JP2010168655A - Stainless steel having excellent oil stain resistance and reduced fingerprint visibility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stainless steel which has a pure surface free from a surface covering layer such as a coating on the surface, wherein the pure surface is excellent in both oil stain resistance and reduced fingerprint visibility. <P>SOLUTION: The stainless steel has the pure surface free from the formation of a surface covering layer such as a coating, wherein the surface roughness of the pure surface has the value obtained by dividing a shortwave length roughness (Ra1) as the arithmetic average roughness of a roughness curve in which a wavelength zone is defined by λc contour curve filter=0.025 mm and a λs contour curve filter=2.5 μm, by a length of short wave (RSm1) as the average length of a roughness curve element in the same roughness curve is ≤0.0030, and also, a long wavelength roughness (Ra2) as the arithmetic average roughness of a roughness curve in which a wavelength zone is defined by a λc contour curve filter=0.8 mm and a λs contour curve filter=2.5 μm is ≥0.5 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a stainless steel excellent in both the property that oil stains are difficult to adhere (oil stain resistance) and the property that fingerprints are not noticeable (fingerprint visibility), and a method for producing the same.

Stainless steel does not rust even if it is not coated unless it has a high chlorine ion concentration in everyday environments. From design applications such as handrails and fences, food manufacturing equipment such as cutting machines, washing machines, mixers and heat exchangers Widely used in hygiene applications such as food and food showcases.
In these applications, various surface skin finishes such as hairline polishing finish, # 400 polishing finish, 2B finish, and bright annealing finish are selected and used.

  In the selection of the stainless steel surface skin, the difficulty of attaching dirt is an important criterion for judgment depending on the application. Since the stainless steel surface generally repels water well, it is difficult for water-based stains to adhere to it, and even if it adheres, it can be easily washed off with water, but oil stains that are oily stains tend to adhere. Therefore, in hygiene applications, it is important that oil stains are difficult to adhere.

  For example, in hairline finishing, the surface roughness is large, and light is irregularly reflected on the surface, so that fingerprints attached to the surface are not noticeable. Therefore, it is frequently used in design applications such as handrails and fences. On the other hand, since dirt such as oil stains is easily caught on the unevenness of the surface, it is not so often used in hygiene applications such as food production equipment.

  On the other hand, the surface roughness is extremely small in the bright annealing finish and the mirror finish. Therefore, it is difficult for oil stains to be caught on the surface irregularities, and it is frequently used in hygiene applications such as food production equipment. However, there is a drawback that fingerprints attached to the surface are very conspicuous. In applications that combine design and hygiene applications such as food showcases, tableware, and kitchen equipment that shows cooking scenes in hotels, etc. It gives a filth to the viewer.

  As described above, when the irregularities on the surface of the stainless steel are increased, the fingerprints are less noticeable. However, the oil stains are easily attached. When the irregularities are reduced, the oil stains are less likely to be adhered, but the fingerprints are easily noticeable. Therefore, in conventional stainless steel, it should be satisfied in food showcases, tableware, kitchen equipment showing cooking scenery, etc., the requirement for design applications that the attached fingerprints are not noticeable and oil stains are difficult to adhere The requirements for hygiene applications cannot be met with high satisfaction at the same time.

As a technique for making an attached fingerprint inconspicuous, there are generally known a method for forming irregularities on a stainless steel surface and a method for coating a stainless steel surface.
Patent Document 1 is an invention that pays attention to the relationship between the shape of surface irregularities and the difficulty of attaching fingerprints. The surface area ratio of microscopic irregularities on the surface is defined as 30% or less and substantially uniform. The present invention relates to a metal plate characterized by being distributed.
However, Patent Document 1 focuses only on the difficulty of attaching fingerprints, and does not allow description of the difficulty of attaching oil stains.

In Patent Document 2, a hydrophilic film represented by a specific chemical formula is provided on the surface of a stainless steel container so that oil stains are less likely to adhere and fingerprints during handling are less noticeable.
However, when a coating layer such as a film is formed on the metal surface, the coating layer may be peeled off and mixed into food. From the viewpoint of food safety, it is necessary to avoid contamination of the food with foreign substances, which is difficult to use in the field of food.
Also, various proposals have been made in Patent Documents 3 to 7 to be described later, but all of them still have problems.

JP-A-6-335705 Japanese Patent Laid-Open No. 2003-310411 JP-A-7-113142 JP-A-11-226606 Japanese Patent Laid-Open No. 2005-240062 Japanese Patent No. 3739887 Japanese Patent No. 3587180

  The present invention has been made in view of such conventional problems, and has a solid surface that does not have a surface coating layer such as a coating on the surface, and oil stains are difficult to adhere to the solid surface, that is, fingerprints are not noticeable. It is an object of the present invention to provide a stainless steel excellent in both oil-resistant soil adhesion and fingerprint resistance.

