, so as to effectively increase the strength of the steel structure.

[0022] In some embodiments, the mass percentage of chromium is 7% to 9%, and the mass percentage of cobalt is 7% to 14%.

[0023] In some embodiments, the steel further comprises niobium, and the mass percentage of the niobium is trace amount to 1%.

[0024] Among them, niobium can be dissolved in steel, causing lattice distortion of the crystal, thus playing a role in solid solution strengthening. It is also a carbide-forming element, which can play a role in grain refinement and precipitation strengthening.

[0025] In the embodiment of the present application, the steel structure also includes niobium, and the steel structure can form iron niobium (Fe 2 Nb) and niobium carbide (NbC), the formed ferroniobium and niobium carbide increase the strength of the steel structure. In addition, the mass percentage of niobium is less than or equal to 1%, avoiding the precipitation of brittle phase along the grain boundary caused by excessive niobium content, which is beneficial to improve the strength and toughness of the steel structure.

[0026] In some embodiments, the steel further comprises tantalum, and the mass percentage of the tantalum is trace amount to 2%.

[0027] In some embodiments, the steel further includes tantalum and niobium, wherein the ratio of the mass percentage of the tantalum to the mass percentage of the niobium is 1-2:1, and the mass percentage of the tantalum plus the mass percentage of the niobium is a trace amount to 1.5%.

[0028] In some embodiments, the steel further comprises tungsten, the mass percentage of which is trace to 2%. Exemplarily, the steel structure comprises the following components in mass percentage: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7%, oxygen: trace to 0.4%, carbon: trace to 0.35%; tungsten: trace to 2%, and the remainder is iron and unavoidable impurities.

[0029] Tungsten can not only promote the formation of strengthening phases, such as Laves phase, tungsten carbide, etc., thereby increasing the strength of the steel structure, but also delay overaging and ensure process stability. In some embodiments, tungsten and molybdenum are added simultaneously during the preparation of the steel structure.

[0030] In the embodiment of the present application, the mass percentage of tungsten is less than or equal to 2%. Since the secondary hardening effect of tungsten is weak, it is avoided to add too much tungsten to affect the strength and toughness of the steel structure.

[0031] In some other embodiments, the steel structure also includes niobium and tungsten. Exemplarily, the steel structure includes the following components in mass percentage: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4 to 7%, oxygen: trace to 0.4%, carbon: trace to 0.35%, niobium: trace to 1%, tungsten: trace to 2%, and the balance is iron and unavoidable impurities.

[0032] In another embodiment, the steel further comprises boron, and the percentage of boron is trace amount -0.01%. Boron can also refine the grains, so that the toughness and strength of the material are improved.

[0033] In another embodiment, the steel further comprises rare earth elements, and the mass percentage of the rare earth elements is: trace amount to 0.5%. Rare earth elements can purify grain boundaries, refine grains, increase the toughness of steel materials, and improve their density during sintering.

[0034] In another embodiment, the steel further includes other elements, including one or more of nitrogen, rhenium, copper, aluminum, titanium, sulfur, phosphorus, hydrogen, zirconium, magnesium, calcium, yttrium, vanadium, scandium and zinc, and the mass percentage of the other elements is ≤1%.

[0035] In a second aspect, the present application provides a steel structure, wherein the material used in the steel structure includes the steel described above.

[0036] In the embodiment of the present application, the material used for the steel structure includes the steel as described above, so that the strength of the steel structure is increased. This steel structure does not need to be further guaranteed by increasing the thickness of the steel structure, which is conducive to the miniaturization of the steel structure, and thus is conducive to the miniaturization of the electronic equipment using this steel structure.

[0037] In a third aspect, the present application provides a method for preparing a steel structure. The method for preparing a steel structure comprises:

[0038] Forming steel powder into a green body of a steel structure, the steel powder comprising the following components in percentage by mass: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7% and iron: 50% to 80%;

[0039] Sintering the green billet of the steel structure component to form a sintered billet of the steel structure component; and

[0040] The sintered blank of the steel structure is heat treated.

[0041] Before forming the steel powder into a green body of the steel structure, the method for preparing the steel structure further comprises: mixing the steel powder uniformly to make the green body of the formed steel structure uniform.

[0042] In the embodiments of the present application, the steel structural parts formed by the preparation method of the steel structural parts provided in the present application have the characteristics of yield strength greater than or equal to 1300Mpa and elongation greater than or equal to 3%, that is, the formed steel structural parts have the characteristics of high strength and high toughness at the same time, so that the steel structural parts are not easily deformed or broken under high-intensity forces.

[0043] Furthermore, the steel structural parts formed by the method for preparing steel structural parts provided by the present application can effectively obtain three-dimensional complex and precise steel structural parts at one time. Compared with traditional mechanical processing, such as computerised numerical control machine (CNC) forming complex and precise steel structural parts does not require additional processing, which improves the production efficiency of preparing complex and precise steel structural parts, reduces the cost of preparing steel structural parts, and is conducive to the large-scale production of steel structural parts.

[0044] In some embodiments, steel powder particles with certain particle size requirements are prepared by atomization. The steel powder particles have a small particle size to facilitate the forming process of steel structures. Exemplarily, at least 90% of the steel powder has a particle size less than or equal to 35 μm, and at most 10% of the steel powder has a particle size less than or equal to 4.5 μm. 50% of the steel powder has a particle size in the range of 5 μm to 15 μm.

[0045] In the embodiment of the present application, 90% of the steel powder has a particle size less than or equal to 35 μm, so as to avoid the steel powder having a particle size that is too large and is not conducive to the subsequent forming of the steel powder; at the same time, at most 10% of the steel powder has a particle size that is less than or equal to 4.5 μm, so as to avoid the steel powder having a particle size that is too small and is not conducive to the subsequent forming of the steel powder.

[0046] In some embodiments, the steel powder further comprises silicon and manganese, the mass percentage of silicon is a trace amount to 0.5%, and the mass percentage of manganese is a trace amount to 0.5%.

[0047] Silicon can be used as a deoxidizer for molten steel during the preparation of steel powder, and can also increase the fluidity of the molten steel. At the same time, a small amount of silicon is retained in the matrix and can exist in the form of oxide inclusions to improve the strength of the matrix. Its content is defined as trace ~ 0.5%.

[0048] Manganese has the effect of deoxidation and desulfurization in steel. During the preparation of steel powder, it can remove oxygen and sulfur in molten steel. It is also an element that ensures hardenability. Similar to the role of silicon, when the manganese content is too high, it will significantly reduce the toughness of the steel. Therefore, the manganese content is controlled to a trace amount of 0.5% in this application.

[0049] In the embodiment of the present application, the steel structure also includes silicon and manganese, and the mass percentage of silicon or manganese is trace amount to 0.5%, so as to effectively increase the strength of the steel structure.

