JP3227418B2 - Ferritic stainless steel with excellent antibacterial and ridging resistance - 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 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 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 in an amount of 1 to 10. 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 used for forming a thin plate of tableware, kitchenware, bathware, electric parts, and the like. There was a problem to offer.

[0005]

It is well known that when a ferritic stainless steel sheet is pressed, a surface defect called ridging occurs, but a ferritic stainless steel sheet having excellent antibacterial properties is also pressed. In applications, it is required to have excellent ridging resistance. The present invention advantageously solves the above-mentioned problems of the conventional materials, and is suitable for a thin steel sheet having a thickness of 2.0 mm or less. An object of the present invention is to provide a ferritic stainless steel sheet having excellent properties.

[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 was expected that it was possible to obtain characteristics excellent in moldability, workability, and corrosion resistance.

First, the experimental results on which the present invention is based will be described. % By weight, C: 0.06%, N: 0.025%,
Si: 0.03%, Mn: 0.05%, P: 0.03%, S: 0.002%,
Cr: 0 to 3% of Ag is added to ferritic stainless steel containing 16.2% (0% means no addition), and the initial bacterial count (E. coli) is 2.0 × 10 ^{5 to} 1.0 × 10 ⁶ cfu / ml. The antibacterial properties were investigated. The antibacterial properties were evaluated according to a test method for a study group on inorganic antibacterial agents such as silver. As a result, as shown in FIG. 1, the number of E. coli decreased as the amount of Ag in steel increased,
A new finding was obtained that bacteria decreased by 99% or more when the amount of Ag added was 0.0005% or more.

Further, the present inventors added 0.15% by weight of V and 0 to 3% of Ag (0% means no addition) to the ferritic stainless steel having the above-described composition by weight. The antibacterial properties were investigated. As a result, as shown in FIG.
It has been found that the ferritic stainless steel to which N is added in combination has remarkably improved antibacterial properties as compared with the material without V added.

The present inventors have also found that ferritic stainless steel to which V and Ag are added in combination has remarkably improved ridging resistance in addition to antibacterial properties. The ridging resistance of a ferritic stainless steel containing no Ag and a ferritic stainless steel containing Ag was investigated by changing the V content. The result is shown in FIG. From FIG. 2, it can be seen that adding resistance is significantly improved by adding Ag and V in combination. Further, with respect to the V-free material and the V: 0.015% by weight material, the crystal orientation distribution in the cross section of the sheet thickness was determined by EBSD (Electron Back Scattering Diffrac
As a result of the measurement by the method, it was found that the addition of V: 0.015% by weight makes the randomization of the crystal orientation in the cross section of the plate thickness more remarkable than that of the material without V added. From these facts, the present inventors have found that V is effective in controlling the crystal orientation distribution in the cross section of the Ag-added ferritic stainless steel, and that the randomization of the crystal orientation by the addition of V improves the ridging resistance. I found something to be done. Furthermore, the conventional measures against ridging have focused on controlling the texture in the center plane of the plate thickness.However, the present inventors consider that the occurrence of ridging depends on the amount of plastic deformation of each crystal grain in the plane of the plate thickness. Sum was the most contributing.

The present invention has been made based on the above findings. That is, the present invention provides a method for preparing C:
Over 0.02% to 0.10%, N: 0.02 to 0.10%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.08% or less, S: 0.02% or less, Cr: 10 to 35%, Ag: 0.0005 to 0.30 %, V: 0.01-0.
It is a ferritic stainless steel excellent in antibacterial property and ridging resistance, characterized by containing 30% and the balance being Fe and inevitable impurities.

In the present invention, C: more than 0.02% to 0.10%, N: 0.02 to 0.10%, Si: 1.0% or less, Mn: 1.0% by weight.
0% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.3
%, Cr: 10 to 35%, Ag: 0.0005 to 0.30%, V: 0.01
It is a ferritic stainless steel excellent in antibacterial property and ridging resistance, characterized by containing 0.30% and the balance being Fe and unavoidable impurities.

In the present invention, each of the above-mentioned compositions may further contain one or two types of W: 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.

