JP3224210B2 - Austenitic stainless steel with excellent antibacterial properties and press formability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel having antibacterial properties and excellent press formability, and in particular, toilets, bathtubs, sinks, dishes, beer barrels, medical equipment, electric appliances or The present invention relates to an antibacterial material suitable for use in sanitary articles and the like. Recently, antibacterial stainless steel containing Cu or Ag is often used as a material for building materials, home appliances, sinks, and the like. However, the quality characteristics of such materials are that they have good press-formability in addition to their antibacterial properties.

[0002]

2. Description of the Related Art As an antibacterial austenitic stainless steel, it contains Cu and the surface of the steel is subjected to heat treatment or antibacterial treatment with an acid solution to form a surface layer.
It is common to concentrate Cu (see JP-A-8-60302).
JP-A-5-53738, JP-A-8-104953, and JP-A-8-229107). On the other hand, in order to improve the press formability of austenitic stainless steel, for example, as disclosed in Japanese Patent Publication No. 1-40102, a method of adding Al and Cu in combination is effective.

[0003]

The stainless steel used for home appliances, sinks, medical equipment, sanitary goods, beer barrels, etc. has a larger amount of dirt, which is a nutrient source of various bacteria, than the interior materials for buildings. , Because the germs are less killed,
Higher antibacterial properties are required. Furthermore, the stainless steel used for these applications needs to be excellent in deep drawability and overhang property during press forming. Generally, to increase the antibacterial properties of stainless steel,
It is effective to increase the content of Cu. However, an unnecessarily increase in Cu not only deteriorates hot workability but also impairs press formability. Therefore, in order to obtain stainless steel excellent in both antibacterial properties and press moldability of our products, there was a limit only by devising the component composition of increasing Cu. That is, it has been difficult to simultaneously improve both of the above-mentioned characteristics only by controlling the alloy components.

An object of the present invention is to provide an austenitic stainless steel having antibacterial properties and excellent press formability. Another object of the present invention is to provide an antibacterial material used for toilets, bathtubs, sinks, dishes, beer barrels, medical instruments, sanitary articles, and the like.

[0005]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have performed austenitic stainless steel without special antibacterial treatment as described above.
Various investigations were made on the conditions under which the material itself exhibited sufficiently stable antibacterial properties and did not have to sacrifice press moldability. As a result, they conceived of an austenitic stainless steel having the following gist configuration.

Therefore, the contents studied in developing the austenitic stainless steel according to the present invention will be described below. First, the inventors designed an alloy on the premise of the antibacterial properties of austenitic stainless steel, recognizing that Cu is effective. And it turned out that antibacterial property improves further not only by simply adding Cu but also by providing a working layer on the steel surface. It was also found that providing a working layer on the steel itself, such as deep drawing and overhanging, was also effective for antibacterial properties.

On the other hand, as a result of intensive studies to improve the press formability of austenitic stainless steel, the inventors have found that the press formability of austenitic stainless steel is the same as that of antibacterial properties, with the addition of Cu, especially with Al. In addition to the effective addition of Cu, the two properties of antibacterial properties and press moldability are simultaneously satisfied without sacrificing the other by delicately balancing the appropriate C and Ni equivalents. I figured out what could be done. Furthermore, it has been found that the addition of Mo to the austenitic stainless steel of the present invention can improve the corrosion resistance and the addition of B can also improve the hot workability. In addition, the weldability of the austenitic stainless steel of the present invention can be improved by adding Nb, Ti, Zr, V, Ta, and the like.

The present invention developed based on such an idea,
The composition of the steel is as follows: C: 0.01 to 0.10 wt%, Si: 2.0 wt% or less, Mn: 3.0 wt% or less, Ni: 6.0 to 12.0 wt%, Cr: 15.0
~ 19.0wt%, Cu: 1.0 ~ 4.0wt%, Al: 0.2 ~ 2.5wt%
And N: 0.08 wt% or less, and the following Ni equivalent is 21.0
Adjusted to fall within the range of ~ 22.5, Ni equivalent (wt%) = 12.6 (C + N) + 0.35Si + 1.05Mn + Ni + 0.65Cr + 0.6 Cu-0.41Al The balance consists of iron and unavoidable impurities. Is an austenitic stainless steel excellent in antibacterial properties and press moldability, characterized in that it has an antibacterial working layer as a work-induced transformation layer composed of 3 to 60 vol% martensite phase on the surface.

