Cerium-nitrogen synergistic microalloyed superaustenitic stainless steel and preparation and application thereof

Abstract

The invention belongs to the field of anti-corrosion and anti-fouling new materials for engineering facilities and equipment in a harsh marine environment, and particularly relates to a cerium-nitrogen synergistic microalloyed marine anti-microbial corrosion super austenitic stainless steel and a preparation method of the cerium-nitrogen synergistic microalloyed marine anti-microbial corrosion super austenitic stainless steel. The steel comprises the following chemical components in percentage by mass: 22.8-23.2% of Cr, 24.8-25.2% of Ni, 5.4-5.6% of Mo, 0.18-0.22% of N, 0.4-2.0% of Ce, less than or equal to 0.025% of C, less than or equal to 0.4% of S i, less than or equal to 0.5% of Mn, less than or equal to 0.015% of P, less than or equal to 0.003% of S and the balance of Fe and inevitable trace impurities, and the steel meets the condition that PREN =% Cr + 3.3 *% Mo + 16 *% N > = 45.

Description

Technical Field

[0001] The present invention belongs to the field of new corrosion-resistant and antifouling materials for engineering facilities and equipment in harsh marine environments, and specifically relates to a cerium-nitrogen synergistically microalloyed marine microbial corrosion-resistant super austenitic stainless steel and a preparation method thereof. Background Art

[0002] The high salinity, high humidity, and microbial activity in the marine environment pose severe challenges to metal materials. In particular, the synergistic effects of chloride ion attack and microorganisms such as sulfate-reducing bacteria (SRB) lead to pitting, crevice corrosion, and microbial-induced corrosion in conventional stainless steel. For example, the widely used 316L austenitic stainless steel has a PREN value of only 25-30, and its pitting potential in a 3.5% NaCl solution is typically less than 0.3 V (SCE), making it unable to meet the long-term service requirements of deep-sea equipment. Although high-molybdenum super austenitic stainless steels (such as 254SMO, with a PREN ≥ 42) improve corrosion resistance by increasing Mo and N content, their poor hot workability limits their large-scale application. Even more challenging, the biofilms formed by marine microorganisms on the material surface secrete acidic metabolites (such as H2S and organic acids), which lower the local pH to below 2, accelerate the dissolution of the passive film, and induce intergranular corrosion. Therefore, the development of new stainless steels that combine high corrosion resistance, resistance to microbial adhesion, and manageable costs has become an urgent need in the field of marine engineering materials.

[0003] Existing MIC-resistant stainless steel mostly relies on surface coatings (such as Ag / Cu coatings) or biocide release strategies, but the coatings are easy to peel off, and the environmental toxicity of biocides does not meet the standards of green marine equipment. In recent years, the biological toxicity effects of rare earth elements have attracted attention: Ce 3+ Competitive replacement of Ca in bacterial cell membranes 2+ , disrupting the integrity of the film. However, Ce has a low solid solubility in conventional stainless steels, and its bioactivity is poor when present as CeO2 particles. Furthermore, while nitrogen can enhance the self-repair ability of the passive film, its inhibitory effect on microbial metabolism is minimal. Microalloying of rare earth elements with nitrogen has been introduced into stainless steel design, aiming to improve performance through grain boundary purification and passive film modification. However, single rare earth additions exceeding 0.1% are prone to forming coarse CeO2 inclusions, leading to microcracks during hot rolling. Nitrogen contents exceeding 0.25% can induce cold rolling brittleness, and nitrogen yields fluctuate widely in conventional smelting processes. Studies have found that while Ce addition alone can refine grains, solid solubility of rare earth Ce exceeding 0.3% induces lattice distortion, reducing the charge transfer resistance of the passive film by 30%. Furthermore, when nitrogen is used alone for strengthening, the Cr2N precipitates it promotes can act as Cl- permeation channels, increasing pitting corrosion susceptibility. Therefore, how to precisely control the Ce / N ratio to achieve synergistic effects while avoiding side effects has become a key difficulty in achieving technological breakthroughs. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of synergistic effect of chloride ion corrosion and microbial corrosion in marine environment, and propose a cerium-nitrogen synergistic microalloyed super austenitic stainless steel and its preparation and application.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A cerium-nitrogen synergistic microalloyed super austenitic stainless steel has the following chemical composition, by mass percentage: Cr: 22.8-23.2%, Ni: 24.8-25.2%, Mo: 5.4-5.6%, N: 0.18-0.22%, Ce: 0.4-2.0%, C≤0.025%, Si≤0.4%, Mn≤0.5%, P≤0.015%, S≤0.003%, the balance being Fe and unavoidable trace impurities, and satisfying PREN=%Cr+3.3×%Mo+16×%N≥45.

