JPH08104953A - Austenitic stainless steel having antibacterial property - Google Patents

Abstract

PURPOSE: To produce an austenitic stainless steel increased in antibacterial properties without impairing its appearance, workability or the like. CONSTITUTION: This austenitic stainless steel has a fundamental compsn. contg., by weight, 0.015 to 0.070% C, 0.5 to 2.0% Si, 0.5 to 2.0% Mn, 0.015 to 0.040% P, <=0.01% S and 15 to 32% Cr, and the balance Fe, in which the content of Cu contained in the fundamental compsn. is regulated to the range of 1.1 to 3.5% and the value of X defined by the formula of X=Cu%/(C%+Si%+Mn%+ P%+S%+Cr%+Cu%) is regulated to the range of 0.05 to 0.15. Thus, in the case the content of Cu contained in the stainless steel exceeds 1.1%, the concn. of Cu in the surface layer part is regulated to >=0.1 atomic %, and Cu ionized by moisture on the surface of the steel shows an antibacterial effect.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an austenitic stainless steel having enhanced antibacterial properties.

[0002]

2. Description of the Related Art Austenitic stainless steel, which is excellent in corrosion resistance, is used as a hard material used in places where various bacteria are easily propagated and where the generation of various bacteria is undesirable. However, there is an increasing tendency to be concerned about the adverse effects of contamination, malodor, slimyness, etc. due to the propagation of various bacteria on human bodies, animals, products and the like. Especially in kitchens, medical institutions, buildings where many people gather, where cleanliness is required, there is a strong demand for materials that are resistant to various bacteria. In order to meet this type of requirement, a method of coating and laminating a resin containing an antibacterial agent on the surface of stainless steel, a method of plating an antibacterial agent component in a matrix, and the like are disclosed in JP-A-5-228202. 6-10191, etc.

[0003]

When a resin containing an antibacterial agent is applied and laminated on the surface of stainless steel, the metallic luster peculiar to stainless steel is lost and the commercial value is lowered. Moreover,
The antibacterial film is damaged during processing and during use, such as cracking, chipping, and abrasion, and when exposed to a humid atmosphere, the antibacterial components are eluted and the appearance is deteriorated, and the original antibacterial action is impaired. Be done. In addition, when the antibacterial agent is exhausted, the remaining film is rather a nutrient for miscellaneous bacteria, which also promotes the growth of miscellaneous bacteria. In the case of applying a composite plating mixed with an antibacterial agent component, the adhesion of the plating layer is not sufficient, and there is a drawback that the workability is reduced. In addition, the appearance may be deteriorated due to dissolution, wear, and defects of the film, and the antibacterial action may be decreased.

In addition, since the antibacterial agent is used in each of the methods, the eluted antibacterial agent may adversely affect the human body and the environment. Therefore, it is desired to impart antibacterial properties to the stainless steel itself, instead of coating the antibacterial agent component. The present invention has been devised in order to meet such a requirement, and imparts antibacterial properties to austenitic stainless steel itself by including Cu in a content such that it is easily ionized when exposed to a humid atmosphere. The purpose of the present invention is to provide austenitic stainless steel that maintains excellent antibacterial properties for a long period of time without sacrificing various characteristics such as the beautiful appearance and workability peculiar to stainless steel, and is safe for the human body and environment. To do.

[0005]

In order to achieve the object, the austenitic stainless steel of the present invention has C: 0.
015-0.070 wt%, Si: 0.5-2.0 wt%, Mn: 0.5-2.0 wt%, P: 0.015-wt%
0.040% by weight, S: 0.01% by weight or less and Cr:
The basic composition is 15 to 32% by weight and the balance is Fe, and the Cu content in the basic composition is in the range of 1.1 to 3.5% by weight, and is defined by the following formula (1). The X value is in the range of 0.05 to 0.15. X = Cu% / (C% + Si% + Mn% + P% + S% + Cr% + Cu%) (1) This austenitic stainless steel further has Ni: 7.
0 to 26.0 wt%, Ti: 0.075 to 0.35 wt%, N: 0.09 to 0.15 wt%, Mo: 0.1
It may contain one or more of 5.1% by weight.

