JPH10140295A - Stainless steel material excellent in antibacterial property and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferritic and an austenitic stainless steel, having antibacterial characteristic against various bacteria, such as colibacillus, yellow staphylococcus, and MRSA, and their production. SOLUTION: The stainless steels excellent in antibacterial characteristicis are obtained by allowing a Cu phase to appear or forming a Cu-enriched layer at the surface of a ferritic stainless steel, containing >1-5% Cu and 0.1-5% Ni and satisfying Cu(%)>=Ni(%)>=0.1×Cu,(%), or an austenitic stainless steel containing >1-5% Cu. These steels can be produced by performing heating to 600-950 deg.C and holding for 1-20hr to allow a Cu phase to appear at the surface of the steel or by carrying out holding at 800-1150 deg.C for 20sec-20hr and acid pickling treatment to form a Cu-enriched layer at the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel material having excellent antibacterial properties and a method for producing the same.
The present invention relates to ferritic and austenitic stainless steel materials used as materials for sanitary appliances such as bathtubs, household electric appliances, toilet seats, and the like, and methods for producing them. In particular, the present invention relates to ferritic and austenitic stainless steel materials suitable for instruments requiring an antibacterial effect against Escherichia coli, Staphylococcus aureus, and MRSA (methicillin-resistant Staphylococcus aureus), and methods for producing them.

[0002]

2. Description of the Related Art Ferritic and austenitic stainless steels are materials having a beautiful metallic luster with a clean feeling, good long-term corrosion resistance, excellent oxidation resistance at high temperatures, and easy maintenance. . for that reason,
Ferritic and austenitic stainless steel materials (hereinafter, both may be abbreviated as stainless steel) are kitchen utensils such as sinks, pans, kettles, dishes,
It is used for various purposes as a material for tableware such as spoons and spoons, or equipment such as hospitals and cafeterias where good hygiene is strictly required. In recent years, as the MRSA nosocomial infection problem in hospitals becomes a major social problem, it is desired that the materials of the instruments themselves have antibacterial properties.

[0003] Originally, metals are said to have more or less an effect of inhibiting the growth and growth of fungi, ie, antibacterial properties. For example, "Study on the Effect of Metals and Metal Ions on Microorganisms", page 913 of the Journal of the Japanese Society of Hygienic Infectious Diseases, Vol. 25 (1929) states that metals have an effect of inhibiting fungal growth and a sterilizing effect. Examples of such materials include mercury, silver, copper, zinc, lead, and bismuth, and it has been described that an antibacterial inorganic material in which these metals are supported on an inorganic carrier such as zeolite or glass has been developed. I have.

[0004] Further, on page 92 of "The Story of Copper" published by the Japan Standards Association (the first edition of the first edition issued on November 15, 1985), it is called "Sterilizing action of trace copper".
It is alleged that in 1993, botanist Negeri discovered that one in ten million traces of copper killed Spirogyra. The publication also states that the brass train had no bacteria on the handle, and that a bronze 10-yen coin and a brass 5-yen coin in a petri dish of an incubator It is reported that Salmonella typhi has been killed. In addition, the publication states that Escherichia coli, Staphylococcus aures, Streptococcus group D, and Gram-negative Pseudomonas species all significantly grew and proliferated on aluminum and stainless steel surfaces. It describes that it does not have a fungus growth inhibiting effect or a sterilizing effect.

[0005] As a method for imparting antibacterial properties to a stainless steel material, JP-A-8-60302 and JP-A-8-603 have been proposed.
No. 03, a noble potential is applied to a Cu-containing ferritic stainless steel material or an austenitic stainless steel material by an alternating electrolytic treatment method to elute Cu, and then a low potential is applied to the surface of the stainless steel material. Cu
A method for imparting antibacterial properties by precipitating is disclosed. However, in the alternating electrolytic treatment method, since Cu is present on the surface of stainless steel by electrodeposition, if the surface is rubbed with a wire brush,
However, there is a disadvantage that the antibacterial property is reduced due to the scraping. Further, the alternating electrolytic treatment method has a disadvantage that it takes time and effort.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a stainless steel material which itself has antibacterial properties and a method for producing the same. That is, an object of the present invention is to provide a stainless steel material having an antibacterial property that suppresses the occurrence, growth and proliferation of various fungi such as Escherichia coli, Staphylococcus aureus and MRSA, and a method for producing the same.

[0007]

The features of the steel material and the manufacturing method of the present invention are as follows: (a) a special chemical composition containing 1 to 5% of Cu, which exceeds the solid solubility limit of the base stainless steel. Using stainless steel as a material, (b) performing a heat treatment to expose a phase of Cu on the surface of the steel material, or a heat treatment and pickling to form a Cu-rich layer on the surface of the steel material It is to apply. The gist of the present invention is the following stainless steel materials having excellent antibacterial properties (,,
,) And their production methods (,).

