Austenitic stainless steel materials and antibacterial / antiviral components

Abstract

This invention provides austenitic stainless steel materials and antibacterial / antiviral components that exhibit not only antibacterial and antiviral properties but also excellent corrosion resistance. [Solution] An austenitic stainless steel material comprising a base material and a surface modification layer formed on the surface of the base material. The base material contains Al: 0.0010 to 0.0500 mass%. The surface modification layer contains a Cu-enriched phase with a Cu concentration of 5% or more, and in a 50 μm square depth-direction cross-sectional area, there are 20 or more Cu-enriched phases with a major axis of 50 to 500 nm and 10 or fewer Cu-enriched phases with a major axis exceeding 500 nm.

Description

[Technical Field]

[0001] This invention relates to austenitic 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 more likely the antibacterial properties are to be lost prematurely, meaning the antibacterial properties are not 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 achieve.

[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 raises concerns that the presence of a continuous Cu-enriched phase at the grain boundaries may reduce corrosion resistance. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 3232532 [Patent Document 2] Patent No. 7260678 [Overview of the project] [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 an austenitic stainless steel material and an antibacterial / antiviral component that exhibits excellent antibacterial and antiviral properties as well as 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 modification layer formed on the surface of the base material. As a result, they discovered that by controlling the Al content of the base material and precipitating a Cu-enriched phase of appropriate size, it is possible to improve corrosion resistance in addition to antibacterial and antiviral properties, thus completing the present invention.

[0009] That is, the present invention is an austenitic stainless steel material including a base material and a surface modified layer formed on the surface of the base material, wherein the base material contains 0.0010 to 0.0500% by mass of Al, and the surface modified layer contains a Cu-enriched phase with a Cu concentration of 5% or more, and in a depth direction cross-sectional area of 50 μm square, there are 20 or more of the Cu-enriched phases with a major diameter of 50 to 500 nm and 10 or less of the Cu-enriched phases with a major diameter exceeding 500 nm. The present invention relates to an austenitic stainless steel material.

Effects of the Invention

[0010] According to the present invention, it is possible to provide an austenitic stainless steel material and an antibacterial / antiviral member that are excellent not only in antibacterial and antiviral properties but also in corrosion resistance.

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements can be appropriately added to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention, and such modified and improved embodiments also fall within the scope of the present invention.

[0012] Here, the “%” indication in this specification means “% by mass” unless otherwise specified. In addition, the “stainless steel material” in this specification means a material formed from stainless steel, and its shape is not particularly limited. Examples of the shape include plate-like (including strip-like), rod-like, wire-like, tubular, etc. Also, various shaped steels with a T-shaped or I-shaped cross-sectional shape may be used. In addition, the "austenitic system" in this specification means a material whose 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, ferrite phase, martensite phase, etc.). However, the "austenitic system" does not include a duplex structure of ferrite phase and austenite phase, a duplex structure of ferrite phase and martensite phase, and a duplex structure of ferrite phase, austenite phase and martensite phase.

[0013] The austenitic 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 base material contains Al: 0.0010 to 0.0500%. By containing Al in the base material, the amount of water-soluble inclusions that become corrosion initiation points can be reduced, and the corrosion resistance can be improved. Here, the water-soluble inclusions mainly mean composite inclusions of sulfides of Mn, Ca and Mg and oxides of Ca and Mg. This composite inclusion is likely to become a corrosion initiation point by dissolving in water and exposing the substrate where the passive film does not exist. In particular, coarse inclusions (10 μm or more) are likely to act as corrosion initiation points because they form deep pits during dissolution. Therefore, by containing 0.0010% or more of Al, non-water-soluble oxides mainly composed of Al can be formed, and the formation of coarse water-soluble inclusions that become corrosion initiation points can be suppressed. In addition, by containing Al, it also contributes to the improvement of oxidation resistance. However, when the Al content exceeds 0.0500%, an Al oxide film is likely to be formed even in a non-oxidizing atmosphere during Cu diffusion heat treatment, and segregation also deteriorates the manufacturability. From the viewpoint of stably ensuring the above effects of Al, the Al content is preferably 0.0015 to 0.0400%, and more preferably 0.0020 to 0.0300%.

[0014] The surface modification layer contains a Cu-enriched phase (ε-Cu phase) with a Cu concentration of 5% or more. The inclusion of such a Cu-enriched phase in the surface modification layer facilitates the elution of Cu. Therefore, for example, when a person's hand touches the surface of an austenitic stainless steel material, the moisture from the hand can elute Cu ions from the Cu-enriched phase. As a result, bacteria can be killed if they adhere to the surface, and viruses can be inactivated and eventually killed if they adhere to the surface. Herein, in this specification, "surface modified layer" refers to the surface layer where the Cu-enriched phase is present. The surface modified layer is defined as the region from the surface to the depth where the Cu-enriched phase is present, as observed by scanning electron microscope (SEM) in a cross-sectional area in the thickness direction of an austenitic stainless steel material. The thickness of the surface modified layer is not particularly limited, but is typically 3 to 100 μm.

