JPH11279744A - Stainless steel product excellent in antibacterial property and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stainless steel product having good antibacterial properties even in the case it is a grinding-finished material. SOLUTION: This stainless steel product is the one using a stainless steel contg., by weight, >=0.5% Cu as a base material, and in which a passive film in which the atomic ratio of Fe/Cr is regulated to <=0.4 is formed on the surface of the base material after grinding finish. As the base material, the stainless steel in which the secondary phases essentially consisting of Cu are precipitately dispersed in the ratio of >=0.2 vol.% is preferably used. It is produced by subjecting the stainless steel contg. >=0.5% Cu to grinding finish, thereafter executing bright annealing in a reducing gas atmosphere and reducing the passive film formed on the surface of the base material. Heat treatment such as aging treatment of precipitation-dispersing the secondary phases essentially consisting of Cu in the ratio of >=0.2 vol.%, slow cooling after the annealing or the like can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel product which exhibits excellent antibacterial properties after being polished and is used for various equipment and instruments which have high sanitary requirements and a method for producing the same.

[0002]

2. Description of the Related Art SUS430 and SUS304 are representative of various equipment used in kitchen equipment, hospitals, etc., and pipes used as handrails in transportation such as buses and trains, because they are required to have corrosion resistance in a general environment. Used stainless steel is mainly used. However, hospital infections caused by Staphylococcus aureus, etc., and food poisoning caused by Escherichia coli such as O-157 have recently become a problem. Is required. Along with this, the materials used for various machines and instruments are not limited to the characteristics of general structural materials, and are maintenance-free with functions such as antibacterial properties that do not need to prevent contamination such as periodic disinfection. Material is desired. Examples of the material provided with antibacterial properties include an antibacterial coat formed by an organic film or plating (JP-A-5-228202).
Japanese Patent Application Laid-Open No. Hei 6-10191), an antibacterial stainless steel to which Cu having a strong antibacterial action is added (Japanese Patent Application No. Hei 6-101191).
-210558) and the like.

[0003]

The antibacterial coat has a reduced antibacterial property as the film disappears. Organic substances with reduced antibacterial properties may become a source of nutrients and may instead propagate bacteria and germs. In the case of performing composite plating in which an antimicrobial agent component is mixed, the plating layer tends to be insufficient in adhesion, and the workability may be reduced in some cases. In addition, dissolution of the coating, wear,
The appearance and the antibacterial action are also reduced due to defects and the like. In stainless steel to which Cu is added, Cu is present in the passive film formed on the surface, and the antimicrobial property is exhibited by the elution of Cu as ions. C
The elution of u ions is promoted by uniformly and finely dispersing and precipitating a second phase mainly composed of Cu (hereinafter, referred to as a Cu-rich phase) by heat treatment such as aging treatment, so that more favorable antibacterial properties are exhibited ( JP-A-9-195509). However, when stainless steel is mechanically polished to improve the antiglare property, the antibacterial property may be reduced.

[0004]

SUMMARY OF THE INVENTION The present invention has been devised in order to solve such a problem, and has an excellent appearance of a polished finish by regulating Fe contained in a passive film. It is an object of the present invention to provide a stainless steel product which maintains good and exhibits good antibacterial properties. The stainless steel product of the present invention contains 0.5% by weight in order to achieve the object.
A passivation film in which the above stainless steel containing Cu is used as a base material and the atomic ratio of Fe / Cr is adjusted to 0.4 or less after polishing is formed on the base material surface.
As the stainless steel used as the substrate, it is preferable that the second phase mainly composed of Cu is precipitated and dispersed at a rate of 0.2% by volume or more. This stainless steel product is obtained by polishing and finishing a stainless steel containing 0.5% by weight or more of Cu and then performing bright annealing in a reducing gas atmosphere to reduce a passive film formed on the surface of the base material. Manufactured. Prior to the polishing, heat treatment such as aging treatment in which the second phase mainly composed of Cu is precipitated and dispersed at a rate of 0.2% by volume or more, and slow cooling after annealing can be performed.

