JP4606929B2 - Clear coated stainless steel sheet with excellent design and method for producing the material - Google Patents

Description

  The present invention relates to a clear-coated stainless steel sheet that is excellent in the excellent design characteristics unique to a metal material possessed by stainless steel and is used in parts such as home appliances, building materials, and automobiles that are not colored yellow during coating.

  Stainless steel has been used barely in the fields of home appliances, kitchens, automobiles, and building materials because it has excellent corrosion resistance and design properties. Recently, application of the clear-coated stainless steel sheet to which functions such as contamination resistance and corrosion resistance have been added while taking advantage of the excellent design such as the metallic luster of the stainless steel sheet has been increasing.

  These clear-coated stainless steel sheets have been designed to be applied in addition to colorless clear coating, as well as clear-coated steel sheets added with a pigment coating such as a clear coating or a pearl tone or a metallic tone in addition to a colorless clear coating. However, the addition of these pigments lowers the transparency of the clear film and lowers the texture with the metallic luster unique to stainless steel.

  On the other hand, a colorless clear-coated stainless steel sheet has a problem that it becomes yellowish due to the chromate treatment of the base treatment, impairs the design, and looks black depending on the viewing angle. To deal with these problems, Patent Document 1 and Patent Document 2 examine the composition of the treatment solution and the amount of coating applied to the chromate film, and Patent Document 3 describes the appearance of the underlying stainless steel plate with phosphoric acid and silica, and the resistance of the coating film. Studies have been made on improving the contamination and seizure resistance.

JP-A-5-106057 JP-A-11-269660 JP-A-8-281864 JP-A-56-259 JP 62-156253 A Japanese Patent Laid-Open No. 11-254585

  Only by improving the chromate treatment method as described above, a clear coated stainless steel sheet having excellent whiteness and high transparency cannot be obtained. It is an object of the present invention to provide a clear-coated stainless steel sheet excellent in whiteness and a method for producing the same by examining chemical treatment conditions, material surface characteristics, and coating conditions.

  As a result of the study by the present inventors, the yellowish coloring (yellowing) of the colorless clear-coated stainless steel plate is caused by chromate treatment, and temper color coloring occurs on the stainless steel plate surface during baking of the clear coating film. It has been found that this temper color coloring also causes yellowing. And by changing the chemical conversion treatment from chromate treatment to non-chromate treatment and optimizing the thickness of the chemical conversion treatment film, and further using a stainless steel plate with excellent temper color resistance as a stainless steel plate applied to a clear coated stainless steel plate, It became clear that yellowing prevention at the time of clear painting can be realized.

It is known that the temper color of a stainless steel plate can be suppressed by bright annealing a stainless steel plate with increased Si and Al to form an oxide film containing SiO ₂ and Al ₂ O ₃ on the surface of the steel plate. That is, as the Si or Al content increases, an oxide film enriched with Si and Al is easily formed, and the temper color resistance is improved. As such stainless steel, high Si steel (Patent Documents 4 and 5), high Al steel (Patent Document 5) and the like are known. Patent Document 6 is known as a heat-resistant transparent coated stainless steel plate in which Al or Si on the surface of a ferritic stainless steel plate is regulated to 4.5 to 6 atomic%.

  As a result of intensive studies on the means for solving the above problems, the present inventors have studied the chemical conversion treatment conditions, the material surface characteristics, and the coating conditions, as described above, and used a ferrite stainless steel sheet having excellent whiteness. A painted stainless steel sheet and its manufacturing method were established.

