Colored stainless steel plate and colored stainless steel coil

Abstract

A color coating layer is formed on the surface of a stainless steel plate by a chemical coloring method or an electrolytic coloring method. Thereafter, a colored stainless steel plate having the color coating layer is cold-rolled, the thickness of the color coating layer is adjusted to between 0.05 μm and 1.0 μm, and an entire plate thickness is adjusted to 0.5 mm or less. By the cold rolling a Vickers hardness Hv is between 250 and 550 to form a deformed band. As surface roughness, an arithmetic average roughness Ra is adjusted to between 0.05 μm and 5.0 μm. In this manner, the strength and rigidity of a thin colored stainless steel plate can be secured, and a color stainless steel plate and a colored stainless steel coil which do not easily cause galling and are excellent in press moldability can be obtained.

Claims

1. A colored stainless steel plate, comprising: a stainless steel plate; and a color coating layer on the stainless steel plate having a thickness in a range of 0.05 μm to 1.0 μm, wherein a total thickness of the stainless steel plate and the color coating layer is equal to or less 0.5 mm, the color coating layer is formed by a hydro oxide of chromium, and the color coating layer has a Vickers hardness Hv in a range of 250 to 550.

2. A colored stainless steel coil obtained by winding the colored stainless steel plate according to claim 1 in the form of a coil.

3. The colored stainless steel plate according to claim 1, wherein the color coating layer has an arithmetic average roughness Ra in a range of 0.05 μm to 5.0 μm.

4. A colored stainless steel coil obtained by winding the colored stainless steel plate according to claim 3 in the form of a coil.

5. A colored stainless steel plate, comprising: a stainless steel plate; and a color coating layer on the stainless steel plate having a thickness in a range of 0.05 μm to 1.0 μm, wherein a total thickness of the stainless steel plate and the color coating layer is equal to or less 0.5 mm, the color coating layer is formed by a hydro oxide of chromium, and the color coating layer has a deformed band formed on a surface of the color coating layer by cold rolling, the deformed band having a wave-like striped pattern that is observable by an optical microscope or a scanning electron microscope.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a sectional view of an example of a colored stainless steel plate or a colored stainless steel plate according to the invention.

(2) FIG. 2 is a flow chart showing steps in manufacturing the colored stainless steel plate or the colored stainless steel band according to the invention.

(3) FIG. 3 is a flow chart showing an example of a chemical coloring step of the colored stainless steel plate according to the invention.

(4) FIGS. 4A and 4B are diagrams showing an example of a device used in a chemical coloring step and a hard film processing step of the colored stainless steel plate according to the invention, in which FIG. 4A is a diagram showing an example of a chemical coloring device which dips a stainless steel plate to color the stainless steel plate and FIG. 4B is a diagram showing a hard film processing step of performing hard film processing to the resultant stainless steel plate.

(5) FIGS. 5A and 5B are diagrams showing an example of an electrolytic coloring device used in an electrolytic coloring step of the colored stainless steel plate according to the invention, in which FIG. 5A is an illustration thereof and FIG. 5B is a diagram showing a bath thereof and a periphery thereof.

(6) FIG. 6 is a diagram showing an outline of a coil coloring method used in continuous coloring of the colored stainless steel strip according to the invention.

(7) FIG. 7 is a diagram of a 4-roller rolling machine used in a rolling step of the colored stainless steel strip according to the invention.

(8) FIG. 8A is a plan view of a vessel of a smart phone serving as an example using the colored stainless steel plate according to the invention.

(9) FIG. 8B is a perspective view of the vessel of the smart phone serving as an example using the colored stainless steel plate according to the invention.

(10) FIGS. 9A and 9B are diagrams showing a color coating layer surface of the colored stainless steel plate, in which FIG. 9A is a diagram showing a photograph obtained by photographing the color coating layer surface before rolling and FIG. 9B is a diagram showing a photograph obtained by photographing the color coating layer surface after rolling.

(11) FIG. 10 is a diagram showing a coloring principle of stainless steel.

(12) FIG. 11 is a diagram showing a relationship between a hardness and a rolling rate of stainless steel.

DESCRIPTION OF THE EMBODIMENTS

(13) As shown in FIG. 1, a color stainless steel plate 1 according to the invention of the present application has a color coating layer 11 on a surface of a stainless steel plate 10. The total thickness of the color stainless steel plate 1 including the stainless steel plate 10 and the color coating layer 11 is 0.5 mm or less, the thickness of the color coating layer 11 ranges from 0.05 μm or more to 1.0 μm or less, a Vickers hardness Hv on a surface 3 of the color coating layer ranges from 250 or more to 550 or less, a surface roughness of the surface 3 of the color coating layer ranges 0.05 μm or more to 5.0 μm or less as an arithmetic average roughness Ra.

