JP2005240062A - Hydrophilic stainless steel plate, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrophilic stainless steel plate having excellent pollution resistance, maintenance-free, and recyclability at low cost. <P>SOLUTION: A belt-polished stainless steel plate in which the center line mean roughness Ra of profile in the direction orthogonal to the rolling direction exceeds 0.30 μm is subjected to the finish bright annealing under the condition of the temperature and the humidity to satisfy the relationship D ≤ 0.067 × T-107, D ≤ -40, and T ≥ 850, where T (°C) is the temperature and D(°C) is the dew point in the hydrogen-nitrogen mixing gas atmosphere in which the nitrogen ratio is ≤ 15 vol.%, and the stainless steel plate is obtained, in which the film deposited on the surface thereof is formed of oxides mainly consisting of SiO<SB>2</SB>having a composition consisting of, by atom, except C, ≥ 12% Si, ≤ 5% Nb, ≤ 10% N, and the balance Al, Mn, Cr, Fe and O. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a stainless steel plate suitable for commercial or household refrigerators, freezers, ice makers, sinks, tables, shelves, kitchen equipment such as wagons, etc., and various stains adhering to the steel plate surface are not noticeable, and The present invention relates to a hydrophilic stainless steel plate that can be easily removed by wiping with a cloth or the like.

Conventionally, a stainless steel plate is excellent in corrosion resistance and has a beautiful appearance and cleanliness with various design properties such as a polished finish and a gloss finish, and thus has been used in various commercial and household kitchen appliances.
However, in these applications, dirt such as dirt is likely to adhere because it is exposed to contact with human hand skin, and there are many opportunities to get dirty with foods, seasonings and the like. For this reason, if maintenance such as cleaning with a detergent is not always taken care of, there is a problem that not only the appearance is lost but also rust is likely to be generated starting from dirt.

As one means for solving such a problem, there is a technique for making the surface of a stainless steel plate hydrophilic so that attached dirt can be removed by simple water washing.
As a means for hydrophilizing the surface of a stainless steel plate, a method for increasing the hydrophilicity by forming appropriate irregularities on the surface, a method for coating the surface with a hydrophilic substance, or a method for concentrating a specific element on the surface by heat treatment. A method for imparting hydrophilicity has been proposed.
For example, Patent Document 1 discloses a stainless steel plate having a high-strength multiphase structure in which hydrophilicity is enhanced by forming fine irregularities on the surface by pickling. Patent Document 2 discloses a stainless steel plate for an offset printing press to which hydrophilicity is imparted by forming a roughened surface by spray etching of a ferric chloride solution.

Patent Document 3 discloses a hydrophilic vinyl monomer-containing hydrophilic sliding surface treatment agent that is applied to impart hydrophilicity to the surface of a base material such as stainless steel, glass, or plastic. Similarly, a surface treating agent containing a fluorinated vinyl monomer is shown. Patent Document 5 discloses a method for producing hydrophilized stainless steel, in which a hydrophilic glass such as sodium silicate, colloidal silica, alumina sol or the like is applied to the surface.
Patent Documents 6 and 7 disclose a member or stainless steel in which a layer containing an optical semiconductor such as anatase-type titanium oxide is formed on the surface.

Furthermore, in Patent Document 8, a polished stainless steel plate is brightly annealed so that the atomic concentration ratio (Cr + Si + Al) / Fe in the surface oxide film is 0.4 or more, and the center line roughness in the direction perpendicular to the polishing surface is increased. It has been shown that when the thickness Ra is set to 0.30 μm or less, the soil removability is improved.
Furthermore, in Patent Document 9, the center line average roughness Ra of the metal surface is set to 0.5 μm or more, and the maximum amplitude in a wavelength region of 10 μm or less is set to 0.02 μm or less in the power spectrum analysis of the surface roughness. And / or when a three-dimensional surface analysis is performed in which the surface is replaced with a 1 μm pitch micro-plane, the proportion of micro-planes whose normals form an angle of less than 5 degrees with respect to the normal of the macro average surface It is shown that the fingerprint is less noticeable by being 50% or less of the plane.

