JP6240423B2 - Ferritic stainless steel sheet with excellent antibacterial properties and method for producing the same - Google Patents

Description

  The present invention relates to a ferritic stainless steel plate excellent in antibacterial properties and a method for producing the same, and more specifically, a currant such as a handrail and a faucet, a metal coin, a metal container, a metal tableware, a bathtub, a household electric appliance, a toilet seat, and a medical device The present invention relates to a ferritic stainless steel sheet that is suitably used as a material for sanitary equipment such as appliances and heating equipment and building materials for buildings, and a method for producing the same.

  Ferritic stainless steel sheets have been widely used for household appliances such as kitchen equipment and microwave oven side panels, mainly sinks, but recently, medical instruments such as hand-washing bats from the standpoint of cleanliness, design, and beauty. It has also been used in interior building materials such as handrails. That is, the use of stainless steel sheets is increasing in places where germs are likely to occur or where germs are not preferred. On the other hand, in recent years, there has been a growing tendency to be concerned about the adverse effects on human bodies caused by the propagation of such bacteria, especially for medical equipment and kitchen equipment where cleanliness is essential, and for building materials for many people. Strong antibacterial requirements. From such a flow, attempts have been made to provide antibacterial properties to the ferritic stainless steel itself that is used in sites where these cleanliness is required.

  Examples of such attempts include Patent Document 1 and Patent Document 2. These disclose techniques for providing antibacterial properties by a method in which a resin containing an antibacterial agent is applied and laminated on the surface of stainless steel and a method in which a matrix containing an antibacterial component is plated.

Moreover, as a method of giving antibacterial properties to the stainless steel material itself, Patent Documents 3 to 5 can be cited. In Patent Literature 3 and Patent Literature 4, Cu is eluted in the electrolyte by applying a noble potential to the ferritic stainless steel material or austenitic stainless steel material containing Cu by an alternating electrolytic treatment method, and then a base potential is applied. By doing so, Cu is deposited on the surface of the stainless steel material to provide antibacterial properties.
Moreover, in patent document 5, after polishing finishing the surface of the ferritic stainless steel material, austenitic stainless steel plate, and martensitic stainless steel plate containing Cu, the steel surface layer is subjected to bright annealing or nitric hydrofluoric acid washing. A method of forming a layer in which Cu is concentrated to 3% by mass or more is disclosed.

Recently, antibacterial stainless steel has been used in various applications. For example, ferritic stainless steel is often used for metal coins because of its good workability and low cost performance. Ferritic stainless steel with low raw material costs is advantageous from an economical point of view.
When ferritic stainless steel is applied to a metal coin or the like, softening of, for example, about Hv 190 or less may be required for punching or stamping. In particular, ferritic stainless steel containing Cu for antibacterial properties often has a problem of hardening due to solid solution strengthening or precipitation strengthening.

  For example, Patent Document 6 discloses the Hv hardness of ferritic stainless steel containing 0.66% or more of Cu. For example, 16.87Cr-0.66Cu is Hv171, and 13.57Cr-1.08Cu is Hv166.

  Moreover, as a manufacturing method of Cu containing ferritic stainless steel, patent document 7 is limited to the cooling rate after hot rolling, and is made to cool at 3 degrees C / s or more to the coiling temperature of 500-300 degreeC after hot rolling. Therefore, a technique for controlling the Cu clustering existing in the hot-rolled sheet to a maximum of 5 nm or less and avoiding toughness failure is proposed.

Japanese Patent Laid-Open No. 5-228202 JP-A-6-10191 JP-A-8-60302 JP-A-8-60303 JP-A-11-172380 JP 2003-213378 A International Publication No. 2012/108479

  However, as shown in Patent Document 1 and Patent Document 2, when a resin containing an antibacterial agent is applied to the surface or a plating layer containing an antibacterial component is applied, the surface gloss peculiar to stainless steel is lost. Is called. Therefore, commercial value is lost in applications where surface gloss is required. In addition, the antibacterial resin film and plating layers containing antibacterial components are susceptible to damage due to cracking and chipping during press processing and use, and the antibacterial components elute when exposed to a humid atmosphere. In addition, the appearance is deteriorated and the original antibacterial action is lost.

  There are also problems in the above-mentioned Patent Documents 3 to 5 in which the stainless steel material itself has antibacterial properties. In other words, the alternating electrolytic treatment methods disclosed in Patent Document 3 and Patent Document 4 deposit Cu on the surface of stainless steel by electrodeposition. Therefore, Cu is easily peeled off from the steel surface. For example, if the surface is rubbed with a wire brush, a steel scrubber or the like, the Cu on the surface is scraped and the antibacterial property is lowered.

  In addition, when the present inventors have examined the prior art disclosed that antibacterial properties can be obtained by controlling the surface Cu concentration to a certain value or more as in Patent Document 5, these prior arts have the same plate width within the same plate surface. It has been found that the antibacterial properties can vary greatly in direction. In other words, the antibacterial stainless steel obtained by the method of the prior art is found to have a portion having good antibacterial properties and a portion having a bad antibacterial property on the plate surface, and is used for a final product imparted with antibacterial properties. , It turns out that the yield will deteriorate.

  As described above, the conventionally disclosed technique for causing the stainless steel itself to exhibit antibacterial properties is likely to be deteriorated in antibacterial properties or unsatisfactory in terms of yield.

In addition, when the ferritic stainless steel sheet is required to be softened, it is necessary to control the hardness. The above-described conventional technology related to hardness has the following problems.
The ferritic stainless steel described in Patent Document 6 has a Cu concentration of 0.66 to 1.08% and Hv of 190 or less. However, the ferritic stainless steel described in Patent Document 6 does not satisfy the formula (a) of the present invention, which will be described later, and cannot cope with the case where high corrosion resistance is required in addition to softening. It was.

  Patent Document 7 relates to softening of a cold-rolled material, although the cooling rate from hot rolling to winding is specified to be 3 ° C./s or more in order to control Cu clustering to 5 nm or less and improve toughness. The technology is not disclosed.

As mentioned above, about the Cu containing ferritic stainless steel, the technique which makes antibacterial property and softening compatible is not disclosed until now.
Accordingly, an object of the present invention is to provide a ferritic stainless steel sheet that has both antibacterial properties and softening and a method for producing the same.

  In order to solve the above-mentioned antibacterial problem, the present inventors have intensively studied the difference between a portion having a good antibacterial property and a portion having a bad antibacterial property within the plate surface. As a result, the following knowledge was obtained.

(I) In order to develop antibacterial properties, the Cu maximum concentration of the Cu concentrated layer on the steel surface needs to be at least 10% by mass.
(Ii) It was also found that control of the Cu concentration on the steel surface is a necessary condition for the development of antibacterial properties, but it is not sufficient. That is, according to the evaluation results of the present inventors, even when the maximum Cu concentration on the steel surface was 10% by mass or more, there were cases where the antibacterial property was poor. This means that there are antibacterial expression factors other than the maximum Cu concentration on the steel surface, and the antibacterial variation has increased in the plate surface because they have not been grasped in the past. It was speculated that it was. Therefore, the present inventors conducted an investigation with a view to the component composition of the steel surface layer part in order to investigate the factor, and antibacterial property is Fe, which is the main component of the Cu concentrated layer on the steel surface. It has been found that it is strongly related to the existence state of Cr. Cu in the Cu-enriched layer on the steel surface is a factor that affects antibacterial properties, but it is evaluated that the antibacterial properties are manifested by the dissolution of the Cu from the steel surface and reducing the cell activity of the bacteria. Therefore, it was assumed that the relationship with Fe and Cr existing around Cu in the Cu enriched layer greatly affects the antibacterial properties. In order to stably obtain antibacterial properties, it has been found that it is necessary to further control the Fe / Cr ratio in addition to the conventionally known Cu maximum concentration of the Cu concentrated layer.
(Iii) Further, according to the evaluation results of the present inventors, if the Cu maximum concentration on the steel surface is 18% by mass or more, even if the Fe / Cr ratio is not controlled, there are places where the antibacterial properties are poor. It was not found and sufficient antibacterial properties were obtained.

