A kind of corrosion-resistant ultra-high strength stainless steel and preparation method thereof

Abstract

The present application relates to the technical field of stainless steel, and specifically discloses a corrosion-resistant ultra-high strength stainless steel and a preparation method thereof. The corrosion-resistant ultra-high strength stainless steel disclosed in the present application, in terms of weight percentage, has the following elemental composition: C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.0~1.5%, Al: 1.5~1.9%, Cu: 0.2~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the remainder is Fe and unavoidable impurities. The stainless steel obtained by using the technical solution of the present application has excellent tensile strength, yield strength, fracture toughness, and excellent corrosion resistance.

Description

Technical Field

[0001] The present application relates to the technical field of stainless steel, and in particular to a corrosion-resistant ultra-high strength stainless steel and a preparation method thereof. Background Art

[0002] Failure analysis results of key load-bearing structural parts of aircraft show that corrosion and wear are important factors leading to structural failure and cracking. Therefore, the durability design concept emphasizes the ability of structural parts to resist external damage such as cracking, stress corrosion cracking, corrosion, and wear within the specified service life. The materials currently used to manufacture landing gear support rods, bearing brackets, shafts and connectors for commercial aircraft are all non-stainless steel, with anti-corrosion coatings on the surface. These coatings require a lot of maintenance costs, and due to environmental regulations, some of these coatings may be banned in the near future. For rail components or connectors, long-term use, especially after the surface protective layer is damaged, is very likely to cause catastrophic corrosion failure, hydrogen embrittlement and stress corrosion cracking of key aircraft components. Metal corrosion not only affects aircraft safety, but also the high cost of corrosion maintenance seriously affects the economy of civil aircraft.

[0003] Although high-strength stainless steels such as PH13-8Mo, 15-5PH and 17-4PH have good corrosion resistance, their strength is relatively low due to the use of single-phase intermetallic compound strengthening. At present, 1900MPa-level ultra-high strength stainless steels are generally designed with carbide strengthening and high Co element (12.0 wt.%~15.0 wt.%). For example, foreign Ferrium S53 steel is strengthened with carbide, and the Co content exceeds 12.0 wt.%. Although the Co element can promote the precipitation of Mo-rich, Ti-rich and Ni-rich second phases during aging, stabilize the dislocation structure in the martensitic matrix, obtain high dislocation density, provide more nucleation sites for the precipitation of the second phase, increase its dispersion and strengthening effect, and make the steel obtain ultra-high strength. However, high Co design will increase the raw material cost of the steel itself. At the same time, the precipitation of carbides and the design of high Co elements will lead to the formation of Cr-rich carbides and α-(Cr,Fe) phases in the steel, resulting in Cr-poor areas in the matrix. The formation of Cr-poor areas will reduce the intrinsic pitting corrosion resistance of the steel. Pitting pits are usually the locations where cracks initiate during the service of the material, resulting in reduced corrosion damage resistance of the steel and affecting the service life and safety of key load-bearing components.

[0004] Therefore, in order to ensure that the steel has good corrosion resistance, a new type of high-strength stainless steel needs to be provided. Summary of the invention

[0005] In order to solve the above technical problems, the present application provides a corrosion-resistant ultra-high strength stainless steel and a preparation method thereof.

[0006] The present application provides a corrosion-resistant ultra-high-strength stainless steel. The element composition of the corrosion-resistant ultra-high-strength stainless steel is, by weight percentage, C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.0~1.5%, Al: 1.5~1.9%, Cu: 0.2~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the balance is Fe and unavoidable impurities.

[0007] In view of the embarrassing situation that existing ultra-high strength steel and high-strength stainless steel cannot take into account excellent mechanical properties, corrosion resistance and low cost control. The characteristics of the steel type provided by the technical solution of this application are that its design concept abandons the expensive Co element, adopts a Co-free ultra-low carbon alloy system, accurately designs the content of chemical elements Cr, Ni, Mo, Ti, Al, and Cu, and uses NiAl and Ni3Ti intermetallic compounds for composite strengthening. At the same time, a Cu-rich phase can be formed during the aging process to improve the strength of the steel, promote the formation of reverse transformation austenite, and improve the toughness and plasticity of the steel; and this application controls Si≤0.02%, thereby ensuring the best combination of strength and toughness; while taking into account the high strength of 1900MPa, it has excellent corrosion resistance, which not only meets the lightweight design requirements of the aircraft, reduces the cost of raw materials, repairs and maintenance, but also improves the service life and safety of the key load-bearing components of the aircraft.

