DESCRIPTION
TITLE OF INVENTION: PLATED STEEL SHEET
TECHNICAL FIELD
[0001] The present invention relates to a plated
steel sheet provided with a Zn-Ni alloy plating
layer.
BACKGROUND ART
[0002] A steel sheet used for fuel tanks of an
automobile, a motorcycle, and so on is required to
have corrosion resistance to fuel such as gasoline on
a surface thereof. A Sn-Pb based plated steel sheet
has been broadly used as the steel sheet for fuel
tanks. In recent years, due to a restriction on Pb,
a plated steel sheet as an alternative to the Sn-Pb
based plated steel sheet has been developed (Patent
Literatures 1 to 4).
[0003] A Zn-Ni based plated steel sheet, which is
one alternative material to the Sn-Pb based plated
steel sheet, has the advantage of exhibiting good
corrosion resistance to gasoline at low cost, and in
recent years, the use of the Zn-Ni based plated steel
sheet in emerging countries has been increasing.
[0004] However, fuel tanks manufactured by using the
Zn-Ni based plated steel sheet sometimes cannot
obtain sufficient corrosion resistance to fuel. The
corrosion resistance to a fuel containing alcohol in
particular is liable to be insufficient, and thus a
hole is sometimes formed for a short period of time.
[0005] A corrosion-resistant member for biofuel
- 1 -
containing alcohol is described in Patent Literature
5. However, even when a fuel tank is manufactured by
using the materials described in Patent Literature 5
to a reproducible extent, sufficient corrosion
resistance cannot be obtained.
CITATION LIST
PATENT LITERATURE
[0006] Patent Literature 1: Japanese Laid-open
Patent Publication No. 09-241866
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2001-341228
Patent Literature 3: Japanese Patent No. 3859941
Patent Literature 4: Japanese Laid-open Patent
Publication No. 2004-360019
Patent Literature 5: Japanese Laid-open Patent
Publication No. 2011-026669
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0007] An object of the present invention is to
provide a plated steel sheet capable of obtaining
excellent corrosion resistance to various fuels.
SOLUTION TO PROBLEM
[0008] As a result of earnest examination conducted
for the purpose of solving the above-described
object, the present inventors have found out that a
crack occurs in a plating layer in working a plated
steel sheet into a fuel tank, and excellent corrosion
resistance can be obtained even when a crack occurs
in a plating layer by providing a specific pre-
- 2 -
plating layer between the plating layer and a steel
sheet, though details will be described later.
[0009] The present invention has been made based on
the above-described findings, and the gist thereof is
as follows.
[0010] (1)
A plated steel sheet, includes:
a steel sheet;
a pre-plating layer on at least one surface of
the steel sheet, the pre-plating layer containing Al,
Cu, In, Zn, Sn, or Sb, or any combination thereof;
and
a plating layer of a Zn-Ni alloy on the preplating
layer, a Ni content of the Zn-Ni alloy being
5 mass% to 15 mass%, wherein
a coating weight of the pre-plating layer is 0.5
g/m2 or more, and
a coating weight of the plating layer is 5 g/m2
or more.
[0011] (2)
The plated steel sheet according to (1), further
comprising a chromate-free film of 10 mg/m2 or more on
the plating layer.
[0012] (3)
The plated steel sheet according to (2), wherein
the chromate-free film contains a fluoro compound of
hexafluorotitanic acid or hexafluorozirconic acid or
both of them, phosphoric acid, and a vanadium
compound.
- 3 -
[0013] (4)
The plated steel sheet according to (2), wherein
the chromate-free film is formed by using a treatment
solution containing a salt of Zr or Ti or both of
them, or a treatment solution containing a silane
coupling agent.
[0014] (5)
The plated steel sheet according to (4), wherein
the treatment solution containing the silane coupling
agent contains a first silane coupling agent
containing a single amino group in a molecule and a
second silane coupling agent containing a single
glycidyl group in a molecule.
ADVANTAGEOUS EFFECTS OF INVENTION
[0015] According to the present invention, an
appropriate pre-plating layer is included, so that
excellent corrosion resistance can be obtained to
various fuels such as gasoline and a composite fuel.
BRIEF DESCRIPTION OF DRAWINGS
[0016] [Fig. 1] Fig. 1 is a view illustrating an
appearance of a plating layer on a vertical wall of a
cylindrical cup.
[Fig. 2] Fig. 2 is a view illustrating an
appearance of an inner surface of the cylindrical
cup.
[Fig. 3] Fig. 3 is a cross-sectional view
illustrating a structure of a plated steel sheet
according to an embodiment of the present invention.
[Fig. 4] Fig. 4 is a cross-sectional view
- 4 -
illustrating a structure of a plated steel sheet
according to a modified example of the embodiment.