In weight%, more than 1% and less than 5% of Cu,
Ni is contained at 0.1% or more and 5% or less, and Cu (%) ≧
A ferritic stainless steel material in which a Cu phase is exposed on the surface of a ferritic stainless steel satisfying a condition of Ni (%) ≧ 0.1 × Cu (%). (Invention) More than 1% and less than 5% of Cu and 0.1% of Ni by weight%.
% To 5% and Cu (%) ≧ Ni (%) ≧
A ferritic stainless steel material having a Cu-enriched layer on the surface of a ferritic stainless steel satisfying a condition of 0.1 × Cu (%). (Invention) An austenitic stainless steel material in which a Cu phase is exposed on the surface of an austenitic stainless steel containing 1% to 5% by weight of Cu in weight%. (Invention) An austenitic stainless steel material comprising a Cu-enriched layer on the surface of an austenitic stainless steel containing 1% to 5% Cu by weight. (Invention) A method for producing a stainless steel material according to the invention or the above, wherein the stainless steel having the chemical composition described in the invention or is heated to a temperature in a range of 600 ° C. or more and 950 ° C. or less and held for 1 to 20 hours. (Invention) A stainless steel having the chemical composition described in the invention or is heated in an oxidizing atmosphere to a temperature in the range of 800 ° C. or more and 1150 ° C. or less and maintained for 20 seconds to 20 hours. Or a method for producing a stainless steel material by removing oxide scale by heating. (Invention) The invention and "the Cu phase is exposed on the surface" will be described.

[0009] Cu present beyond the solid solubility limit in steel
The atoms are kept at a temperature in the range of not less than 600 ° C. and not more than 950 ° C. for 1 to 20 hours, for example, by the heat treatment of the invention, so that the amount of Cu atoms exceeding the solid solubility limit becomes , And grows greatly with the passage of time. In the present invention, this Cu precipitation phase is referred to as “Cu
Phase ”.

[0010] Some phases of Cu are present in the steel, while others are exposed on the surface of the steel. The Cu atoms in the Cu phase exposed on the surface of the steel exhibit antibacterial properties.

The size and shape of the Cu phase vary depending on the heat treatment temperature or heat treatment time, and if heat treatment is performed at a low temperature for a short period of time, the Cu precipitates as particles of about 10 nm or more.
If heat treatment is performed at a high temperature for a long time, a rod having a length of about 2 μm or less precipitates.

The Cu phase has a size of 0.5 to 1 μm,
It is desirable that the particles are uniformly deposited at a density of 1 / μm ² or more on the surface of the steel in order to exhibit antibacterial properties.

Although the phase of Cu may be composed of only Cu, Ni, T which forms an intermetallic compound in addition to Cu may be used.
It may be a phase containing i, Fe, Si, P or S.

The invention and "provided with Cu-rich layer on surface" will be described.

The stainless steel having Cu and Ni in the range specified in the present invention is subjected to, for example, the heat treatment of the present invention, that is, in an oxidizing atmosphere such as the air, at 800 ° C. or more,
Holding for 0 seconds to 20 hours generates oxide scales of Fe and Cr on the surface of the steel. Thereafter, by pickling, Fe and Cr in the oxide scale and a part of the base metal are dissolved and removed, and a Cu-rich layer is formed on the surface of the steel. In the steel of the present invention, since Cu is contained in a large amount of 1 to 5% by weight, compared with the surface composition after pickling treatment of a conventional stainless steel containing only a trace amount of Cu,
The Cu concentration is significantly higher. In the present invention, the formation of a Cu-rich layer on the surface after pickling is defined as a state “provided with a Cu-rich layer on the surface”.

Since Cu is exposed on the surface of the Cu-enriched layer, the Cu exerts antibacterial properties.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The stainless steel material of the present invention (hereinafter referred to as "the stainless steel material")
It may be abbreviated as the steel material of the present invention. ) Exerts antibacterial properties, the chemical composition of the steel of the present invention, and the method for producing the steel of the present invention. In addition,% display used in the description of the chemical composition means% by weight.

(1) Antibacterial property of the steel material of the present invention The steel material of the present invention, as an element exhibiting antibacterial properties, does not cause a significant cost increase in production on a commercial scale.
u. The Cu is previously contained in the stainless steel material in a larger amount (more than 1% and less than 5%) as compared with the conventional stainless steel, and the Cu phase is exposed on the surface by a subsequent heat treatment or pickling treatment. Or C on the surface
forming an enriched layer of u.

When the steel material of the present invention is put to practical use, Cu ions are eluted from the Cu phase or Cu in the Cu-enriched layer due to moisture in the air. When a microorganism contacts the steel material of the present invention, Cu ions diffuse and reach the cell membrane of the microorganism, and are adsorbed by the protein.

The Cu ion adsorbed on the protein exerts an antibacterial action that destroys the SH group radicals and the like of the constituents and disables the energy metabolism function of the microorganism.

