KR20210073117A - Colored stainless steel and manufacturing method thereof - Google Patents

Abstract

Disclosed are colored stainless steel and a manufacturing method thereof which can realize various colors. According to one embodiment of the present invention, the thickness of an oxide layer of the surface of the colored stainless steel is one among (a) to (e) below. The value of an L*a*b* color system in accordance with the thickness of the oxide layer can be (a) higher than or equal to 5nm and lower than 10nm (the a* value is higher or equal to -0.5 and lower than +0.25, and the b* value is higher than +2.5 and lower than or equal to +10), (b) higher than or equal to 10nm and lower than 15nm (the a* value is -1 to 0, and the b* value is higher than +10 and lower than or equal to +20), (c) higher than or equal to 15nm and lower than 30nm (the a* value is +0.25 to +15, and the b* value is +1 to +30), (d) higher than or equal to 30nm and lower than 40nm (the a* value is +5 to +20, and the b* value is -20 to -5), and (e) higher than or equal to 40nm (the a* value is higher than or equal to 0 and lower than +5, and the b* value is -10 to -5).

Description

Colored stainless steel and its manufacturing method {COLORED STAINLESS STEEL AND MANUFACTURING METHOD THEREOF}

The present invention relates to a colored stainless steel and a manufacturing method thereof, and more particularly, to a colored stainless steel capable of implementing various colors and a manufacturing method thereof.

In general, stainless steel is used where corrosion resistance is required, and recently, its use is expanding to industrial fields where visual elements such as interior and exterior materials, decoration, and metal crafts are important.

To this end, various color development methods have been developed to color or develop various colors on the surface of stainless steel to satisfy customers' aesthetic satisfaction, and representative methods include chemical coloring method and sputtering method.

Among them, the chemical coloring method is a method of obtaining a color by immersing stainless steel in an acidic solution to form an oxide such as chromium oxide or chromium hydroxide on the surface of the stainless steel, and hexavalent chromium is used. Hexavalent chromium causes pollution problems as a highly toxic environmental pollutant, and the cost of its manufacture, use, treatment, disposal, etc. continues to rise due to strong global regulations on the use of hexavalent chromium.

A sputtering method has been developed to solve this problem, but since the sputtering method is performed under a vacuum environment, the environmental conditions are difficult, continuous operation is impossible during coiling operation, and the production speed is slow, which limits the application of the mass production process. There is this.

Unexamined Patent Publication No. 1998-069090 (published date: October 26, 1998)

The present invention is devised to solve the problems of the above-described conventional method for color development of stainless steel, and while ensuring corrosion resistance of stainless steel, it does not cause environmental problems, and color stainless steel with improved production speed by continuous operation during coil operation and It is intended to provide a manufacturing method thereof.

As a means for achieving the above object, in the color stainless steel according to an example of the present invention, the oxide layer on the surface has one of the following (a) to (e) thickness values, and L* according to the thickness of the oxide layer The value of a*b* colorimetric system is (a) 5 nm or more and less than 10 nm: a* value is -0.5 or more and less than +0.25, b* value is more than +2.5 and less than +10, (b) 10 nm or more and less than 15 nm: a* value is -1 to 0, b* value greater than +10 +20 or less, (c) 15 nm or more and less than 30 nm: a* value is +0.25 to +15, b* value is +1 to +30, (d) 30 nm or more and less than 40 nm: a* value is +5 to +20, b* value is -20 to -5, (e) 40 nm or more: a* value: 0 to less than +5, b* value: -10 to - 5 can be satisfied.

In each colored stainless steel according to an embodiment of the present invention, the oxide layer may include a Fe-Cr composite oxide.

In addition, as another means for achieving the above object, the method for manufacturing a colored stainless steel according to an example of the present invention is to heat-treat a cold-rolled steel sheet to form an oxide layer having a thickness value of one of the following (a) to (e) on the surface and the value of the L*a*b* color system according to the thicknesses (a) to (e) of the oxide layer is (a) 5 nm or more and less than 10 nm: a* value is -0.5 or more and less than +0.25, and b* value is greater than +2.5 and less than +10, (b) greater than or equal to 10 nm and less than 15 nm: a* value is from -1 to 0, b* value greater than +10 and less than or equal to +20; (c) greater than or equal to 15 nm and less than or equal to 30 nm: a* value is + 0.25 to +15, b* value from +1 to +30, (d) 30 nm to less than 40 nm: a* value is +5 to +20, b* value is -20 to -5, (e) 40 nm or more : a* value: 0 or more and less than +5, b* value: -10 to -5 may be satisfied.

