High-strength and high-toughness corrosion-resistant austenitic antibacterial stainless steel

Abstract

The application discloses a high-strength high-toughness corrosion-resistant austenitic antibacterial stainless steel. The chemical composition of the high-strength high-toughness corrosion-resistant austenitic antibacterial stainless steel is as follows: C is less than or equal to 0.03; Si is 0.3-0.6; Mn is 0.4-0.8; S is less than or equal to 0.02; P is less than or equal to 0.02; Cr is 17-18.5; Ni is 12-14; Mo is 2.0-3.0; Cu is 4.0; and the balance is Fe. The Cu element is added to the austenitic stainless steel base body, and through corresponding processing methods and heat treatment, the material is allowed to precipitate copper-rich phases (epsilon-Cu) in the base body and the surface passivation film contains a certain amount of Cu ions in a relatively short time. The method can not only endow the material with high-efficiency and rapid sterilization performance and high-strength high-toughness mechanical performance, but also greatly reduce the influence of epsilon-Cu precipitation on the corrosion resistance of the material, and the method is simple and suitable for industrial production.

Description

Technical Field

[0001] This invention provides a high-strength, high-toughness, and corrosion-resistant austenitic antibacterial stainless steel, belonging to the field of austenitic antibacterial stainless steel preparation. Background Technology

[0002] With social progress and the improvement of people's living standards, people are paying more and more attention to the quality of life and living environment.

[0003] Antibacterial products are gaining increasing attention. Consequently, in recent years, antibacterial functionality has become a key objective for traditional enterprises seeking to transform into high-tech products and enhance their added value. Driven by this trend, the antibacterial industry has flourished, making the research of various antibacterial materials imperative.

[0004] Antibacterial stainless steel possesses the dual characteristics of both structural and antibacterial functional materials. It can be used as both a structural and decorative material, while also exhibiting self-cleaning properties that inhibit and sterilize bacteria, greatly expanding the application areas of antibacterial materials. Antibacterial stainless steel can be classified according to its microstructure into austenitic antibacterial stainless steel, duplex antibacterial stainless steel, martensitic antibacterial stainless steel, and ferritic antibacterial stainless steel. In recent years, with the significant advancements in vacuum metallurgy technology and the unique advantages of ferritic stainless steel, my country has begun to vigorously develop ferritic stainless steel. Designing and developing ferritic stainless steel with excellent comprehensive performance has become one of the main research directions in the stainless steel field today.

[0005] Cu-containing antibacterial stainless steel is generally designed with a supersaturated Cu content. Therefore, after aging heat treatment, Cu exists in the iron matrix as a precipitated second phase, rather than forming an intermetallic phase with iron. However, after solution heat treatment, the stacking fault energy of the material increases, making it easier for partial dislocations to form full dislocations. This prevents the accumulation of partial dislocations on the same slip plane, leading to a decrease in material strength, i.e., a "softening" effect. This "softening" effect not only offsets the solid solution strengthening caused by the addition of Cu but also reduces the material's plasticity. Aging heat treatment requires long-term holding, consuming a large amount of electricity. Furthermore, the precipitation of some second phases on the stainless steel surface damages the continuity of the passivation film that requires Cr and Fe to form, making it more susceptible to pitting corrosion. The generated second phase has the same FCC structure as austenite, with extremely low mismatch, resulting in negligible "second phase strengthening" effect. After these two heat treatments, the final aged material properties are reduced in strength, plasticity, and corrosion resistance, with only antibacterial properties gained, making it a net loss. Summary of the Invention

[0006] The purpose of this invention is to provide a high-strength, high-toughness, corrosion-resistant austenitic antibacterial stainless steel.

[0007] A high-strength, high-toughness, and corrosion-resistant austenitic antibacterial stainless steel is produced by adding Cu to the austenitic matrix, completely dissolving it, subjecting it to severe deformation, and replacing the traditional aging method with annealing heat treatment. This process imparts an internal layered heterogeneous structure and precipitates ε-Cu to the austenitic stainless steel, while simultaneously achieving excellent mechanical and antibacterial properties with minimal loss of corrosion resistance.

