JPH09256116A - High strength martensitic stainless steel excellent in antibacterial characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a martensitic stainless steel having continuous antibacterial characteristic and high strength. SOLUTION: This high strength martensitic stainless steel has a composition containing, by weight, 0.2-0.8% C, <=3% Si, 10-20% Cr, and 0.4-5% Cu. At least one or more annealing treatments among hot rolled plate annealing, process annealing in the course of cold rolling, and finish annealing are carried out by performing heat treatment consisting of soaking at 500-900 deg.C for >=1hr, and secondary phases composed essentially of Cu are precipitated by >=0.2vol.% in a matrix. Then, after heat treatment consisting of soaking at 800-1000 deg.C for <=10min, hardening treatment is carried out. This steel can further contain either or both of <=4% Mo and <=1% V. Moreover, in the case where higher strength is required, cold rolling can be applied at <=60% rolling rate after the finish annealing and before the hardening treatment for the cold rolled sheet.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high-strength martensitic stainless steel suitable for applications requiring antibacterial properties in the field of knife products such as knives and scissors.

[0002]

2. Description of the Related Art In addition to high strength required for knives such as kitchen knives and scissors, corrosion resistance is often required from the viewpoint of maintenance. Conventionally, SUS420J2 is used for applications requiring both high strength and corrosion resistance. The martensitic stainless steel represented by is used. However, as hospital-acquired infection with Staphylococcus aureus has been highlighted, there has been a great deal of interest in hygiene in recent years, and improvement of hygiene in the environment used by unspecified large numbers of people such as buses and trains has been improved. Not only in the demand, but also in blade applications where there are many opportunities to come into contact with food and drink, maintenance-free materials with antibacterial properties that do not require infection prevention by periodic disinfection etc. are further desired. There is. As a material to which an antibacterial property has been given so far, JP-A-5-22820 and JP-A-6-101 are known.
As disclosed in Japanese Patent Publication No. 91, etc., an antibacterial coat formed by an organic film or plating is generally used.

[0003]

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 be a source of nutrients and may propagate bacteria and various 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, above all, when sharpness deteriorates in blade applications, it is essential to lose the coating and plating layer because the work of sharpening is performed, and these antibacterial coating means solve the problem of imparting antibacterial properties in blade applications. Not done.

Incidentally, it is known that metal elements such as Ag and Cu exhibit an effective antibacterial action. But,
Since Ag is very expensive and has poor corrosion resistance, it is not used in applications where it is 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 is improved by increasing the Cu concentration on the surface of stainless steel, and Japanese Patent Application Nos. Hei 6-209121 and Hei 7 -55069. However, since these proposals also utilize the antibacterial property of the Cu concentrated layer on the surface, the antibacterial property is lost along with the disappearance of the Cu concentrated layer on the surface by polishing as in the case of the above antibacterial coat. There's a problem.

Therefore, the present inventors have made further studies,
It was found that it is possible to continuously obtain antibacterial properties by precipitating a predetermined amount of the second phase mainly composed of Cu in the matrix, and proposed it in Japanese Patent Application No. 7-347735. However, even in these proposals, the high strength required for use as a cutting tool was not satisfied at the same time. The present invention provides a high-strength martensitic stainless steel having high strength and excellent corrosion resistance, and imparting durable antibacterial properties.

[0006]

