Stainless steel material, its manufacturing method, and antibacterial / antiviral component

Abstract

A stainless steel material having an ε-Cu phase exposed on the surface. The area ratio of the ε-Cu phase on the surface of the stainless steel material is 0.1 to 4.0%, the average particle size is 10 to 300 nm, and the maximum interparticle distance is 100 to 1000 nm.

Description

Technical Field

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

[0002] Since stainless steel materials have excellent corrosion resistance, they are used in a wide range of applications such as kitchen equipment, household electrical appliances, medical instruments, interior building materials, and transmission equipment, and are mostly used in environments where bacterial growth or virus attachment is likely to occur. In recent years, there has been an increasing tendency to worry about the adverse effects on the human body caused by such bacterial growth or virus attachment. In particular, in addition to medical instruments or kitchen equipment that require high cleanliness, antibacterial and antiviral properties are also required for various components used in buildings or transmission equipment where a large number of people gather.

[0003] As metal elements having antibacterial / antiviral properties, Ag, Cu, etc. are known, and thus stainless steel materials imparted with antibacterial / antiviral properties by adding these metal elements have been proposed.

[0004] For example, in Patent Document 1, a ferritic stainless steel material having excellent antibacterial properties is proposed, which contains C: 0.1% by weight or less, Si: 2% by weight or less, Mn: 2% by weight or less, Cr: 10 to 30% by weight, and Cu: 0.4 to 3% by weight, and a Cu-rich phase (ε-Cu phase) precipitates in the matrix at a ratio of 0.2% by volume or more. This ferritic stainless steel material is manufactured by cold-rolling a ferritic stainless steel containing C: 0.1% by weight or less, Si: 2% by weight or less, Mn: 2% by weight or less, Cr: 10 to 30% by weight, and Cu: 0.4 to 3% by weight, and performing aging treatment at 500 to 800°C after final annealing, whereby the Cu-rich phase (ε-Cu phase) precipitates to 0.2% by volume or more.

[0005] In addition, in Patent Document 2, an austenitic stainless steel material having excellent antibacterial properties is proposed, which has a composition containing C: 0.1% by weight or less, Si: 2% by weight or less, Mn: 5% by weight or less, Cr: 10 to 30% by weight, Ni: 5 to 15% by weight, and Cu: 1.0 to 5.0% by weight, and a second phase (ε-Cu phase) mainly composed of Cu is dispersed in the matrix at a ratio of 0.2% by volume or more. This austenitic stainless steel material is manufactured by performing heat treatment one or more times in a temperature range of 500 to 900°C during the period from hot rolling to the final product of an austenitic stainless steel containing C: 0.1% by weight or less, Si: 2% by weight or less, Mn: 5% by weight or less, Cr: 10 to 30% by weight, Ni: 5 to 15% by weight, and Cu: 1.0 to 5.0% by weight.

[0006] Prior Art Documents

[0007] Patent document

[0008] Patent Document 1: Japanese Patent Laid-Open No. 9-170053

[0009] Patent Document 2: Japanese Patent Laid-Open No. 9-176800 Summary of the Invention

[0010] In the stainless steel materials described in Patent Documents 1 and 2, the distribution state of the ε-Cu phase on the surface is not properly controlled, so the expected antibacterial property cannot be obtained, and the antibacterial property is likely to be lost at an early stage.

[0011] In addition, since viruses are smaller than bacteria, when viruses adhere between the ε-Cu phases on the surface, almost no antiviral property can be obtained.

[0012] An object of the present invention is to provide a stainless steel material, a manufacturing method thereof, and an antibacterial / antiviral member that can maintain antibacterial and antiviral properties for a long time.

[0013] The inventor of the present invention conducted in-depth research to solve the above problems, and as a result, found that the distribution state of the ε-Cu phase on the surface of the stainless steel material (particularly the area ratio of the ε-Cu phase on the surface, the average particle diameter of the ε-Cu phase, and the maximum interparticle distance of the ε-Cu phase) is closely related to antibacterial and antiviral properties and their persistence, thereby completing the present invention.

[0014] That is, the present invention is a stainless steel material having an ε-Cu phase exposed on the surface,

[0015] wherein the area ratio of the ε-Cu phase on the surface is 0.1 to 4.0%, the average particle diameter is 10 to 300 nm, and the maximum interparticle distance is 100 to 1000 nm.

[0016] In addition, the present invention is a manufacturing method of a stainless steel material, comprising

[0017] Hot rolling process, which hot-rolls a slab to obtain a hot-rolled material, the slab having a ferritic composition or an austenitic composition, the ferritic composition containing, by mass basis, C: 0.10% or less, Si: 4.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00% or less, Cr: 10.00 - 32.00% and Cu: 0.40 - 4.00%, with the balance being Fe and impurities, the austenitic composition containing, by mass basis, C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 - 20.00%, Cr: 10.00 - 32.00% and Cu: 2.00 - 6.00%, with the balance being Fe and impurities, when the composition of the slab is the ferritic system, the final hot rolling finishing temperature is set to 700 - 900°C, and when it is the austenitic system, the final hot rolling finishing temperature is set to 850 - 1050°C;

[0018] Cooling process, which cools the hot-rolled material obtained in the hot rolling process at an average cooling rate of 0.2 - 5°C / second between 900 - 500°C; and

[0019] Heat treatment process, which heats the hot-rolled material cooled in the cooling process at 750 - 850°C for 4 hours or more.

[0020] Furthermore, the present invention is an antibacterial / antiviral member comprising the aforementioned stainless steel material.

[0021] According to the present invention, a stainless steel material capable of maintaining antibacterial and antiviral properties for a long time, its manufacturing method, and an antibacterial / antiviral member can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic view of the surface of a typical stainless steel material of the present invention. DETAILED DESCRIPTION

[0023] The present invention is a stainless steel material having an ε-Cu phase exposed on the surface. The area ratio of this ε-Cu phase is 0.1 - 4.0%, the average particle size is 10 - 300 nm, and the maximum inter-particle distance is 100 - 1000 nm.

[0024] Here, in Figure 1 shows a schematic view of the surface of a typical stainless steel material of the present invention.

[0025] As Figure 1 shown, the ε-Cu phase 11 of the stainless steel material 10 is exposed on the matrix surface. In addition, on the matrix surface where the ε-Cu phase 11 is not exposed, a passive film 12 is formed.

[0026] By exposing the ε-Cu phase 11 on the surface of the parent phase, when moisture contacts the surface of the stainless steel material 10, Cu ions can be dissolved from the ε-Cu phase 11. For example, when a human hand contacts the surface of the stainless steel material 10, Cu ions can be dissolved from the ε-Cu phase 11 by the moisture on the hand. Therefore, even if bacteria adhere to the surface, sterilization can be achieved, and even if viruses adhere to the surface, they will be inactivated and ultimately eliminated.

[0027] In addition, on the surface of the parent phase where the ε-Cu phase 11 is not exposed, a passive film 12 is formed, so the corrosion resistance is also good.

[0028] The composition of the stainless steel material of the present invention is not particularly limited, but the preferred composition contains C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 20.00% or less, Cr: 10.00 - 32.00%, Cu: 0.40 - 6.00%, and the balance is composed of Fe and impurities.

[0029] Here, the “%” notation for components in this specification refers to “mass %” unless otherwise specified.

[0030] The metal structure of the stainless steel material of the present invention is not particularly limited, but it is preferably ferritic or austenitic.

[0031] Hereinafter, for the embodiments of the present invention, ferritic stainless steel materials and austenitic stainless steel materials will be taken as examples for specific description. The present invention is not limited to the following embodiments, and it should be understood that within the scope of not departing from the gist of the present invention, after appropriately making changes, improvements, etc. to the following embodiments based on the general knowledge of those skilled in the art, they also fall within the scope of the present invention.

[0032] (Embodiment 1)

[0033] The ferritic stainless steel material of Embodiment 1 of the present invention has a composition containing C: 0.10% or less, Si: 4.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00% or less, Cr: 10.00 - 32.00%, Cu: 0.40 - 4.00%, and the balance is composed of Fe and impurities.

[0034] Here, in this specification, “steel material” refers to materials in various forms such as steel plates. In addition, “steel plate” is a concept that includes steel strips. Further, “impurities” refer to components mixed in due to various reasons such as raw materials like ores and scraps, and manufacturing processes during the industrial production of stainless steel materials, and are components that are allowed within the range that does not cause adverse effects on the present invention.

[0035] In addition, the ferritic stainless steel material of Embodiment 1 of the present invention may further contain one or more selected from the following: Nb: 1.00% or less, Ti: 0.60% or less, V: 1.00% or less, W: 2.00% or less, Mo: 3.00% or less, N: 0.050% or less, Sn: 0.50% or less, Al: 5.00% or less, Zr: 0.50% or less, Co: 0.50% or less, B: 0.010% or less, Ca: 0.10% or less, REM: 0.20% or less.