[0008] The tensile strength of the stainless steel provided in the present application is greater than 1900 MPa, the yield strength is greater than 1720 MPa, and the fracture toughness is greater than 40 MPa·m 1 / 2 The acidic salt spray corrosion rate in 3.5% NaCl solution (PH=3) is less than 0.005g / m 2 , which meets the urgent needs of commercial aircraft for low-cost, long-life and high-strength materials for key load-bearing components.

[0009] This application proposes a new type of low-cost, corrosion-resistant ultra-high strength stainless steel through alloy composition design and high-cleanliness smelting, forging and heat treatment processes. Its standard chemical formula is 00Cr10Ni12Mo2Al1Ti1CuE. This application adopts Co-free alloying design and Al / Ti composite strengthening alloy design ideas to achieve a tensile strength of 1900MPa while taking into account excellent corrosion resistance. It has potential uses in the manufacture of aircraft shafts, connectors and fasteners, as well as high-speed racing drive shafts, torsion bars and fasteners.

[0010] The basis for adopting the above ingredients in this application is as follows:

[0011] Chromium: Cr plays a decisive role in the corrosion resistance of the material, can improve hardenability, and produce solid solution strengthening. If the Cr content is too high, it will not be possible to obtain the entire martensitic structure after solid solution quenching treatment, and ferrite will be generated in the matrix, which will affect the thermoplasticity of the steel, resulting in a decrease in corrosion resistance, deterioration of transverse toughness, and reduced strength. In addition, Cr can affect the structure and properties of steel together with other elements. The ratio of Cr to Ni determines the structure and type of stainless steel at room temperature. The content of Cr and Ni should be kept within the appropriate range to obtain the best combination of strength and toughness. Therefore, the Cr content is controlled at 9.5~10.0wt.%.

[0012] Nickel: Ni is an important toughening element in the stainless steel in this application, and it is also an important strengthening element. Ni is an austenite stabilizing element, which can improve the toughness of steel. At the same time, Ni can also improve the hardenability of steel, produce solid solution strengthening, maintain high dislocation lath martensite, improve the resistance of the martensite matrix to cleavage fracture, reduce the plastic-brittle transition temperature, and ensure that the steel has sufficient toughness. In addition, Ni forms Ni (Al, Mo) phase and Ni3 (Ti, Mo) phase with Al, Ti, and Mo elements, and is the main strengthening element in steel. However, its content in steel cannot be too high. If the Ni content is too high, the reverse transformation austenite content in the steel will be too high, which will lead to poor yield strength. Therefore, its content is controlled at Ni12.2~13.2wt.%.

[0013] Molybdenum: The addition of Mo is mainly to increase the tempering stability and the second phase strengthening effect, and to form Ni (Al, Mo) phase and Ni3 (Ti, Mo) phase with Ni, Al and Ti elements in the steel, thereby improving the strength of the steel. Considering the strength and toughness ratio of the steel, the Mo content in the steel should not be too high. In this application, the Mo content is controlled at 2.0~2.2wt.%.

[0014] Titanium and aluminum: Ti and Al are the main strengthening elements in steel. They form intermetallic compounds Ni (Al, Mo) phase and Ni3 (Ti, Mo) phase with Ni and Mo elements in steel to improve the strength of steel. Due to the different sizes of the two precipitated phases and the mismatch with the matrix, the strengthening increments produced are different, and the effects on the toughness and pitting corrosion resistance of the steel are also different. In order to ensure that the invented steel has excellent strength, toughness and corrosion resistance, the Ti content is controlled at 1.0~1.5%, and the Al content is controlled at 1.5~1.9%.

[0015] Copper: Cu is the main strengthening element in steel. During the aging process, Cu-rich phase can be formed to improve the strength of the steel. At the same time, Cu can promote the formation of reverse transformation austenite and improve the toughness and plasticity of the steel. In this application, the Cu content is controlled at 0.2-1.0wt.%.