The high-strength martensitic stainless steel of the present invention has the following objects and advantages.
C: 0.2 to 0.8% by weight, Si: 3% by weight or less, C
r: 10 to 20% by weight, Cu: 0.4 to 5% by weight, and at least one or more of intermediate annealing or finish annealing in the hot-rolled sheet annealing or cold-rolling step is 50.
The second phase mainly composed of Cu, which is obtained by performing heat treatment at 0 to 900 ° C. for 1 hour or more of soaking, then heat treatment at 800 to 1000 ° C. for 10 minutes or less, and then quenching treatment, mainly composed of Cu (hereinafter C
u rich phase) 0.2% by volume in the matrix
It is characterized by the above existence. This martensitic stainless steel can further contain one or two of Mo: 4 wt% or less and V: 1 wt% or less. Further, when higher strength is required, higher strength is achieved by performing cold rolling at a rolling rate of 60% or less after finish annealing of the cold rolled sheet and before quenching.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Stainless steel has excellent corrosion resistance because its surface is covered with a hydroxide mainly called Cr called a passive film. The present inventors added Cu expressing effective antibacterial property to martensitic stainless steel, measured the amount of Cu contained in the passive film, and measured the antibacterial property by dropping a liquid containing Staphylococcus aureus. investigated. As a result, it was found that the stainless steel containing a certain amount of Cu or more has antibacterial properties. However, if only a few percent or less of Cu is dissolved in steel,
Antibacterial properties and their persistence may not always be sufficient. Therefore, as a result of further studies, if a part of Cu is finely and uniformly precipitated as a Cu-rich phase such as ε-Cu even if the Cu content is the same, Cu is eluted in the use environment. It has been found that it becomes easier and the antibacterial property is improved. It was found that the amount of precipitation should be 0.2 vol% or more. Further, even if the surface is damaged during polishing, processing or use, the internal Cu-rich phase appears on the new surface, so that it has an excellent antibacterial action.

As means for precipitating the Cu-rich phase,
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 studying various conditions, annealing of martensitic stainless steel containing Cu was soaked at a temperature of 500 to 900 ° C.
It was found that a Cu-rich phase was precipitated in the matrix in an amount of 0.2 vol% or more when the treatment was carried out for more than an hour.

Next, in the martensitic stainless steel containing Cu, at least one or more of the intermediate annealing or the finish annealing in the hot-rolled sheet annealing or the cold-rolling step is performed at 500 to 900 ° C. for a soaking time of 1 hour or more. Heat treatment is performed to precipitate a Cu-rich phase in the matrix in an amount of 0.2 vol% or more, and quenching treatment is performed at 800 to 1000 ° C.
If done within a minute, HV500-600 which is required for high strength without solid solution disappearance of Cu-rich phase
Turned out to be Further, after the finish annealing of the cold rolled sheet and before the quenching treatment, cold rolling is performed at a rolling rate of 60% or less, whereby the strength can be further enhanced.
The high-strength martensitic stainless steel of the present invention is 100 to 600 ° C for the purpose of further improving toughness.
It is also possible to perform tempering treatment in the temperature range of.

The reasons for limiting the content of alloying elements contained in the high-strength martensitic stainless steel of the present invention and the conditions for imparting properties will be described below. C: 0.2 to 0.8% by weight It is an alloying element effective in increasing the strength after quenching and tempering of martensitic stainless steel. In order to obtain the strength after quenching and tempering, 0.2 wt% or more is necessary.
Further, it also has an effect of forming Cr carbide effective as a precipitation site of the Cu-rich phase and uniformly dispersing the fine Cu-rich phase. However, when a large amount of C exceeding 0.8% by weight is contained, corrosion resistance and toughness deteriorate.

Si: 3.0 wt% or less It is an alloying element effective as a deoxidizing agent, and has an effect of increasing temper softening resistance and improving antibacterial property. However, these effects are saturated at 3.0% by weight, and if contained in a large amount, manufacturability is impaired.

Cr: 10 to 20% by weight It is an alloying element necessary for maintaining the corrosion resistance of martensitic stainless steel, and 10% by weight or more of Cr is required in order to ensure the necessary corrosion resistance. However, the inclusion of a large amount of Cr in excess of 20% by weight lowers the hardness after quenching, causes coarse eutectic carbide formation, and deteriorates workability and toughness.

Cu: 0.4 to 5.0% by weight and Cu
Rich phase: 0.2 vol% or more It is the most important alloying element in the stainless steel of the present invention, and in order to maintain good antibacterial property, 0.2 vol% or more of Cu rich phase should be precipitated. Necessary, 0.4% by weight or more of C in order to precipitate 0.2% by volume or more of Cu-rich phase in this system martensitic stainless steel.
u content is required. However, an excessive Cu content exceeding 5.0% by weight deteriorates manufacturability, workability, and corrosion resistance. The Cu-rich phase is not particularly limited in the size of the precipitate, but since it exerts the antibacterial property evenly on the entire product surface, it maintains good antibacterial property even when it is sharpened as a product blade. In order to do so, it is preferable that the precipitation phase is appropriately dispersed both on the surface and inside.

