The present invention relates to a plated steel
material having excellent corrosion resistance, having a
colorless appearance, and further having excellent gloss.
Background Art
10 COO021 Zinc is excellent in corrosion resistance in
the atmospheric environment (sacrificial corrosion
ability etc.) and inhibits corrosion of a steel material,
so is being widely used as plating for steel materials.
For example, electrogalvanized steel materials are being
15 widely used in the field of indoor home electrical
appliances.
COO031 Many such plated steel materials containing
zinc are known (for example, see Japanese Patent
Publication No. 63-14890A). Japanese Patent Publication
20 No. 63-14890A discloses a decorative galvanized steel
material obtained by plating a zinc or zinc-alloy film on
a steel material by a specific coating weight and further
forming a glossy zinc or glossy zinc-alloy film on that
surface by a specific coating weight.
2 5 Summary of Invention
Technical Problem'
[0004] The above decorative galvanized steel material
takes on a colored tinge due to the plating layer
containing a large amount of an q-phase (Zn). If a plated
3 0 steel material takes on a colored tinge, that is, if it
exhibits color, there is the defect that when used with a
clear coating, the clean feel or luxury feel of the
industrial product on which it is used will be impaired.
[0005] Further, the above decorative galvanized steel
35 material has a surface with a gloss of a surface
glossiness Gs60° by the 60' specular gloss method of about
60 due to the fact that the plating layer is not suitably
controlled in average crystal grain size or surface
roughness.
[0006] In recent years, in particular in applications
of home electrical appliances given a clear coating, due
5 to the clean feel and luxury feel, galvanized steel
materials without a colored tinge, in other words,
colorless appearance, and further having an excellent
gloss in surface appearance have been rising in demand.
[0007] Method of Evaluation of Colorless Appearance
10 In this regard, to evaluate if the surface of a plated
steel material is colorless in appearance, it is
necessary that { (2a*) '+ (b*)2 )0.555.0 be satisfied by the
later explained CIELAB color system.
[OOOS] Normally, the color of an object changes
15 depending on the light source (sunlight, fluorescent
light, LED, etc.) If making the light source the color
measurement use standard illuminant D65 and using a
viewing angle loo, it is possible to reproduce the color
of an object under daylight. When measuring the color of
20 the surface of a plated steel material covered by a
plating including zinc by the later explained SCI method
under these measurement conditions, by the CIELAB color
system, if { (2a*)'+ (b*)2 }0.5550., the material can be made
to feel colorless in appearance.
25 [OOOS] The light source is described in the JIS 28720
"Color Measurement Standard Illuminant (Standard Light)
and Standard Light Source'' (corresponding foreign
standard: ISO/CIE 10526). Here, "CIE" is the abbreviation
for the "Commission Internationale de 1'Eclairage
30 (France) ". The CIE develops standards and measurement
techniques for all sorts of matters relating to science
and technology and handicrafts in the fields of light and
illumination, provides guidelines for the preparation of
international standards and national industrial
3 5 standards, and promotes tieups and exchanges with other
international organizations.
[OOlO] The color measurement use standard illuminant
D65 is used when displaying the color of an object
illuminated by daylight. The viewing angle (viewing angle
10') is defined by JIS 28723 "Method of Visual Comparison
5 of Surface Color" (corresponding foreign standard ISO/DIS
3668).
[OOll] When measuring color, the method of measuring
the color while excluding the specular components is
called the SCE (specular components exclude) method,
10 while the method where there is no optical trap and of
measuring the color without excluding the specular
components is called the SCI (specular components
include) method. In the SCI method, the specular
components are included in the measurement, so the color
15 of the material itself is evaluated without regard to the
surface conditions. This is based on the JIS 28722
"Method of Measurement of Color - Reflected and
Transmitted Object Color".
[00121 The CIELAB color space was proposed in 1976 for
20 measuring the color difference due to the differences in
the senses and hardware. In Japan, it is the equivalent
color space prescribed in JIS 28729 "Color Specification
- L*a*b* Color System and L*u*v* Color System".
[0013] The three coordinates of CIELAB correspond to
2 5 the lightness of the color (indicated as L*, meaning
black when its value is 0 and diffuse white when loo), a
position between red and green (indicated as a*, meaning
close to green if its value is negative and close to red
if positive), and a position between yellow and blue
3 0 (indicated as b*, meaning close to blue if its value is
negative and close to yellow if positive).
[00141 Method of Evaluation of Gloss
Next, the gloss can be evaluated by the surface
glossiness measured by the specular gloss method. This
35 surface glossiness is obtained by measuring the specular
reflection light beams a from the surface of a plated
steel material with respect to a prescribed incident
angle (in this Description, 60") and calculating a ratio
a/p based on the specular reflection light beams P of a
glass surface with a refractive index n = 1.567 under the
same conditions and is indicated as "Gs60°".
5 [0015] In recent years, the surface glossiness Gs60°0f
plated steel suitable for use for home electrical
appliances given a clear coating has been deemed 80 or
more. If having such a value of surface glossiness, steel
can be evaluated as excellent in aesthetic nature as
10 well.
[0016] From the definition of colorless appearance and
the definition of gloss shown above, the surface of a
plated steel material preferably satisfies
{ (2a*)2+(b*)2]0.5<50. (preferably 53.5) and the surface
15 glossiness Gs60° is preferably 80 or more (preferably 85
or more) .
[0017] The present invention was made in consideration
of the above situation and has as its object the
provision of a plated steel material having excellent
20 corrosion resistance (sacrificial corrosion ability),
having a colorless appearance (satisfying
{ (2a*)'+ (b*)2 )0.5<5.0 (preferably 53.5)) , and having
excellent gloss (surface glossiness Gs60° of 80 or more
(preferably 85 or more) ) .