[0016] The purpose and advantage of the above technical solution provided by the present application are, firstly, to ensure corrosion resistance, more than 9.5wt.% Cr and more than 12.2wt.% Ni are added to the steel, while avoiding the lateral performance of the steel caused by excessive Cr content, which will be affected by δ-ferrite, and the strength will be reduced due to excessive Ni content, which will lead to reverse transformation of austenite. Therefore, the Cr content is less than 10.0wt.%, and the Ni content is less than 13.2wt.%; secondly, to ensure that the steel has ultra-high strength, Mo: 2.0~2.2%, Ti: 1.0~1.5 %, Al: 1.5~1.9%, Cu: 0.2~1.0%, to achieve the purpose of composite strengthening of Ni (Al, Mo) phase, Ni3 (Ti, Mo) phase and Cu-rich phase. Small addition of the above elements will lead to insufficient strength, and excessive addition will cause a significant decrease in toughness; third, to ensure the high toughness of the steel, add an appropriate amount of Ni and Cu. Too much addition will cause a decrease in yield strength, and too little will affect the toughness of the steel; fourth, high fatigue performance must strictly control the content of C, Si, Mn, S, P, N, O and five harmful elements in the steel.

[0017] Preferably, the element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.3~1.5%, Al: 1.5~1.6%, Cu: 0.5~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the remainder is Fe and unavoidable impurities.

[0018] The present application further limits the Ti content to 1.3-1.5%, the Al content to 1.5-1.6%, and the Cu content to 0.5-1.0%, thereby achieving the purpose of composite strengthening of Ni (Al, Mo) phase, Ni3 (Ti, Mo) phase and Cu-rich phase, thereby further improving the strength of stainless steel.

[0019] Preferably, the element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.3~1.5%, Al: 1.7~1.9%, Cu: 0.5~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the rest is Fe and unavoidable impurities.

[0020] The present application further limits the Ti content to 1.3-1.5%, the Al content to 1.7-1.9%, and the Cu content to 0.5-1.0%, and compositely strengthens the Ni (Al, Mo) precipitation phase, the Ni3 (Ti, Mo) phase, and the Cu-rich phase, thereby further improving the strength and toughness of the stainless steel.

[0021] Preferably, the element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.1~1.3%, Al: 1.7~1.9%, Cu: 0.2~0.4%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the rest are Fe and unavoidable impurity elements.

[0022] The present application further limits the Ti content to 1.1-1.3%, the Al content to 1.7-1.9%, and the Cu content to 0.2-0.4%, thereby further improving the toughness of the stainless steel.

[0023] Preferably, the element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C≤0.005%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.0~1.5%, Al: 1.5~1.9%, Cu: 0.2~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the rest is Fe and unavoidable impurities.

[0024] The present application reduces the formation of TiC inclusions by controlling the C content to ≤0.005%, and can further improve the plasticity, toughness and corrosion resistance of stainless steel.

[0025] In a preferred technical solution, the element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C: 0.001%, Cr: 9.75%, Ni: 12.58%, Mo: 2.14%, Ti: 1.48%, Al: 1.56%, Cu: 0.95%, Si: 0.012%, Mn: 0.0027%, S: 0.0016%, P < 0.005%, N: 0.0014%, O: 0.0012%, and the rest are Fe and unavoidable impurity elements.

[0026] In a preferred technical solution, the element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C: 0.0023%, Cr: 9.55%, Ni: 12.79%, Mo: 2.11%, Ti: 1.47%, Al: 1.82%, Cu: 0.54%, Si: 0.015%, Mn: 0.0072%, S: 0.0028%, P < 0.005%, N: 0.0013%, O: 0.0012%, and the rest are Fe and unavoidable impurity elements.

[0027] In a preferred technical solution, the element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C: 0.001%, Cr: 9.75%, Ni: 12.58%, Mo: 2.14%, Ti: 1.48%, Al: 1.56%, Cu: 0.95%, Si: 0.012%, Mn: 0.0027%, S: 0.0016%, P < 0.005%, N: 0.0014%, O: 0.0012%, and the rest are Fe and unavoidable impurity elements.