(14) In the colored stainless steel plate 1, a deformed band 5 is formed by plastic deformation performed by cold rolling after coloring. Steps formed on the surface 3 of the color coating layer by the deformed band 5 make a fine unevenness, and recessed portions serve as oil sumps 7. Since oil drops of press forming oil used in press molding after cold rolling are held in the oil sumps 7, oil shortage of press lubricant may be prevented in press working to bring about lubricant effect in press working. The deformed band 5 can be observed as a wave-like striped pattern in an enlarged image obtained by an optical microscope or a scanning electronic microscope.

(15) The colored stainless steel plate, as shown in FIG. 2, first, a color coating layer is formed on the stainless steel plate surface by a chemical coloring method or an electrolytic coloring method (each of the methods is performed in a batch process). Alternatively, in a colored stainless steel strip serving as an uncut steel plate obtained before the colored stainless steel plate is cut out, on the stainless steel strip surface serving as an uncut steel plate obtained before the stainless steel plate is cut out, a color coating layer is formed by a coil coloring method (continuous coloring method) (coloring step 20). The colored stainless steel plate or the colored stainless steel strip having a thickness of 0.5 mm or less fabricated as described above is rolled by cold rolling (rolling step 21) to manufacture a colored stainless steel plate or a colored stainless steel strip on which a color coating layer is prepared to have a thickness of 0.05 μm or more to 1.0 μm or less. Furthermore, the colored stainless steel strip manufactured as described above is winded (winding step) to manufacture a color stainless steel coil.

(16) As described above, when a color stainless steel plate (including a colored stainless steel strip) or a colored stainless steel coil according to the invention of the present application is to be manufactured, a color coating layer is formed on the stainless steel plate (including stainless steel strip). The color coating layer can be formed by a batch process performed by a chemical coloring method or an electrolytic coloring method when the stainless steel plate is used, and can be formed by a continuous coloring method performed by a coil coloring method when the stainless steel strip is used.

(17) In the chemical coloring method, in an ordinary coloring method onto a stainless steel plate surface, the stainless steel plate is dipped in a high-temperature solution containing a high-concentration bichromate.sulfuric acid for about 10 minutes or more to 1000 minutes or less by a natural dipping method to form an oxide layer.

(18) The method called an inco (INCO) method, for example, as shown in FIG. 3, includes a degreasing step 30, a water washing step 31, a surface activating step 32, a water washing step 33, an oxidizing (coloring) step 34, a water washing step 35, a hard film processing (drying) step 36, a water washing step 37, and a drying step 38.

(19) FIGS. 4A and 4B show devices used in the oxidizing (coloring) step 34 and the hard film processing step 36, respectively. More specifically, FIG. 4A shows a chemical coloring device, and FIG. 4B shows a hard film processing device. The chemical coloring device is configured such that a stainless steel plate 45, for example, SUS304 is dipped in an oxidizing solution 43, for example, a solution obtained by dissolving chromium oxide CrO.sub.3 serving as a strong oxidant in sulfuric acid, filled in an outer tank 41 lined with a lining 42. The hard film processing device includes a tank similar to the coloring tank of the chemical coloring device, a platinum electrode 44 serving as a counter electrode of the stainless steel plate 45, and a DC power supply 46 applying a potential across the platinum electrode 44 and the stainless steel plate 45.

(20) In chemical coloring, in the degreasing step 30, oil, fat, and the like on the surface of the stainless steel plate 45 are removed by using alkali. In the water washing step 31, the alkali component remaining on the surface of the stainless steel plate 45 is removed by water washing. In the surface activating step 32, the degreased surface of the stainless steel plate 45 is well etched with 10% hydrochloric acid to activate the surface. In the water washing step 33, the hydrochloric acid component remaining on the surface of the stainless steel plate 45 is removed by water washing. In the oxidizing (coloring) step 34, by using the chemical coloring device as shown in FIG. 4A, the stainless steel plate 45 is dipped in 8% chromium oxide CrO.sub.3 and a sulfuric acid aqueous solution to oxidize the stainless steel plate 45 at a temperature of 80° C. and a spontaneous potential, i.e., without application of a potential for 5 to 15 minutes depending on the thickness of an oxide layer. In the water washing step 35, the chromium oxide CrO.sub.3 component and the sulfuric acid component remaining on the surface of the stainless steel plate 45 are removed by water washing. A hard film processing to improve corrosion resistance of the oxide layer (color coating layer) formed on the surface of the stainless steel plate 45 is performed in the hard film processing step 36. In the hard film processing step 36, a hard film processing device, as shown in FIG. 4B, having a tank similar to that in the oxidizing (coloring) step 34 is used, the stainless steel plate 45 is dipped in 5% chromium oxide CrO.sub.3 and phosphoric acid solution, and a potential is applied to the stainless steel plate 45 for 2 to 5 minutes such that a current density of 0.01 A/cm.sup.2 is obtained at ordinary temperature. In the water washing step 37, the chromium oxide CrO.sub.3 component and the phosphoric acid component remaining on the surface of the stainless steel plate 45 are removed by water washing. In the drying step 38, moisture on the surface of the stainless steel 45 is removed to finish all the steps.