[0007] The mass ratio of Ce to N is 2.5:1 to 11:1, and Ce-N composite compound dispersed phase is synergistically formed in the microstructure.

[0008] The Ce-N composite compound dispersed phase is distributed in a continuous network along the austenite grain boundary, and the grain boundary coverage is ≥75%.

[0009] The Ce element is distributed in a bimodal manner, wherein 0.5-2.0% is supersaturated solid solution Ce, and the remainder is dispersedly distributed in the form of CeO2 nanoparticles, with a particle size of 20-50nm and a spacing of ≤200nm.

[0010] A method for preparing super austenitic stainless steel with cerium-nitrogen synergistic microalloying is characterized in that the Ce element is added in stages. In the first stage, it is added in the form of a Ce-Fe master alloy to achieve uniform microalloying of the matrix, and in the second stage, it is added in the form of CeO2 nanoparticles to achieve dispersion strengthening.

[0011] The following steps are involved:

[0012] (1) Batching and charging: Calculate the raw material ratio based on the elemental composition, and load the materials in layers according to melting point and chemical activity. Place the molybdenum-iron alloy at the bottom of the crucible, cover it with metallic chromium, place the chromium nitride particles in the charging hopper, vacuum seal it for standby use, and place the Ce-Fe master alloy in a dedicated charging bin;

[0013] (2) Melting: heating in stages, first raising the temperature to 1200°C at 10°C / min, holding for 30 minutes to pre-melt the low-melting-point metal, and then raising the temperature to 1550-1570°C at 5°C / min; simultaneously, introducing N2-Ar mixed gas into the vacuum induction furnace, controlling the N partial pressure to 0.15-0.25atm, and performing electromagnetic stirring during this period to promote uniform composition;

[0014] (3) Nitrogen alloying, deoxidation and desulfurization: After melting, fill N2 to 0.06atm, add Cr2N in three times, then add Al for pre-deoxidation, and evacuate to 5×10 -3 Pa, then Si-Ca alloy was added for deep desulfurization, and maintained for 10 min to complete deoxidation and desulfurization;

[0015] (4) Cerium microalloying: Ce element is added in stages: in the first stage, Ce-Fe master alloy is added to achieve uniform microalloying of the matrix: after deoxidation and desulfurization, Ar protection is added and Ce-Fe master alloy is added; in the second stage, CeO2 nanoparticles are added to achieve dispersion strengthening: CeO2 nanoparticles are added, the carrier gas is Ar, and the injection pressure is 0.3MPa;

[0016] (5) Casting and demolding: reduce the temperature to 1450℃ at 3℃ / min, fill with N2 to 0.07atm, cast at a speed of 15-20mm / min, slowly cool to 800℃ in the ingot mold and then demold to obtain super austenitic stainless steel with cerium-nitrogen synergistic microalloying.

[0017] In step (3), Cr2N is added every 2 minutes.

[0018] In step (4), the amount of Ce-Fe master alloy added in the first stage is 30%-50% of the total Ce content based on Ce content; the amount of CeO2 nanoparticles added in the first stage is 50%-70% of the total Ce content based on Ce content.

[0019] The cerium-nitrogen synergistically microalloyed super austenitic stainless steel is used to resist marine microbial corrosion.

