Metastable-state austenitic stainless steel, and preparation method therefor and use thereof

Abstract

Provided are metastable-state austenitic stainless steel, and a preparation method therefor and the use thereof. The metastable-state austenitic stainless steel comprises the following element components in percentages by mass: 0.05-0.15% of C, 0.3-0.7% of Si, 6.0-9.0% of Mn, 16.5-19.0% of Cr, 1.0-3.0% of Ni, 0.20-0.30% of N, and the balance of Fe, wherein the value of 8Ni-Mn is larger than 0 and less than 30, with the element symbols in the formula representing the mass percentages of the element ×100. The metastable-state austenitic stainless steel has a relatively high strength in a solution annealing state and a cold work hardening state, and the deformation-induced martensite content is relatively low when a relatively high strength is achieved in a cold work hardening state.

Description

A metastable austenitic stainless steel and a preparation method and application thereof

[0001] Cross-reference to Related Applications

[0002] The present application is based on and claims priority to Chinese Patent Application No. 202410876777.8, filed on July 1, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure belongs to the technical field of stainless steel, and particularly relates to a metastable austenitic stainless steel and a preparation method and application thereof. BACKGROUND

[0004] Appearance parts or deep drawing parts on automobiles often use 300 series austenitic stainless steel, such as 301, 304, etc., which has good corrosion resistance and forming performance. The 300 series austenitic stainless steel contains expensive alloy elements such as Ni and Mo, although it has good corrosion resistance, but its price is high and fluctuates greatly, and it is difficult to be used in large quantities on automobiles. The economic 400 series ferritic stainless steel is difficult to meet the complex forming requirements and strength requirements.

[0005] Mo-saving and Ni-saving austenitic stainless steel has good corrosion resistance, certain strength and forming performance, and will be widely used on automobiles. The Mo-saving and Ni-saving austenitic stainless steel is a typical metastable austenitic stainless steel, and after solid solution treatment, the main organization at room temperature is single-phase austenite, and during cold deformation treatment, a large amount of deformation-induced martensite organization is generated, so that the strength is increased. However, the metastable austenitic stainless steel currently has a high content of deformation-induced martensite organization formed when reaching high strength, which can cause high residual stress in the stainless steel material, and the risk of delayed cracking of the material is large, and further improvement is needed. SUMMARY

[0006] In view of the deficiencies in the related art, the purpose of the present disclosure is to provide a metastable austenitic stainless steel and a preparation method and application thereof. The metastable austenitic stainless steel can achieve different strength levels through different processing methods, realize the normalization of stainless steel for automobiles, and the metastable austenitic stainless steel can reach a high strength at a low content of deformation-induced martensite after cold hardening treatment.

[0007] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0008] In a first aspect, the present disclosure provides a metastable austenitic stainless steel, which comprises the following mass percentage of element components:

[0009] C 0.05-0.15%, Si 0.3-0.7%, Mn 6.0-9.0%, Cr 16.5-19.0%, Ni 1.0-3.0%, and N 0.20-0.30%, with the balance being Fe;

[0010] wherein 0 < 8Ni-Mn < 30, and the element symbols in the formula represent the mass percentage of the element x 100.

[0011] In some embodiments of the present disclosure, the mass percentage of C can be 0.05%, 0.055%, 0.06%, 0.065%, 0.07%, 0.075%, 0.08%, 0.085%, 0.09%, 0.095%, 0.1%, 0.105%, 0.11%, 0.115%, 0.12%, 0.125%, 0.13%, 0.135%, 0.14%, 0.145%, or 0.15%, etc.

[0012] In some embodiments of the present disclosure, the mass percentage of Si can be 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, or 0.7%, etc.

[0013] In some embodiments of the present disclosure, the mass percentage of Mn can be 6.0%, 6.2%, 6.3%, 6.5%, 6.6%, 6.8%, 7%, 7.2%, 7.3%, 7.5%, 7.6%, 7.8%, 8%, 8.2%, 8.3%, 8.5%, 8.6%, 8.8%, or 9%, etc.

