Stainless steel materials and antibacterial / antiviral components

Abstract

To provide stainless steel materials and antibacterial / antiviral components that are excellent not only in antibacterial and antiviral properties but also in corrosion resistance. [Solution] A stainless steel material comprising a base material and a surface modification layer formed on the surface of the base material. The surface modification layer has 20 or more Cu-enriched phases with a Cu concentration of 4% or more present at the grain boundaries in a 50 μm square surface region, and the Cr concentration within the crystal grains on the surface is Cr concentration of the base material - 3% by mass or more.

Description

[Technical Field]

[0001] This invention relates to stainless steel materials and antibacterial / antiviral components. [Background technology]

[0002] Stainless steel is used in a wide range of applications, including kitchen equipment, home appliances, medical equipment, interior building materials, and transportation equipment, due to its excellent corrosion resistance. It is increasingly used in environments where bacterial growth and viral adhesion are likely to occur. In recent years, there has been a growing concern about the adverse effects on human health caused by such bacterial growth and viral adhesion. In particular, antibacterial and antiviral properties are required not only for medical equipment and kitchen equipment where cleanliness is essential, but also for various components used in buildings and transportation equipment where many people gather.

[0003] Since metal elements such as Ag and Cu are known to possess antibacterial and antiviral properties, stainless steel materials and methods for manufacturing them have been proposed that impart antibacterial and antiviral properties by adding these metal elements. For example, Patent Document 1 proposes an austenitic stainless steel material with excellent antibacterial properties, comprising C: 0.1% by weight or less, Si: 2% by weight or less, Mn: 5% by weight or less, Cr: 10-30% by weight, Ni: 5-15% by weight, and Cu: 1.0-5.0% by weight, with the remainder being substantially Fe, and having a Cu-enriched phase (Cu-rich phase) precipitated by aging treatment dispersed in the matrix at a rate of 0.2% by volume or more. This austenitic stainless steel material exhibits antibacterial properties when the Cu-enriched phase dissolves in moisture adhering to the surface. Therefore, the finer the Cu-enriched phase, the faster the dissolution is completed, and the antibacterial properties cannot be said to be sufficient. Therefore, one might consider increasing the amount of added Cu in order to increase the precipitation rate of the Cu-enriched phase and enlarge the Cu-enriched phase. However, increasing the amount of added Cu reduces processability and manufacturability, making this difficult to implement.

[0004] On the other hand, Patent Document 2 proposes a method for forming a Cu-enriched phase (Cu grain boundary layer) that extends continuously from the surface of the stainless steel material along the grain boundaries to a depth of 10 to 200 μm by applying Cu plating treatment to the stainless steel material and then performing heat treatment in an oxidizing atmosphere. This method can increase the size of the Cu-enriched phase and enhance antibacterial properties. However, this method tends to reduce the corrosion resistance of stainless steel. This is because when stainless steel is plated with Cu and then heat-treated, the Cu becomes uniformly dissolved within the crystal grains, reducing the Cr concentration within the grains. Furthermore, the Cu dissolved within the crystal grains is not a Cu-enriched phase (ε-Cu phase), and therefore does not contribute to improving antibacterial properties. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 3232532 [Patent Document 2] Patent No. 7260678 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The austenitic stainless steel material described in Patent Document 1 does not have sufficient antibacterial and antiviral properties, and the stainless steel material described in Patent Document 2 does not have sufficient corrosion resistance. Thus, conventional stainless steel materials have not been able to achieve both antibacterial and antiviral properties and corrosion resistance.

[0007] The present invention aims to provide stainless steel materials and antibacterial / antiviral components that are excellent not only in antibacterial and antiviral properties but also in corrosion resistance. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the inventors diligently researched stainless steel materials including a base material and a surface-modified layer formed on the surface of the base material. As a result, they discovered that by controlling the number of Cu-enriched phases present at the grain boundaries in the surface-modified layer and the Cr concentration within the surface grains, it is possible to improve corrosion resistance in addition to antibacterial and antiviral properties, thus completing the present invention.

[0009] In other words, the present invention relates to a stainless steel material comprising a base material and a surface modification layer formed on the surface of the base material, The surface modification layer relates to a stainless steel material in which, within a 50 μm square surface region, there are 20 or more Cu-enriched phases present at the grain boundaries with a Cu concentration of 4% or more, and the Cr concentration within the surface grains is Cr concentration of the base material minus 3% by mass or more. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide stainless steel materials and antibacterial / antiviral components that are excellent not only in antibacterial and antiviral properties but also in corrosion resistance. [Modes for carrying out the invention]

[0011] The embodiments of the present invention will be described in detail below. The present invention is not limited to the embodiments described below, and it should be understood that modifications, improvements, etc., made to the embodiments described below, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention, also fall within the scope of the present invention.

