Stainless steel material for metal injection molding processing and preparation method and application thereof

Abstract

The invention belongs to the technical field of powder metallurgy materials and intelligent manufacturing, and relates to a metal material, in particular to a stainless steel material for metal injection molding processing and a preparation method and application thereof, and the stainless steel material is composed of the following chemical elements: 6.0-8.0 wt% of Cr, 6.0-9.0 wt% of Ni, 14.0-18.0 wt% of Co, 5.5-6.5 wt% of Mo, 0.05-0.5 wt% of Nb, 0.05-0.5 wt% of V, less than or equal to 0.03 wt% of C, and the balance Fe and inevitable impurity elements. According to the invention, V with a specific content is added into the material, V is added in a matched manner, and the contents of other components are adjusted, so that the yield strength of a steel structural member can reach more than 2100MPa and the ductility can reach more than 5% under the composition within a specific range, and compared with an existing metal injection molded steel member, the steel structural member has the advantages that the yield strength is obviously improved, and the service life is prolonged. And the impact toughness of the material can be obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy materials and intelligent manufacturing, relates to a metal material, and particularly relates to a stainless steel material for metal injection molding processing, a preparation method thereof and an application thereof. Background Art

[0002] Metal Injection Molding (abbreviated as MIM) is a new powder metallurgy near-net shaping technology derived from the powder metallurgy and plastic injection molding industries. In recent years, this technology has developed to maximize the content of solid particles and completely remove the binder during the subsequent sintering process and densify the green compact. The basic process steps of metal injection molding are: first, select metal powders and binders that meet the requirements of MIM, then mix the powders and binders into a uniform feedstock at a certain temperature by an appropriate method, granulate it, and then injection mold it. The obtained green compact is sintered and densified after debinding to become the final product.

[0003] MIM can manufacture metal parts with complex shapes, including fine internal structures, thin-wall structures, precision holes, etc., and can achieve highly precise forming, with excellent dimensional control and surface quality. Therefore, MIM has been widely used in the manufacturing of some components with high precision requirements.

[0004] In the "3C" application field, especially in the application fields of folding screen mobile phones and computers, in order to achieve the lightweight of wearable devices, high-strength martensitic steel and ultra-high-strength steel have begun to be applied to the folding screen hinge design. Since the structure of such components is complex, they are generally designed and manufactured by the metal injection molding method. However, the sintering density of injection molding sintered parts can generally only reach 96% - 99.5% of the theoretical density, unable to reach the density of casting materials, nor can the material properties be further improved by hot and cold deformation (rolling, forging) methods. Therefore, for ultra-high-strength steel materials produced by the injection molding method, even for well-sintered sintered materials, there is a porosity of 0.5 - 3% in the sintered matrix. The porosity of this material can be reduced to near zero and the density can be increased to near the theoretical density by the hot isostatic pressing method. However, this method greatly increases the processing cost and is difficult to achieve low-cost mass production.

[0005] At present, in many patents on injection-molded ultra-high-strength steel, generally only the yield strength of the material is concerned, while its elongation rate is far from being emphasized enough in material development. Such voids in the matrix of injection-molded sintered materials are themselves a kind of defect of the material. Compared with materials with a density of 100% such as casting and forging, their properties such as strength and elongation rate decrease significantly, especially the elongation rate of the material. In practical applications, even for materials with an elongation rate of 5%, due to the existence of sintering voids, the material still has the possibility of brittle fracture and cannot pass the anti-drop test. For example, for materials with a yield strength of 1500 MPa, the impact value of the material with an elongation rate of 5% is only 8 J / cm 2 , while the latter can reach 40 J / cm 2 or more. During the tensile fracture test, the former is close to brittle fracture, while the latter is generally a plastic fracture with necking dimples.

[0006] Therefore, in the "3C" applications, ultra-high-strength steel materials with higher elongation rate and better toughness are often required to improve the application reliability of the materials to meet a wide range of application requirements.

[0007] However, due to the multi-void characteristics of the matrix of injection-molded sintered materials, this common material defect makes it very difficult to improve the elongation rate and toughness of injection-molded ultra-high-strength steel. When the elongation rate of the material is based on 6%, it becomes very difficult to further improve the elongation performance.

