JP3223418B2 - Ferritic stainless steel excellent in antibacterial property and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to kitchen appliances, electric appliances,
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 devices, and chemical devices, and a method for producing the same.

[0002]

2. Description of the Related Art Corrosion resistance in general environments is required for various equipment used in kitchen equipment and hospitals, and handrail pipes for transportation such as buses and trains.
Stainless steel represented by 304 is mainly used. However, in recent years, hospital infections due to Staphylococcus aureus have become a problem, and there is a demand for improved hygiene even in environments used by an unspecified number of people, such as buses and trains. Along with this, the materials used for various machines and instruments are not limited to the properties of general structural materials, and are maintenance-free with functions such as antibacterial properties that do not require regular disinfection and other infection prevention. Material is desired. As a material having antibacterial properties, an antibacterial coat formed by an organic film or plating is generally used as disclosed in JP-A-5-228202 and JP-A-6-10191. However, the antibacterial coat has a drawback in that the antibacterial property decreases as the film disappears. The organic matter having lost the antibacterial property may become a nutrient source and may propagate bacteria and various 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 the dissolution, abrasion, chipping or the like of the film, and the antibacterial effect may be reduced.

[0003]

By the way, Ag, Cu
It is known that such metal elements 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 studied various improvements in antibacterial properties by adding Cu, and found that the antibacterial properties were improved by increasing the Cu concentration on the surface of stainless steel.
No. 53738 and JP-A-8-225895.
The present invention has been devised in order to further enhance the action of Cu previously proposed, and a second phase mainly comprising Cu (hereinafter, referred to as Cu).
By depositing a predetermined amount of Cu-rich phase),
It is intended to impart excellent antibacterial properties to ferritic stainless steel.

[0004]

The ferritic stainless steel of the present invention contains C: 0.1% by weight or less and Si: 2% by weight.
In the following, Mn: 2% by weight or less, Cr: 10 to 30% by weight and Cu: 0.4 to 3% by weight, the balance being substantially Fe
And the Cu-rich phase precipitated by the aging treatment is 0.1%.
It is characterized by being dispersed in the matrix at a rate of 2% by volume or more. Ferritic stainless steel of the present invention,
It may contain 0.02 to 1% by weight of Nb and / or Ti. Further, Mo: 3% by weight or less, Al: 1% by weight or less, Zr: 1% by weight or less, V: 1% by weight or less, B: 0.
05% by weight or less, rare earth metal element (REM): 0.05
It may contain one or two or more kinds by weight. This ferritic stainless steel is obtained by cold rolling a ferritic stainless steel having a predetermined composition and performing final annealing.
Aging treatment is performed at 0 to 800 ° C. to reduce the Cu-rich phase to 0.2.
It is produced by precipitating at least volume%.

[0005]

Since stainless steel is covered with a hydroxide mainly composed of Cr called a passive film, it exhibits excellent corrosion resistance. The present inventors have developed a C-type compound exhibiting 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 of the dropping solution containing Staphylococcus aureus was investigated. As a result, it was found that stainless steel containing Cu to a certain degree or more had antibacterial properties. However, less than several percent of C in steel
Simply dissolving u as a solid solution may not always provide sufficient antibacterial properties and its durability. Therefore, as a result of further study, even if the Cu content is the same, if a part of Cu is precipitated as a Cu-rich phase as shown in FIG. It has been found that the properties are also improved. In providing effective antibacterial properties,
It is necessary to precipitate the Cu-rich phase at a rate of 0.2% by volume or more. Cu-rich phases are those having an FCC structure or H
Some have a CP structure.

Means for precipitating a Cu-rich phase include:
It is conceivable that isothermal heating such as aging is performed in a temperature range where the Cu-rich phase is likely to precipitate, and that the passage time in the precipitation temperature range is made as long as possible by slow cooling. Therefore, as a result of examining various conditions, it was found that after final annealing, 500-800 °
It has been found that when aging treatment is carried out within the range, precipitation is promoted, and good antibacterial properties can be obtained even when the Cu addition amount is low. When elements that easily form carbonitrides and precipitates, such as Ti and Nb, are added, Cu
The rich phase is easily dispersed uniformly in the matrix, and the antibacterial property and the productivity are improved. Cu rich phase precipitation and surface Cu
As a result of further investigation of the relationship with the concentration, a Cu-rich phase was present on a part of the surface, and there was no passive film mainly composed of Cr in this part. It was presumed that this became easier.