In each color stainless steel manufacturing method according to an example of the present invention, the temperature of the heat treatment may be 650 to 850 °C.

In the manufacturing method of each colored stainless steel according to an example of the present invention, the holding time of the heat treatment may be 10 to 100 seconds.

According to the present invention, various colors can be implemented on the surface of stainless steel by using the Fe-Cr composite oxide layer formed by oxidizing Fe and Cr contained in the base material through heat treatment after cold rolling annealing. Accordingly, the present invention secures the corrosion resistance of stainless steel and at the same time does not cause environmental problems because it does not use a chemical color development method in an acidic solution, and provides color stainless steel with improved production speed due to continuous operation during coil operation can do.

In addition, according to the present invention, since various colors are realized by oxidizing Fe and Cr contained in the base material, it is possible to improve durability due to excellent adhesion between the oxide and the base material.

1 is a graph showing changes in a* value and b* value according to the holding time of heat treatment when the temperature of heat treatment is 650°C.
2 is a photograph of the surface of Examples and Comparative Examples. 2A is a surface photograph of Comparative Example 1, FIG. 2B is Example 3, FIG. 2C is Example 6, and FIG. 2D is Example 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention are described below. However, the embodiment of the present invention may be modified in various other forms, and the technical idea of the present invention is not limited to the embodiment described below. Further, the embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art.

The terms used in this application are only used to describe specific examples. Therefore, for example, a singular expression includes a plural expression unless the context clearly requires it to be singular. In addition, terms such as "comprises" or "comprises" used in the present application are used to clearly indicate that there is a feature, step, function, component, or a combination thereof described in the specification, and other features It should be noted that it is not intended to preliminarily exclude the existence of elements, steps, functions, components, or combinations thereof.

Meanwhile, unless otherwise defined, all terms used herein should be regarded as having the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Accordingly, unless explicitly defined herein, certain terms should not be construed in an unduly idealistic or formal sense. For example, a singular expression herein includes a plural expression unless the context clearly dictates otherwise.

In addition, in this specification, "about", "substantially", etc. are used in or close to the numerical value when manufacturing and material tolerances inherent in the stated meaning are presented, and are used in a precise sense to aid the understanding of the present invention. or absolute figures are used to prevent unreasonable use by unscrupulous infringers of the mentioned disclosure.

In general, stainless steel means an alloy steel containing chromium. The rheological definition of stainless steel is an alloy steel containing 11% or more of chromium, but in this specification, "stainless steel" is interpreted as any alloy steel containing 9 to 30% by weight of chromium. When the Cr content is too low (less than 9% by weight), the growth rate of the Fe-Cr composite oxide is too fast, so it is difficult to control the surface color according to the heat treatment holding time. When the Cr content is excessively high than 30% by weight, Fe-Cr This is because, since the growth of the composite oxide is slow, the duration of heat treatment for realizing the color of the surface may be prolonged.

In addition, "color stainless steel" in the present specification means stainless steel in which a color is implemented according to the color development method of stainless steel disclosed in the present specification. However, at this time, the stainless steel is not interpreted limited to the stainless steel in which the color is implemented according to the color development method of some embodiments disclosed in the present specification, but those skilled in the art clearly from the technical idea disclosed in the present specification. All stainless steels that are colored in a perceptible way of color development.

In addition, each color in the present specification may be expressed using "color coordinates", and "color coordinates" means coordinates in the CIE Lab color space, which is a color value stipulated by the International Commission on Illumination (CIE). . An arbitrary position in the CIE color space may be expressed by three coordinate values L*, a*, b*.

Here, the L* value represents the brightness, and when L* = 0, it represents black, and when L* = 100, it represents white. In addition, the a* value indicates whether the color having the corresponding color coordinate is biased between pure red (pure magenta) and pure green (pure green), and the b* value indicates that the color having the corresponding color coordinate is pure yellow and Shows which side of pure blue is biased.

