Ultrahigh-strength metastable austenitic stainless steel for sheet spring and preparation method and application thereof

Abstract

The invention discloses ultrahigh-strength metastable austenitic stainless steel for a sheet spring and a preparation method and application of the ultrahigh-strength metastable austenitic stainless steel, and belongs to the field of metal material component design and heat treatment. The ultrahigh-strength metastable austenitic stainless steel comprises the following chemical components in percentage by weight: 0.05%-0.3% of C, 0.2%-2% of Si, 0.2%-2% of Mn, 12%-20% of Cr and 5%-10% of Ni, and the content of reversed austenite in a phase structure of the metastable austenitic stainless steel is 10%-23%. According to the ultra-high-strength metastable austenitic stainless steel prepared through the method, 10%-23% of reversed austenite is introduced after short-time annealing treatment, the plasticity is improved, the total elongation rate can be nearly doubled compared with the total elongation rate in a cold rolling state, and therefore the considerable elongation rate is reserved while ultra-high strength is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of metal material composition design and heat treatment, and particularly relates to a super-high strength metastable austenitic stainless steel for leaf springs, and a preparation method and application thereof. Background Art

[0002] As a precision component, spring materials are widely used in various precision instruments and heavy machinery, etc. The service environment is complex and diverse, and corrosion cracking is one of the main failure modes of spring materials, causing great losses in production and life. The emergence of stainless steel spring materials can effectively solve this problem and effectively extend the service life of spring devices. For leaf springs, the load during service should be less than its yield strength, and a high yield ratio is very necessary for leaf springs. However, the low yield strength limits the further application of austenitic stainless steel.

[0003] At present, there are clear standards for the strength grades of stainless steel spring materials in various standards, but there is no clear definition for their plasticity requirements. The spring materials produced by the traditional process of cold rolling + low-temperature aging can reach the standard in terms of strength, but the total elongation is only about 2%, making it difficult to effectively combine strength and plasticity. Although the maraging stainless steel proposed in Chinese Patent CN118389964A can achieve a strength level of 2 GPa, the extremely long aging time and the addition of a large amount of alloying elements result in a very long production cycle and high production costs. In the present invention, a large amount of strain-induced martensite is generated in the metastable austenitic stainless steel after cold deformation processing, and a certain amount of reverse-transformed austenite is introduced by short-time annealing in the two-phase region, so that the elongation can be doubled, and at the same time, the stress drop when reaching the tensile strength under the traditional process is eliminated, realizing the effective combination of strength and plasticity. Summary of the Invention

[0004] The research purpose of the present invention is to provide a super-high strength metastable austenitic stainless steel for leaf springs, and a preparation method and application thereof. Through the process of melting - heat treatment - hot deformation - cold deformation - short-time annealing, a large amount of strain-induced martensite is introduced to increase the yield and tensile strength of the material, and at the same time, a small amount of reverse-transformed austenite is introduced to improve the plasticity of the material, realizing a good match between the strength and plasticity of the super-high strength metastable austenitic stainless steel for leaf springs.

[0005] The object of the present invention is achieved by the following technical solutions: The present invention provides a super-high strength metastable austenitic stainless steel for leaf springs. By weight percentage, its chemical composition includes C: 0.05% - 0.3%, Si: 0.2% - 2%, Mn: 0.2% - 2%, Cr: 12% - 20%, Ni: 5% - 10%, and the content of reverse-transformed austenite in the phase structure of the super-high strength metastable austenitic stainless steel is 10% - 23%; The tensile strength of the ultra-high strength metastable austenitic stainless steel for thin plate springs is 1800 MPa - 2056 MPa, the yield strength is 1670 MPa - 1860 MPa. When the tensile strength is between 1800 MPa - 1950 MPa, the total elongation is 5% - 7%. When the tensile strength is between 1950 MPa - 2056 MPa, the total elongation is 4% - 5%.

