U.S. patent application number 13/980595 was filed with the patent office on 2014-01-16 for hot dipped galvanized steel sheet with excellent deep drawing properties and ultra-low temperature adhesive brittleness, and preparation method thereof.
This patent application is currently assigned to POSCO. The applicant listed for this patent is Moon-Hi Hong, Ju-Youn Lee, Seung-Bok Lee, Jun-Woo Park, Hyun-Jun Tark. Invention is credited to Moon-Hi Hong, Ju-Youn Lee, Seung-Bok Lee, Jun-Woo Park, Hyun-Jun Tark.
Application Number | 20140017516 13/980595 |
Document ID | / |
Family ID | 46515890 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140017516 |
Kind Code |
A1 |
Lee; Seung-Bok ; et
al. |
January 16, 2014 |
HOT DIPPED GALVANIZED STEEL SHEET WITH EXCELLENT DEEP DRAWING
PROPERTIES AND ULTRA-LOW TEMPERATURE ADHESIVE BRITTLENESS, AND
PREPARATION METHOD THEREOF
Abstract
Provided is a hot dipped galvanized steel sheet with excellent
deep drawing properties and ultra-low temperature adhesive
brittleness, wherein the average diameter of crystal particles of a
hot-dip galvanizing layer is 150-400 .mu.m, and the degree of the
preferred orientation with respect to the (0001) face of the
hot-dip galvanizing layer is 3,000-20,000 cps (counter per second),
and a preparation method thereof.
Inventors: |
Lee; Seung-Bok; (Gwangyang,
KR) ; Park; Jun-Woo; (Gwangyang, KR) ; Tark;
Hyun-Jun; (Gwangyang, KR) ; Hong; Moon-Hi;
(Gwangyang, KR) ; Lee; Ju-Youn; (Gwangyang,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Seung-Bok
Park; Jun-Woo
Tark; Hyun-Jun
Hong; Moon-Hi
Lee; Ju-Youn |
Gwangyang
Gwangyang
Gwangyang
Gwangyang
Gwangyang |
|
KR
KR
KR
KR
KR |
|
|
Assignee: |
POSCO
Pohang
KR
|
Family ID: |
46515890 |
Appl. No.: |
13/980595 |
Filed: |
January 20, 2011 |
PCT Filed: |
January 20, 2011 |
PCT NO: |
PCT/KR11/00414 |
371 Date: |
September 24, 2013 |
Current U.S.
Class: |
428/659 ;
427/292 |
Current CPC
Class: |
C23C 2/06 20130101; Y10T
428/12799 20150115; C23C 2/28 20130101; C23C 2/02 20130101; C23C
2/18 20130101; C23C 2/26 20130101 |
Class at
Publication: |
428/659 ;
427/292 |
International
Class: |
C23C 2/02 20060101
C23C002/02 |
Claims
1. A hot-dipped galvanized steel sheet with improved deep drawing
properties and low-temperature adhesive brittleness, the hot-dipped
galvanized steel sheet comprising a zinc plating layer, wherein
grains of the zinc plating layer have an average particle diameter
of 150 .mu.m to 400 .mu.m, and intensity of preferred orientation
of (0001) planes of the zinc plating layer is from 3000 cps (count
per second) to 20000 cps.
2. The hot-dipped galvanized steel sheet of claim 1, wherein the
grains of the zinc plating layer have a diameter of 30 .mu.m or
greater and a diameter deviation equal to or less than 40% of the
average particle diameter thereof.
3. The hot-dipped galvanized steel sheet of claim 1, wherein the
zinc plating layer comprises 30% or more, by volume fraction, of
crystallographic twins.
4. A method of manufacturing a hot-dipped galvanized steel sheet,
the method comprising: applying molten zinc to a steel sheet;
adjusting the amount of the molten zinc applied to the steel sheet;
spraying an aqueous solution on the steel sheet; cooling the steel
sheet; and performing a skin pass milling process on the steel
sheet, wherein the spraying of the aqueous solution comprises
spraying electrically charged demi-water (demineralized water) on
the steel sheet.