[Fig. 5] Fig. 5 is a cross-sectional view
illustrating a structure of a plated steel sheet
according to another modified example of the
embodiment.
[Fig. 6] Fig. 6 is a cross-sectional view
illustrating a structure of a plated steel sheet
according to another modified example of the
embodiment.
[Fig. 7] Fig. 7 is a cross-sectional vie1v
illustrating a structure of a plated steel sheet
according to another modified example of the
embodiment.
[Fig. 8] Fig. 8 is a cross-sectional view
illustrating a structure of a plated steel sheet
according to another modified example of the
embodiment.
DESCRIPTION OF EMBODIMENTS
[0017] First, there will be explained a process
leading to achievement of the present invention led
by the present inventors. In the present invention,
a Zn-Ni alloy is a binary alloy substantially
composed of Zn and Ni and may contain impurities
therein, but does not contain other elements added
intentionally.
[0018] (First Experiment)
The present inventors conducted an experiment
(first experiment) for confirming an appearance of
- 5 -
damage of a plating layer caused by working in a
conventional Zn-Ni based plated steel sheet. In the
first experiment, a B-containing ultralow carbon Ti
steel sheet was prepared as a base steel sheet, and a
plating layer of a Zn-Ni alloy with a Ni content
being 12 mass% was formed on both surfaces thereof.
A plating solution is used for formation of the
plating layer. The plating solution was obtained in
a manner that an aqueous solution containing zinc
sulfate: 180 g/L, nickel sulfate: 200 g/L, and sodium
sulfate: 100 g/L was prepared, and pH of the aqueous
solution was adjusted to 1.2 with sulfuric acid. A
coating weight of the plating layer was 30 g/m2 per·
one surface. Then, a film was formed on surfaces of
the plating layers so as to have a coating weight of
500 mg/m2 per one surface with use of a treatment
solution containing a silane coupling agent. In this
manner, a plated steel sheet was manufactured.
Thereafter, a sample was cut out from the plated
steel sheet, a cylindrical cup having a 100 mm
diameter was formed of the sample with a drawing
ratio of 2.2, and the appearance of the plating layer
on the vertical wall of the cylindrical cup was
observed.
[0019) Fig. 1 illustrates the appearance of the
plating layer on the vertical wall. As illustrated
in Fig. 1, many cracks occurred in the plating layer
and the base steel sheet was exposed at many places.
The reason why many cracks occurred was because the
- 6 -
Zn-Ni alloy plating layer is formed of an
intermetallic compound represented as Ni 5 Zn 21 and is
poor in ductility.
[0020] (Second experiment)
Next, the present inventors conducted an
experiment (second experiment) for confirming
corrosion resistance of the Zn-Ni based plated steel
sheet after forming. In the second experiment,
another sample was cut out from a different portion
of the plated steel sheet manufactured in the first
experiment, and another cylindrical cup having a 100
mm diameter was formed of the sample with a drawing
ratio of 2.2. A composite fuel containing gasoline:
ethanol: water 69: 29: 2 by volume ratio was
prepared, and 100 mg of acetic acid and 100 mg of
NaCl per 1 L of the composite fuel were added to the
composite fuel, to produce a corrosive solution.
Then, 100 mL of the corrosive solution was put into
the cylindrical cup to be sealed, the cylindrical cup
with the corrosive solution enclosed therein was left
to stand at 45°C, and the appearance of the inner
surface of the cylindrical cup was observed after
1000 hours elapsed.
[0021] Fig. 2 illustrates the appearance of the
inner surface of the cylindrical cup. As illustrated
in Fig. 2, corrosion occurred significantly and a
large amount of pitting was generated on the vertical
wall where many cracks occurred in the plating layer.
The depth of pitting was 100 pm or more.
- 7 -
[0022] Through a series of these experiments, it was
confirmed that cracks are likely to occur in the Zn-
Ni alloy plating layer and corrosion progresses at
each of crack occurring places. Only the formation
of a chromate film fails to prevent such cracks, and
even the method described in Patent Literature 1, for
example, fails to obtain sufficient corrosion
resistance.
[0023] As a result that the present inventors
further conducted earnest examination repeatedly in
order to study the reason of such a phenomenon, it
was revealed that an oxygen reduction reaction
(cathode reaction) being part of corrosion reaction
progresses quickly on the surface of the base steel
sheet exposed from the crack, and as a result, a
dissolution reaction (anode reaction) of the Zn-Ni
alloy plating layer, which is a paired reaction, is
promoted. It was also revealed that these reactions
are significant when alcohol is contained in a fuel
in particular.