The first invention is a stainless steel having a solid surface on which a surface coating layer such as paint is not formed,
The surface roughness of the solid surface is the short wavelength roughness (Ra1) which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by λc contour curve filter = 0.025 mm and λs contour curve filter = 2.5 μm. Is divided by the short wavelength length (RSm1), which is the average length of the roughness curve elements in the roughness curve, is 0.0030 or less,
In addition, the long wavelength roughness (Ra2), which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by λc contour curve filter = 0.8 mm and λs contour curve filter = 2.5 μm, is 0.5 μm or more. It is in stainless steel excellent in oil-resistant soil adhesion and fingerprint resistance.

  The first invention focuses on the value obtained by dividing the short wavelength roughness (Ra1) by the short wavelength length (RSm1), that is, the inclination of the short wavelength unevenness. It has been found that even if the amplitude of the short wavelength unevenness is large, if the inclination is small, oil stains are hardly attached.

Here, the average length of the roughness curve element is defined in JIS B 0601: 2001, similar to the arithmetic average roughness of the roughness curve. Generally, the roughness curve element is as follows using a roughness measuring machine. Ask.
First, the surface of the object to be measured is traced with a probe using a roughness measuring machine, and the unevenness of the surface of the object to be measured is obtained as a contour curve. Thereafter, a band filter called a contour curve filter is used to remove a component having a longer wavelength than the roughness component (swell) and a component having a shorter wavelength than the roughness component. That is, a specific wavelength band is extracted from the contour curve to obtain a roughness curve. In the roughness curve thus obtained, an arithmetic average roughness (Ra) obtained by evaluating the amplitude of the roughness curve using a predetermined formula defined in JIS B 0601 is JIS B 0601. The average length (RSm) of the roughness curve elements is obtained by evaluating the interval between the peaks and valleys of the roughness curve using the predetermined formula defined in (1). A general roughness measuring machine extracts a wavelength band defined as roughness from a contour curve measurement, obtains a roughness curve, and calculates an arithmetic average roughness of the roughness curve and an average length of the roughness curve elements. Work automatically.

In calculating the arithmetic average roughness, the reference length was λc, the evaluation length was five times the reference length, and the average value of the values for each reference length was the arithmetic average roughness.
In obtaining the average length of the roughness curve element, the reference length was λc, and the average length (RSm) was obtained with respect to the total evaluation length that is five times the reference length. When identifying and determining the minimum height necessary for determining the length of the roughness curve element, the unevenness that is less than 10% of the maximum height of the entire evaluation length is determined as noise, and the minimum length is identified. At the time of determination, unevenness of less than 1% of the evaluation length was determined as noise.

As described above, as a result of intensive studies, the inventors have found that the difficulty of attaching oil stains is greatly influenced by the short wavelength roughness, and further by the value obtained by dividing the short wavelength roughness by the short wavelength length, and the long wavelength It has been found that there is a tendency not to be affected by roughness, and that oil dirt is less likely to adhere by reducing the value obtained by dividing the short wavelength roughness (Ra1) by the short wavelength length (RSm1).
On the other hand, the fingerprint visibility has been found to be less noticeable by increasing the long wavelength roughness (Ra2).

  Specifically, the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by the contour curve filter of λc contour curve filter = 0.025 mm and λs contour curve filter = 2.5 μm is the short wavelength roughness (Ra1). The average length of the roughness curve elements in the roughness curve is the short wavelength length (RSm1), and the wavelength band in the contour curve filter of λc contour curve filter = 0.8 mm and λs contour curve filter = 2.5 μm When the arithmetic mean roughness of the roughness curve defined by is defined as the long wavelength roughness (Ra2), the value obtained by dividing the short wavelength roughness (Ra1) by the short wavelength length (RSm1) is 0.0030 or less. By making the surface roughness characteristics both satisfying the conditions and the condition that the long wavelength roughness (Ra2) is 0.5 μm or more, more preferably 2.0 μm or more, the adhesion of oil stains on the solid surface is difficult. Attached fingerprint It is possible to achieve both inconspicuous difficulty.

For the value obtained by dividing the short wavelength roughness (Ra1) by the short wavelength length (RSm1), an upper limit value is defined. Since it is technically difficult to make the inclination too small and the cost is high, the lower limit is preferably set to 0.0001.
In addition, the above long wavelength roughness (Ra2) defines a lower limit value. If the value is larger than that, there is basically no problem, but it is technically difficult to provide a very large long wavelength roughness. Therefore, the upper limit is preferably set to 30 μm.

