Austenitic stainless steel material, its manufacturing method, and antibacterial and antiviral component

Abstract

To provide an austenitic stainless steel capable of maintaining antibacterial and antivirus properties for a long period.SOLUTION: An austenitic stainless steel has a composition of C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00-20.00%, Cr: 10.00-32.00%, Cu: 2.00-6.00%, and the balance of Fe and impurities on the mass base. The ε-Cu phase of the austenitic stainless steel is exposed on the surface. The ε-Cu phase has an area ratio of 0.1-4.0%, an average particle diameter of 10-300 nm, and a maximum distance between particles of 100-1,000 nm on the surface of the austenitic stainless steel.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an austenitic stainless steel material, a method for producing the same, and an antibacterial and antiviral member. [Background technology]

[0002] Due to their excellent corrosion resistance, stainless steel materials are used in a wide range of applications, such as kitchen equipment, home appliances, medical instruments, interior building materials, and transportation equipment, and are often used in environments where bacterial proliferation and viral adhesion are likely to occur. In recent years, there has been a growing concern about the adverse effects on the human body caused by such bacterial proliferation and viral adhesion, and antibacterial and antiviral properties are being required not only for medical instruments and kitchen equipment, where cleanliness is essential, but also for various components used in buildings and transportation equipment where large numbers of people gather.

[0003] Metal elements such as Ag and Cu are known to have antibacterial and antiviral properties, and stainless steel materials that have been given antibacterial and antiviral properties by adding these metal elements have been proposed. For example, Patent Document 1 proposes an austenitic stainless steel material with excellent antibacterial properties, which has a composition containing up to 0.1 wt% C, up to 2 wt% Si, up to 5 wt% Mn, 10-30 wt% Cr, 5-15 wt% Ni, and 1.0-5.0 wt% Cu, with a Cu-based second phase (ε-Cu phase) dispersed in the matrix at a rate of 0.2 volume % or more. This austenitic stainless steel material is produced by subjecting an austenitic stainless steel containing up to 0.1 wt% C, up to 2 wt% Si, up to 5 wt% Mn, 10-30 wt% Cr, 5-15 wt% Ni, and 1.0-5.0 wt% Cu to one or more heat treatments in the temperature range of 500-900°C after hot rolling and before being made into a final product. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-176800 Summary of the Invention [Problem to be solved by the invention]

[0005] The austenitic stainless steel material described in Patent Document 1 does not have an appropriately controlled distribution state of the ε-Cu phase on the surface, so the desired antibacterial properties may not be obtained or the antibacterial properties may be easily lost early. Furthermore, since viruses are smaller than bacteria, when viruses are attached between the ε-Cu phases on the surface, the antiviral properties may be almost nonexistent.

[0006] An object of the present invention is to provide an austenitic stainless steel material capable of maintaining antibacterial and antiviral properties for a long period of time, a method for producing the same, and an antibacterial and antiviral member. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, they discovered that the distribution of the ε-Cu phase on the surface of an austenitic stainless steel material having a specific composition (in particular, the area ratio of the ε-Cu phase on the surface, the average particle size of the ε-Cu phase, and the maximum interparticle distance of the ε-Cu phase) is closely related to the antibacterial and antiviral properties, as well as the duration of these properties, and have completed the present invention.

[0008] That is, the present invention provides a steel sheet having a composition containing, by mass, C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 to 20.00%, Cr: 10.00 to 32.00%, Cu: 2.00 to 6.00%, and the balance being Fe and impurities; The ε-Cu phase is exposed on the surface. The austenitic stainless steel material has an area ratio of the ε-Cu phase on the surface of 0.1 to 4.0%, an average particle size of 10 to 300 nm, and a maximum interparticle distance of 100 to 1000 nm.

[0009] The present invention also provides A method for producing the austenitic stainless steel material, a hot rolling process for obtaining a hot-rolled material by hot rolling a slab having a composition containing, by mass, C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 to 20.00%, Cr: 10.00 to 32.00%, Cu: 2.00 to 6.00%, and the balance being Fe and impurities, wherein the finish hot rolling temperature is 850 to 1050°C; a cooling step of cooling the hot-rolled material obtained in the hot rolling step to between 900 and 500 ° C. at an average cooling rate of 0.2 to 5 ° C. / second; a heat treatment step of heating the hot-rolled material cooled in the cooling step at 750 to 850°C for 4 hours or more; Including How to eat It is the law.

[0010] Furthermore, the present invention relates to an antibacterial and antiviral member containing the austenitic stainless steel material. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an austenitic stainless steel material capable of maintaining antibacterial and antiviral properties for a long period of time, a method for producing the same, and an antibacterial and antiviral member. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of the surface of an austenitic stainless steel material according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following is a detailed description of the embodiments of the present invention. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements made to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention are also within the scope of the present invention. In addition, in this specification, the "% " display regarding components means "mass % " unless otherwise specified.

