High-toughness low-density stainless steel and method for producing the same

Abstract

The application discloses a kind of high tough low-density stainless steel and preparation method thereof, belong to steel alloy material technical field.The high tough low-density stainless steel of the application includes following chemical components by mass percentage: C:0.01~0.08wt.%, Cr:10~20wt.%, Ni:8~40wt.%, Al:7~15wt.%, the rest is Fe and inevitable impurities.The application is in a large number of addition Al element to reduce density, while regulating C, Al, Cr and Ni content satisfies (Creq-Nieq) / Creq<0.6 to make austenite volume fraction greater than 80%, guarantee stainless steel plasticity and toughness.Meanwhile, a large number of B2 reinforcing phase is formed under the condition of high Ni and high Al, and after multi-pass hot rolling and annealing treatment, layered heterogeneous structure is formed along the rolling direction, so that high tough, high corrosion-resistant low-density stainless steel is obtained.

Description

Technical Field

[0001] This invention relates to the field of steel alloy materials technology, and in particular to a high-strength, high-toughness, low-density stainless steel and its preparation method. Background Technology

[0002] Currently, increasingly severe energy consumption and environmental pressures are placing higher demands on equipment efficiency, driving the rapid development of lightweight steel materials. There are two main approaches to achieving lightweight steel: one is to reduce the material's density through alloying with lightweight elements; the other is to increase the material's strength and then replace conventional steel with thinner, higher-strength steel. For example, adding an appropriate amount of Al to steel materials can achieve lightweighting by increasing lattice distortion and reducing the average atomic mass. Studies have shown that for every 1 wt% increase in Al content, the density of steel can decrease by approximately 1.3%.

[0003] In recent years, Fe-Mn-Al-C steel has become an important research direction for lightweight steel materials due to its combination of low density and high strength, attracting widespread attention. However, the high Mn and Al content in Fe-Mn-Al-C steel makes smelting difficult and easily leads to the formation of coarse κ carbides in the Fe-Mn-Al-C steel matrix, severely deteriorating its ductility, toughness, and corrosion resistance. Furthermore, the literature (JoonohMoon, et al. Scientific Reports, (2020) 10:12140) found that Fe-Mn-Al-C steel exhibits high Cl content in its matrix. － The pitting potential in corrosive environments is approximately -100mV, far lower than the 300mV of 304 stainless steel. Therefore, existing Fe-Mn-Al-C steels cannot simultaneously achieve both low density and corrosion resistance, making them unsuitable for use in harsh corrosive environments, such as high-salt, high-humidity marine environments and high-temperature, high-pressure steam oxidation environments.

[0004] In contrast, directly adding Al to stainless steel systems offers the potential to balance low density and corrosion resistance. Patents (CN102758149A, CN102747307A, CN114836671A) disclose three types of high-aluminum stainless steel plates: 304L+Al, 316L+Al, and 310S+Al, and their preparation methods. However, the Al content added in these inventions is all below 5 wt.%, a relatively small amount, making it difficult to reduce the density to 7.5 g / cm³. 3 Furthermore, the composition design of these schemes is based on existing grades 304L, 316L and 310S, without effective control over the matrix structure and reinforcing phase, resulting in insufficient mechanical properties and corrosion resistance, which still need further improvement. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength, high-toughness, low-density stainless steel and its preparation method, thereby solving the aforementioned problems in the background art. This invention reduces density by adding a large amount of Al, while controlling the content of C, Cr, and Ni to obtain a fully austenitic or austenitic-based ferrite duplex microstructure. Furthermore, it designs and controls the formation of a layered heterogeneous structure of the B2 reinforcing phase through hot rolling and annealing processes, thus obtaining a high-strength, high-toughness, low-density stainless steel with excellent corrosion resistance.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of this invention is to provide a high-strength, high-toughness, low-density stainless steel, comprising the following chemical components by mass percentage:

[0008] C: 0.01–0.08 wt.%, Cr: 10–20 wt.%, Ni: 8–40 wt.%, Al: 7–15 wt.%, with the remainder being Fe and unavoidable impurities;

[0009] Meanwhile, the addition amounts of Cr and Ni satisfy (Creq-Nieq) / Creq<0.6, where Nieq=%Ni+30×%C, and Creq=%Cr+5.5×%Al;

[0010] %Ni, %C, %Al and %Cr are 100 times the mass percentages of Ni, C, Al and Cr, respectively;

[0011] The high-strength, low-density stainless steel has an austenite volume fraction of over 80%.