  In the first invention, the short wavelength roughness (Ra1) is preferably 0.05 μm or less (claim 2). In this case, as shown in the examples described later, a value obtained by dividing the short wavelength roughness (Ra1) by the short wavelength length (RSm1) can be surely made 0.0030 or less.

  When the stainless steel metal surface is exposed, the stainless steel surface is covered with an oxide film containing several nm of Cr called a passive film. This passive film is always present on the surface of stainless steel in a state where corrosion resistance is maintained. Natural oxidation of the metal surface by oxygen in the air or water, or pickling using a specific chemical artificially. Or by electrolytic polishing or the like. The passive film is related to a mechanism in which stainless steel is less likely to rust than carbon steel or the like, and is different from a surface coating layer such as coating. The passive film present on the surface of the stainless steel is a general and natural state when the metal surface of the stainless steel is exposed, and is not included in the surface coating layer such as the coating.

The second invention is a roughness whose wavelength band is defined by a λc contour curve filter = 0.8 mm and a λs contour curve filter = 2.5 μm on a solid surface on which a surface coating layer such as a coating in stainless steel is not formed. Shot processing is performed so as to obtain a skin roughness with a long wavelength roughness (Ra2) of 0.6 μm or more, which is the arithmetic average roughness of the curve,
Thereafter, the short wavelength roughness (Ra1), which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by λc contour curve filter = 0.025 mm and λs contour curve filter = 2.5 μm, Oil stain resistance, characterized in that electropolishing is performed until a skin roughness is obtained in which the value divided by the short wavelength length (RSm1), which is the average length of the roughness curve elements, is 0.0030 or less, and It exists in the manufacturing method of stainless steel excellent in fingerprint-proof visibility (Claim 3).

  The production method according to the present invention is a method for producing the stainless steel of the first invention, and the inventors have used the shot processing and the electropolishing process appropriately for the first time, so that the oil-resistant dirt adheres. It has been found that stainless steel having excellent properties and fingerprint visibility can be produced relatively easily.

The shot process is a process of projecting particles onto the surface of a material, and is also called a shot blast process, and irregularities can be formed on the surface of a material having a complicated shape.
The electropolishing process has a feature of smoothing the unevenness of the short wavelength in preference to the unevenness of the long wavelength on the surface, and can be processed even on the surface of the material having a complicated shape.

  In the present invention, using these two processing features, first, shot processing is performed to give irregularities to the solid surface of stainless steel. The surface roughness of the solid surface after the shot processing is an arithmetic average roughness of a roughness curve in which a wavelength band is defined by λc contour curve filter = 0.8 mm and λs contour curve filter = 2.5 μm. Irregularities having a long wavelength roughness component are formed so that the wavelength roughness (Ra2) is 0.6 μm or more, more preferably 2.3 μm or more. Note that a large short wavelength roughness component exists on the solid surface of the stainless steel at this point.

  After the shot processing, the electrolytic polishing is performed. As a result, the short wavelength roughness (Ra1) which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by the λc contour curve filter = 0.025 mm and the λs contour curve filter = 2.5 μm is equal to the roughness. The value divided by the short wavelength length (RSm1), which is the average length of the roughness curve elements in the curve, is 0.0030 or less. Electropolishing is characterized by smoothing by prioritizing short-wavelength roughness over long-wavelength roughness by selecting appropriate conditions. The above value can be reduced without significant influence.

  Although the long wavelength roughness does not have a great influence by the electrolytic polishing, there is a tendency to slightly decrease. Therefore, after the shot processing, in order to ensure the long wavelength roughness of 0.5 μm or more, more preferably 2.0 μm or more after the electrolytic polishing. The long wavelength roughness (Ra2) is preferably 0.6 μm or more, more preferably 2.3 μm or more.

  The long wavelength roughness (Ra2) adjusted by the shot processing is set to 0.6 μm or more as described above, but the upper limit is technically difficult to provide a very long long wavelength roughness by the shot processing. Because of high cost, the thickness is preferably 31 μm.

  As an example of shot processing that satisfies the above conditions, for example, a spherical steel shot with a diameter of about 0.4 mm and a hardness of HRC 40-50 is cast on a stainless steel surface with an impeller-type steel shot machine at a projection speed of 80 m / sec. And processing to project to. The long wavelength roughness (Ra2) can be adjusted by changing the conditions of shot grain shape, size, hardness, and shot grain projection speed. Optimal conditions can be determined relatively easily.

Moreover, as an example of the electropolishing which satisfies the above conditions, for example, an electropolishing liquid of sulfuric acid 25% -phosphoric acid 60% -phosphorous acid 3% -remaining water 50 ° C. is used, and the current density is 3 with the material as the anode. And a method of electrolysis at 67 A / dm ^{2 for} 40 minutes. This example is an example, and the optimum condition varies depending on the material and the like. The short wavelength roughness (Ra1) can be adjusted by changing the conditions of the composition, temperature, current density, and electrolysis time of the electropolishing liquid. The optimum condition can be obtained.

