U.S. patent application number 15/037068 was filed with the patent office on 2016-10-20 for hot-dip zn-alloy-plated steel sheet.
This patent application is currently assigned to Nisshin Steel Co., Ltd.. The applicant listed for this patent is NISSHIN STEEL CO., LTD.. Invention is credited to Masanori MATSUNO, Atsuo SHIMIZU, Hirofumi TAKETSU, Masaya YAMAMOTO.
Application Number | 20160305003 15/037068 |
Document ID | / |
Family ID | 53273112 |
Filed Date | 2016-10-20 |
United States Patent
Application |
20160305003 |
Kind Code |
A1 |
SHIMIZU; Atsuo ; et
al. |
October 20, 2016 |
HOT-DIP ZN-ALLOY-PLATED STEEL SHEET
Abstract
This hot-dip Zn-alloy-plated steel sheet comprises: a steel
sheet; a hot-dip Zn-alloy-plated layer arranged on a surface of the
steel sheet; and a complex oxide coating film arranged on a surface
of the hot-dip Zn-alloy-plated layer. The complex oxide coating
film includes vanadium and a constituent component of the hot-dip
Zn-alloy-plated layer, and the entire surface of the coating film
satisfies the following formula (1):
S[Hydroxide]/(S[Hydroxide]+S[Oxide]).times.100.ltoreq.40. In
formula (1): S[Oxide] is the area exhibited by a peak having a
center at approximately 1022 eV ascribable to a Zn oxide in an
intensity profile in XPS analysis of the surface of the complex
oxide coating film; and S[Hydroxide] is the area exhibited by a
peak having a center at approximately 1023 eV ascribable to a Zn
hydroxide in an intensity profile in XPS analysis of the surface of
the complex oxide coating film.
Inventors: |
SHIMIZU; Atsuo; (Osaka,
JP) ; MATSUNO; Masanori; (Osaka, JP) ;
YAMAMOTO; Masaya; (Osaka, JP) ; TAKETSU;
Hirofumi; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISSHIN STEEL CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
Nisshin Steel Co., Ltd.
Tokyo
JP
|
Family ID: |
53273112 |
Appl. No.: |
15/037068 |
Filed: |
November 13, 2014 |
PCT Filed: |
November 13, 2014 |
PCT NO: |
PCT/JP2014/005701 |
371 Date: |
May 17, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 2/06 20130101; C22C
18/00 20130101; C23C 2/20 20130101; C23C 2/40 20130101; C22C 18/04
20130101; C23C 2/26 20130101 |
International
Class: |
C23C 2/06 20060101
C23C002/06; C22C 18/00 20060101 C22C018/00; C23C 2/26 20060101
C23C002/26; C22C 18/04 20060101 C22C018/04; C23C 2/40 20060101
C23C002/40; C23C 2/20 20060101 C23C002/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2013 |
JP |
2013-250139 |
Claims
1. A hot-dip Zn alloy-plated steel sheet comprising: a steel sheet;
a hot-dip Zn alloy plating layer disposed on a surface of the steel
sheet; and a composite oxide film disposed on a surface of the
hot-dip Zn alloy plating layer; wherein the composite oxide film
comprises constituent components of the hot-dip Zn alloy plating
layer and vanadium, and the composite oxide film satisfies, at a
whole of a surface of the composite oxide film, following Equation
1: S [ Hydroxide ] S [ Hydroxide ] + S [ Oxide ] .times. 100
.ltoreq. 40 ( Equation 1 ) ##EQU00003## S[Oxide] is a peak area
derived from Zn oxide and centered at approximately 1022 eV in an
intensity profile of the XPS analysis of the surface of the
composite oxide film; and S[Hydroxide] is a peak area derived from
Zn hydroxide and centered at approximately 1023 eV in the intensity
profile of the XPS analysis of the surface of the composite oxide
film.
2. The hot-dip Zn alloy-plated steel sheet according to claim 1,
wherein: the hot-dip Zn alloy plating layer comprises 1.0 to 22.0%
by mass of Al, 0.1 to 10.0% by mass of Mg, and the balance of the
hot-dip Zn alloy plating layer being Zn and unavoidable
impurities.
3. The hot-dip Zn alloy-plated steel sheet according to claim 2,
wherein: the hot-dip Zn alloy plating layer further comprises at
least one selected from the group consisting of 0.001 to 2.0% by
mass of Si, 0.001 to 0.1% by mass of Ti, and 0.001 to 0.045% by
mass of B.
4. The hot-dip Zn alloy-plated steel sheet according to claim 1,
wherein an adhering amount of the vanadium contained in the
composite oxide film is in the range of 0.01 to 10.0
mg/m.sup.2.
5. The hot-dip Zn alloy-plated steel sheet according to claim 2,
wherein an adhering amount of the vanadium contained in the
composite oxide film is in the range of 0.01 to 10.0
mg/m.sup.2.
6. The hot-dip Zn alloy-plated steel sheet according to claim 3,
wherein an adhering amount of the vanadium contained in the
composite oxide film is in the range of 0.01 to 10.0 mg/m.sup.2.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hot-dip Zn alloy-plated
steel sheet excellent in blackening resistance.
BACKGROUND ART
[0002] As plated steel sheet excellent in corrosion resistance, a
hot-dip Zn alloy-plated steel sheet having a base steel sheet with
a surface coated with a hot-dip Zn alloy plating layer including Al
and Mg is known. The composition of the plating layer of a hot-dip
Zn alloy-plated steel sheet includes, for example, 4.0 to 15.0% by
mass of Al, 1.0 to 4.0% by mass of Mg, 0.002 to 0.1% by mass of Ti,
0.001 to 0.045% by mass of B, and the balance of Zn and unavoidable
impurities. The hot-dip Zn alloy-plated steel sheet includes a
plating layer of mixed metal structure of [primary crystal Al] and
[single phase Zn] in a matrix of [Al/Zn/Zn.sub.2Mg ternary eutectic
structure], having sufficient corrosion resistance and surface
appearance as an industrial product.
[0003] The hot-dip Zn alloy-plated steel sheet described above can
be continuously produced by the following steps. First, a base
steel sheet (steel strip) is passed through a furnace, dipped in a
hot-dip Zn alloy plating bath, and then passed through, for
example, a gas wiping apparatus, such that the amount of the molten
metal adhered to the surface of the base steel sheet is adjusted to
a specified amount. Subsequently, the steel strip with the
specified amount of molten metal adhered thereto is passed through
an air jet cooler and a mist cooling zone, so that the molten metal
is cooled to form a hot-dip Zn alloy plating layer. Further, the
steel strip with the hot-dip Zn alloy plating layer is passed
through a water quenching zone, so as to come in contact with
cooling water. A hot-dip Zn alloy-plated steel sheet is thus
obtained.
