JP2005232511A - Austenitic stainless steel having excellent antibacterial property and hot workability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide austenitic stainless steel having excellent hot workability and corrosion resistance, and having excellent antibacterial properties. <P>SOLUTION: The austenitic stainless steel has a composition comprising, by mass, 0.01 to 0.1% C, ≤2.0% Si, ≤2.0% Mn, ≤0.08% P, ≤0.02% S, 10 to 35% Cr, 6 to 15% Ni and 0.01 to 0.1% N, and further comprising 0.001 to 0.09% Ag and >0.30 to 4.0% Cu so as to satisfy Ag/(Ag+Cu)<0.07 (wherein, Ag and Cu denote the content (mass%) of each element). Thus, the austenitic stainless steel having excellent hot workability and antibacterial properties is produced without reducing its corrosion resistance. Further, B and/or Al may be incorporated therein. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an austenitic stainless steel excellent in antibacterial properties and suitable for daily life-related products such as kitchens, medical equipment, and building materials, and more particularly to further improvement of antibacterial properties and hot workability.

  It has been conventionally known that silver and copper are effective in suppressing the growth of pathogenic bacteria represented by E. coli and Salmonella and preventing food poisoning caused by the pathogenic bacteria. In recent years, materials having a bacterial growth suppression effect (hereinafter referred to as antibacterial properties) using silver and / or copper have been proposed.

  For example, Patent Document 1 contains 1.1 to 3.5% by weight of Cu and has antibacterial properties in which Cu% / (C% + Si% + Mn% + P% + S% + Cr% + Cu%) is in the range of 0.05 to 0.15. Austenitic stainless steel has been proposed. In the technique described in Patent Document 1, in order to develop antibacterial properties, Cu needs to be dissolved out from the steel sheet surface as ions, and for that purpose, Cu needs to be present on the steel sheet surface as coarse precipitates. is there. In order to make Cu exist as a precipitate, a method of performing an aging treatment after hot rolling, and a method of increasing the Cu content to facilitate the precipitation of Cu during aging are conceivable. However, performing an aging treatment causes a decrease in productivity and an increase in production cost, and an increase in Cu content has a problem of reducing hot workability. Furthermore, in Cu-containing austenitic stainless steel, coarse Cu precipitates exist on the surface of the steel sheet, and the antibacterial properties are improved by dissolving Cu as ions from the surface of the steel sheet, resulting in a significant destruction of the passive film. There is a problem that the corrosion resistance is lowered.

  Patent Document 2 proposes an austenitic stainless steel excellent in antibacterial properties containing 0.0005 to 0.50% Ag and 0.01 to 0.30% W. Since Ag has a lower solid solution in Fe than Cu and can be precipitated in steel even when added in an amount less than Cu, antibacterial properties can be ensured with a smaller added amount than Cu. According to the technique described in Patent Document 2, antibacterial properties are improved by the combined addition of Ag and W compared to the addition of Ag alone. However, the technique described in Patent Document 2 has a problem in that the manufacturing cost becomes excessively high because a complex addition of Ag and W is required.

  Further, Patent Document 3 proposes an austenitic stainless steel excellent in antibacterial properties in which Cu: 0.5 to 4.0% and Ag: 0.05 to 1.0% are added in combination. According to the technique described in Patent Document 3, by containing Ag and Cu simultaneously, the yield of Ag is improved, and antibacterial properties can be improved without necessarily requiring an aging treatment for Cu precipitation. Therefore, it is said that the Cu content can be relatively reduced. However, the technique described in Patent Document 3 has a problem in that the low melting point Ag—Cu phase is precipitated at the grain boundary, so that the hot workability is still low and the occurrence of shave on the steel surface becomes significant. It was.

Patent Document 4 discloses a stainless steel excellent in antibacterial property containing 0.0001 to 1 wt% of Ag and containing one or more of silver particles, silver oxide and silver sulfide particles in a total area ratio of 0.001% or more. Steel has been proposed. The stainless steel material manufactured by the technique described in Patent Document 4 has excellent workability and corrosion resistance, and can retain excellent antibacterial properties even when subjected to general-purpose surface processing including polishing. However, the technique described in Patent Document 4 requires a large amount of Ag in order to further improve antibacterial properties, leading to a rise in material costs and difficulty in stably dispersing Ag uniformly. was there. Furthermore, when a large amount of Ag is contained, there is a problem that hot workability is lowered and the steel sheet is frequently cracked.
JP-A-8-104953 JP 11-172379 A JP-A-10-259457 Japanese Patent Laid-Open No. 11-264057

  The present invention advantageously solves the above-described problems of the prior art, has excellent hot workability, can suppress the occurrence of surface defects such as ear cracks and dents during hot working, and further reduces the corrosion resistance. The object is to propose an austenitic stainless steel having excellent antibacterial properties without accompanying it.