In the second aspect of the invention, it is preferable that the electrolytic polishing is performed until a skin roughness with which the short wavelength roughness (Ra1) is 0.05 μm or less is obtained (claim 4). In this case, a value obtained by dividing the short wavelength roughness (Ra1) by the short wavelength length (RSm1) can be easily set to 0.0030 or less.
Note that the short wavelength roughness (Ra1) adjusted by the electrolytic polishing is preferably 0.05 μm or less as described above, but the lower limit thereof is too small even if the electrolytic polishing treatment is performed. Since it is difficult to achieve and the cost is high, 0.01 μm is preferable.

  The first invention and the second invention are inventions that focus on the surface roughness of the solid surface of stainless steel, and are not limited to the steel type as long as the stainless steel does not have a coating layer such as a coating. The composition (steel type) is not particularly limited.

In general, there are many cases where the roughness is obtained without particularly indicating the above-mentioned λc in the measurement of the surface roughness. In this case, it can be interpreted that the value of λc is determined according to the rule according to JIS B 0633: 2001, and the arithmetic average roughness is obtained according to JIS B 0601.
According to the rules defined in JIS B 0633, the value of λc (= reference length) is set to five levels in the range of 0.08 to 8 mm, and the upper and lower limits of the Ra value are determined for each level. When the Ra value measured and obtained at a certain λc value is in the upper and lower limit range defined by the standard, the value measured at the smallest λc is determined to be adopted as the arithmetic average roughness Ra of the surface.

And since the following patent documents 3-7 have some which prescribed | regulated Ra which does not prescribe | regulate the value of (lambda) c, a difference with the technique described in these literatures is demonstrated based on the said interpretation.
Patent Document 3 (Japanese Patent Laid-Open No. 7-113142) is a patent document relating to a stainless steel sheet for construction having a surface roughness Ra of 0.5 to 10 μm and having a convex portion on the surface of a steel material and excellent in contamination resistance and corrosion resistance. .
The arithmetic average roughness Ra in this patent document does not indicate the reference length, that is, the value of the λc contour curve filter. Therefore, from JISB0633, the value of λc used at Ra = 0.5 to 10 μm is λc = 0.8 mm or 2.5 mm, which is equal to or longer than the long wavelength roughness in the present invention. It can be said. Therefore, the short wavelength roughness in the present invention is not mentioned and is different from the present invention.

Patent Document 4 (Japanese Patent Laid-Open No. 11-226606) is characterized in that Ra is 0.5 μm or more and the maximum amplitude in a wavelength region of 10 μm or less is 0.02 μm or less in the power spectrum analysis of the surface roughness. It relates to a metal surface where fingerprints are difficult to stand out.
This patent document 4 can be said to be similar to the present invention in that it focuses on two parameters, a long-wavelength surface undulation and a short-wavelength surface undulation. However, Patent Document 4 focuses only on the effect of long-wavelength surface undulations and short-wavelength surface undulations on the conspicuousness of fingerprints, which is a “design need”, and the adhesion of oil stains to which the present invention is focused. There is no mention of the relationship with “sanitary needs” such as the difficulty of working. In this technique, since the surface undulation of the short wavelength focuses on the amplitude of each wavelength component decomposed by the power spectrum analysis, it is impossible to achieve both “design needs” and “sanitary needs”.

  Further, Patent Document 4 does not specifically show how to obtain a desired surface roughness, and a special surface treatment is applied when manufacturing by rolling transfer described in the examples. A rolled roll is required. In addition, the unevenness of the roll surface for transferring the surface undulations creates a difference in the roll peripheral speed depending on the location, and the fine scratches caused thereby increase the surface undulations of short wavelengths, which greatly increases the manufacturing cost. Inevitable.

  Further, Patent Document 4 shows that a desired surface roughness can be obtained by either or a combination of shot processing and electropolishing processing, but no specific description is recognized. That is, it is not clear how to control the roughness of which wavelength by shot processing and how to control the roughness of which wavelength by electrolytic polishing. In general, in electropolishing, unevenness may increase or decrease depending on electrolysis conditions. There is an increase / decrease in the unevenness in the range that can be visually recognized, and an increase / decrease in the unevenness that can only be seen visually as a mirror surface or a cloudy feeling, and it is impossible to unambiguously describe not only the increase / decrease in roughness but also the wavelength range.