When the surface of the steel material of the present invention is contaminated, if the surface is cleaned by brush polishing or buffing to expose the Cu phase and the Cu-rich layer, the antibacterial property is further enhanced.

(2) Chemical composition of the steel of the present invention (A) Ferritic stainless steel The ferritic stainless steel used for the ferritic stainless steel of the present invention is based on a normal ferritic stainless steel and contains 1% of Cu. Up to 5%, Ni is contained at 0.1% or more and 5% or less. In addition, Cu and Ni
The relationship between the contents is Cu (%) ≧ Ni (%) ≧ 0.1 × C
u (%). The chemical composition of the ferritic stainless steel of the present invention may be the same as that of ordinary ferritic stainless steel except for the contents of Cu and Ni. For example, SUS405, SUS430, SUS4
34, ferrite stainless steel specified in JIS such as SUSXM27 contains Cu and Ni in the amounts specified as described above.

Specifically, for example, there is a ferritic stainless steel having the following chemical composition.

I) C: 0.04% or less, Si: 0.28%
Hereinafter, Mn: 0.3% or less, P: less than 0.03%, S:
0.002% or less, Cu: more than 1% and 5% or less, Ni:
0.1% or more and 5% or less, and Cu (%) ≧ Ni (%) ≧
0.1 × Cu (%), Cr: 14 to 22
%, N: 0.04% or less, Mo: 0 to 2.5%, Ca:
0 to 0.03%, Ce: 0 to 0.03%, La: 0 to 0%
0.03%, Y: 0 to 0.03%, REM: 0 to 0.0
3%, balance being Fe and unavoidable impurities.

Ii) C: 0.02% or less, Si: 0.28
%, Mn: 0.3% or less, P: less than 0.03%,
S: 0.002% or less, Cu: more than 1% and 5% or less, N
i: 0.1% or more and 5% or less, and Cu (%) ≧ Ni
(%) ≧ 0.1 × Cu (%), Cr: 1
4 to 22%, N: 0.02% or less, Mo: 0 to 2.5
%, Ca: 0 to 0.03%, Ce: 0 to 0.03%, L
a: 0 to 0.03%, Y: 0 to 0.03%, REM: 0
0.03%, Nb: 0.1% or more, less than 0.8%,
In addition, the condition of Nb (%) ≧ 12 × C (%) + 0.1 is satisfied, and the balance is Fe and inevitable impurities.

Iii) C: 0.02% or less, Si: 0.28
%, Mn: 0.3% or less, P: less than 0.03%,
S: 0.002% or less, Cu: more than 1% and 5% or less, N
i: 0.1% or more and 5% or less, and Cu (%) ≧ Ni
(%) ≧ 0.1 × Cu (%), Cr: 1
4 to 22%, N: 0.02% or less, Mo: 0 to 2.5
%, Ca: 0 to 0.03%, Ce: 0 to 0.03%, L
a: 0 to 0.03%, Y: 0 to 0.03%, REM: 0
0.03%, Nb: 0.1% or more, less than 0.8%,
And Nb (%) ≧ 12 × C (%) + 0.1, Ti: 0
0.2%, and the condition of Nb (%)> 2 × Ti (%) is satisfied, and the balance is Fe and inevitable impurities.

Iv) C: 0.02% or less, Si: 0.28
%, Mn: 0.3% or less, P: less than 0.03%,
S: 0.002% or less, Cu: more than 1% and 5% or less, N
i: 0.1% or more and 5% or less, and Cu (%) ≧ Ni
(%) ≧ 0.1 × Cu (%), Cr: 1
4 to 22%, N: 0.02% or less, Mo: 0 to 2.5
%, Ca: 0 to 0.03%, Ce: 0 to 0.03%, L
a: 0 to 0.03%, Y: 0 to 0.03%, REM: 0
0.03%, Nb: 0.01% or more, less than 0.1%,
Ti: 0.01 to 0.2% or less, the balance being Fe and inevitable impurities.

Next, the contents and functions of the elements essentially contained in the ferritic stainless steel material of the present invention and the elements optionally contained therein will be described.

Cu: more than 1% and not more than 5% Cu is the most important alloying element for exhibiting the antibacterial effect in the ferritic stainless steel material of the present invention. Cu is indispensable for obtaining antibacterial properties by exposing the phase of Cu to the surface of the steel material, or for obtaining antibacterial properties by forming a Cu-rich layer. Cu ions slightly eluted from Cu on the surface suppress the growth and growth of fungi such as Escherichia coli, Staphylococcus aureus and MRSA attached to the surface,
Develop antibacterial effects such as sterilization and sterilization.

In order to exhibit these antibacterial effects, Cu must be used.
Requires a content of more than 1%. If the content exceeds 5%, not only does the effect become saturated, but also the production cost increases, cracks during hot rolling, and depending on the Cr content, the cold workability decreases due to the use of duplex stainless steel. Occurs. Therefore, the content of Cu is set to more than 1% and 5% or less.