[0020] The principle of the present invention is:

[0021] The Ce and N in super-austenitic stainless steel synergistically form a fine Ce-N composite compound dispersed phase in the microstructure. This dispersed phase is distributed in a continuous network along the austenite grain boundaries, with a grain boundary coverage of ≥75%. Ce improves material density by refining grains and purifying grain boundaries, while N enhances austenite stability and the repair ability of the passive film, forming a dynamic protective layer at the corrosion interface. The Ce element is distributed in a bimodal manner, with 0.5-2.0% being supersaturated solid-solution Ce and the remainder dispersed in the form of CeO2 nanoparticles with a particle size of 20-50nm and a spacing of ≤200nm. The supersaturated solid-solution Ce element is evenly distributed in the matrix, avoiding local depletion, significantly improving the density and stability of the stainless steel passivation film, and effectively blocking the intrusion of chloride ions, thereby significantly enhancing corrosion resistance.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention utilizes the unique chemical properties of cerium to develop a new microbial inhibition function. In the marine environment, cerium is Ce. 3+ Replaces Ca in bacterial cell membranes 2+ , destroying the cell membrane structure, reducing the attachment of marine microorganisms, reducing the risk of corrosion caused by microorganisms, and significantly enhancing the resistance to microbial corrosion. Through the design of high cerium content and the uniform distribution of cerium elements in the matrix, comprehensive inhibition of microbial attachment is achieved, providing a more reliable material choice for fields such as marine engineering and shipbuilding.

[0024] 2. The present invention achieves a significant improvement in material performance by precisely controlling the content range of key alloying elements and the cerium / nitrogen ratio, combined with phased addition and gas-shielded smelting processes. Its main components are an optimized combination of chromium, nickel, molybdenum, nitrogen and cerium, supplemented by strict control of impurity elements to ensure that the material has excellent corrosion resistance and structural stability. A step-by-step addition strategy is adopted to achieve uniform solid solution of cerium through an intermediate alloy, and then the grain boundaries are strengthened by nanoparticles, combined with nitrogen partial pressure control technology, to effectively improve the yield and distribution uniformity of nitrogen elements. The cerium-nitrogen synergistic microalloyed super austenitic stainless steel material of the present invention has corrosion resistance far exceeding that of traditional stainless steel in harsh marine environments, while avoiding the cost and processing difficulties brought about by high alloying.

[0025] 3. The synergistic effect of cerium and nitrogen in the present invention constructs a multi-level protection system. Microscopically, cerium and nitrogen form a composite compound dispersed phase, which can inhibit the growth of harmful inclusions Mns, reduce the pitting source caused by the dissolution of MnS, and reduce local corrosion. At the same time, cerium oxides (CeO2, Ce2O3) are embedded in the inner layer of the passivation film to form a Ce-O-Cr-N composite structure, which enhances the self-repair ability of the passivation film. The solid solution cerium combines with the matrix elements to form a stable composite phase, which enhances the density of the passivation film; the nitrogen element promotes the formation of a gradient passivation film, significantly improving the self-repair ability. In a microbial corrosion environment, the cerium-nitrogen synergistic phase forms a dynamic protective layer through chemical transformation, blocking the corrosion path of microbial metabolites. The material achieves long-term corrosion resistance and anti-microbial adhesion functions through the synergistic mechanism of "grain boundary strengthening-passivation film repair-chemical slow release". It is suitable for harsh environments such as deep-sea equipment and ship pipelines, and provides an efficient and sustainable corrosion protection solution for the field of marine engineering.

