DESCRIPTION
Title of the Invention
STEEL SHEET FOR CONTAINER EXCELLENT IN CORROSION
RESISTANCE
5
Technical Field
[0001]
The present invention relates to a steel sheet for
containers, in particular to a steel sheet for containers
10 which can be used for producing two-piece cans and threepiece
cans and is excellent in corrosion resistance,
adhesion, and weldability.
Background Art
15 [0002]
Containers made of iron used mainly in the field of
beverage cans may be classified as two-piece cans and
three-piece cans.
Two-piece cans are can bodies in which the can
20 bottom and the can wall have been formed as a single
piece, and are represented by DrD (draw and redraw) cans,
DI (drawing and ironing) cans, etc. These cans may be
formed by drawing, ironing, bending and reverse bending,
or a combination thereof. Steel sheets to be used for
25 these can bodies may include tin plates (Sn-plated steel
sheets) and TFS (electrolytic chromate-treated steel
sheets (tin-free steel)), and these steel sheets may be
used depending on the applications and processing methods
used therefor.
30 Three-piece cans are can bodies in which the can
wall and the can bottom thereof have been formed as
separate pieces. Three-piece cans may be mainly in the
form of welded cans in which the can wall is formed by
welding. As the material for the can wall, lightly
35 coated Sn-plated steel sheets and Ni-plated steel sheets
may be employed. As the material for the can bottom,
TFS, etc, may be employed.
- 2 -
#
[0003]
In both the two-piece can and the three-piece can,
the outside surface of the can is provided with printing,
in order to appeal to consumers for commercial value of
5 the canned goods. On the other hand, the inside surface
of the can is coated with a resin so as to ensure the
corrosion resistance of the can body. In the case of the
two-piece can in the prior art, after the formation of
the can body, the inside surface of the can is coated,
10 for example, by spraying and the outside surface of the
can is subjected to curved surface printing. Recently,
it is common to use laminated two-piece cans in which the
can is formed from a steel sheet which has preliminarily
been laminated with a PET film (Patent Document 1 and
15 Patent Document 2).
In addition, with respect to the welded cans for
constituting the three-piece cans, the can body is
hitherto produced by welding steel sheets, in which the
outside surface of the can, as well as the inside surface
20 of the can, has preliminarily been printed. However,
instead of the painting or painting finish, it is common
to use three-piece cans which are produced by using steel
sheets (i.e., laminated steel sheets), which have
preliminarily been provided with lamination with a
25 printed PET film (Patent Document 3 and Patent Document
4) .
[0004]
In the production of two-piece cans, a steel sheet
for a container is subjected to drawing, ironing, or
30 bending and reverse bending. In the production of threepiece
cans, a steel sheet for a container is subjected to
neck forming or flanging. Further, in some cases, the
steel sheet for a container is also subjected to
expanding for the purpose of imparting a design to the
35 can. Therefore, the laminated steel sheet used as a
steel sheet for a container must have excellent adhesion
to a film so that the laminated steel sheet can follow
- 3 -
these processes.
[0005]
Sn-plated steel sheets have excellent corrosion
resistance, even with respect to an acidic content, due
5 to the excellent sacrificial anticorrosive effects of the
Sn. However, Sn-plated steel sheets do not exhibit a
stable adhesion with a film because they have brittle Sn
oxides present on their outermost surface layer. As a
result, when Sn-plated sheets have been subjected to the
10 above-described processings, there are problems that
peeling of the film is caused, corrosion begins at sites
where the adhesion strength between the film and the
steel sheet is not sufficient.
[0006]
15 Thus, a Ni-plated steel sheet which not only has
excellent processability and adhesion, but also is
capable of being welded is used as a laminated steel
sheet for a container (Patent Documents 5). Ni-plated
steel sheets have been disclosed for a long time (for
20 example, Patent Documents 9). Some Ni-plated steel
sheets have dull surfaces as in the case of Sn-plated
steel sheets, while there are also ones which have been
subjected to bright plating by Ni plating methods in
which a brightening agent is added (Patent Document 6 and
25 Patent Document 7).
[0007]
However, since Ni does not exhibit any sacrificial
anticorrosive effect such as Sn, it is known that in the
case of Ni-plated steel sheets, highly corrosive
30 contents, such as acidic drinks, cause pitting corrosion
(or perforation corrosion), in which the corrosion grows
in the sheet depth direction due to defects in the Ni
plating layer, such as pinholes, leading to perforation.