[0009] Also, the present onset Ming, the component composition of the steel, C: 0.
01 to 0.10 wt%, Si: 2.0 wt% or less, Mn: 3.0 wt% or less,
Ni: 6.0 to 12.0 wt%, Cr: 15.1 to 19.0 wt%, Mo: 8.0 wt%
% Or less, Cu: 1.0 to 4.0 wt%, Al: 0.2 to 2.5 wt% and N: 0.08 wt% or less, and the following Ni equivalent is 21.0 to 2%.
Adjusted to fall within the range of 2.5, Ni equivalent (wt%) = 12.6 (C + N) + 0.35Si + 1.05Mn + Ni + 0.65Cr + 0.98Mo + 0.6Cu-0.41Al The balance consists of iron and unavoidable impurities. This is an austenitic stainless steel having excellent antibacterial properties and press formability, characterized in that it has an antibacterial working layer, which is a work-induced transformation layer composed of 3 to 60 vol% martensite phase, on the surface of the steel.

In the present invention, it is preferable that the steel having each of the above component compositions further contain B: 0.020 wt% or less.

Further, in the present invention, one or more kinds of weldability improving elements selected from Nb, Ti, Zr, V and Ta are further added to the steel having each of the above component compositions.
It is preferred that the content be 1.0 wt% or less.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention is characterized in that an austenitic stainless steel having good press formability is imparted with antibacterial properties. In this regard, conventional antibacterial stainless steels are often found in martensitic stainless steels. This is because, in the case of martensitic stainless steel with a small solid solution limit of Cu, if the added amount of Cu exceeds 0.3 wt%, part of the Cu does not form a solid solution in the crystal and tends to segregate on the steel surface. This is because, as a result, it is understood that an increase in the Cu concentration on the steel surface exhibits an antibacterial effect.

That is, in a humid environment in which the Cu concentration on the stainless steel surface is high and bacteria can easily grow, even a small amount of water on the stainless steel surface ionizes a very small amount of Cu. Since Cu has a high antibacterial effect, it reacts efficiently with respiratory and metabolic enzymes of bacterial cells existing near the steel surface even in a very small amount, and is inactivated. As a result, the growth of bacteria is suppressed and sterilization is performed. In this sense, it can be said that a martensitic stainless steel in which the presence of surface precipitated Cu is remarkable is more effective as the antibacterial stainless steel.

On the other hand, in the case of an austenitic stainless steel as in the present invention, Cu generally forms a solid solution up to about 5%, so that a general Cu content is such as that of a martensitic stainless steel. There is no precipitation of Cu, which is disadvantageous for imparting antibacterial properties.

Therefore, in the present invention, various experiments were conducted in order to utilize Cu dissolved in austenite ground for antibacterial properties. As a result, by processing austenitic stainless steel, strain is forcibly introduced into the surface and liberation occurs.
It has been found that it is good to precipitate Cu. In general,
The martensite phase can be induced by processing unstable austenite (work-induced transformation). That is, martensitic transformation is induced by the introduction of processing strain and progresses, and large plasticity is generated, which is caused by transformation-induced plasticity (TR
IP), this TRIP is considered to be a type of superplastic.

That is, it is considered that free Cu exceeding the solid solubility limit is generated due to martensite generated by work-induced transformation on the surface of austenitic stainless steel, and this free Cu plays an antibacterial action. At the same time, in the component design according to the present invention, the TRIP can simultaneously improve the press formability based on superplasticity. In addition, in order to exert the effective action of the present invention,
When processing a base material having a Cu content of 0.05 to 10 wt%, it is preferable that the amount of the free Cu exhibiting the antibacterial property occupying in the processed layer on the base material surface is more than 0.05 wt%, It is more preferably at least 1.0 wt% and at most 10 wt%, more preferably at most 8 wt%, further preferably at most 5 wt%. If the amount of free Cu precipitated on the surface of the processing layer is within this range,
Good antibacterial properties.

As a method (re-working) for forming a work layer by work-induced transformation on the surface of stainless steel, austenitic stainless steel after final annealing is subjected to surface processing such as skin pass rolling, shot blasting, polishing, and the like. It is preferable to apply a method of finally forming a processed martensite phase on the surface, such as rolling, deep drawing, overhanging, bending, and the like, and a method of combining these methods. Further, the antibacterial processed layer of the present invention preferably has a thickness of at least 1 μm at the surface layer.

