JPH08104952A - Martensitic stainless steel having antibacterial property - Google Patents

Abstract

PURPOSE: To produce a martensitic stainless steel increased in antibacterial properties without impairing its appearance, workability or the like. CONSTITUTION: This martensitic stainless steel has a fundamental compsn. contg., by weight, 0.015 to 0.070% C, 0.05 to 2.0% Si, 0.10 to 1.0% Mn, 0.015 to 0.040% P, <=0.01% S and 12 to 17% Cr, and the balance Fe, in which the content of Cu contained in the fundamental compsn. is regulated to the range of 0.3 to 5% and the value of X (=Cu%/(C%+Si%+Mn%+P%+S%+Cr%+Cu%)) is regulated to the range of 0.035 to 0.23. Thus, Cu exceeding the limit of solid solution precipitates onto the grain boundaries to increase the concn. of Cu in the surface layer part, and Cu ionized by moisture on the surface of the steel shows an antibacterial effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to martensitic stainless steel having enhanced antibacterial properties.

[0002]

2. Description of the Related Art Martensitic stainless steel having excellent corrosion resistance is used as a hard material used in a place where various bacteria are easily propagated or where the generation of various bacteria is not preferable. 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 kind of demand, there is a method of coating and laminating a resin containing an antibacterial agent on the surface of martensitic stainless steel, a method of plating an antibacterial agent component in a matrix, and the like.
It is introduced in Japanese Unexamined Patent Publication No. 228202, Japanese Unexamined Patent Publication No. 6-10191, and the like.

[0003]

When a resin containing an antibacterial agent is applied and laminated on the surface of martensitic 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 or 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. Is damaged. 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 to meet such a requirement, and by containing Cu in a content such that it is easily ionized when exposed to a humid atmosphere, the martensitic stainless steel itself has antibacterial properties. In order to provide martensitic stainless steel that maintains excellent antibacterial properties for a long period of time without sacrificing the beautiful appearance and workability of stainless steel, and is safe for the human body and environment. To aim.

[0005]

In order to achieve the object, the martensitic stainless steel of the present invention has C: 0.
015 to 0.070% by weight, Si: 0.05 to 2.0% by weight, Mn: 0.10 to 1.0% by weight, P: 0.015
~ 0.040% by weight, S: 0.01% by weight or less and Cr
The basic composition is 12 to 17% by weight with the balance being Fe, the Cu content in the basic composition is in the range of 0.3 to 5% by weight, and the X value defined by the formula (1) is 0.03
It is characterized by being in the range of 5 to 0.23. X = Cu% / (C% + Si% + Mn% + P% + S% + Cr% + Cu%) (1)

This martensitic stainless steel further contains Ni: 0.05 to 8.0 wt% and Al: 0.5 to 1.
5% by weight, Ti: 0.15 to 0.65% by weight, N: 0.
008 to 0.030% by weight, Mo: 0.30 to 2.5% by weight, Nb: 0.10 to 0.50% by weight, Ta: 0.1
It may contain 0 to 0.50% by weight of one type or two or more types. Cu is known to exhibit very good antibacterial properties. The antibacterial property of Cu is considered to be due to ionized Cu efficiently reacting with the thiols in the respiration and metabolic enzymes of cells to inactivate the thiols, and antibacterial silica gel, antibacterial zeolite, etc. It is used as an antibacterial agent carrying Cu. However, regarding Cu contained in the martensitic stainless steel itself. It has not been examined from the viewpoint of antibacterial properties. The present inventors have found that Cu contained in the martensitic 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 can be obtained. However, it was confirmed that excellent antibacterial properties were expressed.

The mechanism by which Cu contained in martensitic stainless steel exhibits antibacterial properties is presumed as follows. Martensitic stainless steel has a lower solid solution limit of Cu than other structures such as austenite. Generally, when the amount of Cu added is 0.3% by weight or more, Cu
Is not solid-solved in the crystal and segregates easily on the steel surface. As a result, the Cu concentration on the surface of the stainless steel becomes high, and in a humid environment where bacteria are likely to grow, even a slight amount of water on the surface of the stainless steel ionizes a very small amount of Cu. Since Cu has a high antibacterial effect, even if it is an extremely small amount, Cu efficiently reacts with the respiratory and metabolic enzymes of bacterial cells existing near the steel surface and is inactivated. 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, as long as the Cu content in steel exceeds the solid solubility limit of 0.3% by weight and satisfies the above-mentioned formula (1), sufficient antibacterial properties can be exhibited 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 martensitic stainless steel increases. From the viewpoint of antibacterial properties, the higher the Cu content, the more preferable. Further, by including Cu in a supersaturated state in the martensite phase and finely dispersing and precipitating a Cu-rich phase in the subsequent aging treatment, the hardness is effectively increased. However, when a large amount of Cu exceeding 5% by weight is contained, the hot workability of stainless steel is impaired. Therefore, Cu of the martensitic stainless steel to be the base steel
Content is 0.3-5% by weight, preferably 2.5% by weight
It is required to be within the following range. The martensitic stainless steel containing Cu in this range has the same appearance as that of ordinary 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, as Cu is widely used for tableware, containers, etc., Cu is harmless to the human body in a normal use environment, so that martensitic stainless steel containing Cu also has an adverse effect on the human body and the environment. Never give.