Therefore, there has been a need to improve the corrosion
35 resistance of Ni-plated steel sheets. In order to reduce
pitting corrosion, a Ni-plated steel sheet was developed
in which the steel components were adjusted so that the
- 4 -
*
electric potential of a steel sheet to be plated was more
noble (Patent Document 8).
Citation List
Patent Document
5 [0008]
Patent Document 1
Japanese Unexamined Patent Publication (Kokai) No.
2000-263696
Patent Document 2
10 Japanese Unexamined Patent Publication (Kokai) No.
2000-334886
Patent Document 3
Japanese Patent No. 3,060,073
Patent Document 4
15 Japanese Patent No. 2,998,043
Patent Document 5
Japanese Unexamined Patent Publication (Kokai) No.
2007-231394
Patent Document 6
20 Japanese Unexamined Patent Publication (Kokai) No.
2000-26992
Patent Document 7
Japanese Unexamined Patent Publication (Kokai) No.
2005-149735
25 Patent Document 8
Japanese Unexamined Patent Publication (Kokai) No.
60(1985)-145380
Patent Document 9
Japanese Unexamined Patent Publication (Kokai) No.
30 56(1981)-169788
Summary of Invention
Technical Problem
[0009]
In the invention described in Patent Document 8, the
35 reduction of pitting corrosion has been accomplished with
effects, but there is a need for further improvement of
corrosion resistance. In addition, the invention
- 5 - t
described in Patent Document 8 specifies the steel
components in a limited range and is only applied to some
applications. Therefore, there is a need for a Ni-plated
steel sheet which can be applied to a wide variety of
5 contents and can shapes.
The present invention has been made in view of the
circumstances as described above and an object thereof is
to provide a steel sheet for a container excellent in
corrosion resistance.
10 Solution to Problem
[0010]
The present inventors have devoted themselves to
research and found that holding Co in a particular range
to a Ni plating layer results in the suppression of
15 pitting corrosion of base iron, thereby exerting
extremely excellent effects to achieve the abovementioned
aim.
[0011]
A steel sheet for the container of the present
20 invention is based on the above findings and includes a
steel sheet; a Ni plating layer which is formed on a
surface of the steel sheet in an amount of plating
deposition containing a Ni amount of 0.3 to 3 g/m2 and
contains Co in the range of 0.1 to 100 ppm; and a
25 chromate coating layer which is formed on a surface of
the Ni plating layer in an amount of coating deposition
containing a converted Cr amount of 1 to 40 mg/m2.
According to the present invention, a steel sheet
for a container excellent in corrosion resistance,
30 adhesion, and weldability, which includes a steel sheet;
a Ni plating layer which is formed on a surface of the
steel sheet in an amount of plating deposition containing
a Ni amount of 0.3 to 3 g/m2 and contains Co in the range
of 0.1 to 100 ppm; and a chromate coating layer which is
35 formed on a surface of the Ni plating layer in an amount
of coating deposition containing a converted Cr amount of
1 to 4 0 mg/m2, is provided.
- 6 -
According to the findings of the present inventors,
reasons why the steel sheet for the container according
to the present invention having the above-described
features exerts excellent effects as presumed to be as
5 follows.
When investigations were performed about effects on
corrosion resistance of elements which were added in fine
amounts to a Ni plating layer, in order to reduce the
pitting corrosion, the present inventors found a
10 phenomenon that the corrosion grows along the interface
between the Ni plating layer and the base iron during
growing the corrosion due to defects in the Ni plating
layer such as pinholes, by including the fine amounts of
Co in a Ni plating layer (see Fig. 1).
15 The present inventors carried on further studies and
also found that the corrosion tends to grow along the
interface between the Ni plating layer and the base iron,
resulting in the suppression of pitting corrosion in the
"depth" direction of the base iron.