5. The method of claim 4, wherein the spraying of the electrically
charged demi-water is performed using a nozzle at a demi-water
injection pressure of 0.3 kgf/cm.sup.2 to 5.0 kgf/cm.sup.2 and an
air injection pressure of 0.5 kgf/cm.sup.2 to 7.0 kgf/cm.sup.2.
6. The method of claim 5, wherein the spraying of the electrically
charged demi-water is performed at a demi-water pressure/air
pressure ratio of 1/10 to 8/10.
7. The method of claim 4, wherein the skin pass milling process is
performed at an elongation of 5% or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hot-dipped galvanized
steel sheet, and more particularly, to a hot-dipped galvanized
steel sheet having improved deep drawing properties and
low-temperature adhesive brittleness, and a method of manufacturing
the hot-dipped galvanized steel sheet.
BACKGROUND ART
[0002] In general, steel sheets are galvanized by passing a steel
sheet through molten zinc contained in a bath and solidifying the
molten zinc applied to the steel sheet. When molten zinc applied to
a steel sheet solidifies, coarse dendritic crystal grains, called
spangles, are formed on the surface of the molten zinc. Generation
of such spangles is a characteristic of zinc solidification.
[0003] In detail, when molten zinc solidifies, crystals start to
rapidly grow from solidification nuclei in the shape of dendrites
to form the basic structure of a zinc plating layer, and pools of
molten zinc remaining between the dendrites are subject to
solidification. Due to this solidification mechanism, spangles are
generated. The size of spangles may be determined by the basic
structure of the zinc plating layer formed in an initial stage of
plating.
[0004] Such spangles decrease the adhesive strength of paint on a
zinc plating layer and the corrosion resistance of a steel sheet,
and even though a zinc plating layer is painted, spangles still
make the surface of the zinc plating layer uneven and spoils the
appearance of a zinc-plated steel sheet because spangles can be
seen through paint.
[0005] Therefore, an inorganic salt solution may be sprayed on a
steel sheet before molten zinc applied to the steel sheet is
solidified, so as to minimize the size of spangles formed on the
steel sheet. At this time, the inorganic salt solution is sprayed
on the steel sheet through an electrode disposed on the front side
of a nozzle. Since the inorganic salt solution is sprayed through
the electrode, droplets of the inorganic salt solution are charged
with static electricity and are thus easily attached to the steel
sheet by electrical attraction to minify the metallographic
structure of a zinc plating layer. A phosphate solution is widely
used as the inorganic salt solution.
[0006] A plating layer having spangles of 150 .mu.m or less can be
formed on a steel sheet by spraying droplets of a phosphate
solution charged with electricity as described above. In this case,
the steel sheet can have a aesthetically-pleasing appearance,
improved image clarity after painting, and high corrosion
resistance, and the plating layer can be prevented from breaking
into flaking during a press process.
[0007] In addition, when molten zinc solidifies, spangles are
formed to have different shapes depending on how hexagonal crystals
of zinc are formed on the surface of a steel sheet. In other words,
since hexagonal crystals of zinc grow in different angles in
different regions of a steel sheet, spangles have different
shapes.
[0008] FIG. 1A illustrates a hot-dipped galvanized steel sheet on
which spangles having a size of 150 .mu.m or less are formed, and
FIG. 1B illustrates a hot-dipped galvanized steel sheet on which
spangles having a size of 400 .mu.m or greater are formed.
Referring to the hot-dipped galvanized steel sheet of FIG. 1B on
which spangles having a size of 400 .mu.m or greater are formed,
relatively large zinc crystals are randomly oriented, advantageous
in terms of brittleness but disadvantageous in terms of the
appearance of the steel sheet.
