JP3227405B2 - Ferritic stainless steel with excellent antibacterial properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a ferritic stainless steel, which is particularly excellent in antibacterial properties and is used in daily life related articles,
The present invention relates to a ferritic stainless steel suitable for use in medical equipment and the like.

[0002]

2. Description of the Related Art It has been known that silver and copper have an effect of suppressing the growth of pathogenic bacteria such as Escherichia coli and Salmonella which cause food poisoning. Recently, bacterial growth suppression effect using these metals (hereinafter referred to as antibacterial)
Materials having the following have been proposed. For example, JP-A-8-
No. 49085 discloses a stainless steel sheet having excellent antibacterial properties in which a metal layer or an alloy layer of Cr, Ti, Ni, Fe or the like containing Ag and / or Cu is formed on the surface of a stainless steel substrate by magnet sputtering. Have been. In this steel plate, it is preferable to form a metal layer or an alloy layer containing 19 to 60% by weight of Ag.

Further, Japanese Patent Application Laid-Open No. 8-156175 proposes a coated steel sheet which can suppress the propagation of bacteria by applying a pigment containing silver. However, in the above-described method of forming a metal layer or an alloy layer containing an antibacterial metal on the surface of a steel sheet or a method of applying a pigment containing an antibacterial metal, a layer containing the antibacterial metal is formed by drawing or polishing the surface. Is peeled or removed, and the effect cannot be expected.In addition, in applications where the surface is constantly rubbed such as in steel plates used for interiors of washing machines, there is also a problem that antibacterial properties cannot be maintained for a long time. there were. Also,
In the above-described method, the number of production steps increases as compared to the conventional method for forming a coating or a metal layer or an alloy layer, and the surface area per unit weight increases as the plate thickness decreases, so that the coating amount per unit weight or the metal layer or The number of alloy layers increases, which is disadvantageous in cost.

Japanese Patent Application Laid-Open No. 8-239726 discloses that, by weight, 10 to 80% of iron, 1 to 10% of aluminum, or one or more of chromium, nickel, manganese, and silver are used. An antimicrobial, marine-resistant biological material is disclosed, comprising 15% with the balance copper and unavoidable impurities. However, this material is a copper-based alloy or an iron-based alloy containing 1 to 10% of aluminum and has low workability, and is particularly suitable for forming thin plates such as tableware, kitchenware, bathware, and electric parts. There was a problem in offering.

[0005]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems of the conventional materials, and is excellent in formability, workability and corrosion resistance suitable for a thin steel sheet having a thickness of 1 mm or less. It is an object of the present invention to provide a ferritic stainless steel sheet having excellent antibacterial properties even after forming.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have controlled the chemical composition of ferritic stainless steel to an appropriate range, and furthermore, contained less unit than Cu in the steel. By adding an appropriate amount of Ag, which has high antibacterial properties per atom and high safety to the human body, stable antibacterial properties can be obtained even in applications where the surface is rubbed or shaved during molding, polishing or use. It has been found that they can be expected, have good moldability and workability, and have sufficient characteristics for corrosion resistance.

First, the experimental results on which the present invention is based will be described. For the steel sheet containing Ag in ferritic stainless steel, the initial bacterial count (Escherichia coli) was 1 × 10 ⁶ cfu
The antibacterial property was evaluated as / ml. As a result, as shown in FIG. 1, the number of bacteria decreases as the amount of Ag in steel increases,
A new finding was obtained that the bacteria decreased by 99.9% or more when the amount of Ag added was 0.0005 wt% or more.

Further, the present inventors have found that when Ag is added to ferritic stainless steel and V or W is further added, pitting corrosion resistance as well as antibacterial property is remarkably improved. As shown in FIG. 2, the ferritic stainless steel in which Ag and V or W are added in combination has a significantly higher pitting potential _Vc200 , which is an indicator of pitting corrosion resistance, than in the case where no Ag is added. Is improved.

The present invention has been made based on the above findings. That is, in the present invention, C: 0.02% or less, N: 0.04% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.3% by weight% Hereinafter, Cr: 12 to 35%, Ag: 0.0005 to 0.30%, V: 0.01 to 0.
It is a ferritic stainless steel with excellent antibacterial properties, containing 30% and the balance being Fe and unavoidable impurities. In addition, the present invention provides, in weight%, C: 0.02% or less;
N: 0.04% or less, Si: 1.0% or less, Mn: 1.0% or less,
P: 0.08% or less, S: 0.02% or less, Al: 0.3% or less, C
r: 12 to 35%, Ag: 0.0005 to 0.30%, W: 0.01 to 0.30%
With the balance being Fe and unavoidable impurities.
Ferritic stainless steel with excellent antibacterial properties
You. In addition, the present invention relates to the following:
0.04% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.
08% or less, S: 0.02% or less, Al: 0.3% or less, Cr: 12 to
35%, Ag: 0.0005 to 0.30%, V: 0.01 to 0.30% and
W: 0.01 to 0.30%, the balance being Fe and unavoidable impurities
Ferrite based with excellent antibacterial properties characterized by consisting of
Stainless steel.