[0004] The hot-dip Zn alloy-plated steel sheet thus produced,
however, allows the surface of the plating layer to be blackened
over time in some cases. Since the progress of blackening of a
hot-dip Zn alloy-plated steel sheet spoils the appearance with a
dark gray color without metallic luster, a method for suppressing
the blackening has been needed.
[0005] As a method for preventing the blackening, adjusting of the
temperature of the surface of a plating layer in the water
quenching zone has been proposed (e.g. refer to PTL 1). In the
invention described in PTL 1, the temperature of the surface of a
plating layer is adjusted at lower than 105.degree. C. when
contacted with cooling water in the water quenching zone so that
blackening of the surface of a plating layer is prevented.
Alternatively, instead of the temperature control of the surface of
a plating layer at lower than 105.degree. C., readily oxidizable
elements (rare earth elements, Y, Zr or Si) are added into a
plating bath and the temperature of the surface of a plating layer
is adjusted at 105 to 300.degree. C. so that blackening of the
surface of the plating layer is prevented.
CITATION LIST
Patent Literature
PTL 1
Japanese Patent Application Laid-Open No. 2002-226958
SUMMARY OF INVENTION
Technical Problem
[0006] In the invention described in PTL 1, since the surface of a
plating layer is required to be cooled to a specified temperature
before passed through a water quenching zone, the production of a
hot-dip Zn alloy-plated steel sheet is restricted in some cases.
For example, the feed rate of a plated steel sheet having a large
thickness is required to be slow so that the plated steel sheet is
cooled to a specified temperature, resulting in reduced
productivity. In addition, in the case of adding readily oxidizable
elements into a plating bath, the readily oxidizable elements tend
to form a dross. Consequently, complicated concentration control of
the readily oxidizable elements is required, resulting in a
complicated production process, which has been a problem.
[0007] An object of the present invention is to provide a hot-dip
Zn alloy-plated steel sheet excellent in blackening resistance
which can be produced without reduction in productivity and without
complicated control of the components of a plating bath.
Solution to Problem
[0008] The present inventors have found that the problem can be
solved by forming a composite oxide film containing the constituent
components of a plating layer and vanadium on the surface of the
plating layer and reducing the ratio of Zn hydroxide contained in
the composite oxide film, and accomplished the present invention
through further study.
[0009] The present invention relates to the following hot-dip Zn
alloy-plated steel sheet.
[0010] [1] A hot-dip Zn alloy-plated steel sheet comprising: a
steel sheet; a hot-dip Zn alloy plating layer disposed on a surface
of the steel sheet; and a composite oxide film disposed on a
surface of the hot-dip Zn alloy plating layer; wherein the
composite oxide film comprises constituent components of the
hot-dip Zn alloy plating layer and vanadium, and the composite
oxide film satisfies, at the whole of a surface of the composite
oxide film, following Equation 1:
S [ Hydroxide ] S [ Hydroxide ] + S [ Oxide ] .times. 100 .ltoreq.
40 ( Equation 1 ) ##EQU00001##
[0011] S[Oxide] is a peak area derived from Zn oxide and centered
at approximately 1022 eV in an intensity profile of the XPS
analysis of the surface of the composite oxide film; and
S[Hydroxide] is a peak area derived from Zn hydroxide and centered
at approximately 1023 eV in the intensity profile of the XPS
analysis of the surface of the composite oxide film.
[0012] [2] The hot-dip Zn alloy-plated steel sheet according to
claim 1, wherein: the hot-dip Zn alloy plating layer comprises 1.0
to 22.0% by mass of Al, 0.1 to 10.0% by mass of Mg, and the balance
of the hot-dip Zn alloy plating layer being Zn and unavoidable
impurities.
[0013] [3] The hot-dip Zn alloy-plated steel sheet according to
claim 2, wherein: the hot-dip Zn alloy plating layer further
comprises at least one selected from the group consisting of 0.001
to 2.0% by mass of Si, 0.001 to 0.1% by mass of Ti, and 0.001 to
0.045% by mass of B.
[0014] [4] The hot-dip Zn alloy-plated steel sheet according to any
one of claims 1 to 3, wherein the adhering amount of the vanadium
contained in the composite oxide film is in the range of 0.01 to
10.0 mg/m.sup.2.
Advantageous Effects of Invention
[0015] According to the present invention, a hot-dip Zn
alloy-plated steel sheet excellent in blackening resistance can be
easily produced at high productivity.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIGS. 1A to 1D illustrate the intensity profiles of the
chemical binding energy corresponding to the 2p orbitals of Zn at
the surface of a composite oxide film.
[0017] FIG. 2A illustrates an exemplary method for contacting a
cooling aqueous solution with the surface of a hot-dip Zn alloy
plating layer by a spraying process;
[0018] FIG. 2B illustrates an exemplary method for contacting a
cooling aqueous solution with the surface of a hot-dip Zn alloy
plating layer by a dipping process; and
[0019] FIG. 3 is a schematic diagram illustrating the configuration
of a part of the production line of a hot-dip Zn alloy-plated steel
sheet.
DESCRIPTION OF EMBODIMENTS
[0020] (Hot-Dip Zn Alloy-Plated Steel Sheet of the Present
Invention)
[0021] The hot-dip Zn alloy-plated steel sheet of the present
invention includes a base steel sheet, a hot-dip Zn alloy plating
layer, and a composite oxide film. The hot-dip Zn alloy-plated
steel sheet of the present invention is excellent in blackening
resistance, by virtue of a specified composite oxide film.
[0022] The type of the base steel sheet is not particularly
limited. For example, a steel sheet made of low-carbon steel,
medium-carbon steel, high-carbon steel, alloy steel or the like may
be used as the base steel sheet. When excellent press formability
is required, a steel sheet for deep drawing made of low-carbon
Ti-alloyed steel, low-carbon Nb-alloyed steel or the like is
preferably used as the base steel sheet. Alternatively, a
high-strength steel sheet containing P, Si, Mn and the like may be
used.
[0023] The hot-dip Zn alloy plating layer is disposed on the
surface of a base steel sheet. The composition of the hot-dip Zn
alloy plating layer may be appropriately selected depending on the
purpose. For example, the plating layer includes 1.0 to 22.0% by
mass of Al, 0.1 to 10.0% by mass of Mg, and the balance of Zn and
unavoidable impurities. The plating layer may further include at
least one selected from the group consisting of 0.001 to 2.0% by
mass of Si, 0.001 to 0.1% by mass of Ti, and 0.001 to 0.045% by
mass of B. Examples of the hot-dip Zn alloy plating include a
molten Zn--0.18% by mass of Al--0.09% by mass of Sb alloy plating,
a molten Zn--0.18% by mass of Al--0.06% by mass of Sb alloy
plating, a molten Zn--0.18% by mass Al alloy plating, a molten
Zn--1% by mass of Al--1% by mass of Mg alloy plating, a molten
Zn--1.5% by mass of Al--1.5% by mass of Mg alloy plating, a molten
Zn--2.5% by mass of Al--3% by mass of Mg alloy plating, a molten
Zn--2.5% by mass of Al--3% by mass of Mg--0.4% by mass of Si alloy
plating, a molten Zn--3.5% by mass of Al--3% by mass of Mg alloy
plating, a molten Zn--4% by mass of Al--0.75% by mass of Mg alloy
plating, a molten Zn--6% by mass of Al--3% by mass of Mg--0.05% by
mass of Ti--0.003% by mass of B alloy plating, a molten Zn--6% by
mass of Al--3% by mass of Mg--0.02% by mass of Si--0.05% by mass of
Ti--0.003% by mass of B alloy plating, a molten Zn--11% by mass of
Al--3% by mass of Mg alloy plating, a molten Zn--11% by mass of
Al--3% by mass of Mg--0.2% by mass of Si alloy plating, and a
molten Zn--55% by mass of Al--1.6% by mass of Si alloy plating.