[0008] In the applicant's previous research, referring to Chinese Patent Application CN118109759A, the strength and elongation rate of injection-molded sintered materials were studied, and a stainless steel material was optimized. The mass percentage content of each chemical element is: Cr 7.0-9.0 wt%, Ni 7.0-9.0 wt%, Co 9.0-15.0 wt%, Mo 5.5-7.0 wt%, Nb 0.05-0.5 wt%, C≤0.03 wt%, the balance is Fe, and inevitable impurity elements. The steel structure formed by injection molding using this high-toughness and high-strength stainless steel raw material has a yield strength greater than 1900 MPa, especially a yield strength greater than 2000 MPa, and at the same time an elongation rate greater than 5%.

[0009] The applicant intends to further improve the yield strength and elongation rate of this material to meet higher requirements in usage scenarios. Summary of the Invention

[0010] The object of the present invention is to supplement the metal injection molding materials in the prior art, and to provide a metal injection molding material with a yield strength greater than 1900 MPa and an elongation greater than 7%, or a yield strength greater than 2100 MPa and an elongation greater than 5%.

[0011] In the first aspect of the present invention, a stainless steel material for metal injection molding is provided.

[0012] The technical solution adopted by the first aspect of the present invention to solve its technical problems is as follows:

[0013] A stainless steel material for metal injection molding is composed of the following chemical elements:

[0014] Cr 6.0 - 8.0 wt%, Ni 6.0 - 9.0 wt%, Co 14.0 - 18.0 wt%, Mo 5.5 - 6.5 wt%, Nb 0.05 - 0.5 wt%, V 0.05 - 0.5 wt%, C ≤ 0.03 wt%, the balance is Fe, and inevitable impurity elements.

[0015] The Cr element mainly provides the corrosion resistance of stainless steel. Chromium forms a stable chromium oxide layer with oxygen, which can prevent the surface of stainless steel from reacting with oxygen and water in the environment, thus protecting stainless steel from corrosion. Chromium is also a ferrite-forming element in the material, and excessive chromium will reduce the material strength.

[0016] The Ni element is also a toughening element in ultra-high strength stainless steel, which improves the fracture resistance of martensitic steel, increases the plasticity and toughness of the material. Nickel can improve the passivation tendency of stainless steel and improve the corrosion resistance of martensitic stainless steel. However, the austenitizing tendency of nickel is relatively large, and excessive nickel makes it difficult for the material to form a martensitic structure, reducing the mechanical properties.

[0017] As an important strengthening element, the Co element will promote the formation of dispersed precipitation phases during the aging process of the material. The increase of Co is beneficial to improving the toughness and strength of the material within a certain range. An appropriate high cobalt content will increase the martensite transformation temperature of the material, and it is easier to achieve martensite transformation during the air quenching process after solution heat treatment, which is beneficial to improving the material properties and stability. However, for this kind of martensitic stainless steel with good toughness required in reality, the material needs to retain an appropriate amount of retained austenite phase on the basis of the martensite matrix to truly make the material have toughness and ductility on the basis of high strength. Excessive cobalt content not only excessively promotes the formation of brittle dispersed phases, but also promotes the full transformation of retained austenite into martensite, ultimately making the material brittle. Therefore, from the perspective of technical characteristics, excessive cobalt is detrimental to the toughness of the material. Excessive cobalt content will also increase the material cost.

[0018] Mo is the most important solid-solution strengthening element in martensitic stainless steel. Its solid-solution strengthening effect can improve the yield strength and tensile strength of martensitic stainless steel. However, excessive Mo will form brittle phases in the material, which will significantly reduce the toughness of the material while increasing the strength, and eventually evolve into brittle materials.

[0019] The Nb element is an important strengthening element. It can not only refine the grains, improve the toughness and strength of the material, but also form NbC with the C element to form dispersion strengthening, further enhancing the strength of the material. However, excessive Nb elements will lead to excessive precipitation of carbides in the material, which will aggregate between grain boundaries, resulting in a decrease in the toughness of the material. At the same time, it will reduce the content of C elements in the matrix, leading to a significant decrease in the strength of the material.

[0020] Generally, the Fe\Ni\Cr\Co\Mo series of ultra-high-strength martensitic stainless steel is a type of ultra-high-strength stainless steel with element substitution solid solution. Mo is the strengthening core, forming a reinforcing material with the basic solid-solution structure of (Fe / Cr / Ni / Co)Mo. The strength and toughness of the material depend on factors such as the elemental composition ratio, phase structure, grain size, dislocation density, and material defects in the material.