[0026] 4. The present invention forms Ce-N phase strengthened grain boundary at microscopic level and constructs Ce at mesoscopic level. 3+ The dual protection of slow release and nitrogen-enhanced passive film achieves long-term anti-microbial corrosion performance on a macro scale. The cerium-nitrogen synergistic microalloyed super austenitic stainless steel of the present invention has both excellent corrosion resistance and anti-microbial properties, and its passive film low-frequency impedance reaches 1×10 6 Ω·cm 2, the pitting potential in 3.5% NaCl solution is >1.2V, and through Ce 3+ Ion replacement of microbial cell membrane Ca 2+ The unique mechanism of the product has an inhibition rate of ≥99.5% against sulfate-reducing bacteria and can be widely used in harsh marine environments such as deep-sea equipment and ship pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 These are the performance data of the super austenitic stainless steel prepared in Example 1 of the present invention, where (A) is the electrochemical open circuit potential, (B) is the electrochemical resistance value, (C) is the electrochemical polarization curve, and (D) is the SEM image after antibacterial treatment.

[0028] Figure 2 These are the performance data of the super austenitic stainless steel prepared in Example 2 of the present invention, where (A) is the electrochemical open circuit potential, (B) is the electrochemical resistance value, (C) is the electrochemical polarization curve, and (D) is the SEM image after antibacterial treatment.

[0029] Figure 3 These are the performance data of the super austenitic stainless steel prepared in Example 3 of the present invention, where (A) is the electrochemical open circuit potential, (B) is the electrochemical resistance value, (C) is the electrochemical polarization curve, and (D) is the SEM image after antibacterial treatment.

[0030] Figure 4 These are the performance data of the super austenitic stainless steel prepared in Example 4 of the present invention, where (A) is the electrochemical open circuit potential, (B) is the electrochemical resistance value, (C) is the electrochemical polarization curve, and (D) is the SEM image after antibacterial treatment. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] The preparation method of the super austenitic stainless steel of cerium-nitrogen synergistic microalloying in the following embodiment is as follows:

[0033] (1) Batching and charging: Calculate the raw material ratio based on the elemental composition of the required steel grade. Load the materials in layers according to melting point and chemical activity. Place the molybdenum-iron alloy (block, 10-30 mm) on the bottom of the crucible, cover it with metal chromium blocks (50-100 mm), place chromium nitride particles (1-3 mm) in the feeding hopper, vacuum seal it for standby use, and pre-bake the Ce-Fe master alloy at 200°C for 2 hours and place it in a dedicated feeding bin.

[0034] (2) Melting: Staged heating: Initially, the temperature was raised to 1200°C at 10°C / min, and kept at this temperature for 30 min to pre-melt the low-melting-point metal. Later, the temperature was raised to 1560°C at 5°C / min to ensure the formation of a molten pool. At the same time, N2-Ar mixed gas was introduced into the vacuum induction furnace, and the N partial pressure was controlled at 0.18 atm. During this period, electromagnetic stirring was performed to promote uniform composition.

[0035] (3) Nitrogen alloying, deoxidation and desulfurization: After melting, fill with N2 to 0.06atm, N2 flow rate is 2L / min, add Cr2N through a vibrating feeder in 3 times, each time interval is 2min, first add Al (pure aluminum wire, φ2mm) for pre-deoxidation, and evacuate to 5×10 - 3 Pa, then Si-Ca alloy (Ca: 28%, particle size 3-5 mm) was added for deep desulfurization, and maintained for 10 min to complete deoxidation and desulfurization;

[0036] (4) Cerium microalloying: Ce elements are added in stages: in the first stage, Ce-Fe master alloy is added to achieve uniform microalloying of the matrix: after deoxidation and desulfurization, the temperature of the molten steel is maintained at 1540 ° C, Ar is added for protection, Ce-Fe master alloy (30% Ce content) is added, the electromagnetic stirring frequency is accelerated to promote diffusion; in the second stage, dispersion strengthening is achieved by adding CeO2 nanoparticles: the molten steel is cooled to 1520 ° C, CeO2 nanoparticles (70% Ce content) (particle size 50 nm) are added by aerosol spraying, the carrier gas is Ar, the injection pressure is 0.3 MPa, and ultrasonic assistance is used to make the particle distribution more uniform;

[0037] (5) Casting and demolding: The temperature was lowered to 1450℃ at 3℃ / min, filled with N2 to 0.07atm, and the casting speed was 17mm / min. The ingot mold was slowly cooled (200℃ / h) to 800℃ before demolding to obtain a super austenitic stainless steel material with cerium-nitrogen synergistic microalloying.

