High-toughness ultrahigh-strength martensitic stainless steel material, and manufacturing method therefor and use thereof

Abstract

The present invention relates to the technical field of powder metallurgy materials and intelligent manufacturing, and relates to a high-toughness ultrahigh-strength martensitic stainless steel material, and a manufacturing method therefor and a use thereof. The material is composed of the following chemical elements: 7.0-9.0 wt% of Cr, 7.1-9.0 wt% of Ni, 9.0-14.0 wt% of Co, 5.5-7.0 wt% of Mo, 0.05-0.5 wt% of Nb, less than or equal to 0.03 wt% of C, the balance being Fe, and inevitable impurity elements. According to the material of the present invention, by using an injection molding process, the yield strength of the martensitic stainless steel reaches 1900 MPa or above, and the elongation is greater than 5%, and particularly, the elongation is greater than 5% while the yield strength is greater than 2000 MPa.

Description

A high-toughness, ultra-high-strength martensitic stainless steel material and its preparation method and application Technical Field

[0001] The present invention belongs to the field of powder metallurgy materials and intelligent manufacturing technology, and relates to a metal material, in particular to a high-toughness, ultra-high-strength martensitic stainless steel material, and a preparation method and application thereof. Background Art

[0002] Metal Injection Molding (MIM) is a novel powder metallurgy near-net-shape forming technology derived from the powder metallurgy and plastic injection molding industries. In recent years, this technology has evolved to maximize the solid particle content and completely remove the binder during the subsequent sintering process, resulting in densification of the preform. The basic MIM process involves selecting metal powder and a binder that meet MIM requirements. The powder and binder are then mixed into a uniform feed using an appropriate method at a specific temperature. After granulation, the feed is then injection molded. The resulting preform is then degreased and sintered to densify it into the final product.

[0003] MIM can produce metal parts with complex shapes, including small internal structures, thin-walled structures, and precise holes. It can also achieve highly precise forming with excellent dimensional control and surface quality. Therefore, MIM has been widely used in the manufacture of parts with high precision requirements.

[0004] In the "3C" (3C) application sector, particularly in foldable phones and computers, high-strength martensitic steels and ultra-high-strength steels are being used in foldable hinge designs to achieve lightweight wearable devices. Due to the complex structure of these components, they are generally designed and manufactured using metal injection molding. However, the sintered density of injection-molded sintered parts generally only reaches 96% to 99.5% of the theoretical density, failing to reach the density of cast materials, and further improvement in material properties through hot and cold deformation (calendering, forging) is not possible. Therefore, even ultra-high-strength steel materials produced by injection molding have a porosity of 0.5-3% within the sintered matrix. Hot isostatic pressing (HIP) can reduce this porosity to near zero and increase the density to near theoretical density. However, this method significantly increases processing costs, making it difficult to achieve low-cost, large-scale production.

[0005] At present, many patents on injection molded ultra-high strength steel generally only focus on the yield strength of the material, while its elongation is far from enough valued in material development. This void in the matrix of injection molded sintered materials is itself a defect of the material. Compared with materials with a density of 100% such as casting and forging, its performance such as strength and elongation has declined significantly, especially the elongation of the material. In practical applications, even for materials with an elongation of 5%, due to the presence of sintering voids, the material is still likely to fracture brittlely, and the material cannot pass the drop test. For example, for a material with a yield strength of 1500MPa, the impact value of a material with an elongation of 5% is only 8J / cm compared to a material with an elongation of 8%. 2 , while the latter can reach 40J / cm 2 In the tensile fracture test, the former is close to brittle fracture, while the latter is generally plastic fracture with diameter-shrinkage dimples.

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

[0007] However, due to the widespread voids in the matrix of injection-molded sintered materials, this common material defect makes it very difficult to improve the elongation and toughness of injection-molded ultra-high-strength steel. Once the material's elongation is above 6%, further improvement in elongation becomes very difficult.

[0008] In the prior art, the injection molding materials are described as follows.

[0009] CN103981436A discloses a high-strength maraging steel produced by metal powder injection molding and a method for manufacturing the same. The maraging steel comprises, by weight, 17-19% Ni, 8-10% Co, 4.5-6.5% Mo, and ≤0.08% C, with the remainder being iron and unavoidable impurities. This results in a tensile strength exceeding 1500 MPa, an elongation exceeding 10%, and an impact strength of 50 J / cm. 2 Above, the hardness of the material is HRC40-48.