Although blackening of a plating layer can be suppressed by
addition of Si as described in PTL 1, in the case of the hot-dip Zn
alloy-plated steel sheet of the present invention, blackening of a
plating layer can be suppressed without addition of Si to the
plating layer.
[0024] The amount of the hot-dip Zn alloy plating layer adhered is
not specifically limited. The amount of the plating layer adhered
may be, for example, approximately 60 to 500 g/m.sup.2.
[0025] The composite oxide film is disposed on the surface of a
hot-dip Zn alloy plating layer, preferably on the entire surface.
The composite oxide film mainly contains constituent components of
the hot-dip Zn alloy plating layer (e.g. Zn, Al and Mg) and
vanadium. The composite oxide film satisfies, at the entire
surface, the following equation 2.
S [ Hydroxide ] S [ Hydroxide ] + S [ Oxide ] .times. 100 .ltoreq.
40 ( Equation 2 ) ##EQU00002##
[0026] wherein S[Oxide] is a peak area derived from the Zn oxide
and centered at approximately 1022 eV in the intensity profile of
the XPS analysis of the surface of a composite oxide film; and
S[Hydroxide] is a peak area derived from the Zn hydroxide and
centered at approximately 1023 eV in the intensity profile of the
XPS analysis of the surface of a composite oxide film.
[0027] The equation 2 indicates that the ratio of the peak area
derived from the Zn hydroxide and centered at approximately 1023 eV
(hereinafter referred to as "hydroxide ratio") is 40% or less
relative to the total of the peak area derived from the Zn oxide
and centered at approximately 1022 eV and a peak area derived from
the Zn hydroxide and centered at approximately 1023 eV in the
intensity profile measured in the XPS analysis.
[0028] FIGS. 1A to 1D illustrate the intensity profiles of the
chemical bonding energy corresponding to the 2p orbitals of Zn at
the surface of the composite oxide film of a hot-dip Zn
alloy-plated steel sheet. FIG. 1A illustrates the intensity profile
with a Zn hydroxide ratio of approximately 80%, FIG. 1B illustrates
the intensity profile with a Zn hydroxide ratio of approximately
40%, FIG. 1C illustrates the intensity profile with a Zn hydroxide
ratio of approximately 15%, and FIG. 1D illustrates the intensity
profile with a Zn hydroxide ratio of approximately 10%. A dotted
line is the base line, a broken line is the intensity profile
derived from Zn oxide (a peak centered at approximately 1022 eV),
and a dashed dotted line is the intensity profile derived from Zn
hydroxide (a peak centered at approximately 1023 eV). In the
hot-dip Zn alloy-plated steel sheet of the present invention, the
Zn hydroxide ratio is 40% or less over the entire surface of the
plating layer as shown in FIGS. 1B to 1D.
[0029] The XPS analysis of the surface of the composite oxide film
of a hot-dip Zn alloy-plated steel sheet of the present invention
is performed using an XPS analyzer (AXIS Nova, produced by Kratos
Group PLC.). The peak area derived from Zn oxide and centered at
approximately 1022 eV and the peak area derived from Zn hydroxide
and centered at approximately 1023 eV are calculated using software
(Vision 2) attached to the XPS analyzer.
[0030] The position of the peak derived from Zn oxide is precisely
at 1021.6 eV, and the position of the peak derived from Zn
hydroxide is precisely at 1023.3 eV. These values may change in
some cases due to characteristics of XPS analysis, contamination of
a sample, and charging of a sample. Those skilled in the art,
however, are capable of distinguishing the peak derived from Zn
oxide from the peak derived from Zn hydroxide.
[0031] The adhering amount of the vanadium in the composite oxide
film is not specifically limited, but preferably in the range of
0.01 to 10.0 mg/m.sup.2. With an adhering amount of the vanadium of
0.01 mg/m.sup.2 or more, the blackening resistance can be further
improved. With an adhering amount of the vanadium of 10.0
mg/m.sup.2 or less, the reactivity with a chemical conversion
liquid for chemical conversion treatment can be improved. The
adhering amount of vanadium in a composite oxide film can be
measured using an ICP emission analyzer.
[0032] (Producing Method of Hot-Dip Zn Alloy-Plated Steel Sheet of
the Present Invention)
[0033] The producing method of a hot-dip Zn alloy-plated steel
sheet of the present invention is not specifically limited. For
example, the hot-dip Zn alloy-plated steel sheet of the present
invention may be produced by: (1) a first step of forming a hot-dip
Zn alloy plating layer (hereinafter, also referred to as "plating
layer") on the surface of a base steel sheet; and (2) a second step
of contacting a specified aqueous solution with the surface of the
plating layer for cooling of the base steel sheet and the plating
layer at a raised temperature through formation of the plating
layer, and for forming a composite oxide film. Each of the steps is
described as follows.
[0034] (1) First Step
[0035] In the first step, a base steel sheet is dipped in a hot-dip
Zn alloy plating bath, so that a hot-dip Zn alloy plating layer is
formed on the surface of the base steel sheet.
[0036] First, a base steel sheet is dipped in a hot-dip Zn alloy
plating bath, and a specified amount of molten metal is allowed to
adhere to the surface of the base steel sheet by gas wiping or the
like. As described above, the type of the base steel sheet is not
specifically limited. The composition of the plating bath is
appropriately selected depending on the composition of the hot-dip
Zn alloy plating layer to be formed.
[0037] Subsequently, the molten metal adhered to the surface of a
base steel sheet is cooled to a temperature equal to or more than
100.degree. C. and equal to or less than the solidifying point of
the plating layer so as to be solidified. A plated steel sheet is
thus formed, having a plating layer with a composition
approximately the same as the composition of the plating bath, on
the surface of the base steel sheet.