  Further, in order to soften the antibacterial material (steel plate), the present inventors further studied the influence of heat treatment on the hardness of the Cu-containing ferritic stainless steel plate. Specifically, various studies were made on the solid solution / precipitation form of Cu and the heat treatment (heating / cooling conditions) exerted on them, and the following knowledge was obtained.

(A) From the comparison of the structure of the hard material and the soft material, a large difference was found in the precipitation form of Cu. In the hard material, fine Cu particles of 10 to 100 nm were observed. On the other hand, Cu precipitation was hardly observed in the soft material. The soft material Cu is solid-dissolved in ferrite, but the hardening allowance due to the solid-solution strengthening is small. Therefore, it is considered that the main cause of hardening is due to Cu precipitation strengthening, and the suppression of precipitation is effective for softening.
Note that the size of the Cu precipitate was on a nanometer scale, and the structure was observed using a TEM (transmission electron microscope) suitable for observing the structure of a minute region. As a sample preparation, a thin film sample was prepared by an electropolishing method, and was magnified up to 200,000 times by TEM to observe a Cu precipitate.
(B) Based on 1.5% Cu-containing ferritic stainless steel for softening by suppressing Cu precipitation, heat treatment conditions effective for softening (the following (b-1) and b-2) ) Was found. Moreover, this heat treatment condition is also effective for softening in the ferritic stainless steel having Cu: 0.3 to 1.7% by mass.
(B-1) About finishing annealing, it was found that the solution temperature was 900 to 1100 ° C., and cooling to less than 500 ° C. satisfied the following formula (a) regarding the hardness Hv to soften. A solution temperature of 900 to 1100 ° C. is considered effective for softening because the Cu precipitate is dissolved again. An average cooling rate of 3 ° C./s or more also suppresses Cu precipitation.
Hv ≦ 40 × (Cu−0.3) +135 (a)
Conversely, when the above formula (a) is not satisfied, Cu precipitates are observed at a high density in the steel. Even if it is softened to Hv 190 or less, the deposited Cu reduces the corrosion resistance.
(B-2) Also from the viewpoint of suppressing Cu precipitation, hot-rolled sheet annealing is performed not by batch annealing but by continuous annealing, and is cooled at an average cooling rate of 1 ° C./s or higher up to 400 ° C. after heating at 800 to 1100 ° C. . Thereby, it can soften in the range which satisfy | fills the said (a) formula regarding the hardness which this invention prescribes | regulates.
In addition, most of the Cu precipitates defined in the present invention are sufficiently small, and coarse precipitates of about 10 to 1000 nm are only partially observed. On the other hand, in the prior art, Cu precipitates are controlled to improve antibacterial properties and high temperature characteristics, but the size is almost 10 to 1000 nm and the precipitation density is very high.

The present invention has been obtained based on the above knowledge, and the contents thereof are as follows.
(1) By mass%, C: 0.050% or less, Cr: 10.0 to 30.0%, Si: 2.00% or less, P: 0.030% or less, S: 0.010% or less, Stainless steel sheet containing Mn: 2.00% or less, N: 0.050% or less, Ni: 2.0% or less, and Cu : 0.3-1.7% , the balance being Fe and inevitable impurities A Cu-enriched layer is formed on the surface of the Cu-enriched layer, and the Cu-enriched layer has a Cu maximum concentration Cm of 10.0% by mass or more, and the Fe / Cr ratio at a depth position from the steel sheet surface showing the Cu-enriched concentration Cm There Ri der 2.4 above, ferritic stainless steel sheet cross-sectional hardness and excellent antibacterial satisfying the following equation (a) in Vickers hardness scale of the stainless steel plate.
Hv hardness ≦ 40 × (Cu−0.3) +135 (a)
(2) By mass%, C: 0.050% or less, Cr: 10.0 to 30.0%, Si: 2.00% or less, P: 0.030% or less, S: 0.010% or less, Mn: 2.00% or less, N: 0.050% or less, Ni: 2.0% or less, and Cu0.1% or more 2. In antibacterial properties, containing 0% or less , the balance being Fe and inevitable impurities , a Cu concentrated layer is formed on the surface of the stainless steel plate, and the Cu maximum concentration Cm of the Cu concentrated layer is 18.0% by mass or more Excellent ferritic stainless steel sheet.
(3) the Cu is a 0.3 to 1.7 percent by mass%, the antimicrobial described before SL (2) cross-sectional hardness of the stainless steel sheet satisfying the following formula (b) in Vickers hardness scale Excellent ferritic stainless steel sheet.
Hv hardness ≦ 40 × (Cu−0.3) +135 ( b)
(4 ) The composition according to any one of (1) to (3), further containing one or more of Ti: 0.50% or less and Nb: 1.00% or less in mass%. Ferritic stainless steel plate with excellent antibacterial properties.
( 5 ) In mass%, Sn: 1.00% or less, Mo: 1.00% or less, Al: 1.000% or less, Mg: 0.010% or less, Co: 1.000% or less, V : 0.50% or less, Zr: 0.10% or less, REM: 0.100% or less, La: 0.100% or less, B: 0.0100% or less, Ca: 0.010% or less Or the ferritic stainless steel plate excellent in antibacterial property as described in any one of said (1)-(4) containing 2 or more types.
( 6 ) The ferritic stainless steel sheet having excellent antibacterial properties according to any one of (1) to ( 5 ), which is for metal coins.
( 7 ) A method for producing a stainless steel plate including a hot rolling step, a hot-rolled sheet annealing step, a cold rolling step, a finish annealing step, and a finish pickling step, wherein the stainless steel plate is the above (1) , ( 4) It has the component composition as described in any one of (5) , and the finish pickling step is dipped in a 5.0 to 35.0 mass% sulfuric acid aqueous solution, and 1.0 to 1.0 look containing a pickling step of immersing in an acid solution containing a 15.0 wt% nitric acid and hydrofluoric acid solution of 0.5 to 5.0 wt%, the finish annealing step, at annealing temperature 900 to 1100 ° C. performed, the step of cooling at an average cooling rate of more than 3 ° C. / sec to 400 ° C. the is Dressings containing (1), (4) antimicrobial excellent ferritic stainless steel sheet according to any one of - (6) Manufacturing method.
( 8 ) A method for producing a stainless steel plate including a hot rolling step, a cold rolling step, and a finish pickling step, wherein the stainless steel plate is described in any one of (2) to (5) above. The finish pickling step has a pickling step of immersing in a 5.0 to 35.0% by mass sulfuric acid aqueous solution, 1.0 to 15.0% by mass nitric acid, and 0.5 to 5%. A pickling step of immersing in an acid solution containing 0.0 mass% hydrofluoric acid aqueous solution, and the hot rolling step is performed at a heating temperature of 1150 to 1300 ° C., a finish rolling temperature of 800 to 1000 ° C., and a winding temperature of 600 ° C. The manufacturing method of the ferritic stainless steel plate excellent in antibacterial property as described in any one of said (2)-(6) performed below.
( 9 ) Further, including a hot-rolled sheet annealing step and a finish annealing step , the finish annealing step is performed at an annealing temperature of 900 to 1100 ° C, and includes a step of cooling to 400 ° C at an average cooling rate of 3 ° C / second or more. The method for producing a ferritic stainless steel sheet having excellent antibacterial properties as described in (8 ) above.
( 10 ) In the hot-rolled sheet annealing step, continuous annealing is performed. The continuous annealing is performed at an annealing temperature of 800 to 1100 ° C, and then cooled to 400 ° C at an average cooling rate of 1 ° C / second or more (7 ) Or (9) , a method for producing a ferritic stainless steel sheet having excellent antibacterial properties.