[0024) Then, as a result that the present inventors
further conducted earnest examination based on these
findings, it was found out that providing a specific
pre-plating layer between a steel sheet and a plating
layer makes it possible to effectively suppress
corrosion of the Zn-Ni based plated steel sheet.
[0025] Next, there will be explained the pre-plating
layer.
[0026] (Third experiment)
- 8 -
The present inventors conducted an experiment
(third experiment) for specifying materials capable
of being used for the pre-plating layer. In the
third experiment, first, similarly to the first
experiment, B-containing ultralow carbon Ti steel
sheets were prepared as a base steel sheet, and a
pre-plating layer of each of Al, Ag, Co, Cr, Cu, In,
Mn, Ni, Zn, Sn, Sb, and Pt was formed on both
surfaces of each of them. Each coating weight of the
pre-plating layers was l g/m2
. In formation of the
pre-plating layers, electroplating of each of the
steel sheets was performed in a solution containing
Al, Ag, Co, Cr, Cu, In, Mn, Ni, Zn, Sn, Sb, or Pt as
sulfate, chloride salt, nitrate, formate, or acetate.
An organid solvent (dimethyl sulfone) bath was used
when the pre-plating layer of Al was formed, and a
bath using water as a solvent was used when the preplating
layers of the other metals were formed.
Then, a plating layer of a Zn-Ni alloy containing Ni:
12 mass% and Zn: 88 mass% was formed on each of the
pre-plating layers. The coating weight of the
plating layer was 30 g/m2 per one surface. In this
manner, plated steel sheets were manufactured.
Thereafter, similarly to the second experiment,
cylindrical cups and a corrosive solution were
prepared, and corrosion resistance evaluations were
performed with use of these. For comparison, the
corrosion resistance evaluation was performed also
for a plated steel sheet not having had pre-plating
- 9 -
layers formed thereon but having had Zn-Ni alloy
plating layers formed thereon. These results are
listed in Table 1. In Table 1, 0 indicates no
corrosion, 6 indicates that corrosion having a depth
of 20 pm or less existed, and X indicates that
corrosion having a depth of greater than 20 pm
existed.
[0027] [Table 1]
METAL
CORROSION
RESISTANCE
AI 0
Ag D.
Co D.
Cr D.
Cu 0
In 0
Mn D.
Ni D.
Zn 0
Sn 0
Sb 0
Pt X
None D.
[0028] As listed in Table 1, when the pre-plating
layers of Al, Cu, In, Zn, Sn, and Sb were formed,
more excellent corrosion resistance than in the case
of no pre-plating layer being formed was obtained.
[0029] (Forth experiment and Fifth experiment)
Further, the present inventors conducted an
experiment related to the oxygen reduction reaction
and an experiment related to the appearance of the
plating layer after working for clarifying
- 10 -
characteristics of the above-described metals
suitable for the pre-plating layer.
[0030] In the experiment related to the oxygen
reduction reaction (fourth experiment), first,
similarly to the first experiment, B-containing
ultralow carbon Ti steel sheets were prepared as a
base steel sheet, and a pre-plating layer of each of
Al, Ag, Co, Cr, Cu, Fe, In, Mn, Ni, Zn, Sn, Sb, and
Pt was formed on both surfaces of each of them. Each
coating weight of the pre-plating layers was 1 g/m2
•
Then, an oxygen reduction current was measured with a
potential of -600 mV (Ag/AgCl electrode reference)
with use of an aqueous solution obtained by
dissolving 50 g/L of Na 2S04 and performing air
bubbling for 30 minutes or more to saturate dissolved
oxygen. The potential of -600 mV (Ag/AgCl electrode
reference) corresponds to a corrosion potential of
the Zn-Ni alloy containing Ni: 12 mass% and Zn: 88
mass%. These results are listed in Table 2. In
Table 2, 0 indicates that the oxygen reduction
current was smaller by one digit or more than in the
case of using Fe for the pre-plating layer, X
indicates that it was larger by one digit or more,
and 8 indicates that it was between these.
[0031] In the experiment related to the appearance
of the plating layer after working (fifth
experiment), first, similarly to the fourth
experiment, a pre-plating layer was formed on both
surfaces of each of base steel sheets. Then, a
- 11 -
sample was cut out from each of the base steel sheets
each having had the pre-plating layers formed
thereon, and a cylindrical cup having a 100 mm
diameter was formed of each of the samples with a
drawing ratio of 2.2. Then, each area ratio of the
pre-plating layers remaining on vertical walls of the
cylindrical cups was measured. These results are
listed in Table 2. In Table 2, 0 indicates that the
area ratio of the remaining pre-plating layer was 95%
or more, ~ indicates that it was 90% or more and less
than 95%, and X indicates that it was less than 90%.