[0014] The austenitic stainless steel material according to an embodiment of the present invention contains C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 to 20.00%, Cr: 10.00 to 32.00%, Cu: 2.00 to 6.00%, and the balance consists of Fe and impurities. Here, in this specification, "steel material" means materials in various forms such as steel plates. Also, "steel plate" is a concept including steel strips. Further, "impurities" mean components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when industrially manufacturing stainless steel materials, and are allowed within a range that does not adversely affect the present invention.

[0015] Moreover, the austenitic stainless steel material according to an embodiment of the present invention can further contain one or more selected from Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, and W: 2.00% or less. Moreover, the austenitic stainless steel material according to an embodiment of the present invention can further contain one or more selected from Mo: 6.00% or less, N: 0.350% or less, and Sn: 0.500% or less. Moreover, the austenitic stainless steel material according to an embodiment of the present invention can further contain one or more selected from Al: 5.00% or less, Zr: 0.500% or less, and Co: 0.500% or less. Furthermore, the austenitic stainless steel material according to an embodiment of the present invention can further contain one or more selected from B: 0.0200% or less, Ca: 0.10% or less, and REM: 0.20% or less. Hereinafter, each component will be described in detail.

[0016] <C: 0.12% or less> C is an austenite-forming element, which is effective in improving the strength of austenitic stainless steels and uniformly dispersing and precipitating the ε-Cu phase by forming Cr carbides. However, if the C content is too high, in addition to becoming hard and reducing the workability, sensitization occurs when subjected to thermal effects such as welding, resulting in a decrease in the corrosion resistance of austenitic stainless steel materials. Therefore, the upper limit value of the C content is controlled to 0.12%, preferably 0.10%, more preferably 0.09%, and even more preferably 0.08%. On the other hand, the lower limit value of the C content is not particularly limited, but is preferably 0.001%, more preferably 0.003%, and even more preferably 0.005%.

[0017] <Si: 4.00% or less> Si is an element effective in improving the corrosion resistance and strength of austenitic stainless steel materials. However, if the Si content is too high, it becomes hardened and the workability of austenitic stainless steel materials decreases. Also, since Si is a ferrite phase (α-phase) forming element, it causes destabilization of the austenite phase and formation of the ferrite phase. Therefore, the upper limit value of the Si content is controlled to 4.00%, preferably 3.00%, more preferably 2.00%, and even more preferably 1.50%. On the other hand, the lower limit value of the Si content is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0018] <Mn: 6.00% or less> Mn is an austenite phase (γ-phase) forming element. Also, Mn forms MnS, and MnS acts as a nucleus for the ε-Cu phase. However, if the Mn content is too high, the corrosion resistance of austenitic stainless steel materials decreases. Therefore, the upper limit value of the Mn content is controlled to 6.00%, preferably 4.00%, more preferably 3.00%, and even more preferably 2.50%. On the other hand, the lower limit value of the Mn content is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0019] <P: 0.050% or less> If the content of P is too high, the corrosion resistance and workability of austenitic stainless steel materials will deteriorate. Therefore, the upper limit value of the content of P is controlled to 0.050%, preferably 0.040%, more preferably 0.035%. On the other hand, the lower limit value of the content of P is not particularly limited, but refining costs will occur for reduction, so it is preferably 0.001%, more preferably 0.005%, still more preferably 0.010%.

[0020] <S: 0.030% or less> If the content of S is too high, the hot workability will decrease, resulting in a decline in the manufacturability of austenitic stainless steel materials and also having an adverse effect on the corrosion resistance. Therefore, the upper limit value of the content of S is controlled to 0.030%, preferably 0.020%, more preferably 0.010%. On the other hand, the lower limit value of the content of S is not particularly limited, but refining costs will occur for reduction, so it is preferably 0.0001%, more preferably 0.0002%, still more preferably 0.0003%.

[0021] <Ni: 4.00 - 20.00%> Ni, like Mn, is an austenite phase (γ-phase) forming element, which improves corrosion resistance and workability. Since Ni is expensive, if the content is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit value of the content of Ni is controlled to less than 20.00%, preferably 15.00% or less, more preferably 12.00% or less, still more preferably 10.00% or less. On the other hand, if the content of Ni is too low, the corrosion resistance of austenitic stainless steel materials will deteriorate. Therefore, the lower limit value of the content of Ni is controlled to 4.00%, preferably 6.00%, more preferably 8.00%, still more preferably 8.50%.

[0022] <Cr: 10.00 - 32.00%> Cr is an important element for maintaining the corrosion resistance of austenitic stainless steel materials. However, if the Cr content is too high, it will lead to an increase in refining costs, harden due to solid solution strengthening, and reduce the workability of austenitic stainless steel materials. Therefore, the upper limit value of the Cr content is controlled at 32.00%, preferably 25.00%, more preferably 22.00%, and even more preferably 20.00%. On the other hand, if the Cr content is too low, sufficient corrosion resistance cannot be obtained. Therefore, the lower limit value of the Cr content is controlled at 10.00%, preferably 14.00%, more preferably 15.00%, and even more preferably 18.00%.