  In order to achieve the above-mentioned problems, the present inventors have conducted extensive research on various factors affecting the hot workability, antibacterial properties, and corrosion resistance of austenitic stainless steel. As a result, by adding Ag and Cu in an appropriate ratio, antibacterial properties can be improved without reducing corrosion resistance, and segregation of the low melting point Cu-Ag phase to the grain boundary is suppressed, resulting in hot It has been found that processability is improved and generation of surface defects such as ear cracks and whiskers during hot working can be prevented.

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) In mass%, C: 0.01 to 0.1%, Si: 2.0% or less, Mn: 2.0% or less, P: 0.08% or less, S: 0.02% or less, Cr: 10 to 35%, Ni: 6 to 15 %, N: 0.01-0.1%, Ag: 0.001-0.09%, Cu: more than 0.30%, 4.0% or less, the following formula (1)
Ag / (Ag + Cu) <0.07 (1)
(Where Ag, Cu: content of each element (mass%))
An austenitic stainless steel excellent in hot workability and antibacterial properties, characterized by having a composition comprising the balance Fe and inevitable impurities.
(2) The austenitic stainless steel according to (1), further containing B: 0.0003 to 0.001% in mass% in addition to the above composition.
(3) The austenitic stainless steel according to (1) or (2), further containing, in addition to the above composition, mass: Al: 0.30% or less.

  According to the present invention, without reducing the corrosion resistance of the austenitic stainless steel, antibacterial properties are improved, and further, hot workability is remarkably improved to suppress the occurrence of surface defects such as ear cracks and heges, Processes such as surface care can be omitted, productivity can be improved, and manufacturing costs can be reduced, resulting in a remarkable industrial effect.

  First, the reason for limiting the chemical composition of the steel of the present invention will be described. Hereinafter, mass% in the composition is simply expressed as%.

Ag: 0.001 to 0.09%
Ag is an element that has the effect of suppressing the growth of bacteria and improves the antibacterial properties of austenitic stainless steel. In the present invention, it is necessary to contain 0.001% or more. On the other hand, a large content exceeding 0.09% can further improve the antibacterial properties, but it reduces the hot workability, increases surface defects, and increases the amount of expensive Ag added, resulting in production costs. Increase. For this reason, Ag was limited to the range of 0.001 to 0.09%. From the viewpoint of antibacterial properties, 0.02 to 0.09% is preferable. Further, it is more preferably 0.03 to 0.08% from the viewpoint of hot workability.

Cu: more than 0.30% and less than 4.0%
Cu, like Ag, is an element that improves antibacterial properties, but a large amount is required when added alone. In the present invention, Ag and Cu are added in combination. By adding Ag and Cu in combination, there is no decrease in corrosion resistance observed when Cu alone is added, there is little decrease in hot workability, and the antibacterial properties are remarkable with a small amount of content compared to the case where it is added alone. To improve. Such an effect is recognized when the content exceeds 0.30%, but when the content exceeds 4.0%, the hot workability deteriorates significantly. For this reason, Cu was limited to the range of more than 0.30% and 4.0% or less. From the viewpoint of antibacterial properties and hot workability, it is preferably 0.5 to 4.0%.

Ag / (Ag + Cu) <0.07 (1)
In the present invention, Ag and Cu are each contained within the above-described range and satisfying the expression (1). In addition, Ag and Cu in (1) Formula are content (mass%) of each element. Ag content and the ratio of Ag content and Cu content, Ag / Ag + Cu is made less than 0.07, so that Ag is dissolved in Cu phase and Cu (Ag) solid solution (melting point is 1084.87 ℃ for pure Cu) ) And segregation of the low melting point (779.1 ° C.) Ag—Cu phase to the grain boundary is suppressed. When Ag / (Ag + Cu) is 0.07 or more, the hot workability decreases, and surface defects such as ear cracks and scabs increase on the steel surface during hot working. For this reason, Ag / (Ag + Cu) was limited to less than 0.07. In addition, Ag / (Ag + Cu) is preferably 0.010 to 0.065 from the viewpoint of antibacterial properties and hot workability.

C: 0.01 to 0.1%
C is an element effective for improving formability and crackability. In the present invention, C is required to be contained in an amount of 0.01% or more. However, if it exceeds 0.1%, the steel is remarkably hardened and the formability is lowered. For this reason, C was limited to the range of 0.01 to 0.1%. In addition, Preferably it is 0.02 to 0.08%.