[0012] When (Creq-Nieq) / Creq≤0.5 in stainless steel, the matrix is ​​a fully austenitic structure; when 0.5<(Creq-Nieq) / Creq<0.6 in stainless steel, the matrix is ​​a dual-phase structure of austenite and ferrite, with the volume fraction of austenite exceeding 80%, and the B2 reinforcing phase is uniformly distributed in the matrix along the rolling direction, forming a layered heterogeneous structure.

[0013] When the ratio of (Creq-Nieq) / Creq is ≥0.6, the volume fraction of austenite will be lower than 80% and the volume fraction of ferrite will be too high, which will reduce the plasticity and toughness.

[0014] The second technical solution of the present invention provides a method for preparing the above-mentioned high-strength, high-toughness, low-density stainless steel, comprising the following steps:

[0015] The raw materials are fed according to the chemical composition design requirements, and the smelting process yields the cast billet.

[0016] The cast billet is subjected to heat treatment to obtain a heat-treated cast billet;

[0017] The heat-treated billet is hot-rolled to obtain a hot-rolled plate;

[0018] The hot-rolled plate is annealed and cooled to obtain the high-strength, low-density stainless steel.

[0019] Preferably, the heat treatment temperature is T = 800 + (%Ni + %Al) × 10℃, and the holding time is t = h1 × (1.2 ~ 1.4) min, where h1 is the thickness of the billet in mm.

[0020] Preferably, the final rolling temperature of the hot rolling is 900-1000℃; the hot rolling includes rough rolling and finish rolling, specifically: first, the heat-treated billet is rough rolled to obtain a rough rolled billet with a thickness of 15-30mm, and then finish rolled to obtain a hot rolled plate with a thickness of 2-10mm.

[0021] Preferably, the rough rolling process consists of 4 to 7 passes; the finish rolling process consists of 4 to 7 passes; and during the hot rolling process, the pass interval is ≤20s, and the pass deformation is 15 to 35%.

[0022] Preferably, the annealing temperature is 700-1100℃, and the holding time is t = h2 × (5-10) min, where h2 is the thickness of the hot-rolled plate in mm.

[0023] Preferably, the cooling method is water cooling.

[0024] More preferably, the preparation method includes the following steps:

[0025] (1) Smelt steel according to the above chemical composition requirements, and obtain low-density stainless steel billet by ingot casting. The billet thickness is 100-250mm.

[0026] (2) Place the billet into the heating furnace and heat it to T = 800 + (%Ni + %Al) × 10℃. Hold it for t = (1.2 ~ 1.4) × h, where h is the billet thickness in mm.

[0027] (3) The billet is hot rolled in two stages: rough rolling and finish rolling. The final rolling temperature of both stages is 900-1000℃. The thickness of the rough rolled billet is 15-30mm, and the thickness of the final hot rolled plate is 2-10mm.

[0028] (4) The hot-rolled plate is annealed at a temperature of 700-1100℃ and a holding time of t = (5-10) × h, where h is the thickness of the hot-rolled plate in mm. Finally, it is water-cooled to room temperature to obtain the high-strength, high-toughness, low-density stainless steel.

[0029] The third technical solution of the present invention provides an application of the above-mentioned high-strength, high-toughness, low-density stainless steel in the field of lightweight steel materials.

[0030] Fourth technical solution of the present invention: A method for improving the mechanical properties and corrosion resistance of stainless steel, wherein the chemical composition of the stainless steel, by mass percentage, is controlled to meet the following requirements:

[0031] C: 0.01–0.08 wt.%, Cr: 10–20 wt.%, Ni: 8–40 wt.%, Al: 7–15 wt.%, with the remainder being Fe and unavoidable impurities;

[0032] Meanwhile, the addition amounts of Cr and Ni satisfy (Creq-Nieq) / Creq<0.6, where Nieq=%Ni+30×%C, and Creq=%Cr+5.5×%Al;

[0033] %Ni, %C, %Al and %Cr are 100 times the mass percentages of Ni, C, Al and Cr, respectively;

[0034] And ensure that the volume fraction of austenite in stainless steel is above 80%.