25 Solution to Problem
[0018] The inventors engaged in repeated intensive
research to improve the aesthetic nature of the
appearance of a plating layer when forming a layer based
on zinc as the outermost plating layer of a plated steel
3 0 material, that is, the first plating layer, to give that
plating layer excellent corrosion resistance (sacrificial
corrosion ability). As a result, the inventors obtained
the discovery that by limiting the ratio of elements
other than zinc included in the first plating layer and,
35 in particular, including specific intermetallic compound
phases in that plating layer, it is possible to make the
plating layer colorless in surface appearance and
excellent in gloss and thereby completed the present
invention. The gist is as follows:
[0019] [I] A plated steel material comprising a steel
5 material and a first plating layer directly or indirectly
formed on the surface of the steel material, , wherein
the first plating layer containing a total content of 5.0
to 20 mass% of at least one element of Fe, Ni, and Co,
0.1 to 20 mass% of carbon, and Zn, in the first plating
10 layer, a total amount of a 8-phase (FeZn~o), r-phase
(Fe3Zn7), and rl-phase (FeZn4) is 50% or more,
a surface of the first plating layer satisfies
{ (2a*) '+ (b*)2 ]o.5<5.0 by the SCI method in spectral
colorimetry of a light source D65 light and a 10" viewing
15 field, and
a plating surface glossiness by the 60° specular gloss
method Gs60° is 80 or more.
[00201 [2] The plated steel material according to [I],
wherein, in the first plating layer, the total amount of
20 the 6-phase (Ni3Zn~z),y -phase (Ni5Znz1),a nd y-phase
(CosZn2~i)s 30% or more, and the surface of the first
plating layer further satisfies { (a*)'+ (b*)2 }0.553.0 by the
SCI method in spectral colorimetry of a light source D65
light and a lo0 viewing field.
2 5 [0021] [3] The plated steel material according to [I]
or [2], wherein the steel material and the first plating
layer are provided with a second plating layer between
them, and the second plating layer includes a content of
0 to 20 mass% of at least one element among Mg, Al, Si,
3 0 Ti, V, Cr, Mn, Co, Ni, Cu, Sn, and Fe and includes Zn.
[0022] [41 The plated steel material according to [I],
wherein the first plating layer further includes at least
one of 0.01 to 3 mass% of nitrogen and 0.01 to 3 mass% of
sulfur.
35 COO231 [5] The plated steel material according to [I],
wherein an amount of deposition of the first plating
layer on the steel material is 5 to 50 g/m2 per side.
COO241 [6] The plated steel material according to [3],
wherein an amount of deposition of the first plating
layer on the second plating layer is 2 to 10 g/m2 per
5 side.
COO251 [7] The plated steel material according to [3],
wherein an amount of deposition of the second plating
layer on the steel material is 5 to 50 g/m2 per side.
[00261 [8] The plated steel material according to [I]
10 or [2], wherein the first plating layer has an average
crystal grain size of 5 to 80 nrn.
[00271 [91 The plated steel material according to [I]
or [2], wherein the first plating layer has a surface
roughness of Ra80 nm or less.
15 [00281 [lo] The plated steel material according to [I]
or [2], wherein the first plating layer has a largest
content of Fe after Zn and in the intermetallic compound,
any of the 6-phase (FeZnlo) , r-phase (Fe3Zn~), and r1-phase
(FeZn*) is the main layer.
2 0 Advantageous Effect of Invention
[0029] The plated steel material according to the
present invention is predicated on using a layer based on
zinc for an outermost plating layer (first plating layer)
of a plated steel material to give that plating layer an
25 excellent corrosion resistance (sacrificial corrosion
ability) and further improves the ratio of elements other
than zinc included in the plating layer, in particular
the types of intermetallic compound phases included in
the plating layer. As a result, according to the plated
30 steel material, it is possible to realize an excellent
corrosion resistance and a colorless appearance with an
excellent gloss.
Description of Embodiments
[0030] Below, the plated steel material (and method of
3 5 production) according to the present invention will be
explained in detail. Note that, these embodiments do not
limit the present invention. Further, the component
elements of the above embodiments include ones which a
person skilled in the art could easily substitute for or
which are substantially the same. Furthermore, the
various examples included in the above embodiments can be
5 freely combined within a range self evident to a person
skilled in the art.
[0031] Plated Steel Material
The plated steel material according to the present
invention comprises a steel material and a first plating
10 layer directly or indirectly formed on the surface of the
above steel material. The steel material is not
particularly limited. For example, a hot rolled steel
sheet or cold rolled steel sheet can be used. Note that
the type of the steel is also not particularly limited.
15 [0032] The first plating layer contains a total
content of 5.0 to 20 mass% of at least one element among
Fe, Ni, and Co, 0.1 to 20 mass% of carbon, and Zn. Here,
the above "total content" means the total of the contents
of Fe, Ni, and Co. Further, the first plating layer
20 contains a total amount of the 6-phase (FeZnlo), r-phase
(Fe3Zn7), and rl-phase (FeZn4) of 50% or more. Here, the
"total amount" means the area rate.
100331 The carbon referred to here is believed to be
the carbon derived from the at least one type of additive
2 5 of the diallylamine polymer and diallyldialkylammonium
salt polymer added to the plating bath when forming the
first plating layer by electroplating (below, sometimes
simply referred to as "the additives").
[00341 Note that, first plating layer may include as
30 components at least one element among Fe, Ni, and Co,
carbon and Zn and also impurities. Here, the "impurities"
are not intentionally added as components of the first
plating layer but enter in the raw materials or in the
production process and mean Al, Mg, Si, Ti, V, Cr, Mn,
35 Cu, Sn, Nb, Pb, Cd, Ca, Pb, Y, La, Ce, Sr, Sb, 0, P, etc.
Even if these elements are included as impurities in a
total of 1% or so, the effects of the present invention
are not impaired.
COO351 Functional Effect Etc.
By making the first plating layer one based on zinc, it
is possible to give that plating layer an excellent
5 corrosion resistance (sacrificial corrosion ability).
[0036] Further, by making the first plating layer
contain a total content of Fe, Ni, and Co of 20 mass% or
less, the inequality ( (2a*12+( b*)2 )0.5<5.0 is satisfied and
the plating layer can be evaluated as being colorless in
10 appearance. Note that, by making the above total content
17 mass% or less, the above effect can be exhibited at a
further higher level (left side 54.5 in above
inequality), while by making it 15 mass% or less, the
above effect can be realized at an extremely high level
15 (left side 53.5 in above inequality).