[0036] Hereinafter, each component will be described in detail.

[0037] <C: 0.10% or less>

[0038] C is an element effective for increasing the strength of the ferritic stainless steel material and for uniformly dispersing and precipitating the ε-Cu phase by the formation of Cr carbides. However, when the C content is excessive, it becomes hard and the workability deteriorates. In addition, sensitization occurs when affected by heat such as welding, and the corrosion resistance of the ferritic stainless steel material decreases. Therefore, the upper limit value of the C content is controlled to 0.10%, preferably 0.06%, more preferably 0.04%, and further preferably 0.03%. On the other hand, the lower limit value of the C content is not particularly limited, preferably 0.001%, more preferably 0.003%, and further preferably 0.005%.

[0039] <Si: 4.00% or less>

[0040] Si is a ferrite phase (α-phase) forming element and is an element effective for improving the corrosion resistance and strength of the ferritic stainless steel material. However, when the Si content is excessive, it becomes hard and the workability of the ferritic stainless steel material decreases. Therefore, the upper limit value of the Si content is controlled to 4.00%, preferably 2.00%, more preferably 1.50%, and further preferably 1.00%. On the other hand, the lower limit value of the Si content is not particularly limited, preferably 0.01%, more preferably 0.05%, and further preferably 0.10%.

[0041] <Mn: 2.00% or less>

[0042] Mn is an element that improves the heat resistance of ferritic stainless steel materials. However, when the Mn content is excessive, the corrosion resistance of ferritic stainless steel materials decreases. In addition, Mn is an austenite phase (γ-phase) forming element, so at high temperatures, the γ-phase is formed (martensite phase at room temperature), and the workability of ferritic stainless steel materials also decreases. Therefore, the upper limit value of the Mn content is controlled to 2.00%, preferably 1.50%, more preferably 1.20%, and further preferably 1.00%. On the other hand, the lower limit value of the Mn content is not particularly limited, preferably 0.01%, more preferably 0.05%, and further preferably 0.10%.

[0043] <P: 0.050% or less>

[0044] When the P content is excessive, the corrosion resistance or workability of ferritic stainless steel materials decreases. Therefore, the upper limit value of the P content is controlled to 0.050%, preferably 0.040%, and more preferably 0.030%. On the other hand, the lower limit value of the P content is not particularly limited. Since the reduction of the P content increases the refining cost, it is preferably 0.001%, more preferably 0.005%, and further preferably 0.010%.

[0045] <S: 0.030% or less>

[0046] When the S content is excessive, the hot workability decreases, the manufacturability of ferritic stainless steel materials decreases, and it has an adverse effect on the corrosion resistance. Therefore, the upper limit value of the S content is controlled to 0.030%, preferably 0.020%, and more preferably 0.010%. On the other hand, the lower limit value of the S content is not particularly limited. Since the reduction of the S content increases the refining cost, it is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0003%.

[0047] <Ni: 4.00% or less>

[0048] Ni is an element that improves the corrosion resistance of ferritic stainless steel materials. However, like Mn, Ni is an austenite phase (γ-phase) forming element. Therefore, when its content is excessive, the γ-phase is formed at high temperatures (martensite phase at room temperature), and the workability of ferritic stainless steel materials decreases. In addition, Ni is a high-price element, so it also increases the manufacturing cost. Therefore, the upper limit value of the Ni content is controlled to 4.00%, preferably 2.00%, more preferably 1.00%, and further preferably 0.60%. On the other hand, the lower limit value of the Ni content is not particularly limited, preferably 0.005%, more preferably 0.01%, and further preferably 0.03%.

[0049] <Cr: 10.00 - 32.00%>

[0050] Cr is an important element for maintaining the corrosion resistance of ferritic stainless steel materials. However, when the Cr content is excessive, it causes an increase in refining costs and hardens due to solid solution strengthening, reducing the workability of ferritic stainless steel materials. Therefore, the upper limit value of the Cr content is controlled to 32.00%, preferably 22.00%, more preferably 20.00%, and further preferably 18.00%. On the other hand, when the Cr content is too low, sufficient corrosion resistance cannot be obtained. Therefore, the lower limit value of the Cr content is controlled to 10.00%, preferably 14.00%, more preferably 15.00%, and further preferably 16.00%.

[0051] <Cu: 0.40 - 4.00%>

[0052] Cu is an element necessary for the precipitation of the ε-Cu phase that imparts antibacterial and antiviral properties. In addition, Cu is also an element that improves the workability of ferritic stainless steel materials. To achieve such effects, the lower limit value of the Cu content is controlled to 0.40%, preferably 0.70%, more preferably 1.00%, and further preferably 1.30%. On the other hand, when the Cu content is excessive, the corrosion resistance of ferritic stainless steel materials decreases, and a low melting point phase is formed during casting, resulting in a reduction in hot workability. Therefore, the upper limit value of the Cu content is controlled to 4.00%, preferably 3.00%, more preferably 2.00%, and further preferably 1.70%.

[0053] <Nb: 1.00% or less>

[0054] Nb is an element that forms precipitates and exhibits the effect of uniformly precipitating the ε-Cu phase around them, and is added as needed. However, when the Nb content is excessive, the workability of ferritic stainless steel materials decreases. Therefore, the upper limit value of the Nb content is controlled to 1.00%, preferably 0.80%, more preferably 0.60%, and further preferably 0.55%. On the other hand, the lower limit value of the Nb content is not particularly limited, and from the perspective of obtaining the effects brought by Nb, it is preferably 0.05%, more preferably 0.10%, further preferably 0.20%, and particularly preferably 0.25%.

[0055] <Ti: 0.60% or less>

[0056] Ti is an element that forms precipitates in the same way as Nb and exhibits the effect of uniformly precipitating the ε-Cu phase around them, and is added as needed. However, when the Ti content is excessive, it causes surface defects, resulting in a reduction in quality, and the workability of ferritic stainless steel materials decreases. Therefore, the upper limit value of the Ti content is controlled to 0.60%, preferably 0.30%. On the other hand, the lower limit value of the Ti content is not particularly limited, and from the perspective of obtaining the effects brought by Ti, it is preferably 0.01%, more preferably 0.03%.

[0057] <V: 1.00% or less>

[0058] V forms precipitates in the same way as Nb and Ti, and has the effect of uniformly precipitating the ε-Cu phase around it, and is added as needed. However, when the V content is too high, it causes surface defects, resulting in a decrease in quality and a decrease in the workability of ferritic stainless steel materials. Therefore, the upper limit value of the V content is controlled to 1.00%, preferably 0.50%. On the other hand, the lower limit value of the V content is not particularly limited, and from the viewpoint of obtaining the effect brought by V, it is preferably 0.01%, more preferably 0.03%.

[0059] <W: 2.00% or less>

[0060] W forms precipitates in the same way as Nb, Ti, and V, and has the effect of uniformly precipitating the ε-Cu phase around it, and is added as needed. However, when the W content is too high, it causes surface defects, resulting in a decrease in quality and a decrease in the workability of ferritic stainless steel materials. Therefore, the upper limit value of the W content is controlled to 2.00%, preferably 1.00%. On the other hand, the lower limit value of the W content is not particularly limited, and from the viewpoint of obtaining the effect brought by W, it is preferably 0.01%, more preferably 0.03%.

[0061] <Mo: 3.00% or less>

[0062] Mo is an element that improves the corrosion resistance of ferritic stainless steel materials and is added as needed. However, when the Mo content is too high, it causes an increase in manufacturing cost. Therefore, the upper limit value of the Mo content is controlled to 3.00%, preferably 2.00%, more preferably 1.50%, and further preferably 1.00%. On the other hand, the lower limit value of the Mo content is not particularly limited, and from the viewpoint of obtaining the effect brought by Mo, it is preferably 0.01%, more preferably 0.03%, and further preferably 0.10%.

[0063] <N: 0.050% or less>

[0064] N, like Mo, is an element that improves the corrosion resistance of ferritic stainless steel materials and is added as needed. However, when the N content is too high, it hardens and reduces the workability of ferritic stainless steel materials. Therefore, the upper limit value of the N content is controlled to 0.050%, preferably 0.030%, more preferably 0.025%, and further preferably 0.015%. On the other hand, the lower limit value of the N content is not particularly limited, and from the viewpoint of obtaining the effect brought by N, it is preferably 0.001%, preferably 0.003%.