JP-A-11-279706 JP-A-9-39426 JP 2002-80831 A JP 2002-105433 A JP 11-256355 A JP-A-10-121269 JP 2001-207243 A Japanese Patent Laid-Open No. 10-259418 JP-A-11-226606

However, since the techniques proposed in Patent Documents 1 and 2 are methods for imparting hydrophilicity by adjusting the surface irregularity form, design on the appearance such as polishing finish or mirror finish is required. It is not applicable for use.
Moreover, in the technique proposed by the cited documents 3-7, when the application as a hydrophilization process of a stainless steel plate is considered, since the equipment and apparatus for apply | coating a processing agent are needed separately, it leads to a cost increase. It will be. In addition, since non-metallic resin and ceramics are coated, problems such as inferior recyclability and increased environmental load are involved.
Furthermore, in the technique proposed in Patent Document 8, it is attempted to improve the dirt removal property by reducing the roughness of the polishing marks, but it cannot always be said to be sufficient for severe demands in recent years, and the attached dirt is not sufficient. It has the disadvantage of being conspicuous.
Furthermore, the technique proposed in Patent Document 9 requires a dedicated rolling roll that has been subjected to special surface processing in order to obtain a desired surface roughness, or requires secondary processing such as electrolytic polishing. Therefore, an increase in manufacturing cost is inevitable.

As described above, the conventional techniques often increase the cost by imparting hydrophilicity, or increase the environmental load from the viewpoint of recycling. Further, the level of hydrophilicity obtained by the above technique is not always sufficient for the stain resistance and maintenance-free properties that have been required in recent years.
Accordingly, the present invention has been devised to solve such problems, and provides a hydrophilic stainless steel sheet that is excellent in contamination resistance, maintenance-free properties, low cost, and excellent in recyclability. For the purpose.

In order to achieve the purpose of the hydrophilic stainless steel sheet of the present invention, the film formed on the surface, except for C, is Si: 12 atomic% or more, Nb: 5 atomic% or less, N: 10 atomic% or less, and the balance is The center line average roughness Ra in the direction perpendicular to the rolling direction on the surface of the steel sheet exceeds 0.30 μm and is made of an oxide mainly composed of SiO ₂ having a composition of Al, Mn, Cr, Fe, O. It is characterized by.
As stainless steel, what contains 0.20-2.0 mass% Si in steel is preferable.
The stainless steel sheet having such surface characteristics is a hydrogen-nitrogen having a nitrogen ratio of 15% by volume or less, which is a belt-polished stainless steel sheet having a center line average roughness Ra in a direction perpendicular to the rolling direction exceeding 0.30 μm. Finish in a mixed gas atmosphere at a temperature and humidity condition satisfying the relationship of D ≦ 0.067 × T−107, D ≦ −40, and T ≧ 850 between the temperature T (° C.) and the dew point D (° C.). Obtained by bright annealing.

As a result of investigating and researching the oxide film formed on the surface of the steel sheet when the stainless steel sheet is brightly annealed, the present inventors first made a hydrophilic property by optimizing the composition of the surface oxide film. I found that it can be improved significantly.
It has been found that the composition of the surface oxide film can be optimized by adjusting the nitrogen content, temperature and dew point in the atmosphere during finish bright annealing.
In addition, as a result of detailed examination of the effect of surface roughness on how noticeable dirt is noticed, it was found that the attached dirt becomes less noticeable by appropriately adjusting the surface roughness when belt-polishing the steel strip. It was.
Therefore, according to the present invention, it is possible to obtain a stainless steel plate excellent in hydrophilicity only by simple means of adjusting belt polishing conditions and adjusting bright annealing. As a result, various stains adhering to the surface of the steel plate are hardly noticeable and can be easily removed by wiping with a cloth or the like, so that it is possible to provide a stainless steel plate suitable for various kitchen appliances at a low cost.