[0014] In some embodiments of the present disclosure, the mass percentage of Cr can be 16.5%, 16.8%, 17%, 17.2%, 17.5%, 17.8%, 18%, 18.2%, 18.5%, 18.8%, or 19%, etc.

[0015] In some embodiments of the present disclosure, the mass percentage of Ni can be 1%, 1.2%, 1.3%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.3%, 2.5%, 2.6%, 2.8%, or 3%, etc.

[0016] In some embodiments of the present disclosure, the mass percentage of N can be 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, or 0.3%, etc.

[0017] Ni, Mn are both austenite forming elements. Mn can reduce the critical quenching speed of the stainless steel, increase the stability of austenite during cooling, inhibit the decomposition of austenite, and make the austenite formed at high temperature stably remain at room temperature. However, too high Mn can reduce the corrosion resistance of the stainless steel.

[0018] N is a strong austenite forming element, which can significantly improve the strength of the stainless steel, and can also improve the corrosion resistance.

[0019] Cr is beneficial to improve the corrosion resistance of the stainless steel.

[0020] By controlling 0 < 8 < 30, the corrosion resistance and cold work hardening strength of the stainless steel can be improved.

[0021] In the present disclosure, by the cooperation of the above-mentioned elements in a specific ratio, a metastable austenitic stainless steel is obtained, which can achieve different strength levels through different processing methods, realizing the normalization of the stainless steel for automobiles. After cold work hardening treatment, the metastable austenitic stainless steel can achieve a higher strength at a lower deformation-induced martensite content.

[0022] In the embodiments of the present disclosure, the metastable austenitic stainless steel further comprises one or more of the following mass percentage of element components: Mo 0.01-2.5%, Cu 0.01-3.5%, V 0-0.2%.

[0023] In some embodiments of the present disclosure, the mass percentage of Mo can be 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, or 2.5%, etc.

[0024] In some embodiments of the present disclosure, the mass percentage of Cu can be 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, or 3.5%, etc.

[0025] In some embodiments of the present disclosure, the mass percentage of V can be 0%, 0.02%, 0.03%, 0.05%, 0.06%, 0.08%, 0.1%, 0.12%, 0.13%, 0.15%, 0.16%, 0.18%, or 0.2%, etc.

[0026] Mo can make the passive film on the surface of the stainless steel more dense, thereby improving the resistance of the stainless steel to chloride ion corrosion.

[0027] Cu can improve the deep drawing performance of stainless steel, and can also play a role in precipitation strengthening. After special treatment, it can also play a role in sterilization.

[0028] In addition, the content of P and S should also be controlled, and the lower the content is, the better, so as to prevent the toughness of the material from being reduced.

[0029] In the embodiment of the present disclosure, the metastable austenitic stainless steel has a martensite transformation point temperature Md30 of 50% martensite at 30% cold deformation, which satisfies -16.5℃≤Md30≤40℃; Md30 may be, for example, -16.5℃, -16℃, -15℃, -13℃, -10℃, -8℃, -5℃, -2℃, 0℃, 2℃, 5℃, 8℃, 10℃, 12℃, 15℃, 18℃, 20℃, 22℃, 25℃, 28℃, 30℃, 32℃, 35℃, 38℃, or 40℃, etc.

[0030] wherein Md30=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)-13.7Cr-18.5Mo, and in the formula, the element symbols represent the mass percentage of the element × 100.

[0031] In the present disclosure, by controlling Md30 within the above range, it is beneficial for the cold rolling and forming of the stainless steel coil, and it is also beneficial for the formation of deformation-induced martensite under different cold work hardening states, thereby obtaining metastable austenitic stainless steel with different strength levels.

[0032] In the embodiment of the present disclosure, the metastable austenitic stainless steel has a PREN value of point corrosion resistance equivalent value PREN>15.0; which may be, for example, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30, etc.