[0050] In some embodiments, the steel powder further comprises niobium, and the mass percentage of the niobium is trace amount to 1%.

[0051] Niobium can be dissolved in steel, causing lattice distortion, thus playing a role in solid solution strengthening. It is also a carbide-forming element, which can refine grains and strengthen by precipitation.

[0052] In the embodiment of the present application, the steel structure also includes niobium, and the steel structure can form iron niobium (Fe 2 Nb) and niobium carbide (NbC), the formed ferroniobium and niobium carbide increase the strength of the steel structure. In addition, the mass percentage of niobium is less than or equal to 1%, avoiding the precipitation of brittle phase along the grain boundary caused by excessive niobium content, which is beneficial to improve the strength and toughness of the steel structure.

[0053] In some embodiments, the steel further comprises tantalum, and the mass percentage of the tantalum is trace amount to 2%.

[0054] In some embodiments, the steel also includes tantalum and niobium, wherein the mass percentage of the tantalum to the mass percentage of the niobium is in a ratio of 1 to 2:1, and the mass percentage of the tantalum plus the mass percentage of the niobium is a trace amount to 1.5%.

[0055] In another embodiment, the steel further comprises boron, and the percentage of boron is trace amount -0.01%. Boron can also refine the grains, so that the toughness and strength of the material are improved.

[0056] In another embodiment, the steel further comprises rare earth elements, and the mass percentage of the rare earth elements is: trace amount to 0.5%. Rare earth elements can purify grain boundaries, refine grains, increase the toughness of steel materials, and improve their density during sintering.

[0057] In another embodiment, the steel further includes other elements, and the other elements include one or more of nitrogen, rhenium, copper, aluminum, titanium, sulfur, phosphorus, hydrogen, zirconium, magnesium, calcium, yttrium, vanadium, scandium and zinc. The mass percentage of the other elements is ≤1%, that is, the sum of all other elements is less than or equal to 1%.

[0058] In some embodiments, the steel powder further includes tungsten, and the mass percentage of the tungsten is trace amount to 2%.

[0059] Tungsten can not only promote the formation of strengthening phases, such as Laves phase, tungsten carbide, etc., thereby increasing the strength of the steel structure, but also delay overaging and ensure process stability. In some embodiments, tungsten and molybdenum are added simultaneously during the preparation of the steel structure.

[0060] In the embodiment of the present application, the mass percentage of tungsten is less than or equal to 2%. Since the secondary hardening effect of tungsten is relatively weak, it is avoided to add too much tungsten to affect the strength and toughness of the steel structure.

[0061] In some embodiments, the “forming steel powder into a green body of a steel structure” comprises:

[0062] mixing the steel powder with a binder to form a paste feed;

[0063] granulating the paste feed to form feed granules; and

[0064] The feed particles are formed into the green body of the steel structure by pressing or injection molding.

[0065] In the embodiment of the present application, the green billet of the steel structure is formed by injection molding, which not only has high forming efficiency and low cost, but also can effectively obtain the green billet of three-dimensional complex and precise steel structure at one time, thereby improving the production efficiency of preparing complex and precise steel structure parts.

[0066] Moreover, in the embodiment of the present application, a binder is mixed in the steel powder, so that the formed paste feed has a certain fluidity, and can fill a complex-shaped mold cavity under pressure to form complex and precise steel structures in one go, thereby improving the production efficiency of complex and precise steel structures. In the embodiment of the present application, the steel powder is mixed with the binder, and the steel powder has a certain fluidity, which reduces or avoids defects such as cracks or corner loss in the green billet of the steel structure. At the same time, the steel powder is mixed with the binder, and the green billet of the steel structure after forming has a certain strength, and can maintain its shape when it is removed from the mold cavity, which reduces or avoids the deformation of the green billet of the steel structure, thereby improving the yield rate of the prepared steel structure.

[0067] In the embodiment of the present application, the feed particles are formed into a green billet of a steel structure by injection molding, that is, the green billet of the steel structure is formed by metal injection molding. In other embodiments, the feed particles can also be formed into a green billet of a steel structure by pressing, which is not limited in the present application.

[0068] In some embodiments, after “forming the feed particles into the green body of the steel structure by pressing or injection molding”, “forming the steel powder into the green body of the steel structure” further comprises:

[0069] Degreasing removes the binder in the green body of the steel structure.

[0070] In some embodiments, the binder comprises a thermoplastic binder.

[0071] The use of a thermoplastic binder as the binder is beneficial to the subsequent degreasing process, thereby improving the reliability of the steel structure. For example, the binder mainly includes polyformaldehyde (POM). As the main component of the binder, the weight percentage of polyformaldehyde is greater than or equal to 80%.

[0072] In the embodiment of the present application, the binder is polyoxymethylene. Based on the high strength of polyoxymethylene, the strength of the formed paste feed is guaranteed, so that the green billet of the steel structure formed by the paste feed has a certain strength, avoiding or reducing the defects caused by demolding the green billet of the steel structure. In addition, polyoxymethylene is suitable for nitric acid catalytic decomposition, the product after degreasing is gaseous, and the degreasing efficiency is high, avoiding the subsequent degreasing process to cause defects such as cracking or deformation of the green billet of the steel structure.

[0073] In some embodiments, the binder in the green steel structure is removed by catalytic degreasing. Catalytic degreasing to remove the binder utilizes the property that polymers can be rapidly degraded in a specific atmosphere, so that the green steel structure is degreased in the corresponding atmosphere to decompose the binder and remove the binder.

[0074] In the embodiment of the present application, the binder in the green body of the steel structure is removed by catalytic degreasing, which not only enables rapid and defect-free degreasing, but also increases the efficiency of degreasing, thereby improving the efficiency of preparing the steel structure.

[0075] It can be understood that the binder not only has the characteristics of enhancing fluidity to be suitable for injection molding and maintaining the shape of the block, but also has the characteristics of being easy to remove, non-polluting, non-toxic, and cost-effective, which is beneficial to the degreasing removal process.

[0076] In a fourth aspect, the present application further provides a steel structure. The steel structure is formed by the preparation method described above.

[0077] In the embodiment of the present application, the steel structure formed by the preparation method of the steel structure provided by the present application can effectively obtain three-dimensional complex and precise steel structure at one time. Compared with the traditional mechanical processing to form complex and precise steel structure, no additional processing is required, which improves the production efficiency of preparing complex and precise steel structure, reduces the cost of preparing steel structure, and is conducive to the large-scale production of steel structure. In addition, the prepared steel structure has the characteristics of yield strength greater than or equal to 1300Mpa and elongation greater than or equal to 5%, that is, the formed steel structure has the characteristics of high strength and high toughness at the same time, so that the steel structure is not easy to deform or break under high-intensity force.

