JPH09249948A - Stainless steel excellent in antibacterial property and designing property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an oxidized film for coloring on a stainless steel surface without deteriorating antibacterial properties of which Cu-enriched phases impart. SOLUTION: This stainless steel is the one contg., by weight, 0.8% C, <=3% Si, <=15% Mn, 10 to 30% Cr, <=15% Ni and 0.4 to 5.0% Cu, in which secondary phases essentially consisting of Cu are dispersed into the matrix in the ratio of 0.2vol.% and an oxidized film having <=200nm thickness is formed by heat treatment at <=900 deg.C. Moreover, the stainless steel may contain one or >= two kinds among 0.02 to 1% Nb, 0.02 to 1% Ti, <=3% Mo, <=1% Al, <=1% Zr, <=1% V, <=0.05% B and <=0.05% rare earth elements(REM).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to kitchen equipment, electric appliances,
The present invention relates to a stainless steel which is used in a wide range of fields such as building materials, various machines, chemical equipment, etc., where antibacterial properties are required, and has excellent antibacterial properties and design.

[0002]

2. Description of the Related Art Since various equipment used in kitchen equipment, hospitals, and pipes for handrails of transportation means such as buses and trains are required to have corrosion resistance in a general environment, SUS is required.
The stainless steel represented by 304 is mainly used. However, nosocomial infection with Staphylococcus aureus has become a problem. In addition, contamination due to the propagation of various bacteria, foul odor,
There is a growing tendency to worry about the adverse effects of slime, etc. on the human body, animals and products. In particular, kitchen appliances, medical institutions, buildings where a large number of people gather, and the like are required to have improved hygiene. Along with this, maintenance-free materials with functions such as antibacterial properties that do not stop at the properties of general structural materials as materials used for various machines and instruments and do not require infection prevention such as regular disinfection. Materials are desired.

As a material imparted with antibacterial properties, there is disclosed in Japanese Patent Laid-Open No.
As disclosed in JP-A-22820, JP-A-6-10191 and the like, an antibacterial coat formed by an organic film or plating is generally used. However, the antibacterial coat has a drawback that the antibacterial property is lowered as the film disappears. The organic matter having lost the antibacterial property may serve as a nutrient source and may propagate bacteria and various bacteria. In the case of applying a composite plating mixed with an antibacterial agent component, the adhesion of the plating layer is not sufficient, and there is a drawback that the workability is reduced. In addition, film dissolution, wear,
The appearance may be deteriorated due to defects and the antibacterial action may be decreased.

[0004]

In order to exhibit excellent antibacterial properties over a long period of time, it is desired that the material itself exhibit antibacterial properties. From the above viewpoints, the present inventors proposed in Japanese Patent Application No. 7-347735 Japanese Patent Application No. 7-347735 a stainless steel having antibacterial properties imparted by containing Cu. However, there is a strong demand for designability of stainless steel sheets used for interiors and exteriors. As a means for improving the design, there is known a method of heating stainless steel and coloring it by utilizing the interference color of the oxide film formed on the surface thereof. When colored by this method, the surface of stainless steel is covered with an oxide film. Therefore, the action of the Cu-rich phase having an antibacterial action is hindered by the oxide film, and the antibacterial property may be deteriorated. The present invention has been devised to solve such a problem, and by forming an oxide film having a specified thickness on the surface of stainless steel, stainless steel having improved design without impairing antibacterial properties. The purpose is to provide.

[0005]

In order to achieve the object, the stainless steel of the present invention is C: 0.8% by weight or less,
Si: 3 wt% or less, Mn: 5 wt% or less, Cr: 10
~ 30 wt%, Ni: 15 wt% or less, Cu: 0.4 ~
The second phase containing 5.0% by weight and mainly containing Cu is 0.2
Dispersed in the matrix at a volume ratio of 90% or more, and 90%
Heat treatment at a temperature of 0 ° C. or lower makes the thickness 200 nm
The following oxide films are formed. The stainless steel used is Nb: 0.02-1% by weight, Ti: 0.02-1% by weight, Mo: 3% by weight or less,
Al: 1 wt% or less, Zr: 1 wt% or less, V: 1 wt% or less, B: 0.05 wt% or less, rare earth element (RE
M): 0.05% by weight or less of one kind or two or more kinds may be contained.