  According to the ferritic stainless steel plate excellent in antibacterial properties of the present invention and the manufacturing method thereof, in order to demonstrate good antibacterial properties throughout the entire plate surface, it is possible to obtain better antibacterial properties than in the past with a good yield. I can do it. Moreover, according to the desirable form of this invention, Cu maximum density | concentration of the steel surface can be highly concentrated so that an example is not seen conventionally, and thereby further favorable antimicrobial property can be obtained. In addition, the Cu content of ferritic stainless steel is limited to 0.3 to 1.7%, and it is possible to sufficiently soften by controlling the conditions of hot-rolled sheet annealing and finish annealing. Can be compatible with antibacterial. The ferritic stainless steel sheet of the present invention having these characteristics can be suitably used as, for example, a metal coin.

FIG. 1 is a graph showing an example of the concentration distribution of C, O and main elements in the depth direction from the surface of the stainless steel according to the present invention. FIG. 2 is a graph showing an example of the concentration distribution of O and main elements in the depth direction from the surface of the stainless steel according to the present invention. FIG. 3 is a graph showing the relationship between the maximum Cu concentration, Fe / Cr ratio, and antibacterial evaluation for the examples and comparative examples of the present invention.

  Hereinafter, the ferritic stainless steel plate excellent in antibacterial properties and a method for producing the same according to an embodiment of the present invention will be described in detail. Unless otherwise noted, the element content% means mass%.

The ferritic stainless steel plate according to the first embodiment contains, by mass%, Cu in a range of 0.1% to 5.0%, a Cu concentrated layer is formed on the surface of the stainless steel plate, and the Cu maximum of the Cu concentrated layer is A ferritic stainless steel sheet having a concentration Cm of 10.0% by mass or more and an Fe / Cr ratio of 2.4 or more at a depth position from the steel sheet surface showing the maximum Cu concentration Cm.
Further, the ferritic stainless steel sheet of the second embodiment contains 0.1% to 5.0% by mass of Cu, and a Cu concentrated layer is formed on the surface of the stainless steel sheet. This is a ferritic stainless steel sheet having a maximum Cu concentration Cm of 18.0% by mass or more.

  In the ferritic stainless steel sheet of the first embodiment or the second embodiment, in mass%, C: 0.050% or less, Cr: 10.0 to 30.0%, Si: 2.00% or less, P: 0.030% or less, S: 0.010% or less, Mn: 2.00% or less, N: 0.050% or less, Ni: 2.0% or less may be contained.

  Moreover, in the ferritic stainless steel plate of 1st Embodiment or 2nd Embodiment, it is the mass%, and also contains 1 type or 2 types of Ti: 0.5% or less and Nb: 1.00% or less. May be.

  Furthermore, in the ferritic stainless steel sheet of the first embodiment or the second embodiment, the mass percentage is Sn: 1.00% or less, Mo: 1.00% or less, Al: 1.000% or less, Mg: 0.010% or less, Co: 1.000% or less, V: 0.50% or less, Zr: 0.10% or less, REM: 0.100% or less, La: 0.100% or less, B: One or more of 0.0100% or less and Ca: 0.010% or less may be contained.

  Here, Cu concentration layer means the area | region which shows Cu density | concentration higher than the average Cu density | concentration in a ferritic stainless steel plate among the surface layers of a ferritic stainless steel plate. Specifically, the ferritic stainless steel plate of this embodiment is an element constituting an element or oxide that is concentrated on the surface by a pickling process to a depth of about 800 nm from the steel plate surface by glow discharge emission analysis (GDS). Is detected. Details of the detection element will be described later. When the concentration distributions of O, Fe, Cr, Si, Mn, Nb, Ti, Al, and Cu are measured, Cu, Fe, and Cr show concentration distributions in the depth direction as shown in FIG. In FIG. 2, the Cu concentration from the surface to a depth of 30 nm is larger than the Cu concentration at a depth of more than 30 nm. In FIG. 2, if the Cu concentration at a depth of more than 30 nm is regarded as the average Cu concentration of the stainless steel plate, the Cu concentrated layer in FIG. 2 is a region from the surface to a depth of 30 nm. The Cu enriched layer may be determined in this way.

  Further, the Cu concentration obtained by GDS analysis is represented by the concentration of Cu with respect to the total amount of O, Fe, Cr, Si, Mn, Nb, Ti, Al, and Cu. In the Cu concentrated layer, the concentration at which the Cu concentration is maximum is defined as the Cu maximum concentration Cm. Furthermore, the ratio of the Fe concentration and the Cr concentration at the depth from the steel plate surface showing the maximum Cu concentration Cm is referred to as the Fe / Cr ratio in this embodiment. In the example of FIG. 2, the maximum Cu concentration Cm is 75.0%, and the Fe / Cr ratio is 2.9.

  Since O, Fe, Cr, Si, Mn, Nb, Ti, Al, and Cu are elements that are concentrated on the surface by the pickling process or elements that constitute oxides, they were used to calculate the Cu concentration.

  Note that P, S, N, and Ni are not considered in the calculation of the Cu concentration because they do not concentrate on the surface by the pickling process and do not form oxides on the surface.

  Ti, Nb, and Al are optional added elements in the present invention, but are elements that constitute oxides, and therefore are considered when calculating the Cu concentration. When these elements are not contained, the Cu concentration is calculated assuming that the concentration of these elements is 0%.

  In addition, since C is a contaminating element, after detection by GDS analysis, Cu concentration is calculated by removing C.

Next, the Cu content of the ferritic stainless steel sheet will be described.
Cu is the most important element for improving antibacterial properties in the ferritic stainless steel sheet of the present embodiment. In this embodiment, it is necessary to set the Cu maximum concentration Cm of the Cu concentrated layer to 10.0% or more. However, when the Cu content of the steel is less than 0.1%, the production of this embodiment described later is performed. Even if the method is applied, a Cm value of 10.0% or more cannot be obtained. Therefore, the lower limit was made 0.1%. On the other hand, if the Cu content is too large, cracking of the slab occurs during the production process, so the upper limit was made 5.0% or less. Preferably it is 0.1-1.7%, Most preferably, it is 0.2-1.5%.

  In order to obtain antibacterial properties in this embodiment, it is necessary to strictly control the element distribution of the steel surface layer. First, the Cu maximum concentration Cm of the Cu concentrated layer on the steel surface needs to be 10.0% or more. When it is less than 10.0%, antibacterial properties are not exhibited even if other regulations are satisfied. Preferably it is 11.0% or more, More preferably, it is 18.0% or more. On the other hand, no matter how high the maximum Cu concentration Cm does not adversely affect antibacterial properties, the upper limit is not specified.