[0021] The present invention also adds V to the Fe\Ni\Cr\Co\Mo system. The addition of V can refine the grains, improve the toughness and strength of the material, and also improve the impact toughness of the material. In this technical solution, 0.05 - 0.5wt% of V is added, and the Co content is increased. By adjusting and improving the raw material composition and its content, the most suitable composition is optimized. Combining with the injection molding process, the yield strength of the martensitic stainless steel reaches more than 1900MPa, and the elongation is greater than 7%. In particular, when the yield strength is greater than 2100MPa, the elongation is greater than 5%.

[0022] The martensitic stainless steel material of the present invention can also achieve the selection of different strength and toughness ranges by controlling the temperature conditions of aging treatment. For example, when the aging temperature range is controlled at 530 - 540°C and held for 4 - 6 hours, the yield strength of the obtained material can be more than 2100MPa, and the elongation is more than 5%. When the aging temperature range is in the 540 - 550°C temperature zone for 4 - 6 hours of vacuum aging, the yield strength of the obtained material can be 1800Mpa to 1900MPa, and the elongation is more than 7%. According to the actual use requirements, ultra-high-strength or ultra-high-toughness performance materials can be prepared, which further broadens the scope of use of the material.

[0023] In one embodiment of the present invention, the mass percentage contents of Cr, Ni, Co, Mo, Nb, and V elements are as follows: Cr 6.0 - 6.8 wt%, Ni 7.5 - 9.0 wt%, Co 15.5 - 18.0 wt%, Mo 5.5 - 6.5 wt%, Nb 0.05 - 0.5 wt%, V 0.05 - 0.5 wt%.

[0024] In one embodiment of the present invention, the mass percentage contents of Cr, Ni, Co, Mo, Nb, and V elements are as follows: Cr 7.0 - 8.0 wt%, Ni 6.0 - 7.5 wt%, Co 15.5 - 18.0 wt%, Mo 5.5 - 6.5 wt%, Nb 0.05 - 0.5 wt%, V 0.05 - 0.5 wt%.

[0025] In the second aspect of the present invention, there is provided a steel structure member formed by a metal injection molding process using the above-mentioned high-toughness and high-strength stainless steel raw material.

[0026] For the above-mentioned steel structure member, while its yield strength is above 2100 MPa, the elongation rate can reach above 5%. Or while the yield strength is 1800 - 1900 MPa, the elongation rate can reach above 7%.

[0027] In the third aspect of the present invention, there is provided a preparation method for a steel structure member, including the following steps:

[0028] S1: Mix and granulate the high-toughness and high-strength stainless steel powder raw material with a particle size D90 less than 40 microns and a binder such as POM to obtain a feed particle raw material; the high-toughness and high-strength stainless steel raw material is composed of the following chemical elements: Cr 6.0 - 8.0 wt%, Ni 6.0 - 9.0 wt%, Co 14.0 - 18.0 wt%, Mo 5.5 - 6.5 wt%, Nb 0.05 - 0.5 wt%, V 0.05 - 0.5 wt%, C ≤ 0.03 wt%, the balance is Fe, and inevitable impurity elements;

[0029] S2: Inject the particle raw material into a green body.

[0030] S3: Catalytically debind the green body.

[0031] S4: After catalytic debinding, the green body is subjected to thermal debinding and sintering in a negative pressure environment to obtain a sintered part, and the sintering temperature range is 1350 - 1370 °C;

[0032] S5: The sintered part is successively subjected to solution treatment and vacuum aging treatment to obtain the steel structure member.

[0033] In one embodiment of the present invention, in step S5, the vacuum aging treatment operation is as follows: aging treatment is carried out at 530 - 540 °C for 4 - 6 hours; or aging treatment is carried out at 540 - 550 °C for 4 - 6 hours.

[0034] In one embodiment of the present invention, in step S1, the granulation temperature is 175 - 200 °C.

[0035] In one embodiment of the present invention, in step S5, the solution treatment operation is as follows: in a vacuum environment, the temperature is raised to 1040 - 1085 °C at a heating rate of 5 - 10 °C / min, held for 60 - 120 minutes, and then quenched to room temperature by high-pressure gas.

[0036] In one embodiment of the present invention, in step S5, high-pressure inert gas of 6 atm - 10 atm is used for gas quenching to room temperature. The inert gas is nitrogen or argon.