20 [0012]
The phenomenon described above was presumed,
according to the findings of the present inventors, to
proceed as follows. In a Ni-plated steel sheet added Co
in fine amounts, by dissolving the Co which is
25 electrochemically less noble than Ni, in the Ni plating
layer, the dissolved Co ions precipitate at the base iron
side between the Ni plating layer and the base iron. The
corrosion would mainly occur between the precipitates Co
and the base iron and grow on the interface between the
30 Ni plating layer and the base iron.
In addition, according to the findings of the
present inventors, it is considered that the ionized Co
may result in a lessened passivation effect of the
chromate layer or the Zr-containing coating layer on the
35 Ni plating layer, and oxygen- or hydrogen-reducing
reactions, which is corresponding to pitting corrosion of
the base iron (Fe-oxidizing reaction), may occur.
- 7 - t
[0013]
By taking advantage of the above-described
phenomenon, the present inventors have arrived at the
invention of a steel sheet for a container excellent in
5 corrosion resistance, adhesion, and weldability, which
has the above-described features.
[0014]
The present invention may include, for example, the
following aspects:
10 [1] A steel sheet for a container excellent in corrosion
resistance, adhesion, and weldability, the steel sheet
including:
a steel sheet;
a Ni plating layer which is formed on a surface of
15 the steel sheet in an amount of plating deposition
containing a Ni amount of 0.3 to 3 g/m2 and contains Co in
the range of 0.1 to 100 ppm; and
a chromate coating layer which is formed on a
surface of the Ni plating layer in an amount of coating
20 deposition containing a converted Cr amount of 1 to 40
mg/m2.
[2] The steel sheet for the container according to [1],
wherein the Ni amount in the Ni plating layer is 0.35 to
2.8 g/m2.
25 [3] The steel sheet for the container according to [1] or
[2], wherein the Co content in the Ni plating layer is
0.3 to 92 ppm.
[4] The steel sheet for the container according to any
one of [1] to [3], wherein the amount as the converted Cr
30 amount of deposition of the chromate coating layer is 1.2
to 38 mg/m2.
[5] A steel sheet for the container excellent in
corrosion resistance, adhesion, and weldability, the
steel sheet including:
35 a steel sheet;
a Ni plating layer which is formed on a surface of
the steel sheet in an amount of plating deposition
- 8 -
containing a Ni amount of 0.3 to 3 g/m and contains Co in
the range of 0.1 to 100 ppm; and
a Zr-containing coating layer which is formed on a
surface of the Ni plating layer in an amount of coating
5 deposition containing a Zr amount of 1 to 40 mg/m2.
[6] The steel sheet for the container according to [5],
wherein the Ni amount in the Ni plating layer is 0.42 to
2.4 g/m2.
[7] The steel sheet for the container according to [5] or
10 [6], wherein the Co content in the Ni plating layer is
0.1 to 89 ppm.
[8] The steel sheet for the container according to any
one of [5] to [7], wherein
the amount as the converted Zr amount of deposition of
15 the Zr-containing coating layer is 1 to 37 mg/m2.
Advantageous Effects of Invention
[0015]
According to the present invention, a steel sheet
for the container is excellent in corrosion resistance,
20 and additionally in adhesion with a laminated resin film
and weldability is provided.
Brief Description of Drawings
[0016]
Fig. 1 is a graph showing a relationship between the
25 Co concentration in a Ni plating and the depth of pitting
corrosion.
Fig. 2(a) is an SE (scanning electron microscope)
image showing an example of corrosion of a Ni-Co plating,
and Fig. 2(b) is a schematic cross-section view showing
30 an (estimated) corrosion behavior of the Ni-Co plating.
Fig. 3(a) is an SE image showing an example of
corrosion of a Ni plating, and Fig. 3 (b) is a schematic
cross-section view showing an (estimated) corrosion
behavior of the Ni plating.
35 Description of Embodiments
[0017]
The following will describe in details a steel sheet
- 9 -
for the container excellent in corrosion resistance,
adhesion, and weldability, which are embodiments of the
present invention.
[0018]
5 A steel sheet for the container excellent in
corrosion resistance, adhesion, and weldability according
to an embodiment of the present invention features
comprising a steel sheet; a Ni plating layer which is
formed on a surface of the steel sheet in an amount of
10 plating deposition containing a Ni amount of 0.3 to 3 g/m2
and contains Co in the range of 0.1 to 100 ppm; and a
chromate coating layer or a Zr-containing coating layer
which is formed on a surface of the Ni plating layer.