[0006] The present invention provides a preparation method for an ultra-high strength metastable austenitic stainless steel for thin plate springs, comprising the following steps: (1) Smelting: According to the designed components, an argon oxygen decarburization furnace and a ladle refining furnace are used to produce metastable austenitic stainless steel, and after the components meet the standards, it is poured into an ingot; (2) Forging: The ingot is forged to obtain a metastable austenitic stainless steel billet; (3) Homogenization: Under the protection of an inert atmosphere, the metastable austenitic stainless steel billet is heated and held to make the composition uniform; (4) Hot rolling: The homogenized metastable austenitic stainless steel billet is subjected to multi-pass hot rolling to reduce the thickness, and cooled to room temperature to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, the metastable austenitic stainless steel sheet is rolled in multiple passes with a constant reduction amount to further reduce the thickness; a large amount of strain-induced martensite is introduced to increase the yield and tensile strength of the material; (6) Annealing: Under the protection of an inert atmosphere, the cold-rolled metastable austenitic stainless steel sheet is subjected to short-time annealing treatment to introduce reverse-transformed austenite, and the content of reverse-transformed austenite is 10% - 23% to obtain an ultra-high strength metastable austenitic stainless steel for thin plate springs; the introduction of reverse-transformed austenite improves the plasticity of the material.

[0007] Further, in step (2), the forging temperature is between 900°C - 1100°C, the initial forging temperature is 1100°C, and the final forging temperature is ≥900°C.

[0008] Further, in step (3), the homogenization treatment temperature is 1100°C - 1300°C, and the holding time is 1 h - 3 h.

[0009] Further, in step (4), the hot rolling temperature is between 950°C - 1300°C, the final rolling temperature is ≥950°C, the thickness reduction is 70% - 90%, and the cooling method is water cooling.

[0010] Further, in step (5), the cold rolling is carried out in multiple passes with a single-pass cold deformation of 0.1 mm until the reduced thickness is 60% - 75%.

[0011] Further, in step (6), the short-time annealing temperature is 500°C - 750°C, and the holding time is 1 s - 600 s.

[0012] Application of a super high strength metastable austenitic stainless steel for leaf springs, wherein the super high strength metastable austenitic stainless steel is used to manufacture leaf springs that take into account both super high strength and plasticity.

[0013] Furthermore, the leaf springs are applied to various deployment devices, energy storage devices, etc.

[0014] The advantages and beneficial effects of the present invention are: The present invention changes the traditional relatively long aging or tempering heat treatment process, adopts a short-time annealing process with faster speed and higher efficiency, greatly improves the production efficiency, and designs a super high strength metastable austenitic stainless steel prepared by the short-time annealing process; For the super high strength metastable austenitic stainless steel prepared by the present invention, the mechanical properties of the material change after short-time annealing treatment. Compared with the cold-rolled state, the total elongation can be increased by nearly one time; For the super high strength metastable austenitic stainless steel prepared by the present invention, more than 10% of reverse transformation austenite is introduced after short-time annealing treatment, improving the plasticity, so that a considerable elongation is retained while achieving super high strength; The super high strength metastable austenitic stainless steel prepared by the present invention has a yield strength ≥ 1670 MPa, a tensile strength ≥ 1800 MPa, and a total elongation ≥ 4%. When used for leaf springs, it can meet the requirements of good matching of strength and plasticity. Description of the Drawings

[0015] Figure 1 It is a schematic flow chart of the preparation method of the super high strength metastable austenitic stainless steel for scroll springs of the present invention; Figure 2 It is the mechanical property curve of the super high strength metastable austenitic stainless steel for scroll springs in Example 1; Figure 3 It is the X-ray diffraction (XRD) pattern of the super high strength metastable austenitic stainless steel for scroll springs prepared in Example 1 before and after short-time annealing. Detailed Embodiments

[0016] The following combines examples to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0017] The embodiments of the present invention are prepared according to Figure 1 the shown process to prepare a super high strength metastable austenitic stainless steel for scroll springs.