[0037] On the other hand, by making the first plating
layer contain a total content of Fe, Ni, and Co of 5.0
mass% or more and making the content of carbon 0.1 to 20
mass%, the first plating layer can be made smaller in
2 0 crystal grain size and refined. Further, by making the
first plating layer contain 0.1 to 20 mass%, the surface
of the first plating layer becomes further smoother. Due
to these actions, the surface glossiness according to the
60" specular gloss method Gs60° becomes 80 or more and the
25 surface of the first plating layer has an excellent
gloss.
COO381 Note that, by making the total content of the
Fe, Ni, and Co 6.0 mass% or more, the above effect can be
realized at a further higher level (plated surface
30 glossiness of 85 or more), while by making it 7.0 mass%
or more, the above effect can be realized at an extremely
high level (plated surface glossiness of 90 or more).
COO391 Further, if the carbon in the first plating
layer is less than 0.1 mass%, the smoothness becomes
35 insufficient and the inconvenience arises that gloss
cannot be obtained. If the carbon exceeds 20 mass%, the
inconveniences arise that parts are formed where the
additives are excessively adsorbed, fine relief shapes
are formed and the gloss is impaired, and, furthermore,
the surface no longer becomes colorless in appearance.
5 When making the content of the carbon in the first
plating layer 0.5 to 10 mass%, the above effect is
realized at a higher level, when making it 0.2 to 5
mass%, the above effect is realized at a further higher
level, and when making it 0.3 to 3 mass%, the above
10 effect is realized at a still higher level. Note that,
the content of the carbon in the first plating layer can
be measured by analyzing the plating layer by glow
discharge emission atomic spectrometry (GDS) which
enables high frequency analysis.
15 [0040] Further, by making the total amount of the
types of phases of the first plating layer, that is, the
&-phase (FeZnlo), r-phase (Fe3Zn7), and rl-phase (FeZn4),
50% or more, it is possible to make the crystal grains of
the first plating layer finer. That is, the various above
2 0 intermetallic compound phases enable the crystallization
overpotential to be made larger compared with zinc alone
(q-phase), so the crystal nuclei are formed before the
crystal growth. Due to this, together with the above
total content of Fe, Ni, and Co and lower limit value of
25 the carbon content, the refining of the first plating
layer is effective at a higher level and excellent gloss
is realized at the surface of the first plating layer.
[0041] As explained above, the plated steel material
according to the present invention is predicated on
3 0 making the outermost plating layer one based on zinc to
realize an excellent corrosion resistance (sacrificial
corrosion ability) and further improves the ratio of
elements other than zinc included in the plating layer,
in particular the types of the intermetallic compound
3 5 phases included in the plating layer. As a result,
according to the plated steel material according to the
present invention, it is possible to realize excellent
corrosion resistance and a colorless appearance with
excellent gloss.
LO0421 Preferred Embodiments
In the plated steel sheet shown above, the above first
5 plating layer preferably has a total amount of the 6-phase
(Ni3Zn22), y-phase (NisZnzl), and y-phase (Co5Znz1) of 30% or
more and the surface of the above first plating layer
preferably further satisfies ( (a*) '+ (b*)2 ]0.5<3.5 by the
SCI method in spectral colorimetry using a light source
10 065 light and 10" viewing field. Here, the above "total
amount" means the area rate. By further satisfying the
above inequality, the plating layer can be evaluated as
exhibiting colorlessness at a further higher level. Note
that, by making the total amount of the 6-phase (Ni3ZnZ2),
15 y-phase (NisZnz~), and y-phase (CosZnzl) 35% or more, the
above effect can be realized at a further higher level
(left side <2.5 in above inequality), while by making it
40% or more, the above effect can be realized at an
extremely high level (left side <2.0 in above
20 inequality).
100431 Further, in the above plated steel sheet,
preferably the steel material and the first plating layer
are provided with the second plating layer between them
and the second plating layer includes a content of 0 to
25 20 mass% of at least one element of Mg, Al, Si, Ti, V,
Cr, Mn, Co, Ni, Cu, Sn, and Fe and includes Zn. Here, the
above "content" means the respective contents of Mg, Al,
Si, Ti, V, Cr, Mn, Co, Ni, Cu, Sn, and Fe.
[00441 The second plating layer is baser in rest
30 potential in a corrosive environment (for example, in 35'C
5 mass% NaCl solution) after removing the effects of the
surface oxide film compared with the first plating layer.
Due to this, the sacrificial corrosion ability can be
further raised.
35 [0045] Note that, as the elements in the second
plating layer other than zinc, as explained above, Mg,
Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Sn, and Fe may be
mentioned, but from the viewpoint of the corrosion
resistance, Mg, Al, Si, Mn, Ni, and Co are preferable.
Further, the second plating layer may contain as metal
5 elements, in addition to the above, impurities which
enter in the raw materials or in the production process.
[00461 Further, in the above plated steel sheet, the
above first plating layer preferably further contains at
least one of 0.01 to 3 mass% of nitrogen and 0.01 to 3
10 mass% of sulfur, more preferably contains at least one of
0.03 to 1 mass% of nitrogen and 0.03 to 1 mass% of
sulfur. Nitrogen and sulfur are also believed to be
elements derived from the additives added to the plating
bath when forming the first plating layer by the
15 electroplating method. By making the first plating layer
formed on the steel material using a galvanization bath
containing the additives contain at least one of 0.01 to
3 mass% of nitrogen and 0.01 to 3 mass% of sulfur, the
surface of the first plating layer becomes further
2 0 smoother and extremely high gloss is exhibited. Further,
these nitrogen and sulfur can be measured in the same way
as carbon by GDS.
100471 Furthermore, in the above plated steel sheet,
the amount of deposition of the above first plating layer
25 on the above steel material is preferably 5 to 50 g/m2 per
side. Note that, this is the mode for plated steel sheet
in the case of the second plating layer not being
contained. By making the above amount of deposition 5 g/m2
or more per side, a further excellent corrosion
30 resistance (sacrificial corrosion ability) can be
exhibited. On the other hand, even if making the above
amount of deposition over 50 g/m2 per surface, no further
improvement in the corrosion resistance can be
anticipated, so by making the deposition 50 g/mZ or less,
35 it is possible to save on the plating materials. Note
that, the more preferable range of the amount of
deposition is 10 to 20 g/m2 per side. Due to this, the
above effects can be realized on respectively further
higher levels.