[0038] (2) Second Step
[0039] In the second step, a specified cooling aqueous solution is
contacted with the surface of the hot-dip Zn alloy plating layer,
so that the base steel sheet and the plating layer at a raised
temperature through formation of the hot-dip Zn alloy plating layer
are cooled. In this step, a composite oxide film is formed on the
surface of the plating layer. From the viewpoint of productivity,
the second step is performed preferably by water quenching (water
cooling). In this case, the temperature of the surface of the
hot-dip Zn alloy plating layer when the cooling aqueous solution is
to be contacted with the surface of the hot-dip Zn alloy plating
layer is equal to or more than 100.degree. C. and approximately
equal to or less than the solidifying point of the plating
layer.
[0040] The cooling aqueous solution is formed of an aqueous
solution containing a vanadium compound. The concentration of the
vanadium compound in the cooling aqueous solution is preferably
0.01 g/L or more in terms of V element. When a concentration of the
vanadium compound is less than 0.01 g/L in terms of V element,
blackening of the surface of a composite oxide film may not be
sufficiently prevented.
[0041] The method for preparing the aqueous solution (cooling
aqueous solution) containing a vanadium compound is not
specifically limited. For example, a vanadium compound and a
dissolution promoter on an as needed basis, may be dissolved in
water (solvent). Preferable examples of the vanadium compound
include acetylacetone vanadyl, vanadium acetylacetonate, vanadium
oxysulfate, vanadium pentoxide, and ammonium vanadate. These
vanadium compounds may be used singly or in combination.
[0042] In the case of adding a dissolution promoter, the amount of
the dissolution promoter added is not specifically limited. For
example, 90 to 130 parts by mass of the dissolution promoter may be
added to 100 parts by mass of the vanadium compound. With an
excessively small amount of the dissolution promoter added, the
vanadium compound cannot be sufficiently dissolved in some cases.
On the other hand, with an excessively large amount of the
dissolution promoter added, the effect is saturated, resulting in a
cost disadvantage.
[0043] Examples of the dissolution promoter include 2-aminoethanol,
tetraethylammonium hydroxide, ethylene diamine,
2,2'-iminodiethanol, and 1-amino-2-propanol.
[0044] The method for contacting the cooling aqueous solution with
the surface of a hot-dip Zn alloy plating layer is not specifically
limited. Examples of the method for contacting the cooling aqueous
solution with the surface of a hot-dip Zn alloy plating layer
include a spraying process and a dipping process.
[0045] FIGS. 2A and 2B illustrate exemplary methods for contacting
a cooling aqueous solution with the surface of a hot-dip Zn alloy
plating layer. FIG. 2A illustrates an exemplary method for
contacting a cooling aqueous solution with the surface of a hot-dip
Zn alloy plating layer by a spraying process. FIG. 2B illustrates
an exemplary method for contacting a cooling aqueous solution with
the surface of a hot-dip Zn alloy plating layer by a dipping
process.
[0046] As shown in FIG. 2A, cooling for spraying process includes a
plurality of spray nozzles 110, squeeze rollers 120 disposed
downstream of spray nozzles 110 in the feed direction of a steel
strip S, and housing 130 which covers the nozzles and the rollers.
Spray nozzles 110 are disposed on both sides of the steel strip S.
The steel strip S is cooled by a cooling aqueous solution supplied
from spray nozzles 110 such that a water film is temporarily formed
on the surface of the plating layer, inside housing 130.
[0047] The cooling aqueous solution is then removed with squeeze
roller 120. The adhering amount of vanadium in the composite oxide
film can be adjusted by controlling the opening of squeeze rollers
120.
[0048] As shown in FIG. 2B, cooling apparatus 200 for dipping
process includes dip tank 210 in which a cooling aqueous solution
is stored, dip roller 220 disposed inside dip tank 210, and squeeze
rollers 230 disposed downstream of dip roller 220 in the feed
direction of the steel strip S so as to remove the extra cooling
aqueous solution adhered to the steel strip S. The steel strip S
fed into dip tank 210 is then contacted with the cooling aqueous
solution so as to be cooled. The steel strip S is then subjected to
a turn of direction by the rotating dip roller 220, and pulled
upward. The cooling aqueous solution is removed with squeeze roller
230. The adhering amount of vanadium in the composite oxide film
can be adjusted by controlling the opening of squeeze rollers
230.
[0049] According to the procedure described above, a hot-dip Zn
alloy-plated steel sheet of the present invention can be
produced.
[0050] Although the composite oxide film was formed through contact
with an aqueous solution containing a vanadium compound in the
water quenching step, it is conceivable that a composite oxide film
can be also formed by applying an aqueous solution containing a
vanadium compound to a cooled hot-dip Zn alloy-plated steel sheet
and drying the applied aqueous solution (post-treatment method).
Accordingly, the present inventors tried to form a composite oxide
film by applying an aqueous solution containing a vanadium compound
(the same aqueous solution as that used in the producing method
described above) to a hot-dip Zn alloy-plated steel sheet cooled to
normal temperature with a general industrial water, and drying the
applied aqueous solution. Although a composite oxide film
containing constituent components of a plating layer and vanadium
was also formed on the surface of the plating layer through such a
post-treatment method, the composite oxide film had a Zn hydroxide
ratio of more than 40%. The hot-dip Zn alloy-plated steel sheet
thus produced had no outstanding difference in blackening
resistance compared with a hot-dip Zn alloy-plated steel plate
having no composite oxide film.
[0051] The reason is not clear why the hot-dip Zn alloy-plated
steel sheet of the present invention has higher blackening
resistance than a hot-dip Zn alloy-plated steel sheet having no
composite oxide film. As described above, the hot-dip Zn
alloy-plated steel sheet produced by the post-treatment method has
a Zn hydroxide ratio of more than 40% in the composite oxide film,
which is different from that of the hot-dip Zn alloy-plated steel
sheet of the present invention. Furthermore, the blackening
resistance is notably different between the hot-dip Zn alloy-plated
steel sheet of the present invention and the hot-dip Zn
alloy-plated steel sheet produced by the post-treatment method. It
is therefore conceivable that the stability of Zn contained in the
composite oxide film is different between the hot-dip Zn
alloy-plated steel sheet of the present invention and the hot-dip
Zn alloy-plated steel sheet produced by the post-treatment method,
and the Zn contained in the composite oxide film of the hot-dip Zn
alloy-plated steel sheet of the present invention is more difficult
to transform into an oxygen-deficient zinc oxide as the source of
blackening. This may be the reason why the hot-dip Zn alloy-plated
steel sheet of the present invention has higher blackening
resistance.
[0052] (Production Line)
[0053] The hot-dip Zn alloy-plated steel sheet of the present
invention may be produced, for example, in the following production
line.
[0054] FIG. 3 is a schematic diagram illustrating a part of
production line 300 of a hot-dip Zn alloy-plated steel sheet.
Production line 300 forms a plating layer and a composite oxide
film on the surface of a base steel sheet (steel strip), and can
continuously produce hot-dip Zn alloy-plated steel sheets of the
present invention. Production line 300 may further form a chemical
conversion coating on the surface of the composite oxide film on an
as needed basis, and can continuously produce plated steel sheets
with chemical conversion treatment.