Moreover, as a result of examining the relationship between various antibacterial properties and the steel surface layer state, it is necessary to appropriately control the presence state of Fe and Cr, which are main components of the Cu concentrated layer of the steel surface layer, according to the Cu maximum concentration Cm. I discovered that. Therefore, the Cu maximum concentration Cm and the Fe / Cr ratio will be further described with reference to the graph of FIG.
FIG. 3 shows test numbers in Tables 2 to 15 of Examples described later. Among the data of 1 to 551, the Cu maximum concentration Cm: around 5 to 40% by mass and the data of Fe / Cr ratio: around 1 to 6 are extracted and plotted, and the Cu maximum concentration Cm, Fe It is a graph which shows the result of having investigated the relationship with / Cr ratio and antibacterial evaluation. In the graph of FIG. 3, “◯” indicates that the antibacterial property is excellent (Example of the present invention), “●” indicates that the antibacterial property is particularly excellent (Invention example), and “×” indicates that the antibacterial property is excellent. What was inferior (this invention comparative example) is shown.

(A) When Cu maximum concentration Cm is 10.0% or more and less than 18.0% (stainless steel plate of the first embodiment)
In the ferritic stainless steel sheet of the first embodiment, the Fe / Cr ratio needs to be 2.4 or more. As shown in FIG. 3, when the Fe / Cr ratio is less than 2.4, antibacterial properties are not exhibited even if the Cu maximum concentration Cm is 10.0% or more. The reason for this is unknown, but according to the inventors' estimation, the Fe / Cr ratio becomes 2.4 or more, the bond between Fe and Cr becomes unstable, and the Cu in the Cu concentrated layer is also unstable. It is thought that it becomes. Cu is an element that is less oxidized than Fe and Cr at room temperature, that is, does not like the bond with oxygen. When Fe and Cr are in an unstable state, oxygen bonded to Fe and Cr is released, so that the amount of oxygen around Cu increases. Therefore, it is considered that Cu, which dislikes bonding with oxygen, easily dissolves in water as ions from the steel surface. Cu dissolved as ions reduces the cell activity of the fungus, and thus exhibits antibacterial properties. Therefore, it is thought that antibacterial expression may be achieved by setting the Fe / Cr ratio of the steel surface layer within the above range. The Fe / Cr ratio is more preferably 2.6 or more and 9.5 or less, and further preferably 3.0 or more and 9.0 or less. In addition, what is necessary is just to control pickling conditions in the manufacturing method of this embodiment mentioned later, in order to make Cu maximum density | concentration Cm 10.0% or more and to make Fe / Cr ratio 2.4 or more.

(B) When Cu maximum concentration Cm is 18.0% or more (stainless steel plate of the second embodiment)
In the ferritic stainless steel sheet of the present invention, antibacterial properties are further improved by increasing the Cu maximum concentration Cm. Specifically, when the Cu maximum concentration Cm is controlled to 18.0% or more as in the ferritic stainless steel plate of the second embodiment, the antibacterial property is further improved. As apparent from the graph of FIG. 3, when the Cu maximum concentration Cm is higher than 18.0% as compared with the first embodiment, it is not necessary to control the Fe / Cr ratio. The reason for this is unknown, but according to the inventors' estimation, when the Cu maximum concentration Cm is 18.0% or more, the Cu concentration of the Cu concentrated layer on the steel surface layer is increased while the Fe concentration and the Cr concentration are increased. This is considered to be because the influence of Fe or Cr in the Cu concentrated layer is reduced. Therefore, regardless of the Fe / Cr ratio, Cu in the Cu-concentrated layer is presumed to exhibit antibacterial properties because it dissolves into the water as ions from the steel surface and reduces the cell activity of the fungus.

  In addition, what is necessary is just to control rolling conditions with pickling conditions in the manufacturing method of this embodiment mentioned later in order to make Cu maximum density | concentration Cm 18.0% or more. In addition, when there is too much Fe in the steel surface layer, the corrosion resistance of the ferritic stainless steel sheet is reduced, so Fe / Cr is preferably 10.0 or less. On the other hand, if there is too little Fe in the steel surface layer, Cr that is relatively abundant on the steel surface is likely to be oxidized, so Fe / Cr is preferably 0.4 or more. The preferable range of Fe / Cr is 0.4-10.0, More preferably, it is 0.5-9.5.

(Softening of ferritic stainless steel sheet)
As described above, in addition to the antibacterial expression by Cu control on the steel surface, in the case of softening, it is effective to suppress Cu precipitation in finish annealing. Hereinafter, specific conditions for achieving softening in the ferritic stainless steel plates of the first and second embodiments will be described.
First, in order to achieve both antibacterial properties and softening, the Cu content is preferably set to 0.3 to 1.7%. If the Cu content is less than 0.3%, it is well below the Cu solid solubility limit, so that hardening due to Cu precipitation hardly occurs. On the other hand, if the C content exceeds 1.7%, even if Cu precipitation is suppressed, it is difficult to achieve the softening defined in the present invention because the hardening allowance due to the solid solution strengthening of Cu is large.
The precipitation form of Cu is 10 to 100 nm granular or rod-like, although it is affected by the Cu content and the like. Hard stainless steel sheets are characterized by a high Cu precipitation density, although the size of Cu precipitates varies. On the other hand, a soft stainless steel plate has a low Cu precipitation density and a small precipitation size. Therefore, Cu precipitation was considered as the main factor of hardening. In order to confirm this, a re-heat treatment was performed using a hard stainless steel plate as a raw material under the conditions specified in the present invention, and the structures before and after the heat treatment were compared. As a result, even with the same component, there was a difference that the soft material had a smaller Cu precipitation density and a smaller Cu precipitation size than the hard material.
Moreover, it is important for Cu precipitation control for such softening to re-dissolve Cu and not to precipitate Cu as much as possible in the cooling process. Factors related to this include solution temperature and cooling rate, and softening was achieved by manufacturing according to hot-rolled sheet annealing conditions and finish annealing conditions described later.
The cross-sectional hardness of the soft stainless steel plate of the present invention satisfies the following formula (a) on the Vickers hardness scale. The formula (a) is a result of various Vickers hardness measurement results plotted on a graph in which each axis is Cu concentration and Vickers hardness, and each plot is classified according to the corrosion resistance evaluation result, and Vickers hardness (Hv hardness, (Also referred to as Hv) is 190 or less and can be derived as a range having corrosion resistance. When the formula (a) is not satisfied, even if Hv is 190 or less, the corrosion resistance is deteriorated. This is presumably due to excessive precipitation of Cu.
Hv hardness ≦ 40 × (Cu−0.3) +135 (a)
In addition, "Cu" in (a) Formula shows content (mass%).

  Next, other chemical components of the ferritic stainless steel plates of the first and second embodiments will be described. The essential feature of the present invention is the control of the element concentration distribution in the surface layer of the steel sheet as described above. Hereinafter, the corrosion resistance, workability and manufacturability, etc., including the component composition of steel that can be used when considering elements other than antibacterial properties, in solving the problems of the present invention as an antibacterial stainless steel plate, The component composition is not limited to the following components.

  C is an impurity element that is inevitably mixed in from the dissolved raw material and the like. If the amount of C exceeds 0.050%, the toughness and cold workability of steel deteriorate, so the upper limit is preferably made 0.050% or less. The C amount is preferably 0.040% or less, and more preferably 0.020% or less. In addition, excessively reducing the amount of C leads to an increase in manufacturing cost, so 0.001% or more is preferable.