[0033] wherein PREN=Cr+3.3Mo-Mn+30N, and in the formula, the element symbols represent the mass percentage of the element × 100.

[0034] In the present disclosure, by controlling PREN>15.0, it is beneficial to improve the corrosion resistance of the stainless steel, so that it meets the requirement of no red rust for at least 720h in the neutral salt spray test.

[0035] In the embodiment of the present disclosure, the metastable austenitic stainless steel is in a solid solution annealing state, and the microstructure of the metastable austenitic stainless steel in the solid solution annealing state includes: 95vol% or more of austenite, 0.01-5vol% of δ ferrite, and 0.5vol% or less of carbonitride; wherein the grain size of the austenite is ≤25μm.

[0036] In the embodiments of the present disclosure, the metastable austenitic stainless steel is in a cold work hardened state, and the microstructure of the metastable austenitic stainless steel in the cold work hardened state with a reduction of 30% includes 59.5-90 vol% of austenite, 10-40 vol% of martensite, and 0.5 vol% or less of carbonitride.

[0037] The metastable austenitic stainless steel provided by the present disclosure can achieve a high strength at a low deformation-induced martensite content in a cold work hardened state. The low martensite content helps to maintain the strength and elongation of the cold work hardened state in an optimal state, and ensures that no cracking occurs during subsequent cold forming (such as stamping, bending, etc.).

[0038] In a second aspect, the present disclosure provides a preparation method of the metastable austenitic stainless steel according to the first aspect, the metastable austenitic stainless steel being in a solid solution annealed state, and the preparation method comprising the following steps performed in sequence:

[0039] smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, second annealing, and second pickling; or, smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, and bright annealing.

[0040] Alternatively, the metastable austenitic stainless steel is in a cold work hardened state, and the preparation method comprises the following steps performed in sequence: smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, second annealing, second pickling, and second cold rolling; or, smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, bright annealing, and second cold rolling.

[0041] In the present disclosure, unless otherwise specified, annealing is performed in air. The bright annealing is performed in an inert atmosphere, and the use of bright annealing instead of second annealing and second pickling can directly obtain a BA (Bright Annealing) surface.

[0042] In the embodiments of the present disclosure, the step of hot rolling includes heating the steel billet obtained after casting by using a heating furnace, controlling the temperature of the heating furnace to be 1200-1250℃, controlling the heating time to be 200-240 min, controlling the opening rolling temperature to be 1100-1150℃, and rolling to the required thickness through rough rolling and finish rolling.

[0043] In the embodiments of the present disclosure, the temperature of the first annealing is 1100-1150℃ (for example, it can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, etc.), the annealing time is 3-10 min (for example, it can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min, etc.), and the cooling mode is air cooling.

[0044] In embodiments of the present disclosure, the preparation method further comprises: performing mechanical descaling between the first annealing and the first pickling. The mechanical descaling can be performed by a shot blasting machine.

[0045] In embodiments of the present disclosure, the step of the first pickling comprises: sulfuric acid pickling and mixed acid pickling, wherein the concentration of the sulfuric acid is 250-400 g / L (for example, it can be 250 g / L, 260 g / L, 280 g / L, 300 g / L, 320 g / L, 330 g / L, 350 g / L, 360 g / L, 380 g / L or 400 g / L, etc.), the mixed acid comprises nitric acid and hydrofluoric acid, the concentration of the nitric acid is 140-240 g / L (for example, it can be 140 g / L, 150 g / L, 160 g / L, 180 g / L, 200 g / L, 220 g / L, 230 g / L or 240 g / L, etc.), and the concentration of the hydrofluoric acid is 10-25 g / L (for example, it can be 10 g / L, 12 g / L, 13 g / L, 15 g / L, 16 g / L, 18 g / L, 20 g / L, 22 g / L, 23 g / L or 25 g / L, etc.).

[0046] In embodiments of the present disclosure, the reduction rate of the first cold rolling is 55-65% (for example, it can be 55%, 56%, 58%, 60%, 62%, 63% or 65%, etc.).

