High-strength high-plasticity austenitic stainless steel and method for producing the same

Abstract

This invention provides a high-strength, high-ductility austenitic stainless steel and its production method. The composition is: C 0.045%-0.085%, N 0.10%-0.40%, Si 0.90%-1.55%, Cr 16%-20.1%, Ni 7.5%-12.5%, Mn 1.5%-3.5%, Mo 1.5%-3.0%, Nb 0.08%-0.22%, Ti 0.015-0.065%, O≤0.005%, P≤0.003%, S≤0.003%, with the remainder being Fe and unavoidable impurities. Compared with existing technologies, this invention obtains a reasonable grain size and second-phase particles through nitrogen, titanium, and niobium alloying, combined with low-temperature rolling and appropriate annealing and aging heat treatment, thus developing an austenitic stainless steel with excellent mechanical properties. It achieves excellent ductility at a high strength level, with a strength-ductility product as high as 60 GPa·s.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel manufacturing technology, specifically relating to a high-strength, high-plasticity austenitic stainless steel and its production method. The produced austenitic stainless steel has the characteristics of high strength and high plasticity, which is beneficial to the safety and lightweight of components and meets the requirements of energy conservation, emission reduction, and green environmental protection. Background Technology

[0002] Austenitic stainless steel is the most widely used type of stainless steel, accounting for approximately 70% of the total. It possesses excellent formability and good corrosion resistance, making it widely applicable in nuclear power, petrochemicals, transportation, and construction. However, its yield strength is relatively low, typically only around 200 MPa. This not only limits its further application in many fields but also hinders energy conservation and emission reduction throughout its entire lifecycle. Improving the strength and toughness of austenitic stainless steel can not only enhance service safety but also reduce its usage under the same service conditions, which is of great significance for energy conservation, emission reduction, environmental protection, and low carbon emissions.

[0003] The invention patent (publication number CN113755753A, publication date: December 7, 2021) discloses a multi-type strengthened austenitic stainless steel based on a heterogeneous structure. Through multiple strengthening methods based on the heterogeneous structure (including fine-grain strengthening, second-phase strengthening, precipitation strengthening, solid solution strengthening, and non-uniform deformation strengthening), the austenite can maintain a uniform elongation of over 20% while achieving a 125 steel grade (862 MPa). However, the composite heterogeneous structure (multiphase microstructure) strengthening using coarse-grained retained austenite + fine-grained inverted austenite + retained martensite employed in this disclosed technology has a relatively complex preparation process, and results in lower elongation and less outstanding strength.

[0004] The invention patent (CN113231648A, publication date: August 10, 2021) discloses a high-strength austenitic stainless steel and its preparation method. Through powder mixing, ball milling, laser melting and forming, and heat treatment, it utilizes oxide metallurgy technology and dispersion strengthening theory to introduce various particles of different sizes (micron particles: TiN, submicron particles: Al2O3, nanoparticles: Y-Al-O) into the steel to strengthen the austenitic stainless steel, achieving a high-temperature (650℃) strength of 440 MPa. However, the preparation process of this disclosed technology is overly cumbersome, and the highest room-temperature yield strength is only 694 MPa. Furthermore, the introduction of a large number of particles inevitably reduces corrosion resistance.

[0005] The invention patent (CN112553533A, publication date: March 26, 2021) discloses an economical high-strength austenitic stainless steel. Although it is economical, it has a variety of alloy components (14 kinds) and contains rare earth elements. The components also need to meet specific quantitative relationships, making it difficult to smelt. In addition, the strength is not ideal, with the highest yield strength being 620MPa and the highest tensile strength being 850MPa.

[0006] The invention patent (CN109837470A, publication date: June 4, 2019) discloses a high-strength nitrogen-containing economical austenitic stainless steel and its manufacturing method. This disclosed technology achieves a maximum tensile strength of 1103 MPa, but the elongation is less than 40%, with a maximum of 39.01%. Moreover, the preparation process requires "secondary cold rolling + secondary flexible annealing", which is relatively complicated.

[0007] The invention patent (CN108866419A, publication date: November 23, 2018) discloses a high-strength, high-corrosion-resistant austenitic stainless steel and its manufacturing method. Although the solid solution yield strength can reach more than 500MPa, the elongation is low, with a maximum of 42%, and the alloy element content is too high: Cr: 28-35%, Ni: 26-32%, Mo: 3-8%, N: 0.2-0.5%, resulting in high cost and poor practicality.

[0008] In summary, the current research and development of high-strength austenitic stainless steel mainly adopts two technical routes: nitrogen alloying and microstructure control. Nitrogen can stabilize austenite, strengthen through solid solution, refine grains, improve strain hardening, strengthen through precipitation, and enhance corrosion resistance. Adding nitrogen to increase strength is an effective method. However, high-nitrogen austenitic stainless steel is difficult to smelt, has poor formability in machining and stamping, hindering its widespread application; furthermore, it easily forms Cr2N, reducing the corrosion resistance of austenitic stainless steel. Microstructure control mainly focuses on grain size and phase composition and proportion, including methods such as grain refinement, obtaining gradient structures, and forming multiphase structures. While strength can also be improved through grain size and phase composition and proportion control, the improvement is either not significant or comes at the cost of substantial sacrifice in plasticity, or the manufacturing process is complex.