[0028] According to the test analysis, the tensile strength of the corrosion-resistant ultra-high strength stainless steel is ≥1900MPa, the yield strength is ≥1720MPa, and the fracture toughness is ≥40MPam. 1 / 2 , acidic / PH=3 salt spray corrosion rate in 3.5% NaCl solution ≤0.005g / m 2 .

[0029] In a second aspect, the present application provides a method for preparing the above-mentioned corrosion-resistant ultra-high strength stainless steel, which specifically comprises the following steps in sequence:

[0030] Vacuum induction melting, high temperature homogenization treatment, forging, preliminary heat treatment, final heat treatment;

[0031] In the vacuum induction melting step: the vacuum degree during the refining period is less than 3 Pa, and the molten steel is stirred at the same time until the oxygen content is less than 0.0015wt.% and the nitrogen content is less than 0.0015wt.%, and then poured in a vacuum atmosphere;

[0032] In the high temperature homogenization step: the homogenization treatment is performed in a temperature range of 1200-1220° C. for a holding time of not less than 40 hours;

[0033] In the forging step: the steel ingot is heated in a temperature range of 1160-1180°C, the holding time is not less than 3 hours, the start forging temperature is 1180°C, and the final forging temperature is ≥950°C;

[0034] In the preliminary heat treatment step: normalizing temperature 830-850°C, holding time 50-70min, air cooling to room temperature, high temperature tempering temperature 650-670°C, holding time 11-13h;

[0035] The final heat treatment process is to carry out the following processes in sequence: solution treatment temperature 840-860°C, holding time 70-110min, oil cooling to room temperature; cryogenic treatment temperature -70~-76°C, holding time 7-9h; aging treatment temperature 500-520°C, holding time 7-9h, air cooling.

[0036] As described in the above technical solution, the manufacturing process of the new ultra-high strength stainless steel of the present application is: according to the chemical composition ratio of the steel of the present application → vacuum induction melting → high temperature homogenization treatment → forging → preliminary heat treatment → final heat treatment, the selection and control principles of the main processes are as follows:

[0037] (1) Vacuum induction melting

[0038] The material requirements are that the charge should be composed of low-carbon refined steel, high-purity metal Cr, Ni plate, metal Mo, metal Ti, metal Al and metal Cu, etc., and should be clean, dry and rust-free. Induction heating and melting of alloy materials with low S and P content under vacuum conditions can avoid atmospheric oxidation and pollution, more effectively control the gas content in steel, reduce the content of non-metallic inclusions in steel, and make the steel purer. In addition, the use of vacuum induction melting helps to control the alloy composition more accurately. The alloy elements in the invention steel can be accurately controlled within a narrow range. At the same time, the burning and oxidation of the alloy can be avoided, that is, the yield and qualified rate of the steel can be improved. The key point of the process is that the vacuum degree is less than 3Pa during the refining period, and the molten steel is stirred at the same time until the oxygen content is less than 0.0015wt.% and the nitrogen content is less than 0.0015wt.%, and then it is cast into electrode rods in a vacuum atmosphere.

[0039] (2) High temperature homogenization treatment

[0040] The content of alloying elements in the invention steel is relatively high, and it is difficult to avoid the segregation of elements at the head, tail and cross-section of the ingot. In order to solve the problem of sufficient diffusion of elements inside the ingot and improve dendrite segregation, high-temperature homogenization treatment is required to effectively reduce segregation, which is an important process link. After a large number of experimental studies, the best homogenization effect is achieved when the ingot is in the temperature range of 1200~1220℃ and the insulation time is not less than 40h.

[0041] (3) Forging

[0042] The steel ingot is heated at 1160-1180℃, and the holding time is not less than 3h. The start forging temperature is 1180℃. The steel ingot is a single-phase austenite structure in this temperature range. The austenite structure is easy to deform, so it has good thermoplasticity and is easy to process. The final forging temperature is ≥950℃. If the temperature is too low, carbides will precipitate, the plasticity will decrease significantly, and it is easy to cause forging cracks or microcracks. The steel ingot must be roughened and stretched to ensure that the transverse and longitudinal properties of the product are close to and meet the standards, and reduce the tendency of anisotropy.