Ni: 0.1% or more and 5% or less Ni is a very important element for improving the hot workability of the ferritic stainless steel material of the present invention. In particular, in the ferritic stainless steel material of the present invention, since the Cu content is large, a crack called copper checking tends to occur during hot working. Therefore, Ni is set to 0.
1% or more and 5% or less, and Cu (%) ≧ Ni (%) ≧
The condition of 0.1 × Cu (%) was satisfied. Under these conditions, the melting point of the Cu-based intermetallic compound can be increased, and cracks on the steel end face and surface flaws can be reduced. The lower limit of the Ni content defined by the above formula is particularly important, and by satisfying 0.1 × Cu (%),
This has the effect of improving hot workability. Cu (%) ≧ N
The reason why i is set to i (%) is that when Ni is added in a necessary amount or more, not only the production cost is increased, but also cold workability is reduced due to the formation of duplex stainless steel.

C, N: C and N form a compound with Cr in steel, generate Cr-based carbide or carbonitride in the heat affected zone by welding, and deteriorate the intergranular corrosion resistance. Therefore, the lower the content, the better, and preferably 0.04% or less.

Si: Si is an element used as a deoxidizing agent. In order to obtain this effect, the content is 0.1 to
It is desirable to set it to 0.2%. When the content exceeds 0.28%, the hot workability decreases.

Mn: Mn has a deoxidizing effect. Mn is also an element that fixes S, which is a harmful element in steel. In order to obtain these effects, the content is preferably 0.05% or more. However, if the content exceeds 0.3%, the effect is saturated, so the upper limit is preferably set to 0.3%.

P: If the P content exceeds 0.03%, the hot workability tends to deteriorate. Desirably 0.015
% Or less. However, since the refining cost is high for low phosphorus reduction, it is preferably set to 0.025% or less in production on a commercial scale.

S: S deteriorates hot workability, so its content is preferably 0.002% or less. More preferably, it is 0.001% or less.

Cr: Cr is the most important element for ensuring the corrosion resistance of the ferritic stainless steel of the present invention. 14% to suppress rust on the surface
It is preferable to contain the above. The upper limit of the content is 2
It is preferably set to 2%. Addition of more than this saturates the corrosion resistance improving effect, leading to an increase in manufacturing cost.

Mo: Mo is an element for improving corrosion resistance, and is contained as necessary. However, even if the content exceeds 2.5%, the effect of improving the corrosion resistance is small.

Ca, Ce, La, Y, REM: All of these are elements that affect the form of S in steel, and are added as necessary to improve hot workability. Y
Has an effect of suppressing oxidation at a high temperature and also has an effect of preventing abnormal oxidation in a heating stage before hot rolling. However, if the content exceeds 0.03%, a problem occurs in that the nozzle for injecting the molten steel is clogged during the casting operation, so the content is preferably 0.03% or less.

Nb: Nb combines with C and N in steel to form Nb carbonitride. This Nb carbonitride is formed preferentially over Cr carbonitride and has the effect of preventing the deterioration of intergranular corrosion resistance due to the precipitation of Cr carbonitride at the grain boundary. Is desirably contained.

Ti: Ti, like Nb, combines with C and N in steel to form a carbonitride of Ti. This Ti
Carbonitrides are preferentially formed over Cr carbonitrides,
This has the effect of preventing deterioration of intergranular corrosion resistance due to precipitation of Cr carbonitrides at the grain boundaries. Therefore, it is desirable to contain up to 0.2%.

(B) Austenitic stainless steel material The austenitic stainless steel used for the austenitic stainless steel material of the present invention is based on austenitic stainless steel and contains more than 1% to 5% of Cu. . The chemical composition of the austenitic stainless steel material of the present invention is the same as that of ordinary austenitic stainless steel, except for the content of Cu. For example, austenitic stainless steel specified by JIS such as SUS304 and SUS316L contains Cu in the amount specified as described above.

Specifically, there is, for example, an austenitic stainless steel having the following chemical composition.

C: 0.04% or less, Si: 2% or less, M
n: 2.5% or less, P: less than 0.025%, S: 0.0
02% or less, Cu: more than 1% and 5% or less, Ni: 7% to 20%, Cr: 15 to 22%, N: 0.04% or less, Nb: 0 to 0.8% or less, Ti: 0 to 0.25%,
Mo: 0 to 2.5%, Ca: 0 to 0.03%, Ce: 0
~ 0.03%, La: 0 ~ 0.03%, Y: 0 ~ 0.0
3%, REM: 0 to 0.03%, balance Fe and unavoidable impurities.

Next, the contents and effects of the elements essentially contained in the austenitic stainless steel material of the present invention and the elements optionally contained therein will be described.