[0032) [Table 2)
OXYGEN METAL REDUCTION AREA CURRENT RATIO
AI 0 0
Ag /::,. 0
Co /::,. X
Or /::,. X
Cu 0 0
Fe /::,. 0
In 0 0
Mn /::,. X
Ni /::,. X
Zn 0 0
Sn 0 0
Sb 0 0
Pt X 0
[0033) As listed in Table 2, the oxygen reduction
current of the metals (0 in Table 1) that were each
used for the pre-plating layer to achieve an
improvement in corrosion resistance, which was
revealed by the third experiment, was smaller by one
- 12 -
digit or more than that of Fe, and the area ratio of
the pre-plating layers remaining after working was
95% or more.
[0034) (Sixth experiment)
The present inventors conducted an experiment
related to the coating weight necessary for the preplating
layer (sixth experiment). In the sixth
experiment, first, similarly to the fifth experiment,
a pre-plating layer was formed on both surfaces of
each of base steel sheets. Al, Cu, In, Zn, Sn, and
Sb, each of which improved corrosion resistance, were
used as the element, and each coating weight was
changed in a range of 0 g/m2 to 1.0 g/m2
. Then, a
sample was cut out from each of the base steel sheets
each having had the pre-plating layers formed thereon
and a cylindrical cup having a 100 mm diameter was
formed of each of the samples with a drawing ratio of
2. 2. Then, each area ratio of the pre-plating layers
remaining on vertical walls of the cylindrical cups
\·Jas measured. Results related to Al are listed in
Table 3. In Table 3, 0 indicates that the area ratio
of the remaining pre-plating layer was 95% or more, 6
indicates that it was 90% or more and less than 95%,
and x indicates that it was less than 90%. Further,
with regard also to Cu, In, Zn, Sn, and Sb, the
similar results were obtained.
[0035) [Table 3)
- 13 -
COATING
WEIGHT AREA
(v:/m2)
RATIO
0.1 X
0.2 X
0.3 X
0.4 b.
0.5 0
0.6 0
0.7 0
0.8 0
0.9 0
1.0 0
[0036] As listed in Table 3, it was revealed that
the coating weight needs to be 0.5 g/m2 or more in
order that the pre-plating layer should remain after
working in an area ratio of 95% or more.
[0037] These experiments revealed that the state of
the base steel sheet being coated with the preplating
layer is maintained and exposure of the base
steel sheet from cracks is suppressed even if cracks
occur in the Zn-Ni alloy plating layer by working, by
providing the pre-plating layer of Al, Cu, In, Zn,
Sn, or Sb, and that, due to the exposure suppression,
progress of the oxygen reduction reaction (cathode
reaction) slows down and the dissolution reaction of
the plating layer (anode reaction) is suppressed.
[0038] Next, there will be explained an embodiment
of the present invention. Fig. 3 is a crosssectional
view illustrating a plated steel sheet
according to the embodiment of the present invention.
[0039] As illustrated in Fig. 3, a plated steel
- 14 -
sheet 1 according to the embodiment includes a steel
sheet (base steel sheet) 2, a pre-plating layer 3 on
one surface of the steel sheet 2, and a plating layer
4 on the pre-plating layer 3. The pre-plating layer
3 contains Al, Cu, In, Zn, Sn, or Sb, or any
combination thereof, and a coating weight of the preplating
layer 3 is 0.5 g/m2 or more. The plating
layer 4 is made of a Zn-Ni alloy containing Ni: 5
mass% to 15 mass% and Zn: 85 mass% to 95 mass%, and a
coating weight of the plating layer 4 is 5 g/m2 or
more.
[0040] The steel type and the composition of the
steel sheet 2 are not limited. For example, a
normally used ultralow carbon steel such as an IF
(interstitial free) steel, an ultralow carbon Ti
steel containing Ti and a small amount of Nb, and an
ultralow carbon Ti-Nb steel may be used for the steel
sheet 2. A steel containing a strengthening element
such as Si, Mn, P, and a steel containing B as a
grain boundary strengthening element may also be used
for the steel sheet 2. A steel containing Cr such as
a stainless steel may also be used for the steel
sheet 2. The steel containing Cr is suitable when
the plated steel sheet 1 is used under a condition
where rust is likely to occur on an end surface such
as outdoors.