[0047] In embodiments of the present disclosure, the temperature of the second annealing is 1100-1150℃ (for example, it can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, etc.), the annealing time is 1-3 min (for example, it can be 1 min, 1.2 min, 1.5 min, 1.8 min, 2 min, 2.2 min, 2.5 min, 2.8 min or 3 min, etc.), the cooling rate is 90-110℃ / s (for example, it can be 90℃ / s, 92℃ / s, 95℃ / s, 98℃ / s, 100℃ / s, 102℃ / s, 105℃ / s, 108℃ / s or 110℃ / s, etc.), and the cooling mode is a combination of air cooling and water cooling.

[0048] In embodiments of the present disclosure, the second pickling step comprises: sodium sulfate electrolysis and mixed acid pickling; wherein the concentration of sodium sulfate in the sodium sulfate electrolysis is 160-200 g / L (for example, it can be 160 g / L, 170 g / L, 180 g / L, 190 g / L or 200 g / L, etc.), and the current is 3000-4000 A (for example, it can be 3000 A, 3200 A, 3300 A, 3500 A, 3600 A, 3800 A or 4000 A, etc.); the mixed acid comprises nitric acid and hydrofluoric acid, the concentration of the nitric acid is 140-240 g / L (for example, it can be 140 g / L, 150 g / L, 160 g / L, 180 g / L, 200 g / L, 220 g / L, 230 g / L or 240 g / L, etc.), and the concentration of the hydrofluoric acid is 10-25 g / L (for example, it can be 10 g / L, 12 g / L, 13 g / L, 15 g / L, 16 g / L, 18 g / L, 20 g / L, 22 g / L, 23 g / L or 25 g / L, etc.).

[0049] In embodiments of the present disclosure, the bright annealing is carried out in an inert atmosphere, the temperature of the bright annealing is 1100-1150℃ (for example, it can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, etc.), the annealing time is 1-3 min (for example, it can be 1 min, 1.2 min, 1.5 min, 1.8 min, 2 min, 2.2 min, 2.5 min, 2.8 min or 3 min, etc.), the cooling rate is 90-110℃ / s (for example, it can be 90℃ / s, 92℃ / s, 95℃ / s, 98℃ / s, 100℃ / s, 102℃ / s, 105℃ / s, 108℃ / s or 110℃ / s, etc.), and the cooling mode is a combination of air cooling and water cooling.

[0050] Generally, as the reduction rate during cold rolling increases, the content of deformation-induced martensite increases, and the strength of the metastable austenitic stainless steel increases. In the present disclosure, the reduction rate of the second cold rolling is not particularly limited, and those skilled in the art can select the reduction rate according to the required strength of the stainless steel.

[0051] In embodiments of the present disclosure, the preparation method further comprises the following steps: after the solid solution annealing, pickling and bright annealing are carried out.

[0052] In a third aspect, the present disclosure provides a use of the metastable austenitic stainless steel according to the first aspect, when the metastable austenitic stainless steel is in a solid solution annealing state, the metastable austenitic stainless steel is used for an oil tank, a battery pack bottom guard plate, a stainless steel hub, a cross beam, a seat, an interior trim and / or an exterior trim of a vehicle.

[0053] Or, when the metastable austenitic stainless steel is in a cold work hardened state, the metastable austenitic stainless steel is used for the battery pack bottom guard plate, front and rear bumpers and / or body outer plate of the automobile.

[0054] The metastable austenitic stainless steel provided by the present disclosure has a yield strength of 400 MPa or more, a tensile strength of 750 MPa or more, an elongation of 50% or more, a pitting potential Epit (according to GB / T 17899) of 230 mv or more, and no intergranular corrosion sensitivity in a solid solution annealed state; and when the tensile strength reaches 1300 MPa, the reduction rate is not more than 30%, the elongation is 10% or more, the martensite content is 40% or less, and there is no intergranular corrosion sensitivity in a cold work hardened state.

