JPH11269615A - Ni-containing stainless steel excellent in antibacterial property and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Ni-contg. stainless steel having antibacterial properties excellent in quick-acting properties and maintainability. SOLUTION: Relating to a stainless steel contg. 10 to 40 wt.% Ni, Ni atoms are concentrated on a surface film by >=0.6 atomic %. In the producing method, Ni atoms are concentrated on the surface film by bright annealing or ordinary annealing and pickling at >=950 deg.C. Or, after bright annealing or ordinary annealing and pickling at >=1000 deg.C, grinding is executed to expose Ni atoms of >=0.6 atomic % to the surface film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a stainless steel suitable for applications requiring antibacterial properties and corrosion resistance in a wide range of fields such as kitchen equipment, electric equipment, building materials, mechanical equipment and chemical equipment. The present invention relates to steel and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, various equipment used in kitchen appliances and hospitals, and pipes for railings of transportation means such as buses and trains 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 become a problem in recent years. Is required. Along with this, even as a material used for various machines and instruments, it is not limited to the characteristics as a general structural material, but also has a maintenance free function provided with a function such as antibacterial property which does not need to prevent infection such as periodic disinfection.
Material is desired. Examples of the material having antibacterial properties include JP-A-5-228202 and JP-A-6-101.
No. 91, etc., an antibacterial coating by an organic film or plating, and a strong antibacterial action as disclosed in JP-A-9-195509, JP-A-9-176800, etc. There is an antibacterial stainless steel to which Cu or Ag is added.

[0003]

However, there is a possibility that the antibacterial coat of the antibacterial coat decreases in accordance with the disappearance of the film. Organic substances with reduced antibacterial properties may become a source of nutrients and may propagate bacteria and various germs. In the case of performing composite plating in which an antibacterial agent component is mixed, the adhesion of the plating layer is not sufficient, and the workability may be reduced. Also,
The appearance may be reduced due to dissolution, abrasion, chipping, etc. of the film, and the antibacterial action may be reduced. Also, Cu
Alternatively, in stainless steel to which Ag is added, Cu, Ag
When a large amount of is added, there is a concern that the productivity may decrease such as the hot workability.

In order to solve the above-mentioned problems, the present invention focuses on Ni as a metal element having an antibacterial action other than Cu or Ag. For stainless steel containing Ni, bright annealing or ordinary annealing pickling is performed. Alternatively, it is an object to impart antibacterial properties without impairing the productivity by concentrating or exposing Ni atoms to the surface film by polishing after annealing.

[0005]

According to the present invention, in order to achieve the object, in a stainless steel containing 10 to 40% by weight of Ni, 0.6 atomic% or more of Ni atoms are concentrated in a surface film. It is characterized by. As this means, 9
Ni atoms are enriched in the surface film by 0.6 atomic% or more by bright annealing or annealing and pickling at 50 ° C. or more, or Ni atoms are reduced to 0 in the surface layer by bright annealing or annealing and pickling at 1000 ° C. or more. .6 at% or more
Thereafter, the surface film generated during annealing is removed by polishing, and the surface layer portion in which Ni atoms are enriched by 0.6 atomic% or more is exposed as a new surface, thereby providing antibacterial properties.

[0006]

Embodiments of the present invention will be described below. Stainless steel is made of C, called a passive film.
Since the surface is covered with a hydroxide mainly composed of r,
Has excellent corrosion resistance. The present inventors have added Ni exhibiting effective antibacterial properties to stainless steel, measured the amount of Ni contained in the passive film, dropped a solution containing Staphylococcus aureus, and then adhered with a polyethylene film. The antibacterial properties were investigated in the following ways. As a result, it was found that stainless steel containing 10% by weight or more of Ni had antibacterial properties. However, simply adding Ni to steel may not always provide sufficient antibacterial properties and its durability. Therefore, as a result of further study, even if the Ni content is the same, stable and excellent antibacterial properties are obtained only when the surface film is enriched with 0.6 atomic% or more of Ni atoms, Moreover, they have found that they exhibit a fast-acting antibacterial action.

As a means for enriching Ni atoms in the surface film, a method of enriching Ni in the surface film during annealing can be considered. At this time, when bright annealing or annealing pickling is performed at 950 ° C. or more, diffusion of Ni is easily caused by annealing at a high temperature, and Ni is diffused and concentrated to the surface film, and antibacterial properties are considered to be exhibited. .

