JP3229577B2 - Austenitic stainless steel with excellent antibacterial properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an austenitic stainless steel, and more particularly to an austenitic stainless steel which has excellent antibacterial properties and is suitable for use in daily necessities, medical equipment and building materials.

[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 represented by Escherichia coli and Salmonella. Recently, materials using these metals to have an effect of inhibiting bacterial growth (hereinafter referred to as antibacterial properties) have been proposed. For example, Japanese Patent Application Laid-Open No. 8-49085 discloses an antibacterial property in which a metal layer or an alloy layer of Cr, Ti, Ni, Fe, etc. containing Ag and / or Cu is formed on the surface of a stainless steel substrate by magnet sputtering. An excellent stainless steel sheet is disclosed. 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 in a method of applying a pigment containing an antibacterial metal, the layer containing the antibacterial metal is formed by drawing or polishing the surface. There is a problem that the effect cannot be expected due to peeling or removal, and there is also a problem that antibacterial properties cannot be maintained for a long period of time in applications where the surface is constantly rubbed such as in steel plates used for interiors of washing machines. Was. 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.

In order to solve the above-mentioned problem, Japanese Patent Application Laid-Open No.
Japanese Patent No. 4953 proposes an austenitic stainless steel in which Cu is added in an amount of 1.1 to 3.5% by weight to improve antibacterial properties.

[0005]

SUMMARY OF THE INVENTION
In the steel material described in Japanese Patent Application Laid-Open No. 8-104953, Cu must be dissolved as ions from the surface of the steel sheet in order to exhibit antibacterial properties. However, Cu dissolved as Cu ions
In the ion elution zone, the passive film on the steel sheet surface is destroyed,
Corrosion resistance will be significantly degraded. That is,
In the case of the Cu-added austenitic stainless steel described in JP-A-8-104953, there remains a problem that it is difficult to achieve both antibacterial properties and corrosion resistance.

The present invention advantageously solves the above problems,
It is an object of the present invention to provide an austenitic stainless steel excellent in antibacterial properties and also excellent in corrosion resistance.

[0007]

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

First, the experimental results on which the present invention is based will be described. % By weight, C: 0.05%, N: 0.025%,
Si: 0.3%, Mn: 1.05%, P: 0.03%, S: 0.004%,
Austenitic stainless steel containing Cr: 18.1% and Ni: 8.05% contains 0 to 1.0% Ag (0 means no addition), W
Was added at 0 to 0.03%, and the antibacterial property was investigated. The antibacterial properties were evaluated according to a test method for a study group on inorganic antibacterial agents such as silver. As a control, the same test was performed by directly dropping a bacterial solution onto a sterilized petri dish. As a result, as shown in FIG. 1, the number of Escherichia coli decreases as the amount of Ag in steel increases (indicated by a black circle), and the amount of Escherichia coli decreases by 99% or more when the amount of Ag added is 0.0005% by weight or more. W: 0.02% by weight in addition to Ag
When the compound is added (marked with ○), the antibacterial property is further improved as compared with the material without W added (marked with ●). It was found that the antibacterial property was significantly improved. By the combined addition of Ag and W, antibacterial properties higher than that of Cu-added steel are obtained with an addition amount of 1/100 or less of conventional Cu addition.

Further, the corrosion resistance of the austenitic stainless steel to which Ag was added (containing 0.02 wt% W) was investigated by a salt dry-wet combined cycle test. The corrosion resistance was evaluated by the rusting area ratio after 100 cycles of the combined salt-dry and wet cycle. The result is shown in FIG. As shown in FIG.
It can be seen that in the range of 05 to 0.5% by weight, corrosion resistance superior to that of the material without Ag is exhibited.

The present invention has been made based on the above findings. That is, the present invention provides a method for preparing C:
0.01% to 0.10%, N: 0.01 to 0.10%, Si: 2.0% or less,
Mn: 2.0% or less, P: 0.08% or less, S: 0.02% or less, C
r: 10 to 20%, Ni: 6.0 to 10.0%, Ag: 0.0005 to 0.50
%, W: 0.01 to 0.30%, and is an austenitic stainless steel with excellent antibacterial properties, characterized by the balance of Fe and inevitable impurities.

In the present invention, C: 0.01% by weight%
0.10%, N: 0.01 to 0.10%, Si: 2.0% or less, Mn: 2.0
%, P: 0.08% or less, S: 0.02% or less, Al: 0.3%
Below, Cr: 10-20%, Ni: 6.0-10.0%, Ag: 0.0005-
Austenitic stainless steel with excellent antibacterial properties, containing 0.50%, W: 0.01 to 0.30%, and the balance consisting of Fe and unavoidable impurities.

In the present invention, each of the above-mentioned compositions may further contain one or more of V: 0.01 to 0.30% and Co: 0.01 to 0.30% by weight. In the present invention,
Each of the above compositions may further contain Mo: 3.0% or less by weight%. Further, in the present invention, Ti: 0.01 to 1.0%, Nb: 0.01 to 1.0%,
One or more of Zr: 0.01 to 1.0% may be contained.