[0035] The stainless steel obtained according to the preparation process defined in this invention can have a yield strength ≥350MPa, tensile strength ≥700MPa, room temperature elongation ≥30%, and room temperature impact toughness ≥200J / cm. 2 Its density reaches 6.5–7.3 g / cm³. 3 .

[0036] Furthermore, the stainless steel obtained by this invention is in Cl － Pitting potential ≥300mV, corrosion current ≤10mV in corrosive environments - 5 A / cm 2 .

[0037] Unlike Fe-Mn-Al-C steel and existing fixed-grade stainless steel systems, this invention, while adding a large amount of Al to reduce density, achieves a fully austenitic or austenitic-based ferrite dual-phase microstructure by cleverly controlling the C, Cr, and Ni contents. The high Ni and high Al content promotes the formation of a large amount of B2 reinforcing phase, which, after multiple hot rolling and annealing processes, forms a layered heterogeneous structure distributed along the rolling direction, thus obtaining a low-density stainless steel with high strength, toughness, and corrosion resistance, showing promising application prospects in marine engineering equipment, aerospace, and the automotive industry.

[0038] In this invention, to ensure the excellent corrosion resistance and ductility of low-density stainless steel, the austenite volume fraction should be greater than 80%. Therefore, the chemical composition of the stainless steel should satisfy (Creq-Nieq) / Creq<0.6, where Nieq=(%Ni+30×%C), and Creq=(%Cr+5.5×%Al). To ensure the thermoplasticity of the stainless steel during rolling, the temperature before rolling should be controlled at T=800+(%Ni+%Al)×10℃, thereby inhibiting the premature formation of the B2 reinforcing phase and preventing hot working cracking. To obtain a layered heterogeneous structure, the stainless steel needs to undergo multiple hot rolling passes. Since the B2 reinforcing phase is a hard and brittle phase, the final rolling temperature should be controlled within the range of 900~1000℃ to ensure that the stainless steel has sufficient thermoplasticity.

[0039] The beneficial technical effects of the present invention are as follows:

[0040] (1) In the stainless steel embodiment of the present invention, the density is reduced to 6.5-7.5 g / cm³ by increasing the Al addition amount to 7-15 wt.%. 3 At the same time, no κ or M appeared. 23 The precipitation of carbides such as C6, and in Cl － The pitting potential in corrosive environments exceeds 300mV, reaching the level of 304 stainless steel;

[0041] (2) The B2 reinforcing phase is distributed along the rolling direction to form a layered heterostructure, and the C element is completely dissolved into the matrix. The synergistic effect of the two achieves the strengthening and toughening of stainless steel.

[0042] (3) The preparation method of the high-strength and tough low-density stainless steel of the present invention has low processing difficulty and low production cost, and can be applied industrially. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a metallographic image of the microstructure of the high-strength, high-toughness, low-density stainless steel of Embodiment 1 of the present invention.

[0045] Figure 2 This is a tensile curve of the high-strength, high-toughness, low-density stainless steel of Embodiment 1 of the present invention.

[0046] Figure 3 This is a Tafel polarization curve of the high-strength, high-toughness, low-density stainless steel of Embodiment 1 of the present invention. Detailed Implementation

[0047] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0048] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0049] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0050] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0051] The test site for the samples in this invention is the longitudinal section of high-strength, high-toughness, low-density stainless steel. The microstructure is examined using a Carl Zeiss Axiolab5 metallographic microscope. The methods for determining the dimensions and properties of the room-temperature tensile specimens are based on GB / T228-2002, and the equipment used is a ZWICK Z100HT tensile testing machine. The methods for testing the electrochemical sample dimensions and Tafel polarization curves are based on GB / T 17899-1999, and the equipment used is a Princeton Parstat 3000. The density of the stainless steel is determined by the Archimedes displacement method according to GB / T 1423-1996.