As a means for concentrating Ni atoms in the surface film, there is a method of bright annealing or annealing at 1000 ° C. or more. As described above, since Ni tends to be enriched not only in the surface film but also in the surface layer portion, even if the surface film is removed by polishing after performing bright annealing at 1000 ° C. or more or ordinary annealing and pickling, The antibacterial property is exhibited by using a newly generated surface as a surface layer portion where Ni is concentrated.

The mechanism by which Ni atoms contained in stainless steel exhibit antibacterial properties is presumed as follows. Generally, as the Ni content increases, the amount of Ni atoms in the surface film or surface layer after bright annealing or after annealing and pickling also increases. In a humid environment where bacteria can easily grow, even a small amount of moisture on the surface of stainless steel causes a trace amount of Ni
It is thought that even if the amount is extremely small, it reacts efficiently with the respiratory system and metabolic enzymes of bacterial cells near the steel surface to inactivate it, thereby suppressing the growth of bacteria and sterilizing it. .

Therefore, in order to develop the antibacterial properties of stainless steel, it is necessary to enrich Ni atoms in the surface layer. The present inventors have added Ni atoms to the surface coating in an amount of 0.1%.
It has been found that antimicrobial properties are exhibited by concentrating at least 6 atomic%. Furthermore, in the Ni-containing stainless steel of the present invention, it has been found that the antimicrobial action lasts for a long time because the Ni atomic weight of the surface film is much larger than the eluted Ni ions. Moreover, since the steel material itself is provided with antibacterial properties, it has a surface that is resistant to scratches, abrasion, etc., and high-level stable antibacterial properties are maintained. Further, since Ni is harmless to the human body and the like under a normal use environment, the stainless steel to which Ni is added does not adversely affect the human body and the environment.

The reasons for limiting the component range and the production method of the present invention are described below.

Ni: 10 to 40% by weight Ni is an element generally used for obtaining the strength, ductility, and toughness of a given stainless steel, but in the present invention, when the Ni content is less than 10% by weight. In addition, the concentration of Ni atoms in the surface film or surface layer after bright annealing or annealing pickling is small, and sufficient antibacterial properties cannot be obtained in any of the bright annealing state, the annealing pickling state, and the polishing state thereafter. On the other hand, the higher the Ni content, the higher the Ni content of the surface film, and the higher the antibacterial effect. However, if the Ni content exceeds 40% by weight, the effect is saturated and the cost of steel material increases. Therefore, in the present invention, the Ni content is 1
It was set to 0 to 40% by weight.

[0013] Bright annealing conditions: 9 without polishing
Heating to 50 ° C. or higher, and 1000 ° C. or higher when applied sufficiently diffuses Ni into the surface film and the surface layer. In addition, bright annealing does not require pickling after annealing, so that the Ni-enriched surface film is not removed. The effect becomes remarkable as the annealing temperature increases, and annealing at 950 ° C. or more causes a sufficient concentration of Ni in the surface film to exhibit antibacterial properties. However, when polishing is performed after bright annealing, the Ni-enriched layer in the surface film is removed during polishing. However, this problem can be solved by enriching Ni not only in the surface film but also in the lower layer. When annealing is performed at a higher temperature, Ni is sufficiently concentrated in the newly formed film even if the surface film formed during bright annealing is removed by polishing.
Antibacterial properties are obtained. The concentration of Ni on the surface layer is 1000
The effect is remarkable above ℃.

Atmospheric annealing conditions: 9 when no polishing is performed
Pickling after air annealing at 50 ° C. or higher, and at 1000 ° C. or higher in the same manner as in bright annealing Thicken. Although the surface film is removed by the subsequent pickling, a new surface film is formed at the same time as the surface layer is exposed, and Ni atoms are concentrated in the film. The effect becomes remarkable by annealing at 950 ° C. or more, and an effective antibacterial property is obtained. When performing polishing, it is necessary to concentrate Ni on the surface layer, as in the case of bright annealing, and it is necessary to perform annealing at 1000 ° C. or higher after polishing to obtain a sufficient antibacterial action. Polishing after bright annealing and annealing pickling: Ni is concentrated in the surface layer in both bright annealing and annealing pickling. Therefore, if necessary, even if the surface film of the steel material is removed by polishing and a new surface film is formed based on the Ni-enriched surface layer, the Ni film is concentrated in the film, so that the antibacterial property is obtained. Is expressed.