[0038] Example 1

[0039] The chemical composition of the cerium-nitrogen synergistic microalloyed super austenitic stainless steel is: Fe-22.97Cr-24.89Ni-5.57Mo-0.19N-0.48Ce.

[0040] The performance of Fe-22.97Cr-24.89Ni-5.57Mo-0.19N-0.48Ce material was tested. Figure 1 (A) It can be seen that the open circuit potential range of Fe-22.97Cr-24.89Ni-5.57Mo-0.19N-0.48Ce material is around -180mV, which has good corrosion resistance. Figure 1(B) It can be seen that the capacitance ring radius in the impedance spectrum of the Fe-22.97Cr-24.89Ni-5.57Mo-0.19N-0.48Ce material becomes larger, which shows good corrosion resistance. Figure 1 (C) It can be seen that the self-corrosion potential of Fe-22.97Cr-24.89Ni-5.57Mo-0.19N-0.48Ce material is -0.536mV, the passivation current density is reduced, and the pitting potential is increased. Figure 1 (D) It can be seen that after 28 days of SRB test, the surface of the Fe-22.97Cr-24.89Ni-5.57Mo-0.19N-0.48Ce material has only slight corrosion.

[0041] Example 2

[0042] The chemical composition of the cerium-nitrogen synergistic microalloyed super austenitic stainless steel is: Fe-23.09Cr-25.16Ni-5.48Mo-0.2N-1.02Ce.

[0043] The performance of Fe-23.09Cr-25.16Ni-5.48Mo-0.2N-1.02Ce material was tested. Figure 2 (A) It can be seen that the open circuit potential range of Fe-23.09Cr-25.16Ni-5.48Mo-0.2N-1.02Ce material is around -160mV, which has good corrosion resistance. Figure 2 (B) It can be seen that the capacitance ring radius in the impedance spectrum of the Fe-23.09Cr-25.16Ni-5.48Mo-0.2N-1.02Ce material becomes larger, and it has good corrosion resistance. Figure 2 (C) It can be seen that the self-corrosion potential is -0.469mV, the passivation current density decreases, and the pitting potential increases. Figure 2 (D) It can be seen that there is no corrosion on the surface of the sample of Fe-23.09Cr-25.16Ni-5.48Mo-0.2N-1.02Ce material after 28 days of SRB test.

[0044] Example 3

[0045] The chemical composition of the cerium-nitrogen synergistic microalloyed super austenitic stainless steel is: Fe-22.98Cr-25.06Ni-5.52Mo-0.19N-1.48Ce.

[0046] The performance test of Fe-22.98Cr-25.06Ni-5.52Mo-0.19N-1.48Ce material was carried out. Figure 3(A) It can be seen that the open circuit potential range of the Fe-22.98Cr-25.06Ni-5.52Mo-0.19N-1.48Ce material is around -260mV, which has good corrosion resistance. Figure 3 (B) It can be seen that the capacitance ring radius in the impedance spectrum of the Fe-22.98Cr-25.06Ni-5.52Mo-0.19N-1.48Ce material becomes larger, which shows good corrosion resistance. Figure 3 (C) It can be seen that the self-corrosion potential is -0.624mV, the passivation current density decreases, and the pitting potential increases. Figure 3 (D) It can be seen that after 28 days of SRB test, the surface of the Fe-22.98Cr-25.06Ni-5.52Mo-0.19N-1.48Ce sample has only slight corrosion.

[0047] Example 4

[0048] The chemical composition of the super austenitic stainless steel with cerium-nitrogen synergistic microalloying is: Fe-23.12Cr-24.89Ni-5.53Mo-0.21N-1.97Ce.