[0010] The low-cobalt martensitic stainless steel powder disclosed in CN114480943A has the following chemical composition, by mass percentage: Ni: 9-13%, Mo: 9-13%, Co: 4-8%, Ti: 1.5-2.5%, Al: 1-2%, Nb: 0.2-0.5%, Mn: <1%, C: ≤0.03%, O: ≤0.03%, and Fe: the balance. It has a tensile strength of approximately 2050 MPa and an elongation of approximately 5%.

[0011] CN111250694A discloses a method for injection molding high-strength, high-toughness metal parts. The specific metal elements and mass percentages of the alloy powder used are: nickel, 17% to 18%; cobalt, 8.5% to 9.5%; molybdenum, 4.5% to 5.0%; and the balance is iron. The resulting high-strength, high-toughness rotating shaft part has a yield strength of 1350 MPa and an elongation of 6%.

[0012] CN115740427A discloses an MIM powder for 1800 MPa-grade ultra-high-strength, high-toughness steel. The powder comprises the following metal powders by weight: C 0.0-0.6%, Cr 2.0-3.5%, Ni 11.0-14.0%, Co 14.0-17.0%, and Mo 1.5-2.5%. The MIM powder has a particle size of ≤50 μm. By improving the raw material composition, thermal degreasing, and sintering processes, the resulting ultra-high-strength, high-toughness steel parts exhibit a yield strength ≥1800 MPa, an elongation ≥5%, and a hardness of 52-58 HRC.

[0013] WO2023025252A1 discloses steel, steel structures, electronic equipment, and methods for manufacturing steel structures. The steel includes Fe (weight percentage >60.67%), Cr (weight percentage 8.01% to 8.99%), Ni (weight percentage 6% to 7%), Co (weight percentage 15.01% to 15.99%), Mo (weight percentage 5.5% to 6.5%), Nb (weight percentage ≤0.5%), O (weight percentage ≤0.3%), and C (weight percentage <0.05%). Steel structures made with this composition have a yield strength of approximately 1900 MPa and an elongation of 4-6%.

[0014] From the above-mentioned prior art, it can be seen that for metal injection molding materials, strength and elongation are important properties that are generally of concern. Generally speaking, the strength of steel products is inversely related to their elongation. In practical applications, steel products usually need to have certain strength and elongation at the same time to meet different requirements. The existing technology is unable to provide high-toughness metal injection molding materials with a yield strength greater than 2000MPa and an elongation greater than 5%. In the "3C" application field, steel structures with such performance are urgently needed. Summary of the Invention

[0015] The purpose of the present invention is to supplement the metal injection molding materials in the prior art and provide a metal injection molding material with a yield strength greater than 1900 MPa, especially a yield strength greater than 2000 MPa, and an elongation greater than 5%.

[0016] A first aspect of the present invention provides a high-toughness and ultra-high-strength martensitic stainless steel material.

[0017] The technical solution adopted by the first aspect of the present invention to solve the technical problem is:

[0018] A high-toughness, ultra-high-strength martensitic stainless steel material composed of the following chemical elements:

[0019] Cr 7.0~9.0wt%, Ni 7.1~9.0wt%, Co 9.0~14.0wt%, Mo 5.5~7.0wt%, Nb 0.05~0.5wt%, C≤0.03wt%, the balance is Fe and inevitable impurity elements.

[0020] Cr primarily contributes to stainless steel's corrosion resistance. Chromium reacts with oxygen to form a stable chromium oxide layer, which prevents the stainless steel surface from reacting with oxygen and water in the environment, thereby protecting the stainless steel from corrosion. Chromium is also a ferritizing element in the material, and excessive chromium content can reduce the material's strength.

[0021] Nickel is also a toughening element in ultra-high-strength stainless steel, improving the fracture resistance of martensitic steel and increasing the material's plasticity and toughness. Nickel can also increase the passivation tendency of stainless steel and improve the corrosion resistance of martensitic stainless steel. However, nickel has a strong tendency to austenitize. Excessive nickel content makes it difficult for the material to form martensitic structure, reducing mechanical properties.