[0055] As shown in FIG. 3, production line 300 includes furnace
310, plating bath 320, air jet cooler 340, mist cooling zone 350,
water quenching zone 360, skin pass mill 370, and tension leveler
380.
[0056] The steel strip S fed from a feeding reel not shown in
drawing through a predetermined step is heated in furnace 310. The
heated steel strip S is dipped in plating bath 320, so that molten
metal is adhered to both sides of the steel strip S. An excess
amount of molten metal is then removed with a wiping apparatus
having wiping nozzle 330, allowing a specified amount of molten
metal to be adhered to the surface of the steel strip S.
[0057] The steel strip S with a specified amount of molten metal
adhered thereto is cooled to the solidifying point of the molten
metal or lower by air jet cooler 340 or in mist cooling zone 350.
Air jet cooler 340 is a facility for cooling the steel strip S by
spraying a gas. Mist cooling zone 350 is a facility for cooling the
steel strip S by spraying atomized fluid (e.g. cooling water) and a
gas. The molten metal is thereby solidified, so that a hot-dip Zn
alloy plating layer is formed on the surface of the steel strip S.
When the steel strip s is cooled in mist cooling zone 350, no water
film is formed on the surface of the plating layer. The temperature
after cooling is not specifically limited, and may be, for example,
100 to 250.degree. C.
[0058] The hot-dip Zn alloy-plated steel sheet cooled to a
specified temperature is further cooled in water quenching zone
360. Water quenching zone 360 is a facility for cooling the steel
strip S through contact with a large amount of cooling water in
comparison with mist cooling zone 350, supplying an amount of water
to form a temporary water film on the surface of the plating layer.
For example, water quenching zone 360 includes headers having 10
flat spray nozzles disposed at intervals of 150 mm in the width
direction of the steel strip S, which are disposed in 7 rows in the
feeding direction of the base steel sheet S. In water quenching
zone 360, an aqueous solution containing a vanadium compound is
used as cooling aqueous solution. The steel strip S is cooled in
water quenching zone 360, with the cooling aqueous solution in an
amount to temporarily form a water film on the surface of the
plating layer being supplied. For example, the cooling aqueous
solution has a water temperature of approximately 20.degree. C., a
water pressure of approximately 2.5 kgf/cm.sup.2, and a water
quantity of approximately 150 m.sup.3/h. The phrase "a water film
is temporarily formed" means a state allowing a water film in
contact with a hot-dip Zn alloy-plated steel sheet to be visually
observed for approximately one second or more. Through cooling
using an aqueous solution of a vanadium compound in water quenching
zone 360, a composite oxide film containing the constituent
components of a plating layer and vanadium with a Zn hydroxide of
40% or more is formed on the surface of the plating layer.
[0059] The water-cooled hot-dip Zn alloy-plated steel sheet is
rolled for thermal refining by skin pass mill 370, corrected to
flat by tension leveler 380, and then wound onto tension reel
390.
[0060] When a chemical conversion coating is further formed on the
surface of a plating layer, a specified chemical conversion
treatment liquid is applied to the surface of the hot-dip Zn
alloy-plated steel sheet corrected by tension leveler 380, with
roll coater 400. The hot-dip Zn alloy-plated steel sheet through
the chemical conversion treatment is dried and cooled in drying
zone 410 and air cooling zone 420, and then wound onto tension reel
390.
[0061] As described above, the hot-dip Zn alloy-plated steel sheet
of the present invention has excellent blackening resistance and
can be easily produced at high productivity.
[0062] The present invention is described in detail with reference
to Examples as follows. The present invention is, however, not
limited to the Examples.
Examples
Experiment 1
[0063] In Experiment 1, the blackening resistance of a hot-dip Zn
alloy-plated steel sheet was examined for the hot-dip Zn
alloy-plated steel sheet cooled using a cooling water containing a
metal compound after plating.
[0064] 1. Production of Hot-Dip Zn Alloy-Plated Steel Sheet
[0065] Using production line 300 shown in FIG. 3, hot-dip Zn
alloy-plated steel sheets were produced. A hot-rolled steel strip
with a sheet thickness of 2.3 mm was prepared as base steel sheet
(steel strip) S. Plating was applied to the base steel sheet using
the plating bath compositions and conditions described in Table 1,
so that 14 types of hot-dip Zn alloy-plated steel sheets having
different plating layer compositions from each other were produced.
The composition of the plating bath and the composition of the
plating layer are approximately the same.
TABLE-US-00001 TABLE 1 Plating conditions Sheet Bath Adhering
passing Plating Plating bath composition (balance: Zn) (% by mass)
temperature amount speed No. Al Mg Si Ti B Sb (.degree. C.)
(g/m.sup.2) (m/min) 1 0.18 -- -- -- -- 0.09 430 90 80 2 0.18 -- --
-- -- 0.06 430 90 80 3 0.18 -- -- -- -- -- 430 90 80 4 1 1 -- -- --
-- 430 90 80 5 1.5 1.5 -- -- -- -- 430 90 80 6 2.5 3 -- -- -- --
430 90 80 7 2.5 3 0.4 -- -- -- 430 90 80 8 3.5 3 -- -- -- -- 430 90
80 9 4 0.75 -- -- -- -- 430 90 80 10 6 3 -- 0.05 0.003 -- 430 90 80
11 6 3 0.02 0.05 0.003 -- 430 90 80 12 11 3 -- -- -- -- 450 90 80
13 11 3 0.2 -- -- -- 450 90 80 14 55 -- 1.6 -- -- -- 600 90 80
[0066] In production of a hot-dip Zn alloy-plated steel sheet, the
cooling conditions in air jet cooler 340 were changed, such that
the temperature of the steel sheet (the surface of plating layer)
is adjusted at 200.degree. C. immediately before passing through
water quenching zone 360. In water quenching zone 360, any one of
the aqueous solution described in Table 2 was used as cooling
aqueous solution for formation of the composite oxide film. Each of
the cooing aqueous solutions was prepared by dissolving the metal
compound described in Table 2 and a dissolution promotor on an as
needed basis at a specified ratio in a water having a pH of 7.6,
and adjusting the water temperature to 20.degree. C. The
concentration of the metal compound in each of the cooling aqueous
solutions was 250 mg/L in terms of metal element in any case. The
spray apparatus in water quenching zone 360 for use includes
headers having 10 flat spray nozzles disposed at intervals of 150
mm in the width direction, which are disposed in 7 rows in the
feeding direction of the base steel sheet S. Each of the cooling
aqueous solutions supplied from water quenching zone 360 was under
conditions with a water pressure of 2.5 kgf/cm.sup.2 and a water
quantity of 150 m.sup.3/h.