Further, in the present invention, each of the above-mentioned compositions may further contain one or more of Cu: 1.0% or less and Ni: 1.0% or less by weight%. Further, in the present invention, each of the above compositions further contains, by weight%, Ca: 0.0003 to 0.0030%,
B: One or two types of 0.0003 to 0.0030% may be contained.

[0014]

Next, the reasons for limiting the chemical composition of the steel of the present invention will be described. C: more than 0.02 to 0.10% C is an element that lowers elongation and r-value and deteriorates workability, but an extreme reduction degrades ridging resistance and increases polishing load after press working. Therefore, considering the balance of the r value, elongation and ridging resistance, C is more than 0.02 to 0.
Limited to 10% range. When C is 0.02% or less, ridging resistance is deteriorated. On the other hand, when C exceeds 0.10%, the r value and elongation are reduced and corrosion resistance is deteriorated. In addition, a preferable range is a range of 0.03 to 0.07%.

N: 0.02 to 0.10% N, like C, is an element that lowers elongation, lowers the r value, and degrades workability, but an extreme reduction degrades ridging resistance and causes polishing after pressing. Increase the load. For this reason, considering the balance of r value, elongation and ridging resistance,
N was limited to the range of 0.02 to 0.10%. When N is less than 0.02%, ridging resistance is deteriorated. On the other hand, when N exceeds 0.10%, r
Value and elongation are reduced, and corrosion resistance is deteriorated. In addition, a preferable range is a range of 0.03 to 0.07%.

Si: 1.0% or less Si is an element effective for deoxidation, but 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 is an effective element that combines with S in steel to form MnS to improve hot workability. However, excessive addition causes reduction in cold workability and corrosion resistance. , 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 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.
Limited to the following. In addition, it is preferably 0.10% or less.

Cr: 10 to 35% 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 35%, 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 35%. Note that a preferable range from the viewpoint of workability is 11 to 22%.

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. Further, the ridging resistance can be improved by the combined addition with V. These effects are observed at the addition of 0.0005% or more, but when added over 0.30%, they have the effect of increasing antibacterial properties, but increase the surface defects during hot rolling,
A large amount of expensive Ag is added, which is disadvantageous in cost. Further, the workability tends to decrease. For this reason, Ag was limited to the range of 0.0005 to 0.30%.

V: 0.01 to 0.30% By adding V in combination with Ag, the antibacterial property is remarkably improved as compared with the case of adding Ag alone. V is added in combination with Ag to randomize the crystal orientation distribution in the cross section of the plate thickness and improve ridging resistance. If V is less than 0.01%, the randomization of the crystal orientation in the cross section of the sheet thickness is insufficient, while if it exceeds 0.30%, the effect of the randomization is saturated and the ductility is rather reduced. For this reason, V is limited to the range of 0.01 to 0.30%. Incidentally, it is preferably in the range of 0.015 to 0.20%.

W: 0.01 to 0.30%, Co: 0.01 to 0.30%
W 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 W and Co
Limited to the range of 0.01 to 0.30%. Since the addition of W and Co tends to harden the material, the total amount of W 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. When the thin plate is applied to an application that requires particularly good workability, 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, 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 types of Cu: 1.0% or less, Ni: 1.0% or less Cu and Ni are effective elements for improving the corrosion resistance to acids and 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 sum of the amounts of u and Ni added is 0.01 to 1.5%. If 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 1.5%.
%, The effect of improving corrosion resistance and crevice corrosion resistance is saturated, and 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. 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,
Perform hot rolling, and further perform hot rolled sheet annealing at 800 to
The product is preferably pickled and cold-rolled to obtain a product having a predetermined thickness, or further subjected to annealing at 800 to 950 ° C. and pickling to obtain a product.

[0028]

EXAMPLES 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 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 830 to 1025 ° C and pickling treatment to obtain cold-rolled annealed sheets.