[0065] <Sn: 0.50% or less>

[0066] Sn, like Mo and N, is an element that improves the corrosion resistance of ferritic stainless steel materials and is added as needed. However, when the Sn content is excessive, the manufacturing cost increases. Therefore, the upper limit value of the Sn content is controlled at 0.50%, preferably 0.30%. On the other hand, the lower limit value of the Sn content is not particularly limited, and from the perspective of obtaining the effects brought by Sn, it is preferably 0.01%, more preferably 0.03%.

[0067] <Al: 5.00% or less>

[0068] Al is an element used for deoxidation in the refining process and is added as needed. In addition, Al is also an element that improves the corrosion resistance or oxidation resistance of ferritic stainless steel materials. However, when the Al content is excessive, the amount of inclusions generated increases and the quality deteriorates. Therefore, the upper limit value of the Al content is 5.00%, preferably 3.00%, more preferably 2.00%, and further preferably 1.00%. On the other hand, the lower limit value of the Al content is not particularly limited, and from the perspective of obtaining the effects brought by Al, it is preferably 0.01%, more preferably 0.05%.

[0069] <Zr: 0.50% or less>

[0070] Zr, like Al, is an element that improves the oxidation resistance of ferritic stainless steel materials and is added as needed. However, when the Zr content is excessive, the manufacturing cost increases. Therefore, the upper limit value of the Zr content is controlled at 0.50%, preferably 0.30%. On the other hand, the lower limit value of the Zr content is not particularly limited, and from the perspective of obtaining the effects brought by Zr, it is preferably 0.01%, more preferably 0.03%.

[0071] <Co: 0.50% or less>

[0072] Co, like Al and Zr, is an element that improves the oxidation resistance of ferritic stainless steel materials and is added as needed. However, when the Co content is excessive, the manufacturing cost increases. Therefore, the upper limit value of the Co content is controlled at 0.50%, preferably 0.30%. On the other hand, the lower limit value of the Co content is not particularly limited, and from the perspective of obtaining the effects brought by Co, it is preferably 0.01%, more preferably 0.03%.

[0073] <B: 0.010% or less>

[0074] B is an element that improves the hot workability of ferritic stainless steel materials and is added as needed. In addition, B is also an element that improves the secondary workability of ferritic stainless steel materials through grain boundary strengthening. However, when the B content is excessive, it causes a decrease in weldability or fatigue strength. Therefore, the upper limit value of the B content is controlled to 0.010%, preferably 0.070%. On the other hand, the lower limit value of the B content is not particularly limited, and from the viewpoint of obtaining the effects brought by B, it is preferably 0.001%, more preferably 0.002%.

[0075] <Ca: 0.10% or less>

[0076] Ca is an element that improves the hot workability of ferritic stainless steel materials and is added as needed. In addition, Ca is also an element that improves the intergranular oxidation resistance by forming sulfides to inhibit the grain boundary segregation of S. However, when the Ca content is excessive, it causes a decrease in workability. Therefore, the upper limit value of the Ca content is controlled to 0.10%, preferably 0.05%. On the other hand, the lower limit value of the Ca content is not particularly limited, and from the viewpoint of obtaining the effects brought by Ca, it is preferably 0.001%, more preferably 0.003%.

[0077] <REM: 0.20% or less>

[0078] REM (rare earth element) is an element that improves the hot workability of ferritic stainless steel materials and is added as needed. In addition, REM is also an element that improves the corrosion resistance by forming sulfides that are difficult to dissolve and inhibiting the formation of MnS as the starting point of corrosion. However, when the REM content is excessive, it causes an increase in manufacturing cost. Therefore, the upper limit value of the REM content is controlled to 0.20%, preferably 0.10%. On the other hand, the lower limit value of the REM content is not particularly limited, and from the viewpoint of obtaining the effects brought by REM, it is preferably 0.001%, more preferably 0.01%.

[0079] Furthermore, in this specification, "REM" refers to the general term for two elements, scandium (Sc) and yttrium (Y), and 15 elements from lanthanum (La) to lutetium (Lu) (lanthanide elements). They can be used alone or as a mixture of two or more.

[0080] Next, the characteristics of the ε-Cu phase exposed on the surface of the ferritic stainless steel material in Embodiment 1 of the present invention will be described in detail.

[0081] <Area ratio: 0.1 - 4.0%>

[0082] The larger the area ratio of the ε-Cu phase exposed on the surface, the more Cu ions are dissolved, so the antibacterial and antiviral properties can be improved. The area ratio of this ε-Cu phase mainly depends on the crystal structure and Cu content. Therefore, when considering the Cu content in the ferritic stainless steel material, the upper limit value of the area ratio of the ε-Cu phase is controlled to 4.0%, preferably 2.0%, more preferably 1.9%, and further preferably 1.8%. On the other hand, from the viewpoint of ensuring antibacterial and antiviral properties, the lower limit value of the area ratio of the ε-Cu phase is controlled to 0.1%, preferably 0.3%, and more preferably 0.6%.

[0083] Here, the "area ratio of the ε-Cu phase exposed on the surface" in this specification can be calculated by observing the surface of the stainless steel material with TEM (transmission electron microscope). Specifically, on the surface of the stainless steel material, after taking TEM images at three or more randomly selected positions, the area of the ε-Cu phase is measured by image analysis of the TEM images, and the area of the ε-Cu phase is divided by the field of view area, whereby the "area ratio of the ε-Cu phase exposed on the surface" can be calculated. The field of view area is not particularly limited, and preferably the total of the shooting positions is 10μm 2 The above.

[0084] <Average particle size: 10 - 300nm>

[0085] The larger the average particle size of the ε-Cu phase exposed on the surface, the more Cu ions can be dissolved in the long term, so the persistence of antibacterial and antiviral properties is improved. However, when the average particle size of the ε-Cu phase is too large, the inter-particle distance of the ε-Cu phase exposed on the surface tends to increase. Therefore, when bacteria or viruses adhere between the particles of the ε-Cu phase exposed on the surface, sufficient antibacterial and antiviral properties may not be obtained. Therefore, the upper limit value of the average particle size of the ε-Cu phase is controlled to 300nm, preferably 250nm, and more preferably 200nm. On the other hand, from the viewpoint of ensuring the persistence of Cu ion dissolution, the lower limit value of the average particle size of the ε-Cu phase is controlled to 10nm, preferably 30nm, and more preferably 50nm.

[0086] Here, the "average particle size of the ε-Cu phase exposed on the surface" in this specification can be calculated by observing the surface of the stainless steel material with TEM (transmission electron microscope). Specifically, on the surface of the stainless steel material, after taking TEM images at three or more randomly selected positions, the equivalent circle diameter of the ε-Cu phase is obtained by image analysis of the TEM images, and its average value is taken as the "average particle size of the ε-Cu phase exposed on the surface".

[0087] <Maximum inter-particle distance: 100 - 1000nm>

[0088] Generally, the size of bacteria is 0.5 to 3 μm, while the size of viruses is very small, being 10 to 200 nm. Therefore, when the maximum interparticle distance of the ε-Cu phase exposed on the surface is too large, especially when viruses adhere between the particles of the ε-Cu phase exposed on the surface, sufficient antiviral properties cannot be obtained. Therefore, the upper limit value of the maximum interparticle distance of the ε-Cu phase is controlled to 1000 nm, preferably 800 nm, more preferably 500 nm. On the other hand, the smaller the maximum interparticle distance of the ε-Cu phase exposed on the surface, the more the antibacterial and antiviral properties can be improved. However, when forming a relatively large ε-Cu phase with an average particle size of 10 to 300 nm, considering the growth process of the ε-Cu phase caused by heat treatment, it is considered that the lower limit value of the maximum interparticle distance of the ε-Cu phase is limited to 100 nm. Therefore, the lower limit value of the maximum interparticle distance of the ε-Cu phase is controlled to 100 nm, preferably 150 nm, more preferably 200 nm.

[0089] Here, the "maximum interparticle distance of the ε-Cu phase exposed on the surface" in this specification can be calculated by observing the surface of the stainless steel material with TEM (transmission electron microscope). Specifically, on the surface of the stainless steel material, after taking TEM images at three or more randomly selected positions, the TEM images are subjected to image analysis to obtain the centroid (parent point) positions of the ε-Cu phase, and Voronoi division is performed. Then, the distance between the centroids of the ε-Cu phase in adjacent Voronoi regions is measured as the interparticle distance, and the maximum value thereof can be used as the "maximum interparticle distance of the ε-Cu phase exposed on the surface".

[0090] The ferritic stainless steel material of Embodiment 1 of the present invention preferably has a Vickers hardness of 160 Hv or less. By controlling the Vickers hardness to such a value, workability can be ensured, and thus it can be used for various purposes.

[0091] Furthermore, the lower limit value of the Vickers hardness is not particularly limited and is generally 100 Hv.