Ni atoms in the surface film: not less than 0.6 atomic% Ni atoms in the surface film are ionized in a very small amount under a humid environment where bacteria can easily grow, and the respiratory system of bacterial cells existing near the steel surface and the like. Reacts efficiently with metabolic enzymes to inactivate. The antibacterial effect is remarkable when the concentration of Ni atoms in the surface film is 0.6 atomic% or more in any of the bright annealing state, the normal annealing pickling state, and the polishing state thereafter.
If it is less than 6 atomic%, a sufficient antibacterial effect may not be obtained stably depending on the use environment. Therefore, in the present invention, the Ni content of the surface film is set to 0.6 atomic% or more.

[0016]

EXAMPLES Example 1 A 30 kg stainless steel having the composition shown in Table 1 was melted in a vacuum melting furnace and subjected to hot rolling. Then, subjected to hot-rolled sheet annealing, followed by cold rolling, and then performed air annealing pickling or bright annealing,
Finally, a cold-rolled annealed sheet of 0.8 to 1.2 mm was obtained. The annealing temperature of bright annealing or atmospheric annealing was set to 1050 ° C. when polishing was not performed thereafter and 1100 ° C. when polishing was performed. The surface Ni concentration was measured using an X-ray electron spectrometer, and the surface of the degreased sample was irradiated with MgKα radiation to obtain Fe, Cr, Ni,
The relative sensitivity index was calculated from the integrated intensity of each peak of C, O, Si, and Mn.

In the antibacterial test, Staphylococcus aureus
IFO12732 (Staphylococcus aureus) on an agar plate at 37 ±
The test bacterium pre-cultured at 1 ° C. for 16 to 24 hours was inoculated again to a normal agar medium and cultured at 37 ± 1 ° C. for 16 to 24 hours. Thereafter, the cells were uniformly dispersed in a 1/500 normal broth medium, which was diluted 500 times with purified water and adjusted to pH 7.0 ± 0.2 with purified water, and the number of bacteria per ml was 2.0 × 105 to 1.0.
The bacterial solution was adjusted to be × 106. 0.5 ml of the bacterial solution was dropped on the surface of the test piece, and a polyethylene film was placed on the surface of the solution to adhere the solution. These are 35 ± 1 ° C., relative humidity 9
It stored for 6 hours or 24 hours under the condition of 0% or more.
After saving, SCDLP (Soybean Casein Digest Broth wit
h Lecithin and Polysorbate 80, manufactured by Nippon Pharmaceutical Co., Ltd.)
The surviving bacteria were washed out of the test piece with the medium, and the viable cell count of the washed solution was determined by the pour plate culture method (35 ° C, 2 ° C) using a standard agar medium.
The number of viable bacteria was counted and the value was converted per sample. According to this test method, it can be said that as the viable cell count decreases 6 hours and 24 hours after the initial viable cell count, the material has a stronger antibacterial property. Further, in order to confirm that there was no abnormality in the test, as a reference, a bacterial solution was directly dropped on a plastic dish, and the number of bacteria was similarly counted.
The evaluation of the antibacterial test was as follows: 生: No viable bacteria were detected after the test, を: 95% or more died compared to the reference viable count, 、: Died in the range of 60 to less than 95% Was evaluated as Δ, and those having a killed amount of less than 60% were evaluated as ×. Table 1 shows the evaluation results together with the surface Ni concentration.

[0018]

[Table 1]

Note 1) Annealing pickling refers to a pickling step using a mixed acid after ordinary short annealing. Note 2) The presence or absence of polishing refers to the presence or absence of a step of polishing the material with # 400 emery paper. Note 3) The surface Ni concentration indicates the measured value of the surface film by an X-ray electron spectrometer. Note 4) The antibacterial property is measured by dropping the bacterial solution and contacting with a film.
After standing for 4 hours, those without viable bacteria were detected as ◎,
Those that killed 95% or more were rated as ○, those that died in the range of 60 to less than 95% were rated as Δ, and those that killed less than 60% were rated X.