[0009] However, referring to the hot-dipped galvanized steel sheet
of FIG. 1A on which spangles having a size of 150 .mu.m or less are
formed, the spangles have the same crystallographic orientation in
a manner such that the basal planes of zinc, (0001) planes, are
parallel to the surface of the steel sheet. The above-mentioned
crystallographic orientation of zinc in which the basal planes of
zinc crystals are parallel to the surface of the steel sheet is
known to be most effective in preventing corrosion, a black patina,
and chemical instability. Until recently, there have been many
efforts to improve such properties.
[0010] For example, Japanese Patent Application Laid-open
Publication No.: 1999-100653 discloses a technique for adjusting
the size of spangles to be within 60 .mu.m to 1000 .mu.m by
spraying mist through a nozzle, and Japanese Patent Application
Laid-open Publication No.: 1996-188863 discloses a technique for
adjusting the size of spangles to be 50 .mu.m or less and the level
of surface roughness to be within 0.4 .mu.m to 1.0 .mu.m. In
addition, U.S. Pat. No. 4,500,561 discloses a technique for
decreasing the size of spangles to 1000 .mu.m or less by using
droplets passed through an electric field.
[0011] Many automobile manufacturers have recently attempted to use
structural adhesives for joining steel sheets, in addition to or
instead of using common existing welding methods such as spot
welding, for the purpose of reducing manufacturing costs, improving
stability, reducing work time, and making processes
eco-friendly.
[0012] Unlike mechanical joining methods such as spot welding,
structural adhesives are used after determining whether plated
steel sheets can be joined using the structural adhesives at a low
temperature of -40.degree. C. for the case of using automobiles in
polar regions. However, if an adhesive is used for a galvanized
steel sheet in which the (0001) planes of zinc crystals are
parallel to the surface of the steel sheet and thus spangles are
not formed, a zinc plating layer may easily be stripped from the
steel sheet at a low temperature of -40.degree. C. or during a deep
drawing process.
[0013] The brittleness of a zinc plating layer increases if
spangles of the zinc plating layer are small, and the (0001) planes
(basal planes) of the zinc plating layer function as slip planes or
cleavage planes. Therefore, if a zinc plating layer formed on a
steel sheet has small spangles or the (0001) planes of zinc
crystals of the zinc plating layer are parallel to the surface of
the steel sheet, the zinc plating layer may easily be stripped from
the steel sheet when the steel sheet is impacted.
[0014] Therefore, to deal with the recent methods of joining
hot-dipped galvanized steel sheets using structural adhesives, it
is necessary to develop a hot-dipped galvanized steel sheet having
an improved appearance, deep drawing properties, and adhesive
brittleness at a low temperature.
DISCLOSURE
Technical Problem
[0015] Aspects of the present invention provide a hot-dipped
galvanized steel sheet having improved deep drawing properties and
low-temperature adhesive brittleness by controlling the structure
and grain size of a zinc plating layer, and a method of
manufacturing the hot-dipped galvanized steel sheet.
Technical Solution
[0016] According to an aspect of the present invention, there is
provided a hot-dipped galvanized steel sheet with improved deep
drawing properties and low-temperature adhesive brittleness, the
hot-dipped galvanized steel sheet including a zinc plating layer,
wherein grains of the zinc plating layer have an average particle
diameter of 150 .mu.m to 400 .mu.m, and intensity of preferred
orientation of (0001) planes of the zinc plating layer is from 3000
cps (count per second) to 20000 cps.
[0017] According to another aspect of the present invention, there
is provided a method of manufacturing a hot-dipped galvanized steel
sheet, the method including: applying molten zinc to a steel sheet;
adjusting the amount of the molten zinc applied to the steel sheet;
spraying an aqueous solution on the steel sheet; cooling the steel
sheet; and performing a skin pass milling process on the steel
sheet, wherein the spraying of the aqueous solution includes
spraying electrically charged demi-water (demineralized water) on
the steel sheet.
Advantageous Effects
[0018] According to the present invention, owing to the spraying of
electrically charged demi-water and a high reduction ratio of the
skin pass milling process, grains of the zinc plating layer of the
hot-dipped galvanized steel sheet can have a reduced size
deviation, the intensity of orientation of the (0001) planes of
zinc crystals of the zinc plating layer can be lowered, and the
volume fraction of crystallographic twins of the zinc plating layer
can be increased. Therefore, the hot-dipped galvanized steel sheet
can have improved properties such as deep drawing properties,
bending properties, and adhesive brittleness.