[00481 As opposed to this, in the above plated steel
sheet, the amount of deposition of the first plating
5 layer on the second plating layer is preferably 2 to 10
g/m2 per side. Note that, this is a mode of plated steel
sheet in the case of including the second plating layer.
If providing the second plating layer, by making the
above amount of deposition 2 g/m2 or more per side, so the
10 patterns or color arising due to the second layer of
plating are concealed, the appearance becomes colorless,
and a good gloss can be realized. On the other hand, even
if the above amount of deposition exceeds 10 g/m2 per
side, no further improvement in colorlessness or gloss
15 can be expected, so by making the amount 10 g/mZ or less,
the plating material can be saved. Note that, the more
preferable range of the upper limit value of the above
amount of deposition is 6 g/m2 per side. Due to this, the
above effect can be realized at a further higher level.
20 [0049] Next, in the above plated steel sheet, the
above first plating layer preferably has an average
crystal grain size of 5 to 80 nm. The average crystal
grain size of the first plating layer also has an effect
on the optical characteristics of the surface of the
25 plated steel sheet. In general, if the first plating
layer is excessively large in average crystal grain size,
a sufficient gloss is not realized. For this reason, the
average crystal grain size of the plating layer is
preferably 80 nm or less, more preferably 30 nm or less.
30 As opposed to this, the lower limit value of the above
average crystal grain size does not particularly have to
be set, but if 5 nm or more, industrial production is
easy.
[0050] The average crystal grain size of the first
35 plating layer may be found by directly finding the
average value of the crystal grain size from a
transmission-type electron micrograph, but may also be
found by analysis of the shape of the X-ray diffraction
peaks. Alternatively, the following formula (Scherrer's
equation) may also be used to simply find the crystal
grain size ( D ) .
5 D= ( 0 . 9 ~/) ( pcose)
Note that, in the above equation, h is the X-ray
wavelength, P is the half width (rad), and 0 is the Bragg
angle of the diffraction line.
[0051] Furthermore, in the above plated steel sheet,
10 when the surface roughness of the first plating layer is
measured by an SPM (scanning probe microscope), it is
preferably an Ra (arithmetic average roughness) of 80 nm
or less. The surface roughness of the first plating layer
of the plated steel sheet has an effect on the optical
15 characteristics of the plated steel sheet. That is, in
general, the lower a plating layer in surface roughness,
the higher the plated steel r?aterial in glossiness. For
this reason, when the roughness of the surface of the
first plating layer is excessively high, that surface
2 0 will not become a mirror surface and the outermost
surface of the plated steel sheet will not have excellent
gloss.
[0052] This can be easily understood from the abovementioned
correlation between the average crystal grain
25 size of the first plating layer and surface roughness of
the first plating layer. That is, by making the first
plating layer finer in structure (making the average
crystal grain size smaller), it is possible to lower the
roughness of the plating layer (make the layer smoother)
30 and in turn possible to increase the glossiness of the
surface of the first plating layer.
100531 Further, the surface roughness of the first
plating layer is closely related to the wavelength at the
region of light visible to humans (380 nm to 810 nm) . If
35 a roughness of about one-tenth the wavelength at that
visible light region, light of substantially the entire
wavelength of the visible light region is reflected
straight. As a result, the color of the plated steel
sheet becomes the object color and a highly glossy
appearance is exhibited. Furthermore, the surface
5 roughness of the first plating layer depends on the
hairlines of the steel material before plating (long
lines given by polishing for the purpose of obtaining a
beautiful appearance of the product), the embossing
(working of steel material to form relief letters,
10 designs, etc.), and other patterning, but the location of
measurement of roughness may also be the projecting parts
of the patterns since micropatterns do not have an effect
on perception of gloss. Note that, the lower limit value
of the roughness of the first plating layer does not have
15 to be particularly set, but if the plating layer surface
is excessively smooth, this becomes the case of marring
and load shifting, so the Ra (arithmetic average
roughness) is preferably made 5 nm or more.
100541 Note that, the glossiness of the first plating
20 layer depends not only on the average crystal grain size
or surface roughness of the plating layer itself.
explained above, but also the roughness of the plated
base material. In general, the lower the plated base
material in roughness, the higher the plated steel
25 material in glossiness. The roughness of the plated base
material has to be controlled from viewpoints other than
the glossiness of the plated steel material (for example,
the lubrication at the time of press forming). Further,
if making the first plating layer sufficiently thick, the
30 effect on the above glossiness due to the roughness of
the plated base material becomes smaller. Due to the
above, in the present invention, the roughness of the
plated base material is not in the end limited.
100551 The roughness of the plated base material of
35 the first plating layer can be adjusted by various
methods. As specific methods of adjustment, transfer by
rolling, shot blasting, polishing, etc. may be mentioned,
but the invention is not limited to these. Other known
means can also be applied.
LO0561 In addition, in the above plated steel sheet,
the above first plating layer contains a large amount of
5 Fe after Zn. In the above intermetallic compound phases,
preferably any of the 6-phase (FeZn~o), r-phase (Fe,Zn.l),
and rl-phase (FeZn4) is a main phase (phase with largest
area rate). That is, by increasing the content of Fe
after Zn, the formation of the q-phase (Zn-phase) is
10 suppressed, the intermetallic compound phase with the
large crystallization overpotential compared with the 11-
phase (Zn-phase) becomes the main phase and finely
precipitates, so the plated surface glossiness by the 60"
specular gloss method Gs60° becomes 80 or more and the
15 surface of the plating layer has further better gloss.
100571 Such a plating phase configuration may be
directly found from the diffracted image of a
transmission-type electron microscope or may be found
from the X-ray diffraction pattern. The plating layer
20 formed by electroplating is large in strain and is
influenced by the orientation of the substrate, so is
often different from the values in usual documents etc.
However, the presence of the 11-phase in the present
invention can be judged comparing the maximum value of
25 the peak strength at 45. lo to 46. lo with the maximum value
of the peak strength at 48.0° to 52.0' by the 20/0 method
using Co for the target. If the maximum value of the peak
strength at 45.1' to 46.1° is 20% or less of the maximum
value of the peak strength at 48.0" to 52.0°, an amount of
3 0 the ?]-phase (Zn) having a detrimental effect on the gloss
is just not present. If 10% or less, no substantive
effect is seen. Further, if there is the second plating
layer, it is possible to change the incident angle of the
X-rays to remove the effect of the second plating layer.