[0009] Therefore, it is extremely urgent to develop an austenitic stainless steel that is simple to prepare, has high strength and high plasticity. This is of great significance for the service safety of austenitic stainless steel, energy conservation and emission reduction throughout its entire life cycle, and green manufacturing. Summary of the Invention

[0010] The purpose of this invention is to provide a high-strength, high-ductility austenitic stainless steel and its production method. By alloying with N, Ti, and Nb and combining with appropriate rolling, annealing, and aging heat treatment processes, the solid solution strengthening of N, the precipitation strengthening of Ti / Nb carbonitrides, the enhancement and plasticization of nano-precipitates, and the fine grain strengthening effect of rolling and annealing are fully utilized to develop austenitic stainless steel with excellent mechanical properties. The strength of austenitic stainless steel is improved while ensuring high ductility. Moreover, the production process of this invention is simple and suitable for industrial production.

[0011] The specific technical solution of this invention is as follows:

[0012] This invention provides a high-strength, high-ductility austenitic stainless steel, comprising the following components by weight percentage:

[0013] C: 0.045%-0.085%, N: 0.10%-0.40%, Si: 0.90%-1.55%, Cr: 16%-20.1%, Ni: 7.5%-12.5%, Mn: 1.5%-3.5%, Mo: 1.5%-3.0%, Nb: 0.08%-0.22%, Ti: 0.015-0.065%, O≤0.005%, P+S≤0.005%, with the remainder being Fe and unavoidable impurities.

[0014] The composition of the high-strength, high-ductility austenitic stainless steel meets the following requirements: P≤0.003%, S≤0.003%.

[0015] The composition of the high-strength, high-ductility austenitic stainless steel meets the following requirements: Cr eq =%Cr+1.5×%Si+%Mo,Ni eq =%Ni+30×(%C+%N)+0.5×(%Mn+%Co+%Cu), 0.75≤Ni eq / Cr eq ≤1.50;

[0016] The composition of the high-strength, high-ductility austenitic stainless steel meets the following requirement: 50 mJ / m 2 ≤γ SEF ≤70mJ / m 2 ;γ SEF =(-53)+6.5×%Ni+0.7×%Cr+3.2×%Mn+9.3×%Mo; γ SEF The unit is mJ / m 2 It refers to the stacking fault energy of austenite.

[0017] This invention controls the above-mentioned components and 0.75≤Ni eq / Cr eq ≤1.50 and 50 mJ / m 2 ≤γSEF (mJ / m 2 ≤70mJ / m 2 The purpose is to: (1) obtain fine niobium / titanium carbonitride particles; (2) avoid the precipitation of TiN particles in the liquid phase; (3) obtain an austenitic structure with a volume fraction of more than 95% in the cast and forged samples; (4) suppress the transformation of austenite to martensite during low-temperature rolling to obtain a stable austenitic structure; (5) improve the solid solubility of nitrogen; and (6) avoid the formation of Cr2N as much as possible.

[0018] When calculating the above formula, multiply the content of each element by 100% and substitute it into the formula.

[0019] The composition of the high-strength, high-plasticity austenitic stainless steel meets the requirements of low carbon, medium nitrogen, trace titanium, low manganese, and low levels of impurity elements such as oxygen, phosphorus, and sulfur.

[0020] The microstructure of the high-strength and high-plasticity austenitic stainless steel consists of polygonal austenite and ferrite, wherein the volume ratio of ferrite is 0.2-1.2% and its average grain size is 1.7-4.2 μm; the size range of the nano-second phase particles is 10-20 nm.

[0021] The yield strength σ of the high-strength, high-ductility austenitic stainless steel 0.2 =600-757MPa, tensile strength σ b = 977-1051 MPa, elongation 39-61%, strength-ductility product 38-60 GPa·%; preferably 42-60 GPa·%.

[0022] The present invention provides a method for producing high-strength, high-plasticity austenitic stainless steel, comprising the following processes: smelting, casting, forging, solution treatment, low-temperature rolling, and annealing.

[0023] The smelting equipment is one of a vacuum induction furnace, a VOD furnace, or an AOD furnace. If a vacuum induction furnace is used, smelting begins when the vacuum level reaches below 90 Pa. During the smelting process, high-purity nitrogen is introduced at a pressure of 0.2-0.3 MPa.

[0024] The casting process is either continuous casting or ingot casting, with full protection during the casting process.

[0025] The forging process involves heating at 1050-1150℃, holding for 45-60 minutes, and water cooling.

[0026] The solid solution is heated at 1150-1200℃, held for 2-3 hours, and cooled by water.

[0027] The low-temperature rolling process involves preheating the sample in liquid nitrogen for 10-15 minutes before rolling, rolling at least 10 passes, controlling the total cold rolling reduction rate to 70%-75%, preheating the sample in liquid nitrogen for 5 minutes every 4 passes during rolling, and controlling the thickness of the low-temperature rolled plate to 2.5-3.5 mm.