[0037] In one embodiment of the present invention, in step S3, nitric acid or oxalic acid is used to catalytically degrease the green body; the temperature condition for nitric acid degreasing is 110 °C ± 5 °C, and the temperature condition for oxalic acid degreasing is 130 °C ± 5 °C.

[0038] In the fourth aspect of the present invention, a steel structure member is provided, which is made by the above preparation method.

[0039] In one embodiment of the present invention, while the yield strength of the steel structure member is between 2000 MPa and 2100 MPa, the elongation rate can reach more than 5%. Or while the yield strength is greater than 1800 Mpa to 1900 MPa, the elongation rate can reach more than 7%.

[0040] In the fifth aspect of the present invention, the applications of the above high-toughness and high-strength stainless steel raw material and the above steel structure member in 3C products, automotive products, aviation products, and medical products are provided.

[0041] In particular, the applications of the above high-toughness and high-strength stainless steel raw material and the above steel structure member in the manufacturing of 3C products and their components.

[0042] The "3C products" referred to in the present invention are the general term for computer, communication, and consumer electronic products, also known as "information appliances". For example, computers, tablets, mobile phones, or digital audio players, etc. These products have complex structures, high precision requirements, and high requirements for strength and toughness. The stainless steel of the present invention is particularly suitable for products in these fields.

[0043] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0044] In the present invention, by adding a specific content of V to the material and adjusting the contents of other components in combination with the addition of V, it is possible to achieve a yield strength of more than 2100 MPa and an elongation of more than 5% in a steel structural member under a specific composition range. Or, when the yield strength is 1800 Mpa to 1900 MPa, the elongation can reach more than 7%. In particular, when the yield strength is more than 2100 MPa, the elongation can reach more than 5%. Compared with existing steel structural members formed by metal injection molding, there is a significant improvement, and the impact toughness of the material can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is the tensile curve diagram of the steel structural member obtained by using the method provided in Example 7 for the raw materials of Example 1 of the present invention.

[0046] Figure 2 is the tensile curve diagram of the steel structural member obtained by using the method provided in Example 8 for the raw materials of Example 1 of the present invention.

[0047] Figure 3 is the backscattered electron diffraction (EBSD) phase test diagram in the scanning electron microscope of the steel structural member provided in Example 3 of the present invention. The figure shows that the high-strength steel material of the present invention is almost entirely martensite. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The following are specific examples to further illustrate the technical solutions of the present invention. It should be understood that the implementation of the present invention is not limited to the following examples, and any formal modification and / or change made to the present invention will fall within the protection scope of the present invention. The parameter ranges involved include the endpoint values unless otherwise specified.

[0049] In the present invention, unless otherwise specified, all parts and percentages are in weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following examples are conventional methods in the art unless otherwise specified.

[0050] The structural parts of "3C" products are generally small and precise parts with complex three-dimensional structures, and they bear the requirements of smooth operation and structural reliability of the mechanism. Therefore, the requirements for materials are multi-dimensional. The preparation process is required to be convenient for forming precise and complex structures to provide greater freedom in structural design, and there are also relatively high requirements for the strength (such as yield strength and tensile strength) and toughness (such as elongation) of the materials.

[0051] In this specific embodiment, it is aimed to provide a stainless steel material with higher strength and better toughness for injection molding to form a steel structure body. When the yield strength of the formed steel structure body is greater than 2100 MPa, the elongation is greater than 5%.

[0052] Testing methods for tensile strength, yield strength, and elongation: The material is injection-molded and sintered into mechanical property tensile test specimens, and tested according to the national standard for tensile testing of metallic materials GB / T 228.1-2010. The diameter of the sintered specimen is Ф3.20±0.05, and the gauge length of the specimen is 25mm; the elongation is calculated by measuring the length after fracture; the tensile strength and yield strength are collected by the microcomputer of the testing machine.

[0053] Testing method for impact toughness: The material is injection-molded and sintered into Charpy impact test specimens, and tested according to the national standard for non-notched impact specimens of sintered metallic materials (excluding hard alloys) GB / T 5318-2017.

[0054] The core of the present invention is to provide a high-toughness and high-strength stainless steel raw material, which is composed of the following chemical elements: Cr 6.0-8.0 wt%, Ni 6.0-9.0 wt%, Co 14.0-18.0 wt%, Mo 5.5-6.5 wt%, Nb 0.05-0.5 wt%, V 0.05-0.5 wt%, C≤0.03 wt%, the balance is Fe, and inevitable impurity elements. Inevitable impurity elements such as Mn, Si, P, S and other elements.