The chromate coating layer is formed on a surface of
15 the Ni plating layer in an amount of coating deposition
containing a converted Cr amount of 1 to 40 mg/m2. The
Zr-containing coating layer is formed on a surface of the
Ni plating layer in an amount of coating deposition
containing a Zr amount of 1 to 4 0 mg/m2.
20 [0019]
The steel sheet is a material plate for plating from
the steel sheet for the container and can be, by way of
example, steel sheets produced through hot rolling, acid
cleaning, cold rolling, annealing, temper rolling, and
25 other common processes from usual processes of producing
steel slabs.
[0020]
A steel sheet as a material plate for plating has a
Ni plating layer formed which contains Co in fine
30 amounts, in order to ensure corrosion resistance,
adhesion, and weldability. Since Ni is a metal which has
adhesion to the steel sheet together with forge
weldability (property of joining a steel sheet(s) at
lower melting temperature of the steel sheet(s)), the Ni
35 plating layer begins to exert practical properties of
adhesion and welding by increasing the Ni amount to 0.3
g/m2 or more as the amount of plating deposition in
- 10 -
applying Ni plating to the steel sheet. Further
increasing the amount of Ni plating deposition improves
adhesion and welding properties, whereas amounts of
deposition of more than 3 g/m2 leads to saturation of
5 improvement effect on adhesion and welding properties,
and this is industrially disadvantageous. Therefore, the
amount of deposition of the Ni plating layer needs to be
from 0.3 to 3 g/m2.
[0021]
10 The Co content in the Ni plating layer which is too
low is not preferable because the direction of growth of
corrosion is the sheet-depth direction of the steel sheet
and pitting corrosion becomes dominant. At the Co
content of 0.1 ppm or more in the Ni plating layer, the
15 corrosion begins to grow along the interface the Ni
plating layer and the base iron. On the other hand, at
the Co content in the Ni plating layer which become
excessive, the forge weldability of Ni is inhibited,
resulting in deteriorated weldability. Therefore, the Co
20 content in the Ni plating layer needs to be 100 ppm or
less.
[0022]
In addition to Co, the Ni plating layer contains
inevitable impurities and the remaining Ni.
25 [0023]
As methods by which the above-described Ni-plating
layer containing Co is formed on the steel sheet, are
industrially useful, without being particularly limited
to, methods by which a solution in which cobalt sulfate
30 or cobalt chloride is dissolved in a known acidic nickelplating
solution composed of nickel sulfate or nickel
chloride is used as a plating bath and cathode
electrolysis is carried out.
[0024]
35 Onto the Ni plating layer, chromate treatment is
applied in order to enhance corrosion resistance and
adhesion by a resin film, particularly, secondary
- 11 -
9
adhesion after processing. Chromate treatment results in
the formation of a chromate coating composed of hydrated
Cr oxide or of hydrated Cr oxide and metallic Cr.
[0025]
5 The metallic Cr or hydrated Cr oxide making up the
chromate coating are excellent in chemical stability and
will improve the corrosion resistance of the steel sheet
for the container in proportion to the amount of the
chromate coating. In addition, the hydrated Cr oxide
10 exhibits excellent adhesion even under a steam atmosphere
by forming strong chemical bonding with functional groups
of a resin film and will improve the adhesion with the
resin film with increasing amounts of the chromate
coating layer. The chromate coating layer containing the
15 converted metallic Cr amount of 1 mg/m2 or more is needed
to exert sufficient degrees of corrosion resistance and
adhesion.
[0026]
Although the increase in the amount of deposition of
20 the chromate coating layer also increases improvement
effect on corrosion resistance and adhesion, increasing
the amount of deposition of the chromate coating layer
results in highly increased electric resistance of the
steel sheet for the container, thereby causing
25 deterioration of its weldability, due to the fact that
the hydrated Cr oxide in the chromate coating layer is an
electric insulator. Specifically, weldability is
extremely deteriorated when the amount of deposition of
the chromate coating layer exceeds 4 0 mg/m2 equivalent to
30 the converted metallic Cr. Therefore, the amount of the
deposition of the chromate coating layer containing the
converted metallic Cr needs to be 40 mg/m2 or less.
