Method for producing antibacterial silver-containing stainless steel by surface alloying

Abstract

Ultimately, a silver antibacterial alloy layer can be formed on the surface of stainless steel, giving the stainless steel antibacterial properties and further improving its corrosion resistance. In addition, this method can be applied to various types of stainless steel, and since the concentration of the antibacterial alloying element and the thickness of the alloy layer can be adjusted by process parameters, it can be adapted to different usage conditions and provides a highly versatile method for producing antibacterial silver-containing stainless steel by surface alloying. [Solution] The method for producing antibacterial silver-containing stainless steel by surface alloying includes coating the surface of stainless steel with at least one diffusion-auxiliary medium layer. Next, coating the diffusion-auxiliary medium layer with at least one silver-containing silver antibacterial metal layer, wherein the silver concentration in the silver antibacterial metal layer is at least 0.2 wt.%. Next, the stainless steel is heat-treated to diffuse the silver antibacterial metal into the stainless steel.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing antibacterial silver-containing stainless steel by surface alloying. In particular, a silver antibacterial metal layer containing silver is coated on the surface of stainless steel, and then heat treatment is carried out to diffuse the silver antibacterial metal into the interior of the stainless steel to form a silver antibacterial alloy layer having a certain thickness. Accordingly, the present invention not only maintains the mechanical properties of stainless steel but also has excellent corrosion resistance and antibacterial properties.

Background Art

[0002] Stainless steel is widely applied in areas such as household goods, kitchen utensils, and medical devices due to its beauty and excellent corrosion resistance. With the increasing awareness of hygiene and safety, stainless steel with antibacterial functions has attracted more and more attention. Currently, the antibacterial technology of stainless steel is mainly divided into the following two types, which are (i) the surface coating type and (ii) the alloy type.

[0003] Among them, the surface coating type achieves an antibacterial effect by coating an antibacterial substance on the surface of stainless steel. Its antibacterial durability is determined by the adhesion and thickness of the coating. However, the coating layer wears during the use process, and the antibacterial effect gradually weakens and finally disappears. The other alloy type technology directly incorporates antibacterial elements into the stainless steel substrate, so it has better antibacterial durability. Its antibacterial effect is closely related to the content, phase composition, and distribution of the antibacterial elements. Since the surface coating type has problems such as peeling of the coating layer and insufficient abrasion resistance, currently, alloy type antibacterial stainless steel products are mainly mainstream in the market.

[0004] Currently, the alloy type antibacterial stainless steel products sold in the market are mainly produced by the smelting method. The manufacturing process mixes antibacterial elements and a stainless steel substrate at high temperature, uniformly dissolves the antibacterial elements inside the substrate, and imparts an antibacterial function to the entire stainless steel. The advantage of this manufacturing process is that antimicrobial elements are uniformly distributed within the stainless steel, giving the material antimicrobial properties. However, while the antimicrobial mechanism primarily acts on the material surface, ensuring a sufficient concentration of antimicrobial elements throughout the entire material usually requires adding large amounts of these elements. This not only significantly increases raw material costs but also alters the material's inherent mechanical properties and affects subsequent processing steps. For example, it is difficult to produce suitable antimicrobial products using ferritic and martensitic steel types with this technology.

[0005] Due to the aforementioned problems, a method for manufacturing surface alloy type stainless steel was developed. The technology typically involves treating the surface of stainless steel using methods such as ion implantation and shot peening to modify the steel surface and form an antibacterial alloy layer of a certain thickness. This imparts antibacterial properties and durability to the material while simultaneously maintaining the mechanical properties of the base material. However, these manufacturing processes are usually costly, which limits large-scale production and thus hinders widespread application.

[0006] To address the aforementioned challenges, we primarily used a special auxiliary medium to effectively diffuse copper elements onto the surface of stainless steel during the heat treatment process, thereby forming an antibacterial alloy layer. (See Patent Document 1 as an example.) Compared to copper, silver has a very low solid solubility in stainless steel, making it difficult to diffuse it onto the surface of stainless steel using that method. Therefore, developing silver-based antibacterial stainless steel products presents a significant technical challenge. However, silver possesses excellent antibacterial properties and is also viewed by consumers as a noble material, so its market potential is high. How to effectively diffuse silver into stainless steel is a crucial issue that needs to be addressed today. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Taiwan Patent No. I17863TW: "Method for manufacturing antibacterial stainless steel by surface alloying" [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The inventors further researched the diffusion of silver into stainless steel and the antimicrobial treatment of stainless steel surfaces, and the object of this invention is to provide a method for producing antimicrobial silver-containing stainless steel by surface alloying that improves the aforementioned problems. [Means for solving the problem]

[0009] The object of this invention is to improve the aforementioned problems, and to achieve this object, the inventor provides a method for producing antibacterial silver-containing stainless steel by surface alloying, which is, A layer of diffusion-enhancing medium is coated onto the surface of stainless steel. The diffusion aid medium layer is coated with at least one silver-containing silver antibacterial metal layer, and the concentration of silver in the silver antibacterial metal layer is at least 0.2 wt.%. The stainless steel is heat-treated to diffuse the silver antibacterial metal into the stainless steel. This includes the following step.