[0006]

The stainless steel has excellent corrosion resistance because it is covered with a hydroxide mainly called Cr called a passive film. The present inventors have found that C that exhibits effective antibacterial properties.
C added to stainless steel by adding u to C
The u amount was measured, and the antibacterial property by dropping the liquid containing Staphylococcus aureus was investigated. As a result, for example, Japanese Patent Application No. 6
As mentioned in No. 210558, C above a certain level
It was found that the stainless steel containing u has antibacterial properties. However, the antibacterial property and the sustainability thereof may not always be sufficient if only a few% or less of Cu is dissolved in steel. Therefore, as a result of further studies, if the second phase mainly composed of Cu (hereinafter, referred to as Cu-rich phase) is finely and uniformly deposited even if the Cu content is the same, Cu is eluted. It was found that the antibacterial property is improved as well as the antibacterial property, and the application was filed as Japanese Patent Application No. 7-347735. The Cu-rich phase is precipitated by heat treatment at a temperature of 900 ° C. or lower for 0.1 hour or longer, and the amount of precipitation is controlled by adjusting the addition amount of Cu and the heat treatment conditions.

Stainless steel having antibacterial properties may be used for purposes that are designed by coloring. In such a case, the oxide film formed for coloring may deteriorate the antibacterial property. Therefore, as a result of various studies on a coloring method and a treatment condition capable of maintaining the antibacterial property even after the coloring treatment, the antibacterial property can be maintained by performing a heat treatment at a temperature of 900 ° C. or less to form an oxide film of 200 nm or less. , It was found that color development occurs due to light interference and the design is improved. This is because the size of the Cu-rich phase exposed on the stainless steel surface is 200 nm or more.
This is because the Cu-rich phase does not diffuse and remains on the stainless steel surface even when heat-treated at a temperature of 00 ° C. or less. Moreover, by regulating the thickness of the oxide film to 200 nm or less, it is presumed that the Cu-rich phase is not covered with the oxide film, Cu can be eluted and the antibacterial property is maintained. It

The alloy components and contents contained in the stainless steel used in the present invention will be described below. C: 0.8% by weight or less In addition to improving the strength of stainless steel, in the present invention,
It is an effective alloying element that uniformly disperses the precipitation of Cu-rich phase by the formation of Cr carbide. However, since excessive addition of C deteriorates manufacturability and corrosion resistance, the upper limit is 0.8% by weight.
Regulated to. Si: 3 wt% or less It is an alloying element that improves corrosion resistance and strength and exhibits an antibacterial action. However, excessive addition causes deterioration of manufacturability, so the upper limit was limited to 3 wt%. Mn: 5 wt% or less An alloying element that improves manufacturability and fixes harmful S in steel as MnS. However, since the corrosion resistance deteriorates due to excessive addition, the upper limit was limited to 5% by weight.

Cr: 10 to 30 wt% An alloying element important for maintaining the corrosion resistance of stainless steel, and 10 wt% or more is required. But 3
A large amount of Cr exceeding 0% by weight deteriorates manufacturability. Cu: 0.4-5.0 wt% and Cu-rich phase:
0.2% by volume or more It is the most important alloying element in the stainless steel of the present invention, and it is necessary that 0.2% by volume or more of Cu-rich phase is precipitated in order to maintain good antibacterial property. 0.2
In order to precipitate a Cu-rich phase of volume% or more,
It is necessary to add 4 wt% or more of Cu. However, since the excessive addition reduces the manufacturability and corrosion resistance, the upper limit of the Cu content was restricted to 5.0% by weight. Further, the Cu-rich phase is not particularly limited in the size of the precipitate, but in order to exert the antibacterial property evenly on the entire surface of the product, the precipitate phase is appropriately dispersed and distributed. preferable.

Nb, Ti: 0.02 to 1% by weight It is an alloying element that is added as needed, and acts as a precipitate to uniformly precipitate a Cu-rich phase around it. Such an effect becomes remarkable at 0.02% by weight or more. However, excessive addition of more than 1% by weight reduces manufacturability and workability. Mo: 3% by weight or less An alloying element added as necessary, which improves corrosion resistance and strength and exhibits an antibacterial action. However, excessive addition of more than 3% by weight reduces manufacturability and workability. Al: 1% by weight or less An alloying element added as necessary, and exhibits an effect of improving corrosion resistance, similar to Mo. However, excessive addition of more than 1% by weight reduces manufacturability and workability.

Zr: 1% by weight or less An alloying element added as necessary, which forms a carbonitride and has an effect of improving the strength of the steel material. But,
Excessive addition of more than 1% by weight reduces manufacturability and workability. V: 1% by weight or less An alloying element added as necessary, which forms a carbonitride similar to Zr and has an effect of improving the strength of steel. However, excessive addition of more than 1% by weight reduces manufacturability and workability. B, REM: 0.05 wt% or less It is an alloying element added as necessary and has an effect of improving hot workability. However, excessive addition of more than 0.05% by weight causes deterioration of hot workability.

Thickness of oxide film: 200 nm or less In order to keep the Cu-rich phase on the surface of the stainless steel and keep Cu in a state where Cu can be eluted, it is necessary to regulate the thickness of the coloring oxide film to 200 nm or less. When the oxide film grows to a thickness of more than 200 nm, the Cu-rich phase is covered with the oxide film, and the antibacterial property tends to decrease.
Examples of the heat treatment for forming an oxide film having a thickness of 200 nm or less on stainless steel include short-time annealing of 10 minutes or less in a temperature range of 400 to 900 ° C. and batch treatment of a temperature of less than 400 ° C. for about 1 hour. As the atmosphere for heating, air, a mixed gas of oxygen and an inert gas, or the like is used.