[0027]
A method for chromate treatment may be carried out
35 by any method, such as dipping, spraying, electrolysis,
and other treatments using aqueous solutions of sodium,
potassium, ammonium salts of various Cr acids. It is
- 12 -
industrially excellent to apply cathode electrolysis
treatment in an aqueous solution in which sulfate ions,
fluoride ions (including complex ions) or a mixture
thereof are added as plating assistant to the Cr acid.
5 [0028]
A Zr-containing coating layer may be formed on the
Ni plating layer, instead of the above-described chromate
coating layer. The Zr-containing coating layer is a
coating composed of Zr compounds such as Zr oxide, Zr
10 phosphate, Zr hydroxide, Zr fluoride, or the like, or a
complex coating composed thereof. When the Zr-containing
coating layer is formed in an amount of coating
deposition containing the converted metallic Zr amount of
1 mg/m2 or more, a dramatic improvement in adhesion with a
15 resin film and in corrosion resistance is observed as in
the case of the above-described chromate coating layer.
On the other hand, when the amount of deposition of the
Zr-containing coating layer containing the converted
metallic Zr amount exceeds 40 mg/m2, weldability and
20 appearance properties are deteriorated. Particularly,
when the amount of deposition of the Zr-containing
coating layer containing the converted metallic Zr
exceeds 40 mg/m2, weldability is extremely deteriorated
because the Zr-containing coating layer is an electric
25 insulator and has a very high electric resistance,
thereby causing deterioration of the weldability.
Therefore, the amount of deposition of the Zr-containing
coating layer containing the converted metallic Zr amount
needs to be from 1 to 4 0 mg/m2.
30 In embodiments of the present invention using the
chromate coating layer, the following ranges are
preferable:
Ni amount in the Ni plating layer (g/m2) : 0.35 to 2.8
(more preferably, 0.6 to 2.4; further preferably, 0.8 to
35 1-8),
Co content in the Ni plating layer (ppm): 0.3 to 92 (more
preferably, 0.3 to 25; further preferably, 0.3 to 24),
- 13 -
*
an amount as the converted Cr amount of deposition of the
chromate coating layer (mg/m2) : 1.2 to 38 (more
preferably, 4 to 22; further preferably, 5 to 22).
[0029]
5 As a method for forming the Zr-containing coating
layer, for example, a method by which a steel sheet after
formation of the Ni plating layer is subjected to dipping
treatment in an acidic solution having as the main
components Zr fluoride, Zr phosphate, and hydrofluoric
10 acid, or to cathode electrolysis treatment, may be used.
In embodiments of the present invention using the
Zr-containing coating layer, the following ranges are
preferable:
Ni amount in the Ni plating layer (g/m2) : 0.42 to 2.4
15 (more preferably, 0.8 to 2.4; further preferably, 1.1 to
2.4),
Co content in the Ni plating layer (ppm): 0.1 to 89
(more preferably, 0.2 to 89; further preferably, 0.2 to
47),
20 an amount as the converted Zr amount of deposition of the
Zr-containing coating layer (mg/m2) : 1 to 37 (more
preferably, 12 to 37; further preferably, 12 to 28).
[0030]
According to embodiments of the present invention,
25 it is possible to improve resistance to pitting corrosion
of the steel sheet for the container and
enhance weldability, and adhesion to a resin film or to
the processed resin film.
Examples
30 [0031]
The present invention will be described in detail.
First, Examples and Comparative Examples of the
present invention are described, and their results are
shown in Table 1. Sample pieces were prepared by the
35 methods described in (1) and performed an evaluation of
items (A) to (D) described in (2).
[0032]
- 14 -
*
(1) Method for preparing sample pieces
Steel sheet (material plate for plating):
A Temper-Grade 3 (T-3) tin cold-rolled steel sheet
having a sheet thickness of 0.2 mm was used as a material
5 plate for plating.
[0033]
Conditions for Ni plating:
Cobalt sulfate was added in an amount of 0.1 to 1%
to an aqueous solution which contained nickel sulfate in
10 a concentration of 20%, nickel chloride in a
concentration of 15%, and boric acid in a concentration
of 1% and was adjusted to pH=2, and cathode electrolysis
was performed at 5 A/dm2 to form a Ni plating layer on the
steel sheet. The amount of Ni deposition was controlled
15 by the time of electrolysis.