Next, the conditions of the chemical components necessary for imparting both the antibacterial property and the press moldability of the austenitic stainless steel according to the present invention will be described. C: 0.20 wt% or less Since C is a component that deteriorates corrosion resistance, basically
Limit to 0.20 wt% or less. However, in order to secure a predetermined deep drawability, the content of C is required to be 0.01 to 0.10 wt%. The reason is that C is a powerful austenite-forming element, and at the same time, is very effective for strengthening the austenite phase and the work-induced martensite phase, and is an essential component for improving deep drawability and overhanging property. , At least 0.01 wt%, preferably at least 0.03 wt%.
However, if it exceeds 0.10 wt%, both the susceptibility to season cracking and the intergranular corrosion sensitivity increase, so the upper limit is made 0.10 wt%, preferably 0.08 wt%. However, in applications that do not require deep drawability, C may be C ≦ 0.01 wt%.

Si: 2.0% by weight or less Si is an effective deoxidizing agent and is an essential component in the steel making process. However, if it exceeds 2.0% by weight, cracks tend to occur at the time, so that the content is 2.0% by weight or less. I do. It is preferably at most 1.0 wt%. Note that the lower limit is preferably set to 0.05 wt% or more in order to ensure deoxidation during the steelmaking operation.

Mn: 10 wt% or less Mn is a component used as a deoxidizing and desulfurizing agent during refining. However, if the content exceeds 10% by weight, the deoxidizing effect decreases, so the upper limit is 10% by weight. It is preferably at most 8.0 wt%, more preferably at most 6.0 wt%. Mn is
A component that contributes to the stabilization of the austenite phase.
More than wt% is effective, but if it exceeds 3.0 wt%, the austenite phase becomes too stable and deep drawability deteriorates.
When considering deep drawing, 3.0 wt% or less, preferably
More than 1.0 wt% to 3.0 wt%.

Ni: 4.0 to 28.0 wt% Ni is a component for stabilizing the austenite phase.
4.0 wt% is required. If it is 28.0 wt% or more, the high-temperature strength increases and the hot workability deteriorates. Preferably, 4.0-
16.0 wt%. However, when considering deep drawability,
Limited to 6.0-12.0 wt%. The reason is that Ni is 6.0 wt.
%, The workability-induced martensite layer is easily formed, thereby deteriorating the press workability. On the other hand, if it exceeds 12.0 wt%, a martensite phase is less likely to be formed during the press working, so that the content of 6.0 to 12.0 wt% is reduced. Range. Preferably 6.0
To 10.0 wt%.

Cr: 12.0 to 25.0 wt% If Cr is less than 12.0 wt%, the corrosion resistance becomes insufficient, and if it exceeds 25.0 wt%, the hot workability is reduced.
Limited to the range of ~ 25.0 wt%. Preferably 13.0-20.0wt
%, More preferably 15.0 to 19.0% by weight.

Cu: 0.05-10.0 wt% Cu is an effective component for imparting antibacterial properties of austenitic stainless steel and for improving deep drawability.
That is, if the amount is less than 0.05% by weight, it is difficult to obtain these effects. On the other hand, if the amount exceeds 10.0% by weight, hot workability is impaired, so the amount is limited to the range of 0.05 to 10.0% by weight. A preferred lower limit is 0.10 wt%, more preferably 0.2 wt%, and even more preferably 0.3 wt%. The preferred upper limit is 7 wt.
%, More preferably 5% by weight.

Al ≦ 5.0 wt% Al supplementally improves the antibacterial property in the coexistence of Cu and at the same time effectively acts on the improvement of hot workability. In particular, in consideration of hot workability, it is necessary to be 5.0 wt% or less, preferably 4.0 wt% or less, more preferably
3.0 wt% or less. Further, Al is a component that is effective for refining austenite grains and can improve press formability when coexisted with Cu. If the Al content is less than 0.2 wt%, no improvement in deep drawing properties is observed, and the susceptibility to time cracking is further increased. On the other hand, if the content exceeds 2.5 wt%, hot workability and deep drawability deteriorate, so when considering deep drawability, the content is limited to 0.2 to 2.5 wt%. It is to be noted that both the deep drawability and the time cracking resistance are most improved in Al:
It is in the range of 0.5 to 1.0 wt%.