The features of the present invention will be described in detail below.
First, in order to impart excellent hydrophilicity to the surface, it is necessary to optimize the composition of the surface oxide film. It is a film made of an oxide mainly composed of SiO ₂ , except for C, Si: 12 atomic% or more, Nb: 5 atomic% or less, N: 10 atomic% or less, and the balance is made of Al, Mn, Cr, Fe, O It is essential to have a composition.
The oxide film composition is identified by comparing the peak height ratios for the three main oxides SiO ₂ , Cr ₂ O ₃ and Fe ₂ O ₃ by analyzing the oxygen spectrum by X-ray photoelectron spectroscopy (XPS). Do it. That is, in the oxygen spectra as shown in FIGS. 1 and ₂ , the peak height ratio of SiO _{2 at} the binding energy 532.5 eV position; hSiO ₂ , the peak height ratio of Cr ₂ O _{3 at} the binding energy 530.9 eV position; hCr The peak height ratio of Fe ₂ O _{3 at} the position of ₂ O ₃ and a binding energy of 530.3 eV; where hFe ₂ O ₃ is used, hSiO ₂ , hCr ₂ O ₃ , and hFe ₂ O ₃ are compared.
When hSiO ₂ ≧ (hCr ₂ O ₃ + hFe ₂ O ₃ ) / 2, this is determined to be an oxide film mainly composed of SiO ₂ . Illustrated FIG. 1 represents an oxygen spectrum in the case of an oxide mainly composed of SiO ₂ , and FIG. 2 represents an oxygen spectrum in the case of an oxide mainly composed of Cr ₂ O ₃ and Fe ₂ O ₃ .

Even in the case where an oxide film mainly composed of SiO ₂ is formed, in order to have excellent hydrophilicity, a surface film is formed of Si, Nb, N, Al, Mn, Cr, Fe, O excluding C. When the element is used, the amount of Si in the film needs to be 12% or more in atomic%. If it is less than 12 atomic%, the oxide film is mainly composed of Cr and Fe oxide, and hydrophilicity cannot be obtained. Preferably, the Si amount in the film is 15 atomic% or more.
In addition, the analysis value of the surface film composition in this specification is a value calculated by a semi-quantitative analysis value based on the integrated area of each element spectrum by X-ray photoelectron spectroscopy.

The reason why the hydrophilicity is improved by the oxide film mainly composed of SiO ₂ can be considered as follows.
In general, it is known that SiO ₂ has a relatively large ionic bond among oxides. In these oxides, since —OH groups polarized on the outermost surface are arranged, it is considered that hydrophilicity is exhibited by an attractive force acting on polarized water molecules. On the contrary, it is considered that an oxide film mainly composed of an oxide such as Cr or Fe having a small ionic bond in the film has a low affinity for water molecules and a hydrophilic property cannot be obtained.

By the way, Nb may be added to stainless steel for the purpose of fixing the contained C and N and improving the corrosion resistance and workability.
This Nb reacts with nitrogen to form a nitride depending on the annealing conditions during bright annealing, and Nb nitride is mixed in the surface film. As the amount of Nb nitride in the surface film increases, the hydrophilicity decreases. This is thought to be due to the fact that the ionic bond of Nb nitride is small, so that the affinity with water molecules decreases as the surface occupancy increases. The present inventors have confirmed from various preliminary experiments that the desired hydrophilicity cannot be obtained when the Nb content in the film exceeds 5 atomic% and the N content exceeds 10 atomic%.
Therefore, in the present invention, the Nb content in the coating is defined as 5 atomic% or less, and the N content is defined as 10 atomic% or less.

As described above, in order to impart hydrophilicity to the stainless steel plate, it is preferable to increase the amount of SiO _{2 in} the surface film after bright annealing. In general, as the stainless steel plate as the original plate, the one having a larger content of Si is preferable. If the amount of Si contained in the steel is small, the Si ratio in the coating becomes low and an oxide coating mainly composed of SiO ₂ cannot be formed. In order to obtain hydrophilicity, the original plate preferably has a Si content of 0.20% by mass or more. In addition, since cold workability will fall when Si content exceeds 2.0 mass%, it is preferable to use a Si content 2.0 mass% or less as an original plate.