[0052] The present invention relates to a high-strength, high-toughness, low-density stainless steel, the chemical composition of which, by mass percentage, includes the following chemical components:

[0053] C: 0.01–0.08 wt.%, Cr: 10–20 wt.%, Ni: 8–40 wt.%, Al: 7–15 wt.%, with the remainder being Fe and unavoidable impurities;

[0054] Meanwhile, the addition amounts of Cr and Ni satisfy (Creq-Nieq) / Creq<0.6, where Nieq=%Ni+30×%C, and Creq=%Cr+5.5×%Al;

[0055] %Ni, %C, %Al and %Cr are 100 times the mass percentages of Ni, C, Al and Cr, respectively.

[0056] The main functions of each component are as follows: C primarily acts as a solid solution strengthener; Cr ensures corrosion resistance; Ni further enhances corrosion resistance and improves processability; and Al significantly reduces density and improves high-temperature oxidation resistance. The synergistic effect of these elements further enhances the product's performance without causing negative impacts.

[0057] In this invention, %Ni, %C, %Al and %Cr are the mass percentages of Ni, C, Al and Cr, respectively.

[0058] The annealing process in this invention is performed under an argon atmosphere.

[0059] Unless otherwise specified, "room temperature" in this invention refers to 10-30°C.

[0060] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0061] Example 1

[0062] A high-strength, low-density stainless steel, by weight percentage, is composed of the following chemical components:

[0063] C 0.01%, Cr 18.5%, Ni 34.5%, Al 7.2%, the remainder being Fe and unavoidable impurities; (Creq-Nieq) / Creq<0.7, where Nieq=34.5+30×0.01=34.8, Creq=18.5+7.2×5.5=58.1, (48.75-24.5) / 48.75=0.4<0.6.

[0064] The specific preparation steps for high-strength, high-toughness, low-density stainless steel are as follows:

[0065] Low-density stainless steel molten steel is smelted according to the set composition, and the molten steel is cast into a billet with a thickness of 200mm through ingot casting; the billet is placed in a heating furnace and heated to T=800+(34.8+7.2)×10℃=1217℃, and held for t=1.2×200=240min.

[0066] The billet is hot rolled in two stages: roughing and finishing. The roughing stage consists of 7 passes with a billet thickness of 19.2 mm, and the finishing stage consists of 5 passes with a final hot-rolled plate thickness of 5.5 mm. The final rolling temperature for both stages is 980℃. The pass interval is 10 s, and the pass deformation is 21%.

[0067] The hot-rolled sheet was annealed at 1100℃ for t = 6 × 5.5 = 33 min; finally, it was water-cooled to room temperature to obtain a high-strength, high-toughness, low-density stainless steel with the following microstructure: Figure 1 As shown.

[0068] Depend on Figure 1 As can be seen, the high-strength and low-density stainless steel matrix of Example 1 is a single austenitic structure, with the B2 reinforcing phase distributed along the rolling direction to form a layered heterogeneous structure.

[0069] The tensile curve of the high-strength, high-toughness, low-density stainless steel in Example 1 is as follows: Figure 2 As shown, its yield strength is 352.5 MPa, tensile strength is 724.8 MPa, and room temperature elongation is 41.5%.

[0070] Example 1 shows that the high-strength, low-density stainless steel has a room temperature impact toughness of 254 J / cm. 2 Its density is 7.21 g / cm³. 3 .

[0071] Example 1: High-strength, low-density stainless steel in Cl － Tafel polarization curves in corrosive environments are as follows Figure 3 As shown, its pitting potential is 315.5 mV, and its corrosion current is 6.3 × 10⁻⁶ mV. -6 A / cm 2 .

[0072] Example 2

[0073] A high-strength, low-density stainless steel, by weight percentage, is composed of the following chemical components:

[0074] C 0.02%, Cr 16.8%, Ni 32.6%, Al 9.8%, the remainder being Fe and unavoidable impurities; (Creq-Nieq) / Creq<0.7, where Nieq=32.6+30×0.02=33.2, Creq=16.8+9.8×5.5=70.7, 0.5<(70.7-33.2) / 70.7=0.53<0.6.

[0075] The specific preparation steps for high-strength, high-toughness, low-density stainless steel are as follows:

[0076] Low-density stainless steel is smelted according to the set composition. The molten steel is then cast into a billet with a thickness of 180mm. The billet is placed in a heating furnace and heated to T=800+(32.6+9.8)×10℃=1224℃. The holding time is t=1.2×180=216min.