[0012] Herein, unless otherwise specified, the "%" notation in this specification means "mass%". Furthermore, in this specification, "stainless steel material" means a material formed from stainless steel, and its shape is not particularly limited. Examples of shapes include plates (including strips), rods, wires, and tubes. It may also be various types of shaped steel, such as T-shaped and I-shaped cross-sections.

[0013] The stainless steel material according to an embodiment of the present invention includes a base material and a surface modified layer formed on the surface of the base material. The surface modified layer contains a Cu-enriched phase (ε-Cu phase) with a Cu concentration of 4% or more. Since the surface modified layer contains such a Cu-enriched phase, the elution of Cu becomes easy. Therefore, for example, when a person's hand touches the surface of the stainless steel material, Cu ions can be eluted from the Cu-enriched phase by the moisture of the hand. Therefore, even if bacteria adhere to the surface, they can be sterilized, and even if viruses adhere to the surface, they can be inactivated and eventually killed. Here, in this specification, the "surface modified layer" means the surface layer where the Cu-enriched phase exists. The surface modified layer is observed by SEM (scanning electron microscope) in the cross-section in the thickness direction of the stainless steel material, and the region from the surface to the depth where the Cu-enriched phase exists is defined as the surface modified layer. The thickness of the surface modified layer is not particularly limited, but is typically 3 to 100 μm.

[0014] In the surface region of 50 μm square of the surface modified layer, there are 20 or more Cu-enriched phases present at grain boundaries. By dispersing and precipitating the Cu-enriched phase in the surface region of the surface modified layer in this way, the amount of Cu elution increases, so the antibacterial and antiviral properties are improved. If the number of Cu-enriched phases is less than 20, the amount of Cu elution decreases, so the antibacterial and antiviral properties cannot be sufficiently ensured. From the viewpoint of improving not only the antibacterial and antiviral properties but also the corrosion resistance, the Cu-enriched phase is preferably 25 or more, more preferably 30 or more, and still more preferably 45 or more. On the other hand, the upper limit of the number of Cu-enriched phases is not particularly limited, but if it is too large, the corrosion resistance tends to decrease. Therefore, the number of Cu-enriched phases is preferably 100 or less, more preferably 80 or less.

[0015] Here, the number of Cu-enriched phases present at the grain boundaries in the 50-μm square surface area of the surface modification layer is determined by observing the surface of the surface modification layer with a SEM (scanning electron microscope). Specifically, the number of Cu-enriched phases present at the grain boundaries in the 50-μm square surface area of the surface modification layer is determined as follows. First, a sample with dimensions of 15 mm × 15 mm × the thickness of the steel material is cut out from the stainless steel material by cutting or the like, and the 50-μm square area on the surface of the surface modification layer is observed with a SEM. In the backscattered electron image of the SEM, the Cu-enriched phases (it is confirmed by EDX analysis that the Cu concentration is 4% or more) are identified based on the difference in contrast, and the number of Cu-enriched phases is measured. This operation is performed in 10 non-overlapping fields of view to obtain the number of Cu-enriched phases respectively, and their average value is obtained.

[0016] The surface modification layer has a Cr concentration in the surface grains that is equal to or higher than the Cr concentration of the base material minus 3 mass%. If the Cr concentration in the surface grains is within this range, it can be said that the Cr-depleted layer has been sufficiently removed, and thus the corrosion resistance of the stainless steel material can be ensured. If the Cr concentration in the surface grains is less than the Cr concentration of the base material minus 3 mass%, the Cr-depleted layer remains, and thus the corrosion resistance of the stainless steel material cannot be ensured. Note that the upper limit of the Cr concentration in the surface grains is not particularly limited, but is generally equal to or lower than the Cr concentration of the base material. Here, in this specification, the "Cr concentration of the base material" means the Cr concentration in the stainless steel material before the surface modification layer is formed.

[0017] Here, the Cr concentration in the surface grains of the surface modification layer is the ratio of the Cr concentration to the total concentration of Fe, Cr, Ni, Cu, Si, Mo, and Mn determined by AES (Auger electron spectroscopy) analysis within the surface grains of the surface (Z-plane) of the surface modification layer, that is, Cr / (Fe + Cr + Ni + Cu + Si + Mo + Mn) × 100 (where each element represents the concentration of each element). The AES analysis is performed by cutting out a sample with dimensions of 10 mm × 10 mm × the thickness of the steel material from the stainless steel material and conducting the analysis within the surface grains of the surface (Z-plane) of the surface modification layer. The AES analysis is performed within the surface grains that are 5 μm or more away from the grain boundaries, and point analysis is performed on 10 different surface grains.