  Cr needs to be added in an amount of 10.0% or more in order to improve corrosion resistance and high-temperature oxidation resistance. On the other hand, if the Cr content exceeds 30.0%, the formability may deteriorate, so the range of 10.0 to 30.0% is preferable. The amount of Cr is preferably 12.0 to 27.0%, and most preferably 13.0 to 25.0%.

  Si acts as a deoxidizing element and improves high-temperature oxidation resistance. In order to obtain this effect, Si may be contained by 0.01% or more. However, when a large amount of Si is added, the steel sheet may become hard and ductility may deteriorate. Therefore, the Si content is preferably 2.00% or less. The amount of Si is preferably 0.01 to 1.50%, and more preferably 0.10 to 1.20%.

  P is an element inevitably mixed from the raw material. P is a grain boundary segregation element, and if it is contained too much, the cold workability and toughness of the steel sheet are deteriorated.

  S, like P, is an element inevitably mixed from the raw material. Since S is an element that degrades corrosion resistance and moldability, it is preferable to make it 0.010% or less.

  Mn acts as a deoxidizer. Further, grain boundary embrittlement due to segregation of S to the crystal grain boundary can be prevented. In order to obtain these effects, Mn may be contained by 0.10% or more. However, if the amount is too large, the cold workability of the steel sheet is lowered. Therefore, the Mn content should be 2.00% or less. The amount of Mn is preferably 0.10 to 1.80%, more preferably 0.12 to 1.50%.

  Since N deteriorates moldability when the content increases, it is preferable to make N 0.05% or less. The N amount is preferably 0.040% or less, and more preferably 0.030% or less. On the other hand, excessively reducing the amount of N leads to an increase in manufacturing cost, so 0.001% or more is preferable.

  Ni improves the hot workability of the ferritic stainless steel sheet of the present embodiment. In order to obtain this effect, Ni may be contained by 0.1% or more. However, if Ni is excessively contained, the stability of ferrite is reduced, so the Ni content is preferably 2.0% or less. The amount of Ni is preferably 1.5% or less, and more preferably 1.2% or less.

  The ferritic stainless steel plates of the first and second embodiments are composed of Fe and impurities inevitably mixed in addition to the above-described component elements.

  Further, the ferritic stainless steel plates of the first and second embodiments may further contain Ti and Nb as optional components. Since Ti and Nb are carbonitride-forming elements, Ti and Nb are elements that improve formability, and one or both of them may be contained as necessary. In order to obtain the effect of improving the formability, 0.002% or more of Ti and 0.002% or more of Nb may be contained. However, excessive addition of Ti and Nb leads to deterioration of workability and toughness. Therefore, when these are contained, Ti is preferably 0.50% or less and Nb: 1.00% or less. More preferably, Ti: 0.45% or less, Nb: 0.95% or less, still more preferably Ti: 0.40% or less, Nb: 0.90% or less.

  Furthermore, the ferritic stainless steel sheets of the first and second embodiments may contain one or more elements shown below as required.

  Sn is an element effective for improving the corrosion resistance. In order to obtain this effect, 0.005% or more of Sn may be contained. However, if it exceeds 1.00%, the toughness deteriorates, so the content is made 1.00% or less. The Sn amount is preferably 0.60% or less, and more preferably 0.50% or less.

  Mo is an effective element for improving the corrosion resistance. In order to obtain this effect, Mo may be contained by 0.002% or more. However, if it exceeds 1.00%, toughness deteriorates, so it is made 1.00% or less. The amount of Mo is preferably 0.70% or less, and more preferably 0.50% or less.

  Al, like Mo, exhibits an effect of improving the corrosion resistance. In order to obtain this effect, 0.002% or more of Al may be contained. However, if it is contained excessively exceeding 1.000%, manufacturability and workability are lowered. The amount of Al is preferably 0.300% or less, and more preferably 0.100% or less.

  Mg forms Mg oxide in molten steel and acts as a deoxidizer, and also acts as a crystallization nucleus of TiN, and can finely produce a ferrite phase during solidification. By making the solidification structure finer, it is possible to prevent surface defects of the steel sheet due to the coarse solidification structure, and to improve workability, it is contained as necessary. In order to obtain this effect, 0.001% or more of Mg may be contained. However, if it exceeds 0.010% and is contained excessively, manufacturability and workability are lowered. The amount of Mg is preferably 0.009% or less, and more preferably 0.008% or less.

  Co exhibits the effect of improving the corrosion resistance like Mo. In order to obtain this effect, 0.002% or more of Co may be contained. However, if it is contained excessively exceeding 1.000%, it leads to an increase in alloy cost and a decrease in manufacturability. The amount of Co is preferably 0.400% or less, and more preferably 0.200% or less.

  V exhibits the effect | action which forms carbonitride and improves the intensity | strength of steel materials. In order to obtain this effect, V may be contained by 0.002% or more. However, if it exceeds 0.50% and it contains excessively, manufacturability and workability will be reduced. The amount of V is preferably 0.20% or less, and more preferably 0.10% or less.

  Zr forms carbonitride like V, and exhibits the effect | action which improves the intensity | strength of steel materials. In order to obtain this effect, Zr may be contained by 0.003% or more. However, if it exceeds 0.10% and is contained excessively, manufacturability and workability are lowered. The amount of Zr is preferably 0.08% or less, more preferably 0.05% or less.

  REM, La, B, and Ca are all elements that affect the form of S in the steel, and are included as necessary to improve hot workability. In order to obtain this effect, REM: 0.003% or more, La: 0.002% or more, B: 0.0002% or more, Ca: 0.002% or more may be contained. The upper limit of these elements is REM: 0.100% or less, La: 0.100% or less, B: 0.0100% or less, Ca: 0.010% or less, and preferable upper limits are REM: 0.00. 080% or less, La: 0.095% or less, B: 0.0095% or less, Ca: 0.009% or less, and more preferable ranges are REM: 0.050% or less, La: 0.050%, respectively. Hereinafter, B: 0.0060% or less, Ca: 0.007% or less. In addition, REM as used in the field of this invention means Sc, Y, and the element of atomic number 58-71.

  As described above, the ferritic stainless steel sheet of the present invention described above can be suitably applied to coin applications that require antibacterial properties. Further, the softened ferritic stainless steel sheet of the present invention can be applied even when further softening is required for coin applications.

  Next, the manufacturing method of the ferritic stainless steel of this embodiment is demonstrated.

  In order to manufacture the ferritic stainless steel of the first embodiment, a hot rolling process, a cold rolling process, and a finish pickling process are sequentially performed on the stainless steel having the above component composition. Here, in the finishing pickling step, the pickling step immersed in a 5.0 to 35.0% by mass sulfuric acid aqueous solution, 1.0 to 15.0% by mass nitric acid and 0.5 to 5.0% by mass. A pickling step of immersing in an acid solution containing a hydrofluoric acid aqueous solution. The pickling step of immersing in an aqueous sulfuric acid solution and the pickling step of immersing in an acid solution containing nitric acid and an aqueous hydrofluoric acid solution may be performed in this order, or in reverse order.

  Moreover, in order to manufacture the ferritic stainless steel of the second embodiment, in addition to the manufacturing conditions of the first embodiment, in the hot rolling step, a heating temperature of 1150 to 1300 ° C. and a finish hot rolling temperature of 800 to 1000 ° C. The hot rolling is performed under the condition where the coiling temperature is 600 ° C. or less.