[0092] Here, the "Vickers hardness" in this specification can be measured according to JIS Z2244:2009. In the measurement of the Vickers hardness, the measurement load is set to 10 kg, and the measurement is performed at five or more randomly selected positions, and the average value thereof is used as the result of the Vickers hardness.

[0093] The ferritic stainless steel material of Embodiment 1 of the present invention preferably has an antibacterial activity value of 2.0 or more in the antibacterial test according to JIS Z2801:2010. If the antibacterial activity value is such, high antibacterial properties can be objectively ensured.

[0094] Here, the "antibacterial test" in this specification is performed according to JIS Z2801:2010 using Staphylococcus aureus as the bacterium.

[0095] In the ferritic stainless steel material of Embodiment 1 of the present invention, in the antiviral test according to ISO 21702:2019, the antiviral activity value is preferably 2.0 or more. With such an antiviral activity value, high antiviral properties can be objectively ensured.

[0096] Here, the "antiviral test" in this specification is carried out using influenza A virus as the virus according to ISO 21702:2019.

[0097] The type of the ferritic stainless steel material of Embodiment 1 of the present invention is not particularly limited, and a hot-rolled material or a cold-rolled material is preferred.

[0098] In the case of a hot-rolled material, its thickness is generally 3 mm or more. In addition, in the case of a cold-rolled material, its thickness is generally less than 3 mm.

[0099] The ferritic stainless steel material of Embodiment 1 of the present invention can be manufactured by a method including a hot-rolling process, a cooling process, and a heat treatment process.

[0100] The hot-rolling process is a process of hot-rolling a slab having the above composition to obtain a hot-rolled material. Specifically, after rough-rolling the slab having the above composition, a hot-rolled material is obtained by final hot-rolling. This hot-rolled material can also be wound into a coil shape.

[0101] Furthermore, the slab having the above composition is not particularly limited. For example, stainless steel having the above composition can be melted and obtained by forging or casting.

[0102] The final hot-rolling is carried out such that the final hot-rolling end temperature becomes 700 to 900 °C. By controlling the final hot-rolling end temperature within this temperature range, fine "seeds" of the ε-Cu phase can be easily precipitated in a small amount and uniformly from the end of the final hot-rolling to the cooling process. As a result, by growing the ε-Cu phase in the heat treatment process, the distribution state of the ε-Cu phase on the surface can be controlled as described above. In contrast, when the final hot-rolling end temperature is less than 700 °C, fine "seeds" of the ε-Cu phase do not precipitate sufficiently from the end of the final hot-rolling to the cooling process. As a result, when the ε-Cu phase grows in the heat treatment process, the average particle diameter or the maximum inter-particle distance of the ε-Cu phase on the surface becomes too large. In addition, when the final hot-rolling end temperature exceeds 900 °C, the structure coarsens and the workability and toughness decrease.

[0103] Furthermore, other conditions in the hot-rolling process can be appropriately set according to the composition of the slab and are not particularly limited.

[0104] The cooling process is a process for precipitating fine "seeds" of the ε-Cu phase, which is carried out by cooling the hot-rolled material obtained in the hot-rolling process at an average cooling rate of 0.2 to 5 °C / second between 900 and 500 °C. By slowly cooling under such conditions, fine "seeds" of the ε-Cu phase can be precipitated in a small amount and uniformly within the precipitation temperature range (900 to 500 °C) of the ε-Cu phase. These fine "seeds" of the ε-Cu phase preferentially grow in the heat treatment process, thus becoming a state in which relatively large ε-Cu phases are uniformly dispersed. As a result, the distribution state of the ε-Cu phase on the surface can be controlled as described above. From the viewpoint of stably obtaining such an effect, the average cooling rate is preferably 1 to 5 °C / second, more preferably 2 to 4 °C / second. In contrast, when cooling between 900 and 500 °C at an average cooling rate greater than 5 °C / second, the fine "seeds" of the ε-Cu phase do not precipitate sufficiently. As a result, when the ε-Cu phase grows in the heat treatment process, the average particle diameter or the maximum inter-particle distance of the ε-Cu phase on the surface becomes too large. In addition, when cooling between 900 and 500 °C at an average cooling rate less than 0.2 °C / second, the precipitation amount of the fine "seeds" of the ε-Cu phase increases. As a result, a state is formed in which a large amount of relatively small ε-Cu phases precipitate in the heat treatment process.

[0105] Furthermore, the cooling method in the cooling process is not particularly limited, and methods known in the art can be used. For example, as long as the hot-rolled material wound into a coil shape is placed in a heat preservation box, slow cooling can be achieved through reheating under the above cooling conditions. In addition, fine adjustment of the cooling temperature can be carried out by controlling the supply amount of the gas (such as Ar gas) supplied to the heat preservation box.

[0106] The heat treatment process is a process for growing the fine "seeds" of the ε-Cu phase precipitated in the cooling process, which is carried out by heating the hot-rolled material cooled in the cooling process at 750 to 850 °C for 4 hours or more. By performing heat treatment under such conditions, the distribution state of the ε-Cu phase on the surface can be controlled as described above. From the viewpoint of stably obtaining such an effect, the heating time is preferably 6 to 48 hours, more preferably 8 to 36 hours. In contrast, when the heating temperature is less than 750 °C and / or the heating time is less than 4 hours, the fine "seeds" of the ε-Cu phase do not grow sufficiently, and the average particle diameter of the ε-Cu phase becomes too small. In addition, when the heating temperature exceeds 850 °C, the ε-Cu phase dissolves in the matrix phase.

[0107] After the heat treatment process, if necessary, a surface removal process of pickling and / or polishing can be further carried out. By performing the surface removal process, the oxide scale and Cr-depleted layer formed on the surface can be removed.

[0108] The thickness of the surface layer removed in the surface layer removal process can be appropriately adjusted according to the composition of the slab, etc., and is not particularly limited. For example, in the case of removing the Cr-depleted layer, it is preferable to remove the surface layer with a thickness of 10 μm or more.

[0109] In the case where the ferritic stainless steel material is a cold-rolled material, a cold rolling / annealing process of performing cold rolling followed by annealing treatment within 300 seconds can also be further performed after the heat treatment process. Furthermore, in the case of performing the surface layer removal process after the heat treatment process, the cold rolling / annealing process can be performed after the surface layer removal process, or the surface layer removal process can be performed after the cold rolling / annealing process.

[0110] By making the annealing treatment a short time within 300 seconds, it is possible to remove the strain generated by cold rolling while suppressing the influence on the ε-Cu phase exposed on the surface.

[0111] Furthermore, the conditions of cold rolling and annealing treatment can be appropriately adjusted according to the composition of the slab, etc., and are not particularly limited.

[0112] The ferritic stainless steel material of Embodiment 1 of the present invention can maintain antibacterial and antiviral properties for a long time, and thus can be used for antibacterial / antiviral components. In addition, since the ferritic stainless steel material of Embodiment 1 of the present invention can make the Vickers hardness 160 Hv or less, it is also easy to process into a shape suitable for antibacterial / antiviral components.

[0113] (Embodiment 2)

[0114] The austenitic stainless steel material of Embodiment 2 of the present invention has a composition containing C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 to 20.00%, Cr: 10.00 to 32.00%, and Cu: 2.00 to 6.00%, and the balance is composed of Fe and impurities.

[0115] In addition, the austenitic stainless steel material of Embodiment 2 of the present invention may further contain one or more selected from the following: Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, W: 2.00% or less, Mo: 6.00% or less, N: 0.350% or less, Sn: 0.50% or less, Al: 5.00% or less, Zr: 0.50% or less, Co: 0.50% or less, B: 0.020% or less, Ca: 0.10% or less, REM: 0.20% or less.

[0116] Hereinafter, each component will be described in detail.

[0117] <C: 0.12% or less>

[0118] C is an austenite-forming element, which is effective in increasing the strength of austenitic stainless steel materials and in uniformly dispersing and precipitating the ε-Cu phase through the formation of Cr carbides. However, when the C content is excessive, it becomes hard and the workability deteriorates, and sensitization occurs when it is affected by heat such as welding, reducing the corrosion resistance of the austenitic stainless steel material. Therefore, the upper limit of the C content is controlled to 0.12%, preferably 0.10%, more preferably 0.09%, and further preferably 0.08%. On the other hand, the lower limit of the C content is not particularly limited, preferably 0.001%, more preferably 0.003%, and further preferably 0.005%.