[0015] The surface-modified layer has 20 or more Cu-enriched phases with a major axis of 50-500 nm in a 50 μm square depth-direction cross-sectional area. Dispersing and precipitating Cu-enriched phases of this size increases the amount of Cu eluted, thereby improving antibacterial and antiviral properties. Cu-enriched phases with a major axis of less than 50 nm do not exhibit sufficient antibacterial and antiviral properties because the Cu elutes quickly. On the other hand, Cu-enriched phases with a major axis exceeding 500 nm cause a decrease in corrosion resistance. Furthermore, if there are fewer than 20 Cu-enriched phases with a major axis of 50-500 nm, the amount of Cu eluted is small, and sufficient antibacterial and antiviral properties cannot be ensured. From the viewpoint of improving not only antibacterial and antiviral properties but also corrosion resistance, the number of Cu-enriched phases with a major axis of 50-500 nm is preferably 32 or more, more preferably 35 or more. The upper limit of the number of Cu-enriched phases with a major axis of 50 to 500 nm is not particularly limited, but is typically 100 or less, preferably 80 or less.

[0016] Here, the number of Cu-enriched phases with a major axis of 50-500 nm in a 50 μm square depth-direction cross-sectional region can be determined by observing the depth-direction cross-section of austenitic stainless steel material with a scanning electron microscope (SEM). Specifically, the number of Cu-enriched phases with a major axis of 50-500 nm in a 50 μm square depth-direction cross-sectional region can be determined as follows: First, a 15 mm × 15 mm × thickness of the steel material sample, including the surface of the austenitic stainless steel material, is cut out by cutting or other means. The L-section (depth-direction cross-section parallel to the rolling direction) is buffed to a mirror finish, and then finished with colloidal polishing to remove strain from the surface layer. In the surface-treated layer of the L-section treated in this way, a 50 μm square region is observed with an SEM. In the backscattered electron image of the SEM, the Cu-enriched phase (the Cu concentration of 5% or more is confirmed by EDX analysis) is identified from the difference in contrast, and the number of Cu-enriched phases with a major axis of 50-500 nm is measured. This operation is performed in 10 non-overlapping fields to determine the number of Cu-enriched phases with a major axis of 50-500 nm in each field, and then the average value is calculated. Note that the major axis of the Cu-enriched phase refers to the diameter of the longest portion in the backscattered electron image obtained by SEM.

[0017] In the surface-modified layer, in a 50 μm square depth-direction cross-sectional area, there are 10 or fewer Cu-enriched phases with a major axis exceeding 500 nm. As described above, Cu-enriched phases with a major axis exceeding 500 nm cause a decrease in corrosion resistance. Therefore, it is necessary to control the number of Cu-enriched phases with a major axis exceeding 500 nm to 10 or fewer. From the viewpoint of stably improving corrosion resistance, the number of Cu-enriched phases with a major axis exceeding 500 nm is preferably 8 or fewer, more preferably 5 or fewer. Here, the number of Cu-enriched phases with a major axis exceeding 500 nm in a 50 μm square depth-direction cross-sectional region can be determined by observing the depth-direction cross-section of the austenitic stainless steel material with a scanning electron microscope (SEM), similar to the number of Cu-enriched phases with a major axis between 50 and 500 nm.

[0018] In the embodiment of the present invention, the austenitic stainless steel material preferably has an average grain size of 15 to 60 μm. By controlling the average grain size of the base material within this range, it becomes easier to disperse and precipitate a Cu-enriched phase of appropriate size by heat treatment after Cu plating. If the average grain size of the base material is less than 5 μm, Cu diffusion to the grain boundaries is prioritized, so the number of Cu-enriched phases of appropriate size tends to fall outside the above range. Also, if the average grain size of the base material exceeds 60 μm, Cu becomes concentrated at specific grain boundaries, forming a coarse Cu-enriched phase, which tends to reduce corrosion resistance. From the viewpoint of facilitating the stable dispersion and precipitation of a Cu-enriched phase of appropriate size, the average grain size of the base material is more preferably 16 to 50 μm, and even more preferably 17 to 40 μm.