[0006] Cu is known to exhibit a very good antibacterial property. The antibacterial property of Cu is that ionized Cu efficiently reacts with thiols in respiration and metabolic enzymes of cells,
It is considered to be caused by inactivating thiol, and Cu such as antibacterial silica gel, antibacterial zeolite, etc.
Is used as an antibacterial agent. However, regarding Cu contained in the austenitic stainless steel itself. It has not been examined from the viewpoint of antibacterial properties. The present inventors have found that Cu contained in the austenitic stainless steel itself also has antibacterial properties, and by setting the content of Cu contained in the steel to a level at which it is easily ionized, the steel itself is It was confirmed that excellent antibacterial properties are expressed even if there is.

The mechanism by which Cu contained in austenitic stainless steel develops antibacterial properties is presumed as follows. In the austenitic stainless steel, the Cu concentration in the surface layer portion increases as the Cu content increases. Generally, when the added amount of Cu is 1.1% by weight or more, the Cu concentration in the surface layer portion is 0.1 atom% or more, and a slight amount of water on the surface of the stainless steel in a humid environment where bacteria are likely to grow. Also ionizes a very small amount of Cu. Since Cu has a high antibacterial effect, even if it is a trace amount, it reacts efficiently with the respiratory and metabolic enzymes of bacterial cells existing near the steel surface,
Inactivate. As a result, bacterial growth is suppressed and sterilized.

[0008] The ionization reaction of Cu is affected by the environment of use such as the pH of the atmosphere in contact with the steel surface and the salt concentration in water, and as a result, the antibacterial effect of Cu changes. However, when the Cu content in steel exceeds 1.1% by weight, the above formula (1)
As long as the above is satisfied, sufficient antibacterial properties can be expressed in a normal environment. The relation of the equation (1) is empirically obtained from many experiments conducted by the present inventors.

The antibacterial effect of Cu becomes stronger as the amount of Cu contained in the austenitic stainless steel increases. From the viewpoint of antibacterial properties, the higher the Cu content, the more preferable. However, if a large amount of Cu exceeding 3.5 wt% is contained, the hot workability of stainless steel is impaired. Therefore, the Cu content of the austenitic stainless steel to be the base steel is required to be in the range of 1.1 to 3.5% by weight. The appearance of the austenitic stainless steel containing Cu in this range is the same as that of the normal one not containing Cu. Moreover, since the steel material itself is provided with antibacterial properties, it has a surface resistant to flaws, abrasion, etc., and the highly stable antibacterial properties are maintained for a long period of time. Further, since Cu is harmless to the human body under the normal use environment as widely used in tableware, containers, etc., Cu-added austenitic stainless steel also has an adverse effect on the human body and environment. There is no such thing.

The effect of addition of alloying elements other than Cu will be described. C: 0.015 to 0.070% by weight If the C content exceeds 0.070% by weight, the material is significantly hardened even when drawing is performed, and the sensitivity to time cracking becomes sensitive. Therefore, the appropriate amount range of C is 0.015
It was set to 0.070% by weight. Si: 0.5 to 2.0 wt% The higher the Si content, the higher the pitting corrosion resistance and the higher the work hardenability of the austenite phase. Such curing is
It becomes remarkable at 0.5 wt% or more of Si. But 2.0
If a large amount of Si in excess of wt% is contained, hot workability deteriorates due to the formation of δ ferrite, which causes hot cracking. S: 0.01% by weight or less It is a harmful impurity and forms a FeS—S eutectic film having a low melting point at a grain boundary, which adversely affects red hot embrittlement and hot workability. However, when the content is as low as 0.01% by weight or less, it is fixed as a sulfide and the adverse effect of S is suppressed.

P: 0.015 to 0.040% by weight Since it has many harmful effects, it promotes the precipitation of carbides in the coexistence with C and lowers the toughness. Regarding corrosion resistance, the susceptibility to pitting corrosion increases as the P content increases, and intergranular corrosion easily occurs. Therefore, the appropriate amount range of P is 0.015 to 0.040.
Weight% is set. Cr: 15 to 32% by weight It is an alloying element effective in improving the corrosion resistance, and when the content is 15% by weight or more, the hardening of Cr becomes remarkable. However, a large amount of Cr content exceeding 32% by weight promotes the formation of δ ferrite and deteriorates the hot workability. Ni: 7.0 to 26.0 wt% This is a basic element of austenitic stainless steel, and the higher the content, the lower the hardness and tensile strength, and the toughness is improved. If the Ni content is less than 7.0% by weight, the austenite phase becomes unstable, work-induced martensite is likely to be formed, and work hardening reduces ductility. However, if a large amount of Ni is contained in excess of 26.0% by weight,
Steel cost increases.