[0077] The billet is hot rolled in two stages: roughing and finishing. The roughing stage consists of 7 passes with a billet thickness of 18.0 mm, and the finishing stage consists of 5 passes with a final hot-rolled plate thickness of 4.8 mm. The final rolling temperature for both stages is 960℃. The pass interval is 12 s, and the pass deformation is 23.5%.

[0078] The hot-rolled sheet was annealed at 1100℃ for t = 5 × 4.8 = 24 min; finally, it was water-cooled to room temperature to obtain high-strength, high-toughness, low-density stainless steel.

[0079] The high-strength, low-density stainless steel matrix of Example 2 is composed of austenitic and ferritic structures, with an austenitic volume fraction of 91.2%. The B2 reinforcing phase is distributed along the rolling direction, forming a layered heterogeneous structure.

[0080] The high-strength, low-density stainless steel of Example 2 has a yield strength of 420.5 MPa, a tensile strength of 890.6 MPa, a room temperature elongation of 36.5%, and a room temperature impact toughness of 223 J / cm. 2 Its density is 7.06 g / cm³. 3 , in Cl － The pitting potential in the corrosive environment is 311.2 mV, and the corrosion current is 7.9 × 10⁻⁶ mV. -6 A / cm 2 .

[0081] Example 3

[0082] A high-strength, low-density stainless steel, by weight percentage, is composed of the following chemical components:

[0083] C 0.01%, Cr 15.6%, Ni 35.1%, Al 13.2%, the remainder being Fe and unavoidable impurities; (Creq-Nieq) / Creq<0.7, where Nieq=35.1+30×0.01=35.4, Creq=15.6+13.2×5.5=88.2, 0.5<(88.2-35.4) / 88.2=0.59<0.6.

[0084] The specific preparation steps for high-strength, high-toughness, low-density stainless steel are as follows:

[0085] Low-density stainless steel molten steel is smelted according to the set composition, and the molten steel is cast into a billet with a thickness of 190mm by ingot casting; the billet is placed in a heating furnace and heated to T=800+(38.1+13.2)×10℃=1313℃, and held for t=1.2×190=228min.

[0086] The billet is hot rolled in two stages: roughing and finishing. The roughing stage consists of 5 passes, with a billet thickness of 29.8 mm. The finishing stage consists of 4 passes, with a final hot-rolled plate thickness of 9.4 mm. The final rolling temperature for both stages is 950℃. The pass interval is 13 s, and the pass deformation is 25%.

[0087] The hot-rolled plate was annealed at 800℃ for t = 5 × 9.4 = 47 min; finally, it was water-cooled to room temperature to obtain high-strength, high-toughness, low-density stainless steel.

[0088] The high-strength, low-density stainless steel matrix of Example 3 is composed of austenitic and ferritic structures, with an austenitic volume fraction of 80.6%. The B2 reinforcing phase is distributed along the rolling direction, forming a layered heterogeneous structure.

[0089] The high-strength, low-density stainless steel of Example 3 has a yield strength of 478.4 MPa, a tensile strength of 948.6 MPa, a room temperature elongation of 31.3%, and a room temperature impact toughness of 201 J / cm. 2 Its density is 6.72 g / cm³. 3 , in Cl － The pitting potential in the corrosive environment is 302.6 mV, and the corrosion current is 9.2 × 10⁻⁶ mV. -6 A / cm 2 .

[0090] Comparative Example 1

[0091] The only difference from Example 1 is that the chemical composition of the stainless steel is modified as follows:

[0092] C 0.03%, Cr 23.1%, Ni 10.2%, Al 8.8%, the remainder being Fe and unavoidable impurities; where Nieq=10.2+30×0.03=11.1, Creq=23.1+8.8×5.5=71.8, (71.8-11.1) / 71.8=0.85>0.6.

[0093] Measurements showed that the stainless steel matrix of Comparative Example 1 was a dual-phase structure of austenite and ferrite, with an austenite volume fraction of only 26.3%. The B2 reinforcing phase was distributed along the rolling direction, forming a layered heterogeneous structure.