3 5 [0058] Method of Production of Plated Steel Material
Below, the method of production of the plated steel sheet
according to the present invention will be explained in
detail.
[00591 Method of Formation of First Plating Layer
5 The plated steel material according to the present
invention is produced by using a plating bath containing
zinc sulfate, sodium sulfate, and sulfuric acid and
further having at least one type of diallylamine polymer
and diallyldialkylammonium salt polymer added to it when
10 forming the above first plating layer (outermost plating
layer) so as to electrogalvanize the steel material (or
the later explained second plating layer). Further, the
plating bath directly or indirectly forms on the steel
material a zinc alloy layer containing not only Zn, but
15 also at least one element of Fe, Co, and Ni.
[0060] The plating bath, as explained above, has not
only Zn, but also at least one element among Fe, Co, and
Ni (element X) added to it. The molar concentration ratio
and the molar concentrations of the element X and L% in
20 the plating bath are adjusted so that both satisfy the
following two formulas. By adjusting the composition etc.
of the plating bath in this way, coarsening of the
crystal grains is suppressed and it is possible to form a
first plating layer having excellent corrosion resistance
25 (sacrificial corrosion ability) and having a colorless
appearance with excellent gloss
~n~'+~~~7m2o0l/.l iter
[00621 If the molar concentration ratio and molar
3 0 concentrations in the plating bath are outside the scope
of at least one of the above two formulas, the first
plating layer is liable to fall in gloss and also the
plating layer is liable to no longer be colorless and to
no longer satisfy { (2a*)'+ (b*)2)0.5_<05.. Further, by using
3 5 a plating bath satisfying both of the above two formulas,
refinement of the crystal grains of the obtained first
plating layer can be promoted. Note that, the plating
bath further unavoidably has mixed into it so4' and C1
forming counter ions to the metal ions in the plating
bath (zn2+,~ e ~ c+o,2+ , ~i'+) .
5 [0063] Further, in alloy plating the first plating
layer, nickel sulfate or nickel chloride may be added to
the plating solution to form a Zn-Ni-based plating layer,
iron sulfate or iron chloride may be added to form a Zn-
Fe-based plating layer, and cobalt sulfate or cobalt
10 chloride may be added to form a Zn-Co-based plating
layer.
[00641 In the above electroplating, by making the
current density 5 to 15 kA/m2, it is possible to control
the product of the current density and the conduction
15 time, that is the coulombs, to realize the target plating
deposition amount. By making the current density 5 kP./m2
or more, the film-forming speed becomes sufficient and
further coarse crystal grains become difficult to form
whereby the first plated surface becomes smoother in
20 state. Further, by making the current density 5 kA/m2 or
more, formation of the q-phase can be suppressed and a
colorless appearance can be obtained. On the other hand,
by making the current density 15 kA/m2 or less, the steel
material surface (or the second plating layer surface)
25 can be smoothly supplied with Zn, Fe, Co, Ni, and other
metal elements and a uniform, good bondability first
plating layer can be obtained. If making the current
density 7 kiX/m2 to 12 kA/mZ, the above effects are
realized at a further higher level, so this is
30 preferable.
[0065] Further, the known art can be used for control
of the bath temperature or the relative flow rate between
the plated material constituted by the steel material (or
the second plating layer) and the plating solution.
3 5 Specifically, at the time of electroplating, the relative
solution flow rate between the plating bath and the
plated material (steel material or the second plating
layer) is preferably made 0.5 m/sec or more. The larger
the relative solution flow rate, the thinner the
diffusion layer between the plated material and the
plating solution and the easier the supply of metal ions.
5 This is particularly effective in the case of plating by
a high current density. There are various ways of
thinking regarding the relative solution flow rate, but
when the plated material is steel sheet, there is the
method of running the sheet at a high speed and the
10 method of imparting a counterflow. Note that, no upper
limit is particularly set on the relative solution flow
rate, but if becoming 5 m/sec or more, there will be
issues such as the plating solution being carried away or
the pump capacity giving rise to a counterflow, so this
15 is not preferable.
100661 The pH of the plating bath is preferably 1 to 3
in range. By making the pH of the plating bath 1 or more,
the generation of hydrogen resulting in a competitive
reaction at the time of electroplating can be suppressed
20 and a remarkable drop in the current efficiency can be
suppressed. Further, by making the pH of the plating bath
3 or less, the metal elements (Zn, Fe, Co, Ni) in the
plating bath can be stably maintained in the dissolved
state. Note that, if making the pH 1.5 to 2.5 in range,
25 the above effects are realized at a further higher level.
[00671 The plating bath temperature is preferably made
40 to 60°C from the viewpoints of the current efficiency
and evaporation of the plating solution. That is, by
making the plating bath temperature 40°C or more, it is
30 possible to realize excellent current efficiency, while
by making it 60° or less, it is possible to suppress
evaporation of the plating solution.
100681 The plating bath preferably contains gloss
additives including at least one type of a diallylamine
3 5 polymer and diallyldialkylamrnonium salt polymer (below,
sometimes simply referred to as the "additives") in an
amount of 0.1 g/liter to 10 g/liter. These additives do
not cause the precipitation of the 11-phase (Zn-phase) in
the first plating layer, but cause the precipitation and
growth of only specific intermetallic compound phases (6-
5 phase (FeZnl~,) r-phase (Fe3Zn7), rl-phase (FeZn4), 6-phase
(Ni3Znz2), y-phase (NisZnz~),a nd y-phase (CosZn21)) .
Furthermore, they are used for refining the crystal grain
size of the first plating layer.
[00691 Specifically, as examples of the diallylamine
10 polymer, a diallylamine hydrochloride polymer,
diallylamine polymer, methyldiallylamine hydrochloride
polymer, methyldiallylamine amide sulfide polymer,
methyldiallylamine succinate polymer, diallylamine
hydrochloride-sulfur dioxide copolymer, diallylamine
15 acetate-sulfur dioxide copolymer, and methyldiallylamine
hydrochloride-sulfur dioxide copolymer may be mentioned.