Cu: more than 1% and not more than 5% Cu is the most important alloying element for exhibiting the antibacterial effect in the austenitic stainless steel material of the present invention. The phase of Cu on the surface of the stainless steel material or Cu concentrated in the surface layer exerts the same antibacterial properties as the above-described ferritic stainless steel material of the present invention.

To exhibit these antibacterial effects, Cu
Requires a content of more than 1%. If the content exceeds 5%, not only the effect is saturated, but also the production cost increases and cracks occur during hot rolling. Therefore Cu
Is more than 1% and 5% or less.

C, N: C and N combine with Cr in the steel to form a carbonitride of Cr, and form a Cr-based carbide or carbonitride in the weld heat affected zone, resulting in intergranular corrosion resistance. Deterioration of performance. Therefore, the lower the content, the better.
Preferably, it is not more than 04%.

Si: Si is an element used as a deoxidizing agent. In order to obtain this effect, the content is 0.1 to
1.5% is desirable. If the content exceeds 2%, the hot workability decreases. Therefore, it is preferable that the content be at most 2%.

Mn: Mn exhibits a deoxidizing effect when coexisting with Si. Mn is also an element that fixes S, which is a harmful element in steel. To obtain this effect, 0.05
% Is preferably contained. On the other hand, Mn is also an element that stabilizes the austenite structure. In order to obtain this effect, the content is preferably 0.1% or more. However, even if the content exceeds 2.5%, the effect is saturated, so that it is not preferable to contain more than 2.5%.

P: If the P content exceeds 0.025%, the hot workability tends to deteriorate. Desirably 0.01
5% or less. However, since the refining cost is high for low phosphorus reduction, it is preferably set to 0.025% or less in production on a commercial scale.

S: S deteriorates hot workability, so its content is preferably 0.002% or less. More preferably, it is 0.001% or less.

Ni: Ni is an element that stabilizes the austenite structure and improves corrosion resistance. If the content is less than 7%, the effect cannot be obtained. On the other hand, if the content exceeds 20%, the effect is saturated and only the raw material cost increases.

Cr: Cr is the most important element for ensuring corrosion resistance in the austenitic stainless steel material of the present invention. In order to suppress rust on the surface, the content is preferably 15% or more. The upper limit of the content is preferably set to 22%. Even if added more, the effect of improving the corrosion resistance is small, and the cost of raw materials increases.

Mo: Mo is an element for improving the corrosion resistance, and may be contained if necessary. However, 2.5%
However, the effect of improving the corrosion resistance is small even if it is contained in excess, and there is a problem that the raw material cost is significantly increased.

Nb: Nb combines with C and N in steel to form Nb carbonitride. This Nb carbonitride is formed preferentially over Cr carbonitride and has an effect of preventing deterioration of intergranular corrosion resistance due to precipitation of grain boundary of Cr carbonitride, so that it is 0.8% or less. Is desirably contained.

Ti: Ti, like Nb, combines with C and N in steel to form Nb carbonitride. This Nb
Carbonitrides are preferentially formed over Cr carbonitrides,
Since it has the effect of preventing deterioration of intergranular corrosion resistance due to precipitation of Cr carbonitride at the grain boundary, it is desirable to contain 0.25% or less.

Ca, Ce, La, Y, REM: All are elements that affect the form of S in steel and are added when it is necessary to improve hot workability. Y has an effect of suppressing oxidation at a high temperature, and also has an effect of preventing abnormal oxidation in a heating step before hot rolling. However,
If the content of each of them exceeds 0.03%, there arises a problem that a nozzle for injecting molten steel is clogged during the casting operation.

(3) Manufacturing Method (A) Invention The invention and the steel of the invention are obtained by heating a stainless steel having the chemical composition of the steel of the invention to a temperature in the range of 600 ° C. to 950 ° C. and holding for 1 to 20 hours. It can be manufactured by the method of the present invention. By performing this heat treatment, the Cu phase can be exposed on the surface of the stainless steel material.

The furnace used for the heat treatment may be an ordinary heating furnace. The atmosphere during the heat treatment may be any of an oxidizing atmosphere such as the air or a non-oxidizing atmosphere such as an argon gas. However, in order to expose the Cu phase on the surface of the stainless steel, no oxide scale is generated. The heat treatment is preferably performed in a non-oxidizing atmosphere which is an atmosphere.

When the heat treatment temperature is lower than 600 ° C., Cu does not precipitate. On the other hand, at a temperature exceeding 1150 ° C., the once precipitated Cu will be dissolved again. Preferably, 850 ° C
As described above, heat treatment is performed at a temperature of 1000 ° C. or lower. In the heat treatment for less than 1 hour, even if Cu precipitates, the grown C
It is difficult to become u phase. Even if the heat treatment is performed for more than 20 hours, the growth of the Cu phase hardly occurs, so that the heating energy is wasted.

The cooling after heating is not particularly limited, and various cooling methods such as furnace cooling, air cooling and water cooling can be used. The cooling rate is desirably 10 to 100 ° C./sec.