The gist of the present invention is as follows.
(1) A ferritic stainless steel sheet in which the stainless steel sheet contains Si: 0.2 to 0.8% by mass%, and the steel sheet has Cr, Si, Al, and Fe atomic concentrations at a depth of up to 50% from the surface. It has a surface oxide film with a ratio (Cr + Si + Al) / Fe of 0.6 or more, and the chemical conversion treatment agent for the coating film is composed of one or two types of aminosilane type and epoxysilane type, and the amount of the chemical conversion treatment agent is 2 ~ a 8 mg / m ^2, clear coated stainless steel plate having excellent whiteness, wherein the clear coating film thickness has 1~10μm of the coating film.
(2) The clear coated stainless steel sheet having excellent whiteness according to claim 1, wherein the stainless steel sheet further contains Al: 0.005 to 0.15% by mass.
(3) The clear-coated stainless steel plate having excellent whiteness according to claim 1 or 2, wherein the stainless steel plate further contains Nb: 0.1 to 0.7% by mass.
(4) Perform final bright annealing on the cold-rolled ferritic stainless steel sheet under conditions where the final bright annealing temperature T1 (° C.) and the dew point T2 (° C.) of the annealing atmosphere satisfy formulas 1 and 2. Do have manufacturing method of the clear coated stainless steel plate having excellent whiteness according to any one of and performing the subsequent coating deposition and clear coating of the chemical conversion treatment agent (1) to (3).
750 ≦ T1 ≦ 5 × T2 + 1200 (1) −70 ≦ T2 ≦ −30 (2) (5) The surface of a cold-rolled ferritic stainless steel plate is subjected to final bright annealing after surface polishing ( A method for producing a clear-coated stainless steel sheet having excellent whiteness as described in 4).

  According to the present invention in which the relationship between the design and color tone of the clear coated stainless steel sheet was examined, b * (chromaticity, yellow / blue degree, JIS Z 8729) was in the range of 0 to 2, and the whiteness was excellent. It becomes possible to manufacture clear coated steel sheets. In general clear-coated stainless steel sheet, b * is yellowish, about 4 to 6, and looks dark depending on the viewing angle. On the other hand, the clear-coated stainless steel sheet of the present invention is whitish and does not appear in a dark color tone depending on the viewing direction.

  As a result of studying the pretreatment in the design of the clear coated stainless steel sheet and the characteristics of the material surface, the present inventors have found that the following two points are important for obtaining a clear coated stainless steel sheet having excellent whiteness. . First of all, an aminosilane-based or epoxysilane-based chemical conversion treatment agent is used as a chemical conversion treatment agent as a pretreatment instead of a chromate treatment agent, and the adhesion amount of the chemical conversion treatment agent is set to an optimum range. Second, as a stainless steel plate material, the surface is enriched with Cr, Si, and Al components to prevent discoloration of the material due to temper color coloring during paint baking. The colorless clear paint may be any of polyester resin, acrylic resin, acrylic urethane resin, epoxy-modified polyester resin, and the like.

  The clear chemical conversion treatment of the present invention will be described.

The clear chemical conversion treatment agent of the present invention comprises one or two types of aminosilane type and epoxysilane type. The reason for selecting the aminosilane type and the epoxysilane type is that when these are used, the adhesion is good and yellow coloring can be prevented as compared with the case where the chromate treatment agent is used. It is processed so that the amount of chemical conversion treatment is 2 to 20 mg / m ² (measured by the amount of SiO _{2 by} fluorescent X-ray), and the surface temperature (MT) of the stainless steel plate is baked and dried at 60 to 140 ° C. The

Fig. 1 rolls E-206 (aminosilane) from Nihon Parkerizing Co., Ltd. at 100 ° C., changing the adhesion amount from 2 mg / m ² to 50 mg / m ^{2 and} applying a 2 μm acrylic urethane resin clear paint. The change in the color tone of the clear coated stainless steel sheet coated at 200 ° C. was investigated. As a stainless steel plate material used for clear coating, an SUS430 / bright annealed material having an atomic concentration ratio (Cr + Si + Al) / Fe (described later) of 0.6 or more at a depth from the surface to 50 mm is used, resulting in temper color coloring. Yellowing is minimized. The vertical axis (Δb *) in FIG. 1 shows the b * (2) of the steel plate material from b * (1) when the coating amount of the chemical conversion treatment agent is changed and the clear coating is baked as shown on the horizontal axis. Is subtracted. That is, Δb * = b * (1) −b * (2).

As a result, as shown in FIG. 1, when the adhesion amount of the chemical conversion treatment agent exceeds 20 mg / m ² , the gloss of the clear coated stainless steel is lowered and slightly yellowish. When the adhesion amount is 20 mg / m ² or less, Δb * is 0.3 or less, and the change in color tone due to the chemical conversion treatment is small. On the other hand, when the chemical conversion treatment is less than 2 mg / m ² , the coating becomes non-uniform, and the adhesion between the clear coating and the stainless steel decreases. Therefore, the deposition amount of the chemical conversion treatment agent in the present invention was 2 to 20 mg / m ^2. Note that the deposition amount of the chemical conversion treatment agent can either be determined by measuring the amount of SiO ₂ by a fluorescent X-ray for clear coated stainless steel surface.