[0010] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, the thickness of the diffusion-assisted medium layer shall be between 0.05 μm and 5.00 μm.

[0011] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, the thickness of the silver antibacterial metal layer shall be between 0.02 μm and 2.00 μm.

[0012] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, the heat treatment involves heating to 500°C or higher in a protective atmosphere for at least 1 minute, and then lowering the temperature to room temperature after the heat treatment is complete.

[0013] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, after heat treatment, the temperature is lowered to room temperature by at least one or a combination of furnace cooling, air cooling, or quenching.

[0014] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, the diffusion auxiliary medium layer shall be at least one of copper, cobalt, nickel, zinc, molybdenum, chromium, or titanium, or a combination thereof.

[0015] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, the stainless steel shall be at least one or a combination thereof from among ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, or duplex stainless steel.

[0016] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, the diffusion-assisted medium layer or the silver antibacterial metal layer is coated using at least one or a combination thereof from physical vapor deposition, chemical vapor deposition, electroplating, or autocatalytic plating.

[0017] In the method for producing antibacterial silver-containing stainless steel by surface alloying described above, the diffusion-aiding medium layer and the silver antibacterial metal layer are applied as multi-layer overlapping coatings to the surface of the stainless steel.

[0018] Among the methods for manufacturing antibacterial silver-containing stainless steel by the above-mentioned surface alloying, the diffusion-assisting medium layer and the silver antibacterial metal layer are coated by co-electroplating, and the diffusion-assisting medium layer and the silver antibacterial metal layer are simultaneously coated on the surface of the stainless steel.

Advantages of the Invention

[0019] The method for manufacturing antibacterial silver-containing stainless steel by surface alloying of the present invention is applied to various stainless steels, and the antibacterial metal layer of the silver coating and the heat treatment are used to diffuse the silver antibacterial metal layer into the stainless steel. Compared with the Taiwan Invention Patent Certificate No. I17863TW applied by the applicant last time, the present invention diffuses the silver (Ag) element with better antibacterial properties onto the surface of the stainless steel to form a silver antibacterial alloy layer on the surface of the stainless steel. It has further excellent electrochemical performance and effectively improves the corrosion resistance of the base material. By installing the diffusion-assisting medium layer, the silver element can be effectively diffused onto the stainless steel substrate, and its fine structure is different from that of copper-containing stainless steel. Moreover, the present invention is applicable to austenitic, ferritic and martensitic stainless steel types, and can be further adjusted according to the differences in the chemical composition, thickness and grain size of the silver antibacterial alloy layer, etc. in the manufacturing process parameters, as well as the usage cases, to improve the applicability and performance of the present invention.