[0022] As an important strengthening element, the Co element promotes the formation of dispersed precipitates 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. A suitably high Co content can increase the martensitic transformation temperature of the material, making it easier to achieve martensitic transformation during the gas quenching process after solution heat treatment, which is beneficial to improving material performance and stability. However, as a practical demand for this kind of martensitic stainless steel with good toughness, the material needs to retain an appropriate retained austenite phase on the basis of the martensitic matrix in order to truly make the material have toughness and ductility on the basis of high strength. Excessive Co content not only promotes the formation of dispersed phase brittleness in a transitional manner, but also prompts the retained austenite to fully transform into martensite, ultimately making the material brittle. Therefore, from a technical perspective, excessive Co content is detrimental to the toughness of the material. Excessive Co content will also increase material costs.

[0023] Mo is the main 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 content will form a brittle phase in the material. While increasing the strength, the toughness of the material is greatly reduced, until it becomes brittle.

[0024] In general, the Fe\Ni\Cr\Co\Mo family of ultra-high-strength martensitic stainless steels is a type of element substitutional solid solution stainless steel. Mo is the core reinforcement, forming a basic solid solution structure of (Fe / Cr / Ni / Co)Mo. The strength and toughness of the material are determined by factors such as the elemental composition ratio, phase structure, grain size, dislocation density, and material defects.

[0025] The present invention also adds Nb to the Fe\Ni\Cr\Co\Mo system. The addition of Nb is generally believed to increase the strength of the material, but excessive Nb addition will reduce the toughness of the material. In this technical solution, 0.05-0.5wt% Nb is added. By adjusting and improving the raw material composition and its content, optimizing the most suitable composition, and combining it with the injection molding process, the yield strength of the martensitic stainless steel reaches above 1900 MPa, while the elongation is greater than 5%, especially the yield strength is greater than 2000 MPa and the elongation is greater than 5%.

[0026] 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 the aging treatment. For example, when the aging temperature range is controlled at 520-535°C, the material yield strength that can be obtained is 1900-2100 MPa, and the elongation is more than 5%. When the aging temperature range is 540-560°C and the vacuum aging is performed for 4-6 hours, the material yield strength that can be obtained is 1600-1800 MPa, and the elongation is more than 8%. According to actual use requirements, the preparation of ultra-high strength or ultra-high toughness performance materials can be selected, which further broadens the scope of use of the material.

[0027] In one embodiment of the present invention, the mass percentages of Cr, Ni, Co, Mo, and Nb are as follows: Cr 7.0-9.0 wt%, Ni 7.5-8.0 wt%, Co 9.5-14.0 wt%, Mo 5.8-6.5 wt%, and Nb 0.15-0.4 wt%. In particular, when the Ni content is between 7.5 and 8.0 wt%, the material exhibits a yield strength greater than 2000 MPa and an elongation greater than 5%.

[0028] In one embodiment of the present invention, the mass percentage contents of Cr, Ni, Co, and Mo are: Cr 8.0-9.0 wt%, Ni 7.5-8.0 wt%, Co 9.5-14.0 wt%, Mo 5.8-6.5 wt%, and Nb 0.2-0.4 wt%.

[0029] In one embodiment of the present invention, the mass percentage contents of Cr, Ni, Co, and Mo are: Cr 8.0-9.0 wt%, Ni 7.5-7.8.0 wt%, Co 10.0-13.0 wt%, Mo 6.0-6.5 wt%, and Nb 0.2-0.35 wt%.

[0030] A second aspect of the present invention provides a steel structure, which is formed by a metal injection molding process using the high-toughness and high-strength stainless steel raw material mentioned above.

[0031] The above-mentioned steel structure has a yield strength of 1900 MPa to 2100 MPa and an elongation of more than 5%, or a yield strength of greater than 1600 MPa to 1800 MPa and an elongation of more than 8%, especially 8% to 9%.

[0032] A third aspect of the present invention provides a method for preparing a steel structure, comprising the following steps:

[0033] S1: A high-toughness, high-strength stainless steel powder raw material with a particle size D90 less than 40 microns is mixed with a binder such as POM to form a granular feed material; the high-toughness, high-strength stainless steel raw material is composed of the following chemical elements: Cr 7.0-9.0wt%, Ni 7.1-9.0wt%, Co 9.0-14.0wt%, Mo 5.5-7.0wt%, C ≤ 0.03wt%, Nb 0.05-0.5wt%, with the balance being Fe and unavoidable impurity elements;

[0034] S2: injection molding the granular raw material into a green body;

[0035] S3: catalytically debinding the green body;

[0036] S4: After catalytic debinding, the green body is subjected to thermal debinding and sintering in a negative pressure environment to obtain a sintered part. The sintering temperature range is 1360~1380℃.