[0055] In some embodiments, the mass percentage contents of Cr, Ni, Co, Mo, and Nb elements are: Cr 6.0-6.8 wt%, Ni 7.5-9.0 wt%, Co 15.5-18.0 wt%, Mo 5.5-6.5 wt%, Nb 0.05-0.5 wt%, V 0.05-0.5 wt%.

[0056] In some embodiments, the mass percentage contents of Cr, Ni, Co, and Mo elements are: Cr 7.0-8.0 wt%, Ni 6.0-7.5 wt%, Co 15.5-18.0 wt%, Mo 5.5-6.5 wt%, Nb 0.05-0.5 wt%, V 0.05-0.5 wt%.

[0057] Using the above high-toughness and high-strength stainless steel raw material, a steel structure body with a specific structure is prepared by a metal injection molding process, and the method is as follows:

[0058] (1) Preparation of raw materials:

[0059] Prepare stainless steel raw materials and a binder. The stainless steel raw materials are the above-mentioned high-toughness and high-strength stainless steel raw materials, containing 6.0 - 8.0 wt% Cr, 6.0 - 9.0 wt% Ni, 14.0 - 18.0 wt% Co, 5.5 - 6.5 wt% Mo, 0.05 - 0.5 wt% Nb, 0.05 - 0.5 wt% V, C ≤ 0.03 wt%, with the balance being Fe and inevitable impurity elements. The stainless steel raw materials can be in the form of pre-alloyed powder or pure metal powder. The powder raw materials can be prepared by atomization method, reduction method, mechanical grinding method, etc. The powder size D90 is less than 40 μm, especially between 0.5 and 40 μm, and more preferably 2 to 18 μm, which can be adjusted accordingly as needed.

[0060] Any available metal powder binder can be used as the binder, such as an organic binder. The role of the binder is to form the metal powder particles and enable injection into various complex-structured parts, making the mixture have rheological properties and lubricity after heating. The binder is the carrier that drives the powder to flow. However, the presence of the organic binder will affect the properties of the steel. Therefore, the requirements for the binder are as follows: ① Use less amount, and a smaller amount of binder can make the mixture have better rheological properties; ② Do not react, and do not undergo any chemical reaction with the metal powder during the process of removing the binder; ③ Easy to remove, and it is easy to remove in the subsequent debinding process without residue in the product.

[0061] The addition ratio of the stainless steel raw materials and the binder depends on the actual situation. Generally, the mass ratio of the stainless steel raw materials to the binder added is 9 - 11:1.

[0062] (2) Feed preparation: Mix the above-mentioned high-toughness and high-strength stainless steel raw material powder with the binder, and mix and granulate in a plasticizing internal mixer under the temperature condition of 170 - 190 °C to make a cylindrical metal powder feed with a length of 3 - 6 mm.

[0063] (3) Injection molding: Make the above-mentioned metal powder feed into a green body in an injection molding machine.

[0064] (4) Catalytic debinding: In a special catalytic debinding furnace for injection molding, use nitric acid or oxalic acid to conduct catalytic debinding on the green body. The temperature condition for nitric acid debinding is 110 °C ± 5 °C, and the temperature condition for oxalic acid debinding is 130 °C ± 5 °C.

[0065] (5) Thermal debinding and sintering: Conduct thermal debinding and sintering on the acid-debound green body in a negative-pressure sintering furnace for MIM. The sintering temperature range is 1360 - 1380 °C.

[0066] (6) Solution heat treatment: The sintered green compact is heated in a vacuum environment at a heating rate of 5 - 10 °C / min to 1040 °C - 1085 °C, held for 60 - 120 min, and then quenched to room temperature with high-pressure gas at 6 atm - 10 atm;

[0067] (7) Age hardening: The samples after solution heat treatment are aged at 530 - 540 °C for 4 - 6 h; or aged at 540 - 550 °C for 4 - 6 h.

[0068] The steel structure part is made by the above method, so that the steel structure part has high strength and high ductility, is not prone to fracture and deformation, and has a long service life.

[0069] In this specific embodiment, a steel structure part is also provided. The material used for the steel structure part includes the above-mentioned steel. The material used for the steel structure part includes the above-mentioned stainless steel raw material, which increases the strength and toughness of the steel structure part. This steel structure part does not need to increase the thickness of the steel structure part to further ensure the reliability of the steel structure part, which is beneficial to the miniaturization of the steel structure part.