[0018] Example 1 For a metastable austenitic stainless steel for leaf springs of the present invention, by weight percentage, its chemical composition includes C: 0.11%, Cr: 16.48%, Mn: 0.73%, Si: 0.69%, Ni: 6.68%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 10%; its yield strength is 1851 MPa, tensile strength is 2056 MPa, and total elongation is 4.3%.

[0019] A preparation method of a metastable austenitic stainless steel with ultra-high strength for scroll springs of the present invention includes the following steps: (1) Smelting: According to the designed components C: 0.11 wt.%, Cr: 16.48 wt.%, Mn: 0.73 wt.%, Si: 0.69 wt.%, Ni: 6.68 wt.%, use an argon-oxygen decarburization furnace and a ladle refining furnace to produce metastable austenitic stainless steel, and pour it into an ingot after the composition meets the standards; (2) Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet; (3) Homogenization: Heat-treat the forged metastable austenitic stainless steel billet, heat it to 1200 °C in an argon protection atmosphere, and hold for 2 h to make the components therein uniform; (4) Hot rolling: Start rolling the homogenized metastable austenitic stainless steel billet at 1200 °C, keep the final rolling temperature ≥ 950 °C, reduce the thickness by 85%, and cool it to room temperature with water after hot rolling to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, roll the metastable austenitic stainless steel sheet with a single-pass reduction of 0.1 mm in multiple passes until the thickness is reduced by 70%; perform mechanical property tests after cold rolling treatment, the yield strength is 2130 MPa, the tensile strength is 2280 MPa, and the total elongation is 2.2%; (6) Annealing: Keep the cold-rolled metastable austenitic stainless steel sheet in a muffle furnace at 600 °C for 120 s, and cool it to room temperature with water to obtain a metastable austenitic stainless steel with ultra-high strength for scroll springs, and perform mechanical property tests. As Figure 2 shown, the yield strength is 1851 MPa, the tensile strength is 2056 MPa, and the total elongation is 4.3%; as Figure 3 shown, the XRD data before and after short-time annealing show that obvious austenite peaks appear after short-time annealing, and it is calculated that 10% reverse-transformed austenite has been introduced.

[0020] The prepared metastable austenitic stainless steel with ultra-high strength is used to make leaf springs, which has both ultra-high strength and good plasticity, and can be used in various deployment devices or energy storage devices.

[0021] Example 2 For a metastable austenitic stainless steel for thin plate springs of the present invention, by weight percentage, its chemical composition includes C: 0.3%, Cr: 20%, Mn: 2%, Si: 2%, Ni: 10%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 17%; its yield strength is 1900 MPa, tensile strength is 2015 MPa, and total elongation is 4.0%.

[0022] A preparation method of a super high strength metastable austenitic stainless steel spring prepared by a short-time annealing process is as follows: (1) Smelting: According to the designed components C: 0.3 wt.%, Cr: 20 wt.%, Mn: 2 wt.%, Si: 2 wt.%, Ni: 10 wt.%, use an argon oxygen decarburization furnace and a ladle refining furnace to produce metastable austenitic stainless steel, and pour it into an ingot after the composition meets the standards; (2) Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet; (3) Homogenization: Heat-treat the forged metastable austenitic stainless steel billet, heat it to 1200 °C under an argon protection atmosphere, and hold for 3 h to make the components therein uniform; (4) Hot rolling: Start rolling the homogenized metastable austenitic stainless steel billet at 1200 °C, keep the final rolling temperature ≥ 950 °C, reduce the thickness by 90%, and cool it to room temperature by water cooling after hot rolling to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, roll the metastable austenitic stainless steel sheet with a single-pass reduction of 0.1 mm in multiple passes until the thickness is reduced by 75%; (6) Annealing: Keep the cold-rolled metastable austenitic stainless steel sheet in a muffle furnace at 700 °C for 60 s to obtain a super high strength metastable austenitic stainless steel for thin plate springs, and conduct mechanical property tests. The yield strength is 1900 MPa, the tensile strength is 2015 MPa, and the total elongation is 4.0%.