As is clear from Table 1, the steel of the present invention has a Ni concentration of 0.6 atomic% or more in the surface film even in the bright annealing or normal annealing pickling state or the polishing state thereafter, and has a sufficient antibacterial property. Has the property. On the other hand, in each of the comparative steels, the Ni concentration of the surface film is less than 0.6 atomic%, and sufficient antibacterial properties are not necessarily obtained.

Example 2: Inventive steels A2 and A shown in Table 1
For 4 and A8, a plate material having a thickness of 2 mm was cut out from the ingot after 30 kg of vacuum melting, and one surface of the plate material was polished with # 400 emery paper. The antibacterial properties when the film was kept in contact for 24 hours after dropping the bacteria were investigated. Regarding A2 and A8, some samples were polished and then subjected to bright annealing or air-annealed pickling, and some of them were further polished to investigate their antibacterial properties. The results of the investigation are shown in Table 2 together with the Ni content of the material.

[0022]

[Table 2]

Note 1) The antibacterial property was evaluated by dropping a bacterial solution, adhering the film to the film, and allowing the film to stand for 24 hours. Those that died within the range of less than △ were evaluated as △, and those that died less than 60% were evaluated as ×.

As shown in Table 2, the Ni atom concentration of the surface coating of the steel ingot of the present invention cut out and polished was determined by the bright annealed state of the same sample, the normal annealed pickling state, or the polishing after annealing. It is smaller than the Ni atom concentration of the surface film in the state in which it was made. As a result, A2 and A8 whose Ni content is at least 10% by weight but less than 14% by weight as defined in the present invention cannot obtain sufficient antibacterial properties with a plate material cut out from an ingot and polished. In A2, the surface Ni concentration is increased by bright annealing or annealing pickling,
If the annealing temperature is lower than the temperature specified in the present invention, the surface Ni concentration is less than 0.6 atomic%, and sufficient antibacterial properties cannot be obtained. The reason for this is that the sheet material cut out from the ingot was not subjected to a heat treatment such as annealing, so that the concentration of Ni atoms in the surface film did not occur. Alternatively, it is estimated that Ni was not concentrated enough to obtain sufficient antibacterial properties in the surface layer. According to this survey, 0.6 atomic% was added to the surface layer.
To obtain sufficient antibacterial properties by enriching the above Ni atoms,
It has been confirmed that bright annealing or normal annealing in the temperature range defined by the present invention is effective.

As shown in A4, when the Ni content is sufficiently high, excellent antibacterial properties can be obtained in a polished state without any annealing. However, as described above, by performing bright annealing or annealing pickling, the surface Ni can be further increased.
In view of the fact that the concentration can be increased, more excellent antibacterial properties can be imparted, and the decrease in workability due to the large amount of Ni content can be improved, the present invention provides that bright annealing or acid pickling is performed even when a large amount of Ni is contained. did.

Example 3: Steel types A2, A4 and A5 in the steel of the present invention listed in Table 1 and steel type B1 in a comparative steel in which sufficient antibacterial activity was not recognized after 24 hours were as follows:
After the bacterial solution was dropped onto the surface of the sample manufactured under the same manufacturing conditions as the sample used in Example 1, the film was closely adhered and stored for 6 hours, and the test piece was immersed in running tap water for 3 or 10 days. Table 3 shows the results of the same antibacterial test for storage for 24 hours. At this time, when the antibacterial property is developed in 6 hours, which is shorter than the normal storage time of 24 hours, the antibacterial property can be regarded as having an immediate effect on the antibacterial property. If no decrease in antibacterial activity is observed, the antibacterial activity is considered to be persistent.

[0027]

[Table 3]

Note 1) The antibacterial property was evaluated by dropping a bacterial solution, adhering the film to the film, and allowing it to stand for 24 hours. ◎: No viable bacteria were detected, ○: 95% or more died, ○: 60-95% Those that died within the range of less than △ were evaluated as △, and those that died less than 60% were evaluated as ×.