(B) Invention The steel of the invention and the invention is obtained by holding a stainless steel having the chemical composition specified in the present invention at 800 ° C. or higher and 1150 ° C. for 20 seconds to 20 hours in an oxidizing atmosphere such as air. And then removing the oxide scale by pickling (invention). By performing the heat treatment and the pickling, a Cu-enriched layer can be formed on the surface of the stainless steel material.

The furnace used for the heat treatment may be an ordinary heating furnace. If the heating temperature is lower than 800 ° C., a sufficient oxide scale cannot be formed on the surface layer of the stainless steel material. Further, even if the heating is performed at a temperature exceeding 1150 ° C., the growth of the oxide scale hardly occurs, so that the heating energy is wasted. On the other hand, even if the heating temperature is in this range,
If the time is maintained for less than 20 seconds, a sufficient oxide scale cannot be formed. In addition, heating energy for more than 20 hours is a waste of heating energy.

The cooling after heating is not particularly limited, and various cooling methods such as furnace cooling, air cooling and water cooling can be used. The cooling rate is desirably 10 to 100 ° C./sec.

The pickling treatment step of the present invention is not required to be special, except for the type of acid used.
A process of pickling the surface of a normal stainless steel material may be used. As for the acid used for pickling, Fe and Cr dissolve, but C
u must be an insoluble acid. Such acids include, for example, a mixture of nitric acid and hydrofluoric acid.

[0067]

【Example】

(Example 1) A ferritic stainless steel material of the present invention was manufactured by the manufacturing method of the present invention, and the antibacterial property was investigated. Further, in order to confirm the practicality of the ferritic stainless steel material of the present invention, corrosion resistance and room-temperature tensile strength were investigated.

A steel having the chemical composition shown in Table 1 was melted under vacuum
0 kg was melted, and a cold-rolled sheet having a sheet thickness of 1.0 mm was produced by an ordinary method. In addition, a steel material for comparison (hereinafter, referred to as a comparative steel material) outside the range of the chemical composition specified in the present invention was similarly processed into a cold-rolled plate.

[0069]

[Table 1]

(A) Antibacterial test of steel material of the invention A phase of Cu is formed on cold-rolled steel plates 1 to 12 and comparative steel materials 13 to 16 satisfying the chemical composition specified in the present invention. For this purpose, a heat treatment was performed at 800 ° C. for 12 hours in the air. In order to measure the density and the size of the Cu phase precipitated by the heat treatment, the thin film sample was observed with a transmission electron microscope. Table 2 shows the results. Invention steel materials 1 to 12
On the surface of the (invention), there is 1 phase of Cu of 0.1 to 1 μm.
Particles / μm ² or more. On the other hand, although the Cu phase was formed in the comparative steel materials 13 to 16, the density was less than 1 piece / μm ² .

[0071]

[Table 2]

The steel material 1 of the present invention in which the Cu phase was precipitated
-12 and comparative steel materials 13-16 were subjected to an antibacterial test.

The bacterium used in the test was Escherichia coli I
FO 3301 (Escherichia coli) and Staphylococcus aureus (Staphylococcus aureus). After the two kinds of bacteria were enriched in a peptone medium, they were diluted with sterile phosphate buffered saline to prepare a bacterial solution. Inventive steel materials 1 to 12 and comparative steel materials 13 to 16
Was cut into 50 mm squares, and 1 ml of each bacterial solution was applied to the surface thereof, and allowed to stand at 25 ° C. for 24 hours. Then, the bacterial solution was wiped off and sprinkled into a diluent. A predetermined amount of the shake-out solution was mixed with a measurement medium, cultured at 37 ° C. for 48 hours, and the number of generated colonies was counted. The results are shown in Table 3. The steel material of the present invention shows excellent antibacterial properties when the number of colonies after culture is 30 or less. However, the comparative steel had no antibacterial effect at 1300 or more.

[0074]

[Table 3]

(B) Antibacterial test of steel material of the present invention A cold rolled steel plate of steel materials 1 to 12 and a comparative steel material of 13 to 16 satisfying the chemical composition specified in the present invention were subjected to 950 ° C in air at 950 ° C. Heat treatment was performed for 2 hours to form an oxide scale on the surface of the steel material. Thereafter, the oxide scale was removed by washing with a mixed solution of nitric acid and hydrofluoric acid. Next, the amount of Cu from the surface layer of the Cu-rich layer formed on these surfaces to 50 Å was measured by XPS. Table 4 shows the results. The content of Cu from the surface layer of the Cu-rich layer of the steel materials 1 to 12 (invention) of the present invention to 50 Å was 6% or more. Comparative steel materials 13 to 16 were less than 3%.

The steel materials 1 to 12 of the present invention and the comparative steel materials 13 to 16
An antibacterial test was carried out on the same method as in Example 1. Table 5 shows the test results. The steel material of the present invention has less than 10 colonies after culturing, and shows excellent antibacterial properties. On the other hand, the comparative steel has no antibacterial properties.