Hereinafter, the alloying elements contained in the ferritic stainless steel of the present invention and the contents thereof will be described. C: 0.1% by weight or less While improving the strength of ferritic stainless steel,
In the present invention, it is an effective alloying element for uniformly dispersing the precipitation of the ε-Cu phase by generating Cr carbide. However, since excessive addition of C deteriorates the productivity and the corrosion resistance, the upper limit is restricted to 0.1% by weight. Si: 2% by weight or less An alloy element that improves corrosion resistance and strength, but the upper limit is 2% by weight because excessive addition causes deterioration of productivity.
Regulated. Mn: 2% by weight or less 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 is regulated to 2% by weight.

[0008] Cr: 10 to 30% by weight An important alloying element for maintaining the corrosion resistance of ferritic stainless steel, and 10% by weight or more is required. However, a large amount of Cr exceeding 30% by weight deteriorates manufacturability. Cu: 0.4 to 3% by weight and Cu-rich phase: 0.2
% By volume or more It is the most important alloying element in the ferritic stainless steel of the present invention.
It is necessary that a Cu-rich phase of at least volume% is precipitated. In order to precipitate a Cu-rich phase of 0.2% by volume or more, it is necessary to add 0.4% by weight or more of Cu. However, because of excessive addition, the productivity and corrosion resistance decrease,
The upper limit of the Cu content was regulated to 3% by weight. In addition, the size of the precipitate is not particularly limited in the Cu-rich phase, but in order to exhibit the antibacterial property evenly over the entire product surface, the precipitate phase must be appropriately dispersed and distributed. preferable.

Nb and / or Ti: 0.02 to 1% by weight Alloying element that is added as required, and serves as a precipitate to uniformly precipitate an ε-Cu phase around the precipitate. Such an effect becomes significant at 0.02% by weight or more. However, excessive addition exceeding 1% by weight lowers the productivity and processability. Mo: 3% by weight or less Mo is an alloy element that is added as necessary, and has an effect of improving corrosion resistance and strength. However, excessive addition exceeding 3% by weight lowers the productivity and processability. Al: 1% by weight or less Al is an alloying element that is added as necessary, and exhibits an effect of improving corrosion resistance similarly to Mo. However, excessive addition exceeding 1% by weight lowers the productivity and processability.

Zr: 1% by weight or less Zr is an alloying element that is added as necessary, and forms a carbonitride and has an effect of improving the strength of a steel material. But,
Excessive addition exceeding 1% by weight lowers the productivity and processability. V: 1% by weight or less An alloy element that is added as necessary, and forms a carbonitride similarly to Zr, and has an effect of improving the strength of steel. However, excessive addition exceeding 1% by weight lowers the productivity and processability. B: 0.05% by weight or less An alloy element that is added as necessary, and has an effect of improving hot workability. However, an excessive addition exceeding 0.05% by weight causes a reduction in hot workability.

Rare earth metal element (REM): 0.05% by weight or less An alloy element added as necessary, and has an effect of improving hot workability similarly to B. However, an excessive addition exceeding 0.05% by weight causes a reduction in hot workability. Aging treatment: 500-800 ° C To precipitate a Cu-rich phase, 500-800 ° C
Is effective. The lower the aging temperature, the lower the amount of solute Cu in the matrix and the greater the amount of Cu-rich phase deposited. However, if the aging treatment temperature is too low, the diffusion rate becomes slow, and the amount of precipitation decreases on the contrary. As a result of performing various aging treatments by changing temperature conditions and examining a temperature range effective for antibacterial properties, it was found that 500 to 800 ° C is an industrially effective temperature range.

