JP2711953B2 - Chrome plated steel sheet with excellent gloss and corrosion resistance and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a chromium-plated steel sheet, and more particularly, to a chromium-plated steel sheet having excellent gloss and corrosion resistance of a processed portion, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, there are steel sheets and steel strips which have been subjected to metal plating with a glossy surface, which are obtained by plating zinc, tin, aluminum, nickel and copper by a thermal or electrolytic method. For naked indoor use, decorative chrome-plated products and stainless steel plates, which are plated after processing, are often used instead of surface-treated steel plates.

For this reason, various relatively inexpensive pre-plated steel sheets and steel strips have been disclosed as plated steel sheets having excellent surface gloss and corrosion resistance. Particularly, a nickel-plated steel sheet discloses a steel sheet subjected to a diffusion treatment after nickel plating, and a Zn-Ni alloy-plated steel sheet further using this steel sheet as a base. For example, (1) JP-A-57-171692 discloses that the plating amount is 15
g / m ² (approximately 1.7 μm) or less, and then subjected to permeation and diffusion to form an Fe—Ni alloy layer, thereby reducing corrosion current caused by electrical contact with the surface Zn—Ni alloy plating layer. In addition, the corrosion resistance, paintability and weldability have been improved to prevent corrosion in automotive body applications. (2) JP-A-61-235594 discloses that 9 to 62 g / m ² per side is used.
After nickel plating, at 600-800 ° C
Fe-Ni having a thickness of 4 μm or less in which a diffusion treatment is performed for 15 hours and the steel base of the plated steel sheet and the nickel plating layer are firmly bonded.
Workability and corrosion resistance are improved by forming an alloy layer and increasing the adhesion of the plating layer. Japanese Patent Application Laid-Open No. 62-243714 discloses (3) a nickel-plated steel sheet having a further gloss. This is a method in which a stainless steel sheet is subjected to a dull nickel plating, then diffusion annealing and then gloss-finished by temper rolling and buff polishing, and its main purpose is to impart electrical conductivity to the stainless steel sheet. Among them, (1) is a steel sheet excellent in corrosion resistance by Zn-Ni alloy plating of the surface layer, but is inferior in glossiness. In the method (2), the corrosion resistance is improved by diffusion. The nickel-plated diffused steel sheet was overhanged by 5 mm with an Erichsen tester, and the salt spray test was carried out. As a result, red rust occurred in 20 hours, and the corrosion resistance was insufficient for naked indoor use and the gloss was poor. Have. (3) is excellent in both corrosion resistance and gloss, but has a problem that the price is high because a stainless steel plate is used for the base material.

In order to further improve the corrosion resistance of nickel-plated steel sheets, there are many chromium-plated surface-treated steel sheets on which chromium is formed, including "canned steel sheets having excellent corrosion resistance", including those for cans having different purposes. It has been disclosed. For example, (4) JP-A-61-76660 discloses that after coating a steel plate surface with nickel to a thickness of 2 to 10 μm,
A steel plate plated with chrome to a thickness of 2 to 10 μm is 800
A steel sheet having excellent corrosion resistance is obtained by heat treatment at a temperature of about 1,200 ° C. Also, (5) JP-A-61-79
758 discloses a glossy surface layer chromium steel sheet, but nickel or chromium is continuously deposited or sputtered in a vacuum chamber instead of an electroplating method, for example, nickel having a thickness of 10 μm and chromium having a thickness of 23 μm are deposited. After being adhered, nickel and chromium are further diffused into the base iron in an alloying furnace to obtain a portion having a Ni-Cr alloy layer with a glossiness equal to that of stainless steel. But,
In the method (4), if the heat treatment is performed in a general non-oxidizing atmosphere, the chromium on the surface is oxidized. Therefore, the method needs to be performed in a reducing atmosphere or a hydrogen atmosphere.
Plating to 10 μm requires a large electrolytic cell and rectifier due to low plating current efficiency, and increases the manufacturing cost. Also, the method (5) has a drawback that the amount of adhesion is large and the equipment cost and the production cost are high.