[0019] Here, the average grain size of the base material as used herein refers to the average value of the grain size (equivalent diameter of a circle) of grains surrounded by grain boundaries with a crystal orientation difference of 2° or more. The average grain size of a crystal grain can be determined by analyzing the cross-section of the base material of an austenitic stainless steel by EBSD (Electron Back Scattering Diffraction). Specifically, the average grain size of a crystal grain is determined as follows: First, a sample measuring 15 mm × 15 mm × the thickness of the steel is cut from the austenitic stainless steel by cutting or other means. The L-section (depth-direction cross-section parallel to the rolling direction) is polished to a mirror finish by mechanical polishing, followed by electropolishing. In the base material region extending to a depth of 200 μm or more from the surface of the L-section treated in this way, EBSD analysis is performed on an 80 μm square region at a magnification of 1000x in a field of view, with step intervals of 0.2 μm, to identify grain boundaries with a crystal orientation difference of 2° or more. Then, the area of ​​each crystal grain enclosed by these grain boundaries is calculated as S [μm²]. 2 Let D [μm] be the diameter of a circle having the same area as the crystal grain, and calculate the crystal grain size (average value of crystal grain size per field of view) [μm] using the following formula (A). Perform this operation for five non-overlapping fields of view to determine the crystal grain size for each field, and take their average value as the average crystal grain size.

[0020]

number

[0021] The austenitic stainless steel material according to the embodiment of the present invention contains 1.0 inclusion per mm² of inclusions present in the base material that have a diameter of 5 μm or more, a sulfur concentration of 2% by mass or more, and satisfy the following formula (1). 2 The following is preferable: (Ca+Mg+Mn) / (Al+Ca+Mg+Mn)≧0.5 ···(1) In the formula, each element represents the mass %) of that element contained in the base material. Because these inclusions are water-soluble and easily become corrosion initiation sites, their quantity should be kept at 1.0 particles / mm³. 2 By controlling the following, corrosion resistance can be stably improved.

[0022] Number density of a given inclusion present in the base material (pieces / mm²) 2 The number density (number of inclusions / mm³) is determined by performing SEM observation and EDX analysis on the base material of austenitic stainless steel. Specifically, the number density of a given inclusion present in the base material is determined as follows: First, a sample of 30 mm × 30 mm × the thickness of the base material is cut from the base material from which the surface modification layer has been removed, and the surface is mirror polished. Next, an 80 μm square area is photographed on the surface using SEM to identify the inclusions, and the composition of these inclusions is analyzed by EDX to determine the number of inclusions that have a diameter of 5 μm or more, an S concentration of 2 mass% or more, and satisfy the above formula (1). The number of inclusions is then divided by the observation area to determine the number density (number of inclusions / mm³) of the given inclusions. 2 ) is obtained. Note that the diameter of the inclusion is considered to be the equivalent diameter of a circle.

[0023] The base material of the austenitic stainless steel material according to the embodiment of the present invention is not particularly limited as long as it contains Al: 0.0010 to 0.0500%, but further contains C: 0.100% or less, Si: 1.00% or less, Mn: 3.00% or less, Cr: 13.00 to 30.00%, Ni: 6.00 to 20.00%, P: 0.100% or less, S: 0.0300% or less, Cu: 4.00% or less, N: 0.100% or less, Mo: 8.00% or less, and the balance is preferably composed of Fe and impurities. Further, the base material of the austenitic stainless steel material according to the embodiment of the present invention can further contain 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, Mg: 0.0100% or less, B: 0.0100% or less.

[0024] 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 industrially manufacturing the austenitic stainless steel material, 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, "xx% or less" includes being xx% or less, but means including an amount exceeding 0% (especially exceeding the impurity level). Hereinafter, each component will be described in detail.

[0025] <C: 0.100% or less> C is an element that improves the strength of austenitic stainless steel. However, if the C content is too high, in addition to becoming hard and causing a decrease in workability, sensitization occurs when subjected to thermal effects such as welding, resulting in a decrease in the corrosion resistance of the austenitic stainless steel. Therefore, the upper limit value of the C content is controlled to 0.100%, preferably 0.080%, more preferably 0.070%. On the other hand, the lower limit value of the C content is not particularly limited, but from the perspective of suppressing refining costs, it is preferably 0.001%, more preferably 0.003%, and even more preferably 0.005%.

[0026] <Si: 1.00% or less> Si is an element effective in improving the corrosion resistance of austenitic stainless steel. 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 becomes hardened, resulting in a decrease in the workability of the stainless steel, 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 perspective of obtaining the effect of Si, it is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0027] <Mn: 3.00% or less> Mn is an element that improves the heat resistance of austenitic stainless steel. However, if the Mn content is too high, MnS, which serves as 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 3.00%, preferably 2.90%, more preferably 2.80%, and even more preferably 2.60%. On the other hand, the lower limit value of the Mn content is not particularly limited, but from the perspective of obtaining the effect of Mn, it is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0028] <Cr: 13.00 - 30.00%> Cr is an important element for ensuring the corrosion resistance and oxidation resistance of austenitic stainless steel materials. However, if the Cr content is too high, it will lead to an increase in refining costs, hardening due to solid solution strengthening (a decrease in toughness), and a decrease in the workability of austenitic stainless steel materials. Therefore, the upper limit value of the Cr content is controlled to 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 value of the Cr content is controlled to 13.00%, preferably 14.00%, more preferably 15.00%, still more preferably 16.00%.