[0028] The annealing process is carried out at a temperature of 950-1100℃ for 1-120 minutes. The annealing furnace can be one of a box furnace, a bell furnace, or a continuous annealing furnace.

[0029] When the annealing temperature is ≤1000℃, aging treatment is required after annealing; when the annealing temperature is >1000℃, aging treatment is not required.

[0030] The aging treatment is carried out at a temperature of 300-600℃ for 5-40 hours.

[0031] This invention achieves a reasonable grain size and second-phase particles through nitrogen, titanium, and niobium alloying combined with low-temperature rolling and appropriate annealing and aging heat treatment. It fully utilizes the solid solution strengthening of nitrogen, the precipitation strengthening and plasticizing effect of titanium-niobium carbonitrides, and the grain-refining strengthening effect of the fine grains obtained by low-temperature rolling and heat treatment. This results in the development of austenitic stainless steel with excellent mechanical properties, achieving a high strength level (tensile strength σ). b It exhibits excellent plasticity (elongation up to 61%) with a strength-ductility product of up to 60 GPa·s (approximately 977-1051 MPa).

[0032] The design concept and principle of this invention:

[0033] Because ordinary austenitic stainless steel lacks strong carbonitride-forming elements and exhibits no γ→α phase transformation during hot working, traditional TMCP steel grain refinement techniques and precipitation strengthening principles are ineffective. In comparison, grain refinement through recrystallization, combined with nitrogen solid solution strengthening and niobium-titanium carbonitride precipitation strengthening, is an ideal choice. Firstly, austenitic stainless steel has a low stacking fault energy and a high degree of dislocation multiplication during cold deformation (easily forming partial dislocations), resulting in a strong recrystallization driving force, which promotes grain refinement and significantly enhances grain strengthening. Secondly, the addition of nitrogen not only provides solid solution strengthening but also saves nickel, reduces costs, and improves pitting corrosion resistance, resulting in improved overall performance. Thirdly, fine, dispersed niobium-titanium carbonitride particles not only provide good precipitation strengthening but also overcome the reduction in plasticity caused by grain refinement at a certain grain size, achieving both enhancement and plasticity improvement simultaneously. Achieving the above effects requires the combination of the composition optimization design as described in this invention with process parameters such as solution treatment, low-temperature rolling, annealing, and aging treatment. The addition of a certain amount of manganese can promote nitrogen solution dissolution, thus strengthening the solution and reducing or preventing the formation of Cr2N. According to thermodynamic calculations based on the phase diagram, solution treatment at 1150-1200℃ can ensure the dissolution of coarse precipitates (as follows). Figure 12 As shown, obtaining single-phase austenite is beneficial for low-temperature rolling; low-temperature rolling with liquid nitrogen insulation ensures the effective accumulation of dislocations during rolling, thereby increasing the recrystallization driving force during subsequent annealing and avoiding recovery or even recrystallization due to the temperature rise of the steel plate during rolling; annealing at 950-1100℃ for 1-120min avoids the precipitation of coarse Laves or sigma phases while ensuring the acquisition of samples with different grain sizes, achieving fine-grain strengthening; aging treatment at 300-600℃ for 5-40h ensures the acquisition of second-phase particles with different numbers and nanoscale sizes, achieving precipitation strengthening and plasticity improvement or enhancement. In summary, this invention is unique in terms of the optimized design of key alloying elements (nitrogen, titanium, niobium), the formulation of solid solution, annealing and aging process parameters, and the control of grain size and second-phase particles.

[0034] Compared with the prior art, the present invention has the following technical effects: First, the optimized alloy composition can ensure the superior thermodynamic stability of austenite. The stacking fault energy of the stainless steel of the present invention is calculated to be 52.6 mJ / m. 2The stacking fault energy is higher than that of ordinary austenitic stainless steel, and martensitic transformation does not occur even under large strain (75.1%). The ultrafine-grained austenite is obtained through recrystallization of austenite, rather than through reverse martensitic transformation. No magnetic phase was detected in the rolled sample by ferrite analysis and XRD, and no BCC phase was detected by EBSD. Therefore, the initial dislocation density inside the grain size is low, which ensures high strain hardening ability and thus improves uniform elongation. Second, the grain boundary stability is high. The grains do not grow significantly after high-temperature annealing (1100℃) or long-term aging (40h) treatment and can still maintain a fine size. Third, the optimized alloy composition design and reasonable preparation process parameters, and only the reasonable combination of annealing and aging treatment can obtain products with better comprehensive performance. Fourth, fewer alloying elements are added, resulting in low production cost. Fifth, the average grain size of the austenitic stainless steel prepared by this invention is 1.7-4.2μm, σ 0.2 =600-757MPa, tensile strength σ b =977-1051MPa, elongation 39-61%; strength-ductility product 38-60GPa·%. These are performance indicators that cannot be achieved by publicly available technologies. Attached Figure Description

[0035] Figure 1a The tensile stress-strain curve of the high-strength, high-ductility austenitic stainless steel sheet from Example 1, annealed at 950℃ for 1 hour and then aged at 550℃ for 7 hours, shows the excellent comprehensive tensile mechanical properties of the steel sheet, with a yield strength σ 0.2 =712MPa, tensile strength σ b =1040MPa, elongation 40.5%, strength-ductility product 42.120GPa·%;

[0036] Figure 1b The microstructure of the high-strength, high-plasticity austenitic stainless steel plate from Example 1, after annealing at 950°C for 1 hour and aging at 550°C for 7 hours, shows that the steel plate has relatively fine and uniform grains with an average grain size of 2.4 μm.