[0055] The metastable austenitic stainless steel provided by the present disclosure has high strength in a solid solution annealed state and a cold work hardened state, and has a low deformation-induced martensite content when reaching a high strength in a cold work hardened state; the metastable austenitic stainless steel can reach different strength levels through one composition and different processing methods, thereby meeting the performance requirements of various automobile parts.

[0056] The metastable austenitic stainless steel provided by the present disclosure can be widely used in automobile oil tanks, battery pack bottom guard plates, stainless steel hubs, cross beams, interior and exterior decorations, front and rear bumpers, body outer plates and other components in a solid solution annealed state and a cold work hardened state with different reductions, thereby eliminating the need for the traditional automobile sheet metal or galvanized sheet metal forming process that requires overall electrophoretic treatment, saving costs while reducing processes and pollution. BRIEF DESCRIPTION OF DRAWINGS

[0057] FIG. 1 is a metallographic micrograph of the metastable austenitic stainless steel provided by Example 2 of the present disclosure in a solid solution annealed state;

[0058] FIG. 2 is a metallographic micrograph of the metastable austenitic stainless steel provided by Example 2 of the present disclosure in a cold work hardened state. DETAILED DESCRIPTION

[0059] The technical solutions of the present disclosure will be further described below by way of exemplary embodiments in conjunction with the accompanying drawings. Those skilled in the art should understand that the exemplary embodiments are only to help understand the present disclosure and should not be regarded as a limitation on the present disclosure.

[0060] Examples 1-8 and Comparative Examples 1-3

[0061] Examples 1-8 and Comparative Examples 1-3 each provide a metastable austenitic stainless steel, and the preparation method is as follows:

[0062] Solid solution annealed state:

[0063] (1) Smelting and casting: smelting, AOD (argon oxygen decarburization), LF (ladle) refining, and continuous casting into slab are sequentially performed according to the composition of the metastable austenitic stainless steel.

[0064] (2) Hot rolling: the slab obtained after casting is heated using a walking beam furnace, the heating temperature of the furnace is 1200°C, the heating time is 220 min, the starting rolling temperature is 1120°C, and after rough rolling and finish rolling to the desired thickness, the steel is coiled.

[0065] (3) First annealing and first pickling: annealing is performed in a horizontal annealing furnace, the temperature of the furnace is 1120°C, the annealing time is 3 min, and the cooling method is air cooling. After annealing, the steel coil is mechanically descaled by a shot blasting machine, and then pickled in a sulfuric acid section and a mixed acid section (nitric acid + hydrofluoric acid) to obtain a steel coil with a surface meeting the requirements; the concentration of sulfuric acid in the sulfuric acid section is 300 g / L, the concentration of nitric acid in the mixed acid section is 160 g / L, and the concentration of hydrofluoric acid is 15 g / L.

[0066] (4) First cold rolling: the steel is rolled to the desired thickness by a conventional continuous rolling mill or a reversible single rolling mill; the cold rolling reduction rate is required to be 60%.

[0067] (5) Second annealing and second pickling: annealing is performed in a horizontal annealing furnace, the annealing temperature is 1120°C, the annealing time is 2 min, the cooling rate is controlled at 100°C / s, and the cooling method is a combination of air cooling and water cooling. Pickling is performed using a sodium sulfate electrolysis and mixed acid (nitric acid + hydrofluoric acid) pickling process; in the electrolysis section, the concentration of sodium sulfate is 160 g / L, and the current is 3000 A; in the mixed acid section, the concentration of nitric acid is 160 g / L, and the concentration of hydrofluoric acid is 15 g / L.

[0068] Cold work hardened state:

[0069] (1) First, obtain a solid solution annealed stainless steel by the same method as described above for preparing the solid solution annealed stainless steel;

[0070] (2) Second cold rolling: the solid solution annealed stainless steel is cold rolled with a total reduction of 30%.

[0071] In the metastable austenitic stainless steel provided in the above examples and comparative examples, the mass percentage (%) of the elements is shown in Table 1 below.