[0005]

The surface of stainless steel is covered with a passive film composed of a hydroxide mainly composed of Cr. In the stainless steel to which Cu is added to improve the antibacterial property, the passive film contains Cu that elutes as ions effective for the antibacterial property. However, if this stainless steel is mechanically polished to a polished finish, the antibacterial properties may be reduced.
The present inventors have investigated and studied in detail the effect of mechanical polishing on the reduction of antibacterial activity. As a result, the passivation film formed on the stainless steel surface after mechanical polishing is Cr or C
It was found that a large amount of Fe was contained in addition to u, and that this Fe content had an adverse effect on antibacterial properties. In other words, Fe contained in the passivation film is preferentially eluted as ions and suppresses elution of Cu having a lower ionization tendency than Fe. Even in stainless steel with a Cu-rich phase precipitated, Fe
Preferentially dissolves the ionization of the Cu-rich phase.

[0006] Based on such findings, various experiments were conducted to remove the Fe content in the passivation film that is inhibiting the ionization of Cu. As a result, when bright annealing is performed in a reducing atmosphere after mechanical polishing, the passive film formed during mechanical polishing temporarily disappears by a reduction reaction, and Cr and Cu are newly added.
The formation of a passive film mainly composed of
The newly formed passivation film exhibits good antibacterial properties because it is not affected by the Fe content. Even in stainless steel in which a Cu-rich phase is uniformly and finely precipitated, reduction annealing and passivation of a passive film occur due to bright annealing. In addition, since the passivation film generated by the reduction annealing is not formed on the Cu-rich phase, the ratio of the Cu-rich phase exposed on the stainless steel surface is increased, and the antibacterial property is further improved. Even if bright annealing is performed after mechanical polishing, the obtained stainless steel product is
It shows the same anti-glare properties as a generally manufactured polished finish, and has no problem in terms of design.

Embodiment

[0007] The stainless steel to which the present invention is applied is 0.1 mm.
The steel type is not specified as long as it contains 5% by weight or more of Cu, and a ferritic material such as SUS430J1L,
Austenitic type such as SUS304J1 and SUS316J1L, martensite type such as SUS630, SUS3
There are two-phase systems such as 29J1. In order to increase the concentration of Cu in the passive film effective for antibacterial properties and to precipitate a Cu-rich phase on the substrate, the larger the amount of Cu added, the more preferable, and the amount of Cu ions effective for maintaining antibacterial properties is secured. 0.5 from above
A Cu content of at least% by weight is required. The upper limit of the Cu content is not particularly limited, but properties such as hot workability tend to decrease in stainless steel to which an excessive amount of Cu is added. Therefore, the Cu content is preferably restricted to 5% by weight or less.

[0008] Alloy components other than Cu include Cr, Ni, C, Si, Mn, Mo, and the like usually contained in stainless steel.
Al and the like. The content of these alloy elements differs depending on the steel type, but C: 0.001 to 0.5% by weight, Si:
0.1 to 3.0% by weight, Mn: 0.1 to 4.0% by weight,
Cr: 10.0 to 30.0% by weight, Ni: 0.05 to 1
5.0% by weight, Mo: 0.01 to 7.0% by weight, Al:
It is adjusted in the range of 0.01 to 7.0% by weight. In addition, Ti, Nb, V, and Zr are used individually or in combination in an amount of 0.01 to 1.0% by weight as a property improving element such as workability. Singly or in combination of 0.0005 to 0.05% by weight.

When the Cu-added stainless steel is aged or cooled slowly, a Cu-rich phase precipitates in the matrix. C
The u-rich phase effectively improves the antibacterial property since a passivation film mainly composed of Cr is not formed thereon. In order to impart antibacterial properties to the entire surface of stainless steel, it is necessary to uniformly disperse a fine Cu-rich phase in a matrix. Fine Cu rich phase is 500-900 ° C × 10
After aging treatment for minutes to 100 hours, or after annealing, the temperature range of 900 to 500 ° C. where a Cu-rich phase is apt to precipitate is gradually cooled to uniformly precipitate and disperse in the matrix. When 0.2 volume% or more of Cu-rich phase is precipitated and dispersed in the matrix, the antibacterial property is remarkably improved.