Si: 2.0% or less
Si is an element effective for improving corrosion resistance, and is preferably contained in an amount of 0.1% or more. However, excessive inclusion causes a decrease in ductility and deteriorates cold workability. For this reason, Si was limited to 2.0% or less. In addition, Preferably it is 0.2 to 0.8%.

Mn: 2.0% or less
Mn combines with S to form MnS and is an effective element for improving hot workability. In the present invention, Mn is preferably contained in an amount of 0.4% or more. Decreases the corrosion resistance. For this reason, Mn was limited to 2.0% or less. In addition, Preferably it is 0.2 to 0.8%.

P: 0.08% or less P is an element that deteriorates hot workability and promotes the occurrence of pitting corrosion, and is desirably reduced as much as possible in the present invention. If it exceeds 0.08%, the adverse effect becomes remarkable. For this reason, P was limited to 0.08% or less. In addition, Preferably it is 0.04% or less.

S: 0.02% or less S forms MnS and serves as an initial rusting start point, and S is an element that segregates at the grain boundaries and promotes embrittlement of grain boundaries, and is preferably reduced as much as possible. If it exceeds 0.02%, the adverse effect becomes significant. For this reason, S was limited to 0.02% or less. In addition, Preferably it is 0.008% or less.

Cr: 10-35%
Cr is an element that contributes to improving corrosion resistance. If it is less than 10%, sufficient corrosion resistance cannot be ensured. On the other hand, a large content exceeding 35% promotes the formation of δ-ferrite and degrades hot workability and cold workability. For this reason, Cr was limited to the range of 10 to 35%. In addition, from a viewpoint of workability, it is preferably 11 to 30%.

Ni: 6-15%
Ni is an austenite stabilizing element and needs to be contained in an amount of 6% or more in the present invention. On the other hand, if the content exceeds 15%, the steel material costs will increase. For this reason, Ni was limited to the range of 6 to 15%. In addition, Preferably it is 7 to 10%.

N: 0.01 to 0.1%
N, like C, is an element effective for improving formability and cracking. In the present invention, N is required to be contained in an amount of 0.01% or more, but if it exceeds 0.1%, the steel is remarkably hardened and formability is increased. Reduce. For this reason, N was limited to the range of 0.01 to 0.1%. In addition, Preferably it is 0.02 to 0.08%.

  In the present invention, in addition to the above basic composition, B: 0.0003 to 0.001% and / or Al: 0.30% or less can be selected and contained.

B: 0.0003-0.001%
B is an element that suppresses nozzle clogging during continuous casting, and can be selected and contained as necessary. However, excessive inclusion causes the amount of inclusions to become an origin of destruction. For this reason, it is preferable to limit to B: 0.0003-0.001%.

Al: 0.30% or less
Al is an element effective as a deoxidizer and can be added as necessary. When added, it is preferable to be more than 0.003% and 0.30% or less. If it is 0.003% or less, the effect is small. On the other hand, if it exceeds 0.30%, the amount of non-metallic inclusions is increased, surface flaws occur frequently, and workability is reduced. For this reason, when Al is added, the content is preferably 0.30% or less, and more preferably 0.10% or less. In addition, when not adding Al, it is 0.003% or less.

  The balance other than the components described above consists of Fe and inevitable impurities.

  Next, a method for producing the steel of the present invention will be described.

  The steel of the present invention can be applied to all commonly known melting methods, and the melting method need not be limited. For example, it is preferable to use a converter, an electric furnace, a vacuum melting furnace or the like, and further, secondary refining may be performed by SS-VOD or the like. Moreover, it is preferable to make the obtained molten steel into raw materials for rolling, such as a slab, using a continuous casting method from quality. The cast rolling material is further hot-rolled to obtain a hot-rolled sheet having a predetermined thickness. A hot rolled sheet or the like may be used as a product. Further, for example, the hot-rolled sheet may be annealed and pickled at 900 to 1150 ° C., and then cold-rolled to obtain a cold-rolled sheet having a predetermined thickness. It is preferable that the cold-rolled sheet is further annealed and pickled at 900 to 1150 ° C. to obtain a product.

  Steel having the composition shown in Table 1 was melted by a converter-secondary refining (SS-VOD), and a 200 mm thick slab was formed by a continuous casting method.

  These slabs were heated to 1260 ° C. and then hot rolled into hot rolled sheets having a thickness of 4 mm.