(21) In the electrolytic coloring method, for example, an electrolytic coloring device 50 as shown in FIG. 5 is used. In the electrolytic coloring device 50, in an aqueous solution (liquid temperature of 50 to 90° C.) 66 filled in a bath 64 and obtained by adding chromium oxide CrO.sub.3 to a sulfuric acid aqueous solution or sulfuric acid, one output of a polarity changing switch 54 switching the polarities of a constant current power supply 52 is connected to a stainless steel plate 60 by a connecting tool 58a through an ammeter 56, and the other output of the polarity changing switch 54 is connected a counter-electrode plate 62 by a connecting tool 58b. The polarities of the constant current power supply 52 are alternatively switched by the polarity changing switch 54, and anode electrolytic treatment and cathode electrolytic treatment are alternately repeated every 5 seconds. With the treatment, an oxide layer (color coating layer) is formed on the surface of the stainless steel plate 60, and the stainless surface is colored. As the aqueous solution 66, an aqueous solution containing at least one of sodium hydrate and potassium hydrate and having a temperature of 80 to 100° C. may be used.

(22) The above is an example of the case of alternating electrolytic treatment.

(23) When the anode electrolytic treatment is performed as DC electrolytic treatment, the polarity changing switch 54 is fixed to an anode side. Alternatively, the polarity changing switch 54 may be omitted, the positive terminal of the constant current power supply 52 is connected to the stainless steel plate 60 by the connecting tool 58a through the ammeter 56, and the negative terminal of the constant current power supply 52 may be connected to the counter electrode plate 62 by the connecting tool 58b.

(24) When the cathode electrolytic treatment is performed as DC electrolytic treatment, the polarity changing switch 54 is fixed to the cathode side. Alternatively, the polarity changing switch 54 is omitted, the negative terminal of the constant current power supply 52 may be connected to the stainless steel plate 60 by the connecting tool 58a through the ammeter 56, and the positive terminal of the constant current power supply 52 may be connected to the counter-electrode plate 62 by the connecting tool 58b.

(25) The stainless steel plate can create various colors such as bronze, blue, gold, red and green by the colors of an interference film of a color coating layer containing chromium (hydro) oxide having 1.5 μm or less at most as a main component and the colors of the color coating layer itself.

(26) In this manner, the color stainless steel plate colored in the coloring step by the chemical coloring method or the electrolytic coloring method is cold-rolled in a rolling step by, for example, 4-roller rolling machine to form a deformed band. Furthermore, the color stainless steel plate is rolled by a coarsened roll as a final pass to simultaneously coarsen color layer forming surfaces formed on one or two surfaces of the color stainless steel plate.

(27) With the cold rolling after the coloring process, Vickers hardnesses Hv on the front and rear surfaces of the color stainless steel plate increase to 250 or more to 550 or less. The surface roughness of the roll in the final cold-rolling is controlled to make arithmetic average roughnesses Ra on both the surfaces 0.05 μm or more to 5.0 μm or less as surface roughnesses. Recessed portions of fine unevenness obtained by the deformed band 5 serve as the oil sumps 7 of press forming oil used in cold-rolling. Oil drops of press forming oil used in press molding after the cold rolling are held in the oil sumps 7 to prevent oil shortage. In addition, control of the surface roughness on the color surface obtained by coarsening the roll of the final rolling in the cold rolling further reinforces prevention of oil shortage of the press forming oil in the pressing. For this reason, the cold-rolled color stainless steel plate according to the present application is improved in press moldability and galling resistance. As a result, high-volume production capability is also improved.