Mo: 4.0 wt% or less An element which is added as required, exhibits an action of improving corrosion resistance, and precipitates as an intermetallic compound such as Fe ₂ Mo to form a fine Cu-rich phase nucleus. It becomes a site and facilitates precipitation. Further, Mo and the compound containing Mo also exhibit the action of improving the antibacterial property. But,
Excessive Mo content exceeding 4.0% by weight deteriorates manufacturability and processability.

V: 1.0% by weight or less Forming a carbide serving as a precipitation site and facilitating precipitation of a fine Cu-rich phase. Further, the formation of the carbide improves the wear resistance and the temper softening resistance.
However, an excessive content exceeding 1.0% by weight deteriorates manufacturability and workability.

In addition to the above alloying elements, the high-strength martensitic stainless steel of the present invention is Nb of 0.5% by weight or less and 1.0% by weight or less of Nb which contributes to grain refinement and improves low temperature toughness. Ti, 0.3% by weight or less of Ta, Zr, 1.0% by weight or less of Al for improving temper softening resistance, 2.0
One or more of W by weight% or less, 2.0% by weight or less Ni effective for improving strength and toughness, and 0.01% by weight or less B by which hot workability is improved can be contained. .

Annealing condition: temperature: 500 to 900 ° C., time: 1 hour or more This is an important treatment for precipitating a Cu-rich phase. The lower the annealing temperature, the smaller the amount of solid solution Cu in the matrix, so the amount of precipitation of the Cu-rich phase increases, but if the temperature is too low, the diffusion rate is slow and the amount of precipitation decreases. As a result of conducting annealing under various conditions and examining temperature conditions effective for antibacterial properties, it was found that a temperature range of 500 to 900 ° C. is industrially effective. In the heat treatment within the above temperature range, a treatment time of 1 hour or more is required to precipitate a Cu-rich phase of 0.2 volume% or more.

Cold rolling conditions: Rolling rate 60% or less Cold rolling is performed for the purpose of obtaining high strength (high hardness) of the product after quenching and tempering, but when the rolling rate is high, toughness is obtained. The upper limit is set to 60% because of the adverse effect of deterioration. This cold rolling may be omitted if the strength required for product use is low.

Quenching treatment: temperature; 800 to 1000 ° C.,
Time: within 10 minutes In order not to eliminate the solid solution of the Cu-rich phase that has been precipitated by 0.2 vol% or more by annealing, it is necessary to avoid the treatment at high temperature, and in order to obtain the effect of quenching, the temperature must be high. It is useless if it is too low, and the quenching temperature is 800-
1000 ° C is suitable. If the treatment time is too long, the Cu-rich phase disappears as a solid solution.

Although this quenching treatment must secure the strength required for use in cutting tools, the quenching treatment temperature range in the present invention is characterized by being lower than the treatment temperature indicated in JIS G3404. This is because the steel of the present invention contains 0.2% by weight or more of C, so that even if the quenching treatment temperature is low, the amount of solid solution C for obtaining hardness HV500 or more can be satisfied and sufficient necessary strength can be obtained. Is.
Furthermore, since the quenching temperature is relatively low, undissolved carbides remain, and the growth of austenite grains during heating is relatively slow, and the structure after quenching becomes fine grains, and good toughness is ensured. It is also possible to omit the tempering process after the quenching process. As described above, the steel of the present invention can omit the tempering treatment after the quenching treatment, but can be tempered in the temperature range of 100 to 600 ° C when further improvement in toughness is required. . 500 ° C
If the tempering treatment is performed at the above temperature, the precipitation of the Cu-rich phase is promoted, so that the effect of further improving the antibacterial property can be obtained.

[0021]

EXAMPLES Steels of the present invention and comparative steels having the compositions shown in Table 1 were melted in a vacuum melting furnace of 30 kg, forged and hot rolled, and then annealed to obtain hot rolled annealed sheets. Hot-rolled sheet annealing is 500-9
It was applied at 00 ° C. for 12 hours. Then, a cold rolled plate having a plate thickness of 1.5 mm was obtained by cold rolling. The finish annealing of cold rolled sheet is 75
Continuous annealing was performed at 0 ° C. for 1 minute. Steel No. M
About part of -1, in the intermediate annealing or finish annealing in the cold rolling process, soaking at 800 ° C for 12 hours, steel N
o. K-2 is 12 at 750 ° C in finish annealing.
Time processed. Steel No. Part of M-2 and M-6
For, the cold rolling was performed at a cold rolling rate of 10 to 50% before the quenching treatment. Steel No. For M-5, M-6 and K-2, 150-500 after quenching treatment
A soaking process at 30 ° C. for 30 minutes was performed.