DESCRIPTION OF DRAWINGS
[0019] FIG. 1A is a schematic view illustrating the
crystallographic structure of a hot-dipped galvanized steel sheet
of the related art on which spangles having a size of 150 .mu.m or
less are formed, and FIG. 1B is a schematic view illustrating the
crystallographic structure of a hot-dipped galvanized steel sheet
of the related art on which spangles having a size of 400 .mu.m or
greater are formed.
[0020] FIG. 2A is an X-ray analysis graph illustrating the
crystallographic orientation of (0001) planes of a hot-dipped
galvanized steel sheet of the related art on which spangles having
a size of 150 .mu.m or less are formed, and FIG. 2B is an X-ray
analysis graph illustrating the crystallographic orientation of
(0001) planes of a hot-dipped galvanized steel sheet of the related
art on which spangles having a size of 400 .mu.m or greater are
formed.
[0021] FIGS. 3A and 3B are images illustrating evaluation results
of low-temperature adhesive brittleness of Comparative Samples 1
and Inventive Samples 1.
BEST MODE
[0022] Hereinafter, the present invention will be described in
detail.
[0023] According to embodiments of the invention, crystal grains of
a zinc plating layer of a hot-dipped galvanized steel sheet have an
average particle diameter of 150 .mu.m to 400 .mu.m.
[0024] If the average particle diameter of the crystal grains is
less than 150 .mu.m, the hot-dipped galvanized steel sheet may have
a beautiful appearance owing to small spangles but the zinc plating
layer may have unsatisfactory low-temperature adhesive brittleness.
On the other hand, if the average particle diameter of the crystal
grains is greater than 400 .mu.m, even though the zinc plating
layer may have satisfactory low-temperature adhesive brittleness,
the hot-dipped galvanized steel sheet may have a poor appearance
and image clarity, and the zinc plating layer may easily be
separated from the hot-dipped galvanized steel sheet during a
continuous press process due to coarse spangles.
[0025] In the embodiments of the invention, it may be preferable
that the crystal grains of the zinc plating layer of the hot-dipped
galvanized steel sheet have a minimum diameter of 30 .mu.m and the
deviation of the diameters of the crystal grains be 40% or less of
the average particle diameter of the crystal grains.
[0026] If the zinc plating layer includes crystal grains having a
diameter of 30 .mu.m or less, the crystal grains may be more
brittle than surrounding crystal grains, and thus cracks may start
from the crystal grains. In addition, when the hot-dipped
galvanized steel sheet is bent, the zinc plating layer may be
separated from the hot-dipped galvanized steel sheet, and thus the
formability of the hot-dipped galvanized steel sheet may be
deteriorated.
[0027] As described above, in the embodiments of the invention, it
may be preferable that the deviation of the diameters of the
crystal grains of the zinc plating layer be 40% or less of the
average particle diameter of the crystal grains. That is, it may be
preferable that the size of spangles formed on the zinc plating
layer be uniform within that range. If the deviation is greater
than 40% and thus the size of zinc crystals is not uniform, when
the hot-dipped galvanized steel sheet undergoes plastic
deformation, the zinc plating layer may receive non-uniformly
applied force and may thus be partially separated from the
hot-dipped galvanized steel sheet. Therefore, to prevent problems
related to adhesive brittleness, it may be preferable that the
deviation of the diameters of crystal grains be 40% or less of the
average particle diameter of the crystal grains.
