JPH0366394B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to colored stainless steel whose surface is partially coated with copper. Stainless steel is a material that has excellent corrosion resistance and is resistant to dirt, giving it a clean feel. Taking advantage of this feature, we can use metal surfaces that touch the human eye as they are, and for this reason, in applications where the color tone of the surface is important, for example.
Stainless steel is mainly used for household items such as interior and exterior parts of buildings, kitchen items, and Western tableware. On the other hand, copper exhibits a unique red color, which is called ``Akagane'', and as it ages, it can change color to a deep green due to so-called patina, giving it a luxurious feel. It is widely used in architectural exterior parts such as roofing materials. The copper-coated colored stainless steel according to the present invention is ideal as a material for these interior and exterior parts of buildings and household kitchen items. [Conventional technology] Stainless steel has excellent corrosion resistance and is resistant to dirt, giving it a clean appearance, but the surface color is achromatic, a metallic color (silver white),
This results in giving a bad impression of being cold. The color of most metals is so-called metallic color (silver-white), except for gold, copper, and some copper alloys.
Although the hue varies slightly depending on the type of metal or surface finish, the basic tone is all silvery-white and achromatic. Of course, the same goes for stainless steel. For this reason, we focus on household goods and architectural interior and exterior products.
There is a strong demand for coloring stainless steel. On the other hand, the conventional coloring technology for stainless steel has mainly been done by painting, and in some cases by surface treatment by chemical treatment using the interference effect of oxide film such as the Inco method, or dry process such as CVD (Japan Institute of Metals Bulletin) Volume 23, No. 10 (1984), P812}. Painting has the advantage that there is a wide range of colors to choose from, since the essence of color development lies in pigments. However, since the skin of stainless steel is hidden, the cleanliness and beauty that stainless steel originally has must be sacrificed. In addition, surface treatment technologies using chemical treatments such as the Inco method and dry processes such as CVD are coloring technologies that take advantage of the characteristics of stainless steel, but they are not suitable for general use because the coloring costs are significantly large and expensive. . Colored stainless steel coated with copper includes so-called copper cladding and plating materials. However, although these materials are technically perfected materials, they are expensive because they require special processes and equipment for manufacturing. It is clear that the colored stainless steel made by this technique can only have the same color tone of the copper itself, since the surface is made entirely of copper. [Problems to be Solved by the Invention] The present invention provides a colored stainless steel that eliminates the drawbacks of stainless steel colored using conventional techniques and has a surface that has a high-quality appearance. In other words, the key to coloring stainless steel so that it does not feel cold while still making the most of its cleanliness lies in the question of what to use and how to increase the variety of colors. [Means for Solving the Problems] In order to solve the above problems, the present invention first utilizes the red color of copper as a warm and luxurious color. Second, copper itself only has a single color tone, but by introducing the perspective that the resolution of the human eye is not necessarily good, we thought about increasing the variety of colors by making differences in hue appear. Ta. In other words, on the surface of the stainless steel, we created a fine mosaic of the silvery white color of the base stainless steel itself and the red color of copper, which gives a warm feel. That is, the surface is visually a mixture of the silvery white of stainless steel and the red of copper, and by changing the area ratio, the variety of colors is increased, albeit only in red. The colored stainless steel according to the present invention is microscopically only a mixture of silver white and copper red. Therefore, there will be color unevenness on a microscopic level, but since the individual sizes are less than the resolution of the naked eye, to the naked eye it appears to be colored in a mixture of these colors. Next, an example of the manufacturing method by which the colored stainless steel of the present invention coated with red copper in a mosaic pattern will be described in detail. As a result of investigating copper-coated stainless steel manufactured by plating and cladding, the present inventor found that adhesion is poor when oxides exist at the interface between the two metals, and very good when they are absent. It has also been found that it is quite difficult to maintain good adhesion because a so-called passive film exists on the surface of stainless steel in extreme environments. Based on this knowledge, they decided that in order to adhere without leaving any oxides at the interface, copper should be bonded to the stainless steel without a passive film on the surface. Keeping stainless steel surfaces free of passive films is nearly impossible under normal circumstances. In the manufacturing process of clad steel using vacuum,
If a new surface is generated by rolling, it is assumed that the surface is without a passive film, but keeping it in a vacuum will complicate the manufacturing process and will inevitably lead to a significant increase in costs. . In addition to such a special environment, the condition for keeping the surface of stainless steel free of a passive film is when the surface of stainless steel releases hydrogen gas and dissolves, that is, it is in an active dissolution state. In order to bond copper to a surface undergoing active dissolution, it is necessary to have atomic copper or copper ions present near the interface where the active dissolution is occurring. However, it is not always easy to mix copper ions into the solution and bring them close to the interface by diffusion, as hydrogen gas may be generated at the interface. Therefore, we thought that it would be easier if atomic or ionic copper was liberated from the steel and appeared as a result of active dissolution. For this purpose, copper was added to the steel. The following is an explanation based on the survey results. A mirror-finished plate of copper-added 17Cr stainless steel shown in Table 1 was immersed in an aqueous H ₂ SO ₄ solution for active dissolution. FIG. 1 is a diagram showing the relationship between the amount of copper added to steel and the color of the surface after active dissolution. In addition, Fig. 2 shows the relationship between the degree of surface coverage (ratio) of copper deposited on the surface and the degree of color using steel No. 3 in the same table with a 5.7% copper additive. The copper coverage was determined by observing the surface using an optical microscope, and measuring the area of red precipitates that are copper by image analysis. Regarding the degree of color, a grade of A was given to the same level as when no coloring was observed with the naked eye, and a grade of E was given to the case where the color was the same as that of copper. During that time, the colors were graded into three levels: pale red, flesh-colored, and copper plate-like red, and these were classified as color ranks. In this classification, a grade B is a level at which it is intuitively recognized that the color is colored, and a grade D is a level at which it can be judged that the color is clearly different from copper itself. As is clear from Figure 1, when the amount of copper added is 2% or more,