[0029] <Ni: 6.00~20.00%> Ni is an element that improves the corrosion resistance (especially intergranular corrosion resistance) of austenitic stainless steel materials. To obtain this effect, the lower limit value of the Ni content is controlled to 6.00%, preferably 7.00%, more preferably 8.00%. On the other hand, 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 20.00%, preferably 19.80%, more preferably 19.50%.

[0030] <P: 0.100% or less> Since austenitic stainless steel materials have a high Cu content, if 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, if the P content is high, it will also cause a decrease in weldability and workability. Therefore, the upper limit value of the P content is controlled to 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit value 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%, still more preferably 0.010%.

[0031] <S: 0.0300% or less> Similar to P, when the content of S is high, it is easy to form an intermetallic compound with a low melting point with Cu, which may cause cracking during hot rolling. In addition, when the content of S is high, it is easy to generate MnS as a corrosion initiation point, and the toughness of the welded part decreases when welding is performed. Therefore, the upper limit of the content of S is controlled to 0.0300%, preferably 0.0200%, more preferably 0.0100%. On the other hand, the lower limit of the content of S is not particularly limited, but in order to reduce it, refining cost is incurred, so it is preferably 0.0001%, more preferably 0.0005%, still more preferably 0.0010%.

[0032] <Cu: 4.00% or less> Cu is an element that improves the workability of austenitic stainless steel materials. However, if the content of Cu is too high, the austenite phase becomes unstable and the manufacturing cost also increases. Therefore, the upper limit of the content of Cu is controlled to 4.00%, preferably 3.00%, more preferably 2.50%. On the other hand, the lower limit of the content of Cu is not particularly limited, but from the perspective of obtaining the effect of Cu, it is preferably 0.01%, more preferably 0.05%, still more preferably 0.10%.

[0033] <N: 0.100% or less> N is an element effective in improving the corrosion resistance of austenitic stainless steel materials. However, if the content of N is too high, in addition to becoming hard and the workability decreasing, sensitization occurs when affected by heat such as welding, and the corrosion resistance of austenitic stainless steel materials decreases. Therefore, the upper limit of the content of N is controlled to 0.100%, preferably 0.080%, more preferably 0.050%, still more preferably 0.040%. On the other hand, the lower limit of the content of N is not particularly limited, but from the perspective of suppressing the refining cost, it is preferably 0.001%, more preferably 0.003%, still more preferably 0.005%.

[0034] <Mo: 8.00% or less> Mo is an element effective in improving the corrosion resistance and oxidation resistance of austenitic stainless steel materials. However, if the Mo content is too high, it will lead to a decrease in workability and an increase in manufacturing costs. Therefore, the upper limit value of the Mo content is controlled to 8.00%, preferably 5.00%, more preferably 3.00%. On the other hand, the lower limit value 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%.

[0035] <Ti: 1.00% or less> Ti is an element that affects the intergranular corrosion resistance (sensitization suppression effect) of austenitic stainless steel materials. Also, Ti is an element effective in fixing C and N. However, if the Ti content is too high, in addition to an increase in manufacturing costs, the workability and surface quality of austenitic stainless steel materials will decrease. 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 perspective of obtaining the effect of Ti, it is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0036] <Nb: 1.00% or less> Nb, similar to Ti, is an element that affects the intergranular corrosion resistance (sensitization suppression effect) of austenitic stainless steel materials. Also, Nb is an element effective in fixing C and N. However, if the Nb content is too high, in addition to an increase in manufacturing costs, the workability and surface quality of austenitic stainless steel materials will decrease. 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 these carbonitrides. From the perspective 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%, and even more preferably 0.05%.

[0037] <Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less> Zr, Co, V and W are elements effective in improving the oxidation resistance of austenitic stainless steel materials. However, if the contents of these elements are too high, it will lead to a decrease in workability and toughness and an increase in manufacturing cost. Therefore, the upper limit values of the contents of these elements are all controlled to 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, the lower limit values of the contents of these elements are not particularly limited, but from the viewpoint of obtaining the effects of these elements, they are preferably 0.01%, more preferably 0.03%, still more preferably 0.05%.