[0037] Figure 2a The tensile stress-strain curve of the high-strength, high-ductility austenitic stainless steel in Example 2, annealed at 1050℃ for 2 min, shows the good comprehensive mechanical properties of the steel plate, with a yield strength σ 0.2 =707MPa, tensile strength σ b =1020MPa, elongation 53.5%, strength-ductility product 54.570GPa·%;

[0038] Figure 2bThe image shows the microstructure of the high-strength, high-plasticity austenitic stainless steel plate after annealing at 1050℃ for 2 minutes in Example 2. It shows that the grains of the steel plate are relatively fine and uniform, with an average grain size of 3.3 μm.

[0039] Figure 3 The tensile stress-strain curve of the high-strength, high-ductility austenitic stainless steel sheet from Example 3, annealed at 1050℃ for 2 minutes and then aged at 550℃ for 40 hours, shows the good comprehensive tensile mechanical properties of the steel sheet, with a yield strength σ 0.2 =724MPa, tensile strength σ b =1045MPa, elongation 49%, strength-ductility product 51.120GPa·%;

[0040] Figure 4a The tensile stress-strain curve of the high-strength, high-ductility austenitic stainless steel sheet from Example 4, annealed at 1100℃ for 1 min, shows that the steel sheet exhibits high ductility at a high strength level, with a yield strength σ... 0.2 =600MPa, tensile strength σ b =977MPa, elongation 61%, strength-ductility product 59.597GPa·%;

[0041] Figure 4b The microstructure of the high-strength, high-plasticity austenitic stainless steel plate annealed at 1100℃ for 1 min in Example 4 is shown. It shows that the grains of the steel plate are relatively fine and uniform, with an average grain size of 4.2 μm.

[0042] Figure 5a The tensile stress-strain curve of the high-strength, high-ductility austenitic stainless steel sheet from Example 5, annealed at 1100℃ for 1 min and then aged at 550℃ for 16 h, shows the good comprehensive tensile mechanical properties of the steel sheet, with a yield strength σ 0.2 =676MPa, tensile strength σ b =1011MPa, elongation 51.5%, strength-ductility product 52.067GPa·%;

[0043] Figure 5b The microstructure of the high-strength, high-plasticity austenitic stainless steel sheet from Example 5, which was annealed at 1100℃ for 1 min and then aged at 550℃ for 16 h, shows that the steel sheet has relatively fine and uniform grains with an average grain size of 4.2 μm.

[0044] Figure 6 The tensile stress-strain curve of the high-strength, high-plasticity austenitic stainless steel plate of Comparative Example 1, which was annealed at 950℃ for 1 hour and then aged at 550℃ for 1 hour, shows that the elongation after fracture of the steel plate under this condition is 34%. It can be seen that the steel plate with an aging time of less than 5 hours has poor plasticity and low strength-ductility product, and does not achieve the mechanical performance effect of the present invention.

[0045] Figure 7 The tensile stress-strain curve of the high-strength, high-plasticity austenitic stainless steel plate annealed at 950℃ for 1 hour without aging treatment is shown in Comparative Example 2. The yield strength of the steel plate under this condition is 671 MPa, the tensile strength is 986 MPa, and the elongation after fracture is 37%. It can be seen that the steel plate without aging treatment has lower strength, poorer elongation after fracture, and lower strength-ductility product, and does not achieve the mechanical performance effect of the present invention.

[0046] Figure 8 Figure 1 shows the morphology and statistical results of the second-phase particles in the sample of the example; Figure 2 shows the morphology of the second-phase particles in the sample after annealing at 950℃ for 1 h and then aging at 550℃ for 7 h, and Figure 3 shows the corresponding statistical results of the second-phase particle size; Figure 4 shows the morphology of the second-phase particles in the sample after annealing at 950℃ for 1 h and then aging at 550℃ for 40 h, and Figure 55 shows the corresponding statistical results of the second-phase particle size.

[0047] Figure 9 The TEM microstructure of the sample in Comparative Example 2 shows the presence of coarse second-phase particles with an average size of approximately 98 nm, while no fine nano-second-phase particles were found.

[0048] Figure 10 The tensile stress-strain curve of the high-strength, high-plasticity austenitic stainless steel plate annealed at 850℃ for 1 hour without aging treatment, as shown in Comparative Example 3, reveals that the elongation after fracture of the steel plate under this condition is only 33.5%, the yield strength is 774 MPa, and the tensile strength is 1086 MPa. It can be seen that the mechanical properties of the steel plate are poor when the annealing temperature is 850℃, and the mechanical properties effect of the present invention is not achieved.