Further, Mn which stabilizes austenite:
0.5 to 2.0% by weight, Ti: 0.075 to 0.35% by weight, which makes the crystal grains finer and suppresses coarsening at the time of recrystallization.
Mo for improving high temperature strength, creep rupture strength, toughness, etc .:
You may add 1 type (s) or 2 or more types, such as 0.1-5.1 weight% and N: 0.009-0.15 weight% which refines a crystal grain and improves toughness.

[0013]

【Example】

Example 1: Various stainless steels whose components are shown in Table 1 were melted. In Table 1, test numbers 1 to 8 are C according to the present invention.
1 shows an austenitic stainless steel whose u content is adjusted. Test numbers 9 and 10 are SUS304 containing 0.31 wt% Cu and SU containing 0.29 wt% Cu, respectively.
Cu-Ni-C containing S316 and Cu 0.99 wt%
It is a comparative example using r steel.

[0014]

[Table 1]

The antibacterial property of each test piece was investigated as follows. Escherichia coli IFO 33
01 (E. coli) and Staphylococcus a
ureus IFO 12732 (Staphylococcus aureus) in ordinary broth medium at 35 ° C., 16-20
After culturing with shaking for a period of time, a culture solution was prepared. The bacterial solution was prepared by diluting the culture solution 20,000 times with sterile phosphate buffer. Drop 1 ml of the bacterial solution on the surface of the test piece, and
Stored at 24 ° C for 24 hours. After storage, the test piece was washed out with SCDLP medium, and the number of viable cells in the obtained liquid was measured by the pour plate culture method (culture at 35 ° C. for 2 days) using a standard agar medium. According to this test method, it can be said that a material having a stronger antibacterial property is obtained as the viable cell count after 24 hours is decreased from the initial viable cell count. In addition, in order to confirm that there was no abnormality in the test, the bacterial solution was directly dropped on the petri dish as a reference, and the number of bacteria was measured in the same manner. The test results are evaluated as highly reliable when there is no significant increase or decrease in the reference viable cell count.

[0016]

[Table 2]

As is clear from Table 2 showing the test results,
In the test numbers 1 to 8 in which the Cu content is 1.1% by weight or more,
It can be seen that all the test pieces had a small number of viable cells after 24 hours and exhibited good antibacterial properties. In contrast, in Test Nos. 9 and 10 having a low Cu content, a large amount of Escherichia coli and Staphylococcus aureus survived even after 24 hours. Also, Cu
With respect to the austenitic stainless steel whose content was maintained at a constant value of 1.5% by weight, the effect of other alloy components on the antibacterial action was investigated. As a result, even if the Cu content is the same, when the composition range defined in the present invention and the relational expression (1) described above are satisfied as shown in Table 3 and FIG. 1, the antibacterial property is maintained at a high level. It turned out that On the other hand, in the case where the specified component range or the relational expression (1) is not satisfied, the antibacterial property has a large variation, the reliability is low, and the austenite structure is not formed in some cases.

[0018]

[Table 3]

[0019]

As described above, the austenitic stainless steel of the present invention has a C content in relation to other alloy components.
When the u content is 1.1% by weight or more, the appearance,
Maintains high and stable antibacterial properties for a long time without impairing the originally required properties such as processability. Also, C
The surface can be hardened by utilizing the precipitation hardening of u. The stainless steel thus improved in antibacterial property is used in a wide range of fields such as cutting tools, Western tableware, medical equipment, sanitary equipment, food-related equipment, etc. that emphasize hygiene.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of the relationship between alloy components on antibacterial properties.

Claims (2)

[Claims] 1. C: 0.015 to 0.070% by weight, S
i: 0.5 to 2.0% by weight, Mn: 0.5 to 2.0% by weight, P: 0.015 to 0.040% by weight, S: 0.01
% Or less and Cr: 15 to 32% by weight with the balance being F
e is a basic composition, the content of Cu contained in the basic composition is in the range of 1.1 to 3.5% by weight, and the formula X = Cu
% / (C% + Si% + Mn% + P% + S% + Cr% + C
An austenitic stainless steel having antibacterial properties, characterized in that the X value defined by u%) is in the range of 0.05 to 0.15. 2. Ni: 7.0 to 26.0% by weight, T
i: 0.075 to 0.35% by weight, N: 0.09 to 0.
15% by weight, Mo: 0.1 to 5.1% by weight of one or two
The austenitic stainless steel according to claim 1, containing at least one kind.