[0038] <REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less> REM (rare earth elements), Ca and Sn are elements effective in improving the oxidation resistance of austenitic stainless steel materials. However, if the contents of these elements are too high, it will lead to an increase in manufacturing cost. Therefore, the upper limit values of the contents of these elements are all controlled to 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit values of the contents of these elements are not particularly limited, but from the viewpoint of obtaining the effects of these elements, they are preferably 0.001%, more preferably 0.003%, still more preferably 0.005%. Note that REM refers to the general term of 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.

[0039] <Mg: 0.0100% or less> Mg is an element effective as a deoxidizing element. In particular, Mg forms an oxide together with Si and reduces oxygen in the matrix phase. Also, Mg is an element that improves hot workability and the cleanliness of stainless steel. However, if the content of Mg is too high, the manufacturability decreases, and the oxides in the stainless steel increase and combine with sulfides to form soluble inclusions, which become the starting points of corrosion and reduce the weather resistance. Therefore, the upper limit value of the content of Mg is set to 0.0100%. Considering manufacturability and oxidation resistance, the content of Mg is preferably 0.0090% or less. On the other hand, the lower limit value of the content of Mg is not particularly limited, but from the viewpoint of obtaining the effects of Mg, it is preferably 0.0003%.

[0040] <B: 0.0100% or less> B is an element effective for improving the secondary workability of austenitic stainless steel materials. However, if the content of B is too high, it causes a decrease in fatigue strength. Therefore, the upper limit value of the content of B is controlled to 0.0100%, preferably 0.0070%. On the other hand, the lower limit value of the content of B is not particularly limited, but from the viewpoint of obtaining the effects of B, it is preferably 0.0001%, more preferably 0.0003%.

[0041] The type of austenitic 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 (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. Also, in the case of a cold-rolled material or a cold-rolled annealed material, its thickness is generally less than 3 mm.

[0042] The austenitic stainless steel material according to the embodiment of the present invention has a chromaticity index a in the CIE L * a * b * color space of the surface of the surface modified layer * is preferably 3.0 or less. CIEL * a * b *Chromatics index a in color space * The chromatic index a indicates that a value of 0 represents achromaticity, and the color becomes more reddish as the value increases in the positive direction, and more greenish as the value increases in the negative direction. The surface of austenitic stainless steel (base material) has a silvery-white stainless steel texture (chromatic index a * Although it has a value of 0 or greater, as the Cu plating remains, the surface color takes on a reddish copper hue. Therefore, the chromatic index a is used as an index to determine the surface color. * Use a * If the value exceeds 3.0, it indicates that there is a large amount of residual Cu plating and that the Cu diffusion heat treatment is insufficient. Therefore, it can be considered that a surface modification layer with appropriately sized Cu-enriched phase precipitated has not been formed. Here, the chromanetics index a * This is determined by measuring the surface color tone of the surface modified layer in accordance with JIS Z8722:2009.

[0043] The austenitic stainless steel material according to the embodiment of the present invention has an initial Cu elution amount of 0.50 μg / cm³. 2 It is preferable that the initial Cu elution amount is within this range. If the initial Cu elution amount is within this range, it can be said that the antibacterial and antiviral properties are excellent. The initial Cu elution amount is 1.00 μg / cm³. 2 It is more preferable that the concentration be greater than or equal to 2.00 μg / cm³. 2 It is even more preferable that the concentration be greater than or equal to 3.00 μg / cm³. 2 The above is particularly preferable. The upper limit of the initial Cu elution amount is not particularly limited, as a higher value results in superior antibacterial and antiviral properties, but for example, 10.00 μg / cm³ is preferable. 2 That is the case.

[0044] Here, the initial 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 an austenitic stainless steel material 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 The result is determined and taken as the initial amount of Cu eluted.

[0045] The austenitic stainless steel material according to the embodiment of the present invention exhibits a Cu elution amount of 0.10 μg / cm³ after immersion in stirred pure water for 100 hours. 2 The above is preferable. With a Cu elution amount within this range, a Cu-enriched phase is present on the surface to the extent that it can exhibit antibacterial and antiviral properties over a long period of time, and it can be said that it has excellent persistence of antibacterial and antiviral properties. The Cu elution amount after immersion in stirred pure water for 100 hours was 0.20 μg / cm³. 2 It is more preferable that the concentration be greater than or equal to 0.30 μg / cm³. 2 The above is even more preferable. The upper limit of the amount of Cu eluted after 100 hours of immersion in stirred pure water is not particularly limited, as a higher value results in superior persistence of antibacterial and antiviral properties; for example, 5.00 μg / cm³. 2 That is the case. The amount of Cu eluted after immersion in stirred pure water for 100 hours can be measured in the same manner as above after immersing the above sample in stirred pure water (water temperature: 18-25°C) for 100 hours.