[0018] The composition of the base material of the stainless steel material according to the embodiment of the present invention is not particularly limited, but C: 0.100% or less, Si: 1.00% or less, Mn: 5.00% or less, Ni: 35.00% or less, Cr: 13.00 to 30.00%, P: 0.100% or less, S: 0.0300% or less, Cu: 4.00% or less, N: 0.300% or less, Mo: 8.00% or less are further included, and the balance is preferably composed of Fe and impurities. Further, the base material of the stainless steel material according to the embodiment of the present invention can further include one or more selected from Ti: 1.00% or less, Nb: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, Al: 0.100% or less, B: 0.0100% or less.

[0019] Here, in this specification, "impurities" means components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when the stainless steel material is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. For example, impurities include inevitable impurities. Regarding the content of each element, including "xx% or less" means that it is xx% or less, but includes an amount exceeding 0% (especially exceeding the impurity level). Hereinafter, each component will be described in detail.

[0020] <C: 0.100% or less> C is an element that improves the strength of the stainless steel material. However, if the content of C is too high, in addition to becoming hard and the workability deteriorating, sensitization occurs when it is affected by heat such as welding, and the corrosion resistance of the stainless steel material decreases. Therefore, the upper limit value of the content of C is controlled to 0.100%, preferably 0.090%, more preferably 0.080%, and still more preferably 0.075%. On the other hand, the lower limit value of the content of C is not particularly limited, but from the viewpoint of suppressing refining costs, it is preferably 0.001%, more preferably 0.003%, and still more preferably 0.005%.

[0021] <Si: less than 1.00%> Si is an element effective in improving the corrosion resistance of stainless steel materials. However, if the Si content is too high, an Al oxide film is likely to form even in a non-oxidizing atmosphere during Cu diffusion heat treatment. Also, it hardens and the workability of the stainless steel material decreases, and when welding is performed, the toughness of the welded part decreases. Therefore, the upper limit value of the Si content is controlled to 1.00%, preferably 0.90%, more preferably 0.80%, and even more preferably 0.70%. On the other hand, the lower limit value of the Si content is not particularly limited, but from the viewpoint of obtaining the effect of Si, it is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0022] <Mn: less than 5.00%> Mn is an element that improves the heat resistance of stainless steel materials. However, if the Mn content is too high, MnS, which is a corrosion initiation point, is likely to be generated, and the austenite phase becomes unstable. Therefore, the upper limit value of the Mn content is controlled to 5.00%, preferably 4.50%, more preferably 4.00%, and even more preferably 3.50%. On the other hand, the lower limit value of the Mn content is not particularly limited, but from the viewpoint of obtaining the effect of Mn, it is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0023] <Ni: less than 35.00%> Ni is an element that improves the corrosion resistance (especially intergranular corrosion resistance) of stainless steel materials. However, if the Ni content is too high, the austenite phase becomes unstable like Mn, and the manufacturing cost also increases. Therefore, the upper limit value of the Ni content is controlled to 35.00%, preferably 30.00%, more preferably 25.00%, and even more preferably 20.00%. On the other hand, the lower limit value of the Ni content is not particularly limited, but when the stainless steel material is austenitic, it is controlled to 6.00%, preferably 7.00%, more preferably 7.50%.

[0024] <Cr: 13.00 - 30.00%> Cr is an important element for ensuring the corrosion resistance and oxidation resistance of stainless steel materials. However, if the Cr content is too high, it will lead to an increase in refining costs, hardening (decrease in toughness) due to solid solution strengthening, and a decrease in the workability of stainless steel materials. Therefore, the upper limit of the Cr content is controlled at 30.00%, preferably 28.00%, more preferably 26.00%. On the other hand, if the Cr content is too low, sufficient corrosion resistance cannot be obtained. Therefore, the lower limit of the Cr content is controlled at 13.00%, preferably 14.00%, more preferably 15.00%, and still more preferably 16.00%.

[0025] <P: 0.100% or less> When the Cu content is high and the P content is high, it is easy to form Cu and low-melting-point intermetallic compounds. This intermetallic compound causes cracks and the like during hot rolling, so it is desirable to reduce the P content. Also, when the P content is high, it also causes a decrease in weldability and workability. Therefore, the upper limit of the P content is controlled at 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit of the P content is not particularly limited, but since refining costs are incurred for reduction, it is preferably 0.001%, more preferably 0.005%, and still more preferably 0.010%.

[0026] <S: 0.0300% or less> Similar to P, when the S content is high, it is easy to form Cu and low-melting-point intermetallic compounds, which causes cracks and the like during hot rolling. Also, when the S content is high, MnS, which serves as a corrosion initiation point, is likely to be generated, and the toughness of the welded part decreases when welding is performed. Therefore, the upper limit of the S content is controlled at 0.0300%, preferably 0.0200%, more preferably 0.0100%. On the other hand, the lower limit of the S content is not particularly limited, but since refining costs are incurred for reduction, it is preferably 0.0001%, more preferably 0.0005%, and still more preferably 0.0010%.