The effect of addition of alloying elements other than Cu will be described. C: 0.015 to 0.070 wt% As the C content increases, quenching aging and strain aging become remarkable, and C dissolved in supersaturation of martensite develops strength. However, the impact resistance decreases as the C content increases, and further increases the pitting corrosion sensitivity. Therefore, the optimum range of C is set to 0.015 to 0.070% by weight. Si: 0.05 to 2.0% by weight It is an alloying element that improves pitting corrosion resistance, and its effect becomes remarkable when the content is 0.05% by weight or more. However, a Si content exceeding 2.0% by weight forms δ ferrite, impairs hot workability, and causes hot cracking. S: 0.01 wt% or less FeS-Fe, which is a harmful impurity and has a low melting point at the grain boundaries.
Form a eutectic film, which causes problems in red hot brittleness and hot workability. When the S content is low, it is fixed as a sulfide, so in the present invention, the upper limit of the S content is set to 0.01% by weight.

P: 0.015 to 0.040% by weight P has many harmful effects, and when coexisting with C, promotes precipitation of carbides and reduces toughness. Regarding the corrosion resistance, as the P content increases, the pitting corrosion sensitivity becomes higher, causing intergranular corrosion. Therefore, the appropriate range of P content is 0.015 to 0.
It was set to 040% by weight. Cr: 12 to 17% by weight It is an alloy element effective for improving the corrosion resistance, and the effect of Cr addition becomes remarkable when the content is 12% by weight or more. But 17
If a large amount of Cr is contained in excess of weight%, the hot workability is deteriorated due to the formation of δ ferrite. Ni: 0.05 to 8.0 wt% Addition of 0.05 wt% or more of Ni increases the precipitation hardenability. However, since it is a strong austenite forming element, if a large amount of Ni exceeding 8.0 wt% is included,
The strength is likely to decrease due to the retained austenite.

Further, Ti: 0.1 for improving the precipitation hardenability.
5 to 0.65% by weight, Mn: 0.10 to 1.0% by weight for improving hardenability and creep strength, Mo: 0.30 to 2.5% by weight for improving temper embrittlement and creep resistance, N: 0.008 to 0.03 for improving strain aging and quenching aging
0% by weight, Nb: 0.10 to 0.50% by weight for improving secondary hardening of tempering and refinement of crystal grains, Ta: 0.10 to 0.50% by weight for improving toughness and refinement of crystal grains , Al for improving the precipitation hardenability: 0.15 to 1.5% by weight or the like may be added alone or in combination.

[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.
The martensitic stainless steel with adjusted u content is shown. Test Nos. 9 and 10 are comparative examples using SUS403 and stainless steel melted so as to fall outside the scope of the present invention.

[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] Table 2: Antibacterial evaluation of various stainless steels

As is clear from Table 2 showing the test results,
In the test numbers 1 to 8 in which the Cu content is 0.3% 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 martensitic stainless steel whose content was maintained at a constant value of 0.71% by weight, the influence of other alloy components on the antibacterial action was investigated. As a result, even if the Cu content is the same, as shown in Table 3 and FIG. 1, when the composition range and the relational expression (1) defined in the present invention are satisfied, the antibacterial property is maintained at a high level. It has been found. On the other hand, in the case where the specified component range and the relational expression (1) are not satisfied, the antibacterial property has a large variation and the reliability is low,
Some did not exhibit a martensite structure.

[0018]

[Table 3]

[0019]

As described above, the martensitic stainless steel of the present invention has a C content in relation to other alloy components.
By making the u content 0.3% 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.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hiromitsu Fukumoto 7-1 Takatani Shinmachi, Ichikawa City, Chiba Nisshin Steel Co., Ltd.

Claims (2)

[Claims] 1. C: 0.015 to 0.070% by weight, S
i: 0.05 to 2.0% by weight, Mn: 0.10 to 1.0
% By weight, P: 0.015 to 0.040% by weight, S: 0.
01 wt% or less and Cr 12 to 17 wt% and the balance is Fe as a basic composition, the content of Cu contained in the basic composition is in the range of 0.3 to 5 wt%, and X = Cu% /
(C% + Si% + Mn% + P% + S% + Cr% + Cu
%) Defined by X) is in the range of 0.035 to 0.23, which is a martensitic stainless steel having antibacterial properties. 2. Ni: 0.05 to 8.0% by weight, A
1: 0.5 to 1.5% by weight, Ti: 0.15 to 0.65
% By weight, N: 0.008 to 0.030% by weight, Mo:
The martensite system according to claim 1, containing one or more of 0.30 to 2.5% by weight, Nb: 0.10 to 0.50% by weight, and Ta: 0.10 to 0.50% by weight. Stainless steel.