Specifically, the a* value has a range of -a to +a, the maximum value of a* (a* max) represents pure red (pure magenta), and the minimum value of a* (a* min) is pure green. (pure green). For example, a negative value of a* means a color biased toward pure green, and a positive value means a color biased toward pure red. When a*=80 and a*=50 are compared, it means that a*=80 is closer to pure red than a*=50. In addition, the b* value has a range from -b to +b. The maximum value of b* (b* max) represents pure yellow, and the minimum value of b* (b* min) represents pure blue. For example, a negative b* value indicates a color biased toward pure yellow, and a positive number indicates a color biased toward pure blue. When b*=80 and b*=50 are compared, it means that b*=80 is closer to pure yellow than b*=50.

Color stainless steel according to an embodiment of the present invention can implement various colors by controlling the thickness of the oxide layer on the surface. The oxide layer may include a Fe-Cr composite oxide, and in this specification, the Fe-Cr composite oxide means a composite oxide of Fe and/or Cr, and is interpreted as a concept including a single oxide of Fe and a single oxide of Cr.

For example, when the thickness of the oxide layer is less than 5 nm, a transparent color like the surface color of general stainless steel is implemented, and the color stainless steel desired by the present invention cannot be obtained.

For example, when the thickness of the oxide layer is 5 nm or more and less than 10 nm, a light brown color may be implemented. In this case, the a* value of the L*a*b* color space may be greater than or equal to -0.5 and less than +0.25, and the value of b* may be greater than or equal to +2.5 and less than or equal to +10.

For example, when the thickness of the oxide layer is 10 nm or more and less than 15 nm, brown color may be realized. In this case, the a* value of the L*a*b* color space may be -1 to 0, and the b* value may be greater than +10 and less than or equal to +20.

For example, when the thickness of the oxide layer is 15 nm or more and less than 30 nm, a dark brown color may be implemented. In this case, the a* value of the L*a*b* color space may be +0.25 to +15, and the b* value may be +1 to +30.

For example, when the thickness of the oxide layer is 30 nm or more and less than 40 nm, purple may be realized. In this case, the a* value of the L*a*b* color space may be +5 to +20, and the b* value may be -20 to -5.

For example, when the thickness of the oxide layer is 40 nm or more, blue may be realized. In this case, the a* value of the L*a*b* color space may be 0 or more and less than +5, and the b* value may be -10 to -5.

Referring to the above example, it can be seen that brown is implemented in a relatively wide thickness range compared to other colors in which the oxide layer has a thickness of 5 nm or more and less than 30 nm, so that the chromaticity of brown can be particularly finely adjusted.

According to an example, in the method of forming the oxide layer on the surface, the final cold-rolled steel sheet manufactured according to the general stainless steel manufacturing process is additionally heat-treated to oxidize Fe and Cr among the elements contained in the stainless steel base material to form a Fe-Cr composite oxide. A layer may be formed on the surface.

As used herein, the cold-rolled steel sheet means a cold-rolled steel sheet as a final product that has undergone cold rolling, annealing heat treatment, and pickling processes. However, it is necessary to note that this is for helping the understanding of the present invention, and the spirit of the present invention is not necessarily limited thereto. If it is obvious from the point of view of a person skilled in the art to mean a cold-rolled steel sheet as a final product, it corresponds to the cold-rolled steel sheet of the present invention.

The temperature of the heat treatment may be 650 to 850 °C according to an example. At a heat treatment temperature of less than 650 °C, the heat treatment holding time for surface color development is too long, so it may be difficult to apply the mass production process. On the other hand, at a heat treatment temperature exceeding 850° C., the surface color development is too fast, and color control may be difficult.

The holding time of the heat treatment corresponds to a key configuration capable of controlling the thickness of the oxide layer by growing the Fe-Cr composite oxide in the present invention. The holding time of the heat treatment may be 10 seconds to 100 seconds according to an example. If the holding time is less than 10 seconds, it may be difficult to realize the color because the time for surface color development is too short. On the other hand, if the holding time exceeds 100 seconds, it may be difficult to apply the mass production process due to a decrease in the production speed.