[0037] S5: The sintered component is subjected to solution treatment and vacuum aging treatment in sequence to obtain the steel structure component.

[0038] In one embodiment of the present invention, in step S5, the vacuum aging treatment is performed at 520-535° C. for 4-6 hours; or at 540-560° C. for 4-6 hours.

[0039] In one embodiment of the present invention, in step S1, the granulation temperature is 175-200°C.

[0040] In one embodiment of the present invention, in step S5, the solution treatment operation is: heating to 1040-1085°C at a heating rate of 5-10°C / min under a vacuum environment, keeping the temperature for 60-120 minutes, and then quenching to room temperature with high-pressure gas.

[0041] In one embodiment of the present invention, in step S5, high-pressure inert gas at 6 atm to 10 atm is used for gas quenching to room temperature. The inert gas is nitrogen or argon.

[0042] 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.

[0043] A fourth aspect of the present invention provides a steel structure member manufactured using the above-mentioned preparation method.

[0044] In one embodiment of the present invention, the steel structure has a yield strength of 1900 MPa to 2100 MPa and an elongation of 5% or more, or has a yield strength of 1600 MPa to 1800 MPa and an elongation of 8% or more, particularly 8% to 9%.

[0045] The fifth aspect of the present invention provides applications of the above-mentioned high-toughness and high-strength stainless steel raw materials and the above-mentioned steel structural parts in 3C products, automotive products, aviation products, and medical products.

[0046] In particular, the application of the above-mentioned high-toughness and high-strength stainless steel raw materials and the above-mentioned steel structural parts in the manufacturing of 3C products and their components.

[0047] The "3C products" referred to in this invention are a collective term for computer, communication, and consumer electronic products, also known as "information appliances." Examples include computers, tablet computers, mobile phones, and digital audio players. These products have complex structures and require high precision, strength, and toughness. The stainless steel of this invention is particularly suitable for use in these fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG1 is a tensile curve diagram of the steel structure provided by Example 9 according to Example 3 of the present invention.

[0049] FIG2 is a tensile curve diagram of the steel structure provided by Example 10 according to Example 3 of the present invention.

[0050] Figure 3 is a scanning electron microscopy (EBSD) image of a steel structure provided in Example 3 of the present invention. The lower half is a partial enlargement of the upper half. The image shows a certain proportion of retained austenite within the martensite matrix.

[0051] Figure 4 shows a scanning electron microscopy (EBSD) image of the steel structure provided in Comparative Example 1 of the present invention. The lower half is a partial magnification of the upper half. The image shows that the material is primarily martensite, with very little retained austenite. Implementation Method

[0052] The technical solution of the present invention will be further described in detail below through specific examples. It should be understood that the implementation of the present invention is not limited to the following examples, and any formal modifications and / or changes made to the present invention will fall within the scope of protection of the present invention. The parameter ranges involved include endpoint values ​​unless otherwise specified.

[0053] In the present invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. The methods in the following examples are all conventional methods in the art unless otherwise specified.

[0054] The structural components of "3C" products are generally small precision parts with complex three-dimensional structures. They are responsible for the smooth operation of the mechanism and the reliability of the structure. Therefore, the requirements for materials are multi-dimensional. The preparation process is required to facilitate the formation of precise and complex structures to provide greater freedom in structural design. There are also high requirements for the strength (such as yield strength and tensile strength) and toughness (such as elongation) of the material.

[0055] In this specific embodiment, a stainless steel material with higher strength and better toughness is provided for use in injection molding to form a steel structure. The yield strength of the formed steel structure is greater than 1900 MPa and the elongation is greater than 7%.

[0056] Tensile strength, yield strength, and elongation testing methods: Materials are injected and sintered into mechanical tensile test bars. Testing is performed according to the national standard for tensile testing of metallic materials, GB / T228.1-2010. The sintered bars have a diameter of 3.20 ± 0.05 mm and a standard length of 25 mm. Elongation is calculated by measuring the fracture length. Tensile strength and yield strength are recorded using a microcomputer on the testing machine.