[0041] As described above, the pre-plating layer 3
contains Al, Cu, In, Zn, Sn, or Sb, or any
combination thereof. That is, the pre-plating layer
- 15 -
3 may contain Al, Cu, In, Zn, Sn, or Sb alone, or may
also contain two or more of these elements. The preplating
layer 3 may also contain metals such as Cr,
Mo, Nb, and Fe. However, when the total amount of
the metals such as Cr, Mo, Nb, and Fe is greater than
10 mass%, the pre-plating layer 3 is brittle and is
likely to peel off during working. For example, when
the total amount of the metals is greater than 10
mass% and the same experiment as the fifth experiment
is conducted, the area ratio of the remaining preplating
layer is likely to decrease. Thus, the total
amount of the metal other than Al, Cu, In, Zn, Sn,
and Sb is preferable to be 10 mass% or less. The
method of forming the pre-plating layer 3 is not
limited, and an electrolytic treatment method is
preferable. This is because the electrolytic
treatment method is the most excellent in uniformity
and exhibits a corrosion resistance improving effect
most effectively under the present situation. Salt
of the above-described six kinds of metals contained
in an electrolytic treatment solution is not limited
and, for example, sulfate, chloride salt, nitrate,
formate, or acetate may be used.
[0042) The coating weight of the pre-plating layer 3
is 0.5 g/m2 or more. When the coating weight of the
pre-plating layer 3 is less than 0.5 g/m2
, a region
where sufficient corrosion resistance is not obtained
is possibly made on the plated steel sheet. For the
purpose of obtaining more excellent corrosion
- 16 -
resistance, the coating weight of the pre-plating
layer 3 is preferable to be 0.8 g/m2 or more. The
upper limit of the coating weight of the pre-plating
layer 3 is not limited, and the effect of the coating
weight of the pre-plating layer 3 is saturated if the
coating weight is about 5.0 g/m2
, and the pre-plating
layer 3 is likely to peel off if the coating weight
is greater than 100.0 g/m2
• Thus, the coating weight
of the pre-plating layer 3 is preferable to be 100.0
g/m2 or less from a viewpoint of suppression of
peeling, and is preferable to be 5.0 g/m2 or less from
an economic viewpoint.
[0043] The Ni content of the Zn-Ni alloy for the
plating layer 4 is 5 mass% to 15 mass%. When the Ni
content is less than 5 mass%, the Zn content results
in being greater than 95 mass%, and sufficient
corrosion resistance to degraded gasoline cannot be
obtained, red rust occurs early, and pitting occurs,
similarly to normal Zn plating. Thus, the Ni content
is 5 mass% or more. For the purpose of obtaining
more excellent corrosion resistance to degraded
gasoline, the Ni content is preferable to be 7 mass%
or more. On the other hand, when the content ratio
of Ni is greater than 15 mass%, the plating layer 4
hardens too much, thereby causing peeling during
working, resulting in that sufficient corrosion
resistance cannot be obtained. Thus, the Ni content
is 15 mass% or less. For the purpose of more
suppressing the peeling during working, the Ni
- 17 -
content is preferable to be 13 mass% or less.
[0044] The coating weight of the plating layer 4 is
5 g/m2 or more. When the coating weight of the
plating layer 4 is less than 5 g/m2
, sufficient
corrosion resistance cannot be obtained to both
degraded gasoline and a composite fuel of gasoline
and alcohol. For the purpose of obtaining more
excellent corrosion resistance, the coating weight of
the plating layer 4 is preferable to be 10 g/m2 or
more. The upper limit of the coating weight of the
plating layer 4 is not limited, and the effect of the
coating weight of the plating layer 4 is saturated
when the coating weight is about 60 g/m2
, and the
plating layer 4 is likely to peel off when the
coating weight is greater than 100 g/m2
• Thus, the
coating weight of the plating layer 4 is preferable
to be 100 g/m2 or less from a viewpoint of suppression
of peeling, and is preferable to be 60 g/m2 or less
from an economic viewpoint.
[0045] The plated steel sheet 1 exhibits excellent
corrosion resistance to gasoline and a composite fuel
of gasoline and alcohol in a fuel tank formed so as
to make the pre-plating layer 3 and the plating layer
4 inside.
[0046] As illustrated in Fig. 4, the plated steel
sheet 1 may include a pre-plating layer 5 and a
plating layer 6 on the pre-plating layer 5 on the
other surface of the steel sheet 2. If the preplating
layer 5 is provided with the same
- 18 -
constitution as that of the pre-plating layer 3 and
the plating layer 6 is provided with the same
constitution as that of the plating layer 4,
excellent corrosion resistance is exhibited also in a
fuel tank formed so as to make the pre-plating layer
5 and the plating layer 6 inside. As illustrated in
Fig. 5, the plating layer 6 may be formed without the
pre-plating layer 5. As illustrated in Fig. 6, the
pre-plating layer 5 may be formed without the plating
layer 6. In the example illustrated in Fig. 5 or
Fig. 6, the plated steel sheet l exhibits excellent
corrosion resistance in a fuel tank formed so as to
make the pre-plating layer 3 and the plating layer 4
inside.