[0005] Although there have been few reports on glossy chromium-plated steel sheets, this is because the chromium-plated layer is hard and excellent in wear resistance but inferior in toughness.
Cracks are formed in the plating layer, and the corrosion resistance of the processed part is extremely deteriorated. Another reason is that when continuously manufacturing wide steel sheets such as steel sheets, the cathode generated during plating is intermittently energized using multiple tanks. This is presumably because the film becomes uneven and surface color abnormalities easily occur.

As a countermeasure for the latter color tone abnormality, a two-step current plating method and a strip which perform plating at a low current density at the time of plating in the second and subsequent tanks to make the cathode film uniform and then perform plating at the original current density are known. It has been reported that the chromium plating electrolytic bath is washed with sulfuric acid each time it leaves the electrolytic bath, the cathode film is completely removed, and then the chromium plating is continued.However, any of these methods requires an extra treatment tank or rectifier. In addition, there is a disadvantage that the equipment cost and the production price are high.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive chromium-plated steel sheet which solves the above-mentioned drawbacks, that is, has a high glossiness by electroplating and has excellent corrosion resistance in a processed portion, and a method of manufacturing the same. is there.

[0008]

SUMMARY OF THE INVENTION The present invention relates to (a) a low-carbon steel sheet or a strip of low-carbon steel having a thickness of 1 to 4 μm as cold rolled or after annealing and temper rolling. After producing semi-bright nickel by electrolytic plating,
By diffusing at a temperature of 450 ° C. or more and 850 ° C. or less in a non-oxidizing atmosphere (in the case of using an unannealed material as a plating base plate, it also serves as a recrystallization treatment), and at least one surface diffuses the base iron to the surface layer Without plating, a part of the plated nickel is formed into a Ni—Fe alloy layer having a thickness of 0.5 to 4 μm, and further, a thickness of 0.8 to 4 μm is formed on one or both sides where the base iron does not diffuse to the surface layer. Bright nickel plating of 2 μm and bright chrome plating of 0.05 to 0.15 μm in thickness are sequentially generated (see FIG. 1), and (b) one or both sides of the bright chromium plating layer further provided with bright nickel plating the by forming a hydrated chromium oxide per side 5 to 25 mg / m ^2, chromium plated steel sheet and strip having more excellent gloss and processing corrosion resistance is further improved corrosion resistance (FIG. 2 ginseng ) And its is a manufacturing method. Hereinafter, the present invention will be described in detail.

[0009] The plating base plate component may be a low carbon steel generally used for surface-treated steel plates such as tinplate and TFS (tin-free steel), and is not particularly limited. After cold rolling manufactured in a normal process, a steel sheet which has been subjected to annealing or temper rolling can be used as it is, but there is a relationship between the surface roughness of the original sheet and the gloss after plating.

FIG. 3 shows a 1 μm thick plate directly on a low carbon steel plate.
In this figure, the effect of the roughness of the original plate on the surface gloss when bright nickel plating is performed is described. The glossiness was measured using a gloss meter “VG-2PD” manufactured by Nippon Denshoku Co., Ltd. (reflection angle: 20
The average roughness of the original plate is 0.2 μm
When it exceeds, the glossiness after plating sharply decreased. The original plate roughness is preferably as small as possible for glossiness.
If the thickness is less than μm, it is uneconomical in terms of surface scratches and productivity during coil transfer. On the other hand, if the thickness is 0.2 μm or more, the desired glossy steel sheet cannot be obtained even if bright nickel plating is performed in the subsequent step. Therefore, it is recommended that the original plate has an average roughness of 0.2 μm or less, preferably 0.05 to 0.10 μm.

[0011] The plating base plate is subjected to electroless plating with a matte or semi-bright nickel plating having a thickness of 1 to 4 µm. The conditions of the plating bath are not particularly limited, and a general watt bath or sulfamic acid bath is used. Any other plating bath may be used. If the Ni coating amount is less than 1 μm, sufficient corrosion resistance cannot be obtained even if the diffusion process in the next step is performed. On the other hand, if the thickness is more than 4 μm, the production cost increases and the price becomes a problem in terms of application.