[0057] The core of the present invention is to provide a high-toughness and high-strength stainless steel raw material composed of the following chemical elements:

[0058] Cr 7.0~9.0wt%, Ni 7.1~9.0wt%, Co 9.0~14.0wt%, Mo 5.5~7.0wt%, Nb 0.05~0.5wt%, C ≤ 0.03wt%, the balance is Fe and unavoidable impurity elements. Unavoidable impurity elements such as Mn, Si, P, S, etc.

[0059] In some embodiments, the mass percentage contents of Cr, Ni, Co, Mo, and Nb are: Cr 7.0-9.0 wt%, Ni 7.5-8.0 wt%, Co 9.5-14.0 wt%, Mo 5.8-6.5 wt%, and Nb 0.15-0.4 wt%.

[0060] In some embodiments, the mass percentage contents of Cr, Ni, Co, and Mo elements are: Cr 8.0-9.0 wt%, Ni 7.5-8.0 wt%, Co 9.5-14.0 wt%, Mo 5.8-6.5 wt%, and Nb 0.2-0.4 wt%.

[0061] In some embodiments, the mass percentage content of Cr, Ni, Co, and Mo is: Cr 8.0-9.0wt%, Ni 7.5-8.0wt%, Co 10.0-13.0wt%, Mo 6.0-6.5wt%, and Nb 0.2-0.35wt%. The above high-toughness and high-strength stainless steel raw material is used to prepare a steel structure with a specific structure through a metal injection molding process, as follows:

[0062] (1) Raw material preparation:

[0063] Prepare stainless steel raw material and binder. The stainless steel raw material uses the high-toughness, high-strength stainless steel raw material described above, containing 7.0-9.0wt% Cr, 7.0-9.0wt% Ni, 9.0-15.0wt% Co, 5.5-7.0wt% Mo, 0.05-0.5wt% Nb, C ≤ 0.03wt%, the balance being Fe, and unavoidable impurities. The stainless steel raw material can be in the form of pre-alloyed powder or pure metal powder. The powder raw material can be prepared by atomization, reduction, mechanical grinding, or other methods. The powder size D90 is less than 40μm, particularly between 0.5 and 40μm, more preferably between 2 and 18μm, and can be adjusted accordingly as needed.

[0064] Any available binder for metal powders, such as an organic binder, can be used. The binder's function is to shape the metal powder particles and enable injection molding into various complex structural parts. It also imparts rheological and lubricious properties to the mixture after heating, acting as a carrier that drives the powder flow. However, the presence of organic binders can affect the properties of the steel. Therefore, the binder requirements are: 1. Low dosage—a small amount of binder can improve the rheological properties of the mixture; 2. Non-reactive—no chemical reaction with the metal powder during binder removal; and 3. Easy to remove during the subsequent degreasing process, leaving no residue in the finished product.

[0065] The addition ratio of stainless steel raw materials and binders depends on the actual situation. Generally, the mass ratio of stainless steel raw materials and binders is 9-11:1.

[0066] (2) Feed preparation: The high-toughness and high-strength stainless steel raw material powder is mixed with a binder, and granulated in a plasticizing internal mixer at a temperature of 170-190°C to prepare a cylindrical metal powder feed with a length of 3-6 mm;

[0067] (3) Injection molding: The above metal powder is fed into an injection molding machine to form a green body;

[0068] (4) Catalytic degreasing: In a special catalytic degreasing furnace for injection molding, the green body is catalytically degreased with nitric acid or oxalic acid; the temperature condition for nitric acid degreasing is 110℃±5℃, and the temperature condition for oxalic acid degreasing is 130℃±5℃;

[0069] (5) Thermal debinding and sintering: The acid-debinded green body is thermally debinded and sintered in a MIM negative pressure sintering furnace. The sintering temperature range is 1360~1380℃.

[0070] (6) Solution heat treatment: The sintered green body is heated to 1040-1085°C in a vacuum environment at a heating rate of 5-10°C / min, kept at this temperature for 60-120 min, and then quenched to room temperature using high-pressure gas at 6atm-10atm;

[0071] (7) Age hardening: After solution heat treatment, the sample is aged at 520~535℃ for 4~6h; or aged at 540~560℃ for 4~6h.