  The reason for pickling the surface of the stainless steel sheet is to remove the scale film adhering by heat treatment and to increase the Cu concentration on the surface by preferentially pickling and dissolving Fe and Cr. Conventionally, various acid solutions have been proposed as such acids. However, when the present inventors repeatedly conducted the experiment, when the sulfuric acid pickling step with a specific concentration and the nitric hydrofluoric acid pickling step with a specific concentration were performed, compared with the case of using another acid solution. It has been found that the scale removal efficiency and the promotion of Cu concentration in the steel surface layer are significantly improved. Moreover, in this case, the other surface characteristics described above were also obtained, and it was found that antibacterial properties were exhibited. The production method of the present invention based on this knowledge makes it possible to reliably obtain stainless steel having excellent antibacterial properties.

  The acid solution used for pickling must be under the following conditions. That is, the aqueous sulfuric acid solution needs to have a concentration in the range of 5.0 to 35.0% by mass. When the concentration of the sulfuric acid aqueous solution is less than 5.0% by mass, the dissolution reaction of the scale and the steel by the aqueous acid solution hardly proceeds, so that Cu may not be concentrated on the surface. On the other hand, when the concentration of the sulfuric acid aqueous solution exceeds 35.0% by mass, the dissolution reaction with the acid aqueous solution proceeds remarkably, resulting in significant unevenness due to dissolution. This level of unevenness results in a streak or uneven pattern on the product plate, thus reducing product quality. Therefore, the concentration of the sulfuric acid aqueous solution is preferably 6.0 to 34.0% by mass, and more preferably 8.0 to 33.0% by mass.

  The nitric hydrofluoric acid aqueous solution needs to have a nitric acid concentration of 1.0 to 15.0 mass% and a hydrofluoric acid concentration of 0.5 to 5.0 mass%. When the nitric acid concentration is less than 1.0% by mass, since the dissolution reaction hardly proceeds as in the case of sulfuric acid, Cu does not concentrate on the surface. On the other hand, when the nitric acid concentration exceeds 15.0% by mass, the dissolution reaction proceeds remarkably and the product quality is lowered.

  Also for hydrofluoric acid, for the same reason as sulfuric acid and nitric acid, concentrations of less than 0.5% by mass and more than 5.0% by mass are not suitable as aqueous solution concentrations.

  Preferably, the nitric acid concentration is 1.2 to 14.5% by mass, the hydrofluoric acid concentration is 0.7 to 4.7% by mass, and more preferably the nitric acid concentration is 1.5 to 14.0% by mass. The concentration is 0.9 to 4.5% by mass.

  In addition, the time for immersing the steel sheet in these acid solutions is appropriately selected within a range of 10 to 1000 seconds for each of the sulfuric acid aqueous solution and the nitric hydrofluoric acid aqueous solution in consideration of the Cu maximum concentration Cm and other physical properties in the Cu concentrated layer. That's fine. Also, the temperature of each acid aqueous solution is not particularly limited as long as it is a general condition. For example, what is necessary is just to carry out in the range of 40-80 degreeC.

  A feature of the manufacturing method of the present embodiment is that it has been found that the physical properties of the steel surface layer can be strictly controlled within the above-described range by finishing pickling with an aqueous sulfuric acid solution and an aqueous nitric hydrofluoric acid solution. Therefore, for example, the pickling order of the sulfuric acid aqueous solution and the nitric hydrofluoric acid aqueous solution can be reversed. In addition to the sulfuric acid aqueous solution and the nitric hydrofluoric acid aqueous solution, third and fourth pickling treatments may be performed as long as the physical property range of the ferritic stainless steel plate of the present embodiment is not deviated.

Next, the hot rolling process will be described.
As a result of investigations by the present inventors, it has been found that the surface layer Cu is concentrated in the hot rolling stage by strictly controlling various conditions of the hot rolling process. Therefore, it was found that by subjecting the cold-rolled sheet with the surface Cu concentration concentrated by hot rolling to the finish pickling, the surface Cu concentration can be further increased and the antibacterial properties can be further improved.

  Specifically, when hot rolling, the maximum temperature of Cu is obtained by performing heating at 1150 to 1300 ° C., finishing temperature of 800 to 1000 ° C., winding temperature of 600 ° C. or less, and finishing pickling under the above-mentioned conditions. It was found that Cm can be increased to 18.0%.

  In order to increase the Cu maximum concentration by pickling finishing after the hot rolling process, it is important to increase the Cu concentration in the surface layer during hot-rolled sheet production and to make Cu present in a solid solution state. When the heating temperature is 1150 ° C. or higher, Cu precipitates slightly remaining in the slab can be re-dissolved in a normal holding time. However, if it exceeds 1300 ° C., it causes surface flaws due to grain coarsening, and heating energy is useless.

  Next, the range of finishing temperature and winding temperature will be described. When the ferritic stainless steel sheet of the present embodiment is manufactured by a conventional hot-rolled sheet manufacturing process, Cu contained in the steel is produced as a Cu precipitate during cooling, so the amount of Cu dissolved in the steel is reduced. To do. On the other hand, the finishing temperature at the time of hot-rolled sheet production is set to 800 to 1000 ° C., normal equipment such as water spraying is used, the hot-rolled sheet is cooled relatively quickly, and wound at 600 ° C. or less to obtain Cu precipitates. Was not generated. The hot-rolled stainless steel sheet thus obtained has been found to be a cold-rolled sheet having a high Cu concentration even with normal pickling, and the maximum Cu concentration Cm is 18.0 by pickling as defined above. It turned out that it becomes a ferritic stainless steel plate which has Cu of the high concentration which is not more than% as a surface layer.

  The reason for this is unknown, but the present inventors presume as follows. During slab heating at 1150 to 1300 ° C., Fe and Cr that are easily oxidized compared to Cu are preferentially oxidized. For this reason, Cu that has not been oxidized remains immediately below the scale, so that the surface Cu concentration also increases. Furthermore, by setting the finish hot rolling temperature to 800 to 1000 ° C. and winding at 600 ° C. or less, the Cu precipitate temperature range is passed in a short time, and Cu precipitation is suppressed. Therefore, a hot rolled stainless steel sheet having a high surface Cu concentration and no Cu precipitates can be produced.

  Moreover, if the steel plate temperature is 600 ° C. or less, the Cu diffusion rate in the steel is slowed and the formation of Cu precipitates is suppressed, but Cu precipitates are generated when held for a long time, so that the finish It is preferable to perform water injection winding after hot rolling and to cool the coil with water.

  More preferable conditions in the hot rolling step are heating temperature above 1200 ° C., finish rolling temperature: above 800 ° C., winding temperature: 600 ° C. or less, most preferably heating temperature of 1250 to 1300 ° C., finishing rolling temperature, respectively. : 900 to 1000 ° C, winding temperature: 500 ° C or lower.

  Moreover, the stainless steel plate having antibacterial properties according to the present embodiment described above is annealed at 900 to 1100 ° C. under the condition of the finish annealing step after cold rolling, and 400 ° C. at an average cooling rate of 3 ° C./second or more. It can be made soft to below the hardness prescribed | regulated by this invention by cooling to.