[0119] <Si: 4.00% or less>

[0120] Si is an element effective in improving the corrosion resistance and strength of austenitic stainless steel materials. However, when the Si content is excessive, it becomes hard and the workability of the austenitic stainless steel material deteriorates. In addition, Si is a ferrite-phase (α-phase) forming element, and thus causes the destabilization of the austenite phase (γ-phase) or the formation of the ferrite phase. Therefore, the upper limit of the Si content is controlled to 4.00%, preferably 3.00%, more preferably 2.00%, and further preferably 1.50%. On the other hand, the lower limit of the Si content is not particularly limited, preferably 0.01%, more preferably 0.05%, and further preferably 0.10%.

[0121] <Mn: 6.00% or less>

[0122] Mn is an austenite-phase (γ-phase) forming element. In addition, Mn forms MnS, and MnS acts as a nucleus for the ε-Cu phase. However, when the Mn content is excessive, the corrosion resistance of the austenitic stainless steel material deteriorates. Therefore, the upper limit of the Mn content is controlled to 6.00%, preferably 4.00%, more preferably 3.00%, and further preferably 2.50%. On the other hand, the lower limit of the Mn content is not particularly limited, preferably 0.01%, more preferably 0.05%, and further preferably 0.10%.

[0123] <P: 0.050% or less>

[0124] When the P content is excessive, the corrosion resistance or workability of the austenitic stainless steel material deteriorates. Therefore, the upper limit of the P content is controlled to 0.050%, preferably 0.040%, and more preferably 0.035%. On the other hand, the lower limit of the P content is not particularly limited. Since reducing the P content increases the refining cost, it is preferably 0.001%, more preferably 0.005%, and further preferably 0.010%.

[0125] <S: 0.030% or less>

[0126] When the S content is excessive, the hot workability deteriorates, the manufacturability of austenitic stainless steel materials decreases, and the corrosion resistance is also adversely affected. Therefore, the upper limit value of the S content is controlled to 0.030%, preferably 0.020%, more preferably 0.010%. On the other hand, the lower limit value of the S content is not particularly limited. Since the refining cost increases as the S content decreases, it is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0003%.

[0127] <Ni: 4.00 to 20.00%>

[0128] Like Mn, Ni is an austenite phase (γ-phase) forming element, which improves the corrosion resistance and workability. Since Ni is an expensive element, when the content is excessive, the manufacturing cost increases. Therefore, the upper limit value of the Ni content is controlled to be less than 20.00%, preferably 15.00% or less, more preferably 12.00% or less, and further preferably 10.00% or less. On the other hand, when the Ni content is too low, the corrosion resistance of the austenitic stainless steel material decreases. Therefore, the lower limit value of the Ni content is controlled to 4.00%, preferably 6.00%, more preferably 8.00%, and further preferably 8.50%.

[0129] <Cr: 10.00 to 32.00%>

[0130] Cr is an important element for maintaining the corrosion resistance of austenitic stainless steel materials. However, when the Cr content is excessive, it leads to an increase in the refining cost and hardening due to solid solution strengthening, and the workability of the austenitic stainless steel material decreases. Therefore, the upper limit value of the Cr content is controlled to 32.00%, preferably 25.00%, more preferably 22.00%, and further preferably 20.00%. On the other hand, when the Cr content is too low, sufficient corrosion resistance cannot be obtained. Therefore, the lower limit value of the Cr content is controlled to 10.00%, preferably 14.00%, more preferably 15.00%, and further preferably 18.00%.

[0131] <Cu: 2.00 to 6.00%>

[0132] Cu is an element necessary for precipitating the ε-Cu phase that imparts antibacterial and antiviral properties. In addition, Cu is also an element that improves the workability of austenitic stainless steel materials. To obtain such an effect, the lower limit value of the Cu content is controlled to 2.00%, preferably 2.50%, more preferably 3.00%, and further preferably 3.60%. On the other hand, when the Cu content is excessive, the corrosion resistance of the austenitic stainless steel material decreases, and a low melting point phase is formed during casting, resulting in a decrease in hot workability. Therefore, the upper limit value of the Cu content is controlled to 6.00%, preferably 5.00%, more preferably 4.80%, and further preferably 4.50%.

[0133] <Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, W: 2.00% or less>

[0134] Nb, Ti, V, and W are elements that reduce sensitization caused by grain boundary segregation of C and N by forming carbides and / or nitrides, thereby improving intergranular corrosion resistance, and are added as needed. However, when the contents of Nb, Ti, V, and W are excessive, they cause surface defects, resulting in a reduction in quality and a decrease in the workability of austenitic stainless steel materials. Therefore, the upper limit values of the contents of Nb, Ti, and V are all controlled to be 1.00%, preferably 0.50%. In addition, the upper limit value of the W content is controlled to be 2.00%, preferably 1.50%. On the other hand, the lower limit values of the contents of Nb, Ti, V, and W are not particularly limited, and from the viewpoint of obtaining the effects brought by these elements, they are 0.01%, preferably 0.02%.

[0135] <Mo: 6.00% or less>

[0136] Mo is an element that improves the corrosion resistance of austenitic stainless steel materials and is added as needed. However, when the Mo content is excessive, it causes an increase in manufacturing cost. Therefore, the upper limit value of the Mo content is controlled to be 6.00%, preferably 5.00%, more preferably 3.00%, and further preferably 2.00%. On the other hand, the lower limit value of the Mo content is not particularly limited, and from the viewpoint of obtaining the effects brought by Mo, it is preferably 0.01%, more preferably 0.03%, and further preferably 0.10%.

[0137] <N: 0.350% or less>

[0138] Similar to Mo, N is an element that improves the corrosion resistance of austenitic stainless steel materials and is added as needed. However, when the N content is excessive, it causes hardening and a decrease in the workability of austenitic stainless steel materials. Therefore, the upper limit value of the N content is controlled to be 0.350%, preferably 0.200%, more preferably 0.150%, and further preferably 0.050%. On the other hand, the lower limit value of the N content is not particularly limited, and from the viewpoint of obtaining the effects brought by N, it is preferably 0.001%, preferably 0.003%.

[0139] <Sn: 0.50% or less>

[0140] Sn, like Mo and N, is an element that improves the corrosion resistance of austenitic stainless steel materials and is added as needed. However, when the Sn content is excessive, it causes a decrease in the hot workability of austenitic stainless steel materials. Therefore, the upper limit value of the Sn content is controlled to 0.50%, preferably 0.30%. On the other hand, the lower limit value of the Sn content is not particularly limited, and from the viewpoint of obtaining the effect of Sn, it is preferably 0.01%, more preferably 0.02%.

[0141] <Al: 5.00% or less>

[0142] Al is an element used for deoxidation in the refining process and is added as needed. In addition, Al is also an element that improves the corrosion resistance and oxidation resistance of austenitic stainless steel materials. However, when the Al content is excessive, the amount of inclusions generated increases and the quality deteriorates. Therefore, the upper limit value of the Al content is 5.00%, preferably 3.00%, more preferably 2.00%, and further preferably 1.00%. On the other hand, the lower limit value of the Al content is not particularly limited, and from the viewpoint of obtaining the effect brought by Al, it is preferably 0.01%, more preferably 0.03%.

[0143] <Zr: 0.50% or less>

[0144] Zr, like Al, is an element that improves the oxidation resistance of austenitic stainless steel materials and is added as needed. However, when the Zr content is excessive, it causes an increase in manufacturing costs. Therefore, the upper limit value of the Zr content is controlled to 0.50%, preferably 0.30%. On the other hand, the lower limit value of the Zr content is not particularly limited, and from the viewpoint of obtaining the effect brought by Zr, it is preferably 0.01%, more preferably 0.03%.

[0145] <Co: 0.50% or less>

[0146] Co, like Al and Zr, is an element that improves the oxidation resistance of austenitic stainless steel materials and is added as needed. However, when the Co content is excessive, it causes an increase in manufacturing costs. Therefore, the upper limit value of the Co content is controlled to 0.50%, preferably 0.30%. On the other hand, the lower limit value of the Co content is not particularly limited, and from the viewpoint of obtaining the effect brought by Co, it is preferably 0.01%, more preferably 0.03%.

[0147] <B: 0.020% or less>

[0148] B is an element that improves hot workability and is added as needed. However, when the B content is excessive, the corrosion resistance and weldability of austenitic stainless steel materials decrease. Therefore, the upper limit value of the B content is controlled to 0.020%, preferably 0.015%, more preferably 0.010%, and further preferably 0.005%. On the other hand, the lower limit value of the B content is not particularly limited, and from the viewpoint of obtaining the effects brought by B, it is controlled to 0.0001%, preferably 0.0003%, and more preferably 0.0005%.

[0149] <Ca: 0.10% or less>

[0150] Ca, like B, is an element that improves the hot workability of austenitic stainless steel materials and is added as needed. In addition, Ca is also an element that improves intergranular oxidation resistance by forming sulfides to inhibit the grain boundary segregation of S. However, when the Ca content is excessive, it causes a decrease in workability. Therefore, the upper limit value of the Ca content is controlled to 0.10%, preferably 0.05%. On the other hand, the lower limit value of the Ca content is not particularly limited, and from the viewpoint of obtaining the effects brought by Ca, it is preferably 0.001%, and more preferably 0.003%.