[0043] (4) Preliminary heat treatment: Preliminary heat treatment includes normalizing + high-temperature tempering. Since martensitic phase transformation will occur when the forging blank is cooled to room temperature after forging, martensitic stainless steel is highly sensitive to cracks. In addition, a large amount of residual stress is distributed in the forging rod after forging, which will cause cracking or microcracks. In addition, the irregular grains of the forging blank after forging require normalizing to obtain all equiaxed grains. At the same time, high-temperature tempering can produce a large amount of austenite, thereby reducing the risk of residual stress causing cracking of the forging blank. After experimental research, the preliminary heat treatment process is as follows: normalizing temperature 840℃, holding time 60min, air cooling to room temperature, high-temperature tempering temperature 660℃, holding time 12h.

[0044] (5) Final heat treatment

[0045] The final heat treatment process of the ultra-high strength stainless steel of the present invention is solution quenching, cold treatment and aging treatment. The optimal comprehensive performance can be obtained by adopting the preferred heat treatment system; the specific process is: solution treatment temperature is 850°C, holding time is 1.5h, and oil cooling to room temperature; deep cold treatment temperature is -73°C, holding time is 8h; aging treatment temperature is 510°C, holding time is 8h, and air cooling.

[0046] In summary, the technical solution of this application has the following effects:

[0047] The main feature of the corrosion-resistant ultra-high strength stainless steel provided in this application is that it adopts the alloy design of composite strengthening of Ni (Al, Mo) phase, Ni3 (Ti, Mo) phase and Cu-rich phase, and a large amount of dispersed and fine second phase ( Figure 1 ), at this time, the steel has ultra-high strength (tensile strength ≥1900MPa, yield strength ≥1720MPa) and greatly guarantees the fracture toughness of the steel (≥40MPa·m 1 / 2 ).

[0048] The main features of the corrosion-resistant ultra-high strength stainless steel provided in the present application are the use of a Co-free ultra-low carbon alloy design, and the use of Ni (Al, Mo) phase, Ni3 (Ti, Mo) phase and Cu-rich phase composite strengthening to ensure that the steel strength reaches 1900MPa while having excellent corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 1a is a transmission electron microscope image of the composite precipitated phase of the stainless steel in Example 1, wherein Figure 1a is a bright field image and Figure 1b is a dark field image.

[0050] Figure 2 This is the salt spray corrosion morphology of 15-5PH stainless steel.

[0051] Figure 3 This is the salt spray corrosion morphology of Custom465 stainless steel.

[0052] Figure 4 This is the salt spray corrosion morphology of Ferrium S53 stainless steel.

[0053] Figure 5 This is the salt spray corrosion morphology of the stainless steel in Example 1. DETAILED DESCRIPTION

[0054] The present application is further described in detail below in conjunction with examples, comparative examples and performance testing experiments. These examples should not be construed as limiting the scope of protection claimed in the present application. Example Example 1

[0055] Example 1 provides an ultra-high strength stainless steel.

[0056] The chemical composition of the ultra-high strength stainless steel in this embodiment is calculated by weight percentage: C: 0.001%, Cr: 9.75%, Ni: 12.58%, Mo: 2.14%, Ti: 1.48%, Al: 1.56%, Cu: 0.95%, Si: 0.012%, Mn: 0.0027%, S: 0.0016%, P: 0.003%, N: 0.0014%, O: 0.0012%, and the rest are Fe and unavoidable impurity elements.

[0057] The preparation method of the ultra-high strength stainless steel in this embodiment is specifically as follows: the ingredients are subjected to vacuum induction melting, vacuuming is performed until the whole is melted, the composition is determined, oxygen is extracted, the vacuum degree during the refining period is less than 3.0 Pa, and the molten steel is stirred until the oxygen content is less than 0.0015wt% and the nitrogen content is less than 0.0015wt%, and then the steel is poured in a vacuum atmosphere, and the steel ingot is heated to 1200°C during high temperature homogenization, and the heat preservation time is 40h. The steel ingot is heated to 11 80℃, keep warm for 3h, start forging at 1180℃, final forging temperature 950℃, and the steel should be slowly air-cooled to room temperature after forging; during the preliminary heat treatment, first normalize at 840℃, keep warm for 1h, air-cool to room temperature, high temperature tempering temperature is 660℃, and the holding time is 12h; during the final heat treatment, the solution temperature is 850℃, keep warm for 1h, oil-cool to room temperature, and then deep cryogenic treatment is performed at -73℃, keep warm for 8h, the aging temperature is 510℃, and air-cool after keeping warm for 8h.