  In the manufacturing method of the second invention of the present application, long wavelength roughness is given to a solid surface in shot processing, and short wavelength roughness inevitably generated in shot processing is electropolished under electropolishing conditions in which the short wavelength roughness is reduced. It is processed and removed, and is a much more advanced and specific technique than the description in Patent Document 4. In addition, there is a merit that the degree of freedom of the shape of the steel material is high as compared with the transfer by the rolling roll.

Patent Document 5 (JP 2005-240062) is, Ra having film comprising an oxide of SiO ₂ mainly is related more stainless steel 0.30 .mu.m. The invention of Patent Document 5 is related to a stainless steel having a coating made of an oxide mainly composed of SiO _2, and is different from the present invention relating to a general stainless steel surface, ie, a surface mainly composed of Cr oxide. It is.

  The invention of Patent Document 6 (Patent No. 3739887) is an invention related to a polished stainless steel sheet excellent in dirt removal property and a method for producing the same, characterized in that Ra is 0.30 μm or less. It can be said that it is similar to the present invention that the smaller the roughness Ra, the better. However, the invention of Patent Document 6 is an invention relating to “removability of dirt”, that is, ease of removing attached dirt, and “difficulty to adhere oil dirt” of the present invention refers to a point of interest regarding dirt. Different. This is also clear from the fact that, in the example of Patent Document 6, evaluation is performed by applying petrolatum, wiping with a cloth, and performing ultrasonic cleaning with acetone. On the other hand, the present invention does not focus on wiping and cleaning properties, but the cohesiveness of oil (whether thinly spread or gathered) on the solid surface of stainless steel has a short wavelength roughness, and further a short wavelength roughness. This is based on the knowledge greatly influenced by the value divided by the short wavelength length, and is greatly different from the invention of Patent Document 6.

  In the invention of Patent Document 6, the roughness Ra is not designated as the reference length, that is, the value of the λc contour curve filter. From this, according to JISB0633, the value of λc used when Ra = 0.30 μm or less can be interpreted as λc = 0.8 mm or less. In the invention of Patent Document 6, λc corresponding to the largest roughness Ra = 0.30 μm is 0.8 mm, which is the same as the value of λc in the long wavelength roughness of the present invention. However, in the present invention, Ra = 0.5 μm or more at λc = 0.8 mm, more preferably 2.0 μm or more is a necessary element for the invention, and the invention is also different from Patent Document 6 in the roughness range. It can be said that.

Patent Document 7 (Japanese Patent No. 3587180) has a ten-point average roughness Rz of 3.5 μm or more and 6.5 μm.
Hereinafter, the present invention relates to a stainless steel plate having a surface having an average spacing Sm of 120 μm or more and 250 μm or less and a convex area ratio of 15% or more and 45% or less and excellent in stain resistance and corrosion resistance. This invention does not pay attention to short wavelength roughness, and stain resistance is intended for suspended dust and the like, and is different from the present invention. That is, the agglomeration property (whether thinly spread or gathered) of the steel surface in the present invention is not touched on the knowledge that is greatly influenced by the short wavelength roughness, and is different from the present invention.

  The stainless steel excellent in oil stain resistance and fingerprint resistance according to the embodiment of the present invention and the manufacturing method thereof will be described more specifically.

As shown in Table 2, SUS304 stainless steel sheets with various surface finishes including the present invention were prepared or prepared. For these steel plates, measurement of long wavelength roughness (Ra2), measurement of short wavelength roughness (Ra1), measurement of short wavelength length (RSm1), evaluation test for adhesion resistance to oil stains, and fingerprint visibility resistance An evaluation test was conducted.
For reference, the arithmetic mean roughness when measured according to the rules defined in 7.2 of JIS B 0633: 2001 is also shown together without particularly indicating λc.

First, the test piece used for the evaluation test will be described.
Sample No. 1, sample no. 2 and Sample No. 8 to 21 show examples of the present invention. 3 shows a comparative example. Sample No. 4 to Sample No. 7 is a conventional example and is a general surface-finished stainless steel available in the market. Regardless of the examples, comparative examples, and conventional examples, the material is all SUS304.
Sample No. 1 to 3 and sample no. Table 1 shows the manufacturing steps of 8-21.

<Sample No. 1>
Sample No. The material No. 1 is obtained by subjecting a pickled finish to steel shot processing and then electrolytic polishing.
In the above shot processing, on a solid surface of stainless steel, an impeller-type steel shot machine is used, the diameter defined by JIS Z 0311: 2004 is about 0.4 mm (grain size number 040), and the hardness is HRC 40-50 spherical. By projecting steel shot grains at a projection speed of 80 m / sec and a projection density of 312 kg / m ² , a long wavelength roughness necessary for fingerprint resistance visibility was imparted to the surface.
Sample No. The surface roughness after the above-described shot processing and before the subsequent electropolishing processing was 0.19 μm for the short wavelength roughness (Ra1) and 4.95 μm for the long wavelength roughness (Ra2). It was.