[0046] In the embodiment of the present invention, the austenitic stainless steel material preferably has a rating number of 5.0 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 6.0 or higher is more preferable, and 6.5 or higher is even more preferable. The rating number was determined using two samples, and the average value was used as the result.

[0047] The method for manufacturing an austenitic stainless steel material according to the embodiments of the present invention is not particularly limited as long as it can produce an austenitic stainless steel material having the above-described characteristics. A typical method for manufacturing an austenitic stainless steel material according to the embodiments of the present invention will be described below. A method for producing an austenitic stainless steel material according to an embodiment of the present invention includes a Cu plating step and a Cu diffusion heat treatment step.

[0048] The Cu plating process involves applying a Cu plating treatment to an austenitic stainless steel material (base material). The base material used for Cu plating is not particularly limited as long as it is an austenitic stainless steel material containing Al: 0.0010 to 0.0500%. Preferably, the base material used for Cu plating further contains C: 0.100% or less, Si: 1.00% or less, Mn: 3.00% or less, Cr: 13.00 to 30.00%, Ni: 6.00 to 20.00%, P: 0.100% or less, S: 0.0300% or less, Cu: 4.00% or less, N: 0.100% or less, and Mo: 8.00% or less, with the remainder consisting of 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, Mg: 0.0100% or less, and B: 0.0100% or less.

[0049] The base material used in the Cu plating process may be hot-rolled material or hot-rolled annealed material, or cold-rolled material or cold-rolled annealed material. For example, hot-rolled material can be obtained by hot-rolling an austenitic stainless steel slab. Hot-rolled material can be annealed to obtain hot-rolled annealed material. Cold-rolled material can be obtained by cold-rolling a hot-rolled annealed material. Cold-rolled material can be annealed to obtain cold-rolled annealed material. 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 austenitic 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.

[0050] The base material used in the Cu plating process preferably has an average grain size of 15 to 60 μm after the Cu plating and diffusion heat treatment processes. Typically, the average grain size of the base material used in Cu plating is hardly affected by the Cu plating and diffusion heat treatment processes, and can therefore be set to 15 to 60 μm. By controlling the average grain size of the base material used in Cu plating to this range, it becomes easier to disperse and precipitate a Cu-enriched phase of appropriate size through the Cu diffusion heat treatment process.

[0051] The base material used for Cu plating must have inclusions with a diameter of 5 μm or more, a sulfur concentration of 2% by mass or more, and satisfy the following formula (1) at a rate of 1.0 inclusions / mm². 2 The following is preferable: (Ca+Mg+Mn) / (Al+Ca+Mg+Mn)≧0.5 ···(1) In the formula, each element represents the mass %) of that element contained in the base material. Because these inclusions are water-soluble and easily become corrosion initiation sites, their quantity should be kept at 1.0 particles / mm³. 2 By controlling the following, corrosion resistance can be stably improved.

[0052] The method for the Cu plating process 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 0.25 μm. By controlling the thickness within this range, a Cu-enriched phase with a major axis of 50 to 500 nm can be sufficiently 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. If the thickness of the Cu plating exceeds 0.25 μm, there will be a large amount of Cu-enriched phase with a major axis exceeding 500 nm, resulting in reduced corrosion resistance. In addition, Cu plating will remain on the surface after the Cu diffusion heat treatment process. From the viewpoint of stably depositing a Cu-enriched phase of an appropriate size, the thickness of the Cu plating is preferably 0.05 to 0.23 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).

[0053] The Cu diffusion heat treatment process involves heating a Cu-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, forming a surface modification layer on the surface of the base material. Cu atoms diffuse more easily into grain boundaries than into crystal grains, but because the average crystal grain size of the base material is controlled within an appropriate range, the Cu-enriched phase also precipitates easily within the crystal grains.

[0054] 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, argon gas, hydrogen gas, nitrogen gas, etc., can be used as the non-oxidizing atmosphere. 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 such a 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 -40 to -100°C, and more preferably -50 to -80°C.

[0055] The heating temperature for the Cu diffusion heat treatment process is set to 900-1050°C. By controlling the heating temperature within this range, it is possible to reduce the precipitation of Cu-enriched phase with a major axis exceeding 500 nm while increasing the precipitation of Cu-enriched phase with a major axis of 50-500 nm. 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 1050°C, significant penetration into the grain boundaries will result in increased precipitation of Cu-enriched phase with a major axis exceeding 500 nm. In particular, since the melting point of Cu is 1083°C, if the heating temperature is higher than the melting point of Cu, the Cu-enriched phase that has precipitated may disappear by evaporation or solid solution. From the viewpoint of stably precipitating Cu-enriched phase of an appropriate size, the heating temperature is preferably 950-1050°C, more preferably 1000-1050°C.