[0047) As illustrated in Fig. 7, the plated steel
sheet 1 illustrated in Fig. 3 may include a chromatefree
film 7 on the plating layer 4. The chromatefree
film 7 contributes to a rust prevention effect.
When the coating weight of the chromate-free film 7
is less than 10 mg/m2
, a sufficient rust prevention
effect is not be obtained. Thus, the coating weight
of the chromate-free film 7 is preferable to be 10
mg/m2 or more, and is more preferable to be 15 mg/m2
or more for the purpose of obtaining a more excellent
rust prevention effect. On the other hand, the rust
prevention effect of the chromate-free film 7 is
saturated when the coating weight is about 1000 mg/m2
•
Thus, the coating weight of the chromate-free film 7
is, from an economic viewpoint, preferable to be 1000
- 19 -
mg/m2 or less, and more preferable to be 900 mg/m2 or
less.
[ 0 0 4 8 l The chromate-free film 7 can be formed by a
chromate-free treatment (non-chromate treatment). As
a treatment solution to be used for the chromate-free
treatment, a treatment solution not containing
hexavalent chrome, which is harmful environmentally,
for example, a treatment solution containing a salt
of Zr or Ti or both of them, a treatment solution
containing a silane coupling agent are exemplified.
The chromate-free film (conversion treatment film) 7
containing 5 mass% or more of Ti, Zr, P, Ce, Si, Al,
Li, or the like as a main component and not
containing chrome canbe formed on the plating layer 4
by the chromate-free treatment using the treatment
solution. That is, the chromate-free film 7
contains, for example, Ti, Zr, P, Ce, Si, Al, or Li,
or any combination thereof.
[0049] The treatment solution containing a silane
coupling agent is especially effective For formation
of the chromate-free film 7. For example, it is
preferable that a treatment solution containing a
first silane coupling agent containing a single amino
group in a molecule, a second silane coupling agent
containing a single glycidyl group in a molecule, a
fluoro compound of hexafluorotitanic acid or
hexafluorozirconic acid, or both of them, phosphoric
acid, and a vanadium compound is used. A composite
film containing a fluoro compound of
- 20 -
hexafluorotitanic acid or hexafluorozirconic acid or
both of them, phosphoric acid, and a vanadium
compound can be formed as the chromate-free film 7 by
using the treatment solution.
[0050] As for a compounding ratio of the abovedescribed
treatment solution, the following four
relations are preferably satisfied where "A" denotes
a solid content mass of the first silane coupling
agent, "B" denotes a solid content mass of the second
silane coupling agent, "X" denotes a solid content
mass of the fluoro compound, "Y" denotes a solid
content mass of the phosphoric acid, and "Z" denotes
a solid content mass of the vanadium compound.
0.5 ~ A/B ~ 1.7
0.02 ~ X/(A +B) ~ 0.07
0.03 ~ Y/(A + B) ~ 0.12
0.05 ~ Z/(A +B) ~ 0.17
[0051] As illustrated in Fig. 8, the plated steel
sheet 1 illustrated in Fig. 4 may include a chromatefree
film 8 on the plating layer 6. Similarly, the
plated steel sheet 1 illustrated in Fig. 5 or Fig. 6
may include a chromate-free film 8 on the plating
layer 6 or the pre-plating layer 5. The chromatefree
film 8 is preferably composed in the same manner
as that of the chromate-free film 7.
EXAMPLE
[0052] Next, examples of the present invention will
be explained, but conditions of the examples are
condition examples employed for confirming the
- 21 -
applicability and effects of the present invention,
and the present invention is not limited to these
condition examples. The present invention can employ
various conditions as long as the object of the
present invention is achieved without departing from
the spirit of the present invention.
[0053] First, steels 1·1ere each smelted by refining
and a vacuum degassing treatment in a normal
converter to obtain steel materials. Then, on each
of the steel materials, hot rolling, cold rolling,
and continuous annealing were performed under normal
conditions, and thus ultralow carbon steel sheets
each having a sheet thickn~ss of 0.8 mm were
manufactured.
[0054] Thereafter, a pre-plating layer of each of
Zn, Sb, Sn, In, Cu, a Zn-Sb alloy, a Sn-Cu alloy, a
Sn-Sb-In alloy, Co, Mn, Cr, and Ni was formed by
electroplating on both surfaces of each of the
ultralow carbon steel sheets. A solution containing
each of the metals to be contained in the pre-plating
layers as sulfate, chloride salt, nitrate, formate,
or acetate was used in electroplating. A coating
weight of the pre-plating layers was varied in a
range of 0 g/m2 to 6 g/m2
• The composition and the
coating weight of the pre-plating layers are listed
in Table 4.