[0034]
Conditions for chromate treatment:
Cathode electrolysis was performed at 10 A/dm2 in an
aqueous solution which contained chromium(VI) oxide in a
20 concentration of 10%, sulfuric acid in a concentration of
0.2%, and ammonium fluoride in a concentration of 0.1%,
followed by washing with water for 10 seconds, to form a
chromate coating layer on the Ni plating layer. The
amount of Cr deposition in the chromate coating layer was
25 controlled by the period of time of electrolysis.
[0035]
Conditions for Zr-containing coating layer
treatment:
Cathode electrolysis was performed at 10 A/dm2 in an
30 aqueous solution which contained zirconium fluoride in a
concentration of 5%, phosphoric acid in a concentration
of 4%, and hydrofluoric acid in a concentration of 5%, to
form a Zr-containing coating layer on the Ni plating
layer. The amount of Zr deposition in the Zr-containing
35 coating layer was controlled by the time of electrolysis.

Amounts of Ni, Zr, and Cr were determined with
- 15 -
fluorescent X-ray. For Co, a plating layer was dissolved
in 10% hydrochloric acid, and the Co concentration was
determined by atomic absorption analysis and calculated.
[0036]
5 (2) Methods for evaluation of sample pieces
(A) Weldability
After laminated a 15 pm thick PET film onto a test
piece, welding was performed under conditions of a lap of
0.5 mm, a welding pressure of 45 kgf, a welding wire
10 speed of 80 m/min, and varying currents. The range of
conditions for suitable welding was considered by the
range of suitable currents determined by the minimum
current value which sufficient welding strength was
obtained, and the maximum current value which welding
15 defects such as expulsion and surface flash began to
appear, and a welding state. Evaluation was done on a
four-grade scale (AA: very wide, A: wide, B: practically
no problems, C: narrow).
[0037]
20 (B) Adhesion
After laminated a 15 |jm thick PET film onto a sample
piece, a cup was fabricated in a DrD press. The cup was
formed into a DI can in a DI machine. Peeling levels of
the film on the can wall of the formed DI can were
25 observed. Evaluation was holistically done on a fourgrade
scale (AA: not peeled at all, A: slight floating of
the film, B: large peeling, C: the film was peeled during
DI forming and finally the drum was broken).
[0038]
30 (C) Secondary adhesion
A 15 |jm thick PET film was laminated onto a sample
piece, from which a cup was fabricated in a DrD press.
The cup was formed into a DI can in a DI machine. The DI
can was subjected to heat treatment for 10 minutes at a
35 temperature (around 240°C) exceeding the melting point of
the PET film, followed by further treatment under a steam
- 16 -
*
atmosphere at 125°C for 30 minutes (retort treatment).
Peeling levels of the film on the can wall of the retorttreated
DI can were observed. Evaluation was
holistically done on a four-grade scale (AA: not peeled
5 at all, A: slight floating of the film, B: large peeling,
C: the film was peeled during DI forming and finally the
drum was broken).
[0039]
(D) Corrosion resistance
10 After a welded can laminated with a PET film was
fabricated a repair paint is applied on the weld. The
weld can was filled with a testing solution of a mixture
of 1.5% citric acid and 1.5% salt, fitted with a top, and
set in a temperature-controlled room at 55°C for one
15 month. Evaluation was done by assessing corrosion levels
at film scuffing sites inside the welded can on a fourgrade
scale (AA: no pitting corrosion, A: slight pitting
corrosion with practically no problems, B: grown pitting
corrosion, C: perforation due to pitting corrosion). In
20 addition, 10 corrosion sites were observed under an
optical microscope to determine the average value of
corrosion depths.
[0040]
Table 1 shows the results of evaluation of
25 weldability, adhesion, secondary adhesion, and corrosion
resistance for Examples 1 to 11 and Comparative Examples
1 to 7 in which the amount of deposition of the Ni
plating layer, the Co content, and the chromate coating
layer or Zr-containing coating layer were changed. In
30 Table 1, numerical values which were not ranged in those
of the present invention were underlined.
[0041]
- 17 -
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- 18 -
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[0042]
As shown in Table 1, all of the steel sheets of
Examples 1 to 11 have excellent in weldability, adhesion,
secondary adhesion, and corrosion resistance.
5 Comparative Example 1 had a decreased amount of
deposition of the Ni plating layer and resulted in
decreased weldability and corrosion resistance.