[0023] <Cu: 2.00 - 6.00%> Cu is an element necessary for precipitating the ε-Cu phase that provides antibacterial and antiviral properties. Also, Cu is an element that improves the workability of austenitic stainless steel materials. To obtain such effects, the lower limit value of the Cu content is controlled at 2.00%, preferably 2.50%, more preferably 3.00%, and even more preferably 3.60%. On the other hand, if the Cu content is too high, the corrosion resistance of austenitic stainless steel materials will decrease, and a low melting point phase will be formed during casting, leading to a decrease in hot workability. Therefore, the upper limit value of the Cu content is controlled at 6.00%, preferably 5.00%, more preferably 4.80%, and even more preferably 4.50%.

[0024] <Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, W: 2.00% or less> Nb, Ti, V, and W are elements that reduce sensitization due to grain boundary segregation of C and N by forming carbides and nitrides, improving intergranular corrosion resistance, and are added as necessary. However, if the contents of Nb, Ti, V, and W are too high, it will cause surface defects, leading to quality degradation, and the workability of austenitic stainless steel materials will decrease. Therefore, the upper limit values of the contents of Nb, Ti, and V are all controlled at 1.00%, preferably 0.50%. Also, the upper limit value of the content of W is controlled at 2.00%, preferably 1.50%. On the other hand, the lower limit values of the contents of Nb, Ti, V, and W are not particularly limited, but from the perspective of obtaining the effects of these elements, they are 0.01%, preferably 0.02%.

[0025] <Mo: 6.00% or less> Mo is an element that improves the corrosion resistance of austenitic stainless steel materials and is added as necessary. However, if the content of Mo is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit value of the content of Mo is controlled at 6.00%, preferably 5.00%, more preferably 3.00%, and even more preferably 2.00%. On the other hand, the lower limit value of the content of Mo is not particularly limited, but from the perspective of obtaining the effects of Mo, it is preferably 0.01%, more preferably 0.03%, and even more preferably 0.10%.

[0026] <N: 0.350% or less> N is an element that improves the corrosion resistance of austenitic stainless steel materials in the same way as Mo and is added as necessary. However, if the content of N is too high, it will harden and the workability of austenitic stainless steel materials will decrease. Therefore, the upper limit value of the content of N is controlled at 0.350%, preferably 0.200%, more preferably 0.150%, and even more preferably 0.050%. On the other hand, the lower limit value of the content of N is not particularly limited, but from the perspective of obtaining the effects of N, it is preferably 0.001%, preferably 0.003%.

[0027] <Sn: 0.500% or less> Sn, like Mo and N, is an element that improves the corrosion resistance of austenitic stainless steel materials and is added as necessary. However, if the Sn content is too high, it will cause a decrease in the hot workability of austenitic stainless steel materials. Therefore, the upper limit value of the Sn content is controlled to 0.500%, preferably 0.300%. On the other hand, the lower limit value of the Sn content is not particularly limited, but from the perspective of obtaining the effect of Sn, it is preferably 0.010%, more preferably 0.020%.

[0028] <Al: 5.00% or less> Al is an element used for deoxidation in the refining process and is added as necessary. Also, Al is an element that improves the corrosion resistance and heat resistance of austenitic stainless steel materials. However, if the Al content is too high, the amount of inclusions generated will increase and the quality will deteriorate. Therefore, the upper limit value of the Al content is 5.00%, preferably 3.00%, more preferably 2.00%, still more preferably 1.00%. On the other hand, the lower limit value of the Al content is not particularly limited, but from the perspective of obtaining the effect of Al, it is preferably 0.01%, more preferably 0.03%.

[0029] <Zr: 0.500% or less> Zr, like Al, is an element that improves the oxidation resistance of austenitic stainless steel materials and is added as necessary. However, if the Zr content is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit value of the Zr content is controlled to 0.500%, preferably 0.300%. On the other hand, the lower limit value of the Zr content is not particularly limited, but from the perspective of obtaining the effect of Zr, it is preferably 0.010%, more preferably 0.030%.

[0030] <Co: 0.500% or less> Co, like Al and Zr, is an element that improves the oxidation resistance of austenitic stainless steel materials and is added as necessary. However, if the Co content is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit value of the Co content is controlled at 0.500%, preferably 0.300%. On the other hand, the lower limit value of the Co content is not particularly limited, but from the perspective of obtaining the effect of Co, it is preferably 0.010%, more preferably 0.030%.

[0031] <B: 0.0200% or less> B is an element that improves hot workability and is added as necessary. However, if the B content is too high, the corrosion resistance and weldability of austenitic stainless steel materials will decrease. Therefore, the upper limit value of the B content is controlled at 0.0200%, preferably 0.0150%, more preferably 0.0100%, and even more preferably 0.0050%. On the other hand, the lower limit value of the B content is not particularly limited, but from the perspective of obtaining the effect of B, it is controlled at 0.0001%, preferably 0.0003%, more preferably 0.0005%.