[0049] Figure 11 The tensile stress-strain curve of the high-strength, high-plasticity austenitic stainless steel plate annealed at 900℃ for 2 hours without aging treatment is shown in Comparative Example 4. The plate under this condition has a yield strength of 686 MPa, a tensile strength of 1000 MPa, and an elongation after fracture of 36%. It can be seen that the mechanical properties of the steel plate annealed at 900℃ for 2 hours are poor and do not achieve the mechanical properties effect of the present invention.

[0050] Figure 12 Thermodynamic calculations were performed to determine the dissolution of the precipitated phase after solid solution treatment.

[0051] Figure 13 This is a performance comparison between the present invention and existing technologies. Detailed Implementation

[0052] The present invention will be described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0053] Example 1

[0054] A high-strength, high-ductility austenitic stainless steel comprises the following components by weight percentage:

[0055] C: 0.07%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.22%, Ti: 0.05%, O: 0.005%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0056] The composition of the high-strength, high-ductility austenitic stainless steel described in Example 1 conforms to: Ni eq / Cr eq =0.963, γ SEF =55.22mJ / m 2 .

[0057] The production method of high-strength and high-plasticity austenitic stainless steel described in Example 1 includes smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging treatment.

[0058] Specifically, the process involves: smelting in a vacuum induction furnace and casting in a cast iron mold. High-purity nitrogen is used throughout the smelting process, maintained at a pressure of 0.2 MPa, with continuous protective casting. The cast billet is held at 1100℃ for 45 minutes in a heating furnace before forging to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet is then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature to obtain a solution-treated steel sample. The solution-treated steel sample is held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to achieve a steel plate thickness of 3.5 mm. During rolling, the sample is held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel plate is then annealed at 950℃ for 1 hour in a nitrogen atmosphere to obtain an annealed plate. The annealed plate is further aged at 550℃ for 7 hours to obtain an aged plate.

[0059] Figure 8 Figure (a) shows the morphology of the second-phase particles in the sample of Example 1, which was annealed at 950°C for 1 hour and then aged at 550°C for 7 hours. Figure (c) shows the corresponding statistical results of the second-phase particle size, with an average particle size of 14.1 nm. Figure (b) shows the morphology of the second-phase particles in the sample of Example 1, which was annealed at 950°C for 1 hour and then aged at 550°C for 40 hours. Figure (d) shows the corresponding statistical results of the second-phase particle size, with an average particle size of 11.5 nm.

[0060] The high-strength, high-ductility austenitic stainless steel finished plate has an average grain size of 2.4 μm and a yield strength σ 0.2 =712MPa, tensile strength σb =1040MPa, elongation 40.5%, strength-ductility product 42.120GPa·%. Test conditions: room temperature tensile test, tensile testing machine model DNS50, test tensile speed 0.9mm / min. The following examples and comparative examples were also conducted under these conditions.

[0061] Example 2

[0062] A high-strength, high-ductility austenitic stainless steel comprises the following components by weight percentage:

[0063] C: 0.06%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.20%, Ti: 0.06%, O: 0.004%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0064] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq =0.951, γ SEF =55.22mJ / m 2 .

[0065] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0066] Specifically, the process involves vacuum induction furnace smelting and casting in cast iron molds. High-purity nitrogen is used throughout the smelting process, maintained at a pressure of 0.2 MPa, with full protection during casting. The cast billet is held at 1100℃ for 45 minutes in a heating furnace before forging to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet is then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature to obtain a solution-treated steel sample. This sample is held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to achieve a thickness of 3.5 mm. During rolling, the sample is held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel plate is then annealed at 1050℃ for 2 minutes in a nitrogen atmosphere to obtain an annealed plate.

[0067] The high-strength, high-ductility austenitic stainless steel finished plate has an average grain size of 3.3 μm and a yield strength σ. 0.2 =707MPa, tensile strength σ b =1020MPa, elongation 53.5%, strength-ductility product 54.570GPa·%.

[0068] Example 3

[0069] A high-strength, high-ductility austenitic stainless steel comprises the following components by weight percentage:

[0070] C: 0.06%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.20%, Ti: 0.06%, O: 0.004%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0071] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq =0.951, γ SEF =55.22mJ / m 2 .

[0072] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0073] The specific process involves vacuum induction furnace smelting and casting in cast iron molds. High-purity nitrogen is used throughout the smelting process, maintained at a pressure of 0.2 MPa, with full-process protective casting. The cast billet is held at 1100℃ for 45 minutes in a heating furnace before forging to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet is then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature, yielding a solution-treated steel sample. This sample is held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to achieve a thickness of 3.5 mm. During rolling, the sample is held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel sheet is annealed at 1050℃ for 2 minutes in an air atmosphere to obtain an annealed plate. The annealed plate is further aged at 550℃ for 40 hours to obtain an aged plate.

[0074] The high-strength, high-ductility austenitic stainless steel finished plate has an average grain size of 3.3 μm and a yield strength σ. 0.2 =724MPa, tensile strength σ b =1045MPa, elongation 49%, strength-ductility product 51.205GPa·%.

[0075] Example 4

[0076] A high-strength, high-ductility austenitic stainless steel and its preparation method, comprising the following components by mass percentage:

[0077] C: 0.06%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.20%, Ti: 0.06%, O: 0.004%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0078] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq =0.951, γ SEF =55.22mJ / m 2 .

