Corrosion-resistant and antimicrobial bifunctional austenitic stainless steel containing rare earth element lanthanum and preparation and application of corrosion-resistant and antimicrobial bifunctional austenitic stainless steel

Abstract

The invention belongs to the field of novel corrosion-resistant materials for engineering facilities and equipment in a marine environment, has double functions of corrosion resistance and microorganism resistance, and relates to corrosion-resistant and microorganism-resistant double-function austenitic stainless steel containing rare earth element La as well as preparation and application of the corrosion-resistant and microorganism-resistant double-function austenitic stainless steel. The stainless steel comprises the following chemical components in percentage by weight: 19.5-20.5% of Cr, 17.5-18.5% of Ni, 5.5-6.5% of Mo, 0.75-0.85% of Cu, 0.5-2.0% of La, 0.18-0.22% of N, less than or equal to 0.03% of C, less than or equal to 0.5% of S i, less than or equal to 0.8% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S and the balance of Fe and inevitable trace impurities, and PREN =% Cr + 3.3 *% Mo + 16 *% N > = 45.

Description

Technical Field

[0001] The present invention belongs to the field of new corrosion-resistant materials for engineering facilities and equipment in marine environments, has dual functions of corrosion resistance and antimicrobial properties, and relates to a corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La, and its preparation and application. Background Art

[0002] As marine engineering equipment expands into deep-sea and offshore areas, traditional austenitic stainless steel faces severe challenges from the coupling of microbial corrosion and high chloride ion erosion in long-term seawater environments. Substances such as hydrogen sulfide and organic acids produced by the metabolism of marine microorganisms can easily form localized corrosion micro-batteries on the surface of the material, accelerating the rupture of the passivation film and inducing preferential dissolution of grain boundaries. Although conventional high-alloy stainless steel has improved its pitting resistance through the use of molybdenum and nitrogen elements, its resistance mechanism to microbial corrosion is insufficient. Existing solutions mostly rely on the release of ions from antibacterial elements such as copper and silver, but this can easily lead to a decrease in the corrosion resistance of the matrix, and it can fail due to ion depletion during long-term immersion, making it difficult to meet the long-term service requirements of marine equipment.

[0003] In recent years, the functional application of rare earth elements in marine steel has attracted much attention. Studies have shown that lanthanum (La) can improve corrosion resistance through grain boundary purification and nano-precipitation phase regulation, but its solid solubility in the austenite matrix is ​​extremely low. The traditional single addition method is prone to cause segregation, and excessive La is prone to form coarse precipitates, which in turn reduces the toughness of the material. At the same time, nitrogen (N) acts as an austenite stabilizer, and its synergistic effect with rare earths can optimize the structure of the passivation film, but the existing technology still has gaps in the research on the dynamic repair ability of the passivation film synergistically regulated by La-N. For example, conventional smelting processes make it difficult to achieve a gradient distribution of La and precise penetration of N, resulting in a single protective layer structure that cannot effectively block the synergistic effect of Cl- penetration and microbial attachment. Summary of the Invention

[0004] The purpose of the present invention is to provide a corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing rare earth lanthanum (La) and its preparation and application, which is particularly suitable for long-term protection of marine engineering equipment.

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

[0006] Disclosed is a corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La. The chemical composition of the stainless steel is as follows by weight: 19.5-20.5% of Cr, 17.5-18.5% of Ni, 5.5-6.5% of Mo, 0.75-0.85% of Cu, 0.5-2.0% of La, 0.18-0.22% of N, ≤0.03% of C, ≤0.5% of Si, ≤0.8% of Mn, ≤0.02% of P, ≤0.005% of S, with the balance being Fe and unavoidable trace impurities, and satisfying PREN=%Cr+3.3×%Mo+16×%N≥45.

[0007] The mass ratio of La to N is 2.3-9.4.

[0008] In the microstructure, La-N composite dispersed phase is formed, which is distributed in a continuous network along the austenite grain boundaries with a grain boundary coverage of ≥80%. La refines the grains and forms a dispersed strengthening phase to improve the density of the material. N enhances the stability of austenite, promotes the repair of the passivation film, and forms a dynamic protective layer to prevent corrosion.