(28) The coil coloring method, for example, as shown in FIG. 6, includes an uncoiler step 61, a degreasing step 63, a coloring tank step 65, and a coiler step 67. First, from a stainless steel coil obtained by winding a stainless steel band in the form of a coil, the stainless steel band is turned out in the uncoiler step 61. An oil film adhering to the surface of the turned-out stainless steel band is removed in the degreasing step 63. Thereafter, the degreased stainless steel band is continuously colored in the coloring tank step 65. The color stainless steel band after the continuous coloring is winded in the form of a coil in the coiler (winding) step 67 to obtain a color stainless steel coil.

(29) The colored color stainless steel band is turned out from the color stainless steel coil, and the rolling step is executed. In the rolling step, a color stainless steel band having a color coating layer formed by any one of the coloring methods, for example, a black color coating layer is cold-rolled. In the cold rolling, for example, a 4-roller rolling machine 70 as shown in FIG. 7 or a multistage rolling machine having stages larger than 4 is used. For example, in the 4-roller rolling machine, the color stainless steel band 1 turned out from the color stainless steel coil formed as described above passes between a pair of upper and lower work rolls (drive rolls) 71a and 71b rotationally driven by a motor 75 to perform cold rolling. The pair of upper and lower work rolls (drive rolls) 71a and 71b are supported by a pair of upper and lower backup rolls (non-driving rolls) 73a and 73b, respectively.

(30) FIG. 7 shows one reverse-type 4-roller rolling machine. However, this is merely an example, and cold-rolling in a cluster mill, Sendzimir mill, multistage rolling machine, or the like can be used without a particular problem. A plurality of rolling machines may be serially arranged, and special rolling machine, a special rolling technique, and a special rolling condition are not necessary. When dull rolling is performed, the rolling is performed in only a final pass.

(31) Cold rolling is performed by the 4-roller rolling machine to roll the color stainless steel plate by a coarsened roll as a final pass, thereby forming a deformed band. As a result, the front surface (front surface of the color coating layer) and the rear surface (surface on a side on which the color coating layer of the colored stainless steel strip is not formed) of the colored stainless steel strip are simultaneously coarsened, a thin color stainless steel strip in which the thickness of the color coating layer and the whole thickness are desired thicknesses can be obtained. By cold rolling after the coloring process, the Vickers hardnesses Hv of the front surface and the rear surface of the color stainless steel band increase to 250 or more to 550 or less. In addition, a fine unevenness having an arithmetic average roughness Ra of 0.05 μm or more to 5.0 μm or less as a surface roughness is observed on each of the front and rear surfaces of the colored stainless steel strip. Recessed portions of the fine unevenness obtained by the deformed band 5 serve as the oil sumps 7 of press forming oil used in cold rolling to prevent oil shortage, so that the color stainless steel band is improved in press moldability and galling resistance. As a result, high-volume production capability is also improved.

(32) Furthermore, the colored stainless steel strip cold-rolled by the 4-roller rolling machine 70 is winded on, for example, an iron core 78 by the coiler device 76 in the form of a coil (winding step) to obtain a color stainless steel coil 77.

(33) After the cold rolling, a correction process such as a leveler, a tension leveler, or tension annealing for the color stainless steel plate or the colored stainless steel strip may be necessary. These correction processes do not spoil the effect of the invention of the present application, and is included in the scope of rights of the invention of the present application.

(34) In the above explanation, the colored stainless steel plate obtained after the continuous coloring is temporarily winded in the form of a coil to form a colored stainless steel coil. Thereafter, the colored stainless steel strip is turned out from the colored stainless steel coil and then winded in the form of a coil again after cold rolling is executed, so that a color stainless steel coil is formed. However, a continuously colored color stainless steel band may be immediately cold-rolled, and the cold-rolled colored stainless steel strip may be winded in the form of a coil to form a colored stainless steel coil. Each of the series of processes does not spoil the effect of the invention of the present application, and is included in the scope of rights of the invention of the present application.

EMBODIMENTS

(35) By using steel plates of SUS304, SUS316, and SUS443J1, chemical coloring processes were performed under conditions shown in Table 1A. Electrolytic coloring processes were performed under conditions shown in Table 1B and Table 1C. As thicknesses of color coating layers, color coating thicknesses were adjusted by changing coloring process times. The thicknesses of the color coating layers were measured by sputtering performed by a high-frequency glow discharge emission surface analyzing device (GD-Profiler2 available from Horiba, Ltd.). In hardness measurement, with respect to a steel plate surface, an average of Vickers hardnesses at 5 points was measured by using a hardness measurement device (FM-ARS900 available from FUTURE-TECH CORP.), and a measurement load was set to 50 g. With respect to a surface roughness, an average of arithmetic average roughnesses Ra at 5 points was measured by using a surface roughness measurement device (HANDYSURF E-35A available from Tokyo Seimitsu Co., Ltd.).