[0008] This invention replaces the traditional long-term high-temperature aging process by adding 4 wt.% Cu, first using a special forging process to eliminate segregation, and then combining the preparation process of antibacterial stainless steel with layered heterogeneous structure.

[0009] High-quality Cu fraction can enhance the nucleation kinetics of copper-rich phases. At the same time, large deformation rolling of the material introduces high-density dislocations, which promotes the nucleation of copper-rich phases during the subsequent annealing process.

[0010] By simply holding the material at 750℃ for 25 minutes, it can achieve more than 99% antibacterial properties while maintaining excellent strength and plasticity and minimal loss of corrosion resistance.

[0011] This invention has significant advantages over existing technologies:

[0012] 1. This invention adds Cu to an austenitic stainless steel matrix and designs matching processing and heat treatment methods to impart antibacterial properties, high strength, and high toughness to the stainless steel with minimal energy loss. Furthermore, the addition of Cu and the formation of a copper-rich phase improve the material's thermal stability. 2. Firstly, the potentiodynamic polarization curve shows that the pitting potential decreases with increasing annealing time; however, the size of the pits exhibits a pattern of "first increasing, then decreasing," which coincides with the change in self-corrosion current density obtained from the potentiodynamic polarization curve. 3. Electrochemical impedance spectroscopy (EIS) measurements show that the impedance spectrum of the material exhibits a trend of "first decreasing, then increasing" with increasing annealing time, consistent with the above phenomena. ICP-MS and XPS tests revealed an "increased concentration of copper ions" and that "when held at 750℃ for 25 min, Cu..." 1+ Cu 2+ The phenomenon of "a higher proportion" is due to the deposition of elemental Cu formed during the anodic dissolution process, leading to Cu... 1+ The higher Cu content also inhibits the anodic reaction, lowers the critical current density, and promotes passivation. Simultaneously, Cu has a stronger affinity for oxygen, promoting oxygen adsorption and further enhancing the passivation process; 4. The solid-solid Cu element precipitates as ε-Cu after rolling and annealing heat treatment, uniformly and diffusely distributed throughout the stainless steel matrix, releasing free Cu... 1+ and Cu 2+ It acts on the bacterial cell membrane, causing a strong killing effect on bacteria. Attached Figure Description

[0013] Figure 1 Metallographic diagrams of different forging and solution treatment processes.

[0014] Figure 2 The antibacterial results are shown in the following figures: experimental group (no material added for cultivation), no copper added (Cu element eliminated based on the stainless steel composition of this invention), solution-treated state, rolled state, and samples held at 750℃ for 10 min and 750℃ for 25 min. The bacterial strain is Escherichia coli (Gram-negative bacteria), and the bacterial concentration is 10. 5 CFU / mL, culture time 24h.

[0015] Figure 3 This is a graph of potentiodynamic polarization.

[0016] Figure 4 The image shows the copper ion precipitation concentration measured by ICP-MS and the pitting pits generated after the measurement of the potentiodynamic polarization curve.

[0017] Figure 5 Nyquist measured by EIS (a) and analog circuit diagram (b).

[0018] Figure 6 This is a graph showing the XPS results.

[0019] Figure 7 A stretched pattern resembling a dog bone.

[0020] Figure 8 This is a stretch curve graph. Detailed Implementation

[0021] The present application will be further described below with reference to the accompanying drawings.

[0022] A high-strength, high-toughness, corrosion-resistant austenitic antibacterial stainless steel has the following chemical composition (wt.%): C≤0.03; Si:0.3-0.6; Mn:0.4-0.8; S≤0.02; P≤0.02; Cr:17-18.5; Ni:12-14; Mo:2.0-3.0; Cu:4.0; balance Fe.

