Patent Description:
As a terminal mobile phone is more and more functional and integrated, people are no longer satisfied with a screen size of about <NUM> inches. Foldable-screen mobile phones are beginning to appear in the public eye and are becoming one of main directions for future smartphone development. Foldable-screen mobile phones are generally thick and heavy, which affects consumer experience to some extent. A design and a structure of a built-in metal structural part of the foldable-screen mobile phone significantly affect a thickness and a weight of the mobile phone. Therefore, weight reduction and thinning of the built-in structure of the foldable-screen mobile phone are important research topics in the industry.

In the industry, miniature and complex structural parts in the foldable-screen mobile phone are mostly made of injection molded stainless steel, but strength of the stainless steel is relatively low (yield strength is less than <NUM> MPa). As the structural parts of the mobile phone continue to be thinned, strength of an existing material is difficult to meet a requirement, and the material is prone to a failure such as fracture. However, for conventional high-strength profile steel (yield strength <NUM> MPa), a method of smelting and casting + plastic processing is used to prepare a blank, and a miniature and complex structural part is produced by using a machining method, which is low in efficiency and high in costs. Therefore, development of injection molded ultrahigh-strength alloy materials attracts much attention in the industry.

Document <CIT> discloses steel, steel structure parts, electronic equipment and preparation method of steel structure parts.

To resolve the foregoing technical problem, this application provides an injection molded alloy material and a processing method. By using the alloy material molded by using the component, strength of the alloy material can be improved, a structure of a terminal product is thinned, production costs of the product are reduced, and production efficiency of the product is improved.

According to a first aspect, an embodiment of this application provides an injection molded alloy material. The injection molded alloy material includes the following components: carbon (C) occupying ≤ <NUM>% of a total weight of the alloy material, nickel (Ni) occupying <NUM>-<NUM>% of the total weight of the alloy material, chromium (Cr) occupying <NUM>-<NUM>% of the total weight of the alloy material, molybdenum (Mo) occupying <NUM>-<NUM>% of the total weight of the alloy material, cobalt (Co) occupying <NUM>-<NUM>% of the total weight of the alloy material, vanadium (V) occupying ≤ <NUM>% of the total weight of the alloy material, and a remaining component of iron (Fe). The alloy material prepared by using the alloy components in this solution can be used to prepare an alloy structural part with yield strength of more than <NUM> MPa, which is beneficial to thinning of the product, that is, a size of an entire structure can be reduced, and user experience can be improved. In addition, production costs can be reduced, and production efficiency can be improved.

Based on the first aspect, the injection molded alloy material provided in this embodiment of this application may further include the following components: carbon (C) occupying ≤ <NUM>% of a total weight of the alloy material, nickel (Ni) occupying <NUM>-<NUM>% of the total weight of the alloy material, chromium (Cr) occupying <NUM>-<NUM>% of the total weight of the alloy material, molybdenum (Mo) occupying <NUM>-<NUM>% of the total weight of the alloy material, cobalt (Co) occupying <NUM>-<NUM>% of the total weight of the alloy material, and a remaining component of iron (Fe). The alloy material prepared by using the alloy components in this solution can be used to prepare a metal structural part with yield strength of <NUM> MPa, tensile strength of <NUM> MPa, an elongation rate of <NUM>%, hardness of <NUM> HV, and corrosion resistance of <NUM> in a neutral salt spray test.

According to a second aspect, this application provides a processing method for an injection molded alloy material, including the following steps:.