  The clear coating thickness is in the range of 1 μm to 10 μm. This is because it is difficult to obtain a stable color tone at 1 μm or less, and it becomes difficult to produce one coat at 10 μm or more, and the coating cost increases. Preferably, it is in the range of 2 μm to 5 μm.

  Next, the material of the clear coated stainless steel sheet of the present invention will be described.

  In the present invention, by using a steel plate having a surface oxide film having a Cr, Si, Al, Fe atomic concentration ratio (Cr + Si + Al) / Fe of 0.6 or more at a depth of 50 mm from the surface, a temper during coating baking is used. It is characterized by preventing coloration and preventing yellowing. By using a ferritic stainless steel plate containing 0.2% by mass or more of Si and subjecting this steel plate to bright annealing at a predetermined temperature and atmosphere, the atomic concentration ratio on the surface of the steel plate can be made within the above preferred range.

  The stainless steel of the clear coated stainless steel plate is a ferritic stainless steel plate containing Si: 0.2 to 0.8% by mass. Since the diffusion rate of elements in ferritic stainless steel is faster than that of austenite, Cr and Si are easily concentrated in the film. Therefore, the present invention is limited to ferritic stainless steel sheets. In particular, special steel types (Cr—Al steel and Cr—Si steel) containing Al and Si are relatively easy and are described in Patent Documents 4 and 5. However, in the ferritic stainless steel of the present invention, that is, a steel containing Si: 0.2 to 0.8%, a technique for concentrating Cr, Si, and Al described below is essential.

  In the present invention, in order to form a surface oxide film in which Si is concentrated on the surface of the stainless steel plate, it is essential that Si is contained in an amount of 0.2% or more. In this case, Si is deoxidized during melting of steel. Those used as elements are also included. The upper limit of 0.8% of Si particularly indicates that the present invention is a general-purpose ferritic stainless steel. If Si is further contained, the component range of general-purpose ferritic stainless steel, for example, SUS430 or Nb-added SUS430J1L is exceeded. That is, addition of Si exceeding 0.8% is not suitable for general-purpose use because it degrades workability due to the solid solution hardening action.

  In the present invention, it is desirable to contain a trace amount of Al of 0.005% or more and 0.15% or less. This is because Al, like Si, has the effect of suppressing an increase in b * during baking of the clear coating film by being concentrated in the bright annealed coating as described below. Al is added in an amount of 0.005% or more as a deoxidizing element. Addition of a large amount of Al deteriorates workability. Therefore, Al is preferably 0.005 to 0.15%.

  In the present invention, the content of Cr, which is a basic component of a ferritic stainless steel sheet, can be in the range of 16.0 to 20.0 mass%. Furthermore, in order to obtain a clear stainless steel plate having excellent whiteness, the Cr content should be as high as possible. This is because it has the effect of promoting the concentration of Cr in the film during bright annealing. Furthermore, in this invention, it is desirable to contain 0.1-0.7% of Nb. This is because the oxide of Nb is thermodynamically more stable than Cr oxide and is considered to have the same action as Cr.

  Next, a technique for concentrating Cr, Si, and Al in the surface oxide film in ferritic stainless steel containing Si: 0.2 to 0.8% will be described.

After cold rolling annealing of SUS430, which is a ferritic stainless steel, no. 4. The polished material was bright annealed, and the ratio of Cr, Si, Al, and Fe in the oxide film was changed by changing the temperature and atmosphere of the bright anneal. An aminosilane-based chemical conversion treatment agent is applied as a chemical conversion treatment to a material in which the atomic concentration ratio (Cr + Si + Al) / Fe is adjusted in the range of 0.15 to 3.5 so that the amount of adhesion is 10 mg / m ^2. After baking and drying, a 2 μm acrylic urethane resin-based clear paint was roll-coated. FIG. 2 shows the relationship between the atomic concentration ratio (Cr + Si + Al) / Fe and Δb * when the baking temperature after applying the clear paint is 224 ° C. Evaluation was performed by Δb *, which is a difference in b * between the baking and the reference material (clear coated stainless steel plate material). As is clear from FIG. 2, a material in which the atomic concentration ratio (Cr + Si + Al) / Fe is adjusted to 0.6 or more has little color tone change due to painting and baking, and Δb * is less than 1 and there is little color change.