(36) TABLE-US-00001 TABLE 1A Chemical coloring condition Reaction Coloring Coloring Temperature time condition method Chemical solution (° C.) (min.) Condition 1 Chemical CrO.sub.3 250 g/L 50-100 10-120 coloring H.sub.2SO.sub.4 500 g/L Aqueous solution

(37) TABLE-US-00002 TABLE 1B Anode Cathode Chemical current current Coloring Coloring solution density density condition method Polarity Chemical solution temperature (A/dm.sup.2) (A/dm.sup.2) Condition 2 Anode DC H.sub.2SO.sub.4 500 g/L 50-90° C. 0.04 — electrolytic Aqueous solution Condition 3 Anode DC CrO.sub.3 250 g/L 50-90° C. — 0.01-0.5 electrolytic H.sub.2SO.sub.4 500 g/L Aqueous solution

(38) TABLE-US-00003 TABLE 1C Anode Cathode Anode energization Cathode energization Chemical current time per unit current time per unit Coloring Coloring Chemical solution density alternating density alternating condition method Polarity solution temperature (A/dm.sup.2) cycle (sec.) (A/dm.sup.2) cycle (sec.) Condition 4 Alternating Alternating H.sub.2SO.sub.4 500 g/L 50-90° C. 0.2-0.5 0.1-15 0.2-0.5 0.1-15 electrolytic Aqueous solution Condition 5 Alternating Alternating CrO.sub.3 250 g/L 50-90° C. 0.1-0.3 0.1-15 0.2-0.4 0.1-15 electrolytic H.sub.2SO.sub.4 500 g/L Aqueous solution Condition 6 Alternating Alternating NaOH 40 g/L 50-90° C. 1.0 5 1.0 10 electrolytic Aqueous solution

Experimental Example 1

(39) Coloring processes were performed to steel plates of a BA material and a ½H material of SUS304 each having a thickness of 0.3 mm and 200-mm width×300-mm length under the conditions shown in Table 1A, Table 1B, and Table 1C. Thereafter, by using a small 4-roller rolling machine in a laboratory, reverse-type multi-pass cold rolling was performed to the steel plates to obtain 0.2-mm thicknesses at room temperature. On the other hand, by using steel plates of a BA material and a ½H material of SUS304 each having a thickness of 0.3 mm, cold rolling was laboratorily performed to obtain 0.2-mm thicknesses. Thereafter, coloring was performed under the condition in Table 1.

(40) As a galling resistance test evaluation method, a cylindrical swift deep drawing test was performed. In this case, a punch diameter was set to 40 mm, a punch progressing rate was set to 60 mm/min, a blank holding force was set to 12 kN, and blank diameters are changed into 72 mm, 78 mm, and 84 mm to perform the test. In order to easily detect a seizure difference, low-viscosity press forming oil (viscosity of 25 centistokes) was applied to perform the test, and the presence/absence of galling or the like was examined.

(41) Table 2 shows results of cylindrical swift deep drawing tests for the BA material and the ½H material of SUS304. In Table 2, with respect to galling characteristics, a material which is not galled in the cylindrical swift deep drawing test is indicated by “∘”, and a material which is galled is indicated by “x”. In Table 2, with respect press moldability, as a result of the cylindrical swift deep drawing test, a material which can perfectly pass drawing-out processing and is not cracked is indicated by “⊚”. In addition, a material which can perfectly pass drawing-out processing but is cracked at a punch corner portion is indicated by “∘”. Furthermore, a material which is cracked in the middle of drawing-out processing and cannot pass the drawing-out processing is indicated by “x”.

(42) In Table 2, an example in which the thickness of a color coating layer falls within the range of 0.05 μm or more to 1.0 μm or less and cold rolling is performed after a coloring process is used as the example. On the other hand, an example in which the thickness of a color coating layer falls outside the range of 0.05 μm or more to 1.0 μm or less or an example in which the thickness falls within the range and a coloring process is performed after cold rolling is used as a comparative example.