N: 1.0 wt% or less, 0.08 wt% or less N is generally controlled to 1.0 wt% or less, preferably 0.5 wt% or less to improve workability. However, for those requiring consideration for deep drawability, the content is set to 0.08 wt% or less.
Preferably, it is 0.07 wt% or less, more preferably 0.05 wt% or less, further 0.03 wt% or less, 0.02 wt% or less, 0.01 wt%
%, The hot workability is gradually improved. Further, N is an austenite forming element and is effective in improving corrosion resistance. However, in a component system containing Al, when N exceeds 0.08 wt%, the time cracking resistance and deep drawability deteriorate, When considering deep drawability,
0.08 wt% or less. Preferably, it is 0.05 wt% or less.

Mo: 8.0 wt% or less Mo is generally well known as a component for improving the corrosion resistance of stainless steel. Therefore, in the present invention,
We decided to improve corrosion resistance by using appropriate Mo. In order to improve this corrosion resistance, at least 0.03wt
% Or more is effective. But 8.0wt%
Exceeding the above range deteriorates hot workability and deep drawability. Therefore, Mo is limited to 8.0 wt% or less. Preferably, it is 5.0 wt% or less, more preferably 3.0 wt% or less, still more preferably 0.03-3.0 wt%, even more preferably.
The range is 0.1 to 1.0 wt%.

B: 0.020 wt% or less B is a very effective component for improving the hot workability. If it is less than 0.0010 wt%, the effect is poor.
If it exceeds 0.020 wt%, the corrosion resistance deteriorates.
Hereinafter, it is preferably limited to the range of 0.0010 to 0.020 wt%.

Nb, Ti, Zr, V, Ta: 1.0 wt% or less These elements are effective elements for improving the weldability, and are added at 1.0 wt% or less for the improvement. More preferably, the range of 0.2 to 1.0 wt% is effective.

Next, in the present invention, Ni equivalent represented by the following formula is controlled as a means for improving the press formability such as deep drawability and overhanging property while simultaneously forming an austenitic structure. In general, the Ni equivalent is an index indicating that the transformation-induced martensitic transformation is difficult to occur, and the higher the Ni equivalent, the more stable the austenite phase. Therefore, in order to obtain an austenite structure, the content needs to be 20 wt% or more. However, if this Ni equivalent is less than 21.0 wt%,
The martensite phase already forms in the solution heat treatment, and both the deep drawability and the overhang property deteriorate.
On the other hand, when the Ni equivalent exceeds 22.5 wt%, the amount of work-induced martensite generated decreases.

FIG. 1 shows the relationship between the Ni equivalent and the molding height (mm) represented by the following formula.
High moldability is shown within the range of wt%. Therefore, this
The Ni equivalent is in the range of 21.0 to 22.5 wt%. Ni equivalent (wt%) = 12.6 (C + N) + 0.35Si + 1.05Mn + Ni + 0.
65Cr + 0.98Mo + 0.6Cu-0.4Al The above Ni equivalent equation in the present invention is obtained by calculating the relative amount of martensite of a test piece having a 30% elongation in a tensile test using a ferrite scope, and obtaining an index of austenite stability. This is a modified formula that adds Cu and Al terms to Hirayama's Ni equivalent equation. Note that the lower limit of the Ni equivalent may be 20.0 wt%, provided that the Ni equivalent is controlled only in response to a request to make the structure an austenitic ground.

[0031]

【Example】

Example 1 An austenitic stainless steel having the composition shown in Table 1 was melted and subjected to hot rolling and cold rolling by a conventional method to finish a 1.0 mm thick thin plate.

[0032]

[Table 1]

The material shown in Table 1 was subjected to a deep drawing process and a rolling process (a reduction ratio of 3 to 80%) to generate a work-induced martensite phase, and a work layer was provided as a test material. . A ferrite meter was used to measure the amount of martensite in the processed layer. The amount of free Cu present on the surface of the processed layer was measured by AES (Auger Ele
ctron Spectroscopy). Staphylococcus aureus (IFO 12732) was used for the antibacterial test. These test bacteria are Trypticase Soy Ager
(BBL) on an agar plate medium at 35 ° C for 18 to 24 hours, and the growing colonies are suspended in 1/100 concentration of normal broth medium for about 10 ⁶
The one adjusted to CFU / ml was used. In this test, 0.5 ml of the test bacterium suspension was uniformly contacted with a test plate of 5 × 5 cm, and a polyethylene film of the same size as the test plate was placed thereon, and the humidity was 95% and the temperature was 35 ° C. for 24 hours. After the specified time has elapsed, wipe off the bacterial solution on the test plate SCDLP
The adherent bacteria were shaken out by adding 10 ml of bouillon medium, and a dilution line was prepared using the shaking liquid as a stock solution, and a dilution plate with an agar medium was used, and the number of colonies after culturing was measured. In addition, although this test condition basically conforms to the standard and evaluation method by the research group for inorganic antibacterial agents such as silver,
Normal broth medium concentration 1/500 to high concentration (1/10
0) to simulate more severe stains. Tables 3 and 4 show the results. The evaluation criteria are based on Table 2.