In the present invention, each of the above compositions may further contain 0.01 to 0.30 % by weight of Co. Further, in the present invention, each of the above compositions is further added with
o: may contain 3.0% or less. In the present invention,
In addition to each of the above compositions, Ti: 0.01 to 1.0% by weight,
One or more of Nb: 0.01 to 1.0% and Zr: 0.01 to 1.0% may be contained.

In the present invention, each of the above-mentioned compositions may further contain one or more of Cu: 1% or less and Ni: 1% or less by weight. Further, in the present invention, each of the above compositions further contains, by weight%, Ca: 0.0003 to 0.0030%, and B:
One or two of 0.0003 to 0.0030% may be contained.

[0012]

Next, the reasons for limiting the chemical composition of the steel of the present invention will be described. C: 0.02% or less, N: 0.04% or less C and N are elements that lower elongation and r value and deteriorate workability, and combine with Cr to form a carbonitride and form a deCr phase. Therefore, it is reduced as much as possible. Reduction of these elements is effective for improving workability and corrosion resistance.
% And N can be tolerated up to 0.04%, so each is set as the upper limit. It is preferable that C is 0.0005% or more and N is 0.0010% or more in consideration of actual manufacturability (decarburization and denitrification ability in steel making).

Si: 1.0% or less Si is an effective element for deoxidation. However, excessive addition causes a reduction in cold workability and ductility, so it was limited to 1.0% or less. Incidentally, Si is preferably in the range of 0.03 to 0.5%. Mn: 1.0% or less Mn combines with S in steel to form MnS and is an effective element for improving hot workability. However, excessive addition causes reduction in cold workability and corrosion resistance. To invite, it was limited to 1.0% or less. In addition, it is preferably in the range of 0.03 to 0.50%.

P: 0.08% or less P is a harmful element that degrades hot workability and promotes the occurrence of pitting corrosion, and it is desirable to reduce P as much as possible. If it exceeds 0.08%, its adverse effect becomes remarkable,
P was limited to 0.08% or less. In addition, it is preferably 0.03% or less. S: 0.02% or less S is segregated at crystal grain boundaries to promote grain boundary embrittlement,
It is a harmful element that combines with Mn to form MnS and becomes an initial rusting starting point, and it is desirable to reduce it as much as possible. If it exceeds 0.02%, the adverse effect becomes remarkable, so S was limited to 0.02% or less. Incidentally, the content is preferably 0.008% or less.

Al: 0.30% or less Al is an effective element for deoxidation, but excessive addition increases alumina-based inclusions, increases the number of surface flaws, and lowers workability. Limited to the following.
In addition, it is preferably 0.10% or less. Cr: 12 to 35% Cr is an element effective for improving corrosion resistance, and if it is less than 12%, sufficient corrosion resistance cannot be secured. On the other hand, if it exceeds 35%, the cold workability is reduced, and the working of the cold rolled sheet becomes difficult. For this reason, Cr is limited to the range of 12 to 35%. In addition, a preferable range from the viewpoint of workability is 12 to 25%.

Ag: 0.0005 to 0.30% Ag is the most important element in the present invention, and has an effect of suppressing the growth of bacteria and is an element that enhances antibacterial properties. Also,
In addition, it has the effect of improving corrosion resistance and workability. These effects are observed when added at 0.0005% or more. However, when added over 0.30%, they have the effect of increasing antibacterial properties, but they have the effect of improving workability and manufacturability (specifically, cracks and surface damage during hot rolling). Ag) and expensive
Is added in a large amount, which is disadvantageous in terms of cost. Therefore, the amount of Ag added is limited to the range of 0.0005 to 0.30%.

V: 0.01 to 0.30% V has the effect of improving corrosion resistance in a chloride-containing solution environment, and is particularly remarkable when Ag is added in combination with Ag. This effect is observed when 0.01% or more is added, but when it exceeds 0.30%, it saturates, so that V becomes 0.01 to 0.30%.
Limited to the range. In addition, since the addition of a large amount of V hardens the material, it is preferably set to 0.15% or less.