It was observed that copper precipitated on the surface depending on the amount dissolved in the acid, giving it a red color characteristic of copper. That is, when the amount dissolved was small, the color was pale red, and when the amount dissolved was large, the color was quite deep red. Furthermore, after a fairly long immersion, hydrogen gas evolution was significantly reduced and almost the entire surface was coated with copper. The mechanism of precipitation on the surface is currently under research, but in principle the copper deposited on the surface is equivalent to a type of plating (that is, the copper that has become ions is reduced and deposited), and the copper deposited on the surface It is thought that some of the atomic copper present in the stainless steel is liberated from the lattice of the stainless steel due to the dissolution of iron, etc., and is precipitated and adsorbed on the active dissolution surface. Copper deposited by this method has significantly superior adhesion compared to ordinary plating, and has excellent adhesion properties such as tight bending,
No peeling occurred in evaluation tests such as bending back from t/2 to 180°. In addition, regarding the type of acid used for dissolution, in the case of acids such as sulfuric acid and hydrochloric acid that generate hydrogen gas and cause active dissolution, the precipitation was equally good with both single acids and mixed acids, and copper-coated steel sheets were obtained. However, in the case of acids such as nitric acid, which passivates stainless steel or dissolves it by releasing nitrogen oxides such as NO gas, no copper precipitation was observed. Further, even in solutions with strong oxidizing effects such as solutions containing ferric chloride, no precipitation of copper was observed. In the case of a solution containing copper sulfate, copper precipitation was observed depending on the conditions, but the adhesion was poor. On the other hand, it was found that the relationship between the surface coverage of copper and the surface color shown in FIG. 2 changes from white to red as the amount of red precipitate, ie, copper, increases.
Furthermore, to the human eye, if the copper surface coverage is less than 5%, copper deposits can hardly be discerned, and it is only when the copper surface coverage exceeds 5% that it is felt that it has turned red, unlike the base stainless steel. It was confirmed that when this area was coated, it became indistinguishable from copper itself. Next, the limiting conditions of the present invention will be shown. The target steel was set at the upper limit because if more than 0.15% of C was added, it would exhibit quench hardening properties and would not be used for decorative purposes that require coloring. On the other hand, the lower the C content, the better the workability, but the lower limit was set at 0.005% because of the cost involved in reducing C. When Si is added in excess of 2%, it not only deteriorates the workability under heating but also increases the strength at room temperature.
The upper limit was set because it would be difficult to process for decoration. However, if it is less than 0.01%, deoxidation is insufficient and deterioration of workability and corrosion resistance due to inclusions is unavoidable, so the lower limit was set. If Mn is added in an amount exceeding 2%, quench hardenability appears, so the upper limit was set. However, if it is less than 0.01%, the unavoidable impurity S cannot be fixed as MnS, and FeS
is formed and the hot workability deteriorates, so the lower limit was set. P and S are unavoidable impurities and should be reduced from the viewpoint of corrosion resistance and hot workability, but both
If it is 0.04% or less, it will have no effect on the colorability of the present invention, so the upper limit was set at 0.04%. Ni, which is mixed as an unavoidable impurity, has no effect on the present invention, but if it is mixed in more than 0.6%, quench hardenability appears, so the upper limit was set. However, if it is reduced to less than 0.01%, the acid resistance will deteriorate, promoting surface roughness during the pickling and descaling process after hot processing, and impairing the beauty of the surface.
It was set as the lower limit. If the Cr content is less than 10%, the basic corrosion resistance of stainless steel will be insufficient, so 10% is set as the lower limit. In addition, if it exceeds 30%, the corrosion resistance improves accordingly, but the corrosion resistance exceeds the level required for the application of the present invention, and not only does the quality become excessive, but the hot workability deteriorates significantly, making it difficult to make stainless steel. The upper limit was set at 30% because it would be difficult to manufacture the product itself. When the Cu content is less than 2%, even if melted for a long time, copper will not precipitate and the red color characteristic of copper will not appear, but rather the black corrosion products that are seen when dissolving ordinary stainless steel in acid will appear. If it exceeds 20%, the hot workability deteriorates significantly, making it difficult to manufacture the stainless steel itself, so the upper limit is set at 20%. Al is essential as a deoxidizing agent for steel, but 0.2
If added in excess of %, hot and cold workability will be significantly degraded, so the upper limit was set. but,
If it is less than 0.001%, deoxidation is insufficient and deterioration of workability and corrosion resistance due to inclusions is unavoidable, so the lower limit was set. Furthermore, since colored stainless steel, which appears red to the human eye as a copper coating, has a copper phase covering 5% or more of the surface, 5% was set as the lower limit of the copper coverage. [Function] According to the present invention, it is possible to freely select an intermediate color between red and silvery white by changing the surface coverage of copper, and it is possible to obtain a colored stainless steel that has the warm feel and luxurious feel of copper. It will be done. In addition, since copper is present in the surface layer of the steel of the present invention, it is possible to generate a patina in the same way as with copper alone, and depending on the application, it is also possible to create a more calm and luxurious feel. [Example] Copper-added and copper-free 17Cr stainless steels having the chemical compositions shown in Table 1 were melted and hot-rolled, hot-rolled plate annealed, cold rolled, and cold-rolled plate annealed to a thickness of 1.0 mm.
A thin plate was manufactured. The thin plates were mirror-polished and then immersed in an acid solution under the conditions shown in Table 2. The color of the surface after washing with water is also shown in Table 2. Red precipitates were deposited on the dissolution surface corresponding to the present invention, and it was clearly recognized that it was coated with copper. Then, perform 180° close bending.