[0079] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0080] Specifically, the process involves vacuum induction furnace smelting and casting in cast iron molds. High-purity nitrogen is used throughout the smelting process, maintained at a pressure of 0.2 MPa, with continuous protective casting. The cast billet is held at 1100℃ for 45 minutes in a heating furnace before forging to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet is then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature to obtain a solution-treated steel sample. The solution-treated steel sample is held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to achieve a steel plate thickness of 3.5 mm. During rolling, the sample is held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel plate is then annealed to obtain an annealed plate at 1100℃ for 1 minute in a nitrogen atmosphere.

[0081] The high-strength, high-ductility austenitic stainless steel finished plate has an average grain size of 4.2 μm and a yield strength σ. 0.2 =600MPa, tensile strength σ b =977MPa, elongation 61%, strength-ductility product 59.597GPa·%.

[0082] Example 5

[0083] A high-strength, high-ductility austenitic stainless steel and its preparation method, comprising the following components by mass percentage:

[0084] C: 0.06%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.20%, Ti: 0.06%, O: 0.004%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0085] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Nieq / Cr eq =0.951, γ SEF =55.22mJ / m 2 .

[0086] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0087] Specifically, a vacuum induction furnace was used for smelting, followed by casting in an iron mold. High-purity nitrogen was used throughout the smelting process, maintaining a pressure of 0.2 MPa for continuous protection during casting. The cast billet was held at 1100℃ for 45 minutes in a furnace before forging to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet was then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature, yielding a solution-treated steel sample. This sample was held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to achieve a thickness of 3.5 mm. During rolling, the sample was held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel sheet was annealed at 1100℃ for 1 minute in a nitrogen atmosphere to obtain an annealed plate. The annealed plate was further aged at 550℃ for 16 hours to obtain an aged plate.

[0088] The high-strength, high-ductility austenitic stainless steel finished plate has an average grain size of 4.2 μm and a yield strength σ. 0.2 =676MPa, tensile strength σ b =1011MPa, elongation 51.5%, strength-ductility product 52.067GPa·%.

[0089] Comparative Example 1

[0090] A high-strength, high-ductility austenitic stainless steel and its preparation method, comprising the following components by mass percentage:

[0091] C: 0.07%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.22%, Ti: 0.05%, O: 0.005%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0092] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq =0.963, γ SEF =55.22mJ / m 2 .

[0093] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0094] Specifically, a vacuum induction furnace was used for smelting, followed by casting in an iron mold. High-purity nitrogen was used throughout the smelting process, maintaining a pressure of 0.2 MPa, with full protection during casting. The cast billet was held at 1100℃ for 45 minutes in a furnace before forging to a thickness of 14 mm, and then water-cooled to room temperature. The forged billet was then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature, yielding a solution-treated steel sample. This sample was held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to produce a steel plate with a thickness of 3.5 mm. During rolling, the sample was held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel plate was annealed at 950℃ for 1 hour in a nitrogen atmosphere to obtain an annealed plate. The annealed plate was further aged at 550℃ to obtain an aged plate. The time is 1 hour .

[0095] The high-strength, high-ductility austenitic stainless steel finished plate has an average grain size of 2.4 μm and a yield strength σ 0.2 =713MPa, tensile strength σ b =1037MPa, elongation is 34％ Strong plastic volume is 35.258 GPa·% .

[0096] The relatively short aging time in Comparative Example 1 resulted in an insufficient number of second-phase particles. This is because the precipitation of second-phase particles is a diffusion-type phase transition, occurring through nucleation and growth. The short treatment time and insufficient diffusion prevented the effective precipitation of second-phase particles, leading to a low number. Insufficient second-phase particles cannot provide an effective source for dislocation multiplication, thus failing to improve the sample's plasticity and potentially causing cracks at the interface between the second-phase particles and the matrix due to stress concentration, thereby reducing plasticity.

[0097] Comparative Example 2

[0098] A high-strength, high-ductility austenitic stainless steel and its preparation method, comprising the following components by mass percentage:

[0099] C: 0.07%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.22%, Ti: 0.05%, O: 0.005%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0100] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq =0.963, γSEF =55.22mJ / m 2 .

[0101] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0102] Specifically, a vacuum induction furnace was used for smelting, followed by casting in an iron mold. High-purity nitrogen was used throughout the smelting process, maintaining a pressure of 0.2 MPa for continuous protection during casting. The cast billet was held at 1100℃ for 45 minutes in a furnace before forging to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet was then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature, yielding a solution-treated steel sample. This sample was held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to achieve a thickness of 3.5 mm. During rolling, the sample was held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel plate was then annealed at 950℃ for 1 hour in a nitrogen atmosphere to obtain an annealed plate.

[0103] Figure 9 The TEM microstructure of the sample in Comparative Example 2 shows the presence of coarse second-phase particles with an average size of approximately 98 nm, while no fine nano-second-phase particles were found.