Next, in order to improve corrosion resistance by reducing plating pinholes and to improve workability by removing distortion of the plating layer,
Diffusion annealing is performed, but when the plating base sheet is an unannealed material, it can also serve as a recrystallization treatment. This diffusion process, in general non-oxidizing atmosphere for preventing oxidation of the end surface and the plating pinhole nickel plating layer and the plating is not generated, for example, N ₂ gas, Ar gas, H ₂ gas further H ₂ -N ₂ mixed gas atmosphere, but a box type annealing furnace,
It can be carried out using any of a continuous annealing furnace.

The diffusion conditions, ie, the annealing temperature and time,
It is appropriately determined depending on the annealing furnace to be used, the chemical composition of the nickel-plated steel sheet, the amount of plating film, the target material, the thickness of the alloy layer, and the like. The lower limit of the diffusion is that the thickness of the diffusion layer is 0.5 μm.
The above conditions and the upper limit are determined under conditions that do not allow the base iron to diffuse to the surface layer through nickel plated on one or both sides requiring high corrosion resistance. Although the diffusion rate of nickel has been reported in the literature as experimental results, various investigations have shown that the lower limit temperature is higher than the recrystallization temperature (about 550 ° C) when using an unannealed steel sheet, When a tempered rolled steel sheet was used, the temperature was preferably 450 ° C. or more and the upper limit was 850 ° C. or less. If the temperature is lower than 450 ° C., the diffusion rate of nickel becomes slow. As a result, the diffusion takes a long time, resulting in poor productivity. If the temperature is higher than 850 ° C., the diffusion rate of nickel becomes too high, and it is difficult to control the thickness of the nickel diffusion layer. And the structure of the steel itself becomes coarse and the mechanical properties deteriorate.

FIG. 4 shows the results of a survey on the diffusion conditions of the nickel-plated steel sheet and the thickness of the formed Fe—Ni alloy layer. The diffusion conditions for obtaining the Fe—Ni alloy layer without diffusing the base iron to the surface layer are shown in FIG. More configurable. For example,
When the nickel plating thickness is 1 μm and the soaking temperature is 800 ° C. in a continuous annealing furnace, it is 10 seconds to 24 seconds, and when the soaking temperature is 500 ° C. in a box type annealing furnace, 3 hours to 21 hours.
Time range. 800 when the plating amount is 4 μm
At ℃, the lower limit is 10 seconds, and the upper limit is 2 minutes or less in the case of a normal continuous annealing furnace. When the temperature is soaked at 600 ° C. in a box-type annealing furnace, the upper limit is 12 hours, but the lower limit is no particular problem under any normal operating conditions. However, from the viewpoint of corrosion resistance and productivity during annealing, the thickness of the alloy layer can be assured to be 0.5 μm where there is no plating pinhole, and if the plating distortion of the plating layer can be removed, the thicker the nickel layer, the better. Preferably, the diffusion conditions are determined so as to be 5 to 1.0 μm.

Bright nickel plating having a thickness of 0.8 to 2 μm is performed to brighten the nickel-plated steel sheet after the diffusion treatment. In this case, after the diffusion treatment, a method of performing an activation treatment by pickling and then performing plating, and after the diffusion treatment, performing a cold rolling or a temper rolling for material and shape correction, and then performing an activation treatment by degreasing and pickling. There is a method in which plating is performed thereon, but the latter method is preferable for improving gloss and shape. In this case, the surface roughness of the steel sheet is preferably 0.05 to 0.10 μm as described above. For the subsequent bright nickel plating, a general Watt bath, sulfamic acid bath, or any other bright nickel plating bath may be used, but if the thickness is 0.8 μm or less, a predetermined luster cannot be obtained. Further, even if it is formed with a thickness of 2 μm or more, the effect is saturated and uneconomical, so the range is 0.8 to 2 μm.
Preferably it is 1.0 to 1.5 μm.