As can be seen from Table 3, the comparative steel does not have a rapid antibacterial effect. As shown in Comparative Steel B1, when immersed in running water for 3 or 10 days,
Antibacterial properties are lower than before immersion. As a result of examining the Ni atom concentration of the surface film of the sample after immersing the comparative steel B1 in running water for 10 days, the Ni atom concentration was 0.40 atomic%, which was 0.1% higher than before immersion.
It was reduced by 10 atomic%. That is, in the comparative steel B1, the Ni of the surface film is eluted into the running water when immersed in the running water, and the N of the surface film is reduced.
It can be said that the antimicrobial action was reduced because the i-atom concentration was reduced. On the other hand, in the steel of the present invention, a quick effect of the antibacterial action was recognized. In addition, the antimicrobial activity was hardly impaired even when immersed in running water for 10 days, and the decrease in the Ni atom concentration of the surface coating of any of the steels of the present invention was 0.05% or less. It was confirmed that the compound had sufficient durability for the action.

Example 4: Steel A of the present invention used in Example 1
Using stainless steel plates of 1, A8 and comparative steel B1,
A plurality of sinks for sinks having a length of 640 mm and a width of 440 mm having a depth of 180 mm were manufactured by press molding. Thereafter, the inner surface of the sink was roughly polished and buff-polished in the same manner as a normal product for a part of the product to obtain a final product. A part of the side surface of the unpolished product and the final product is cut out, the concentration of Ni atoms in the surface film on the inner surface of the sink, and the antibacterial property when the film is adhered and stored for 24 hours under the droplets of bacteria. investigated. Table 4 shows the survey results

[0031]

[Table 4]

Note 1) The antibacterial property was evaluated by dropping a bacterial solution, adhering the film to the film, and allowing the film to stand for 24 hours. ◎: No viable bacteria were detected, ○: 95% or more died, ○: 60-95% Those that died within the range of less than △ were evaluated as △, and those that died less than 60% were evaluated as ×.

As shown in Table 4, when the steel of the present invention and the comparative steel were processed into products, the Ni atom concentration of the surface film on the processed surface was slightly reduced as compared with before the processing, but the amount of the reduction was at most. 0.04%. Further, the Ni atom concentration of the surface film of the polished final product was not much different from that before the processing, though there was a slight change. Therefore, it was confirmed that the steel of the present invention exhibited excellent antibacterial properties even in a processed and polished product.

[0034]

As described above, in the Ni-containing stainless steel of the present invention, the amount of Ni in the surface film is controlled by bright annealing or ordinary annealing and pickling, while controlling the amount of Ni in the material. By polishing after bright annealing or ordinary annealing and pickling, N on the newly formed surface film
By concentrating the i-atoms, excellent antibacterial properties having a quick effect and a long lasting effect are exhibited. In this way, stainless steel with antibacterial properties is used in areas where antibacterial properties are required, such as kitchen equipment, equipment used in hospitals, handrails of transportation such as buses and trains, and living environments. Be improved.

Claims (5)

[Claims] 1. A stainless steel containing 10 to 40% by weight of Ni, wherein Ni atoms are contained in a surface film at 0.6 atomic%.
Ni with excellent antibacterial properties characterized by being concentrated above
Contains stainless steel. 2. A stainless steel containing 10 to 40% by weight of Ni is brightly annealed at 950 ° C. or higher to obtain N.
A method for producing a Ni-containing stainless steel having excellent antibacterial properties, wherein i atoms are concentrated in a surface film by 0.6 atomic% or more. 3. A stainless steel containing 10 to 40% by weight of Ni is annealed at 950 ° C. or higher and pickled to concentrate Ni atoms in the surface coating by 0.6 at% or more. A method for producing Ni-containing stainless steel having excellent antibacterial properties. 4. A stainless steel containing 10 to 40% by weight of Ni is brightly annealed at 1000 ° C. or more to enrich Ni atoms in the surface layer by 0.6 atomic% or more.
Polishing removes the surface film generated during bright annealing,
A method for producing a Ni-containing stainless steel having excellent antibacterial properties, characterized by exposing a surface layer in which i atoms are concentrated at 0.6 atomic% or more as a new surface. 5. A stainless steel containing 10 to 40% by weight of Ni is annealed and pickled at 1000 ° C. or more to concentrate 0.6% or more of Ni atoms in the surface layer portion.
A method for producing a Ni-containing stainless steel excellent in antibacterial properties, characterized by removing a surface film generated during annealing by polishing and exposing a surface layer in which Ni atoms are enriched by 0.6 atomic% or more as a new surface.