JP2005232510A - Ferritic stainless steel having excellent antibacterial property and hot workability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ferritic stainless steel having excellent hot workability and corrosion resistance, and having excellent antibacterial properties. <P>SOLUTION: The ferritic stainless steel has a composition comprising, by mass, ≤0.1% C, ≤1.0% Si, ≤1.0% Mn, ≤0.08% P, ≤0.02% S, 10 to 35% Cr and ≤0.10% N, and further comprising 0.001 to 0.09% Ag and 0.05 to 2.0% Cu so as to satisfy Ag/(Ag+Cu)<0.07 (wherein, Ag and Cu are the content (mass%) of each element). Thus, the ferritic stainless steel having excellent hot workability and antibacterial properties is obtained. Further, one or more kinds of metals selected from Ti and Nb, and Al may be incorporated therein. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to ferritic stainless steel excellent in antibacterial properties, suitable for daily life-related products such as kitchens, medical equipment, electrical equipment, chemical 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 for Cu to be present as a precipitate, a method of applying an aging treatment after hot rolling, and a method of increasing the Cu content to facilitate precipitation of Cu during aging are required. . 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, the presence of coarse Cu precipitates on the surface of the steel sheet, and the antibacterial property being improved by dissolving Cu from the steel sheet surface as ions, greatly destroys the passive film and is associated with a decrease in corrosion resistance. There's a problem.

  In Patent Document 2, C, N, Si, Mn, P, S, Al, and V are adjusted to an appropriate range, Cr is contained in an amount of 12 to 35%, and further, V is 0.01 to 0.30% and Ag is contained. By adding 0.0005 to 0.30%, a ferritic stainless steel having sufficient workability and corrosion resistance and improved antibacterial properties has been proposed. Ag has a solid solution amount in Fe less than Cu, and even if added in an amount less than Cu, it precipitates in the steel and exhibits antibacterial properties. Therefore, excellent antibacterial properties can be ensured with a smaller added amount than Cu. According to the technique described in Patent Document 2, pitting corrosion resistance is markedly improved by the combined addition of Ag and V, together with antibacterial properties. However, the technique described in Patent Document 2 requires a large amount of Ag to be further improved in antibacterial properties, leading to an increase in material costs and a small amount of solid solution of Ag in steel. Therefore, there is a problem that it is difficult to uniformly disperse a large amount of Ag.

  Patent Document 3 proposes a ferritic stainless steel excellent in antibacterial properties in which Cu: 0.5 to 3.0% and Ag: 0.10 to 1.0% are added in combination. According to the technique described in Patent Document 3, by containing Ag and Cu at the same time, the yield of Ag is improved, and a long-term aging treatment for Cu precipitation is not required, and the solid solution limit or less is required. Even if it is Cu content of, it is said that the antibacterial property of ferritic stainless steel can be improved. 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% of Ag and containing one or more kinds 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 to be further improved in antibacterial properties, resulting in an increase in material cost and difficulty in stable and uniform dispersion of Ag. 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 11-12692 A Japanese Patent Laid-Open No. 11-256284 Japanese Patent Laid-Open No. 11-264057

  The present invention advantageously solves the above-mentioned problems of the prior art, has excellent hot workability capable of suppressing 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 a ferritic stainless steel having excellent antibacterial properties without accompanying it.

  In order to achieve the above-described problems, the present inventors have intensively studied various factors affecting the hot workability, antibacterial properties, and corrosion resistance of ferritic 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: 0.1% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.08% or less, S: 0.02% or less, Cr: 10 to 35%, N: 0.10% or less In addition, Ag: 0.001-0.09%, Cu: 0.05-2.0%, the following formula (1)
Ag / (Ag + Cu) <0.07 (1)
(Where Ag, Cu: content of each element (mass%))
And ferritic stainless steel excellent in hot workability and antibacterial properties, characterized by having a composition comprising the balance Fe and inevitable impurities.
(2) In (1), in addition to the above-mentioned composition, the composition further comprises mass%, Nb: 1% or less, Ti: 1% or less selected from 1% or less. Ferritic stainless steel.
(3) The ferritic 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 ferritic stainless steel, antibacterial properties are improved, and further, hot workability is remarkably improved and the occurrence of surface defects such as ear cracks and scabs is suppressed, 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 reasons 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 ferritic 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 decreases the hot workability, causes an increase in surface defects, and increases the amount of expensive Ag added. Incurs an increase. For this reason, Ag was limited to the range of 0.001 to 0.09%. In addition, it is preferable to set it as 0.03-0.09% from a viewpoint of antibacterial property and hot workability. More preferably, it is 0.04 to 0.08%.

Cu: 0.05-2.0%
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 is 0.05% or more. On the other hand, when the content exceeds 2.0%, the hot workability deteriorates significantly. For this reason, Cu was limited to the range of 0.05 to 2.0%. In addition, it is preferable to set it as 0.4 to 2.0% from a viewpoint of hot workability.

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. By adjusting the ratio of Ag content, Ag content and Cu content, Ag / (Ag + Cu) to less than 0.07, Ag is dissolved in the high melting point Cu phase, and the Cu (Ag) solid solution becomes The segregation of the low melting point Cu—Ag phase (melting point 779 ° C.) to the grain boundary during hot working 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. From the viewpoint of preventing surface defects, Ag / (Ag + Cu) is preferably 0.020 to 0.060.