[0010] The Fe atom contained in the ordinary passivation film is
It exists in a stable state, and hardly elutes in an environment containing moisture such that antibacterial properties are exhibited. However, the polished stainless steel contains about 0.6 to 0.7 Fe at an atomic ratio of Fe / Cr under normal polishing and finishing conditions. In this passive film, Fe is preferentially oxidized simultaneously with Cr during cooling after polishing, and the passivation film is present in a state close to the oxide film, so that the bonding state of Fe becomes unstable.
It is presumed that Fe elutes preferentially in an environment containing water due to the behavior of Fe after such polishing finish, and Cu elution is suppressed. The bonding state of Fe is Cu
Irrespective of the addition amount of Cu or the presence of a Cu-rich phase, the relation is established with Fe, Cr in the passive film and oxygen that makes these exist as a film. In order to stabilize the bonding state of Fe in the passivation film, the presence of Cr has an effect. From the results of investigations and studies by the present inventors, if the atomic ratio of Fe / Cr is set to 0.4 or less, Fe Was found to be in a stable binding state. Thereby, the adverse effect of the Fe component on the elution of Cu is suppressed, and good antibacterial properties are obtained.

In order to reduce the Fe content, a method of eliminating a passivation film formed after mechanical polishing and forming a new passivation film is adopted. A typical example is bright annealing after mechanical polishing. Bright annealing is to heat-treat stainless steel in a reducing gas atmosphere, and the heat reduction at this time reduces the Fe-based passive film formed after mechanical polishing. The annealing atmosphere is more effective as the concentration and temperature of the reducing gas are higher from the viewpoint of reducing the passive film mainly composed of Fe. However, when the reducing gas or the heating temperature is increased, not only the production cost is increased, but also as the heating temperature is increased, the re-solid solution of the Cu-rich phase is promoted, and the antibacterial property is rather reduced. In addition, the passivation film mainly composed of Fe generated by mechanical polishing also has different physical properties depending on the type of steel. Considering these conditions comprehensively, the annealing conditions are not determined unconditionally, but are generally 75% by volume or more of hydrogen and 2%.
Using a reducing gas containing 5% by volume or less of nitrogen, 800
Reduction heating at a temperature of at least 30 ° C. for at least 30 seconds is preferred.

[0012]

EXAMPLES Various stainless steels having the compositions shown in Table 1 were melted and subjected to hot rolling, annealing and cold rolling to produce stainless steel sheets having a thickness of 0.6 mm. For the steel types A, B, and C, aging treatment was performed at 800 ° C. for 24 hours after cold rolling to precipitate a Cu-rich phase.

[0013]

Each stainless steel plate was mechanically polished using a belt-type mechanical polishing machine to obtain a # 320 or # 120 polished finish. In Test Nos. 1 to 4 according to the present invention, after mechanical polishing, bright annealing was performed by heating to 900 to 1050 ° C. in a reducing gas atmosphere of 75% H ₂ + 25% N ₂ . A test piece was cut out from the bright annealed stainless steel plate and subjected to the following tests. For comparison, the same test was performed on test numbers 6 to 8 that were not subjected to bright annealing, and the effect of bright annealing was comparatively investigated. Each test piece was observed with an X-ray photoelectron analyzer, and Fe and Cr in the passive film were quantified. The metal structure was observed with a transmission electron microscope,
The u-rich phase was quantified. In antibacterial tests, Staphy
lococcus aureus IFO12732
A test bacterium obtained by culturing (Staphylococcus aureus) on a normal agar medium was again inoculated on the normal agar medium, and a culture solution cultured at 35 ° C. for 16 to 20 hours was prepared. The culture was incubated with phosphate buffer for 20 minutes.
It was diluted 000-fold to prepare a bacterial solution. 1 ml of bacterial solution 5c
Drop on the surface of a test piece of mx 5 cm, 25 ° C, relative humidity 9
It was allowed to stand in a humid atmosphere of 0% or more for 24 hours.