If the solution temperature (finish annealing temperature) is equal to or higher than the temperature at which Cu can be dissolved, the influence on hardness is small. Therefore, in order to grasp the influence of the solution temperature on the hardness, solution heat treatment (finish annealing) was performed at various temperatures within a range of 700 to 1100 ° C., and then water cooling was performed. As a result, it was found that the hardness hardly changed at a solution temperature of 900 ° C. or higher. Further, the effect of the solution temperature was less than Hv10.
Moreover, it becomes Hv hardness which satisfy | fills the following formula (a) prescribed | regulated by this invention by making the average cooling rate at the time of cooling after solution heat treatment into 3 degrees C / second or more, and it can soften.
Hv hardness ≦ 40 × (Cu−0.3) +135 (a)

In order to grasp the influence of the average cooling rate on the hardness, it was cooled by various cooling methods after the solution heat treatment at 900 to 1100 ° C. As a result, it turned out that it softens by cooling to the cooling end temperature mentioned later with the average cooling rate of 3 degrees C / sec or more. The average cooling rate of 3 ° C./second or more can be controlled by ordinary equipment such as gas blowing. Moreover, Cu precipitation tends to be suppressed as the cooling rate increases, and is effective for softening. Therefore, the upper limit of the average cooling rate is not particularly set, and may be appropriately determined in consideration of the performance of the cooling equipment to be used.

In the cooling after the solution heat treatment, the cooling end temperature is 400 ° C. or less.
In order to grasp the influence of the cooling end temperature on the hardness, cooling is controlled to various temperatures at a cooling rate of 3 ° C./second or more after the solution heat treatment at 900 to 1100 ° C., and then natural cooling (average cooling rate of 3 ° C. / Less than a second). As a result, when the cooling end temperature was 400 ° C. or lower, it was possible to soften to Hv hardness satisfying the above formula (a) defined by the present invention.
On the other hand, when the cooling rate end temperature was 500 to 700 ° C., significant hardening was confirmed. In this hardened specimen, Cu deposits of 10 to 100 nm were observed. From this, the temperature range of 500 to 700 ° C. is considered as a nose temperature range for Cu precipitation, and it is effective for softening to quickly pass the Cu precipitation nose temperature range, that is, to increase the cooling rate.
From the above, more preferable conditions in the finish annealing step according to the present embodiment are heating temperature (finish annealing temperature): 910 to 1080 ° C., cooling completion temperature: 390 ° C. or less, average cooling rate: 3.2 ° C./second or more. Most preferably, the heating temperature is 920 to 1060 ° C., the cooling completion temperature is 380 ° C. or less, and the average cooling rate is 3.5 ° C./second or more.

In order to soften, by further adding hot-rolled sheet annealing conditions after hot rolling, it becomes a more preferable form by suppressing Cu precipitation.
By prescribing the hot-rolled sheet annealing conditions, the size of the Cu precipitates is controlled to a size that can be solutionized by finish annealing, which is a subsequent process. In addition, hot-rolled sheet annealing is performed not by batch annealing but by continuous annealing. After heating to 800 to 1100 ° C., cooling to 400 ° C. is performed at an average cooling rate of 1 ° C./second or more.
If the heating temperature is less than 800 ° C., recrystallization is insufficient, while if it exceeds 1100 ° C., the crystal grains become coarse, which adversely affects the subsequent productivity. The cooling end temperature was set to 400 ° C. in order to suppress Cu precipitation. At an average cooling rate of 1 ° C./second or less, Cu precipitates are coarsened, and Cu precipitates cannot be sufficiently solutioned even by subsequent finish annealing.
Preferred conditions in the hot-rolled sheet annealing step are heating temperature 810 to 1090 ° C., cooling temperature: 390 ° C. or less, average cooling rate: 1.1 ° C./second or more, most preferably heating temperature 820 to 1080 ° C., cooling respectively. Temperature: 380 ° C. or lower, average cooling rate: 1.2 ° C./second or higher.

  As described above, according to the ferritic stainless steel plate having excellent antibacterial properties according to the first and second embodiments and the manufacturing method thereof, good antibacterial properties are exhibited over the entire area of the plate surface. Good antibacterial properties can be obtained with good yield. In addition, according to the ferritic stainless steel sheet and the manufacturing method thereof according to the second embodiment, the maximum Cu concentration on the steel surface can be increased to an unprecedented level, thereby obtaining even better antibacterial properties. I can do it. In order to achieve both antibacterial properties and softening, the Cu content of the Cu-containing ferritic stainless steel is preferably 0.3 to 1.7%.

Example 1
Steels having the compositions shown in Table 1A and Table 1B are melted by vacuum melting, hot-rolled at a heating temperature of 1100 to 1350 ° C and a finishing hot rolling temperature of 700 to 1020 ° C, and at a winding temperature of 400 to 700 ° C. Winded up. Next, hot-rolled sheet annealing is performed in the atmosphere at 980 ° C. for 10 seconds, and after normal pickling, cold rolling is performed and finish annealing is performed, and a sheet thickness of 1.0 to 1.3 mm is cooled. It was a sheet. Then, it pickled with 40-80 degreeC sulfuric acid and nitric hydrofluoric acid, and manufactured the ferritic stainless steel plate. In Tables 1A and 1B, the column labeled “-” indicates that measurement was not performed because the element was not added.

  The following evaluation was performed about the obtained ferritic stainless steel sheet. In this example, in order to confirm whether or not good antibacterial properties were expressed in the entire plate surface, evaluation was performed covering the plate width direction in which a difference in antibacterial properties occurred. That is, a large number of 50 mm square test pieces were cut out in the plate width direction at arbitrary points in the length direction of each steel plate. And all these test pieces were evaluated.

(Measurement of surface component concentration)
For each of the above test pieces, the C, O, Fe, Cr, Si, Mn, Nb, Ti, Al, and Cu concentration distribution from the steel surface to about 800 nm was measured by glow discharge emission analysis (GDS). The Cu, Fe, and Cr concentrations in the Cu enriched layer changed in the depth direction as shown in the example of FIG. Next, when the concentration distribution was calculated again excluding C, it changed in the depth direction as in the example shown in FIG. 2, and it was found that a Cu concentrated layer was formed on the stainless steel surface. Further, the maximum Cu concentration of the Cu concentrated layer was Cm. Furthermore, the Fe / Cr ratio obtained from the ratio of the Fe concentration and the Cr concentration at the depth where the maximum Cu concentration Cm was obtained was also obtained.
FIG. 2 is an example of the steel of the present invention, and the maximum Cu concentration Cm was 75.0%. Moreover, Fe / Cr ratio calculated from the density | concentration of Fe and Cr in the position where Cu maximum density | concentration Cm is obtained was 2.9.

(Antimicrobial evaluation)
Antibacterial evaluation was in accordance with ISO 22196. 1 ml of the test bacterial solution was applied to each of the above-mentioned test pieces, and after standing at 25 ° C. for 36 hours, the bacterial solution was wiped off and shaken out into the diluted solution. A predetermined amount of the shake-out solution was mixed with the measurement medium and cultured at 35 ° C. for 24 hours, and the steel having an antibacterial activity value of 2.0 or more was evaluated as having excellent antibacterial properties to suppress the growth of bacteria. . In addition, when the antibacterial activity value was 4.0 or more, it was evaluated as having particularly excellent antibacterial properties. In the table, there is only one numerical value for each steel material, but among the measured specimens, the one with the lowest antibacterial property in the antibacterial evaluation is described, and the result of the surface component concentration The measurement result of the test piece with the lowest antibacterial property is shown. This is because if the antibacterial activity is the lowest in the plate width direction of each steel material and the antibacterial activity value is 2.0 or more, the entire plate surface of the steel material is antibacterial.