[0028] In the embodiments of the invention, it may be preferable
that the intensity of preferred orientation of the (0001) planes of
the zinc plating layer of the hot-dipped galvanized steel sheet be
from 3000 cps to 20000 cps (count per second). When the hot-dipped
galvanized steel sheet of the embodiments of the invention was
irradiated with X-rays generated under the conditions of 20 KV and
10 mA, the intensity of preferred orientation of the zinc plating
layer of the hot-dipped galvanized steel sheet was measured to be
from 3000 cps to 20000 cps. In detail, the maximum intensity of the
(0001) planes of zinc crystals was measured to be from 3000 cps to
20000 cps (the tilt angle of a sample was 5.degree., and intensity
values measured at intervals of 5.degree. in a rotational angle of
0.degree. to 360.degree. were averaged).
[0029] Referring to FIG. 2A, the intensity of preferred orientation
of a hot-dipped galvanized steel sheet of the related art on which
spangles having a size of 150 .mu.m or less are formed is greater
than 20,000 cps, and referring to FIG. 2B, the intensity of
preferred orientation of a hot-dipped galvanized steel sheet of the
related art on which spangles having a size of 400 .mu.m or greater
is formed on is less than 3000 cps.
[0030] In the embodiments of the invention, the intensity of
preferred orientation of (0001) planes is adjusted to be within the
range of 3000 cps to 20000 cps. If the intensity of preferred
orientation of (0001) planes is less than 3000 cps, it is
advantageous in terms of the brittleness of a zinc plating layer
but disadvantageous in terms of appearance due to coarse spangles.
On the other hand, if the intensity of preferred orientation of
(0001) planes is greater than 20000 cps, the appearance of a zinc
plating layer may be good, owing to small spangles but the deep
drawing properties and low-temperature brittleness of the zinc
plating layer may be deteriorated.
[0031] In the embodiments of the invention, it may be preferable
that the volume fraction of crystallographic twins of the zinc
plating layer of the hot-dipped galvanized steel sheet be 30% or
greater. Crystallographic twins may be present in the zinc plating
layer when the hot-dipped galvanized steel sheet is processed
through a skin pass milling process, and in zinc crystals having a
hexagonal close-packed (HCP) structure, crystallographic twins
function as an important plastic deformation mechanism to
facilitate a deep drawing process and improve brittleness
characteristics. If the volume fraction of crystallographic twins
of the zinc plating layer is less than 30%, plastic deformation may
be less facilitated, and the workability of the hot-dipped
galvanized steel sheet may be deteriorated particularly when the
size of the zinc crystals of the zinc plating layer is from 150
.mu.m to 400 .mu.m.
[0032] A method of manufacturing a hot-dipped galvanized steel
sheet will now be described in detail according to an embodiment of
the invention.
[0033] In an embodiment of the invention, a method of manufacturing
a hot-dipped galvanized steel sheet includes: applying molten zinc
to a steel sheet; adjusting the amount of the molten zinc applied
to the steel sheet; spraying an aqueous solution on the steel
sheet; cooling the steel sheet; and performing a skin pass milling
process on the steel sheet.
[0034] The spraying of the aqueous solution is performed by
spraying electrically charged demi-water (demineralized water) on
the steel sheet.
[0035] In the embodiment of the invention, the applying of the
molten zinc is performed by passing the steel sheet through a zinc
plating solution to attach molten zinc to the steel sheet. In the
embodiment of the invention, the applying of the molten zinc is not
limited to a particular method or process. That is, molten zinc may
be applied to the steel sheet using any zinc plating solution and
process conditions that are commonly used for manufacturing
hot-dipped galvanized steel sheets in the art to which the present
invention pertains. The zinc plating solution may include aluminum
(Al), antimony (Sb), and/or lead (Pb). However, the embodiment of
the invention is not limited thereto. The steel sheet may be any
kind of steel sheet. That is, any steel sheet used for
manufacturing a hot-dipped galvanized steel sheet in the related
art may be used.
[0036] In the adjusting of the amount of the molten zinc after the
applying of the molten zinc to the steel sheet, the steel sheet is
air-wiped to remove an excessive amount of the zinc plating
solution from the steel sheet. The amount of the molten zinc
applied to the steel sheet may be adjusted to be any degree
considered appropriate by those of skill in the art to which the
present invention pertains. That is, the amount of the molten zinc
applied to the steel sheet is not limited to any particular degree.