[0009] The La element exists in a bimodal state, in which 0.7-2.0% of the La element is in a supersaturated solid solution state; the remaining La element is dispersed in the form of La2O3 nanoparticles with a particle size of 30-50nm and a spacing of ≤200nm; and La and Cu form nanoscale Cu-La intermetallic compounds, which are evenly distributed in the matrix, improving the stability and density of the stainless steel passivation film, thereby significantly enhancing the corrosion resistance.

[0010] A method for preparing the corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La comprises the following steps: firstly smelting the base metals Fe, Cr, Ni, Mo, and Cu, introducing high-purity nitrogen gas after they are completely melted to achieve nitrogen alloying, then adding the rare earth element La in stages, and subsequently performing low-superheat casting to obtain the corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La.

[0011] The rare earth element La is added in stages. In the first stage, it is added in the form of La-Fe composite master alloy to achieve solid solution strengthening at the lattice level. In the second stage, La2O3 nanoparticles are introduced for interface modification.

[0012] Specifically, the following steps are included:

[0013] (1) Prepare raw materials: prepare raw materials according to the target composition ratio;

[0014] (2) Adding raw materials: First, add 80-90% Fe as the base metal into a vacuum induction melting furnace, heat it to 1550-1570°C to ensure complete melting, then cool it to 1500-1520°C and add high-purity metal Cr, stir it electromagnetically for 10-15 minutes, then add Ni raw material, stir it electromagnetically for 10-15 minutes, heat it to 1550-1570°C and add Mo raw material, stir it electromagnetically for 15-20 minutes, then cool it to 1480-1500°C and add Cu raw material, stir it electromagnetically for 5-10 minutes;

[0015] (3) Nitrogen alloying: cooling to 1450-1480℃, adding nitrogen, using pulsed nitrogen injection process, adjusting nitrogen partial pressure to 0.15-0.25atm, and electromagnetic stirring for 10-15min;

[0016] (4) Introduction of rare earth element La: Cooling to 1420-1450℃, adding rare earth element La in stages. In the first stage, 60% of the total La is added in the form of La-Fe composite master alloy to achieve solid solution strengthening at the lattice level. In the second stage, La2O3 nanoparticles are introduced for interface modification, adding 40% of the total La.

[0017] (5) Low superheat casting: The pressure in the vacuum induction furnace is maintained at 0.07-0.08 atm, and the temperature of the molten steel is controlled in the range of 1430-1490 ° C for low superheat casting. After the ingot is cooled, it is solution treated at 1200 ° C for 1 hour, and then rapidly water-cooled to obtain a corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing rare earth element La.

[0018] In step (2), Mo was added in two batches, with an interval of 3 minutes between each batch.

[0019] The corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La is applied to marine microbial corrosion.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention uses a core alloy system of Cr, Ni, Mo, Cu, La, and N in specific proportions. While maintaining the original corrosion resistance of austenitic stainless steel, it significantly enhances its ability to resist the attachment of marine microorganisms and biocorrosion, solving the problem of localized corrosion failure caused by microbial metabolites (such as hydrogen sulfide and organic acids) in traditional austenitic stainless steel during long-term service in marine environments.

[0022] 2. The present invention achieves precise control of La content through a phased alloying process: first, a La-Fe composite master alloy is used for lattice solid solution strengthening. Then, La2O3 nanoparticles are dispersed throughout the matrix via plasma-assisted atomization. Combined with pulsed nitrogen injection and electromagnetic oscillation temperature control, a La-N synergistic gradient melt environment is created. Within the microstructure, La exhibits a multi-morphological distribution: La added as a La-Fe composite master alloy achieves solid solution strengthening at the lattice level. La added in the second phase is dispersed as La2O3 nanoparticles for interface modification. The remaining La combines with Cu to form a nanoscale Cu-La intermetallic compound, which is uniformly distributed throughout the matrix and exhibits both antibacterial and corrosion resistance.

[0023] 2. The present invention constructs a "sandwich" composite protection system through La / N mass ratio (2.3-9.4) regulation and interface engineering: the outer layer is La-O-Cr composite oxide, which blocks Cl- penetration; the middle nitrogen-rich transition layer disperses the corrosion current through the Cr2N precipitation phase network; the inner layer is a nano-precipitation strengthening matrix. 2+ Selectively released from the micropores of the passivation film, La2O3 nanoparticles disrupt microbial cell membranes. La2O3 nanoparticles are embedded in the passivation film to form a Cu-La-O composite structure, synergistically improving density. This material exhibits excellent resistance to microbial corrosion in simulated seawater environments, making it suitable for harsh corrosive environments such as deep-sea pipelines and ship ballast tanks, with an inhibition rate of ≥99.0% against sulfate-reducing bacteria. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Performance data of the Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material 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 potentiodynamic polarization curve, and (D) is the surface morphology of the material after 28 days of corrosion in a sulfate-reducing bacteria environment.