[0058] Figure 1 The figure shows the transmission electron micrograph of the strengthening phase of the stainless steel in Example 1; the analysis results show that the nano-precipitated phase is spherical or short rod-shaped and dispersed on the martensite mass, which can significantly improve the strength of the steel while maintaining a good strength-toughness match. Example 2

[0059] This embodiment provides an ultra-high strength stainless steel.

[0060] The chemical composition of the ultra-high strength stainless steel in this embodiment is calculated in weight percentage: The chemical composition of the ultra-high strength stainless steel is calculated in mass percentage: C: 0.0023%, Cr: 9.55%, Ni: 12.79%, Mo: 2.11%, Ti: 1.47%, Al: 1.82%, Cu: 0.54%, Si: 0.015%, Mn: 0.0072%, S: 0.0028%, P: 0.003%, N: 0.0013%, O: 0.0012%, and the rest are Fe and unavoidable impurity elements.

[0061] The preparation method of the ultra-high strength stainless steel in this embodiment is the same as that in Embodiment 1. Example 3

[0062] This embodiment provides an ultra-high strength stainless steel.

[0063] The chemical composition of the ultra-high strength stainless steel in this embodiment is calculated in weight percentage: The chemical composition of the ultra-high strength stainless steel is calculated in mass percentage: C: 0.0031%, Cr: 10.0%, Ni: 12.56%, Mo: 2.12%, Ti: 1.2%, Al: 1.83%, Cu: 0.21%, Si: 0.019%, Mn: 0.0093%, S: 0.0022%, P: 0.003%, N: 0.0014%, O: 0.0011%, and the rest are Fe and unavoidable impurity elements.

[0064] The preparation method of the ultra-high strength stainless steel in this embodiment is the same as that in Embodiment 1. Comparative Example Comparative Example 1

[0065] This comparative example provides a stainless steel.

[0066] The chemical composition of the stainless steel in this comparative example is calculated in weight percentage: the chemical composition of the ultra-high strength stainless steel is calculated in mass percentage: C: 0.0031%, Cr: 10.0%, Ni: 11.83%, Mo: 1.92%, Ti: 0.92%, Al: 1.12%, Cu: 0.16%, Si: 0.019%, Mn: 0.0093%, S: 0.0022%, P: 0.003%, N: 0.0014%, O: 0.0011%, and the rest are Fe and unavoidable impurity elements.

[0067] The preparation method of the stainless steel in this comparative example is the same as that in Example 1. Comparative Example 2

[0068] This comparative example provides a stainless steel.

[0069] The chemical composition of the stainless steel in this comparative example is calculated in weight percentage: the chemical composition of the ultra-high strength stainless steel is calculated in mass percentage: C: 0.0031%, Cr: 10.0%, Ni: 13.41%, Mo: 2.32%, Ti: 1.49%, Al: 1.95%, Cu: 1.00%, Si: 0.019%, Mn: 0.0093%, S: 0.0022%, P: 0.003%, N: 0.0014%, O: 0.0011%, and the rest are Fe and unavoidable impurity elements.

[0070] The preparation method of the stainless steel in this comparative example is the same as that in Example 1. Comparative Example 3

[0071] This comparative example provides a stainless steel.

[0072] The chemical composition of the stainless steel in this comparative example is calculated in weight percentage: the chemical composition of the ultra-high strength stainless steel is calculated in mass percentage: C: 0.0020%, Cr: 10.0%, Ni: 12.28%, Mo: 2.01%, Ti: 1.17, Al: 1.47%, Si: 0.057%, Mn: 0.0093%, S: 0.0012%, P: 0.003%, N: 0.0022%, O: 0.0011%, and the rest are Fe and unavoidable impurity elements.