[0078] In a fifth aspect, the present application further provides an electronic device, wherein the electronic device comprises the steel structure as described above.

[0079] In some embodiments, the electronic device further includes a flexible display screen and a folding device for supporting the flexible display screen, wherein the folding device is used to drive the flexible display screen to deform; wherein the folding device includes the steel structure.

[0080] In the embodiment of the present application, the steel structure is applied to the folding device in the electronic device, which reduces the risk of the steel structure in the electronic device falling from a height and breaking, thereby reducing the phenomenon that the display screen of the flexible display screen is affected by the breaking of the steel structure; at the same time, it also avoids or reduces the risk of the folding device getting stuck, thereby improving the quality of the electronic device. At the same time, the strength of the steel structure is relatively large, and the steel structure does not need to increase the thickness to ensure the reliability of the steel structure, which is conducive to the miniaturization of the folding device, and thus conducive to the miniaturization of the electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] In order to illustrate the technical solutions in the embodiments of the present application or the background technology, the drawings required for use in the embodiments of the present application or the background technology will be described below.

[0082] Figure 1 is a schematic diagram of the structure of an electronic device provided by an embodiment of the present application in a state;

[0083] Figure 2 is a schematic diagram of the structure of an electronic device provided by an embodiment of the present application in another state;

[0084] Figure 3 It is a schematic diagram of the process of the steel structure preparation method provided in this application;

[0085] Figure 4 yes Figure 3 Schematic diagram of the process of step S120. DETAILED DESCRIPTION

[0086] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0087] See also Figure 1 , Figure 1 1 is a schematic diagram of the structure of the electronic device 100 in one state provided in an embodiment of the present application. The electronic device 100 may be a mobile phone, a tablet computer, an e-reader, a laptop computer, a vehicle-mounted device, a wearable device, or a rollable and foldable electronic newspaper. In the embodiment of the present application, the electronic device 100 is described as a mobile phone.

[0088] like Figure 1 As shown, in some embodiments, the electronic device 100 includes a housing 10, a flexible display screen 20, and a folding device 30. The folding device 30 is installed on the housing 10. The flexible display screen 20 is used to display images. The folding device 30 is used to drive the flexible display screen 20 to deform. Exemplarily, the folding device 30 is connected to the flexible display screen 20 and is used to drive the flexible display screen 20 to fold or unfold. The folding device 30 includes a rotating shaft, which can rotate under the action of a driving force to drive the flexible display screen 20 to bend.

[0089] The present application does not limit the types of the flexible display screen 20 and the folding device 30. Those skilled in the art can select the types of the flexible display screen 20 and the folding device 30 according to actual needs. The flexible display screen 20 is made of soft material and is a deformable and bendable panel with display function. Figure 1 The shapes and thicknesses of the flexible display screen 20 and the folding device 30 are only examples and are not limited in this application.

[0090] Please also read Figure 1 and Figure 2 , Figure 2 1 is a schematic diagram of the structure of the electronic device 100 provided in an embodiment of the present application in another state. Under the action of the driving force, the folding device 30 can rotate to drive the flexible display screen 20 to bend or unfold. Figure 1 As shown, in one state, the electronic device 100 is in an unfolded state, and the flexible display screen 20 is located in the same plane. Figure 2 As shown, in another state, the electronic device 100 is in a folded state, and a portion of the structure of the flexible display screen 20 and another portion of the structure of the flexible display screen 20 are located in different planes. The electronic device 100 provided in the present application can be folded or unfolded according to different usage scenarios, and the electronic device 100 presents different forms to meet different needs of users.

[0091] Among them, the folding device 30 includes a steel structure. The steel structure is a structure with a certain appearance shape. Exemplarily, the steel structure can be but is not limited to complex force-bearing structures such as rotating shafts, gears, sliders, slide grooves or connecting rods in the folding device 30. The steel structure has a certain strength to ensure the mechanical strength of the folding device 30 and prevent the folding device 30 from deforming due to force, thereby ensuring the reliability of the electronic device 100. The material used for the steel structure includes steel. The steel structure can be obtained by one-time forming of steel powder, or it can be formed into a steel structure with a certain shape by processing sheet steel, and the present application does not limit this.

[0092] In traditional technology, the steel structure in the folding device is easy to deform under high stress, and there is even a risk of breaking, which will not only cause the folding device to get stuck, making it impossible for the electronic device to switch between folding and unfolding, but also the broken steel structure may hold up the flexible display screen, affecting the display screen of the flexible display screen, thereby affecting the quality of the electronic device. For example, in traditional technology, the material used in the folding device is 17-4PH or 420w, which is insufficient in strength and poor in toughness. When the electronic device falls from a height, the steel structure in the folding device is easy to break, affecting the service life of the electronic device.

[0093] Based on the risk of fracture of steel structures in electronic devices in traditional technology, the present application provides a steel structure with greater strength and higher elongation to reduce the risk of fracture and failure of the steel structure during the fall of the electronic device 100; at the same time, the strength of the steel structure is greater, and the steel structure does not need to increase the thickness to ensure the reliability of the steel structure, which is conducive to the miniaturization of the steel structure, and thus to the miniaturization of the electronic device 100. Exemplarily, the yield strength of the steel structure provided by the present application is greater than or equal to 1300Mpa, and the elongation is greater than or equal to 3%.

[0094] Yield strength is the yield limit of metal materials when yielding occurs, that is, the stress that resists micro plastic deformation. It can be understood that the greater the yield strength of steel structures, the greater the mechanical strength of steel structures. Elongation (δ) is an indicator that describes the plastic properties of materials. The elongation value is the percentage of the total deformation length of the specimen after tensile fracture to the original length.

[0095] In the embodiment of the present application, the yield strength of the steel structure is greater than or equal to 1300 MPa, so that the mechanical structure strength of the folding device 30 using this steel structure is relatively large, reducing or avoiding the risk of the electronic device 100 falling from a height and breaking, improving the reliability of the folding device 30, and thus improving the quality of the electronic device 100.

[0096] In some embodiments, the yield strength of the steel structure is less than or equal to 2000 MPa, and the elongation is less than or equal to 12%. It is understandable that the greater the yield strength and elongation of the steel structure, the more difficult the preparation method of the steel structure is.

[0097] In the embodiment of the present application, the yield strength of the steel structure is less than or equal to 2000Mpa, and the elongation is less than or equal to 12%. While ensuring that the steel structure has strong mechanical strength, the difficulty of the steel structure preparation method is reduced, which is beneficial to reducing the production cost of the steel structure.

[0098] Among them, in the embodiment of the present application, the steel structural part is described as the folding device 30 of the electronic device 100. In other embodiments, the steel structural part can also be other structural parts with more complex shapes in the electronic device 100, such as gears, etc., and the present application is not limited thereto.