[0077]

[Table 4]

[0078]

[Table 5]

(C) Corrosion resistance test of steel material of the invention Cold rolled sheets of steel materials 1 to 12 of the present invention and comparative steel materials 13 to 16
Was subjected to a corrosion resistance test.

The corrosion resistance was evaluated by a salt spray test according to JIS Z2371.

The results are shown in Table 6.

[0082]

[Table 6]

All the steel materials of the present invention exhibited good corrosion resistance.
In the comparative steel materials, no. No. 13 shows good corrosion resistance, but No. 13 having a low Cr content. In No. 13, severe rust of 50 points or more was observed. The steel material of the present invention was found to have the same or higher corrosion resistance than the comparative steel material, which is a conventional steel.

(D) Tensile test of steel of the invention Cold rolled sheets of steels 1 to 12 of the invention and comparative steels 13 to 16
Was subjected to a room temperature tensile test.

The workability at room temperature was evaluated by measuring the tensile strength and elongation of each test piece in accordance with JIS Z 2441. The results are shown in Table 6.

The steel material of the present invention has a tensile strength of 450 MPa.
As described above, the elongation was 20% or more, and the workability at room temperature was excellent. The comparative steel has a tensile strength of 450 MPa or more. No. 13 does not have sufficient elongation. Thus, it was found that the steel material of the present invention has the same or higher normal-temperature workability than the comparative steel material.

(E) Practice of the Invention Steel 6 having the chemical composition specified in the present invention shown in Table 1 was melted in a vacuum of 20 kg by a vacuum melting method, and the sheet thickness was 1.0 mm.
Was manufactured.

In order to form a Cu phase on a cold-rolled sheet,
Heat treatment was performed at various temperatures and times in the atmosphere.

The heat-treated cold-rolled sheet was subjected to a test for investigating the same antibacterial properties as described above. The results are shown in Table 7.

The cold-rolled sheet heat-treated at a temperature outside the temperature specified in the present invention was poor in antibacterial activity because no Cu phase was precipitated or the once precipitated Cu phase was dissolved. On the other hand, the cold rolled sheet produced by the method of the present invention exhibited excellent antibacterial properties.

[0091]

[Table 7]

(F) Practice of the Invention 20 kg of steel 6 having the chemical composition specified in the present invention shown in Table 1 was melted by vacuum melting, and the thickness was 1.0 mm by a usual method.
Was manufactured.

[0093] In order to form a Cu-enriched layer on the cold-rolled sheet, heat treatment is performed in the air at various temperatures and times, and then the oxide scale is removed by pickling with a mixed solution of nitric acid and hydrofluoric acid. did. Next, a test for investigating the same antibacterial properties as above was conducted. The results are shown in Table 8.

[0094]

[Table 8]

The anti-bacterial properties of the cold-rolled sheet heat-treated under the conditions deviating from the temperature specified in the present invention were poor because the Cu-enriched layer was not formed. On the other hand, the cold rolled sheet produced by the method of the present invention exhibited excellent antibacterial properties.

Example 2 Next, the antibacterial properties of the austenitic stainless steel material of the present invention manufactured by the manufacturing method of the present invention were examined. Further, in order to confirm the practicality of the austenitic stainless steel material of the present invention, corrosion resistance and workability were investigated.

50 kg of steels A to E having the chemical compositions shown in Table 9 were melted by vacuum melting, and the thickness was 1.0 mm by a usual method.
Was manufactured.

[0098]

[Table 9]

The obtained cold-rolled sheets of steels A to E were each divided, and a part thereof was subjected to heat treatment at various temperatures and times in the air to expose a Cu phase on the steel surface ( Invention steel materials 21 to 25: invention and comparison steel materials 26 to 30). The remaining part is subjected to heat treatment at various temperatures and times in the air to form oxide scale on the surface, and then pickling with a mixed solution of nitric acid and hydrofluoric acid to remove the oxide scale, and to form a surface layer. Cu was concentrated (steel materials 31 to 35 of the present invention: invention and comparative steel materials 36 to 40).

The size and density of the Cu phase on the steel surfaces of the steel materials 21 to 25 of the present invention and the comparative steel materials 26 to 30 were determined by EPM.
A. The results are shown in Table 10.

[0101]

[Table 10]

On the surfaces of the steel materials 21 to 25 of the present invention, a Cu phase was exposed at a density of 1 / μm ² or more. On the other hand, no Cu phase was detected on the surfaces of the comparative steel materials 26 to 35.

The steel materials 31 to 35 of the present invention and the comparative steel materials 3
The Cu content of the Cu-enriched layer on the surface of 6 to 40 was determined by XPS.
Was measured by The results are shown in Table 11. C from the surface of the steel materials 31 to 35 of the present invention to 50 Å
The u content was 10% or more. On the other hand, comparative steel materials 36-
That of 40 was at most 6.5%.