The results of evaluation are shown in Table 2-15. Tables 2 to 8 (Test Nos. 1 to 276) show the evaluation results when pickling in this order using nitric hydrofluoric acid as the first pickling solution and sulfuric acid as the second pickling solution. Tables 9 to 15 (Test Nos. 277 to 551) show that the pickling order is changed, the first pickling solution is sulfuric acid, and the second pickling solution is nitric hydrofluoric acid. It is an evaluation result. In Tables 2 to 15 , the column labeled “-” represents that the processing was not performed.

Test No. manufactured by the manufacturing method satisfying the hot rolling conditions specified by the method of the present invention. 181-206, No. About 457-481, maximum Cu density | concentration Cm exceeded 18%, and the especially outstanding antimicrobial property was expressed (antimicrobial evaluation:-).

  On the other hand, test No. which is a comparative example manufactured under conditions deviating from the pickling conditions defined by the method of the present invention. 207-276, no. In the steel sheets of 482 to 551, the antibacterial activity value was less than 2.0 (antibacterial evaluation: x). In particular, test no. 207-221 and test no. In the steel plates of 497 to 511, only the nitric hydrofluoric acid treatment was performed as the pickling treatment, so that the maximum Cu concentration Cm was less than 10%, and the antibacterial property was lower than that of the present invention example.

(Example 2)
Next, in order to confirm the softening effect of the present invention, the conditions of the hot-rolled sheet annealing step and the finish annealing step were changed to the conditions shown in Table 16 when manufacturing some of the steel types in Tables 1A and 1B.
In Example 2, the hot rolling step, the cold rolling step, and the finish pickling step were performed under conditions within the scope of the present invention.
About each steel plate after manufacture, cross-sectional hardness and corrosion resistance were evaluated. In addition, the cross-sectional hardness measured the average value by performing N5 of the Vickers hardness test in the center of board thickness. Corrosion resistance was tested in accordance with JISZ2371 by continuously spraying 308K, 5% NaOH solution for 72 hours, and the rusting condition was observed.
The evaluation results are shown in Table 16 .

In the example which does not satisfy the preferable finish annealing conditions of the present invention, the cross-sectional Hv hardness exceeded 190, or the result of not satisfying the formula (a) was obtained.
On the other hand, Test No. which is an example of the present invention produced under the preferable finish annealing condition of the present invention. The Hv hardness of the steel plates 552, 555, 556, 559, 560, 563, 564, 567, 568, 571, 572, 575, 576, 579, 580, 583 is 190 or less, and the formula (a) Met. As a result, as compared with other examples that deviated from the preferable production conditions of the present invention, dot-like rusting was remarkably reduced, and the corrosion resistance was further improved. From this result, it was found that a steel sheet applicable to softening and high corrosion resistance, for example, for coins can be manufactured under the preferable manufacturing conditions of the present invention.

Claims (10)

% By mass
C: 0.050% or less,
Cr: 10.0 to 30.0%,
Si: 2.00% or less,
P: 0.030% or less,
S: 0.010% or less,
Mn: 2.00% or less,
N: 0.050% or less,
Ni: 2.0% or less, and Cu : 0.3-1.7% , the balance consists of Fe and inevitable impurities ,
A Cu concentrated layer is formed on the surface of the stainless steel plate, the Cu maximum concentration Cm of the Cu concentrated layer is 10.0% by mass or more, and Fe / Fe at a depth position from the steel plate surface showing the Cu maximum concentration Cm. Ri der Cr ratio is 2.4 or more,
A ferritic stainless steel sheet having excellent antibacterial properties in which the cross-sectional hardness of the stainless steel sheet satisfies the following formula (a) on the Vickers hardness scale .
Hv hardness ≦ 40 × (Cu−0.3) +135 (a) % By mass
C: 0.050% or less,
Cr: 10.0 to 30.0%,
Si: 2.00% or less,
P: 0.030% or less,
S: 0.010% or less,
Mn: 2.00% or less,
N: 0.050% or less,
Ni: 2.0% or less, and Cu : 0.1% or more 2 . Containing 0% or less , the balance consisting of Fe and inevitable impurities ,
A ferritic stainless steel plate having excellent antibacterial properties, wherein a Cu concentrated layer is formed on the surface of the stainless steel plate, and the Cu maximum concentration Cm of the Cu concentrated layer is 18.0% by mass or more. The ferritic stainless steel having excellent antibacterial properties according to claim 2 , wherein the Cu is 0.3 to 1.7% by mass and the cross-sectional hardness of the stainless steel plate satisfies the following formula ( b ) on a Vickers hardness scale. steel sheet.
Hv hardness ≦ 40 × (Cu−0.3) +135 ( b ) In mass%,
Ti: 0.50% or less,
Nb: 1.00% or less,
The ferritic stainless steel sheet excellent in antibacterial property according to any one of claims 1 to 3 , comprising one or more of the following. In mass%,
Sn: 1.00% or less,
Mo: 1.00% or less,
Al: 1.000% or less,
Mg: 0.010% or less,
Co: 1.000% or less,
V: 0.50% or less,
Zr: 0.10% or less,
REM: 0.100% or less,
La: 0.100% or less,
B: 0.0100% or less,
Ca: 0.010% or less,
The ferritic stainless steel plate excellent in antibacterial property as described in any one of Claims 1-4 containing 1 type (s) or 2 or more types. The ferritic stainless steel sheet having excellent antibacterial properties according to any one of claims 1 to 5 , which is for metal coins. A method for producing a stainless steel sheet including a hot rolling step, a hot rolled sheet annealing step, a cold rolling step, a finish annealing step, and a finish pickling step,
The stainless steel plate has the component composition according to any one of claims 1 , 4 , and 5 ,
The pickling step wherein the finishing pickling step is immersed in a 5.0 to 35.0% by weight sulfuric acid aqueous solution;
1.0 to 15.0 saw including a pickling step of immersing in an acid solution containing a mass% of hydrofluoric acid solution of nitric acid and 0.5 to 5.0 wt%,
The finish annealing step is performed at an annealing temperature of 900 to 1100 ° C., antimicrobial according the step of cooling at an average cooling rate of more than 3 ° C. / sec to 400 ° C. to any one of claims 1,4～6 is Dressings containing Of ferritic stainless steel sheet with excellent properties. A method for producing a stainless steel sheet including a hot rolling step, a cold rolling step, and a finish pickling step,
The stainless steel sheet has the component composition according to any one of claims 2 to 5,
The pickling step wherein the finishing pickling step is immersed in a 5.0 to 35.0% by weight sulfuric acid aqueous solution;
A pickling step of immersing in an acid solution containing 1.0 to 15.0% by mass nitric acid and 0.5 to 5.0% by mass hydrofluoric acid aqueous solution,
The ferrite system excellent in antibacterial properties according to any one of claims 2 to 6, wherein the hot rolling step is performed at a heating temperature of 1150 to 1300 ° C, a finish rolling temperature of 800 to 1000 ° C, and a winding temperature of 600 ° C or less. Manufacturing method of stainless steel sheet. Furthermore, it includes a hot-rolled sheet annealing step and a finish annealing step, and the finish annealing step includes an annealing temperature of 900 to 1100 ° C. and cooling to 400 ° C. at an average cooling rate of 3 ° C./second or more. 8. A method for producing a ferritic stainless steel sheet having excellent antibacterial properties according to 8 . In the hot rolled sheet annealing step, carried out in continuous annealing, the continuous annealing, the annealing temperature is performed at 800 to 1100 ° C., and then to claim 7 or 9 is cooled at an average cooling rate of more than 1 ° C. / sec to 400 ° C. The manufacturing method of the ferritic stainless steel plate excellent in the antimicrobial property of description.

Images