[0023] Cu is the most important component in this invention and the fundamental reason why the material possesses excellent antibacterial properties. The antibacterial performance of Cu-containing metal materials mainly depends on the toxic stress effect of Cu on bacterial cells. Regarding its stress mechanism, it is generally believed that the dissolution level of antibacterial Cu is the key factor determining the antibacterial effect of the material. Cu ions can induce depolarization of bacterial cell membranes. Generally, bacterial cells with intact cell membranes and metabolic activity can form a potential difference of 100mV~200mV (depending on the bacterial species) inside and outside the cell. Dissolved Cu ions can bind to negatively charged regions inside and outside the cell membranes of Gram-negative or Gram-positive bacteria, such as lipopolysaccharides, peptidoglycans, or carboxyl groups, thereby reducing this potential difference and causing membrane depolarization. When the potential difference drops to zero, the cell membrane ruptures, and contents leak out. In addition, Cu can catalyze the Fenton reaction to produce reactive oxygen species (ROS). Increased ROS levels can cause oxidative damage to cells, including degradation of intracellular DNA and peroxidation of phospholipids.

[0024] The present invention provides the processing and heat treatment methods required for the aforementioned austenitic antibacterial stainless steel, which is also the most important part of this invention: After the molten steel is cast and cooled in a vacuum induction furnace, it is placed in a high-temperature furnace at 1100℃ and held for 0.5 hours, then removed for forging. The forging adopts a three-upsetting process, with the initial forging temperature controlled at 1100℃ and the final forging temperature controlled at 900℃, with a 5-minute interval between each upsetting. After the final upsetting, the steel is rapidly cooled. Then, it undergoes solution heat treatment in a high-temperature furnace at 1100℃ for 0.5 hours, and is then rapidly water-cooled to obtain a solution-treated structure.

[0025] The material was wire-cut into 50×50×10mm cuboids and subjected to intense plastic deformation, i.e., rolling. Each rolling pass reduced the material by 0.2mm, resulting in a final thickness of 1.3mm from 10mm, representing 87% reduction. The high-density dislocations generated during rolling provided more nucleation sites and additional energy for ε-Cu precipitation, while the high-density grain boundaries offered better corrosion resistance. After rolling, an annealing heat treatment was performed: the material was placed in a 750℃ atmosphere and held for 0min (CR state), 5min, 10min, 15min, 20min, and 25min respectively. After the holding time, the material was removed and air-cooled.

[0026] The elemental composition of austenitic antibacterial stainless steel is shown in Table 1 (the same material was used in the solution-treated, rolled, and subsequent heat-treated states: experimental group). The solution-treated state refers to the material obtained by water cooling after forging at 1100℃ for 30 minutes. The rolled state refers to the state where a 10mm diameter sheet was rolled to 1.3mm. The subsequently annealed state refers to the sample that underwent annealing heat treatment based on the rolled state.

[0027] Table 1 Chemical composition of materials

[0028] Material C Si Mn P S Cr Ni Mo Cu Fe experimental group 0.028 0.52 0.81 0.011 0.01 18.25 13.74 3.07 4.08 Bal. No copper added 0.022 0.49 0.79 0.01 0.01 18.14 13.65 3.01 / Bal.

[0029] (1) Forging and solution treatment processes

[0030] After trying multiple sets of parameters, the forging process with an initial forging temperature of 1100℃, a final forging temperature of 900℃ plus three upsettings, and a solution treatment process with a holding temperature of 1100℃ for 30 minutes were finally determined. Specific control group parameters are shown in Table 2, and metallographic diagrams are shown below. Figure 1 As can be seen from the information in the figure, the initial forging temperature and the final forging temperature must be controlled during forging to control precipitation. Then, in the solution treatment stage, the temperature must be held at 1100℃ for 30 minutes to produce the target structure; otherwise, precipitation of varying degrees will occur.

[0031] Table 2 Process parameters for the control group

[0032] Forging process Corresponding diagram 1100℃ heat treatment for 30 minutes + three upsetting processes + water cooling Figure 1 （a） 1100℃ hold for 30 min + triple upsetting + water cooling + 1100℃ hold for 30 min solution treatment Figure 1 （b） 1100℃ hold for 30 min + triple upsetting + water cooling + 1200℃ hold for 30 min solution treatment Figure 1 （c） 1050℃ heat treatment for 30 minutes + three upsetting processes + water cooling Figure 1 （d） 1000℃ heat treatment for 30 minutes + three-stage forging + water cooling Figure 1 （e） 1100℃ holding for 30 minutes + three upsetting processes + initial forging at 1100℃ + final forging at 900℃ + water cooling Figure 1 （f） 1100℃ holding for 30 min + three upsetting + initial forging at 1100℃ + final forging at 900℃ + water cooling + 1100℃ holding for 30 min solution treatment Figure 1 （g）