[0104]

[Table 11]

(A) Antibacterial test of the invention and the steel of the invention The steel 21 to 25 of the invention (invention), the steel 31 to 35 of the invention (invention), and the comparative steel 2 formed on the cold-rolled plate
Antibacterial tests were performed on 6 to 30 and comparative steel materials 36 to 40. The bacteria used were Escherichia coli IFO 3301 (Escherichia coli), Staphylococcus aureus (Staphylococcus aureus) and Methicillin Resistant Staphylococcus aureus.
(Methicillin-resistant Staphylococcus aureus). These bacteria were enriched in a peptone medium and then diluted with sterile phosphate buffered saline to prepare a bacterial solution. The steel material of the present invention and the comparative steel material were cut into 50 mm squares, 1 ml of each bacterial solution was smeared on the surface, and allowed to stand at 25 ° C. for 24 hours, and the bacterial solution was wiped off.
Shake into diluent. A predetermined amount of the shake-out solution was mixed with a measurement medium, cultured at 37 ° C. for 48 hours, and the number of colonies generated was counted. The results are shown in Table 12. Invention Steel Material 21
25 and the steel materials 31 to 35 of the present invention exhibited antibacterial properties against any bacteria, but the comparative steel materials 26 to 30 and the comparative steel materials 36 to 40 were insufficient in antibacterial properties.

[0106]

[Table 12]

(B) Corrosion resistance test of the invention and the steel of the invention Cold-rolled sheets of the steels 21 to 30 of the invention and comparative steels 31 to 3
The corrosion resistance test was performed on the cold-rolled sheet No. 5.

The corrosion resistance was evaluated by a salt spray test according to JIS Z2371.

Table 13 shows the results.

[0110]

[Table 13]

Both the steel of the present invention and the comparative steel exhibited good corrosion resistance. Therefore, it was found that the steel material of the present invention has the same level of corrosion resistance as the comparative steel material, which is a conventional steel.

(C) Tensile test of the invention and the steel material of the invention The room temperature tensile test was carried out on the cold rolled plates of the steel materials 21 to 25, 31 to 35 of the present invention and the comparative steel materials 26 to 30, 36 to 40. Was carried out.

The workability at room temperature was evaluated by measuring the tensile strength and elongation of each test piece according to JIS Z 2441. The results are shown in Table 13.

The steel material of the present invention has a tensile strength of 500 MPa.
As described above, the elongation was 35% or more, and it was found that the steel had comparable room-temperature workability as compared with the comparative steel as a conventional steel.

[0115]

The stainless steel material of the present invention has excellent antibacterial properties, and also has a performance that can be used as a practical material. Further, according to the manufacturing method of the present invention, the steel material of the present invention can be manufactured at low cost. By using the stainless steel material of the present invention as a material, the antibacterial properties of curbs such as handrails and faucets, metal tableware, kitchen utensils, bathtubs, and electric appliances can be significantly improved.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // A61L 2/16 A61L 2/16 A

Claims (6)

[Claims] 1. The method according to claim 1, wherein the content of Cu is not less than 1% and not more than 5%,
0.1% or more and 5% or less, and Cu (%) ≧ Ni
A ferritic stainless steel excellent in antibacterial properties, characterized in that a Cu phase is exposed on the surface of a ferritic stainless steel satisfying the condition of (%) ≧ 0.1 × Cu (%). 2. The composition according to claim 1, wherein the content of Cu is more than 1% and not more than 5% by weight.
0.1% or more and 5% or less, and Cu (%) ≧ Ni
(%) ≧ 0.1 × Cu (%) A ferritic stainless steel material excellent in antibacterial properties, characterized by comprising a Cu-rich layer on the surface of a ferritic stainless steel. 3. An austenitic stainless steel material excellent in antibacterial properties, characterized in that a Cu phase is exposed on the surface of an austenitic stainless steel containing 1% to 5% by weight of Cu in weight%. 4. An austenitic stainless steel material excellent in antibacterial properties, characterized by comprising a Cu-enriched layer on the surface of an austenitic stainless steel containing 1% to 5% Cu by weight. 5. The stainless steel having the chemical composition according to claim 1 or 3, wherein the stainless steel is heated to a temperature in the range of 600 ° C. to 950 ° C., and subjected to heat treatment for 1 to 20 hours. Item 4. The method for producing a stainless steel material having excellent antibacterial properties according to item 1 or 3. 6. A stainless steel having the chemical composition according to claim 2 or more, in an oxidizing atmosphere at 800 ° C. or higher.
The stainless steel having excellent antibacterial properties according to claim 2 or 4, wherein the stainless steel is heated to a temperature of 150 ° C or less and maintained for 20 seconds to 20 hours, and then the surface is pickled to remove oxide scale. Method of manufacturing steel.