In the present invention, each of the above-mentioned compositions may further contain 1.0% or less by weight of Cu. Further, in the present invention, each of the above-mentioned compositions further contains C
a: 0.0003~0.0030%, B: 0.0003~0.0030 % of one or
Or two or more kinds may be contained.

[0014]

Next, the reasons for limiting the chemical composition of the steel of the present invention will be described. C: 0.01 to 0.10% C is an element effective for improving the formability and the cracking property, but if less than 0.01%, these effects are not recognized. On the other hand, if it exceeds 0.10%, the steel is hardened significantly and the formability is reduced. For this reason, C was limited to the range of 0.01 to 0.10%. In addition, it is preferably 0.02 to 0.08%.

N: 0.01 to 0.10% N, like C, is an element effective for improving the formability and the cracking property, but if it is less than 0.01%, these effects are not recognized. On the other hand, 0.10% If it exceeds, the steel is hardened significantly and the formability is lowered. For this reason, N was limited to the range of 0.01 to 0.10%. In addition, it is preferably 0.02 to 0.08%.

Si: 2.0% or less Si is an element effective for improving corrosion resistance. However, excessive addition causes a reduction in cold workability and ductility, so it was limited to 2.0% or less. Incidentally, Si is preferably in the range of 0.2 to 0.8%. Mn: 2.0% 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. , 2.0% or less.
The content is preferably in the range of 0.5 to 1.5%.

P: 0.08% or less P is a harmful element that degrades hot workability and promotes the occurrence of pitting corrosion, and is desirably reduced as much as possible.
When the content exceeds 0.08%, the adverse effect becomes remarkable.
Limited to 0.08% or less. In addition, it is preferably 0.04% or less. S: 0.02% or less S is a harmful element that combines with Mn to form MnS and serves as an initial rusting starting point, segregates at crystal grain boundaries and promotes grain boundary embrittlement, and is desirably reduced 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 element effective for deoxidation, but can be added if necessary. Al may not be added in some cases.
0.30% or less. Excessive addition of Al increases the amount of aluminum-based nonmetallic inclusions, increases the number of surface flaws, and reduces workability.
Or less, preferably limited to 0.10% or less.

Cr: 10 to 20% Cr is an element effective for improving corrosion resistance, and if it is less than 10%, sufficient corrosion resistance cannot be secured. On the other hand, if it exceeds 20%, the cold workability is reduced, and the workability of the cold rolled sheet is impaired. For this reason, Cr was limited to the range of 10 to 20%. Note that a preferable range from the viewpoint of workability is 11 to 19%.

Ag: 0.0005 to 0.50% 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. Further, the antibacterial property can be further improved by the complex addition with W. These effects are observed when added at 0.0005% or more, but when added over 0.50%, they have the effect of enhancing antibacterial properties, but increase corrosion resistance, increase surface defects during hot rolling, and increase the cost. A large amount of Ag is added, which is disadvantageous in cost. For this reason, Ag was limited to the range of 0.0005 to 0.50%.

W: 0.01 to 0.30% When W is added in combination with Ag, the antibacterial property is remarkably improved as compared with the case of adding Ag alone. If W is less than 0.01%, the effect of improving antibacterial properties is insufficient, while if it exceeds 0.30%, ductility is rather reduced. For this reason, W is limited to the range of 0.01 to 0.30%. Incidentally, it is preferably in the range of 0.015 to 0.20%.

V: 0.01 to 0.30%, Co: 0.01 to 0.30%
V or Co has the effect of improving corrosion resistance in a chloride-containing solution environment. These effects are particularly significant for Ag
And the combined addition tends to increase significantly.
These effects are observed at the addition of 0.01% or more.
%, The effect saturates, so both V and Co
Limited to the range of 0.01 to 0.30%. In addition, since the addition of V and Co tends to harden the material, the total amount of V and Co is 0.
It is preferably at most 30%.

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. From the viewpoint of achieving both antibacterial properties and corrosion resistance, the amount of Mo added is preferably in the range of 0.1 to 2.0%.

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, C and N in the steel are fixed and precipitated as carbonitrides to refine crystal grains. However, excessive addition tends to reduce these properties, so Ti, Nb,
Zr was limited to the range of 0.01 to 1.0%.

Cu: 1.0% or less Cu is an element that improves antibacterial properties. However, compared to Ag, Cu does not significantly improve antibacterial properties when added in a small amount. On the other hand, when added in a large amount to the extent that antibacterial properties are exhibited. Corrosion resistance is significantly deteriorated.
However, Cu is an effective element for improving the corrosion resistance to acids and improving the crevice corrosion resistance if added in an appropriate amount, and is particularly desirable to be added to steel materials for building materials and kitchen appliances. However, if added in excess, hot cracking is likely to occur, so the content was limited to 1.0% or less. Preferably, the content is 0.1 to 0.8%.

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. The steel of the present invention can be applied to all commonly used melting methods, 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 900-1150 ° 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 900 to 1150 ° C. to obtain a product.