[0023] Use the prepared super high strength metastable austenitic stainless steel to make a scroll spring, which has both super high strength and good plasticity, and can be used in deployment devices in the aerospace field.

[0024] Example 3 For a metastable austenitic stainless steel for thin plate springs of the present invention, by weight percentage, its chemical composition includes C: 0.05%, Cr: 12%, Mn: 0.2%, Si: 0.2%, Ni: 5%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 11%; its yield strength is 1860 MPa, tensile strength is 2032 MPa, and total elongation is 4.0%.

[0025] A preparation method of a super-high-strength metastable austenitic stainless steel spring prepared by a short-time annealing process is as follows: (1) Smelting: Produce metastable austenitic stainless steel by an argon oxygen decarburization furnace and a ladle refining furnace according to the designed components C: 0.05 wt.%, Cr: 12 wt.%, Mn: 0.2 wt.%, Si: 0.2 wt.%, Ni: 5 wt.%. After the components meet the standards, pour them into steel ingots; (2) Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet; (3) Homogenization: Heat-treat the forged metastable austenitic stainless steel billet, heat it to 1100 °C under an argon protection atmosphere, and hold for 1 h to make the components uniform; (4) Hot rolling: Start rolling the homogenized metastable austenitic stainless steel billet at 1100 °C, keep the final rolling temperature ≥ 950 °C, reduce the thickness by 70%, and cool it to room temperature by water cooling after hot rolling to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, roll the metastable austenitic stainless steel sheet in multiple passes with a single-pass deformation of 0.1 mm until the thickness is reduced by 60%; (6) Annealing: Keep the cold-rolled metastable austenitic stainless steel sheet in a muffle furnace at 500 °C for 600 s to obtain a super-high-strength metastable austenitic stainless steel for thin plate springs, and conduct mechanical property tests. The yield strength is 1860 MPa, the tensile strength is 2032 MPa, and the total elongation is 4.0%.

[0026] Example 4 A super-high-strength metastable austenitic stainless steel for thin plate springs of the present invention, by weight percentage, its chemical composition includes C: 0.21%, Cr: 17.48%, Mn: 1.73%, Si: 1.69%, Ni: 8.68%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 15%; its yield strength is 1850 MPa, the tensile strength is 2000 MPa, and the total elongation is 4.0%.

[0027] A preparation method of a super-high-strength metastable austenitic stainless steel for scroll springs of the present invention includes the following steps: (1) Smelting: Produce metastable austenitic stainless steel by an argon oxygen decarburization furnace and a ladle refining furnace according to the designed components C: 0.21 wt.%, Cr: 17.48 wt.%, Mn: 1.73 wt.%, Si: 1.69 wt.%, Ni: 8.68 wt.%. After the components meet the standards, pour them into ingots; (2) Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet; (3) Homogenization: The forged metastable austenitic stainless steel billet is heat-treated, heated to 1200 °C in an argon-protected atmosphere, and held for 3 h to make the composition uniform therein; (4) Hot rolling: The homogenized metastable austenitic stainless steel billet is rolled starting at 1200 °C, maintaining the final rolling temperature ≥ 950 °C, reducing the thickness by 85%, and water-cooled to room temperature after hot rolling to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, the metastable austenitic stainless steel sheet is rolled in multiple passes with a single-pass reduction of 0.1 mm until the thickness is reduced by 70%; (6) Annealing: The cold-rolled metastable austenitic stainless steel sheet is held in a muffle furnace at 600 °C for 400 s and water-cooled to room temperature to obtain a super-high-strength metastable austenitic stainless steel for leaf springs, and mechanical property tests are carried out. The yield strength is 1850 MPa, the tensile strength is 2000 MPa, and the total elongation is 4.0%; The prepared super-high-strength metastable austenitic stainless steel is used to make leaf springs, which has both super-high strength and good plasticity and can be used in various deployment devices or energy storage devices.