For example, the amount of the molten zinc applied to the steel
sheet may be adjusted according to the purpose of the steel
sheet.
[0037] After the adjusting of the amount of the molten zinc applied
to the steel sheet, the spraying of the aqueous solution is
performed by spraying electrically charged demi-water on the steel
sheet to solidify the molten zinc. The electrically charged
demi-water is sprayed so as to form a uniform zinc plating layer
having uniformly sized spangles. If a solution is electrically
charged and sprayed in the form of mist, droplets of the solution
collide with a molten zinc plating layer and absorb heat from the
molten zinc plating layer to facilitate solidification of the
molten zinc plating layer. However, if an inorganic solution such
as a phosphate solution is sprayed, regions of the molten zinc
plating layer colliding with nuclear particles such as phosphate
nuclear particles may lose heat much more quickly than other
regions. Thus, relatively small spangles may be formed on the
regions, and relatively large spangles may be formed on the other
regions to increase the deviation of the sizes of the spangles.
[0038] If the deviation in the sizes of spangles is large, the zinc
plating layer of the hot-dipped galvanized steel sheet may not be
uniformly stressed during a deep drawing process, and thus cracks
may start from relatively small spangles. In addition, when the
hot-dipped galvanized steel sheet is bent, the zinc plating layer
may be separated from the hot-dipped galvanized steel sheet. That
is, a large deviation of the sizes of spangles may deteriorate the
formability of the hot-dipped galvanized steel sheet.
[0039] In the embodiment of the invention, it may be preferable
that electrically charged demi-water be sprayed through a nozzle at
a demi-water injection pressure of 0.3 kgf/cm.sup.2 to 5.0
kgf/cm.sup.2, an air injection pressure of 0.5 kgf/cm.sup.2 to 7.0
kgf/cm.sup.2, and a demi-water pressure/air pressure ratio of 1/10
to 8/10.
[0040] If the demi-water is sprayed at a pressure of lower than 0.3
kgf/cm.sup.2, spangles may not be minified. If the demi-water is
sprayed at a pressure of greater than 5.0 kgf/cm.sup.2, pitting
marks may be formed on the steel sheet while the steel sheet
collide with droplets of the demi-water, and thus the appearance of
the steel sheet may be spoiled.
[0041] It may be preferable that the front side of the nozzle may
be charged to have a voltage of -1 KV to -25 KV. If the front side
of the nozzle is charged to have a voltage of less than -1 KV,
electrical attraction may not be sufficient to minify droplets and
spangles. On the other hand, if the front side of the nozzle is
charged to a voltage of greater than -25 KV, spangles smaller than
150 pm may be formed on the zinc plating layer, and thus deep
drawing properties and adhesive brittleness may be
deteriorated.
[0042] In the embodiment of the invention, after the spraying of
demi-water, a skin pass milling process is performed on the steel
sheet. During the skin pass milling process, crystallographic twins
are formed in the zinc plating layer. The skin pass milling process
may be performed at an elongation of 5% or less.
[0043] In the embodiment of the invention, as described above, it
may be preferable that the skin pass milling process be performed
at an elongation of 5% or less. During the skin pass milling
process, crystallographic twins are formed, which function as an
important processing mechanism in zinc crystals having an HCP
structure because the HCP structure has few deformation mechanisms.
In addition, owing to physical deformation by the skin pass milling
process, the intensity of preferred orientation of the (0001)
planes of zinc crystals may be lowered. In other words, if the skin
pass milling process is not performed, the bonding between the zinc
plating layer and the steel sheet may not be firm, and the
formability of the steel sheet may not be good. On the other hand,
if the skin pass milling process is performed at an elongation of
greater than 5%, the properties of the steel sheet may be
deteriorated even though the formability and adhesiveness of the
zinc plating layer are improved.
MODE FOR INVENTION
[0044] An example of the present invention will now be described in
detail. However, the present invention is not limited thereto.