[0099] In other embodiments, the steel structure may also be the middle frame or back cover of the electronic device 100, which is not limited in the present application. For example, the steel structure is the middle frame of the electronic device 100. Since the steel structure has a large yield strength and is not easily deformed, when the electronic device 100 falls from a height, the middle frame of the electronic device 100 is not easily deformed, which reduces the risk of deformation of the appearance of the electronic device 100, thereby facilitating the aesthetic appearance of the electronic device 100.

[0100] In some embodiments, the steel structural member includes the following components in mass percentage: chromium (Cr): 7% to 11%, nickel (Ni): 2% to 7.5%, cobalt (Co): 6% to 15%, molybdenum (Mo): 4% to 7%, oxygen (O): trace amount to 0.4%, carbon (C): trace amount to 0.35% and iron: 50% to 80%.

[0101] Wherein, the range A to B means including the endpoints A, B and any value between A and B. Trace refers to the content of a substance below one part per million in chemistry. It can be understood that trace refers to the extremely small content of a substance component in chemistry, so little that there is only a trace. The meaning of the term trace has changed with the development of trace analysis technology. In the embodiments of the present application, the lower limits of the content of oxygen and carbon are not limited.

[0102] Carbon is one of the most common elements in steel and is one of the elements that stabilize austenite. At the same time, it can also improve the hardenability of steel. In the Fe-Cr-Ni-Co-Mo system, MC (such as Mo) can also be generated. 2 C.W. 2 C) Carbides, which increase the strength of the matrix. Too much carbon will combine with the chromium in the matrix to form a series of complex carbides, making the structure difficult to control. Therefore, the carbon content is defined as less than or equal to 0.35%.

[0103] Chromium plays a decisive role in the corrosion resistance of steel. In the embodiment of the present application, the mass percentage of chromium is less than or equal to 11%, which avoids the formation of ferrite in the steel structure with too high chromium content, resulting in low strength of the steel structure; at the same time, the mass percentage of chromium is greater than or equal to 7%, which avoids the reduction of Ms point of steel due to too low chromium content, inhibits the precipitation of Laves phase, and thus reduces the strength of the steel structure. Laves phase is a chemical formula mainly AB 2 The Laves phase is a second phase in steel. When the second phase is evenly distributed in the matrix phase as fine dispersed particles, it will produce a significant strengthening effect, which is called second phase strengthening.

[0104] Nickel is an important austenite stabilizing element in steel and an important toughening element in steel. In the embodiment of the present application, the mass percentage of nickel is greater than or equal to 2%, which improves the cleavage fracture resistance of the martensite structure in the steel structure and ensures that the steel structure has sufficient toughness; at the same time, the mass percentage of nickel is less than or equal to 7.5%, avoiding the presence of excessive nickel, which inhibits the transformation of austenite into martensite during the quenching process, thereby improving the strength of the steel structure.

[0105] The cobalt element promotes the formation of austenite in the process of preparing steel, which is beneficial to improving the toughness of steel structures; at the same time, cobalt can delay the recovery of the martensite dislocation substructure, maintain the high dislocation density of the martensite lath, and promote the formation of precipitation phases. As an austenite stabilizing element, when its content is too high, it will lead to the formation of stable austenite in the alloy, which cannot be transformed into martensite during the quenching process, hindering the matrix from obtaining high strength. Therefore, the cobalt content is defined as 6% to 15%.

[0106] Molybdenum can promote the formation of strengthening phases, such as Laves phase, molybdenum carbide, etc., thereby increasing the strength of steel structures. At the same time, molybdenum is a ferrite stabilizing element. Too much molybdenum will cause excessive austenite to form in the alloy, which will then transform into stable ferrite, resulting in reduced matrix strength. Therefore, the molybdenum content is defined as 4-7%.

[0107] Oxygen elements are easy to form inclusions in steel. A small amount of oxide inclusions in a dispersed state can increase the strength of the matrix. Due to the special powder making and sintering process of molding, the oxygen content can be strictly controlled from the powder preparation and sintering process, and its content is defined as trace ~0.4%.

[0108] In the embodiment of the present application, by limiting the mass percentage of each component in the steel structure, the formed steel structure can rely on the Fe-Co-Ni-Cr-Mo phase, the Fe-Co-Cr-Mo phase and the carbide (such as: Mo 2 C.W. 2 C) Strengthening is achieved so that the yield strength of the formed steel structure is greater than or equal to 1300Mpa, and the elongation is greater than or equal to 3%, that is, the formed steel structure has the characteristics of high strength and high toughness, so that the steel structure is not easy to deform or break under high-intensity forces. The mass percentage of each component in the steel structure is different, and the composition of the strengthening phase is also different, that is, the Fe-Co-Ni-Cr-Mo phase, Fe-Co-Cr-Mo phase or carbide formed is different. The strengthening phase can be but is not limited to (Fe, Co, Ni) 17 Cr 8 Mo 18 ,(Fe,Co) 15 Cr 8 Mo 4 or(Fe,Co) 16 Cr 8 Mo 18 wait.

[0109] Moreover, in the embodiments of the present application, the carbon content in the steel structural parts is relatively low (less than or equal to 0.35%), which is easy to control during the process of preparing the steel structural parts, such as the sintering process, thereby reducing the difficulty of producing the steel structural parts, and is beneficial to reducing the production cost of the steel structural parts and ensuring the production quality of the steel structural parts.

[0110] The steel structure provided by the present application is further described in the following with multiple embodiments:

[0111] Embodiment 1:

[0112] Steel structural parts include the following components in mass percentage: chromium (Cr): 7% to 11%, nickel (Ni): 2% to 7.5%, cobalt (Co): 6% to 15%, molybdenum (Mo): 4% to 7%, oxygen (O): trace amount to 0.4%, carbon (C): trace amount to 0.35%, silicon (Si): trace amount to 0.5%, manganese (Mn): trace amount to 0.5%, and the balance is iron and unavoidable impurities.

[0113] Silicon can be used as a deoxidizer for molten steel during the preparation of steel powder, and can also increase the fluidity of the molten steel. At the same time, a small amount of silicon is retained in the matrix and can exist in the form of oxide inclusions to improve the strength of the matrix. Its content is defined as trace ~ 0.5%.

[0114] Manganese has the effect of deoxidation and desulfurization in steel. During the preparation of steel powder, it can remove oxygen and sulfur in molten steel. It is also an element that ensures hardenability. Similar to the role of silicon, when the manganese content is too high, it will significantly reduce the toughness of the steel. Therefore, the manganese content is controlled to a trace amount of 0.5% in this application.

[0115] In the embodiment of the present application, the steel structure also includes silicon and manganese, and the mass percentage of silicon or manganese is trace amount to 0.5%, so as to effectively increase the strength of the steel structure.