[0028] Example 5 A super-high-strength metastable austenitic stainless steel for leaf springs according to the present invention, by weight percentage, its chemical composition includes C: 0.21%, Cr: 15%, Mn: 0.8%, Si: 0.8%, Ni: 9%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 17%; its yield strength is 1780 MPa, the tensile strength is 2011 MPa, and the total elongation is 4.2%.

[0029] A preparation method of a super-high-strength metastable austenitic stainless steel for scroll springs according to the present invention includes the following steps: (1) Smelting: According to the designed components C: 0.21 wt.%, Cr: 15 wt.%, Mn: 0.8 wt.%, Si: 0.8 wt.%, Ni: 9 wt.%, an argon-oxygen decarburization furnace and a ladle refining furnace are used to produce metastable austenitic stainless steel, and after the composition meets the standards, it is cast into an ingot; (2) Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet; (3) Homogenization: The forged metastable austenitic stainless steel billet is heat-treated, heated to 1200 °C in an argon-protected atmosphere, and held for 2 h to make the composition uniform therein; (4) Hot rolling: The homogenized metastable austenitic stainless steel billet is rolled starting at 1200 °C, maintaining the final rolling temperature ≥ 950 °C, reducing the thickness by 85%, and water-cooled to room temperature after hot rolling to obtain a metastable austenitic stainless steel sheet; (5)Cold rolling: At room temperature, the metastable austenitic stainless steel sheet is rolled in multiple passes with a single-pass reduction of 0.1 mm until the thickness is reduced by 75%. (6)Annealing: The cold-rolled metastable austenitic stainless steel sheet is kept in a muffle furnace at 600 °C for 600 s and then water-cooled to room temperature to obtain a super-high-strength metastable austenitic stainless steel for leaf springs. Mechanical property tests are carried out, with a yield strength of 1780 MPa, a tensile strength of 2011 MPa, and a total elongation of 4.2%. The prepared super-high-strength metastable austenitic stainless steel is used to make leaf springs, which has both super-high strength and good plasticity and can be used in various deployment devices or energy storage devices.

[0030] Example 6 A super-high-strength metastable austenitic stainless steel for leaf springs according to the present invention, by weight percentage, its chemical composition includes C: 0.17%, Cr: 15%, Mn: 2%, Si: 0.8%, Ni: 10%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 20%; its yield strength is 1750 MPa, its tensile strength is 1900 MPa, and its total elongation is 5.7%.

[0031] A preparation method of a super-high-strength metastable austenitic stainless steel for scroll springs according to the present invention includes the following steps: (1)Smelting: According to the designed components C: 0.17 wt.%, Cr: 15 wt.%, Mn: 2 wt.%, Si: 0.8 wt.%, Ni: 10 wt.%, an argon-oxygen decarburization furnace and a ladle refining furnace are used to produce metastable austenitic stainless steel, and after the composition meets the standard, it is cast into an ingot. (2)Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet. (3)Homogenization: The forged metastable austenitic stainless steel billet is heat-treated, heated to 1300 °C in an argon protective atmosphere, and kept for 2 h to make the components therein uniform. (4)Hot rolling: The homogenized metastable austenitic stainless steel billet is rolled at 1300 °C, keeping the final rolling temperature ≥ 950 °C, and the thickness is reduced by 85%. After hot rolling, it is water-cooled to room temperature to obtain a metastable austenitic stainless steel sheet. (5)Cold rolling: At room temperature, the metastable austenitic stainless steel sheet is rolled in multiple passes with a single-pass reduction of 0.1 mm until the thickness is reduced by 75%. (6)Annealing: The cold-rolled metastable austenitic stainless steel sheet is kept in a muffle furnace at 750 °C for 1 s and then water-cooled to room temperature to obtain a super-high-strength metastable austenitic stainless steel for leaf springs. Mechanical property tests are carried out, with a yield strength of 1750 MPa, a tensile strength of 1900 MPa, and a total elongation of 5.7%. The prepared ultra-high-strength metastable austenitic stainless steel is used to make leaf springs, which has both ultra-high strength and good plasticity, and can be used in various deployment devices or energy storage devices.