[0073] The preparation method of the stainless steel in this comparative example is the same as that in Example 1.

[0074] Performance testing

[0075] Test Example 1

[0076] This test example investigated the room temperature mechanical properties of stainless steel.

[0077] Tensile strength R m , yield strength R p0.2 , elongation after fracture A and section reduction Z are measured by the method described in ASTM E8; fracture toughness K IC The test results are measured by the method described in GB / T 4161, and the salt spray corrosion performance is measured by the method described in GJ 150.11A.

[0078] Test results: Table 1-2 shows the room temperature mechanical properties of common stainless steel varieties in the prior art, and longitudinal parallel stainless steel specimens in Examples 1-3 and Comparative Examples 1-3.

[0079] Table 1 Room temperature mechanical properties and strengthening systems of common stainless steel varieties in the prior art

[0080]

[0081] Table 2 Room temperature mechanical properties of stainless steel in Examples 1-3 and Comparative Examples 1-3

[0082]

[0083] Combining Table 1 with Table 2, by comparing the room temperature mechanical properties of common stainless steel varieties in the prior art, Examples 1-3 and Comparative Examples 1-3, it can be seen that the stainless steel obtained using the technical solution provided in the present application has excellent mechanical properties.

[0084] Test Example 2

[0085] This test example investigated the salt spray corrosion performance of stainless steel.

[0086] Stainless steel salt spray corrosion rate: The test standard adopts GJB150.11A-2009. The concentration of sodium chloride solution is 50g / L, the temperature in the salt spray chamber is 35℃±2℃, and the pH values ​​are 3.0, 5.0, and 7.0 respectively. Test results: as shown in Table 3.

[0087] Table 3 Salt spray corrosion rate performance results of stainless steel in Examples 1-3 and Comparative Examples 1-2

[0088]

[0089] Combined with Table 3, by comparing the salt spray corrosion rate performance of common stainless steel varieties in the prior art, Examples 1-3 and Comparative Examples 1-3, it can be seen that the stainless steel obtained using the technical solution provided by the present application has excellent corrosion resistance.

[0090] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A corrosion-resistant ultra-high strength stainless steel, characterized in that: The element composition of the corrosion-resistant ultra-high strength stainless steel is, by weight percentage, C≤0.01%, Cr: 9.5-10.0%, Ni: 12.2-13.2%, Mo: 2.0-2.2%, Ti: 1.0-1.5%, Al: 1.5-1.9%, Cu: 0.2-1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the balance is Fe and unavoidable impurities; The method for preparing the corrosion-resistant ultra-high strength stainless steel is characterized in that it specifically comprises the following steps in sequence: Vacuum induction melting, high temperature homogenization treatment, forging, preliminary heat treatment, final heat treatment; In the vacuum induction melting step: the vacuum degree during the refining period is less than 3 Pa, and the molten steel is stirred at the same time until the oxygen content is less than 0.0015wt.% and the nitrogen content is less than 0.0015wt.%, and then poured in a vacuum atmosphere; In the high temperature homogenization step: the homogenization treatment is performed in a temperature range of 1200-1220° C. for a holding time of not less than 40 hours; In the forging step: the steel ingot is heated in a temperature range of 1160-1180° C., the holding time is not less than 3 hours, the start forging temperature is 1170-1190° C., and the final forging temperature is ≥950° C.; In the preliminary heat treatment step: normalizing temperature 830-850°C, holding time 50-70min, air cooling to room temperature, high temperature tempering temperature 650-670°C, holding time 11-13h; The final heat treatment process is to carry out the following processes in sequence: solution treatment temperature 840-860°C, holding time 70-110min, oil cooling to room temperature; cryogenic treatment temperature -70~-76°C, holding time 7-9h; aging treatment temperature 500-520°C, holding time 7-9h, air cooling.

2. The corrosion-resistant ultra-high strength stainless steel according to claim 1, characterized in that: Measured in weight percentage, the element composition of the corrosion-resistant ultra-high strength stainless steel is: C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.3~1.5%, Al: 1.5~1.6%, Cu: 0.5~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the remainder is Fe and unavoidable impurities.