[0032] <Ca: 0.10% or less> Ca, like B, is an element that improves the hot workability of austenitic stainless steel materials and is added as necessary. Also, Ca is an element that improves intergranular oxidation resistance by forming sulfides and suppressing the grain boundary segregation of S. However, if the Ca content is too high, it will cause a decrease in workability. Therefore, the upper limit value of the Ca content is controlled at 0.10%, preferably 0.05%. On the other hand, the lower limit value of the Ca content is not particularly limited, but from the perspective of obtaining the effect of Ca, it is preferably 0.001%, more preferably 0.003%.

[0033] <REM: 0.20% or less> Like B and Ca, REM (rare earth elements) are elements that improve the hot workability of austenitic stainless steel materials and are added as needed. REM also forms sulfides that are difficult to dissolve and inhibits the formation of MnS, which acts as a corrosion starting point, thereby improving corrosion resistance. However, an excessive REM content leads to increased manufacturing costs. Therefore, the upper limit of the REM content is controlled to 0.20%, preferably 0.10%. On the other hand, the lower limit of the REM content is not particularly limited, but is preferably 0.001%, more preferably 0.01%, from the viewpoint of obtaining the effects of REM. REM is a collective term for two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu). These may be used alone or as a mixture.

[0034] In the austenitic stainless steel material according to the embodiment of the present invention, the ε-Cu phase is exposed on the surface. FIG. 1 shows a schematic diagram of the surface of an austenitic stainless steel material according to an embodiment of the present invention. As shown in Fig. 1, an ε-Cu phase 11 is exposed on the surface of the parent phase of an austenitic stainless steel material 10. In addition, a passive film 12 is formed on the surface of the parent phase where the ε-Cu phase 11 is not exposed.

[0035] By exposing the ε-Cu phase 11 on the surface of the parent phase, when moisture comes into contact with the surface of the austenitic stainless steel material 10, Cu ions can be eluted from the ε-Cu phase 11. For example, when a person's hand touches the surface of the austenitic stainless steel material, the moisture on the hand can elute Cu ions from the ε-Cu phase 11. Therefore, even if bacteria adhere to the surface, they can be killed, and even if viruses adhere to the surface, they can be inactivated and eventually killed. Furthermore, since the passive film 12 is formed on the surface of the parent phase where the ε-Cu phase 11 is not exposed, the corrosion resistance is also good. The characteristics of the ε-Cu phase exposed on the surface will be explained in detail below.

[0036] <Area ratio: 0.1~4.0%> The greater the area fraction of the ε-Cu phase exposed on the surface, the greater the amount of Cu ions eluted, resulting in improved antibacterial and antiviral properties. The area fraction of the ε-Cu phase mainly depends on the crystal structure and Cu content. Therefore, the upper limit of the area fraction of the ε-Cu phase is controlled to 4.0%, preferably 3.0%, and more preferably 2.0%, taking into account the Cu content in the austenitic stainless steel material. On the other hand, the lower limit of the area fraction of the ε-Cu phase is controlled to 0.1%, preferably 0.3%, and more preferably 0.6%, from the viewpoint of ensuring antibacterial and antiviral properties.

[0037] Here, the "area ratio of the ε-Cu phase exposed on the surface" in this specification can be calculated by observing the surface of an austenitic stainless steel material with a TEM (transmission electron microscope). Specifically, TEM images are taken at three or more randomly selected locations on the surface of the austenitic stainless steel material, and the TEM images are then analyzed to measure the area of the ε-Cu phase. The area of the ε-Cu phase is then divided by the area of the field of view to calculate the "area ratio of the ε-Cu phase exposed on the surface." The area of the field of view is not particularly limited, but is preferably 10 μm in total for the locations photographed. 2 It is preferable that this is equal to or greater than this.

[0038] <Average particle size: 10~300nm> The larger the average particle size of the ε-Cu phase exposed on the surface, the longer Cu ions can be eluted, thereby improving the durability of antibacterial and antiviral properties. However, if the average particle size of the ε-Cu phase is too large, the interparticle distance of the ε-Cu phase exposed on the surface tends to be large. Therefore, when bacteria or viruses adhere between the ε-Cu phase particles exposed on the surface, sufficient antibacterial and antiviral properties may not be obtained. Therefore, the upper limit of the average particle size of the ε-Cu phase is controlled to 300 nm, preferably 250 nm, more preferably 200 nm, and even more preferably 150 nm. On the other hand, the lower limit of the average particle size of the ε-Cu phase is controlled to 10 nm, preferably 20 nm, and more preferably 30 nm, from the viewpoint of ensuring the durability of Cu ion elution.