[0067] As Comparative Example, a composite oxide film was formed by
using a water containing no metal compound instead of using any one
of the aqueous solutions described in Table 2 in water quenching
zone 360, then applying any of the aqueous solutions described in
Table 2 by a roll coat method or a spray ringer roll method, and
drying the applied aqueous solution (post-treatment method).
TABLE-US-00002 TABLE 2 Metal compound (A) Dissolution promoter (B)
Cooling Amount Ratio of water added amount Category No. Name (mg/L)
Name added (B/A) Example 1 Vanadium 1709 Tetraethylammonium 1.1
acetylacetonate hydroxide 2 Acetylacetonate vanadyl 1301 Ethylene
diamine 1.3 3 Ammonium metavanadate 574 -- -- 4 Sodium metavanadate
598 -- -- 5 Divanadium tetroxide 407 2,2'-Iminodiethanol 0.9 6
Vanadium pentoxide 446 1-Amino-2-propanol 1.1 Comparative 7
Ammonium chromate 606 -- -- Example 8 Potassium chromate 467 -- --
9 Sodium silicate 1087 -- --
[0068] 2. Evaluation of Hot-Dip Zn Alloy-Plated Steel Sheet
[0069] (1) Measurement of Zn(OH).sub.2 Ratio on Surface of
Composite Oxide Film
[0070] For each of the hot-dip Zn alloy-plated steel sheets, the Zn
hydroxide ratio on the surface of the composite oxide film was
measured using an XPS analyzer (AXIS Nova, produced by Kratos Group
PLC.). The Zn hydroxide ratio was calculated using software (Vision
2) attached to the XPS analyzer.
[0071] (2) Measurement of Adhering Amount of V on Surface of
Composite Oxide Film
[0072] For each of the hot-dip Zn alloy-plated steel sheets, the
adhering amount of vanadium on the surface of the composite oxide
film was measured using an ICP emission analyzer (ICPS-8100,
produced by Shimadzu Corporation).
[0073] (3) Treatment for Accelerating Deterioration of Gloss
[0074] A test piece was cut out from each of the produced hot-dip
Zn alloy-plated steel sheets. Each of the test pieces was placed in
a thermo-hygrostat (LHU-113, produced by Espec Corp.), and
subjected to a treatment for accelerating deterioration of the
gloss at a temperature 70.degree. C., with a relative humidity of
90%, for 72 hours.
[0075] (4) Measurement of Degree of Blackening
[0076] The brightness (L* value) at the surface of the plating
layer for each of the hot-dip Zn alloy-plated steel sheets was
measured before and after the treatment for accelerating
deterioration of the gloss. The brightness (L* value) at the
surface of the plating layer was measured using a spectroscopic
color difference meter (TC-1800, produced by Tokyo Denshoku Co.,
Ltd), by spectral reflectance measurement in accordance with JIS K
5600. The measurement conditions are as follows:
[0077] Optical condition: d/8.degree. method (double beam optical
system)
[0078] Field of view: 2-degree field of view
[0079] Measurement method: reflectometry
[0080] Standard illuminant: C
[0081] Color system: CIELAB
[0082] Measurement wavelength: 380 to 780 nm
[0083] Measurement wavelength interval: 5 nm
[0084] Spectroscope: 1,200/mm diffraction grating
[0085] Lighting: halogen lamp (voltage: 12 V, power: 50 W, rating
life: 2,000 hours)
[0086] Measurement area: 7.25 mm diameter
[0087] Detection element: photomultiplier tube (R928 produced by
Hamamatsu Photonics K.K.)
[0088] Reflectance: 0 to 150%
[0089] Measurement temperature: 23.degree. C.
[0090] Standard plate: white
[0091] For each of the plated steel sheets, the evaluation was
ranked as "A" for a difference in L* values (.DELTA.L*) between
before and after the treatment for accelerating deterioration of
the gloss of less than 1, "B" for a difference of 1 or more and
less than 3, "C" for a difference of 3 or more and less than 7, and
"D" for a difference of 7 or more. It can be determined that a
plated steel sheet evaluated as "A" or "B" has blackening
resistance.
[0092] (4) Evaluation Results
[0093] For each of the plated steel sheets, the relation between
the type of the cooling aqueous solution for use and the method for
forming the composite oxide film (a water quenching method (WQ), a
roll coat method (RC), or a spray ringer roll method (SP)), and the
Zn hydroxide ratio, the adhering amount of V and the evaluation
results of the degree of blackening is described in Table 3 to
Table 6.
TABLE-US-00003 TABLE 3 Cool- Adhering Black- Test Plat- ing Treat-
Amount ening Cate- piece ing water ment Hydroxide of V test gory
No. No. No. method Ratio (%) (mg/m.sup.2) result Ex. 1 11 1 WQ 7
0.004 B Ex. 2 11 2 WQ 11 0.004 B Ex. 3 11 3 WQ 7 0.005 B Ex. 4 11 4
WQ 13 0.004 B Ex. 5 11 5 WQ 7 0.005 B Ex. 6 11 6 WQ 25 0.005 B Ex.
7 11 1 WQ 6 0.01 A Ex. 8 11 2 WQ 11 0.017 A Ex. 9 11 3 WQ 16 0.013
A Ex. 10 11 4 WQ 19 0.022 A Ex. 11 11 5 WQ 23 0.029 A Ex. 12 11 6
WQ 24 0.027 A Ex. 13 11 1 WQ 8 0.13 A Ex. 14 11 2 WQ 18 0.18 A Ex.
15 11 3 WQ 21 0.17 A Ex. 16 11 4 WQ 14 0.12 A Ex. 17 11 5 WQ 25
0.16 A Ex. 18 11 6 WQ 18 0.18 A Ex. 19 11 1 WQ 22 1.02 A Ex. 20 11
2 WQ 7 1.01 A Ex. 21 11 3 WQ 23 0.96 A Ex. 22 11 4 WQ 7 0.96 A Ex.
23 11 5 WQ 5 0.98 A Ex. 24 11 6 WQ 19 1.01 A Ex. 25 11 1 WQ 20 7.95
A Ex. 26 11 2 WQ 16 7.98 A Ex. 27 11 3 WQ 6 8.02 A Ex. 28 11 4 WQ
21 8.05 A Ex. 29 11 5 WQ 6 8.01 A Ex. 30 11 6 WQ 18 8.04 A
TABLE-US-00004 TABLE 4 Cool- Adhering Black- Test Plat- ing Treat-
Amount ening piece ing water ment Hydroxide of V test Category No.
No. No. method Ratio (%) (mg/m.sup.2) result Ex. 31 11 1 WQ 13
15.04 A Ex. 32 11 2 WQ 8 14.97 A Ex. 33 11 3 WQ 17 14.98 A Ex. 34
11 4 WQ 5 14.99 A Ex. 35 11 5 WQ 14 14.97 A Ex. 36 11 6 WQ 17 14.96
A Comp. Ex. 37 11 7 WQ 19 0 C Comp. Ex. 38 11 8 WQ 9 0 C Comp. Ex.