  The appearance of the dirt adhering to the surface of the steel sheet varies depending on the glossiness and image clarity of the surface. That is, the visibility of adhesion dirt is affected by the surface roughness of the steel sheet. As the surface roughness in the direction perpendicular to the rolling direction increases, the present inventors make it difficult to visually check the attached dirt. When the center line average roughness Ra exceeds 0.30 μm, there is almost no wiping trace of dirt. I found it to be inconspicuous. At this time, there is no upper limit of Ra, and finishing roughness can be selected according to the application. In general, from the viewpoint of design properties, it is desirable to stop at 1.0 μm or less, preferably about 0.5 μm.

  The following reasons can be considered as the reason why the adherent stains are not conspicuous in a steel sheet having a specific surface roughness. That is, when the surface roughness is small, reflection of the background on the steel plate surface and regular reflection of light rays increase, so even a slight amount of adhering dirt can be easily recognized by the naked eye as preventing the reflection or regular reflection. On the other hand, when the surface roughness is large, reflection and regular reflection decrease, and conversely, irregular reflection due to polishing eyes increases, so that it is difficult to recognize attached dirt. The present inventors have confirmed that the critical value is 0.30 μm in terms of centerline average roughness Ra.

Next, the manufacturing method of the stainless steel plate which has the above surface characteristics is demonstrated.
The stainless steel hot-rolled steel strip, which has been hot-rolled after soaking as usual, is annealed, cold-rolled, polished with a belt, and then subjected to bright finish annealing.
When polishing the belt, it is preferable to use a rough polishing belt of # 150 or less, for example, so that the center line average roughness Ra in the direction perpendicular to the rolling direction exceeds 0.30 μm.

It is the annealing conditions when performing the finish bright annealing that has the greatest influence on the composition of the film formed on the surface of the stainless steel plate.
When the nitrogen ratio in the atmosphere gas composed of hydrogen-nitrogen increases, the amount of Nb nitride produced increases and the hydrophilicity decreases. Although depending on the Nb content of the material, the influence of Nb nitride is not recognized if the nitrogen ratio is 15 vol% or less.

In order to form an oxide film mainly composed of SiO ₂ , assuming that the temperature T (° C.) and the dew point D (° C.), D ≦ 0.067 × T−107, D ≦ −40, and T ≧ 850. It is necessary to anneal at the temperature and humidity conditions that satisfy the conditions.
When the dew point D (° C.) exceeds −40 ° C., the oxide film becomes too thick and coloration with an interference color (temper color) occurs. Further, when the temperature T (° C.) is less than 850 ° C., Si is not sufficiently concentrated in the oxide film, and an oxide film mainly composed of SiO ₂ is not formed. Further, when bright annealing is performed under a condition where the dew point D (° C.) exceeds 0.067 × T-107, the oxide film becomes an oxide mainly composed of Cr and Fe, and the desired hydrophilicity cannot be obtained. These conditions were experimentally confirmed by repeating various preliminary experiments.

  The stainless steel sheet in the present invention includes any steel type such as austenite, ferrite, martensite, ferrite + martensite, austenite + ferrite, or high Mn austenite according to the general stainless steel classification. May be applied.