[0039] Here, the "average particle size of the ε-Cu phase exposed on the surface" in this specification can be calculated by observing the surface of the austenitic stainless steel material with a TEM (transmission electron microscope). Specifically, TEM images are taken at three or more randomly selected locations on the surface of the austenitic stainless steel material, and the TEM images are then analyzed to determine the circle-equivalent diameters of the ε-Cu phase, and the average value thereof can be used as the "average particle size of the ε-Cu phase exposed on the surface."

[0040] <Maximum interparticle distance: 100~1000nm> Generally, bacteria are 0.5 to 3 μm in size, while viruses are very small, ranging from 10 to 200 nm. Therefore, if the maximum interparticle distance of the ε-Cu phase exposed on the surface is too large, sufficient antiviral properties may not be obtained, especially when viruses adhere between the particles of the ε-Cu phase exposed on the surface. Therefore, the upper limit of the maximum interparticle distance of the ε-Cu phase is controlled to 1000 nm, preferably 800 nm, and more preferably 500 nm. On the other hand, the smaller the maximum interparticle distance of the ε-Cu phase exposed on the surface, the higher the antibacterial and antiviral properties. However, when the ε-Cu phase has a relatively large average particle size of 10 to 300 nm, taking into account the growth process of the ε-Cu phase during heat treatment, the lower limit of the maximum interparticle distance of the ε-Cu phase is considered to be 100 nm. Therefore, the lower limit of the maximum interparticle distance of the ε-Cu phase is controlled to 100 nm, preferably 150 nm, and more preferably 200 nm.

[0041] Here, the "maximum interparticle distance of the ε-Cu phase exposed on the surface" in this specification can be calculated by observing the surface of an austenitic stainless steel material with a TEM (transmission electron microscope). Specifically, TEM images are taken at three or more randomly selected locations on the surface of the austenitic stainless steel material, and the TEM images are then subjected to image analysis to determine the positions of the centers of gravity (generator points) of the ε-Cu phase and perform Voronoi tessellation. Next, the distance between the centers of gravity of the ε-Cu phase in adjacent Voronoi regions is measured as the interparticle distance, and the maximum value thereof can be taken as the "maximum interparticle distance of the ε-Cu phase exposed on the surface."

[0042] The austenitic stainless steel material according to the embodiment of the present invention preferably has a Vickers hardness of 190 Hv or less, more preferably 180 Hv or less. By controlling the Vickers hardness to such a level, workability can be ensured, making it possible to use the material in a variety of applications. The lower limit of the Vickers hardness is not particularly limited, but is generally 100 Hv. Here, the Vickers hardness can be measured in accordance with JIS Z2244: 2009. In measuring the Vickers hardness, the measurement load is 10 kg, and measurements are made at five or more randomly selected locations, and the average value is taken as the Vickers hardness result.

[0043] The austenitic stainless steel material according to the embodiment of the present invention preferably has an antibacterial activity value of 2.0 or more in an antibacterial test in accordance with JIS Z2801: 2010. Such an antibacterial activity value can objectively guarantee high antibacterial properties. The "antibacterial test" in the present invention is performed in accordance with JIS Z2801:2010 using Staphylococcus aureus as the bacterium.

[0044] The austenitic stainless steel material according to the embodiment of the present invention preferably has an antiviral activity value of 2.0 or more in an antiviral test in accordance with ISO 21702: 2019. Such an antiviral activity value can objectively guarantee high antiviral properties. Antiviral testing is performed in accordance with ISO 21702:2019 using influenza A virus as the virus.

[0045] The type of austenitic stainless steel material according to the embodiment of the present invention is not particularly limited, but is preferably a hot-rolled material or a cold-rolled material. In the case of hot-rolled materials, the thickness is generally 3 mm or more, and in the case of cold-rolled materials, the thickness is generally less than 3 mm.

[0046] The austenitic stainless steel material according to the embodiment of the present invention can be produced by a method including a hot rolling step, a cooling step, and a heat treatment step. The hot rolling process is a process in which a slab having the above composition is hot rolled to obtain a hot rolled material. Specifically, the slab having the above composition is rough rolled and then finish hot rolled to obtain a hot rolled material. This hot rolled material may be wound into a coil. The slab having the above composition is not particularly limited, but can be obtained, for example, by melting stainless steel having the above composition and forging or casting it.

[0047] Finish hot rolling is performed so that the finish hot rolling end temperature is 850 to 1050°C. Controlling the finish hot rolling end temperature within this temperature range facilitates the uniform precipitation of small amounts of fine ε-Cu phase "seeds" from the end of finish hot rolling to the cooling process. As a result, by growing the ε-Cu phase in the heat treatment process, it becomes possible to control the distribution of the ε-Cu phase on the surface as described above. On the other hand, if the finish hot rolling end temperature is less than 850°C, the fine ε-Cu phase "seeds" do not precipitate sufficiently from the end of finish hot rolling to the cooling process. As a result, if the ε-Cu phase is grown in the heat treatment process, the average particle size and maximum interparticle distance of the ε-Cu phase on the surface become too large. Furthermore, if the finish hot rolling end temperature exceeds 1050°C, the microstructure becomes coarse, resulting in reduced workability and toughness. Furthermore, multiple rolling processes and heat treatments are required to restore the coarsened microstructure to a fine structure, which increases production costs. Other conditions in the hot rolling process may be appropriately set depending on the composition of the slab, and are not particularly limited.