[0151] <REM: 0.20% or less>

[0152] REM (rare earth element), like B and Ca, is an element that improves the hot workability of austenitic stainless steel materials and is added as needed. In addition, REM is also an element that improves corrosion resistance by forming sulfides that are difficult to dissolve and inhibiting the formation of MnS as the starting point of corrosion. However, when the REM content is excessive, it causes an increase in manufacturing cost. Therefore, the upper limit value of the REM content is controlled to 0.20%, preferably 0.10%. On the other hand, the lower limit value of the REM content is not particularly limited, and from the viewpoint of obtaining the effects brought by REM, it is preferably 0.001%, and more preferably 0.01%.

[0153] Furthermore, REM can be used as a single type or as a mixture of two or more types.

[0154] Next, the characteristics of the ε-Cu phase exposed on the surface of the austenitic stainless steel material in the second embodiment of the present invention will be described in detail.

[0155] <Area ratio: 0.1 - 4.0%>

[0156] The larger the area ratio of the ε-Cu phase exposed on the surface, the more Cu ions are dissolved, and thus the antibacterial and antiviral properties can be improved. The area ratio of this ε-Cu phase mainly depends on the crystal structure and Cu content. Therefore, when considering the Cu content in austenitic stainless steel materials, the upper limit value of the area ratio of the ε-Cu phase is controlled to 4.0%, preferably 3.0%, more preferably 2.0%. On the other hand, from the perspective of ensuring antibacterial and antiviral properties, the lower limit value of the area ratio of the ε-Cu phase is controlled to 0.1%, preferably 0.3%, more preferably 0.6%.

[0157] <Average particle size: 10 - 300 nm>

[0158] The larger the average particle size of the ε-Cu phase exposed on the surface, the more Cu ions can be dissolved over a long period, and thus the persistence of antibacterial and antiviral properties is improved. However, when the average particle size of the ε-Cu phase is too large, the inter-particle distance of the ε-Cu phase exposed on the surface tends to increase. Therefore, when bacteria or viruses attach between the particles of the ε-Cu phase exposed on the surface, sufficient antibacterial and antiviral properties cannot be obtained. Therefore, the upper limit value of the average particle size of the ε-Cu phase is controlled to 300 nm, preferably 250 nm, more preferably 200 nm, and further preferably 150 nm. On the other hand, from the perspective of ensuring the persistence of Cu ion dissolution, the lower limit value of the average particle size of the ε-Cu phase is controlled to 10 nm, preferably 20 nm, more preferably 30 nm.

[0159] <Maximum inter-particle distance: 100 - 1000 nm>

[0160] Generally, the size of bacteria is 0.5 - 3 μm, while the size of viruses is very small, 10 - 200 nm. Therefore, when the maximum inter-particle distance of the ε-Cu phase exposed on the surface is too large, especially when viruses attach between the particles of the ε-Cu phase exposed on the surface, sufficient antiviral properties cannot be obtained. Therefore, the upper limit value of the maximum inter-particle distance of the ε-Cu phase is controlled to 1000 nm, preferably 800 nm, more preferably 500 nm. On the other hand, the smaller the maximum inter-particle distance of the ε-Cu phase exposed on the surface, the more the antibacterial and antiviral properties can be improved. However, in the case of forming a relatively large ε-Cu phase with an average particle size of 10 - 300 nm, considering the growth process of the ε-Cu phase caused by heat treatment, it is considered that the lower limit value of the maximum inter-particle distance of the ε-Cu phase is limited to 100 nm. Therefore, the lower limit value of the maximum inter-particle distance of the ε-Cu phase is controlled to 100 nm, preferably 150 nm, more preferably 200 nm.

[0161] The Vickers hardness of the austenitic stainless steel material of Embodiment 2 of the present invention is preferably 190 Hv or less, more preferably 180 Hv or less. By controlling the Vickers hardness to such a level, workability can be ensured, and thus it can be used for various purposes.

[0162] Furthermore, the lower limit value of the Vickers hardness is not particularly limited and is generally 100 Hv.

[0163] The austenitic stainless steel material of Embodiment 2 of the present invention preferably has an antibacterial activity value of 2.0 or more in the antibacterial test according to JIS Z2801:2010. If the antibacterial activity value is such, high antibacterial property can be objectively ensured.

[0164] The austenitic stainless steel material of Embodiment 2 of the present invention preferably has an antiviral activity value of 2.0 or more in the antiviral test according to ISO 21702:2019. If the antiviral activity value is such, high antiviral property can be objectively ensured.

[0165] The type of the austenitic stainless steel material of Embodiment 2 of the present invention is not particularly limited, and a hot-rolled material or a cold-rolled material is preferred.

[0166] In the case of a hot-rolled material, its thickness is generally 3 mm or more. In the case of a cold-rolled material, its thickness is generally less than 3 mm.

[0167] The austenitic stainless steel material of Embodiment 2 of the present invention can be manufactured by a method including a hot-rolling process, a cooling process, and a heat treatment process.

[0168] The hot-rolling process is a process of hot-rolling a slab having the above composition to obtain a hot-rolled material. Specifically, after rough-rolling the slab having the above composition, a hot-rolled material is obtained by final hot-rolling. This hot-rolled material can also be wound into a coil shape.

[0169] Furthermore, the slab having the above composition is not particularly limited, and can be obtained, for example, by melting, forging, or casting the stainless steel having the above composition.

[0170] The final hot rolling is carried out in such a manner that the final hot rolling finishing temperature becomes 850 to 1050 °C. By controlling the final hot rolling finishing temperature within this temperature range, it is easy for a small amount of fine "seeds" of the ε-Cu phase to precipitate uniformly from the end of the final hot rolling to the cooling process. As a result, by growing the ε-Cu phase in the heat treatment process, the distribution state of the ε-Cu phase on the surface can be controlled as described above. In contrast, when the final hot rolling finishing temperature is less than 850 °C, fine "seeds" of the ε-Cu phase do not precipitate sufficiently from the end of the final hot rolling to the cooling process. As a result, when the ε-Cu phase grows in the heat treatment process, the average particle diameter and the maximum inter-particle distance of the ε-Cu phase on the surface become too large. In addition, when the final hot rolling finishing temperature exceeds 1050 °C, the structure coarsens, resulting in a decrease in workability and toughness. In addition, in order to return the coarsened structure to a fine structure, multiple rolling treatments and heat treatments are required, increasing the manufacturing cost.

[0171] Furthermore, other conditions in the hot rolling process can be appropriately set according to the composition of the slab and are not particularly limited.

[0172] The cooling process is a process for precipitating fine "seeds" of the ε-Cu phase, which is carried out by cooling the hot rolled material obtained in the hot rolling process at an average cooling rate of 0.2 to 5 °C / second between 900 and 500 °C. By cooling slowly under such conditions, fine "seeds" of the ε-Cu phase can be precipitated in a small amount and uniformly within the precipitation temperature range (900 to 500 °C) of the ε-Cu phase. These fine "seeds" of the ε-Cu phase preferentially grow in the heat treatment process, resulting in a state where relatively large ε-Cu phases are uniformly dispersed. As a result, the distribution state of the ε-Cu phase on the surface can be controlled as described above. From the viewpoint of stably obtaining such an effect, the average cooling rate is preferably 1 to 5 °C / second, more preferably 2 to 4 °C / second. In contrast, when cooling between 900 and 500 °C at an average cooling rate greater than 5 °C / second, fine "seeds" of the ε-Cu phase do not precipitate sufficiently. As a result, when the ε-Cu phase grows in the heat treatment process, the average particle diameter and the maximum inter-particle distance of the ε-Cu phase on the surface become too large. In addition, when cooling between 900 and 500 °C at an average cooling rate less than 0.2 °C / second, the precipitation amount of fine "seeds" of the ε-Cu phase increases. As a result, a state is formed in which a large amount of relatively small ε-Cu phases precipitate in the heat treatment process.

[0173] Furthermore, the cooling method in the cooling process is not particularly limited, and methods known in the art can be used. For example, as long as the hot rolled material wound into a coil shape is placed in a heat preservation box, it can be slowly cooled by reheating under the above cooling conditions. In addition, fine adjustment of the cooling temperature can be carried out by controlling the supply amount of the gas (such as Ar gas) supplied to the heat preservation box.