(43) TABLE-US-00004 TABLE 2 Thickness Arithmetic Vickers of color average Cold-rolling hardness Coloring coating roughness Steel type method Hv Coloring method condition layer (μm) (Ra .Math. μm) Comparative SUS304 BA Cold rolling 450 Electrolytic coloring Condition 4 0.04 0.02 example material after coloring Comparative process Chemical coloring Condition 1 0.04 0.03 example Example Electrolytic coloring Condition 2 0.05 0.03 Example Electrolytic coloring Condition 3 0.12 0.02 Example Chemical coloring Condition 1 0.13 0.03 Example Electrolytic coloring Condition 6 0.35 0.02 Example Electrolytic coloring Condition 5 0.52 0.03 Example Electrolytic coloring Condition 5 0.84 0.02 Example Electrolytic coloring Condition 5 0.95 0.02 Comparative Electrolytic coloring Condition 5 1.05 0.02 example Comparative Coloring 452 Electrolytic coloring Condition 5 0.04 0.03 example process after Electrolytic coloring Condition 6 0.10 0.03 cold rolling Electrolytic coloring Condition 5 0.55 0.02 Comparative SUS304 Cold rolling 520 Chemical coloring Condition 1 0.04 0.02 example 1/2H after coloring Example material process Chemical coloring Condition 1 0.06 0.02 Electrolytic coloring Condition 4 0.15 0.03 Electrolytic coloring Condition 4 0.45 0.03 Comparative Coloring 523 Electrolytic coloring Condition 3 0.04 0.02 example process after Electrolytic coloring Condition 3 0.07 0.02 cold rolling Electrolytic coloring Condition 3 0.14 0.02 Blank diameter (mm) 72 78 84 Galling Galling Galling Press characteristics Press moldability characteristics Press moldability characteristics moldability Comparative X X X X X X example Comparative X X X X X X example Example ◯ ◯ ◯ ◯ ◯ ◯ Example ◯ ⊚ ◯ ⊚ ◯ ⊚ Example ◯ ⊚ ◯ ⊚ ◯ ⊚ Example ◯ ⊚ ◯ ⊚ ◯ ⊚ Example ◯ ⊚ ◯ ⊚ ◯ ⊚ Example ◯ ⊚ ◯ ⊚ ◯ ⊚ Example ◯ ⊚ ◯ ⊚ ◯ ⊚ Comparative X X X X X X example Comparative X X X X X X example ◯ ⊚ ◯ X ◯ X ◯ ⊚ ◯ X ◯ X Comparative X X X X X X example Example ◯ ◯ ◯ ◯ ◯ ◯ ◯ ⊚ ◯ ⊚ ◯ ◯ ◯ ⊚ ◯ ⊚ ◯ ◯ Comparative X X X X X X example ◯ ◯ ◯ X X X ◯ ◯ ◯ X X X

(44) In this experiment, a limiting drawing ratio is small because low-viscosity press forming oil is used. On the other hand, in Comparative example, it is clarified that, when the thickness of the color coating layer is less than 0.05 μm, galling occurs at a punch corner portion by seizure between the stainless steel plate and a press mold to deteriorate press moldability. In contrast to this, in the embodiments of the present invention, any galling was not observed. In addition, even though a blank diameter increases to make the press moldability severe, the press moldability and the deep drawing characteristics are considerably preferable more than those of Comparative example in which coloring is performed after cold rolling.

Experimental Example 2

(45) By using steel plates of a BA material having a 0.3-mm thickness of SUS316 and SUS443J1, electrolytic coloring was performed under conditions in Table 1, and the thicknesses of color coating layers were also changed. Thereafter, multi-pass cold rolling was performed to laboratorily obtain a 0.2-mm thickness. In the final pass of cold rolling, steel plates in which surface roughnesses of roll surfaces were changed at 8 levels by shot blast or electrolytic etching were used, and arithmetic average roughnesses Ra on the surfaces of color coating layers of cold-rolled color stainless steel plates were changed. Press moldabilities were evaluated by using these steel plates. A cylindrical swift deep drawing test was performed as a press moldability test to calculate a limiting drawing ratio. In this case, low-viscosity press forming oil (viscosity of 25 centistokes) was used, a punch diameter was set to 40 mm, a punch progress rate was set to 60 mm/min, a blank holding force was changed within the range of 12 kN or more to 20 kN or less, and a blank diameter was changed within the range of 60 mm or more to 100 mm or less to perform the test.

(46) In a deep drawing test, a ratio of blank diameter/punch diameter serves as a drawing ratio, and a limit value at which the steel plate can be drawn without being broken is a limiting drawing ratio. Since the punch diameter is constant, when the blank diameter increases, deep drawing becomes difficult. As a matter of course, when the limiting drawing ratio is high, deep drawing characteristics are good.