[0025] Figure 2 Performance data of the Fe-19.97Cr-18.16Ni-5.97Mo-0.79Cu-0.19N-0.98La material 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 potentiodynamic polarization curve, and (D) is the surface morphology of the material after 28 days of corrosion in a sulfate-reducing bacteria environment.

[0026] Figure 3Performance data of the Fe-20.13Cr-17.97Ni-6.02Mo-0.81Cu-0.21N-1.48La material 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 potentiodynamic polarization curve, and (D) is the surface morphology of the material after 28 days of corrosion in a sulfate-reducing bacteria environment.

[0027] Figure 4 Performance data of the Fe-20.26Cr-18.15Ni-5.93Mo-0.79Cu-0.19N-1.98La material 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 potentiodynamic polarization curve, and (D) is the surface morphology of the corrosion reaction in a sulfate-reducing bacteria environment for 28 days. DETAILED DESCRIPTION

[0028] 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.

[0029] The present invention uses La-Fe composite master alloys to achieve solid solution strengthening at the lattice level in austenitic stainless steel, thereby improving the mechanical properties and corrosion resistance of the steel. At the same time, plasma-assisted atomization technology is used to introduce La2O3 nanoparticles into the melt for interface modification. This ensures that the rare earth elements are evenly distributed in the steel, further optimizing the performance of the steel. During the vacuum melting process, a pulsed N2 injection process is used to promote the dissolution of nitrogen, and electromagnetic oscillation technology is used to ensure that the temperature fluctuation of the melt does not exceed ±15°C, thereby avoiding compositional inhomogeneities and fluctuations in physical properties caused by temperature fluctuations. After the above steps are completed, low-superheat casting is performed to reduce segregation and the formation of pores, thereby ensuring the quality and uniformity of the ingot. After the ingot is cooled, a rapid water cooling treatment is then performed to optimize the organizational structure of the steel and enhance the comprehensive mechanical properties of the steel, especially its stability and corrosion resistance under high temperature conditions.

[0030] The preparation method of the corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La in the following embodiment is as follows:

[0031] (1) Prepare raw materials: prepare industrial pure iron, metallic chromium, electrolytic nickel, molybdenum iron alloy, electrolytic copper and other raw materials according to the designed target composition ratio.

[0032] (2) Adding raw materials: First, add 90% Fe as the base metal into the vacuum induction melting furnace, heat it to 1570℃ to ensure complete melting, and reserve 10% Fe to be added after the La element is added to fine-tune the final composition. Subsequently, cool it to 1500℃ and add high-purity metal Cr. Electromagnetic stirring is performed for 10 minutes to ensure that Cr is completely dissolved. Then, Ni raw materials are added at one time and electromagnetic stirring is performed for 10 minutes to ensure that Ni is fully dissolved. Heat it to 1570℃ and add Mo raw materials: add Mo in two batches, with an interval of 3 minutes between each batch. Electromagnetic stirring is performed for 15 minutes to promote uniform diffusion of Mo. Then, cool it to 1500℃ and add Cu at one time. Electromagnetic stirring is performed for 5 minutes to ensure that Cu is evenly distributed.

[0033] (3) Nitrogen alloying: Cool the melt to 1450°C and add nitrogen to avoid nitrogen volatilization or uneven precipitation due to excessive temperature. The total addition amount is 0.2 wt.%. A pulsed N2 injection process is used to dynamically adjust the nitrogen partial pressure at 0.20 atm to promote nitrogen dissolution. Electromagnetic stirring is performed for 10 minutes to ensure that the temperature fluctuation of the melt does not exceed ±15°C to avoid compositional inhomogeneity and physical property fluctuations caused by temperature fluctuations. Nitrogen alloying significantly improves the strength, corrosion resistance, and high-temperature stability of austenitic stainless steel.

[0034] (4) Introduction of rare earth element La: Cooling to 1420℃ to prevent La from oxidation and burning. A phased La addition strategy is adopted. In the first phase, La-Fe composite master alloy is added to achieve solid solution strengthening at the lattice level, adding 60% of the total La content; in the second phase, plasma-assisted atomization technology is used to introduce La. a2 O3 nanoparticles were used for interface modification, and 40% of the total amount of La was added.