The alloy components in the solutions of the first aspect are separately prepared according to the steps of the processing method, so that effects of the foregoing solutions can be implemented.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, a granularity specification of the alloy material powder in step <NUM> includes: a laser granularity D50: <NUM>-<NUM>, and a tap density ≥ <NUM>/cm<NUM>.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, the alloy powder and the polymer binder are poured into a Σ-type kneader for mixing according to a volume ratio of <NUM>:<NUM>-<NUM>:<NUM> in step <NUM>, where a mixing temperature is <NUM>-<NUM>, and a mixing time is <NUM>-<NUM>.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, degreasing processing in step <NUM> includes performing acid catalyst catalytic degreasing or solvent degreasing treatment on the injection molded green body to remove the polymer binder, where a degreasing temperature is <NUM>-<NUM>, a catalytic time is <NUM>-<NUM>; and a catalytic medium is nitric acid or oxalic acid, and a protective atmosphere is nitrogen.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, sintering in step <NUM> includes two steps; the first step includes: thermal degreasing, and a process of thermal degreasing includes: increasing a temperature in a furnace chamber from a room temperature to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes; and the second step includes: heating the temperature in the furnace chamber from <NUM>-<NUM> to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes, where an atmosphere is vacuum, a protective atmosphere is argon, and a partial pressure of the argon is <NUM>-<NUM> KPa.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, shaping in step <NUM> includes performing cold shaping on a sintered product.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, heat treatment in step <NUM> includes solution treatment and aging treatment.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, the solution treatment includes: heating a temperature in a furnace chamber from a room temperature to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes, where an atmosphere is vacuum; and after temperature preserving is completed, using a high-pressure inert gas to rapidly cool the furnace chamber to a temperature below <NUM>, where the inert gas is nitrogen or argon, and a pressure is > <NUM> bar.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, the aging treatment includes: heating a temperature in a furnace chamber from a room temperature to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes, where an atmosphere is vacuum, and the furnace temperature is cooled after temperature preserving is completed.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, heat treatment in step <NUM> further includes subzero treatment.

Based on the second aspect, in the processing method for an injection molded alloy material provided in this application, the subzero treatment includes: performing cryogenic insulation at a temperature lower than -<NUM>, and a time of the cryogenic insulation is greater than <NUM>.

By using the processing method in this solution and combining the alloy components in the first aspect, a metal structural part whose yield strength reaches <NUM> MPa can be prepared. In addition, production costs of the metal structural part can be reduced, and production efficiency of the metal structural part can be improved.

All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of this application without making creative efforts shall fall within the protection scope of this application.

The term "and/or" in this specification merely describes an association relationship for describing associated objects, and represents that three relationships may exist.

The terms "first", "second", and the like in the specification and claims of embodiments of this application are used to distinguish between different objects, and are not used to indicate a specific sequence of objects. For example, a first target object and a second target object are used to distinguish between different target objects, but are not used to describe a specific sequence of the target objects.

In the embodiments of this application, words such as "an example" or "for example" are used to represent giving an example, an illustration, or a description. Any embodiment or design solution described as "example" or "for example" in embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design solutions. Specifically, the words such as "example" or "for example" are used to present related concepts in a specific manner.

In the descriptions of embodiments of this application, unless otherwise specified, "a plurality of" means two or more. For example, a plurality of processing units refer to two or more processing units. A plurality of systems refer to two or more systems; and a plurality of systems refer to two or more systems.

An injection molded alloy material provided in embodiments of this application may be used to prepare structural parts of various types of terminals, and is particularly applied to a structural part of a foldable-screen style terminal. As a terminal mobile phone is more and more functional and integrated, a user is no longer satisfied with a screen size of about <NUM> inches. A mobile phone is used as an example. Based on a requirement of a user for a large screen, a foldable-screen mobile phone emerges accordingly. However, a structural part of a foldable-screen mobile phone (especially a rotating shaft) obtained after production and assembly by using an existing structural material is relatively thick and heavy as a whole, and user experience is affected to some extent. As a result, the mobile phone is relatively thick and heavy.

To resolve the problem that the structure of the foldable-screen mobile phone is thick and heavy, an injection molding manner of a stainless steel material is mostly used currently. However, yield strength of the existing stainless steel material is lower than <NUM> MPa, that is, the strength of the existing stainless steel material is relatively low. With improvements to continuous thinning of the mobile phone structural part, it is difficult for the strength of the existing stainless steel material to meet a requirement, and the structural part molded by using the existing stainless steel material is prone to failure problems such as fracture. If the existing stainless steel material is replaced with conventional high-strength profile steel, and a product blank is prepared by sequentially performing smelting and casting and plastic processing, it is further necessary to produce a required miniature and complex structural part by using a machining method, and there is a problem of low production efficiency and high production costs. For example, if a <NUM> stainless steel powder is used, mixing, injection molding, degreasing, sintering, shaping, heat treatment, and surface treatment are sequentially performed, and finally, a <NUM> stainless steel structural part is molded. Yield strength of the <NUM> stainless steel structural part is <NUM> MPa, and the molded structural part is prone to a failure problem of deformation or fracture. For example, heat treatment includes quenching and tempering. For example, if a <NUM>-4PH stainless steel powder is used, mixing, injection molding, degreasing, sintering, shaping, heat treatment, and surface treatment are sequentially performed, and finally, a <NUM>-4PH stainless steel structural part is molded. Yield strength of the <NUM>-4PH stainless steel structural part is <NUM> MPa, and the molded structural part also is prone to a failure problem of deformation or fracture. If high-strength profile steel is used, the high-strength profile steel is sequentially melted and cast and plastically processed to obtain high-strength profile, and then CNC processing, heat treatment, and surface treatment are performed to finally mold a high-strength profile steel structural part. Yield strength of the high-strength profile steel structural part is <NUM> MPa. Although the strength of the structural part is increased, machining costs are high, machining efficiency is low, and it is difficult to process a micro and three-dimensional structural part.