  Next, a material in which the atomic concentration ratio (Cr + Si + Al) / Fe is adjusted to 0.6 or more and a material in which the atomic concentration ratio (Cr + Si + Al) / Fe is adjusted to less than 0.6 are prepared, and the baking temperature is 150 ° C. to 250 ° C. Until I saw the change in color. Except for the difference in baking temperature and the difference in variety, the same as in the case of FIG. In FIG. 3, the atomic concentration ratio (Cr + Si + Al) / Fe is about 3 for the materials of ◯ and Δ. For ● and ▲, the atomic concentration ratio (Cr + Si + Al) / Fe is about 0.4 and 0.2, respectively. As a result, as shown in FIG. 3, in the material in which (Cr + Si + Al) / Fe is adjusted to 0.6 or more by bright annealing, there is little change in color tone due to painting and baking. On the other hand, after polishing finish, materials that are not brightly annealed or processed under bright annealing conditions outside the scope of the present invention and whose atomic concentration ratio (Cr + Si + Al) / Fe is adjusted to less than 0.6 are yellowish during coating and baking. Discoloration is large, especially when the baking temperature is as high as 200 ° C. or higher.

In the present invention, the components in the surface oxide film were analyzed by AES (Auger electron spectroscopy), and the atomic concentration ratio (Cr + Si + Al) / Fe at the highest oxygen concentration was obtained. In the present invention, it is extremely important to control the (Cr + Si + Al) / Fe to be 0.6 or more to obtain a surface oxide film enriched with Cr or Si. In this case, Si is concentrated in the outer layer of the surface oxide film, and Al is concentrated in the inner layer near the bulk. The reason for this is that the bright annealing condition is a reducing condition for Cr and an oxidizing condition for Si and Al, and Al ₂ O ₃ has a lower dissociation pressure than SiO ₂ . Further, depending on the method of measuring the surface oxide film, the appropriate range of (Cr + Si + Al) / Fe may be different, but the necessary surface oxide film structure is the same as described above.

  The atomic concentration ratio (Cr + Si + Al) / Fe in the surface oxide film of the cold-rolled annealed material and the polished finish is about 0.2. Therefore, the present inventors performed bright annealing on the stainless steel plate, and formed an oxide film in which the atomic concentration ratio of Cr, Si, Al, Fe (Cr + Si + Al) / Fe is 0.6 or more at a depth of 50 mm from the surface. The bright annealing conditions to be formed were examined.

Bright annealing is generally performed in a reducing atmosphere in which hydrogen and nitrogen are mixed in a ratio of H ₂ : N ₂ = (1 to 9): 1. At that time, the annealing temperature T1 (° C.) and the atmospheric dew point T 2 (° C. ) Changes the components in the oxide film after annealing.

For cold-rolled SUS430J1L and SUS430 steel plates, cold rolling annealing or no. FIG. 4 shows the results of bright annealing at various annealing temperatures T1 (° C.) and atmospheric dew points T2 (° C.) after mechanical polishing equivalent to 4 finishing (JIS G 0203 No. 5349). The range in which the annealing temperature T1 is on the horizontal axis and the atmospheric dew point T2 is on the vertical axis, and the (Cr + Si + Al) / Fe atomic concentration ratio at a depth of 50 mm from each surface is stably 0.6 or more,
750 ≦ T1 ≦ 5 · T2 + 1200 Equation 1 −70 ≦ T2 ≦ −30 Equation 2

  In the range of Formulas 1 and 2, Cr is a condition for reduction, while Si and Al are conditions for oxidation. Therefore, concentration by selective oxidation of active ingredients (Si, Al) into the film is effective. Done. When the bright annealing temperature T1 (° C.) is lower than 750 ° C., the diffusion movement of effective elements (Si, Al) centering on Cr is slowed down, and an oxide film having a sufficient atomic concentration ratio is not obtained. Further, when the temperature T1 (° C.) exceeds (5 × T2 +1200) ° C., the condition is on the reduction side further than the range of the formula 1, so that selective oxidation of Si and Al is suppressed and oxidation with a sufficient atomic concentration ratio is achieved. It does not become a film. Therefore, the bright annealing temperature T1 (° C.) is preferably in the range of one set determined from the relationship with the dew point. Preferably 800 degreeC or more and 1000 degrees C or less are good. More preferably, it is 800 degreeC or more and 900 degrees C or less.