【table】

【table】

〔Effect of the invention〕

According to the present invention, it was possible to obtain a colored stainless steel that exhibits an intermediate color between the red of copper and the silvery white of stainless steel, and has a warm feel and a luxurious feel, without impairing the cleanliness inherent to stainless steel. . Furthermore, since copper is present on the surface, it is possible to generate a patina, and depending on the application, it is possible to create a more calm and luxurious look. As a result, it can be widely applied to interior and exterior parts of buildings, household goods, kitchen goods, etc. As described above, the present invention makes it possible to provide stainless steel with functions not previously available, which not only expands the range of materials to choose from, but also has the potential to create new uses, which has enormous industrial and social effects. There are things that aren't there.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of copper added in steel and the color of the surface after acid dissolution. FIG. 2 is a diagram showing changes in red hue depending on the degree of surface coverage of copper.

Claims (1)

[Claims] 1. The substrate is C: 0.005% or more and 0.15% or less, Si: 0.01% or more and 2% or less, Mn: 0.01% or more and 2% or less, P: 0.04% or less, S: 0.04% or less, Ni: Stainless steel containing 0.01% to 0.6%, Cr: 10% to 30%, Al: 0.001% to 0.2%, Cu: 2% to 20%, with the balance being unavoidable impurities and iron. The copper phase precipitated on the surface accounts for 5% of the surface.
Colored stainless steel coated with copper, characterized by being coated with the above.