[0048] The cooling process, which is intended to precipitate fine ε-Cu phase "seeds," involves cooling the hot-rolled material obtained in the hot-rolling process between 900 and 500°C at an average cooling rate of 0.2 to 5°C / s. Slow cooling under these conditions allows for the uniform precipitation of small amounts of fine ε-Cu phase "seeds" in the ε-Cu phase precipitation temperature range (900 to 500°C). These fine ε-Cu phase "seeds" preferentially grow during the heat treatment process, resulting in the uniform dispersion of relatively large ε-Cu phases. As a result, the distribution of the ε-Cu phase on the surface can be controlled as described above. In contrast, cooling between 900 and 500°C at an average cooling rate greater than 5°C / s does not result in sufficient precipitation of the fine ε-Cu phase "seeds." Consequently, if the ε-Cu phase is grown during the heat treatment process, the average particle size and maximum interparticle distance of the ε-Cu phase on the surface become excessively large. Furthermore, if the average cooling rate between 900 and 500°C is less than 0.2°C / s, the amount of fine ε-Cu phase "seeds" precipitated increases, resulting in a state in which a large amount of relatively small ε-Cu phase precipitates during the heat treatment process. The cooling method in the cooling step is not particularly limited, and any method known in the art can be used. For example, simply placing the coiled hot-rolled material in an insulating box allows for gradual cooling under the above cooling conditions by recuperation. The cooling temperature can be finely adjusted by controlling the amount of gas (e.g., Ar gas) supplied to the insulating box.

[0049] The heat treatment process is a process for growing the fine "seeds" of the ε-Cu phase precipitated in the cooling process. The hot-rolled material cooled in the cooling process is heated at 750 to 850°C for at least 4 hours. By performing the heat treatment under these conditions, it becomes possible to control the distribution of the ε-Cu phase on the surface as described above. If the heating temperature is less than 750°C or the heating time is less than 4 hours, the fine "seeds" of the ε-Cu phase do not grow sufficiently, and the average particle size of the ε-Cu phase becomes too small. Furthermore, if the heating temperature exceeds 850°C, the ε-Cu phase dissolves in the matrix.

[0050] After the heat treatment step, a surface layer removal step of pickling and / or polishing may be further carried out as necessary. By carrying out the surface layer removal step, scale formed on the surface and Cr-depleted layers can be removed. The thickness of the surface layer removed in the surface layer removal step is not particularly limited and may be adjusted appropriately depending on the composition of the slab, etc. For example, when removing a Cr-depleted layer, it is preferable to remove a surface layer with a thickness of 10 μm or more.

[0051] When the austenitic stainless steel material is a cold-rolled material, the heat treatment step may be followed by a cold rolling / annealing step in which cold rolling is performed and then annealing is performed for 300 seconds or less. When a surface layer removal step is performed after the heat treatment step, the cold rolling / annealing step may be performed after the surface layer removal step, or the surface layer removal step may be performed after the cold rolling / annealing step. By performing the annealing treatment for a short time of 300 seconds or less, it is possible to remove the strain generated by the cold rolling while suppressing the influence on the ε-Cu phase exposed on the surface. The conditions for the cold rolling and annealing treatment are not particularly limited and may be adjusted appropriately depending on the composition of the slab, etc.

[0052] The austenitic stainless steel material according to the embodiment of the present invention can maintain its antibacterial and antiviral properties for a long period of time, and can therefore be used for antibacterial and antiviral components. Furthermore, the austenitic stainless steel material according to the embodiment of the present invention can have a Vickers hardness of 190 Hv or less, and can therefore be easily processed into shapes suitable for antibacterial and antiviral components.

[0053] An antibacterial and antiviral member according to an embodiment of the present invention includes the above-mentioned austenitic stainless steel material. The above-mentioned austenitic stainless steel material used in this antibacterial and antiviral member may be processed into various shapes by methods known in the technical field. The antibacterial and antiviral member according to the embodiment of the present invention may further include a member other than the above-mentioned austenitic stainless steel material. Examples of antibacterial and antiviral materials include, but are not limited to, various materials that require antibacterial and antiviral properties and are used in kitchen equipment, home appliances, medical equipment, interior building materials for buildings, transportation equipment, laboratory equipment, sanitary equipment, etc. [Example]

[0054] The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited to these examples.