[0072] Table 1

[0073] The microstructure and composition of the metastable austenitic stainless steel provided in the above examples are detected by metallographic method.

[0074] The metallographic micrograph of the metastable austenitic stainless steel provided by Example 2 in a solid solution annealing state is shown in Figure 1, and the microstructure is: 99.2 vol% of austenite, 0.5 vol% of δ ferrite and 0.3 vol% of carbonitride;

[0075] The metallographic micrograph of the metastable austenitic stainless steel provided by Example 2 in a cold work hardening state is shown in Figure 2, and the microstructure is: 82 vol% of austenite, 17.7 vol% of martensite and 0.3 vol% of carbonitride.

[0076] The properties of the metastable austenitic stainless steel provided by the above examples and comparative examples are tested, and the test method is as follows:

[0077] Yield strength, tensile strength, elongation: tested according to the method of GB / T 228.1, A50 standard sample;

[0078] Pitting potential Epit: tested according to the method of GB / T 17897;

[0079] Intergranular corrosion sensitivity: tested according to method E in GB / T4334;

[0080] The results of the above property tests are shown in Table 2 below.

[0081] Table 2

[0082] As can be seen from the test results in Table 2, the metastable austenitic stainless steel provided by the present disclosure has a yield strength of more than 400 MPa, a tensile strength of more than 750 MPa, an elongation of more than 50%, a pitting potential Epit (according to GB / T 17897) of more than 230 mv in a solid solution annealing state; in a cold work hardening state with a reduction of 30%, the yield strength is more than 1000 MPa, the tensile strength is more than 1300 MPa, the elongation is more than 10%, there is no intergranular corrosion sensitivity, and the martensite content is less than 40% when the strength reaches 1300 MPa after cold work hardening.

[0083] Among them, Comparative Example 1 has too high Ni content, too low Mn content, and too small Md30 value, which makes it difficult to transform martensite during secondary cold rolling, and the finished material has a tensile strength of less than 1200 MPa after cold work hardening to the limit, which does not meet the design requirements.

[0084] Comparative Example 2 has too large Md30 value, which makes it easy to transform martensite and transform a large amount of martensite during secondary cold rolling, and the elongation of the finished material is less than the target value of >10%, and the intergranular corrosion sensitivity is poor.

[0085] Comparative Example 3 has a significantly reduced corrosion resistance, especially at the edge of the material, due to 8Ni-Mn < 0, and cannot meet the requirement of no intergranular corrosion.

[0086] In the present disclosure, the terms "first", "second", "third", etc. are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or an indicated number of technical features. Thus, a feature defined with "first", "second", etc. can explicitly or implicitly include at least one of the feature. In the description of the present disclosure, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly and specifically limited.

[0087] In the present disclosure, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like mean that the particular feature, structure, material, or characteristic being described is included in at least one embodiment or example of the present disclosure. Illustrative expressions of the above terms in the present specification are not necessarily directed to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics being described can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the description of a particular feature, structure, material, or characteristic in the specification can be combined with the description of other features, structures, materials, or characteristics in one or more embodiments or examples, if such a combination is not mutually inconsistent and within the scope of the present disclosure.

[0088] The above description is merely that of specific embodiments of the present disclosure to enable those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to these embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A metastable austenitic stainless steel, wherein, The metastable austenitic stainless steel comprises the following mass percentage of element components: C 0.05-0.15%, Si 0.3-0.7%, Mn 6.0-9.0%, Cr 16.5-19.0%, Ni 1.0-3.0%, N 0.20-0.30%, and the balance of Fe; wherein, 0<8Ni-Mn<30, the element symbols in the formula represent the mass percentage of the element x 100.

2. The metastable austenitic stainless steel according to claim 1, wherein, The metastable austenitic stainless steel further comprises one or more of the following mass percentage of element components: Mo 0.01-2.5%, Cu 0.01-3.5%, V 0-0.2%.