[0070] In this specific embodiment, the application of the above-mentioned high-toughness and high-strength stainless steel raw material and steel structure body is also provided, which is mainly used in applications such as 3C products, automotive products, aerospace products, and medical products.

[0071] 3C products usually include hardware devices such as smart phones, tablet computers, laptop computers, digital cameras, etc. Emerging consumer electronic devices include smart wearable devices, unmanned aerial vehicles, etc. It is usually used for precision and complex parts such as power interface parts, card tray camera rings, and buttons in 3C products.

[0072] Automotive products use some complex-shaped, bimetallic parts and groups of micro-miniature parts produced by the MIIM process, such as turbocharger parts, adjusting rings, fuel injector parts, blades, gearboxes, power steering components, etc.

[0073] Automotive products use the MIIM process to produce, for example, a large number of fasteners, screws, seat belt components, wing flap screw seals, micro switches, connectors, solenoids, radiators, optical connectors, and patch panels, etc.

[0074] Medical products are produced by the MIIM process, such as surgical knife handles, scissors, forceps, dental parts, orthopedic joint parts, etc.

[0075] The above specific applications are only listed and do not limit the protection scope of the present invention.

[0076] The following is further elaborated through various embodiments.

[0077] Example 1

[0078] A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0079] Cr 6.1 wt%, Ni 8.7 wt%, Co 16.5 wt%, Mo 5.6 wt%, Nb 0.45 wt%, V 0.09 wt%, the balance is Fe, and inevitable impurity elements.

[0080] Example 2

[0081] A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0082] Cr 6.8 wt%, Ni 7.8 wt%, Co 15.7 wt%, Mo 6.3 wt%, Nb 0.08 wt%, V 0.46 wt%, the balance is Fe, and inevitable impurity elements.

[0083] Example 3

[0084] A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0085] Cr 6.6 wt%, Ni 8.0 wt%, Co 17.6 wt%, Mo 6.0 wt%, Nb 0.3 wt%, V 0.15 wt%, the balance is Fe, and inevitable impurity elements.

[0086] Example 4

[0087] A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0088] Cr 7.9 wt%, Ni 6.2 wt%, Co 17.7 wt%, Mo 5.7 wt%, Nb 0.47 wt%, V 0.10 wt%, the balance is Fe, and inevitable impurity elements.

[0089] Example 5

[0090] A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0091] Cr 7.3 wt%, Ni 7.3 wt%, Co 15.6 wt%, Mo 6.4 wt%, Nb 0.28 wt%, V 0.21 wt%, the balance is Fe, and inevitable impurity elements.

[0092] Example 6

[0093] A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0094] Cr 7.6 wt%, Ni 6.4 wt%, Co 16.2 wt%, Mo 6.1 wt%, Nb 0.15 wt%, V 0.43 wt%, the balance is Fe, and inevitable impurity elements.

[0095] Comparative Example 1

[0096] A martensitic stainless steel raw material, consisting of the following chemical elements:

[0097] Cr 9.2 wt%, Ni 7.4 wt%, Co 15.3 wt%, Mo 5.8 wt%, Nb 0.32 wt%, V 0.23 wt%, the balance is Fe, and inevitable impurity elements.

[0098] Comparative Example 2

[0099] Cr 6.5 wt%, Ni 5.2 wt%, Co 14.5 wt%, Mo 5.9 wt%, Nb 0.25 wt%, V 0.31 wt%, the balance is Fe, and inevitable impurity elements.

[0100] Comparative Example 3

[0101] A stainless steel raw material, consisting of the following chemical elements:

[0102] Cr 6.8 wt%, Ni 7.3 wt%, Co 20.4 wt%, Mo 6.4 wt%, Nb 0.48 wt%, V 0.25 wt%, the balance is Fe, and inevitable impurity elements.

[0103] Comparative Example 4

[0104] A stainless steel raw material, consisting of the following chemical elements:

[0105] Cr 7.3 wt%, Ni 7.6 wt%, Co 16.2 wt%, Mo 7.5 wt%, Nb 0.37 wt%, V 0.19 wt%, the balance is Fe, and inevitable impurity elements.

[0106] Comparative Example 5

[0107] A stainless steel raw material, consisting of the following chemical elements:

[0108] Cr 7.5 wt%, Ni 6.7 wt%, Co 17.1 wt%, Mo 6.2 wt%, Nb 0.55 wt%, V 0.19 wt% the balance is Fe, and inevitable impurity elements.