[0116] Please refer to Table 1, which is a table of component contents of the steel structure provided by the present application in various embodiments of Example 1. Table 1 reflects the yield strength and elongation corresponding to the content of each component in the steel structure in different embodiments.

[0117] Table 1

[0118]

[0119] In some embodiments, based on the cobalt content being in the range of 6% to 15% and the nickel content being in the range of 2% to 7.5%, when the cobalt content is higher, the nickel content is correspondingly reduced; or, when the nickel content is higher, the cobalt content is correspondingly lower.

[0120] In this embodiment, appropriately increasing the nickel content is beneficial to improving the toughness of the steel structure, and too much nickel will cause the strength of the steel structure to decrease. When the nickel content is low, increasing the cobalt content promotes the precipitation of the strengthening phase, which is beneficial to improving the strength of the steel structure.

[0121] Embodiment 2

[0122] In Example 2, the steel structure also includes niobium (Nb). The mass percentage of niobium is trace to 1%. It can be understood that the present application does not limit the specific lower limit of niobium. Among them, the steel structure in Example 2 includes the components of Example 1. That is, in Example 2, the steel structure includes the following components in mass percentage: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7%, oxygen: trace to 0.4%, carbon: trace to 0.35%; niobium: trace to 1%, and the remainder is iron and unavoidable impurities.

[0123] Among them, niobium can be dissolved in steel, causing lattice distortion, thus playing a role in solid solution strengthening. It is also a carbide-forming element, which can refine grains and strengthen precipitation. Tantalum and niobium have similar roles in steel. Therefore, in the material preparation process, they can be replaced with each other in a certain ratio, and the replacement ratio is about 1 to 2:1.

[0124] In the embodiment of the present application, the steel structure also includes niobium, and the steel structure can form iron niobium (Fe 2 Nb) and niobium carbide (NbC), the formed ferroniobium and niobium carbide increase the strength of the steel structure. In addition, the mass percentage of niobium is less than or equal to 1%, avoiding the precipitation of brittle phase along the grain boundary caused by excessive niobium content, which is beneficial to improve the strength and toughness of the steel structure.

[0125] Please refer to Table 2, which is a table of component contents of the steel structure provided by the present application in various implementations of Example 2. Table 2 reflects the yield strength and elongation corresponding to the content of each component in the steel structure in different implementations.

[0126] Table 2

[0127]

[0128] Embodiment 3

[0129] In Example 3, the steel structure also includes tungsten (W). The mass percentage of tungsten is trace to 2%. It is understandable that the present application does not limit the specific lower limit of tungsten. Among them, the steel structure in Example 3 includes the various components of the steel structure in the aforementioned embodiments. Exemplarily, in Example 3, the steel structure includes the following components in mass percentage: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7%, oxygen: trace to 0.4%, carbon: trace to 0.35%; tungsten: trace to 2%, the remainder is iron and unavoidable impurities.

[0130] Tungsten can not only promote the formation of strengthening phases, such as Laves phase, tungsten carbide, etc., thereby increasing the strength of the steel structure, but also delay overaging and ensure process stability. In some embodiments, tungsten and molybdenum are added simultaneously during the preparation of the steel structure.

[0131] In the embodiment of the present application, the mass percentage of tungsten is less than or equal to 2%. Since the secondary hardening effect of tungsten is relatively weak, it is avoided to add too much tungsten to affect the strength and toughness of the steel structure.

[0132] Please refer to Table 3, which is a table of component contents of the steel structure provided by the present application in various implementations of Example 3. Table 3 reflects the yield strength and elongation corresponding to the content of each component in the steel structure in different implementations.

[0133] Table 3

[0134]

[0135] Embodiment 4

[0136] In the fourth embodiment, the steel structure also includes niobium and tungsten. The mass percentage of niobium is trace to 1%, and the mass percentage of tungsten is trace to 2%. Among them, the steel structure in the fourth embodiment includes the components of the steel structure in the above-mentioned embodiments. Exemplarily, in the fourth embodiment, the steel structure includes the following components in mass percentage: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4 to 7%, oxygen: trace to 0.4%, carbon: trace to 0.35%; niobium: trace to 1%; tungsten: trace to 2%, and the remainder is iron and unavoidable impurities.

[0137] Please refer to Table 4, which is a table of component contents of the steel structure provided by the present application in each implementation manner in Example 4. Table 4 reflects the yield strength and elongation corresponding to the content of each component of the steel structure.

[0138] Table 4

[0139]

[0140] In some embodiments, the mass percentage of chromium is 7% to 9%, and the mass percentage of cobalt is 7% to 14%.

[0141] The present application also provides a steel. The steel provided in the present application may be a steel structure with a certain complex shape, or may be an unprocessed plate steel, which is not limited in the present application. The steel structure is made of steel, and the mass percentage of each component in the steel is the same as the mass percentage of each component in the above-mentioned steel structure. It can be understood that the above-mentioned steel structure is a presentation form of steel. The mass percentages of steel in different embodiments can refer to the mass percentages of the above-mentioned steel structure in any of the embodiments one to four, and the present application does not repeat them here. For example, steel includes the following mass percentages of components: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7%, oxygen: trace to 0.4%, carbon: trace to 0.35%, and the remainder is iron and unavoidable impurities. In some embodiments, steel may also include niobium with a mass percentage of trace to 1%. In some other embodiments, steel may also include tungsten with a mass percentage of trace to 2%.

[0142] The present application also provides a method for preparing a steel structure. In conventional technology, steel structures with relatively complex structures are usually processed and formed by computerised numerical control machines (CNC), but this forming method is inefficient and costly. A computerised numerical control machine is an automated machine equipped with a program control system, which is used for large-scale processing of parts. Metal injection molding (MIM) is a new type of powder metallurgy near-net forming technology derived from the plastic injection molding industry. Based on metal injection molding technology, products of various complex shapes can be produced with low production costs, and it is widely used in the production of steel structures with relatively complex structures.

[0143] However, in traditional technology, some steel structures in electronic devices, such as the hinge assembly in folding mobile phones, are formed by metal injection molding. However, due to the limited strength and low elongation of the formed steel structures, the folding device is easily deformed under high force and even has the risk of breaking. Not only will the folding device be stuck, making it impossible for the electronic device to switch between folding and unfolding, but the broken steel structure may support the flexible display screen, affecting the display screen of the flexible display screen, thereby affecting the quality of the electronic device. For example, in traditional technology, one of the materials used for molding the steel structure in the folding device is 17-4PH, which is insufficient in strength, restricting the design freedom of the product, and reliability must be ensured by increasing the thickness of the product; another material is 420w, which is insufficient in strength and poor in toughness. At the same time, the excessively high carbon content makes the subsequent sintering process difficult to control, making production extremely difficult, affecting production and product quality.