Based on this, embodiments of this application may provide an alloy material and a processing method that can improve product production efficiency, reduce product production costs, and increase yield strength of a structural part. Specifically, a solution of an injection molded alloy material in this application is as follows:.

Embodiments of this application provide an injection molded alloy material, including the following components: carbon (C) occupying ≤ <NUM>% of a total weight of the alloy material, nickel (Ni) occupying <NUM>-<NUM>% of the total weight of the alloy material, chromium (Cr) occupying <NUM>-<NUM>% of the total weight of the alloy material, molybdenum (Mo) occupying <NUM>-<NUM>% of the total weight of the alloy material, cobalt (Co) occupying <NUM>-<NUM>% of the total weight of the alloy material, vanadium (V) occupying ≤ <NUM>% of the total weight of the alloy material, and a remaining component of iron (Fe). For example, the remaining component may further include impurities, for example, trace Mn and Si. The alloy material in this solution is sequentially subjected to a high-strength steel powder, mixing, injection molding, degreasing, sintering, shaping, heat treatment, and surface treatment, and finally a high-strength alloy structural part is molded. After the foregoing series of molding processes and heat treatment, yield strength of the high-strength alloy structural part may reach more than <NUM> MPa, and hardness of a surface material and hardness of a core material may reach <NUM>-<NUM> HV.

For example, a molding method for injection molding of an alloy material powder in this embodiment of this application includes but is not limited to powder making, mixing, injection molding, degreasing, sintering, and heat treatment. For example, heat treatment includes quenching and tempering.

For example, a structural shape of a metal part obtained by means of injection molding of the alloy material powder in this embodiment of this application is corresponding to a cavity structure of a used injection mold. The molding method of injection molding, which eliminates a need for subsequent machining or requires only a small amount of machining, makes it ideal for bulk preparation of miniature and complex three-dimensional mobile phone metal structural parts.

For example, a high-strength steel powder is prepared by using a high-pressure water atomization method or a gas atomization method. Specifically, a granularity feature D50 of the high-strength steel powder is <NUM>-<NUM>, and a tap density of the high-strength steel powder is ≥ <NUM>/cm<NUM>.

For example, a mixing process includes: pouring the high-strength steel powder and a polymer binder according to a volume ratio of <NUM>:<NUM>-<NUM>:<NUM> into a mixing machine for mixing. Specifically, a mixing temperature is <NUM>-<NUM>, and a mixing time is <NUM>-<NUM>. For example, the polymer binder may be at least one of polyformaldehyde, high-density polyethylene, polypropylene, paraffin, ethylene-vinyl acetate copolymer EVA, polymethyl methacrylate PMMA, stearic acid SA, or an antioxidant.

For example, the mixing process may alternatively include: pouring the high-strength steel powder and a polymer binder according to a volume ratio of <NUM>:<NUM>-<NUM>:<NUM> into a mixing machine for mixing. Specifically, a mixing temperature is <NUM>-<NUM>, and a mixing time is <NUM>-<NUM>. For example, the polymer binder mainly includes a main filler, a skeleton agent, and a lubricant/an activator. The main filler is polyoxymethylene, which accounts for <NUM>-<NUM>% by weight. The skeleton agent is one or more of high-density polyethylene, polypropylene, and the like, and accounts for <NUM>-<NUM>% by weight. The lubricant/the activator is one or more of ethylene-vinyl acetate copolymer EVA, polymethyl methacrylate PMMA, stearic acid SA, and the like, and accounts for <NUM>-<NUM>% by weight.