[0022]

[Table 1]

Precipitated Cu-rich phase (ε in the present invention steel
-Cu phase is precipitated) was determined by SEM-EDX. The antibacterial test was as follows. Staphylo
cocus aureus IFO 12732 (staphylococcus aureus) in a normal broth medium at 35 ° C. for 16 to 24
After culturing with shaking for a period of time, a culture solution was prepared. The culture was diluted 20,000-fold with sterile phosphate buffer to prepare a bacterial solution.
1 ml of the bacterial solution was dropped on a # 400 polished surface of a test piece of 5 cm × 5 cm and stored at 25 ° C. for 24 hours. After saving,
9 ml of SCDLP medium (Nippon Pharmaceutical Co., Ltd.)
The cells were washed away with and the number of viable cells in the obtained liquid was counted by the pour plate culture method (35 ° C., 2 days culture) using a standard agar medium. 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.

⊚ when no viable bacteria were detected, ○ when 60% or more of the reference viable cells were killed, ○, 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. Table 2 shows the hardness and antibacterial property evaluation results of each steel and the measurement results of the ε-Cu phase precipitation amount. As shown in Table 2, Cu containing 0.4 wt% or more of Cu and 0.2 vol% or more of the ε-Cu phase precipitated had excellent antibacterial properties. Further, all of the materials within the composition range of the present invention, which have been subjected to the quenching treatment after heating at 800 to 1000 ° C., have a hardness of HV500 to 600, which is a sufficient value for use as a cutting tool.

On the other hand, comparative steels K-1 to K containing a small amount of Cu
-3, the amount of precipitation of the ε-Cu phase is less than 0.2% by volume even when hot-rolled sheet annealing, intermediate annealing in the cold rolling step or finish annealing, soaking at 500 to 900 ° C. for 12 hours of soaking. Inferior antibacterial property. Even if the added amount of Cu is 0.4% by weight or more, the comparative example steel No. having the annealing temperature of the hot rolled sheet of less than 500 ° C. Comparative example steel No. M-3 in which the annealing temperature of the M-3 and hot-rolled sheet exceeds 900 ° C. In M-1, the precipitation amount of the ε-Cu phase was 0.
It is less than 2% by volume and the antibacterial property is poor. Further, the Cu addition amount was 0.4% by weight or more, and the annealing temperature of the hot-rolled sheet was within the range of the present invention, but the quenching temperature was 750 ° C., which is outside the range of the present invention. M-4 has excellent antibacterial properties, but has low hardness and is not suitable for use as a knife.

[0026]

[Table 2]

[0027]

As described above, the high-strength martensitic stainless steel of the present invention exhibits excellent antibacterial properties even with a solid material, and has corrosion resistance and high strength suitable for use in cutlery. Therefore, this stainless steel is used in a wide range of fields such as cutting blade applications and can improve the living environment.

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Claims (3)

[Claims] 1. A composition comprising C: 0.2 to 0.8% by weight, Si: 3% by weight or less, Cr: 10 to 20% by weight, Cu: 0.4 to 5% by weight, and hot rolled. At least one or more of the intermediate annealing or finish annealing in the sheet annealing or cold rolling step is performed by heat treatment at 500 to 900 ° C. for 1 hour or more soaking, and the second phase mainly composed of Cu is added to the matrix in an amount of 0.2.
After precipitating more than volume%, soak 1 at 800-1000 ° C
A high-strength martensitic stainless steel with excellent antibacterial properties, which is obtained by quenching after heat treatment within 0 minutes. 2. The high-strength martensitic stainless steel with excellent antibacterial properties according to claim 1, further comprising one or two of Mo: 4% by weight or less and V: 1% by weight or less. 3. After the finish annealing of the cold rolled sheet and before the quenching treatment, 60
The high-strength martensitic stainless steel excellent in antibacterial properties according to claim 1 or 2, which is cold-rolled at a rolling ratio of not more than%.