Comparative Examples 2 and 3 had a Co content in the
Ni plating layer, which was not ranged in that of the
10 present invention and resulted in decreased corrosion
resistance (Comparative Example 2) and decreased
weldability (Comparative Example 3), respectively.
Comparative Examples 4 and 5 had an amount of
deposition of the chromate coating layer, which was not
15 ranged in that of the present invention and resulted in
decreased secondary adhesion (Comparative Example 4) and
decreased weldability (Comparative Example 5),
respectively.
Comparative Examples 6 and 7 had an amount of
20 deposition of the Zr-containing coating layer, which was
not ranged in that of the present invention and resulted
in decreased secondary adhesion (Comparative Example 6)
and decreased weldability (Comparative Example 7),
respectively.
25 [0043]
As a material plate for plating were used a
plurality of Temper-Grade 3 (T-3) tin cold-rolled steel
sheets having a sheet thickness of 0.2 mm and subjected
to plating under Ni plating conditions similar to those
30 described above, thereby to form a Ni plating layer on
each of the steel sheets. For all of the Ni plating
layers, the amount of Ni deposition was set at a fixed
amount of 0.7 g/m2.
Subseguently, a chromate coating layer was formed on
35 each of the Ni plating layers under chromate treatment
conditions similar to those described above. For all of
the chromate coating layers, the amount of Cr deposition
- 19 -
in each of the chromate coating layers was set at a fixed
amount of 8 g/m2.
For a variety of the obtained steel sheets, the
corrosion resistance test was performed as described
5 above and the depth of pitting corrosion was determined.
The results are shown in Fig. 1.
[0044]
As shown in Fig. 1, it was found that a Co content
in the Ni plating layer was in the range of 0.1 to 100
10 ppm, the depth of pitting corrosion was in the range of
0.02 to 0.08 mm and the corrosion resistance to pitting
corrosion was greatly improved. At the Co content in the
range of 0.1 to 100 ppm, the corrosion was observed to
grow along the between the Ni plating layer and the base
15 iron. At the Co content in the range of less than 0.1
ppm, on the other hand, the corrosion was observed to
grow along in the sheet-depth direction.

CLAIMS
Claim 1
A steel sheet for a container excellent in corrosion
resistance, adhesion, and weldability, the steel sheet
5 comprising:
a steel sheet;
a Ni plating layer which is formed on a surface of
the steel sheet in an amount of plating deposition
containing a Ni amount of 0.3 to 3 g/m^ and contains Co in
10 the range of 0.1 to 100 ppm; and
a chromate coating layer which is formed on a
surface of the Ni plating layer in an amount of coating
deposition containing a converted Cr amount of 1 to 40
mg/m^.
15 Claim 2
The steel sheet for the container according to claim
1, wherein the Ni amount in the Ni plating layer is 0.35
to 2.8 g/m^.
Claim 3
20 The steel sheet for the container according to
claims 1 or 2, wherein the Co content in the Ni plating
layer is 0.3 to 92 ppm.
Claim 4
The steel sheet for the container according to
25 claims 1 or 2, wherein the amount as the converted Cr
amount of deposition of the chromate coating layer is 1.2
to 38 mg/m^.
Claim 5
A steel sheet for a container excellent in corrosion
30 resistance, adhesion, and weldability, the steel sheet
comprising:
a steel sheet;
a Ni plating layer which is formed on a surface of
the steel sheet in an amount of plating deposition
35 containing a Ni amount of 0.3 to 3 g/m^ and contains Co in
the range of 0.1 to 100 ppm; and
a Zr-containing coating layer which is formed on a
- 21 -
^ surface of the Ni plating layer in an amount of coating
deposition containing a converted metallic Zr amount of 1
to 4 0 mg/m^.
Claim 6
5 The steel sheet for the container according to claim
5, wherein the Ni amount in the Ni plating layer is 0.42
to 2.4 g/m^.
Claim 7
The steel sheet for the container according to
10 claims^ 5 or 6, wherein the Co content in the Ni plating
layer is 0.1 to 8 9 ppm.
Claim 8
The steel sheet for the container according to
claims 5 or 6, wherein the amount as the converted Zr
15 amount of deposition of the Zr-containing coating layer
is 1 to 37 mg/m^.