Next, SCDLP (Soybean C)
asein Digest Broth with L
ecitin and Polysorbate 8
The bacteria were washed out from the test pieces with 10 ml of a medium (0, manufactured by Nippon Pharmaceutical Co., Ltd.), and the number of viable bacteria in the wash was counted by a pour plate method (cultured at 35 ° C. for 2 days) using a standard agar medium. The counted number of viable bacteria was converted into one test piece, and a bacteria reduction rate [= (viable bacteria before test−viable bacteria after test) / viable bacteria before test × 100 (%)] was determined. Was. Those having a sterilization rate of 99% or more were determined to have antibacterial properties. Also,
In order to investigate metal ions eluted in the antibacterial test solution, an antibacterial test solution to which no bacteria were added was prepared in the same manner, and 5 cm × 5
cm test piece was immersed in 25 ml of the antibacterial test solution at 25 ° C.
After standing for 24 hours, the amounts of Fe and Cu ions eluted in the antibacterial test solution were analyzed by ion chromatography.

The test results are shown in Table 2 together with the production conditions. As is clear from Table 2, in Test No. 5 using steel type D to which Cu was not added, since bright annealing was performed after mechanical polishing, the Fe content in the passivation film was low, and the elution amount of Fe was small. No antibacterial properties due to no elution. In Test Nos. 6 to 8 using steel types A to C to which 0.5% by weight or more of Cu was added, since bright annealing was not performed after polishing, the passivation film after mechanical polishing contained a large amount of Fe, The elution amount of Fe which inhibits the elution of Cu was large, and the antibacterial property was poor. On the other hand, in Test Nos. 1 to 4 using steel types A to C containing 0.5% by weight or more of Cu as the base material and performing bright annealing after mechanical polishing, the Fe content in the passive film is reduced by bright annealing. Was. It can be seen that the amount of Fe eluted was small with the decrease of Fe content, and the elution of Cu was actively progressing. As a result, excellent antibacterial properties were obtained in the polishing finish.

[0017]

[0018]

As described above, the stainless steel product of the present invention is based on a stainless steel containing 0.5% by weight or more of Cu and has a Fe / Cr atomic ratio of 0.1% on the surface.
4 or less passive films are formed. Since the Fe content in the passive film is small, the elution of Cu effective for antibacterial properties is not hindered, and good antibacterial properties are exhibited even after mechanical polishing. Above all, in stainless steel in which a Cu-rich phase is precipitated, the amount of the Cu-rich phase exposed on the surface increases, so that the antibacterial property is significantly improved. Such stainless steel products exhibiting excellent antibacterial properties are used in a wide variety of fields as handrails in various equipment used in kitchen appliances, hospitals, and the like, and in transportation such as buses and trains.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Suzuki 4976 Nomura Minamicho, Ninanyo-shi, Yamaguchi Prefecture Inside Nisshin Steel R & D Laboratory (72) Inventor Sadayuki Nakamura 4976 Nomura Minamicho, Shinnanyo-shi, Yamaguchi Prefecture Nissin Steel Technology Co., Ltd.

Claims (5)

[Claims] 1. A passivation film having a base material of stainless steel containing 0.5% by weight or more of Cu and having a Fe / Cr atomic ratio adjusted to 0.4 or less after polishing is formed on the surface of the base material. Has stainless steel products with excellent antibacterial properties. 2. The volume of the second phase mainly composed of Cu is 0.2% by volume.
2. The method according to claim 1, wherein the base material is precipitated and dispersed in the above ratio.
The stainless steel product described. 3. After polishing and polishing a stainless steel containing 0.5% by weight or more of Cu, bright annealing is performed in a reducing gas atmosphere to reduce a passive film formed on the substrate surface. Method of manufacturing stainless steel products with excellent antibacterial properties. 4. The stainless steel having excellent antibacterial properties according to claim 3, wherein the stainless steel is subjected to a heat treatment for precipitating and dispersing a second phase mainly composed of Cu at a rate of 0.2% by volume or more before polishing. Product manufacturing method. 5. The bright anneal of mechanically polished stainless steel in a reducing gas atmosphere having a reducing ability to reduce the Fe / Cr of the passive film to an atomic ratio of 0.4 or less. 2. A method for producing a stainless steel product having excellent antibacterial properties according to item 1.