[0174] The heat treatment process is a process for growing fine "seeds" of the ε-Cu phase precipitated in the cooling process, which is carried out by heating the hot-rolled material cooled in the cooling process at 750 to 850 °C for 4 hours or more. By performing the heat treatment under such conditions, the distribution state of the ε-Cu phase on the surface can be controlled as described above. From the viewpoint of stably obtaining such an effect, the heating time is preferably 6 to 48 hours, more preferably 8 to 36 hours. In contrast, when the heating temperature is less than 750 °C and / or the heating time is less than 4 hours, the fine "seeds" of the ε-Cu phase do not grow sufficiently, and the average particle size of the ε-Cu phase becomes too small. In addition, when the heating temperature exceeds 850 °C, the ε-Cu phase dissolves in the matrix phase.

[0175] After the heat treatment process, a surface removal process of pickling and / or polishing may be further carried out as needed. By performing the surface removal process, the scale and Cr-depleted layer formed on the surface can be removed.

[0176] The thickness of the surface layer removed in the surface removal process may be appropriately adjusted according to the composition of the slab, etc., and is not particularly limited. For example, in the case of removing the Cr-depleted layer, it is preferable to remove a surface layer with a thickness of 10 μm or more.

[0177] In the case where the austenitic stainless steel material is a cold-rolled material, a cold rolling / annealing process of performing cold rolling followed by annealing treatment within 300 seconds may be carried out after the heat treatment process. Furthermore, in the case where a surface removal process is carried out after the heat treatment process, the cold rolling / annealing process may be carried out after the surface removal process, or the surface removal process may be carried out after the cold rolling / annealing process.

[0178] By making the annealing treatment a short time within 300 seconds, it is possible to remove the strain generated during cold rolling while suppressing the influence on the ε-Cu phase exposed on the surface.

[0179] Furthermore, the conditions of cold rolling and annealing treatment may be appropriately adjusted according to the composition of the slab, etc., and are not particularly limited.

[0180] The austenitic stainless steel material of Embodiment 2 of the present invention can maintain antibacterial and antiviral properties for a long time, and thus can be used for antibacterial / antiviral components. In addition, the austenitic stainless steel material of Embodiment 2 of the present invention can make the Vickers hardness 190 Hv or less, and thus is also easily processed into a shape suitable for antibacterial / antiviral components.

[0181] The antibacterial / antiviral component of the present invention includes the above stainless steel material (for example, the ferritic stainless steel material of Embodiment 1 of the present invention and / or the austenitic stainless steel material of Embodiment 2 of the present invention). The above stainless steel material used for the antibacterial / antiviral component can also be processed into various shapes by methods known in the art.

[0182] The antibacterial / antiviral component of the present invention may further include components other than the above-mentioned stainless steel materials.

[0183] The antibacterial / antiviral component is not particularly limited, and various components requiring antibacterial and / or antiviral properties for kitchen equipment, household electrical appliances, medical instruments, interior building materials of buildings, transmission equipment, experimental instruments, sanitary appliances, etc. can be cited.

[0184] Examples

[0185] The following examples are listed to illustrate the content of the present invention in detail, but the present invention is not construed as being limited thereto.

[0186] <Ferritic stainless steel material>

[0187] After melting and forging stainless steels having ferritic compositions of Steel Grades A to J shown in Table 1 (the balance being Fe and impurities) to form slabs, the final hot rolling end temperature was controlled as shown in Table 2, and hot pressing was performed to a thickness of 3 mm to obtain hot-rolled materials. The hot-rolled materials were wound into coil shapes, quickly placed in a heat preservation box, and cooled between 900 and 500 °C at the average cooling rate shown in Table 2. The average cooling rate was adjusted by the supply amount of Ar gas supplied to the heat preservation box. Then, using a batch annealing furnace, the cooled hot-rolled materials were heat-treated at 800 °C in an atmospheric atmosphere for the heating time shown in Table 2. Then, the heat-treated hot-rolled materials were cut into 100 mm (rolling direction) × 100 mm (width direction) by cutting, pickled to remove scale, and polished with a P400 polishing wheel (#400) to obtain ferritic stainless steel materials.

[0188] Table 1

[0189]

[0190] Table 2

[0191]

[0192] The following evaluations were performed on the obtained ferritic stainless steel materials.

[0193] (Area ratio of ε-Cu phase exposed on the surface)

[0194] Circular plates with a diameter of 3 mm were cut from the ferritic stainless steel materials. After one side was ground to a thickness of 0.5 mm, test pieces were prepared by electro-polishing the ground surface. For the electro-polished surface of the test pieces, 10 randomly selected positions (total field area: 15 μm 2After taking a TEM image, the TEM image is subjected to image analysis to measure the area of the ε-Cu phase. The area ratio of the ε-Cu phase is calculated by dividing the measured area of the ε-Cu phase by the field of view area.

[0195] (Average particle diameter of the ε-Cu phase exposed on the surface)

[0196] The equivalent circle diameters of 30 ε-Cu phases are obtained by performing image analysis on the TEM image obtained in the same manner as the above area ratio, and their average value is calculated. Thus, the average particle diameter of the ε-Cu phase is obtained.

[0197] (Maximum interparticle distance of the ε-Cu phase exposed on the surface)

[0198] The TEM image obtained in the same manner as the above area ratio is subjected to image analysis, and the distance between the centroids of the ε-Cu phases in adjacent Voronoi regions is measured as the interparticle distance according to the above method, and its maximum value is obtained. Thus, the maximum interparticle distance of the ε-Cu phase is obtained.

[0199] (Antibacterial test: Antibacterial activity value)

[0200] After cutting a test piece of 50 mm (rolling direction) × 50 mm (width direction) from a ferritic stainless steel material, an antibacterial test is carried out according to JIS Z2801:2010 to obtain the antibacterial activity value (initial). In the antibacterial test, Staphylococcus aureus is used as the bacterium, and a 40 mm × 40 mm polyethylene film is used as the sealing film. In addition, the inoculation amount of the bacterial solution is set to 0.4 mL. Before the test starts, the entire surface of the test piece is gently wiped with a Japanese Pharmacopoeia gauze soaked with ethanol with a purity of more than 99%, and the test is carried out after sufficient drying.

[0201] In addition, in order to evaluate the persistence of the antibacterial effect, the test piece is immersed in 500 mL of water and kept at 80 °C in a thermostatic bath for 16 hours, and then an antibacterial test is carried out in the same manner as above to obtain the antibacterial activity value (after water immersion).

[0202] (Antiviral test: Antiviral activity value)

[0203] After cutting a test piece of 50 mm (rolling direction) × 50 mm (width direction) from a ferritic stainless steel material, an antiviral test is carried out according to ISO 21702:2019 to obtain the antiviral activity value (initial). In the antiviral test, influenza A virus is used as the virus, and a 40 mm × 40 mm polyethylene film is used as the sealing film. In addition, the inoculation amount of the virus suspension (test solution) is set to 0.4 mL. Before the test starts, the entire surface of the test piece is gently wiped with a Japanese Pharmacopoeia gauze soaked with ethanol with a purity of more than 99%, and the test is carried out after sufficient drying.

[0204] In addition, in order to evaluate the persistence of the antiviral effect, the test piece was immersed in 500 mL of water and kept at 80°C in a constant temperature bath for 16 hours, and then the antiviral test was carried out in the same manner as above to obtain the antiviral activity value (after water immersion).

[0205] (Vickers hardness)

[0206] The Vickers hardness was measured in accordance with JIS Z2244:2009. The measurement was performed using a Vickers hardness tester HV-100 manufactured by Mitutoyo Corporation. The measurement load was set to 10 kg, and the Vickers hardness of the surface was measured at 10 randomly selected positions, and the average value was taken as the result.

[0207] The above evaluation results are shown in Table 3.

[0208] Table 3

[0209]

[0210] As shown in Table 3, the ferritic stainless steel materials of No. 1-1 to 1-11 (Examples of the present invention), having a predetermined composition and the distribution state of ε-Cu phase on the surface, thus the results of the antibacterial activity value (initial and after water immersion), the antiviral activity value (initial and after water immersion), and the Vickers hardness are all good.

[0211] In contrast, for the ferritic stainless steel material of No. 1-12 (Comparative Example), the final hot rolling end temperature was too low and the average cooling rate was too large, so the maximum inter-particle distance of the ε-Cu phase became too large. As a result, antiviral property (antiviral activity value of 2.0 or more) could not be obtained.

[0212] For the ferritic stainless steel materials of No. 1-13 and 1-14 (Comparative Examples), the average cooling rate was too large, so the average particle size and / or the maximum inter-particle distance of the ε-Cu phase became large. As a result, antiviral property (antiviral activity value of 2.0 or more) could not be obtained.