Brief Description of the Drawings

[0020] [Figure 1] It is a flowchart of the present invention. [Figure 2a] It is a cross-sectional tissue image of the test body of the present invention No.1 (420J2 SS) before heat treatment. [Figure 2b] It is a cross-sectional tissue image of the test body of the present invention No.1 (420J2 SS) after heat treatment. [Figure 2c] It is a surface tissue image of the test body of the present invention No.1 (420J2 SS) after heat treatment. [Figure 2d] It is a cross-sectional tissue image of the test body of the present invention No.10 (420J2 SS) after heat treatment. [Figure 3]In the embodiment of the present invention, the diagrams compare the effects of silver diffusion on the diffusion-enhancing media layer of 420J2. The left diagram shows that the diffusion-enhancing media layer was used on test specimen No. 1, while the right diagram shows that the diffusion-enhancing media was not used on test specimen No. 10. [Figure 4a] This is a cross-sectional microstructure image of specimen No. 2 (304L SS) of the present invention before heat treatment. [Figure 4b] This is a cross-sectional microstructure image of specimen No. 2 (304L SS) of the present invention after heat treatment. [Figure 4c] This is an image of the surface structure of specimen No. 2 (304L SS) of the present invention after heat treatment. [Figure 4d] This is a cross-sectional microstructure image of specimen No. 11 (304L SS) after heat treatment according to the present invention. [Figure 5] In the embodiments of the present invention, the diagram shows a comparison of the effects of silver diffusion when 304L uses a diffusion-enhancing media layer. Of these, test specimen No. 2 in the left figure uses the diffusion-enhancing media layer, while test specimen No. 11 in the right figure does not use the media. [Figure 6] In an embodiment of the present invention, this is a comparative diagram of the effect of different thicknesses of the 304L diffusion-auxiliary medium layer on the silver diffusion depth, where the thickness of the diffusion-auxiliary medium layer film for each test specimen is 0.40 μm for test specimen No. 3, 0.50 μm for test specimen No. 4, and 0.60 μm for test specimen No. 5. [Figure 7] In the embodiments of the present invention, the diagrams compare the effects of silver diffusion structure on 420J2 under different heat treatment conditions. Of these, specimen No. 1 in the left diagram was held at 800°C for 2 hours, and specimen No. 6 in the right diagram was held at 900°C for 2 hours. [Figure 8] In the embodiments of the present invention, the effects of silver diffusion structure under different heat treatment conditions are compared for 304L, with specimen No. 2 held at 800°C for 2 hours, specimen No. 3 held at 900°C for 2 hours, and specimen No. 7 held at 900°C for 5 hours. [Figure 9] This is a surface image of test specimen No. 8 (420J2 SS) after polishing, in an embodiment of the present invention. [Figure 10]In the examples of the present invention, the results of the antimicrobial test of test specimen No. 8 (420J2 SS) are shown, with test specimen No. 12 being a control group sample that has not been treated with antimicrobial agents. [Figure 11] In the embodiment of the present invention, the images show the surface of test specimens No. 3, No. 4, and No. 5 of 304L SS after polishing. The thickness of the diffusion-enhancing media layer used for each test specimen was 0.40 μm for test specimen No. 3, 0.50 μm for test specimen No. 4, and 0.60 μm for test specimen No. 5. [Figure 12] In the embodiment of the present invention, the antimicrobial test results for test specimens No. 3, No. 4, and No. 5 of 304L SS are shown, with the thickness of the diffusion aid media layer used for each test specimen being 0.40 μm for test specimen No. 3, 0.50 μm for test specimen No. 4, and 0.60 μm for test specimen No. 5. [Figure 13] In an embodiment of the present invention, this is a comparative diagram of the periodic polarization curve measurements of 420J2 after silver diffusion. Of these, test specimens No. 8 and No. 9 both underwent silver antibacterial treatment. Test specimen No. 8 had a diffusion aid medium layer of 0.30 μm, test specimen No. 9 had a diffusion aid medium layer of 0.40 μm, and test specimen No. 12 is a cured 420J2 material without silver antibacterial treatment. [Figure 14] In the embodiments of the present invention, this is a comparative diagram of the periodic polarization curve measurements of 304L after silver diffusion. Of these, specimens No. 3, No. 4 and No. 5 all underwent silver antibacterial treatment. Specimen No. 3 had a diffusion aid medium layer of 0.30 μm, specimen No. 4 had a diffusion aid medium layer of 0.40 μm, specimen No. 5 had a diffusion aid medium layer of 0.50 μm, and specimen No. 13 is 304L material without silver antibacterial treatment. [Modes for carrying out the invention]

[0021] (One embodiment) To provide a deeper understanding of the present invention, several good embodiments of the inventor's technical means are described in detail below, along with diagrams.

[0022] As shown in Figure 1, the present invention is a method for producing antibacterial silver-containing stainless steel by surface alloying, and it includes the following:

[0023] (Step) S001: Coat the surface of the stainless steel with at least one infiltration promoter layer. As an example, the diffusion-enhancing medium layer may be at least one or a combination thereof from copper, cobalt, nickel, zinc, molybdenum, chromium, or titanium. Specific examples of stainless steel include at least one or a combination thereof from among ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, or duplex stainless steel. As an example of coating a diffusion-enhancing medium layer onto the surface of stainless steel, the coating is performed using at least one or a combination of the following methods: physical vapor deposition, chemical vapor deposition, electroplating, or autocatalytic plating. However, the above-described examples are not limited thereto. The stainless steel used as the base material can be in any structure or shape, such as block material, sheet material, or semi-finished products.

[0024] The diffusion-enhancing medium layer can have any thickness, but a thickness between 0.05 μm and 5.00 μm is preferable. If the thickness of the diffusion-enhancing medium layer is insufficient, the diffusion of metal elements may not be effectively promoted. Furthermore, if the thickness of the diffusion-enhancing medium layer exceeds 5.00 μm, the subsequent diffusion of the silver antibacterial metal may be inhibited.

[0025] (Step) S002: The diffusion-aiding medium layer is coated with at least one silver-containing silver antibacterial metal layer, and the silver concentration in the silver antibacterial metal layer is at least 0.2 wt.%. After coating the diffusion aid medium with a silver antibacterial metal layer, the diffusion aid medium is positioned between the silver antibacterial metal layer and the stainless steel by further coating with a silver antibacterial metal layer. In other embodiments, the silver antibacterial metal layer may be coated between the diffusion aid medium layer and the stainless steel. As can be seen here, the silver antibacterial metal layer may be coated on the upper or lower end of the diffusion aid medium layer on stainless steel, and its position is not limited. Regarding the coating of the silver antibacterial metal layer, as described above, as one example, the coating may be performed by at least one or a combination thereof from the following methods: physical vapor deposition, chemical vapor deposition, electrolytic plating, or electroless plating.

