JPH09195009A - Ferritic stainless steel excellent in antibacterial property and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a ferritic stainless steel having antibacterial properties with maintainability. SOLUTION: This ferritic stainless steel has a compsn. contg. <=0.1% C, <=2% Si, <=2% Mn, 10 to 30% Cr and 0.4 to 3% Cu, and in which Cu enriched phases are precipitated into the matrix by >=0.2vol.%. Furthermore, 0.02 to 1% Nb and/or Ti may be incorporated, and one or >= two kinds among <=3% Mo, <=1% Al, <=1% Zr, <=1% V, <=0.05% B and <=0.05% rare earth metal elements (REM) may be added. The Cu enriched phases are precipitated by >=0.2vol.%, after final annealing, by executing batch annealing at 500 to 900 deg.C or executing cooling at a rate of <=10 deg.C/min in the temp. range of 900 to 500 deg.C in the cooling stage after the final annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to kitchen equipment, electric equipment,
The present invention relates to a ferritic stainless steel suitable for applications requiring antibacterial properties in a wide range of fields such as building materials, mechanical equipment, and chemical equipment, and a method for producing the same.

[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 due to Staphylococcus aureus has become a problem in recent years, and there is a demand for improved hygiene even in an environment used by an unspecified number of people such as buses and trains. 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 having an antibacterial property, an organic film or an antibacterial coat formed by plating is generally used as disclosed in JP-A-5-22820 and JP-A-6-10191. However, the antibacterial coat has a drawback that the antibacterial property is lowered as the film disappears. The organic substances that have lost their antibacterial properties are
There is also a risk that it will serve as a nutrient source and will propagate bacteria and other germs. 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, the appearance may be deteriorated due to dissolution, wear, and defects of the film, and the antibacterial action may be decreased.

[0003]

By the way, Ag, Cu
It is known that the metal elements such as the above exhibit an effective antibacterial action. However, Ag is extremely expensive and has poor corrosion resistance, and therefore is not used in applications exposed to an environment where corrosion is expected. On the other hand, since Cu is a relatively inexpensive element and is also effective as an antibacterial component, it has been studied to add it to a material such as stainless steel to impart antibacterial properties. The present inventors also conducted various studies on the improvement of antibacterial property by adding Cu, and found that the antibacterial property was improved by increasing the Cu concentration on the surface of stainless steel, and Japanese Patent Application No. 6-
No. 209121 and Japanese Patent Application No. 7-55069.
The present invention has been devised in order to further enhance the action of Cu previously proposed, and a second phase (hereinafter,
By depositing a predetermined amount of Cu-rich phase)
The purpose is to impart excellent antibacterial properties to ferritic stainless steel.

[0004]

In order to achieve the object, the ferritic stainless steel of the present invention has C: 0.1% by weight or less, Si: 2% by weight or less, Mn: 2% by weight or less,
Cr: 10 to 30% by weight and Cu: 0.4 to 3% by weight, and by performing batch annealing at 500 to 900 ° C. after hot rolling, or 900 to 500 ° C. in the cooling process after hot rolling.
The Cu-rich phase is precipitated in the matrix at a rate of 0.2% by volume or more by cooling the temperature range of 10 at a rate of 10 ° C./minute or less. The ferritic stainless steel of the present invention contains 0.02 to 1% by weight of Nb.
And / or Ti may be included. Further, Mo: 3 wt% or less, Al: 1 wt% or less, Zr: 1 wt% or less,
V: 1% by weight or less, B: 0.05% by weight or less, rare earth metal element (REM): 0.05% by weight or less, and one or more kinds may be included. This ferritic stainless steel is manufactured by hot rolling a ferritic stainless steel having a predetermined composition and then controlling the temperature in a batch annealing or cooling process.

[0005]

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.
u was added to ferritic stainless steel, the amount of Cu contained in the passivation film was measured, and the antibacterial property by dropping the liquid containing Staphylococcus aureus was investigated. As a result, it was found that the stainless steel containing a certain amount of Cu or more has antibacterial properties. However, the C content in steel is less than a few percent.
The antibacterial property and its durability may not always be sufficient if u is simply dissolved. Therefore, as a result of further studies, even if the Cu content is the same, if a part of Cu is precipitated as a Cu-rich phase, the Cu concentration on the surface is increased and the antibacterial property is also improved. There was found. In order to impart effective antibacterial properties, it is necessary to precipitate the Cu-rich phase at a ratio of 0.2% by volume or more. Cu
The rich phase includes those having an FCC structure and those having an HCP structure.