[0144] Please continue reading Figure 3 , Figure 3: is a flow chart of the method for preparing a steel structure provided in the present application. The method for preparing a steel structure provided in the present application includes but is not limited to preparing the above-mentioned steel structure. The above-mentioned steel structure can be obtained by the method for preparing a steel structure provided in the present application, or by other preparation methods.

[0145] The method for preparing the steel structure comprises:

[0146] S110: Mixing steel powder, the steel powder includes the following components in percentage by mass: chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7% and iron: 50% to 80%.

[0147] In some embodiments, the steel powder further comprises carbon and oxygen. The present application does not limit the content of carbon and oxygen in the steel powder, and those skilled in the art can select the content of carbon and oxygen according to actual needs. For example, the carbon content is less than or equal to 0.35%, and the oxygen content is less than or equal to 0.45%.

[0148] In some embodiments, steel powder particles with certain particle size requirements are prepared by atomization. The steel powder particles have a small particle size to facilitate the forming process of steel structures. Exemplarily, at least 90% of the steel powder has a particle size less than or equal to 35 μm, and at most 10% of the steel powder has a particle size less than or equal to 4.5 μm. 50% of the steel powder has a particle size in the range of 5 μm to 15 μm.

[0149] In the embodiment of the present application, 90% of the steel powder has a particle size less than or equal to 35 μm, so as to avoid the steel powder having a particle size that is too large and is not conducive to the subsequent forming of the steel powder; at the same time, at most 10% of the steel powder has a particle size that is less than or equal to 4.5 μm, so as to avoid the steel powder having a particle size that is too small and is not conducive to the subsequent forming of the steel powder.

[0150] In some embodiments, the steel powder further comprises silicon and manganese, wherein the mass percentage of silicon is a trace amount to 0.5%, and the mass percentage of manganese is a trace amount to 0.5%.

[0151] Silicon can be used as a deoxidizer for molten steel during the preparation of steel powder, and it can also increase the fluidity of the molten steel. At the same time, a small amount of silicon is retained in the matrix and can exist in the form of oxide inclusions to improve the strength of the matrix. Its content is defined as trace amounts to 0.5%. Manganese has the effect of deoxidation and desulfurization in steel. During the preparation of steel powder, it can remove oxygen and sulfur from the molten steel, and it is also an element that ensures hardenability. Similar to the effect of silicon, when the manganese content is too high, the toughness of the steel will be significantly reduced. Therefore, this application controls the manganese content to a trace amount to 0.5%.

[0152] In the embodiment of the present application, the steel structure also includes silicon and manganese, and the mass percentage of silicon or manganese is trace amount to 0.5%, so as to effectively increase the strength of the prepared steel structure.

[0153] In some embodiments, the steel powder further comprises niobium, the mass percentage of which is trace to 1%. Niobium can be dissolved in steel to cause lattice distortion, thereby playing a role in solid solution strengthening, and is also a carbide-forming element, which can play a role in grain refinement and precipitation strengthening.

[0154] In the embodiment of the present application, the steel powder also includes niobium, so that the steel structure finally prepared can form iron niobium (Fe 2 Nb) and niobium carbide (NbC), the formed iron niobide and niobium carbide increase the strength of the steel structure. In addition, the mass percentage of niobium is less than or equal to 1%, avoiding the precipitation of brittle phase along the grain boundary caused by excessive niobium content, which is beneficial to improve the strength and toughness of the prepared steel structure.

[0155] In some embodiments, the steel powder further includes tungsten, and the mass percentage of tungsten is a trace amount of 2%.

[0156] Tungsten can not only promote the formation of strengthening phases, such as Laves phase, tungsten carbide, etc., thereby increasing the strength of the prepared steel structure, but also delay overaging and ensure process stability. In some embodiments, tungsten and molybdenum are added simultaneously during the preparation of the steel structure.

[0157] In the embodiment of the present application, the mass percentage of tungsten is less than or equal to 2%. Since the secondary hardening effect of tungsten is weak, it is avoided to add too much tungsten to affect the strength and toughness of the prepared steel structure.

[0158] S120: forming the steel powder into a green body of a steel structure.

[0159] Please also read Figure 3 and Figure 4 , Figure 4 yes Figure 3 In some embodiments, forming the steel powder into a green body of a steel structure comprises:

[0160] S121: Mix steel powder and binder to form a paste feed.

[0161] The steel powder is mixed with a binder, so that the formed paste feed has a certain fluidity, and can fill the mold cavity of complex shape under pressure to form complex and precise steel structures in one go, thereby improving the production efficiency of complex and precise steel structures.

[0162] In the embodiment of the present application, mixing steel powder and binder not only enhances the fluidity of steel powder, but also makes the steel powder have a certain strength, which is convenient for subsequent transfer and handling operations and is beneficial to maintaining the shape of the product, thereby improving the yield of steel structural parts.

[0163] In some embodiments, after the steel powder and the binder are mixed according to the target ratio, they are added to the internal mixer for mixing to form a uniform paste feed. The mixing of the steel powder and the binder is completed under the combined action of thermal effect and shear force, so the temperature of the mixture cannot be too high to avoid the decomposition of the binder or the separation of the steel powder and the binder due to too low viscosity.

[0164] This application does not limit the ratio of steel powder to binder, and the conditions for mixing in the internal mixer. Those skilled in the art can select the ratio of steel powder to binder, and the conditions for mixing in the internal mixer according to actual needs. Exemplarily, the steel powder and the binder are mixed in a volume ratio of 62:38. The parameters of the mixture in the internal mixer are: temperature at 170°C to 210°C, time for 2 to 4 hours, and blade speed of 15 to 30 r / min.

[0165] In some embodiments, the binder includes a thermoplastic binder. The use of a thermoplastic binder is beneficial to the subsequent degreasing process, thereby improving the reliability of the steel structure. Exemplarily, the binder mainly includes polyformaldehyde (POM). Polyformaldehyde is the main component of the binder, and its weight percentage is greater than or equal to 80%.

[0166] In the embodiment of the present application, the binder is polyoxymethylene. Based on the high strength of polyoxymethylene, the strength of the formed paste feed is guaranteed, so that the green billet of the steel structure formed by the paste feed has a certain strength, avoiding or reducing the defects caused by demolding the green billet of the steel structure. In addition, polyoxymethylene is suitable for nitric acid catalytic decomposition, the product after degreasing is gaseous, and the degreasing efficiency is high, avoiding the subsequent degreasing process to cause defects such as cracking or deformation of the green billet of the steel structure.

[0167] In some embodiments, the binder further comprises ethylene vinylacetate (EVA), polyethylene (PE), ceresine wax (CW) and stearic acid (SA).