For example, an injection molding process includes: performing injection molding by using an injection molding machine and an injection mold, to obtain a green body. Specifically, an injection temperature is <NUM>-<NUM>.

For example, a degreasing process includes catalytic degreasing. Specifically, catalytic degreasing includes: performing acid catalyst catalytic degreasing or solvent degreasing on the injection molded green body to remove the polymer binder. For example, a degreasing temperature is <NUM>-<NUM>, a catalytic degreasing time is <NUM>-<NUM>, and a catalytic medium may be nitric acid or oxalic acid.

For example, a sintering process is defined as follows: Sintering includes two steps; the first step includes: thermal degreasing, and a process of thermal degreasing includes: increasing a temperature in a furnace chamber from a room temperature to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes; and the second step includes: heating the temperature in the furnace chamber from <NUM>-<NUM> to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes, where an atmosphere is vacuum, a protective atmosphere is argon, and a partial pressure of the argon is <NUM>-<NUM> KPa.

For example, a heat treatment process includes: sequentially performing solution treatment and aging treatment. Specifically, the solution treatment includes: heating a temperature in a furnace chamber from a room temperature to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes, where an atmosphere is vacuum; and after temperature preserving is completed, using a high-pressure inert gas to rapidly cool the furnace chamber to a temperature below <NUM>, where the inert gas is nitrogen or argon, and a pressure is > <NUM> bar. Specifically, the aging treatment includes: heating a temperature in a furnace chamber from a room temperature to <NUM>-<NUM>, and preserving the temperature at <NUM>-<NUM> for <NUM>-<NUM> minutes, where an atmosphere is vacuum, and the furnace temperature is cooled after temperature preserving is completed.

For example, the heat treatment process may alternatively include: sequentially performing solution treatment, subzero treatment, and aging treatment. Content of solution treatment and aging treatment is the same as that in the previous solution, and details are not described herein again. In addition, the subzero treatment includes: performing cryogenic insulation at a temperature lower than -<NUM>, and a time of the cryogenic insulation is greater than <NUM>.

The foregoing alloy material composition and molding method can be used to prepare an alloy structural part with yield strength of more than <NUM> MPa, which is beneficial to thinning of the product, that is, a size of an entire structure can be reduced, and user experience can be improved. By using the injection molding process, the preparation method is relatively low in costs and high in production efficiency, and is suitable for bulk preparation of miniature and complex three-dimensional mobile phone metal structural parts. In addition, a sintered structural part has hardness of < <NUM> HV and yield strength of < <NUM> MPa, and is easy for product shaping.

Further, to further show an effect of the solution of the alloy powder and the processing method for the alloy powder, an embodiment of this application provides a specific molding process of the following first solution:.

Specifically, a solution treatment device uses a vacuum high-pressure gas quenching furnace. Solution treatment includes:.

Specifically, an aging treatment device uses a vacuum heat treatment furnace. Aging treatment includes:
The temperature in the furnace chamber is increased from the room temperature to <NUM>, the heating time is <NUM> minutes, and the heating rate is <NUM>/minute. The temperature is preserved at <NUM> for <NUM> minutes; and the atmosphere is vacuum.

According to the alloy material and the processing method in the first solution, a metal structural part with yield strength of <NUM> MPa, tensile strength of <NUM> MPa, an elongation rate of <NUM>%, hardness of <NUM> HV, and corrosion resistance of <NUM> in a neutral salt spray test.

Further, to further show an effect of the solution of the alloy powder and the processing method for the alloy powder, an embodiment of this application provides a specific molding process of the following second solution:.

Specifically, an aging treatment device uses a vacuum heat treatment furnace. Aging treatment includes:
The temperature in the furnace chamber is increased from the room temperature to <NUM>, the heating time is <NUM> minutes, and the heating rate is <NUM>/minute. The temperature is preserved at <NUM> for <NUM> minutes; and the atmosphere is vacuum. After temperature preserving is completed, a fan is opened to cool the furnace temperature.

According to the alloy material and the processing method in the second solution, a metal structural part with yield strength of <NUM> MPa, tensile strength of <NUM> MPa, an elongation rate of <NUM>%, hardness of <NUM> HV, and corrosion resistance of <NUM> in a neutral salt spray test.

Further, to further show an effect of the solution of the alloy powder and the processing method for the alloy powder, an embodiment of this application provides a specific molding process of the following third solution:.