[0027] <Cu: 4.00% or less> Cu is an element that improves the workability of stainless steel materials. However, if the Cu content is too high, the austenite phase becomes unstable and the manufacturing cost also increases. Therefore, the upper limit of the Cu content is controlled at 4.00%, preferably 3.00%, more preferably 2.50%. On the other hand, the lower limit of the Cu content is not particularly limited, but from the perspective of obtaining the effect of Cu, it is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0028] <N: 0.300% or less> N is an element effective in improving the corrosion resistance of stainless steel materials. However, if the N content is too high, in addition to becoming hard and the workability decreasing, sensitization occurs when subjected to heat effects such as welding, and the corrosion resistance of the stainless steel material decreases. Therefore, the upper limit of the N content is controlled at 0.300%, preferably 0.200%, more preferably 0.100%, and even more preferably 0.050%. On the other hand, the lower limit of the N content is not particularly limited, but from the perspective of suppressing the refining cost, it is preferably 0.001%, more preferably 0.003%, and even more preferably 0.005%.

[0029] <Mo: 8.00% or less> Mo is an element effective in improving the corrosion resistance and oxidation resistance of stainless steel materials. However, if the Mo content is too high, it leads to a decrease in workability and an increase in manufacturing cost. Therefore, the upper limit of the Mo content is controlled at 8.00%, preferably 5.00%, more preferably 3.00%. On the other hand, the lower limit of the Mo content is not particularly limited, but from the perspective of obtaining the effect of Mo, it is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0030] <Ti: 1.00% or less> Ti is an element that affects the intergranular corrosion resistance (sensitization suppression effect) of stainless steel materials. Also, Ti is an element effective for immobilizing C and N. However, if the Ti content is too high, in addition to an increase in manufacturing cost, the workability and surface quality of stainless steel materials will deteriorate. Therefore, the upper limit value of the Ti content is 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, the lower limit value of the Ti content is not particularly limited, but from the viewpoint of obtaining the effect of Ti, it is preferably 0.01%, more preferably 0.03%, still more preferably 0.05%.

[0031] <Nb: 1.00% or less> Similar to Ti, Nb is an element that affects the intergranular corrosion resistance (sensitization suppression effect) of stainless steel materials. Also, Nb is an element effective for immobilizing C and N. However, if the Nb content is too high, in addition to an increase in manufacturing cost, the workability and surface quality of stainless steel materials will deteriorate. Therefore, the upper limit value of the Nb content is 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, since Nb generates carbonitrides such as NbC and NbN, the coarsening of crystal grains can be effectively suppressed by the pinning effect of this carbonitride. From the viewpoint of obtaining this effect, the lower limit value of the Nb content is not particularly limited, but it is preferably 0.01%, more preferably 0.03%, still more preferably 0.05%.

[0032] <Zr: 1.00% or less, Co:​​​​​<REM: Below 0.100%, Ca: Below 0.100%, Sn: Below 0.100%, Al: Below 0.100%> REM (rare earth elements), Ca, Sn, and Al are elements effective in improving the oxidation resistance of stainless steel materials. However, if the content of these elements is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit of the content of these elements is controlled to 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit of the content of these elements is not particularly limited, but from the perspective of obtaining the effects of these elements, it is preferably 0.001%, more preferably 0.003%, and still more preferably 0.005%. Note that REM refers to the general 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] <B: Below 0.0100%> B is an element effective in improving the secondary processing properties of stainless steel materials. However, if the content of B is too high, it will cause a decrease in fatigue strength. Therefore, the upper limit of the content of B is controlled to 0.0100%, preferably 0.0070%. On the other hand, the lower limit of the content of B is not particularly limited, but from the perspective of obtaining the effects of B, it is preferably 0.0001%, more preferably 0.0003%.

[0035] The steel type of the stainless steel material according to the embodiment of the present invention is not particularly limited and may be any of austenitic, ferritic, martensitic, duplex, etc. Among them, the stainless steel material according to the embodiment of the present invention is preferably austenitic. Here, the "austenitic system" in this specification means that the metal structure is mainly the austenite phase at room temperature. Therefore, the "austenitic system" includes those that slightly contain phases other than the austenite phase (for example, the ferrite phase, the martensite phase, etc.). However, the "austenitic system" does not include a duplex structure of the ferrite phase and the austenite phase, a duplex structure of the ferrite phase and the martensite phase, and a duplex structure of the ferrite phase, the austenite phase, and the martensite phase.

[0036] The type of the stainless steel material according to the embodiment of the present invention is not particularly limited, and it may be a hot-rolled material or a hot-rolled annealed material, or it may be a cold-rolled material or a cold-rolled annealed material, but it is preferably a cold-rolled material or a cold-rolled annealed material. In the case of a hot-rolled material or a hot-rolled annealed material, its thickness is generally 3 mm or more. In the case of a cold-rolled material or a cold-rolled annealed material, its thickness is generally less than 3 mm.