[0109] Comparative Example 6

[0110] Cr 6.3 wt%, Ni 8.5 wt%, Co 16.8 wt%, Mo 5.8 wt%, Nb 0.40 wt%, the balance being Fe, and inevitable impurity elements.

[0111] Comparative Example 7

[0112] Cr 6.5 wt%, Ni 8.3 wt%, Co 16.7 wt%, Mo 5.9 wt%, Nb 0.32 wt%, V 1.02 wt%, the balance being Fe, and inevitable impurity elements.

[0113] Example 7

[0114] A preparation method for a high-toughness and high-strength steel structure member:

[0115] (1) Raw material preparation:

[0116] Prepare high-toughness and high-strength stainless steel raw materials and a binder, and use the atomization method to prepare metal powders with a particle size of D95 30 μm.

[0117] The binder used is a binder with a composition of POM, EVA, PE, PP, CW, SA in a weight ratio of 78:1:4:2:2:1.

[0118] (2) Feed preparation: Mix the above-mentioned high-toughness and high-strength stainless steel raw material powders and the binder in a mass ratio of 10:1, and mix and granulate them in a plasticizing internal mixer under the temperature condition of 170 °C to make cylindrical metal powder feeds with a length of 4 mm;

[0119] (3) Injection molding: Inject and mold the above-mentioned metal powder feeds in an injection molding machine to form a green test bar, with a molding temperature of 180 °C and a molding pressure of 85 MPa.

[0120] (4) Catalytic debinding: In a special catalytic debinding furnace for injection molding, use nitric acid to perform catalytic debinding on the green body; the temperature condition for nitric acid debinding is 112 °C, and the debinding time is 7 h.

[0121] (5) Thermal debinding and sintering: Perform thermal debinding and sintering on the catalytically debound green body in a negative-pressure sintering furnace for MIM, with a sintering temperature of 1375 °C and a sintering time of 5 h.

[0122] (6) Solution heat treatment: Heat the sintered green body in a vacuum environment to 1050 °C at a heating rate of 8 °C / min, hold for 75 min, and then quickly cool to room temperature with high-pressure nitrogen gas at 7 atm;

[0123] (7) Aging treatment: The sample after solution heat treatment is subjected to aging treatment at 535 °C, hold for 4 h, to obtain a steel structure member.

[0124] Example 8

[0125] A preparation method for a high-toughness and high-strength steel structural member:

[0126] (1) Raw material preparation:

[0127] Prepare high-toughness and high-strength stainless steel raw materials and a binder, and use the atomization method to prepare metal powder with a particle size of D95 30μm powder.

[0128] The binder used is a binder with a composition of POM, EVA, PE, PP, CW, and SA in a weight ratio of 78:1:4:2:2:1.

[0129] (2) Feed preparation: Mix the above-mentioned high-toughness and high-strength stainless steel raw material powder and the binder in a mass ratio of 10:1, and mix and granulate in a plasticizing internal mixer under the temperature condition of 170°C to make a cylindrical metal powder feed with a length of 4 mm;

[0130] (3) Injection molding: Inject the above-mentioned metal powder feed in an injection molding machine to form a green test strip, with a molding temperature of 180°C and a molding pressure of 85 MPa.

[0131] (4) Catalytic debinding: In a special catalytic debinding furnace for injection molding, use nitric acid to perform catalytic debinding on the green body; the temperature condition for nitric acid debinding is 112°C, and the debinding time is 7 h.

[0132] (5) Thermal debinding and sintering: Perform thermal debinding and sintering on the catalytically debound green body in a negative pressure sintering furnace for MIM, with a sintering temperature of 1375°C and a sintering time of 5 h.

[0133] (6) Solution heat treatment: Heat the sintered green body in a vacuum environment at a heating rate of 8°C / min to 1050°C, hold for 75 min, and then rapidly cool to room temperature with high-pressure nitrogen gas at 7 atm;

[0134] (7) Aging treatment: The sample after solution heat treatment is subjected to aging treatment at 545°C, hold for 4 h, to obtain a steel structural member.

[0135] For the stainless steel raw materials of Examples 1-6 and Comparative Examples 1-8, the preparation methods of Examples 7-8 are respectively adopted, and the performance test results (yield strength and elongation) of the obtained steel structural members are shown in Table 1 below:

[0136] Table 1 Performance test results of the steel structural members corresponding to the preparation methods of each example and each comparative example using the preparation method of Example 7 (aging treatment at 535°C, hold for 4 h)

[0137]

[0138] Note: " / " represents brittle fracture of the material, and the yield strength cannot be tested.