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

As shown in Tables 3 and 4, each of the steels of the present invention exhibited excellent antibacterial properties.

FIG. 2 is a graph showing the relationship between the limiting drawing ratio (LDR) and the C content of a steel containing Cu and Al in which the Ni equivalent is kept constant at 22%. When the C content was 0.03 wt% or more, LDR ≧ 2.20, and when the C content exceeded 0.05 wt%, LDR = 2.30, which was a very high LDR. However, when C = 0.13 wt%, cracking occurred. From FIG. 2, C ≧ 0.03 wt% is necessary in order to obtain a steel having LDR ≧ 2.20, and further, in order to obtain a higher LDR, C is more than 0.05 and 0.10%.
It has been found that it is desirable to set the range of wt%. Tables 3 and 4 show the results.
Good antibacterial properties are obtained.

[0039]

As described above, in the present invention, free Cu is deposited by performing secondary processing such as overhanging, rolling or deep drawing, and an antibacterial processed layer is formed on the surface. An austenitic stainless steel excellent in both properties and press formability can be obtained. In particular,
This stainless steel is suitably used as a material for food-related equipment, medical equipment, sanitary goods, and sinks and beer barrels, which have a large amount of dirt that becomes a nutrient when bacteria grow.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of Ni equivalent on the molding height.

FIG. 2 is a graph showing a relationship between a limiting aperture ratio and C.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-229107 (JP, A) JP-A-8-104953 (JP, A) JP-A-10-140295 (JP, A) JP-A-9-09 176800 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 9/46-9/48 C21D 8/00-8/10 A01N 59/20

Claims (4)

(57) [Claims] 1. A steel composition comprising: C: 0.01 to 0.10 wt%;
Si: 2.0 wt% or less, Mn: 3.0 wt% or less, Ni: 6.0 to 12.0
wt%, Cr: 15.0-19.0wt%, Cu: 1.0-4.0wt%, Al:
It is adjusted so that it contains 0.2 to 2.5 wt% and N: 0.08 wt% or less, and the following Ni equivalent falls within the range of 21.0 to 22.5. Ni equivalent (wt%) = 12.6 (C + N) + 0.35Si + 1. 05Mn + Ni + 0.65Cr + 0.6 Cu -0.41Al Ri name than the remainder iron and unavoidable impurities, and the table of the steel
The surface is made of 3-60 vol% martensite phase
Characterized by having an antibacterial processed layer that is an induced transformation layer
Austenitic stainless steel with excellent antibacterial properties and press formability . 2. A steel composition comprising: C: 0.01 to 0.10 wt%;
Si: 2.0 wt% or less, Mn: 3.0 wt% or less, Ni: 6.0 to 12.0
wt%, Cr: 15.0 to 19.0 wt%, Mo: 8.0 wt% or less, Cu: 1.
0 to 4.0 wt%, Al: 0.2 to 2.5 wt% and N: 0.08 wt%
The following Ni equivalent is adjusted so that the following Ni equivalent falls within the range of 21.0 to 22.5, Ni equivalent (wt%) = 12.6 (C + N) + 0.35Si + 1.05Mn + Ni + 0.65Cr + 0.98Mo + 0.6Cu-0.41Al Ri Na than the remainder iron and unavoidable impurities, and the table of the steel
The surface is made of 3-60 vol% martensite phase
Characterized by having an antibacterial processed layer that is an induced transformation layer
Austenitic stainless steel with excellent antibacterial properties and press formability . 3. An apparatus according to claim 1 or stainless steel as described in 2, further B: 0.020 antibacterial and press formability in excellent austenitic stainless steel, characterized in that the additional inclusion wt% or less. 4. A stainless steel as claimed in any one of claims 1 to 3, more Nb, Ti, Zr, V and
An austenitic stainless steel excellent in antibacterial properties and press formability, characterized by containing one or more kinds of weldability improving elements selected from Ta among 1.0 wt% or less.