[0056] 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, making it difficult to stably precipitate a Cu-enriched phase of an appropriate size.

[0057] The austenitic 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 austenitic stainless steel material according to the embodiment of the present invention can be used in antibacterial and antiviral components.

[0058] The antibacterial and antiviral member according to the embodiment of the present invention includes the above-described austenitic stainless steel material. The above-described austenitic 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 austenitic stainless steel material described above. Antibacterial and antiviral materials are not particularly limited, but examples include various materials used in kitchen equipment, home appliances, medical devices, interior building materials, transportation equipment, laboratory equipment, and sanitary equipment, where antibacterial and antiviral properties are required. [Examples]

[0059] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0060] Austenitic stainless steel having the compositions of steel grades A to I shown in Table 1 (the remainder being Fe and impurities) was melted and forged to form austenitic stainless steel slabs, which were 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 to 1200°C, pickled, and then cold-rolled and annealed sheets (base material) were obtained.

[0061] [Table 1]

[0062] Next, the cold-rolled and annealed sheet (base material) was subjected to Cu plating by electroplating. The Cu plating conditions were as follows: Anode: Pt plate Electrolyte composition: copper sulfate 200g / L and sulfuric acid 50g / L Electrolyte temperature: 40℃ Current density: 5A / dm 2 Plating time: Maximum 60 seconds Table 2 shows the thickness of the Cu plating formed in this manner. The plating thickness was measured using a cross-sectional observation method.

[0063] Next, a Cu-plated cold-rolled annealed sheet was subjected to Cu diffusion heat treatment for 4 minutes in an electric furnace under a hydrogen gas atmosphere with the dew point shown in Table 2, at the heating temperature shown in Table 2, to form a surface modification layer on the surface of the cold-rolled annealed sheet (base material). The dew point was adjusted by changing the amount of water vapor introduced into the electric furnace.

[0064] Table 2 shows the results of measuring the average grain size of the base material and the number density of inclusions with a diameter of 5 μm or more, an S concentration of 2 mass% or more, and satisfying the above formula (1) using the austenitic stainless steel sheet obtained as described above. Note that the difference in average grain size for the same steel type in Table 2 is due to the difference in annealing temperature after cold rolling. The average grain size of the base material and the number density of the specified inclusions were measured according to the method described above. A JXA-8900 manufactured by JEOL Ltd. was used for EBSD analysis. A Schottky scanning electron microscope SU5000 manufactured by Hitachi High-Tech Corporation was used for SEM.

[0065] [Table 2]

[0066] Furthermore, the following further evaluations were conducted on austenitic stainless steel sheets.

[0067] (Number of Cu-enriched phases) The number of Cu-enriched phases with a major axis of 50-500 nm and Cu-enriched phases with a major axis exceeding 500 nm in the surface modification layer of an austenitic stainless steel sheet 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.

[0068] (Chromanetics Index a * ) The color tone of the surface modification layer of an austenitic 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.

[0069] (Initial Cu elution amount) The initial amount of Cu leaching from austenitic stainless steel sheets was determined according to the method described above. For ICP analysis, a Shimadzu ICPE-9800 was used.

[0070] (Amount of Cu leached after immersion in stirred pure water for 100 hours) The amount of Cu eluted from an austenitic stainless steel plate after immersion in stirred pure water for 100 hours was determined according to the method described above. In this test, the austenitic stainless steel plate sample was placed in a beaker containing 1 L of pure water, and the pure water was stirred at 600 rpm. For ICP analysis, a Shimadzu ICPE-9800 was used. In the following, this amount of leaching will be referred to as "the amount of Cu leached after immersion in pure water."

[0071] (corrosion resistance) After cutting a 50 mm (width direction) x 100 mm (rolling direction) test specimen from the austenitic stainless steel sheet obtained as described above, three sides of the test specimen (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 20 mmφ x 10 mm polyethylene tubes were bonded onto a 70 mm x 150 mm bakelite plate, and the uncoated side of the test specimen 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 specimen was at a 75° angle to the horizontal plane, and the uncoated side of the measurement specimen 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 specimen was determined, and the rating number (RN) was calculated.

[0072] The results of each of the above evaluations are shown in Table 3.