The short wavelength roughness produced by shot processing is detrimental to the difficulty of oil stains. Therefore, the electrolytic polishing process was subsequently performed to reduce the short wavelength roughness.
Sample No. The electropolishing process for the test piece 1 was a general one that regenerated the passive film by dipping in nitric acid after electropolishing using a mixed acid composed of sulfuric acid and phosphoric acid. The purpose of immersing in nitric acid is to regenerate the passive film on the surface of the stainless steel, impart the original corrosion resistance to the stainless steel, and prevent rust. The passive film has a thickness of several nm, and is not limited to the present invention, and is generally present on the surface of stainless steel not only in the present invention but also in the comparative example and the conventional example. More specifically, the electropolishing is carried out using an electropolishing liquid of sulfuric acid 25% -phosphoric acid 60% -phosphorous acid 3% -remaining water at 50 ° C. with the material as the anode at a current density of 3.67 A / dm ² . Electrolysis was performed.
Sample No. The final short wavelength roughness (Ra1), short wavelength length (RSm1) and long wavelength roughness (Ra2) of 1 are as shown in Table 2 described later.

<Sample No. 2>
Sample No. The material of Sample No. 2 After performing the same shot processing as in the case of No. 1, The electropolishing in the case of No. 1 was performed in two parts. And the corrosion resistance finally obtained is improved by putting a 30% nitric acid dipping step in the middle of the electrolytic polishing twice and finally performing a 5% nitric acid dipping step. Sample No. As a result of the electropolishing process in FIG. As compared with the first step, excellent corrosion resistance can be obtained.

  The first 38-minute electropolishing is intended to reduce the short wavelength roughness generated during the shot processing, which is the previous process, by electropolishing. The subsequent 30% nitric acid immersion process is for removing Cu deposited on the surface after the first electrolysis process, and is compared with the substrate in the second 2 minute electropolishing and 5% nitric acid immersion process performed after that. Thus, a passive film having a high Cr concentration and excellent corrosion resistance is obtained on the solid surface of stainless steel.

  Sample No. The surface roughness after the above-described shot processing and before the subsequent electropolishing processing was 0.28 μm for the short wavelength roughness (Ra1) and 4.29 μm for the long wavelength roughness (Ra2). It was. The final short wavelength roughness (Ra1), short wavelength length (RSm1), and long wavelength roughness (Ra2) values are as shown in Table 2 described later.

<Sample No. 8-21>
Sample No. The materials of Nos. 8 to 21 are sample Nos. In the same manner as in No. 1, the steel pickling finish was subjected to steel shot processing, followed by electrolytic polishing.
In the above shot processing, a high carbon cast steel shot defined by JIS Z 0311: 2004 is projected on a solid surface of stainless steel under the shot conditions shown in Table 3 using an impeller-type steel shot machine. The surface was given a long wavelength roughness necessary for the properties.

Sample No. Table 3 shows the surface state in the state after the above-described shot processing of 8 to 21 and before the subsequent electropolishing processing.
As shown in Table 1, sample no. The electropolishing time of 8 to 14 was 20 minutes, and sample No. The electropolishing time for 15-21 is 40 minutes.
Sample No. The final short wavelength roughness (Ra1), short wavelength length (RSm1) and long wavelength roughness (Ra2) values of 8 to 21 are as shown in Table 2 described later.

<Sample No. 3>
Sample No. The material of Sample No. 3 After performing the same shot processing as in the case of No. 1, This is a comparative example in which the electropolishing time in the electropolishing process of 1 is shortened and the effect of reducing the short wavelength roughness by electropolishing is suppressed.

  Sample No. The surface roughness in the state after the above shot processing of 3 and before the subsequent electropolishing processing is 0.19 μm for the short wavelength roughness (Ra1), 18.2 for the short wavelength length (RSm1), The long wavelength roughness (Ra2) was 4.88 μm. The final values of the short wavelength roughness (Ra1) and the long wavelength roughness (Ra2) are as shown in Table 2 described later.

Next, evaluation conditions will be described.
Sample No. above. 1 to 3 and sample no. In addition to the samples 8 to 21, a commercially available sample No. Four types of samples 4 to 7 were prepared, and each evaluation test was performed as follows.
In each evaluation test, a SUS304 stainless steel plate with various surface finishes was cut into a length of 150 mm and a width of 100 mm, the surface was washed with acetone, washed with a neutral detergent, and naturally dried. Respectively. In addition, the test piece was cut so that the direction of the test piece length direction was the polishing direction for the surface irregularities such as hairline polishing finish and # 400 finish.
The roughness was measured using a surface roughness measuring device SE3500 manufactured by Kosaka Laboratory.