[0012]

EXAMPLE A 30 kg ferritic stainless steel having the composition shown in Tables 1 and 2 was melted in a vacuum melting furnace, forged and hot-rolled, and then annealed to obtain a hot-rolled annealed plate. And cold rolling and annealing are repeatedly performed, and finally board thickness 0.5-1.
A 0 mm cold-rolled annealed plate was obtained. Some plates were aged for 1 hour. The obtained test material was observed with a transmission electron microscope. For example, when a specimen obtained by aging a K4 steel at 800 ° C. for 1 hour was observed after forming a thin film sample, as shown in the observation results of FIG. 1, the Cu-rich phase (ε-Cu phase) was uniform. And it was finely dispersed and precipitated. As described above, those having a structure in which the ε-Cu phase was uniformly and finely dispersed and precipitated exhibited more excellent antibacterial properties. Also,
From the observation results, the amount of the precipitated ε-Cu phase was determined.

For the antibacterial test, Staphylococ
us aureus 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 was diluted 20,000-fold with sterile phosphate buffer to prepare a bacterial solution. 5cm ×
1 ml of the bacterial solution was dropped on a surface of a 5-cm test piece polished with # 400, and stored at 25 ° C. for 24 hours. After storage, the test piece was washed off with 9 ml of SCDLP medium (manufactured by Nippon Pharmaceutical Co., Ltd.), and the number of viable cells was counted on the obtained liquid by a pour plate method (cultured at 35 ° C. for 2 days) using a standard agar medium. . Further, as a reference, a bacterial solution was directly dropped on a petri dish, and the number of viable bacteria was similarly counted. ◎: No viable bacteria detected, ○: 95% or more died compared to the reference viable count, ○: 60-95% range died, Δ: Less than 60% Was evaluated as x. The evaluation results are shown in Tables 1 and 2 together with the ε-Cu phase.

[0014]

[0015]

As is evident from Table 1, the material to which 0.4% by weight or more of Cu is added and the ε-Cu phase is precipitated in 0.2% by volume or more exhibits excellent antibacterial properties. I understand. On the other hand, in K14 to K16 of Table 2 in which the Cu content was less than 0.4% by weight, the amount of the precipitated ε-Cu phase was small, and the antibacterial properties were low. In Test Nos. K1 and K2 in Table 2 where the aging treatment for ε-Cu phase precipitation was not performed even at the same level of Cu content, although the antibacterial properties were slightly improved, sufficient antibacterial properties were obtained. Did not. K3 of Table 2 aged at 400 ° C. and K4 of Table 2 aged at 900 ° C., even when Cu of 0.4% by weight or more was added.
In this case, the precipitation amount of the ε-Cu phase was less than 0.2% by volume, and the antibacterial properties were insufficient. Further, in K17 and K18 of Table 2 which were aged in the temperature range specified in the present invention,
Antibacterial properties were also inferior due to insufficient Cu content.

[0017]

As described above, the ferritic stainless steel of the present invention regulates the Cu content of the material and precipitates a predetermined amount of the Cu-rich phase, thereby providing an excellent antibacterial effect with a solid material. Has been expressed. Ferritic stainless steel thus imparted antibacterial properties maintains excellent properties over a long period of time, so it can be used for kitchen equipment, equipment used in hospitals, and handrails for transportation such as buses and trains. Used in areas where antimicrobial properties are required, and living environment is improved.

[Brief description of the drawings]

FIG. 1 Microstructure of a Cu-containing ferritic stainless steel specimen aged at 800 ° C. for 1 hour observed by a transmission electron microscope

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naoto Okubo 4976 Nomura Minamicho, Shinnanyo-shi, Yamaguchi Prefecture Nissin Steel Engineering Co., Ltd. (56) References JP-A-5-17850 (JP, A) JP-A Heihei 7-90503 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 6/00-6/00 102

Claims (2)

(57) [Claims] 1. C: 0.1% by weight or less, Si: 2% by weight
In the following, Mn: 2% by weight or less, Cr: 10 to 30% by weight and Cu: 0.4 to 3% by weight, the balance being substantially Fe
And the Cu-rich phase precipitated by the aging treatment is 0.1%.
Ferritic stainless steel with excellent antibacterial properties dispersed in the matrix at a rate of 2% by volume or more . 2. A ferrite having the composition according to claim 1.
After cold rolling stainless steel and final annealing, 500 ~
Aging treatment at 800 ° C, 0.2 volume of Cu rich phase
% Of ferrite stainless steel with excellent antibacterial properties
Steel manufacturing method.