[0073] [Table 3]

[0074] As shown in Table 3, the austenitic stainless steel sheets of Examples 1 to 6 contained 0.0010 to 0.0500% Al in the base material, and in the surface modified layer, there were 20 or more Cu-enriched phases with a major axis of 50 to 500 nm and 10 or fewer Cu-enriched phases with a major axis exceeding 500 nm. As a result, the amount of Cu eluted initially and after immersion in pure water was high, and the rating number (RN) was also high. In contrast, the austenitic stainless steel sheet of Comparative Example 1 had a small amount of Cu-enriched phase with a major axis of 50-500 nm, resulting in a small amount of Cu leaching both initially and after immersion in pure water. This is thought to be due to the average grain size of the base material being too small. The austenitic stainless steel sheet in Comparative Example 2 had a low rating number (RN) because it contained too much Cu-enriched phase with a major axis exceeding 500 nm. This is thought to be due to the base material having too large an average grain size. The austenitic stainless steel sheet in Comparative Example 3 had a small amount of Cu-enriched phase with a major axis of 50-500 nm, resulting in low Cu elution both initially and after immersion in pure water. This is thought to be due to the insufficient thickness of the Cu plating formed during the Cu plating process. The austenitic stainless steel sheet in Comparative Example 4 had a low rating number (RN) because it contained too much Cu-enriched phase with a major axis exceeding 500 nm. This is thought to be due to the excessive thickness of the Cu plating formed during the Cu plating process.

[0075] The austenitic stainless steel sheet in Comparative Example 5 had a low rating number (RN) because it contained too much Cu-enriched phase with a major axis exceeding 500 nm. This is thought to be due to the heating temperature in the Cu diffusion heat treatment process being too low. The austenitic stainless steel sheet in Comparative Example 6 had a small amount of Cu-enriched phase with a major axis of 50-500 nm, resulting in low Cu elution both initially and after immersion in pure water. This is thought to be due to the heating temperature in the Cu diffusion heat treatment process being too high. The austenitic stainless steel sheet in Comparative Example 7 had a small amount of Cu-enriched phase with a major axis of 50-500 nm and a large amount of Cu-enriched phase with a major axis of 500 nm, resulting in a smaller rating number (RN). This is thought to be due to the dew point of the atmosphere during the Cu diffusion heat treatment process being too high. The austenitic stainless steel sheet in Comparative Example 8 had a small amount of Cu-enriched phase with a major axis of 50-500 nm and a large amount of Cu-enriched phase with a major axis of more than 500 nm, resulting in a smaller rating number (RN). In Comparative Example 9, the austenitic stainless steel sheet had too much Al content in the base material, resulting in a small amount of Cu-enriched phase with a major axis of 50-500 nm and a large amount of Cu-enriched phase with a major axis of more than 500 nm, which led to a small rating number (RN). The austenitic stainless steel sheet in Comparative Example 10 had a low rating number (RN) because the Al content of the base material was too low.

[0076] As can be seen from the above results, the present invention provides an austenitic stainless steel material and an antibacterial / antiviral component that is excellent not only in antibacterial and antiviral properties but also in corrosion resistance.

Claims

1. An austenitic stainless steel material comprising a base material and a surface modification layer formed on the surface of the base material, The aforementioned base material contains Al: 0.0010 to 0.0500% by mass, The surface-modified layer contains a Cu-enriched phase with a Cu concentration of 5% or more, and in a 50 μm square depth-direction cross-sectional region, there are 20 or more Cu-enriched phases with a major axis of 50 to 500 nm and 10 or fewer Cu-enriched phases with a major axis exceeding 500 nm, in an austenitic stainless steel material.

2. The austenitic stainless steel material according to claim 1, wherein the average grain size of the base material is 15 to 60 μm.

3. CIE L of the surface of the surface modified layer * a * b * Chromanetics index a in color space * The austenitic stainless steel material according to claim 1 or 2, wherein the ratio is 3.0 or less.

4. The base material contains 1.0 inclusion per mm² that has a diameter of 5 μm or more, an S concentration of 2% by mass or more, and satisfies the following formula (1). 2 The austenitic stainless steel material according to claim 1 or 2, which is as follows: (Ca+Mg+Mn) / (Al+Ca+Mg+Mn)≧0.5...(1) In the formula, each element represents the mass percentage of that element contained in the base material.

5. The austenitic 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: 3.00% or less, Cr: 13.00 to 30.00%, Ni: 6.00 to 20.00%, P: 0.100% or less, S: 0.0300% or less, Cu: 4.00% or less, N: 0.100% or less, Mo: 8.00% or less, with the remainder being Fe and impurities.

6. The austenitic stainless steel material according to claim 5, 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, Mg: 0.0100% or less, and B: 0.0100% or less.

7. The initial Cu elution rate was 0.50 μg / cm³. 2 The austenitic stainless steel material according to claim 1 or 2.

8. The austenitic stainless steel material according to claim 1 or 2, wherein the surface of the surface-modified layer has a rating number of 5.0 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.

9. An austenitic stainless steel material according to claim 1 or 2, used in antibacterial and antiviral components.

10. An antibacterial and antiviral member comprising an austenitic stainless steel material as described in claim 1 or 2.

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