(47) These results are shown in Table 3. With respect to galling resistance, a color coating layer having a layer thickness of 0.05 μm or more is effective. However, it is clear that, when the arithmetic average roughness Ra falls within the range of the scope of claims of the present invention, each of the steel types has a very high limiting drawing ratio.

(48) In this Table 3, an example in which the thickness of a color coating layer falls within the range of 0.05 μm or more to 1.0 μm or less and an arithmetic average roughness is 0.05 μm or more to 5.0 μm or less is used as the example. In contrast to this, an example in which the thickness of a color coating layer falls outside the range of 0.05 μm or more to 1.0 μm or less or an arithmetic average roughness falls outside the range of 0.05 μm or more to 5.0 μm or less is used as the comparative example.

(49) TABLE-US-00005 TABLE 3 Arithmetic average Thickness of color roughness of Limiting Presence/absence Steel type Hv coating layer surface, Ra (μm) drawing ratio of galling Comparative SUS316 349 0.04 0.03 1.70 Presence example Comparative 0.06 0.04 1.75 Absence example Example 0.05 0.11 1.95 Absence Example 0.15 0.04 1.90 Absence Example 0.16 0.15 2.00 Absence Example 0.25 0.56 2.05 Absence Example 0.26 4.8 2.00 Absence Comparative 0.21 5.5 1.75 Absence example Comparative SUS443J1 275 0.04 0.04 1.75 Presence example Example 0.09 0.15 1.95 Absence Example 0.21 0.60 2.05 Absence Example 0.26 1.50 2.10 Absence Example 0.23 4.90 2.05 Absence Comparative 0.28 5.05 1.85 Absence example

Experimental Example 3

(50) A steel band (about 300 kg) of a BA material having a width of 320 mm and a thickness of 0.3 mm of SUS304 was divided by four divided steel strips, and two of the four divided steel strips were electrolytically colored under the conditions in Table 4 and had color coating layers having thicknesses set at two levels. Cold rolling was performed by using a 4-roller rolling machine (work roll diameter of 80 mm), and the surface roughness of the roll in the final pass was adjusted to obtain a steel plate having a thickness of 0.2 mm. On the other hand, the remaining two of the four divided steel strips were cold-rolled in the same manner as described above to form steel strips having two levels of surface roughnesses and electrolytically colored under the conditions in Table 4 to obtain two levels of color coating layer thicknesses. As evaluation of press moldability and galling, the same cylindrical swift deep drawing test as in Experimental Example 2 was performed to calculate a limiting drawing ratio, so that the presence/absence of galling was checked.

(51) TABLE-US-00006 TABLE 4 Anode Anode energization Cathode Cathode Total current time per unit current energization energization Coloring Chemical density alternating density time per unit process method Polarity solution (A/dm.sup.2) cycle (sec.) (A/dm.sup.2) cycle (sec.) time (min.) Alternating Alternating H.sub.2SO.sub.4 500 g/L 0.2-0.5 0.1-15 0.2-0.5 0.1-15 5-60 electrolyte Aqueous solution

(52) These results are shown in Table 5. In this Table 5, an example in which the thickness of a color coating layer falls within the range of 0.05 μm or more to 1.0 μm or less and cold rolling is performed after a coloring process is used as the example. An example in which the thickness of a color coating layer falls outside the range of 0.05 μm or more to 1.0 μm or less or an example in which the thickness falls within the range and a coloring process is performed after cold rolling is used as the comparative example.

(53) In Comparative Example 3-1 in which the layer thickness of the color coating layer is small, galling occurs. In Comparative Example 3-2 in which coloring is performed after cold rolling, galling does not occur because the layer thickness of the color coating layer is sufficient. However, when the arithmetic average roughness is adjusted within the range of the scope of claims, a limiting drawing ratio is somewhat improved. The limiting drawing ratio is low as in Comparative Example 3-1. On the other hand, in each of Examples 3-1 and 3-2, galling does not occur. It is understood that the limiting drawing ratio in Example 3-2 in which the arithmetic average roughness is adjusted within the range of the scope of claims is very high.