[0033] (2) Antibacterial performance test

[0034] According to Appendix C of GB / T21510-2008 "Test Methods for Antibacterial Properties of Nano-Inorganic Materials" regarding the film application method for the antibacterial properties of hard surface materials such as plastics, ceramics, paint films, sheets, and metals, the bactericidal rate of the metal components shown in Table 1 after action on Escherichia coli was quantitatively tested. The bactericidal rate was calculated using the following formula: Bactericidal rate (%) = [(Number of viable bacteria in the sample without copper - Number of viable bacteria in the experimentally tested antibacterial stainless steel) / Number of viable bacteria in the sample without copper] × 100%.

[0035] Table 3 shows the colony count, bacterial concentration, and antibacterial rate at different dilution ratios.

[0036] Table 3 Antibacterial rate

[0037] Grouping Colony count Dilution factor Bacterial concentration (CFU / mL) Antibacterial rate No copper added 89 <![CDATA[10 1 ]]> 1.78 x 10 5 ]] / solid solution 46 <![CDATA[10 1 ]]> <![CDATA[9.2×10 4 ]]> 48.31% Rolled state 35 <![CDATA[10 1 ]]> <![CDATA[7×10 4 ]]> 60.67% 750-10 163 <![CDATA[10 0 ]]> <![CDATA[3.26×10 4 ]]> 81.69% 750-25 5 <![CDATA[10 0 ]]> <![CDATA[10 3 ]]> 99.44%

[0038] Note: Colony counts are the results of colony counting at the corresponding dilutions for each group. The counting principle is based on the national standard GB4789.2-2016, selecting colony counts between 30 CFU and 300 CFU. If no colonies grow at the lowest dilution, it proves that the sample has a significant antibacterial effect. The bacterial concentration (CFU / mL) is calculated as follows: Colony count × dilution factor × 20 (950 μL sterile PBS rinsed with 50 μL co-culture medium) × 10 (0.1 mL spread).

[0039] (3) Potentiodynamic polarization curve

[0040] A polarization curve is a curve obtained by plotting electrode potential on the x-axis and the current flowing through the electrode on the y-axis. It characterizes the functional relationship between the driving potential of the corrosion galvanic cell reaction and the reaction rate current. The pitting corrosion sites and self-corrosion current density of the experimental group can be determined from the polarization curve. Detailed values ​​are shown in Table 4.

[0041] Table 4 Pitting potentials (E) of each experimental group b ) and self-corrosion current density (i corr )value

[0042] Commercial CR solid solution Copper-free 750-5 750-10 750-15 750-20 750-25 <![CDATA[E b (mV)]]> 692 688 740 803 576 529 482 383 365 <![CDATA[i corr (nA / cm2)]]> 134 169 158 147 67 72 81 69 53

[0043] (4) ICP-Ms and pitting corrosion

[0044] Inductively coupled plasma mass spectrometry (ICP-MS) can detect the concentration of elements precipitated in solution with sensitivity at the ppb level, effectively detecting the concentration of copper ions released from materials. The density and size of pitting corrosion directly reflect the material's resistance to pitting corrosion and the rate of pit expansion, such as... Figure 4 As shown.

[0045] (5) EIS

[0046] The sample was cut into 10×10×1.5mm cubes. Copper conductive adhesive was used to connect the sample to copper wires, followed by epoxy resin embedding and sealing of the gaps with silicone rubber. Electrochemical impedance spectroscopy (EIS) measurements were performed using a Garmy Reference 600+ electrochemical workstation and a traditional three-electrode system (sample as working electrode, calomel electrode as reference electrode, and platinum electrode as counter electrode). The parameters are shown in Table 5. The Nyquist plot (a) and the fitted circuit diagram (b) are shown in Table 5. Figure 5 As shown in Table 6, the measurement results were fitted using ZSimpWin software, where Q1 is a constant phase angle element. The obtained impedance values ​​are all within 10%. -3 Level. As can be seen from the chart, the processing and heat treatment method of the present invention reduces the negative impact of ε-Cu precipitation on the corrosion resistance of the material, exhibiting superior corrosion resistance.