[0037] The stainless steel material according to the embodiment of the present invention has a chromaticity index a * , * , * , * , * , a * b * in the CIE L * color space preferably of 1.5 or less. CIE L * a​​​​​​​​​​​​​​​This is determined by measuring the surface color tone of the surface modified layer in accordance with JIS Z8722:2009.

[0038] The stainless steel material according to the embodiment of the present invention has a Cu elution amount of 0.10 μg / cm³. 2 It is preferable that the amount of Cu eluted is above this range. A Cu elution amount within this range can be said to exhibit excellent antibacterial and antiviral properties. The Cu elution amount is 0.15 μg / cm³. 2 It is more preferable that the concentration be greater than or equal to 0.20 μg / cm³. 2 More preferably, the concentration is 0.30 μg / cm³. 2 The above is particularly preferable. The upper limit of the Cu elution amount is not particularly limited, as higher values ​​result in superior antibacterial and antiviral properties, but for example, 10.00 μg / cm³ is preferable. 2 That is the case.

[0039] Here, the amount of Cu eluted in this specification is determined as follows. First, a sample measuring 33 mm × 33 mm × the thickness of the steel material is cut from a stainless steel plate by cutting or other means, and the surface is degreased with acetone. Next, the sample is immersed in 25 mL of 5% nitric acid aqueous solution (liquid temperature: 18~25°C) for 2 hours. At this time, the sample is left standing upright in a container of nitric acid aqueous solution so that the surface modified layer is approximately parallel to the vertical direction. Then, the Cu concentration in the nitric acid aqueous solution after the test is analyzed by ICP. The Cu concentration per unit area (μg / cm³) is obtained by dividing the obtained Cu concentration by the surface area of ​​the sample (however, the surface area is the area of ​​the two faces (front and back) perpendicular to the thickness direction of the sample, and the area of ​​the four faces (end faces) parallel to the thickness direction of the sample is excluded). 2 ) is calculated, and this result is taken as the amount of Cu eluted.

[0040] In the embodiment of the present invention, the stainless steel material preferably has a rating number of 7.0 or higher as defined in JIS G0595:2004 on the surface of the surface-modified layer after five cycles of a wet-dry cycle test, in which a 5% aqueous solution containing NaCl is sprayed at 35°C for 2 hours, then held in a dry atmosphere at 60°C and 30% relative humidity for 4 hours, and then held in a wet atmosphere at 50°C and 95% relative humidity for 2 hours constitutes one cycle. A rating number within this range indicates excellent corrosion resistance. A rating number of 7.5 or higher is more preferable. The rating number was determined using two samples, and the average value was used as the result.

[0041] The method for manufacturing stainless steel materials according to the embodiments of the present invention is not particularly limited as long as it can produce stainless steel materials having the above-described characteristics. A typical method for manufacturing stainless steel materials according to the embodiments of the present invention will be described below. A method for manufacturing stainless steel material according to an embodiment of the present invention includes a Cu plating step, a Cu diffusion heat treatment step, and a polishing step.

[0042] The Cu plating process is a process in which a Cu plating treatment is applied to a stainless steel material (base material). The base material used for the Cu plating process is not particularly limited, but it preferably contains C: 0.100% or less, Si: 1.00% or less, Mn: 5.00% or less, Ni: 35.00% or less, Cr: 13.00-30.00%, P: 0.100% or less, S: 0.0300% or less, Cu: 4.00% or less, N: 0.300% or less, and Mo: 8.00% or less, with the remainder being Fe and impurities. Furthermore, the base material used for Cu plating may further include one or more selected from Ti: 1.00% or less, Nb: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, Al: 0.100% or less, and B: 0.0100% or less.

[0043] The type of steel used as the base material for Cu plating is not limited and may be austenitic, ferritic, martensitic, or duplex. Among these, austenitic steel is preferred for the base material used for Cu plating. The type of base material used in the Cu plating process is not particularly limited, but it may be a hot-rolled material or a hot-rolled annealed material, or a cold-rolled material or a cold-rolled annealed material, although a cold-rolled material or a cold-rolled annealed material is preferred. For example, a hot-rolled material can be obtained by hot-rolling a stainless steel slab. A hot-rolled material can be made into a hot-rolled annealed material by annealing. A cold-rolled material can be obtained by cold-rolling a hot-rolled annealed material. A cold-rolled material can also be made into a cold-rolled annealed material by annealing. Pickling may be performed after annealing. The conditions for hot-rolling, cold-rolling, annealing, and pickling are not particularly limited and can be adjusted according to the composition. The stainless steel slab is not particularly limited, but for example, it can be obtained by melting stainless steel having the above composition and then forging or casting it.