[0104] The high-strength, high-ductility austenitic stainless steel finished plate has an average grain size of 2.4 μm and a yield strength σ 0.2 =671MPa, tensile strength σ b =986MPa, The elongation rate is 37%. The strength-plasticity product was 36.482 GPa·%. Comparative Example 2, without aging treatment, did not precipitate nano-second phase particles and had coarse precipitates, resulting in low elongation.

[0105] Comparative Example 3

[0106] A high-strength, high-ductility austenitic stainless steel and its preparation method, comprising the following components by mass percentage:

[0107] C: 0.06%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.20%, Ti: 0.06%, O: 0.004%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0108] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq =0.951, γ SEF =55.22mJ / m 2.

[0109] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0110] Specifically, a vacuum induction furnace was used for smelting, followed by casting in an iron mold. High-purity nitrogen was used throughout the smelting process, maintained at a pressure of 0.2 MPa, with full-process protective casting. The cast billet was held at 1100℃ for 45 minutes in a furnace before forging to a thickness of 14 mm, and then water-cooled to room temperature. The forged billet was then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature to obtain a solution-treated steel sample. This sample was held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to produce a steel plate with a thickness of 3.5 mm. During rolling, the sample was held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel plate was then annealed to obtain an annealed plate. The annealing temperature was 850℃ and the time was 1 hour. The atmosphere used is nitrogen.

[0111] The average grain size of the high-strength, high-ductility austenitic stainless steel finished plate is 1.1μm Yield strength s 0.2 = 774MPa ,tensile strength s b =1086MPa , The elongation rate is 33.5%. The strength-plasticity product is 36.381 GPa·%.

[0112] The annealing temperature in Comparative Example 3 was 850℃. 800-900℃ is a sensitive temperature for the precipitation of sigma phase in austenitic stainless steel. In the experiment of this application, sigma phase was also observed to precipitate in the steel sample at this temperature. sigma phase is brittle and hard, which is not conducive to plasticity. Therefore, the elongation of the sample annealed at this temperature is low.

[0113] Comparative Example 4

[0114] A high-strength, high-ductility austenitic stainless steel and its preparation method, comprising the following components by mass percentage:

[0115] C: 0.06%, N: 0.39%, Si: 1.55%, Cr: 20.1%, Ni: 9.1%, Mn: 2.8%, Mo: 2.8%, Nb: 0.20%, Ti: 0.06%, O: 0.004%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0116] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq =0.951, γ SEF =55.22mJ / m 2 .

[0117] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0118] Specifically, vacuum induction furnace smelting and cast iron mold pouring are adopted. High-purity nitrogen is used during the smelting process, and the nitrogen pressure is maintained at 0.2MPa. The pouring process is protected throughout.

[0119] The cast billet was held at 1100℃ for 45 minutes in a furnace and then forged to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet was then held at 1200℃ for 3 hours in a box furnace, followed by water cooling to room temperature to obtain a solution-treated steel sample. The solution-treated steel sample was held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to produce a steel plate with a thickness of 3.5 mm. During the rolling process, the sample was held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel plate was then annealed to obtain an annealed plate at a temperature of [missing information - likely a specific temperature range]. 900℃, for 2 hours The atmosphere is created using air.

[0120] The average grain size of the high-strength, high-ductility austenitic stainless steel finished plate is 1.8μm, Yield strength σ 0.2 =686MPa, tensile strength σ b =1000MPa, elongation It is 36%. The strength-ductility product is 36 GPa·%. The annealing temperature in Comparative Example 4 is 900℃. At this temperature, the sigma phase precipitates in the steel sample. The sigma phase is brittle and hard, which is detrimental to plasticity. Therefore, the elongation of the sample annealed at this temperature is low.

[0121] Comparative Example 5

[0122] A high-strength, high-ductility austenitic stainless steel and its preparation method, comprising the following components by mass percentage:

[0123] C: 0.06%, N: 0.15%, Si: 1.35%, Cr: 18.5%, Ni: 8.0%, Mn: 2.0%, Mo: 2.0%, Nb: 0.20%, Ti: 0.03%, O: 0.004%, P+S = 0.0049%, with the remainder being Fe and unavoidable impurities.

[0124] The composition of the high-strength, high-ductility austenitic stainless steel conforms to: Ni eq / Cr eq S0.679 , γ SEF =36.95mJ / m 2 。

[0125] The preparation method of the high-strength and high-plasticity austenitic stainless steel is achieved through smelting, casting, forging, solution treatment, low-temperature rolling, annealing, and aging processes.

[0126] The specific process involves vacuum induction furnace smelting and casting in cast iron molds. High-purity nitrogen is used throughout the smelting process, maintained at a pressure of 0.2 MPa, with full protection during casting. The cast billet is held at 1100℃ for 45 minutes in a heating furnace before forging to a thickness of 14 mm, followed by water cooling to room temperature. The forged billet is then held at 1200℃ for 3 hours in a box-type resistance furnace, followed by water cooling to room temperature to obtain a solution-treated steel sample. This sample is held in liquid nitrogen for 15 minutes and then subjected to low-temperature rolling, undergoing at least 10 passes to achieve a thickness of 3.5 mm. During rolling, the sample is held in liquid nitrogen for 5 minutes every 4 passes. The low-temperature rolled steel sheet is annealed at 950℃ for 1 hour in either nitrogen or air. The annealed sheet is further aged at 550℃ for 7 hours to obtain an aged sheet.