As means for precipitating the Cu-rich phase,
It is conceivable to apply isothermal heating such as aging in a temperature region where the Cu-rich phase is likely to precipitate, and to gradually increase the passage time in the precipitation temperature region by slow cooling. In general, if the precipitation treatment is performed at the final stage of the manufacturing process, the target steel can be easily obtained. However, the exclusive precipitation treatment causes an increase in manufacturing cost and is not preferable as a manufacturing condition. Therefore, as a result of various studies on conditions for precipitating a Cu-rich phase without impairing manufacturability, it was found that after hot rolling, it was 500 to 900 ° C
It was found that the Cu-rich phase is precipitated by performing the batch annealing in the range of 10 to 100 ° C. or cooling the temperature range of 900 to 500 ° C. at a rate of 10 ° C./min or less in the cooling process after hot rolling. This Cu-rich phase is highly likely to remain even after short-time annealing such as intermediate annealing and finish annealing,
Antibacterial properties are easily obtained even when the amount added is low. Further, when carbonitrides such as Ti and Nb, and alloy components that easily form precipitates are added, the precipitates are used as precipitation sites to form C.
The u-rich phase is easily dispersed uniformly in the matrix, resulting in improved antibacterial properties and manufacturability.

The alloying elements contained in the ferritic stainless steel of the present invention and their contents will be described below. C: 0.1 wt% or less While improving the strength of ferritic stainless steel,
In the present invention, it is an effective alloying element that uniformly disperses the precipitation of the Cu-rich phase by the formation of Cr carbide. But C
Since the excessive addition of 1 deteriorates manufacturability and corrosion resistance, the upper limit was regulated to 0.1% by weight. Si: 2 wt% or less It is an alloying element that improves corrosion resistance and strength, and also exhibits an action of improving antibacterial property. However, excessive addition causes deterioration of manufacturability, so the upper limit was limited to 2% by weight. Mn: 2 wt% or less It is 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 2% by weight.

Cr: 10 to 30 wt% An alloying element important for maintaining the corrosion resistance of ferritic stainless steel, and 10 wt% or more is required. However, a large amount of Cr exceeding 30% by weight deteriorates manufacturability. Cu: 0.4-3 wt% and Cu-rich phase: 0.2
Volume% or more It is the most important alloying element in the ferritic stainless steel of the present invention, and is 0.2 in order to maintain good antibacterial property.
It is necessary that the Cu-rich phase of volume% or more is deposited. In order to precipitate a Cu-rich phase of 0.2 vol% or more, 0.4 wt% or more of Cu must be added. However, since excessive addition reduces productivity and corrosion resistance,
The upper limit of the Cu content was regulated to 3% by weight. In addition, the Cu-rich phase is not particularly limited in the size of the precipitate, but in order to uniformly exert the antibacterial property on the entire surface of the product, the precipitate phase is appropriately dispersed and distributed on the surface and inside. It is preferable that

Nb and / or Ti: 0.02 to 1% by weight It is an alloying element that is added as required, and acts as a precipitate to uniformly precipitate the 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 wt% or less It is an alloying element added as necessary, and has an effect of improving corrosion resistance and strength, and also improving antibacterial property. 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: 0.05% by weight 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.

Rare earth metal element (REM): not more than 0.05% by weight It is an alloy element added as required, and exhibits an effect of improving hot workability like B. However, excessive addition of more than 0.05% by weight causes deterioration of hot workability. Batch annealing conditions: 500 to 900 ° C. Batch annealing, which is generally performed for a relatively long time, is an effective treatment for precipitating a Cu-rich phase. The lower the annealing temperature, the smaller the amount of solid solution Cu in the matrix,
The precipitation amount of the u-rich phase increases. However, if the annealing temperature is too low, the diffusion rate becomes slow and the amount of precipitation decreases conversely. As a result of conducting various batch annealings under different temperature conditions and examining a temperature range effective for antibacterial properties, it was found that 500 to 900 ° C. is an industrially effective temperature range. Cooling condition after hot rolling: a temperature range of 900 to 500 ° C. is 10
Since hot rolling of ferritic stainless steel cooled at a rate of ℃ / min or less is generally completed at around 900 ℃, Cu
Rich phase may precipitate. Therefore, as a result of studying the conditions for precipitating a Cu-rich phase under the cooling conditions after hot rolling, when the temperature range of 900 to 500 ° C. is gradually cooled at a rate of 10 ° C./min or less, 0 required for improving antibacterial properties is obtained. .2% by volume
It was found that the above Cu-rich phase was precipitated.