[0055] Stainless steels having the compositions of steel grades A to J shown in Table 1 (the balance being Fe and impurities) were melted and forged into slabs. The finish hot rolling temperature was controlled as shown in Table 2, and hot-rolled to a thickness of 3 mm to obtain hot-rolled materials. The hot-rolled materials were then wound into coils, quickly placed in an insulating box, and cooled between 900 and 500°C at the average cooling rate shown in Table 2. The average cooling rate was adjusted by adjusting the amount of Ar gas supplied to the insulating box. The cooled hot-rolled materials were then heat-treated in a batch annealing furnace at 800°C for 24 hours in an air atmosphere. The heat-treated hot-rolled materials were then cut into 100 mm (rolling direction) x 100 mm (width direction) pieces by cutting, pickling to remove scale, and polishing with a P400 buff (#400) to obtain austenitic stainless steel materials.

[0056] [Table 1]

[0057] [Table 2]

[0058] The resulting austenitic stainless steel materials were evaluated as follows.

[0059] (area ratio of ε-Cu phase exposed on the surface) A 3 mm diameter disk was cut out from an austenitic stainless steel material, one side was ground to a thickness of 0.5 mm, and the ground surface was then electrolytically polished to prepare a test specimen. Ten randomly selected points (total field area: 15 μm) were measured on the electrolytically polished surface of this test specimen. 2 ) and then analyzed the TEM images to measure the area of the ε-Cu phase. The area fraction of the ε-Cu phase was calculated by dividing the measured area of the ε-Cu phase by the area of the field of view.

[0060] (Average particle size of the ε-Cu phase exposed on the surface) The TEM images obtained in the same manner as the above area ratio were analyzed to determine the circle-equivalent diameters of the ε-Cu phase (30 particles), and the average value was calculated to obtain the average particle diameter of the ε-Cu phase.

[0061] (Maximum interparticle distance of ε-Cu phase exposed on the surface) The TEM images obtained in the same manner as for the above area ratio were subjected to image analysis, and the distance between the centers of gravity of the ε-Cu phase in adjacent Voronoi regions was measured as the interparticle distance according to the above method. The maximum value of this distance was calculated to obtain the maximum interparticle distance of the ε-Cu phase.

[0062] (Antibacterial test: antibacterial activity value) Test pieces measuring 50 mm (rolling direction) x 50 mm (width direction) were cut from the austenitic stainless steel material and subjected to antibacterial tests in accordance with JIS Z2801:2010 to determine the initial antibacterial activity value. Staphylococcus aureus was used as the bacteria in the antibacterial test, and a 40 mm x 40 mm polyethylene film was used as the adhesive film. The inoculation volume of the bacterial solution was 0.4 mL. Just before the start of the test, the entire surface of the test piece was lightly wiped with local gauze absorbed with ethanol of 99% purity or higher, and the test was then conducted after the piece had thoroughly dried. In addition, to evaluate the durability of the antibacterial effect, the test piece was immersed in 500 mL of water and kept in a thermostatic chamber at 80°C for 16 hours, after which the antibacterial test was carried out in the same manner as above, and the antibacterial activity value (after immersion in water) was determined.

[0063] (Antiviral test: antiviral activity value) Test pieces measuring 50 mm (rolling direction) x 50 mm (width direction) were cut from the austenitic stainless steel material and subjected to antiviral tests in accordance with ISO 21702:2019 to determine the antiviral activity value. In the antiviral test, influenza A virus was used as the virus, and a 40 mm x 40 mm polyethylene film was used as the adhesive film. The inoculation volume of the virus suspension (test solution) was 0.4 mL. Just before the test began, the entire surface of the test piece was lightly wiped with local gauze absorbed with ethanol of 99% purity or higher, and then allowed to dry thoroughly before the test. To evaluate the durability of the antiviral effect, the test piece was immersed in 500 mL of water and kept in a thermostatic chamber at 80°C for 16 hours, after which the antiviral test was carried out in the same manner as above, and the antiviral activity value (after immersion in water) was determined.

[0064] (Vickers hardness) Vickers hardness was measured in accordance with JIS Z2244: 2009. Measurements were performed using a Mitutoyo Vickers hardness tester HV-100 with a measurement load of 10 kg, measuring the Vickers hardness of the surface at 10 randomly selected points, and the average value was used as the result.

[0065] The results of the above evaluations are shown in Table 3.

[0066] [Table 3]

[0067] As shown in Table 3, the austenitic stainless steel materials Nos. 1 to 7 (examples of the present invention) had the specified composition and the distribution of the ε-Cu phase on the surface, and therefore the results of the antibacterial activity value (initial and after water immersion), the antiviral activity value (initial and after water immersion), and the Vickers hardness were all good. In contrast, the austenitic stainless steel material No. 8 (comparative example) had an excessively low finish hot rolling temperature and an excessively high average cooling rate, resulting in an excessively large average particle size of the ε-Cu phase. As a result, antiviral properties (antiviral activity value of 2.0 or more) were not obtained. In the austenitic stainless steel materials Nos. 9 and 10 (comparative examples), the average cooling rate was too high, which increased the maximum interparticle distance of the ε-Cu phase. As a result, antiviral properties (antiviral activity value of 2.0 or more) were not obtained.