[0032] Example 7 For the ultra-high-strength metastable austenitic stainless steel used for leaf springs in the present invention, by weight percentage, its chemical composition includes C: 0.19%, Cr: 13.2%, Mn: 1.5%, Si: 1.8%, Ni: 7%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 23%; its yield strength is 1670 MPa, tensile strength is 1800 MPa, and total elongation is 7%.

[0033] A preparation method of ultra-high-strength metastable austenitic stainless steel for volute springs in the present invention includes the following steps: (1) Smelting: According to the designed components C: 0.19 wt.%, Cr: 13.2 wt.%, Mn: 1.5 wt.%, Si: 1.8 wt.%, Ni: 7 wt.%, an argon-oxygen decarburization furnace and a ladle refining furnace are used to produce metastable austenitic stainless steel, and after the components meet the standards, it is cast into an ingot; (2) Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet; (3) Homogenization: Heat-treat the forged metastable austenitic stainless steel billet, heat it to 1250 °C under an argon protection atmosphere, and hold for 1 h to make the components therein uniform; (4) Hot rolling: Start rolling the homogenized metastable austenitic stainless steel billet at 1250 °C, keep the final rolling temperature ≥ 950 °C, reduce the thickness by 80%, and cool it to room temperature with water after hot rolling to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, roll the metastable austenitic stainless steel sheet with a single-pass reduction of 0.1 mm in multiple passes until the thickness is reduced by 70%; (6) Annealing: Keep the cold-rolled metastable austenitic stainless steel sheet in a muffle furnace at 750 °C for 10 s, and cool it to room temperature with water to obtain the ultra-high-strength metastable austenitic stainless steel for leaf springs, and conduct mechanical property tests. The yield strength is 1670 MPa, the tensile strength is 1800 MPa, and the total elongation is 7%; The prepared ultra-high-strength metastable austenitic stainless steel is used to make leaf springs, which has both ultra-high strength and good plasticity, and can be used in various deployment devices or energy storage devices.

[0034] Example 8 The present invention relates to a metastable austenitic stainless steel with ultra-high strength for leaf springs. By weight percentage, its chemical composition includes C: 0.22%, Cr: 14.2%, Mn: 1.3%, Si: 1.5%, Ni: 6.8%, and the content of reverse-transformed austenite in the metastable austenitic stainless steel phase structure is 19%; its yield strength is 1730 MPa, tensile strength is 1950 MPa, and total elongation is 5%.

[0035] A preparation method of a metastable austenitic stainless steel with ultra-high strength for volute springs according to the present invention includes the following steps: (1) Smelting: According to the designed components C: 0.22 wt.%, Cr: 14.2 wt.%, Mn: 1.3 wt.%, Si: 1.5 wt.%, Ni: 6.8 wt.%, use an argon-oxygen decarburization furnace and a ladle refining furnace to produce metastable austenitic stainless steel, and pour it into an ingot after the components meet the standards; (2) Forging: Start forging at 1100 °C, and the final forging temperature ≥ 900 °C to obtain a metastable austenitic stainless steel billet; (3) Homogenization: Heat-treat the forged metastable austenitic stainless steel billet, heat it to 1260 °C in an argon-protected atmosphere, and hold for 1 h to make the components therein uniform; (4) Hot rolling: Start rolling the homogenized metastable austenitic stainless steel billet at 1250 °C, keep the final rolling temperature ≥ 950 °C, reduce the thickness by 83%, and water-cool to room temperature after hot rolling to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, roll the metastable austenitic stainless steel sheet with a single-pass reduction of 0.1 mm in multiple passes until the thickness is reduced by 70%; (6) Annealing: Keep the cold-rolled metastable austenitic stainless steel sheet in a muffle furnace at 650 °C for 30 s, water-cool to room temperature to obtain a metastable austenitic stainless steel with ultra-high strength for leaf springs, and conduct mechanical property tests. The yield strength is 1730 MPa, the tensile strength is 1950 MPa, and the total elongation is 5%; The prepared metastable austenitic stainless steel with ultra-high strength is used to make leaf springs, which has both ultra-high strength and good plasticity, and can be used in various deployment devices or energy storage devices.