W: 0.01 to 0.30%, Co: 0.01 to 0.30 % W and Co are not as remarkable as V, but have an effect of improving pitting corrosion resistance by adding Ag and a composite, and the effect is 0.01% or more. However, when the content exceeds 0.30%, the material is hardened. Therefore, both W and Co are limited to the range of 0.01 to 0.30%. Note that the addition of W and Co is more preferably 0.15% or less in order to suppress hardening of the material.

Mo: 3.0% or less Mo is an element which improves corrosion resistance and rust resistance.
If added in excess of, precipitation of the σ phase and χ phase is promoted, and the corrosion resistance and workability are significantly reduced. For this reason, Mo was limited to 3.0% or less. In addition, from the viewpoint of workability, 0.1 to 2.0%
It is preferable to set it in the range.

Ti: 0.01-1.0%, Nb: 0.01-1.0%, Z
r: 0.01 to 1.0% of one or more of Ti, Nb, and Zr are carbonitride forming elements. They suppress grain boundary precipitation of Cr carbonitride during welding and heat treatment and improve corrosion resistance. Let it. Further, it fixes C and N in steel and improves ductility and workability as a carbonitride. However, excessive addition tends to reduce these properties, so that Ti
1.0%, Nb is limited to 0.01 to 1.0%, and Zr is limited to 0.01 to 1.0%.

One or two kinds of Cu: 1% or less, Ni: 1% or less Cu and Ni are effective elements for improving the corrosion resistance to an acid and improving the crevice corrosion resistance. It is desirable to add it to steel materials for kitchen appliances. However, if added in excess, hot cracking is likely to occur, so Cu,
Ni addition was limited to 1.0% or less. Furthermore, C
It is preferable that the total amount of u and Ni be 0.01 to 2.0%. When the total of these elements is less than 0.01%, no effect of improving corrosion resistance in acid is observed, and the total of these elements is 2.0% or less.
%, The workability is reduced.

Ca: 0.0003-0.0030%, B: 0.0003-0.00
30% of one or two types of Ca and B are elements that have the effect of suppressing nozzle clogging due to Ti-based inclusions during casting. However, if they are added excessively, inclusions that become the starting points of brittle fracture increase. , Ca,
B was limited to the range of 0.0003 to 0.0030%. In addition, a preferable range is 0.0005 to 0.0010%.

The balance is Fe and inevitable impurities. For the steel of the present invention, all known melting methods can be applied, and there is no need to limit the melting method. For example, as a steelmaking method,
Melted in converters, electric furnaces, etc., and SS-VOD (Strongly
It is preferable to perform secondary refining by cuum oxygen decarburization). The casting method is preferably a continuous casting method in terms of productivity and quality. In addition, in order to make a hot-rolled sheet of a predetermined thickness,
Hot rolling, hot rolled sheet annealing at 850-1025 ° C,
It is preferable to perform pickling and cold rolling to obtain a product having a predetermined thickness, or to further perform annealing and pickling at 800 to 950 ° C. to obtain a product.

[0024]

EXAMPLES Steel having the chemical composition shown in Table 1 was melted by converter-secondary refining (SS-VOD) and made into a slab 260 mm thick by continuous casting. After heating these slabs to 1150 ° C,
A hot-rolled sheet having a thickness of 4 mm was formed by hot rolling. After subjecting these hot rolled sheets to hot rolled sheet annealing at 850 to 1025 ° C and pickling,
Cold-rolled sheets with a thickness of 0.6 mm were obtained by cold rolling. Further, these cold-rolled sheets were subjected to cold-rolled sheet annealing at 800 to 950 ° C and pickling treatment to obtain product sheets.

For the product sheet, the tensile properties (yield strength: Y
S, tensile strength: TS, elongation: El), workability, pitting resistance, and antibacterial properties were tested. The workability was evaluated by an Erichsen value by performing an Erichsen test in accordance with JIS regulations. As the Erichsen value, a test piece having graphite grease applied to both surfaces was used, and the average value was used as the number of repetitions of three.

The pitting resistance was determined by using a 3.0% NaCl solution (25%).
C), and the pitting potential was measured and evaluated. Measurement is 10
The average value _Vc.200 of the potential when the voltage reached 200 μA / cm ² was determined by using the electrokinetic method of mV / min. The number of measurements for the same product plate was eight. The antibacterial properties were evaluated using a test method for the study group on inorganic antibacterial agents such as silver. The procedure of the test method for the study group for inorganic antibacterial agents such as silver is as follows.