[0094] The stainless steel in Comparative Example 1 has a yield strength of 391.4 MPa, a tensile strength of 850.6 MPa, a room temperature elongation of only 5.6%, and a room temperature impact toughness of 98.2 J / cm². 2 Its density is 6.98 g / cm³. 3 , in Cl － The pitting potential in the corrosive environment is 103.1 mV, and the corrosion current is 4.1 × 10⁻⁶ mV. -5 A / cm 2 .

[0095] Comparative Example 2

[0096] The only difference from Example 1 is that the heating temperature during the furnace heating stage is adjusted to 1100℃ or 1300℃ respectively, which does not satisfy T=800+(%Ni+%Al)×10℃.

[0097] Measurements showed that when the stainless steel in Comparative Example 2 was heated to too low a temperature (1100℃), the B2 reinforcing phase formed at the initial stage of hot rolling, leading to severe hot cracking during the process. When the heating temperature was too high (1300℃), the stainless steel overheated, resulting in a liquid phase and subsequent hot cracking. Therefore, both excessively high and low heating temperatures can lead to the failure of hot-rolled stainless steel sheet preparation.

[0098] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-strength, high-toughness, low-density stainless steel, characterized in that, By mass percentage, it includes the following chemical components: C: 0.01~0.08 wt.%, Cr: 10~20 wt.%, Ni: 8~40 wt.%, Al: 7~15 wt.%, the remainder being Fe and unavoidable impurities; Meanwhile, the addition amounts of Cr and Ni satisfy (Creq-Nieq) / Creq<0.6, where Nieq=%Ni+30×%C, and Creq=%Cr+5.5×%Al; %Ni, %C, %Al, and %Cr are 100 times the mass percentages of Ni, C, Al, and Cr, respectively. The high-strength, low-density stainless steel has an austenite volume fraction of over 80%.

2. A method for preparing the high-strength, high-toughness, low-density stainless steel according to claim 1, characterized in that, Includes the following steps: The raw materials are fed according to the chemical composition design requirements, and the smelting process yields the cast billet. The cast billet is subjected to heat treatment to obtain a heat-treated cast billet; The heat-treated billet is hot-rolled to obtain a hot-rolled plate; The hot-rolled plate is annealed and cooled to obtain the high-strength, low-density stainless steel.

3. The preparation method according to claim 2, characterized in that, The heat treatment temperature is T=800+(%Ni+%Al)×10℃, and the holding time is t=h1×(1.2~1.4)min, where h1 is the thickness of the billet in mm.

4. The preparation method according to claim 2, characterized in that, The final rolling temperature of the hot rolling is 900~1000℃; the hot rolling includes rough rolling and finish rolling, specifically: first, the heat-treated billet is rough rolled to obtain a rough rolled billet with a thickness of 15~30mm, and then finish rolled to obtain a hot rolled plate with a thickness of 2~10mm.

5. The preparation method according to claim 4, characterized in that, The roughing rolling process consists of 4 to 7 passes; the finishing rolling process consists of 4 to 7 passes; during the hot rolling process, the pass interval is ≤20s, and the pass deformation is 15 to 35%.

6. The preparation method according to claim 2, characterized in that, The annealing temperature is 700~1100℃, and the holding time is t=h2×(5~10)min, where h2 is the thickness of the hot-rolled plate in mm.

7. The preparation method according to claim 2, characterized in that, The cooling method is water cooling.

8. The application of the high-strength, high-toughness, low-density stainless steel according to claim 1 in the field of lightweight steel materials.

9. A method for improving the mechanical properties and corrosion resistance of stainless steel, characterized in that, By mass percentage, the chemical composition of stainless steel shall meet the following requirements: C: 0.01~0.08 wt.%, Cr: 10~20 wt.%, Ni: 8~40 wt.%, Al: 7~15 wt.%, the remainder being Fe and unavoidable impurities; Meanwhile, the addition amounts of Cr and Ni satisfy (Creq-Nieq) / Creq<0.6, where Nieq=%Ni+30×%C, and Creq=%Cr+5.5×%Al; %Ni, %C, %Al, and %Cr are 100 times the mass percentages of Ni, C, Al, and Cr, respectively. And ensure that the volume fraction of austenite in stainless steel is above 80%.

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