(54) TABLE-US-00007 TABLE 5 Thickness of Arithmetic average Cold rolling color coating roughness Ra Limiting method layer (μm) (μm) Hv drawing ratio Galling Comparative Coloring process 0.04 0.04 425 1.75 Presence example 3-1 after cold rolling Comparative Coloring process 0.25 0.55 430 1.85 Absence example 3-2 after cold rolling Example 3-1 Cold rolling after 0.16 0.03 440 2.05 Absence coloring process Example 3-2 Cold rolling after 0.41 0.46 435 2.20 Absence coloring process

Experimental Example 4

(55) A vessel for smart phone was manufactured by way of trial by using Example 3-2 in Table 5. FIG. 8A and FIG. 8B are diagrams showing a trial product of the vessel for smart phone. In the drawings, a vessel 80 has, for example, has an approximately rectangular base 81 having a height of 137 mm, a width of 74 mm, and a rising (thickness) of 1 mm. Three peripheral edges 82 including long sides S1 and S3 of the base 81 and one short side S2 adjacent to the long sides form a narrow-frame shape bent to slightly protrude in vertical directions to the main surface of the base 81. A peripheral edge 83 of the remaining short side S4 of the base 81 corresponds to the bottom surface of the smart phone. The peripheral edge 83 has a large width unlike the narrow-frame shape of the peripheral edges 82. Corner portions C1 and C2 of the base 81 are cutouts cut at 45 degrees. Support portions 84 and 85 near the corner portions and a support portion 86 formed at a position slightly distant from the support portion 84 is wider and higher than the peripheral edge 82. This shape is a shape suitable for engagement with the smart phone body.

(56) As described above, the vessel for smart phone, unlike a building material required to have surface flatness, is required to satisfy both a small thickness and high strength. Even in the vessel for smart phone can be achieved by press working of a colored stainless steel plate. At this time, according to the manufacturing method, galling does not easily occur, and press moldability is also improved. For this reason, even though the shape near the corner portion is complicated, working can be performed without deteriorating productivity. In addition, a vessel colored in a color except for black can be achieved by changing the thickness of the color coating layer.

(57) A stainless steel plate having a thickness of 0.5 mm or more can also be coarsened and colored.

(58) As described above, although the embodiment of the present invention is disclosed in the above description, the present invention is not limited to the embodiment.

(59) More specifically, the embodiment as described above can be variously changed with respect to mechanisms, shapes, materials, quantities, positions, arrangements, and the like without departing from the technical idea and the scope of the present invention, and these changes are included in the present invention.

(60) For example, a colored stainless steel plate according to another embodiment of the invention of the present application is a colored stainless steel plate including a stainless steel plate having at least one main surface to be colored and a color coating layer formed on the main surface to be colored of the stainless steel plate, wherein the colored stainless steel plate is a plastic deformed laminated body in which main surfaces are adjusted in hardness by plastic deformation performed by cold rolling to control the hardness of at least one main surface and the thickness of the color coating layer, and fine unevenness serving as oil sumps of press forming oil is formed on at least one main surface by the cold rolling.

(61) The fine unevenness is formed by coarsening at least one main surface of the plastic deformed laminated body by the cold rolling.

(62) The coarsening is performed such that a deformed band formed in the plastic deformed laminated body by cold molding forms steps in at least one main surface of the plastic deformed laminated body.

(63) Furthermore, the deformed band is formed such that the cold rolling is executed to the plastic deformation laminated body by a mill roll having a coarsened surface.

INDUSTRIAL APPLICABILITY

(64) A color stainless steel plate, a color stainless steel coil, and a method of manufacturing the same according to the invention are used in press products press-molded by molds in an application of molded articles requiring high strength and high rigidity of thin color stainless. According to the invention, since a color cold-rolled thin stainless steel plate or thin steel band which does not easily cause galling and is excellent in press moldability can be obtained, the life time of a press mold or the like and productivity are improved to considerably contribute to metal working industry segments.

REFERENCE NUMERALS

(65) 1 colored stainless steel plate 3 surface of color coating layer 5 deformed band 7 oil sump 10 stainless steel plate 11 color coating layer 20 coloring step 21 rolling step 30 degreasing step 31, 33, 35, 37 water washing step 32 surface activating step 34 oxidizing step 36 hard film processing step 38 drying step 41 outer tank 42 lining 43 oxidizing solution 44 platinum electrode 45 stainless steel plate 46 DC power supply 50 electrolytic coloring device 52 constant current power supply 54 polarity changing switch 56 ammeter 58a, 58b connecting tool 60 stainless steel plate 61 uncoiler step 62 counter-electrode plate 63 degreasing step 64 bath 65 coloring tank step 66 aqueous solution 67 coiler step 70 four-roller rolling machine 71a, 71b work roll 73a, 73b backup roll 75 motor 76 coiler device 77 colored stainless steel coil 78 core 80 vessel 81 base 82, 83 peripheral edge 84, 85, 86 support portion 100 stainless steel 101 stainless material 102 oxide layer S1, S3 long side S2, S4 short side C1, C2 corner portion