For the diallylamine polymer, these may be used
independently or two or more types of these may be mixed
and used.
20 [00701 Further, as examples of the
diallyldialkylammonium salt polymer, a
diallyldimethylammonium chloride polymer,
diallylmethylethylammonium ethyl sulfate polymer,
diallylmethylethylammonium ethyl sulfate-sulfur dioxide
2 5 copolymer, diallyldimethylammonium chloride-sulfur
dioxide copolymer, diallyldimethylammonium chlorideacrylamide
copolymer, and partial 3-chloro-2-
hydroxypropylated diallylamine hydrochloridediallyldimethylammonium
chloride copolymer may be
3 0 mentioned. For the diallyldialkylammonium salt polymer,
these may be used independently or two or more types of
these may be mixed and used.
[00711 Furthermore, the diallylamine polymer and
diallyldialkylammonium salt polymer may be mixed for use
35 as the additive. The mixed state is not limited to two
types. Three or more types of polymers may also be mixed.
100721 In particular, among the diallylamine polymers
and diallyldialkylammonium salt polymers, polymers having
five-member ring structures are preferable. By the above
polymers having five-member ring structures, in the first
5 plating layer, specific intermetallic compound phases (6-
phase (FeZnlo) , r-phase (Fe3Zn7), rl-phase (FeZn*), &-phase
(Ni3Zn22), y-phase (NisZnzl), and y-phase (CosZnzl)) can be
made to efficiently precipitate and grow and the crystal
grain size of the first plating layer can be made finer
10 by a higher level. Note that by what kind of mechanism
these phenomena arise is not certain, but the phenomena
were empirically found by the inventors.
100731 Whether the above polymer includes five-member
ring structures can be evaluated by the following method.
15 That is, the first plating layer is dissolved and the
metal ions removed so that the organic matter is not
allowed to coprecipitate. The result is refined so as not
to destroy the structures and the five-member ring
structures are identified. Specifically, various nuclear
20 magnetic resonance (NMR) spectroscopic methods may be
used to identify the five-member ring structures.
100741 The amount of the additives in the plating bath
is made 0.1 g/liter to 10 g/liter in range. If including
the above-mentioned additives in the plating bath for
25 electroplating, when forming the first plating layer, the
additives will pack locations where the current
concentrates and plating growth at those parts will be
obstructed, but at parts where the additives are not
packed, growth of the first plating layer will be
30 promoted, the surface of the plating layer formed becomes
smooth, and high gloss can be realized. If the amount of
the additives in the plating bath is made less than 0.1
g/liter, the above amount of packing of the additives is
insufficient, so the above effect is not obtained. On the
35 other hand, if making the amount of the additives over 10
g/liter in the plating bath, the amount of packing of the
additives will be too large and conversely the additives
will become uneven, so the above effect will not be
obtained. Note that, if making the amount of the
additives 0.2 g/liter to 4 g/liter, the above effects are
5 realized at respectively further higher levels.
[0075] Further, the average molecular weight of the
additives according to the present invention is
preferably made 1000 to 10000 in range. By making the
average molecular weight of the additives 1000 or more,
10 it is possible to keep the first plating layer from
excessively growing. On the other hand, by making the
average molecular weight 10000 or less, it is possible to
avoid the additives from becoming insoluble in the
plating bath. If making the average molecular weight of
15 the additives 2000 to 6000 in range, the above effects
are realized at higher levels.
100761 The above gave descriptions relating to a
method of forming a first plating layer, but these
descriptions can also be applied in the same way to the
20 case of directly forming a plating layer on a steel
material of course and also the case of forming a first
plating layer on the later explained second plating
layer.
[00771 Method of Forming Second Plating Layer
25 Next, in the plated steel sheet according to the present
invention, the steel material and the first plating layer
may have a second plating layer interposed between them.
Due to this, the plated steel material is further raised
in corrosion resistance (sacrificial corrosion ability).
30 The second plating layer can be formed using a plating
bath containing zinc sulfate, sodium sulfate, and
sulfuric acid to electrogalvanize the steel material.
Further, the plating bath may have added to it, in
addition to Zn, one or more elements of Mg, Al, Si, Ti,
3 5 V, Cr, Mn, Co, Ni, Cu, Sn, and Fe.
[00781 As the conditions for forming the second
plating layer, by making the current density 1 to 20 k~/m'
(more preferably 5 to 15 k~/m'), it is possible to realize
the desired coating weight. Further, by making the
relative solution flow rate between the plating bath and
plated material (steel material) at the time of
5 electroplating 0.5 m/sec or more, it is possible to
facilitate the supply of metal ions. Furthermore, by
making the pH of the plating bath 1 or more, it is
possible to suppress the generation of hydrogen which
would competitively react at the time of electroplating
10 and possible to keep the current efficiency from
remarkably falling, while by making the pH 3 or less, it
is possible to maintain the elements in the plating bath
(Zn, Mg, Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Sn, and Fe)
in the dissolved state. Note that, if making the pH 2 or
15 less in range, the above effects are exhibited to a
further higher level.
[0079] In addition, when forming the second plating
layer, the plating bath temperature may be made 40 to 60°C
from the viewpoint of current efficiency and evaporation
20 of the plating solution. Additives may be suitably added
to the plating bath.
[00801 Further, the second plating layer may be formed
by using a hot dip coating bath containing zinc to hot
dip coat the steel material. Further, a hot dip
25 galvanization bath may also have added to it, in addition
to Zn, at least one element of Mg, Al, Si, Ti, V, Cr, Mn,
Co, Ni, Cu, and Sn.
[0081] As the conditions for forming the second
plating layer in the case of using a hot dip coating
30 bath, a steel material annealed for reduction is dipped
into the coating bath heated to 400°C to 650°C and is
pulled up after a predetermined time. Wiping may be
performed for keeping down the amount of deposition of
the plating. Further, if including Fe in the plating
3 5 coating, it is sufficient to pull up the material from
the coating bath and then heat to 450°C or more for
alloying.
[0082] Method of Surface Treatment of First Plating
Layer
Furthermore, the plated steel material according to the
5 present invention may have the outermost plating layer,
that is, the first plating layer, further treated on its
surface in various ways for the purpose of improving the
various characteristics.