[0168] Among them, those skilled in the art can select the ratio of each component in the binder according to the actual process requirements. In some embodiments, the weight percentage of each component in the binder is as follows: polyoxymethylene: 80% to 95%, ethylene-vinyl acetate copolymer: 0.5% to 1.5%, polyethylene: 2% to 9%, CW: 1% to 3%, SA: 0.5% to 1.5%. Exemplarily, polyoxymethylene: ethylene-vinyl acetate copolymer: polyethylene: CW: SA = 89:1:5:2:1. This application does not limit the specific content of each component in the binder.

[0169] S122: Granulate the paste feed to form feed granules.

[0170] The paste feed can be granulated by a granulator to form feed pellets. For example, after the paste feed is moved into the granulator, the screw of the granulator extrude the gradually cooled paste feed through the die head, and the rotating blade cuts the strip feed into cylindrical pellets of 2 mm to 3 mm in length to obtain feed pellets that can be directly used for molding.

[0171] S123: Forming the feed particles into green bodies of steel structural parts by injection molding.

[0172] Feeding particles are added to the hopper of the injection molding machine, and injection molding is performed under certain temperature and pressure conditions to obtain a green billet of a steel structure. The present application does not limit the temperature or pressure conditions of the injection molding, and those skilled in the art can select them according to actual conditions. For example, the temperature of the injection molding is 170°C to 220°C, and the pressure of the injection molding is 150MPa to 200MPa.

[0173] In the embodiment of the present application, the green billet of the steel structure is formed by injection molding, which not only has high forming efficiency and low cost, but also can effectively obtain the green billet of three-dimensional complex and precise steel structure at one time, thereby improving the production efficiency of preparing complex and precise steel structure parts.

[0174] Furthermore, in the embodiment of the present application, the steel powder is mixed with the binder, and the steel powder has a certain fluidity, which reduces or avoids defects such as cracks or corner loss in the green body of the steel structure. At the same time, the steel powder is mixed with the binder, and the green body of the steel structure after being formed has a certain strength, and can maintain its shape when it is released from the mold cavity, which reduces or avoids the deformation of the green body of the steel structure, thereby improving the yield rate of the steel structure.

[0175] In the embodiment of the present application, the feed particles are formed into a green billet of a steel structure by injection molding, that is, the green billet of the steel structure is formed by metal injection molding (MIM). In other embodiments, the feed particles can also be formed into a green billet of a steel structure by pressing, which is not limited in the present application.

[0176] S130: Degreasing to remove the binder in the green body of the steel structure.

[0177] In some embodiments, the binder in the green steel structure is removed by catalytic degreasing. Catalytic degreasing to remove the binder utilizes the property that polymers can be rapidly degraded in a specific atmosphere, so that the green steel structure is degreased in the corresponding atmosphere to decompose the binder and remove the binder.

[0178] In the embodiment of the present application, the binder in the green body of the steel structure is removed by catalytic degreasing, which not only enables rapid and defect-free degreasing, but also increases the efficiency of degreasing, thereby improving the efficiency of preparing the steel structure.

[0179] It can be understood that the binder not only has the characteristics of enhancing fluidity to be suitable for injection molding and maintaining the shape of the block, but also has the characteristics of being easy to remove, non-polluting, non-toxic, and cost-effective, which is beneficial to the degreasing removal process.

[0180] Among them, in the embodiments of the present application, catalytic degreasing to remove the binder is taken as an example for description. In other implementations, other degreasing methods, such as solvent degreasing, may also be used, and the present application is not limited to this.

[0181] In some embodiments, the green body of the steel structure is placed flat on an alumina ceramic plate, placed in a catalytic degreasing furnace, and catalytically degreased under certain conditions. Among them, the present application does not limit the time, temperature, specific atmosphere and other conditions of degreasing, and those skilled in the art can select the degreasing conditions according to actual needs. Exemplarily, the temperature of catalytic degreasing is set to 110°C to 130°C, the amount of fuming nitric acid introduced is 0.5g / min to 3.5g / min, and the time is 2h to 4h.

[0182] S140: Sintering the green billet of the steel structure component after degreasing to form a sintered billet of the steel structure component.

[0183] Among them, the green body of sintered steel structural parts needs to be in an atmosphere of protective gas, such as Ar, H 2 Or vacuum to avoid the introduction of impurities during sintering in air. This application does not limit the temperature or time of sintering the green body of the steel structure, and those skilled in the art can set the sintering conditions according to actual needs. For example, the sintering temperature is 1200℃~1400℃, and the time is 1.5h~4h.

[0184] In the embodiment of the present application, sintering the green billet of the steel structure can reduce or eliminate the pores in the green billet of the steel structure to densify the green billet of the steel structure, so that the sintered billet of the formed steel structure reaches full densification or close to full densification, thereby enhancing the strength of the steel structure.

[0185] Moreover, in the embodiment of the present application, the carbon content in the steel powder is less than or equal to 0.35%, that is, the carbon content is low, which makes it easy to realize the sintering process of the green body of the steel structure, reducing the process difficulty of preparing the steel structure. At the same time, the steel powder does not rely on the strengthening of active elements such as aluminum (Al) or titanium (Ti), and has a low carbon content. For the steel structure through injection molding or metal injection molding process, the sintering process is easy to realize, and stable control is easy to produce.

[0186] In some embodiments, during the sintering process, the oxygen or carbon content in the final steel structure is adjusted by controlling the sintering temperature, time and pressure of the protective gas, so that the final steel structure has the characteristics of high strength and high toughness.

[0187] In the embodiment of the present application, during the process of preparing the steel structural parts, not only the oxygen and carbon contents in the original steel powder can be adjusted, but also the oxygen and carbon contents of the final steel structural parts can be adjusted through the sintering process, thereby effectively controlling the oxygen or carbon content in the final prepared steel structural parts.

[0188] S150: Sintered billet for heat-treated steel structural parts.

[0189] In the embodiment of the present application, heat treatment is performed on the sintered blank of the steel structure, which is beneficial to the solution treatment and aging treatment of the steel structure, promotes the precipitation of strengthening phases, and enables the final steel structure to achieve the required strength.

[0190] Please refer to Table 5, which is a table of component contents in various embodiments of the method for preparing steel structural parts provided in this application. Table 5 reflects the content of each component in the steel powder before preparing the steel structural parts, as well as the content of each component in the prepared steel structural parts product and the yield strength and elongation corresponding to each component.

[0191] Table 5

[0192]

[0193]

[0194]

[0195] According to Table 5, the steel structural parts formed by the preparation method of the steel structural parts provided in the present application have the characteristics of a yield strength greater than or equal to 1300 MPa and an elongation greater than or equal to 5%, that is, the formed steel structural parts have the characteristics of high strength and high toughness at the same time, so that the steel structural parts are not easily deformed or broken under high-intensity forces.