Claims

1. An ultra-high strength metastable austenitic stainless steel for leaf springs, characterized in that: The chemical composition thereof includes, by weight percentage, C: 0.05%-0.3%, Si: 0.2%-2%, Mn: 0.2%-2%, Cr: 12%-20%, Ni: 5%-10%, and the content of reversed austenite in the phase structure of the ultra-high strength metastable austenitic stainless steel is 10%-23%; The ultra-high strength metastable austenitic stainless steel used for the thin leaf spring has a tensile strength of 1800MPa-2056MPa, a yield strength of 1670MPa-1860MPa, and a total elongation of 5%-7% when the tensile strength is 1800MPa-1950MPa; and a total elongation of 4%-5% when the tensile strength is 1950MPa-2056MPa.

2. A method for preparing the ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 1, characterized in that: The following steps are involved: (1) Smelting: According to the designed composition, argon oxygen decarburization furnace and ladle refining furnace are used to produce metastable austenitic stainless steel, and after the composition meets the standard, it is cast into ingots; (2) Forging: Forging the steel ingot to obtain a metastable austenitic stainless steel billet; (3) Homogenization: Under the protection of inert atmosphere, heating and heat preservation are performed to make the composition of the metastable austenitic stainless steel billet uniform; (4) Hot rolling: The metastable austenitic stainless steel billet after homogenization is subjected to multiple hot rolling processes to reduce the thickness, and then cooled to room temperature to obtain a metastable austenitic stainless steel sheet; (5) Cold rolling: At room temperature, the metastable austenitic stainless steel sheet is rolled multiple times with a constant downward pressure to continue to reduce the thickness; (6) Annealing: Under the protection of an inert atmosphere, the cold-rolled metastable austenitic stainless steel sheet is subjected to a short-time annealing treatment to introduce reverse austenite, and the reverse austenite content is 10%-23%, thereby obtaining ultra-high strength metastable austenitic stainless steel for thin leaf springs.

3. The method for preparing ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 2, characterized in that: In step (2), the forging temperature is between 900°C and 1100°C, the initial forging temperature is 1100°C, and the final forging temperature is ≥900°C.

4. The method for preparing ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 2, characterized in that: The homogenization treatment temperature in step (3) is 1100°C-1300°C, and the insulation time is 1h-3h.

5. The method for preparing ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 2, characterized in that: In step (4), the hot rolling temperature is between 950°C and 1300°C, the final rolling temperature is ≥950°C, the thinning thickness is 70%-90%, and the cooling method is water cooling.

6. The method for preparing ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 2, characterized in that: Step (5) cold rolling is performed by cold deformation of 0.1 mm in a single pass and multiple passes until the thickness is reduced to 60%-75%.

7. The method for preparing ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 2, characterized in that: The short-term annealing temperature in step (6) is 500°C-750°C, and the holding time is 1s-600s.

8. An application of the ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 1, characterized in that: The ultra-high strength metastable austenitic stainless steel is used to manufacture a thin leaf spring having both ultra-high strength and plasticity.

9. The use of ultra-high strength metastable austenitic stainless steel for leaf springs according to claim 8, characterized in that: The thin leaf spring is applied to various deployment devices and energy storage devices.

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