[0013]

Example Austenitic and ferritic stainless steels shown in Table 1 were melted and cast into a slab having a thickness of 200 mm, and then hot rolled to a thickness of 4.5 mm. Ferrite-based stainless steel is subjected to batch annealing at 800 ° C. for 24 hours, and austenitic stainless steel is subjected to batch annealing at 800 ° C. for 100 hours to precipitate a Cu-rich phase at a ratio of 0.2 vol% or more, followed by cold rolling and annealing. Repeatedly, finally the plate thickness was 0.
A bright annealed material of 7 mm was obtained.

[0014]

The cold-rolled annealed sheet thus obtained was subjected to an oxidation treatment at various coloring temperatures in the atmosphere, and the thickness of the produced oxide film was measured by a glow discharge emission spectrometer. Further, a test piece of 5 cm × 5 cm was cut out from the plate after coloring and used for an antibacterial test. For antibacterial tests, Staph
ylococcus aureus IFO12732
(Staphylococcus aureus) in normal broth medium at 35 ° C, 16
The culture was prepared by shaking culture for -24 hours. The culture solution was diluted 20,000 times with sterile phosphate buffer solution to prepare a bacterial solution. 1 ml of the bacterial solution was dropped on a # 400 polished surface of a test piece of 5 cm × 5 cm and stored at 25 ° C. for 24 hours. After storage, the test piece is used as a SCDLP medium (manufactured by Nippon Pharmaceutical Co., Ltd.)
After washing off with 9 ml, the number of viable bacteria in the obtained liquid was counted by the pour plate culture method (culture at 35 ° C. for 2 days) using a standard agar medium. As a reference, the bacterial solution was directly dropped on the petri dish, and the number of viable bacteria was counted in the same manner.

Those in which viable bacteria were not detected are marked with ⊚, and those in which 95% or more of them were killed compared with the reference viable count were marked with ○, 60.
What was killed in the range of less than 95% was evaluated as Δ, and what killed less than 60% was evaluated as x. The survey results are also shown in Table 2. As shown in the test results of Table 2, Cu
Was added in an amount of 0.4% by weight or more, a Cu-rich phase was precipitated in the base material in an amount of 0.2% by volume or more, and a colored film having a thickness of 200 nm or less was formed. On the other hand, even if Cu is added in an amount of 0.4% by weight or more, if the Cu-rich phase precipitated in the base material is less than 0.2% by volume, further, the Cu-rich phase is 0.2% by volume or more. Even if it was present, the antibacterial properties were inferior as seen in Comparative Examples in the case where the coloring treatment was performed at a temperature exceeding 900 ° C. or the case where a colored film having a thickness exceeding 200 nm was formed.
From this result, the heating temperature during coloring was set to 900 ° C. or lower,
It is confirmed that setting the thickness of the colored oxide film to 200 nm or less is effective in improving both antibacterial properties and design properties.

[0017]

[0018]

As described above, the stainless steel of the present invention has a Cu content of 0.4% by weight and a Cu-rich phase precipitated in the base material of 0.2% by volume or more, and is 400 to 9
Since the colored oxide film having a thickness of 200 nm or less is formed by the heat treatment at 00 ° C., the design is improved without impairing the antibacterial property exhibited by the Cu-rich phase. Therefore, antibacterial,
As a stainless steel product that requires design, it is used in a wide range of fields such as kitchen equipment, electrical products, building materials, various machines, and chemical equipment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadayuki Nakamura 4976 Nomura-Minamimachi, Shinnanyo-shi, Yamaguchi Nisshin Steel Co., Ltd.

Claims (2)

[Claims] 1. C: 0.8 wt% or less, Si: 3 wt%
Below, Mn: 5 wt% or less, Cr: 10 to 30 wt%,
Ni: 15% by weight or less, Cu: 0.4 to 5.0% by weight, the second phase mainly composed of Cu is dispersed in the matrix at a ratio of 0.2% by volume or more, and at 900 ° C. or less. Stainless steel excellent in antibacterial properties and design, in which an oxide film having a thickness of 200 nm or less is formed by heat treatment at a temperature. 2. Nb: 0.02-1% by weight, Ti: 0.
02 to 1% by weight, Mo: 3% by weight or less, Al: 1% by weight
Below, Zr: 1 wt% or less, V: 1 wt% or less, B:
0.05 wt% or less, rare earth element (REM): 0.05
The stainless steel according to claim 1, wherein the stainless steel contains one kind or two or more kinds in an amount of not more than wt%.