[0044] The method for copper plating is not particularly limited, and known electroplating or electroless plating methods can be used. The thickness of the Cu plating formed by the Cu plating process should be 0.03 to 1.00 μm. By controlling the thickness within this range, the Cu-enriched phase can be sufficiently dispersed and deposited by the Cu diffusion heat treatment process described later. If the thickness of the Cu plating is less than 0.03 μm, the amount of Cu-enriched phase deposited will be small, and sufficient antibacterial and antiviral properties will not be obtained. Also, if the thickness of the Cu plating exceeds 0.25 μm, the Cu-enriched phase will precipitate continuously along the grain boundaries, reducing corrosion resistance. Furthermore, Cu plating will remain on the surface after the Cu diffusion heat treatment process. From the viewpoint of stably dispersing and depositing the Cu-enriched phase, the thickness of the Cu plating is preferably 0.05 to 0.50 μm, more preferably 0.08 to 0.20 μm. Furthermore, the conditions for the Cu plating process are not particularly limited; they can be selected to control the thickness of the Cu plating within the above-mentioned range (electrolyte and its temperature, current density).

[0045] This process involves heating a copper-plated base material in a non-oxidizing atmosphere. By performing this process, Cu atoms in the Cu plating diffuse from the surface of the base material into the metal structure inside the base material, and a surface modification layer is formed on the surface of the base material. Since Cu atoms diffuse more easily into grain boundaries than within crystal grains, the amount of Cu-enriched phase deposited at and around the grain boundaries increases.

[0046] The atmosphere during the Cu diffusion heat treatment process is kept non-oxidizing to suppress the formation of an oxide film. While not particularly limited, the non-oxidizing atmosphere can be Alcon gas, hydrogen gas, nitrogen gas, etc. These gases can be used individually or in combination of two or more. Furthermore, the atmosphere during the Cu diffusion heat treatment process is set to have a dew point of -30°C or lower. By controlling the atmosphere to this dew point range, the formation of oxide films can be suppressed, reducing the precipitation of Cu-enriched phases with a major axis exceeding 500 nm, while increasing the precipitation of Cu-enriched phases with a major axis of 50 to 500 nm. The dew point is preferably -35 to -100°C, and more preferably -40 to -80°C.

[0047] The heating temperature in the Cu diffusion heat treatment process should be between 900 and 1200°C. By controlling the heating temperature within this range, the Cu-enriched phase can be sufficiently dispersed and precipitated. If the heating temperature is below 900°C, the amount of Cu-enriched phase precipitated by Cu diffusion will be small, and sufficient antibacterial and antiviral properties will not be obtained. If the heating temperature exceeds 1200°C, the Cu-enriched phase will precipitate continuously along the grain boundaries, reducing corrosion resistance. From the viewpoint of stably dispersing and precipitating the Cu-enriched phase, the heating temperature is preferably between 950 and 1150°C, and more preferably between 1000 and 1100°C.

[0048] The heating time in the Cu diffusion heat treatment process is not particularly limited and can be set appropriately according to the heating temperature. The heating temperature can be, for example, 1 second to 60 minutes, preferably 1 to 600 seconds, and more preferably 1 to 180 seconds. Here, the heating temperature in this specification refers to the holding time after reaching the predetermined heating temperature. If the heating time is less than 1 second, the amount of Cu-enriched phase precipitated by Cu diffusion tends to be small. Also, if the heating time exceeds 60 minutes, Cu diffusion proceeds excessively, causing Cu to diffuse not only to the surface but also to the interior, resulting in a decrease in the Cu-enriched phase on the surface.

[0049] The polishing process involves polishing the surface of the surface-modified layer to remove the chromium-poorened layer. When using wet polishing with water, the Cu-enriched phase precipitated at the grain boundaries of the surface-modified layer dissolves, impairing its antibacterial and antiviral properties. Furthermore, when using dry polishing, significant heat is generated at the contact surface between the abrasive and the surface-modified layer, leading to a rapid temperature increase on the surface of the modified layer, which causes the Cu-enriched phase precipitated at the grain boundaries to dissolve. Therefore, as a polishing method, wet polishing using an oily solvent is performed in order to remove the Cr-enriched phase while maintaining the Cu-enriched phase precipitated at the grain boundaries. The oily solvent is not particularly limited, and alcohols or mineral oils that are liquid at room temperature (25°C) can be used. Alternatively, various oils and fats such as fatty acids or petroleum-based oils that are solid at room temperature but become liquid due to the heat generated during polishing may also be used. The abrasive particles used in wet polishing with an oily solvent are not particularly limited, but alumina, chromium oxide, etc., can be used. However, the size of the abrasive particles should be such that their average particle size is 50 μm or less, from the viewpoint of retaining as much of the Cu-enriched phase precipitated at the grain boundaries as possible. If the average particle size of the abrasive particles exceeds 50 μm, a large amount of the Cu-enriched phase will be removed, impairing the antibacterial and antiviral properties. Here, the "average particle size" of the abrasive refers to the average value of the longest side of 10 arbitrarily selected abrasive grains observed using a scanning electron microscope (SEM).