C: 0.1% or less, N: 0.10% or less C and N are elements that deteriorate workability, and also combine with Cr to form carbonitrides, thereby forming a Cr-free layer and reducing corrosion resistance. It is desirable to reduce as much as possible. Since such adverse effects are allowable up to 0.1% for C and up to 0.10% for N, the upper limit was set for each. In consideration of manufacturability in actual operation, C is preferably 0.0010% or more and N is preferably 0.0060% or more.

Si: 1.0% or less
Si is an element that acts as a deoxidizer and is preferably contained in an amount of 0.10% or more. However, excessive inclusion causes a decrease in cold workability and ductility. For this reason, Si was limited to 1.0% or less. In addition, Preferably it is 0.20 to 0.35%.

Mn: 1.0% or less
Mn is an effective element that combines with S to form MnS to improve hot workability. In the present invention, Mn is preferably contained in an amount of 0.1% or more. On the other hand, if the content exceeds 1.0%, cold workability and corrosion resistance are lowered. For this reason, Mn was limited to 1.0% or less. In addition, Preferably it is 0.1 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 0.035% or less.

S: 0.02% or less S is segregated at the grain boundary to promote embrittlement of the grain boundary, and combines with Mn to form MnS to be an initial rusting start point. Therefore, S 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 0.005% 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, if it contains a large amount exceeding 35%, the cold workability deteriorates and it becomes difficult to process cold rolled sheets. For this reason, Cr was limited to the range of 10 to 35%. From the viewpoint of corrosion resistance and cold workability, it is preferably 15.0 to 19.0%.

  In the present invention, in addition to the basic composition described above, Nb: 1% or less, Ti: 1% or less selected from 1% or less, Al: 0.3% or less, if necessary. Can be contained.

Nb: 1% or less, Ti: 1% or less selected from 1% or less
Ti and Nb are both carbonitride-forming elements, and have the effect of suppressing the grain boundary precipitation of Cr carbonitride during welding and heat treatment and improving the corrosion resistance. In addition, C and N in the steel are fixed and precipitated as carbonitride to refine the crystal grains. Such an effect becomes remarkable when Ti: 0.05% or more and Nb: 0.05% or more are contained. On the other hand, excessive inclusion deteriorates these characteristics. For this reason, it is preferable to limit to Ti: 1% or less and Ti: 1% or less, respectively.

Al: 0.30% or less
Al is an element effective as a deoxidizer and can be added as necessary. When added, the content is preferably 0.30% or less. If it exceeds 0.30%, the amount of non-metallic inclusions increases, surface flaws occur frequently, and workability decreases. For this reason, when adding Al, it is preferable to set it as 0.30% or less. More preferably, it is 0.050% or less. If not added, 0.005% or less is acceptable as an inevitable impurity.

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

  Below, the manufacturing method of the ferritic stainless steel plate which has this invention steel composition is demonstrated. In addition, a steel plate shall also contain a steel strip.

  First, molten steel having the above composition is melted. For the melting of the steel of the present invention, all known melting methods can be applied, and there is no need to limit the melting method. As the melting method, for example, a converter, an electric furnace, a vacuum melting furnace or the like is preferably used, 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 continuous casting condition may be a normal casting condition for stainless steel, and is not particularly limited.

  The cast rolling material is further hot-rolled to obtain a hot-rolled sheet (hot-rolled steel sheet) having a predetermined thickness. Since the steel of the present invention is excellent in hot workability, the hot rolling conditions need not be particularly limited. Further, it is preferable to subject the hot-rolled sheet to, for example, hot-rolled sheet annealing at 900 to 1150 ° C. and pickling, and then to cold-rolled sheet (cold-rolled steel sheet) having a predetermined thickness by cold rolling. It is preferable that the cold-rolled plate is further annealed and pickled at 900 to 1150 ° C. to obtain a product plate.

  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 1150 ° C. and then hot rolled into hot rolled sheets with a thickness of 4 mm.

First, the following tests were conducted using these slabs and hot-rolled sheets to evaluate hot workability. Special heat treatment such as aging treatment is not performed.
(1) Hot workability A greeble test piece (10φ × 120 mm) was taken from a position about 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 1100 ° C corresponding to the slab heating temperature in 30s, hold at that temperature for 60s, cool to 1050 ° C in the hot rolling temperature range at 50 ° C / min, and hold at that temperature for 10s. 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 the 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 850 to 120 ° C. and pickling treatment, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 1.0 mm. Furthermore, these cold-rolled sheets were subjected to cold-rolled sheet annealing at 800 to 950 ° C. and pickling treatment to obtain cold-rolled annealed sheets.

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 activity is expressed by the following formula: Bacterial eradication 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.

In all of the examples of the present invention, hot workability is remarkably improved and generation of lashes is suppressed. Further, in all of the examples of the present invention, the antibacterial properties are remarkably improved without lowering the corrosion resistance.
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: 0.1% or less, Si: 1.0% or less,
Mn: 1.0% or less, P: 0.08% or less,
S: 0.02% or less, Cr: 10 to 35%,
N: 0.10% or less, Ag: 0.001 to 0.09%, Cu: 0.05 to 2.0% are included so as to satisfy the following formula (1), and the composition is composed of the remaining Fe and inevitable impurities. Ferritic stainless steel with excellent hot workability and antibacterial properties.
Record
Ag / (Ag + Cu) <0.07 (1)
(Where Ag, Cu: content of each element (mass%))   2. The composition according to claim 1, wherein in addition to the composition, the composition further includes one or two kinds selected from mass%, Nb: 1% or less, and Ti: 1% or less. Ferritic stainless steel.   The ferritic stainless steel according to claim 1 or 2, further comprising, in addition to the composition, mass% and Al: 0.30% or less.