  The bright annealing dew point T2 (° C) exceeds -30 ° C, and the oxidation of Fe becomes intense. Concentration of Fe on the oxide film on the surface is inevitable, and the color changes due to the temper color. It is not preferable. Moreover, a gas dew point of less than -70 ° C is very difficult industrially. Accordingly, the dew point of bright annealing is preferably in the range of the two formulas. Preferably, -60 degreeC or more and less than -35 degreeC are good.

  Although the thing of patent document 5 says that there is little temper color coloring in Si density | concentration 0.3%, the Example of Si density | concentration 0.3% in the same literature is temper color coloring grade 3 (yellow). Therefore, it is not possible to obtain a clear coated stainless steel sheet having excellent whiteness. In the present invention, the atomic concentration ratio (Cr + Si + Al) / Fe in the oxide film is clearly defined as 0.6 or more, and the manufacturing conditions capable of realizing this atomic concentration ratio are clarified, whereby the Si concentration is reduced to 0. Even with a low Si concentration of 8% or less, it was possible to obtain a clear coated stainless steel plate with excellent whiteness.

  A polished finish with a surface pattern peculiar to stainless steel with a polished surface is useful as a member that places importance on design. However, the surface coating of stainless steel that has undergone surface polishing has very little concentration of Cr, Si, and Al, so it turns yellow when applying a clear coating, and a highly designed clear coating with excellent whiteness Stainless steel sheets cannot be obtained. Therefore, it is necessary to perform bright annealing in order to concentrate Cr, Si, and Al in the surface film. However, if bright annealing is performed after surface polishing of a ferritic stainless steel sheet that has been subjected to normal softening annealing, the manufacturing process is complicated. This increases the cost. Therefore, in the present invention, it is desirable to subject the cold-rolled ferritic stainless steel sheet to the final bright annealing after surface polishing. Brightening of softening annealing for material preparation and concentration of Cr, Si, Al in the surface film (high (Cr + Si + Al) / Fe) by one manufacturing process of cold rolling-surface polishing-bright annealing It can be performed simultaneously by annealing. In particular, in the ferritic stainless steel sheet of the present invention, the recrystallization temperature may be controlled and adjusted by the Nb content in order to match the softening temperature with the concentration temperature of Cr, Si, Al in the surface film. Is possible. Further, in the case of an austenitic stainless steel sheet, since the solution annealing is usually 1000 ° C. or higher, it does not coincide with the temperature at which Cr, Si, Al is concentrated in the surface film. Therefore, after the cold rolling-polishing, it is necessary to provide two annealing steps, ie, solution annealing and bright annealing for forming an oxide film.

  Table 1 shows examples and comparative examples of the present invention. The surface finish of ferritic stainless steel sheet is No. There were three types: 4 (polishing finish for fine eyes), HL (polishing finish for hairline), and 2B (skin that was lightly rolled after pickling). These ferritic stainless steel plates were brightly annealed under the conditions shown in Table 1. The ferritic stainless steel sheet with 2B finish is a manufacturing process in which annealing is performed after cold rolling, while other surface finishing products are not annealed after cold rolling. Softening is also performed at the same time.

  For each ferritic stainless steel sheet after bright annealing, the atomic concentration ratio of Cr, Si, Al, Fe in the oxide film at a depth of 50 mm from the surface was measured by AES (Auger Electron Spectroscopy), and the atomic concentration ratio (Cr + Si + Al) / Fe was determined.

To ferritic stainless steel sheet each after bright annealing, chemical treatment as Nippon Parkerizing Co. chemical conversion treatment agent for (E-206) used as one of the aminosilane and epoxysilane, the deposition amount 2 mg / m ² To 50 mg / m ² . As a comparison, the chemical conversion treatment agent was chromated. Thereafter, the acrylic urethane resin-based clear film was treated at a baking temperature of 220 ° C. for 1 to 10 μm.

  The color tone after clear coating was measured by b * (JIS Z8729), and the degree of discoloration was evaluated.