[0083] To prevent discoloration of the first plating
10 layer and improve the adhesion with the later explained
paint, the first plating layer may be treated by chromate
treatment or chromate-free treatment (nonchromate
treatment) for primary rustproofing to form a rustproof
coating layer. In the case of chromate treatment, for
15 example, it is possible to use a chromate treatment
solution containing chromic acid and a reaction promoter
as main ingredients. The chromate deposition is made 1 to
200 mg/m2. If the chromate deposition is less than 1
mg/m2, a sufficient rustproofing effect cannot be
20 obtained, while if over 200 mg/m2, the rustproofing effect
ends up becoming saturated.
LO0841 On the other hand, in the case of chromate-free
treatment, it is possible to use a treatment solution not
containing the toxic hexavalent chrome in the treatment
25 solution, but containing salts of Zr, Ti, etc., a
treatment solution containing a silane coupling agent,
etc. In chromate-free treatment, a chromate-free
treatment layer mainly comprising Ti, Zr, P, Ce, Si, Al,
Li, etc. and not containing chrome is formed. The amount
30 of deposition of the chromate-free treatment layer is
preferably made 1 to 1000 mg/m2. If the amount of
deposition of the chromate-free treatment layer is less
than 1 mg/m2, a sufficient rustproofing effect is not
obtained, while if over 1000 mg/m2, the rustproofing
3 5 effect is saturated.
[0085] Further, to realize prevention of discoloration
and resistance to scratching of the plated steel material
at a higher level, it is preferable to form a coating
film of 0.5 to 100 pm thickness after the chromate
treatment etc. The coating film can be formed by a known
coating method. As the coating film material, an acrylic-
5 based bake-on paint, urethane-based paint, epoxy-based
paint, polyester-based paint, polyether sulfone-based
paint, melamine alkyd-based paint, etc. may be mentioned.
For forming the coating film, these paints may be used
independently or mixtures of these paints may be used. As
10 the coating method, the roll coater method, curtain
coater method, spray gun method, electrostatic method,
etc. may be mentioned. Among these coating methods, the
roll coater method and curtain coater method are
preferable from the viewpoints of productivity and
15 uniformity. Note that, to make use of the high glossiness
of the plated steel sheet according to the present
invention, it is preferable to use a clear paint to which
no coloring pigment is added so as to avoid scattering
and absorption of light.
20 [00861 According to the method of production of a
plated steel material according to the present invention
, shown above, when forming the outermost plating layer
constituted by the first plating layer (first plating
layer), by adding to the galvanization bath at least one
25 type of a diallylamine polymer and diallyldialkylammonium
salt polymer in specific amounts and adjusting the
composition of the plating bath for plating, it is
possible to obtain a plated steel material having an
excellent corrosion resistance (sacrificial corrosion
30 ability) which is colorless in appearance and further has
an excellent gloss.
Examples
[0087] Below, the effects of the present invention
will be specifically explained by invention examples.
35 Note that the present invention is not limited to the
conditions used in the following invention examples.
Further, the underlined parts in Tables 1 to 6-2 mean
values outside the scope of the present invention.
[0088] Annealed and adjusted steel sheets of
thicknesses of 0.6 mm (respectively containing as
chemical compositions C: 0.001%, Si: 0.01%, Mn: 0.1%, P:
5 0.008%, and S: 0.004%) were degreased by electrolysis
using a concentration 30 g/liter Na4Si04 treatment
solution under conditions of a treatment solution of 60°C,
current density of 20~/dm', and treatment time of 10
seconds and then rinsed. Next, the electrolytically
10 degreased steel materials were dipped in concentration 50
g / liter 60°C HzSO4 aqueous solution for 10 seconds and
further rinsed to perform plating pretreatment. Note
that, the Ra (arithmetic average roughness) in the Ldirection
of the steel sheets (direction parallel to
15 rolling direction) was 0.6 pm.
[0089] Next, using plating baths having the
compositions shown in Table 1 and containing the
additives shown in Table 2, Table 3-1, and Table 3-2,
electroplating was performed under the various conditions
20 of Table 2, Table 3-1, and Table 3-2, whereby first
plating layers were formed on the steel sheets and Test
Examples 1 to 74 showing the different properties in
Table 4, Table 5-1, and Table 5-2 were obtained.
[0090] Next, Test Examples 75 to 125 having the same
25 steel sheets and first plating layers as specific test
examples shown in Table 4 (Test Examples 1, 3, 8, 9, 12,
and 19) and second plating layers of the compositions
shown in Table 6-1 and Table 6-2 between them were
obtained. The mode of formation of the second plating
30 layer was made a mode based on the mode of formation of
the first plating layer.
[00911 Note that, in Table 4 to Table 6-2, the modes
of the intermetallic compound phases are indicated as "A"
when making any of the 6-phase (FeZnl~),r -phase (Fe3Zn7),
3 5 and rl-phase (FeZn4) as the main phase, as "B" v~hen
including at least one intermetallic compound phase among
the &phase (FeZnla) , r-phase (Fe3Zn7), rl-phase (FeZn4), 6-
phase (Ni3Znzz), y-phase (Ni5Znzl), and y-phase (CosZn2,),
and as "C" when not corresponding to the above A or B.
Further, in these tables, the X-ray diffraction strength
5 is indicated as "A" when the maximum value of the peak
strength from 45.1" to 46.1' is 10% of the maximum value
of the peak strength from 48.0' to 52.0° or less, as "B"
when over 10% to 20%. and as "C" when over 20%.
i*:Equation (2) left side is sum of Zn2'+x2' where "X" indicates an element X (any one of Fe, Ni, and Co)

[0095] Table 3-2
Test Bath no. Btaytphe A~dydiptei ve Am't of Current
Average density
addition molecular (@./m21
pH Bath Remarks
temp.
Inv. ex.
Inv. ex.
Inv. ex.
Ref. ex.
Inv. ex.
5 0 Inv. ex.
5 0 Inv. ex.
50 Inv. ex.
2 1 50 1 Inv. e:;.
2 150 I Inv. ex.

[0097] Table 5-1
[0098] Table 5-2
Test
no.