[0072] The steel structure is manufactured by the above method, so that the steel structure has high strength and high ductility, is not prone to breakage and deformation, and has a long service life.

[0073] This embodiment also provides a steel structure, wherein the material used for the steel structure includes the aforementioned steel. The steel structure, which includes the aforementioned stainless steel raw material, increases the strength and toughness of the steel structure. This eliminates the need to increase the thickness of the steel structure to further ensure its reliability, thereby facilitating miniaturization of the steel structure.

[0074] In this specific embodiment, the application of the above-mentioned high-toughness and high-strength stainless steel raw materials and steel structures is also provided, which are mainly used in applications in 3C products, automotive products, aviation products, medical products, etc.

[0075] 3C products typically include hardware devices such as smartphones, tablets, laptops, and digital cameras, while emerging consumer electronics devices include smart wearable devices and drones. These components are typically used for sophisticated and complex components such as power connectors, card trays, camera rings, and buttons within 3C products.

[0076] Some automotive products use MIIM technology to produce complex-shaped, bimetallic parts and grouped micro parts, such as turbocharger parts, adjustment rings, fuel injector parts, blades, gearboxes, power steering components, etc.

[0077] Automotive products produced using the MIIM process include a large number of fasteners, screws, seat belt components, wing flap screw seals, micro switches, connectors, solenoids, heat sinks, optical connectors and patch panels.

[0078] Medical products are produced using the MIIM process, such as surgical knife handles, scissors, tweezers, dental parts, orthopedic joint parts, etc.

[0079] The above specific applications are merely examples and do not limit the scope of protection of the present invention.

[0080] The invention is further described below through various embodiments. Example 1 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0081] Cr 7.0wt%, Ni 8.0wt%, Co 9.0wt%, Mo 6.2wt%, Nb 0.05wt%, C 0.015wt%, the balance is Fe and inevitable impurity elements. Example 2 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0082] Cr 7.0wt%, Ni 7.1wt%, Co 10.3wt%, Mo 5.5wt%, Nb 0.5wt%, C 0.01wt%, the balance is Fe and inevitable impurity elements. Example 3 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0083] Cr 8.5wt%, Ni 7.5wt%, Co 10.5wt%, Mo 6.0wt%, Nb 0.3wt%, C 0.012wt%, the balance is Fe and inevitable impurity elements. Example 4 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0084] Cr 8.5wt%, Ni 7.5wt%, Co 14.0wt%, Mo 6.5wt%, Nb 0.32wt%, C 0.01wt%, the balance is Fe and inevitable impurity elements. Example 5 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0085] Cr 9.0wt%, Ni 8.0wt%, Co 11.0wt%, Mo 6.6wt%, Nb 0.28wt%, C≤0.02wt%, the balance is Fe, and inevitable impurity elements. Example 6 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0086] Cr 8.0wt%, Ni 7.5wt%, Co 13.2wt%, Mo 6.0wt%, Nb 0.25wt%, C≤0.02wt%, the balance is Fe, and inevitable impurity elements. Example 7 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0087] Cr 8.0wt%, Ni 7.8wt%, Co 14.0wt%, Mo 6.4wt%, Nb 0.25wt%, C≤0.02wt%, the balance is Fe, and inevitable impurity elements. Example 8 A high-toughness and high-strength stainless steel material is composed of the following chemical elements:

[0088] Cr 7.8wt%, Ni 9.0wt%, Co 12.0wt%, Mo 7.0wt%, Nb 0.22wt%, C≤0.03wt%, the balance is Fe, and inevitable impurity elements.

[0089] Comparative Example 1

[0090] A martensitic stainless steel raw material composed of the following chemical elements:

[0091] Cr 8.5wt%, Ni 6.5wt%, Co 15.5wt%, Mo 6.0wt%, Nb 0.32wt%, C 0.005wt%, the balance is Fe and inevitable impurity elements.

[0092] Comparative Example 2

[0093] Cr 7.0wt%, Ni 8.0wt%, Co 9.0wt%, Mo 6.0wt%, C 0.015wt%, the balance is Fe, and inevitable impurity elements.

[0094] Comparative Example 3

[0095] A stainless steel raw material composed of the following chemical elements:

[0096] Cr 6.5wt%, Ni 6.5wt%, Co 9.0wt%, Mo 6.3wt%, Nb 0.25wt%, C 0.015wt%, the balance is Fe and inevitable impurity elements.