[0012]

EXAMPLE Ferritic stainless steels having the compositions shown in Tables 1 and 2 were melted in a 30 kg vacuum melting furnace, and various cooling conditions after forging and hot rolling were controlled. Next, batch annealing or short-time annealing was performed, cold rolling and short-time annealing were repeated, and finally a cold-rolled annealed plate having a plate thickness of 0.7 mm was obtained. For comparison, some plates were aged for 1 hour after the final annealing. The obtained test material was observed with a transmission electron microscope to quantify the amount of precipitation of Cu-rich ε-Cu phase.
For antibacterial tests, Staphylococcus aur
Eus IFO12732 (Staphylococcus aureus) was shake-cultured in a normal broth medium at 35 ° C. for 16 to 24 hours to prepare a culture solution. The culture solution was sterilized with a phosphate buffer solution of 20,000
It was diluted to 0 times to prepare a bacterial solution. 1 ml of the bacterial solution was dropped on the surface of a 5 cm × 5 cm test piece that was polished # 400.
Stored at 24 ° C for 24 hours. After storage, the test piece was washed with 9 ml of SCDLP medium (manufactured by Nippon Pharmaceutical Co., Ltd.), and the obtained solution was subjected to the pour plate culture method using standard agar medium (35
The viable cell count was counted by culturing at 2 ° C for 2 days. 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 with no viable bacteria detected were ◎, and those with 95% or more dead compared to the reference number of viable bacteria were ○, 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. Evaluation results
It is shown in Tables 1 and 2 together with the ε-Cu phase.

[0013]

[0014]

As is clear from Table 1, in the case where 0.4% by weight or more of Cu was added and the material was subjected to hot-rolling followed by slow cooling or batch annealing, a large amount of ε-Cu phase was precipitated, and after the final annealing. However, a large amount of ε-Cu phase remained. Also, ε−
Table 1 shows that the antibacterial property is excellent when the Cu phase is precipitated in an amount of 0.2 vol% or more. On the other hand, even if the Cu content is 0.4% by weight or more, as shown in Table 2, when the cooling rate after hot rolling is fast or the annealing after hot rolling is short. The precipitation amount of ε-Cu phase is low,
The amount of precipitation of the ε-Cu phase after the final annealing was less than 0.2% by volume, and the antibacterial property was poor.

[0016]

As described above, in the ferritic stainless steel of the present invention, the Cu content of the raw material is regulated, and a predetermined amount of C is obtained by batch annealing or slow cooling after annealing.
It deposits a u-rich phase and exhibits excellent antibacterial properties in solid wood. Since the ferritic stainless steel with antibacterial properties thus maintained has excellent properties for a long period of time, it can be used for kitchen equipment, equipment used in hospitals, railings of transportation means such as buses and trains, etc. It is used in fields where antibacterial properties are required and improves the living environment.

Continued on the front page (72) Inventor Sadayuki Nakamura 4976 Nomura Minamicho, Shinnanyo-shi, Yamaguchi Pref. Nisshin Steel Co., Ltd.

Claims (5)

[Claims] 1. C: 0.1% by weight or less, Si: 2% by weight
Hereinafter, a Cu-rich phase containing Mn: 2 wt% or less, Cr: 10 to 30 wt% and Cu: 0.4 to 3 wt% and dispersed in a matrix at a ratio of 0.2 vol% or more is a heat. A ferritic stainless steel that has been precipitated by batch annealing at 500 to 900 ° C. after rolling and is present in a proportion of 0.2% by volume or more even after final annealing. 2. C: 0.1% by weight or less, Si: 2% by weight
Hereinafter, a Cu-rich phase containing Mn: 2 wt% or less, Cr: 10 to 30 wt% and Cu: 0.4 to 3 wt% and dispersed in a matrix at a ratio of 0.2 vol% or more is a heat. In the cooling process after rolling, the temperature range of 900 to 500 ° C.
A ferritic stainless steel that is precipitated by cooling at a rate of ℃ / min or less and that is present in a proportion of 0.2% by volume or more even after the final annealing. 3. Nb: 0.02 to 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 metal element (REM): 0.
The ferritic stainless steel according to claim 1 or 2, which contains one or more of 0.05% by weight or less. 4. After hot rolling the ferritic stainless steel having the composition according to any one of claims 1 to 3, 500 to 9
0.2% by volume of Cu-rich phase by batch annealing at 00 ℃
A method for producing a ferritic stainless steel having excellent antibacterial properties, which is deposited as described above. 5. After hot rolling the ferritic stainless steel having the composition according to claim 1, 900 to 5
The temperature range of 00 ° C is cooled at a rate of 10 ° C / minute or less, and C
A method for producing a ferritic stainless steel excellent in antibacterial property, which deposits a u-rich phase in an amount of 0.2 vol% or more.