[0026] Regarding the arrangement of the silver antibacterial metal layer coating, its thickness may be adjusted according to the needs, but a good example would be a thickness of 0.02 μm to 2.00 μm. However, if the thickness of the silver antibacterial metal layer is less than 0.02 μm, a silver alloy layer of sufficient concentration cannot be formed on the surface of the stainless steel, and a good antibacterial effect cannot be obtained. Furthermore, if the thickness of the silver antibacterial metal layer exceeds 2.00 μm, the excess antibacterial layer will remain on the surface of the stainless steel in the form of silver deposits, and it will be necessary to remove these residues using a different surface treatment method.

[0027] Furthermore, in other embodiments of the coating sequence described above, the diffusion-aiding medium layer and the silver antibacterial metal layer may be multilayer-layered coatings on the surface of the stainless steel. In other words, at least one of the diffusion-enhancing medium layer and the silver antibacterial metal layer may be installed in multiple layers, with the multiple layers overlapping each other. For example, when multiple diffusion-enhancing medium layers and silver antibacterial metal layers are installed simultaneously, four layers can be arranged in the order of diffusion-enhancing medium layer-silver antibacterial metal layer-diffusion-enhancing medium layer-silver antibacterial metal layer, starting from the stainless steel area. However, this is merely an example and is not limited to it.

[0028] As a good example, the diffusion-enhancing medium layer and the silver antimicrobial metal layer are coated by co-plating, and the diffusion-enhancing medium layer and the silver antimicrobial metal layer are simultaneously coated on the surface of the stainless steel, further advancing the diffusion of silver and ensuring uniform diffusion within the stainless steel. However, this is merely an example and is not limited thereto.

[0029] After the coating of the diffusion-enhancing medium layer and the silver antibacterial metal layer is completed, it is determined whether or not an additional protective layer needs to be coated on the outside of the silver antibacterial metal layer, based on the subsequent heat treatment conditions of the finished product. The protective layer is manufactured from a high-melting-point material. Specifically, the protective layer may be a metal layer (e.g., chromium, molybdenum, tungsten, nickel, titanium) or a ceramic (e.g., nitride or oxide). However, this is merely an example and is not limited to these. These measures prevent the volatilization of silver elements during high-temperature heat treatment and simultaneously avoid oxidation problems caused by trace amounts of oxygen remaining in the ambient atmosphere. The protective layer can also be coated by any of the following methods, for example, by at least one or a combination thereof, of the aforementioned physical vapor deposition, chemical vapor deposition, electroplating, or electroless plating. Furthermore, the thickness can also be changed, with the best options being between 0.05 μm and 5.00 μm. In the case of a protective layer with a thickness of less than 0.05 μm, silver will volatilize from tiny defects on the surface of the plating layer, resulting in poor protective effect. Furthermore, if the protective layer is thicker than 5.00 μm, the excess protective layer will remain on the surface of the stainless steel and will have to be removed by an additional surface treatment method. However, the above is merely one example and is not limited to this.

[0030] (Step S) S003: Heat treatment is performed on the stainless steel to diffuse the silver antibacterial metal into the stainless steel, and finally a silver antibacterial alloy layer is formed on the surface of the stainless steel.

[0031] In order to mitigate the problem of substrate oxidation during the heat treatment process, one example involves performing the heat treatment in a protective atmosphere. The protective atmosphere is a vacuum, or at least one of nitrogen, argon, or hydrogen, or a combination thereof. In other embodiments, a recyclable atmosphere may be selected. In the heat treatment process, any heating rate can be used to reach the target temperature.

[0032] As an example of heat treatment, the material is heated to 500°C or higher in a protective atmosphere for at least one minute.

[0033] The heat treatment temperature should be adjusted according to the type, thickness, shape, and structure of the steel material. If the heating temperature is below 500°C, the diffusion rate of silver is very low, and it is not possible to effectively achieve the antibacterial depth effect. As the heating temperature increases, the diffusion rate also increases accordingly, and the diffusion distance effectively extends.

[0034] However, it is important to note that the melting point of silver is 961°C. If the temperature exceeds this range, too much silver will volatilize into the environment, resulting in insufficient silver content to diffuse into the substrate, which can lead to problems such as adhesion to the sample and contamination of the furnace body. Therefore, when the heat treatment temperature exceeds 800°C, as mentioned above, it is necessary to install a protective layer to overcome the problem of silver volatilization.

[0035] The heat treatment time must be set to at least one minute to ensure sufficient time for the antimicrobial elements to diffuse fully into the stainless steel. The length of the heat treatment time is adjusted according to the type of stainless steel and the target thickness of the silver antimicrobial alloy layer. As the heat treatment time increases, the diffusion distance of the silver antimicrobial elements also increases, resulting in a thicker silver antimicrobial alloy layer. However, if the heat treatment time is too long, the diffusion distance increases, but the effect gradually decreases, ultimately resulting in energy waste. Therefore, by setting the heat treatment time in this embodiment between 1 minute and 100 hours, a good diffusion effect and resource utilization efficiency can be achieved.