[0213] For the ferritic stainless steel material of No. 1-15 (Comparative Example), the average cooling rate was too small, so the maximum inter-particle distance of the ε-Cu phase became small. As a result, the antibacterial activity value and the antiviral activity value after water immersion were low, and the maintenance effect of antibacterial and antiviral properties was insufficient.

[0214] For the ferritic stainless steel materials of No. 1-16 and 1-17 (Comparative Examples), they did not have the predetermined composition, so the distribution state of the ε-Cu phase on the surface could not be properly controlled. As a result, antibacterial property (antibacterial activity value of 2.0 or more) and antiviral property (antiviral activity value of 2.0 or more) could not be obtained.

[0215] No.1 - 18 (Comparative Example) Cracking occurred during hot rolling, and it was impossible to manufacture ferritic stainless steel materials.

[0216] <Austenitic stainless steel material>

[0217] After melting and forging stainless steels having the austenitic compositions of steel types a - j shown in Table 4 (the balance being Fe and impurities) to form slabs, the final hot rolling end temperature was controlled as shown in Table 5, and hot pressing was performed to a thickness of 3 mm to obtain hot - rolled materials. The hot - rolled materials were wound into a coil shape, quickly placed in an insulation box, and then cooled between 900 - 500 °C at the average cooling rate shown in Table 5. The average cooling rate was adjusted by the supply amount of Ar gas supplied to the insulation box. Next, using a batch annealing furnace, the cooled hot - rolled materials were heat - treated in an air atmosphere at 800 °C for the heating time shown in Table 5. Then, the heat - treated hot - rolled materials were cut into 100 mm (rolling direction) × 100 mm (width direction) by machining, pickled to remove scale, and polished with a P400 polishing wheel (#400) to obtain austenitic stainless steel materials.

[0218] Table 4

[0219]

[0220] Table 5

[0221]

[0222] The obtained austenitic stainless steel materials were evaluated in the same manner as the above - mentioned ferritic stainless steel materials. The evaluation results are shown in Table 6.

[0223] Table 6

[0224]

[0225] As shown in Table 6, the austenitic stainless steel materials of No.2 - 1 to 2 - 11 (Examples of the present invention), having a predetermined composition and the distribution state of ε - Cu phase on the surface, thus have good results for antibacterial activity values (initial and after water immersion), antiviral activity values (initial and after water immersion), and Vickers hardness.

[0226] In contrast, for the austenitic stainless steel material of No.2 - 12 (Comparative Example), the final hot rolling end temperature was too low and the average cooling rate was too high, so the average particle size of the ε - Cu phase became too large. As a result, antiviral properties (antiviral activity value of 2.0 or more) were not obtained.

[0227] The austenitic stainless steel materials of No. 2-13 and 2-14 (comparative examples) have an excessively high average cooling rate, so the maximum inter-particle distance of the ε-Cu phase becomes larger. As a result, antiviral properties (antiviral activity value of 2.0 or more) cannot be obtained.

[0228] The austenitic stainless steel material of No. 2-15 (comparative example) has an excessively low average cooling rate, so the average particle size of the ε-Cu phase becomes smaller. As a result, the antibacterial activity value and the antiviral activity value after water immersion are low, and the maintenance effect of antibacterial and antiviral properties is insufficient.

[0229] The austenitic stainless steel materials of No. 2-16 and 2-17 (comparative examples) do not have a predetermined composition, so the distribution state of the ε-Cu phase on the surface cannot be properly controlled. As a result, antibacterial properties (antibacterial activity value of 2.0 or more) and antiviral properties (antiviral activity value of 2.0 or more) cannot be obtained.

[0230] No. 2-18 (comparative example) does not have a predetermined composition, so cracking occurs during hot rolling, and an austenitic stainless steel material cannot be manufactured.

[0231] From the above results, it can be seen that according to the present invention, a stainless steel material capable of maintaining antibacterial and antiviral properties for a long time, a manufacturing method thereof, and an antibacterial / antiviral member can be provided.

[0232] Explanation of reference numerals

[0233] 10 Stainless steel material

[0234] 11 ε-Cu phase

[0235] 12 Passive film

Claims

1. A stainless steel material having an ε-Cu phase exposed on the surface, wherein the area ratio of the ε-Cu phase on the surface is 0.1 to 4.0%, the average particle size is 10 to 300 nm, and the maximum inter-particle distance is 200 to 1000 nm, and the composition of the stainless steel material contains, by mass basis, C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 0.01 to 20.00%, Cr: 10.00 to 32.00%, and Cu: 0.40 to 6.00%, with the balance being composed of Fe and impurities.

2. The stainless steel material according to claim 1, which is a ferritic stainless steel material with a C content of 0.10% or less, an Mn content of 2.00% or less, an Ni content of 4.00% or less, and a Cu content of 0.40 to 4.00%.

3. The stainless steel material according to claim 2, further contains, by mass basis, one or more selected from the following: Nb: 1.00% or less, Ti: 0.60% or less, V: 1.00% or less, W: 2.00% or less, Mo: 3.00% or less, N: 0.050% or less, Sn: 0.50% or less, Al: 5.00% or less, Zr: 0.50% or less, Co: 0.50% or less, B: 0.010% or less, Ca: 0.10% or less, REM: 0.20% or less.

4. The stainless steel material according to claim 2 or 3, having a Vickers hardness of 160 Hv or less.

5. The stainless steel material according to claim 1, which is an austenitic stainless steel material with an Ni content of 4.00 to 20.00% and a Cu content of 2.00 to 6.00%.

6. The stainless steel material according to claim 5, further contains, by mass basis, one or more selected from the following: Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, W: 2.00% or less, Mo: 6.00% or less, N: 0.350% or less, Sn: 0.50% or less, Al: 5.00% or less, Zr: 0.50% or less, Co: 0.50% or less, B: 0.020% or less, Ca: 0.10% or less, REM: 0.20% or less.

7. The stainless steel material according to claim 5 or 6, having a Vickers hardness of 190 Hv or less.

8. The stainless steel material according to any one of claims 1 to 3, 5 to 6, has an antibacterial activity value of 2.0 or more in the antibacterial test conducted according to JIS Z2801:2010.

9. The stainless steel material according to any one of claims 1 to 3, 5 to 6, has an antiviral activity value of 2.0 or more in the antiviral test conducted according to ISO 21702:2019.

10. A manufacturing method of a stainless steel material, comprising Hot rolling process, which hot-rolls a slab to obtain a hot-rolled material, the slab having a ferritic composition or an austenitic composition, the ferritic composition containing, by mass basis, C: 0.10% or less, Si: 4.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00% or less, Cr: 10.00 - 32.00% and Cu: 0.40 - 4.00%, with the balance being composed of Fe and impurities, the austenitic composition containing, by mass basis, C: 0.12% or less, Si: 4.00% or less, Mn: 6.00% or less, P: 0.050% or less, S: 0.030% or less, Ni: 4.00 - 20.00%, Cr: 10.00 - 32.00% and Cu: 2.00 - 6.00%, with the balance being composed of Fe and impurities, when the composition of the slab is the ferritic system, the final hot rolling end temperature is set to 700 - 900 °C, and when it is the austenitic system, the final hot rolling end temperature is set to 850 - 1050 °C; Cooling process, which cools the hot-rolled material obtained in the hot rolling process at an average cooling rate of 0.2 - 5 °C / second between 900 - 500 °C; and Heat treatment process, which heats the hot-rolled material cooled in the cooling process at 750 - 850 °C for 4 hours or more.

11. The method for manufacturing a stainless steel material according to claim 10, The slab having the ferritic composition further contains, by mass basis, one or more selected from the following: Nb: 1.00% or less, Ti: 0.60% or less, V: 1.00% or less, W: 2.00% or less, Mo: 3.00% or less, N: 0.050% or less, Sn: 0.50% or less, Al: 5.00% or less, Zr: 0.50% or less, Co: 0.50% or less, B: 0.010% or less, Ca: 0.10% or less, REM: 0.20% or less, The slab having the austenitic composition further contains, by mass basis, one or more selected from the following: Nb: 1.00% or less, Ti: 1.00% or less, V: 1.00% or less, W: 2.00% or less, Mo: 6.00% or less, N: 0.350% or less, Sn: 0.50% or less, Al: 5.00% or less, Zr: 0.50% or less, Co: 0.50% or less, B: 0.020% or less, Ca: 0.10% or less, REM: 0.20% or less.

12. The method for manufacturing a stainless steel material according to claim 10 or 11, after the heat treatment process, further includes a surface removal process of performing pickling and / or grinding.

13. The method for manufacturing a stainless steel material according to claim 10 or 11, after the heat treatment process, further includes a cold rolling / annealing process of performing cold rolling and then an annealing treatment within 300 seconds.

14. An antibacterial / antiviral component comprising the stainless steel material according to any one of claims 1 to 9.

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