Next, bright chromium plating is performed. In the case of a wide steel plate, plating is performed intermittently using multiple tanks, so that a plating bath or a surge bath for TFS (tin-free steel), which is generally used, is used. It is difficult to obtain a glossy chromium plating layer at a current density of several tens A / dm ² or more which is usually applied to TFS, but a part of hexavalent chromium in the bath is reduced to trivalent chromium using methyl alcohol or ethyl alcohol. By increasing the trivalent chromium ion concentration, it is possible to obtain a chromium plating layer with excellent brightness even in a relatively high current density region without intermittent plating without the above-described low current pretreatment and post treatment with sulfuric acid pickling. I found something.

The reason why the luster was obtained even in the high current density region by increasing the trivalent chromium ion concentration in the bath is that the metal chromium does not precipitate from the trivalent chromium ion. It is considered that the concentration of hexavalent chromium ions in the vicinity of the cathode surface is relatively reduced to suppress abnormal deposition of protruding metallic chromium, and as a result, the deposited surface has a function of forming a smooth and glossy film.

Tables 1 and 2 show the effect of increasing the amount of trivalent chromium ions on the surface gloss for obtaining bright chromium plating from a low concentration plating bath and a high concentration plating bath on a bright nickel steel sheet. is there. In the table, 1) Both nickel plating and chromium plating were plated in a circulation cell. 2) Electrolysis time "On: 4, Off: 10, cycle:
“5” indicates that “immersion in an electrolyte for 10 seconds after energization for 4 seconds” is repeated 5 times as one cycle. 3) Gloss determination symbols "○", "△", and "x" are gloss meters "VG-2PD" manufactured by Nippon Denshoku Co., Ltd. (reflection angle: 20).
The glossiness range measured in ゜) is shown, and the meaning is as follows. “○”: Glossiness at a reflection angle of 20 ° is 1200 or more “△”: Glossiness at a reflection angle of 20 ° is 1000 or more and less than 1200 “×”: Glossy at a reflection angle of 20 ° Degree less than 1000

[0019]

A chromium hydrated oxide can be formed on the chromium plating to further improve the corrosion resistance. This chromium hydrated oxide is formed in two ways, namely, a one-step method for removing a part of the chromium hydrated oxide layer formed at the same time as the formation of metallic chromium and a method for substantially removing the chromium hydrated oxide once formed. After that, any of the two-step methods of generating in another electrolytic cell can be used.
If this chromium hydrated oxide layer is thin, its effect is not recognized, and if it is excessive, the surface becomes darker and the gloss deteriorates.
m ² , preferably 10 to ²⁰ mg / m ² .

FIGS. 6 and 7 show glow discharge emission spectrometry (GD).
It is an example of a cross-sectional analysis result in the thickness direction of the treated steel sheet by S = Glow Discharge Spectroscopy). 6 shows the results of analysis of a 2 μm-thick nickel-plated undiffused steel sheet using an annealed and temper-rolled steel sheet, and FIG. 7 shows a 500 μC nickel-plated 2 μm-thick steel sheet.
Diffusion treatment for 8 hours, bright nickel plating 1.5 μm thick, bright chrome plating 0.1 μm thick and 15
It is the analysis result of the steel plate which performed the electrolytic chromic acid treatment of mg / m < ² >. In the analysis elements, S is a component element contained in the brightener added to the bright nickel plating bath and is attached to the coating together with metallic nickel.