These cold-rolled annealed sheets were tested for workability, antibacterial properties, and pitting resistance. The workability was evaluated based on the r value and the ridging height. The test method is shown below. (1) Workability (i) r value Using a JIS No. 13B test piece collected from each cold-rolled annealed sheet,
After giving the% tensile strain, the r value in each direction was determined by a three-point method, and evaluated by the average value calculated by r value = (r _L + 2r _D + r _C ) / 4. Note that r _L is a rolling direction, r _D is a direction at 45 degrees to the rolling method, and r _C is an r value in a direction at 90 degrees to the rolling direction.

(Ii) Ridging height Using a JIS No. 5 test piece taken from the rolling direction of each cold-rolled annealed sheet, applying a 20% tensile strain, and then measuring the ridging height generated on the test piece by a surface roughness meter. The thickness (μm) was measured. (2) Antibacterial property The antibacterial property was 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 is 2.
It was adjusted to 0 × 10 ^{5 to} 1.0 × 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 boion medium is meat extract 5.0g, sodium chloride 5.0g, peptone 10.0g, purified water
1.000ml, 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 .

The surface of the test piece is covered with a coating film. 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 (%)
= (Control bacterial count-bacterial count after test) / (control bacterial count) x 10
0 The number of bacteria in the control is the number of viable bacteria after the test in which an antibacterial test was performed in a sterilized petri dish, and the number of bacteria after the test is the measured number of viable bacteria. (3) Pitting corrosion resistance Pitting corrosion resistance was evaluated by immersing a product plate in a 3.0% NaCl solution (25 ° C) and measuring the pitting potential. The measurement was performed using the electrokinetic method of 20 mV / min, and an average value V _c.10 of the potential when it reached 10 μA / cm ² was determined. The number of measurements on the same product plate was 8
Times.

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, the comparative example (N
In o.7), the growth of bacteria cannot be suppressed, and no improvement in antibacterial properties is observed. In the present invention, the pitting corrosion potential V _c.10 is 117 to 183, which is a comparative example (No. 7, V _c.10 = 93).
And the pitting corrosion resistance is improved.

Further, in the example of the present invention, the r value is 1.27 to 1.91.
Comparative Examples (No. 7, No. 8), which are higher than Comparative Examples No. 7 (1.01) and No. 8 (0.90), and the ridging height is 3 to 10 μm.
Of 18 to 27 μm, and the workability is improved. In Comparative Example No. 8 in which the amount of Ag added was high, the antibacterial property was good, but the processability was deteriorated.

[0039]

According to the present invention, it is possible to provide a ferritic stainless steel thin plate having improved antibacterial properties of ferritic stainless steel, excellent ridging resistance and corrosion resistance, and excellent in cost. Furthermore, it is possible to apply the present invention to a member which is subjected to molding and polishing so as to emphasize hygiene, for example, a member used in an environment where a particularly high humidity such as a kitchen and a bath tub is liable to propagate bacteria, and the like. A remarkable effect can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the effect of a combined addition of Ag and V on ridging resistance.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshihiro Yazawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (72) Inventor Keijiro Shigeru 585 Tomicho, Funabashi City, Chiba Prefecture Sumitomo Osaka Cement Co., Ltd. (56) References JP-A-10-259456 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (6)

(57) [Claims] 1. In weight%, C: more than 0.02% to 0.10%, N: 0.02 to 0.10%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.08% or less, S: 0.02% or less, Cr : 10 to 35%, Ag: 0.0005 to 0.30%, V: 0.01 to 0.30%, or further contains Al: 0.3% or less, the balance
A ferritic stainless steel with excellent antibacterial properties and ridging resistance characterized by Fe and unavoidable impurities. 2. In addition, W: 0.01 to 0.30% by weight%,
The ferritic stainless steel according to claim 1, wherein one or two types of Co: 0.01 to 0.30% are contained. 3. The ferritic 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 ferritic 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 composition according to claim 1, further comprising: Cu: 1.0% or less,
The ferritic stainless steel according to any one of claims 1 to 4, wherein one or two kinds of i: 1.0% or less are contained. 6. Further, in weight%, Ca: 0.0003 to 0.0030.
%, B: 0.0003 to 0.0030% , one or two of which are contained, the ferritic stainless steel according to any one of claims 1 to 5.