3. The corrosion-resistant ultra-high strength stainless steel according to claim 1, characterized in that: Measured in weight percentage, the element composition of the corrosion-resistant ultra-high strength stainless steel is: C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.3~1.5%, Al: 1.7~1.9%, Cu: 0.5~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the rest is Fe and unavoidable impurities.

4. The corrosion-resistant ultra-high strength stainless steel according to claim 1, characterized in that: Measured in weight percentage, the element composition of the corrosion-resistant ultra-high strength stainless steel is: C≤0.01%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.1~1.3%, Al: 1.7~1.9%, Cu: 0.2~0.4%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the rest are Fe and unavoidable impurity elements.

5. The corrosion-resistant ultra-high strength stainless steel according to claim 1, characterized in that: Measured in weight percentage, the element composition of the corrosion-resistant ultra-high strength stainless steel is: C≤0.005%, Cr: 9.5~10.0%, Ni: 12.2~13.2%, Mo: 2.0~2.2%, Ti: 1.0~1.5%, Al: 1.5~1.9%, Cu: 0.2~1.0%, Si≤0.02%, Mn≤0.05%, S≤0.003%, P≤0.005%, N≤0.0015%, O≤0.0015%, and the rest is Fe and unavoidable impurities.

6. The corrosion-resistant ultra-high strength stainless steel according to claim 2, characterized in that: Measured by weight percentage, the element composition of the corrosion-resistant ultra-high strength stainless steel is: C: 0.001%, Cr: 9.75%, Ni: 12.58%, Mo: 2.14%, Ti: 1.48%, Al: 1.56%, Cu: 0.95%, Si: 0.012%, Mn: 0.0027%, S: 0.0016%, P < 0.005%, N: 0.0014%, O: 0.0012%, and the rest is Fe and unavoidable impurity elements.

7. The corrosion-resistant ultra-high strength stainless steel according to claim 3, characterized in that: Measured by weight percentage, the element composition of the corrosion-resistant ultra-high strength stainless steel is: C: 0.0023%, Cr: 9.55%, Ni: 12.79%, Mo: 2.11%, Ti: 1.47%, Al: 1.82%, Cu: 0.54%, Si: 0.015%, Mn: 0.0072%, S: 0.0028%, P < 0.005%, N: 0.0013%, O: 0.0012%, and the rest is Fe and unavoidable impurity elements.

8. The corrosion-resistant ultra-high strength stainless steel according to claim 4, characterized in that: Measured by weight percentage, the element composition of the corrosion-resistant ultra-high strength stainless steel is: C: 0.0031%, Cr: 10.0%, Ni: 12.56%, Mo: 2.12%, Ti: 1.2%, Al: 1.83%, Cu: 0.21%, Si: 0.019%, Mn: 0.0093%, S: 0.0022%, P < 0.005%, N: 0.0014%, O ≤ 0.0011%, and the rest are Fe and unavoidable impurity elements.

9. The method for preparing the corrosion-resistant ultra-high strength stainless steel according to any one of claims 1 to 8, characterized in that: Specifically, the following steps are performed in sequence: Vacuum induction melting, high temperature homogenization treatment, forging, preliminary heat treatment, final heat treatment; In the vacuum induction melting step: the vacuum degree during the refining period is less than 3 Pa, and the molten steel is stirred at the same time until the oxygen content is less than 0.0015wt.% and the nitrogen content is less than 0.0015wt.%, and then poured in a vacuum atmosphere; In the high temperature homogenization step: the homogenization treatment is performed in a temperature range of 1200-1220° C. for a holding time of not less than 40 hours; In the forging step: the steel ingot is heated in a temperature range of 1160-1180° C., the holding time is not less than 3 hours, the start forging temperature is 1170-1190° C., and the final forging temperature is ≥950° C.; In the preliminary heat treatment step: normalizing temperature 830-850°C, holding time 50-70min, air cooling to room temperature, high temperature tempering temperature 650-670°C, holding time 11-13h; The final heat treatment process is to carry out the following processes in sequence: solution treatment temperature 840-860°C, holding time 70-110min, oil cooling to room temperature; cryogenic treatment temperature -70~-76°C, holding time 7-9h; aging treatment temperature 500-520°C, holding time 7-9h, air cooling.

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