The following tests were carried out using slabs and hot-rolled sheets to evaluate hot workability.
(1) Hot workability A greeble test piece (10φ × 120 mm) was sampled from a position 10 mm below the surface of the obtained slab, and a greeble test (hot tensile test) was performed. In the greeble test, heat up to 1200 ° C corresponding to the slab heating temperature for 30 s, hold at that temperature for 60 s, cool to 1100 ° C in the hot rolling temperature range at 50 ° C / min and hold at that temperature for 10 s. From this, tensile deformation was performed at a speed of 100 mm / s, and the cross-sectional area reduction rate (RA) after deformation was measured to evaluate hot workability in the hot rolling temperature range. In addition, the case where RA was 80% or more was judged to have sufficient hot workability. Moreover, the surface of the obtained hot-rolled sheet was observed visually, and the presence or absence of scabs was observed. The case where no whisker was observed was marked with ◯, and the others were marked with x.

  The obtained results are shown in Table 2.

  Next, the obtained hot-rolled sheet was subjected to hot-rolled sheet annealing at 1050 ° C. and pickling treatment, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 1.0 mm. Further, these cold-rolled sheets were subjected to cold-rolled sheet annealing at 1050 ° C. and pickling treatment to obtain cold-rolled annealed sheets having a thickness of 1.0 mm.

These cold-rolled annealed plates were evaluated for antibacterial properties and corrosion resistance. The test method was as follows.
(2) Antibacterial test Antibacterial property was evaluated using the film adhesion method established by the Antibacterial Product Technology Association in accordance with the provisions of JIS Z 2801. The procedure is as follows.

(B) Wash and degrease a 25 cm ² specimen with 99.5% ethanol-containing absorbent cotton.

(B) Disperse E. coli in 1/500 NB solution. (The number of bacteria was adjusted to 2 × 10 ^{6 to} 6 × 10 ⁶ cfu / ml. The 1/500 NB solution is obtained by diluting a normal buion medium (NB) 500 times with sterilized purified water. (Normal Buion medium means meat extract 5.0 g, sodium chloride 5.0 g, peptone 10.0 g, purified water 1000 ml, pH: 7.0 ± 0.2.)
(C) inoculating the bacterial suspension to the test piece at a rate of 0.5 ml / 25 cm ² (each 3 pictures).

  (D) Cover the surface of the test piece with a coating film.

  (E) The test piece is stored for 24 hours under conditions of temperature: 35 ± 1.0 ° C. and RH (relative humidity): 90% or more.

  (F) The viable cell count is measured by an agar culture method (35 ± 1.0 ° C., 40 to 48 h). Antibacterial properties were evaluated by the number of bacteria and the number of bacteria sterilized after the test.

Antibacterial activity is expressed by the following formula: Bacterial sterilization rate (%) = (number of bacteria in control-number of bacteria after test) / (number of bacteria in control) x 100
The sterilization rate defined in (1) was evaluated. In addition, the number of control bacteria was the number of viable bacteria after the test in which an antibacterial test was performed in a sterilized petri dish, and was 6 × 10 ⁶ cfu / ml. Moreover, the number of bacteria after a test is the number of live bacteria measured.
(3) Corrosion resistance test Corrosion resistance was evaluated by a salt dry and wet combined cycle test. (B) After spraying a 5.0% NaCl aqueous solution (temperature: 35 ° C) for 0.5 h on a test piece (size: 50 x 80 mm), humidity: 40% or less, temperature: Hold for 1.0 h in a dry atmosphere at 60 ° C.

(B) Hold for 1.0 h in a humid atmosphere of humidity: 95% or more, temperature: 40 ° C.
After combining 100 times to repeat 100 cycles, the rusting area ratio (%) on the surface of the test piece was measured.

  The test results obtained are shown in Table 2.

All of the examples of the present invention show a sterilization rate of 99% or more, and the antibacterial property is remarkably improved without lowering the corrosion resistance, and the hot workability is remarkably improved and the occurrence of lashes is suppressed. Yes.
On the other hand, in the comparative example and the conventional example which are out of the scope of the present invention, any one of corrosion resistance, antibacterial property and hot workability, or two or more characteristics are deteriorated.

Claims (3)

mass%
C: 0.01 to 0.1%, Si: 2.0% or less,
Mn: 2.0% or less, P: 0.08% or less,
S: 0.02% or less, Cr: 10 to 35%,
Ni: 6-15%, N: 0.01-0.1%
Further including Ag: 0.001 to 0.09%, Cu: more than 0.30% to 4.0% or less so as to satisfy the following formula (1), and having a composition composed of the balance Fe and inevitable impurities: Austenitic stainless steel with excellent hot workability and antibacterial properties.
Record
Ag / (Ag + Cu) <0.07 (1)
Here, Ag, Cu: Content of each element (mass%)   The austenitic stainless steel according to claim 1, further comprising B: 0.0003 to 0.001% in mass% in addition to the composition.   The austenitic stainless steel according to claim 1, further comprising, in addition to the composition, mass% and Al: 0.30% or less.