[0035] (5) Low superheat casting: After the above steps are completed, the pressure in the vacuum induction furnace is maintained at 0.07 atm, and the molten steel temperature is controlled at 1450°C for low superheat casting. After the ingot is cooled, it is solution treated at 1200°C for 1 hour, followed by rapid water cooling to obtain a corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La.

[0036] Example 1

[0037] The actual chemical composition of the corrosion-resistant and antimicrobial dual-functional austenitic stainless steel containing the rare earth element La is: Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La.

[0038] The performance test of Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material was carried out. Figure 1(A) It can be seen that the open circuit potential of the Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material is -282mV, which has good corrosion resistance. Figure 1 (B) It can be seen that the electrochemical impedance spectroscopy shows that the impedance behavior of the material is mainly controlled by the charge transfer process, the arc radius is large, the electrode surface reaction kinetics is slow, and it has good corrosion resistance. Figure 1 (C) It can be seen that the passivation area appears during anodic polarization, indicating that there is a stable passivation film on the surface of the Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material, and the self-corrosion potential is -522mV. Figure 1 (D) It can be seen that after 28 days of corrosion by sulfate-reducing bacteria, the corrosion marks on the surface of Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material are relatively small.

[0039] Example 2

[0040] The actual chemical composition of the corrosion-resistant and antimicrobial dual-functional austenitic stainless steel containing the rare earth element La is: Fe-19.97Cr-18.16Ni-5.97Mo-0.79Cu-0.19N-0.98La.

[0041] The performance of Fe-19.97Cr-18.16Ni-5.97Mo-0.79Cu-0.19N-0.98La material was tested. Figure 2 (A) It can be seen that the open circuit potential of the Fe-19.97Cr-18.16Ni-5.97Mo-0.79Cu-0.19N-0.98La material is -428mV, which has good corrosion resistance. Figure 2 (B) It can be seen that the electrochemical impedance spectroscopy shows that the impedance behavior of the material is mainly controlled by the charge transfer process, the arc radius is large, the electrode surface reaction kinetics is slow, and it has good corrosion resistance. Figure 2 (C) It can be seen that there is no passivation area in the anode of the Fe-19.97Cr-18.16Ni-5.97Mo-0.79Cu-0.19N-0.98La material, indicating that the material has been in a dissolved state and the self-corrosion potential is -659mV. Figure 2 (D) It can be seen that after 28 days of sulfate-reducing bacteria corrosion, the surface of Fe-19.97Cr-18.16Ni-5.97Mo-0.79Cu-0.19N-0.98La was slightly corroded, and the material has good anti-microbial corrosion performance.

[0042] Example 3

[0043] The actual chemical composition of the corrosion-resistant and antimicrobial dual-functional austenitic stainless steel containing the rare earth element La is: Fe-20.13Cr-17.97Ni-6.02Mo-0.81Cu-0.21N-1.48La.

[0044] The performance of Fe-20.13Cr-17.97Ni-6.02Mo-0.81Cu-0.21N-1.48La material was tested. Figure 3 (A) It can be seen that the open circuit potential of the Fe-20.13Cr-17.97Ni-6.02Mo-0.81Cu-0.21N-1.48La material is -478mV, which has good corrosion resistance. Figure 3 (B) It can be seen that the impedance behavior of the Fe-20.13Cr-17.97Ni-6.02Mo-0.81Cu-0.21N-1.48La material is mainly controlled by the charge transfer process, the arc radius is large, the electrode surface reaction kinetics is slow, and it has good corrosion resistance. Figure 3 (C) It can be seen that the anodic polarization curve fluctuates, the material has multiple passivation zones, has excellent corrosion resistance, and the self-corrosion potential is -731mV. Figure 3 (D) As can be seen, after 28 days of sulfate-reducing bacteria corrosion, the surface corrosion marks are minimal, indicating that the Fe-20.13Cr-17.97Ni-6.02Mo-0.81Cu-0.21N-1.48La material exhibits excellent resistance to microbial corrosion. For the Fe-20.13Cr-17.97Ni-6.02Mo-0.81Cu-0.21N-1.48La material, cell staining and fluorescence observation revealed an inhibition rate of ≥95.0%.