3. The metastable austenitic stainless steel according to claim 1 or 2, wherein The metastable austenitic stainless steel has a martensite transformation point temperature Md30 of 50% martensite under 30% cold deformation, satisfying -16.5℃≤Md30≤40℃.

4. The metastable austenitic stainless steel according to any one of claims 1 to 3, wherein, The metastable austenitic stainless steel has a pitting corrosion resistance equivalent value PREN>15.

0.

5. The metastable austenitic stainless steel according to any one of claims 1 to 4, wherein, The metastable austenitic stainless steel is in a solid solution annealing state, and the microstructure of the metastable austenitic stainless steel in the solid solution annealing state comprises: 95vol% or more of austenite, 0.01-5vol% of δ ferrite, and 0.5vol% or less of carbonitride; wherein the grain size of the austenite is ≤25μm.

6. The metastable austenitic stainless steel according to any one of claims 1 to 4, wherein, The metastable austenitic stainless steel is in a cold work hardening state, and the microstructure of the metastable austenitic stainless steel in the cold work hardening state with a reduction of 30% comprises: 59.5-90vol% of austenite, 10-40vol% of martensite, and 0.5vol% or less of carbonitride.

7. A method of producing a metastable austenitic stainless steel as claimed in any one of claims 1 to 6, wherein, The metastable austenitic stainless steel is in a solid solution annealing state, and the preparation method comprises the following steps performed in sequence: smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, second annealing, and second pickling; or, smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, and bright annealing. Alternatively, the metastable austenitic stainless steel is in a cold work hardening state, and the preparation method comprises the following steps performed in sequence: smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, second annealing, second pickling, and second cold rolling; or, smelting, casting, hot rolling, first annealing, first pickling, first cold rolling, bright annealing, and second cold rolling.

8. The production method according to claim 7, wherein The step of hot rolling comprises: heating the steel billet obtained after casting by using a heating furnace, controlling the temperature of the heating furnace to be 1200-1250℃, controlling the heating time to be 200-240min, and controlling the open rolling temperature to be 1100-1150℃, and then performing rough rolling and finish rolling to the required thickness; Preferably, the temperature of the first annealing is 1100-1150℃, the annealing time is 3-10min, and the cooling mode is air cooling; Preferably, the preparation method further comprises: performing mechanical dephosphorization between the first annealing and the first pickling; Preferably, the step of first pickling comprises: sulfuric acid pickling and mixed acid pickling, wherein the concentration of the sulfuric acid is 250-400g / L, the mixed acid comprises nitric acid and hydrofluoric acid, the concentration of the nitric acid is 140-240g / L, and the concentration of the hydrofluoric acid is 10-25g / L; Preferably, the reduction ratio of the first cold rolling is 55-65%.

9. The production method according to claim 7 or 8, wherein The second annealing is performed at a temperature of 1100-1150℃, for 1-3 minutes, at a cooling rate of 90-110℃ / s, and by combining air cooling and water cooling. Preferably, the second pickling comprises: sodium sulfate electrolysis and mixed acid pickling; wherein the concentration of sodium sulfate in the sodium sulfate electrolysis is 160-200g / L, and the current is 3000-4000A; the mixed acid comprises nitric acid and hydrofluoric acid, the concentration of the nitric acid is 140-240g / L, and the concentration of the hydrofluoric acid is 10-25g / L. Preferably, the bright annealing is performed in an inert atmosphere, at a temperature of 1100-1150℃, for 1-3 minutes, at a cooling rate of 90-110℃ / s, and by combining air cooling and water cooling.

10. Use of a metastable austenitic stainless steel as claimed in any one of claims 1 to 6, wherein The metastable austenitic stainless steel is in a solid solution annealed state, and is used for the oil tank, battery pack bottom guard plate, stainless steel hub, cross beam, seat, interior and / or exterior of a vehicle. Alternatively, the metastable austenitic stainless steel is in a cold work hardened state, and is used for the battery pack bottom guard plate, front and rear bumpers and / or vehicle body outer plate of a vehicle.

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