[0047] Table 5 EIS Parameters

[0048] Electrolyte solution EIS frequency range (Hz) EIS signal <![CDATA[Area region (mm 2 )]]> 0.9 wt.% NaCl <![CDATA[0.01-10 5 ]]> 10mV sine wave 80.4

[0049] Grouping <![CDATA[R s (Ω·cm 2 )]]> <![CDATA[R ct (kΩ·cm 2 )]]> <![CDATA[Q1(Ω -1 S n cm -2 )]]> Chi-sqr CR 27.45 437.3 2.858 1.38 750-5 25.61 420.7 2.892 1.02 750-10 26.66 285.8 2.827 2.73 750-15 24.26 209 3.28 1.94 750-20 25.34 316 2.871 1.37 750-25 26.33 420.5 3.124 1.35 solid solution 26.86 534.9 2.634 1.56

[0050] Table 6 Impedance Values

[0051] (6) XPS

[0052] X-ray photoelectron spectroscopy (XPS) is an advanced analytical technique used in the microscopic analysis of electronic materials and devices, and it is often used in conjunction with Auger electron spectroscopy (AES). Because it can measure the inner-shell electron binding energy and chemical shift of atoms more accurately than Auger electron spectroscopy, it provides information not only on molecular structure and atomic valence states for chemical research, but also on the elemental composition and content, chemical state, molecular structure, and chemical bonds of various compounds in electronic materials research. When analyzing electronic materials, it provides not only overall chemical information, but also information on surface, micro-region, and depth distribution. Peak fitting of the measurement results yields the surface Cu... 1+ and Cu 2+ The relative content was plotted as a curve, such as... Figure 6 As shown, the changes in ion valence states can be observed quite intuitively.

[0053] (7) Mechanical property testing

[0054] According to the national standard GB 6397-86 for tensile test specimens of metals, the sample is wire-cut as follows. Figure 7 The "dog bone" shaped tensile specimen shown was characterized for mechanical properties using a universal tensile testing machine. The mechanical properties are as follows: Figure 8 As shown in Table 3, the specific data are as follows. The data shows that the sample 750-25 with the highest antibacterial rate has a tensile strength of 945.67 MPa and an elongation at break of 25.81%, achieving a good balance between strength and plasticity.

[0055] Table 7 Tensile Data

[0056] Grouping Tensile strength (MPa) Elongation at break (%) Yield strength (MPa) Uniform elongation (%) CR 1241.13 9.86 1185.42 1.65 750-5 1103.41 14.13 1003.69 3.86 750-10 1023.97 15.72 922.93 6.97 750-15 967.74 19.11 820.62 11.77 750-20 947.35 26.45 758.72 15.54 750-25 945.67 25.81 758.25 16.48 solid solution 508.12 37.25 247.26 51.72

[0057] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength, high-toughness, corrosion-resistant austenitic antibacterial stainless steel, characterized in that, The austenitic antibacterial stainless steel has the following mass percentage (wt.%): C≤0.03; Si:0.3-0.6; Mn:0.4-0.8; S≤0.02; P≤0.02; Cr:17-18.5; Ni:12-14; Mo:2.0-3.0; Cu:4.0; with the balance being Fe. This austenitic antibacterial stainless steel is smelted, then cast, forged, solution-treated, and cold-rolled before being shaped and annealed. The forging process uses a three-upsetting technique, with an initial forging temperature of 1100℃ and a final forging temperature of 900℃. The heat treatment involves annealing at 750℃ for 20-25 minutes and then air-cooling to room temperature.

2. The method for preparing austenitic antibacterial stainless steel according to claim 1, characterized in that: The specific processing procedure for austenitic antibacterial stainless steel is as follows: after the molten steel is cast and cooled in a vacuum induction furnace, it is placed in a high-temperature furnace for heat preservation and then taken out for forging; after forging, it is quickly cooled; after solution heat treatment, it is taken out and quickly water-cooled to obtain a solution structure, and then cold-rolled; after rolling, it is annealed.

3. The method for preparing austenitic antibacterial stainless steel according to claim 1 or 2, characterized in that: During the cold rolling process, the reduction is over 80%.

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