[0049] The performance test of Fe-23.12Cr-24.89Ni-5.53Mo-0.21N-1.97Ce material was carried out. Figure 4 (A) It can be seen that the open circuit potential range of Fe-23.12Cr-24.89Ni-5.53Mo-0.21N-1.97Ce material is around -320mV, which has good corrosion resistance. Figure 4 (B) It can be seen that the capacitance ring radius in the impedance spectrum of the Fe-23.12Cr-24.89Ni-5.53Mo-0.21N-1.97Ce material becomes larger, and it has good corrosion resistance. Figure 4 (C) It can be seen that the self-corrosion potential is -0.793mV, the passivation current density decreases, and the pitting potential increases. Figure 4 (D) It can be seen that after 28 days of SRB test, the surface of the Fe-23.12Cr-24.89Ni-5.53Mo-0.21N-1.97Ce sample has only slight corrosion.

[0050] Comparative Example 1

[0051] Performance testing of 153MA stainless steel (commercially available, with a Ce content of 0.03-0.08%, a N content of 0.12-0.18%, and a Ce / N mass ratio of less than 2.5) revealed that electrochemical impedance spectroscopy (EIS) showed that the passivation film resistance was only 30-50% of that of the material in Example 1. The increased defect density resulted in a sharp increase in the sulfate-reducing bacteria (SRB) corrosion current density (Icorr), and the biofilm coverage of SRB bacteria reached as high as 80%.

[0052] Since the Ce / N mass ratio of the comparative example 1 material is less than 2.5, the resistance of the passivation film is reduced and the biofilm coverage of SRB bacteria is increased. It is also found that when the Ce / N mass ratio is greater than 11, intergranular sensitization is aggravated, the stability of the passivation film decreases, and the intergranular corrosion rate increases. Excessive Ce causes inclusion coarsening (such as CeO2, Ce2O3), destroys the continuity of the passivation film, and increases the self-corrosion current density (such as 0Cr17Mo steel, the self-corrosion current density increases by about 30%). At the same time, excessive Ce can cause grain boundary segregation and weaken the antibacterial durability (the antibacterial rate drops from 99% to 85%). Therefore, the present invention controls the Ce / N mass ratio to be 2.5-11, and Ce and N synergistically optimize the passivation film (such as CeO2 and Cr2O3 composite film), so that the pitting corrosion resistance potential is increased by 50-100mV. At the same time, the coverage can be controlled to <5% by the Ce / N synergistic effect, and the microbial corrosion rate is reduced by 63%.

[0053] Comparative Example 2

[0054] This method differs from Example 1 in that elemental Ce is added in the form of a Ce-Fe master alloy during tapping from the vacuum induction furnace, without secondary dispersion strengthening. This method achieves uniform cerium distribution through argon purging and stirring, but does not introduce nano-oxide particles. The single addition of metallic Ce primarily forms oxysulfide inclusions such as Ce₂O₂S or CeS, which can be as large as 1-5 μm. Coarse inclusions can act as corrosion initiation sites, reducing the stability of the passive film and significantly degrading corrosion resistance.

[0055] Therefore, the embodiment of the present invention adopts a staged addition of Ce: the first stage is to achieve uniform microalloying of the matrix with Ce-Fe master alloy, and the second stage is to achieve CeO2 nanoparticle dispersion strengthening. The Ce-Fe master alloy is used to achieve solid solution of cerium, refine the grains, and inhibit the coarsening of Cr2N at the grain boundaries. CeO2 nanoparticles act as heterogeneous nucleation cores and are evenly dispersed in the matrix to improve creep resistance and corrosion resistance. In the staged process, Ce 3+ The sustained release of CeO2 promotes the densification of Cr / Fe oxides in the passivation film, and CeO2 nanoparticles generate reactive oxygen species (ROS) through photocatalysis, which inhibits the attachment of sulfate-reducing bacteria (SRB).

[0056] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the spirit and scope of protection of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the scope of protection of the present invention.