[0036] In this embodiment, the stainless steel material after diffusion heat treatment can be cooled to room temperature by any temperature cooling rate or method, based on the target microstructure. As one example, the temperature cooling treatment of stainless steel having a silver antibacterial alloy layer is carried out by natural cooling, or by at least one of furnace cooling, air cooling, or quenching, and finally lowered to room temperature.

[0037] Regarding the silver antibacterial alloy layer, the silver concentration in the surface treatment material for stainless steel gradually decreases from the steel surface to the substrate, resulting in differences in structure and composition. During the heat treatment process, silver has very low solubility among the iron and chromium elements in the substrate, so it diffuses into the stainless steel along the grain boundaries. As a result, a microstructure containing a large amount of high-density silver is observed at the grain boundaries on the surface of the stainless steel. As the depth increases, the silver-rich phase gradually decreases, but the original stainless steel composition, structure, and performance within the substrate are maintained.

[0038] In particular, it should be explained that since the silver element hardly dissolves in the iron matrix and exists at grain boundaries in the form of a precipitated phase, in this invention, the diffusion depth or the thickness of the antibacterial alloy layer is determined by analyzing a combination of microscopic images and chemical components, and measuring the deepest location where the silver precipitated phase exists. Furthermore, when the silver content exceeds 0.2 wt%, a very excellent antibacterial effect is obtained. Therefore, the effective depth of the silver antibacterial alloy layer and the diffusion depth of silver are directly proportional. Accordingly, in this invention, the thickness of the silver antibacterial alloy layer is measured by observing the microstructure with a scanning electron microscope (SEM), and performing elemental analysis by combining energy-dispersive X-ray spectroscopy (EDS) or wavelength-dispersive X-ray spectroscopy (WDS) to measure the diffusion depth of the silver element.

[0039] Based on these, the present invention will be further explained by giving the following several embodiments, however, these are merely examples and do not limit the scope of the claims of the present invention.

[0040] [Materials used, precursors, and diffusion heat treatment] In the embodiments of the present invention, martensitic 420J2 stainless steel (SUS 420J2) and austenitic 304L stainless steel (SUS 304L) were selected, and the differences between them for different steel grades of the present invention were compared. Their chemical compositions are shown in Tables 1 and 2 below, respectively. The test samples are preprocessed using the following method. First, the stainless steel plate is cut to a size of 20 cm in length, 5 cm in width, and 2 mm in thickness. Then, the surface is polished with a grinding wheel and a nylon wheel to remove rust and defects from the surface. In this embodiment, the test piece is cleaned using ultrasonic vibration to ensure the removal of grease and dirt from the material surface, thereby forming a stainless steel base material.

[0041] Next, a precursor (diffusion-enhancing medium layer and silver antibacterial metal layer) is sputtered onto the test specimen using a physical vapor deposition method, followed by diffusion heat treatment. Detailed examples of the operating parameters for the manufacturing of surface-silver-containing stainless steel are shown separately in Table 3 below. However, this example is merely one example and is not limited thereto.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

[0045] [Influence of the diffusion aid layer]

[0046] Figure 2a shows the microstructure of the cross-section of specimen No. 1 after sputtering. The precursor was layered on the 420J2 substrate surface in the following order: a diffusion aid medium layer, a silver antibacterial metal layer, and a protective layer. The material is heat-treated and lightly polished to remove any residue. The SEM cross-sectional image in Figure 2b clearly shows that the silver-rich phase is distributed on the stainless steel grain boundaries, indicating that the silver diffused from the grain boundaries to the substrate surface. Calculations from the substrate surface indicate that the silver-rich phase is located at a depth of approximately 6-7 μm, demonstrating that the present invention successfully diffused silver into the interior of the stainless steel substrate. Furthermore, observation of the sample surface revealed that, as shown in Figure 2c, the silver-rich phase was diffusely embedded in the surface of the stainless steel, proving that the silver definitely diffused into the stainless steel and was not merely adhering to the surface. The test specimen that did not undergo diffusion-assisted media treatment (test specimen No. 10 control group) showed no silver-rich phase as shown in the SEM cross-sectional image after heat treatment in Figure 2d. In addition, a comparison of the EDS component analysis results of the two test specimens, No. 1 and No. 10, is shown in Figure 3, and the components at each point are shown in Tables 4 and 5. However, this embodiment is merely an example, and the present invention is not limited thereto.

[0047] [Table 4]

[0048] [Table 5]

[0049] As can be seen from the data, the light-colored area of ​​test specimen No. 1 is a silver-rich structure, and even after penetrating deeply into the substrate along the silver-rich area, a considerable amount of silver component can be identified, proving that the silver successfully diffused into the stainless steel substrate, with a diffusion distance of 6.09 μm. In this embodiment, no clear silver-rich structure was observed in the substrate of test specimen No. 10, which was not treated with a diffusion-enhancing medium. No effective silver signal was detected in the component analysis, indicating that when the diffusion-enhancing medium layer is not used, the silver element does not easily diffuse into the substrate.