[0045] Example 4

[0046] The actual chemical composition of the corrosion-resistant and antimicrobial dual-functional austenitic stainless steel containing the rare earth element La is: Fe-20.26Cr-18.15Ni-5.93Mo-0.79Cu-0.19N-1.98La.

[0047] The performance test of Fe-20.26Cr-18.15Ni-5.93Mo-0.79Cu-0.19N-1.98La material was carried out. Figure 4 (A) It can be seen that the open circuit potential of the Fe-20.26Cr-18.15Ni-5.93Mo-0.79Cu-0.19N-1.98La material is -463mV, which has good corrosion resistance. Figure 4(B) It can be seen that the impedance behavior of the Fe-20.26Cr-18.15Ni-5.93Mo-0.79Cu-0.19N-1.98La material is mainly controlled by the charge transfer process. In the low-frequency region, the material exhibits a certain Warburg impedance characteristic. The electrode reaction is mainly controlled by the diffusion of substances, and the corrosion resistance is good. Figure 4 (C) It can be seen that the anodic polarization curve fluctuates, the material has multiple passivation zones, has excellent corrosion resistance, and the self-corrosion potential is -774mV. Figure 4 (D) It can be seen that after 28 days of sulfate-reducing bacteria corrosion, the corrosion marks on the surface are relatively small, and the anti-microbial corrosion performance of the Fe-20.26Cr-18.15Ni-5.93Mo-0.79Cu-0.19N-1.98La material is significant.

[0048] Comparative Example 1

[0049] The comparative composition is Fe-20Cr-18Ni-6Mo-0.8Cu-0.2N-0.3La super austenitic stainless steel, in which 0.3wt% La is added (weight ratio La / N=1.5<2.3), and the open circuit potential is -564mV. The open circuit potential of Example 1 Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material is -282mV. Compared with Comparative Example 1, the corrosion tendency is significantly reduced. Comparative Example 1 material Fe-20Cr-18Ni-6Mo-0.8Cu-0.2N-0.3La weight ratio La / N=1.5<2.3, due to La 3+ The ion release is insufficient, and the antibacterial rate is only 58%. Example 1 is composed of Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material. After staining cells and performing fluorescence observation, the antibacterial rate of the material is ≥90.0%.

[0050] Comparative Example 2

[0051] The comparative composition is Fe-20Cr-24Ni-6Mo-0.8Cu-0.13N-1.3La super austenitic stainless steel, with 1.3wt.% La added (weight ratio La / N = 10 > 9.4). Due to the high La / N ratio, La combines with N (LaN inclusions), reducing the solid solution N content (0.15% → 0.09%) and failing to synergize with Ni to stabilize austenite, resulting in a pitting potential of 0.15V. In contrast, the pitting potential of Example 1, the Fe-19.93Cr-18.04Ni-6.05Mo-0.81Cu-0.21N-0.49La material, is 0.7V. The high N activity enhances the passive film and improves the material's corrosion resistance. When La / N = 10 > 9.4, La and Cu form La-Cu-O composite inclusions (confirmed by EDS analysis), hindering the precipitation of the ε-Cu phase and rendering Cu's antibacterial effect ineffective. The material of the present invention with La / N=2.3-9.4 will promote the precipitation of nano-sized oxide La2O3 and ε-Cu phase.

[0052] Comparative Example 3

[0053] Comparative Example 1 Material Preparation Process: All rare earth elements La were added in the form of La-Fe composite master alloy at one time during smelting. The charge transfer resistance (Rct) in 3.5% NaCl was 3200Ω / cm 2 , and in Example 1, due to the phased rare earth element La, the charge transfer resistance (Rct) reaches 12000Ω / cm 2 , an increase of 173%.

[0054] Comparative Example 4

[0055] Compared to 316L stainless steel, the one-time La addition process makes sulfide (such as MnS) inclusions the preferred corrosion path. When the stainless steel grain boundary sulfur content reaches 0.0050wt.%, the pitting corrosion propagation rate increases by 3 times. In Example 2, the composition of Fe-19.97Cr-18.16Ni-5.97Mo-0.79Cu-0.19N-0.98La material, the La added in stages preferentially reacts with sulfur and oxygen to form a La2O2S dispersion phase <10nm, reducing the sulfur content from 0.0050wt.% to 12wt.%. The staged process refines the size of La-Si-O inclusions from 1-5μm (one-time addition) to 0.2-0.5μm, reducing the stress concentration effect.