  In the measurement of the long wavelength roughness (Ra2), λc = 0.8 mm, λs = 2.5 μm, in order to measure the long wavelength roughness component using a roughness measuring instrument equipped with a probe having a tip radius of 2 μm, Arithmetic average roughness was obtained according to JIS B 0601: 2001 at a reference length of 0.8 mm and an evaluation length of 4.0 mm, and was regarded as long wavelength roughness, and an average value measured at three locations was regarded as final long wavelength roughness.

  In the measurement of the short wavelength roughness (Ra1), λc = 0.025 mm, λs = 2.5 μm, in order to measure the roughness component of the short wavelength using a roughness measuring instrument equipped with a probe having a tip radius of 2 μm, Arithmetic average roughness was determined according to JIS B 0601: 2001 at a reference length of 0.025 mm and an evaluation length of 0.125 mm, and was defined as short wavelength roughness, and an average value measured at three locations was defined as final short wavelength roughness.

In the measurement of the short wavelength length (RSm1), a roughness measuring machine equipped with a probe having a tip radius of 2 μm is used, and in order to measure the short wavelength roughness component, λc = 0.025 mm and λs = 2.5 μm. The roughness curve is obtained, and the average length RSm of the roughness curve element is obtained according to JIS B 0601: 2001 with respect to the evaluation length full length which is 5 times λc, and the average value obtained by measuring three points is finally obtained. It was a short wavelength length.
When identifying and determining the minimum height necessary to obtain the length of the roughness curve element, the unevenness having a maximum height of less than 10% in the entire evaluation length is determined as noise, and the minimum length is identified and determined. In this case, unevenness of less than 1% of the evaluation length was judged as noise.

For reference, for comparison with the prior art, use a roughness measuring machine equipped with a probe having a tip radius of 2 μm and measure λc according to the rules defined in 7.2 of JIS B 0633: 2001. The arithmetic average roughness was determined according to JIS B 0601: 2001.
These results are shown in Table 2.

  The oil stain resistance evaluation test was performed using an artificial contaminant mixed with 61.5% olive oil, 38% oleic acid, and 0.5% oil red by mass ratio. This artificial pollutant is the same as that listed as oleophilic artificial pollutant-2 in the JIS L 1919: 2006 textile product antifouling test method.

  In the oil stain resistance evaluation test, the longitudinal direction of the test piece is the vertical direction, and is inclined at an angle of 45 ° with respect to the vertical. Next, 1 mL of artificial pollutant is dropped on the center of the inclined test piece using a micropipette, and the test piece is allowed to stand for one minute as the dropped artificial pollutant drips down the surface of the test piece. The width of the artificial pollutant adhered after standing was visually judged using the calipers in the following three stages.

The evaluation criteria were as follows.
○: The width of the remaining artificial contamination is within 5 mm.
Δ: The width of the remaining artificial contamination is 5 mm or more and 10 mm or less.
X: The width of the remaining artificial contamination is 10 mm or more.

  The evaluation test for anti-fingerprint visibility was performed visually. Press the finger of a human hand against the test piece for 3 seconds, visually observe the degree of the fingerprint trace that is noticeable, give 5 points where the fingerprint trace is not obvious at all, and 1 point that clearly shows the fingerprint trace. Were scored in 5 grades of 5 to 1 points. The average of the scores given by 20 evaluators was calculated, and the final score (average value) of each test piece was obtained. In Table 2, in addition to this final score, four or more samples are indicated by ◎, three or more and less than four by ◯, two or more by three and less by Δ, and less than two by ×.

  As is known from Table 2, Example 1 (Sample No. 1), Example 2 (Sample No. 2), and Example 8 (Sample No. 8) to Example 21 (Sample No. 21) are made of stainless steel. The steel surface is subjected to appropriate shot polishing and then subjected to appropriate electropolishing. In either case, the short wavelength roughness (Ra1), which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by λc contour curve filter = 0.025 mm and λs contour curve filter = 2.5 μm, is the same roughness. The value divided by the short wavelength length (RSm1) which is the average length of the roughness curve elements in the curve is 0.0030 or less, and the λc contour curve filter = 0.8 mm and the λs contour curve filter = 2.5 μm. The long wavelength roughness (Ra2), which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined, is 0.5 μm or more (2.0 μm or more).

  In the evaluation test of the oil stain resistance of the test pieces of Examples 1, 2, and 8 to 21, the oil stain dropped on the test piece leaning diagonally first wets the stainless steel surface, and the width Although the oil stains hang down gradually, the width of the belt-like stains decreases, and after 1 minute, the width becomes 5 mm or less, indicating that the oil stains are difficult to adhere. . Moreover, since the irregularities on the surface of the steel material produced by the long wavelength roughness diffusely reflect light, the attached fingerprints are not noticeable.