[0050] As shown in Figure 4a, specimen No. 2 uses austenitic 304L stainless steel, and the image shows the cross-sectional microstructure of the substrate after sputtering. The precursor also has a layered structure and is stacked on the substrate surface. After heat treatment of the test specimen, the SEM cross-sectional image is shown in Figure 4b. The silver-rich phase is similarly distributed along the grain boundaries of the stainless steel, and calculations from the substrate surface indicate that the silver-rich phase exists in a depth range of approximately 5-6 μm. Furthermore, an SEM image of the surface of the test specimen is shown in Figure 4c. In this embodiment, the polishing process was omitted from the surface, so the presence of a large amount of silver-rich phase can be observed, and these silver-rich phase structures are distributed in a network structure, and their distribution is closely related to the crystalline structure of the substrate. As shown in Figure 4d, the SEM cross-sectional image of the test specimen (control group No. 11) that was not treated with a diffusion-enhancing medium shows no diffusion of the silver-rich phase into the substrate.

[0051] Furthermore, comparing the analysis results of the EDS components for two test specimens, No. 2 and No. 11, it is clear that the light-colored area within the substrate of test specimen No. 2 has a high proportion of silver content, as shown in Figure 5 and Tables 6 and 7 below. This proves that the area has a silver-rich phase structure, and from the image, its diffusion distance is observed to reach 5.56 μm. On the other hand, in test specimen No. 11, which did not have the auxiliary media treatment added, the phenomenon of silver diffusing from the substrate grain boundaries into the interior was not observed. This proves that the diffusion auxiliary media layer is related to the silver diffusion treatment. However, the present invention is not limited to these values.

[0052] [Table 6]

[0053] [Table 7]

[0054] In this embodiment, it was confirmed that the present invention successfully diffused the silver element into the stainless steel substrate structure using a diffusion-assisted media layer. Furthermore, the present invention can successfully diffuse silver in both martensitic (No. 1) and austenitic (No. 2) steels, demonstrating its broad applicability. However, the present invention is not limited to these.

[0055] [Effect of diffusion aid layer thickness]

[0056] Figure 6 shows a comparative diagram of the effects of different thicknesses of diffusion-adjusting media layers on the diffusion of silver. Test specimens No. 3, No. 4, and No. 5 all used 304L stainless steel as the base material. After applying a diffusion-enhancing medium layer to different thicknesses, a silver antibacterial metal layer and a protective layer were sputtered onto the specimens. Following diffusion heat treatment, the change in silver element distribution was analyzed by SEM / EDS. The analysis results showed that the silver diffusion depth of No. 3 was 12.71 μm. No. 4 is 16.63 μm, The thickness of No. 5 was 19.17 μm. This result indicates that the diffusion depth of silver into the stainless steel base material increases with increasing thickness of the diffusion-enhancing medium layer. The results described above show that adjusting the thickness of the diffusion-enhancing medium layer affects the diffusion depth of silver into the substrate. This result indicates that by controlling the thickness of the diffusion-enhancing medium layer, the diffusion depth of silver can be precisely adjusted according to the needs of subsequent products, which has great potential for subsequent and future applications.

[0057] [Influence of heat treatment conditions on microstructure]

[0058] In this embodiment, as shown in Figures 7 and 8, the effects of different heat treatment conditions on the silver diffusion distribution are demonstrated. However, the present invention is not limited to these conditions. In this embodiment, test specimens No. 1 and No. 6 were produced using 420J2 as the substrate, sputtered in proportion to the precursor, and heat-treated at 800°C and 900°C for 2 hours, respectively. The SEM surface images are shown. The crystal grains of specimen No. 1 are relatively small, with a high grain boundary ratio, and the silver-rich phase forms a granular structure, dispersed at the grain boundaries. In specimen No. 6, which was heat-treated at high temperatures, the microstructure showed significant grain growth, and the silver-rich phase further aggregated, distributing in a network-like pattern along the grain boundaries.

[0059] The results shown in Figure 8, using 304L as the test substrate, indicate that in test specimen No. 2, held at 800°C for 2 hours, the grain structure was small, a large amount of silver-rich phase was distributed on the surface, and some areas had a porous structure. In this embodiment, as shown in Figure 8, in test specimen No. 3, where the temperature was raised to 900°C and held for 2 hours, the crystal grain size increased, the silver-rich phase was more uniformly distributed along the grain boundaries, the surface became even flatter, and no porous structure appeared, indicating that the representative silver was uniformly diffused inside the substrate. Furthermore, in specimen No. 7, which was held at 900°C for 5 hours, the silver-rich phase on the grain boundaries became even finer, indicating that even more silver had diffused into the deeper parts of the substrate. Moreover, the height of the silver-rich phase and the stainless steel substrate were the same, indicating a stable network structure. However, the present invention is not limited to these conditions.