In addition, although the reasons for limiting the temperature and holding time of the heat treatment have been described above, it may be appropriately adjusted within a limited numerical range according to a desired surface color. Hereinafter, an example for appropriately adjusting the temperature and holding time of the heat treatment will be described.

The a* and b* values of the L*a*b* color system on the surface of the colored stainless steel according to the present invention change depending on the temperature and holding time of the heat treatment. According to an example of the present invention, it is possible to determine a suitable temperature and holding time of the heat treatment in consideration of the change trend of the a* value and b* value according to the temperature and the holding time of the heat treatment. Hereinafter, an example of controlling the holding time of the heat treatment when the temperature of the heat treatment is 650° C. will be described to help the understanding of the present invention, but it is necessary to note that the technical idea of the present invention is not limited thereto.

1 is a graph showing changes in the a* value and b* value according to the holding time of the heat treatment when the temperature of the heat treatment is 650 °C. Referring to FIG. 1 , in the brown region, the a* value and the b* value increased as the heat treatment time increased. In the dark brown region, the a* value increased as the heat treatment time increased, while the b* value decreased. In the purple and blue regions, the a* value decreased as the heat treatment time increased, while the b* value increased.

In addition, referring to FIG. 1 , it can be seen that the holding time of the heat treatment occupies most of the brown region and the dark brown region compared to the holding time of the entire heat treatment. This is because, when the temperature of the heat treatment is 650° C., the growth rate of the oxide layer according to the holding time of the heat treatment is relatively slower than when the temperature is high, so the degree of change in the surface color development is not large. In other words, when the temperature of the heat treatment is 650° C., since the specific gravity of the heat treatment holding time in the brown region and the dark brown region is large, the chromaticity of brown among colors can be finely adjusted by adjusting the heat treatment holding time. Referring to the above, it can be seen that it is preferable to control the temperature of the heat treatment to 650 to 750° C. from the viewpoint of being able to finely control the chromaticity of the brown color to be implemented.

Although not shown separately as shown in FIG. 1, in the section of the heat treatment temperature of 750 to 850° C., where the growth rate of the oxide layer is relatively fast, the specific gravity of the heat treatment holding time in the purple and blue regions increases, so the heat treatment holding time is adjusted to brown, Various colors such as purple and blue can be implemented. Referring to the above content, it can be seen that it is preferable to control the temperature of the heat treatment to 750 to 850 °C from the viewpoint that various colors can be implemented.

According to the present invention, various colors can be implemented on the surface of stainless steel by using the Fe-Cr composite oxide layer formed by oxidizing Fe and Cr contained in the base material through heat treatment after cold rolling annealing. Accordingly, the present invention secures the corrosion resistance of stainless steel and at the same time does not cause environmental problems because it does not use a chemical color development method in an acidic solution, and provides color stainless steel with improved production speed due to continuous operation during coil operation can do.

In addition, according to the present invention, since various colors are realized by oxidizing Fe and Cr contained in the base material, it is possible to improve durability due to excellent adhesion between the oxide and the base material.

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.

{Example}

In an embodiment of the present invention, STS430-based steel containing 13% by weight of Cr was used as stainless steel. However, it should be noted that the stainless steel of the present invention is not limited to the above-mentioned steel type. The reason is that if the stainless steel contains Fe and Cr, a Fe-Cr composite oxide can be formed through heat treatment, and the Fe-Cr composite oxide can be grown through the heat treatment holding time.

A cold-rolled steel sheet manufactured by using the above STS430-based steel type according to a conventional stainless steel manufacturing process was heat-treated according to the heat treatment conditions shown in Table 1 below to manufacture color stainless steel. The heat treatment was carried out in the atmosphere, and the a* and b* values were measured using a colorimeter.