[0056] Comparative Example 5

[0057] Comparative Example 4's material preparation process, in which all the rare earth element La was added at once during smelting in the form of a La-Fe composite master alloy, resulted in a surface biofilm coverage of 45% after immersion in a 3.5% NaCl solution for 30 days. SEM images showed bacteria clustering around coarse La-Mo-N precipitates (200-500 nm). In contrast, Example 4, which added the rare earth element La in stages and circulated in a 3.5% NaCl solution for 30 days, achieved a biofilm inhibition rate of ≥99.0% against marine sulfate-reducing bacteria.

[0058] 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 corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La, characterized in that: The chemical composition of the stainless steel is as follows by weight: Cr 19.5-20.5%, Ni 17.5-18.5%, Mo 5.5-6.5%, Cu 0.75-0.85%, La 0.5-2.0%, N0.18-0.22%, C≤0.03%, Si≤0.5%, Mn≤0.8%, P≤0.02%, S≤0.005%, the balance being Fe and unavoidable trace impurities, and satisfying PREN=%Cr+3.3×%Mo+16×%N≥45.

2. The corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La according to claim 1, characterized in that: In the microstructure, a La-N composite dispersed phase is formed, and the dispersed phase is distributed in a continuous network along the austenite grain boundaries, with a grain boundary coverage of ≥80%.

3. The corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La according to claim 1, characterized in that: The La element exists in a bimodal state, in which 0.7-2.0% of the La element is in a supersaturated solid solution state; the remaining La element is dispersed in the form of La2O3 nanoparticles with a particle size of 30-50nm and a spacing of ≤200nm; and La and Cu form nanoscale Cu-La intermetallic compounds that are uniformly distributed in the matrix.

4. A method for preparing the corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La according to claim 1, characterized in that: The matrix metals Fe, Cr, Ni, Mo, and Cu are first smelted, and after they are completely melted, high-purity nitrogen is introduced to achieve nitrogen alloying. Then, the rare earth element La is added in stages, and then low-superheat casting is performed to obtain the corrosion-resistant and antimicrobial dual-functional austenitic stainless steel containing the rare earth element La.

5. The method for preparing the corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La according to claim 4, characterized in that: The rare earth element La is added in stages. In the first stage, it is added in the form of La-Fe composite master alloy to achieve solid solution strengthening at the lattice level. In the second stage, La2O3 nanoparticles are introduced for interface modification.

6. The preparation method according to claim 5, characterized in that The following steps are involved: (1) Prepare raw materials: prepare raw materials according to the target composition ratio; (2) Adding raw materials: First, add 80-90% Fe as the base metal into a vacuum induction melting furnace, heat it to 1550-1570°C to ensure complete melting, then cool it to 1500-1520°C and add high-purity metal Cr, stir it electromagnetically for 10-15 minutes, then add Ni raw material, stir it electromagnetically for 10-15 minutes, heat it to 1550-1570°C and add Mo raw material, stir it electromagnetically for 15-20 minutes, then cool it to 1480-1500°C and add Cu raw material, stir it electromagnetically for 5-10 minutes; (3) Nitrogen alloying: cooling to 1450-1480℃, adding nitrogen, using pulsed nitrogen injection process, adjusting nitrogen partial pressure to 0.15-0.25atm, and electromagnetic stirring for 10-15min; (4) Introduction of rare earth element La: Cooling to 1420-1450°C, rare earth element La is added in stages: in the first stage, 60% of the total La is added in the form of La-Fe composite master alloy to achieve solid solution strengthening at the lattice level; in the second stage, La2O3 nanoparticles are introduced for interface modification, adding 40% of the total La; (5) Low superheat casting: The pressure in the vacuum induction furnace is maintained at 0.07-0.08 atm, and the temperature of the molten steel is controlled in the range of 1430-1490 ° C for low superheat casting. After the ingot is cooled, it is solution treated at 1200 ° C for 1 hour, and then rapidly water-cooled to obtain a corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing rare earth element La.

7. The preparation method according to claim 6, characterized in that In step (2), Mo was added in two batches, with an interval of 3 min between each batch.

8. A corrosion-resistant and antimicrobial dual-function austenitic stainless steel containing the rare earth element La as claimed in claim 1, wherein the stainless steel is applied to marine microbial corrosion.

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