[0139] Table 2 shows the performance test results of the steel structure parts corresponding to the preparation methods of each example and each comparative example using Example 8 (aging treatment at 545 °C for 4 h).

[0140]

[0141] In summary, the materials of each example are the stainless steel materials of the present invention. The obtained steel structure parts have excellent plasticity. Within the composition range described in the present invention, steel structure parts with a yield strength of about 2100 MPa and an elongation rate of more than 5% can be obtained. At the same time, the impact toughness of the steel is also significantly improved and can reach 120 J / cm. 2 Above. The temperature of the aging treatment can also be changed to obtain high-toughness steel structure parts with a yield strength of about 1900 MPa and an elongation rate of more than 7%. It can be applied to aerospace, medical devices, especially the application scenarios in "3C" intelligent wearable devices that require both high strength and high toughness.

[0142] In this specification, each example is described in a progressive manner. The key point of each example is to illustrate the differences from other examples. The same or similar parts among the examples can be referred to each other. For the devices disclosed in the examples, since they correspond to the methods disclosed in the examples, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0143] The high-toughness and high-strength stainless steel raw materials, steel structure parts, and their preparation methods and applications provided by the present invention have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The descriptions of the above examples are only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A stainless steel material for metal injection molding processing, characterized in that, Composed of the following chemical elements: Cr 6.0 - 8.0 wt%, Ni 6.0 - 9.0 wt%, Co 14.0 - 18.0 wt%, Mo 5.5 - 6.5 wt%, Nb 0.05 - 0.5 wt%, V 0.05 - 0.5 wt%, C ≤ 0.03 wt%, the balance is Fe, and inevitable impurity elements.

2. The stainless steel material according to claim 1, characterized in that, The mass percentage contents of Cr, Ni, Co, Mo, Nb, and V elements are: Cr 6.0 - 6.8 wt%, Ni 7.5 - 9.0 wt%, Co 15.5 - 18.0 wt%, Mo 5.5 - 6.5 wt%, Nb 0.05 - 0.5 wt%, V 0.05 - 0.5 wt%.

3. The stainless steel material according to claim 1, characterized in that The mass percentage contents of Cr, Ni, Co, Mo, Nb, and V elements are: Cr 7.0 - 8.0 wt%, Ni 6.0 - 7.5 wt%, Co 15.5 - 18.0 wt%, Mo 5.5 - 6.5 wt%, Nb 0.05 - 0.5 wt%, V 0.05 - 0.5 wt%.

4. The application of a stainless steel material for metal injection molding processing according to claim 1, which is used to manufacture 3C products and their components through metal injection molding processing.

5. A steel structure member, characterized in that, Formed by using the stainless steel material for metal injection molding processing according to any one of claims 1 - 3 through a metal injection molding process.

6. The preparation method of the steel structure member according to claim 5, characterized in that Including the following steps: S1: Mix the stainless steel material with a binder and granulate to obtain a feedstock granule raw material; S2: Inject the feedstock granule raw material into a green body; S3: Catalytically debind the green body; S4: After catalytic debinding, the green body is thermally debound and sintered in a negative pressure environment to obtain a sintered part, and the sintering temperature range is 1350 - 1370 °C; S5: The sintered part is successively subjected to solution treatment and vacuum aging treatment to obtain the steel structure part.

7. The preparation method according to claim 6, characterized in that, In step S5, the aging treatment operation is: aging treatment is carried out at 490 - 515 °C for 4 - 6 h; or aging treatment is carried out at 540 - 560 °C for 4 - 6 h.

8. The preparation method according to claim 6, wherein In step S5, the solution treatment operation is: in a vacuum environment, it is heated to 1040 °C - 1085 °C at a heating rate of 5 - 10 °C / min, held for 60 - 120 min, and then quenched to room temperature with a high-pressure inert gas of 6 - 10 atm.

9. A steel structure member, characterized in that, Formed by using the preparation method according to any one of claims 6 - 8.

10. The steel structure member according to claim 9, wherein, The yield strength of this steel structure part is between 2000 MPa and 2100 MPa, and the elongation is more than 5%; or the yield strength is greater than 1800 Mpa to 1900 MPa, and the elongation is more than 7%.

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