In the present invention example, a chemical conversion treatment having an atomic concentration ratio in the oxide film on the surface of the ferritic stainless steel sheet of 0.6 or more and consisting of one or two types of aminosilane type and epoxysilane type, the adhesion amount is 2 to 20 mg / By making m ² , a clear coated steel sheet having excellent b * with a b * of 2 or less can be obtained, whereas in a comparative example, a clear coated steel sheet with a b * exceeding 2 is obtained, Depending on the viewing angle, it looks dark.

  In Comparative Example 20, since the Si component of the stainless steel plate deviated from the lower limit, (Cr + Si + Al) / Fe in the oxide film deviated from the lower limit, and b * was 2 or more, resulting in poor whiteness. In Comparative Examples 21 to 25, one of the temperature T1 and the dew point T2 under the bright annealing condition deviated from the upper and lower limits, so (Cr + Si + Al) / Fe in the oxide film deviated from the lower limit, and b * was 2 or more, resulting in poor whiteness. In particular, Comparative Example 25 did not measure (Cr + Si + Al) / Fe because the temper color of the stainless steel plate material was clearly observed. In Comparative Examples 26 to 32, the material (Cr + Si + Al) / Fe is 0.6 or more, but the conditions of the chemical conversion treatment agent are out of the scope of the present invention. In Comparative Example 26, the adhesion amount of the chemical conversion treatment agent deviated from the lower limit, resulting in poor adhesion. In Comparative Example 27, the adhesion amount of the chemical conversion treatment agent deviated from the upper limit, and in Comparative Example 28, the chemical conversion treatment agent was a chromate agent and not the non-chromate treatment agent of the present invention. Inferior. In Comparative Examples 29 and 31, the clear paint thickness is outside the lower limit, and the color tone is unstable. In Comparative Examples 30 and 32, the clear paint thickness is outside the upper limit, and it is difficult to manufacture.

It is a figure which shows the relationship between a chemical conversion treatment adhesion amount and discoloration (DELTA) b * of a clear coating stainless steel plate. It is a figure which shows the relationship of the discoloration (DELTA) b * of the clear coating stainless steel plate by 224 degreeC baking, and atomic concentration ratio (Cr + Si + Al) / Fe of Cr, Si, Al, and Fe in the oxide film in the depth from the surface to 50 mm. It is a figure which shows the relationship between the baking temperature of a polished finish stainless steel plate and the steel plate which gave the bright annealing of the range of this invention after grinding | polishing, and discoloration (DELTA) b * of a clear coating stainless steel plate. It is the figure which shows the relationship of the atomic concentration ratio (Cr + Si + Al) / Fe of Cr, Si, Al, and Fe in the oxide film in the depth from the surface to the annealing temperature T1 (° C.) and dew point T 2 (° C.) of bright annealing. is there.

Claims (5)

The stainless steel plate is a ferritic stainless steel plate containing Si: 0.2 to 0.8% by mass%, and the steel plate has a Cr, Si, Al, Fe atomic concentration ratio (Cr + Si + Al at a depth of 50 mm from the surface thereof. ) / Fe has a surface oxide film of 0.6 or more,
The chemical conversion treatment agent for the coating film is composed of one or two types of aminosilane and epoxysilane, the amount of the chemical conversion treatment agent is 2 to 8 mg / m ² , and the clear coating film thickness is 1 to 10 μm. A clear-coated stainless steel sheet with excellent whiteness, characterized by having a coating film.   The clear coated stainless steel sheet having excellent whiteness according to claim 1, wherein the stainless steel sheet further contains Al: 0.005 to 0.15% by mass.   The said stainless steel plate contains Nb: 0.1-0.7% further by the mass%, The clear coated stainless steel plate excellent in the whiteness of Claim 1 or 2 characterized by the above-mentioned. For rolling the ferritic stainless steel sheet was cold performs a final bright annealing, the final temperature T1 (° C.) of bright annealing and dew point T2 (° C.) of the annealing atmosphere rows that have the condition which satisfies the equation (1) and 2 where 4. The method for producing a clear coated stainless steel sheet having excellent whiteness according to any one of claims 1 to 3 , wherein the chemical conversion treatment agent is subsequently applied and a clear paint is applied .
750 ≦ T1 ≦ 5 × T2 + 1200 Equation 1 −70 ≦ T2 ≦ −30 Equation 2 The method for producing a clear coated stainless steel sheet excellent in whiteness according to claim 4, wherein the bright bright annealing is performed after surface polishing of the cold rolled ferritic stainless steel sheet.

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