This step may include: sequentially performing solution treatment, subzero treatment, and aging treatment on a shaped product.

Specifically, content of solution treatment and aging treatment is the same as that in the first solution, and details are not described herein again. In addition, a temperature of subzero treatment is -<NUM>, and the temperature is preserved for <NUM>.

According to the alloy material and the processing method in the third solution, a metal structural part with yield strength of <NUM> MPa, tensile strength of <NUM> MPa, an elongation rate of <NUM>%, hardness of <NUM> HV, and corrosion resistance of <NUM> in a neutral salt spray test.

Further, to further show an effect of the solution of the alloy powder and the processing method for the alloy powder, an embodiment of this application provides a specific molding process of the following fourth solution:
Content of steps d1-d6 is the same as content of a1-a6 in the first solution, and details are not described herein again.

Step d7 includes that a temperature of aging treatment is <NUM>. Remaining content is the same as content of a7 in the first solution, and details are not described herein again.

According to the alloy material and the processing method in the fourth solution, a metal structural part with yield strength of <NUM> MPa, tensile strength of <NUM> MPa, an elongation rate of <NUM>%, hardness of <NUM> HV, and corrosion resistance of <NUM> in a neutral salt spray test.

Further, to further show an effect of the solution of the alloy powder and the processing method for the alloy powder, an embodiment of this application provides a specific molding process of the following fifth solution:.

Content of steps f1-f6 is the same as content of a1-a6 in the first solution, and details are not described herein again.

Step f7 includes that a temperature of aging treatment is <NUM>. Remaining content is the same as content of a7 in the first solution, and details are not described herein again.

According to the alloy material and the processing method in the fifth solution, a metal structural part with yield strength of <NUM> MPa, tensile strength of <NUM> MPa, an elongation rate of <NUM>%, hardness of <NUM> HV, and corrosion resistance of <NUM> in a neutral salt spray test.

Product performance comparison of the five solutions is shown in Table <NUM> below:.

In conclusion, an alloy composition of a structural part material is designed, combined with a matching molding process and a heat treatment system, to implement full dispersion strengthening of a maraging MIM steel reinforcement phase, so that yield strength of the material can reach <NUM> MPa, and counter bending/extrusion resistance of a metal structural part of a mobile phone is greatly improved, and the metal structural part is thinned/weight-reduced. Specifically, an effect of an alloy element is as follows: A design of nickel element (Ni) content ensures not only plasticity and corrosion resistance of the material, but also sintering activity and stability. A design of cobalt element (Co) content can maintain high dislocation content of martensite, provide more nucleation positions of a second phase strengthening phase, precipitate more strengthening phases, and have higher strength. A design of molybdenum element (Mo) content: Molybdenum is a synthetic element of a main strengthening phase Fe2Mo. High molybdenum content can provide more precipitated strengthening phases, and molybdenum can also improve corrosion resistance. A design of chromium element (Cr) content improves corrosion resistance.

To realize comprehensive mechanical properties of high strength and high toughness of alloy materials, and meet requirements of mass production processability, the carbon content is set to be less than <NUM>%, so as to ensure that a main structure of a base material is lath-shaped martensite, which is conducive to toughness and plasticity of the material, stability of a sintering process, and shapability after sintering; and
a proper content proportion of nickel, chromium, cobalt, and molybdenum is set to ensure that the structure at a room temperature is mainly lath-shaped martensite, containing a small amount of residual austenite and a small amount of ferrite; a proper content proportion of nickel, chromium, cobalt, and molybdenum is set to ensure that a martensite formation temperature (Ms point) is higher than <NUM> after rapid cooling; and a proper content proportion of cobalt and molybdenum is set to ensure sufficient dispersion strengthening phase formation on the base material after heat treatment.

Claim 1:
An injection molded alloy material, comprising the following components: carbon (C) occupying ≦ <NUM>% of a total weight of the alloy material, nickel (Ni) occupying <NUM>-<NUM>% of the total weight of the alloy material, chromium (Cr) occupying <NUM>-<NUM>% of the total weight of the alloy material, molybdenum (Mo) occupying <NUM>-<NUM>% of the total weight of the alloy material, cobalt (Co) occupying <NUM>-<NUM>% of the total weight of the alloy material, vanadium (V) occupying ≦ <NUM>% of the total weight of the alloy material, and a remaining component of iron (Fe).