Element X content
(mass81
[!a'):+ !b'I'lu" 1 (2a')" i(b')'lY" Presence of
intermetallic
Diffraction
strength of
Carbon
content
~ ~ 6 0 'De position
!9/m:)
Crystal
grain size
Roughness
Ba (nml
Remarks

[OlOl] Plated steel sheets with amounts of deposition
of the first plating layers after plating such as shown
in Table 4, Table 5-1, and Table 5-2 or plated steel
sheets with amounts of deposition of the first and the
5 second plating layers such as shown in Table 6-1 and
Table 6-2 were rinsed and dried. Next, a Konica-Minolta
CM-2500d as a measurement device was used to measure "a*"
and "b*" b y a light source D65, 10" viewing field, and the
SCI method. Further, a glossimeter was used to measure
10 the Gs60° based on the Rats (arithmetic average roughness)
in the L-direction (rolling direction) and C-direction
(direction perpendicular to rolling direction). The
"Gs60°" shown in Table 4 to Table 6-2 is the average value
of the values measured based on the different Ra's in the
15 L-direction and the C-direction. Furthermore, the carbon
content (mass%) contained in the first plating layer was
measured with a HORIBA high frequency glow discharge
emission surface analyzer. The average crystal grain size
(nm) of the plating layer was evaluated by analysis of
2 0 the shapes of the X-ray diffraction peaks. Note that,
when finding the average crystal grain size, Scherrer's
equation { (D= (0.9h) / (pcos6) ) ) was used. The X-ray
diffraction was measured using Co for the target and
performing measurement at an accelerated voltage of 30
25 kV, current of 100 mA, scan speed of l"/min, and scan axis
of 28. The above results of evaluation are shown together
in Table 4 to Table 6-2.
[0102] The method of analysis of the first and the
second plating layer were as follov~s. That is, the
30 contents of the elements were analyzed from the surface
in the depth direction by glow discharge emission atomic
spectrometry (GDS).
[0103] Further, the interface between the plating
layer/steel base material etc. at this time was
3 5 determined as follov~s: That is, when analyzed from the
surface, the place where the total of the metal elements
exceeded 70 mass% was judged as the outermost surface of
the first plating layer, the region where the total of
Fe, Ni, and Co was 5 to 20 mass% and the carbon was 0.1
to 20 mass% was judged as the first plating layer, and
5 the region from there to a depth where the Fe derived
from the steel base material exceeded 50 mass% was judged
as the second plating layer. Further, when there was no
second plating layer, the region from where the total of
the metal elements exceeded 70 mass% to a depth where the
10 Fe derived from the steel base material exceeded 50 mass%
was judged as the first plating layer. According to Table
4 to Table 6-2, the invention examples (improved in at
least one of the ratio of elements other than zinc
included in the plating layer, in particular the types of
15 the intermetallic compound phases contained in the
plating layer) all had { (~a*)(~b+*) 2 }0.5~50. and Gs60°>80.
For this reason, the plated steel materials of the
invention examples all can be said to have excellent
corrosion resistance and be colorless in appearance with
20 excellent gloss.
[01041 As opposed to this, the comparative examples
(not improved in at least one of the ratio of elements
other than zinc included in the plating layer, in
particular the types of the intermetallic compound phases
25 contained in the plating layer) all failed to satisfy at
least one of { (2a*12+( b*)2 }0.555.0 and Gs60°t80. For this
reason, the plated steel materials of the comparative
examples all cannot be said to have excellent corrosion
resistance and be colorless in appearance with excellent
30 gloss.

CLAIMS
Claim 1. A plated steel material comprising a steel
material and a first plating layer directly or indirectly
formed on the surface of the steel material,
5 wherein said first plating layer containing a
total content of 5.0 to 20 mass% of at least one element
of Fe, Ni, and Co, 0.1 to 20 mass% of carbon, and Zn,
in said first plating layer, a total amount of
a &phase (FeZnlo) , r-phase (Fe3Zn7), and i'1-phase (FeZn4)
10 is 50% or more,
a surface of said first plating layer satisfies
{ (2a*)'+(b*) 0 by the SCI method in spectral
colorimetry of a light source D65 light and a 10" viewing
field, and
15 a plating surface glossiness by the 60° specular
gloss method Gs60° is 80 or more.
Claim 2. The plated steel sheet according to claim
1, wherein,
in said first plating layer, the total amount
20 of the &-phase (Ni~Znzz),y -phase (NisZnz~),a nd y-phase
(CosZnzl) is 30% or more, and
the surface of said first plating layer further
satisfies { (a*)'+ (b*)2 }0.5<3. 0 by the SCI method in
spectral colorimetry of a light source D65 light and a 10"
25 viewing field.
Claim 3. The plated steel material according to
claim 1 or 2, wherein,
said steel material and said first plating
layer are provided with a second plating layer between
them, and
said second plating layer includes a content of
0 to 20 mass% of at least one element among Mg, Al, Si,
Ti, V, Cr, Mn, Co, Ni, Cu, Sn, and Fe and includes Zn.
Claim 4. The plated steel material according to
3 5 claim 1 or 2, wherein said first plating layer further
includes at least one of 0.01 to 3 mass% of nitrogen and
0.01 to 3 mass% of sulfur.
Claim 5. The plated steel material according to
claim 1 or 2, wherein an amount of deposition of said
first plating layer on said steel material is 5 to 50 g/m2
5 per side.
Claim 6. The plated steel material according to
claim 3, wherein an amount of deposition of said first
plating layer on said second plating layer is 2 to 10 g/mZ
per side.
10 Claim 7. The plated steel material according to
claim 3, wherein an amount of deposition of said second
plating layer on said steel material is 5 to 50 g/mZ per
side.
Claim 8. The plated steel material according to
15 claim 1 or 2, wherein said first plating layer has an
average crystal grain size of 5 to 80 nm.
Claim 9. The plated steel material according to
claim 1 or 2, wherein said first plating layer has a
surface roughness of Ra80 nm or less.
20 Claim 10. The plated steel material according to
claim 1 or 2, wherein said first plating layer has a
largest content of Fe after Zn and in said intermetallic
compound, any of the 6-phase (F.eZnlo),r -phase (Fe3Zn,),
and rl-phase (FeZn.,) is the main layer.