[0050] Wet polishing using oily solvents may be carried out by preparing the solvent and abrasive separately as described above, but commercially available solid abrasives contain various oils and abrasives, so it is easier to apply this solid abrasive to a buffing pad and polish using a grinder. The conditions during polishing are not particularly limited and can be adjusted as appropriate depending on the state of the surface modification layer and the type of polishing equipment used.

[0051] The stainless steel material according to the embodiment of the present invention has excellent antibacterial and antiviral properties as well as corrosion resistance, and can therefore be used in various applications where these properties are required. Typically, the stainless steel material according to the embodiment of the present invention can be used in antibacterial and antiviral components.

[0052] The antibacterial and antiviral member according to the embodiment of the present invention includes the above-described stainless steel material. The above-described stainless steel material used in this antibacterial and antiviral member may be processed into various shapes by methods known in the art. The antibacterial and antiviral member according to the embodiment of the present invention may further include members other than the stainless steel material described above. Antibacterial and antiviral materials are not limited to any particular type, but examples include various materials used in kitchen equipment, home appliances, medical devices, interior building materials, transportation equipment, laboratory equipment, sanitary equipment, etc., where antibacterial and antiviral properties are required. [Examples]

[0053] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0054] Stainless steel having the compositions of steel grades A to F shown in Table 1 (the remainder being Fe and impurities) was melted, forged to form stainless steel slabs, and then hot-rolled to obtain hot-rolled sheets with a thickness of 3 mm. Next, the hot-rolled sheets were annealed at 1100°C, pickled, and cold-rolled to obtain cold-rolled sheets with a thickness of 1 mm. Next, the cold-rolled sheets were annealed at 1000°C and pickled to obtain cold-rolled and annealed sheets (base material).

[0055] [Table 1]

[0056] Next, the cold-rolled annealed sheet (base material) was subjected to Cu plating by electroplating. The Cu plating conditions were as follows, and the plating time was controlled so that the Cu plating thickness was 0.10 μm. The plating thickness was measured as follows: First, a 10 mm (rolling direction) × 10 mm (width direction) sample was cut from the Cu-plated cold-rolled annealed sheet by cutting or other means, and the L-section (depth-direction section parallel to the rolling direction) was polished to a mirror finish by mechanical polishing. Next, this L-section was observed with an SEM, and the Cu plating thickness was measured at 10 different points at least 1 mm away from the edge, and the average value was taken as the result of the Cu plating thickness. Anode: Pt plate Electrolyte composition: copper sulfate 200g / L and sulfuric acid 50g / L Electrolyte temperature: 40℃ Current density: 5A / dm 2

[0057] Next, a cold-rolled and annealed sheet coated with copper was subjected to a copper diffusion heat treatment in an electric furnace at 1060°C for 1 minute under a hydrogen gas atmosphere with a dew point of -55°C, forming a surface modification layer on the surface of the cold-rolled and annealed sheet (base material). The dew point was adjusted by the amount of water vapor introduced into the electric furnace. Next, a 300 mm (rolling direction) x 100 mm (width direction) sample was cut from the base material on which the surface modification layer had formed, and the surface of the surface modification layer was polished using the following method. Note that polishing was not performed on Comparative Example 1. Polishing method A: Wet polishing using a solid abrasive (Blue Bar K-1 manufactured by Koyo Co., Ltd.: average particle size of abrasive grains 30 μm). Polishing method B: Wet polishing using solid abrasive (White Bar 1300 manufactured by Koyo Co., Ltd.: average particle size of abrasive grains 45 μm) Polishing method C: Wet polishing using solid abrasive (Sizer 46 manufactured by Koyo Co., Ltd.: average particle size of abrasive grains 60 μm) Polishing method D: Dry polishing using #600 SiC abrasive paper (average particle size of abrasive grains: 30 μm) Polishing method E: Wet polishing using #600 SiC abrasive paper (average particle size of abrasive grains 30 μm) while applying water. The average particle size of the abrasive grains in the solid abrasive was calculated by peeling off abrasive grains from a buff or abrasive paper coated with the solid abrasive using carbon tape, collecting them, observing 10 arbitrarily selected abrasive grains with a scanning electron microscope (SEM), and determining the average of their longest sides. A Schottky scanning electron microscope SU5000 manufactured by Hitachi High-Tech Corporation was used for the SEM.

[0058] The stainless steel sheets obtained as described above were evaluated as follows.

[0059] (Number of Cu-enriched phases) The number of Cu-enriched phases present at the grain boundaries on the surface of the surface-modified layer was determined according to the method described above. A Schottky scanning electron microscope SU5000 manufactured by Hitachi High-Tech Corporation was used for the SEM.