[0127] The average grain size of the high-strength, high-ductility austenitic stainless steel finished plate is 1.3μm, Yield strength σ 0.2 =731MPa, Tensile strength σ b =1103MPa , The elongation was 33%, and the strength-ductility product was 36.399 GPa·%.

[0128] Although the composition of Comparative Example 5 is within the scope of this invention, Ni eq / Cr eq和 γ SEF (mJ / m 2 The product does not meet the requirements of this invention. Even if it is produced according to the method of this application, the composition results in a different tissue than the sample of this invention, so the performance is poor.

[0129] The underlined data above are data that do not meet the requirements of this invention.

[0130] The austenitic stainless steel prepared by this invention has an average grain size of 1.7-4.2 μm and σ 0.2 =600-757MPa, tensile strength σ b =977-1051MPa, elongation 39-61%; strength-ductility product 38-60GPa·%, which are performance indicators that cannot be achieved by existing publicly available technologies.

[0131] As can be seen from the above comparative examples, the elongation and strength-ductility product of austenitic stainless steel obtained by technical solutions not defined in the claims of this invention are relatively low, far from achieving the effect obtained by technical solutions defined in the claims of this invention.

[0132] The embodiments described above are merely typical embodiments of the present invention and are illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A high-strength high-plasticity austenitic stainless steel, characterized by, The high-strength and high-plasticity austenitic stainless steel has the following mass percentage components: C: 0.045%-0.085%, N: 0.10%-0.40%, Si: 0.90%-1.55%, Cr: 16%-20.1%, Ni: 7.5%-12.5%, Mn: 1.5%-3.5%, Mo: 1.5%-3.0%, Nb: 0.08%-0.22%, Ti: 0.015-0.065%, O≤0.005%, P≤0.003%, S≤0.003%, and the rest is Fe and inevitable impurities; The high-strength high-plasticity austenitic stainless steel has a composition satisfying: 0.75 ≤ Ni eq / Cr eq ≤ 1.50, Cr eq = %Cr + 1.5 × %Si + %Mo, Ni eq = %Ni + 30 × (%C + %N) + 0.5 × (%Mn + %Co + %Cu); 50 mJ / m 2 ≤ γ SEF ≤ 70 mJ / m 2 ; γ SEF = (-53) + 6.5 × %Ni + 0.7 × %Cr + 3.2 × %Mn + 9.3 × %Mo; γ SEF refers to an austenite stacking fault energy, and has a unit of mJ / m 2 . The production method of the high-strength and high-plasticity austenitic stainless steel comprises the following processes: smelting, pouring, forging, solid solution, low-temperature rolling, annealing; The low-temperature rolling is performed by liquid nitrogen insulation for 10-15 minutes before rolling, the rolling pass is not less than 10 passes, the total cold rolling reduction is controlled to be 70%-75%, the sample is insulated in liquid nitrogen for 5 minutes every 4 passes during the rolling process, and the low-temperature rolling plate thickness is controlled to be 2.5-3.5 mm. The annealing is performed at an annealing treatment temperature of 950-1100℃ for 1-120 minutes; when the annealing temperature is ≤1000℃, aging treatment is performed at an aging treatment temperature of 300-600℃ for 5-40 hours.

2. The high-strength high-plasticity austenitic stainless steel according to claim 1, characterized by, The microstructure of the high-strength and high-plasticity austenitic stainless steel is polygonal austenite and ferrite, the volume ratio of the ferrite is 0.2-1.2%, the average grain size is 1.7-4.2 μm, and the size range of the nanometer second phase particles is 10-20 nm.

3. The high-strength high-plasticity austenitic stainless steel according to claim 1 or 2, characterized by, The high-strength high-plasticity austenitic stainless steel has yield strength σ 0.2 = 600-757 MPa, tensile strength σ b = 977-1051 MPa, elongation of 39-61%, and product of strength and plasticity of 38-60 GPa·%.

4. A method of producing the high-strength high-plasticity austenitic stainless steel according to any one of claims 1 to 3, characterized by, The production method comprises the following processes: smelting, pouring, forging, solid solution, low-temperature rolling, annealing; The low-temperature rolling is performed by liquid nitrogen insulation for 10-15 minutes before rolling, the rolling pass is not less than 10 passes, the total cold rolling reduction is controlled to be 70%-75%, the sample is insulated in liquid nitrogen for 5 minutes every 4 passes during the rolling process, and the low-temperature rolling plate thickness is controlled to be 2.5-3.5 mm. The annealing is performed at an annealing treatment temperature of 950-1100℃ for 1-120 minutes; when the annealing temperature is ≤1000℃, aging treatment is performed at an aging treatment temperature of 300-600℃ for 5-40 hours.

5. The production method according to claim 4, characterized by, The forging is performed at a heating temperature of 1050-1150℃ for 45-60 minutes, and the cooling mode is water cooling.

6. The production method according to claim 4, characterized by, The solid solution is performed at a heating temperature of 1150-1200℃ for 2-3 hours, and the cooling mode is water cooling.

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