[0055] Subsequently, a Zn-Ni alloy plating layer was
formed on each of the pre-plating layers. A plating
solution to be used for formation of the plating
- 22 -
layer was produced in a manner that an aqueous
solution containing zinc sulfate: 180 g/L, sodium
sulfate: 100 g/L, and sodium sulfate was prepared and
pH of the aqueous solution was adjusted to 1.2 with
sulfuric acid. The amount of nickel sulfate was
varied in a range of 0 g/L to 300 g/L. The Ni
content of the Zn-Ni alloy was varied in a range of 0
mass% to 20 mass%, and the coating weight was varied
in a range of 3 g/m2 to 50 g/m2
. The Ni content and
the coating weight of the plating layer are listed in
Table 4.
[0056] Then, a chromate-free film was formed by a
chromate-free treatment on each of the plating
layers. The main component of a treatment solution
used for the chromate-free treatment and the coating
weight of the chromate-free film are listed in Table
4 .
[0057] In this manner, various plated steel sheets
were manufactured.
[0058] Thereafter, workability, resistance to
degraded gasoline, and resistance to a composite fuel
of gasoline. and alcohol were examined for the plated
steel sheets.
[0059] (Workability)
In the examination of workability, a forming test
was performed using a cylindrical punch having a
diameter of 50 mm with a drawing ratio of 2.3 by a
hydraulic forming tester. A blank holding pressure
was set to 500 kg/cm2
. Then, the workability was
- 23 -
evaluated based on the following standards.
0: formable and no plating layer peeling
X: formable and plating layer peeled
[0060] (Resistance to degraded gasoline)
In the examination of the r~sistance to degraded
gasoline, a cylindrical cup having a diameter of 100
mm was formed of the plated steel sheet, and a
corrosive solution produced in the following manner
was put into the inside of the cup to be sealed. In
production of the corrosive solution, degraded
gasoline was prepared by a method in conformity with
JIS K 2287, and to this degraded gasoline, 10 vol% of
water was added. The corrosive solution was twophase
separated into a gasoline phase and a water
phase and was adjusted with use of a formic acid
reagent and an acetic acid reagent so that the
concentration of formic acid became 100 mg/L and the
concentration of acetic acid became 200 mg/L in the
water phase being the lower phase side. Thereafter,
the cylindrical cup with the corrosive solution
enclosed therein was left to stand at 45"C, and after
1000 hours elapsed, a corrosion depth of the
cylindrical cup was measured. Then, the workability
was evaluated based on the following standards.
0: no corrosion
6: corrosion having a depth of 20 ~m or less
exists
X: corrosion having a depth of greater than 20
~m exists
- 24 -
[0061] (Resistance to a composite fuel)
In the examination of the resistance to a
composite fuel, a cylindrical cup having a diameter
of 100 mm was formed of the plated steel sheet, and a
corrosive solution produced in the following manner
was put into the inside of the cup to be sealed. In
production of the corrosive solution, a composite
fuel containing gasoline: ethanol: water ~ 69: 29: 2
by volume ratio was prepared, and to this entire
composite fuel, acetic acid: 100 mg/L and NaCl: 100
mg/L were added. Then, the cylindrical cup with the
corrosive solution enclosed therein was left to stand
at 45°C, and after 1000 hours elapsed, a corrosion
depth of the cylindrical cup was measured. Then, the
workability was evaluated based on the following
standards.
@: no corrosion
0: corrosion having a depth of less than 5 ~m
exists
6: corrosion having a depth of not less than 5
~m nor more than 20 ~m exists
X: corrosion having a depth of greater than 20
~m exists
[0062]
4 .
[0063]
These evaluation results are listed in Table
[Table 4]
- 25 -
1'0
m
EXAMPLE
COMPARATIVE
EXAMPLE
SAMPLE
No.