EXAMPLE
[0045] Hot-dipped galvanized steel sheets were treated with a
phosphate solution or demi-water under the conditions shown in
Table 1 to adjust the size of spangles. Thereafter, the steel
sheets were treated through a skin pass milling process at an
elongation of 1.0% and a roll pressure of 200 tons to 240 tons, and
the adhesive brittleness, appearance, and image clarity of the
hot-dipped galvanized steel sheets were measured as shown in Table
1.
[0046] The hot-dipped galvanized steel sheets were prepared by
performing a hot-dip galvanization process on soft IF steel sheets
having a thickness of 0.67 mm to form zinc plating layers on the
steel sheets at a plating density of 70 g/m.sup.2.
[0047] Sizes and size deviations of spangles formed on the zinc
plating layers were measured and analyzed using an optical
microscope and an image analyzer before the hot-dipped galvanized
steel sheets were treated through the skin pass milling process.
The measured and analyzed results are shown in the "spangle size"
and "spangle size deviation" columns of Table 1 below. Adhesive
brittleness was measured by bonding two hot-dipped galvanized steel
sheets with an adhesive for automotive structural parts (Sealer
Terokal 5089 by Henkel Korea, Ltd.), keeping the bonded hot-dipped
galvanized steel sheets at -40.degree. C., impacting the hot-dipped
galvanized steel sheets with a wedge, and observing separation of
zinc plating layers of the hot-dipped galvanized steel sheets. In
Table 1, O denotes the case where a zinc plating layer was not
stripped off, .DELTA. denotes the case where 20% or less of a zinc
plating layer was stripped off, and X denotes the case where 50% or
more of a zinc plating layer was stripped off. Appearance and image
clarity were measured with the naked eye, and results thereof are
denoted as good (O), fair (.DELTA.), and poor (X) in Table 1.
TABLE-US-00001 TABLE 1 Spangle Spangle size Preferred Spraying size
deviation orientation Adhesive Image No. Solution (.mu.m) (.mu.m)
(cps) brittleness Appearance quality *CS1 Demi-water 150 99 28670 x
.smallcircle. .smallcircle. **IS1 Demi-water 250 81 10190
.smallcircle. .smallcircle. .smallcircle. IS2 Demi-water 350 126
4800 .smallcircle. .smallcircle. .smallcircle. IS3 Demi-water 400
-- 3253 .smallcircle. .smallcircle. .quadrature. CS2 Phosphate 150
-- 44214 x .smallcircle. .smallcircle. CS3 Phosphate 250 106 11850
x .smallcircle. .smallcircle. CS4 Phosphate 350 141 4215
.quadrature. .smallcircle. .quadrature. CS5 Phosphate 700 -- 1540
.smallcircle. .quadrature. x CS6 -- 1000 -- 954 .smallcircle. x x
*CS: Comparative Sample **IS: Inventive Sample
[0048] Referring to Table 1, Inventive Samples treated with
demi-water have spangles within a preferable size range, intensity
of preferred orientation within the range of 3000 cps to 20000 cps,
size deviations within a preferable range, good adhesive
brittleness, and good appearance.
[0049] Although Comparative Sample 1 treated with demi-water has
spangles within a preferable size range, Comparative Sample 1 has
an unacceptably large spangle size deviation, an unacceptably high
degree of intensity of preferred orientation, and poor adhesive
brittleness. Comparative Samples 2 to 5 treated with a phosphate
solution have unsatisfactory adhesive brittleness or appearance.
Comparative Sample 6, a general hot-dipped galvanized steel sheet
has poor appearance.
[0050] FIGS. 3A and 3B are images for evaluating adhesive
brittleness of Comparative Samples 1 and Inventive Samples 1.
Adhesive brittleness was evaluated based on whether a blue adhesive
remained. Referring to Comparative Samples 1 shown in FIG. 3A, as
indicated by circles, an adhesive does not remain after zinc
plating layers are fractured. Referring to Inventive Samples 1
shown in FIG. 3B, an adhesive remains owing to improved adhesive
brittleness.
* * * * *