  Comparative Example 3 (Sample No. 3) was obtained by subjecting stainless steel to shot machining as in Example 1 and then performing electropolishing, but the electropolishing time was short and inappropriate. The uneven component of the short wavelength roughness that is sometimes generated cannot be sufficiently reduced. The long wavelength roughness is 3.0 μm or more, and the attached fingerprint is not noticeable, but the short wavelength roughness is 0.09 μm, and the value obtained by dividing the short wavelength roughness by the short wavelength length is 0.0044. Since it is large, it is inferior to oil stains.

  In the evaluation test of oil stain resistance of the test piece of Comparative Example 3, the oil stain dripped on the test piece leaning diagonally wets the stainless steel surface and drips down into a wide band. The width of the strip-like dirt does not decrease so much even with time, and the width is 10 mm or more even after one minute, indicating that the oil dirt is likely to adhere. In addition, since the irregularities on the surface of the steel material produced by the long wavelength roughness diffusely reflect light, the attached fingerprint is not noticeable.

Conventional examples 4 to 7 are materials having a surface finish generally used.
The bright annealed test piece shown in Conventional Example 7 is a test piece having a surface state close to a mirror surface. Therefore, the short wavelength roughness is as small as 0.02 μm, the value obtained by dividing the short wavelength roughness by the short wavelength length is as small as 0.0019, and oil stains are difficult to adhere, and in hygiene applications such as food production equipment Is used a lot. However, since the long wavelength roughness is small, the attached fingerprint is very conspicuous, and it is used in applications that combine hygiene and design applications such as food showcases, tableware, and kitchen equipment that shows cooking scenes in hotels, etc. There are difficult drawbacks.

The test piece of # 400 polishing finish shown in Conventional Example 5 is similar to Conventional Example 7, although the short wavelength roughness and the value obtained by dividing the short wavelength roughness by the short wavelength length satisfy the present invention. Does not satisfy the present invention and oil stains are difficult to adhere, but the attached fingerprints are conspicuous.
The hairline polishing finish specimen shown in Conventional Example 4 and the 2B finish specimen shown in Conventional Example 6 are both short wavelength roughness, short wavelength roughness divided by short wavelength length, and long wavelength roughness. Not satisfying the present invention, oil stains are easily attached, and attached fingerprints are also conspicuous.

  The hairline polishing finish shown in Conventional Example 4 has the largest long-wavelength roughness among the conventional examples, and the score of 2.9 in the evaluation of the conspicuousness of the attached fingerprint, and the most adhered fingerprint in the conventional example. Inconspicuous. Therefore, it is frequently used in design applications. However, since dirt adheres to the polishing eye, it is not used much in hygiene applications such as food production equipment.

Claims (4)

Stainless steel with a solid surface that does not have a surface coating layer such as paint,
The surface roughness of the solid surface is the short wavelength roughness (Ra1) which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by λc contour curve filter = 0.025 mm and λs contour curve filter = 2.5 μm. Is divided by the short wavelength length (RSm1), which is the average length of the roughness curve elements in the roughness curve, is 0.0030 or less,
In addition, the long wavelength roughness (Ra2), which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by λc contour curve filter = 0.8 mm and λs contour curve filter = 2.5 μm, is 0.5 μm or more. Stainless steel with excellent adhesion to oil stains and fingerprint resistance.   2. The stainless steel according to claim 1, wherein the short wavelength roughness (Ra1) is 0.05 [mu] m or less, and is excellent in oil stain resistance and fingerprint resistance. Arithmetic average roughness of a roughness curve in which a wavelength band is defined by a λc contour curve filter = 0.8 mm and a λs contour curve filter = 2.5 μm on a solid surface on which a surface coating layer such as paint is not formed in stainless steel The long wavelength roughness (Ra2) is shot processing so as to obtain a skin roughness of 0.6 μm or more,
Thereafter, the short wavelength roughness (Ra1), which is the arithmetic mean roughness of the roughness curve in which the wavelength band is defined by λc contour curve filter = 0.025 mm and λs contour curve filter = 2.5 μm, Oil stain resistance, characterized in that electropolishing is performed until a skin roughness is obtained in which the value divided by the short wavelength length (RSm1), which is the average length of the roughness curve elements, is 0.0030 or less, and Stainless steel manufacturing method with excellent fingerprint visibility.   In Claim 3, the shot processing is performed until the skin roughness with the short wavelength roughness (Ra1) of 0.05 μm or less is obtained. Stainless steel manufacturing method with excellent fingerprint visibility.