[0022]

Example: Cold rolled steel sheet (sheet thickness: 0.3 mm,
Tables 3 to 5 show the results of various investigations using annealed and temper-rolled steel sheets (sheet thickness: 0.3 mm, surface average roughness: 0.1 μm) as plating base sheets. . After subjecting the base plate to a cleaning treatment and an activation treatment by alkali degreasing and sulfuric acid washing, as a base nickel plating, a matte plating is performed in a sulfamic acid bath, and a semi-glossy plating is performed in a Watts bath, and then diffusion treatment is performed. After the cleaning treatment and the activation treatment by alkali degreasing and sulfuric acid washing were performed again, bright nickel plating and bright chromium plating were continuously performed without drying. Further, the electrolytic chromic acid treatment was similarly performed continuously without drying after the bright chromium plating. Table 3 shows these electroplating conditions, and Tables 4 and 5 show the prepared film thickness and diffusion conditions and the evaluation results of the prepared plated steel sheets. The gloss and corrosion resistance in the table were evaluated by the following methods. * 1: Glossiness After plating, Nippon Denshoku Co., Ltd. gloss meter “VG-2PD”
(Reflection angle: 20 °)
Displayed with "x". The meaning is as follows. “○”: Glossiness at a reflection angle of 20 ° is 1200 or more “△”: Glossiness at a reflection angle of 20 ° is 1000 or more and less than 1200 “×”: Glossy at a reflection angle of 20 ° Degree less than 1000 * 2: Corrosion resistance Salted spray test (JI) on (1) flat plate part, (2) Erichsen 5 mm overhang part with plated steel sheet bare
SZ2371), and the red rust generation area ratio after 96 hours was measured and expressed by the following score. “A”: 0 to 0.1% “O”: 0.1 to 0.5% “Δ”: 0.5 to 2.5% “X”: 2.5% or more

[0023]

[0024]

As described above, the bright chromium-plated steel sheet manufactured by the method of the present invention is excellent in glossiness and work corrosion resistance and can be widely applied to general indoor use.

[0025]

[Brief description of the drawings]

FIG. 1 is a schematic view of a cross section of a coating of a single-sided chromium-plated steel sheet of the present invention.

FIG. 2 is a schematic view of a cross section of a coating film of a single-sided chromium-plated steel sheet in which a chromium hydrated oxide is formed on a surface layer of the present invention.

FIG. 3 is a drawing showing the effect of original plate roughness on surface gloss after bright nickel plating.

FIG. 4 shows diffusion annealing conditions and N in nickel-plated steel sheets.
It is a drawing which shows the relationship of i-Fe alloy layer thickness.

FIG. 5 is an example of an analysis result by glow discharge emission analysis of a cross section of an undiffused steel sheet after nickel plating.

FIG. 6 shows a diffusion treatment after nickel plating according to the method of the present invention;
Further, it is an analysis example by glow discharge optical emission spectrometry of a section of a chromium-plated steel sheet which has been subjected to bright nickel plating, bright chromium plating and electrolytic chromic acid treatment.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C25D 5/50 C25D 5/50

Claims (4)

(57) [Claims] 1. A low-carbon steel sheet is coated with nickel on both sides in a thickness of 1 to 4 μm, and then a 0.5 to 4 μm thick Ni—Fe alloy layer is formed without diffusing the base iron to the surface layer. And at least one surface has a thickness of 0.8 to 2
μm bright nickel plating and thickness 0.05-0.15μ
Chromium-plated steel sheet with excellent glossiness and corrosion resistance with a chrome-plated layer of m. ^2. The chromium chromium having excellent gloss and corrosion resistance according to claim 1, wherein 5 to 25 mg / m ² of hydrated chromium oxide per one side in terms of chromium metal is further formed on both sides of the plated steel sheet. Plated steel sheet. 3. The chromium hydrate oxide of 5 to 25 mg / m ² per one side in terms of chromium metal is further formed on the surface on the chromium plating layer side, which is excellent in glossiness and corrosion resistance. Chrome plated steel sheet. 4. After a low-carbon steel sheet is subjected to a matte or semi-bright nickel plating having a thickness of 1 to 4 μm, a part of the plated nickel is removed without the base iron of at least one surface being diffused to the surface layer. 0.5 to 4 μm thick Fe
-Brightness by sequentially forming bright nickel plating of 0.8 to 2 μm thickness and bright chrome plating of 0.05 to 0.15 μm thickness on one or both sides where the base iron does not diffuse to the surface layer as a Ni alloy layer For producing chrome-plated steel sheets with excellent corrosion resistance.