[0196] Moreover, in the embodiments of the present application, the steel structural parts formed by the method for preparing steel structural parts provided by the present application can effectively obtain three-dimensional complex and precise steel structural parts at one time. Compared with traditional mechanical processing, such as computerized numerical control machine (CNC) forming complex and precise steel structural parts does not require additional processing, which improves the production efficiency of preparing complex and precise steel structural parts, reduces the cost of preparing steel structural parts, and is conducive to the large-scale production of steel structural parts.

[0197] Among them, according to Table 5, it can be seen that the mass percentage of each component in the steel structure formed by the preparation method of the steel structure provided by the present application is somewhat different from the mass percentage of each component in the steel powder. Since the preparation method of the steel structure includes a sintering process, the carbon and oxygen content in the steel structure after sintering is different from the carbon and oxygen content in the steel powder, resulting in a slight change in the content of metal elements (chromium, nickel, cobalt, molybdenum or iron, etc.) in the final steel structure and the content of metal elements in the steel powder. Among them, the final formed steel structure includes chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7% and iron: 50% to 80%, so that the steel structure includes Fe-Co-Ni-Cr-Mo phase, Fe-Co-Cr-Mo phase and carbide (such as: Mo 2 C.W. 2 C) isoenhanced phase.

[0198] In some embodiments, the steel structural parts formed by the steel structural parts preparation method provided in the present application have the characteristics of a yield strength less than or equal to 2000Mpa and an elongation less than or equal to 12%. The formed steel structural parts reduce the difficulty of the steel structural parts preparation process while ensuring the mechanical strength, which is beneficial to reduce the production cost of the steel structural parts.

[0199] In the embodiment of the present application, by limiting the mass percentage of each component in the steel powder, the formed steel structure can depend on the Fe-Co-Ni-Cr-Mo phase, Fe-Co-Cr-Mo phase and carbides (such as Mo 2 C.W. 2C) Strengthening is achieved so that the yield strength of the steel structure prepared by metal injection molding technology is greater than or equal to 1300Mpa, and the elongation is greater than or equal to 5%, that is, the formed steel structure has the characteristics of high strength and high toughness at the same time, making it difficult for the steel structure to deform or break under high-intensity forces.

[0200] Exemplarily, the steel structure includes the following components in mass percentage: chromium (Cr): 7% to 11%, nickel (Ni): 2% to 7.5%, cobalt (Co): 6% to 15%, molybdenum (Mo): 4% to 7%, oxygen (O): trace to 0.4%, carbon (C): trace to 0.35% and iron: 50% to 80%. Among them, the mass percentages of the components in the steel structure are different, and the composition of the strengthening phase is also different, that is, the Fe-Co-Ni-Cr-Mo phase, Fe-Co-Cr-Mo phase or carbide formed are different. The strengthening phase can be but is not limited to (Fe, Co, Ni) 17 Cr 8 Mo 18 ,(Fe,Co) 15 Cr 8 Mo 4 or(Fe,Co) 16 Cr 8 Mo 18 wait.

[0201] The above are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application; in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A steel powder, characterized in that The steel powder is used for metal powder injection molding, and includes the following components in mass percentage: Chromium: 7% to 11%, nickel: 2% to 7.5%, cobalt: 6% to 15%, molybdenum: 4% to 7% and iron: 50% to 80%.

2. The steel powder according to claim 1, characterized in that The steel powder also includes the following components in percentage by mass: Oxygen: trace ~0.4%, Carbon: trace ~0.35%.

3. The steel powder according to any one of claims 1 to 2, characterized in that The steel powder further comprises niobium, and the mass percentage of the niobium is a trace amount to 1%.

4. The steel powder according to any one of claims 1 to 3, characterized in that The steel powder further comprises tantalum, and the mass percentage of the tantalum is a trace amount to 2%.

5. The steel powder according to any one of claims 1 to 4, characterized in that The steel powder also includes tantalum and niobium, wherein the mass percentage of the tantalum and the mass percentage of the niobium is in a ratio of 1 to 2:1, and the mass percentage of the tantalum plus the mass percentage of the niobium is a trace amount to 1.5%.

6. The steel powder according to any one of claims 1 to 5, characterized in that The steel powder further comprises tungsten, and the mass percentage of the tungsten is a trace amount to 2%.

7. The steel powder according to any one of claims 1 to 6, characterized in that The steel powder further comprises manganese, and the mass percentage of manganese is a trace amount to 0.5%.

8. The steel powder according to any one of claims 1 to 7, characterized in that The steel powder further comprises silicon, and the mass percentage of silicon is a trace amount to 0.5%.

9. The steel powder according to any one of claims 1 to 8, characterized in that The steel powder does not include titanium and aluminum.

10. The steel powder according to any one of claims 1 to 9, characterized in that The steel powder also includes boron in a trace amount of 0.01%.

11. The steel powder according to any one of claims 1 to 10, characterized in that The steel powder further comprises rare earth elements, and the mass percentage of the rare earth elements is trace amount to 0.5%.

12. A feed particle, characterized in that: The feed particles comprise the steel powder according to any one of claims 1 to 11 and a binder.

13. The feed granules according to claim 12, characterized in that The binder includes polyoxymethylene in an amount greater than or equal to 80% by weight.

14. The feed granules according to claim 13, characterized in that The binder also includes ethylene-vinyl acetate copolymer, polyethylene, microcrystalline wax and stearic acid.

15. The feed granules according to claim 14, characterized in that The weight percentages of the components in the binder are as follows: polyoxymethylene: 80% to 95%, ethylene-vinyl acetate copolymer: 0.5% to 1.5%, polyethylene: 2% to 9%, microcrystalline wax: 1% to 3%, and stearic acid: 0.5% to 1.5%.

16. The feed granule according to any one of claims 12 to 15, characterized in that The length of the feed particles is 2 mm to 3 mm.

17. A steel structure, characterized in that: The steel structure is obtained by processing the steel powder according to any one of claims 1 to 11; or The steel structure is obtained by processing the feed particles according to any one of claims 12 to 16.

18. A method for preparing feed particles, characterized in that: include: Mixing the steel powder according to any one of claims 1 to 11 with a binder to form a paste feed; The paste feed is granulated to form feed granules.

19. A method for preparing a steel structure, characterized in that: include: Forming the feed particles according to any one of claims 12 to 16 into a green body of a steel structure by pressing or injection molding; Sintering the green billet of the steel structure component to form a sintered billet of the steel structure component; The sintered blank of the steel structure is heat treated to form a steel structure.

20. An electronic device, characterized in that: Comprising the steel structural member as claimed in claim 19.

21. The electronic device according to claim 20, characterized in that: The electronic device further includes a flexible display screen and a folding device for supporting the flexible display screen, wherein the folding device is used to drive the flexible display screen to deform; wherein the folding device includes the steel structure.

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