[0060] (Cr concentration within crystal grains) The Cr concentration within the crystal grains on the surface of the surface-modified layer was determined according to the method described above. An FE-AES (JUMP-9510F manufactured by JEOL Ltd.) was used for AES analysis.

[0061] (Chromanetics Index a * ) The color tone of the surface modification layer of the stainless steel sheet is determined according to the method described above, and the chromatic index a * The following was calculated. A Konica Minolta CM-700d spectrophotometer was used.

[0062] (Cu elution amount) The amount of Cu leaching from the stainless steel sheet was determined according to the method described above. For ICP analysis, a Shimadzu ICPE-9800 was used.

[0063] (corrosion resistance) After cutting a 50mm (width direction) x 100mm (rolling direction) test piece from the stainless steel plate obtained as described above, three sides of the test piece (excluding one side in the width direction) were coated with resin (one-component condensation type RTV rubber KE44 manufactured by Shin-Etsu Chemical Co., Ltd.). Next, two 20mmφ x 10mm polyethylene tubes were bonded onto a 70mm x 150mm bakelite plate, and the uncoated side of the test piece was placed on top and bonded. The measurement sample obtained in this way was subjected to the wet-dry cycle test described above for 5 cycles. The sample was placed in the apparatus so that the surface of the measurement test piece was at a 75° angle to the horizontal plane, and the uncoated side of the measurement test piece was facing downwards. After the wet-dry cycle test, the measurement sample was washed with water and dried, the rust area ratio on the surface of the test piece was determined, and the rating number (RN) was calculated.

[0064] The results of each of the above evaluations are shown in Table 2.

[0065] [Table 2]

[0066] As shown in Table 2, the stainless steel sheets of Examples 1 to 6 had 20 or more Cu-enriched phases present at the grain boundaries, and the Cr concentration within the grains was 3% by mass or more of the Cr concentration of the base material. Therefore, they had a high amount of Cu elution and a high rating number (RN). In contrast, the stainless steel plate of Comparative Example 1 had a Cr-poorened layer formed on its surface because it had not been polished after Cu diffusion heat treatment, resulting in a lower rating number (RN). In Comparative Example 2, the stainless steel plate had too large an average particle size of abrasive grains used for polishing, resulting in a large amount of the Cu-enriched phase being removed and a low amount of Cu elution. In Comparative Example 3, the stainless steel plate underwent dry polishing, which resulted in the Cu-enriched phase dissolving into the crystal grains and disappearing, thus reducing the amount of Cu leached. In Comparative Example 4, the stainless steel plate was wet-polished while water was applied, which caused the Cu-enriched phase to dissolve into the water and be removed, resulting in a reduced amount of dissolved Cu.

[0067] As can be seen from the above results, the present invention provides stainless steel materials and antibacterial / antiviral components that are excellent not only in antibacterial and antiviral properties but also in corrosion resistance.

Claims

1. A stainless steel material comprising a base material and a surface modification layer formed on the surface of the base material, The surface-modified layer is a stainless steel material in which, within a 50 μm square surface region, there are 20 or more Cu-enriched phases present at the grain boundaries with a Cu concentration of 4% or more, and the Cr concentration within the surface grains is the Cr concentration of the base material minus 3% by mass or more.

2. CIE L of the surface of the surface modified layer * a * b * Chromanetics index a in color space * The stainless steel material according to claim 1, wherein the ratio is 1.5 or less.

3. The stainless steel material according to claim 1 or 2, wherein the base material further comprises, by mass, C: 0.100% or less, Si: 1.00% or less, Mn: 5.00% or less, Ni: 35.00% or less, Cr: 13.00 to 30.00%, P: 0.100% or less, S: 0.0300% or less, Cu: 4.00% or less, N: 0.300% or less, Mo: 8.00% or less, with the remainder being Fe and impurities.

4. The stainless steel material according to claim 3, wherein the base material further comprises one or more selected by mass from Ti: 1.00% or less, Nb: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, Al: 0.100% or less, and B: 0.0100% or less.

5. The stainless steel material according to claim 3, wherein the base material is an austenitic stainless steel with Ni content of 6.00 to 35.00% by mass.

6. Cu elution amount: 0.10 μg / cm³ 2 The stainless steel material according to claim 1 or 2.

7. The stainless steel material according to claim 1 or 2, wherein the surface of the surface-modified layer has a rating number of 7.0 or higher as defined in JIS G0595:2004, after performing five cycles of a wet-dry cycle test, in which an aqueous solution containing 5% by mass of NaCl is sprayed at 35°C for two hours, the material is held in a dry atmosphere at 60°C and 30% relative humidity for four hours, and the material is held in a wet atmosphere at 50°C and 95% relative humidity for two hours.

8. A stainless steel material according to claim 1 or 2, used in antibacterial and antiviral components.

9. An antibacterial and antiviral member comprising the stainless steel material described in claim 1 or 2.

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