39 11 9 WQ 24 0 D Comp. Ex. 40 11 1 RC 76 1.03 D Comp. Ex. 41 11 2
RC 76 0.96 D Comp. Ex. 42 11 3 RC 65 0.99 D Comp. Ex. 43 11 4 RC 71
7.96 D Comp. Ex. 44 11 5 RC 83 7.96 D Comp. Ex. 45 11 6 RC 76 8.01
D Comp. Ex. 46 11 1 SP 76 1.06 D Comp. Ex. 47 11 2 SP 76 1.05 D
Comp. Ex. 48 11 3 SP 65 1.01 D Comp. Ex. 49 11 4 SP 71 8.03 D Comp.
Ex. 50 11 5 SP 83 8.03 D Comp. Ex. 51 11 6 SP 76 8.03 D
TABLE-US-00005 TABLE 5 Cool- Adhering Black- Test Plat- ing Treat-
Amount ening Cate- piece ing water ment Hydroxide of V test gory
No. No. No. method Ratio (%) (mg/m.sup.2) result Ex. 52 9 1 WQ 11
0.005 B Ex. 53 14 2 WQ 12 0.004 B Ex. 54 2 3 WQ 7 0.007 B Ex. 55 10
4 WQ 12 0.005 B Ex. 56 1 5 WQ 15 0.003 B Ex. 57 12 6 WQ 22 0.005 B
Ex. 58 5 1 WQ 14 0.024 A Ex. 59 8 2 WQ 8 0.019 A Ex. 60 13 3 WQ 11
0.022 A Ex. 61 3 4 WQ 14 0.017 A Ex. 62 10 5 WQ 8 0.021 A Ex. 63 4
6 WQ 24 0.023 A Ex. 64 13 1 WQ 20 0.221 A Ex. 65 7 2 WQ 21 0.239 A
Ex. 66 12 3 WQ 6 0.217 A Ex. 67 9 4 WQ 5 0.224 A Ex. 68 7 5 WQ 16
0.189 A Ex. 69 5 6 WQ 12 0.24 A Ex. 70 12 1 WQ 15 1.08 A Ex. 71 9 2
WQ 6 1.05 A Ex. 72 4 3 WQ 9 0.98 A Ex. 73 1 4 WQ 14 0.97 A Ex. 74
14 5 WQ 8 0.95 A Ex. 75 3 6 WQ 10 1.04 A Ex. 76 10 1 WQ 10 7.85 A
Ex. 77 8 2 WQ 6 7.81 A Ex. 78 13 3 WQ 19 8.19 A Ex. 79 10 4 WQ 22
7.81 A Ex. 80 6 5 WQ 8 8.12 A Ex. 81 12 6 WQ 15 8.09 A
TABLE-US-00006 TABLE 6 Cool- Adhering Black- Test Plat- ing Treat-
Amount ening piece ing water ment Hydroxide of V test Category No.
No. No. method Ratio (%) (mg/m2) result Ex. 82 5 1 WQ 24 15.16 A
Ex. 83 9 2 WQ 24 15.01 A Ex. 84 1 3 WQ 18 15.08 A Ex. 85 2 4 WQ 6
14.96 A Ex. 86 13 5 WQ 12 15.05 A Ex. 87 6 6 WQ 11 15.04 A Comp.
Ex. 88 13 7 WQ 20 0 C Comp. Ex. 89 12 8 WQ 5 0 C Comp. Ex. 90 10 9
WQ 12 0 D Comp. Ex. 91 9 1 RC 72 1.02 D Comp. Ex. 92 14 2 RC 70
0.96 D Comp. Ex. 93 12 3 RC 88 0.91 D Comp. Ex. 94 8 4 RC 74 0.97 D
Comp. Ex. 95 9 5 RC 67 0.91 D Comp. Ex. 96 5 6 RC 65 1.08 D Comp.
Ex. 97 9 1 SP 72 0.99 D Comp. Ex. 98 14 2 SP 70 0.96 D Comp. Ex. 99
12 3 SP 88 0.83 D Comp. Ex. 100 8 4 SP 74 0.88 D Comp. Ex. 101 9 5
SP 67 0.81 D Comp. Ex. 102 5 6 SP 65 1.07 D
[0094] As shown in Table 3 to Table 6, in the case of cooling using
an aqueous solution containing vanadium in water quenching zone
360, a composite oxide film containing vanadium was formed having
the surface with a Zn hydroxide ratio of 40% or less, and excellent
blackening resistance. In contrast, in the case of cooling using an
aqueous solution containing no vanadium in water quenching zone
360, a composite oxide film containing no vanadium was formed, and
blackening was insufficiently suppressed. In the case of
application of an aqueous solution containing vanadium by a roll
coat method or a spray ringer roll method, a composite oxide film
was formed, having the surface with a Zn hydroxide ratio of more
than 40%, and blackening was insufficiently suppressed.
[0095] From the comparison of the blackening resistance of the test
pieces Nos. 1 to 6 and Nos. 52 to 57 with the blackening resistance
of the test pieces Nos. 7 to 36 and Nos. 58 to 87, it is found that
the blackening resistance is particularly excellent in the case of
an adhering amount of vanadium in the composite oxide film of 0.01
mg/m.sup.2 or more.
[0096] From the results described above, it is found that the
cooling using an aqueous solution containing vanadium in water
quenching zone 360 allows a composite oxide film to be formed,
which contains vanadium and has the surface with a Zn hydroxide
ratio of 40% or less. The plated steel sheet having such a
composite oxide film is excellent in blackening resistance.
Experiment 2
[0097] In Experiment 2, the 102 types of hot-dip Zn alloy-plated
steel sheets produced in Experiment 1 were subjected to a chemical
conversion treatment under the following chemical conversion
treatment conditions A to C. Blackening resistance was measured
when the treatment for accelerating deterioration of the gloss was
carried out in the same manner as in Experiment 1. The appearance
after the chemical conversion treatment was also evaluated.
[0098] In chemical conversion treatment conditions A, ZINCHROME
3387N (chrome concentration: 10 g/L, produced by Nihon Parkerizing
Co., Ltd.) was used as chemical conversion treatment liquid. The
chemical conversion treatment liquid was applied to have an
adhering amount of chromium of 10 mg/m.sup.2 by a spray ringer roll
method.
[0099] In chemical conversion treatment conditions B, an aqueous
solution containing 50 g/L of magnesium phosphate, 10 g/L of
potassium fluorotitanate, and 3 g/L of an organic acid was used as
chemical conversion treatment liquid. The chemical conversion
treatment liquid was applied to have an adhering amount of metal
components of 50 mg/m.sup.2 by a roll coat method.
[0100] In chemical conversion treatment conditions C, an aqueous
solution containing 20 g/L of a urethane resin, 3 g/L of ammonium
dihydrogen phosphate, and 1 g/L of vanadium pentoxide was used as
chemical conversion treatment liquid. The chemical conversion
treatment liquid was applied to have a dried film thickness of 2
.mu.m by a roll coat method.