1
2
3
4
5
6
i
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
PRE-PLATING LAYER
COATING
COMPOSmON AMOUNT
Cvm2
)
Zn 0.5
Zn 1.0
Zn 2.0
Sb 0.5
Sn 1.0
In 5.0
Cu 1.2
90MASS%Zn
-10MASS%Sb 1.5
95MASS%Sn 1.0 -5MASS%Cu
90MASS%Sn-5MASS%Sb 6.0 -5MASS%!n
Sn 1.0
Sn 1.0
NONE 0.0
Zn 0.4
Sn 0.2
Co 1.0
Mn 1.0
Cr 1.0
Sn 1.0
Sn 1.0
Sn 1.0
Sn 1.0
N; 44.0
N; 1.0
~~~---------------- ------
PLATING LAYER
COATING
N; CONTENT AMOUNT
(MASS%)
(•1m2
)
5 5
10 10
15 15
10 20
15 20
15 25
15 20
10 30
5 20
10 60
10 20
10 20
10 20
10 20
10 20
10 20
10 20
10 20
0 20
4 20
16 20
10 4
13 59
10 20
~J~
I CHTRROEMAATTMEE-FNRTE E I RESISTANCE RESISTTOA NCE
MAIN COATING WORKABILJTY TO DEGRADED COMPOS:TE REMARKS
COMPONENT AMOUNT GASOLJNE FUEL
(•1m2
)
Zr 10 0 0 © EXAMPLE
Zr 300 0 0 © EXAMPLE
Zr 600 0 0 © EXAMPLE
r; 10 0 0 © EXAMPLE
T; 300 0 0 © EXAMPLE
T; 600 0 0 © EXAMPLE
SILANE COUPLJNG 10 0 0 © EXAMPLE
AGENT
SILANE COUPLJNG 300 0 0 © EXAMPLE
AGENT
SILANE COUPLJNG 600 0 0 © EXAMPLE
AGENT
SILANE COUPUNG 50 0 0 © EXAMPLE
AGENT
T; 6 0 0 0 EXAMPLE
p 300 0 0 0 EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
T; 300 0 X X COMPARATIVE
EXAMPLE
T; 300 0 £,. £,. COMPARATIVE
EXAMPLE
T; 300 X X X COMPARATIVE
EXAMPLE
T; 300 0 £,. £,. COMPARATIVE
EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
Zr 300 0 0 X COMPARATIVE
EXAMPLE
[0064] As listed in Table 4, in Examples No. l to
No. 12 each falling within the present invention
range, in terms of all of the workability, the
resistance to the degraded gasoline, and the
resistance to .the composite fuel, good results were
obtained. In Examples No. l to No. 10, a preferable
chromate-free film was included, so that the
resistance to the composite fuel was particularly
excellent.
[0065] On the other hand, in Comparative examples
No. 13 to No. 15, no pre-plating layer was formed or
the coating weight of the pre-plating layer was
small, so that sufficient resistance to the composite
fuel could not be obtained. In Comparative examples
No. 16 to No. 18, No. 23, and No. 24, the metal
contained in the pre-plating layer was not
appropriate, so that sufficient resistance to the
composite fuel could not be obtained. In Comparative
examples No. 19 and No. 20, the Ni content of the Zn-
Ni alloy of the plating layer was low, so that
sufficient resistance to the degraded gasoline and
sufficient resistance to the composite fuel could not
be obtained. In Comparative example No. 21, the Ni
content of the Zn-Ni alloy of the plating layer was
high, so that sufficient workability could not be
I obtained and peeling of the plating layer occurred.
In association with this, sufficient resistance to
the degraded gasoline and sufficient resistance to
the composite fuel also could not be obtained. In
- 27 -
Comparative example No. 22, the coating weight of the
plating layer was small, so that sufficient
resistance to the degraded gasoline and sufficient
resistance to the composite fuel could not be
obtained.
INDUSTRIAL APPLICABILITY
[0066] The present invention can be utilized in
industries related to fuel tanks of an automobile, a
motor cycle, and the like, for example.

CLAIMS
[Claim 1] A plated steel sheet, comprising:
a steel sheet;
a pre-plating layer on at least one surface of
the steel sheet, the pre-plating layer containing Al,
Cu, In, Zn, Sn, or Sb, or any combination thereof;
and
a plating layer of a Zn-Ni alloy on the preplating
layer, a Ni content of the Zn-Ni alloy being
5 mass% to 15 mass%, wherein
a coating weight of the pre-plating layer is 0.5
g/m2 or more, and
a coating weight of the plating layer is 5 g/m2
or more.
[Claim 2] The plated steel sheet according to claim
1, further comprising a chromate-free film of 10 mg/m2
or more on the plating layer.
[Claim 3] The plated steel sheet according to claim
2, wherein the chromate-free film contains a fluoro
compound of hexafluorotitanic acid or
hexafluorozirconic acid or both of them, phosphoric
acid, and a vanadium compound.
[Claim 4] The plated steel sheet according to claim
2, wherein the chromate-free film is formed by using
a treatment solution containing a salt of Zr or Ti or
both of them, or a treatment solution containing a
silane coupling agent.
[Claim 5] The plated steel sheet according to claim
4, wherein the treatment solution containing the
- 29 -
silane coupling agent contains a first silane
coupling agent containing a single amino group in a
molecule and a second silane coupling agent
containing a single glycidyl group in a molecule.