In Table 1 below, the oxide layer thickness means the oxide layer thickness of the Fe-Cr composite oxide. In Table 1, the oxide layer thickness was measured using a Glow Discharge Spectrometer (GDS).

division heat treatment temperature
(℃) holding time (sec) a* value b* value Oxide layer thickness (nm) surface color Comparative Example 1 - - 0.05 1.14 3.5 Transparency Example 1 650 10 0.09 2.69 7.1 light brown Example 2 650 15 -0.04 6.9 9.6 light brown Example 3 650 20 -0.27 14.28 10.8 Brown Example 4 650 25 -0.25 17.5 12.1 Brown Example 5 650 30 0.27 21.42 16.5 mum Example 6 650 35 1.5 25.49 18.3 mum Example 7 650 60 9.8 1.4 23.5 mum Example 8 650 80 19.44 -18.01 36.7 purple Example 9 650 100 2.3 -5.7 45.2 blue Example 10 700 10 -0.35 7.83 8.4 light brown Example 11 700 30 2.42 26.81 19.5 mum Example 12 750 10 -0.72 12.86 10.6 Brown Example 13 750 30 10.08 9.69 20.1 mum Example 14 800 10 -0.62 15.04 11.8 Brown Example 15 800 30 8.81 -7.22 34.7 purple Example 16 850 10 -0.58 12.69 11.3 Brown Example 17 850 30 4.23 -9.52 43.4 blue

The physical properties of each invention example and comparative example steel having the alloy composition of Table 1 are evaluated below.

Referring to Table 1, Examples 1 to 17 satisfy the heat treatment conditions of the present invention, which are the heat treatment conditions of 650 to 850° C., and the heat treatment holding time of 10 to 100 seconds, and various colors were expressed. 2b, the surface of Example 3 is brown, and with reference to FIG. 2c, dark brown is implemented on the surface of Example 6, and with reference to FIG. 2d, purple is implemented on the surface of Example 8 Able to know.

On the other hand, Comparative Example 1, which was not subjected to heat treatment after cold rolling, had an oxide layer thickness of 3.5 nm and a thickness of an oxide layer of general stainless steel. This implementation could not obtain the color stainless steel desired by the present invention.

In the foregoing, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art will not depart from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

Claims (5)

The oxide layer on the surface has a thickness value of one of the following (a) to (e),
The value of the L*a*b* color system according to the thicknesses (a) to (e) of the oxide layer is
(a) greater than or equal to 5 nm and less than 10 nm: a* value greater than or equal to -0.5 and less than +0.25, and b* value greater than or equal to +2.5 and less than or equal to +10;
(b) greater than or equal to 10 nm and less than 15 nm: the value of a* is from -1 to 0, and the value of b* is greater than +10 and less than or equal to +20;
(c) greater than or equal to 15 nm and less than 30 nm: the a* value is from +0.25 to +15, and the b* value is from +1 to +30;
(d) greater than or equal to 30 nm and less than 40 nm: the a* value is from +5 to +20, and the b* value is from -20 to -5;
(e) 40 nm or more: a* value: 0 or more and less than +5, b* value: -10 to -5;
color stainless steel that satisfies According to claim 1,
The oxide layer is a colored stainless steel comprising a Fe-Cr composite oxide. An oxide layer having a thickness value of one of the following (a) to (e) is formed on the surface by heat-treating the cold-rolled steel sheet,
The value of the L*a*b* color system according to the thicknesses (a) to (e) of the oxide layer is
(a) greater than or equal to 5 nm and less than 10 nm: a* value greater than or equal to -0.5 and less than +0.25, and b* value greater than or equal to +2.5 and less than or equal to +10;
(b) greater than or equal to 10 nm and less than 15 nm: the value of a* is from -1 to 0, and the value of b* is greater than +10 and less than or equal to +20;
(c) greater than or equal to 15 nm and less than 30 nm: the a* value is from +0.25 to +15, and the b* value is from +1 to +30;
(d) greater than or equal to 30 nm and less than 40 nm: the a* value is from +5 to +20, and the b* value is from -20 to -5;
(e) 40 nm or more: a* value: 0 or more and less than +5, b* value: -10 to -5;
A manufacturing method of colored stainless steel that satisfies 4. The method of claim 3,
The temperature of the heat treatment is 650 to 850 ℃ method of producing a color stainless steel. 4. The method of claim 3,
The holding time of the heat treatment is a method of manufacturing a color stainless steel of 10 to 100 seconds.

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