[0101] In the evaluation of the appearance for each of the plated
steel sheets after the chemical conversion treatment, the
evaluation was ranked as "B" for the chemical conversion treatment
coating having no white turbidity, and "D" for the chemical
conversion treatment coating having white turbidity.
[0102] For each of the plated steel sheets, the relation between
the type of the original sheet for the chemical conversion
treatment and the type of chemical conversion treatment, and the
evaluation results of the degree of blackening and the appearance
is described in Table 7 to Table 10.
TABLE-US-00007 TABLE 7 Original sheet for conversion Black- Test
Chemical treatment ening piece conversion (test piece test Appear-
Category No. treatment No.) result ance Ex. 103 A 1 B B Ex. 104 B 2
B B Ex. 105 C 3 B B Ex. 106 A 4 B B Ex. 107 B 5 B B Ex. 108 C 6 B B
Ex. 109 A 7 A B Ex. 110 B 8 A B Ex. 111 C 9 A B Ex. 112 A 10 A B
Ex. 113 B 11 A B Ex. 114 C 12 A B Ex. 115 A 13 A B Ex. 116 B 14 A B
Ex. 117 C 15 A B Ex. 118 A 16 A B Ex. 119 B 17 A B Ex. 120 C 18 A B
Ex. 121 A 19 A B Ex. 122 B 20 A B Ex. 123 C 21 A B Ex. 124 A 22 A B
Ex. 125 B 23 A B Ex. 126 C 24 A B Ex. 127 A 25 A B Ex. 128 B 26 A B
Ex. 129 C 27 A B Ex. 130 A 28 A B Ex. 131 B 29 A B Ex. 132 C 30 A
B
TABLE-US-00008 TABLE 8 Original sheet for chemical conversion
Black- Test Chemical treatment ening piece conversion (test test
Appear- Category No. treatment piece No.) result ance Ex. 133 A 31
A D Ex. 134 B 32 A D Ex. 135 C 33 A D Ex. 136 A 34 A D Ex. 137 B 35
A D Ex. 138 C 36 A D Comp. Ex. 139 A 37 D B Comp. Ex. 140 B 38 D B
Comp. Ex. 141 C 39 D B Comp. Ex. 142 A 40 D B Comp. Ex. 143 B 41 D
B Comp. Ex. 144 C 42 D B Comp. Ex. 145 A 43 D B Comp. Ex. 146 B 44
D B Comp. Ex. 147 C 45 D B Comp. Ex. 148 A 46 D B Comp. Ex. 149 B
47 D B Comp. Ex. 150 C 48 D B Comp. Ex. 151 A 49 D B Comp. Ex. 152
B 50 D B Comp. Ex. 153 C 51 D B
TABLE-US-00009 TABLE 9 Original sheet for chemical conversion
Black- Test Chemical treatment ening piece conversion (test test
Appear- Category No. treatment piece No.) result ance Ex. 154 A 52
B B Ex. 155 B 53 B B Ex. 156 C 54 B B Ex. 157 A 55 B B Ex. 158 B 56
B B Ex. 159 C 57 B B Ex. 160 A 58 A B Ex. 161 B 59 A B Ex. 162 C 60
A B Ex. 163 A 61 A B Ex. 164 B 62 A B Ex. 165 C 63 A B Ex. 166 A 64
A B Ex. 167 B 65 A B Ex. 168 C 66 A B Ex. 169 A 67 A B Ex. 170 B 68
A B Ex. 171 C 69 A B Ex. 172 A 70 A B Ex. 173 B 71 A B Ex. 174 C 72
A B Ex. 175 A 73 A B Ex. 176 B 74 A B Ex. 177 C 75 A B Ex. 178 A 76
A B Ex. 179 B 77 A B Ex. 180 C 78 A B Ex. 181 A 79 A B Ex. 182 B 80
A B Ex. 183 C 81 A B
TABLE-US-00010 TABLE 10 Original sheet for chemical conversion
Black- Test Chemical treatment ening piece conversion (test test
Appear- Category No. treatment piece No.) result ance Ex. 184 A 82
A D Ex. 185 B 83 A D Ex. 186 C 84 A D Ex. 187 A 85 A D Ex. 188 B 86
A D Ex. 189 C 87 A D Ex. 190 A 88 D B Ex. 191 B 89 D B Comp. Ex.
192 C 90 D B Comp. Ex. 193 A 91 D B Comp. Ex. 194 B 92 D B Comp.
Ex. 195 C 93 D B Comp. Ex. 196 A 94 D B Comp. Ex. 197 B 95 D B
Comp. Ex. 198 C 96 D B Comp. Ex. 199 A 97 D B Comp. Ex. 200 B 98 D
B Comp. Ex. 201 C 99 D B Comp. Ex. 202 A 100 D B Comp. Ex. 203 B
101 D B Comp. Ex. 204 C 102 D B
[0103] As shown in Table 7 to Table 10, the plated steel sheets
having a composite oxide film including vanadium, with the surface
having a Zn hydroxide ratio of 40% or less, had excellent
blackening resistance even when a chemical conversion coating is
formed. In contrast, in the case of an adhering amount of vanadium
in the composite oxide film of more than 10.0 mg/m.sup.2 (test
piece Nos. 31 to 36 and Nos. 82 to 87), the reactivity between the
chemical conversion treatment liquid and the surface of the plating
layer (composite oxide film) was decreased, and the chemical
conversion treatment coating had white turbidity.
[0104] From the results, it is found that in the case of chemical
conversion treatment, the adhering amount of vanadium in the
composite oxide film is preferably adjusted to 10.0 mg/m.sup.2 or
less.
[0105] This application claims priority based on Japanese patent
Application No. 2013-250139, filed on Dec. 3, 2013, the entire
contents of which including the specification and the drawings are
incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0106] The hot-dip Zn alloy-plated steel sheet obtained by the
production method of the present invention is excellent in
blackening resistance, and useful as plated steel sheet for use in,
for example, roof materials and exterior materials for buildings,
home appliances, and automobiles.
REFERENCE SIGNS LIST
[0107] 100, 200 Cooling apparatus [0108] 110 Spray nozzle [0109]
120, 230 Squeeze roll [0110] 130 Housing [0111] 210 Dip tank [0112]
220 Dip roller [0113] 300 Production line [0114] 310 Furnace [0115]
320 Plating bath [0116] 330 Wiping nozzle [0117] 340 Air jet cooler
[0118] 350 Mist cooling zone [0119] 360 Water quenching zone [0120]
370 Skin pass mill [0121] 380 Tension leveler [0122] 390 Tension
reel [0123] 400 Roll coater [0124] 410 Drying zone [0125] 420 Air
cooling zone [0126] S: Steel strip
* * * * *