[0060] In summary, the present invention demonstrates that by adjusting the heat treatment parameters, the distribution and morphology of the silver-rich phase can be controlled and applied to different application needs. For example, 304L stainless steel is commonly used in a wide variety of household products. In this embodiment, for products requiring plastic deformation (e.g., cups, cans), it is preferable to set a high silver-rich ratio on the surface in order to maintain a sufficient silver concentration even after deformation. For example, in flat products that do not require processing, such as cutting boards and refrigerator interiors, the proportion of the silver phase can be appropriately reduced, while maintaining even better corrosion resistance.

[0061] [Antibacterial test]

[0062] In this embodiment, the antimicrobial property test will be conducted in accordance with JIS Z2801 standards. ATCC 8739 E. coli will be used as the test species, and the concentration will be 2.5 × 10⁻⁶. 5 ~10 6 A bacterial suspension with a CFU / ml concentration was collected and inoculated onto antimicrobially treated and untreated stainless steel test pieces, respectively. The test area was 40 mm x 40 mm, and the samples were incubated at 37°C for 24 hours. Next, after eluting the bacterial suspension with phosphate-buffered saline (PBS), the number of colonies is calculated using the standard plate count method. Then, the antimicrobial activity of the antimicrobially treated test specimens is obtained by counting the colonies on the two test specimens using the following mathematical formula 1.

[0063] (mathematical formula 1) Antimicrobial activity = (Number of colonies on untreated stainless steel specimens - Number of colonies on antimicrobial treated stainless steel specimens) / Number of colonies on untreated stainless steel specimens × 100%

[0064] Since 420J2 belongs to the category of cutlery steel, it is usually subjected to rapid quenching in actual use. Therefore, an antibacterial test was performed on the rapidly quenched specimen No. 8, and specimen No. 12 was used as the untreated control group. Test specimen No. 8 was first polished with #2000 sandpaper, then polished with aluminum oxide powder, and a microscopic image of the surface after polishing is shown in Figure 9. Subsequently, an antibacterial test was performed following the procedure described above, and the test was repeated three times to confirm the reproducibility of the results. The test results are shown in Figure 10. The antibacterial rate of test specimen No. 8 reached 99.99%, indicating that an antibacterial effect was generated on the material surface, and proving that the present invention is applicable to martensitic steel.

[0065] Next, in this embodiment, test specimens No. 3, No. 4, and No. 5 were selected from 304L stainless steel and subjected to antimicrobial testing, while test specimen No. 13 was used as an untreated control group. The test specimens were first polished with #2000 sandpaper to achieve a consistent surface texture. Figure 11 shows the surfaces after polishing. Subsequently, an antibacterial test was conducted following the procedure described above, and the test was repeated three times to confirm the reproducibility of the results. The test results are shown in Figure 12 and Table 8 below, with the antibacterial rates being 97.45% for No. 3, 99.70% for No. 4, and 99.46% for No. 5. This data shows that each test specimen exhibits excellent antibacterial activity. Furthermore, even when the proportion of the diffusion aid layer was increased to deepen the diffusion depth of silver, the surface after diffusion maintained its excellent antibacterial performance, demonstrating the superior antibacterial capabilities of the silver element. In addition, the reproducibility test of antibacterial performance demonstrates the stability and reliability of the present invention and represents the potential of the antibacterial product. It should be noted that the present invention is not limited to these values.

[0066] [Table 8]

[0067] [Corrosion resistance test]

[0068] In this embodiment, a cyclic polarization measurement is performed as a corrosion resistance test under the following conditions. The corrosion resistance test is measured and analyzed using a periodic polarization curve, and the test solution is 3.5 wt% NaCl deoxygenated with nitrogen at 25°C. (aq) Prepare an aqueous solution. Since 420J2 is a tool steel, it is usually subjected to rapid quenching in actual use. Because there is a significant difference in corrosion resistance between the annealed and hardened structures, all test specimens in this test will be rapidly air-cooled. Tests were conducted using 420J2 test specimens No. 8 and No. 9 with different thicknesses of diffusion-enhancing media layers, while the standard 420J2 test specimen No. 12 served as the control group. The hardness of all three test specimens after rapid cooling reached HRC 52, confirming that the material had hardened. The corrosion resistance test results are shown in Figure 13 and Table 9. According to the data, the passivation current density of these test specimens is even lower than that of test specimen No. 12, indicating that the passivation film on the silver-containing surface is more stable and the corrosion rate is reduced. However, the present invention is not limited to these conditions.

[0069] [Table 9]

[0070] Tests were conducted on 304L stainless steel specimens No. 3, No. 4, and No. 5 with different thicknesses of auxiliary media layers, while specimen No. 13, a silver-treated 304L stainless steel specimen, served as a control group. The test results are shown in Figure 14. According to the data, a decrease in passivation current density was observed in all three sets of samples, which is consistent with the performance of the aforementioned 420J2 substrate, proving that the passivation film on the surface of the silver-containing 304L stainless steel is even more stable.