[0028]

EXAMPLE Steel having the chemical composition shown in Table 1 was melted by converter-secondary refining (SS-VOD) and made into a 200 mm thick slab by continuous casting. After heating these slabs to 1260 ° 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 1050 ° C and pickling treatment, they are cold-rolled into cold-rolled sheets, and further subjected to cold-rolled sheet annealing at 1050 ° C and pickling treatment. A cold-rolled annealed sheet having a thickness of 1.0 mm was obtained.

These cold rolled annealed sheets were tested for antibacterial properties and corrosion resistance. The test method is shown below. (1) Antibacterial property The antibacterial property was evaluated by using a test method for a 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 is 2
It was adjusted to × 10 ^{6 to} 6 × 10 ⁶ cfu / ml. The 1/500 NB solution is a solution obtained by diluting a normal Bion medium (NB) 500 times with sterilized purified water. Ordinary Bion medium is a meat extract 5.
0 g, sodium chloride 5.0 g, peptone 10.0 g, purified water 1.00
0 ml, pH: 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 put 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). The antibacterial activity was evaluated based on the number of bacteria and the bacteria reduction rate after the test.

The sterilization rate is defined by the following equation. Sterilization rate (%) = (number of control cells-number of cells after test) / (number of control cells) x 100 The number of control cells is the number of viable cells after the antibacterial test in a sterilized petri dish. And 9.30 × 10 ⁷ cfu / ml. The number of bacteria after the test is the number of viable bacteria measured. (2) Corrosion resistance The corrosion resistance was evaluated by a salt-dry / wet combined cycle test.

The test piece is sprayed with a 5.0% aqueous NaCl solution (temperature: 35 ° C.) for 0.5 hours after the following treatment, and then kept in a dry atmosphere at a humidity of 40% or less and a temperature of 60 ° C. for 1.0 hour. Hold for 1.0hr in a humid atmosphere with a humidity of 95% or more and a temperature of 40 ° C. Were combined into one cycle, and after repeating 100 cycles, the rusting area ratio (%) on the surface of the test piece was measured.

Table 2 shows the test results.

[0035]

[Table 1]

[0036]

[Table 2]

From Table 2, it can be seen that the antibacterial property, which is an effect of suppressing the growth of bacteria, was remarkably improved in the examples of the present invention. is decreasing. On the other hand, in Comparative Example (No. 1) in which Ag and W were not added, the growth of bacteria could not be suppressed, and no improvement in antibacterial properties was observed. In the present invention, the rusting area ratio (%) is 2 to 21%, which is the conventional example (No. 14: 82%).
Compared to the comparative example (No. 1: 52%), the corrosion resistance was significantly reduced and the corrosion resistance was improved.

On the other hand, in the comparative examples out of the range of the present invention, No. 6 in which the corrosion resistance was reduced and the Cu addition amount was large, and N in which the Ag addition amount was large.
In o.13, the rusting area ratio was 74% and 65%, which was higher than that of the present invention.

[0039]

According to the present invention, the antibacterial properties of austenitic stainless steel are improved, and the corrosion resistance is further improved.
An austenitic stainless steel sheet excellent in cost can be provided, and a remarkable industrial effect can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the effect of Ag addition on corrosion resistance.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Misako Tochihara 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (72) Yoshihiro Yazawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Inside the Technical Research Institute, Inc. (72) Inventor Takashi Oku 585 Tomicho, Funabashi-shi, Chiba Sumitomo Osaka Cement Co., Ltd.New Materials Division (72) Inventor Keijiro Shigeru 585 Tomicho, Funabashi-shi, Chiba Sumitomo Osaka Cement In the Materials Division (72) Inventor Yoshitomo Inoue 585 Tomimachi, Funabashi-shi, Chiba Sumitomo Osaka Cement Co., Ltd. New Materials Division (56) References JP-A-10-259457 (JP, A) JP-A-10-259456 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 A61L 2/16

Claims (6)

(57) [Claims] 1. In weight%, C: 0.01% to 0.10%, N: 0.01 to 0.10%, Si: 2.0% or less, Mn: 2.0% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.3% or less Cr: 10 to 20%, Ni: 6.0 to 10.0%, Ag: 0.0005 to 0.50%, W: 0.01 to 0.30%, with excellent antibacterial properties characterized by the balance of Fe and unavoidable impurities Austenitic stainless steel. 2. V: 0.01 to 0.30% by weight,
The austenitic stainless steel according to claim 1, wherein one or two types of Co: 0.01 to 0.30% are contained. 3. The austenitic stainless steel according to claim 1, further comprising Mo: 3.0% or less by weight. 4. Ti: 0.01 to 1.0% by weight.
The austenitic stainless steel according to any one of claims 1 to 3, comprising one or more of Nb: 0.01 to 1.0% and Zr: 0.01 to 1.0%. 5. The austenitic stainless steel according to claim 1, further comprising Cu: 1.0% or less by weight. 6. Further, in weight%, Ca: 0.0003 to 0.0030.
The austenitic stainless steel according to any one of claims 1 to 5, wherein the steel contains one or two kinds of B, 0.0003 to 0.0030%.