[0068] In the austenitic stainless steel material No. 11 (comparative example), the average cooling rate was too slow, which resulted in a small average particle size of the ε-Cu phase. As a result, the antibacterial activity value and antiviral activity value after water immersion were low, and the antibacterial and antiviral properties were not sufficiently maintained. The austenitic stainless steel materials Nos. 12 and 13 (comparative examples) did not have the predetermined composition, and therefore the distribution of the ε-Cu phase on the surface could not be appropriately controlled, and as a result, antibacterial properties (antibacterial activity value of 2.0 or more) and antiviral properties (antiviral activity value of 2.0 or more) could not be obtained. No. 14 (comparative example) did not have the specified composition, and therefore cracks occurred during hot rolling, making it impossible to produce an austenitic stainless steel material.

[0069] As can be seen from the above results, the present invention can provide an austenitic stainless steel material capable of maintaining antibacterial and antiviral properties for a long period of time, a method for producing the same, and an antibacterial and antiviral member. [Explanation of symbols]

[0070] 10 Austenitic stainless steel 11 ε-Cu phase 12 Passive film

Claims

1. The composition includes, on a mass basis, C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 to 20.00%, Cr: 10.00 to 32.00%, Cu: 2.00 to 6.00%, and the balance being Fe and impurities; The ε-Cu phase is exposed on the surface, The austenitic stainless steel material has an area ratio of the ε-Cu phase on the surface of 0.1 to 4.0%, an average particle size of 10 to 300 nm, and a maximum interparticle distance of 100 to 1000 nm.

2. 2. The austenitic stainless steel material according to claim 1, further comprising, on a mass basis, one or more selected from Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, and W: 2.00% or less.

3. 3. The austenitic stainless steel material according to claim 1, further comprising, on a mass basis, one or more selected from Mo: 6.00% or less, N: 0.350% or less, and Sn: 0.500% or less.

4. The austenitic stainless steel material according to any one of claims 1 to 3, further comprising, on a mass basis, one or more selected from Al: 5.00% or less, Zr: 0.500% or less, and Co: 0.500% or less.

5. The austenitic stainless steel material according to any one of claims 1 to 4, further comprising, on a mass basis, one or more selected from B: 0.0200% or less, Ca: 0.10% or less, and REM: 0.20% or less.

6. The austenitic stainless steel material according to any one of claims 1 to 5, having a Vickers hardness of 190 Hv or less.

7. The austenitic stainless steel material according to any one of claims 1 to 6, having an antibacterial activity value of 2.0 or more in an antibacterial test in accordance with JIS Z2801:2010.

8. The austenitic stainless steel material according to any one of claims 1 to 7, having an antiviral activity value of 2.0 or more in an antiviral test in accordance with ISO 21702: 2019.

9. The austenitic stainless steel material according to any one of claims 1 to 8, which is used for an antibacterial and antiviral component.

10. A method for producing the austenitic stainless steel material of claim 1, comprising: a hot rolling process for obtaining a hot-rolled material by hot rolling a slab having a composition containing, on a mass basis, C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 to 20.00%, Cr: 10.00 to 32.00%, Cu: 2.00 to 6.00%, with the balance being Fe and impurities, wherein the hot rolling finish temperature is 850 to 1050°C; A cooling step of cooling the hot-rolled material obtained in the hot rolling step to between 900 and 500 ° C. at an average cooling rate of 0.2 to 5 ° C. / second; a heat treatment step of heating the hot-rolled material cooled in the cooling step at 750 to 850°C for 4 hours or more; A method comprising:

11. A method for producing the austenitic stainless steel material according to claim 2, comprising: The method according to claim 10, wherein the slab further contains, by mass, one or more selected from Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, and W: 2.00% or less.

12. A method for producing the austenitic stainless steel material of claim 3, comprising: The method according to claim 10 or 11, wherein the slab further contains, by mass, one or more selected from Mo: 6.00% or less, N: 0.350% or less, and Sn: 0.500% or less.

13. A method for producing the austenitic stainless steel material of claim 4, comprising: The method according to any one of claims 10 to 12, wherein the slab further contains, by mass, one or more selected from Al: 5.00% or less, Zr: 0.500% or less, and Co: 0.500% or less.

14. A method for producing the austenitic stainless steel material of claim 5, comprising: The method according to any one of claims 10 to 13, wherein the slab further contains, by mass, one or more selected from B: 0.0200% or less, Ca: 0.10% or less, and REM: 0.20% or less.

15. The method according to any one of claims 10 to 14, further comprising a surface layer removal step of pickling and / or polishing after the heat treatment step.

16. The method according to any one of claims 10 to 15, further comprising a cold rolling / annealing step of performing cold rolling and then annealing for 300 seconds or less after the heat treatment step.

17. An antibacterial and antiviral member comprising the austenitic stainless steel material according to any one of claims 1 to 9.

Images