[0071] In this embodiment, the aforementioned experiments combined show that all stainless steel materials subjected to silver diffusion treatment (for example, 304L and 420J2) exhibited a decrease in passivation current density, demonstrating that silver effectively enhances the stability of the surface passivation film. By diffusing silver onto the surface of stainless steel through the present invention, not only is the stainless steel endowed with antibacterial properties, but the stability and repair capabilities of the passivation film are also improved, further enhancing the corrosion resistance of the stainless steel. However, the present invention is not limited to these compositions or conditions.

[0072] [Metal elution test]

[0073] Stainless steel is widely used in various household products, and in particular, 300-series austenitic stainless steel is commonly used in food containers. Therefore, when the present invention is applied to the manufacture of food or drinking water containers, it is necessary to ensure that the amount of silver element leached out complies with safety standards. This test was conducted according to ASTM D5673 standards. Deionized water was dropped onto the surfaces of test specimens No. 3, No. 4, and No. 5, and the specimens were sealed in petri dishes for 7 days. Subsequently, the amount of silver ions eluted was measured using an inductively coupled plasma mass spectrometer (ICP-MS). The test results are shown in Table 10. First, a standard sample with a silver ion concentration of 0.100 ppm was used for correction, and after correction, the effective quantitative concentration range was set to 0.01 to 1.00 ppm. Subsequently, tests were conducted on three sets of test specimens. The data shows that the silver ion release from the three sets of test specimens was less than 0.01 ppm, below the quantitative range, and therefore displayed as Not Detected (ND). According to ASTM D5673 standards, the amount of silver ions released by this invention is less than 0.05 ppm, which falls within the safe range. Therefore, these test results prove that the present invention possesses antibacterial properties while simultaneously ensuring the safety of food and drinking water.

[0074] [Table 10]

[0075] The technical means disclosed in this invention effectively solves known problems and achieves the expected objectives and effects. Furthermore, prior to filing, it was not seen in any prior art or publicly disclosed. It also satisfies the invention requirements under patent law, demonstrating long-term progress.

[0076] In this embodiment, the above are merely some good examples of the present invention and do not limit the scope of the claims. That is, all the same effect changes and modifications shown in the claims and specification of the present invention are considered to fall within the scope of the claims. However, the present invention is not limited to these descriptions. [Explanation of symbols]

[0077] [The present invention] S001~S003: Step

Claims

1. In a method for producing antibacterial silver-containing stainless steel by surface alloying, among them, A layer of diffusion-enhancing medium is coated onto the surface of stainless steel. The diffusion-aiding medium layer is coated with at least one silver-containing silver antibacterial metal layer, and the concentration of silver in the silver antibacterial metal layer is at least 0.2 wt.%. The aforementioned stainless steel is subjected to heat treatment to diffuse the silver antibacterial metal into the stainless steel. A method for producing antibacterial silver-containing stainless steel by surface alloying, characterized by including the following step.

2. The method for producing antibacterial silver-containing stainless steel by surface alloying according to claim 1, characterized in that the thickness of the diffusion-auxiliary medium layer is between 0.05 μm and 5.00 μm.

3. The method for producing antibacterial silver-containing stainless steel by surface alloying according to claim 1, characterized in that the thickness of the silver antibacterial metal layer is between 0.02 μm and 2.00 μm.

4. The method for producing antibacterial silver-containing stainless steel by surface alloying according to claim 1, characterized in that the heat treatment is performed by heating to 500°C or higher in a protective atmosphere for a heating time of 1 minute or more, and then lowering to room temperature after the heat treatment is completed.

5. The method for producing antibacterial silver-containing stainless steel by surface alloying according to claim 4, characterized in that, after the heat treatment, the material is cooled to room temperature by at least one or a combination thereof, from furnace cooling, air cooling, or quenching.

6. The method for producing antibacterial silver-containing stainless steel by surface alloying according to claim 1, characterized in that the diffusion-enhancing medium layer is at least one or a combination thereof from copper, cobalt, nickel, zinc, molybdenum, chromium, or titanium.

7. A method for producing antibacterial silver-containing stainless steel by surface alloying according to any one of claims 1 to 6, characterized in that the stainless steel is at least one or a combination thereof from among ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, or duplex stainless steel.

8. A method for producing antibacterial silver-containing stainless steel by surface alloying according to any one of claims 1 to 6, characterized in that the diffusion-auxiliary medium layer or the silver antibacterial metal layer is coated by at least one or a combination thereof from physical vapor deposition, chemical vapor deposition, electroplating, or electroless plating.

9. A method for producing antibacterial silver-containing stainless steel by surface alloying according to any one of claims 1 to 6, characterized in that the diffusion-aiding medium layer and the silver antibacterial metal layer are multilayer-layered coatings on the surface of the stainless steel.

10. A method for producing antibacterial silver-containing stainless steel by surface alloying according to any one of claims 1 to 6, characterized in that the diffusion-auxiliary medium layer and the silver antibacterial metal layer are coated by co-plating, and the diffusion-auxiliary medium layer and the silver antibacterial metal layer are simultaneously coated on the surface of the stainless steel.

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