Claims

1. A super austenitic stainless steel with cerium-nitrogen synergistic microalloying, characterized in that: The cerium-nitrogen synergistic microalloyed super austenitic stainless steel has a chemical composition, in terms of mass percentage, of Cr: 22.8-23.2%, Ni: 24.8-25.2%, Mo: 5.4-5.6%, N: 0.18-0.22%, Ce: 0.4-2.0%, C≤0.025%, Si≤0.4%, Mn≤0.5%, P≤0.015%, S≤0.003%, and the balance is Fe and unavoidable trace impurities, and satisfies PREN=%Cr+3.3×%Mo+16×%N≥45.

2. The cerium-nitrogen synergistic microalloyed super austenitic stainless steel according to claim 1, characterized in that: The mass ratio of Ce to N is 2.5:1 to 11:1, and Ce-N composite compound dispersed phase is synergistically formed in the microstructure.

3. The cerium-nitrogen synergistically microalloyed super austenitic stainless steel according to claim 2, characterized in that: The Ce-N composite compound dispersed phase is distributed in a continuous network along the austenite grain boundary, and the grain boundary coverage is ≥75%.

4. The cerium-nitrogen synergistic microalloyed super austenitic stainless steel according to claim 2, characterized in that: The Ce element is distributed in a bimodal manner, wherein 0.5-2.0% is supersaturated solid solution Ce, and the remainder is dispersedly distributed in the form of CeO2 nanoparticles, with a particle size of 20-50nm and a spacing of ≤200nm.

5. A method for preparing the cerium-nitrogen synergistic microalloyed super austenitic stainless steel according to claim 1, characterized in that: The Ce element is added in stages. In the first stage, it is added in the form of Ce-Fe master alloy to achieve uniform microalloying of the matrix. In the second stage, it is added in the form of CeO2 nanoparticles to achieve dispersion strengthening.

6. The preparation method according to claim 5, characterized in that The following steps are involved: (1) Batching and charging: Calculate the raw material ratio based on the elemental composition, and load the materials in layers according to melting point and chemical activity. Place the molybdenum-iron alloy at the bottom of the crucible, cover it with metallic chromium, place the chromium nitride particles in the charging hopper, vacuum seal it for standby use, and place the Ce-Fe master alloy in a dedicated charging bin; (2) Melting: heating in stages, first raising the temperature to 1200°C at 10°C / min, holding for 30 minutes to pre-melt the low-melting-point metal, and then raising the temperature to 1550-1570°C at 5°C / min; simultaneously, introducing N2-Ar mixed gas into the vacuum induction furnace, controlling the N partial pressure to 0.15-0.25atm, and performing electromagnetic stirring during this period to promote uniform composition; (3) Nitrogen alloying, deoxidation and desulfurization: After melting, fill N2 to 0.06atm, add Cr2N in three times, then add Al for pre-deoxidation, and evacuate to 5×10 -3 Pa, then Si-Ca alloy was added for deep desulfurization, and maintained for 10 min to complete deoxidation and desulfurization; (4) Cerium microalloying: Ce element is added in stages: in the first stage, Ce-Fe master alloy is added to achieve uniform microalloying of the matrix: after deoxidation and desulfurization, Ar protection is added and Ce-Fe master alloy is added; in the second stage, CeO2 nanoparticles are added to achieve dispersion strengthening: CeO2 nanoparticles are added, the carrier gas is Ar, and the injection pressure is 0.3MPa; (5) Casting and demolding: reduce the temperature to 1450℃ at 3℃ / min, fill with N2 to 0.07atm, cast at a speed of 15-20mm / min, slowly cool to 800℃ in the ingot mold and then demold to obtain super austenitic stainless steel with cerium-nitrogen synergistic microalloying.

7. The preparation method according to claim 6, characterized in that In step (3), Cr2N is added every 2 minutes.

8. The preparation method according to claim 6, characterized in that In step (4), the amount of Ce-Fe master alloy added in the first stage is 30%-50% of the total Ce content based on Ce content; the amount of CeO2 nanoparticles added in the first stage is 50%-70% of the total Ce content based on Ce content.

9. The cerium-nitrogen synergistically microalloyed super austenitic stainless steel according to claim 1 is used for resisting marine microbial corrosion.

Images