For ferritic stainless steels containing about 17.8% by mass of Cr, about 0.4% by mass of Nb, and other elements within the range of SUS430, three types of steels with different Si contents are used. Prepared (see Table 1). These steels were melted by a conventional method and formed into a hot-rolled steel strip having a plate thickness of 3 mm by forging and hot rolling. After solution treatment and pickling, and finish cold rolling to 0.8 mm thickness, cut plate samples were collected from steel plates subjected to belt polishing and finish bright annealing under various conditions shown in Table 2 did.
About each sample, the oxide peak height ratio was measured from the atomic ratio and oxygen spectrum in the outermost surface of a film | membrane by the X ray photoelectron spectroscopy about the surface. Moreover, centerline average roughness Ra in the direction perpendicular to the rolling direction was measured by a conventional method using a stylus type surface roughness meter. Further, the contact angle of each sample with a 0.1 ml droplet of ion-exchanged water was measured by a sessile drop method, and the case where the contact angle was 50 degrees or less was evaluated as having excellent hydrophilicity. In addition, after attaching beef tallow to the steel plate surface at room temperature, it is wiped off manually with gauze moistened with water, and the wiping traces are observed with the naked eye. evaluated. That is, the case where almost no wiping trace was visible was marked with ◎, the case where it was slightly visible was marked with ◯, and the case where it was conspicuous was marked with ×.

Table 3 shows the surface film composition, oxide peak height ratio and centerline average roughness Ra of each sample, and the contact angle of each sample and the ease of noticeable adhesion.
Test No. which is an example of the present invention. In Nos. 1 to 6, an appropriate oxide film mainly composed of SiO ₂ was formed, and the contact angle was 50 degrees or less, indicating excellent hydrophilicity. Further, Ra exceeded 0.30 μm, and the attached dirt was not noticeable. Even if it is made of a steel type with a relatively small Si content, if it is subjected to cold rolling and bright annealing under appropriate conditions (see Test Nos. 5 and 6), the surface is mainly composed of SiO _2. An oxide film is formed and desired hydrophilicity can be exhibited.

In contrast, Test No. of the comparative example. In Nos. 7 and 8, although an oxide film mainly composed of SiO ₂ is formed on the surface, the attached dirt is conspicuous because Ra is small and out of the scope of the present invention. In addition, Test No. In No. 9, since the nitrogen ratio of the bright annealing atmosphere gas is high, the ratio of Nb and N in the surface film is high, and the contact angle is large. Furthermore, test no. 10 to 12, the conditions of the bright annealing temperature and humidity are outside the scope of the present invention, so the Si ratio on the outermost surface of the film is low, an oxide film mainly composed of Cr and Fe is formed, and the contact angle exceeds 50 degrees. It is like that.
Thus, when brightly annealing a belt-polished stainless steel sheet, if both the surface roughness and the composition of the oxide film formed on the steel sheet surface are adjusted within an appropriate range, stainless steel with excellent hydrophilicity can be obtained. I understand that

Oxygen spectrum measured by X-ray photoelectron spectroscopy on the surface of a steel sheet with an oxide film mainly composed of SiO ₂ Oxygen spectrum by X-ray photoelectron spectroscopy of steel sheet surface with oxide film mainly composed of Cr and Fe oxide The figure which shows the range of this invention of the relationship between the temperature T and the dew point D in bright annealing

Claims (3)

SiO ₂ having a composition in which the film formed on the surface is composed of Si: 12 atomic% or more, Nb: 5 atomic% or less, N: 10 atomic% or less, with the balance being Al, Mn, Cr, Fe, O except for C. A hydrophilic stainless steel sheet comprising a main oxide and having a center line average roughness Ra in a direction perpendicular to the rolling direction on the steel sheet surface exceeding 0.30 μm.   The hydrophilic stainless steel sheet according to claim 1, wherein the steel contains 0.20 to 2.0 mass% of Si.   A stainless steel sheet, belt-polished so that the center line average roughness Ra in the direction perpendicular to the rolling direction exceeds 0.30 μm, in a hydrogen-nitrogen mixed gas atmosphere with a nitrogen ratio of 15% by volume or less, temperature T (° C.) The finish bright annealing is performed at a temperature and humidity conditions satisfying the relationship of D ≦ 0.067 × T−107, D ≦ −40, and T ≧ 850 between the temperature and the dew point D (° C.). Or the manufacturing method of the hydrophilic stainless steel plate of 2.

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