[0097] Comparative Example 4

[0098] A stainless steel raw material composed of the following chemical elements:

[0099] Cr 7.0wt%, Ni 9.3wt%, Co 9.0wt%, Mo 5.7wt%, Nb 0.05wt%, C 0.015wt%, the balance is Fe and inevitable impurity elements.

[0100] Comparative Example 5

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

[0102] Cr 7.8wt%, Ni 9.1wt%, Co 12.0wt%, Mo 7.5wt%, C 0.015wt%, Nb 0.22wt%, the balance being Fe and inevitable impurity elements.

[0103] Example 9 A method for preparing a high-toughness and high-strength steel component:

[0104] (1) Raw material preparation:

[0105] Prepare high-toughness and high-strength stainless steel raw materials and binders, and use an atomization method to prepare metal powder with a particle size of D95 30μm.

[0106] The adhesive comprises POM, EVA, PE, PP, CW and SA in a weight ratio of 78:1:4:2:2:1.

[0107] (2) Feed preparation: The high-toughness and high-strength stainless steel raw material powder and the binder are mixed at a mass ratio of 10:1, mixed and granulated in a plasticizing internal mixer at a temperature of 170°C to prepare cylindrical metal powder feed with a length of 4 mm;

[0108] (3) Injection molding: The above metal powder is fed into an injection molding machine and injection molded into a test bar green body. The molding temperature is 180°C and the molding pressure is 85 MPa.

[0109] (4) Catalytic degreasing: In a special catalytic degreasing furnace for injection molding, the green body is catalytically degreased with nitric acid; the temperature condition of nitric acid degreasing is 112 ° C, and the degreasing time is 7 hours.

[0110] (5) Thermal debinding and sintering: The catalytically debinded green body is thermally debinded and sintered in a MIM negative pressure sintering furnace at a sintering temperature of 1375 °C and a sintering time of 5 h.

[0111] (6) Solution heat treatment: The sintered green body was heated to 1050 °C at a rate of 8 °C / min in a vacuum environment, kept at this temperature for 75 min, and then quenched to room temperature using 7 atm high-pressure nitrogen gas.

[0112] (7) Aging treatment: After solution heat treatment, the sample was aged at 530 °C for 4 h to obtain a steel structure.

[0113] Example 10 A method for preparing a high-toughness and high-strength steel component:

[0114] (1) Raw material preparation:

[0115] Prepare high-toughness and high-strength stainless steel raw materials and binders, and use an atomization method to prepare metal powder with a particle size of D95 30μm.

[0116] The adhesive comprises POM, EVA, PE, PP, CW and SA in a weight ratio of 78:1:4:2:2:1.

[0117] (2) Feed preparation: The high-toughness and high-strength stainless steel raw material powder and the binder are mixed at a mass ratio of 10:1, mixed and granulated in a plasticizing internal mixer at a temperature of 170°C to prepare cylindrical metal powder feed with a length of 4 mm;

[0118] (3) Injection molding: The above metal powder is fed into an injection molding machine and injection molded into a test bar green body. The molding temperature is 180°C and the molding pressure is 85 MPa.

[0119] (4) Catalytic degreasing: In a special catalytic degreasing furnace for injection molding, the green body is catalytically degreased with nitric acid; the temperature condition of nitric acid degreasing is 112 ° C, and the degreasing time is 7 hours.

[0120] (5) Thermal debinding and sintering: The catalytically debinded green body is thermally debinded and sintered in a MIM negative pressure sintering furnace at a sintering temperature of 1375 °C and a sintering time of 5 h.

[0121] (6) Solution heat treatment: The sintered green body was heated to 1050 °C at a rate of 8 °C / min in a vacuum environment, kept at this temperature for 75 min, and then quenched to room temperature using 7 atm high-pressure nitrogen gas.

[0122] (7) Aging treatment: After solution heat treatment, the sample was aged at 550 °C for 4 h to obtain a steel structure.