A 25 cm ² specimen is washed and degreased with absorbent cotton containing 99.5% ethanol. E. coli is dispersed in a 1/500 NB solution. (The number of bacteria used was about 2 × 10 ⁶ cfu / ml. The 1/500 NB solution is a normal Bion medium (NB) diluted 500 times with sterile purified water. , Meat extract 5.0g, sodium chloride 5.0g, peptone 10.0g, purified water 1.000ml, pH:
It means 7.0 ± 0.2. ) Inoculate the test sample (3 each) with the bacterial solution at a rate of 0.5 ml / 25 cm ² .

A coating film is placed on the surface of the test piece. Test specimens at temperature (35 ± 1.0 ℃), RH (relative humidity) 90%
Store for 24 hours under the above conditions. The number of viable cells is measured by an agar culture method (35 ± 1.0 ° C, 40 to 48 hours). Table 2 shows the test results of the product plate.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

From Table 2, it can be seen that the antibacterial property, which is an effect of inhibiting the growth of bacteria, was remarkably improved in the examples of the present invention in which Ag was added within the scope of the present invention. E. coli and Staphylococcus aureus have been reduced by more than 99.9%. On the other hand, comparative examples (No. 1, No. 2,
In Nos. 22 to 24), the growth of bacteria cannot be suppressed, and no improvement in antibacterial properties is observed.

In the example of the present invention, the pitting potential V _c.200 is
105-250 and Comparative Example without Ag addition (No. 1, V _c.200 = 10
Compared with 0), the pitting corrosion resistance is improved. In particular,
Inventive Examples Nos. 11 to 21 to which V and W are added have markedly improved pitting corrosion resistance. Furthermore, in the present invention example, the Erichsen value is 10.8 to
11.6, which is higher than that of Comparative Example No. 1 (10.1), and the workability is also improved. In Comparative Examples No. 9 to No. 10 in which the added amount of Ag exceeds the range of the present invention, the tendency of the workability to decrease is observed.

[0035]

According to the present invention, it is possible to provide a ferritic stainless steel sheet having improved antibacterial properties of ferritic stainless steel, excellent corrosion resistance, excellent workability, and excellent cost. Furthermore, it is subjected to molding and polishing,
The present invention can be applied to a member in which hygiene is emphasized, for example, a member used in a humid environment such as a kitchen, a bathtub or the like where bacteria can easily propagate in a humid environment, and a remarkable industrial effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of Ag on antibacterial properties.

FIG. 2 is a graph showing the effect of a combined addition of Ag, V and W on pitting corrosion resistance.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takeshi Yokota 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. In-company (72) Inventor Keijiro Shigeru 585 Tomicho, Funabashi-shi, Chiba Sumitomo Osaka Cement Co., Ltd. (72) Inventor Yoshitomo Inoue 585 Tomicho, Funabashi-shi, Chiba Pref. Kaihei 10-259456 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (8)

(57) [Claims] 1. In weight%, C: 0.02% or less, N: 0.04% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.3% or less , Cr: 12-35%, Ag: 0.0005-0.30%, V: 0.01-0.30%, the ferrite stainless steel having excellent antibacterial properties characterized by the balance of Fe and inevitable impurities. 2. In% by weight, C: 0.02% or less, N: 0.04% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.3% or less, Cr: 12-35%, Ag: 0.0005 to 0.30%, W: 0.01 to 0.30% And the balance consists of Fe and unavoidable impurities.
Ferritic stainless steel with excellent antibacterial properties. 3. In% by weight, C: 0.02% or less, N: 0.04% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.3% or less , Cr: 12-35%, Ag : 0.0005-0.30%, V: 0.01-0.30% , W : 0.01-0.30%, with the balance being Fe and unavoidable impurities.
Ferritic stainless steel with excellent antibacterial properties. 4. Further, in weight%, Co: 0.01 to 0.30% of <br/> any of 3 to claims 1, characterized in that it contains
Excellent ferritic stainless steel antibacterial described. 5. Further, in wt%, Mo: no claim 1, characterized in that it contains 3.0% or less to a ferritic stainless steel having excellent antibacterial <br/> according to any one of 4. 6. The composition according to claim 1, further comprising: Ti: 0.01 to 1.0% by weight.
Nb: 0.01~1.0%, Zr: 0.01~1.0 % of claims 1, characterized in that it contains one or two or more to 5 Neu
Ferritic stainless steel with excellent antibacterial properties as described in any of the above. 7. In addition, Cu: 1% or less, Ni:
The ferritic stainless steel having excellent antibacterial properties according to any one of claims 1 to 6 , containing 1% or less of 1 or 2 types. 8. Further, in weight%, Ca: 0.0003 to 0.0030
%, B: 0.0003% to 0.0030% of one or two kinds of ferrite stainless steels having excellent antibacterial properties according to any one of claims 1 to 7 .