[0123] The high-toughness and high-strength stainless steel raw materials of Examples 1-8 and the comparative examples were prepared using the methods of Examples 9-10, and the performance test results (yield strength and elongation) of the obtained steel structures are shown in Table 1 below:

[0124]

[0125]

[0126] In summary, the stainless steel materials of the present invention used in each embodiment have excellent plasticity in the obtained steel structures. Within the composition range described in the present invention, ultra-high strength and high toughness steel structures with a yield strength greater than 1900 MPa and an elongation of more than 5% can be obtained. The yield strength of Examples 3, 4, 6, and 7 is even greater than 2000 MPa, and the elongation is all above 5%. The temperature of the aging treatment can also be changed to obtain a high-toughness steel structure with a yield strength greater than 1600 MPa and an elongation of more than 8%. It can be used in aerospace, medical equipment, and especially in "3C" smart wearable devices where both high strength and high toughness are required.

[0127] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from the other embodiments. Reference can be made to the descriptions of the identical or similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and the relevant parts can be referred to the descriptions of the methods.

[0128] The above is a detailed introduction to the high-toughness and high-strength stainless steel raw materials, steel structural parts, and their preparation methods and applications provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the methods of the present invention and its core ideas. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A high-toughness ultra-high-strength martensitic stainless steel material, characterized in that: It is composed of the following chemical elements: Cr 7.0~9.0wt%, Ni 7.1~9.0wt%, Co 9.0~14.0wt%, Mo 5.5~7.0wt%, Nb 0.05~0.5wt%, C≤0.03wt%, the balance is Fe, and inevitable impurity elements.

2. The high-toughness and high-strength stainless steel material according to claim 1, characterized in that: The mass percentage contents of Cr, Ni, Co, Mo and Nb elements are: Cr 8.0~9.0wt%, Ni 7.1~8.0wt%, Co 9.5~14.0wt%, Mo 5.7~6.5wt%, and Nb 0.15~0.4wt%.

3. The high-toughness and high-strength stainless steel material according to claim 1, characterized in that: The mass percentage contents of Cr, Ni, Co, Mo and Nb elements are: Cr 8.0~9.0wt%, Ni 7.1~8.0wt%, Co 9.5~14.0wt%, Mo 5.8~6.5wt%, and Nb 0.2~0.4wt%.

4. The high-toughness and high-strength stainless steel material according to claim 1, characterized in that: The mass percentage contents of Cr, Ni, Co, Mo and Nb elements are: Cr 8.0~9.0wt%, Ni 7.1~8.0wt%, Co 10.0~13.0wt%, Mo 6.0~6.4wt%, and Nb 0.2~0.35wt%.

5. Application of the high-toughness ultra-high-strength martensitic stainless steel material as claimed in claim 1 for the manufacture of 3C products and their components.

6. A steel structure, characterized in that: The high-toughness and high-strength stainless steel material according to any one of claims 1 to 4 is formed by a metal injection molding process.

7. The method for preparing a steel structure according to claim 6, characterized in that: The steps include: S1: mixing the high-toughness and high-strength stainless steel raw material with a binder and granulating to obtain a feed granular raw material; S2: injection molding the feed granular raw material into a green body; S3: catalytically degreasing the green body; S4: After catalytic debinding, the green body is subjected to thermal debinding and sintering in a negative pressure environment to obtain a sintered part. The sintering temperature ranges from 1360 to 1380°C. S5: The sintered part is subjected to solution treatment and aging treatment in sequence to obtain the steel structure part.

8. The preparation method according to claim 7, characterized in that In step S5, the aging treatment operation is: aging treatment at 520-535°C for 4-6 hours; or aging treatment at 540-560°C for 4-6 hours.

9. The preparation method according to claim 7, characterized in that: In step S1, the granulation temperature is 175-200°C.

10. The preparation method according to claim 7, characterized in that In step S5, the solution treatment operation is: heating the temperature to 1050°C-1085°C at a heating rate of 5-10°C / min in a vacuum environment, keeping the temperature for 60-120 minutes, and then quenching to room temperature with 6-10atm high-pressure inert gas.

11. The preparation method according to claim 7, characterized in that In step S3, nitric acid or oxalic acid is used to perform catalytic degreasing on 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.

12. A steel structure, made by the preparation method according to any one of claims 7 to 11.

13. The steel structure according to claim 12, characterized in that: The yield strength of the steel structure is 1900~2100MPa, and the elongation is 5% or above; or the yield strength is 1600~1800MPa, and the elongation is 8% or above.

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